Examensarbete vid Institutionen för geovetenskaper ISSN 1650-6553 Nr 193
Investigating Magma Plumbing Beneath Anak Krakatau Volcano, Indonesia: Evidence for Multiple
Magma Storage Regions
Börje Dahrén
Copyright © Börje Dahrén och institutionen för geovetenskaper, Berggrundsgeologi, Uppsala universitet. Tryckt hos Institutionen för geovetenskaper Geotryckeriet, Uppsala universitet, Uppsala 2010
iii
Referat
Att öka förståelsen för transport och lagring av magma är en stor utmaning för petrologer och
vulkanologer. Detta gäller speciellt för explosiva vulkaner, där förståelsen av magma-
lagringssystem är mycket viktig för att förutse dynamiska förändringar och därigenom också i
riskförebyggande arbete. Denna studie syftar till att undersöka magma-lagringssystemet vid
Anak Krakatau, den aktiva vulkanen som befinner sig på kanten av kalderan från Krakataus
förödande utbrott år 1883. För detta ändamål tillämpas a.) klinopyroxen-smälta
termobarometri (Putirka et al., 2003; Putirka, 2008), b.) plagioklas-smälta termobarometri
(Putirka, 2005; Putirka, 2008), c.) klinopyroxen-barometri (Nimis & Ulmer, 1998; Nimis,
1999; Putirka, 2008) samt d.) olivin-smälta termometri (Putirka et al., 2007). Tidigare
seismiska (Harjono et al., 1989) och petrologiska (Camus et al., 1987; Mandeville et al.,
1996a; Gardner et al., under granskning, J. Petrol.) studier har undersökt denna frågeställning.
De petrologiska studierna påvisar ytligt förvar av magma, vid ett djup av 2-8 km. Den
seismiska studien, å andra sidan, identifierade två områden med magmalagring, på djup av ~9
respektive ≥22 km.
Denna studie visar att klinopyroxen för närvarande kristalliserar i mitt i jordskorpan under
Anak Krakatau (8-12 km), en nivå tidigare identifierad av seismiska undersökningar (Harjono
et al., 1989). Plagioklas visar på ett ytligare förvar (4-6 km), vilket överenstämmer med
tidigare petrologiska undersökningar (Camus et al., 1987; Mandeville et al., 1996a; Gardner et
al., under granskning, J. Petrol.). Klinopyroxen äldre än 1981 uppvisar större
kristallisationsdjup (8-22 km), vilket antyder att magma-förvaringssystemet närmat sig ytan
under de senaste ~40 åren. Dessutom sammanfaller de identifierade djupen för lagring av
magma med de dominerande litologiska gränserna i skorpan, vilket indikerar att lagringen
styrs av diskontinuiteter och densitetsskillnader i skorpan. Denna studie visar således att
petrologiska metoder är tillräckligt känsliga för att identifiera magma-lagringsnivåer, även där
seismiska metoder misslyckas på grund av begränsningar i upplösning. Kombinerade
seismiska och petrologiska studier har därför högre potential att uppnå en mer komplett
karaktärisering av magma-lagringssystem vid aktiva vulkaniska komplex.
Nyckelord:
Anak Krakatau; termobarometri; magma-lagringssystem; klinopyroxen; plagioklas.
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Abstract
Improving our understanding of magma plumbing and storage remains one of the major
challenges for petrologists and volcanologists today. This is especially true for explosive
volcanoes, where constraints on magma plumbing are essential for predicting dynamic
changes in future activity and thus for hazard mitigation. This study aims to investigate the
magma plumbing system at Anak Krakatau; the post-collapse cone situated on the rim of the
1883 Krakatau caldera. Since 1927, Anak Krakatau has been highly active, growing at a rate
of ~8 cm/week. The methods employed are a.) clinopyroxene-melt thermo-barometry (Putirka
et al., 2003; Putirka, 2008), b.) plagioclase-melt thermo-barometry (Putirka, 2005), c.)
clinopyroxene composition barometry (Nimis & and Ulmer, 1998; Nimis, 1999; Putirka,
2008) and d.) olivine-melt thermometry (Putirka et al., 2007). Previously, both seismic
(Harjono et al., 1989) and petrological studies (Camus et al., 1987; Mandeville et al., 1996a;
Gardner et al., in review, J. Petrol.) have addressed the magma plumbing beneath Anak
Krakatau. Interestingly, petrological studies indicate shallow magma storage in the region of
2-8 km, while the seismic evidence points towards a mid-crustal and a deep storage, at 9 and
22 km respectively.
This study shows that clinopyroxene presently crystallizes in a mid-crustal storage region
(8-12 km), a previously identified depth level for magma storage, using seismic methods
(Harjono et al., 1989). Plagioclases, in turn, form at shallower depths (4-6 km), in concert
with previous petrological studies (Camus et al., 1987; Mandeville et al., 1996a; Gardner et
al., in review, J. Petrol.). Pre-1981 clinopyroxenes record deeper levels of storage (8-22 km),
indicating that there may have been an overall shallowing of the plumbing system over the
last ~40 years. The magma storage regions detected coincide with major lithological
boundaries in the crust, implying that magma ascent and storage at Anak Krakatau is probably
controlled by crustal discontinuities and/or density contrasts. Therefore, this study shows that
petrology has the sensitivity to detect magma bodies in the crust where seismic surveys fail
due to limited resolution. Combined geophysical and petrological surveys offer an increased
potential for the thorough characterization of magma plumbing at active volcanic complexes.
Keywords
Anak Krakatau; thermobarometry; magma plumbing; clinopyroxene; plagioclase.
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Table of Contents
1. Introduction ........................................................................................................................ 1
2. Field work........................................................................................................................... 2
3. Geotectonic setting ............................................................................................................. 5
4. Previous estimates of magma storage depth ....................................................................... 9
5. Bulk rock geochemistry.................................................................................................... 11
6. Analytical method ............................................................................................................ 14
7. Petrography and mineral chemistry .................................................................................. 15
7.1 Plagioclase phenocrysts .............................................................................................. 15
7.2 Clinopyroxene phenocrysts ........................................................................................ 18
7.3 Olivine ........................................................................................................................ 19
7.4 Groundmass ................................................................................................................ 20
8. Estimates of bedrock density and pre-eruptive volatile content ....................................... 21
9. Method.............................................................................................................................. 22
9.1 Clinopyroxene-melt thermo-barometers .................................................................... 22
9.2 Clinopyroxene barometers ......................................................................................... 23
9.3 Plagioclase-melt thermobarometers ........................................................................... 24
9.4 Olivine-melt thermometers ........................................................................................ 24
10. Results ............................................................................................................................ 26
10.1 Pressures and temperatures from clinopyroxene-melt thermobarometry ................ 26
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10.2 Pressure estimates from clinopyroxene barometry .................................................. 29
10.3 Pressures and temperatures from plagioclase-melt thermobarometry ..................... 30
10.4 Temperature estimates from olivine-melt thermometry ........................................... 31
11. Discussion ...................................................................................................................... 34
12. Conclusions .................................................................................................................... 39
References ............................................................................................................................ 41
Appendix 1 – Chemical composition of analysed clinopyroxene phenocrysts ........................ 46
Appendix 2 – Chemical composition of analysed plagioclase phenocrysts ............................. 50
Appendix 3 – Chemical composition of analysed olivine ........................................................ 53
Appendix 4 – Chemical composition of analysed orthopyroxene ........................................... 54
Appendix 5 – Chemical composition of analysed titanomagnetite .......................................... 55
Appendix 6 – Chemical composition of analysed glass and groundmass ................................ 56
1
1. Introduction
The Krakatau volcano complex, western Java (Indonesia), is one of the most infamous
volcanoes worldwide due to the cataclysmic eruption of 1883, being the latest in a sequence
of caldera forming events (van Bemmelen, 1949; Camus et al., 1987). In 1927, a new volcanic
cone breached the ocean surface, earning the name Anak Krakatau, “child of Krakatau”. The
aim of this investigation is to constrain the depth of magma storage region(s) beneath Anak
Krakatau, which is approached by employing pressure and temperature modelling calculations
that use measured mineral and rock composition data and calibrated thermodynamic
formulations. The focus will be on a.) clinopyroxene-melt thermo-barometry (Putirka et al.,
2003; Putirka, 2008), and b.) plagioclase-melt thermo-barometry (Putirka, 2005). This will be
complemented by a.) clinopyroxene composition barometry (Nimis, 1999; Putirka, 2008) and
b.) olivine-melt thermometry (Putirka et al., 2007). The mineral dataset consists of electron
microprobe (EPMA) and X-ray fluorescence (XRF) analyses of minerals and rocks erupted
between 1883 and 2002. The results will serve as an independent test of previous estimates of
magma storage depths derived by geophysical means, plagioclase-melt geobarometry and in-
situ isotope stratigraphy (Camus et al., 1987; Harjono et al., 1989; Mandeville et al., 1996a;
Gardner et al., in review, J. Petrol.). Improved knowledge of the magma plumbing system
beneath Anak Krakatau will allow for better understanding and prediction of future activity at
this highly dynamic volcanic complex.
2
2. Field work
In September and October 2008, field work was carried out on the Indonesian islands of Java
and Bali, to sample rocks and fumarole gases at 16 active volcanoes. The expedition was part
of a project funded by Vetenskapsrådet and Uppsala University. Also, my participation on the
trip was made possible by additional funding from Otterborgs donationsfond.
See Fig. 1 map of the field area. According to the Global Volcanism Program, run by the
Smithsonian Institute, Krakatau was more or less active between October 2007 and October
2009. Our visit, however, took place during a period of relative quiescence. Notably, a new
crater formed in 2007, situated on the southern flank, just below the old summit crater (Fig.
2). Although no eruptions took place during our visit of Anak Krakatau, the evidence of
recent eruptions were abundant. The southern flank below the newly formed crater was
covered in volcanic ash, and was devoid of vegetation. Volcanic bombs of varying size, with
fresh bomb sags (Fig. 3) were scattered around the volcanic cone, especially on the terrace on
the eastern flank (Fig. 2). See Fig. 2-7 below for pictures taken during the expedition.
Figure 1. Map of the Sunda Straits, after Gardner et al. (in review, J. Petrol.). The location of the other volcanoes in
the north-south trending volcanic lineament is marked with triangles. Inset (b) is a close up on the Krakatau complex,
the dashed line indicating the outline of the pre-1883 Krakatau island.
3
Figure 2. The southern flank of Anak Krakatau. Visible is the 1960’s crater rim (black), the pre-2007 summit
crater (blue), as well as the currently active crater (red).
Figure 3. Picture taken on the terrace
on the eastern flank (visible in Fig. 2),
just below the main active cone. This
area was strewn with countless
volcanic bombs, ranging in size from
centimetres to several meters in
diameter. Many of the bombs had
fresh bomb sags implying that they
were recently erupted. This
particular bomb was erupted in late
2001/early 2002. In the bottom right
corner, one can see destroyed solar
panel, associated with the KrakMon
surveillance system operating on the
Krakatau islands.
Figure 4. A view from inside the
active Anak Krakatau crater. Note
the fumaroles on the far crater wall.
Other fumaroles, located in the
summit crater, were sampled to be
used in other studies (e.g. Blythe et
al., 2009).
4
Figure 5. A view from the top of Anak
Krakatau towards Rakata (Fig. 1), one
of the three islets remaining after the
collapse of the old Krakatau island in
1883.
Figure 6. A part of the 1883 caldera
wall on the island of Rakata. In other
words this is a view inside the pre-1883
Krakatau volcano (approximately in the
centre of Fig. 5). Below the volcanic
rocks, one can see the top of a sequence
of what is likely sedimentary rocks,
and/or pyroclastic deposits. Note also
the dyke swarm cutting trough the
rocks of the old Krakatau edifice.
Figure 7. View from beach of Rakata,
were the expedition spent the night
after the excursion to Anak Krakatau.
The boat in the middle left of the image
was used for transportation from the
mainland
5
3. Geotectonic setting
Anak Krakatau (Anak) is located in the Sunda Strait between the Indonesian islands of
Sumatra and Java (Fig. 1). Geologically, Anak is a part of the Sunda arc where the Indo-
Australian plate is subducted beneath the Eurasian plate. In west Java, this occurs at a rate of
67±7 mm per year (Tregoning et al., 1994). The Sunda arc is an active volcanic region with
the Krakatau complex being one of the most active parts. Since 1927, Anak has had numerous
eruptions, and has grown to a height of ~315m (Hoffmann-Rothe et al., 2006), which converts
to an average of 8 cm per week. Anak is a part of a volcanic lineament (Nishimura &
Harjono, 1992), with Panaitan to the south and Sukadana to the north (Fig. 1). This lineament
is related to a north-south trending fracture zone, manifested in a shallow seismic belt with
foci depths predominantly in the range of 0-20 km (Harjono et al., 1989; Nishimura &
Harjono, 1992; Špičák et al., 2002). Furthermore, the Krakatau complex is located at the
intersection of the volcanic lineament and a fault (Nishimura & Harjono, 1992; Deplus et al.,
1995), both of which would contribute to a heavily fractured bedrock facilitating magma
transport. The projection of this fault is seen in the bathymetric map (Deplus et al., 1995), as
indicated by the depressions labeled B and C (Fig. 8). The whole of the Sunda Strait is
subjected to extensive faulting and rifting, attributed to the clockwise rotation of Sumatra
relative to Java by 20° during the late Cenozoic (Ninkovich, 1976; Nishimura et al., 1986;
Harjono et al., 1991). The angle of subduction changes from near perpendicular (13°) in front
of Java to oblique (55°) in front of Sumatra (Jarrard, 1986). The Sumatran rotation has
resulted in extension, as reported in Harjono et al. (1991) and associated thinning of the crust
to ~20 km in the Sunda Strait, as compared to 25-30 km in Sumatra and west Java (Nishimura
& Harjono, 1992). The micro-seismic study by Harjono et al. (1989) estimated the crustal
thickness directly below Anak Krakatau to be ~22 km. The magmatism in the Sunda Strait is
thus not strictly subduction zone related, but must also be considered to be to some degree
extensional. The influence of the rifting is manifested in Sukadana (Fig. 1), where an 0.8-1.2
Ma old MORB-type basalt is found (Nishimura & Harjono, 1992).
The bimodal nature of the Krakatau complex, with extended periods of basaltic and/or
basaltic-andesitic eruptions culminating in colossal caldera forming ignimbrite eruptions (Fig.
9), was discussed by Van Bemmelen (1949), and has since been strengthened by findings of
other authors (Camus et al., 1987; Mandeville et al., 1996a).
6
The formation of the most recent caldera occurred on the 23rd
of August 1883, when the
Krakatau island collapsed (Mandeville et al., 1996). This resulted in a submarine caldera ~100
m deeper than the surrounding sea floor (Fig. 8). Note also that Anak is situated on the north-
eastern rim of this caldera. The volume of products of the 1883 eruption has been estimated to
be 17-25 km3 (Deplus et al., 1995), ~20 km
3 (Rampino & Self, 1982) or 12.5 km
3 (Mandeville
et al., 1996a). There is evidence of at least two more large ignimbrite eruptions at Krakatau.
Ninkovich, (1979) located two major dacitic ashfalls near the trench ~350 km south and
southwest of Krakatau, which he associated with Krakatau and attributed to 60,000 BC and
“recent”. The “recent” ashfall has not been radiometrically dated. However, two estimates,
from correlations with historical documents are suggested in the literature, namely 416 AD
(Camus et al., 1987) and 535 AD (Wohletz, 2000).
Figure 1. Bathymetric map
(Deplus et al., 1995) of the
Krakatau complex. Isolines
indicate 20 m contours. The
depression labeled “A” is the
~240 m deep caldera from the
1883 eruption. Note the
location of Anak Krakatau on
the north-eastern rim of the
caldera. The east-west trending
fault intersecting the volcanic
lineament is visible as the
depressions labeled “B” and
“C”.
Figure 2. The bimodal cyclicity of Krakatau, as reported in van Bemmelen (1949). The composition of the present day
eruption products are still dominated by basaltic-andesites (~55 wt% SiO2).
7
Drill cores obtained during hydrocarbon exploration by Pertamina-Aminoil provides
information on the bedrock at depth in the Sunda Strait. The closest of these wells (C-1SX) is
located ~30 km southeast of Anak (Fig. 1). The C-1SX well penetrated a continuous
sedimentary sequence of Quaternary to upper Pliocene age. The lithology is dominated by
marine clays and clay-dominated siliciclastic rocks interbedded with volcanoclastic material
to a depth of at least 3000 m (Nishimura & Harjono, 1992; Mandeville et al., 1996a).
Findings by (Lelgemann et al., 2000) suggest that the extension and rapid subsidence of the
Sunda Strait have created space for up to 6 km graben fill. Thus, the total depth of the
sediments and sedimentary rocks below Krakatau can be constrained to between 3 to 6 km.
The Pertamina-Aminoil wells all failed to reach the basement below the sedimentary
sequence, but other wells to the southeast of Sumatra and northwest of Java have drilled
Cretaceous granites and quartz-monzonites (Hamilton, 1979). The assumption of a
sedimentary sequence
underlain by a plutonic
basement below
Krakatau (Harjono et
al., 1991) is supported
by the findings of
sedimentary
(Mandeville et al.,
1996b; Gardner et al., in
review, J. Petrol.),
granitic (Oba et al.,
1983) as well as dioritic,
gabbroic and meta-basic
(Oba et al., 1983;
Gardner et al., in
review, J. Petrol.)
xenoliths in Krakatau
lavas and pyroclastic
flows. The crustal
velocity model used in
the micro-seismic study
Figure 3. Stratigraphy of the bedrock below Anak Krakatau. The lithology is
inferred from findings of xenoliths (Oba et al., 1983; Camus et al., 1987;
Mandeville et al., 1996b; Gardner et al., in review, J. Petrol.) and seismic
studies (Harjono et al., 1989; Kopp et al., 2001).
8
by Harjono et al. (1989) identifies three boundaries in the crust below Krakatau with
distinguishable crustal velocities, which could correspond with lithological boundaries. These
boundaries would be at depths of roughly 4, 9 and 22 km respectively, with the lowermost
boundary representing the Moho. The upper boundary (4 km) very likely represent the
sedimentary-plutonic crustal boundary. The middle boundary (9 km) represent a density
contrast, possibly caused by a change in lithology from a light density plutonic rock (e.g.
granite) to a higher density plutonic rock (e.g. diorite or gabbro). See Fig. 10 for a schematic
stratigraphy of the bedrock below Anak Krakatau.
9
4. Previous estimates of magma storage depth
The methods previously employed to estimate magma storage depth beneath Krakatau are a.)
plagioclase-melt thermobarometry, b.) chlorine content in melt inclusions, c.) loci of seismic
attenuation zones, and d.) in-situ crystal isotope stratigraphy. The results of these studies will
be outlined below.
Mandeville et al. (1996a)
employed plagioclase-melt
thermobarometry (Housh & Luhr,
1991) to estimate the depth of the
pre-1883 magma chamber. Their
results indicate shallow depths of
crystallization for plagioclase, with
pressure estimates in the range of 1
to 2 kbar (~4 to 8 km). This was
complemented by analysing
chlorine content in melt inclusions
(Metrich & Rutherford, 1992),
resulting in an independent
estimate of 1 kbar (~4 km).
Camus et al. (1987) estimated
depth of crystallization for
plagioclase in rocks erupted
between 1883 and 1981, using
plagioclase-melt thermobarometry (Kudo & and Weill, 1970), resulting in estimates of 0.5 to
2 kbar (~2 to 8 km).
Gardner et al. (in review, J. Petrol.) have carried out in situ 87
Sr/86
Sr analyses on
plagioclase from the 2002 eruptions, employing LA-ICPMS, and conclude that crystallization
of many plagioclase grains must have taken place during assimilation of sedimentary country-
rock. This constrains the depth of final crystallization to within the upper three or four
kilometres simply on stratigraphic grounds - from drill hole evidence - in agreement with the
plagioclase-melt thermobarometry results discussed above.
Harjono et al. (1989) analysed the seismic signature from 14 earthquakes near Anak
Krakatau during 1984, using data from analogue seismograms. Two seismic attenuation zones
Figure 11. The two seismic attenuation zones detected below Anak
Krakatau, redrawn from Harjono et al. (1989). Circles represent
earthquake foci with (open circles) and without (filled circles) S-
wave attenuation. The inferred magma storage regions are
represented by the red shapes. Note that the resolution in this
study is too low to conclude whether or not the two attenuation
zones are connected.
10
beneath the volcanic edifice were identified in that study, one a small and irregular zone at a
depth of approximately 9 km, and another much larger one at 22 km (Fig. 11). Note that the
seismic attenuation zones coincide with the lower boundary of the medium and lower crustal
velocity zones discussed above. However, it was not possible to resolve whether the two
attenuation zones are connected or not, nor if these represent large volume chambers or a
plexus of smaller pockets and chambers.
The present study uses, for the first time, barometry based on clinopyroxene, to provide an
independent and complementary test to these isotopic, geophysical and geobarometric
constraints, with the aim to establish a model of the plumbing system beneath Anak Krakatau.
11
5. Bulk rock geochemistry
Bulk rock chemistry of flows, bombs and ash erupted from Krakatau and Anak is plotted in
Fig. 12. The bulk rock data was supplied by Mairi Gardner, a final year PhD student at
University College Cork, Ireland, who works with Prof. Troll on other aspects of Anak
(Gardner et al., in review, J. Petrol.), or otherwise taken from the literature (Zen &
Hadikusumo, 1964; Self, 1982; Camus et al., 1987; Mandeville et al., 1996a). All oxides have
been normalized to 100%, (volatile free) and iron content is reported as FeOt. Note that the
bulk rock analyses of lava flows and bombs erupted between 1990 and 2002 carried out by
Gardner et al. (in review, J. Petrol.), were done on the exact same samples that were used for
the petrographic and microprobe analyses in this study. Analyses of rocks erupted during the
1883 eruption as well as the time period 1960-1981 are also plotted in Fig. 12. Note that, in
the TAS diagram (Le Bas et al., 1986) below, all Krakatau rocks plot in the subalkaline field
(Fig. 12).
Figure 12. TAS diagram (Le Bas et al., 1986) plotting bulk composition of rocks from Anak Krakatau (black circles)
and Krakatau (red circles). The data was taken from the literature. (Zen & Hadikusumo, 1964; Self, 1982; Camus et
al., 1987; Mandeville et al., 1996a; Gardner et al., in review, J. Petrol.). The Krakatau rocks include products from
the ignimbrite eruption in 1883 as well as older basaltic dyke rocks. The vast majority of the rocks erupted from Anak
Krakatau plot in a very narrow region in the basaltic-andesite field, with rocks from single events plotting in the
basaltic and andesitic fields.
12
Using the classification of Peccerillo and Taylor (1976), the rock suite plots mostly within
the medium-K part of the calc-alkaline series (Fig. 13), in concert with the findings of other
authors (Camus et al., 1987). Note, however, that when using the definition of Peacock
(1931), the rock suite would be classified as calcic rather than calc-alkaline, with an alkali
lime index of 61.6.
Figure 43. K2O vs SiO2 plot (Peccerillo & Taylor, 1976) for rocks from Anak Krakatau (black circles) and Krakatau (red
circles). Except for two of the basaltic dyke rocks from pre-1883, all rocks plot within the calc-alkaline series, and there
almost exclusively within the medium-K part.
The rocks plot in two main groups on a TAS diagram. The pumices and obsidians of the
1883 eruption plot in the dacite-rhyolite field, while the lava flows and bombs from Anak
belong to a rather homogenous suite of basaltic-andesites. The exceptions to this would be the
1960-1963 and 1981 eruptions (basalts and acidic-andesites, respectively), representing single
events. Note also that several basaltic dyke rocks from the island of Rakata with a similar
composition to the 1963 basaltic flows have been reported (Camus et al., 1987). The early
history of Anak is not well documented, as very few analyses have been performed on rocks
0
1
2
3
4
48 53 58 63 68
Arc tholeiite series
Calc-alkaline series
High-Kcalc-alkaline series
Shoshonite series
SiO2
K2O
13
erupted between 1927 and 1960. However, there are indications that the early Anak rocks did
not differ significantly from the more recent ones, as silica content in ashes and bombs
erupted in the period 1928-1935 has been reported to be in the range of 51.81 to 54.76 wt. %
(van Bemmelen, 1949), overlapping with the SiO2 content of the recent basaltic-andesites
(Fig. 12). This corresponds well with the observation of Camus et al. (1987), that the
composition of the tuff ring and lava flows on Anak appeared to belong invariably to the
basaltic-andesite suite. Field observations in 2008 also support this as the lava bombs of the
2007-2008 eruptions appear to be virtually identical in composition to the 2002 bombs. Thus,
all bulk rock analyses and field observations indicate that the bulk of Anak Krakatau island is
made up of basaltic-andesites, with minor components of basalt plus sparse acidic-andesite.
This suggests the presence of a steady state magma storage system under the volcano,
presently producing basaltic-andesite from parental basalt with limited variation of the final
product.
14
6. Analytical method
Mineral chemistry as well as glass and groundmass composition was analysed at Uppsala
University (Sweden) using a Cameca SX 50 Electron Probe Microanalyser (EPMA), equipped
with three crystal spectrometers (WDS), secondary (SE) and backscattered electron detectors
(BSE). The EPMA is an advanced microchemical instrument that is used to determine the
chemical composition of e.g. mineral samples. The sample, prepared as a thin section, is
beamed with high energy electrons with an accelerating voltage of 20 kV and a current of 15
nA, causing the sample to emit characteristic X-ray signatures, allowing the determination of
chemical composition. The electron beam is focused using several electromagnetic lenses.
The diameter of the beam is commonly 1-2 µm, though a beam size of up to 25 µm was used
for the analysis of groundmass composition. The wide beam analyses of groundmass included
glass and microcrysts, but avoided phenocrysts. Glass compositions were analysed both in the
groundmass and in melt inclusions. International reference materials were used for calibration
and standardisation (e.g. Andersson, 1997).
Figure 14. Schematic illustration of an Electron Probe Microanalyser (EPMA).
Image adopted from Bundesanstalt für Geowissenschaften und Rohstoffe, Hannover
(www.bgr.bund.de)
15
7. Petrography and mineral chemistry
The lavas examined are all highly porphyritic, dark, and partly vesicular. Plutonic as well as
sedimentary xenoliths occur. The homogeneity of the bulk chemistry of the rocks is reflected
in the petrographic features, as all thin sections examined share the same characteristics,
outlined below. The analysed dataset consists of 152 clinopyroxene, 121 plagioclase, 19
olivine, 26 orthopyroxene and 4 titanomagnetite spot analyses where collected from 15
clinopyroxene, 12 plagioclase, 4 olivine and 4 titanomagnetite mineral grains. The relatively
small number of analysed minerals was considered adequate due to the relatively homogenous
mineral chemistry, especially regarding clinopyroxene. Also, 14 analyses of glass in
groundmass and melt inclusions where collected as well as another 14 wide beam (~10x10
µm) analyses of groundmass, in order to be able to calculate an average groundmass
composition including both glass and microcrystalline phases. Mineral chemistry of
clinopyroxene from Mandeville et al. (1996) and Camus et al. (1987) will be included in the
model calculations in order to increase the temporal resolution of the data set. The modal
composition is, on average, 70% groundmass, 25% plagioclase, 4% clinopyroxene and less
than 1% olivine crystals, as determined from point counting (4 thin sections, 144 points each).
These mineral phases will be outlined below. Representative microphotographs and electron
backscatter images of the rocks analysed are displayed in Fig. 15.
7.1 Plagioclase phenocrysts
Plagioclase is the volumetrically dominant phenocryst phase, making up approximately one
fourth of the total rock volume. Plagioclase phenocrysts are mostly subhedral, but a few are
anhedral. Sieve-like textures are a common feature with numerous melt inclusions present.
The size of the plagioclase crystals are on the order of 0.5-2 mm. Numerous plagioclase
crystals, when viewed under polarized light, appear to have experienced stages of growth
and/or dissolution, as shown by cores that have been partially resorbed at some point before
growth re-commenced (Fig 13a, 13d). Normal as well as reverse zoning has been
documented.
16
Figure 15a. Subhedral plagioclase crystal with highly
sieve-textured core and rim regions. This implies a
dynamic magmatic system. Crossed polars.
Figure 15b. Sieve-textured plagioclase crystal with
numerous melt inclusions. Crossed polars. Note also the
very thin overgrowth rim.
Figure 15c. Several intergrown anhedral plagioclase
crystals, all with a sieve-texture. Crossed polars.
Figure 15d. Plagioclase crystal. Note that the
anomalously dark brown colour of the plagioclase is due
to the thin section being thicker than normal (~100 µm).
The outer regions are sieve-textured with a very thin
overgrowth of the rims, just like the plagioclase in Fig.
15b. Crossed polars
Figure 15e. A plagioclase crystal with sieve-like texture,
having grown around several small clinopyroxenes.
Again, note the sieve-texture and the thin overgrowth on
the rims. Crossed polars.
Figure 15f. A plagioclase crystal intergrown with several
smaller clinopyroxene crystals. Crossed polars.
17
Figure 15g. Euhedral clinopyroxene crystal. Dark brown,
vesicular groundmass consisting of acicular plagioclase,
orthopyroxene, titanomagnetite and glass. Crossed
polars.
Figure 15h. Euhedral clinopyroxene crystal. Crossed
polars.
Figure 15i. Euhedral, clinopyroxene crystal. Crossed
polars.
Figure 15j. Euhedral, twinned clinopyroxene crystal. In
the bottom left corner, there is a tiny, partly resorbed
olivine with very high colours. Note that the olivine rim is
covered in discontinuous phases, as can also be seen in
Fig. 15k below. Crossed polars.
Figure 15k. BSE image of a partly resorbed olivine
(center of image), covered in discontinuous growth of
orthopyroxene and titanomagnetite. The olivine crystal is
surrounded by the groundmass composed of acicular
plagioclase (dark grey laths), anhedral orthopyroxene
(light grey), titanomagnetite (white crystals) and glass
(irregular dark grey fields).
Figure 15l. BSE image. Intergrown plagioclase (bottom)
and clinopyroxene (top). Note the abundance of melt
inclusions and vesicles in the plagioclase. The
clinopyroxene have several inclusions of opaque
minerals, likely titanomagnetite.
18
The lowest anorthite
concentrations (An45) as
well as the highest
(An80) were found in
plagioclase cores. The
rims do also vary
widely in their
composition, with
extremes of An79 and
An55. It is noteworthy
that the An% variation
between different grains
is often greater than
within individual grains. Although the number of analysed individual grains (n=12) is
insufficient to distinguish between different plagioclase generations, there seems to be two
main groupings, in the range of An45-70 and An58-80 respectively. Other authors have
independently reached similar conclusions, finding two plagioclase populations in Anak
Krakatau lavas of An55-60 and An75-90 (Gardner et al., in review, J. Petrol.) and An40-55 and
An75-90 (Camus et al., 1987). The composition of all plagioclase datapoints analysed for this
study is illustrated in Fig. 16.
7.2 Clinopyroxene phenocrysts
Clinopyroxene is the second most abundant mineral phase, though markedly less common
than plagioclase, making up approximately 4% of the total rock volume. The clinopyroxene
crystals are, with few exceptions, euhedral. Most grains have melt inclusions, though
considerably fewer than found in plagioclase. The clinopyroxene crystals are slightly smaller
than plagioclase, in the region of 0.2-1.0 mm. Also, it is common to find plagioclase that has
grown around clinopyroxene, implying that the main phase of plagioclase growth occurred
after clinopyroxene crystallization, the two mineral phases may thus possibly record different
levels of magma storage and crystallisation.
The overall composition of pyroxenes, in terms of the endmember mineral components as
defined by (Morimoto et al., 1988), is plotted in Fig. 17. It is apparent that all the
Figure 16. Composition of all analyzed plagioclase crystals (n=121).
Composition of plagioclase varies between An45 and An80.
19
clinopyroxenes belong to the same compositional family. Therefore, the average composition
of each individual clinopyroxene grain was calculated, which will be used in the
thermobarometric model calculations. Note also that the core-rim variations are minor and
unsystematic, though a tendency of normal zoning towards slightly Fe-richer rims is often
observed. However, the opposite has also been found in a few grains. This would indicate that
the clinopyroxenes are close to equilibrium with the basaltic-andesite host rock. Interestingly,
Camus et al. (1987) noted that the variation in composition of the clinopyroxenes found in the
1981 acid-andesites relative to the ones in the earlier basaltic-andesites does not differ
significantly, implying a common source region for the clinopyroxenes, despite the
differences in bulk chemistry between the eruptions. Moreover, in terms of major elements,
the composition of the recent (1990-2002) and the old (1883-1981) clinopyroxenes is very
similar. There is, however, one notable distinction between the two, namely the Na2O
component. The clinopyroxenes from the recent eruptions have Na2O contents of 0.20 ± 0.06
(n=152, range = 0.042-0.40, 1 std), which contrasts the older clinopyroxenes that fall between
0.31-0.50 % (n=15). Although
Na2O is a minor component in
clinopyroxene, this is an
interesting distinction, as the
jadeite (NaAlSi2O6) component
of clinopyroxene is supposed to
increase (under equilibrium)
with increasing pressure under
which the melt has crystallised
(Putirka et al., 1996; 2003;
Putirka, 2008). This implies that
the older rocks may have formed
at a deeper level than the recent
ones.
7.3 Olivine
Olivine is rather uncommon (<1 wt. %) and has not been identified in all thin sections. The
olivines found are very small, with diameters in the order of 0.02 to 0.15 mm, and are best
Figure 17. Composition of clinopyroxenes (filled circles, n=168) and
orthopyroxenes (open circles, n=26). The clinopyroxene dataset
include composition of minerals analyzed for this study (n=153) and
older clinopyroxenes (n=15) reported in the literature (Camus et al.,
1987; Mandeville et al., 1996a). All clinopyroxenes plot in a narrow
region in the augite field, implying a common source. The
composition of the orthopyroxenes found in the groundmass (n=26)
is slightly more heterogeneous, spreading over the enstatite and
pigeonite fields.
20
identified using electron backscatter images and EPMA analyses. All olivines observed are
anhedral (resorbed), frequently with rims covered by over-growths of orthopyroxene and
occasional titanomagnetite (Appendix A, image 11). There is a gradual normal zoning in all
the olivines investigated towards more Fe-rich rims. Forsterite content is in the range of Fo63-
80, with most olivine rims below Fo69.
7.4 Groundmass
The groundmass consists of 35% glass, 40% microcrystalline laths of plagioclase, 20%
orthopyroxene and 5% opaque phases, as determined by point counting on high magnification
electron backscatter images (7 images, 88 points each). The glass is dark brown to black, and
not transparent under plain-polarized light. The plagioclase in the groundmass, present as
anhedral laths and needles (An59-68), is chemically very similar to the larger plagioclase
phenocrysts. The orthopyroxenes occur in two modes: as a discontinuous phase on the rims of
partly resorbed olivine, and as microcrysts in the groundmass. No clinopyroxene has been
identified in the groundmass. Only four EPMA analyses were performed on the opaque
phases, all of which were identified as titanomagnetite. Although this is a small number of
analyses, our data coincide with the findings of Camus et al. (1987), who identified
titanomagnetite as the only opaque phase in basaltic-andesites from Anak.
21
8. Estimates of bedrock density and pre-eruptive volatile content
The H2O content is a very influential parameter in a number of the thermobarometers that will
be used. The pre-eruptive volatile content of a rock can be approximated from the mass
deficiency in EPMA analyses of groundmass glass and melt inclusions („the difference
method‟), as described in Devine et al. (1995), provided that the volatiles make up >1%. The
mass deficiency in the glass inclusions ranges from 1.2 % to 4.9 % (average = 2.4 %).
However, the precision of estimating volatile concentrations using the difference method is
not very high, reported to be ±0.5 % (Devine et al., 1995). Mandeville et al. (1996a) estimated
the pre-eruptive volatile content in the 1883 eruptive products to be 4 ± 0.5 wt. %. Due to the
enrichment of H2O in magmas during fractional crystallisation, it would be reasonable to
assume that the water content in the recently erupted basaltic-andesites are lower than in the
considerably more felsic magma of the 1883 eruption. Therefore, the pre-eruptive H2O
content will be approximated to be in the range of 2 to 4 wt. % for the thermobarometric
calculations to follow. Furthermore, for the reasons stated above, the higher end of that range
(3-4 wt. %) will be considered for basaltic-andesite bulk rock compositions, while the lower
end (2 to 3 wt. %) will be considered for basaltic bulk compositions. Note that the H2O
estimates henceforth will be labeled as XH2O, were X is the estimate in weight percent.
For the conversion of pressure estimates (kbar) to depth (km), the approximate densities of
the respective stratigraphic units below Krakatau need to be established. In the seismic study
by Kopp et al. (2001), a seismic line over the Java trench, ending just ~10 km south of
Krakatau, was investigated. The stratigraphy proposed for the area close to the Krakatau
complex by Kopp et al. (2001) will be used as density constraint applicable for the bedrock
directly below Krakatau also (table 1). In Kopp et al. (2001), two different densities are
suggested for different parts of the sedimentary succession, 2.23 and 2.4 g cm-3
, respectively.
For our purpose, an average of the two will be used.
Table 1. Densities of country rock below Anak Krakatau.
Inferred rock types Depth
(km)
Density (g cm-3
)
Sedimentary succession 0-4 2.32
Granitoids 4-9 2.8
Diorite/gabbro 9-22 2.95
Mantle >22 3.37
22
9. Method
The available rock forming mineral phases in the rocks are, plagioclase > clinopyroxene >
orthopyroxene > titanomagnetite > olivine. This allows the use of a number of igneous
thermometers and barometers. The focus will be on the clinopyroxene-melt thermobarometry
(Putirka et al., 1996; 2003; Putirka, 2008) and plagioclase-melt thermobarometry (Putirka,
2005) but will be complemented by other appropriate methods outlined below.
9.1 Clinopyroxene-melt thermo-barometers
Two models based on clinopyroxene-melt equilibria have been applied. The first and most
established model is a thermobarometer developed by Putirka et al. (1996), and later
calibrated for a wider selection of compositions and P-T conditions (Putirka, 1999; Putirka et
al., 2003), including the application to hydrous magmas. This clinopyroxene-melt
thermobarometer is an experimental regression model based on the jadeite-
diopside/hedenbergite exchange equilibria between clinopyroxene and co-existing melt. The
model has proved to be able to recreate P-T conditions for a wide range of magma
compositions, within a reasonable margin of error, and has been widely used in the last
decade (Shaw & Klügel, 2002; Putirka & Condit, 2003; Schwarz et al., 2004; Caprarelli &
Riedel, 2005; Klügel et al., 2005; Galipp et al., 2006; Mordick & Glazner, 2006; Longpré et
al., 2008; Barker et al., 2009). The Putirka et al. (2003) thermobarometer will henceforth be
termed PTB03. The standard errors of estimate (SEE) for PTB03 are ± 33 °C and ± 1.7 kbar
(Putirka et al., 2003). The second clinopyroxene-melt model to be used for comparison is a
barometer based on the Al partitioning between melt and clinopyroxene, and was recently
presented by Putirka (2008, eqn. 32c). That model is noteworthy as it is especially calibrated
for hydrous systems, requiring the input of a specific H2O estimate. This model will be named
PTB08. PTB08 also requires the input of a temperature estimate, which will be provided by
the PTB03 model. Note that PTB08 is not as firmly tested as PTB03, and is thus not
considered quite as reliable, even though the reported SEE of ±1.5 kbar (Putirka, 2008) is
even better than for PTB03. As PTB03 and PTB08 are based on different clinopyroxene-melt
exchange equilibria (Na and Al, respectively), any overlap of the two models would strongly
imply that the results are reliable.
23
Both PTB03 and PTB08 require the input of a mineral composition data and that of a co-
existing melt. The importance of finding a suitable nominal melt, representing the equilibrium
conditions of clinopyroxene formation, needs to be stressed, as it is the single largest source
of error in mineral-melt equilibria models. This is especially true as there is no definite right
or wrong when it comes to choosing a nominal melt, meaning that testing whether the
nominal melt of choice represents an equilibrium melt is exceedingly important. Tests of
equilibrium are often performed (Klügel & Klein, 2005; Longpré et al., 2008; Barker et al.,
2009) using the Fe-Mg exchange coefficients, Kd[FeMg], between clinopyroxene and liquid
(Duke, 1976). The Kd[FeMg] expected for a clinopyroxene-melt system in equilibrium would
be 0.28 ± 0.08 (Putirka, 2008), and clinopyroxene-melt pairs that fall outside these boundaries
will not be considered. As a further equilibrium test, it is useful to take into account the
exchange equilibria of other components, such as Na-Al and Ca-Al, as initially suggested by
Rhodes et al. (1979) and later expanded on by Putirka (1999). The Putirka (1999) model
predicts the relative amounts of different clinopyroxene mineral components that would
crystallize from a given nominal melt at the estimated P-T conditions. The predicted mineral
components (PMC) can then be compared to the observed mineral components (OMC). If the
clinopyroxene and melt compositions are approaching an equilibrium pair, the PMC should
closely match the OMC. Here, the focus will be on the dioipside+hedenbergite component
(DiHd), as it is the main component of the analysed clinopyroxenes, and it will provide a
good complement to the other equilibrium tests that will be performed (Putirka, personal
communication Aug. 2009).
9.2 Clinopyroxene barometers
To test the results of the Putirka clinopyroxene-melt thermobarometry (PTB03 and PTB08), a
clinopyroxene barometer not requiring the input of a coexisting melt would be ideal. The
clinopyroxene composition barometer developed by Nimis (1995; 1999) and Nimis & Ulmer
(1998) is widely used, despite having a tendency of systematically underestimating pressures
when applied on hydrous systems (Putirka, 2008). To eliminate the systematic error, this
barometer was re-calibrated for hydrous systems by Putirka (2008, eqn. 32b), with the added
requirement of an H2O estimate in addition to the temperature estimate already needed. This
barometer will be called NimCal08. The SEE for NimCal08 is at 2.6 kbar (Putirka, 2008).
24
9.3 Plagioclase-melt thermobarometers
Plagioclase-melt thermobarometry has been one of the preferred methods for petrologists to
estimate pressures and temperatures of igneous systems, likely due to the abundance of
plagioclase phenocryst in igneous rocks of varying composition and tectonic setting. Since the
first thermometer was formulated (Kudo & and Weill, 1970), the approach has been
developed further by various authors and a geobarometer has been incorporated (Housh &
Luhr, 1991; Sugawara, 2001; Ghiorso et al., 2002; Putirka, 2005; Putirka, 2008). Putirka
(2005) calibrated the plagioclase-melt thermobarometer for hydrous systems, requiring the
input of a H2O estimate in the modelling calculations. The thermometer in Putirka (2005) was
later improved slightly (Putirka, 2008, eqn. 24a). Despite all this, the accuracy of plagioclase-
melt geobarometry remains underwhelming, reproducing pressures within <3 kbar in most
cases and, occasionally and apparently randomly, produces very poor results from some data
sets. SEE for the plagioclase-melt thermometer is ± 36 °C and ± 2.47 kbar (Putirka, 2008).
The results of the plagioclase-melt thermobarometer will therefore be evaluated in reference
to the findings of Gardner et al. (in review, J. Petrol.), who argue for shallow crustal
plagioclase growth in the Anak magma plumbing system.
The recommended equilibrium test for plagioclase-melt thermobarometry uses the ratio of
the partitioning coefficients of the anorthite and albite components, Kd[An-Ab]. This is
expected to be 0.10 ± 0.05 at low temperatures (T < 1050 °C), or 0.27 ± 0.11 at high
temperatures (T > 1050 °C) (Putirka, 2008). Due to the highly variable composition, only the
plagioclase datapoints closest to equilibrium with the selected nominal melt will be
considered reliable. As a further test for equilibrium, the temperature estimate will be
compared to a plagioclase saturation surface temperature calculated for the nominal melt
(Putirka, 2008, eqn. 26). The plagioclase saturation surface temperature would be the lowest
possible temperature for the nominal melt before plagioclase would start crystallizing. A close
match between the temperature estimates of the plagioclase-melt and plagioclase saturation
thermometers is expected for equilibrium conditions (Putirka, 2008).
9.4 Olivine-melt thermometers
Olivine-melt thermometers (Beattie 1993; Putirka 2007, eqn. 4) will also be tested on the few
olivines found. To test for olivine-melt equilibrium, the test proposed by Roeder and Emslie
25
(1970) has been used, where the partitioning coefficient of Fe and Mg between olivine and
liquid (Kd[FeMg]) should approach 0.30 ± 0.03. Though this value has since been shown to
vary with pressure and silica- and alkali-content, it remains generally valid at pressures below
20 to 30 kbar (Putirka, 2008). As reported by Putirka (2008), the two models that most
successfully manage to recreate temperatures for olivine-melt equilibria are the Beattie (1993)
and Putirka (2007, eqn. 4) models, henceforth labeled BO93 and PO07, respectively. Though
BO93 is the overall more successful olivine-melt thermometer, it has a tendency of
systematically overestimating temperatures for hydrous systems, a problem the PO07
thermometer is calibrated to avoid (Putirka et al., 2007; Putirka, 2008). PO07 may therefore
be considered the most suitable model (Putirka, 2008). The SEE of PO07 is ± 29 °C (Putirka,
2008). In this study, the main reason for employing olivine-melt thermometry is to provide an
independent test for the reliability of the clinopyroxene-melt thermobarometry. The
temperature estimates from clinopyroxene-melt and olivine-melt thermometry will be
compared and a close match would indicate a high reliability of the results (Longpré et al.,
2008; Putirka, personal communication Aug. 2009). This approach assumes that the
clinopyroxenes and olivines are coeval, and will only be applicable if both clinopyroxene and
olivine perform adequate equilibrium tests using the same nominal melt.
26
10. Results
In this section, the results of the thermobarometric models described above are presented. .
The methods employed are a.) clinopyroxene-melt thermo-barometry (Putirka et al., 2003;
Putirka, 2008) b.) clinopyroxene composition barometry (Nimis & and Ulmer, 1998; Nimis,
1999; Putirka, 2008) c.) plagioclase-melt thermo-barometry (Putirka, 2005) and d.) olivine-
melt thermometry (Putirka et al., 2007). The clinopyroxene-melt thermobarometry (PTB03
and PTB08) as well as the plagioclase-melt thermobarometry is considered most reliable
(Putirka, 2008). The other models mentioned will mainly be used for reference, as overlap in
results between different models is a very strong indication of reliable results.
10.1 Pressures and temperatures from clinopyroxene-melt
thermobarometry
The first, and arguably most important
step, when employing a mineral-melt
equilibrium model is to find a suitable
nominal melt. As mentioned above, the
clinopyroxenes exhibit no obvious signs of
being out of equilibrium with the host melt,
as they are euhedral and lack any major
compositional zoning. However, euhedral
habitus and the lack of zoning does not by
itself verify that the clinopyroxene was in
equilibrium with the host melt, especially
considering the sluggishness of
clinopyroxene re-equilibration, that is on the
order of months to years for a 5-10µm rim
(Cashman, 1990), and the rather short repose
time at Anak Krakatau volcano, often with tens of smaller eruptions during a single year.
The most commonly used nominal melts are: a.) bulk rock composition (Caprarelli &
Riedel, 2005; Putirka & Condit, 2003; Putirka et al., 2003) and b.) groundmass or groundmass
glass (Shaw & Klügel, 2002; Klügel et al., 2005; Longpré et al., 2008). In
Figure 18. Test for equilibrium using the Kd[FeMg]
between clinopyroxene and melt. The 1963 basalt and
2002 bulk rock both result in Kd[FeMg] values close to
the ideal of 0.28 (Putirka, 2008), and are selected as the
two viable nominal melt options.
60
65
70
75
80
0 20 40 60
10
0xM
g# c
px
100xMg# melt
1963 Basalt
Melt inclusions
2002 bulk rock
Groundmass
Glass
Out of equilibrium Out of equilibrium
27
addition to these options, two
more nominal melts will be
evaluated here. These are melt
inclusions (in plagioclase and
clinopyroxene) and a more
primitive bulk rock from a lava
flow from the eruptive period
1960-1963 (henceforth labeled
1963 basalt) reported in Zen and
Hadikusumo (1964). In Fig. 18,
the Kd[FeMg] of the five
nominal melt options outlined
above are compared. It is
apparent that groundmass and
glass are far from equilibrium
conditions with the
clinopyroxene.
Of the remaining three
options, the 1963 basalt and the
bulk rock fit well within the
expected boundaries, while
inclusions appear to be only
slightly out of equilibrium. In
Fig. 19, the observed and
predicted DiHd components are
plotted, using the (a) 1963 basalt
and (b) 2002 bulk rock. Both
result in a very good match. It is
thus not possible, using only
these methods, to determine whether the 1963 basalt or 2002 bulk rock is the better nominal
melt. Both of those nominal melts will be used therefore, resulting in six sets of P-T estimates
using the PTB03 and PTB08 models with different input of nominal melts and H2O estimates.
The results of these model calculations are summarised in Fig. 20a-b. The average P estimate
of -0.57 kbar (range = -1.81 to 0.43) gained from PTB03 using the 2002 bulk rock as nominal
Figure 19. The predicted vs. observed mineral components of
diopside+hedenbergite, using nominal melts (a) 1963 basalt and (b)
2002 bulk rock. Both nominal melts result in very similar results, in
terms of predicted mineral compositions, indicating that both need
to be considered viable nominal melts. Clinopyroxenes analyzed for
this thesis and older clinopyroxenes (erupted 1883-1981) are
represented by black and red circles respectively.
0,60 0,80 1,00
Ob
se
rve
d c
px C
om
po
ne
nts
Predicted px Components
Nominal melt: 2002 bulk rock
0,60 0,70 0,80 0,90 1,00
Ob
se
rve
d c
px C
om
po
ne
nts
Predicted cpx Components
Nominal melt: 1963 basalt
28
melt is an impossible result. Also, using the 2002 bulk rock as nominal melt, there is no
overlap of the results from the PTB03 and PTB08 calibrations. This indicate that the 2002
bulk rock is not suitable as a nominal melt composition from which the clinopyroxene has
crystallized, and will therefore not be considered further. The three sets of calculated
pressures using the 1963 basalt as nominal melt are in a narrow range (0.59 to 3.77 kbar) with
a high degree of overlap between PTB03 and PTB08 results. PTB03 and PTB08 were also
employed using representative clinopyroxene compositions reported in the literature (Camus
et al., 1987; Mandeville et al., 1996a). These clinopyroxenes come from rocks erupted
between 1883 and 1981. The results of the old clinopyroxenes are plotted in Fig. 20c,
spreading over a much larger P-T interval, and the majority of them record higher pressures
and temperatures as compared to the more recent ones. This indicates that the bulk of the
clinopyroxenes prior to the acidic-andesite eruption of 1981 crystallized at a greater depth
compared to the recently erupted clinopyroxenes. Note that the old clinopyroxenes did not
perform quite as well in the equilibrium test as the more recent clinopyroxenes. However, the
difference in this equilibrium test between old and recent clinopyroxenes is very slight, and all
datapoints are within the allowed 5% deviation. All results of clinopyroxene-melt
thermobarometry, using the 1963 basalt as nominal melt, are reported in table 2.
Figure 20. Results of PTB03 (filled circles) and PTB08
using 2H2O (filled triangles) and 3H2O (open triangles).
Recent and old clinopyroxenes are displayed in black
symbols and red symbols respectively, Note that, when
using the 1963 basalt (a), results of the PTB03 and PTB08
models are overlapping. The 2002 bulk rock (b) does not
produce an overlap. This is a strong indication that the
1963 basalt is the most suitable nominal melt. The
pressures and temperatures calculated for the old
clinopyroxenes (c) are consistently higher than for the
recent clinopyroxenes. SEE for PTB03 are ± 33 °C and ±
1.7 kbar. SEE for PTB08 is ± 1.5 kbar
0
1
2
3
4
5
1090 1100 1110 1120 1130
P (
kb
ar)
T (° C)
(a)
Nominal melt:1963 basalt
0
1
2
3
4
5
6
7
8
1100 1120 1140 1160
P (
kb
ar)
T (° C)
(c)
Nominal melt:1963 basalt
-2
-1
0
1
2
3
4
5
1080 1090 1100 1110 1120
P (
kb
ar)
T (°C)
(b)
Nominal melt:2002 bulk rock
29
10.2 Pressure estimates from clinopyroxene barometry
The NimCal08 barometer (Putirka, 2008, eqn. 32b), using temperature estimates calculated
using the PTB03 model, yields pressures slightly lower than the PTB03 and PTB08 models.
Estimates of 2H2O and 3H2O result in average pressures of 1.03 kbar (-0.57 to 2.14) and 1.48
kbar (-0.11 to 2.59) respectively. As mentioned above, this model is not deemed very precise
nor accurate, with a tendency of systematically underestimating pressure (Putirka, 2008).
Despite this, the overall overlap with model results from PTB03 and PTB08 lends further
credence to these results. The results of the NimCal08 barometer is plotted in Fig. 21, and
table 2, for comparison with the PTB03 and PTB08 models.
Figure 21. Results of the
NimCal08 barometer.
Results using 2H2O and
3H2O are represented by
filled and open squares
respectively. The partial
overlap with results from
the PTB03 and PTB08
models lends further
credence to these results.
SEE for NimCal08 is at
2.6 kbar.
Table 2. Clinopyroxene-melt thermobarometry and clinopyroxene barometry.
Model Nominal
melt
XH2O (%) Recent clinopyroxenes
(1990-2002)
Old clinopyroxenes
(1883-1981)
P (kbar) T (°C) P (kbar) T (°C)
PTB03 1963 basalt N/A 2.74
(1.46 to 3.77) 1116
(1102 to 1123)
4.85
(2.64 to 7.52)
1131
(1113 to 1154)
PTB08 1963 basalt 2 1.92
(0.59 to 2.83)
N/A 2.78
(1.15 to 5.61)
N/A
3 2.59
(1.26 to 3.50)
3.45
(1.82 to 6.28)
NimCal08 N/A 2 1.03
(-0.57 to 2.14)
N/A 2.41
(-1.72 to 5.66)
N/A
3 1.48
(-0.11 to 2.59)
2.86
(-1.27 to 6.11)
-1
0
1
2
3
1100 1110 1120 1130
P (
kb
ar)
T (°C)
30
10.3 Pressures and temperatures from plagioclase-melt
thermobarometry
Of all the potential nominal
melts, the 2002 bulk rock
performed best in the Kd[ab-an]
equilibrium test with the
plagioclase (Fig. 22), with the
majority of the datapoints falling
within the field of equilibrium.
The plagioclase-melt pairs
outside the field of equilibrium
will not be considered for the
model calculations. However, at
>3.5H2O the temperature
estimates calculated are all below
1050, requiring equilibrium
conditions of Kd[Ab-An] that
differ from 0.27 ± 0.11 (Putirka,
2008), i.e. the plagioclase is not in equilibrium with the bulk rock at >3.5H2O. This effectively
constrains pre-eruptive H2O content in the basaltic-andesite to ≤3.5H2O. A further indication
that the 2002 bulk rock is a suitable nominal melt for plagioclase-melt thermobarometry is the
fact that the plagioclase saturation surface temperatures calculated are only on average ~10 °C
higher than the temperature estimated using the plagioclase-melt thermometer. The results of
plagioclase-melt thermobarometry, using 2002 bulk rock, 3H2O and 3.5H2O, is displayed in
table 3 and Fig. 23. Note that there is no systematic difference between P-T estimates for
plagioclase cores and rims. However, there is a strong correlation with An content and P-T
estimates. High An contents, resulting in low Kd[An-Ab], correspond to low pressure
estimates and vice versa. Plagioclase with medium An content appears to be closest to
equilibrium with the bulk rock, with a range of An62-68 yielding Kd[An-Ab] values very close
to the ideal of 0.27 (0.24-0.30) determined by Putirka (2008). These “best fit” plagioclases
result in a very tight range of temperature and pressure estimates, where T = 1065 to 1071 °C
Figure 22. Equilibrium test for plagioclase and three nominal melt
options. The 2002 bulk rock result in the best fit, and will be used
in the plagioclase-melt thermobarometry.
0
10
20
30
40
50
0 5 10 15
1000 x
An
x A
b l
iq
1000 x Ab x An liq
2002 Bulk rock
Groundmass
1963 Basalt
31
and P = 1.24 to 1.81 kbar (assuming 3H2O), or 1049 to 1055 °C and 0.72 to 1.24 kbar
(assuming 3.5H2O). These two sets of P-T estimates are considered the most reliable.
Table 3. Results from plagioclase-melt thermobarometry.
T (°C) Saturation surface
T (°C)
P (kbar)
Kd[An-Ab] =
0.16-0.38
P (kbar)
Kd[An-Ab] =
0.24-0.30
Nominal melt XH2O (%)
1051
(1044 to 1060)
1061 1.06 (0.33 to 1.75) 1.01 (0.72 to 1.24) 2002 Bulk rock 3.5
1067
(1059 to 1076)
1076 1.61 (0.80 to 2.35) 1.56 (1.24 to 1.81) 2002 Bulk rock 3
10.4 Temperature estimates from olivine-melt thermometry
As the olivine phase is clearly not stable in the basaltic-andesite host rock, neither bulk
rock chemistry nor groundmass can be considered as feasible nominal melts for olivine-
melt thermometry. However, the more primitive bulk rock of the 1963 basalt seems to
better represent the magma that gave rise to initial olivine crystallization. Three bulk rock
compositions from the 1963 lava flow (Zen & Hadikusumo, 1964) will be compared:
analysis No. 4, 5, and an average of the two. Analysis No 5 has the highest magnesium
Figure 23. Results of plagioclase-
melt thermobarometry, using
3.5H2O (red triangles) and 3H2O
(blue circles). Only the
plagioclase compositions closest
to equilibrium with the 2002 bulk
rock have been used in this plot.
The dotted lines indicate the
respective estimated saturation
surface temperatures (Putirka,
2008), very close to the calculated
temperatures. Note also that
there is no systematic difference
between P-T estimates for
plagioclase cores and rims. SEE
for the plagioclase-melt
thermobarometer are ± 36 °C
and ± 2.47 kbar
0
0,5
1
1,5
2
1040 1050 1060 1070 1080
P (
kb
ar)
T (° C)
3H2O
3.5H2O
32
number of the three. Using the Kd[FeMg] of Roeder and Emslie (1970) as discriminant,
the olivines are divided into three classes by being close to equilibrium with the three
different bulk rocks (Fig. 24). The Forsterite content of these three classes would be Fo75-
76, Fo70-72 and Fo69-67. Note that olivines above Fo77 and below Fo67 are out of equilibrium
with all nominal melts tested, and are thus discarded. This results in three sets of
temperatures (see table 4) in the range of 1106 to 1153 °C. The results, and a comparison
with the temperatures estimated for clinopyroxene using PTB03, are plotted in Fig. 25.
Note that the temperatures estimated for olivine are overlapping with temperatures
estimated for clinopyroxene, suggesting that the olivine-melt and clinopyroxene-melt
models are consistent with each other (Longpré et al., 2008; Putirka, personal
communication Aug. 2009).
Figure 24. Test for olivine-
melt equilibrium. The
olivines are divided into
three compositional groups
based on their forsterite
content and which nominal
melt produces the best fit.
Note that the average bulk
composition was used as
nominal melt in the PTB03
model.
60
65
70
75
80
35 40 45 50 55
10
0xM
g#
Oliv
ine
100xMg# Liquid
1963 basalt (no:4)
1963 basalt (average)
1963 basalt (no:5)
outside equilibrium
outside equilibrium
33
Table 4. Results of olivine-melt thermometry
Figure 25. Results of
olivine-melt
thermobarometry. The
overlap of temperatures
estimated for olivine
(PO07) and clinopyroxene
(PTB03) is a strong
indication that the results
are reasonable. The SEE
for PO07 is at ± 29 °C.
Model T (°C) Fo75-76 T (°C) Fo70-72 T (°C) Fo67-69
PO07 1153 (1152 to 1153) 1131 (1127 to 1139) 1110 (1106 to 1112)
1090
1100
1110
1120
1130
1140
1150
1160T
(°C
)
Olivine composition
Fo76-75 Fo72-70 Fo69-67
cpx temperature(PTB03)
34
11. Discussion
The clinopyroxene-melt and plagioclase-melt thermobarometry resulted in two distinct sets
of P-T estimates with very little overlap, indicative of two distinct magma crystallisation
(storage) regions. In Fig. 26, the results from plagioclase-melt and clinopyroxene-melt
barometry are displayed as histograms, with the pressure estimates converted to depth. It is
evident that the calculated depths of plagioclase and clinopyroxene crystallization are focused
to in the region of 4-6 and 8-12 km respectively. Fig. 27 combines all results from
clinopyroxene-melt and plagioclase-melt barometry in one plot.
The depths calculated for plagioclase crystallization (4-6 km) fit well with previously
calculated depths as well as evidence from crystal isotope stratigraphy (Camus et al., 1987;
Mandeville et al., 1996a; Gardner et al., in review, J. Petrol.). In turn, the zone of
clinopyroxene crystallization (8-12 km) coincide very well with the findings of Harjono et al.
(1989), identifying a magma chamber system at a depth of ~9 km, with an unknown vertical
extension. These contrasting depths calculated for plagioclase and clinopyroxene
crystallization are not contradictory, as plagioclase should represent a later stage of
crystallization than clinopyroxene, but rather it indicates a shallow and a deeper magma
storage region. Also, a lack of seismic attenuation zones at depths less than 9 km does not
exclude shallower magma storage. A diffuse zone of small pockets of magma, e.g. as
discussed in Gardner et al. (in review, J. Petrol.) would likely be outside the detection limit of
the micro-seismic study of Harjono et al. (1989).
In this study, no strong evidence of the very deep storage zone (>22 km), detected by
Harjono et al. (1989), has been found. This implies that crystalline phases potentially formed
in the deep storage region very rarely survive ascent and crustal storage, due to resorption in
the progressively evolving melts, or remain in deep seated cumulates. A few of the old
clinopyroxenes analyzed, however, do record depths of crystallization greater than 18 km (fig.
20, 26, 27 and table 5), implying that they might have formed in this very deep storage region.
Therefore, there are strong lines of thermobarometric, geophysical and isotopic evidence
for up to three distinct magma storage regions below Anak, at depths of approximately 4-6
and 8-12 km plus a probable very deep storage region at ≥22 km, as discussed in Harjono et
al. (1989). These three zones fit remarkably well with the three lithological boundaries (Fig.
10) inferred for the bedrock below Anak Krakatau, based on evidence from drill holes,
xenoliths and micro-seismic studies. Additionally, there are indications of a shallowing of the
35
plumbing system over recent years (fig. 20, 26, 27 and table 5), with respect to clinopyroxene
crystallization.
Key factors controlling the ascent of silicate magmas may be a.) fractures, states of stress
and mechanical properties of the lithosphere, and b.) density contrasts between magma and
rock, where light density lithologies act as barriers for denser magma (Putirka et al., 2003, and
Figure 26. Calculated pressures from (a) plagioclase-melt
barometry, (b) PTB03 and PTB08 for recent
clinopyroxene, and (c) PTB03 and PTB08 for old
clinopyroxene. Plagioclase record depths of crystallisation
that considerably shallower than clinopyroxene, and pre-
1981 clinopyroxenes record deeper levels of crystallisation
than recent clinopyroxenes.
Figure 27. All results from clinopyroxene-melt and
plagioclase-melt barometry (fig. 26). The clinopyroxene
and plagioclase record distinctly different depths of
crystallisation with very little overlap. The old
clinopyroxene appear to have crystallised partly at
deeper levels, and are spread over a larger interval.
36
references therein). The bedrock beneath Anak is heavily fractured and faulted, which would
provide ample vertical pathways for magma ascent. Results of the mineral-melt
thermobarometry (this thesis) and geophysical investigations (Harjono et al., 1989), however,
strongly indicate that magma storage below Anak is chiefly controlled by discontinuities and
lateral lithological boundaries in the crust, where density contrasts between the different
lithologies plays an important role.
The magma evolution and plumbing system beneath Anak is thus envisaged in the
following manner:
1) Partial melting of the mantle wedge and transport of magma up to the mantle-lower
crust boundary, where magma ascent is halted due to the density contrast with the lower crust.
The initial melt composition may also, to some extent, be influenced by decompressional
melting, due to the extensional character of the Sunda Straits (Harjono et al., 1991). The
extent of the seismic attenuation zone (Fig. 11) detected by Harjono et al (1989) implies that
this storage region is large-scale and likely interconnected. This would, in part, account for
the semi-continuous supply and semi-homogenous character of the Anak basaltic-andesites.
Analogous to this would be the “deep crustal hot zones” proposed by e.g. Annen et al. (2006).
2) Ascent of basalt either when magma density has decreased to below that of the lower
crust (~2.95 g cm-3
), or when replenishment of fresh basalt and associated volatile release into
the magma chambers from below forces ascent to higher levels.
3) The ascending magma stalls at a mid-crustal level due to density contrast, at a depth of
~9 km, where crystallization of clinopyroxene takes place. The euhedral habitus and
homogenous composition of all observed and analyzed clinopyroxenes would indicate a
sizeable and stable storage region with a continuous supply of magma. The bulk composition
of the magma at this level is likely close to the evolved basalt documented in Zen &
Hadikusumo (1964), as indicated by clinopyroxene being in apparent equilibrium with this
bulk composition at the calculated thermodynamic conditions.
4) Again, ascent of magma is triggered by either evolving the magma towards a less dense,
basaltic-andesitic composition, with a magma density lower than that of the middle crust
(~2.75 g cm-3
), or when replenishment of fresh magma and associated release of gases from
below forces ascent.
5) At a depth of ~4 km, the magma ascent is stalled once more again, at a major
lithological boundary. The main phase of plagioclase crystallization takes place at this level.
The large compositional variation of plagioclase (An45-80), the sieve-like textures and complex
zoning patterns would suggest a highly dynamic magma system. The sieve-like textures, in
37
particular, could be an indication of rapid growth and/or dissolution, which in turn can be
related to events like magma mixing, replenishment, and assimilation of country rock (e.g.
Tepley et al., 1999; Troll et al., 2004). This shallow storage region is likely made up of a
plexus of more or less interconnected pockets of magma dispersed in the crust, as it was not
detected in the low resolution micro-seismic study of Harjono et al. (1989), but has been
detected by Gardner et al. (in review, J. Petrol.) using in situ (LA-ICPMS) 87
Sr/86
Sr analyses
on plagioclase to show sediment contamination in plagioclase growth zones. This storage
region is likely where the magma evolves to its final pre-eruptive composition (i.e. basaltic-
andesite) before being erupted, as indicated by plagioclase being close to equilibrium with
this bulk composition at the calculated thermodynamic conditions. See Fig. 28 for a schematic
illustration of the current magma plumbing system beneath Anak Krakatau.
Thermal preconditioning of the upper crust by mafic to intermediate magmas has been
suggested to be a major factor in the production of rhyolitic magmas in the Taupo Volcanic
Zone (Price et al., 2005). This petrogenic model could potentially be applicable to the
Figure 28. The magma
plumbing system at
Anak Krakatau. Three
magma storage regions
have been identified, of
which the upper two
have been verified by
thermobarometric
model calculations in
this study. Only the
mid-crustal storage
level (at ~8-12 km
depth) has been
detected by both
seismic and
thermobarometric
studies. Therefore,
combined geophysical
and petrological
surveys provide the
highest potential for the
thorough
characterization of
magma plumbing at
active volcanic
complexes.
38
Krakatau complex, considering its history of recurring major dacitic-rhyolitic eruptions with
intermittent periods of mafic-intermediate magmatism. In this model, a steep geothermal
gradient and continuous heating of the crust would eventually lead to large scale assimilation
of country rocks, as well as recycling of co-magmatic plutons and intrusives. The idea that the
uppermost magma storage region (~4-6 km) detected is made up of a plexus of magma
pockets, as discussed above, means that the surface-to-volume ratio of the magma volume
stored at that level is high, leading to an efficient heat transfer from magma to crust. The high
magma throughput at Anak Krakatau, evident in the average extrusive growth of 8 cm/week,
would further add to the efficient heating of the crust. In concert with these speculations, the
geothermal gradient in one of the 3 km deep wells, ~30 km south-southeast of Krakatau has
been estimated to be as high as 67 °C/km (Nishimura et al., 1986).
With the model proposed by Price et al. (2005) and the cyclicity of van Bemmelen (1949)
in mind, the shallowing of the plumbing system detected in this study could be an indication
that Krakatau is presently in the process of evolving towards a new major caldera forming
eruption.
Table 5. Calculated pressures converted to depth
Model Mineral phase Nominal melt XH2O
(%)
Time of eruption Depth (km)
PTB03 Clinopyroxene 1963 basalt N/A 1990-2002 10.59 (6.15 to 14.14)
1883-1981 17.85 (10.24 to 26.85)
PTB08 Clinopyroxene 1963 basalt 2 1990-2002 10.05 (5.45 to 13.20)
1883-1981 13.04 (7.39 to 22.78)
PTB08 Clinopyroxene 1963 basalt 3 1990-2002 7.70 (2.58 to 10.88)
1883-1981 10.73 (5.08 to 20.51)
Plagioclase-melt Plagioclase 2002 bulk rock 3 1990-2002 6.39 (5.22 to 7.26)
Plagioclase-melt Plagioclase 2002 bulk rock 3.5 1990-2002 4.35 (3.16 to 5.19)
Figure 29. The cyclicity of Krakatau, redrawn and modified from van Bemmelen (1949). The red hatched area
represents the inferred recent shallowing of the magma plumbing system.
39
12. Conclusions
Our results imply that clinopyroxene presently crystallizes in a mid-crustal storage region (8-
12 km), a magma storage region previously identified in the micro-seismic study by Harjono
et al. (1989). Plagioclase, in turn, form at shallower depths (4-6 km), very much in concert
with previous estimates based on plagioclase barometry and chlorine in fluid inclusions
(Camus et al., 1987; Mandeville et al., 1996a; Gardner et al., in review, J. Petrol.).
Clinopyroxenes erupted between 1981-1883 record deeper levels of storage, indicating that
there may have been a shallowing of the plumbing system over the last ~40 years. This study
demonstrates that petrology can detect magma bodies in the crust where seismic surveys fail
due to limitations in resolution, and vice versa in the case of the ~22 km system.
Consequently, a combination of geophysical and petrological surveys offers the highest
potential for a thorough characterization of magma plumbing at active volcanic complexes.
The magma storage regions detected beneath Krakatau coincide with major lithological
boundaries in the crust, implying that magma ascent at Anak is controlled by discontinuities
in the crust. This, in turn, indicates that density contrasts between magma and bedrock is an
important parameter controlling magma ascent at this particular volcanic complex. However,
the extensional character and heavily faulted bedrock in the Sunda Straits (Nishimura et al.,
1986), is likely fundamental in providing vertical pathways for magma to ascend, meaning
that other factors such as stratigraphy, play a significant role too.
The compelling evidence presented in this study of widespread and shallow magma storage
at this highly active volcano, coupled with the documented caldera forming eruptions at the
Krakatau complex in the recent past, means that continuous seismic and petrologic monitoring
of Anak Krakatau remain of utmost importance. This is especially true considering that
Indonesia today has the world‟s fourth largest population, with a much more densely
populated proximal area compared to that in 1883, when the latest major ignimbrite eruption
claimed 36,000 lives.
40
Acknowledgement
For the opportunity to work on this project, for all the discussions, counselling and for
providing endless inspiration, I would like to thank my supervisors Prof. Valentin R. Troll
and Dr. Ulf Bertil Andersson.
When working at the EPMA facilities at Uppsala University, I was greatly helped by
specialist technician Hans Harryson.
I would also like to thank Jane Chadwick, Mairi Gardner, Frances Deegan, Lara Blythe,
Abigail Barker, Peter Dahlin and Axel Andersson. You have all been of great help.
A heartfelt thanks goes to all the participants in the field trip to Java and Bali in 2008. You all
made the trip memorable.
Kristina, thank you for everything not geology.
The project was made possible by funding provided by Vetenskapsrådet, Uppsala University
and Otterborgs donationsfond.
41
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46
Appendix 1 – Chemical composition of analysed clinopyroxene phenocrysts
SiO2 TiO2 Al2O3 FeO MnO MgO CaO Na2O K2O Cr2O3 SUM
AK-LF 3-PX p1 51.94 0.47 1.56 9.66 0.75 15.06 20.06 0.32 0.00 0.00 99.80
AK-LF 3-PX 51.40 0.50 1.49 8.53 0.48 15.63 20.55 0.27 0.00 0.00 98.85
AK-LF 3-PX p3 51.37 0.70 1.89 9.14 0.34 15.62 20.09 0.30 0.00 0.00 99.44
AK-LF 3-PX p4 51.41 0.68 2.26 9.42 0.36 15.91 19.41 0.13 0.00 0.00 99.57
AK-LF 3-PX p5 51.34 0.64 2.16 8.96 0.33 15.54 19.54 0.17 0.00 0.00 98.68
AK-LF 3-PX p6 51.01 0.80 2.21 9.18 0.46 14.45 20.22 0.21 0.00 0.00 98.56
AK-LF 3-PX tr Pl>rim 51.70 0.64 2.05 9.75 0.31 15.28 19.84 0.27 0.01 0.00 99.85
AK-LF 3-PX tr Pl>rim 51.96 0.68 2.01 9.34 0.34 15.32 20.39 0.20 0.00 0.00 100.23
AK-LF 3-PX tr Pl>rim 51.67 0.58 1.93 9.23 0.36 15.84 19.99 0.29 0.00 0.00 99.89
AK-LF 3-PX tr Pl>rim 52.38 0.47 1.63 9.01 0.42 15.53 20.24 0.21 0.00 0.01 99.91
AK-LF 3-PX tr Pl>rim 51.21 0.66 2.26 9.93 0.54 14.71 20.30 0.23 0.00 0.01 99.84
AK-LF 3-PX tr Pl>rim 52.68 0.46 1.41 9.43 0.62 15.78 19.77 0.17 0.01 0.00 100.34
AK-LF 3-PX tr Pl>rim 52.86 0.45 1.14 9.22 0.59 15.90 19.83 0.09 0.00 0.00 100.08
AK-LF 3-PX tr Pl>rim 52.64 0.40 1.15 9.45 0.52 15.60 20.08 0.14 0.00 0.00 99.98
AK-LF 3-PX tr Pl>rim 52.67 0.45 1.28 9.52 0.59 15.59 19.77 0.18 0.00 0.00 100.05
AK-LF 3-PX tr Pl>rim 52.41 0.44 1.39 9.53 0.67 15.15 19.90 0.19 0.00 0.00 99.68
AK-LF 3-PX tr Pl>rim 52.04 0.43 1.36 9.07 0.60 15.60 20.43 0.17 0.00 0.00 99.70
AK-LF 3-PX tr Pl>rim 51.07 0.53 1.54 9.06 0.46 15.53 20.64 0.10 0.00 0.00 98.95
AK-LF 3-PX tr Pl>rim 51.39 0.57 1.75 8.60 0.44 15.87 20.38 0.23 0.00 0.01 99.25
AK-LF 3-PX tr Pl>rim 52.11 0.63 1.85 8.93 0.30 15.45 20.57 0.17 0.00 0.00 100.00
AK-LF 3-PX tr Pl>rim 51.74 0.57 1.70 10.08 0.36 15.83 18.93 0.22 0.01 0.00 99.44
AK-LF 3-PX tr Pl>rim 51.29 0.69 2.04 9.59 0.27 15.44 19.83 0.04 0.00 0.02 99.22
AK-LF 3-PX tr Pl>rim 51.53 0.61 1.87 9.50 0.35 15.55 19.90 0.20 0.01 0.00 99.52
AK-LF 3-PX tr Pl>rim 51.89 0.69 2.14 9.87 0.34 15.36 19.50 0.25 0.00 0.00 100.06
AK-LF 3-PX tr Pl>rim 52.18 0.55 1.63 10.93 0.34 16.50 17.82 0.09 0.00 0.00 100.04
AK-LF6-PX p11 52.32 0.65 2.04 9.71 0.34 15.40 19.93 0.26 0.00 0.01 100.66
AK-LF6-PX p12 51.01 0.80 3.15 9.92 0.26 15.30 19.55 0.17 0.00 0.00 100.15
AK-LF6-PX p13 52.02 0.66 1.93 9.45 0.32 15.59 20.01 0.18 0.02 0.00 100.18
AK-LF6-PX p14 52.16 0.68 2.16 9.60 0.35 15.62 19.91 0.21 0.00 0.00 100.68
AK-LF1-PX p16 51.61 0.64 2.06 9.71 0.33 15.46 20.13 0.20 0.00 0.03 100.17
AK-LF1-PX p17 52.31 0.63 2.09 9.11 0.31 15.32 20.47 0.20 0.00 0.01 100.45
AK-LF1-PX p18 51.43 0.69 2.17 9.44 0.27 15.40 20.30 0.22 0.00 0.00 99.92
AK-LF6-PX tr R-R 50.82 0.68 2.36 9.12 0.32 15.22 20.07 0.40 0.00 0.01 99.01
AK-LF6-PX tr R-R 51.55 0.86 2.71 9.33 0.41 15.78 19.81 0.27 0.00 0.00 100.72
AK-LF6-PX tr R-R 50.17 0.74 2.71 8.74 0.28 15.65 20.29 0.17 0.00 0.00 98.74
AK-LF6-PX tr R-R 50.26 0.65 2.59 8.42 0.29 15.67 20.63 0.21 0.00 0.00 98.72
AK-LF6-PX tr R-R 51.96 0.70 2.26 8.41 0.24 15.55 20.67 0.15 0.01 0.03 99.98
AK-LF6-PX tr R-R 52.47 0.59 1.89 8.51 0.47 16.02 20.42 0.19 0.00 0.00 100.56
AK-LF6-PX tr R-R 51.98 0.55 1.71 8.79 0.48 16.20 19.98 0.11 0.00 0.00 99.80
AK-LF6-PX tr R-R 51.65 0.61 2.11 8.78 0.35 15.78 20.39 0.21 0.00 0.00 99.89
AK-LF6-PX tr R-R 51.25 0.45 1.56 9.24 0.54 15.26 20.57 0.27 0.00 0.00 99.12
AK-LF6-PX tr R-R 51.66 0.65 2.08 9.79 0.29 15.67 20.03 0.18 0.00 0.00 100.35
47
AK-LF6-PX tr R-R 51.57 0.62 2.32 9.79 0.26 15.54 19.83 0.23 0.00 0.00 100.17
AK-LF6-PX tr R-R 51.09 0.37 1.31 9.18 0.57 15.23 20.35 0.08 0.00 0.00 98.19
AK-LF6-PX tr R-R 52.78 0.41 1.33 8.49 0.41 15.65 20.91 0.17 0.00 0.00 100.15
AK-LF6-PX tr R-R 51.62 0.73 2.71 8.30 0.25 15.16 20.92 0.17 0.00 0.00 99.86
AK-LF6-PX tr R-R 52.15 0.65 2.24 8.73 0.26 15.31 20.28 0.23 0.02 0.00 99.86
AK-LF6-PX tr R-R 51.28 0.60 2.04 8.90 0.36 15.12 20.49 0.11 0.00 0.00 98.89
AK-LF6-PX tr R-R 51.84 0.66 2.26 9.27 0.27 15.21 19.97 0.13 0.00 0.00 99.62
AK-LF6-PX tr R-R 51.22 0.71 2.55 9.45 0.30 15.52 19.92 0.14 0.00 0.00 99.82
AK-LF6-PX tr R-R 51.36 0.75 2.22 10.56 0.32 16.11 18.30 0.06 0.06 0.01 99.76
AK-LF6-PX tr R-R 51.21 0.79 2.30 10.24 0.40 15.25 19.26 0.10 0.00 0.00 99.56
AK-LF6-PX tr R-R 51.72 0.79 2.42 10.49 0.32 15.21 19.01 0.20 0.00 0.03 100.19
AK-LF6-PX tr R-R 51.74 0.68 2.02 9.27 0.29 15.25 20.14 0.23 0.00 0.02 99.64
AK-LF6-PX tr R-R 51.55 0.60 1.86 9.44 0.45 14.99 20.16 0.29 0.00 0.00 99.34
AK-LF6-PX tr R-R 51.14 0.64 2.28 9.58 0.28 15.33 19.79 0.24 0.00 0.00 99.27
AK-LF6-PX tr R-R 52.13 0.64 2.21 9.62 0.26 15.37 19.88 0.11 0.00 0.00 100.21
AK-LF6-PX tr R-R 52.04 0.65 2.21 10.00 0.30 15.57 19.92 0.25 0.00 0.00 100.95
AK-LF6-PX tr R-R 52.13 0.65 2.19 9.90 0.34 15.37 19.73 0.21 0.00 0.00 100.52
AK-LF6-PX tr R-R 52.16 0.64 2.11 9.60 0.36 15.71 19.91 0.15 0.00 0.00 100.65
AK-LF6-PX tr R-R 52.15 0.64 2.02 9.59 0.41 15.38 20.44 0.22 0.00 0.01 100.86
AK-LF6-PX tr R-R 51.34 0.60 2.10 9.43 0.53 14.97 20.36 0.32 0.00 0.00 99.65
AK-LF6-PX tr R-R 51.33 0.81 2.44 9.79 0.37 14.77 19.94 0.24 0.00 0.00 99.68
AK-LF6-PX tr R-R 50.62 0.74 2.79 9.26 0.29 15.42 20.28 0.19 0.00 0.01 99.61
2_AK14px p1 50.71 0.73 2.70 9.24 0.36 15.57 19.96 0.23 0.00 0.03 99.53
2_AK14px p2 50.88 0.75 2.49 10.05 0.34 15.83 18.95 0.27 0.00 0.01 99.56
2_AK14px p5 50.52 0.70 2.30 9.22 0.29 15.57 20.10 0.16 0.00 0.02 98.91
2_AK12px p8 51.74 0.65 2.34 8.68 0.34 15.33 20.53 0.25 0.00 0.02 99.88
2_AK12px p9 51.15 0.66 2.08 9.24 0.30 14.93 19.78 0.21 0.00 0.04 98.38
2_AK12px p10 51.53 0.68 2.20 9.60 0.27 15.16 19.65 0.24 0.00 0.00 99.32
2_AK12px p13 50.75 0.83 3.09 8.58 0.29 15.07 20.30 0.28 0.00 0.00 99.18
2AK14px tr1 49.92 0.83 3.08 8.86 0.28 15.27 20.32 0.31 0.00 0.00 98.87
2AK14px tr1 50.59 0.60 2.17 8.38 0.33 15.43 20.35 0.13 0.00 0.06 98.04
2AK14px tr1 50.91 0.61 2.17 8.34 0.31 15.78 20.34 0.18 0.00 0.00 98.65
2AK14px tr1 50.95 0.60 2.23 8.12 0.34 15.77 20.09 0.16 0.00 0.00 98.25
2AK14px tr1 51.65 0.62 2.10 8.33 0.28 15.85 20.31 0.12 0.00 0.00 99.26
2AK14px tr1 51.52 0.61 2.18 8.37 0.35 15.73 20.15 0.14 0.00 0.06 99.10
2AK14px tr1 51.53 0.62 2.06 8.32 0.28 15.67 20.17 0.12 0.00 0.01 98.77
2AK14px tr1 50.67 0.63 2.33 8.22 0.30 15.75 20.56 0.26 0.01 0.03 98.74
2AK14px tr1 51.09 0.63 2.34 8.34 0.35 15.45 20.63 0.24 0.00 0.00 99.08
2AK14px tr1 53.16 0.67 2.46 8.53 0.31 16.45 20.23 0.15 0.00 0.00 101.95
2AK14px tr1 51.53 0.62 2.03 8.94 0.44 15.45 20.00 0.18 0.00 0.02 99.20
2AK14px tr1 51.06 0.68 2.08 9.13 0.30 15.44 20.02 0.16 0.01 0.00 98.87
2AK14px tr1 50.99 0.78 2.79 9.43 0.26 15.19 19.61 0.21 0.00 0.03 99.29
2AK14px tr1 51.10 0.72 2.30 9.05 0.30 15.62 19.93 0.30 0.01 0.00 99.33
2AK14px tr1 51.13 0.64 2.21 8.81 0.30 15.47 19.93 0.15 0.00 0.05 98.70
2AK14px tr1 50.57 0.66 2.56 8.99 0.24 15.40 20.20 0.21 0.00 0.00 98.82
2AK14px tr1 51.11 0.74 1.45 12.78 0.46 15.00 17.39 0.16 0.00 0.05 99.15
48
2_AK1XC 1px p15 50.68 0.65 2.31 8.54 0.22 15.50 20.69 0.23 0.00 0.02 98.83
2_AK1XC 1px p17 52.00 0.67 2.24 8.46 0.26 15.65 20.97 0.17 0.00 0.00 100.43
2_AK1XC 1px p18 51.55 0.62 2.41 8.21 0.21 15.31 20.78 0.20 0.01 0.11 99.40
2_AKIXC 1px p19 51.57 0.69 2.04 9.75 0.41 14.92 20.04 0.18 0.00 0.05 99.64
2_AKIXC 1px p20 52.49 0.61 1.83 8.51 0.28 15.88 20.13 0.18 0.00 0.00 99.93
2_AKIXC 1px p21 51.09 0.67 2.08 9.58 0.33 15.26 20.15 0.24 0.00 0.06 99.47
2_AKIXC 1px p22 51.92 0.69 2.05 8.55 0.34 15.78 20.81 0.23 0.00 0.00 100.36
2_AKIXC 1px p23 51.43 0.71 2.27 9.11 0.36 15.31 19.85 0.23 0.00 0.00 99.27
2_AKIXC 1px p24 51.77 0.72 2.27 9.13 0.29 15.72 20.14 0.26 0.01 0.01 100.33
2_AKIXC 1px p25 51.29 0.74 2.49 9.05 0.27 15.35 19.77 0.22 0.00 0.00 99.18
3_AKXIC 04 6px p1 50.80 0.63 2.30 9.46 0.37 15.36 19.79 0.25 0.00 0.00 98.96
3_AKXIC 04 6px p2 51.04 0.75 2.60 9.34 0.32 15.51 19.63 0.14 0.00 0.03 99.37
3_AKXIC 04 6px p3 51.50 0.63 2.20 9.04 0.30 15.51 20.03 0.19 0.00 0.00 99.40
3_AKXIC 04 6px p4 52.17 0.55 1.93 8.82 0.32 16.15 20.00 0.17 0.00 0.00 100.10
3_AKXIC 04 2px p5 51.85 0.49 1.40 8.75 0.56 15.00 20.85 0.19 0.00 0.00 99.08
3 AKXIC 04 2px tr1 52.01 0.54 1.48 8.70 0.44 15.36 20.98 0.21 0.00 0.04 99.76
3 AKXIC 04 2px tr1 51.58 0.54 1.38 8.89 0.46 15.51 20.89 0.21 0.00 0.00 99.45
3 AKXIC 04 2px tr1 50.32 0.67 2.68 8.84 0.47 14.63 21.09 0.26 0.00 0.00 98.95
3 AKXIC 04 2px tr1 51.89 0.53 1.54 8.74 0.54 15.40 20.88 0.18 0.00 0.00 99.69
3 AKXIC 04 2px tr1 51.73 0.47 1.36 8.93 0.52 15.21 20.78 0.30 0.00 0.02 99.34
3 AKXIC 04 2px tr1 51.99 0.59 1.63 8.52 0.42 15.11 20.61 0.15 0.00 0.00 99.02
3 AKXIC 04 2px tr1 49.05 0.70 2.63 8.51 0.48 13.88 20.90 0.18 0.00 0.00 96.33
3 AKXIC 04 2px tr1 51.77 0.55 1.56 9.19 0.44 15.05 20.48 0.16 0.00 0.00 99.20
3 AKXIC 04 2px tr1 51.98 0.44 1.20 9.11 0.50 15.07 20.75 0.26 0.00 0.01 99.32
3 AKXIC 04 2px tr1 51.86 0.58 1.42 8.88 0.57 14.68 20.88 0.23 0.00 0.00 99.10
3 AKXIC 04 2px tr1 51.76 0.45 1.23 9.35 0.60 15.32 20.67 0.24 0.00 0.00 99.61
3 AKXIC 04 2px tr1 53.46 0.43 1.34 8.94 0.50 15.96 20.60 0.22 0.00 0.00 101.45
3 AKXIC 04 2px tr1 51.03 0.75 1.59 11.82 0.41 14.96 18.24 0.18 0.02 0.02 99.01
4_AKXIC 11 p40 52.20 0.63 1.93 9.15 0.27 15.76 19.89 0.26 0.00 0.00 100.08
4_AKXIC 11 p41 51.87 0.60 2.06 8.86 0.28 15.60 20.24 0.10 0.00 0.02 99.62
4_AKXIC 11 p42 52.07 0.56 1.92 8.83 0.32 15.43 20.05 0.21 0.01 0.01 99.40
4_AKXIC 11 p43 51.37 0.73 2.39 9.87 0.35 15.17 19.44 0.20 0.00 0.01 99.54
4_AKXIC 11 p44 51.93 0.68 2.25 8.75 0.24 15.34 20.25 0.22 0.01 0.00 99.68
4_AKXIC 11 p52 52.59 0.53 1.89 9.79 0.38 15.97 18.81 0.23 0.01 0.00 100.19
4_AKXCI 11 p53 52.17 0.61 2.11 9.69 0.29 15.97 19.20 0.21 0.00 0.11 100.36
4_AKXCI 11 p54 52.25 0.62 2.05 9.33 0.33 15.06 19.89 0.21 0.01 0.00 99.76
4_AKXCI 11 p55 52.37 0.63 2.25 9.54 0.38 15.05 19.84 0.25 0.00 0.05 100.35
4_AKXCI 11 p56 52.41 0.82 2.88 10.08 0.31 14.88 18.72 0.20 0.00 0.02 100.33
4_AKXCI 11 p56b 51.75 0.70 2.73 9.80 0.31 15.31 19.42 0.09 0.00 0.02 100.14
4_AKXCI 11 tr2 C-R 52.26 0.63 1.79 8.72 0.46 15.21 20.64 0.23 0.00 0.00 99.93
4_AKXCI 11 tr2 C-R 52.73 0.49 1.61 9.04 0.48 15.14 20.45 0.23 0.00 0.00 100.17
4_AKXCI 11 tr2 C-R 52.25 0.66 2.09 9.47 0.65 14.89 20.09 0.26 0.00 0.00 100.36
4_AKXCI 11 tr2 C-R 51.77 0.57 2.06 9.26 0.52 14.63 20.17 0.18 0.00 0.00 99.17
4_AKXCI 11 tr2 C-R 51.84 0.63 2.04 9.31 0.53 14.52 20.38 0.25 0.00 0.00 99.50
4_AKXCI 11 tr2 C-R 51.88 0.62 1.97 9.24 0.45 14.99 20.25 0.20 0.00 0.00 99.60
4_AKXCI 11 tr2 C-R 52.31 0.56 1.75 9.26 0.48 15.00 20.45 0.24 0.01 0.00 100.05
49
4_AKXCI 11 tr2 C-R 51.92 0.59 1.86 8.69 0.53 14.74 20.79 0.18 0.00 0.00 99.30
4_AKXCI 11 tr2 C-R 51.80 0.54 1.80 8.67 0.51 14.91 20.96 0.22 0.00 0.00 99.43
4_AKXCI 11 tr2 C-R 52.65 0.55 1.88 8.26 0.40 15.09 20.83 0.18 0.00 0.00 99.83
4_AKXCI 11 tr2 C-R 50.96 0.76 2.69 8.69 0.36 14.90 20.85 0.28 0.00 0.03 99.52
4_AKXCI 11 tr2 C-R 51.45 0.82 2.75 8.56 0.33 15.00 20.65 0.18 0.02 0.03 99.79
4_AKXCI 11 tr2 C-R 51.45 0.79 2.73 8.69 0.39 15.23 20.58 0.30 0.00 0.05 100.22
4_AKXCI 11 tr2 C-R 51.23 0.82 2.64 8.87 0.33 15.24 20.73 0.19 0.01 0.00 100.07
4_AKXCI 11 tr2 C-R 52.56 0.55 1.69 8.55 0.41 15.05 20.18 0.19 0.00 0.06 99.23
4_AKXCI 11 tr2 C-R 50.90 0.63 2.02 9.18 0.37 14.65 19.87 0.34 0.00 0.00 97.94
4_AKXCI 11 tr2 C-R 50.92 0.67 2.35 9.39 0.28 15.24 19.80 0.23 0.02 0.06 98.95
4_AKXCI 11 tr2 C-R 51.71 0.71 2.24 8.82 0.27 15.10 20.14 0.14 0.00 0.00 99.12
4_AKXCI 11 tr2 C-R 50.90 0.89 3.16 10.08 0.34 14.65 19.65 0.30 0.00 0.03 100.00
4_AKXCI 11 tr2 C-R 50.45 1.05 2.64 10.88 0.41 14.75 18.46 0.10 0.01 0.00 98.75
50
Appendix 2 – Chemical composition of analysed plagioclase phenocrysts
SiO2 TiO2 Al2O3 FeO MnO MgO CaO Na2O K2O Cr2O3 SUM
3_AKXIC 04 1fsp p8 50,25 0,02 30,74 0,62 0,00 0,00 14,56 3,21 0,06 0,00 99,46
3_AKXIC 04 1fsp p9 50,23 0,02 31,03 0,67 0,05 0,00 14,66 3,24 0,08 0,00 99,98
3_AKXIC 04 1fsp p10 52,17 0,04 28,76 0,59 0,00 0,00 12,53 4,50 0,11 0,00 98,70
3 AKXIC 04 2fsp tr2 52,35 0,03 27,85 0,62 0,00 0,00 11,95 4,93 0,12 0,00 97,84
3 AKXIC 04 2fsp tr2 50,92 0,04 29,09 0,62 0,00 0,00 13,08 4,09 0,10 0,01 97,94
3 AKXIC 04 2fsp tr2 50,97 0,08 28,56 0,57 0,02 0,00 12,84 4,25 0,11 0,00 97,39
3 AKXIC 04 2fsp tr2 51,71 0,03 28,24 0,53 0,04 0,00 12,45 4,56 0,10 0,00 97,67
3 AKXIC 04 2fsp tr2 51,79 0,05 28,37 0,57 0,00 0,00 12,42 4,44 0,12 0,00 97,78
3 AKXIC 04 2fsp tr2 52,86 0,01 27,45 0,55 0,00 0,00 11,63 4,90 0,13 0,00 97,53
3 AKXIC 04 2fsp tr2 52,75 0,03 26,92 0,64 0,00 0,00 11,40 5,10 0,13 0,00 96,97
3 AKXIC 04 2fsp tr2 52,26 0,03 28,06 0,63 0,01 0,00 12,35 4,40 0,08 0,00 97,81
3 AKXIC 04 2fsp tr2 53,44 0,02 27,27 0,60 0,02 0,00 11,12 5,21 0,15 0,00 97,82
3 AKXIC 04 2fsp tr2 52,91 0,03 27,51 0,56 0,00 0,00 11,11 5,16 0,14 0,02 97,44
3 AKXIC 04 2fsp tr2 53,03 0,00 27,48 0,57 0,00 0,00 11,27 5,21 0,13 0,00 97,69
3 AKXIC 04 2fsp tr2 52,58 0,02 27,25 0,63 0,00 0,02 11,33 5,12 0,12 0,00 97,07
3 AKXIC 04 2fsp tr2 51,79 0,00 28,44 0,53 0,00 0,00 12,20 4,73 0,10 0,00 97,78
3 AKXIC 04 2fsp tr2 49,56 0,03 29,40 0,72 0,00 0,00 14,05 3,59 0,06 0,00 97,41
3 AKXIC 04 2fsp tr2 50,16 0,06 29,63 0,80 0,00 0,01 13,98 3,61 0,07 0,02 98,34
3_AKXIC 04 2fsp p24 53,77 0,03 28,30 0,60 0,00 0,00 11,77 4,80 0,13 0,02 99,41
3_AKXIC 04 2fsp p26 53,25 0,03 27,88 0,59 0,01 0,00 11,66 4,93 0,12 0,00 98,47
3_AKXIC 04 2fsp p27 52,38 0,02 28,84 0,63 0,01 0,00 12,58 4,41 0,10 0,00 98,98
3_AK1 1 fsp p11 49,11 0,03 30,35 0,59 0,00 0,00 14,72 3,04 0,08 0,02 97,93
3_AK1 1 fsp p12 48,24 0,02 31,81 0,67 0,00 0,00 15,68 2,67 0,02 0,02 99,13
3_AK1 1 fsp p13 50,94 0,06 30,06 0,74 0,00 0,00 13,90 3,84 0,09 0,00 99,62
4_AKLF 1Fsp p1 49,00 0,01 30,27 0,80 0,01 0,00 15,39 2,91 0,08 0,00 98,47
4_AKLF 1Fsp p2 49,84 0,00 30,10 0,72 0,01 0,00 14,82 3,18 0,09 0,00 98,76
4_AKLF 1Fsp p3 48,67 0,03 31,48 0,75 0,00 0,00 15,86 2,56 0,07 0,00 99,42
4_AKLF 1Fsp p5 47,80 0,03 31,83 0,66 0,00 0,00 16,19 2,36 0,03 0,00 98,90
4_AKLF 1Fsp p6 51,49 0,06 29,76 0,76 0,00 0,04 13,57 3,87 0,08 0,00 99,63
4_AKLF 1Fsp p7 53,31 0,06 28,61 0,71 0,04 0,00 12,30 4,71 0,13 0,00 99,86
4_AKLF 1Fsp p8 51,55 0,03 30,15 0,69 0,03 0,00 13,94 3,65 0,08 0,00 100,12
4_AKLF 1Fsp p9 53,29 0,06 29,22 0,73 0,00 0,00 12,83 4,33 0,12 0,00 100,57
4_AKLF p18 52,55 0,02 28,74 0,58 0,00 0,02 12,69 4,44 0,10 0,00 99,15
4_AKLF p19 53,34 0,05 28,77 0,56 0,00 0,00 12,46 4,59 0,13 0,00 99,91
4_AKLF p20 54,16 0,01 28,03 0,66 0,00 0,00 11,45 4,84 0,14 0,01 99,31
4_AKLF p21 50,90 0,02 30,35 0,62 0,00 0,00 13,90 3,57 0,07 0,00 99,44
4_AKLF p22 52,45 0,04 29,20 0,69 0,02 0,00 12,84 4,17 0,10 0,00 99,51
4_AKLF p31 50,24 0,02 30,66 0,54 0,04 0,00 14,37 3,37 0,08 0,00 99,32
4_AKLF p32 49,65 0,02 30,69 0,57 0,00 0,00 14,71 3,32 0,06 0,00 99,03
4_AKLF p33 49,67 0,00 31,33 0,61 0,00 0,00 14,89 2,81 0,07 0,00 99,37
4_AKLF p34 50,27 0,03 30,41 0,63 0,00 0,00 14,23 3,57 0,12 0,03 99,29
51
4_AKXIC 11 p36 47,80 0,01 31,96 0,58 0,00 0,00 16,17 2,18 0,02 0,00 98,72
4_AKXIC 11 p37 48,25 0,01 31,72 0,56 0,02 0,00 15,77 2,34 0,05 0,00 98,71
4_AKXIC 11 p38 50,17 0,01 30,76 0,60 0,00 0,00 14,35 3,33 0,07 0,00 99,30
4_AKXIC 11 p39 52,46 0,05 29,57 0,66 0,00 0,00 13,30 4,05 0,09 0,00 100,18
4_AKXIC 11 p48 50,69 0,04 30,16 0,61 0,01 0,00 14,08 3,72 0,07 0,00 99,39
4_AKXIC 11 p49 51,78 0,03 29,58 0,56 0,00 0,00 13,44 3,90 0,10 0,00 99,38
4_AKXIC 11 p50 52,07 0,04 29,63 0,58 0,00 0,00 13,21 3,98 0,11 0,00 99,62
4_AKXIC 11 p51 53,15 0,04 29,11 0,74 0,00 0,00 12,80 4,19 0,12 0,00 100,16
4_AKXCI 11 tr2 C-R 49,09 0,01 31,63 0,76 0,01 0,00 15,43 2,83 0,04 0,00 99,81
4_AKXCI 11 tr2 C-R 50,85 0,05 29,94 0,58 0,02 0,00 14,06 3,53 0,08 0,00 99,11
4_AKXCI 11 tr2 C-R 50,27 0,03 29,84 0,61 0,00 0,00 14,29 3,29 0,10 0,00 98,44
4_AKXCI 11 tr2 C-R 49,76 0,01 31,00 0,66 0,00 0,00 14,78 3,24 0,07 0,00 99,52
4_AKXCI 11 tr2 C-R 50,74 0,02 30,40 0,76 0,00 0,00 14,19 3,50 0,08 0,00 99,70
4_AKXCI 11 tr2 C-R 50,60 0,05 29,75 0,63 0,00 0,00 14,00 3,63 0,11 0,01 98,77
4_AKXCI 11 tr2 C-R 50,71 0,02 30,49 0,64 0,01 0,00 14,10 3,43 0,06 0,00 99,47
4_AKXCI 11 tr2 C-R 50,33 0,03 30,27 0,68 0,02 0,00 14,69 3,18 0,08 0,00 99,28
4_AKXCI 11 tr2 C-R 48,56 0,02 31,22 0,72 0,00 0,00 15,73 2,59 0,06 0,00 98,91
4_AKXCI 11 tr2 C-R 49,31 0,03 30,74 0,72 0,00 0,00 15,31 2,88 0,06 0,02 99,09
4_AKXCI 11 tr2 C-R 48,22 0,00 31,95 0,70 0,00 0,00 16,13 2,28 0,06 0,01 99,36
4_AKXCI 11 tr2 C-R 48,73 0,00 31,40 0,75 0,00 0,00 15,75 2,55 0,05 0,00 99,22
4_AKXCI 11 tr2 C-R 48,66 0,04 30,90 0,72 0,00 0,00 15,56 2,51 0,05 0,02 98,47
4_AKXCI 11 tr2 C-R 48,52 0,01 31,05 0,72 0,01 0,00 15,68 2,41 0,03 0,02 98,45 4_AKXCI 11 tr3 C-R 56,48 0,04 26,36 0,54 0,00 0,00 10,10 5,95 0,18 0,00 99,66
4_AKXCI 11 tr3 C-R 56,17 0,05 26,12 0,47 0,00 0,00 10,14 5,65 0,19 0,00 98,78
4_AKXCI 11 tr3 C-R 56,10 0,04 26,81 0,52 0,00 0,00 10,56 5,72 0,17 0,01 99,92
4_AKXCI 11 tr3 C-R 55,80 0,03 26,53 0,51 0,00 0,00 10,61 5,68 0,17 0,00 99,33
4_AKXCI 11 tr3 C-R 54,85 0,03 26,97 0,53 0,00 0,00 11,04 5,39 0,14 0,05 98,99
4_AKXCI 11 tr3 C-R 54,86 0,04 27,10 0,47 0,00 0,00 10,93 5,15 0,15 0,00 98,69
4_AKXCI 11 tr3 C-R 55,09 0,02 27,47 0,54 0,00 0,01 11,12 4,96 0,16 0,03 99,40
4_AKXCI 11 tr3 C-R 54,65 0,05 27,46 0,50 0,02 0,00 11,24 5,09 0,12 0,01 99,13
4_AKXCI 11 tr3 C-R 54,48 0,02 26,70 0,45 0,00 0,00 11,19 5,12 0,14 0,00 98,10
4_AKXCI 11 tr3 C-R 54,58 0,06 27,15 0,55 0,00 0,00 11,30 5,22 0,11 0,00 98,96
4_AKXCI 11 tr3 C-R 55,05 0,08 26,82 0,43 0,00 0,00 11,31 5,04 0,13 0,00 98,84
4_AKXCI 11 tr3 C-R 54,63 0,03 26,61 0,49 0,01 0,00 11,20 5,20 0,13 0,00 98,31
4_AKXCI 11 tr3 C-R 54,49 0,05 27,41 0,58 0,04 0,00 11,22 5,21 0,18 0,01 99,18
4_AKXCI 11 tr3 C-R 55,03 0,01 27,23 0,56 0,00 0,00 10,99 5,39 0,13 0,00 99,34
4_AKXCI 11 tr3 C-R 54,30 0,04 26,54 0,55 0,00 0,00 11,02 5,34 0,15 0,00 97,93
4_AKXCI 11 tr3 C-R 55,80 0,06 27,18 0,59 0,00 0,00 10,93 5,44 0,16 0,00 100,16
4_AKXCI 11 tr3 C-R 55,14 0,03 27,21 0,44 0,02 0,00 10,74 5,55 0,14 0,00 99,27
4_AKXCI 11 tr3 C-R 57,05 0,01 25,77 0,48 0,02 0,00 9,73 6,31 0,20 0,00 99,57
4_AKXCI 11 tr3 C-R 55,13 0,03 26,87 0,48 0,00 0,00 10,87 5,53 0,14 0,00 99,04
4_AKXCI 11 tr3 C-R 54,86 0,02 26,70 0,54 0,00 0,00 11,13 5,37 0,16 0,06 98,83
4_AKXCI 11 tr3 C-R 55,25 0,00 26,90 0,44 0,00 0,00 10,67 5,77 0,16 0,08 99,25
4_AKXCI 11 tr3 C-R 55,25 0,02 26,60 0,52 0,02 0,00 10,70 5,44 0,17 0,00 98,73
4_AKXCI 11 tr3 C-R 56,41 0,02 26,39 0,52 0,00 0,00 10,08 6,03 0,14 0,02 99,62
4_AKXCI 11 tr3 C-R 56,56 0,02 26,07 0,54 0,00 0,00 10,07 5,85 0,19 0,00 99,31
52
4_AKXCI 11 tr3 C-R 55,34 0,00 26,58 0,59 0,00 0,01 10,59 5,48 0,14 0,08 98,82
4_AKXCI 11 tr3 C-R 53,79 0,02 28,20 0,46 0,00 0,00 11,90 4,68 0,10 0,00 99,14
4_AKXCI 11 tr3 C-R 52,94 0,03 28,49 0,57 0,02 0,00 12,64 4,56 0,13 0,00 99,38
4_AKXCI 11 tr3 C-R 53,25 0,04 28,12 0,51 0,02 0,00 12,15 4,53 0,13 0,00 98,75
4_AKXCI 11 tr3 C-R 54,26 0,04 27,04 0,51 0,01 0,00 11,90 4,87 0,11 0,01 98,75
4_AKXCI 11 tr3 C-R 54,73 0,01 27,48 0,53 0,00 0,01 11,47 4,94 0,15 0,00 99,33
4_AKXCI 11 tr3 C-R 53,82 0,05 27,70 0,48 0,00 0,00 12,08 4,66 0,08 0,00 98,87
4_AKXCI 11 tr3 C-R 51,24 0,04 28,81 0,56 0,00 0,00 11,96 4,03 0,10 0,00 96,74
4_AKXCI 11 tr3 C-R 52,90 0,04 27,22 0,54 0,00 0,00 12,04 4,77 0,12 0,00 97,63
4_AKXCI 11 tr3 C-R 54,39 0,04 27,52 0,45 0,00 0,00 11,50 4,96 0,15 0,00 99,00
4_AKXCI 11 tr3 C-R 54,34 0,07 27,65 0,53 0,00 0,00 11,37 5,11 0,14 0,00 99,22
4_AKXCI 11 tr3 C-R 53,84 0,05 27,16 0,67 0,00 0,00 11,82 4,70 0,15 0,00 98,40
4_AKXCI 11 tr3 C-R 54,01 0,05 26,87 0,51 0,02 0,00 11,64 4,96 0,15 0,05 98,27
4_AKXCI 11 tr3 C-R 52,87 0,06 27,63 0,56 0,00 0,01 12,68 4,29 0,11 0,02 98,23
4_AKXCI 11 tr3 C-R 52,45 0,09 27,67 0,57 0,06 0,00 12,67 4,29 0,13 0,00 97,95
4_AKXCI 11 tr3 C-R 53,05 0,01 28,04 0,56 0,00 0,00 12,61 4,47 0,10 0,00 98,85
4_AKXCI 11 tr3 C-R 52,65 0,02 28,02 0,55 0,01 0,00 12,57 4,43 0,13 0,00 98,37
4_AKXCI 11 tr3 C-R 48,15 0,06 26,71 0,64 0,00 0,00 12,27 3,52 0,09 0,05 91,47
4_AKXCI 11 tr3 C-R 54,10 0,06 29,01 0,50 0,00 0,00 12,42 4,55 0,12 0,02 100,78
4_AKXCI 11 tr3 C-R 51,52 0,03 29,43 0,58 0,03 0,00 13,66 3,59 0,08 0,01 98,93
4_AKXCI 11 tr3 C-R 54,60 0,03 27,65 0,53 0,00 0,00 11,58 4,90 0,15 0,00 99,43
4_AKXCI 11 tr3 C-R 53,42 0,07 28,03 0,54 0,00 0,00 12,08 4,81 0,10 0,00 99,05
4_AKXCI 11 tr3 C-R 51,06 0,06 25,88 0,57 0,00 0,00 11,59 4,38 0,14 0,01 93,69
4_AKXCI 11 tr3 C-R 55,54 0,04 27,06 0,54 0,00 0,00 10,85 5,49 0,17 0,01 99,71
4_AKXCI 11 tr3 C-R 53,01 0,05 27,67 0,53 0,00 0,00 12,04 4,63 0,14 0,00 98,07
4_AKXCI 11 tr3 C-R 53,94 0,02 27,14 0,55 0,00 0,00 11,31 5,11 0,10 0,01 98,18
4_AKXCI 11 tr3 C-R 55,27 0,07 27,12 0,47 0,00 0,00 11,07 5,23 0,15 0,00 99,39
4_AKXCI 11 tr3 C-R 53,24 0,07 27,87 0,59 0,04 0,00 12,17 4,47 0,11 0,00 98,56
4_AKXCI 11 tr3 C-R 52,59 0,06 28,17 0,66 0,00 0,00 12,75 4,06 0,11 0,00 98,41
4_AKXCI 11 tr3 C-R 53,53 0,05 27,73 0,72 0,01 0,00 12,12 4,70 0,13 0,00 98,98
4_AKXCI 11 tr3 C-R 52,87 0,09 27,64 0,59 0,00 0,00 12,39 4,64 0,14 0,00 98,35
4_AKXCI 11 tr3 C-R 52,23 0,02 27,86 0,66 0,05 0,00 12,84 4,16 0,11 0,00 97,93
4_AKXCI 11 tr3 C-R 53,09 0,05 28,00 0,75 0,01 0,00 12,76 4,40 0,13 0,00 99,18
53
Appendix 3 – Chemical composition of analysed olivine
SiO2 TiO2 Al2O3 FeO MnO MgO CaO Na2O K2O Cr2O3 SUM
AK-LF7-PX p19 37.92 0.03 0.00 26.59 0.54 36.72 0.16 0.00 0.00 0.00 101.95
3_AKXIC 04 p28 36.47 0.00 0.00 25.92 0.49 35.63 0.17 0.00 0.02 0.01 98.71
3_AKXIC 04 p29 37.28 0.02 0.00 26.28 0.44 36.05 0.16 0.00 0.00 0.01 100.25
3_AKXIC 04 p30 37.10 0.03 0.00 25.94 0.50 35.37 0.19 0.00 0.00 0.05 99.18
3_AKXIC 04 p33 36.61 0.03 0.00 28.88 0.53 33.41 0.20 0.00 0.00 0.00 99.66
3_AKXIC 04 p34 38.40 0.00 0.03 22.29 0.38 39.94 0.19 0.00 0.00 0.06 101.29
3_AKXIC 04 p35 37.08 0.02 0.00 25.23 0.42 36.73 0.21 0.00 0.00 0.00 99.70
3_AKXIC 04 p36 36.29 0.13 0.02 32.52 0.61 31.32 0.24 0.00 0.00 0.03 101.17
4_AKLF p10 39.29 0.00 0.03 19.20 0.36 41.43 0.17 0.00 0.00 0.00 100.49
4_AKLF p11 39.68 0.06 0.00 18.96 0.29 41.51 0.19 0.00 0.00 0.02 100.70
4_AKLF p12 39.14 0.01 0.00 20.34 0.38 40.31 0.16 0.00 0.00 0.00 100.34
4_AKLF p13 37.75 0.01 0.00 22.08 0.36 38.88 0.15 0.00 0.01 0.02 99.25
4_AKLF p14 37.41 0.00 0.03 24.83 0.47 36.39 0.20 0.00 0.00 0.00 99.34
4_AKLF p27 37.25 0.05 0.02 27.66 0.72 33.87 0.20 0.00 0.00 0.00 99.77
4_AKLF p28 37.28 0.03 0.00 27.95 0.63 33.29 0.18 0.00 0.01 0.00 99.35
4_AKLF p29 37.10 0.03 0.00 29.70 0.68 32.79 0.25 0.00 0.01 0.05 100.59
4_AKXCI 11 p59 37.39 0.00 0.03 29.93 0.63 32.54 0.17 0.00 0.00 0.01 100.68
4_AKXCI 11 p60 37.83 0.00 0.08 27.39 0.49 35.06 0.16 0.00 0.00 0.00 101.01
4_AKXCI 11 p61 37.43 0.01 0.00 29.32 0.50 33.74 0.17 0.00 0.00 0.00 101.17
54
Appendix 4 – Chemical composition of analysed orthopyroxene
SiO2 TiO2 Al2O3 FeO MnO MgO CaO Na2O K2O Cr2O3 SUM
AK-LF7-PX p20 54.16 0.20 0.69 16.99 0.48 26.48 1.68 0.00 0.00 0.00 100.67
2_AK14px p3 53.43 0.31 1.00 16.51 0.53 25.99 1.72 0.00 0.00 0.00 99.48
2_AK14px p4 53.88 0.28 0.96 16.88 0.57 25.84 1.63 0.00 0.00 0.00 100.03
3_AK1 1 9px p17 52.16 0.42 0.67 20.50 0.67 20.25 4.79 0.00 0.01 0.00 99.47
3_AK1 1 9px p18 52.15 0.37 0.79 20.80 0.65 20.81 3.72 0.00 0.00 0.00 99.29
3_AKXIC 04 1 p20 52.21 0.28 0.70 18.59 0.56 24.70 2.07 0.00 0.00 0.04 99.16
3_AKXIC 04 2 p22 51.84 0.46 1.54 18.47 0.60 24.03 2.26 0.00 0.01 0.04 99.24
3_AKXIC 04 2 p23 52.90 0.43 0.76 20.03 0.68 20.76 4.63 0.00 0.00 0.00 100.18
3_AKXIC 04 p31 50.73 0.92 2.08 14.24 0.57 15.57 14.78 0.13 0.01 0.00 99.03
3_AKXIC 04 p32 53.19 0.33 0.75 18.59 0.59 23.86 2.06 0.00 0.01 0.00 99.38
3_AKXIC 04 p37 52.75 0.47 0.83 19.53 0.70 20.68 4.94 0.00 0.02 0.00 99.91
4_AKXCI 11 p63 54.22 0.36 0.73 18.97 0.62 21.89 4.07 0.00 0.00 0.00 100.86
4_AKXCI 11 p64 54.45 0.35 0.65 19.69 0.69 23.44 2.17 0.00 0.02 0.00 101.46
4_AKXCI 11 p65 53.11 0.33 0.81 19.33 0.66 21.73 3.83 0.00 0.03 0.00 99.81
4_AKLF p30 54.35 0.88 2.81 18.86 0.53 17.74 4.06 0.32 0.59 0.02 100.16
4_AKLF p15 46.89 0.44 1.13 23.94 0.63 22.07 4.07 0.00 0.00 0.00 99.17
AK-LF8-PX tr R-R 54.13 0.31 0.96 17.35 0.55 25.90 1.74 0.00 0.00 0.05 100.99
AK-LF8-PX tr R-R 53.65 0.26 0.80 17.40 0.49 26.13 1.69 0.00 0.01 0.01 100.44
AK-LF8-PX tr R-R 54.29 0.23 0.76 16.89 0.44 26.55 1.58 0.00 0.00 0.00 100.74
AK-LF8-PX tr R-R 54.82 0.24 0.74 16.88 0.50 26.23 1.56 0.00 0.00 0.01 100.98
AK-LF8-PX tr R-R 52.93 0.26 0.80 16.76 0.56 26.23 1.65 0.00 0.00 0.00 99.19
AK-LF8-PX tr R-R 53.82 0.23 0.74 17.04 0.49 25.86 1.64 0.00 0.00 0.01 99.83
AK-LF8-PX tr R-R 53.82 0.35 1.39 16.57 0.54 25.54 1.67 0.00 0.00 0.00 99.87
AK-LF8-PX tr R-R 54.12 0.32 1.39 17.34 0.48 25.73 1.68 0.00 0.00 0.00 101.07
AK-LF8-PX tr R-R 54.57 0.33 1.26 17.39 0.50 26.11 1.58 0.00 0.02 0.00 101.77
AK-LF8-PX tr R-R 54.39 0.34 1.22 17.69 0.56 25.53 1.75 0.00 0.02 0.01 101.52
55
Appendix 5 – Chemical composition of analysed titanomagnetite
SiO2 TiO2 Al2O3 FeO MnO MgO CaO Na2O K2O Cr2O3 SUM
4_AKLF p16 0.13 10.89 3.39 72.83 0.433843 3.19 0.08 0.00 0.01 3.11 94.06
4_AKLF p17 0.10 12.34 3.69 75.75 0.396398 3.18 0.03 0.00 0.00 0.04 95.52
4_AKLF p35 0.10 10.70 3.15 76.34 0.408019 2.99 0.14 0.00 0.00 0.24 94.06
4_AKXCI 11 p66 0.18 18.43 1.92 72.64 0.463541 1.37 0.14 0.00 0.02 0.05 95.22
56
Appendix 6 – Chemical composition of analysed glass and groundmass
SiO2 TiO2 Al2O3 FeO MnO MgO CaO Na2O K2O Cr2O3 SUM Note
AK-LF6-PX p15 57.28 2.62 12.76 12.76 0.27 1.09 4.57 4.63 1.91 0.00 97.89 1
2_AK12px p11 57.68 1.65 16.29 7.67 0.19 1.26 2.77 7.59 2.04 0.00 97.14 1
3_AK1 1 fsp p14 64.83 1.08 16.18 4.60 0.07 0.25 4.72 5.28 1.80 0.01 98.82 1
3_AKXIC 04 2fsp p25 61.31 1.92 9.91 11.29 0.23 1.91 3.50 3.99 2.92 0.02 97.01 1
3_AKXIC 04 2px p7 63.31 1.75 13.84 7.43 0.20 0.72 3.90 4.95 2.15 0.00 98.26 1
4_AKLF p23 60.86 1.63 11.11 10.44 0.22 3.51 4.62 2.96 2.68 0.00 98.03 1
4_AKLF p24 63.86 1.34 13.84 7.07 0.14 1.87 2.73 4.10 3.41 0.05 98.41 1
3_AK1 1 fsp p15 66.35 1.40 12.61 6.54 0.13 0.85 3.10 4.96 1.88 0.02 97.84 2
3_AK1 1 fsp p16 68.41 1.51 12.15 6.69 0.13 0.82 3.06 3.63 1.63 0.00 98.04 2
3_AKXIC 04 p19 67.93 1.61 12.36 4.95 0.11 0.42 3.11 2.73 2.54 0.00 95.78 2
3_AKXIC 04 p21 68.44 1.84 11.65 5.94 0.13 0.30 2.77 3.99 3.19 0.00 98.25 2
2_AK14px p7 60.46 0.67 19.37 3.99 0.09 0.87 6.31 5.22 1.40 0.00 98.38 3
2_AK12px p14 62.36 0.87 18.59 4.22 0.08 0.33 5.78 5.27 1.53 0.01 99.05 3
2_AKIXC 1px p26 59.82 0.68 18.10 4.20 0.06 0.73 7.51 4.90 1.04 0.00 97.04 3
2_AKIXC 1px p27 57.66 0.50 20.90 2.57 0.05 0.26 9.00 4.99 0.67 0.00 96.61 3
AK-LF 3-PX p8 57.49 1.49 16.08 8.08 0.11 1.65 6.51 4.62 1.52 0.00 97.54 3
AK-LF 3-PX p9 57.84 1.36 15.54 7.89 0.11 2.53 6.50 4.73 1.43 0.00 97.93 3
2_AK14px p6 62.72 1.10 14.46 7.40 0.21 2.17 4.95 4.94 1.79 0.01 99.75 3
2_AKIXC 1px p28 59.99 0.92 15.03 6.23 0.15 2.39 6.16 4.41 1.30 0.00 96.57 3
4_AKXIC 11 p45 64.50 2.14 11.50 10.20 0.20 1.84 3.30 4.20 2.79 0.00 100.67 3
4_AKXIC 11 p46 61.55 3.00 13.07 12.08 0.11 1.07 3.16 4.44 2.26 0.00 100.76 3
4_AKXCI 11 p57 63.37 0.00 15.34 8.17 0.13 1.11 4.53 4.84 1.88 0.00 99.37 3
4_AKXCI 11 p58 63.09 1.24 13.64 6.53 0.12 1.30 4.90 4.60 2.26 0.00 97.68 3
4_AKLF p25 58.11 1.54 12.75 11.32 0.25 4.62 6.01 3.66 1.44 0.00 99.69 3
4_AKLF p26 58.77 2.10 14.28 11.78 0.19 2.14 5.25 4.72 1.71 0.05 100.98 3
1: Melt inclusions
2: Groundmass glass
3: Groundmass
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