Post on 27-Aug-2020
ANISOTROPY OF MAGNETIC SUSCEPTIBILITY STUDIES IN LAVA FLOWS OF
THE EASTERN ANATOLIA REGION, TURKEY Hakan Ucar and Mualla Cengiz Cinku
Istanbul University, Faculty of Engineering, Dept. of Geophysical Engineering, 34320, Avcilar, Istanbul, Turkey
(hakan.ucar@ogr.iu.edu.tr)
1) SUMMARY
In this study, anisotropy of magnetic susceptibility measurements were carried out on 21 different sites from
the Eastern Anatolian Region to determine the determine the flow direction of lavas. In total, 133 volcanic
samples from Pliocene-Quaternary ages were measured on 18 different measurement position by using
Bartington MS2B susceptibility device and AMS-BAR software. As a result of the AMS measurements,
magnetic lineations associated with a magma flow in horizontal direction have been determined. The magma
flow directions are generally towards the volcano vent.
Detailed rock magnetic experiments, including thermomagnetic measurements, acquisition of isothermal
remanent magnetization (IRM), and thermal demagnetization of three-axes composite IRM, were conducted on
each pilot sample. Thermomagnetic experiments were performed on representative samples by heating in air,
using an Bartington MS2 susceptibility bridge fitted with an oven unit. IRMs were acquired using an ASC
pulse magnetizer (Model IM-10-30). Steps of 1, 0.4, and 0.12 T were imparted along the Z-, Y-, and X-axis,
respectively. Subsequently, samples were thermally demagnetized to identify the magnetic carriers based on
their coercivity and unblocking behaviour. As a result of this measurements, most of the samples are
characterized by titanomagnetite.
2) AIM OF THE STUDY
This study was carried out to determine the relationship between magma flow directions of the
samples(Pliocene-Quaternaty ages) from three volcanoes(Tendurek, Suphan and Girekol) and magnetic
lineation with the help of AMS measurements.
3) GEOLOGICAL SETTING OF THE REGION
Eastern Anatolia comprises one of the high plateaus of the Alpine-Himalaya mountain belt with an average
elevation of ~2 km above the sea level. Available geochronologic data indicate that the volcanism started in the
south of the region around the north of Lake Van and continued towards the norths in a age interval of 15.0 Ma
to 0.4 Ma. The products are exposed as stratovolcanoes like Ağrı, Tendürek, Süphan and Girekol with the
eruption of andesitic to rhyolitic lavas, ignimbrites and basaltic lava flows (Pearce vd., 1990; Keskin vd.,
1998).
4) SAMPLING AREA
Figure 1: Plate motions of Turkey and its
environment. According to GPS measurements,
Arabian Plate moves towards Northwest at a rate of
18±2 mm every year. As a result of this movement,
Anatolian block moves towards West at a rate of
24±2 mm across North Anatolian Fault(NAF) and
9±2 mm across East Anatolian Fault(EAF) every
year. Also, West Anatolian Region moves towards
Southwest at a rate of 30±1 mm every year(Okay
and Tüysüz, 1999).
Figure 2: Tectonic units, distribution of collision-
related volcanic products and volcanic centers across
Eastern Anatolia. E-K-P: the Erzurum-Kars Plateau;
NATF and EATF: North and East Anatolian
Transform Faults. I : The Pontide unit which is
represented basically by a magmatic arc, II :
Northwestern Iran Unit, III : The Eastern Anatolian
Accretionary Complex (EAAC), IV : The Bitlis-
Poturge Massif (BPM) and V : Arabian Plate. Green
areas : Ophiolitic melange, Pink and red areas :
Volcanic units which is related to the collision, White
areas : Young units (Keskin et al., 2003)
Figure 3: Geological setting of the region and locations of the samples(modified after MTA, 2002)
5)
Figure 4: Lavas belonging to
Tendurek volcano.
Figure 5: Lavas belonging to
Girekol volcano. Figure 6: Lavas belonging to
Suphan volcano
6)
7) THERMOMAGNETIC MEASUREMENTS, IRM AND THERMAL DEMAGNETIZATION OF
THREE-AXES COMPOSITE IRM Figure 7: The results of the
thermomagnetic analysis
reveal three different types of
behaviour (Fig. 7a, d, g).
Most samples with minor
alteration are characterized by
a single ferromagnetic phase
and Curie temperatures
between 550 and 580 °C,
indicating the presence of Ti-
poor titanomagnetites (Fig.
7a). In the second group, low
Curie temperatures between
260 and 280 °C are observed
that are typical of titanium-
rich titanomagnetite or low-
temperature oxidized titano-
maghemite (Fig. 7d).
The increase in magnetization seen in the cooling curve suggests oxidation of high-titanomagnetite/
titanomaghemite to low-Ti magnetite. The third group is defined by two different thermomagnetic phases during
heating and a single phase in the cooling curve. The cooling curves show a loss in magnetization, indicating
oxidation of Ti-poor titanomagnetite to Ti-rich titanomagnetite. The Curie temperatures for these types of samples
are 550 and 580 °C (Fig. 7g). In the heating curves, a decrease in susceptibility between 320 and 350 °C shows
the transformation of titanomaghematite to magnetite, and a Curie point between 550 and 580 °C. Typical
examples of IRM acquisition and thermal decay experiments are shown in Fig. 7. IRM curves show rapid
acquisition of magnetization to about 300 mT in general, suggesting the existence of low-coercivity ferromagnets
(Fig. 7b, e, h). Thermal demagnetization of the cross-component IRM shows that the low-coercivity component is
gradually unblocked beneath 400 °C (Fig. 7i) and 600 °C, showing the existence of Ti-poor magnetite (Fig. 7c).
Another group, is characterized by the thermomagnetic curves, a slower increase in IRM, and a higher unblocking
temperature (Fig. 7e, f). (Hisarlı et al., 2016)
8) AMS MEASUREMENTS
Figure 8: Lineations are in horizontal direction and have low inclination angles for D31, D27, D10, D12, D13, D14, D2, D5, D8,
D6, D20, D22 sites. Blue squares : Kmin(Foliation), Green triangles : Kint, Red circles : Kmax(Lineation).
Figure 9: Lineations are in horizontal direction and have low
inclination angles for D1, D18, D21, D3, D7, D42, D43 sites.
Blue squares : Kmin(Foliation), Green triangles : Kint, Red
circles : Kmax(Lineation).
Figure 10: Graph representation of Flinn diagram
(Lineations – Foliations)
9) MAGNETIC LINEATION AND
MAGMA FLOW DIRECTION
Figure 11: In the Tendürek volcano, the
magnetic lineations represent a magma flow in
the horizontal direction, and the lineations are
generally towards the volcano vent.
Figure 12: In the Süphan volcano, the
magnetic lineations represent a magma
flow in the horizontal direction, and
lineations(arrows with red point) are
generally towards the volcano vent.
Figure 13: In the Girekol volcano,
the magnetic lineations(arrows with
red point) represent a magma flow in
the horizontal direction.
11) CONCLUSIONS
According to the thermomagnetic measurements, isothermal remanent magnetization
(IRM) and thermal demagnetization of three-axes composite IRM, most of the samples
are characterized by titanomagnetite.
When percentages of susceptibility and SiO2 of specimens were evaluated, it was
determined that generally basic specimens have high susceptibility and susceptibility
decreases relatively for acidic specimens.
Three different volcanoes was investigated to determine the relationship between magma
flow direction and magnetic lineation. In the Tendurek, Girekol and Suphan volcanoes,
magnetic lineations are associated with a magma flow in the horizontal direction, and the
lineations are generally towards the volcano vent. It is understood that the magnetic
lineations correspond to magma flow direction.
10) SUSCEPTIBILITY AND
CHEMISTRY OF VOLCANISM
Figure 14: Graph representation of
volcanic rocks obtained due to
susceptibility and SiO2 component.
12) REFERANCES 1) Keskin, M., Pearce, J.A. and Mitchell, J.G. (1998). Volcano-stratigraphy and geochemistry of collision-related volcanism on the Erzurum-Kars
Plateau, North Eastern Turkey, Journal of Volcanology and Geothermal Research, V.85/1-4, pp. 355-404.
2) Keskin, M. (2003). Magma generation by slab steepening and breakoff beneath a subduction–accretion complex: an alternative model for
collision-related volcanism in Eastern Anatolia, Turkey. Geophysical Research Letters 30 (24).
3) MTA (2002) Geological map of Turkey (1:500000 scale). General Directorate of Mineral Research and Exploration, Ankara
4) Okay, A.I. and Tüysüz, O. (1999). Tethyan Sutures Of Northern Turkey. In: Durand, B., Jolivet, L., Horváth, F. & Séranne, M. (Eds), The
Mediterranean Basins: Tertiary Extension Within The Alpine Orogen. Geological Society, London, Special Publications,156, 475-515.
5) Pearce, J.A., Bender, J.F., De Long, S.E., Kidd, W.S.F., Low, P.J., Güner, Y., Saroglu, F., Yilmaz, Y., Moorbath, S. and Mitchell, J.G. (1990).
Genesis of collision volcanism in Eastern Anatolia, Turkey, J. Volcanol. Geotherm. Res., 44, 189-229.
6) Hisarlı, Z. M., Çinku, M. C., Ustaömer, T., Keskin, M., & Orbay, N. (2016). Neotectonic deformation in the Eurasia–Arabia collision zone, the
East Anatolian Plateau, E Turkey: evidence from palaeomagnetic study of Neogene–Quaternary volcanic rocks. International Journal of Earth
Sciences, 105(1), 139-165.