The volatile content of the Earth Mantle; highlights, progress and future directions

Alberto Saal1, Erik Hauri2, Greg Hirth1, Marc Parmentier1, Don Forsyth1

1. Dept. of Geological Sciences, Brown University2. Dept. of Terrestrial Magnetism, Carnegie Institution of Washington

AcknowledgementRajdeep Dasgupta, Marc Hirschmann, Katie Kelly, Alison Shaw, Terry Plank, Liz Cottrell, Paul Asimow, Hans Keppler, Shun-Ichiro Karato, Cyril Aubaud

Possible Loci of Hydrous Melting in the Mantle

Volatiles have significant effect on the mantle solidus, the composition and physical properties of melt, magma crystallization and differentiation, style of magma eruption, generation of mantle heterogeneity, seismic and electrical properties of minerals, rheology of the mantle

Hirschmann CIDER 2009

Cameca 6F:

Low detection limits C 1ppm H2O 2 ppm; F 0.1 ppm; S 0.3 ppm; Cl 0.03 ppm

High spatial resolution 10-20µm

Cameca NanoSims:

Low detection limits C 0.13 ppm H2O 0.4 ppm; F 0.1 ppm; S 0.3 ppm; Cl 0.03 ppm

High spatial resolution 4-20µm

Concentrations of C, H2O, F, S, Cl collected together

Hauri et al., unpublished; 2002; 2006Koga et al., 2003; Aubaud et al., 2004

Highlights Technical Aspects:

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H2O ppm

F p

pm

Water in samples from the Moon

• Solubility of volatiles in NAM.Kohlstedt et al. (1996); Kawamoto et al. (1995); Bolfan-Casanova et al. (2000); Smyth et al. (2003); Mierdel K, Keppler H (2004); Komabayashi et al. (2005); Rauch & Keppler (2002); Smyth et al (2005); Mierdel et al. (2007); Jacobsen (2005).

• Partitioning of volatiles between NAM and melt. Koga et al., (2003); Aubaud et al., (2004); (2008); Hauri et al., (2006), Tenner, et al (2009); O'Leary et al. (2009); Hirschmann (2006).

• The influence of volatiles (water) on mantle wedge melting. Grove et al., (2006); Kushiro et al., (1968); Mysen & Boettcher (1975).

• Effect of volatiles on rheology, seismic anisotropy and electrical conductivity as a way to map water content from geophysical observations. Karato (2001); Mei &Kohlstedt (2000); Hirth & Kohlstedt (2003); Jacobsen (2006)

• Trace element partitioning between slab fluids and minerals. Green & Adam, (2007); Kessel et al. (2004); (2005); Schmidt et al. (2004); Manning (2004); Johnson and Plank (1999); Keppler (1996).

• Carbonated peridotite/eclogite solidus. Understanding the importance of CO2 flux on the onset of silicate melting and deep carbonatite generation. Dasgupta et al., (2004); (2005); (2006); (2007a); (2007b); Dasgupta and Hirschmann (2007)

Highlights Experimental Work:

• Volatiles in submarine glasses.Dixon et al. (2002); Worman et al. (2006); Cartigny et al (2008); Stroncik& Haase(2004); many others

• Volatiles in melt inclusions. Wallace (2005); Saal et al. (2002); Portnyagin et al.(2009);Metrich and Wallace (2008); many others

• Water in pyroxenes.Wade et al. (2008)

• How water drive melting in the mantle.Kelley et al. (2006), Langmuir et al (2006); Portnyagin et al.(2009); Asimow & Langmuir (2004); Plank et al. (2009); Hirschman (2006).

• Correlation pre-eruptive H2O contents with melt oxidation state.Kelley & Cottrell (2009)

• Hydrogen isotope fractionations in melt inclusions from arc lavas to OIB.Shaw et al., (2008); Hauri (2002)

Highlights Observations and Modeling:

PriestleyMcKenzie, 2006

What is the Asthenosphere?

Progress Report:

Ritsema: S40FR: 125 Km

• The unique physical properties of the Asthenosphere have been attributed to either mineral properties at relevant temperature, pressure, and water content or to the presence of a low melt fraction.

• We rely on the composition of the asthenosphere to understand the parameters controlling the observed physical properties of this mechanically weak region of the upper mantle.

• We resort to the geochemical studies of Mid-Ocean Ridge Basalts (MORB) to unravel the composition of the Asthenosphere.

• It is important to determine to what extent the geochemical variations in axial MORB do represent a homogeneous mantle composition and variations in the physical conditions of magma generation and transport; or alternatively, they are inherited from mixing processes during the aggregation of melts originated from an heterogeneous mantle.

• Lavas from intra-transform faults and seamounts share a common mantle source with axial MORB, they represent smaller melt volumes tapped locally from areas lacking steady-state magma chambers and along-axis transport. Thus, they are melts experiencing relatively less mixing and differentiation, and their compositions provide insight into the heterogeneity of the Asthenosphere.

Axial, seamount and intra-transform basalts

Seamounts

Intra-transform

Ridge axis

Trace element composition normalized to Primitive MantleT

race

Ele

me

nts

/PM

Enriched

Normal

Depleted

Normalization values from McDonough and Sun 1995

Significant fractionation of very incompatible elements

Enriched

Normal

Depleted

Essentially a two component Asthenosphere EnrichedNormalDepleted

Mixing or residence time of the enriched component in the upper mantle

Workman et al., 2006

Volatiles: Fluorine

Volatiles: Fluorine

Enriched

Normal

Depleted

Volatiles: Chlorine

Enriched

Normal

Depleted

Stoncik & Haase (2004)

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H2O/Ce

Cl/K

seawater

Mantle source

Cl-Contamination and Water

Mantle values for OIBStoncik and Haase (2004)

Volatiles: Water

Enriched

Normal

Depleted

Volatiles: Carbon dioxide

Cartigny et al. 2008

CO 2/N

b ~600

Degassing

10%

90%

Saal et al. 2002

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10000

0.1 1 10 100Nb [ppm]

CO

2 [p

pm]

Iceland NVZ

Siqueiros MI

MORB

Depleted

Enriched ?

CO 2/N

b ~300

Volatiles: Carbon dioxide

Enriched

Normal

Depleted

Cl50

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CO

2

Cl assimilation of Host Glasses

CO2= 22(±14) + Cl x 57(±8))

Cl assimilation of Host Glasses

CO2 Degassing

Host Glasses

Melt Inclusions

MORB

100

1000

10000

1 10 100 1000Cl

CO

2

Using average Cl content of 150 ppm for Enriched Cl uncontaminated lava we get 8600±1000 CO2

Using the average Nb content of 15 ppm for the Enriched Cl uncontamina-ted lava, we get a CO2/Nb of 570±70 consistent with the CO2/Nb for the Enriched mantle by Cartigny et al., (2008)

Thus, given the Nb content of a melt we can use the CO2-Nb-Cl relationship to estimate the primitive CO2 and Cl contents for degassed and chlorine-contaminated basalt magmas, and hence constrain degassing and contamination histories

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Nb/La

CO

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2O

MORB 10% enriched + 90% depleted

Enriched

Depleted

Volatiles: CO2/H2O

The new data on intra-transform and seamount lavas from the EPR, indicate the presence of a two mantle component forming the Asthenosphere: An incompatible trace element and volatile enriched mantle immersed in a very depleted mantle, which is significantly more depleted than the estimated average MORB source.

Such heterogeneity should be considered when interpreting the physical properties of the Asthenosphere

Progress Report Conclusions:

Approximate concentrations

Depleted Mantle H2O 50 ppm; CO2 20 ppm; Cl 1 ppm; F 7 ppm

Enriched Mantle H2O 500 ppm; CO2 420 ppm; Cl 10 ppm; F 18 ppm

Total Mantle H2O 366 ppm; CO2 301 ppm; Cl 7 ppm; F 15 ppm

The key points are: (a) The H/C ratio of the bulk silicate Earth is superchondritic, owing chiefly to the high H/C ratio of the exosphere. (b) the H/C ratio of the mantle is lower than that of the exosphere, which requires significant H/C fractionation during ingassing or outgassing at some point in Earth history.

Hirschmann and Dasgupta (2009)

Volatile Budget!

Future work:

• Hydrogen solubility and the influence of hydrogen on physical properties of lower mantle minerals.

• Constraining the influence of mixed volatiles in the properties of planetary cores melting, crystallization, and geochemical

• Volatile heterogeneity in the Earth's mantle, are they coupled to major element?

• Understanding effects of mixed volatiles on mantle melting,

• What are the solidus temperatures of peridotite at low water fugacity

• S and Cl isotopes

• The effect of redox states on volatile-present melting

• Behavior of volatiles during early Earth differentiation accretion, giant impact, and core-mantle segregation

• Damp/carbonated mantle solidus at high pressure

• What are the properties of fluids in subduction zones? (e.g., mineral solubilities).

• Partitioning of noble gases during melting at all pressures.

• Mass balance: is the mantle outgassing or ingassing.

Pahlevan and Stevenson (2007) suggested that the proto-Earth and proto-lunar disk would have diffusively equilibrated after the giant impact, and that the volatile depletion of the Moon may be explained by hydrodynamic escape driven by an outflow of hydrous materials previously accreted to the Earth.

m = 2x10-3 ME

m = 2x10-2 ME

2000 K

Volatile-rich-meteorite bombardment during the lunar magma ocean

Ryder, 2002

Many models have proposed significant accretion of material during and after the LMO

Our results suggest that either hydrodynamic escape was not complete or a significant amount of water was accreted to the Earth-Moon system very soon after the giant impact.

Marty, 2008

Earth’s zircons as old as 4,325 Ma with oxygen isotopes of 6.5 ‰ provide evidence for the presence of liquid water near Earth’s surface within ~230 Ma of Earth’s accretion.

This observation strongly suggests that either the Earth had significant amounts of water before the giant impact, or the material accreted to the Earth and Moon within a narrow time window after the giant impact but before 4.3 Ga was rich in volatiles

Valley et al., 2002; Cavosie et al., 2005

Future Work funded by the LASER

To characterize the volatile contents of the different Lunar volcanic glasses compositional groups defined by Delano (1986). Specially those showing different proportion of KREEP component.

To determine the volatile contents in lunar Mare basalts melt inclusions and pyroxenes

melt inclusionspyroxenes

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MELT INCLUSION

196 µ

Why are melt inclusions important to the study of volatiles in magmatic systems?

They have a more primitive (pre-eruptive) volatile content than glasses, before shallow level degassing or contamination occurred

Histogram of Nd isotopic ratios in basalts

Warren et al., 2008

Nor

mal

ized

Fre

que

ncy

(%)

Enriched

Normal

Depleted

The problem with the calculation of CO2

a) Difference of 0.1 gr/cm3 in density of melt used gives a difference of 450 ppm CO2.

b) Difference in the melt-glass transition temperature used, the calculated CO2 content will significantly vary ~ 1000 ppm CO2 for each 100oC difference! (e.g., 1000 rather than 700 oC will produce a calculated CO2 content of 10000 ppm and 13000 respectively)

c) Difference of 1% vesicularity will produce a difference of 600 ppm CO2

d) Considers not bubble accumulation!

e) d13C fractionation (D) between measured gas and dissolved carbon vary widely, between 2 and 8 per mil. Such variations cannot be modeled neither by equilibrium nor Rayleigh fractionation. If this is the case, what evidence do we have that the carbon content in the popping rocks is the primordial content?

H2O-CO2 saturation model.

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Isobars and Isopleth

100 bars

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XH2OV

= 0.1

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500 bars

600 bars

Melt Inclusion

Host Glass

H2O wt%

400 bars

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0 0.03 0.06 0.09 0.12 0.15H2O [wt%]

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The generation of the enriched MORB require two-stage-melting: an ancient low degree melting (~ 1%) that metasomatise the deplete mantle, which later undergoes large extent of melting (~6-10%)

Halliday et al., (1995); Niu and O’Hara (2003)

Donnelly et al., (2004)Phipps-Morgan and Morgan (1999)

Dasgupta and Hirschmann 2006

0.4% H2O

Dry

0.75% H2O+ Aug

+ Plag

Olivine

Major elements suggest peridotitic sources for both components

Enriched

Normal

Depleted

Fractionation Corrections and Water Content

0.70230.70240.70250.70260.70270.70280.70290.7030

1818.218.418.618.81919.219.4

00.511.522.533.54[La/Sm]N

0.512950.513000.513050.513100.513150.51320

0.7024 0.7026 0.7028 0.7030

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5.0

0.087Sr/86Sr

Al72

Ca72Fe72

Na72Ti72

[A] [B]

Dasgupta and Hirschmann 2007

Dasgupta et al 2009