A novel in situ approach to study trace element partitioning between silicate and iron rich liquids at extreme conditions

Details A novel in situ approach to study trace element partitioning between silicate and iron rich liquids at extreme conditions A novel in situ approach to study trace element partitioning between silicate and iron rich liquids at extreme conditions

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p11a1575p&link_type=abstract

American Geophysical Union, Fall Meeting 2011, abstract #P11A-1575

Other

[1015] Geochemistry / Composition Of The Core, [5410] Planetary Sciences: Solid Surface Planets / Composition, [5430] Planetary Sciences: Solid Surface Planets / Interiors

Scientific paper

From early partitioning studies [1] it has been emphasized that the Earth s mantle (and crust) should be depleted of highly siderophile elements (HSE) and noble metals. However, these elements are found in excess in the Earth s upper mantle and crust (close to the chondrite abundance) and this phenomenon has been a long-lasting problem in the interpretation of geochemical signatures of the Earth s mantle and the geochemistry of core-mantle differentiation. This inconsistency has been explained either by a differentiation model with a chemical equilibrium at the bottom of a silicate magma ocean while a metallic core forms at a depth of 1100 km [2] or by the so called late veneer hypothesis. The later postulates an enrichment of HSE in the Earth s mantle by an intensive meteorite bombardment 100±50 My after the Earth s accretion [3]. So far, all the metal-silicate partitioning studies make use of classical HP-HT techniques, e.g., multi-anvil press, and therefore are limited in PT conditions in the Earth s mantle (max. 15-20 GPa/2200°C). There are obvious needs for experiments at much higher pressures and temperatures as it remains unclear if determined metal-silicate partition coefficients of HSE can be extrapolated to much higher pressures and temperatures. Using Palladium as an example, it has recently been shown that the partition coefficient decreases with increasing pressure (1.5 to 15 GPa) and temperature (1400 to 2200 °C) [2]. Here, we present the first preliminary data on metal-silicate trace element partitioning from a new experimental approach obtaining in situ information at high pressures and temperatures up to 50 GPa and 4400 K. Experiments were performed at the high pressure beamline ID27 (ESRF, Grenoble, France) using double-side laser-heated diamond-anvil cells (DAC). The set-up enables analysis of samples before, during and after laser heating by means of XRF and XRD. The full details of the experimental techniques and setup are discussed in this presentation. The sample chamber was loaded with a trace element (HSE: Pd, Ru; Zr (metal incompatible)) doped chondrite glass chip placed next to a trace element free metal foil (Fe90Ni10) very close to early Earth composition. Laser heating was used to sequentially increase the temperature at the interface of the chondrite glass and the metal foil, until the observation of S(Q) in the diffraction data, confirming the onset of melt. Time resolved fluorescence analysis was used to follow the evolution of the varying concentration of the trace elements in the laser heating spot. First qualitative analysis verifies existing data and shows a strong partitioning of HSE (Pd, Ru) into the metal liquid with increasing temperature whereas Zr prefers the silicate melt. To fully understand the results obtain during these first in situ partitioning experiments, recovered samples are currently investigated with other probes to get quantitative data analyses. [1] Ertel et al (1999). Geochemica and Cosmochimica Acta, 63, 2439-2449 [2] Righter et al. (2008). Nature Geoscience 1, 321-323 [3] Holzheid et al. (2000). Nature, 406, 396-399

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