Fractionation of highly siderophile elements in the lower oceanic crust
Final Report Abstract
The data on 735b and published data on the lower crustal Wadi Tayin section in the Oman ophiolite indicate that primitive Mg rich lithologies hold the key to understanding the behavior of HSE during magmatic fractionation processes in the oceanic crust and during magma transport in the mantle. Low abundances of the PGE and Re in the most abundant lithologies at 735b (olivine gabbro) hint that most of the fractionation of these elements occurs, either near the Moho, or below. HSE patterns and abundances in the lower crust drilled at 735b and in the Wadi Tayin section of the Oman ophiolite differ substantially. The cause and controls on these differences are not clear, but are likely caused by differences in spreading rate or mantle composition. The peridotite like HSE composition of some troctolites found at relatively high stratigraphic levels in the 735b crust supports the sill model for the formation of layer 3 of very slow spreading oceanic crust. Several open questions that result from the present study and comparison with MORB data and the lower crustal data from Oman can be addressed by further study of cumulates from the deepest level of the oceanic crust and troctolites and dunites that have formed in faster spreading oceanic crust: What are the compositions, processes and fractionation of HSE in cumulates near the base of the oceanic crust? Are there significant differences in HSE and chalcogen element composition between very slow, slow and fast spreading lower crust? Which geodynamic processes control these differences? Is the radiogenic initial Os isotopic composition of lower crustal gabbros and troctolites caused by contamination of magma with seawater in the lower crust, or are these signatures inherited from enriched mantle reservoirs?
Publications
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(2012) Fractionation of highly siderophile elements in the lower oceanic crust at ODP Site 735b, SW Indian Ridge. Goldschmidt Conference Montreal
Meyer, C. and Becker, H.
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(2012) Fractionation of highly siderophile elements in the lower oceanic crust at ODP Site 735b, SW Indian Ridge. SPP IODP/ICDP-Colloquium, Kiel
Meyer, C. and Becker, H.
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(2013) Composition of the Oceanic Crust: Where have all the noble metals gone? Goldschmidt Conference Florence
Becker, H. and Meyer, C.
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(2013) Fractionation of highly siderophile and chalcogen elements in the lower oceanic crust at Site 735B. SPP IODP/ICDP-Colloquium, Freiberg
Becker, H. and Meyer, C.
