What is it about?
Mantle xenoliths Re-Os isotope dating and PGE distribution were applied to clearing up the East Antarctic mantle evolution. In view of the geochemical features, the Re–Os isotope system of mantle xenoliths is of special importance in the interpretation of mantle processes along with the evaluation of the age of the mantle protolith (harzburgite). The concentrations and proportions of the platinum group elements (PGE)—Os, Ir, Ru, Rh, Pt, and Pd — along with their refractories and different sensibility to variations in the redox conditions, as well as pronounced sidero- and chalcophile properties, allow one to characterize the geochemical processes in the mantle that are inaccessible to study using other groups of elements.
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Why is it important?
The treated xenoliths represent the mantle section of the East Antarctic Craton down to depths of 60–80 km. The osmium isotope composition of these nodules testifies to the beginning of the formation of the lithospheric mantle in the considered region of the craton 2400 Ma ago. The absence of any signs of Early Archeozoic lithosphere points either to partial destruction of the lithosphere at the convergent boundary of the plates in the Late Archean or to thermal erosion of the Archean lithosphere under the effect of a deep-seated plume in the Mesozoic during rift formation.
Perspectives
The most important result of this study is the evidence from the rhenium–osmium isotope systematics of mantle nodules that the formation of the lithospheric mantle in the considered area of the East Antarctic Craton began 2400 Ma ago or earlier. The nonfractionated mode of EPG distribution in mantle peridotite of Jetty Oasis, as well as certain similarities to the model PGE distribution for the upper primitive mantle, points to the possibility of the retention of the primary geochemical characteristics. The absence of any traces of a more ancient lithospheric mantle complementary to the Early Archean continental crust might have resulted either from partial delamination of the lithosphere at the convergent boundary of the plates in the Late Archean or from the thermal erosion of the deep-seated Archean lithosphere under the action of an ascending plume in the Mesozoic in the course of rifting.
Boris V Belyatsky
Karpinsky Geological Institute (VSEGEI)
Read the Original
This page is a summary of: The Age and Evolution of the Lithospheric Mantle in the East Antarctic Craton: Osmium Isotope Composition and the Distribution of Platinum Group Elements in Spinel Lherzolite Nodules, Doklady Earth Sciences, April 2019, Pleiades Publishing Ltd,
DOI: 10.1134/s1028334x19040226.
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