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High Pressure Mantle Geochemistry


The majority of eclogites and garnet pyroxenites studied show that the Lu–Hf system records ‘older’ mantle events than the Sm–Nd system, but neither necessarily records the protolith age. Both the Lu–Hf and the Sm–Nd systems are prone to being reset by entrainment in high-temperature kimberlite and/or basaltic magmas. In addition new mineralogical, trace element and Nd-Hf-Sr-O isotopic data for eclogites and garnet pyroxenites reveal some similarities but also important chemical and isotopic differences that support a distinct provenance (i.e., age and process). Continental and oceanic garnet pyroxenites have relatively homogeneous O isotope compositions identical to peridotitic mantle and P-type solid inclusions in diamonds. In contrast on- and off-craton continental eclogites have heterogeneous O isotopes with similarities to E-type solid inclusions in diamonds. Cratonic eclogites and garnet pyroxenites have heterogeneous Hf–Nd–Sr–(O) isotope ratios that define a positive Hf–Nd isotope array and a negative Nd–Sr isotope array. Isotopic variability encompasses depleted (mid-ocean ridge basalt and ocean-island basalt) to enriched mantle compositions (Group I and II kimberlites) and overlaps with cratonic garnet peridotite xenoliths.


Staff: Funding: Brazilian Government






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