DCO Project Summary

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Project Title
DMGC - The Nature of Diamond Forming Liquids in the Mantle and Direct Estimates of Deep Mantle Stresses from Diamond Plasticity
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11121/5621-4594-2813-8282-CC
Description

Thermodynamic parameters have been calibrated for a geobarometer suitable for use on eclogitic mantle xenoliths. The barometer is based on the incorporation of 4-fold Al in omphacitic clinopyroxene coexisting with garnet and has been calibrated using the results of piston cylinder and multi-anvil experiments performed between pressures of 2.5 to 7 GPa and temperatures from 900°C to 1550°C. Starting materials were hydrous and anhydrous synthetic mixtures of basaltic bulk compositions that yielded a homogeneous bimineralic garnet-clinopyroxene phase assemblage. The experimental dataset was expanded by employing results from some previous experimental studies conducted in eclogitic systems, which widened the range of applicable conditions and compositions. The calibration reproduces experimental pressures to within 0.4 GPa at the 95% confidence interval. The barometer was then tested with natural eclogites from various mantle xenolith locations covering a wide P-T-X regime. The barometer allows precise and accurate pressures for bimineralic eclogite xenoliths to be determined without invoking additional accessory phases.  In addition, high-pressure deformation experiments have been performed in single crystals of diamond at 10 GPa and 1600°C. Samples are under analysis.

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