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Mobility of Chromium in High-Temperature Crustal and Upper Mantle Fluids
Speaker Miss Jingyi Huang, Johns Hopkins University
Date 25 July 2019 (Thursday)
Time 14:30 - 16:00
Venue Room 4503 (Lift 25-26), HKUST

Chromium is mobile in ultramafic magmas but its mobility in high temperature fluids has long been unclear. Studies of some chromium-rich ophiolites have suggested chromium mobility in upper mantle fluids. However, the mechanism is poorly understood because Cr(III) is so insoluble in water. We used previous estimates of aqueous Cr-species and published experimental and ab initio studies of the solubility of πΆπ‘Ÿ2𝑂3 in 𝐻𝐢𝑙 and 𝐾𝐢𝑙 fluids at 500 -1,200 °C and 0.1 -6.0 GPa together with the Deep Earth Water Model to calibrate a thermodynamic equation of state for the Cr(II) complex πΆπ‘ŸπΆπ‘™(𝑂𝐻)0. Our model predicted low Cr solubilities (0.15 π‘šπ‘”βˆ™π‘˜π‘”H2O-1) in a mid-ocean ridge fluid and very high solubilities (3,500 π‘šπ‘”βˆ™π‘˜π‘”H2O-1) in saline, peridotitic diamond-forming fluid consistent with expectations for these environments. In pelitic, mafic eclogitic, and serpentinite fluids, predicted Cr solubilities varied widely depending on the oxygen fugacity and Cl concentration. The predicted predominance of Cr(II) in deep fluids and Cr(III) in minerals suggests that precipitation of Cr-mineral components is a redox reaction.