Redox state at ultrahigh-pressure metamorphism: Constraint from the chinese continental scientific drilling eclogites
Journal
Island Arc
Journal Volume
22
Journal Issue
1
Pages
25-36
Date Issued
2013
Author(s)
Abstract
In order to estimate the fluid composition, C-species of the CCSD (Chinese Continental Scientific Drilling) eclogites were investigated. Graphite is always recognized with pyrite in the eclogites, suggesting their growth from the H2O-rich (CO2-poor) fluids released during metamorphism. The studied eclogites contain vacancy (CaEs component =Ca0.5□0.5AlSi2O6) in clinopyroxene. Therefore, Fe3+ content in clinopyroxene cannot be calculated based on their chemical composition determined by an electron probe micro analyzer. We estimated Fe3+/ΣFe based on the Mössbauer analysis and calculated the pressure-temperature (P-T) conditions from the assemblage of phengite-garnet-clinopyroxene-(coesite) as P=3-4 GPa, and T=650-780°C. The P-T-values obtained in this study show lower values than those which were previously reported elsewhere for the CCSD eclogites, suggesting that the effect of Fe3+ estimation is significant. © 2013 Wiley Publishing Asia Pty Ltd.
Type
journal article