Pitfalls in geothermobarometry of eclogites: Fe3+ and changes in the mineral chemistry of omphacite at ultrahigh pressures

Journal article

Authors/Editors

Research Areas

No matching items found.

Publication Details

Author list: Proyer A, Dachs E, McCammon C

Publisher: Springer

Place: NEW YORK

Publication year: 2004

Journal: Contributions to Mineralogy and Petrology (0010-7999)

Journal acronym: CONTRIB MINERAL PETR

Volume number: 147

Issue number: 3

Start page: 305

End page: 318

Number of pages: 14

ISSN: 0010-7999

eISSN: 1432-0967

Languages: English-Great Britain (EN-GB)

View in Web of Science | View on publisher site | View citing articles in Web of Science

Abstract

The relatively low-variance mineral assemblage of a talc-kyanite eclogite from Dabie Shan enabled application of both conventional geothermobarometers (garnet-clinopyroxene geothermometer and the garnet-omphacite-phengite geobarometer) and a multi-equilibrium method to determine peak P-T conditions (THERMOCALC, "average PT"). The results were highly discrepant: 840 degreesC / 31.1 kbar vs. 590 degreesC / 29.8 kbar. Mossbauer spectroscopy showed that Fe3+/Fe-total in omphacite was significantly higher than the value obtained from standard formula recalculation. When the activities were corrected for Fe endmembers, geothermobarometry gave consistent results (606 degreesC / 31.3 kbar vs. 585 degreesC / 30.8 kbar). These are close to those obtained earlier by "average PT", confirming the robustness of the multi-equilibrium approach. The high Fe3+ concentration in omphacite is best explained using a Ca-eskola endmember Ca-0.5[](0.5)AlSi2O6 and allowing corresponding vacancies in the omphacite structure.

Keywords

No matching items found.

Documents

No matching items found.