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The (Na–Ca)amphibole–albite–chlorite–epidote–quartz geothermobarometer in the system S–A–F–M–C–N–H 2 O. 1. An empirical calibration
Author(s) -
TRIBOULET C.
Publication year - 1992
Publication title -
journal of metamorphic geology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.639
H-Index - 114
eISSN - 1525-1314
pISSN - 0263-4929
DOI - 10.1111/j.1525-1314.1992.tb00104.x
Subject(s) - amphibole , tremolite , epidote , geology , plagioclase , albite , greenschist , chlorite , geochemistry , mineralogy , metamorphic facies , mineral , quartz , metamorphic rock , chemistry , materials science , facies , metallurgy , asbestos , paleontology , organic chemistry , structural basin
The proposed geothermobarometer is based on an empirical calibration which takes account of two equilibria involving the tremolite, edenite, pargasite and hastingsite components in amphiboles. It has applications to assemblages found in metabasic rocks of widely different chemical compositions (magnesian to Fe‐rich metabasalts), and for metamorphism ranging from lower greenschist to highest amphibolite facies. Knowing the Si (T1) , Al iv , Al vi , Fe 3+ , Fe 2+ , Mg, Ca, Na M4 , Na A and A vacancy in an amphibole, and the Al 3+ and X Mg in coexisting epidote and chlorite, it is possible to calculate two values of In K d for this assemblage. These equilibria involve edenite‐tremolite and (pargasite/hastingsite)‐tremolite end‐members in amphibole (the calculation program is given). For these equilibria, the isopleths (iso‐values of K d ) have been calculated for 0.27 < X Mg < 0.75 and 0 < X Fe3+ = Fe 3+ /(Fe 3+ + Al vi ) < 0.8. It is then possible to determine pressure and temperature directly when X Mg , X Fe3+ , In K d for tremoliteedenite and In K d for (pargasite/hastingsite)‐tremolite are known. Application of this geothermobarometer is limited to Ca‐free plagioclase assemblages, and complete P–T paths can be drawn only if all the minerals are considered together. Phase relations at successive stages of crystallization can be constrained by studying the relationships between the coexisting minerals, their zoning and the metamorphic fabrics.