1988/03/01 by Somnath Dasgupta, P. K. Bhattacharya, G. Chattopadhyay +4
paper · doi:10.1180/minmag.1988.052.364.09
crossref issued 1988/03/01 · crossref published 1988/03/01 · crossref published-print 1988/03/01 · crossref created 2006/12/07 · crossref published-online 2018/07/05 · crossref deposited 2021/02/05 · crossref indexed 2026/07/30
Abstract Mg-Mn amphibole (tirodite), with or without pyroxmangite in the total absence of pyroxenes and high-calcic pyroxenoids, occurs in the Mn silicate rocks of the Sausar Group, India. The rocks were metamorphosed to amphibolite facies condition ( T ∼ 650°C, P ∼ 6 kbar). Tirodite-pyroxmangite pairs developed in both carbonate-free and rhodochrosite-bearing assemblages. Also tirodite coexists with either kutnahorite or manganoan calcite in the absence of pyroxmangite. Mineral reactions inferred from modal abundances and compositions of the phases indicate stabilization of the amphibole alone from a bivalent cation-bearing residual unbuffered X CO 2 system with X Mn X CO 2 assemblages with X Mn > 0.35. Pyroxenes and high-calcic pyroxenoids did not appear in the present situation, though they occur elsewhere in rocks with broadly similar contents of immobile components. Closely associated assemblages of diverse mineralogy suggest that the X Mn and X CO 2 , rather than the physical conditions of metamorphism, are the decisive factors in promoting the observed phase assemblages.