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Quantitative phase petrology of cordierite–orthoamphibole gneisses and related rocks
Author(s) -
DIENER J. F. A.,
POWELL R.,
WHITE R. W.
Publication year - 2008
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.1525-1314.2008.00791.x
Subject(s) - cordierite , geology , metamorphic rock , mineral , gneiss , geochemistry , phase (matter) , mineralogy , materials science , chemistry , metallurgy , ceramic , organic chemistry
Cordierite–orthoamphibole gneisses and rocks of similar composition commonly contain low‐variance mineral assemblages that can provide useful information about the metamorphic evolution of a terrane. New calculated petrogenetic grids and pseudosections are presented in the FeO–MgO–Al 2 O 3 –SiO 2 –H 2 O (FMASH), Na 2 O–CaO–K 2 O–FeO–MgO–Al 2 O 3 –SiO 2 –H 2 O (NCKFMASH) and Na 2 O–CaO–K 2 O–FeO–MgO–Al 2 O 3 –SiO 2 –H 2 O–TiO 2 –Fe 2 O 3 (NCKFMASHTO) chemical systems to investigate quantitatively the phase relations in these rocks. Although the bulk compositions of cordierite–orthoamphibole gneisses are close to FMASH, calculations in this system do not adequately account for the observed range of mineral assemblages. Calculations in NCKFMASH and NCKFMASHTO highlight the role of minor constituents such as Ca, Na and Fe 3+ in the mineral assemblage evolution of such rocks and these systems are more appropriate for interpreting the evolution of natural examples.