6533b822fe1ef96bd127cbab

RESEARCH PRODUCT

Quantitative phase petrology of cordierite-orthoamphibole gneisses and related rocks

Johann F.a. DienerRichard WhiteRoger Powell

subject

MineralMetamorphic rockGeochemistryGeologyCordieriteengineering.materialGedriteGeochemistry and PetrologyAnthophylliteWhiteschistengineeringPetrologyGeologyTerraneGneiss

description

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-Al2O3-SiO2-H2O (FMASH), Na2O-CaO-K2O-FeO-MgO-Al2 O3- SiO2-H2O (NCKFMASH) and Na2O-CaO-K2O-FeO-MgO-Al2O3- SiO2-H2O-TiO2-Fe2 O3 (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 Fe3+ in the mineral assemblage evolution of such rocks and these systems are more appropriate for interpreting the evolution of natural examples. © 2008 Blackwell Publishing Ltd.

https://doi.org/10.1111/j.1525-1314.2008.00791.x