ISSN:
1525-1314
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Geosciences
Notes:
Petrogenetic grids in the KFMASH and KMnFMASH model systems calculated with the software thermocalc 3.1 are presented for the P–T range 0.5–12 kbar and 450–900 °C, for assemblages involving garnet, muscovite, chloritoid, biotite, chlorite, staurolite, cordierite, spinel, orthopyroxene, K-feldspar, Al2SiO5 phases, quartz, water and melt. Based on calculated compatibility diagrams and P–T and T–MMn [Mn/(Mg + Fe + Mn)] pseudosections for different metapelitic bulk compositions, the principal conclusions are that the addition of Mn to the KFMASH system: (i) enhances the stability of garnet, and, to a lesser extent, aluminosilicates; (ii) reduces the stability of staurolite, cordierite and, to a lesser extent, chlorite; and (iii) extends the medium pressure stability of muscovite and the low-P stability field of K-feldspar. The influence of Mn on individual mineral stabilities is strongly related to rock composition, in particular, to the relative contents of Al2O3 and K2O. For metapelites of a range of compositions and MMn values, P–T pseudosections in the KFMASH system, in most cases, do not adequately predict the mineral assemblages observed in natural assemblages under medium and low-pressure conditions. In contrast, the P–T pseudosections in the KMnFMASH system generally provide more satisfactory results, suggesting that MnO is one of the non-KFMASH components that should not be neglected in documenting the phase equilibria of medium- and low-P metapelites.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1525-1314.2004.00530.x
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