Pyroxene exsolution in granulites from Fyfe Hills, Enderby Land, Antarctica: evidence for 1000oC metamorphic temperatures in Archean continental crust.

Abstract

Orthopyroxene (Opx) and augite (Aug) in metasedimentary and meta-igneous gneisses in a supracrustal succession at Fyfe Hills exhibit intimate exsolution intergrowths. The textural relations and compositional data suggest the following phase relations at peak conditions: Opx-Aug (for 031XFe Opx <0.43), Opx-Aug-Pgt (for 031XFe Opx = 0.5-0.43), Opx-Pgt (for 031XFe Opx >0.5), Aug-Pgt (for 031XFe Aug >0.48), where XFe = Fe2+/(Fe2+ + Mg). A peak metamorphic T of = or >1000oC at 9 kbar is indicated. -J.A.Z.