A clinopyroxene-orthopyroxene-plagioclase symplectite formed by garnet breakdown in granulite facies, Guaxupe, Minas Gerais, Brazil

In mafic granulites, garnet can form by reactions such as Opx + Pl = Cpx Grt + Qtz; Opx + Pl = Grt + Qtz. As a result of isothermal decompression (I TD), garnet can then break down to a characteristic orthopyroxene-plagiocla se symplectite. Mafic, iron-rich garnet-pyroxene granulite from the Guaxupe Massif has symplectite that formed by near-isothermal decompression, as a consequence of uplift of the granulite facies terrane. This symplectite was found to consist of vermicular clinopyroxene-orthopyroxene-plagioclase, wi th clinopyroxene clearly growing from the garnet that is breaking down, mod al amounts of clinopyroxene being less than orthopyroxene. Electron probe a nalyses show dear differences between core (Cpx(1)), rim, and symplectite c linopyroxene (Cpx(2)). Considering also the presence of magnetite in the sy mplectite texture, garnet breakdown is thought to be better represented by a reaction such as Cpx(1) + Grt +O-2 = Cpx(2) + Opx + Pl +Mr + Qtz.