Minerals from ultramophites of Karabash massif (South Urals)

In this paper we present the estimation of PT-metamorphic conditions of ultramafic rocks from Karabash massif because it is very important in understanding the ultramafic rocks formation and geodynamic history of the Urals. For the first time we have studied compositions of accessory minerals for Karabash massif ultramafic rocks and defined the multiple emplacement mechanism of the formation. We took samples from serpentinous harzburgites and dunites weighing more than 150 kg each and studied the minerals. From the fractions the accessory minerals were selected and analyzed by scanning electron microscope REMMA-202M in the mode of secondary electrons operated at 20 kV. We found garnets (Alm-Prp, Prp-Alm Spess-Alm and Adr-Grs of compositions); alumobronzite with the highest concentration of aluminum (Al IV = 0.25-0.41 f. c. & Al VI = 0.41-0.44 f. c.); amphiboles (tschermakite, hornblende and tremolite) and also phlogopite, kyanite and muscovite. Alm-Prp (Prp 43Grs 28) and alumobronzite (Si 4+ = 1.59-1.75 f. c.) testify to the high-temperature (T = 1050-1350 °C) and high-pressure (P ³ 27-30 kbar) metamorphic conditions of ultramafic protoliths. The composition of tschermakite, hornblende and phlogopite testify to the transformation of the ultramafic rocks in the conditions of low temperature and middle pressure (T=600-700 °C & P = 10-11 kbar) due to their raising and influence of Al, K, Ca, H 2O-fluids. Kyanite+muscovite and Adr-Grs minerals association reflects the late metamorphism.