Abstract
Petrological study of the ultramafic rocks from the Nidar Ophiolite Complex (NOC) of the Indus Suture Zone is carried out. The study of Cr-spinels along with olivine and pyroxenes emphasizes the genesis and tectonic setting of the ultramafites. Olivine from the harzburgite is Mg-rich, with the molar ratio Mg# [Mg/(Mg + Fe2+)] varying between 0.91 and 0.94 and olivine in dunite between 0.92 and 0.94. Clinopyroxene from the harzburgite is TiO2 and Na2O-poor diopside (Wo47–50En47–50Fs2–4). Spinel in harzburgite shows wide Cr#, molar ratio varied between 0.26 and 0.72, and significantly higher in dunites with Cr# ranges from 0.69–0.85. Cr# of the peridotite spinel follow a depletion trend. Calculated equilibrium conditions of the samples are 800–900°C temperature, 32 and 40 kbar pressure, oxygen fugacity −0.09 to 0.55 log units above the FMQ buffer. Residual nature of the harzburgites and the presence of high and low Cr# spinels may be due to the genetic artifact of the different ultramafic units.
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