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peridotites; Nidar Ophiolite Complex (NOC); supra-subduction zone (SSZ); partial melting

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# [$\rm{Mg/(Mg + Fe^{2+}}$)] varying between 0.91 and 0.94 and olivine in dunite between 0.92 and 0.94. Clinopyroxene from the harzburgite is $\rm{TiO_{2}}$ and $\rm{Na_{2}O}$-poor diopside ($\rm{Wo_{47–50}En_{47–50}Fs_{2–4}}$). 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 $800–900^{0}\rm{C}$ temperature, 32 and 40 kbar pressure, oxygen fugacity -0.09 to 0.55 log units above the FMQ buAer. 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.

RANJIT NAYAK^{1 2} BIDYANANDA MAIBAM³

1. Department of Earth and Atmospheric Sciences, NIT Rourkela, Rourkela 769 008, India.
2. Department of Geology, Addis Ababa Science and Technology University, Addis Ababa, Ethiopia.
3. Department of Earth Sciences, Manipur University, Canchipur, Imphal 795 003, India.

Published

10 January 2020

Manuscript received

12 March 2019

Manuscript revised

24 September 2019

Accepted

9 October 2019

Early published

Unedited version published online

Final version published online

9 January 2020

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