Low-titanium clinopyroxene composition of Nidar ophiolite gabbros, southeastern Ladakh Himalaya, India: implications to geotectonic setting

The Nidar ophiolite complex is one of the wellpreserved ophiolite sequences of the Indus Tsangpo Suture Zone (ITSZ) towards the southeastern part of Ladakh Himalaya, India. This study presents petrography and clinopyroxene mineral chemistry of gabbroic rocks from the Nidar ophiolite. These gabbros are massive, essentially composed of plagioclase and clinopyroxene with minor amounts of olivine, orthopyroxene, hornblende and magnetite. The clinopyroxenes are very low in TiO2 (0.05-0.77 wt%) and Na2O (0.12-0.85 wt%) but rich in SiO2 (52-55 wt%). It is observed that there is a wide variation of CaO (12.26-23.88 wt%) and in the Wo- En-Fs ternary diagram, clinopyroxene shows augitic to diopside compositional variation. These low-titanium clinopyroxenes are inferred to be tholeiitic in nature with an island-arc boninitic affinities.