Petrology and geochemistry of Proterozoic olivine tholeiite intrusives from the Central Crystallines of the Western Arunachal Himalaya, India: evidence for a depleted mantle

Abstract

A number of plugs and dykes of mafic rocks are encountered between Se La and Jung areas of the Central Crystalline rocks of western Arunanchal Himalaya. These mafic intrusives are emplaced within the Paleoproterozoic high to medium grade schists and gneisses of Se La Group. These mafic reeks are Dietamorphosed and composed of hornblende (~70%) and plagioclase showing granoblastic texture. Geo-chemically they show olivine tholeiitic characteristics. Appreciable amount of normative hypersthene and olivine is present in all samples. The geochemistry of high-field strength (+ rare-earth) elements suggests that these mafic rocks are co-genetic and derived from olivine tholeiite melt generated from a depleted lher-zolite mantle source. These mafic rocks show very close geochemical similarities with mafic rocks reported from the western Himalaya. The satellite imageries suggest that these mafic intrusive rocks are exposed at intersection of major lineaments. The asso­ciation of these mafic rocks with major lineaments, mostly fault planes, advocates that these originally deep seated intrusions have been upthrown and exposed along the fault planes.