Geology of Ali Khanzai Block of Zhob Ophiolite, Balochistan, Pakistan

Abstract

Abstract The Zhob Ophiolite is divided into Naweoba, Omzha and Ali Khanzai blocks. Ali Khanzai Block is further divided into ultramafic, mafic, and lava units which are surrounded by sedimentary rocks successions. The ultramafic unit contains ultramafic tectonic and ultramafic cumulate, mafic rock unit consists of foliated and layered gabbros and mafic dykes are doleritic in composition. Volcanic–volcaniclastic–pelagic rocks unit consists of thick volcanic pillow basalt, hyaloclastite, bedded chert, pelagic limestone and hemipelagic mudstone. The metamorphic sole rocks are tectonically high distorted and dismembered, comprising of amphibolite and greenschist facies. They might have formed through the process of early intra-oceanic obduction of the ophiolite. All units make thrusted contacts and are highly deformed. Petrography and geochemical studies divide the Ali Khanzai Block into rock types such as gabbro, olivine gabbro, dolerite, basalt, basaltic andesite and basaltic trachy-andesite, chert, mudstone, and limestone, dunite, serpentinite, harzburgite, and wehrlite. Mafic dyke intrusions crosscut mantle rocks of block. The mantle rocks are altered, deformed, and deeply weathered, maybe residual melting of enriched mantle peridotite. The contact relationship of dolerite dykes with peridotite indicta that they are late magmatic intrusions. The Crustal gabbros are partially chloritic and sericitic and occur within mantle peridotite,, they may have formed from fractional crystallization in a magma chamber. The volcanic-volcaniclastic-pelagic sediments surround mantle and crustal rock units. It might be a mélange in nature is much like that of the Bagh Complex found beneath the Muslim Bagh Ophiolite, and other ophiolites around the world.