Petrography and Mapping of the Gwal Melange of Khanozai Region, Balochistan, Pakistan

Abstract

Abstract The Gwal mélange is mapped on a large scale and is divided into the lithological units such as ultramafic, mafic, volcanic, volcanoclastic rocks, pelagic sediments and ophicarbonates. Petrographically, the mapped rocks are classified as harzburgite, dunite, wehrlite, serpentinite, gabbro, basalt, and andesite. These rocks are quite deformed and altered into the secondary minerals. Harzburgite is a layered mantle peridotite consists of olivine and orthopyroxene while dunite lacks the presence of any pyroxene. Serpentinite is the secondary product after peridotite is the product of post magmatic stages. The mesh structure is usually observed when olivine is completely altered to serpentine. The volcanic rocks are structurally sheeted and pillow type while the volcanoclastic rocks are essentially hyaloclastites associated with pelagic sediments. The Ophicarbonate is composed of serpentinite fragments and carbonate minerals, most probably calcite. Minor to trace amounts of opaque minerals are also present in association with major components. The gabbros may be a fragment of the main crustal rocks and have been formed in a magma chamber by fraction crystallization. The origin of ophicarbonate may be due to gas seeps originated by mantle or as the surficial process where ultramafic rocks and carbonates are mixed through processes of gravity, tectonic crushing and sedimentary reworking. The Gwal mélange may the southern extension of Bagh Complex found beneath the Muslim Bagh Ophiolite. The mantle peridotite of the mélange is much like that of the Khanozai peridotite and may represent its detached blocks. Volcanic and volcanoclastic rocks may be the representatives of the uppermost part of ophiolite crust which might have trimmed off from subducting slab and are, now, part of the Gwal accretionary wedge. The mélange may have tectonically emplacement over the Indian platform sediments along with overlying the ophiolite sheet during the Late Cretaceous.