Provenance And Tectonic Setting Of Miocene-pliocene Gaj Formation Of Khirthar Range Southern Indus Basin Sindh Pakistan

The petrography of clastic sedimentary rocks provides important knowledge for understanding the tectonic background,provenance,paleo-weathering,and paleoclimate of sedimentary basins,as well as reconstructing their paleogeographic history.The Gaj Formation is well exposed in southern Indus Basin,Pakistan,and the formation is regarded as the best exposure to study the basin evolution during India-Eurasian collision.It is assumed that there are significant constraints on the collision and pre-collision tectonic configuration between the Indian and Eurasian plates.We have applied the petrography of Gaj Formation from Khirthar Range,Southern Indus Basin,Pakistan to determine the provenance,tectonic settings,source of weathering and its climatic conditions.Several problems hindered especially on provenance and tectonics,and mineralogical research of Gaj Formation,southern Indus Basin.These samples include limestone,sand,sandstone,and mudstone.The samples are fresh rock samples,collected from sections of Gaj formation,packed,labeled and stored in big bags.The stratum studied is composed of limestone,mudstone and sandstone and a small amount of sand.Limestone is yellowish brown,off-white and yellowish.These fine-grained layers are essentially laterite,loose,laminated,cracked and woody layers.Sandstone is brownish-yellow,gray in color,loose,muddy/earth colored,layered,iron,calcareous,and sub-round to round.Petrographic analyses of descriptive sandstone samples from the Khirthar Range of Gaj formation,much observed fossils and bio-clastic with contain calcite;contain abundant quartz with variable proportions and subordinate feldspars of lithic grains.In the understudied Gaj formation,monocrystalline quartz predominates over polycrystalline quartz.The feldspar content mostly ranges from 10 to 13%,in sandstones and the Gaj formation,individually.There is a wide degree of variation in the abundance of lithic grains(5 to 31%).The analyzed sandstones petrographic data were further processed through different provenance discriminatory diagrams,which suggested a Magmatic arc,Recycled Orogens,and Provenance and Tectonic Setting of Miocene Pliocene Khirthar Range of Gaj Formation Southern Indus Basin Sindh Pakistan.The recycled orogen sediments are assumed to come from Himalayan tectonic units,active continental margin orogen sediments from the Asian active continental margin(the Trans-Himalaya and Karakoram),and magmatic arc orogen sediments from the Kohistan-Ladakh arc in the study area's regional tectonic scenario.According to the above-mentioned properties,the Gaj Formation was most likely formed by a Shallow Marine environment.The minerological results demonstrate that the Gaj formation sediments are dominated by mature sublitharenites derived predominantly from quartz sedimentary and felsic rocks with minor arc related mafic inputs.The chemical index of alteration and plagioclase index of alteration of the Khirthar Range indicate the sediments experienced low to high weathering conditions in the southern Indus Basin during Mio-Pliocene time.The provenance characteristics suggest that the Miocene sediments were deposited in a passive margin,instead of a foreland basin.Therefore,we propose that India might be have collided with Eurasia in the Mio-Pliocene Time.