pjg.01.2021.25.34
ABSTRACT
GEOLOGY OF ALI KHANZAI BLOCK OF ZHOB OPHIOLITE, BALOCHISTAN, PAKISTAN
Journal: Pakistan Journal of Geology (PJG)
Author: Saeed Ur Rehman, M. Ishaq Kakar, Muhammad Ayoub Khan, Abdul Naeem
This is an open access journal distributed under the Creative Commons Attribution License CC BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited
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.
| Pages | 25-34 |
| Year | 2021 |
| Issue | 1 |
| Volume | 5 |
The Siwalik sediments are widely distributed in foreland areas of Pakistan, India, Nepal and Bhutan. In Pakistan they are composed of four formations (Chinji Formation, Nagri Formation, Dhok Pathan Formation, Soan Formation) These post tectonic deposits contain vast phylogenetic trends of modern vertebrate species especially dating back to Miocene-Pliocene. Our study encompasses the Miocene-Pliocene Nagri Formation exposed at Kanati Section, District Khushab. The purpose of the study is to establish depositional modal based of Lithofacies and Petrographical studies. The Nagri Formation in the Kanati Section is 47 m thick and predominantly contains sandstone, silt and clay with sub-ordinate conglomerates. Four Lithofacies were established. These are Conglomerate Facies (N1) interpreted as channel floor deposits, Sandstone Facies with cross beds and extraclasts (N2), where extraclasts were deposited by the lateral movement of channel, Siltstone and Claystone/Mudstone Facies (N3) which were interpreted as crevasse splay deposits, and Clay Facies (N4) interpreted as flood channel deposits. The clay exposed here was mostly brick red in color showing oxidizing conditions due to subaerial exposure. Spheroidal weathering was quite common in sandstone. Petrographic analysis for sandstone thin sections revealed mostly moderate amount of quartz (59.53%), lithic fragments (39.9%) with minimal amount of feldspar (0.55%). The petrographic results for Nagri sandstone were plotted on a QFL diagram from where it was interpreted as belonging to Lithic Arenites. The provenance of this sandstone was established to be of Recycled Orogen based on the studies.
