Elemental Geochemistry And Zircon U-Pb Dating Of The Rocks From Nagar Parkar Igneous Complex,Sindh,Pakistan

The Nagar Parkar Igneous Complex lies at the southern extremity of Pakistan along the Pakistan-India border in the deserts of Thar Parkar near the great Rann of Kutch in Sindh province.The igneous complex comprises of metamorphic rocks,plutonic igneous rocks,and volcanic igneous rocks;the exposures of these rocks are in the form of plutons amid desert plains.The granites of various varieties are the major lithologic units as they occupy major volume of exposures.The present study was undertaken in order to determine the elemental compositions and absolute ages of the rocks exposed in the Nagar Parkar Igneous Complex.For this purpose,the fieldworks for collecting the representative samples were conducted around the Nagar Parkar area,a total of twenty eight samples belonging to nine different plutons exposed in the area were collected and transported to University of Science and Technology of China for the said analytical purposes.The whole rock elemental composition concentrations were determined through XRF,ICP-MS,and ICP-AES techniques following standard procedures at ALS laboratories Guangzhou.Meanwhile,for the age dating,mechanically crushed samples were sieved and zircon crystal separations were performed,the separated zircon crystals were mount on epoxy disks and polished till exposure of desired crystal structure,then the carbon coating of epoxy mount crystals was performed and CL images were acquired through Gatan Chroma CL mounted Tescan SEM.The desired spots were marked on CL images and the 235U-207Pb ablation analyses on the zircon crystals were conducted using LA-ICP-MS at CAS key laboratory for crust-mantle materials and environments in the University of Science and Technology of China following specified conditions and parameters.The acquired results were processed for common lead(Pb)corrections and finally the concordia diagrams and weighted average age diagrams were prepared using computer based specified software applications.The elemental concentration results were used against various discrimination diagrams and plots in order to determine the classification,tectonic evolution settings affinity and the provenance environments.The trace element behaviours were observed in the sample chondrite and sample primitive mantle diagram plots after normalizing the data values,the enrichment and depletion anomalies helped in concluding the origin source for the magma.The plutonic rocks in the complex are a result of partial melting from lower continental crust derived magma with assimilation and contamination from the surrounding rocks;which has experienced the impact of metamorphism due to the magma activity.The area was then subjected to the uplifting because of the Nagar Parkar fault re-activation and related rifting activities in the nearby Rajasthan and Kutch regions.The subject region after uplifting experienced the volcanic activity which is evident from the occurrence of enriched mantle source derived magma volcanic rocks.The tectonic discrimination diagrams categorize the area as active continental margin with the WPG origin settings for the rocks exposed there.The granites are of medium to high potash calcic alkaline nature and typically are A-type granites.The zircon 235U-207Pb ablation results of the samples suggest the existence of three major magmatic activity phases i.e.,(a)Metamorphism:in the form orthogneiss of 884±6 Ma age and amphibolite of 818±7 Ma age,(b)Plutonic:the plutonic magma activity phase lasted from 815 Ma to 730 Ma with several episodic pulse activities in between producing felsic,intermediate,and mafic rocks,and(c)Volcanic:with 283.22±2.0 Ma age for trachyte.The Nagar Parkar Igneous Complex rocks represent bimodal origin,formed during the times of rifting phase for the Gondwanaland in this region,and is regionally connected to the Malani Igneous Suite(in India)which is a post-Delhi magmatic event in the Rajasthan craton region of the Indian shield.