Petro-geochemical,Geochronological And Hf Isotopic Investigation Of The Southern Part Of Paleo-Island Arc (Kohistan Island Arc,Northern Pakistan)

The southwestern part of the Kohistan Island Arc?KIA?is not well studied in context of geochronology and Hf isotope.In order to know the detail geology of this part of KIA?Swat Valley?,present research work has taken place,to investigate the evolution of the magma,and magma segregation of mantle and crust.To study the genetic relationship of Metaplutonic Complex with overlying and/or intruded Chilas Complex in the Swat Valley.The present investigation includes petrography,whole-rock geochemistry,U-Pb dating,Hf isotope and trace element of the zircon grains.The use of zircon geochronometer helps in understanding of the geodynamic processes of deep earth and its trace elements take good part in comprehending the origin of the rocks and crystallization environments.The in-situ Hf isotope geochemistry is used with LA-MC-ICPMS for the selected zircons for better interpretation of continental crust development from the mantle source.The slight variations in source regions of magmatic rocks are well shown by hafnium isotopes in zircons.The present research work having the geological span of time from 83 to 87 Ma and ?_Hf?t?ranging from?-6.82 to+11.9?.The zircon ?_Hf?t?values of Metaplutonic Complex?-6.8 to+10.1?reveal possibly subduction control while Chilas Complex?+7.58⁺11.97?shows depleted mantle.As zircon trace elements geochemistry distinguished the oceanic and continental fields for KIA rocks,the Metaplutonic and Chilas Complexes are plotted in the continental arc setting with subduction influence whereas some of the samples?i.e Nb/Sc?plotted slightly outside the defined field.The negative anomaly of the HFS elements of the whole-rock is supporting the non-MORB tectonic environment.The tectonic settings of Island arc are interpreted for these southern KIA rocks based on whole-rock enriched LILE?U,Ba,Sr,Pb?and depleted HFSE?Nb,Y,Zr?.