Petrogeochemical Characteristics And Origin Of Closepet Batholith,Dharwar Craton,South-central India

Closepet batholith is a huge late-Neoarchean composite intrusion outcropped in the Eastern Dharwar Craton,the south-central part of Indian Peninsula.It can be subdivided into the northern intrusion zone,central transfer zone and southern root zone.The integrated study on geochronology,petrogenesis and tectonic setting of porphyritic monzogranite,biotite monzogranite,brick red granite,porphyritic quartz monzonite and mafic microgranular enclave in the south and central have been researched to provide evidence for deciphering the origin of Closepet batholith.The zircon U-Pb geochronology of Closepet batholith indicates three magmatic events.The first event dated at ca.2545Ma includes porphyritic monzogranite and minor biotite monzogranite mainly from the transfer zone.The magma shows high contents of SiO₂?69.71%⁷2.91%?,K₂O?3.71%⁴.54%?,and low contents of TiO₂?0.23%⁰.37%?,MgO?0.34%⁰.68%?,Cr?4.17⁷.31 ppm?,Ni?3.65⁵.71 ppm?.The?_Nd?t?is-1.7 and zircon?_Hf?t?range from-7.60 to+3.05,demonstrating the result of partial melting of old crust with the input of the small juvenile materials.While the biotite monzogranite has?_Nd?t?of-5.7,probably derived the magma end-member partial melted from crustal materials,and partial melting of the crust caused by heating of the ascending asthenospheric mantle metasomatized by subduction slabs.The second event occurred in 2512²520 Ma and mainly exposed in the root zone.They are composed mainly of the porphyritic quartz monzonite with mafic microgranular enclave.Of which,the mafic microgranular enclave have low SiO₂ contents?57.08%⁵7.67%?,high MgO contents?4.29%⁴.44%?,Mg^#values of 56,Cr?94⁹8ppm?and Ni?80⁸6ppm?contents.They have relatively enrichment of Nd(?_Nd?t?=0.4)and Hf isotopes(?_Hf?t?=-4.27⁺1.55)in the mafic microgranular enclave.All indicate the geochemical characteristics of High-Ti sanukitoid and suggeste result from the derivation from enriched mantle.While,the porphyritic quartz monzonite have relatively low SiO₂?64.13%⁶7.07%?contents,high TiO₂?3.73%⁵.13%?,TFe₂O₃?3.73%⁵.13%?,and CaO?2.70%³.61%?contents,belonging to metaluminous high-k calcic-alkaline granites.They have?_Hf?t?=-3.68^-8.40,?_Nd?t?=-5.6^-2.5,and high Sr?423⁷12 ppm?,Ba?720¹122 ppm?and HFSE contents,low MgO?1.04%¹.56%?,Cr?6.97¹9.44 ppm?and Ni?7.39²0.7 ppm?contents.Thier REE pattern is similar to those of the mafic microgranular enclave,indicating they are products of magma-mixing between sanukitoid magmatism and crustal-derived magma.This magmatic event may be related to partial melting of asthenospheric mantle metasomatized by subduction plate.Finally,the third event occurred in 2500²512 Ma.They are represented by non-deformation brick red granites,and clearly intrude into other plutons.The granular granites have low MgO?0.34%⁰.38%??Cr?3.47⁵.27 ppm?,and Ni?2.97⁴.17 ppm?contents and Rb/Sr of 0.55⁰.56,indicating the characteristics of crust source.This magmatic event may be resulted from partial melting from crustal materials in a later magmatic event of asthenospheric mantle upwelling.