Geochemistry and U-Pb SHRIMP zircon chronology of granitoids and microgranular enclaves from Jhirgadandi Pluton of Mahakoshal Belt, Central India Tectonic Zone, India

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• 作者：Sita Bora^a ; Santosh Kumar^a ; ^{skyadavan@yahoo.com} ; Keewook Yi^b ; Namhoon Kim^b ; Tae Ho Lee^b
• 关键词：Geochemistry ; Geochronology ; Jhirgadandi Pluton ; Mahakoshal Belt ; Central India Tectonic Zone
• 刊名：Journal of Asian Earth Sciences
• 出版年：2013
• 出版时间：July, 2013
• 年：2013
• 卷：70-71
• 期：Complete
• 页码：99-114
• 全文大小：4853 K

文摘

The northern part of Central India Tectonic Zone (CITZ) is delineated by an arc-shaped supracrustal belt commonly referred to as Mahakoshal Belt, which is considered as a product of intense rifting of sialic crust that occurred at ca 2400-2600 Ma. Several granitoid plutons intrude the Parsoi Formation of Mahakoshal Belt. Among these, an elliptical small stock-like granitoid body trending E-W is exposed in and around Jhirgadandi region of Mahakoshal Belt, referred herein as Jhirgadandi Pluton. It is composed of minor amount of mafic rocks (diorite) and predominant granitoids. Country-rock pelitic xenoliths and microgranular enclaves (ME) are commonly hosted in granitoids but are absent in diorite. The ME exhibit typical magmatic texture with a Bt(¡ÀCpx ¡À Hbl)-Pl-Kf-Qtz-Mag-Ap assemblage, similar to that in host granitoids but with contrasting mineral proportions. Whole-rock molar Al₂O₃/(CaO + Na₂O + K₂O) (A/CNK) ratios of diorite (0.63-0.72), ME (0.69-1.21) and granitoids (0.83-1.05) suggest their nature largely metaluminous (I-type) to rarely peraluminous (S-type) granitoids. On most binary plots involving silica, two distinct compositional paths can be recognized; one formed by an array of differentiating diorite and ME, and another by fractionating granitoids gradually depleting in compatible elements. It is most likely that ME were generated by progressive and concurrent mixing of coeval pristine mafic (diorite) and granitoid magmas and fractionation processes. However, coherent and identical trace elements (except for Sr, Th, Y and Ni) and REE patterns for ME-granitoid pairs most likely suggest partial to near-complete chemical equilibration through varying degrees of diffusion process across the ME - partly crystalline host granitoid boundary. High-precision U-Pb SHRIMP zircon ²⁰⁶Pb/²³⁸U ages for ME (1758 ¡À 19 Ma) and host granitoid (1753 ¡À 9.1 Ma) from Jhirgadandi Pluton further support the notion that they were coeval. The obtained age (¡«1750 Ma) of Jhirgadandi Pluton also points to the existence and role of Super-Columbian continental component in the evolution of Mahakoshal Belt of the CITZ.