Physico-chemical conditions of four calc-alkaline granitoid plutons of Chhotanagpur Gneissic Complex, eastern India: Tectonic implications

Abstract

Chhotanagpur Gneissic Complex, eastern India, are investigated. The plutons, as a whole, are composed of varying proportions of Qtz-Pl-Kfs-Bt-Hbl±Px-Ttn-Mag-Ap-Zrn±Ep. The composition of biotite is consistent with those of calc-alkaline granitoids. Hornblende-plagioclase thermometry, aluminium-in-hornblende barometry and the assemblage sphene-magnetite-quartz were used to determine the P , T and f O2 during the crystallisation of the parent magmas in different plutons. The plutons are crystallised under varying pressures (6.2-2.4 kbar) and a wide range of temperatures (896-718 • C) from highly oxidised magmas (log f O2 −11.2 to −15.4 bar). The water content of the magma of different plutons varied from 5.0 to 6.5 wt%, consistent with the calc-alkaline nature of the magma. Calc-alkaline nature, high oxygen fugacity and high H 2 O melt suggest that these plutons were emplaced in subduction zone environment. The depths of emplacement of these plutons seem to increase from west to east. Petrologic compositions of these granitoids continuously change from enderbite (opx-tonalite: Sarpahari) in the east to monzogranite (Raghunathpur) to syenogranite (Sindurpur) to alkali feldspar granite (Agarpur) in the west. The water contents of the parental magmas of different plutons also increase systematically from east to west. No substantial increase in the depth of emplacement is found in these plutons lying south and north of the major shear zone passing through the study area suggesting the strike-slip nature of the east-west shear zone.

Discovery of Early Tonian Calc‐alkaline and Shoshonitic Metamafic Rocks from the North Purulia Shear Zone, Chhotanagpur Gneissic Complex, Eastern India: Implications of Proterozoic Sub‐continental Lithospheric Mantle

“…The early Tonian mafic and felsic magmatism in the study area occurred along extensional shear zones of the North Purulia Shear Zone, implying that tectonic structures controlled the emplacement and elongated lenticular shape of the plutons Bhattacharyya, 2010, 2014;Das et al, 2020;Roy et al, 2021). The foliated granite plutons following the foliation of the shear zone indicate that granite emplacement was coeval with shearing (Goswami and Bhattacharyya, 2014;Goswami et al, 2018;Das et al, 2020). Moreover, the mafic granulites were metamorphosed and uplifted within 990-950 Ma (Karmakar et al, 2011).…”

Petrogenesis of the post-collisional porphyritic granitoids from Jhalida, Chhotanagpur Gneissic Complex, eastern India

“…The extensive occurrences of potassic porphyritic granitoids within the migmatitic complex of the CGC attracted the attention of many workers, and suggested their late tectonic emplacement (Sen, 1956;Sengupta & Sarkar, 1964, 1968Mazumdar, 1988;Goswami & Bhattacharyya, 2014). Recently, Goswami et al (2018) discussed the physicochemical conditions of crystallization of four calcalkaline plutons, all lying on the EW-to ENE-WSW-trending North Purulia Shear Zone (NPSZ) in Purulia district, West Bengal. Among these plutons, the porphyritic granitoid batholith of Raghunathpur is well-studied and is suggested to be emplaced in a post-collisional tectonic setting (Goswami & Bhattacharyya, 2014) at c. 998 ± 10 Ma (Chakraborty et al 2019a).…”