Mineral chemistry of tourmaline from Mashak Pahar, South Purulia Shear Zone (SPSZ), eastern Indian Shield
Santanu Acharjee Jyotisankar Ray Payel Dey Debapriya Bhattacharyya Mousumi Banerjee Basab Chattopadhyay Shyamal Sengupta A K Bhatt D Chowdhury A K Dwivedi Sanjoy Mahato Arka Ranjan Jana P B Maithani P V Ramesh Babu
The area of investigation at and around Mashak Pahar, Bankura district, West Bengal, India comprises a number of rock types namely: granite gneiss, migmatized quartz tourmaline gneiss, quartz pebbleconglomerate, ferruginous quartzite, quartz tourmaline veins (as veins) and graphite schists. Interestingly, the study area lies in the region extending South Purulia Shear Zone (∼Tamar–Porapahar Shear Zone) which marks the boundary between two contrasting tectonic blocks of eastern India, namely, the Chhotanagpur Gneissic Terrane (CGC) to the north and Singhbhum Group of rocks to the south. The rocks of the study area are poly-phasedly deformed by three phases of folding, namely, F1, F2 and F3. All the tourmalines are classified to be of ‘Alkali Group’. Chemistry of tourmalines from migmatized quartz tourmaline gneiss and those from quartz tourmaline veins are in conformity with their relation to (earthquake induced) shear system evolution in this terrain. In general, the compositional evolutionof tourmaline during prograde metamorphism (∼400°–730°C) has been supported by both petrographic and chemical evidences. Assessment of mineral–chemical data of constituent tourmaline grains clearly suggests compositional variations across zonal boundaries within tourmaline that was controlled by changing metamorphic milieu in this terrane. Field and petrographic evidences clearly indicate activation of earlier and later shears in this region accompanied by infiltration of boron and formation of zoned tourmaline crystals.
Santanu Acharjee1 Jyotisankar Ray1 Payel Dey1 Debapriya Bhattacharyya1 Mousumi Banerjee1 Basab Chattopadhyay2 Shyamal Sengupta2 A K Bhatt3 D Chowdhury3 A K Dwivedi3 Sanjoy Mahato1 Arka Ranjan Jana1 P B Maithani3 P V Ramesh Babu3
Volume 129, 2020
Continuous Article Publishing mode
Click here for Editorial Note on CAP Mode