Polyphase deformation and garnet growth in pelitic schists of Sausar Group in Ramtek area, Maharashtra, India: A study of porphyroblast-matrix relationship

Abstract

Polyphase deformation and metamorphism of pelitic schists of Chorbaoli Formation of Sausar Group in and around Ramtek area, Nagpur district, Maharashtra, India has led to the development of garnet and staurolite porphyroblasts in a predominantly quartz-mica matrix. Microstructural study of oriented thin sections of these rocks shows that garnet and staurolite have different growth histories and these porphyroblasts share a complex relationship with the matrix. Garnet shows at least two phases of growth -first intertectonic between D 1 and D 2 (pre-D 2 phase) and then syn-tectonic to post-tectonic with respect to D 2 deformation. Growth of later phase of garnet on the earlier (pre-D 2 ) garnet grains has led to the discordance of quartz inclusion trails between core and rim portion of the same garnet grain. Staurolite develops only syn-D 2 and shows close association with garnet of the later phase. The peak metamorphic temperature thus coincided with D 2 deformation, which developed the dominant crenulation schistosity (S 2 ), regionally persistent in the terrain. The metamorphic grade reached up to middle amphibolite facies in the study area, which is higher than the adjoining southern parts of Sausar Fold Belt.

Automated petrography analysis by QEMSCAN® of a garnet-staurolite schist of the San Lorenzo Formation, Sierra Nevada de Santa Marta massif

“…This relationship between deformation and development of progressive schistosity surfaces has been reported in different studies (e.g., Bell and Rubenach, 1983;Ríos et al, 2003;Chattopadhyay and Ghosh, 2007;Vinagre et al, 2016;Castellanos et al, 2001Castellanos et al, , 2004Castellanos et al, , 2016aCastellanos et al, , 2016bGarcía et al, 2017). Our observations suggest that during a first step of deformation (D 1 ), the original structure of the protholith was affected as revealed by a first metamorphic foliation (S 1 ).…”

Mineragraphic Study of Manganese Ore Deposits of Kandri, Mansar, Beldongri and Satak Mines, Nagpur District (Maharashtra) Central India

“…Generalised geological map of study area (Nagpur) in Central India, India. After Chattopadhyay and Ghosh[22]. Inset: Map of India showing position of study area (N = Nagpur).…”