Evolution of high‐Mg–Al granulites from Sunkarametta, Eastern Ghats, India: evidence for a lower crustal heating–cooling trajectory

Abstract

A suite of high‐Mg–Al granulites from Sunkarametta, Eastern Ghats Belt, India, shows contrasting prograde assemblages of extremely aluminous orthopyroxene+cordierite+sapphirine and similarly aluminous orthopyroxene+Ti‐rich spinel in closely associated domains. Textural and compositional characteristics indicate that both were derived from prograde dehydration–melting of biotite–plagioclase–quartz‐bearing protoliths. The former assemblage was stabilized at relatively more magnesian bulk composition. Geothermobarometric data and petrogenetic grid considerations place ‘peak’ metamorphic conditions at c. 950 °C and 9 kbar. Subsequent to peak metamorphism, the rocks cooled to c. 700–750 °C, with slight lowering of pressure, and the retrograde reactions also involved melt–solid interaction. The inferred P–T trajectory is one of heating–cooling at lower crustal (25–30 km) depths.

Significance of post‐peak metamorphic reaction microstructures in the ultrahigh temperature Eastern Ghats Province, India

“…M2) of a complex overall counter‐clockwise P–T loop (analogous to Figure a,b; Bose et al., ; Dasgupta et al., ; Pal & Bose, ; Sarkar et al., ; Sengupta et al., ). Other (or sometimes the same) studies infer that late cordierite develops along an effectually near‐isobaric cooling path post‐M1 (Bose & Das, ; Bose et al., ; Das, Bhattacharya, et al., ; Kamineni & Rao, ; Korhonen et al., ; Mohan et al., ; Sarkar et al., ; Shaw & Arima, ). In these studies, the late cordierite was interpreted as either the result of negatively sloped reactions in P–T space and/or expanded (i.e.…”

“…Late cordierite is a common feature of many (62%) of the studies listed in Table . In evaluating photomicrographs and accompanying descriptions in the published studies, the late cordierite is commonly not developed to great extent, typically being confined to narrow coronas or symplectites on higher pressure post‐peak M1 assemblages such as orthopyroxene–sillimanite, garnet–sillimanite and sapphirine–orthopyroxene, amongst others (Table ; Bose et al., , ; Das, Bose, et al., ; Dasgupta et al., ; Dharma Rao et al., ; Grew, ; Grew et al., ; Kamineni & Rao, ; Mohan et al., ; Pal & Bose, ; Prakash et al., ; Sarkar et al., ; Sengupta et al., ; Shaw & Arima, ). Late cordierite was interpreted in numerous studies to reflect the down‐pressure segment (i.e.…”

“…The M1 event in the EGP was interpreted to involve UHT metamorphism followed by near‐isobaric cooling (e.g. Bhowmik, ; Bose & Das, ; Bose, Das, Dasgupta, Miura, & Fukuoka, ; Bose, Fukuoka, Sengupta, & Dasgupta, ; Das, Bhattacharya, Raith, Bhadra, and Banerjee, ; Das, Bose, Ohnishi, & Dasgupta, ; Dasgupta & Ehl, ; Dasgupta & Sengupta, , ; Dasgupta, Sengupta, Fukuoka, & Bhattacharya, ; Dasgupta et al., ; Dharma Rao et al., ; Grew, ; Kamineni & Rao, , 1988b; Korhonen, Brown, et al., ; Korhonen et al., ; Lal, Ackermand, & Upadhyay, ; Mohan, Tripathi, & Motoyoshi, ; Mukhopadhyay & Bhattacharya, ; Nasipuri, Bhattacharya, & Das, ; Pal & Bose, ; Prakash et al., ; Sarkar, Dasgupta, & Fukuoka, ; Sengupta, Karmakar, Dasgupta, & Fukuoka, ; Sengupta, Raith, & Dasgupta, ; Sengupta et al., ; Shaw & Arima, , ). Most researchers consider M1 to be characterized by an overall counter‐clockwise P–T path (see Table and preceding references).…”

The Eastern Ghats Belt … A polycyclic granulite terrain

“…North of the Godavari Rift also an early UHT (~1000°C) metamorphic event (M 1 ) at crustal depths of 30-35km (8-10 kb) is reported from high-Mg-Al granulites in several areas (Fig.6), like Anantagiri (Sengupta et al 1990), Anakapalle (Dasgupta et al 1994;Rickers et al 2001b;Sanyal and Fukuoka, 1995), Araku , Paderu (Bhattacharya and Kar, 2002;Lal et al 1987;Pal and Bose, 1997), Rayagada (Shaw and Arima, 1996a, 1996b, 1998, G. Madugula (Mohan et al 1997), Vizianagram (Kamineni and Rao, 1988a), Sunkarametta (Bose et al 2000), Rajamundry , Kakanuru (Kamineni and Rao, 1988b), Deobhog Neogi and Das, 2000), from calc-granulites of Borra (Bhowmik et al 1995), Garividi and Rajamundry (Dasgupta et al 1992;Dasgupta, 1993), Anakapalle (Sengupta et al 1997a) and also from mafic granulites from Araku-Anantagiri areas Dasgupta et al 1993).…”

“…This temperature was attained at a deeper level in the prograde phase in the granitoid gneiss prior to its emplacement at a shallower level during D 1 deformation. Sen et al (1995), 4 -Rayagada, Shaw and Arima (1996), 5 -Salur, Mukhopadhyay and Bhattacharya (1997), 6 -Garbham, Dasgupta et al (1992), 7 -Vizianagram, Sarkar et al (2003), 8 -Visakhapatnam, Fonarev et al (1995), 9 -Anakapalle, Dasgupta et al (1994), Sanyal and Fukoaka (1995), 10 -Sankarimetta, Bose et al (2000). 11 -A: Borra - Bhowmik et al (1995), B: Borra - Bhowmik et al (1997), C: Anantagiri: Sengupta et al (1991), D: Araku, Sengupta et al (1991), E: Dasgupta et al (1991), 12 -A: Paderu, Lal et al (1987), B: Pal and Bose (1997), C: Bhattacharya et al (2003), 13 -G. Madugula, Mohan et al (1997), 14 -Gokavaram, Dasgupta et al (1999), 15 -Rajamundry - , 16 -A: Deobhog, , B: Bhawanaipatna, Das et al (2006), 18 -Kondapalle, Sengupta et al (1999).19 -Chimakurty, Dasgupta et al (1997).…”