Pressure‐temperature‐time evolution of ultrahigh‐temperature granulites from the Trivandrum Block, southern India: Implications for long‐lived high‐grade metamorphism

Abstract

The Southern Granulite Terrane in India comprises a number of Archean to Neoproterozoic magmatic arcs and supracrustal units that underwent latest Neoproterozoic to Cambrian high‐grade metamorphism. Here, we present a new petrological and geochronological data from khondalites in the western part of the Trivandrum Block and discuss pressure‐temperature‐time (P–T–t) path of the block for unravelling the duration and heat source of high‐grade metamorphism. Phase equilibria modelling of the khondalite indicates peak P–T condition of 920°C–1,030°C and 6.0–7.6 kbar, suggesting ultrahigh‐temperature (UHT) metamorphism. Prograde and retrograde P–T conditions of ~750°C/~7 kbar and ~750°C/~4 kbar, respectively, were also obtained, based on which a clockwise P–T path with geotherm‐parallel slow cooling is inferred. Zircon and monazite U–Pb geochronology and rare‐earth elements (REE) patterns suggest that heavy rare‐earth elements (HREE)‐depleted zircons grew together with garnet during prograde partial melting at >810°C or during fluid activity at around 582 ± 17 Ma, which was followed by peak UHT metamorphism at 555.1 ± 8.1 Ma as inferred from the dominant monazite ages. Relatively HREE‐enriched zircons (527.3 ± 8.0 Ma) and monazites (501.9 ± 8.5 Ma) were probably formed by garnet breakdown during retrograde metamorphism. The growth of HREE‐enriched zircons at 489 ± 12 Ma might be related to later fluid infiltration and hydration of garnet to form biotite at <770°C/~4 kbar. Our results suggest that high‐grade metamorphism continued at least 90 Myr, from 582 to 489 Ma, suggesting a long‐lived thermal event possibly related to the input of radiogenic heat from the crust and/or magmatic heat from syntectonic to post‐tectonic intrusions.

Prolonged Neoproterozoic high‐grade metamorphism of the Wanni Complex, Sri Lanka: New insights from petrology, phase equilibria modelling, and zircon U–Pb geochronology of partially melted cordierite gneiss from Walpita

“…They suggested that such long-lived high post-peak temperatures require a significant contribution from crustal heat production. Similar prolonged high-grade metamorphism of >90 Myr has been reported from the Trivandrum Block in southern India based on LA-ICP-MS zircon/monazite U-Pb geochronology of khondalites (Kadowaki et al, 2019). Although heat source of such protracted high-T and UHT metamorphism is a subject of ongoing debate, previous studies argued the effect of radiogenic heat from the crustal rocks (e.g., Fitzsimons, 2016;He et al, 2018;Morrissey, Hand, Raimondo, & Kelsey, 2014).…”

“…Although heat source of such protracted high-T and UHT metamorphism is a subject of ongoing debate, previous studies argued the effect of radiogenic heat from the crustal rocks (e.g., Fitzsimons, 2016;He et al, 2018;Morrissey, Hand, Raimondo, & Kelsey, 2014). Kadowaki et al (2019) also suggested that continuous magmatic heat input (e.g., charnockite…”

Tectonometamorphic evolution of the Trivandrum and Southern Madurai blocks in the Southern Granulite Terrane, south India: correlation with south-central Madagascar

“…The dominant lithologies in the TB are anatectic garnet-biotite ± graphite gneisses, garnetbearing leptynitic gneisses, garnet-biotite-sillimanite ± cordierite (khondalite) gneisses, granitic and tonalitic orthogneisses, and non-garnetiferous and garnetiferous charnockites (quartzo-feldspathic gneisses with orthopyroxenes), together with minor amounts of quartzites and calc-silicates (Chacko et al 1987;Santosh et al 1993Bindu, 1997;Nandakumar & Harley, 2000;Satishkumar et al 2002;Shabeer et al 2002;Endo et al 2013;Sreejith & Ravindra Kumar, 2013;Ravindra Kumar & Sreejith, 2016). Khondalites, leptynites, calc-silicates and quartzites form the metapelitic suite, whereas charnockites, garnet-biotite gneisses and mafic granulites are mostly orthogneisses (Braun, 2006;Tadokoro et al 2008;Kröner et al 2012;Endo et al 2013;Sreejith & Ravindra Kumar, 2013;Harley & Nandakumar, 2014;Taylor et al 2014;Kadowaki et al 2019). The garnet-biotite gneisses commonly show arrested charnockitization (Ravindra Kumar et al 1985;Hansen et al 1987;Raith & Srikantappa, 1993).…”

Neoarchean arc magmatism and Paleoproterozoic granulite‐facies metamorphism in the Bhavani Suture Zone, South India

“…The Archean (3,600–2,500 Ma) Dharwar Craton is dominantly composed of tonalitic–trondhjemitic–granodioritic gneiss and greenstone belts (Jayananda, Santosh, & Aadhiseshan, ; Wang & Santosh, ). The SGT comprises Paleoarchean to Late Neoproterozoic crustal blocks that are dissected by transcrustal shear and/or suture zones, making the SGT a complex orogen formed by multiple subduction–accretion–collision history (e.g., Chetty & Bhaskar Rao, ; Chetty, Mohanty, & Yellappa, ; Collins, Clark, & Plavsa, ; Drury, Harris, Holt, Reeves‐Smith, & Wightman, ; Kadowaki et al, ; Praveen et al, ; Santosh et al, ; Santosh et al, ; Santosh et al, ; Santosh, Shaji, et al, ).…”