Ultrahigh‐temperature mafic granulites from the Madurai Block, southern India: Constraints from conventional thermobarometry, pseudosection analysis, and rare earth element‐based thermometry

Abstract

Ultra-high temperature (UHT) regional metamorphism is the most extreme form of crustal metamorphism with temperatures exceeding 900 C at moderate pressures of 7-13 kbar (Harley, 1998). UHT crustal metamorphism has so far been recognized from more than 50 localities worldwide (compiled in Kelsey, 2008;Kelsey & Hand, 2015), presenting a very exciting phenomenon, as it implies that the Earth's crust is mechanically capable of attaining and withstanding extreme thermal conditions on a regional scale (Harley, 2004;Kelsey, 2008) during 'normal' tectonic events. Although UHT metamorphism is now considered normal in the continuum of regional crustal processes, the number of occurrences is extremely low compared to the extent of metamorphic rock exposures, possibly because of the difficulty of its preservation and recognition in the rock record (cf. Kelsey & Hand, 2015).UHT metamorphism is classically recognized on the basis of diagnostic mineral assemblages such as Spr + Qz, Spl + Qz, Opx + Sil + Qz, Osm, etc., that typically develops in a Mg-Al rich metapelitic granulite (Harley, 1998;Kelsey & Hand, 2015). On the contrary, the most common mineral assemblage in mafic granulites is Opx + Cpx + Pl ± Grt, which has a broad stability range and, therefore, not diag-

Long‐lived high‐grade metamorphism in southern India: Constraints from charnockites and sapphirine‐bearing semipelitic granulites from the Madurai Block

“…Compilation of P – T evolution paths from the Madurai Block (Raith et al, 1997 [1]; Sajeev et al, 2006 [2]; Santosh & Sajeev, 2006 [3]; Tsunogae & Santosh, 2006 [4], Tsunogae & Santosh, 2011 [7]; Braun et al, 2007 [5]; Tadokoro et al, 2007 [6]; Tsunogae et al, 2008 [8]; Raith et al, 2010 [9]; Brandt et al, 2011 [10]; Clark et al, 2015 [11]; Prakash et al, 2017 [12]; Li et al, 2020 [13]; Tiwari & Sarkar, 2020 [14]; Ray et al, 2021 [15]), this study, the Trivandrum Block (Chacko et al, 1987 [1]; Nandakumar & Harley, 2000 [2]; Cenki et al, 2002 [3]; Ishii et al, 2006 [4]; Tadokoro et al, 2008 [5]) and Sri Lanka (Perera, 1984, 1994 [9]; Kriegsman, 1995 [7]; Kriegsman & Schumacher, 1999 [8]; Sajeev & Osanai, 2004 [2]; Sajeev et al, 2007 [3]; Dharmapriya et al, 2015 [1], Dharmapriya et al, 2015 [6], Dharmapriya et al, 2017 [4]; Takamura et al, 2015 [5]). Dominantly clockwise P – T evolution from all the domains should be noted.…”

“…UHT metamorphism in the MB is dominantly reported from metapelites and Mg–Al granulites (e.g. Brandt et al, 2011; Dev et al, 2021, 2022; Lal et al, 1984; Prakash et al, 2017; Raith et al, 1997; Santosh & Sajeev, 2006; Sato et al, 2009; Sato & Santosh, 2007; Tateishi et al, 2004; Tiwari & Sarkar, 2020; Tsunogae et al, 2008; Tsunogae & Santosh, 2003) along with mafic granulites from a few localities (Prakash et al, 2007, 2010; Ray et al, 2021; Sajeev & Santosh, 2006). However, there are no reports of UHT metamorphism from the charnockites which form the most dominant lithology within the MB.…”

“…Following the discovery of diagnostic Spr + Qz assemblage from pelitic granulites by Tateishi et al (2004), multiple studies have reported UHT metamorphism from various rock types and characterized the metamorphic P – T evolution. Obtained P – T paths from the MB are predominantly clockwise with near isothermal decompression to varying degrees (Brandt et al, 2011; Prakash et al, 2017; Raith et al, 1997; Ray et al, 2021; Tamashiro et al, 2004; Tiwari & Sarkar, 2020); however, anti‐clockwise P – T trajectories are also reported (Santosh & Sajeev, 2006; Tsunogae & Santosh, 2006, 2011). The diverse P – T trajectories have been attributed to different styles of tectonism, which would have contributed to heat input and subsequent exhumation.…”

Age and petrogenesis of mafic granulites from central Madurai block, south India: implications on regional tectonics

“…1b) are limited to field mapping and thermobarometric studies (Geological Survey of India (GSI), unpub. data; Prakash et al 2007; Ray et al 2021). For the present study, mafic granulite samples were collected from eight newly identified locations along the central part of the Madurai block within the Kambam UHT belt (blue circles in Fig.…”