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

Abstract

Detailed structural investigations across the Achankovil terrane boundary shear zone (AKSZ) system show distinct differences in the geometry of superposed fold structures between the Trivandrum (TB) and Southern Madurai (SMB) blocks separated by the AKSZ. The metamorphic temperatures and pressures estimated from the SMB and TB have a similar range, that is, 600–880°C and 5–8 kbar. The similar clockwise P-T paths retrieved by phase equilibrium modelling from both the blocks represent the last deformation and metamorphism shared between them during their accretion along the AKSZ. The distinct evolutionary history of the SMB and TB prior to their amalgamation is supported by the contrasting structural, metamorphic and chronological patterns, particularly the lack of prominent middle Neoproterozoic ages and the presence of Palaeoproterozoic ages in the TB, and vice versa in the SMB. The prominent 600–500 Ma monazite ages in the TB, SMB and AKSZ attest to their timing of accretion along the AKSZ. The study corroborates the S-directed subduction model proposed for terrane accretion along the AKSZ, and provides further insight into the subduction–accretion–collision tectonics associated with the late Neoproterozoic – Cambrian evolutionary history of this region. The tectonothermal histories and geochronology of the SMB and TB are compared to the once adjoined crustal domains of Madagascar within Gondwanaland. It is suggested that the TB is equivalent to the Androyan and Anosyan domains of southern Madagascar, the SMB is equivalent to the Antananarivo and Itremo–Ikalamavony blocks of the central Madagascar, and the sinistral AKSZ is contiguous with the Ranotsara Shear Zone in southern Madagascar.

Geochemical internal variations of Salem Dolerite dykes from Southern Granulite Terrane: Implications of petrogenetic processes in the dyke conduits

“…The studied wide Salem dolerite dykes (figure 2) formed during the Proterozoic period within the charnockite regions of Southern Granulite Terrane (SGT) were intensely metamorphosed (Ghosh et al, 2004;Collins et al, 2007) during the late Archean to early Proterozoic and dissected by several crustal-scale shear zones (figure 2) (Drury and Holt, 1980;Collins et al, 2014)) run in different orientations tracked back to the Gondwana Sutures (Sato et al, 2011;Santosh et al, 2012) and the SGT comprises Coorg block (Roberts and Santosh, 2018), Nilgiri block, Salem block, Madras block to be found in the north and Madurai block, Trivandrum block and Nagercoil block in the south contains cumulates of rocks from more felsic to ultramafic (Devaraju et al, 2007;Clark et al, 2009;Santosh et al, 2009Santosh et al, , 2015Santosh et al, , 2016Santosh et al, , 2017Yellappa, 2021;Praharaj and Rekha, 2022;Kakkassery et al, 2022). Several authors discussed the emplacement of peninsular dyke swarms in India (Ernst and Srivastava, 2008;Radhakrishna et al, 2013;Dash et al, 2013;Pivarunas et al, 2019;Srivastava et al, 2014Srivastava et al, , 2019Srivastava et al, , 2021.…”