PSEUDOSECTION MODELLING, GEOCHRONOLOGICAL CONSTRAINTS AND DECOMPRESSIVE TEXTURES OF GRANULITES FROM MADURAI BLOCK, SOUTH INDIA: WITH A PARALLEL STUDY OF GRENVILLIAN OAXACAN COMPLEX, MEXICO

The Southern Granulite Terrain (SGT), one of the most notable tectonic divisions of the Indian peninsula. Mg-Al granulite from Usilampatti in the Madurai block of southern India preserves a variety of mineral textures and reactions that help in reconstructing a three-stage metamorphic evolution. Usilampatti area constitutes part of the granulite-facies rocks of the Madurai block in the SGT. We report the occurrence of coexisting sapphirine + quartz in garnet-orthopyroxene bearing granulite from a new locality in southern India, presenting evidence for UHT metamorphism (Yadav et al. 2021). The P-T evolution of the Mg-Al granulite has been constrained using TWQ and Perplex_X programs. SHRIMP U-Pb ages from zircon and monazite associated with sapphirine-bearing Mg-Al granulites suggest a widespread Ediacaran (545±60 Ma) tectonothermal event. The sapphirine-quartz association and the related textures reported here are important in understanding the tectonometamorphic evolution of the lower continental crust in the SGT and the various processes involved in UHT metamorphism.

The Oaxacan Complex (OC) occupies the central Region of the state of Oaxaca in southern Mexico. The OC represents the most extensive, lithologically dissimilar, and high-grade metamorphic outcrop. It is the largest and southernmost exposure of Grenville-age (Anderson and Silver 1971). The OC consists of metamorphic rocks derived from sedimentary and igneous protoliths. All these rocks were involved in a tectonothermal event during the Grenville orogeny, named by some authors as the Zapotecan event, with an age of 990 ± 10 Ma (Solari et al., 2003, 2014). A detailed inspection of the mineralogical and microstructural characteristics (e.g., rutile dense lamellar inclusions in quartz, rare sapphirine, ubiquitous mesoperthites, and wollastonite-fassaite calc-silicates) of the Oaxacan Complex suggest UHT metamorphism (Ortega-Gutiérrez et al. 2018), rather than typical granulite facies conditions. Other studies also suggest UHT conditions (Culí et al. 2020; Salazar et al. 2022). The Oaxacan Complex is very similar to the southern Indian granulite terrane. It is very interesting to know about the tectonometamorphic evolution of both terranes.