Early Palaeoproterozoic structural reconstitution of a suite of rocks from the Mahadevi Layered Complex, Tamil Nadu, India

Abstract

The Palghat-Cauvery Shear Zone (PCSZ) of the Granulite Terrane of South India is perceived to be a late Neoproterozoic transcontinental shear zone that develops extensive mylonite and sheath folds. The Mahadevi Layered Complex (MLC), the area of present study, is situated in the eastern part of the PCSZ. The studied area exposes vast expanse of felsic orthogneisses with large enclaves of mafic granulite interlayered with meta-BIF. Our study records two distinct deformational events (D 1-2 ) that produced E-W closing regional folds with gently curved fold axis. The curved fold axes results in the regional dome-and-basin structure. Kinematic markers suggest that a weak shear couple was accompanied with the D 2 deformation. Preponderance of the granoblastic fabric in the rocks, restriction of mylonites only in local conjugate shear zones, and the structures produced during D 1-2 deformations are at variance with the view that (a) existence of a sheath fold as previously reported from the area and (b) the PCSZ marks the zone of intense shear deformation. Preliminary petrological information from the studied area shows that D 1-2 deformational events were accompanied by high-pressure granulite-facies metamorphism that was followed by a steeply decompressive retrograde P-T path. The U-Pb zircon ages from the felsic orthogneiss fixes the date of emplacement of its magmatic protolith and the regional high-pressure metamorphism at ≥2,530 and ca. 2,479 Ma, respectively. Integrating all the information it is suggested that the evolution of the MLC occurred in a continent-continent/arc collisional setting at the dawn of the Proterozoic Eon. This study does not support the existence of a "mega sheath fold" in the MLC as has been published in the recent literature. KEYWORDS continent-continent/arc collision, Early Palaeoproterozoic, Granulite Terrane of South India, highpressure metamorphism, Mahadevi Layered Complex, structure, U-Pb zircon chronology

Ultrahigh temperature metamorphism and isobaric cooling of Neoarchean ultramafic‐mafic granulites in the southern granulite terrain, India: Phase equilibrium modelling and SHRIMP zircon U–Pb dating

“…Zircon U–Pb geochronological studies on the metamorphic rocks from the Namakkal Block, the Shevaroy Block, the Madras Block, and the Nallamalai shear zone have yielded metamorphic ages from ca. 2540 to 2440 Ma (Table S6; Figure 16a) (Anderson et al, 2012; Clark et al, 2009; George et al, 2019; Glorie et al, 2014; Li, Santosh, Ganguly, et al, 2018; Mohan et al, 2013; Peng et al, 2019; Peucat et al, 2013; Saitoh et al, 2011; Sato et al, 2011; Talukdar et al, 2020), which can be roughly subdivided into two groups, that is, ca. 2540–2510 and ca.…”

“…These results reflect multiple reworking events that occurred in the lower mafic continental crust. Zircon and monazite U – Pb analyses on various metamorphic rocks have yielded abundant late Neoarchean to early Paleoproterozoic metamorphic ages, ranging from 2526 to 2442 Ma (Anderson et al, 2012; George et al, 2019; Glorie et al, 2014; Mohan et al, 2013; Peng et al, 2019; Saitoh et al, 2011; Sato et al, 2011; Talukdar et al, 2020).…”

Validation of clinopyroxene-garnet magnesium isotope geothermometer to constrain the peak metamorphic temperature in ultrahigh-temperature ultramafic-mafic granulites

“…Ma (Saitoh et al 2011;Sato et al 2011;Anderson et al 2012;Mohan et al 2013;Glorie et al 2014;George et al 2019;Peng et al 2019;Talukdar et al 2020). Phase equilibrium modelling yielded a P-T condition of 22 kbar at 980 °C for the garnet pyroxenite from the Jambumalai Hills in the Kolli-massif (Figure 2), and an isothermal decompression P-T path was obtained based on the presence of plagioclase corona around the garnet (George et al 2019).…”

Deformation mechanisms and characteristics of the meta-BIFs from an early Proterozoic shear system of the Southern Granulite Terrane (SGT), India

“…The present structural architecture of the BIFs results from two phases of deformations, D 1 and D 2 , both of which occurred at granulite facies conditions. The gneissosity of the host orthogneiss developed during D 1 , whereas the N-S compression induced folding characterizes D 2 (Talukdar et al, 2020). The latter also produced the E-W trending linear fabric, particularly at the hinges, with a gentle easterly plunge, defined by the elongated streaks of magnetite and quartz alterations (Talukdar, 2015).…”