Paleoproterozoic/Mesoproterozoic tectonism in the northern fringe of the Western Dharwar Craton (India): Its relevance to Gondwanaland and Columbia supercontinent reconstructions

Abstract

A newly discovered suite of Paleoproterozoic/Mesoproterozoic amphibolite facies supracrustals

P–T path reconstruction in a multi‐layered garnet‐bearing schist: Evidence for 2.2–2.1 Ga near‐isothermal loading in the northern margin of the Western Dharwar Craton (India), and regional implications

“…This however does not preclude the possibility of migration of fluids across the layers. But for such an eventuality, the dominant fraction of fluids needs to migrate along grain boundaries parallel to the layers (dominated by weak-to-shear phyllosilicate minerals), rather than across the layers where grain boundary controlled porosity networks are likely to be shorter and more circuitous.The temperature-pressure estimates made in this study (510-665 C and 6-9 kbar) overlap with the P-T values obtained in previous studies from this area, for example, 600 ± 40 C, 7.3 ± 1.2 kbar(Rekha & Bhattacharya, 2013) and 490-620 C and 6.4-7.9 kbar(Rekha & Bhattacharya, 2014). P-T paths reconstructed in the F I G U R E 1 2 Comparative diagram showing the stability fields of mineral assemblages and P-T paths from Layer-1A, 1B, 3 and 4.…”

“…Since the different layers are likely to have experienced same P-T evolutionary histories, it is unusual for the temperatures to vary in the scale of thin section. We suggest that the differences in the P-T paths may be an artefact of assuming the composition of the fluid to be same or similar in the different layers, and therefore, the P-T paths, although topologically correct, are somewhat idealized Rekha and Bhattacharya (2014). demarcated steeply dipping WNW-striking transpressional shear zones with dextral sense of shearing and north-down kinematics.…”

Restoration of Late Neoarchean–Early Cambrian tectonics in the Rengali orogen and its environs (eastern India): The Antarctic connection

“…However, the thin rims mantling older cores in the "type a" monazites in the matrix are invariably Pan African in age (505-610 Ma). These monazites rims often truncate chemical zones in the older cores, and therefore, these Pan African metamorphic rims are inferred to have precipitated by fluid-aided dissolution-precipitation (Rasmussen et al, 2005;Rasmussen and Muhling, 2007;Rekha and Bhattacharya, 2014). We suggest that the lack of Pan African rims in monazites included within the porphyroblasts is because these monazites were shielded from…”

“…Rekha and Bhattacharya, 2014). By contrast, "type b" chemically-homogeneous metamorphic monazites yield tightlyconstrained ages varying between 505 ± 10 Ma and 610 ± 15 Ma, with the mean age population at 535 ± 4 Ma (Fig.…”

Early Neoproterozoic Deformation Kinematics in the Chottanagpur Gneiss Complex (Eastern India): Evidence from the Curvilinear Hundru Falls Shear ZoneAnalysis

“…The technique has high spatial resolution (beam diameter~1 μm) and can be used to date texturally constrained in situ monazite [113][114][115][116]. Also, monazites tend to grow readily, unlike zircons, by fluid-induced dissolutionprecipitation processes in a wide range of temperature, and especially at low temperatures [114,[117][118][119][120][121] well below 14 Lithosphere the blocking temperature of intracrystalline U, Pb diffusion at T < 850°C [122][123][124][125]. As a consequence, the ages of the deformation fabric at greenschist/amphibolite facies can be readily obtained from structurally and texturally constrained monazite grains; also, older magmatic and high-T metamorphic dates may be preserved especially in dry assemblages where fluid activity is limited as in weakly strained rocks, and in monazites sequestered within robust grains lodged in strain shadow zones of subsequent low-T events.…”