Tectonostratigraphic development of the c. 300 km-long Nellore schist belt (NSB) of southern India is described in relation to the post-Neoarchaean growth of the Dharwar cratonic nucleus. Lying along the eastern margin of the Dharwar cratonic nucleus, the NSB comprises several geologically and geochemically distinct tracts of deformed Palaeoproterozoic to Mesoproterozoic volcanosedimentary successions: the Vinjamuru Group, the Kandra ophiolite complex (KOC), the Kanigiri ophiolitic melange (KOM) and the Udaigiri Group, arranged in relative order of younging. The high-grade Eastern Ghats belt occurs further to the east of the NSB with a tectonic contact. Thrust-transported oceanic crust remnants occur in the 1.9 Ga KOC, 1.34 Ga KOM, and the Vinjamuru Group, which show multiple deformation, amphibolite facies metamorphism and granitic intrusions. The available geological, geochemical and geochronological data have been examined to tentatively constrain the relative age of the different tectonostratigraphic units of the NSB, tectonic juxtaposition and implications in relation to global events in the Proterozoic. Subduction-related ocean closures outboard and east of the Dharwar Craton, evidenced by the KOC and KOM, possibly had links with the assembly of Columbia and its final dispersal, respectively.

A new U-Pb zircon SHRIMP age of 1284 Ma from the Kanigiri granite, India, is reported to help constrain the middle to late Mesoproterozoic tectonic evolution of the Nellore schist belt (NSB). The Kanigiri granite has whole-rock chemical characteristics of A-type granites and is marked by light rare earth element enrichment, a strong negative Eu anomaly, and negative Ba, Sr, P, Ti, and Yb anomalies, indicating feldspar, apatite, and ilmenite/magnetite fractionation. Samples show Y/Nb versus Yb/Ta ratios in the range for granites associated with ocean island basalts. This two-mica granite is peraluminous and alkali-calcic to calc-alkalic, and it has high annite to phlogopite proportions (92%-98%). Strong alignment of flattened mafic microgranular enclaves in the granite, together with relatively high-to moderate-temperature crystal plastic deformation fabric in shear zones within the granite, suggest overprinting of subsolidus deformation over a relict magmatic fabric, a feature not very common in true anorogenic granites but reported in late-to postorogenic granites elsewhere. An intrusive relationship with the 1334 Ma Kanigiri ophiolitic mélange, within the NSB, indicates that there is a ≤50 m.yr. gap between the Mesoproterozoic subduction-accretion, represented by the ophiolite mélange and late-to postorogenic granite emplacement. Although the Kanigiri granite occurs in close proximity to mafic and felsic alkaline plutons belonging to the 1250-1400 Ma Prakasam alkaline province (PAkP) in the northern NSB and there is overlap in age, the Atype granitic magma source is apparently unrelated to PAkP alkaline magmatism. Our work further substantiates the observation that A-type granites originate in varied tectonic settings, not necessarily only in a rift-related (intraplate) setting.

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The tectonic deformation of the outer Indo-Burman Ranges (i.e., Chittagong Tripura Fold Belt, CTFB) is associated with the oblique convergence of Indo-Burmese plates since the latest Miocene. This article presents detailed field evidence of deformation structures and their kinematics in the exposed Tertiary successions in the CTFB. We combine observations made in this study with the published structural, geodetic, and seismic data sets to present an overview of the active tectonic framework of the region and its strain partitioning. To determine the kinematic evolution, décollement depth, and amount of strain, we combined geologic field mapping, structural analysis of fifteen anticlines, fracture/lineament analysis, and paleostress analysis of faults that define the ∼100 km wide CTFB. Structural data and kinematic analyses suggest subhorizontal plane strain with approximately 10% east-west shortening (oriented ~65°) that is perpendicular to the axial plane (oriented ~155°) of the CTFB anticlines. No evidence of significant transpression or strike-slip faulting has been observed in the CTFB and, therefore, suggests that full slip-partitioning is normal to the outer belt and parallel to the inner belt of the IBR. Paleostress analysis results are in good agreement with the present-day stress regime, and this implies that past and present deformation is dynamically related with the normal component of India-Burma oblique vector velocity motion.

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