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[Display omitted] • Granitoids of Chitradurga belt were emplaced at ∼ 3.2 Ga, ∼3.0 Ga and ∼ 2.6 Ga. • Two metamorphic events are documented at ∼ 3.0 Ga and ∼ 2.56 Ga. • Nd isotopes infer juvenile crustal addition at 3.2 Ga, reworking at 3.0 Ga and 2.6 Ga. • Role of convergent margin tectonics in the evolution of Chitradurga granitoids. The Chitradurga Greenstone Belt is one of the largest belts in the central part of the Western Dharwar Craton (WDC). We present new SHRIMP U-Pb zircon and titanite ages, whole-rock geochemical and Sm-Nd isotopic data for granitoids that developed at both its eastern and western margins, and for those that are intrusive into the belt. Western margin TTG samples yield emplacement ages ofca. 3.21 Ga and are of the high-Al TTG type characterized by weakly negative ɛNd t values. Eastern margin granite samples yield emplacement ages of ∼ 3.0 Ga and 2.56 Ga with negative ɛNd t values. The granites intrusive into the belt are of Neoarchean age (∼2.61 Ga) with more-evolved Nd isotopic signatures consistent with the involvement of older crustal material. Metamorphic events are documented at ca. 3.0 Ga and ca. 2.5 Ga. The ca. 3.0 Ga event is synchronous with the diapiric emplacement of trondhjemites and high-K granitic plutons in the WDC. The peak metamorphic event at ∼ 2.5 Ga is the major tectono-thermal event evident throughout the Dharwar Craton. Geochemical systematics imply the involvement of convergent margin tectonics in the evolution of studied granitoids. The role of horizontal tectonics in the crustal growth of WDC is evident from at least 3.2 Ga, whereas signatures for the reworking of the older crust are more prominent from ∼ 3.0 Ga. [ABSTRACT FROM AUTHOR]

New zircon U-Pb ages for a felsic volcanic rock (2,588 ± 10 Ma) and an intrusive granite (≥2,555 ± 6 Ma) in the Gadag greenstone belt in the Western Dharwar Craton, southern India, are similar to dates for equivalent rocks in the Eastern Dharwar Craton and indicates docking of the two cratons prior to this time. The zircons in the intrusive granite are strongly overprinted, and coexisting titanites yielded two different age populations: the dominant group gives an age of 2,566 ± 7 Ma, interpreted as the emplacement age, whereas the minor group gives an age of 2,516 ± 10 Ma, reflecting a hydrothermal overprint. In situ U-Pb dating of monazite and xenotime in gold reefs of the Gadag (2,522 ± 6 Ma) and Ajjanahalli (2,520 ± 9 Ma) gold deposits reveal a previously undated episode of gold mineralization at 2.52 Ga, substantially younger than the 2.55 Ga Hutti deposit in the eastern Dharwar Craton. The new dates confirm that both the younger greenstone belts and lode gold mineralization in the Dharwar Craton are about 100-120 My, younger than in other well-dated Archaean cratons. Although gold mineralization across the craton postdates most of the magmatic activity and metamorphism at upper crustal levels, widespread thermal reworking of the lower-middle crust, involving partial melting, metamorphism, and lower crustal granitoid intrusion, occurred concurrently with gold mineralization. It is likely that the large-scale hydrothermal fluid flow that produced widespread gold deposition was also part of this tectono-thermal event during the final stages of cratonization of the Dharwar Craton in southern India. [ABSTRACT FROM AUTHOR]

The Andaman ophiolites are well exposed in the Andaman group of islands, which is part of the Sunda-Burmese double-chain arc system in the Bay of Bengal, India. Plagiogranites occurring on the eastern margin of the southern part of South Andaman Island appear as interstitial vermicular and micrographic intergrowths of quartz and plagioclase. They are tonalitic to trondhjemitic in composition, and their Rb, Yb, Ta, and Y abundances are characteristic of a volcanic-arc affinity. Sensitive high-resolution ion microprobe U-Pb dating of zircons from a plagiogranite within the Andaman ophiolite has yielded a weighted mean 206Pb/238U age of 93.6 ± 1.3 Ma, interpreted as the age of its crystallization. The subduction-related plagiogranite has intruded a gabbro unit of the Andaman ophiolites as well as extrusives of the East Coast Volcanics at this time. Since the Andaman ophiolitic rocks predate the plagiogranite, they cannot have been generated in the currently active Late Miocene Andaman-Java subduction zone and were most likely obducted onto the leading edge of the Eurasian continent at an earlier phase of subduction activity during early Cretaceous time. [ABSTRACT FROM AUTHOR]

The Hutti orogenic gold deposit, in the eastern Dharwar craton of South India, is located in a cuspate greenstone belt which is tectonically juxtaposed against tonalite-trondhjemite-granodiorite (TFG) basement on its western margin. The host rocks to gold mineralization are mafic and felsic volcanic rocks metamorphosed to the amphibolite facies. Mineralization is confined to nine, broadly parallel, quartz reefs within north-south--to north-northwest-south-southeast-trending shear zones that dip approximately 70°W. Six of these 2- to 10-m-thick, boudinaged veins have been mined to a depth of over 810 m. Free gold occurs in the veins and alteration haloes and is spatially and temporally associated with quartz and disseminated pyrite and arsenopyrite which, in turn, are closely associated with hydrothermal monazite and xenotime in the biotite-plagioclase wall-rock alteration around veins. Gold is considered to have been deposited during D2 to D3 deformation, broadly coincident with the emplacement of syntectonic granitoids. The history of volcanism, granitic magmatism, and gold mineralization is defined by U-Pb geochronology of magmatic zircons and hydrothermal monazite and xenotime. The felsic volcanic host rocks have a U-Pb zircon age of 2587 ± 7 Ma, about 40 m.y. older than the age of gold mineralization at 2547 ± 10 Ma determined from hydrothermal monazite. The syntectonic Kavital granitoid has a U-Pb zircon age of 2545 ± 7 Ma, which overlaps with the timing of gold deposition and is consistent with structural interpretations. The Ramagiri and Kolar gold deposits elsewhere in the Dharwar craton are considered to have a similar structural timing, and the Hutti geochronology suggests that gold mineralization occurred throughout the Dharwar craton some 80 to 120 m.y. later than the major peak of Late Archean world-class orogenic gold mineralization in most other Archean cratons. [ABSTRACT FROM AUTHOR]

Examines the bedding-plane markings for implications of early evolution of animals in Vindhyan, India. Query on the biological origin of the markings; Estimation on the inclusive dates of the deposit of sediments; Suggestion on the evolution of complex metazoans.

• The Bababudan Group is an intracontinental rift to passive-margin succession. • The Chitradurga Group is divided into unconformity bound Stages I and II. • Stage I is the sedimentary and volcanic record of an extensional back-arc basin. • Stage II is the sedimentary and volcanic record of a transtensional back-arc basin. • Stratigraphic equivalents in the Eastern Dharwar Craton are near-arc basins. The Dharwar Supergroup comprises the unconformity bound Bababudan and Chitradurga groups. The Bababudan Group, which is best preserved in the Western Dharwar Craton, records a divergent margin comprising a basalt-dominant intracontinental rift sequence, a shale-BIF drift sequence, and a sandstone-shale thermal-subsidence sequence. The rift stage evolved from ∼2765 Ma to ∼2720 Ma, whereas the succession was folded, uplifted and eroded during development of a convergent continental margin from ∼2680 Ma. Ocean opening was to the east or southeast. The Chitradurga Group records a two-stage back-arc basin behind an east-facing continental arc. Stage I evolved between ∼2609 Ma and ∼2582 Ma, and Stage II between ∼2582 Ma and ∼2540 Ma. The two stages are separated by a subaerial unconformity. Stage I comprises siliciclastic fluvial, shallow-marine and deep-marine sedimentary rocks and bimodal volcanic rocks. Stage I is best preserved in the Western Dharwar Craton, but there are equivalents in the Eastern Dharwar Craton. Stage II in the Western Dharwar Craton comprises deep-marine turbidites of siliciclastic and volcaniclastic provenance, and basaltic and felsic volcanic rocks. Volcanic Stage II sequences in the Eastern Dharwar Craton define an arc-adjacent position. Tectonically driven cyclic uplift and erosion were responsible for the mismatch between preserved stratigraphic thickness and time, particularly for Stage II sequences. A remnant of a <2540 Ma late-stage basin in the northeast of the Eastern Dharwar Craton defines a syncollisional tectonic setting. The Dharwar Supergroup was deformed in a SW-verging hinterland magmatic fold/thrust belt from ∼2540 Ma. [ABSTRACT FROM AUTHOR]