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Two linear NE–SW trending belts of platformal orthoquartzite-carbonate sequence, namely, the East Jahazpur Belt (EJB) and the West Jahazpur Belt (WJB), within a vast tract of slate–argillite–metagreywacke and subordinate metavolcanics of Hindoli Group (HG) together occur sandwiched between Vindhyan sediments to the east and Banded Gneissic Complex-II (BGC-II) to the west, at the eastern boundary of Aravalli Craton, Rajasthan, India. A NE–SW trending crustal-scale transpressive shear separates this low-grade supracrustal sequence from the gneisses of older Mangalwar Complex (BGC-II) to the west and the Great Boundary Fault (GBF) restricts it in the east against the Vindhyan rocks. A lensoid body of strongly deformed and mylonitised Jahazpur Granite (JG), is the basement for the supracrustal rocks and occupies the core of a SE verging D1-antiformal nappe defined by the EJB (Jahazpur Group-I) rocks. This large scale D1 thrust nappe structure in the EJB is manifested by stacking of early recumbent folds in the carbonate and quartzite units and a prominent zone of brecciation and ferruginisation all along the eastern margin of EJB. In the WJB (Jahazpur Group-II), D1 is represented by large scale isoclinal reclined fold geometry, likely to be influenced by the major transpressive shear and refolding at its western margin. D2 deformation phase, variably superposed over the D1 structures, together controls the NE–SW disposition of Hindoli and Jahazpur rocks. Based on the structural patterns and lithostratigraphic characters, we propose a revised stratigraphy of the Hindoli–Jahazpur rocks. Whole rock Rb–Sr dating of the strongly deformed and mylonitised Jahazpur Granite constrained the age of the tectono-metamorphic event that affected these rocks. Two suites of mylonitised Jahazpur Granite from two different localities yielded ages of 1423 ± 52 and 1393 ± 33 Ma, using Sector 54 TIMS. The tectonism that resulted in folding, thrust nappe, shearing and mylonitisation involving basement JG of Neoarchean age and the overlying Paleoproterozoic Jahazpur–Hindoli supracrustal sequences, therefore, represents a Mesoproterozoic (~1.4 Ga) orogeny that is correlatable with the breaking-up of Columbian Supercontinent along the eastern margin of the Aravalli craton. [ABSTRACT FROM AUTHOR]

Late Neoproterozoic (c. 555 Ma) high-pressure–ultrahigh-temperature (HP–UHT) metamorphism has been documented for MgAl-rich migmatitic granulites from the Palni Hills in the Southern Granulite Terrane (South India). Conspicuous reaction textures indicate a clockwise P–T evolution, which is constrained through P–T pseudosection modelling and thermobarometry. The transformation of sillimanite to kyanite, which coexisted with orthopyroxene and/or garnet, records an early stage of loading. During subsequent heating to UHT conditions at deep-crustal levels (c. 1000°C, 13·0 kbar) kyanite was transformed to sillimanite, and distinct peak-temperature assemblages (orthopyroxene + sillimanite + mesoperthite + rutile ± garnet ± quartz ± sapphirine, garnet + biotite + sillimanite + spinel + corundum + rutile + plagioclase and garnet + orthopyroxene + rutile + plagioclase ± quartz) formed in specific bulk compositions through biotite-dehydration-melting reactions. A sequence of corona and sapphirine-bearing symplectite textures records subsequent isothermal decompression of the order of c. 6 kbar at persistent extreme temperatures (1010–920°C). UHT decompression is consistent with the uniformly high Al contents of porphyroblastic, coronitic and symplectitic orthopyroxene (up to 10·4 wt % Al2O3). Regrowth of garnet and biotite documents post-decompressional cooling to subsolidus conditions of <800°C at mid-crustal levels (c. 6 kbar). HP–UHT metamorphism and the clockwise P–T path of the Palni Hills granulites is attributed to a single late Neoproterozoic tectono-metamorphic event, which has been consistently dated at c. 555 Ma through laser ablation inductively coupled plasma mass spectrometry U–Pb analyses of zircon and in situ electron microprobe U–Th–total Pb analyses of monazite. The MgAl-rich granulites occur as enclaves in enderbitic orthogneiss. The intrusion of the orthogneiss in the late Archean (2534 ± 28 Ma) marks the beginning of voluminous granitoid emplacement in the Southern Granulite Terrane between 2530 and 2440 Ma, which presumably caused a first high-grade metamorphic event in the early Paleoproterozoic (2469 ± 13 Ma), recorded by zircon cores in the MgAl-rich granulites. The clockwise P–T–t evolution indicates that HP–UHT metamorphism in the central part of the Southern Granulite Terrane is related to collisional tectonics during the final assembly of Gondwana in the late Neoproterozoic. Extreme heating is ascribed to upwelling of the asthenosphere during delamination of the thickened lithospheric mantle. Fast uplift of the rocks followed by mid-crustal isobaric cooling reflects extension of the hot overthickened crust and its subsequent cooling to a normal geotherm. [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]

U-Pb zircon dating indicates that the Balugaon Anorthosite Massif of the Chilka Lake Domain, Eastern Ghats Belt, India, crystallized at 983.0 ± 2.5 Ma, ∼200 m.yr. earlier than previously inferred from ferrodiorite that intruded the massif. An integration of the new date with published structural data indicates that the anorthosite intruded a crust that was deformed twice before the intrusion. Furthermore, U-Th-Pb chemical dating of monazite cores (714 ± 11 Ma) and rims (655 ± 12 Ma) yields results consistent with progressive high-grade metamorphism of the anorthosite, and monazite + allanite rims (463 ± 22 Ma) around apatite indicate low-grade pan-African thermal activity. The 714- 655-Ma dates possibly correspond to convergence and oblique collision between the Eastern Ghats-Rayner Block and western Australia in the mid-Neoproterozoic. [ABSTRACT FROM AUTHOR]

The arc sequence in the lower Shyok area comprises volcanics (Shyok Volcanics) and intra-arc basin sediments (Hundiri, Saltoro Flysch and Saltoro Molasse formations). Biostratigraphic investigations on the Hundiri Formation indicate that this lithounit contains several Aptian-early Albian orbitolinids comprising Mesorbitolina, Orbitolina, Praeorbitolina, Palorbitolinoides, Palorbitolina, ?Neorbitolinopsis and Paracoskinolina. The orbitolinid taxa from the Shyok tectonic belt are comparable with those known to occur in Ladakh, Chitral, Burzil Pass (Indo-Pak region), Afghanistan, South Tibet and Myanmar. Fossil data suggest the existence of transgressive Neo-Tethys sea during Early Cretaceous, north of the Indian Plate. [ABSTRACT FROM AUTHOR]

Recent fossil discoveries, phylogenetic analyses, revised reconstructions of continental drift, and accumulating molecular evidence have all yielded new information relating to anthropoid origins within the broader context of primate evolution. There is an emerging consensus among molecular studies that four superorders of eutherian mammals can be recognized: Afrotheria, Euarchontoglires (to which primates belong), Laurasiatheria, and Xenarthra. Overall, molecular phylogenies for mammals agree with some statistical analyses of the primate fossil record in indicating an early origin for primates around 85 Ma ago, and the divergence of haplorhines and strepsirrhines at ca. 77 Ma. Such an ancient date for the origin of haplorhines is some 17 Ma prior to the first known possible primate, and some 22 Ma before the earliest fossil evidence of undoubted euprimates. Because anthropoid fossils date back at least to the late Eocene and perhaps to the middle Eocene, and given indications of an early origin for primates it is unlikely that ancestral anthropoids arose within any other currently known clade of fossil primates (adapiforms, omomyiforms, strepsirrhines, or tarsiiforms). Implications of new molecular, morphological, and biogeographic lines of evidence are explored with respect to the likely time and place of the origin of anthropoids. Four competing, testable hypotheses are reviewed in detail: 1) the Paratethyan hypothesis, 2) the continental Asian hypothesis, 3) the Indo-Madagascar hypothesis, and 4) the African hypothesis. A case is made that current evidence best supports a relatively ancient Gondwanan origin for primates, as well as a Gondwanan (African or Indo-Madagascan) origin for anthropoids at least as old as that of any other currently documented major primate clade. Available fossil evidence at present seems to be most compatible with the African hypothesis, but it is noteworthy that primates are included not in Afrotheria but in Euarchontoglires. [ABSTRACT FROM AUTHOR]

Presents an uranium-lead isotope study of zircon and titanite from rocks in and around the Ramagiri Schist Belt of the eastern Dharwar Craton, India, to determine the geological history of the terranes that constitute the belt. Inference of the minimum age of the crust's magmatic precursors; Evidence for accretionary origin of the eastern Dharwar Craton.

Estimates the age of the Rajamundry Traps in India around the late Cretaceous-early Paleocene with the use of K-Argon dating. Geochronological and geochemical analysis; Equivalence in the stratigraphy of the Rajamundy Traps and the Deccan Traps.

Reports seven new U-Pb (zircon) dates for felsic volcanic and plutonic units in the eastern and western Caledonian Highlands, Canada. Magmatic evolution in the Caledonian Highlands; Relationships with adjacent areas in Southern New Brunswick; Regional implications; Importance of geochronological data.

The article presents information on an Acheulian assemblage that has been found at Bori in the state of Maharashtra, India. Acheulian sites were first reported from India over a century ago. Dating of the Acheulian in India is very difficult because most of it occurs in a near surface context or stratified in the quaternary alluvium along the rivers. The first absolute dating of the Acheulian in India furnished minimum ages of about 1000, 000 years for a number of sites. The dated tephra occurs within the alluvium exposed by the river Kukdi near the village of Bori. The tephra sequence is dominated by clays and silts, with gravels at the base and at the top of the sequence and immediately follows the tephra layer. Artefacts are generally found in a gravel which cuts into the tephra at sections 3, 4, 7 and 9. When the raw material used is soft as is basalt then the artefacts incorporated into gravels are abraded. The association of an Acheulian assemblage with dated tephra pushes back the age of the Acheulian in India from the late Middle Pleistocene to the early Middle Pleistocene.

Presents comments on the work of several authors led by Julia de Sigoyer on issues about the dating of the Indian continental subduction and collisional thickening of eclogites in the northwest Himalaya. Points of arguments; Clarifications made by the authors led by de Sigoyer.

Discusses the debate of the age of the first multicellular animals. Original age dating 600 million years old; Difficulties in dating fossil worm tracks found in central India; Details on the tracks; Workshop held in Lucknow, India in February 1999.