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[en] The radiometric age data obtained by different dating methods have been interpreted in terms of possible orogenic activities prevailing in the Himalaya. In general, the age data confirm four main events, the Precambrian, the Late Precambrian-Cambrian Assyntian (Caledonian), the Late Palaeozoic-Hercynian and the Late Cretaceous-Tertiary Himalayan orogeny. The mineral dates are particularly significant in delineating different phases of the last i.e. the Himalayan orogeny which indicates main activity of the young Himalayan metamorphism around 70 to 50 Ma and followed by a momentous phase of major uplift during 25 to 10 Ma, which was responsible for the rise of the deeper part of the Himalaya into great folds and thrust slices and the formation of nappe structures. (author)
[en] Two major regions of India, the Peninsular Indian Shield and the Himalayan Orogen, host a variety of uranium deposits and occurrences. The uranium provinces identified in the Indian Shield include four contiguous regions. The most predominant uranium mineralizations are of the hydrothermal disseminated and vein types, the quartz-pebble conglomerate type and the sandstone type. Uranium also occurs in association with phosphorites and black shales in the Himalayan region and parts of the Indian Shield. Some of the hydrothermal deposits have peneconcordant gradational stratabound characteristics suggestive of an initial syngenetic character and subsequent remobilization into zones of major tectonic and later magmatic activity. Many of the provinces are intimately associated with polymetallic mineralization, especially copper, nickel and molybdenum, as exemplified by the Singhbhum uranium-copper belt of eastern India. A broad time-bound character can be assigned to the mineralizations. Early quartz-pebble conglomerate mineralization during the period 2600 to 2900 million years (Ma) is followed by subsequent hydrothermal shear controlled mineralization in the time ranges 1600 to 1400 and 1200 to 700 Ma. In the Phanerozoic, uranium has been recycled into sedimentary basins from the earlier belts of Precambrian mineralization. This has resulted in sediments highly enriched in uranium in the Permo-Carboniferous, Cretaceous and Mio-Plio-Pleistocene sedimentary sequences. The geological knowledge gained by exploration efforts in the Indian subcontinent, with regard to the uranium potential in specific tectonic and lithostratigraphic horizons, has relevance in identifying favourable target areas in the adjoining countries of South-East Asia. 57 refs, 3 figs, 6 tabs
[en] Complete text of publication follows. Paleomagnetic study in southern Tibet and the Higher Himalayan Crystalline (HHC) was twofold: (1) the recognition of vertical and horizontal block rotations and (2) the examination of the high grade metamorphic rocks (gneisses) from the HHC for their suitability for paleomagnetic investigations. Toward the separation of local and regional tectonic effects, the results from southern Tibet reflect a regional trend in agreement with oroclinal bending and rotational under-thrusting. On the other hand, measured 'anomalous inclinations' are interpreted as a consequence of extensional tectonic, and the circular distribution of magnetic remanences is attributed to long wavelength folding within the study area as well as doming in the crust. The examination of the high grade metamorphic rocks was successful: The high quota of isolated stable and well grouping secondary magnetic remanences, demonstrate their suitability for paleomagnetic investigations. A high potential source is therefore established which enable considerable contributions within the thermo-tectonic evolution of an orogen. Data suggest no significant vertical rotation on a regional scale versus India. A regional trend comparable to that obtained for south Tibet, and expressed as a dispersion of remanence vector directions on a small circle is observed. The new findings are in disagreement with the hypothesis of a uniform clockwise rotation increasing to the east of the Himalayan arc. A major effect, inferred from paleomagnetic data, attributed to long wavelength folding, doming and associated low/high normal faults/thrust system became more evident. In summary, paleomagnetism is a potential applied method in deciphering deformation processes on local-, meso- and regional scale.
[en] Complete text of publication follows. Magnetotelluric surveys were conducted over two profiles for mapping the major tectonic features over the eastern syntaxial bend. These studies over the main frontal thrust and Main boundary thrust of the Himalaya and the Mishmi thrust in the Indo Burman range have shown that the signatures of these thrusts at deeper level are not coincident with their corresponding surface expressions. Thus main frontal and the main boundary thrusts are traced about 20 km south of the surface manifestations where as the Mishmi thrust at deeper levels is about 25 km west of the location observed on the surface. The global positioning studies (Gan, W, et al. (2007) J. Geophys. Res. Article No: B08416) are indicative of eastward (transverse to the strike) movements of the sedimentary overburden north of the main frontal thrust, in this region. Another conspicuous feature is the south dipping thrust / reverse fault delineated to the north of the Main frontal thrust earlier observed in the Tawang-Bomdilla region (Gokarn et al, 2008, 19th EM induction workshop, Beijing China). Its signatures at shallow depth in this region are however obscured by the presence of then supracrustal deposits of the Abhor volcanics and Yinkiang formations occurring in small discrete patches in the close vicinity of this feature.