A B C D E F G H I J K L M N O P Q R S T U V W X Y Z All
Ray, K. K.
- Geology of Great Nicobar Island
Authors
1 Geological Survey of India, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 16, No 2 (1975), Pagination: 135-142Abstract
The Joint Scientific Expedition to the Great Nicobar Island provided opportunity for obtaining a comprehensive knowledge of the major geological features of the island. The various rock formations were examined and their stratigraphic sequence was established. Major structural features were noted and the geological history of the island is reviewed. This reveals a close similarity with the geology of Andaman Islands. Other aspects studied are economic geology, nature of soils and water resources.
- Unusual Composition from the Cumulate Section of Andaman Ophiolite
Authors
1 Geological Survey of India, 4, Chowringhee Lane, Calcutta, IN
2 I.T.C., Kanaalweg, 3, Delft, NL
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 30, No 4 (1987), Pagination: 249-254Abstract
Mafic and acid cumulates from Andaman ophiolite contain hornblende and magnetite as primary cumulus phases. Four samples with higher SiO2range, contain in addition apatite and quartz crystallised from intercumulus liquid. These have lower Ni, Cr and higher total REE abundances than ophiolitic gabbros and plot away from the field of ophiolitic cumulates in the AFM diagram. Strong negative Eu-anomaly is in striking contrast to ophiolitic cumulates.No volcanic rocks are associated with these cumulates. Volcanic rocks occurring in a different thrust slice are similar to 'transitional' ridge basalts. It is suggested that the cumulates have crystallised from melts more evolved than ridge tholeiites and possibly from melts similar to basaltic andesites of Andaman ophiolite. in a shallow magma chamber.
- Tectono-Stratigraphy and Emplacement History of the Ophiolite Assemblage from the Naga Hills and Andaman Island-Arc, India
Authors
1 Geological Survey of India, Calcutta, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 33, No 1 (1989), Pagination: 4-18Abstract
The oceanic pelagic sediments from the ophiolite assemblages of Naga Hills (NHO) and Andaman islands (ANO) broadly correspond to Late Cretaneous to Paleocene age. Late Cretaceous ocean floor represented in ANO was dominantly below the carbonate-compensation-depth (CCD), whereas it was uneven but mainly above CCD during Paleocene-Early Eocene. Maestrichtian to Paleocene ocean floor appears to be dominantly above the CCD in NHO. The NHO and ANO have closely similar postemplacement ophiolite-derived mid- and mid-late Eocene cover sediments respectively. Emplacement of the Naga Hills ophiolites during mid-Eocene, was possibly caused due to initial collision of an ocean-island chain with the subduction zone beneath the Central Burmese continent. Emplacement of the Andaman ophiolites occurred during early-mid-Eocene and may have been caused by a similar situation. The Chin Hills ophiolites were also mainly emplaced during early Eocene. The accreted ophiolites of the Indo-Burman range and Andaman islands were thrust westward over the Paleogene turbidite pile, deposited on the down going Indian plate during late Oligocene, due to terminal India-Burma continent-continent collision. In the southern Manipur sector of Naga Hills, the olistostromal upper Disang Formation (mid to late mid-Eocene) tectonically flooring the NHO, stratigraphically underlies the flyschoid to molassic Barail (Oligocene) sediments. In Andaman islands, the Lipa Formation with early Eocene and older olistoliths, forms the dominant constituent of the lower tectonic sedimentary melange flooring the ophiolites. Towards west, the sedimentary melange overrides the Archipelago Group. (Neogene) which unconformably overlies the Andarnan Flysch of Eocene-Oligocene age. The ischolar_main-zone of the collisional suture appears to be concealed below younger sediments in the Central Burma basin and in the Andaman Sea, parts of the latter being created as a back-arc marginal basin. There is thus no straightforward relation between the Late Oligocene collision suture and the present subduction zone along the trench to the west of Andaman-Nicobar islands.- Geochronology and Geochemistry of the Lingtse Gneiss, Darjeeling - Sikkim Himalaya: Revisited
Authors
1 Indian School of Mines, Dhanbad - 826 004, Bihar, IN
2 Department of Geology and Geophysics, The University of Western Australia, Nedlands, W.A. 6907, AU
3 Geological Survey of India, 27, J.L. Nehru Road, Calcutta - 700016, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 48, No 5 (1996), Pagination: 497-506Abstract
Foliated augen gneisses with streaky character, such as the Lingtse Gneiss of Sikkim-Darjeeling area, occur throughout the Himalaya. The Lingtse Gneiss is highly deformed and Occurs as thin tabular bodies. Considerable textural variation is noticed depending on the intensity of deformation and grain growth. The rocks are peraluminous and show fractionated REE pattern (Lan/Lun = 1.2-6.8). These gneisses were previously dated at 1075 and 2034 Ma by Rb-Sr method. The results of the present isotopic age determination by Rb-Sr and Pb/Pb methods indicate ages of 1678 ± 44 Ma and 1792 ± 45 Ma respectively. The variability and scatter of isotopic composition are believed to reflect imprints of tectono-thermal events.Keywords
Geochronology, Geochemistry, Lingtse Gneiss, Sikkim Himalaya.- Implication of the Mobile Belt of the Indies Archipelago on the Concept of Continental Drift Between India and Australia
Authors
1 Geological Survey of India, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 17, No 3 (1976), Pagination: 309-321Abstract
The Indies mobile belt stretching from northern Burma through the Indonesian to the Australasian archipelagoes is essentially Upper Mesozoic-Cainozoic in age. It is intercontinental in a sense that it is situated between the continents of India and Australia on one side and Sino-Sunda continent on the other, but essentially intracontinental because subsurface continuity of the continental mass and pre-geosynclinal sedimentary formations can be envisaged between the two sectors of continental mass below the geosyncline.
Studies of the geology of the various parts of the Indonesian mobile belt especially the transverse vertical gelogical cross sections of various segments of the belt in Assam-Burma, Andaman-Nicobar, Mentawal-Sumatra and Australasian sectors, suggest spatial continuity of the continental crust and pre-geosynclinal geological formations below the Upper-Mesozoic-Cainozoic geosynclinal formations of the mobile belt.
Absence of any imprint on the Indonesian mobile belt expected due to continental drift between India and Australia corroborates the view of the non-existence of such continental drift.