http://pucir.inflibnet.ac.in:8080/jspui/handle/123456789/593 2026-05-22T07:22:30Z http://pucir.inflibnet.ac.in:8080/jspui/handle/123456789/599 Title: An appraisal of crustal structure of the Indo-Burmese subduction region Authors: Bharali, Bulbul Abstract: We analyzed teleseismic receiver functions of 9 sites to determine the crustal structure beneath the Indo-Burmese subduction region (IBR), which is seismically one of the most active subduction zones of the Indian subcontinent. The receiver function analysis of the primary and reverberated phases allowed us to image the down going Moho beneath the Burmese micro plate parallel to the subducting slab. We observed that this subduction zone is characterized by sharp dip of a thick (˜45 km) crust in the Indian Territory, which steeply bends down to ˜57 km in the Burmese Territory separated by the Churachandpur Mao Fault (CMF). The Imphal valley, located in the central part of the IBR, has a sedimentary thickness of 2.5 km. The Poisson’s ratio values correlate well with the tectonic units comprises the subduction region. We observed high Poisson’s ratio values throughout the region, which reflects bulk mafic to ultramafic crustal composition. Our observations of Poisson’s ratio beneath the IBR reveal that the Indian crust along the IBR is oceanic in nature, which is possibly the Tethyan oceanic crust of Southeast Asia. 2019-01-01T00:00:00Z http://pucir.inflibnet.ac.in:8080/jspui/handle/123456789/595 Title: Petrography and whole-rock geochemistry of Oligocene Barail Sandstones of Surma basin: Implications for tectono-provenance and paleoclimatic condition Authors: Bharali, Bulbul Abstract: The Oligocene Barail Sandstones of Surma basin from parts of Champhai District of Mizoram, northeast India has been studied for their tectono-provenance setting using petrography and geochemistry. The studied sandstones are poor to moderately sorted, subarkosic to sub-litharenite and show dominance of quartz (avg. 54.46%) followed by feldspars (avg. 7.22%), rock fragments (avg. 4.98%), mica (avg. 5.89%), matrix (avg. 14.47%) and cement (avg. 12.98%). Dominance of polycrystalline and undulatory monocrystalline quartz indicates contribution from medium grade metamorphic sources, primarily of granite gneisses. High concentration of SiO2 with moderate to low concentration of Al2O3, Fe2O3, MgO, Na2O and K2O resembles the composition of upper continental crust. Moreover, moderate to high concentration of Th and V, depleted value of Ni along with TiO2/Zr suggests derivation of sediments from felsic sources. The ratios of Eu/Eu* (avg. 0.63) and LaN/LuN bears resemblance with the upper continental crust. Overall analyses show that the sediments were derived from the felsic terrain of neighbouring orogens probably represented by granite-gneisses and have undergone a moderate degree of weathering (avg. values of CIA: 70.20, CIW: 81.03, PIA: 77.63, WIP: 38.45, ICV: 1.06, Iw = 2) in a semi-humid to humid climatic conditions [Qp/(F + RF):Qt/(F + RF) = 0.20]. 2020-04-24T00:00:00Z http://pucir.inflibnet.ac.in:8080/jspui/handle/123456789/594 Title: Oblique slip faulting associated with evolving central Indo-Burmese region from Early Pleistocene deformational sequences Authors: Bharali, Bulbul Abstract: The Indo-Burmese Ranges (IBR) marks as the boundary between the rigid Burmese Plate and the north-easterly moving, obliquely converging Indian plate. This results in upliftment of Mizoram fold belt alongside of IBR, in the eastern most part of the Indian subcontinent. NS trending fault generated fold belt appears around the region due to the NE stress component from Indian plate movement. There are many linear tectonic features formed due to this process. On the eastern margin of the fold belt in the greater elevated part of IBR, EeW and NWeSE lineament patterns intersect the NS lineaments, and deformed the ridges obliquely to create complex geotectonic settings. In this study, a pristine attempt has been made to understand the geodynamic evolutionary mechanisms for the area to reveal the cause for such surficial convolutions. The arcuate subduction zone along the IBR causes the slab to flex and bend at depth. This relates to differential dipping of the slab and the greater dip surface occurred beneath the study area. The easterly dipping slab can accommodate great amount of sediments and therefore the region having maximum dip upholds the highest Tertiary sediment thickness, above the basement. Champhai district of Mizoram, India had been considered for this study as it has in the zone of convergence with highest slab dip underneath. The surface exposures have sufficient neotectonic evidences which inferred the signs from Early Pleistocene neotectonic to present active tectonic deformational history. Sequential offset of the antecedent rivers carries the signatures of the varying stress component within them. The geodynamic processes produce some tectonic features through the mode of earthquake generation. Epicentral plots and focal mechanism solutions for the area indicate seismic activity associated with the thrust and oblique strike-slip movement along with their correlation for the lineament distribution. The evolutionary model indicates syn-tectonic upliftment of the study area along with evolving IBR during Late Oligocene thrusting events. A Paleo-lake adjacent to the Champhai town is believed to be the source of some northerly flowing rivers that was located on the ridge. Late Pleistocene seismic events produce some contractional strike-slip faults that later transformed to oblique slip component that shaped the area. This study is also important for understanding the earthquake events and related deformation pattern in IBR. This also might be used to locate potential geohazard sites for safer construction as well as to understand the petroleum migration pathways. Copyright © 2018, Guangzhou Institute of Geochemistry. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 2018-05-07T00:00:00Z