Articles written in Journal of Earth System Science

    • Active tectonics in the Assam seismic gap between the meizoseismal zone of AD 1934 and 1950 earthquakes along eastern Himalayan front, India

      Arjun Pandey Ishwar Singh Rajeeb Lochan Mishra Priyanka Singh Rao Hari B Srivastava R Jayangondaperumal

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      The Assam Seismic Gap has witnessed a long seismic quiescence since the Mw∼8.4 great Assam earthquake of AD 1950. Owing to its improper connectivity over the last decades, this segment of the Himalaya has long remained inadequately explored by geoscientists. Recent geodetic measurements inthe eastern Himalaya using GPS document a discrepancy between the geologic and geodetic convergence rates. West to east increase in convergence rate added with shorter time span earthquakes like the 1697 Sadiya, 1714 (Mw∼8) Bhutan and 1950 (Mw∼8.4) Tibet–Assam, makes this discrepancy more compositeand crucial in terms of seismic hazard assessment. To understand the scenario of palaeoearthquake surface rupturing and deformation of youngest landforms between the meizoseismal areas of Mw∼8.1 1934 and 1950 earthquakes, the area between the Manas and Dhanshiri Rivers along the Himalayan Frontal Thrust(HFT) was traversed. The general deformation pattern reflects north-dipping thrust faults. However, back facing scarps were also observed in conjugation to the discontinuous scarps along the frontal thrust. Preliminary mapping along with the published literature suggests that, in the eastern Himalayan front the deformation is taking place largely by the thrust sheet translation without producing a prominent fault-related folds, unlike that of the central and western Himalayas.

    • Grain-scale anatomy of the Bundelkhand granite: Implications for the interplay of magmatic to sub-magmatic deformation mechanisms


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      Grain-scale structures of the granitoid rocks from the north-western part of the Bundelkhand craton, central India are analysed with the aid of an optical microscope and electron probe micro analyser. Although field-based studies and quick microscopic observations suggest an overall porphyritic texture ofthe Bundelkhand granitoid, detailed microstructural observations reveal a significant deviation from the first-order igneous porphyritic texture. Here, we show that the Bundelkhand granitoid has three distinct grain-scale structures: (i) original pristine igneous structures, (ii) ductile deformation-related structures, and (iii) brittle fracturing-related structures. Based on microstructural evidences, we argue that the deformation-induced structures (both brittle and ductile) are not restricted to solid state, rather thesestructures initiated in the sub-magmatic stage and nucleated in partially crystallised magma during the magmatic to sub-magmatic event of the crystallisation history.

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