Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

M. I. Bhat ¹, T. Ahmad ¹

Affiliations
1 Wadia Institute of Himalayan Geology, 33, General Mahadeo Singh Road, Dehra Dun 248 001, IN

Abstract

The Late Palaeozoic Abor Volcanics of the eastern Himalayas have typical continental tholeiite chemistry in terms of rather high and variable Fe/Mg ratios and incompatible trace elements, except P, abundances. The compatible trace elements (Ni, Cr, Co) are low for their specific MgO levels. Variable abundances of incompatible elements at constant Mg numbers, lack of significant Eu anomalies and large range in the ratios of more incompatible to less incompatible elements (e.g. La/Yb) suggest that fractionation was not significant in their compositional evolution. Fe-Mg relations indicate that the melts were generated from a mantle source with enriched Fe/Mg ratio compared to pyrolitic mantle; melting was followed by separation of an immiscible sulphide phase which resulted in lowering of Ni and P contents, and some clinopyroxene fractionation. Model calculations on REE data suggest that the source was enriched by about l1x and 4x chondrite in light REE (La) and heavy REE (Yb) respectively. This enrichment of the source was probably due to an undersaturated silicate melt and a CO₂-rich fluid phase.

Keywords

Petrogenesis, Abor Volcanics, Geochemistry, Himalaya.

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V. C. Thakur ¹, R. Jayangondaperumal ², P. K. Champatiray ³, M. I. Bhat ⁴, M. A. Malik ⁵

Affiliations
1 Wadia Institute of Himalayan Geology, Dehra Dun - 248 001, IN
2 Wadia Institute of Himalayan Geology, Dehra Dun - 248 001
3 Indian Institute of Remote Sensing, Dehra Dun - 248 001, IN
4 Kashmir University Srinagar - 190 006, IN
5 Jammu University, Jammu - 180 006, IN

Abstract

The 8 October 2005 Muzaffarabad earthquake was the deadhest earthquake In the history of Indian subcontinent Its epicenter located 10 km northeast of Muzaffarabad lies in the lndus Kohistan Seismic Zone (IKSZ), which represents northwestern continuation of the microseismicity and moderate earthquakes belt of Garhwal, Kumaun and Nepal A multi-institution team undertook post earthquake studies along the LOC and adjoining areas in Tangdhar, Un and Poonch sectors of Kashmir, India The Tangdhar area lying on the hanging wall and the Un area close to the rupture zone have suffered much more damage In comparision to the Poonch region located on the footwall An isoseismal map of the earthquake affected region has been prepared on the basis of our observations and website data The opened-up cracks and lateral spreads mapped In the Tangdhar and Un reglonishow both right-lateral as well as left-lateral strike-slip and vertical motions of a few cm to 30 cm The Mw 7 6 Muzaffarabad earthquake has ruptured a segment -80 km x 50 km west of the closure of Kashrmr Valley An earlier mapped active fault of en echelon nature, trending NW-SE and extending from Balakot to Muzaffarabad and further southeast along the eastern bank of river Jhelum, coincldes with linear trend of the aftershocks belt and the rupture plane of the earthquake The knowledge gamed through ths earthquake implies that a selismic gap of a similar size of unruptured segment that lies between the 1555 Kashmir (Mw 7 5) and 1905 Kangra (Mw 7 8) earthquakes, where there is no historical record of a large earthquake for more than 500 years, may be ripe for a large event.

Keywords

Himalayan Seismicity, kashmir Earthquakes, Earthquake Hazard, Active Faults.

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