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

Prabha Pandey ¹, R. S. Rawat ²

Affiliations
1 National Geophysical Research Institute, Hyderabad - 500007, IN
2 Wadia Institute of Himalayan Geology, Dehra Dun - 248001, IN

Abstract

Pre-Himalayan granites are important in the study of evolution of Himalaya. Amritpur Granite Series (AGS) in the Kumaun Lesser Himalaya is one such Pre-Himalayan, Precambrian granite and is of three types, viz. Porphyritic Amritpur Granite (PAG), Equigranular Amritpur Granite (EAG) and Amritpur Porphyry (AP). The field, mineralogical and geochemical characteristics of AGS are consistent with those of S-type granites. The AGS is peraluminous with A/CNK (>1.1) and high normative corundum. besides high (⁸⁷Sr/⁸⁶Sr) ratio of 0.7117+0.0044. Major and trace element geochemistry of AGS indicates a syn-collisional regime and anatexis associated with pre-Himalayan collision during Precambrian times. The melt produced by anatexis has intruded into the Precambrian Bhimtal-Bhowalj Formation.

Keywords

Geochemistry, Tectonic Setting, S-Type Granites, Kumaun Himalaya.

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Prabha Pandey ¹, Anand K. Pandey ²

Affiliations
1 Department of Geology, Banaras Hindu University, Varanasi - 22 1 005, IN
2 National Geophysical Research Institute, Uppal Road, Hyderabad - 500 007, IN

Abstract

The Hinna fault, in the meizoseismal region of 1991 Uttarkashi earthquake, has been observed as a N-S trending lineament in the satellite imagery and aerial photographs. The stratigraphic and structural expression of the fault has been studied in soft sediments to assess the activity of fault. The Hinna fault occurs as a principal Low-Angle reverse fault dipping towards east and has not ruptured the surface in the trench section. The correlative stratigraphic horizons occur on both side of the main fault with the beds occurring as monoclinal drape over the principal fault. The hanging wall shows warping with development of extensional faults. Extensional faults are produced by the bending moment of strata. The faults also displace the liquefaction features in the soft sediments suggesting their formation prior to faulting event. The tips of the principal reverse fault and the related secondary faults are covered by -3 in thick gravel unit. This suggests that the fault was active prior to the deposition of gravel unit and was not ruptured during 1991-Uttarkashi earthquake.

Keywords

Active Faulting, Soft Sediment Deformation, Earthquake, Garhwal Himalaya.

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