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

M. S. Pandian ¹, S. K. Dutta ²

Affiliations
1 Department of Earth Sciences, Pondicherry University, Pondicherry - 605 014, IN
2 State Remote Sensing Application Centre, Vivek Vihar, Itanagar - 791 113, IN

Abstract

In Sewariya-Alniawas-Govindgarh areas of central Rajasthan, the Delhi metasediments are intruded by an older, biotite granite (Sewariya granite) which is equivalent to Erinpura granite occurring further south, and an younger, tourmaline leucogranite (Govindgarh granite) which is geochemically specialised. Sewariya granite hosts wolframite bearing quartz veins along its sheared contact with mica schist of Barotiya Group. Govindgarh granite occurs in the form of small intrusive bodies within rocks of Barotiya Group, essentially along a major ductile shear zone at the western margin of South Delhi fold belt. Our study reveals that leucogranite magmatism yielded tungsten mineralisation in Sewariya area.

Keywords

Economic Geology, Leucogranite, Tungsten, Tourmaline, Aravalli Craton, Rajasthan.

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M. S. Pandian ¹, B. K. Bhadra ¹

Affiliations
1 Department of Earth Sciences, Pondicherry University, Pondicherry, IN

Abstract

Earthquake of magnitude 3.9 occurred in Tiruppattur area of Tamil Nadu on 31 January 1997. The epicentral location lies on a seismically active N45°E fault zone, along which many late Proterozoic alkaline intrusives are emplaced. The earthquake resulted in the opening of few fractures on the surface and as a secondary effect, induced liquefaction of soil at the base of Elagiri Hills. Excessive rainfall which preceded this event could have possibly played a role in causing the earthquake.

Keywords

Earthquake, Liquefaction of Soil, Granulile Terrain, Tamil Nadu.

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Jyoti Shah ¹, Deepak C. Srivastava ¹, M. S. Pandian ², Supratik Sarkar ³, Mainak Choudhari ³, V. Subramanian ⁴

Affiliations
1 Department of Earth Sciences, IIT Roorkee, Roorkee - 247 667, IN
2 Department of Earth Sciences, Pondicherry University, Pondicherry - 605 014, IN
3 Reliance Industries Ltd, Navi Mumbai - 470 110, IN
4 Department of Geology, National College, Tiruchirapalli - 620001, IN

Abstract

This paper presents the results of field studies, and palaeostress analyses of the mesoscale fractures and veins in Cauvery basin. It shows that different sedimentary sequences (119-64 Ma) are cut by tensile structures that belong to two successive phases of post-Palaeocene brittle tectonics (I) an early phase during which bedding parallel fractures and veins were developed due to horizontally directed maximum compression and vertical extension, and (II) a late phase of hydraulic fracturing in a tectonic regime of vertically directed maximum compression. Dynamic analyses imply triaxial and axial compression deviatoric states of palaeostress during first and second phases of fracturing, respectively. Very high pore-fluid pressure and low differential stress, during the second phase of fracturing, resulted into hydraulic brecciation as a consequence of simultaneous extension in different orientations. We suggest that the development of the mesoscale extensional (mode I) fractures in Cauvery basin is due to reactivation of large-Scale normal faults in the basement rocks.

Keywords

Extensional Fracturing, Hydraulic Fracturing, Pore-Fluid Pressure, Cauvery Basin, Tamil Nadu.

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M. S. Pandian ¹, O. P. Varma ²

Affiliations
1 Department of Earth Sciences, Pondicherry University, Pondicherry- 605 014, IN
2 35-A, Civil Lines, Roorkee-247 667, IN

Abstract

Post-Delhi acid magmatism at Degana has yielded three intrusive bodies of topaz granite, the earliest one emplaced within phyllite of Delhi Supergroup and the other two successively in the core of previous intrusive, along with two generations of aplites. Wolframite mineralisation has occurred at two different stages during the magmatism: (1) greisen-bordered vein-type ore bodies hosted by the earliest granite intrusive and adjoining phyllite rcpresent the first stage, and (2) stockwork ore bodies hosted by an intrusion breecia developed at a later stage following the emplacement of other two granite bodies. Presence of topaz, Li-mica and fluorite is a characteristic feature of these granites and wolframite deposits. The granites are strongly peraluminous and geochemically specialised with enrichment of Li, F, Rb and depleted in Sr, K-As dating of zinnwaldite from wolframite bearing lode indicates an age of 860±25 Ma.

Keywords

Neoproterozoic, Topaz Granite, Tungsten Deposit, Delhi Fold Belt, Degana, Rajasthan.

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