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CONTROL ID: 1485967 TITLE: Geological and geophysical variations across the Talchir Gondwana basin – evidence for episodic reactivation of the North Orissa Boundary Fault, India. PRESENTATION TYPE: Assigned by Committee (Oral or Poster) CURRENT SECTION/FOCUS GROUP: Tectonophysics CURRENT SESSION: T049. Understanding Deformation Phases of the India-Asia Continental Collision 1
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AUTHORS (FIRST NAME, LAST NAME): Animesh Mandal , Surajit Misra , William Kumar Mohanty , Saibal 1 Gupta INSTITUTIONS (ALL): 1. Geology and Geophysics, Indian Institute of Technology Kharagpur, Kharagpur, West Bengal, India. ABSTRACT BODY: The Talchir basin is a late Paleozoic-Mesozoic age Gondwana basin that trends NW-SE and is oriented perpendicular to the eastern cost of Peninsular India. The basin straddles the Proterozoic contact between granulites of the Eastern Ghats Mobile Belt (EGMB) and amphibolite facies rocks of the Rengali Province. At present, the northern part of the basin experiences periodic moderate seismicity by reactivation of faults located within the basin and to its north. The precise location of these faults and their relationship with pre-existing basement anisotropies remains uncertain. Geological studies to the north and south of the basin establish that the two terranes preserve early structural discrepancies, but were juxtaposed by a transpressional deformation along WNW-ESE trending Proterozoic shear zones, the southernmost of which defines the northern boundary of the Talchir basin. All total 300 gravity observations were conducted along transects that cut north to south across the basin. The Bouguer anomalies decrease systematically northwards from the EGMB, through the basin, into the Rengali Province, which is typical of suture zones along such terrane boundaries. The sharp rise in gravity across the northern and southern boundary of the basin suggests the presence of steep faults with a sharp density difference on both the sides, forming a characteristic graben structure. However, 2-D Bouguer gravity models depict distinct upper crustal structures to the north and south of the Talchir basin. This indicates that the northern fault boundary of the Talchir basin coincides with the Proterozoic suture zone. Recent seismicity also shows highest activity over the northern margin of the basin. It therefore appears that the area has been periodically reactivated from the Proterozoic time to the present, making it a seismically vulnerable zone for over 500 million years. (Keywords: Talchir basin, Rengali Province, Gravity, 2-D model, reactivation, seismicity)
INDEX TERMS: [8122] TECTONOPHYSICS / Dynamics: gravity and tectonics. (No Table Selected) (No Image Selected)
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