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Thakur, S. S.
- Low Pressure Granulite Facies Sukma Supracrustal Rocks near Nagaras, Southern Bastar Craton
Authors
1 Department of Earth Sciences, Indian Institute of Technology, Powai, Mumbai - 400076, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 69, No 1 (2007), Pagination: 75-79Abstract
This communication discusses the metamorphism of low pressure granulites in the Sukma supracrustal suite near Nagaras in the southern Bastar craton. The area shows occurrence of Mg-Al rocks,of both amphibolite and granulite facies. Amphibolite facies Mg-Al schist usually contains cordierite and a low-Ca amphibole, which is commonly cummingtonite and rarely gedrite. Low-Ca amphibole and sillimanite are never found together in the same rock. Mg-Al granulite is characterised by the presence of orthopyroxene in lieu of low-Ca amphibole. Most of the Mg-Al rocks are silica saturated.Keywords
Cummingtonite, Cordierite, Granulite, Bastar Craton.- Deformation Pattern in a Proterozoic Low Pressure Metamorphic Belt near Ramanujganj, Western Chhotanagpur Terrane
Authors
1 Department of Earth Sciences, Indian Institute of Technology, Powai, Mumbai - 400 076, IN
2 Intersight Consulting Pvt Ltd, 12th Main Road, Vasanthnagar, Bangalore - 560 052, IN
3 Geological Survey of India, Sector 33B, Chandigarh - 160 047, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 70, No 2 (2007), Pagination: 207-216Abstract
The Ramanujganj area in eastern India exposes a Proterozoic metasedimentary belt (-35 km x 18 km) which has been mapped in detail in terms of two pelitic and two psammitic lithounits. Dominant rock types in the belt include porphyroblastic argillite, phyllite and pelitic schist, feldspathic quartzite and orthoquartzite. The belt has an elongated oval shape with broadly NW-SE trend. Folds of three generations (F1, F2 and F3) have been recorded F1 folds are rarely preserved as small isoclinal folds on bedding(So)associated with an axial planar cleavage (S1) F2 folds involve transposed So+S1 surfaces and vary from open to isoclinal, with steeply inclined axial plane and moderate plunge. Several large scale F2 closures with NW to NNW striking axial planes are exposed F3 folds are steeply inclined to upright in nature with NE striking axial planes. Large scale F3 folds are usually broad warps. Interference patterns of dome and basin type and hook type are observed in the area F1 and F2 folds are broadly coaxial in nature, and their superposition has resulted in hook shaped pattern F2 and F3 folds have superposed to produce dome-and-basin structures on both outcrop scale and large scale. The regional structure of the area is an elongate basin resulting mainly from the interference of F3 folds on F2 structures.
The western and northern parts of the area are occupied by biotite quartzofeldspathic orthogneiss which intruded during or before F1 deformation. In the eastern part mesocratic granodiorite intruded after F1 deformation and before or during F2 deformation. The Ramanujganj pelites are commonly characterised by large porphyroblasts of andalusite (chiastolite), whereas biotite and garnet form relatively small porphyroblasts. Andalusite occurs in the southeastern and central parts of the area, and transforms to sillimanite as we go towards northwest. This indicates increasing grade of metamorphism from southeast towards northwest. The metamorphism is of low pressure type.
Keywords
Structral Analysis, Polyphase Deformation, Pelite, Chhotanagpur Gneissic Complex.- Structural Pattern in Sukma Supracrustal Rocks near Nagaras, Southern Bastar Craton
Authors
1 Department of Earth Sciences, Indian Institute of Technology, Powai, Mumbai- 400 076, IN