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Sarkar, S. N.
- Structural Analysis of a Part of the Sausar Group Rocks in Chikla-Sitekesa Area, Bhandara District, Maharashtra
Authors
1 Indian School of Mines, Dhanbad 826004, IN
2 CMPDI, Ranchi, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 18, No 12 (1977), Pagination: 627-643Abstract
Systematic analysis of structural geometry of a part of the Sausar Group rocks in Chikla-Sitekesa area throws new light on the tectonic pattern and evolution of the area. The country rocks mainly include Tirodi gneiss, Sitasaongi, Lohangi, Mansar, Chorbaoli and Junewani Formations and three ore-horizons of the Sausar Group in which four types of s-planes (S1-S4) and six types of linear structures (L1-L6) have been recognised.
For tectonic analysis the area has been subdivided into three sectors and 15 subareas and selective and synoptic π and lineation diagrams of megafabric elements (1500 s-planes and 516 lineations) have been critically studied along with the structural maps. The results indicate that the rocks of the area exhibit triclinic symmetry in megascopic, mesoscopic and macroscopic scale with reference to all structural elements, though there are domains of monoclinic symmetry with reference to one or more fabric elements.
Kinematic analysis indicates the generation of isoclinal (B1) folds and ischolar_mainless hinges with axial planes mostly dipping SSE due to rotational stress (P1) along N168°N348° with anticlockwise rotation sense when looking ENE. Considerable variation in the orientation of the first fold axes may be due to inhomogeneity of rock pile, irregular distribution of stresses and different degrees and phases of deformation. Subhorizontal stress (P2) acting along N10°-N190° with deformation plane dipping steeply westward is responsible for the generation of east to southeast plunging L5 puckers and minor (B2) folds along with steeply dipping S3 planes on S2, Stress (P3) acting along N146°-N326° seems to have generated widely spaced kink bands and gentle superimposed L6 folds on S2 in Sector-I and Sector-III and macroscopic scale anti formal B3 fold (Alesur: antiform) in Sector-II. The rocks represent B1 Λ B2Λ B3 tectonites formed during successive deformation phases (F1-F3) of the Sausar orogenic cycle.
- Multiple Deformation and Interference Structures in the Archaean Iron Ore Group Rocks Around Barda-Ulugutu Area, Singhbhum District, Bihar
Authors
1 Department of Earth Sciences, University of Roorkee, Roorkee, U. P., IN
2 Indian School of Mines, Dhanbad, Bihar, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 26, No 7 (1985), Pagination: 453-464Abstract
Systematic structural analysis of the Archaean Iron Ore Group rocks around Barda and Ulugutu throws new light on the tectonic pattern and structural evolution of the area. The polyphase tectonics (D1-D3) is evident by the style and over-printing relationship between three types of s-planes (SO-S2), folds (F1-F3), and related lineations. Folds (F1) showing complex geometries, related lineations showing variable plunges and slaty cleavages (S1) have developed synchronously during the earliest tectonic phase (D1). The concomitant evolution of a new set of structures and deformation of preexisting D1 structures took place during the second phase (D2). The numerous smallscale culminations - depressions of F2 folds are attributed to the variable orientations of s-surfaces prior to F2 folding. Critical field evidences suggest the evolution of both F1 and F2 folds through similar deformational plans including buckling and post-buckle flattening. The concentric warps (F3) are envisaged to have developed under flexural conditions during D3 phase in local domains.
En-echelon arrangement of elliptical interference structures are ascribed to the nonorthogonal axial surfaces of F1 and F2 folds, and axial migrations during F2 folding. The co-existence of type-1 and type-2 patterns is due to F2-flexure of alternating tight and open folds (F1) within the same layer. That the bedding (sO) has been successively subjected to layer parallel compression is implied by buckling nature of repeated folding. Therefore, finite strain-ellipse of the whole area corresponds to constrictional field (1>λ1>λ2)·
- Rb-Sr whole-Rock and Mineral Isochron Ages of the Tirodi Gneiss, Sausar Group, Rhandara District, Maharashtra
Authors
1 Indian School of Mines, Dhanbad 826 004, IN
2 Physical Research Laboratory, Ahmedabad 380 009, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 27, No 1 (1986), Pagination: 30-37Abstract
Six whole rock samples of the Tirodi gneiss belonging to the basal part of the Sausar Group rocks in the Dongri Buzurg area yield a good Rb-Sr isochron corresponding to an age of 1525±70 Ma and an initial Sr ratio of 0.7148±0.0033. Mineral isachrons for two of these rocks give concordant but younger ages at 860 Ma in good agreement with the previously reported K/Ar ages on minerals separated from the Sausar Group rocks. The 1525 Ma event is interpreted to mark the main phase of regional metamorphism of the Sausar Group of rocks including the granitization of the basal Tirodi unit. The deposition of the sediments of the Sausar Group and their basement must therefore be even older. The good agreement of the RblSr and K/Ar mineral ages at about 860 Ma indicates the latest thermal overprint on the Sausar - rocks, The regional metamorphism of the Tirodi gneiss at about 1500 Ma ago is also reflected in the Rb/Sr and K/Ar mineral ages of the Amgaon gneiss and Dongargarh granite to the east of the Tirodi gneiss.- Factorial Correspondence Analysis of Spatially Related Multi-Metallic Data along Gangpur-Singhbhum Metallo-Tectonic Belt
Authors
1 Geological Survey of India, ER, 12 Russel St., Calcutta-700071, IN
2 Department of Geology, Presidency College, Calcutta-700073, IN
3 95A, Ballygunge Gardens, Calcutta-700019, IN