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Chatterjee, N.
- Structural Pattern of Rocks Around Dariba, Alwar District, Rajasthan, with Special Reference to Copper Occurrence
Authors
1 Department of Geology, Presidency College, Calcutta, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 12, No 1 (1971), Pagination: 43-50Abstract
The structural pattern of Delhi system of rocks around Dariba is dominated by open, asymmetrical folds which occur on both major and minor scales. A set of axial plane cleavages, which grades from discrete fractures to slaty cleavage, is consistently developed with the folds. The axial traces of the major fold range in trend from NNE-SSW to WNW-ESE. Although the fold axes vary both in direction and amount of plunge, the axial planes are consistently inclined westwards. The copper ore bodies which have been explored so far, occur in the eastern ridge of Dariba. Mineralisation is practically confined to phyllites ana schists. The lenticular ore bodies have been explored uptil now on the limbs of major overturned synformal fold in the eastern ridge. The axial plane cleavage has been observed to be the main structural plane controlling the distribution of the disseminated sulphides in the rock.
- Ore Microscopic Observations on Sulphide Minerals from Dariba Copper Mine, Alwar District, Rajasthan
Authors
1 Department of Geology, Presidency College, Calcutta, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 13, No 2 (1972), Pagination: 178-181Abstract
No Abstract.Full Text
- Plume Generated Mesoproterozoic Mafic-Ultramafic Magmatism in the Chotanagpur Mobile Belt of Eastern Indian Shield Margin
Authors
1 G/608, Raheja Residency, Koramangala, Bangalore - 560 034, IN
2 Department of Geology, Patna University, Patna - 800 005, IN
3 Department of Earth, Atmospheric and Planetary Sciences, MIT, Cambridge, Massachusetts 02139, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 66, No 6 (2005), Pagination: 725-740Abstract
The Chotanagpur gneiss-Granulite complex (CGGC)-a mobile belt north of the Archaean Singhbhum cratonic nucleus and contiguous orogenic belt with the Singhbhum Proterozoic basin, is a vast tract of high-Grade rocks and gneisses with enclaves of granulite and metasedimentary rocks, and intrusive granites of Proterozoic age. Pervasive intrusions of mantle-Derived rocks of varied composition ranging from mafic-Ultramafic, sodic-Ultrapotassic alkaline rocks, massif anorthosite to younger tholentic basalts (Rajmahal) and dolerite at different geological periods ranging from Late Paleoproterozoic to Early Tertiary, give evidence of an active mantle in the prolonged history of evolution of this mobile belt. The present study is limited to metamorphosed mafic-Ultramafic rocks at the eastern sector of CGGC. The mafic-Ultramafic suite is represented by amphibolite, basic granulite and hornblendite. Compositions of the primary amphibole in these rocks range from hornblende to pargasitic hornblende, and plagioclase from An40 to An59. Positive correlation of Mg# between clinopyroxene and hornblende, and clinopyroxene and orthopyroxene, indicating that the Fe-Mg exchange KD is constant between the ferromagnesian minerals, and the rocks to have attained equilibrium conditions of metamorphism. Calculated post-Peak metamorphic equilibrium pressures and temperatures are 3 8-5 4 kb and 643- 781°C, similar to conditions in the surrounding country rocks.
Chemically, the metabasic rocks studied are associated with the Bengal anorthosite massif at Saltora and have been grouped into low-Ti and high-Ti tholeiites. The former shows similarity with transitional basalts derived from T-MORB, while the latter is rich in incompatible elements and shows affinity with basalts derived from E-MORB or from recycled mantle fed by subducted oceanic crust. The nepheline normative ultramafic rock is the most depleted in incompatible elements and shows similarity in trace element contents with MORB. All these rocks show variable crustal contamination. Nevertheless, the bulk chemical compositions of the low-Ti rocks preserve evidence of low-Pressure fractional crystallisation involving olivine, plagioclase and clinopyroxene. The intra-cratonic Mesoproterozoic bi-Modal (tholeiitic-alkaline) magmatism in CGGC is analogous to Phanerozoic magma generation(Rajmahal tholentes-Ultrapotassic mafic-Ultramafic intrusions in the Gondwana basins) in a rift setting (Damodar graben /Shield margin faults) accompanied with crustal thinning. The trace element geochemistry of mafic-Ultramafic rocks gives evidence of plume-Generated magmatism in the Eastern Indian Shield margin during Mesoproterozoic time, which is correlatable with the global thermal event in the Precambrian shields.