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Authors
Affiliations
1 Geological Survey of India, Jhalana Dungri, Jaipur-302 004, IN
2 Geological Survey of India, Calcutta-700 016, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 52, No 4 (1998), Pagination: 417-432
Abstract
The Precambrian Khetri Fold Belt in northern Rajasthan, India, is bifurcated by the transverse Kantli Fault into the North Khetri Belt (NKB) and the South Khetri Belt (SKB). A new stratigraphic and structural framework has been proposed for the NKB and the SKB. The NKB and the SKB evolved independently and show different basement-cover relationships. The Proterozoic cover sequence on either side of the Kantli Fault differ significantly from each other in litho-characteristics, specially in the content of felsic-volcanics. The 1832 ± 3 Ma old synsedimentary felsic volcanism in Proterozoic sequence is considered to be coeval with the Jasrapura Granite dated at 1844 ± 7 Ma.
Geochronological data from several granite bodies suggest a plutonic event around 1500 ± 200 Ma which constrains the third phase of deformation in the basement rocks. TWo types of granites are recognised; one akin to the Hercynian-type peraluminuous, compositionally restricted ilmenite-bearing S-type granite and the other Caledonian-type, compositionally restricted I-type granite.
Both forceful ballooning and forceful permitted type processes were responsible for the plutonic activity. Significant amongst the first-type are the Udaipurwati Granite and the Chapoli Granite; the former shows stretching of the sodium-rich early consolidated intrusion as a result of inflation of the potassium-rich central part of the magma balloon.
A general readjustment of the isotopic systems within minerals occurred around 700 - 800 Ma or even later, possibly a Pan-African event, which has been correlated with widespread granitic activity in western Rajasthan.
Keywords
Stratigraphy, Proterozoic, Granite Emplacement Mechanism, Khetri Copper Belt, Rajasthan.
