Western Dharwar Craton

The Western Dharwar craton is bounded on the west by the Arabian sea, covered in the north by the Deccan basalts, and separated on the east from the Eastern Dharwar craton by the Closepet granite and a major fault zone along the eastern margin of the Chitradurga schist belt.

Singhbhum Craton Geology

Simplified geologic-tectonic map of India. Main Archean terranes are Granulite, Western Dharwar, Eastern Dharwar, Bhandara, Singhbhum, and Aravalli. Other locations on map include Delhi, Patna, Ahmedabad, Calcutta, Nagpur, Mumbai, Hyderabad, Madras, and Bangalore. (modeled after J. Rogers and S.M. Naqvi, 1987)

The Western Dharwar craton is the best known of the Archean cratons of India, hosting several large gold deposits in the mafic volcanic/schist belts, especially in the Chitradurga belt. structures in the Western Dharwar craton, including the main schist belts, strike generally northward, with a broad convex arc facing east toward the Eastern Dharwar craton. Greenstone belts in the northern part of the craton are generally larger and less metamorphosed than those in the south.

Rocks in the Western Dharwar craton are diverse in age and type. The so-called Peninsular Gneiss forms much of the craton and is made up of tonalitic-trondhjemitic gneiss with many inclusions of older sedimentary and igneous rocks. Several generations of igneous dikes and plutons intrude the Peninsular Gneiss, which has yielded isotopic ages of 3.4 to 3.0 billion years, with younger granites intruding the gneiss between 3.0 and 2.9 billion years ago. The term Dharwar has been used to describe mafic volcanic and sedimentary schist belts engulfed by quartz-feldspar gneisses of the Peninsular gneiss. There are three main types of mafic rocks included in this general classification: high-grade mafic rocks caught as enclaves in gneisses in the southern part of the craton, coherent belts of amphibolite facies metamorphic grade, and belts preserved at low meta-morphic grade. The term Sargurs describes the highly deformed greenstone fragments that are generally older than 3.0 billion years. The high-grade schist belts of the Western Dharwar craton contain numerous fragments of ultramafic/mafic layered igneous complexes and include komatiites, basalts, and other magma types. Some of these may be examples of Archean ophiolites, and others may be intrusions into the continental crust. Other rock types include quartzites, conglomerates, greywacke and sandstones, banded-iron formations, mica schists, metamorphosed mafic volcanic rocks, chert, carbonates, and rare layers of evaporites. The 2.3-2.5-billion-year-old Closepet granite on the eastern side of the craton is rich in potassium feldspar, and its highly elongate shape (about 360 miles long by 30 miles wide [600 km by 50 km]) suggests that it may have intruded along a convergent continental margin type of tectonic setting, perhaps during the collision of the Eastern and Western Dharwar cratons.

Most rocks in the Western Dharwar craton are complexly deformed, with layered rocks typically preserving two or three folding generations. older folds are generally tight to isoclinal, whereas younger folds are more open and upright, and fold interference patterns are common in the older rocks. The cause of the early deformation events in the schist and greenstone belts is not well known, but some of the younger events appear to be related to the collision of the Western Dharwar craton with other blocks, such as the Eastern Dharwar craton and the formation of supercontinents in the Proterozoic.

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Responses

  • ida
    What is the name of dharwar schists?
    3 years ago

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