are known therein. The territory of India, characterized by widespread ancient rock complexes and well-known mineral deposits, is distinguished by an in-depth knowledge of the stratigraphy, tectonics, petrology, geochemistry, metallogeny, and isotope geochronology of Precambrian complexes. The most important publications used for compilation of the map and the metallogenic database include
The Archaean Peninsular Gneiss of southern India is considered by a number of workers to be the basement upon which the Dharwar supracrnstai rocks were deposited. However, the Peninsular Gneiss in its present state is a composite gneiss formed by synkinematic migmatization during successive episodes of folding (DhFI, DhFI, and DhF2) that affected the Dharwar supracrustal rocks. An even earlier phase of migniatization and deformation (DhF,) is evident from relict fabrics in small enclaves of gneissic tonalites and amphibolites within the Peninsular Gneiss. We consider these enclaves to represent the original basement for the Dharwar supracrustal rocks. Tonalitic pebbles in conglomerates of the Dharwar Supergroup confirm the inferenoe that the supracrustal rocks were deposited on a gneissic basement. Whole rock Rb-Sr ages of gneisses showing only the DhF1 structures fall in the range of 310(O3200 Ma. Where the later deformation (DhF 2) has been associated with considerable recrystallization, the Rb-Sr ages are between 2500 Ma and 2700 Ma. Significantly, a new Rb-Sr analysis of tonafitic gneiss pebbles in the Kaldurga conglomerate of the Dharwar sequence is consistent with an age of ,,-2500 Ma and not that of 3300 Ma reported earlier by Venkatasubramanian and Narayanaswamy (1974). Pb-Pb ages based on direct evaporation of detrital zircon grains from the metasedimentary rocks of the Dharwar sequence fall into two groups, 3300-3100Ma, and 2800-3000 Ma. Stratigraphic, structural, textural and geochronologic data, therefore, indicate that the Peninsular Gneiss of the Dharwar craton evolved over a protracted period of time ranging from > 3300 Ma to 2500 Ma.
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