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In this case, data of U–Pb SHRIMP of Zircons from amphibolite facies gneisses from Kobaladurga and Kober single zircon evaporation ages of grey gneisses have been considered Thus, three major episodes, namely, 3.4 Ga., 3.3–3.2 Ga., and 3.0–2.9 Ga ., are accreted to form the Peninsular Gneiss of the region, dated 2500 to 3400 million years.
The craton mainly consists of Archaean granitic complexes, but also includes rocks from the Dodoma System in the central area, and belts of greenstone to the south and east of Lake Victoria. Gneisses, schists, quartzites, migmatites, amphibolites and granulite are also found.
Gneiss (/ n aɪ s / nice) is a common and widely distributed type of metamorphic rock.It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks.
A considerable area of peninsular India, the Indian Shield, consists of Archean gneisses and schists which are the oldest rocks found in India. The Precambrian rocks of India have been classified into two systems, namely the Dharwar system and the Archaean system (gneiss and schists). The Dharwar System
Archaean.– The metamorphic rocks compose the main mass of the tableland, and are exposed in every deep valley in Tigre and along the valley of the Blue Nile. Mica-schists form the prevalent rocks. Hornblende schists also occur and a compact feldspathic rock in the Suris defile. The folia of the schists strike north and south. [6] Triassic.–
The location map of the Dharwar Craton. The shaded area represents the Dharwar Craton. Generated from GeoMapApp (Ryan et al., 2009). [1]The Dharwar Craton is an Archean continental crust craton formed between 3.6-2.5 billion years ago (), which is located in southern India and considered the oldest part of the Indian peninsula.
The original sedimentary succession transformed into migmatites at its base, followed by gneisses, micaschists and finally sericite schists and chlorite schists at the top, the schists at the top only being metamorphosed under greenschist facies conditions. The volcanogenic material was metamorphosed to leptynites and amphibolites.
The oldest part of the Lewisian complex is a group of gneisses of Archaean age that formed in the interval 3.0–2.7 Ga. These gneisses are found throughout the outcrop of the Lewisian complex in the mainland. The dominant lithology of the Scourie complex is banded grey gneisses, typically granodioritic, tonalitic or trondhjemitic in composition.