Rb-Sr geochronology and petrogenesis of granitoids from the Chhotanagpur granite gneiss complex of Raikera-Kunkuri region,Central India |
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Authors: | Yamuna Singh Veena Krishna |
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Institution: | 1.Department of Atomic Energy,Atomic Minerals Directorate for Exploration and Research,Begumpet, Hyderabad,India |
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Abstract: | The Precambrian Chhotanagpur granite gneiss complex (CGGC) terrain covers more than 80,000 sq km area, and is dominated by
granitoid gneisses and migmatites. Recent geochronological data indicate that the CGGC terrain has witnessed five tectonomagmatic
thermal events at: (i) 2.5–2.4 Ga, (ii) 2.2–2.0 Ga, (iii) 1.6–1.4 Ga, (iv) 1.2–1.0 Ga, and (v) 0.9–0.8 Ga. Of these, the third
and the fourth events are widespread. The whole-rock Rb-Sr isotopic analysis of twenty granite samples from the CGGC of Raikera-Kunkuri
region, Jashpur district, Chhattisgarh, Central India, yields two distinct isochrons. The eleven samples of grey granites
define an isochron age of 1005±51 Ma with moderate initial 87Sr/86Sr ratio of 0.7047±0.0065, which corresponds to the fourth tectonomagmatic event. On the other hand, the nine samples of pink
granites indicate younger isochron age of 815±47 Ma with a higher initial 87Sr/86Sr ratio of 0.7539±0.0066 that matches with the fifth phase of the thermal event. The data suggest emplacement of large bodies
of grey granite at ∼1005 Ma that evolved possibly from precursors of tonalitic-granodioritic composition. Furthermore, the
younger age (∼815 Ma) suggests the age of metasomatism, involving isotopic resetting, that resulted in genesis of pink granite
bodies of limited areal extent. By analogy, the age of metasomatism (∼815 Ma) may also be taken to represent the age of Y-mineralisation
in the Raikera-Kunkuri region of the CGGC terrain. |
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