Current Science

T. Radhakrishna ¹, Ram Chandra ²

Affiliations
1 National Centre for Earth Science Studies, Thiruvananthapuram 695 031, IN
2 Centre of Excellence in Geology, Institute of Earth Science, Bundelkhand University, Jhansi 284 128, IN

Abstract

A reassessment of the recent palaeomagnetic data on Proterozoic mafic dykes in the Bundelkhand and Bastar cratons permits a robust estimate of 1.466 Ga (Calymmian) pole (λ = 49.4°N; Φ; = 132.9°E; A₉₅ = 6.6°; N = 11) for the Indian shield. The pole corresponds to a mean direction of D = 40.5°; I = 56.4° (α₉₅ = 5.5°; K = 70). The Indian pole at c. 1.65 Ga (Statherian) is suggested to have been situated at λ = 59.6°N and Φ = 47.9°E (A₉₅ = 8.1°; N = 6); it is estimated from a mean direction of D = 336.4°; I = 66.0°N (α₉₅ = 5.3°; K = 159). The 1.466-Ga-old dykes are confined to the Eastern Ghats orogenic front in the easternmost part of the Bastar craton. Geochemically, the shoshonitic/high-K calc-alkaline affinity of these dykes is uniquely distinct from the tholeiitic composition found in Mesoor Palaeoproterozoic dykes in other parts of the Indian shield. Testing the existing pre-Rodinia Mesoproterozoic tectonic reconstructions negates the Columbia reconstructions in which the Indian shield is shown in juxtaposition with North China/Laurentia. On the other hand, palaeomagnetic and geological data suggest that the linkages between the Indian shield and Western Australia proposed earlier for the Palaeoproterozoic appear to persist during the Mesoproterozoic as well. The linkages may be further extended into Baltica.

Keywords

Geodynamics, Mafic Dykes, Orogenic Belts, Palaeomagnetism, Tectonic Reconstructions.

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