Petrogenesis of the 1.85 Ga Sonakhan mafic dyke swarm, Bastar Craton, India

Abstract

The NNW trending tholeiitic Sonakhan mafic dyke swarm of the Northern Bastar Craton is comprised of basalt to basaltic andesite (SiO2 = 46.3 wt% to 55.3 wt%; Mg# = 37 to 70) dykes. A single basaltic dyke yielded a weighted-mean 207Pb/206Pb baddeleyite age of 1851.1 ± 2.6 Ma. The Sr and Nd isotopes (87Sr/86Sri = 0.70396 to 0.70855; εNd(t) = −5.7 to +2.0) are variable which is a consequence of crustal contamination. Trace element modeling suggests the dykes were likely derived by partial melting of a spinel-bearing mantle source. The Sonakhan dykes are 30 million years younger than the 1.88 Ga Bastar-Cuddapah dykes (Bastanar-Hampi swarm) of the southern and central Bastar Craton indicating they represent a distinct period of magmatism. However, much like the 1.88 Ga dykes, the Sonakhan dykes appear to be correlative with dykes from the Yilgarn Craton (Yalgoo dyke = 1854 ± 5 Ma) of Western Australia. The temporal and compositional similarity of the Sonakhan dykes with the Yalgoo dyke is evidence that they are petrologically related and may represent different branches of the same dyke swarm. The existence of two distinct Paleoproterozoic dyke swarms in the Bastar Craton that each have a correlative unit in the Yilgarn Craton is supportive of a link between India and Australia before 1.9 Ga. Moreover, it suggests that the break-up of India and Western Australia was protracted and lasted for at least 30 million years.