Cryogenian (∼830 Ma) mafic magmatism and metamorphism in the northern Madurai Block, southern India: A magmatic link between Sri Lanka and Madagascar?

The northern Madurai Block, southern India, lies directly south of, and partly deformed by, the Palghat–Cauvery Shear Zone System (PCSS) – a potential suture of the Neoproterozoic Mozambique Ocean. The Kadavur gabbro-anorthosite complex lies south of the PCSS, in the northern Madurai Block, and crystallized at 829 ± 14 Ma (LA-ICPMS zircon data) in a supra-subduction zone setting. The complex contains zircon εHf(t) values of −12.5 to −8.6 that represent Palaeoproterozoic T(DM) model ages (2.3–2.5 Ga). These broadly agree with a whole rock neodymium T(DM) model age of 2287 Ma. Oxygen isotope δ18O ratios range from 5.82‰ and 6.74‰. The parental magma for the gabbro-anorthosites are interpreted to be derived from a juvenile Neoproterozoic mantle contaminated by Mesoarchaean igneous infra-crustal sources. The gabbro-anorthosites intrude quartzites with dominantly Palaeoproterozoic detrital zircons that contain Neoarchaean and Mesoarchaean hafnium model ages. These quartzite zircons contain metamorphic rims that yield an age of 843 ± 23 Ma demonstrating the autochthonous nature of the gabbro-anorthosite complex. Later felsic magmatism is recorded by the 766 ± 8 Ma crystallisation age of the protolith of a felsic gneiss.Cryogenian magmatism in the Madurai Block is interpreted to form part of an extensive arc magmatic province within the southern East African Orogen that can be traced from central Madagascar, through southern India to the Wanni Complex of Sri Lanka. This province is interpreted to have formed above a south/west dipping subduction system as the Mozambique Ocean was subducted under the Neoproterozoic continent Azania.

► The Kadavur gabbro-anorthosite complex, north Madurai Block, crystallized at 829 ± 14 Ma and represents Cryogenian subduction magmatism.
► Hf, Nd and O isotopes show that the parent magma was derived from the mixing of mantle-derived melt with lower continental crust.
► Kadavur correlates with similar magmatism in Sri Lanka and Madagascar, supporting the Azania model for the origin of southern India.