Understanding the Neoproterozoic geodynamics of NW India: clues from tectonomagmatic studies of the Cryogenian Sindreth Basin at the eastern Malani Igneous Province

The 770 to 750 Ma Malani Igneous Suite (MIS) in NW India is regarded as one of the largest (>50.000 km2) felsic igneous provinces in the world. Its geodynamics in the context of break-up history of Rodinia and subsequent amalgamation of continental blocks to form Gondwana has been attempted in a number of recent studies but not resolved yet and contrasting models (plume-, rift-, subduction-, mantle delamination- related) have been proposed. Coeval (765 to 767 Ma) small basins (Sindreth, Punargath) situated along the eastern margin of the MIS show overlap in ages, therefore, the order of geological events cannot be established in these basins. Existing models of basin formation propose active subduction setting (either back-arc basin or accretionary sediments over a subduction zone) and implications have been discussed in the context of global crustal dynamics. Reconnaissance studies by our German-Indian research group have noted field geological evidence and collected data that clearly contradict such interpretations. Instead of an inferred ocean floor setting for the Sindreth Basin we have observed conglomerate, fanglomerate, debris flow and lake deposits derived from the nearby continental provenance, intercalated with mafic and felsic lava flows. The sequence is unmetamorphosed but shows tilting (inversion) and faulting. Our reconnaissance findings indicate a fault-related basin formation. Preliminary magnetic fabric studies point to intrusion of felsic dykes (MIS sensu stricto) into this inverted basin. These findings need to be substantiated through a detailed field and laboratory work that would allow establishing a model of basin formation and basin inversion. Magnetic fabric studies combined with measurements of natural remanent magnetization will provide constraints for deciphering the geometric interrelationship of basin inversion and the MIS. Satellite pictures will be evaluated to resolve the relationship between faulting and ascent of magma on a larger areal scale. The Sindreth Basin and its surrounding area represent a transition zone between the undeformed MIS sensu stricto in the west and corridor of coeval Cryogenian ductile deformation, anatexis and granite intrusion in the east, main target of our research in the last years. The latter region has been linked to Neoproterozoic age magmatic belts and shear zones in Madagascar and south India, thus underlining the global significance of this region.