Variations in the crustal structure and composition beneath the Malani Igneous Province, NW India, through receiver function analysis

The crust beneath the Malani igneous province(MIP) in northwestern India was shaped by several Neoproterozoic magmatic events, Cretaceous Barmer-Sanchor rifting, pre-Deccan alkaline magmatism and sedimentation. The structure and composition of the crust beneath MIP are investigated through P receiver function(RF) studies using teleseismic data recorded by 21 broadband stations deployed in MIP. About 1851 RFs corresponding to 750 events (M≥5.5) were constructed using the iterative time domain deconvolution technique. The H-k grid search for crustal thickness(H) and Vp/Vs ratio(k) reveals large variations of ≈ 10km in crustal thickness and ≈ 0.05 in the crustal Poisson's ratio(σ) across MIP. The error estimation done by bootstrap analysis gives a mean value of crustal thickness and Poisson's ratio of 38.2 ± 3 km and 0.28 ± 0.02, respectively. The Poisson's ratio (σ) shows a strong correlation with the local geology, with the alkaline complexes being characterized by a high σ of 0.31 while the Erinpura granites are characterized by a low σ of 0.26. Modelling the RFs using the Neighbourhood algorithm revealed a variation in the crustal thickness from 34 km to 43.5km. Northern and southern segments of MIP are characterized by a thicker ( > 37km) and thinner (< 37km) crust, respectively. A zone of crustal thinning (32.8km to 35.4km) is mapped that is centred beneath the southern part of the Barmer rift, encompassing the sites of pre-Deccan alkaline magmatism and lies above the cylindrical zone of a low velocity upper mantle anomaly hypothesised to be a plume conduit. The average crustal shear velocities are 3.7 ± 0.1km, with several stations underlain by high lower crustal velocities ≥ 3.9 km/s indicating underplating. Overall, MIP is characterized by a thick crust with intermediate crustal composition and underplating at the base of the crust suggesting signatures of magmatic events.