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Abstract

We use ambient noise tomography to image the crustal-scale anisotropic structure beneath the Marwar craton of northwestern India to understand the impact of magmatism, crustal growth, and melt distribution. The study region was shaped by several magmatic events that include the Neoproterozoic Erinpura and Malani volcanism, Cretaceous Barmer-Sanchor rifting, and pre-Deccan volcanism. Correlograms of ~300 paths from 29 broadband seismic stations were computed for the vertical and transverse components. Rayleigh and Love wave group velocity dispersion curves of the fundamental mode were computed for the period ranging from 4s to 40s using the frequency-time analysis method. The 3D shear velocity tomography model was constructed by regionalizing the dispersion data to obtain local dispersion curves which were then inverted using a non-linear trans-dimensional Bayesian approach. The geometry of the Barmer-Sanchor rift is clearly delineated by an elliptical zone of low group velocity anomalies. The tomograms reveal low shear velocities (<3km/s) corresponding to thick sediments (~4km) in the rift. The crustal thickness beneath the rift varies from 30km to 34km while the region away from the rift has an average crustal thickness of 39km. The lower crust is characterized by high shear velocities ranging from 3.8km/s - 4.25 km/s that indicate magmatic underplating. Overall, the study region is characterized by positive radial anisotropy (~8%) that decreases away from the rift, crustal thinning beneath the rift, and a high velocity lower crust that reflects magmatic intrusion linked to rifting and magmatic events.