Variations in the crustal thickness and Poisson’s ratio beneath the Malani Igneous province in Northwestern India

Abstract:

The Malani igneous province(MIP) in northwestern India is a 750 Ma bi-model volcanic province which also hosts the 65 Ma alkaline complexes related to the Deccan volcanism. The variation in the average crustal thickness and Poisson’s ratio in MIP is investigated using P receiver functions. The receiverfunctions(RF) were constructed at 23 triaxial broadband seismic stations which were operated in phases during 2011- 2017. A total of about 8000 waveforms with high signal to noise ratio > 5 corresponding to around 2000 teleseismic events with magnitude ≥ 5.5 were used. The delay times of the P-to-s conversions from the Moho in the stacked RFs exhibit a large variation of about 1sec from 4.85s to 5.85s from western to eastern segments of MIP. The average crustal thickness and Poisson’s ratio estimated through H-k slant stacking was 38.5 ± 2 km and 0.27 ± 0.01 respectively. The error estimation is done by bootstrap analysis giving a mean value within 2σ distribution, which is 95% confidence interval. The results indicate large variations in the depth to the Moho from 34 km beneath the Barmer-Sanchor rift to 48 km beneath the Erinpura granite adjoining the Aravalli-Delhi fold belt. The Poisson’s ratio is observed to vary from 0.26 to 0.29 indicating intermediate to mafic composition. High values of Poisson’s ratio (≈0.30) may be related to the existence of high-velocity lower crust with a mafic or ultramafic composition. This study indicates significant heterogeneity in the crust beneath MIP corresponding to the imprints of several tectonic episodes