Concealed architecture, volcanism and tectonics of Deccan LIP related alkaline complexes of Rajasthan, NW India: Constrained from high resolution aero-geophysical data

Abstract

In the north-western Indian shield two important alkaline complexes (Sarnu-Dandali and Mer-Mundwara) are linked to end-Cretaceous Deccan large igneous province (LIP) bear significance for REE mineralization, CO2 outgassing and mass extinctions near the K-Pg boundary. Although both of them bear numerous similarities, but, the geomorphology and magmatic emplacement are quite conflicting. Here, the subsurface crustal architecture of these two alkaline complexes is reported for the first time on the basis of high resolution airborne geophysical anomaly data (magnetic and spectrometric). Aeromagnetic anomalies distinguish prominent NW-SE and E-W trending linear deep seated crustal structures in the Sarnu-Dandali alkaline complex. The E-W trending structure mimics the older tectonic tendencies of the regional crustal-scale Narmada-Tapti tectonic zone. The NW-SE trending linear are linked to subsurface rift-oblique networks of fault systems of the petroliferous Barmer basin. The ensemble of numerous fracture patterns at various depths may attest to the rejuvenation of fracture systems and recurrent magmatism, leading to the polychronous nature of Sarnu-Dandali alkaline complex. On the contrary, the Mer-Mundwara alkaline complex exhibits broad magnetic circular features representing the deeper sections of a magmatic plumbing system. The geometry also resembles the subsurface magma chambers for Deccan basalt volcanism, occurring as rootless cones. Paleo stress pattern is derived from the fractures and when compared with the results obtained from geophysical data, these analyses demonstrate a high degree of compliance, reinforcing the validity and accuracy of both methods. Further, the inversion modeling, profile depth analysis and computed Euler depth solutions led us to infer that the subsurface magma sources of the Sarnu-Dandali are deeper than those of the Mer-Mundwara alkaline complex.