Effect of local topography/structure on lava flow direction: A view from Ananthagiri Hills from Deccan Basalts, India

Abstract

Deccan Trap lavas may have erupted through multiple centers, the most prominent of which may have been a shield volcano-like structure in the Western Ghats. The lava transportation and emplacement mechanism provides crucial information on the source and how lava is associated with crustal rocks. Here, we present the results of Anisotropy of magnetic susceptibility (AMS), rock magnetism, and petrology to understand the lava flow directions of Deccan basalts at Ananthagiri Hills. We collected 48 oriented block rock samples from 6 sites and prepared 432 specimens for the detailed investigation. Rock magnetic study indicates that the Pseudo-single domain of titanomagnetite is the primary carrier magnetic mineral. Under the microscope, the volcanic rocks of the Ananthagiri predominantly contain plagioclase and pyroxene phenocrysts that are surrounded by plagioclase, pyroxene, and other opaques, including magnetite and titanomagnetite in the matrix. The AMS principal susceptibility axes are closely clustered with well-developed magnetic lineation and foliation. The magnetic lineation (K₁) aligns best with microscopic flow indicators along NE-SW, indicating the lava flow direction. The pole of magnetic foliation (K₃) clustered at the center with an almost sub-vertical direction, whereas K₁ and K₂ are shallow plunging NE-SW and NW-SE directed, respectively. The degree and shape parameters indicate a mixed oblate and prolate nature; most sites are oblate. Based on all these observations, it is inferred that the local paleo-topography and structures before the Deccan eruption at ∼65 Ma in the basement Dharwar craton affect the lava flow in the study region with an anomalous SW-directed flow.