Kinematic Reconstruction of Rajmahal Trap: Implications for Cretaceous to Present Day Geodynamics of Indian plate

Abstract

The Rajmahal Trap is one of the two major Large Igneous Provinces (LIPs) that erupted in the Mesozoic. The trap was the product of the Kerguelen hotspot that initiated around 117 Ma, which is currently located in the Indian Ocean. Earlier studies on the paleogeographic location of the Rajmahal trap eruption show that its location does not coincide with the present-day location of the Kerguelen Hotspot. Presently, the hotspot has shifted approximately 700 km towards the South from the paleo-latitude location. This shift of the location is attributed to numerous reasons such as multiple diapir-single plume model or the migration of the hotspot beneath the mantle or the complex plume-ridge interaction. The history of the Kerguelen hotspot is long lived, spatially as well as temporally. The first magmatic activity by the hotspot is supposed to be the eruption of Comei LIP, second activity by the hotspot, was the eruption of Bunbury basalts (Western Australia) at 129 Ma, another volumetrically small Large Igneous province was formed at 117 Ma named Rajmahal basalts (India). Next eruption was one of the largest LIP formed by Kerguelen hotspot at 110 Ma was South Kerguelen plateau. At 95 Ma, two LIPs, Broken Ridge and the Central Kerguelen Plateau, were formed. From 91 Ma to 50 Ma, the formation of Ninety East Ridge took place and by 41 Ma, the Kerguelen hotspot formed the North Kerguelen Plateau and in the present day, the Kerguelen hotspot is supposed to be present beneath the North Kerguelen plateau. The observations were made in GPlates, while reconstructing the Indian plate movement with the help of GPlates directory. The kinematic analysis for the Rajmahal trap with respect to the geoid, the Australian plate and the Antarctic plate was calculated, after which the kinematic reconstruction of the Indian plate was simulated since 117 Ma, showing the major tectonic events during the Indian plate migration. The kinematic analysis for the Rajmahal trap suggests the absolute change in the velocity magnitude from 117 Ma. The variation in absolute velocity magnitude shows drastic changes at specific points in time due to different tectonic activities. At 90 Ma, the velocity increases suddenly due to the Morondova plume activity. From 78 Ma to 62 Ma, the plate motion is accelerated by the reunion hotspot activity thereby creating an intra-oceanic subduction zone. From 62 Ma, the activity by the reunion hotspot is reduced and the double subduction process is at its peak leading to a drop of the velocity at 56 Ma. At around 56 Ma the Indian oceanic plate collides with the Eurasian plate and the velocity decreases. Due to the slab pull mechanism, the velocity again rises at 50 Ma. From 50 Ma to 43 Ma, the velocity drops due to continental collision of the Indian plate against the Eurasia plate. Since 45 Ma, the velocity is almost constant with a value of approximately 5cm/yr. Since 117 Ma, the highest velocity observed is 16.87 cm/yr at 62 Ma and lowest velocity observed is 3.71 cm/yr at 95 Ma. The comparative velocity magnitude analysis between the Indian plate and the Rajmahal trap showed a slight difference of 0.2 cm/yr in the velocities since the India-Eurasia collision at 56 Ma.