Anisotropy of magnetic susceptibility study to locate the feeder zone and lava flow directions of the Rajmahal Traps (India): Implications to Kerguelen mantle plume interaction with Indian Plate

M.R. Kapawar, Venkateshwarlu Mamilla, S.J. Sangode

Rajmahal Traps (RT) represents the earliest eruption from the Kerguelen hotspot activity over Indian Plate. Petrofabric studies such as anisotropy of magnetic susceptibility (AMS) provide fundamental data on the paleoflow directions, viscosity controls of fabrics, and overall flow dynamics of the lava. This study is first attempt to investigate the regional fabrics for understanding the style of eruption of the RT volcanism and its relation to the plume activity as well as to understand the magma emplacement dynamics and tectonics of the region.

 

The feeder zone for RT was located in the NE quadrant of the volcanic province and along the Narmada-Son-Brahmaputra Transform (NSBT) fault.  From the AMS fabrics, site-wise flow directions determined and the average lava flow direction for the RT is inferred from NE to SW. The AMS fabrics suggest that the entire lava sequence of RT (indeed the RBS province) was fed from the feeder zone location parallel to the elongated NSBT fault located in the Comei-Cona region of Tibet NE of RT, and served as a plume source instead of Kerguelen hotspot’s direct involvement for the genesis of RT (RBS province). The results further suggest that the NSBT system provide the major topographic control for the lava flow channel distribution in the Rajmahal province. It implies that the fracture zone was available during the lava emplacement, which records the earliest Kerguelen plume activity.

Figure: (Left) - The inferred lava flow directions for individual sites of RT. (Right) - A sketch map (a) showing the Narmada-Son-Brahmaputra transform (NSBT) fault trending NE-SW, the younger E-W trending Dauki fault (DF) forms triple junction (grey ellipse) with NSBT in the NE of RT exposures. The ~132 Ma Comei-Cona (CC; red dashed ellipse) resulted from the Kerguelen mantle plume served as a plume center (feeder zone) for ~120 Ma RT (RBS province). A plate tectonic reconstruction (b) at ~120 Ma showing India, Australia, and Antarctica as a single eastern Gondwana configuration.

 

Citation

Physics of the Earth and Planetary Interiors, V. 313, 2021, 106692; https://doi.org/ 10.1016/j.pepi.2021.106692 external link.