Timing the Mikir Hill uplift in Assam Basin: Record of stress propagation along the eastern margin of the Indian Plate

Abstract

The Shillong Plateau-Mikir Hill complex is a comparatively small but significant geological feature located in the NE part of India. It mostly constitutes of Precambrian basement rocks and is covered by Cretaceous, Tertiary and Quaternary sediments. There are several studies that estimate the exhumation timing of these basement complexes, either by directly dating the basement rocks or indirectly by dating the sediments. The present study tried to use the available seismic and well data to establish a relative chronology of exhumation and uplift of the Mikir Hill with respect to other tectonic and geological events. The study finds that the Mikir Hill upliftment started at the end of deposition of Nazira sandstone at ∼3.6 Ma (Early Pliocene) and stopped by the end of Pleistocene (∼0.012 Ma) which is marked by a prominent unconformity at the top of Namsang Formation. These observations are broadly in agreement with the timing of the surface uplift of the Mikir Hill and Shillong Plateau from previous authors. The study also shows that the structures formed in the Assam foreland along the Naga Thrust front, the frontal thrust of the Schuppen belt, shows a progressive younging in deformation from the NE to the SW. This shows a broad correlation in their formation with the eastern subduction history of the Indian plate.