Deep Seismic Reflection Imaging of Mesozoic Kachchh Rift, NW India: Implications for Evolution

• Published in: Tectonics (Washington, D.C.) D.C.), 2023-11, Vol.42 (11), p.n/a
• Main Authors: Mandal, Biswajit, Vijaya Rao, V., Karuppannan, P., Laxminarayana, K., Chopra, Sumer, Ravi Kumar, M., Kumar, Prakash
• Format: Article
• Language: English
• Subjects: Accretion; Basins; Compression; Crustal structure; Crustal thickness; deep seismic reflection study; Earthquakes; Evolution; Fault lines; Graben; Heterogeneity; mantle plume; Mantle plumes; Mesozoic; Moho; Oceanic crust; Plate boundaries; Reflection; Rheology; Rifting; Seismic activity; Seismic data; Seismic reflection profiling; Seismicity; Seismological data; Tectonics; underplating; Uplift
• ISSN: 0278-7407; 1944-9194
• DOI: 10.1029/2023TC007992

Deep crustal seismic reflection profiling is carried out for first time across various tectonic domains of seismically active Mesozoic Kachchh rift basin, formed during the breakup of Gondwanaland. The seismic data, processed using the common reflection surface stack approach, provided maiden images of the shallow and deep sub‐surface structures in the region. These images reveal a 15 km thick subhorizontal lower crustal reflection fabric and crustal‐scale domal‐type structure extending from the surface to the Moho. We interpret the earlier structure represent magmatic underplating and the latter as the Kachchh Mainland uplift. We find large variations in the thickness of sediments from 150 m to 6.5 km and crustal thickness from 45 to 35 km from north to south, with a Moho up warp of 4 km beneath the Kachchh Mainland fault. The Kachchh rift basin exhibits an unusually thick crust of 45 km, contrary to many rift basins. We interpret the syn‐rifting and the Reunion mantle plume activity, manifested as Deccan volcanics, are responsible for magmatic underplating and crustal thickening. Uplift in the region is multi‐genetic in origin. Present study illuminated new faults and nature of various other faults. Moderate to large earthquakes in the region are attributed to the regional and local stresses resulting from the plate boundary and heterogeneous crustal structure. Based on the mafic lower crust and distribution of aftershocks through the entire crust, we interpret the lower crust is brittle, contrary to most models of continental rheology. Plain Language Summary Crustal evolution takes place at orogenic belts and extensional areas. Present study area, the Kachchh rift basin located on the NW part of the Indian Shield underwent extensional activity during its formation. It was formed during different stages of rifting/breaking processes of the Gondwanaland during the Mesozoic. Crustal thickness varies according to the tectonic activity of the region. In general rift basins exhibit 33–35 km thick crust, whereas the present study imaged an unusually 45 km thick crust beneath the Kachchh basin. We attribute this thickness to the accretion of 15 km mantle material in the lower crust, the magmatic underplating, during rifting and Reunion mantle plume activities. The Kachchh basin exhibits crustal heterogeneity due to uplift (horst) and depression (graben) type of structures formed during basin evolution. The peninsular India is in a state of compression between t