Crustal structure beneath the Sub-Himalayan fold–thrust belt, Kangra recess, northwest India, from seismic reflection profiling: Implications for Late Paleoproterozoic orogenesis and modern earthquake hazard

• Published in: Earth and planetary science letters Vol. 308; no. 1; pp. 218 - 228
• Main Authors: Rajendra Prasad, B., Klemperer, Simon L., Vijaya Rao, V., Tewari, H.C., Khare, Prakash
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.08.2011
• Subjects: deep seismic reflection profiling; Kangra recess; Main Himalayan Thrust; Sub-Himalaya; Ulleri-Wangtu gneiss; Vindhyan Supergroup; India; Sub-Himalaya; Ulleri-Wangtu gneiss; Kangra recess; deep seismic reflection profiling; Main Himalayan Thrust; Vindhyan Supergroup
• ISSN: 0012-821X; 1385-013X
• DOI: 10.1016/j.epsl.2011.05.052

Most compressional orogens include salients and recesses along their strike, the age and origin of which can be hard to ascertain. In the Kangra recess in the trace of the Main Boundary Thrust (MBT), the largest such recess within the active Himalayan orogen, the Sub-Himalayan sedimentary fold-thrust belt increases in width to as much as 90 km (the Kangra Basin), but narrows to as little as 10 km in the adjoining Nahan salient of the MBT (the Subathu Basin) to the southeast. New seismic reflection profiling places the Himalayan décollement at 6–8 km depth above thin but reflective Meso- to Neoproterozoic Vindhyan (Lesser Himalayan Series-equivalent) strata. These data show that the Vindhyan sedimentary rocks are thinner in the Kangra recess than further southeast, allowing the hypothesis that the width of the Lesser Himalayan thrust belt, and the existence of the Kangra recess, could be related to the pre-deformation basin thickness. This hypothesis obviates the need for control of the Kangra recess by a lateral ramp in the Main Himalayan Thrust, so making it more likely that the Kangra segment could rupture as part of an earthquake far larger than the devastating 1905 M = 7.8 Kangra earthquake. Below the Proterozoic sedimentary rocks, our reflection data show a west–southwest-dipping reflective fabric spanning a 30 km-crustal thickness, which we infer corresponds to a widespread “Ulleri-Wangtu” orogenic event at c. 1850 Ma affecting a pre-Tethyan Indian continental margin, thickening the basement by c. 20%. The deepest 10 km of this ~ 50 km-thick crust shows a more horizontal, arguably younger, reflectivity, though the Moho is not clearly marked by strong reflectors. [Display omitted] ► We present the first crustal seismic reflection profile across the Sub-Himalaya. ► An ~ 1850 Ma orogeny thickened Indian crust by ~ 20%, imprinting a WSW-dipping fabric. ► Vindhyan sedimentary rocks are thinner beneath the Kangra recess than to the SE. ► The Kangra recess may be due to thin Vindhyans, and not to a lateral ramp in the MHT. ► Absent a lateral ramp, future earthquakes may more likely break across this region.