A review on out-of-sequence deformation in the Himalaya

Abstract

Abstract Out-of-sequence deformation in the Himalaya has been caused mainly by thrusting. Out-of-sequence thrusts, usually north- to NE-dipping foreshear planes, occur inside the Sub-Himalaya (SH), Lesser Himalaya (LH) and Greater Himalayan Crystalline (GHC) sequences. Where absolute dates are available, the youngest slip within the SH occurred near the Janauri Anticline (India) at c. AD 1400–1460. The Munsiari Thrust (India) activated within the LH at c. 1–2 Ma and the Main Central Thrust zone in the Marsyandi valley (Nepal) in the GHC was formed during the Holocene ( c. 0.3 ka). Except for the Riasi Thrust (Kashmir, India), the Paonta Thrust (Himachal Pradesh, India) in the Siwalik and the Tons Thrust (Garhwal region, India) within the Main Central Thrust zone, crustal shortening related to out-of-sequence thrusting in the Himalaya has been insignificant. The major litho-/stratigraphic contacts within the SH and the GHC at some places acted as out-of-sequence thrusts. Out-of-sequence thrusts in the SH have been detected mainly based on geomorphological observations. However, more quantitative geochronological studies have detected out-of-sequence thrusting from c. 22 Ma up to Holocene age in the GHC based on age jumps, especially within the Main Central Thrust zone. Crustal channel flow (specifically for the GHC) and/or the critical taper model with or without erosion can be used to explain the Himalayan out-of-sequence thrusts.