Extensional tectonics in the Himalayan orogen, Zanskar, NW India

Abstract

Large-scale nappes of the deformed Higher Himalayan Crystallines (HHC) were thrust southward over the Lesser Himalayan Proterozoic foreland during the Late Cenozoic. Critical evaluation of shear fabrics, reveals that the HHC underwent an earlier phase of ductile shearing with top-to-southwest overthrust-type sense of movement. On which was superposed layer-parallel NE-trending extension. As a consequence, the Zanskar Shear Zone (ZSZ) along the northern boundary of the HHC is re-interpreted as a complex ductile shear zone with an initial top-to-southwest sense of thrusting followed by the later superposition of top to northeast-directed extension. This period of extension is recognized across the whole of the HHC and is the result of the uplift and exhumation of the HHC by southwestward directed thrusting and ramping along numerous thrusts including the Main Central Thrust (MCT).

Doming in compressional orogenic settings: New geochronological constraints from the NW Himalaya

“…This event was likely coeval with the SW directed nappe tectonics (e.g., Nyimaling-Tsarap nappe) responsible for the middle Eocene low-grade metamorphism in the Tethyan Himalaya constrained by 40 Ar/ 39 Ar white mica ages (circa 45 -42 Ma [Bonhomme and Garzanti, 1991;Wiesmayr and Grasemann, 1999;Schlup et al, 2003]). This interpretation is consistent with the observations by Patel et al [1993] that the extensional ZSZ reactivates a former thrust.…”

“…BT, Baralacha La Thrust; DTFZ, Dutung-Thaktote Fault Zone; HHCZ, High Himalayan Crystalline Zone; JD, Jahla Detachment; KSZ, Khanjar Shear Zone; LHC, Lesser Himalayan Crystalline; LT, Lagudarsi La Thrust; MBT, Main Boundary Thrust; MCT, Main Central Thrust; MTZ, Miyar Thrust; PT, Parang Thrust; SD, Sangla Detachment; SF, Sarchu Fault; ZSZ, Zanskar Shear Zone. a consequence, the tectonometamorphic evolution of this part of the range is well constrained [e.g., Honegger et al, 1982;Kündig, 1989;Stäubli, 1989;Patel et al, 1993;Dèzes, 1999;Searle et al, 1999;Walker et al, 1999;Stephenson et al, 2000;Epard and Steck, 2004]. In contrast, the timing of the metamorphic and tectonic evolution of the southern limb of the Gianbul dome is still poorly constrained.…”

Integrated tectonostratigraphic analysis of the Himalaya and implications for its tectonic reconstruction

“…Although known geologic relationships support this interpretation, other aspects of the complex are also consistent with the possibility that it may have rooted along the South Tibetan Fault System as a remnant of early south-verging thrusting that pre-dated recent north-verging normal movement associated with gravitational collapse [29]. The metamorphic grade associated with the structurally lowest levels of the complex is similar to that found within the southernmost parts of the Tethyan zone adjacent to the GH and the South Tibetan Fault System.…”

“…Additionally, relatively un-deformed Silurian strata in the Himalaya are preserved only in the TH; they are absent in the LH, where Permian strata rest directly on the Lower Cambrian. Middle Cambrian to Lower Permian strata are also cut-out below a Permian unconformity south of the extension of the MCT (the P^K fault) in Pakistan, whereas to the north of the fault a full pre-Permian Tethyan succession exists [29]. Whether the Kathmandu Complex represents (1) a part of the GH that roots back to the MCT and escaped strong metamorphism, or (2) a part of the TH that moved along the STDS, remains an unresolved problem.…”

Higher Himalayan Shear Zone, Zanskar Indian Himalaya: microstructural studies and extrusion mechanism by a combination of simple shear and channel flow

“…d A schematic cross-section of the Zanskar Shear Zone along the NE-SW geographic direction. The structures reported by Patel et al (1993) are shown: 1 top-to-SW sense of ductile shearing, 3 top-to-NE (down) extensional ductile shearing, 1 0 Top-to-SW sense of brittle shearing represented by duplexes, and 2 0 Northeasterly steeply dipping brittle faulting. Ductile shearing represented by 1 and 3 are subsequently referred as 'shearing-1' and 'shearing-3', respectively.…”