Timing of slip along the Zanskar normal fault, Greater Himalayan Range, NW, India: Constraints from apatite and zircon (U-Th)/He thermochronometry

Brett Shurtleff
November 2012

Research Objectives

I propose to document the timing and slip along the Zanskar fault, a moderately northeast- dipping northwest-striking normal fault bounding the northeastern flank of the Greater Himalaya Range, India using low-temperature (U-Th)/He thermochronology. The Zanskar fault is the far western extent of the ~2200 km long South Tibetan Detachment System (STDS), a shallow north dipping normal sense shear zone. The Zanskar Shear Zone (ZSZ) fault is unique in that it accommodates extension parallel to contractional deformation due to the collision between India and Asia (Figure 1) (Herren, 1987; Searle, 1986). Along this segment of the STDS, the Zanskar fault juxtaposes unmetamorphosed to weakly metamorphosed Tethyan sediments in the hanging wall upon metasedimentary, igneous, and migmatites of the Greater Himalaya Sequence (GHS) in its footwall (Figure 2) (Searle, 1986, and references therein). Structurally below the STDS and defining the base of the GHS is the Main Central Thrust (MCT) fault. Thrust fault slip history along this north-dipping thrust-fault zone, which accommodated much of the Indo-Asian convergence, is broadly synchronous with slip along the STDS. Geochronologic data from the central (Nepal) and eastern (Bhutan) segments of the STDS (Figure 1) indicate a normal slip history that is between ~23 Ma to ~12 Ma (Godin et al., 2006 and references therein). However, the timing of slip along the Zanskar segment of the STDS has long been debated (Harrison et al., 1997). Geochronologic data from the Zanskar region along the STDS suggest a normal slip history between ~26 Ma (Dèzes et al., 1999; Robyr et al., 2002) and ~8 Ma (Kumar et al., 1995), somewhat younger than farther to the east.

The Zanskar fault near Padum, India displays well-developed triangular facets (Figure 3) suggesting that normal slip along this part of the STDS could be Pliocene in age or younger. If true, then this slip history is younger than what has been previously documented elsewhere along the ZSZ segment of the STDS. To test this hypothesis, I propose to use (U-Th)/He thermochronology, a low-temperature thermochronology dating technique, on rock samples collected from the footwall of the Zanskar fault. (U-Th)/He thermochronology on apatite and zircon grains will constrain the time-temperature cooling history of footwall rocks as they were exhumed, during normal slip, through temperatures of ~180-60°C. Apatite and zircon (U-Th)/He ages will allow me to document the timing of normal slip along the Zanskar fault, which will have spatial-temporal implications for the tectonic evolution of the Himalayan orogen.

Full Thesis Proposal (PDF format)