4.2.6 Phase D6: High-angle normal faults

The last tectonic phase D6 occurred under brittle conditions and is expressed by ultramylonites, pseudotachylites and cataclastites associated with high-angle normal faults. These young faults cross-cut the Zanskar Shear Zone and propagate through the overlying sedimentary series of the Tethys Himalaya. Normal displacement along these faults is documented in the Tethys Himalaya by the juxtaposition of younger series in the hanging wall against older series in the footwall. The most prominent of these high-angle normal faults is the Sarchu Fault (chapter 5.3.2) which juxtaposes low-grade metamorphic sedimentary series in the hanging wall against amphibolite facies metasediments in the footwall (Fig 4.10).

In the Tethys Himalaya, these faults are always masked by quaternary scree. Within the ZSZ however, a clear cross-cutting relation can be established between the narrow high-angle ultramylonitic D6 faults and the low-angle mylonitic foliation associated with D4.

Along most of the ZSZ, the high-angle faults dip towards the NE at an angle between 50° and 70°. Less pronounced conjugated faults dipping towards the SW are also frequently observed. Towards the southeastern end of the HHCS, high-angle normal faults are also observed around the Gumburanjun and Kamirup leucogranitic bodies (Fig 4.11). High-angle faults have also been reported in the Miyar valley, along the southern edge of the Gianbul dome, but so far only in the high-grade rocks (Steck, oral comm.).