Syn-convergent low-angle normal-sense detachments (LANDs) are found in many orogens
around the world. However, those tectonic processes which result in their formation are
little known. The South Tibetan detachment system (STDS) is the best-studied example
worldwide of a syn-convergent LAND, and formed in the Miocene due to the continental
collision of India and Asia. In Bhutan, eastern Himalaya, the STDS is duplicated.
Here I investigate the tectonic history of the inner STDS and particularly the
outer STDS in Bhutan, to determine whether the duplicated STDS can be explained
by or used to constrain models of Himalayan orogenesis. A range of geochronometric,
thermochronologic, petrologic, structural, thermobarometric, thermometric, and isotopic
tools are used to constrain: the onset and cessation of motion on the outer STDS; the
cessation of motion on the inner STDS; the peak metamorphic conditions in the hanging
wall and footwall of the outer STDS; the pressure-temperature-time paths of tectonites in
the hanging wall and footwall of the outer STDS; the structural history of the hanging wall
rocks of the outer STDS, and; the paleogeographic affinity of the hanging wall rocks of
the outer STDS.
The results of these studies are compared to thermo-mechanical models of Himalayan-
type continental collision. Similarities in model predictions of the type and timing
of structures, peak metamorphic conditions of hanging wall and footwall tectonites,
pressure-temperature-time paths, and other regional tectonic observations lead to two main
conclusions. 1. The STDS is a system of three main types of LANDs: those that formed
during channel flow of low-viscosity mid-crustal rocks, those that formed by extrusion
of cooled channel rocks to the surface, and those that formed by destabilization of the
upper crust above a dome of mid-crustal channel rocks. 2. The STDS was duplicated by
underthrusting of a crustal ramp into the Himalayan orogen since early Miocene. The
underthrusting led to extrusion of a dome of weak mid-crustal above a previously-extruded
channel. The crustal ramp may be local to the eastern Himalaya due to higher convergence
and/or erosion rates, or due to local underthrusting of relatively strong crust behind weaker
crust.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:NSHD.ca#10222/13153 |
| Date | 12 August 2010 |
| Creators | Kellett, Dawn |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
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