This thesis integrates structural, metamorphic and geochronological data to critically examine key aspects of the tectonothermal evolution of the mid-crustal portion of the Himalayan orogen . in the Makalu - Kharta region of southern Tibet. U(-Th)-Pb ages indicate that in the southern area prograde metamorphism of the mid-crustal Greater Himalayan Series (GHS) peaked at least as early as -38.9 Ma. Subsequent sillimanite grade metamorphism at -28.0 Ma was followed by at least two phases of leucogranite emplacement at -20.8 Ma and -16.7 Ma. To the north, approximately 40 km in the down-tectonic transport direction, prograde metamorphism was occurring at -25.4 Ma and lasted until -16.1 Ma. Immediately following metamorphism, two phases of leucogranite were emplaced at -15.2 Ma and -12.6 Ma, with an intervening phase of ductile deformation. These two outcrops record a northward propagation of peak metamorphism, leucogranite intrusion and deformation events that are -5 - 7 Ma younger in the down-tectonic transport direction. The top of the GHS is bounded by the South Tibetan Detachment System (STDS), a large-scale, north-dipping low-angle normal fault characterised by a -1 OOOm thick zone of distributed ductile shear. Macro- and micro-structural observations indicate that this segment of the STDS records a progression from ductile- to brittle-deformation without development of a single discrete detachment fault, and therefore provides important insight into the early ductile history of the STDS and associated exhumation of the GHS. Lying to the east and structurally beneath the GHS, the Ama Drime massif (ADM) is an anomalous region of elevated topography extending -70km northward from the crest of the High Himalaya. The ADM is bounded by north-striking normal-faults and is cored by 1800 Ma. gneisses, granulitized mafic eclogites and -12 Ma syn-kinematic leucosomes that record crustal-scale east-west extension and ductile exhumation of mid-crustal material that was enhanced by focused surface denudation acting on the Himalayan range front.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:491354 |
| Date | January 2007 |
| Creators | Cottle, John M. |
| Publisher | University of Oxford |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
Page generated in 0.022 seconds