title of the thesis - Department of Geology - Queen's University

1996; Hodges et al., 2001; Beaumont et al., 2001, 2004, 2006; Jamieson et al., 2004; Godin et al.,
2006a).
The channel-flow model stipulates that ductile extrusion of the GHS occurred normal to
the trend of the orogen towards the topographic front of the Himalaya via flow in a low-viscosity
channel, potentially coupled to focused surface denudation (Beaumont et al., 2001). However,
this process is controversial and adamantly debated (Grujic, 2006; Harrison, 2006; Harris, 2007;
Kohn, 2008). Alternative models have employed wedge-type extrusion (Burchfiel and Royden,
1985; Grujic et al., 1996; Kohn, 2008) and tectonic wedging (Yin, 2006; Webb et al., 2007, 2011)
to explain the presence of the enigmatic GHS.
By middle Miocene time, motion along the MCT and STDS waned, and shortening was
accommodated south of the GHS, along the Main Boundary thrust and the Lesser Himalayan
imbricate thrust belt (Fig. 1.2; Schelling, 1992; Meigs et al., 1995; Huyghe et al., 2001). From
this time forward, deformation has progressed southward in a typical in-sequence foreland
propagating style.
The onset of orogen-parallel extension throughout the Himalaya and Tibetan plateau
broadly coincides with the cessation of south-directed extrusion of the GHS (Jessup and Cottle,
2010), and on-going orogen-perpendicular shortening in the foreland (Huyghe et al., 2001).
Orogen-parallel extension is indicated by structures that accommodate extension and translation
in an orientation roughly parallel to the Himalayan arc. These structures are typically east-west or
ESE-WNW trending strike-slip faults and north-south or NNE-SSW striking normal faults.
Extensional deformation has been active from middle Miocene up to present day and is
commonly manifested throughout central and southern Tibet as east-west oriented strike-slip
faults and north-south oriented normal faults (Fig. 1.3; Armijo et al., 1986, 1989; Taylor et al.,
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