T24B-06
Discussion starter: the case for channel flow during the development and emplacements of Himalaya middle crust

Tuesday, 15 December 2015: 17:10
302 (Moscone South)
Dawn Kellett1, John M Cottle2, Laurent Godin3, Djordje Grujic4, Kyle Larson5 and Renaud Soucy La Roche3, (1)Geological Survey of Canada, Natural Resources Canada, Ottawa, ON, Canada, (2)University of California Santa Barbara, Santa Barbara, CA, United States, (3)Queen's University, Geological Sciences & Geological Engineering, Kingston, ON, Canada, (4)Dalhousie University, Halifax, NS, Canada, (5)University of British Columbia, Vancouver, BC, Canada
Abstract:
The Himalayan orogen has been the key testing ground for geodynamic models of channel flow, the gravity-driven lateral flow of a layer of melt-weakened crust, since it was first proposed as an important tectonic process for the middle crust of large hot orogens. Over the last fifteen years, there has been a dedicated international effort to test field and analytical predictions of the channel flow model in the Himalaya, in particular discerning and comparing predictive characteristics of channel flow with that of a flow-absent critical Coulomb wedge. A range of structural, metamorphic and geological features of the Himalayan orogen are compatible with predictions from geodynamic models of channel flow. However, the longevity of flow, interaction with external critical Coulomb wedge processes, and overall amount of convergence accommodated by flow remain unresolved. Towards this end, documented tectonometamorphic discontinuities may record the complex interplay of channel flow and critical Coulomb wedge processes in time and space.

Recent research in favour of preservation of a branch line of opposing-sense structures bounding the exposed middle crust of the Himalaya has been offered as evidence against active extrusion of a mid-crustal channel. Further, flow-absent wedge extrusion/duplexing has been proposed as a mechanism for producing the paired normal and thrust sense shear zones, the Himalaya’s inverted metamorphic sequence, and the tectonometamorphic discontinuities. Although duplexing shares geometric similarities with tunnelling channel flow, as a process it fails to explain the development and emplacement of Himalayan middle crust on rheological, structural and geological grounds.

Outstanding questions that should drive discussion and future research: is evidence for a branch line compelling? Is evidence for channel flow active extrusion compelling? Are there along strike differences and how can these be explained in light of this discussion? Is duplexing a possible outcome of shortening a non-Coulomb layer?

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