HR: 1645h
AN: T34C-04 INVITED    [Abstracts]
TI: Channel Flow in the Deep Crust and its Topographic Expression
AU: * Royden, L
EM: lhroyden@mit.edu
AF: MIT, MIT 54-826, Cambridge, MA 02139, United States
AB: Crustal channel flow occurs when lateral flow in the mid to deep crust occurs more rapidly or in a different direction than surface motions, measured with respect to the underlying mantle. Because channel flow accomplishes lateral transfer of crustal material with little development of surface geologic structures, documenting and constraining channel flow remains a challenge. Channel flow may transfer lower crustal material over length scales of hundreds up to perhaps a thousand kilometers. It can occur along strike, such as in the central Andes, across strike, such as may have occurred across the early Paleozoic passive margin of western North America; it always occurs down the regional topographic gradient. Channel flow requires more than the existence of a weak lower crust. Either the lower crust must be weak enough (low enough viscosity) that flow does not cause stresses in the upper crust to exceed the brittle yield criteria, or, if not, it occurs only if the ratio of upper crustal to lower crustal viscosity exceeds a value that scales linearly with the flow-length squared and with the channel thickness. Channel flow on length scales of 100 km is easily developed, while channel flow on length scales of 1000 km should be relatively rare. Because a deep crustal channel is effectively a crustal asthenosphere, the conditions necessary for channel flow ensure that the regional topographic gradient above the channel is very low. It thus provides a natural mechanism for establishing areas of low relief at high elevation that is independent of the density structure within the underlying mantle. Probably most low relief, high elelvation regions on Earth are underlain by areas of channel flow, including Tibet, Altiplano and much of the high central Andes, the Iranian Plateau, and the high areas of eastern Turkey.
DE: 1213 Earth's interior: dynamics (1507, 7207, 7208, 8115, 8120)
DE: 8168 Stresses: general
SC: Tectonophysics [T]
MN: 2007 Fall Meeting