How Far Does the Keel Go? Archean Basement Control on the Laramide Orogeny
Abstract
The Wyoming province, the type locality of the Laramide orogeny, is characterized by uplifts of Archean basement and surrounding basins associated with flat-slab subduction. Laramide flat-slab subduction has been attributed to: 1) features of the subducting plate (e.g. Shatzky conjugate) or 2) interactions between both upper and lower plates in the context of global plate kinematics and local geometry of the North American craton. This last set of models attribute initial low-angle subduction to increased rate and orthogonality of convergence, which contributed to propagating shear stress into the crust; slab flattening is subsequently enhanced by differential pressure in the mantle associated with constricted asthenospheric return flow in the vicinity of the deep keel of the Wyoming craton. The first set of models predict a NE trend of deformation and uplift along a relatively narrow corridor trending approximately N15°E from the early late Cretaceous to the Paleocene (ca. 90-60 Ma). The second set of models are consistent with the timing and structural evolution of mountain ranges and adjoining basins along the full breadth of the Rocky Mountains, explain the onset of early of deformation in the late Cretaceous in SW Montana and the culmination of contractile deformation in the middle and late Eocene, and are consistent with the sweep of magmatism in the northern Rocky Mountains and Great Plains.
The timing of exhumation of Laramide uplifts can be used as proxy for the timing of deformation and to provide constraints on the spatio-temporal evolution of the Laramide orogeny, which in turn can help test existing models of the Laramide. New thermochronological data show that the northern Laramide region of Montana was active no later than ca. 80 Ma and as early as ca. 100 Ma and earlier than areas in Wyoming. Exhumation of Laramide ranges in Wyoming (e.g., Gros Ventre and Wind River Ranges) mostly occurred in the Paleogene and may be associated with removal of depleted mantle lithosphere. This when combined with the Laramide basins history supports a general model for the Laramide orogeny involving a combination of initial slab shallowing owing to increased convergence rate, followed by slab flattening in response to interaction with the Archean craton lithospheric keel.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.T12A..04C
- Keywords:
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- 7205 Continental crust;
- SEISMOLOGY;
- 8103 Continental cratons;
- TECTONOPHYSICS;
- 8120 Dynamics of lithosphere and mantle: general;
- TECTONOPHYSICS;
- 8159 Rheology: crust and lithosphere;
- TECTONOPHYSICS