HR: 0800h
AN: V51B-0555    [Abstracts]
TI: Yellowstone Hotspot Melting And Its Relation To Pre-Existing Crustal Structures And Great Basin Extension
AU: * Glen, J M
EM: jglen@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., MS 989, Menlo Park, CA 94025
AU: Ponce, D A
AF: U.S. Geological Survey, 345 Middlefield Rd., MS 989, Menlo Park, CA 94025
AU: Sepulveda, E
AF: Laboratoire d'Optique Physique, ESPCI, 10 Rue Vauquelin, Paris, 75005 France
AB: Topography and geophysical data suggest that the path of Yellowstone hotspot (YSHS) volcanism was controlled by pre-existing crustal structures associated with the Snake River Plain (SRP), and that Great Basin (GB) extension is intimately tied to hotspot melting. From its point of inception (Glen and Ponce, 2002), the YSHS migrated south to the southern Snake River Plain (SRP) where it began a steady migration northeast along the eastern SRP to its present position under the Yellowstone caldera. In doing so, however, it had to move through a 90$\deg$ counter-clockwise turn that is not consistent with a fixed hotspot and its predicted path based on plate motions, and assuming a fixed hotspot. We present evidence suggesting that the SRPs western and eastern branches form a continuous deep crustal structure that guided YSHS volcanism along a track from its inception in eastern Oregon to its present position under the Yellowstone caldera. The western and eastern segments of the SRP, which are interpreted to have different origins and ages, nonetheless form a single topographic depression that curves 180$\deg$ along a circular arc. Also associated with the SRP is a broad and continuous gravity anomaly indicating a relatively deep-seated crustal structure extending across the western and eastern SRP. Heat flow data, which show an uninterrupted corridor of high heat flow values extending from Yellowstone caldera through the SRP to the inferred inception point of the hotspot, might reflect either the thermal footprint of the hotspot's path or the control on heat flow by a regional-scale crustal discontinuity. While the path of the hotspot could have been directed by crustal structures, the location and timing of mid- to late-Tertiary extension in the GB might, in turn, have been controlled by hotspot melting. Well known is the age-progressive hotspot track along the eastern SRP, presently marked by active volcanism at the Yellowstone caldera. Less well known, is a second age-progressive track trending northwest across the Oregon Plateau ending at the historically active Newberry craters. The present locations of these active melting fronts, at Yellowstone and Newberry, coincide with the eastern and western margins, respectively, of the GB. This remarkable correlation, while suggesting a link between hotspot melting and GB extension, does not reveal whether melting controls the bounds of GB extension or whether GB extension controls the propagation of hotspot volcanism. Another characteristic of GB extension, however, that might reflect a causal relation between magmatism and rifting, is the geometry and orientation of basins and ranges in the GB. The trends of basins and ranges fan out from north-northwest in the eastern GB to northeast in the west. When extrapolated, these trends intersect near the SRP close to where the age-progressive YSHS trend began $\sim$ 12-14 Ma, suggesting a relationship between the formation of the GB and this period of the hotspot's path. We infer that this fracturing pattern is related to the SRP, perhaps induced by the $\sim$ 12-14 m.y. old hotspot, and that subsequent extension in the GB exploited these pre-existing crustal weaknesses.
DE: 8109 Continental tectonics--extensional (0905)
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8121 Dynamics, convection currents and mantle plumes
DE: 8122 Dynamics, gravity and tectonics
DE: 8159 Rheology--crust and lithosphere
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting