Your query was:

"S22A-0419"

HR: 0830h
AN: S22A-0419
TI: Consequences of Removal of Cold Mantle Lithosphere: Uplift, Extension and Contraction in California (and Maybe Even Changes to the San Andreas)
AU: * Jones, C H
EM: cjones@cires.colorado.edu
AF: Dept. Geol. Sci. & CIRES, Univ. Colorado at Boulder, CB 399, Boulder, CO 80309-0399 United States
AU: Farmer, G L
EM: farmer@terra.colorado.edu
AF: Dept. Geol. Sci. & CIRES, Univ. Colorado at Boulder, CB 399, Boulder, CO 80309-0399 United States
AU: Unruh, J R
EM: unruh@lettis.com
AF: Wm. Lettis & Assoc., 1777 Botelho Dr., Suite 262, Walnut Creek, CA 94596 United States
AU: Molnar, P
EM: molnar@terra.colorado.edu
AF: Dept. Geol. Sci. & CIRES, Univ. Colorado at Boulder, CB 399, Boulder, CO 80309-0399 United States
AB: Volcanic rocks and associated xenoliths from the Sierra Nevada of California indicate that the entire mantle lithosphere was removed about 3.5 Ma, including about 30 km of eclogites and garnet pyroxenites. Such removal is surprising in that the Sierra has long been noted for its low surface heat flow, which, when combined with temperature information from xenoliths, indicates that this mantle lithosphere was very cold at the time of removal. One means of exploring the magnitude of this event is to examine the tectonic consequences. Replacing such a thick, dense body with more buoyant asthenosphere should drive uplift, which is consistent with uplift of the Sierran crest by more than 1 km between 3 and 8 Ma. Removal will also increase the gravitational potential energy of the Sierran lithosphere by at least 1.2 * 10$^{12}$ N/m, which is capable of inducing extension. Such extension within 50 km of the east edge of the modern Sierra initiated between 5 and 3 Ma. If there are no changes in Pacific-North American plate motions [e.g., {\it Atwater and Stock}, 1998], then new extension must shut down extension elsewhere or increase compression. The California Coast Ranges date to about 3-5 Ma and largely have been created through shortening normal to the Sierran axis. Potentially this could influence San Andreas rates, as narrowing of the rigid Sierran block permits strike-slip motion to increase on the east side. A decrease of 12 mm/yr on the San Andreas at $\sim4$ Ma [{\it Dickinson}, 1996] suggests that slip on the Eastern California Shear Zone became viable about this time. All of these effects extend the length of the Sierra, indicating that removal affected the entire Sierra. If the removal occurred as a Rayleigh-Taylor instability, existing models can be reconciled with the cold temperatures if the high stress limit of {\it Evans and Goetze} (1979) is used and, probably, the top boundary of the lithosphere weakened prior to removal. However, the removal of the entire lithosphere is unexpected and suggests that the physics of these systems, including the lithospheric rheology, need additional study.
DE: 8110 Continental tectonics--general (0905)
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8159 Rheology--crust and lithosphere
SC: Seismology [S]
MN: 2003 Fall Meeting