HR: 17:00h
AN: G14A-05    [Abstracts]
TI: The Development of the San Andreas Plate Boundary through Northern California: Insights from GPS, Crustal Structure, and Lithospheric Modeling
AU: * Furlong, K P
EM: kevin@geodyn.psu.edu
AF: Dept. Geosciences, Penn State University, University Park, PA 16802, United States
AU: Williams, T
EM: williams@unavco.org
AF: UNAVCO-PBO, N. California Operations, Richmond, CA 94801, United States
AU: Hayes, G P
EM: ghayes@geosc.psu.edu
AF: Dept. Geosciences, Penn State University, University Park, PA 16802, United States
AB: The San Andreas plate boundary lengthens in the wake of the Mendocino triple junction (MTJ), and over the last ca. 7-10 Ma it has developed into a localized plate boundary shear zone between the North America and Pacific plates. The pathway from a diffuse deformation swath to a few major fault related plate boundary structures reflects the interplay of thermal and deformational processes acting on the inherited structures of the Cascadia forearc. Furlong and Govers (1998) proposed the Mendocino Crustal Conveyor (MCC) model (supported by numerical modeling) that argued for temporal and spatial variations in lithospheric deformation in association with MTJ passage, which have led to the formation of the main plate boundary structures. The general concept of faults developing and eventually coalescing into a primary plate boundary structure after MTJ passage serves as the framework for most tectonic and geodetic analyses of the fault system. What has been less well understood or quantified is specifically how the fault systems form, what drives fault localization, and how does the concomitant crustal evolution play a role in the plate boundary development. The substantial augmentation of the geodetic data for northern California through a combination of campaign and most recently (through the PBO component of EarthScope) continuous GPS observations in concert with seismological analyses of crustal structure now allows us to test, calibrate, and refine the MCC model. Specifically, the (1) crustal thickening at and north of the MTJ, predicted by MCC processes, is clearly seen in the crustal velocity and GPS derived strain fields, (2) the approx, E-W extent of MCC deformation is delineated by the GPS data to occur primarily through the core of the northern Coast Ranges – consistent with the topographic and fluvial evolution of the region, (3) compatible with seismic observations, the GPS data imply that the upper crust is only a minor participant in the MCC crustal thinning that occurs approximately 200 km south of the MTJ (i.e. ca. 4-5 million years after MTJ passage), and (4) development of the precursor faults to the San Andreas plate boundary structures appear to be driven by the combination of MCC crustal deformation and the development of localized shear within the MTJ-formed slab window. Further structural complexities arise in developing these precursor faults in the upper crust with its pre- existing convergent margin structures, which are either overprinted or reactivated as a result of their orientation and segmentation. The addition of GPS observations to the existing catalog of geophysical and tectonic characteristics of the northern San Andreas system allow us to place the transition from a mature convergent margin to an active translational plate boundary into a physically constrained framework. The MCC model of plate boundary evolution is consistent with these kinematic and structural constraints and thus provides a useful framework model for unraveling the processes that drive the development of the San Andreas plate boundary after MTJ passage and the cessation/removal of subduction from the western margin of North America.
DE: 1209 Tectonic deformation (6924)
DE: 1236 Rheology of the lithosphere and mantle (7218, 8160)
DE: 7218 Lithosphere (1236)
DE: 8111 Continental tectonics: strike-slip and transform
DE: 8158 Plate motions: present and recent (3040)
SC: Geodesy [G]
MN: 2007 Fall Meeting