Geodynamic Origins of Broad and Focused Deformation in the Central California Coast Ranges Illustrated by the Monterey and Big Sur Segments of the San Gregorio-Hosgri Fault
Abstract
The spatial distribution and geodynamic drivers of uplift and erosion in the central and northern California Coast Ranges are incompletely known. To explain time-space patterns, previous workers have invoked either: (1) dynamic topography migrating northward with the Mendicino Triple Junction; (2) oblique convergence across restraining segments of the North American - Pacific plate boundary; or (3) basal traction imparted by vestiges of the Farallon plate that have been remobilized in slow subduction during the past ~5 m.y.
None of these models, in isolation, satisfactorily explains the spatial distribution of plate boundary strain. We note that although restraining segments of plate boundary faults tend to localize some fraction of the total strain, the average width of the Coast Ranges is relative constant north of the Western Transverse Ranges lacking a clear correlation with obliquity. Recent seismic work has strengthened the case for a dipping and slowly subducting slab beneath coastal California. Slow subduction provides the most compelling mechanism for the generation of the uniform breadth of the Coast Ranges. In such a model, neutral (e.g. Monterey Bay) and restraining (e.g., Big Sur) segments of the plate boundary are aptly considered lateral and oblique fault ramps that sole onto the plate interface in the subduction zone. Here, we focus our analysis on the Monterey and Big Sur segments of the San Gregorio - Hosgri (SGH) Fault. Paradoxically the intermediate Monterey segment of the SGH fault is restraining geometry with respect to Pacific/North America motion, yet the land surface adjacent to this segment of the fault shows little evidence of horizontal shortening. If the plate boundary is vertical and operates in a vise-like manner, the neutral orientation for a strike-slip fault is predicted to follow a small circle. However, this assumption is invalid if the plate boundary includes a component of subduction. For an oblique subduction boundary, the neutral orientation for a strike-slip fault (defined the strain field) is parallel to the trend of the subduction zone boundary. If this model is correct, then the San Andreas Fault shares characteristic with other oblique subduction zones (e.g. Sumatra) and oblique transform margins (e.g., Queen Charlotte Fault).- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.T23F0447H
- Keywords:
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- 4302 Geological;
- NATURAL HAZARDS;
- 8106 Continental margins: transform;
- TECTONOPHYSICS;
- 8170 Subduction zone processes;
- TECTONOPHYSICS;
- 8175 Tectonics and landscape evolution;
- TECTONOPHYSICS