Structure contour diagram of the weathered surface atop the San Bernardino Mountains: Supplement 5 from "The neotectonics of the San Bernardino Mountains and adjacent San Andreas Fault : a case study of uplift associated with strike-slip fault systems" (Thesis)

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The San Bernardino Mountains have uplifted over the last few million years at the hub of structural systems along the southern San Andreas fault zone and represent an excellent opportunity to study the interplay between orogeny and transpressive strike-slip faulting. To attain a better understanding of the complex architecture of deformation in this range, I have constrained several basic kinematic aspects of its development. First, the timing and magnitude of rock uplift and exhumation of fault blocks have been constrained using the thermochronometry of radiogenic helium in apatite (Chapter 2). This has shown that small crustal slivers within the San Andreas fault zone were exhumed several kilometers over the last few million years, due to slip-partitioning along geometrically-complex, high-angle faults. Second, a detailed constraint on the vertical deformation field of the largest fault block in the range has been determined using a deeply weathered granite surface as a structural datum (Chapter 3). A structural analysis of this deformation pattern has provided the total displacements, slip rates, and subsurface geometries of the major thrust faults within the range (Chapter 4). As a whole, the San Bernardino Mountains appear to have uplifted within a complex system of both high and low-angle faults. The total horizontal plate motion accommodated by this uplift is on the order of 6 km and is focused tightly about a restraining bend in the San Andreas fault zone at San Gorgonio Pass. This suggests the entire range has been built due to convergence associated with a small geometric perturbation of a major strike-slip system. To acquire a different perspective on the relationship of strike-slip faulting and uplift, I have also studied the deformation pattern around a restraining bend resulting from a single fault rupture. Structural analysis of surficial breaks at a slip gap during the 1992 Landers earthquake has revealed how complex, secondary thrust and normal faulting were induced to accommodate simple strike-slip motion where a through-going connection between two dextral fault segments has yet to develop (Chapter 5). This illustrates a single episode in the incremental evolution of a transpressive orogenic system.

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