TERTIARY EXTENSION AND CONTRACTION OF LOWER-PLATE ROCKS IN THE CENTRAL MOJAVE METAMORPHIC CORE COMPLEX, SOUTHERN CALIFORNIA

Several authors recently have proposed the “rolling‐hinge” model for the formation of extensional detachment faults in metamorphic core complexes. In this model, isostatic uplift of the denuded footwall of a major normal fault causes the near‐surface part of the fault to rotate from a higher to a lower dip. For the rolling‐hinge model to be acceptable, the footwalls of detachment faults must have undergone the strain pattern dictated by the rolling hinge. In this paper, the structural development of the footwall of the central Mojave metamorphic core complex is used as a field test. Tertiary structures in the lower plate of the core complex record NE‐directed ductile extensional shear followed by cataclastic NE‐side up shear with a significant component of contraction along the previous extension direction. This strain history agrees with the rolling‐hinge model, and particularly with a version of the model in which footwall uplift occurs by a combination of elastic flexure and flexurally driven upper‐crustal failure. Similar late‐stage layer‐parallel contraction appears to be present in some other tectonically denuded terranes of the Basin and Range, suggesting that the flexural‐failure rolling‐hinge model for extensional terranes may be widely applicable. Copyright 1990 by the American Geophysical Union.