STRAIN ACCOMMODATION ABOUT STRIKE-SLIP-FAULT DISCONTINUITIES IN GRANITIC ROCK UNDER BRITTLE-TO-DUCTILE CONDITIONS

Brittle and ductile structures adjacent to fault terminations and eche lon fault steps of left-lateral strike-slip faults in the Lake Edison Granodiorite of the central Sierra Nevada, California are related to s tress perturbations caused by fault slip. The structures associated wi th fault terminations change from dilatant splay fractures only, to sp lay fractures and ductile fabrics on opposing sides of the fault, to d uctile fabrics ahead of the fault with decreasing distance from a youn ger neighboring pluton and, presumably, with increased temperatures. T he distributions of deformation mechanisms correlate with the inferred local magnitudes and spatial distributions of the maximum tensile str ess, the mean stress, and the maximum shear stress. Displacements alon g the faults are transferred across echelon stepovers by mineralized d ilatant fractures in extensional steps. To accommodate slip transfer a cross contractional steps, rock apparently was squeezed vertically out of the step by ductile flow; concentrations of mobile and immobile el ements indicate that diffusive mass transfer was not significant. Incr eased mean stress in contractional steps apparently enhanced crystal-p lastic how of quartz. A how law that includes a pressure effect throug h correlation with pressure-dependent solidus temperatures is more suc cessful than other experimentally derived flow laws in predicting the observed distribution of ductile fabrics.