ROCK FABRIC ANALYSIS OF THE SIERRA CREST SHEAR ZONE SYSTEM, CALIFORNIA: IMPLICATIONS FOR CRUSTAL-SCALE TRANSPRESSIONAL SHEAR ZONES

Abstract

Crustal-scale tabular shear zones are common features of transpressional orogens and arcs. Though foliation development in shear zones is well understood, the development of another rock fabric element, lineation, is not. Computer modeling shows that monoclinic solutions for lineations are unstable; triclinic models better explain the variation of lineation in natural transpressional zones. This thesis investigates an example of natural lineation variation in three segments of the Sierra Crest shear zone system, Sierra Nevada, California. Field data collected during large-scale mapping indicate an early (Paleozoic?) generation of deformation overprinted by a Cretaceous, dextral, reverse (west-over east), steeply-dipping shear zone active for ~20 Ma. A third generation of deformation overprints previous fabrics. Estimates of shear zone volume reduction are correlated with volumetrically-complementary emplacement of the Sierra Nevada batholith across strike. Disagreement between single-domain model predictions and field observations is interpreted as being due to heterogeneous strain localization on many scales.