Crustal Structure of Strike-slip Fault Systems from a down-plunge section in the eastern Chugach Mountains, Alaska

University Of New Orleans, New Orleans LA

Investigators

Abstract

Near-surface fault patterns of strike-slip systems are now reasonably well understood, in large part because of extensive societal interest (seismic hazard) and a wealth of subsurface information obtained from petroleum exploration. What happens to these faults at depth, however, is poorly understood. One approach to resolve these questions is geophysical imaging, but these studies are expensive and typically ambiguous because of imaging problems of structures ranging from low to high angle in crystalline rocks that often lack sufficient variation in physical properties for clear imaging. A much higher resolution technique to resolve these issues is to examine well-exposed down-plunge sections of strike-slip shear zones. Such a structure exists in eastern Chugach Mountains of southern Alaska, and this project proposes to examine this structure in detail to investigate the three-dimensional architecture of strike-slip systems at mid to lower crustal depths. Previous NSF funded research by the PI and V.B. Sisson has documented the structural geometry of the lower and upper portions of the system, but a mid-crustal portion of the system has not been examined in detail. In light of recent theoretical developments (e.g. Teyssier et al., in press) the PI's initial conclusions require re-evaluation because the classic hypothesis of steep shear zones penetrating through the crustal column predicts a different geometry than a crustal column in which the upper and lower crust are detached along a broad zone of distributed flow. This project will test these alternative predictions through a combination of field structural studies, kinematic analyses (finite and incremental strain, shear-sense determination, and strain path information through growth fibers and development of quartz LPO's).