Title

Controls on Fault Geometry During Early Stages of Extension in the Larkspur Hills, Northwest Basin and Range

Presenter Information

Diana Strickley
Anne Egger

Document Type

Oral Presentation

Location

SURC Room 140

Start Date

15-5-2014

End Date

15-5-2014

Keywords

Fault initiation, Pre-existing structures, extension

Abstract

Detailed analyses of normal faults in domains of the Larkspur Hills, northwest Basin and Range, offer insight into factors controlling fault initiation, growth, and distribution in extensional regimes. N-trending faults in the southernmost domain share trends of major range-bounding structures and Pliocene linear volcanic vents; in contrast, NNW- and NNE- trending faults dominate further north and into south-central Oregon. Stress analyses and comparison with experimental and field data suggest that preexisting structures control fault geometries in the northern domains, while faults form perpendicular to σ3 in the southern domain. NNW-trending structures were favorably oriented to slip under E-W extension, so reactivated and continued as the dominant fault orientation in northern domains. NNE structures have the most offset, however, possibly due to pre-existing NE-oriented structures that reactivated as links between newer segments, forming structures with zig-zag traces and an average orientation optimal to slip. The change in fault orientations is abrupt, occurring across a major NNE structure. A regional transition is thus captured within the Larkspur Hills, suggesting they overlie a structural boundary at depth that separates isotropic crust from crust with a pre-existing NW-trending fabric.

For her work on this project, Diana Strickley was nominated for the SOURCE 2014 Scholar of the Year Award.

Faculty Mentor(s)

Egger, Anne

Additional Mentoring Department

Geological Sciences

This document is currently not available here.

Share

COinS
 
May 15th, 1:50 PM May 15th, 2:10 PM

Controls on Fault Geometry During Early Stages of Extension in the Larkspur Hills, Northwest Basin and Range

SURC Room 140

Detailed analyses of normal faults in domains of the Larkspur Hills, northwest Basin and Range, offer insight into factors controlling fault initiation, growth, and distribution in extensional regimes. N-trending faults in the southernmost domain share trends of major range-bounding structures and Pliocene linear volcanic vents; in contrast, NNW- and NNE- trending faults dominate further north and into south-central Oregon. Stress analyses and comparison with experimental and field data suggest that preexisting structures control fault geometries in the northern domains, while faults form perpendicular to σ3 in the southern domain. NNW-trending structures were favorably oriented to slip under E-W extension, so reactivated and continued as the dominant fault orientation in northern domains. NNE structures have the most offset, however, possibly due to pre-existing NE-oriented structures that reactivated as links between newer segments, forming structures with zig-zag traces and an average orientation optimal to slip. The change in fault orientations is abrupt, occurring across a major NNE structure. A regional transition is thus captured within the Larkspur Hills, suggesting they overlie a structural boundary at depth that separates isotropic crust from crust with a pre-existing NW-trending fabric.

For her work on this project, Diana Strickley was nominated for the SOURCE 2014 Scholar of the Year Award.