USArray
A Continental-scale Seismic Observatory

W Idaho Shear

Deformation and Magmatic Modification of a Steep Continental Margin, Western Idaho-eastern Oregon (passive broadband and active source studies)

Principal Investigators and Institutions:

Raymond Russo, (P.I. Passive Broadband study) University of Florida

John Hole, (P.I. Active source study) Virginia Polytechnic Institute

Funding Source:

NSF EarthScope

Field Dates: 

Passive Experiment: 5/2011 – 5/2013

Active Experiment 7/2012 - 9/2012

Equipment Used:

Passive Experiment: Gurlap CMG3T/Raftek130 Datalogger 

Active Experiment: TEXANS

Data Status:

Passive Experiment: Archived 1 Service

Network Code:  

Passive Expoeriment: XT

Description:

Much of the land area of Washington, Oregon, and California was added to continental North America during the last 200 million years. Exactly how this dominantly oceanic lithosphere accreted to the continent is not well understood, although it is clear that the processes involved differed from north to south along North America's former western margin. In the Idaho-Oregon border region, the boundary between oceanic and continental lithospheres is well exposed in a very narrow zone of high deformation known as the western Idaho shear zone. This project is providing insight into how this sharp boundary formed, how it has controlled subsequent deformation and magmatism regionally, and the role it has played in the formation of North America. Because the Oregon-Idaho segment separates distinct styles of mountain building in California and the southern Canadian Cordillera, a better understanding of this complex region is critical for developing a coherent model for the tectonic evolution of western North America and ultimately helping us understand proceses by which continents are created and evolve through time.

Research scientists from the University of Wisconsin, Virginia Tech, The University of Florida, and Washington State University are integrating the results of seismological, geochemical, geochronologic, and structural geologic studies in order to investigate three major issues associated with the evolution of this continental margin: 1) How do fundamental lithospheric structures, such as the continental-oceanic lithosphere boundary exposed in the western Idaho shear zone, guide subsequent deformation and magmatism?; 2) How do magmatism and extensional deformation modify (destabilize) the continental lithosphere, and at what lithospheric levels?; and 3) What are the tectonic implications of this destabilization for evolving magmatism, deformation, and lithospheric strength? A swath of broadband passive seismic instruments and a seismic refraction line will delineate the current geometry of the major geologic units and their boundaries to several hundred kilometers depth. Geochemistry and geochronology will characterize post- western Idaho shear zone magmatism to provide the timing of events and the tectonic context in which these processes occurred. Structural geology will provide the kinematic and dynamic deformation path by which the continent was modified, by defining the major tectonic boundaries and establishing the kinematic history of the major structures.