Paleomagnetic rotations and the Cenozoic tectonics of the Cascade Arc, Washington, Oregon, and California

Journal Article · Sat Nov 10 04:00:00 EST 1990 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/JB095iB12p19409· OSTI ID:5195891

Wells, R E ^[1]

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1. Geological Survey, Menlo Park, CA (USA)

Paleomagnetic results from Cenozoic (62-12 Ma) volcanic rocks of the Cascade arc and adjacent indicate that moderate to large clockwise rotations are an important component of the tectonic history of the arc. Two mechanisms of rotation are suggested by the regional pattern of paleomagnetic rotations. The progressive increase in rotation toward the coast in arc and forearc rocks results from distributed dextral shear, which is likely driven by oblique subduction of oceanic plates to the west. Simple shear rotation is accommodated in the upper crust by strike-slip faulting. The right-lateral Mount St. Helens seismic zone may be an active manifestation of this process. Dextral shear probably obscures a subequal contribution to arc and forearc rotation that is driven by intraarc or backarc extension. This rotation is suggested by the average southward increase in continental margin rotations into the region outboard of the Basin and Range. The southward increase in rotation parallels a change in the arc tectonic regime from largely compressional in northern Washington to extensional in Oregon. Concomitant with this change is a southward increase in the volume of eruptive rocks and the number of basaltic vents in the arc. A progressive eastward shift of the arc volcanic front with time in the rotated arc terrane is the result of the westward pivoting of the arc block in front of a zone of extension since Eocene time. Westward migration of bimodal Basin and Range volcanism since at least 16 Ma is tracking westward rotation of the frontal arc block and growth of the Basin and Range in its wake.

• OSTI ID: 5195891
• Journal Information: Journal of Geophysical Research; (United States), Journal Name: Journal of Geophysical Research; (United States) Vol. 95:B12; ISSN 0148-0227; ISSN JGREA
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
CALIFORNIA
CASCADE MOUNTAINS
CENOZOIC ERA
COMPRESSION
CONTINENTAL MARGIN
DEVELOPED COUNTRIES
EARTH CRUST
EOCENE EPOCH
FEDERAL REGION IX
FEDERAL REGION X
GEOLOGIC AGES
GEOLOGIC FAULTS
GEOLOGIC FRACTURES
GEOLOGIC HISTORY
GEOLOGIC STRUCTURES
IGNEOUS ROCKS
MAGNETISM
MOTION
MOUNTAINS
MT ST HELENS
NORTH AMERICA
OCEANIC CRUST
OREGON
PALEOMAGNETISM
ROCKS
ROTATION
SEDIMENTARY BASINS
SLIP
SUBDUCTION ZONES
TECTONICS
TERTIARY PERIOD
USA
VOLCANIC REGIONS
VOLCANIC ROCKS
WASHINGTON