Deep crustal structure of the Cascade Range and surrounding regions from seismic refraction and magnetotelluric data

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

DOI:https://doi.org/10.1029/JB095iB12p19419· OSTI ID:5226760

Stanley, W D ^[1]; Mooney, W D; Fuis, G S ^[2]

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1. Geological Survey, Denver, CO (USA)
2. Geological Survey, Menlo Park, CA (USA)

Analysis of three MT and two seismic refraction profiles in Oregon and a coincident MT and refraction profile in northern California show a high degree of correlation between resistivity and velocity models. The main feature that is evident in both data sets is a highly conductive (2-20 ohm m) zone that occurs at depths of 6-20 km and largely within a midcrustal velocity layer of 6.4-6.6 km/s, overlying a lower crust with velocities of 7.0-7.4 km/s. Although this conductor and the midcrustal zone of 6.4-6.6 km/s velocities are generally rather horizontal, important structures do occur. For instance, near the boundary of Western Cascades and High Cascades the MT midcrustal conductor rises to within 6 km of the surface. In addition, on the coincident MT-refraction profile in northern California a significant westward downdip occurs on both the MT deep conductor and the 6.4-km/s velocity layer, with both occurring at very similar depths. However, in the Columbia Plateau of Washington, no deep crustal conductors occur shallower than 25 km; also, the velocity structure is quite different, with a 6.8-km/s midcrust and a 7.5-km/s lower crust. Complex accretionary structures occur on MT models for the southern Washington Cascades. The accretionary structures in the southern Washington Cascades have been shown to be related to stress release in the area of Mount St. Helens. In order to explain the similar structures in the MT and refraction models for Oregon and California, the authors propose a model involving the effects of metamorphic zonation to produce the velocity structure, combined with metamorphically produced fluids and partial melt to produce the deep conductor.

• OSTI ID: 5226760
• Journal Information: Journal of Geophysical Research; (United States), Vol. 95:B12; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
CALIFORNIA
VOLCANIC REGIONS
OREGON
GEOMORPHOLOGY
WASHINGTON
CASCADE MOUNTAINS
CONTINENTAL CRUST
DATA ANALYSIS
DEPTH
ELECTRIC CONDUCTIVITY
GEOLOGIC MODELS
GEOLOGIC STRUCTURES
MAGNETOTELLURIC SURVEYS
METAMORPHISM
MT ST HELENS
REFRACTIVITY
SEISMIC SURVEYS
STRESS RELAXATION
WAVE PROPAGATION
DEVELOPED COUNTRIES
DIMENSIONS
EARTH CRUST
ELECTRICAL PROPERTIES
ELECTRICAL SURVEYS
ELECTROMAGNETIC SURVEYS
FEDERAL REGION IX
FEDERAL REGION X
GEOLOGY
GEOPHYSICAL SURVEYS
MOUNTAINS
NORTH AMERICA
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
RELAXATION
SURVEYS
USA
580000* - Geosciences