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McCarthy, Jill, 1987

Seismic reflection imaging of plate boundaries: Examples from the central Aleutians, the north Atlantic, and the Basin and Range Province of the western U.S.

Bibliographic Reference

McCarthy, Jill, 1987, Seismic reflection imaging of plate boundaries: Examples from the central Aleutians, the north Atlantic, and the Basin and Range Province of the western U.S.: Palo Alto, California, Stanford University, Ph.D. dissertation, 155 p., illust., maps.


This thesis uses the seismic reflection technique to study the processes controlling the structural and geologic evolution of convergent and strike-slip margins, oceanic spreading centers, and continental rift zones. Studies from four separate tectonic settings are presented: the central Aleutian subduction complex, the paleo-North Atlantic spreading center, and the basin and Range extensional province. Seismic reflection studies from the central Aleutians subduction complex document the importance of both sediment accretion and sediment subduction in the evolution of this rapidly converging plate margin. The accreted sediment can be divided into a few discrete structural blocks that each have their own internal structure, including monoclinal sequences, antiforms, synforms, and faulted folds. Underlying this accreted complex, and separated by an acoustically defined decollement surface, is a 1-km-thick section of underthrust trench fill overlying oceanic lithosphere. Structural associations imaged on the seismic reflection profiles indicate that subduction of the igneous oceanic crust, with its rough, irregular surface, may also promote the development of structures observed in the accretionary prism. A seismic reflection study in the western North Atlantic images steeply dipping reflections or packets of reflections, continuous laterally for up to 5-7 km, that terminate downdip against the subhorizontal reflection Moho. These reflections are ascribed to mafic-ultramafic layering preserved in the dominantly gabbroic oceanic crust. The lithologic contacts mapped on the reflection profile combined with thermal modeling are used to constrain the geometry of the Mesozoic magma chamber responsible for this observed layering. Reflection profiles from the northern Snake Range metamorphic core complex of eastern Nevada provide new constraints to the processes associated with continental extension in both the upper and lower crust of this highly extended region. The lack of a reflection from the northern Snake Range decollement and the predominant subhorizontal reflectivity ranging from 4.0 s to the Moho suggest that extension has not been localized along a major low-angle normal fault, but has been distributed throughout the entire crust down to the Moho. Magmatism and intrusion associated with extension are also inferred.

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