Date of Award

2006

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Geology

Abstract

This dissertation consists of four independent, yet related projects: (1) the petrology, geochemistry, and original tectonic setting of the Galice Formation, Klamath Mountains, Oregon-California; (2) the geochemistry, tectonic setting, and possible regional correlations of the Iron Mountain and Esmeralda Peaks units of the Ingalls ophiolite complex, central Cascades, Washington; (3) the provenance and original tectonic setting of sedimentary serpentinites and ophiolite breccias within the sedimentary rocks of the Ingalls ophiolite complex; and (4) geology, tectonics, and possible regional correlations of pre-Cenozoic rocks, central Cascades, Washington. This research indicates that the Galice Formation represents continuous Late Jurassic deposition (Oxfordian-Kimmeridgian), within the Josephine backarc basin. Source; areas for the Galice Formation included active Jurassic arcs, older Klamath terranes, and the North American craton. The Early Jurassic Iron Mountain unit of the Ingalls ophiolite complex originated as a seamount in close proximity to an oceanic spreading ridge. The Late Jurassic Esmeralda Peaks unit of the Ingalls ophiolite complex originated in a backarc basin that included a fracture zone. The Iron Mountain unit is the rifted basement of the Esmeralda Peaks unit, and both units correlate to similar rocks within the Klamath Mountains. Cr-spinel compositions, geochemistry, and petrography indicate that sedimentary serpentinites and ophiolite breccias within the Ingalls sedimentary rocks were locally derived. These rocks were originally deposited in a Late Jurassic fracture zone. The Manastash inlier consists of the Hereford Meadow amphibolite, Lookout Mountain Formation, Quartz Mountain stock, and Helena-Haystack mélange. Hereford Meadow amphibolite is, in part, a dismembered pre-Jurassic ophiolite that originated in a supra-subduction zone setting. The Lookout Mountain Formation is Late Jurassic in age, had cratonic sources, and was originally located in the Klamath Mountains region, Oregon-California. The Quartz Mountain stock is Late Jurassic in age, and the remnants of an island arc. The Helena-Haystack mélange is a major suture between Cascade terranes, and suggests that ∼98 km of right-lateral displacement has occurred along the Straight Creek fault. The De Roux unit consists of metaigneous and metasedimentary rocks. Metaigneous rocks have calc-alkaline, within-plate, and mid-ocean ridge basalt affinities. The De Roux unit correlates with other Cascade mélanges.

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