The geology, geochronology, structure and geochemistry of the Wild Rogue Wilderness remnant of the Coast Range ophiolite, southwest Oregon: Implications for the magmatic and tectonic evolution of the Coast Range ophiolite
Stefan Bernhard Kosanke 2000
A Dissertation submitted to the State University of New York at Albany in partial fulfillment of the requirements for the degree of Doctor of Philosophy
College of Sciences and Mathematics, Department of Geological Sciences
Advisor: G.D. Harper

The Wild Rogue Wilderness ophiolite (WRWO) has been correlated with the Coast Range ophiolite (CRO) and overlying Great Valley Sequence in California. The WRWO occurs on the east limb of a large Cretaceous syncline within a folded thrust sheet. The basement units strike NE, are subvertical and fault bounded and include from east to west: (1) a sheeted dike complex having gabbro screens; (2) a ductily, but heterogeneously deformed metatonalite containing abundant mylonites; (3) a heterogeneously deformed metagabbro having a relic magmatic foliation overprinted by solid-state deformation at amphibolite facies and lower grade conditions; (4) a 0.5-0.9 km wide, high-strain zone consisting of mafic and silicic ultramylonites and mylonites; (5) undeformed pillow basalts cut by mafic and silicic dikes; (6) quartz gabbro to tonalite (Half Moon Bar diorite); (7) poorly exposed metavolcanic rocks, including at least some volcaniclastics in the uppermost section of this unit.
The following events have been identified in the Wild Rogue Wilderness: (1) preophiolite deformation and (regional?) amphibolite facies metamorphism (unit 3; ~171 Ma); (2) formation of the ophiolite, related normal faulting and subseafloor hydrothermal alteration (units 1, 2, and 5; ~164 Ma); (3) Post-ophiolite arc-related magmatism (units 6 and 7; 153-160 Ma); and (4) Nevadan-age ductile deformation (unit 4 and mylonites in units 2 and 3; ~149 Ma).
The trace-element analysis indicates that the WRWO consists of rocks having magmatic affinities to normal mid-ocean ridge basalt island-arc tholeiite, calc-alkaline basalt and boninite. Compositional variations within units and between units cannot be explained with differences in the degree of partial melting and/or fractionation. A highly heterogeneous source is inferred, which was probably variably depleted by previous melting and variably re-enriched with a subduction component.
The evolution of the WRWO is similar to that of the CRO and the Josephine ophiolite, which is consistent with previously proposed models that invoke rifting of the volcanic arc built on western N. America. The geochemical diversity of the WRWO is indicative of formation in a fore-arc or intra-arc setting similar to that of the Miocene Tonga are, SW Pacific. Rift-propagation and melting of heterogeneous, inherited mantle may have played an important role in the magmatic evolution of the WRWO.

Kosanke, S.B., 2000. The geology, geochronology, structure and geochemistry of the Wild Rogue Wilderness remnant of the Coast Range ophiolite, southwest Oregon: Implications for the magmatic and tectonic evolution of the Coast Range ophiolite.
Unpublished PhD dissertation, State University of New York at Albany. 754pp., +xxii (2 vols); 1 folded plate (map)
University at Albany Science Library call number:  SCIENCE MIC Film QE 40 Z899 2000 K67
Copies of this PhD dissertation can be ordered from Proquest UMI

        Front matter (title, table of contents, abstract, acknowledgements) - 0.25MB pdf file
        Photo and figure pages in dissertation (colour and greyscale photos and diagrams with captions): - 44.9MB pdf file

        Plate 1 - Geological map of the Wild Rogue Wilderness, southwest Oregon
                (coloured geological map; scale ~1:24,000) - 1.3MB pdf file
        Simplified geological map and cross-sections of the Wild Rogue Wilderness, with geological age and geochemical affinities of units
            (Figs 2.2a, b; 5.1; 7.2 combination) - 0.3MB pdf file

        Data tables and lists; sample locations:
                Fig 5.1 - Sample locations on simplified geological map
                Table 2.1 -  40Ar/39Ar ages; U/Pb zircon ages
                Tables 3.1-3.4 -  Hornblende compositions and paleotemperature estimates
                Tables 5.1-5.7 -  Major and trace element geochemical compositions of igneous and metaigneous samples
                Appendix A -  Petrographic summary descriptions of samples
                Appendix B -  Age spectra and related diagrams for the 40Ar/39Ar dated samples
                Appendix C -  Electron microprobe compositions of clinopyroxene, plagioclase, and Cr-spinel
                Appendix D -  Fault slip and sense of shear data
                Appendix E -  Quality check of the trace element analysis by ICP-MS at Union College
                Appendix F -  ICP-MS geochemical data for samples (Wild Rogue Wilderness; Snow Camp Mountain; Black Mountain; Llanada)

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