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Abstract: The Coast Range Ophiolite Debate - A Perspective from its Northern Neighbor, the Josephine Ophiolite, SW Oregon


In contrast to the controversy surrounding the origin of the Coast Range ophiolite, the origin of the Josephine ophiolite is well constrained. Given that the two ophiolites are similar in many ways, a clear understanding of the Josephine ocean basin may provide an analogy for the Coast Range ophiolite and its basin. The past 25 years of research in the region has shown that the Josephine ophiolite formed in a suprasubduction ocean basin along the margin of western North America. The discovery of a screen of Rattlesnake Creek terrane rocks contained within the Josephine ophiolite provides unequivocal proof that this basin formed when older Klamath Mountains terranes rifted apart between 170 and 162 Ma. Structural and faunal evidence suggest that the Josephine ophiolite spreading ridges were north-south directed which must have carried the Rattlesnake Creek screen and an overlapping island arc complex (the Rogue arc) northward relative to the older Klamath Mountains terranes. Thus, the Late Jurassic geometry of the Josephine basin may have looked very similar to the modern Andaman Sea region with an elongate transform dominated basin (the Josephine ophiolite) bordered on the north and south by active arcs constructed on older oceanic material (the Rogue arc and older Klamath terranes). Carrying this further, the Coast Range ophiolite basin may have formed in an analogous setting with the Klamath and Sierran terranes forming its northern and eastern borders, respectively. Under this scenario the paired Coast Range ophiolite-Josephine ophiolite basin system may have represented approximately 2000 kilometers of the interarc, and fore-arc region of the Cordilleran plate edge.

Search and Discovery Article #90945©1997 AAPG Pacific Section Meeting, Bakersfield, California