Abstract
The Upper Jurassic Galice Formation of the Klamath Mountains, OregonCalifornia, overlies the ca. 162-Ma Josephine ophiolite and the slightly younger Rogue–Chetco volcano-plutonic arc complex. The Galice Formation that overlies the Josephine ophiolite consists of a siliceous hemipelagic sequence, which grades upward into a thick turbidite sequence. Bedded hemipelagic rocks and scarce sandstone, however, also occur at several localities within the Josephine ophiolite pillow basalts. Corrected paleoflow current data suggest that the Galice Formation was derived predominantly from the east and north. Detrital modes of sandstones from the Galice Formation indicate an arc source as well as a predominantly chert-argillite source with minor metamorphic rocks. A sandstone located ~20 m below the top of the Josephine ophiolite has detrital modes and heavy mineral suites similar to the turbidite sandstones. Detrital Cr-spinel compositions from the turbidite and intra-pillow lava sandstones are also similar, indicating supra-subduction zone mantle peridotite and volcanic sources. Published detrital zircon data from a turbidite sandstone chiefly give a bimodal age distribution of 153 Ma and ca. 227 Ma but with a minor Proterozoic component. Whole-rock geochemistry from intra-pillow lava sedimentary rocks, the hemipelagic sequence, and the turbidites suggest a mixture between mafic and cratonic sources. It is suggested that the source area for the intra-pillow lava sedimentary rocks, hemipelagic sequence, and turbidites resulted from the mixing of arc and accreted terranes. These data indicate that the source areas for the Galice Formation were already established by ca. 162 Ma, probably during a Middle Jurassic orogeny that predated formation of the Josephine basin.
Published Version
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