40Ar/39Ar dating of detrital micas from Oligocene-Pleistocene sandstones of the Olympic Peninsula, Klamath Mountains, and northern California Coast Ranges: provenance and paleodrainage patterns

Abstract

Sandstones of the Eocene-Miocene Hoh assemblage of the Olympic Peninsula and Late Oligocene - Miocene Weaverville Formation (Klamath Mountains) were studied to determine if the Hoh sandstones could be tectonically transported equivalents of the Weaverville Formation. Distinct Hoh sandstone types exposed between La Push and the Hoh River include (1) highly brecciated and veined, quartz-poor, mica-poor volcaniclastic sandstone preserved in mélange blocks; and (2) relatively unveined and unbrecciated, quartzose micaceous sandstone preserved in mélange blocks and bounding turbidites. 40Ar/39Ar laser heating analyses of single crystals of detrital muscovite grains from quartzose Hoh sandstones yield Late Cretaceous - early Tertiary ages, consistent with contributions to Hoh detritus from the Idaho batholith. Volcaniclastic mélange block sandstones could be derived from older Tertiary volcanic terranes of the northeast Olympic Peninsula, or from Mesozoic accretionary terranes. Analyses of muscovites from the fluviatile Weaverville Formation of the Klamath Mountains, California, yield Pennsylvanian ages with a possible source within the Klamath Central Metamorphic terrane. No provenance link was detected between the Hoh assemblage and Weaverville Formation. Analyses of muscovites from Pliocene and Pleistocene sandstones of the Wildcat Group of the northern California Coast Ranges yield both Cretaceous - early Tertiary and Pennsylvanian ages, suggesting derivation from both local and distant sources. Although an ancestral "Snake River" paleodrainage system to the Klamath Mountains region was shutoff during Weaverville sedimentation, it may have been reestablished in the Late Miocene when Idaho-derived sediments were again transported to northwestern California.