Geologic sketch of the Klamath Mountains and Coast Ranges of northern California and southern Oregon
No abstract available.
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Research about Klamath Mountains
Source-linked reports with geographic coverage including Klamath Mountains.
Submarine chert-argillite slide-breccia of Paleozoic age in the southern Klamath Mountains, California
A unique chert-argillite breccia—a breccia with an argillite matrix, in which nearly all the fragments are chert—underlies an area of at least 60 sq mi in the southern Klamath Mountains of California. Rocks of this composition have not been reported previously, in the Klamath Mountains or elsewhere, but in northwestern Trinity County they make up a large part of the western Paleozoic and Triassic belt. The remainder of the belt consists of northerly trending sinuous zones of two other principal lithologies: radiolarian chert, rhythmically interbedded with slate or phyllite, crops out in three zones in the eastern, central, and western parts of the area; and massive metabasalt and metadiabase intruded by gabbro and serpentinite occur in a zone about 3 mi wide in the eastern part of the area. Although the predominance of chert fragments makes the chert-argillite breccia apparently unique, rocks that are generally similar, consisting of angular to subangular clasts in a pelitic matrix, have been studied in many localities. Field relations and petrographic features of the chert-argillite breccia—specifically the angularity of clasts, absence of a sandy matrix, preservation of Radiolaria in both chert clasts and pelitic matrix, presence of contorted flow laminae in the matrix, large size of some of the exotic blocks, close association with chert, pillow lava, and limestone, absence of stretching or slickensiding of clasts, and overall dimensions of the unit measurable in miles—variously preclude origin of the rock as a normal sedimentary conglomerate, a tectonic breccia, a tillite, or a subaerial mudflow, but include features common to numerous submarine-slide deposits. We interpret the chert-argillite breccia as the result of uplift and subsequent sliding of a thick deposit of inter-layered chert and pelitic ooze. Brittle fracturing of the chert and mobilization of water-saturated ooze produced the observed features. Fossiliferous limestone blocks within the slide-breccia indicate that it is no older than Silurian or Devonian, and it predates Jurassic metamorphism and plutonism. The relation of the breccia to a major northwest-trending fault zone, and to serpentinite within this zone, suggests that the formation of the breccia was generally synchronous with the faulting and ultramafic intrusion. Rocks of the central metamorphic belt, east of the mapped area, were metamorphosed during a Devonian orogeny, and we suggest that the submarine slide-breccia was formed as a frontal effect of the same orogeny.
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Blueschist metamorphism in the Yreka-Fort Jones area, Klamath Mountains, California
Blueschist is plentiful in the Yreka-Fort Jones area, eastern Klamath Mountains, adjacent to a belt of serpentinite that marks the boundary between two fundamental lithologic units, an eastern belt of early Paleozoic sedimentary and metamorphic rocks, and a western greenstone-chert assemblage of late Paleozoic and Triassic(?) age. The blueschists, which contain lawsonite and glaucophane or crossite, occur with phyllitic quartzite and siliceous phyllite of the Stuart Fork Formation, which is overthrust northwestward on the greenstone-chert terrane. The blueschist facies metamorphism probably was synchronous with Middle and Late Jurassic metamorphism of the Stuart Fork Formation. The blueschist-serpentinite terrane possibly marks the site of collision between the eastern Klamath plate and an oceanic western Paleozoic and Triassic plate.
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Isotopic age of the Nevadan Orogeny and older Plutonic and metamorphic events in the Klamath Mountains, California
Several metamorphic and plutonic events have been recognized in the Klamath Mountains utilizing potassium-argon and rubidium-strontium mineral and whole-rock ages. The oldest known metamorphic event in the region produced the Abrams Mica Schist and the co-extensive Salmon Hornblende Schist. Strontium evolution diagrams indicate that the age of primary metamorphism of the Abrams Mica Schist is approximately 380 m.y. (Devonian). The Stuart Fork Formation of Davis and Lipman (1962), the schists of Condrey Mountain, and related schists were produced during a Middle and Late Jurassic metamorphic event. Granitic plutonic rocks are divided into four groups that are different in age and somewhat different in chemical characteristics. The oldest pluton, the Pit River stock, has a minimum age of 246 m.y. (Permian) and is grouped with the Castle Crags pluton. The other three plutonic groups are Middle and Late Jurassic and are characterized by the following ranges in isotopic age: 165 to 167 m.y., 145 to 155 m.y., and 127 to 140 m.y. The principal lode gold deposits in the California part of the Klamath Mountains seem to be related to the youngest group of plutons. If the Nevadan orogeny in this area is restricted to a Middle and Late Jurassic deformational, metamorphic, and plutonic event, the orogeny includes the emplacement of plutons of the three younger groups and the metamorphic development of the Stuart Fork Formation, schists of Condrey Mountain, and related schists.
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