10.6: Chapter Summary — Read — Invisible Network

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10.1 Assembling a Continent

The Klamath Mountains have historical significance in the development of the idea of terrane accretion.
Terranes are composed of ancient island arcs.
Melange forms through the accretion of sediments and other oceanic crustal rocks in an accretionary wedge.
The Klamath Mountains are composed of several accreted terranes, with a general pattern of alternation between terrane and mélange.
Large east-dipping thrust faults separate terranes.
The sequence of terranes in the Klamath Mountains is similar to the sequence of terranes in the Sierra Nevada.

The McCloud Limestone formed in a coral reef during the Permian Period.
Permian coral reef communities were composed of many species that went extinct in the end-Permian mass extinction.
Comparison of fossil species found in different geologic units can help geologists understand the paleoenvironment.

Obduction is the uplift of oceanic lithosphere onto continental lithosphere and it is less common by far than subduction.
The Josephine Ophiolite formed in a back-arc basin and was obducted when a tectonic change resulted in the collapse of the back-arc basin and accretion of the island arc.
Ophiolites themselves are rare, but the ophiolite sequence makes up most of the crust on earth (the oceanic crust).
The ophiolite sequence forms as magma cools within a magma chamber and lava erupts on the ocean floor at mid ocean ridges (or back-arc spreading ridges).
The ultramafic chemistry of ophiolites produce unique soils and correspondingly unique ecosystems.

The story of the Klamath mountains involves alternation of island arc volcanism and continental arc volcanism.
Continental arc volcanism resulted in emplacement of plutons that cross-cut older accreted terranes.
Dating of plutons in combination with cross cutting relationships allows for the dating of accretion events.
Zoned plutons result from the slow cooling of magma chambers from outside inwards.

During the Cretaceous Period, when the Sierra Nevada volcanic arc was forming, the Klamath province was part of the forearc basin, much like the Great Valley.
The topographic difference between the Klamath Mountains and the Great Valley is the result of Neogene uplift.
The uplift of the current mountain range is a much younger event than the events involving the accretion of the bedrock.
Normal faults in the southern Klamath, such as the La Grange Fault contributed to mountain uplift.
The Weaverville Formation is composed of sedimentary fill formed in Neogene grabens and basins.
Glacial erosional features formed during the Pleistocene Epoch.
Small glaciers were still present in the Klamath Mountains at the start of the 21st century.

10.6: Chapter Summary is shared under a CC BY-NC 4.0 license and was authored, remixed, and/or curated by Emily Wright.