Coast Range Ophiolite

Coast Range Ophiolite
Stratigraphic range: middle Jurassic to late Jurassic
Type igneous, metamorphic
Underlies Franciscan Formation, various Great Valley Sequence formations
Overlies basement
Lithology
Primary basalt, gabbro, peridotite, schist
Location
Region California Coast Ranges
Country United States
Type section
Named for California Coast Ranges

The Coast Range Ophiolite is an ophiolite of Middle to Late Jurassic age located in the California Coast Ranges. They form the basement of the extreme western margin of central and northern California. Exposures straddle the coast from Santa Barbara County up to San Francisco. The formation then trends inland up to the southern end of the Klamath Mountains.[1]

It is arguably the most extensive ophiolite terrane in the United States, and is one of the most studied ophiolites in the North America; however, Canada has many much larger and more famous ophiolites, including the one at Gros Morne National Park.

Description

As indicated by the name, the ophiolite is defined by the presence of ultramafic rocks in the California Coast Ranges. Pillow lavas and oceanic basalts are among the most common rocks found within the formation. There are a number of exposures that straddle the Mohorovičić discontinuity. Metamorphosed peridotite, in the form of a serpentine rock, is an indicator of the formation.[2]

Distribution

In general, the ophiolite is exposed near the boundary between the sequences of rocks associated with the Coast Ranges, and rocks associated with the Great Valley Sequence. Where it is exposed, it generally underlies the various sedimentary rocks of the Great Valley Sequence, and may be coextensive with the contemporaneous (but slightly younger on average) Franciscan Assemblage, as would be expected by an observational application of the law of superposition. However, in many localities, the ultramafic rocks of the ophiolite can be found intruding or on top of the local country rock.[1]

Origin and Tectonics

The Coast Range Ophiolite is characterized by obduction of oceanic crust onto land.[3] Most of the rocks in the ophiolite were part of an accretionary wedge on the continental margin of Laurasia that was thrust onto land during the Jurassic through the influence of subduction.[4] The exact origins of the rocks found in the ophiolite are a matter of debate; some geologists hypothesize that the rock primarily consist of mid-ocean lithosphere, while others assert different ideas related to island arc terranes associated with the Nevadan orogeny.[5]

See also

References

  1. 1 2 Bailey, et al.
  2. Bailey, et al.
  3. Shervais
  4. Encyclopedia Britannica
  5. Dickinson et al.

Sources


Jurassic Period
Lower/Early Jurassic Middle Jurassic Upper/Late Jurassic
Hettangian | Sinemurian
Pliensbachian | Toarcian
Aalenian | Bajocian
Bathonian | Callovian
Oxfordian | Kimmeridgian
Tithonian
Preceded by Proterozoic Eon Phanerozoic Eon
Paleozoic Era Mesozoic Era Cenozoic Era
Cambrian Ordovician Silurian Devonian Carboniferous Permian Triassic Jurassic Cretaceous Paleogene Neogene 4ry
This article is issued from Wikipedia - version of the Friday, December 04, 2015. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.