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.Bailey, et al. It is arguably the most extensive ophiolite terrane in the United States, and is one of the most studied ophiolites in the North America.

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 ancient

Mohorovičić discontinuity The Mohorovičić discontinuity ( , ), usually referred to as the Moho discontinuity or the Moho, is the boundary between the Earth's crust and the mantle. It is defined by the distinct change in velocity of seismic waves as they pass through ch ...

. Metamorphosed

peridotite Peridotite ( ) is a dense, coarse-grained igneous rock consisting mostly of the silicate minerals olivine and pyroxene. Peridotite is ultramafic, as the rock contains less than 45% silica. It is high in magnesium (Mg2+), reflecting the high prop ...

, in the form of a

serpentine Serpentine may refer to: Shapes * Serpentine shape, a shape resembling a serpent * Serpentine curve, a mathematical curve * Serpentine, a type of riding figure Science and nature * Serpentine subgroup, a group of minerals * Serpentinite, a ...

rock, is an indicator of the formation.

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 The Franciscan Complex or Franciscan Assemblage is a geologic term for a late Mesozoic terrane of heterogeneous rocks found throughout the California Coast Ranges, and particularly on the San Francisco Peninsula. It was named by geologist Andrew ...

, 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 Country rock is a genre of music which fuses rock and country. It was developed by rock musicians who began to record country-flavored records in the late 1960s and early 1970s. These musicians recorded rock records using country themes, vocal s ...

Origin and Tectonics

The Coast Range Ophiolite is characterized by obduction of oceanic crust onto land. Most of the rocks in the ophiolite were part of an accretionary wedge on the continental margin of

Laurasia Laurasia () was the more northern of two large landmasses that formed part of the Pangaea supercontinent from around ( Mya), the other being Gondwana. It separated from Gondwana (beginning in the late Triassic period) during the breakup of Pan ...

that was thrust onto land during the Jurassic through the influence of subduction. The exact origins of the rocks found in the ophiolite are a matter of debate; some geologists hypothesize that the rock primarily consists of mid-ocean lithosphere, while others assert different ideas related to island arc terranes associated with the

Nevadan orogeny The Nevadan orogeny occurred along the western margin of North America during the Middle Jurassic to Early Cretaceous time which is approximately from 155 Ma to 145 Ma. Throughout the duration of this orogeny there were at least two different ki ...

.Dickinson et al.

References

Sources

* *{{cite Q, Q97990697, author-mask1=Dickinson, W. R., , author-mask2=Hopson, C. A., , author-mask3=Saleeby, J. B., , author-mask4=Schweickert, R. A., , author-mask5=Ingersoll, R. V., , author-mask6=Pessagno Jr, E. A., , author-mask7=Mattinson, J. M., , author-mask8=Luyendyk, B. P., , author-mask9=Beebe, W., , author-mask10=Hull, D. M., , author-mask11=Muñoz, I. M. & , author-mask12=Blome, C. D. *Shervais, J. (n.d.). John W. Shervais: Research Projects - Ophiolites and Oceanic Crust. Retrieved September 6, 2014. Ophiolites Natural history of the California Coast Ranges Ophiolite, Coast Range Jurassic California Middle Jurassic North America Late Jurassic North America Geologic formations of California Geology of Monterey County, California Geology of San Francisco Geology of San Luis Obispo County, California Geology of Santa Barbara County, California Geology of California

Description

Distribution

Origin and Tectonics

See also

References

Sources