California, with a fault zone running through it, is home to large beds of metamorphic rocks. The Western Metamorphic Belt runs for over 200 miles through the Sierra region and includes a diverse crop of metamorphic rocks that are clues to the complex geological history of the state.
State Rock
Metamorphic rocks are often formed near boundaries of tectonic plates in the Earth's crust. When the plates push against each other, the pressure and heat forms metamorphic rocks. The San Andreas Fault runs through the state of California, leading to an abundance of metamorphic rock. Serpentinite results from the pressure of shearing and is so common in California that it was named the state rock. Some forms of serpentine, the mineral that makes up serpentinite, are used as fire retardants.
Western Metamorphic Belt
The Western Metamorphic Belt extends through the Sierra region for 200 miles. The belt, consisting of many types of metamorphic rocks, was formed in the Paleozoic to Jurassic period along what used to be the western border of North America. There were multiple subduction zones in which one plate slid beneath another, producing the conditions for the formation of large areas of metamorphic rocks. Later, the Franciscan subduction zone formed what is now the coast of California.
Types of Rock in Metamorphic Belt
There are a diverse catalog of metamorphic rocks in the Western Metamorphic Belt. Scientists have had trouble putting together all of the clues to decode the geological history of California. Scientists study the rocks in efforts to determine all of the events that produced the types of rock present, as well as their physical properties. Examples of rock include quartzite, schist, slate, greenstone, serpentinite, chert, marble and phyllite. The rocks have undergone various physical and chemical changes, including mixing with granite and other igneous rocks.
Round Valley
Another major metamorphic outlay includes Round Valley near Bishop, California. The rocks in this region resulted from contact metamorphism, which usually is the product of molten magma or lava. The lava is formed form the intense heat and pressure of two plate boundaries meeting each other. Round Valley has historical significance as being a major source of tungsten during World War I. The tungsten was found in the form of sheelite, a type of metamorphic rock.
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