The Franciscan Assemblage is a geological term for an accreted terrane of heterogeneous rocks found on and near the San Francisco Peninsula. Geology (from Greek γη gê, "earth" and λόγος Logos, "speech" lit A terrane in Geology is a fragment of crustal material formed on or broken off from one Tectonic plate and accreted — " sutured " In Geology, rock is a naturally occurring aggregate of Minerals and/or Mineraloids The Earth's outer solid layer the ‘ Lithosphere The San Francisco Peninsula in California separates the San Francisco Bay from the Pacific Ocean. It was named by geologist Andrew Lawson who also named the San Andreas Fault which bounds the Franciscan Assemblage. Andrew Cowper Lawson (1861-1952 was a professor of geology at the University of California Berkeley. The San Andreas Fault is a geologic Transform fault that runs a length of roughly 800 miles (1300 km through California in the United States.
Also known as the "Franciscan Formation," "Franciscan Series," "Franciscan Group," "Franciscan assemblage," or "Franciscan Complex," it includes altered mafic volcanic rocks (greenstones), deep-sea cherts, greywacke sandstones, limestones, serpentinites, shales, and high-pressure metamorphic rocks, all of them faulted and mixed in a seemingly chaotic manner. Mafic is an adjective describing a Silicate mineral or rock that is rich in magnesium and iron the term was derived by contracting "magnesium" and "ferric" Plate tectonics and hotspots Divergent plate boundaries At the Chert (ˈtʃɝt is a fine-grained Silica -rich Microcrystalline, Cryptocrystalline or Microfibrous Sedimentary rock that may contain Greywacke ( German grauwacke, signifying a grey earthy rock is a variety of Sandstone generally characterized by its hardness dark color and poorly-sorted Sandstone is a Sedimentary rock composed mainly of Sand -size Mineral or rock grains. Limestone is a Sedimentary rock composed largely of the Mineral Calcite ( Calcium carbonate: CaCO3 Serpentinite is a rock composed of one or more Serpentine Minerals Minerals in this group are formed by serpentinization a hydration and metamorphic Shale (also called mudstone) is a fine-grained Sedimentary rock whose original constituents were Clay minerals or Muds It is characterized by Metamorphic rock is the result of the transformation of an existing rock type the protolith, in a process called Metamorphism, which means "change In Geology a fault, or fault line, is a planar rock fracture which shows evidence of relative movement
It forms the major component of the Pacific Coast Ranges of California. The Pacific Coast Ranges are the series of Mountain ranges that stretch along the west coast of North America from Alaska to northern and central Mexico California ( is a US state on the West Coast of the United States, along the Pacific Ocean.
Wentworth and others (1984) interpreted the juxtaposition of the Franciscan Assemblage and the section consisting of the Coast Range ophiolite and the Great Valley sequence to have happened through landward movement of the Franciscan Assemblage as a tectonic wedge. An Ophiolite is a section of the Earth's Oceanic crust and the underlying upper mantle that has been uplifted or emplaced to be exposed within Continental This article discusses the geologic usage for the philosophical or architectural usage see Architectonics ' Or see Plate tectonics.
References
- Wentworth, C. M. , Blake, M. C. Jr. , Jones, D. L. , Walter, A. W. , and Zoback, M. D. 1984. Tectonic wedging associated with emplacement of the Franciscan assemblage, California Coast Ranges. In Blake, M. C. , ed. , Franciscan geology of northern California. Pacific Section, Society of Economic Paleontologists and Mineralogists, Field Trip Guidebook 43, p. 163-173.
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