Gradient franciscain

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Roadcut showing Franciscan chert rock in Glen Canyon Park. The remarkable folding of the stacked layers indicates the tectonic forces that lifted up the coastal mountain ranges, and which warped the originally planar layers of this rock into the fantastic shapes they now present. The chert itself in this area is rich with fossils of radiolarian creatures. ©2007 Eric A. Schiff.
Roadcut showing Franciscan chert rock in Glen Canyon Park. The remarkable folding of the stacked layers indicates the tectonic forces that lifted up the coastal mountain ranges, and which warped the originally planar layers of this rock into the fantastic shapes they now present. The chert itself in this area is rich with fossils of radiolarian creatures. ©2007 Eric A. Schiff.

Un gradient franciscain, ou métamorphisme haute pression-basse température de gradient prograde (parfois aussi appelé métamorphisme franciscain), est un terme géologique désignant un assemblage hétérogène de roches typique de la péninsule de San Francisco ou de ses environs. Le terme de Franciscan Assemblage est dû au géologiste Andrew Lawson, qui nomma également la faille de San Andreas qui retient ce gradient.

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