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News: Underwater caves off Yucatan yield three old skeletons—remains date to 11,000 B.C.
http://www.edgarcayce.org/am/11,000b.c.yucata.html
 
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Metamorphism

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Author Topic: Metamorphism  (Read 1691 times)
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Rebecca
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« on: May 29, 2007, 10:55:49 pm »



Contact Metamorphism:
>>>High Temp./Low Pressure
>>>Typical Rocks: hornfels, quartzite, marble, skarn
     Contact metamorphism occurs in the " country rock" (the rock intruded by and surrounding an igneous intrusion). Rocks are " baked" into a ceramic from heat escaping from intrusives, often enhanced by hydrothermal fluids. The intensity of metamorphism decreases with distance from the intrusion, until at some distance away the rock is unaltered country rock.
     The metamorphism often occurs in aureoles, or zones surrounding the intrusion. Close to the intrusion is the hydrothermal (or metasomatic) aureole where minerals from the hot fluids have their greatest effect. Further away is the thermal aureole where heat is the primary effect. The dimensions of the aureoles are dependent on the size of the intrusive body and the amount of water present. In the absence of fluids, the aureole is very small.
     The assemblage of new minerals that grow in the country rock depend on the composition of the country rock. For a complex sedimentary parent of sandstones and shales, anhydrous (without water) minerals such as garnet and pyroxene occur closest to the intrusion, then hydrous (water rich) minerals such as amphibole and epidote, and at the lowest intensity, chlorite and serpentinite occur.
     When an magma intrudes into carbonates such as limestone and dolostone the carbonate reacts with silica from the hydrothermal fluids to form SKARN. Many special lime-bearing silicate minerals form here.
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