GEOL 104 Lecture : GEOL 104 Lect6
17 Feb 2012
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Heat is needed to speed up chemical reactions. Metamorphism occurs at about ~100c to 800c - above 800c we have melting. Sometimes the geothermal gradient isnt followed, such as when a. Lithostatic (confining) pressure is applied equally in all directions in the earth"s crust due to the weight of overlaying rocks - thus pressure increases with depth. Confining pressure increases at a rate at about 250bars per km. Directed pressure is not equal in all directions. Can occur with two plates coming together. Water trapped in pores of sedimentary rocks during formation. Dehydration of water bearing minerals like gypsum. These fluids enhance the growth of new minerals by increasing the rate of chemical reactions, because ions can move readily and rapidly through the fluid. Water and co2 are generally present in regions where metamorphism occurs. Fluids may sometimes be involved in the chemical reactions, such as the formation of serpentine from olivine. The fluids help move the ions around.
