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Earth 121 Final Exam Review (AFTER midterm only)

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Earth Sciences
Keith Delaney

Chapter 7 Metamorphic Rocks transformation results from exposure of preexisting solid rock to heat pressure and fluid chemical activity to change the mineral composition and texture chemical composition reflects parent rock but texture and mineral makeup depends on metamorphic processes involvedControlling Factors in Metamorphism 1 Composition of the parent rock 2 Heatincreases therate of chemical rxns most powerful agentContact metamorphismintrusive magmas Regional metamorphismdeep burial upper crust is 2030Ckm 12k reaches 245C water doesnt boil because of the increase pressure3 PressureConfining pressureuniform stresssqueezing of the rock from all directions increases with depth Directed pressuredifferential stressminerals align in the direction of least stress Tensional stresspulling apart motion crustal stretching Shear stressforces parallel but in opposite direction Foliation platy minerals become more aligned parallel to direction of least stress under pressure Shallow depthslow pressure and tempelastic then brittle fractures Deep depthshigh pressure and tempelastic then ductile 4Chemically active fluidsenhance rxn rate an increase in metamorphic grade is indicated by minerals that are stable at progressively higher temperatures and pressures index minerals form within a narrow range of TP and are used to define grades of metamorphismFacies assemblage of minerals that can be used to designate a particular set of metamorphic environmental conditions recorded in the rock Burial metamorphismalteration of rock by increase in TP rocks become dense but not distorted occurs at temps 200C Contact metamorphismaureole zone contacted rocks are altered minerals crystallize in random directions hornfels quartzite and marble commonly produced togetherRegional Metamorphism majority of metamorphic rocks characteristically foliatedoccurs over a large area tremendous TP and deformation in the crust shortened and thickened
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