chap10 - Chapter 10 Metamorphic Rocks Geology 11 Principles...

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Unformatted text preview: Chapter 10 Metamorphic Rocks Geology 11 Principles of Geology A. M. P. Tengonciang National Institute of Geological Sciences University of the Philippines, Diliman 10.1 What is metamorphism? Greek: meta (change) and morphe (form) change of form All the mineralogical, chemical and structural adjustments of solid rocks to physical and chemical conditions at depths below the region of sedimentation and diagenesis Solid rocks squeezed, stretched, bent, heated Limits of metamorphism Temperature Geothermal gradient ~ 30C/km At 5 km, T is approximately 150C Upper limit of diagenesis Lower limit of metamorphic processes Pressure Pressure in the crust increases with depth at 300 atm/km Remember: pressure at sea level is 1 atm (1.03 kg/cm 2 or 14.7 lb/in 2 ) At 5 km, P is about 1500 times greater than atmospheric pressure Metamorphism begins at 5 km because the T and P are high enough for recrystallization and growth of minerals to start. 10.1 Factors that affect metamorphism 1. Rock composition of parent rock (protolith) Affects mineral assemblage of resulting metamorphic rock Reactivity of rock to metamorphic agent/s affects degree of metamorphism 2. Influence of pore fluids Pore fluids gas (CO 2 ) or water w/ dissolved salts &/or gases Speed up recrystallization by providing a medium for dissolution, transfer and precipitation Act as reservoirs during the growth of new minerals Speed up chemical reactions Veins produced by expelled pore fluids from pore spaces and hydrous minerals that flow through fractures in a rock 3. Effects of pressure Differential stress (stress not equal in all directions); compare to igneous rocks that relatively form under uniform stress Foliation alignment of flat minerals, e.g. micas, perpendicular to the direction of maximum stress; produces slaty cleavage Schistosity foliation in coarse-grained rocks; not necessarily planar 10.1 Factors that affect 10....
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chap10 - Chapter 10 Metamorphic Rocks Geology 11 Principles...

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