Understanding Earth Fifth Edition Chapter 6: Metamorphic Rocks Copyright 2007 by W. H. Freeman & Company John Grotzinger, Thomas H. Jordan, Frank Press, Raymond Siever, Concepts you will need to know for the exams CHAPTER 6 METAMORPHIC ROCKS Controls on metamorphism by: P,T, fluids Isotherm Geothermal gradient Confining pressure Directed pressure Regional metamorphism Contact metamorphism High-P metamorphism Burial or low-grade metamorphism Foliated texture Crystal Growth Pressure-Temperature Paths (pro-grade and retrograde metamorphism) Factors that control the type and and degree Metamorphism Heat Pressure Fluids Temperature increases with depth A typical continental geothermal gradient is 30 degrees C per kilometer Where is the 1300 degree isotherm? Old lithosphere km New lithosphere (Divergent) - 30 km Volcanic regions (Convergent)- 50 km 150 Confining Pressure Confining pressure is the same in all directions (incl. 3rd dimension) Confining pressure implies that there is little more in one direction that in the other directions. In water, that is one ton per m2 each meter of depth 10 m ~ 1 atm or 10 tons of pressure Directed Pressure When one pressure is greater than the other three (incl. 3rd dimension) If directed pressure is great enough rocks can break and/or fold Fluids Accelerate chemical reactions Dissolve ions and move them from one mineral to another metasomatism(A change in rock composition by fluid transport is metasomatism) Pressure Temperature Fluids metasomatism) (Impacts) Contact Burial (low-P, low-T), low-grade TYPES OF METAMORPHISM Increasing grade Regional Metamorphism Subduction Zones Mountain belts shock, contact, regional, and burial Types of metamorphism Depth, km Asthenosphere Continental mantle lithosphere Continental crust Regional metamorphism Oceanic crust Oceanic lithosphere Shockmetamorphism Depth, km Asthenosphere Continental mantle lithosphere Continental crust Regional metamorphism Oceanic crust Oceanic lithosphere Shockmetamorphism Regionalmetamorphism Depth, km Asthenosphere Continental mantle lithosphere Continental crust Regional metamorphism Oceanic crust Oceanic lithosphere Shockmetamorphism Regionalmetamorphism Regionalhigh-pressuremetamorphism Depth, km Asthenosphere Continental mantle lithosphere Continental crust Regional metamorphism Oceanic crust Oceanic lithosphere Shockmetamorphism Regionalmetamorphism Regionalhigh-pressuremetamorphism Contactmetamorphism Depth, km Asthenosphere Continental crust Regional metamorphism Oceanic crust Oceanic lithosphere Shockmetamorphism Regionalmetamorphism Regionalhigh-pressuremetamorphism Contactmetamorphism Burialmetamorphism Continental mantle lithosphere Depth, km Asthenosphere Continental crust Regional metamorphism Oceanic crust Oceanic lithosphere Shockmetamorphism Regionalmetamorphism Regionalhigh-pressuremetamorphism Contactmetamorphism Continental mantle lithosphere Water Seafloormetamorphism Textures to distinguish metamorphic rocks