John Grotzinger Thomas H Jordan Frank Press Raymond

John Grotzinger, Thomas H. Jordan, Frank Press, Raymond Siever, Understanding Earth Fifth Edition Chapter 6: Metamorphic Rocks Copyright © 2007 by W. H. Freeman & Company

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 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 - 150 km New lithosphere (Divergent) - 30 km Volcanic regions (Convergent)- 50 km

Confining Pressure Confining pressure is the same in all directions (incl. 3 rd dimension) In water, that is one ton per m 2 each meter of depth 10 m ~ 1 atm or 10 tons of pressure Confining pressure implies that there is little more in one direction that in the other directions.

Directed Pressure When one pressure is greater than the other three (incl. 3 rd 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 • (A change in rock composition by fluid transport is metasomatism) metasomatism

TYPES OF METAMORPHISM Pressure (Impacts) Subduction Zones e Regional Metamorphism d ra Burial e r c g g in s a In Mountain belts (low-P, low-T), low-grade Fluids metasomatism) Contact Temperature

Types of metamorphism shock, contact, regional, and burial

Shock metamorphism Depth, km 0 Con tine 35 nta l cr Con ust tine nta lm 75 ant le As th en osp he re Regional metamorphism lith osp Oceanic crust Oceanic lithosphere her e

Regional metamorphism Shock metamorphism Depth, km 0 Con tine 35 nta l cr Con ust tine nta lm 75 ant le As th en osp he re Regional metamorphism lith osp Oceanic crust Oceanic lithosphere her e

Regional metamorphism Shock metamorphism Depth, km 0 Con tine 35 nta l cr Con ust tine nta lm 75 ant le As th en osp he re Regional high-pressure metamorphism Regional metamorphism lith osp Oceanic crust Oceanic lithosphere her e

Regional metamorphism Shock metamorphism Depth, km 0 Con tine 35 nta l cr Con ust tine nta lm 75 ant le As th en osp he re Regional high-pressure metamorphism Contact metamorphism Regional metamorphism lith osp Oceanic crust Oceanic lithosphere her e

Regional metamorphism Shock metamorphism Depth, km 0 Con tine 35 nta l cr Con ust tine nta lm 75 ant le As th en osp he re Regional high-pressure metamorphism Contact metamorphism Regional metamorphism lith osp Oceanic crust Oceanic lithosphere her e

Regional metamorphism Shock metamorphism Depth, km 0 Con tine 35 nta l cr Con ust tine nta lm 75 ant le As th en osp Regional high-pressure metamorphism Contact metamorphism Regional metamorphism lith osp Oceanic crust Oceanic lithosphere her e he re Water Seafloor metamorphism

Textures to distinguish metamorphic rocks