吉林大学：《地球科学概论》课程PPT教学课件（英文版）Chapter 8：Metamorphism and Metamorphic Rocks - New Rocks from Old

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Chapter 8: Metamorphism and Metamorphic Rocks:New Rocks from Old

What is Metamorphism? 1) Metamorphism is the change in form that happens in earth's crustal rocks in response to changes in temperature and pressure

What is Metamorphism? (1) ◼ Metamorphism is the change in form that happens in Earth’s crustal rocks in response to changes in temperature and pressure

What is Metamorphism?(2) There are six major factors in metamorphism: a Chemical composition The change in temperature The change in pressure The presence or absence of fluids How long a rock is subjected to high pressure or high temperature a whether the rock is simply compressed or is twisted and broken during metamorphism

What is Metamorphism? (2) ◼ There are six major factors in metamorphism: ◼ Chemical composition. ◼ The change in temperature. ◼ The change in pressure. ◼ The presence or absence of fluids. ◼ How long a rock is subjected to high pressure or high temperature. ◼ Whether the rock is simply compressed or is twisted and broken during metamorphism

Chemical composition of Original rock a The greatest factor in determining the mineral assemblage of a metamorphic roc k a The chemical composition of the original rock controls the mineralogy of the metamorphosed rock

Chemical Composition of Original Rock ◼ The greatest factor in determining the mineral assemblage of a metamorphic rock. ◼ The chemical composition of the original rock controls the mineralogy of the metamorphosed rock

Temperature And Pressure (1) a The heat source is earths internal heat Rock can be heated by burial or by nearby igneous intrusion Burial is inevitably accompanied by an increase in pressure due to the weight of the overlying rocks。 An intrusion may be shallow, resulting in low pressure, or deep, resulting in high pressure

Temperature And Pressure (1) ◼ The heat source is Earth’s internal heat. ◼ Rock can be heated by burial or by nearby igneous intrusion. ◼ Burial is inevitably accompanied by an increase in pressure due to the weight of the overlying rocks. ◼ An intrusion may be shallow, resulting in low pressure, or deep, resulting in high pressure

收 a grain of garnet in a garnet-biotite gneiss, the small inclusions are relicts from early assemblage formed under p-Tconditions different from those that formed the gneiss

A grain of garnet in a garnet-biotite gneiss, the small inclusions are relicts from early assemblage formed under P-T conditions different from those that formed the gneiss

Temperature A ETROGRADE C P-T path for a body of rock undergoing metamorphism along a subduction zone

P-T path for a body of rock undergoing metamorphism along a subduction zone

Temperature And Pressure(2) Low-grade metamorphism is the result of metamorphic processes that occur at temperatures from about 100oc to 500oC and at relatively low pressures. High-grade metamorphism is the result of metamorphic processes at high temperatures(above 500C), and at high p ressure

Temperature And Pressure (2) ◼ Low-grade metamorphism is the result of metamorphic processes that occur at temperatures from about 100oC to 500oC, and at relatively low pressures. ◼ High-grade metamorphism is the result of metamorphic processes at high temperatures (above 500oC), and at high pressure

Region of Temperature(C diagenesis 200 400 600 Region of tow-grade 2000 amorphism Continental crust 4000 Increasi 15E grade of 200° C metamorphism 6000 metamorphism 400°C 3 8000Pressure and conditions 600°C o 10,000in the crust not found 800C Melting starts 12000 Mantle The metamorphic grade

The metamorphic grade

Stress Stress is applied pressure that results in deformation in a solid, and the development of new textures a Uniform stress occurs if pressure is equal in all directions Differential stress occurs if pressure is different in different directions a Texture is controlled by differential versus uniform stress

Stress ◼ Stress is applied pressure that results in deformation in a solid, and the development of new textures. ◼ Uniform stress occurs if pressure is equal in all directions. ◼ Differential stress occurs if pressure is different in different directions. ◼ Texture is controlled by differential versus uniform stress