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WSU GEOLOGY 101 - Metamorphism

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Geo. 101 – 1st Edition Lecture 14 Outline of Last Lecture I. Sedimentary Rocks EnvironmentOutline of Current Lecture I. MetamorphismII. Metamorphic Rocka. Factors Controlling Iti. Temperature, Pressure, FluidsCurrent Lecture- Metamorphism: A Process of Changeo To change form- Metamorphic Rocks: changed rockso A rock whose mineralogy, texture or composition (or all three) has changed due to increased temperatures, pressures, or moving fluids (like hot water).The Rock Cycle and Metamorphic Rock:- What happens when rocks get buried and are heated up?o Delicate features are obliteratedo Minerals or grains in the rock may become deformed Deformation: if buried deep enough, the rock can undergo plastic deformation.- Factors Controlling Metamorphismo Temperature: Minerals convert to new higher temperature minerals- Diffusion: the movement of atoms due to thermal energy (heat)o Forms new minerals Fluids are released- EX: Clay = Mica + H20 Recrystallization:- Crystals grow larger or change shape Rocks become weaker and easier to deformo Pressure: Confining Pressure: general pressure applied equally in all directionsThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute. Directed Pressure: (differential stress) unequal pressure, greater in one direction (think: converging plates)- The mineral grains will become aligned when acted on by directedpressure- Directed pressure results in foliationo Foliation: preferred orientation of platy (flat) or elongated mineralso Looks layeredo Fluids Released during recrystallization- H20, CO2, plus dissolved ionsClassification of Metamorphic Rocks:- Foliated Rocks:o Nature of foliationo Size of crystalso The degree to which minerals are segregated in different mineral bands These features tell about the Metamorphic Grade of the rocko EX: Slate, Phyllite, Schist, Gneiss, Migmatite (grain size from fine to coarse)- Non-Foliated Rocks:o Highest grade of coal moves from the conditions of sedimentary rocks to metamorphic rocks EX: Quartzite, Marble, Hornfels, Coal- Metamorphic Grade:o The degree to which a rock has changed from the parent rock or protolith (The original rock type) Low Grade = Low Pressure and Low Temperature (200-400°C)- May still contain features of parent rocko Fossils, sedimentary structures etc High Grade = High Pressure and High Temperature (500-800°C)- Features of parent rock are usually destroyedIndex Minerals:- Index minerals are characterized minerals that define metamorphic zones formed under a restricted range of temperatures and pressures.o Prograde Path: rock during subduction or burial to high temp and high deptho Retrograde Path: rock during its journey back to the


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