What do you like better: Igneous or Sedimentary rocks???
Pressure: Two Types of pressure: Confining Pressure Directed Pressure
Imposed by Surrounding Rocks, Uniform in All Directions. A. Confining Pressure: Imposed by Surrounding Rocks, Increases with Depth. Uniform in All Directions.
This diver is experiencing "Confining Pressure"
Effects of Confining Pressure
B. Directed Pressure / Stress Connected to plate tectonics & mountain building processes. NOT Uniform in All Directions. Results in Deformation.
Directed Pressure / Stress is applied in a specific direction! ...it causes mineral crystals to align PERPENDICULAR to the stress!
Why would the minerals want to align parallel to the stress? Domino demo– is it more stable like this or flat (parallel)
ex. Slatey Cleavage Schistocity & Gneissic Banding Results of Pressure! As pressure increases rocks become more Compact & Dense. Mineral Crystals become aligned parallel to each other. Mineral crystals line up perpendicular to the stress. Results in compositional & textural banding ex. Slatey Cleavage Schistocity & Gneissic Banding
Show slate. Which way did the pressure push on it Show slate. Which way did the pressure push on it? – looking for top/bottom minerals from perpendicular to stress
Increase in Pressure ? Which way does pressure increase?
Effects of Pressure! Turn to a partner. What do you think are some of the effects of pressure
Often creates “Rock Cleavage” ex. Slate breaks easily into flat layers! Mineral crystals & rock/fossil fragments become stretched & deformed. Porosity is greatly reduced. Mineral crystals INCREASE in SIZE due to recrystallization! Recrystallization of many minerals occurs = Porphyroblasts!
Large mineral crystals in a fine grained groundmass Porphyroblasts Garnet porphyroblast! Large mineral crystals in a fine grained groundmass
Chemical Reaction: Permeable rocks allow fluids to flow through pore space. Fluids (or materials dissolved in them) which flow through pore spaces can react with the original rock. Reaction produces new mineral assemblages, and therefore new METAMORPHOSED rocks. Often fluids migrate away from an area of heating caused by the intrusion of magma. What are permeable rocks?? Note fluids are going to change the chemical composition of the rock= new minerals form!
These fluids then leave one area and enter another. These fluids often carry various dissolved gasses and minerals. Areas that GAIN fluids & areas that LOSE fluids will end up being changed chemically = METAMORPHOSED! The fluids are moving in and out of rocks– grabbing these different dissolved gases and minerals Note: any rocks that have had any interaction with the fluids will change!
Parent Rocks: The metamorphic changes depend on the original mineral composition of the “Parent Rock”. This initial “Parent Rock Composition” interacts in a complex way with temperature, pressure, and chemical reactions. Ex. A shale parent rock can become slate, phyllite, schist, or gneiss, depending on the temperature, pressure, and chemical reactions it undergoes!! What is parent rock? Activity: what is it’s common parent rock? https://quizlet.com/17641795/parent-rocks-of-metamorphic-rocks-flash-cards/ Show rocks- example of shale (undergoing pressure/ temperature) and becoming slate!! Pass the rocks around
Parent Rocks! Your Task In a group, go to one of the stations At each station is a group of parent rocks and a group of metamorphic rocks In your group, you have to match the parent rocks to the metamorphic rocks.