Metamorphic Rocks the Earth Science Journal Issue 12 November 2013

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METAMORPHIC ROCKS THE EARTH SCIENCE JOURNAL ISSUE 12 NOVEMBER 2013 IN THIS ISSUE Plate Tectonics P.1 Foliated Rocks P.1 Contact Metamorphism P.2 Metamorphic Rocks Non-foliated Rocks P.2 What is a metamorphic rock? The word metamorphic can be broken down to help explain its meaning. The prefix meta- means after, and -morph means shape or form, so in combination, the word metamorphic means “after shape” which fits exactly what metamorphic rocks are. Foliated Rocks When a rock is exposed to the extreme heat and/or pressures that exist beneath the surface of When minerals align from directed the Earth, its physical properties change, and indeed, its shape may as well. Most of the time heat and pressure during metamor- the chemical makeup of the rock remains the same, and it resembles very closely its parent phism they fall into the classification rock, or the rock it was before metamorphism. Mineral colors are often a good indicator of of foliated rocks. Foliation characteristics range from flaky, crystals what the parent rock looked like before metamorphism. composed of the mineral mica in the So how does metamorphism happen? Metamorphism occurs in one of two ways: regionally, metamorphic rock schist, to extreme bands of alternating light and dark or locally (contact). Regional metamorphism occurs over large areas as rocks are exposed to minerals in the metamorphic rock extreme pressures and heat. Typically regional metamorphism is found along folded mountain gneiss. belts and during tectonic plate collisions where pressures can exceed millions of tons. Local or contact metamorphism is much different and is also on a much smaller scale. If an intrusion of magma makes its way through layers of rock, it will heat its surroundings. This heat is sufficient enough to change the characteristics of the rock around the intrusion causing the formation of metamorphic rocks. Local metamorphism is common in areas with volcanic activity and along plate boundaries. Non-foliated Rocks Non-foliated metamorphic rocks do not have the mineral alignment that foliated rocks do and will often have a color and texture similar to that of their parent rock. The sample below is quartzite, which is a metamorphic rock formed from a quartz sandstone. Quartzite is slightly more dense and very resistant to weather- ing, so it is a popular choice for use in building materials. Contact Metamorphism The diagram above depicts an igneous intrusion pushing through horizontal rock strata (layers). Along the intrusion are a series of hachure marks that indicate contact metamorphism of the surrounding sedimentary rocks. In order to identify what rocks the preexisting sedimentary rocks change into, you must use both the Scheme for Sedimentary Rock Identifi- cation and the Scheme for Metamorphic Rock Identification. First identify the sedimentary rock that the intrusion goes through. Then look under the ‘Comments’ column on the Scheme for Metamorphic Rock Identification chart and determine which metamorphic rock formed from the previously identified sedimentary rock. A few examples are below. Sandstone to Quartzite Shale to Slate Limestone to Marble Conglomerate to Metaconglomerate THE EARTH SCIENCE JOURNAL Created By: Dave Burgess Rochester STEM High School I do not own any rights to the images in this journal. All images used for educational purposes only. .

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The Sierra Nevada Batholith a Synthesis. of Recent Work Across the Central Part
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