Common intrusive igneous rocks are: granite, diorite, gabbro, and peridotite. The La Sal Mountains were formed by widespread igneous activity that began about 40 million years ago. Caldera explosions erupted thousands of cubic miles of volcanic rocks from several locations.
Volcanoes spewed ash and lava. For 20 million years these extrusive volcanic rocks smoothed the landscape, filling depressions with accumulations of ash, flows, and debris literally miles thick. These mostly pastel-colored extrusive rocks still blanket much of the high areas of central and southwestern Utah. Not all of the molten rising igneous material erupted as volcanic rocks; some material, along with its mineral-bearing fluids, congealed in the earth's crust.
Several of these intruded masses having been exposed by erosion or encountered out by exploration drilling became great mining districts, such as at Alta, Brighton, Bingham, Park City, and Cedar City. In the Colorado Plateau, bodies of intrusive rocks domed the overlying sedimentary rocks to form the Abajo and Henry Mountains as well as the La Sal Mountains.
NOTE: This paragraph on laccoliths borrowed from here. Rocks which have undergone these sorts of changes are called metamorphic rocks. Agents of Matamorphosis. The three primary agents which metamorphose rock are temperature, pressure, and fluids.
High temperatures can change rock by changing the structure of the minerals which make up the rocks; changing the structure of the minerals changes them into new minerals remember the definition of a mineral.
This increase in temperature with increase in depth is called the geotherm. Intrusions Another source of high temperatures inside the Earth is magma intruding cooler rock.
These temperature increases are localized near the intrusion, but also metamorphose rock this is called contact metamorphism. Pressure or more properly, stress can also change rock. There are two main kinds I want you to know about: Confining Pressure Pressure due to the weight of overlying rock. This kind of pressure is roughly the same in all directions this is like water pressure when scuba diving , and is the kind which compacts rock during diagenesis.
Confining pressure changes rock by compaction and by changing the crystal structure of minerals from relatively open forms to more densely-packed forms. One mineral which does this is olivine, which changes from olivine isolated silica tetrahedra to spinel a much more tightly-bonded structure to perovskite a still more highly compressed structure.
This kind of pressure is usually due to tectonic forces. It changes rocks by changing the structure of minerals and by changing the orientation of mineral grains, particularly platy minerals like mica or clay. Fluids which metamorphose rock are not pore fluids remaining from when sedimentary rocks were deposited. Instead, they come from two main sources: hydrothermal fluids from magmatic intrusions and dehydration of minerals, like clay, which contain water in their structures hydrous minerals.
Whatever the source, fluids contain ions dissolved from other rock or from their original source. As fluids percolate through rocks, they can exchange ions with the existing minerals and thus change the chemical makeup of those minerals. The other way fluids change minerals is by hydrating minerals which previously did not contain water. Either way, fluids change the chemical makeup of minerals, turning them into new minerals, which changes the rocks which were made of the previous minerals.
This process of change by fluids is called metasomatism. Types of Rock Metamorphism. Some kinds of metamorphism: Burial Bury rocks deeply enough and they will warm up and change. This form of metamorphism is found anywhere where sediments and rocks are buried deeply, and should strike you as being pretty similar to diagenesis, which we discussed last time.
The line between diagenesis and burial metamorphism is fuzzy. Regional Caused by widespread moderate-to-high temperatures and pressures, as opposed to localized changes along faults or near magmatic intrusions.
You find this type of metamorphism in mountain building regions and near subduction zone volcanism. Contact Caused by high temperatures near magmatic intrusions. Found in volcanic regions subduction zones, hot spots and mountain building zones.
Cataclastic Caused by grinding along fault zones. Found along major faults like the San Andreas Fault in California , in mountain building zones, and in deformation regions associated with subduction zones. Hydrothermal Caused by hot fluids percolating through rocks. Found anywhere where hot fluids can percolate through rocks, notably along mid-ocean ridges.
Metamorphic Rocks and Rock Textures. Three major texture and rock types for metamorphic rocks that you need to know: Foliated Rocks Characterized by parallel planes formed through directed pressure and preferred growth orientations of certain platy minerals.
Two common kinds are schist and gneiss, which have been used in a great many really bad geological puns. Non-foliated Rocks Don't have those planes, usually because they are made of mineral grains which are cubic or spherical, and therefore have no preferred orientation.
Two common examples are marble and amphibolites. Deformational Caused by cataclastic metamorphism. The most common rock of this kind is called a mylonite; there is a big mylonite belt in the mountains south of Palm Springs, CA. Metamorphic Grade. Granite is an igneous rock that forms when magma cools relatively slowly underground. It is usually composed primarily of the minerals quartz, feldspar, and mica. When granite is subjected to intense heat and pressure, it changes into a metamorphic rock called gneiss.
Slate is another common metamorphic rock that forms from shale. Limestone, a sedimentary rock , will change into the metamorphic rock marble if the right conditions are met. This happens due to geologic uplift and the erosion of the rock and soil above them. At the surface, metamorphic rocks will be exposed to weathering processes and may break down into sediment.
These sediments could then be compressed to form sedimentary rocks, which would start the entire cycle anew. Any rock type can become any other.
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The Rights Holder for media is the person or group credited. Tyson Brown, National Geographic Society. National Geographic Society. For information on user permissions, please read our Terms of Service. Related questions How do igneous rocks form? What are some common characteristics of sedimentary rocks? What are some examples of igneous rocks? How can igneous rocks become metamorphic rocks?
The minerals can form crystals when they cool. Igneous rock can form underground, where the magma cools slowly. Or, igneous rock can form above ground, where the magma cools quickly. When it pours out on Earth's surface, magma is called lava. Yes, the same liquid rock matter that you see coming out of volcanoes. On Earth's surface, wind and water can break rock into pieces. They can also carry rock pieces to another place. Usually, the rock pieces, called sediments, drop from the wind or water to make a layer.
The layer can be buried under other layers of sediments. After a long time the sediments can be cemented together to make sedimentary rock.
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