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GEOL G190 - Chapter 5 Subduction Zones
Terms in this set (46)
A mountain range formed as sedimentary strata and hard crust are scraped off the top of a subducting plate. Folded and thrust-faulted mountains and steep valleys. Sedimentary layers (sandstone and shale) scraped off the ocean floor. Basalt from the oceanic crust.
A block of crust with characteristic igneous and metamorphic rocks and sedimentary rock cover, that is bounded by faults and distinctly different than surrounding crustal blocks. It is an unexpected section of landscape that is out of the ordinary of what is common with the forearc basin (trench, accretionary wedge, forearc basin, volcanic arc). The Oregon Caves, NM in the Klamath Mountains with all of its limestone exists because it was possibly inland or an area of continental crust that was scraped along with the subduction of the oceanic plate, and because it was buoyant and thick, it was not pulled down into the trench or subduction zone, it was pushed along the top of the continental crust, and stayed there.
A region of focused activity of earthquakes from near Earth's surface extended downward and inward along a subduction zone.
A large (12 mile diameter) mountain formed during numerous eruptions of a variety of volcanic materials (lava flows, ash, pumice, cinders, mudflows) that pile up into a relatively steep volcano (strato-volcano).
A fine-grained, light-to-dark colored igneous rock with about 60% silica. It is in-between mafic and felsic. Because it's fine grained, it cooled fast and is very viscous because of its high silica content formed by hydration melting (making it igneous). This is found frequently in areas of volcanic arcs because it is formed through the subduction process.
An extensive, igneous intrusive rock body, commonly with granite or granodiorite composition. It typically forms as a region of magma chamber cools. An extensive chain of volcanoes developed as the Farallon Plate subducted beneath the western edge of North America. These structures, including the Sierra Nevada, are eroded remnants of magma chambers that fed the ancient volcanoes.
A sheetlike, igneous intrusive rock body formed where magma cuts across rock layers.
A coarse-grained, light-to-dark colored igneous rock with about 60% silica (an intrusive equivalent of andesite).
Depression between the uplifted (accretionary wedge) and volcanic (volcanic arc) mountain ranges formed above a subduction zone.
A coarse-grained, generally light-colored igneous rock with about 65% silica (less silica than granite, but more than diorite). Most of the rock at Yosemite National Park has this. It is a coarse-grained, intrusive and plutonic rock with composition between Granite (70%) and Diorite (60%). (after solidification of magma).
A coarse-grained, generally light-colored igneous rock with about 70% silica.
Change from solid to liquid that occurs when a material is heated and loses water (dehydrates). The change occurs where a plate subducts and loses water as it heats up; the water rises and wets (hydrates) hot rock in its path, causing some of the rock to melt.
A mass of solid material and water that moves swiftly downslope, commonly as a result of volcanic processes (volcanic mudflow). The deposits of a volcanic mudflow. Big threat at Mt. Rainier NP, WA. Deposits show along the Nisqually River, just outside the park.
An accumulation of molten rock below Earth's surface.
An igneous rock that solidified from magma that cooled within the Earth (intrusive rock).
A depression on the ocean floor formed where one lithospheric plate descends (sub ducts) beneath another.
A sequence of thick sandstone and thin shale layers deposited by a turbidity flow. These are found in the Olympic NP because of the submarine landslides common in that area and how the sediments flow and settle. How they are compressed can tell us the age of teh turbidite.
A current of water saturated with sediment that rushes down a continental slope, dropping the sediment on the deep floor of the ocean.
The chain of volcanoes that forms on the overriding plate at a subduction zone. Steep, composite volcanoes, Stratification of lava flows, ash, pumice, cinders, mudflows. Andesite-to-rhyolite composition, with some basalt. Explosive eruptions.
A convergent plate boundary where one plate slides deeply beneath another.
A break in the Earth along which the blocks on either side of the break slid horizontally past one another. The break forms when the rocks are subjected to shearing streesses. At a right-lateral strike-slip, the block across the fault line appears to move to the right. At a left-lateral strike-slip fault, the block across the fault line appears to move to the left.
Olympic National Park
Active, accretionary wedge, (Coast Ranges), subduction zone-related. Three basic types of rock found in the accretionary wedge: igneous rock (basalt), sedimentary rock (sandstone and shale), and metamorphic rock (slate). Also found are uplifted and tilted turbidite (sandstone and shale layers). Second Beach - has the Sea Stacks. It is dynamic in equilibrium because its elevation is not changing (even thought it's still actively forming) because the forces of erosion are equally strong as the forces of continental uplift. The rate of it actively building up is the same as the mountain ranges being actively broken down.
Mount Rainier National Park, WA
Subduction Zone-related. Last recorded eruption: ~1850's. Most significant hazard: Lahars!
Mt. St. Helens National VM
Active, accretionary wedge, subduction zone-related. Contain materials that were manufactured in the sea, then scrapped off the subducting Juan de Fuca Plate and incorporated into the accretionary wedge. National Park lands in the Pacific Northwest. (Juan de Fuca is NOT the Pacific Plate).
Active, volcanic arc, subduction zone-related. Steep composite volcanoes built on a base of broad shields.
Subduction Zone-related, disrupt the natural depression (Puget Sound/Willamette Valley/Great Valley) between the Coastal Ranges and the Cascades. NP in the Pacific Northwest.
Crater Lake National Park
Active, volcanic arc, (Cascades), subduction zone. The composite volcano Mount Mazama (12,000') erupted spewing pumice and gas-laden materials flowing down the sides of the mountain. High-silica eruptions. Rainfall and snowmelt partially filled in the caldera, forming this National Park.
Lassen Volcanic National Park
Active, volcanic arc (Cascades), straddles the Cascade Volcanic Arc and Basin & Range Continental Rift Zone. Pacific Northwest.
Kings Canyon National Park
Ancient, volcanic arc, (Sierra Nevada), subduction zone-related
Sequoia National Park & General Sherman Tree
Ancient subduction zone, General Sherman, >2300 years old, 275 feet tall (Redwood tree).
Yosemite National Park Half Dome
Ancient, volcanic arc, (SierraNevada), subduction zone-related. Coarse-grained Granodiorite rock is here (65% composition, intrusive, plutonic).
Ancient Volcanic Arc
Cooled remains of granitic magma chambers. Great climbing rock!
Topography in balance: erosion equal to uplift. Mountains stay about the same elevation. Dynamic equilibrium. ex. Olympic National Park, WA The Juande de Fuca plate subducting into the North American Plate.
Northern Hemisphere - colder side.
Formed by lava erupting into cold ocean water forming new pillows on top of the oceanic crust.
HOH Rain Forest, Olympic National Park
West side of the park gets lots of fog and rain where the moisture drops there fore causing the trees to grow much faster.
The southern portion of the Juan de Fuca Plate. Near the National Park Lands in the Costal Ranges.
A tree that fell down and had shoots of new trees coming out from it and feeding from it. Once this tree has decomposed and has fed the new trees, it leaves behind space underneath the new trees (like a tunnel or cave).
Redwood National Park & State Parks, CA
Sedimentary rocks deposited in the sea, metamorphosed and deformed as they were subducted, then uplifted as part of the accretionary wedge.
This plate was completely sub ducted in the California region, leaving only fragments known as the Juan de Fuca and Cocos plates. 18 million years ago.
Vesuvian eruptions, ex. Mount Vesuvius AD79 description of eruption written by Pliny the younger to Pliny the Elder. These eruptions are marked by columns of gas and volcanic ash high into the stratosphere. Large amounts of pumice and very powerful gas eruptions. Lava: Rhyolitic and rich in Silicates.
"Glowing Cloud" swiftly moving pyroclastic flow, dense cloud of hot gasses, ashes, lava fragments from the collapse of a growing lava dome or flow. It is highly distructive, fast moving, incadescent mass of gas and particles in volcanic eruptions.
Small intrusive body (a few to tens of km across) that seems to represent one fossilized magma chamber. Coarse-grained igneous rock.
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