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2.5: Types of Plate Boundaries - Geosciences

2.5: Types of Plate Boundaries - Geosciences


Categorization of plate boundaries is based off of how two plates move relative to each other. There are essentially three types of plate boundaries, which are divergent, convergent, and transform. In the case of divergent plate boundaries, two of earth’s plates move away from each other. Spreading centers and areas where new ocean floor are generally located at divergent plate boundaries. An example of a divergent plate boundary is the Mid-Atlantic Ridge. Depending on what type of lithospheric crust each diverging plate is, whether oceanic or continental, varying geographic features are formed. For example, when two continental plates diverge from each other, an ocean basin is created due to the separation of land. On the other hand, if two oceanic plates diverged, a mid ocean ridge would form, which is also known as a spreading center. Divergent plate boundaries are commonly associated with shallow earthquakes.

When two plates move towards each other, the boundary is known as a convergent boundary. As previously mentioned, depending on what type of crust each converging plate is, different geographic features are formed. When two continental crusted plates converge, they eventually collide and end up producing mountains; this was how the Himalayan Mountains were created. Neither continental crust will subduct underneath one another because of their similar densities. When two oceanic plates converge, the denser plate will end up sinking below the less dense plate, leading to the formation of an oceanic subduction zone. When an oceanic plate converges with a continental plate, the oceanic crust will always subduct under the continental crust; this is because oceanic crust is naturally denser. Convergent boundaries are commonly associated with larger earthquakes and higher volcanic activity. Whenever a subduction zone is formed, the subducted plate will end up being partially melted by the earth’s internal magma and molten. This melting leads to heat being transferred upwards and uplifting the crust, eventually developing into a volcano. Subduction zones are the reason why oceanic crust older than 200 million years old cannot be found. Old, dense crust tends to be subducted back into the earth. An example of a subduction zone formed from a convergent boundary is the Chile-Peru trench.

The last type of plate boundary is the transform boundary, which is where two plates slide past one another. Unlike the other two types of plate boundaries in which new seafloor is created at divergent boundaries and where old seafloor is subducted at convergent boundaries, transform plate boundaries neither create nor destroy the seafloor. The rubbing caused by the sliding is what causes earthquakes along the transform faults; one example would be the San Andreas fault.


Tectonic Plates and Plate Boundaries

The Earth’s outer shell, the lithosphere, consisting of the crust and uppermost mantle, is divided into a patchwork of large tectonic plates that move slowly relatively to each other. There are 7-8 major plates and many minor plates. Varying between 0 to 100mm per year, the movement of a plate is driven by convection in the underlying hot and viscous mantle.

Earthquakes, volcanic activity, mountain-building, and oceanic trench formation occur along plate boundaries in zones that may be anything from a few kilometres to a few hundred kilometres wide. To watch a simulated fly-by along New Zealand's plate boundary check out this video.

There are three main types of plate boundaries:

1. Convergent boundaries: where two plates are colliding.

Subduction zones occur when one or both of the tectonic plates are composed of oceanic crust. The denser plate is subducted underneath the less dense plate. The plate being forced under is eventually melted and destroyed.

i. Where oceanic crust meets ocean crust
Island arcs and oceanic trenches occur when both of the plates are made of oceanic crust. Zones of active seafloor spreading can also occur behind the island arc, known as back-arc basins. These are often associated with submarine volcanoes.

ii. Where oceanic crust meets continental crust
The denser oceanic plate is subducted, often forming a mountain range on the continent. The Andes is an example of this type of collision.

iii. Where continental crust meets continental crust
Both continental crusts are too light to subduct so a continent-continent collision occurs, creating especially large mountain ranges. The most spectacular example of this is the Himalayas.

2. Divergent boundaries – where two plates are moving apart.

The space created can also fill with new crustal material sourced from molten magma that forms below. Divergent boundaries can form within continents but will eventually open up and become ocean basins.

i. On land
Divergent boundaries within continents initially produce rifts, which produce rift valleys.

ii. Under the sea
The most active divergent plate boundaries are between oceanic plates and are often called mid-oceanic ridges.

3. Transform boundaries – where plates slide passed each other.

The relative motion of the plates is horizontal. They can occur underwater or on land, and crust is neither destroyed nor created.

Because of friction, the plates cannot simply glide past each other. Rather, stress builds up in both plates and when it exceeds the threshold of the rocks, the energy is released – causing earthquakes.


Introduction

Subduction zones form where a plate with thinner (less-buoyant) oceanic crust descends beneath a plate with thicker (more-buoyant) continental crust. Two parallel mountain ranges commonly develop above such a subduction zone – a coastal range consisting of sedimentary strata and hard rock lifted out of the sea (accretionary wedge), and a volcanic range farther inland (volcanic arc). Ancient magma chamber rocks can be exposed if subduction stops and the volcanoes erode away.

Buoyancy

Where tectonic plates converge, the one with dense, thin oceanic crust subducts beneath the one with thick, more buoyant continental crust.

Subduction Zone—Two Parallel Mountain Ranges

  • An accretionary wedge forms between the converging plates as material is scraped off the subducting plate.
  • A forearc basin develops in the low area between the two mountain ranges.
  • Farther inland, the subducting plate reaches depths where it “sweats” hot water. The rising water melts rock in its path, forming a volcanic arc on the overrriding plate.
  • Near their boundary, the plates can lock together for centuries, then suddenly let go as a giant earthquake. If the seafloor rises or falls, giant sea waves (a tsunami) can form.

Cascadia Subduction Zone

  • The Coast Range and Cascades are the two parallel mountain ranges that form the Cascadia Subduction Zone in the Pacific Northwest.
  • The forearc basin is the Willamette Valley in Oregon and Puget Sound in Washington.

Images above modified from “Oregon's Island in the Sky: Geology Road Guide to Marys Peak, by Robert J. Lillie, Wells Creek Publishers, 75 pp., 2017, www.amazon.com/dp/1540611965.

Many National Park Service sites are found in active and ancient subduction zones. Visitors can witness mountains as they are forming, and sometimes experience the accompanying earthquake and volcanic activity. Parks in the Cascadia Subduction Zone dramatically display the two distinct mountain ranges – the Coast Range just above where the Juan de Fuca Plate begins to subduct, and the volcanic Cascade Range farther inland, where the top of the plate is deeper. Sites in the Sierra Nevada Mountains reveal the eroded roots of an ancient volcanic range that formed when the subduction zone extended much farther south. And very large parks in the Southern Alaska Subduction Zone display magnificent mountains, rock layers and active volcanoes that tell the story ongoing plate convergence along the North Pacific Coast.

Redwood National and State Parks, California

The Coastal Ranges are forming as material from the ocean is scraped off the top of the subducting Juan de Fuca Plate.

Mount Rainier National Park, Washington

Mount Rainier is a 14,000 foot (4,300 meter) volcano in the Cascade Range developed above the place where the subducting Juan de Fuca Plate reaches sufficient depth to release hot fluids into the overriding North American Plate.

Photo courtesy of Robert J. Lillie.

Yosemite National Park, California

The light-colored granite rocks are the cooled remnants of magma chambers that fed ancient volcanoes when the subduction zone extended through California and into Mexico.

Photo courtesy of Robert J. Lillie.

Kenai Fjords National Park, Alaska

The rock layers are lifting out of the sea as the Pacific Plate subducts beneath southern Alaska.

Photo courtesy of Robert J. Lillie.


Looking ahead

Automated plate paleo-boundary creation is already being developed using machine learning techniques to better integrate numerous sources of information and their uncertainties, by our team at Halliburton in collaboration with academic partners. Recent advances in the generation of closed plate boundaries (Matthews et al., 2017 Merdith et al 2021) and the reconstruction of consumed oceanic seafloor (Williams et al., 2019 Karlsen et al., 2020) get our community closer to a solution. Full integration of all of these within a “dynamic plate boundaries” approach and its application to a wider variety of geodynamic contexts are still to come.


7 Types of Boundaries You May Need

Boundaries help us focus on whats most important to us.

And boundaries improve relationships by creating clear expectations and responsibilities.

But it can be hard to figure out what boundaries you need to set.

One way to identify your boundaries is to think about the areas of your life where youre experiencing problems. Do you constantly feel exhausted? Do you feel uncomfortable around your coworker Kevin? Do you feel resentful of your mothers intrusions? Each of these problems is telling you that youre lacking boundaries in this area of your life.

Ive identified seven common types of boundaries. Understanding each type can help you clarify the specific boundaries that you may need.

Physical boundaries protect your space and body, your right to not be touched, to have privacy, and to meet your physical needs such as resting or eating. They tell others how close they can get to you, what kind of physical touch (if any) is okay, how much privacy you need, and how to behave in your personal space. A physical boundary clearly defines that your body and personal space belong to you.

When someone sits uncomfortably close to you, you move away or say, I need a little more personal space.

We dont keep or consume alcohol at our house.

Sexual boundaries protect your right to consent, to ask for what you like sexually, and to honesty about your partners sexual history. They define what kind of sexual touch and intimacy you want, how often, when, where, and with whom.

Id like to be touched like this.

Thuy has a personal policy of not having sex on the first date.

Emotional or mental boundaries protect your right to have your own feelings and thoughts, to not have your feelings criticized or invalidated, and not have to take care of other people’s feelings. Emotional boundaries differentiate your feelings from other peoples, so youre accountable for your own feelings, but not responsible for how others feel. Emotional boundaries also allow us to create emotional safety by respecting each other’s feelings, not oversharing personal information thats inappropriate for the nature or level of closeness in the relationship.

I dont feel comfortable discussing this.

I feel embarrassed and powerless when you chastise me in front of our kids. Id like you to stop.

Spiritual boundaries protect your right to believe in what you want, worship as you wish, and practice your spiritual or religious beliefs.

Im going to take a moment and say a silent prayer before we eat.

Paul goes to church alone because his partner doesnt share his beliefs.

Financial and material boundaries protect your financial resources and possessions, your right to spend your money as you choose, to not give or loan your money or possessions if you dont want to, and your right to be paid by an employer as agreed.

Im on a budget, so I brought my lunch from home and wont be ordering lunch today.

Please dont borrow my car without asking.

Time boundaries protect how you spend your time. They protect you from agreeing to do things you don’t want to do, having people waste your time, and being overworked.

I reserve my evenings for family time. Ill respond to all work emails first thing in the morning.

Dad, I dont have time to take you shopping this week. Ill place an order for you with the grocery delivery service.

Non-negotiable boundaries are deal-breakers, things that you absolutely must have in order to feel safe. They usually pertain to safety issues such as physical violence, emotional abuse, drug or alcohol use, fidelity, and life-threatening health issues.

Mom, if you dont install a fence around your pool, my children will not be able to come to your house.

Infidelity is a deal-breaker for me and I will not continue in this relationship if you cheat on me.

We all need some non-negotiable boundaries, but we also need to be careful that we dont put too many of our boundaries into this category. If a non-negotiable boundary is going to have any meaning, you have to be willing to follow through on it. Its counter-productive to set non-negotiable boundaries that you dont enforce.

After reading about the seven types of boundaries, I hope you gained greater clarity about the boundaries you need to set. I encourage you to write them down so that you can hold yourself accountable for creating boundaries to protect yourself, maintain (or establish) your individuality, and ensure that you use your time, energy, and resources for what matters most to you.


Continental Hotspot

The Pacific Northwest of the United States has a variety of active tectonic settings, including plate convergence at the Cascadia Subduction Zone and divergence in the Basin and Range Continental Rift Zone. But superimposed on these active tectonic features is a line of volcanic activity stretching from the Columbia Plateau of eastern Oregon and Washington all the way to the Yellowstone Plateau at the intersection of Wyoming, Idaho and Montana.

Shaded relief map of United States, highlighting National Park Service sites at a Continental Hotspot. Letters are abbreviations for NPS sites listed below. Sites in the the Columbia Plateau of Oregon and Washington, the Snake River Plain of Idaho, and the Yellowstone Plateau of Wyoming lie along the track of the Yellowstone Hotspot that is currently beneath Yellowstone National Park.

Modified from “Parks and Plates: The Geology of our National Parks, Monuments and Seashores,” by Robert J. Lillie, New York, W. W. Norton and Company, 298 pp., 2005, www.amazon.com/dp/0134905172.

Continental Hotspot

Continental [4 parks]

  • CRMO—Craters of the Moon National Monument, Idaho—[ Geodiversity Atlas ] [Park Home]
  • HAFE—Hagerman Fossil Beds National Monument , Idaho —[Geodiversity Atlas] [Park Home]
  • JODA—John Day Fossil Beds National Monument, Oregon—[Geodiversity Atlas] [Park Home]
  • YELL—Yellowstone National Park, Wyoming, Idaho & Montana—[ Geodiversity Atlas ] [Park Home]

The Greater Pacific Northwest Has all Three Types of Plate Boundaries and a Hotspot


The Yellowstone Hotspot track is superimposed on other tectonic provinces of the Pacific Northwest. The hotspot first surfaced 17 million years ago as massive outpourings of fluid basalt lava in the Columbia Plateau and Steens Basalt region. Surfacing of the hotspot was affected by subduction that is now manifest as the Cascadia Subduction Zone where the Juan de Fuca Plate descends beneath the edge of the continent. Since then the North American Plate has been moving west-southwest over the hotspot, so that a chain of explosive rhyolite volcanic centers (pink blobs) extends across the Snake River Plain to Yellowstone. This line of supervolcanoes is concurrent with continental rifting forming the Basin and Range Province.
Modified from “Oregon's Island in the Sky: Geology Road Guide to Marys Peak, by Robert J. Lillie, Wells Creek Publishers, 75 pp., 2017, www.amazon.com/dp/1540611965.

Volcanic Activity along Columbia Plateau – Yellowstone Hotspot Track

The Columbia Plateau has been the site of enormous volcanic eruptions, unsurpassed anywhere on Earth during the past 17 million years. Lava from large fissures in northeastern Oregon and southeastern Washington was so fluid that it flowed considerable distances, forming the numerous layers of basalt familiar to visitors to the Columbia Gorge. Some of the lava traveled more than 300 miles (500 kilometers) all the way to the Pacific Ocean. This vast volcanism resulted from the rise of hot material from deep within Earth’s mantle. Over the past 17 million years the North American continent has continued to drift west-southwest over this hotspot. The spectacular hot springs, geysers, and other hydrothermal features of Yellowstone National Park are the current manifestation of the hotspot activity.

Columbia Plateau, Oregon

Columns of basalt represent vast outpourings of fluid lava that covered large portions of Oregon, Washington, and Idaho as the hotspot surfaced 17 million years ago.

Photo courtesy of Robert J. Lillie.

Yellowstone Plateau, Wyoming

Geysers, hot springs and other geothermal features in Yellowstone National Park are reminders that the supervolcano that lies directly above the hotspot is still very much alive.

Photo courtesy of Robert J. Lillie.

NPS Sites along Columbia Plateau – Yellowstone Hotspot Track

A rising mantle plume has a massive head as much as 500 miles (800 kilometers) in diameter. The volume of basaltic magma that rises initially through the overriding plate can be so enormous that it matters little what kind of crust is capping the plate – huge volumes of basaltic lava pour out on the surface. The numerous lava flows that poured out in the Columbia Plateau and the Steens Basalt region of southeastern Oregon are thought to represent the original surfacing of the Yellowstone Hotspot that began 17 million years ago. Since then the North American Plate has continued to move in a west-southwestward direction over the Yellowstone Hotspot. Starting near the Oregon/Nevada/Idaho juncture 16 million years ago, a line of rhyolite magma centers—supervolcanoes—formed across what is now the Snake River Plain of southern Idaho. Yellowstone National Park today lies directly over the hotspot.

Shaded relief map of the Pacific Northwest highlighting National Park Service sites along the Yellowstone Hotspot track. Letters are abbreviations for NPS sites listed near the top of this page. The Yellowstone Hotspot surfaced 17 million years ago as massive outpourings of basalt lava in the Columbia Plateau–Steens Basalt region. Since then the North American Plate has moved west-southwestward, forming a chain of supervolcanoes across southern Idaho to Yellowstone National Park. The Yellowstone Plateau is a broad region of high elevation directly above the hotspot, while the Snake River Plain has gradually subsided as that portion of the plate moved away from the hotspot.

Modified from “Parks and Plates: The Geology of our National Parks, Monuments and Seashores,” by Robert J. Lillie, New York, W. W. Norton and Company, 298 pp., 2005, www.amazon.com/dp/0134905172.

Columbia Plateau —Yellowstone Hotspot Track

Volcanic rocks in the Pacific Northwest show the effects of a tectonic plate riding over a deep-mantle hotspot.

Numbers are the Age of Initial Volcanism (Millions of Years Ago). Letters are abbreviations for National Park Service sites listed near the top of this page.

A hotspot is like the hot wax rising in a lava lamp.

When you turn the lamp on the heated wax rises because it expands and becomes less dense than the oil.

A broad “head” developes, connected to the vat of wax by a narrow “stem.”

The Columbia Plateau and Steens Basalt are the initial surfacing of the giant plume head.

When magma from the plume head reaches the surface, it flows across the surface as basalt.

Illustrations above modified from “Beauty from the Beast: Plate Tectonics and the Landscapes of the Pacific Northwest,” by Robert J. Lillie, Wells Creek Publishers, 92 pp., 2015, www.amazon.com/dp/1512211893.

When only the stem remains, the magma mixes with melted continental crust and is enriched in silica, forming the rhyolite lavas that poured out across southern Idaho and Yellowstone.

Along with black lights and hookahs, lava lamps are iconic fixtures of the psychedelic 1960’s. Observing what happens when we turn on a lava lamp can help us understand the evolution of the Columbia Plateau–Yellowstone Hotspot track. It’s not clear exactly why deep mantle material heats up. But when it does it expands like the hot wax in a lava lamp. The wax rises as it becomes less dense than the surrounding oil. At times the rising wax develops a mushroom shape, with a large head and narrow stem. Similarly, deep within the Earth heated mantle becomes less dense than the surrounding material. Although it is still solid, the heated mantle can rise slowly toward the surface. And like the wax in a lava lamp, it can develop a mushroom shape. The magma melting off the mantle at a hotspot initially has a low-silica, basalt composition. When the Yellowstone Hotspot initially reached the surface 17 million years ago, it was shaped like a mushroom, with a large head and narrow stem. The massive outpourings of basalt lava covered the Columbia Plateau and Steens Basalt regions.

After a few million years, the mushroom head of the hotspot dissipates, leaving only a thin stem. Plate motion carries the region of extensive basalt lava away, but the magma rising from the stem must somehow work its way to the surface. That’s when the thickness and composition of continental crust come into play. The basaltic melt from the hotspot stem may, in fact, form two levels of magma chambers within the overriding plate. The lowest is at the base of the crust, retaining a low-silica (basalt/gabbro) composition. Magma rising from that level melts its way through thick, silica-rich continental crust, forming high-silica (rhyolite/granite) magma chambers in the upper part of the crust. A narrow chain of explosive, rhyolite volcanoes forms on the surface of the moving plate.

The areas of rhyolite underlying the Snake River Plain form discrete areas of volcanic activity, rather than one long ridge. This situation is analogous to that seen in the Pacific Ocean, where discrete islands form over the Hawaiian Hotspot. “Islands” of rhyolite, progressively younger to the northeast, extend across the Snake River Plain of southern Idaho. Similar to the Big Island of Hawaii, a very high region, the Yellowstone Plateau, lies directly above the hotspot.

John Day Fossil Beds

John Day Fossil Beds National Monument in northeastern Oregon contains incredible examples of mammal, plant, and other fossils. Those fossils are preserved in sedimentary layers that were deposited from 54 to 6 million years ago. Within the fossil beds are lava flows—part of the enormous volume of basalt that formed the Columbia Plateau of northeastern Oregon and southeastern Washington. The fluid lavas poured out of long fissures, much like those seen erupting from rift zones on the flanks of shield volcanoes in Hawaii and Iceland. More than 20 such flows, totaling about 1,600 feet (500 meters) thickness, can be seen in Picture Gorge within the monument.


Data Sources

GPS and GNSS

The "filtered" versions of the two above data sources simply remove sites that have velocity sigmas larger than 2 mm/yr NE and 6 mm/yr vertical.

The GEM Strain Rate Map Project compiles velocity data from thousands of GPS/GNSS stations around the world, and models plate motions and crustal strain. The GSRM report is "A geodetic plate motion and Global Strain Rate Model," Kreemer, C., G. Blewitt, E.C. Klein, 2014, Geochemistry, Geophysics, Geosystems, 15, 3849-3889, doi:10.1002/2014GC005407.

Vertical speeds which are precisely zero are not plotted, as is the case for GEM data in 2015.

Earthquakes

Earthquake location data comes from the United States Geological Survey (USGS). You can search their catalog with the USGS Earthquake Search. There are three sets of earthquakes from this source: 4200 North American earthquakes with magnitudes of 4.5 or more, 6387 earthquakes in the western U.S. (lower 48 states) with magnitudes of 3.5 or more, and 10286 global earthquakes of magnitude 5.5 or more, all sets for the years 1995 through 2014. How many earthquakes are shown depends on the "How many markers displayed" choice. Color indicates depth of earthquakes (see the Key above). To find recent earthquakes, see Earthquakes from the USGS Earthquake Hazards Program.

Volcanoes

Smithsonian Global Volcanism Program.
All volcanoes are always shown, regardless of the "How many markers displayed" choice.

Tectonic Plates

From the USGS web site Global Geologic Setting of the 1906 Earthquake, the Tectonic Plate Boundaries data file (https://earthquake.usgs.gov/regional/nca/virtualtour/kml/Earths_Tectonic_Plates.kmz), and from the KMZ file Earth's Tectonic Plates. All plate boundaries are always shown, regardless of the "How many markers displayed" choice.

If you have questions about the data values, please check with the data providers listed above. Ask UNAVCO (send mail to: dataunavco.org ) about this map tool and its displays.

Last modified: 2021-01-13 16:31:58 America/Denver

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The Geodetic Facility for the Advancement of Geosciences (GAGE) is a facility funded by the National Science Foundation and NASA and operated by UNAVCO. Any opinions, findings, and conclusions or recommendations expressed in this material do not necessarily reflect the views of the National Science Foundation.


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