Reporting in the April 28 issue of the journal Nature, the eight-member team reports that uplift occurred as bottom portions of the lithosphere -- the upper layer of the Earth -- deteriorated, peeled and collapsed into magnetic, liquid-rich material, allowing the thick, underlying layer of fragile rock -- the asthenosphere -- to ascend and push up remaining surface material.
The images they created document the process of delamination. They also make a case for how much of the western half of the United States and, perhaps, many similar areas around the globe have formed, said co-author Eugene D. Humphreys, professor of geological sciences at the University of Oregon. The process is ongoing, he added, with the western half of the Grand Canyon still rising ever so slowly on the geological clock.
"This is the first time this process has actually been imaged, and it gives us insight into how tectonic plates can disintegrate and give surface uplift," Humphreys said.
UO doctoral student Brandon M. Schmandt applied UO-developed tomography techniques, similar to those used in CAT scans, with USArray data collected by Rice University geologists, including lead author Alan Levander. Their computation was pulled together using interface imaging techniques developed by Levander.
Researchers, including scientists from the University of Southern California and the University of New Mexico, created depth maps of underground features. They did this by calculating seismic secondary waves (S waves) and primary waves (P waves), which travel differently in response to earthquakes anywhere in the world. These waves were monitored at the USArray stations, which were inserted into the ground throughout the west in 2004.
Much of the western United States rose upward in the absence of horizontal tectonics in which plates collide, forcing one to descend and the other to rise. The Colorado Plateau covers much of an area known as the Four Corners -- southwestern Colorado, northwestern New Mexico, northeastern Arizona and southeastern Utah.
"Most geologists learned that vertical motions, like mountain building, are the result of horizontal motions such as thrust faulting, such as the Himalayas." Humphreys said. "More recently we are finding that changes in the density distribution beneath an area -- like the base of a relatively dense plate falling off -- can have a strong effect on surface uplift, too. This has been surprising to many, and for the base of a plate -- in this case, the lithosphere, in geology terminology -- falling off in particular, the question is: How does it do that?"
The two alternative theories have centered on a dripping process, or melting of the lithosphere's underside, or the peeling that occurs in delamination. In 2000, geologists argued that the Sierra Nevada mountain range is the result of the latter.
"We had to find a trigger to cause the lithosphere to become dense enough to fall off," Levander said. The partially molten asthenosphere is "hot and somewhat buoyant, and if there's a topographic gradient along the asthenosphere's upper surface, as there is under the Colorado Plateau, the asthenosphere will flow with it and undergo a small amount of decompression melting as it rises."
It melts enough, he said, to infiltrate the lithosphere's base and solidify. "It's at such a depth that it freezes as a dense phase. At some point, it exceeds the density of the asthenosphere underneath and starts to drip." The heat also reduces the viscosity of the mantle lithosphere.
It's possible, Humphreys said, that mountainous areas of southern and northern Africa and western Saudi Arabia resulted from the same process.
Co-authors with Levander, Schmandt and Humphreys were USC geologist Meghan Miller, Rice graduate student Kaijian Liu, Rice geologist Cin-Ty A. Lee, and geologist Karl E. Karlstrom and doctoral student Ryan Scott Crow, both of the University of New Mexico. National Science Foundation EarthScope grants and the Alexander von Humboldt Foundation Research Prize to Levander funded the research.About the University of Oregon
Media Contacts: Jim Barlow, director of science and research communications, 541-346-3481, firstname.lastname@example.org; and Mike Williams, senior media relations specialist, Rice University, 713-348-6728, email@example.com
Source: Eugene Humphreys, professor of geological sciences, 541-346-5575, firstname.lastname@example.orgLinks:
Layers' Interaction: http://comm.uoregon.edu/files/pmr/uploads/images/The_Interaction.mp3
UO Science on Facebook: http://www.facebook.com/UniversityOfOregonScience
Jim Barlow | EurekAlert!
In times of climate change: What a lake’s colour can tell about its condition
21.09.2017 | Leibniz-Institut für Gewässerökologie und Binnenfischerei (IGB)
Did marine sponges trigger the ‘Cambrian explosion’ through ‘ecosystem engineering’?
21.09.2017 | Helmholtz-Zentrum Potsdam - Deutsches GeoForschungsZentrum GFZ
Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.
A warming planet
Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.
The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...
Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...
Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!
When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole...
For the first time, physicists have successfully imaged spiral magnetic ordering in a multiferroic material. These materials are considered highly promising candidates for future data storage media. The researchers were able to prove their findings using unique quantum sensors that were developed at Basel University and that can analyze electromagnetic fields on the nanometer scale. The results – obtained by scientists from the University of Basel’s Department of Physics, the Swiss Nanoscience Institute, the University of Montpellier and several laboratories from University Paris-Saclay – were recently published in the journal Nature.
Multiferroics are materials that simultaneously react to electric and magnetic fields. These two properties are rarely found together, and their combined...
19.09.2017 | Event News
12.09.2017 | Event News
06.09.2017 | Event News
22.09.2017 | Life Sciences
22.09.2017 | Medical Engineering
22.09.2017 | Physics and Astronomy