When and why that second uplift happened are still debated. Almost all modern Colorado mountain ranges have thrust faults at their bases.
Thrust faults occur when the crust is compressed, which happens when tectonic plates converge. Movement on a thrust fault stacks one slab of rock atop another. That stacking forms mountains. During the Laramide Orogeny, a plate consisting of oceanic material was converging with continental North America off the coast of California. The best explanation for those attributes is that the mantle beneath the Rockies is unusually warm.
That warm mantle is also the reason Colorado has so many hot springs. Geophysicist Gordon Eaton has called this heat-induced swelling the Alvarado Ridge.
While geophysicists have documented the warmth of the mantle beneath the Colorado Rockies, they have been unable to deduce when the mantle warmed up. The when and the why of that mantle heating and the associated second uplift event are the subject of current disagreement and research. About 38 million years ago, soon after the Laramide Orogeny ended, Colorado erupted in a volcanic episode of giant proportions that lasted until about 24 million years ago; geologists call this episode the Ignimbrite Flare-up.
It is one of fifteen giant caldera volcanoes in the San Juans, and more big Ignimbrite Flare-up volcanoes or their eroded remnants form peaks in the Elk, West Elk, Sawatch, and Front Ranges. Later activity also helps explain the raising of the Alvarado Ridge. About 28 million years ago, just as the Ignimbrite Flare-up was winding down, the Colorado Rockies were stretched and split along the north-south trending Rio Grande Rift.
Such stretching thins the crust, bringing hot mantle closer to the surface, which in turn causes thermal expansion and associated surface uplift. For that reason, many geologists think the Alvarado Ridge rose about 28 million years ago, simultaneous with formation of the Rio Grande Rift. Their primary evidence is that before 5 million years ago, sand and gravel were accumulating across the western Great Plains, producing the Ogallala Formation, the rock unit that forms the important Ogallala Aquifer.
Sometime after 5 million years ago, the Ogallala Formation was tilted up to the west and the Arkansas and South Platte Rivers began to erode it. Both the tilting and the erosion might indicate that the Alvarado Ridge rose in the more recent geological past.
The modern Rockies might have risen 40, 28, or 5 million years ago. The mountains did not achieve their current grandeur until big glaciers sculpted them during the Pleistocene Ice Ages, which began about 2. About every , years, the planet cools by about 5 degrees Celsius, which is enough to cause large glaciers to form.
Those glacial intervals alternate with interglacial intervals, when the Earth receives more sunlight and the glaciers melt away. The Earth has been in an interglacial interval for about the last 10, years, and the peak of the most recent glacial interval was about 20, years agowere.
Without the combination of the Laramide Orogeny, the post-Laramide uplift of the Alvarado Ridge, and the sculpting action of the Pleistocene glaciers, Colorado would not boast the mountain landscape that brings pleasure to so many locals and visitors today.
Eugene Humphreys et al. Denver: Colorado Geological Survey, You are here Home. Rocky Mountains. View of Rocky Mountains from Mt. The spectacular scenery of the park lies within the Blue Ridge Province, with a small portion on the northwest in the Valley and Ridge Province. Parks in the Washington DC area reveal a lot about the geology and tectonic evolution of the Appalachian Mountains. The Ouachita Mountains of western Arkansas and southeastern Oklahoma are a classic example of a soft continental collision.
Plate convergence ceased soon after the ocean separating ancient North America from Gondwanaland closed. The crust beneath the growing mountains remained relatively thin.
Peaks never attained heights anywhere near those of the modern Himalayas and Alps, nor of the ancient Appalachians. The low buoyancy of thin crust allowed the accumulation of thick sedimentary layers as the ancient ocean closed about million years ago.
Without thick crust and high mountains, there has been only small amounts of erosion and isostatic rebound, so that a pile of sedimentary layers as much as 12 miles 20 kilometers thick still lies beneath the Ouachita Mountains.
Hot Springs National Park in Arkansas preserves evidence of the soft continental collision that formed the Ouachita Mountains. Rocks are not the hard igneous and metamorphic variety found in the Appalachian Mountains, but rather softer sedimentary layers scraped off the seafloor and thrust over the edge of the continent as the ocean between North and South America closed.
The originally horizontal rocks are folded and faulted, much as the strata in the Valley and Ridge Province of the Appalachians. The sandstone, shale and chert layers are part of a thick pile of sediments that were deformed and uplifted as Gondwanaland collided with the southern edge of ancient North America million years ago.
Photo courtesy of Robert J. Congress established Hot Springs National Reservation in to preserve and protect the region of thermal waters around Hot Springs Mountain in Arkansas. The thermal waters for which Hot Springs National Park is named are not due to the presence of shallow magma beneath the area, as at Yellowstone. Rather, the hot springs occur because there are cracks in chert layers outside the park that allow rainwater to circulate slowly downward, where it is heated due to the normal increase in temperature with depth in the Earth.
The area of southwest Texas where the Rio Grande River takes a sharp turn to the north displays the effects of three superimposed tectonic episodes. Earlier compression of the North American continent from 80 to 40 million years ago formed the Laramide Uplifts, which include the frontal ranges of the Rocky Mountains. And before that, the soft continental collision that formed the Ouachita Mountains million years also formed the Marathon Mountains.
The northernmost part of Big Bend National Park, around Persimmon Gap, lies in the Marathon Mountains and includes rocks and structures similar to those found in the Ouachitas.
The park thus preserves the westernmost vestiges of the oceanic closure and continental collision found not only in the Appalachians of the U.
Northern Alaska was the site of continental collision that progressed to a stage somewhere between the soft collision seen in the Ouachita and Marathon mountains, and the hard collision observed in the Appalachians and Himalayas. In its prime, about million years ago, the Brooks Range probably had mountains as high as the Alps of Europe.
Gates of the Arctic National Park and Preserve reveals mountains much higher than those seen in the Appalachians, because the Brooks Range is still young—erosion has not worn the landscape down quite as much. Today The Arctic Ocean opens on the north.
After eroding away up to 10 miles 16 kilometers of rock, there is still a small crustal root that maintains mountain heights much greater than those seen today in the Appalachians. Plate Tectonics and Our National Parks. Divergent Plate Boundaries. Convergent Plate Boundaries. Transform Plate Boundaries. Oceanic Hotspots. Continental Hotspots. Text and Illustrations by Robert J. Explore This Park. Introduction Sometimes an entire ocean closes as tectonic plates converge, causing blocks of thick continental crust to collide.
Collisional Mountain Range Development. A plate capped by thin oceanic crust subducts beneath one capped by thick continental crust, forming an accretionary wedge and volcanic arc on the overriding plate. The ocean closes as a continent with thick crust approaches the subduction zone. A collisional mountain range forms as an entire ocean closes and blocks of thick continental crust collide.
Letters are abbreviations for parks listed below. Ouachita Mountains [1 park]. Marathon Mountains [2 parks]. Brooks Range [4 parks]. Shenandoah National Park, Virginia. The rugged Appalachian Mountains are the eroded remnants of much higher mountains that formed as continents collided million years ago. NPS photo. Hot Springs National Park, Arkansas. The mineral springs rise up in the center of the Ouachita Mountains, an extension of the Appalachian Mountains that surface in Arkansas and Oklahoma.
NPS sites in northern Alaska are vast wilderness areas that lie in the Brooks Range, a collisional mountain range that is younger and higher than the Appalachian Mountains. Tectonic Development of the Appalachian—Ouachita—Marathon Mountain Range The Appalachian Mountains, along with the Caledonide Mountains in Greenland, the British Isles and Scandinavia, as well as the Atlas Mountains in northeastern Africa, are parts of a continental collision zone that formed to million years ago.
The Appalachian Mountains formed from terrane accretion and the collision of Gondwanaland with ancient North America as the Iapetus Ocean closed. Note that Shenandoah National Park lies within the state of Virginia highlighted on the map.
Old Continent Rips Apart. The notion that only part of the oceanic plate got pulled up by suction helps explain why the Colorado Plateau south of the Rockies appears relatively undisturbed, even though it was also riding atop the subducting plate.
The authors suggest the lithosphere under the plateau wasn't as thick, so it didn't interfere as much with the oceanic plate's progress. So far there's no solid evidence for an odd landmass under Wyoming. But the new hypothesis "sort of challenges this idea that we understand what's going on," said Basil Tikoff , a structural geologist at the University of Wisconsin in Madison who was not involved with the paper. If all it took to create the Rockies was the grinding of one plate against another, then we should see major, far-inland mountain ranges on most continents, he added.
The fact that we don't seems to counter the flat-slab hypothesis, according to Tikoff. Mihai Ducea , a geoscientist at the University of Arizona, called the new research a "paradigm-shifting paper, something we've been waiting for a long time to explain most of the observations we have out here in the West.
In addition to the Rockies, the Colorado Mineral Belt—a swath of igneous rocks and precious metals reaching from southwest Colorado to Boulder—could have formed when the extraordinary tension from suction caused parts of the mantle to melt and rise to the surface.
In the flat-slab hypothesis, the mineral belt "was sort of written off as a fluke as to how the continent had been built, instead of a fundamental clue," study leader Jones said. Ducea, who reviewed the paper before publication, said he'd like to apply the study to the Andes Mountains, which could turn out to be a "living laboratory" for testing the new hypothesis.
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