The geology of the Rocky Mountains is an intermittent series of mountains with different geological origins. Collectively it forms the Rocky Mountains, a mountain system that stretches from northern British Columbia through the center of New Mexico and which is part of a large mountain system known as the Cordillera of North America.
The core of mountain rocks, in many places, is formed from pieces of continental crust that are over a billion years old. In the south, the older mountains formed 300 million years ago, then eroded. Older range rocks were reformed into the Rocky Mountains.
The Rocky Mountains formed during the intense period of tectonic plate activity that resulted in many rugged landscapes in western North America. The Laramide orogeny, about 80-55 million years ago, was the last of three episodes and was responsible for raising the Rocky Mountains. The ensuing erosion by glaciers has created the shape of today's mountains.
Video Geology of the Rocky Mountains
Stone bells
The rocks in the Rocky Mountains formed before the mountains were raised by tectonic powers. The oldest rocks are Precambrian metamorphic rocks that form the core of the North American continent. There is also a Precambrian sediment argillit, since 1.7 billion years ago. During Paleozoikum, western North America lies beneath the shallow seas, depositing many miles of limestone and dolomite.
In the southern Rocky Mountains, near present-day Colorado, these ancestral rocks are disrupted by a mountain building of about 300 Ma, during Pennsylvania. This mountain building produces the Ancestral Rocky Mountains. This increase creates two large islands in the mountains, known by geologists as Frontrangia and Uncompahgria, located approximately in the current location in the Front Line and the San Juan Mountains. They are mostly composed of Precambrian metamorphic rocks, forced upward through layers of limestone laid out in shallow seas. Mountains eroded throughout the early Paleozoic and Mesozoicum, leaving extensive sedimentary sedimentary rocks.
The mesozoic deposition in the Rockies occurs in a mixture of ocean, transition, and continental environment as local sea level changes. At the Mesozoic closure, 10,000 to 15,000 feet (3000 to 4500 m) of sediment are collected in 15 known formations. The most extensive non-sea formations are stored in the Cretaceous period when the western part of the Western Interior Seaway covers the area.
Maps Geology of the Rocky Mountains
Terran and subduction
Terranes began colliding with the western edge of North America at the age of Mississippian (about 350 million years ago), causing Antler orogeny. During the last half of the Mesozoic Era, most areas of California, British Columbia, Oregon, and Washington are currently being added to North America. Western North America suffers from recurrent collisions when the Kula and Farallon plates are submerged beneath continental shores. The slices of the continental crust, carried along by the subduction ocean plate, are swept into subduction zones and etched to the western edge of North America.
It represents various tectonic environments. Some ancient island arches, similar to Japanese, Indonesian and Aleutians; the other are pieces of oceanic crust that are flanked to the boundary of the continent while others represent small islands in the middle of the sea are isolated.
The magma produced on top of the subduction plate rises to the North American continental crust of about 200 to 300 miles (300 to 500 km) inland. Large volcanic volcanoes, known as the Sierran Arc, grow as lava and ash spewed out from dozens of individual volcanoes. Below the surface, large mass of molten rock is injected and hardened in place.
For 270 million years, the effects of plate collisions are highly focused near the edge of the North American plate boundary, deep in the west of the Rocky Mountain region. It was not until 80 MA that this effect began to reach the Rockies.
Rockies Cultivation
The Rocky Mountains are currently raised in Laramide orogeny from between 80 and 55 Ma. For the Canadian Rockies, the mountain buildings are analogous to the carpets being pushed on hardwood floors: carpet bunches and forming wrinkles (mountains). In Canada, subduction of the Kula plates and terran that hit the continent is the foot pushing the tapestry, the ancestral stone is a tapestry, and the Canadian shield in the middle of the continent is hardwood floor.
Further south, the growth of the Rocky Mountains in the United States is a geological puzzle. Mountain buildings are usually focused between 200 to 400 mil (300 to 600 km) of land from the subduction zone boundary. Geologists continue to gather evidence to explain the rise of the Rocky Mountains farther inland; the answer most likely lies in the unusual subduction of the Farallon plate, or perhaps because of the subduction of the plains.
In a typical subduction zone, the oceanic plate usually sinks at a fairly steep angle, and the volcanic arc grows over the subduction plate. During the growth of the Rocky Mountains, the angle of the subduction plate may have been significantly leveled, moving the melt focus and building mountains further inland than normally expected. It is postulated that the shallow angle of the subduction plate greatly improves friction and other interactions with the thick continental mass above it. The tremendous impulse piled the crust sheets on top of each other, building an incredibly wide and high range of Rocky Mountain.
The southern Rockies are currently forced upward through the remaining layers of Pennsylvanian and Permian rocks from the Ancestral Rocky Mountains. The remains of the sediments are often tilted at steep angles along the sides of the modern line; they are now seen in many places throughout the Rockies, and are clearly displayed along the Dakota Hogback, the early Cretaceous sandstone formation that stretches on the eastern side of the modern Rockies.
Current landscape
Soon after Laramide orogeny, the Rockies like Tibet: the plateau, maybe 6,000 meters (20,000 feet) above sea level. In the last 60 million years, erosion has stripped away the high stones, revealing the ancestral rocks beneath them, and forming the current Rockies landscape.
The period of glaciation occurred from the Pleistocene Epoch (1.8 million-70,000 years ago) to the Holocene Epoch (less than 11,000 years ago). The ice age left their mark in the Rockies, forming a large glacial landscape, like U-shaped valleys and cirques. Recent glacial episodes include the Bull Lake Glaciation which began about 150,000 years ago and the Pinedale Glaciation that may remain at full glaciations up to 15,000-20,000 years ago. Ninety percent of Yellowstone National Park is covered by ice during Glide Pinedale. The small ice age is a period of glacial faces that lasted several centuries from about 1550 to 1860. For example, Agassiz and the Jackson Glacier in Glacier National Park reached the most advanced position around 1860 during the Small Ice Age.
All the geological processes, above, have left behind a complex collection of exposed rocks on the surface. For example, in the Rockies of Colorado, there is extensive granite and gneiss dating back to the Ancestral Rockies. In the middle Canadian Rockies, the main range consists of Precambrian bricks, while the front range consists of Paleozoic and dolomite limestone. The volcanic rocks from Cenozoic (66 million-1.8 million years ago) occurred in the San Juan Mountains and elsewhere. Severe millenium erosion in the Wyoming Basin converts the intermountain basin into a relatively flat field. Tetons and other north-central ranges contain rocks folded and damaged during the Paleozoic and Mesozoic ages composed of frozen and metamorphic Proterozoic and Arkeian rock cores ranging from 1.2 billion (eg Tetons) to over 3.3 billion years ( Beartooth Mountains)..
See also
- Aspen anomaly
- Canadian Rocky Mountains
- The geology of the Grand Teton area
References
External links
- Southern Rockies Geology
Source of the article : Wikipedia
0 Comments