Where to find igneous rocks in colorado

Contact metamorphism of the Leadville limestone created the Yule Marble. Regional metamorphism occurs because pressure and temperature change over a broad area. Different pressure and temperature combinations create a variety of minerals.

In the course of a drive through Big Thompson Canyon from Loveland to Estes Park, you traverse all of the mineral zones of regional metamorphism. The presence of biotite near the mouth of the canyon signals an area of low-grade metamorphic rocks. Farther up the canyon are the garnet and staurolite zones indicative of formations subjected to higher temperatures.

Within five miles, you reach the community of Drake in the highest sillimanite temperature and pressure zone of regional metamorphism. Exposed in the hills above Drake are coarse-grained pegmatites that are vein-like offshoots of the batholith. The high-grade rocks and pegmatites are indicators that you are approaching the square-mile granitic batholith that surrounds Estes Park. Around Estes Park and Rocky Mountain National Park, the metamorphic rocks were raised to temperatures and pressures at or near their melting point.

This gave rise to migmatites , an intimate mixture of igneous and metamorphic rocks. Migmatites are found throughout much of the Front Range. The Archaean rocks of the Owiyukuts Complex are the oldest in Colorado. They were metamorphosed about 2. That means that the original rocks were even older. Rocks are subjected to intense pressures and temperatures during metamorphism.

This makes them quite ductile and allows them to fold into weird and wonderful shapes. Sometimes they are folded multiple times such that early formed folds will be re-folded. The metamorphic rocks in Colorado endured three, and perhaps four, periods of ductile deformation. The oldest folds in Colorado are in Precambrian metamorphic rocks. The layers were folded during different regional metamorphic events. When previously folded rocks were again subjected to heat and pressure, they were refolded and became refolded folds.

Early geologists studying the Precambrian structures of the Front Range found many clues indicating two periods of folding, but were unable to find a place where they could see both sets of folds in the same outcrop. Finally, they found an outcrop in Clear Creek Canyon east of Blackhawk that has both sets of folds. It is fairly easy to pick out large-scale many sq km anticline and synclines. However, it requires careful searching to discern the smaller-scale cm-sized or less tight folds that were folded once during an earlier period of folding, then folded again and tightened by a second period of folding.

However, there are places in Colorado where the original features can be discerned, even in high-grade metamorphic rocks. Igneous rock is formed from magma that has cooled and become solid. Molten rock is extraordinarily hot, sometimes exceeding 2, degrees Fahrenheit.

If this molten and partially crystallized material magma solidifies underground before it reaches the surface, the rock is intrusive or plutonic. Magma that reaches the surface forms a variety of volcanic landforms and deposits.

In the southwestern part of the state, ash-flow tuffs cover thousands of square miles. The tuff is created from the ash that is blown from the volcano to blanket the landscape. An ash-flow eruption creates a roughly circular depression called a caldera.

The Rocky Mountains of Colorado boast spectacular views of numerous plutonic or intrusive rocks. These rocks were formed long ago as magma rose from deep sources and solidified before making it all the way to the surface. As the magma rose, in many places, it brought with it precious minerals such as gold, silver, lead, and molybdenum used in hardening steel. After millions of years, erosional processes stripped off the overlying rocks, exposing them as we see today.

Both complexes contain abundant rare earth elements. A batholith is an intrusive mass of solidified magma usually granitic in composition and defined as having a minimum size greater than 40 mi 2 km 2 and no known floor. These are emplaced deep in the crust and are irregular in shape.

It was generally thought that the batholiths fell into three age groups: the Routt plutonic suite at about 1. With more age dating, and more advanced dating techniques, we are discovering that the intrusions were more spread out in time.

Dikes are formed when magma a mixture of molten material and crystals rises from below and cuts across pre-existing strata. The magma may follow pre-existing cracks or faults, or may create its own path upward. The magma crystallizes underground and becomes a dike, which is a plutonic or intrusive rock. Erosion cuts into the earth and allows us to observe the dikes. The magma in a dike may or may not have reached the surface.

If the magma pours out onto the surface then it becomes a volcanic or extrusive rock. All extrusive rocks must of necessity have intrusive feeders, usually dikes or plugs. Laccoliths are mushroom-shaped bodies with a flat floor and a domed roof. Thus, they appear to have begun forming in the same way as sills; however, as magma continued to intrude, it pushed up the overlying layers rather than continuing to spread out laterally.

Colorado has many laccoliths and is the first place in the world where they were recognized and named. Corry lists more than 80 by name and location, and it is estimated that there are between , globally. Magma that moves upward and cuts across pre-existing layers of rock forms what are generally known as plutons. The largest plutons are batholiths , such as the granitic rocks of Pikes Peak, which are part of a 1,square-mile batholith. Smaller plutons take a variety of shapes, each with its own name, such as stocks , plugs , dikes and sills.

A volcanic plug, also called a volcanic neck or lava neck, is a volcanic landform created when magma hardens within a vent on an active volcano. If rising volatile-charged magma is trapped beneath a plug, the resulting extreme build-up of pressure can sometimes lead to an explosive eruption. Eons later, erosion can reveal the more resistant plug forming residual landforms. For example, Edinburgh Castle in Scotland is built upon an ancient volcanic plug.

Sills form by magma squeezing between, and parallel to, the layers of the host rock, rather than cross-cut existing layers of strata as dikes do. Paleogene andesite sill in a quarry southwest of Lyons. The sill intrudes the upper Paleozoic Fountain Formation. Note the vertical columnar jointing in the sill. Primary use of andesite in this sill is for commercial aggregate. Colorado has sills of many different sizes and ages intruded into an astonishing variety of surrounding rocks.

Volcanic or extrusive rocks have cooled from molten material that either flowed out onto the surface of the earth or were blasted up into the air and settled back onto the surface of the earth.

Volcanic igneous rocks are widespread throughout Colorado. At one time, about sixty percent of Colorado was covered by volcanic rocks but much of that coverage has since eroded. Volcanic rocks come in a variety of forms, depending on the type of eruption from which it originated.

For example, in a violent eruption ash fall, ash flow, and lava flow may occur, all of which produce different types of volcanic igneous rock. Many of these rocks originated in the San Juan volcanic field, which is in the southwestern region of the state.

There, many large caldera eruptions generated hundreds of cubic miles of pyroclastic debris. When volcanic debris is ejected into the atmosphere it eventually settles back down to the surface as ash fall. Volcanic igneous rocks that result from this process are usually of uniform in grain size, which are tiny flakes of glass. Some ash ejected into the atmosphere may float for years before settling back down to the surface. Ash falls provide very good age datums that may be correlated for thousands of miles in some cases.

A very important ash fall deposit in Colorado is the Lava Creek B ash that was created by Yellowstone Caldera around , years ago.

This ash has been instrumental in providing age constraints on numerous formations around Colorado, such as the Browns Park Formation. Ash flows follow explosive volcanic eruptions and occur when dense ash sinks and flows down the flanks of an erupting volcano.

These scorching hot flows can travel hundreds of miles per hour, knocking down trees and obliterating anything else in their path. Ash flows can form volcanic igneous rocks such as welded tuffs, where the incredible temperature of the flow causes ash to fuse together. Ash flows may also contain various sizes of other pyroclastic material. Between 25 and 37 million years ago when ash flows were erupting with gusto, it is estimated that two-thirds of the state was covered with ash flow deposits.

The Fish Canyon Tuff surrounding the present-day site of Creede, Colorado is one of the largest ash flows in the world. It contains approximately 1, cubic miles of material that was deposited red hot and has a welded zone more than a half-mile thick. The Rocky Mountains of the Southwest consist of multiple mountain ranges resulting from both the Sevier and Laramide orogenies, which uplifted numerous discrete blocks of terrain along thrust faults that accommodated compressional shortening and thickening of the crust.

The overlying sediments were subsequently eroded to expose deeper Precambrian rock as well as Paleozoic and Mesozoic sedimentary formations. The thrust-faulted uplift also produced adjacent basins, which subsequently accumulated sediments eroded from the surrounding mountains. In the Southwest, the Rockies are located in central and western Colorado, north-central New Mexico, and northeastern Utah.

Precambrian rocks are well exposed in the Rocky Mountains, where 1. These ancient rocks are typically metamorphosed and deformed, but occasionally some of the original sedimentary and volcanic textures can still be observed, including bedding, cross-bedding, and pillow lavas. Coarse-grained, dark-colored metamorphic rocks are ubiquitous.

Many of these Precambrian rock units can be seen in exposures along roads that wind through the mountains. For example, the Uinta Mountains, an east-west segment of the southern Rockies in northeastern Utah, are made of uplifted and metamorphosed sedimentary rocks deposited in a shallow marine basin over million years ago. These are part of a thick 4- to 7-kilometer [13, to 24,foot] sequence of rocks known as the Uinta Mountain Group that were uplifted during the Laramide Orogeny Figure 2.

Figure 2. Schist—metamorphosed sediment—is fairly common in the Rocky Mountains, and can be found throughout the region. It is usually composed of shale and siltstone that have been compressed to form relatively large crystals especially micas that are layered into sheet-like structures. Gneisses—metamorphosed rhyolite or granite—are common in the Colorado Rockies Figure 2. In contrast, the Precambrian rocks of New Mexico have a higher ratio of sedimentary units, including more quartzite and conglomerate, than is found in Colorado.

Quartzite—metamorphosed sandstone—is very resistant to erosion, so it forms steep slopes and is often found at the core of ridges or mountains. This rock ranges in color from white and gray to pink and purple, depending on the amounts of iron and other minor minerals that were deposited with the sand grains.

When rocks are subjected to high enough temperatures or pressures, their characteristics begin to change. The weight of overlying rock can cause minerals to realign perpendicularly to the direction of pressure, layering them in a pattern called foliation , as exemplified in gneiss and schist.

Recrystallization, as seen in marble and quartzite, results as rock is heated to high temperatures. Individual grains reform as interlocking crystals, making the resulting metamorphic rock much harder than its parent rock.

Contact metamorphism describes a metamorphic rock that has been altered by direct contact with magma. Changes that occur due to contact metamorphism are greatest at the point of contact. The farther away the rock is from the point of contact, the less pronounced the change. Regional or dynamic metamorphism describes a metamorphic rock that has been altered due to deep burial and great pressure. This type of metamorphic rock tends to occur in long belts.

Different types of metamorphic rock are created depending on the gradients of heat and pressure applied. A gneiss is a very highly metamorphosed rock with alternating bands of dark and light minerals. The dark bands are mafic and higher in magnesium and iron, while the lighter bands are felsic and higher in silicates. These bands may form because extreme temperature and pressure cause a chemical reaction that forces the different elements into separate layers.

Banding may also occur when a set of varied protoliths are subjected to extreme shearing and sliding forces, causing them to stretch into stacked sheets. See Chapter 5: Mineral Resources to learn about rhodo-chrosite, diamonds, and other rare Rocky Mountain minerals. Natural regions of Colorado [Map]. Griffin, K. National Park Service Educational Resources.

Hopkins, R. Mineralogical Society of America. The Rock Cycle [Figure]. Lufkin, J. Geology of Colorado and Major Prehistoric Events. GEO-Volution , Biennial Geotechnical Seminar McCreary, J.

McKinney, M. Environmental Science: Systems and Solutions 4 th ed. Raynolds, R. Colorado Stratigraphy Chart. Map Series MS The Rock Cycle. Mineralogical Society of America There are three types of rock incorporated in this process:. Igneous Rock Formations located throughout Colorado. CGS South Table Mountain, Golden, Colorado. Sedimentary Rock Formations throughout Colorado.

Book Cliffs, Western Colorado. Metamorphic Rocks. Metamorphic Rock Formations throughout Colorado. Painted Wall in the Black Canyon of the Gunnison. Generalized Geology of Colorado.

Glenwood Canyon First hard-shelled animals e. Table 2: Hydrogeologic units throughout Colorado. Colorado Stratigraphic Chart. Natural regions of Colorado. Encyclopedia Britannica Online n. Colorado Plateau. Southern Rocky Mountains. Great Plains. The Colorado Piedmont is an area along the base of the foothills of the Front Range in north central Colorado located just under 5, feet elevation. The area is characterized by a broad, hilly valley stretching north and northeast of Denver in the South Platte River valley and southward from Colorado Springs in the Arkansas River valley.

The Raton Basin is a geologic structural basin in southern Colorado and northern New Mexico that is bound by the Sangre de Cristo Mountains and Culebra Range to the west, the south edge of the Wet Mountains to the north, the Apishapa Arch to the northeast, the Las Animas Uplift to the east and the Sierra Grande uplift to the south and southeast. The lowest elevation is approximately 6, feet along the Purgatoire River, while the highest elevation rises to over 13, feet at the Spanish Peaks.

Hydrogeology of Colorado An aquifer is a groundwater reservoir composed of geologic units that are saturated with water and sufficiently permeable to yield water in usable amounts to wells and springs. Consolidated Sedimentary Rock Aquifers. Poorly Consolidated to Unconsolidated Sediments.

Colorado's poorly consolidated to unconsolidated sediment aquifers. Recreated from CGS Volcanic and Crystalline Rock Aquifers. Additional Resources.

Geologic Tour. Geology and National Parks.