Monzonite is an igneous intrusive rock. It is composed of equal amounts of plagioclase and alkali feldspar. It may contain minor amounts of hornblende and other minerals, if quartz constitutes greater than 5%, the rock is termed a quartz monzonite. If the rock has a percentage of alkali feldspar, it grades into a syenite. With an increase in calcic plagioclase and mafic minerals the rock becomes a diorite. The volcanic equivalent is the latite, monzonite was originally named after the Monzoni range in Val di Fassa where it is abundant. As rock definitions have been systematized and codified, this association has lost any relevance to the rocks definition
The House Range is a north-south trending mountain range in Millard County, of west-central Utah. The House Range was named in 1859 by James H. Simpson and it was named by Simpson because. of its well-defined stratification and the resemblance of portions of its outline to domes, minarets and other structures. The House Range is bounded by Tule Valley to the west, Whirlwind Valley and Sevier Desert to the east, the range has three notable passes, Skull Rock Pass, Marjum Canyon, and Sand Pass. The highest point in the House Range is Swasey Peak, at 9,669 feet, other notable peaks include Notch Peak, a frequent climbing and base-jumping hotspot, and the very square Tatow Knob. It is known for one of the tallest limestone cliffs in the world, the geology of the House Range is dominated by gray Cambrian to Devonian carbonate rock which was intruded by a pink Jurassic granitoid in the central part of the range. In the Wheeler Amphitheater, away from the intrusion, the Lagerstätte that contains the well-preserved fauna is found in the Cambrian section of the range, evidence of Lake Bonnevilles presence is found both in shorelines and white marls at the base of the range.
The main structural component to the range is a large basin-bounding fault on the west side. The range is known for a fossil Lagerstätte of Cambrian age, which has an array of Burgess Shale type fauna, including Elrathia kingii, the Swasey Limestone was deposited in the Bathyuriscus–Elrathina zone. This is overlain in turn by the Bolaspidella zone Wheeler Shale and Marjum Formation, the Cedaria zone Weeks Formation
Notch Peak is a distinctive summit located on Sawtooth Mountain in the House Range, west of Delta, United States. The peak and the area are part of the Notch Peak Wilderness Study Area. Bristlecone pines, estimated to be 3,000 to 4,000 years old, are located on the ridges surrounding Notch Peak, Notch Peak is one of the highest peaks in the House Range, reaching 9,658 feet NAVD88. The northwest face of the mountain is a carbonate rock cliff with 2,200 feet of vertical rise. Overall, the summit rises about 4,450 feet above Tule Valley, the significance of this cliff is debatable, mainly because of the variation in the definition of the term cliff. It is the highest carbonate rock cliff in North America and/or the second highest pure vertical drop in the United States after El Capitan, one of the more popular uses of the area is the hike to Notch Peak so you can look down the notch in person. The summit can be reached by following a trail from the east side of the mountain in Sawtooth Canyon, the hike is about 7.5 miles round trip, with 2,600 feet elevation gain.
The north face of Notch Peak is divided by a large shelf into an upper and lower wall, there are several rock climbing routes on the limestone cliffs. The Swiss Route, Direct North West Ridge, and Book of Saturdays ascend the upper wall, on the lower wall Appetite for Destruction and Western Hardman reach 900 feet of vertical. Climbing on all of these routes is adventurous with rockfall hazard, in addition to the face of Notch Peak, the granite found in the canyon below the notch is used for climbing. This part of the House Range is chiefly made up of a passive margin sequence of Cambrian to Ordovician carbonate rocks, the top of the range is the type section for the aptly named Notch Peak Dolomite. At the base of the range is the pink/orange Notch Peak granite and monzonite, around Notch Peak, especially from the west side, white Lake Bonneville fossiliferous marls occur. Because of the intrusion, a hike up the canyon below the notch can clearly show a well-developed metamorphic aureole, small quantities of tungsten and placer gold have been found around the Notch Peak area
In geology and related fields, a stratum is a layer of sedimentary rock or soil with internally consistent characteristics that distinguish it from other layers. The stratum is the unit in a stratigraphic column and forms the basis of the study of stratigraphy. Each layer is one of a number of parallel layers that lie one upon another. They may extend over hundreds of thousands of kilometers of the Earths surface. Strata are typically seen as bands of different colored or differently structured material exposed in cliffs, road cuts, individual bands may vary in thickness from a few millimeters to a kilometer or more. Each band represents a mode of deposition, river silt, beach sand, coal swamp, sand dune, lava bed. Geologists study rock strata and categorize them by the material of beds, each distinct layer is typically assigned to the name of sheet, usually based on a town, mountain, or region where the formation is exposed and available for study. For example, the Burgess Shale is an exposure of dark, occasionally fossiliferous.
Slight distinctions in material in a formation may be described as members, formations are collected into groups while groups may be collected into supergroups. Archaeological horizon Geologic formation Geologic map Geologic unit Law of superposition Bed GeoWhen Database
Igneous rock, or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or lava, the magma can be derived from partial melts of existing rocks in either a planets mantle or crust. Typically, the melting is caused by one or more of three processes, an increase in temperature, a decrease in pressure, or a change in composition, solidification into rock occurs either below the surface as intrusive rocks or on the surface as extrusive rocks. Igneous rock may form with crystallization to form granular, crystalline rocks and metamorphic rocks make up 90–95% of the top 16 km of the Earths crust by volume. Igneous rocks form about 15% of the Earths current land surface, most of the Earths oceanic crust is made of igneous rock. In terms of modes of occurrence, igneous rocks can be either intrusive or extrusive, the mineral grains in such rocks can generally be identified with the naked eye.
Intrusive rocks can be classified according to the shape and size of the intrusive body, typical intrusive formations are batholiths, laccoliths and dikes. When the magma solidifies within the earths crust, it cools slowly forming coarse textured rocks, such as granite, the central cores of major mountain ranges consist of intrusive igneous rocks, usually granite. When exposed by erosion, these cores may occupy huge areas of the Earths surface, intrusive igneous rocks that form at depth within the crust are termed plutonic rocks and are usually coarse-grained. Intrusive igneous rocks that form near the surface are termed subvolcanic or hypabyssal rocks, hypabyssal rocks are less common than plutonic or volcanic rocks and often form dikes, laccoliths, lopoliths, or phacoliths. Extrusive igneous rocks, known as rocks, are formed at the crusts surface as a result of the partial melting of rocks within the mantle. Extrusive igneous rocks cool and solidify quicker than intrusive igneous rocks and they are formed by the cooling of molten magma on the earths surface.
The magma, which is brought to the surface through fissures or volcanic eruptions, hence such rocks are smooth and fine-grained. Basalt is an extrusive igneous rock and forms lava flows, lava sheets. Some kinds of basalt solidify to form long polygonal columns, the Giants Causeway in Antrim, Northern Ireland is an example. The molten rock, with or without suspended crystals and gas bubbles, is called magma and it rises because it is less dense than the rock from which it was created. When magma reaches the surface from beneath water or air, it is called lava, eruptions of volcanoes into air are termed subaerial, whereas those occurring underneath the ocean are termed submarine. Black smokers and mid-ocean ridge basalt are examples of volcanic activity
A dike or dyke, in geological usage, is a sheet of rock that formed in a fracture in a pre-existing rock body. Dikes can be either magmatic or sedimentary in origin, magmatic dikes form when magma intrudes into a crack crystallizes as a sheet intrusion, either cutting across layers of rock or through an unlayered mass of rock. Clastic dikes are formed when sediment fills a pre-existing crack, an intrusive dike is an igneous body with a very high aspect ratio, which means that its thickness is usually much smaller than the other two dimensions. Thickness can vary from sub-centimeter scale to many meters, and the dimensions can extend over many kilometres. A dike is an intrusion into an opening cross-cutting fissure, shouldering aside other pre-existing layers or bodies of rock, near-horizontal, or conformable intrusions, along bedding planes between strata are called intrusive sills. Sometimes dikes appear in swarms, consisting of several to hundreds of dikes emplaced more or less contemporaneously during a single intrusive event, the worlds largest dike swarm is the Mackenzie dike swarm in the Northwest Territories, Canada.
Dikes often form as either radial or concentric swarms around plutonic intrusives, the latter are known as ring dikes. Pegmatite dikes comprise extremely coarse crystalline granitic rocks - often associated with granite intrusions or metamorphic segregations. Aplite dikes are fine-grained or sugary-textured intrusives of granitic composition, in contrast to magmatic dikes, a sill is a magmatic sheet intrusion that forms within and parallel to the bedding of layered rock. Sedimentary dikes or clastic dikes are vertical bodies of rock that cut off other rock layers. Driven by the pressure the sediment breaks through overlying layers. When a soil is under permafrost conditions the water is totally frozen. When cracks are formed in rocks, they may fill up with sediments that fall in from above. The result is a body of sediment that cuts through horizontal layers. Batholith Ring dike Fissure vent Laccolith Runamo, formerly interpreted as a runic inscription
Devils Tower is a laccolithic butte composed of igneous rock in the Bear Lodge Mountains near Hulett and Sundance in Crook County, northeastern Wyoming, above the Belle Fourche River. It rises dramatically 1,267 feet above the Belle Fourche River, the summit is 5,112 feet above sea level. Devils Tower was the first declared United States National Monument, established on September 24,1906, the Monuments boundary encloses an area of 1,347 acres. In recent years, about 1% of the Monuments 400,000 annual visitors climbed Devils Tower, the name Devils Tower originated in 1875 during an expedition led by Colonel Richard Irving Dodge, when his interpreter reportedly misinterpreted a native name to mean Bad Gods Tower. All information signs in that use the name Devils Tower. Native American names for the monolith include, Bears House or Bears Lodge, Aloft on a Rock, Tree Rock, Great Gray Horn, and Brown Buffalo Horn. In November 2014, one Arvol Looking Horse again proposed renaming the geographical feature Bear Lodge, a second proposal was submitted to request that the US acknowledge the offensive mistake and to rename the monument and sacred site Bear Lodge National Historic Landmark.
The formal public comment period ended in fall 2015, local state senator Ogden Driskill opposed the change. The landscape surrounding Devils Tower is composed mostly of sedimentary rocks, the oldest rocks visible in Devils Tower National Monument were laid down in a shallow sea during the Triassic period,225 to 195 million years ago. This dark red sandstone and maroon siltstone, interbedded with shale, oxidation of iron minerals causes the redness of the rocks. This rock layer is known as the Spearfish Formation, above the Spearfish formation is a thin band of white gypsum, called the Gypsum Springs Formation. This layer of gypsum was deposited during the Jurassic period,195 to 136 million years ago, created as sea levels and climates repeatedly changed, gray-green shales were interbedded with fine-grained sandstones and sometimes thin beds of red mudstone. This composition, called the Stockade Beaver member, is part of the Sundance Formation, the Hulett Sandstone member, part of the Sundance formation, is composed of yellow fine-grained sandstone.
Resistant to weathering, it forms the vertical cliffs which encircle the Tower itself. During the Paleocene Epoch,56 to 66 million years ago, the Rocky Mountains, magma rose through the crust, intruding into the existing sedimentary rock layers. Geologists Carpenter and Russell studied Devils Tower in the late 19th century, modern geologists agree that it was formed by the intrusion of igneous material, but not on exactly how that process took place. Several believe the molten rock comprising the Tower might not have surfaced, in 1907, scientists Darton and OHarra decided that Devils Tower must be an eroded remnant of a laccolith. A laccolith is a mass of igneous rock which is intruded through sedimentary rock beds without reaching the surface
A phacolith is a pluton parallel to the bedding plane or foliation of folded country rock. More specifically, it is a typically lens-shaped pluton that occupies either the crest of an anticline or the trough of a syncline. In rare cases the body may extend as a sill from the crest of an anticline through the trough of an adjacent syncline, in intensely folded terrain the hinge of folds would be areas of reduced pressure and thus potential sites for magma migration and emplacement. The term was coined and initially defined by Alfred Harker in his The Natural History of Igneous Rocks in 1909, young Mind Over Magma, The Story of Igneous Petrology, page 335, Princeton University Press
A batholith is a large emplacement of igneous intrusive rock that forms from cooled magma deep in the Earths crust. Batholiths are almost always made mostly of felsic or intermediate rock-types, such as granite, quartz monzonite, although they may appear uniform, batholiths are in fact structures with complex histories and compositions. Individual plutons are crystallized from magma that traveled toward the surface from a zone of partial melting near the base of the Earths crust, these plutons have been considered to form by ascent of relatively buoyant magma in large masses called plutonic diapirs. Because the diapirs are liquified and very hot, they tend to rise through the native country rock, pushing it aside. Most diapirs do not reach the surface to form volcanoes, but instead slow down, cool, an alternate view is that plutons commonly are formed not by diapiric ascent of large magma diapirs, but rather by aggregation of smaller volumes of magma that ascended as dikes. A batholith is formed when many plutons converge to form an expanse of granitic rock.
Some batholiths are mammoth, paralleling past and present subduction zones, one such batholith is the Sierra Nevada Batholith, which is a continuous granitic formation that makes up much of the Sierra Nevada in California. An even larger batholith, the Coast Plutonic Complex is found predominantly in the Coast Mountains of western Canada, a batholith is an exposed area of continuous plutonic rock that covers an area larger than 100 square kilometers. Areas smaller than 100 square kilometers are called stocks, the majority of batholiths visible at the surface have areas far greater than 100 square kilometers. These areas are exposed to the surface through the process of erosion accelerated by continental uplift acting over many tens of millions to hundreds of millions of years and this process has removed several tens of square kilometers of overlying rock in many areas, exposing the once deeply buried batholiths. Batholiths exposed at the surface are subjected to pressure differences between their former location deep in the earth and their new location at or near the surface.
As a result, their crystal structure expands slightly over time and this manifests itself by a form of mass wasting called exfoliation. This form of weathering causes convex and relatively thin sheets of rock to slough off the surfaces of batholiths. The result is clean and rounded rock faces. A well-known result of this process is Half Dome, located in Yosemite Valley,4, pp. 4–11 Idaho Batholith The Cornubian Batholith
A pegmatite is a holocrystalline, intrusive igneous rock composed of interlocking phaneritic crystals usually larger than 2.5 cm in size, such rocks are referred to as pegmatitic. The word pegmatite derives from Homeric Greek, πεγνυμι, which means “to bind together”, in reference to the crystals of quartz. Most pegmatites are composed of quartz and mica, having a similar composition as granite. Crystal size is the most striking feature of pegmatites, with usually over 5 cm in size. Individual crystals over 10 metres long have been found, and many of the worlds largest crystals were found within pegmatites and these include, microcline and tourmaline. Similarly, crystal texture and form within pegmatitic rock may be taken to extreme size, perthite feldspar within a pegmatite often shows gigantic perthitic texture visible to the naked eye. The single feature that is diagnostic to all pegmatites is their large size crystal components, Pegmatite bodies are usually of minor size compared to typical intrusive rock bodies.
Pegmatite body size is on the order of magnitude of one to a few hundred meters, compared to typical igneous rocks they are rather inhomogeneous and may show zones with different mineral assemblages. Crystal size and mineral assemblages are usually oriented parallel to the rock or even concentric for pegmatite lenses. Crystal growth rates in pegmatite must be slow to allow gigantic crystals to grow within the confines and pressures of the Earths crust. The mineralogy of a pegmatite is in most cases dominated by some form of feldspar, often with mica and usually with quartz and this is because of the difficulty in counting and sampling mineral grains in a rock which may have crystals from centimeters to meters across. Garnet, commonly almandine or spessartine, is a common mineral within pegmatites intruding mafic, pegmatites associated with granitic domes within the Archaean Yilgarn Craton intruding ultramafic and mafic rocks contain red and brown almandine garnet. Syenite pegmatites are quartz depleted and contain large feldspathoid crystals instead, Pegmatite is difficult to sample representatively due to the large size of the constituent mineral crystals.
Often, bulk samples of some 50–60 kg of rock must be crushed to obtain a meaningful, pegmatite is often characterised by sampling the individual minerals which comprise the pegmatite, and comparisons are made according to mineral chemistry. Occasionally, enrichment in the trace elements will result in crystallisation of equally unusual and rare minerals such as beryl, columbite, zinnwaldite. Pegmatites are the source of lithium either as spodumene, lithiophyllite or usually from lepidolite. The primary source for caesium is pollucite, a mineral from a zoned pegmatite, the majority of the worlds beryllium is sourced from non-gem quality beryl within pegmatite. Tantalum, rare-earth elements are sourced from a few pegmatites worldwide, bismuth and tin have been won from pegmatite, but this is not yet an important source of these metals
In geology, a sill is a tabular sheet intrusion that has intruded between older layers of sedimentary rock, beds of volcanic lava or tuff, or even along the direction of foliation in metamorphic rock. The term sill is synonymous with concordant intrusive sheet and this means that the sill does not cut across preexisting rocks, in contrast to dikes, discordant intrusive sheets which do cut across older rocks. Sills are fed by dikes, except in locations where they form in nearly vertical beds attached directly to a magma source. These planes or weakened areas allow the intrusion of a thin body of magma paralleling the existing bedding planes, concordant fracture zone. Sills parallel beds and foliations in the country rock. They can be emplaced in a horizontal orientation, although tectonic processes may cause subsequent rotation of horizontal sills into near vertical orientations. Sills can be confused with solidified lava flows, there are differences between them. Intruded sills will show partial melting and incorporation of the country rock.
On both contact surfaces of the rock into which the sill has intruded, evidence of heating will be observed. Lava flows will show this evidence only on the side of the flow. In addition, lava flows will show evidence of vesicles where gases escaped into the atmosphere. Because sills generally form at shallow depths below the surface, the pressure of overlying rock prevents this from happening much, lava flows will typically show evidence of weathering on their upper surface, whereas sills, if still covered by country rock, typically do not. Certain layered intrusions are a variety of sill that often contain important ore deposits, phanerozoic examples are usually smaller and include the Rùm peridotite complex of Scotland and the Skaergaard igneous complex of east Greenland. These intrusions often contain concentrations of gold, chromium, despite their concordant nature, many large sills change stratigraphic level within the intruded sequence, with each concordant part of the intrusion linked by relatively short dike-like segments.
Such sills are known as transgressive, examples include the Whin Sill, the geometry of large sill complexes in sedimentary basins has become clearer with the availability of 3D seismic reflection data. Such data has shown that many sills have a saucer shape. Sill may refer to the rise in depth near the mouth of a fjord caused by the moraine of the previous glacier. Sill swarm Batholith Stock Dike Laccolith Sheet intrusion