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Boulder Batholith
The Boulder Batholith is a relatively small batholith in southwestern Montana, United States, exposed at the surface as granite (more specifically quartz monzonite) and serving as the host rock for rich mineralized deposits at Butte and other locations. The batholith lies roughly between Butte and Helena, and between the Deer Lodge (Upper Clark Fork) Valley and the Broadwater (Upper Missouri) Valley. The volcanic Elkhorn Mountains are a large mass of forested lava associated with the batholith. The batholith is composed of at least seven, and possibly as many as 14, discrete rock masses called plutons, which had formed beneath the Earth's surface during a period of magma intrusion about 73 to 78 million years ago (Late Cretaceous time). The rising buoyant plutons resulted from subduction along what was then the west coast of North America, which was near today's border between Montana and Idaho. Regional uplift brought the deep-seated granite to the surface, where erosion expo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Idaho Batholith
The Idaho Batholith is a granitic and granodioritic batholith of Cretaceous- Paleogene age that covers approximately of central Idaho and adjacent Montana. The batholith has two lobes that are separate from each other geographically and geologically. The Bitterroot lobe is the smaller lobe and the larger lobe is the Atlanta lobe. The Bitterroot lobe is in the north and is separated from the larger Atlanta lobe in the south by the Belt Supergroup metamorphic rocks that compose the Salmon River Arch. Much of the Atlanta and Bitterroot lobes are in the Idaho Batholith ecoregion. The overall intrusive event that created the Idaho batholith lasted for around 55 million years from Late Cretaceous to the Eocene (98 to 43 Ma) of magmatism and includes the younger Challis suite which is not considered to be part of the Idaho Batholith. The Challis suite intruded both the Atlanta and Bitterroot lobes of the Idaho Batholith as well as the surrounding areas to the east of the Atlant ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Subduction
Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the heavier plate dives beneath the second plate and sinks into the mantle. A region where this process occurs is known as a subduction zone, and its surface expression is known as an arc-trench complex. The process of subduction has created most of the Earth's continental crust. Rates of subduction are typically measured in centimeters per year, with the average rate of convergence being approximately two to eight centimeters per year along most plate boundaries. Subduction is possible because the cold oceanic lithosphere is slightly denser than the underlying asthenosphere, the hot, ductile layer in the upper mantle underlying the cold, rigid lithosphere. Once initiated, stable subduction is driven mostly by the negative buoyancy of the de ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Batholiths Of North America
A batholith () is a large mass of intrusive igneous rock (also called plutonic rock), larger than in area, that forms from cooled magma deep in Earth's crust. Batholiths are almost always made mostly of felsic or intermediate rock types, such as granite, quartz monzonite, or diorite (see also ''granite dome''). Formation Although they may appear uniform, batholiths are in fact structures with complex histories and compositions. They are composed of multiple masses, or ''plutons'', bodies of igneous rock of irregular dimensions (typically at least several kilometers) that can be distinguished from adjacent igneous rock by some combination of criteria including age, composition, texture, or mappable structures. Individual plutons are solidified from magma that traveled toward the surface from a zone of partial melting near the base of the Earth's crust. Traditionally, these plutons have been considered to form by ascent of relatively buoyant magma in large masses called ''p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spheroidal Weathering
Spheroidal weathering is a form of chemical weathering that affects jointed bedrock and results in the formation of concentric or spherical layers of highly decayed rock within weathered bedrock that is known as '' saprolite.'' When saprolite is exposed by physical erosion, these concentric layers peel (spall) off as concentric shells much like the layers of a peeled onion. Within saprolite, spheroidal weathering often creates rounded boulders, known as ''corestones'' or ''woolsack'', of relatively unweathered rock. Spheroidal weathering is also called onion skin weathering, concentric weathering, spherical weathering, or woolsack weathering.Fairbridge, RW (1968) ''Spheroidal Weathering.'' in RW Fairbridge, ed., pp. 1041–1044, The Encyclopedia of Geomorphology, Encyclopedia of Earth Sciences, vol. III. Reinhold Book Corporation, New York, New York. Ollier, C.D. (1971). ''Causes of spheroidal weathering. ''Earth-Science Reviews 7:127–141.Neuendorf, KKE, JP Mehl Jr., and JA ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hydrothermal Vein
In geology, a vein is a distinct sheetlike body of crystallized minerals within a rock. Veins form when mineral constituents carried by an aqueous solution within the rock mass are deposited through precipitation. The hydraulic flow involved is usually due to hydrothermal circulation. Veins are classically thought of as being the ones in the body not the rock veins and arteries planar fractures in rocks, with the crystal growth occurring normal to the walls of the cavity, and the crystal protruding into open space. This certainly is the method for the formation of some veins. However, it is rare in geology for significant open space to remain open in large volumes of rock, especially several kilometers below the surface. Thus, there are two main mechanisms considered likely for the formation of veins: ''open-space filling'' and ''crack-seal growth''. Open space filling Open space filling is the hallmark of epithermal vein systems, such as a stockwork, in greisens or in certa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Volcanics
Volcanic rock (often shortened to volcanics in scientific contexts) is a rock formed from lava erupted from a volcano. In other words, it differs from other igneous rock by being of volcanic origin. Like all rock types, the concept of volcanic rock is artificial, and in nature volcanic rocks grade into hypabyssal and metamorphic rocks and constitute an important element of some sediments and sedimentary rocks. For these reasons, in geology, volcanics and shallow hypabyssal rocks are not always treated as distinct. In the context of Precambrian shield geology, the term "volcanic" is often applied to what are strictly metavolcanic rocks. Volcanic rocks and sediment that form from magma erupted into the air are called "volcaniclastics," and these are technically sedimentary rocks. Volcanic rocks are among the most common rock types on Earth's surface, particularly in the oceans. On land, they are very common at plate boundaries and in flood basalt provinces. It has been estimated ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sedimentary Rock
Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles to settle in place. The particles that form a sedimentary rock are called sediment, and may be composed of geological detritus (minerals) or biological detritus (organic matter). The geological detritus originated from weathering and erosion of existing rocks, or from the solidification of molten lava blobs erupted by volcanoes. The geological detritus is transported to the place of deposition by water, wind, ice or mass movement, which are called agents of denudation. Biological detritus was formed by bodies and parts (mainly shells) of dead aquatic organisms, as well as their fecal mass, suspended in water and slowly piling up on the floor of water bodies (marine snow). Sedimentation may also occur as dissolved minerals precipitate from ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mesoproterozoic
The Mesoproterozoic Era is a geologic era that occurred from . The Mesoproterozoic was the first era of Earth's history for which a fairly definitive geological record survives. Continents existed during the preceding era (the Paleoproterozoic), but little is known about them. The continental masses of the Mesoproterozoic were more or less the same ones that exist today, although their arrangement on the Earth's surface was different. Major events and characteristics The major events of this era are the breakup of the Columbia supercontinent, the formation of the Rodinia supercontinent, and the evolution of sexual reproduction. This era is marked by the further development of continental plates and plate tectonics. The supercontinent of Columbia broke up between 1500 and 1350 million years ago, and the fragments reassembled into the supercontinent of Rodinia around 1100 to 900 million years ago, on the time boundary between the Mesoproterozoic and the subsequent Neoproterozoi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Syenogranite
Syenogranite is a fine to coarse grained intrusive igneous rock of the same general composition as granite. They are characteristically felsic. The feldspar component of syenogranite is predominantly alkaline in character (usually orthoclase). For example, the syenogranite in the Salmon Mountains in Idaho is pink to tan and composed of 45–55% alkali feldspar, 15–20% plagioclase, 15–20% quartz, 5–8% biotite, 3–5% hornblende, and accessory magnetite (Evans and Green, 2003). Syenogranite is similar to syenite, however the major difference is its higher content of quartz (15-25%) usually at the expense of some alkali feldspar (45-50%), the domination of biotite over hornblende and the presence of muscovite and rutile as additional accessories in the syenogranite. Some syenogranite contain rare idiomorphic amphibole (Fe-hornblende and Fe-edenite), biotite (annite 25%-35%), plagioclase (An3), along with K-feldspar and quartz. (Mafti, 2001). In the Sao Jose do Campestr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Monzogranite
Monzogranites are biotite granite rocks that are considered to be the final fractionation product of magma. Monzogranites are characteristically felsic (SiO2 > 73%, and FeO + MgO + TiO2 < 2.4), weakly (Al2O3/ (CaO + Na2O + K2O) = 0.98–1.11), and contain , , and as accessory |
Granodiorite
Granodiorite () is a coarse-grained (phaneritic) intrusive igneous rock similar to granite, but containing more plagioclase feldspar than orthoclase feldspar. The term banatite is sometimes used informally for various rocks ranging from granite to diorite, including granodiorite. Composition According to the QAPF diagram, granodiorite has a greater than 20% quartz by volume, and between 65% and 90% of the feldspar is plagioclase. A greater amount of plagioclase would designate the rock as tonalite. Granodiorite is felsic to intermediate in composition. It is the intrusive igneous equivalent of the extrusive igneous dacite. It contains a large amount of sodium (Na) and calcium (Ca) rich plagioclase, potassium feldspar, quartz, and minor amounts of muscovite mica as the lighter colored mineral components. Biotite and amphiboles often in the form of hornblende are more abundant in granodiorite than in granite, giving it a more distinct two-toned or overall darker appearan ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Idaho
Idaho ( ) is a state in the Pacific Northwest region of the Western United States. To the north, it shares a small portion of the Canada–United States border with the province of British Columbia. It borders the states of Montana and Wyoming to the east, Nevada and Utah to the south, and Washington and Oregon to the west. The state's capital and largest city is Boise. With an area of , Idaho is the 14th largest state by land area, but with a population of approximately 1.8 million, it ranks as the 13th least populous and the 7th least densely populated of the 50 U.S. states. For thousands of years, and prior to European colonization, Idaho has been inhabited by native peoples. In the early 19th century, Idaho was considered part of the Oregon Country, an area of dispute between the U.S. and the British Empire. It officially became U.S. territory with the signing of the Oregon Treaty of 1846, but a separate Idaho Territory was not organized until 1863, instead ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
