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Bearhead Rhyolite
The Keres Group is a group of geologic formations exposed in and around the Jemez Mountains of northern New Mexico. Radiometric dating gives it an age of 13 to 6 million years, corresponding to the Miocene epoch. Geology The Jemez Mountains lie on the intersection of the western margin of the Rio Grande Rift and the Jemez Lineament. Here magma produced from the fertile rock of an ancient subduction zone has repeatedly found its way to the surface along faults produced by rifting. This has produced a long-lived volcanic field, with the earliest eruptions beginning at least 13 million years ago in both the northern (Polvadera Group) and southern (Keres Group) portions of the volcanic field. High-silica eruptions of the Tewa Group began about 1.85 million years ago and continued almost to the present day. The Keres Group is a sequence of basalt, andesite, dacite, and rhyolite flows that underlie the southern Jemez Mountains. It overlaps the Polvadera Group to the north and has a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Group (geology)
In geology, a group is a lithostratigraphic unit consisting of a series of related formations that have been classified together to form a group. Formations are the fundamental unit of stratigraphy. Groups may sometimes be combined into supergroups. Groups are useful for showing relationships between formations, and they are also useful for small-scale mapping or for studying the stratigraphy of large regions. Geologists exploring a new area have sometimes defined groups when they believe the strata within the groups can be divided into formations during subsequent investigations of the area. It is possible for only some of the strata making up a group to be divided into formations. An example of a group is the Glen Canyon Group, which includes (in ascending order) the Wingate Sandstone, the Moenave Formation, the Kayenta Formation, and the Navajo Sandstone. Each of the formations can be distinguished from its neighbor by its lithology, but all were deposited in the same vast ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Jemez Lineament
The Jemez Lineament is a chain of late Cenozoic volcanic fields, long, reaching from the Springerville and White Mountains volcanic fields in East-Central Arizona to the Raton-Clayton volcanic field in Northeastern New Mexico. The lineament was long interpreted as a hotspot trace (Raton hotspot) due to its resemblance in length and direction to the Yellowstone hot spot trace, but there is no systematic progression in age along the trace and it is now interpreted as a hydrous subduction zone scar. This formed about 1.7 billion years ago, when oceanic crust was subducting under what was then the southern edge of North America. The arrival of a large island arc in the subduction zone shifted subduction further south, leaving remnants of oceanic crust at the top of the Earth's mantle along the former subduction zone. These are rich in hydrous minerals that lower the melting temperature of the rock containing them. This hydrous subduction scar now separates basement rock of th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Abiquiu Formation
The Abiquiu Formation is a geologic formation found in northern New Mexico. Radiometric dating constrains its age to between 18 million and 27 million years, corresponding to the late Oligocene to Miocene epochs. The formation is composed mostly of volcanic debris from the Latir volcanic field, and records the early stages of the opening of the Rio Grande rift in northern New Mexico. Artist Georgia O'Keeffe drew inspiration from her study of the formation at Plaza Blanca. Description The Abiquiu Formation consists of light-gray to yellowish-gray, locally crossbedded, thin to thick beds of tuffaceous sandstone, pebbly sandstone, and siltstone. There are also a few gravel beds and lenses of mudstone. The clasts are mostly of volcanic rock, including Amalia Tuff and trachyandesite and trachydacite possibly also from the Latir volcanic field. The formation is exposed in a broad belt from the southwest flank of the Tusas Mountains to the Jarosa area in the northwest Jemez Mou ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chinle Formation
The Chinle Formation is an Upper Triassic continental geological formation of fluvial, lacustrine, and palustrine to eolian deposits spread across the U.S. states of Nevada, Utah, northern Arizona, western New Mexico, and western Colorado. In New Mexico, it is often raised to the status of a geological group, the Chinle Group. Some authors have controversially considered the Chinle to be synonymous to the Dockum Group of eastern Colorado and New Mexico, western Texas, the Oklahoma panhandle, and southwestern Kansas. The Chinle Formation is part of the Colorado Plateau, Basin and Range, and the southern section of the Interior Plains.GEOLEX database entry for Chinle USGS (viewed 19 March 2006) A probable separate depositional basin within the Chinle is found in northwestern Colorado and northeastern Ut ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Abo Formation
The Abo Formation is a geologic formation in New Mexico. It contains fossils characteristic of the Cisuralian epoch of the Permian period. Description The Abo Formation consists of fluvial redbed mudstones and sandstones, including river channel deposits in its lower beds (Scholle Member) and distinctive sandstone sheets in its upper beds (Cañon de Espinoso Member.) Its depositional environment was typical of the "wet red beds" of tropical Pangaea. It is extensively exposed in the mountains and other uplifts bordering the Rio Grande Rift, with a thickness of at the type section. It is also present in the subsurface in the Raton Basin. The base of the Abo is gradational with the Madera Group, and is usually placed at the first massive marine limestone bed below the fluvial sediments of the Abo. It is overlain by the Yeso Formation, with the base of the Yeso placed at the first massive sandstone bed showing frosted grains and other eolian features. The transition zone between th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Permian
The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Paleozoic Era; the following Triassic Period belongs to the Mesozoic Era. The concept of the Permian was introduced in 1841 by geologist Sir Roderick Murchison, who named it after the region of Perm in Russia. The Permian witnessed the diversification of the two groups of amniotes, the synapsids and the sauropsids ( reptiles). The world at the time was dominated by the supercontinent Pangaea, which had formed due to the collision of Euramerica and Gondwana during the Carboniferous. Pangaea was surrounded by the superocean Panthalassa. The Carboniferous rainforest collapse left behind vast regions of desert within the continental interior. Amniotes, which could better cope with these drier conditions, rose to dominance in place of their am ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Valles Caldera
Valles Caldera (or Jemez Caldera) is a wide volcanic caldera in the Jemez Mountains of northern New Mexico. Hot springs, streams, fumaroles, natural gas seeps and volcanic domes dot the caldera floor landscape. The highest point in the caldera is Redondo Peak, an resurgent lava dome located entirely within the caldera. Also within the caldera are several grass valleys, or ''valles'', the largest of which is Valle Grande ( ), the only one accessible by a paved road. In 1975, Valles Caldera was designated as a National Natural Landmark by the National Park Service with much of the caldera being within the Valles Caldera National Preserve, a unit of the National Park System. History Use of Valles Caldera dates back to the prehistoric times: spear points dating to 11,000 years ago have been discovered.Anscheutz, Kurt F. and Merlan, Thomas (2007)"More than a scenic mountain landscape: Valles Caldera National Preserve land use history" U.S. Department of Agriculture Rocky Mountain ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Composite Volcano
A stratovolcano, also known as a composite volcano, is a conical volcano built up by many layers (strata) of hardened lava and tephra. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile with a summit crater and periodic intervals of explosive eruptions and effusive eruptions, although some have collapsed summit craters called calderas. The lava flowing from stratovolcanoes typically cools and hardens before spreading far, due to high viscosity. The magma forming this lava is often felsic, having high-to-intermediate levels of silica (as in rhyolite, dacite, or andesite), with lesser amounts of less-viscous mafic magma. Extensive felsic lava flows are uncommon, but have travelled as far as . Stratovolcanoes are sometimes called composite volcanoes because of their composite stratified structure, built up from sequential outpourings of erupted materials. They are among the most common types of volcanoes, in contrast to the less common shield volcanoes ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Andesite
Andesite () is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predominantly of sodium-rich plagioclase plus pyroxene or hornblende. Andesite is the extrusive equivalent of plutonic diorite. Characteristic of subduction zones, andesite represents the dominant rock type in island arcs. The average composition of the continental crust is andesitic. Along with basalts, andesites are a component of the Martian crust. The name ''andesite'' is derived from the Andes mountain range, where this rock type is found in abundance. It was first applied by Christian Leopold von Buch in 1826. Description Andesite is an aphanitic (fine-grained) igneous rock that is intermediate in its content of silica and low in alkali metals. It has less than 20% quartz and 10% feldspathoid by volume, with at least 65% of the fe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Basalt
Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial planet, rocky planet or natural satellite, moon. More than 90% of all volcanic rock on Earth is basalt. Rapid-cooling, fine-grained basalt is chemically equivalent to slow-cooling, coarse-grained gabbro. The eruption of basalt lava is observed by geologists at about 20 volcanoes per year. Basalt is also an important rock type on other planetary bodies in the Solar System. For example, the bulk of the plains of volcanism on Venus, Venus, which cover ~80% of the surface, are basaltic; the lunar mare, lunar maria are plains of flood-basaltic lava flows; and basalt is a common rock on the surface of Mars. Molten basalt lava has a low viscosity due to its relatively low silica content (between 45% and 52%), resulting in rapidly moving lava flo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Volcanic Field
A volcanic field is an area of Earth's crust that is prone to localized volcanic activity. The type and number of volcanoes required to be called a "field" is not well-defined. Volcanic fields usually consist of clusters of up to 100 volcanoes such as cinder cones. Lava flows may also occur. They may occur as a monogenetic volcanic field or a polygenetic volcanic field. Description Alexander von Humboldt observed in 1823 that geologically young volcanoes are not distributed uniformly across the Earth's surface, but tend to be clustered into specific regions. Young volcanoes are rarely found within cratons, but are characteristic of subduction zones, rift zones, or in ocean basins. Intraplate volcanoes are clustered along hotspot traces. Within regions of volcanic activity, volcanic fields are clusters of volcanoes that share a common magma source. Scoria cones are particularly prone to cluster into volcanic fields, which are typically in diameter and consist of several tens ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
