Английская Википедия:Cima volcanic field

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Cima volcanic field is a volcanic field in San Bernardino County, California, close to the border with Nevada.Шаблон:SfnШаблон:Sfn The volcanic field covers a surface area of Шаблон:Cvt within the Mojave National Preserve west of the Cima Dome and consists of about 40 volcanic cones with about 60 lava flows. The volcanic cones range from simple cones over multi-cratered mountains to eroded hills, and lava flows are up to Шаблон:Cvt long. At least one lava tube exists in the field and can be visited.

Volcanic activity in the field commenced in the Late Miocene and after a pause between 3 and 1 million years ago continued into the latest Pleistocene. The youngest cone is known as the Black Tank cone and formed about 15,000 years before present, although it is possible that it was formed through two separate eruption events; formerly it was considered to be of historical age.

Geography and geology

The Cima volcanic field lies in the eastern Mojave Desert of California,Шаблон:SfnШаблон:Sfn between the Shadow Valley in the northeast, the Cima Dome in the east and the Soda Lake Valley in the southwest.Шаблон:Sfn Southwest of the field is Kelbaker Road which crosses some lava flows,[1] and dirt roads such as the Indian Springs Trail and the Aiken Mine Road crisscross between the volcanoes.Шаблон:Sfn

Interstate 15 passes north of the field and just south of older volcanic units,Шаблон:Sfn while California State Route 127 runs west and southwest of the field,Шаблон:Sfn The city of Las Vegas is Шаблон:Convert northeast of the area.Шаблон:Sfn The Cima volcanoes are part of the Mojave National Preserve and since 1973 they make up the Cinder Cones National Natural Landmark.[1]Шаблон:Sfn

During the Holocene and until recent times, humans engraved petroglyphs into the lava flows.[2] One cinder cone was quarried to obtain materials for road construction.Шаблон:Sfn The volcanic field has been the subject of soil sciences and landscape development research.Шаблон:Sfn

Regional

Volcanism is widespread in the western United States and occurs in various forms at various places. Among the better known are the Cascade volcanoes created by subduction off the western coast of North America,Шаблон:Sfn which include the caldera of Mount Mazama (created by a large eruption in the early Holocene)Шаблон:Sfn as well as stratovolcanoes such as Mount St. Helens and mafic volcanic fields.Шаблон:Sfn Other volcanic centres in the United States are those associated with Yellowstone Caldera and Snake River Plain,Шаблон:Sfn those along the margins of the Colorado Plateau,Шаблон:Sfn volcanoes linked to the Rio Grande Rift and Jemez lineament,Шаблон:Sfn and finally volcanoes in the western Basin and Range Province such as the Cima volcanic fieldШаблон:Sfn where the crust is extending.Шаблон:Sfn

Generally, volcanic activity was widespread in the dry regions of the western United States during the Tertiary and Quaternary, forming several volcanic fields.Шаблон:Sfn An earlier phase of felsicШаблон:Efn volcanism during the Tertiary was followed during the Quaternary by more basaltic volcanism,Шаблон:Sfn often in the form of short-lived volcanic vents.Шаблон:Sfn Examples of this kind of volcanism are the Cima volcanic field, the San Francisco volcanic field (Arizona), the Southwest Nevada volcanic field (Nevada) and the Zuni-Bandera volcanic field (New Mexico).Шаблон:Sfn

The Cima volcanic field is part of the Mojave Desert, which in turn belongs to the Basin and Range Province and features both mountains exceeding Шаблон:Convert height which trend in southeast–northwest direction, with broad valleys between the mountains.Шаблон:Sfn Other volcanoes there include Dish Hill, Amboy Crater and Pisgah Crater.Шаблон:Sfn

Local

There are about 40 cones in the Cima volcanic field. The cones are as much as Шаблон:Convert wide and Шаблон:Convert high,Шаблон:Sfn and are concentrated between elevations of Шаблон:ConvertШаблон:SfnШаблон:Sfn on a south-southwest tilting slope.Шаблон:SfnШаблон:SfnШаблон:Sfn Some cones are well preserved with intact craters,Шаблон:Sfn while others have been reduced to hills by erosion.Шаблон:Sfn Some cones have more than one crater.Шаблон:Sfn North of the main field lie two outcrops of older volcanic rocks (Miocene to Pliocene);Шаблон:Sfn other than this separate older outcrop volcanic activity appears to have occurred without any preferential alignment.Шаблон:Sfn Several washes such as Willow Wash, Black Tank Wash and Indian Creek cross through the field and have eroded lava flows.Шаблон:Sfn

The youngest cone (Шаблон:Coord) in the southwestern part of the field is called Black Tank cone.Шаблон:Sfn The Black Tank cone is the source of a Шаблон:Convert long lava flow, which at first forms a levee-bound channel and then narrows out into a lobate shape.Шаблон:Sfn It also shows traces of a lava tubeШаблон:Sfn and has a volume of Шаблон:Convert. This flow may have been preceded by a previous lava flow which was later buried by the main flow.Шаблон:Sfn An older vent lies just south-southwest of the Black Tank Cone.Шаблон:Sfn

The field presents black and red volcanic rocksШаблон:Sfn in the form of cinders, exposed feeder dikes and lava bombs, as well as agglutinates which are exposed in gullies and eroded vents. Bombs and cinders cover the less eroded cones, which are also sometimes surrounded by base surge deposits.Шаблон:Sfn At some vents, tuff rings formed through phreatomagmatic activity.Шаблон:Sfn Erosion has dug gullies and larger valleys in the older cones,Шаблон:Sfn including one Шаблон:Convert deep gorge.Шаблон:Sfn

Volcanic material covers a surface area of about Шаблон:Convert[3]Шаблон:SfnШаблон:Sfn within an area of Шаблон:Circa Шаблон:Convert.Шаблон:Sfn The volcanic field was emplaced on a basement of Tertiary age, which comprises both crystalline bedrock and thick gravel deposits.Шаблон:Sfn Other rock formations in the area are of ProterozoicШаблон:EndashPaleozoic to Mesozoic (Teutonia batholith) age, and the region is considered to be part of the Ivanpah uplift.Шаблон:EfnШаблон:SfnШаблон:Sfn

Lava flows

Файл:NPS mojave-lava-tube-trail-map.gif
Map of the road to the lava tube

The cones have given rise to about 60 lava flows. Lava flows reach lengths of Шаблон:Convert, thicknesses of Шаблон:Convert and have surface features similar to pahoehoe or aa lava depending on how steep the slopes they flowed down were.Шаблон:SfnШаблон:Sfn The lava flows display structures like levees, finger-like and lobe-like edges at the lava flow margins, spines and spiresШаблон:Sfn and material from the cones that was rafted away by the lavas.[4] One can distinguish between long, gently sloping flows which dominate the field, and shorter, steeper rougher flows covered by blocks with sizes of up to Шаблон:Convert.Шаблон:Sfn[5] One major lava tube lies in the Cima field and is accessibleШаблон:Sfn[6] through a skylight; it is Шаблон:Convert long and Шаблон:Convert wide.Шаблон:Sfn In some places flows surrounded basement outcrops, forming kipukas.Шаблон:Efn In accordance to the slope of the area, most lavas flowed westward.Шаблон:Sfn

Younger flows often show crisp lava flow featuresШаблон:Sfn while older flows are almost always mantled with younger material and have lost their original surface features.Шаблон:Sfn The oldest flows have flat or gentle surfaces and their source vents are heavily degraded.Шаблон:Sfn Lava flows are also in part covered by wind-transported or erosional materialШаблон:Sfn and desert varnish.Шаблон:Sfn

Composition

The field has erupted alkali basalt, basanite and hawaiite.Шаблон:Sfn Phenocrysts include clinopyroxene, olivine and plagioclase. There are also xenoliths including dunite, gabbro, granite,Шаблон:SfnШаблон:Sfn and notably ultramafic to mafic xenolithsШаблон:Sfn such as peridotite derived from the mantle.Шаблон:Sfn The rock composition has not changed much during the history of the Cima volcanoes,Шаблон:Sfn but three distinct groups have been identified.Шаблон:Sfn Temperatures of Шаблон:Convert have been estimated for the lava erupted by the Black Tank cone.Шаблон:Sfn

The magma erupted in the field ultimately appears to originate from the lithospheric or asthenospheric mantle with little contribution of crustal components,Шаблон:Sfn unlike earlier felsic volcanism.Шаблон:Sfn Upwelling of asthenosphere material appears to be responsible for the volcanism at the end,Шаблон:Sfn possibly associated with the change in the tectonics of the region from subduction-dominated to tectonics of a transform boundary.Шаблон:Sfn Fractional crystallization, magma ponding in the crust, differences in the mantle sources and partial melting processes have been invoked to explain certain compositional differences in the erupted rocks.Шаблон:Sfn Xenoliths indicate that magma ascent to the surface is rapid, with no stalling, and processes of magma formation to surface eruption take only a few days.Шаблон:Sfn

Climate and vegetation

The climate of the area is warm and dry with average temperatures of Шаблон:Convert and average precipitation amounting to Шаблон:Convert.Шаблон:Sfn Most precipitation falls during winter, with only small amounts of rain falling during summer as monsoonal rainfall.Шаблон:Sfn Before the beginning of the Holocene, the climate was wetter and this facilitated the development of soils on lava flows. During the Holocene, playasШаблон:Efn became sources for wind-blown dust which accumulates on the lava.Шаблон:Sfn

Vegetation in the area is classified as scrub, with plants including brittle bush, creosote bush, Mormon tea and white bursage. Joshua trees grow at higher elevations.Шаблон:Sfn[5] Some of these species arrived during the Holocene, while others became established during the Pleistocene or appeared and disappeared repeatedly.[5] Vegetation grows in clusters separated by soil covered by desert pavement.Шаблон:Sfn The youngest cone is unvegetatedШаблон:Sfn and little vegetation has developed on other recent volcanic vents and lava flows.[7]

Eruptive history

Early research postulated a Pleistocene age for the northern part of the field and a Holocene age for the southern; later radiometric dates indicated Miocene ages for the northern parts of the field. More recent research showed Miocene ages for the northern volcanics and Pleistocene ages for the southern.Шаблон:Sfn An eruption rate of 8 events per 100,000 years and a magma output of Шаблон:Convert has been estimated for the Cima field.[8]

According to potassium-argon dating, volcanic activity started in the Miocene and continued to the end of the Pleistocene.Шаблон:Sfn Activity has been subdivided into five phases, the first between 7.6 and 6.5 million years ago, the second between 5.1 and 3.6 million years ago, the third between 1.1 and 0.6 million years ago, the fourth between 750,000 and 200,000 years ago and the fifth and last between 200,000 and 10,000 years ago.Шаблон:SfnШаблон:SfnШаблон:Sfn The radiometric ages have been corroborated by morphological and paleomagnetic information.Шаблон:Sfn Volcanic activity paused between 3 and 1 million years ago.Шаблон:Sfn

The oldest volcanic phase left a heavily dissected volcano in the southeastern part of the field, while the subsequent phase involved lava flows in the northern part of the field that take the form of eroded mesas. The final three phases formed lava flows and the volcanoes in the southern part of the field.Шаблон:Sfn Eruptions commenced as maar-forming eruptions and continued with the growth of cinder cones and lava flows.Шаблон:Sfn Unlike regular cinder cones which usually erupt only once, some cones at Cima experienced more than one eruption and were active over hundreds of thousands of years.Шаблон:Sfn

The Black Tank cone,Шаблон:Sfn the youngest cone in the field, has been dated to 15,000 ± 5,000 years before present by several methods.Шаблон:SfnШаблон:Sfn Some evidence suggested a historical age for one of the southern lava flows,Шаблон:Sfn with earlier radiocarbon dating yielding an age of 330–480 years.[3]Шаблон:Sfn Several chronological data imply that the lava flow was formed during two separate eruptive episodes, one 20,000 years ago and the other 11,500 - 13,000 years ago.Шаблон:Sfn The lava flow was probably laid down in less than a week of time,Шаблон:Sfn and the growth of the cone was influenced by wind, which transported tephra east-southeastwards where it fell out and formed a tephra blanket.Шаблон:Sfn

See also

Шаблон:Portal

Шаблон:Clearboth

Notes

Шаблон:Notelist

References

Шаблон:Reflist

Sources

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Шаблон:Refend

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Разное

  1. ↑ 1,0 1,1 Ошибка цитирования Неверный тег <ref>; для сносок USGS не указан текст
  2. ↑ Ошибка цитирования Неверный тег <ref>; для сносок WhitleyDorn1987 не указан текст
  3. ↑ 3,0 3,1 Ошибка цитирования Неверный тег <ref>; для сносок GVP не указан текст
  4. ↑ Ошибка цитирования Неверный тег <ref>; для сносок ValentineGregg2008 не указан текст
  5. ↑ 5,0 5,1 5,2 Ошибка цитирования Неверный тег <ref>; для сносок BalmackiWigand2019 не указан текст
  6. ↑ Ошибка цитирования Неверный тег <ref>; для сносок NPS не указан текст
  7. ↑ Ошибка цитирования Неверный тег <ref>; для сносок USGS2004 не указан текст
  8. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Browne2017 не указан текст
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