The Ocate volcanic field (also known as the Mora volcanic field) is a monogenetic

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 ...

that extends from the southern Cimarron Range of the

Sangre de Cristo Mountains The Sangre de Cristo Mountains ( Spanish for " Blood of Christ") are the southernmost subrange of the Rocky Mountains. They are located in southern Colorado and northern New Mexico in the United States. The mountains run from Poncha Pass in South- ...

to the vicinity of

Wagon Mound, New Mexico Wagon Mound is a village in Mora County, New Mexico, United States. It is named after and located at the foot of a butte called Wagon Mound, which was a landmark for covered wagon trains and traders going up and down the Santa Fe Trail and is ...

. The town of Wagon Mound is named after The Wagon Mound, a prominent landmark that is a highly eroded

volcanic neck A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plates are ...

of the volcanic field.

Description

About 8.12 million years ago,

basaltic Basalt (; ) is an 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 surface of a rocky planet or moon. More than ...

volcano A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plates ...

es began to erupt in the Ocate area. Fourteen eruptive pulses have been identified using

Ar-Ar dating Arar or Ar-Ar may refer to: Geography and history * Arar, Saudi Arabia, the capital of Al Hudud ash Shamaliyah (The Northern Border) province ** Arar border crossing, a Saudi-Iraqi border crossing near Arar, Saudi Arabia and Nukhayb, Iraq * Arar ...

, with the most recent taking place around 0.67 to 0.95 Mya. The lavas erupted in the field are mostly alkali olivine basalt or transitional olivine basalt, with smaller quantities of

basaltic andesite Basaltic andesite is a volcanic rock that is intermediate in composition between basalt and andesite. It is composed predominantly of augite and plagioclase. Basaltic andesite can be found in volcanoes around the world, including in Central Am ...

s, olivine

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 predo ...

s, and

dacite Dacite () is a volcanic rock formed by rapid solidification of lava that is high in silica and low in alkali metal oxides. It has a fine-grained ( aphanitic) to porphyritic texture and is intermediate in composition between andesite and rhyo ...

s. The basaltic lavas were generated from heterogeneous source regions in the mantle, while the more silica-rich andesites and dacites formed from fractional crystallization of basaltic magma and mixing with silica-rich magma from

partial melting Partial melting occurs when only a portion of a solid is melted. For mixed substances, such as a rock containing several different minerals or a mineral that displays solid solution, this melt can be different from the bulk composition of the soli ...

of crust. The volcanic field lies along the

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 ...

, a zone of young volcanic activity stretching from central Arizona to northeastern New Mexico. The lineament is thought to be a zone of weakness in the lower crust and upper

mantle A mantle is a piece of clothing, a type of cloak. Several other meanings are derived from that. Mantle may refer to: *Mantle (clothing), a cloak-like garment worn mainly by women as fashionable outerwear **Mantle (vesture), an Eastern Orthodox ve ...

. The vents in the eastern part of the field are aligned roughly east to west, perpendicular to the direction of least compression in the southern

Great Plains The Great Plains (french: Grandes Plaines), sometimes simply "the Plains", is a broad expanse of flatland in North America. It is located west of the Mississippi River and east of the Rocky Mountains, much of it covered in prairie, steppe, a ...

. Vents in the western part of the field are aligned more randomly, probably because of recent tectonic disturbance of this area. An unusual feature of the Ocate volcanic field is that the oldest basaltic flows form the highest mesas, and the youngest flows form surfaces lower in elevation. This

reverse stratigraphy Reverse stratigraphy (sometimes known as inverted stratigraphy) is the result of a process whereby one sediment is unearthed by human or natural actions and moved elsewhere, whereby the latest material will be deposited on the bottom of the new s ...

occurred because after the older flows were erupted about 8.3–5.7 m.y. ago on a relatively flat

alluvial plain An alluvial plain is a largely flat landform created by the deposition of sediment over a long period of time by one or more rivers coming from highland regions, from which alluvial soil forms. A floodplain is part of the process, being the smal ...

, the entire area was uplifted, and

canyon A canyon (from ; archaic British English spelling: ''cañon''), or gorge, is a deep cleft between escarpments or cliffs resulting from weathering and the erosive activity of a river over geologic time scales. Rivers have a natural tendency to cu ...

s were cut into the older basalt flows. Younger basalt flows then filled the major stream canyons. When uplift ceased, the youngest basalt flows of the Ocate volcanic field flowed on top of intermediate-aged flows.

History of investigation

During the

Wheeler Survey The Wheeler Survey, carried out in 1872-1879, was one of the "Four Great Surveys" conducted by the US government after the Civil War primarily to document the geology and natural resources of the American West. Supervised by First Lieutenant (lat ...

of 1878 to 1879, J.J. Stevenson studied the basalt flows of the Ocate volcanic field, giving the name ''Ocate Mesa'' to the main lava-capped mesa that nearly surrounds the town of Ocate, New Mexico. Stevenson also recognized that the basalt-capped mesas south of Ocate Mesa were once continuous with Ocate Mesa prior to erosion. N.H. Darton included the outline of the field in his geologic map of New Mexico in 1928. More detailed mapping took place from the 1950s on. In 1988, J. Michael O'Neill and Harald H. Mehnert carried out the first detailed geologic study of the area and gave it the name of the Ocate volcanic field.

Footnotes

References

* * * * * Volcanic fields of New Mexico Miocene volcanism Landforms of Mora County, New Mexico Pliocene volcanism Pleistocene volcanism Monogenetic volcanic fields

External links

* {{cite gvp, name=Ocate, vn=327819, access-date=2021-06-28

Description

History of investigation

See also

Footnotes

References

External links