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 Earth's crust, crust that is prone to localized volcano, volcanic activity. The type and number of volcanoes required to be called a "field" is not well-defined. Volcanic fields usually consist of clusters ...

that extends from the southern Cimarron Range of the

Sangre de Cristo Mountains The Sangre de Cristo Mountains (Spanish language, Spanish for "Blood of Christ") are the southernmost mountain range, subrange of the Rocky Mountains. They are located in southern Colorado and northern New Mexico in the United States. The mountai ...

to the vicinity of Wagon Mound, New Mexico. The town of Wagon Mound is named after The Wagon Mound, a prominent landmark that is a highly eroded volcanic neck 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 90% ...

volcano A volcano is commonly defined as a vent or fissure 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 oft ...

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 andesites, 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 predomina ...

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 rhyolite. ...

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 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 w ...

, 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. 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 is a broad expanse of plain, flatland in North America. The region stretches east of the Rocky Mountains, much of it covered in prairie, steppe, and grassland. They are the western part of the Interior Plains, which include th ...

. 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 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 plain (an essentially flat landform) created by the deposition of sediment over a long period by one or more rivers coming from highland regions, from which alluvial soil forms. A ''floodplain'' is part of the process, bei ...

, the entire area was uplifted, and

canyon A canyon (; archaic British English spelling: ''cañon''), gorge or chasm, 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 t ...

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 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