The most famous example of a volcanic neck; unusual near-surface preservation of mafic mid-Tertiary volcanoes
The Navajo volcanic field is a diffuse group of intrusions, dikes, and some extrusive rocks of early Neogene (mid-Cenozoic) age scattered between Gallup and Farmington, New Mexico and Window Rock, Arizona. The most famous intrusion is Ship Rock. Intrusive rocks in the Navajo volcanic field, like most of those elsewhere within Colorado Plateaus province, include some unusual ultramfic petrographies such as minette, vogesite, and kimberlite as well as altered and serpentinized basaltic tuff and tuff breccia.
As a rule these types of volcanic rocks are indicative of derivation of magmas from deep within the continental lithosphere and from a mantle source that is somewhat different in composition than "typical" mantle. Minette consists of alkali feldspar, biotite or phlogopite, and diopside. Diopside (pyroxene), phlogopitic biotite and olivine occur as phenocrysts in many hand samples.
The Buell Park diatreme, which consists of kimberlite, is also part of the field. Kimberlite is the host rock for diamonds in many places in the world, because kimberlite is erupted from great depths where diamonds are initially formed. Both Buell Park and the Green Knobs are ultramafic beccias and consists mostly of serpentinized olivine and pyroxene.
The Beast, an isolated intrusion, is typical of the scattered smaller volcanic intrusions throughout the Navajo volcanic field.
View Navajo Volcanic Field/Shiprock in a larger map
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Beaumont, E.C., Preliminary geologic map of the Ship Rock and Hogback quadrangles, San Juan County, New Mexico. U. S. Geol. Survey Coal Investigation Map C-29, scale 1:48,000, 1955.
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Goff, F, Green Knobs ultramafic diatreme and carbon dioxide sequestration investigation. NM Geological Society Field Conference Guidebook 54, 16-17, 2003.
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Naeser, C.W., Geochronology of the Navajo-Hopi diatremes, Four Corners area [Colorado]. Jour. Geophys. Res., 76, 4978-4985, 1971.
Nicholls, J. W., Studies of the volcanic petrology of the Navajo-Hopi area, Arizona. Berkely, Univ. California, Ph.D. thesis, 107p., 1969.
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Williams, H., Pliocene volcanoes of the Navajo-Hopi country. Geol. Soc. America Bulletin, 47, 111-171, 1936.
Delaney, P. T., and D. Pollard, Deformation of host rocks and flow of magma during growth of minette dikes and breccia-bearing intrusions near Ship Rock, New Mexico. U. S. Geol. Survey Professional Paper 1201, 61p., 1981.
New Mexico Volcano Directory
A map of volcanoes and volcanic features around the state, with detailed discussion of each site.
Volcanoes of New Mexico
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