Several youthful maars and significant neotechtonic structures; Zuni Salt lake maar is a classic youthful hydromagmatic crater
Mostly alkali basalts and intermediate compositions
Information about the Red Hill field is sparse, but existing geologic mapping and age determinations show that the area has been active over times significant enough for inversion of topography to occur. As a result, areas of younger volcanism are surrounded by basalt capped mesas on both sides of Highway 60 about 24 miles east of the border with Arizona and Springerville field.
Red Hill volcanic field and Zuni Salt Lake maar. Photo L. Crumpler
Red Hill cone and flow. Photo L. Crumpler
Red Hill cone. Photo L. Crumpler
Zuni Salt Lake maar is a youthful example of a classic magma-water steam-blast (phreatomagmatic) eruption. These typically result in broad flat-floored craters that resemble Meteor Crater in many ways. The water that results in all of the volence is usually groundwater and the rate at which the water is re-supplied as it is used by the explosiuons gcontrols the relative importance of explosions versus regular pyroclastic eruptions. SO, as at Zuni Salt Lake it is fairly common to see evidence for scoria and dark ash, or eeven lava flows, that have been buried by subsequent steam-blast products. Another thing that tends to happen in these types of eruptions is the alteration of volcanic materials before they cool and solidify. In other words, small droplets of pyroclastic material may be caught up in an environment of such high temperature and w=gases that the glass itself is altered before it has time to solidify. The result is a lot of yellowish staining to the dusty-appearing ash particles, a type of ash we call "palagonite." Then there are accretionary lapilli that appear common around maars. ZSL has some classic deposits of those.
Zuni Salt Lake. Photo L. Crumpler
This low level oblique from the south gives a somewhat better view of the floor and the two dark scoria cones.
Photo L. Crumpler
Phreatic tuffs on the western rim of Zuni Salt Lake Maar. Insets, bomb sags. Example on right is from Zuni Salt Lake maar. Example on left is from Mars! Photo L. Crumpler
Note the small spherical blobs, some of which appear to have shell-like exteriors. These are classic accretionary lapilli from a deposit on the west crater rim of Zuni Salt Lake. Accretionary lapilli are literally volcanic hailstones. Instead of water ice accumulating on a small grain of ice in a thunderstorm circulation cell, these are bits of pyroclasts and country rock that get coated with many layers of mud and ash as they churn within a violent eruption column.
Zuni Salt Lake panoraa from the noirth rim. Photo L. Cumpler
View Red Hill Volcanic in a larger map
Chamberlin, R.M., Steven M. Cather, Orin J. Anderson, and Glen E. Jones, 1994. RECONNAISSANCE GEOLOGIC MAP OF THE QUEMADO 30 x 60 MINUTE QUADRANGLE, CATRON COUNTY, NEW MEXICO. New Mexico Bureau of Mines and Mineral Resources Open-file Report 406.
Bradbury, J. P., 1966, Pleistocene-Recent geologic history of Zuni Salt lake, New Mexico: New Mexico Geological Society 17th Field Conference Guidebook, Taos-Raton-Spanish Peaks Country, New Mexico and Colorado, p. 119.
Crumpler, L. S., and J. C. Aubele, 1990, Red Hill volcanic field, New Mexico; in Wood, C. A., and Kienle, J. (eds), Volcanoes of North America: Cambridge University Press, Cambridge, p. 307-308.
Cummings, D., 1968, Geologic map of the Zuni Salt Lake volcanic crater, Catron County, New Mexico: U. S. Geological Surevy, Miscellaneous Geologic Investigations Map I-544, scale 1:6,000.
Darton, N. H., 1906, The Zuni salt lake: Geological Society of America Bulletin, v. 16, p. 564.
Hoffer, J. M., and Corbitt, L. L., 1989, A preliminary note on some unusual explosion-collapse craters, Quemado basalt field, Catron County, New Mexico: New Mexico Geological Society, 40th Field Conference Guidebook, p. 157-158.
Horning, R. R., Dunbar, N.W., Kyle, P. R., and Baldridge, W. S., 1996, Evolution of igneous veins intruding basanite at El Porticito, Quemado, NM: New Mexico Geology, v.18, p. 53.
McIntosh, W. C., 1994, 40Ar/39Ar geochronology of late Miocene to Pleistocene basalts of the Zuni Bandera, Red Hill-Quemado and Potrillo Volcanic Fields: New Mexico Geology, v. 16, p. 6061.
McIntosh, W. C., and Cather, S. M., 1994, 40Ar/39Ar geochronology of basaltic rocks and constraints on Late Cenozoic stratigraphy and landscape development in the Red Hill-Quemado area, New Mexico: New Mexico Geological Society 45th Field Conference Guidebook, p. 209-224.
All text and photo credit due to Dr. Larry Crumpler, New Mexico Museum of Natural History and Science
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