Earth and Planetary Sciences ETDs

Publication Date

12-1975

Abstract

The Datil Mountains, Catron County, New Mexico, are an uplifted fault-block located along the northwestern margin of the San Augustin Plains, a Basin and Range structural basin.

No pre-Tertiary rocks occur in the study-area. All of the volcanic rocks are probably Oligocene in age, although the base of the lowest unit may be late Eocene. The oldest rocks belong to the Spears Formation and are divided into three members: A lower unit composed of andesite breccia flows and interbedded volcaniclastic conglomerate, 700+ ft (220+m); a feldspathic volcaniclastic sandstone, 100 ft (30 m); and upper porphyritic andesite flow rock, 100 ft (30 m).

The rocks above the Spears Formation composed mainly of rhyolite ash-flow tuff. The lowest of these is the rhyolite tuff of Datil Well, 50 ft (15 m). Above the tuff of Datil Well, two different stratigraphic sections occur on opposite sides of a major fault; these are here termed the northern and southern stratigraphic sections. In the northern section, the sequence consists of a lower sedimentary unit, 110 (35 m), rhyolite tuff of Main Canyon, 200 ft (60 m), a middle sedimentary unit, 100 ft (20 m), rhyolite tuff of Blue Canyon, 100 ft (30 m), an upper sedimentary unit, 300 ft (100 m), Hells Mesa Rhyolite, 200 ft (60 m), A-L Peak Rhyolite, 20 ft (6 m), basaltic andesite of Twin Peaks, 50 ft (15 m), and rhyolite tuff of Wahoo canyon, 50 ft (15 m).

In the southern section, the sequence consists of rhyolite tuff of Horse Springs, 200+ (60 +m) rhyolite tuff of Ary Ranch, 300 ft (90 m), rhyolite tuff of Crosby Mountain, 300 ft (90 m), A-L Peak Rhyolite, basaltic andesite of Twin Peaks, and tuff of Wahoo Canyon.

The rhyolite ash-flow tuff units in the area are part of what has been called the “Datil Formation” (now Datil Group) and were erupted from several known and unknown ash-flow tuff caldrons. Known cauldrons include the proposed Horse Mountain cauldron, (source of the tuff of Horse Springs and tuff of Crosby Mountain), a proposed cauldron in the Magdalena Mountains, (source of Hells Mesa Rhyolite), the Mt. Withington cauldron, (source of the A-L Peak Rhyolite), and the proposed Luera cauldron, (source of the tuff of Wahoo Canyon).

Within the map-area, the Datil Mountains are characterized by north- and northeast-trending faultblocks bounded by high-angle faults, which are generally downfaulted step-like toward the San Augustin Plains. The possible effect of the Capitan lineament is seen in the westward bending of the faults in the central part of the map-area. Basin and Range faulting in the area is Miocene in age. Total structural relief is about 2300 ft (700 m).

Degree Name

Earth and Planetary Sciences

Level of Degree

Masters

Department Name

Department of Earth and Planetary Sciences

First Committee Member (Chair)

Wolfgang Eugene Elston

Second Committee Member

Lee A. Woodward

Third Committee Member

Jonathan Ferris Callender

Language

English

Document Type

Thesis

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