Earth and Planetary Sciences ETDs

Publication Date

10-10-1968

Abstract

The San Mateo Mountains of south-central New Mexico consist of a series of uplifted blocks of Tertiary volcanic rocks which cover an area approximately 45 miles long by 20 miles wide. Faulted blocks of older, Paleozoic and Precambrian, rocks and post-volcanic intrusives are found along the eastern and southern borders of the range. Only late Paleozoic, Pennsylvanian and Permian sediments occur in the mapped area. More than 7,000 feet of Tertiary volcanic rocks unconformably overlies all older rocks, divided into the Lower Volcanic and Datil Groups. The lower Volcanic Group is composed of a series of deeply altered andesites, tuffaceous andesites, conglomerate, and lake beds. The Datil Group is subdivided into the Rock Spring Formation, Vicks Peak Rhyolite, and Indian Creek Rhyolite. The Rock Spring Formation consists of a cyclic eruptive sequence of four volatile-rich tuffaceous latites each in turn followed by less extensive, volatile-poor, andesite and latite flows or flow breccia. The Vicks Peak Rhyolite (2,000 feet) and Indian Creek Rhyolite (2,000 feet) overlie the Rock Spring Formation. Lineation of stretched pumice fragments in the Vicks Peak Rhyolite shows a strong southeasterly orientation (130-140°). Stocklike bodies of quartz rhyolite are intruded into the Tertiary volcanic rocks along the southern border fault zone and are most fully developed where this zone is cross-cut by major north-south faulting. A large sill of sanidine rhyolite occurs in the northern part of the map area. Block mosaic faulting has taken place over broad areas occupied by the Vicks Peak Rhyolite. Culmination of normal faulting of Basin-and-Range type took place along the Rio Grande in middle Miocene time and development of major north-south structures in the San Mateo Mountains probably took place at this time. Hydrothermal alteration of rocks over wide areas is closely associated with north-south fault zones and intrusions of rhyolitic rocks. Alteration is especially widespread in the Lower Volcanic Group and in porous tuffaceous or less densely welded materials of the younger rocks. Cyclic phenomena and overall eruptive sequence of volcanic rocks may indicate their origin in one or a series of closely related magma chambers where differentiating processes took place. A predominance of andesite flows in the Lower Volcanic Group is succeeded by voluminous latitic pyroclastic materials of the early Datil Group. Later Datil volcanic rocks are mainly rhyolitic pyroclastics and lava flows. Lastly quartz-rich intrusives were injected along the southern border fault zone and in northern parts of the map area. Thinning of andesite flows in the Lower Volcanic Group, interpretation of cooling unit sequence, and lineation of pumice fragments in the Vicks Peak Rhyolite indicate a possible eruptive center to the north of the area mapped. Although hydrothermal alteration of rocks is widespread in the San Mateo Mountains, the rocks are not highly mineralized. A few hypogene deposits of gold and fluorspar­uranium are known, but nothing of major value has been discovered to date.

Degree Name

Earth and Planetary Sciences

Level of Degree

Doctoral

Department Name

Department of Earth and Planetary Sciences

First Committee Member (Chair)

Vincent Cooper Kelley

Second Committee Member

J. Paul Fitzsimmons

Third Committee Member

Wolfgang Eugene Elston

Fourth Committee Member

William Clarence Martin

Project Sponsors

The Society of the Sigma Xi, New Mexico Geological Society, and the DePauw University Geology Department

Language

English

Document Type

Dissertation

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Geology Commons

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