Precambrian Geology of South-Central New Mexico William R

New Mexico Geological Society Downloaded from: http://nmgs.nmt.edu/publications/guidebooks/15 Precambrian geology of south-central New Mexico William R. Muehlberger and R. E. Denison, 1964, pp. 62-69 in: Ruidoso Country (New Mexico), Ash, S. R.; Davis, L. R.; [eds.], New Mexico Geological Society 15th Annual Fall Field Conference Guidebook, 195 p. This is one of many related papers that were included in the 1964 NMGS Fall Field Conference Guidebook. Annual NMGS Fall Field Conference Guidebooks Every fall since 1950, the New Mexico Geological Society (NMGS) has held an annual Fall Field Conference that explores some region of New Mexico (or surrounding states). Always well attended, these conferences provide a guidebook to participants. Besides detailed road logs, the guidebooks contain many well written, edited, and peer-reviewed geoscience papers. These books have set the national standard for geologic guidebooks and are an essential geologic reference for anyone working in or around New Mexico. Free Downloads NMGS has decided to make peer-reviewed papers from our Fall Field Conference guidebooks available for free download. Non-members will have access to guidebook papers two years after publication. Members have access to all papers. This is in keeping with our mission of promoting interest, research, and cooperation regarding geology in New Mexico. However, guidebook sales represent a significant proportion of our operating budget. Therefore, only research papers are available for download. Road logs, mini-papers, maps, stratigraphic charts, and other selected content are available only in the printed guidebooks. Copyright Information Publications of the New Mexico Geological Society, printed and electronic, are protected by the copyright laws of the United States. No material from the NMGS website, or printed and electronic publications, may be reprinted or redistributed without NMGS permission. Contact us for permission to reprint portions of any of our publications. One printed copy of any materials from the NMGS website or our print and electronic publications may be made for individual use without our permission. Teachers and students may make unlimited copies for educational use. Any other use of these materials requires explicit permission. This page is intentionally left blank to maintain order of facing pages. NEW MEXICO GEOLOGICAL SOCIETY • FIFTEENTH FIELD CONFERENCE PRECAMBRIAN GEOLOGY OF SOUTH-CENTRAL NEW MEXICO William R. Muehlberger and Rodger E. Denison Department of Geology and Crustal Studies Laboratory The University of Texas, Austin, Texas INTRODUCTION include individual studies on outcrop belts in the southern Manzano (Stark, 1956), Los Pinos (Stark and Dap- The Ruidoso country contains no Precambrian out- ples, 1946), San Andres (Kottlowski and others, 1956, crops and no .wells in the region to penetrate to it. To Kottlowski, 1959), and Organ Mountains (Dunham, interpret the Precambrian geology of the actual field trip (1961), and Flawn (1956). area we have therefore selected the larger area shown The basement rocks in this area can be placed into in figure 1, which gives sufficient regional control for in- petrographically allied rock groups. Some of the state- terpolation into the Ruidoso country. The extensive out- 1935) ; Bent dome (Bachman, 1960) ; and regional sub- crop belt of the San Andres Mountains, Sierra Oscura, surface studies by Foster (1959), Foster and Stipp Los Pinos and southern Manzano Mountains form the ments made concerning these groups are defensible only western flank; the exposures in southern Torrance in light of our larger study to make a geologic map of County as well as the numerous wells in that area form the buried basement of North America. This project is the northern; a line of wells along the western margins an outgrowth of the AAPG Basement Rocks Committee of some of the Precambrian belts in eastern New Mexico project to prepare a map at a scale of 1:5,000,000 show- forms the eastern flank; the southern line has been drawn ing the wells that penetrate the basement, contours on in Otero County north of the Tertiary intrusive rocks the surface of the buried basement, and gross lithology that extend into Trans-Pecos Texas. This contribution of the exposed basement. We are making a petrographic furnishes petrographic descriptions of basement well and study of sample materials from each basement well, and outcrop samples (Denison) and a synthesis of Precam- isotopic age determinations of selected samples in order brian history in the map area (both authors). to work out the geologic history of the Precambrian. PREVIOUS WORK AND PRESENT PROJECT ACKNOWLEDGEMENTS Numerous studies have touched on various aspects of the map area. The most complete general references Our sincere thanks to Roy W. Foster, New Mexico Precambrian Outcrop Tertiary Intrusive Rock Quaternary Volcanic Rock I I- •• Wells to Basement Described in Appendix 50 iCHAVES Miles OTERO DORIA Figure 1. Map of south-central New Mexico showing ANA locations of wells to basement, Precambrian outcrops, Tertiary intrusive rock and Quaternary volcanic rock. 62 NEW MEXICO GEOLOGICAL SOCIETY • FIFTEENTH FIELD CONFERENCE Bureau of Mines and Mineral Resources, who picked and the wells in Torrance and Lincoln Counties that the sample materials from the wells and collected sam- penetrated either granite, granite gneiss, or granodiorite ples from the Sierra Oscura and San Andres Mountains. gneiss. This also includes metasedimentary rock exposed In addition we have obtained samples from various com- in the San Andres Mountains in a band straddling the pany files and individuals which have made isotopic age Sierra-Dona Ana county lines. determinations possible. In areas of such sparse control 3. Sediment and diabase belt (III). The belt south and complex geology, each basement well is valuable and of the central diagonal and also possibly the area of the needed. Isotopic age determinations for our program field conference are underlain by Precambrian sediment- have been made by members of the Isotope Geology ary rocks that have been extensively intruded and contact Branch, U.S. Geological Survey, S. S. Goldich, Chief. metamorphosed by sills and dikes of diabase. The se- This work has been performed under Contract AF 49 quence consists largely of quartzite and siltstone, and in a (638)-1115 of the Air Force Office of Scientific Research small portion of the area impure limestone. Some of these as part of the Advanced Research Projects Agency Pro- rocks also crop out in the San Andres Mountains where ject VELA UNIFORM. they overlie the older metamorphic rocks and underlie the Bliss Sandstone (Kottlowski, 1959, p. 261) . This Precambrian sedimentary sequence resembles those found in the Franklin Mountains near El Paso (Harbour, 1960) and in the Van Horn region of Trans-Pecos Texas ( King and Flawn, 1953) . The total thickness is un- known but is probably not great. 4. Southeast granite gneiss area (IV). A group of wells penetrate granite gneisses in southern Chaves and northwest Eddy Counties. This is the western edge of a complex igneous-metamorphic suite of basement rocks in southeast New Mexico. DESCRIPTION OF INDIVIDUAL AREAS Northwest metamorphic area (I).—The Los Pinos and southern Manzano Mountains have been mapped and described by Stark and Dapples (1946) and Stark (1956). The following summary is abstracted from their work. The trend of metamorphic rocks essentially par- allels the length of the range. The Precambrian stratigraphic sequence consists of a lower metaclastic series unconformably overlain by about 7,000 feet of quartzite, muscovite schist, and quartzite in ascending stratigraphic order. These have been named Sais Quartzite, Blue Springs Muscovite Schist, and White Ridge Quartzite, respectively. This sequence is in turn overlain unconformably by the Sevilleta Rhyolite, which is at least 4,000 feet thick. All of these units . have been tightly folded into an asymmetric syncline whose axis strikes Figure 2. Map of south-central New Mexico showing northeast across the range. Regional cleavage was de- Precambrian subdivisions described in text: 1, North- veloped during this folding episode. Cross folding, fault- west metamorphic area; II, Central granite belt; ing and small crenulations were later developed on ear- III, Sediment and diabase belt; IV, Southeast gran- lier schistosity. Granitic rocks that intruded this meta- ite gneiss area. sedimentary sequence have been divided into a gray equi- granular biotitic granite and a younger porphyritic pink granite that is gneissic in places. Granitic rocks of this REGIONAL STATEMENT character have an isotopic age of about 1.35 b.y. in the The Precambrian rocks of the map area are divisible Sandia Mountains near Albuquerque (Tilton, Wetherill, into four geologic units. and Davis, 1962) . 1. Northwest metamorphic area (I).— This includes Southern Torrance County includes the southern- the southern Manzano and Los Pinos Mountains (the most portion of the Estancia basin wherein most wells band of black shown in fig. 1) in northeastern Socorro have penetrated metasedimentary rocks that are very County, and most of southern Torrance County. The similar to the Precambrian rocks in the Los Pinos and basement rocks are dominantly metasedimentary and Manzano Mountains. The Pedernal uplift consists of metavolcanic with minor intrusive granitic masses. granitic rocks flanked by these metasedimentary units. 2. Central granite belt (//).—The area north of a The trend of this belt appears to be south-southwestward line drawn from the southwest to the northeast corner under the Jornada del Muerto and may well connect of the map area and south of the Northwest metamor- with the metasedimentary rocks of the central San An- phic area includes practically all of the Precambrian dres Mountains. North of the map area this metasedi- outcrops in the San Andres Mountains and Sierra Oscura mentary terrane extends under the Galisteo basin and is 63 NEW MEXICO GEOLOGICAL SOCIETY • FIFTEENTH FIELD CONFERENCE exposed in the high mountains of the upper Pecos River dikes of pale pink aplite (Kottlowski, 1959, p.

Load more