DOCSLIB.ORG

The Petrology and Geochemistry of the Ocate Volcanic Field, North-Central New Mexico

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
The Petrology and Geochemistry of the Ocate Volcanic Field, North-Central New Mexico The petrology and geochemistry of the Ocate volcanic field, north-central New Mexico ROGER L. NIELSEN Department of Geology, University of Maryland, College Park, Maryland 20742 MICHAEL A. E>UNGAN Department of Geological Sciences, Southern Methodist University, Dallas, Texas 75275 ABSTRACT INTRODUCTION The Ocate volcanic field in north-central New Mexico is on the The Ocate volcanic field is one of several dominantly basaltic eastern flank of the Sangre de Cristo Mountains. It is a suite of Pliocene-Pleistocene eruptive complexes that defines the Jemez trend or Pliocene-Pleistocene basaltic and intermediate lavas which were lineament in northern New Mexico (Fig. 1). The Ocate field lies between erupted in five pulses over a period of ~7 m.y. (8.3-0.8 m.y. B.P.) the Taos Plateau volcanic field on the west and the Raton-Clayton field to during rejuvenation of the Rio Grande Rift. Geochemical and petro- the east. These three volcanic fields developed contemporaneously and are graphic criteria sire used to define five major rock types: alkali olivine characterized by comparable temporal evolution trends and by similar basalt (AOB), transitional olivine basalt (TOB), xenocrystic basaltic assemblages of volcanic rock types. The Ocate lavas range from mafic andesite (XBA), olivine andesites (OA), and dacite. The timing and alkali to tholeiitic basalts, to andesites and dacites, representing a wide eruptive volume:; of these five lava types define a complex temporal range of major- and trace-element content. sequence in which the transitional basalts and intermediate rocks are The objectives of this study were to develop a model for the pedo- closely associated during the maximum in basaltic activity (4.5-2.0 genesis of the variety of magma compositions observed in the Ocate field m.y. B.P.). and to fit them into a regional model for the origin of Pliocene-Pleistocene The alkali olivine basalts have higher incompatible and com- volcanism in northern New Mexico. Toward that end, we have employed patible trace-element abundances and higher normative nepheline petrographic data, mineral and bulk chemistry, and have performed mass- (>2%) than do the TOB lavas. The two basalt types apparently were balance (Stormer and Nicholls, 1978) and phase-equilibria calculations derived from physically discrete or heterogeneous source regions. The (Nielsen and Dungan, 1983) in order to evaluate the roles of mixing and AOB lavas could be the products of smaller degrees of melting from fractional crystallization. Utilizing data from this investigation and from similar sources, source heterogeneity, and/or melting at greater depth. investigations on the other Pliocene-Pleistocene volcanic fields in northern The intermediate lavas were generated from basaltic parent New Mexico (Bachman, 1953; Dungan and others, 1983a; Stormer, 1972; magmas by varying degrees of fractionation, assimilation of crustal Phelps and others, 1983), we have attempted to evaluate the Ocate field in material, and miring with silicic melts derived by crustal anatexis. The terms of its place in the regional geology and to develop a large-scale XBA lavas and ilacites are characterized by disequilibrium phase as- model for the evolution of volcanism in New Mexico during the past semblages which include olivine coexisting with biotite and quartz, 10 m.y. melt inclusions of K- and Si-rich glass, and a bimodal distribution of plagioclase phenocryst compositions with modes at An^ and An25- The high concentration of Mg, Ni, and Cr in the intermediate lavas is inconsistent with simple fractionation of basaltic parent magmas. The linear trends defined on variation diagrams are consistent with mixing Utah\Colo._ mafic and silicic end members. The lack of continuity between two 'ÁrTz'jÑMe*: tpvM hybrid types may be a reflection of contrasting subvolcanic environ- V RCVF ments in which Che hybridization took place. I OVF ! / SAxial Rift Basins The olivine andesites show little petrographic evidence for Figure 1. Location mixing. Chemical variations within this group define highly nonlinear map. trends more consistent with extensive crystal fractionation. Calculated I 0 IQOkm liquid lines of descent from available mafic parent magmas (assuming Late Cenozoic Volcanic Fields perfect fractions!) crystallization) do not satisfactorily produce the ob- Northern New Mexico and served intermediate compositions. If assimilation of a silicic crystal Southern Colorado component is paired with crystal fractionation, such that the mass of Raton-Clayton 7.5 - 0.01 m.y. crustal material is approximately equal to 50% of the fractionated Ocate 8.1 -0.8 m.y. Taos Plateau 4.5-1.8 solids, the major- and trace-element characteristics of the olivine an- desites can be successfully modeled. Additional material for this article, Tables A and B, may be secured free of charge by requesting Supplementary Data 85-12 front the GSA Documents Secretary. Geological Society of America Bulletin, v. 96, p. 296-312, 15 figs., 5 tables, March 1985. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/96/3/296/3434418/i0016-7606-96-3-296.pdf by guest on 01 October 2021 OCATE VOLCANIC FIELD, NEW MEXICO 297 GEOLOGIC SETTING TABLE 1. APPROXIMATE AGES. VOLUME, AND CHARACTER OF THE FIVE MAJOR VOLCANIC EPISODES IN THE OCATE VOLCANIC FIELD The Ocate volcanic field lies astride the physiographic and geologic boundary between the southern Sangre de Cristo range of the Rocky Mountains and the High Plains province to the east. Volcanism in the Taos Age (m.y.) 8.1 5.5 4.8-4.0 3.2 3.0 2.2-2.0 1.4-0.8 Plateau and in the Ocate and the Raton-Clayton volcanic fields was coin- Elevation to drainage 600-200 m 300-100 m 150-50 m 50-20 m 30-10 m Volume (km3) cident with a major tectonic rejuvenation of the northern Rio Grande Rift (approx.) 3.9 31 23 28 4.0 during late Cenozoic time. Volcanism along the Jemez lineament was Appro* volume % of each accompanied by regional uplift and activation of major high-angle faults. rock type In contrast to the Taos Plateau field, which erupted within an actively AOB 40 20 10 10 20 subsiding rift basin (San Luis Valley), the Ocate and Raton-Clayton lavas TOB 40 50 80 60 50 were erupted on the uplifted eastern flank of the rift. Subsequent erosion XBA 10 20 10 25 30 has inverted the topography. Broad lava flows cap mesa surfaces at eleva- OA 10 >10 > 5 > 5 tions up to 600 m above the present-day drainages; the oldest lavas occupy Dacite > 2 _ 2 the highest local elevations. The correlation between age of eruption and terrace level has been documented by O'Neill and Mehnert (1980), who demonstrated that the levels would exist, and the observed interfingering of flows from separate Ocate volcanics were erupted in a series of five pulses during the period volcanic centers would not be present. 8.3 to 0.8 m.y. B.P., using K/Ar whole-rock dates of the capping flows. In Table 1, we have listed estimates of the total volume of volcanic We concur with the conclusions of O'Neill and Mehnert that the volcan- rocks produced during the five episodes and the proportions of the five ism occurred in five pulses, although we acknowledge that it is possible rock types present in each magmatic pulse. Greater uncertainties are at- that volcanic activity was more continuous than the existing dates indicate tached to older episodes, particularly the first phase, which may have been (Fig. 2). This is particularly true for the youngest events, for which only substantially eroded. The much lower volume of lavas that erupted during one or two dates are available. There are remarkably few terrace levels this event, compared to subsequent events, must be taken as a minimum within the area, considering that the elevations of the five surfaces decrease value. greatly (as much as 1,500 m) from the northwest to the southeast. If AGE (m.y) volcanic activity had been continuous, rather than episodic, more terrace Figure 2. Sketch map of the Ocate volcanic field, north-cen- tral New Mexico. The approxi- mate distribution of the lavas of each eruptive episode is shown by patterns indicated in the key. Heavy lines delineate the major fault zones (after O'Neill and Mehnert, 1980). Key to loca- tions: OM - Ortega Mesa; SM - Sierra Montuoso; LCF - Lost Cabin fault; RMF - Range Margin fault of the Sangre de Cristo Mountains; CM - Cerro Montoso; CP - Cerro Pelon; CN - Cerro Negro; MC - Maxon Crater; MR - Mora River; OC - Ocate; WM - Wagon Mound; CH - Charette Mesa; LG - La Grulla Mesa; CO - Cerro del Oro. miles Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/96/3/296/3434418/i0016-7606-96-3-296.pdf by guest on 01 October 2021 Figure 3. Pyroxene compositions (circles) in terms of En, Fs, and Wo as calculated by the method of Cammeron and Papike (1981). Olivine (triangles) are molar Fo. Filled symbols are rims and groundmass compositions, open are phenocryst compositions. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/96/3/296/3434418/i0016-7606-96-3-296.pdf by guest on 01 October 2021 OCATE VOLCANIC FIELD, NEW MEXICO 299 The temporal evolution pattern which emerges from these estimates ANALYTICAL METHODS of eruptive volumes clearly indicates that the middle three phases of the Ocate field were far more voluminous than were the first or last episodes. Major-element, whole-rock compositions were obtained by XRF The TOB lavas, which are the dominant basalt type in the field as a whole, analysis at the Johnson Space Center in Houston and at the Department of are, on the average, four times more abundant than are alkali basalts. The Geology at the University of Massachusetts, Amherst.
Load more

Recommended publications
  • Baylor Geological Studies
    BAYLORGEOLOGICA L STUDIES PAUL N. DOLLIVER Creative thinking is more important than elaborate FRANK PH.D. PROFESSOR OF GEOLOGY BAYLOR UNIVERSITY 1929-1934 Objectives of Geological Training at Baylor The training of a geologist in a university covers but a few years; his education continues throughout his active life. The purposes of train­ ing geologists at Baylor University are to provide a sound basis of understanding and to foster a truly geological point of view, both of which are essential for continued professional growth. The staff considers geology to be unique among sciences since it is primarily a field science. All geologic research in­ cluding that done in laboratories must be firmly supported by field observations. The student is encouraged to develop an inquiring ob­ jective attitude and to examine critically all geological concepts and principles. The development of a mature and professional attitude toward geology and geological research is a principal concern of the department. Frontis. Sunset over the Canadian River from near the abandoned settlement of Old Tascosa, Texas. The rampart-like cliffs on the horizon first inspired the name "Llano Estacado" (Palisaded Plain) among Coronado's men. THE BAYLOR UNIVERSITY PRESS WACO, TEXAS BAYLOR GEOLOGICAL STUDIES BULLETIN NO. 42 Cenozoic Evolution of the Canadian River Basin Paul N. DoUiver BAYLOR UNIVERSITY Department of Geology Waco, Texas Spring 1984 Baylor Geological Studies EDITORIAL STAFF Jean M. Spencer Jenness, M.S., Editor environmental and medical geology O. T. Ph.D., Advisor, Cartographic Editor what have you Peter M. Allen, Ph.D. urban and environmental geology, hydrology Harold H. Beaver, Ph.D.
    [Show full text]
  • Long-Term Volumetric Eruption Rates and Magma Budgets
    Article Geochemistry 3 Volume 7, Number 1 Geophysics XX Month 2006 GeosystemsG XXXXXX, doi:10.1029/2005GC001002 G ISSN: 1525-2027 AN ELECTRONIC JOURNAL OF THE EARTH SCIENCES Published by AGU and the Geochemical Society 1 Long-term volumetric eruption rates and magma budgets 2 Scott M. White 3 Department of Geological Sciences, University of South Carolina, 700 Sumter Street, Columbia, South Carolina 29208, 4 USA ([email protected]) 5 Joy A. Crisp 6 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, USA 7 ([email protected]) 8 Frank J. Spera 9 Department of Earth Science, University of California, Santa Barbara, Santa Barbara, California 93106, USA 10 ([email protected]) 11 [1] A global compilation of 170 time-averaged volumetric volcanic output rates (Qe) is evaluated in terms 12 of composition and petrotectonic setting to advance the understanding of long-term rates of magma 13 generation and eruption on Earth. Repose periods between successive eruptions at a given site and 4 14 intrusive:extrusive ratios were compiled for selected volcanic centers where long-term (>10 years) data 15 were available. More silicic compositions, rhyolites and andesites, have a more limited range of eruption À1 3 16 rates than basalts. Even when high Qe values contributed by flood basalts (9 ± 2 Â 10 km /yr) are 17 removed, there is a trend in decreasing average Qe with lava composition from basaltic eruptions (2.6 ± À2 3 À3 3 À3 3 18 1.0 Â 10 km /yr) to andesites (2.3 ± 0.8 Â 10 km /yr) and rhyolites (4.0 ± 1.4 Â 10 km /yr).
    [Show full text]
  • Facts and Hypotheses Regarding the Miocene–Holocene Jemez Lineament, New Mexico, Arizona and Colorado Fraser Goff and Shari A
    New Mexico Geological Society Downloaded from: https://nmgs.nmt.edu/publications/guidebooks/72 Facts and hypotheses regarding the Miocene–Holocene Jemez Lineament, New Mexico, Arizona and Colorado Fraser Goff and Shari A. Kelley, 2021, pp. 101-116 in: Geology of the Mount Taylor area, Frey, Bonnie A.; Kelley, Shari A.; Zeigler, Kate E.; McLemore, Virginia T.; Goff, Fraser; Ulmer-Scholle, Dana S., New Mexico Geological Society 72nd Annual Fall Field Conference Guidebook, 310 p. This is one of many related papers that were included in the 2021 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. 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, Color Plates, 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.
    [Show full text]
  • Petrology and Physiographic Evolution of the Oeate Volcanic Field, North-Central New Mexico A
    Petrology and Physiographic Evolution of the Oeate Volcanic Field, North-Central New Mexico A. The Ocate Volcanic Field Description of Vdlcanic Vents and the Geochrondlogy, Petrography, and Whole-Rock Chemistry of Associated Flows B. Late Cenozoic Physiographic Evolution of the Ocate Volcanic Field U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1478 Petrology and Physiographic Evolution of the Ocate Volcanic Field, North-Central New Mexico A. The Ocate Volcanic Field Description of Volcanic Vents and the Geochronology, Petrography, and Whole-Rock Chemistry of Associated Flows By J. MICHAEL O'NEILL and HARALD H. MEHNERT B. Late Cenozoic Physiographic Evolution of the Ocate Volcanic Field By J. MICHAEL O'NEILL U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 147 UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1988 DEPARTMENT OF THE INTERIOR DONALD PAUL MODEL, Secretary U.S. GEOLOGICAL SURVEY Dallas L. Peck, Director Library of Congress Cataloging-in-Publication Data Petrology and physiographic evolution of the Ocate volcanic field, north-central New Mexico. (U.S. Geological Survey professional paper ; 1478-A.B) Bibliography: p. Supt. of Docs, no.: I 19.16:1778A,B Contents: Pt. A. The Ocate volcanic field description of volcanic vents and the geochronology, petrography, and whole-rock chemistry of associated flows / by J. Michael O'Neill and Harald H. Mehnert Pt. B. Late Cenozoic physiographic evolution of the Ocate volcanic field / by J. Michael O'Neill. 1. Volcanic ash, tuff, etc. Sangre de Cristo Mountains (Colo. and N.M.) 2. Volcanic ash, tuff, etc. New Mexico. 3. Geology, Stratigraphic Cenozoic. I. O'Neill, J. Michael. Ocate volcanic field description of volcanic vents and the geochronology, petrography, and whole-rock chemistry of associated flows.
    [Show full text]
  • Nevada, Las Vegas Las Vegas Nevidi.89154
    CENTER FOR VOLCANIC AND TECrONIC STUDIES1 DEPARTMENT OF GEOSCIENCE University of Nevada, Las Vegas Las Vegas Nevidi.89154 Report No. 56 ANNUAL REPORT for the Period 10/1/90 to 9/30/91 Submitted to the Nudlear Waste Project Office State of Nevada December 14, 1991 'Eugene L Smith-Principal hvestigator. Daniel Feuerbach-Research Associate Terry aaumann-Research Associate 0 9210020232 911231 PDR WASTE WM-11 PDR INTRODUCION The annual report of the Center for Volcanic and Tectonic Studies (CVTS) contains a series of papers, maps, reprints and theses that review the progress made by the CVF`S between October 1, 1990 and September 30, 1991. During this period CVIS staff focused on several topics that had direct relevance to volcanic hazards related to the proposed high-level nuclear waste repository at Yucca Mountain, Nevada. These topics included: (1) The role of the mantle in controlling the location and composition of Pliocene- Holocene volcanism. (2) The nature of boundaries between compositionally different mantle domains. These domain boundaries may control the location of surface faults and volcanism. (3) The detailed geology of the Pliocene volcanic cones in Crater Flat (4) The detailed geology of bedrock to the east of Crater Flat on Yucca Mountain. (5) The structural controls and emplacement mechansims of Pliocene/Quaternary basaltic volcanic centers and dikes. (6) The study of young felsic volcanism in the southern Basin and Range. (7) Estimating the probability of disruption of the proposed repository by volcanic eruption (this topic is being studied by Dr. C Ho-UNLV). Activities CV1S presented papers at several professional meetings including (a) The Geological Society of America Cordilleran Section Meeting in San Francisco- March 25-27, 1991.
    [Show full text]
  • The Origin of the Wilson Ridge Pluton And
    UNLV Retrospective Theses & Dissertations 1-1-1988 The origin of the Wilson Ridge pluton and its enclaves, northwestern Arizona: Implications for the generation of a calc- alkaline intermediate pluton in an extensional environment Lance Louis Larsen University of Nevada, Las Vegas Follow this and additional works at: https://digitalscholarship.unlv.edu/rtds Repository Citation Larsen, Lance Louis, "The origin of the Wilson Ridge pluton and its enclaves, northwestern Arizona: Implications for the generation of a calc-alkaline intermediate pluton in an extensional environment" (1988). UNLV Retrospective Theses & Dissertations. 58. http://dx.doi.org/10.25669/trxh-n4m2 This Thesis is protected by copyright and/or related rights. It has been brought to you by Digital Scholarship@UNLV with permission from the rights-holder(s). You are free to use this Thesis in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s) directly, unless additional rights are indicated by a Creative Commons license in the record and/ or on the work itself. This Thesis has been accepted for inclusion in UNLV Retrospective Theses & Dissertations by an authorized administrator of Digital Scholarship@UNLV. For more information, please contact [email protected]. INFORMATION TO USERS The most advanced technology has been used to photo­ graph and reproduce this manuscript from the microfilm master. UMI films the text directly from the original or copy submitted. Thus, some thesis and dissertation copies are in typewriter face, while others may be from any type of computer printer.
    [Show full text]
  • NMBGMR OFR 541: a Geologic Study of Capulin Volcano National
    A Geologic Study of the Capulin Volcano National Monument and surrounding areas, Union and Colfax Counties, New Mexico by William O. Sayre and Michael H. Ort New Mexico Bureau of Geology and Mineral Resources, New Mexico Tech Socorro, New Mexico 87801 Open-file Report 541 August, 2011 A geologic study of Capulin Volcano National Monument and surrounding areas Final Report Cooperative Agreement CA7029-2-0017 December 4, 1999 Submitted to: Capulin Volcano National Monument P. O. Box 80 Capulin, New Mexico 88414 Submitted by: William O. Sayre, Ph.D., P.G. College of Santa Fe 1600 St. Michael’s Drive Santa Fe, New Mexico 87505-7634 and Michael H. Ort, Ph.D. Department of Geology PO Box 4099 Northern Arizona University Flagstaff, Arizona 86011 Table of Contents Executive Summary ........................................................................................................ 2 Introduction ..................................................................................................................... 2 Body of Report .............................................................................................................. 17 Discussion and Conclusions ......................................................................................... 22 Recommendations for Future Work .............................................................................. 64 References .................................................................................................................... 65 Appendices…………………………………………………………………………………….
    [Show full text]
  • U.S. DEPARTMENT of the INTERIOR U.S.GEOLOGICAL SURVEY ALK.BIB a Selected Bibliography of Alkaline Igneous Rocks and Related Mine
    U.S. DEPARTMENT OF THE INTERIOR U.S.GEOLOGICAL SURVEY ALK.BIB A selected bibliography of alkaline igneous rocks and related mineral deposits, with an emphasis on western North America compiled by Felix E. Mutschler, D. Chad Johnson, and Thomas C. Mooney Open-File Report 94-624 1994 This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards and stratigraphic nomenclature. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. INTRODUCTION This bibliography contains 3,406 references on alkaline igneous rocks and related mineral deposits compiled in conjunction with ongoing studies of alkaline igneous rocks, metallogeny, and tectonics in western North America. Much of the literature on these topics is not readily recovered by searches of current bibliographies and computerized reference systems. We hope that by making this bibliography available, it will help other workers to access this occasionally hard to find literature. The bibliography is available in two formats: (1) paper hardcopy and (2) Apple Macintosh computer-readable 3.5 inch double density diskette. The computer-readable version of the bibliography is a 725 KB WORD (version 5.0) document. Individual literature citations are arranged alphabetically by author(s) and the order of items in each citation follows the standard U.S. Geological Survey format. Version 3.4 1 February 1994 BIBLIOGRAPHY Abbott, J. G., Gordey, S. P., and Tempelman-Kluit, D. J., 1986, Setting of stratiform, sediment- hosted lead-zinc deposits in Yukon and northeastern British Columbia, in Morin, J.
    [Show full text]
  • Topography of the Southwestern US
    Chapter 4: Topography of the topography • the landscape Southwestern US of an area, including the presence or absence of hills and the slopes between high and low areas. Does your region have rolling hills? Mountainous areas? Flat land where you never have to bike up a hill? The answers to these questions can help others understand the basic topography of your region. The term topography is used to describe the shape of the land surface as measured by how elevation— geologic time scale • a height above sea level—varies over large and small areas. Over geologic standard timeline used to time, topography changes as a result of weathering and erosion, as well as describe the age of rocks and fossils, and the events that the type and structure of the underlying bedrock. It is also a story of plate formed them. tectonics, volcanoes, folding, faulting, uplift, and mountain building. The Southwest’s topographic zones are under the influence of the destructive surface processes of weathering and erosion. Weathering includes both the plate tectonics • the process mechanical and chemical processes that break down a rock. There are two by which the plates of the types of weathering: physical and chemical. Physical weathering describes the Earth’s crust move and physical or mechanical breakdown of a rock, during which the rock is broken interact with one another at their boundaries. into smaller pieces but no chemical changes take place. Water, ice, and wind all contribute to physical weathering, sculpting the landscape into characteristic forms determined by the climate. In most areas, water is the primary agent of erosion.
    [Show full text]
  • Fort Union National Monument Geologic Resources Inventory Report
    National Park Service U.S. Department of the Interior Natural Resource Stewardship and Science Fort Union National Monument Geologic Resources Inventory Report Natural Resource Report NPS/NRSS/GRD/NRR—2012/580 ON THE COVER Local materials, such as sandstone exposed in nearby cliffs and clay from the “adobe fields,” were used in the construction of Fort Union. Graneros Shale (geologic map unit Kgs), which underlies most of the national monument, yielded the clay. Dakota Sandstone (Kd) provided the building stone. Photograph by Katie KellerLynn (Colorado State University). THIS PAGE The Turkey Mountains fill the northern horizon at Fort Union National Monument. The mountains are composed of an igneous intrusion called a “laccolith.” Photograph by Katie KellerLynn (Colorado State University). Fort Union National Monument Geologic Resources Inventory Report Natural Resource Report NPS/NRSS/GRD/NRR—2012/580 National Park Service Geologic Resources Division PO Box 25287 Denver, CO 80225 September 2012 U.S. Department of the Interior National Park Service Natural Resource Stewardship and Science Fort Collins, Colorado The National Park Service, Natural Resource Stewardship and Science office in Fort Collins, Colorado publishes a range of reports that address natural resource topics of interest and applicability to a broad audience in the National Park Service and others in natural resource management, including scientists, conservation and environmental constituencies, and the public. The Natural Resource Report Series is used to disseminate high-priority, current natural resource management information with managerial application. The series targets a general, diverse audience, and may contain NPS policy considerations or address sensitive issues of management applicability. All manuscripts in the series receive the appropriate level of peer review to ensure that the information is scientifically credible, technically accurate, appropriately written for the intended audience, and designed and published in a professional manner.
    [Show full text]
  • Volcanic and Sedimentary Stratigraphy of the Rio Grande Gorge and the Late Cenozoic Geologic Evolution of the Southern San Luis Valley M
    New Mexico Geological Society Downloaded from: http://nmgs.nmt.edu/publications/guidebooks/35 Volcanic and sedimentary stratigraphy of the Rio Grande gorge and the late Cenozoic geologic evolution of the southern San Luis Valley M. A. Dungan, W. R. Muehlberger, L. Leininger, C. Peterson, Nancy J. McMilan, G. Gunn, M. Lindstrom, and L. Haskin, 1984, pp. 157-170 in: Rio Grande Rift (Northern New Mexico), Baldridge, W. S.; Dickerson, P. W.; Riecker, R. E.; Zidek, J.; [eds.], New Mexico Geological Society 35th Annual Fall Field Conference Guidebook, 379 p. This is one of many related papers that were included in the 1984 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.
    [Show full text]
  • The Egan Range Volcanic Complex: Implications for the Evolution of a Mid-Tertiary Synextensional Volcanic System
    AN ABSTRACT OF THE THESIS OF Todd C. Feeley for the degree of Master of Science in Geology presented onJune 2. 1989. Title: The Egan Range Volcanic Complex: Implications for the Evolution of a Mid-Tertiary Synextensional Volcanic System. Abstract approved: Redacted for Privacy Dr. Anita L. *Under The Egan Range volcanic complex (ERVC),located approximately 30 km northwest of Ely, Nevada,lies astride a boundary separating a zone of high crustal extension (approximately 300% extension) to the east,including the Snake Range metamorphic core complex, anda relatively unextended domain (approximately 15% extension)to the west, including the Butte Mountains. The volcanic and minor sedimentary rocks of the ERVChave been divided into three stratigraphic groups: the early, middle, and late groups. Two new 40Ar-39Ar age determinations indicate that the volcanic rocks were erupted approximately35 Ma ago and were coeval with other mid-Tertiary volcanicrocks in east-central Nevada. Volcanic rocks of the earlygroup range from basaltic andesite (54% Si02) to rhyodacite (70% Si02),although the bulk of the lavas are two-pyroxene andesitesand dacites. Apparent compositional gaps are present at56 to 58% Si02 and 66 to 68% Si02, although thesemay be an artifact of incomplete sampling. Textural evidence, including plagioclase with sieved cores mantled by normally and reversely zoned rims, olivine coexisting with quartz surrounded by augite coronas, and quenched inclusions of basaltic andesite, suggest that thesemagmas represent incomplete mixtures of mafic and silicicmagmas. Volcanic rocks of the middle group are exposed ina northwest trending belt of outcrops in the north-eastern to central-western region of the studyarea.
    [Show full text]