DOCSLIB.ORG

The Geology and Geochemistry of Cenozoic Topaz Rhyolites from the Western United States

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
The Geology and Geochemistry of Cenozoic Topaz Rhyolites from the Western United States The Geology and Geochemistry of Cenozoic Topaz Rhyolites from the Western United States Eric H. Christiansen Department of Geology University of Iowa Iowa City, Iowa 52242 Michael F. Sheridan Donald M. Burt Arizona State University Tempe, Arizona 85287 SFEE'It':' FAFE., 205 © 1986 The Geological Society of America, Inc. All rights reserved. All materials subject to this copyright and included in this volume may be photocopied for the noncommercial purpose of scientific or educational advancement. Published by The Geological Society of America, Inc. 3300 Penrose Place, P.O. Box 9140, Boulder, Colorado 80301 GSA Books Science Editor Campbell Craddock Printed in U.S.A. Library ofCongress Cataloging-in-Publication Data Christiansen, Eric H The geology and geochemistry of Cenozoic topaz rhyolites from the western United States. (Special paper; 205) Bibliography: p. 1. Rhyolite-West (U.S.) 2. Topaz. 3. Ore­ deposits-West (U.S.) 4. Geology, Stratigraphic­ Crenozoic. 5. Geology-West (U.S.) I. Sheridan, Michael F. II. Burt, Donald M., 1943- . m. Title. IV. Series: Special paper (Geological Society of America); 205. QE462.R4C48 1986 552'.2 86-273 ISBN 0-8137-2205-5 Contents Acknowledgments v Abstract I Introduction ;................................................ 3 Cenozoic topaz rhyoUtes from the western United States 3 1. Thomas Range, west-central Utah 3 2. Spor Mountain, west-central Utah 10 3. Honeycomb Hills, west-central Utah ........................•......... 13 4. Smelter Knolls, west-central Utah 14 5. Keg Mountain, west-central Utah 15 6. Mineral Mountains, western Utah 15 7. Wah Wah Mountains and vicinity, southwestern Utah and southeastern Nevada 17 8. Wilson Creek Range, southeastern Nevada 19 9. Kane Springs Wash, southeastern Nevada......... .. 19 Topaz rhyolites in the eastern Great Basin: A summary 21 10. Cortez Mountains, north-central Nevada 21 11. Sheep Creek Range, north-central Nevada 23 12. Jarbidge, northern Nevada '" 24 13. Blackfoot lava field, southeastern Idaho 25 14. Elkhorn Mountains, western Montana 26 15. Little Belt Mountains, central Montana 27 16. Specimen Mountain, north-central Colorado 29 17. Chalk Mountain, central Colorado 30 18. Nathrop, central Colorado 31 19. Silver Cliff-Rosita, central Colorado 32 20. Tomichi Dome, central Colorado 34 21. Boston Peak, central Colorado. ................ .. .................. .. 35 22. Lake City, southwestern Colorado 36 Topaz rhyolites in Colorado: A summary 37 23. East Grants Ridge, west-central New Mexico ....•...................... 37 24. Black Range, southwestern New Mexico 39 25. Saddle Mountain, eastern Arizona 41 26. Burro Creek, western Arizona 41 Other "topaz rhyolite" occurrences 42 Other Cenozoic occurrences, western United States 42 Mexican topaz rhyolites '. .......................... .. 42 Precambrian topaz rhyolites -. ................. .. 42 iii iv Contents Principal characteristics of topaz rhyolites 43 Distribution and ages .....................................•......... 43 Mode of emplacement 44 Mineralogy 46 Fe-Ti oxides and titanite 46 Feldspar 47 Mafic silicates 48 Geochemistry and differentiation trends 50 Isotopic composition 59 Magma-tectonic setting 59 Ore deposits 61 Beryllium 61 Climax-type molybdenum deposits 62 Tin ' 63 Uranium 64 Fluorite 64 Comparison with other types ofrhyolitic rocks 64 Calc-alkaline rhyolites 64 Peralkaline rhyolites 66 Aluminous bimodal rhyolites 67 Ongonites 67 Petrogenetic modelfor topaz rhyolites 69 References cited 74 Acknowledgments . This work was partially supported by U.S. DOE Subcontract #79-270-E from Bendix Field Engineering Corporation. Additional support was provided by Arizona· State Univer­ sity, the University of Iowa, the U.S. Geological Survey, and the National Aeronautics and Space Administration (grant NAGW-537). A large number of people have helped with the new analytical work presented in this report. They include D. McRoberts, M. Druecker, J. Edie, J. V. Bikun, B. Correa, K. Evans, A. Yates, R. Satkin, K. Hon, D. Lambert, C. E. Hedge, K. Futa, A. Bartel, D. R. Shawe, J. S. Stuckless, L. Jones, R. T. Wilson, W. Rehrig, G. Goles, and G. Pine. The technical reviews by W. Nash and W. Hildreth, and editorial assistance of C. Craddock and L. Gregonis are greatly appreciated. We are also indebted to the authors of many of the articles cited herein for helpful discussions and for recording the presence of topaz in the rhyolites they have studied. v Geological Society of America Special Paper 205 1986 The Geology and Geochemistry ofCenozoic Topaz Rhyolites from the Western United States ABSTRACT High-silica, topaz-bearing rhyolites of Cenozoic age are widely distributed across the western United States and Mexico. Topaz rhyolites are characteristically enriched in fluorine (>0.2 wt%) and contain topaz crystallized during post-magmatic vapor-phase alteration. In the United States, their ages span much of the Cenozoic Era (50 to 0.06 Ma). Their emplacement followed or was contemporaneous with calc-alkaline and ba­ saltic magmatism in the Basin and Range province, along the Rio Grande rift, and in Montana, and coincided with episodes of extensional tectonism in these regions. Nearly all topaz rhyolites extruded as small, endogenous lava domes with or with­ out lava flows; no topaz-bearing ash-flow tuffs have yet been identified with certainty in the western United States. Most domes are underlain by a precursory blanket of non­ welded tephra. A few are small, shallowly emplaced intrusive plugs. Volumes of rock «1 to 100 km3) in individual complexes composed of 1 to many separate extrusions suggest that the lavas were erupted from small to medium sized magma bodies. In addition to topaz, these rhyolites also contain garnet, bixbyite, pseudobrookite, hematite, and fluorite in cavities or in their devitrified groundmasses. All ofthese phases may form during vapor-phase crystallization. Magmatic phenocrysts include sanidine (ca. Orso), quartz, sodic plagioclase (usually oligoclase), and F- and Fe-rich biotite in order of usual abundance. Fe-rich hornblende or clinopyroxene occur in a few lavas. Common magmatic accessory minerals include magnetite, ilmenite, zircon, apatite, allan­ ite, and fluorite. Titanite and REE-rich phosphates have been identified in a few lavas. The rhyolites crystallized over a wide temperature interval (850 to 600°C, with most at the lower end of this range) and at variable oxygen fugacities. Titanite-bearing lavas crystallized above the NNO buffer under oxidizing conditions. Most others appear to have crystallized near the QFM oxygen buffer. For individual complexes, temperatures correlate negatively with F-content. All topaz rhyolites are high-SiOz rhyolites with elevated F, Na, K, Fe/Mg and low Ti, Mg, Ca, and P. Samples with F concentrations of about 1% have notably lower Si and higher AI and Na than other topaz rhyolite glasses. Most glasses from topaz rhyo­ lites are metaluminous, but many appear to be slightly peraluminous. Fluorine concen­ trations in glasses range from slightly less than 0.2 to more than 1.0 wt%, and F/ Cl ratios are high (3 to 10) compared to F-rich peralkaline glasses «3). Topaz rhyolites are characteristically enriched in incompatible lithophile elements (Rb, U, Th, Ta, Nb, Y, Be, Li, and Cs). Elements compatible in feldspars (Sr, Eu, Ba), ferromagnesian minerals (Ti, . Co, Ni, Cr), and zircon (Zr, Hi) are depleted. The REE patterns ofmost topaz rhyolites are almost flat (La/YbN = 1 to 3) and have pronounced negative Eu anomalies (Eu/Eu* = 0.01 to 0.02). Both of these parameters decrease with differentiation as indicated by increasing F, U, Cs, and other incompatible elements. Titanite-bearing rhyolites have prominent middle REE depletions. Initial Sr-isotope ratios range from 0.705 to over 0.710. Geochemical trends at individual complexes are interpreted as arising from frac­ tional crystallization of an initially more "mafic" rhyolite with about 0.2% fluorine. Extensive fractionation of sanidine, quartz, plagioclase, biotite, and Fe-Ti oxides (in 1 2 Christiansen, Sheridan, and Burt proportions consistent with their modes) produced much ofthe trace element patterns. Zircon, apatite, and a REE-rich phase (allanite, monazite, or titanite) were minor but important fractionating phases. No liquid-state fractionation is required to explain the geochemical trends. The high F content and FICI ratios oftopaz rhyolite melts may have modified phase relations so as to produce Na and AI enrichments for highly evolved magmas. Topaz rhyolites are intimately related to economic deposits of lithophile elements (i.e. Be, U, F, Li, and Sn). The volcanic rocks were probably ore- and, in some cases, fluid-sources for these mineral deposits. In their age, tectonic setting, mineralogy, chem­ istry, and style ofemplacement, topaz rhyolites bear resemblance to the rhyolitic stocks associated with Climax-type Mo deposits, and some may be surface manifestations of such deposits. In their chemical composition and mineralogy, topaz rhyolites are distinct from both peralkaline rhyolites and calc-alkaline rhyolites with which they may be spatially and temporally associated. Some of the compositional differences between topaz rhyolites and peralkaline rhyolites may be attributed to the relative effects of F and CI, on melt structure and phase relationships in their parental magmas. The F/CI ratios ofthe melt or its source may determine the alumina saturation ofthe magma series. Topaz rhyolites are distinguishable from calc-alkaline rhyolites by lower Sr, Ba, and Eu,
Load more

Recommended publications
  • The Central Kenya Peralkaline Province: Insights Into the Evolution of Peralkaline Salic Magmas
    The central Kenya peralkaline province: Insights into the evolution of peralkaline salic magmas. Ray Macdonald, Bruno Scaillet To cite this version: Ray Macdonald, Bruno Scaillet. The central Kenya peralkaline province: Insights into the evolution of peralkaline salic magmas.. Lithos, Elsevier, 2006, 91, pp.1-4, 59-73. 10.1016/j.lithos.2006.03.009. hal-00077416 HAL Id: hal-00077416 https://hal-insu.archives-ouvertes.fr/hal-00077416 Submitted on 10 Jul 2006 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. The central Kenya peralkaline province: Insights into the evolution of peralkaline salic magmas R. Macdonalda, and B. Scailletb aEnvironment Centre, Lancaster University, Lancaster LA1 4YQ, UK bISTO-CNRS, 1a rue de la Férollerie, 45071 Orléans cedex 2, France Abstract The central Kenya peralkaline province comprises five young (< 1 Ma) volcanic complexes dominated by peralkaline trachytes and rhyolites. The geological and geochemical evolution of each complex is described and issues related to the development of peralkalinity in salic magmas are highlighted. The peralkaline trachytes may have formed by fractionation of basaltic magma via metaluminous trachyte and in turn generated pantellerite by the same mechanism. Comenditic rhyolites are thought to have formed by volatile-induced crustal anatexis and may themselves have been parental to pantelleritic melts by crystal fractionation.
    [Show full text]
  • Geologic Map of the Central San Juan Caldera Cluster, Southwestern Colorado by Peter W
    Geologic Map of the Central San Juan Caldera Cluster, Southwestern Colorado By Peter W. Lipman Pamphlet to accompany Geologic Investigations Series I–2799 dacite Ceobolla Creek Tuff Nelson Mountain Tuff, rhyolite Rat Creek Tuff, dacite Cebolla Creek Tuff Rat Creek Tuff, rhyolite Wheeler Geologic Monument (Half Moon Pass quadrangle) provides exceptional exposures of three outflow tuff sheets erupted from the San Luis caldera complex. Lowest sheet is Rat Creek Tuff, which is nonwelded throughout but grades upward from light-tan rhyolite (~74% SiO2) into pale brown dacite (~66% SiO2) that contains sparse dark-brown andesitic scoria. Distinctive hornblende-rich middle Cebolla Creek Tuff contains basal surge beds, overlain by vitrophyre of uniform mafic dacite that becomes less welded upward. Uppermost Nelson Mountain Tuff consists of nonwelded to weakly welded, crystal-poor rhyolite, which grades upward to a densely welded caprock of crystal-rich dacite (~68% SiO2). White arrows show contacts between outflow units. 2006 U.S. Department of the Interior U.S. Geological Survey CONTENTS Geologic setting . 1 Volcanism . 1 Structure . 2 Methods of study . 3 Description of map units . 4 Surficial deposits . 4 Glacial deposits . 4 Postcaldera volcanic rocks . 4 Hinsdale Formation . 4 Los Pinos Formation . 5 Oligocene volcanic rocks . 5 Rocks of the Creede Caldera cycle . 5 Creede Formation . 5 Fisher Dacite . 5 Snowshoe Mountain Tuff . 6 Rocks of the San Luis caldera complex . 7 Rocks of the Nelson Mountain caldera cycle . 7 Rocks of the Cebolla Creek caldera cycle . 9 Rocks of the Rat Creek caldera cycle . 10 Lava flows premonitory(?) to San Luis caldera complex . .11 Rocks of the South River caldera cycle .
    [Show full text]
  • The Hydrous Component in Andradite Garnet
    American Mineralogist, Volume 83, pages 835±840, 1998 The hydrous component in andradite garnet GEORG AMTHAUER* AND GEORGE R. ROSSMAN² Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, U.S.A. ABSTRACT Twenty-two andradite samples from a variety of geological environments and two syn- thetic hydroandradite samples were studied by Fourier transform IR spectroscopy. Their 2 spectra show that H enters andradite in the form of OH . Amounts up to 6 wt% H2O occur in these samples; those from low-temperature formations contain the most OH2. Some 42 ↔ 42 features in the absorption spectra indicate the hydrogarnet substitution (SiO4) (O4H4) whereas others indicate additional types of OH2 incorporation. The complexity of the spectra due to multi-site distribution of OH2 increases with increasing complexity of the garnet composition. 42 ↔ 42 INTRODUCTION tution (O4H4) (SiO4) . This observation has been Systematic studies have shown that hydroxide is a con®rmed by XRD of a hydrous andradite with a Si de- common minor component of grossular and pyrope-al- ®ciency of about 50%, and a high OH content (Arm- mandine-spessartite garnets (Aines and Rossman 1985; bruster 1995). The structure of this particular sample with Rossman and Aines 1991). Comparable surveys of an- space group Ia3d is composed of disordered microdo- dradite garnet have not been previously presented. Sev- mains containing (SiO4) and (O4H4) tetrahedral units. eral reports indicate that appreciable amounts of OH2 can The aim of the present investigation was to perform a be incorporated in both natural and synthetic andradite- Fourier transform infrared (FTIR) study on different sam- rich garnet (Flint et al.
    [Show full text]
  • Stratigraphy and Geochemistry of Volcanic Rocks in the Lava Mountains, California: Implications for the Miocene Development of the Garlock Fault
    Geological Society of America Memoir 195 2002 Stratigraphy and geochemistry of volcanic rocks in the Lava Mountains, California: Implications for the Miocene development of the Garlock fault Eugene I. Smith Alexander Sa´nchez Deborah L. Keenan Department of Geoscience, University of Nevada, Las Vegas, Nevada 89154-4010, USA Francis C. Monastero Geothermal Program Office, Naval Air Weapons Station, China Lake, California 93555-6001, USA ABSTRACT Volcanism in the Lava Mountains occurred between 11.7 and 5.8 Ma and was contemporaneous with sinistral motion on the Garlock fault. Volcanic rocks, equiv- alent in age and chemistry to those in the Lava Mountains, crop out 40 km to the southwest in the El Paso Mountains across the Garlock fault. Three chemical groups of volcanic rocks erupted in the Lava Mountains over a period of 5 m.y. These are (1) andesite of Summit Diggings, Almond Mountain volcanic section, and Lava Moun- tains Andesite, (2) basalt of Teagle Wash, and (3) tuffs in the northeastern Lava Moun- tains and dacite in the Summit Range. Volcanic rocks of each group have distinctive chemical signatures useful for correlation of units across the Garlock fault. Our work demonstrated that tuffs in the Almond Mountain volcanic section may be equivalent to a tuff in member 5 of the Miocene Dove Spring Formation, El Paso Mountains. The basalt of Teagle Wash probably correlates with basalt flows in member 4, and tuffs in the northeast Lava Mountains may be equivalent to tuff of member 2. Cor- relation of these units across the Garlock fault implies that the Lava Mountains were situated south of the El Paso Mountains between 10.3 and 11.6 Ma and that 32–40 km of offset occurred on the Garlock fault in ϳ10.4 m.y., resulting in a displacement rate of 3.1 to 3.8 mm/yr.
    [Show full text]
  • (2000), Voluminous Lava-Like Precursor to a Major Ash-Flow
    Journal of Volcanology and Geothermal Research 98 (2000) 153–171 www.elsevier.nl/locate/jvolgeores Voluminous lava-like precursor to a major ash-flow tuff: low-column pyroclastic eruption of the Pagosa Peak Dacite, San Juan volcanic field, Colorado O. Bachmanna,*, M.A. Dungana, P.W. Lipmanb aSection des Sciences de la Terre de l’Universite´ de Gene`ve, 13, Rue des Maraıˆchers, 1211 Geneva 4, Switzerland bUS Geological Survey, 345 Middlefield Rd, Menlo Park, CA, USA Received 26 May 1999; received in revised form 8 November 1999; accepted 8 November 1999 Abstract The Pagosa Peak Dacite is an unusual pyroclastic deposit that immediately predated eruption of the enormous Fish Canyon Tuff (ϳ5000 km3) from the La Garita caldera at 28 Ma. The Pagosa Peak Dacite is thick (to 1 km), voluminous (Ͼ200 km3), and has a high aspect ratio (1:50) similar to those of silicic lava flows. It contains a high proportion (40–60%) of juvenile clasts (to 3–4 m) emplaced as viscous magma that was less vesiculated than typical pumice. Accidental lithic fragments are absent above the basal 5–10% of the unit. Thick densely welded proximal deposits flowed rheomorphically due to gravitational spreading, despite the very high viscosity of the crystal-rich magma, resulting in a macroscopic appearance similar to flow- layered silicic lava. Although it is a separate depositional unit, the Pagosa Peak Dacite is indistinguishable from the overlying Fish Canyon Tuff in bulk-rock chemistry, phenocryst compositions, and 40Ar/39Ar age. The unusual characteristics of this deposit are interpreted as consequences of eruption by low-column pyroclastic fountaining and lateral transport as dense, poorly inflated pyroclastic flows.
    [Show full text]
  • Rulemaking for Colorado Roadless Areas Map 2
    MAP 2 Inventoried Roadless Areas MAP 2 IRA acres 114 Porphyry Peak 3,400 233 Treasure Mountain 20,900 194 115 Puma 8,500 234 Turkey Creek 22,300 193 Platte River Inventoried Roadless Area rounded 116 Purgatoire 13,200 235 West Needle 2,500 Wilderness Names to nearest 207 117 Rampart West 23,700 236 West Needle Wilderness 5,900 4 100 acres ** Map Key ** 24 118 Romley 6,900 237 Williams Creek White Fir Natural Area 500 209 Arapaho-Roosevelt National Forest 119 Sangre de Cristo 32,600 White River National Forest 187 204 193 Mount 1 Bard Creek 25,400 120 Scraggy Peaks 8,200 238 Adam Mountain 8,200 195 197 21 Major Roads Zirkel 2 Byers Peak 10,100 121 Sheep Rock 2,200 239 Ashcroft 900 Wilderness 210 205 24 76 208 Rawah 10 25 3 Cache La Poudre Adjacent Areas 3,200 122 Silverheels 6,600 240 Assignation Ridge 13,300 Wilderness 9 11 4 Cherokee Park 7,800 123 Spanish Peaks 5,700 241 Baldy Mountain 6,000 Inventoried Roadless Areas 5 3 5 Comanche Peak Adjacent Areas 46,000 124 Spanish Peaks- proposed 1,300 242 Basalt Mountain A 14,000 196 5 3 3 5 5 Cache La Poudre 6 Copper Mountain 13,500 125 Square Top Mountain 5,900 243 Basalt Mountain B 7,400 5 3 3 3 214 Wilderness 7 Crosier Mountain 7,200 126 St. Charles Peak 11,600 244 Berry Creek 8,600 National Forest System Wilderness & Comanche Peak 28 200 24 8 Gold Run 6,500 245 Big Ridge To South Fork A 35,300 191 Wilderness 127 Starvation Creek 8,200 19 5 9 Green Ridge - East 26,700 128 Tanner Peak 17,800 246 Big Ridge To South Fork B 6,000 Other Congressionally Designated Lands 24 Fort 19 5 10 Green Ridge
    [Show full text]
  • Evolution of the Magma System of Pantelleria (Italy) from 190 Ka to Present
    Eastern Kentucky University Encompass EKU Faculty and Staff Scholarship Faculty and Staff Scholarship Collection 2021 Evolution of the magma system of Pantelleria (Italy) from 190 ka to present. Nina J. Jordan University of Leicester John C. White Eastern Kentucky University, [email protected] Ray Macdonald University of Warsaw Silvio G. Rotolo Universita degli Studi di Palermo Follow this and additional works at: https://encompass.eku.edu/fs_research Part of the Geochemistry Commons, Geology Commons, and the Volcanology Commons Recommended Citation Nina J. Jordan; John C. White; Ray Macdonald; Silvio G. Rotolo. Evolution of the magma system of Pantelleria (Italy) from 190 ka to present. Comptes Rendus. Géoscience, Online first (2021), pp. 1-17. doi : 10.5802/crgeos.50. This Article is brought to you for free and open access by the Faculty and Staff Scholarship Collection at Encompass. It has been accepted for inclusion in EKU Faculty and Staff Scholarship by an authorized administrator of Encompass. For more information, please contact [email protected]. Comptes Rendus Géoscience Sciences de la Planète Nina J. Jordan, John C. White, Ray Macdonald and Silvio G. Rotolo Evolution of the magma system of Pantelleria (Italy) from 190 ka to present Online first (2021) <https://doi.org/10.5802/crgeos.50> Part of the Special Issue: Perspectives on alcaline magmas Guest editor: Bruno Scaillet (Institut des Sciences de la Terre d’Orléans, CNRS, France) © Académie des sciences, Paris and the authors, 2021. Some rights reserved. This article is licensed under the Creative Commons Attribution 4.0 International License. http://creativecommons.org/licenses/by/4.0/ Les Comptes Rendus.
    [Show full text]
  • Acknowledgments
    DATING TECHNIQUES 3 Schultz's definition (1937, p.79) of the Coso should be clarified because the lava flows in the Coso Range have a wide age range. We believe that the lava flows referred to by Schultz are the rhyodacite flows on the Haiwee Ridge (fig. 1) described in the section on Pliocene rhyodacite lava flows. Parts of the Coso Formation have been described by Hopper (1947), Power (1959, 1961), Bacon and Duffield (1978), Duffield, Bacon, and Roquemore (1979), Duffield, Bacon, and Dalrymple (1980), and Giovannetti (1979a, b). Deposits mapped as the Coso (fig. 1) Occur in the Haiwee Reservoir (Stinson, 1977a), Keeler (Stinson, 1977b), and Darwin (Hall and MacKevett, 1962) 15-minute quadrangles and have been mapped in the Coso volcanic field (Duffield and Bacon, 1981). Potassium-argon dating of volcanic rocks intercalated with, and overlying, the Coso Formation has been used by Evernden, Savage, Curtis, and James (1964), Bacon, Giovannetti, Duffield, and Dalrymple (1979), and Duffield, Bacon, and Dalrymple (1980) to constrain the age of the Coso. In this report, we review these potassium-argon ages and present additional data that provide more accurate limits on the age of the Coso Formation. ACKNOWLEDGMENTS We thank C. A. Repenning for advice on paleontologic aspects of this study. G. R. Roquemore contributed valuable observations offieldrela- tions of pyroclastic rocks near Sugar Loaf. J. Metz painstakingly prepared and analyzed glass fractions of tuffs. C. E. Meyer and M. J. Woodward kindly determined fission-track ages of zircons. Part of this report is based on the second author's M. S.
    [Show full text]
  • Spanish Peaks Wilderness
    Mt. Bierstadt Field Trip Trip date: 6/17/2006 Ralph Swain, USFS R2 Wilderness Program Manager Observations: 1). The parking lot was nearly full (approximately 35 + vehicles) at 8:00 am on a Saturday morning. I observed better-than-average compliance with the dog on leash regulation. Perhaps this was due to my Forest Service truck being at the entrance to the parking lot and the two green Forest Service trucks (Dan and Tom) in the lot! 2). District Ranger Dan Lovato informed us of the District’s intent to only allow 40 vehicles in the lower parking lot. Additional vehicles will have to drive to the upper parking lot. This was new information for me and I’m currently checking in with Steve Priest of the South Platte Ranger District to learn more about the parking situation at Mt. Bierstadt. 3). I observed users of all types and abilities hiking the 14er. Some runners, 14 parties with dogs (of which 10 were in compliance with the dog-leash regulation), and a new- born baby being carried to the top by mom and dad (that’s a first for me)! Management Issues: 1). Capacity issue: I counted 107 people on the hike, including our group of 14 people. The main issue for Mt. Bierstadt, being a 14er hike in a congressionally designated wilderness, is a social issue of how many people are appropriate? Thinking back to Dr. Cordell’s opening Forum discuss on demographic trends and the growth coming to the west, including front-range Denver, the use on Mt.
    [Show full text]
  • Alkalic-Type Epithermal Gold Deposit Model
    Alkalic-Type Epithermal Gold Deposit Model Chapter R of Mineral Deposit Models for Resource Assessment Scientific Investigations Report 2010–5070–R U.S. Department of the Interior U.S. Geological Survey Cover. Photographs of alkalic-type epithermal gold deposits and ores. Upper left: Cripple Creek, Colorado—One of the largest alkalic-type epithermal gold deposits in the world showing the Cresson open pit looking southwest. Note the green funnel-shaped area along the pit wall is lamprophyre of the Cresson Pipe, a common alkaline rock type in these deposits. The Cresson Pipe was mined by historic underground methods and produced some of the richest ores in the district. The holes that are visible along several benches in the pit (bottom portion of photograph) are historic underground mine levels. (Photograph by Karen Kelley, USGS, April, 2002). Upper right: High-grade gold ore from the Porgera deposit in Papua New Guinea showing native gold intergrown with gold-silver telluride minerals (silvery) and pyrite. (Photograph by Jeremy Richards, University of Alberta, Canada, 2013, used with permission). Lower left: Mayflower Mine, Montana—High-grade hessite, petzite, benleonardite, and coloradoite in limestone. (Photograph by Paul Spry, Iowa State University, 1995, used with permission). Lower right: View of north rim of Navilawa Caldera, which hosts the Banana Creek prospect, Fiji, from the portal of the Tuvatu prospect. (Photograph by Paul Spry, Iowa State University, 2007, used with permission). Alkalic-Type Epithermal Gold Deposit Model By Karen D. Kelley, Paul G. Spry, Virginia T. McLemore, David L. Fey, and Eric D. Anderson Chapter R of Mineral Deposit Models for Resource Assessment Scientific Investigations Report 2010–5070–R U.S.
    [Show full text]
  • Volcanic Vistas Discover National Forests in Central Oregon Summer 2009 Celebrating the Re-Opening of Lava Lands Visitor Center Inside
    Volcanic Vistas Discover National Forests in Central Oregon Summer 2009 Celebrating the re-opening of Lava Lands Visitor Center Inside.... Be Safe! 2 LAWRENCE A. CHITWOOD Go To Special Places 3 EXHIBIT HALL Lava Lands Visitor Center 4-5 DEDICATED MAY 30, 2009 Experience Today 6 For a Better Tomorrow 7 The Exhibit Hall at Lava Lands Visitor Center is dedicated in memory of Explore Newberry Volcano 8-9 Larry Chitwood with deep gratitude for his significant contributions enlightening many students of the landscape now and in the future. Forest Restoration 10 Discover the Natural World 11-13 Lawrence A. Chitwood Discovery in the Kids Corner 14 (August 4, 1942 - January 4, 2008) Take the Road Less Traveled 15 Larry was a geologist for the Deschutes National Forest from 1972 until his Get High on Nature 16 retirement in June 2007. Larry was deeply involved in the creation of Newberry National Volcanic Monument and with the exhibits dedicated in 2009 at Lava Lands What's Your Interest? Visitor Center. He was well known throughout the The Deschutes and Ochoco National Forests are a recre- geologic and scientific communities for his enthusiastic support for those wishing ation haven. There are 2.5 million acres of forest including to learn more about Central Oregon. seven wilderness areas comprising 200,000 acres, six rivers, Larry was a gifted storyteller and an ever- 157 lakes and reservoirs, approximately 1,600 miles of trails, flowing source of knowledge. Lava Lands Visitor Center and the unique landscape of Newberry National Volcanic Monument. Explore snow- capped mountains or splash through whitewater rapids; there is something for everyone.
    [Show full text]
  • Subduction Cycles Under Western North America During the Mesozoic and Cenozoic Eras
    .. Geological Society of America Special Paper 299 1995 Subduction cycles under western North America during the Mesozoic and Cenozoic eras Peter L. Ward U.S. Geological Survey, 345 Middlefield Road, MS 977, Menlo Park, California 94025 ABSTRACT An extensive review of geologic and tectonic features of western North America suggests that the interaction of oceanic plates with the continent follows a broad cycli- cal pattern. In a typical cycle, periods of rapid subduction (7-15 cdyr), andesitic vol- canism, and trench-normal contraction are followed by a shift to trench-normal extension, the onset of voluminous silicic volcanism, formation of large calderas, and the creation of major batholiths. Extension becomes pervasive in metamorphic core complexes, and there is a shift to fundamentally basaltic volcanism, formation of flood basalts, widespread rifting, rotation of terranes, and extensive circulation of flu- ids throughout the plate margin. Strike-slip faulting becomes widespread with the creation of new tectonostratigraphic terranes. A new subduction zone forms and the cycle repeats. Each cycle is 50-80 m.y. long; cycles since the Triassic have ended and begun at approximately 225, 152, 92, 44, and 15 Ma. The youngest two cycles are diachronous, one from Oregon to Alaska, the other from central Mexico to Califor- nia. The transitions from one cycle to the next cycle are characterized by rapid and pervasive changes termed, in this chapter, “major chaotic tectonic events.” These events appear to be related to the necking or breaking apart of the formerly sub- ducted slab at shallow depth, the resulting delamination of the plate margin, and the onset of a new subduction cycle.
    [Show full text]