DOCSLIB.ORG

Mechanisms of Intrusion of the Coastal Batholith of Peru Into Its Own Volcanic Ejecta

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Mechanisms of Intrusion of the Coastal Batholith of Peru Into Its Own Volcanic Ejecta Cauldron Subsidence and Fluidization: Mechanisms of Intrusion of the Coastal Batholith of Peru into Its Own Volcanic Ejecta JOHN S. MYERS Geological Survey of Greenland, 0stervoldgade 10, Copenhagen, Denmark ABSTRACT 10 to 60 km inland, and has subvertical walls and a flat roof. It was emplaced be- The Coastal Batholith of Peru shows how tween Late Albian and Eocene time (about diorite, tonalite, granodiorite, and granite 100 to 50 m.y. ago) into two groups of magmas rose through their last few volcanic rocks which were erupted from the kilometers by a process of magmatic stop- rising batholith. ing by their fluidized upper surface. The Structures and features relating to intru- magmas successively displaced both older, sive mechanisms are described together, more basic plutons and their own volcanic drawing on examples from different units debris downward and canje to rest within 3 of the batholith because the structure and km of the Earth's surface after loosing vol- intrusion mechanism of most plutons are atiles by eruptions through fissures and cal- broadly similar. A more complete account deras. There was a continuous association of the batholith, the volcanic rocks, and the between volcanic eruptions and plutonic in- regional geology is in press (Myers, in trusions from at least 100 to 30 m.y. ago in press). Plutonic rock names follow the a narrow belt parallel with the continental margin. The batholith is 50 km wide, more than 1,100 km long, and probably 15 km or less thick. It has steep walls and an extensively preserved flat roof exposed in mountainous desert with relief of 4,500 m. It consists of plutons and sheets which were intruded in five distinct episodes into the same tabular belt by repeated cauldron subsidence. Each subsidence was preceded by the formation Figure 1. Map showing the extent of the of small shear zones which were fractured Coastal Batholith of Peru (after Bellido and and fluidized, and accompanied by the rise others, 1972) and locations of the area described and of section A-B of Figure 12. of corrosive, turbulent gas-liquid-solid mix- tures. Individual plutons form relatively thin tabular bodies with flat roofs and relief of more than 4,500 m. This paper de- floors and steep walls which pass down- scribes the structure of the batholith and ward into ring dikes and upward into ring evidence of the mechanism of its intrusion. dikes and calderas. Key words: structural Earlier descriptions of other parts of the geology, igneous rocks, batholiths, vol- Coastal Batholith were made by Jenks canism. (1948), Cossio (1964), Cossio and Jaén (1967), and Stewart (in Garcia, 1968). Part INTRODUCTION of the batholith lying immediately south of this area was described by Cobbing and The Coastal Batholith of Peru is one of Pitcher (1972) and Cobbing (1973a). These the largest and best exposed of a chain of studies showed the batholith to consist of a Mesozoic and Tertiary batholiths which number of plutons of which tonalite, occur along the western margin of the granodiorite, and adamellite far exceed feftvj Coastal Batholith American continent. It forms an almost basic rocks and granite in total volume. The continuous outcrop 1,100 km long and 50 earliest intrusions are more basic than I" Calipuy Voleantes km wide on the western flank of the Andes younger ones and local basic to acid dif- j v v | Casma Voleantes between latitudes 8° and 16° south (Fig. 1). ferentiation sequences occur within some The 80-km-long section of it which lies be- composite plutons. K-Ar minimum ages, • ' Crttacvous shtlf stdiments tween latitudes 10° and 10° 30' south was mostly of biotite and hornblende obtained Pr«-Crttac«ous rocks mapped on the scale of 1:50,000 during 12 from a wide area of the Coastal Batholith, Figure 2. Part of northern Peru showing the months spent in the field in 1968-1970. range from about 100 to 10 m.y. (Stewart close association of the Casma and Calipuy The shapes of the intrusions and the struc- and others, 1974). Groups of volcanic rocks with the Coastal ture of their country rocks can be clearly Between latitudes 10° and 10° 30' south, Batholith (after Cobbing, 1973b); the area de- observed here in mountainous desert with the batholith lies parallel with the coastline. scribed is outlined. Geological Society of America Bulletin, v. 86, p. 1209-1220, 12 figs., September 1975, Doc. no. 50903. 1209 1210 J. S. MYERS definitions recommended by the Interna- with amphibolite facies metamorphism. Dikes of microdiorite were intruded be- tional Union of Geological Sciences (Streck- Biotite forms a prominent schistosity, tween and during the emplacement of all eisen, 1973). The term "host rock" is used hornblende crystals are elongate parallel the complexes. In the Sayán area (Fig. 1), to include any rock into which a pluton, with fold axes, and cordierite contains the dikes intruded between the Santa Rosa dike, or sheet was intruded, whereas the spiral inclusion trails of opaque minerals. and Puscao — San Jeronimo Complexes give term "country rock" is restricted to non- The Tapacocha fold belt is an anticlinorium K-Ar whole-rock ages of 72 to 68 m.y. A plutonic rocks, mostly volcanic, into which of isoclinal folds associated with green- fifth group of plutons at Sayán, younger the batholith was emplaced. schist facies metamorphism. than the Puscao — San Jeronimo Com- plexes, give K-Ar mineral ages of ~30 m.y. VOLCANIC COUNTRY ROCKS Calipuy Group (P. A. Wilson, 1974, personal commun.). The Coastal Batholith was intruded into The Calipuy Group is a sequence of ter- Major Structures the Casma Group of volcanic rocks which restrial andesite, dacite and rhyolite, lava, are chiefly marine and Middle to Upper and pyroclastic flows which extends for at The batholith has steep walls, subparallel Albian, and the Calipuy Group of terrestri- least 600 km along the western cordillera of with the coast and continental margin, and al volcanic rocks which unconformably northern Peru (Fig. 2). The rocks were first a flat roof. The roof is extensively preserved overlie them and are Late Cretaceous to described in detail by Cossio (1964) and in the northeastern part of the area (Fig. 3). early Tertiary in age (Fig. 2). Cossio and Jaén (1967) and are extensively Individual plutons have similar flat roofs intruded by the Coastal Batholith. In the and steep outward-dipping or vertical walls Casma Group northeast part of the area described, they (Figs. 4, 5, and 6). The plutons generally overlie the Tapacocha fold belt with form rectangular bodies with long sides The Casma Group is a sequence of ande- marked unconformity (Fig. 3) and their av- parallel to the batholith and short sides site lava and pyroclastic flows, andesite pil- erage thickness is in the order of 2 km. The normal to it [for example, the Huampi low lava, tuff, dikes, and sills, with smaller rocks are probably Late Cretaceous to early Piruroc granodiorite (Fig. 4); the Con- amounts of dacitic pyroclastic flows, chert, Tertiary in age, and they formed the land taderas, Llagumpe, and Maria Cristina plu- and volcaniclastic sediments. The sequence surface during intrusion of most of the tons of the Puscao unit, and northernmost extends for at least 500 km along the batholith. San Jeronimo pluton (Fig. 5)]. The transi- coastal region of northern Peru and inland tion from steep walls to flat roof generally to just beyond the eastern margin of the COASTAL BATHOLITH occurs within a vertical distance of 50 m Coastal Batholith (Fig. 2). In the area de- (Fig. 4, localities B and D). This relation- scribed here, it comprises six formations The batholith is a heterogeneous mass of ship is most clearly seen on a large scale in with a total thickness of about 6.5 km, al- coarse-grained igneous rocks which was in- the dome-shaped outcrops of the Puca Jirca though the actual thickness in any one place truded as numerous plutons and sheets. and Chasquitambo plutons of the Puscao is probably in the order of 3 to 4 km. The Each pluton is a distinct mappable intrusive unit. The Puca Jirca pluton forms a subcir- stratigraphic sequence is summarized in the body with steep walls and a flat roof. Many cular dome-shaped outcrop, 5 km in diame- legend of Figure 3 and described in detail in plutons are composed of identical rock ter, through which a valley cuts a section Myers (1974, and in press). Fossils indicate types, and each major mappable rock type 700 m deep (Fig. 5). At the highest levels that most of the lower part of the volcanic is called a magma unit. This unit is the fun- exposed, the contacts dip outward at 5°; sequence is late Middle Albian in age. In the damental division of the batholith and is whereas in the valley floor, they dip at 30° northeast corner of the area, the Casma analogous to the lithostratigraphic term to 40° outward. The Chasquitambo pluton Group conformably overlies a thick se- "formation." In the same way, a "com- crops out over an area of 300 sq km be- quence of shale and siltstone of probable plex" (or super-unit of Cobbing and tween altitudes of 400 and 2,400 m (Fig. 5). Hauterivian to Middle Albian age (Huayl- Pitcher, 1972) is a group of related units, At the highest topographic levels, its con- lapainpa Group). and a "subunit" is a division of a unit, tact dips at less than 10° outward; at the analogous to the lithostratigraphic terms lowest levels exposed, its contact dips Regional Deformation and Metamorphism "group" and "member." steeply Outward.
Load more

Recommended publications
  • Impinging Ring Dike Complexes in the Sierra Nevada Batholith, California: Roots of the Early Cretaceous Volcanic Arc
    Impinging ring dike complexes in the Sierra Nevada batholith, California: Roots of the Early Cretaceous volcanic arc Diane Clemens-Knott* Division of Geological and Planetary Sciences, California Institute of Technology, Jason B. Saleeby } Pasadena, California 91125 ABSTRACT and Tilton, 1991, for a recent review). Specifically, the crust varied from rel- atively thin, accreted ophiolite and marine metasedimentary rocks on the In this paper we interpret new and previously published U-Pb zircon west, to altered volcanic and volcaniclastic rocks in the center, to a thicker data in light of structures mapped within ~360 km2 of the southwestern wedge of continental margin metasedimentary rocks on the east (Saleeby, Sierra Nevada batholith. Traces of intrusive contacts and igneous foli- 1981). In addition to crustal heterogeneity, the proportion of crust assimilated ations reveal the presence of two ring dike complexes: the eastern ring by depleted mantle-derived magmas may have increased eastward (DePaolo, complex and the western ring(?) complex. These subvolcanic com- 1981). More recent studies suggest that the lateral variations are due, in part, plexes formed during overlapping periods: the eastern ring complex to variations within the mantle (Silver and Chappell, 1988): for example, between 123 and 117 Ma (n = 5) and the western ring complex between parental magmas of western Sierran plutons were derived from depleted 120 and 115 Ma (n = 5). Each complex may have been emplaced dur- mantle and parental magmas of central and eastern Sierran plutons may have ing a minimum of two events, each 2 to 3 m.y. long and separated by 3 been derived from enriched mantle (Coleman et al., 1992; Beard and to 4 m.y.
    [Show full text]
  • The Rio Ca~Ete Basin : Central Coastal Ranges of Peru
    Third ISAG, St Malo (France), 17-1 9/91]996 STRATIGRAPHY, SEDIMENTOLOGY AND TECTONIC EVOLUTION OF THE RIO CA~ETEBASIN : CENTRAL COASTAL RANGES OF PERU Antenor M. Aleman Amoco Production CO Houston, Texas 77293 KEY WORDS: Lima stratigraphy, frontal arc, arc extension. Central Coastal Ranges evolution. ABSTRACT The Rio Caiiete Basin in the Central Coastal Ranges of Peru (C.C.R.P.) represents a fault-bounded frontal-arc Late Jurasic (Tithonian) to Albian sequence formed by aborted intra-arc spreading process during the early evolution of the Andes (Fig.1). The sequence, exposed in the Lima area, consists of more than 6000 meters of volcaniclastic sedimentary rocks, lava flows, lime mudstones, shales, quartz rich sandstones and subordinated fossiliferous limestones and evaporites. The stratigraphy records several episodes of volcanism and extension along and across the basin and provides new insight in the evolution and crustal growth of the Central Andes. INTRODUCTION Four widespread groups and one areally restricted formation mark important stages in the stratigraphic, sediimentologic and tectonic evolution of the Rio Caiiete Basin. The Puente Piedra Group consists of volcaniclastic debris, basaltic to andesitic lava flows, shales and subordinate limestones that document the presence of a Jurassic volcanic arc (Fig.2). The overlying quartz rich sandstones and shales of the Morro Solar Group (fig.3) records an abrupt change in sedimentation and tectonic style. Ensialic extension accompanied by subsidence of the volcanic arc and concomitant uplift of the Paleozoic (o Precambrian "Coastal Cordillera" (Paracas Block) explains the change of source and provenance. The areally restricted Pucusana Formation (Fig.4), made up of alkaline lavas, volcanic breccias and lapillistones, is interpreted (o represent a localized volcanic center perhaps related to subduction of oceanic fractures.
    [Show full text]
  • Geology of the Pilanesberg Ring Dike Complex 28 July 2015
    Geology of the Pilanesberg Ring Dike complex 28 July 2015 sustain critical watering holes for the animals. The largest body of water in the park, Mankwe Lake, is visible in the lowlands just east of the center. Several phases of geologic activity created the landscape over hundreds of millions of years. The process began about 1.3 billion years ago, when primitive organisms like algae were the only lifeforms on Earth and huge volcanic eruptions were common. During this period, magma pooled up near the surface in a large hot spot that bulged with immense pressure. The pressure helped push up a volcanic structure that was several thousand meters tall. Acquired June 19, 2015. Over time, tubes of magma radiated outward from the main magma chamber beneath the volcano. Eventually this created massive cracks in the Earth's surface around the volcano at regular While big game animals such as lions, leopards, intervals. (In cross section, the magma tubes would elephants, rhinos, and water buffaloes draw most have looked something like the branches of a tree visitors to Pilanesberg National Park, the land extending from a common trunk. From above, the these animals live on is just as compelling. radial cracks gave the surface the appearance of a Pilanesberg is located in one of the world's largest broken window. A good illustration of the magma and best preserved alkaline ring dike complexes—a tubes is available here.) After several violent rare circular feature that emerged from the eruptions sent lava bursting from the volcano, the subterranean plumbing of an ancient volcano.
    [Show full text]
  • Mineralogy and Geochemistry of Carbonaceous Mudstone As a Vector to Ore: a Case Study at the Lagunas Norte High-Sulfidation Gold Deposit, Peru
    MINERALOGY AND GEOCHEMISTRY OF CARBONACEOUS MUDSTONE AS A VECTOR TO ORE: A CASE STUDY AT THE LAGUNAS NORTE HIGH-SULFIDATION GOLD DEPOSIT, PERU by Harry Hanneman A thesis submitted to the Faculty and Board of Trustees of the Colorado School of Mines in partial fulfillment of the requirements for the degree of Master of Science (Geology). Golden, Colorado Date ________________ Signed: ________________________ Harry Hanneman Signed: ________________________ Dr. Thomas Monecke Thesis Advisor Golden, Colorado Date ________________ Signed: ________________________ Dr. Paul Santi Professor and Head Department of Geology and Geological Engineering ii ABSTRACT The Lagunas Norte Au deposit in the Alto Chicama district of Peru is a ~14 Moz high- sulfidation epithermal deposit that is hosted by an atypical host-rock succession for this deposit type. Approximately 80% of the ore body is contained in the Lower Cretaceous Chimu Formation, which is composed of quartz arenite with interbedded carbonaceous mudstone, siltstone, and coal seams. The remainder of the ore is hosted by the Miocene volcanic rocks of the Calipuy Group, forming an irregular and thin veneer on the deformed sedimentary rocks of the basement. The host rock succession of the Lagunas Norte deposit has been affected by widespread hydrothermal alteration. The alteration is cryptic within most of sedimentary rocks as the quartz arenite was largely inert to alteration by the strongly acidic fluids. Vuggy textures associated with residual quartz alteration can only be recognized in the overlying Miocene volcanic rocks. However, the present study shows that mudstone of the Chimu Formation records acid-type alteration due to its originally high clay mineral content.
    [Show full text]
  • Part 629 – Glossary of Landform and Geologic Terms
    Title 430 – National Soil Survey Handbook Part 629 – Glossary of Landform and Geologic Terms Subpart A – General Information 629.0 Definition and Purpose This glossary provides the NCSS soil survey program, soil scientists, and natural resource specialists with landform, geologic, and related terms and their definitions to— (1) Improve soil landscape description with a standard, single source landform and geologic glossary. (2) Enhance geomorphic content and clarity of soil map unit descriptions by use of accurate, defined terms. (3) Establish consistent geomorphic term usage in soil science and the National Cooperative Soil Survey (NCSS). (4) Provide standard geomorphic definitions for databases and soil survey technical publications. (5) Train soil scientists and related professionals in soils as landscape and geomorphic entities. 629.1 Responsibilities This glossary serves as the official NCSS reference for landform, geologic, and related terms. The staff of the National Soil Survey Center, located in Lincoln, NE, is responsible for maintaining and updating this glossary. Soil Science Division staff and NCSS participants are encouraged to propose additions and changes to the glossary for use in pedon descriptions, soil map unit descriptions, and soil survey publications. The Glossary of Geology (GG, 2005) serves as a major source for many glossary terms. The American Geologic Institute (AGI) granted the USDA Natural Resources Conservation Service (formerly the Soil Conservation Service) permission (in letters dated September 11, 1985, and September 22, 1993) to use existing definitions. Sources of, and modifications to, original definitions are explained immediately below. 629.2 Definitions A. Reference Codes Sources from which definitions were taken, whole or in part, are identified by a code (e.g., GG) following each definition.
    [Show full text]
  • Washington Division of Geology and Earth Resources Open File Report
    OF~ 76-~ PETR)3ENFSIS OF THE MXJNT STUART BATHOLITH PID:rrnIC EQJI\7ALENT OF THE HIGH-AIJ.JMINA BASALT ASSO:IATION by Erik H. Erikson Jr. Depart:rrent of Geology Eastern Washington State College Cheney ,Wc::.shington 99004 June 1, 1976 Abstract. The 1-bunt Stuart batholith is a Late Cretaceous calc-alkaline pluton · . canposed of intrusive phases ranging in canposition fran two-pyroxene gabbro to granite. This batholith appears to represent the plutonic counterpart of the high-alumina basalt association. Mineralogical, petrological and chrono­ logical characteristics are consistent with a m:::rlel in which the intrusive series evolved fran one batch of magnesian high-alumina basalt by successive crystal fractionation of ascending residual magrna. ' canputer m:::rleling of this intrusive sequence provides a quanti- tative evaluation of the sequential change of magrna CCIIlfX)sition. These calculations indicate that this intrusive suite is consanguineous, and that subtraction of early-fonned crystals £ran the oldest magrna is capable of reprcducing the entire magrna series with a remainder of 2-3% granitic liquid. Increasing f()tash discrepancies prcduced by the rrodeling may reflect the increasing effects of volatile transfer in progressively rrore hydrous and silicic melts. Mass-balances between the arrounts of curn-ulate and residual liquid ccnpare favorably with the observed arrounts of intenrediate rocks exposed in the batholith, but not with the mafic rocks. Ma.fie cum: ulates must lie at depth. Mafic magmas probably fractionated by crystal settling, while quartz diorite and rrore granitic magrnas underwent a process of inward crystallization producing exposed gradationally zoned plutons.Aat present erosional levels.
    [Show full text]
  • Tectonic Evolution of the Northern Sierra Nevada
    TECTONIC EVOLUTION OF THE NORTHERN SIERRA NEVADA BATHOLITH A DISSERTATION SUBMITTED TO THE DEPARTMENT OF GEOLOGICAL AND ENVIRONMENTAL SCIENCES AND THE COMMITTEE ON GRADUATE STUDIES OF STANFORD UNIVERSITY IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY Nicholas James Van Buer December 2011 © 2011 by Nicholas James Van Buer. All Rights Reserved. Re-distributed by Stanford University under license with the author. This work is licensed under a Creative Commons Attribution- Noncommercial 3.0 United States License. http://creativecommons.org/licenses/by-nc/3.0/us/ This dissertation is online at: http://purl.stanford.edu/xb187vq0064 Includes supplemental files: 1. Plate 1. Geologic Map of the Jayhawk Well 7.5' Quadrangle, Pershing County, Nevada (jayhawkwell.pdf) 2. Plate 2. Geologic Map of the Juniper Pass 7.5' Quadrangle, Pershing County, Nevada (Juniperpass.pdf) 3. Plate 3. Geologic Map of the Tohakum Peak NE 7.5' Quadrangle, Pershing County, Nevada (TohakumpkNE.pdf) 4. Plate 4. Geologic Map of the Tunnel Spring 7.5' Quadrangle, Pershing County, Nevada (tunnelspr.pdf) 5. Plate 5. Geologic Map of the Bob Spring 7.5' Quadrangle, Pershing County, Nevada (bobspring.pdf) 6. Plate 6. Geologic Map of the Tohakum Peak SE 7.5' Quadrangle, Pershing County, Nevada (TohakumpkSE.pdf) 7. Plate 7. Geologic Map of the Sage Hen Spring 7.5' Quadrangle, Pershing County, Nevada (SageHenSpr.pdf) 8. Plate 8. Geologic Map of the Bluewing Spring 7.5' Quadrangle, Pershing County, Nevada (BluewingSpr.pdf) ii I certify that I have read this dissertation and that, in my opinion, it is fully adequate in scope and quality as a dissertation for the degree of Doctor of Philosophy.
    [Show full text]
  • University of Nevada Reno Dike Emplacement and Deformation In
    M’ MES Lf&SARY 3201 University of Nevada Reno Dike Emplacement and Deformation in the Donner Summit Pluton, Central Sierra Nevada, California Ch vS> C* This thesis is submitted in partial fulfillment of the requirements for the degree of Master of Science in Geological Engineering. by Kathleen Andrea Ward Dr. Richard Schultz/ Thesis Advisor December 1993 H ACKNOWLEDGEMENTS <Whew> I bet some of you out there figured I would never get done. But here I am with a completed M.S. thesis in geological engineering. I am not even sure where to begin and who to thank first, because each and every one of the following people have contributed so much to my life and my thesis. My mom and dad and Erika and Christy have always been supportive about my schoolwork. Without them close by in Sacramento with a guest room I would have gone crazy. I love them more than they can ever imagine. And no one will ever find a better field assistant than my sister Erika. Christina and Robert - What an incredible pair! Always had an extra room for me too, even in Florida. My grandma, who put up with me no matter what my mood. I love you. My e-mail account was priceless. The constant cheer and love I received from Becky, Kevin, and Erika helped me through many stressful times. The other graduate students who enjoyed the M.S. thesis ride with me, I salute each and every one of you. Especially Paul and Li (the two hardest workers in the department). Reno Mountain Sports, the entire crew, have been my constant sanctuary always making me take time out to smell the roses, or ski the powder...
    [Show full text]
  • Measurement of Radon in Soils of Lima City - Peru During the Period 2016-2017
    EARTH SCIENCES RESEARCH JOURNAL Earth Sci. Res. J. Vol. 23, No. 3 (September, 2019): 171-183 ENVIRONMENTAL GEOLOGY ENVIRONMENTAL Measurement of radon in soils of Lima City - Peru during the period 2016-2017 Lázaro Luís Vilcapoma1, María Elena López Herrera1, Patrizia Pereyra1, Daniel Francisco Palacios1, Bertin Pérez1, Jhonny Rojas1, Laszlo Sajo-Bohus2 1Pontificia Universidad Católica del Perú, Lima, Peru 2Universidad Simón Bolívar, Caracas, Venezuela * Corresponding author: [email protected] ABSTRACT Keywords: soil gas radon; emanation; Lima; LR- Lima City is situated on alluvial fan deposits of rivers flowing through geological formations that contain different 115 detector; Niño Costero; river floods; alluvial levels of uranium. In this paper, a study is made on the average spatial and temporal behavior of radon gas in soils of deposits; igneous rocks. Lima City. Radon concentration was determined using the LR-115 type 2 track detector during 36 periods, of 14 days each, in twenty holes distributed in the fifteen districts of Lima City. Radon concentration in soil pores ranged from 0.1 to 64.3 kBq/m3 with an average value of 5.6 kBq/m3. The average radon concentration in soil gas was about two times lower in winter than in the other seasons. High radon values during October/November 2017 were related to the earthquakes perceived in Lima City in that period. The highest radon concentrations were found in areas of alluvial deposits whose parental material has been removed from the Quilmaná and Huarangal volcanics by the Chillón and Huaycoloro Rivers. Soil gas radon concentrations were even higher in areas closer to volcanic and less distant from rivers.
    [Show full text]
  • The Mogollon-Datil Volcanic Field, Southwestern New Mexico Wolfgang E
    New Mexico Geological Society Downloaded from: http://nmgs.nmt.edu/publications/guidebooks/59 When batholiths exploded: The Mogollon-Datil volcanic field, southwestern New Mexico Wolfgang E. (Wolf) Elston, 2008, pp. 117-128 in: Geology of the Gila Wilderness-Silver City area, Mack, Greg, Witcher, James, Lueth, Virgil W.; [eds.], New Mexico Geological Society 59th Annual Fall Field Conference Guidebook, 210 p. This is one of many related papers that were included in the 2008 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.
    [Show full text]
  • The Great Eucrite Intrusion of Ardnamurchan, Scotland: Reevaluating the Ring-Dike Concept
    The Great Eucrite intrusion of Ardnamurchan, Scotland: Reevaluating the ring-dike concept B. O'Driscoll* Department of Geology, Museum Building, Trinity College, Dublin 2, Ireland V.R. Troll R.J. Reavy Department of Geology, University College Cork, Cork, Ireland P. Turner School of Geography, Earth, and Environmental Sciences, University of Birmingham, Birmingham B15 2TT, UK ABSTRACT Ring-dikes are cylindrical sheet intrusions that develop at a subvolcanic level due to ascent of magma along steep outward- dipping ring fractures. Magma ascent is triggered by central block subsidence, and fully formed ring-dikes are composed of a ¯at- lying sill-like roof as well as steeply outward-dipping walls on all sides. The Great Eucrite of the Ardnamurchan Paleocene igneous complex, NW Scotland, is a spectacular gabbro intrusion that has Figure 1. Schematic diagram showing subvolcanic level and been cited as one of the classic examples of a ring-dike for the past ring-fault system along which ring-dikes are emplaced (after 70 yr. We combine ®eld observations, detailed structural measure- Walter and Troll, 2001). Inset: Bell-jar geometry of typical ring- ments of primary magmatic features, and anisotropy of magnetic dike intrusion and expected magma ¯ow directions during susceptibility data in a reinvestigation of this intrusive body. Mag- emplacement. matic layering and macroscopic planar crystal arrangements dip inward, and magnetic lineations plunge consistently toward the Three distinct foci of activity have been recognized in the Ard- center of the intrusion, in contrast to what would be expected for namurchan complex (centers 1, 2, and 3; Fig. 2). Each of these is a ring-dike.
    [Show full text]
  • The Boulder Creek Batholith, Front Range, Colorado
    I u The Boulder Creek Batholith, Front Range, Colorado By DOLORES J. GABLE GEOLOGICAL SURVEY PROFESSIONAL PAPER 1101 A study of differentiation, assimilation, and origin of a granodiorite batholith showing interrelated differences in chemistry and mineralogy in the batholith and cogenetic rock types UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1980 UNITED STATES DEPARTMENT OF THE INTERIOR CECIL D. ANDRUS, Secretary GEOLOGICAL SURVEY H. William Menard, Director Library of Congress Cataloging in Publication Data Gable, Dolores J. 1922- The Boulder Creek batholith, Front Range, Colorado (Geological Survey Professional Paper 1101) Bibliography: p. 85 Supt. of Docs. No.: I 19.16:1101 1. Batholiths Colorado Boulder region. I. Title. II. Series: United States Geological Survey Professional Paper 1101. QE611.5.U6G3 551.8; 8 78-24482 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 CONTENTS Page Page Abstract................................................ 1 Origin of the Boulder Creek Granodiorite and the Twin Introduction ............................................ 1 Spruce Quartz Monzonite .......................... 62 Previous work........................................... 2 Mineralogy, petrology, and chemistry of minerals in the Techniques used in this study ............................ 2 batholith.......................................... 64 Geologic setting ......................................... 3 Biotite ...'........................................... 64 The batholith ..........................................
    [Show full text]