DOCSLIB.ORG

Geochemistry of the Granite-Gabbro Complex on Vinalhaven Ismnd, Maine

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Geochemistry of the Granite-Gabbro Complex on Vinalhaven Ismnd, Maine Maine Geological Survey Studies in Maine Geology: Volume 4 1989 Geochemistry of the Granite-Gabbro Complex on Vinalhaven Ismnd, Maine Christopher B. Mitchell IEP, Inc. P.O. Box 1136 Portsmouth, New Hampshire 03801 J. Michael Rhodes Department ofGeology and Geography University of Massachusetts Amherst, Massachusetts 01003 ABSTRACT The bimodal granite-gabbro association on Vinalhaven Island, Maine has spectacular textural and structural relationships that are interpreted to have resulted from commingling of contemporaneous mafic and felsic liquids. During this process, the felsic and mafic magmas retained their identities and produced composite zones of chilled basaltic pillows in a granite matrix. Approximately 100 samples have been analyzed for whole-rock major and trace element abundances. These data have been used to classify the rocks and evaluate their relationships. The granites are homogeneous, high Si Oz (72.55-77.35 wt % ), two-feldspar, biotite ±hornblende, I-type, crustal, minimum-melt granites, with similar compositions to other granites from the Maine coastal lithotectonic belt. The mafic rocks, medium-grained gab bros to diorites and fine-grained chilled basalt pillows, have a range in composition (MgO 4.09-11.11 wt % ) that can be explained by varying amounts of crystal fractionation of the proposed parental magma composition accompanied by crystal accumulation and contamination by the surrounding granite melt. The parental composition calculated for the mafic rocks is similar to type I MORB that has been enriched in K, Sr, Rb, Ba, and Al. The mafic magma is probably the product of partial melting and was enriched in these elements during emplacement. A second group of mafic samples is enriched relative to the other mafic samples, in high field-strength elements Ti02, Zr, Nb, along with Sr. The physical differences in composition, temperature, and viscosity between the mafic and felsic magmas allowed the mafic magmas to chill as pillows, which helped prevent mixing between the basalt and the granite melt in the composite zones. The mechanical breakdown of some of the pillow-granite contacts has aided selective mixing, which has produced limited hybridization. These contaminated samples are not the result of simple two-component mixing of the observed granite and proposed parental basalt composition. INTRODUCTION The Island of Vinalhaven lies 15 miles east of Rockland, south western most exposure of the Bays-of-Maine Igneous Com­ Maine at the southern end of Penobscot Bay. It is made up of a plex (Chapman, I 962a). 361 ± 7 Ma Devonian granite-gabbro association, intruding the The Bays-of-Maine Igneous Complex is a large, essentially 393 ± 6 Ma Silurian-Early Devonian(?) Vinalhaven rhyolite and bimodal Devonian granite-gabbro association that trends 280 km Thorofare andesite (Brookins, 1976). The intrusive rocks are the east-northeast, parallel to tectonic strike, from southern 45 C. B. Mitchell and J. M. Rhodes Penobscot Bay along the coast of Maine into New Brunswick, et al., 1965; Walker and Skelhom 1966; Wiebe 1973, 1974, 1979, Canada. According to Chapman (l 962a) it consists of earlier 1980, 1984; Yoder, 1973; Gamble, 1979; Taylor et al., 1980; Reid gabbroic phases, closely followed by at least two later granitic et al., 1983; Marshall and Sparks, 1984; Cantagrel et al., 1984; phases. Chapman (1962a, 1968) has placed the granites of Vogel et al., 1984; Whalen and Currie, 1984; Brown and Becker, Vinalhaven into the younger group termed the Maine coastal 1986), suggesting that the textures formed are the result of plutons, cutting the earlier phases of the complex. He suggested interaction when both magmas were liquid or largely liquid at that the Maine coastal plutons are post-orogenic and were the same time. Despite the overwhelming field and petrographic emplaced in association with cauldron subsidence. These evidence for the commingling of mafic and silicic magmas, plutons straddle the proposed Acadian suture, and therefore must attempts to document the degree ofliquid-liquid interaction with have been emplaced in the late stages of, or after, the Acadian geochemical data have failed to support simple two-component orogeny (Berry, 1986). Both these conclusions are in accord mixing processes (Gamble, 1979; Taylor et al., 1980; Vogel et with that of Loiselle and Wones ( 1979) who state that the coastal al., 1984; Whalen and Currie, 1984). plutons are anorogenic or A-type granites. This study shows that Other alternatives such as fluidization have been suggested the granites on Vinalhaven were closely associated with the for net-veining of mafic and felsic magmas (Reynolds, 1954). emplacement of the "earlier" mafic phase and that intimate Chapman (1962b) suggested that the composite dikes of Mt. commingling of the two magmas took place during their Desert Island, Maine were formed by net-veining, with a granite emplacement (Mitchell, 1986). liquid intruding a solid gabbro host. Taylor et al. (1980) ex­ amined the Mt. Desert dikes and interpreted those dikes as having formed through commingling. The Association of Mafic and F elsic Magmas The well developed textural relationships and spectacular shoreline exposures on Vinalhaven Island make this an excellent The relationship between coexisting felsic and mafic mag­ location to study the commingling of mafic and felsic magmas. mas has been a long-standing controversy in geology (e.g. Hol­ The purpose of this study is twofold: first to describe the mes, 1931 ; Walker and Skelhom, 1966; Yoder, 1973). Such chemistry of the intrusive rocks on Vinalhaven Island in order to associations have been explained through fractional crystal­ place them in the regional and tectonic setting, and second to lization of a parental basaltic magma, various degrees of partial relate the chemical variatfon in the zones of commingling to the melting of single or multiple sources, restite contamination, and massive granite-gabbro association that makes up the majority magma-mixing. Each theory has prevailed at some time in the of the island. past, with magma-mixing receiving considerable attention in the Throughout this paper the term commingling will be used current literature. to describe magmas which have mechanically mixed, but have The intimate association of mafic and felsic magmas is well retained their compositional identity. The terms hybridized and documented throughout the geologic record. These associations contaminated will be used interchangeably to describe situations manifest themselves as mixed magma ejecta, net-veined com­ where the magmas have interacted in such a manner that their plexes, composite dikes and sills, and dikes of incompletely compositions have been changed. mixed, commingled mafic "pillows" in granite hosts. Examples include commingling in the Precambrian Tigalak intrusion, Labrador, Canada (Wiebe and Wild, 1983), the Tertiary Marsco Methods suite on the Isle of Skye, Scotland (Harker, 1904; Wager et al., 1965; Vogel et al., 1984), and mixed magma ejecta in the 1875 During the summers of 1984 and 1985, over 100 samples eruption of Askja, Iceland (Sigurdsson and Sparks, 1981 ). were collected from the granite-gabbro complex on Vinalhaven. Bunsen (1851) first recognized the association of basalt and Sample size for chemical analysis was based on the guidelines rhyolite in the lavas of Iceland. He suggested that the mixing of of Clanton and Fletcher ( 1976) and ranged from approximately these magmas could be responsible for the genesis of the range 100 grams for fine-grained mafic material to 2,000 grams for of igneous rocks of Iceland and other similar associations. In his medium-grained granite. Samples were analyzed for bulk rock classic work on the Tertiary igneous rocks of Skye, Harker chemistry major (Si, Ti, Al, Fe, Mn, Mg, Ca, Na, K, P) and trace ( 1904) interpreted the composite dikes, sills, and ring dikes as a (V, Cr, Ni, Zn, Ga, Sr, Y, Zr, Nb, Ba, La, Ce, Pb, Th, U) elements consequence of the simultaneous intrusion of mafic and felsic using X-ray fluorescence spectrometry (XRF) at the Department magmas. Wager and Bailey ( 1953) examined the details of of Geology and Geography, University of Massachusetts, Am­ net-veined complexes and attributed the textures to the chilling herst. Standard petrographic thin sections were examined for of mafic magma against a cooler felsic magma, which produced textural relations and mineralogical data. chilled margins on the mafic unit. They called this incomplete Major elements analyses were done following modifica­ mixing of compositionally distinct magmas "commingling." tions of the methods of Norrish and Hutton (1969). Trace-ele­ Many subsequent studies support the commingling ment abundances were determined using the methods of Norrish hypothesis (Gibson and Walker 1963; Blake et al., 1965; Wager and Chappell ( 1967). Mass absorption coefficients for the 46 Granite-gabbro complex on Vinalhaven Island, Maine TABLE I. REPRESENTATIVE ANALYSES FROM THE VINALHAVEN GRANITE-GABBRO ASSOCIATION. MGA VG. average of 11 medium grained granites; FGA VG, average of 6 fine grained granites; M, representative granite matrix material (VH-62); E, repre- sentative evolved sample (VH-51): P, five-pillow average representing the starting liquid composition; C, representative cumulate sample (VH-49). Analytical precision estimates ( l cr) expressed as weight percentage or ppm. Complete Vinalhaven analyses are given in Appendix A, Table A I. Sample MCA VG I-std FGAVG I-std M E p c Analytical Precision Si02 74.37 0.62 73.83 0.59 6 l.71 53.34 48.94 47.58 0.16 Ti02 0.32 0.03 0.30 0.02 I.62 2.25 l.26 0.89 0.005 Alz03 13.00 0.18 13.58 0.12 14.26 13.89 17.11 17.69 0.06 Fe20 3* 2.06 0.14 1.91 0. 17 8.59 12.03 9.95 9.18 O.D3 MnO 0.04 0.01 0.04 0.01 0.16 0.20 0.1 7 0.15 0.005 MgO 0.28 0.05 0.39 0.05 1.9 1 5.55 8.26 11.11 0.04 CaO I.IO 0.09 1.23 0.1 I 4.41 7.89 10.82 10.84 0.03 Na20 3.45 0.16 3.56 0.17 3.62 3.2 1 2.70 2.48 0.09 KzO 5.07 0.07 5.08 0.15 3.
Load more

Recommended publications
  • Bedrock Geology Glossary from the Roadside Geology of Minnesota, Richard W
    Minnesota Bedrock Geology Glossary From the Roadside Geology of Minnesota, Richard W. Ojakangas Sedimentary Rock Types in Minnesota Rocks that formed from the consolidation of loose sediment Conglomerate: A coarse-grained sedimentary rock composed of pebbles, cobbles, or boul- ders set in a fine-grained matrix of silt and sand. Dolostone: A sedimentary rock composed of the mineral dolomite, a calcium magnesium car- bonate. Graywacke: A sedimentary rock made primarily of mud and sand, often deposited by turbidi- ty currents. Iron-formation: A thinly bedded sedimentary rock containing more than 15 percent iron. Limestone: A sedimentary rock composed of calcium carbonate. Mudstone: A sedimentary rock composed of mud. Sandstone: A sedimentary rock made primarily of sand. Shale: A deposit of clay, silt, or mud solidified into more or less a solid rock. Siltstone: A sedimentary rock made primarily of sand. Igneous and Volcanic Rock Types in Minnesota Rocks that solidified from cooling of molten magma Basalt: A black or dark grey volcanic rock that consists mainly of microscopic crystals of pla- gioclase feldspar, pyroxene, and perhaps olivine. Diorite: A plutonic igneous rock intermediate in composition between granite and gabbro. Gabbro: A dark igneous rock consisting mainly of plagioclase and pyroxene in crystals large enough to see with a simple magnifier. Gabbro has the same composition as basalt but contains much larger mineral grains because it cooled at depth over a longer period of time. Granite: An igneous rock composed mostly of orthoclase feldspar and quartz in grains large enough to see without using a magnifier. Most granites also contain mica and amphibole Rhyolite: A felsic (light-colored) volcanic rock, the extrusive equivalent of granite.
    [Show full text]
  • The Geology, Petrography and Geochemistry of Gabbroic Rocks Of
    The Geology, Petrography and Geochemistry of Gabbroic Rocks of the Pants Lake Intrusive Suite on the Donner/Teck South Voisey's Bay Property, North-Central Labrador, Canada Heather E. MacDonald A thesis submitted in conformity with the requirements for the degree of Mastet's of Science Graduate Department of the Department of Geology University of Toronto O Copyright by Heather E. MacDonald, 1999 National Library Bibliothèque nationale 1*1 of Canada du Canada Acquisitions and Acquisitions et Bibliographie Services services bibliographiques 395 Wellingtori Street 395. rue Wellington OttawaON K1A ON4 OnawaON KlAONQ Canada Canada The author has granted a non- L'auteur a accordé une licence non exclusive licence allowing the exclusive permettant à la National Library of Canada to Bibliothèque nationale du Canada de reproduce, loan, distribute or seii reproduire, prêter, distribuer ou copies of this thesis in microform, vendre des copies de cette thèse sous paper or electronic formats. la forme de rnicrofiche/film, de reproduction sur papier ou sur format électronique. The author retains ownership of the L'auteur consewe la propriété du copyright in this thesis. Neither the droit d'auteur qui protège cette thèse. thesis nor substantiai extracts fiom it Ni la thèse ni des extraits substantiels may be printed or otherwise de celle-ci ne doivent être imprimés reproduced without the author's ou autrement reproduits sans son permission. autorisation. The Geology, Petrography and Ceochernistry of Gabbroic Rocks of the Pants Lake Intrusive Suite on the Donner/Teck South Voisey's Bay Property, North-Central Labrador, Canada Heather E. MacDonald Master's of Science, 1999 Department of Geology University of Toronto Abstract The South Voisey's Bay property held by Donner Minerals Limited in North-Central Labrador hosts Ni-Cu-Co mineralization within gabbroic rocks of the Pants Lake Intrusive Suite (PLIS).
    [Show full text]
  • Module 7 Igneous Rocks IGNEOUS ROCKS
    Module 7 Igneous Rocks IGNEOUS ROCKS ▪ Igneous Rocks form by crystallization of molten rock material IGNEOUS ROCKS ▪ Igneous Rocks form by crystallization of molten rock material ▪ Molten rock material below Earth’s surface is called magma ▪ Molten rock material erupted above Earth’s surface is called lava ▪ The name changes because the composition of the molten material changes as it is erupted due to escape of volatile gases Rocks Cycle Consolidation Crystallization Rock Forming Minerals 1200ºC Olivine High Ca-rich Pyroxene Ca-Na-rich Amphibole Intermediate Na-Ca-rich Continuous branch Continuous Discontinuous branch Discontinuous Biotite Na-rich Plagioclase feldspar of liquid increases liquid of 2 Temperature decreases Temperature SiO Low K-feldspar Muscovite Quartz 700ºC BOWEN’S REACTION SERIES Rock Forming Minerals Olivine Ca-rich Pyroxene Ca-Na-rich Amphibole Na-Ca-rich Continuous branch Continuous Discontinuous branch Discontinuous Biotite Na-rich Plagioclase feldspar K-feldspar Muscovite Quartz BOWEN’S REACTION SERIES Rock Forming Minerals High Temperature Mineral Suite Olivine • Isolated Tetrahedra Structure • Iron, magnesium, silicon, oxygen • Bowen’s Discontinuous Series Augite • Single Chain Structure (Pyroxene) • Iron, magnesium, calcium, silicon, aluminium, oxygen • Bowen’s Discontinuos Series Calcium Feldspar • Framework Silicate Structure (Plagioclase) • Calcium, silicon, aluminium, oxygen • Bowen’s Continuous Series Rock Forming Minerals Intermediate Temperature Mineral Suite Hornblende • Double Chain Structure (Amphibole)
    [Show full text]
  • A Geochemical Study of the Riddle Peaks Gabbro, North Cascades: Evidence for Amphibole Accumulation in the Mid-Crust of an Arc
    Western Washington University Western CEDAR WWU Graduate School Collection WWU Graduate and Undergraduate Scholarship 2014 A geochemical study of the Riddle Peaks gabbro, North Cascades: evidence for amphibole accumulation in the mid-crust of an arc Angela C. Cota Western Washington University Follow this and additional works at: https://cedar.wwu.edu/wwuet Part of the Geology Commons Recommended Citation Cota, Angela C., "A geochemical study of the Riddle Peaks gabbro, North Cascades: evidence for amphibole accumulation in the mid-crust of an arc" (2014). WWU Graduate School Collection. 362. https://cedar.wwu.edu/wwuet/362 This Masters Thesis is brought to you for free and open access by the WWU Graduate and Undergraduate Scholarship at Western CEDAR. It has been accepted for inclusion in WWU Graduate School Collection by an authorized administrator of Western CEDAR. For more information, please contact [email protected]. A GEOCHEMICAL STUDY OF THE RIDDLE PEAKS GABBRO, NORTH CASCADES: EVIDENCE FOR AMPHIBOLE ACCUMULATION IN THE MID CRUST OF AN ARC By Angela C. Cota Submitted for Partial Completion Of the Requirements for the Degree Master of Science Kathleen L. Kitto, Dean of the Graduate School ADVISORY COMMITTEE Chair, Dr. Susan DeBari Dr. Elizabeth Schermer Dr. Robert Miller MASTER’S THESIS In presenting this thesis in partial fulfillment of the requirements for a master’s degree at Western Washington University, I grant to Western Washington University the nonexclusive royalty‐free right to archive, reproduce, distribute, and display the thesis in any and all forms, including electronic format, via any digital library mechanisms maintained by WWU. I represent and warrant this is my original work, and does not infringe or violate any rights of others.
    [Show full text]
  • Petrology, Geochemistry of Hornblende Gabbro and Associated
    Petrology, geochemistry of hornblende gabbro and associated dolerite dyke of Paharpur, Puruliya, West Bengal: Implication for petrogenetic process and tectonic setting Aditi Mandal, Arijit Ray∗, Mayukhee Debnath and Sankar Prasad Paul Presidency University, Kolkata 700 073, India. ∗Corresponding author. e-mail: [email protected] Paharpur gabbroic intrusive is an arcuate body running east–west paralleling the foliation of Chhota- nagpur Granite Gneiss which acts as country rock. The main gabbroic body is intruded by a number of dolerite dykes running north–south. It is composed of clinopyroxene (Wo48En40Fs12–Wo51En40Fs09,mg no. 72–82), plagioclase (An52–An90), hornblende (magnesian hornblende to ferro-tschermackite), orthopy- roxene (En76–En79) and ilmenite. Hornblende occurs as large poikilitic grain and constitutes around 60% of the rock. Both gabbro and associated dolerite dykes, show relatively primitive character (mg no. 65– 73). Primitive mantle-normalized and MORB-normalized spider diagrams indicate enrichment in Rb, Ba, Th, La, Sr and depletion in Nb, Zr, Y, Ti and Nd. The LILE enrichment and Nb, Ti, Zr, Y depletion suggest arc like geochemical signature for the gabbroic and doleritic rocks of Paharpur. Flat to slightly LREE fractionated pattern and variable degree of REE enrichment is observed. An early stage fraction- ation of clinopyroxene, plagioclase, orthopyroxene, ilmenite and late stage reaction of cumulate pile and evolved melt/hydrous fluid is suggested for magmatic evolution of gabbro. Associated dolerite dykes, which are geochemically similar to the gabbro, have tholeiitic with boninitic character. The mineralogi- cal and chemical compositions of intrusive rocks also have some similarity with mafic rocks of ophiolite complex of subduction zone.
    [Show full text]
  • Micro-Gabbro 0.34 Grams
    61224,6 Micro-Gabbro 0.34 grams Introduction 61224 contained several white and off-white particles as well as 3 peppered black and white rock fragments that appeared to fit together as one (figure 1). Thin section studies showed this to be a shocked lunar gabbro (albiet very fine-grained for a gabbro). Petrography Marvin and Warren (1980) describe 61224,6 and liken it to a eucritic meteorite – accept that the Fe/Mn ratio Figure 1: Group photo for 61224,6. Scale in mm. proves it is lunar in origin. Marvin (1972) originally called it “gabbroic microporphry”. The gabbroic texture and mineral mode is illustrated in figure 2. Grain size is about 1- 2 mm. Marvin and Mosie (1980) wrote 61224,6: “is a coarse- grained, pristine, plutonic gabbro with a cumulate texture in which chains of anhedral hyperthene and augite grains coexist with plagioclase (An83). The plagioclase has been shocked in situ to a leafy, optically-randomized state, and the grain boundaries are occupied by a selvage of pyroxene-plagioclase glass containing minute cyrstallites”. Mineralogical Mode 40 % plagioclase 60% pyroxene Mineralogy Olivine: none Pyroxene: Marvin and Warren (1980) and Takeda et al. (1981) studied the composition and structure of pyroxene (figures 3 and 4). The Fe/Mn ratio of pyroxene seems to indicate that this is a lunar gabbro, not a meteorite (figure 5). Bersch et al. (1983) give precise analyses of high- and low-Ca pyroxene in 61224,6. Plagioclase: Marvin and Warren (1980) reported plagioclase as An79-87. Selvage glass: Marvin and Warren (1980) reported the composition of shock-melted glass in 61224,6.
    [Show full text]
  • A) Diorite B) Gabbro C) Andesite D) Pumice 1. the Photograph Below
    1. The photograph below shows an igneous rock with 4. The photograph below shows the intergrown crystals mineral crystals ranging in size from 2 to 6 of a pegmatite rock. millimeters. The rock is composed of 58% plagioclase feldspar, 26% amphibole, and 16% biotite. What is the name of this rock? A) diorite B) gabbro Which characteristic provides the best evidence that this pegmatite solidified deep underground? C) andesite D) pumice 2. Which igneous rock is dark colored, cooled rapidly on A) low density Earth's surface, and is composed mainly of B) light color plagioclase feldspar, olivine, and pyroxene? C) felsic composition D) very coarse texture A) obsidian B) rhyolite C) gabbro D) scoria 3. Which intrusive igneous rock could be composed of approximately 60% pyroxene, 25% plagioclase feldspar, 10% olivine, and 5% amphibole? A) granite B) rhyolite C) gabbro D) basalt 5. The graph below shows the relationship between the cooling time of magma and the size of the crystals produced. Which graph correctly shows the relative positions of the igneous rocks granite, rhyolite, and pumice? A) B) C) D) 6. The diagrams below show the crystals of four different rocks viewed through the same hand lens. Which crystals most likely formed from molten material that cooled and solidified most rapidly? A) B) C) D) 7. "Which granite sample most likely formed from magma that cooled and solidified at the slowest rate?" A) " " B) " " C) " " D) " " Base your answers to questions 8 and 9 on the diagram below and on your knowledge of Earth science. The diagram represents a portion of the scheme for igneous rock identification.
    [Show full text]
  • Petrography and Engineering Properties of Igneous Rocks
    ENGINEERil~G MONOGRAPHS No. I United States Department of the Interior BUREAU OF RECLAMATION PETROGRAPIIY AND ENGINEERING· PROPER11ES OF IGNEOUS ROCKS hy Rit~bard C. 1\lielenz Denver, Colorado October 1948 95 cents (R.evised September 1961) United States Department of the Interior STEWART L. UDALL, Secretacy Bureau of Reclamation FLOYD E. DOMINY, Commissioner G~T BLOODGOOD, Assistant Commissioner and Chief Engineer Engineering Monograph No. 1 PETROGRAPHY AND ENGINEERING PROPERTIRES ·OF IGNEOUS RO<;:KS by Richard C. Mielenz Revised 1959. by William Y. Holland Head. Petrographic Laboratory Section Chemical Engineering Laboratory Branch Commissioner's Office. Denver Technical Infortnation Branch Denver Federal Center Denver, Colorado ENGINEERING MONOGRAPHS are published in limited editions for the technical staff of the Bureau of Reclamation and interested technical circles in Government and private agencies. Their purpose is to record devel­ opments, innovations, .and progress in the engineering and scientific techniques and practices that are employed in the planning, design, construction, and operation of Rec­ lamation structures and equipment. Copies 'may be obtained from the Bureau of Recla- · mation, Denver Federal Center, Denver, Colon.do, and Washington, D. C. Excavation and concreting of altered zones in rhyolite dike in the spillway foundation. Davis Damsite. Arizona-Nevada. Fl'ontispiece CONTENTS Page Introduction . 1 General Basis of Classification of Rocks . 1 Relation of the Petrographic Character to the Engineering Properties of Rocks . 3 Engineering J?roperties of Igneous Rocks ................................ :. 4 Plutonic Rocks . 4 Hypabyssal Rocks . 6 Volcanic Rocks..... 7 Application of Petrography to Engineering Problems of the Bureau of Reclamation . 8 A Mineralogic and Textural Classification of Igneous Rocks .
    [Show full text]
  • Mafic-Ultramafic Igneous Rocks and Associated Carbonatites of the Gem Park Complex, Custer and Fremont Counties, Colorado
    Mafic-Ultramafic Igneous Rocks And Associated Carbonatites of the Gem Park Complex, Custer and Fremont Counties, Colorado GEOLOGICAL SURVEY PROFESSIONAL PAPER 649 MAFIG-ULTRAMAFIC IGNEOUS ROCKS AND ASSOCIATED CARBONATITES OF THE GEM PARK COMPLEX, CUSTER AND FREMONT COUNTIES, COLORADO S a wa tc h C r i s t o Range S a n g r e d a Range rh p I e x * '*w 5 tp" *,. ' j^.*f\ A- j*s'j»- ' ^«K*£ DEMOB R^TjC MQ^NTAIN. \3 1 /T* :S>- * >." " '"' _J^ ^: '-V*^ Bdj^|*°C,j^B^*' * X* -H'c;"",.,,,,'*^ ,,' -aCr* Gem Park, Colo. View northwestward from Democratic Mounta GEM MOUNTAIN Sawatch Range ark -Cbtrfplex -« "*» +** 4ifa. ving pyroxenite and gabbro of the Gem Park Complex. Mafic-Ultramafic Igneous Rocks And Associated Carbonatites of the Gem Park Complex, Custer and Fremont Counties, Colorado By RAYMOND L. PARKER and WILLIAM N. SHARP GEOLOGICAL SURVEY PROFESSIONAL PAPER 649 The Gem Park Complex its geology and mineralogy, and its niobium distribution UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1970 UNITED STATES DEPARTMENT OF THE INTERIOR WALTER J. HIGKEL, Secretary GEOLOGICAL SURVEY William T. Pecora, Director Library of Congress catalog-card No. 79-608291 For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, B.C. 20402 (Paper cover) CONTENTS Pag-e Abstract __ _-_---__---__-_--..---__-_____-_______-____ Gem Park Complex Continued Introduction __________________________________________ 1 Carbonatite dikes_--______---------_--__-__-___-__- 7 General geology-______________________________________ 1 Attitude, orientation, and distribution of dikes.___ 7 Precambrian rocks.________________________________ 3 Composition of dikes.-______..______..__-_____-__ P Cambrian rocks.__________________________________ 3 Carbonatite in rocks that enclose the complex.
    [Show full text]
  • Hayward Fault Rocks: Porosity, Density and Strength Measurements by C.A
    Hayward Fault Rocks: Porosity, Density and Strength Measurements by C.A. Morrow and D.A. Lockner1 Open-File Report 01–421 2001 This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards or with the North American Stratigraphic Code. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. U.S. DEPARTMENT OF THE INTERIOR U.S. GEOLOGICAL SURVEY 1Menlo Park, Calif. 2 Abstract Porosity, density and strength measurements were conducted on rock samples collected from the Hayward Fault region in Northern California as part of the Hayward Fault Working Group’s efforts to create a working model of the Hayward Fault. The rocks included in this study were both fine and coarse grained gabbros, altered keratophyre, basalt, sandstone, and serpentinite from various rock formations adjacent to the Hayward Fault. Densities ranged from a low of 2.25 gm/cc (altered keratophyre) to 3.05 gm/cc (fine gabbro), with an average of 2.6 gm/cc, typical of many other rocks. Porosities were generally around 1% or less, with the exception of the sandstone (7.6%) and altered keratophyre (13.5%). Failure and frictional sliding tests were conducted on intact rock cylinders at room temperature under effective pressure conditions of up to 192 MPa, simulating depths of burial to 12 km. Axial shortening of the samples progressed at a rate of 0.1 µm/sec (fine samples) or 0.2 µm/sec (porous samples) for 6 mm of displacement.
    [Show full text]
  • The Metamorphism of the Cambrian Basic Volcanic Rocks of Tasmania and Its Relationship to the Geosynclinal Environ­ Ment
    PAPlilllS AND PROCEEDINGS OF THE ROYAL SOCI>lTY OF TASMANIA, VOLUMB 88 The Metamorphism of the Cambrian Basic Volcanic Rocks of Tasmania and its Relationship to the Geosynclinal Environ­ ment By BERYL SCOTT, B.SC., PH.D. (With 4 Plates and 2 Text Ji'igwres) ABSTRACT A spilitic suite comprising picrite basalts, spilites, keratophyres, albite dolerites and associated pyroclastics of Middle and Upper Cambrian age, outcrops on the North-Vi/est and West Coast of Tasmania. The spilites and keratophyres are considered to have been normal basalts which later suffered soda metasomatism as a result of geosynclinal depOl::,ition and orogeny. Hydrothermal alteration of the volcanics has also given rise to a variety of other rock types which includes porphyries, variolite, spherulitic quartz rock and jasper. INTRODlJCTION While the author was resident in Tasmania, a detailed petrographie study was made of the Cambrian volcanle rocks of the State and the results were submitted to the University of Tasmania as a thesis for the degree of Doctor of Philosophy in 1952. Several papers have already been published on this work (Scott, 1952), but after leaving Tasmania it was thought necessary to publish a general summary of the whole study even though the interpretations may not be eonelusive. Mueh confusion exists in the literature dealing with the volcanics of the 'Vest Coast of Tasmania. The igneous rocks have been referred to as porphyroids, keratophyres, quartz and feldspar porphyries, andesites, melaphyres and syenites. The present author believes that the greater part of the volcanics was essentially basic in composition, probably basalts and porphyritic basalts, with or without amygdales, and their corresponding pyroclastics.
    [Show full text]
  • Glossary of Geological Terms
    GLOSSARY OF GEOLOGICAL TERMS These terms relate to prospecting and exploration, to the regional geology of Newfoundland and Labrador, and to some of the geological environments and mineral occurrences preserved in the province. Some common rocks, textures and structural terms are also defined. You may come across some of these terms when reading company assessment files, government reports or papers from journals. Underlined words in definitions are explained elsewhere in the glossary. New material will be added as needed - check back often. - A - A-HORIZON SOIL: the uppermost layer of soil also referred to as topsoil. This is the layer of mineral soil with the most organic matter accumulation and soil life. This layer is not usually selected in soil surveys. ADIT: an opening that is driven horizontally (into the side of a mountain or hill) to access a mineral deposit. AIRBORNE SURVEY: a geophysical survey done from the air by systematically crossing an area or mineral property using aircraft outfitted with a variety of sensitive instruments designed to measure variations in the earth=s magnetic, gravitational, electro-magnetic fields, and/or the radiation (Radiometric Surveys) emitted by rocks at or near the surface. These surveys detect anomalies. AIRBORNE MAGNETIC (or AEROMAG) SURVEYS: regional or local magnetic surveys that measures deviations in the earth=s magnetic field and carried out by flying a magnetometer along flight lines on a pre-determined grid pattern. The lower the aircraft and the closer the flight lines, the more sensitive is the survey and the more detail in the resultant maps. Aeromag maps produced from these surveys are important exploration tools and have played a major role in many major discoveries (e.g., the Olympic Dam deposit in Australia).
    [Show full text]