DOCSLIB.ORG

CONTENTS. United States Geological Survey LETTER of TRANSMITTAL

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
CONTENTS. United States Geological Survey LETTER of TRANSMITTAL Part I.—THE WESTERN PART OF THE DISTRICT DEPARTMENT OF THE INTERIOR By J. MORGAN CLEMENS MONOGRAPHS OF THE CONTENTS. United States Geological Survey LETTER OF TRANSMITTAL......................................................4 VOLUME XXXVI INTRODUCTION, BY CHARLES RICHARD VAN HISE ..................5 OUTLINE OF MONOGRAPH. ...................................................9 PART I.—THE WESTERN PART OF THE CRYSTAL FALLS DISTRICT, BY J. MORGAN CLEMENTS. CHAPTER I.—INTRODUCTION..............................................13 Previous work in the district................................... 14 Mode of work. ........................................................18 Magnetic observations. ..............................................18 CHAPTER II.—GEOGRAPHICAL LIMITS, STRUCTURE AND WASHINGTON STRATIGRAPHY, AND PHYSIOGRAPHY...................................19 GOVERNMENT PRINTING OFFICE Geographical limits. ...............................................19 1899 Structure and stratigraphy. ....................................19 UNITED STATES GEOLOGICAL SURVEY Physiography.........................................................21 CHARLES B. WALCOTT, DIRECTOR Topography................................................................21 Drainage. ...................................................................21 Timber and soil...........................................................24 THE CHAPTER III.—THE ARCHEAN.............................................25 CRYSTAL FALLS IRON-BEARING DISTRICT OF Distribution, exposures, and topography............... 25 Relations to overlying formations. .........................25 MICHIGAN Petrographicai characters......................................26 Biotite-granite (granitite).............................................26 BY Gneissoid biotite-granite, border facies of granite......27 J. MORGAN CLEMENTS and HENRY LLOYD SMYTH Acid dikes in Archean.................................................28 WITH Basic dikes in Archean...............................................28 A CHAPTER ON THE STURGEON RIVER TONGUE Schistose dikes. .....................................................28 BY Massive dikes.........................................................29 WILLIAM SHIRLEY BAYLEY Résumé. ................................................................29 AND CHAPTER IV.—THE LOWER HURONIAN SERIES....................30 AN INTRODUCTION Section 1.—The Randville dolomite.............................30 BY CHARLES RICHARD VAN HISE Distribution, exposures, and topography............... 30 Petrographical characters......................................30 Relations to underlying and overlying formations. 31 Thickness. .............................................................31 Section 2.—The Mansfield slate. .................................31 Distributions, exposures, and topography............. 31 Possible continuation of the Mansfield slate. .............32 Petrographical characters......................................32 Graywacke. ................................................................32 Clay slate and phyllite. ...............................................33 Origin of clay slate and phyllite...............................33 Present composition necessarily different from that WASHINGTON of rock from which derived. ....................................33 GOVERNMENT PRINTING OFFICE Analysis of Mansfield slate.....................................33 1899 Comments on analysis,..........................................34 Comparison of analysis of Mansfield clay slate with analyses of clays....................................................34 Comparison of analysis of Mansfield clay slate with analyses of other clay slates. .................................34 Siderite-slate, chert, ferruginous chert, and iron ores. 34 Monographs of the USGS Vol. XXXVI – Part I – Page 1 of 133 Relations of siderite-slate, ferruginous chert, and ore CHAPTER V.—THE UPPER HURONIAN SERIES. ....................73 bodies to clay slates. ..................................................35 Distribution, exposures, and topography............... 73 Relations of Mansfield slate to adjacent Magnetic lines. ...........................................................74 formations. .............................................................35 Thickness. .............................................................74 Relations to intrusives. ...............................................35 Folding...................................................................74 Relations to volcanics.................................................35 Crystal Falls syncline. ................................................74 Structure of the Mansfield area..............................36 Time of folding of the Upper Huronian. ......................75 Thickness...............................................................36 Relations to other series........................................ 76 Ore deposits...........................................................36 Relations to intrusives. ..........................................76 General description of Mansfield mine deposit...........37 Correlation. ............................................................76 Relations to surrounding beds....................................37 Petrographical characters......................................77 Composition of ore. ....................................................38 Microscopical character of the ores and associated Sedimentary rocks. ....................................................77 Microscopical description of certain of the chert bands.................................................................38 sedimentaries.........................................................78 Origin of the ore deposits. ..........................................38 Igneous rocks.............................................................81 Conditions favorable for ore concentration.................39 Exploration. ................................................................39 Ore deposits. .........................................................81 History of opening of the district.................................81 Section 3.—The Hemlock formation............................ 39 Distribution. ................................................................81 Distribution, exposures, and topography. ..............40 Western half of sec. 34, T. 46 N., R. 33 W.............81 Thickness...............................................................40 Sec. 20, T. 45 N., R. 33 W. ....................................81 Relations to adjacent formations. ..........................40 The Amasa area.....................................................82 Relations to intrusives............................................41 The Crystal Falls area. ...........................................82 Volcanic origin........................................................41 Character of the ore. ..................................................84 Classification..........................................................42 Relations to adjacent rocks. .......................................84 Acid volcanics. .......................................................42 Origin. ........................................................................85 Acid lavas...................................................................42 Size of the ore bodies. ...............................................85 Rhyolite-porphyry. ..................................................43 Methods of mining......................................................85 Texture of the porphyries....................................43 Prospecting. ...............................................................86 Aporhyolite-porphyry. .............................................45 Production of ore from the crystal falls area...............86 Schistose acid lavas...............................................45 CHAPTER VI.—THE INTRUSIVES. ........................................86 Acid pyroclastics.........................................................48 Order of treatment. ................................................87 Basic volcanics. .....................................................48 Age of the intrusives..............................................87 Basic lavas. ................................................................48 Relations of folding and the distribution of the General characters.................................................48 intrusives....................................................................87 Nomenclature. ........................................................49 Metabasalts. ...........................................................50 Section I.—Unrelated intrusives...................................88 Nonporphyritic metabasalt. .................................50 Classification. ........................................................88 Petrographical characters...............................50 Acid intrusives. ......................................................88 Chemical composition.....................................52 Geographical distribution and exposures of granites. 88 Porphyritic metabasalt. .......................................52 Biotite-granite.............................................................88 Petrographical characters...............................52 Micropegmatites.....................................................89 Chemical composition.....................................53 Muscovite-biotite-granite.
Load more

Recommended publications
  • Marmara Region, an In- Tense Vo
    Mineral Res. Expl. Bull., 120, 97-118, 1998 FEATURES OF THE TERTIARY VOLCANISM AROUND SEA OF MARMARA Tuncay ERCAN*; Ahmet TÜRKECAN*; Herve GUILLOU"; Muharrem SATIR*"; Dilek SEVİN*** and Fuat SAROĞLU***** ABSTRACT.- In the region around the sea of Marmara, limited by the boundaries of the 1:500 000 scale Istanbul Quadrangle, the volcanism starting in Upper Cretaceous and intermittently continuing through the end of Upper Miocene has been differentiated into five different stages, namely Upper Cretaceous, Eocene, Oligocene, Lower-Middle Miocene and Upper Miocene, and the volcanic outcrops situated in the region have been dated. Together with the detailed petrographic studies, nine samples from different areas and stages have been dated by K/Ar method, resulting in that the oldest and the youngest lava is of 74.3 ± 1.0 million years old (Upper Cretaceous) and 8.9±0.2 years old (Upper Miocene), respectively. Of these, belonging to the first four stages are mostly calcalkaline (some of the Eocene aged samples are tholeiitic) and are of basalt, basaltic andesite, trachyandesite, andesite, dacite, rhyolite type, whereas that of belonging to the fifth stage are alkaline and of basanite, basalt and trachybasalt types. The pyroclastics of various size and the tuffs of the first four volcanism stages crop out in a wide area. The Upper Cretaceous volcanics have completely formed beneath the sea. On the other hand, some of Eocene volcanics have formed beneath the sea which are seen intercalated with sediments while the others have formed on land. The lavas of Oligocene, Lower-Middle Miocene and Upper Miocene age have formed on land and are observed to be intercalated with lacustrine sediments, in places.
    [Show full text]
  • Basaltic Macadam-Breccias in the Girvan-Ballantrae Complex, Ayrshire
    Downloaded from http://sjg.lyellcollection.org/ at University of Nairobi, Kenya on April 12, 2016 Basaltic macadam-breccias in the Girvan-Ballantrae Complex, Ayrshire A. D. LEWIS1 and T. W. BLOXAM2 department of Geology, University of Nairobi, Nairobi, Kenya ^Department of Geology, University College, Swansea SYNOPSIS Many supposed "volcanic agglomerates and tuffs" in the Girvan-Ballantrae complex of southern Ayrshire are considered to be non-pyroclastic in origin. These macadam breccias are accumulations of lava breccia derived mainly from the autoclastic disintegration of pillow basalts during, or shortly after, extrusion. The breccia-forming process is considered to be mainly a func­ tion of supercooling, glass formation and retention of volatiles, all of which are directly related to external hydrostatic pressure. INTRODUCTION Throughout the Girvan-Ballantrae igneous complex of southern Ayrshire a group of fragmental rocks, generally referred to as "volcanic breccia, agglomerate and tuff" (Peach and Home 1899; Geol. Surv. Scotland, 1" sheet 7), are closely associated with Ordovician basaltic pillow lavas. The most extensive exposures of these particular volcaniclastic rocks occur on Knockdolian and Sallachan Hills [NX 113 848; NX 128 848] about three kilometres north-east of Ballantrae; around Knockormal Hill [NX 132 881]; Lochton Hill [NX 133 875]; Carleton Hill [NX 128 893] and on the coast at Pinbain [NX 137 916] (Fig. 1). The most extensive exposures on Knockdolian Hill have been briefly mentioned by Pringle (1948, p. 11) who notes that these "agglomerates and breccias" are unusual in ". the absence of any fine-grained matrix, the rock being composed of angular fragments of a vesicular lava presenting the appearance of consolidated macadam".
    [Show full text]
  • Implications for the Obduction Process
    Lithos 112 (2009) 163–187 Contents lists available at ScienceDirect Lithos journal homepage: www.elsevier.com/locate/lithos Jurassic back-arc and Cretaceous hot-spot series In the Armenian ophiolites — Implications for the obduction process Yann Rolland a,⁎, Ghazar Galoyan a,b, Delphine Bosch c, Marc Sosson a, Michel Corsini a, Michel Fornari a, Chrystèle Verati a a Géosciences Azur, Université de Nice Sophia Antipolis, CNRS, IRD, Parc Valrose, 06108 Nice cedex 2, France b Institute of Geological Sciences, National Academy of Sciences of Armenia, 24a Baghramian avenue, Yerevan, 375019, Armenia c Géosciences Montpellier, CNRS UMR-5243, Université de Montpellier II, Place E. Bataillon, 34095 Montpellier Cedex 05, France article info abstract Article history: The identification of a large OIB-type volcanic sequence on top of an obducted nappe in the Lesser Caucaus of Received 2 July 2008 Armenia helps us explain the obduction processes in the Caucasus region that are related to dramatic change Accepted 16 February 2009 in the global tectonics of the Tethyan region in the late Lower Cretaceous. The ophiolitic nappe preserves Available online 10 March 2009 three distinct magmatic series, obducted in a single tectonic slice over the South Armenian Block during the Coniacian–Santonian (88–83 Ma), the same time as the Oman ophiolite. Similar geological, petrological, Keywords: geochemical and age features for various Armenian ophiolitic massifs (Sevan, Stepanavan, and Vedi) argue Nd–Sr–Pb isotopes for the presence of a single large obducted ophiolite unit. The ophiolite, shows evidence for a slow-spreading Armenian ophiolite Back-arc oceanic environment in Lower to Middle Jurassic.
    [Show full text]
  • Petrography and Mineralogy of the Quartz and Quartz-Feldspar Sulphide Veins in the Pan-African Syenitic Massif of Guider (North Cameroon)
    Open Journal of Geology, 2020, 10, 235-259 https://www.scirp.org/journal/ojg ISSN Online: 2161-7589 ISSN Print: 2161-7570 Petrography and Mineralogy of the Quartz and Quartz-Feldspar Sulphide Veins in the Pan-African Syenitic Massif of Guider (North Cameroon) Marguerite Boyabe1, Daouda Dawai1*, Rigobert Tchameni2, Periclex Martial Fosso Tchunte2 1Department of Earth Sciences, Faculty of Science, University of Maroua, Maroua, Cameroon 2Department of Earth Sciences, Faculty of Science, University of Ngaoundéré, Ngaoundéré, Cameroon How to cite this paper: Boyabe, M., Da- Abstract wai, D., Tchameni, R. and Tchunte, P.M.F. (2020) Petrography and Mineralogy of the In the syenitic pluton of Guider (593 ± 4 Ma) in the North-West Cameroon Quartz and Quartz-Feldspar Sulphide Veins domain of Central African Fold Belt, mineralized N-S to NE-SW vertical or in the Pan-African Syenitic Massif of Guider sub-vertical quartz and quartz feldspar veins has been recently identified. In (North Cameroon). Open Journal of Geol- ogy, 10, 235-259. this contribution, we present petrography and mineralogy of these veins, in https://doi.org/10.4236/ojg.2020.103013 order to constrain their genesis and emplacement mechanisms based on de- tailed field work, petrographic studies and chemical characterization of min- Received: February 1, 2020 erals by using an electron probe microanalyser (EPMA). Field observations Accepted: March 17, 2020 Published: March 20, 2020 and vein microstructures show that the emplacement of the veins has been controlled by the dextral N-S trending strike-slip shear zones related to the Copyright © 2020 by author(s) and regional D2 deformation phase.
    [Show full text]
  • 2019 Deer Management Unit (Or Area Or Zone) Polygons “Current” (Rev. 2019 Aug. 28)
    MICHIGAN DEPARTMENT OF NATURAL RESOURCES – www.michigan.gov/dnr Wildlife Division FGDC Geospatial Metadata for 2019 Deer Management Unit (or area or zone) polygons “current” (rev. 2019 Aug. 28) By M. Strong, DNR Wildlife Division, Lansing, MI. Description: This file is a shorter summary of longer FGDC geospatial data metadata with important comments, constraints, and qualifiers to accompany geographic information system files (ESRI format shapefile or layer). See the longer more-complete documentation of this data set’s metadata, approximates and follows the FGDC and NBII Metadata Standards at primary required levels, where applicable and appropriate; additional details added if needed. However, these metadata below should include all the mandatory FGDC compliant elements for this data set (a single layer). Some text may be duplicated, but will be improved with next update of these metadata. Data summary/abstract for "deer_management_unit_polygons_current": Description summary: This is the most current white-tailed deer (species Odocoileus virgininus) related management unit, area, or zone polygons; these deer management units (DMUs), special management areas or zones, and other specifically defined polygons are tools DNR staff, particularly DNR Wildlife Division staff, use to manage, represent and depict the extent of deer populations, hunting quotas, open/closed DMUs for applying for drawings or hunting licenses, and other related geospatial activities regarding white-tailed deer. It is your responsibility as a user of these data, to ensure, if you are using these data to determine, plan or do recreational activities, that you personally investigate all regulations or rules related to those activities (acts, place, etc.) before doing those activities or face legal repercussions; if questions, contact DNR offices (http:///www.michigan.gov/dnr ).
    [Show full text]
  • The Petrology and Geochemistry of Archean Volcanics, Western
    THE PETROLOGY AND GEOCHEMISTRY OF ARCHEAN VOLCANICS, WESTERN VERMILION DISTRICT, NORTHEASTERN MTNNESOTA A THESIS SUBMITTED TO THE FACULTY OF THE GRADUATE SCHOOL OF THE UNIVERISTY OF MINNESOTA FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DECEMBER 1977 TABLE OF CONTENTS i Page LIST OF TABLES ••••.•••••••.•••••••••••••••••••••••••• , ••••••• iv LIST 0}' FIGURES •••••••••.••••••••.. ••••••••••••••••••••••••••• v LIST OF APPENDICES ••••••••••••••••••••••••. ••••••••••••••••••• x DEDICATION ••••••••••••••••••••••••••••••••••••••••••••••••••• xi ACKNOWLEDGEMENTS ••••••••••••••••••••••••••••••••••••••••••••• xii ABS TRACT ••••••••••••••••••••••••••••• , ••••••••••••••••••••••• xiii INTRODUCTION ••••••••••••••••••••••••••••••••••• , ••••••••••••• THE VERMILION DISTRICT ••••••••••••••••••••••••••••••••••••••• 3 General Geology ..••••...•......•...••.........•...•...••• 3 Stratigraphy .....••..••......•.•...•....•.........••..•. 5 Structural Geology ..... .. .. •...• • ..........•.........•.. 8 Metamorphism. ......•....•.............•• • ..••..•......• 9 Geochronology ...•.....•...•....•........ ; .•..•.......... 10 Previous Petrologic and Geochemical Studies .•......•.•... 12 NATURE OF THE PRESENT STUDY •••••••••••••••••••••••••••••••••• 16 Specific Objectives ......••••..•..•..........•.........• 16 Methods of Study ..........•.•.....•....••....•.•.....•.. 18 GEOLOGY OF VERNILION DISTRICT VOLCANIC ROCKS ••••••••••••••••• 21 Ely Greenstone ......•••...•.........•..•. , .•...•........ 21 Lower Ely. Greens tone Member ............•.....•.......•.• 23 Pillowed
    [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]
  • Crystal Falls Township Master Plan
    CRYSTAL FALLS TOWNSHIP MASTER PLAN January 2003 Updated 2010 Updated January 2017 Township Officials Master Plan 2017 Crystal Falls Township Iron County, Michigan Planning Commission Curtis Stebic, Chair and Secretary Diane Kut Kenneth West Patrick Olsen Dan Lato Board of Trustees Thomas Lesandrini, Supervisor Nancy Niemi, Clerk Donna Gustafson, Treasurer Joanne Seppala, Trustee Diane Kut, Trustee Zoning Administrator Cary Gustafson With Assistance From: GEI Consultants of Michigan, P.C. 990 Lalley Road Iron River, MI 49935 Table of Contents Chapter 1 Introduction .................................................................................................................... 1 Regional Location and Context .............................................................................. 3 Brief History ........................................................................................................... 4 Chapter II Existing Conditions ....................................................................................................... 6 Demographics ......................................................................................................... 6 Population ............................................................................................................... 6 Housing ................................................................................................................... 8 Income................................................................................................................... 11 Economic
    [Show full text]
  • TABLE of CONTENTS. Lake Huron Drainage in Northern Peninsula
    MICHIGAN GEOLOGICAL AND BIOLOGICAL SURVEY General Geological Features .........................................4 Altitudes and Reliefs. .....................................................6 Publication 7. The Drainage Systems...................................................7 Geological Series 5. CHAPTER II. Glacial Features of the Northern Peninsula ..........................................................................7 SURFACE GEOLOGY OF THE NORTHERN The Moraines and their Significance..............................7 PENINSULA OF MICHIGAN. The Outwash Aprons. ....................................................8 Features Inside the Moraines.........................................9 WITH NOTES ON AGRICULTURAL CONDITIONS AND Drumlins................................................................... 9 WATER POWER Eskers...................................................................... 9 Kames.................................................................... 10 BY FRANK LEVERETT Effect of the Ice Sheet on Rock Surfaces. ...................10 CHAPTER III. Lake History...........................................11 Lake History of the Peninsula ......................................11 Abandoned Shore Lines........................................ 11 Earlier Investigations and Discussions.......................11 Nature of the Present Investigations. .........................12 Lake Ontonagon.........................................................12 Lake Duluth................................................................13 Lake
    [Show full text]
  • On the Variolitic Structure
    On the variolitic structure. By Harald Carstens Abstract. The article presents detailed descriptions of the variolitic structure in selected minor intrusions and lavas. The evidence indicates that the varioles formed by liquid segrega tion rather than by spherulitic crystallization. Introduction. The commonly accepted opinion on the origin of varioles is reflected in modem petrographic textbooks which traditionally state that the variolitic structure of basic igneous rocks is equivalent to the spherulitic structure of silicious lavas and intrusions, which are presumably formed by rapid crystallization in a viscous magma or by devitrification of glass around scattered nuclei. The spheroidal shape of varioles by this hypo thesis is thus accounted for by the crystallization of one mineral from numerous centers with equal velocity in all directions. A number of observations presented below are, however, inconsistent with this view. Petrographic literature of this century conveys the impression that varioles are a structural curiosity. This is probably not so. Studies of minor intrusions and lavas from Norway have shown that in certain rocks this structure exists almost invariably. Certain types of lamprophyres and spilitic pillow lavas are particularly prone to a variolitic development. The variolitic structures of some Norwegian rocks, one monchiquite, a few vogesites, and a glassy augitite lava, are described below. The Nor wegian pillow lavas are altered and not suitable for detailed treatment. 27 Minor intrusions. a) Monchiquite dyke, Hamar The dyke is exposed in a limestone quarry at Furuberget about 3 km north of Hamar. The dyke is obviously connected with the Permian volcanism of the Oslo region and has intruded into a Middle Ordovician limestone.
    [Show full text]
  • 1993 Enrolled Senate Bill 0508
    Act No. 75 Public Acts of 1993 Approved by the Governor July 01, 1993 Filed with the Secretary of State July 01, 1993 STATE OF MICHIGAN 87TH LEGISLATURE REGULAR SESSION OF 1993 Introduced by Senators Gast, Ehlers, Schwarz, Arthurhultz, Cisky, Geake, Emmons, Faust, Berryman, McManus, Vaughn, Conroy, DeGrow, Koivisto, Pollack, Dingell, Hart, Pridnia, Dunaskiss and Wartner ENROLLED SENATE BILL No. 508 AN ACT to make appropriations to the department of natural resources to provide for the acquisition of land; to provide for the development of public recreation facilities; to provide for the powers and duties of certain state agencies and officials; and to provide for the expenditure of appropriations. The People of the State of Michigan enact: Sec. 1. There is appropriated for the department of natural resources to supplement former appropriations for the fiscal year ending September 30, 1993, the sum of $15,819,250.00 for land acquisition and grants and $4,455,850.00 for public recreation facility development and grants as provided in section 35 of article IX of the state constitution of 1963 and the Michigan natural resources trust fund act, Act No. 101 of the Public Acts of 1985, being sections 318.501 to 318.516 of the Michigan Compiled Laws, from the following funds: For Fiscal Year Ending Sept. 30, 1993 GROSS APPROPRIATIONS....................................................................................................................... $ 20,275,100 Appropriated from: Special revenue funds: Michigan natural resources trust fund......................................................................................................
    [Show full text]
  • Geochemistry of Archaean Volcanic Rocks from Iron Ore Supergroup, Singhbhum, Eastern India
    Geochemistry of Archaean volcanic rocks from Iron Ore Supergroup, Singhbhum, eastern India S SENGUPTA*, S K ACHARYYA*, J B DESMETH** * Geological Survey of India, 27, Jawaharlal Nehru Road, Calcutta 700016 ** ITC, Kanaalweg 3 2628EB, Delft, The Netherlands Mafic-ultramafic rocks of Archaean age constitute a significant component of the Eastern Indian Craton. These occur in two different modes. In the eastern belt these occur as a long, linear enclave within the Singhbhum granite and the primary banding in them is subvertical. In the more extensive western belt along the periphery of the Singhbhum granite, the disposition of the primary banding is subhorizontal. The major rock type in both the belts is meta-basalt with minor peridotitic komatiite and basaltic komatiite occurring in the eastern belt. Rare ultramafic rocks with cumulate textures are present in both the belts. The larger volume of the basaltic rocks preclude the possibility of their being derived by fractional crystallization of the high-MgO components. On the basis of trace element and REE characters the rocks may be classified into three groups. One of the groups shows a tholeiitic trend and include samples mostly from the eastern belt while the second consisting mostly of samples from the western belt shows a calc-alkaline trend. The third group includes samples having elemental ratios intermediate between these two groups. Zr/Nb ratios for the tholeiitic and calc-alkaline samples are different suggesting their sources to be different. The tholeiitic samples have been generated from a source having chondritic REE characters, while the calc-alkaline samples have been generated from a source with LREE enriched character.
    [Show full text]