Naming Metamorphic Rocks
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Origin, Texture, and Classification of Metamorphic Rocks - Teklewold Ayalew
GEOLOGY – Vol. II - Origin, Texture, and Classification of Metamorphic Rocks - Teklewold Ayalew ORIGIN, TEXTURE, AND CLASSIFICATION OF METAMORPHIC ROCKS Teklewold Ayalew Addis Ababa University, Ethiopia Keywords: aluminosilicates, assemblage, fabric, foliation, gneissose banding, index mineral, isograd, lineation, lithosphere, metamorphic facies, metasomatism, orogenic belt, schistosity Contents 1. Introduction 2. Occurrence 2.1. Orogenic Metamorphism 2.2. Contact Metamorphism 2.3. Ocean Floor Metamorphism 3. Classification 4. Minerals of Metamorphic Rocks 5. Metamorphic Facies 5.1. Facies of Very Low Grade 5.2. Greenschist Facies 5.3. Amphibolite Facies 5.4. Granulite Facies 5.5. Hornblende Hornfels Facies 5.6. Pyroxene Hornfels Facies 5.7. Blueschist Facies 5.8. Eclogite Facies 6. Tectonic Setting of Metamorphic Facies 7. Textures 7.1. Layering, Banding, and Fabric Development 8. Kinetics 8.1. Diffusion 8.2. Nucleation 8.3. Crystal Growth AcknowledgmentUNESCO – EOLSS Glossary Bibliography Biographical SketchSAMPLE CHAPTERS Summary Metamorphic rocks are igneous, sedimentary, or other metamorphic rocks whose texture and composition has been changed by metamorphism. Metamorphism occurs as a response to changes in the physical or chemical environment of any pre-existing rock, such as variations in pressure or temperature, strain, or the infiltration of fluids. It involves recrystallization of existing minerals into new grains and/or the appearance of new mineral phases and breakdown of others. Metamorphic processes take place ©Encyclopedia of Life Support Systems (EOLSS) GEOLOGY – Vol. II - Origin, Texture, and Classification of Metamorphic Rocks - Teklewold Ayalew essentially in the solid state. The rock mass does not normally disaggregate and lose coherence entirely; however small amounts of fluids are frequently present and may play an important catalytic role. -
Actually Consists of 2 Cleavages
Types of foliations • Crenulation Cleavage- – Actually consists of 2 cleavages – The first may be a slaty cleavage or schistosity that becomes microfolded – Fold axial planes typically form at high angle to the σ1 of the second compressional phase 1 Progressive development (a → c) of a crenulation cleavage for both asymmetric (top) and symmetric (bottom) situations. From Spry (1969) Metamorphic Textures. Pergamon. Oxford. 2 Figure 23.24a. Symmetrical crenulation cleavages in amphibole-quartz-rich schist. Note concentration of quartz in hinge areas. From Borradaile et al. (1982) Atlas of Deformational and Metamorphic Rock Fabrics. Springer-Verlag. 3 Figure 23.24b. Asymmetric crenulation cleavages in mica-quartz-rich schist. Note horizontal compositional layering (relict bedding) and preferential dissolution of quartz from one limb of the folds. From Borradaile et al. (1982) Atlas of Deformational and Metamorphic Rock Fabrics. Springer-Verlag. 4 Figure 23.25. Stages in the development of crenulation cleavage as a function of temperature and intensity of the second deformation. From Passchier and Trouw (1996) Microtectonics. Springer-Verlag. Development of S2 micas depends upon T and the intensity of the second deformation 5 Types of lineations a. Preferred orientation of elongated mineral aggregates b. Preferred orientation of elongate minerals c. Lineation defined by platy minerals d. Fold axes (especially of crenulations) e. Intersecting planar elements. Figure 23.26. Types of fabric elements that define a lineation. From Turner and Weiss (1963) Structural 6 Analysis of Metamorphic Tectonites. McGraw Hill. Analysis of Deformed Rocks • If two or more geometric elements are present, we can add a numeric subscript to denote the chronological sequence in which they were developed and superimposed- • Deformational events: D1 D2 D3 … • Metamorphic events: M1 M2 M3 … • Foliations: So S1 S2 S3 … • Lineations: Lo L1 L2 L3 … • Plot on a metamorphism-deformation-time plot showing the crystallization of each mineral 7 Deformation vs. -
Rocks and Geology: General Information
Rocks and Geology: General Information Rocks are the foundation of the earth. Rock provides the firmament beneath our oceans and seas and it covers 28% of the earth's surface that we all call home. When we travel any distance in any given direction, it is impossible not to see the tremendous variety in color, texture, and shape of the rocks around us. Rocks are composed of one or more minerals. Limestone, for example, is composed primarily of the mineral calcite. Granite can be made up of the minerals quartz, orthoclase and plagioclase feldspars, hornblende, and biotite mica. Rocks are classified by their mineral composition as well as the environment in which they were formed. There are three major classifications of rocks: igneous, sedimentary and metamorphic. A question: Which kind of rock came first? Think about it....... The following sections describe the conditions and processes that create the landscape we admire and live on here on "terra firma." IGNEOUS ROCKS The millions of tons of molten rock that poured out of the volcano Paracutin in Mexico, and from the eruption of Mount St. Helens in Washington State illustrate one of the methods of igneous rock formation. Igneous (from fire) rocks are formed when bodies of hot liquid rock called magma located beneath the earth's crust, find their way upward through the crust by way of fissures or faults. If the magma reaches the earth's surface, it forms extrusive igneous rocks or volcanic rocks. If the magma cools before it reaches the surface, it forms bodies of rock called intrusive igneous rocks or plutonic rocks. -
Megaliths and Geology: a Journey Through Monuments, Landscapes and Peoples
Megaliths and Geology Megálitos e Geologia MEGA-TALKS 2 19-20 November 2015 (Redondo, Portugal) Edited by Rui Boaventura, Rui Mataloto and André Pereira Access Archaeology aeopr ch es r s A A y c g c e o l s o s e A a r c Ah Archaeopress Publishing Ltd Summertown Pavilion 18-24 Middle Way Summertown Oxford OX2 7LG www.archaeopress.com ISBN 978-1-78969-641-7 ISBN 978-1-78969-642-4 (e-Pdf) © the individual authors and Archaeopress 2020 Financial support for the meeting Mega-Talks 2 has been provided by the project Moving megaliths in the Neolithic (PTDC/EPH-ARQ/3971/2012), funded by FCT (Fundação para a Ciência e a Tecnologia, Portugal) and the Municipality of Redondo (Portugal). All rights reserved. No part of this book may be reproduced, stored in retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying or otherwise, without the prior written permission of the copyright owners. This book is available direct from Archaeopress or from our website www.archaeopress.com Contents Introduction: Megaliths and Geology: a journey through monuments, landscapes and peoples ........................... iii Moving megaliths in the Neolithic - a multi analytical case study of dolmens in Freixo-Redondo (Alentejo, Portugal). Rui Boaventura, Patrícia Moita, Jorge Pedro, Rui Mataloto, Luis Almeida, Pedro Nogueira, Jaime Máximo, André Pereira, José Francisco Santos & Sara Ribeiro ............................................................... 1 Funerary megalithism in the south of Beira Interior: architectures, spoils and cultural sequences. João Luís Cardoso .................................................................................................................................................................. 25 A look at Proença-a-Nova’s Megalithism (Beira Baixa Intermunicipal Community, UNESCO Global Geopark Naturtejo, Portugal). -
Towards a Unified Nomenclature in Metamorphic Petrology
8. Amphibolite and Granulite Recommendations by the IUGS Subcommission on the Systematics of Metamorphic Rocks: Web version 01.02.07 1José Coutinho, 2Hans Kräutner, 3Francesco Sassi, 4Rolf Schmid and 5Sisir Sen. 1 J. Coutinho, University of São Paulo, São Paulo, Brazil 2 L M University, Munich, Germany 3 F. Sassi, Department of Mineralogy and Petrography, University of Padova, Italy 4 R. Schmid, ETH-Centre, Zürich, Switzerland 5 S. Sen, Indian Institute of Technology, Kharagpur, India Introduction This paper summarises the results of the discussions by the SCMR, and the response to circulars distributed by the SCMR, which demonstrated the highly variable usage of the terms granulite and amphibolite. It presents those definitions which currently seem to be the most appropriate ones. Some notes are included in order to explain the reasoning behind the suggested definitions. In considering the definitions it is important to remember that some of them are a compromise of highly different, even conflicting, opinions and traditions. The names amphibolite and granulite have been used in geological literature for nearly 200 years: amphibolite since Brongniart (1813), granulite since Weiss (1803). Although Brongniart described amphibolite as a rock composed of amphibole and plagioclase, in those early days the meaning of the term was variable. Only later (e.g. Rosenbusch, 1898) was it fixed as metamorphic rock consisting of hornblende and plagioclase, and of medium to high metamorphic grade. In contrast, the use of the name granulite was highly variable, a position which was further complicated by the introduction of the facies principle (Eskola, 1920, 1952) when the name granulite was proposed for all rocks of the granulite facies. -
A Systematic Nomenclature for Metamorphic Rocks
A systematic nomenclature for metamorphic rocks: 1. HOW TO NAME A METAMORPHIC ROCK Recommendations by the IUGS Subcommission on the Systematics of Metamorphic Rocks: Web version 1/4/04. Rolf Schmid1, Douglas Fettes2, Ben Harte3, Eleutheria Davis4, Jacqueline Desmons5, Hans- Joachim Meyer-Marsilius† and Jaakko Siivola6 1 Institut für Mineralogie und Petrographie, ETH-Centre, CH-8092, Zürich, Switzerland, [email protected] 2 British Geological Survey, Murchison House, West Mains Road, Edinburgh, United Kingdom, [email protected] 3 Grant Institute of Geology, Edinburgh, United Kingdom, [email protected] 4 Patission 339A, 11144 Athens, Greece 5 3, rue de Houdemont 54500, Vandoeuvre-lès-Nancy, France, [email protected] 6 Tasakalliontie 12c, 02760 Espoo, Finland ABSTRACT The usage of some common terms in metamorphic petrology has developed differently in different countries and a range of specialised rock names have been applied locally. The Subcommission on the Systematics of Metamorphic Rocks (SCMR) aims to provide systematic schemes for terminology and rock definitions that are widely acceptable and suitable for international use. This first paper explains the basic classification scheme for common metamorphic rocks proposed by the SCMR, and lays out the general principles which were used by the SCMR when defining terms for metamorphic rocks, their features, conditions of formation and processes. Subsequent papers discuss and present more detailed terminology for particular metamorphic rock groups and processes. The SCMR recognises the very wide usage of some rock names (for example, amphibolite, marble, hornfels) and the existence of many name sets related to specific types of metamorphism (for example, high P/T rocks, migmatites, impactites). -
Metamorphic Rocks
Metamorphic Rocks Geology 200 Geology for Environmental Scientists Regionally metamorphosed rocks shot through with migmatite dikes. Black Canyon of the Gunnison, Colorado Metamorphic rocks from Greenland, 3.8 Ga (billion years old) Major Concepts • Metamorphic rocks can be formed from any rock type: igneous, sedimentary, or existing metamorphic rocks. • Involves recrystallization in the solid state, often with little change in overall chemical composition. • Driving forces are changes in temperature, pressure, and pore fluids. • New minerals and new textures are formed. Major Concepts • During metamorphism platy minerals grow in the direction of least stress producing foliation. • Rocks with only one, non-platy, mineral produce nonfoliated rocks such as quartzite or marble. • Two types of metamorphism: contact and regional. Metamorphism of a Granite to a Gneiss Asbestos, a metamorphic amphibole mineral. The fibrous crystals grow parallel to least stress. Two major types of metamorphism -- contact and regional Major Concepts • Foliated rocks - slate, phyllite, schist, gneiss, mylonite • Non-foliated rocks - quartzite, marble, hornfels, greenstone, granulite • Mineral zones are used to recognize metamorphic facies produced by systematic pressure and temperature changes. Origin of Metamorphic Rocks • Below 200oC rocks remain unchanged. • As temperature rises, crystal lattices are broken down and reformed with different combinations of atoms. New minerals are formed. • The mineral composition of a rock provides a key to the temperature of formation (Fig. 6.5) Fig. 6.5. Different minerals of the same composition, Al2SiO5, are stable at different temperatures and pressures. Where does the heat come from? • Hot magma ranges from 700-12000C. Causes contact metamorphism. • Deep burial - temperature increases 15-300C for every kilometer of depth in the crust. -
Metamorphism and the Origin of Granitic Rocks Northgate District Colorado
Metamorphism and the Origin of Granitic Rocks Northgate District Colorado GEOLOGICAL SURVEY PROFESSIONAL PAPER 274-M Metamorphism and the Origin of Granitic Rocks Northgate District Colorado By T. A. STEVEN SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY GEOLOGICAL SURVEY PROFESSIONAL PAPER 274-M A discussion of the progressive metamorphism, granitixation, and local rheomorphism of a layered sequence of rocks, and of the later emplacement and deuteric alteration of an unrelated granitic stock UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1957 UNITED STATES DEPARTMENT OF THE INTERIOR FRED A. SEATON, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director For sale by the Superintendent of Documents, U. S. Government Printing Office Washington 25, D. C. CONTENTS Page Page Abstract_________________________________ 335 Pre-Cambrian geology—Continued Introduction-_______________________________________ 335 Dacite porphyry—____ ——— __ —— _____________ 364 Acknowledgments__ ___--_____-____-_____-______-_ 336 Intrusive quartz monzonite_-____--_-__-_--_-_-_. 365 Geologic setting._______ — _________________________ 336 Petrography ________—— —— _______________ 365 Pre-Cambrian geology—___________________________ 337 Main body of the stock____________— 366 Hornblende gneiss___-_________-_-_____-________ 338 Marginal dikes_________-____-__-__——— 366 Quartz monzonite gneiss_________________________ 342 Satellitic dikes___-___.__________ 367 Biotite-garnet gneiss___________________________ 345 Wall-rock alteration_________ _ __——_ 368 Pegmatite_________________________________ -
Download the Scanned
THn AMERIceN M INERALoGIST JOURNAL OF THE MINERALOGICAL SOCIETY OF AMERICA Vol.22 DECEMBER, 1937 No. 12,Part 1 DEVELOPMENT OF PLAGIOCLASE PORPHYROBLASTSI G. E. Gootsrooo, U niver si.tyoJ W ashington, S eattle, W ashington. Assrnacr Porphyroblastic textures are common to hornfels in the Cornucopia area oJ the Wal- lowa Mountains of northeastern Oregon. Recent petrographic studies indicate that they are also common to some of the rocks of the Cascades of Washington. Plagioclase porphyro- blasts range from initial allotrioblastic forms to fully developed idioblastic crystals. They exhibit many characteristic features which may include poikioblastic structures, helizitic inclusions and complex aggregates. The arrangement within the crystal of inclusions of either identifiable minerals or turbid material, is apparently directly related to the stage of development of the porphyroblast. This included matter differs chiefly in its arrange- ment from the products of endogenetic or subsequent alteration. Recognition of these metamorphic textures and structures is one of the points essential to the interpretation of recrystallization-replacement as applied to igneous-appearing rocks which are believed to have been formed in situ by processesof additive hydrothermal metamorphism. In a previous paper the writer outlined the development of qaartz porphyroblasts in a siliceoushornfels.2 The quartz porphyroblasts in the siliceoushornfels were too small (0.5 mm.) to be conspicuousin the hand specimens,but were readily seenunder crossednicols, although in plane light they merged almost completely with the groundmass of the horn- fels, and contained the sameabundance of small inclusions as the ground- mass. The siliceoushornfels is not the most abundant; biotitic and horn- blendic varieties are far more common. -
Nucleation and Growth History in the Garnet Zone
Spear and Daniel Geological Materials Research v.1, n.1, p.1 Three-dimensional imaging of garnet porphyroblast sizes and chemical zoning: Nucleation and growth history in the garnet zone Frank S. Spear and Christopher G. Daniel Department of Earth and Environmental Sciences, Rensselaer Polytechnic Institute, Troy, New York 12180 <[email protected]> (Received July 1, 1998; Published October 30, 1998) Abstract The three-dimensional (3-D) growth history of two garnet zone samples (Grt + Chl + Bt + Ms + Pl + Qtz + Ilm) from southwestern Maine was examined by serial sectioning and 3-D reconstructions of compositional zoning from backscatter images and X-ray maps. Mn, Fe, Mg, and Ca zoning is broadly concentric. The concentration of Mn in garnet cores generally correlates with size (d = 50 to 750 microns), indicating progressive nucleation. In detail, all elements show irregular, patchy zoning in the cores. Assuming constancy of Mn on the rims of all garnet crystals in a rock volume plus no subsequent diffusional modification, Mn concentration can be used as a Òtime lineÓ for garnet growth. Examination of the evolution of individual garnet crystals reveals that multiple nuclei formed simultaneously in the core regions and that nuclei expanded by growth in amoeba-shape forms along preexisting mineral grain boundaries (primarily quartz and plagioclase), dissolving the interior grains until the grains were either gone or encapsulated, at which time dissolution ceased. Amoeba-shaped garnet crystals coalesced as they grew and, simultaneously, new nuclei appeared in the nearby matrix. The net result was a single garnet porphyroblast that formed by the growth and coalescence of multiple nuclei. -
Metamorphic Rocks -- Rocks That Change by Cindy Grigg
Metamorphic Rocks -- Rocks that Change By Cindy Grigg 1 Rocks can be put into three main groups. They are grouped by how the rocks formed. Metamorphic (met-uh-MOR-fic) rocks are changed by the heat and pressure inside Earth. "Metamorphic" comes from a Greek word that means "change of form." Metamorphic rocks can be formed from other metamorphic rocks. They can form from sedimentary and igneous rocks, too. 2 The temperature deep inside the Earth is much hotter than temperatures near or on the surface. The weight of tons of land and rocks on top presses down on the rocks underneath. This pressure, along with heat, causes the rocks inside the Earth to go through a physical or chemical change. Movement of Earth's plates causes pressure on rocky material under the surface, resulting in folding. Water can dissolve and redeposit minerals. This can also cause a change in rocks. Minerals react with each other at high heat. Atoms rearrange, and new minerals are created from old ones. Grains in rocks are pressed and made more compact. Rocks morph into other kinds of rocks. 3 Some metamorphic rocks are slate, schist, gneiss, marble, and quartzite. Sandstone is a sedimentary rock. It is made of grains of sand pressed together. Sandstone is fairly soft. It crumbles easily. When sandstone changes into the metamorphic rock quartzite, is becomes one of the hardest rocks. 4 The sedimentary rock shale changes into slate. The mineral grains in shale change directions because of the heat and pressure. Slate, a metamorphic rock, can be changed by continued heat and pressure into a rock called schist. -
Petrologic Significance of Fe-Rich Staurolite in Pelitic Schists of the Silgará Formation, Santander Massif
EARTH SCIENCES RESEARCH JOURNAL Earth Sci. Res. J. Vol. 20, No. 1 (March, 2016): C1 - C7 PETROLOGY Petrologic significance of Fe-rich staurolite in pelitic schists of the Silgará Formation, Santander Massif Carlos Alberto Ríos R.1*, Oscar Mauricio Castellanos A.2 1*. Escuela de Geología, Universidad Industrial de Santander, Bucaramanga, Colombia, e-mail: [email protected] 2. Programa de Geología, Universidad de Pamplona, Colombia ABSTRACT Keywords: Staurolite, pelitic schists, Silgará Medium grade metapelites of the Silgará Formation at the Santander Massif (Colombian Andes) have been Formation, metamorphism, Santander Massif. affected by a medium-pressure/high-temperature Barrovian type of metamorphism, developing a sequence of metamorphic zones (biotite, garnet, staurolite and sillimanite). These rocks record a complex tectono- metamorphic evolution and reaction history. Metapelitic rocks from the staurolite zone are typically foliated, medium- to coarse-grained, pelitic to semipelitic schists that contain the mineral assemblage biotite + garnet + staurolite ± kyanite; all contain muscovite + quartz + plagioclase with minor K-feldspar, tourmaline, apatite, zircon, epidote, calcite, and Fe–Ti oxides. Field and microscopic evidences reveal that Fe-rich staurolite in pelitic schists is involved in several chemical reactions, which explains its formation and transformation to other minerals, which are very important to elucidate the reaction history of the Silgará Formation metapelites. Significado Petrológico de Estaurolita Rica en Fe en Esquistos Pelíticos de la Formación Silgará, Macizo de Santander RESUMEN Palabras clave: Estaurolita, esquistos pelíticos, Medium grade metapelites of the Silgará Formation en el Macizo de Santander (Andes Colombianos) han sido Formación Silgará, metamorfismo, Macizo de afectadas por un metamorfismo de tipo Barroviense, el cual se ha producido en condiciones de media presión y Santander.