DOCSLIB.ORG

The Diversity of Magmatism at a Convergent Plate

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
The Diversity of Magmatism at a Convergent Plate 1 Flow of partially molten crust controlling construction, growth and collapse of the Variscan orogenic belt: 2 the geologic record of the French Massif Central 3 4 Vanderhaeghe Olivier1, Laurent Oscar1,2, Gardien Véronique3, Moyen Jean-François4, Gébelin Aude5, Chelle- 5 Michou Cyril2, Couzinié Simon4,6, Villaros Arnaud7,8, Bellanger Mathieu9. 6 1. GET, UPS, CNRS, IRD, 14 avenue E. Belin, F-31400 Toulouse, France 7 2. ETH Zürich, Institute for Geochemistry and Petrology, Clausiusstrasse 25, CH-8038 Zürich, Switzerland 8 3. Université Lyon 1, ENS de Lyon, CNRS, UMR 5276 LGL-TPE, F-69622, Villeurbanne, France 9 4. Université de Lyon, Laboratoire Magmas et Volcans, UJM-UCA-CNRS-IRD, 23 rue Dr. Paul Michelon, 10 42023 Saint Etienne 11 5. School of Geography, Earth and Environmental Sciences, Plymouth University, Plymouth,UK 12 6. CRPG, Université de Lorraine, CNRS, UMR7358, 15 rue Notre Dame des Pauvres, F-54501 13 Vandoeuvre-lès-Nancy, France 14 7. Univ d’Orléans, ISTO, UMR 7327, 45071, Orléans, France ; CNRS, ISTO, UMR 7327, 45071 Orléans, 15 France ; BRGM, ISTO, UMR 7327, BP 36009, 45060 Orléans, France 16 8. University of Stellenbosch, Department of Earth Sciences, 7602 Matieland, South Africa 17 9. TLS Geothermics, 91 chemin de Gabardie 31200 Toulouse. 18 19 [email protected] 20 +33(0)5 61 33 47 34 21 22 Key words: 23 Variscan belt; French Massif Central; Flow of partially molten crust; Orogenic magmatism; Orogenic plateau; 24 Gravitational collapse. 25 26 Abstract 27 We present here a tectonic-geodynamic model for the generation and flow of partially molten rocks and for 28 magmatism during the Variscan orogenic evolution from the Silurian to the late Carboniferous based on a synthesis 29 of geological data from the French Massif Central. Eclogite facies metamorphism of mafic and ultramafic rocks 30 records the subduction of the Gondwana hyperextended margin. Part of these eclogites are forming boudins- 31 enclaves in felsic HP granulite facies migmatites partly retrogressed into amphibolite facies attesting for 1 32 continental subduction followed by thermal relaxation and decompression. We propose that HP partial melting 33 has triggered mechanical decoupling of the partially molten continental rocks from the subducting slab. This would 34 have allowed buoyancy-driven exhumation and entrainment of pieces of oceanic lithosphere and subcontinental 35 mantle. Geochronological data of the eclogite-bearing HP migmatites points to diachronous emplacement of 36 distinct nappes from middle to late Devonian. These nappes were thrusted onto metapelites and orthogneisses 37 affected by MP/MT greenschist to amphibolite facies metamorphism reaching partial melting attributed to the late 38 Devonian to early Carboniferous thickening of the crust. The emplacement of laccoliths rooted into strike-slip 39 transcurrent shear zones capped by low-angle detachments from c. 345 to c. 310 Ma is concomitant with the 40 southward propagation of the Variscan deformation front marked by deposition of clastic sediments in foreland 41 basins. We attribute these features to horizontal growth of the Variscan belt and formation of an orogenic plateau 42 by gravity-driven lateral flow of the partially molten orogenic root. The diversity of the magmatic rocks points to 43 various crustal sources with modest, but systematic mantle-derived input. In the eastern French Massif Central, 44 the southward decrease in age of the mantle- and crustal-derived plutonic rocks from c. 345 Ma to c. 310 Ma 45 suggests southward retreat of a northward subducting slab toward the Paleotethys free boundary. Late 46 Carboniferous destruction of the Variscan belt is dominantly achieved by gravitational collapse accommodated by 47 the activation of low-angle detachments and the exhumation-crystallization of the partially molten orogenic root 48 forming crustal-scale LP migmatite domes from c. 305 Ma to c. 295 Ma, coeval with orogen-parallel flow in the 49 external zone. Laccoliths emplaced along low-angle detachments and intrusive dykes with sharp contacts 50 correspond to the segregation of the last melt fraction leaving behind a thick accumulation of refractory LP felsic 51 and mafic granulites in the lower crust. 52 This model points to the primordial role of partial melting and magmatism in the tectonic-geodynamic evolution 53 of the Variscan orogenic belt. In particular, partial melting and magma transfer (i) triggers mechanical decoupling 54 of subducted units from the downgoing slab and their syn-orogenic exhumation; (ii) the development of an 55 orogenic plateau by lateral flow of the low-viscosity partially molten crust; and, (iii) the formation of metamorphic 56 core complexes and domes that accommodate post-orogenic exhumation during gravitational collapse. All these 57 processes contribute to differentiation and stabilisation of the orogenic crust. 58 Index 59 1. Introduction ....................................................................................................................................................................... 4 60 2. Geology of the French Massif Central: a window through the Variscan belt .................................................................... 6 61 2.1. The Variscan belt: continental blocs, oceanic sutures, allochthonous terranes and paleogeographic reconstructions ... 6 62 2.2. The main lithologic-tectonic units of the French Massif Central ....................................................................................... 8 63 Metamorphic nappes ....................................................................................................................................................... 9 64 Protoliths age for the high-grade rocks, basement of the Devonian to Carboniferous volcanic and sedimentary units 11 2 65 Migmatites and granulites .............................................................................................................................................. 12 66 Late Devonian to Carboniferous plutonic rocks ............................................................................................................. 13 67 Carboniferous volcanic and sedimentary deposits ........................................................................................................ 15 68 2.3. Architecture and P-T-t record of nappes of the western and eastern French Massif Central ......................................... 16 69 Western French Massif Central (W-FMC)...................................................................................................................... 17 70 Eastern French Massif Central (E-FMC) ........................................................................................................................ 21 71 3. Previous tectonic-geodynamic reconstructions and debated issues .............................................................................. 27 72 Monocyclic doubly-vergent orogen model ..................................................................................................................... 27 73 Polycyclic orogenic model.............................................................................................................................................. 27 74 Collision versus syn-orogenic extension during the Carboniferous ............................................................................... 28 75 Impact of partial melting and magmatism on Variscan tectonics? ................................................................................. 29 76 4. A new model for the geodynamic-tectonic evolution of the Variscan belt of Western Europe ........................................ 31 77 4.1. Pre-Variscan configuration: the North Gondwana hyper-extended margin .................................................................... 31 78 4.2. Late Silurian to Devonian subduction and HP partial melting of terranes issued from the North Gondwana margin ..... 32 79 4.3. Middle Devonian to early Carboniferous syn-orogenic exhumation of the partially molten subducted crustal units with 80 mantle enclaves ....................................................................................................................................................................... 34 81 4.4. Late Devonian exhumation of nappes in between retreating slabs ................................................................................ 37 82 4.5. Carboniferous (c. 345-310 Ma) building of an orogenic plateau by lateral flow of the partially molten orogenic root ..... 39 83 4.6. Late Carboniferous to Permian (c. 305-295 Ma) gravitational collapse and exhumation of the partially molten root of the 84 Variscan orogenic belt .............................................................................................................................................................. 41 85 4.7. Pertinence of the proposed geodynamic-tectonic model compared to physical modeling of the dynamics of orogenic 86 belts 46 87 5. Conclusion ...................................................................................................................................................................... 47 88 6. References: .................................................................................................................................................................... 56 89 90 91 92 3 93 1. Introduction 94 95 Migmatites and granites are the main constituents of the continental crust and their petrogenesis and emplacement 96
Load more

Recommended publications
  • The Origin of Formation of the Amphibolite- Granulite Transition
    The Origin of Formation of the Amphibolite- Granulite Transition Facies by Gregory o. Carpenter Advisor: Dr. M. Barton May 28, 1987 Table of Contents Page ABSTRACT . 1 QUESTION OF THE TRANSITION FACIES ORIGIN • . 2 DEFINING THE FACIES INVOLVED • • • • • • • • • • 3 Amphibolite Facies • • • • • • • • • • 3 Granulite Facies • • • • • • • • • • • 5 Amphibolite-Granulite Transition Facies 6 CONDITIONS OF FORMATION FOR THE FACIES INVOLVED • • • • • • • • • • • • • • • • • 8 Amphibolite Facies • • • • • • • • 9 Granulite Facies • • • • • • • • • •• 11 Amphibolite-Granulite Transition Facies •• 13 ACTIVITIES OF C02 AND H20 . • • • • • • 1 7 HYPOTHESES OF FORMATION • • • • • • • • •• 19 Deep Crust Model • • • • • • • • • 20 Orogeny Model • • • • • • • • • • • • • 20 The Earth • • • • • • • • • • • • 20 Plate Tectonics ••••••••••• 21 Orogenic Events ••••••••• 22 Continent-Continent Collision •••• 22 Continent-Ocean Collision • • • • 24 CONCLUSION • . • 24 BIBLIOGRAPHY • • . • • • • 26 List of Illustrations Figure 1. Precambrian shields, platform sediments and Phanerozoic fold mountain belts 2. Metamorphic facies placement 3. Temperature and pressure conditions for metamorphic facies 4. Temperature and pressure conditions for metamorphic facies 5. Transformation processes with depth 6. Temperature versus depth of a descending continental plate 7. Cross-section of the earth 8. Cross-section of the earth 9. Collision zones 10. Convection currents Table 1. Metamorphic facies ABSTRACT The origin of formation of the amphibolite­ granulite transition
    [Show full text]
  • Oregon Geologic Digital Compilation Rules for Lithology Merge Information Entry
    State of Oregon Department of Geology and Mineral Industries Vicki S. McConnell, State Geologist OREGON GEOLOGIC DIGITAL COMPILATION RULES FOR LITHOLOGY MERGE INFORMATION ENTRY G E O L O G Y F A N O D T N M I E N M E T R R A A L P I E N D D U N S O T G R E I R E S O 1937 2006 Revisions: Feburary 2, 2005 January 1, 2006 NOTICE The Oregon Department of Geology and Mineral Industries is publishing this paper because the infor- mation furthers the mission of the Department. To facilitate timely distribution of the information, this report is published as received from the authors and has not been edited to our usual standards. Oregon Department of Geology and Mineral Industries Oregon Geologic Digital Compilation Published in conformance with ORS 516.030 For copies of this publication or other information about Oregon’s geology and natural resources, contact: Nature of the Northwest Information Center 800 NE Oregon Street #5 Portland, Oregon 97232 (971) 673-1555 http://www.naturenw.org Oregon Department of Geology and Mineral Industries - Oregon Geologic Digital Compilation i RULES FOR LITHOLOGY MERGE INFORMATION ENTRY The lithology merge unit contains 5 parts, separated by periods: Major characteristic.Lithology.Layering.Crystals/Grains.Engineering Lithology Merge Unit label (Lith_Mrg_U field in GIS polygon file): major_characteristic.LITHOLOGY.Layering.Crystals/Grains.Engineering major characteristic - lower case, places the unit into a general category .LITHOLOGY - in upper case, generally the compositional/common chemical lithologic name(s)
    [Show full text]
  • 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).
    [Show full text]
  • Role of Water in the Formation of Granulite and Amphibolite Facies Rocks Tobacco Root Mountains Montana
    University of Montana ScholarWorks at University of Montana Graduate Student Theses, Dissertations, & Professional Papers Graduate School 1988 Role of water in the formation of granulite and amphibolite facies rocks Tobacco Root Mountains Montana Linda M. Angeloni The University of Montana Follow this and additional works at: https://scholarworks.umt.edu/etd Let us know how access to this document benefits ou.y Recommended Citation Angeloni, Linda M., "Role of water in the formation of granulite and amphibolite facies rocks Tobacco Root Mountains Montana" (1988). Graduate Student Theses, Dissertations, & Professional Papers. 8115. https://scholarworks.umt.edu/etd/8115 This Thesis is brought to you for free and open access by the Graduate School at ScholarWorks at University of Montana. It has been accepted for inclusion in Graduate Student Theses, Dissertations, & Professional Papers by an authorized administrator of ScholarWorks at University of Montana. For more information, please contact [email protected]. COPYRIGHT ACT OF 1976 Th is is an unpublished manuscript in which copyright SUBSISTS. Any further r e p r in t in g of its contents must be APPROVED BY THE AUTHOR. Ma n s f ie l d Library Un iv e r s it y of Montana Date : t , 9 C B_ THE ROLE OF WATER IN THE FORMATION OF GRANULITE AND AMPHIBOLITE FACIES ROCKS, TOBACCO ROOT MOUNTAINS, MONTANA By Linda Marie Angeloni B.S., University of California, Santa Cruz, 1982 Presented in partial fulfillment of the requirements for the degree of Master of Science University of Montana 1988 Approved by Chairman, Board of Examiners Dean, Graduate School Date UMI Number: EP38916 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted.
    [Show full text]
  • Geologic Map of Washington - Northwest Quadrant
    GEOLOGIC MAP OF WASHINGTON - NORTHWEST QUADRANT by JOE D. DRAGOVICH, ROBERT L. LOGAN, HENRY W. SCHASSE, TIMOTHY J. WALSH, WILLIAM S. LINGLEY, JR., DAVID K . NORMAN, WENDY J. GERSTEL, THOMAS J. LAPEN, J. ERIC SCHUSTER, AND KAREN D. MEYERS WASHINGTON DIVISION Of GEOLOGY AND EARTH RESOURCES GEOLOGIC MAP GM-50 2002 •• WASHINGTON STATE DEPARTMENTOF 4 r Natural Resources Doug Sutherland· Commissioner of Pubhc Lands Division ol Geology and Earth Resources Ron Telssera, Slate Geologist WASHINGTON DIVISION OF GEOLOGY AND EARTH RESOURCES Ron Teissere, State Geologist David K. Norman, Assistant State Geologist GEOLOGIC MAP OF WASHINGTON­ NORTHWEST QUADRANT by Joe D. Dragovich, Robert L. Logan, Henry W. Schasse, Timothy J. Walsh, William S. Lingley, Jr., David K. Norman, Wendy J. Gerstel, Thomas J. Lapen, J. Eric Schuster, and Karen D. Meyers This publication is dedicated to Rowland W. Tabor, U.S. Geological Survey, retired, in recognition and appreciation of his fundamental contributions to geologic mapping and geologic understanding in the Cascade Range and Olympic Mountains. WASHINGTON DIVISION OF GEOLOGY AND EARTH RESOURCES GEOLOGIC MAP GM-50 2002 Envelope photo: View to the northeast from Hurricane Ridge in the Olympic Mountains across the eastern Strait of Juan de Fuca to the northern Cascade Range. The Dungeness River lowland, capped by late Pleistocene glacial sedi­ ments, is in the center foreground. Holocene Dungeness Spit is in the lower left foreground. Fidalgo Island and Mount Erie, composed of Jurassic intrusive and Jurassic to Cretaceous sedimentary rocks of the Fidalgo Complex, are visible as the first high point of land directly across the strait from Dungeness Spit.
    [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]
  • Petrology and Geochemical Characteristics of Phlogopite Pyroxenite Related to Durbachites, Moldanubian Zone, Bohemian Massif
    Journal of Geosciences, 60 (2015), 73–90 DOI: 10.3190/jgeosci.191 Original paper Petrology and geochemical characteristics of phlogopite pyroxenite related to durbachites, Moldanubian Zone, Bohemian Massif Jakub TRUBAČ1*, Stanislav VRÁNA2, Eva HALUZOVÁ3, Lukáš ACKERMAN3 1 Institute of Geochemistry, Mineralogy and Mineral Resources, Charles University, Albertov 6, 128 43 Prague 2, Czech Republic; [email protected] 2 Czech Geological Survey, Klárov 3, 118 21 Prague 1, Czech Republic 3 Institute of Geology v.v.i., The Czech Academy of Sciences, Rozvojová 269, 165 00 Prague 6, Czech Republic; * Corresponding author The phlogopite pyroxenite with a high content of pyrrhotite forms a body of circular outline about 1 km in diameter at Přední Zvonková in Moldanubian Zone (Šumava/Bohemian Forest/Böhmerwald), Czech Republic. The contours of pyroxenite body are indicated by magnetometry and gravity data. Loose blocks up to 70 cm in size scattered on fields in the flat terrain indicate that the rock is at least partly exposed at the current erosion level. The best preserved sample SV235A is a medium-grained rock containing 27 vol. % phlogopite, 23 % diopside, 25 % enstatite, abundant apatite (7 %), minor plagioclase (3 %, An39–42), and pyrrhotite (3 %). Tendency to sulphide segregation is indicated by several mm pyrrhotite aggregates enclosing individual grains of pyroxenes, phlogopite and apatite. In the mg# vs. MgO diagram the studied pyroxenites plot along the linear trend defined by granitoid durbachites (me- lanocratic quartz syenites, quartz monzodiorites to melagranites), biotite–amphibole quartz diorites and biotite–amphi- bole ultramafic rocks (all from the Moldanubian Zone in southern and south–central Bohemia), after the whole-rock compositions of pyroxenites are corrected for the respective content of pyrrhotite.
    [Show full text]
  • Early Carboniferous P–T Path from the Upper Gneiss Unit of Haut-Allier (French Massif Central) – Reconstructed by Geothermobarometry and EMP–Th–U–Pb Monazite Dating
    Journal of Geosciences, 59 (2014), 327–349 DOI: 10.3190/jgeosci.178 Original paper Early Carboniferous P–T path from the Upper Gneiss Unit of Haut-Allier (French Massif Central) – reconstructed by geothermobarometry and EMP–Th–U–Pb monazite dating Bernhard SCHULZ* Institute of Mineralogy, Department Economic Geology and Petrology, TU Bergakademie Freiberg, Brennhausgasse 14, D-09596 Freiberg/Saxony, Germany; [email protected] * Corresponding author In the Haut-Allier region (French Massif Central), a Variscan inverted metamorphic sequence is made up by crustal nappes. A high-grade Upper Gneiss Unit (UGU) was thrusted over a Lower Gneiss Unit (LGU) and an amphibolite- -facies para-autochthonous Micaschist Unit (MU). Growth-zoned garnets with distinct Mn–Mg–Fe–Ca and trace-ele- ment zonation trends occur in kyanite garnet gneisses at Agnat (UGU). The porphyroblasts have been characterised by automated energy-dispersive X-ray spectral mapping with SEM, by electron microprobe and LA-ICPMS analyses. Microstructurally-controlled geothermobarometry based on cation exchange and net transfer reactions was used to re- construct a syn-deformational and clockwise P–T path for garnet crystallization in the UGU. The P–T path passed maximal pressures at 700 °C/13 kbar and then maximal temperatures at ~800 °C/11 kbar in the stability field of kyanite + K-feldspar. The final stage of the P–T path is a marked decompression from 10 to 5 kbar at 700–750 °C. The timing of this P–T evolution in the UGU has been constrained by electron-microprobe Th–U–Pb monazite dating (CHIME). A detailed interpretation of ages and Y-contents of monazites enclosed in a syncrystalline-rotated Mg-rich garnet allowed to relate a marked pressure decrease along a late stage of the P–T path to ~330 Ma.
    [Show full text]
  • Retrograde Metamorphism of Amphibolite, Bighorn Mountains, Wyoming
    Retrograde Metamorphism of Amphibolite, Bighorn Mountains, Wyoming R. A. HEIMLICH Department of Geology, Kent State University, Kent, Ohio 44242 ABSTRACT and minéralogie descriptions of an schist zones, and no chemical data are actinolite-plagioclase rock and chlorite- available. It is the purpose of this paper to Twenty well-defined zones of schistose talc-actinolite schist from several of the describe the petrographic, mineralogic, and rocks occur within a thick amphibolite zones north-northwest of Hazelton Peak. chemical changes that accompanied the body in the southern Bighorn Mountains, Williams (1962) also described the petrog- formation of the schist bodies. Wyoming. The zones are 2 to 12 m thick raphy of chlorite-actinolite-talc schist from and as much as 300 m long. Many of the a few of the zones. LABORATORY METHODS zones are parallel to the strike of the am- However, no over-all petrographic or Modes of the schist and the amphibolite phibolite body. However, a significant minéralogie study has been made of these were determined on the basis of 1,200 number are oriented across its trend and at an angle to the strike of its foliation. Lo- cally, the strike of amphibolite foliation is deflected near the schist zones, and blocks of amphibolite occur isolated within one of the zones. Adjacent to the schist, the amphibolite is typically a massive or layered, granoblastic aggregate of hornblende, andesine, some quartz, and minor accessories. The schist bodies consist of tremolite or magnesian ac- tinolite, chlorite, talc, and local sodic oligoclase. Chemical analyses of schist and adjacent amphibolite indicate that the schist contains smaller amounts of TiC)2, A1203, CaO, Na20, K20, and greater amounts of MgO and H20.
    [Show full text]
  • Amphibolite Vs. Banded Amphibolite: a Case Study in the São Martinho
    Cadernos Lab. Xeolóxico de Laxe ISSN: 0213-4497 Coruña. 2003. Vol. 28, pp. 213-229 Amphibolite vs. banded amphibolite: a case study in the São Martinho-Arronches area, Tomar Cordoba Shear Zone, NE Ossa Morena Zone, Portugal Anfibolita versus anfibolita bandeada: el caso de São Martinho-zona de Arronches, Zona de Cizalla de Tomar Cordoba, Zona NE de Ossa Morena, Portugal DE OLIVEIRA, D. P. S.1; WIECHOWSKI, A.2; ROBB, L. J.3 & INVERNO, C. M. C.4 Abstract Amphibolites and banded amphibolites form an integral part of the Série Negra rocks that outcrop within the Tomar Cordoba Shear Zone that forms the boundary between the Ossa Morena Zone and the Central Iberian Zone. The terms amphiboli- te and “amphibole schist” (here changed to banded amphibolite) have been regularly used by exploration geologists when referring to the amphibolitic-type lithologies, with or without a marked schistosity, that outcrop in the Ossa Morena Zone, e.g. in the vicinity of the São Martinho gold prospect. In this study the term amphibolite is used for homogeneous, massive-texture rocks at the mesoscopic scale whereas ban- ded amphibolite refers to rocks that exhibit a distinct banding at the outcrop scale. Microscopically both rock types show a schistosity, which is better defined in the banded amphibolites. These rock types have a rather similar mineralogy. Geochemically, in terms of their major element composition, there is little differen- ce between them. However, each exhibits a distinct mineral chemistry: the amphi- boles in the amphibolites are actinolite-magnesiohornblende while those in the ban- ded amphibolites are mostly magnesiohornblende and minor tschermakite.
    [Show full text]
  • 2021 SEG CODES Student Chapter Field Trip Report King Island, Tasmania, Australia
    1 CODES SEG STUDENT CHAPTER, KING ISLAND FIELDTRIP 2021 __________________________________________________________________________________ 2021 SEG CODES Student Chapter Field Trip Report King Island, Tasmania, Australia 2021 SEG-CODES Student Chapter Field Trip Participants at Grassy Mine Written and compiled by Carlos Díaz Castro, Nathaly Guerrero Ramirez, Max Hohl, Rhiannon Jones, Peter Berger, Thomas Schaap, Zebedee Zivkovic, Karla Morales, Xin Ni Seow, Tobias Staal, Alex Farrar and Hannah Moore 2 CODES SEG STUDENT CHAPTER, KING ISLAND FIELDTRIP 2021 __________________________________________________________________________________ Contents Introduction 3 Trip Leaders and organisers 5 Day 1 – Grassy area, Dolphin open pit mine 6 Historical context 6 Skarn mineralization at King Island 7 SEG-CODES student chapter crew activities 9 Naracoopa 12 Day 2 – Stokes Point and Cape Wickham 15 Stokes Point 15 Cape Wickham 16 Day 3 – City of Melbourne Bay 18 City of Melbourne Bay south: volcanics and tillites 18 City of Melbourne Bay north: cap carbonate 20 Acknowledgements 23 References 23 3 CODES SEG STUDENT CHAPTER, KING ISLAND FIELDTRIP 2021 __________________________________________________________________________________ Introduction When the Society of Economic Geologists UTAS student chapter met up at the start of 2021, the student chapter’s committee noted a general eagerness amongst the members to get out into the field. Indeed, many of the society’s postgraduate members had their research fieldwork postponed in 2020 due to travel and fieldwork restrictions established to reduce the spread of COVID-19. Discussions led to fundraising efforts, and the group secured sponsorship from the Geological Society of Australia and a travel grant from the Society of Economic Geologists to lead a field trip to King Island.
    [Show full text]
  • THE PRECAMBRIAN ROCKS of TASMANIA, PART VII NOTES on the PETROLOGY of SOME ROCKS from the PORT DAVEY-BATHURST HARBOUR AREA by A
    PAPERS AND PROCEEDINGS OF THE ROYAL SOCIETY OF TASMANIA, VOLUME 99. THE PRECAMBRIAN ROCKS OF TASMANIA, PART VII NOTES ON THE PETROLOGY OF SOME ROCKS FROM THE PORT DAVEY-BATHURST HARBOUR AREA By A. SPRY' and W. E. BAKER' (With two plates and two text figurea.) ABSTRACT No formal stratigraphic terms will be used in Petrological examination SUggests ,that the rocks this paper and it seems that, until formal strati­ of the Port Davey-Bathurst HaDbour area may be graphic terms can be useti in an ,accurate, under­ divided into .two main groups: the regionally meta­ standable manner, the stratigraphic names for this morphosed schists, quartzites, phyllites and amphi­ area may have to be abandoned. bolites which are probably older Precambrian, and the essentially unmetamorphosed sediments which PRINCIPLES are probably younger Precambrian. The latter can be divided into three main types; subgreywacke The rocks are divided into a number of litho­ sandstones and slates (Ua. Bay, Bramble Cove and logical assemblages using the amount of meta­ north eastern Bathurst Harbour), greywacke sand­ morphism and deformation as criteria following stones, slates and conglomerates (Joe Page Bay) Spry (1962a) because the structural and strati­ and orthoconglomerates and quartzites (Mts. graphic relations are not yet clear from field Rugby, Berry, &c.). studies. The low ,to medium-grade metamorphics strongly resemble rocks at Frenchmans Cap, the upper Mersey-Forbh area and Ulverstone, and INTRODUCTION are assigned to the Older Precambrian (Spry The geology of the remote south-western corner 1962a) , Moderately deformed but unmeta­ of Tasmania is complex 'and observations by morphosed sediments resemble rocks between Twelvetrees (1906, 1908, 1909), Baker (957), Zeehan and Corinna and along the North-West Stefanski (1957), and Taylor (1959) have left Coast (Spry 1957a, 1964) and may be Younger major problems of structure and stratigraphy un­ Precambrian.
    [Show full text]