DOCSLIB.ORG

Bulletin of the Geological Society of Denmark, Vol. 39/3-4 Pp. 199-211

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Bulletin of the Geological Society of Denmark, Vol. 39/3-4 Pp. 199-211 Tectonostratigraphic terranes within Archaean gneiss complexes: examples from Western Australia and southern West Greenland ALLEN P. NVTMAN Nutman, A. P.: Tectonostratigraphic terranes within Archaean gneiss complexes: examples from Western Australia and southern West Greenland. Bull. geol. Soc. Denmark, vol. 39, pp. 199-211. Copenhagen, December 20th, 1991. https://doi.org/10.37570/bgsd-1991-39-09 New field work and isotopic data show that the Godthabsfjord region of West Greenland consists of a collage of tectonostratigraphic terranes, which evolved separately prior to tectonic juxtaposition in the late Archaean. In WesternA ustralia the Narryer Gneiss Complex, which lies on the northwesternm argin of the Yilgarn Craton, is, unlike the Godthabsfjord region, very poorly exposed (less than 1 % ). In consequence it is impossible to follow geological boundaries in this complex, and instead the complex has been studied by a very extensive use of within-grain zircon U-Pb geochronology on the ion microprobe SHRIMP. The zircon geochronology suggests that the Narryer Gneiss Complex also consists of several discrete terranes of early to mid Archaean gneisses. In both the Godthabsfjord region and the Narryer Gneiss Complex, late Archaean juxtaposition of terranes was accompanied by intrusion of crustally­ derived granites, deformation, and amphibolite facies metamorphism. Thus some Archaean high grade gneiss complexes consist of terranes that underwent independent evolution until they were brought together at a later time. In this respect their anatomy resembles post-Archaean orogenic belts that formed as a consequence of plate tectonic processes. Allen P. Nutman, Research School of Earth Sciences, Australian National University, G.P.O. Box 4, Canberra ACT 2601, Australia.June 8th, 1990. Introduction: CADS and terranes itic and tonalitic magma into supracrustal se­ quences dominated by mafic rocks; older conti­ The purpose of this paper is to review the lines of nental crust may or may not be present. These evidence supporting the application of the tecto­ trondhjemitic and tonalitic rocks are now pre­ nostratigraphic terrane concept (sensu Coney, served as the "grey gneisses" ubiquitous in Ar­ Jones & Monger 1980) to the Archaean evolution chaean high grade gneiss complexes. Whole rock of the Godthabsfjord region, and then demon­ Rb-Sr, Sm-Nd and Pb isotopic studies (see e.g. strate how this concept has been applied to the Taylor et al. 1980; Moorbath & Taylor 1986; early Archaean Narryer Gneiss Complex of Moorbath et al. 1986) demonstrated that the pro­ Western Australia. Implications of recognition of toliths of these grey gneisses are dominated by tectonostratigraphic terranes in Archaean gneiss juvenile additions to the crust. The second phase complexes for the evolution of the crust are then (differentiation) of a CADS involves ultrameta­ discussed. morphism and partial melting in the depth of the In the late 1970s and early 1980s crustal accre­ new crust to give rise to a geochemically stratified tion differentiation superevents (CADS) were rec­ crust by the extraction from the lower crust of ognised as the most important factor in the pro­ granitic melt and LIL elements (see e.g. Fyfe duction of Archaean sialic crust (see e.g. Wells 1973; Wells 1979). Following a CADS the new 1979, 1980; Moorbath & Ta ylor 1986). From un­ crust is stable and may survive for a long time. certainties on Rb-Sr and Pb-Pb whole rock dating The intensive studies in the 1970s of the God­ (e.g. Moorbath & Pankhurst 1976; Ta ylor et al. thabsfjord region, southern West Greenland, 1980), CADS took less than - 200 million years. gave rise to much of the data which was firstused The first phase (crustal accretion) of a CADS to formulate the idea of CADS. The proposed involves injection of predominantly trondhjem- mid Archaean CADS in the Godthabsfjord re- 200 Nutman: Archaean gneiss complexes Davis Strait 25 km 1 I Tasiusarsuaq terrane 1 2800 Ma Iliveralik granite Undivided rnid to late Archaean supracrustal rnetamorphisrn rocks and gabbro-anorthosite cornplexes Akia terrane r Kangimut sammisoq Mid-Archaeangneisses, including 3050-2980 Ma A TinissAq Nfik gneisses. Granulite facies rnetarnorphisrn at -3000 Ma in the west. @$# 2550 Ma Qôrqut granite cornplex Akulleq terrane ' Terrane boundary 0Færingehavn sub-terrane, dominantly >3600 Ma Arnitsoq gneisses 2' Proterozoic fault Tre Brodre sub-terrane,dorninantly Permanent ice 1 2750-2800 Ma Ikkattoq gneisses Fig. 1. Geological sketch map of the Godthåbsfjord region, West Greenland. gion entailed (1) tectonic intercalation of the lite and amphibolite facies assemblages found in "Malene supracrustal rocks" and the early Ar- the southern half of the region as having formed chaean Amitsoq gneisses (cut by the Ameralik at different structural levels during a single - dykes), (2) intrusion of the voluminous protoliths 2800 Ma metamorphic peak. Coe (1980) inter- of the (type) Nuk gneisses of Nuuk and south- preted this purported synchronous regional meta- western Godthåbsfjord and what were presurned morphic peak as marking "cratonisation" at - to be their equivalents elsewhere in the region, 2800 Ma following a CADS. Late Archaean and (3) folding and granulite facies metamor- shearing, granite emplacement and retrogression phism (see e.g. McGregor 1973, 1979; Bndgwa- were regarded as evidence of local reworking of ter et al. 1974; Chadwick & Nutman 1979; Wells crust formed in a single mid Archaean CADS, 1979; Coe 1980; McGregor et al. 1983,1986; Dy- rather than evidence of a much more complex mek 1984; Robertson 1986; Moorbath et al. crustal evolution for the Godthåbsfjord region 1986). Wells (1976, 1979) interpreted the granu- (Bridgwater et al, 1976; McGregor et al. 1983). Bulletin of the Geological Society of Denmark 201 e AKULLEQ TERRANE TASIU- AKIA TERRANE Færingehavn Isukasia Tre Br~dre TERME 1 4500 i sub-terrane sub-terrane sub-terrane 4000 -* some Isua - early g -111111111111111 3500 sialic 111111111111111 crust * -- t 3000 *-p 11111111111111 g,a a *-t-a t*- g,a -t (Mal -k stratigraphic position of supracrustal ' rocks not yet dated t unpublished protoliths of Archaean grey gneisses SHRIMP results granite unique to a terrane deformed granites found in several terranes Qôrqut granite complex and pegmatites, mostly undeformed dated supracrustal rocks g a documented granulite (g) and amphibolite (a) facies metamorphism Fig. 2. Terrane chronology in the Godthåbsfjord region. tH. Baadsgaard, M.J. Duke and A.P. Nutman, unpublished SHRIMP within-grain zircon U-Pb data. In the mid 1980s C.R.L. Friend, V.R. McGre- are dorninated by mid Archaean gneisses (Fig. gor and the writer carried out remapping of se- 1). The Akulleq terrane, which forms most of lected areas in order to resolve the limit of Ar- Godthåbsfjord and the coastal strip south of chaean granulite facies metamorphism and the Nuuk, contains a wide variety of rocks, ranging extent of the early Archaean Amitsoq gneisses. from early to late Archaean in age (McGregor et The data gathered during this work showed that al. 1991 - this volume). The Akulleq terrane is a several associations of rocks are present in the conglomeration of the Tre Brodre and Fzringe- Godthåbsfjord region, each with its own early havn terranes described in previous publications history (Friend et al. 1987). Furthermore, "Niik (e.g. Nutman et al. 1989), which are now reduced gneisses" dorninating different associations with to sub-terrane status. The reason for this is that contrasting structural and metamorphic history, although tectonic boundaries have been identi- are now known from U-Pb zircon geochronology fied between the Tre Brodre and F~ringehavn to be of different ages (Nutman et al. 1989; sub-terranes (Friend et al. 1987), these sub-ter- Schiotte et al. 1989; H. Baadsgaard, pers. ranes contain the same lithologies but in different comm.). This suggested that the region did not proportions. This is discussed by McGregor et al. develop during a single CADS, and that it might (1991 - this volume). instead consist of a collage of tectonostrati- graphic terranes (sensu Coney et al. 1980) that were assembled in the late Archaean with amphi- The Godthåbsfjord region bolite facies metamorphism, folding, and em- placement of crustally denved granites (Fig. 2). The evidence for tectonostratigraphic terranes in The Akia terrane and Tasiusarsuaq terrane, to the the Godthåbsfjord region is demonstrated by re- north and south of Godthåbsfjord respectively, sults from part of the F~ringehavn- Tre Brodre 202 Nutman: Archaean gneiss complexes - paragneiss and amphibolite - metagabbro and anorthosite Fig. 3. Detailed map of part of the Færingehavn-Tre Brbdre area, West Greenland, illustrating evidence for tectonostratigraphic terranes. area as shown in Fig. 3. The eastern terrane in than 20 m wide, which are locally discordant to this area contains the controversial "old gneisses" lithological units within the terranes (Fig 3; at Titiissiq and Kangimut sammissoq (see Friend et al. 1987). The zones of flaggy rocks Schi~tteet al. 1989 and McGregor et al. 1991 - separating the terranes consist of finely-layered this volume - for discussion). Three lines of evi- quartzo-feldspathic and quartz-nch rocks, mica- dente to support the tectonostratigraphic terrane and amphibole-rich schistose rocks, and (locally model for the region are considered here: struc- discordant) seams of fuchsite-bearing quartz tural, isotopic and metamorphic. rocks. The schistose rocks commonly contain thin, disrupted
Load more

Recommended publications
  • Facies and Mafic
    Metamorphic Facies and Metamorphosed Mafic Rocks l V.M. Goldschmidt (1911, 1912a), contact Metamorphic Facies and metamorphosed pelitic, calcareous, and Metamorphosed Mafic Rocks psammitic hornfelses in the Oslo region l Relatively simple mineral assemblages Reading: Winter Chapter 25. (< 6 major minerals) in the inner zones of the aureoles around granitoid intrusives l Equilibrium mineral assemblage related to Xbulk Metamorphic Facies Metamorphic Facies l Pentii Eskola (1914, 1915) Orijärvi, S. l Certain mineral pairs (e.g. anorthite + hypersthene) Finland were consistently present in rocks of appropriate l Rocks with K-feldspar + cordierite at Oslo composition, whereas the compositionally contained the compositionally equivalent pair equivalent pair (diopside + andalusite) was not biotite + muscovite at Orijärvi l If two alternative assemblages are X-equivalent, l Eskola: difference must reflect differing we must be able to relate them by a reaction physical conditions l In this case the reaction is simple: l Finnish rocks (more hydrous and lower MgSiO3 + CaAl2Si2O8 = CaMgSi2O6 + Al2SiO5 volume assemblage) equilibrated at lower En An Di Als temperatures and higher pressures than the Norwegian ones Metamorphic Facies Metamorphic Facies Oslo: Ksp + Cord l Eskola (1915) developed the concept of Orijärvi: Bi + Mu metamorphic facies: Reaction: “In any rock or metamorphic formation which has 2 KMg3AlSi 3O10(OH)2 + 6 KAl2AlSi 3O10(OH)2 + 15 SiO2 arrived at a chemical equilibrium through Bt Ms Qtz metamorphism at constant temperature and =
    [Show full text]
  • Metamorphism
    Title page INTRODUCING METAMORPHISM Ian Sanders DUNEDIN EDINBURGH LONDON Contents Contents v Preface ix Acknowledgements x 1 Introduction 1 1.1 What is metamorphism? 1 1.1.1 Protoliths 1 1.1.2 Changes to the minerals 1 1.1.3 Changes to the texture 3 1.1.4 Naming metamorphic rocks 3 1.2 Metamorphic rocks – made under mountains 3 1.2.1 Mountain building 3 1.2.2 Directed stress, pressure and temperature in a mountain’s roots 4 1.2.3 Exhumation of a mountain’s roots 6 1.3 Metamorphism in local settings 6 1.3.1 Contact metamorphism 7 1.3.2 Hydrothermal metamorphism 7 1.3.3 Dynamic metamorphism 9 1.3.4 Shock metamorphism 9 2 The petrography of metamorphic rocks 11 2.1 Quartzite and metapsammite 11 2.1.1 Quartzite 11 2.1.2 Metapsammite 13 2.2 Metapelite 13 2.2.1 Slate 14 2.2.2 Phyllite and low-grade schist 16 2.2.3 Minerals and textures of medium-grade schist 17 2.2.4 The regional distribution of minerals in low- and medium-grade schist 20 2.2.5 Pelitic gneiss and migmatite 22 2.2.6 Metapelite in a contact aureole 23 2.2.7 The significance of Al2SiO5 for inferring metamorphic conditions 23 2.3 Marble 24 2.3.1 Pure calcite marble 24 2.3.2 Impure marble 26 2.3.3 Metasediments with mixed compositions 29 CONTENTS 2.4 Metabasite 30 2.4.1 Six kinds of metabasite from regional metamorphic belts 31 2.4.2 The ACF triangle for minerals in metabasites 36 2.4.3 P–T stability of metabasites, and metamorphic facies 38 vi 2.4.4 A metabasite made by contact metamorphism 40 2.5 Metagranite 41 2.5.1 Granitic gneiss and orthogneiss 41 2.5.2 Dynamic metamorphism
    [Show full text]
  • PRELIMINARY EVALUATION of BEDROCK POTENTIAL for NATURALLY OCCURRING ASBESTOS in ALASKA by Diana N
    Alaska Division of Geological & Geophysical Surveys MISCELLANEOUS PUBLICATION 157 PRELIMINARY EVALUATION OF BEDROCK POTENTIAL FOR NATURALLY OCCURRING ASBESTOS IN ALASKA by Diana N. Solie and Jennifer E. Athey Tremolite (UAMES 34960) displaying the soft, friable fibers of asbestiform minerals. Sample collected from the Cosmos Hills area, Kobuk District, Alaska, by Eskil Anderson. Image courtesy of the University of Alaska Museum Earth Sciences Department. June 2015 Released by STATE OF ALASKA DEPARTMENT OF NATURAL RESOURCES Division of Geological & Geophysical Surveys 3354 College Road, Fairbanks, Alaska 99709-3707 907-451-5020 dggs.alaska.gov [email protected] $2.00 (text only) $13.00 (per map sheet) TABLE OF CONTENTS Abstract ................................................................................................................................................................................................................................. 1 Introduction ........................................................................................................................................................................................................................ 1 General geology of asbestos ......................................................................................................................................................................................... 2 Naturally occurring asbestos potential in Alaska ..............................................................................................................................................
    [Show full text]
  • Streaming of Saline Fluids Through Archean Crust
    Lithos 346–347 (2019) 105157 Contents lists available at ScienceDirect Lithos journal homepage: www.elsevier.com/locate/lithos Streaming of saline fluids through Archean crust: Another view of charnockite-granite relations in southern India Robert C. Newton a,⁎, Leonid Ya. Aranovich b, Jacques L.R. Touret c a Dept. of Earth, Planetary and Spaces, University of California at Los Angeles, Los Angeles, CA 90095, USA b Inst. of Ore Deposits, Petrography, Mineralogy and Geochemistry, Russian Academy of Science, Moscow RU-119017, Russia c 121 rue de la Réunion, F-75020 Paris, France article info abstract Article history: The complementary roles of granites and rocks of the granulite facies have long been a key issue in models of the Received 27 June 2019 evolution of the continental crust. “Dehydration melting”,orfluid-absent melting of a lower crust containing H2O Received in revised form 25 July 2019 only in the small amounts present in biotite and amphibole, has raised problems of excessively high tempera- Accepted 26 July 2019 tures and restricted amounts of granite production, factors seemingly incapable of explaining voluminous bodies Available online 29 July 2019 of granite like the Archean Closepet Granite of South India. The existence of incipient granulite-facies metamor- phism (charnockite formation) and closely associated migmatization (melting) in 2.5 Ga-old gneisses in a quarry Keywords: fl Charnockite exposure in southern India and elsewhere, with structural, chemical and mineral-inclusion evidence of uid ac- Granite tion, has encouraged a wetter approach, in consideration of aqueous fluids for rock melting which maintain suf- Saline fluids ficiently low H2O activity for granulite-facies metamorphism.
    [Show full text]
  • 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]
  • Nature and Origin of Fluids in Granulite Facies Metamorphism R.C
    129 NATURE AND ORIGIN OF FLUIDS IN GRANULITE FACIES METAMORPHISM R.C. Newton, Department of the Geophysical Sciences, University of Chicago, Chicago, IL 60637, USA Orthopyroxene, the definitive mineral of the granulite facies, may originate in prograde dehydration reactions in rock systems open to fluids or may be a premetamorphic relic of igneous intrusions or their contact aureoles which persisted through fluid-deficient metamorphism. Terrains showing evidence of open-system orthopyroxene-forming reactions are those of South India and southern Norway. An example of fluid-deficient granulite facies metamorphism is the Adirondack Highlands of New York, where metamorphic pyroxene commonly resulted from dry recrystallization of pyroxenes of plutonic charnockites and anorthosites. The metamorphism recorded by the presence of orthopyroxene in different terrains may thus have been conservative or may have involved fluids of different origins pervasive on various length-scales. Metamorphism with pervasive metasomatism is signaled by monotonous H20, C02 and 02 fugacities over large areas, nearly independent of lithology, by scarcity of relict textures, and by pronounced depletion of Rb and other large ion lithophile (LILE) elements in the highest grade areas, such as the southernmost part of the Bamble, South Norway, terrain (1). Primary hornblende is rare or absent in quartzofeldspathic gneisses and orthopyroxene is ubiquitous in acid and basic rocks in the charnockitic terrains. Pronounced major and minor element redistributions took place
    [Show full text]
  • 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.
    [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]
  • The Granulite-Granite Linkage: Inferences Froll} S
    the Granulite-Granite Linkage: Inferences froll} s lDEPARTAMENTO DE PETROLOGIA Y GEOQUIMICA, FACULTAD DE CIENCIAS GEOLOGICAS, UNIVERSIDAD COMPLUTENSE, 28040 MADRID, SPAIN 2 DEPARTMENT OF GEOLOGY, BIRKBECK COLLEGE, MALIT STREET, LONDON WCIE 7HX, UK 3CNRS UMR 6524, D EPARTEMENT DES SCIENCES DE LA TERRE, UNIVERSITE BLAISE PASCAL, 5 RUE KESSLER, F-63038 CLERMONT-FERRAND, FRANCE 4DEPARTAMENTO DE GEOLOGIA, FACULTAD DE CIENCIAS DEL MAR, UNIVERSIDAD DE CADIZ, 1151O PUERTO REAL ''-'""JJHC,J. SPAIN if the xenoliths is lower than that outcropping mid-crustal A contribution the granites reduces the mantle contribution in models ifgranite nature if the lower continental crust in contrasts with the more mqficffJ7f!r:r-,Cf1LUflf con7iJo:ntum and estimaud in other European Herrynian areas) a non- Thermobarometric calculations based on min- crust in this Herrynian eral paragenesis indicate conditions around 850-950°(;, 7-11 th us the xenoliths lower con- this high-T high-P assemi'JLCl!.'!e IS a by Ket;vpftlUC coronas) trf111.'in(J'rt in the KEY WORDS: filsi;; lower continental crust; Sr-Nd .L.LO,'OYJ<,"-M& Iberian Belt alkaline magma. Felsic mela1!!J'leOlIS exhibit restitic mineral with up to 50% 37% sillimanite. Major and trace element mO,rJelLWP idea that the taU�-l1erc�vnuzn {J19JaLumlnollS INTRODUCTION The study of lower-crustal xenoliths has been a 8 Nd calculaud at an (J1)erage Herrynian age tool in understanding the process of anatexis involved in if300 Ma) are in the range O' 706-0' 712) and -1,4 to -8'2, the genesis of felsic (Downes & Duthou, These values match the isowpic if the Ruiz et Miller et 1992; Hanchar et outcrobtnnp late TIe Sr 1994; Pankhurst & Rapela, It is clear that granite sources in orogenic areas are not the outcropping An alkaline ultrabasic dyke swarm was intruded into metamorphic rocks but are located in deeper crustal the region in Mesozoic times (Villaseca & Nuez, levels.
    [Show full text]
  • Earth's Oldest Rocks
    Chapter 12 The Oldest Terrestrial Mineral Record: Thirty Years of Research on Hadean Zircon From Jack Hills, Western Australia Aaron J. Cavosie1, John W. Valley2 and Simon A. Wilde3 1Curtin University, Perth, WA, Australia; 2University of WisconsineMadison, Madison, WI, United States; 3Curtin University of Technology, Perth, WA, Australia Chapter Outline 1. Introduction 255 3.4.1 Lithium 266 2. Jack Hills Metasedimentary Rocks 256 3.4.2 Ti Thermometry 266 2.1 Age of Deposition 257 3.4.3 Rare Earth Elements, Yttrium and Phosphorous 266 2.2 Metamorphism 258 3.4.4 Other Trace Elements (Al, Sc, Sm/Nd, Xe) 267 2.3 Geology of Adjacent Rocks 258 3.5 Hafnium Isotopic Compositions 267 3. Studies of Jack Hills Zircon 259 3.6 Mineral Inclusion Studies 268 3.1 Images of Jack Hills Zircon 259 4. Early Earth Processes Recorded by Jack Hills Zircon 270 3.2 Age of the Hadean Zircon Population 259 4.1 Derivation of Jack Hills Zircon From Early Mafic 3.2.1 The UePb Story 259 Crust (εHf) 270 3.2.2 U Abundance, Radiation Damage, and Pb Loss 261 4.2 Existence of >4300 Ma Granitoid 270 3.2.3 The Oldest Grains in the Jack Hills 262 4.3 Significance of Surface Alteration on the Early Earth 271 3.2.4 Distribution of Hadean Grains 264 4.4 Impact Events Recorded in Jack Hills Zircon? 271 3.3 Oxygen Isotopes 264 Acknowledgments 273 3.4 Trace Elements 266 References 273 1. INTRODUCTION Little is known of the early Earth because of the absence of a rock record for the first 500 million years after accretion.
    [Show full text]
  • Proterozoic Deformation in the Northwest of the Archean Yilgarn Craton, Western Australia Catherine V
    Available online at www.sciencedirect.com Precambrian Research 162 (2008) 354–384 Proterozoic deformation in the northwest of the Archean Yilgarn Craton, Western Australia Catherine V. Spaggiari a,∗, Jo-Anne Wartho b,1, Simon A. Wilde b a Geological Survey of Western Australia, Department of Industry and Resources, 100 Plain Street, East Perth, Western Australia 6004, Australia b Department of Applied Geology, Curtin University, GPO Box U1987, Perth, Western Australia 6845, Australia Received 31 January 2007; received in revised form 19 September 2007; accepted 16 October 2007 Abstract The Narryer Terrane within the northwestern Yilgarn Craton contains the oldest crust in Australia. The Jack Hills greenstone belt is located within the southern part of the Narryer Terrane, and structures cutting it and surrounding rocks have been dated using the 40Ar/39Ar technique. The results show that east-trending, dextral, transpressive shearing was related to the 1830–1780 Ma Capricorn Orogeny, followed by further deformation and/or cooling between c. 1760 and 1740 Ma. These results confirm that major deformation has affected the northwestern part of the Yilgarn Craton in an intracratonic setting during the Proterozoic. Proterozoic structures have been interpreted to extend south beyond the Narryer Terrane into the northern part of the Youanmi Terrane (Murchison Domain), and include the Yalgar Fault, previously interpreted as the boundary between the Narryer and Youanmi Terranes. Terrane amalgamation pre-dated the emplacement of c. 2660 Ma granites in both terranes, and the current expression of the Yalgar Fault must represent a younger, reworked, post-amalgamation structure, possibly controlled by the tectonic boundary. However, new aeromagnetic and gravity imagery does not show the eastern part of the Yalgar Fault as a major structure.
    [Show full text]
  • Heterogeneous Hadean Crust with Ambient Mantle Affinity Recorded in Detrital Zircons of the Green Sandstone Bed, South Africa
    Heterogeneous Hadean crust with ambient mantle affinity recorded in detrital zircons of the Green Sandstone Bed, South Africa Nadja Drabona,1,2, Benjamin L. Byerlyb,3, Gary R. Byerlyc, Joseph L. Woodend,4, C. Brenhin Kellere, and Donald R. Lowea aDepartment of Geological Sciences, Stanford University, Stanford, CA 94305; bDepartment of Earth Sciences, University of California, Santa Barbara, CA 93106; cDepartment of Geology and Geophysics, Louisiana State University, Baton Rouge, LA 70803; dPrivate address, Marietta, GA 30064; and eDepartment of Earth Sciences, Dartmouth College, Hanover, NH 03755 Edited by Albrecht W. Hofmann, Max Planck Institute for Chemistry, Mainz, Germany, and approved January 4, 2021 (received for review March 10, 2020) The nature of Earth’s earliest crust and the processes by which it While the crustal rocks in which Hadean zircon formed have formed remain major issues in Precambrian geology. Due to the been lost, the trace and rare earth element (REE) geochemistry of absence of a rock record older than ∼4.02 Ga, the only direct re- these zircons can be used to characterize their parental magma cord of the Hadean is from rare detrital zircon and that largely compositions. Zircon crystallizes as a ubiquitous accessory mineral from a single area: the Jack Hills and Mount Narryer region of in silica-rich, differentiated magmas formed in a number of crustal Western Australia. Here, we report on the geochemistry of environments. Since zircon compositions are influenced by varia- Hadean detrital zircons as old as 4.15 Ga from the newly discov- tions in melt composition, coexisting mineral assemblage, and trace ered Green Sandstone Bed in the Barberton greenstone belt, element partitioning as a function of magmatic processes, temper- South Africa.
    [Show full text]