DOCSLIB.ORG

Archaean to Early Proterozoic Tectonics and Crustal Evolution: a Review

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Archaean to Early Proterozoic Tectonics and Crustal Evolution: a Review RevistaBrasileira de Geociências 12(1-3): 15-31, Mer.câet., 1982 - Silo Paulo ARCHAEAN TO EARLY PROTEROZOIC TECTONICS AND CRUSTAL EVOLUTION: A REVIEW ALFRED KRONER' ABSTRACT Hypothesis on the formation and evolution of the Earth's continental crust in the Early Precambrian have to account for the independent and directionally consistent motion of crustal segments of considerable dimensions since at least 3,5 Ga ago, and at minimum veJocities comparable to those of today. It seems established, therefore, that plate tectonics has governed lithospheric evolution since the generation of rigid crustal segmenta, and it is speculated that a change in style of pia te interaction, 'rather than a change in fundamental mechanisms, has deter­ mined non-uniformitarian crustal evolution towards the present Wilson cycle. Uncertainties in the reliable reconstruction of Archaean tectonic settings are caused by low­ -temperature rock alteration that may obliterate primary magma tic trends, by the variable possible sources and melting processes for the generation of bimodal and calc-alkaline associations, and by disagreement on the interpretation of rocks with "primitive" isotopic characteristics. It is sug~ gested that magmatic underplating played a major role in lithospheric growth and. that reworking of continental crust during large-scale crustal differentiation was more important in the Archaean than recognized by most currently popular models. The generation and survival of first continental crust is seen in analogy with the evolution of Iceland, and later greenstone belt development was probably largely .intracontinental, following a rift-and-sag mede] in response to crustal rearrangements. Most high-grade terrains are considered to be older than neighbouring or overlying greenstone associations and were brought to the surface through low-angle thrusting. Archaean lithospheric growth built stable cratons that experienced little internal deformation in ear1y Proterozoic times. Less stabilized crust reacts to large-scale distortions predominantly by stretching, elongate basin-formation and "ensialic" orogeny through mechanisms ranging from crust restacking to transform shearing, finally gcnerating mobile belts. Locally, modern-type con­ vergent plate margins become recognizable at about 2.2 Ga ago while the full Wilson cycle is finally established in the late Proterozoic. ' INTRODUCTION Some 20 years of plate teetonies, crustal sutures merely by tiny occurrences of mafic-ultra­ eombined with new insights into the fine strueture of the mafic rocks, nappe tectonics and the presence of'calc-alkaline lithosphere as derived from seismie data, the application rock assemblages (e.g. Burke et al., 1977) and by inferring of multi-element geoehemieal and isotopie studies, and teetonie processes almost exclusively from geochemical data paleomagnetism have profoundly influeneed present think­ (e.g. Taylor, 1967; Glikson, 1972; Tarney, 1976) and thus ing on the origin and evolution of the Earth's continental postulating uniformitarian crustal evolution back to the crust. Early Arehaean (Burke et al., 1976; Burke, 1981), is now Although there is now general agreernent on how the succeeded by more realistic models that recognize funda­ Earth worked for the last 200 Ma beeause of observable mentai changes in the Earth's internal processes following evidenee in the oeeans and eontinents (e.g. Bird, 1980; Con­ global cooling and concomitant changes in lithospheric die, 1982a), it has proved diffieult to extend this history behaviour through time (Baer, 1981; Goodwin, 1981a; into more ancient times in view of the lost oceanic record Króner, 1981 a). It is also satisfying to see that modern and the ambiguity and eomplexity of the pre-Mesozoic rock workers place increasing importance on field relationships relationships in the continents (Dewey, 1982). However, pre­ rather than on conceptual interpretations, particularly as served eharaeteristie rock assemblages uniquely identifying regards such controversial problems as the evolution of modern Wilson eyclc processes have now been abundantly Arehaean greenstone-granitoid-gneiss terrains and Pro­ recognized in continental terrains as old as ea. 800-900 Ma terozoic mobile belts. and provide strong evidence for the conclusion that the The plate tectonie eoneept is now flexible enough to present global teetonic regime has governed the evolution aecomodate such previously rejected models. as "ensialic" of the lithosphere at least sinee the Late Precambrian (Baer, orogeny (Bally, 1981; Dewey, 1982; Króner, in press), while 1977; Krõner, 1977). adversaries of Precambrian piate motion have toaccept the Profound disagreement on the older erustal history, how­ dominance of horizontal tectonics in continental crust for­ ever, prevails to the present day, but it seems clear that mation sinee the earliest Arehaean (Myers, 1976) and the the earlier period of dogmatism that followed the introdue­ growing evidence for independent motion of rigid litho­ tion of the plate teetonic concept is now giving way to a . spheric plates ofconsiderable dimensions since at least 3.5 Ga more balaneed approaeh in attempts to decipher the Pre­ ago (Krõner and McWilliams, in press). The conclusion cambrian evolution of the continents. Thus, the early is inescapable, therefore, that oceanic crust has been recy­ enthusiasm of postulating vanished oeeans and defining cled back into the mantle since plates move around, although '" Institut für Geowissenschaften, Johannes-Gutenberg~Universitat,Saarstr. 21, 6500 Mainz, West Germany 16 Revisto Brasileiro de Geociêncías, Volume 12 (1-3), 1982 the detailed process of aneient subduction as well as the is seen in the widespread occurrence of MgO-rich komatiitic mechanism that triggered it remain speculative (Hargraves, volcanic rocks in Archaean terrains thatare commonly ascri­ 1981; Krôner, 1981a; Lambert, 1981). bed to high degrees ef partial melting in the mantle (Green, Uniformitarianists acknowledge significant difTerences 1975,1981). Since there is no evidence that signiticant heat between Archaean and younger terrains (e.g. Sleep and was lost by conduction through the Archaean continental Windley, 1982), yet they appeallargely to crustal-evolution crust (Tarney and Windley, 1977), the greater heat flux must models that are based on processes occurring along modern havebeen removed via theoceaniccrust, either byan increa­ plate boundaries in explaining crustal growth through time sed rate ofplate production or by an increased totallength of (e.g. Windley, 1979; Moorbath, 1978), in line with the oceanic ridges (Biekle, 1978). About six times the current glo­ dogma: comparable rocks imply cornparable origins (Dic­ bal oceanic crust formation rate of 3km'!a would thus be kinson, 1981). required by 2.8Ga ago or an average age ofocean crust at the The crucial questions not answered by these models are time of subduction of only ca. 20Ma (Sleep and Windley, why crusta I growth took place episodically rather than 1982). continuously (DePaolo, 1981) and why 70%-85% of the 1t is also argued that plate motion would have been faster present continental crust apparently formed in Archaean due to a lower viscosity in the mantle. Hager and O'Connell times despite the lack of evidence for signiticantly faster (1980), for example, calculated that a temperature increase plate motion in the early Precambrian as compared to later of 100'C in the mantle results in a viscosity decrease by a periods. The present Wilson cycleand associated subduction­ factor of 10, Ieading to a 3·fold increase in platevelocities. -related continental margin and island-arc magmatísm, there­ The high calc-alkaline magma generation rate of the Ar­ fore, appear to be less efficient continent-building mecha­ chaean (Moorbath, 1978) is seen as a consequence of this nisms than required by the Archaean rate of crustal growth. postulated greater plate motion (Dewey and Windley, 1981). This paper reviews the situation and speculates on alterna­ However, presently available palaeomagnetie data for tive processes that seem compatible with the geological, Achaean rocks do not support this concept in that they geochemical and palaeomagnetic data as well as the general fail to reveal signiticantly higher minimum continental ve­ concept of piate tectonics. locities with respect to the poles in the early Precambrian. These data come from the Superior Province in Canada (Dunlop, 1981), the Pilbara Block of western Australia PRECAMBRIAN PLATE MOTION It has been a wide­ (McElhinny and Senanayake, 1980) and the Kaapvaal Iy held opinion that higher heat flow in the Precambrian craton of southern Africa (Krõner and McWilliams, in resulted in faster plate motion and that this explains the press) (Fig. I). The reader should be aware of the Iimitations decreasing rate of crust-forrnation through time (e.g. Bickle, of palaeomagnetie data in that they only record longitudinal 1978; Dewey and Windley, 1981; Park, 1981; Smith, 1981). motion with respect to the poles and that motion is also The argument goes Iike this: Archaean terrestrial heat flow difficult to detect in cases where palaeomagnetic and rota­ was two-three times present rates (Lambert, 1981)and requi­ tion poles are in close proximity (McWilliams, 1981). red upper mantle temperatures to have been up to 150'C The Canadian results imply a minimum average veloeity higher than now (Davies, 1979; Cook and Turcotte, 1981; of about 2cm!a for the period 2.8 to 2.5 Ga ago (Ullrich Smith, 1981). Direct
Load more

Recommended publications
  • Two Contrasting Phanerozoic Orogenic Systems Revealed by Hafnium Isotope Data William J
    ARTICLES PUBLISHED ONLINE: 17 APRIL 2011 | DOI: 10.1038/NGEO1127 Two contrasting Phanerozoic orogenic systems revealed by hafnium isotope data William J. Collins1*(, Elena A. Belousova2, Anthony I. S. Kemp1 and J. Brendan Murphy3 Two fundamentally different orogenic systems have existed on Earth throughout the Phanerozoic. Circum-Pacific accretionary orogens are the external orogenic system formed around the Pacific rim, where oceanic lithosphere semicontinuously subducts beneath continental lithosphere. In contrast, the internal orogenic system is found in Europe and Asia as the collage of collisional mountain belts, formed during the collision between continental crustal fragments. External orogenic systems form at the boundary of large underlying mantle convection cells, whereas internal orogens form within one supercell. Here we present a compilation of hafnium isotope data from zircon minerals collected from orogens worldwide. We find that the range of hafnium isotope signatures for the external orogenic system narrows and trends towards more radiogenic compositions since 550 Myr ago. By contrast, the range of signatures from the internal orogenic system broadens since 550 Myr ago. We suggest that for the external system, the lower crust and lithospheric mantle beneath the overriding continent is removed during subduction and replaced by newly formed crust, which generates the radiogenic hafnium signature when remelted. For the internal orogenic system, the lower crust and lithospheric mantle is instead eventually replaced by more continental lithosphere from a collided continental fragment. Our suggested model provides a simple basis for unravelling the global geodynamic evolution of the ancient Earth. resent-day orogens of contrasting character can be reduced to which probably began by the Early Ordovician12, and the Early two types on Earth, dominantly accretionary or dominantly Paleozoic accretionary orogens in the easternmost Altaids of Pcollisional, because only the latter are associated with Wilson Asia13.
    [Show full text]
  • Wilson Cycle Guide
    Wilson Cycle Description Lynn S. Fichter and Eric Pyle Department of Geology and Environmental Science James Madison University Layout of this Guide For each stage represented in this Wilson Cycle, several pieces of information are provided: Description of Process: a description of the forces acting on a particular location, and the results of those forces; Composition: the particular rock types that result from these forces, including chemical make up, major minerals present, and texture (grain size and orientation), expressed in photographs, verbal descriptions, and categorical graphs; Specific Locations, Present and Past: the map locations of examples of the environment, with current and past locations represented. Stage A: Stable Continental Craton Description of Process: This stage represents the basis of all existing continents, showing in a simplified fashion both continental crust and adjacent oceanic crust, both of which lie over the mantle. You will notice that the continental crust is considerably thicker than the ocean crust. Continental crust is less dense than oceanic crust (approximately 2.7 g/cm3 vs. 3.3 g/cm3), and so “rides” higher over the mantle. Continental crust is also more rigid that oceanic crust. Furthermore, the development of continental crust involves considerable thickening. Composition: This diagram represents considerable simplification, in that the internal structure has not been shown, but is represented as a crystalline “basement” for the continent. This basement material represents a variety of rock types, including granites and diorites, gneisses and schists, and various sedimentary rocks. Taken as a whole, the average composition of the basement rock is the same as a granodiorite – enriched in sodium, potassium and silica-rich minerals, such as alkali feldspar, sodium plagioclase, and quartz, and depleted in iron/magnesium, silica poor minerals, such as olivine, pyroxene, and amphibole.
    [Show full text]
  • Connecting the Deep Earth and the Atmosphere
    In Mantle Convection and Surface Expression (Cottaar, S. et al., eds.) AGU Monograph 2020 (in press) Connecting the Deep Earth and the Atmosphere Trond H. Torsvik1,2, Henrik H. Svensen1, Bernhard Steinberger3,1, Dana L. Royer4, Dougal A. Jerram1,5,6, Morgan T. Jones1 & Mathew Domeier1 1Centre for Earth Evolution and Dynamics (CEED), University of Oslo, 0315 Oslo, Norway; 2School of Geosciences, University of Witwatersrand, Johannesburg 2050, South Africa; 3Helmholtz Centre Potsdam, GFZ, Telegrafenberg, 14473 Potsdam, Germany; 4Department of Earth and Environmental Sciences, Wesleyan University, Middletown, Connecticut 06459, USA; 5DougalEARTH Ltd.1, Solihull, UK; 6Visiting Fellow, Earth, Environmental and Biological Sciences, Queensland University of Technology, Brisbane, Queensland, Australia. Abstract Most hotspots, kimberlites, and large igneous provinces (LIPs) are sourced by plumes that rise from the margins of two large low shear-wave velocity provinces in the lowermost mantle. These thermochemical provinces have likely been quasi-stable for hundreds of millions, perhaps billions of years, and plume heads rise through the mantle in about 30 Myr or less. LIPs provide a direct link between the deep Earth and the atmosphere but environmental consequences depend on both their volumes and the composition of the crustal rocks they are emplaced through. LIP activity can alter the plate tectonic setting by creating and modifying plate boundaries and hence changing the paleogeography and its long-term forcing on climate. Extensive blankets of LIP-lava on the Earth’s surface can also enhance silicate weathering and potentially lead to CO2 drawdown (cooling), but we find no clear relationship between LIPs and post-emplacement variation in atmospheric CO2 proxies on very long (>10 Myrs) time- scales.
    [Show full text]
  • Proterozoic First-Order Sedimentary Sequences of the Sao Francisco
    Marine and Petroleum Geology 33 (2012) 127e139 Contents lists available at SciVerse ScienceDirect Marine and Petroleum Geology journal homepage: www.elsevier.com/locate/marpetgeo Proterozoic first-order sedimentary sequences of the São Francisco craton, eastern Brazil Fernando F. Alkmima,*, Marcelo A. Martins-Netob a Departamento de Geologia, Escola de Minas, Universidade Federal de Ouro Preto, Morro do Cruzeiro, 35.400.000 Ouro Preto, MG, Brazil b Vicenza Mineração, Av. Agulhas Negras, 580, Mangabeiras, 30210-340 Belo Horizonte, MG, Brazil article info abstract Article history: The São Francisco craton in eastern Brazil hosts sedimentary sequences deposited between the Paleo- Received 4 May 2010 archean (w3300 Ma) and Late Neoproterozoic (w580 Ma). Proterozoic successions occurring in this Received in revised form region comprise five 1st-order sedimentary sequences, which besides episodes of global significance 15 August 2011 record major basin-forming events. The ca. 8000 m-thick Minas-Itacolomi 1st-order sequence, exposed Accepted 18 August 2011 in the Brazilian mining district of the Quadrilátero Ferrífero and containing as marker bed the Lake Available online 5 September 2011 Superior-type Cauê Banded Iron Formation, tracks the operation of a Wilson cycle in the Paleoproterozoic Era. The quartz-arenite dominated Espinhaço I and II sequences record at least two major rift-sag basin- Keywords: First-order sequences forming events, which affected the host continent of the São Francisco craton at around 1.75 Ga and Proterozoic 1.57 Ga. The Macaúbas sequence and its correlatives in the extracratonic domains witness the individ- São Francisco craton ualization of a São Francisco-Congo plate in synchronicity with the break-up of Rodinia in the Cryogenian Brazil period.
    [Show full text]
  • 20170601173846853169.Pdf
    Gondwana Research 35 (2016) 40–58 Contents lists available at ScienceDirect Gondwana Research journal homepage: www.elsevier.com/locate/gr Geologic and geochemical insights into the formation of the Taiyangshan porphyry copper–molybdenum deposit, Western Qinling Orogenic Belt, China Kun-Feng Qiu a,b,⁎,RyanD.Taylorb,Yao-HuiSonga,c,Hao-ChengYua,d,Kai-RuiSonga,NanLia a State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China b U.S. Geological Survey, Box 25046, Mail Stop 973, Denver Federal Center, Denver, CO 80225-0046, USA c Airborne Survey and Remote Sensing Center of Nuclear Industry, Shijiazhuang 050000, China d The 7th Gold Detachment of Chinese Armed Police Force, Yantai 264004, China article info abstract Article history: Taiyangshan is a poorly studied copper–molybdenum deposit located in the Triassic Western Qinling collisional Received 24 January 2016 belt of northwest China. The intrusions exposed in the vicinity of the Taiyangshan deposit record episodic Received in revised form 24 March 2016 magmatism over 20–30 million years. Pre-mineralization quartz diorite porphyries, which host some of the de- Accepted 31 March 2016 posit, were emplaced at 226.6 ± 6.2 Ma. Syn-collisional monzonite and quartz monzonite porphyries, which also Available online 2 May 2016 host mineralization, were emplaced at 218.0 ± 6.1 Ma and 215.0 ± 5.8 Ma, respectively. Mineralization occurred Handling Editor: F. Pirajno during the transition from a syn-collisional to a post-collisional setting at ca. 208 Ma. A barren post- mineralization granite porphyry marked the end of post-collisional magmatism at 200.7 ± 5.1 Ma.
    [Show full text]
  • Ultrahigh-Pressure Metamorphic Rocks in the Dabie–Sulu Orogenic Belt: Compositional Inheritance and Metamorphic Modification
    Downloaded from http://sp.lyellcollection.org/ by guest on September 30, 2021 Ultrahigh-pressure metamorphic rocks in the Dabie–Sulu orogenic belt: compositional inheritance and metamorphic modification YONG-FEI ZHENG*, ZI-FU ZHAO & REN-XU CHEN CAS Key Laboratory of Crust–Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China Y.-F.Z., 0000-0003-0332-4871; R.-X.C., 0000-0003-1517-8373 *Correspondence: [email protected] Abstract: The Dabie–Sulu orogenic belt in east-central China contains one of the largest ultrahigh-pressure (UHP) metamorphic terranes in the world. The UHP eclogites are associated with gneiss, peridotite and marble. But all these rocks underwent in situ UHP metamorphism during the continental collision in the Triassic. Although fluid action is not significant during cold subduction, it becomes prominent during hot exhumation of UHP slices. Whereas the composition of UHP metamorphic rocks is primarily inherited from their protoliths, they were locally modified by partial melting to varying extents. The partial melting of UHP rocks is highly heterogeneous along the collisional orogen, and achieves a maximum during rifting orogeny at the post-colli- sional stage. This paper outlines the petrographical features and geochemical compositions of UHP metamor- phic rocks, and presents an overview of collisional modification and post-collisional reworking of the subducted continental crust. Further discussions are devoted to continental subduction tectonics, as well as to subduction style, subduction polarity and exhumation mechanism. The results also provide insights into the initiation of continental rifting in a Wilson cycle.
    [Show full text]
  • Large Evaporite Provinces: Geothermal Rather Than Solar Origin?
    Large Evaporite Provinces: Geothermal rather than Solar Origin? Zhanjie Qin Chinese Academy of Sciences Chunan Tang ( [email protected] ) Dalian University of Technology Xiying Zhang Chinese Academy of Sciences Tiantian Chen Northeastern University Xiangjun Liu Northwest Normal University Yongshou Li Chinese Academy of Sciences Zhen Chen Sun Yat-Sen University Lianting Jiang South China Sea Institute of Oceanology, Chinese Academy of Sciences Article Keywords: Large evaporite provinces (LEPs), evaporites, salt deposits, evaporitic basins Posted Date: October 8th, 2020 DOI: https://doi.org/10.21203/rs.3.rs-80284/v2 License: This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License Large Evaporite Provinces: Geothermal rather than Solar Origin? Z.J. Qin1,2, C.A. Tang3,4*, T.T. Chen5, X.J. Liu6, Y.S. Li1,2, Z. Chen7, L.T. Jiang8, X.Y. Zhang1,2 1Key Laboratory of Comprehensive and Highly Efficient Utilization of Salt Lake Resources, Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008, China 2Qinghai Provincial Key Laboratory of Geology and Environment of Salt Lakes, Xining 810008, China 3 State Key Laboratory of Coastal & Offshore Engineering, Dalian University of Technology, Dalian 116024, China 4 State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences (Wuhan) 430074, China 5School of Resources and Civil Engineering, Northeastern University, Shenyang 110819, China 6College of Geography and Environmental Science, Northwest Normal University, Lanzhou 730070, China 7School of Earth Sciences and Geological Engineering, Sun Yat-sen University, Guangzhou 510275, China 8Key Laboratory of Ocean and Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China *Correspondence to: [email protected] Large evaporite provinces (LEPs) represent prodigious volumes of evaporites widely developed from the Sinian to Neogene.
    [Show full text]
  • A Decade of Plate Tectonics
    478 Nature Vol. 279 7 June, 1979 search could reveal information on versity of Oxford) was consistent with A decade of variations in intensity of the field m this interpretation. Moorbath argued plate tectonics space and time, which can del,imit strongly that isotopic data pointed to changes in the strength of the dipole continental ,growth by irreversible dif­ from A. Hallam and non-dipole field components with ferentiation of the upper mantle J. Tuzo WILSON is widely acknowledged time. throughout geologica,I time, rather as one of the founding fathers of the Seismological data originally pro­ than by reworking and regeneration .-,f new global tectonics. Because he has vided strong evidence for the delimita­ much older crust. Intriguingly enough, been successively Professor of Geophy­ tion and character of plate boundaries, Tuzo Wi.lson was once most widely sics and Principal of Erindale College and attention is now being directed known for his notiion of continental in tJhe University of Toronto, before more to seismicity within plates. L. R. accretion, albeit at a tune when he was taking up his present position of Direc­ Sykes (Lamont-Doherty Geological a staunch opponent of continental tor of the Ontario Science Centre, it is Observatory, New York) indicated drift. appropriate that the university recently that intraplate earthquakes tend to Other aspects of subduction were held a conference* to honour his multi­ be ,concentrated along ,pre-existing dealt with by W. S. Fyfe (University farious contributions to earth science. zones of weakness affected by the of Western Onta11io), who argued for Although various topics were discussed, youngest orogeny that predates the substantial subduction of sediments, a including the early thermal history of opening of the present oceans.
    [Show full text]
  • Back to the Future II: Tidal Evolution of Four Supercontinent Scenarios
    Earth Syst. Dynam., 11, 291–299, 2020 https://doi.org/10.5194/esd-11-291-2020 © Author(s) 2020. This work is distributed under the Creative Commons Attribution 4.0 License. Back to the future II: tidal evolution of four supercontinent scenarios Hannah S. Davies1,2, J. A. Mattias Green3, and Joao C. Duarte1,2,4 1Instituto Dom Luiz (IDL), Faculdade de Ciências, Universidade de Lisboa, Campo Grande, 1749-016, Lisbon, Portugal 2Departamento de Geologia, Faculdade de Ciências, Universidade de Lisboa, Campo Grande, 1749-016, Lisbon, Portugal 3School of Ocean Sciences, Bangor University, Askew St, Menai Bridge LL59 5AB, UK 4School of Earth, Atmosphere and Environment, Monash University, Melbourne, VIC 3800, Australia Correspondence: Hannah S. Davies ([email protected]) Received: 7 October 2019 – Discussion started: 25 October 2019 Revised: 3 February 2020 – Accepted: 8 February 2020 – Published: 20 March 2020 Abstract. The Earth is currently 180 Myr into a supercontinent cycle that began with the break-up of Pangaea and which will end around 200–250 Myr (million years) in the future, as the next supercontinent forms. As the continents move around the planet they change the geometry of ocean basins, and thereby modify their resonant properties. In doing so, oceans move through tidal resonance, causing the global tides to be profoundly affected. Here, we use a dedicated and established global tidal model to simulate the evolution of tides during four future supercontinent scenarios. We show that the number of tidal resonances on Earth varies between one and five in a supercontinent cycle and that they last for no longer than 20 Myr.
    [Show full text]
  • Wilson Cycle Studies Nasa Grant Nag5-585
    WILSON CYCLE STUDIES NASA GRANT NAG5-585 Semi -Annual Report July 15, 1986 - January 15, 1987 Activity concentrated on the study of regional 1 ineaments in continental evolution and an extended abstract (Appendix 1 attached) was prepared that will be presented at a forthcoming US-India workshop on continental 1 ineaments to be held in Bangalore in April 1987 (attendance is at no cost to the project). (6ASB-CH-180353) WILSCN CYClE SPUDIES ~a1-15a24 Semiannual Regort, 15 Jul. 19E6 - 15 Jan. 1587 (Houston Univ.) 7 F CSCL OBG Unclas 63/46 43555 . REGIONAL LINEAMENTS AND CONTINENTAL EVOLUTION Kevin Burke, Lunar and Planetary Institute, 3303 Nasa Road I, Houston, TX 77058 and Department of Geosciences, University of Houston, Houston, TX 77001 rnd Cel:l Sen&, Lunar Planetary Institute and Istanbul Technical University. 1. SUMMARY Lineaments within continents are attributable to a small number of processes of conti- nent formation and modification, but interactions among these processes may produce complex patterns. 2. FORMATlON AND MODIFICATION OF THE CONTINENTAL CRUST Continents originate by the sweeping together of island arcs (Burke and SengEr, 1986). Continental and island arc crusts are dominated by rocks of comparable compositional and density ranges (SOz 50-7096; 2.6-2.9 gm/cc), evidence of the operation of this process is abundant in the geological record, and can be seen in action today in Indonesia. Misgivings have been voiced about the simple idea of assembling continents by colliding arcs, because some arcs do not closely resemble average continental material and because much continental material is very old (> 2.5 Ga) and the world is likely to have operated in a different way in the remote past.
    [Show full text]
  • Supercontinent Cycle and Thermochemical Structure in the Mantle: Inference from Two-Dimensional Numerical Simulations of Mantle Convection
    geosciences Article Supercontinent Cycle and Thermochemical Structure in the Mantle: Inference from Two-Dimensional Numerical Simulations of Mantle Convection Masanori Kameyama * ID and Akari Harada Geodynamics Research Center, Ehime University, 2–5 Bunkyo-cho, Matsuyama 790-8577, Ehime, Japan; [email protected] * Correspondence: [email protected] Received: 27 September 2017; Accepted: 30 November 2017; Published: 5 December 2017 Abstract: In this study, we conduct numerical simulations of thermochemical mantle convection in a 2D spherical annulus with a highly viscous lid drifting along the top surface, in order to investigate the interrelation between the motion of the surface (super)continent and the behavior of chemical heterogeneities imposed in the lowermost mantle. Our calculations show that assembly and dispersal of supercontinents occur in a cyclic manner when a sufficient amount of chemically-distinct dense material resides in the base of the mantle against the convective mixing. The motion of surface continents is significantly driven by strong ascending plumes originating around the dense materials in the lowermost mantle. The hot dense materials horizontally move in response to the motion of continents at the top surface, which in turn horizontally move the ascending plumes leading to the breakup of newly-formed supercontinents. We also found that the motion of dense materials in the base of the mantle is driven toward the region beneath a newly-formed supercontinent largely by the horizontal flow induced by cold descending flows from the top surface occurring away from the (super)continent. Our findings imply that the dynamic behavior of cold descending plumes is the key to the understanding of the relationship between the supercontinent cycle on the Earth’s surface and the thermochemical structures in the lowermost mantle, through modulating not only the positions of chemically-dense materials, but also the occurrence of ascending plumes around them.
    [Show full text]
  • Supercontinent Reconstruction the Palaeomagnetically Viable, Long
    Geological Society, London, Special Publications The palaeomagnetically viable, long-lived and all-inclusive Rodinia supercontinent reconstruction David A. D. Evans Geological Society, London, Special Publications 2009; v. 327; p. 371-404 doi:10.1144/SP327.16 Email alerting click here to receive free email alerts when new articles cite this service article Permission click here to seek permission to re-use all or part of this article request Subscribe click here to subscribe to Geological Society, London, Special Publications or the Lyell Collection Notes Downloaded by on 21 December 2009 © 2009 Geological Society of London The palaeomagnetically viable, long-lived and all-inclusive Rodinia supercontinent reconstruction DAVID A. D. EVANS Department of Geology & Geophysics, Yale University, New Haven, CT 06520-8109, USA (e-mail: [email protected]) Abstract: Palaeomagnetic apparent polar wander (APW) paths from the world’s cratons at 1300–700 Ma can constrain the palaeogeographic possibilities for a long-lived and all-inclusive Rodinia supercontinent. Laurentia’s APW path is the most complete and forms the basis for super- position by other cratons’ APW paths to identify possible durations of those cratons’ inclusion in Rodinia, and also to generate reconstructions that are constrained both in latitude and longitude relative to Laurentia. Baltica reconstructs adjacent to the SE margin of Greenland, in a standard and geographically ‘upright’ position, between c. 1050 and 600 Ma. Australia reconstructs adja- cent to the pre-Caspian margin of Baltica, geographically ‘inverted’ such that cratonic portions of Queensland are juxtaposed with that margin via collision at c. 1100 Ma. Arctic North America reconstructs opposite to the CONgo þ Sa˜o Francisco craton at its DAmaride–Lufilian margin (the ‘ANACONDA’ fit) throughout the interval 1235–755 Ma according to palaeomag- netic poles of those ages from both cratons, and the reconstruction was probably established during the c.
    [Show full text]