DOCSLIB.ORG

The Evolution of the Island Arc of Japan and the Formation of Granites in the Circum-Pacific Belt

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
The Evolution of the Island Arc of Japan and the Formation of Granites in the Circum-Pacific Belt JOURNALOF GEOMAGNETISMAND GEOELECTRICITY VOL. 23, No. 3, 4, 1971 The Evolution of the Island Arc of Japan and the Formation of Granites in the Circum-Pacific Belt Naoto KAWAI, Tadashi NAKAJIMA and Kimio HIROOKa+ Department of Material Physics, Faculty of Engineering Science, Osaka University, Osaka, Japan (Received April 27, 1971) Abstract From a palaeomagnetic study and radiometric investigation of Cretaceous intrusive rocks it was recently suggested that the Palaeozoic basin formed in the northeastern Japan was severely deformed at the end of Mesozoic era. This resulted in a narrowing and shortening of the entire length of the Japanese islands. The northeastern block moved southwestward by approximately 200km and southwestern northeastward by 150km, whereas the middle block remained relative- ly unmoved but was compressed between the two blocks. As the compressional forces increased, first the Palaeozoic sediments of the central block were uplifted, and subsequently the "median line" was formed. Along the latter line, the northern half of the southern block moved eastward relative to the southern half. A strong uniaxial stress superimposed upon a hydrostatic one oc- curred associated with the relative movement. The sediments as the results recrystallized to form the three major metamorphic belts. During and after these movements, the compressed zone in the middle of the island was push- ed to the east to form a great warp in the island. Such a simple model of a bend accompanied by a tension crack as predicted by Kawai, Ito and Kume several years ago was reconsidered. The contraction of the basin was finally related to the eastward drift of Asian continent upon the Creta- ceous Pacific sea floor. The drift of the continents around the Pacific resulted in the narrowing of the ocean as well as the shortening of the coastal line. That of the Japanese islands is a part of the shortening that occurred around the Pacific zone. We suggest that the heat of friction was accumulated at the deep-seismic plane (Benioff zone) at which the down and west going ocean floor and the up-thrusting mantle have been conflicting. The mantle nearby the deep-seismic plane was, therefore, warmed up until it partially melted. An acidic and migmatitic magma initiated at the friction interface was intruded into the pre-exist- ing fracture zone occupying the front. Production of frictional heat was, we believe, succeeded even in the Tertiary period when effective drift was no longer evident but the retardation of the motion of the continent was much stronger. Heat required to cause the Tertiary volcanic activity might be due to this friction. 1. Palaeomagnetic Results and Radiometric Dating of Igneous Rocks Sedimentary and igneous rocks ranging in age from Triassic to the Recent were collected from various localities in Japan. The directions of natural remanent magnet- ism of these rocks were measured. The results obtained show that the directions found + Present Address: Faculty of Education , Fukui University 267 268 N. KAWAI, T. NAKAJIMA and K. HIROOKA were nearly parallel or antiparallel in the late Tertiary rocks regardless of the localities from which the rock specimens were collected, although there exist local differences in the direction of the remanent magnetism in pre-Tertiary rocks. Rocks from the northeastern Japan are all found to have northwesterly directions. In contrast those from the southwestern Japan have northeasterly directions. In order to reconcile the discrepancy, Kawai et al. (1961) proposed an occurrence of a land mass motion with which it is possible to bend a comparatively straight pre- Cretaceous land to form the present bow-shaped island arc. They assumed an anti- clockwise rotation of the northern Japan by about 50° relative to the southern Japan. This great bend was estimated to have been made at the end of Mesozoic era. Recently an extensive survey was carried out with the aim of determining the geo- logical age of a number of igneous rocks intruded during the time of the deformation. Thus, it became possible not only to know when the bending was initiated and came to the end but also to clarify the relation between the plastic deformation and the igneous activity. Granites and granodiorites whose ages were already determined by Kawano and Ueda (1964, 1966) were collected from the northeastern Japan. After AC. and thermal cleaning the remanent magnetism was measured under an astatic magnetometer. In Table 1 are tabulated the results of the measurements, localities from which the rocks were collected, and the geologic ages determined. In Fig. 1 are shown the dis- tribution of magnetic declinations and the localities of the collected rocks. The intrusive rocks in the northeastern Japan, according to the K-Ar dating of Kawano's results (1967), can be classified into the following three major groups; KITAKAMI MASSIF of the ages ranging from 120m.y. to 110m.y., ABUKUMA MASSIF of the ages ranging from 100m.y. to 90m.y. and ASAHI-TIDE MASSIF of the ages ranging from 70m.y. to 55m.y. The granitic rocks of Kitakami Massif were collected from the following localities, Sugo, Akabane, Ochiai, Hosozawa, Hitokabe, Senmaya, Tono, Yoshihama and Otomo in Iwate Pref. and also from Kinkazan in Miyagi Pref. The rocks of Abukuma Massif were collected from Abukuma, Shiobite, Tsushima and Hirusone in Fukushima Pref. On the other hand the rocks of Asahi-Tide Massif were collected from Nogawa Dam, Yakuwa Dam, Suganodai, Sekigawa and Ootorigawa in Yamagata Pref., respectively. In the Kitakami Massif, the oldest rock (121m.y.) has the most westerly declination of 61°W, and the youngest (106m.y.) has declination of 35°W. In Abukuma Massif, declinations of the oldest (101m.y.) and youngest (92 m.y.) rocks are 33°W and 7°E, respectively. In the above two districtss the rocks having intermediate age have intermediate declination as shown in the Schmidt's equal area projection (Fig. 2). On the other hand, Asahi-Tide intrusive rocks have almost easterly declinations. In Figs. 3 and 4 are shown the changes of magnetic declinations and incli- nations, respectively, with geologic age in the northeastern Japan. In Fig. 3, it can be seen that the change of declination occurred twice, once in a range extending from 120 to 115m.y. and then in a range from 100 to 85m.y. The Evolution of the Island Arc of Japan and the Formation of Granites in the Circum-Pacific Belt 269 Fig. 1 Directions of remanent magnetization of Cretaceous rocks in Japan A detailed palaeomagnetic research of the southwestern Japan had already been carried out by Kawai et al. (1961) and also followed by Sasajima et al. (1966, 1968). The results are summarized in Table 2. The localities from which the rocks were collected are all in the regions west of the geotectonic structure, the "Fossa Magna", and north of the "median line" as shown in Figs. 1 and 8. In Figs. 5 and 6 are shown the changes of declination and inclination, respectively, with geologic time in the southwestern Japan. As shown in Fig. 5, no abrupt change of declination occurred in the southwestern Japan. The declination decreased gradually from 60°E to 40°E in a range from the Cretaceous to the Paleogene, and this gradual change has continued to the present. It seems 270 N. KAWAI, T. NAKAJIMA and K. HIROOKA Fig. 2 Direction of N.R.M. of granitic rocks from the northeastern Japan (plotted on a Schmidt's equal area projection) AM, SB, YM, etc, are the abbreviations of the localities of the sampling sites tabulated in Table 1, and the numbers annexed to them in the brackets are the determined ages in million years. Fig. 3 Change in declination of N.R.M, with geologic time in the northeastern Japan. The Evolution of the Island Acr of Japan and the Formation of Granites in the Circum-Pacific Belt 271 Fig. 4 Change in inclination of N.R.M, with geologic time in the northeastern Japan Fig. 5 Change in declination of N.R.M, with geologic time in the southwestern Japan (Sasajima et al. 1966 and 1968) 272 N. KAWAI, T. NAKAJIMA and K. HIROOKA Fig. 6 Change in inclination of N.R.M, with geologic time in the southwestern Japan (Sasajima et al. 1966 and 1968) Fig. 7 Change in declination in Japan (summarized from Fig. 3 and Fig. 5) The Evolution of the Island Arc of Japan and the Formation of Granites in the Circum-Pacific Belt 273 reasonable to consider that this continuous curve is the result of the so-called "polar wan- dering". In Fig. 7 are summarized the changes of declination in both the northeastern and southwestern Japan. Mean declinations of the remanent vectors in Kitakami district differ by 85° and that in Abukuma district differ by 50° from the mean declination of the southwestern Japan. On the other hand, the mean declination of the rocks in Asahi- Iide does not show a large difference from the southwestern Japan. In contrast to the remarkable differences in declination in the above-mentioned districts, one cannot find any large difference in the inclination of the magnetic vectors over the entire island as shown in Figs. 4 and 6. In order to explain the facts mentioned above the present authors (1969) proposed an occurrence of an extreme plastic deformation in which are involved not only a great bend in the middle of the island but also other subsidiary bends at other places. At the present stage of our study in which the sequence of the Cretaceous intrusion was well clarified by means of radiometric age determination, it is possible to discuss the land mass deformation much more in detail as will be shown in the following para- graphs.
Load more

Recommended publications
  • Kinematic Reconstruction of the Caribbean Region Since the Early Jurassic
    Earth-Science Reviews 138 (2014) 102–136 Contents lists available at ScienceDirect Earth-Science Reviews journal homepage: www.elsevier.com/locate/earscirev Kinematic reconstruction of the Caribbean region since the Early Jurassic Lydian M. Boschman a,⁎, Douwe J.J. van Hinsbergen a, Trond H. Torsvik b,c,d, Wim Spakman a,b, James L. Pindell e,f a Department of Earth Sciences, Utrecht University, Budapestlaan 4, 3584 CD Utrecht, The Netherlands b Center for Earth Evolution and Dynamics (CEED), University of Oslo, Sem Sælands vei 24, NO-0316 Oslo, Norway c Center for Geodynamics, Geological Survey of Norway (NGU), Leiv Eirikssons vei 39, 7491 Trondheim, Norway d School of Geosciences, University of the Witwatersrand, WITS 2050 Johannesburg, South Africa e Tectonic Analysis Ltd., Chestnut House, Duncton, West Sussex, GU28 OLH, England, UK f School of Earth and Ocean Sciences, Cardiff University, Park Place, Cardiff CF10 3YE, UK article info abstract Article history: The Caribbean oceanic crust was formed west of the North and South American continents, probably from Late Received 4 December 2013 Jurassic through Early Cretaceous time. Its subsequent evolution has resulted from a complex tectonic history Accepted 9 August 2014 governed by the interplay of the North American, South American and (Paleo-)Pacific plates. During its entire Available online 23 August 2014 tectonic evolution, the Caribbean plate was largely surrounded by subduction and transform boundaries, and the oceanic crust has been overlain by the Caribbean Large Igneous Province (CLIP) since ~90 Ma. The consequent Keywords: absence of passive margins and measurable marine magnetic anomalies hampers a quantitative integration into GPlates Apparent Polar Wander Path the global circuit of plate motions.
    [Show full text]
  • A Dangling Slab, Amplified Arc Volcanism, Mantle Flow and Seismic Anisotropy in the Kamchatka Plate Corner
    AGU Geodynamics Series Volume 30, PLATE BOUNDARY ZONES Edited by Seth Stein and Jeffrey T. Freymueller, p. 295-324 1 A Dangling Slab, Amplified Arc Volcanism, Mantle Flow and Seismic Anisotropy in the Kamchatka Plate Corner Jeffrey Park,1 Yadim Levin,1 Mark Brandon,1 Jonathan Lees,2 Valerie Peyton,3 Evgenii Gordeev ) 4 Alexei Ozerov ,4 Book chapter in press with "Plate Boundary Zones," edited by Seth Stein and Jeffrey Freymuller Abstract The Kamchatka peninsula in Russian East Asia lies at the junction of a transcurrent plate boundary, aligned with the western Aleutian Islands, and a steeply-dipping subduction zone with near-normal convergence. Seismicity patterns and P-wave tomography argue that subducting Pacific lithosphere terminates at the Aleutian junction, and that the downdip extension (>150km depth) of the slab edge is missing. Seismic observables of elastic anisotropy (SKS splitting and Love-Rayleigh scattering) are consistent \Vith asthenospheric strain that rotates from trench-parallel beneath the descending slab to trench-normal beyond its edge. Present-day arc volcanism is concentrated near the slab edge, in the Klyuchevskoy and Sheveluch eruptive centers. Loss of the downdip slab edge, whether from thermo-convective or ductile instability, and subsequent "slab-window" mantle return flow is indicated by widespread Quaternary volcanism in the Sredinny Range inland of Klyuchevskoy and Sheveluch, as well as the inferred Quaternary uplift of the central Kamchatka depression. The slab beneath Klyuchevskoy has shallower dip (35°) than the subduction zone farther south (55°) suggesting a transient lofting of the slab edge, either from asthenospheric flow or the loss of downdip load.
    [Show full text]
  • Arc Dacite Genesis Pathways: Evidence from Mafic Enclaves and Their Hosts in Aegean Lavas ⁎ G.F
    Lithos 95 (2007) 346–362 www.elsevier.com/locate/lithos Arc dacite genesis pathways: Evidence from mafic enclaves and their hosts in Aegean lavas ⁎ G.F. Zellmer a,b, , S.P. Turner c a Institute of Earth Sciences, Academia Sinica, 128 Academia Road, Section 2, Nankang, Taipei 11529, Taiwan, ROC b Lamont-Doherty Earth Observatory, 61 Route 9W, Palisades, New York 10964, USA c GEMOC, Department of Earth and Planetary Sciences, Macquarie University, Sydney, NSW 2109, Australia Received 4 January 2006; accepted 17 August 2006 Available online 25 September 2006 Abstract Mafic enclaves are commonly found in intermediate arc magmas, and their occurrence has been linked to eruption triggering by pre-eruptive magma mixing processes. New major, trace, Sr–Nd and U–Th isotope data of rocks from Nisyros in the Aegean volcanic arc are presented here. Pre-caldera samples display major and trace element trends that are consistent with fractionation of magnetite and apatite within intermediate compositions, and zircon within felsic compositions, and preclude extensive hybrid- ization between mafic and felsic magmas. In contrast, post-caldera dacites form a mixing trend towards their mafic enclaves. In terms of U-series isotopes, most samples show small 238U excesses of up to ∼10%. Mafic enclaves have significantly higher U/Th ratios than their dacitic host lavas, precluding simple models that relate the mafic and felsic magmas by fractionation or aging alone. A more complicated petrogenetic scenario is required. The post-caldera dacites are interpreted to represent material remobilized from a young igneous protolith following influx of fresh mafic magma, consistent with the U–Th data and with Sr–Nd isotope constraints that point to very limited (b10%) assimilation of old crust at Nisyros.
    [Show full text]
  • Exploring Submarine Arc Volcanoes Steven Carey University of Rhode Island, [email protected]
    University of Rhode Island DigitalCommons@URI Graduate School of Oceanography Faculty Graduate School of Oceanography Publications 2007 Exploring Submarine Arc Volcanoes Steven Carey University of Rhode Island, [email protected] Haraldur Sigurdsson University of Rhode Island Follow this and additional works at: https://digitalcommons.uri.edu/gsofacpubs Terms of Use All rights reserved under copyright. Citation/Publisher Attribution Carey, S., and H. Sigurdsson. 2007. Exploring submarine arc volcanoes. Oceanography 20(4):80–89, https://doi.org/10.5670/ oceanog.2007.08. Available at: https://doi.org/10.5670/oceanog.2007.08 This Article is brought to you for free and open access by the Graduate School of Oceanography at DigitalCommons@URI. It has been accepted for inclusion in Graduate School of Oceanography Faculty Publications by an authorized administrator of DigitalCommons@URI. For more information, please contact [email protected]. This article has This been published in or collective redistirbution of any portion of this article by photocopy machine, reposting, or other means is permitted only with the approval of The approval portionthe ofwith any permitted articleonly photocopy by is of machine, reposting, this means or collective or other redistirbution SP ec I A L Iss U E On Ocean E X P L O R ATIO N Oceanography , Volume 20, Number 4, a quarterly journal of The 20, Number 4, a quarterly , Volume O ceanography Society. Copyright 2007 by The 2007 by Copyright Society. ceanography Exploring O ceanography Society. All rights All reserved. Society. ceanography O Submarine Arc Volcanoes or Th e [email protected] Send Society. ceanography to: correspondence all B Y S T even C A R E Y an D H A R A LDUR SIGURD ss O N Three quarters of Earth’s volcanic activ- although a significant part of arc volca- tion of tsunamis (Latter, 1981).
    [Show full text]
  • Viscous Volcanos 2016 Grades 6-8 (Earth Science)
    2016 Deepwater Exploration of the Marianas Viscous Volcanoes Focus Serpentine mud volcanoes Grade Level 6-8 (Earth Science) Focus Question What are serpentine mud volcanoes and how are they different from magma volcanoes? Learning Objectives • Students will describe mud volcanoes, contrast them with magma volcanoes, and explain how these structures, the Mariana Islands, and the Mariana Trench are related to the motion of tectonic plates. Materials For each serpentine mud volcano model: q Plastic tubing, approximately 1/4” outer diameter, 1/8” inside diameter q 2-liter plastic soda bottle q Fast-setting epoxy glue q Air-cure modeling clay, approximately 500 ml q Fine sand, table salt, or finely ground coffee q Drill and drill bit to match outside diameter of plastic tubing For each sediment-derived mud volcano model: q 2-liter plastic soda bottle q Cardboard or acrylic disk, diameter slightly smaller than soda bottle diameter q Fine sand or clay q Drill and drill bits, 3/8” and 1/2” For each magma volcano model: q Modeling materials, depending upon techniques chosen (see Learning Procedure, Step 1d and Step 4. Image captions/credits on Page 2. Audio-Visual Materials q (Optional) Interactive whiteboard Teaching Time If you need assistance with this document, please contact NOAA 1 Two or three 45-minute class periods Fisheries at (808) 725-5000. www.oceanexplorer.noaa.gov Viscous Volcanos 2016 Grades 6-8 (Earth Science) Seating Arrangement Groups of two to four students Maximum Number of Students 30 Key Words Mariana Arc Serpentine Mud volcano Mariana Trench Magma volcano Tectonic plate Images from Page 1 top to bottom: This Google Earth map shows the operating area of the 2016 Deepwater Background Information Exploration of the Marianas Expedition.
    [Show full text]
  • 53. Petrologic Evolution of the Mariana Arc and Back-Arc Basin System— a Synthesis of Drilling Results in the South Philippine Sea1
    53. PETROLOGIC EVOLUTION OF THE MARIANA ARC AND BACK-ARC BASIN SYSTEM— A SYNTHESIS OF DRILLING RESULTS IN THE SOUTH PHILIPPINE SEA1 James H. Natland, Deep Sea Drilling Project, Scripps Institution of Oceanography, La Jolla, California and John Tarney, Department of Geology, University of Leicester, LEI 7RH, United Kingdom ABSTRACT The results of Deep Sea Drilling Project Leg 60 pertaining to the petrologic evolution of the Mariana Trough and Mariana arc are summarized in Part I. The rocks recovered at five principal sites are exceptionally diverse, including gabbros and calc-alkalic andesites derived from the West Mariana Ridge; fresh and hydrothermally altered basalts in the Mariana Trough; and interbedded boninites and arc tholeiites in the forearc region between the modern arc and the trench. Part I outlines the stratigraphy, alteration, and petrology of these rock suites and summarizes hypotheses on their origin. Part II integrates these results with those of previous DSDP legs in the region, and with island sampling, to present a composite 40-m.y. history of the Mariana arc system. Arc volcanism began in the Eocene, probably as a result of a change to the west in the motion of the Pacific plate. A north-south-trending fracture zone was transformed into a trench-subduction complex, trapping a portion of the Pacific plate in the Philippine Sea. The crust of this basin, drilled in Hole 447 (Leg 59), has the composition of typical ocean floor basalt. The earliest Eocene arc was built up dominantly of arc tholeiite and boninitic lavas, with lesser calc-alkalic lavas, based on the results of Leg 60 drilling at Sites 458 and 459 in the forearc region; Leg 59, Site 448, on the Palau-Kyushu Ridge; and exposures on the islands of Palau, Guam, and Saipan.
    [Show full text]
  • Inherited Zircons Reveal a Gondwana Continental Fragment Beneath East Java, Indonesia ⁎ H.R
    Earth and Planetary Science Letters 258 (2007) 269–282 www.elsevier.com/locate/epsl The deep crust beneath island arcs: Inherited zircons reveal a Gondwana continental fragment beneath East Java, Indonesia ⁎ H.R. Smyth a, , P.J. Hamilton b, R. Hall a, P.D. Kinny b a SE Asia Research Group, Royal Holloway University of London, Egham, Surrey TW200EX, UK b Department of Applied Geology, Curtin University of Technology, Perth 6845, Australia Received 21 November 2006; received in revised form 21 March 2007; accepted 21 March 2007 Available online 1 April 2007 Editor: R.W. Carlson Abstract Inherited zircons in Cenozoic sedimentary and igneous rocks of East Java range in age from Archean to Cenozoic. The distribution of zircons reveals two different basement types at depth. The igneous rocks of the Early Cenozoic arc, found along the southeast coast, contain only Archean to Cambrian zircons. In contrast, clastic rocks of north and west of East Java contain Cretaceous zircons, which are not found in the arc rocks to the south. The presence of Cretaceous zircons supports previous interpretations that much of East Java is underlain by arc and ophiolitic rocks, accreted to the Southeast Asian margin during Cretaceous subduction. However, such accreted material cannot account for the older zircons. The age populations of Archean to Cambrian zircons in the arc rocks are similar to Gondwana crust. We interpret the East Java Early Cenozoic arc to be underlain by a continental fragment of Gondwana origin and not Cretaceous material as previously suggested. Melts rising through the crust, feeding the Early Cenozoic arc, picked up the ancient zircons through assimilation or partial melting.
    [Show full text]
  • Seismotectonic Modeling of the Repeating M 7-Class Disastrous Odawara Earthquake in the Izu Collision Zone, Central Japan
    Earth Planets Space, 56, 843–858, 2004 Seismotectonic modeling of the repeating M 7-class disastrous Odawara earthquake in the Izu collision zone, central Japan Katsuhiko Ishibashi Research Center for Urban Safety and Security/Department of Earth and Planetary Sciences, Kobe University, Kobe 657-8501, Japan (Received February 16, 2004; Revised July 15, 2004; Accepted July 21, 2004) Odawara City in central Japan, in the northernmost margin of the Philippine Sea (PHS) plate, suffered from severe earthquake disasters five times during the last 400 years with a mean repeat time of 73 years; in 1633, 1703, 1782, 1853 and 1923. In this region, non-volcanic Izu outer arc (IOA), the easternmost part of the PHS plate, has been subducted beneath Honshu (Japanese main island), and volcanic Izu inner arc (IIA) on the west of IOA has made multiple collision against Honshu. I hypothesize ‘West-Sagami-Bay Fracture’ (WSBF) beneath Odawara, a north-south striking tear fault within the PHS plate that has separated the descending IOA crust from the buoyant IIA crust, through examinations of multiple collision process and the PHS plate configuration. WSBF is considered a blind causative fault of the 1633, 1782 and 1853 M 7 Odawara earthquakes, and is inferred to have ruptured also during the 1703 and 1923 great Kanto earthquakes simultaneously with the interplate main fault. A presumable asperity on WSBF just beneath Odawara seems to control the temporal regularity of earthquake occurrence. Though WSBF has not yet been detected directly, it is considered an essential tectonic element in this region, which might be a fracture zone with a few or several kilometer thickness actually.
    [Show full text]
  • Aleutian Island Arc Magma Production Rates and Mechanisms
    https://doi.org/10.5194/se-2019-179 Preprint. Discussion started: 4 December 2019 c Author(s) 2019. CC BY 4.0 License. Aleutian island arc magma production rates and mechanisms Yongliang Bai1, Diya Zhang1, Dongdong Dong2, Shiguo Wu3, Zhenjie Wang1 1College of Ocean and Space Information, China University of Petroleum, Qingdao 266580, China 2Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 5 266071, China 3Institute of Deep-sea Science and Engineering, Chinese Academy of Sciences, Sanya 572000, China Correspondence to: Yongliang Bai ([email protected]) Abstract. The variation in island arc magma production rates and their influencing mechanisms are of great significance since island arc magma is considered a main source of continental crust growth. The island arc magma directly originates from the 10 molten mantle wedge, and the mantle melting is driven by fluids or melts from the subducted slab. Slab dehydration flux mainly depends on the slab thermal structures, and subducted slab melting requires a sufficiently high temperature. For the Aleutian subduction system, the subducted Pacific Plate has diverse thermal structures due to the existing fracture zones, ridges and slab window, so it is an ideal region for arc magma production rate research. However, the previous estimations are based on seismic profiles that only provide magma production rates at specific regions of the Aleutian arc, and these results are 15 controversial. Here, we design a magma production rate estimation method based on gravity inversion constrained by deep seismic profiles. The first overview map of magma production rates along the Aleutian arc strike demonstrates that the magma production rates have the same trend as the slab dips, and the peaks correspond to the subduction of the fracture zones and ridges.
    [Show full text]
  • Geodynamic Evolution of the Palaeozoic Gondwana Margin in Western Argentina (Famatina-System)
    Second ISAG, Oxford (UK),21-231911993 531 GEODYNAMIC EVOLUTION OF THE PALMOZOIC GONDWWA MARGIN IN WESTERN ARGENTINA (FAJVWTINA-SYSTEM) . Rolf Mannheim Jnstitut fiir Allgemeine und Angewandte Geologie Luisenstr. 37,80333 München 2, Germany Los caracteres geoquimicos de los basaltos ordovicicos del Sistema deFamatina (SF) son comparables a los de basaltos calcoalcalinos modernos de arcos de islas oceinicos. Observaciones sedimentoi6gicas prueban la existencia de una Cuenca de retroarco entre el arc0 voldnico (SF) al oeste y el craton (Sierras Pampeanas) al este en el Ordovicico (relacionado a coordenadas actuales). Durante la colision del arco con el continentese intruyeron granitoides anatécticos corticales en el SF (Orogénesis Famatiniana). Como indicadores de un estadio poscolisional aparecen leucogranitos peralcalinos (Devonico?). En el mismo ambiente geotecthico del SF se intruyeronbasaltos de subducci6n. Los caracteres geoquimicos de estos basaltos correspondena los de basaltos calcoalcalinos de un borde continental activo como delactual tipo Chile. KEY WORDS: Famatina-Systern, island arc - back arc, collision, nlagmatism INTRODUCTION The Famatina System 0's) representsa lithostrati- graphically and structurally independent unit within the NW-argentinian Sierras (fjg.1). It is characterized by Lower Middleto Ordovician volcanosedimentary scquences, which areintruded by calcalkaline granitoids of Upper Ordovician to Devonian age and by syn- to postplutonic volcanic dykes. Accordingto Aceiiolaza and Toselli (1954) andToselli etal. (1991) the xnagnlatic characteristics of the FS advocate for a destructiv plate margin. In the concept of Willner et al. (1957) and Rapela et al. (1990) the Ordovician wcstem Gondwana margin included a volcanic arc in the region of the FS and a several.hundred km largezone of intrusion situated in the back of the arc.
    [Show full text]
  • Andesite and Dacite Genesis Via Contrasting Processes: the Geology and Geochemistry of El Valle Volcano, Panama Marc J
    Contrib Mineral Petrol (1991) 106:309-324 Contributions to Mineralogy and Petrology Springer-Verlag 1991 Andesite and dacite genesis via contrasting processes: the geology and geochemistry of El Valle Volcano, Panama Marc J. Defant 1, Lee F. Clark i Robert H. Stewart t, Mark S. Drummond 2, Jelle Z. de Boer 3, Ren~ C. Maury 4, Herv~ Bellon 5, Thomas E. Jackson 1, and Juan F. Restrepo 1 1 Department of Geology,University of South Florida, Tampa, FL 33620, USA 2 Department of Geology,University of Alabama at Birmingham,Birmingham, AL 35294, USA 3 Department of Earth and EnvironmentalSciences, Wesleyan University,Middletown, CT 06457, USA 4 Laboratoire de P6trologie et UA 1278, Universit6 de Bretagne Occidentale, 29287 Brest, France 5 Laboratoire de G~ochimieet de G~ochronologieet UA 1278, Universit6 de Bretagne Occidentale, 29287 Brest, France Received November 29, 1989/Accepted July 6, 1990 Abstract. The easternmost stratovolcano along the Cen- geochemical characteristics of subducted-lithosphere tral American arc is E1 Valle volcano, Panama. Several melting is generated apparently only where relatively hot andesitic and dacitic lava flows, which range in age 5- crust is subducted, based on recent work. The young 10 Ma, are termed the old group. After a long period dacite-genesis at E1 Valle volcano is related to the sub- of quiescence (approximately 3.4 Ma), volcanic activity duction of relatively hot lithosphere. resumed approximately 1.55 Ma with the emplacement of dacitic domes and the deposition of dacitic pyroclastic flows 0.9-0.2 Ma. These are referred to as the young group. All of the samples analyzed are calc-alkaline an- desites and dacites.
    [Show full text]
  • Subduction Zones
    AccessScience from McGraw-Hill Education Page 1 of 11 www.accessscience.com Subduction zones Contributed by: R. J. Stern, S. H. Bloomer Publication year: 2019 Regions where portions of the Earth’s tectonic plates sink beneath other plates, into the Earth’s interior. Subduction zones are defined by deep oceanic trenches, lines of volcanoes parallel to the trenches and zones of large earthquakes that extend from the trenches landward. Plate tectonic theory recognizes that the Earth’s solid surface is composed of a mosaic of interacting lithospheric plates, with the lithosphere consisting of the crust (continental or oceanic) and associated underlying mantle, for a total thickness that varies with age but that is typically about 100 km (60 mi). Oceanic lithosphere is created by seafloor spreading at mid-ocean ridges (divergent, or accretionary, plate boundaries) and destroyed at subduction zones (at convergent, or destructive, plate boundaries). At subduction zones, the oceanic lithosphere dives beneath another plate, which may be either oceanic or continental. Part of the material on the subducted plate is recycled back to the surface (by being scraped off the subducting plate and accreted to the overriding plate, or by melting and rising as magma) and the remainder is mixed back into the Earth’s deeper mantle. This process balances the creation of lithosphere that occurs at the mid-ocean ridge system. The convergence of two plates occurs at rates of 1–10 cm∕yr (0.4–4 in.∕yr) or 10–100 km (6–60 mi) per million years (Fig. 1). During subduction, stress and phase changes in the upper part of the cold descending plate produce earthquakes in the upper portion of the plate, in a narrow band called the Wadati-Benioff zone (named after the Japanese and U.S.
    [Show full text]