DOCSLIB.ORG

3.16 Oceanic Plateaus A.C.Kerr Cardiffuniversity,Wales,UK

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
3.16 Oceanic Plateaus A.C.Kerr Cardiffuniversity,Wales,UK 3.16 Oceanic Plateaus A.C.Kerr CardiffUniversity,Wales,UK 3.16.1 INTRODUCTION 537 3.16.2 FORMATION OF OCEANIC PLATEAUS 539 3.16.3 PRESERVATIONOFOCEANIC PLATEAUS 540 3.16.4GEOCHEMISTRY OF CRETACEOUSOCEANICPLATEAUS 540 3.16.4.1 GeneralChemicalCharacteristics 540 3.16.4.2 MantlePlumeSource Regions ofOceanic Plateaus 541 3.16.4.3 Caribbean–ColombianOceanic Plateau(, 90 Ma) 544 3.16.4.4OntongJavaPlateau(, 122 and , 90 Ma) 548 3.16.5THE INFLUENCE OF CONTINENTALCRUST ON OCEANIC PLATEAUS 549 3.16.5.1 The NorthAtlantic Igneous Province ( , 60 Ma to Present Day) 549 3.16.5.2 The KerguelenIgneous Province ( , 133 Ma to Present Day) 550 3.16.6 IDENTIFICATION OF OCEANIC PLATEAUS IN THE GEOLOGICAL RECORD 551 3.16.6.1 Diagnostic FeaturesofOceanic Plateaus 552 3.16.6.2 Mafic Triassic Accreted Terranesinthe NorthAmericanCordillera 553 3.16.6.3 Carboniferous to CretaceousAccreted Oceanic Plateaus inJapan 554 3.16.7 PRECAMBRIAN OCEANICPLATEAUS 556 3.16.8ENVIRONMENTAL IMPACT OF OCEANICPLATEAU FORMATION557 3.16.8.1 Cenomanian–TuronianBoundary (CTB)Extinction Event 558 3.16.8.2 LinksbetweenCTB Oceanic PlateauVolcanism andEnvironmentalPerturbation 558 3.16.9 CONCLUDING STATEMENTS 560 REFERENCES 561 3.16.1 INTRODUCTION knowledge ofthe oceanbasins hasimproved over the last 25years,many moreoceanic plateaus Although the existence oflarge continentalflood havebeenidentified (Figure1).Coffinand basalt provinceshasbeenknownfor some Eldholm (1992) introduced the term “large igneous considerabletime, e.g.,Holmes(1918),the provinces” (LIPs) asageneric term encompassing recognition thatsimilarfloodbasalt provinces oceanic plateaus,continentalfloodbasalt alsoexist belowthe oceans isrelatively recent. In provinces,andthoseprovinceswhich form at the early 1970s increasingamounts ofevidence the continent–oceanboundary (volcanic rifted fromseismic reflection andrefraction studies margins). revealed thatthe crust inseverallarge portions of LIPsaregenerallybelieved to be formed by the oceanfloorissignificantly thickerthan decompression meltingofupwellinghottermantle, “normal” oceanic crust,which is6–7kmthick. knownasmantleplumes. Although ideasabout Oneofthe first areasofsuch over-thickened crust hotpots andmantleplumeshavebeenaroundfor to be identified wasthe Caribbeanplate(Edgar almost 40years (Wilson,1963),itisonly inthe etal.,1971)which Donnelly (1973) proposed to be past 15years thatLIPshavebecomethe focus of an“oceanic floodbasalt province”. Theterm major research.Oneofthe mainreasons for the oceanic plateauwascoined byKroenke (1974), increased research activity intoLIPsisthe andwasprompted bythe discovery ofalarge area realization thatsignificant proportions ofthese ofthickened crust(. 30 km) inthe western Pacific LIPserupted overarelatively short time, often known asthe OntongJavaplateau(OJP). Asour less than2–3Myr (see reviewinCoffin,1994). 537 538 Oceanic Plateaus Thishasimportant implications for mantlepro- Pacific, whileinthe IndianOceanthe Kerguelen cessesandsource regions (Hart etal.,1992; Stein plateauwasdeveloping.Theareas,volume andHofmann,1994),aswell asenvironmental maximum thicknessesandagesofthe largerof effects on the globalbiosphere(e.g.,Caldeiraand theseplateaus aregiveninTable1. TheOntong Rampino,1990; Courtillot etal.,1996; Kerr, Javaisthe largest ofthe Cretaceous plateaus. 1998). Oceanic plateaus canalsobecomeaccreted Itcovers anarea of1.9 106 km 2 ,andhasan to continentalmargins,andithasbeenproposed estimatedtotalvolum£ eof4.4 107 km 3 thattheseplateaus havebeensignificant contri- (EldholmandCoffin,2000). Althou£ gh early butors to the growthofcontinentalcrust (e.g., seismic refraction datasuggested thatthe OJP Abbott,1996; Albarede, 1998). wasasthick as43km(Furomoto etal .,1976),a The most recent major phaseofoceanic morerecent synthesisbased on existingseismic plateauformation wasinthe Cretaceous when andnewgravity data(Gladczenko etal.,1997) the OntongJava, Manihiki, Hess Rise, andthe hasindicated the averagethickness to Caribbean–Colombianplateaus formed inthe be , 32 km. Figure1 Mapshowingall major oceanic plateaus,andotherlarge igneous provincesdiscussed inthe text (afterSaunders etal.,1992). Table1 Agesanddimensions ofJurassic–Cretaceous oceanic plateaus. Oceanic plateauMeanage Area Thickness range Volume (Ma) (106 km 2 ) (km) (106 km 3 ) Hikurangi early-mid Cretaceous 0.7 10–152.7 ShatskyRise1470.2 10–282.5 MagellanRise145 0.510 1.8 Manihiki 123 0.8 . 20 8.8 OntongJava121(90) 1.9 15–32 44.4 Hess Rise99 0.8 . 159.1 Caribbean88 1.1 8–20 4.4 SouthKerguelen110 1.0 , 22 6.0 CentralKerguelen/BrokenRidge 861.0 19–21 9.1 SierraLeoneRise , 73 0.9 . 10 2.5 MaudRise , . 73 0.2 . 10 1.2 AfterEldholm andCoffin(2000). Formation ofOceanic Plateaus 539 3.16.2 FORMATION OF OCEANIC PLATEAUS The production oflarge volumes(. 106 km 3 ) ofmelt inaperiodasshort as2–3Myr implies magmaproduction ratesupto25%higherthan thoseobserved atpresent-daymidoceanridges (Eldholm andCoffin,2000),andisgenerally believed to necessitateahigh flux ofhotter-than- ambient asthenospheric mantlebelowthese provinces(e.g.,McKenzie andBickle, 1988). Numericalandphysicalmodels show thatthis hottermantlecommonly takesthe form ofa mantleplumewhich ascendsbythermalbuoy- ancythrough the overlyingmantle(Loper,1983; McKenzie andBickle, 1988;Campbell etal., 1989; FarnetaniandRichards,1995). Physical constraints demandthatmantleplumesmust ascendfrom aboundary layerwithinthe Earth, eitherthe core–mantleboundary ( D 00)orthe 670 kmdiscontinuity. Large ascendingmantle plumesare, on average, 200 8 Chotterthanthe ambient uppermantle(McKenzie andBickle, 1988)andundergodecompression meltingas theyapproachthe baseofthe lithosphere. PhysicalmodelingexperimentsbyGriffithsand Campbell (1990) haveshown thatmantleplumes arelikely to ascendthrough the mantlefrom their source boundary layerinthe form ofalarge semi-spherical“head”fed from the source region Figure2 Cartoon to illustratehow mantleplumesare byanarrowerplumetail(Figure2). Alterna- believed to (a)risethrough the asthenospherefrom either tively,numericalmodelingbyFarnetaniand the 670 kmdiscontinuity or D 00 and(b)flattenalongthe Richards(1995)suggested thatplumeheads baseofthe lithosphereandundergodecompression startinginthe mantleonly riseabout three meltingto produce aLIP (afterSaunders etal.,1992). plumehead diameters beforespreadingout. In eithercase, asthe plumeapproachesthe baseof the lithosphere, itspreadsout overabroadly circulararea (whichcanbe asmuch as1000 km indiameter) andundergoesadiabatic decompres- sion,producingmelt overmostofthe area covered bythe flattened-out plumehead (Campbell andGriffiths,1990). Theamount of melt producediscritically dependent on the thickness ofthe preexistinglithosphere, since the baseofthe rigid, nonconvectinglithospherewill actasa“lid”onthe upwellingplumemantleand on the extent ofdecompression melting.Thus,a mantleplumeascendingbelow thick continental lithosphere( . 50km) will produce asmaller thickness ofmelt thanaplumewhich ascends Figure3 Schematic diagramshowinghow original beneathoceanic lithosphere( # 7km) (Figure3). lithospheric thickness andmantlepotentialtemperature Anothersignificant factor indeterminingthe affectthe amount ofmelt produced (melt thickness) and amount ofmelt generated byamantleplumeis how thesefactors relateto continentalfloodbasalts the temperatureofthe plume: generallythe (CFB),volcanic rifted margins (VRM),off –ridge and higherthe temperature, the moremelt will be ridge–centered oceanic plateaus (OP),andmidocean produced(Figure3). ridges(MOR). Theinitial 40 Ar/39Arstep-heatingagesfor LIPs supportmodels ofrapid formation anderuption, Caribbeanplateau,95–86Ma: Kerr etal.,1997a; ofteninless than2–3Myr (Richards etal.,1989). Sinton etal.,1998;Hauff etal.,2000b). Never- Asmoreage datahavebecomeavailable, awider theless,itstill appears thatsubstantialproportions age-range hasemergedfor someLIPs(e.g.,the oftheseprovinceswereformed overgeologically 540 Oceanic Plateaus short timeperiods(e.g.,the OntongJavaplateau accreted oceanic plateausections. For example, formed on two occasions:122^ 3and90^ 4Ma; the OntongJavaplateaucollided withthe Neal etal.,1997). westward-dippingSolomon Islandssubduction Theoretically,oceanic plateaus canform any- zoneat10–20 Ma, resultinginareversalinthe whereinthe oceanbasins; however,most oceanic polarity ofsubduction from west to east,and plateaus appeartohaveformed atornear the upliftandexposureofthe deepersections of midoceanridges(e.g.,Kerguelen,Manihiki and the plateauonthe Solomon Islands(Neal etal., OntongJava),i.e.,regions thatareconduciveto 1997; Petterson etal.,1999). Asecondexampleis voluminous decompression melting(Eldholm and the Caribbean–Colombianoceanic plateau,which Coffin,2000). Atfirst glance, itappears somewhat formed inthe Pacific at , 90 Ma (Sinton etal., coincidentalthatplumesofdeepmantleorigin 1998;Hauff etal.,2000a). Within10Myr the reach the baseofthe lithosphereatamidocean eastward-movingFarallon platehad broughtthe ridge.However,aspointed out bySaunders etal. southern portion ofthe plateauinto collision with (1996),alikely explanation for thisobservation continentalnorthwestern SouthAmerica,resulting isthatmantleplumescan“capture”oceanic inthe accretion ofslicesofthe plateauontothe spreadingcenters (cf.present-dayIceland). continentalmargin(Kerr etal.,1997b). This accretion wasaccompanied byback-steppingof the subduction zonewest ofthe accreted plateau 3.16.3 PRESERVATION OF OCEANIC slices. Shortly afterits formation the northern PLATEAUS portion ofthe plateaubegantomoveinto the The oldest insitu oceanic crustisJurassic inage proto-CaribbeanseawaybetweenNorthandSouth
Load more

Recommended publications
  • Ocean Trench
    R E S O U R C E L I B R A R Y E N C Y C L O P E D I C E N T RY Ocean trench Ocean trenches are long, narrow depressions on the seafloor. These chasms are the deepest parts of the ocean—and some of the deepest natural spots on Earth. G R A D E S 5 - 12+ S U B J E C T S Earth Science, Geology, Geography, Physical Geography C O N T E N T S 11 Images, 1 Video, 2 Links For the complete encyclopedic entry with media resources, visit: http://www.nationalgeographic.org/encyclopedia/ocean-trench/ Ocean trenches are long, narrow depressions on the seafloor. These chasms are the deepest parts of the ocean—and some of the deepest natural spots on Earth. Ocean trenches are found in every ocean basin on the planet, although the deepest ocean trenches ring the Pacific as part of the so-called “Ring of Fire” that also includes active volcanoes and earthquake zones. Ocean trenches are a result of tectonic activity, which describes the movement of the Earth’s lithosphere. In particular, ocean trenches are a feature of convergent plate boundaries, where two or more tectonic plates meet. At many convergent plate boundaries, dense lithosphere melts or slides beneath less-dense lithosphere in a process called subduction, creating a trench. Ocean trenches occupy the deepest layer of the ocean, the hadalpelagic zone. The intense pressure, lack of sunlight, and frigid temperatures of the hadalpelagic zone make ocean trenches some of the most unique habitats on Earth.
    [Show full text]
  • Geologists Suggest Horseshoe Abyssal Plain May Be Start of a Subduction Zone 8 May 2019, by Bob Yirka
    Geologists suggest Horseshoe Abyssal Plain may be start of a subduction zone 8 May 2019, by Bob Yirka against one another. Over by the Iberian Peninsula, the opposite appears to be happening—the African and Eurasian plates are pulling apart as the former creeps east toward the Americas. Duarte noted that back in 2012, other researchers conducting seismic wave tests found what appeared to be a dense mass of unknown material beneath the epicenter of the 1969 quake. Some in the field suggested it could be the start of a subduction zone. Then, last year, another team conducted high-resolution imaging of the area and also found evidence of the mass, confirming that it truly existed. Other research has shown that the area just above the mass experiences routine tiny earthquakes. Duarte suggests the evidence to date indicates that the bottom of the plate is peeling away. This could happen, he explained, due to serpentinization in which water percolates through plate fractures and reacts with material beneath the surface, resulting A composite image of the Western hemisphere of the in the formation of soft green minerals. The soft Earth. Credit: NASA mineral layer, he suggests, is peeling away. And if that is the case, then it is likely the area is in the process of creating a subduction zone. He reports that he and his team members built models of their A team of geologists led by João Duarte gave a ideas and that they confirmed what he suspected. presentation at this past month's European The earthquakes were the result of the process of Geosciences Union meeting that included a birthing a new subduction zone.
    [Show full text]
  • Subsidence and Growth of Pacific Cretaceous Plateaus
    ELSEVIER Earth and Planetary Science Letters 161 (1998) 85±100 Subsidence and growth of Paci®c Cretaceous plateaus Garrett Ito a,Ł, Peter D. Clift b a School of Ocean and Earth Science and Technology, POST 713, University of Hawaii at Manoa, Honolulu, HI 96822, USA b Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA Received 10 November 1997; revised version received 11 May 1998; accepted 4 June 1998 Abstract The Ontong Java, Manihiki, and Shatsky oceanic plateaus are among the Earth's largest igneous provinces and are commonly believed to have erupted rapidly during the surfacing of giant heads of initiating mantle plumes. We investigate this hypothesis by using sediment descriptions of Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) drill cores to constrain plateau subsidence histories which re¯ect mantle thermal and crustal accretionary processes. We ®nd that total plateau subsidence is comparable to that expected of normal sea¯oor but less than predictions of thermal models of hotspot-affected lithosphere. If crustal emplacement was rapid, then uncertainties in paleo-water depths allow for the anomalous subsidence predicted for plumes with only moderate temperature anomalies and volumes, comparable to the sources of modern-day hotspots such as Hawaii and Iceland. Rapid emplacement over a plume head of high temperature and volume, however, is dif®cult to reconcile with the subsidence reconstructions. An alternative possibility that reconciles low subsidence over a high-temperature, high-volume plume source is a scenario in which plateau subsidence is the superposition of (1) subsidence due to the cooling of the plume source, and (2) uplift due to prolonged crustal growth in the form of magmatic underplating.
    [Show full text]
  • Geometrical Effects of a Subducted Seamount on Stopping Megathrust
    GEOPHYSICAL RESEARCH LETTERS, VOL. 40, 1–6, doi:10.1002/grl.50509, 2013 Geometrical effects of a subducted seamount on stopping megathrust ruptures Hongfeng Yang,1,2 Yajing Liu,1,3 and Jian Lin1 Received 6 March 2013; revised 18 April 2013; accepted 25 April 2013. [1] We have numerically simulated dynamic ruptures along rich sediments into seismogenic zone [Bangs et al., 2006]. a “slip-weakening” megathrust fault with a subducted The presence of entrained fluid-rich sediments in the vicinity seamount of realistic geometry, demonstrating that of a subducted seamount would reduce effective normal seamounts can act as a barrier to earthquake ruptures. Such stress and lubricate the thrust interface, leading to little barrier effect is calculated to be stronger for increased elastic strain accumulation and thus inhibiting coseismic seamount normal stress relative to the ambient level, for ruptures [Mochizuki et al., 2008; Singh et al., 2011]. Further- larger seamount height-to-width ratio, and for shorter more, it was proposed that seamount subduction may create seamount-to-nucleation distance. As the seamount height a complex fracture network in the overriding plate, making it increases from 0 to 40% of its basal width, the required unfavorable for the generation of large earthquakes [Wang increase in the effective normal stress on the seamount to and Bilek, 2011]. Thus, the specific mechanisms for stop ruptures drops by as much as ~20%. We further subducted seamounts to stop coseismic ruptures could be demonstrate that when a seamount is subducted adjacent to complex and remain open for debate. the earthquake nucleation zone, coseismic ruptures can be [3] Previous numerical studies have modeled a subducted stopped even if the seamount has a lower effective normal seamount as a patch under elevated effective normal stress stress than the ambient level.
    [Show full text]
  • S41598-020-76691-1 1 Vol.:(0123456789)
    www.nature.com/scientificreports OPEN Rifting of the oceanic Azores Plateau with episodic volcanic activity B. Storch1*, K. M. Haase1, R. H. W. Romer1, C. Beier1,2 & A. A. P. Koppers3 Extension of the Azores Plateau along the Terceira Rift exposes a lava sequence on the steep northern fank of the Hirondelle Basin. Unlike typical tholeiitic basalts of oceanic plateaus, the 1.2 km vertical submarine stratigraphic profle reveals two successive compositionally distinct basanitic to alkali basaltic eruptive units. The lower unit is volumetrically more extensive with ~ 1060 m of the crustal profle forming between ~ 2.02 and ~ 1.66 Ma, followed by a second unit erupting the uppermost ~ 30 m of lavas in ~ 100 kyrs. The age of ~ 1.56 Ma of the youngest in-situ sample at the top of the profle implies that the 35 km-wide Hirondelle Basin opened after this time along normal faults. This rifting phase was followed by alkaline volcanism at D. João de Castro seamount in the basin center indicating episodic volcanic activity along the Terceira Rift. The mantle source compositions of the two lava units change towards less radiogenic Nd, Hf, and Pb isotope ratios. A change to less SiO2-undersaturated magmas may indicate increasing degrees of partial melting beneath D. João de Castro seamount, possibly caused by lithospheric thinning within the past 1.5 million years. Our results suggest that rifting of oceanic lithosphere alternates between magmatically and tectonically dominated phases. Oceanic plateaus with a crustal thickness to 30 km cover large areas in the oceans and these bathymetric swells afect oceanic currents and marine life 1,2.
    [Show full text]
  • Active Continental Margin
    Encyclopedia of Marine Geosciences DOI 10.1007/978-94-007-6644-0_102-2 # Springer Science+Business Media Dordrecht 2014 Active Continental Margin Serge Lallemand* Géosciences Montpellier, University of Montpellier, Montpellier, France Synonyms Convergent boundary; Convergent margin; Destructive margin; Ocean-continent subduction; Oceanic subduction zone; Subduction zone Definition An active continental margin refers to the submerged edge of a continent overriding an oceanic lithosphere at a convergent plate boundary by opposition with a passive continental margin which is the remaining scar at the edge of a continent following continental break-up. The term “active” stresses the importance of the tectonic activity (seismicity, volcanism, mountain building) associated with plate convergence along that boundary. Today, people typically refer to a “subduction zone” rather than an “active margin.” Generalities Active continental margins, i.e., when an oceanic plate subducts beneath a continent, represent about two-thirds of the modern convergent margins. Their cumulated length has been estimated to 45,000 km (Lallemand et al., 2005). Most of them are located in the circum-Pacific (Japan, Kurils, Aleutians, and North, Middle, and South America), Southeast Asia (Ryukyus, Philippines, New Guinea), Indian Ocean (Java, Sumatra, Andaman, Makran), Mediterranean region (Aegea, Cala- bria), or Antilles. They are generally “active” over tens (Tonga, Mariana) or hundreds (Japan, South America) of millions of years. This longevity has consequences on their internal structure, especially in terms of continental growth by tectonic accretion of oceanic terranes, or by arc magmatism, but also sometimes in terms of continental consumption by tectonic erosion. Morphology A continental margin generally extends from the coast down to the abyssal plain (see Fig.
    [Show full text]
  • Distribution and Sedimentary Characteristics of Tsunami Deposits
    Sedimentary Geology 200 (2007) 372–386 www.elsevier.com/locate/sedgeo Distribution and sedimentary characteristics of tsunami deposits along the Cascadia margin of western North America ⁎ Robert Peters a, , Bruce Jaffe a, Guy Gelfenbaum b a USGS Pacific Science Center, 400 Natural Bridges Drive, Santa Cruz, CA 95060, United States b USGS 345 Middlefield Road, Menlo Park, CA 94025, United States Abstract Tsunami deposits have been found at more than 60 sites along the Cascadia margin of Western North America, and here we review and synthesize their distribution and sedimentary characteristics based on the published record. Cascadia tsunami deposits are best preserved, and most easily identified, in low-energy coastal environments such as tidal marshes, back-barrier marshes and coastal lakes where they occur as anomalous layers of sand within peat and mud. They extend up to a kilometer inland in open coastal settings and several kilometers up river valleys. They are distinguished from other sediments by a combination of sedimentary character and stratigraphic context. Recurrence intervals range from 300–1000 years with an average of 500–600 years. The tsunami deposits have been used to help evaluate and mitigate tsunami hazards in Cascadia. They show that the Cascadia subduction zone is prone to great earthquakes that generate large tsunamis. The inclusion of tsunami deposits on inundation maps, used in conjunction with results from inundation models, allows a more accurate assessment of areas subject to tsunami inundation. The application of sediment transport models can help estimate tsunami flow velocity and wave height, parameters which are necessary to help establish evacuation routes and plan development in tsunami prone areas.
    [Show full text]
  • Subduction Zones”
    EGU Journal Logos (RGB) Open Access Open Access Open Access Advances in Annales Nonlinear Processes Geosciences Geophysicae in Geophysics Open Access Open Access Natural Hazards Natural Hazards and Earth System and Earth System Sciences Sciences Discussions Open Access Open Access Atmospheric Atmospheric Chemistry Chemistry and Physics and Physics Discussions Open Access Open Access Atmospheric Atmospheric Measurement Measurement Techniques Techniques Discussions Open Access Open Access Biogeosciences Biogeosciences Discussions Open Access Open Access Climate Climate of the Past of the Past Discussions Open Access Open Access Earth System Earth System Dynamics Dynamics Discussions Open Access Geoscientific Geoscientific Open Access Instrumentation Instrumentation Methods and Methods and Data Systems Data Systems Discussions Open Access Open Access Geoscientific Geoscientific Model Development Model Development Discussions Open Access Open Access Hydrology and Hydrology and Earth System Earth System Sciences Sciences Discussions Open Access Open Access Ocean Science Ocean Science Discussions Open Access Solid Earth, 4, 129–133, 2013 Open Access www.solid-earth.net/4/129/2013/ Solid Earth doi:10.5194/se-4-129-2013 Solid Earth Discussions © Author(s) 2013. CC Attribution 3.0 License. Open Access Open Access The Cryosphere The Cryosphere Discussions Introduction to the special issue on “Subduction Zones” S. J. H. Buiter1,2, F. Funiciello3, and J. van Hunen4 1Geological Survey of Norway, Geodynamics Team, Leiv Eirikssons vei 39, 7040 Trondheim, Norway 2University of Oslo, The Centre for Earth Evolution and Dynamics, 0316 Oslo, Norway 3Universita` Roma Tre, Dipartimento di Scienze, L.go S. Leonardo Murialdo 1, 00146, Rome, Italy 4Durham University, Department of Earth Sciences, Durham DH1 3LE, UK Correspondence to: S.
    [Show full text]
  • Mantle Hydration and Cl-Rich Fluids in the Subduction Forearc Bruno Reynard1,2
    Reynard Progress in Earth and Planetary Science (2016) 3:9 Progress in Earth and DOI 10.1186/s40645-016-0090-9 Planetary Science REVIEW Open Access Mantle hydration and Cl-rich fluids in the subduction forearc Bruno Reynard1,2 Abstract In the forearc region, aqueous fluids are released from the subducting slab at a rate depending on its thermal state. Escaping fluids tend to rise vertically unless they meet permeability barriers such as the deformed plate interface or the Moho of the overriding plate. Channeling of fluids along the plate interface and Moho may result in fluid overpressure in the oceanic crust, precipitation of quartz from fluids, and low Poisson ratio areas associated with tremors. Above the subducting plate, the forearc mantle wedge is the place of intense reactions between dehydration fluids from the subducting slab and ultramafic rocks leading to extensive serpentinization. The plate interface is mechanically decoupled, most likely in relation to serpentinization, thereby isolating the forearc mantle wedge from convection as a cold, potentially serpentinized and buoyant, body. Geophysical studies are unique probes to the interactions between fluids and rocks in the forearc mantle, and experimental constrains on rock properties allow inferring fluid migration and fluid-rock reactions from geophysical data. Seismic velocities reveal a high degree of serpentinization of the forearc mantle in hot subduction zones, and little serpentinization in the coldest subduction zones because the warmer the subduction zone, the higher the amount of water released by dehydration of hydrothermally altered oceanic lithosphere. Interpretation of seismic data from petrophysical constrain is limited by complex effects due to anisotropy that needs to be assessed both in the analysis and interpretation of seismic data.
    [Show full text]
  • From Oceanic Plateaus to Allochthonous Terranes: Numerical Modelling
    Gondwana Research 25 (2014) 494–508 Contents lists available at ScienceDirect Gondwana Research journal homepage: www.elsevier.com/locate/gr From oceanic plateaus to allochthonous terranes: Numerical modelling Katharina Vogt a,⁎, Taras V. Gerya a,b a Geophysical Fluid Dynamics Group, Institute of Geophysics, Department of Earth Sciences, Swiss Federal Institute of Technology (ETH-Zurich), Sonneggstrasse, 5, 8092 Zurich, Switzerland b Adjunct Professor of Geology Department, Moscow State University, 119899 Moscow, Russia article info abstract Article history: Large segments of the continental crust are known to have formed through the amalgamation of oceanic pla- Received 29 April 2012 teaus and continental fragments. However, mechanisms responsible for terrane accretion remain poorly un- Received in revised form 25 August 2012 derstood. We have therefore analysed the interactions of oceanic plateaus with the leading edge of the Accepted 4 November 2012 continental margin using a thermomechanical–petrological model of an oceanic-continental subduction Available online 23 November 2012 zone with spontaneously moving plates. This model includes partial melting of crustal and mantle lithologies and accounts for complex rheological behaviour including viscous creep and plastic yielding. Our results in- Keywords: Crustal growth dicate that oceanic plateaus may either be lost by subduction or accreted onto continental margins. Complete Subduction subduction of oceanic plateaus is common in models with old (>40 Ma) oceanic lithosphere whereas models Terrane accretion with younger lithosphere often result in terrane accretion. Three distinct modes of terrane accretion were Oceanic plateau identified depending on the rheological structure of the lower crust and oceanic cooling age: frontal plateau accretion, basal plateau accretion and underplating plateaus.
    [Show full text]
  • OCEAN SUBDUCTION Show That Hardly Any Commercial Enhancement Finney B, Gregory-Eaves I, Sweetman J, Douglas MSV Program Can Be Regarded As Clearly Successful
    1982 OCEAN SUBDUCTION show that hardly any commercial enhancement Finney B, Gregory-Eaves I, Sweetman J, Douglas MSV program can be regarded as clearly successful. and Smol JP (2000) Impacts of climatic change and Model simulations suggest, however, that stock- Rshing on PaciRc salmon over the past 300 years. enhancement may be possible if releases can be Science 290: 795}799. made that match closely the current ecological Giske J and Salvanes AGV (1999) A model for enhance- and environmental conditions. However, this ment potentials in open ecosystems. In: Howell BR, Moksness E and Svasand T (eds) Stock Enhancement requires improvements of assessment methods of and Sea Ranching. Blackwell Fishing, News Books. these factors beyond present knowledge. Marine Howell BR, Moksness E and Svasand T (1999) Stock systems tend to have strong nonlinear dynamics, Enhancement and Sea Ranching. Blackwell Fishing, and unless one is able to predict these dynamics News Books. over a relevant time horizon, release efforts are Kareiva P, Marvier M and McClure M (2000) Recovery not likely to increase the abundance of the target and management options for spring/summer chinnook population. salmon in the Columbia River basin. Science 290: 977}979. Mills D (1989) Ecology and Management of Atlantic See also Salmon. London: Chapman & Hall. Ricker WE (1981) Changes in the average size and Mariculture, Environmental, Economic and Social average age of PaciRc salmon. Canadian Journal of Impacts of. Salmonid Farming. Salmon Fisheries: Fisheries and Aquatic Science 38: 1636}1656. Atlantic; Paci\c. Salmonids. Salvanes AGV, Aksnes DL, FossaJH and Giske J (1995) Simulated carrying capacities of Rsh in Norwegian Further Reading fjords.
    [Show full text]
  • Controls of Subduction Geometry, Location of Magmatic Arcs, and Tectonics of Arc and Back-Arc Regions
    Controls of subduction geometry, location of magmatic arcs, and tectonics of arc and back-arc regions TIMOTHY A. CROSS Exxon Production Research Company, P.O. Box 2189, Houston, Texas 77001 REX H. PILGER, JR. Department of Geology, Louisiana State University, Baton Rouge, Louisiana 70803 ABSTRACT States), intra-arc extension (for example, convergence rate, direction and rate of the Basin and Range province), foreland absolute upper-plate motion, age of the de- Most variation in geometry and angle of fold and thrust belts, and Laramide-style scending plate, and subduction of aseismic inclination of subducted oceanic lithosphere tectonics. ridges, oceanic plateaus, or intraplate is caused by four interdependent factors. island-seamount chains. It is crucial to Combinations of (1) rapid absolute upper- INTRODUCTION recognize that, in the natural system of the plate motion toward the trench and active Earth, the major factors may interact and, overriding of the subducted plate, (2) rapid Since Luyendyk's (1970) pioneer attempt therefore, are interdependent variables. De- relative plate convergence, and (3) subduc- to relate subduction-zone geometry to some pending on the associations among them, in tion of intraplate island-seamount chains, fundamental aspect(s) of plate kinematics a historical and spatial context, their aseismic ridges, and oceanic plateaus and dynamics, subsequent investigations effects on the geometry of subducted litho- (anomalously low-density oceanic litho- have suggested an increasing variety and sphere can be additive, or by contrast, one sphere) cause low-angle subduction. Under complexity among possible controls and variable can act in opposition to another conditions of low-angle subduction, the resultant configurations of subduction variable and result in total or partial cancel- upper surface of the subducted plate is in zones.
    [Show full text]