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Deformation of Accretionary Wedges in Response to Seamount Subduction: Insights from Sandbox Experiments S Dominguez, J Malavieille, Serge E

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Deformation of Accretionary Wedges in Response to Seamount Subduction: Insights from Sandbox Experiments S Dominguez, J Malavieille, Serge E Deformation of accretionary wedges in response to seamount subduction: Insights from sandbox experiments S Dominguez, J Malavieille, Serge E. Lallemand To cite this version: S Dominguez, J Malavieille, Serge E. Lallemand. Deformation of accretionary wedges in response to seamount subduction: Insights from sandbox experiments. Tectonics, American Geophysical Union (AGU), 2010, 19 (1), pp.192-196. 10.1029/1999TC900055. hal-01261523 HAL Id: hal-01261523 https://hal.archives-ouvertes.fr/hal-01261523 Submitted on 28 Jan 2016 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. TECTONICS, VOL. 19, NO. 1, PAGES 182-196 FEBRUARY 2000 Deformation of accretionary wedgesin responseto seamount subduction- Insights from sandbox experiments S. Dominguez,J. Malavieille, and S. E. Lallemand Laboratoirede G6ophysique,Tectonique et S6dimentologie,UMR 5573, CNRS Institutdes Sciences de la Terre, de l'Eau et de I'Espacede Montpe!!ier Universit6de Montpellier II, Montpellier,France Abstract. Sandboxexperiments, using a two-dimensional and al., 1998, 1999; Park et al., 1999], the subduction of these a three-dimensional approach, are used to study the volcanic highs strongly deformsthe overriding plate margin deformation of margins in response to seamount subduction. and also influences the seismicity across the subduction Successivemechanisms of deformationare activated during interfaceand the magmaticactivity of the volcanic arc [Nut the subduction of conical seamounts. First, reactivation of the and Ben-Avraham, 1981; McGeary, 1985; Tatchef, 1989]. frontal thrusts and compactionof the accretionarywedge is Recent works propose that when these volcanic highs reach observed. Then, back thrusting and, conjugate strike-slip the seismogeniczone, they modify,the seismiccoupling and faulting develops above the leading slope of the subducted favor the nucleation of strong earthquakes [Christensen and seamount.The basal d6collementis deflectedupward in the Lay; 1988; Cloos, 1992; Scholtz and Small, 1997]. Small wake of the subducting high, and a large shadow zone and Abbott[1998] evensuggest that the subductionof very develops behind the seamounttrailing slope. Consequently, largeseamounts (e.g., the Louisvilleridge in the Tonga- frontal accretionis inhibited and part of the frontal margin is KermadecTrench) could fracturethe surroundingoceanic dragged into the subduction zone. When the main crust. d6collement returns to its basal level in the wake of the Geophysicaldata recordedduring oceanographiccruises seamount,the margin records a rapid subsidence and a new allow detailed studiesof the morphologyand structureof accretionarywedge develops, closing the margin reentrant. convergent margins. Nevertheless,while seismic profiles The sediments underthrusted in the wake of the seamount into succeedin resolvingthe geologicstructure of the upperplate the shadowzone, are underplated beneaththe rear part of the in relativelyundeformed regions of a margin,interpretation accretionarywedge. Substantialshortening and thickening of becomes difficult when the subduction of a seamount occurs. the deformable seaward termination of the upper plate In suchareas the accretionarywedge and the fi'ontalmargin basement, associated with basal erosion is observed. areso stronglydeformed that the internalstructure is poorly Seamount subduction induces significant material transfer resolved. within the accretionary wedge, favors large tectonic erosion Sandboxexperiments already have been used to study of the frontal margin and thickening of the rear part of the sedimentaryaccretionary wedges and seamountsubduction margin. The subduction and underplating of relatively [Davis et al., 1983; Malavieille, 1984; Lallemand et al., undeformed, water-ladden sediments, associated with fluid 1992; Kukowskiet al., 1994; Gutschef et al., 1998l. It expulsion along the fractures affecting the margin could appearsfrom thesestudies that analogexperiments aflbrd good modify the fluid pressure along the basal ddcollement. tools to complementthe marine observations. Consequently, significant variations of the effective basal We have usedsimilar sandbox experiments to investigate friction and local mechanicalcoupling betweenthe two plates the structuralevolution of the overridingplate marginin could be expected around the subductingseamount. responseto seamountsubduction. We analyze structuresin two andthree dimensions, the evolution in time and spaceof 1. Introduction the stressfield induced by the seamount,and we estimatethe amount of material transfer within the margin. The main 1.1. Geologic Setting purpose of this experimentalstudy is to improve our understandingof the deIbrmationmechanisms occurring Large domainsof oceanicplates (Figure 1) are characterized during seamount subduction and to propose some by a very rough seafloor covered by numerous seamounts, quantitativeresults. Indeed, since fluids and pore pressureare aseismicridges, and volcanic plateaus [Batiza, 1982; Smith not considered,angles of reposeand angles of taperare greater and Jordan, 1988; Wessel and Lyons, 1997]. As revealed by than those observed in nature. Nevertheless, as demonstrated marine data and large-scale observations [Ballance et al., by morphologiccomparisons between previous experiments 1989; Collot and Fisher, 1989, 1991; Fisher et al., 1991; and natural cases[Dominguez e! al., 1998], we believe that Lallemand et al., 1990; von Huene and Scholl, 1991; von the mechanismsobserved in such sandboxexperiments are Huene et al., 1995; Moore and Sender, 1995; Dominguez et analog to those occurringin subductionzones. Figure2 summarizesthe main morphologicti:atures induced Copyright2000 by theAmerican Geophysical Union. by seamount subduction, presented in previous works [Dominguezet al., 1994, 1998]. The accretionarywedge is Papernumber 1999TC900055. indented,and a large reentrantdevelop associatedwith a 0278-7407/00/1999TC00055512.00 critical frontal slope, where massivesedimentary sliding 182 DOMINGUEZET AL.: SANDBOXEXPERIMENTS OF SEAMOUNTSUBDUCTION 183 120' 130' 140' 150' 160' 170'40' 40' 30' 20' 20' 10' 120' 130' 140' 150' 160' 170' Figure1. Shadedview of the Pacific and Philippine Plates showing themorphologic features ofthe seafloor. Areasof high density ofseamounts areoutlined aswell as regions ofseamount orridge subduction (circles). occurs.Landward of the reentrant,the margin is uplifted sedimentaryrocks and marinesediments. The basal friction above the subductedseamount and shows a characteristic along the sand-mylar interfaceis intermediate(Ob=20ø). faultnetwork. Seaward dipping back thrusts and conjugated Scaling is such as I cm in the sandboxexperiment is strike-slipfaults, related to the indentationof the margin, equivalentto I km in nature [Lallemandet al., 1992]. The propagatelandward as the seamountsubduct. cohesion of the sand and the cohesion of the rock powder, used in our experiments,are 20 Pa and about 100 Pa, 1.2. Experimental Setup respectively,and scaleto 2 and 10 MPa [Gutschef eta!., Thetwo experimental devices used to performthe sandbox 1998]. Thesecohesion values are very close to values of experiments(Figure 2)are comparableto those used by unconsolidated marine sediments and lithified sedimentary Malavieilleet al. [1991] andDominguez et al. [1994; 1998]. rocks [Hoshinoet al., 1972]. Both consistof an inclinedrigid plate on which a mylar sheet, The shapeof the subductinghigh is conicalwith a slopeof simulatingthe subductingoceanic plate slides,is located. 20ø. It consistsof a rigid corecovered by a 2 cmthick layer of This sheet is pulled beneath a rigid backstopwhich cohesive rock powder with a thin (< I cm)sand cover, representsthe undeformablepart of the overridingplate. A simulating a volcanoclasticcover. The friction along the cohesivesand wedge is built in front of this backstopto interfacebetween the rigid core and the cohesive layer is simulatethe morecompacted inner part of the accretionary moderateto high (closeto •b=25ø). ,wedgeand the morecohesive seaward termination of the The first device, used to study in cross sections the overridingplate [yonHuene and Scholl,1991]. The oceanic differentstages of a seamountsubduction, has two lateral sedimentscarried by the subductingplate are built by glasspanes. They allow the deformationto be observedin real sprinklinghorizontal layers of coloredsand on the mylarfilm. time on both sides of the experiment.The second device, The sandlayers and backstop wedge are composedof granular dedicated to the study of the margin structure in three material(sand and rock powder). The sand used in our dimensions,is very muchlarger to avoid boundaryeffects. On experimentsis well-sortedeolian quartz sand with a grain thisapparatus the modelcan be impregnatedwith waterat the sizeof about250 ILtm.Its physical•properties (angle of internal endof the experimentto increasethe sandcohesion and to cut frictionOs of 30ø anda very low cohesion)satisfy the Mohr- vertical and also horizontal cross sections. Coulombcriteria [Dahlen, 1984, 1990; Dahlen and Suppe, The results of three
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