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Sample records for subduction complex hispaniola

  1. Diverse melanges of an ancient subduction complex

    Energy Technology Data Exchange (ETDEWEB)

    Lash, G.G.

    1987-07-01

    Three lithologically and structurally diverse melanges occur within an early Paleozoic (Early-Middle Ordovician) subduction complex in the central Appalachian orogen. Type I melange, characterized by horizons of variably deformed sandstone and scaly mudstone that alternate with coherent sandstone-rich sequences, is interpreted to reflect accretion-related deformation of water-saturated trench deposits. Type II melange, composed of exotic radiolaria-bearing mudstone clasts in a scaly mudstone matrix, can be explained by remobilization and mixing of inner-trench slope sediments. Type III melange is a poorly sorted polymict assemblage of native lithology clasts in a scaly mudstone matrix. Evidence of forceful injection of matrix mud into clasts and inferred discordant contacts between melange and surrounding bedded deposits suggest that the type III melange formed from mud diapirism. The close association of these melanges points out the diversity of tectonic and sedimentary processes previously documented from modern convergent margins that may be reflected in older subduction complexes.

  2. Neotectonics of a subduction/strike-slip transition: the northeastern Dominican Republic

    Energy Technology Data Exchange (ETDEWEB)

    Winslow, M.A.; McCann, W.R.

    1985-01-01

    The Septentrional fault system in the northeastern Dominican Republic marks the zone where the North American-Carribean plate boundary is evolving from subduction to strike-slip motion, and where terranes appear to be forming and migrating laterally in a subduction complex/forearc region. On the Island of Hispaniola, slip vectors are oblique to the strike of the Puerto Rico trench, and oblique subduction thrusts the upper plate over normal seafloor. The offshore geology and seismicity of the northern Caribbean suggest that uplift, broad crustal warping, thrusting, and strike-slip faulting (ie. collisional tectonics) should be present in the northern part of the Dominican Republic. The high topography (>1000m), high levels of seismicity, and large earthquakes support the hypothesis of contemporary deformation in Hispaniola. In this region, the subduction regime dies out toward the west, and deformation is transferred to onshore, oblique-slip faults. As this change in tectonic style has occurred in Neogene to Recent times, we are investigating the modern evolution of a plate boundary. We have already documented: (1) the presence of a strike-slip faulting in the northeastern Dominican Republic; (2) an anomalous push-up structure; and (3) a region of numerous splay faults. In conclusion, recent seismicity suggest a wide zone of deformation and variations in interplate motions near Hispaniola. This island lies at the western limit of active underthrusting and at the eastern limit of onshore faulting, i.e., at an important transition from a subduction to strike-slip regime.

  3. Complex Subduction Imaged by Diffractional Tomography of USArray Receiver Functions

    Science.gov (United States)

    Zhou, Y.

    2016-12-01

    Subduction of a large oceanic plate beneath a continental plate is a complex process. In the Western United States, fragmentation of the Farallon slab has been reported in recent tomographic models. In this study, we measure finite-frequency travel times of P410s and P660s receiver functions recorded at USArray Transportable Array (TA) stations for teleseismic events occurred between 2015 and 2011. We calculate the finite-frequency sensitivities of receiver functions to depth perturbations of the 410-km and 660-km discontinuities to obtain high resolution mantle transition zone models based on diffractional tomography. The high-resolution discontinuity models reveal several interesting anomalies associated with complex subduction of the Farallon plate. In particular, we observe a linear feature in both the 410-km and 660-km discontinuity models. This mantle transition zone anomaly is roughly located in the western Snake River Plain and aligns with a major slab gap imaged in an earlier finite-frequency S-wave velocity model. We show that non-stationary upwellings generated by eastward propagation of a slab tearing event, together with a westward motion of the North American plate at a rate of about 1 to 1.5 centimeters per year (comparable to the half spreading rate of the Mid-Atlantic Ridge) in the past 16 million years can explain the age-progressive Snake River Plain / Yellowstone volcanic track. The slab to the west of the anomaly shows a near vertical subduction, it is heavily fragmented and the 410-km and 660-km discontinuity topography indicates that the southern fragment north of the Mendocino triple junction has subducted down to the mantle transition zone.

  4. Retrograde lawsonite formation in the Franciscan subduction complex

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    Myers, S.; Mulcahy, S. R.

    2016-12-01

    Lawsonite [CaAl2Si2O7(OH)2·H2O] is an index mineral of low-temperature subduction zones, contains a significant amount of water, and is an important host of rare-earth and trace elements in mafic protoliths. For these reasons, numerous studies have investigated the consequences of lawsonite breakdown during prograde subduction. In the Franciscan subduction complex, however, lawsonite in mafic blueschist largely formed along a retrograde path from pre-existing eclogite. In order to asses the conditions and significance of retrograde lawsonite formation we examined the petrology and geochemistry of lawsonite-bearing assemblages in Franciscan mafic rocks. All of the samples have the common assemblage: lawsonite, glaucophane, and sphene. Quartz is generally absent. Muscovite, chlorite, and relict epidote and rutile are variably present. Different index minerals calcite, aragonite, albite, and jadeitic pyroxene are present within lawsonite assemblages. Garnet occurs in equilibrium with lawsonite, as a relict mineral in lawsonite and the matrix, or is completely absent. Major element compositions vary from typical basalts and are strongly correlated with one another. Chondrite normalized REE compositions are variably LREE depleted or enriched, MREE are flat to enriched, and HREE are generally flat. Trace elements normalized to NMORB show variably enriched and depleted LILE. The petrology suggests lawsonite, glaucophane, and sphene formed from multiple retrograde reactions involving garnet, clinopyroxene, epidote, and rutile, together with significant hydration. Important index minerals imply lawsonite formed over a wide range of pressures within the subduction zone. The major, REE, and trace element compositions suggest lawsonite assemblages were derived from different protoliths or experienced variable amounts of metasomatism and interaction with crustally derived material and serpentinite.

  5. Multiscale Architecture of a Subduction Complex and Insight into Large-scale Material Movement in Subduction Systems

    Science.gov (United States)

    Wakabayashi, J.

    2014-12-01

    The >1000 km by >100 km Franciscan complex of California records >100 Ma of subduction history that terminated with conversion to a transform margin. It affords an ideal natural laboratory to study the rock record of subduction-interface and related processes exhumed from 10-70 km. The Franciscan comprises coherent and block-in-matrix (mélange) units forming a nappe stack that youngs structurally downward in accretion age, indicating progressive subduction accretion. Gaps in accretion ages indicate periods of non-accretion or subduction erosion. The Franciscan comprises siliciclastic trench fill rocks, with lesser volcanic and pelagic rocks and serpentinite derived from the downgoing plate, as well as serpentinite and felsic-intermediate igneous blocks derived as detritus from the upper plate. The Franciscan records subduction, accretion, and metamorphism (including HP), spanning an extended period of subduction, rather than a single event superimposed on pre-formed stratigraphy. Melanges (serpentinite and siliciclastic matrix) with exotic blocks, that include high-grade metamorphic blocks, and felsic-intermediate igneous blocks from the upper plate, are mostly/entirely of sedimentary origin, whereas block-in-matrix rocks formed by tectonism lack exotic blocks and comprise disrupted ocean plate stratigraphy. Mélanges with exotic blocks are interbedded with coherent sandstones. Many blocks-in-melange record two HP burial events followed by surface exposure, and some record three. Paleomegathrust horizons, separating nappes accreted at different times, appear restricted to narrow fault zones of structures, are accommodated by discrete faults or narrow shear zones, rather than by significant penetrative strain. Exhumation of Franciscan HP units, both coherent and mélange, was accommodated by significant extension of the overlying plate, and possibly extension within the subduction complex, with cross-sectional extrusion, and like subduction burial, took place at

  6. Molecular modelling of rare earth element complexation in subduction zone fluids

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    van Sijl, J.; Allan, N.L.; Davies, G.R.; van Westrenen, W.

    2009-01-01

    Complexation of (trace) elements in fluids plays a critical role in determining element mobility in subduction zones, but to date, the atomic-scale processes controlling elemental solubilities are poorly understood. As a first step towards computer simulation of element complexation in subduction

  7. Blueschist facies pseudotachylytes from Corsica: First account of fossil earthquakes from a subduction complex

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    Andersen, T. B.; Austrheim, H.

    2003-04-01

    Pseudotachylytes (PST) are products of deformation at extreme slip-rates along faults or in impact structures. Fault-plane PSTs are considered to represent fossil earthquakes. Tectonics in subduction zones, generate >80% of the seismic energy. Earthquake rocks should therefore also be common in old subduction complexes. Blueschist terrains are formed in the upper 15 to 50 km by tectonic burial in accreationary complexes and subduction zones. In spite of the very common earthquakes recorded from present-day subduction complexes, we are unaware of previous accounts of fossil earthquakes from exhumed subduction complexes. With a working hypothesis predicting fossil earthquakes to be preserved in subduction complexes, we have re-examined parts of the Alpine blueschist-eclogite terrain in Corsica. Within blueschist facies ophiolite gabbro and peridotite of Cape Corse, we discovered a number of faults decorated with ultra-fine fault rocks including PSTs. Detailed probe and SEM-studies reveal that some of the PSTs have quench textures proving the former presence of a melt. Quenched minerals, including fassaitic pyroxene are found as spherulites and dendrites. Fassaite has previously been described from UHP complexes and from PSTs formed in HP experiments. Other devitrification minerals include glaucophane, barroisite and zoisite as well as pumpellyite and albite. Our hypothesis -- fossil earthquakes in the form of frictional heat generated PST and ultra-cataclasite may be preserved within subduction complexes -- has been confirmed. Whilst most models view the properties of subducted lithosphere as a function of temperature, it is increasingly recognized that the rheological properties of rocks depend on their metamorphic status and importantly on fluids. Fluids from dehydration reactions in subduction complexes may reduce the effective stress to allow rapid brittle failure, which in turn may produce frictional heating and additional dehydration. It is, however, also

  8. Historical perspective on seismic hazard to Hispaniola and the northeast Caribbean region

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    ten Brink, Uri S.; Bakun, W.H.; Flores, C.H.

    2011-01-01

    We evaluate the long-term seismic activity of the North-American/Caribbean plate boundary from 500 years of historical earthquake damage reports. The 2010 Haiti earthquakes and other earthquakes were used to derive regional attenuation relationships between earthquake intensity, magnitude, and distance from the reported damage to the epicenter, for Hispaniola and for Puerto Rico and the Virgin Islands. The attenuation relationship for Hispaniola earthquakes and northern Lesser Antilles earthquakes is similar to that for California earthquakes, indicating a relatively rapid attenuation of damage intensity with distance. Intensities in Puerto Rico and the Virgin Islands decrease less rapidly with distance. We use the intensity-magnitude relationships to systematically search for the location and intensity magnitude MI which best fit all the reported damage for historical earthquakes. Many events occurred in the 20th-century along the plate-boundary segment from central Hispaniola to the NW tip of Puerto Rico, but earlier events from this segment were not identified. The remaining plate boundary to the east to Guadeloupe is probably not associated with M > 8 historical subduction-zone earthquakes. The May 2, 1787 earthquake, previously assigned an M 8–8.25, is probably only MI 6.9 and could be located north, west or SW of Puerto Rico. An MI 6.9 earthquake on July 11, 1785 was probably located north or east of the Virgin Islands. We located MI I 7.7) and May 7, 1842 (MI 7.6) earthquakes ruptured the Septentrional Fault in northern Hispaniola. If so, the recurrence interval on the central Septentrional Fault is ~300 years, and only 170 years has elapsed since the last event. The recurrence interval of large earthquakes along the Hispaniola subduction segment is likely longer than the historical record. Intra-arc M ≥ 7.0 earthquakes may occur every 75–100 years in the 410-km-long segment between the Virgin Islands and Guadeloupe.

  9. The herpetogeography of Hispaniola, West Indies

    NARCIS (Netherlands)

    Schwartz, Albert

    1980-01-01

    The modern West Indian island of Hispaniola is in actuality a fusion of two formerly separate islands, each of which presumably supported a distinctive herpetofauna. With the union of these two paleoislands, there has been extensive to small interchange of these faunas; the purpose of the present

  10. Cholera in United States Associated with Epidemic in Hispaniola

    Science.gov (United States)

    Heiman, Katherine E.; Schmitz, Ann; Török, Tom; Apostolou, Andria; Hanson, Heather; Gounder, Prabhu; Bohm, Susan; Kurkjian, Katie; Parsons, Michele; Talkington, Deborah; Stroika, Steven; Madoff, Lawrence C.; Elson, Franny; Sweat, David; Cantu, Venessa; Akwari, Okey; Mahon, Barbara E.; Mintz, Eric D.

    2011-01-01

    Cholera is rare in the United States (annual average 6 cases). Since epidemic cholera began in Hispaniola in 2010, a total of 23 cholera cases caused by toxigenic Vibrio cholerae O1 have been confirmed in the United States. Twenty-two case-patients reported travel to Hispaniola and 1 reported consumption of seafood from Haiti. PMID:22204035

  11. Sediment-derived fluids in subduction zones: Isotopic evidence from veins in blueschist and eclogite of the Franciscan Complex, California

    Energy Technology Data Exchange (ETDEWEB)

    Nelson, B.K. (Univ. of Washington, Seattle (United States))

    1991-10-01

    Isotopic analyses of minerals from veins that cut high-grade blueschist and eclogite blocks in the central belt of the Franciscan Complex provide constraints on the chronology of metamorphic events and on the origin and movement of fluids within the subduction zone. A Rb-Sr age of 153 {plus minus}1 Ma obtained for minerals from veins and open cavities that formed contemporaneously with retrograde blueschist facies metamorphism is a minimum age for the prograde metamorphism. The veining precedes the last episode of sedimentary-matrix melange formation by a minimum 15 to 20 Ma, during which time the blocks must have been stored within the subduction complex at low temperatures and without undergoing penetrative deformation. Initial Nd-isotope compositions ({epsilon}{sub Nd}) of the vein minerals range from +10.8 to {minus}2.4, indicating that some fluids were derived predominantly from dehydration of subducted mid-ocean ridge basalt, but that other fluids had a component derived from subducted sediment. The provenance of the subducted sediment was within old continental crust, thus associating the Franciscan paleo-subduction complex with a continental craton by the time of vein formation.

  12. Ins and outs of a complex subduction zone: C cycling along the Sunda margin, Indonesia

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    House, B. M.; Bebout, G. E.; Hilton, D. R.

    2016-12-01

    Subduction of C in marine sediments and altered oceanic crust is the main mechanism for reintroducing C into the deep earth and removing it from communication with the ocean and atmosphere. However, detailed studies of individual margins - which are necessary to understanding global C cycling - are sparse. The thick, C-rich sediment column along the Sunda margin, Indonesia makes understanding this margin crucial for constructing global C cycling budgets. Furthermore it is an ideal location to compare cycling of organic and carbonate C due to the abrupt transition from carbonate-dominated sediments in the SE to sediments rich in organic C from the Nicobar Fan in the NW. To quantify and characterize C available for subduction, we analyzed samples from DSDP 211, 260, 261, and ODP 765, all outboard of the trench, as well as piston and gravity cores of locally-sourced terrigenous trench fill. We created a 3-D model of overall sediment thickness and the thicknesses of geochemically distinct sedimentary units using archived and published seismic profiles to infer unit thicknesses at and along the 2500 km trench. This model vastly improves estimates of the C available for subduction and also reveals that the Christmas Island Seamount Province serves as a barrier to turbidite flow, dividing the regions of the trench dominated by organic and inorganic C input. Incorporating best estimates for the depth of the decollement indicates that the terrigenous trench fill, with up to 1.5 wt % organic C, is entirely accreted as is the thick section of carbonate-rich turbidites that dominate the southeastern portion of the margin (DSDP 261/ODP 765). Organic C accounts for most of the C bypassing the accretionary complex NW of the Christmas Island Seamount Province, and C inputs to the trench are lower there than to the SE where carbonate units near the base of the sediment column are the dominant C source. Release of C from altered oceanic crust - a C reservoir up to 10 times greater

  13. Mantle peridotite in newly discovered far-inland subduction complex, southwest Arizona: Initial report

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    Haxel, Gordon B.; Jacobson, Carl E.; Wittke, James H.

    2015-01-01

    The latest Cretaceous to early Palaeogene Orocopia Schist and related units are generally considered a low-angle subduction complex that underlies much of southern California and Arizona. A recently discovered exposure of Orocopia Schist at Cemetery Ridge west of Phoenix, Arizona, lies exceptionally far inland from the continental margin. Unexpectedly, this body of Orocopia Schist contains numerous blocks, as large as ~300 m, of variably serpentinized mantle peridotite. These are unique; elsewhere in the Orocopia and related schists, peridotite is rare and completely serpentinized. Peridotite and metaperidotite at Cemetery Ridge are of three principal types: (1) serpentinite and tremolite serpentinite, derived from dunite; (2) partially serpentinized harzburgite and olivine orthopyroxenite (collectively, harzburgite); and (3) granoblastic or schistose metasomatic rocks, derived from serpentinite, made largely of actinolite, calcic plagioclase, hercynite, and chlorite. In the serpentinite, paucity of relict olivine, relatively abundant magnetite (5%), and elevated Fe3+/Fe indicate advanced serpentinization. Harzburgite contains abundant orthopyroxene, only slightly serpentinized, and minor to moderate (1–15%) relict olivine. Mantle tectonite fabric is locally preserved. Several petrographic and geochemical characteristics of the peridotite at Cemetery Ridge are ambiguously similar to either abyssal or mantle-wedge (suprasubduction) peridotites and serpentinites. Least ambiguous are orthopyroxene compositions. Orthopyroxene is distinctively depleted in Al2O3, Cr2O3, and CaO, indicating mantle-wedge affinities. Initial interpretation of field and petrologic data suggests that the peridotite blocks in the Orocopia Schist subduction complex at Cemetery Ridge may be derived from the leading corner or edge of a mantle wedge, presumably in (pre-San Andreas fault) southwest California. However, derivation from a subducting plate is not precluded.

  14. The genus Leptostylopsis of Hispaniola (Coleoptera, Cerambycidae, Acanthocinini

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    Steven Lingafelter

    2009-08-01

    Full Text Available The generic differences and similarities between Leptostylus LeConte and Leptostylopsis Dillon (Coleoptera: Cerambycidae: Acanthocinini are discussed. Leptostylopsis is redescribed and the following species are transferred from Leptostylus to Leptostylopsis: Leptostylopsis annulipes (Fisher 1942, comb. n.; Leptostylopsis poeyi (Fisher 1925, comb. n.; and Leptostylopsis viridicomus (Fisher 1942, comb. n. Leptostylopsis hispaniolae (Fisher 1942 is a syn. n. of Leptostylopsis annulipes (Fisher 1942. Seven new species of Leptostylopsis from Hispaniola are diagnosed, described, and illustrated: L. basifulvus Lingafelter and Micheli, sp. n.; L. caliginosus Lingafelter and Micheli, sp. n.; L. chlorescens Lingafelter and Micheli, sp. n.; L. humerofulvus Lingafelter and Micheli, sp. n.; L. perfasciatus Lingafelter and Micheli, sp. n.; L. puntacanaensis Lingafelter and Micheli, sp. n.; and L. thomasi Lingafelter and Micheli, sp. n. Redescriptions and distributional data are provided for the six previously described species known from Hispaniola, and a dichotomous key to all thirteen species of Leptostylopsis from Hispaniola is provided.

  15. The Mesozoic accretionary complex in Northeast China: Evidence for the accretion history of Paleo-Pacific subduction

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    Zhou, Jian-Bo; Li, Long

    2017-09-01

    The Mesozoic accretionary complex in Northeast China, which mainly consists of the Jilin-Heilongjiang high-pressure (HP) metamorphic belt and the Nadanhada accretionary complex, are the key area to understand the Paleo-Pacific subduction-accretion. The Jilin-Heilongjiang HP belt is a HP metamorphic zone between the Jiamusi and Songliao blocks and consists of the Heilongjiang blueschist belt and the Zhangguangcai Complex. Previously published and our new geochronological data indicate that the collision between the Jiamusi and Songliao blocks along the Jilin-Heilongjiang HP belt occurred between 210 and 180 Ma, suggesting that the Jilin-Heilongjiang HP belt is an important unit for characterizing the geodynamic switch from the north-south closure of the Central Asian Orogenic Belt to the onset of westward accretion related to subduction of Paleo-Pacific plate in the Latest Triassic to Early Jurassic. Early Permian igneous rocks with arc affinity in the eastern margin of the Jiamusi Block are more likely related to the Mongol-Okhotsk subduction rather than the Paleo-Pacific subduction or the collision between the Jiamusi and Khanka blocks as previously considered. The Nadanhada accretionary complex lies to the east of the Jiamusi Block, and is composed of the Yuejinshan and Raohe complexes. Compilation of published geochronological data indicate that the Yuejinshan Complex was probably formed between 210 Ma and 180 Ma, similar to ages for the Jilin-Heilongjiang HP belt along the western margin of the Jiamusi-Khanka Block. The Raohe Complex was formed later in the Late Jurassic to Early Cretaceous (170-137 Ma), likely more related to the subduction-accretion of Paleo-Pacific plate. The final accretion in the target area took place in the Early Cretaceous (137-130 Ma).

  16. New Evaluation of Seismic Hazard in Cental America and la Hispaniola

    Science.gov (United States)

    Benito, B.; Camacho, E. I.; Rojas, W.; Climent, A.; Alvarado-Induni, G.; Marroquin, G.; Molina, E.; Talavera, E.; Belizaire, D.; Pierristal, G.; Torres, Y.; Huerfano, V.; Polanco, E.; García, R.; Zevallos, F.

    2013-05-01

    The results from seismic hazard studies carried out in two seismic scenarios, Central America Region (CA) and La Hispaniola Island, are presented here. Both cases follow the Probabilistic Seismic Hazard Assessment (PSHA) methodology and they are developed in terms of PGA, and SA (T), for T of 0.1, 0.2, 0.5, 1 and 2s. In both anaysis, hybrid zonation models are considered, integrated by seismogenic zones and faults where data of slip rate and recurrence time are available. First, we present a new evaluation of seismic hazard in CA, starting with the results of a previous study by Benito et al (2011). Some improvements are now included, such as: updated catalogue till 2011, corrections in the zonning model in particular for subduction regime taken into account the variation of the dip in Costa Rica and Panama, and modelization of some faults as independent units for the hazard estimation. The results allow us to carry out a sensitivity analysis comparing the ones obtained with and without faults. In a second part we present the results of the PSHA in La Hispaniola, carried out as part of the cooperative project SISMO-HAITI supported by UPM and developed in cooperation with ONEV. It started a few months after the 2010 event, as an answer to a required help from the Haitian government to UPM. The study was aimed at obtaining results suitable for seismic design purposes and started with the elaboration of a seismic catalogue for the Hispaniola, requiring an exhaustive revision of data reported by around 30 seismic agencies, apart from these from Puerto Rico and Dominican Republic Seismic Networks. Seismotectonic models for the region were reviewed and a new regional zonation was proposed, taking into account different geophysical data. Attenuation models for subduction and crustal zones were also reviewed and the more suitable were calibrated with data recorded inside the Caribbean plate. As a result of the PSHA, different maps were generated for the quoted parameters

  17. Middle Ordovician subduction of continental crust in the Scandinavian Caledonides - an example from Tjeliken, Seve Nappe Complex, Sweden

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    Fassmer, Kathrin; Andersson, Barbro; Klonowska, Iwona; Walczak, Katarzyna; Froitzheim, Nikolaus; Majka, Jarosław; Fonseca, Raul

    2017-04-01

    The Seve Nappe Complex (SNC) in the Scandinavian Caledonides represents the distal part of the margin of Baltica, which was subducted to depth of UHP metamorphism during the Caledonian orogeny. In contrast to the ages determined for the Western Gneiss Complex in Western Norway (ca. 420 - 400 Ma) which is interpreted to represent the subducted Baltican basement , the ages in the SNC and related nappes are overall older (ca. 500-430 Ma), with a general trend of higher ages in the North (Norrbotten) than in the South (Jämtland). As the previously published ages in the SNC are quite diverging it is difficult to reconstruct the tectonometamorphic history of this unit. Therefore exact dating with different methods is necessary to get a better constraint on the exact timing of subduction. We present new age determinations on an eclogite and a garnet-phengite schist from Tjeliken in northern Jämtland, Sweden. There the SNC can be divided into three tectonic units, an Eastern, Middle and Western belt. The locality of Mt. Tjeliken is situated in the Eastern Belt. Thermodynamic modelling of the eclogite yielded a pressure of 25-26 kbar at 650-700 °C (Majka et al. 2014). Previous dating produced diverging ages of 460±4 Ma (Sm-Nd mineral isochrones, Brueckner & Van Roermund 2007) and 446±1 Ma (U-Pb zircon dating, Root & Corfu 2012). In this study metamorphic rims of zircons from the garnet-phengite schist were dated using secondary ion mass spectrometry (SIMS) and yielded a concordia age of 458.9 ± 2.5 Ma. Lu-Hf garnet-whole rock dating yielded 458.5 ± 1.1 Ma for the eclogite. Garnet in the eclogite shows a prograde major-element zoning and a concentration of Lu in the cores, indicating that this age is related to garnet growth during pressure increase, i.e. subduction. The identical ages from both rock types confirm subduction of the outer margin of Baltica during the Middle Ordovician in a fast subduction-exhumation cycle. The fact that Sm-Nd and Lu-Hf dating yielded

  18. Thermal Evolution of the Permo−Triassic Karakaya Subduction-accretion Complex Between the Biga Peninsula and the Tokat Massif (Anatolia)

    OpenAIRE

    FEDERICI, ILARIA; CAVAZZA, WILLIAM; Okay, Aral I.; Beyssac, Olivier

    2014-01-01

    The results of the combined application of a series of analytical methods (clay mineralogy, vitrinite reflectance, Raman microspectroscopy) placed tight constraints on the thermal evolution of the Karakaya Complex of northern Anatolia, a mostly Permo-Triassic subduction-accretion complex resulting from the progressive closure of the Palaeotethys. The thermal evolution of the Karakaya Complex is the result of Permian-Triassic subduction-accretion processes, and was not significantly affected b...

  19. Eclogite inclusions from subducted metaigneous continental crust (Malpica-Tui Allochthonous Complex, NW Spain): Petrofabric, geochronology, and calculated seismic properties

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    Puelles, P.; Beranoaguirre, A.; Ábalos, B.; Gil Ibarguchi, J. I.; García de Madinabeitia, S.; Rodríguez, J.; Fernández-Armas, S.

    2017-07-01

    This study describes the strain geometry, crystal-plastic deformational features, isotopic age of metamorphism, and calculated seismic properties of two medium-temperature eclogite types from the Malpica-Tui Allochthonous Complex of Variscan NW Iberia. The eclogite types are eclogites with coronitic garnets and eclogites with a planolinear fabric. Both of them were buried, deformed and recrystallized under maximum pressure and temperature of 2.6 GPa and 610-640°C, and subsequently exhumed in a late Devonian subduction channel. The metamorphic peak of the subduction-exhumation cycle occurred 375 Ma ago. Omphacite petrofabric ties eclogites with coronitic garnet to noncoaxial constrictional strain and eclogites with planolinear fabrics to noncoaxial flattening strain and stretching along the lineation. We also used omphacite crystallographic preferred orientations to calculate and constrain the seismic properties of the eclogites. The slight variations in petrophysical properties observed are interpreted to result from variations in the strain regime recorded by pristine eclogites, or from variations in the modal proportions of the constituent high-pressure minerals. We foresee that eclogite in subduction metamorphic complexes might be either seismically undetectable or detected as planar features with high impedance contrasts relative to their host rocks.

  20. Genetic diversity and differentiation of Pseudophoenix (Arecaceae) in Hispaniola

    Science.gov (United States)

    Technical Abstract Pseudophoenix ekmanii Burret, P. lediniana Read, and P. vinifera (Mart.) Becc. (Arecaceae) are endemic to Hispaniola. The more wide-ranging P. sargentii H.Wendl. ex Sarg. occurs on this island as well. The population genetic diversity and structure of Pseudophoenix was investigate...

  1. Middle Ordovician subduction of continental crust in the Scandinavian Caledonides: an example from Tjeliken, Seve Nappe Complex, Sweden

    Science.gov (United States)

    Fassmer, Kathrin; Klonowska, Iwona; Walczak, Katarzyna; Andersson, Barbro; Froitzheim, Nikolaus; Majka, Jarosław; Fonseca, Raúl O. C.; Münker, Carsten; Janák, Marian; Whitehouse, Martin

    2017-12-01

    The Seve Nappe Complex of the Scandinavian Caledonides is thought to be derived from the distal passive margin of Baltica which collided with Laurentia in the Scandian Phase of the Caledonian Orogeny at 430-400 Ma. Parts of the Seve Nappe Complex were affected by pre-Scandian high- and ultrahigh-pressure metamorphism, in a tectonic framework that is still unclear, partly due to uncertainties about the exact timing. Previous age determinations yielded between 505 and 446 Ma, with a general trend of older ages in the North (Norrbotten) than in the South (Jämtland). New age determinations were performed on eclogite and garnet-phengite gneiss at Tjeliken in northern Jämtland. Thermodynamic modelling yielded peak metamorphic conditions of 25-27 kbar/680-760 °C for the garnet-phengite gneiss, similar to published peak metamorphic conditions of the eclogite (25-26 kbar/650-700 °C). Metamorphic rims of zircons from the garnet-phengite gneiss were dated using secondary ion mass spectrometry and yielded a concordia age of 458.9 ± 2.5 Ma. Lu-Hf garnet-whole rock dating yielded 458 ± 1.0 Ma for the eclogite. Garnet in the eclogite shows prograde major-element zoning and concentration of Lu in the cores, indicating that this age is related to garnet growth during pressure increase, i.e. subduction. The identical ages from both rock types, coinciding with published Sm-Nd ages from the eclogite, confirm subduction of the Seve Nappe Complex in Northern Jämtland during the Middle Ordovician in a fast subduction-exhumation cycle.

  2. Structural context and variation of ocean plate stratigraphy, Franciscan Complex, California: insight into mélange origins and subduction-accretion processes

    Science.gov (United States)

    Wakabayashi, John

    2017-12-01

    The transfer (accretion) of materials from a subducting oceanic plate to a subduction-accretionary complex has produced rock assemblages recording the history of the subducted oceanic plate from formation to arrival at the trench. These rock assemblages, comprising oceanic igneous rocks progressively overlain by pelagic sedimentary rocks (chert and/or limestone) and trench-fill clastic sedimentary rocks (mostly sandstone, shale/mudstone), have been called ocean plate stratigraphy (OPS). During accretion of OPS, megathrust slip is accommodated by imbricate faults and penetrative strain, shortening the unit and leading to tectonic repetition of the OPS sequence, whereas OPS accreted at different times are separated by non-accretionary megathrust horizons. The Franciscan subduction complex of California accreted episodically over a period of over 150 million years and incorporated OPS units with a variety of characteristics separated by non-accretionary megathrust horizons. Most Franciscan OPS comprises MORB (mid-ocean-ridge basalt) progressively overlain by chert and trench-fill clastic sedimentary rocks that are composed of variable proportions of turbidites and siliciclastic and serpentinite-matrix olistostromes (sedimentary mélanges). Volumetrically, the trench-fill component predominates in most Franciscan OPS, but some units have a significant component of igneous and pelagic rocks. Ocean island basalt (OIB) overlain by limestone is less common than MORB-chert assemblages, as are abyssal serpentinized peridotite slabs. The earliest accreted OPS comprises metabasite of supra-subduction zone affinity imbricated with smaller amounts of metaultramafic rocks and metachert, but lacking a clastic component. Most deformation of Franciscan OPS is localized along discrete faults rather than being distributed in the form of penetrative strain. This deformation locally results in block-in-matrix tectonic mélanges, in contrast to the sedimentary mélanges making up part of

  3. Structures and microfabrics of the Franciscan Complex (California): Inferences on the rheology and kinematics of a subduction channel

    Science.gov (United States)

    Krohe, A.; Wassmann, S.; Trepmann, C.; Stoeckhert, B.

    2009-12-01

    The characteristic feature of the Franciscan Subduction Complex (FSC) is a chaotic mélange structure with centimeter- to about one kilometer-sized tectonic blocks composed of metabasalts, floating in a matrix of oceanic meta-sediments or, locally, serpentinites. Investigating map scale structures, microfabrics, and P-T-histories of the FSC, we try to gain information on the mechanical properties of rocks and their influence on the kinematics of material transport in a subduction channel. Structures and microfabrics indicate that metabasalts from the oceanic crust as well as mantle-derived ultramafic rocks (i) underwent fragmentation and sealing under high pore fluid pressure, (ii) remaining internally undeformed, or (iii) deform by dissolution precipitation creep. Importantly, microfabrics which would indicate crystal plastic deformation or dislocation creep are systematically absent. This means that, during the entire P-T history, differential stresses generally remained too low to activate crystal plastic deformation or dislocation creep. Hence the material in the subduction channel is characterized by a low strength, being either limited by brittle failure at high pore fluid pressure, or a Newton viscosity, which is expected for dissolution precipitation creep. We interpret the characteristic mélange structure as to reflect this mechanical state of the system: Brittle failure at quasi-lithostatic fluid pressures down to great depths is recorded in the tectonic blocks by the widespread occurrence of aragonite-bearing veins. This leads to fragmentation into the blocks of variable size and moderate aspect ratios, which behave as rigid inclusions in a flowing matrix with distributed deformation by dissolution precipitation creep. In contrast, a power law rheology characteristic for dislocation creep, would favor strain localization into shear zones at sites of stress concentration. However, such shear zones formed at high-P metamorphic conditions are not

  4. Isotopic investigation of metasomatism in subduction zones: the Franciscan Complex, California

    Energy Technology Data Exchange (ETDEWEB)

    Nelson, B.K.; Depaolo, D.J.

    1985-01-01

    Metasomatizing fluids associated with metamorphism in subduction zones may be an important agent for the chemical modification of subducted rocks and of the overlying mantle wedge, both of which may be sources for island arc magmas. To characterize the timing of metasomatism and the source and nature of the fluids, the authors measured Sm-Nd and Rb-Sr isotope ratios of vein-filling minerals and actinolitic rinds cross-cutting meta-basaltic blocks from the Franciscan Central belt. 12 of 14 unmetasomatized samples of greenstone, blueschist and eclogite blocks have measured element of/sub ND/=+8 to +11, indicating MOR protoliths. Measured element of/sub Sr/ values scatter, but initial element of/sub Sr/ for whole rocks and garnets at 150 m.y. are +1 to +16. In element of/sub Nd=element of/sub Sr/ space the initial ratios are shifted to higher element of/sub Sr/ values with respect to unaltered MORB, suggesting seawater-hydrothermal alteration of the protolith. Foliated actinolite +/- white mica rinds from an eclogite and blueschist, both with element of/sub Nd/=+9, have element of/sub Nd/ of +6 and +1 respectively. The Rb-Sr age of the aragonite-glaucophane pair is 153.6 +/- 2.4 m.y., with initial /sup 87/Sr//sup 86/Sr = 0.7052 and element of/sub Nd/ = +6.3. The Rb-Sr age of a white mica-zoisite pair from a vein in a Tiburon eclogite is 151.9 +/- 0.4 m.y., initial /sup 87/Sr//sup 86/Sr = 0.7050 and element of/sub Nd/=+6.7. The vein fluids had similar isotopic compositions, but some rind-forming fluids had element of/sub Nd/<+1 suggesting a component derived from continental crust. Jadeitic metagreywacke, such as that from Pacheco Pass may be a source for low element of/sub Nd/ fluids. Beyond alteration at a MOR, subduction-related metasomatism may further modify eclogite returned to the mantle.

  5. On the initiation of subduction

    Science.gov (United States)

    Mueller, Steve; Phillips, Roger J.

    1991-01-01

    Estimates of shear resistance associated with lithospheric thrusting and convergence represent lower bounds on the force necessary to promote trench formation. Three environments proposed as preferential sites of incipient subduction are investigated: passive continental margins, transform faults/fracture zones, and extinct ridges. None of these are predicted to convert into subduction zones simply by the accumulation of local gravitational stresses. Subduction cannot initiate through the foundering of dense oceanic lithosphere immediately adjacent to passive continental margins. The attempted subduction of buoyant material at a mature trench can result in large compressional forces in both subducting and overriding plates. This is the only tectonic force sufficient to trigger the nucleation of a new subduction zone. The ubiquitous distribution of transform faults and fracture zones, combined with the common proximity of these features to mature subduction complexes, suggests that they may represent the most likely sites of trench formation if they are even marginally weaker than normal oceanic lithosphere.

  6. Mercury concentrations in tropical resident and migrant songbirds on Hispaniola.

    Science.gov (United States)

    Townsend, Jason M; Rimmer, Christopher C; Driscoll, Charles T; McFarland, Kent P; Iñigo-Elias, Eduardo

    2013-01-01

    Despite growing concerns over mercury (Hg) exposure to humans and wildlife on a global scale, little is known about Hg bioaccumulation in the New World tropics. From 2005 to 2011, we monitored Hg concentrations in blood of nine avian species occupying a geographic range of tropical wet broadleaf sites on the island of Hispaniola, including eight passerines (two Nearctic-Neotropical migrant and six resident species) and one top order predatory accipiter. Invertivorous songbirds were further differentiated by foraging guild, with six species of ground-foragers and two species of foliage-gleaners. Blood Hg concentrations were orders of magnitude higher in birds sampled in central and southern cloud forest sites (1,000-1,800 m elevation) than in northern and northeastern rainforest sites (50-500 m elevation), with migratory and resident species both showing 2-20× greater blood Hg concentrations in cloud forests than in rainforests. Within cloud forest sites, ground-foraging species had higher Hg concentrations than foliage-gleaning species. Top order predatory sharp-shinned hawks (Accipiter striatus) had the highest blood Hg concentrations among all species, suggesting that Hg biomagnification is occurring in terrestrial forests of Hispaniola. Two migrant songbird species overwintering on the island had higher blood Hg concentrations than have been recorded on their North American breeding grounds. Future studies should seek to elucidate sources of variation in atmospheric Hg deposition on Hispaniola and to quantify the dynamics of Hg cycling in tropical forest ecosystems, which may differ in important ways from patterns documented in temperate forest ecosystems.

  7. Prospects for malaria elimination in Mesoamerica and Hispaniola.

    Science.gov (United States)

    Herrera, Sócrates; Ochoa-Orozco, Sergio Andrés; González, Iveth J; Peinado, Lucrecia; Quiñones, Martha L; Arévalo-Herrera, Myriam

    2015-05-01

    Malaria remains endemic in 21 countries of the American continent with an estimated 427,000 cases per year. Approximately 10% of these occur in the Mesoamerican and Caribbean regions. During the last decade, malaria transmission in Mesoamerica showed a decrease of ~85%; whereas, in the Caribbean region, Hispaniola (comprising the Dominican Republic [DR] and Haiti) presented an overall rise in malaria transmission, primarily due to a steady increase in Haiti, while DR experienced a significant transmission decrease in this period. The significant malaria reduction observed recently in the region prompted the launch of an initiative for Malaria Elimination in Mesoamerica and Hispaniola (EMMIE) with the active involvement of the National Malaria Control Programs (NMCPs) of nine countries, the Regional Coordination Mechanism (RCM) for Mesoamerica, and the Council of Health Ministries of Central America and Dominican Republic (COMISCA). The EMMIE initiative is supported by the Global Fund for Aids, Tuberculosis and Malaria (GFATM) with active participation of multiple partners including Ministries of Health, bilateral and multilateral agencies, as well as research centers. EMMIE's main goal is to achieve elimination of malaria transmission in the region by 2020. Here we discuss the prospects, challenges, and research needs associated with this initiative that, if successful, could represent a paradigm for other malaria-affected regions.

  8. Prospects for malaria elimination in Mesoamerica and Hispaniola.

    Directory of Open Access Journals (Sweden)

    Sócrates Herrera

    2015-05-01

    Full Text Available Malaria remains endemic in 21 countries of the American continent with an estimated 427,000 cases per year. Approximately 10% of these occur in the Mesoamerican and Caribbean regions. During the last decade, malaria transmission in Mesoamerica showed a decrease of ~85%; whereas, in the Caribbean region, Hispaniola (comprising the Dominican Republic [DR] and Haiti presented an overall rise in malaria transmission, primarily due to a steady increase in Haiti, while DR experienced a significant transmission decrease in this period. The significant malaria reduction observed recently in the region prompted the launch of an initiative for Malaria Elimination in Mesoamerica and Hispaniola (EMMIE with the active involvement of the National Malaria Control Programs (NMCPs of nine countries, the Regional Coordination Mechanism (RCM for Mesoamerica, and the Council of Health Ministries of Central America and Dominican Republic (COMISCA. The EMMIE initiative is supported by the Global Fund for Aids, Tuberculosis and Malaria (GFATM with active participation of multiple partners including Ministries of Health, bilateral and multilateral agencies, as well as research centers. EMMIE's main goal is to achieve elimination of malaria transmission in the region by 2020. Here we discuss the prospects, challenges, and research needs associated with this initiative that, if successful, could represent a paradigm for other malaria-affected regions.

  9. Prospects for Malaria Elimination in Mesoamerica and Hispaniola

    Science.gov (United States)

    Herrera, Sócrates; Ochoa-Orozco, Sergio Andrés; González, Iveth J.; Peinado, Lucrecia; Quiñones, Martha L.; Arévalo-Herrera, Myriam

    2015-01-01

    Malaria remains endemic in 21 countries of the American continent with an estimated 427,000 cases per year. Approximately 10% of these occur in the Mesoamerican and Caribbean regions. During the last decade, malaria transmission in Mesoamerica showed a decrease of ~85%; whereas, in the Caribbean region, Hispaniola (comprising the Dominican Republic [DR] and Haiti) presented an overall rise in malaria transmission, primarily due to a steady increase in Haiti, while DR experienced a significant transmission decrease in this period. The significant malaria reduction observed recently in the region prompted the launch of an initiative for Malaria Elimination in Mesoamerica and Hispaniola (EMMIE) with the active involvement of the National Malaria Control Programs (NMCPs) of nine countries, the Regional Coordination Mechanism (RCM) for Mesoamerica, and the Council of Health Ministries of Central America and Dominican Republic (COMISCA). The EMMIE initiative is supported by the Global Fund for Aids, Tuberculosis and Malaria (GFATM) with active participation of multiple partners including Ministries of Health, bilateral and multilateral agencies, as well as research centers. EMMIE’s main goal is to achieve elimination of malaria transmission in the region by 2020. Here we discuss the prospects, challenges, and research needs associated with this initiative that, if successful, could represent a paradigm for other malaria-affected regions. PMID:25973753

  10. Late extensional shear zones and associated recumbent folds in the Alpujarride subduction complex, Betic Cordillera, southern Spain

    Energy Technology Data Exchange (ETDEWEB)

    Orozco, M.; Alonso-Chaves, F.; Platt, J.

    2017-11-01

    The existence in the Alpujarride Complex (Betic Cordillera, southern Spain) of a relatively continuous extensional event (following crustal thickening) is based on detailed structural studies and is consistent with the P-T paths and geochronological data established for the Alpujarride rocks. According to our research, the Alpujarride Complex contains two large-scale shear zones accommodating early Miocene extension. The shear zones contain km-scale recumbent folds, some with sheath fold geometry, and megaboudinage structures, and are closely associated with detachment faults. Large-scale folds and boudins cause dome-like undulations in the detachments, which are inferred to overlap in time with the deformation in the shear zones. One shear zone in the eastern part of the orogen is top-N; the other, in the western part, is top-E. The change in the shear direction may represent a temporal evolution in the direction of shear, possibly related to a change in the subduction direction in space and time.

  11. A discussion of numerical subduction initiation

    Science.gov (United States)

    Buiter, Susanne; Ellis, Susan

    2016-04-01

    In nature, subduction can initiate in various ways: Shortening can localise at oceanic transform faults, extinct spreading centres, or inherited passive margin faults; or, alternatively, subduction can be triggered from existing subduction systems by along-strike trench propagation, polarity reversals, or trench jumps. Numerical studies that specifically address subduction initiation have highlighted the roles of sediment loading, rheological strength contrasts, strain softening, and continental topographic gradients, among others. Usually, however, numerical models that aim to investigate subduction dynamics prefer to bypass the subduction initiation phase and its complexities, and focus instead on the stages during which the slab is descending into the mantle. However, even in these models, subduction still needs to begin. It is disturbingly easy to define initial model geometries that do not result in subduction. The specific combination of initial model geometries and values for rheological parameters that successfully initiates subduction has even been referred to as 'the sweet spot' in model space. One cause of subduction initiation failure is when the subducting and overriding plates lock, resulting in either indentation or severe dragging downwards of the overriding plate. This may point to a difficulty in maintaining a weak subduction interface during model evolution. A second factor that may cause difficulties is that initial model geometry and stresses need to balance, as otherwise the first model stages may show spurious deformation associated with reaching equilibrium. A third requirement that may cause problems is that the surface needs to have sufficient displacement freedom to allow the overriding plate to overthrust the subducting plate. That also implies an exclusion of sharp corners in the subduction interface near the surface. It is the interplay of subduction interface geometry, interface strength and subducting plate rheology that determines

  12. Geochemistry of jadeitites and jadeite-lawsonite rocks in a serpentinite mélange (Rio San Juan Complex, northern Dominican Republic): Constraints on fluid composition in a subduction channel environment

    Science.gov (United States)

    Baese, Rauno; Maresch, Walter V.; Schenk, Volker; Schertl, Hans-Peter

    2010-05-01

    Jadeitites are excellent rock types for obtaining information on fluid composition in subduction zones. Recent studies indicate that many jadeitites appear to have formed by direct precipitation from a fluid [1]. In almost all localities worldwide (see e.g. Harlow and Sorensen, 2005) jadeitites are found either as allochthonous blocks or as veins and lenses directly within the serpentinite country rock of serpentinite mélanges. In the Rio San Juan Complex on the other hand jadeitite also frequently occurs as veins (cm to some dm in thickness) within lawsonite-blueschist blocks [2,3,4] entrained in the serpentinite mélange. The mélange of the Rio San Juan Complex also contains blocks (m to 10m scale) of different metamorphic grade and lithology (eclogites, blueschists, orthogneisses and very low grade rocks) showing contrasting but interrelated P-T-t paths. The consistency of such interrelated P-T-t paths with those obtained by numerical models led Krebs et al. [5] to interpret the mélange of the Rio San Juan Complex as a former subduction channel. So far, two types of jadeitite have been found in the blueschist blocks: either as discordant veins cutting the foliation, or as concordant layers. In some cases the jadeitites contain large amounts of lawsonite and should then better be called jadeite-lawsonite rocks. The latter rock type may form a network of thin (contact between vein and host rock is very sharp and petrographically no sign of a depletion zone near the vein can be recognized, indicating that the infiltrating fluid originated from an external source and was not released from the adjoining host rock. A mineralogical center-to-rim zonation has been identified in the jadeitite veins. Near the contact to the blueschist, lawsonite is the dominant mineral phase and towards the center the amount of jadeite increases. Major and trace element concentrations also change from centers to rims. Ca/Na varies from 0.75-0.77 in the center to 1.03-1.29 in the rim

  13. Isla Hispaniola: A trans-boundary flood risk mitigation plan

    Science.gov (United States)

    Brandimarte, Luigia; Brath, Armando; Castellarin, Attilio; Baldassarre, Giuliano Di

    It is sadly known that over the past decades Isla Hispaniola (Haiti and the Dominican Republic) has been exposed to the devastating passage of several hurricanes and tropical storms. Territories that are economically weak and extremely poor in terms of natural resources have been shaken by severe flood events that caused the loss of thousands of human lives, displacement of people and damage to the environment. On May 24th 2004, the flooding of the trans-boundary river Soliette killed over 1000 Haitian and Dominican people, wiping out villages and leaving behind desolation and poverty. After this catastrophic flood event, the General Direction for Development and Cooperation of the Italian Department of Foreign Affairs funded through the Istituto Italo-Latino Americano (IILA, www.iila.org) an international cooperation initiative (ICI), coordinated and directed by the University of Bologna. The ICI involved Haitian and Dominican institutions and was twofold: (a) institutional capacity building on flood risk management and mitigation measures and policies; (b) hydrological and hydraulic analysis of the May 2004 flood event aimed at formulating a suitable and affordable flood risk mitigation plan, consisting of structural and non-structural measures.

  14. Evidence of Meso-Archaean subduction from the Torckler-Tango Layered Complex, Rauer Group, Prydz bay, East Antarctica

    Science.gov (United States)

    McCallum, C. A.; Harley, S. L.

    2010-12-01

    The Archaean Torckler Tango Layered complex (TTLC) of the Rauer Group, East Antarctica, consists of a series of elongate mega-boudins that can be traced over a strike length of 7 km, enclosed within and intruded by c. 2.8 Ga homogeneous tonalitic orthogneisses. Despite later granulite facies metamorphism (860-900°C, 0.7 GPa) original igneous structures and layering features of the TTLC are very well preserved. Graded and cross stratified layering is evident, as are load-cast structures and geopetal structures. Isotopic and LILE signatures indicate that crustal contamination has been negligible and that metamorphic disturbances have been minor. As a result, the whole rock chemistry of the TTLC is considered to reflect its igneous protoliths. This whole rock geochemistry is distinctive, with high MgO (av. 15.8 wt%), high Mg# (av. 79.1) low TiO2 (av.< 0.33 wt%), and high SiO2 (av. 52.5 wt%). The TTLC can be subdivided into two geochemical groupings based upon Al2O3 and Cr abundances, which provide clear evidence for the crystal fractionation and accumulation processes active within the complex. Trace-element and REE element ratios show coherent trends. Based on its systematic major element (Al2O3/TiO2 ~40), trace element ratios Ti/Zr vs. Zr (Ti/Zr ~34-59 at Zr ~15-40 ppm), and negative HSFE anomalies, the TTLC is similar in geochemistry to both modern, neo-Proterozoic and Archaean boninitic rocks. Magmatic zircons define an intrusive age for the TTLC of ca. 3280 ± 22 Ma. HSFE ratios, and whole rock Nd isotope ratios recalculated back to this age, are consistent with a juvenile depleted source for the primary magma. The TTLC is therefore interpreted as the intrusive equivalent of a boninite, produced through the shallow melting of refractory mantle and supportive of the operation of subduction-like processes in the early-mid Archaean.

  15. Trace element composition of rutile in eclogite from the Karakaya Complex, NW Anatolia: Implications for rutile growth during subduction zone metamorphism

    Science.gov (United States)

    Şengün, Fırat

    2017-04-01

    High-pressure/low-temperature (HP/LT) eclogite-facies terranes are widely regarded to represent exhumed fragments of subducted slabs. Therefore, the metamorphic studies of eclogites and associated high-pressure rocks yield crucial information about their P-T evolution and associated tectonometamorphic processes at depth in subduction zones. Especially rutile in eclogites record chemical history of subduction zones and also constrain metamorphic temperatures of subduction zone processes. Eclogites occur as a tectonic slice within metabasite-phyllite-marble intercalation of the Karakaya Complex. In this study, trace element geochemistry of rutiles and Zr-in-rutile thermometry have been investigated. The main mineralogical composition eclogites are composed of omphacite, garnet, glaucophane, epidote and quartz. Core-rim analyses through rutile grains yield remarkable trace element zoning with lower contents of Nb, Ta and Zr in the core than in the rim. The variations in Nb, Ta and Zr can be ascribed to the growth zoning rather than diffusion effect. The Nb/Ta and Zr/Hf ratios increase with a decrease in Ta and Hf contents, which could be ascribed to the effect of metamorphic dehydration at subduction zones on rutile Nb/Ta differentiation. The rutile grains from eclogites in the Karakaya Complex are characterized by subchondritic Nb/Ta and Zr/Hf ratios. It can be noted that the subchondritic Nb/Ta ratios may record rutile growth from local sinks of aqueous fluids from metamorphic dehydration. The Zr contents of the all rutile grains vary between 81 and 160 ppm with the average of 123 ppm. The Zr-in-rutile thermometer yielded the metamorphic temperature of 559-604 oC (average 585 oC) for eclogites occurring in the Karakaya Complex. This average temperature suggests the peak growth temperature of rutile. Moreover, Zr contents and calculated temperatures in both inclusion rutile and matrix rutile from eclogites are identical to each other, which suggests that rutiles in

  16. Subduction of shallowly formed arc cumulates: Evidence from clinopyroxene compositions of garnet peridotites in the Rio San Juan Complex, northern Dominican Republic

    Science.gov (United States)

    Hattori, K.; Tubrett, M.; Saumur, B.-M.; Guillot, S.

    2009-04-01

    Garnet peridotites are very rare in oceanic subduction complexes, with only two reported occurrences. One is in the Sambagawa metamorphic belt in Shikoku, Japan, and the other example is in the southern part of the Rio Juan Complex, northern Dominican Republic. In both locations, garnet peridotite occurs in close association with eclogites in high metamorphic grade of the terranes. The Rio Juan Complex represents rocks formed during the southwestern subduction of the Proto-Caribbean oceanic plate below the Carribean Plate during late Cretaceous to early Eocene. Garnet peridotites (clinopyroxene[Cpx]-bearing dunite, wehrlite, olivine clinopyroxenite) occur as large (The rocks are all low in Ir-group PGE (Ir, Ru, Os), indicating that they are cumulates of a melt, since these remain in the residue during partial melting. A cumulate origin of the ultramafic rocks is consistent with relatively low Mg contents of olivine (Fo 74-83) compared to olivine in mantle peridotites. Extended trace element plots of the bulk rocks show a so-called "arc geochemical signature" with high fluid-mobile element concentrations, such as Sr, U, and Pb, and low HFSE, such as Nb and Zr, indicating that formation of the parental magmas were related to subduction. Two representative garnet-bearing samples (wehrlite and clinopyroxenite) were selected for trace element analysis of Cpx grains using a LA HR ICP-MS. The data show a negatively sloped normalized pattern of REE; low contents of light REE (0.1-0.3 of the primitive mantle values) and similar concentrations of middle to heavy REE (1-2 of the primitive mantle values). Extended trace element patterns of Cpx are similar between two samples and also to that of the bulk rocks, with low Nb and Zr and high fluid-mobile elements. The Y and heavy REE patterns of Cpx do not show anomalies between the samples. As these elements would be preferentially incorporated into garnet, the lack of anomalies indicates early crystallization of Cpx and later

  17. Paleo-Pacific subduction-accretion: Evidence from Geochemical and U-Pb zircon dating of the Nadanhada accretionary complex, NE China

    Science.gov (United States)

    Zhou, Jian-Bo; Cao, Jia-Lin; Wilde, Simon A.; Zhao, Guo-Chun; Zhang, Jin-Jiang; Wang, Bin

    2014-12-01

    The Nadanhada Terrane, located along the eastern margin of Eurasia, contains a typical accretionary complex related to paleo-Pacific plate subduction-accretion. The Yuejinshan Complex is the first stage accretion complex that consists of meta-clastic rocks and metamafic-ultramafic rocks, whereas the Raohe Complex forms the main parts of the terrane and consists of limestone, bedded chert, and mafic-ultramafic rocks embedded as olistolith blocks in a weakly sheared matrix of clastic meta-sedimentary rocks. Geochemical data indicate that the Yuejinshan metabasalts have normal mid-ocean ridge basalt (N-MORB) affinity, whereas the Raohe basaltic pillow lavas have an affinity to ocean island basalts (OIB). Sensitive high-resolution ion microprobe (SHRIMP) U-Pb zircon analyses of gabbro in the Raohe Complex yield a weighted mean 206Pb/238U zircon age of 216 ± 5 Ma, whereas two samples of granite intruded into the complex yield weighted mean 206Pb/238U zircon ages of 128 ± 2 and 129 ± 2 Ma. Laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) U-Pb zircon analyses of basaltic pillow lava in the Raohe Complex define a weighted mean age of 167 ± 1 Ma. Two sandstone samples in the Raohe Complex record younger concordant zircon weighted mean ages of 167 ± 17 and 137 ± 3 Ma. These new data support the view that accretion of the Raohe Complex was between 170 and 137 Ma, and that final emplacement of the Raohe Complex took place at 137-130 Ma. The accretion of the Yuejinshan Complex probably occurred between the 210 and 180 Ma, suggesting that paleo-Pacific plate subduction was initiated in the Late Triassic to Early Jurassic.

  18. Deformation of mantle pyroxenites provides clues to geodynamic processes in subduction zones: Case study of the Cabo Ortegal Complex, Spain

    Science.gov (United States)

    Henry, Hadrien; Tilhac, Romain; Griffin, William L.; O'Reilly, Suzanne Y.; Satsukawa, Takako; Kaczmarek, Mary-Alix; Grégoire, Michel; Ceuleneer, Georges

    2017-08-01

    In the Herbeira massif, Cabo Ortegal Complex, Spain, a well exposed assemblage of deformed dunites and pyroxenites offers a unique opportunity to investigate key upper mantle tectonic processes. Four types of pyroxenites are recognized: clinopyroxenites with enclosed dunitic lenses (type-1), massive websterites (type-2), foliated and commonly highly amphibolitized clinopyroxenites (type-3) and orthopyroxenites (type-4). Field and petrological observations together with EBSD analysis provide new insights on the physical behavior of the pyroxenes and their conditions of deformation and reveal the unexpected journey of the Cabo Ortegal pyroxenites. We show that, during deformation, type-1 pyroxenites, due to their enclosed dunitic lenses, are more likely to localize the deformation than types-2 and -4 pyroxenites and may latter act as preferred pathway for fluid/melt percolation, eventually resulting in type-3 pyroxenites. All pyroxenite types display a similar response to deformation. Orthopyroxene deformed mostly by dislocation creep; it shows kink bands and undulose extinction and its fabric is dominated by [001](100). Clinopyroxene displays subgrain rotation, dynamic recrystallization and fabric with [010] axes clustering next to the foliation pole and [001] axes clustering next to the lineation suggesting activation of [001]{110} and [001](100) in some samples. These observations are in good agreement with deformation at temperatures greater than 1000 °C. Olivine in type-1 and type-4 pyroxenites shows [100](010) or [001](010) fabrics that are consistent with deformation at temperatures >1000 °C and may indicate deformation in a hydrous environment. The amphibole [001](100) fabric gives insights on a lower-temperature deformation episode (∼800 to 500 °C). Our results, interpreted in the light of published experimental data, together with the regional geological and geochemical studies are consistent with the following tectonic evolution of the Cabo Ortegal

  19. Evolving metasomatic agent in the North Andean subduction, deduced from magma composition of the long-lived Pichincha volcanic complex (Ecuador)

    Science.gov (United States)

    Samaniego, P.; Robin, C.; Chazot, G.; Bourdon, E. P.; Jo, C.

    2009-12-01

    Geochemical studies of long-lived volcanic complexes are crucial for the understanding of the nature and composition of the subduction component of arc magmatism. The Pichincha Volcanic Complex (Northern Andean Volcanic Zone) consists of: (1) an older, highly eroded edifice, the Rucu Pichincha, whose lavas are mostly andesites, erupted from 1100 to 150 ka; and (2) a younger, essentially dacitic, Guagua Pichincha composite edifice, with three main construction phases (Basal Guagua Pichincha, Toaza and Cristal) which formed over the last 60 ka. This structural evolution was accompanied by a progressive increase of most incompatible trace element abundances and ratios, as well as by a sharp decrease of fluid-mobile to fluid-immobile element ratios. Geochemical data indicate that fractional crystallization of an amphibole-rich cumulate could account for the evolution from the Guagua Pichincha andesites to dacites. However, in order to explain the passage from the Rucu Pichincha andesites to Guagua Pichincha dacites, the mineralogical and geochemical data indicate the predominance of magma mixing processes between a mafic, trace-element depleted, mantle-derived end-member, and a siliceous, trace-element enriched, adakitic end-member. The systematic variation of trace element abundances and ratios in primitive samples of this volcanic complex leads us to propose that the Rucu Pichincha magmas came from a hydrous-fluid metasomatized mantle wedge, whereas Guagua Pichincha magmas are related to partial melting of a siliceous-melt metasomatized mantle. This temporal evolution implies a change from dehydration to partial melting of the slab, which may be associated with an increase in the geothermal gradient along the slab due to the presence of the subducted Carnegie Ridge at the subduction system. This work emphasizes the importance of studying arc-magma systems over long periods of time (of at least 1 million of years), in order to evaluate the potential variations of the

  20. Evolving metasomatic agent in the Northern Andean subduction zone, deduced from magma composition of the long-lived Pichincha volcanic complex (Ecuador)

    Science.gov (United States)

    Samaniego, Pablo; Robin, Claude; Chazot, Gilles; Bourdon, Erwan; Cotten, Joseph

    2010-08-01

    Geochemical studies of long-lived volcanic complexes are crucial for the understanding of the nature and composition of the subduction component of arc magmatism. The Pichincha Volcanic Complex (Northern Andean Volcanic Zone) consists of: (1) an old, highly eroded edifice, the Rucu Pichincha, whose lavas are mostly andesites, erupted from 1,100 to 150 ka; and (2) a younger, essentially dacitic, Guagua Pichincha composite edifice, with three main construction phases (Basal Guagua Pichincha, Toaza, and Cristal) which developed over the last 60 ka. This structural evolution was accompanied by a progressive increase of most incompatible trace element abundances and ratios, as well as by a sharp decrease of fluid-mobile to fluid-immobile element ratios. Geochemical data indicate that fractional crystallization of an amphibole-rich cumulate may account for the evolution from the Guagua Pichincha andesites to dacites. However, in order to explain the transition between the Rucu Pichincha andesites and Guagua Pichincha dacites, the mineralogical and geochemical data indicate the predominance of magma mixing processes between a mafic, trace-element depleted, mantle-derived end-member, and a siliceous, trace-element enriched, adakitic end-member. The systematic variation of trace element abundances and ratios in primitive samples leads us to propose that the Rucu Pichincha magmas came from a hydrous-fluid metasomatized mantle wedge, whereas Guagua Pichincha magmas are related to partial melting of a siliceous-melt metasomatized mantle. This temporal evolution implies a change from dehydration to partial melting of the slab, which may be associated with an increase in the geothermal gradient along the slab due to the presence of the subducted Carnegie Ridge at the subduction system. This work emphasizes the importance of studying arc-magma systems over long periods of time (of at least 1 million of years), in order to evaluate the potential variations of the slab contribution

  1. The Compositions And Sources Of Fluids Through Time In A 1.8 Gya UHP Subduction Complex

    Science.gov (United States)

    Glassley, W. E.; Korstgård, J.; Sorensen, K.

    2016-12-01

    The HP and UHP history of a 1.8 Gya terrain in West Greenland (Glassley et al., 2014) is only preserved in pods, lenses and tectonic slices that escaped hydration during transit to lower P-T conditions from the UHP environment. The terrain consists of a tectonic assemblage of metasomatically altered pillow basalts, ultramafic bodies, exhalative and chemical oceanic metasediments, pelites, and quartzo-feldspathic gneisses, that are the preserved remnants of a subduction channel. Only those rocks that escaped significant hydration during decompression preserve evidence of the sequence of recrystallization episodes under evolving fluid conditions. The highest-pressure mineral assemblages exhibit no evidence of fluid presence, implying very low activities of potential fluid components. During ascent from UHP conditions, recrystallization involved a sequence of fluid-sensitive mineral assemblages (graphite precipitation > carbonate precipitation > OH-bearing mineral growth) as well as exsolution features involving oxides. Buffering mineral assemblages, e.g., QFM, developed as decompression progressed. Carbon isotope measurements on graphite document a biogenic origin (∂C13 = -24.6) for the C in the precipitated graphite. The results, when placed in a time sequence correlating with P-T trajectory suggest that the subduction channel may have been zoned with respect to the dominant fluid components. The results demonstrate that: 1) The extent of recrystallization during decompression is mainly a reflection of local rock chemistry/mineralogy and fluid activity; 2) Preservation of the prograde P-T-t path during subduction is a very sensitive function of the fluid composition and activity during decompression.

  2. High-pressure mafic oceanic rocks from the Makbal Complex, Tianshan Mountains (Kazakhstan & Kyrgyzstan): Implications for the metamorphic evolution of a fossil subduction zone

    Science.gov (United States)

    Meyer, Melanie; Klemd, Reiner; Konopelko, Dmitry

    2013-09-01

    The Makbal Complex in the western Tianshan Mountains of Kazakhstan and Kyrgyzstan consists of HP/UHP metasedimentary host rocks which enclose various HP mafic blocks or boudins. These mafic rocks comprise rare eclogites (sensu stricto and sensu lato), garnet amphibolites (retrograded eclogites) and a newly discovered glaucophanite (glaucophane-garnet-omphacite bearing rock). So far the Makbal Complex has been interpreted to predominantly consist of continental lithologies and the mafic rocks were considered as dismembered dikes intruding continental metasediments. This interpretation is mainly based on the geological relationship and bulk rock chemistry of the different rock types. It was further suggested that the continental lithologies of the Makbal Complex underwent eclogite-facies metamorphism in a former subduction zone. In the present study we combined conventional geothermometry, P-T pseudosection modeling and major and trace element whole rock geochemistry for different mafic samples (glaucophanite and eclogites (sensu lato)) in order to shed light on both the metamorphic evolution and the protoliths of the mafic HP rocks in the Makbal Complex. Prograde to peak-pressure clockwise P-T paths of glaucophanite and eclogites (sensu lato) were modeled using garnet isopleth thermobarometry. The results show that the glaucophanite and eclogite (sensu lato) samples experienced similar prograde P-T paths and slightly different peak metamorphic conditions at ~ 560 °C at 2.4 GPa for the former and between ~ 520 °C at 2.2 GPa and ~ 555 °C at ~ 2.5 GPa for the latter, corresponding to burial depths between 70 and 85 km. Whole rock major and trace element analyses and petrological evidence imply that the various rock types at the Makbal Complex most likely originated from different precursor rocks. Eclogites (sensu lato) are believed to represent strongly retrogressed former eclogite-facies rocks that had never been eclogites (sensu stricto, i.e. > 70 vol.% garnet and

  3. Contribution to the study of the genus Helicopsyche (Trichoptera) from Cuba, Hispaniola, and Puerto Rico

    NARCIS (Netherlands)

    Botosaneanu, L.; Flint, O.S.

    1991-01-01

    Seven new species and one new subspecies of Helicopsyche von Sieboid are described from Cuba, Hispaniola, and Puerto Rico based on adults; additionally four species and one subspecies belonging to the fauna of these islands are redescribed. Both sexes are described when correct association of

  4. Taxonomic Revision of Hispaniola Tiger Beetles in the Genus Brasiella Rivalier 1954 (Coleoptera, Carabidae, Cicindelinae)

    Science.gov (United States)

    Acciavatti, Robert E.

    2011-01-01

    Abstract The Brasiella tiger beetle fauna on Hispaniola, the second largest island of the Greater Antilles, has more species diversity than currently recognized as all populations previously have been assigned to the insular endemic Brasiella dominicana (Mandl). A comparative study of adult morphology, particularly male genitalic and female abdominal characters, for available Brasiella specimens from populations on Hispaniola, proposes eight additional new species also endemic to this island. Except for three sympatric species in the Sierra de Baoruco in southern Dominican Republic occurring in different habitats, all the Brasiella on Hispaniola appear to be allopatric. Most species occur in the major mountainous regions of Hispaniola. Two species, however, are known only from river floodplains in the southern coastal plain of the Dominican Republic. Brasiella dominicana (Mandl) and Brasiella ocoa, new species, occur along river floodplains emanating from the eastern end of the Cordillera Central in the Dominican Republic. Two new Brasiella species, Brasiella bellorum, and Brasiella philipi, occur in the Cordillera Central, Dominican Republic, the former species from central portions, and the latter species from north slopes of this mountain range, respectively. Three new Brasiella species, Brasiella rawlinsi, Brasiella iviei, and Brasiella youngi, are isolated in the Sierra de Baoruco, Dominican Republic, where each occupies a different habitat along an altitudinal gradient. The two new Brasiella species in Haiti are Brasiella darlingtoniana, in the Massif de la Selle, and Brasiella davidsoni, in the Massif de la Hotte. All nine Brasiella species on Hispaniola, along with Brasiella viridicollis (Dejean) and its two subspecies on Cuba, belong to the viridicollis species group of the genus Brasiella based on criteria presented in earlier published phylogenetic studies of Brazilian and West Indian tiger beetles. The subspecies Brasiella viridicollis fernandozayasi

  5. Primary fluids entrapped at blueschist to eclogite transition: evidence from the Tianshan meta-subduction complex in northwestern China

    Science.gov (United States)

    Gao, Jun; Klemd, Reiner

    2001-06-01

    The Tianshan is the first locality worldwide where primary fluids at blueschist to eclogite transition have been documented. Veins containing high-pressure minerals in massive host eclogites transitional to blueschists, or eclogite boudins surrounded by blueschists, indicate that a free fluid phase was present at the time of eclogitization. The high-pressure veins are predominantly composed of omphacite fibers with minor quartz or calcite. The transition from blueschist- to eclogite-facies parageneses occurs as "dehydration" halos around these veins. Clinozoisite, paragonite, glaucophane, and omphacite inclusions preserved in garnet porphyroblasts in wall eclogites document the transformation of blueschist to eclogite. C-axis-parallel, non-planar populations of fluid inclusions were trapped during the growth of omphacite in high-pressure veins and dehydrated wall rocks. Low salinity H2O + NaCl +/- solid-bearing inclusions are preserved in omphacite fibers in veins and matrix omphacite of wall rocks. None of the isochores of these low salinity aqueous fluid inclusions intersect peak eclogite-facies metamorphic conditions, suggesting that, although the textural evidence constrains the entrapment of fluid inclusions to peak metamorphic conditions, their densities must have been modified during exhumation. The fluids are interpreted to have been derived from the host blueschist as a result of dehydration reactions such as 13 Gln+5 Czo=9 Prp+26 Jd+12 Di+19 Qtz+15 H2O and Gln+Pg=Prp+3 Jd+2 Otz+2 H2O. The similarity of vein and wall rock mineral compositions, fluid inclusion characteristics and O-isotope data also favor an internal source for the fluids. The major element composition of veins indicate that Si, Na, and Ca-rich aqueous fluids were released during dehydration at a depth of 50+/-10 km within a Paleozoic subduction zone.

  6. Three-dimensional dynamic laboratory models of subduction with an overriding plate and variable interplate rheology

    NARCIS (Netherlands)

    Duarte, João C.; Schellart, Wouter P.; Cruden, Alexander R.

    2013-01-01

    Subduction zones are complex 3-D features in which one tectonic plate sinks underneath another into the deep mantle. During subduction the overriding plate (OP) remains in physical contact with the subducting plate and stresses generated at the subduction zone interface and by mantle flowforce the

  7. Early Cretaceous wedge extrusion in the Indo-Burma Range accretionary complex: implications for the Mesozoic subduction of Neotethys in SE Asia

    Science.gov (United States)

    Zhang, Ji'en; Xiao, Wenjiao; Windley, Brian F.; Cai, Fulong; Sein, Kyaing; Naing, Soe

    2017-06-01

    The Indo-Burma Range (IBR) of Myanmar, the eastern extension of the Yarlung-Tsangpo Neotethyan belt of Tibet in China, contains mélanges with serpentinite, greenschist facies basalt, chert, sericite schist, silty slate and unmetamorphosed Triassic sandstone, mudstone and siltstone interbedded with chert in the east, and farther north high-pressure blueschist and eclogite blocks in the Naga Hills mélange. Our detailed mapping of the Mindat and Magwe sections in the middle IBR revealed a major 18 km antiformal isocline in a mélange in which greenschist facies rocks in the core decrease in grade eastwards and westwards symmetrically `outwards' to lower grade sericite schist and silty slate, and at the margins to unmetamorphosed sediments, and these metamorphic rocks are structurally repeated in small-scale imbricated thrust stacks. In the Mindat section the lower western boundary of the isoclinal mélange is a thrust on which the metamorphic rocks have been transported over unmetamorphosed sediments of the Triassic Pane Chaung Group, and the upper eastern boundary is a normal fault. These relations demonstrate that the IBR metamorphic rocks were exhumed by wedge extrusion in a subduction-generated accretionary complex. Along strike to the north in the Naga Hills is a comparable isoclinal mélange in which central eclogite lenses are succeeded `outwards' by layers of glaucophane schist and glaucophanite, and to lower grade greenschist facies sericite schist and slate towards the margins. In the Natchaung area (from west to east) unmetamorphosed Triassic sediments overlie quartzites, sericite schists, actinolite schists and meta-volcanic amphibolites derived from MORB-type basalt, which are in fault contact with peridotite. Olivine in the peridotite has undulatory extinction suggesting deformation at 600-700 °C, similar to the peak temperature of the amphibolite; these relations suggest generation in a metamorphic sole. The amphibolites have U/Pb zircon ages of 119

  8. Plume-induced subduction

    Science.gov (United States)

    Gerya, T.; Stern, R. J.; Baes, M.; Sobolev, S. V.; Whattam, S. A.

    2016-12-01

    Dominant present-day subduction initiation mechanisms require acting plate forces and/or pre-existing zones of lithospheric weakness, which are themselves consequences of plate tectonics. In contrast, recently discovered plume-induced subduction initiation could have started the first subduction zone without pre-existing plate tectonics. Here, we investigate this new mechanism with high-resolution 3D numerical thermomechanical modeling experiments. We show that typical plume-induced subduction dynamics is subdivided into five different stages: (1) oceanic plateau formation by arrival of a mantle plume head; (2) formation of an incipient trench and a descending nearly-circular slab at the plateau margins; (3) tearing of the circular slab; (4) formation of several self-sustained retreating subduction zones and (5) cooling and spreading of the new lithosphere formed between the retreating subduction zones. At the final stage of plume-induced subduction initiation, a mosaic of independently moving, growing and cooling small oceanic plates heading toward individual retreating subduction zones forms. The plates are separated by spreading centers, triple junctions and transform faults and thus the newly formed multi-slab subduction system operates as an embryonic plate tectonic cell. We demonstrate that three key physical factors combine to trigger self-sustained plume-induced subduction: (1) old negatively buoyant oceanic lithosphere; (2) intense weakening of the lithosphere by plume-derived magmas; and (3) lubrication of the forming subduction interface by hydrated oceanic crust. We furthermore discuss that plume-induced subduction, which is rare at present day conditions, may have been common in the Precambrian time and likely started global plate tectonics on Earth.

  9. Isotope and trace element studies of the Xingdi II mafic-ultramafic complex in the northern rim of the Tarim Craton: Evidence for emplacement in a Neoproterozoic subduction zone

    Science.gov (United States)

    Chen, Hongjin; Chen, Yanjing; Ripley, Edward M.; Li, Chusi; Deng, Xiaohua; Yue, Suwei; Zheng, Zhen; Fu, Bin

    2017-05-01

    The Xingdi II mafic-ultramafic complex is located in the northern rim of the Tarim Craton, Northern Xinjiang, NW China. This complex is mainly composed of gabbro, gabbronorite, websterite and lherzolite, plus minor granodiorites and granites. The geodynamic setting of this complex and other Neoproterozoic mafic-ultramafic complexes in the region is debated, with opinions varying from mantle plume to a continental arc. A new zircon U-Pb age from this study reveals > 7-myr difference for two gabbroic intrusive phases in the Xingdi II mafic-ultramafic complex and up to a 21-myr difference between this complex and the nearby mafic-ultramafic complexes that occur crystals from the Xingdi II mafic-ultramafic complex are between - 2.8 and - 7.0. The trace element and isotope data together indicate that this complex formed from multiple pulses of contaminated subduction-related basaltic magma that were emplaced separately with a time gap of at least 7 myr. The results from this study support the viewpoint that in the Neoproterozoic the northern rim of the Tarim Craton was an active continental margin that belongs to the Circum-Rodinia Subduction System.

  10. The genus Loxosceles Heineken & Lowe (Araneae: Sicariidae) in Cuba and Hispaniola, West Indies.

    Science.gov (United States)

    Ruiz, Alexander Sánchez; Brescovit, Antonio D

    2013-10-30

    The three known species of the genus Loxosceles Heineken & Lowe from Cuba and Hispaniola are revised and two new species, Loxosceles maisi sp. nov. and Loxosceles mogote sp. nov., are described from the eastern region of Cuba. These new species are included in the reclusa group, and are considered close to Loxosceles taino Gertsch & Ennik as they have a greatly thickened male palpal tibia, a projecting cymbium, and large receptacles in the female genitalia. The distribution ranges of the known Cuban and Hispaniolan species are extended.

  11. Metallogeny of subduction zones

    Directory of Open Access Journals (Sweden)

    Sorokhtin N. O.

    2017-03-01

    Full Text Available The paper deals with the multistage mechanism of the Earth's crust enrichment in ore elements in underthrust zones. The processes of metamorphism and the formation of hydrothermal solutions at pulling of the watered oceanic lithospheric plate into the subduction zone have been described. Some physical and chemical transformation regularities of structural-material complexes in these areas and mechanisms of the formation of ore deposits have been discussed. Spatio-temporal patterns of the localization of a number of endogenetic and exogenetic deposits have been described using metallogeny of the Ural and the Verkhoyansk-Kolyma Fold Belts as an example. It has been shown that in nature there are several effective mechanisms of the enrichment of the crust in ore minerals. One of them is the process of pulling into subduction zone of metalliferous sediments and ferromanganese crusts as well as seabed nodules, their metamorphic transformation, partial melting and transition of ore components into magmatic melts and mineralized fluids. In the future this leads to the release of ore material by magmas and hydrothermal solutions into the folded formations of island-arc and Andean types and the formation of igneous, metasomatic and hydrothermal deposits. Another, yet no less powerful natural mechanism of a conveyor enrichment of the crust in ore elements is the process of destruction and sedimentation of mineral deposits formed in the folded areas as well as the formation of placers and their transfer to the marginal parts of the continent. Later, during the collision of active and passive margins of two lithospheric plates, such as the collision of the Kolyma Massif with the eastern part of the Siberian craton in the middle of the Mesozoic there was a thrusting of a younger lithospheric plate over a more ancient one. As a result, the sedimentary sequences of the passive margin of the Siberian plate were submerged and partially melted by the basic magmas

  12. Hypolestes hatuey sp. nov.: a new species of the enigmatic genus Hypolestes (Odonata, Hypolestidae) from Hispaniola.

    Science.gov (United States)

    Torres-Cambas, Yusdiel; Lorenzo-Carballa, M Olalla; Ferreira, Sónia; Cordero-Rivera, Adolfo

    2015-08-14

    Both sexes of Hypolestes hatuey Torres-Cambas, sp. nov. (Odonata: Zygoptera: Hypolestidae) from Hispaniola are described and illustrated here. This newly described species differs from H. trinitatis and H. clara, the other two species within the genus, by the morphology of the genital ligula and male cerci. Females of H. hatuey sp. nov. differ from H. clara by the shape of the female antehumeral stripe and wing venation. Morphological distinctiveness in males is supported by genetic differences in the 16S mitochondrial gene. Following the categories and criteria of the IUCN Red List of Threatened Species, we suggest this species should be listed as Data Deficient (DD), given that available data on its distribution are too limited to assess its risk of extinction.

  13. Introduction to the structures and processes of subduction zones

    Science.gov (United States)

    Zheng, Yong-Fei; Zhao, Zi-Fu

    2017-09-01

    Subduction zones have been the focus of many studies since the advent of plate tectonics in 1960s. Workings within subduction zones beneath volcanic arcs have been of particular interest because they prime the source of arc magmas. The results from magmatic products have been used to decipher the structures and processes of subduction zones. In doing so, many progresses have been made on modern oceanic subduction zones, but less progresses on ancient oceanic subduction zones. On the other hand, continental subduction zones have been studied since findings of coesite in metamorphic rocks of supracrustal origin in 1980s. It turns out that high-pressure to ultrahigh-pressure metamorphic rocks in collisional orogens provide a direct target to investigate the tectonism of subduction zones, whereas oceanic and continental arc volcanic rocks in accretionary orogens provide an indirect target to investigate the geochemistry of subduction zones. Nevertheless, metamorphic dehydration and partial melting at high-pressure to ultrahigh-pressure conditions are tectonically applicable to subduction zone processes at forearc to subarc depths, and crustal metasomatism is the physicochemical mechanism for geochemical transfer from the slab to the mantle in subduction channels. Taken together, these provide us with an excellent opportunity to find how the metamorphic, metasomatic and magmatic products are a function of the structures and processes in both oceanic and continental subduction zones. Because of the change in the thermal structures of subduction zones, different styles of metamorphism, metasomatism and magmatism are produced at convergent plate margins. In addition, juvenile and ancient crustal rocks have often suffered reworking in episodes independent of either accretionary or collisional orogeny, leading to continental rifting metamorphism and thus rifting orogeny for mountain building in intracontinental settings. This brings complexity to distinguish the syn-subduction

  14. Tracing source terranes using U-Pb-Hf isotopic analysis of detrital zircons: provenance of the Orhanlar Unit of the Palaeotethyan Karakaya subduction-accretion complex, NW Turkey

    Science.gov (United States)

    Ustaömer, Timur; Ayda Ustaömer, Petek; Robertson, Alastair; Gerdes, Axel

    2016-04-01

    Sandstones of the Late Palaeozoic-Early Mesozoic Karakaya Complex are interpreted to have accumulated along an active continental margin related to northward subduction of Palaeotethys. The age of deposition and provenance of the sandstones are currently being determined using radiometric dating of detrital zircons, coupled with dating of potential source terranes. Our previous work shows that the U-Pb-Hf isotopic characteristics of the sandstones of all but one of the main tectonostratigraphic units of the Karakaya Complex are compatible with a provenance that was dominated by Triassic and Permo-Carboniferous magmatic arc-type rocks, together with a minor contribution from Lower to Mid-Devonian igneous rocks (Ustaömer et al. 2015). However, one of the tectono-stratigraphic units, the Orhanlar Unit, which occurs in a structurally high position, differs in sedimentary facies and composition from the other units of the Karakaya Complex. Here, we report new isotopic age data for the sandstones of the Orhanlar Unit and also from an extensive, associated tectonic slice of continental metamorphic rocks (part of the regional Sakarya Terrane). Our main aim is to assess the provenance of the Orhanlar Unit sandstones in relation to the tectonic development of the Karakaya Complex as a whole. The Orhanlar Unit is composed of shales, sandstone turbidites and debris-flow deposits, which include blocks of Devonian radiolarian chert and Carboniferous and Permian neritic limestones. The sandstones are dominated by rock fragments, principally volcanic and plutonic rocks of basic-to-intermediate composition, metamorphic rocks and chert, together with common quartz, feldspar and mica. This modal composition contrasts significantly with the dominantly arkosic composition of the other Karakaya Complex sandstones. The detrital zircons were dated by the U-Pb method, coupled with determination of Lu-Hf isotopic compositions using a laser ablation microprobe attached to a multicollector

  15. New myrmecomorphous longhorned beetles from Haiti and the Dominican Republic with a key to Anaglyptini and Tillomorphini of Hispaniola (Coleoptera: Cerambycidae: Cerambycinae)

    Science.gov (United States)

    First records of the tribes Anaglyptini and Tillomorphini (Coleoptera: Cerambycidae: Cerambycinae) are documented for Hispaniola. A new genus of highly myrmecomorphic longhorned beetle (Licracantha, new genus) is described and illustrated based on one species (Licracantha formicaria, new species) a...

  16. Geochronology of diamond-bearing zircons from garnet peridotite in the North Qaidam UHPM belt, Northern Tibetan Plateau: A record of complex histories from oceanic lithosphere subduction to continental collision [rapid communication

    Science.gov (United States)

    Song, Shuguang; Zhang, Lifei; Niu, Yaoling; Su, Li; Jian, Ping; Liu, Dunyi

    2005-05-01

    We report the results of a comprehensive study of zircons separated from the Lüliangshan peridotite massif within the 400-km-long North Qaidam UHPM belt, northern Tibetan Plateau, NW China. The peridotite massif is dominated by garnet lherzolite with minor amounts of interlayered garnet-bearing dunite and cross-cutting garnet pyroxenite dikes. Most zircons from the garnet lherzolite show rather complex zoning. One diamond and a few graphite inclusions are identified in some zircons by Raman spectroscopy. SHRIMP dating on these zircons show four major age groups: (a) 484-444 Ma (weighted mean age, 457 ± 22 Ma) for cores of most crystals, whose morphology and rare earth element (REE) systematics (i.e., very high [Lu / Sm] CN = 88-230) suggest a magmatic origin, consistent with the protolith being magmatic cumulate; (b) 435-414 Ma with a mean of 423 ± 5 Ma, which, given by mantle portions of zircon crystals, is interpreted to record the event of ultrahigh-pressure metamorphism (UHPM) at depths greater than 200 km in an Andean-type subduction zone; (c) 402-384 Ma (mean age 397 ± 6 Ma) for near-rim portions of zircon crystals; and (d) 368-349 Ma for outermost rims, which is interpreted as representing some post-orogenic thermal events. Inherited cores in two zircon crystals were identified using CL and found to be Proterozoic. Morphology and CL images show that zircons from dunite and garnet pyroxenite are of metamorphic origin. The mean age of dunite zircons is 420 ± 5 Ma, which overlaps the mantle age of the garnet lherzolite zircon (see (b) above). The mean age of garnet pyroxenite zircons is 399 ± 8 Ma, which overlaps ages of near-rim domains in garnet lherzolite zircons (see (c) above). Some garnet pyroxenite zircons also recorded a retrograde event at 358 ± 7 Ma. All these data suggest that the Lüliangshan garnet peridotite massif is not a fragment of ancient lithospheric mantle, but a peridotite body with long and complex histories from Early Ordovician

  17. Buoyant subduction on Venus: Implications for subduction around coronae

    Science.gov (United States)

    Burt, J. D.; Head, J. W.

    1993-01-01

    Potentially low lithospheric densities, caused by high Venus surface and perhaps mantle temperatures, could inhibit the development of negative buoyancy-driven subduction and a global system of plate tectonics/crustal recycling on that planet. No evidence for a global plate tectonic system was found so far, however, specific features strongly resembling terrestrial subduction zones in planform and topographic cross-section were described, including trenches around large coronae and chasmata in eastern Aphrodite Terra. The cause for the absence, or an altered expression, of plate tectonics on Venus remains to be found. Slab buoyancy may play a role in this difference, with higher lithospheric temperatures and a tendency toward positive buoyancy acting to oppose the descent of slabs and favoring under thrusting instead. The effect of slab buoyancy on subduction was explored and the conditions which would lead to under thrusting versus those allowing the formation of trenches and self-perpetuating subduction were defined. Applying a finite element code to assess the effects of buoyant forces on slabs subducting into a viscous mantle, it was found that mantle flow induced by horizontal motion of the convergent lithosphere greatly influences subduction angle, while buoyancy forces produce a lesser effect. Induced mantle flow tends to decrease subduction angle to near an under thrusting position when the subducting lithosphere converges on a stationary overriding lithosphere. When the overriding lithosphere is in motion, as in the case of an expanding corona, subduction angles are expected to increase. An initial stage involved estimating the changes in slab buoyancy due to slab healing and pressurization over the course of subduction. Modeling a slab, descending at a fixed angle and heated by conduction, radioactivity, and the heat released in phase changes, slab material density changes due to changing temperature, phase, and pressure were derived.

  18. Crustal structure of western Hispaniola (Haiti) from a teleseismic receiver function study

    Science.gov (United States)

    Corbeau, J.; Rolandone, F.; Leroy, S.; Guerrier, K.; Keir, D.; Stuart, G.; Clouard, V.; Gallacher, R.; Ulysse, S.; Boisson, D.; Bien-aimé Momplaisir, R.; Saint Preux, F.; Prépetit, C.; Saurel, J.-M.; Mercier de Lépinay, B.; Meyer, B.

    2017-07-01

    Haiti, located at the northern Caribbean plate boundary, records a geological history of terrane accretion from Cretaceous island arc formations to the Eocene to Recent oblique collision with the Bahamas platform. Little is presently known about the underlying crustal structure of the island. We analyze P-waveforms arriving at 27 temporary broadband seismic stations deployed over a distance of 200 km across the major terrane boundaries in Haiti to determine the crustal structure of western Hispaniola. We compute teleseismic receiver functions using the Extended-Time Multi-Taper method and determine crustal thickness and bulk composition (Vp/Vs) using the H-k stacking method. Three distinctive and fault-bounded crustal domains, defined by their characteristic Moho depth distributions and bulk crustal Vp/Vs, are imaged across Haiti. We relate these domains to three crustal terranes that have been accreted along the plate boundary during the northeastwards displacement of the Caribbean plate and are presently being deformed in a localized fold and thrust belt. In the northern domain, made up of volcanic arc facies, the crust has a thickness of 23 km and Vp/Vs of 1.75 ± 0.1 typical of average continental crust. The crust in the southern domain is part of the Caribbean Large Igneous Province (Caribbean LIP), and is 22 km thick with Vp/Vs of 1.80 ± 0.03 consistent with plume-related rocks of late Cretaceous age. Significantly thicker, the crust in central Haiti has values of Moho depths averaging 41 km and with Vp/Vs of 1.80 ± 0.05. We propose that the central domain is likely constructed of an island arc upper crust with fragments of dense material originating from mafic lavas or LIP material. We produce a crustal profile along a N-S transect across Haiti accounting for the surface geology, shallow structural history, and new seismological constraints provided by variations of crustal thickness and bulk composition.

  19. Ablative subduction - A two-sided alternative to the conventional subduction model

    Science.gov (United States)

    Tao, Winston C.; O'Connell, Richard J.

    1992-01-01

    The plausibility of a two-sided fluid-based model of lithospheric subduction that is based upon current views of lithospheric structure is examined. In this model the viscous lower lithosphere flows downward, and the brittle upper lithosphere deforms in passive response. This process is potentially double-sided, since it is found that even a buoyant plate can be dragged downward by a dense descending neighbor. Thus an apparent overriding plate may be worn away by a process of viscous ablation, with the rate of ablation a function of plate buoyancy. This process, called 'ablative subduction,' makes it possible to simply interpret observations concerning slab profiles, interplate seismicity, back arc tectonics, and complex processes such as double subduction and subduction polarity reversal. When experiments modeling the evolution of simple fluid 'slabs' are performed, slab profile is found to be strongly influenced by ablation in the overriding plate. When ablation is weak, as when a buoyant continent borders the trench, deformable slabs adopt shallow Andean-style profiles.

  20. Boron cycling in subduction zones

    OpenAIRE

    Palmer, Martin R.

    2017-01-01

    Subduction zones are geologically dramatic features, with much of the drama being driven by the movement of water. The “light and lively” nature of boron, coupled with its wide variations in isotopic composition shown by the different geo-players in this drama, make it an ideal tracer for the role and movement of water during subduction. The utility of boron ranges from monitoring how the fluids that are expelled from the accretionary prism influence seawater chemistry, to the subduction of c...

  1. Faulting and strain partitioning in Jamaica from GPS and structural data: Implications for Gonave and Hispaniola microplate kinematics, northern Caribbean

    Science.gov (United States)

    Benford, Bryn

    A series of small microplates separate the Caribbean and North America plates in the northern Caribbean. My dissertation focuses on understanding the structural evolution and neotectonic deformation of Jamaica, and how it relates to the overall microplates and tectonics of the northern Caribbean. Jamaica, which lies along the same seismically active plate boundary as Haiti, has had twelve earthquakes with Modified Mercalli intensities of VII to X since 1667. However, remarkably little is known about which faults presently constitute the most significant seismic hazards. This research provides insight into tectonic processes and facilitates mitigation of geological hazards in the region. Two chapters focus on characterizing deformation in Jamaica through modeling GPS velocities and through field mapping. The best-fitting models based on GPS velocities place most strike-slip motion on faults in central Jamaica and suggest that faults in northern Jamaica have minimal motion. I estimate 4--5 mm yr-1 of slip for faults near the capital city of Kingston of southeastern Jamaica, implying significant seismic hazard. Field mapping combined with present-day topography, focal mechanisms, geology, gravity, and well and borehole data indicate that east-west contraction is accommodated by reactivated, NNW-striking reverse faults, which are bound by E-striking strike-slip faults in southern Jamaica. The other two chapters of my thesis focuses on understanding the behavior of the microplates along the Caribbean-North America plate boundary: I model GPS velocities and use shear-wave splitting to understand the crustal and mantle behaviors, respectively of the microplates. The GPS data require an independently moving Hispaniola microplate between the Mona Passage and a likely diffuse boundary just west of or within western Hispaniola. The new microplate angular velocities predict 6.8+/-1.0 mm yr-1 of left-lateral slip and 5.7+/-1 mm yr-1 of convergent motion surrounding the

  2. An Alpine-style Ordovician collision complex in the Sierra de Pie de Palo, Argentina: Record of subduction of Cuyania beneath the Famatina arc

    Science.gov (United States)

    van Staal, C. R.; Vujovich, G. I.; Currie, K. L.; Naipauer, M.

    2011-03-01

    The Caucete Group and structurally overlying Pie de Palo Complex in western Argentina are characterised by two generations of west-verging folds and thrust-related shear zones, which formed under amphibolite facies conditions. The Caucete Group is separated from the Pie de Palo Complex by the Pirquitas thrust. These structures are interpreted to have formed as a result of a progressive deformation, generated during Middle Ordovician, underthrusting of the Laurentian-derived Cuyania microcontinent beneath the active Famatina margin. Geometrical relationships are most simply explained if the Pie de Palo Complex was basement to the Caucete Group prior to Ordovician orogenesis. We propose that this basement-cover relationship was established during Cambrian rifting of the Cuyania microcontinent from Laurentia. The Pirquitas fault may have been initiated during this extension prior to its long-lived remobilization as a thrust. We cannot rule out the possibility that the Pie de Palo Complex was exotic with respect to the Caucete Group, but for this to be possible we have to introduce an extra generation of structures, for which no evidence is preserved. The deformation was characterised by early strain localization followed by a more homogeneously distributed non-coaxial flow during F 2. Thermal softening probably dominated over fabric softening during this stage.

  3. Seismicity and the subduction process

    Science.gov (United States)

    Ruff, L.; Kanamori, H.

    1980-01-01

    There is considerable variation between subduction zones in the largest characteristic earthquake within each zone. Assuming that coupling between downgoing and upper plates is directly related to characteristic earthquake size, tests for correlations between variation in coupling and other physical features of subduction zones are conducted: the lateral extent and penetration depth of Benioff zones, age of subducting lithosphere, convergence rate, and back-arc spreading. Using linear multivariate regression, coupling is correlated with two variables: convergence rate and lithosphere age. Secondary correlations within the data set are penetration depth versus lithosphere age, and lateral extent versus convergence rate. Taken together, the observed correlations suggest a simple qualitative model where convergence rate and lithosphere age determine the horizontal and sinking rates, respectively, of slabs: these parameters influence the seismic coupling in the subduction zone. In the limit of a fast sinking rate and slow convergence rate, back-arc spreading occurs and thereby appears to be a passive process.

  4. Discovery of a Giant Chameleon-Like Lizard (Anolis) on Hispaniola and Its Significance to Understanding Replicated Adaptive Radiations.

    Science.gov (United States)

    Mahler, D Luke; Lambert, Shea M; Geneva, Anthony J; Ng, Julienne; Hedges, S Blair; Losos, Jonathan B; Glor, Richard E

    2016-09-01

    We report a new chameleon-like Anolis species from Hispaniola that is ecomorphologically similar to congeners found only on Cuba. Lizards from both clades possess short limbs and a short tail and utilize relatively narrow perches, leading us to recognize a novel example of ecomorphological matching among islands in the well-known Greater Antillean anole radiation. This discovery supports the hypothesis that the assembly of island faunas can be substantially deterministic and highlights the continued potential for basic discovery to reveal new insights in well-studied groups. Restricted to a threatened band of midelevation transitional forest near the border of the Dominican Republic and Haiti, this new species appears to be highly endangered.

  5. Taxonomy of the Loggerhead Kingbird (Tyrannus caudifasciatus) complex (Aves: Tyrannidae)

    Science.gov (United States)

    Orlando H. Garrido; James W. Wiley; George B. Reynard

    2009-01-01

    We examined the complex of populations of the Loggerhead Kingbird (Tyrannus caudifasciatus), a West Indian endemic. We separate populations in Puerto Rico and Isla Vieques (T. taylori), and Hispaniola (T. gabbii) as distinct species. Subspecific distinction is assigned to populations in Cuba, Isla de Pinos, and Cuban satellites (T. caudifasciatus caudifasciatus);...

  6. Subduction processes related to the Sea of Okhotsk

    Science.gov (United States)

    Zabarinskaya, Ludmila P.; Sergeyeva, Nataliya

    2017-04-01

    It is obviously important to study a role of subduction processes in tectonic activity within the continental margins. They are marked by earthquakes, volcanic eruptions, tsunami and other natural disasters hazardous to the people,plants and animals that inhabit such regions. The northwest part of the Sea of Okhotsk including the northern part of Sakhalin Island and the Deryugin Basin is the area of the recent intensive tectonic movements. The geological and geophysical data have made it possible to construct the geodynamic model of a deep structure of a lithosphere for this region. This geodynamic model has confirmed the existence of the ophiolite complex in the region under consideration. It located between the North Sakhalin sedimentary basin and the Deryugin basin. The Deryugin basin was formed on the side of an ancient deep trench after subducting the Okhotsk Sea Plate under Sakhalin in the Late Cretaceous-Paleogene. The North Sakhalin Basin with oil and gas resources was formed on the side of back-arc basin at that time. Approximately in the Miocene period the subduction process, apparently, has stopped. The remains of the subduction zone in the form of ophiolite complex have been identified according to geological and geophysical data. On a surface the subduction zone is shown as deep faults stretched along Sakhalin.

  7. Subduction-driven recycling of continental margin lithosphere.

    Science.gov (United States)

    Levander, A; Bezada, M J; Niu, F; Humphreys, E D; Palomeras, I; Thurner, S M; Masy, J; Schmitz, M; Gallart, J; Carbonell, R; Miller, M S

    2014-11-13

    Whereas subduction recycling of oceanic lithosphere is one of the central themes of plate tectonics, the recycling of continental lithosphere appears to be far more complicated and less well understood. Delamination and convective downwelling are two widely recognized processes invoked to explain the removal of lithospheric mantle under or adjacent to orogenic belts. Here we relate oceanic plate subduction to removal of adjacent continental lithosphere in certain plate tectonic settings. We have developed teleseismic body wave images from dense broadband seismic experiments that show higher than expected volumes of anomalously fast mantle associated with the subducted Atlantic slab under northeastern South America and the Alboran slab beneath the Gibraltar arc region; the anomalies are under, and are aligned with, the continental margins at depths greater than 200 kilometres. Rayleigh wave analysis finds that the lithospheric mantle under the continental margins is significantly thinner than expected, and that thin lithosphere extends from the orogens adjacent to the subduction zones inland to the edges of nearby cratonic cores. Taking these data together, here we describe a process that can lead to the loss of continental lithosphere adjacent to a subduction zone. Subducting oceanic plates can viscously entrain and remove the bottom of the continental thermal boundary layer lithosphere from adjacent continental margins. This drives surface tectonics and pre-conditions the margins for further deformation by creating topography along the lithosphere-asthenosphere boundary. This can lead to development of secondary downwellings under the continental interior, probably under both South America and the Gibraltar arc, and to delamination of the entire lithospheric mantle, as around the Gibraltar arc. This process reconciles numerous, sometimes mutually exclusive, geodynamic models proposed to explain the complex oceanic-continental tectonics of these subduction zones.

  8. Fluid flux and melting reactions in subduction zones

    Science.gov (United States)

    Bouilhol, Pierre; Magni, Valentina; van Hunen, Jeroen; Kaislaniemi, Lars

    2014-05-01

    Understanding the metamorphic reactions that occurs within the slab is a must to constrain subduction zone processes. Slab dehydration reactions ultimately permit the mantle wedge to melt, by lowering its solidus, thus forming arcs above descending slabs. Alternatively the slab crust may cross its solidus in warm hydrated slabs. Moreover, slab dehydration allows chemical fractionation to occur between residual phases and transferred fluid phase, giving arc magmas part of their typical subduction zone chemical characteristics. To better comprehend such complex thermo-chemical open system, we are using a numerical model that reproduces the thermo-mechanical behaviour of a subducting slab and computes the thermodynamic equilibrium paragenesis at each P-T-X conditions of the system. Hence we generate a "paragenetic map" of a subduction system, allowing us to track the fate of water during dehydration and subsequent re-hydration or melting reactions. Here we highlight the role of dehydration and re-hydration reactions occurring in the slab's igneous crust and mantle and the mantle wedge for different slab configuration hence presenting the evolution of a subduction paragenetic map for different regimes. We intend to show the key roles of a) antigorite and chlorite breakdown in the hydrated part of the slab mantle, b) amphibole and lawsonite in the slab crust, and c) the role of amphibole and chlorite in the mantle wedge. Our results show the crucial role of dehydration and re-hydration reactions on slab and mantle wedge melting potential.

  9. Processes and consequences of deep subduction

    NARCIS (Netherlands)

    Rubie, David C.; Hilst, R.D. van der

    2001-01-01

    Subduction of slabs of oceanic lithosphere into the deep mantle involves a wide range of geophysical and geochemical processes and is of major importance for the physical and chemical evolution of the Earth. For example, subduction and subduction-related volcanism are major processes through

  10. Building a Subduction Zone Observatory

    Science.gov (United States)

    Gomberg, Joan S.; Bodin, Paul; Bourgeois, Jody; Cashman, Susan; Cowan, Darrel; Creager, Kenneth C.; Crowell, Brendan; Duvall, Alison; Frankel, Arthur; Gonzalez, Frank; Houston, Heidi; Johnson, Paul; Kelsey, Harvey; Miller, Una; Roland, Emily C.; Schmidt, David; Staisch, Lydia; Vidale, John; Wilcock, William; Wirth, Erin

    2016-01-01

    Subduction zones contain many of Earth’s most remarkable geologic structures, from the deepest oceanic trenches to glacier-covered mountains and steaming volcanoes. These environments formed through spectacular events: Nature’s largest earthquakes, tsunamis, and volcanic eruptions are born here.

  11. Thermal buoyancy on Venus - Underthrusting vs subduction

    Science.gov (United States)

    Burt, Jeffrey D.; Head, James W.

    1992-01-01

    The thermal and buoyancy consequences of the subduction endmember are modeled in an attempt to evaluate the conditions distinguishing underthrusting and subduction. Thermal changes in slabs subducting into the Venusian mantle with a range of initial geotherms are used to predict density changes and, thus, slab buoyancy. Based on a model for subduction-induced mantle flow, it is then argued that the angle of the slab dip helps differentiate between underthrusting and subduction. Mantle flow applies torques to the slab which, in combination with torques due to slab buoyancy, act to change the angle of slab dip.

  12. Viscous Dissipation and Criticality of Subducting Slabs

    Science.gov (United States)

    Riedel, Mike; Karato, Shun; Yuen, Dave

    2016-04-01

    Rheology of subducting lithosphere appears to be complicated. In the shallow part, deformation is largely accomodated by brittle failure, whereas at greater depth, at higher confining pressures, ductile creep is expected to control slab strength. The amount of viscous dissipation ΔQ during subduction at greater depth, as constrained by experimental rock mechanics, can be estimated on the basis of a simple bending moment equation [1,2] 2ɛ˙0(z) ∫ +h/2 2 M (z) = h ṡ -h/2 4μ(y,z)y dy , (1) for a complex multi-phase rheology in the mantle transition zone, including the effects of a metastable phase transition as well as the pressure, temperature, grain-size and stress dependency of the relevant creep mechanisms; μ is here the effective viscosity and ɛ˙0(z) is a (reference) strain rate. Numerical analysis shows that the maximum bending moment, Mcrit, that can be sustained by a slab is of the order of 1019 Nm per m according to Mcrit˜=σp ∗h2/4, where σp is the Peierl's stress limit of slab materials and h is the slab thickness. Near Mcrit, the amount of viscous dissipation grows strongly as a consequence of a lattice instability of mantle minerals (dislocation glide in olivine), suggesting that thermo-mechanical instabilities become prone to occur at places where a critical shear-heating rate is exceeded, see figure. This implies that the lithosphere behaves in such cases like a perfectly plastic solid [3]. Recently available detailed data related to deep seismicity [4,5] seems to provide support to our conclusion. It shows, e.g., that thermal shear instabilities, and not transformational faulting, is likely the dominating mechanism for deep-focus earthquakes at the bottom of the transition zone, in accordance with this suggested "deep criticality" model. These new findings are therefore briefly outlined and possible implications are discussed. References [1] Riedel, M. R., Karato, S., Yuen, D. A. Criticality of Subducting Slabs. University of Minnesota

  13. A model for the termination of the Ryukyu subduction zone against Taiwan: A junction of collision, subduction/separation, and subduction boundaries

    Science.gov (United States)

    Wu, F.T.; Liang, W.-T.; Lee, J.-C.; Benz, H.; Villasenor, A.

    2009-01-01

    The NW moving Philippine Sea plate (PSP) collides with the Eurasian plate (EUP) in the vicinity of Taiwan, and at the same time, it subducts toward the north along SW Ryukyu. The Ryukyu subduction zone terminates against eastern Taiwan. While the Ryukyu Trench is a linear bathym??trie low about 100 km east of Taiwan, closer to Taiwan, it cannot be clearly identified bathymetrically owing to the deformation related to the collision, making the location of the intersection of the Ryukyu with Taiwan difficult to decipher. We propose a model for this complex of boundaries on the basis of seismicity and 3-D velocity structures. In this model the intersection is placed at the latitude of about 23.7??N, placing the northern part of the Coastal Range on EUP. As PSP gets deeper along the subduction zone it collides with EUP on the Taiwan side only where they are in direct contact. Thus, the Eurasian plate on the Taiwan side is being pushed and compressed by the NW moving Philippine Sea plate, at increasing depth toward the north. Offshore of northeastern Taiwan the wedge-shaped EUP on top of the Ryukyu subducting plate is connected to the EUP on the Ryukyu side and coupled to the NW moving PSP by friction at the plate interface. The two sides of the EUP above the western end of the subduction zone are not subjected to the same forces, and a difference in motions can be expected. The deformation of Taiwan as revealed by continuous GPS measurements, geodetic movement along the east coast of Taiwan, and the formation of the Hoping Basin can be understood in terms of the proposed model. Copyright 2009 by the American Geophysical Union.

  14. Horizontal mantle flow controls subduction dynamics.

    Science.gov (United States)

    Ficini, E; Dal Zilio, L; Doglioni, C; Gerya, T V

    2017-08-08

    It is generally accepted that subduction is driven by downgoing-plate negative buoyancy. Yet plate age -the main control on buoyancy- exhibits little correlation with most of the present-day subduction velocities and slab dips. "West"-directed subduction zones are on average steeper (~65°) than "East"-directed (~27°). Also, a "westerly"-directed net rotation of the lithosphere relative to the mantle has been detected in the hotspot reference frame. Thus, the existence of an "easterly"-directed horizontal mantle wind could explain this subduction asymmetry, favouring steepening or lifting of slab dip angles. Here we test this hypothesis using high-resolution two-dimensional numerical thermomechanical models of oceanic plate subduction interacting with a mantle flow. Results show that when subduction polarity is opposite to that of the mantle flow, the descending slab dips subvertically and the hinge retreats, thus leading to the development of a back-arc basin. In contrast, concordance between mantle flow and subduction polarity results in shallow dipping subduction, hinge advance and pronounced topography of the overriding plate, regardless of their age-dependent negative buoyancy. Our results are consistent with seismicity data and tomographic images of subduction zones. Thus, our models may explain why subduction asymmetry is a common feature of convergent margins on Earth.

  15. On the role of the Beata Ridge in the structure of southern Hispaniola: new constrains from the correlation between offshore and onshore structures

    Science.gov (United States)

    Granja Bruña, J.; Hernaiz-Huerta, P.; Carbó-Gorosabel, A.; Llanes Estrada, M.; Pérez-Valera, F.; Abad, M.; Gómez Ballesteros, M.; Druet, M.; Munoz Martin, A.; Martín-Dávila, J.; Pazos, A.; Catalan, M.; ten Brink, U. S.

    2011-12-01

    The Beata Ridge is a thickened aseismic crust block that forms a NNE-SSW trending bathymetric high located in the interior of the Caribbean Large Igneous Province (CLIP). This ridge is impinging into the Greater Antilles island arc in south-central Hispaniola Island. The impingement has resulted into the following main consequences for the southern region of Hispaniola: uplifting and accretion of part of the CLIP to the island arc, an associated localized strain partitioning and a sharp structural change between both sides of the ridge, with frontal thrusting in the Los Muertos convergent margin (to the east) against dominant left-lateral strike-slip tectonics in the Enriquillo-Plantain Garden fault zone (to the west). Two hypotheses have been suggested to explain the impingement as a result of: 1) the continuous motion of the aseismic ridge toward the NE against the Greater Antilles, at least from the Miocene; or 2) the thickened ridge acting as a fixed obstacle in the foreland area impeding the overthrusting of the island arc over the Caribbean plateau. Several works have tried to restore the situation prior to the impingement of the Beata Ridge into the island arc and to correlate the tectonic units observed on both sides of the region of impingement: the offshore imbricate structures observed in Los Muertos convergent margin with the onshore Peralta fold-and-thrust belt and/or the E-W transcurrent Enriquillo fault system in southern Hispaniola. However as a result of the huge lateral and vertical offset caused by the impingement of the aseismic ridge there is not a tectonic model which can successfully explain this transition. A detailed interpretation of the deep and shallow structure of western Los Muertos convergent margin and northern Beata Ridge has been made using the new data obtained from the CARIBENORTE research cruise carried out in the spring of 2009 in the southern insular slope of Hispaniola. On the other hand a complete geothematic survey of the

  16. Subduction and vertical coastal motions in the eastern Mediterranean

    Science.gov (United States)

    Howell, Andy; Jackson, James; Copley, Alex; McKenzie, Dan; Nissen, Ed

    2017-10-01

    Convergence in the eastern Mediterranean of oceanic Nubia with Anatolia and the Aegean is complex and poorly understood. Large volumes of sediment obscure the shallow structure of the subduction zone, and since much of the convergence is accommodated aseismically, there are limited earthquake data to constrain its kinematics. We present new source models for recent earthquakes, combining these with field observations, published GPS velocities and reflection-seismic data to investigate faulting in three areas: the Florence Rise, SW Turkey and the Pliny and Strabo Trenches. The depths and locations of earthquakes reveal the geometry of the subducting Nubian plate NE of the Florence Rise, a bathymetric high that is probably formed by deformation of sediment at the surface projection of the Anatolia-Nubia subduction interface. In SW Turkey, the presence of a strike-slip shear zone has often been inferred despite an absence of strike-slip earthquakes. We show that the GPS-derived strain-rate field is consistent with extension on the orthogonal systems of normal faults observed in the region and that strike-slip faulting is not required to explain observed GPS velocities. Further SW, the Pliny and Strabo Trenches are also often interpreted as strike-slip shear zones, but almost all nearby earthquakes have either reverse-faulting or normal-faulting focal mechanisms. Oblique convergence across the trenches may be accommodated either by a partitioned system of strike-slip and reverse faults or by oblique slip on the Aegean-Nubia subduction interface. The observed late-Quaternary vertical motions of coastlines close to the subduction zone are influenced by the interplay between: (1) thickening of the material overriding the subduction interface associated with convergence, which promotes coastal uplift; and (2) subsidence due to extension and associated crustal thinning. Long-wavelength gravity data suggest that some of the observed topographic contrasts in the eastern

  17. Subduction dynamics: Constraints from gravity field observations

    Science.gov (United States)

    Mcadoo, D. C.

    1985-01-01

    Satellite systems do the best job of resolving the long wavelength components of the Earth's gravity field. Over the oceans, satellite-borne radar altimeters such as SEASAT provide the best resolution observations of the intermediate wavelength components. Satellite observations of gravity contributed to the understanding of the dynamics of subduction. Large, long wavelength geoidal highs generally occur over subduction zones. These highs are attributed to the superposition of two effects of subduction: (1) the positive mass anomalies of subducting slabs themselves; and (2) the surface deformations such as the trenches convectively inducted by these slabs as they sink into the mantle. Models of this subduction process suggest that the mantle behaves as a nonNewtonian fluid, its effective viscosity increases significantly with depth, and that large positive mass anomalies may occur beneath the seismically defined Benioff zones.

  18. Reevaluating plate driving forces from 3-D models of subduction

    Science.gov (United States)

    Stegman, D. R.; Freeman, J.; Schellart, W. P.; Moresi, L.; May, D.; Turnbull, R.

    2004-12-01

    Subducting lithospheric slabs mechanically attached to tectonic plates provide the main driving force for surface plate motion. Numerical models historically simulate slab dynamics as a 2-D process and further simplify the problem into either a density driven model (no heat transfer) or a corner-flow problem (thermal convection) [Christensen, 2001; Enns et al., (in revision); van Keken, 2003]. Recent 3-D global models of density driven flow incorporating a history of plate motion (Conrad and Lithgow-Bertelloni, 2002) have succussfully ruled out slab "suction" (basal shear traction induced by downward flow of the slabs) as a major driving force, but exact partitioning of the remaining forces acting on the slab remain unconstrained. A survey of trenches around the world reveals that over half of the slabs presently subducted in the upper mantle have a discontinuous edge (either a slab tip on a young slab, or the side edge of a slab with finite width) around which mantle can flow: prime examples being slabs in the Mediterranean and Carribean. However, even slabs with a wide lateral extent (and where a 2-D approximation may seem appropriate), show signs of having 3-D complexity. For example, on the surface Tonga appears relatively symmetric, but when the history of subduction is considered, the slab has a twisted, 3-D structure due to significant eastward retreat of just the northern part of an originally N-S oriented trench edge. Similarly the widest slabs, South American and Kamchatka, show seismic anisotropy attributed to trench parallel mantle flow (Russo and Silver, 1994; Peyton, et al., 2001, respectively), while the Aleutian trench has oblique subduction varying in magnitude from west to east, and medium width Central American slab likely has a slab window allowing 3-D flow (Johnston and Thorkelson, 1997). Recent laboratory experiments of subduction have demonstrated the full complexity of flow occuring in 3-D geometry (Kincaid and Griffiths, 2003; Schellart

  19. Thermobarometric and fluid expulsion history of subduction zones

    Energy Technology Data Exchange (ETDEWEB)

    Ernst, W.G. (Univ. of California, Los Angeles (United States))

    1990-06-10

    Phanerozoic, unmetamorphosed, weathered, and altered lithotectonic complexes subjected to subduction exhibit the prograde metamorphic facies sequence: zeolite {r arrow} prehnite-pumpellyite {r arrow} glaucophane schist {r arrow} eclogite. Parageneses reflect relatively high-P trajectories, accompanied by semicontinuous devolatilization. The thermal evolution of convergent plate junctions results in early production of high-rank blueschists, high-P amphibolites, and eclogites at depth. Inclusion studies suggest that two-phase immiscible volatiles are evolved in turn during progressive metamorphism of the subducted sections. Expulsion of pore fluids and transitions from weathered and altered supracrustal rocks to zeolite facies assemblages release far more fluid than the better understood higher-grade transformations. Many blueschist parageneses (e.g., Western Alps) have been partially overprinted by later greenschist and/or epidote-amphibolite facies assemblages. Less common blueschist terranes (e.g., Franciscan belt of western California) preserve metamorphic aragonite and other high-P minerals, and lack a low-pressure overprint; physical conditions during retrogression approximately retraced the prograde path or, for early formed high-grade blocks, reflect somewhat higher pressures and lower temperatures. The ease with which volatiles are expelled from a subduction complex and migrate upward along the plate junction zone is roughly proportional to the sandstone/shale ratio: low-permeability mudstones tend to maintain P{sub fluid} values approaching lithostatic, lose strength, and deform chaotically (forming melange belts), whereas permeable sandstone-rich sections retain structural/stratigraphic coherence and fail brittlely (forming coherent terranes).

  20. Kinematics of Late Cretaceous subduction initiation in the Neo-Tethys Ocean reconstructed from ophiolites of Turkey, Cyprus, and Syria

    Science.gov (United States)

    Maffione, Marco; van Hinsbergen, Douwe J. J.; de Gelder, Giovanni I. N. O.; van der Goes, Freek C.; Morris, Antony

    2017-05-01

    Formation of new subduction zones represents one of the cornerstones of plate tectonics, yet both the kinematics and geodynamics governing this process remain enigmatic. A major subduction initiation event occurred in the Late Cretaceous, within the Neo-Tethys Ocean between Gondwana and Eurasia. Suprasubduction zone ophiolites (i.e., emerged fragments of ancient oceanic lithosphere formed at suprasubduction spreading centers) were generated during this subduction event and are today distributed in the eastern Mediterranean region along three E-W trending ophiolitic belts. Several models have been proposed to explain the formation of these ophiolites and the evolution of the associated intra-Neo-Tethyan subduction zone. Here we present new paleospreading directions from six Upper Cretaceous ophiolites of Turkey, Cyprus, and Syria, calculated by using new and published paleomagnetic data from sheeted dyke complexes. Our results show that NNE-SSW subduction zones were formed within the Neo-Tethys during the Late Cretaceous, which we propose were part of a major step-shaped subduction system composed of NNE-SSW and WNW-ESE segments. We infer that this subduction system developed within old (Triassic?) lithosphere, along fracture zones and perpendicular weakness zones, since the Neo-Tethyan spreading ridge formed during Gondwana fragmentation would have already been subducted at the Pontides subduction zone by the Late Cretaceous. Our new results provide an alternative kinematic model of Cretaceous Neo-Tethyan subduction initiation and call for future research on the mechanisms of subduction inception within old (and cold) lithosphere and the formation of metamorphic soles below suprasubduction zone ophiolites in the absence of nearby spreading ridges.

  1. Origin and dynamics of depositionary subduction margins

    Science.gov (United States)

    Vannucchi, Paola; Morgan, Jason P.; Silver, Eli; Kluesner, Jared W.

    2016-01-01

    Here we propose a new framework for forearc evolution that focuses on the potential feedbacks between subduction tectonics, sedimentation, and geomorphology that take place during an extreme event of subduction erosion. These feedbacks can lead to the creation of a “depositionary forearc,” a forearc structure that extends the traditional division of forearcs into accretionary or erosive subduction margins by demonstrating a mode of rapid basin accretion during an erosive event at a subduction margin. A depositionary mode of forearc evolution occurs when terrigenous sediments are deposited directly on the forearc while it is being removed from below by subduction erosion. In the most extreme case, an entire forearc can be removed by a single subduction erosion event followed by depositionary replacement without involving transfer of sediments from the incoming plate. We need to further recognize that subduction forearcs are often shaped by interactions between slow, long-term processes, and sudden extreme events reflecting the sudden influences of large-scale morphological variations in the incoming plate. Both types of processes contribute to the large-scale architecture of the forearc, with extreme events associated with a replacive depositionary mode that rapidly creates sections of a typical forearc margin. The persistent upward diversion of the megathrust is likely to affect its geometry, frictional nature, and hydrogeology. Therefore, the stresses along the fault and individual earthquake rupture characteristics are also expected to be more variable in these erosive systems than in systems with long-lived megathrust surfaces.

  2. Origin and dynamics of depositionary subduction margins

    Science.gov (United States)

    Vannucchi, Paola; Morgan, Jason P.; Silver, Eli A.; Kluesner, Jared W.

    2016-06-01

    Here we propose a new framework for forearc evolution that focuses on the potential feedbacks between subduction tectonics, sedimentation, and geomorphology that take place during an extreme event of subduction erosion. These feedbacks can lead to the creation of a "depositionary forearc," a forearc structure that extends the traditional division of forearcs into accretionary or erosive subduction margins by demonstrating a mode of rapid basin accretion during an erosive event at a subduction margin. A depositionary mode of forearc evolution occurs when terrigenous sediments are deposited directly on the forearc while it is being removed from below by subduction erosion. In the most extreme case, an entire forearc can be removed by a single subduction erosion event followed by depositionary replacement without involving transfer of sediments from the incoming plate. We need to further recognize that subduction forearcs are often shaped by interactions between slow, long-term processes, and sudden extreme events reflecting the sudden influences of large-scale morphological variations in the incoming plate. Both types of processes contribute to the large-scale architecture of the forearc, with extreme events associated with a replacive depositionary mode that rapidly creates sections of a typical forearc margin. The persistent upward diversion of the megathrust is likely to affect its geometry, frictional nature, and hydrogeology. Therefore, the stresses along the fault and individual earthquake rupture characteristics are also expected to be more variable in these erosive systems than in systems with long-lived megathrust surfaces.

  3. The Two Subduction Zones of the Southern Caribbean: Lithosphere Tearing and Continental Margin Recycling in the East, Flat Slab Subduction and Laramide-Style Uplifts in the West

    Science.gov (United States)

    Levander, A.; Bezada, M. J.; Niu, F.; Schmitz, M.

    2015-12-01

    The southern Caribbean plate boundary is a complex strike-slip fault system bounded by oppositely vergent subduction zones, the Antilles subduction zone in the east, and a currently locked Caribbean-South American subduction zone in the west (Bilham and Mencin, 2013). Finite-frequency teleseismic P-wave tomography images both the Atlanic (ATL) and the Caribbean (CAR) plates subducting steeply in opposite directions to transition zone depths under northern South America. Ps receiver functions show a depressed 660 discontinuity and thickened transition zone associated with each subducting plate. In the east the oceanic (ATL) part of the South American (SA) plate subducts westward beneath the CAR, initiating the El Pilar-San Sebastian strike slip system, a subduction-transform edge propagator (STEP) fault (Govers and Wortel, 2005). The point at which the ATL tears away from SA as it descends into the mantle is evidenced by the Paria cluster seismicity at depths of 60-110 km (Russo et al, 1993). Body wave tomography and lithosphere-asthenosphere boundary (LAB) thickness determined from Sp and Ps receiver functions and Rayleigh waves suggest that the descending ATL also viscously removes the bottom third to half of the SA continental margin lithospheric mantle as it descends. This has left thinned continental lithosphere under northern SA in the wake of the eastward migrating Antilles subduction zone. The thinned lithosphere occupies ~70% of the length of the El Pilar-San Sebastian fault system, from ~64oW to ~69oW, and extends inland several hundred kilometers. In northwestern SA the CAR subducts east-southeast at low angle under northern Colombia and western Venezuela. The subducting CAR is at least 200 km wide, extending from northernmost Colombia as far south as the Bucaramanga nest seismicity. The CAR descends steeply under Lake Maracaibo and the Merida Andes. This flat slab is associated with three Neogene basement cored, Laramide-style uplifts: the Santa Marta

  4. Dynamics of intraoceanic subduction initiation: 2D thermomechanical modeling

    Science.gov (United States)

    Zhou, X.; Gerya, T.; LI, Z.; Stern, R. J.

    2016-12-01

    Intraoceanic subduction initiation occurs in previous weak zones which could be transform faults or old fracture zones, and concurrents with the change of plate motions. It is an important process to understand the beginning of plate tectonics. However, the dynamic process during (after) subduction initiation remain obscure. The process of suducting slabs move from down to downdip is also not revealed clearly. In order to obtain better understanding of the transitional process of subducting slab motion, we use finite difference and marker-in-cell methods to establish a series of self-sustainable subduction initiation models and explore many visco-plastic parameters to qualify the dynamical process of subduction initiation. The following parameters are systematic tested: (1) the age of the subducting slab; (2) friction coefficient of the mantle material; (3) the mantle potential temperature; (4) the age of the overriding slab. We find out the critical age of the oceanic lithosphere which can produce subduction initiation. And the age of subducting slab plays important roles during subduction initiation. The young subducting slab induces fast trench retreat and then trench begin to advance. For the old subducting slab, it induces relative slower trench retreat and then stop moving. The age of overriding slabs impacts coupling with the subducting slab. The friction coefficient of lithosphere also impacts the backarc spreading and subduction velocity. Stronger subducted plate gives lower subduction velocity and faster trench retreat velocity. The mantle potential temperature changes the critical age of subducted slabs.

  5. Multiple subduction imprints in the mantle below Italy detected in a single lava flow

    Science.gov (United States)

    Nikogosian, Igor; Ersoy, Özlem; Whitehouse, Martin; Mason, Paul R. D.; de Hoog, Jan C. M.; Wortel, Rinus; van Bergen, Manfred J.

    2016-09-01

    Post-collisional magmatism reflects the regional subduction history prior to collision but the link between the two is complex and often poorly understood. The collision of continents along a convergent plate boundary commonly marks the onset of a variety of transitional geodynamic processes. Typical responses include delamination of subducting lithosphere, crustal thickening in the overriding plate, slab detachment and asthenospheric upwelling, or the complete termination of convergence. A prominent example is the Western-Central Mediterranean, where the ongoing slow convergence of Africa and Europe (Eurasia) has been accommodated by a variety of spreading and subduction systems that dispersed remnants of subducted lithosphere into the mantle, creating a compositionally wide spectrum of magmatism. Using lead isotope compositions of a set of melt inclusions in magmatic olivine crystals we detect exceptional heterogeneity in the mantle domain below Central Italy, which we attribute to the presence of continental material, introduced initially by Alpine and subsequently by Apennine subduction. We show that superimposed subduction imprints of a mantle source can be tapped during a melting episode millions of years later, and are recorded in a single lava flow.

  6. Influence of Initial Geometry and Boundary Conditions on Flat Subduction Models and Resulting Topography

    Science.gov (United States)

    Nelson, P.; Moucha, R.

    2014-12-01

    Numerical investigations of surface deformation in response to flat slab subduction began with seminal papers by Bird (1988) and Mitrovica et al. (1989). Recently, a number of numerical studies have begun to explore the complexity in the dynamics of flat-slab subduction initiation and continuation, but did not address the corresponding surface deformation (English et al., 2003; Pérez-Campos et al., 2008; Liu et al., 2010; Jones et al., 2011; Arrial and Billen, 2013; Vogt and Gerya, 2014). Herein, we explore the conditions that lead to flat-slab subduction and characterize the resulting surface deformation using a 2D finite-difference marker-in-cell method. We specifically explore how initial model geometry and boundary conditions affect the evolution of the angle at which a slab subducts in the presence/absence of a buoyant oceanic plateau and the resulting surface topography. In our simulations, the surface is tracked through time as an internal erosion/sedimentation surface. The top boundary of the crust is overlaid by a "sticky" (viscous 10^17 Pa.s) water/air layer with correspondingly stratified densities. We apply a coupled surface processes model that solves the sediment transport/diffusion erosion equation at each time step to account for the corresponding crustal mass flux and its effect on crustal deformation. Model results show the initial angle of subduction has a substantial impact on the subduction angle of the slab and hence the evolution of topography. The results also indicate plate velocity and the presence of an oceanic plateau in a forced subduction only have a moderate effect on the angle of subduction.

  7. Silicate dissolution boosts the CO2 concentrations in subduction fluids.

    Science.gov (United States)

    Tumiati, S; Tiraboschi, C; Sverjensky, D A; Pettke, T; Recchia, S; Ulmer, P; Miozzi, F; Poli, S

    2017-09-20

    Estimates of dissolved CO2 in subduction-zone fluids are based on thermodynamic models, relying on a very sparse experimental data base. Here, we present experimental data at 1-3 GPa, 800 °C, and ∆FMQ ≈ -0.5 for the volatiles and solute contents of graphite-saturated fluids in the systems COH, SiO2-COH ( + quartz/coesite) and MgO-SiO2-COH ( + forsterite and enstatite). The CO2 content of fluids interacting with silicates exceeds the amounts measured in the pure COH system by up to 30 mol%, as a consequence of a decrease in water activity probably associated with the formation of organic complexes containing Si-O-C and Si-O-Mg bonds. The interaction of deep aqueous fluids with silicates is a novel mechanism for controlling the composition of subduction COH fluids, promoting the deep CO2 transfer from the slab-mantle interface to the overlying mantle wedge, in particular where fluids are stable over melts.Current estimates of dissolved CO2 in subduction-zone fluids based on thermodynamic models rely on a very sparse experimental data base. Here, the authors show that experimental graphite-saturated COH fluids interacting with silicates at 1-3 GPa and 800 °C display unpredictably high CO2 contents.

  8. Crust and subduction zone structure of Southwestern Mexico

    Science.gov (United States)

    Suhardja, Sandy Kurniawan; Grand, Stephen P.; Wilson, David; Guzman-Speziale, Marco; Gomez-Gonzalez, Juan Martin; Dominguez-Reyes, Tonatiuh; Ni, James

    2015-02-01

    Southwestern Mexico is a region of complex active tectonics with subduction of the young Rivera and Cocos plates to the south and widespread magmatism and rifting in the continental interior. Here we use receiver function analysis on data recorded by a 50 station temporary deployment of seismometers known as the MARS (MApping the Rivera Subduction zone) array to investigate crustal structure as well as the nature of the subduction interface near the coast. The array was deployed in the Mexican states of Jalisco, Colima, and Michoacan. Crustal thickness varies from 20 km near the coast to 42 km in the continental interior. The Rivera plate has steeper dip than the Cocos plate and is also deeper along the coast than previous estimates have shown. Inland, there is not a correlation between the thickness of the crust and topography indicating that the high topography in northern Jalisco and Michoacan is likely supported by buoyant mantle. High crustal Vp/Vs ratios (greater than 1.82) are found beneath the trenchward edge of magmatism including below the Central Jalisco Volcanic Lineament and the Michoacan-Guanajuato Volcanic Field implying a new arc is forming closer to the trench than the Trans Mexican Volcanic Belt. Elsewhere in the region, crustal Vp/Vs ratios are normal. The subducting Rivera and Cocos plates are marked by a dipping shear wave low-velocity layer. We estimate the thickness of the low-velocity layer to be 3 to 4 km with an unusually high Vp/Vs ratio of 2.0 to 2.1 and a drop in S velocity of 25%. We postulate that the low-velocity zone is the upper oceanic crust with high pore pressures. The low-velocity zone ends from 45 to 50 km depth and likely marks the basalt to eclogite transition.

  9. A subduction zone reference frame based on slab geometry and subduction partitioning of plate motion and trench migration

    NARCIS (Netherlands)

    Schellart, W. P.

    2011-01-01

    The geometry of subducted slabs that interact with the transition zone depends critically on the partitioning of the subduction velocity (v S⊥) at the surface into its subducting plate motion component (vSP⊥) and trench migration component (vT⊥). Geodynamic models of progressive subduction

  10. The earthquake cycle in subduction zones

    Science.gov (United States)

    Melosh, H. J.; Fleitout, L.

    1982-01-01

    A simplified model of a subduction zone is presented, which incorporates the mechanical asymmetry induced by the subducted slab to anchor the subducting plate during post-seismic rebound and thus throw most of the coseismic stream release into the overthrust plate. The model predicts that the trench moves with respect to the deep mantle toward the subducting plate at a velocity equal to one-half of the convergence rate. A strong extensional pulse is propagated into the overthrust plate shortly after the earthquake, and although this extension changes into compression before the next earthquake in the cycle, the period of strong extension following the earthquake may be responsible for extensional tectonic features in the back-arc region.

  11. Seismic coupling and uncoupling at subduction zones

    Science.gov (United States)

    Ruff, L.; Kanamori, H.

    1983-01-01

    Some of the correlations concerning the properties of subduction zones are reviewed. A quantitative global comparison of many subduction zones reveals that the largest earthquakes occur in zones with young lithosphere and fast convergence rates. Maximum earthquake size is directly related to the asperity distribution on the fault plane. This observation can be translated into a simple model of seismic coupling where the horizontal compressive stress between two plates is proportional to the ratio of the summed asperity area to the total area of the contact surface. Plate age and rate can control asperity distribution directly through the horizontal compressive stress associated with the vertical and horizontal velocities of subducting slabs. The basalt to eclogite phase change in the down-going oceanic crust may be largely responsible for the uncoupling of subduction zones below a depth of about 40 km.

  12. A numerical reference model for themomechanical subduction

    DEFF Research Database (Denmark)

    Quinquis, Matthieu; Chemia, Zurab; Tosi, Nicola

    2010-01-01

    response to systematic variations in input parameters, numerical studies often start from a 'reference' subduction model. However, the reference model often varies between different numerical studies, making it difficult to compare results directly. We aim therefore to define a numerical reference model......, and initial temperature distribution. We will show results of the evolution and dynamics of the subduction reference model using different numerical codes: a finite element code, SULEC, and two finite difference codes, YACC and FDcon....

  13. Kinematics of subduction and subduction-induced flow in the upper mantle

    NARCIS (Netherlands)

    Schellart, W. P.

    2004-01-01

    Results of fluid dynamical experiments are presented to model the kinematics of lithospheric subduction in the upper mantle. The experiments model a dense highviscosity plate (subducting lithosphere) overlying a less dense low-viscosity layer (upper mantle). The overriding lithosphere is not

  14. Seamount subduction at the North-Ecuadorian convergent margin : effects on structures, inter-seismic coupling and seismogenesis

    OpenAIRE

    Marcaillou, Boris; Collot, Jean-Yves; Ribodetti, Alessandra; d'Acremont, E.; Mahamat, A. A.; Alvarado, A.

    2016-01-01

    At the North-Ecuadorian convergent margin (1 degrees S-1.5 degrees N), the subduction of the rough Nazca oceanic plate leads to tectonic erosion of the upper plate and complex seismogenic behavior of the megathrust. We used three selected pre-stack depth migrated, multi-channel seismic reflection lines collected during the SISTEUR cruise to investigate the margin structure and decipher the impact of the subducted Atacames seamounts on tectonic erosion, interseismic coupling, and seismogenesis...

  15. Thermobarometric and fluid expulsion history of subduction zones

    Science.gov (United States)

    Ernst, W. G.

    1990-06-01

    Phanerozoic, unmetamorphosed, weathered, and altered lithotectonic complexes subjected to subduction exhibit the prograde metamorphic facies sequence: zeolite → prehnite-pumpellyite → glaucophane schist → eclogite. Parageneses reflect relatively high-P trajectories, accompanied by semicontinuous devolatilization. The thermal evolution of convergent plate junctions results in early production of high-rank blueschists, high-P amphibolites, and eclogues at depth within narrow subduction zones while the hanging wall lithosphere is still hot. Protracted underflow drains heat from the nonsubducted plate and, even at profound depths, generates very low-T/high-P parageneses. Inclusion studies suggest that two-phase immiscible volatiles (liquid H2O, and gaseous high-hydrocarbons, CH4 and CO2) are evolved in turn during progressive metamorphism of the subducted sections. Expulsion of pore fluids and transitions from weathered and altered supracrustal rocks to zeolite facies assemblages release far more fluid than the better understood higher-grade transformations. Many blueschist parageneses, such as those of the internal Western Alps, have been partially overprinted by later greenschist and/or epidote-amphibolite facies assemblages. Alpine-type postblueschist metamorphic paths involved fairly rapid, nearly adiabatic decompression; some terranes even underwent modest continued heating and fluid evolution during early stages of ascent. Uplift probably occurred as a consequence of the underthrusting of low-density island arc or microcontinental crust along the convergent plate junction, resulting in marked deceleration or cessation of lithospheric underflow, decoupling, and nearly isothermal rise of the recrystallized subduction complex. Other, less common blueschist terranes, such as the eastern Franciscan belt of western California, preserve metamorphic aragonite and other high-P minerals, and lack a low-pressure overprint; physical conditions during retrogression

  16. Intrinsic and Extrinsic Factors in Subduction Dynamics

    Science.gov (United States)

    Billen, Magali; Arredondo, Katrina

    2014-05-01

    Since the realization that tectonic plates sink into the mantle, in a process we now call subduction, our understanding of this process has improved dramatically through the combined application of observations, theory and modeling. During that time independent research groups focusing on different aspects of subduction have identified factors with a significant impact on subduction, such as three-dimensionality, slab rollback, rheology of the slab and mantle and magnitude of phase changes. However, as each group makes progress we often wonder how these different factors interact as we all strive to understand the real world subduction system. These factors can be divided in two groups: intrinsic factors, including the age of the slab, its thermal structure, composition, and rheology, and extrinsic factors including others forces on plates, overall mantle flow, structure of the overriding plate, rheology of the mantle and phase changes. In addition, while modeling has been a powerful tool for understanding subduction, all models make important (but often necessary) approximations, such as using two dimensions, imposed boundary conditions, and approximations of the conservation equations and material properties. Here we present results of a study in which the "training wheels" are systematically removed from 2D models of subduction to build a more realistic model of subduction and to better understand how combined effects of intrinsic and extrinsic factors contribute to the dynamics. We find that a change from the Boussinesq to the extended Boussinesq form of the conservation equations has a dramatic effect on slab evolution in particular when phase changes are included. Allowing for free (dynamically-driven) subduction and trench motion is numerically challenging, but also an important factor that allows for more direct comparison to observations of plate kinematics. Finally, compositional layering of the slab and compositionally-controlled phase changes also have

  17. Long distance transport of eclogite and blueschist during early Pacific Ocean subduction rollback

    Science.gov (United States)

    Tamblyn, Renee; Hand, Martin; Kelsey, David; Phillips, Glen; Anczkiewicz, Robert

    2017-04-01

    The Tasmanides in eastern Australia represent a period of continental crustal growth on the western margin of the Pacific Ocean associated with slab rollback from the Cambrian until the Triassic. During rollback numerical models predict that subduction products can become trapped in the forearc (Geyra et al., 2002), and can migrate with the trench as it retreats. In a long-lived subduction controlled regime such as the Tasmanides, this should result in an accumulation of subduction products with protracted geochronological and metamorphic histories. U-Pb, Lu-Hf, Sm-Nd and Ar-Ar geochronology and phase equilibria modelling of lawsonite-eclogite and garnet blueschist in the Southern New England Fold Belt in Australia demonstrate that high-P low-T rocks remained within a subduction setting for c. 40 Ma, from c. 500 to 460 Ma. High-P metamorphic rocks initially formed close to the Australian cratonic margin during the late Cambrian, and were subsequently transported over 1500 Ma oceanward, during which time subducted material continued to accumulate, resulting in the development of complex mélange which records eclogite and blueschist metamorphism and partial exhumation over 40 Ma. The duration of refrigerated metamorphism approximates the extensional evolution of the upper plate which culminated in the development of the Lachlan Fold Belt. The protracted record of eclogite and blueschist metamorphism indicates that rapid exhumation is not necessarily required for preservation of high-pressure metamorphic rocks from subduction systems. Reference: Gerya, T. V., Stockhert, B., & Perchuk, A. L. (2002). Exhumation of high-pressure metamorphic rocks in a subduction channel: A numerical simulation. Tectonics, 21(6), 6-1-6-19. doi:10.1029/2002tc001406

  18. Seismic anisotropy in the Hellenic subduction zone: Effects of slab segmentation and subslab mantle flow

    Science.gov (United States)

    Evangelidis, C. P.

    2017-12-01

    The segmentation and differentiation of subducting slabs have considerable effects on mantle convection and tectonics. The Hellenic subduction zone is a complex convergent margin with strong curvature and fast slab rollback. The upper mantle seismic anisotropy in the region is studied focusing at its western and eastern edges in order to explore the effects of possible slab segmentation on mantle flow and fabrics. Complementary to new SKS shear-wave splitting measurements in regions not adequately sampled so far, the source-side splitting technique is applied to constrain the depth of anisotropy and to densify measurements. In the western Hellenic arc, a trench-normal subslab anisotropy is observed near the trench. In the forearc domain, source-side and SKS measurements reveal a trench-parallel pattern. This indicates subslab trench-parallel mantle flow, associated with return flow due to the fast slab rollback. The passage from continental to oceanic subduction in the western Hellenic zone is illustrated by a forearc transitional anisotropy pattern. This indicates subslab mantle flow parallel to a NE-SW smooth ramp that possibly connects the two subducted slabs. A young tear fault initiated at the Kefalonia Transform Fault is likely not entirely developed, as this trench-parallel anisotropy pattern is observed along the entire western Hellenic subduction system, even following this horizontal offset between the two slabs. At the eastern side of the Hellenic subduction zone, subslab source-side anisotropy measurements show a general trench-normal pattern. These are associated with mantle flow through a possible ongoing tearing of the oceanic lithosphere in the area. Although the exact geometry of this slab tear is relatively unknown, SKS trench-parallel measurements imply that the tear has not reached the surface yet. Further exploration of the Hellenic subduction system is necessary; denser seismic networks should be deployed at both its edges in order to achieve

  19. Subduction zone forearc serpentinites as incubators for deep microbial life

    Science.gov (United States)

    Plümper, Oliver; King, Helen E.; Geisler, Thorsten; Liu, Yang; Pabst, Sonja; Savov, Ivan P.; Rost, Detlef; Zack, Thomas

    2017-04-01

    Serpentinization-fueled systems in the cool, hydrated forearc mantle of subduction zones may provide an environment that supports deep chemolithoautotrophic life. Here, we examine serpentinite clasts expelled from mud volcanoes above the Izu-Bonin-Mariana subduction zone forearc (Pacific Ocean) that contain complex organic matter and nanosized Ni-Fe alloys. Using time-of-flight secondary ion mass spectrometry and Raman spectroscopy, we determined that the organic matter consists of a mixture of aliphatic and aromatic compounds and functional groups such as amides. Although an abiotic or subduction slab-derived fluid origin cannot be excluded, the similarities between the molecular signatures identified in the clasts and those of bacteria-derived biopolymers from other serpentinizing systems hint at the possibility of deep microbial life within the forearc. To test this hypothesis, we coupled the currently known temperature limit for life, 122 °C, with a heat conduction model that predicts a potential depth limit for life within the forearc at ˜10,000 m below the seafloor. This is deeper than the 122 °C isotherm in known oceanic serpentinizing regions and an order of magnitude deeper than the downhole temperature at the serpentinized Atlantis Massif oceanic core complex, Mid-Atlantic Ridge. We suggest that the organic-rich serpentinites may be indicators for microbial life deep within or below the mud volcano. Thus, the hydrated forearc mantle may represent one of Earth’s largest hidden microbial ecosystems. These types of protected ecosystems may have allowed the deep biosphere to thrive, despite violent phases during Earth’s history such as the late heavy bombardment and global mass extinctions.

  20. Subduction zone forearc serpentinites as incubators for deep microbial life.

    Science.gov (United States)

    Plümper, Oliver; King, Helen E; Geisler, Thorsten; Liu, Yang; Pabst, Sonja; Savov, Ivan P; Rost, Detlef; Zack, Thomas

    2017-04-25

    Serpentinization-fueled systems in the cool, hydrated forearc mantle of subduction zones may provide an environment that supports deep chemolithoautotrophic life. Here, we examine serpentinite clasts expelled from mud volcanoes above the Izu-Bonin-Mariana subduction zone forearc (Pacific Ocean) that contain complex organic matter and nanosized Ni-Fe alloys. Using time-of-flight secondary ion mass spectrometry and Raman spectroscopy, we determined that the organic matter consists of a mixture of aliphatic and aromatic compounds and functional groups such as amides. Although an abiotic or subduction slab-derived fluid origin cannot be excluded, the similarities between the molecular signatures identified in the clasts and those of bacteria-derived biopolymers from other serpentinizing systems hint at the possibility of deep microbial life within the forearc. To test this hypothesis, we coupled the currently known temperature limit for life, 122 °C, with a heat conduction model that predicts a potential depth limit for life within the forearc at ∼10,000 m below the seafloor. This is deeper than the 122 °C isotherm in known oceanic serpentinizing regions and an order of magnitude deeper than the downhole temperature at the serpentinized Atlantis Massif oceanic core complex, Mid-Atlantic Ridge. We suggest that the organic-rich serpentinites may be indicators for microbial life deep within or below the mud volcano. Thus, the hydrated forearc mantle may represent one of Earth's largest hidden microbial ecosystems. These types of protected ecosystems may have allowed the deep biosphere to thrive, despite violent phases during Earth's history such as the late heavy bombardment and global mass extinctions.

  1. Tectonic implications of tomographic images of subducted lithosphere beneath northwestern South America

    NARCIS (Netherlands)

    Hilst, R.D. van der; Mann, P.

    1994-01-01

    We used seismic tomography to investigate the complex structure of the upper mantle below northwestern South America. Images of slab structure not delineated by previous seismicity studies help us to refine existing tectonic models of subducted Caribbean-Pacific lithosphere beneath the study area.

  2. Strength of stick-slip and creeping subduction megathrusts from heat flow observations.

    Science.gov (United States)

    Gao, Xiang; Wang, Kelin

    2014-08-29

    Subduction faults, called megathrusts, can generate large and hazardous earthquakes. The mode of slip and seismicity of a megathrust is controlled by the structural complexity of the fault zone. However, the relative strength of a megathrust based on the mode of slip is far from clear. The fault strength affects surface heat flow by frictional heating during slip. We model heat-flow data for a number of subduction zones to determine the fault strength. We find that smooth megathrusts that produce great earthquakes tend to be weaker and therefore dissipate less heat than geometrically rough megathrusts that slip mainly by creeping. Copyright © 2014, American Association for the Advancement of Science.

  3. Evidence for retrograde lithospheric subduction on Venus

    Science.gov (United States)

    Sandwell, David T.; Schubert, Gerald

    1992-01-01

    Annular moats and outer rises around large Venus coronas such as Artemis, Latona, and Eithinoha are similar in arcuate planform and topography to the trenches and outer rises of terrestrial subduction zones. On earth, trenches and outer rises are modeled as the flexural response of a thin elastic lithosphere to the bending moment of the subducted slab; this lithospheric flexure model also accounts for the trenches and outer rises outboard of the major coronas on Venus. Accordingly, it is proposed that retrograde lithospheric subduction may be occurring on the margins of the large Venus coronas while compensating back-arc extension is occurring in the expanding coronas interiors. Similar processes may be taking place at other deep arcuate trenches or chasmata on Venus such as those in the Dali-Diana chasmata area of aestern Aphrodite Terra.

  4. Seismic Structure of the Subducted Cocos Plate

    Science.gov (United States)

    Clayton, R. W.; Davis, P. M.; Perez-Campos, X.

    2007-05-01

    The Meso-American Subduction Experiment (MASE) was designed to determine the critical parameters to necessary to simulate the subduction process in Central Mexico . A preliminary analysis of the data shows a 200km section of the slab that is subhorizontal and to within the resolution of the receiver functions it underplates the continental crust with no intervening asthenosphere. This is an interesting situation because the short-term (GPS) and long-term (geologic) strain measurements show almost no compressive strain in this region. This would imply that the crust is decoupled from the subducting slab. Near the coast, the receiver functions show that the slab cuts through the crust at an approximately a 15-degree angle, and under the Trans-Mexican Volcanic Belt the slab becomes detached from the crust, but its geometry at depth is not yet determined from the receiver functions, but a well-developed mantle wedge is apparent from the attenuation of regional earthquakes.

  5. Subduction zones seen by GOCE gravity gradients

    DEFF Research Database (Denmark)

    Švarc, Mario; Herceg, Matija; Cammarano, Fabio

    In this study, the GOCE (Gravity field and steady state Ocean Circulation Explorer) gradiometry data were used to study geologic structures and mass variations within the lithosphere in areas of known subduction zones. The advantage of gravity gradiometry over other gravity methods...... is that gradients are extremely sensitive to localized density contrasts within regional geological settings, which makes it ideally suited for detecting subduction zones. Second order gravity gradients of disturbing potential were extracted from global geopotential model, the fifth release GOCE model ‘EGM_TIM_RL05......’. In order to remove the signal which mainly corresponds to the gravity signal of the lower mantle, long wavelength part of the gravity signal was removed up to degree and order 60. Because the areas with notable topography differences coincide with subduction zones, topography correction was also performed...

  6. Thermal impact of magmatism in subduction zones

    Science.gov (United States)

    Rees Jones, David W.; Katz, Richard F.; Tian, Meng; Rudge, John F.

    2018-01-01

    Magmatism in subduction zones builds continental crust and causes most of Earth's subaerial volcanism. The production rate and composition of magmas are controlled by the thermal structure of subduction zones. A range of geochemical and heat flow evidence has recently converged to indicate that subduction zones are hotter at lithospheric depths beneath the arc than predicted by canonical thermomechanical models, which neglect magmatism. We show that this discrepancy can be resolved by consideration of the heat transported by magma. In our one- and two-dimensional numerical models and scaling analysis, magmatic transport of sensible and latent heat locally alters the thermal structure of canonical models by ∼300 K, increasing predicted surface heat flow and mid-lithospheric temperatures to observed values. We find the advection of sensible heat to be larger than the deposition of latent heat. Based on these results we conclude that thermal transport by magma migration affects the chemistry and the location of arc volcanoes.

  7. Subduction zones dynamics and structure from coupled geodynamic and seismological modelling

    Science.gov (United States)

    Faccenda, Manuele

    2017-04-01

    The present-day structure of subduction settings is mainly determined by means of seismological methods. The interpretation of seismological data (e.g., isotropic and anisotropic velocity anomalies) is however non-unique, as different processes occurring simultaneously at subduction zones can be invoked to explain the observations. A further complication arises when regional tomographic seismic models ignore seismic anisotropy, in which case apparent seismic anomalies due to non-uniform sampling of anisotropic areas will appear. In order to decrease the uncertainties related to the interpretation of seismological observations, geodynamic modelling can be exploited to reproduce the micro and macro scale dynamics and structure of subduction settings, yielding a valuable first-order approximation of the rock isotropic and anisotropic elastic properties. The model output can be subsequently tested against observations by performing seismological synthetics (e.g., SKS splitting, travel-time tomography, receiver functions, azimuthal and radial anisotropy). When the misfit between the modelled and measured seismic parameters is low, the geodynamic model likely provides a good approximation of the recent dynamics and present-day structure of the subduction setting. Such a model can then be used to give a more robust and thermomechanically-based interpretation of the observables and/or further improve the seismological model by providing a-priori information for subsequent inversions. The methodology is still in its infancy, but we envisage that future developments could substantially improve seismological models and, overall, our understanding of complex subduction settings.

  8. Subduction trench migration since the Cretaceous

    Science.gov (United States)

    Williams, S.; Flament, N. E.; Müller, D.; Butterworth, N. P.

    2015-12-01

    Much of our knowledge about subduction zone processes is derived from analyzing present-day Earth. Several studies of contemporary plate motions have investigated the balance between retreating and advancing trenches and shown that subduction zone kinematics are sensitive to the choice of Absolute Plate Motion (APM) model (or "reference frame"). For past times, the absolute motions of the lithospheric plates relative to the Earth's deep interior over tens of millions of years are commonly constrained using observations from paleomagnetism and age-progressive seamount trails. In contrast, a reference frame linking surface plate motions to subducted slab remnants mapped from seismic tomography has recently been proposed. APM models derived using different methodologies, different subsets of hotspots, or differing assumptions of hotspot motion, have contrasting implications for parameters that describe the long term state of the plate-mantle system, such as the balance between advance and retreat of subduction zones, plate velocities, and net lithospheric rotation. Here we quantitatively compare the subduction zone kinematics, net lithospheric rotation and fit to hotspot trails derived the last 130 Myr for a range of alternative reference frames and a single relative plate motion model. We find that hotspot and tomographic slab-remnant reference frames yield similar results for the last 70 Myr. For the period between 130 and 70 Ma, when hotspot trails become scarce, hotspot reference frames yield a much more dispersed distribution of slab advance and retreat velocities, which is considered geodynamically less plausible. By contrast, plate motions calculated using the slab-remnant reference frame, or using a reference frame designed to minimise net rotation, yield more consistent subduction zone kinematics for times older than 70 Ma. Introducing the global minimisation of trench migration rates as a key criterion in the construction of APM models forms the foundation

  9. Depth-dependent rupture mode along the Ecuador-Colombia subduction zone

    Science.gov (United States)

    Yoshimoto, Masahiro; Kumagai, Hiroyuki; Acero, Wilson; Ponce, Gabriela; Vásconez, Freddy; Arrais, Santiago; Ruiz, Mario; Alvarado, Alexandra; Pedraza García, Patricia; Dionicio, Viviana; Chamorro, Orlando; Maeda, Yuta; Nakano, Masaru

    2017-03-01

    A large earthquake (Mw 7.7) occurred on 16 April 2016 within the source region of the 1906 earthquake in the Ecuador-Colombia subduction zone. The 1906 event has been interpreted as a megathrust earthquake (Mw 8.8) that ruptured the source regions of smaller earthquakes in 1942, 1958, and 1979 in this subduction. Our seismic analysis indicated that the spatial distribution of the 2016 earthquake and its aftershocks correlated with patches of high interplate coupling strength and was similar to those of the 1942 earthquake and its aftershocks, suggesting that the 2016 and 1942 earthquakes ruptured the same asperity. Our analysis of tsunami waveforms of the 1906 event indicated Mw around 8.4 and showed that large slip occurred near the trench off the source regions of the above three historical and the 2016 earthquakes, suggesting that a depth-dependent complex rupture mode exists along this subduction zone.

  10. Metamorphic zirconology of continental subduction zones

    Science.gov (United States)

    Chen, Ren-Xu; Zheng, Yong-Fei

    2017-09-01

    Zircon is widely used to date geological events and trace geochemical sources in high-pressure (HP) to ultrahigh-pressure (UHP) metamorphic rocks of continental subduction zones. However, protolith zircons may be modified by three different types of metamorphic recrystallization via mechanisms of solid-state transformation, metasomatic alteration and dissolution reprecipitation; new zircon growth may be induced by dehydration reactions below the wet solidus of crustal rocks (metamorphic zircon) or peritectic reactions above the wet solidus (peritectic zircon). As a consequence, there are different origins of zircon domains in high-grade metamorphic rocks from collisional orogens. Thus, determining the nature of individual zircon domains is substantial to correct interpretation of their origin in studies of isotopic geochronology and geochemical tracing. We advocate an integrated study of zircon mineragraphy (internal structure and external morphology), U-Pb ages, mineral inclusions, trace elements, and Lu-Hf and O isotope compositions. Only in this way we are in a position to advance the simple zircon applications to metamorphic zirconology, enabling discrimination between the different origins of zircon and providing constraints on the property of fluid activity at subduction-zone conditions. The metamorphic recrystallization of protolith zircons and the new growth of metamorphic and peritectic zircons are prominent in HP to UHP metamorphic rocks of collisional orogens. These different types of recrystallized and grown zircons can be distinguished by their differences in element and isotope compositions. While the protolith nature of metamorphosed rocks dictates water availability, the P-T conditions of subduction zones dictate the property of subduction-zone fluids. The fluids of different properties may be produced at different positions of subducting and exhuming crustal slices, and they may physically and chemically mix with each other in continental

  11. Testing Alternative Tectono-Stratigraphic Interpretations of the Late Palaeozoic−Early Mesozoic Karakaya Complex in NW Turkey: Support for an Accretionary Origin Related to Northward Subduction of Palaeotethys

    OpenAIRE

    USTAÖMER, ALASTAIR HARRY FORBES ROBERTSON & TİMUR

    2012-01-01

    Lower Carboniferous-Upper Triassic rocks of the Karakaya Complex exposed E-W across Turkey are critical to reconstructions of Palaeotethys in the Eastern Mediterranean region. Despite decades of research, the origin and emplacement of the Karakaya Complex remains controversial because it is mapped either as an overall stratigraphic succession of sedimentary olistostromes or as a stack of thrust sheets and mélange. Tectonic models include a continental rift, a back-arc rift, a marginal oceanic...

  12. Influence of the subducting plate velocity on the geometry of the slab and migration of the subduction hinge

    NARCIS (Netherlands)

    Schellart, Wouter P.

    2005-01-01

    Geological observations indicate that along two active continental margins (East Asia and Mediterranean) major phases of overriding plate extension, resulting from subduction hinge-retreat, occurred synchronously with a reduction in subducting plate velocity. In this paper, results of fluid

  13. Mantle hydration and Cl-rich fluids in the subduction forearc

    Science.gov (United States)

    Reynard, Bruno

    2016-12-01

    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. Electrical conductivity increases with increasing fluid content and temperature of the subduction. However, the forearc mantle of Northern Cascadia, the hottest subduction zone where extensive serpentinization was first demonstrated, shows only modest electrical conductivity. Electrical conductivity may vary not only with the thermal state of the subduction zone, but also with time for

  14. Stress orientations in subduction zones and the strength of subduction megathrust faults.

    Science.gov (United States)

    Hardebeck, Jeanne L

    2015-09-11

    Subduction zone megathrust faults produce most of the world's largest earthquakes. Although the physical properties of these faults are difficult to observe directly, their frictional strength can be estimated indirectly by constraining the orientations of the stresses that act on them. A global investigation of stress orientations in subduction zones finds that the maximum compressive stress axis plunges systematically trenchward, consistently making an angle of 45° to 60° with respect to the subduction megathrust fault. These angles indicate that the megathrust fault is not substantially weaker than its surroundings. Together with several other lines of evidence, this implies that subduction zone megathrusts are weak faults in a low-stress environment. The deforming outer accretionary wedge may decouple the stress state along the megathrust from the constraints of the free surface. Copyright © 2015, American Association for the Advancement of Science.

  15. Stress orientations in subduction zones and the strength of subduction megathrust faults

    Science.gov (United States)

    Hardebeck, Jeanne L.

    2015-01-01

    Subduction zone megathrust faults produce most of the world’s largest earthquakes. Although the physical properties of these faults are difficult to observe directly, their frictional strength can be estimated indirectly by constraining the orientations of the stresses that act on them. A global investigation of stress orientations in subduction zones finds that the maximum compressive stress axis plunges systematically trenchward, consistently making a 45°-60° angle to the subduction megathrust fault. These angles indicate that the megathrust fault is not substantially weaker than its surroundings. Together with several other lines of evidence, this implies that subduction zone megathrusts are weak faults in a low-stress environment. The deforming outer accretionary wedge may decouple the stress state along the megathrust from the constraints of the free surface.

  16. Subduction and volatile recycling in Earth's mantle

    Science.gov (United States)

    King, S. D.; Ita, J. J.; Staudigel, H.

    1994-01-01

    The subduction of water and other volatiles into the mantle from oceanic sediments and altered oceanic crust is the major source of volatile recycling in the mantle. Until now, the geotherms that have been used to estimate the amount of volatiles that are recycled at subduction zones have been produced using the hypothesis that the slab is rigid and undergoes no internal deformation. On the other hand, most fluid dynamical mantle flow calculations assume that the slab has no greater strength than the surrounding mantle. Both of these views are inconsistent with laboratory work on the deformation of mantle minerals at high pressures. We consider the effects of the strength of the slab using two-dimensional calculations of a slab-like thermal downwelling with an endothermic phase change. Because the rheology and composition of subducting slabs are uncertain, we consider a range of Clapeyron slopes which bound current laboratory estimates of the spinel to perovskite plus magnesiowustite phase transition and simple temperature-dependent rheologies based on an Arrhenius law diffusion mechanism. In uniform viscosity convection models, subducted material piles up above the phase change until the pile becomes gravitationally unstable and sinks into the lower mantle (the avalanche). Strong slabs moderate the 'catastrophic' effects of the instabilities seen in many constant-viscosity convection calculations; however, even in the strongest slabs we consider, there is some retardation of the slab descent due to the presence of the phase change.

  17. Earth's oldest mantle fabrics indicate Eoarchaean subduction.

    Science.gov (United States)

    Kaczmarek, Mary-Alix; Reddy, Steven M; Nutman, Allen P; Friend, Clark R L; Bennett, Vickie C

    2016-02-16

    The extension of subduction processes into the Eoarchaean era (4.0-3.6 Ga) is controversial. The oldest reported terrestrial olivine, from two dunite lenses within the ∼3,720 Ma Isua supracrustal belt in Greenland, record a shape-preferred orientation of olivine crystals defining a weak foliation and a well-defined lattice-preferred orientation (LPO). [001] parallel to the maximum finite elongation direction and (010) perpendicular to the foliation plane define a B-type LPO. In the modern Earth such fabrics are associated with deformation of mantle rocks in the hanging wall of subduction systems; an interpretation supported by experiments. Here we show that the presence of B-type fabrics in the studied Isua dunites is consistent with a mantle origin and a supra-subduction mantle wedge setting, the latter supported by compositional data from nearby mafic rocks. Our results provide independent microstructural data consistent with the operation of Eoarchaean subduction and indicate that microstructural analyses of ancient ultramafic rocks provide a valuable record of Archaean geodynamics.

  18. Earthquake nucleation in weak subducted carbonates

    NARCIS (Netherlands)

    Kurzawski, Robert M.; Stipp, Michael; Niemeijer, André R.; Spiers, Chirstopher J.; Behrmann, Jan H.

    Ocean-floor carbonate- and clay-rich sediments form major inputs to subduction zones, especially at low-latitude convergent plate margins. Therefore, knowledge of their frictional behaviour is fundamental for understanding plate-boundary earthquakes. Here we report results of mechanical tests

  19. Global correlations between maximum magnitudes of subduction zone interface thrust earthquakes and physical parameters of subduction zones

    NARCIS (Netherlands)

    Schellart, W. P.; Rawlinson, N.

    2013-01-01

    The maximum earthquake magnitude recorded for subduction zone plate boundaries varies considerably on Earth, with some subduction zone segments producing giant subduction zone thrust earthquakes (e.g. Chile, Alaska, Sumatra-Andaman, Japan) and others producing relatively small earthquakes (e.g.

  20. Dynamics of intraoceanic subduction initiation : 1. Oceanic detachment fault inversion and the formation of supra-subduction zone ophiolites

    NARCIS (Netherlands)

    Maffione, Marco; Thieulot, Cedric|info:eu-repo/dai/nl/270177493; van Hinsbergen, Douwe J.J.|info:eu-repo/dai/nl/269263624; Morris, Antony; Plümper, Oliver|info:eu-repo/dai/nl/37155960X; Spakman, Wim|info:eu-repo/dai/nl/074103164

    Subduction initiation is a critical link in the plate tectonic cycle. Intraoceanic subduction zones can form along transform faults and fracture zones, but how subduction nucleates parallel to mid-ocean ridges, as in e.g., the Neotethys Ocean during the Jurassic, remains a matter of debate. In

  1. Slab2 - Updated subduction zone geometries and modeling tools

    Science.gov (United States)

    Portner, D. E.; Hayes, G. P.; Furtney, M.; Moore, G.; Flamme, H. E.; Hearne, M. G.

    2016-12-01

    The U.S. Geological Survey database of global subduction zone geometries (Slab1.0) combines a variety of geophysical data sets (earthquake hypocenters, moment tensors, active-source seismic survey images of the shallow subduction zone, bathymetry, trench locations, and sediment thickness information) to image the shape of subducting slabs in three dimensions, at approximately 85% of the world's convergent margins. The database is used extensively for a variety of purposes from earthquake source imaging to magnetotelluric modeling. Gaps in Slab1.0 exist where input data are sparse and/or where slabs are geometrically complex (and difficult to image with an automated approach). Slab1.0 also does not include information on the uncertainty in the modeled geometrical parameters, or the input data used to image them, and provides no means for others to reproduce the models it describes. Now near completion, Slab2 will update and replace Slab1.0 by: (1) extending modeled slab geometries to the full extent of all known global subduction zones; (2) incorporating regional data sets (e.g., tomography models) that may describe slab geometry more comprehensively than do previously used teleseismic data; (3) providing information on the uncertainties in each modeled slab surface; (4) modifying our modeling approach to a fully-three dimensional data interpolation, rather than following the 2-D to 3-D steps of Slab1.0; (5) adding further layers to the base geometry dataset, such as historic moment release, earthquake tectonic providence, and interface coupling; (6) migrating the slab modeling code base to a more universally distributable language, Python; and (7) providing the code base and input data we use to create our models, such that the community can both reproduce the slab geometries, and add their own data sets to ours to further improve upon those models in the future. In this presentation we will describe our progress made in creating Slab2, and provide information on

  2. Li isotopic constraints from the Erro-Tobbio serpentinites on Alpine subduction processes

    Science.gov (United States)

    Chu, M.-F.; Scambelluri, M.; Griffin, W. L.; O'Reilly, S. Y.; Pearson, N. J.

    2012-04-01

    Subduction zones represent a unique feature of the dynamic Earth and provide important constraints on how plate tectonics works. Subduction of serpentinized oceanic lithosphere, characterized by releasing water into the mantle wedge via dehydration, i.e. breakdown of hydrous minerals, plays a critical role in not only the generation of continental crust but also the Earth's water cycle. To track the recycling of water or fluid released by subduction, the stable isotope system of Li, a lithophile and mobile element, shows its high potential because 7Li, relative to 6Li, preferentially moves into the fluid phase when fractionation occurs. Here we present new Li abundance and isotopic compositions of the Erro-Tobbio serpentinized peridotite complex, a remnant mantle slice of the Alpine subduction. Our data indicate that most of the serpentinized ultramafic rocks have uniform Li concentrations, around 1 ppm. These rocks, however, show variable Li isotopic compositions. Among them, the high-pressure antigorite-bearing metaperidotites, formed under a low-strain condition, have a limited range in Li isotopic values, with δ7Li = +1.5 to +4.0, similar to those of serpentinized peridotites. In contrast, apparently heavier Li isotopes, up to +10.0, are observed in the high-pressure serpentinite mylonites that also contain antigorite but formed in high-strain domains. We note that O-H isotope ratios of the high-pressure ultramafic rocks reported in previous study (Früh-Green et al., 2001, Contrib. Mineral Petrol. 141: 145-159) show insignificant variations between the low- and high-strain domains. This demonstrates the superiority of Li isotope than conventional stable isotope systems in offering critical information about fluid-releasing processes in subduction zones. Moreover, our new data unsupport the general assumption that fluid released from subducted slabs is in favor of extracting 7Li than 6Li, thus capable of forming the much lighter δ7Li values observed in

  3. Zagros blueschists: Episodic underplating and long-lived cooling of a subduction zone

    Science.gov (United States)

    Angiboust, Samuel; Agard, Philippe; Glodny, Johannes; Omrani, Jafar; Oncken, Onno

    2016-06-01

    Pressure-temperature-time (P- T- t) trajectories of high-pressure rocks provide important constraints to understand the tectonic evolution of convergent margins. New field observations and P- T- t constraints for the evolution of the only known blueschist-facies exposure along the Zagros suture zone in Southern Iran are reported here. These blueschists, now exposed in tectonic windows under the Sanandaj-Sirjan zone (upper plate), constitute accreted fragments of the Tethyan domain during N-directed Cretaceous subduction. Three units were identified in the field: from top to bottom, the Ashin unit (mafic and felsic gneisses), the Seghin complex (mafic tuffs and ultramafics) and the Siah Kuh massif (coherent volcanic edifice). Microstructural observations, P- T estimates and Rb-Sr deformation ages indicate that the Ashin unit possibly underwent burial down to 30-35 km and 550 °C along a relatively warm P- T gradient (c. 17°/km) and was ultimately deformed between 85 and 100 Ma. The Seghin complex exhibits remarkably well-preserved HP-LT assemblages comprising lawsonite, glaucophane, aragonite, omphacite and garnet. P- T- t reconstruction indicates that this slice was subducted down to c. 50 km at temperatures of c. 500 °C along a very cold subduction gradient (c. 7°/km). Deformation in the Seghin complex stopped at around 65 Ma, close to peak metamorphic conditions. Field relationships and estimates of the P- T trajectory followed by the Siah Kuh volcanic edifice indicate that this massif was lately subducted down to 15 km depth along the same very cold gradient. This slice-stack represents a well-preserved field example (i) highlighting the existence of transient underplating processes juxtaposing pluri-kilometric tectonic slices along the subduction channel and (ii) imaging the discontinuous down-stepping of the active main subduction thrust with ongoing accretion. The Zagros blueschists also record an apparent cooling of the Zagros subduction zone between 90

  4. Subduction zone earthquakes and stress in slabs

    Science.gov (United States)

    Vassiliou, M. S.; Hager, B. H.

    1988-01-01

    Simple viscous fluid models of subducting slabs are used to explain observations of the distribution of earthquakes as a function of depth and the orientation of stress axes of deep (greater than 300 km) and intermediate (70-300 km) earthquakes. Results suggest the following features in the distribution of earthquakes with depth: (1) an exponential decrease from shallow depths down to 250 to 300 km, (2) a minimum near 250 to 300 km, and (3) a deep peak below 300 km. Many shallow subducting slabs show only the first characteristic, while deeper extending regions tend to show all three features, with the deep peak varying in position and intensity. These data, combined with the results on the stress orientations of various-depth earthquakes, are consistent with the existence of a barrier of some sort at 670-km depth and a uniform viscosity mantle above this barrier.

  5. The hidden simplicity of subduction megathrust earthquakes

    Science.gov (United States)

    Meier, M.-A.; Ampuero, J. P.; Heaton, T. H.

    2017-09-01

    The largest observed earthquakes occur on subduction interfaces and frequently cause widespread damage and loss of life. Understanding the rupture behavior of megathrust events is crucial for earthquake rupture physics, as well as for earthquake early-warning systems. However, the large variability in behavior between individual events seemingly defies a description with a simple unifying model. Here we use three source time function (STF) data sets for subduction zone earthquakes, with moment magnitude Mw ≥ 7, and show that such large ruptures share a typical universal behavior. The median STF is scalable between events with different sizes, grows linearly, and is nearly triangular. The deviations from the median behavior are multiplicative and Gaussian—that is, they are proportionally larger for larger events. Our observations suggest that earthquake magnitudes cannot be predicted from the characteristics of rupture onsets.

  6. Subduction related fluids fractionate Nb/Ta

    Science.gov (United States)

    Salters, V. J.; Bizimis, M.; Sachi-Kocher, A.; Taylor, R.; Savov, I. P.; Stern, C. R.

    2009-12-01

    Key differences between the chemical composition of terrestrial materials and those of meteorites have led to the suggestion that a `hidden’ high Nb/Ta reservoir exists in the Earth’s mantle. In order to test this hypothesis we must identify the processes that can create such a reservoir. It has been suggested that during subduction Nb is more refractory then Ta resulting in low Nb/Ta in the subducted slab, which then serves as a reservoir for the high Nb/Ta. Here we report high precision HFSE data on products of the subduction processes thought to fractionate Nb from Ta: boninites (hydrous melting), adakites (slab melting), oceanic island arc basalts and supra subduction zone peridotites. We developed a new method for the high precision determination of Nb, Ta, Zr, Hf concentrations based on a modified version of standard addition. All analyses were performed on a single collector ICPMS (ELEMENT 1), using Y and Yb as internal standards to correct for instrumental drift during the unspiked -spiked sample sequence. Concentrations are calculated using a York- type regression that accounts for all measured and propagated errors. Long-term reproducibility (multiple dissolutions and multiple spike solutions) for the standards BHVO-1, BIR-1 AGV-1 and BCR-1 are better than 0.8% (1s) for Nb/Ta and Zr/Hf ratios. The advantages of this method compared to previous methods are fast throughput, no column chemistry and low blanks. While the Zr/Hf ratios in subduction-related volcanics and ocean island basalts vary by less than a factor of two, the Nb/Ta ratio varies by a factor of four. Most of the Nb/Ta variation is observed in subduction related rocks. Samples with the highest Nb/Ta ratio (up to 19.5) are adakites from the Austral Volcanic Zone (Andes) which are thought to represent eclogitic melts from subducted oceanic crust which was most likely dehydrated. The lowest Nb/Ta (5) was found in boninites from Chichi-Jima, Bonin Island. Samples from Chichi-Jima and from the

  7. Volcanism and Subduction: The Kamchatka Region

    Science.gov (United States)

    Eichelberger, John; Gordeev, Evgenii; Izbekov, Pavel; Kasahara, Minoru; Lees, Jonathan

    The Kamchatka Peninsula and contiguous North Pacific Rim is among the most active regions in the world. Kamchatka itself contains 29 active volcanoes, 4 now in a state of semi-continuous eruption, and I has experienced 14 magnitude 7 or greater earthquakes since accurate recording began in 1962. At its heart is the uniquely acute subduction cusp where the Kamchatka and Aleutian Arcs and Emperor Seamount Chain meet. Volcanism and Subduction covers coupled magmatism and tectonics in this spectacular region, where the torn North Pacific slab dives into hot mantle. Senior Russian and American authors grapple with the dynamics of the cusp with perspectives from the west and east of it, respectively, while careful tephrostratigraphy yields a remarkably precise record of behavior of storied volcanoes such as Kliuchevskoi and Shiveluch. Towards the south, Japanese researchers elucidate subduction earthquake processes with unprecedented geodetic resolution. Looking eastward, new insights on caldera formation, monitoring, and magma ascent are presented for the Aleutians. This is one of the first books of its kind printed in the English language. Students and scientists beginning research in the region will find in this book a useful context and introduction to the region's scientific leaders. Others who wish to apply lessons learned in the North Pacific to their areas of interest will find the volume a valuable reference.

  8. Regional differences in subduction ground motions

    CERN Document Server

    Beauval, Céline; Abrahamson, N; Theodulidis, N; Delavaud, E; Rodriguez, L; Scherbaum, F; Haendel, A

    2012-01-01

    A few ground-motion prediction models have been published in the last years, for predicting ground motions produced by interface and intraslab earthquakes. When one must carry out a probabilistic seismic hazard analysis in a region including a subduction zone, GMPEs must be selected to feed a logic tree. In the present study, the aim is to identify which models provide the best fit to the dataset M6+, global or local models. The subduction regions considered are Japan, Taiwan, Central and South America, and Greece. Most of the data comes from the database built to develop the new BCHydro subduction global GMPE (Abrahamson et al., submitted). We show that this model is among best-fitting models in all cases, followed closely by Zhao et al. (2006), whereas the local Lin and Lee (2008) is well predicting the data in Taiwan and also in Greece. The Scherbaum et al. (2009) LLH method prove to be efficient in providing one number quantifying the overall fit, but additional analysis on the between-event and within-ev...

  9. Great earthquakes hazard in slow subduction zones

    Science.gov (United States)

    Marcaillou, B.; Gutscher, M.; Westbrook, G. K.

    2008-12-01

    Research on the Sumatra-Andaman earthquake of 2004 has challenged two popular paradigms; that the strongest subduction earthquakes strike in regions of rapid plate convergence and that rupture occurs primarily along the contact between the basement of the overriding plate and the downgoing plate. Subduction zones presenting similar structural and geodynamic characteristics (slow convergence and thick wedges of accreted sediment) may be capable of generating great megathrust earthquakes (M>8.5) despite an absence of thrust type earthquakes over the past 40 years. Existing deep seismic sounding data and hypocenters are used to constrain the geometry of several key slow subduction zones (Antilles, Hellenic, Sumatra). This geometry forms the basis for numerical modelling of fore-arc thermal structure, which is applied to calculate the estimated width of the seismogenic portion of the subduction fault plane. The margins with the thickest accretionary wedges are commonly found to have the widest (predicted) seismogenic zone. Furthermore, for these margins there exists a substantial (20-60 km wide) region above the up-dip limit for which the contribution to tsunami generation is poorly understood. As the rigidity (mu) of these high-porosity sediments is low, co-seismic slip here can be expected to be slow. Accordingly, the contribution to seismic moment will be low, but the contribution to tsunami generation may be very high. Indeed, recent seismological data from Nankai indicate very low frequency shallow-thrust earthquakes beneath this portion of the accretionary wedge, long-considered to be "aseismic". We propose that thick accumulations of sediment on the downgoing plate and the presence of a thick accretionary wedge can increase the maximum size of the potential rupture fault plane in two ways; 1) by thermally insulating the downgoing plate and thereby increasing the total downdip length of the fault which can rupture seismically and 2) by "smoothing out" the

  10. Subduction of oceanic plate irregularities and seismicity distribution along the Mexican Subduction Zone

    Science.gov (United States)

    Manea, Marina; Constantin Manea, Vlad; Gerya, Taras; Wong, Raul-Valenzuela; Radulian, Mircea

    2017-04-01

    It is known that oceanic plates morphology is not a simple one, but rather complicated by a series of irregularities as seamounts, fracture zones and mid-ocean ridges. These features present on the oceanic floor form part of the fabric of oceanic crust, and once formed they move together with the oceanic plates until eventually enter a subduction zone. Offshore Mexico the oceanic Cocos plate seafloor is littered with relatively small but numerous seamounts and seamount chains, and also large fracture zones. In this study we investigate the relationship between these oceanic irregularities located in the vicinity of the trench in Mexico and the distribution of subduction seismicity, including the rupture history of large subduction zone earthquakes. Since the interseismic locking degree is influenced by the rheological properties of crustal and mantle rocks, any variations along strike will result in significant changes in seismic behavior due to a change in frictional stability. Our preliminary study shows a direct relationship between the presence of seamounts chains on the incoming oceanic plate and the subduction seismicity distribution. We also found a clear relationship between the subduction of the Tehuantepec fracture zone (TFZ) and the low seismic activity in the region where this fracture zone intersects the trench. This region is also long term conspicuously quiet and considered a seismic gap where no significant large earthquake has occurred in more than 100 years. Using high-resolution three-dimensional coupled petrological-thermomechanical numerical simulations specifically tailored for the subduction of the Cocos plate in the region of TFZ we show that the weakened serpentinized fracture zone is partially scraped out in the forearc region because of its low strength and positive buoyancy. The presence of serpentinite in the fore arc apparently lowers the degree of interseismic locking, producing a seismic gap in southern Mexico.

  11. What's happening inside the subduction factory?

    Science.gov (United States)

    Penniston-Dorland, S. C.; Bebout, G. E.; Gorman, J. K.; Piccoli, P. M.; Walker, R. J.

    2012-12-01

    Much research has focused on the inputs and outputs of the 'subduction factory,' however a variety of metamorphic processes occur within the subducting slab and at its interface with the mantle wedge that contribute to creating the mixed signals observed in arc magmas. Subduction-related metamorphic rocks from the Catalina Schist represent a range of metamorphic grades and provide a natural laboratory to investigate these processes. Hybrid rock types such as reaction zones or 'rinds' between mafic (crustal) and ultramafic (mantle) rocks have attracted recent interest since they have a different bulk chemistry and mineralogy compared to the original inputs to the subduction factory. Here we explore the mineralogical and geochemical differences between the metamorphic rocks, their reaction zones, and endmember subduction input lithologies over a range of metamorphic grades including lawsonite albite, lawsonite blueschist, and amphibolite facies (with peak T ranging from ~ 275 to ~ 750°C and peak P ranging up to ~1.1 GPa). The results shed light on chemical changes occurring within the subduction zone and the processes happening inside the 'subduction factory', including mass transfer of elements by both fluid infiltration and mechanical mixing. Elements commonly enriched in arc magmatic rocks, such as the LILE (e.g. Ba, K), are enriched in metamafic rocks at all metamorphic grades relative to likely MORB protoliths. These enrichments are interpreted as the product of metamorphic fluid infiltration. Many major- and trace-element concentrations in reaction rinds fall between those of metamafic blocks and surrounding ultramafic-rich mélange matrix (including TiO2, MgO, FeO, Al2O3, Zr, Ni and Cr). Spatial distributions of these elements within the rinds suggest that the intermediate concentrations may be due to mechanical mixing of crustal and mantle materials. Rind concentrations of the highly siderophile elements (HSE: including Os, Ir, Ru, Pt, Pd, Re) as well as

  12. Velocities of Subducted Sediments and Continents

    Science.gov (United States)

    Hacker, B. R.; van Keken, P. E.; Abers, G. A.; Seward, G.

    2009-12-01

    The growing capability to measure seismic velocities in subduction zones has led to unusual observations. For example, although most minerals have VP/ VS ratios around 1.77, ratios 1.8 have been observed. Here we explore the velocities of subducted sediments and continental crust from trench to sub-arc depths using two methods. (1) Mineralogy was calculated as a function of P & T for a range of subducted sediment compositions using Perple_X, and rock velocities were calculated using the methodology of Hacker & Abers [2004]. Calculated slab-top temperatures have 3 distinct depth intervals with different dP/dT gradients that are determined by how coupling between the slab and mantle wedge is modeled. These three depth intervals show concomitant changes in VP and VS: velocities initially increase with depth, then decrease beyond the modeled decoupling depth where induced flow in the wedge causes rapid heating, and increase again at depth. Subducted limestones, composed chiefly of aragonite, show monotonic increases in VP/ VS from 1.63 to 1.72. Cherts show large jumps in VP/ VS from 1.55-1.65 to 1.75 associated with the quartz-coesite transition. Terrigenous sediments dominated by quartz and mica show similar, but more-subdued, transitions from ~1.67 to 1.78. Pelagic sediments dominated by mica and clinopyroxene show near-monotonic increases in VP/ VS from 1.74 to 1.80. Subducted continental crust that is too dry to transform to high-pressure minerals has a VP/ VS ratio of 1.68-1.70. (2) Velocity anisotropy calculations were made for the same P-T dependent mineralogies using the Christoffel equation and crystal preferred orientations measured via electron-backscatter diffraction for typical constituent phases. The calculated velocity anisotropies range from 5-30%. For quartz-rich rocks, the calculated velocities show a distinct depth dependence because crystal slip systems and CPOs change with temperature. In such rocks, the fast VP direction varies from slab-normal at

  13. Extensive decarbonation of continuously hydrated subducting slabs

    Science.gov (United States)

    Arzilli, Fabio; Burton, Mike; La Spina, Giuseppe; Macpherson, Colin G.

    2017-04-01

    CO2 release from subducting slabs is a key element of Earth's carbon cycle, consigning slab carbon either to mantle burial or recycling to the surface through arc volcanism, however, what controls subducted carbon's fate is poorly understood. Fluids mobilized by devolatilization of subducting slabs play a fundamental role in the melting of mantle wedges and in global geochemical cycles [1]. The effect of such fluids on decarbonation in subducting lithologies has been investigated recently [2-5], but several thermodynamic models [2-3], and experimental studies [6] suggest that carbon-bearing phases are stable at sub-arc depths (80-140 km; 2.6-4.5 GPa), implying that this carbon can be carried to mantle depths of >140 km. This is inconsistent with observations of voluminous CO2 release from arc volcanoes [7-10], located above slabs that are at 2.6-4.5 GPa pressure. The aim of this study is to re-evaluate the role of metamorphic decarbonation, showing if decarbonation reactions could be feasible at sub-arc depths combined with a continuous hydration scenario. We used the PerpleX software combined with a custom-designed algorithm to simulate a pervasive fluid infiltration characterized by "continuous hydration" combined with a distillation model, in which is possible to remove CO2 when decarbonation occurs, to obtain an open-system scenario. This is performed by repeatedly flushing the sediment with pure H2O at 0.5, 1.0 or 5 wt.% until no further decarbonation occurs. Here we show that continuous hydrated of sediment veneers on subducting slabs by H2O released from oceanic crust and serpentinised mantle lithosphere [11-13], produces extensive slab decarbonation over a narrow, sub-arc pressure range, even for low temperature subduction pathways. This explains the location of CO2-rich volcanism, quantitatively links the sedimentary composition of slab material to the degree of decarbonation and greatly increases estimates for the magnitude of carbon flux through the arc

  14. Constraining the hydration of the subducting Nazca plate beneath Northern Chile using subduction zone guided waves

    Science.gov (United States)

    Garth, Tom; Rietbrock, Andreas

    2017-09-01

    Guided wave dispersion is observed from earthquakes at 180-280 km depth recorded at stations in the fore-arc of Northern Chile, where the 44 Ma Nazca plate subducts beneath South America. Characteristic P-wave dispersion is observed at several stations in the Chilean fore-arc with high frequency energy (>5 Hz) arriving up to 3 s after low frequency (first motion dispersion observed at multiple stations, or the extended P-wave coda observed in arrivals from intermediate depth events within the Nazca plate. These signals can however be accurately accounted for if dipping low velocity fault zones are included within the subducting lithospheric mantle. A grid search over possible LVL and faults zone parameters (width, velocity contrast and separation distance) was carried out to constrain the best fitting model parameters. Our results imply that fault zone structures of 0.5-1.0 km thickness, and 5-10 km spacing, consistent with observations at the outer rise are present within the subducted slab at intermediate depths. We propose that these low velocity fault zone structures represent the hydrated structure within the lithospheric mantle. They may be formed initially by normal faults at the outer rise, which act as a pathway for fluids to penetrate the deeper slab due to the bending and unbending stresses within the subducting plate. Our observations suggest that the lithospheric mantle is 5-15% serpentinised, and therefore may transport approximately 13-42 Tg/Myr of water per meter of arc. The guided wave observations also suggest that a thin LVL (∼1 km thick) interpreted as un-eclogitised subducted oceanic crust persists to depths of at least 220 km. Comparison of the inferred seismic velocities with those predicted for various MORB assemblages suggest that this thin LVL may be accounted for by low velocity lawsonite-bearing assemblages, suggesting that some mineral-bound water within the oceanic crust may be transported well beyond the volcanic arc. While older

  15. Control of high oceanic features and subduction channel on earthquake ruptures along the Chile-Peru subduction zone

    Science.gov (United States)

    Contreras-Reyes, Eduardo; Carrizo, Daniel

    2011-05-01

    We discuss the earthquake rupture behavior along the Chile-Peru subduction zone in terms of the buoyancy of the subducting high oceanic features (HOF's), and the effect of the interplay between HOF and subduction channel thickness on the degree of interplate coupling. We show a strong relation between subduction of HOF's and earthquake rupture segments along the Chile-Peru margin, elucidating how these subducting features play a key role in seismic segmentation. Within this context, the extra increase of normal stress at the subduction interface is strongly controlled by the buoyancy of HOF's which is likely caused by crustal thickening and mantle serpentinization beneath hotspot ridges and fracture zones, respectively. Buoyancy of HOF's provide an increase in normal stress estimated to be as high as 10-50 MPa. This significant increase of normal stress will enhance seismic coupling across the subduction interface and hence will affect the seismicity. In particular, several large earthquakes (Mw ≥ 7.5) have occurred in regions characterized by subduction of HOF's including fracture zones (e.g., Nazca, Challenger and Mocha), hotspot ridges (e.g., Nazca, Iquique, and Juan Fernández) and the active Nazca-Antarctic spreading center. For instance, the giant 1960 earthquake (Mw = 9.5) is coincident with the linear projections of the Mocha Fracture Zone and the buoyant Chile Rise, while the active seismic gap of north Chile spatially correlates with the subduction of the Iquique Ridge. Further comparison of rupture characteristics of large underthrusting earthquakes and the locations of subducting features provide evidence that HOF's control earthquake rupture acting as both asperities and barriers. This dual behavior can be partially controlled by the subduction channel thickness. A thick subduction channel smooths the degree of coupling caused by the subducted HOF which allows lateral earthquake rupture propagation. This may explain why the 1960 rupture propagates

  16. Postglacial (after 18 ka) deep-sea sedimentation along the Hikurangi subduction margin (New Zealand): Characterisation, timing and origin of turbidites

    OpenAIRE

    Pouderoux, Hugo; Proust, Jean-Noël; Lamarche, Geoffroy; Orpin, Alan; Neil, Helen

    2012-01-01

    International audience; Recent sedimentation along the Hikurangi subduction margin off northeastern New Zealand is investigated using a series of piston cores collected between 2003 and 2008. The active Hikurangi Margin lies along the Pacific-Australia subduction plate boundary and contains a diverse range of geomorphologic settings. Slope basin stratigraphy is thick and complex, resulting from sustained high rates of sedimentation from adjacent muddy rivers throughout the Quaternary. Turbidi...

  17. Diapiric flow at subduction zones: a recipe for rapid transport.

    Science.gov (United States)

    Hall, P S; Kincaid, C

    2001-06-29

    Recent geochemical studies of uranium-thorium series disequilibrium in rocks from subduction zones require magmas to be transported through the mantle from just above the subducting slab to the surface in as little as approximately 30,000 years. We present a series of laboratory experiments that investigate the characteristic time scales and flow patterns of the diapiric upwelling model of subduction zone magmatism. Results indicate that the interaction between buoyantly upwelling diapirs and subduction-induced flow in the mantle creates a network of low-density, low-viscosity conduits through which buoyant flow is rapid, yielding transport times commensurate with those indicated by uranium-thorium studies.

  18. The characteristics of mantle lithosphere buoyancy revealed from the northern Manila subduction zone to the active collision in Taiwan region

    Science.gov (United States)

    Lo, Chung-Liang; Doo, Wen-Bin; Kuo-Chen, Hao; Hsu, Shu-Kun; Lin, Jing-Yi

    2017-04-01

    It has been widely studied on the complexity tectonic structure in the active Taiwan orogenesis, since the converging between the Philippine Sea plate (PSP) and the Eurasian plate (EU) along with the Manila subduction zone extended from the Philippine to offshore the southern Taiwan and the Ryukyu subduction zone in the east. Considering the separate contribution of the crust and the mantle lithosphere to the topography, we try to examine the mantle lithosphere buoyancy (Hm) behavior from the northern Manila subduction zone to the active collision in Taiwan region. In this study, we present several Hm profiles across the northern Manila subduction zone and the Taiwan island. In order to calculate the Hm, the crust structures are constrained by the forward gravity modeling, in which the density is provided from the multi-channel seismic data and on land seismic data (thanks to the Taiwan Integrated Geodynamic Research (TAIGER) project). The result shows that the Hm across the northern Manila subduction zone displays apparent undulations, and undulates more drastic approaching the north end of the subduction zone. It implies that the plate coupling between the PSP and the EU here is weak. The Hm across the southern Taiwan undulates still, but the amplitudes are smaller with relative gentle undulations. This reflects the contribution from the slab underneath while the initial collision occurs in south Taiwan. Into the central Taiwan, the Hm pattern behaves undulating mild comparing with that across the subduction zone because the slab structure effects not obvious. Besides, the Hm in the central Taiwan primarily is affects by both the thickening crust and high elevation caused by the strong lateral external compression stress.

  19. The zone of influence of the subducting slab in the asthenospheric mantle

    Science.gov (United States)

    MacDougall, Julia G.; Jadamec, Margarete A.; Fischer, Karen M.

    2017-08-01

    Due to the multidisciplinary nature of combined geodynamics and shear wave splitting studies, there is still much to be understood in terms of isolating the contributions from mantle dynamics to the shear wave splitting signal, even in a two-dimensional (2-D) mantle flow framework. This paper investigates the viscous flow, lattice preferred orientation (LPO) development, and predicted shear wave splitting for a suite of buoyancy-driven subduction models using a non-linear rheology to shed light on the nature of the slab-driven asthenospheric flow and plate-mantle coupling. The slab-driven zone of influence in the mantle, LPO fabric, and resulting synthetic splitting are sensitive to slab strength and slab initial slab dip. The non-linear viscosity formulations leads to dynamic reductions in asthenospheric viscosity extending over 600 km into the mantle wedge and over 300 km behind the trench, with peak flow velocities occurring in models with a weaker slab and moderate slab dip. The olivine LPO fabric in the asthenosphere generally increases in alignment strength with increased proximity to the slab but can be transient and spatially variable on small length scales. The results suggest that LPO formed during initial subduction may persist into the steady state subduction regime. Vertical flow fields in the asthenosphere can produce shear wave splitting variations with back azimuth that deviate from the predictions of uniform trench-normal anisotropy, a result that bears on the interpretation of complexity in shear wave splitting observed in real subduction zones. Furthermore, the models demonstrate the corner flow paradigm should not be equated with a 2-D subduction framework.

  20. Seismotectonics of the southern boundary of Anatolia, Eastern Mediterranean region: subduction, collision, and arc jumping

    Energy Technology Data Exchange (ETDEWEB)

    Rotstein, Y.; Kafka, A.L.

    1982-09-10

    The pattern of seismicity and fault plane solutions of earthquakes are used to outline the tectonic features of the southern boundary of Anatolia in the eastern Mediterranean and southeastern Turkey. The results of this study show that this boundary is composed of two distinct parts. One, in southeastern Turkey and Syria, is a wide and complex zone of continental collision. The other, in the Levantine basin of the eastern Mediterranean, is a zone of oceanic subduction. In the region of continental collision three zones of seismicity are observed. Most of the seismic activity in this region follows the Bitlis zone and is associated with a zone of thrusting and mountain building. This appears to be the zone of most active deformation and plate consumption in the plate boundary region between Arabia and Turkey. A less active zone of seismicity to the north of the Bitlis zone is interpreted to have been more active in the past whereas another active zone of seismicity to the south is interpreted to be a zone which may be more active in the future as the main zone of plate consumption jumps to the south. In the subduction zone of the eastern Mediterranean the depth of the subducted slab and the rate of seismicity generally increease from east to west. The zone of present-day convergence between Africa and Turkey in the Levantine basin can be best outlined by the northern edge of the Mediterranean ridge. Deep seismic activity near the Gulf of Antalya is associated with a detached subducted slab north of the Anaximander Mountains that is distinctly different from the seismic trend which is associated with present-day active subduction. Most of the focal mechanisms of the earthquakes along the entire southern boundary of Anatolia indicate that N to NNW thrusting is the dominant mode of seismic deformation.

  1. Three-dimensional structure and seismicity beneath the Central Vanuatu subduction zone

    Science.gov (United States)

    Foix, Oceane; Crawford, Wayne; Pelletier, Bernard; Regnier, Marc; Garaebiti, Esline; Koulakov, Ivan

    2017-04-01

    The 1400-km long Vanuatu subduction zone results from subduction of the oceanic Australian plate (OAP) beneath the North-Fijian microplate (NFM). Seismic and volcanic activity are both high, and several morphologic features enter into subduction, affecting seismicity and probably plate coupling. The Entrecasteaux Ridge, West-Torres plateau, and Bougainville seamount currently enter into subduction below the large forearc islands of Santo and Malekula. This collision coincides with a strongly decreased local convergence velocity rate - 35 mm/yr compared to 120-160 mm/yr to the north and south - and significant uplift on the overriding plate, indicating a high degree of deformation. The close proximity of large uplifted forearc islands to the trench provides excellent coverage of the megathrust seismogenic zone for a seismological study. We used 10 months of seismological data collected using the 30-instrument land and sea ARC-VANUATU seismology network to construct a 3D velocity model — using the LOTOS joint location/model inversion software — and locate 11655 earthquakes using the NonLinLoc software suite. The 3-D model reveals low P and S velocities in the first tens of kilometers beneath both islands, probably due to water infiltration in the heavily faulted upper plate. The model also suggests the presence of a subducted seamount beneath south Santo. The earthquake locations reveal a complex interaction of faults and stress zones related to high and highly variable deformation. Both brittle deformation and the seismogenic zone depth limits vary along-slab and earthquake clusters are identified beneath central and south Santo, at about 10-30 km of depth, and southwest of Malekula island between 10-20 km depth.

  2. Characterizing Seismic Anisotropy across the Peruvian Flat-Slab Subduction Zone: Shear Wave Splitting from PULSE

    Science.gov (United States)

    Eakin, C. M.; Long, M. D.; Beck, S. L.; Wagner, L. S.; Tavera, H.

    2013-12-01

    Although 10% of subduction zones worldwide today exhibit shallow or flat subduction, we are yet to fully understand how and why these slabs go flat. An excellent study location for such a problem is in Peru, where the largest region of flat-subduction currently exists, extending ~1500 km in length (from 3 °S to 15 °S) and ~300 km in width. Across this region we investigate the pattern of seismic anisotropy, an indicator for past and/or ongoing deformation in the upper mantle. To achieve this we conduct shear wave splitting analyzes at 40 broadband stations from the PULSE project (PerU Lithosphere and Slab Experiment). These stations were deployed for 2+ years across the southern half of the Peruvian flat-slab region. We present detailed shear wave splitting results for deep and teleseismic events, making use of a wide variety of available phases that sample the upper mantle directly beneath the stations (such as SKS, SKKS, PKS, sSKS, SKiKS, ScS and local/direct S). We analyze the variability of our results with respect to initial polarizations and ray paths, as well as spatial variability between stations as the underlying slab morphology changes. Preliminary results show predominately NW-SE fast polarizations (trench oblique to sub-parallel) over the flat-slab region east of Lima. These results are consistent with observations of more complex multi-layered anisotropy beneath a nearby permanent station (NNA). Further south, towards the transition to steeper subduction, the splitting pattern becomes increasingly dominated by null measurements. Over to the east however, beyond Cuzco, where the mantle wedge might begin to play a role, we record fast polarizations quasi-parallel to the local slab contours. We carefully evaluate the different possible source locations within the subduction zone for this seismic anisotropy and observe increasing evidence for distinct anisotropy within the slab as well as the sub-slab mantle.

  3. Seismotectonics of the southern boundary of Anatolia, eastern Mediterranean region: Subduction, collision, and arc jumping

    Science.gov (United States)

    Rotstein, Yair; Kafka, Alan L.

    1982-09-01

    The pattern of seismicity and fault plane solutions of earthquakes are used to outline the tectonic features of the southern boundary of Anatolia in the eastern Mediterranean and southeastern Turkey. The results of this study show that this boundary is composed of two distinct parts. One, in southeastern Turkey and Syria, is a wide and complex zone of continental collision. The other, in the Levantine basin of the eastern Mediterranean, is a zone of oceanic subduction. In the region of continental collision three zones of seismicity are observed. Most of the seismic activity in this region follows the Bitlis zone and is associated with a zone of thrusting and mountain building. This appears to be the zone of most active deformation and plate consumption in the plate boundary region between Arabia and Turkey. A less active zone of seismicity to the north of the Bitlis zone is interpreted to have been more active in the past whereas another active zone of seismicity to the south is interpreted to be a zone which may be more active in the future as the main zone of plate consumption jumps to the south. In the subduction zone of the eastern Mediterranean the depth of the subducted slab and the rate of seismicity generally increase from east to west. The zone of present-day convergence between Africa and Turkey in the Levantine basin can be best outlined by the northern edge of the Mediterranean ridge. The subduction zone in this area sequentially jumps to the south as small continental fragments collide with existing zones of subduction. Deep seismic activity near the Gulf of Antalya is associated with a detached subducted slab north of the Anaximander Mountains that is distinctly different from the seismic trend which is associated with present-day active subduction. The plate boundary between Africa and Turkey at the center of the Levantine basin appears to have shifted to the south of the Anaximander Mountains and Florence rise. Most of the focal mechanisms of the

  4. Subduction Zone Concepts and the 2010 Chile Earthqake (Arthur Holmes Medal Lecture)

    Science.gov (United States)

    von Huene, Roland

    2010-05-01

    Knowledge of convergent margin systems evolved from hypothesis testing with marine geophysical technology that improved over decades. Wegener's drift hypothesis, Holmes mantle convection, and marine magnetic anomaly patterns were integrated into an ocean spreading concept that won wide acceptance after ocean drilling confirmed the crustal younging trend toward the Mid-Atlantic ridge. In contrast, the necessary disposal of oceanic and trench sediment at convergent margins remained largely hypothetical. Fresh interpretations of some coastal mountains as exposing ancient convergent margin rock assemblages and the seismologist's "Wadati-Benioff" zone were combined into a widely-accepted hypothesis. A convergent margin upper plate was pictured as an imbricate fan of ocean sediment thrust slices detached from the lower plate. During the 1980s ocean drilling to test the hypothesis revealed what then were counter-intuitive processes of sediment subduction and subduction erosion. Rather than the proposed seaward growth by accretion, many margins had lost material from erosion. In current concepts, individual margins are shaped by the net consequences of subduction accretion, sediment subduction, and subduction erosion. Similarly, recently acquired age data from ancient subduction complexes reveal periods dominated by accretion separated by periods dominated by tectonic erosion. Globally, the recycling of continental crustal material at subduction zones appears largely balanced by magmatic addition at volcanic arcs. The longevity of the original imbricate fan model in text books confirms its pictorial simplicity, because geophysical images and drill core evidence show that it commonly applies to only a relatively small frontal prism. A better understanding of convergent margin dynamics is of urgent societal importance as coastal populations increase rapidly and as recent disastrous earthquakes and tsunamis verify. The shift in convergent margin concepts has developed through

  5. Modeling mantle circulation and density distributions in subduction zones: Implications for seismic studies

    Science.gov (United States)

    Kincaid, C. R.; Druken, K. A.; Griffiths, R. W.; Long, M. D.; Behn, M. D.; Hirth, G.

    2009-12-01

    Subduction of ocean lithosphere drives plate tectonics, large-scale mantle circulation and thermal-chemical recycling processes through arcs. Seismologists have made important advances in our ability to map circulation patterns in subduction zones though anisotropy data/methods and in providing detailed images of mantle density fields. Increasingly, seismic and geodynamic disciplines are combining to extend our understanding of time varying subduction processes and associated vertical mass and energy fluxes. We use laboratory experiments to characterize three-dimensional flow fields in convergent margins for a range in plate forcing conditions and background, buoyancy-driven flow scenarios. Results reveal basic patterns in circulation, buoyant flow morphologies and density distributions that have implications for reconciling seismic data with mantle convection models. Models utilize a glucose working fluid with a temperature dependent viscosity to represent the upper 2000km of the mantle. Subducting lithosphere is modeled with a Phenolic plate and back-arc extension is produced using Mylar sheets. We recreate basic subduction styles observed in previous dynamic subduction models using simplified, kinematic forcing. Slab plate segments, driven by hydraulic pistons, move with various combinations of downdip, rollback and steepening motion. Neutral density finite strain markers are distributed throughout the fluid and used as proxies for tracking the evolution of olivine alignment through space and time in the evolving flow fields. Particle image velocimetry methods are also used to track time varying 3D velocity fields for use in directly calculating anisotropy patterns. Results show that complex plate motions (rollback, steepening, back-arc extension) in convergent margins produce relatively simple anisotropy patterns (e.g., trench-normal alignments) and underscore the importance of initial strain marker orientations on alignment patterns in the wedge. Results also

  6. Imaging of the subducted Kyushu-Palau Ridge in the Hyuga-nada region, western Nankai Trough subduction zone

    Science.gov (United States)

    Yamamoto, Yojiro; Obana, Koichiro; Takahashi, Tsutomu; Nakanishi, Ayako; Kodaira, Shuichi; Kaneda, Yoshiyuki

    2013-03-01

    We performed 3D seismic tomography of the Hyuga-nada region, western Nankai subduction zone, to investigate the relationship of the subducted part of Kyushu-Palau Ridge (KPR) to coseismic rupture propagation, seismicity, and shallow very low frequency earthquakes. Combining active-source and passive-source data recorded both onshore and offshore, we imaged the deep slab from near the trough axis to the coastal area. Our results show the subducted KPR as a low-velocity belt oriented NW-SE extending down the plate boundary to around 30 km depth. At this depth, we suggest that the subducted KPR detaches from the slab and becomes underplated on the overriding continental plate. As the coseismic slip areas of past large earthquakes do not extend into the subducted KPR, we suggest that it may inhibit rupture propagation. The interior of the subducted KPR shows active intraslab seismicity with a wide depth distribution. Shallow very low frequency earthquakes are continuously active above the location of the subducted KPR, whereas they are intermittent to the northeast of the subducted KPR. Thus, the subducted KPR appears to be an important factor in coseismic rupture propagation and seismic phenomena in this region.

  7. The melting of subducted banded iron formations

    Science.gov (United States)

    Kang, Nathan; Schmidt, Max W.

    2017-10-01

    Banded iron formations (BIF) were common shelf and ocean basin sediments 3.5-1.8 Ga ago. To understand the fate of these dense rocks upon subduction, the melting relations of carbonated BIF were determined in Fe-Ca-(Mg)-Si-C-O2 at 950-1400 °C, 6 and 10 GPa, oxidizing (fO2 = hematite-magnetite, HM) and moderately reducing (fO2 ∼CO2-graphite/diamond, CCO) conditions. Solidus temperatures under oxidizing conditions are 950-1025 °C with H2O, and 1050-1150 °C anhydrous, but 250-175 °C higher at graphite saturation (values at 6-10 GPa). The combination of Fe3+ and carbonate leads to a strong melting depression. Solidus curves are steep with 17-20 °C/GPa. Near-solidus melts are ferro-carbonatites with ∼22 wt.% FeOtot, ∼48 wt% CO2 and 1-5 wt.% SiO2 at fO2 ∼ HM and ∼49 wt.% FeOtot, ∼20 wt% CO2 and 19-25 wt.% SiO2 at fO2 ∼ CCO . At elevated subduction geotherms, as likely for the Archean, C-bearing BIF could melt out all carbonate around 6 GPa. Fe-rich carbonatites would rise but stagnate gravitationally near the slab/mantle interface until they react with the mantle through Fe-Mg exchange and partial reduction. The latter would precipitate diamond and yield Fe- and C-rich mantle domains, yet, Fe-Mg is expected to diffusively re-equilibrate over Ga time scales. We propose that the oldest subduction derived diamonds stem from BIF derived melts.

  8. Subducting Plate Breakup by Plume-Lithosphere Interaction

    Science.gov (United States)

    Koptev, A.; Gerya, T.; Jolivet, L.; Leroy, S. D.

    2016-12-01

    We use a 3D high-resolution thermo-mechanical modeling to investigate the impact of active mantle plume on a subducting lithospheric plate. Initial model setup consists of an overriding continental lithosphere and subducting lithospheric plate including oceanic and continental lithosphere. A mantle plume thermal anomaly has been initially seeded at the bottom of the model box underneath the continental segment of subducting plate. Mantle plume impingement on lithospheric bottom leads to thinning of continental lithosphere and decompressional melting of both lithospheric and sublithospheric mantle along stretched trench-parallel zone. Further continental breakup is followed by opening of an oceanic basin separating a newly formed microcontinent from the main subducting continent. Despite continuous push applied at the boundary of subducting plate, plume-induced oceanic basin opens during several Myrs reaching several hundred kilometers wide. Cooling of the mantle plume and beginning of collision between the separated microcontinent and the overriding continental plate lead to gradual closure of newly formed oceanic basin that gets further involved into subduction and collision. The final stage sees continental subduction of main body of subducting plate and simultaneous tectonic exhumation of the upper crust of the subducted microcontinent. This scenario involving a plume-induced rifting of a microcontinent away from main body of subducted plate can be compared to the Mesozoic-Cenozoic development of the African plate characterized by the consecutive separation of the Apulian microcontinent and Arabian plate (in the Jurassic and the Neogene, respectively) during subduction of Neo-Tethys oceanic lithosphere beneath the Eurasian margin.

  9. Dynamics of interplate domain in subduction zones: influence of rheological parameters and subducting plate age

    Directory of Open Access Journals (Sweden)

    D. Arcay

    2012-12-01

    Full Text Available The properties of the subduction interplate domain are likely to affect not only the seismogenic potential of the subduction area but also the overall subduction process, as it influences its viability. Numerical simulations are performed to model the long-term equilibrium state of the subduction interplate when the diving lithosphere interacts with both the overriding plate and the surrounding convective mantle. The thermomechanical model combines a non-Newtonian viscous rheology and a pseudo-brittle rheology. Rock strength here depends on depth, temperature and stress, for both oceanic crust and mantle rocks. I study the evolution through time of, on one hand, the brittle-ductile transition (BDT depth, zBDT, and, on the other hand, of the kinematic decoupling depth, zdec, simulated along the subduction interplate. The results show that both a high friction and a low ductile strength at the asthenospheric wedge tip shallow zBDT. The influence of the weak material activation energy is of second order but not negligible. zBDT becomes dependent on the ductile strength increase with depth (activation volume if the BDT occurs at the interplate decoupling depth. Regarding the interplate decoupling depth, it is shallowed (1 significantly if mantle viscosity at asthenospheric wedge tip is low, (2 if the difference in mantle and interplate activation energy is weak, and (3 if the activation volume is increased. Very low friction coefficients and/or low asthenospheric viscosities promote zBDT = zdec. I then present how the subducting lithosphere age affects the brittle-ductile transition depth and the kinematic decoupling depth in this model. Simulations show that a rheological model in which the respective activation energies of mantle and interplate material are too close hinders the mechanical decoupling at the down-dip extent of the interplate

  10. Contrasting sediment melt and fluid signatures for magma components in the Aeolian Arc: Implications for numerical modeling of subduction systems

    Science.gov (United States)

    Zamboni, Denis; Gazel, Esteban; Ryan, Jeffrey G.; Cannatelli, Claudia; Lucchi, Federico; Atlas, Zachary D.; Trela, Jarek; Mazza, Sarah E.; De Vivo, Benedetto

    2016-06-01

    The complex geodynamic evolution of Aeolian Arc in the southern Tyrrhenian Sea resulted in melts with some of the most pronounced along the arc geochemical variation in incompatible trace elements and radiogenic isotopes worldwide, likely reflecting variations in arc magma source components. Here we elucidate the effects of subducted components on magma sources along different sections of the Aeolian Arc by evaluating systematics of elements depleted in the upper mantle but enriched in the subducting slab, focusing on a new set of B, Be, As, and Li measurements. Based on our new results, we suggest that both hydrous fluids and silicate melts were involved in element transport from the subducting slab to the mantle wedge. Hydrous fluids strongly influence the chemical composition of lavas in the central arc (Salina) while a melt component from subducted sediments probably plays a key role in metasomatic reactions in the mantle wedge below the peripheral islands (Stromboli). We also noted similarities in subducting components between the Aeolian Archipelago, the Phlegrean Fields, and other volcanic arcs/arc segments around the world (e.g., Sunda, Cascades, Mexican Volcanic Belt). We suggest that the presence of melt components in all these locations resulted from an increase in the mantle wedge temperature by inflow of hot asthenospheric material from tears/windows in the slab or from around the edges of the sinking slab.

  11. Noble gases recycled into the mantle through cold subduction zones

    Science.gov (United States)

    Smye, Andrew J.; Jackson, Colin R. M.; Konrad-Schmolke, Matthias; Hesse, Marc A.; Parman, Steve W.; Shuster, David L.; Ballentine, Chris J.

    2017-08-01

    Subduction of hydrous and carbonated oceanic lithosphere replenishes the mantle volatile inventory. Substantial uncertainties exist on the magnitudes of the recycled volatile fluxes and it is unclear whether Earth surface reservoirs are undergoing net-loss or net-gain of H2O and CO2. Here, we use noble gases as tracers for deep volatile cycling. Specifically, we construct and apply a kinetic model to estimate the effect of subduction zone metamorphism on the elemental composition of noble gases in amphibole - a common constituent of altered oceanic crust. We show that progressive dehydration of the slab leads to the extraction of noble gases, linking noble gas recycling to H2O. Noble gases are strongly fractionated within hot subduction zones, whereas minimal fractionation occurs along colder subduction geotherms. In the context of our modelling, this implies that the mantle heavy noble gas inventory is dominated by the injection of noble gases through cold subduction zones. For cold subduction zones, we estimate a present-day bulk recycling efficiency, past the depth of amphibole breakdown, of 5-35% and 60-80% for 36Ar and H2O bound within oceanic crust, respectively. Given that hotter subduction dominates over geologic history, this result highlights the importance of cooler subduction zones in regassing the mantle and in affecting the modern volatile budget of Earth's interior.

  12. GPS Monitoring of Subduction Zone Deformation in Costa Rica

    Science.gov (United States)

    Lundgren, Paul

    1997-01-01

    The subduction of the Cocos plate beneath Costa Rica is among the highest convergence rates in the world. The high subduction rate and nearness of the Nicoya Peninsula, Costa Rica to the Middle America Trench (MAT) provide a unique opportunity to map variations in interseismic strain of the crust above the seismogenic zone in response to variations in seismic coupling.

  13. The subduction dichotomy of strong plates and weak slabs

    Science.gov (United States)

    Petersen, Robert I.; Stegman, Dave R.; Tackley, Paul J.

    2017-03-01

    A key element of plate tectonics on Earth is that the lithosphere is subducting into the mantle. Subduction results from forces that bend and pull the lithosphere into the interior of the Earth. Once subducted, lithospheric slabs are further modified by dynamic forces in the mantle, and their sinking is inhibited by the increase in viscosity of the lower mantle. These forces are resisted by the material strength of the lithosphere. Using geodynamic models, we investigate several subduction models, wherein we control material strength by setting a maximum viscosity for the surface plates and the subducted slabs independently. We find that models characterized by a dichotomy of lithosphere strengths produce a spectrum of results that are comparable to interpretations of observations of subduction on Earth. These models have strong lithospheric plates at the surface, which promotes Earth-like single-sided subduction. At the same time, these models have weakened lithospheric subducted slabs which can more easily bend to either lie flat or fold into a slab pile atop the lower mantle, reproducing the spectrum of slab morphologies that have been interpreted from images of seismic tomography.

  14. Slab detachment of subducted Indo-Australian plate beneath Sunda ...

    Indian Academy of Sciences (India)

    2007). We investigate the northward subduction of the. Indo-Australian plate along the eastern Sunda arc right from northwestern Sumatra, along Java to. Keywords. Slab detachment; subduction zone; Sunda arc; Indo-Australian slab; trench migration. J. Earth Syst. Sci. 120, No. 2, April 2011, pp. 193–204 c Indian Academy ...

  15. The Run-Up of Subduction Zones

    Science.gov (United States)

    Riquelme, S.; Bravo, F. J.; Fuentes, M.; Matias, M.; Medina, M.

    2016-12-01

    Large earthquakes in subduction zones are liable to produce tsunamis that can cause destruction and fatalities. The Run-up is a geophysical parameter that quantifies damage and if critical facilities or population are exposed to. Here we use the coupling for certain subduction regions measured by different techniques (Potency and GPS observations) to define areas where large earthquakes can occur. Taking the slab 1.0 from the United States Geological Survey (USGS), we can define the geometry of the area including its tsunamigenic potential. By using stochastic earthquakes sources for each area with its maximum tsunamigenic potential, we calculate the numerical and analytical run-up for each case. Then, we perform a statistical analysis and calculate the envelope for both methods. Furthermore, we build an index of risk using: the closest slope to the shore in a piecewise linear approach (last slopecriteria) and the outputsfrom tsunami modeling. Results show that there are areas prone to produce higher run-up than others based on the size of the earthquake, geometrical constraints of the source, tectonic setting and the coast last slope. Based on these results, there are zones that have low risk index which can define escape routes or secure coastal areas for tsunami early warning, urban and planning purposes when detailed data is available.

  16. Mapping subduction interface coupling using magnetotellurics: Hikurangi margin, New Zealand

    Science.gov (United States)

    Heise, W.; Caldwell, T. G.; Bannister, S.; Bertrand, E. A.; Ogawa, Y.; Bennie, S. L.; Ichihara, H.

    2017-09-01

    The observation of slow-slip, seismic tremor, and low-frequency earthquakes at subduction margins has provided new insight into the mechanisms by which stress accumulates between large subduction (megathrust) earthquakes. However, the relationship between the physical properties of the subduction interface and the nature of the controls on interplate seismic coupling is not fully understood. Using magnetotelluric data, we show in situ that an electrically resistive patch on the Hikurangi subduction interface corresponds with an area of increased coupling inferred from geodetic data. This resistive patch must reflect a decrease in the fluid or sediment content of the interface shear zone. Together, the magnetotelluric and geodetic data suggest that the frictional coupling of this part on the Hikurangi margin may be controlled by the interface fluid and sediment content: the resistive patch marking a fluid- and sediment-starved area with an increased density of small, seismogenic-asperities, and therefore a greater likelihood of subduction earthquake nucleation.

  17. Dating Subduction Zone Metamorphism with Garnet and Lawsonite Geochronology

    Science.gov (United States)

    Mulcahy, S. R.; Vervoort, J. D.

    2013-12-01

    Lawsonite [CaAl2Si2O7(OH)2 H2O] is a critical index mineral for high- to ultrahigh-pressure metamorphism associated with subduction. Lawsonite is an important carrier of water into the mantle, a likely contributor to subduction zone seismicity, and a bearer of trace elements that link metamorphism to arc magmatism. Due to its limited pressure-temperature stability, lawsonite can serve as a powerful petrogenetic indicator of specific metamorphic events. Lu-Hf dating of lawsonite, therefore provides a potentially powerful new tool for constraining subduction zone processes in a pressure-temperature window where few successful geochronometers exist. Broad application of lawsonite Lu-Hf geochronology requires constraining the role of pressure-temperature path, lawsonite forming reactions, and the Lu and Hf systematics within lawsonite and other blueschist facies minerals. We are working to address the role of the metamorphic path on the applicability of lawsonite Lu-Hf geochronology within the Franciscan Complex of California. The Franciscan Complex preserves mafic high-grade exotic blocks in melange that underwent a counterclockwise pressure-temperature path wherein garnet, which strongly partitions heavy rare-earth elements, formed prior to lawsonite. Coherent mafic rocks within the Franciscan Complex, however, underwent a clockwise pressure-temperature path and lawsonite growth occurred prior to garnet. We sampled exotic blocks of garnet-hornblendite, garnet-epidote amphibolite, garnet-epidote blueschist, and lawsonite blueschist from the Berkeley Hills and Tiburon Peninsula of California. We collected four samples from coherent lawsonite blueschist across the lawsonite-pumpellyite-epidote isograds in Ward Creek, near Cazadero California. High-grade blocks give ages similar to existing Franciscan geochronology: multi-stage garnet in hornblendite gives the following ages: 171×1.3 Ma (MSWD 2.8) for the core and 159.4×0.9 Ma (MSWD 2.0) for the corresponding rim; 166

  18. Subduction zone and crustal dynamics of western Washington; a tectonic model for earthquake hazards evaluation

    Science.gov (United States)

    Stanley, Dal; Villaseñor, Antonio; Benz, Harley

    1999-01-01

    The Cascadia subduction zone is extremely complex in the western Washington region, involving local deformation of the subducting Juan de Fuca plate and complicated block structures in the crust. It has been postulated that the Cascadia subduction zone could be the source for a large thrust earthquake, possibly as large as M9.0. Large intraplate earthquakes from within the subducting Juan de Fuca plate beneath the Puget Sound region have accounted for most of the energy release in this century and future such large earthquakes are expected. Added to these possible hazards is clear evidence for strong crustal deformation events in the Puget Sound region near faults such as the Seattle fault, which passes through the southern Seattle metropolitan area. In order to understand the nature of these individual earthquake sources and their possible interrelationship, we have conducted an extensive seismotectonic study of the region. We have employed P-wave velocity models developed using local earthquake tomography as a key tool in this research. Other information utilized includes geological, paleoseismic, gravity, magnetic, magnetotelluric, deformation, seismicity, focal mechanism and geodetic data. Neotectonic concepts were tested and augmented through use of anelastic (creep) deformation models based on thin-plate, finite-element techniques developed by Peter Bird, UCLA. These programs model anelastic strain rate, stress, and velocity fields for given rheological parameters, variable crust and lithosphere thicknesses, heat flow, and elevation. Known faults in western Washington and the main Cascadia subduction thrust were incorporated in the modeling process. Significant results from the velocity models include delineation of a previously studied arch in the subducting Juan de Fuca plate. The axis of the arch is oriented in the direction of current subduction and asymmetrically deformed due to the effects of a northern buttress mapped in the velocity models. This

  19. Intra-oceanic subduction shaped the assembly of Cordilleran North America.

    Science.gov (United States)

    Sigloch, Karin; Mihalynuk, Mitchell G

    2013-04-04

    The western quarter of North America consists of accreted terranes--crustal blocks added over the past 200 million years--but the reason for this is unclear. The widely accepted explanation posits that the oceanic Farallon plate acted as a conveyor belt, sweeping terranes into the continental margin while subducting under it. Here we show that this hypothesis, which fails to explain many terrane complexities, is also inconsistent with new tomographic images of lower-mantle slabs, and with their locations relative to plate reconstructions. We offer a reinterpretation of North American palaeogeography and test it quantitatively: collision events are clearly recorded by slab geometry, and can be time calibrated and reconciled with plate reconstructions and surface geology. The seas west of Cretaceous North America must have resembled today's western Pacific, strung with island arcs. All proto-Pacific plates initially subducted into almost stationary, intra-oceanic trenches, and accumulated below as massive vertical slab walls. Above the slabs, long-lived volcanic archipelagos and subduction complexes grew. Crustal accretion occurred when North America overrode the archipelagos, causing major episodes of Cordilleran mountain building.

  20. Complexity

    Indian Academy of Sciences (India)

    Rahul Pandit

    2008-10-31

    Oct 31, 2008 ... ”The more complex a thing is, the more you can talk about it.” - attributed to Giorgio Parisi. ▻ ”C'est magnifique, mais ce n'est pas de la science.” (It is magnificent, but not all of it is science.) - attributed ... Earliest examples: theoretical computer science, algorithmic complexity, etc. ▻ Rapid progress after the ...

  1. Mw 8.6 Sumatran earthquake of 11 April 2012: rare seaward expression of oblique subduction

    Science.gov (United States)

    Ishii, Miaki; Kiser, Eric; Geist, Eric L.

    2013-01-01

    The magnitude 8.6 and 8.2 earthquakes off northwestern Sumatra on 11 April 2012 generated small tsunami waves that were recorded by stations around the Indian Ocean. Combining differential travel-time modeling of tsunami waves with results from back projection of seismic data reveals a complex source with a significant trench-parallel component. The oblique plate convergence indicates that ~20-50 m of trench-parallel displacement could have accumulated since the last megathrust earthquake, only part of which has been taken up by the Great Sumatran fault. This suggests that the remaining trench-parallel motion was released during the magnitude 8.6 earthquake on 11 April 2012 within the subducting plate. The magnitude 8.6 earthquake is interpreted to be a result of oblique subduction as well as a reduction in normal stress due to the occurrence of the Sumatra-Andaman earthquake in 2004.

  2. Zinc isotope evidence for sulfate-rich fluid transfer across subduction zones

    Science.gov (United States)

    Pons, Marie-Laure; Debret, Baptiste; Bouilhol, Pierre; Delacour, Adélie; Williams, Helen

    2016-12-01

    Subduction zones modulate the chemical evolution of the Earth's mantle. Water and volatile elements in the slab are released as fluids into the mantle wedge and this process is widely considered to result in the oxidation of the sub-arc mantle. However, the chemical composition and speciation of these fluids, which is critical for the mobility of economically important elements, remain poorly constrained. Sulfur has the potential to act both as oxidizing agent and transport medium. Here we use zinc stable isotopes (δ66Zn) in subducted Alpine serpentinites to decipher the chemical properties of slab-derived fluids. We show that the progressive decrease in δ66Zn with metamorphic grade is correlated with a decrease in sulfur content. As existing theoretical work predicts that Zn-SO42- complexes preferentially incorporate heavy δ66Zn, our results provide strong evidence for the release of oxidized, sulfate-rich, slab serpentinite-derived fluids to the mantle wedge.

  3. Zinc isotope evidence for sulfate-rich fluid transfer across subduction zones.

    Science.gov (United States)

    Pons, Marie-Laure; Debret, Baptiste; Bouilhol, Pierre; Delacour, Adélie; Williams, Helen

    2016-12-16

    Subduction zones modulate the chemical evolution of the Earth's mantle. Water and volatile elements in the slab are released as fluids into the mantle wedge and this process is widely considered to result in the oxidation of the sub-arc mantle. However, the chemical composition and speciation of these fluids, which is critical for the mobility of economically important elements, remain poorly constrained. Sulfur has the potential to act both as oxidizing agent and transport medium. Here we use zinc stable isotopes (δ(66)Zn) in subducted Alpine serpentinites to decipher the chemical properties of slab-derived fluids. We show that the progressive decrease in δ(66)Zn with metamorphic grade is correlated with a decrease in sulfur content. As existing theoretical work predicts that Zn-SO4(2-) complexes preferentially incorporate heavy δ(66)Zn, our results provide strong evidence for the release of oxidized, sulfate-rich, slab serpentinite-derived fluids to the mantle wedge.

  4. Extending the global coverage of Slab1.0 3D subduction zone models

    Science.gov (United States)

    Seidman, L.; Hayes, G. P.

    2013-12-01

    Slab1.0 is a three-dimensional model of subduction zone geometries that covers approximately 85% of global slabs by area. It is built from an automated interpolation of a combined dataset made up from subduction-related earthquakes, moment tensors, interpretations of active source seismic data, and models of bathymetry and sediment thickness. Those subduction zones that are missing from the model are difficult to characterize with this automated approach because of sparse teleseismically located, interplate seismicity (e.g., Cascadia, Hikurangi), complex geometry (e.g., Halmahera, southern Philippine Sea), or some combination of these issues (e.g., Caribbean). Here we attempt to solve this problem with a straightforward modification of the Slab1.0 approach. Instead of constructing a series of automated spline fits to our geophysical data in two-dimensional cross sections, we produce hand-contoured two-dimensional fits; under the assumption that where seismicity is sparse or geometry complex, a human guided by tectonic knowledge can produce a better fit to geometry than can a computer algorithm. These manual 2D sections are then interpolated into a 3D surface in the same way automated 2D fits are processed for Slab1.0. Following this approach, we produce models for slabs in the Caribbean, the Makran, the Manila Trench, the Halmahera Plate, and the Hellenic Arc. We also address regions of current models (e.g., Peru) that were poorly characterized by the original automated approach. These new models thus provide valuable information on subduction zone structure from the trench and into the mantle in regions previously missing from Slab1.0, and help to make existing models more accurate, and thus more useful, than was previously possible. In turn, the models can be used to better characterize associated seismic hazards.

  5. Cascadia subduction tremor muted by crustal faults

    Science.gov (United States)

    Wells, Ray; Blakely, Richard J.; Wech, Aaron G.; McCrory, Patricia A.; Michael, Andrew

    2017-01-01

    Deep, episodic slow slip on the Cascadia subduction megathrust of western North America is accompanied by low-frequency tremor in a zone of high fluid pressure between 30 and 40 km depth. Tremor density (tremor epicenters per square kilometer) varies along strike, and lower tremor density statistically correlates with upper plate faults that accommodate northward motion and rotation of forearc blocks. Upper plate earthquakes occur to 35 km depth beneath the faults. We suggest that the faults extend to the overpressured megathrust, where they provide fracture pathways for fluid escape into the upper plate. This locally reduces megathrust fluid pressure and tremor occurrence beneath the faults. Damping of tremor and related slow slip caused by fluid escape could affect fault properties of the megathrust, possibly influencing the behavior of great earthquakes.

  6. Depositionary Margins: The Destruction and Renovation of Subduction Forearcs

    Science.gov (United States)

    Vannucchi, P.; Morgan, J. P.; Silver, E. A.; Kluesner, J.

    2016-12-01

    A depositionary margin is a new framework for forearc evolution that focuses on the potential feedbacks between subduction tectonics, sedimentation, and geomorphology that take place during an extreme event of subduction erosion. These feedbacks can lead to the creation of a forearc structure that extends the traditional division of forearcs into accretionary or erosive subduction margins by demonstrating a mode of rapid basin accretion during an erosive event at a subduction margin. A depositionary mode of forearc evolution occurs when terrigenous sediments are deposited directly on the forearc while it is being removed from below by subduction erosion. In the most extreme case, an entire forearc can be removed by a single subduction erosion event followed by depositionary replacement without involving transfer of sediments from the incoming plate. We need to further recognize that subduction forearcs are often shaped by interactions between slow, long-term processes and sudden extreme events reflecting the sudden influences of large-scale morphological variations in the incoming plate. Both types of processes contribute to the large-scale architecture of the forearc, with extreme events associated with a replacive depositionary mode that rapidly creates sections of a typical forearc margin. The persistent upward diversion of the megathrust is likely to affect its geometry, frictional nature, and hydrogeology. Therefore, the stresses along the fault and individual earthquake rupture characteristics are also expected to be more variable in these erosive systems than in systems with long-lived megathrust surfaces.

  7. Subducted oceanic relief locks the shallow megathrust in central Ecuador

    Science.gov (United States)

    Collot, Jean-Yves; Sanclemente, Eddy; Nocquet, Jean-Mathieu; Leprêtre, Angélique; Ribodetti, Alessandra; Jarrin, Paul; Chlieh, Mohamed; Graindorge, David; Charvis, Philippe

    2017-05-01

    Whether subducted oceanic reliefs such as seamounts promote seismic rupture or aseismic slip remains controversial. Here we use swath bathymetry, prestack depth-migrated multichannel seismic reflection lines, and wide-angle seismic data collected across the central Ecuador subduction segment to reveal a broad 55 km × 50 km, 1.5-2.0 km high, low height-to-width ratio, multipeaked, sediment-bare, shallow subducted oceanic relief. Owing to La Plata Island and the coastline being located, respectively, 35 km and 50-60 km from the trench, GPS measurements allow us to demonstrate that the subducted oceanic relief spatially correlates to a shallow, 80 km × 55 km locked interplate asperity within a dominantly creeping subduction segment. The oceanic relief geometrical anomaly together with its highly jagged topography, the absence of a subduction channel, and a stiff erosive oceanic margin are found to be long-term geological characteristics associated with the shallow locking of the megathrust. Although the size and level of locking observed at the subducted relief scale could produce an Mw >7+ event, no large earthquakes are known to have happened for several centuries. On the contrary, frequent slow slip events have been recorded since 2010 within the locked patch, and regular seismic swarms have occurred in this area during the last 40 years. These transient processes, together with the rough subducted oceanic topography, suggest that interplate friction might actually be heterogeneous within the locked patch. Additionally, we find that the subducted relief undergoes internal shearing and produces a permanent flexural bulge of the margin, which uplifted La Plata Island.

  8. Carbonation by fluid-rock interactions at High-Pressure conditions: implications for Carbon cycling in subduction zones

    Science.gov (United States)

    Piccoli, Francesca; Vitale Brovarone, Alberto; Beyssac, Olivier; Martinez, Isabelle; Ague, Jay J.; Chaduteau, Carine

    2016-04-01

    Carbonate-bearing lithologies are the main carbon carrier into subduction zones. Their evolution during metamorphism largely controls the fate of carbon regulating its fluxes between shallow and deep reservoirs. In subduction zones, most works have focused on subtractive processes responsible for carbon release from subducting slabs. As an example, several recent works have stressed on the importance of carbonate dissolution as a mean to mobilize large amounts of carbon in subduction zones. By contrast, little is known on additive processes such as rock carbonation at high-pressure (HP) conditions. At shallow depths (e.g. ocean floor and shallow subduction zones, i.e. geo-biosphere and the atmosphere. We report the occurrence of eclogite-facies marbles associated with metasomatic systems in HP metamorphic unit in Alpine Corsica (France). We performed a field-based study on metasomatic marbles. We will present the petrology and geochemistry that characterize carbonate metasomatism together with fluid inclusions study and pseudosection modeling. Altogether, we bring strong evidences for the precipitation of these carbonate-rich assemblages from carbonic fluids during HP metamorphism. We propose that rock carbonation can occur at HP conditions by either vein-injection or chemical replacement mechanisms. Rock carbonation indicates that carbonic fluids produced by decarbonation reactions and carbonate dissolution may not be directly transferred to the mantle wedge, but may have a preferential and complex pathway within the slab and along slab/mantle interface. Rock carbonation by fluid-rock interactions has a potentially great impact on the residence time of carbon and oxygen and on carbonates isotopic signature in subduction zones. Lastly, carbonation may modulate the emission of CO2 at volcanic arcs over geological time scales.

  9. The initiation of subduction: criticality by addition of water?

    Science.gov (United States)

    Regenauer-Lieb, K; Yuen, D A; Branlund, J

    2001-10-19

    Subduction is a major process of plate tectonics; however, its initiation is not understood. We used high-resolution (less than 1 kilometer) finite-element models based on rheological data of the lithosphere to investigate the role played by water on initiating subduction. A solid-fluid thermomechanical instability is needed to drive a cold, stiff, and negatively buoyant lithosphere into the mantle. This instability can be triggered slowly by sedimentary loading over a time span of 100 million years. Our results indicate that subduction can proceed by a double feedback mechanism (thermoelastic and thermal-rheological) promoted by lubrication due to water.

  10. Deformation cycles of subduction earthquakes in a viscoelastic Earth.

    Science.gov (United States)

    Wang, Kelin; Hu, Yan; He, Jiangheng

    2012-04-18

    Subduction zones produce the largest earthquakes. Over the past two decades, space geodesy has revolutionized our view of crustal deformation between consecutive earthquakes. The short time span of modern measurements necessitates comparative studies of subduction zones that are at different stages of the deformation cycle. Piecing together geodetic 'snapshots' from different subduction zones leads to a unifying picture in which the deformation is controlled by both the short-term (years) and long-term (decades and centuries) viscous behaviour of the mantle. Traditional views based on elastic models, such as coseismic deformation being a mirror image of interseismic deformation, are being thoroughly revised.

  11. A record of spontaneous subduction initiation in the Izu-Bonin-Mariana arc

    NARCIS (Netherlands)

    Arculus, Richard J.; Ishizuka, Osamu; Bogus, Kara A.; Gurnis, Michael; Hickey-Vargas, Rosemary; Aljahdali, Mohammed H.; Bandini-Maeder, Alexandre N.; Barth, Andrew P.; Brandl, Philipp A.; Drab, Laureen; Do Monte Guerra, Rodrigo; Hamada, Morihisa; Jiang, Fuqing; Kanayama, Kyoko; Kender, Sev; Kusano, Yuki; Li, He; Loudin, Lorne C.; Maffione, Marco; Marsaglia, Kathleen M.; McCarthy, Anders; Meffre, Sebastién; Morris, Antony; Neuhaus, Martin; Savov, Ivan P.; Sena, Clara; Tepley, Frank J.; Van Der Land, Cees; Yogodzinski, Gene M.; Zhang, Zhaohui

    2015-01-01

    The initiation of tectonic plate subduction into the mantle is poorly understood. If subduction is induced by the push of a distant mid-ocean ridge or subducted slab pull, we expect compression and uplift of the overriding plate. In contrast, spontaneous subduction initiation, driven by subsidence

  12. Deep structure and historical earthquakes in the Calabrian subduction zone (Southern Italy): preliminary results from multi-channel seismic reflection profiles

    Science.gov (United States)

    Gallais, F.; Gutscher, M.; Torelli, L.; Polonia, A.; Riminucci, F.

    2009-12-01

    The Calabrian subduction zone is located in the complex Central Mediterranean area. This subduction is characterized by the presence of deep earthquakes under the Tyrrhenian Sea down to 500 km depth. The Tethyan remnant Ionian slab descends towards the NW at a dip of about 70° and is associated with an active volcanic arc (the Aeolian Islands). Recently reported GPS and seismicity studies suggest that the subduction of the Ionian lithosphere beneath the Calabrian Arc may be locally still active, though at very slow rates (thrust earthquakes, characteristic of active subduction zone, suggests that if subduction is active, the fault plane may be locked since the instrumental period. To seek evidence of continuous tectonic activity of the Calabrian system, we present preliminary results from reprocessed 96-channels seismic reflection profiles (French Archimede cruise, 1997) offshore Sicily. This analysis permits to recognize a well-defined stratigraphy in the Ionian Abyssal Plain, this stratigraphy becomes difficult to follow under the deformed Calabrian Prism. But the joint interpretation with the reprocessed PM01 profile (French PRISMED cruise, 1994) helps constrain this interpretation and to image some characteristic structures of an accretionary wedge (fore/back-thrusts, basal decollement...). This study also include interpretation of a more recent Italian seismic cruise (Calamare, 2008) and CROP profiles. This work will help to prepare a future cruise proposal (CIRCEE, to be submitted in January 2010) to study the Calabrian subduction with OBS, MCS seismic, heat-flow measurements and sediment coring. The goals are : 1/ to image the deep structure of this subduction zone, 2/ to characterize its thermal state to deduce a geometry of the seismogenic part of the plate interface and add new constraints on seismic risk linked with the Calabrian subduction.

  13. The spatial distribution of earthquake stress rotations following large subduction zone earthquakes

    Science.gov (United States)

    Hardebeck, Jeanne L.

    2017-01-01

    Rotations of the principal stress axes due to great subduction zone earthquakes have been used to infer low differential stress and near-complete stress drop. The spatial distribution of coseismic and postseismic stress rotation as a function of depth and along-strike distance is explored for three recent M ≥ 8.8 subduction megathrust earthquakes. In the down-dip direction, the largest coseismic stress rotations are found just above the Moho depth of the overriding plate. This zone has been identified as hosting large patches of large slip in great earthquakes, based on the lack of high-frequency radiated energy. The large continuous slip patches may facilitate near-complete stress drop. There is seismological evidence for high fluid pressures in the subducted slab around the Moho depth of the overriding plate, suggesting low differential stress levels in this zone due to high fluid pressure, also facilitating stress rotations. The coseismic stress rotations have similar along-strike extent as the mainshock rupture. Postseismic stress rotations tend to occur in the same locations as the coseismic stress rotations, probably due to the very low remaining differential stress following the near-complete coseismic stress drop. The spatial complexity of the observed stress changes suggests that an analytical solution for finding the differential stress from the coseismic stress rotation may be overly simplistic, and that modeling of the full spatial distribution of the mainshock static stress changes is necessary.

  14. Tomography of the subducting Pacific slab and the 2015 Bonin deepest earthquake (Mw 7.9).

    Science.gov (United States)

    Zhao, Dapeng; Fujisawa, Moeto; Toyokuni, Genti

    2017-03-15

    On 30 May 2015 an isolated deep earthquake (~670 km, Mw 7.9) occurred to the west of the Bonin Islands. To clarify its causal mechanism and its relationship to the subducting Pacific slab, we determined a detailed P-wave tomography of the deep earthquake source zone using a large number of arrival-time data. Our results show that this large deep event occurred within the subducting Pacific slab which is penetrating into the lower mantle. In the Izu-Bonin region, the Pacific slab is split at ~28° north latitude, i.e., slightly north of the 2015 deep event hypocenter. In the north the slab becomes stagnant in the mantle transition zone, whereas in the south the slab is directly penetrating into the lower mantle. This deep earthquake was caused by joint effects of several factors, including the Pacific slab's fast deep subduction, slab tearing, slab thermal variation, stress changes and phase transformations in the slab, and complex interactions between the slab and the ambient mantle.

  15. Tectonic history of subduction zones inferred from retrograde blueschist P-T paths

    Energy Technology Data Exchange (ETDEWEB)

    Ernst, W.G. (Univ. of California, Los Angeles (USA))

    1988-12-01

    Many Phanerozoic convergent plate junctions are marked by discontinuous blueschist belts, reflecting relatively high-pressure (P) prograde trajectories. Common blueschist paragneisses, such as those of the western Alps, exhibit widespread overprinting by greenschist and/or epidote-amphibolite facies assemblages. For this type of high-P belt, retrograde metamorphism involved fairly rapid, nearly isothermal decompression; some terranes underwent continued heating during early stages of pressure release. Uplift probably occurred as a consequence of the entrance of an island arc, oceanic plateau, or segment of continental crust into the subduction zone (collision), resulting in marked deceleration or cessation of underflow and buoyant, approximately adiabatic rise of the stranded, recrystallized subduction complex. Other high-P belts, such as the Franciscan of western California, preserve metamorphic aragonite and lack a low-P overprint; retrogression approximately retraced the prograde P-T (temperature) path, or for early formed high-grade blocks, occurred at even higher P/T ratios. Parts of this type of metamorphic belt evidently migrated slowly back up the subduction zone in response to isostatic forces during continued plate descent and refrigeration. Upward motion took place as tectonically imbricated slices, as laminar return flow in melange zones, and perhaps partly a lateral spreading/extension of the underplated accretionary prism. Retrograde P-T trajectories of high-P belts therefore provide important constraints on the tectonic evolution of convergent plate junctions.

  16. The spatial distribution of earthquake stress rotations following large subduction zone earthquakes

    Science.gov (United States)

    Hardebeck, Jeanne L.

    2017-05-01

    Rotations of the principal stress axes due to great subduction zone earthquakes have been used to infer low differential stress and near-complete stress drop. The spatial distribution of coseismic and postseismic stress rotation as a function of depth and along-strike distance is explored for three recent M ≥ 8.8 subduction megathrust earthquakes. In the down-dip direction, the largest coseismic stress rotations are found just above the Moho depth of the overriding plate. This zone has been identified as hosting large patches of large slip in great earthquakes, based on the lack of high-frequency radiated energy. The large continuous slip patches may facilitate near-complete stress drop. There is seismological evidence for high fluid pressures in the subducted slab around the Moho depth of the overriding plate, suggesting low differential stress levels in this zone due to high fluid pressure, also facilitating stress rotations. The coseismic stress rotations have similar along-strike extent as the mainshock rupture. Postseismic stress rotations tend to occur in the same locations as the coseismic stress rotations, probably due to the very low remaining differential stress following the near-complete coseismic stress drop. The spatial complexity of the observed stress changes suggests that an analytical solution for finding the differential stress from the coseismic stress rotation may be overly simplistic, and that modeling of the full spatial distribution of the mainshock static stress changes is necessary.[Figure not available: see fulltext.

  17. Extensional reactivation of the Chocolate Mountains subduction thrust in the Gavilan Hills of southeastern California

    Science.gov (United States)

    Oyarzabal, F.R.; Jacobson, C.E.; Haxel, G.B.

    1997-01-01

    The NE vergent Chocolate Mountains fault of south-eastern California has been interpreted as either a subduction thrust responsible for burial and prograde metamorphism of the ensimatic Orocopia Schist or as a normal fault involved in the exhumation of the schist. Our detailed structural analysis in the Gavilan Hills area provides new evidence to confirm the latter view. A zone of deformation is present at the top of the Orocopia Schist in which lineations are parallel to those in the upper plate of the Chocolate Mountains fault but oblique to ones at relatively deep levels in the schist. Both the Orocopia Schist and upper plate contain several generations of shear zones that show a transition from crystalloblastic through mylonitic to cataclastic textures. These structures formed during retrograde metamorphism and are considered to record the exhumation of the Orocopia Schist during early Tertiary time as a result of subduction return flow. The Gatuna fault, which places low-grade, supracrustal metasediments of the Winterhaven Formation above the gneisses of the upper plate, also seems to have been active at this time. Final unroofing of the Orocopia Schist occurred during early to middle Miocene regional extension and may have involved a second phase of movement on the Gatuna fault. Formation of the Chocolate Mountains fault during exhumation indicates that its top-to-the-NE sense of movement provides no constraint on the polarity of the Orocopia Schist subduction zone. This weakens the case for a previous model involving SW dipping subduction, while providing support for the view that the Orocopia Schist is a correlative of the Franciscan Complex.

  18. Breaking the shell: Initiating plate tectonic-like subduction on Europa

    Science.gov (United States)

    Bland, Michael T.; McKinnon, William B.

    2017-10-01

    Europa’s prominent bands have been proposed to form by a seafloor-spreading-like mechanism involving complete separation of Europa’s lithosphere and the emplacement of fresh ice from below [Prockter et al. 2002]. This formation mechanism poses a challenge for Europa’s strain balance: extensional rifting at bands must be offset by lithospheric shortening elsewhere, yet few obvious contractional features have been observed. Kattenhorn and Prockter [2014] suggested that extension on Europa is accommodated by subduction of the lithosphere at linear, tabular zones termed subsumption bands. Subduction of Europa’s lithosphere implicitly requires that lithospheric-scale thrust faults can develop. This contrasts with previous numerical modeling, which found that lithospheric shortening is instead primarily accommodated by folding or passive thickening [Bland and McKinnon 2012, 2013]. Here we reevaluate the conditions required to form large-scale thrust faults using a numerical model of lithospheric shortening on Europa that includes realistic localization of brittle failure (non-associated plasticity). In the absence of strain weakening (wherein brittle failure decreases the subsequent yield strength) essentially all shortening results in folding or thickening, consistent with previous results. With moderate strain weakening, deformation becomes localized within fault-like zones for surface temperatures ≤100 K; however, the resulting surface deformation suggests a complex interplay between folding and faulting. Only if the ice shell weakens very easily does faulting dominate. Large-scale faults preferentially form at cold surface temperatures and high heat fluxes. Cold temperatures promote faulting (as opposed to folding), and high heat fluxes result in a thinner lithosphere, which is more easily subducted. The subsumption bands identified by Kattenhorn and Prockter [2014] are at a relatively high latitude (cold temperature), and are associated with putative

  19. Volatile (Li, B, F and Cl) mobility during amphibole breakdown in subduction zones

    Science.gov (United States)

    Debret, Baptiste; Koga, Kenneth T.; Cattani, Fanny; Nicollet, Christian; Van den Bleeken, Greg; Schwartz, Stephane

    2016-02-01

    Amphiboles are ubiquitous minerals in the altered oceanic crust. During subduction, their breakdown is governed by continuous reactions up to eclogitic facies conditions. Amphiboles thus contribute to slab-derived fluid throughout prograde metamorphism and continuously record information about volatile exchanges occurring between the slab and the mantle wedge. However, the fate of volatile elements and especially halogens, such as F and Cl, in amphibole during subduction is poorly constrained. We studied metagabbros from three different localities in the Western Alps: the Chenaillet ophiolite, the Queyras Schistes Lustrés and the Monviso meta-ophiolitic complexes. These samples record different metamorphic conditions, from greenschist to eclogite facies, and have interacted with different lithologies (e.g. sedimentary rocks, serpentinites) from their formation at mid-oceanic ridge, up to their devolatilization during subduction. In the oceanic crust, the initial halogen budget is mostly stored in magmatic amphibole (F = 300-7000 ppm; Cl = 20-1200 ppm) or in amphibole corona (F = 100-7000 ppm; Cl = 80-2000 ppm) and titanite (F = 200-1500 ppm; Cl glaucophane at the expense of magmatic and amphibole coronas. This episode is accompanied with a decrease of halogen concentrations in amphiboles (glaucophane (up to 600 ppm) whereas halogen concentrations are unaffected. At eclogite facies conditions, metagabbros display low halogens concentrations (< 20 ppm of F and < 100 ppm of Cl) relative to altered oceanic crust (F = 40-650 ppm; Cl = 40-1400 ppm) suggesting that these elements are continuously released by fluids during the first 30-80 km of subduction whatever the tectonic environment (e.g. slab, plate interface) and the considered fluid/rock interactions.

  20. Imprints of an "Arc" Signature onto Subduction Zone Eclogites from Central Guatemala

    Science.gov (United States)

    Simons, K. K.; Sorensen, S. S.; Harlow, G. E.; Brueckner, H. K.; Goldstein, S. L.; Hemming, N. G.; Langmuir, C. H.

    2007-12-01

    High-pressure, low-temperature (HP-LT) rocks associated with the Motagua fault zone in central Guatemala occur as tectonic blocks in serpentinite mélange. Dismembered jadeitite and albitite veins within the melange are crystallization products of subduction fluids at glaucophane) in veins and overgrowths. The low temperatures recorded in these rocks indicate they have only seen an aqueous fluid, not a melt, and therefore, could provide a window into the acquisition of an arc signature at a cold margin. Trace-element patterns for both eclogite and jadeitite resemble arc lavas, with large enrichments in the most fluid mobile elements (e.g. Cs, Tl, Ba, Pb), moderate enrichments in U, Th, Be and LREE and generally little to no enrichment in HFSE and HREE, although enriched Nb in jadeitite indicates some HFSE mobility. Trace-element patterns also have similarities to average subducting sediment (GLOSS), with enrichments in Th, Be, Ba and Li that suggest a sediment contribution. Nd versus Sr isotopes lie to the right of the mantle array, indicating a hydrous fluid contribution from altered ocean crust or sediment. Overall, Guatemalan eclogites resemble counterparts from the Franciscan Complex (CA) and the Dominican Republic. Guatemalan and Franciscan eclogites are interpreted to have had a MORB protolith despite the arc trace element signature because of: 1) similarities in major elements to MORB; 2) HREE and HFSE abundances similar to MORB; and 3) high 143Nd/144Nd that overlap MORB values. The modifications that transformed these eclogites from a MORB trace element pattern to an arc one can be attributed to an aqueous subduction fluid at moderate depths (reactions, and an abundance of alkali-aluminosilicate components in subduction fluids. Together these may act to dissolve and transport trace elements (including elements considered insoluble like Nb) out of the slab and into the mantle wedge. The Guatemala data thus indicate that the arc geochemical fingerprint may be

  1. Subduction-stage P-T path of eclogite from the Sambagawa belt: Prophetic record for oceanic-ridge subduction

    Science.gov (United States)

    Aoya, M.; Uehara, S.; Wallis, S. R.; Enami, M.

    2003-12-01

    The Sambagawa belt in SW Japan is a subduction-type high-P/T metamorphic belt. Subduction-stage P-T paths of its constituent rocks are important because they directly constrain physical conditions of the EarthOs interior at the time exhumation of high-P/T metamorphic rocks became feasible. Although a few examples of subduction-stage P-T paths for the Sambagawa rocks have been recognized, these are limited to relatively low-pressure regions (~10 kbar). To augment these data the subduction-stage P-T path of the Kotsu glaucophane (Gln) eclogite is derived. The tectonic significance of the derived and previously determined P-T paths is further examined using a new thermal model. By using compositions of matrix minerals and rims of porphyroblastic garnet (Grt), the peak-T conditions of the Kotsu Gln eclogite have been estimated as ~20 kbar/ 600° C. However, the dP/dT of the P-T path leading to the peak-T conditions is unknown. Petrological studies focusing on inclusion minerals in Grt show: (1) albite is absent as inclusions within Grt; (2) acmite (Acm) component of cpx decreased during growth of Grt; (3) Tschermakite (Ts) component of amphibole decreased and Gln component increased during growth of Grt; and (4) Grt-Cpx thermometry shows a temperature increase during growth of Grt. Along with mineral textures observed in the matrix, the Gln-formation reaction can be determined as: 4Acm + 2Ts + 2quartz + H2O (R) 2Gln + 2epidote + hematite. P-T curve of this reaction always has a large positive dP/dT (>7.1 kbar/100 ?C) with the Gln stability field on the high-P/T side. To cross this reaction curve into the Gln stability field during a rise in temperature, the Kotsu eclogite must trace a very steep subduction-type P-T path. Compilation of previously obtained subduction-stage P-T paths for the Sambagawa rocks along with the P-T path of the Kotsu Gln eclogite shows that the series of subduction-stage P-T paths are not distributed on a straight line starting from the origin

  2. Subduction, back-arc spreading and global mantle flow

    Science.gov (United States)

    Hager, B. H.; Oconnell, R. J.; Raefsky, A.

    1983-01-01

    It is pointed out that the subducted lithosphere associated with Benioff zones provides the only direct evidence about the flow in the earth's interior associated with plate motions. It is the primary objective of the present investigation to study the relation between the orientation of subducting lithosphere and the flow patterns (both local and global) near subduction zones. Most of the calculations conducted are based on simple flow models for radially symmetric, Newtonian viscous spheres. The investigation is concerned with the possibility that a simple model of global mantle flow could account for some features of subduction zones. It is found that such a model can account for the orientation of the seismic zones, and, in addition, also for features related to back-arc spreading and perhaps the maximum earthquake size.

  3. Reaction-induced rheological weakening enables oceanic plate subduction

    OpenAIRE

    Hirauchi, Ken-ichi; Fukushima, Kumi; Kido, Masanori; Muto, Jun; Okamoto, Atsushi

    2016-01-01

    Earth is the only terrestrial planet in our solar system where an oceanic plate subducts beneath an overriding plate. Although the initiation of plate subduction requires extremely weak boundaries between strong plates, the way in which oceanic mantle rheologically weakens remains unknown. Here we show that shear-enhanced hydration reactions contribute to the generation and maintenance of weak mantle shear zones at mid-lithospheric depths. High-pressure friction experiments on peridotite goug...

  4. Neoarchean Subduction Recorded in the Northern Margin of the Yangtze Craton, South China

    Science.gov (United States)

    Zhang, S. B.; Zheng, Y. F.

    2016-12-01

    The Neoarchean is an important era during which plate tectonics began to operate widely on the earth and the continental crust compositions changed dramatically. However, reliable record of plate subduction has never been reported yet in the Yangtze Craton. Here we report geochemical studies on gneissic tonalite, trondhjemite and amphibolite in the Yudongzi Complex in the northern margin of the Yangtze Craton, which suggests that there is a plate subduction recorded in this area at about 2.7 Ga.The rocks in the Yudongzi Complex are gneissic granite, gneissic tonalite, amphibolite gneiss and magnetite quartzite. Most rocks are enriched in sodic. The gneissic granites show positive Eu anomalies, high (La/Yb)cn and Sr/Y ratios, low Ybcn and Y, resembling typical TTG. The amphibolite and tonalite gneiss show less fractionated REE patterns. SHRIMP zircon U-Pb dating on one gneissic trondhjemite, one amphibolite and one tonalite gave crystallization ages of 2667±21 Ma, 2701±10 Ma and 2697±9 Ma, respectively. They all recorded a metamorphic event at about 2.48 Ga. The SHRIMP zircon oxygen isotope analysis for a trondhjemite and an amphibolite gave δ18O values of 6.2±0.3‰ and 6.3±0.4‰, respectively. The oxygen isotope ratios higher than normal mantle values suggest a source experienced low temperature alteration. The laser fluoration analysis of bulk minerals gave δ18O values of 6.4-8.8‰ for zircon and 12.5-15.2‰ for quartz. The zircon Lu-Hf isotope analysis on the trondhjemite and amphibolite gave similar ɛHf(t) values of 0.08±0.48 and 0.07±0.63, respectively. Whole-rock ɛNd(t) values range from -1.5 to +1.0. These trondhjemite and tonalite can be interpreted as derivation from partial melting of subducted oceanic slab with a garnet-amphibolite residue.Considering the 2.67 Ga A-type granitic rocks at Huji in the interior of the craton, plate subduction took place in the northern edge of the Yangtze Craton. The Yudongzi trondhjemite and tonalite were

  5. Evolution of the Archaean crust by delamination and shallow subduction.

    Science.gov (United States)

    Foley, Stephen F; Buhre, Stephan; Jacob, Dorrit E

    2003-01-16

    The Archaean oceanic crust was probably thicker than present-day oceanic crust owing to higher heat flow and thus higher degrees of melting at mid-ocean ridges. These conditions would also have led to a different bulk composition of oceanic crust in the early Archaean, that would probably have consisted of magnesium-rich picrite (with variably differentiated portions made up of basalt, gabbro, ultramafic cumulates and picrite). It is unclear whether these differences would have influenced crustal subduction and recycling processes, as experiments that have investigated the metamorphic reactions that take place during subduction have to date considered only modern mid-ocean-ridge basalts. Here we present data from high-pressure experiments that show that metamorphism of ultramafic cumulates and picrites produces pyroxenites, which we infer would have delaminated and melted to produce basaltic rocks, rather than continental crust as has previously been thought. Instead, the formation of continental crust requires subduction and melting of garnet-amphibolite--formed only in the upper regions of oceanic crust--which is thought to have first occurred on a large scale during subduction in the late Archaean. We deduce from this that shallow subduction and recycling of oceanic crust took place in the early Archaean, and that this would have resulted in strong depletion of only a thin layer of the uppermost mantle. The misfit between geochemical depletion models and geophysical models for mantle convection (which include deep subduction) might therefore be explained by continuous deepening of this depleted layer through geological time.

  6. Impact-driven subduction on the Hadean Earth

    Science.gov (United States)

    O'Neill, C.; Marchi, S.; Zhang, S.; Bottke, W.

    2017-10-01

    Impact cratering was a dominant geologic process in the early Solar System that probably played an active role in the crustal evolution of the young terrestrial planets. The Earth's interior during the Hadean, 4.56 to 4 billion years ago, may have been too hot to sustain plate tectonics. However, whether large impacts could have triggered tectonism on the early Earth remains unclear. Here we conduct global-scale tectonic simulations of the evolution of the Earth through the Hadean eon under variable impact fluxes. Our simulations show that the thermal anomalies produced by large impacts induce mantle upwellings that are capable of driving transient subduction events. Furthermore, we find that moderate-sized impacts can act as subduction triggers by causing localized lithospheric thinning and mantle upwelling, and modulate tectonic activity. In contrast to contemporary subduction, the simulated localized subduction events are relatively short-lived (less than 10 Myr) with relatively thin, weak plates. We suggest that resurgence in subduction activity induced by an increased impact flux between 4.1 and 4.0 billion years ago may explain the coincident increase in palaeointensity of the magnetic field. We further suggest that transient impact-driven subduction reconciles evidence from Hadean zircons for tectonic activity with other lines of evidence consistent with an Earth that was largely tectonically stagnant from the Hadean into the Archaean.

  7. Subduction initiation and Obduction: insights from analog models

    Science.gov (United States)

    Agard, P.; Zuo, X.; Funiciello, F.; Bellahsen, N.; Faccenna, C.; Savva, D.

    2013-12-01

    Subduction initiation and obduction are two poorly constrained geodynamic processes which are interrelated in a number of natural settings. Subduction initiation can be viewed as the result of a regional-scale change in plate convergence partitioning between the set of existing subduction (and collision or obduction) zones worldwide. Intraoceanic subduction initiation may also ultimately lead to obduction of dense oceanic "ophiolites" atop light continental plates. A classic example is the short-lived Peri-Arabic obduction, which took place along thousands of km almost synchronously (within ~5-10 myr), from Turkey to Oman, while the subduction zone beneath Eurasia became temporarily jammed. We herein present analog models designed to study both processes and more specifically (1) subduction initiation through the partitioning of deformation between two convergent zones (a preexisting and a potential one) and, as a consequence, (2) the possible development of obduction, which has so far never been modeled. These models explore the mechanisms of subduction initiation and obduction and test various triggering hypotheses (i.e., plate acceleration, slab crossing the 660 km discontinuity, ridge subduction; Agard et al., 2007). The experimental setup comprises an upper mantle modelled as a low-viscosity transparent Newtonian glucose syrup filling a rigid Plexiglas tank and high-viscosity silicone plates. Convergence is simulated by pushing on a piston at one end of the model with plate tectonics like velocities (1-10 cm/yr) onto (i) a continental margin, (ii) a weakness zone with variable resistance and dip (W), (iii) an oceanic plate - with or without a spreading ridge, (iv) a subduction zone (S) dipping away from the piston and (v) an upper active continental margin, below which the oceanic plate is being subducted at the start of the experiment (as for the Oman case). Several configurations were tested over thirty-five parametric experiments. Special emphasis was

  8. 2D numerical modelling of fluid percolation in the subduction zone

    Science.gov (United States)

    Dymkova, D.; Gerya, T.; Podladchikov, Y.

    2012-04-01

    Subducting slab dehydration and resulting aqueous fluid percolation triggers partial melting in the mantle wedge and is accompanied with the further melt percolation through the porous space to the region above the slab. This problem is a complex coupled chemical, thermal and mechanical process responsible for the magmatic arcs formation and change of the mantle wedge properties. We have created a two-dimensional model of a two-phase flow in a porous media solving a coupled Darcy-Stokes system of equations for two incompressible media for the case of nonlinear visco-plastic rheology of solid matrix. Our system of equation is expanded for the high-porosity limits and stabilized for the case of high porosity contrasts. We use a finite-difference method with fully staggered grid in a combination with marker-in-cell technique for advection of fluid and solid phase. We performed a comparison with a benchmark of a thermal convection in a porous media in a bottom-heated box to verify the interdependency of Rayleigh and Nusselt numbers with earlier obtained ones (Cherkaoui & Wilcock, 1999). We have demonstrated the stability and robustness of the algorithm in case of strongly non-linear visco-plastic rheology of solid including cases with localization of both deformation and porous flow along spontaneously forming shear bands. We have checked our model for the forming of localized porous channels under a simple shear stress (Katz et al, 2006). We have developed a setup of a self-initiating due to gravitational instability subduction. With our coupled fluid-solid flow we have achieved a self-consistent water downward suction by a slab bending predicted by the other models with a simplified fluid kinematical motion implementation (Faccenda et al, 2009). With this setup we have obtained a self-consistent upper crust weakening by a porous fluid pressure which was theoretically assumed in the previously existing subduction models (Gerya & Meilick, 2011; Faccenda et al, 2009

  9. Paleotethyan subduction process revealed from Triassic blueschists in the Lancang tectonic belt of Southwest China

    Science.gov (United States)

    Fan, Weiming; Wang, Yuejun; Zhang, Yanhua; Zhang, Yuzhi; Jourdan, Fred; Zi, Jianwei; Liu, Huichuan

    2015-11-01

    The subduction of the Paleotethyan Ocean and subsequent continental collision along the Lancang tectonic belt of the southeastern Paleotethyan belt is a major tectonic event in Southwest China, but the event of the subduction preceding the final collision is still not well-constrained. The mafic blueschists exposed in the Lancang accretionary complex provide crucial records of the Paleotethyan subduction process. In this paper, we present a set of new petrologic, geochronological and geochemical data for the Suyi mafic blueschists in the Lancang metamorphic zone. The mineral assemblage of these blueschists consists of zoned sodic amphibole (25-30%), albite (15-20%), epidote (25-30%), phengite (5-10%), chlorite (~ 5-10%), and minor amounts of actinolite, apatite, sphene, zircon, ilmenite, quartz and secondary limonite. This suggests a prograde metamorphism from ~ 0.5 to ~ 0.9 GPa and retrograde metamorphic overprinting (back to ~ 0.6 GPa) within the temperature range of 300-450 °C. The Suyi blueschists give a zircon U-Pb age of 260 ± 4 Ma and glaucophane minerals formed during prograde metamorphism yield a 40Ar/39Ar plateau age of 242 ± 5 Ma (MSWD = 0.77; P = 0.54). The blueschists have geochemical compositions of subalkaline basalt and show typical OIB-type REE and multi-elemental patterns and εNd(t) values ranging from + 3.35 to + 4.85. Based on available data, it is inferred that the protolith formed at 260 Ma and originated from a basaltic seamount. The basaltic rocks subducted down to 30-35 km depths beneath the Lincang arc to form the epidote blueschists at ~ 242 Ma. The blueschists were subsequently transported to shallower crustal levels in response to the continuous underthrust of the subducted slab and the continent-continent collision in the middle-late Triassic. These results provide a systematic constraint on the tectonic evolution and temporal framework of the southeastern Paleotethyan belt in Southwest China.

  10. The Geodynamics of Continental Lithosphere Entering a Subduction Zone

    Science.gov (United States)

    Steedman, C. E.; Kaus, B. J.; Becker, T. W.; Okaya, D.; Wu, F. T.

    2006-12-01

    As deformation patterns resulting from subduction of a passive continental margin are insufficiently understood, here we perform 2-D numerical simulations to explore the effects of continental lithosphere entering a subduction zone. The model setup consists of a subduction zone in which the oceanic part of a passive continental margin initially subducts beneath an oceanic plate. A particle-based 2-D visco-elasto-plastic thermo-mechanical finite element code is employed to study the dynamics of the system. A novel new feature of the code is that the resolution of the model can be significantly increased in selected parts of the domain, which allows for self-consistent modelling of mantle-lithosphere interaction. In the present study this feature is employed to study how crustal scale deformation around the subduction zone is influenced by surface processes and by flow in the upper mantle. Using systematic 2-D numerical simulations, we explore the parameters that are dominant in controlling near- surface structures, both with regards to changes in topography over time, and subsurface features such as Moho undulations. The main parameters that have been varied are: the lithospheric density structure; the strength of the lower crust; the amounts of erosion; imposed pushing versus density-driven (slab-pull and ridge- push) convergence; the upper boundary condition (free surface versus free slip); rheology (non-Newtonian versus Newtonian, viscous, visco-elasto-plastic); and finally the effect of an imposed slab breakoff. In all cases we track surface uplift, subduction evolution and rock exhumation history. The results can be compared to evidence from areas such as Taiwan where continental subduction or convergence is thought to be happening. Preliminary results indicate that a low viscosity lower crust may contribute to crustal uplift.

  11. Deep electrical resistivity structure of Costa Rican Subduction Zone

    Science.gov (United States)

    Worzewski, T.; Jegen, M.; Brasse, H.; Taylor, W.

    2009-04-01

    The water content and its distribution play an important role in the subduction process. Water is released from the subducting slab in a series of metamorphic reactions and the hydration of the mantle wedge may trigger the onset of melting, weakening and changes in the dynamics and thermal structure of subduction zones. However, the amount of water carried into the subduction zone and its distribution are not well constrained by existing data and are subject of vigorous current research in SFB574 (Volatiles and Fluids in Subduction Zones: Climate Feedback and Trigger Mechanisms for Natural Disasters). We will show numerical modeling studies which are used to determine the resolution and sensitivity of the MT response to fluids in the crust and subducting slab under the special condition of a coastal setting. In 2007-2008 we conducted a long-period magnetotelluric investigations in northwestern Costa Rica on- and offshore, where the Cocos Plate subducts beneath the Carribean plate. Eleven marine magnetotelluric Stations newly developed and constructed by IFM-GEOMAR and University of Kiel were deployed on the 200 km long marine extension of the profile for several months. We will present the data and its processing, as well as our attempts to eliminate motion induced noise observed on some stations on the cliffy shelf due to tidal waves hitting the shelf and trench parallel- and perpendicular currents. The marine profile was extended landwards by the Free University of Berlin over length of 160 kilometers with further 18 stations. We present preliminary modeling results of land data, which revealed interesting features, inter alia a possible image of fluid release from the downgoing slab in the forearc, as well as ongoing modeling of the combined on- and offshore data sets.

  12. Subduction zone decoupling/retreat modeling explains south Tibet (Xigaze) and other supra-subduction zone ophiolites and their UHP mineral phases

    Science.gov (United States)

    Butler, Jared P.; Beaumont, Christopher

    2017-04-01

    The plate tectonic setting in which proto-ophiolite 'oceanic' lithosphere is created remains controversial with a number of environments suggested. Recent opinions tend to coalesce around supra-subduction zone (SSZ) forearc extension, with a popular conceptual model in which the proto-ophiolite forms during foundering of oceanic lithosphere at the time of spontaneous or induced onset of subduction. This mechanism is favored in intra-oceanic settings where the subducting lithosphere is old and the upper plate is young and thin. We investigate an alternative mechanism; namely, decoupling of the subducting oceanic lithosphere in the forearc of an active continental margin, followed by subduction zone (trench) retreat and creation of a forearc oceanic rift basin, containing proto-ophiolite lithosphere, between the continental margin and the retreating subduction zone. A template of 2D numerical model experiments examines the trade-off between strength of viscous coupling in the lithospheric subduction channel and net slab pull of the subducting lithosphere. Three tectonic styles are observed: 1) C, continuous subduction without forearc decoupling; 2) R, forearc decoupling followed by rapid subduction zone retreat; 3) B, breakoff of subducting lithosphere followed by re-initiation of subduction and in some cases, forearc decoupling (B-R). In one case (BA-B-R; where BA denotes backarc) subduction zone retreat follows backarc rifting. Subduction zone decoupling is analyzed using frictional-plastic yield theory and the Stefan solution for the separation of plates containing a viscous fluid. The numerical model results are used to explain the formation of Xigaze group ophiolites, southern Tibet, which formed in the Lhasa terrane forearc, likely following earlier subduction and not necessarily during subduction initiation. Either there was normal coupled subduction before subduction zone decoupling, or precursor slab breakoff, subduction re-initiation and then decoupling

  13. The Impact of Surface Bending, A Complete Mineralogical Model and Movement of the Overriding Plate on Subduction Zones

    Science.gov (United States)

    Arredondo, Katrina Marie

    Modern observations of subduction zones provide only snapshots of a complex geologic system that can last tens of millions of years. Surface velocity measurements and seismic tomography images provide information on the possible forces acting on the plate and influencing slab shape and behavior. Modern subduction zones exhibit a wide range of behavior, from the rapidly rolling back Tonga subduction zone (where the trench is moving toward the subducting plate) to stationary trenches to trench advance (where the trench is moving toward the overriding plate). Slabs may also stagnate at 660 km while others directly penetrate into the lower mantle. Numerical models can combine observations and laboratory data to test and study possible forces that may explain the wide variety of behavior observed in modern subduction zones. Past numerical model studies have not studied the impact on subduction zone behavior from: composition-dependent phase transitions, a complete mineralogical model and movement of the overriding plate. Here we show that: 1) weakening of the subducting plate can be observed from the forebulge to the trench using highly detailed bathymetry and gravity measurement tracks parallel to the trench, 2) using a complete mineralogy model is important for accurate numerical models because incomplete approximations may overestimate slab stagnation and slab rollback, 3) in free subduction models, the complete mineralogy model creates a strong feedback loop between broad slab folds and trench velocities, and 4) the movement of the overriding plate is very important for slab rollback. Results presented in Chapter 1 indicate that the rheology in the numerical models should produce weakening in the slab as it bends into the trench, which is observed in the models of Chapter 2 and 3. Past published models can be analyzed in relation to Chapter 2 and 3 to determine if their conclusions are skewed by an overestimation of slab stagnation or trench rollback. The presented

  14. Highly oxidising fluids generated during serpentinite breakdown in subduction zones.

    Science.gov (United States)

    Debret, B; Sverjensky, D A

    2017-09-04

    Subduction zones facilitate chemical exchanges between Earth's deep interior and volcanism that affects habitability of the surface environment. Lavas erupted at subduction zones are oxidized and release volatile species. These features may reflect a modification of the oxidation state of the sub-arc mantle by hydrous, oxidizing sulfate and/or carbonate-bearing fluids derived from subducting slabs. But the reason that the fluids are oxidizing has been unclear. Here we use theoretical chemical mass transfer calculations to predict the redox state of fluids generated during serpentinite dehydration. Specifically, the breakdown of antigorite to olivine, enstatite, and chlorite generates fluids with high oxygen fugacities, close to the hematite-magnetite buffer, that can contain significant amounts of sulfate. The migration of these fluids from the slab to the mantle wedge could therefore provide the oxidized source for the genesis of primary arc magmas that release gases to the atmosphere during volcanism. Our results also show that the evolution of oxygen fugacity in serpentinite during subduction is sensitive to the amount of sulfides and potentially metal alloys in bulk rock, possibly producing redox heterogeneities in subducting slabs.

  15. Crustal structure of the Carpathian orogen from receiver function analysis: how craton subduction and active delamination affect the crust

    Science.gov (United States)

    Petrescu, Laura; Tataru, Dragos; Grecu, Bogdan

    2017-04-01

    The Carpathian arc is an uncommon curved collisional system, involving the subduction of the Eastern European craton and the Proterozoic Moesian platform beneath younger European microplates. The Cenozoic collision led to the closure of the Tethys Oceanic basin, portions of which are actively breaking off or delaminating beneath the orogen, generating deep mantle earthquakes. Neogene volcanism, possibly related to subduction slab roll-back, also formed a band of presently extinct volcanoes in the back-arc region. The Carpathian embayment is thus an ideal laboratory to investigate crustal processes related to subduction of cratonic material, multiple plate junctions and active delamination. To better understand how the crustal structure changes from the Eastern European cratonic foreland, across the curved subduction zone, to the younger European microplates, we analyse teleseismic earthquakes recorded at broadband seismic stations located across eastern and southern Carpathians, in Romania and Moldova. We processed data from permanent seismic networks (The Romanian National Seismic Network) as well as data from temporary deployments such as CALIXTO (Carpathian Arc Lithosphere X-Tomography) and SCP (South Carpathian Project). Using extended multi-taper spectral division, we compute and analyse radial and transverse receiver functions. Energy on the transverse component may be an indicator of crustal anisotropy or the existence of intracrustal dipping interfaces. Using phase-weighted H-k stacking of receiver functions, we estimate the crustal thickness and the bulk crustal Poisson's ratio as well as the seismic sharpness of the Moho discontinuity. Furthermore, we invert receiver functions to obtain the S-wave velocity structure of the crust and upper mantle beneath individual stations, which provide concurrent information on the Moho nature. Our results provide a better understanding of crustal structure across complex collisional systems involving the subduction of

  16. Seamount subduction at the North-Ecuadorian convergent margin: Effects on structures, inter-seismic coupling and seismogenesis

    Science.gov (United States)

    Marcaillou, Boris; Collot, Jean-Yves; Ribodetti, Alessandra; d'Acremont, Elia; Mahamat, Ammy-Adoum; Alvarado, Alexandra

    2016-01-01

    At the North-Ecuadorian convergent margin (1°S-1.5°N), the subduction of the rough Nazca oceanic plate leads to tectonic erosion of the upper plate and complex seismogenic behavior of the megathrust. We used three selected pre-stack depth migrated, multi-channel seismic reflection lines collected during the SISTEUR cruise to investigate the margin structure and decipher the impact of the subducted Atacames seamounts on tectonic erosion, interseismic coupling, and seismogenesis in the region of the 1942 Mw7.8 earthquake. This dataset highlights a subducted ∼ 30 × 40 km, double-peak seamount that belongs to the Atacames seamount chain and that is associated with a deep morphologic re-entrant containing mass transport deposits. The seamount subduction uplifted the margin basement by ∼1.6 km and pervasively broke the margin by deep and intense reverse faulting ahead of the seamount, a process that is likely to weaken considerably the margin. In the seamount wake, the basement reverse fault system rotated counter-clockwise. This faulted basement is overlain with slope sediment sliding along listric normal faults that sole out onto the BSR. This superposition of deep tectonic contraction within the basement and shallow gravitational extension deformation within the sediment highlights the key role of gas hydrate on outer slope erosion. In addition to long-term regional basal erosion, the margin basement has thinned locally by an extra 0.8-1 km in response to the subduction of the Atacames seamount chain and hydrofracturing by overpressured fluids at the margin toe. This pervasively and deeply fractured margin segment is associated with a seismically quiet and GPS-modeled low interseismic coupling corridor that terminates downdip near the 1942 epicenter and locked zone. We suggest that the deeply buried double-peak Atacames seamount triggered the 1942 earthquake ahead of its leading flank. This result supports previous studies proposing that subducted seamounts

  17. Trench dynamics: Effects of dynamically migrating trench on subducting slab morphology and characteristics of subduction zones systems

    Science.gov (United States)

    Yoshida, Masaki

    2017-07-01

    Understanding the mechanisms of trench migration (retreat or advance) is crucial to characterizing the driving forces of Earth's tectonics plates, the origins of subducting slab morphologies in the deep mantle, and identifying the characteristics of subduction zones systems, which are among the fundamental issues of solid Earth science. A series of numerical simulations of mantle convection, focusing on plate subduction in a three-dimensional (3-D) regional spherical shell coordinate system, was performed to examine subduction zone characteristics, including geodynamic relationships among trench migration, back-arc stress, and slab morphology. The results show that a subducting slab tends to deflect around the base of the mantle transition zone and form a sub-horizontal slab because its front edge (its 'toe') is subject to resistance from the highly viscous lower mantle. As the sub-horizontal slab starts to penetrate into the lower mantle from its 'heel,' the toe of the slab is drawn into the lower mantle. The results for models with dynamically migrating trenches suggest that trench retreat is the dynamically self-consistent phenomenon in trench migration. The reason for this is that the strong lateral mantle flow that is generated as a sequence of events leading from corner flow at the subduction initiation to return flow of the formation of a sub-horizontal slab in the shallower part of mantle wedge produces the retreat of the subducting slab. In fact, a 'mantle suction force,' which is generated in the mantle wedge to fill space left by the retreating subducting plate, is enhanced by the subsequent trench retreat. Even when upwelling flow with significant positive buoyancy originates just above a mantle phase boundary at a depth of 410 km (as inferred from independent seismic tomographic, geodynamic, geochemical, and mineral physics), reaches the base of the overriding plate, and the overriding plate is slightly thinned, lithospheric stress tends to be

  18. Mapping fluids to subduction megathrust locking and slip behavior

    Science.gov (United States)

    Saffer, Demian M.

    2017-09-01

    In subduction zones, high fluid content and pore pressure are thought to promote aseismic creep, whereas well-drained conditions are thought to promote locking and failure in earthquakes. However, observations directly linking fluid content and seismic coupling remain elusive. Heise et al. (2017) use a magnetotelluric survey to image the electrical resistivity structure of the northern Hikurangi subduction thrust to 30 km depth, as an indicator of interconnected fluid content. The authors document a clear correlation between high resistivity and a distinct geodetically locked patch and between conductive areas and weak coupling. Their study, together with other recent geophysical investigations, provides new evidence for the role of fluids in governing subduction thrust locking.

  19. A Silent Slip Event on the Deeper Cascadia Subduction Interface

    Science.gov (United States)

    Dragert, Herb; Wang, Kelin; James, Thomas S.

    2001-05-01

    Continuous Global Positioning System sites in southwestern British Columbia, Canada, and northwestern Washington state, USA, have been moving landward as a result of the locked state of the Cascadia subduction fault offshore. In the summer of 1999, a cluster of seven sites briefly reversed their direction of motion. No seismicity was associated with this event. The sudden displacements are best explained by ~2 centimeters of aseismic slip over a 50-kilometer-by-300-kilometer area on the subduction interface downdip from the seismogenic zone, a rupture equivalent to an earthquake of moment magnitude 6.7. This provides evidence that slip of the hotter, plastic part of the subduction interface, and hence stress loading of the megathrust earthquake zone, can occur in discrete pulses.

  20. A silent slip event on the deeper Cascadia subduction interface.

    Science.gov (United States)

    Dragert, G; Wang, K; James, T S

    2001-05-25

    Continuous Global Positioning System sites in southwestern British Columbia, Canada, and northwestern Washington state, USA, have been moving landward as a result of the locked state of the Cascadia subduction fault offshore. In the summer of 1999, a cluster of seven sites briefly reversed their direction of motion. No seismicity was associated with this event. The sudden displacements are best explained by approximately 2 centimeters of aseismic slip over a 50-kilometer-by-300-kilometer area on the subduction interface downdip from the seismogenic zone, a rupture equivalent to an earthquake of moment magnitude 6.7. This provides evidence that slip of the hotter, plastic part of the subduction interface, and hence stress loading of the megathrust earthquake zone, can occur in discrete pulses.

  1. Friction and stress coupling on the subduction interfaces

    Science.gov (United States)

    Tan, E.; Lavier, L.; van Avendonk, H.

    2011-12-01

    At a subduction zone, the down-going oceanic plate slides underneath the overriding plate. The frictional resistance to the relative motion between the plates generates great earthquakes along the subduction interface, which can cause tremendous damage in the civil life and property. There is a strong incentive to understand the frictional strength of the subduction interface. One fundamental question of mechanics of subuction is the degree of coupling between the plates, which is linked to the size of earthquakes. It has been noted that the trench-parallel (along-strike) gravity variation correlates positively with the trench-parallel topography anomaly and negatively with the activity of great earthquake (Song and Simons, 2003). Regions with a negative trench-parallel gravity anomaly are more likely to have great earthquakes. The interpretation of such correlation is that strong coupling along subduction interface will drag down the for-arc region of the overriding plate, which generates the gravity and topography anomalies, and could store more strain energy to be released during a great earthquake. We developed a 2D numerical thermo-mechanical code for modeling subduction. The numerical method is based on an explicit finite element method similar to the Fast Lagrangian Analysis of Continua (FLAC) technique. The constitutive law is visco-elasti-plastic with strain weakening. The cohesion and friction angle are reduced with increasing plastic strain after yielding. To track different petrologic phases, Lagrangian particles are distributed in the domain. Basalt-eclogite, sediment-schist and peridotite-serpentinite phase changes are included in the model. Our numerical models show that the degree of coupling negatively correlates with the coefficient of friction. In the low friction case, the subduction interface has very shallow dipping angle, which helps to elastically couple the downing plate with the overriding plate. The topography and gravity anomalies of the

  2. Splay fault branching along the Nankai subduction zone.

    Science.gov (United States)

    Park, Jin-Oh; Tsuru, Tetsuro; Kodaira, Shuichi; Cummins, Phil R; Kaneda, Yoshiyuki

    2002-08-16

    Seismic reflection profiles reveal steeply landward-dipping splay faults in the rupture area of the magnitude (M) 8.1 Tonankai earthquake in the Nankai subduction zone. These splay faults branch upward from the plate-boundary interface (that is, the subduction zone) at a depth of approximately 10 kilometers, approximately 50 to 55 kilometers landward of the trough axis, breaking through the upper crustal plate. Slip on the active splay fault may be an important mechanism that accommodates the elastic strain caused by relative plate motion.

  3. Petrogenetic implications of ophiolitic chromite from Rutland Island, Andaman—a boninitic parentage in supra-subduction setting

    Science.gov (United States)

    Ghosh, Biswajit; Pal, Tapan; Bhattacharya, Anindya; Das, Dipankar

    2009-05-01

    Chromites occurring in different modes have been characterized from ophiolites of Rutland Island, a part of Burma-Andaman-Java subduction complex in the Bay of Bengal. Chromite mainly occurs as massive chromitite pods in mantle ultramafic tectonite and as thin massive chromitite bands together with minor disseminations in crustal ultramafic cumulate. Other than pods chromite also appears as: (a) anhedral restitic grains, (b) strings occurring as exsolved phases and as (c) symplectitic intergrowth with orthopyroxene in mantle tectonite. The chromites occurring as massive chromitite pods and bands contain high Cr (Cr#—73 to 80). Restitic chromite grains in mantle ultramafics are high-Mg (Mg#—58), high-Al (Al2O3—34 wt.%) and intermediate-Cr (Cr#—37) chromites. The bivariant plots of TiO2 wt.% vs 100Cr#, Mg# vs Cr# and Cr-Al-Fe3+ ternary discrimination diagram show that the massive and disseminated chromites fall in the boninitic field. The (Al2O3)melt and (FeO/MgO)melt values for the massive chromitites are estimated as 10 wt.% to 11 wt.% and 0.67-1.78 respectively, corroborating a boninitic parentage. Massive chromitite on Fe2+/Fe3+ vs Al2O3 wt.% and TiO2 wt.% vs Al2O3 wt.% plots occupy mainly the field of supra-subduction zone peridotites. High-Mg olivine (Fo91-93), high-Mg orthopyroxene (En˜90) and high-Cr chromites of Rutland ophiolite are all supportive of boninitic source at supra-subduction zone setting. 57Fe Mössbauer study of chromite of beach placer shows that chromites occur in partly inverse spinel structure with iron distribution as Fe3+(A)Fe2+(A)Fe2+(B) which might be a result of oxidation. The olivine-spinel geothermometry shows 650-700°C re-equilibration temperature which is much lower than near crystallization temperature (950-1,050°C) derived from orthopyroxene-clinopyroxene assemblage. At supra-subduction setting an oxidizing hydrous fluid derived from subducting slab might have a major influence during the formation of Rutland ophiolite

  4. Topographic and sedimentary features in the Yap subduction zone and their implications for the Caroline Ridge subduction

    Science.gov (United States)

    Dong, Dongdong; Zhang, Zhengyi; Bai, Yongliang; Fan, Jianke; Zhang, Guangxu

    2018-01-01

    The Yap subduction zone in the western Pacific presents some unique features compared to normal intra-oceanic subduction zones such as the subduction of an oceanic plateau. However, due to the relative paucity of geophysical data, the detailed structure remains unknown in this area. In this study, we present the latest high-quality swath bathymetry and multi-channel seismic data acquired synchronously in 2015 across the Yap subduction zone. The topographic and sedimentary features are intensively investigated and a modified evolutionary model of the Yap subduction zone is proposed. The two-stage evolution of the Parece Vela Basin (PVB) produced fabrics that are N-S trending and NW-SE trending. Our seismic data clearly reveal landslide deposits at the upper slope break of the forearc, to the north of the Yap Island, which was identified as the fault notch denoting a lithological boundary in previous work. The swath bathymetry and seismic profile reveal detailed horst and graben structures, including a crescent-shaped fault zone near the contact between the Yap Trench and the Caroline Ridge. A simple geometric model is proposed to explain the structure formation, indicating that the higher topography of the Caroline Ridge resulted in enhanced bending-related extension. A seismic angular unconformity (named R1) is identified in the Sorol Trough, marking the onset of rifting in the trough. Based on the sequence thickness and deposition rate by Deep Sea Drilling Project (DSDP), it is deduced that the Sorol Trough formed at 10 Ma or even earlier. A modified model for the Yap subduction zone evolution is proposed, incorporating three major tectonic events: the proto-Yap Arc rupture in the Oligocene, the collision of the Caroline Ridge and the Yap Trench in the late Oligocene or middle Miocene, and the onset of the Sorol Trough rifting in the late Miocene.

  5. Identification of source lithology at south segment of Kamchatka subduction zone

    Science.gov (United States)

    Gavrilenko, M.; Herzberg, C. T.; Portnyagin, M.; Ozerov, A.

    2012-12-01

    Kamchatka peninsula (Russia) is an island-arc with a complex geological history and structure. It has three distinct volcanic fronts, the origin of which is still debated. Moreover, a junction with the Aleutian Arc (at ~56°N) complicates the understanding of geodynamics at the region. However, the south part (from ~53°N) of Kamchatka peninsula is thought to be a "textbook case" of subduction zone with relatively rapid (over 8 cm/yr) near-normal convergence and a steep (over 50°) angle of subduction. Kamchatka is unusual in the world because its volcanoes contain a significant amount of primitive high MgO lavas that are rich in olivine crystals. Furthermore, high precision contents of Ni, Ca, and Mn can help to constrain the source lithology. Straub et al. (2008) reported high Ni contents on olivines from a limited number of samples from the Mexican Volcanic Front, and concluded that pyroxenite melting was important. Portnyagin et al. (2009) reported high precision Ni, Ca, and Mn contents of olivines from a wide range of volcanoes from Kamchatka, and similarly concluded that pyroxenite melting is widespread. We have extended the work of Portnyagin et al. (2009) by analyzing olivine phenocrysts from volcanoes in the southernmost Kamchatka peninsula. Our work confirms that there are regional variations in olivine phenocryst composition that likely arises from variations in pyroxenite composition, the amount of peridotite melt that mixes with pyroxenite melts, and a variable role played by magnetite fractionation. We conclude that pyroxenite melting is likely to be important in subduction zones world-wide, but its significance has been underestimated because of the general rarity of olivine-bearing high MgO lavas.

  6. The long-term seismic cycle at subduction thrusts: benchmarking geodynamic numerical simulations and analogue models

    Science.gov (United States)

    van Dinther, Y.; Gerya, T.; Corbi, F.; Funiciello, F.; Mai, P. M.; Dalguer, L. A.

    2011-12-01

    The physics governing the long-term seismic cycle in subduction zones remains elusive, largely due to its spatial inaccessibility, complex tectonic and geometric setting, and the short observational time span. To improve our understanding of the physics governing this seismic cycle, we benchmark a geodynamic numerical approach with a novel laboratory model. In this work we quantify and compare periodicity and source parameters of slip events (earth-quakes and gel-quakes) as a function of fault rheology (i.e. frictional properties), subduction velocity, slab dip, and seismogenic zone width. Our fluid-dynamic numerical method involves a plane-strain finite-difference scheme with marker-in-cell technique to solve the conservation of momentum, mass, and energy for a visco-elasto-plastic rheology. The simulated gelatin laboratory setup constitutes a triangular, visco-elastic crustal wedge on top of a straight subducting slab that includes a seismogenic zone. Numerical and analogue results show a regular and roughly comparable periodicity of short, rapid wedge velocity reversals. Ruptures nucleating mainly around the bottom of the seismogenic zone, and propagating upward, cause a distinct and rapid drop in stress within the wedge. To mimic the short duration, high speed and regularity of the analogue results, the numerical method requires a form of steady-state velocity-weakening friction for acceleration, and healing. The necessity of including a variable state component into the numerical simulations is subject of ongoing work. Finally, we extend this analysis by observing the role of different friction laws in large-scale, geometrically more realistic models.

  7. Influence of trench width on subduction hinge retreat rates in 3-D models of slab rollback

    NARCIS (Netherlands)

    Stegman, D. R.; Freeman, J.A.; Schellart, W. P.; Moresi, L.; May, D.

    Subduction of tectonic plates limited in lateral extent and with a free-trailing tail, i.e., "free subduction,'' is modeled in a three-dimensional (3-D) geometry. The models use a nonlinear viscoplastic rheology for the subducting plate and exhibit a wide range of behaviors depending on such plate

  8. Review of subduction and its association with geothermal system in Sumatera-Java

    Science.gov (United States)

    Ladiba, A. F.; Putriyana, L.; Sibarani, B. br.; Soekarno, H.

    2017-12-01

    Java and Sumatera have the largest geothermal resources in Indonesia, in which mostly are spatially associated with volcanoes of subduction zones. However, those volcanoes are not distributed in a regular pattern due to the difference of subduction position. Subduction position in java is relatively more perpendicular to the trench than in Sumatera. In addition, Java has a concentration of large productive geothermal field with vapour dominated system in the western part of Java, which may be caused by the various subduction dip along the island. In order to understand the relationship between the subduction process and geothermal system in the subduction zone volcanoes, we examined several kinematic parameters of subduction that potentially relevant to the formation of geothermal system in overriding plate such as slab dip, subduction rate, and direction of subduction. Data and information regarding tectonic setting of Sumatera and Java and productive geothermal field in Sumatera and Java have been collected and evaluated. In conclusion, there are three condition that caused the geothermal fluid to be more likely being in vapour phase, which are: the subduction is in an orthogonal position, the slab dip is high, and rate of subduction is high. Although there are plenty researches of subduction zone volcanoes, only a few of them present information about its formation and implication to the geothermal system. The result of this study may be used as reference in exploration of geothermal field in mutual geologic environment.

  9. Back-arc Extension: Critical Analisys of Subduction-related and Non Subduction-related Driving Mechanisms

    Science.gov (United States)

    Mantovani, E.; Viti, M.; Babbucci, D.; Tamburelli, C.; Albarello, D.

    It is argued that the opening of back arc basins can hardly be explained as an effect of subduction related forces, since this kind of interpretation has not yet provided plausible explanations for several major features of such processes in the world. In particular, it is not clear why back arc extension occurs in some subduction zones and not in others, why extension ceased in zones where subduction has remained active, why the arcs associated with back arc basins are often characterized by a strongly curved shape, why arc-trench-back arc systems do not develop along the entire length of consuming borders and why no significant correlation can be recognized between any parameter of subduction processes and the occurrence of back arc extension. In addition, modelling experiments indicate that the magnitude of the tensional stress induced in the overriding plate by subduction-related forces is significantly lower than the lithospheric strength. These problems are discussed, in particular, for three subduction-related interpretations, the "slab-pull", the "corner flow" and the "sea an- chor" models, which seem to be the most quoted in literature. It is then argued that possible solutions of the above problems may be provided by the extrusion model, which postulates that back arc basins are generated by the forced separation of the arc from the overriding plate, along a sector of the consuming border. This separa- tion is generally caused by the oblique indentation of strong and buoyant structures against the accretionary belt. In this view, subduction and back arc extension are not causally linked one to the other, but rather represent simultaneous effects of the lateral migration of the arc, driven by plate convergence. It is pointed out that the conditions required for the occurrence of this kind of mechanism may be recognized in the tec- tonic contexts where back arc basins developed in the wake of arc-trench migrating systems. On the other hand, in the zones

  10. Mantle enrichment by volatiles as the Nazca plate subducts beneath the Payenia backarc of the Southern Volcanic Zone, Argentina

    DEFF Research Database (Denmark)

    Brandt, Frederik Ejvang

    , minerals, fluid and melt inclusions from the Payenia backarc province of the Andean Southern Volcanic Zone. Major emphasis has been on olivine hosted melt inclusions. The study gives evidence for the role of fluids in the metasomatism of the backarc mantle, and outlines the trend of the variation...... of the metasomatism in Payenia, which is also characterized by a variation in oxidation state and other geochemical parameters of the melt inclusions, and is moreover related to mantle lithological variations. The mantle metasomatism by melts of subducted crust and fluid-borne enrichment is quantitatively modelled......, the origin of Chlorine is explained via slab-derived fluids, and the contrast between backarc and frontal arc magmas is discussed. These results add to the understanding of the origin of the complexities in the mantle wedge under arc-backarc in a subduction zone which has transition to flat slab conditions...

  11. Formation and stability of a double subduction system: a numerical study

    Science.gov (United States)

    Pusok, Adina E.; Stegman, Dave

    2017-04-01

    Examples of double subduction systems can be found in both modern (Izu-Bonin-Marianas and Ryukyu arcs, e.g. Hall [1997]) and ancient (Kohistan arc in Western Himalayas, e.g. Burg [2006], Burg et al. [2006]) tectonic record. A double subduction system has also been proposed to explain the high convergence rate observed for the India-Eurasia convergence [Jagoutz et al., 2015; Holt et al., 2016, 2017]. Rates of convergence across coupled double subduction systems can be significantly faster than across single subduction systems because of slab pull by two slabs. However, despite significant geological and geophysical observations, our understanding about this process is limited, and questions regarding double subduction remain largely unexplored in terms of physical factors controlling its initiation, duration and dynamics. Subduction initiation (of a single system) in itself has been a popular and challenging topic in the research community for the last few years, and various mechanisms (i.e., collapse at a passive margin or transform fault [Gerya et al., 2008; Stern, 2004], driven by compression [Hall et al., 2003; Toth and Gurnis, 1998], due to shear heating under compression [Thielmann and Kaus, 2012] or plume induced initiation [Gerya et al., 2015]) have been proposed. However, initiation of a secondary subduction, and formation of a stable double subduction system has not been studied before. Previous studies of double subduction either introduced weak zones to initiate subduction [Mishin et al., 2008] or both the subduction systems were already initiated [Jagoutz et al., 2015], thus assuming a priori information regarding the initial position of the two subduction zones. In this study, we perform 2D and 3D numerical simulations to investigate i) subduction initiation of a secondary system in an already initiated single subduction system, and ii) the dynamics and stability of the newly formed double subduction system. For this, we employ the code LaMEM [Kaus et

  12. Seismic anisotropy and mantle flow below subducting slabs

    Science.gov (United States)

    Walpole, Jack; Wookey, James; Kendall, J.-Michael; Masters, T.-Guy

    2017-05-01

    Subduction is integral to mantle convection and plate tectonics, yet the role of the subslab mantle in this process is poorly understood. Some propose that decoupling from the slab permits widespread trench parallel flow in the subslab mantle, although the geodynamical feasibility of this has been questioned. Here, we use the source-side shear wave splitting technique to probe anisotropy beneath subducting slabs, enabling us to test petrofabric models and constrain the geometry of mantle fow. Our global dataset contains 6369 high quality measurements - spanning ∼ 40 , 000 km of subduction zone trenches - over the complete range of available source depths (4 to 687 km) - and a large range of angles in the slab reference frame. We find that anisotropy in the subslab mantle is well characterised by tilted transverse isotropy with a slow-symmetry-axis pointing normal to the plane of the slab. This appears incompatible with purely trench-parallel flow models. On the other hand it is compatible with the idea that the asthenosphere is tilted and entrained during subduction. Trench parallel measurements are most commonly associated with shallow events (source depth < 50 km) - suggesting a separate region of anisotropy in the lithospheric slab. This may correspond to the shape preferred orientation of cracks, fractures, and faults opened by slab bending. Meanwhile the deepest events probe the upper lower mantle where splitting is found to be consistent with deformed bridgmanite.

  13. Evolution of passive continental margins and initiation of subduction zones

    NARCIS (Netherlands)

    Cloetingh, Sierd

    1982-01-01

    The initiation of subduction is a key element in plate tectonic schemes for the evolution of the Earth's lithosphere. Nevertheless, up to present, the underlying mechanism has not been very well understood (e.g. Dickinson and Seely, 1979; Hager, 1980; Kanamori, 1980). The insight into the initiation

  14. Evolution of passive continental margins and initiation of subduction zones

    NARCIS (Netherlands)

    Cloetingh, S.A.P.L.

    1982-01-01

    The initiation of subduction is a key element in plate tectonic schemes for the evolution of the Earth's lithosphere. Nevertheless, up to present, the underlying mechanism has not been very well understood (e.g. Dickinson and Seely, 1979; Hager, 1980; Kanamori, 1980). The insight into the

  15. The course of water in Archean subduction systems

    Science.gov (United States)

    Bouilhol, P.; Magni, V.; Van Hunen, J.; Kaislaniemi, L.

    2012-12-01

    The andesitic nature of the bulk continental crust, as well as its characteristic trace element ratios, have a close resemblance to the differentiated crust of volcanic arcs, thus leading to models for formation of continental crust in subduction zone settings. If the modern processes leading to continental crust formation at convergent margins are well constrained, the extrapolation to early Earth conditions is hazardous, because the composition of Earth's early crust can be achieved through several processes. We study the different scenarios that may have operated during early Earth subduction to form differentiated crust. Each scenario (e.g. arc crust melting, slab melting, mantle melting followed by differentiation…) has a common denominator that is the fate of water, because it reflects slab devolatilization and controls the melting process and the stability of minerals such as garnet, amphibole and plagioclase, which are major players in the final melt composition. To this end, we present thermomechanical numerical models that incorporate internally consistent thermodynamic data in order to simulate slab dehydration. Our goal is to track the fate of subducted water in an Archean style subduction regime to better comprehend its modus operandi.

  16. Slab melting versus slab dehydration in subduction-zone magmatism.

    Science.gov (United States)

    Mibe, Kenji; Kawamoto, Tatsuhiko; Matsukage, Kyoko N; Fei, Yingwei; Ono, Shigeaki

    2011-05-17

    The second critical endpoint in the basalt-H(2)O system was directly determined by a high-pressure and high-temperature X-ray radiography technique. We found that the second critical endpoint occurs at around 3.4 GPa and 770 °C (corresponding to a depth of approximately 100 km in a subducting slab), which is much shallower than the previously estimated conditions. Our results indicate that the melting temperature of the subducting oceanic crust can no longer be defined beyond this critical condition and that the fluid released from subducting oceanic crust at depths greater than 100 km under volcanic arcs is supercritical fluid rather than aqueous fluid and/or hydrous melts. The position of the second critical endpoint explains why there is a limitation to the slab depth at which adakitic magmas are produced, as well as the origin of across-arc geochemical variations of trace elements in volcanic rocks in subduction zones.

  17. Surface deformation resulting from subduction and slab detachment

    NARCIS (Netherlands)

    Buiter, S.J.H.

    2000-01-01

    Convergence of lithospheric plates is accommodated at active margins by one plate moving beneath the other into the Earth's mantle. Changes in this subduction process may cause variations in the topography of the Earth's surface near a convergent plate margin. The focus of this thesis lies on

  18. Some consequences of the subduction of young slabs

    NARCIS (Netherlands)

    England, P.; Wortel, R.

    The negative buoyancy force exerted by a subducting oceanic slab depends on its descent velocity, and strongly on its age. For lithosphere close to thermal equilibrium, this force dominates by a large margin the resisting forces arising from friction on the plate boundary and compositional buoyancy.

  19. Fluid Release and the Deformation of Subducting Crust

    Science.gov (United States)

    Maunder, Benjamin; van Hunen, Jeroen; Magni, Valentina; Bouilhol, Pierre

    2014-05-01

    It is known that slab dehydration is crucial in subduction dynamics and for the formation of arc-magmatism. Previous studies of this process have constrained this intake and subsequent release of fluids into the mantle wedge by considering the stability hydrous phases within the slab. Other, more dynamical effects of this hydration state and partial melting have also been suggested, such as the possibility of "cold plumes", crustal delamination, and subduction channel return flow. These processes have been inferred to play a role in the generation of continental crust over time through accumulation and melting beneath the overriding plate. Water content and melt fraction have a strong control on the rheology of the system. Therefore we investigate the effect of these parameters on the dynamics of a subducting slab, with the aim to establish the physical bounds on the delamination process. To do this we use a coupled geodynamical-petrological model that tracks dehydration and melting reactions in order to factor in the rheological effect of metamorphism and magmatism on slab and mantle wedge dynamics. We focus primarily on the strength of the subducting crust and the possibility of delamination. We then extend this investigation by considering whether early earth crust formation could have been the result of such a processes by looking at a hypothetical Archean setting.

  20. Tensor-guided fitting of subduction slab depths

    Science.gov (United States)

    Bazargani, Farhad; Hayes, Gavin P.

    2013-01-01

    Geophysical measurements are often acquired at scattered locations in space. Therefore, interpolating or fitting the sparsely sampled data as a uniform function of space (a procedure commonly known as gridding) is a ubiquitous problem in geophysics. Most gridding methods require a model of spatial correlation for data. This spatial correlation model can often be inferred from some sort of secondary information, which may also be sparsely sampled in space. In this paper, we present a new method to model the geometry of a subducting slab in which we use a data‐fitting approach to address the problem. Earthquakes and active‐source seismic surveys provide estimates of depths of subducting slabs but only at scattered locations. In addition to estimates of depths from earthquake locations, focal mechanisms of subduction zone earthquakes also provide estimates of the strikes of the subducting slab on which they occur. We use these spatially sparse strike samples and the Earth’s curved surface geometry to infer a model for spatial correlation that guides a blended neighbor interpolation of slab depths. We then modify the interpolation method to account for the uncertainties associated with the depth estimates.

  1. Hafnium at subduction zones: isotopic budget of input and output fluxes; L'hafnium dans les zones de subduction: bilan isotopique des flux entrant et sortant

    Energy Technology Data Exchange (ETDEWEB)

    Marini, J.Ch

    2004-05-15

    Subduction zones are the primary regions of mass exchanges between continental crust and mantle of Earth through sediment subduction toward the earth's mantle and by supply of mantellic magmas to volcanic arcs. We analyze these mass exchanges using Hafnium and Neodymium isotopes. At the Izu-Mariana subduction zone, subducting sediments have Hf and Nd isotopes equivalent to Pacific seawater. Altered oceanic crust has Hf and Nd isotopic compositions equivalent to the isotopic budget of unaltered Pacific oceanic crust. At Luzon and Java subduction zones, arc lavas present Hf isotopic ratios highly radiogenic in comparison to their Nd isotopic ratios. Such compositions of the Luzon and Java arc lavas are controlled by a contamination of their sources by the subducted oceanic sediments. (author)

  2. Recycling Revisited: Where did all the Subducted Sediments go?

    Science.gov (United States)

    Hofmann, A. W.; Chauvel, C.; Lewin, E.; Kelemen, P. B.; Hacker, B. R.

    2016-12-01

    Several lines of reasoning have revived the idea [1] that subduction has recycled continent-derived sediments into the mantle on a massive scale. For example, well-known peaks in zircon ages have been reinterpreted as reflecting variable rates of crust destruction via erosion and sediment subduction [2]. In addition, assessment of the trace element budgets of subducted sediments and arc volcanics, as well as geological and geophysical studies of accretionary wedges have led to estimates that about one mass of present-day continental crust has been returned to the mantle [3]. If these ideas are correct, then recycled sedimentary components should be present in MORB and OIB sources. As previously established, Nb/U and 87Sr/86Sr are negatively correlated in all EM2-type OIBs, clearly indicating continental/sedimentary input. However, the MORB source reservoir, being depleted in incompatible elements, is particularly susceptible to "pollution" by subducted sediments. Chauvel et al. [4] modeled the Hf-Nd isotopic array of MORBs+OIBs and concluded that it requires the addition of up to 6 % subducted sediment. We revisit this issue and show that global MORBs show no decrease in Nb/U with increasing 87Sr/86Sr, ruling out extensive addition of recycled sediment into global MORB sources. Instead, the Hf-Nd array can be obtained by recycled alkali basalts derived from subducted seamounts and ocean islands, rather than sediments. Moreover, mantle plumes with clearly identifiable sediment input contribute less than 20% of the total plume flux. We conclude that most of the subducted sediment flux is not returned to the convecting mantle. Instead, its most plausible fate is to be underplated beneath existing continental crust via "relamination" [5]. These results imply that continental recycling is subordinate and the growth of the continental crust has been largely irreversible. [1] Armstrong, 1968, Rev. Geophys. 6, 175. [2] Hawkesworth et al., 2009, Science 323, 49. [3] Porter

  3. Frictional behavior of carbonate-rich sediments in subduction zones

    Science.gov (United States)

    Rabinowitz, H. S.; Savage, H. M.; Carpenter, B. M.; Collettini, C.

    2016-12-01

    Deformation in rocks and sediments is controlled by multiple mechanisms, each governed by its own pressure- (P), temperature- (T), and slip velocity- (v) dependent kinetics. Frictional behavior depends on which of these mechanisms are dominant, and, thus, varies with P, T, and v. Carbonates are a useful material with which to interrogate the PTv controls on friction due to the fact that a wide range of mechanisms can be easily accessed in the lab at geologically relevant conditions. In addition, carbonate-rich layers make up a significant component of subducting sediments around the world and may impact the frictional behavior of shallow subduction zones. In order to investigate the effect of carbonate subduction and the evolution of friction at subduction zone conditions, we conducted deformation experiments on input sediments for two subduction zones, the Hikurangi trench, New Zealand (ODP Site 1124) and the Peru trench (DSDP Site 321), which have carbonate/clay contents of 40/60 wt% and 80/20 wt%, respectively. Samples were saturated with distilled water mixed with 35g/l sea salt and deformed at room temperature. Experiments were conducted at σeff = 1-100 MPa and T = 20-100 °C with sliding velocities of 1-300 μm/s and hold times of 1-1000 s. We test the changes in velocity dependence and healing over these PT conditions to elucidate the frictional behavior of carbonates in subduction zone settings. The mechanical results are complemented by microstructural analysis. In lower stress experiments, there is no obvious shear localization; however, by 25 MPa, pervasive boundary-parallel shears become dominant, particularly in the Peru samples. Optical observations of these shear zones under cross-polarized light show evidence of plastic deformation (CPO development) while SEM-EDS observations indicate phase segregation in the boundary shears. Degree of microstructural localization appears to correspond with the trends observed in velocity-dependence. Our

  4. Mapping seismic azimuthal anisotropy of the Japan subduction zone

    Science.gov (United States)

    Zhao, D.; Liu, X.

    2016-12-01

    We present 3-D images of azimuthal anisotropy tomography of the crust and upper mantle of the Japan subduction zone, which are determined using a large number of high-quality P- and S-wave arrival-time data of local earthquakes and teleseismic events recorded by the dense seismic networks on the Japan Islands. A tomographic method for P-wave velocity azimuthal anisotropy is modified and extended to invert S-wave travel times for 3-D S-wave velocity azimuthal anisotropy. A joint inversion of the P and S wave data is conducted to constrain the 3-D azimuthal anisotropy of the Japan subduction zone. Main findings of this work are summarized as follows. (1) The high-velocity subducting Pacific and Philippine Sea (PHS) slabs exhibit trench-parallel fast-velocity directions (FVDs), which may reflect frozen-in lattice-preferred orientation of aligned anisotropic minerals formed at the mid-ocean ridge as well as shape-preferred orientation such as normal faults produced at the outer-rise area near the trench axis. (2) Significant trench-normal FVDs are revealed in the mantle wedge, which reflects corner flow in the mantle wedge due to the active subduction and dehydration of the oceanic plates. (3) Obvious toroidal FVDs and low-velocity anomalies exist in and around a window (hole) in the aseismic PHS slab beneath Southwest Japan, which may reflect a toroidal mantle flow pattern resulting from hot and wet mantle upwelling caused by the joint effects of deep dehydration of the Pacific slab and the convective circulation process in the mantle wedge above the Pacific slab. (4) Significant low-velocity anomalies with trench-normal FVDs exist in the mantle below the Pacific slab beneath Northeast Japan, which may reflect a subducting oceanic asthenosphere affected by hot mantle upwelling from the deeper mantle. ReferencesLiu, X., D. Zhao (2016) Seismic velocity azimuthal anisotropy of the Japan subduction zone: Constraints from P and S wave traveltimes. J. Geophys. Res. 121, doi

  5. Three-dimensional Thermal Model of the Mexican Subduction Zone

    Science.gov (United States)

    Rosas, J. C.; Pimentel, F. D. C.; Currie, C. A.; He, J.; Harris, R. N.

    2015-12-01

    Along the Mexican section of the Middle America Trench (MAT), the Cocos plate subducts beneath the North American plate. The most important feature of this subduction zone is the flat-slab section below central Mexico, extending approximately 250 km landward from the trench at a depth of 50 km. Further west, the dip changes to 45-50º. This particular geometry has several unique consequences, such as a volcanic arc that is not aligned with the trench and very shallow slab seismicity. For the mantle wedge, the abrupt change in slab geometry could lead to a three-dimensional (3D) mantle wedge flow that departs from the classical 2D subduction-driven corner flow. Evidence of 3D flow in the region comes from seismic anisotropy studies, which show that olivine fast-direction axes have a component that is parallel to the MAT. In other subduction zones, such as Costa Rica-Nicaragua and Japan, 3D flow has been observed to increase temperatures by >50º C relative to corner flow models.For this study, we have created the first 3D finite-element model of the Mexican subduction zone in order to analyze its thermal structure. Our objective is to assess the effects of 3D mantle flow and hydrothermal circulation (HC) in the subducting slab. In this region, low surface heat flow values near the trench indicate that HC may remove heat from the oceanic plate. Our model incorporates the effect of HC through conductivity proxies in the subducting crust and a 2D oceanic geotherm that includes the age variations of the Cocos plate along the MAT. For an isoviscous mantle, our model shows that the slab dip variations induce a flow that departs from 2D corner flow near the transition between the flat-slab and normal-dipping sections. The mantle flows in eastward direction toward the flat slab, and its orientation is consistent with seismic anisotropy studies. The maximum along-margin flow rate is nearly 2 cm/yr, which is >30% of the convergence rate. Temperatures at the location of this

  6. Geologic signature of early Tertiary ridge subduction in Alaska

    Science.gov (United States)

    Bradley, Dwight C.; Kusky, Timothy M.; Haeussler, Peter J.; Goldfarb, Richard J.; Miller, Marti L.; Dumoulin, Julie A.; Nelson, Steven W.; Karl, Susan M.

    2003-01-01

    A mid-Paleocene to early Eocene encounter between an oceanic spreading center and a subduction zone produced a wide range of geologic features in Alaska. The most striking effects are seen in the accretionary prism (Chugach–Prince William terrane), where 61 to 50 Ma near-trench granitic to gabbroic plutons were intruded into accreted trench sediments that had been deposited only a few million years earlier. This short time interval also saw the genesis of ophiolites, some of which contain syngenetic massive sulfide deposits; the rapid burial of these ophiolites beneath trench turbidites, followed immediately by obduction; anomalous high-T, low-P, near-trench metamorphism; intense ductile deformation; motion on transverse strike-slip and normal faults; gold mineralization; and uplift of the accretionary prism above sea level. The magmatic arc experienced a brief flare-up followed by quiescence. In the Alaskan interior, 100 to 600 km landward of the paleotrench, several Paleocene to Eocene sedimentary basins underwent episodes of extensional subsidence, accompanied by bimodal volcanism. Even as far as 1000 km inboard of the paleotrench, the ancestral Brooks Range and its foreland basin experienced a pulse of uplift that followed about 40 million years of quiescence.All of these events - but most especially those in the accretionary prism - can be attributed with varying degrees of confidence to the subduction of an oceanic spreading center. In this model, the ophiolites and allied ore deposits were produced at the soon-to-be subducted ridge. Near-trench magmatism, metamorphism, deformation, and gold mineralization took place in the accretionary prism above a slab window, where hot asthenosphere welled up into the gap between the two subducted, but still diverging, plates. Deformation took place as the critically tapered accretionary prism adjusted its shape to changes in the bathymetry of the incoming plate, changes in the convergence direction before and after

  7. Dynamic Linkages Between the Transition Zone & Surface Plate Motions in 2D Models of Subduction

    Science.gov (United States)

    Arredondo, K.; Billen, M. I.

    2013-12-01

    feedback to other added processes remain important, which could encourage mineralogical research into multiphase systems. Feedback from the compositionally complex slab to the dynamic trench may improve understanding on the mechanics of slab behavior in the upper and lower mantle and surface behavior of the subducting and overriding plates. Běhounková, M., and H. Cízková, Long-wavelength character of subducted slabs in the lower mantle, Earth and Planetary Science Letters, 275, 43-53, 2008. Fukao, Y., M. Obayashi, T. Nakakuki, and the Deep Slab Project Group, Stagnant slab: A review, Annual Reviews of Earth and Planetary Science, 37, 19-46, 2009. Ricard, Y., E. Mattern, and J. Matas, Synthetic tomographic images of slabs from mineral physics, in Earth's Deep Mantle: Structure, Composition, and Evolution, Geophysical Monograph Series, vol. 160, American Geophysical Union, 2005.

  8. Is the Vincent fault in southern California the Laramide subduction zone megathrust?

    Science.gov (United States)

    Xia, H.; Platt, J. P.

    2016-12-01

    The Vincent fault (VF) in the San Gabriel Mountains, southern California separates a Meso-Proterozoic gneiss complex and Mesozoic granitoid rocks in the upper plate from the ocean-affiliated Late Cretaceous Pelona schist in the lower plate, and it has been widely interpreted as the original Laramide subduction megathrust. A 500 to 1000 m thick mylonite zone, consisting of a low-stress (LS) section at the bottom, a high-stress (HS) section at the top, and a weakly deformed section in between, is developed above the VF. Our kinematic, thermobarometric and geochronological analysis of the mylonite zone indicates that the VF is a normal fault. Shear sense indicators including asymmetric porphyroblasts, quartz new grain fabric, mineral fish, and quartz CPO from the HS and the LS sections exhibit a top-to-SE sense of shear on the SW-dipping mylonitic foliation, which is contrary to what one would expect for the Laramide subduction megathrust. A few samples from the LS section were overprinted by HS microstructure, implying that the LS mylonites predate the HS mylonites. TitaniQ thermometer and Si-in-muscovite barometer show that the P-T conditions are 389 ± 6 °C, 5 kbar for the LS mylonites and 329 ± 6 °C, 2.4 kbar for HS mylonites. Considering the temporal sequence of HS and LS mylonites, they are likely to be formed during exhumation. A comparison with the lower plate leads to the same conclusion. The top 80-100 m of the Pelona schist underneath the VF is folded and also mylonitized, forming the Narrows synform and S3 simultaneously. Our previous study found that S3 of the Pelona schist has a top-to-SE sense of shear and similar P-T conditions as the LS mylonite in the upper plate, so S3 of the Pelona schist is likely to be formed together with the LS mylonites in the upper plate. While mylonitization of Pelona schist (S3) overprinted both the subduction-related S1 fabric and the return-flow-related S2 fabric, it is reasonable to argue that the mylonite zone above

  9. Seismicity, topography, and free-air gravity of the Aleutian-Alaska subduction zone

    Science.gov (United States)

    Wells, R. E.; Blakely, R. J.; Scholl, D. W.; Ryan, H. F.

    2011-12-01

    The Aleutian-Alaska subduction zone, extending 3400 km from the Queen Charlotte Fault to Kamchatka, has been the source of six great megathrust earthquakes in the 20th Century. Four earthquakes have ruptured the 2000-km-long Aleutian segment, where the Cenozoic Aleutian arc overlies the subducting Pacific plate. These include the 1946 M 8.6 earthquake off Unimak Is., the 1957 M 8.6 and 1986 M 8.0 earthquakes off the Andreanoff Is., and the 1965 M 8.7 Rat Is. earthquake. The source regions of these earthquakes inferred from waveform inversions underlie the well-defined Aleutian deep-sea terrace. The deep-sea terrace is about 4 km deep and is underlain by Eocene arc framework rocks, which extend nearly to the trench. It is bounded on its seaward and landward margins by strong topographic and fee-air gravity gradients. The main asperities (areas of largest slip) for the great earthquakes and nearly all of the Aleutian thrust CMT solutions lie beneath the Aleutian terrace, between the maximum gradients. Similar deep-sea terraces are characteristic of non-accretionary convergent margins globally (75% of subduction zones), and, where sampled by drilling (e.g., Japan, Peru, Tonga, Central America), are undergoing sustained subsidence. Sustained subsidence requires removal of arc crust beneath the terrace by basal subduction erosion (BSE). BSE is in part linked to the seismic cycle, as it occurs in the same location as the megathrust earthquakes. Along the eastern 1400 km of the Alaskan subduction zone, the Pacific plate subducts beneath the North American continent. The boundary between the Aleutian segment and the continent is well defined in free-air gravity, and the distinctive deep-sea terrace observed along the Aleutian segment is absent. Instead, the Alaskan margin consists of exhumed, underplated accretionary complexes forming outer arc gravity highs. Superimposed on them are broad topographic highs and lows forming forearc basins (Shumagin, Stevenson) and islands

  10. Thermochronological response to rifting and subduction in the Corsica-Sardinia block

    Science.gov (United States)

    Malusà, Marco Giovanni; Danišík, Martin; Kuhlemann, Joachim

    2014-05-01

    The linkage between deep-seated tectonic processes and surface processes provides a key to investigate the geological evolution of complex plate boundaries starting from the analysis of low-temperature geochronological systems. Here, we integrate published thermochronological data from Corsica (Danišík et al., 2007) with a new multi-thermochronological dataset (i.e., zircon and apatite fission track (ZFT and AFT), and apatite (U-Th)/He (AHe) data) from Sardinia, in order to tackle the Western Mediterranean tectonic issue and constrain the problematic transition in space and time between the opposite-dipping Alpine (European) and Apenninic (Adriatic) subductions. Mesozoic AFT ages (169-201 Ma) and AHe ages (133-204 Ma), found on mountain ridges of central Sardinia and on the eastern coast of the island, indicate that rocks now exposed at the surface have resided since Jurassic times at very shallow depth, i.e., above the partial annealing zone of the AFT system (~60-110°C) or even above the partial retention zone of the AHe system (~40-80°C). The observed age pattern and track length distributions are consistent with those predicted after rising of isothermal surfaces during rifting and subsequent thermal relaxation after continental break-up. We demonstrate that the crustal sections now exposed in central and eastern Sardinia were originally located closer to the Tethyan rift axis than crustal sections exposed in NW Sardinia and Corsica, pointing to a NNE trend for the continental crust isopachs of the northern Tethyan margin (ENE before Corsica-Sardinia rotation), with burial depth progressively increasing from SE to NW. In Alpine Corsica, the low-T geochronological evidence of Jurassic rifting was largely obliterated by Cenozoic metamorphism, but it is still recognized in high-T systems. AFT and AHe ages set after Tethyan rifting but not thermally affected by Neogene backarc extension, define a SE-NW trend of decreasing ages from southern Sardinia to northern

  11. Wind-induced subduction at the South Atlantic subtropical front

    Science.gov (United States)

    Calil, Paulo H. R.

    2017-10-01

    The South Atlantic Subtropical Front, associated with the eastward-flowing South Atlantic Current, separates the colder, nutrient-rich waters of the subpolar gyre from the warmer, nutrient-poor waters of the subtropical gyre. Perturbations to the quasi-geostrophic, eastward flow generate meanders and filaments which induce cross-frontal exchange of water properties. Down-front winds transport denser waters from the South over warm waters from the North, inducing convective instability and subduction. Such processes occur over spatial scales of the order of 1 km and thus require high horizontal spatial resolution. In this modeling study, a high-resolution (4 km) regional grid is embedded in a basin-wide configuration (12 km) of the South Atlantic Ocean in order to test the importance of submesoscale processes in water mass subduction along the subtropical front. Stronger and more numerous eddies obtained in the high-resolution run yield more intense zonal jets along the frontal zone. Such stronger jets are more susceptible to instabilities, frontogenesis, and the generation of submesoscale meanders and filaments with O(1) Rossby number. As a consequence, vertical velocities larger than 100 md 1 are obtained in the high-resolution run, one order of magnitude larger than in the low-resolution run. Wind-driven subduction occurs along the frontal region, associated with negative Ertel potential vorticity in the surface layer. Such processes are not observed in the low-resolution run. A passive tracer experiment shows that waters with density characteristics similar to subtropical mode waters are preferentially subducted along the frontal region. The wind-driven buoyancy flux is shown to be much larger than thermal or haline fluxes during the wintertime, which highlights the importance of the frictional component in extracting PV from the surface ocean and inducing subduction, a process that has been overlooked in subtropical mode water formation in the region.

  12. The dynamical control of subduction parameters on surface topography

    Science.gov (United States)

    Crameri, F.; Lithgow-Bertelloni, C. R.; Tackley, P. J.

    2017-04-01

    The long-wavelength surface deflection of Earth's outermost rocky shell is mainly controlled by large-scale dynamic processes like isostasy or mantle flow. The largest topographic amplitudes are therefore observed at plate boundaries due to the presence of large thermal heterogeneities and strong tectonic forces. Distinct vertical surface deflections are particularly apparent at convergent plate boundaries mostly due to the convergence and asymmetric sinking of the plates. Having a mantle convection model with a free surface that is able to reproduce both realistic single-sided subduction and long-wavelength surface topography self-consistently, we are now able to better investigate this interaction. We separate the topographic signal into distinct features and quantify the individual topographic contribution of several controlling subduction parameters. Results are diagnosed by splitting the topographic signal into isostatic and residual components, and by considering various physical aspects like viscous dissipation during plate bending. Performing several systematic suites of experiments, we are then able to quantify the topographic impact of the buoyancy, rheology, and geometry of the subduction-zone system to each and every topographic feature at a subduction zone and to provide corresponding scaling laws. We identify slab dip and, slightly less importantly, slab buoyancy as the major agents controlling surface topography at subduction zones on Earth. Only the island-arc high and the back-arc depression extent are mainly controlled by plate strength. Overall, his modeling study sets the basis to better constrain deep-seated mantle structures and their physical properties via the observed surface topography on present-day Earth and back through time.

  13. Comparing the effects of rheology on the dynamics and topography of 3D subduction-collision models

    Science.gov (United States)

    Pusok, Adina E.; Kaus, Boris; Popov, Anton

    2015-04-01

    continental collision side (trench advance, slab detachment, topographic uplift and lateral extrusion of material). Moreover, different topographic regimes can be identified in the upper plate during continental subduction/collision, which can be determined using the Argand number and an initial buoyancy ratio of the upper plate. Next, we investigate the effect of using more complex (powerlaw viscous and plastic) rheologies and compare the results with linear viscous models. Acknowledgements: Funding was provided by the European Research Council under the European Community's Seventh Framework Program (FP7/2007-2013) / ERC Grant agreement #258830. Numerical computations have been performed on MOGON (ZDV Mainz computing center) and JUQUEEN (Jülich high-performance computing center).

  14. Endoderm convergence controls subduction of the myocardial precursors during heart-tube formation.

    Science.gov (United States)

    Ye, Ding; Xie, Huaping; Hu, Bo; Lin, Fang

    2015-09-01

    Coordination between the endoderm and adjacent cardiac mesoderm is crucial for heart development. We previously showed that myocardial migration is promoted by convergent movement of the endoderm, which itself is controlled by the S1pr2/Gα13 signaling pathway, but it remains unclear how the movements of the two tissues is coordinated. Here, we image live and fixed embryos to follow these movements, revealing previously unappreciated details of strikingly complex and dynamic associations between the endoderm and myocardial precursors. We found that during segmentation the endoderm underwent three distinct phases of movement relative to the midline: rapid convergence, little convergence and slight expansion. During these periods, the myocardial cells exhibited different stage-dependent migratory modes: co-migration with the endoderm, movement from the dorsal to the ventral side of the endoderm (subduction) and migration independent of endoderm convergence. We also found that defects in S1pr2/Gα13-mediated endodermal convergence affected all three modes of myocardial cell migration, probably due to the disruption of fibronectin assembly around the myocardial cells and consequent disorganization of the myocardial epithelium. Moreover, we found that additional cell types within the anterior lateral plate mesoderm (ALPM) also underwent subduction, and that this movement likewise depended on endoderm convergence. Our study delineates for the first time the details of the intricate interplay between the endoderm and ALPM during embryogenesis, highlighting why endoderm movement is essential for heart development, and thus potential underpinnings of congenital heart disease. © 2015. Published by The Company of Biologists Ltd.

  15. The Coupling of Back-arc Extension, Extrusion and Subduction Dynamics in the Eastern Mediterranean

    Science.gov (United States)

    Capitanio, Fabio A.

    2017-04-01

    Extension in the Aegean Sea and lateral Anatolian extrusion are contrasting and seemingly unrelated examples of continental tectonics In the Eastern Mediterranean. It is acknowledged that these must reconcile with the dynamics of Tethys closure and following continental collision along the convergent margin, however the underlying mechanisms have been difficult to pinpoint, thus far. Three-dimensional numerical modelling of the dynamics of subduction and coupling with the mantle and upper plates allows probing the evolution of similar areas, supporting inferences on the ultimate causes for the continental tectonics. I will present models that reproduce the force balance of subducting slabs' buoyancy, mantle flow and upper plate interiors, and emphasise the role of perturbations in the force balance that may have followed slab breakoff, collision and trench land-locking reconstructed during the oceanic closure in the Eastern Mediterranean. These perturbations lead to a range of different margin motions and strain regimes in the upper plate, from rollback and back-arc spreading, to indentation and extrusion along the collisional margin. Different spatial and temporal fingerprints are illustrated for these processes, and while the trench rollback and back-arc spreading are rather stable features, extrusion is transient. When these regimes overlap, rapid and complex rearrangements of the tectonics in the upper plate are the result. The remarkable similarity between the models' and the Eastern Mediterranean tectonic regimes and geophysical observable allows proposing viable driving mechanisms and support inferences on the Miocene-to-Pliocene evolution of this puzzling area.

  16. Subduction Mode Selection During Slab and Mantle Transition Zone Interaction: Numerical Modeling

    Science.gov (United States)

    Shi, Yanan; Wei, Dongping; Li, Zhong-Hai; Liu, Ming-Qi; Liu, Mengxue

    2017-12-01

    Global seismic tomography of the subduction zones shows that the subducting slabs could either stagnate around the 660-km discontinuity, or penetrate into the lower mantle. The stagnating slabs also have various morphologies. These are directly related to the interaction between the subducting slabs and the mantle transition zone (MTZ), the dynamics of which are still debated. Using a 2-D thermo-mechanical model, we systematically investigated the modes of subduction in the mantle transition zone and explored the key constraints of various subduction styles. Four basic subduction modes are obtained in the numerical experiments, including one with slab penetrating through the 660-km discontinuity and three other modes with slab stagnating in the MTZ (i.e. folding, lying and rolling-back). The numerical models indicate that the age of subducting oceanic plate, the thickness of overriding continental lithosphere and the convergence velocity play crucial roles in the dynamics of subducting slab and MTZ interaction. In general, the young subducting slab favors the penetration or folding mode, whereas the old subducting slab tends to result in lying or rolling-back mode, although other parameters can also affect. Our models also show a strong correlation between the subduction mode selection and dip angle of the slab tip when reaching the 660-km phase boundary.

  17. 3D Numerical modelling of topography development associated with curved subduction zones

    Science.gov (United States)

    Munch, Jessica; Ueda, Kosuke; Burg, Jean-Pierre; May, Dave; Gerya, Taras

    2017-04-01

    Curved subduction zones, also called oroclines, are geological features found in various places on Earth. They occur in diverse geodynamic settings: 1) single slab subduction in oceanic domain (e.g. Sandwich trench in the Southern Atlantic); 2) single slab subduction in continental domain, (e.g. Gibraltar-Alboran orocline in the Western Mediterranean) 3); multi-slab subduction (e.g. Caribbean orocline in the South-East of the Gulf of Mexico). These systems present various curvatures, lengths (few hundreds to thousands of km) and ages (less than 35 Ma for Gibraltar Alboran orocline, up to 100 Ma for the Caribbean). Recent studies suggested that the formation of curved subduction systems depends on slab properties (age, length, etc) and may be linked with processes such as retreating subduction and delamination. Plume induced subduction initiation has been proposed for the Caribbean. All of these processes involve deep mechanisms such as mantle and slab dynamics. However, subduction zones always generate topography (trenches, uplifts, etc), which is likely to be influenced by surface processes. Hence, surface processes may also influence the evolution of subduction zones. We focus on different kinds of subduction systems initiated by plume-lithosphere interactions (single slab subduction/multi-slab subduction) and scrutinize their surface expression. We use numerical modeling to examine large-scale subduction initiation and three-dimensional slab retreat. We perform two kinds of simulations: 1) large scale subduction initiation with the 3D-thermomechanical code I3ELVIS (Gerya and Yuen, 2007) in an oceanic domain and 2) large scale subduction initiation in oceanic domain using I3ELVIS coupled with a robust new surface processes model (SPM). One to several retreating slabs form in the absence of surface processes, when the conditions for subduction initiation are reached (c.f. Gerya et al., 2015), and ridges occur in the middle of the extensional domain opened by slab

  18. Dynamic Topography during Flat Subduction: Subsidence or Uplift?

    Science.gov (United States)

    Davila, F. M.; Lithgow-Bertelloni, C. R.

    2011-12-01

    Since the first studies on dynamic topography and basin evolution, low-dipping subduction has been related to intracontinental, long-wavelength and high-amplitude subsidence, whereas retreating to normal subduction systems to uplift. This was proposed to explain the Cretaceous-early Cenozoic topographic evolution of the western US. However, modern flat-slab and slab-retreating segments of South America do not record such a subsidence and uplift patterns. For example, the flat slab of Peru at ˜10°SL, related to the subduction of the Nazca Ridge, underlies an elevated promontory known as the Fitzcarrald Arch. The Argentine flat-slab at ˜31°SL associated to the subduction of the Juan Fernandez Ridge underlies a high-elevated intermontane system known as the Pampean broken foreland. Both upwarping features are younger than 7 Ma and contemporaneous with the arrival of flat subduction to these segments. In order to shed light into this controversy, we calculate dynamic topography along the Andean flat-slab segments using the Hager and O'Connell (1981) instantaneous flow formulation, an accurate reconstruction of the slab geometry along the central Andes and a density contrast between the flat slabs and the country mantle close to zero (△δ≈0) in order to simulate a buoyant oceanic lithosphere. We demonstrate that dynamic subsidence develops only at the leading edge of flat subduction, where the slabs plunge >30°, whereas the flatter slabs reproduce minor or no dynamic topography signals. These results agree with geological and geophysical proxies. Along the Argentine Plains, the account for a accumulated relief of ˜200 m, which might be considered as an "observed dynamic subsidence" signal (given that no tectonic activity has been recorded in this region since the Cretaceous to explain this surface topography). This gives a ˜0.03 mm/yr dynamic subsidence rate that are curiously similar to the exhumations estimated by low-temperature thermochronology along the

  19. An imbalance in the deep water cycle at subduction zones: The potential importance of the fore-arc mantle

    Science.gov (United States)

    Ribeiro, Julia M.; Lee, Cin-Ty A.

    2017-12-01

    The depth of slab dehydration is thought to be controlled by the thermal state of the downgoing slab: cold slabs are thought to mostly dehydrate beneath the arc front while warmer slabs should mostly dehydrate beneath the fore-arc. Cold subduction zone lavas are thus predicted to have interacted with greater extent of water-rich fluids released from the downgoing slab, and should thus display higher water content and be elevated in slab-fluid proxies (i.e., high Ba/Th, H2O/Ce, Rb/Th, etc.) compared to hot subduction zone lavas. Arc lavas, however, display similar slab-fluid signatures regardless of the thermal state of the slab, suggesting more complexity to volatile cycling in subduction zones. Here, we explore whether the serpentinized fore-arc mantle may be an important fluid reservoir in subduction zones and whether it can contribute to arc magma generation by being dragged down with the slab. Using simple mass balance and fluid dynamics calculations, we show that the dragged-down fore-arc mantle could provide enough water (∼7-78% of the total water injected at the trenches) to account for the water outfluxes released beneath the volcanic arc. Hence, we propose that the water captured by arc magmas may not all derive directly from the slab, but a significant component may be indirectly slab-derived via dehydration of dragged-down fore-arc serpentinites. Fore-arc serpentinite dehydration, if universal, could be a process that explains the similar geochemical fingerprint (i.e., in slab fluid proxies) of arc magmas.

  20. Thermal State, Slab Metamorphism, and Interface Seismicity in the Cascadia Subduction Zone Based On 3-D Modeling

    Science.gov (United States)

    Ji, Yingfeng; Yoshioka, Shoichi; Banay, Yuval A.

    2017-09-01

    Giant earthquakes have repeatedly ruptured the Cascadia subduction zone, and similar earthquakes will likely also occur there in the near future. We employ a 3-D time-dependent thermomechanical model that incorporates an up-to-date description of the slab geometry to study the Cascadia subduction thrust. Results show a distinct band of 3-D slab dehydration that extends from Vancouver Island to the Seattle Basin and farther southward to the Klamath Mountains in northern California, where episodic tremors cluster. This distribution appears to include a region of increased dehydration in northern Cascadia. The phenomenon of heterogeneous megathrust seismicity associated with oblique subduction suggests that the presence of fluid-rich interfaces generated by slab dehydration favors megathrust seismogenesis in the northern part of this zone. The thin, relatively weakly metamorphosed Explorer, Juan de Fuca, and Gorda Plates are associated with an anomalous lack of thrust earthquakes, and metamorphism that occurs at temperatures of 500-700°C near the Moho discontinuity may represent a key factor in explaining the presence of the associated episodic tremor and slip (ETS), which requires a young oceanic plate to subduct at a small dip angle, as is the case in Cascadia and southwestern Japan. The 3-D intraslab dehydration distribution suggests that the metamorphosed plate environment is more complex than had previously been believed, despite the existence of channeling vein networks. Slab amphibolization and eclogitization near the continental Moho depth is thus inferred to account for the resultant overpressurization at the interface, facilitating the generation of ETS and the occurrence of small to medium thrust earthquakes beneath Cascadia.

  1. The 2016 Kaikōura earthquake: Simultaneous rupture of the subduction interface and overlying faults

    Science.gov (United States)

    Wang, Teng; Wei, Shengji; Shi, Xuhua; Qiu, Qiang; Li, Linlin; Peng, Dongju; Weldon, Ray J.; Barbot, Sylvain

    2018-01-01

    The distribution of slip during an earthquake and how it propagates among faults in the subduction system play a major role in seismic and tsunami hazards, yet they are poorly understood because offshore observations are often lacking. Here we derive the slip distribution and rupture evolution during the 2016 Mw 7.9 Kaikōura (New Zealand) earthquake that reconcile the surface rupture, space geodetic measurements, seismological and tsunami waveform records. We use twelve fault segments, with eleven in the crust and one on the megathrust interface, to model the geodetic data and match the major features of the complex surface ruptures. Our modeling result indicates that a large portion of the moment is distributed on the subduction interface, making a significant contribution to the far field surface deformation and teleseismic body waves. The inclusion of local strong motion and teleseismic waveform data in the joint inversion reveals a unilateral rupture towards northeast with a relatively low averaged rupture speed of ∼1.5 km/s. The first 30 s of the rupture took place on the crustal faults with oblique slip motion and jumped between fault segments that have large differences in strike and dip. The peak moment release occurred at ∼65 s, corresponding to simultaneous rupture of both plate interface and the overlying splay faults with rake angle changes progressively from thrust to strike-slip. The slip on the Papatea fault produced more than 2 m of offshore uplift, making a major contribution to the tsunami at the Kaikōura station, while the northeastern end of the rupture can explain the main features at the Wellington station. Our inversions and simulations illuminate complex up-dip rupture behavior that should be taken into consideration in both seismic and tsunami hazard assessment. The extreme complex rupture behavior also brings new challenges to the earthquake dynamic simulations and understanding the physics of earthquakes.

  2. Bulk rheology and simulated episodic tremor and slip within a numerically-modeled block-dominated subduction melange

    Science.gov (United States)

    Webber, S.; Ellis, S. M.; Fagereng, A.

    2015-12-01

    We investigate the influence of melange rheology in a subduction thrust interface on stress and slip cycling constrained by observations from an exhumed subduction complex at Chrystalls Beach, New Zealand. A two-phase mélange dominated by large, competent brittle-viscous blocks surrounded by a weak non-linear viscous matrix is numerically modeled, and the evolution of bulk stress are analysed as the domain deforms. The models produce stress cycling behaviour under constant shear strain rate boundary conditions for a wide range of physical conditions that roughly corresponds to depths and strain rates calculated for instrumentally observed episodic tremor and slip (ETS) in presently-deforming subduction thrust interfaces. Stress cycling is accompanied by mixed brittle plastic-viscous deformation, and occurs as a consequence of geometric reorganisation and the progressive development and breakdown of stress bridges as blocks mutually obstruct one another. We argue that periods of low differential stress correspond to periods of rapid mixed-mode deformation and ETS. Stress cycling episodicities are a function of shear strain rate and pressure/temperature conditions at depth. The time period of stress cycling is principally controlled by the geometry (block distribution and density through time) and stress cycling amplitudes are controlled by effective stress. The duration of stress cycling events in the models (months-years) and rapid strain rates are comparable to instrumentally observed ETS. Shear strain rates are 1 - 2 orders of magnitude slower between stress cycling events, suggesting episodic return times within a single model domain are long duration (> centennial timescales), assuming constant flow stress. Finally, we derive a bulk viscous flow law for block dominated subduction mélanges for conditions 300 - 500°C and elevated pore fluid pressures. Bulk flow laws calculated for block-dominated subduction mélanges are non-linear, owing to a combination of

  3. What favors the occurrence of subduction mega-earthquakes?

    Science.gov (United States)

    Brizzi, Silvia; Funiciello, Francesca; Corbi, Fabio; Sandri, Laura; van Zelst, Iris; Heuret, Arnauld; Piromallo, Claudia; van Dinther, Ylona

    2017-04-01

    Most of mega-earthquakes (MEqs; Mw > 8.5) occur at shallow depths along the subduction thrust fault (STF). The contribution of each subduction zone to the globally released seismic moment is not homogenous, as well as the maximum recorded magnitude MMax. Highlighting the ingredients likely responsible for MEqs nucleation has great implications for hazard assessment. In this work, we investigate the conditions favoring the occurrence of MEqs with a multi-disciplinary approach based on: i) multivariate statistics, ii) analogue- and iii) numerical modelling. Previous works have investigated the potential dependence between STF seismicity and various subduction zone parameters using simple regression models. Correlations are generally weak due to the limited instrumental seismic record and multi-parameter influence, which make the forecasting of the potential MMax rather difficult. To unravel the multi-parameter influence, we perform a multivariate statistical study (i.e., Pattern Recognition, PR) of the global database on convergent margins (Heuret et al., 2011), which includes seismological, geometrical, kinematic and physical parameters of 62 subduction segments. PR is based on the classification of objects (i.e., subduction segments) belonging to different classes through the identification of possible repetitive patterns. Tests have been performed using different MMax datasets and combination of inputs to indirectly test the stability of the identified patterns. Results show that the trench-parallel width of the subducting slab (Wtrench) and the sediment thickness at the trench (Tsed) are the most recurring parameters for MEqs occurrence. These features are mostly consistent, independently of the MMax dataset and combination of inputs used for the analysis. MEqs thus seem to be promoted for high Wtrench and Tsed, as their combination may potentially favor extreme (i.e., in the order of thousands of km) trench-parallel rupture propagation. To tackle the

  4. Nonuniform subduction of the Indian crust beneath the Himalayas.

    Science.gov (United States)

    Guo, Xiaoyu; Li, Wenhui; Gao, Rui; Xu, Xiao; Li, Hongqiang; Huang, Xingfu; Ye, Zhuo; Lu, Zhanwu; Klemperer, Simon L

    2017-10-02

    Himalayan tectonic activity is triggered by downward penetration of the Indian plate beneath the Asian plate. The subsurface geometry of this interaction has not been fully investigated. This study presents novel constraints on this geometry provided by two newly obtained, deep seismic reflection profiles. The profiles cover 100- and 60-km transects across the Yarlung-Zangbo suture of the Himalaya-Tibet orogen at c. 88°E. Both profiles show a crustal-scale outline of the subducting Indian crust. This outline clearly shows Indian understhrusting southern Tibet, but only to a limited degree. When combined with a third seismic reflection profile of the western Himalayas, the new profiles reveal progressive, eastward steepening and shortening in the horizontal advance of the subducting Indian crust.

  5. Reaction-induced rheological weakening enables oceanic plate subduction.

    Science.gov (United States)

    Hirauchi, Ken-Ichi; Fukushima, Kumi; Kido, Masanori; Muto, Jun; Okamoto, Atsushi

    2016-08-26

    Earth is the only terrestrial planet in our solar system where an oceanic plate subducts beneath an overriding plate. Although the initiation of plate subduction requires extremely weak boundaries between strong plates, the way in which oceanic mantle rheologically weakens remains unknown. Here we show that shear-enhanced hydration reactions contribute to the generation and maintenance of weak mantle shear zones at mid-lithospheric depths. High-pressure friction experiments on peridotite gouge reveal that in the presence of hydrothermal water, increasing strain and reactions lead to an order-of-magnitude reduction in strength. The rate of deformation is controlled by pressure-solution-accommodated frictional sliding on weak hydrous phyllosilicate (talc), providing a mechanism for the 'cutoff' of the high peak strength at the brittle-plastic transition. Our findings suggest that infiltration of seawater into transform faults with long lengths and low slip rates is an important controlling factor on the initiation of plate tectonics on terrestrial planets.

  6. The dominant surface-topography contributions of individual subduction parameters

    Science.gov (United States)

    Crameri, Fabio; Lithgow-Bertelloni, Carolina; Tackley, Paul

    2017-04-01

    It is no secret, not any longer, that dynamic processes below the plate exert a significant contribution to the elevation of the plate at the surface (e.g., Flament et al., 2013). We have therefore studied* the individual impact each and every major subduction parameter has on surface topography. This allows us to qualitatively compare the different sources amongst each other, and to quantify their actual potential to vertically deflect the surface. The gained knowledge from this compilation is crucial: We might finally be able to link the directly-observable surface topography to the dynamics (buoyancy, rheology, and geometry) of the subduction system. *This study is made possible by the efficient convection code StagYY (Tackley 2008), the largely-automated post-processing and visualisation toolbox StagLab (www.fabiocrameri.ch/software), and crucial model developments (Crameri and Tackley, 2015; Crameri et al., G-cubed, submitted, Crameri and Lithgow-Bertelloni, Tectonophysics, submitted). REFERENCES 
Flament, N., M. Gurnis, and R. D. Müller (2013), A review of observations and models of dynamic topography, Lithosphere, 5(2), 189-210. Crameri, F., and P. J. Tackley (2015), Parameters controlling dynamically self-consistent plate tectonics and single-sided subduction in global models of mantle convection, J. Geophys. Res. Solid Earth, 120(5), 3680-3706. Crameri, F., C. R. Lithgow-Bertelloni, and P. J. Tackley (submitted), The dynamical control of subduction parameters on surface topography, Geochem. Geophys. Geosyst. Crameri, F., and C. R. Lithgow-Bertelloni (submitted), Dynamic Mantle-Transition-Zone Controls on Upper-Plate Tilt, Tectonophysics. Tackley, P.J (2008) Modelling compressible mantle convection with large viscosity contrasts in a three- dimensional spherical shell using the yin-yang grid. Physics of the Earth and Planetary Interiors 171(1-4), 7-18.

  7. Subducting characteristic of the Pacific slab beneath northeast China

    Science.gov (United States)

    Jiang, G.; Zhang, G.; Xu, Y.

    2012-12-01

    The volcanoes locating in northeast China are very active. Some researchers consider that the origin of volcanoes is closely related to the subducting western Pacific plate and the upwelling asthenosphere. The thickness and the existing range of the subducted plate are not clear as far although the seismic tomography results obviously show that the Pacific plate exists below the volcano region. Therefore, in this study, we adopted the method combining the teleseismic tomography with travel time forward modeling to further study the velocity structure beneath northeast China, especially the precise model of subducted Pacific plate. Our results show that (1) the average thickness and velocity perturbation of slab is 85 km and 1%, respectively, and the slab has not been thickened compared with the previous result of the Japan Sea; (2) the Pacific plate subducted into the mantle transition zone with a shallow dip angle, and changed horizontally when it touched the bottom of mantle transition zone, and extended westward to Longitude 127°E and then stops over there; (3) the horizontal slab locates right below the volcano region. These above features help people understand the origin of intraplate volcanoes and the geodynamical process better. (a) Tomographic result along 43°N. Red and blue colors represent the high and low velocity anomalies, respectively, and the scale is shown at the right-bottom; The profile line is shown in (b); The black triangles represent the volcanoes locating near the profile; The black solid and dashed lines show the depths of upper and lower boundaries of Pacific plate, respectively. The red dots represent the deep earthquakes around the profile. (b) Location of profile AA' along 43°N. Black triangles denote volcanoes; White squares represent the stations; Blue contours denote the depth of upper boundary of Pacific plate; Black and red dots represent the deep epicenters.

  8. Ups and downs in western Crete (Hellenic subduction zone).

    Science.gov (United States)

    Tiberti, Mara Monica; Basili, Roberto; Vannoli, Paola

    2014-07-14

    Studies of past sea-level markers are commonly used to unveil the tectonic history and seismic behavior of subduction zones. We present new evidence on vertical motions of the Hellenic subduction zone as resulting from a suite of Late Pleistocene - Holocene shorelines in western Crete (Greece). Shoreline ages obtained by AMS radiocarbon dating of seashells, together with the reappraisal of shoreline ages from previous works, testify a long-term uplift rate of 2.5-2.7 mm/y. This average value, however, includes periods in which the vertical motions vary significantly: 2.6-3.2 mm/y subsidence rate from 42 ka to 23 ka, followed by ~7.7 mm/y sustained uplift rate from 23 ka to present. The last ~5 ky shows a relatively slower uplift rate of 3.0-3.3 mm/y, yet slightly higher than the long-term average. A preliminary tectonic model attempts at explaining these up and down motions by across-strike partitioning of fault activity in the subduction zone.

  9. Water and the oxidation state of subduction zone magmas.

    Science.gov (United States)

    Kelley, Katherine A; Cottrell, Elizabeth

    2009-07-31

    Mantle oxygen fugacity exerts a primary control on mass exchange between Earth's surface and interior at subduction zones, but the major factors controlling mantle oxygen fugacity (such as volatiles and phase assemblages) and how tectonic cycles drive its secular evolution are still debated. We present integrated measurements of redox-sensitive ratios of oxidized iron to total iron (Fe3+/SigmaFe), determined with Fe K-edge micro-x-ray absorption near-edge structure spectroscopy, and pre-eruptive magmatic H2O contents of a global sampling of primitive undegassed basaltic glasses and melt inclusions covering a range of plate tectonic settings. Magmatic Fe3+/SigmaFe ratios increase toward subduction zones (at ridges, 0.13 to 0.17; at back arcs, 0.15 to 0.19; and at arcs, 0.18 to 0.32) and correlate linearly with H2O content and element tracers of slab-derived fluids. These observations indicate a direct link between mass transfer from the subducted plate and oxidation of the mantle wedge.

  10. Extending Alaska's plate boundary: tectonic tremor generated by Yakutat subduction

    Science.gov (United States)

    Wech, Aaron G.

    2016-01-01

    The tectonics of the eastern end of the Alaska-Aleutian subduction zone are complicated by the inclusion of the Yakutat microplate, which is colliding into and subducting beneath continental North America at near-Pacific-plate rates. The interaction among these plates at depth is not well understood, and further east, even less is known about the plate boundary or the source of Wrangell volcanism. The drop-off in Wadati-Benioff zone (WBZ) seismicity could signal the end of the plate boundary, the start of aseismic subduction, or a tear in the downgoing plate. Further compounding the issue is the possible presence of the Wrangell slab, which is faintly outlined by an anemic, eastward-dipping WBZ beneath the Wrangell volcanoes. In this study, I performed a search for tectonic tremor to map slow, plate-boundary slip in south-central Alaska. I identified ∼11,000 tremor epicenters, which continue 85 km east of the inferred Pacific plate edge marked by WBZ seismicity. The tremor zone coincides with the edges of the downgoing Yakutat terrane, and tremors transition from periodic to continuous behavior as they near the aseismic Wrangell slab. I interpret tremor to mark slow, semicontinuous slip occurring at the interface between the Yakutat and North America plates. The slow slip region lengthens the megathrust interface beyond the WBZ and may provide evidence for a connection between the Yakutat slab and the aseismic Wrangell slab.

  11. The relationship between orogenesis, terrane accretion and the subduction of oceanic ridges in the Ecuadorian andes

    Science.gov (United States)

    Spikings, R.; Winkler, W.; Seward, D.; Hughes, R.; Handler, R.; Crowhurst, P.

    2003-04-01

    Oceanic hotspot activity, generating large oceanic igneous plateau provinces, plate rearrangements and the generation of new spreading centers since at least 90 Ma have formed large structural, thickness and density heterogeneities in the approaching and subducting oceanic crust offshore NW South America (SOAM). Various oceanic allochthonous terranes comprise western Ecuador and the relatively thick and buoyant Carnegie Ridge is being subducted. We present 40Ar/39Ar, fission track (FT) and (U-Th/He) data from i) the Eastern Cordillera and the Amotape Complex, which define the palaeo-continental margin, ii) the Western Cordillera, which is built upon allochthonous, oceanic crust and iii) a tectonic mélange at the ocean-continent suture. 40Ar/39Ar ages and FT data from exotic, Triassic blocks within the ocean-continent suture record elevated cooling rates of plateau basalts and the continental margin. 40Ar/39Ar ages and FT data from the palaeo-continental margin show that the entire contemporaneous continental margin was being cooled by rapid tectonic exhumation (combined with geochemical analyses, suggest that these periods of orogenesis were driven by stress imposed by the collision of terranes that originated at the Caribbean Plateau. Distinct periods of rapid cooling and exhumation of fault blocks in the W. Cordillera and the northern E. Cordillera occurred at ˜15 and ˜9 Ma. Cooling at ˜15 Ma was driven by the collision of the Carnegie Ridge with the trench at ˜15 Ma. The elevated, compressive stress field gave rise to a complex transcurrent system, resulting in uplift, exhumation and cooling in the northern E. Cordillera and extension in the southern E. Cordillera. Finally, FT and (U-Th)/He data record rapid cooling in the northern E. Cordillera and parts of the W. Cordillera at ˜6-5 Ma, suggesting that the middle Miocene transcurrent system was reactivated by thrust tectonics during the late Miocene, giving rise to the Interandean Valley, which split the

  12. Deformation fabrics of natural blueschists and implications for seismic anisotropy in subducting oceanic crust

    Science.gov (United States)

    Kim, Daeyeong; Katayama, Ikuo; Michibayashi, Katsuyoshi; Tsujimori, Tatsuki

    2013-09-01

    Investigations of microstructures are crucial if we are to understand the seismic anisotropy of subducting oceanic crust, and here we report on our systematic fabric analyses of glaucophane, lawsonite, and epidote in naturally deformed blueschists from the Diablo Range and Franciscan Complex in California, and the Hida Mountains in Japan. Glaucophanes in the analyzed samples consist of very fine grains that are well aligned along the foliation and have high aspect ratios and strong crystal preferred orientations (CPOs) characterized by a (1 0 0)[0 0 1] pattern. These characteristics, together with a bimodal distribution of grain sizes from some samples, possibly indicate the occurrence of dynamic recrystallization for glaucophane. Although lawsonite and epidote display high aspect ratios and a strong CPO of (0 0 1)[0 1 0], the occurrence of straight grain boundaries and euhedral crystals indicates that rigid body rotation was the dominant deformation mechanism. The P-wave (AVP) and S-wave (AVS) seismic anisotropies of glaucophane (AVP = 20.4%, AVS = 11.5%) and epidote (AVP = 9.0%, AVS = 8.0%) are typical of the crust; consequently, the fastest propagation of P-waves is parallel to the [0 0 1] maxima, and the polarization of S-waves parallel to the foliation can form a trench-parallel seismic anisotropy owing to the slowest VS polarization being normal to the subducting slab. The seismic anisotropy of lawsonite (AVP = 9.6%, AVS = 19.9%) is characterized by the fast propagation of P-waves subnormal to the lawsonite [0 0 1] maxima and polarization of S-waves perpendicular to the foliation and lineation, which can generate a trench-normal anisotropy. The AVS of lawsonite blueschist (5.6-9.2%) is weak compared with that of epidote blueschist (8.4-11.1%). Calculations of the thickness of the anisotropic layer indicate that glaucophane and lawsonite contribute to the trench-parallel and trench-normal seismic anisotropy beneath NE Japan, but not to that beneath the Ryukyu

  13. Reevaluating carbon fluxes in subduction zones, what goes down, mostly comes up.

    Science.gov (United States)

    Kelemen, Peter B; Manning, Craig E

    2015-07-28

    Carbon fluxes in subduction zones can be better constrained by including new estimates of carbon concentration in subducting mantle peridotites, consideration of carbonate solubility in aqueous fluid along subduction geotherms, and diapirism of carbon-bearing metasediments. Whereas previous studies concluded that about half the subducting carbon is returned to the convecting mantle, we find that relatively little carbon may be recycled. If so, input from subduction zones into the overlying plate is larger than output from arc volcanoes plus diffuse venting, and substantial quantities of carbon are stored in the mantle lithosphere and crust. Also, if the subduction zone carbon cycle is nearly closed on time scales of 5-10 Ma, then the carbon content of the mantle lithosphere + crust + ocean + atmosphere must be increasing. Such an increase is consistent with inferences from noble gas data. Carbon in diamonds, which may have been recycled into the convecting mantle, is a small fraction of the global carbon inventory.

  14. Louisville seamount subduction and its implication on mantle flow beneath the central Tonga-Kermadec arc.

    Science.gov (United States)

    Timm, Christian; Bassett, Daniel; Graham, Ian J; Leybourne, Matthew I; de Ronde, Cornel E J; Woodhead, Jon; Layton-Matthews, Daniel; Watts, Anthony B

    2013-01-01

    Subduction of intraplate seamounts beneath a geochemically depleted mantle wedge provides a seldom opportunity to trace element recycling and mantle flow in subduction zones. Here we present trace element and Sr, Nd and Pb isotopic compositions of lavas from the central Tonga-Kermadec arc, west of the contemporary Louisville-Tonga trench intersection, to provide new insights into the effects of Louisville seamount subduction. Elevated (206)Pb/(204)Pb, (208)Pb/(204)Pb, (86)Sr/(87)Sr in lavas from the central Tonga-Kermadec arc front are consistent with localized input of subducted alkaline Louisville material (lavas and volcaniclastics) into sub-arc partial melts. Furthermore, absolute Pacific Plate motion models indicate an anticlockwise rotation in the subducted Louisville seamount chain that, combined with estimates of the timing of fluid release from the subducting slab, suggests primarily trench-normal mantle flow beneath the central Tonga-Kermadec arc system.

  15. Collapse risk of buildings in the Pacific Northwest region due to subduction earthquakes

    Science.gov (United States)

    Raghunandan, Meera; Liel, Abbie B.; Luco, Nicolas

    2015-01-01

    Subduction earthquakes similar to the 2011 Japan and 2010 Chile events will occur in the future in the Cascadia subduction zone in the Pacific Northwest. In this paper, nonlinear dynamic analyses are carried out on 24 buildings designed according to outdated and modern building codes for the cities of Seattle, Washington, and Portland, Oregon. The results indicate that the median collapse capacity of the ductile (post-1970) buildings is approximately 40% less when subjected to ground motions from subduction, as compared to crustal earthquakes. Buildings are more susceptible to earthquake-induced collapse when shaken by subduction records (as compared to crustal records of the same intensity) because the subduction motions tend to be longer in duration due to their larger magnitude and the greater source-to-site distance. As a result, subduction earthquakes are shown to contribute to the majority of the collapse risk of the buildings analyzed.

  16. Geodynamic Modeling of the Subduction Zone around the Japanese Islands

    Science.gov (United States)

    Honda, S.

    2017-06-01

    In this review, which focuses on our research, we describe the development of the thermomechanical modeling of subduction zones, paying special attention to those around the Japanese Islands. Without a sufficient amount of data and observations, models tended to be conceptual and general. However, the increasing power of computational tools has resulted in simple analytical and numerical models becoming more realistic, by incorporating the mantle flow around the subducting slab. The accumulation of observations and data has made it possible to construct regional models to understand the detail of the subduction processes. Recent advancements in the study of the seismic tomography and geology around the Japanese Islands has enabled new aspects of modeling the mantle processes. A good correlation between the seismic velocity anomalies and the finger-like distribution of volcanoes in northeast Japan has been recognized and small-scale convection (SSC) in the mantle wedge has been proposed to explain such a feature. The spatial and temporal evolution of the distribution of past volcanoes may reflect the characteristics of the flow in the mantle wedge, and points to the possibility of the flip-flopping of the finger-like pattern of the volcano distribution and the migration of volcanic activity from the back-arc side to the trench side. These observations are found to be qualitatively consistent with the results of the SSC model. We have also investigated the expected seismic anisotropy in the presence of SSC. The fast direction of the P-wave anisotropy generally shows the trench-normal direction with a reduced magnitude compared to the case without SSC. An analysis of full 3D seismic anisotropy is necessary to confirm the existence and nature of SSC. The 3D mantle flow around the subduction zone of plate-size scale has been modeled. It was found that the trench-parallel flow in the sub-slab mantle around the northern edge of the Pacific plate at the junction between

  17. Characterizing Seismic Anisotropy across the Peruvian Flat-Slab Subduction Zone: Implications for the Dynamics of Flat-Slabs

    Science.gov (United States)

    Eakin, Caroline; Long, Maureen; Beck, Susan; Wagner, Lara; Tavera, Hernando

    2014-05-01

    Although 10% of subduction zones worldwide today exhibit shallow or flat subduction, we are yet to fully understand how and why these slabs go flat. An excellent study location for such a problem is in Peru, where the largest region of flat-subduction currently exists, extending ~1500 km in length (from 3 °S to 15 °S) and ~300 km in width. Across this region we investigate the pattern of seismic anisotropy, an indicator for past and/or ongoing deformation in the upper mantle. To achieve this we conduct shear wave splitting analyzes at 40 broadband stations from the PULSE project (PerU Lithosphere and Slab Experiment). These stations were deployed for 2+ years across the southern half of the Peruvian flat-slab region. We present detailed shear wave splitting results for both teleseismic events (such as SKS, SKKS, PKS, sSKS) that sample the upper mantle column beneath the stations as well as direct S from local events that constrain anisotropy in the upper portion of the subduction zone. We analyze the variability of our results with respect to initial polarizations, ray paths, and frequency content as well as spatial variability between stations as the underlying slab morphology changes. Teleseismic results show predominately NW-SE fast polarizations (trench oblique to sub-parallel) over the flat-slab region east of Lima. These results are consistent with observations of more complex multi-layered anisotropy beneath a nearby permanent station (NNA) that suggests a trench-perpendicular fast direction in the lowest layer in the sub-slab mantle. Further south, towards the transition to steeper subduction, the splitting pattern becomes increasingly dominated by null measurements. Over to the east however, beyond Cuzco, where the mantle wedge might begin to play a role, we record fast polarizations quasi-parallel to the local slab contours. Local S results indicate the presence of weak (delay times typically less than 0.5 seconds) and heterogeneous supra

  18. Subduction of a buoyant plateau at the Manila Trench: Tomographic evidence and geodynamic implications

    Science.gov (United States)

    Fan, Jianke; Zhao, Dapeng; Dong, Dongdong

    2016-02-01

    We determined P-wave tomographic images by inverting a large number of arrival-time data from 2749 local earthquakes and 1462 teleseismic events, which are used to depict the three-dimensional morphology of the subducted Eurasian Plate along the northern segment of the Manila Trench. Dramatic changes in the dip angle of the subducted Eurasian Plate are revealed from the north to the south, being consistent with the partial subduction of a buoyant plateau beneath the Luzon Arc. Slab tears may exist along the edges of the buoyant plateau within the subducted plate induced by the plateau subduction, and the subducted lithosphere may be absent at depths greater than 250 km at ˜19°N and ˜21°N. The subducted buoyant plateau is possibly oriented toward NW-SE, and the subducted plate at ˜21°N is slightly steeper than that at ˜19°N. These results may explain why the western and eastern volcanic chains in the Luzon Arc are separated by ˜50 km at ˜18°N, whereas they converge into a single volcanic chain northward, which may be related to the oblique subduction along the Manila Trench caused by the northwestern movement of the Philippine Sea Plate. A low-velocity zone is revealed at depths of 20-200 km beneath the Manila Accretionary Prism at ˜22°N, suggesting that the subduction along the Manila Trench may stop there and the collision develops northward. The Taiwan Orogeny may originate directly from the subduction of the buoyant plateau, because the initial time of the Taiwan Orogeny is coincident with that of the buoyant plateau subduction.

  19. Plate tectonics on the Earth triggered by plume-induced subduction initiation.

    Science.gov (United States)

    Gerya, T V; Stern, R J; Baes, M; Sobolev, S V; Whattam, S A

    2015-11-12

    Scientific theories of how subduction and plate tectonics began on Earth--and what the tectonic structure of Earth was before this--remain enigmatic and contentious. Understanding viable scenarios for the onset of subduction and plate tectonics is hampered by the fact that subduction initiation processes must have been markedly different before the onset of global plate tectonics because most present-day subduction initiation mechanisms require acting plate forces and existing zones of lithospheric weakness, which are both consequences of plate tectonics. However, plume-induced subduction initiation could have started the first subduction zone without the help of plate tectonics. Here, we test this mechanism using high-resolution three-dimensional numerical thermomechanical modelling. We demonstrate that three key physical factors combine to trigger self-sustained subduction: (1) a strong, negatively buoyant oceanic lithosphere; (2) focused magmatic weakening and thinning of lithosphere above the plume; and (3) lubrication of the slab interface by hydrated crust. We also show that plume-induced subduction could only have been feasible in the hotter early Earth for old oceanic plates. In contrast, younger plates favoured episodic lithospheric drips rather than self-sustained subduction and global plate tectonics.

  20. Porosity and Salt Content Determine if Subduction Can Occur in Europa's Ice Shell

    Science.gov (United States)

    Johnson, Brandon C.; Sheppard, Rachel Y.; Pascuzzo, Alyssa C.; Fisher, Elizabeth A.; Wiggins, Sean E.

    2017-12-01

    Motivated by recent evidence for subduction in Europa's ice shell, we explore the geophysical feasibility of this process. Here we construct a simple model to track the evolution of porosity and temperature within a slab that is forced to subduct. We also vary the initial salt content in Europa's ice shell and determine the buoyancy of our simulated subducting slab. We find that porosity and salt content play a dominant role in determining whether the slab is nonbuoyant and subduction in Europa's ice shell is actually possible. Generally, we find that initially low porosities and high salt contents within the conductive lid are more conducive to subduction. If salt contents are laterally homogenous, and Europa has a reasonable surface porosity of ϕ0 = 0.1, the conductive portion of Europa's shell must have salt contents exceeding 22% for subduction to occur. However, if salt contents are laterally heterogeneous, with salt contents varying by a few percent, subduction may occur for a surface porosity of ϕ0 = 0.1 and overall salt contents of 5%. Thus, we argue that under plausible conditions, subduction in Europa's ice shell is possible. Moreover, assuming that subduction is actively occurring or has occurred in Europa's recent past provides important constraints on the structure and composition of the ice shell.

  1. A new integrated tectonic model for the Mesozoic-Early Cenozoic subduction, spreading, accretion and collision history of Tethys adjacent to the southern margin of Eurasia (NE Turkey)

    Science.gov (United States)

    Robertson, Alastair; Parlak, Osman; Ustaömer, Timur; Taslı, Kemal; İnan, Nurdan; Dumitrica, Paulian; Karaoǧlan, Fatih

    2014-05-01

    Cretaceous age for the E Pontide ophiolites, with important implications for alternative tectonic hypotheses. The two-subduction-zone hypothesis is supported by sedimentological and structural studies of the volcanic-sedimentary melange and of the sedimentary thrust sheets within the suture zone. Geochemical studies of oceanic basaltic rocks in the melange and also new biostratigraphic dating of radiolarites and calcareous microfossils within pelagic and redeposited deep-sea/slope sediments add to the picture. Taken together, the evidence suggests the former existence of both an oceanic and a continental margin subduction complex that are now amalgamated within the suture zone. We propose the following tectonic hypothesis: Fragments of oceanic basaltic lithologies and their deep-sea sedimentary cover accreted to form a Jurassic-Cretaceous intra-oceanic subduction complex. Terrigenous and arc-derived volcaniclastic gravity flows and pelagic carbonates accumulated in a continental margin forearc basin, mainly during the Cretaceous. Subduction melange was first emplaced over the distal Eurasian margin during the Late Cretaceous owing to thickening of the accretionary prism. During suturing, the continental margin forearc basin was emplaced southwards over the oceanic-derived accretionary wedge. The Eurasian continental margin was imbricated and thrust northwards as collision proceeded. Final closure of the adjacent Tethys took place prior to late Middle Eocene. This was followed by marine transgression and the accumulation of non-marine to shallow-marine sediments, including Nummulitic limestones. Regional correlations suggest that the double subduction zone hypothesis, notably involving Jurassic intra-oceanic spreading, is applicable to >1000 km of the Eurasian margin, specifically the Lesser Caucasus and possibly also the Central Pontides.

  2. Post-Eocene Subduction Dynamics and Mantle Flow beneath Western U.S.

    Science.gov (United States)

    Liu, L.; Zhou, Q.; Leonard, T.

    2015-12-01

    Both surface geology and mantle seismic images suggest a complex late Cenozoic history of mantle dynamics over western U.S. We try to understand this history by simulating the Farallon subduction since 40 Ma. Forward subduction models assimilating time dependent seafloor ages, plate kinematics and evolving plate boundaries suggest that the present-day 3D distribution of fast seismic anomalies below western U.S. mostly represent late Cenozoic slabs, which experienced multiple phases of segmentation during subduction because of their young age and small mechanical strength (Liu & Stegman, 2011). A major slab segmentation event occurred around mid-Miocene, with the resulting slab tear and induced asthenosphere upwelling correlating with the Steens-Columbia River flood basalts (SCRB) eruption both in space and in time (Liu & Stegman, 2012). This suggests that a mantle plume is not required for the formation of the SCRB. Segmentation of the Farallon slab generates rapid toroidal flows around the newly formed slab edges beneath the Cascadia arc. These mantle flows may affect both the pattern and composition of arc volcanism through transportation of oceanic asthenosphere material into the mantle wedge. Based on the forward model, we further test the influence of slow seismic anomalies on mantle dynamics. On the one hand, we explicitly input a deep hot anomaly to represent the putative Yellowstone plume. On the other hand, we develop a hybrid scheme that combines the adjoint inverse method with the high-resolution forward simulation approach, so that the present-day mantle seismic structure is entirely consistent with the convection model. Our preliminary results suggest that a hot plume could actively rise up only when it is several hundreds of kilometers away from the slabs, as is the case prior to 20 Ma. Subsequently, the plume is dominated by the surrounding slabs, resulting in an overall downwelling mantle flow. This suggests that a plume might have contributed to

  3. Chemical and oxygen isotope zonings in garnet from subducted continental crust record mineral replacement and metasomatism

    Science.gov (United States)

    Vho, Alice; Rubatto, Daniela; Regis, Daniele; Baumgartner, Lukas; Bouvier, Anne-Sophie

    2017-04-01

    Garnet is a key mineral in metamorphic petrology for constraining pressure, temperature and time paths. Garnet can preserve multiple growth stages due to its wide P-T stability field and the relatively slow diffusivity for major and trace elements at sub-solidus temperatures. Pressure-temperature-time-fluid paths of the host rock may be reconstructed by combining metamorphic petrology with microscale trace element and oxygen isotope measurements in garnet. Subduction zones represent relevant geological settings for geochemical investigation of element exchanges during aqueous fluid-rock interactions. The Sesia Zone consists of a complex continental sequence containing a variety of mono-metamorphic and poly-metamorphic lithologies such as metagranitoids, sediments and mafic boudins. The precursor Varisican-Permian amphibolite-facies basement (6-9 kbar 650-850°C; Lardeaux and Spalla, 1991; Robyr et al., 2013) experienced high pressure metamorphism (15-22 kbar 500-550°C; Regis, et al. 2014; Robyr et al., 2013) during Alpine subduction. In different lithologies of the Internal Complex (Eclogitic Micaschist Complex), including metabasites from the Ivozio Complex, Ti-rich metasediments from Val Malone and pre-Alpine Mn-quartzites associated to metagabbros from Cima Bonze, garnet is abundant and shows a variety of complex textures that cannot be reconciled with typical growth zoning, but indicate resorption and replacement processes and possible metasomatism. In-situ, microscale oxygen isotopes analysis of garnet zones was performed by ion microprobe with the SwissSIMS Cameca IMS 1280-HR at University of Lausanne and SHRIMP-SI at the Australian National University. Each sample has a distinct δ18O composition, and the δ18O values show different degrees of variation between domains. Homogeneously low values of element geochemistry and P-T modelling allows reconstructing the major stages of metasomatism, as well as identifying the nature of the fluid interacting with the

  4. Crustal Gravitational Potential Energy Change and Subduction Earthquakes

    Science.gov (United States)

    Zhu, P. P.

    2017-05-01

    Crustal gravitational potential energy (GPE) change induced by earthquakes is an important subject in geophysics and seismology. For the past forty years the research on this subject stayed in the stage of qualitative estimate. In recent few years the 3D dynamic faulting theory provided a quantitative solution of this subject. The theory deduced a quantitative calculating formula for the crustal GPE change using the mathematic method of tensor analysis under the principal stresses system. This formula contains only the vertical principal stress, rupture area, slip, dip, and rake; it does not include the horizontal principal stresses. It is just involved in simple mathematical operations and does not hold complicated surface or volume integrals. Moreover, the hanging wall vertical moving (up or down) height has a very simple expression containing only slip, dip, and rake. The above results are significant to investigate crustal GPE change. Commonly, the vertical principal stress is related to the gravitational field, substituting the relationship between the vertical principal stress and gravitational force into the above formula yields an alternative formula of crustal GPE change. The alternative formula indicates that even with lack of in situ borehole measured stress data, scientists can still quantitatively calculate crustal GPE change. The 3D dynamic faulting theory can be used for research on continental fault earthquakes; it also can be applied to investigate subduction earthquakes between oceanic and continental plates. Subduction earthquakes hold three types: (a) crust only on the vertical up side of the rupture area; (b) crust and seawater both on the vertical up side of the rupture area; (c) crust only on the vertical up side of the partial rupture area, and crust and seawater both on the vertical up side of the remaining rupture area. For each type we provide its quantitative formula of the crustal GPE change. We also establish a simplified model (called

  5. Stress and Strength of Seismogenic and Creeping Subduction Faults (Invited)

    Science.gov (United States)

    Wang, K.; Bilek, S. L.; Wada, I.; Gao, X.; Brown, L.

    2013-12-01

    Force balance studies of subduction zone forearcs constrained by earthquake focal mechanisms, active faulting, and topography suggest very weak subduction megathrusts. If represented by an effective coefficient of friction μ', the ratio of shear to normal stress at failure, the average μ' value of most megathrusts is about 0.03, seldom exceeding 0.06, an order of magnitude lower than fault strengths predicted by the Byerlee's law with hydrostatic pore fluid pressure. The μ' value required to explain heat flow observations using megathrust frictional heating modeling is usually also about 0.03, regardless of whether the megathrust is seismogenic or creeping. The mechanism for the weakness is not fully understood, although it must be a combined consequence of fault zone material, fault zone fabric, and pore fluid pressure. Prior to March 11, 2011, the Japan Trench was a rare exception where pervasive margin-normal compression of the upper plate made it difficult to infer megathrust strength. But wholesale stress reversal in much of the forearc due to the M 9 Tohoku earthquake dramatically verified the low-strength (μ' = 0.03) prediction of Wang and Suyehiro (1999, GRL 26(35), 2307-2310). This value translates to depth-dependant shear strength of roughly 10 MPa at 10 km and 30 MPa at 30 km. With regard to how fault strength and stress affect earthquake processes, several issues deserve special attention. (1) There is little doubt that no megathrust is 'strongly' locked, but creeping megathrusts can be either weaker or stronger than locked faults. In fact, subduction of extremely rugged seafloor causes creeping, despite strong resistance caused by geometrical incompatibilities. Physical meanings of regarding locked and creeping faults as 'strongly coupled' and 'weakly coupled', respectively, are in serious question. (2) A μ' value of 0.03-0.05 is a spatial average. For a smooth fault, even small changes in pore fluid pressure alone can cause local deviations from

  6. Fractal analysis of the spatial distribution of earthquakes along the Hellenic Subduction Zone

    Science.gov (United States)

    Papadakis, Giorgos; Vallianatos, Filippos; Sammonds, Peter

    2014-05-01

    The Hellenic Subduction Zone (HSZ) is the most seismically active region in Europe. Many destructive earthquakes have taken place along the HSZ in the past. The evolution of such active regions is expressed through seismicity and is characterized by complex phenomenology. The understanding of the tectonic evolution process and the physical state of subducting regimes is crucial in earthquake prediction. In recent years, there is a growing interest concerning an approach to seismicity based on the science of complex systems (Papadakis et al., 2013; Vallianatos et al., 2012). In this study we calculate the fractal dimension of the spatial distribution of earthquakes along the HSZ and we aim to understand the significance of the obtained values to the tectonic and geodynamic evolution of this area. We use the external seismic sources provided by Papaioannou and Papazachos (2000) to create a dataset regarding the subduction zone. According to the aforementioned authors, we define five seismic zones. Then, we structure an earthquake dataset which is based on the updated and extended earthquake catalogue for Greece and the adjacent areas by Makropoulos et al. (2012), covering the period 1976-2009. The fractal dimension of the spatial distribution of earthquakes is calculated for each seismic zone and for the HSZ as a unified system using the box-counting method (Turcotte, 1997; Robertson et al., 1995; Caneva and Smirnov, 2004). Moreover, the variation of the fractal dimension is demonstrated in different time windows. These spatiotemporal variations could be used as an additional index to inform us about the physical state of each seismic zone. As a precursor in earthquake forecasting, the use of the fractal dimension appears to be a very interesting future work. Acknowledgements Giorgos Papadakis wish to acknowledge the Greek State Scholarships Foundation (IKY). References Caneva, A., Smirnov, V., 2004. Using the fractal dimension of earthquake distributions and the

  7. Subduction and exhumation structures preserved in Cerro del Almirez HP metaserpentinites (Betic Cordillera, SE Spain)

    Science.gov (United States)

    Jabaloy-Sánchez, Antonio; López Sánchez-Vizcaíno, Vicente; Gómez-Pugnaire, María Teresa; Padrón-Navarta, José Alberto; Garrido, Carlos J.

    2014-05-01

    The Cerro del Almirez massif (Nevado-Filábride Complex, Betic Cordillera, SE Spain) is composed of antigorite serpentinite and chlorite harzburgite separated by a thin reaction front in a paleo-subduction setting. Structural analysis of ultramafic lithologies and metasedimentary host rocks provides information on the tectonic evolution of this massif during prograde metamorphism in a subduction zone and during subsequent exhumation. Here we report for the first time HP structures related to a subduction event underwent by ultramafic rocks of the Nevado-Filábride Complex. The oldest subduction-related structures are preserved in Atg-serpentinites: a penetrative S1 foliation and associated L1 stretching lineation were formed in a non-coaxial regime with a top-to-the-W sense of shearing. This planar linear fabric is crosscut by olivine ± Ti-clinohumite veins formed during the prograde breakdown of brucite and pre-metamorphic clinopyroxene at temperatures ranging from 465 to 500 ºC [1]. Veins occur as a system of decimetric long joints, some of them hybrid open and sheared veins with associated drag folds. They recorded embrittlement processes due to the release of 6% vol. H2O of the rock. S1 foliation can, however, be simultaneous with or be overgrown by olivine and/or tremolite porphyroblasts, product of the prograde reaction Di + Atg → Fo + Tr + H2O, which occurred at T > 600 ºC and P = 1.7-1.9 GPa [1]. Generation of S1/L1 fabric was followed by static annealing at ca. 680 ºC and 1.6-1.9 GPa [2]. The S1/L1 fabric in Atg-serpentinite is crosscut by the Atg-out isograd and overgrown by the Atg-serpentinite dehydration products that gave place to Chl-harzburgite. Peak metamorphic conditions of the Chl-harzburgite assemblage reached 680-710 ºC and 1.6-1.9 GPa [3]. Prograde Chl-harzburgite is crosscut by sets of conjugate zones associated to grain-size reduction of olivine grains [3]. These grain size reduction zones are interpreted as brittle structures

  8. Foreland sedimentary record of Andean mountain building during advancing and retreating subduction

    Science.gov (United States)

    Horton, Brian K.

    2016-04-01

    As in many ocean-continent (Andean-type) convergent margins, the South American foreland has long-lived (>50-100 Myr) sedimentary records spanning not only protracted crustal shortening, but also periods of neutral to extensional stress conditions. A regional synthesis of Andean basin histories is complemented by new results from the Mesozoic Neuquén basin system and succeeding Cenozoic foreland system of west-central Argentina (34-36°S) showing (1) a Late Cretaceous shift from backarc extension to retroarc contraction and (2) an anomalous mid-Cenozoic (~40-20 Ma) phase of sustained nondeposition. New detrital zircon U-Pb geochronological results from Jurassic through Neogene clastic deposits constrain exhumation of the evolving Andean magmatic arc, retroarc thrust belt, foreland basement uplifts, and distal eastern craton. Abrupt changes in sediment provenance and distal-to-proximal depositional conditions can be reconciled with a complex Mesozoic-Cenozoic history of extension, post-extensional thermal subsidence, punctuated tectonic inversion involving thick- and thin-skinned shortening, alternating phases of erosion and rapid accumulation, and overlapping igneous activity. U-Pb age distributions define the depositional ages of several Cenozoic stratigraphic units and reveal a major late middle Eocene-earliest Miocene (~40-20 Ma) hiatus in the Malargüe foreland basin. This boundary marks an abrupt shift in depositional conditions and sediment sources, from Paleocene-middle Eocene distal fluviolacustrine deposition of sediments from far western volcanic sources (Andean magmatic arc) and subordinate eastern cratonic basement (Permian-Triassic Choiyoi igneous complex) to Miocene-Quaternary proximal fluvial and alluvial-fan deposition of sediments recycled from emerging western sources (Malargüe fold-thrust belt) of Mesozoic basin fill originally derived from basement and magmatic arc sources. Neogene eastward advance of the fold-thrust belt involved thick

  9. Deformation fabrics of blueschist facies phengite-rich, epidote-glaucophane schists from Ring Mountain, California and implications for seismic anisotropy in subduction zone

    Science.gov (United States)

    Jung, H.; HA, Y.; Raymond, L. A.

    2016-12-01

    In many subduction zones, strong seismic anisotropy is observed. A part of the seismic anisotropy can be attributed to the subducting oceanic crust, which is transformed to blueschist facies rocks under high-pressure, high-temperature conditions. Because glaucophane, epidote, and phengite constituting the glaucophane schists are very anisotropic elastically, seismic anisotropy in the oceanic crust in hot subduction zones can be attributed to the lattice preferred orientation (LPO) of these minerals. We studied deformation fabrics and seismic properties of phengite-rich, epidote-glaucophane schists from the Franciscan Complex of Ring Mountain, California. The blueschist samples are mainly composed of glaucophane, epidote, and phengite, with minor garnet, titanite, and chlorite. Some samples contain abundant phengite (up to 40 %). We determined LPOs of minerals using SEM/EBSD and calculated seismic anisotropy of minerals and whole rocks. LPOs of glaucophane have [001] axes aligned subparallel to lineation, and both (110) poles and [100] axes subnormal to foliation. Epidote [001] axes are aligned subnormal to foliation, with both (110) and (010) poles subparallel to lineation. LPOs of phengite are characterized by maxima of [001] axes subnormal to foliation, and both (110) and (010) poles and [100] axes aligned in a girdle subparallel to foliation. Phengite showed much stronger seismic anisotropy (AVP = 42%, max.AVS = 37%) than glaucophane or epidote. Glaucophane schist with abundant phengite showed much stronger seismic anisotropy (AVP = 30%, max.AVS = 23%) than epidote-glaucophane schist without phengite (AVP = 13%, max.AVS = 9%). Therefore, phengite clearly can significantly affect seismic anisotropy of whole rocks. When the subduction angle of phengite-rich blueschist facies rocks is considered for a 2-D corner flow model, the polarization direction of fast S-waves for vertically propagating S-waves changed to a nearly trench-parallel direction for the subduction

  10. Rapid fore-arc extension and detachment-mode spreading following subduction initiation

    Science.gov (United States)

    Morris, Antony; Anderson, Mark W.; Omer, Ahmed; Maffione, Marco; van Hinsbergen, Douwe J. J.

    2017-11-01

    Most ophiolites have geochemical signatures that indicate formation by suprasubduction seafloor spreading above newly initiated subduction zones, and hence they record fore-arc processes operating following subduction initiation. They are frequently underlain by a metamorphic sole formed at the top of the downgoing plate and accreted below the overlying suprasubduction zone lithosphere immediately following ophiolite formation. Paleomagnetic analyses of ophiolites can provide important insights into the enigmatic geodynamic processes operating in this setting via identification of tectonic rotations related to upper plate extension. Here we present net tectonic rotation results from the Late Cretaceous Mersin ophiolite of southern Turkey that document rapid and progressive rotation of ophiolitic rocks and their associated metamorphic sole. Specifically, we demonstrate that lower crustal cumulate rocks and early dykes intruded into the underlying mantle section have undergone extreme rotation around ridge-parallel, shallowly-plunging axes, consistent with oceanic detachment faulting during spreading. Importantly, later dykes cutting the metamorphic sole experienced rotation around the same axis but with a lower magnitude. We show that these rotations occurred via a common mechanism in a pre-obduction, fore-arc setting, and are best explained by combining (hyper)extension resulting from detachment-mode, amagmatic suprasubduction zone spreading in a fore-arc environment with a recently proposed mechanism for exhumation of metamorphic soles driven by upper plate extension. Available age constraints demonstrate that extreme rotation of these units was accommodated rapidly by these processes over a time period of <∼3 Myr, comparable with rates of rotation seen in oceanic core complexes in the modern oceans.

  11. Slow earthquakes linked along dip in the Nankai subduction zone.

    Science.gov (United States)

    Hirose, Hitoshi; Asano, Youichi; Obara, Kazushige; Kimura, Takeshi; Matsuzawa, Takanori; Tanaka, Sachiko; Maeda, Takuto

    2010-12-10

    We identified a strong temporal correlation between three distinct types of slow earthquakes distributed over 100 kilometers along the dip of the subducting oceanic plate at the western margin of the Nankai megathrust rupture zone, southwest Japan. In 2003 and 2010, shallow very-low-frequency earthquakes near the Nankai trough as well as nonvolcanic tremor at depths of 30 to 40 kilometers were triggered by the acceleration of a long-term slow slip event in between. This correlation suggests that the slow slip might extend along-dip between the source areas of deeper and shallower slow earthquakes and thus could modulate the stress buildup on the adjacent megathrust rupture zone.

  12. Tectonics of the IndoBurma Oblique Subduction Zone

    Science.gov (United States)

    Steckler, M. S.; Seeber, L.; Akhter, S. H.; Betka, P. M.; Cai, Y.; Grall, C.; Mondal, D. R.; Gahalaut, V. K.; Gaherty, J. B.; Maung Maung, P.; Ni, J.; Persaud, P.; Sandvol, E. A.; Tun, S. T.

    2016-12-01

    The Ganges-Brahmaputra Delta (GBD) is obliquely colliding with the IndoBurma subduction zone. Most of the 42 mm/y of arc-parallel motion is absorbed in a set of dextral to dextral-convergent faults, the Sagaing, Kabaw and Churachandpur-Mao Faults. The 13-17 mm/y of convergence with the delta has built a 250-km wide active accretionary prism. The upper part of the 19-km sediment thickness consists of a shallowing-up stack of prograding strata that has shifted the shelf edge 3-400 km since the Himalayan orogeny at 50 Ma. The upper 3-5 km sandy shelf to fluvial strata are deformed into a broad fold and thrust belt above an overpressured décollement. It forms a flat shallow roof thrust in the frontal accretionary prism. The structure of the deeper part of the accretionary prism, which must transfer the incoming sediments to the upper plate, is unknown. GPS indicates the downdip end of the megathrust locked zone is 25 km at 92.5°E. The deformation front, marked by nascent detachment folds above the shallow décollement reaches the megacity of Dhaka in the middle of the GBD. The seismogenic potential of this portion of the prism is unknown. Arc volcanism in Myanmar, 500 km east of the deformation front, is sparse. Limited geochemical data on the arc volcanics are consistent with hot slab conditions. One possibility is that the deep GBD slab and basement are metamorphosed and dewatered early in the subduction process whereby most of the fluids are transferred to the growing prism by buoyancy driven migration or accretion of fluid-rich strata. Since it is entirely subaerial this little-studied region crossing Bangladesh, India and Myanmar provides an opportunity for a detailed multidisciplinary geophysical and geological investigation. It has the potential to highlight the role of fluids in subduction zones, the tectonics of extreme accretion and their seismic hazards, and the interplay between driving and resistance forces of a subduction zone during a soft collision.

  13. Modeling Diverse Pathways to Age Progressive Volcanism in Subduction Zones.

    Science.gov (United States)

    Kincaid, C. R.; Szwaja, S.; Sylvia, R. T.; Druken, K. A.

    2015-12-01

    One of the best, and most challenging clues to unraveling mantle circulation patterns in subduction zones comes in the form of age progressive volcanic and geochemical trends. Hard fought geological data from many subduction zones, like Tonga-Lau, the Cascades and Costa-Rica/Nicaragua, reveal striking temporal patterns used in defining mantle flow directions and rates. We summarize results from laboratory subduction models showing a range in circulation and thermal-chemical transport processes. These interaction styles are capable of producing such trends, often reflecting apparent instead of actual mantle velocities. Lab experiments use a glucose working fluid to represent Earth's upper mantle and kinematically driven plates to produce a range in slab sinking and related wedge transport patterns. Kinematic forcing assumes most of the super-adiabatic temperature gradient available to drive major downwellings is in the tabular slabs. Moreover, sinking styles for fully dynamic subduction depend on many complicating factors that are only poorly understood and which can vary widely even for repeated parameter combinations. Kinematic models have the benefit of precise, repeatable control of slab motions and wedge flow responses. Results generated with these techniques show the evolution of near-surface thermal-chemical-rheological heterogeneities leads to age progressive surface expressions in a variety of ways. One set of experiments shows that rollback and back-arc extension combine to produce distinct modes of linear, age progressive melt delivery to the surface through a) erosion of the rheological boundary layer beneath the overriding plate, and deformation and redistribution of both b) mantle residuum produced from decompression melting and c) formerly active, buoyant plumes. Additional experiments consider buoyant diapirs rising in a wedge under the influence of rollback, back-arc spreading and slab-gaps. Strongly deflected diapirs, experiencing variable rise

  14. Effect of the Earth's rotation on subduction processes

    Science.gov (United States)

    Levin, B. W.; Rodkin, M. V.; Sasorova, E. V.

    2017-09-01

    The role played by the Earth's rotation is very important in problems of physics of the atmosphere and ocean. The importance of inertia forces is traditionally estimated by the value of the Rossby number: if this parameter is small, the Coriolis force considerably affects the character of movements. In the case of convection in the Earth's mantle and movements of lithospheric plates, the Rossby number is quite small; therefore, the effect of the Coriolis force is reflected in the character of movements of the lithospheric plates. Analysis of statistical data on subduction zones verifies this suggestion.

  15. Kinematics of subduction and plate convergence under Taiwan and its geomorphic, geodetic and seismic expressions

    Science.gov (United States)

    Suppe, J.; Carena, S.; Kanda, R. V.; Wu, Y.; Huang, H.; Wu, J. E.

    2013-12-01

    Deciphering the kinematics of ongoing subduction and rapid plate convergence under Taiwan is neither trivial nor straightforward. A 3D synthesis of diverse constraints is required, for example tomography, geodesy, tectonic geomorphology, stress inversion, and Philippine Sea plate motions. Eurasian-Philippine Sea plate convergence is ~90mm/y in a mildly oblique 300° azimuth relative to the ~NS nearly vertically subducting Eurasian mantle lithosphere which extends to ~500km depth. If all the current plate convergence were consumed in subduction of Eurasian mantle, the subduction flexural hinge would migrate westward at ~80mm/y, which is fast relative to the ~30mm/y long-term slip rate on the Taiwan main detachment that represents the Eurasian subduction interface under the Taiwan Central Mountains. If this fast simple subduction were occurring, subduction would too quickly outrun the mountain belt in conflict with data. Instead we estimate that subduction of Eurasian lithosphere is proceeding at ~50mm/y with the remaining ~40mm/y convergence at a lithospheric level consumed by secondary subduction above and to the east of the main plate interface. This secondary subduction is largely transient deformation that is most obvious under the Coastal Range, which represents the deforming western margin of the Philippine Sea plate during the last ~1-1.5 Ma. The thrust faults of the Coastal Range function as subduction faults with the long-term net motion of their footwalls moving largely down relative to their only slowly uplifting hanging walls, with a net secondary subduction of ~40-50km in the last ~1-1.5Ma as estimated from seismic tomography and other data. In addition we find evidence for ongoing subduction of the eastern Central Mountains of Taiwan. The crest of the mountains coincides with the western edge of the migrating plate flexure, a band of extensional geodetic strain coincides with the flexure, and an extensional stress state in the upper 5-10km coincides

  16. Is localised dehydration and vein generation the tremor-generating mechanism in subduction zones?

    Science.gov (United States)

    Fagereng, Ake; Meneghini, Francesca; Diener, Johann; Harris, Chris

    2017-04-01

    The phenomena of tectonic, non-volcanic, tremor was first discovered at the down-dip end of the seismogenic zone in Japan early this millennium. Now this low amplitude, low frequency, noise-like seismic signal has been observed at and/or below the deep limit of interseismic coupling along most well-instrumented subduction thrust interfaces. Data and models from these examples suggest a link between tremor and areas of elevated fluid pressure, or at least fluid presence. Tremor locations appear to also correlate with margin-specific locations of metamorphic fluid release, determined by composition and thermal structure. We therefore hypothesise that: (i) tremor on the deep subduction thrust interface is related to localised fluid release; and (ii) accretionary complex rocks exhumed from appropriate pressure - temperature conditions should include a record of this process, and allow a test for the hypothesis. Hydrothermal veins are a record of mineral precipitation at non-equilibrium conditions, commonly caused by fracture, fluid influx, and precipitation of dissolved minerals from this fluid. Quartz veins are ubiquitous in several accretionary complexes, including the Chrystalls Beach Complex, New Zealand, and the Kuiseb Schist of the Namibian Damara Belt. In both locations, representing temperatures of deformation of tremor. In the Chrystalls Beach Complex, quartz δ18O values range from 14.1 ‰ to 17.0 ‰ (n = 18), whereas in the Kuiseb schist, values range from 9.4 ‰ to 17.9 ‰ (n = 30). In the latter, values less than 14.0‰ are associated with long-lived shear zones. Excluding the lower values in the Kuiseb schist, the δ18O values are consistent with metamorphic fluids in near equilibrium with the host rocks. We thus infer that the veins that developed on the prograde path formed at a small range of temperatures from a local fluid source. This interpretation is consistent with the veins forming in response to a spatially localised metamorphic fluid

  17. Areas of Active Tectonic Uplift Are Sensitive to Small Changes in Fold Orientations within a Broad Zone of Left-lateral Transpression and Shearing, Dominican Republic and Haiti (Hispaniola)

    Science.gov (United States)

    Ambrosius, I.; Mann, P.

    2014-12-01

    Previous GPS studies have shown that the island of Hispaniola is a 250 km-wide zone of active, east-west, left-lateral shearing along two major strike-slip zones: the Septentrional-Oriente fault zone through the northern part of the island and the Enriquillo-Plantain Garden fault zone (EPGFZ) through the southern part of the island. The total interplate rate distributed on both faults is 21 mm/yr. Using a high-resolution DEM, we constructed fluvial channel profiles across transpression-related folds of late Miocene to recent age in the area of central and southern Dominican Republic and Haiti to determine controls of areas of relatively high, moderate, and slow uplift inferred from fluvial channel profiles. Fold axes in this area extend for 50-150 km and exhibit two different trends: 1) folds that occupy the area of the Sierra de Neiba-Chaine des Matheux north of the Enriquillo-Cul-de-Sac Valley and EPGFZ and folds that occupy the area of the Sierra de Bahoruco-Massif de la Selle all exhibit more east-west fold axes trending 110; 2) folds that occupy the area northwest of the EPGFZ in the western Chaine des Matheux and Sierra de Neiba all exhibit fold axes with more northwest trends of 125. River channel profiles show that the second group of more northwesterly-trending fold axes show relatively higher rates of tectonic uplift based on their convex-upward river profiles. Our interpretation for regional variations in river profiles and inferred uplift is that uplift is more pronounced on fold axes trending 15 degrees more to the northwest because their axes are more oblique to the interplate direction of east-west shearing. Longterm uplift rates previously measured from a stairstep of late Quaternary coral terraces at the plunging nose of the westernmost Chaine des Matheux have been previously shown to be occurring at a rate of 0.19 mm/yr. Onland exposures of Holocene corals are found only on one locality within the southern area of folds 30 km west of the epicenter

  18. Alteration and dehydration of subducting oceanic crust within subduction zones: implications for décollement step-down and plate-boundary seismogenesis

    Science.gov (United States)

    Kameda, Jun; Inoue, Sayako; Tanikawa, Wataru; Yamaguchi, Asuka; Hamada, Yohei; Hashimoto, Yoshitaka; Kimura, Gaku

    2017-04-01

    The alteration and dehydration of predominantly basaltic subducting oceanic crustal material are thought to be important controls on the mechanical and hydrological properties of the seismogenic plate interface below accretionary prisms. This study focuses on pillow basalts exposed in an ancient accretionary complex within the Shimanto Belt of southwest Japan and provides new quantitative data that provide insight into clay mineral reactions and the associated dehydration of underthrust basalts. Whole-rock and clay-fraction X-ray diffraction analyses indicate that the progressive conversion of saponite to chlorite proceeds under an almost constant bulk-rock mineral assemblage. These clay mineral reactions may persist to deep crustal levels ( 320 °C), possibly contributing to the bulk dehydration of the basalt and supplying fluid to plate-boundary fault systems. This dehydration can also cause fluid pressurization at certain horizons within hydrous basalt sequences, eventually leading to fracturing and subsequent underplating of upper basement rock into the overriding accretionary prism. This dehydration-induced breakage of the basalt can explain variations in the thickness of accreted basalt fragments within accretionary prisms as well as the reported geochemical compositions of mineralized veins associated with exposed basalts in onland locations. This fracturing of intact basalt can also nucleate seismic rupturing that would subsequently propagate along seismogenic plate interfaces.[Figure not available: see fulltext.

  19. A plate tectonics oddity: Caterpillar-walk exhumation of subducted continental crust

    NARCIS (Netherlands)

    Tirel, C.; Brun, J.-P.; Burov, E.; Wortel, M.J.R.; Lebedev, S.

    2013-01-01

    Since plate tectonics began on Earth, grandiose "subduction factories" have continually shaped the continents, accreting continental blocks and new crust at the convergent plate boundaries. An enigmatic product of subduction factories is the high-pressure to ultrahigh-pressure (HP-UHP) metamorphic

  20. Experimental and observational evidence for plume-induced subduction on Venus

    Science.gov (United States)

    Davaille, A.; Smrekar, S. E.; Tomlinson, S.

    2017-04-01

    Why Venus lacks plate tectonics remains an unanswered question in terrestrial planet evolution. There is observational evidence for subduction--a requirement for plate tectonics--on Venus, but it is unclear why the features have characteristics of both mantle plumes and subduction zones. One explanation is that mantle plumes trigger subduction. Here we compare laboratory experiments of plume-induced subduction in a colloidal solution of nanoparticles to observations of proposed subduction sites on Venus. The experimental fluids are heated from below to produce upwelling plumes, which in turn produce tensile fractures in the lithosphere-like skin that forms on the upper surface. Plume material upwells through the fractures and spreads above the skin, analogous to volcanic flooding, and leads to bending and eventual subduction of the skin along arcuate segments. The segments are analogous to the semi-circular trenches seen at two proposed sites of plume-triggered subduction at Quetzalpetlatl and Artemis coronae. Other experimental deformation structures and subsurface density variations are also consistent with topography, radar and gravity data for Venus. Scaling analysis suggests that this regime with limited, plume-induced subduction is favoured by a hot lithosphere, such as that found on early Earth or present-day Venus.

  1. A thermo-mechanical model of horizontal subduction below an overriding plate

    NARCIS (Netherlands)

    Hunen, Jeroen van; Berg, A.P. van den; Vlaar, N.J.

    2000-01-01

    Subduction of young oceanic lithosphere cannot be explained by the gravitational driving mechanisms of slab pull and ridge push. This deficiency of driving forces can be overcome by obduction of an actively overriding plate, which forces the young plate either to subduct or to collide. This

  2. Subduction on the margins of coronae on Venus: Evidence from radiothermal emissivity measurements

    Science.gov (United States)

    Robinson, C. A.

    1993-01-01

    Retrograde subduction has been suggested to occur at three coronae on Venus: Latona, Artemis, and Eithinoha. Using the mineralogical arguments of Klose to explain surface emissivity, a study of radio thermal emissivity of Venus coronae showed that emissivity changes associated with Latona, Artemis, and Ceres imply the same crustal movements predicted by the subduction model of Sandwell and Schubert.

  3. Does subduction polarity changes below the Alps? Inferences from analogue modelling

    NARCIS (Netherlands)

    Luth, S.; Willingshofer, E.; Sokoutis, D.; Cloetingh, S.

    2013-01-01

    The surface expression of a lateral polarity change of continental mantle lithosphere subduction has been studied by using lithosphere-scale physical models. Key parameters investigated were: the degree of lateral coupling between adjacent domains of opposing subduction polarity, the width of the

  4. Subduction in an Eddy-Resolving State Estimate of the Northeast Atlantic Ocean

    Science.gov (United States)

    Gebbie, Geoffrey

    2004-01-01

    Are eddies an important contributor to subduction in the eastern subtropical gyre? Here, an adjoint model is used to combine a regional, eddy-resolving numerical model with observations to produce a state estimate of the ocean circulation. The estimate is a synthesis of a variety of in- situ observations from the Subduction Experiment, TOPEX/POSEIDON altimetry, and the MTI General Circulation Model. The adjoint method is successful because the Northeast Atlantic Ocean is only weakly nonlinear. The state estimate provides a physically-interpretable, eddy-resolving information source to diagnose subduction. Estimates of eddy subduction for the eastern subtropical gyre of the North Atlantic are larger than previously calculated from parameterizations in coarse-resolution models. Furthermore, eddy subduction rates have typical magnitudes of 15% of the total subduction rate. Eddies contribute as much as 1 Sverdrup to water-mass transformation, and hence subduction, in the North Equatorial Current and the Azores Current. The findings of this thesis imply that the inability to resolve or accurately parameterize eddy subduction in climate models would lead to an accumulation of error in the structure of the main thermocline, even in the relatively-quiescent eastern subtropical gyre.

  5. Using open sidewalls for modelling self-consistent lithosphere subduction dynamics

    NARCIS (Netherlands)

    Chertova, M.V.; Geenen, T.; van den Berg, A.; Spakman, W.

    2012-01-01

    Subduction modelling in regional model domains, in 2-D or 3-D, is commonly performed using closed (impermeable) vertical boundaries. Here we investigate the merits of using open boundaries for 2-D modelling of lithosphere subduction. Our experiments are focused on using open and closed (free

  6. A two-way interaction between the Hainan plume and the Manila subduction zone

    NARCIS (Netherlands)

    Mériaux, Catherine A.; Duarte, João C.; Schellart, Wouter P.; Mériaux, Anne Sophie

    2015-01-01

    The interaction between mantle plumes and subducting slabs is well accepted, but the influence of slabs on plumes has more often been portrayed than the reverse. Here we present three-dimensional upper mantle laboratory models in which a compositional plume rises underneath a subducting plate.

  7. Rapid fore-arc extension and detachment-mode spreading following subduction initiation

    NARCIS (Netherlands)

    Morris, Antony; Anderson, Mark W.; Omer, Ahmed; Maffione, Marco; van Hinsbergen, Douwe J.J.|info:eu-repo/dai/nl/269263624

    2017-01-01

    Most ophiolites have geochemical signatures that indicate formation by suprasubduction seafloor spreading above newly initiated subduction zones, and hence they record fore-arc processes operating following subduction initiation. They are frequently underlain by a metamorphic sole formed at the top

  8. Slab melting as a barrier to deep carbon subduction.

    Science.gov (United States)

    Thomson, Andrew R; Walter, Michael J; Kohn, Simon C; Brooker, Richard A

    2016-01-07

    Interactions between crustal and mantle reservoirs dominate the surface inventory of volatile elements over geological time, moderating atmospheric composition and maintaining a life-supporting planet. While volcanoes expel volatile components into surface reservoirs, subduction of oceanic crust is responsible for replenishment of mantle reservoirs. Many natural, 'superdeep' diamonds originating in the deep upper mantle and transition zone host mineral inclusions, indicating an affinity to subducted oceanic crust. Here we show that the majority of slab geotherms will intersect a deep depression along the melting curve of carbonated oceanic crust at depths of approximately 300 to 700 kilometres, creating a barrier to direct carbonate recycling into the deep mantle. Low-degree partial melts are alkaline carbonatites that are highly reactive with reduced ambient mantle, producing diamond. Many inclusions in superdeep diamonds are best explained by carbonate melt-peridotite reaction. A deep carbon barrier may dominate the recycling of carbon in the mantle and contribute to chemical and isotopic heterogeneity of the mantle reservoir.

  9. Dehydration-induced instabilities at intermediate depths in subduction zones

    Science.gov (United States)

    Brantut, Nicolas; Stefanou, Ioannis; Sulem, Jean

    2017-08-01

    We formulate a model for coupled deformation and dehydration of antigorite, based on a porosity-dependent yield criterion and including shear-enhanced compaction. A pore pressure and compaction instability can develop when the net volume change associated with the reaction is negative, i.e., at intermediate depth in subduction zones. The instability criterion is derived in terms of the dependence of the yield criterion on porosity: if that dependence is strong, instabilities are more likely to occur. We also find that the instability is associated with strain localization, over characteristic length scales determined by the hydraulic diffusivity, the elasto-plastic parameters of the rock, and the reaction rate. Typical lower bounds for the localization length are of the order of 10 to 100 for antigorite dehydration and deformation at 3 GPa. The fluid pressure and deformation instability is expected to induce stress buildup in the surrounding rocks forming the subducted slab, which provides a mechanism for the nucleation and propagation of intermediate-depth earthquakes.

  10. The transition zone below the Chile-Argentina flat subduction region

    Science.gov (United States)

    Bonatto, Luciana; Piromallo, Claudia; Badi, Gabriela

    2017-04-01

    We study the fine structure of the upper mantle (below 200 km depth) beneath the western margin of South America, within an area known as the Chile-Argentina flat subduction zone (between 26°S and 36°S). Unlike what happens in most subduction zones, in this region the Nazca Plate subducts with an angle close to the horizontal -initially dips underneath the continent and flattens at a depth of approximately 100 km, remaining almost horizontal for about 300 km before descending more steeply into the mantle. Moreover, the flat slab follows the path of the subducting Juan Fernández Ridge, a hot spot seamount chain on the Nazca Plate. The complex tectonic setting makes this region an excellent laboratory to explore and quantify the relative contributions of thermal and compositional heterogeneities to the mantle discontinuity structure. In this study we combine data available from four past temporary experiments: 18 seismic stations from CHARGE; 43 from SIEMBRA, 12 from ESP and 30 from PUDEL. The research tools are the Pds phases (the direct P wave converted to an S wave while passing through a seismic discontinuity at depth d). These signals arrive in the coda of the P-phase in the radial component and are expected to be coherent with the waveform of the first arrival for conversion at discontinuities thinner than one half of the P-wavelength. In order to extract these converted phases by means of waveform similarity, we use the receiver function (RF) technique, i.e. the deconvolution of the vertical from the radial component in the frequency domain. The Pds phases are then detected on stacked RF (globally and by common conversion point) in the relative time-slowness domain. Since the incidence angle of converted phases is larger than the incidence angle of the P phase, they are expected with negative slowness. This permits to separate them from the multiples, which are instead expected with positive slowness. We measure amplitudes and arrival times for the

  11. Release of mineral-bound water prior to subduction tied to shallow seismogenic slip off Sumatra.

    Science.gov (United States)

    Hüpers, Andre; Torres, Marta E; Owari, Satoko; McNeill, Lisa C; Dugan, Brandon; Henstock, Timothy J; Milliken, Kitty L; Petronotis, Katerina E; Backman, Jan; Bourlange, Sylvain; Chemale, Farid; Chen, Wenhuang; Colson, Tobias A; Frederik, Marina C G; Guèrin, Gilles; Hamahashi, Mari; House, Brian M; Jeppson, Tamara N; Kachovich, Sarah; Kenigsberg, Abby R; Kuranaga, Mebae; Kutterolf, Steffen; Mitchison, Freya L; Mukoyoshi, Hideki; Nair, Nisha; Pickering, Kevin T; Pouderoux, Hugo F A; Shan, Yehua; Song, Insun; Vannucchi, Paola; Vrolijk, Peter J; Yang, Tao; Zhao, Xixi

    2017-05-26

    Plate-boundary fault rupture during the 2004 Sumatra-Andaman subduction earthquake extended closer to the trench than expected, increasing earthquake and tsunami size. International Ocean Discovery Program Expedition 362 sampled incoming sediments offshore northern Sumatra, revealing recent release of fresh water within the deep sediments. Thermal modeling links this freshening to amorphous silica dehydration driven by rapid burial-induced temperature increases in the past 9 million years. Complete dehydration of silicates is expected before plate subduction, contrasting with prevailing models for subduction seismogenesis calling for fluid production during subduction. Shallow slip offshore Sumatra appears driven by diagenetic strengthening of deeply buried fault-forming sediments, contrasting with weakening proposed for the shallow Tohoku-Oki 2011 rupture, but our results are applicable to other thickly sedimented subduction zones including those with limited earthquake records. Copyright © 2017, American Association for the Advancement of Science.

  12. The role of frictional strength on plate coupling at the subduction interface

    KAUST Repository

    Tan, Eh

    2012-10-01

    At a subduction zone the amount of friction between the incoming plate and the forearc is an important factor in controlling the dip angle of subduction and the structure of the forearc. In this paper, we investigate the role of the frictional strength of sediments and of the serpentinized peridotite on the evolution of convergent margins. In numerical models, we vary thickness of a serpentinized layer in the mantle wedge (15 to 25km) and the frictional strength of both the sediments and serpentinized mantle (friction angle 1 to 15, or static friction coefficient 0.017 to 0.27) to control the amount of frictional coupling between the plates. With plastic strain weakening in the lithosphere, our numerical models can attain stable subduction geometry over millions of years. We find that the frictional strength of the sediments and serpentinized peridotite exerts the largest control on the dip angle of the subduction interface at seismogenic depths. In the case of low sediment and serpentinite friction, the subduction interface has a shallow dip, while the subduction zone develops an accretionary prism, a broad forearc high, a deep forearc basin, and a shallow trench. In the high friction case, the subduction interface is steep, the trench is deeper, and the accretionary prism, forearc high and basin are all absent. The resultant free-air gravity and topographic signature of these subduction zone models are consistent with observations. We believe that the low-friction model produces a geometry and forearc structure similar to that of accretionary margins. Conversely, models with high friction angles in sediments and serpentinite develop characteristics of an erosional convergent margin. We find that the strength of the subduction interface is critical in controlling the amount of coupling at the seismogenic zone and perhaps ultimately the size of the largest earthquakes at subduction zones. © 2012. American Geophysical Union. All Rights Reserved.

  13. The link between great earthquakes and the subduction of oceanic fracture zones

    Directory of Open Access Journals (Sweden)

    R. D. Müller

    2012-12-01

    Full Text Available Giant subduction earthquakes are known to occur in areas not previously identified as prone to high seismic risk. This highlights the need to better identify subduction zone segments potentially dominated by relatively long (up to 1000 yr and more recurrence times of giant earthquakes. We construct a model for the geometry of subduction coupling zones and combine it with global geophysical data sets to demonstrate that the occurrence of great (magnitude ≥ 8 subduction earthquakes is strongly biased towards regions associated with intersections of oceanic fracture zones and subduction zones. We use a computational recommendation technology, a type of information filtering system technique widely used in searching, sorting, classifying, and filtering very large, statistically skewed data sets on the Internet, to demonstrate a robust association and rule out a random effect. Fracture zone–subduction zone intersection regions, representing only 25% of the global subduction coupling zone, are linked with 13 of the 15 largest (magnitude Mw ≥ 8.6 and half of the 50 largest (magnitude Mw ≥ 8.4 earthquakes. In contrast, subducting volcanic ridges and chains are only biased towards smaller earthquakes (magnitude < 8. The associations captured by our statistical analysis can be conceptually related to physical differences between subducting fracture zones and volcanic chains/ridges. Fracture zones are characterised by laterally continuous, uplifted ridges that represent normal ocean crust with a high degree of structural integrity, causing strong, persistent coupling in the subduction interface. Smaller volcanic ridges and chains have a relatively fragile heterogeneous internal structure and are separated from the underlying ocean crust by a detachment interface, resulting in weak coupling and relatively small earthquakes, providing a conceptual basis for the observed dichotomy.

  14. Dynamics and Significance of Plume-Induced Subduction Initiation: Numerical Modeling

    Science.gov (United States)

    Gerya, T.; Stern, R. J.; Baes, M.; Sobolev, S. V.; Whattam, S. A.

    2014-12-01

    How did the first subduction zone form? Most present-day subduction initiation mechanisms require acting plate forces and/or preexisting zones of lithospheric weakness, which are themselves the consequence of plate tectonics (Stern 2004). In contrast, spontaneous plume-induced subduction initiation - suggested on the basis of numerical thermo-mechanical experiments (Ueda et al., 2008) and supported by data re-interpretation of how subduction started in Late Cretaceous time around the Caribbean LIP (Whattam and Stern, 2014) - does not require pre-existing lithospheric fabric, such as are created by active plate tectonics and is viable for both stagnant lid and mobile/deformable lid conditions. Here, we present first results of high-resolution 3D numerical thermo-mechanical modeling of plume-induced subduction resulting from mechanical-magmatic interaction of an ascending thermal mantle plume with old, cold, dense oceanic lithosphere. We demonstrate that weakening of the strong lithosphere by plume-induced magmatism is the key factor enabling subduction initiation around the plume head. A large plume head is required to overcome ring confinement, and subduction initiation is further favored when plume activity and lithospheric weakening continues for several tens of Ma. We further discuss possible implications of this scenario for modern plate tectonics as well as for plate tectonics initiation in Precambrian time. ReferencesStern, R.J., 2004. Subduction initiation: spontaneous and induced. EPSL 226, 275-292.Ueda, K., Gerya, T., Sobolev, S.V., 2008. Subduction initiation by thermal-chemical plumes. PEPI 171, 296-312.Whattam, S.A., Stern, R. 2014. Late Cretaceous plume-induced subduction initiation along the southern margin of the Caribbean and NW South America: The first documented example with implications for the onset of plate tectonics. Gondwana Research, (accepted).

  15. Jurassic arc volcanism on Crimea (Ukraine): Implications for the paleo-subduction zone configuration of the Black Sea region

    Science.gov (United States)

    Meijers, M. J. M.; Vrouwe, B.; van Hinsbergen, D. J. J.; Kuiper, K. F.; Wijbrans, J.; Davies, G. R.; Stephenson, R. A.; Kaymakcı, N.; Matenco, L.; Saintot, A.

    2010-10-01

    The early Cretaceous and younger opening of the Black Sea has obliterated much of the older record of Tethyan subduction below southeastern Europe. The earlier Mesozoic evolution was dominated by opening and closure of Tethyan oceans between Gondwana and Laurasia with their consumption, at least in part, accommodated along the southern Eurasian margin. Crimea (Ukraine), a peninsula in the northern Black Sea, represents the northernmost region of southeastern Europe that exposes a record of a pre-Cretaceous Tethyan active margin. To shed new light on the paleosubduction zone configuration of the southeastern European margin in the Jurassic, we report 40Ar/ 39Ar isotope dating on 10 samples and whole rock geochemistry on 31 samples from supposedly Jurassic magmatic rocks from the Crimean peninsula. The samples can be subdivided into two age groups: middle Jurassic (~ 172-158 Ma) and uppermost Jurassic to lowermost Cretaceous (~ 151-142 Ma), that both have a subduction-related geochemical signature. The ages of the younger group are in conflict with previously assigned biostratigraphic ages of the units under- and overlying the volcanic complex. This might suggest a scenario where the latter were juxtaposed by faulting. We argue that the Crimean volcanics represent a fragment of a volcanic arc overlying the southeastern European continental margin. These data therefore provide evidence for Jurassic northwards subduction below the Eurasian margin, preceding the opening of the Black Sea as a back-arc basin. We argue that the corresponding Jurassic trench was already positioned south of the Turkish Pontides and the Caucasus belt, implying a very shallow slab angle in the Jurassic.

  16. Plume-induced roll back subduction around Venus large coronae

    Science.gov (United States)

    Davaille, A.; Smrekar, S. E.; Tomlinson, S. M.

    2016-12-01

    On Venus, possible subduction trenches are mainly associated with large coronae, eventhough the latter are thought to be produced by hot mantle plumes. The mechanism of assocation between subduction and plume has long remained elusive. However, we recently observe the same association in laboratory experiments on thermal convection in colloidal aqueous dispersions of silica nanoparticles, which deform in the Newtonian regime at low solid particle fraction φp, and transition to strain-rate weakening, plasticity, elasticity, and brittle properties as φp increases. Hence, a dense skin akin to a planetary lithosphere grows on the surface when the system is dried from above. When a hot plume rises under the skin, the latter undergoes a flexural deformation which puts it under tension. Cracks then develop, sometimes using pre-existing weaknesses. Plume material (being more buoyant that the laboratory lithosphere) upwells through the cracks and spreads as a axisymmetric gravity current above the broken denser skin. The latter bends and sinks under the conjugate action of its own weight and the plume gravity current. The brittle character of the top experimental lithosphere forbids it to deform viscously to accomodate the sinking motions. Instead, the plate continues to tear as a sheet of paper would do upon intrusion. Several slabs are therefore produced, associated with trenches localized along partial circles on the plume, and strong roll-back is always observed. Depending on the lithospheric strength, roll-back can continue and triggers a complete resurfacing, or it stops when the plume stops spreading. Scalings derived from the experiments suggest that a weaker lithosphere than that present on Earth today is required for such a convective regime. We identified two candidates on Venus. At Artemis and Quetzelpetlatl Coronae, the radar image observations and subsurface density variations inferred from modeling the gravity and topography agree with the predictions from

  17. Melting carbonated epidote eclogites: carbonatites from subducting slabs

    Science.gov (United States)

    Poli, Stefano

    2016-12-01

    Current knowledge on the solidus temperature for carbonated eclogites suggests that carbonatitic liquids should not form from a subducted oceanic lithosphere at sub-arc depth. However, the oceanic crust includes a range of gabbroic rocks, altered on rifts and transforms, with large amounts of anorthite-rich plagioclase forming epidote on metamorphism. Epidote disappearance with pressure depends on the normative anorthite content of the bulk composition; we therefore expect that altered gabbros might display a much wider pressure range where epidote persists, potentially affecting the solidus relationships. A set of experimental data up to 4.6 GPa, and 1000 °C, including new syntheses on mafic eclogites with 36.8 % normative anorthite, is discussed to unravel the effect of variable bulk and volatile compositions in model eclogites, enriched in the normative anorthite component ( An 37 and An 45). Experiments are performed in piston cylinder and multianvil machines. Garnet, clinopyroxene, and coesite form in all syntheses. Lawsonite was found to persist at 3.7 GPa, 750 °C, with both dolomite and magnesite; at 3.8 GPa, 775-800 °C, fluid-saturated conditions, epidote coexists with kyanite, dolomite, and magnesite. The anhydrous assemblage garnet, omphacite, aragonite, and kyanite is found at 4.2 GPa, 850 °C. At 900 °C, a silicate glass of granitoid composition, a carbonatitic precipitate, and Na-carbonate are observed. Precipitates are interpreted as evidence of hydrous carbonatitic liquids at run conditions; these liquids produced are richer in Ca compared to experimental carbonatites from anhydrous experiments, consistently with the dramatic role of H2O in depressing the solidus temperature for CaCO3. The fluid-absent melting of the assemblage epidote + dolomite, enlarged in its pressure stability for An-rich gabbros, is expected to promote the generation of carbonatitic liquids. The subsolidus breakdown of epidote in the presence of carbonates at depths

  18. Isotopic Characteristics of Thermal Fluids from Mexican Subduction Zone

    Science.gov (United States)

    Taran, Y.; Inguaggiato, S.

    2007-05-01

    Chemical (major and trace elements) and isotopic (H,O,N,C,He) composition of waters and gases from thermal springs and geothermal wells of Mexican subduction zone have been measured. Three main geochemical profiles have been realized: (1) along the frontal Trans-Mexican Volcanic Belt (TMVB) zone through high- temperature Acoculco, Los Humeros, Los Azufres and La Primavera hydrothermal systems, Colima and Ceboruco volcanoes; (2) along the for-arc region of Pacific coast (12 groups of hot springs); (3) across the zone, from Pacific coast to TMVB, through the Jalisco Block. Fluids from El Chichon volcano in Chiapanecan arc system and Tacana volcano from the Central America Volcanic Arc have also been sampled. The frontal zone of TMVB is characterized by high 3He/4He ratios, from 7.2Ra in Ceboruco fumaroles to 7.6Ra in gases from Acoculco and Los Humeros calderas (Ra is atmospheric value of 1.4x10-6). These values are significantly higher than those published earlier in 80-s (up to 6.8Ra). Gases from coastal springs are low in 3He, usually < 1Ra with a minimum value of 0.2Ra in the northernmost submarine Punta Mita hot springs and a maximum value of 2.4Ra in La Tuna springs at the southern board of the Colima graben. An important feature of the TMVB thermal fluids is the absence of excess nitrogen in gases and, as a consequence, close to zero d15N values. In contrast, some coastal for-arc gases and gases from the Jalisco Block have high N2/Ar ratios and d15N up to +5 permil. Isotopic composition of carbon of CO2 along TMVB is close to typical "magmatic" values from -3 permil to -5 permil, but d13C of methane varies significantly indicating multiple sources of CH4 in geothermal fluids and a partial temperature control. High 3He/4He ratios and pure atmospheric nitrogen may indicate a low contribution of subducted sediments into the TMVB magmas and magmatic fluids. In contrast, El Chichon and Tacana fluids show some excess nitrogen (N2/Ar up to 500) and variable d15N, but

  19. Dehydration reactions in subducting oceanic crust: implications for arc volcanism

    Science.gov (United States)

    Forneris, J. F.; Holloway, J. R.

    2003-04-01

    In subduction zones, oceanic lithosphere progressively dehydrates as it sinks deep into the underlying mantle. Fluids released from the subducting slab are thought to trigger partial melting in the overlying mantle wedge, leading to the formation of volcanic arcs. Experiments were conducted in the ranges of 2.2--3.4 GPa (70 to 100 km) and 625--750^oC to determine the dehydration reactions that control fluid release from the basaltic layer of the subducting slab. The experimental duration was typically one month, although some experiments were replicated with a shorter run duration (one to two weeks) in order to identify potentially metastable phases. A mixture of a natural mid-ocean ridge basalt glass and mineral seeds was used as the starting material. Oxygen fugacity was buffered within ±1.3 log units of nickel-bunsenite (NiNiO). The results obtained indicate that the transformation of a hydrated eclogite into a nominally dry eclogite occurs through the decomposition of three hydrous phases: amphibole, lawsonite, and zoisite. Chloritoid, a mineral described as an H_2O carrier in previous experimental studies, is found to be metastable in the examined pressure-temperature (P-T) range and therefore should not be involved in the global fluid release from the basaltic crust. A detailed chemical analysis reveals that amphiboles are sodic-calcic (barroisite) at low pressures (2.2 to 2.4 GPa), but become sodic (glaucophane) with increasing pressure. This observation is the first experimental confirmation of the high-pressure stability of glaucophane in metabasalt compositions. At pressures above the stability field of amphibole, zoisite/clinozoisite becomes the stable hydrous phase at temperatures above 645^oC, whereas lawsonite is stable at lower temperatures. H_2O contents of eclogitic assemblages have been estimated based on modal abundance of minerals calculated from electron microprobe analyses. These results indicate that a slab following an intermediate

  20. Deformation of Lawsonite at High Pressure and High Temperature - Implications for Low Velocity Layers in Subduction Zones

    Science.gov (United States)

    Amiguet, E.; Hilairet, N.; Wang, Y.; Gillet, P.

    2014-12-01

    During subduction, the hydrated oceanic crust undergoes a series of metamorphic reactions and transform gradually to blueschists and eclogite at depths of 20-50 km. Detailed seismic observations of subduction zones suggest a complex layered structure with the presence of a Low Velocity Layer (LVL) related to the oceanic crust [1] persisting to considerable depths (100- 250 km).While the transformation from blueschist to eclogite [2] and the presence of glaucophane up to 90-100 km [3] could explain some of these observations, the presence of LVL at greater depths could be related to the presence of the hydrous mineral lawsonite (CaAl2(Si2O7)(OH)2 H2O). Its stability field extends to 8.5 GPa and 1100K corresponding to depths up to 250 km in cold hydrous part of subducting slabs [4]. Because these regions undergo large and heterogeneous deformation, lawsonite plasticity and crystal preferred orientation (CPOs) may strongly influence the dynamic of subduction zones and the seismic properties. We present a deformation study at high presssure and high temperature on lawsonite. Six samples were deformed at 4-10 GPa and 600K to 1000K using a D-DIA apparatus [5] at 13-BMD at GSECARS beamline, APS, in axial compression up to 30% deformation with strain rates of 3.10-4s-1 to 6.10-6s-1. We measured in-situ lattice strains (a proxy for macroscopic stress), texture and strain using synchrotron radiations and calculated the macroscopic stress using lawsonite elastic properties [6]. Results from lattice strain analysis show a dependence of flow stress with temperature and strain rate. Texture analysis coupled with transmission electron microscopy showed that dislocation creep is the dominant deformation mechanism under our deformation conditions. [1] Abers, Earth and Planetary Science Letters, 176, 323-330, 2000 [2] Helffrich et al., Journal of Geophysical Research, 94, 753-763, 1989 [3] Bezacier et al., Tectonophysics, 494, 201-210, 2010 [4] Schmidt & Poli, Earth and Planetary

  1. Recycling of water, carbon, and sulfur during subduction of serpentinites: A stable isotope study of Cerro del Almirez, Spain

    Science.gov (United States)

    Alt, Jeffrey C.; Garrido, Carlos J.; Shanks, Wayne C.; Turchyn, Alexandra; Padrón-Navarta, José Alberto; López Sánchez-Vizcaíno, Vicente; Gómez Pugnaire, María Teresa; Marchesi, Claudio

    2012-01-01

    We use the concentrations and isotope compositions of water, carbon, and sulfur in serpentinites and their dehydration products to trace the cycling of volatiles during subduction. Antigorite serpentinites from the Cerro del Almirez complex, Spain, contain 9–12 wt.% H2O and 910 ± 730 ppm sulfur, and have bulk δ18O values of 8.6 ± 0.4‰, δD = − 54 ± 5‰, and δ34S = 5.0‰, consistent with serpentinization at temperatures of ~ 200 °C by seawater hydrothermal fluids in a seafloor setting. The serpentinites were dehydrated to chlorite–harzburgite (olivine + orthopyroxene + chlorite) at 700 °C and 1.6–1.9 GPa during subduction metamorphism, resulting in loss of water, and sulfur. The chlorite–harzburgites contain 5.7 ± 1.9 wt.% H2O, and have bulk δ18O = 8.0 ± 0.9‰, and δD = − 77 ± 11‰. The rocks contain 650 ± 620 ppm sulfur having δ34S = 1.2‰. Dehydration of serpentinite resulted in loss of 5 wt.% H2O having δ18O = 8–10‰ and δD = − 27 to − 65‰, and loss of 260 ppm sulfur as sulfate, having δ34S = 14.5‰. The contents and δ13C of total carbon in the two rock types overlap, with a broad trend of decreasing carbon contents and δ13C from ~ 1300 to 200 ppm and − 9.6 to − 20.2‰. This reflects mixing between reduced carbon in the rocks (210 ppm, δ13C ≈ − 26‰) and seawater-derived carbonate (δ13C ≈ − 1‰). Our results indicate: 1) Serpentinized oceanic peridotites carry significant amounts of isotopically fractionated water, carbon and sulfur into subduction zones; 2) Subduction of serpentinites to high P and T results in loss of water, and sulfur, which can induce melting and contribute to 18O, D, and 34S enrichments and oxidation of the sub-arc mantle wedge; and 3) Isotopically fractionated water, carbon, and sulfur in serpentinite dehydration products are recycled deeper into the mantle where they can contribute to isotope heterogeneities and may be significant for volatile budgets of the deep Earth.

  2. Does subduction zone magmatism produce average continental crust

    Science.gov (United States)

    Ellam, R. M.; Hawkesworth, C. J.

    1988-01-01

    The question of whether present day subduction zone magmatism produces material of average continental crust composition, which perhaps most would agree is andesitic, is addressed. It was argued that modern andesitic to dacitic rocks in Andean-type settings are produced by plagioclase fractionation of mantle derived basalts, leaving a complementary residue with low Rb/Sr and a positive Eu anomaly. This residue must be removed, for example by delamination, if the average crust produced in these settings is andesitic. The author argued against this, pointing out the absence of evidence for such a signature in the mantle. Either the average crust is not andesitic, a conclusion the author was not entirely comfortable with, or other crust forming processes must be sought. One possibility is that during the Archean, direct slab melting of basaltic or eclogitic oceanic crust produced felsic melts, which together with about 65 percent mafic material, yielded an average crust of andesitic composition.

  3. Geoid anomalies in the vicinity of subduction zones

    Science.gov (United States)

    Mcadoo, D. C.

    1981-01-01

    In the considered investigation, attention is given to the line source model, a surface source model, an application of the model, and a model of the thermal lithosphere associated with marginal basins. It is found that undulations in the altimetrically observed geoid of the southwest Pacific are strongly controlled by positive density anomalies in the subducting slabs of the region and the effects of elevation of the geotherm in behind arc lithosphere (corresponding to young marginal basins). Finer details of slab geometry do not obviously manifest themselves in the observed geoid. Such gravitational effects are quite attenuated at sea level and are apparently mixed with crustal effects, oceanographic noise, etc. It appears that slabs in global composite may contribute substantially to intermediate and long wavelength portions (down to spherical harmonic degree 3 or 4) of the earth's gravity field.

  4. Subduction of the Daiichi Kashima Seamount in the Japan Trench

    Science.gov (United States)

    Lallemand, S.; Culotta, R.; Von Huene, R.

    1989-01-01

    In 1984-1985, the Kaiko consortium collected Seabeam, single-channel seismic and submersible sampling data in the vicinity of the Daiichi-Kashima seamount and the southern Japan trench. We performed a prestack migration of a Shell multichannel seismic profile, that crosses this area, and examined it in the light of this unusually diverse Kaiko dataset. Unlike the frontal structure of the northern Japan trench, where mass-wasting appears to be the dominant tectonic process, the margin in front of the Daiichi-Kashima shows indentation, imbrication, uplift and erosion. Emplacement of the front one-third of the seamount beneath the margin front occurs without accretion. We conclude that the Daiichi-Kashima seamount exemplifies an intermediate stage between the initial collision and subduction of a seamount at a continental margin. ?? 1989.

  5. Experimental Determination of Chloritoid Stability in Subducting Oceanic Crust

    Science.gov (United States)

    Forneris, J.; Holloway, J. R.

    2001-12-01

    Dehydration of subducting oceanic lithosphere is the key process for understanding arc magma generation and transport of H2O into the mantle. To establish when and how H2O may be released from the slab into the overlying mantle it is necessary to determine the stability of hydrous phases in the subducting lithosphere. In the past 10 years, experimental investigations of phase relationships in basaltic compositions representing the crustal component of the slab have led to controversial results. Results obtained by Schmidt and Poli (1998) and Pawley and Holloway (1993) on basaltic compositions under H2O saturated conditions showed the potential importance of hydrous phases other than amphibole (such as chloritoid, epidote and lawsonite) in the dehydration process. However, these results are in disagreement with the experiments of Liu et al. (1996), which showed that no hydrous phases are stable beyond the amphibole breakdown reaction at or above 650° C. In our study, piston-cylinder experiments were conducted between 2.2 GPa and 2.8 GPa at 650° C. The starting material consisted of a natural basaltic glass with blueschist/eclogite seeds and H2O. Samples were pressure-sealed in a thick-walled silver capsule with a gold lining designed to prevent hydrogen diffusion in long-duration experiments. The oxygen fugacity was fixed at or near Ni+NiO. These experiments have been focused on determining the stability field of chloritoid by running long-duration experiments (up to 1 month). Our results are in agreement with results by Liu et al. (1996): Chloritoid appears in short-duration runs (144 hours or less at 2.6 GPa and 650° C) but is not present in longer-duration experiments (696 hours or more under the same conditions). The amphiboles obtained in our run products have a glaucophane composition and seem to be stable up to higher pressures (at least 2.6 GPa) than the more calcic amphiboles obtained by the three other groups. Epidote/zoisite is present up to at least

  6. Dynamical effects of subducting ridges: Insights from 3-D laboratory models

    CERN Document Server

    Martinod, Joseph; Faccenna, Claudio; Labanieh, Shasa; Regard, Vincent; 10.1111/j.1365-246X.2005.02797.x

    2010-01-01

    We model the subduction of buoyant ridges and plateaus to study their effect on slab dynamics. Oceanic ridges parallel to the trench have a stronger effect on the process of subduction because they simultaneously affect a longer trench segment. Large buoyant slab segments sink more slowly into the asthenosphere, and their subduction result in a diminution of the velocity of subduction of the plate. We observe a steeping of the slab below those buoyant anomalies, resulting in smaller radius of curvature of the slab, that augments the energy dissipated in folding the plate and further diminishes the velocity of subduction. When the 3D geometry of a buoyant plateau is modelled, the dip of the slab above the plateau decreases, as a result of the larger velocity of subduction of the dense "normal" oceanic plate on both sides of the plateau. Such a perturbation of the dip of the slab maintains long time after the plateau has been entirely incorporated into the subduction zone. We compare experiments with the presen...

  7. Nitrogen recycling at the Costa Rican subduction zone: The role of incoming plate structure.

    Science.gov (United States)

    Lee, Hyunwoo; Fischer, Tobias P; de Moor, J Maarten; Sharp, Zachary D; Takahata, Naoto; Sano, Yuji

    2017-10-24

    Efficient recycling of subducted sedimentary nitrogen (N) back to the atmosphere through arc volcanism has been advocated for the Central America margin while at other locations mass balance considerations and N contents of high pressure metamorphic rocks imply massive addition of subducted N to the mantle and past the zones of arc magma generation. Here, we report new results of N isotope compositions with gas chemistry and noble gas compositions of forearc and arc front springs in Costa Rica to show that the structure of the incoming plate has a profound effect on the extent of N subduction into the mantle. N isotope compositions of emitted arc gases (9-11 N°) imply less subducted pelagic sediment contribution compared to farther north. The N isotope compositions (δ(15)N = -4.4 to 1.6‰) of forearc springs at 9-11 N° are consistent with previously reported values in volcanic centers (δ(15)N = -3.0 to 1.9‰). We advocate that subduction erosion enhanced by abundant seamount subduction at 9-11 N° introduces overlying forearc crustal materials into the Costa Rican subduction zone, releasing fluids with lighter N isotope signatures. This process supports the recycling of heavier N into the deep mantle in this section of the Central America margin.

  8. Subduction of fracture zones controls mantle melting and geochemical signature above slabs.

    Science.gov (United States)

    Manea, Vlad C; Leeman, William P; Gerya, Taras; Manea, Marina; Zhu, Guizhi

    2014-10-24

    For some volcanic arcs, the geochemistry of volcanic rocks erupting above subducted oceanic fracture zones is consistent with higher than normal fluid inputs to arc magma sources. Here we use enrichment of boron (B/Zr) in volcanic arc lavas as a proxy to evaluate relative along-strike inputs of slab-derived fluids in the Aleutian, Andean, Cascades and Trans-Mexican arcs. Significant B/Zr spikes coincide with subduction of prominent fracture zones in the relatively cool Aleutian and Andean subduction zones where fracture zone subduction locally enhances fluid introduction beneath volcanic arcs. Geodynamic models of subduction have not previously considered how fracture zones may influence the melt and fluid distribution above slabs. Using high-resolution three-dimensional coupled petrological-thermomechanical numerical simulations of subduction, we show that enhanced production of slab-derived fluids and mantle wedge melts concentrate in areas where fracture zones are subducted, resulting in significant along-arc variability in magma source compositions and processes.

  9. Where does subduction initiate and die? Insights from global convection models with continental drift

    Science.gov (United States)

    Ulvrova, Martina; Williams, Simon; Coltice, Nicolas; Tackley, Paul

    2017-04-01

    Plate tectonics is a prominent feature on Earth. Together with the underlying convecting mantle, plates form a self-organized system. In order to understand the dynamics of the coupled system, subduction of the lithospheric plates plays the key role since it links the exterior with the interior of the planet. In this work we study subduction initiation and death with respect to the position of the continental rafts. Using thermo-mechanical numerical calculations we investigate global convection models featuring self-consistent plate tectonics and continental drifting employing a pseudo-plastic rheology and testing the effect of a free surface. We consider uncompressible mantle convection in Boussinesq approximation that is basaly and internaly heated. Our calculations indicate that the presence of the continents alterns stress distribution within a certain distance from the margins. Intra-oceanic subudction initiation is favorable during super-continent cycles while the initiation at passive continental margin prevails when continents are dispersed. The location of subduction initiation is additionally controlled by the lithospheric strength. Very weak lithosphere results in domination of intra-oceanic subduction initiation. The subduction zones die more easily in the vicinity of the continent due to the strong rheological contrast between the oceanic and continental lithosphere. In order to compare our findings with subduction positions through time recorded on Earth, we analyse subduction birth in global plate reconstruction back to 410 My.

  10. Convective Removal of Continental Margin Lithosphere at the Edges of Subducting Oceanic Plates

    Science.gov (United States)

    Levander, A.; Bezada, M. J.; Palomeras, I.; Masy, J.; Humphreys, E.; Niu, F.

    2013-12-01

    Although oceanic lithosphere is continuously recycled to the deeper mantle by subduction, the rates and manner in which different types of continental lithospheric mantle are recycled is unclear. Cratonic mantle can be chemically reworked and essentially decratonized, although the frequency of decratonization is unclear. Lithospheric mantle under or adjacent to orogenic belts can be lost to the deeper mantle by convective downwellings and delamination phenomena. Here we describe how subduction related processes at the edges of oceanic plates adjacent to passive continental margins removes the mantle lithosphere from beneath the margin and from the continental interior. This appears to be a widespread means of recycling non-cratonic continental mantle. Lithospheric removal requires the edge of a subducting oceanic plate to be at a relatively high angle to an adjacent passive continental margin. From Rayleigh wave and body wave tomography, and receiver function images from the BOLIVAR and PICASSO experiments, we infer large-scale removal of continental margin lithospheric mantle from beneath 1) the northern South American plate margin due to Atlantic subduction, and 2) the Iberian and North African margins due to Alboran plate subduction. In both cases lithospheric mantle appears to have been removed several hundred kilometers inland from the subduction zones. This type of ';plate-edge' tectonics either accompanies or pre-conditions continental margins for orogenic activity by thinning and weakening the lithosphere. These processes show the importance of relatively small convective structures, i.e. small subducting plates, in formation of orogenic belts.

  11. Why Do We Need 3-d Numerical Models of Subduction?

    Science.gov (United States)

    Morra, G.; Faccenna, C.; Funiciello, F.; Giardini, D.; Regenauer-Lieb, K.

    We use a set of 2-D and 3-D numerical fluid dynamic experiments, modeled with different strain rate dependent rheologies (viscous, visco-plastic, power law) to ana- lyze the long-term dynamics of the subduction of an oceanic slab into an iso-viscous or stratified mantle. For the lithosphere a fluid dynamic approach has been bench- marked with our previous solid mechanical approach with the aim of overcoming the coherency problem of fluid dynamic calculations. The solid mechanical dichotomy Sstrong before failure and weak where it failsT has been cast into a specialized non- & cedil;linear fluid rheology. Analog 2-D and 3-D experiments are finally compared with the numerical experiments. 2-D numerical experiments are considered with and without free surface to investigate the limitations induced by a closed top boundary. The effect of asymmetric boundary conditions (with and without overriding plate) is analyzed with respect to the possibility of trench retreat. We clearly state the importance for the free surface analysis. 2-D experiments have inherent weaknesses: first they provide an unrealistic simulation of mantle flow (suppression of toroidal flow), second they give rise to the Sclosed boxT problem (interaction of the slab with a boundary, i.e. & cedil;660 km and the left and right box boundaries). 3-D numerical experiments permit to overcome these problems. A natural analysis of the behavior of the mantle flow during subduction and the three-dimensional behavior of the slab is thus possible. Physical observables like trench retreat and toroidal and poloidal flow are compared with the results of our companion analog 3-D experiments.

  12. Earth's first stable continents did not form by subduction.

    Science.gov (United States)

    Johnson, Tim E; Brown, Michael; Gardiner, Nicholas J; Kirkland, Christopher L; Smithies, R Hugh

    2017-03-09

    The geodynamic environment in which Earth's first continents formed and were stabilized remains controversial. Most exposed continental crust that can be dated back to the Archaean eon (4 billion to 2.5 billion years ago) comprises tonalite-trondhjemite-granodiorite rocks (TTGs) that were formed through partial melting of hydrated low-magnesium basaltic rocks; notably, these TTGs have 'arc-like' signatures of trace elements and thus resemble the continental crust produced in modern subduction settings. In the East Pilbara Terrane, Western Australia, low-magnesium basalts of the Coucal Formation at the base of the Pilbara Supergroup have trace-element compositions that are consistent with these being source rocks for TTGs. These basalts may be the remnants of a thick (more than 35 kilometres thick), ancient (more than 3.5 billion years old) basaltic crust that is predicted to have existed if Archaean mantle temperatures were much hotter than today's. Here, using phase equilibria modelling of the Coucal basalts, we confirm their suitability as TTG 'parents', and suggest that TTGs were produced by around 20 per cent to 30 per cent melting of the Coucal basalts along high geothermal gradients (of more than 700 degrees Celsius per gigapascal). We also analyse the trace-element composition of the Coucal basalts, and propose that these rocks were themselves derived from an earlier generation of high-magnesium basaltic rocks, suggesting that the arc-like signature in Archaean TTGs was inherited from an ancestral source lineage. This protracted, multistage process for the production and stabilization of the first continents-coupled with the high geothermal gradients-is incompatible with modern-style plate tectonics, and favours instead the formation of TTGs near the base of thick, plateau-like basaltic crust. Thus subduction was not required to produce TTGs in the early Archaean eon.

  13. Migration of teleseismically triggered tremor in southwestern Japan subduction zone

    Science.gov (United States)

    Kurihara, R.; Obara, K.; Maeda, T.; Takeo, A.

    2016-12-01

    Deep low frequency tremor in subduction zone is sometimes triggered by surface waves from teleseismic earthquakes. In southwestern Japan, a sequence of triggered tremor was reported for the 2004 Sumatra-Andaman earthquake (Miyazawa and Mori, 2006). Such triggered tremor was observed in the ambient tremor zone where the short-term slow slip events episodically occur. However, the triggered tremor is not distributed in the entire source area of ambient tremor, but is concentrated in several fixed spots. In this study, we tried to reveal accurate location of triggered tremor and investigate the spatiotemporal characteristics for understandings of condition and occurrence mechanism of triggered tremor. We detected low frequency earthquakes in tremor sequence triggered by teleseismic wave by using matched filter technique. The data were obtained at 10 NIED Hi-net stations. We used low frequency earthquakes occurred in 2014 detected by JMA as template events. Time duration of the templates is five seconds. We analyzed continuous waveform data for one hour from the origin times of 2004 Sumatra, 2008 Wenchuan, 2012 Sumatra and 2015 Nepal earthquakes. In western Shikoku, detected triggered tremor is concentrated at distant fixed two spots with an average separation of 20 km for analyzed four teleseismic events. Particularly, southwestern spot has a streak-like distribution along the dip direction of the subducting plate. In this spot, we detected along-dip migration of triggered tremor. The migration speed is about 300 km/h for 2008 Wenchuan earthquake and about 20 km/h for 2015 Nepal earthquake. Shelly et al. (2007) reported similar along-dip migration of ambient tremor at velocity from 25 to 150 km/h. Therefore, migrations of triggered tremor detected in this study suggest that the triggered tremor is also associated by slow slip event like as ambient tremor.

  14. Assessment of Optimum Value for Dip Angle and Locking Rate Parameters in Makran Subduction Zone

    Science.gov (United States)

    Safari, A.; Abolghasem, A. M.; Abedini, N.; Mousavi, Z.

    2017-09-01

    Makran subduction zone is one of the convergent areas that have been studied by spatial geodesy. Makran zone is located in the South Eastern of Iran and South of Pakistan forming the part of Eurasian-Arabian plate's border where oceanic crust in the Arabian plate (or in Oman Sea) subducts under the Eurasian plate ( Farhoudi and Karig, 1977). Due to lack of historical and modern tools in the area, a sampling of sparse measurements of the permanent GPS stations and temporary stations (campaign) has been conducted in the past decade. Makran subduction zone from different perspectives has unusual behaviour: For example, the Eastern and Western parts of the region have very different seismicity and also dip angle of subducted plate is in about 2 to 8 degrees that this value due to the dip angle in other subduction zone is very low. In this study, we want to find the best possible value for parameters that differs Makran subduction zone from other subduction zones. Rigid block modelling method was used to determine these parameters. From the velocity vectors calculated from GPS observations in this area, block model is formed. These observations are obtained from GPS stations that a number of them are located in South Eastern Iran and South Western Pakistan and a station located in North Eastern Oman. According to previous studies in which the locking depth of Makran subduction zone is 38km (Frohling, 2016), in the preparation of this model, parameter value of at least 38 km is considered. With this function, the amount of 2 degree value is the best value for dip angle but for the locking rate there is not any specified amount. Because the proposed model is not sensitive to this parameter. So we can not expect big earthquakes in West of Makran or a low seismicity activity in there but the proposed model definitely shows the Makran subduction layer is locked.

  15. Implications for metal and volatile cycles from the pH of subduction zone fluids.

    Science.gov (United States)

    Galvez, Matthieu E; Connolly, James A D; Manning, Craig E

    2016-11-17

    The chemistry of aqueous fluids controls the transport and exchange-the cycles-of metals and volatile elements on Earth. Subduction zones, where oceanic plates sink into the Earth's interior, are the most important geodynamic setting for this fluid-mediated chemical exchange. Characterizing the ionic speciation and pH of fluids equilibrated with rocks at subduction zone conditions has long been a major challenge in Earth science. Here we report thermodynamic predictions of fluid-rock equilibria that tie together models of the thermal structure, mineralogy and fluid speciation of subduction zones. We find that the pH of fluids in subducted crustal lithologies is confined to a mildly alkaline range, modulated by rock volatile and chlorine contents. Cold subduction typical of the Phanerozoic eon favours the preservation of oxidized carbon in subducting slabs. In contrast, the pH of mantle wedge fluids is very sensitive to minor variations in rock composition. These variations may be caused by intramantle differentiation, or by infiltration of fluids enriched in alkali components extracted from the subducted crust. The sensitivity of pH to soluble elements in low abundance in the host rocks, such as carbon, alkali metals and halogens, illustrates a feedback between the chemistry of the Earth's atmosphere-ocean system and the speciation of subduction zone fluids via the composition of the seawater-altered oceanic lithosphere. Our findings provide a perspective on the controlling reactions that have coupled metal and volatile cycles in subduction zones for more than 3 billion years(7).

  16. Investigating the Subduction History of the Southwest Pacific using Coupled Plate Tectonic-Mantle Convection Models

    Science.gov (United States)

    Matthews, K. J.; Flament, N. E.; Williams, S.; Müller, D.; Gurnis, M.

    2014-12-01

    The Late Cretaceous to mid Eocene (~85-45 Ma) evolution of the southwest Pacific has been the subject of starkly contrasting plate reconstruction models, reflecting sparse and ambiguous data. Disparate models of (1) west-dipping subduction and back-arc basin opening to the east of the Lord Howe Rise, (2) east-dipping subduction and back-arc basin closure to the east of the Lord Howe Rise, and (3) tectonic quiescence with no subduction have all been proposed for this time frame. To help resolve this long-standing problem we test a new southwest Pacific reconstruction using global mantle flow models with imposed plate motions. The kinematic model incorporates east to northeast directed rollback of a west-dipping subduction zone between 85 and 55 Ma, accommodating opening of the South Loyalty back-arc basin to the east of New Caledonia. At 55 Ma there is a plate boundary reorganization in the region. West-dipping subduction and back-arc basin spreading end, and there is initiation of northeast dipping subduction within the back-arc basin. Consumption of South Loyalty Basin seafloor continues until 45 Ma, when obduction onto New Caledonia begins. West-dipping Tonga-Kermadec subduction initiates at this time at the relict Late Cretaceous-earliest Eocene subduction boundary. We use the 3D spherical mantle convection code CitcomS coupled to the plate reconstruction software GPlates, with plate motions and evolving plate boundaries imposed since 230 Ma. The predicted present-day mantle structure is compared to S- and P-wave seismic tomography models, which can be used to infer the presence of slab material in the mantle at locations where fast velocity anomalies are imaged. This workflow enables us to assess the forward-modeled subduction history of the region.

  17. Geometry and Evolution of the Cangdong Sag in the Bohai Bay Basin, China: Implications for Subduction of the Pacific Plate.

    Science.gov (United States)

    Luo, Liang; Qi, Jiafu; Li, Hongxiang; Dong, Yueqi; Zhang, Shuai; Zhang, Xichen; Yu, Xiaoxia; Luo, Lingyan

    2017-11-13

    The Cangdong Sag is a complex Cenozoic rift basin at the center of the Bohai Bay Basin. Cenozoic structures in the Cangdong Sag can be subdivided into the Cangdong Fault System in the west and the Xuxi Fault System in the east. The geometry of the boundary faults varies along the axes of half-grabens. According to the cross-sectional strata geometry, unconformity and planar structural pattern, the Cenozoic structural evolution of the Cangdong Sag can be divided into four distinct stages: (1) major Paleocene initial rift, (2) latest Paleocene-early Eocene intensive rift, (3) late Eocene-Oligocene strike-slip superimposed rift, and (4) Neogene to present-day post-rift depression. The extensional deformation was mainly derived from horizontal stress induced by the upwelling of asthenosphere. The strike-slip structure of the Cangdong Sag provides important information related to the subduction of the Western Pacific Plate. It was found that the strike-slip movement of the southern Xuxi Fault Zone was activated during the deposition of the third member of Shahejie Formation to the Dongying Formation; therefore, ~43 Ma probably marks the time when the Western Pacific Plate initially changed its subduction direction from northwest to nearly west.

  18. To what depth can continental crust be subducted: numerical predictions and critical observations

    Science.gov (United States)

    Gerya, T.; Faccenda, M.

    2006-12-01

    We performed systematic two-dimensional numerical modeling of continental collision associated with subduction of the lithospheric mantle. Results of our experiments suggest that two contrasting modes of lithospheric subduction below an orogen can exist: one-sided and double-sided. One-sided subduction brings continental crust subducting atop the slab to the contact with hot asthenosperic mantle wedge below the overriding plate. This can result in strong heating, partial melting and rheological weakening of the crust triggering its delamination from subducting mantle lithosphere in form of compositionally buoyant structures (cold plumes) propagating away from subducting plate, passing through the hot mantle wedge, underplating the overriding lithosphere and producing large amount of relatively felsic syn-orogenic magmas at sub-lithospheric depths. One-sided subduction of the buoyant continental crust can also result in a transient "hot channel effect" triggering formation and exhumation of coesite- and diamond- bearing rocks metamorphosed at 700 to 900oC. Anomalously high temperature is caused by intense viscous and radiogenic heating in the channel composed of deeply subducted radiogenic upper-crustal rocks. Low effective viscosity of the channel subsequent to increased temperature and partial melting permits profound mixing of mantle and crustal rocks. The hot channel exists during few million years only but rapidly produces and exhumes large amounts of ultrahigh-pressure, high-temperature rocks within the orogen. Double-sided subduction can follow the one-sided mode at later stages of orogeny when significant rheological coupling between two plates occurs during the collision. In this case the orogen is characterized by double- verging structure, the layer of subducting continental crust is embedded between two negatively buoyant lithospheric slabs and delamination of the crust does not occur. This mode of subduction can bring crustal rocks from the bottom of an

  19. The Calabrian Arc: three-dimensional modelling of the subduction interface.

    Science.gov (United States)

    Maesano, Francesco E; Tiberti, Mara M; Basili, Roberto

    2017-08-21

    The Calabrian Arc is a one-of-a-kind subduction zone, featuring one of the shortest slab segments (subduction zone, we first made a geological reconstruction of the shallower slab interface (subduction interface, its lateral terminations and down-dip curvature, and a slab tear at 70-100 km depth. Our 3D slab model of the Calabrian Arc will contribute to understanding of the geodynamics of a cornerstone in the Mediterranean tectonic puzzle and estimates of seismic and tsunami hazards in the region.

  20. Uplift in the Fiordland region, New Zealand: implications for incipient subduction.

    Science.gov (United States)

    House, M A; Gurnis, M; Kamp, P J J; Sutherland, R

    2002-09-20

    Low-temperature thermochronometry reveals regional Late Cenozoic denudation in Fiordland, New Zealand, consistent with geodynamic models showing uplift of the overriding plate during incipient subduction. The data show a northward progression of exhumation in response to northward migration of the initiation of subduction. The locus of most recent uplift coincides with a large positive Bouguer gravity anomaly within Fiordland. Thermochronometrically deduced crustal thinning, anomalous gravity, and estimates of surface uplift are all consistent with approximately 2 kilometers of dynamic support. This amount of dynamic support is in accord with geodynamic predictions, suggesting that we have dated the initiation of subduction adjacent to Fiordland.

  1. Numerical Modelling of Subduction Plate Interface, Technical Advances for Outstanding Questions

    Science.gov (United States)

    Le Pourhiet, L.; Ruh, J.; Pranger, C. C.; Zheng, L.; van Dinther, Y.; May, D.; Gerya, T.; Burov, E. B.

    2015-12-01

    The subduction zone interface is the place of the largest earthquakes on earth. Compared to the size of a subduction zone itself, it constitutes a very thin zone (few kilometers) with effective rheological behaviour that varies as a function of pressure, temperature, loading, nature of the material locally embedded within the interface as well as the amount of water, melts and CO2. Capturing the behaviour of this interface and its evolution in time is crucial, yet modelling it is not an easy task. In the last decade, thermo-mechanical models of subduction zone have flourished in the literature. They mostly focused on the long-term dynamics of the subduction; e.g. flat subduction, slab detachment or exhumation. The models were validated models against PTt path of exhumed material as well as topography. The models that could reproduce the data all included a mechanically weak subduction channel made of extremely weak and non cohesive material. While this subduction channel model is very convenient at large scale and might apply to some real subduction zones, it does not capture the many geological field evidences that point out the exhumation of very large slice of almost pristine oceanic crust along localised shear zone. Moreover, modelling of sismological and geodetic data using short term tectonic modelling approach also point out that large localised patches rupture within the subduction interface, which is in accordance with geological data but not with large-scale long-term tectonic models. I will present how high resolution models permit to produce slicing at the subduction interface and give clues on how the plate coupling and effective location of the plate interface vary over a few millions of year time scale. I will then discuss the implication of these new high-resolution long-term models of subduction zone on earthquake generation, report progress in the development of self-consistent thermomechanical codes which can handle large strain, high resolution

  2. Petrochronological investigations to unravel the tectono-metamorphic history of Alpine subduction (Briançonnais, Queyras, Western Alps)

    Science.gov (United States)

    Lanari, Pierre

    2015-04-01

    The study of the tectonic and metamorphic history of the Alpine metamorphic belt involving oceanic and continental subduction processes requires knowledge of detailed Pressure-Temperature-time-deformation (P-T-t-ɛ) paths recorded by different tectono-metamorphic units across the belt. This task is particularly challenging in low-grade rocks, e.g. metapelites, (a) for thermobarometry, and (b) for geochronology. Metapelites at greenschist facies metamorphic conditions show a narrow spectrum of metamorphic minerals, notably quartz, chlorite and K-white mica, in addition to commonly detrital relics inherited from previous metamorphic rocks. To obtain reliable P-T estimates, a multi-method approach is required, which usefully combines Raman study of Carbonaceous Material (RSCM), chemical analysis in standardized X-ray maps, and multi-equilibrium inverse thermodynamic modelling of chlorite and white mica. In order to be able to link each assemblage to a specific metamorphic stage and determine the time scales and rates of metamorphism, it is critical to use in situ dating techniques. In this study, high-resolution geochronology was conducted including single-grain 40Ar/39Ar dating (step heating), where possible in combination with U-Th-Pb age-dating of allanite by LA-ICP-MS analysis. In the French western Alps, the Briançonnais zone is a remnant of the continental subduction wedge, while the Liguro-Piedmontais zone is a fossil oceanic subduction wedge. Metapelites from these two complexes were investigated to constrain the individual P-T-t paths recorded in each tectonic slice. This study focussed on deciphering four tectono-metamorphic units in the Briançonnais zone: (B1) The Internal basement; (B2) the Lower and (B3) Upper Zone Houillère; (B4) the Mesozoic Nappe Stack. These continental units recorded green-schist Alpine metamorphic conditions. In the Liguro-Piedmontais zone, five tectono-metamorphic units are identified: (LP1) the Péouvou; (LP2) Saint-Véran; (LP

  3. Reconstructing Farallon plate subduction beneath North America back to the Late Cretaceous.

    Science.gov (United States)

    Liu, Lijun; Spasojevic, Sonja; Gurnis, Michael

    2008-11-07

    Using an inverse mantle convection model that assimilates seismic structure and plate motions, we reconstruct Farallon plate subduction back to 100 million years ago. Models consistent with stratigraphy constrain the depth dependence of mantle viscosity and buoyancy, requiring that the Farallon slab was flat lying in the Late Cretaceous, consistent with geological reconstructions. The simulation predicts that an extensive zone of shallow-dipping subduction extended beyond the flat-lying slab farther east and north by up to 1000 kilometers. The limited region of flat subduction is consistent with the notion that subduction of an oceanic plateau caused the slab to flatten. The results imply that seismic images of the current mantle provide more constraints on past tectonic events than previously recognized.

  4. Observing mesoscale eddy effects on mode-water subduction and transport in the North Pacific.

    Science.gov (United States)

    Xu, Lixiao; Li, Peiliang; Xie, Shang-Ping; Liu, Qinyu; Liu, Cong; Gao, Wendian

    2016-02-01

    While modelling studies suggest that mesoscale eddies strengthen the subduction of mode waters, this eddy effect has never been observed in the field. Here we report results from a field campaign from March 2014 that captured the eddy effects on mode-water subduction south of the Kuroshio Extension east of Japan. The experiment deployed 17 Argo floats in an anticyclonic eddy (AC) with enhanced daily sampling. Analysis of over 3,000 hydrographic profiles following the AC reveals that potential vorticity and apparent oxygen utilization distributions are asymmetric outside the AC core, with enhanced subduction near the southeastern rim of the AC. There, the southward eddy flow advects newly ventilated mode water from the north into the main thermocline. Our results show that subduction by eddy lateral advection is comparable in magnitude to that by the mean flow--an effect that needs to be better represented in climate models.

  5. Oblique subduction modelling indicates along-trench tectonic transport of sediments.

    Science.gov (United States)

    Malatesta, Cristina; Gerya, Taras; Crispini, Laura; Federico, Laura; Capponi, Giovanni

    2013-01-01

    Convergent plate margins are currently distinguished as 'accretional' or 'erosional', depending on the tendency to accumulate sediments, or not, at the trench. Accretion and erosion can coexist along the same margin and we have noticed that this mostly occurs where subduction is oblique. Here we show that at oblique subduction zones, sediments that enter the trench are first buried, and later migrate laterally parallel to the trench and at various depths. Lateral migration of sediments continues until they reach a physical barrier where they begin to accumulate. The accretionary wedge size decreases along the trench moving away from the barrier. We therefore suggest that the gradual variation of the accretionary wedge size and sediment amount at the trench along one single subduction zone, as observed in many active plate margins worldwide, can be explained by the lateral tectonic migration of sediments driven by obliquity of subduction as well.

  6. A Computer-Based Subduction-Zone-Earthquake Exercise for Introductory-Geology Classes.

    Science.gov (United States)

    Shea, James Herbert

    1991-01-01

    Describes the author's computer-based program for a subduction-zone-earthquake exercise. Instructions for conducting the activity and obtaining the program from the author are provided. Written in IBM QuickBasic. (PR)

  7. Origin and consequences of western Mediterranean subduction, rollback, and slab segmentation

    NARCIS (Netherlands)

    van Hinsbergen, D.J.J.|info:eu-repo/dai/nl/269263624; Vissers, R.L.M.|info:eu-repo/dai/nl/068789203; Spakman, W.|info:eu-repo/dai/nl/074103164

    2014-01-01

    The western Mediterranean recorded subduction rollback, slab segmentation and separation. Here we address the questions of what caused Oligocene rollback initiation, and how its subsequent evolution split up an originally coherent fore arc into circum-southwest Mediterranean segments. We

  8. Chromium isotope signature during continental crust subduction recorded in metamorphic rocks

    National Research Council Canada - National Science Library

    Shen, Ji; Liu, Jia; Qin, Liping; Wang, Shui‐Jiong; Li, Shuguang; Xia, Jiuxing; Ke, Shan; Yang, Jingsui

    2015-01-01

    The chromium isotope compositions of 27 metamorphic mafic rocks with varying metamorphic degrees from eastern China were systematically measured to investigate the Cr isotope behavior during continental crust subduction...

  9. Probing the transition between seismically coupled and decoupled segments along an ancient subduction interface

    National Research Council Canada - National Science Library

    Angiboust, Samuel; Kirsch, Josephine; Oncken, Onno; Glodny, Johannes; Monié, Patrick; Rybacki, Erik

    2015-01-01

    ... as the focus site of episodic tremor and slip features. Exhumed remnants of the former Alpine subduction zone found in the Swiss Alps allow analyzing fluid and deformation processes near the transition zone region (30–40 km paleodepth...

  10. Frictional behaviour of megathrust fault gouges under in-situ subduction zone conditions

    NARCIS (Netherlands)

    den Hartog, S.A.M.

    2013-01-01

    Subduction zone megathrusts generate the largest earthquakes and tsunamis known. Understanding and modelling “seismogenesis” on such faults requires an understanding of the frictional processes that control nucleation and propagation of seismic slip. However, experimental data on the frictional

  11. The Melt Segregation During Ascent of Buoyant Diapirs in Subduction Zones

    Science.gov (United States)

    Zhang, N.; Behn, M. D.; Parmentier, E. M.; Kincaid, C. R.

    2014-12-01

    Cold, low-density diapirs arising from hydrated mantle and/or subducted sediments on the top of subducting slabs may transport key chemical signatures from the slab to the shallow source region for arc magmas. These chemical signatures are strongly influenced by melting of this buoyant material during its ascent. However, to date there have been relatively few quantitative models to constrain melting and melt segregation in an ascending diapir, as well as the induced geochemical signature. Here, we use a two-phase Darcy-Stokes-energy model to investigate thermal evolution, melting, and melt segregation in buoyant diapirs as they ascend through the mantle wedge. Using a simplified 2-D axi-symmetric circular geometry we investigate diapir evolution in three scenarios with increasing complexity. First, we consider a case without melting in which the thermal evolution of the diapir is controlled solely by thermal diffusion during ascent. Our results show that for most cases (e.g., diapir radius ≤ 3.7 km and diapir generation depths of ~ 75 km) thermal diffusion times are smaller than the ascent time—implying that the diapir will thermal equilibrate with the mantle wedge. Secondly, we parameterize melting within the diapir, but without melt segregation, and add the effect of latent heat to the thermal evolution of the diapir. Latent heat significantly buffers heating of the diapir. For the diapir with radius ~3.7 km, the heating from the outside is slowed down ~30%. Finally, we include melt segregation within the diapir in the model. Melting initiates at the boundaries of the diapir as the cold interior warms in response to thermal equilibration with the hot mantle wedge. This forms a high porosity, high permeability rim around the margin of the diapir. As the diapir continues to warm and ascend, new melts migrate into this rim and are focused upward, accumulating at the top of the diapir. The rim thus acts like an annulus melt channel isolating the central part of

  12. Electrical conductivity imaging in the western Pacific subduction zone

    Science.gov (United States)

    Utada, Hisashi; Baba, Kiyoshi; Shimizu, Hisayoshi

    2010-05-01

    Oceanic plate subduction is an important process for the dynamics and evolution of the Earth's interior, as it is regarded as a typical downward flow of the mantle convection that transports materials from the near surface to the deep mantle. Recent seismological study showed evidence suggesting the transportation of a certain amount of water by subduction of old oceanic plate such as the Pacific plate down to 150-200 km depth into the back arc mantle. However it is not well clarified how deep into the mantle the water can be transported. The electromagnetic induction method to image electrical conductivity distribution is a possible tool to answer this question as it is known to be sensitive to the presence of water. Here we show recent result of observational study from the western Pacific subduction zone to examine the electrical conductivity distribution in the upper mantle and in the mantle transition zone (MTZ), which will provide implications how water distributes in the mantle. We take two kinds of approach for imaging the mantle conductivity, (a) semi-global and (b) regional induction approaches. Result may be summarized as follows: (a) Long (5-30 years) time series records from 8 submarine cables and 13 geomagnetic observatories in the north Pacific region were analyzed and long period magnetotelluric (MT) and geomagnetic deep sounding (GDS) responses were estimated in the period range from 1.7 to 35 days. These frequency dependent response functions were inverted to 3-dimensional conductivity distribution in the depth range between 350 and 850 km. Three major features are suggested in the MTZ depth such as, (1) a high conductivity anomaly beneath the Philippine Sea, (2) a high conductivity anomaly beneath the Hawaiian Islands, and (3) a low conductivity anomaly beneath and in the vicinity of northern Japan. (b) A three-year long deployment of ocean bottom electro-magnetometers (OBEM's) was conducted in the Philippine Sea and west Pacific Ocean from 2005

  13. Trading Time with Space - Development of subduction zone parameter database for a maximum magnitude correlation assessment

    Science.gov (United States)

    Schaefer, Andreas; Wenzel, Friedemann

    2017-04-01

    Subduction zones are generally the sources of the earthquakes with the highest magnitudes. Not only in Japan or Chile, but also in Pakistan, the Solomon Islands or for the Lesser Antilles, subduction zones pose a significant hazard for the people. To understand the behavior of subduction zones, especially to identify their capabilities to produce maximum magnitude earthquakes, various physical models have been developed leading to a large number of various datasets, e.g. from geodesy, geomagnetics, structural geology, etc. There have been various studies to utilize this data for the compilation of a subduction zone parameters database, but mostly concentrating on only the major zones. Here, we compile the largest dataset of subduction zone parameters both in parameter diversity but also in the number of considered subduction zones. In total, more than 70 individual sources have been assessed and the aforementioned parametric data have been combined with seismological data and many more sources have been compiled leading to more than 60 individual parameters. Not all parameters have been resolved for each zone, since the data completeness depends on the data availability and quality for each source. In addition, the 3D down-dip geometry of a majority of the subduction zones has been resolved using historical earthquake hypocenter data and centroid moment tensors where available and additionally compared and verified with results from previous studies. With such a database, a statistical study has been undertaken to identify not only correlations between those parameters to estimate a parametric driven way to identify potentials for maximum possible magnitudes, but also to identify similarities between the sources themselves. This identification of similarities leads to a classification system for subduction zones. Here, it could be expected if two sources share enough common characteristics, other characteristics of interest may be similar as well. This concept

  14. Subduction and Slab Advance at Orogen Syntaxes: Predicting Exhumation Rates and Thermochronometric Ages with Numerical Modeling

    Science.gov (United States)

    Nettesheim, Matthias; Ehlers, Todd A.; Whipp, David M.

    2017-04-01

    The change in plate boundary orientation and subducting plate geometry along orogen syntaxes may have major control on the subduction and exhumation dynamics at these locations. Previous work documents that the curvature of subducting plates in 3D at orogen syntaxes forces a buckling and flexural stiffening of the downgoing plate. The geometry of this stiffened plate region, also called indenter, can be observed in various subduction zones around the world (e.g. St. Elias Range, Alaska; Cascadia, USA; Andean syntaxis, South America). The development of a subducting, flexurally stiffened indenter beneath orogen syntaxes influences deformation in the overriding plate and can lead to accelerated and focused rock uplift above its apex. Moreover, the style of deformation in the overriding plate is influenced by the amount of trench or slab advance, which is the amount of overall shortening not accommodated by underthrusting. While many subduction zones exhibit little to no slab advance, the Nazca-South America subduction and especially the early stages of the India-Eurasia collision provide end-member examples. Here, we use a transient, lithospheric-scale, thermomechanical 3D model of an orogen syntaxis to investigate the effects of subducting a flexurally stiffened plate geometry and slab advance on upper plate deformation. A visco-plastic upper-plate rheology is used, along with a buckled, rigid subducting plate. The free surface of the thermomechanical model is coupled to a landscape evolution model that accounts for erosion by fluvial and hillslope processes. The cooling histories of exhumed rocks are used to predict the evolution of low-temperature thermochronometer ages on the surface. With a constant overall shortening for all simulations, the magnitude of slab advance is varied stepwise from no advance, with all shortening accommodated by underthrusting, to full slab advance, i.e. no motion on the megathrust. We show that in models where most shortening is

  15. Subduction-related metasomatism in French Massif Central: evidence from secondary orthopyroxene in mantle xenoliths.

    Science.gov (United States)

    Wagner, Christiane

    2017-04-01

    Peridotite xenoliths from the French Massif Central (FMC) have undergone a complex mantle metasomatic history by percolation of various melts/ fluids from alkali basaltic to carbonatite composition. This contribution argues for the imprint of another type of metasomatism related to subduction-derived melts/fluids. The samples come from the Mont Coupet strombolian volcano, Devès, FMC. They are fresh protogranular spinel lherzolites, with no infiltration of the host basanitic magma, but with evidences of alkali and carbonate-related metasomatism discussed elsewhere [1-3]. This study focuses on secondary orthopyroxene (opx2). It occurs +/- minor secondary clinopyroxene (cpx2) in cross-cutting thin (10 µm-20 µm) veinlets, and also as discontinuous patches developed after primary clinopyroxene (cpx1) at the contact with primary olivine (ol1). Opx2 crystals do not form fibrous radial aggregates. Rare small (<1 µm) rounded chloroapatite is included in opx2 after cpx1. Small (2 µm) pores are observed throughout the veins, at the contact with ol1, along sub-grained boundaries between opx2 and cpx2 in the veinlets, and between opx2 and cpx1. The primary minerals crosscut by the veinlets do not show any compositional zoning and the different elements show sharp profiles between opx 2 and primary minerals. Compared to primary opx, opx2 are characterized by a lower content in Al2O3 (1.7-2.5 wt. %) / 3.2-4.0 wt. %). They are slightly MgO (XMg = 90-91/ 89-90) and CaO richer (0.5 wt. % / 0.3 wt. %), and contain slightly less Cr2O3 (<0.2 wt. % / 0.2-0.3wt. %) and TiO2 (<0.06 wt. % / 0.06-0.14 wt. %), although there is some crossover between the two data sets. Na2O contents (<0.05 wt. %) are comparable. Cpx2 and opx2 from the veinlets are in equilibrium (XMg = 90-92). Al and Ti contents in cpx2 exclude any influence of percolation of the host magma. Moreover, their high Al6/Al4 ratio points to an equilibration at higher pressure than igneous cpx, close to that of cpx1. These

  16. Perovskite inclusions in deep mantle diamonds and the fate of subducted lithosphere

    Science.gov (United States)

    Walter, Michael; Armstrong, Lora

    2010-05-01

    Sublithospheric diamonds are typically Type II, frequently exhibit complex zoning, and sometimes contain mineral inclusions that can potentially reveal deep mantle lithologies and petrologic processes. A considerable number of these diamonds contain inclusions with elemental stoichiometries consistent with transition zone (e.g. majoritic garnet, Ca-perovskite) and lower mantle phases (e.g. Mg-perovskite, Ca-perovskite, (Mg,Fe)-periclase) [1]. Ca-rich perovskites, some containing considerable CaTiO3 component, almost invariably have very low Mg contents, unlike what would be expected in solid lower mantle peridotitic or basaltic lithologies, but have elevated incompatible elements abundances that almost certainly indicate crystallization from a low-degree Ca-rich partial melt [2,3]. High-Ca majoritic garnets also have both major and trace element characteristics indicating the role of low-degree, Ca-rich partial melts [3,4], and in some cases calculated melts likely formed in subducted oceanic crust or lithosphere [3]. Given that diamond crystallized syngenetically with the inclusions, crystallization from carbonated melts is implicated. The reducing conditions expected in the ambient transition zone and lower mantle [5] could promote reduction of the carbonate component in slab-derived, carbonated (oxidized), partial melts. Reduction can lead to diamond and perovskite crystallization from the melt, possibly with H2O as a by-product through a reaction such as: CaCO3 (melt) + SiO2(melt-solid) + CH4(fluid-melt)= CaSiO3(melt-solid)) + 2H2O(melt) + 2Cdiamond Mg-perovskite could crystallize via a similar reaction involving the MgCO3 component of the melt. We speculate that when subducted slabs stall at the base of the transition zone, they may heat up and release low-degree carbonated melts [6]. Such melts may migrate, crystallize and metasomatize the ambient mantle. Trace element abundances in some kimberlites are remarkably similar to liquids that could have coexisted

  17. Softening trigerred by eclogitization, the first step toward exhumation during continental subduction

    Science.gov (United States)

    Jolivet, Laurent; Raimbourg, Hugues; Labrousse, Loïc; Avigad, Dov; Leroy, Yves; Austrheim, Håkon; Andersen, Torgeir B.

    2005-09-01

    Direct observation of peak pressure deformation in exhumed subduction channels is difficult because little evidence of this deformation survives later syn-exhumation deformation. Most ultrahigh-pressure parageneses are found in continental derived metamorphic rocks making continental subduction the best context to observe peak pressure deformation. Whereas many studies have enlightened the main driving parameters of exhumation such as buoyancy forces, low viscosity in the subduction channel, overburden removal by erosion and normal faulting, a basic question is seldom considered: why is a tectonic unit disconnected from the descending lithosphere and why does it start its way towards the surface? This event, seminal to exhumation processes, must involve some deformation and decoupling of the exhumed slice from the descending slab at peak pressure conditions or close to it. Our field observations in the Bergen arc show that Caledonian eclogitization and later amphibolitization of a granulitic terrane was achieved with a consistent component of simple shear compatible with the sense of the Caledonian subduction. Thus, the sequence of deformation preserved in the Bergen Arc documents the decoupling of subducted crustal material from the descending slab at the onset of exhumation. This observation suggests that deformation in the subduction channel is largely controlled by kinematic boundary conditions, i.e. underthrusting of the subducting slab. In this context of simple shear, metamorphic reactions assisted by fracturating, fluid infiltration and ductile deformation lower the resistance of rocks and allow the localisation of shear zones and the decoupling of buoyant tectonic units from the subducting slab. These tectonic units can then be incorporated into the channel circulation and start their upward travel.

  18. Lower slab boundary in the Japan subduction zone

    Science.gov (United States)

    Tonegawa, Takashi; Hirahara, Kazuro; Shibutani, Takuo; Fujii, Naoyuki

    2006-07-01

    We have successfully detected the lower boundary of a subducting slab. The successive imaging of the lower slab boundary beneath northeastern (NE) Japan is attained by receiver function (RF) depth conversion analysis using a recent 3D tomographic velocity model. We use waveforms from 249 teleseismic events collected by Hi-net and J-array short-period stations in NE Japan. RFs are calculated through frequency domain division of radial components by vertical ones with a water level of 0.001 and a 1.0 Hz low-pass Gaussian filter. Assuming that all later phases in the radial RFs are due to Ps phases converted at discontinuities beneath stations, we calculate depth-converted RFs, mapped onto the cross-section with the CCP (common conversion point) stacking. In a cross section, the slab surface and the oceanic Moho can be imaged down to 120 km depth. For the greater depths, the RF amplitudes corresponding to them cannot be seen, because, in the oceanic crust, basalt would be completely metamorphosed to eclogite below this depth. The lower boundary of the Pacific slab can also be traced down to 200 km depth or more. It is parallel to the slab surface and the oceanic Moho, and the thickness between the slab surface and the lower boundary is ˜ 80 km. Finally, we estimate a top-to-bottom slab velocity model that explains the RFs observed at broadband stations with the synthetic RFs. This model exhibits a 13% velocity reduction downwards the lower slab boundary, which would relatively sharp for the base of the thermal boundary layer. Therefore, this sharp discontinuity is presumably considered to be the subducting G (Gutenberg) discontinuity that is formed by the change of the amount of H 2O (water), meaning that the G discontinuity is the chemical boundary at the bottom of the oceanic lithosphere. The G discontinuity depth is controlled by the potential temperature of the asthenospheric mantle beneath the mid-ocean ridge, and hence the observed thickness of 80 km, i.e. the

  19. Geological model of supercritical geothermal reservoir related to subduction system

    Science.gov (United States)

    Tsuchiya, Noriyoshi

    2017-04-01

    Following the Great East Japan Earthquake and the accident at the Fukushima Daiichi Nuclear power station on 3.11 (11th March) 2011, geothermal energy came to be considered one of the most promising sources of renewable energy for the future in Japan. The temperatures of geothermal fields operating in Japan range from 200 to 300 °C (average 250 °C), and the depths range from 1000 to 2000 m (average 1500 m). In conventional geothermal reservoirs, the mechanical behavior of the rocks is presumed to be brittle, and convection of the hydrothermal fluid through existing network is the main method of circulation in the reservoir. In order to minimize induced seismicity, a rock mass that is "beyond brittle" is one possible candidate, because the rock mechanics of "beyond brittle" material is one of plastic deformation rather than brittle failure. Supercritical geothermal resources could be evaluated in terms of present volcanic activities, thermal structure, dimension of hydrothermal circulation, properties of fracture system, depth of heat source, depth of brittle factures zone, dimension of geothermal reservoir. On the basis of the GIS, potential of supercritical geothermal resources could be characterized into the following four categories. 1. Promising: surface manifestation d shallow high temperature, 2 Probability: high geothermal gradient, 3 Possibility: Aseismic zone which indicates an existence of melt, 4 Potential : low velocity zone which indicates magma input. Base on geophysical data for geothermal reservoirs, we have propose adequate tectonic model of development of the supercritical geothermal reservoirs. To understand the geological model of a supercritical geothermal reservoir, granite-porphyry system, which had been formed in subduction zone, was investigated as a natural analog of the supercritical geothermal energy system. Quartz veins, hydrothermal breccia veins, and glassy veins are observed in a granitic body. The glassy veins formed at 500-550

  20. Episodic tremor and slip in Northern Sumatra subduction zone

    Science.gov (United States)

    Sianipar, Dimas; Subakti, Hendri

    2017-07-01

    The first reported observation of non-volcanic tremor in Sunda Arc in Sumbawa, Indonesia open a possibility of discovery of episodic tremor and slip (ETS) from out of Pacific Rim. Non-volcanic tremor gives some important information about dynamic of plate boundaries. The characteristics of these tremors are visually as non-impulsive, high frequency, long-duration and low-amplitude signals. Tectonic tremor occurred in a transition part of brittle-ductile of a fault and frequently associated with the shearing mechanism of slow slip. Tectonic tremor is a seismic case that also very interested, because it shows strong sensitivity to stress changes. Deep non-volcanic tremor is usually associated with episodic slow-slip events. Tectonic tremor is found in close association with geodetically observed slow-slip events (SSE) in subduction zones. One research found that there is possibility of SSE occurrence on Banyak Islands, North Sumatra revealed from coral observation. The SSE occurred on the Banyak Islands portion of the megathrust at 30-55 km depth, within the downdip transition zone. We do a systematic search of episodic tremor and its possible relationship with slow-slip phenomena in Northern Sumatra subduction zone. The spectrogram analysis is done to analyze the potential tremor signals. We use three component broadband seismic stations with 20, 25, and 50 sampling per second (BH* and SH* channels). We apply a butterworth 5 Hz highpass filter to separate the signal as local tremor and teleseismic/regional earthquakes. Before computing spectrogram to avoid high-frequency artifacts to remote triggering, we apply a 0.5 Hz filter. We also convert the binary seismic data into sound waves to make sure that these events meet the tectonic tremor criterion. We successfully examine 3 seismic stations with good recording i.e. GSI, SNSI and KCSI. We find there are many evidences of high frequency episodic tremor like signals. This include an analysis of potential triggered

  1. Lithium Isotopic Fractionation in Subduction Zones: Clues From Clays

    Science.gov (United States)

    Williams, L. B.; Hervig, R. L.

    2003-12-01

    Lithium isotope ratios show such large variations in nature (>30 per mil), that many areas of geosciences are exploring the usefulness of this system in explaining the evolution of particular rocks. Here we show how the lithium isotope ratios change during the transformation of smectite clay minerals to illite during burial metamorphism. Such a transition may be a common feature in the shallow regions of subduction zones and may ultimately affect the Li isotope compositions of fluids contributing to arc magmatism. Lithium is a ubiquitous trace element in natural formation waters that, like B, shows large isotopic fractionation especially during interactions with clay minerals. Lithium is adsorbed in the interlayer region of expandable clay minerals but is easily exchanged. Lithium is also incorporated into the octahedral sites. The substitutions of Li in two crystallographic sites of clay minerals may complicate interpretations of bulk Li-isotope ratios. We suggest that the magnitude of the isotopic fractionation of Li between fluid and clay is different in the interlayer sites of clay minerals than in the octahedral sites of clay minerals. Examination of Li contents and isotope variations in experimental reactions of smectite to illite (300C, 100MPa) shows changes with structural re-arrangement of the clay layers. The Li-isotope trend declines (from ~+6 to -13 per mil, expressed as ratios of 7/6) throughout R1-ordering of the mixed-layered illite smectite (I/S). However, the equilibrium end products of the reaction have R3-ordering and show a heavier isotope ratio (~0 per mil). This observation is very similar to the trends we observed for B-isotopes, where the interlayer B initially overprinted the tetrahedral-layer B isotope composition, but as the interlayer sites were collapsed during illitization, the equilibrium isotope composition was approached. The significant Li and B isotopic changes that occur during ordering of I/S coincides with the temperatures

  2. Kinematics of Late Cretaceous subduction initiation in the Neo-Tethys Ocean reconstructed from ophiolites of Turkey, Cyprus, and Syria

    Science.gov (United States)

    Maffione, Marco; van Hinsbergen, Douwe; de Gelder, Giovanni; van der Goes, Freek; Morris, Antony

    2017-04-01

    Formation of new subduction zones represents one of the cornerstones of plate tectonics, yet both the kinematics and geodynamics governing this process remain enigmatic. A major subduction initiation event occurred in the Late Cretaceous, within the Neo-Tethys Ocean between Gondwana and Eurasia. Supra-subduction zone (SSZ) ophiolites (i.e., emerged fragments of ancient oceanic lithosphere accreted at supra-subduction spreading centers) were generated during this subduction event, and are today distributed in the eastern Mediterranean region along three E-W trending ophiolitic belts. Current models associate these ophiolite belts to simultaneous initiation of multiple, E-W trending subduction zones at 95 Ma. Here we report paleospreading direction data obtained from paleomagnetic analysis of sheeted dyke sections from seven Neo-Tethyan ophiolites of Turkey, Cyprus, and Syria, demonstrating that these ophiolites formed at NNE-SSW striking ridges parallel to the newly formed subduction zones. This subduction system was step-shaped and composed of NNE-SSW and ESE-WNW segments. The eastern subduction segment invaded the SW Mediterranean, leading to a radial obduction pattern similar to the Banda arc. Emplacement age constraints indicate that this subduction system formed close to the Triassic passive and paleo-transform margins of the Anatolide-Tauride continental block. Because the original Triassic-Jurassic Neo-Tethyan spreading ridge must have already subducted below the Pontides before the Late Cretaceous, we infer that the Late Cretaceous Neo-Tethyan subduction system started within ancient lithosphere, along NNE-SSW oriented fracture zones and faults parallel to the E-W trending passive margins. This challenges current concepts suggesting that subduction initiation occurs along active intra-oceanic plate boundaries.

  3. 3D geodynamic models for the development of opposing continental subduction zones: The Hindu Kush-Pamir example

    Science.gov (United States)

    Liao, Jie; Gerya, Taras; Thielmann, Marcel; Webb, A. Alexander G.; Kufner, Sofia-Katerina; Yin, An

    2017-12-01

    The development of opposing continental subduction zones remains scantly explored in three dimensions. The Hindu Kush-Pamir orogenic system at the western end of the Himalayan orogen provides a rare example of continental collision linked to two opposing intra-continental subduction zones. The subducted plates feature a peculiar 3D geometry consisting of two distinct lithospheric fragments with different polarities, subduction angles and slab-curvatures beneath the Hindu Kush and Pamir, respectively. Using 3D geodynamic modeling, we simulate possible development of two opposing continental subduction zones to understand the dynamic evolution of the Hindu Kush-Pamir orogenic system. Our geodynamic model reproduces the major tectonic elements observed: (1) the deeper subduction depth, the steeper dip angle and the southward offset of the Hindu Kush subduction zone relative to the Pamir naturally occur if convergence direction of the subducting Indian plate and dip-direction of the Hindu Kush subduction zone match. (2) The formation of the highly asymmetrically curved Pamir region and the south-dipping subduction is promoted by the initial geometry of the indenting Indian lithosphere together with the existence of a major strike-slip fault on the eastern margin of the Pamir region. (3) Subduction of only the lower continental crust during continental collision can occur if the coupling between upper and lower crusts is weak enough to allow a separation of these two components, and that (4) the subduction of mainly lower crust then facilitates that conditions for intermediate-depth seismicity can be reached. (5) The secondary tectonic features modeled here such as strike-slip-fault growth, north-northwest striking extension zone, and lateral flow of the thickened ductile upper crust are comparable to the current tectonics of the region. (6) Model results are further compared to the potentially similar orogenic system, i.e., the Alpine orogen, in terms of the curved

  4. Dry Juan de Fuca slab revealed by quantification of water entering Cascadia subduction zone

    Science.gov (United States)

    Canales, J. P.; Carbotte, S. M.; Nedimović, M. R.; Carton, H.

    2017-11-01

    Water is carried by subducting slabs as a pore fluid and in structurally bound minerals, yet no comprehensive quantification of water content and how it is stored and distributed at depth within incoming plates exists for any segment of the global subduction system. Here we use seismic data to quantify the amount of pore and structurally bound water in the Juan de Fuca plate entering the Cascadia subduction zone. Specifically, we analyse these water reservoirs in the sediments, crust and lithospheric mantle, and their variations along the central Cascadia margin. We find that the Juan de Fuca lower crust and mantle are drier than at any other subducting plate, with most of the water stored in the sediments and upper crust. Variable but limited bend faulting along the margin limits slab access to water, and a warm thermal structure resulting from a thick sediment cover and young plate age prevents significant serpentinization of the mantle. The dryness of the lower crust and mantle indicates that fluids that facilitate episodic tremor and slip must be sourced from the subducted upper crust, and that decompression rather than hydrous melting must dominate arc magmatism in central Cascadia. Additionally, dry subducted lower crust and mantle can explain the low levels of intermediate-depth seismicity in the Juan de Fuca slab.

  5. The Terminal Stage of Subduction: the Hindu Kush Slab Break-off

    Science.gov (United States)

    Kufner, S. K.; Schurr, B.; Sippl, C.; Yuan, X.; Ratschbacher, L.; Akbar, A. S. M.; Ischuk, A.; Murodkulov, S.; Schneider, F.; Mechie, J.; Tilmann, F. J.

    2016-12-01

    The terminal stage of subduction arrives when the ocean basin is closed and the continental margin arrives at the trench. The opposite forces of the sinking slab and buoyant continent ultimately leads to break-off of the subducted slab. This process, although common in geological history, is rarely observed, because it is short-lived. Here we report new precise earthquake hypocenters, detailed tomographic images and earthquake source mechanisms from the Hindu Kush region in Central Asia, which hint at continental subduction and plate necking. Our images provide a rare glimpse at the ephemeral process of slab break-off: the Hindu Kush slablet in its uppermost section is thinned or already severed and that intermediate depth earthquakes cluster at the neck connecting it to the deeper slab. From a strain rate analysis, we deduce that the deep portion of the slab is in the process of detaching from the shallower fragment at much higher rates than the current convergence rate at the surface. The increased strain rate might arise as the buoyant continental crust, which is dragged into the subduction system in its terminal stage, resists subduction, whereas the earlier subducted mantle lithosphere pulls from underneath.

  6. Connecting the Surface and the Deep: Evolving Role of Subduction Zone Fluids Through Time

    Science.gov (United States)

    Galvez, Matthieu Emmanuel

    2017-04-01

    The speciation of aqueous fluids controls the transport and exchange of metals and volatile elements on Earth. Subduction zones are the most important geodynamic setting for this fluid-mediated chemical exchange. Characterizing the ionic speciation and pH of fluids equilibrated with rocks at subduction zone conditions has been a major challenge in Earth science. I will first present thermodynamic predictions of fluid-rock equilibria that tie together models of mineralogy and fluid speciation along a range of model P-T paths. The pH of fluids in subducted crustal lithologies is uniform and confined to a mildly alkaline range, controlled by rock volatile and chlorine contents. In contrast, the pH of mantle wedge fluids exhibits marked sensitivity to minor variations in rock chemistry. These variations may be caused by intramantle differentiation, or by infiltration of fluids enriched in alkali components extracted from the subducted crust. The sensitivity of pH to carbon, alkali and halogens illustrates a top-down control of Earth's atmosphere - ocean chemistry on the speciation of subduction zone fluids via the hydrothermally altered oceanic lithosphere. These results provide a perspective on the physicochemical mechanisms that have coupled metal and volatile cycles in subduction zones for over 2.5 billion years.

  7. Surface imprint of toroidal flow at retreating slab edges: The first geodetic evidence in the Calabrian subduction system

    Science.gov (United States)

    Palano, M.; Piromallo, C.; Chiarabba, C.

    2017-01-01

    Dense GPS observations can help Earth scientists to capture the surface imprint of mantle toroidal flow at slab edges. We document this process in the Calabrian subduction system, where the Ionian slab rollback took place during the past 30 Ma, following a stepwise process driven by migration of lithospheric tearing. We found rotation rates of 1.29°/Ma (counterclockwise) and 1.74°/Ma (clockwise), for poles located close to the northern and southern slab edges, respectively. These small-scale, opposite rotations occur along complex sets of active faults representing the present-day lithospheric expression of the tearing processes affecting the southeastward retreating Ionian slab at both edges. The observed rotations are likely still young and the process more immature at the northern tear, where it is unable to reorient mantle fabric and therefore is unseen by SKS splitting.

  8. Primary carbonatite melt from deeply subducted oceanic crust

    Energy Technology Data Exchange (ETDEWEB)

    Walter, M.J.; Bulanova, G.P.; Armstrong, L.S.; Keshav, S.; Blundy, J.D.; Gudfinnesson, G.; Lord, O.T.; Lennie, A.R.; Clark, S.M.; Smith, C.B.; Gobbo, L.

    2008-07-01

    Partial melting in the Earth's mantle plays an important part in generating the geochemical and isotopic diversity observed in volcanic rocks at the surface. Identifying the composition of these primary melts in the mantle is crucial for establishing links between mantle geochemical 'reservoirs' and fundamental geodynamic processes. Mineral inclusions in natural diamonds have provided a unique window into such deep mantle processes. Here they provide exper8imental and geochemical evidence that silicate mineral inclusions in diamonds from Juina, Brazil, crystallized from primary and evolved carbonatite melts in the mantle transition zone and deep upper mantle. The incompatible trace element abundances calculated for a melt coexisting with a calcium-titanium-silicate perovskite inclusion indicate deep melting of carbonated oceanic crust, probably at transition-zone depths. Further to perovskite, calcic-majorite garnet inclusions record crystallization in the deep upper mantle from an evolved melt that closely resembles estimates of primitive carbonatite on the basis of volcanic rocks. Small-degree melts of subducted crust can be viewed as agents of chemical mass-transfer in the upper mantle and transition zone, leaving a chemical imprint of ocean crust that can possibly endure for billions of years.

  9. Plume-subduction interaction forms large auriferous provinces.

    Science.gov (United States)

    Tassara, Santiago; González-Jiménez, José M; Reich, Martin; Schilling, Manuel E; Morata, Diego; Begg, Graham; Saunders, Edward; Griffin, William L; O'Reilly, Suzanne Y; Grégoire, Michel; Barra, Fernando; Corgne, Alexandre

    2017-10-10

    Gold enrichment at the crustal or mantle source has been proposed as a key ingredient in the production of giant gold deposits and districts. However, the lithospheric-scale processes controlling gold endowment in a given metallogenic province remain unclear. Here we provide the first direct evidence of native gold in the mantle beneath the Deseado Massif in Patagonia that links an enriched mantle source to the occurrence of a large auriferous province in the overlying crust. A precursor stage of mantle refertilisation by plume-derived melts generated a gold-rich mantle source during the Early Jurassic. The interplay of this enriched mantle domain and subduction-related fluids released during the Middle-Late Jurassic resulted in optimal conditions to produce the ore-forming magmas that generated the gold deposits. Our study highlights that refertilisation of the subcontinental lithospheric mantle is a key factor in forming large metallogenic provinces in the Earth's crust, thus providing an alternative view to current crust-related enrichment models.The lithospheric controls on giant gold deposits remain unclear. Here, the authors show evidence for native gold in the mantle from the Deseado Massif in Patagonia demonstrating that refertilisation of the lithospheric mantle is key in forming metallogenic provinces.

  10. The thermodynamic regime of metamorphism in the ancient subduction zones

    Science.gov (United States)

    Perchuk, L. L.; Aranovich, L. Ya.

    1981-02-01

    Based on mineralogical themometry and baroraetry and computation of mineral reactions modelling metamorphic sequence, a geotherm for metamorphic belts of the subduction zones has been deduced. Relatively low PT-values (3 kbar/200° C) correspond to zeolite and prehnite-pumpellyite metasediments and at higher pressures and temperatures (10 kbar/400 °C) lawsonite-glaucophane assemblages become unstable. The PT-curve achieves maximum at 11 kbar and 470° C to drop down to normal geotherm (Perchuk 1977). High concentration of H2O in the metamorphic fluid has been revealed, the difference between Pf1 and P_{{text{H}}_{text{2}} {text{O}}} being less than 2 kbar. Consideration has also been given to specific thermodynamic regime of zeolite and prehnite-pumpellyite zones of the younger island arcs, where lawsoniteglaucophane zones are absent. Here the geotherm has been found to rise from 0.2kbar/120° C up to 4 kbar/350° C and P_{{text{H}}_{text{2}} {text{O}}}-regime similar to that of glaucophane schists formations.

  11. Subduction Controls of Hf and Nd Isotopes in Lavas of the Aleutian Island Arc

    Energy Technology Data Exchange (ETDEWEB)

    Yogodzinski, Gene; Vervoort, Jeffery; Brown, Shaun Tyler; Gerseny, Megan

    2010-08-29

    The Hf and Nd isotopic compositions of 71 Quaternary lavas collected from locations along the full length of the Aleutian island arc are used to constrain the sources of Aleutian magmas and to provide insight into the geochemical behavior of Nd and Hf and related elements in the Aleutian subduction-magmatic system. Isotopic compositions of Aleutian lavas fall approximately at the center of, and form a trend parallel to, the terrestrial Hf-Nd isotopic array with {var_epsilon}{sub Hf} of +12.0 to +15.5 and {var_epsilon}{sub Nd} of +6.5 to +10.5. Basalts, andesites, and dacites within volcanic centers or in nearby volcanoes generally all have similar isotopic compositions, indicating that there is little measurable effect of crustal or other lithospheric assimilation within the volcanic plumbing systems of Aleutian volcanoes. Hafnium isotopic compositions have a clear pattern of along-arc increase that is continuous from the eastern-most locations near Cold Bay to Piip Seamount in the western-most part of the arc. This pattern is interpreted to reflect a westward decrease in the subducted sediment component present in Aleutian lavas, reflecting progressively lower rates of subduction westward as well as decreasing availability of trench sediment. Binary bulk mixing models (sediment + peridotite) demonstrate that 1-2% of the Hf in Aleutian lavas is derived from subducted sediment, indicating that Hf is mobilized out of the subducted sediment with an efficiency that is similar to that of Sr, Pb and Nd. Low published solubility for Hf and Nd in aqueous subduction fluids lead us to conclude that these elements are mobilized out of the subducted component and transferred to the mantle wedge as bulk sediment or as a silicate melt. Neodymium isotopes also generally increase from east to west, but the pattern is absent in the eastern third of the arc, where the sediment flux is high and increases from east to west, due to the presence of abundant terrigenous sediment in the

  12. The mechanism of forearc basement subduction in eastern Taiwan: Insights from sandbox modeling: Insight from Sandbox

    Science.gov (United States)

    Lu, Chia-Yu

    2015-04-01

    In Taiwan today, the subduction of the Chinese continental margin under the Philippine Sea plate results in the progressive growth of an active orogenic wedge. It is one of the best places to study the complex relationships that occur between the tectono-metamorphic processes controlling deformation (plate rheology and kinematics) and surface processes (erosion and sedimentation). In the Central Range of Taiwan, foliation and lineation traces outline the geometry and kinematics of deformation in both, the foreland and hinterland of the orogenic wedge. The foliation dip and the strain ellipsoids distribution show the fan shape of a large pop-up structure characterizing the effects of oblique plate convergence. On the eastern flank, regionally developed penetrative cleavage dips, isotope data and sedimentary structures demonstrating regional overturned structures. Two mélange units, the Kenting and Lichi mélange are exposed at the south and east of the Central Range respectively. Experiments allow the study of interactions between tectonics and surface processes. Accounting for various boundary conditions and parameters such as sedimentation, erosion, basal friction, and décollement level. We present the results of 2D and 3D sandbox models designed to investigate the complex deformation characterizing the active Taiwan orogenic wedge and to demonstrate the development of those mélanges, overturned structures and mountain frontal thrusts. Models are analyzed using pictures, movies and PIV (Particle Image Velocimetry software). We then characterize the exhumation patterns, the mode of fault propagation and displacement patterns by strain partitioning of those mélanges and overturned structures.

  13. Transfer of subduction fluids into the deforming mantle wedge during nascent subduction: Evidence from trace elements and boron isotopes (Semail ophiolite, Oman)

    Science.gov (United States)

    Prigent, C.; Guillot, S.; Agard, P.; Lemarchand, D.; Soret, M.; Ulrich, M.

    2018-02-01

    The basal part of the Semail ophiolitic mantle was (de)formed at relatively low temperature (LT) directly above the plate interface during "nascent subduction" (the prelude to ophiolite obduction). This subduction-related LT deformation was associated with progressive strain localization and cooling, resulting in the formation of porphyroclastic to ultramylonitic shear zones prior to serpentinization. Using petrological and geochemical analyses (trace elements and B isotopes), we show that these basal peridotites interacted with hydrous fluids percolating by porous flow during mylonitic deformation (from ∼850 down to 650 °C). This process resulted in 1) high-T amphibole crystallization, 2) striking enrichments of minerals in fluid mobile elements (FME; particularly B, Li and Cs with concentrations up to 400 times those of the depleted mantle) and 3) peridotites with an elevated δ11B of up to +25‰. These features indicate that the metasomatic hydrous fluids are most likely derived from the dehydration of subducting crustal amphibolitic materials (i.e., the present-day high-T sole). The rapid decrease in metasomatized peridotite δ11B with increasing distance to the contact with the HT sole (to depleted mantle isotopic values in slab-derived elements to the locus of partial melting in subduction zones.

  14. Analyzing One-Sided vs. Two-Sided Subduction Arising from Mantle Convection Simulations

    Science.gov (United States)

    Kaplan, M. S.; Becker, T. W.

    2013-12-01

    Purely thermal plate tectonic generation models struggle to consistently reproduce one-sided subduction as is observed on Earth (Tackley 2000; Van Heck and Tackley 2008; Foley and Becker 2009), and instead produce two-sided subduction where the subducting slab contains a significant flux of material from both plates. The models of Crameri et al. (2012) demonstrate that the implementation of a free upper surface boundary condition and the inclusion of a weak hydrated crust can facilitate one-sided subduction. We employ a similar model configuration to Crameri et al. (2012) to further investigate the dynamics and energetics which are associated with one-sided vs. two-sided subduction. We use a 2D finite difference code based off of the algorithms of I2ELVIS (Gerya and Yuen 2007) where material parameters are tracked on Lagrangian markers and the Stokes and Energy equations are solved on a Cartesian grid. A free surface is implemented by a low viscosity and density 'sticky air layer' (Schmeling et al., 2008; Crameri et al., 2012) with the stabilization routine of Duretz et al. (2011) to prevent the 'drunken seaman' instability (Kaus et al., 2010). The effects of a weak crust, shear heating, a free surface or free slip upper mechanical boundary condition, plasticity as a function of depth or pressure, and the sticky air layer thermal conductivity on one-sided vs. two-sided subduction are investigated. When we observe one-sided subduction it is transient and can smoothly evolve back to a two-sided configuration. In our models, 'sidedness' is a spectrum, rather than either discretely one or two sided, and the models move between the two regimes throughout the model runs. We observe that the thermal conductivity of the sticky air layer can influence the dynamics of the convective domain. Elevated values of thermal conductivity compared to those of rock must be implemented in the sticky air layer in order to maintain a constant temperature at the surface of the convective

  15. Defining Incipient Subduction by Detecting Serpentenised Mantle in the Regional Magnetic Field

    Science.gov (United States)

    Pires, Rui; Clark, Stuart; Reis, Rui

    2017-04-01

    Keywords: Subduction initiation, Incipient Subduction, Active Margins, Southeast Asia, Mantle wedge The mechanisms of subduction initiation are poorly understood. One idea is to look for incipient subduction zones in the present day and see what features are common in these zones. However, incipient subduction zones are very difficult to detect and debate surrounds particular cases as to whether they qualify as incipient or not. In the analysis conducted in this work, we use the signal of the presence of a mantle wedge in the magnetic anomaly field as an indicator of incipient subduction. Each subduction zone exhibits variations in the particular responses of the system, such as slab-dip angle, maximum earthquake depths and volcanism to various parameters. So far, attempts to reduce the system to a dominate controlling parameter have failed, probably as a result of the limited number of cases and the large variety of controlling parameters. Parameters such as down-going and overriding plate morphology and velocity, mantle flow, the presence of plumes or not, sediment transport into the trench are a few of the parameters that have been studied in the literature. However, one of the characteristics associated with a subduction zones is the presence of a mantelic wedge as a result of the partial melt of the subducting plate and the development of a mantle wedge between the subducting plate and the overriding plate. The wedge is characterised by the presence of water (coming from sediments in the down-going plate) as well as lower temperatures (because the wedge is between two relatively cold lithospheres). As a results a serpentinized mantle wedge is formed that contains hydrous minerals, of which magnetite is an example, that alter the composition and properties of this region. According to Blakely et.al. (2005), this region exhibits both higher magnetic susceptibility and lower densities than the surrounding medium. We analysed five active margin boundaries located

  16. Garnet cannibalism provides clues to extensive hydration of lower crustal fragments in a subduction channel (Sesia Zone, Northwestern Alps)

    Science.gov (United States)

    Giuntoli, Francesco; Lanari, Pierre; Engi, Martin

    2015-04-01

    The extent to which granulites are transformed to eclogites is thought to impose critical limits on the subduction of continental lower crust. Although it is seldom possible to document such densification processes in detail, the transformation is believed to depend on fluid access and deformation. Remarkably complex garnet porphyroblasts are widespread in eclogite facies micaschists in central parts of the Sesia Zone (Western Italian Alps). They occur in polydeformed samples in assemblages involving phengite+quartz+rutile ±paragonite, Na-amphibole, Na-pyroxene, chloritoid. Detailed study of textural and compositional types reveals a rich inventory of growth and partial resorption zones in garnet. These reflect several stages of the polycyclic metamorphic evolution. A most critical observation is that the relict garnet cores indicate growth at 900 °C and 0.9 GPa. This part of the Eclogitic Micaschist Complex thus derived from granulite facies metapelites of Permian age. These dry rocks must have been extensively hydrated during Cretaceous subduction, and garnet records the conditions of these processes. Garnet from micaschist containing rutile, epidote, paragonite and phengite were investigated in detail. Two types of garnet crystals are found in many thin sections: mm-size porphyroclasts and smaller atoll garnets, some 100 µm in diameter. X-ray maps of the porphyroclasts show complex zoning in garnet: a late Paleozoic HT-LP porphyroclastic core is overgrown by several layers of HP-LT Alpine garnet, these show evidence of growth at the expense of earlier garnet generations. Textures indicate 1-2 stages of resorption, with garnet cores that were fractured and then sealed by garnet veins, rimmed by multiple Alpine overgrowth rims with lobate edges. Garnet rim 1 forms peninsula and embayment structures at the expense of the core. Rim 2 surrounds rim 1, both internally and externally, and seems to have grown mainly at the expense of the core. Rim 3 grew mainly at

  17. Kinematics of Late Cretaceous subduction initiation in the Neo-Tethys Ocean reconstructed from ophiolites of Turkey, Cyprus, and Syria

    OpenAIRE

    Maffione, Marco; van Hinsbergen, Douwe J.J.; de Gelder, Giovanni I.N.O.; van der Goes, Freek C.; Morris, Antony

    2017-01-01

    Formation of new subduction zones represents one of the cornerstones of plate tectonics, yet both the kinematics and geodynamics governing this process remain enigmatic. A major subduction initiation event occurred in the Late Cretaceous, within the Neo-Tethys Ocean between Gondwana and Eurasia. Suprasubduction zone ophiolites (i.e., emerged fragments of ancient oceanic lithosphere formed at suprasubduction spreading centers) were generated during this subduction event and are today distribut...

  18. Subduction zone processes and continental crust formation in the southern Central Andes: insights from geochemistry and geochronology

    OpenAIRE

    Jones, Rosemary Ellen

    2014-01-01

    Subduction zones, such as the Andean convergent margin, are the sites at which new continental crust is generated, and where subducting material is either recycled to the crust via arc magmatism or transferred to the deep mantle. The composition of arc magmas and associated new continental crust reflects variable contributions from mantle, crustal and subducted reservoirs. Insights into crustal growth and recycling processes in the southern Central Andes, specifically in the ...

  19. Gravity and Magnetic Anomaly Interpretations and 2.5D Cross-Section Models over the Border Ranges Fault System and Aleutian Subduction Zone, Alaska

    Science.gov (United States)

    Mankhemthong, N.; Doser, D. I.; Baker, M. R.; Kaip, G.; Jones, S.; Eslick, B. E.; Budhathoki, P.

    2011-12-01

    Quaternary glacial covers and lack of dense geophysical data on the Kenai Peninsula cause a location and geometry of the Border Ranges fault system (BRFS) within a recent forearc-accretionary boundary of Aleutian subduction zone in southern Alaska are unclear. Using new ~1,300 gravity collections within the Anchorage and Kenai Peninsula regions complied with prior 1997 gravity and aeromagnetic data help us better imaging these fault and the subduction structures. Cook Inlet forearc basin is corresponded by deep gravity anomaly lows; basin boundaries are characterized by a strong gravity gradient, where are considered to be traces of Border Ranges fault system on the east and Castle Mountain and Bruin Bay fault system on the west and northwest of the forearc basin respectively. Gravity anomaly highs over accreted rocks generally increase southeastward to the Aleutian trench, but show a gravity depression over the Kenai Mountains region. The lineament between gravity high and low in the same terrenes over the Kenai Peninsula is may be another evidence to determine the Southern Edge of the Yakutat Microplate (SEY) as inferred by Eberhart-Phillips et al. (2006). Our 2.5-D models illustrate the main fault of the BRFS dips steeply toward the west with a downslip displacement. Gravity and Magnetic anomaly highs, on the east of the BRFS, probably present a slice of the ultramafic complex emplaced by faults along the boundary of the forearc basin and accretionary wedge terranes. Another magnetic high beneath the basin in the southern forearc basin support a serpentiznied body inferred by Saltus et al. (2001), with a decreasing size toward the north. Regional density-gravity models show the Pacific subducting slab beneath the foreacre-arc teranes with a gentle and flatted dip where the subducting plate is located in north of SEY and dips more steeply where it is located on the south of SEY. The gravity depression over the accreted terrene can be explained by a density low

  20. Carbonation of Subduction Interface Ultramafic Rocks and Implications for Deep Carbon Cycling: Evidence from Hybrid Serpentinite-Marble in the Voltri Massif, Italy

    Science.gov (United States)

    Scambelluri, M.; Bebout, G. E.; Gilio, M.; Belmonte, D.; Campomenosi, N.; Crispini, L.

    2015-12-01

    Release of COH fluids from hydrous minerals and carbonates influences element recycling and magmatism at subduction zones. Contradictory interpretations exist regarding the retention/storage of C in subducting plates and in the forearc to subarc mantle. Multiple lines of evidence indicate mobility of C in forearcs; however, the magnitude of this loss is highly uncertain[1-5]. A poorly constrained fraction of the 40-115 Mt/y of C initially subducted is released into fluids (e.g., by decarbonation, carbonate dissolution), and 18-43 Mt/y is returned at arc volcanoes[2-5, refs. therein]. The imbalance could reflect subduction into the deeper mantle or forearc/subarc storage[4-7]. We examine the fate of C in slab/interface ultramafic rocks, and by analogy serpentinized mantle wedge, via study of fluid-rock evolution of marble and variably carbonated serpentinite (Ligurian Alps). Based on petrography, and major/trace element and C and O isotope compositions, we demonstrate that serpentinite dehydration at 2-2.5 GPa, 550°C released aqueous fluids triggering breakdown of dolomite in nearby marbles, thus releasing C into fluids. Carbonate + olivine veins document flow of COH fluids; interaction of these COH fluids with serpentinite led to formation of high-pressure carbonated ultramafic-rock domains, thus resulting in retention of C in some rocks at an ancient subduction interface. We stress that lithologically complex interfaces could contain sites of both C release and C addition, further confounding estimates of net C loss at forearc and subarc depths [cf 4,5]. Sites of C retention, also including carbonate veins and graphite as reduced carbonate[7], could influence the transfer of slab C to at least the depths beneath volcanic fronts. 1. Poli S et al. 2009 EPSL; 2. Ague and Nicolescu 2014 Nat Geosci; 3. Cook-Collars et al. 2014 Chem Geol; 4. Collins et al. 2015 Chem Geol; 5. Kelemen and Manning 2015 PNAS; 6. Sapienza et al. 2009 CMP; 7 Galvez et al. 2013 Nat Geosci

  1. Metamorphic evolution of the Frido Unit from the southern Apennines (Italy): consequences for the subduction processes in the western Mediterranean area

    Science.gov (United States)

    Laurita, Salvatore; Prosser, Giacomo; Altenberger, Uwe; Bousquet, Romain; Oberhänsli, Roland; Cavalcante, Francesco

    2013-04-01

    The southern Apennine chain is a typical segment of the western Mediterranean orogenic belt. It consists of oceanic- and continent-derived complexes, representing the remnants of the Tethyan oceanic crust and as its eastern (Adriatic) margin. Oceanic subduction was active during the Eocene, followed by involvement of the Adriatic margin during the Oligocene-early Miocene. The Frido Unit represents the uppermost tectonic unit in the nappe pile of the southern Apennine chain. It is a typical ocean-derived unit, made up of metasediments, metabasites, serpentinites and fragments of continental crust rocks. Although HP/LT conditions for metabasites (0.6-0.8 GPa; 350±50°C or 0.8-1.0 GPa; 400-450°C) were already recognized, the extent of the HP-LT overprint and its widespread regional distribution in the sedimentary matrix has never been described in detail. In the present study we define the HP/LT metamorphism of the Frido Unit exposed in the Pollino area (Basilicata) by: i) mapping the occurrence of new and significant index minerals in all rock types (metasediments, gneisses and mafic rocks), to document the areal extent of HP-LT metamorphism in the Frido Unit; ii) constraining P-T evolution and the deformation of both mafic rocks and metasediments during the subduction process. Mapping of index minerals in metasediments (carpholite and aragonite), metabasites and fragments of continental crust rocks (glaucophane, riebeckite, lawsonite, and omphacite/jadeite) reveals widespread HP metamorphism, indicating that the whole Frido Unit underwent HP-LT conditions during subduction. Interestingly, carpholite occurs within a NW-oriented belt, where strongly deformed metabasalts and massive metadolerites show the most widespread HP overprint. By using thermodynamic modelling on a HP metadolerite and by considering the stability field of carpholite and aragonite in metasediments peak PT conditions of 0.9-1.2 GPa at less than 350 °C can be deduced. A very cold retrograde path

  2. Mineralogy, geochronology and geochemistry of early Triassic blueschists in the Lancang metamorphic zone of Southwest China: fingerprints of the Paleotethyan subduction

    Science.gov (United States)

    Wang, Y.; Fan, W.; Zhang, Y.; Cai, Y.; Jourdan, M.

    2013-12-01

    The subduction of the Paleotethyan Ocean and subsequent continental collision along the Lancang tectonic belt of the southeastern Paleotethyan belt is a major tectonic event for Southwest China, but the timing of the subduction and associated thermal structure preceding the final collision are still unknown. The mafic blueschists exposed in the Lancang accretionary complex provide the crucial records of the kinematics and thermal dynamics for the subduction zone. In this paper, we present a set of new mineralogical, geochronological and geochemical data for the Xuyi blueschists and report the presence of high-pressure Na-amphibole in the Lancang metamorphic zone. The mineral assemblage of these blueschists consists of zoned sodic amphibole (25-30 %), albite (15-20 %), epidote (25-30 %), phengite (5-10 %), chlorite (~5-10 %), and minor amounts of actinolite, apatite, sphere, zircon, ilmenite, quartz and secondary limonite. They display a progressive metamorphism from ~0.5 GPa to ~0.9 GPa and retrograde metamorphic overprinting (back to ~0.6 GPa) within the temperature range 300-450°C. The glaucophane and phengite developed during progressive metamorphism yielded the Ar-Ar ages of 246-251 Ma, and the glaucophane overprinted by retrograde metamorphism gave the Ar-Ar plateau ages of 233.2 ×3.1 Ma. The Xuyi blueschists yielded the zircon U-Pb age of 254 × 3 Ma, and are compositionally identical to the subalkaline basalt with typical OIB-type REE and multi-elemental patterns and ɛNd(t) values of +3.35 to +4.85. Based on all the available data, it is inferred that the protolith originated from the basaltic seamount with shallow-marine carbonate cap in the Paleotethyan Ocean till 254 Ma. The seamounts subducted eastward down to 30-35 km depths beneath the Lincang arc and became metamorphosed to form the epidote blueschists at ~246 -251 Ma. The blueschists were subsequently transported to shallower crustal levels in response to the continuous underthrust of the

  3. Origin and consequences of western Mediterranean subduction, rollback, and slab segmentation

    Science.gov (United States)

    van Hinsbergen, Douwe J. J.; Vissers, Reinoud L. M.; Spakman, Wim

    2014-04-01

    The western Mediterranean recorded subduction rollback, slab segmentation and separation. Here we address the questions of what caused Oligocene rollback initiation, and how its subsequent evolution split up an originally coherent fore arc into circum-southwest Mediterranean segments. We kinematically reconstruct western Mediterranean geology from subduction initiation to present, using Atlantic plate reconstructions as boundary condition. We test possible reconstructions against remnants of subducted lithosphere imaged by seismic tomography. Transform motion between Africa and Iberia (including the Baleares) between 120 and 85 Ma was followed by up to 150 km convergence until 30 Ma. Subduction likely initiated along the transform fault that accommodated pre-85 Ma translation. By the 30 Ma inception of rollback, up to 150 km of convergence had formed a small slab below the Baleares. Iberia was disconnected from Sardinia/Calabria through the North Balearic Transform Zone (NBTZ). Subduction below Sardinia/Calabria was slightly faster than below the Baleares, the difference being accommodated in the Pyrenees. A moving triple junction at the trench-NBTZ intersection formed a subduction transform edge propagator fault between the Baleares and Calabria slab segments. Calabria rolled back eastward, whereas the Baleares slab underwent radial (SW-S-SE) rollback. After Kabylides-Africa collision, the western slab segment retreated toward Gibraltar, here reconstructed as the maximum rollback end-member model, and a Kabylides slab detached from Africa. Opening of a slab window below the NBTZ allowed asthenospheric rise to the base of the fore arc creating high-temperature metamorphism. Western Mediterranean rollback commenced only after sufficient slab-pull was created from 100 to 150 km of slow, forced subduction before 30 Ma.

  4. Effect of a weak layer at the base of an oceanic plate on subduction dynamics

    Science.gov (United States)

    Carluccio, Roberta; Kaus, Boris

    2017-04-01

    The plate tectonics model relies on the concept of a relatively rigid lithospheric lid moving over a weaker asthenosphere. In this frame, the lithosphere asthenosphere boundary (LAB) is a first-order discontinuity that accommodates differential motions between tectonic plates and the underlying mantle. Recent seismic studies have revealed the existence of a low velocity and high electrical conductivity layer at the base of subducting tectonic plates. This thin layer has been interpreted as being weak and slightly buoyant and was suggested to affect the dynamics of subducting plates. However, geodynamically, the role of a weak layer at the base of the lithosphere remains poorly studied, especially at subduction zones. Therefore, we here use numerical models to investigate the first-order effects of a weak buoyant layer at the LAB on subduction dynamics. We employ both 2-D and 3-D models in which the slab and mantle are either linear viscous or have a more realistic temperature-dependent visco-elastic-plastic rheology. Results show that a weak layer affects the dynamics of the plates, foremost by increasing the subduction speed. The impact of this effect depends on the thickness of the layer and the viscosity contrast between the mantle and the weak layer. For moderate viscosity contrasts (1000), it can also change the morphology of the subduction itself, perhaps because this changes the overall effective viscosity contrast between the slab the and the mantle. For thinner layers, the overall effect is reduced. Yet, if seismological observations are correct that suggests that this layer is 10 km thick and partially molten, such that the viscosity is 1000 times lower than that of the mantle, our models suggest that this effect should be measurable. Some of our models also show a pile-up of weak material in the bending zone of the subducting plate, consistent with recent seismological observations.

  5. Long streamer waveform tomography imaging of the Sanak Basin, Alaska subduction zone

    Science.gov (United States)

    Roche, Pierre-Henri; Delescluse, Matthias; Becel, Anne; Nedimovic, Mladen; Shillington, Donna; Webb, Spahr; Kuehn, Harold

    2017-04-01

    The Alaska subduction zone is prone to large megathrust earthquakes, including several large tsunamigenic events in the historical record (e.g. the 1964 Mw 9.2 and the 1946 Mw 8.6 earthquakes). Along the Alaska Peninsula trench, seismic coupling varies from fully locked to the east to weakly coupled to the West, with apparent aseismic slip in the Shumagin Gap and Unimak rupture zone. Overlapping the Shumagin gap and the Unimak area, the Sanak basin is a Miocene basin formed by a large-scale normal fault recently imaged by the ALEUT 2011 cruise and clearly rooting in the subduction interface at 30 km depth (Becel et al., submitted). Recent activity on this normal fault is detected at the seafloor of the Sanak Basin by a 5 m scarp in the multibeam bathymetry data. As this normal fault may be associated with faults involved in the 1946 tsunami earthquake, it is particularly important to try to decipher its history in the Sanak basin, where sediments record the fault activity. MCS data processing and interpretation shows evidence for the activity of the fault from Miocene to recent geological times. Very limited knowledge of the sedimentation rates and ages as well as complexities due to submarine landslides and channel depositions make it difficult to quantify the present day fault activity with respect to the Miocene fault activity. In addition, the mechanical behaviour of a normal splay fault system requires low to zero effective friction and probably involves fluids. High-resolution seismic velocity imaging can help with both the interpretation of complex sedimentary deposition and fluid detection. To obtain such a high resolution velocity field, we use two 45-km-long MCS profiles from the ALEUT 2011 cruise acquired with an 8-km-long streamer towed at 12 m depth to enhance low frequencies with shots fired from a large, tuned airgun array (6600 cu.in.). The two profiles extend from the shelf break to mid slope and encompass the normal splay fault emerging at 1 km

  6. Shear wave splitting and the dynamics of the hydrated mantle wedge in subduction regions constrained by the example of the Ryukyu subduction zone

    Science.gov (United States)

    Nagaya, T.; Walker, A.; Wookey, J. M.; Wallis, S.; Ishii, K.; Kendall, J. M.

    2016-12-01

    H2O-rich subduction fluids are a key component of convergent plate margin dynamics, essential to earthquake initiation and magma formation. These fluids in the wedge mantle are dominantly derived from antigorite dragged down by plate motion. However, the accurate distribution of antigorite-rich serpentinite related to the fluid transport in subduction zones has thus far been difficult to determine. Our approach is to model the S-wave splitting of the Ryukyu arc in order to constrain the distribution, amount and orientation of antigorite, while taking into account the geometry of seismic ray paths and the elastic anisotropy of deformed antigorite-bearing mantle. We have also carried out a full assessment of uncertainties associated with our analysis including time delay estimates from the seismic waves themselves, crustal anisotropy, averaging schemes for CPO, and the strength of antigorite CPO patterns. The results suggest the presence of a large-scale flow in the hydrous mantle with a low viscosity and more than 54% of this domain consists of antigorite. Other geophysical observations in the forearc mantle including the low seismic velocity and gravity anomaly are also compatible with our inference of the presence of induced flow in an antigorite-rich, hydrated mantle wedge in the Ryukyu arc. We have also constructed a geodynamic model to examine flow patterns in the hydrated shallow wedge mantle using the distribution and proportion of serpentinite derived from our seismic model and subduction parameters that are close to those of the arc. The results clearly show that convection occurs in the serpentinized mantle wedge and that this domain is associated with a low surface heat flow. S-wave splitting observations in other subduction zones implies this large-scale serpentinization and hydrous mantle flow is likely to be more widespread than generally recognized and the view that the forearc mantle of cold subduction zones lacks significant zones of hydration needs

  7. Geodynamical Analysis of Plate Reconstructions based on Subduction History Models

    Science.gov (United States)

    Quevedo, L. E.; Butterworth, N. P.; Matthews, K. J.; Morra, G.; Müller, R. D.

    2011-12-01

    We present a novel method to produce global subduction history models from plate reconstructions and use their predicted geodynamic behaviour as a quality metric for the physical consistency of absolute motions. We show that modelled slabs constructed by advecting material into the mantle according to absolute and relative plate motions given by a particular reconstruction are better correlated with the present day slab dips observed in mantle tomography than instantaneous kinematic quantities like present convergence rate. A complete simulation incorporating lithospheric thickness derived from oceanic age and a rheological model of the lithosphere was run using the Boundary Element Method-based software BEMEarth to infer the global pattern of mantle flow. The predicted plate motion orientations in the form of Euler pole location for the present day and mid-Cretaceous (125 Ma) were compared with the kinematic model for a set of rheologies and mantle structures, and found to be a robust and efficient indicator of the physical consistency of kinematic reconstructions based on their effect on the balance of plate driving forces. As an application example, during the Early Cretaceous, the predicted motion of the Farallon plate was found to be more consistent with the regional geology of the Western North American Cordillera system than the instantaneous motion suggested by a reconstruction at 125 Ma based on sparse hotspot track data on the Pacific Plate. This suggests that a methodology based on forward geodynamic modellling could be used to predict absolute plate motions in reconstructions for times that are ill-constrained by observations constraining absolute plate motions.

  8. The Southern Tyrrhenian subduction system: recent evolution and neotectonic implications

    Directory of Open Access Journals (Sweden)

    A. Argnani

    2000-06-01

    Full Text Available Geological and geophysical data have been integrated with the aim of presenting a new evolutionary model for the Southern Tyrrhenian and adjacent regions. The Southern Tyrrhenian backarc basin opened within a plate convergence regime because of sinking and rollback of the oceanic Ionian lithosphere. On the basis of seismological observations, I infer that the sinking slab was torn apart on either side in the last 2 Ma and this process controlled the neotectonics of the Southern Apennines - Tyrrhenian region. On the north-eastern side the slab broke off from NW to SE and this process triggered volcanism and NW-SE extension along the Eastern Tyrrhenian margin, and strike-slip tectonics along NW-SE trending faults in Northern Calabria. On the south-western side the slab broke off from W to E along the Aeolian Island alignment, although the tear has currently been reoriented along the NNW-SSE Malta escarpment. During its sinking the subducted slab also detached from the overriding plate, favouring the wedging of the asthenosphere between the two plates and the regional uplift of the Calabrian arc and surroundings. This regional uplift promoted gravitational instability within the orogenic wedge, particularly towards low topography areas; the large-scale sliding of the Calabrian arc towards the Ionian basin can be the cause of CW rotation and graben formation in Calabria. Also the E-dipping extensional faults of the Southern Apennines can be related to accommodation of vertical motions within the fold-and-thrust belt. The pattern of recent seismicity reflects this neotectonics where crustal-scale gravity deformation within the orogenic wedge is responsible for extensional earthquakes in Calabria and the Southern Apennines, whereas Africa plate convergence can account for compressional earthquakes in Sicily.

  9. Constraints on Subduction Zone Processes from Low Frequency Earthquakes

    Science.gov (United States)

    Bostock, M. G.

    2015-12-01

    The discovery of tectonic tremor and constituent low-frequency earthquakes (LFEs) offers seismologists new opportunities to study both deformational processes and structure within the subduction zone forearc. This assertion is especially true for northern Cascadia where i) regular seismicity is sparse, and ii) a relatively transparent overriding plate inflicts minimal distortion upon direct P and S wave arrivals from LFEs. Despite low signal-to-noise ratios, LFEs are highly repetitive and signal can be enhanced through construction of stacked templates. Studies in both Cascadia and Nankai reveal an association between LFE hypocenters and a high Vp/Vs, low-velocity zone (LVZ) that is inferred to represent overpressured upper oceanic crust. Scattered signals within Vancouver Island templates, interpreted to originate at boundaries of the LVZ, place LFEs within the LVZ and suggest that this structure may define a distributed (several km) zone of deformation. A recent analysis of LFE magnitudes indicates that LFEs exhibit scaling relations distinct from both regular earthquakes and longer period (10's of seconds to days) phenomena associated with slow slip. Regular earthquakes generally obey a scaling of moment proportional to duration cubed consistent with self similarity, whereas long period slow slip phenomena exhibit a linear scaling between moment and duration that can be accommodated through constant slip or constant stress drop models. In contrast, LFE durations are nearly constant suggesting that moment is governed by slip alone and that asperity size remains approximately constant. The implied dimensions (~1 km2), the persistance of LFEs in time and their stationarity in space point to structural heterogeneity, perhaps related to pockets of upper oceanic crust impervious to hydrothermal circulation, as a fundamental control.

  10. Phengite-hosted LILE enrichment in eclogite and related rocks: Implications for fluid-mediated mass transfer in subduction zones and arc magma genesis

    Science.gov (United States)

    Sorensen, Sorena S.; Grossman, J.N.; Perfit, M.R.

    1997-01-01

    Geochemical differences between island arc basalts (LAB) and ocean-floor basalts (mid-ocean ridge basalts; MORB) suggest that the large-ion lithophile elements (LILE) K, Ba, Rb and Cs are probably mobilized in subduction zone fluids and melts. This study documents LILE enrichment of eclogite, amphibolite, and epidote ?? garnet blueschist tectonic blocks and related rocks from melanges of two subduction complexes. The samples are from six localities of the Franciscan Complex, California, and related terranes of Oregon and Baja California, and from the Samana Metamorphic Complex, Samana Peninsula, Dominican Republic. Most Franciscan blocks are MORB-like in their contents of rare earth elements (REE) and high field strength elements (HFSE); in contrast, most Samana blocks show an LAB signature of these elements. The whole-rock K2O contents of both groups range from 1 to 3 wt %; K, Ba, Rb, and Cs are all strongly intercorrelated. Many blocks display K/Ba similar to melasomatized transition zones and rinds at their outer margins. Some transition zones and rinds are enriched in LILE compared with host blocks; others are relatively depleted in these elements. Some LILE-rich blocks contain 'early' coarse-grained muscovite that is aligned in the foliation defined by coarse-grained omphacite or amphibole grains. Others display 'late' muscovite in veins and as a partial replacement of garnet; many contain both textural types. The muscovite is phengite that contains ???3??25-3??55 Si per 11 oxygens, and ???0??25-0??50 Mgper 11 oxygens. Lower-Si phengite has a significant paragonite component: Na per 11 oxygens ranges to ???0??12. Ba contents of phengite range to over 1 wt % (0??027 per 11 oxygens). Ba in phengite does not covary strongly with either Na or K. Ba contents of phengite increase from some blocks to their transition zones or rinds, or from blocks to their veins. Averaged KlBa ratios for phengite and host samples define an array which describes other subsamples of

  11. Deformation Patterns and Subduction Behavior of Continental Lithosphere Entering a Trench

    Science.gov (United States)

    Steedman, C. E.; Kaus, B. J.; Becker, T. W.; Okaya, D.

    2007-05-01

    We perform 2-D numerical simulations of continental lithosphere entering a subduction zone, to better understand deformation patterns resulting from subduction of a continental margin. The model consists of a subduction zone in which an attached slab drives subduction of a passive continental margin beneath an oceanic plate. A particle-based 2-D visco-elasto-plastic thermo-mechanical finite element code is employed to study the dynamics of the system. A novel feature of the code is that the resolution of the model can be significantly increased in selected parts of the domain, which allows for self-consistent modelling of mantle-lithosphere interaction. In the present study we employ this feature to study how lithospheric-scale deformation around and within the subduction zone is influenced by surface processes such as erosion, and by flow in the upper mantle. Using systematic 2-D numerical simulations, we explore the parameters that are dominant in controlling near- surface structures, both with regards to changes in topography and trench location, and subsurface features such as Moho undulations. The main parameters that have been varied are: the lithospheric density structure; the lithospheric age and temperature structure; the strength of the lower crust; the presence of a weak zone at the plate interface; the amounts of erosion; the upper boundary condition (free surface versus free slip); rheology (non-Newtonian versus Newtonian, viscous, visco-elasto-plastic); and finally the effect of an imposed slab breakoff. In all cases we track surface uplift, subduction evolution and rock exhumation history. We find that the strength of the overriding plate influences surface uplift and the shape of subsurface deformation, and that the density and thermal structure of the subducting plate affects trench motion. Denser slab roll back, and younger, lighter slabs advance, while neither slab rheology nor the presence of erosion greatly affect trench location. For all cases

  12. Eclogite-, amphibolite- and blueschist-facies rocks from Diego de Almagro Island (Patagonia): Episodic accretion and thermal evolution of the Chilean subduction interface during the Cretaceous

    Science.gov (United States)

    Hyppolito, Thais; Angiboust, Samuel; Juliani, Caetano; Glodny, Johannes; Garcia-Casco, Antonio; Calderón, Mauricio; Chopin, Christian

    2016-11-01

    Few localities in the Patagonian Andes expose remnants of the Mesozoic Chilean paleo-accretionary complex. We focus on the Diego de Almagro Island high-pressure/low-temperature (HP/LT) Complex, a pluri-kilometer thick sequence comprising metavolcanic rocks with oceanic affinities and metasedimentary rocks. In this study, the deepest segments of the Chilean subduction interface in Patagonia are characterized for the first time. Despite its apparent homogeneity, the complex is actually composed of two tectonic units with distinct ages of metamorphism and thermal evolution: the garnet amphibolite (GA) and the underlying blueschist (BS) units. The GA unit mafic rocks exhibit epidote, phengite, titanite, rutile, chloritoid and paragonite inclusions in prograde garnet I, diopside + albite intergrows replacing omphacite inclusions in garnet II, and relict omphacite (XJd45) included in edenitic-pargasitic amphiboles. Thermobarometric results show that these rocks were buried along a relatively cold prograde path (c. 11 °C/km) and reached eclogite-facies near peak pressure conditions (c. 550-600 °C, 1.6 GPa). The GA unit underwent a pervasive stage of amphibolitization during decompression at c. 1.3 GPa. Field and petrological observations, together with multi-mineral Rb-Sr dating, indicate that amphibolitization of the GA unit took place along the subduction interface at c. 120 Ma in a slightly warmer subduction regime (c. 13-14 °C/km), in agreeement with the formation of coetanoeus amphibolites at c. 35 km. The underlying BS unit (i) yields four consistent Rb-Sr deformation ages of c. 80 Ma, i.e. 40 Ma younger than the overlying rocks from the GA unit; (ii) exhibits slightly cooler peak metamorphic conditions (c. 520-550 °C, 1.6 GPa) indicating burial along a prograde path of c. 10 °C/km (iii) does not show amphibolite-facies overprint as seen in the GA unit. After a long residence time under amphibolite-facies conditions, the amphibolitized rocks of the GA unit

  13. Laboratory models of the thermal evolution of the mantle during rollback subduction.

    Science.gov (United States)

    Kincaid, C; Griffiths, R W

    2003-09-04

    The subduction of oceanic lithosphere plays a key role in plate tectonics, the thermal evolution of the mantle and recycling processes between Earth's interior and surface. Information on mantle flow, thermal conditions and chemical transport in subduction zones come from the geochemistry of arc volcanoes, seismic images and geodynamic models. The majority of this work considers subduction as a two-dimensional process, assuming limited variability in the direction parallel to the trench. In contrast, observationally based models increasingly appeal to three-dimensional flow associated with trench migration and the sinking of oceanic plates with a translational component of motion (rollback). Here we report results from laboratory experiments that reveal fundamental differences in three-dimensional mantle circulation and temperature structure in response to subduction with and without a rollback component. Without rollback motion, flow in the mantle wedge is sluggish, there is no mass flux around the plate and plate edges heat up faster than plate centres. In contrast, during rollback subduction flow is driven around and beneath the sinking plate, velocities increase within the mantle wedge and are focused towards the centre of the plate, and the surface of the plate heats more along the centreline.

  14. Postcollisional mafic igneous rocks record crust-mantle interaction during continental deep subduction.

    Science.gov (United States)

    Zhao, Zi-Fu; Dai, Li-Qun; Zheng, Yong-Fei

    2013-12-04

    Findings of coesite and microdiamond in metamorphic rocks of supracrustal protolith led to the recognition of continental subduction to mantle depths. The crust-mantle interaction is expected to take place during subduction of the continental crust beneath the subcontinental lithospheric mantle wedge. This is recorded by postcollisional mafic igneous rocks in the Dabie-Sulu orogenic belt and its adjacent continental margin in the North China Block. These rocks exhibit the geochemical inheritance of whole-rock trace elements and Sr-Nd-Pb isotopes as well as zircon U-Pb ages and Hf-O isotopes from felsic melts derived from the subducted continental crust. Reaction of such melts with the overlying wedge peridotite would transfer the crustal signatures to the mantle sources for postcollisional mafic magmatism. Therefore, postcollisonal mafic igneous rocks above continental subduction zones are an analog to arc volcanics above oceanic subduction zones, providing an additional laboratory for the study of crust-mantle interaction at convergent plate margins.

  15. Seismic reflection imaging of two megathrust shear zones in the northern Cascadia subduction zone.

    Science.gov (United States)

    Calvert, Andrew J

    2004-03-11

    At convergent continental margins, the relative motion between the subducting oceanic plate and the overriding continent is usually accommodated by movement along a single, thin interface known as a megathrust. Great thrust earthquakes occur on the shallow part of this interface where the two plates are locked together. Earthquakes of lower magnitude occur within the underlying oceanic plate, and have been linked to geochemical dehydration reactions caused by the plate's descent. Here I present deep seismic reflection data from the northern Cascadia subduction zone that show that the inter-plate boundary is up to 16 km thick and comprises two megathrust shear zones that bound a >5-km-thick, approximately 110-km-wide region of imbricated crustal rocks. Earthquakes within the subducting plate occur predominantly in two geographic bands where the dip of the plate is inferred to increase as it is forced around the edges of the imbricated inter-plate boundary zone. This implies that seismicity in the subducting slab is controlled primarily by deformation in the upper part of the plate. Slip on the shallower megathrust shear zone, which may occur by aseismic slow slip, will transport crustal rocks into the upper mantle above the subducting oceanic plate and may, in part, provide an explanation for the unusually low seismic wave speeds that are observed there.

  16. Necessity of the Ridge for the Flat Slab Subduction: Insights from the Peruvian Flat Slab

    Science.gov (United States)

    Knezevic Antonijevic, S.; Wagner, L. S.; Beck, S. L.; Long, M. D.; Zandt, G.; Tavera, H.

    2014-12-01

    Flattening of the subducting plate has been linked to the formation of various geological features, including basement-cored uplifts, the cessation of arc volcanism, ignimbrite flare-ups, and the formation of high plateaus and ore deposits [Humphreys et al., 2003; Gutscher et al., 2000; Rosenbaum et al., 2005]. However, the mechanism responsible for the slab flattening is still poorly understood. Here we focus on the Peruvian flat slab, where the Nazca plate starts to bend at ~80 km depth and travels horizontally for several hundred kilometers, at which point steep subduction resumes. Based on a 1500 km long volcanic gap and intermediate depth seismicity patterns, the Peruvian flat slab appears to have the greatest along-strike extent and, therefore, has been suggested as a modern analogue to the putative flat slab during the Laramide orogeny in the western United States (~80-55 Ma). Combining 3D shear wave velocity structure and Rayleigh wave phase anisotropy between ~10° and 18° S, we find that the subducting Nazca plate is not uniformly flat along the entire region, but fails to the north of the subducting Nazca Ridge. Our results show that, in combination with trench retreat, rapid overriding plate motion, and/or presence of a thick cratonic root, the subduction of buoyant overthickened oceanic crust, such as the Nazca Ridge, is necessary for the formation and sustainability of flat slabs. This finding has important implications for the formation of flat slabs both past and present.

  17. Subduction or obduction of continental crust in the northern Norwegian Caledonides? An example from the Nordmannvik Nappe

    Science.gov (United States)

    Faber, Carly; Stünitz, Holger; Jeřábek, Petr; Gasser, Deta; Konopásek, Jiří; Kraus, Katrin

    2017-04-01

    The debate about how and why continental crust is subducted is ongoing (Ingalls et al., 2016). This work uses the tectonmetamorphic history of a the Nordmannvik nappe in the northern Scandinavian Caledonides to discuss mid- to lower-crustal processes involved in the subduction of continental crust during the Caledonian Orogeny. The Nordmannvik Nappe, together with the underlying Kåfjord and Vaddas nappes, constitutes the Reisa Nappe Complex (RNC). The RNC overlies continental rocks of the Kalak Nappe Complex (KNC), and a clear oceanic suture between Baltican basement, the KNC and the RNC is missing. The RNC consists mainly of paragneisses of mostly unknown depositional age. Rare fossils in the Vaddas Nappe indicate that it at least partly consists of Ordovician-Silurian (>460 Ma) metasediments (Binns and Gayer, 1980). Both the Nordmannvik and Vaddas Nappes were intruded by gabbroic melt around 439 Ma at 9 kbar (c. 30 km) (Getsinger et al., 2013). Therefore, the host and intrusive rocks were already buried to positions far deeper than oceanic crust prior to nappe stacking. Nordmannvik nappe rocks show at least two distinct metamorphic fabrics; 1) an early high-grade kyanite-present migmatitic fabric and 2) a pervasive mylonitic fabric. Based on microstructural observations and pseudosection modeling these two fabrics are estimated to have formed at 770-800 °C and 9.4-11 kbar and 580-630 °C and 8-9.8 kbar, respectively. The presence of sillimanite in garnet cores (confirmed by Raman spectra) and garnet core compositions also suggest that an earlier, less well constrained, history exists with metamorphism around 815 °C and 8.7 kbar, similar to that recognized in the KNC, where it is dated to be pre-Caledonian. The lack of ocean floor rocks between the Nordmannvik Nappe and the Baltica basement suggests that the Nordmannvik Nappe and nappe units below were fairly proximal to Baltica prior to the Caledonian Orogeny. Their position below the Lyngen Nappe (Iapetus

  18. A revised subduction inception model to explain the Late Cretaceous, doubly vergent orogen in the pre-collisional western Tethys: evidences from the Northern Apennine

    Science.gov (United States)

    Meneghini, Francesca; Marroni, Michele; Pandolfi, Luca

    2017-04-01

    Orogenic processes are widely demonstrated to be strongly controlled by inherited structures. The paleogeography of the converging margins, and the tectonic processes responsible for their configuration, will influence the location of subduction initiation, the distribution of deformation between upper and lower plate, the shape of the accretionary prism and of the subsequent orogeny, through controlling the development of single or doubly-vergent orogens, and, as a corollary, the modality of exhumation of metamorphosed units. The "alpine age" collisional belts of the Mediterranean area are characterized by tangled architectures derived from the overlapping of several deformation events related to a multiphase, long history that comprises not only the collision of continental margins, but that can be regarded as an heritage of both the rifting-related configuration of the continental margins, and the subduction-related structures. The Northern Apennines is a segment of these collisional belts that originated by the Late Cretaceous-Middle Eocene closure of the northern branch of the western Tethys, and the subsequent Late Eocene-Early Oligocene continental collision between the Europe and Adria plates. Due to a different configuration of the paired Adria and Europe continental margins, inherited from a rifting phase dominated by asymmetric, simple-shear kinematics, the Northern Apennines expose a complex groups of units, referred to as Ligurian Units, that record the incorporation into the subduction factory of either fragments of the Ligure-Piemontese oceanic domain (i.e. Internal Ligurian Units), and various portions of the thinned Adria margin (i.e. External Ligurian Units), describable as an Ocean-Continent Transition Zone (OCTZ). The structural relationships between these groups of Units are crucial for the definition of the pre-collisional evolution of the belt and have been the subject of big debates in the literature, together with the location and

  19. Long-term and Short-term Vertical Deformation Rates across the Forearc in the Central Mexican Subduction Zone

    Science.gov (United States)

    Ramirez-Herrera, M. T.; Gaidzik, K.; Forman, S. L.; Kostoglodov, V.; Burgmann, R.

    2015-12-01

    Spatial scales of the earthquake cycle, from rapid deformation associated with earthquake rupture to slow deformation associated with interseismic and transient slow-slip behavior, span from fractions of a meter to thousands of kilometers (plate boundaries). Similarly, temporal scales range from seconds during an earthquake rupture to thousands of years of strain accumulation between earthquakes. The complexity of the multiple physical processes operating over this vast range of scales and the limited coverage of observations leads most scientists to focus on a narrow space-time window to isolate just one or a few process. We discuss here preliminary results on the vertical crustal deformation associated with both slow and rapid crustal deformation along a profile across the forearc region of the central Mexican subduction zone on the Guerrero sector, where the Cocos plate underthrusts the North American plate. This sector of the subduction zone is characterized by a particular slab geometry (with zones of rapid bending-unbending of the slab), irregular distributed seismicity, exceptionally large slow slip events (SSE) and non-volcanic tremors (NVT). We used the river network and geomorphic features of the Papagayo River to assess Quaternary crustal deformation. The Papagayo drainage network is strongly controlled by Late Cenozoic tectonic, Holocene and recent earthquake cycle processes. This is particularly true for the southern section of the drainage basin; from the dam in La Venta to the river mouth, where W-E structures commonly offset the course of the main river. River terraces occur along the course of the river at different elevations. We measured the height of a series of terraces and obtained OSL ages on quartz extracts to determine long-term rates of deformation. Finally, we discuss associations of the topography and river characteristics with the Cocos slab geometry, slow earthquakes, crustal deformation, and interseismic deformation.

  20. H2O and CO2 devolatilization in subduction zones: implications for the global water and carbon cycles (Invited)

    Science.gov (United States)

    van Keken, P. E.; Hacker, B. R.; Syracuse, E. M.; Abers, G. A.

    2010-12-01

    Subduction of sediments and altered oceanic crust functions as a major carbon sink. Upon subduction the carbon may be released by progressive metamorphic reactions, which can be strongly enhanced by free fluids. Quantification of the CO2 release from subducting slabs is important to determine the provenance of CO2 that is released by the volcanic arc and to constrain the flux of carbon to the deeper mantle. In recent work we used a global set of high resolution thermal models of subduction zones to predict the flux of H2O from the subducting slab (van Keken, Hacker, Syracuse, Abers, Subduction factory 4: Depth-dependent flux of H2O from subducting slabs worldwide, J. Geophys. Res., under review) which provides a new estimate of the dehydration efficiency of the global subducting system. It was found that mineralogically bound water can pass efficiently through old and fast subduction zones (such as in the western Pacific) but that warm subduction zones (such as Cascadia) see nearly complete dehydration of the subducting slab. The top of the slab is sufficiently hot in all subduction zones that the upper crust dehydrates significantly. The degree and depth of dehydration is highly diverse and strongly depends on (p,T) and bulk rock composition. On average about one third of subducted H2O reaches 240 km depth, carried principally and roughly equally in the gabbro and peridotite sections. The present-day global flux of H2O to the deep mantle translates to an addition of about one ocean mass over the age of the Earth. We extend the slab devolatilization work to carbon by providing an update to Gorman et al. (Geochem. Geophys. Geosyst, 2006), who quantified the effects of free fluids on CO2 release. The thermal conditions were based on three end-member subduction zones with linear interpolation to provide a global CO2 flux. We use the new high resolution and global set of models to provide higher resolution predictions for the provenance and pathways of CO2 release to

  1. The initial superposition of oceanic and continental units in the southern Western Alps: constraints on geometrical restoration and kinematics of the continental subduction wedge

    Science.gov (United States)

    Dumont, Thierry; Schwartz, Stéphane; Matthews, Steve; Malusa, Marco; Jouvent, Marine

    2017-04-01

    older in the oceanic rocks (Malusà et al. 2015). Finally, further SE, the Voltri massif shows a huge volume of serpentinized mantle which locally overlies continental basement (strongly metamorphosed), and is interpreted as an exhumed remnant of the subduction channel (Federico et al., 2007). In all these localities the transport directions during initial pulses of stacking were consistently oriented generally towards the NW to N, taking into account the subsequent Oligocene and younger collision-related deformation (complex folds, thrusts, backfolds and backthrusts, and block-rotations). It is thus possible to attempt reconstructing an early stage continental subduction wedge involving these different elements from the subduction channel to the most frontal part of the accretionary complex. However, this early Alpine orogen which was active throughout the Eocene is interpreted to have propagated generally towards the NW to N, prior to subsequent pulses of more westerly directed deformation from the Oligocene onwards within the southern part of the Western Alps arc. It is therefore essential to continually improve high-resolution 3D geophysical imaging to facilitate a better understanding of the complex western termination of the Alpine orogen. References: Dumont T., Schwartz S., Guillot S., Simon-Labric S., Tricart P. & Jourdan S. (2012), Structural and sedimentary record of the Oligocene revolution in the Western Alpine arc. Jour. Geodynamics, doi:10.1016/j.jog.2011.11.006 Federico L., Crispini L., Scambelluri M. & Capponi G. (2007), Ophiolite mélange zone records exhumation in a fossil subduction channel. Geology, 35, p. 499-502 Malusà M.G., Faccenna C., Baldwin S.L., Fitzgerald P.G., Rossetti F., Balestrieri M.L., Danišík M., Ellero A., Ottria G. & Piromallo C. (2015), Contrasting styles of (U)HP rock exhumation along the Cenozoic Adria-Europe plate boundary (Western Alps, Calabria, Corsica). Geochem. Geophys. Geosyst. ,16, p. 1786-1824 Tricart P. & Schwartz S

  2. Imaging subducted high velocity slabs beneath the sea of Okhotsk using depth phases

    Science.gov (United States)

    Bai, K.; Li, D.; Helmberger, D. V.; Sun, D.; Wei, S.

    2014-12-01

    A recent study of a shallow Kuril subduction zone event displays significant waveform multi-pathing for paths propagating down the slab towards Europe(Zhan,Zhongwen 2014). Relatively fast structures (5%) are invoked to simulate such observations requiring numerical methods to capture such proportional distortions. Here, we present results from the reverse direction that is the effects on depth phases of deep events propagating up the slab. In particular the Mw6.7 Sea of Okhotsk deep earthquake occurred at a depth of 640 km is believed to be near the bottom of the slab structure and produced an abundance of depth phases. Differential travel time sP-P analysis shows a systematic decrease of up to 5 seconds from Europe to Australia and then to Pacific which is indicative of a dipping high velocity layer above the source region. Multiple simulations using WKM(An upgraded variation of the traditional WKBJ method) and finite difference methods were conducted in an effort to assess the effects of sharp structure on the whole wave-field. Results obtained from analytical methods, by the WKM code become questionable compared against the finite difference method due to its inability to handle the diffraction phases which become crucial in complex structures. In this example, seismicity clustered within a 45 degree dipping benioff zone at shallow depth but became blurred beyond 400 km. Finite difference simulations showed that a slab shapped structure that follows the benioff zone at shallow depth and steepens beyond 400 km produces a model that can account for the sP-P differential travel times of our 5s for oceanic paths.

  3. Subducting slab ultra-slow velocity layer coincident with silent earthquakes in southern Mexico.

    Science.gov (United States)

    Song, Teh-Ru Alex; Helmberger, Donald V; Brudzinski, Michael R; Clayton, Robert W; Davis, Paul; Pérez-Campos, Xyoli; Singh, Shri K

    2009-04-24

    Great earthquakes have repeatedly occurred on the plate interface in a few shallow-dipping subduction zones where the subducting and overriding plates are strongly locked. Silent earthquakes (or slow slip events) were recently discovered at the down-dip extension of the locked zone and interact with the earthquake cycle. Here, we show that locally observed converted SP arrivals and teleseismic underside reflections that sample the top of the subducting plate in southern Mexico reveal that the ultra-slow velocity layer (USL) varies spatially (3 to 5 kilometers, with an S-wave velocity of approximately 2.0 to 2.7 kilometers per second). Most slow slip patches coincide with the presence of the USL, and they are bounded by the absence of the USL. The extent of the USL delineates the zone of transitional frictional behavior.

  4. The subduction zone flow field from seismic anisotropy: a global view.

    Science.gov (United States)

    Long, Maureen D; Silver, Paul G

    2008-01-18

    Although the morphologies of subducting slabs have been relatively well characterized, the character of the mantle flow field that accompanies subduction remains poorly understood. To analyze this pattern of flow, we compiled observations of seismic anisotropy, as manifested by shear wave splitting. Data from 13 subduction zones reveal systematic variations in both mantle-wedge and subslab anisotropy with the magnitude of trench migration velocity |V(t)|. These variations can be explained by flow along the strike of the trench induced by trench motion. This flow dominates beneath the slab, where its magnitude scales with |V(t)|. In the mantle wedge, this flow interacts with classical corner flow produced by the convergence velocity V(c); their relative influence is governed by the relative magnitude of |V(t)| and V(c).

  5. High-pressure creep of serpentine, interseismic deformation, and initiation of subduction.

    Science.gov (United States)

    Hilairet, Nadege; Reynard, Bruno; Wang, Yanbin; Daniel, Isabelle; Merkel, Sebastien; Nishiyama, Norimasa; Petitgirard, Sylvain

    2007-12-21

    The supposed low viscosity of serpentine may strongly influence subduction-zone dynamics at all time scales, but until now its role could not be quantified because measurements relevant to intermediate-depth settings were lacking. Deformation experiments on the serpentine antigorite at high pressures and temperatures (1 to 4 gigapascals, 200 degrees to 500 degrees C) showed that the viscosity of serpentine is much lower than that of the major mantle-forming minerals. Regardless of the temperature, low-viscosity serpentinized mantle at the slab surface can localize deformation, impede stress buildup, and limit the downdip propagation of large earthquakes at subduction zones. Antigorite enables viscous relaxation with characteristic times comparable to those of long-term postseismic deformations after large earthquakes and slow earthquakes. Antigorite viscosity is sufficiently low to make serpentinized faults in the oceanic lithosphere a site for subduction initiation.

  6. Topography of the Overriding Plate During Progressive Subduction: A Dynamic Model to Explain Forearc Subsidence

    Science.gov (United States)

    Chen, Zhihao; Schellart, Wouter P.; Duarte, João. C.; Strak, Vincent

    2017-10-01

    Overriding plate topography provides constraints on subduction zone geodynamics. We investigate its evolution using fully dynamic laboratory models of subduction with techniques of stereoscopic photogrammetry and particle image velocimetry. Model results show that the topography is characterized by an area of forearc dynamic subsidence, with a magnitude scaling to 1.44-3.97 km in nature, and a local topographic high between the forearc subsided region and the trench. These topographic features rapidly develop during the slab free-sinking phase and gradually decrease during the steady state slab rollback phase. We propose that they result from the variation of the vertical component of the trench suction force along the subduction zone interface, which gradually increases with depth and results from the gradual slab steepening during the initial transient slab sinking phase. The downward mantle flow in the nose of the mantle wedge plays a minor role in driving forearc subsidence.

  7. Subduction of the oceanic Hikurangi Plateau and its impact on the Kermadec arc.

    Science.gov (United States)

    Timm, Christian; Davy, Bryan; Haase, Karsten; Hoernle, Kaj A; Graham, Ian J; de Ronde, Cornel E J; Woodhead, Jon; Bassett, Dan; Hauff, Folkmar; Mortimer, Nick; Seebeck, Hannu C; Wysoczanski, Richard J; Caratori-Tontini, Fabio; Gamble, John A

    2014-09-17

    Large igneous province subduction is a rare process on Earth. A modern example is the subduction of the oceanic Hikurangi Plateau beneath the southern Kermadec arc, offshore New Zealand. This segment of the arc has the largest total lava volume erupted and the highest volcano density of the entire Kermadec arc. Here we show that Kermadec arc lavas south of ~32°S have elevated Pb and Sr and low Nd isotope ratios, which argues, together with increasing seafloor depth, forearc retreat and crustal thinning, for initial Hikurangi Plateau-Kermadec arc collision ~250 km north of its present position. The combined data set indicates that a much larger portion of the Hikurangi Plateau (the missing Ontong Java Nui piece) than previously believed has already been subducted. Oblique plate convergence caused southward migration of the thickened and buoyant oceanic plateau crust, creating a buoyant 'Hikurangi' mélange beneath the Moho that interacts with ascending arc melts.

  8. Thermal effects of variable material properties and metamorphic reactions in a three-component subducting slab

    DEFF Research Database (Denmark)

    Chemia, Zurab; Dolejš, David; Steinle-Neumann, Gerd

    2015-01-01

    We explore the effects of variable material properties, phase transformations, and metamorphic devolatilization reactions on the thermal structure of a subducting slab using thermodynamic phase equilibrium calculations combined with a thermal evolution model. The subducting slab is divided...... within the slab is limited. Two extreme scenarios are considered for a newly forming fluid phase: complete retention in the rock pore space or instantaneous fluid escape due to porosity collapse. Internal heat generation or consumption due to variable heat capacity, compressional work, and energetics...... of progressive metamorphic and devolatilization reactions contribute to the thermal evolution of the slab in addition to the dominating heat flux from the surrounding mantle. They can be considered as a perturbation on the temperature profile obtained in dynamic or kinematic subduction models. Our calculations...

  9. Breaking the oceanic lithosphere of a subducting slab: the 2013 Khash, Iran earthquake

    Science.gov (United States)

    Barnhart, William D.; Hayes, Gavin P.; Samsonov, S.; Fielding, E.; Seidman, L.

    2014-01-01

    [1] Large intermediate depth, intraslab normal faulting earthquakes are a common, dangerous, but poorly understood phenomenon in subduction zones owing to a paucity of near field geophysical observations. Seismological and high quality geodetic observations of the 2013 Mw7.7 Khash, Iran earthquake reveal that at least half of the oceanic lithosphere, including the mantle and entire crust, ruptured in a single earthquake, confirming with unprecedented resolution that large earthquakes can nucleate in and rupture through the oceanic mantle. A rupture width of at least 55 km is required to explain both InSAR observations and teleseismic waveforms, with the majority of slip occurring in the oceanic mantle. Combining our well-constrained earthquake slip distributions with the causative fault orientation and geometry of the local subduction zone, we hypothesize that the Khash earthquake likely occurred as the combined result of slab bending forces and dehydration of hydrous minerals along a preexisting fault formed prior to subduction.

  10. Smectite reactions and slip instabilities in subduction zones

    Science.gov (United States)

    Gadenne, Leslie; Raimbourg, Hugues; Champallier, Remi; Yamamoto, Yuzuru

    2015-04-01

    instabilities in natural conditions, as (1) smectite is a major component of subducted sediments and (2) its transformation into illite may occur over a large depth range.

  11. Seamount subduction underneath an accretionary wedge: modelling mass wasting and wedge collapse

    Science.gov (United States)

    Mannu, Utsav; Ueda, Kosuke; Willett, Sean; Gerya, Taras; Strasser, Michael

    2017-04-01

    Seamounts (h >1 km) and knolls (h = 500 m-1000 m) cover about one-fifth of the total ocean floor area. These topographical highs of the ocean floor eventually get subducted. Subduction of these topographical features leads to severe deformation of the overriding plate and can cause extensive tectonic erosion and mass wasting of the frontal prism, which can ultimately cause a forearc wedge collapse. Large submarine landslides and the corresponding wedge collapse have previously been reported, for instance, in the northern part of the Hikurangi margin where the landslide is known as the giant Ruatoria debris avalanche, and have also been frequently reported in several seismic sections along the Costa Rica margin. Size and frequency relation of landslides suggest that the average size of submarine landslides in margins with rough subducting plates tends to be larger. However, this observation has not yet been tested or explained by physical models. In numerical subduction models, landslides take place, if at all, on a much larger timescale (in the order of 104-105 years, depending on the time steps of the model) than in natural cases. On the other hand, numerical models simulating mass wasting events such as avalanches and submarine landslides, typically model single events at a much smaller spatio-temporal domain, and do not consider long-term occurrence patterns of freely forming landslides. In this contribution, we present a multi-scale nested numerical approach to emulate short-term landslides within long-term progressive subduction. The numerical approach dynamically produces instantaneous submarine landslides and the resulting debris flow in the spatially and temporally refined inner model. Then we apply these convoluted changes in topography (e.g. due to the submarine landslide etc.) back to an outer larger-scale model instance that addresses wedge evolution. We use this approach to study the evolution of the accretionary wedge during seamount subduction.

  12. Record of mid-Archaean subduction from metamorphism in the Barberton terrain, South Africa.

    Science.gov (United States)

    Moyen, Jean-François; Stevens, Gary; Kisters, Alexander

    2006-08-03

    Although plate tectonics is the central geological process of the modern Earth, its form and existence during the Archaean era (4.0-2.5 Gyr ago) are disputed. The existence of subduction during this time is particularly controversial because characteristic subduction-related mineral assemblages, typically documenting apparent geothermal gradients of 15 degrees C km(-1) or less, have not yet been recorded from in situ Archaean rocks (the lowest recorded apparent geothermal gradients are greater than 25 degrees C km(-1)). Despite this absence from the rock record, low Archaean geothermal gradients are suggested by eclogitic nodules in kimberlites and circumstantial evidence for subduction processes, including possible accretion-related structures, has been reported in Archaean terrains. The lack of spatially and temporally well-constrained high-pressure, low-temperature metamorphism continues, however, to cast doubt on the relevance of subduction-driven tectonics during the first 1.5 Gyr of the Earth's history. Here we report garnet-albite-bearing mineral assemblages that record pressures of 1.2-1.5 GPa at temperatures of 600-650 degrees C from supracrustal amphibolites from the mid-Archaean Barberton granitoid-greenstone terrain. These conditions point to apparent geothermal gradients of 12-15 degrees C-similar to those found in recent subduction zones-that coincided with the main phase of terrane accretion in the structurally overlying Barberton greenstone belt. These high-pressure, low-temperature conditions represent metamorphic evidence for cold and strong lithosphere, as well as subduction-driven tectonic processes, during the evolution of the early Earth.

  13. Characterizing Mega-Earthquake Related Tsunami on Subduction Zones without Large Historical Events

    Science.gov (United States)

    Williams, C. R.; Lee, R.; Astill, S.; Farahani, R.; Wilson, P. S.; Mohammed, F.

    2014-12-01

    Due to recent large tsunami events (e.g., Chile 2010 and Japan 2011), the insurance industry is very aware of the importance of managing its exposure to tsunami risk. There are currently few tools available to help establish policies for managing and pricing tsunami risk globally. As a starting point and to help address this issue, Risk Management Solutions Inc. (RMS) is developing a global suite of tsunami inundation footprints. This dataset will include both representations of historical events as well as a series of M9 scenarios on subductions zones that have not historical generated mega earthquakes. The latter set is included to address concerns about the completeness of the historical record for mega earthquakes. This concern stems from the fact that the Tohoku Japan earthquake was considerably larger than had been observed in the historical record. Characterizing the source and rupture pattern for the subduction zones without historical events is a poorly constrained process. In many case, the subduction zones can be segmented based on changes in the characteristics of the subducting slab or major ridge systems. For this project, the unit sources from the NOAA propagation database are utilized to leverage the basin wide modeling included in this dataset. The length of the rupture is characterized based on subduction zone segmentation and the slip per unit source can be determined based on the event magnitude (i.e., M9) and moment balancing. As these events have not occurred historically, there is little to constrain the slip distribution. Sensitivity tests on the potential rupture pattern have been undertaken comparing uniform slip to higher shallow slip and tapered slip models. Subduction zones examined include the Makran Trench, the Lesser Antilles and the Hikurangi Trench. The ultimate goal is to create a series of tsunami footprints to help insurers understand their exposures at risk to tsunami inundation around the world.

  14. Slab1.0: A three-dimensional model of global subduction zone geometries

    Science.gov (United States)

    Hayes, G.P.; Wald, D.J.; Johnson, R.L.

    2012-01-01

    We describe and present a new model of global subduction zone geometries, called Slab1.0. An extension of previous efforts to constrain the two-dimensional non-planar geometry of subduction zones around the focus of large earthquakes, Slab1.0 describes the detailed, non-planar, three-dimensional geometry of approximately 85% of subduction zones worldwide. While the model focuses on the detailed form of each slab from their trenches through the seismogenic zone, where it combines data sets from active source and passive seismology, it also continues to the limits of their seismic extent in the upper-mid mantle, providing a uniform approach to the definition of the entire seismically active slab geometry. Examples are shown for two well-constrained global locations; models for many other regions are available and can be freely downloaded in several formats from our new Slab1.0 website, http://on.doi.gov/ d9ARbS. We describe improvements in our two-dimensional geometry constraint inversion, including the use of average active source seismic data profiles in the shallow trench regions where data are otherwise lacking, derived from the interpolation between other active source seismic data along-strike in the same subduction zone. We include several analyses of the uncertainty and robustness of our three-dimensional interpolation methods. In addition, we use the filtered, subduction-related earthquake data sets compiled to build Slab1.0 in a reassessment of previous analyses of the deep limit of the thrust interface seismogenic zone for all subduction zones included in our global model thus far, concluding that the width of these seismogenic zones is on average 30% larger than previous studies have suggested. Copyright 2011 by the American Geophysical Union.

  15. Probing the transition between seismically coupled and decoupled segments along an ancient subduction interface

    Science.gov (United States)

    Angiboust, Samuel; Kirsch, Josephine; Oncken, Onno; Glodny, Johannes; Monié, Patrick; Rybacki, Erik

    2015-06-01

    The transition zone at the downdip end of seismic coupling along subduction interfaces is often the site of megathrust earthquake nucleation and concentrated postseismic afterslip, as well as the focus site of episodic tremor and slip features. Exhumed remnants of the former Alpine subduction zone found in the Swiss Alps allow analyzing fluid and deformation processes near the transition zone region (30-40 km paleodepth). The Dent Blanche Thrust (DBT) is a lower blueschist-facies shear zone interpreted as a fossilized subduction interface where granitic mylonites overlie a metamorphosed accretionary wedge. We report field observations from the DBT region where multiple, several tens of meters thick foliated cataclastic networks are interlayered within the basal DBT mylonites. Petrological results and microstructural observations indicate that the various cataclasis events took place at near-peak metamorphic conditions (400-500°C, 1.1-1.3 GPa) during subduction of the Tethyan seafloor in Eocene times (42-48 Ma). Some of these networks exhibit mutual crosscutting relationships between mylonites, foliated cataclasites, and vein systems indicating mutual overprinting between brittle deformation and ductile creep. Whole-rock chemical compositions, in situ 40Ar-39Ar age data of recrystallized phengite, and Sr isotopic signatures reveal that DBT rocks also underwent multiple hydrofracturing and metasomatic events via the infiltration of fluids mainly derived from the oceanic metasediments underneath the DBT. From the rock fabrics, we infer strain rate fluctuations of several orders of magnitude beyond subduction strain rates (˜10-12 s-1) accompanied by fluctuation of supralithostatic and quasi-lithostatic fluid pressures (1 ≥ λ > 0.95). DBT brittle-plastic deformation switches highlight the diversity of deformation processes and fluid-rock interactions in the transition zone region of the subduction interface.

  16. Kinematics of Late Cretaceous subduction initiation in the Neo-Tethys Ocean reconstructed from ophiolites of Turkey, Cyprus, and Syria

    NARCIS (Netherlands)

    Maffione, Marco; van Hinsbergen, Douwe J.J.; de Gelder, Giovanni I.N.O.; van der Goes, Freek C.; Morris, Antony

    Formation of new subduction zones represents one of the cornerstones of plate tectonics, yet both the kinematics and geodynamics governing this process remain enigmatic. A major subduction initiation event occurred in the Late Cretaceous, within the Neo-Tethys Ocean between Gondwana and Eurasia.

  17. Rapid conversion of an oceanic spreading center to a subduction zone inferred from high-precision geochronology.

    Science.gov (United States)

    Keenan, Timothy E; Encarnación, John; Buchwaldt, Robert; Fernandez, Dan; Mattinson, James; Rasoazanamparany, Christine; Luetkemeyer, P Benjamin

    2016-11-22

    Where and how subduction zones initiate is a fundamental tectonic problem, yet there are few well-constrained geologic tests that address the tectonic settings and dynamics of the process. Numerical modeling has shown that oceanic spreading centers are some of the weakest parts of the plate tectonic system [Gurnis M, Hall C, Lavier L (2004) Geochem Geophys Geosys 5:Q07001], but previous studies have not favored them for subduction initiation because of the positive buoyancy of young lithosphere. Instead, other weak zones, such as fracture zones, have been invoked. Because these models differ in terms of the ages of crust that are juxtaposed at the site of subduction initiation, they can be tested by dating the protoliths of metamorphosed oceanic crust that is formed by underthrusting at the beginning of subduction and comparing that age with the age of the overlying lithosphere and the timing of subduction initiation itself. In the western Philippines, we find that oceanic crust was less than ∼1 My old when it was underthrust and metamorphosed at the onset of subduction in Palawan, Philippines, implying forced subduction initiation at a spreading center. This result shows that young and positively buoyant, but weak, lithosphere was the preferred site for subduction nucleation despite the proximity of other potential weak zones with older, denser lithosphere and that plate motion rapidly changed from divergence to convergence.

  18. Geodynamic models of continental subduction and obduction of overriding plate forearc oceanic lithosphere on top of continental crust

    NARCIS (Netherlands)

    Edwards, Sarah J.; Schellart, Wouter P.; Duarte, Joao C.

    2015-01-01

    Continental subduction takes place in the final stage of subduction when all oceanic lithosphere is consumed and continental passive margin is pulled into the mantle. When the overriding plate is oceanic, dense forearc oceanic lithosphere might be obducted onto light continental crust forming an

  19. Geophysical detection of relict metasomatism from an Archean (approximately 3.5 Ga) subduction zone.

    Science.gov (United States)

    Chen, Chin-Wu; Rondenay, Stéphane; Evans, Rob L; Snyder, David B

    2009-11-20

    When plate tectonics started on Earth has been uncertain, and its role in the assembly of early continents is not well understood. By synthesizing coincident seismic and electrical profiles, we show that subduction processes formed the Archean Slave craton in Canada. The spatial overlap between a seismic discontinuity and a conductive anomaly at approximately 100 kilometers depth, in conjunction with the occurrence of mantle xenoliths rich in secondary minerals representative of a metasomatic front, supports cratonic assembly by subduction and accretion of lithospheric fragments. Although evidence of cratonic assembly is rarely preserved, these results suggest that plate tectonics was operating as early as Paleoarchean times, approximately 3.5 billion years ago (Ga).

  20. Transient uplift after a 17th-century earthquake along the Kuril subduction zone.

    Science.gov (United States)

    Sawai, Yuki; Satake, Kenji; Kamataki, Takanobu; Nasu, Hiroo; Shishikura, Masanobu; Atwater, Brian F; Horton, Benjamin P; Kelsey, Harvey M; Nagumo, Tamotsu; Yamaguchi, Masaaki

    2004-12-10

    In eastern Hokkaido, 60 to 80 kilometers above a subducting oceanic plate, tidal mudflats changed into freshwater forests during the first decades after a 17th-century tsunami. The mudflats gradually rose by a meter, as judged from fossil diatom assemblages. Both the tsunami and the ensuing uplift exceeded any in the region's 200 years of written history, and both resulted from a shallow plate-boundary earthquake of unusually large size along the Kuril subduction zone. This earthquake probably induced more creep farther down the plate boundary than did any of the region's historical events.

  1. Flat-slab subduction, orogenesis, intraplate deformation, and glacial erosion in southern Alaska: A tectonic-glacial progression from STEEP

    Science.gov (United States)

    Pavlis, T. L.; Gulick, S. S.; Bruhn, R. L.; Christeson, G. L.; Enkelmann, E.; Freymueller, J. T.; Hallet, B.; Horton, B. K.; Hansen, R. A.; Koons, P. O.; Pavlis, G. L.; Ridgway, K. D.; Spotila, J. A.; Van Avendonk, H. J.

    2012-12-01

    The ST. Elias Erosion and tectonics Project (STEEP) is a Continental Dynamics multidisciplinary collaboration involving offshore and onshore studies of a modern example of an oceanic plateau collision with a continental margin in southern Alaska. These studies constrain erosion-tectonic interactions and clarify the timeline of northern Cordilleran orogenesis. At ~55 Ma an oceanic plateau formed on either the Kula-Farallon or Farallon-Resurrection spreading center. From 50-46 Ma, this plateau attempted to subduct beneath an accretionary complex, the Yakutat Group (YG), near offshore British Columbia. The YG was thrust onto the plateau to form what is now the Yakutat Terrane. From ~40 to as late as 33 Ma the Yakutat Terrane was part of North America and the proto-Transition Fault was active moving the remnant Kula Plate towards the Aleutian Trench, slicing off the southern edge of the Yakutat Terrane, and emplacing Pacific crust adjacent to the Terrane. From ~33 to 6 Ma the Yakutat Terrane moved northward with the Pacific Plate. There is some Oligocene paleogeographic uncertainly, but upper plate deformation and basin development starting ~ 20-25 Ma may be Yakutat related. At ~6 Ma the Pacific Plate underwent a clockwise shift in motion reactivating the Transition Fault, albeit at a slow rate, and this motion drove a component of oblique convergence along the Fairweather Fault and orogenesis in the St. Elias. Rejuvenation of the Transition Fault formed a stable triple junction with the Aleutian Trench and the Yakutat-North American subduction front. Uplift in the orogen seeded glacial systems that reached tidewater by ~5.5 Ma and the sediments produced were the glaciomarine, syn-orogenic Yakataga Formation. The eastern syntaxis of the St. Elias orogen began to focus exhumation as thickened crust generated along the transpressive Fairweather system was fed into the fully contractional core of the orogen. Between 4 and 3 Ma, the thicker portions of the Yakutat Terrane

  2. The Ionian Abyssal Plain - closure of a remnant Mesozoic oceanic domain: subbottom structures, deep deformation and the Calabrian subduction zone

    Science.gov (United States)

    Gallais, F.; Gutscher, M.; Graindorge, D.; Klaeschen, D.

    2010-12-01

    The Ionian Abyssal Plain (IAP), located in the Central Mediterranean area is a deep triangular shaped basin, surrounded by the Calabrian subduction zone to the NW, the Mediterranean Ridge to the NE and the Medina Ridges to the South. Available heat flow measurements show very low values under the Ionian Abyssal plain, suggesing a very old age of 180-200 Ma for the basin. The Bouguer gravity anomaly map shows only a strong positive anomaly in this region and the depth of the Moho is around 16 to 18 km corresponding to high refraction velocities of 8.1-8.2 km/s. The Ionian basin is interpreted as one of the oldest basins in the Mediterranean area, and is thought to represent a remnant part of the Mesozoic Tethyan ocean. Due to the complex relative motions of microplates and blocks, currently, the oceanic lithosphere of the Ionian basin is being simultaneously consumed by subduction to the NE beneath the Hellenic system and to the NW beneath Calabria. We present the most relevant lines of the Archimede multi-channel seismic cruise (1997, R/V Le Nadir) crossing the Ionian Abyssal Plain and the Calabrian subduction zone. Interpretation of this seismic dataset is based on correlation with published seismic data and with ESP results. Beneath the IAP, we identify a thick sedimentary cover (> 5km) from the Jurassic to the Plio-Quaternary in age, which overlies the oceanic basement. The Pre-Messinian sequences are affected by a set of NE/SW striking compressional faults with some syn-tectonic basins NW of these faults. These features are interpreted as a re-activated set of normal faults, possibly formed during rifting and/or subsequent accretion of oceanic crust. The orientation of the subbottom structures and the thickness of the Messinian deposits in the south-eastern part of the IAP may be linked with the presence of these faults and their activity through time. On the Calabrian side of the IAP, the Post-Messinian sequences are accreted to the Calabrian wedge. The weak

  3. Diapir versus along-channel ascent of crustal material during plate convergence: Constrained by the thermal structure of subduction zones

    Science.gov (United States)

    Liu, Ming-Qi; Li, Zhong-Hai; Yang, Shao-Hua

    2017-09-01

    Subduction channel processes are crucial for understanding the material and energy exchange between the Earth's crust and mantle. Crustal rocks can be subducted to mantle depths, interact with the mantle wedge, and then exhume to the crustal depth again, which is generally considered as the mechanism for the formation of ultrahigh-pressure metamorphic rocks in nature. In addition, the crustal rocks generally undergo dehydration and melting at subarc depths, giving rise to fluids that metasomatize and weaken the overlying mantle wedge. There are generally two ways for the material ascent from subarc depths: one is along subduction channels; the other is through the mantle wedge by diapir. In order to study the conditions and dynamics of these contrasting material ascent modes, systematic petrological-thermo-mechanical numerical models are constructed with variable thicknesses of the overriding and subducting continental plates, ages of the subducting oceanic plate, as well as the plate convergence rates. The model results suggest that the thermal structures of subduction zones control the thermal condition and fluid/melt activity at the slab-mantle interface in subcontinental subduction channels, which further strongly affect the material transportation and ascent mode. The thick overriding continental plate and the low-angle subduction style induced by young subducting oceanic plate both contribute to the formation of relatively cold subduction channels with strong overriding mantle wedge, where the along-channel exhumation occurs exclusively to result in the exhumation of HP-UHP metamorphic rocks. In contrast, the thin overriding lithosphere and the steep subduction style induced by old subducting oceanic plate are the favorable conditions for hot subduction channels, which lead to significant hydration and metasomatism, melting and weakening of the overriding mantle wedge and thus cause the ascent of mantle wedge-derived melts by diapir through the mantle wedge

  4. Accessory minerals and subduction zone metasomatism: a geochemical comparison of two mélanges (Washington and California, U.S.A.)

    Science.gov (United States)

    Sorensen, Sorena S.; Grossman, Jeffrey N.

    1993-01-01

    The ability of a subducted slab or subducted sediment to contribute many incompatible trace elements to arc source regions may depend on the stabilities of accessory minerals within these rocks, which can only be studied indirectly. In contrast, the role of accessory minerals in lower-T and -P metasomatic processes within paleo-subduction zones can be studied directly in subduction-zone metamorphic terranes.

  5. Incremental Slip Along Dilatant Faults in Ancient Fluid-Rich Subduction Zones

    Science.gov (United States)

    Remitti, F.; Fagereng, A.; Sibson, R. H.; Vannucchi, P.; Bettelli, G.

    2012-12-01

    At a variety of depths in subduction zones a proportion of relative plate motion is accommodated by episodic tremor and slow slip events. These events are accompanied by distinct low frequency seismic signals and/or high levels of micro-seismic activity. Based on theoretical studies and seismic attributes of the source region, fluids overpressured to near-lithostatic values seem likely to be involved in the mechanism behind episodic tremor. Ancient crust surrounding paleoseismic zones, especially if rich in overpressured fluids, should contain widespread relics of this kind of activity. Here we present microstructural observations from two ancient subduction thrust analogues where brittle deformation was accommodated by repeating micro-movements along dilatant faults. The first example is a mélange formed during Triassic-Jurassic tectonic accretion of ocean floor sediments now exposed in the Chrystalls Beach Complex, South Island, NZ. The mélange comprises competent sandstone and chert lenses set in a cleaved mudstone matrix deformed in a continuous-discontinuous style under subgreenschist conditions. Deformation is characterized by a pervasive anastomosing fault-fracture mesh of multiple shearing surfaces, subparallel to cleavage and coated with incrementally developed quartz-calcite slickenfibres. Microstructural observations reveal that slickenfibres grew by 'crack-seal' increments of 10-100 μm. Incremental slip transfer was constant over a single slickenfiber and accommodated by opening of extension fractures that link en echelon slip surfaces. The characteristic spacing of inclusion bands indicates relatively constant growth increments, possibly occurring into regular size cracks. Increments of non-constant growth and, instead, fractures significantly wider than 100 μm, are represented by local veins of euhedral quartz and carbonate. Similar structures are present in the shallow part of an ancient plate interface, now exposed in the Northern Apennines of

  6. Oceanic-style Subduction Controls Late Cenozoic Deformation of the Northern Pamir and Alai

    Science.gov (United States)

    Sobel, E. R.; Chen, J.; Schoenbohm, L. M.; Thiede, R. C.; Stockli, D. F.; Sudo, M.; Strecker, M. R.

    2012-12-01

    The Pamir - Alai represents the preeminent example of an active intracontinental subduction zone in the early stages of continent-continent collision. Such zones are the least understood type of plate boundary because modern examples are few and of limited access, and ancient analogs have been extensively overprinted by subsequent continent-continent collision and erosion processes. In the Pamir, at least 300 km of convergence has apparently occurred between the North Pamir and the South Tien Shan. Published P-wave tomography and earthquake epicenters suggest subduction of a ~300 km-long slab. The MPT and Pamir Frontal Thrusts (PFT) correspond to the updip projection of this subduction zone. We have compiled ca. 260 published and 18 new apatite and zircon (U-Th)/He and fission track, and biotite and muscovite Argon cooling ages from basement samples as well as several detrital samples from key areas in the Pamir region. Our synopsis shows that the hanging wall of the MPT experienced relatively minor amounts of late Cenozoic exhumation. This is incompatible with a model of a huge overthrust such as the Himalayan Main Central Thrust. Rather, the bulk of the convergence is apparently accommodated by underthrusting. The Pamir orogen as a whole is an integral part of the overriding plate in a subduction system, while the remnant basin to the north constitutes the downgoing plate. Herein, we demonstrate that the observed deformation of the upper and lower plates within the Pamir-Alai convergence zone resembles highly arcuate oceanic subduction systems characterized by slab rollback, subduction erosion, subduction accretion, and marginal slab-tear faults. We suggest that the curvature of the North Pamir is genetically linked to the short width and rollback of the south-dipping Alai slab; northward motion (indentation) of the Pamir is accommodated by crustal processes related to slab rollback and intracontinental subduction. Our model relates late Oligocene - early Miocene

  7. Some geophysical and geochemical consequences of slab serpentinization at subduction zones

    Science.gov (United States)

    Phipps Morgan, J.; Ruepke, L. H.; Ranero, C.; Hort, M.

    2002-12-01

    Here we explore the potential impact of slab serpentinization and deserpentinization processes on arc-melting and on water, carbon-dioxide, U, Pb, and noble gas recycling into the deep mantle. We examine the consequences of a scenario in which bend-faulting between the outer rise and trench axis creates the conduits for seawater to reach and react with cold lithospheric mantle to serpentinize it. Water penetration to serpentinize the slab-lithosphere will be inhibited by thick sediments (e.g. Cascades) or thick oceanic crust (subducting oceanic plateaus), while subducting long-offset fracture zones will be especially serpentine-rich because they serpentinized at both the spreading center and subduction zone. If this process occurs, then the incoming lithosphere will typically contain ~500m of altered sediments, ~6 km of partially hydrated oceanic crust, and ~20-55km of partially serpentinized slab mantle. Possible regional geophysical consequences of this scenario are: (1) Fracture Zones preferentially become tears in subducting slabs because they are relatively serpentine rich, thus they deserpentinize more. (2) If so, then their greater deserpentinization should produce greater sub-arc water release which leads to greater arc melting above subducted fracture zones. (3) Regions of little serpentinization will be correlated with flat subduction, lower volumes of slab-water release, and relatively low rates of arc-volcanism. Our thermomechanical modelling implies, depending upon a slab's age and subduction rate, between 30-90% of the slab's chemically bound water is likely to survive sub-arc dehydration to transport its water into the deeper mantle. Possible global geochemical consequences of this scenario are: (1) At current subduction rates, 0.5-1.5 oceans of water would be recycled past the arc-melting region into the deeper mantle during the past Ga. (2) Since 0.3%, 1%, and 3% of the exosphere's Ne, Ar, and Xe are dissolved in the oceans, this implies that at

  8. Incorporating Cutting Edge Scientific Results from the Margins-Geoprisms Program into the Undergraduate Curriculum: The Subduction Factory

    Science.gov (United States)

    Penniston-Dorland, S.; Stern, R. J.; Edwards, B. R.; Kincaid, C. R.

    2014-12-01

    The NSF-MARGINS Program funded a decade of research on continental margin processes. The NSF-GeoPRISMS Mini-lesson Project, funded by NSF-TUES, is designed to integrate fundamental results from the MARGINS program into open-source college-level curriculum. Three Subduction Factory (SubFac) mini-lessons were developed as part of this project. These include hands-on examinations of data sets representing 3 key components of the subduction zone system: 1) Heat transfer in the subducted slab; 2) Metamorphic processes happening at the plate interface; and 3) Typical magmatic products of arc systems above subduction zones. Module 1: "Slab Temperatures Control Melting in Subduction Zones, What Controls Slab Temperature?" allows students to work in groups using beads rolling down slopes as an analog for the mathematics of heat flow. Using this hands-on, exploration-based approach, students develop an intuition for the mathematics of heatflow and learn about heat conduction and advection in the subduction zone environment. Module 2: "Subduction zone metamorphism" introduces students to the metamorphic rocks that form as the subducted slab descends and the mineral reactions that characterize subduction-related metamorphism. This module includes a suite of metamorphic rocks available for instructors to use in a lab, and exercises in which students compare pressure-temperature estimates obtained from metamorphic rocks to predictions from thermal models. Module 3: "Central American Arc Volcanoes, Petrology and Geochemistry" introduces students to basic concepts in igneous petrology using the Central American volcanic arc, a MARGINS Subduction Factory focus site, as an example. The module relates data from two different volcanoes - basaltic Cerro Negro (Nicaragua) and andesitic Ilopango (El Salvador) including hand sample observations and major element geochemistry - to explore processes of mantle and crustal melting and differentiation in arc volcanism.

  9. Mantle constraints on the plate tectonic evolution of the Tonga-Kermadec-Hikurangi subduction zone and the South Fiji Basin region

    NARCIS (Netherlands)

    Schellart, W. P.; Spakman, W.

    The Tonga-Kermadec-Hikurangi subduction zone is a major plate boundary in the Southwest Pacific region, where the Pacific plate subducts westward underneath the Australian plate. Considerable controversy exists regarding the Cenozoic evolution of this subduction zone, its connection with the

  10. Mantle constraints on the plate tectonic evolution of the Tonga-Kermadec-Hikurangi subduction zone and the South Fiji Basin region

    NARCIS (Netherlands)

    Schellart, W.P.; Spakman, W.

    2012-01-01

    The Tonga–Kermadec–Hikurangi subduction zone is a major plate boundary in the Southwest Pacific region, where the Pacific plate subducts westward underneath the Australian plate. Considerable controversy exists regarding the Cenozoic evolution of this subduction zone, its connection with

  11. Multi-stage origin of the Coast Range ophiolite, California: Implications for the life cycle of supra-subduction zone ophiolites

    Science.gov (United States)

    Shervais, J.W.; Kimbrough, D.L.; Renne, P.; Hanan, B.B.; Murchey, B.; Snow, C.A.; Zoglman, Schuman M.M.; Beaman, J.

    2004-01-01

    The Coast Range ophiolite of California is one of the most extensive ophiolite terranes in North America, extending over 700 km from the northernmost Sacramento Valley to the southern Transverse Ranges in central California. This ophiolite, and other ophiolite remnants with similar mid-Jurassic ages, represent a major but short-lived episode of oceanic crust formation that affected much of western North America. The history of this ophiolite is important for models of the tectonic evolution of western North America during the Mesozoic, and a range of conflicting interpretations have arisen. Current petrologic, geochemical, stratigraphic, and radiometric age data all favor the interpretation that the Coast Range ophiolite formed to a large extent by rapid extension in the forearc region of a nascent subduction zone. Closer inspection of these data, however, along with detailed studies of field relationships at several locales, show that formation of the ophiolite was more complex, and requires several stages of formation. Our work shows that exposures of the Coast Range ophiolite preserve evidence for four stages of magmatic development. The first three stages represent formation of the ophiolite above a nascent subduction zone. Rocks associated with the first stage include ophiolite layered gabbros, a sheeted complex, and volcanic rocks vith arc tholeiitic or (roore rarely) low-K calc-alkaline affinities. The second stage is characterized by intrusive wehrlite-clinopyroxenite complexes, intrusive gabbros, Cr-rich diorites, and volcanic rocks with high-Ca boninitic or tholeiitic ankaramite affinities. The third stage includes diorite and quartz diorite plutons, felsic dike and sill complexes, and calc-alkaline volcanic rocks. The first three stages of ophiolite formation were terminated by the intrusion of mid-ocean ridge basalt dikes, and the eruption of mid-ocean ridge basalt or ocean-island basalt volcanic suites. We interpret this final magmatic event (MORB

  12. Stress rotation across the Cascadia megathrust requires a weak subduction plate boundary at seismogenic depths

    Science.gov (United States)

    Li, Duo; McGuire, Jeffrey J.; Liu, Yajing; Hardebeck, Jeanne L.

    2018-01-01

    The Mendocino Triple Junction region is the most seismically active part of the Cascadia Subduction Zone. The northward moving Pacific plate collides with the subducting Gorda plate causing intense internal deformation within it. Here we show that the stress field rotates rapidly with depth across the thrust interface from a strike-slip regime within the subducting plate, reflecting the Pacific plate collision, to a thrust regime in the overriding plate. We utilize a dense focal mechanism dataset, including observations from the Cascadia Initiative ocean bottom seismograph experiment, to constrain the stress orientations. To quantify the implications of this rotation for the strength of the plate boundary, we designed an inversion that solves for the absolute stress tensors in a three-layer model subject to assumptions about the strength of the subducting mantle. Our results indicate that the shear stress on the plate boundary fault is likely no more than about ∼50 MPa at ∼20 km depth. Regardless of the assumed mantle strength, we infer a relatively weak megathrust fault with an effective friction coefficient of ∼0 to 0.2 at seismogenic depths. Such a low value for the effective friction coefficient requires a combination of high fluid pressures and/or fault-zone minerals with low inherent friction in the region where a great earthquake is expected in Cascadia.

  13. Intra-Panthalassa Ocean subduction zones revealed by fossil arcs and mantle structure

    NARCIS (Netherlands)

    Meer, D.G. van der; Torsvik, T.H.; Spakman, W.; Hinsbergen, D.J.J. van; Amaru, M.L.

    2012-01-01

    The vast Panthalassa Ocean once surrounded the supercontinent Pangaea. Subduction has since consumed most of the oceanic plates that formed the ocean floor, so classic plate reconstructions based on magnetic anomalies can be used only to constrain the ocean’s history since the Cretaceous period, and

  14. Thermal structure and intermediate-depth seismicity in the Tohoku-Hokkaido subduction zones

    Energy Technology Data Exchange (ETDEWEB)

    Van Keken, P.E. [Michigan Univ., Ann Arbor, MI (United States). Dept. of Earth and Environmental Sciences; Kita, S.; Nakajima, J. [Tohoku Univ., Sendai (Japan). Research Center for Prediction of Earthquakes and Volcanic Eruptions

    2012-07-01

    The cause of intermediate-depth (>40 km) seismicity in subduction zones is not well understood. The viability of proposed mechanisms, which include dehydration embrittlement, shear instabilities and the presence of fluids in general, depends significantly on local conditions, including pressure, temperature and composition. The wellinstrumented and well-studied subduction zone below Northern Japan (Tohoku and Hokkaido) provides an excellent testing ground to study the conditions under which intermediate-depth seismicity occurs. This study combines new finite element models that predict the dynamics and thermal structure of the Japan subduction system with a high-precision hypocenter data base. The upper plane of seismicity is principally contained in the crustal portion of the subducting slab and appears to thin and deepen within the crust at depths >80 km. The disappearance of seismicity overlaps in most of the region with the predicted phase change of blueschist to hydrous eclogite, which forms a major dehydration front in the crust. The correlation between the thermally predicted blueschist-out boundary and the disappearance of seismicity breaks down in the transition from the northern Japan to Kurile arc below western Hokkaido. Adjusted models that take into account the seismically imaged modified upper mantle structure in this region fail to adequately recover the correlation that is seen below Tohoku and eastern Hokkaido. We conclude that the thermal structure below Western Hokkaido is significantly affected by timedependent, 3-D dynamics of the slab. This study generally supports the role of fluids in the generation of intermediate-depth seismicity. (orig.)

  15. A role for subducted super-hydrated kaolinite in Earth’s deep water cycle

    Energy Technology Data Exchange (ETDEWEB)

    Hwang, Huijeong; Seoung, Donghoon; Lee, Yongjae; Liu, Zhenxian; Liermann, Hanns-Peter; Cynn, Hyunchae; Vogt, Thomas; Kao, Chi-Chang; Mao, Ho-Kwang

    2017-11-20

    Water is the most abundant volatile component in the Earth. It continuously enters the mantle through subduction zones, where it reduces the melting temperature of rocks to generate magmas. The dehydration process in subduction zones, which determines whether water is released from the slab or transported into the deeper mantle, is an essential component of the deep water cycle. Here we use in situ and time-resolved high-pressure/high-temperature synchrotron X-ray diffraction and infrared spectra to characterize the structural and chemical changes of the clay mineral kaolinite. At conditions corresponding to a depth of about 75 km in a cold subducting slab (2.7 GPa and 200 °C), and in the presence of water, we observe the pressure-induced insertion of water into kaolinite. This super-hydrated phase has a unit cell volume that is about 31% larger, a density that is about 8.4% lower than the original kaolinite and, with 29 wt% H2O, the highest water content of any known aluminosilicate mineral in the Earth. As pressure and temperature approach 19 GPa and about 800 °C, we observe the sequential breakdown of super-hydrated kaolinite. The formation and subsequent breakdown of super-hydrated kaolinite in cold slabs subducted below 200 km leads to the release of water that may affect seismicity and help fuel arc volcanism at the surface.

  16. Fossil intermediate-depth earthquakes in subducting slabs linked to differential stress release

    Science.gov (United States)

    Scambelluri, Marco; Pennacchioni, Giorgio; Gilio, Mattia; Bestmann, Michel; Plümper, Oliver; Nestola, Fabrizio

    2017-12-01

    The cause of intermediate-depth (50-300 km) seismicity in subduction zones is uncertain. It is typically attributed either to rock embrittlement associated with fluid pressurization, or to thermal runaway instabilities. Here we document glassy pseudotachylyte fault rocks—the products of frictional melting during coseismic faulting—in the Lanzo Massif ophiolite in the Italian Western Alps. These pseudotachylytes formed at subduction-zone depths of 60-70 km in poorly hydrated to dry oceanic gabbro and mantle peridotite. This rock suite is a fossil analogue to an oceanic lithospheric mantle that undergoes present-day subduction. The pseudotachylytes locally preserve high-pressure minerals that indicate an intermediate-depth seismic environment. These pseudotachylytes are important because they are hosted in a near-anhydrous lithosphere free of coeval ductile deformation, which excludes an origin by dehydration embrittlement or thermal runaway processes. Instead, our observations indicate that seismicity in cold subducting slabs can be explained by the release of differential stresses accumulated in strong dry metastable rocks.

  17. Influence of subduction zone conditions and gouge composition on frictional slip stability of megathrust faults

    NARCIS (Netherlands)

    den Hartog, S.A.M.; Spiers, C.J.

    2013-01-01

    To understand the temperature/depth distribution of destructive earthquakes in subduction megathrusts, and the mechanisms of nucleation of these events, data on the frictional behaviour of phyllosilicate/quartz-rich megathrust fault gouges under in-situ conditions are needed. We performed rotary

  18. Fluid and deformation regime of an advancing subduction system at Marlborough, New Zealand.

    Science.gov (United States)

    Wannamaker, Philip E; Caldwell, T Grant; Jiracek, George R; Maris, Virginie; Hill, Graham J; Ogawa, Yasuo; Bibby, Hugh M; Bennie, Stewart L; Heise, Wiebke

    2009-08-06

    Newly forming subduction zones on Earth can provide insights into the evolution of major fault zone geometries from shallow levels to deep in the lithosphere and into the role of fluids in element transport and in promoting rock failure by several modes. The transpressional subduction regime of New Zealand, which is advancing laterally to the southwest below the Marlborough strike-slip fault system of the northern South Island, is an ideal setting in which to investigate these processes. Here we acquired a dense, high-quality transect of magnetotelluric soundings across the system, yielding an electrical resistivity cross-section to depths beyond 100 km. Our data imply three distinct processes connecting fluid generation along the upper mantle plate interface to rock deformation in the crust as the subduction zone develops. Massive fluid release just inland of the trench induces fault-fracture meshes through the crust above that undoubtedly weaken it as regional shear initiates. Narrow strike-slip faults in the shallow brittle regime of interior Marlborough diffuse in width upon entering the deeper ductile domain aided by fluids and do not project as narrow deformation zones. Deep subduction-generated fluids rise from 100 km or more and invade upper crustal seismogenic zones that have exhibited historic great earthquakes on high-angle thrusts that are poorly oriented for failure under dry conditions. The fluid-deformation connections described in our work emphasize the need to include metamorphic and fluid transport processes in geodynamic models.

  19. Seismic evidence for flow in the hydrated mantle wedge of the Ryukyu subduction zone.

    Science.gov (United States)

    Nagaya, Takayoshi; Walker, Andrew M; Wookey, James; Wallis, Simon R; Ishii, Kazuhiko; Kendall, J-Michael

    2016-07-20

    It is widely accepted that water-rich serpentinite domains are commonly present in the mantle above shallow subducting slabs and play key roles in controlling the geochemical cycling and physical properties of subduction zones. Thermal and petrological models show the dominant serpentine mineral is antigorite. However, there is no good consensus on the amount, distribution and alignment of this mineral. Seismic velocities are commonly used to identify antigorite-rich domains, but antigorite is highly-anisotropic and depending on the seismic ray path, its properties can be very difficult to distinguish from non-hydrated olivine-rich mantle. Here, we utilize this anisotropy and show how an analysis of seismic anisotropy that incorporates measured ray path geometries in the Ryukyu arc can constrain the distribution, orientation and amount of antigorite. We find more than 54% of the wedge must consist of antigorite and the alignment must change from vertically aligned to parallel to the slab. This orientation change suggests convective flow in the hydrated forearc mantle. Shear wave splitting analysis in other subduction zones indicates large-scale serpentinization and forearc mantle convection are likely to be more widespread than generally recognized. The view that the forearc mantle of cold subduction zones is dry needs to be reassessed.

  20. Ediacaran 2,500-km-long synchronous deep continental subduction in the West Gondwana Orogen.

    Science.gov (United States)

    Ganade de Araujo, Carlos E; Rubatto, Daniela; Hermann, Joerg; Cordani, Umberto G; Caby, Renaud; Basei, Miguel A S

    2014-10-16

    The deeply eroded West Gondwana Orogen is a major continental collision zone that exposes numerous occurrences of deeply subducted rocks, such as eclogites. The position of these eclogites marks the suture zone between colliding cratons, and the age of metamorphism constrains the transition from subduction-dominated tectonics to continental collision and mountain building. Here we investigate the metamorphic conditions and age of high-pressure and ultrahigh-pressure eclogites from Mali, Togo and NE-Brazil and demonstrate that continental subduction occurred within 20 million years over at least a 2,500-km-long section of the orogen during the Ediacaran. We consider this to be the earliest evidence of large-scale deep-continental subduction and consequent appearance of Himalayan-scale mountains in the geological record. The rise and subsequent erosion of such mountains in the Late Ediacaran is perfectly timed to deliver sediments and nutrients that are thought to have been necessary for the subsequent evolution of sustainable life on Earth.

  1. Age of the subducting Pacific slab beneath East Asia and its geodynamic implications

    Science.gov (United States)

    Liu, Xin; Zhao, Dapeng; Li, Sanzhong; Wei, Wei

    2017-04-01

    We study the age of the subducting Pacific slab beneath East Asia using a high-resolution model of P-wave tomography and paleo-age data of ancient seafloor. Our results show that the lithosphere age of the subducting slab becomes younger from the Japan Trench (∼130 Ma) to the slab's western edge (∼90 Ma) beneath East China, and the flat (stagnant) slab in the mantle transition zone (MTZ) is the subducted Pacific plate rather than the proposed Izanagi plate which should have already collapsed into the lower mantle. The flat Pacific slab has been in the MTZ for no more than ∼10-20 million years, considerably less than the age of the big mantle wedge beneath East Asia (>110 million years). Hence, the present flat Pacific slab in the MTZ has contributed to the Cenozoic destruction of the East Asian continental lithosphere with extensive intraplate volcanism and back-arc spreading, whereas the destruction of the North China Craton during the Early Cretaceous (∼140-110 Ma) was caused by the subduction of the Izanagi (or the Paleo-Pacific) plate.

  2. Are subduction zones invading the atlantic? Evidence from the southwest iberia margin

    NARCIS (Netherlands)

    Duarte, João C.; Rosas, Filipe M.; Terrinha, Pedro; Schellart, Wouter P.; Boutelier, David; Gutscher, Marc André; Ribeiro, António

    Subduction initiation at passive margins plays a central role in the plate tectonics theory. However, the process by which a passive margin becomes active is not well understood. In this paper we use the southwest Iberia margin (SIM) in the Atlantic Ocean to study the process of passive margin

  3. Dehydration of lawsonite could directly trigger earthquakes in subducting oceanic crust

    Science.gov (United States)

    Okazaki, Keishi; Hirth, Greg

    2016-02-01

    Intermediate-depth earthquakes in cold subduction zones are observed within the subducting oceanic crust, as well as the mantle. In contrast, intermediate-depth earthquakes in hot subduction zones predominantly occur just below the Mohorovičić discontinuity. These observations have stimulated interest in relationships between blueschist-facies metamorphism and seismicity, particularly through dehydration reactions involving the mineral lawsonite. Here we conducted deformation experiments on lawsonite, while monitoring acoustic emissions, in a Griggs-type deformation apparatus. The temperature was increased above the thermal stability of lawsonite, while the sample was deforming, to test whether the lawsonite dehydration reaction induces unstable fault slip. In contrast to similar tests on antigorite, unstable fault slip (that is, stick-slip) occurred during dehydration reactions in the lawsonite and acoustic emission signals were continuously observed. Microstructural observations indicate that strain is highly localized along the fault (R1 and B shears), and that the fault surface develops slickensides (very smooth fault surfaces polished by frictional sliding). The unloading slope during the unstable slip follows the stiffness of the apparatus at all experimental conditions, regardless of the strain rate and temperature ramping rate. A thermomechanical scaling factor for the experiments is within the range estimated for natural subduction zones, indicating the potential for unstable frictional sliding within natural lawsonite layers.

  4. The Othris Ophiolite, Greece: A snapshot of subduction initiation at a mid-ocean ridge

    NARCIS (Netherlands)

    Barth, M.G.; Mason, P.R.D.; Davies, G.R.; Drury, M.R.

    2008-01-01

    The mantle section of the Tethyan-type Othris Ophiolite, Greece, records tectono-magmatic processes characteristic of both mid-ocean ridges and supra-subduction zones. The Othris Ophiolite is a remnant of the Jurassic Neotethys Ocean, which existed between Eurasia and Gondwanaland. Othris

  5. Structure and evolution of subducted lithosphere beneath the Sunda arc, Indonesia

    NARCIS (Netherlands)

    Widiyantoro, Sri; Hilst, R.D. van der

    1996-01-01

    Tomographic imaging reveals seismic anomalies beneath the Sunda island arc, Indonesia, that suggest that the lithospheric slab penetrates to a depth of at least 1500 kilometers. The Sunda slab forms the eastern end of a deep anomaly associated with the past subduction of the plate underlying the

  6. Slab detachment in laterally varying subduction zones: 3-D numerical modeling

    NARCIS (Netherlands)

    Duretz, T.; Gerya, T.V.; Spakman, W.|info:eu-repo/dai/nl/074103164

    Understanding the three-dimensional (3-D) dynamics of subduction-collision systems is a longstanding challenge in geodynamics. We investigate the impact of slab detachment in collision systems that are subjected to along-trench variations. High-resolution thermomechanical numerical models,

  7. Mantle wedge infiltrated with saline fluids from dehydration and decarbonation of subducting slab.

    Science.gov (United States)

    Kawamoto, Tatsuhiko; Yoshikawa, Masako; Kumagai, Yoshitaka; Mirabueno, Ma Hannah T; Okuno, Mitsuru; Kobayashi, Tetsuo

    2013-06-11

    Slab-derived fluids play an important role in heat and material transfer in subduction zones. Dehydration and decarbonation reactions of minerals in the subducting slab have been investigated using phase equilibria and modeling of fluid flow. Nevertheless, direct observations of the fluid chemistry and pressure-temperature conditions of fluids are few. This report describes CO2-bearing saline fluid inclusions in spinel-harzburgite xenoliths collected from the 1991 Pinatubo pumice deposits. The fluid inclusions are filled with saline solutions with 5.1 ± 1.0% (wt) NaCl-equivalent magnesite crystals, CO2-bearing vapor bubbles, and a talc and/or chrysotile layer on the walls. The xenoliths contain tremolite amphibole, which is stable in temperatures lower than 830 °C at the uppermost mantle. The Pinatubo volcano is located at the volcanic front of the Luzon arc associated with subduction of warm oceanic plate. The present observation suggests hydration of forearc mantle and the uppermost mantle by slab-derived CO2-bearing saline fluids. Dehydration and decarbonation take place, and seawater-like saline fluids migrate from the subducting slab to the mantle wedge. The presence of saline fluids is important because they can dissolve more metals than pure H2O and affect the chemical evolution of the mantle wedge.

  8. Subduction of the Tethys Oceans reconstructed from plate kinematics and mantle tomography

    NARCIS (Netherlands)

    Hafkenscheid, Edith

    2004-01-01

    This thesis is concerned with the large-scale history of subduction within the Tethyan region, the Alpine-Himalayan mountain chain that stretches from the Mediterranean to the Indonesian archipelago. We investigate whether we can contribute to a better understanding of the Tethyan evolution by

  9. Stress rotation across the Cascadia megathrust requires a weak subduction plate boundary at seismogenic depths

    Science.gov (United States)

    Li, Duo; McGuire, Jeffrey J.; Liu, Yajing; Hardebeck, Jeanne L.

    2018-03-01

    The Mendocino Triple Junction region is the most seismically active part of the Cascadia Subduction Zone. The northward moving Pacific plate collides with the subducting Gorda plate causing intense internal deformation within it. Here we show that the stress field rotates rapidly with depth across the thrust interface from a strike-slip regime within the subducting plate, reflecting the Pacific plate collision, to a thrust regime in the overriding plate. We utilize a dense focal mechanism dataset, including observations from the Cascadia Initiative ocean bottom seismograph experiment, to constrain the stress orientations. To quantify the implications of this rotation for the strength of the plate boundary, we designed an inversion that solves for the absolute stress tensors in a three-layer model subject to assumptions about the strength of the subducting mantle. Our results indicate that the shear stress on the plate boundary fault is likely no more than about ∼50 MPa at ∼20 km depth. Regardless of the assumed mantle strength, we infer a relatively weak megathrust fault with an effective friction coefficient of ∼0 to 0.2 at seismogenic depths. Such a low value for the effective friction coefficient requires a combination of high fluid pressures and/or fault-zone minerals with low inherent friction in the region where a great earthquake is expected in Cascadia.

  10. Shallow and buoyant lithospheric subduction : causes and implications from thermo-chemical numerical modeling

    NARCIS (Netherlands)

    Hunen, Jeroen van

    2001-01-01

    Where two lithospheric plates converge on the Earth, one of them disappears into the mantle. The dominant driving mechanism for plate motion is regarded to be `slab pull': the subducted plate, the slab, exerts a pulling force on the attached plate at the surface. However, what has been puzzling

  11. Megathrust and accretionary wedge properties and behaviour in the Makran subduction zone

    Science.gov (United States)

    Penney, Camilla; Tavakoli, Farokh; Saadat, Abdolreza; Nankali, Hamid Reza; Sedighi, Morteza; Khorrami, Fateme; Sobouti, Farhad; Rafi, Zahid; Copley, Alex; Jackson, James; Priestley, Keith

    2017-06-01

    We study the Makran subduction zone, along the southern coasts of Iran and Pakistan, to gain insights into the kinematics and dynamics of accretionary prism deformation. By combining techniques from seismology, geodesy and geomorphology, we are able to put constraints on the shape of the subduction interface and the style of strain across the prism. We also address the long-standing tectonic problem of how the right-lateral shear taken up by strike-slip faulting in the Sistan Suture Zone in eastern Iran is accommodated at the zone's southern end. We find that the subduction interface in the western Makran may be locked, accumulating elastic strain, and move in megathrust earthquakes. Such earthquakes, and associated tsunamis, present a significant hazard to populations around the Arabian Sea. The time-dependent strain within the accretionary prism, resulting from the megathrust earthquake cycle, may play an important role in the deformation of the Makran region. By considering the kinematics of the 2013 Balochistan and Minab earthquakes, we infer that the local gravitational and far-field compressive forces in the Makran accretionary prism are in balance. This force balance allows us to calculate the mean shear stress and effective coefficient of friction on the Makran megathrust, which we find to be 5-35 MPa and 0.01-0.03, respectively. These values are similar to those found in other subduction zones, showing that the abnormally high sediment thickness in the offshore Makran does not significantly reduce the shear stress on the megathrust.

  12. Friction on subduction megathrust faults: Beyond the illite-muscovite transition

    NARCIS (Netherlands)

    den Hartog, S.A.M.; Niemeijer, A.R.; Spiers, C.J.

    2013-01-01

    Previous experimental studies addressing subduction megathrust friction have focused on shallow fault gouges, dominated by smectite, illite and quartz. Here, we aim to determine the effect of the transition to muscovite-rich fault rock at depths beyond the illite-dominated region of the seismogenic

  13. Interplay between deformation, fluid release and migration across a nascent subduction interface: evidence from Oman-UAE and implications for warm subduction zones

    Science.gov (United States)

    Agard, Philippe; Prigent, Cécile; Soret, Mathieu; Guillot, Stéphane; Dubacq, Benoît

    2017-04-01

    Frozen-in subduction plate interfaces preserving the first 1-2 My of the subduction history are found beneath ophiolites. These contacts are a key target to study the inception of mantle wedge metasomatism and the mechanical coupling between the upper plate and the top part of the sinking slab shortly after subduction initiation. Combining structural field and EBSD data, detailed petrology, thermodynamic modelling and geochemistry on both sides, i.e. the base of the mantle wedge (Oman-UAE basal peridotites) and the underlying accreted crustal fragments from the subducting slab (metamorphic soles), this study documents the continuous evolution of the plate contact from 1 GPa 900-750°C to 0.6 GPa 750-600°C, with emphasis on strain localization and feedbacks between deformation and fluid migration. In the mantle wedge, the (de)formation of proto-ultramylonitic peridotites is coeval with mantle metasomatism by focused hydrous fluid migration. Peridotite metasomatism results in the precipitation of new minerals (clinopyroxene, amphibole and spinel ± olivine and orthopyroxene) and their enrichment in FMEs (particularly B, Li and Cs, with concentrations up to 40 times that of the PM). Boron concentrations and isotopes (δ11B of metasomatized peridotites up to +25‰) suggest that these fluids with a "subduction signature" are probably sourced from the dehydrating amphibolitic metamorphic sole. Concomitantly, deformation in the lower plate results in the stepwise formation, detachment and accretion to the mylonitic s.l. mantle of successive slices of HT metabasalts from the downgoing slab, equilibrated at amphibolite/granulite conditions (900-750°C). Two major stages may be outlined: - between 900 and 750°C, the garnet-clinopyroxene-amphibole bearing sinking crust (with melting < 6 vol%) gets juxtaposed and mechanically coupled to the mantle, leading to the transfer of subduction fluids and metasomatism (possibly into the arc zone ultimately). Deformation is

  14. Mantle Wedge formation during Subduction Initiation: evidence from the refertilized base of the Oman ophiolitic mantle

    Science.gov (United States)

    Prigent, C.; Guillot, S.; Agard, P.; Godard, M.; Lemarchand, D.; Ulrich, M.

    2015-12-01

    Although the Oman ophiolite is classically regarded as being the direct analog of oceanic lithosphere created at fast spreading ridges, the geodynamic context of its formation is still highly debated. The other alternative end-member model suggests that this ophiolite entirely formed in a supra-subduction zone setting. The latter one is supported by studies on volcanic sequences whereas studies dealing on the mantle section do not involve a significant influence of subduction processes on its structure and composition. We herein focus on basal peridotites from all along the ophiolite strike in order to decipher and characterize potential fluid/melt transfers relate to subduction processes. Samples were taken across the basal banded unit directly overlying the amphibolitic/granulitic metamorphic sole which represents an accreted part of the lower plate. We carried out a petrological, structural and geochemical study on these rocks and their constitutive minerals. Our results show that basal peridotites range from lherzolites to highly depleted harzburgites in composition. Clinopyroxenes (cpx) display melt impregnation textures and co-crystallized with HT/HP amphiboles (amph), spinels and sulfurs. Major and trace elements of the constitutive minerals indicate that these minerals represent trapped incremental partial melt after hydrous melting. Different cpx-bearing lithologies then result from varying degrees of partial melting and melt extraction. Combined with Boron isotopic data, we demonstrate that fluids responsible for hydrous melting of these ophiolitic basal peridotites are subduction-related, most likely derived from dehydration of the metamorphic sole during its formation in subduction initiation. From these observations and thermal constraints, we interpret the occurrence of these basal lherzolites as representing a freezing front developed by thermal re-equilibration (cooling) during subduction processes: subduction-related hydrous partial melts were

  15. Seismotectonics in the Pamir: An oblique transpressional shear and south-directed deep-subduction model

    Directory of Open Access Journals (Sweden)

    Jiasheng Zhang

    2011-01-01

    Full Text Available The 3-D geometry of the seismicity in Hindu Kush–Pamir–western China region has been defined by seismic records for 1975–1999 from the National Earthquake Information Center, the U.S. Geological Survey, and over 16,000 relocated earthquakes since 1975 recorded by the Xinjiang seismic network of China. The results show that most Ms ≥ 5.0 hypocenters in the area are confined to a major intracontinental seismic shear zone (MSSZ. The MSSZ, which dips southwards in Pamir has a north-dipping counterpart in the Hindu Kush to the west; the two tectonic realms are separated by the sinistral Chaman transform fault of the India–Asia collisional zone. We demonstrate that the MSSZ constitutes the upper boundary of a south-dipping, actively subducting Pamir continental plate. Three seismic concentrations are recognized just above the Pamir MSSZ at depths between 45–65 km, 95–120 km, and 180–220 km, suggesting different structural relationships where each occurs. Results from focal mechanism solutions in all three seismological concentrations show orientations of the principal maximum stress to be nearly horizontal in an NNW–SSE direction. The south-dipping Pamir subduction slab is wedge-shaped with a wide upper top and a narrow deeper bottom; the slab has a gentle angle of dip in the upper part and steeper dips in the lower part below an elbow depth of ca. 80–120 km. Most of the deformation related to the earthquakes occurs within the hanging wall of the subducting Pamir slab. Published geologic data and repeated GPS measurements in the Pamir document a broad supra-subduction, upper crustal zone of evolving antithetic (i.e. north-dipping back-thrusts that contribute to north-south crustal shortening and are responsible for exhumation of some ultrahigh-pressure rocks formed during earlier Tethyan plate convergence. An alternating occurrence in activity of Pamir and Chaman seismic zones indicates that there is interaction between

  16. Quantitative Study of Seismogenic Potential Along Manila Trench: Effects of Scaborough Seamount Chain Subduction

    Science.gov (United States)

    Yu, H.; Liu, Y.; Li, D.; Ning, J.; Matsuzawa, T.; Shibazaki, B.; Hsu, Y. J.

    2014-12-01

    Modern seismicity record along the Manila Trench shows only infrequent Mw7 earthquakes, the lack of great earthquakes may indicate the subduction fault is either aseismically slipping or is accumulating strain energy toward rapid release in a megathrust earthquake. We conduct numerical simulations of the plate coupling, earthquake nucleation and dynamic rupture propagation processes along the Manila subduction fault (15-19.5ºN), taking into consideration the effects of plate geometry (including subducted seamounts), fault strength, rate-state frictional properties and pore pressure variations. Specifically, we use the bathymetry to depict the outline of Manila trench along its strike, 2681 background seismicity (1970/02/13 to 2013/09/06) from Chinese Earthquake Network Center and 540 focal mechanism solutions (1976/01/01 to 2013/01/27) from Global CMT project to constrain the geometry of the subducting Sunda/Eurasian slab. The compilation of seismicity and focal mechanism indicates the plate dipping angle gradually changes from 28º (south of the Scaborough Seamount Chain) to 12º (north of it). This geometric anomaly may due to the subducted part of the seamount chain. Preliminary modeling results using gabbro gouge friction data show that the Scaborough Seamount Chain could be a barrier to earthquake rupture propagation. Only earthquakes larger than Mw7 can overcome the barrier to rupture the entire Manila trench. Smaller earthquakes would cease rupturing when it encounters the seamount chain. Moreover, we propose that Manila trench subduction zone has the potential of rupturing in a Mw8 megathrust earthquake, if the simulation period is long enough for an Mw8 earthquake cycle and dynamic rupture overcomes the subducted Scaborough Seamount Chain. Our model parameters will be further constrained by laboratory rock mechanics experiments conducted on IODP Expedition 349, South China Sea (SCS), drilling samples (work in progress at China Earthquake Administration

  17. Counter-intuitive Behavior of Subduction Zones: Weak Faults Rupture, Strong Faults Creep

    Science.gov (United States)

    Wang, K.; Gao, X.; Bilek, S. L.; Brown, L. N.

    2014-12-01

    Subduction interfaces that produce great earthquakes are often said to be "strongly coupled", and those that creep are said to be "weakly coupled". However, the relation between the strength and seismogenic behavior of subduction faults is far from clear. Seismological and geodetic observations of earthquake rupture usually provide information only on stress change, not fault strength. In this study, we infer fault strength by calculating frictional heating along megathrusts and comparing results with heat flow measurements. We find that stick-slip megathrusts that have produced great earthquakes such as at Japan Trench and northern Sumatra have very low apparent friction coefficients (~ 0.02 - 0.03), but megathrusts that creep such as at Northern Hikurangi and Manila Trench have higher values (up to ~0.13). The differnce cannot be explained by coseismic dynamic weakening of the stick-slip megathrusts, because the average stress drop in great earthquakes is usually less than 5 MPa, equivalent to a coseismic reduction of apparent friction coefficient by less than ~0.01. Therefore our results indicate differences in the static strength of different subduction faults. Why are the creeping faults stronger? We think it is related to their creeping mechanism. Very rugged subducting seafloor tends to cause creep and hinder great earthquake rupture (Wang and Bilek, 2014). In contrast, all giant earthquakes have occurred at subduction zones with relatively smooth subducting seafloor. Large geometrical irregularities such as seamounts generate heterogeneous structure and stresses that promote numerous small and medium size earthquakes and aseismic creep. The creeping is a process of breaking and wearing of geometrical irregularities in a deformation zone and is expected to be against relatively large resistance (strong creep). This is different from the creeping of smooth faults due to the presence of weak fault gouge (weak creep) such as along the creeping segment of the

  18. Controls on continental strain partitioning above an oblique subduction zone, Northern Andes

    Science.gov (United States)

    Schütt, Jorina M.; Whipp, David M., Jr.

    2016-04-01

    Strain partitioning is a common process at obliquely convergent plate margins dividing oblique convergence into margin-normal slip on the plate-bounding fault and horizontal shearing on a strike-slip system parallel to the subduction margin. In subduction zones, strain partitioning in the upper continental plate is mainly controlled by the shear forces acting on the plate interface and the strength of the continental crust. The plate interface forces are influenced by the subducting plate dip angle and the obliquity angle between the normal to the plate margin and the convergence velocity vector, and the crustal strength of the continent is strongly affected by the presence or absence of a volcanic arc, with the presence of the volcanic arcs being common at steep subduction zones. Along the ˜7000 km western margin of South America the convergence obliquity, subduction dip angles and presence of a volcanic arc all vary, but strain partitioning is only observed along parts of it. This raises the questions, to what extent do subduction zone characteristics control strain partitioning in the overriding continental plate, and which factors have the largest influence? We address these questions using lithospheric-scale 3D numerical geodynamic experiments to investigate the influence of subduction dip angle, convergence obliquity, and weaknesses in the crust owing to the volcanic arc on strain partitioning behavior. We base the model design on the Northern Volcanic Zone of the Andes (5° N - 2° S), characterized by steep subduction (˜ 35°), a convergence obliquity between 31° -45° and extensive arc volcanism, and where strain partitioning is observed. The numerical modelling software (DOUAR) solves the Stokes flow and heat transfer equations for a viscous-plastic creeping flow to calculate velocity fields, thermal evolution, rock uplift and strain rates in a 1600 km x 1600 km box with depth 160 km. Subduction geometry and material properties are based on a

  19. Spatial and temporal development of exhumation at the St. Elias syntaxis in the Yakutat-North American subduction-collision zone, SE Alaska

    Science.gov (United States)

    Falkowski, Sarah; Enkelmann, Eva; Pfänder, Jörg; Drost, Kerstin; Stübner, Konstanze; Ehlers, Todd

    2015-04-01

    several terranes contributed cobbles with young cooling signals. Unlike at the Himalayan syntaxes, the higher-temperature 40Ar/39Ar cooling ages (~300-500 °C) are not very young but mostly only a few Myr younger than the corresponding crystallization age. This represents cooling after Eocene ridge subduction, which formed the Chugach Metamorphic Complex. This study reveals the longer regional tectonic history, such as various subduction processes and collision of the Yakutat microplate. It also shows that detrital material yields information on exhumation and provenance of otherwise inaccessible parts of a catchment.

  20. High resolution earthquake source mechanisms in a subduction zone: 3-D waveform simulations of aftershocks from the 2010 Mw 8.8 Chile rupture

    Science.gov (United States)

    Hicks, Stephen; Rietbrock, Andreas

    2015-04-01

    The earthquake rupture process is extremely heterogeneous. For subduction zone earthquakes in particular, it is vital to understand how structural variations in the overriding plate and downgoing slab may control slip style. The large-scale 3-D geometry of subduction plate boundaries is rapidly becoming well understood (e.g. Hayes et al., 2012); however, the nature of slip style along any finer-scale structures remains elusive. Regional earthquake moment tensor (RMT) inversion can shed light on faulting mechanisms. However, many traditional regional moment tensor inversions use simplified (1-D) Earth models (e.g. Agurto et al., 2012; Hayes et al., 2013) that only use the lowest frequency parts of the waveform, which may mask source complexity. As a result, we may have to take care when making small-scale interpretations about the causative fault and its slip style. This situation is compounded further by strong lateral variations in subsurface geology, as well as poor station coverage for recording offshore subduction earthquakes. A formal assessment of the resolving capability of RMT inversions in subduction zones is challenging and the application of 3-D waveform simulation techniques in highly heterogeneous media is needed. We generate 3-D waveform simulations of aftershocks from a large earthquake that struck Chile in 2010. The Mw 8.8 Maule earthquake is the sixth largest earthquake ever recorded. Following the earthquake, there was an international deployment of seismic stations in the rupture area, making this one of the best observed aftershock sequences to date. We therefore have a unique opportunity to compare recorded waveforms with simulated waveforms for many earthquakes, shedding light on the effect of 3-D heterogeneity on source imaging. We perform forward simulations using the spectral element wave propagation code, SPEFEM3D (e.g. Komatitsch et al., 2010) for a set of moderate-sized aftershocks (Mw 4.0-5.5). A detailed knowledge of velocity structure

  1. The Calabrian subduction zone (Ionian Sea): Historical seismicity and a new review of the system from multi-channel seismic data

    Science.gov (United States)

    Gallais, Flora; Gutscher, Marc-Andre; Torelli, Luigi; Polonia, Alina; Graindorge, David

    2010-05-01

    The Calabrian subduction zone is included in the long W-E elongated compressive South Mediterranean belt. This subduction is located in the complex Central Mediterranean area and accommodates the African/Eurasian convergence at very slow rates (thrusts events characteristic of active subduction have been recorded during the instrumental era. However, the South Calabrian/East Sicilian region is well-known to have been affected by strong historical seismicity with Mercalli intensities reaching XI. The sources of these events is often linked to the activity of crustal, normal faults in the Calabrian region: 1638, 1783, 1905. Furthermore, important details of the Messina 1908 earthquake (72000 killed) and tsunami remain unresolved, in particular the origin of the tsunami (fault induced or submarine landslide). Moreover, the origin of two of the most destructive earthquakes (1169 and 1693) remains enigmatic. For the 1169 and 1693 (60000 killed and 5 to 10 m tsunami wave) Catania earthquakes, the source faults are the subject of debate and linked alternatively to the activity of the Malta escarpment or of the subduction fault plane (because the isoseismals are open to the sea). In this case, the 1169 earthquake which had similar intensities and a comparable isoseismal pattern, is suggested to have the same source and so the fault plane may have be locked between these two events. To better understand the origins of the 1169 and 1693 major events and seek evidence of activity of Calabrian system, we present new results from reprocessed 96-channels seismic reflection profiles (French Archimede cruise, 1997) offshore Sicily. Interpretation of the seismic dataset is based on correlations with published seismic data and with ESP results and allows us to identify the following thick sedimentary cover (>5km) in the Ionian Abyssal Plain overlying an oceanic crust: Mesozoic (1400 to 1800m) and Tertiary (~1800m) sequences, a Messinian unit (1400m) and the Plio-Quaternary deposits

  2. SubductionGenerator: A program to build three-dimensional plate configurations

    Science.gov (United States)

    Jadamec, M. A.; Kreylos, O.; Billen, M. I.; Turcotte, D. L.; Knepley, M.

    2016-12-01

    Geologic, geochemical, and geophysical data from subduction zones indicate that a two-dimensional paradigm for plate tectonic boundaries is no longer adequate to explain the observations. Many open source software packages exist to simulate the viscous flow of the Earth, such as the dynamics of subduction. However, there are few open source programs that generate the three-dimensional model input. We present an open source software program, SubductionGenerator, that constructs the three-dimensional initial thermal structure and plate boundary structure. A 3D model mesh and tectonic configuration are constructed based on a user specified model domain, slab surface, seafloor age grid file, and shear zone surface. The initial 3D thermal structure for the plates and mantle within the model domain is then constructed using a series of libraries within the code that use a half-space cooling model, plate cooling model, and smoothing functions. The code maps the initial 3D thermal structure and the 3D plate interface onto the mesh nodes using a series of libraries including a k-d tree to increase efficiency. In this way, complicated geometries and multiple plates with variable thickness can be built onto a multi-resolution finite element mesh with a 3D thermal structure and 3D isotropic shear zones oriented at any angle with respect to the grid. SubductionGenerator is aimed at model set-ups more representative of the earth, which can be particularly challenging to construct. Examples include subduction zones where the physical attributes vary in space, such as slab dip and temperature, and overriding plate temperature and thickness. Thus, the program can been used to construct initial tectonic configurations for triple junctions and plate boundary corners.

  3. The ADN project : an integrated seismic monitoring of the northern Ecuadorian subduction

    Science.gov (United States)

    Nocquet, Jean-Mathieu; Yepes, Hugo; Vallee, Martin; Mothes, Patricia; Regnier, Marc; Segovia, Monica; Font, Yvonne; Vaca, Sandro; Bethoux, Nicole; Ramos, Cristina

    2010-05-01

    The subduction of the Nazca plate beneath South America has caused one of the largest megathrust earthquake sequence during the XXth century with three M>7.7 earthquakes that followed the great 1906 (Mw = 8.8) event. Better understanding the processes leading to the occurrence of large subduction earthquakes requires to monitor the ground motion over a large range of frequencies. We present a new network (ADN) developed under a collaboration between the IRD-GeoAzur (Nice, France) and the IG-EPN (Quito, Ecuador). Each station of the ADN network includes a GPS recording at 5 Hz, an accelerometer and a broadband seismometer. CGPS data will quantify the secular deformation induced by elastic locking along the subduction interface, enabling a detailed modelling of the coupling distribution. CGPS will be used to monitor any transient deformation induced by Episodic Slip Event along the subduction, together with broadband seismometers that can detect any tremors or seismic signatures that may accompany them. In case of any significant earthquake, 5 Hz GPS and accelerometer will provide near field data for earthquake source detailed study. Finally, the broadband seismometers will be used for study of the microseismicity and structure of the subduction zone. The network includes 9 stations, operating since 2008 and covering the coastal area from latitude 1.5°S to the Colombian border. In this poster, we will present preliminary assessment of the data, first hypocenters location, magnitude and focal mechanism determination, as well as results about an episodic slip event detected in winter 2008.

  4. Metastability of Subducted Slabs in the Mantle Transition Zone: A Collaborative Geodynamic, Petrologic, and Seismological Approach

    Science.gov (United States)

    Garber, J. M.; Billen, M. I.; Duncan, M. S.; Roy, C.; Ibourichene, A. S.; Olugboji, T.; Celine, C.; Rodríguez-González, J.; Grand, S. P.; Madrigal, P.; Sandiford, D.; Valencia-Cardona, J. J.

    2016-12-01

    Subducted slabs exhibit a range of geometries in the mantle transition zone. Studies of this phenomenon suggest that olivine and/or pyroxene metastability may profoundly alter the slab density profile, leading to slab flattening (e.g., King et al., 2015) and potentially yielding a resolvable seismological signature (e.g., Kawakatsu and Yoshioka, 2011; Yoshioka et al., 2015). Such metastability may also be critical for deep earthquake generation. Geodynamic modelling of this process is typically done with a simplified petrologic model of the downgoing slab, whereas petrologic studies of phase assemblages in subducted slabs typically impose an idealized geodynamic model with an unrealistic thermal structure. Connecting these two approaches should lead to a better understanding of the consequences of metastable assemblages on subducting slabs. Here, we present a new methodology that combines geodynamic, seismic and petrologic approaches to assess the impact of mineral metastability on dynamic subduction models, developed in a collaborative effort begun at the 2016 NSF CIDER summer program in Santa Barbara, CA. We use two parallel approaches to extrapolate equilibrium rock properties to metastable regions and impose these data on extracted time-slices from robust thermo-mechanical geodynamic models, allowing us to quantify the density and buoyancy changes in the slab that result from considering metastable phase assemblages. Our preliminary results suggest that metastable assemblages can yield a 10-30% density decrease over the subducted slab relative to an equilibrium reference model. We then generate a seismic velocity profile of the slab, and compute waveforms based on the 2D finite-difference method (e.g., Vidale & Helmberger, 1987) to determine whether metastable phases could reasonably be detected by different seismic approaches. Continuing analyses will be aimed at coupling the evolution of geodynamic models with phase metastability to model the feedback between

  5. Geometry and seismic properties of the subducting Cocos plate in central Mexico

    Science.gov (United States)

    Kim, Y.; Clayton, R. W.; Jackson, J. M.

    2010-06-01

    The geometry and properties of the interface of the Cocos plate beneath central Mexi