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Sample records for unique subduction complexity

  1. 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.

  2. Diamonds from Dachine, French Guiana: A unique record of early Proterozoic subduction

    Science.gov (United States)

    Smith, Chris B.; Walter, Michael J.; Bulanova, Galina P.; Mikhail, Sami; Burnham, Antony D.; Gobbo, Luiz; Kohn, Simon C.

    2016-11-01

    Diamonds from Dachine, French Guiana, are unique among worldwide diamond populations. The diamonds were transported to the surface in an unusual ultramafic extrusive magma with an affinity to boninite or komatiite, which was emplaced within an arc geological setting at 2.2 Ga. Dachine diamonds have internal and external morphologies indicative of relatively rapid growth from carbon oversaturated fluids or melts, and exhibit internal features consistent with residence in a high-strain environment. On the basis of nitrogen (N) defects the diamonds are categorized as Type Ib-IaA. The unusually low aggregation state of N places severe constraints on the thermal history of the diamonds, effectively ruling out derivation in convecting mantle. The carbon and N isotopic compositions of Dachine diamonds are consistent with a sedimentary source of carbon, with the majority of diamonds having δ13C values + 4‰. The primary carbon was presumably deposited on an early Proterozoic seafloor. Sulphide inclusions have low Ni and Cr and are comparable to lithospheric eclogitic-type sulphide inclusions. Three garnet and one clinopyroxene inclusion are also eclogitic in composition, and one garnet inclusion has a majorite component indicating an origin around 250 km depth. The silicate inclusions are highly depleted in many incompatible trace elements (e.g. LREE, Nb, Hf, Zr), and modelling indicates an eclogitic source lithology that contained a LREE-enriched trace phase such as epidote or allanite, and an HFSE-rich phase such as rutile. Four of the five inclusions are unusually enriched in Mn, as well as Ni and Co, and modelling suggests a protolith with a bulk composition of subducted normal MORB plus about 10% ferromanganese crust component. We suggest a model wherein Dachine diamonds precipitated from remobilized sedimentary carbon at the slab-mantle interface from liquids derived ultimately by deserpentinization of slab peridotite at depths of 200 to 250 km. These fluids may

  3. Survey yields data on unique metamorphic rock complex in China

    Science.gov (United States)

    Schulze, A.; Jiang, M.; Ryberg, T.; Gao, R.

    Seismic data from survey work last year in Dabie Shan, China, are giving scientists their first view of the subsurface structure of a unique metamorphic rock complex. The work, in which a joint Chinese-German research team surveyed possible sites for a super deep borehole, set the stage for more intensive petrological and seismic investigations this year and next.Data were collected by near-vertical seismic imaging at Dabie Shan, the Earth's largest outcrop of ultra-high pressure metamorphic (UHM) rocks, some exhumed from depths of 100 km. Processing so far has revealed unexpectedly strong mid-and lower-crustal reflections, predominantly dipping west to east, indicating the involved tectonic history of the region. Upcoming research will look more closely at the three-dimensional structure of the rock and other matters. Scientific deep drilling is essential in addressing a wide range of major geoscientific problems of global importance. The International Continental Scientific Drilling Programme (ICDP) coordinates such, and one key target of ICDP is the Dabie Shan. To find the most appropriate location for a drill site and to extend the findings of the drilling beyond the drill hole, geophysical methods, especially seismic investigations, play an important role. Integrated interpretation of seismic and drill results in the Dabie Shan will lead to a better understanding of the structure and dynamic processes of the collisional history of the Yangtze and Sino-Korean Cratons. The Dabie Shan is located in the eastern part of the Qinling orogen in Anhui province, central China. The rocks there contain microdiamonds and coesite within a 20-km-thick eclogite zone representing a part of the lower lithosphere of the Yangtze Craton [Okay, 1993]. Such rocks suggest that continental crust had been subducted to depths greater than 100 km and exhumed afterwards [Hackeretal, 1995].

  4. Magmatism of the Shuteen Complex and Carboniferous subduction of the Gurvansaikhan terrane, South Mongolia

    Science.gov (United States)

    Batkhishig, Bayaraa; Noriyoshi, Tsuchiya; Greg, Bignall

    2010-03-01

    The Carboniferous Shuteen Complex, a volcano-plutonic ring complex associated with Cu-Au porphyry mineralization, is located in the Gurvansaikhan island arc terrane of South Mongolia. This paper presents new data on the petrography, major and trace element chemistry, and Sr-Nd isotopic chemistry of the Shuteen Complex. We discuss the relationship between volcanic and plutonic rocks of the complex, and consider their similarity to high-Al 2O 3 trondhjemite-tonalite-granodiorite and adakites. We also consider the origin, magma source, and dynamic processes of the Shuteen Complex; propose a petrogenetic model; and investigate the composition of the subducting slab and the features of arc volcanism at the time. We assess some of the magmatic processes likely to have occurred within the Shuteen Complex, such as Carboniferous slab subduction and partial melting, and examine their influence on magma composition. The Shuteen Complex is geochemically similar to adakite-type rocks. The complex is silica-saturated (SiO 2 ⩾ 56%), rich in Al 2O 3 (⩾15%), MgO (400 ppm), and depleted in high field strength elements. It also has a high Sr/Y value, and ( 87Sr/ 86Sr) I arc setting, and partial melting was the dominant process during petrogenesis. The primary Shuteen magma had an adakitic composition and was probably derived from the partial melting of subducting oceanic crust, possibly with minor local interaction with mantle material. The results of quantitative modelling of mass balance and partial melt equilibrium for the magma source indicate that the subducting slab contained oceanic basalt and a minor component of oceanic sediment, which together with a restite eclogite phase formed the source of the Shuteen magma. The conclusive results of this study provide new insights into the magmatic evolution of the Shuteen Complex.

  5. Complex interactions between diapirs and 4-D subduction driven mantle wedge circulation.

    Science.gov (United States)

    Sylvia, R. T.; Kincaid, C. R.

    2015-12-01

    Analogue laboratory experiments generate 4-D flow of mantle wedge fluid and capture the evolution of buoyant mesoscale diapirs. The mantle is modeled with viscous glucose syrup with an Arrhenius type temperature dependent viscosity. To characterize diapir evolution we experiment with a variety of fluids injected from multiple point sources. Diapirs interact with kinematically induced flow fields forced by subducting plate motions replicating a range of styles observed in dynamic subduction models (e.g., rollback, steepening, gaps). Data is collected using high definition timelapse photography and quantified using image velocimetry techniques. While many studies assume direct vertical connections between the volcanic arc and the deeper mantle source region, our experiments demonstrate the difficulty of creating near vertical conduits. Results highlight extreme curvature of diapir rise paths. Trench-normal deflection occurs as diapirs are advected downward away from the trench before ascending into wedge apex directed return flow. Trench parallel deflections up to 75% of trench length are seen in all cases, exacerbated by complex geometry and rollback motion. Interdiapir interaction is also important; upwellings with similar trajectory coalesce and rapidly accelerate. Moreover, we observe a new mode of interaction whereby recycled diapir material is drawn down along the slab surface and then initiates rapid fluid migration updip along the slab-wedge interface. Variability in trajectory and residence time leads to complex petrologic inferences. Material from disparate source regions can surface at the same location, mix in the wedge, or become fully entrained in creeping flow adding heterogeneity to the mantle. Active diapirism or any other vertical fluid flux mechanism employing rheological weakening lowers viscosity in the recycling mantle wedge affecting both solid and fluid flow characteristics. Many interesting and insightful results have been presented based

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

    Science.gov (United States)

    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

  7. High-pressure metamorphism in the Early Variscan subduction complex of the SW Iberian Massif

    Science.gov (United States)

    Rubio Pascual, Francisco J.; Matas, Jerónimo; Martín Parra, Luis M.

    2013-04-01

    Several units exposed in the boundary area of the Ossa Morena Zone (OMZ) and the South Portuguese Zone (SPZ) preserve petrographic and thermobarometric evidence for an early metamorphic episode (M1), developed under a high-P, low to intermediate-T gradient, related to Early Variscan subduction in the SW Iberian Massif. In the OMZ, these are the Cubito-Moura Unit (Pmin ~ 9.2 kbar and T = 395 ± 45 °C), blueschists from its basal mélange (Pmin ~ 12.4 kbar and T = 310 ± 11 °C), and the underlying Fuenteheridos Group (P = 10.9 ± 0.4 kbar and T = 449 ± 31 °C). The equivalent units in the SPZ are the La Minilla Formation (P = 8.7 ± 0.4 kbar and T = 388 ± 16 °C) and the lawsonite pseudomorphs-bearing Pulo do Lobo Formation. All these units formed part of an approximately NE verging orogenic wedge (present coordinates) developed by the accretion of subducted slabs of the outermost margin of Gondwana and other elements of the Rheic Ocean realm, from at least the Middle Devonian to the lowermost Tournaisian. High-pressure rocks were subsequently emplaced on more internal zones of the OMZ that only experienced a younger high-T, low to intermediate-P metamorphism (M2). This high-T event was coeval with magmatic activity from the uppermost Devonian to the Middle Mississippian, probably as a consequence of transtensional lithospheric thinning and/or delamination of the lower crust and mantle lithosphere of the Gondwana margin. Pre-Late Devonian synorogenic sedimentation in forearc and back-arc basins of the subduction complex evolved to a Late Devonian-Middle Mississippian foreland basin system in early collisional stages. Finally, a new Middle-Late Mississippian fold-and-thrust belt with opposite (SW) vergence and new foreland basins developed during late collisional stages.

  8. Seafloor morphology in the different domains of the Calabrian Arc subduction complex - Ionian Sea

    Science.gov (United States)

    Riminucci, F.; Polonia, A.; Torelli, L.; Mussoni, P.

    2010-05-01

    The Calabrian Arc (CA) is a subduction system that develops along the African-Eurasian plate boundary in the Ionian Sea and connects the E-W trending Sicilian Maghrebian belt with the NW-SE trending Southern Apennines. The first systematic geophysical investigation in the offshore region of the CA was conducted during the 70's by the Institute of Marine Geology (now ISMAR) with the R/V 'Bannock' [1]. In the last 30 years, further geophysical data (high penetration multichannel seismics, CHIRP and multibeam data) has been acquired in the offshore of the CA, down to the Ionian Abyssal Plain. The integrated interpretation of the existing geophysical data [2] has outlined the regional architecture of the subduction complex, the main tectonic features absorbing plate motion and variation of seafloor morphology in the different structural domains. Pre-stack depth migrated seismic profiles has revealed that the accretionary complex is constituted by two distinct wedges whose geometry, structural style and seafloor morphology widely vary. The outermost accretionary wedge has been emplaced in post-messinian times. It is a salt-bearing complex as pointed out by the internal structure of the wedge (acoustically transparent assemblage), very low taper angle and high seismic velocities. The seafloor shows a rough morphology, short wavelength folds and depressions superimposed on a rather constant gentle regional slope. Landward of the outer wedge, the evaporites are no longer present and the transition to the clastic rock assemblage is reflected in a different structural architecture, which shows steeper slopes and a succession of topographic scarps separated by sedimentary basins and mid slope terraces. The topographic scarps are controlled in depth by a series of high angle landward dipping reflectors, that we interpreted as out of sequence thrust faults absorbing shortening at the rear of the wedge. Landward of the inner wedge a mid slope terrace develops (inner plateau

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

    Science.gov (United States)

    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).

  10. Idiopathic Fenestrated Complex Syndactyly in a Unique Crisscross Fashion.

    Science.gov (United States)

    Williams, Benjamin R; Van Heest, Ann E

    2016-12-01

    This case presents surgical treatment of a unique form of syndactyly: an isolated fenestrated, complex, crisscross syndactyly of the right middle and ring fingers. A 2-year-old boy presented with the ring finger lying dorsal and the middle finger lying volar, with the middle phalanges syndactylized. A surgical release was performed with a subsequent z-plasty, 2 years later, for scar elongation. At the age of 4, he has essentially full function of his hand with minimal limitations. This case demonstrates that 2 digits that were syndactylized in a coronal plane (ring finger dorsal and middle finger volar) can be successfully surgically separated.

  11. Complex geometry of the subducted Pacific slab inferred from receiver function

    Science.gov (United States)

    Zhang, Ruiqing; Wu, Qingju; Zhang, Guangcheng

    2014-05-01

    In recent years, slab tear has received considerable attention and been reported in many arc-arc junctures in Pacific plate subdution zones. From 2009 to 2011, we deployed two portable experiments equipped with CMG-3ESPC seismometers and the recorders of REFTEK-130B in NE China. The two linear seismic arrays were designed nearly parallel, and each of them containing about 60 seismic stations extended about 1200 km from west to east spanning all surface geological terrains of NE China. The south one was firstly set up and continually operated over two year, while the north deployment worked only about one year. By using the teleseismic data collected by these two arrays, we calculate the P receiver functions to map topographic variation of the upper mantle discontinuities. Our sampled region is located where the juncture between the subducting Kuril and Japan slabs reaches the 660-km discontinuity. Distinct variation of the 660-km discontinuity is mapped beneath the regions. A deeper-than-normal 660 km discontinuity is observed locally in the southeastern part of our sampled region. The depression of the 660 km discontinuity may be resulted from an oceanic lithospheric slab deflected in the mantle transition zone, in good agreement with the result of earlier tomographic and other seismic studies in this region. The northeastern portion of our sampled region, however, does not show clearly the deflection of the slab. The variation of the tomography of the 660-km discontinuity in our sampled regions may indicate a complex geometry of the subducted Pacific slab.

  12. Complex morphology of subducted lithosphere in the mantle beneath the Tonga trench

    NARCIS (Netherlands)

    Hilst, R.D. van der

    1995-01-01

    At the Tonga trench, old Pacific sea floor subducts at a rapid rate below the Indo-Australia plate, generating most of the world's deep earthquakes and producing a deep slab of former oceanic lithosphere.

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

    Science.gov (United States)

    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.

  14. The Cambrian initiation of intra-oceanic subduction in the southern Paleo-Asian Ocean: Further evidence from the Barleik subduction-related metamorphic complex in the West Junggar region, NW China

    Science.gov (United States)

    Liu, Bo; Han, Bao-Fu; Xu, Zhao; Ren, Rong; Zhang, Jin-Rui; Zhou, Jing; Su, Li; Li, Qiu-Li

    2016-06-01

    In this study, we present new evidence from the Barleik subduction-related metamorphic complex in the southern West Junggar region, northwestern China, for the Cambrian initiation of intra-oceanic subduction in the southern Paleo-Asian Ocean. The Barleik metamorphic complex is mainly composed of blueschist and amphibolite blocks within an ophiolitic mélange and their protoliths are calc-alkaline andesite and alkali and tholeiitic basalts. The calc-alkaline andesite has a zircon U-Pb age of 502 ± 2 Ma, obtained from magmatic cores of zircon grains, and shares geochemical features similar to the 515-485 Ma intra-oceanic arc magmatic rocks in the West Junggar region. By contrast, the alkali and tholeiitic basalts have trace element features similar to ocean island and enriched mid-ocean ridge basalts, respectively. Rutile and sodic-calcic amphibole from the amphibolite have a U-Pb age of 502 ± 25 Ma and a 40Ar/39Ar age of ∼504 Ma, respectively, which are in good agreement within errors with a 40Ar/39Ar age of 492 ± 4 Ma for phengite from the blueschist. These metamorphic ages of ∼500 Ma are interpreted to represent the timing of Pacific-type subduction-related metamorphism and are also compatible with ages of the oldest supra-subduction zone ophiolites (531-512 Ma) and intra-oceanic arc plutons (515-485 Ma) in the southern West Junggar region. Being one of the oldest subduction-related metamorphic complexes (509-490 Ma) in the southern Central Asian Orogenic Belt, the Barleik metamorphic complex, together with the oldest arc plutons, definitely indicate the initial intra-oceanic subduction in the southern Paleo-Asian Ocean at least in the Early Cambrian.

  15. 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 (garnet formation under high pressures. The geochemical data suggest that Cpx-rich cumulates formed at a relatively shallow level in the mantle wedge, and subsequently drug towards the subduction plane by mantle flow, followed by metamorphism that formed garnet in the subduction channel

  16. Gelled Complex Fluids: Combining Unique Structures with Mechanical Stability.

    Science.gov (United States)

    Stubenrauch, Cosima; Gießelmann, Frank

    2016-03-01

    Gelled complex fluids are soft materials in which the microstructure of the complex fluid is combined with the mechanical stability of a gel. To obtain a gelled complex fluid one either adds a gelator to a complex fluid or replaces the solvent in a gel by a complex fluid. The most prominent example of a "natural" gelled complex fluid is the cell. There are various strategies by which one can form a gelled complex fluid; one such strategy is orthogonal self-assembly, that is, the independent but simultaneous formation of two coexisting self-assembled structures within one system. The aim of this Review is to describe the structure and potential applications of various man-made gelled complex fluids and to clarify whether or not the respective system is formed by orthogonal self-assembly.

  17. Paleozoic subduction complex and Paleozoic-Mesozoic island-arc volcano-plutonic assemblages in the northern Sierra terrane

    Science.gov (United States)

    Hanson, Richard E.; Girty, Gary H.; Harwood, David S.; Schweickert, Richard A.

    2000-01-01

    This field trip provides an overview of the stratigraphic and structural evolution of the northern Sierra terrane, which forms a significant part of the wall rocks on the western side of the later Mesozoic Sierra Nevada batholith in California. The terrane consists of a pre-Late Devonian subduction complex (Shoo Fly Complex) overlain by submarine arc-related deposits that record the evolution of three separate island-arc systems in the Late Sevonian-Early Mississippian, Permian, and Late Triassic-Jurassic. The two Paleozoic are packages and the underlying Shoo Fly Complex have an important bearing on plate-tectonic processes affecting the convergent margin outboard of the Paleozoic Cordilleran miogeocline, although their original paleogeographic relations to North America are controversial. The third arc package represents an overlap assemblage that ties the terrane to North America by the Late Triassic and helps constrain the nature and timing of Mesozoic orogenesis. Several of the field-trip stops examine the record of pre-Late Devonian subduction contained in the Shoo Fly Complex, as well as the paleovolcanology of the overlying Devonian to Jurassic arc rocks. Excellent glaciated exposures provide the opportunity to study a cross section through a tilted Devonian volcano-plutonic association. Additional stops focus on plutonic rocks emplaced during the Middle Jurassic arc magmatism in the terrane, and during the main pulse of Cretaceous magmatism in the Sierra Nevada batholith to the east.

  18. Subduction Complex Provenance redefined: modern sands from the Indo-Burman-Andaman-Nicobar Ridge and Barbados Island

    Science.gov (United States)

    Limonta, Mara; Resentini, Alberto; Andò, Sergio; Vezzoli, Giovanni; Bandopadhyay, Pinaki C.; Najman, Yani; Boni, Maria; Bechstädt, Thilo; Garzanti, Eduardo

    2013-04-01

    Subduction complexes large enough to be exposed subaerially and to become significant sources of terrigenous detritus are formed by tectonic accretion above trenches choked with thick sections of remnant-ocean turbidites. They thus need to be connected along strike to a large Alpine-type or Andean-type orogen, where huge volumes of orogenic detritus are produced and conveyed via a major fluvio-deltaic system to the deep sea (Ingersoll et al., 2003). We investigated sediment generation and recycling in the Indo-Burman-Andaman-Nicobar subduction complex, representing the archetype of such settings in the eastern prolongation of the Himalayan collisional system. "Subduction Complex Provenance" is composite, and chiefly consists of detritus recycled from largely turbiditic parent rocks (Recycled Clastic Provenance), with local supply from ultramafic and mafic rocks of forearc lithosphere (Ophiolite Provenance) or recycled paleovolcanic to neovolcanic sources (Volcanic Arc Provenance; Garzanti et al., 2007). In order to specifically investigate the effect of recycling, we characterized the diverse detrital signatures of Cenozoic sandstones deposited during subsequent stages of "soft" and "hard" Himalayan collision and exposed from Bangladesh to the Andaman Islands, and discuss the reasons for compositional discrepancies between parent sandstones and their recycled daughter sands. A companion study was carried out with the same methodologies, rationale and goals on Barbados Island, one of the few other places where a large accretionary prism is subaerially exposed. Also modern Barbados sands are largely multicyclic, reflecting mixing in various proportions of detritus from the basal Scotland Formation (sandstones and mudrocks), their stratigraphic and tectonic cover, the Oceanic Formation (quartzose turbidites and deep-water biogenic oozes including radiolarite), and from the Pleistocene calcarenite and reefal cap, as well as from volcanic layers ultimately derived from

  19. Modern-style Subduction Processes in the Archean:Evidence from the Shangyi Complex in North China Craton

    Institute of Scientific and Technical Information of China (English)

    WANG Renmin; WAN Yusheng; CHENG Suhua; FENG Yonggang

    2009-01-01

    Three fragments of the Arehean oceanic crust have been found between the Archean granulite belt and the Paleo-Proterozoic Hongqiyingzi group in North China craton,which spread and geochronology evidence of the ancient oceanic fragments.The magma crystallizing age of the tonalite in the Shangyi complex is 2512+19 Ma and the geochemical characteristics suggest that the Nb-enriched basalts may be related to crustal contamination and formed in the intra-oceanic arc of the supra subduction zone setting.

  20. Unique advantages of organometallic supporting ligands for uranium complexes

    Energy Technology Data Exchange (ETDEWEB)

    Diaconescu, Paula L. [Univ. of California, Los Angeles, CA (United States); Garcia, Evan [Univ. of California, Los Angeles, CA (United States)

    2014-05-31

    The objective of our research project was to study the reactivity of uranium complexes supported by ferrocene-based ligands. In addition, this research provides training of graduate students as the next generation of actinide scientists.

  1. Deformational evolution of a Cretaceous subduction complex: Elephant Island, South Shetland Islands, Antarctica

    Science.gov (United States)

    Trouw, Rudolph A. J.; Passchier, Cees W.; Valeriano, Claudio M.; Simões, Luiz Sérgio A.; Paciullo, Fabio V. P.; Ribeiro, André

    2000-03-01

    New structural data from Elephant Island and adjacent islands are presented with the objective to improve the understanding of subduction kinematics in the area northeast of the Antarctic Peninsula. On the island, a first deformation phase, D 1, produced a strong SL fabric with steep stretching and mineral lineations, partly defined by relatively high pressure minerals, such as crossite and glaucophane. D 1 is interpreted to record southward subduction along an E-W trench with respect to the present position of the island. A second phase, D 2, led to intense folding with steep E-W-trending axial surfaces. The local presence of sinistral C'-type shear bands related to this phase and the oblique inclination of the L 2 stretching lineations are the main arguments to interpret this phase as representing oblique sinistral transpressive shear along steep, approximately E-W-trending shear zones, with the northern (Pacific) block going down with respect to the southern (Antarctic Peninsula) block. The sinistral strike-slip component may represent a trench-linked strike-slip movement as a consequence of oblique subduction. Lithostatic pressure decreased and temperature increased to peak values during D 2, interpreted to represent the collision of thickened oceanic crust with the active continental margin. The last deformation phase, D 3, is characterised by post-metamorphic kink bands, partially forming conjugate sets consistent with E-W shortening and N-S extension. The rock units that underlie the island probably rotated during D 3, in Cenozoic times, together with the trench, from an NE-SW to the present ENE-WSW position, during the progressive opening of the Scotia Sea. The similarity between the strain orientation of D 3 and that of the sinistral NE-SW Shackleton Fracture Zone is consistent with this interpretation.

  2. Deformation of the Calabrian Arc subduction complex and its relation to STEP activity at depth.

    Science.gov (United States)

    Polonia, Alina; Wortel, Rinus; Nijholt, Nicolai; Govers, Rob; Torelli, Luigi

    2015-04-01

    Propagating tear faults at the edge of subducted slabs ("Subduction transform edge propagator", STEP) are an intrinsic part of lithospheric plate dynamics. The surface expression of a STEP is generally not known yet, and is expected to vary significantly from one region to the other. We choose the Sicily -Calabria-Ionian Sea region, of which the lithosphere-upper mantle structure has the characteristics of a STEP zone, as a study area. The area has a very prominent accretionary wedge, the formation and subsequent deformation of which presumably were affected by the STEP activity at depth. In this contribution, we use seismic data on the near surface structure and deformation in combination with numerical model results to investigate the relation between deep STEP activity and near surface expression. Prominent features in the surface tectonics are the Malta escarpment (with predominantly normal faulting), the newly identified Ionian Fault and Alfeo-Etna fault system, and a distinct longitudinal division of the wedge into a western and an eastern lobe (Polonia et al., Tectonics, 2011). The two lobes are characterized by different structural style, deformation rates and basal detachment depths. Numerical model results indicate that the regional lithospheric structure, such as the orientation of the eastern passive (albeit subsequently activated) margin of Sicily relative to the Calabrian subduction zone, has a profound effect on possible fault activity along the Malta escarpment. Fault activity along the above primary fault structures may have varied in time, implying the possibility of intermittent activity. Interpreting seismicity in the context of a possible STEP, and the accompanying deformation zone at or near the surface, is not (yet) straightforward. Although direct evidence for recognizing all aspects of STEP activity is - as usual - lacking, a comparison with two well-known STEP regions, the northern part of the Tonga subduction zone and southern part of the

  3. UNIQUENESS PROBLEM FOR MEROMORPHIC MAPPINGS IN SEVERAL COMPLEX VARIABLES INTO PN(C) WITH TRUNCATED MULTIPLICITIES

    Institute of Scientific and Technical Information of China (English)

    Zhenhan TU; Zhonghua WANG

    2013-01-01

    This paper proves some uniqueness theorems for meromorphic mappings in several complex variables into the complex projective space PN(C) with truncated multiplicities,and our results improve some earlier work.

  4. The metamorphic and kinematic history of a subduction channel analogue - the subgreenschist Chrystalls Beach Complex, New Zealand - and effects of metamorphic fluid pressure generation on dominant deformation style

    Science.gov (United States)

    Fagereng, A.

    2010-12-01

    Subduction channel shear zones, comprising subducting sediments, fragments of oceanic crust, and material eroded off the upper plate, are commonly inferred to occur along subduction megathrusts. The Chrystalls Beach Complex, an accretionary mélange within the Otago Schist on the South Island of New Zealand, comprises highly sheared trench-fill sedimentary rocks and scattered pillow basalts, and is inferred to have formed during Jurassic subduction under the paleo-Pacific Gondwana margin. Lithologically and structurally, this mélange is analogous to a subduction channel shear zone. Equilibrium mineral assemblages indicate peak P-T conditions in the range 400-550 MPa and 250-300°C. Relatively high pressures of burial and accretion during foliation development are inferred from phengite content and b0 spacing analyses of white mica. Rare lawsonite occurs in a post-foliation vein, and illite `crystallinity' measurements indicate a thermal overprint during exhumation. These P-T estimates and their relative chronology indicate that the mineral assemblages developed along a clockwise P-T path, compatible with published models for rocks deformed along the seismogenic subduction thrust interface and exhumed in an accretionary prism (e.g. Gerya and Stöckhert, 2006). The mélange deformed in a mixed continuous-discontinuos style. Extensive deformation by dissolution-precipitation creep provides evidence for relatively large strains accommodated by viscous flow at temperatures ≤ 300°C. Discontinuous deformation is evident in an extensive fault-fracture mesh involving mutually cross-cutting subvertical extension veins and subhorizontal slickenfibre shear surfaces. For quartz in extension and shear veins, 14.5‰compressive stress. The quartz veins in the Chrystalls Beach Complex are therefore inferred to have precipitated as a result of progressive fluid pressure increase along the prograde P-T path, leading to hydrofracture and fault-fracture mesh generation. At

  5. Dynamic Simulation of the 2011 M9.0 Tohoku Earthquake with Geometric Complexity on a Rate- and State-dependent Subduction Plane

    Science.gov (United States)

    Luo, B.; Duan, B.

    2015-12-01

    The Mw 9.0 Tohoku megathrust earthquake on 11 March 2011 is a great surprise to the scientific community due to its unexpected occurrence on the subduction zone of Japan Trench where earthquakes of magnitude ~7 to 8 are expected based on historical records. Slip distribution and kinematic slip history inverted from seismic data, GPS and tsunami recordings reveal two major aspects of this big event: a strong asperity near the hypocenter and large slip near the trench. To investigate physical conditions of these two aspects, we perform dynamic rupture simulations on a shallow-dipping rate- and state-dependent subduction plane with topographic relief. Although existence of a subducted seamount just up-dip of the hypocenter is still an open question, high Vp anomalies [Zhao et al., 2011] and low Vp/Vs anomalies [Yamamoto et al., 2014] there strongly suggest some kind of topographic relief exists there. We explicitly incorporate a subducted seamount on the subduction surface into our models. Our preliminary results show that the subducted seamount play a significant role in dynamic rupture propagation due to the alteration of the stress state around it. We find that a subducted seamount can act as a strong barrier to many earthquakes, but its ultimate failure after some earthquake cycles results in giant earthquakes. Its failure gives rise to large stress drop, resulting in a strong asperity in slip distribution as revealed in kinematic inversions. Our preliminary results also suggest that the rate- and state- friction law plays an important role in rupture propagation of geometrically complex faults. Although rate-strengthening behavior near the trench impedes rupture propagation, an energetic rupture can break such a barrier and manage to reach the trench, resulting in significant uplift at seafloor and hence devastating tsunami to human society.

  6. Eduction, extension, and exhumation of ultrahigh-pressure rocks in metamorphic core complexes due to subduction initiation

    Science.gov (United States)

    Petersen, Kenni Dinesen; Buck, W. Roger

    2015-09-01

    The controversy over the exhumation of ultrahigh-pressure (UHP) rocks centers on whether it involves rising of pieces of crust detached from subducted continental lithosphere or an entire subducted plate that undergoes "eduction," i.e., reverse subduction. We present a new thermomechanical model of continental subduction showing that these apparently contrasting mechanisms can occur together: crust subducted deep enough is heated and weakened, causing limited diapiric rise, while crust subducted to shallower depths retains strength and is exhumed only by eduction. The model also shows for the first time how eduction followed by seafloor spreading can occur in a zone of regional convergence. This occurs spontaneously when subduction of buoyant crust causes a subduction zone to "lock up" in one place causing a new subduction zone to form in another. The model is consistent with many features of the youngest region of UHP rock exhumation on earth: the D'Entrecasteaux Islands. UHP exhumation and the amount of regional extension, as well as the seismic structure around the islands, can be explained by eduction. Ductile flow fabrics, seen on the islands, would result from exhumation of the most deeply subducted crust heated enough to undergo partial melting. Reversal of motion on the north-dipping continental subduction zone, required by this model, was likely triggered by initiation of the New Britain Trench, as suggested previously. Our model implies that the crust of Goodenough Basin, south of the islands, was exhumed by eduction in the last 5 Ma and this hypothesis can be tested by drilling.

  7. Origin and serpentinization of ultramafic rocks of Manipur Ophiolite Complex in the Indo-Myanmar subduction zone, Northeast India

    Science.gov (United States)

    Ningthoujam, P. S.; Dubey, C. S.; Guillot, S.; Fagion, A.-S.; Shukla, D. P.

    2012-05-01

    The Manipur Ophiolite Complex (MOC) is part of the Manipur-Nagaland ophiolite belt (MNOB). The belt is exposed in the eastern margin of the Indo-Myanmar Ranges (IMRs), which formed by the collision between the India and Myanmar continental plates. Several contrasting views were put forward concerning the origin of the MNOB. The complex represents a dismembered ophiolite sequence with serpentinite as the largest litho-unit formed. Petrography and Raman spectroscopy of the serpentinite suggest that they are serpentinized ultramafic cumulate and peridotite. The serpentinization may have occurred at a condition of low pressure and low temperature metamorphism. Geochemical signatures of the rocks and spinel grains revealed that the protolith be an abyssal peridotite, derived from a less depleted fertile mantle melt at a MORB setting after low degree (10-15%) partial melting. The study concluded that the serpentinite may have been created at a slow-spreading ridge, rather than a supra-subduction-zone setting. These rocks were later obducted and incorporated into the IMR of Indo-Myanmar suture zone.

  8. Internal structure of a thrust associated with subduction underplating from the Okitsu melange in the Shimanto accretionary complex, Japan

    Science.gov (United States)

    Kanaya, T.; Chester, F.; Sakaguchi, A.

    2005-12-01

    The structure of large-displacement, plate-boundary faults in subduction zones is poorly defined relative to other tectonic settings. The thrust faults in the Okitsu melange constitute a duplex, which juxtapose oceanic pillow basalt (hanging walls) and trench-fill-sedimentary rocks (footwalls), and may represent a paleo-underplating zone of a plate-boundary subduction thrust at seismogenic depth. One well exposed duplex-fault, with displacement greater than several kilometers, is examined through structural mapping at scales of 1:100 to 1:1, mesoscale fabric analysis, and geochemical analysis. The duplex-fault zone displays a unique, asymmetric internal structure: brittle deformation dominates in the hanging wall and brittle and ductile deformation is evident in the footwall. The internal structure and surrounding host rocks reflect three accretionary processes: underthrusting, underplating, and uplifting along Out-of-Sequence-Thrusts (OOSTs). On the basis of style of deformation and displacement field, two distinct deformation episodes are identified, which likely correspond to underthrusting and underplating. The elongation of basalt pillows and the boudinage structure of sandstone blocks in shale indicate an elongation of 1.1 to 1.5 parallel to the oceanic crust layer throughout the host rocks of both the hanging wall and footwall, consistent with uniform extension of the crust during underthrusting. Pillow basalt and sedimentary rocks are juxtaposed by a single cataclasite layer composed of decimeter thick ultracataclasite derived from both rock types along the duplex-fault. Mesoscale implosion breccia and micro textures indicative of pressure solution are observed along the master duplex-fault and thought to be products of alternating fast- and slow-rate slip, respectively. Mesoscale fault fabric indicates a paleostress with the maximum principal compression at 15-20° to the master duplex-fault reflecting layer parallel contraction, which is consistent with

  9. Geometry and thermal structure of the Menderes Massif Core Complex (Western Turkey), implications for thermal evolution of Hellenic subduction zone

    Science.gov (United States)

    Roche, Vincent; Jolivet, Laurent; Guillou-Frottier, Laurent; Tuduri, Johann; Bouchot, Vincent; Beccaletto, Laurent; Lahfid, Abdeltif

    2016-04-01

    The eastern Mediterranean region is one of the most promising geothermal areas, with more than 250 geothermal fields discovered in Turkey (Parlaktuna, 2013), in a region of active tectonics and volcanism. Although the potential of these deep geothermal resources has not been systematically investigated yet, the geothermal activity of the western Turkey area is the most recent signature of the high heat flow (120-140 mW/m²; Aydin, 2005, from Teczan, 1995). Based on Turkish data, 2084 MWt are being utilized for direct applications and most of the energy originates from the Menderes Massif (Baba et al., 2015). This large-scale thermal anomaly at the surface is correlated to a long wavelength east-west increase of surface heat flow that could reflect the thermal state of Aegean subduction zone at depth. In order to better understand and characterize the possible connections between large-scale mantle dynamics and surface processes in space and time, we study the structure and thermal evolution of the Menderes Massif. Both the acceleration of the Aegean extension in the Middle Miocene and the recent escape of Anatolia have been proposed to result from several slab tearing events, the first one being located below western Turkey and the Eastern Aegean Sea. These events have triggered the formation of metamorphic complexes with contrasted exhumation P-T paths. While the extension in the Aegean domain is well-characterized with high-temperature domes in the center and east, the succession of several metamorphic events in the Menderes Massif and their significance in terms of geodynamics is still debated. Hence, the exhumation history is key to understanding the temporal and spatial distribution of the thermal signature of the Hellenic slab and its tearing/detachment. The Menderes Massif displays a large variety of metamorphic facies, from the Barrovian type metamorphism in the Eocene (the Main Menderes Metamorphism) to the coeval (?) HP-LT metamorphism on the southernmost

  10. Early Jurassic subduction of the Paleo-Pacific Ocean in NE China: Petrologic and geochemical evidence from the Tumen mafic intrusive complex

    Science.gov (United States)

    Guo, Feng; Li, Hongxia; Fan, Weiming; Li, Jingyan; Zhao, Liang; Huang, Miwei; Xu, Wenliang

    2015-05-01

    Subduction of the Paleo-Pacific Oceanic Plate is widely considered to have caused extensive Mesozoic magmatism, lithospheric deformation and mineralization in East Asia. However, it is still unclear when this subduction began. Here we report an Early Jurassic (~ 187 Ma) mafic intrusive complex (including olivine norite, gabbro, and diorite) from the Tumen area in NE China. The olivine norite contains a mineral assemblage of olivine, pyroxene, Ca-plagioclase, and hornblende that crystallized in a water-saturated parental magma. The rocks in the complex show variable degrees of plagioclase and ferromagnesian mineral accumulation as reflected by positive Sr and Eu anomalies in primitive mantle-normalized incompatible element patterns. Mass-balance calculations indicate that the parental magma was calc-alkaline with arc-type trace element features (i.e., large ion incompatible and light rare earth element enrichment and Nb-Ta depletion). It also had Sr-Nd-Hf isotopic compositions (87Sr/86Sr(i) = 0.7042 to 0.7044, εNd(t) = + 2.5 to + 3.5 and εHf(t) = + 8.4 to + 10.5) similar to those of modern arc basalts. The parental magma was likely derived from 5 to 20% melting of a mantle wedge metasomatized by an addition of 3-4% hydrous sediment melt from the subducting Paleo-Pacific Oceanic slab. The Tumen mafic intrusive complex, together with other contemporaneous mafic intrusions, I-type granitoids, and felsic lavas, constitutes an Early Jurassic N-S-trending arc magmatic belt that was formed by westward subduction of the Paleo-Pacific Ocean.

  11. Melting of a subduction-modified mantle source: A case study from the Archean Marda Volcanic Complex, central Yilgarn Craton, Western Australia

    Science.gov (United States)

    Morris, P. A.; Kirkland, C. L.

    2014-03-01

    Subduction processes on early earth are controversial, with some suggestions that tectonics did not operate until the earth cooled to a sufficient point around the Archean-Proterozoic boundary. One way of addressing this issue is to examine well-preserved successions of Archean supracrustal rocks. Here we discuss petrography, whole-rock chemical and isotopic data combined with zircon Hf isotopes from andesites, high-magnesium andesites (HMA), dacites, high-magnesium dacites (HMD), rhyolites and coeval felsic intrusive rocks of the c. 2730 Ma Marda Volcanic Complex (MVC) in the central Yilgarn Craton of Western Australia. We demonstrate that these rocks result from melting of a metasomatized mantle source, followed by fractional crystallization in a crustal magma chamber. Contamination of komatiite by Archean crust, to produce the Marda Volcanic Complex andesites, is not feasible, as most of these crustal sources are too radiogenic to act as viable contaminants. The ɛNd(2730) of MVC andesites can be produced by mixing 10% Narryer semi-pelite with komatiite, consistent with modelling using Hf isotopes, but to achieve the required trace element concentrations, the mixture needs to be melted by about 25%. The most likely scenario is the modification of a mantle wedge above a subducting plate, coeval with partial melting, producing volcanic rocks with subduction signatures and variable Mg, Cr and Ni contents. Subsequent fractionation of cognate phases can account for the chemistry of dacites and rhyolites.

  12. 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.

  13. Dynamics and Preservation Potential of Subduction Complexes in Continental Sutures: A Case Study from the Sedimentary-Marix Mélange of the Indus-Yarlung Suture Zone in Southern Tibet

    Science.gov (United States)

    Metcalf, K.; Kapp, P. A.; Orme, D. A.

    2015-12-01

    Intra-continental sutures are the geologic record of ancient subduction zones. Subduction complexes are a useful record of ancient continental collisions because they preserve sediments and/or blocks from units which have since eroded and are the first point of contact during collision. The India-Asia collision is one of the most-studied collisional orogens, but how much of the original subduction complex is preserved and what we can determine about the dynamics of the ancient subduction zone along the southern margin of Asia is poorly understood. Compared to other subduction complexes around the world, the complex preserved in the Indus Yarlung Suture Zone (IYSZ) of southern Tibet is anomalous. Blueschist facies metamorphism, a prominent mineral assemblage along intra-continental suture zones, is common in the northwest Himalaya, but not found along the central segment of the IYSZ. Most of the subduction complex is greenschist facies, inconsistent with the geotherm for a subduction zone. We present a metamorphic history for the greenschist facies rocks to reconcile this contradiction. A deep forearc basin (~5-8 km) developed during the Cretaceous, requiring an accretionary subduction zone, a topographic or structural outer forearc high behind which to trap sediment, and/or basal subduction erosion. The preserved subduction complex is almost entirely tectonic sedimentary-matrix mélange with minor outcrops of overlying turbidites. We present evidence from detrital zircon U-Pb geochronology of sandstones that indicate along-strike variability in the provenance of the sedimentary-matrix mélange. For example, both lower and upper plate material are present near the town of Ngamring, while regions along-strike to the west contain little to no upper plate material. The blocks in the sedimentary-matrix mélange are well-mixed throughout kilometers of exposed width. Sandstone blocks of Tethyan affinity, which could have entered the trench only at the onset of collision

  14. 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.

  15. A Matriptase-Prostasin Reciprocal Zymogen Activation Complex with Unique Features

    DEFF Research Database (Denmark)

    Friis, Stine; Uzzun Sales, Katiuchia; Godiksen, Sine

    2013-01-01

    and prostasin form a reciprocal zymogen activation complex with unique features. Prostasin serves as a critical co-factor for matriptase activation. Unexpectedly, however, prostasin-induced matriptase activation requires neither prostasin zymogen conversion nor prostasin catalytic activity. Prostasin zymogen...... conversion to active prostasin is dependent on matriptase but does not require matriptase zymogen conversion. Consistent with these findings, wild type prostasin, activation cleavage site-mutated prostasin, and catalytically inactive prostasin all were biologically active in vivo when overexpressed...... observations regarding these two membrane-anchored serine proteases and their downstream targets....

  16. The Tachakoucht-Iriri-Tourtit arc complex (Moroccan Anti-Atlas): Neoproterozoic records of polyphased subduction-accretion dynamics during the Pan-African orogeny

    Science.gov (United States)

    Triantafyllou, Antoine; Berger, Julien; Baele, Jean-Marc; Diot, Hervé; Ennih, Nasser; Plissart, Gaëlle; Monnier, Christophe; Watlet, Arnaud; Bruguier, Olivier; Spagna, Paul; Vandycke, Sara

    2016-05-01

    We report new mapping, tectonic, metamorphic and U-Pb zircon dating data on the polyphased Tachakoucht-Iriri and Tourtit arc-related units within the Moroccan Pan-African belt (Sirwa window, Anti-Atlas). The studied area contains four different sub-units, from south to north: (1) the Tachakoucht gneisses intruded to its northern part by (2) Iriri intrusions. To the north, the Tachakoucht-Iriri massif is thrusted by (3) the south-verging 760 Ma Khzama ophiolitic sequence intruded by (4) the Tourtit meta-granitic complex. The Tachakoucht gneiss represents former andesitic to dacitic porphyritic rocks crystallized around 740-720 Ma in an intra-oceanic arc setting (IOAS). Subsequently, it has been buried and metamorphosed to 700 °C, 8 kbar in response to early accretion of the arc onto the West African Craton (WAC). This tectono-metamorphic event also led to the dismembering and stacking of back-arc ophiolite onto the arc unit. Subsequently, the Iriri intrusions, a suite of hydrous mafic dykes (hornblende gabbro and fine-grained basalt) and ultramafic (hornblendite) plutons showing subduction zone affinities, intruded the Tachakoucht gneiss under P-T conditions of 750-800 °C and 2-5 kbar. Emplacement of Iriri intrusions led locally to pronounced partial melting of the Tachakoucht gneiss and to the production of leucogranitic melts. These melts crop out into the Iriri-Tachakoucht gneiss contacts as leucogneissic bands (former leucosomes, dated at 651 ± 5 Ma) but also intruded the Khzama ophiolite to form the Tourtit granite (dated at 651 ± 3 Ma). These ages (651-641 Ma) also constrain the timing of Iriri intrusion emplacement. The entire complex has been overprinted by a second deformation event under greenschist to amphibolite facies conditions marked by transposition of primary structures and a development of mylonitic shear zones. These results and those published on the Bou Azzer window show that two phases of subduction-related magmatism occurred in the Anti

  17. Unique optimal solution instance and computational complexity of backbone in the graph bi-partitioning problem

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    As an important tool for heuristic design of NP-hard problems, backbone analysis has become a hot spot in theoretical computer science in recent years. Due to the difficulty in the research on computational complexity of the backbone, many researchers analyzed the backbone by statistic ways. Aiming to increase the backbone size which is usually very small by the existing methods, the unique optimal solution instance construction (UOSIC) is proposed for the graph bi-partitioning problem (GBP). Also, we prove by using the UOSIC that it is NP-hard to obtain the backbone, i.e. no algorithm exists to obtain the backbone of a GBP in polynomial time under the assumption that P ( NP. Our work expands the research area of computational complexity of the backbone. And the UOSIC provides a new way for heuristic design of NP-hard problems.

  18. C1 Polymerization: a unique tool towards polyethylene-based complex macromolecular architectures

    KAUST Repository

    Wang, De

    2017-05-09

    The recent developments in organoborane initiated C1 polymerization (chain grows by one atom at a time) of ylides opens unique horizons towards well-defined/perfectly linear polymethylenes (equivalent to polyethylenes, PE) and PE-based complex macromolecular architectures. The general mechanism of C1 polymerization (polyhomologation) involves the formation of a Lewis complex between a methylide (monomer) and a borane (initiator), followed by migration/insertion of a methylene into the initiator and after oxidation/hydrolysis to afford OH-terminated polyethylenes. This review summarizes efforts towards conventional and newly discovered borane-initiators and ylides (monomers), as well as a combination of polyhomologation with other polymerization methods. Initial efforts dealing with C3 polymerization and the synthesis of the first C1/C3 copolymers are also given. Finally, some thoughts for the future of these polymerizations are presented.

  19. The RTR complex as caretaker of genome stability and its unique meiotic function in plants

    Directory of Open Access Journals (Sweden)

    Alexander eKnoll

    2014-02-01

    Full Text Available The RTR complex consisting of a RecQ helicase, a type IA topoisomerase and the structural protein RMI1 is involved in the processing of DNA recombination intermediates in all eukaryotes. In Arabidopsis thaliana the complex partners RECQ4A, topoisomerase 3α and RMI1 have been shown to be involved in DNA repair and in the suppression of homologous recombination (HR in somatic cells. Interestingly, mutants of AtTOP3A and AtRMI1 are also sterile due to extensive chromosome breakage in meiosis I, a phenotype that seems to be specific for plants. Although both proteins are essential for meiotic recombination it is still elusive on what kind of intermediates they are acting on. Recent data indicate that the pattern of non-crossover (NCO-associated meiotic gene conversion (GC differs between plants and other eukaryotes, as less NCOs in comparison to crossovers (CO could be detected in Arabidopsis. This indicates that NCOs happen either more rarely in plants or that the conversion tract length is significantly shorter than in other organisms. As the TOP3α/RMI1-mediated dissolution of recombination intermediates results exclusively in NCOs, we suggest that the peculiar GC pattern found in plants is connected to the unique role, members of the RTR complex play in plant meiosis.

  20. Structure and reactivity of a unique Y-shaped tricoordinate bis(silyl)platinum(II)-NHC complex

    NARCIS (Netherlands)

    Berthon-Gelloz, G.; de Bruin, B.; Tinant, B.; Markó, I.E.

    2009-01-01

    A unique, three-coordinate Y-shaped bis(silyl)platinum(II) complex was isolated and characterized. DFT studies on a model system shed light on the nature of this unusual coordination mode for platinum(II).

  1. The Elastin Receptor Complex: a unique matricellular receptor with high anti-tumoral potential

    Directory of Open Access Journals (Sweden)

    Amandine eScandolera

    2016-03-01

    Full Text Available Elastin, one of the longest-lived proteins, confers elasticity to tissues with high mechanical constraints. During aging or pathophysiological conditions such as cancer progression, this insoluble polymer of tropoelastin undergoes an important degradation leading to the release of bioactive elastin-derived peptides (EDP, named elastokines. EDP exhibit several biological functions able to drive tumor development by regulating cell proliferation, invasion, survival, angiogenesis, and matrix metalloproteinase expression in various tumor and stromal cells. Although several receptors have been suggested to bind elastokines (αvβ3 and αvβ5 integrins, galectin-3, their main receptor remains the Elastin Receptor Complex (ERC. This heterotrimer comprises a peripheral subunit, named Elastin Binding Protein (EBP, associated to the Protective Protein/Cathepsin A (PPCA. The latter is bound to a membrane-associated protein called Neuraminidase-1 (Neu-1. The pro-tumoral effects of elastokines have been linked to their binding onto EBP. Additionally, Neu-1 sialidase activity is essential for their signal transduction. Consistently, EDP-EBP interaction and Neu-1 activity emerge as original anti-tumoral targets. Interestingly, besides its direct involvement in cancer progression, the ERC also regulates diabetes outcome and thrombosis, an important risk factor for cancer development and a vascular process highly increased in patients suffering from cancer. In this review, we will describe ERC and elastokines involvement in cancer development suggesting that this unique receptor would be a promising therapeutic target. We will also discuss the pharmacological concepts aiming at blocking its pro-tumoral activities. Finally, its emerging role in cancer-associated complications and pathologies such as diabetes and thrombotic events will be also considered.

  2. 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

  3. Unique chemical properties of metal-carbon bonds in metal-carboranyl and metal-carboryne complexes

    Institute of Scientific and Technical Information of China (English)

    QIU ZaoZao; XIE ZuoWei

    2009-01-01

    The metal-carbon bonds in metal-carboranyl and metal-carboryne complexes behave very differently from those in classical organometallic complexes. The unique electronic and steric properties of icosahedral carboranyl moiety make the M-C bond in metal-carboranyl complexes inert toward unsaturated molecules, and on the other hand, the sterically demanding carborane cage can induce unexpected C-C coupling reactions. The M-C bonds in metal-carboryne complexes are, however, active toward various kinds of unsaturated molecules and the reactivity patterns are dependent upon the electronic configurations of the metal ions. This account provides an overview of our recent work in this area.

  4. Unique chemical properties of metal-carbon bonds in metal-carboranyl and metal-carboryne complexes

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    The metal-carbon bonds in metal-carboranyl and metal-carboryne complexes behave very differently from those in classical organometallic complexes. The unique electronic and steric properties of ico-sahedral carboranyl moiety make the M-C bond in metal-carboranyl complexes inert toward unsaturated molecules, and on the other hand, the sterically demanding carborane cage can induce unexpected C-C coupling reactions. The M-C bonds in metal-carboryne complexes are, however, active toward various kinds of unsaturated molecules and the reactivity patterns are dependent upon the electronic configurations of the metal ions. This account provides an overview of our recent work in this area.

  5. Subduction of fracture zones

    Science.gov (United States)

    Constantin Manea, Vlad; Gerya, Taras; Manea, Marina; Zhu, Guizhi; Leeman, William

    2013-04-01

    Since Wilson proposed in 1965 the existence of a new class of faults on the ocean floor, namely transform faults, the geodynamic effects and importance of fracture zone subduction is still little studied. It is known that oceanic plates are characterized by numerous fracture zones, and some of them have the potential to transport into subduction zones large volumes of water-rich serpentinite, providing a fertile water source for magma generated in subduction-related arc volcanoes. In most previous geodynamic studies, subducting plates are considered to be homogeneous, and there is no clear indication how the subduction of a fracture zone influences the melting pattern in the mantle wedge and the slab-derived fluids distribution in the subarc mantle. Here we show that subduction of serpentinized fracture zones plays a significant role in distribution of melt and fluids in the mantle wedge above the slab. Using high-resolution tree-dimensional coupled petrological-termomechanical simulations of subduction, we show that fluids, including melts and water, vary dramatically in the region where a serpentinized fracture zone enters into subduction. Our models show that substantial hydration and partial melting tend to concentrate where fracture zones are being subducted, creating favorable conditions for partially molten hydrous plumes to develop. These results are consistent with the along-arc variability in magma source compositions and processes in several regions, as the Aleutian Arc, the Cascades, the Southern Mexican Volcanic Arc, and the Andean Southern Volcanic Zone.

  6. Unique Ligand-Based Oxidative DNA Cleavage by Zinc(II) Complexes of Hpyramol and Hpyrimol

    NARCIS (Netherlands)

    Maheswari, P.U.; Barends, S.; Özalp-Yaman, S.; de Hoog, P.; Casellas, H.; Teat, S.J.; Massera, C.; Lutz, M.; Spek, A.L.; van Wezel, G.P.; Gamez, P.; Reedijk, J.

    2007-01-01

    The zinc(II) complexes reported here have been synthesised from the ligand 4-methyl-2-N-(2-pyridylmethyl)aminophenol (Hpyramol) with chloride or acetate counterions. All the five complexes have been structurally characterised, and the crystal structures reveal that the ligand Hpyramol gradually unde

  7. Multicolour optical coding from a series of luminescent lanthanide complexes with a unique antenna.

    Science.gov (United States)

    Wartenberg, Nicolas; Raccurt, Olivier; Bourgeat-Lami, Elodie; Imbert, Daniel; Mazzanti, Marinella

    2013-03-04

    The bis-tetrazolate-pyridine ligand H(2)pytz sensitises efficiently the visible and/or near-IR luminescence emission of ten lanthanide cations (Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb). The Ln(III) complexes present sizeable quantum yields in both domains with a single excitation source. The wide range of possible colour combinations in water, organic solvents and the solid state makes the complexes very attractive for labelling and encoding.

  8. Routes to unique palladium A-frame complexes with a bridging fluoro-ligand.

    Science.gov (United States)

    Braun, Thomas; Steffen, Andreas; Schorlemer, Verena; Neumann, Beate; Stammler, Hans-Georg

    2005-10-21

    Treatment of a toluene solution of [PdMe(2)(Cy(2)PCH(2)PCy(2))](1) with pentafluoropyridine in the presence of traces of water affords the generation of the A-frame complexes [(PdMe)(2){mu-kappa(2)(P,P)Cy(2)PCH(2)PCy(2)}(2)(mu-F)][SiMeF(4)]() and [(PdMe)(2){mu-kappa(2)(P,P)Cy(2)PCH(2)PCy(2)}(2)(mu-F)][OC(5)NF(4)](2b). If the reaction is performed in an NMR tube equipped with a PFA inliner, complex 2b is produced, only. Treatment of 1 with pentafluoropyridine in the presence of an excess water yields the pyridyloxy complex [PdMe(OC(5)NF(4))(Cy(2)PCH(2)PCy(2))](3). Compound [(PdMe)(2){mu-kappa(2)(P,P)Cy(2)PCH(2)PCy(2)}(2)(mu-F)][FHF](2c) bearing a bifluoride anion instead of SiMeF(4)(-) or OC(5)NF(4)(-) can be generated by reaction of 1 with substoichiometric amounts of Et(3)N.3HF. The analogous complex [(PdMe)(2){mu-kappa(2)(P,P)Ph(2)PCH(2)PPh(2)}(2)(mu-F)][FHF] (5c) has been synthesized by addition of Ph(2)PCH(2)PPh(2) to a solution of [PdMe(2)(Me(2)NCH(2)CH(2)NMe(2))](4) in THF and subsequent treatment of the reaction mixture with Et(3)N.3HF. The structure of the A-frame complex 5c has been determined by X-ray crystallography.

  9. 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

  10. Dichlorostannylene complexes of group 10 metals, a unique bonding mode stabilized by bridging 2-pyridyldiphenylphosphine ligands

    NARCIS (Netherlands)

    Cabon, Y.; Kleijn, H.; Siegler, M. A.; Spek, A.L.; Klein Gebbink, R.J.M.; Deelman, B.J.

    2010-01-01

    The reaction of tin dichloride with catalytically-relevant group 10 metal precursors [M(Cl)(X)(2-PyPPh2)2] (M = Ni, Pd, Pt; 2-PyPPh2 = 2-pyridyldiphenylphosphine; X = Cl, Me) provides easy access to unprecedented cationic dichlorostannylene complexes [M(X)(2-PyPPh2)2(SnCl2)]+ where the M–Sn bond is

  11. Unique secreted–surface protein complex of Lactobacillus rhamnosus, identified by phage display

    Science.gov (United States)

    Gagic, Dragana; Wen, Wesley; Collett, Michael A; Rakonjac, Jasna

    2013-01-01

    Proteins are the most diverse structures on bacterial surfaces; hence, they are candidates for species- and strain-specific interactions of bacteria with the host, environment, and other microorganisms. Genomics has decoded thousands of bacterial surface and secreted proteins, yet the function of most cannot be predicted because of the enormous variability and a lack of experimental data that would allow deduction of function through homology. Here, we used phage display to identify a pair of interacting extracellular proteins in the probiotic bacterium Lactobacillus rhamnosus HN001. A secreted protein, SpcA, containing two bacterial immunoglobulin-like domains type 3 (Big-3) and a domain distantly related to plant pathogen response domain 1 (PR-1-like) was identified by screening of an L. rhamnosus HN001 library using HN001 cells as bait. The SpcA-“docking” protein, SpcB, was in turn detected by another phage display library screening, using purified SpcA as bait. SpcB is a 3275-residue cell-surface protein that contains general features of large glycosylated Serine-rich adhesins/fibrils from gram-positive bacteria, including the hallmark signal sequence motif KxYKxGKxW. Both proteins are encoded by genes within a L. rhamnosus-unique gene cluster that distinguishes this species from other lactobacilli. To our knowledge, this is the first example of a secreted-docking protein pair identified in lactobacilli. PMID:23233310

  12. Unique cell type-specific junctional complexes in vascular endothelium of human and rat liver sinusoids.

    Directory of Open Access Journals (Sweden)

    Cyrill Géraud

    Full Text Available Liver sinusoidal endothelium is strategically positioned to control access of fluids, macromolecules and cells to the liver parenchyma and to serve clearance functions upstream of the hepatocytes. While clearance of macromolecular debris from the peripheral blood is performed by liver sinusoidal endothelial cells (LSECs using a delicate endocytic receptor system featuring stabilin-1 and -2, the mannose receptor and CD32b, vascular permeability and cell trafficking are controlled by transcellular pores, i.e. the fenestrae, and by intercellular junctional complexes. In contrast to blood vascular and lymphatic endothelial cells in other organs, the junctional complexes of LSECs have not yet been consistently characterized in molecular terms. In a comprehensive analysis, we here show that LSECs express the typical proteins found in endothelial adherens junctions (AJ, i.e. VE-cadherin as well as α-, β-, p120-catenin and plakoglobin. Tight junction (TJ transmembrane proteins typical of endothelial cells, i.e. claudin-5 and occludin, were not expressed by rat LSECs while heterogenous immunreactivity for claudin-5 was detected in human LSECs. In contrast, junctional molecules preferentially associating with TJ such as JAM-A, B and C and zonula occludens proteins ZO-1 and ZO-2 were readily detected in LSECs. Remarkably, among the JAMs JAM-C was considerably over-expressed in LSECs as compared to lung microvascular endothelial cells. In conclusion, we show here that LSECs form a special kind of mixed-type intercellular junctions characterized by co-occurrence of endothelial AJ proteins, and of ZO-1 and -2, and JAMs. The distinct molecular architecture of the intercellular junctional complexes of LSECs corroborates previous ultrastructural findings and provides the molecular basis for further analyses of the endothelial barrier function of liver sinusoids under pathologic conditions ranging from hepatic inflammation to formation of liver metastasis.

  13. Subduction of fore-arc crust beneath an intra-oceanic arc: The high-P Cuaba mafic gneisess and amphibolites of the Rio San Juan Complex, Dominican Republic

    Science.gov (United States)

    Escuder-Viruete, Javier; Castillo-Carrión, Mercedes

    2016-10-01

    The Rio San Juan metamorphic complex (RSJC) exposes a segment of a high-P accretionary prism, built during Late Cretaceous subduction below the intra-oceanic Caribbean island-arc. In this paper we present new detailed maps, tectonostratigraphy, large-scale structure, mineral chemistry, in situ trace element composition of clinopyroxene (Cpx), and bulk rock geochemical data for representative garnet-free peridotites and mafic metaigneous rocks of the Cuaba and Helechal tectonometamorphic units of the southern RSJC. The Cuaba subcomplex is composed of upper foliated amphibolites and lower garnet amphibolites, retrograded (coronitic) eclogites, and heterogeneous metagabbros metamorphosed to upper amphibolite and eclogite-facies conditions. The lenticular bodies of associated peridotites are Cpx-poor harzburgites. The underlying Helechal subcomplex is composed of Cpx-poor harzburgites, Cpx-rich harzbugites, lherzolites and rare dunites. The presented data allow us to argue that the Cuaba subcomplex: (a) represents tectonically deformed and metamorphosed crust of the Caribbean island-arc, (b) contains fragments of its supra-subduction zone mantle, and (c) includes different geochemical groups of mafic protoliths generated by varying melting degrees of diverse mantle sources. These geochemical groups include mid-Ti tholeiites (N-MORB), normal IAT and calc-alkaline rocks, low-Ti IAT, metacumulates of boninitic affinity, and HREE-depleted IAT, that collectively record a multi-stage magmatic evolution for the Caribbean island-arc, prior to the Late Cretaceous high-P metamorphism. Further, these mafic protoliths present comparable geochemical features to mafic igneous rocks of the Puerca Gorda Schists, Cacheal and Puerto Plata complexes, all of them related to the Caribbean island-arc. These relations suggest that the southern RSJC complex represents part of the subducted fore-arc of the Caribbean island-arc, which experienced initial subduction, underplating below the arc

  14. Northward subduction-related orogenesis of the southern Altaids: Constraints from structural and metamorphic analysis of the HP/UHP accretionary complex in Chinese southwestern Tianshan, NW China

    Directory of Open Access Journals (Sweden)

    Mark Scheltens

    2015-03-01

    Full Text Available The Chinese Tianshan belt of the southern Altaids has undergone a complicated geological evolution. Different theories have been proposed to explain its evolution and these are still hotly debated. The major subduction polarity and the way of accretion are the main problems. Southward, northward subduction and multiple subduction models have been proposed. This study focuses on the structural geology of two of the main faults in the region, the South Tianshan Fault and the Nikolaev Line. The dip direction in the Muzhaerte valley is southward and lineations all point towards the NW. Two shear sense motions have been observed within both of these fault zones, a sinistral one, and a dextral one, the latter with an age of 236–251 Ma. Structural analyses on the fault zones show that subduction has been northward rather than southward. The two shear sense directions indicate that the Yili block was first dragged along towards the east due to the clockwise rotation of the Tarim block. After the Tarim block stopped rotating, the Yili block still kept going eastward, inducing the dextral shear senses within the fault zones.

  15. Uniqueness of Solutions to Schrödinger Equations on Complex Semi-Simple Lie Groups

    Indian Academy of Sciences (India)

    Sagun Chanillo

    2007-08-01

    In this note we study the time-dependent Schrödinger equation on complex semi-simple Lie groups. We show that if the initial data is a bi-invariant function that has sufficient decay and the solution has sufficient decay at another fixed value of time, then the solution has to be identically zero for all time. We also derive Strichartz and decay estimates for the Schrödinger equation. Our methods also extend to the wave equation. On the Heisenberg group we show that the failure to obtain a parametrix for our Schrödinger equation is related to the fact that geodesics project to circles on the contact plane at the identity.

  16. Inositol pyrophosphates and their unique metabolic complexity: analysis by gel electrophoresis.

    Directory of Open Access Journals (Sweden)

    Oriana Losito

    Full Text Available BACKGROUND: Inositol pyrophosphates are a recently characterized cell signalling molecules responsible for the pyrophosphorylation of protein substrates. Though likely involved in a wide range of cellular functions, the study of inositol pyrophosphates has suffered from a lack of readily available methods for their analysis. PRINCIPAL FINDING: We describe a novel, sensitive and rapid polyacrylamide gel electrophoresis (PAGE-based method for the analysis of inositol pyrophosphates. Using 4',6-diamidino-2-phenylindole (DAPI and Toluidine Blue we demonstrate the unequivocal detection of various inositol pyrophosphate species. CONCLUSION: The use of the PAGE-based method reveals the likely underestimation of inositol pyrophosphates and their signalling contribution in cells when measured via traditional HPLC-based techniques. PAGE-based analyses also reveals the existence of a number of additional, previously uncharacterised pyrophosphorylated inositol reaction products, defining a more complex metabolism associated with the catalytically flexible kinase class responsible for the production of these highly energetic cell signalling molecules.

  17. 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

  18. Vitamin B12: Unique Metalorganic Compounds and the Most Complex Vitamins

    Directory of Open Access Journals (Sweden)

    Lucio Randaccio

    2010-04-01

    Full Text Available The chemistry and biochemistry of the vitamin B12 compounds (cobalamins, XCbl are described, with particular emphasis on their structural aspects and their relationships with properties and function. A brief history of B12, reveals how much the effort of chemists, biochemists and crystallographers have contributed in the past to understand the basic properties of this very complex vitamin. The properties of the two cobalamins, the two important B12 cofactors Ado- and MeCbl are described, with particular emphasis on how the Co-C bond cleavage is involved in the enzymatic mechanisms. The main structural features of cobalamins are described, with particular reference to the axial fragment. The structure/property relationships in cobalamins are summarized. The recent studies on base-off/base-on equilibrium are emphasized for their relevance to the mode of binding of the cofactor to the protein scaffold. The absorption, transport and cellular uptake of cobalamins and the structure of the B12 transport proteins, IF and TC, in mammals are reviewed. The B12 transport in bacteria and the structure of the so far determined proteins are briefly described. The currently accepted mechanisms for the catalytic cycles of the AdoCbl and MeCbl enzymes are reported. The structure and function of B12 enzymes, particularly the important mammalian enzymes methyltransferase (MetH and methyl-malonyl-coenzymeA mutase (MMCM, are described and briefly discussed. Since fast proliferating cells require higher amount of vitamin B12 than that required by normal cells, the study of B12 conjugates as targeting agents has recently gained importance. Bioconjugates have been studied as potential agents for delivering radioisotopes and NMR probes or as various cytotoxic agents towards cancer cells in humans and the most recent studies are described. Specifically, functionalized bioconjugates are used as “Trojan horses” to carry into the cell the appropriate antitumour or

  19. The Dissociative Subtype of Posttraumatic Stress Disorder: Unique Resting-State Functional Connectivity of Basolateral and Centromedial Amygdala Complexes.

    Science.gov (United States)

    Nicholson, Andrew A; Densmore, Maria; Frewen, Paul A; Théberge, Jean; Neufeld, Richard Wj; McKinnon, Margaret C; Lanius, Ruth A

    2015-09-01

    Previous studies point towards differential connectivity patterns among basolateral (BLA) and centromedial (CMA) amygdala regions in patients with posttraumatic stress disorder (PTSD) as compared with controls. Here we describe the first study to compare directly connectivity patterns of the BLA and CMA complexes between PTSD patients with and without the dissociative subtype (PTSD+DS and PTSD-DS, respectively). Amygdala connectivity to regulatory prefrontal regions and parietal regions involved in consciousness and proprioception were expected to differ between these two groups based on differential limbic regulation and behavioral symptoms. PTSD patients (n=49) with (n=13) and without (n=36) the dissociative subtype and age-matched healthy controls (n=40) underwent resting-state fMRI. Bilateral BLA and CMA connectivity patterns were compared using a seed-based approach via SPM Anatomy Toolbox. Among patients with PTSD, the PTSD+DS group exhibited greater amygdala functional connectivity to prefrontal regions involved in emotion regulation (bilateral BLA and left CMA to the middle frontal gyrus and bilateral CMA to the medial frontal gyrus) as compared with the PTSD-DS group. In addition, the PTSD+DS group showed greater amygdala connectivity to regions involved in consciousness, awareness, and proprioception-implicated in depersonalization and derealization (left BLA to superior parietal lobe and cerebellar culmen; left CMA to dorsal posterior cingulate and precuneus). Differences in amygdala complex connectivity to specific brain regions parallel the unique symptom profiles of the PTSD subgroups and point towards unique biological markers of the dissociative subtype of PTSD.

  20. 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

  1. 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

  2. Contrasting exhumation P-T paths followed by high-P rocks in the northern Caribbean subduction-accretionary complex: Insights from the structural geology, microtextures and equilibrium assemblage diagrams

    Science.gov (United States)

    Escuder-Viruete, Javier; Pérez-Estaún, Andrés

    2013-02-01

    The Río San Juan metamorphic complex exposes a segment of a high-pressure subduction-accretionary complex built during convergence between the Caribbean island arc and the North America continental margin. It is composed of accreted arc- and oceanic-derived metaigneous rocks, serpentinized peridotites and minor metasediments forming a structural pile. Combined structural geology, microtextural relations, multi-equilibrium calculations and thermodynamical modelling, together with published isotopic ages, allow reconstructing the metamorphic P-T-t paths of each nappe/unit and their links to the structural evolution. In all units of the complex, three major stages (M1 to M3) in the tectonothermal evolution have been distinguished. The M1 stage corresponds to the prograde evolution towards the pressure-peak of metamorphism under blueschist or eclogitic-facies conditions. The M2 stage is related to the main retrogressive event and is characterized by the S2-L2 fabric development in all lithologies and at all scales. The M3 stage represents continuous exhumation from ductile to ductile-brittle deformation regimes. However, the shape of the retrograde P-T path, the age of the exhumation-related D2 structures and the tectonic significance of D2 deformation are different in each structural unit. In the upper structural levels of the Jagua Clara serpentinitic-matrix mélange, the counter-clockwise P-T path of the eclogite blocks is typical of rocks exhumed in the early stages of intra-oceanic subduction zones. The clockwise P-T path obtained for the lower Cuaba unit is characterized by a strong isothermal decompression from the garnet-epidote amphibolite and eclogite-facies pressure-peak. This P-T evolution can be explained by rapid exhumation caused by extensional tectonics, in relation to a major modification of convergence conditions across the subduction zone. The P-T path also explains local syn-M2 partial melting processes, because it crosses the wet solidus for IAT

  3. Unique and Interactive Associations Between Maltreatment and Complex Emotion Recognition Deficits and Psychopathic Traits in an Undergraduate Sample.

    Science.gov (United States)

    Waller, Rebecca; McCabe, Hannah K; Dotterer, Hailey L; Neumann, Craig S; Hyde, Luke W

    2017-09-13

    Psychopathy is defined by affective and interpersonal deficits, deviant lifestyle, and antisocial behaviors. Poor recognition of emotions and childhood maltreatment are two risk factors implicated in psychopathy. The current study examined whether childhood maltreatment and complex emotion recognition deficits showed unique and interactive associations with psychopathic traits among 261 undergraduate students. Results indicate that maltreatment was related to higher general psychopathy scores within a bifactor model comprising a general psychopathy factor and four specific factors tapping underlying dimensions of psychopathy (i.e., affective, interpersonal, lifestyle, and antisocial). A significant interaction emerged whereby maltreatment was related to higher antisocial factor scores among individuals showing poor recognition of positive emotions. In an intriguing interaction, more maltreatment was related to lower interpersonal factor scores among individuals with low/mean levels of neutral emotion recognition. The interaction of positive emotion recognition deficits and maltreatment highlights a potential intervention target among antisocial individuals who have experienced maltreatment.

  4. Crystal structure of lactose permease in complex with an affinity inactivator yields unique insight into sugar recognition

    Energy Technology Data Exchange (ETDEWEB)

    Chaptal, Vincent; Kwon, Seunghyug; Sawaya, Michael R.; Guan, Lan; Kaback, H. Ronald; Abramson, Jeff (UCLA); (TTU)

    2011-08-29

    Lactose permease of Escherichia coli (LacY) with a single-Cys residue in place of A122 (helix IV) transports galactopyranosides and is specifically inactivated by methanethiosulfonyl-galactopyranosides (MTS-gal), which behave as unique suicide substrates. In order to study the mechanism of inactivation more precisely, we solved the structure of single-Cys122 LacY in complex with covalently bound MTS-gal. This structure exhibits an inward-facing conformation similar to that observed previously with a slight narrowing of the cytoplasmic cavity. MTS-gal is bound covalently, forming a disulfide bond with C122 and positioned between R144 and W151. E269, a residue essential for binding, coordinates the C-4 hydroxyl of the galactopyranoside moiety. The location of the sugar is in accord with many biochemical studies.

  5. Crystal structure of lactose permease in complex with an affinity inactivator yields unique insight into sugar recognition.

    Science.gov (United States)

    Chaptal, Vincent; Kwon, Seunghyug; Sawaya, Michael R; Guan, Lan; Kaback, H Ronald; Abramson, Jeff

    2011-06-07

    Lactose permease of Escherichia coli (LacY) with a single-Cys residue in place of A122 (helix IV) transports galactopyranosides and is specifically inactivated by methanethiosulfonyl-galactopyranosides (MTS-gal), which behave as unique suicide substrates. In order to study the mechanism of inactivation more precisely, we solved the structure of single-Cys122 LacY in complex with covalently bound MTS-gal. This structure exhibits an inward-facing conformation similar to that observed previously with a slight narrowing of the cytoplasmic cavity. MTS-gal is bound covalently, forming a disulfide bond with C122 and positioned between R144 and W151. E269, a residue essential for binding, coordinates the C-4 hydroxyl of the galactopyranoside moiety. The location of the sugar is in accord with many biochemical studies.

  6. Inside the Subduction Factory

    Science.gov (United States)

    Eiler, John

    Subduction zones helped nucleate and grow the continents, they fertilize and lubricate the earth's interior, they are the site of most subaerial volcanism and many major earthquakes, and they yield a large fraction of the earth's precious metals. They are obvious targets for study—almost anything you learn is likely to impact important problems—yet arriving at a general understanding is notoriously difficult: Each subduction zone is distinct, differing in some important aspect from other subduction zones; fundamental aspects of their mechanics and igneous processes differ from those in other, relatively well-understood parts of the earth; and there are few direct samples of some of their most important metamorphic and metasomatic processes. As a result, even first-order features of subduction zones have generated conflict and apparent paradox. A central question about convergent margins, for instance—how vigorous magmatism can occur where plates sink and the mantle cools—has a host of mutually inconsistent answers: Early suggestions that magmatism resulted from melting subducted crust have been emphatically disproved and recently just as emphatically revived; the idea that melting is fluxed by fluid released from subducted crust is widely held but cannot explain the temperatures and volatile contents of many arc magmas; generations of kinematic and dynamic models have told us the mantle sinks at convergent margins, yet strong evidence suggests that melting there is often driven by upwelling. In contrast, our understanding ofwhy volcanoes appear at ocean ridges and "hotspots"—although still presenting their own chestnuts—are fundamentally solved problems.

  7. Structure of the PSD-95/MAP1A complex reveals a unique target recognition mode of the MAGUK GK domain.

    Science.gov (United States)

    Xia, Yitian; Shang, Yuan; Zhang, Rongguang; Zhu, Jinwei

    2017-08-10

    The PSD-95 family of membrane-associated guanylate kinases (MAGUKs) are major synaptic scaffold proteins and play crucial roles in the dynamic regulation of dendritic remodelling, which is understood to be the foundation of synaptogenesis and synaptic plasticity. The guanylate kinase (GK) domain of MAGUK family proteins functions as a phosphor-peptide binding module. However, the GK domain of PSD-95 has been found to directly bind to a peptide sequence within the C-terminal region of neuronal-specific microtubule-associated protein 1A (MAP1A), although the detailed molecular mechanism governing this phosphorylation-independent interaction at the atomic level is missing. In the present study, we determine the crystal structure of PSD-95 GK in complex with the MAP1A peptide at 2.6-Å resolution. The complex structure reveals that, unlike a linear and elongated conformation in the phosphor-peptide/GK complexes, the MAP1A peptide adopts a unique conformation with a stretch of hydrophobic residues far from each other in the primary sequence clustering and interacting with the 'hydrophobic site' of PSD-95 GK and a highly conserved aspartic acid of MAP1A (D2117) mimicking the phosphor-serine/threonine in binding to the 'phosphor-site' of PSD-95 GK. We demonstrate that the MAP1A peptide may undergo a conformational transition upon binding to PSD-95 GK. Further structural comparison of known DLG GK-mediated complexes reveals the target recognition specificity and versatility of DLG GKs. © 2017 The Author(s). Published by Portland Press Limited on behalf of the Biochemical Society.

  8. Polyoxometalate complexes for oxidative kinetic resolution of secondary alcohols: unique effects of chiral environment, immobilization and aggregation.

    Science.gov (United States)

    Shi, Lei; Wang, Yizhan; Li, Bao; Wu, Lixin

    2014-06-28

    In this paper, the chiral surfactants bearing two long alkyl chains with hydroxyl groups at their terminals were synthesized and employed to encapsulate a catalytically efficient polyoxometalate through electrostatic interaction. The obtained chiral surfactant-encapsulated polyoxometalate complexes, in which a defined chiral microenvironment surrounds the inorganic cluster, were covalently immobilized into the silica matrix via a sol-gel process. Kinetic resolution of racemic aromatic alcohols was selected as the model reaction to evaluate the chiral supramolecular hybrid catalysts. Up to 89% enantiomeric excess was obtained by varying the reaction conditions. Importantly, the change of loading values of the chiral surfactant-encapsulated polyoxometalates leads to mutative inner microstructures ranging from uniform dispersion to subsequent formation of nanocrystalline domains in the silica matrix. Such a structural evolution differentiates the density and stability of the chiral microenvironment, resulting in a regular change of enantioselectivity of the prepared asymmetric catalysts. Moreover, the fixation of the chiral microenvironment surrounding the polyoxometalates by covalent immobilization was proved to have a promoting effect on enantioselectivity. The present research uncovers the unique effect of immobilization on the kinetic resolution. The strategy helps to understand the influencing factors of enantioselectivity, and provides a convenient and efficient approach for the construction of supramolecular asymmetric catalysts based on chiral surfactant-encapsulated polyoxometalate complexes.

  9. 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

    Science.gov (United States)

    Robertson, Alastair; Ustaömer, Timur

    2010-05-01

    The mainly Permian-Triassic rocks of the Karakaya Complex exposed E-W across Turkey are critical to reconstruction of Tethys in the E Mediterranean region. Their origin remains controversial with both stratigraphic layer-cake and accretionary-type settings being advocated. Suggested tectonic settings range from back-arc rift, to accretionary prism- related to either northward or southward subduction. To test alternatives we have studied the contact relations and the internal fabric of each of the main litho-tectonic units making up the Karakaya Complex and related "basement" in nine outcrop areas across NW Turkey, also taking account of existing chemical and dating evidence. Our results show that the Karakaya Complex was assembled by regional-scale thrust faulting without evidence of layer cake-type stratigraphical contacts, or even of deformed sedimentary contacts separating the major lithotectonic units. In several areas (e.g. Havran) the outcrops of meta-siliciclastic sediments of presumed Palaeozoic-age (~Kalabak Unit) are locally cut by Early-Mid Devonian granites. These outcrops represent one or more high-level crustal imbricates made up of basement rocks together with depositionally overlying U. Triassic siliciclastic rocks. Evidence from structurally lower, high pressure-low temperature Karakaya rocks (~Nilüfer Unit) reveals an imbricated, mainly volcaniclastic-carbonate sequence. Both these relatively high-grade Karakaya rocks and the structurally overlying, lower-grade Karakaya rocks (i.e. Çal and Ortaoba units) are interpreted as tectonically emplaced accretionary melange rather than sedimentary "olistostromes". MOR-type basalts (Ortaoba Unit) are locally overlain by red ribbon radiolarites that then pass upwards into feldspar-rich siliciclastics. Triassic oceanic crust and oceanic siliceous sediments were overlain by terrigenous turbidites derived from the north (Sakarya continent), followed by tectonic accretion at a subduction trench bordering the

  10. Crustal growth in subduction zones

    Science.gov (United States)

    Vogt, Katharina; Castro, Antonio; Gerya, Taras

    2015-04-01

    crustal units may collide with continental margins to form collisional orogens and accreted terranes in places where oceanic lithosphere is recycled back into the mantle. We use thermomechanical-petrological models of an oceanic-continental subduction zone to analyse the dynamics of terrane accretion and its implications to arc magmatisim. It is shown that terrane accretion may result in the rapid growth of continental crust, which is in accordance with geological data on some major segments of the continental crust. Direct consequences of terrane accretion may include slab break off, subduction zone transference, structural reworking, formation of high-pressure terranes and partial melting (Vogt and Gerya., 2014), forming complex suture zones of accreted and partially molten units. Castro, A., Vogt, K., Gerya, T., 2013. Generation of new continental crust by sublithospheric silicic-magma relamination in arcs: A test of Taylor's andesite model. Gondwana Research, 23, 1554-1566. Vogt, K., Castro, A., Gerya, T., 2013. Numerical modeling of geochemical variations caused by crustal relamination. Geochemistry, Geophysics, Geosystems, 14, 470-487. Vogt, K., Gerya, T., 2014. From oceanic plateaus to allochthonous terranes: Numerical Modelling. Gondwana Research, 25, 494-508

  11. Unique formation of two high-nuclearity metallamacrocycles from a mononuclear complex [Zn(dmpzdtc)2] (dmpzdtc=3,5-dimethylpyrazole-1-dithiocarboxylate) via CS2 elimination.

    Science.gov (United States)

    Li, Hong-Xi; Wu, Hua-Zhou; Zhang, Wen-Hua; Ren, Zhi-Gang; Zhang, Yong; Lang, Jian-Ping

    2007-12-21

    Dissolution of a mononuclear complex [Zn(dmpzdtc)2] in BrCH2CH2Br or DMF saturated with water followed by CS2 elimination led to the formation of two unique high-nuclearity metallamacrocyclic complexes, [Zn4(micro-dmpz)6(micro-OH)2]2 and [Zn4(micro-dmpz)6(micro-OH)2]4.

  12. Intra oceanic subduction systems

    Institute of Scientific and Technical Information of China (English)

    R.D.Larter; P.T.Leat; Dr.JohnCobbing

    2004-01-01

    The book is the result of a joint meeting ofthe Tectonic Studies Group, the Marine Studies Group and the Volcanic and Magmatic Studies Group hosted by the Geological Society of London in September 2001. It is 382 pages in length and consists of sixteen articles, most of which describe a different example of intra oceanic subduction. All the contributions to this volume are clearly presented and have benefitted from peer review and careful editing.

  13. Unique insula subregion resting-state functional connectivity with amygdala complexes in posttraumatic stress disorder and its dissociative subtype.

    Science.gov (United States)

    Nicholson, Andrew A; Sapru, Iman; Densmore, Maria; Frewen, Paul A; Neufeld, Richard W J; Théberge, Jean; McKinnon, Margaret C; Lanius, Ruth A

    2016-04-30

    The insula and amygdala are implicated in the pathophysiology of posttraumatic stress disorder (PTSD), where both have been shown to be hyper/hypoactive in non-dissociative (PTSD-DS) and dissociative subtype (PTSD+DS) PTSD patients, respectively, during symptom provocation. However, the functional connectivity between individual insula subregions and the amygdala has not been investigated in persons with PTSD, with or without the dissociative subtype. We examined insula subregion (anterior, mid, and posterior) functional connectivity with the bilateral amygdala using a region-of-interest seed-based approach via PickAtlas and SPM8. Resting-state fMRI was conducted with (n=61) PTSD patients (n=44 PTSD-DS; n=17 PTSD+DS), and (n=40) age-matched healthy controls. When compared to controls, the PTSD-DS group displayed increased insula connectivity (bilateral anterior, bilateral mid, and left posterior) to basolateral amygdala clusters in both hemispheres, and the PTSD+DS group displayed increased insula connectivity (bilateral anterior, left mid, and left posterior) to the left basolateral amygdala complex. Moreover, as compared to PTSD-DS, increased insula subregion connectivity (bilateral anterior, left mid, and right posterior) to the left basolateral amygdala was found in PTSD+DS. Depersonalization/derealization symptoms and PTSD symptom severity correlated with insula subregion connectivity to the basolateral amygdala within PTSD patients. This study is an important first step in elucidating patterns of neural connectivity associated with unique symptoms of arousal/interoception, emotional processing, and awareness of bodily states, in PTSD and its dissociative subtype. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

  14. Zircon U-Pb ages and emplacement history of the Nodoushan plutonic complex in the central Urumieh-Dokhtar magmatic belt, Central Iran: Product of Neotethyan subduction during the Paleogene

    Science.gov (United States)

    Shahsavari Alavijeh, Badieh; Rashidnejad-Omran, Nematollah; Corfu, Fernando

    2017-08-01

    The Nodoushan plutonic complex is composed of a wide range of felsic and mafic rocks straddling several of the major orogenic zones in Iran. Diorite porphyry, diorite, granodiorite and granite intrusives belong to the central part of the Urumieh-Dokhtar magmatic belt, which is part of the Alpine-Himalayan orogenic belt. Monzogabbroic members of the complex are instead located within the bordering Sanandaj-Sirjan magmatic-metamorphic zone. These plutons were emplaced into Permian and lower Cretaceous sedimentary units and Eocene calc-alkaline volcanic and subvolcanic rocks. New U-Pb zircon ages reveal that the plutonic complex was assembled incrementally over ca. 15 m.y. during three main episodes at 40.487 ± 0.063 Ma near the Middle/Late Eocene boundary, at 30.52 ± 0.11 Ma and 30.06 ± 0.10 Ma in the Early Oligocene (Middle Rupelian) and at 24.994 ± 0.037 and 24.13 ± 0.19 Ma in the Late Oligocene (latest Chattian). The activity recorded in the Nodoushan plutonic complex represents the final stages of subduction-related magmatism prior to the eventual Miocene collision between the Arabian and Eurasian blocks.

  15. 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 (nephrite and jadeitite) and serpentinite: Metasomatic connections. International Geology Review 47:113-146. 2) Schertl, H.-P., Maresch, W.V., Krebs, M., Draper, G. (2007) The Rio San Juan serpentinite complex and its jadeitites (Dominican Republic). In: Martens U., García-Casco A. (eds) High-pressure belts of Central Guatemala: the Motagua suture and the Chuacús Complex. IGCP 546 Special Contribution, 1. 3) Schertl, H.-P., Krebs, M., Maresch, W.V., Draper, G. (2007) Jadeitite from Hispaniola: a link between Guatemala and Antigua? 20th Colloquium on Latin American Earth Sciences, Kiel, Germany, Abstract

  16. Spatiotemporal evolution of dehydration reactions in subduction zones (Invited)

    Science.gov (United States)

    Padron-Navarta, J.

    2013-12-01

    Large-scale deep water cycling takes place through subduction zones in the Earth, making our planet unique in the solar system. This idiosyncrasy is the result of a precise but unknown balance between in-gassing and out-gassing fluxes of volatiles. Water is incorporated into hydrous minerals during seafloor alteration of the oceanic lithosphere. The cycling of volatiles is triggered by dehydration of these minerals that release fluids from the subducting slab to the mantle wedge and eventually to the crust or to the deep mantle. Whereas the loci of such reactions are reasonably well established, the mechanisms of fluid migration during dehydration reactions are still barely known. One of the challenges is that dehydration reactions are dynamic features evolving in time and space. Experimental data on low-temperature dehydration reactions (i.e. gypsum) and numerical models applied to middle-crust conditions point to a complex spatiotemporal evolution of the dehydration process. The extrapolation of these inferences to subduction settings has not yet been explored but it is essential to understand the dynamism of these settings. Here I propose an alternative approach to tackle this problem through the textural study of high-pressure terrains that experienced dehydration reactions. Spatiotemporal evolution of dehydration reactions should be recorded during mineral nucleation and growth through variations in time and space of the reaction rate. Insights on the fluid migration mechanism could be inferred therefore by noting changes in the texture of prograde assemblages. The dehydration of antigorite in serpentinite is a perfect candidate to test this approach as it releases a significant amount of fluid and produces a concomitant porosity. Unusual alternation of equilibrium and disequilibrium textures observed in Cerro del Almirez (Betic Cordillera, S Spain)[1, 2] attest for a complex fluid migration pattern for one of the most relevant reactions in subduction zones

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

    Science.gov (United States)

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

    1993-03-01

    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. High-pressure granulites of the Podolsko complex, Bohemian Massif: An example of crustal rocks that were subducted to mantle depths and survived a pervasive mid-crustal high-temperature overprint

    Science.gov (United States)

    Faryad, Shah Wali; Žák, Jiří

    2016-03-01

    The Podolsko complex, Bohemian Massif, is a mid-crustal migmatite-granite dome exposed along a tectonic boundary separating the upper crust from the deeply eroded interior of the Variscan orogen, referred to as the Moldanubian Zone. This study examines metamorphic history of mafic and felsic granulites that occur in this complex as minor lenses or layers hosted in pervasively anatectic rocks. The mafic granulite contains garnet with preserved high-Ca cores, which based on pseudosection modelling indicates pressure conditions near the coesite stability field at temperatures of ca. 550-600 °C. The relicts of an earlier eclogite-facies stage have been overprinted by a later granulite-facies assemblage consisting of ternary feldspar, orthopyroxene, and spinel in the mafic granulite and sillimanite and spinel in the felsic granulite. Composition of younger garnet (in rims and as smaller grains) in both granulites suggests that a near isothermal decompression of these rocks was followed by heating that reached temperature of ca. 900 °C at pressure of ca. 0.5 GPa. It is thus concluded that the granulites underwent at least two temporally separate tectonometamorphic events: they were first subducted to mantle depths and exhumed rapidly at relatively low temperatures and then near isobarically heated at mid-crustal levels. The preservation of earlier eclogite-facies garnet in the mafic granulite indicates that the latter event was short-lived and was followed by near isobaric cooling. The geologically brief granulite-facies metamorphism was previously explained as a result of slab break-off and mantle upwelling after the main phase of microplate convergence in the Bohemian Massif. To put the Podolsko complex into a broader tectonic context, we synthesize the available petrologic and structural data from the correlative (U)HP assemblages of the Moldanubian Zone to suggest that they typically do not preserve structural record of the subduction stage, only rarely preserve an

  19. 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.

  20. Late Paleozoic onset of subduction and exhumation at the western margin of Gondwana (Chilenia Terrane): Counterclockwise P-T paths and timing of metamorphism of deep-seated garnet-mica schist and amphibolite of Punta Sirena, Coastal Accretionary Complex, central Chile (34° S)

    Science.gov (United States)

    Hyppolito, T.; García-Casco, A.; Juliani, C.; Meira, V. T.; Hall, C.

    2014-10-01

    In this study, the Paleozoic albite-epidote-amphibolite occurring as meter-sized intercalations within garnet-mica schist at Punta Sirena beach (Pichilemu region, central Chile) is characterized for the first time. These rocks constitute an unusual exposure of subduction-related rocks within the Paleozoic Coastal Accretionary Complex of central Chile. Whereas high pressure (HP) greenschist and cofacial metasediments are the predominant rocks forming the regional metamorphic basement, the garnet-mica schist and amphibolite yield higher P-T conditions (albite-epidote amphibolite facies) and an older metamorphic age. Combining detailed mineral chemistry and textural information, P-T calculations and Ar-Ar ages, including previously published material from the Paleozoic Accretionary Complex of central Chile, we show that the garnet-mica schist and associated amphibolite (locally retrograded to greenschist) are vestiges of the earliest subducted material now forming exotic bodies within the younger HP units of the paleo-accretionary wedge. These rocks are interpreted as having been formed during the onset of subduction at the southwestern margin of Gondwana. However, we show that the garnet-mica schist formed at a slightly greater depth (ca. 40 km) than the amphibolite (ca. 30 km) along the same hot-subduction gradient developed during the onset of subduction. Both lithotypes reached their peak-P conditions at ca. 335-330 Ma and underwent near-isobaric cooling followed by cooling and decompression (i.e., counterclockwise P-T paths). The forced return flow of the garnet-mica schist from the subduction channel started at ca. 320 Ma and triggered the exhumation of fragments of shallower accreted oceanic crust (amphibolite). Cores of phengite (garnet-mica schist) and amphibole (amphibolite) grains have similar chemical compositions in both the S1 and S2 domains, indicating rotation of these grains during the transposition of the burial-related (prograde peak-T) foliation S1

  1. Cratonic lithospheric mantle: Is anything subducted?

    Institute of Scientific and Technical Information of China (English)

    William L. Griffin; Suzanne Y. O'ReiUy

    2007-01-01

    @@ If the subcontinental lithospheric mantle (SCLM) formed through the repeated underthrusting of oceanic slabs, peridotitic SCLM should resemble oceanic peridotites, and mafic rocks (eclogites, s.l.) should be distributed throughout the SCLM. However, cratonic peridotites (both exposed massifs and xenoliths) differ markedly from oceanic and ophiolitic peridotites in their Fe-Cr-Al relationships and abundances of trace elements (Li and B) diagnostic of subduction. "Typical"cratonic peridotites have experienced extensive metaso matism; modelling of their refractory protoliths indicates high-degree melting at high P, perhaps a uniquely Archean process.

  2. Complete 40Ar resetting in an ultracataclasite by reactivation of a fossil seismogenic fault along the subducting plate interface in the Mugi Mélange of the Shimanto accretionary complex, southwest Japan

    Science.gov (United States)

    Tonai, Satoshi; Ito, Shun; Hashimoto, Yoshitaka; Tamura, Hajimu; Tomioka, Naotaka

    2016-08-01

    We used the K-Ar ages of clay-sized mineral grains to investigate the timing of activity on the Minami-Awa Fault, which is a fossil seismogenic fault along a subducting plate interface separating the coherent strata of the Shimanto accretionary complex to the north from the tectonic mélange to the south. The K-Ar ages from the matrix shale of the mélange range from 85 to 48 Ma and decrease with decreasing amount of detrital mica, indicating that they record a mixture of authigenic illite related to burial diagenesis and detrital mica. In contrast, the K-Ar ages of an ultracataclasite within the fault core are significantly younger, ranging from 29 to 23 Ma, and are unrelated to grain size and amount of detrital mica. This indicates that s Ar diffused completely from the ultracataclasite between 29 and 23 Ma, which postdates the formation of authigenic illite by at least several million years. The diffusion of 40Ar in the ultracataclasite was probably caused by frictional heating or high-temperature fluid migration that occurred when the fault was reactivated. The results indicate that seismogenic faults that separate tectonic mélange from coherent strata in accretionary complexes may slip, not only during accretion, but also long after accretion.

  3. Student Performance along Axes of Scenario Novelty and Complexity in Introductory Biology: Lessons from a Unique Factorial Approach to Assessment

    Science.gov (United States)

    Deane-Coe, Kirsten K.; Sarvary, Mark A.; Owens, Thomas G.

    2017-01-01

    In an undergraduate introductory biology laboratory course, we used a summative assessment to directly test the learning objective that students will be able to apply course material to increasingly novel and complex situations. Using a factorial framework, we developed multiple true-false questions to fall along axes of novelty and complexity,…

  4. Molecular Basis of Light Harvesting and Photoprotection in CP24 UNIQUE FEATURES OF THE MOST RECENT ANTENNA COMPLEX

    NARCIS (Netherlands)

    Passarini, Francesca; Wientjes, Emilie; Hienerwadel, Rainer; Croce, Roberta

    2009-01-01

    CP24 is a minor antenna complex of Photosystem II, which is specific for land plants. It has been proposed that this complex is involved in the process of excess energy dissipation, which protects plants from photodamage in high light conditions. Here, we have investigated the functional

  5. Unique Pattern of Component Gene Disruption in the NRF2 Inhibitor KEAP1/CUL3/RBX1 E3-Ubiquitin Ligase Complex in Serous Ovarian Cancer

    Directory of Open Access Journals (Sweden)

    Victor D. Martinez

    2014-01-01

    Full Text Available The NFE2-related factor 2 (NRF2 pathway is critical to initiate responses to oxidative stress; however, constitutive activation occurs in different cancer types, including serous ovarian carcinomas (OVCA. The KEAP1/CUL3/RBX1 E3-ubiquitin ligase complex is a regulator of NRF2 levels. Hence, we investigated the DNA-level mechanisms affecting these genes in OVCA. DNA copy-number loss (CNL, promoter hypermethylation, mRNA expression, and sequence mutation for KEAP1, CUL3, and RBX1 were assessed in a cohort of 568 OVCA from The Cancer Genome Atlas. Almost 90% of cases exhibited loss-of-function alterations in any components of the NRF2 inhibitory complex. CNL is the most prominent mechanism of component disruption, with RBX1 being the most frequently disrupted component. These alterations were associated with reduced mRNA expression of complex components, and NRF2 target gene expression was positively enriched in 90% of samples harboring altered complex components. Disruption occurs through a unique DNA-level alteration pattern in OVCA. We conclude that a remarkably high frequency of DNA and mRNA alterations affects components of the KEAP1/CUL3/RBX1 complex, through a unique pattern of genetic mechanisms. Together, these results suggest a key role for the KEAP1/CUL3/RBX1 complex and NRF2 pathway deregulation in OVCA.

  6. Evolution of a Subduction Zone

    Science.gov (United States)

    Noack, Lena; Van Hoolst, Tim; Dehant, Veronique

    2014-05-01

    The purpose of this study is to understand how Earth's surface might have evolved with time and to examine in a more general way the initiation and continuance of subduction zones and the possible formation of continents on an Earth-like planet. Plate tectonics and continents seem to influence the likelihood of a planet to harbour life, and both are strongly influenced by the planetary interior (e.g. mantle temperature and rheology) and surface conditions (e.g. stabilizing effect of continents, atmospheric temperature), but may also depend on the biosphere. Employing the Fortran convection code CHIC (developed at the Royal Observatory of Belgium), we simulate a subduction zone with a pre-defined weak zone (between oceanic and continental crust) and a fixed plate velocity for the subducting oceanic plate (Quinquis et al. in preparation). In our study we first investigate the main factors that influence the subduction process. We simulate the subduction of an oceanic plate beneath a continental plate (Noack et al., 2013). The crust is separated into an upper crust and a lower crust. We apply mixed Newtonian/non-Newtonian rheology and vary the parameters that are most likely to influence the subduction of the ocanic plate, as for example density of the crust/mantle, surface temperature, plate velocity and subduction angle. The second part of our study concentrates on the long-term evolution of a subduction zone. Even though we model only the upper mantle (until a depth of 670km), the subducted crust is allowed to flow into the lower mantle, where it is no longer subject to our investigation. This way we can model the subduction zone over long time spans, for which we assume a continuous inflow of the oceanic plate into the investigated domain. We include variations in mantle temperatures (via secular cooling and decay of radioactive heat sources) and dehydration of silicates (leading to stiffening of the material). We investigate how the mantle environment influences

  7. Seismic probing of continental subduction zones

    Science.gov (United States)

    Zhao, Liang; Xu, Xiaobing; Malusà, Marco G.

    2017-09-01

    High-resolution images of Earth's interior provide pivotal information for the understanding of a range of geodynamic processes, including continental subduction and exhumation of ultrahigh-pressure (UHP) metamorphic rocks. Here we present a synthesis of available global seismic observations on continental subduction zones, and selected examples of seismic probing from the European Alps, the Himalaya-Tibet and the Qinling-Dabie orogenic belts. Our synthesis and examples show that slabs recognized beneath exhumed continental UHP terranes generally have shallow dip angles (100 km. Slabs underlined by a clear high velocity anomaly from Earth's surface to the mantle are generally Cenozoic in age. Some of these slabs are continuous, whereas other continental subduction zones are located above discontinuous high velocity anomalies possibly suggesting slab breakoff. The density of seismic stations and the quality of recordings are of primary importance to get high-resolution images of the upper mantle to be used as a starting point to provide reliable geodynamic interpretations. In some cases, areas previously indicated as possible site of slab breakoff, such as the European Alps, have been later proven to be located above a continuous slab by using higher quality travel time data from denser seismic arrays. Discriminating between oceanic and continental slabs can be challenging, but valuable information can be provided by combining teleseismic tomography and receiver function analysis. The upper mantle beneath most continental UHP terranes generally shows complex seismic anisotropy patterns that are potentially preserved even in pre-Cenozoic subduction zones. These patterns can be used to provide information on continental slabs that are no longer highlighted by a clear high-velocity anomaly.

  8. The return of sialic material to the mantle indicated by terrigeneous material subducted at convergent margins

    Science.gov (United States)

    von, Huene R.; Scholl, D. W.

    1993-01-01

    At convergent margins where oceanic crust is subducted beneath continental or island-arc crust, sediment on the igneous oceanic crust divides into an accreted and a subducted fraction. Although the subducted fraction is larger, it is obscured in many seismic reflection records because of its depth and the effects of the overlying complex structure. Volumes of accreted and underthrust sediment were quantified at individual margins and global estimates were made of the terrigeneous debris subducted. Also included were debris from subduction erosion. The estimated volume of terrigeneous material subducted beneath continental and island-arc crust is sufficiently large to significantly affect processes along the plate boundary. The possible volume reaching the mantle could have considerable affect on mantle evolution. ?? 1993.

  9. Geodynamics of divergent double subduction: 3-D numerical modeling of a Cenozoic example in the Molucca Sea region, Indonesia

    Science.gov (United States)

    Zhang, Qingwen; Guo, Feng; Zhao, Liang; Wu, Yangming

    2017-05-01

    Geological observations reveal existence of a unique form of plate subduction featuring subduction on both sides of one single oceanic plate, which is termed divergent double subduction (DDS). DDS may play an important role in facilitating tectonic processes like closure of oceanic basins, accretion and amalgamation of magmatic arcs, and growth of continents. However, this type of subduction has been largely a conceptual model and the geodynamics behind DDS are still poorly constrained. The Molucca Sea subduction zone in SE Asia has been considered as a Cenozoic example of DDS based on geophysical and geological data and provides an opportunity for detailed assessment of how DDS occurs. Here we present 3-D numerical modeling with aims to reproduce the geodynamic processes of DDS. Several factors that may have important influences on the evolution of DDS are evaluated, including the geometry of the subducting plate, the order of subduction initiation on both sides, the far-field boundary conditions and thickness of the overriding plates, and the negative buoyancy of the subducting plate. Our results reproduce the observed asymmetrical shape of the subducting Molucca Sea plate and the bending of Halmahera and Sangihe arcs and suggest that DDS is possible if effective escape of the slab-trapped upper mantle overcomes the space problem, otherwise the slab-trapped mantle may hinder the sustainability of subduction. We therefore conclude that DDS is associated with closure of narrow and short oceanic plate, and large-scale double subduction is rare in nature probably owing to space problem.

  10. Unique cleavage of 2-acetamido-2-deoxy-D-glucose from the reducing end of biantennary complex type oligosaccharides.

    Science.gov (United States)

    Murase, Takefumi; Kajihara, Yasuhiro

    2010-08-16

    Basic treatment of a biantennary complex-type sialyloligosaccharide, as well as its asialo form, was found to lead to the specific cleavage of 2-acetamido-2-deoxy-d-glucose (GlcNAc) from the reducing end. The resultant oligosaccharides were identical to those prepared by treatment with endo-beta-glycosidase-M, which cleaves the glycosidic bond between two GlcNAc residues at the reducing end of N-linked oligosaccharides. In addition, mechanistic studies suggested that an elimination reaction in the reducing-end terminal GlcNAc residue causes this specific cleavage reaction.

  11. Changes of the Unique Odontogenic Properties of Rat Apical Bud Cells under the Developing Apical Complex Microenvironment

    Institute of Scientific and Technical Information of China (English)

    Jun Fang; Liang Tang; Xiao-hui Liu; Ling-ying Wen; Yan Jin

    2009-01-01

    Aim To characterize the odontogenic capability of apical bud and phenotypical change of apical bud cells (ABCs) in different microenvironment. Methodology Incisor apical bud tissues from neonatal SD rat were dissected and transplanted into the renal capsules to determine their odontogenic capability. Meanwhile ABCs were cultured and purified by repeated differential trypsinization. Then ABCs were cultured with conditioned medium from developing apical complex cells (DAC-CM). Immunocytochemistry, reverse transcriptase polymerase chain reaction (RT-PCR) and scanning electron microscope (SEM) were performed to compare the biological change of ABC treated with or without DAC-CM. Results First we confirmed the ability of apical bud to form crown-like structure ectopically. Equally important, by using the developing apical complex (DAC) conditioned medium, we found the microenvironment created by root could abrogate the "crown" features of ABCs and promote their proliferation and differentiation. Conclusion ABCs possess odontogenic capability to form crown-like tissues and this property can be affected by root-produced microenvironment.

  12. Mof-associated complexes have overlapping and unique roles in regulating pluripotency in embryonic stem cells and during differentiation

    Science.gov (United States)

    Ravens, Sarina; Fournier, Marjorie; Ye, Tao; Stierle, Matthieu; Dembele, Doulaye; Chavant, Virginie; Tora, Làszlò

    2014-01-01

    The histone acetyltransferase (HAT) Mof is essential for mouse embryonic stem cell (mESC) pluripotency and early development. Mof is the enzymatic subunit of two different HAT complexes, MSL and NSL. The individual contribution of MSL and NSL to transcription regulation in mESCs is not well understood. Our genome-wide analysis show that i) MSL and NSL bind to specific and common sets of expressed genes, ii) NSL binds exclusively at promoters, iii) while MSL binds in gene bodies. Nsl1 regulates proliferation and cellular homeostasis of mESCs. MSL is the main HAT acetylating H4K16 in mESCs, is enriched at many mESC-specific and bivalent genes. MSL is important to keep a subset of bivalent genes silent in mESCs, while developmental genes require MSL for expression during differentiation. Thus, NSL and MSL HAT complexes differentially regulate specific sets of expressed genes in mESCs and during differentiation. DOI: http://dx.doi.org/10.7554/eLife.02104.001 PMID:24898753

  13. TGF-{beta} signals the formation of a unique NF1/Smad4-dependent transcription repressor-complex in human diploid fibroblasts

    Energy Technology Data Exchange (ETDEWEB)

    Luciakova, Katarina, E-mail: katarina.luciakova@savba.sk [Cancer Research Institute, Slovak Academy of Sciences, Bratislava, Vlarska 7, 833 91 Bratislava (Slovakia); Kollarovic, Gabriel; Kretova, Miroslava; Sabova, Ludmila [Cancer Research Institute, Slovak Academy of Sciences, Bratislava, Vlarska 7, 833 91 Bratislava (Slovakia); Nelson, B. Dean [Department of Biochemistry and Biophysics, Arrhenius Laboratories, Stockholm University, S-106 91 Stockholm (Sweden)

    2011-08-05

    Highlights: {yields} TGF-{beta} induces the formation of unique nuclear NF1/Smad4 complexes that repress expression of the ANT-2 gene. {yields} Repression is mediated through an NF1-dependent repressor element in the promoter. {yields} The formation of NF1/Smad4 complexes and the repression of ANT2 are prevented by inhibitors of p38 kinase and TGF-{beta} RI. {yields} NF1/Smad complexes implicate novel role for NF1 and Smad proteins in the regulation of growth. -- Abstract: We earlier reported the formation of a unique nuclear NF1/Smad complex in serum-restricted fibroblasts that acts as an NF1-dependent repressor of the human adenine nucleotide translocase-2 gene (ANT2) [K. Luciakova, G. Kollarovic, P. Barath, B.D. Nelson, Growth-dependent repression of human adenine nucleotide translocator-2 (ANT2) transcription: evidence for the participation of Smad and Sp family proteins in the NF1-dependent repressor complex, Biochem. J. 412 (2008) 123-130]. In the present study, we show that TGF-{beta}, like serum-restriction: (a) induces the formation of NF1/Smad repressor complexes, (b) increases binding of the complexes to the repressor elements (Go elements) in the ANT2 promoter, and (c) inhibits ANT2 expression. Repression of ANT2 by TGF-{beta} is eliminated by mutating the NF1 binding sites in the Go repressor elements. All of the above responses to TGF-{beta} are prevented by inhibitors of TGF-{beta} RI and MAPK p38. These inhibitors also prevent NF1/Smad4 repressor complex formation and repression of ANT2 expression in serum-restricted cells, suggesting that similar signaling pathways are initiated by TGF-{beta} and serum-restriction. The present finding that NF1/Smad4 repressor complexes are formed through TGF-{beta} signaling pathways suggests a new, but much broader, role for these complexes in the initiation or maintenance of the growth-inhibited state.

  14. Unique selectivity reversal in Am(3+)-Eu(3+) extraction in a tripodal TREN-based diglycolamide in ionic liquid: extraction, luminescence, complexation and structural studies.

    Science.gov (United States)

    Leoncini, Andrea; Mohapatra, Prasanta K; Bhattacharyya, Arunasis; Raut, Dhaval R; Sengupta, Arijit; Verma, Parveen K; Tiwari, Nidhi; Bhattacharyya, Dibyendu; Jha, Sambhunath; Wouda, Anna M; Huskens, Jurriaan; Verboom, Willem

    2016-02-14

    An N-pivot diglycolamide extractant (DGA-TREN) was synthesized for the first time and its complexation behaviour was studied towards trivalent lanthanide/actinide ions. The solvent extraction studies suggested a unique selectivity reversal in the extraction of trivalent actinides versus trivalent lanthanides which was observed performing extraction studies in an ionic liquid vis-à-vis a molecular diluent for a tripodal TREN-based diglycolamide ligand (DGA-TREN) vs. a tripodal diglycolamide ligand (T-DGA) which may have great significance in radioactive waste remediation. The nature of the bonding to Eu(3+) ion was investigated by EXAFS as well as by DFT calculations.

  15. 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.

  16. New access to the deep interior of the Nankai accretionary complex and comprehensive characterization of subduction inputs and recent mega splay fault activity (IODP-NanTroSEIZE Expedition 338)

    Science.gov (United States)

    Strasser, Michael; Moore, Gregory F.; Kanagawa, Kyuichi; Dugan, Brandon; Fabbri, Olivier; Toczko, Sean; Maeda, Lena

    2013-04-01

    The Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) is a coordinated, multi-expedition Integrated Ocean Drilling Program (IODP) drilling project designed to investigate fault mechanics and seismogenesis along subduction megathrusts through direct sampling, in situ measurements, and long-term monitoring in conjunction with allied laboratory and numerical modeling studies. IODP Expedition 338 (1 October 2012 - 13 January 2013), extended riser Hole C0002F from 856 meters below the sea floor (mbsf) to 2005 mbsf. Site C0002 is the centerpiece of the NanTroSEIZE project, and is planned to be deepened to eventually reach the seismogenic fault zone during upcoming drilling expeditions. The original Exp. 338 operational plan to case the hole to 3600 mbsf had to be revised as sudden changes in sea conditions resulted in damage to parts of the riser system, thus the hole was suspended at 2005 mbsf but left for future re-entry. The revised operation plan included additional riserless logging and coring of key targets not sampled during previous NanTroSEIZE expeditions, but relevant to comprehensively characterize the alteration stage of the oceanic basement input to the subduction zone, the early stage of Kumano Basin evolution and the recent activity of the shallow mega splay fault zone system and submarine landslides. Here we present preliminary results from IODP Exp. 338: Logging While Drilling (LWD), mud gas monitoring and analysis on cuttings from the deep riser hole characterize two lithological units within the internal accretionary prism, separated by a prominent fault zone at ~1640 mbsf. Internal style of deformation, downhole increase of thermogenically formed formation gas and evidence for mechanical compaction and cementation document a complex structural evolution and provide unprecedented insights into the mechanical state and behavior of the wedge at depth. Additionally, multiple samples of the unconformity between the Kumano Basin and accretionary prism

  17. The Ds1 Transposon Provides Messages That Yield Unique Profiles of Protein Isoforms and Acts Synergistically With Ds to Enrich Proteome Complexity via Exonization.

    Science.gov (United States)

    Charng, Yuh-Chyang; Hsu, Lung-Hsin; Liu, Li-Yu Daisy

    2017-01-01

    In exonization events, Ds1 may provide donor and/or acceptor sites for splicing after inserting into genes and be incorporated into new transcripts with new exon(s). In this study, the protein variants of Ds1 exonization yielding additional functional profile(s) were studied. Unlike Ds exonization, which creates new profiles mostly by incorporating flanking intron sequences with the Ds message, Ds1 exonization additionally creates new profiles through the presence or absence of Ds1 messages. The number of unique functional profiles harboring Ds1 messages is 1.3-fold more than that of functional profiles without Ds1 messages. The highly similar 11 protein isoforms at a single insertion site also contribute to proteome complexity enrichment by exclusively creating new profiles. Particularly, Ds1 exonization produces 459 unique profiles, of which 129 cannot be built by Ds. We thus conclude that Ds and Ds1 are independent but synergistic in their capacity to enrich proteome complexity through exonization.

  18. Subduction & orogeny: Introduction to the special volume

    Science.gov (United States)

    Rolland, Y.; Bosch, D.; Guillot, S.; de Sigoyer, J.; Martinod, J.; Agard, P.; Yamato, P.

    2016-05-01

    Subduction processes play a major role in plate tectonics and the subsequent geological evolution of Earth. This special issue focuses on ongoing research in subduction dynamics to a large extent (oceanic subduction, continental subduction, obduction…) for both past and active subduction zones and into mountain building processes and the early evolution of orogens. It puts together various approaches combining geophysics (imaging of subduction zones), petrology/geochemistry (metamorphic analysis of HP-UHP rocks, fluid geochemistry and magmatic signal, geochronology), seismology and geodesy (present-day evolution of subduction zones, active tectonics), structural geology (structure and evolution of mountain belts), and numerical modelling to provide a full spectrum of tools that can be used to constrain the nature and evolution of subduction processes and orogeny. Studies presented in this special issue range from the long-term (orogenic cycle) to short-term (seismic cycle).

  19. A unique missense allele of BAF155, a core BAF chromatin remodeling complex protein, causes neural tube closure defects in mice.

    Science.gov (United States)

    Harmacek, Laura; Watkins-Chow, Dawn E; Chen, Jianfu; Jones, Kenneth L; Pavan, William J; Salbaum, J Michael; Niswander, Lee

    2014-05-01

    Failure of embryonic neural tube closure results in the second most common class of birth defects known as neural tube defects (NTDs). While NTDs are likely the result of complex multigenic dysfunction, it is not known whether polymorphisms in epigenetic regulators may be risk factors for NTDs. Here we characterized Baf155(msp3) , a unique ENU-induced allele in mice. Homozygous Baf155(mps3) embryos exhibit highly penetrant exencephaly, allowing us to investigate the roles of an assembled, but malfunctional BAF chromatin remodeling complex in vivo at the time of neural tube closure. Evidence of defects in proliferation and apoptosis were found within the neural tube. RNA-Seq analysis revealed that surprisingly few genes showed altered expression in Baf155 mutant neural tissue, given the broad epigenetic role of the BAF complex, but included genes involved in neural development and cell survival. Moreover, gene expression changes between individual mutants were variable even though the NTD was consistently observed. This suggests that inconsistent gene regulation contributes to failed neural tube closure. These results shed light on the role of the BAF complex in the process of neural tube closure and highlight the importance of studying missense alleles to understand epigenetic regulation during critical phases of development.

  20. Unique syndio-selectivity in CO/styrene copolymerization reaction catalyzed by palladium complexes with 2-(2'-oxazolinyl)-1,10-phenanthrolines.

    Science.gov (United States)

    Meduri, Angelo; Cozzula, Daniela; D'Amora, Angela; Zangrando, Ennio; Gladiali, Serafino; Milani, Barbara

    2012-07-07

    The reaction of the neutral Pd complex [Pd(CH(3))Cl(cod)] with the potentially terdentate 2-oxazolinyl phenanthroline ligands 1-3 affords the corresponding cationic dinuclear Pd-complexes 1a-3a, which can be isolated in the solid state in good yields. By treatment with AgPF(6) the complexes 1a-3a were converted into the corresponding hexafluorophosphate derivatives 1b-3b, where both the ligand units feature a terdentate coordination around the two Pd-centres with the phenanthroline fragment of each unit displaying a chelate coordination to one Pd-centre, while the corresponding oxazolinyl pendant acts as a bridging ligand towards the second Pd-centre. The persistence of this dimeric structure of 1b-3b in CD(2)Cl(2) solution was confirmed by (15)N-NMR experiments at natural abundance, which clearly show the binding to the metal of all of the nitrogen donors, as well as the overall C(2) symmetry of the compound. In consequence of the different strengths of the relevant ion-pair, the dimeric structure of the complex undergoes partial fragmentation in the case of the chloride derivatives 1a-3a, as evidenced from the (15)N-NMR spectra. Complexes 1b-3b are active catalysts in styrene alternate carbonylation, where, under very mild conditions (30 °C and 1 atm of CO), they provide oligomers with 3-5 repetitive units as the exclusive or prevailing product. When traces of the CO/styrene polyketones are also formed, their (13)C-NMR characterization shows that they are stereochemically homogeneous with a unique syndio-tacticity. This result implies that Pd-complexes able to induce a complete enantioface discrimination in the insertion step of the alkene during the catalytic cycle of the styrene alternate carbonylation have been produced for the first time.

  1. 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

  2. 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.

  3. Geodynamics of the northern Andes: Subductions and intracontinental deformation (Colombia)

    Science.gov (United States)

    Taboada, Alfredo; Rivera, Luis A.; Fuenzalida, AndréS.; Cisternas, Armando; Philip, Hervé; Bijwaard, Harmen; Olaya, José; Rivera, Clara

    2000-10-01

    New regional seismological data acquired in Colombia during 1993 to 1996 and tectonic field data from the Eastern Cordillera (EC) permit a reexamination of the complex geodynamics of northwestern South America. The effect of the accretion of the Baudó-Panama oceanic arc, which began 12 Myr ago, is highlighted in connection with mountain building in the EC. The Istmina and Ibagué faults in the south and the Santa Marta-Bucaramanga fault to the northeast limit an E-SE moving continental wedge. Progressive indentation of the wedge is absorbed along reverse faults located in the foothills of the Cordilleras (northward of 5°N) and transpressive deformation in the Santander Massif. Crustal seismicity in Colombia is accurately correlated with active faults showing neotectonic morphological evidences. Intermediate seismicity allows to identify a N-NE trending subduction segment beneath the EC, which plunges toward the E-SE. This subduction is interpreted as a remnant of the paleo-Caribbean plateau (PCP) as suggested by geological and tomographic profiles. The PCP shows a low-angle subduction northward of 5.2°N and is limited southward by a major E-W transpressive shear zone. Normal oceanic subduction of the Nazca plate (NP) ends abruptly at the southern limit of the Baudó Range. Northward, the NP subducts beneath the Chocó block, overlapping the southern part of the PCP. Cenozoic shortening in the EC estimated from a balanced section is ˜120 km. Stress analysis of fault slip data in the EC (northward of 4°N), indicates an ˜E-SE orientation of σ1 in agreement with the PCP subduction direction. Northward, near Bucaramanga, two stress solutions were observed: (1) a late Andean N80°E compression and (2) an early Andean NW-SE compression.

  4. 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

  5. The Structure of the RAGE:S100A6 Complex Reveals a Unique Mode of Homodimerization for S100 Proteins.

    Science.gov (United States)

    Yatime, Laure; Betzer, Cristine; Jensen, Rasmus Kjeldsen; Mortensen, Sofia; Jensen, Poul Henning; Andersen, Gregers Rom

    2016-12-06

    S100 proteins are calcium-dependent regulators of homeostatic processes. Upon cellular response to stress, and notably during tumorigenesis, they relocalize to the extracellular environment where they induce pro-inflammatory signals by activating the receptor for advanced glycation end products (RAGE), thereby facilitating tumor growth and metastasis. Despite its importance in sustaining inflammation, the structural basis for RAGE-S100 crosstalk is still unknown. Here we report two crystal structures of the RAGE:S100A6 complex encompassing a full-length RAGE ectodomain. The structures, in combination with a comprehensive interaction analysis, suggest that the primary S100A6 binding site is formed by the RAGE C1 domain. Complex formation with S100A6 induces a unique dimeric conformation of RAGE that appears suited for signal transduction and intracellular effector recruitment. Intriguingly, S100A6 adopts a dimeric conformation radically different from all known S100 dimers. We discuss the physiological relevance of this non-canonical homodimeric form in vivo. Copyright © 2016 Elsevier Ltd. All rights reserved.

  6. Formation of the adakite-like granitoid complex and porphyry copper-gold deposit in Shaxi from southern Tancheng-Lujiang fault belt: A clue to the West Pacific plate subduction

    Institute of Scientific and Technical Information of China (English)

    LAN Xianghua; YANG Xiaoyong; YU Liangfan; ZHANG Qianming

    2009-01-01

    On the basis of the geological and geochemical studies, including chemical analysis of bulk rocks, rare-earth and trace element studies, fluid inclusion, and S and O isotopic analyses, the authors described the geo-logical background of the deposit in detail and presented significant proofs for the conditions of formation of the Shaxi porphyry copper-gold deposit. Compared with other large and supper-large porphyry copper deposits in China and the adjacent Cu-Au mineralized areas, the ore-forming processes and conditions were analyzed; and the possibil-ity of forming large porphyry copper deposits in the Shaxi area was discussed. The present study indicated that the ore-forming fluid and material were mainly of magmatic origin, while meteoric water played a certain role in the ore-forming processes. Interactions between subducting and overriding plates provided a major driving force for the formation of igneous rocks and the deposition of metal elements in East China since Jurassic. Based on the geo-chemical data of the Shaxi intrusive, it is found that the copper (gold) mineralization is closely related to the genesis of adakite-like intrusive in the Shaxi area. This adakite-like intrusive was formed in the subduction environment as a result of the subduction of the West Pacific plate toward the East China continent, where there is a great potential-ity to form a large porphyry copper deposit.

  7. Rheological evolution of subducting slabs

    Science.gov (United States)

    Hirth, G.

    2016-12-01

    The mechanical behavior of subducting lithosphere depends on both the rheological evolution of the slab and how the slab is modified prior to subduction. Geophysical data demonstrate that the combination of thermal evolution and deformation lead to alteration of the slab at both mid-ocean ridges and the outer rise of subduction zones. In addition, the locations of earthquakes in these locations are generally consistent with both extrapolation of laboratory data that constrain the depth to the brittle-plastic transition, and deformation mechanisms inferred from microstructural analysis of mantle rocks recovered from the oceanic lithosphere. However, the frictional properties of both mantle aggregates and their alteration products suggest that linking the location of lithospheric earthquakes to regions that become hydrothermally altered is not straightforward. Furthermore, the inferred link between the location of intermediate-depth seismicity and the conditions of dehydration reactions is challenged by laboratory studies on dehydration embrittlement. In this presentation, I will introduce these apparent discrepancies; provide some possible resolutions for them based on scaling of laboratory data and discuss the implications for how an integrated understanding of slab rheology informs our understanding of the mechanical and geochemical evolution of the slab.

  8. A unique iridium(III) complex-based chemosensor for multi-signal detection and multi-channel imaging of hypochlorous acid in liver injury.

    Science.gov (United States)

    Zhang, Feiyue; Liang, Xiaowen; Zhang, Wenzhu; Wang, Yong-Lei; Wang, Haolu; Mohammed, Yousuf H; Song, Bo; Zhang, Run; Yuan, Jingli

    2017-01-15

    Although hypochlorous acid (HOCl) has long been associated with a number of inflammatory diseases in mammalian bodies, the functions of HOCl in specific organs at abnormal conditions, such as liver injury, remain unclear due to its high reactivity and the lack of effective methods for its detection. Herein, a unique Ir(III) complex-based chemosensor, Ir-Fc, was developed for highly sensitive and selective detection of HOCl. Ir-Fc was designed by incorporating a ferrocene (Fc) quencher to a Ir(III) complex through a HOCl-responsive linker. In the presence of HOCl, the fast cleavage of Fc moiety in less than 1s led to the enhancement of photoluminescence (PL) and electrochemical luminescence (ECL), by which the concentration of HOCl was determined by both PL and ECL analysis. Taking advantages of excellent properties of Ir(III) complexes, optical and electrochemical analyses of the response of Ir-Fc towards HOCl were fully investigated. Followed by the measurements of low cytotoxicity of Ir-Fc by MTT analysis, one-photon (OP), two-photon (TP) and lifetime imaging experiments were conducted to visualise the generation of HOCl in live microphage and HepG2 cells, and in zebrafish and mouse, respectively. Furthermore, the generation and distribution of HOCl in liver cells and liver injury of zebrafish and mouse were investigated. The results demonstrated the applicability of Ir-Fc as an effective chemosensor for imaging of HOCl generation in mitochondria of cells and liver injury in vivo, implying the potential of Ir-Fc for biomedical diagnosis and monitoring applications.

  9. 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

  10. Mantle circulation and the lateral migration of subducted slabs

    Science.gov (United States)

    Garfunkel, Z.; Anderson, C. A.; Schubert, G.

    1986-01-01

    The geometry of transverse migration of subducted lithospheric slabs is examined, and the way in which this influences the flow in the mantle is studied. The migration of subducted slabs generally appears to be retrograde (at rates of 10-25 mm/yr), so that the descent of material is actually steeper than the slab dip. Retrograde slab migration is probably caused by the tendence of negatively buoyant slabs to sink in the surrounding mantle. The properties of the flow driven by such retrograde slab migration are explored in simple two-dimensional models. The results are used as a guide to infer the contribution of retrograde slab motion to the more complex mantle flow and to examine some consequences of the additional component of mantle flow. It is shown that slab migration is an important factor that causes mantle flow to be geometrically complex and time dependent.

  11. A G-quadruplex-binding macrodomain within the "SARS-unique domain" is essential for the activity of the SARS-coronavirus replication-transcription complex.

    Science.gov (United States)

    Kusov, Yuri; Tan, Jinzhi; Alvarez, Enrique; Enjuanes, Luis; Hilgenfeld, Rolf

    2015-10-01

    The multi-domain non-structural protein 3 of SARS-coronavirus is a component of the viral replication/transcription complex (RTC). Among other domains, it contains three sequentially arranged macrodomains: the X domain and subdomains SUD-N as well as SUD-M within the "SARS-unique domain". The X domain was proposed to be an ADP-ribose-1"-phosphatase or a poly(ADP-ribose)-binding protein, whereas SUD-NM binds oligo(G)-nucleotides capable of forming G-quadruplexes. Here, we describe the application of a reverse genetic approach to assess the importance of these macrodomains for the activity of the SARS-CoV RTC. To this end, Renilla luciferase-encoding SARS-CoV replicons with selectively deleted macrodomains were constructed and their ability to modulate the RTC activity was examined. While the SUD-N and the X domains were found to be dispensable, the SUD-M domain was crucial for viral genome replication/transcription. Moreover, alanine replacement of charged amino-acid residues of the SUD-M domain, which are likely involved in G-quadruplex-binding, caused abrogation of RTC activity. Copyright © 2015 Elsevier Inc. All rights reserved.

  12. An Analysis of Unique Aerial Photographs of Atmospheric Eddies in Marine Stratocumulus Clouds Downwind of Complex Terrain Along the California Coast

    Science.gov (United States)

    Muller, B. M.; Herbster, C. G.; Mosher, F. R.

    2013-12-01

    Unique aerial photographs of atmospheric eddies in marine stratocumulus clouds downwind of complex terrain along the California coast are presented and analyzed. While satellite imagery of similar eddies have appeared in the scientific literature since the 1960's, it is believed that these are the first close-up photographs of such eddies, taken from an airplane, to appear in publication. Two photographs by a commercial pilot, flying California coastal routes, are presented: one from July 16, 2006 downwind of Santa Cruz Island, a 740 m peak bordering the Santa Barbara Channel off the California coast; and one from September 12, 2006 near Grover Beach, California, downwind of a headland containing the San Luis Range, a region of complex terrain near San Luis Obispo, California, with ridges ranging approximately from 240 to 550 m elevation. Both eddies occurred in the lee of inversion-penetrating terrain, and were marked by a cyclonic vortex in the clouds with a striking cloud-free 'eye' feature roughly 3 km in diameter. The Santa Cruz Island eddy was 25 km in length and 9-10 km in width, while the Grover Beach eddy was 17 km in length and had a width of 9 km, placing it in the meso-gamma scale of atmospheric features. GOES (Geostationary Operational Environmental Satellite) imagery for both cases was obtained and help to define the lifecycle and motions of the eddies captured in the snapshots. Relevant meteorological observations for the Santa Cruz Island eddy were not located, but in-situ observations from the Diablo Canyon Nuclear Power Plant, California Polytechnic State University (Cal Poly) pier, and the San Luis Obispo County Air Pollution Control District, made possible a more detailed examination of the Grover Beach eddy and its structure. Additionally, we offer speculation on an eddy formation mechanism consistent with the satellite and in-situ observations described in this presentation, and hypotheses from the literature on low Froude number, continuously

  13. Subduction erosion and accretion in the Solomon Sea region

    Science.gov (United States)

    Honza, Eiichi; Miyazaki, Teruki; Lock, Jo

    1989-03-01

    The Solomon Sea region is an area of intense tectonic activity characterized by structural complexity, a high level of seismicity and volcanism, and rapid evolution of plate boundaries. There is little accretion in the eastern New Britain Trench. Accretion gradually increases westward with thick accretion in the western New Britain Trench and in the Trobriand Subduction System. The thick accretion in the western part of the New Britain Trench may be a result of collision from the north of Finisterre-Huon block with New Guinea mainland. The present boundary of the collision is along the Ram-Markham fault. Deformation structures and present day seismicity suggest that the northern block is under compression. Accretion has occurred in the sediment filled trenches in the Solomon Sea. The scale of the accretionary wedge depends on the amount of trench-fill sediment available. It is unlikely that there is no sediment supply to the eastern part of the New Britain Trench where no accretion is observed and subduction erosion may be occurring. There are two possible mechanisms for subduction erosion of sediment; either a rapid rate of subduction relative to the supply of sediment inhibiting sediment accumulation in the trench; or horizontal tensional force superimposed on both the forearc and backarc regions of the arc. Seafloor spreading in both the Manus and Woodlark basins is fan-like with nearby poles in the western margins of the basins. This may be a reflection of a horizontally compressional field in the western part and a tensional field in the eastern part of the Solomon Sea. Therefore it is possible to conclude that the consumption of sediment in the eastern New Britain Trench is related to the horizontal tensional field superimposed on both the forearc and backarc regions of the subduction system. Imbricated thrust and overthrust faults in the western New Britain Trench and Trobriand Trough are not linear over long distance, but form wavy patterns in blocks with

  14. Dynamics of Caribbean and Nazca Plate Subduction Beneath Colombia from Receiver Function Analysis

    Science.gov (United States)

    Porter, R. C.; Warren, L. M.

    2014-12-01

    The tectonics of northwestern South America are controlled by the complex interactions of the South American, Nazca, and Caribbean plates. In order to better understand subduction within the region, we utilize data recorded by the Colombian National Seismic Network to calculate P-to-S receiver functions at a range of frequencies across the nation of Colombia. Where the station spacing was dense enough, receiver functions were stacked using the Common Conversion Point (CCP) method in order to better image lateral changes in crustal and upper mantle structure. Along the Pacific margin of Colombia, where the Nazca plate is subducting beneath South America, the subducting slab dips too steeply to image it with receiver functions. However, layering and strong negative arrivals are observed in the crust above the subducting slab where active volcanoes are present. The presence of these arrivals is possibly indicative of slab dehydration and the presence of partial melt within the crust. In northeastern Colombia, the Caribbean plate is subducting beneath South America at an oblique angle. Along the direction of convergence, the slab extends ~500 km inland with a relatively shallow dip before steepening. Preliminary receiver function images from this region show a shallowly-dipping negative arrival, interpreted as the top of the slab. This arrival is underlain by a positive conversion, interpreted as the down-going oceanic Moho. As the dip of the seismicity associated with the subducting slab steepens, these arrivals are no longer observed within the receiver function stacks. These cross sections of the Caribbean plate subduction are consistent with the idea that phase changes within the downgoing oceanic crust and mantle are controlling the slab buoyancy and, as a result, the angle of subduction. As the receiver functions are refined and further combined with local earthquake locations, we will better be able to understand the location of earthquakes within the subducting

  15. The dynamics of double slab subduction from numerical and semi-analytic models

    Science.gov (United States)

    Holt, A.; Royden, L.; Becker, T. W.

    2015-12-01

    Regional interactions between multiple subducting slabs have been proposed to explain enigmatic slab kinematics in a number of subduction zones, a pertinent example being the rapid pre-collisional plate convergence of India and Eurasia. However, dynamically consistent 3-D numerical models of double subduction have yet to be explored, and so the physics of such double slab systems remain poorly understood. Here we build on the comparison of a fully numerical finite element model (CitcomCU) and a time-dependent semi-analytic subduction models (FAST) presented for single subduction systems (Royden et. al., 2015 AGU Fall Abstract) to explore how subducting slab kinematics, particularly trench and plate motions, can be affected by the presence of an additional slab, with all of the possible slab dip direction permutations. A second subducting slab gives rise to a more complex dynamic pressure and mantle flow fields, and an additional slab pull force that is transmitted across the subduction zone interface. While the general relationships among plate velocity, trench velocity, asthenospheric pressure drop, and plate coupling modes are similar to those observed for the single slab case, we find that multiple subducting slabs can interact with each other and indeed induce slab kinematics that deviate significantly from those observed for the equivalent single slab models. References Jagoutz, O., Royden, L. H., Holt, A. F. & Becker, T. W., 2015, Nature Geo., 8, 10.1038/NGEO2418. Moresi, L. N. & Gurnis, M., 1996, Earth Planet. Sci. Lett., 138, 15-28. Royden, L. H. & Husson, L., 2006, Geophys. J. Int. 167, 881-905. Zhong, S., 2006, J. Geophys. Res., 111, doi: 10.1029/2005JB003972.

  16. Influence of Subducting Plate Geometry on Upper Plate Deformation at Orogen Syntaxes: A Thermomechanical Modeling Approach

    Science.gov (United States)

    Nettesheim, Matthias; Ehlers, Todd; Whipp, David

    2016-04-01

    Syntaxes are short, convex bends in the otherwise slightly concave plate boundaries of subduction zones. These regions are of scientific interest because some syntaxes (e.g., the Himalaya or St. Elias region in Alaska) exhibit exceptionally rapid, focused rock uplift. These areas have led to a hypothesized connection between erosional and tectonic processes (top-down control), but have so far neglected the unique 3D geometry of the subducting plates at these locations. In this study, we contribute to this discussion by exploring the idea that subduction geometry may be sufficient to trigger focused tectonic uplift in the overriding plate (a bottom-up control). For this, we use a fully coupled 3D thermomechanical model that includes thermochronometric age prediction. The downgoing plate is approximated as spherical indenter of high rigidity, whereas both viscous and visco-plastic material properties are used to model deformation in the overriding plate. We also consider the influence of the curvature of the subduction zone and the ratio of subduction velocity to subduction zone advance. We evaluate these models with respect to their effect on the upper plate exhumation rates and localization. Results indicate that increasing curvature of the indenter and a stronger upper crust lead to more focused tectonic uplift, whereas slab advance causes the uplift focus to migrate and thus may hinder the emergence of a positive feedback.

  17. From oceanic subduction to continental collision: An overview of HP-UHP metamorphic rocks in the North Qaidam UHP belt, NW China

    Science.gov (United States)

    Zhang, Guibin; Zhang, Lifei; Christy, Andrew G.

    2013-02-01

    The North Qaidam UHPM belt is unique among "continental type" subduction zones in showing well-preserved subducted oceanic relics that predate continental subduction and collision. We review petrologic, thermobarometric, geochemical and geochronological studies for the Yuka, Luliang Shan, Xitieshan and Dulan terranes in this belt. UHP conditions are demonstrated by coesite inclusions in eclogite and country gneiss, and diamond inclusions from garnet peridotite. The relict subducted oceanic lithology crops out in the Shaliuhe cross-section in Dulan terrane; it originated as the floor of a Paleo-Qilian Ocean that existed between Qaidam and Qilian blocks before the early Ordovician. Whereas most eclogites of this belt are derived from mafic rocks of either a Neoproterozoic continental rift or incipient oceanic basin setting, which were subducted along with continental rocks in the early Paleozoic. The data, especially the two protolith sources for eclogites, demonstrate tectonic evolution of the North Qaidam UHPM belt from oceanic subduction to continental collision.

  18. Origin and dynamics of depositionary subduction margins

    Science.gov (United States)

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

    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.

  19. 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.

  20. Lithospheric Subduction on Earth and Venus?

    Science.gov (United States)

    Sandwell, D. T.; Garcia, E.; Stegman, D. R.; Schubert, G.

    2016-12-01

    There are three mechanisms by which terrestrial planets can shed excess heat: conduction across a surface thermal boundary layer; advection of heat through volcanic pipes; and mobile plates/subduction. On the Earth about 30% is released by conduction and 70% by subduction. The dominant mode of heat transport on Venus is largely unknown. Plate flexure models rule out significant heat loss by conduction and the resurfacing from active volcanism is in discordance with a surface age of 600 Ma. There are 9000 km of trenches on Venus that may have been subduction sites but they do not appear active today and are only 25% of the length of the subduction zones on the Earth. Turcotte and others have proposed an episodic recycling model that has short bursts ( 150 Ma) of plate tectonic activity followed by long periods ( 450 Ma) of stagnant lid convection. This talk will review the arguments for and against subduction zones on Venus and discuss possible new satellite observations that could help resolve the subduction issue. Figure Caption. (a) Global mosaic of Magellan SAR imagery. (b) Zoom of area along the Artemis trench, which has similar topography and fracture patterns as the Aleutian subduction zone on Earth. Trench and outer rise lines were digitized from the matching topography image (not shown). The Magellan SAR imagery and topography, displayed on Google Earth, can be downloaded at http://topex.ucsd.edu/venus/index.html

  1. Dehydration-driven topotaxy in subduction zones

    Science.gov (United States)

    Padrón-Navarta, José Alberto; Tommasi, Andréa; Garrido, Carlos J.

    2014-05-01

    // (100)opx//(001)chl. The relation [010]atg// [001]ol //[001]opx can also be inferred but it is weaker. Similar topotactic relations are observed in the Cerro del Almirez samples, but the CPOs are weaker and more complex. The complexity arises from constant interfacial angles and systematic low-index interfacial contacts between orthopyroxene-olivine-chlorite (e.g. (001)chl // (100)opx). As a consequence the inheritance from the antigorite serpentinite is partially obliterated. Compaction-related microstructural features are also present including: (1) smooth bending of the former foliation and diffuse olivine veinlets perpendicular to it, (2) gradual crystallographic misorientation (up to 15º) of prismatic enstatite due to buckling, (3) localized orthoenstatite(Pbca)/low clinoenstatite (P21/c) inversion, and (4) brittle fracturing of prismatic enstatite wrapped by plastically deformed chlorite. These observations suggest that topotactic crystrallographic relations are dominant in undrained systems, but that the mechanisms allowing for compaction and fluid draining significantly affect the final texture in drained systems. Because the second case prevails in subduction zones, compaction mechanisms need to be better understood for modelling the development of CPOs after foliated protoliths in the slab and the mantle wedge. [1] Putnis, A., 2009. Reviews in Mineralogy and Geochemistry 70, 87-124. [2] Boudier, F., et al. 2010 J. Petrology 51, 495-512.

  2. 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.

  3. Earthquake faulting in subduction zones: insights from fault rocks in accretionary prisms

    Science.gov (United States)

    Ujiie, Kohtaro; Kimura, Gaku

    2014-12-01

    Subduction earthquakes on plate-boundary megathrusts accommodate most of the global seismic moment release, frequently resulting in devastating damage by ground shaking and tsunamis. As many earthquakes occur in deep-sea regions, the dynamics of earthquake faulting in subduction zones is poorly understood. However, the Integrated Ocean Drilling Program (IODP) Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) and fault rock studies in accretionary prisms exhumed from source depths of subduction earthquakes have greatly improved our understanding of earthquake faulting in subduction zones. Here, we review key advances that have been made over the last decade in the studies of fault rocks and in laboratory experiments using fault zone materials, with a particular focus on the Nankai Trough subduction zone and its on-land analog, the Shimanto accretionary complex in Japan. New insights into earthquake faulting in subduction zones are summarized in terms of the following: (1) the occurrence of seismic slip along velocity-strengthening materials both at shallow and deep depths; (2) dynamic weakening of faults by melt lubrication and fluidization, and possible factors controlling coseismic deformation mechanisms; (3) fluid-rock interactions and mineralogical and geochemical changes during earthquakes; and (4) geological and experimental aspects of slow earthquakes.

  4. Carbon dioxide released from subduction zones by fluid-mediated reactions

    Science.gov (United States)

    Ague, Jay J.; Nicolescu, Stefan

    2014-05-01

    The balance between the subduction of carbonate mineral-bearing rocks into Earth's mantle and the return of CO2 to the atmosphere by volcanic and metamorphic degassing is critical to the carbon cycle. Carbon is thought to be released from subducted rocks mostly by simple devolatilization reactions. However, these reactions will also retain large amounts of carbon within the subducting slab and have difficulty in accounting for the mass of CO2 emitted from volcanic arcs. Carbon release may therefore occur via fluid-induced dissolution of calcium carbonate. Here we use carbonate δ18O and δ13C systematics, combined with analyses of rock and fluid inclusion mineralogy and geochemistry, to investigate the alteration of the exhumed Eocene Cycladic subduction complex on the Syros and Tinos islands, Greece. We find that in marble rocks adjacent to two fluid conduits that were active during subduction, the abundance of calcium carbonate drastically decreases approaching the conduits, whereas silicate minerals increase. Up to 60-90% of the CO2 was released from the rocks--far greater than expected via simple devolatilization reactions. The δ18O of the carbonate minerals is 5-10 lighter than is typical for metamorphosed carbonate rocks, implying that isotopically light oxygen was transported by fluid infiltration from the surroundings. We suggest that fluid-mediated carbonate mineral removal, accompanied by silicate mineral precipitation, provides a mechanism for the release of enormous amounts of CO2 from subduction zones.

  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. 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.

  7. A numerical reference model for themomechanical subduction

    DEFF Research Database (Denmark)

    Quinquis, Matthieu; Chemia, Zurab; Tosi, Nicola;

    2010-01-01

    Building an advanced numerical model of subduction requires choosing values for various geometrical parameters and material properties, among others, the initial lithosphere thicknesses, representative lithological types and their mechanical and thermal properties, rheologies, initial temperature...

  8. Orthopyroxene refertilization in subduction environment.

    Science.gov (United States)

    Melchiorre, Massimiliano; Dantas, Celine; Faccini, Barbara; Bonadiman, Costanza; Coltorti, Massimo; Gregoire, Michel

    2010-05-01

    One of the most fascinating and controversial debate in Earth Science concerns the chemical and mineralogical modifications affecting the mantle during melts/fluids percolation. Particularly in subduction settings it is important to well constrain the role and extent of silica enrichment related to subducted slab dehydratation or melting. This topic is addressed in the present study where a new suite of mantle xenoliths from Estancia Sol de Mayo (ESM, Patagonia) are investigated and compared with other xenolith occurrences nearby. ESM peridotites are mainly represented by spinel-bearing protogranular harzburgites and dunites, with minor lherzolites and one wehrlite. They are avoid of modal metasomatic features, such as spongy cpx, reaction rims around spinel and/or orthopyroxene, glassy patches, as well as of any hydrous minerals. The most interesting petrographic features is one dunitic sample cut by a vein of orthopyroxene (secondary orthopyroxenes, opx2). These are texturally and chemically different from those belonging to the typical protogranular peridotites (primary opx, opx1). Opx1 have mg# (MgO/MgO+FeO, at%) between 88.02 and 92.76 and Al2O3 content varying between 1.37 and 2.97 wt% while opx2 in the vein presents a more restricted range of mg# values at about 90 (89.99-90.88) with a significantly higher Al2O3 content (3.02-3.52 wt%). Similar opx veins were also found in two other Patagonian localities, Cerro Fraile (CF) and Gobernador Gregores (GG), together with orthopyroxenites and wehrlites. A comparison between the two generation of opxs from these localities show two clearly separated Al2O3 enrichment trends, which cannot be explained by a simple partial melting process: one at almost constant mg# with Al2O3 values varying from 1.33 and 4.20 wt% and the other reaching 5.03%wt of Al2O3 but with mg# varying from 86.89 to 67.37 (including the pyroxenites). Textural and chemical features suggest that the latter trend may be accounted for a

  9. Subduction History and the Evolution of Earth's Lower Mantle

    Science.gov (United States)

    Bull, Abigail; Shephard, Grace; Torsvik, Trond

    2016-04-01

    Understanding the complex structure, dynamics and evolution of the deep mantle is a fundamental goal in solid Earth geophysics. Close to the core-mantle boundary, seismic images reveal a mantle characterised by (1) higher than average shear wave speeds beneath Asia and encircling the Pacific, consistent with sub ducting lithosphere beneath regions of ancient subduction, and (2) large regions of anomalously low seismic wavespeeds beneath Africa and the Central Pacific. The anomalously slow areas are often referred to as Large Low Shear Velocity Provinces (LLSVPs) due to the reduced velocity of seismic waves passing through them. The origin, composition and long-term evolution of the LLSVPs remain enigmatic. Geochemical inferences of multiple chemical reservoirs at depth, strong seismic contrasts, increased density, and an anticorrelation of shear wave velocity to bulk sound velocity in the anomalous regions imply that heterogeneities in both temperature and composition may be required to explain the seismic observations. Consequently, heterogeneous mantle models place the anomalies into the context of thermochemical piles, characterised by an anomalous component whose intrinsic density is a few percent higher relative to that of the surrounding mantle. Several hypotheses have arisen to explain the LLSVPs in the context of large-scale mantle convection. One end member scenario suggests that the LLSVPs are relatively mobile features over short timescales and thus are strongly affected by supercontinent cycles and Earth's plate motion history. In this scenario, the African LLSVP formed as a result of return flow in the mantle due to circum-Pangean subduction (~240 Ma), contrasting a much older Pacific LLSVP, which may be linked to the Rodinia supercontinent and is implied to have remained largely unchanged since Rodinian breakup (~750-700 Ma). This propounds that Earth's plate motion history plays a controlling role in LLSVP development, suggesting that the location

  10. Spontaneous Nucleation of Subduction Zones in the Western Pacific During Middle Eocene Time: Evidence From the IBM Forearc Ophiolite

    Science.gov (United States)

    Stern, R. J.

    2001-12-01

    Subduction zones nucleate in two fundamentally different ways. Induced nucleation is a response to continuing plate convergence following a collision event and requires the lithosphere to fail under compression; no change in plate motion is expected. Spontaneous nucleation of a subduction zone (SNSZ) manifests failure of old lithosphere due to gravitation instability. SNSZ doesn't require plate convergence to occur but major changes in plate motion are expected. SNSZ is possible where old oceanic lithosphere is unusually dense (old continental margins) or weak (along fracture zones). The western edge of the Pacific plate spontaneously reorganized as a convergent margin during Middle Eocene time ( ~50-42 Ma) and is the best known example of SNSZ. The unusual nature of this episode is preserved in the Izu-Bonin-Mariana (IBM) forearc, where pillow basalts, dyke complexes, gabbro, and harzburgitic mantle define an in situ ophiolite. The IBM forearc ophiolite requires that SNSZ was accompanied by a strongly magmatic episode of seafloor spreading. Spreading so close to the present trench requires asthenospheric upwelling where strong mantle downwelling now occurs. Abundant boninite, formed by melting harzburgite, in IBM forearc sections further demonstrates the unique nature of the IBM subduction initiation event. IBM SNSZ spans the period from beginning of magmatic construction of the IBM `forearc ophiolite' about 50 Ma to the change in Pacific Plate motion at 43 Ma marking the start of true subduction. Events during this stage are very poorly understood but can only be explained by subsidence of part of the lithosphere to a depth such that asthenosphere flowed over it. Stern and Bloomer (1992 BGSA 104, 1621-1636) argue that this occurred along a zone of weakness associated with a N-S fracture zone but this has been criticized on the basis of paleomagnetic models requiring ~90 o CW rotation of the Philippine Sea Plate (PSP) since 43Ma. The youngest parts of the

  11. Complexity in Climatic Controls on Plant Species Distribution: Satellite Data Reveal Unique Climate for Giant Sequoia in the California Sierra Nevada

    OpenAIRE

    Waller, Eric Kindseth

    2014-01-01

    ABSTRACTComplexity in Climatic Controls on Plant Species Distribution: Satellite Data Reveal Unique Climate for Giant Sequoia in the California Sierra NevadabyEric Kindseth WallerDoctor of Philosophy in Environmental Science, Policy, and ManagementUniversity of California, BerkeleyProfessor Dennis D. Baldocchi, ChairA better understanding of the environmental controls on current plant species distribution is essential if the impacts of such diverse challenges as invasive species, changing fir...

  12. Complexity in Climatic Controls on Plant Species Distribution: Satellite Data Reveal Unique Climate for Giant Sequoia in the California Sierra Nevada

    Science.gov (United States)

    Waller, Eric Kindseth

    A better understanding of the environmental controls on current plant species distribution is essential if the impacts of such diverse challenges as invasive species, changing fire regimes, and global climate change are to be predicted and important diversity conserved. Climate, soil, hydrology, various biotic factors fire, history, and chance can all play a role, but disentangling these factors is a daunting task. Increasingly sophisticated statistical models relying on existing distributions and mapped climatic variables, among others, have been developed to try to answer these questions. Any failure to explain pattern with existing mapped climatic variables is often taken as a referendum on climate as a whole, rather than on the limitations of the particular maps or models. Every location has a unique and constantly changing climate so that any distribution could be explained by some aspect of climate. Chapter 1 of this dissertation reviews some of the major flaws in species distribution modeling and addresses concerns that climate may therefore not be predictive of, or even relevant to, species distributions. Despite problems with climate-based models, climate and climate-derived variables still have substantial merit for explaining species distribution patterns. Additional generation of relevant climate variables and improvements in other climate and climate-derived variables are still needed to demonstrate this more effectively. Satellite data have a long history of being used for vegetation mapping and even species distribution mapping. They have great potential for being used for additional climatic information, and for improved mapping of other climate and climate-derived variables. Improving the characterization of cloud cover frequency with satellite data is one way in which the mapping of important climate and climate-derived variables can be improved. An important input to water balance models, solar radiation maps could be vastly improved with a

  13. Terrane Stations: intra-oceanic subduction assembled western North America

    Science.gov (United States)

    Sigloch, K.; Mihalynuk, M. G.

    2012-12-01

    The western quarter of North America consists of accreted terranes, crustal blocks that were added to the margin in a series of collisions over the past 200 million years - but why? The most widely accepted explanation posits a scenario analogous to Andean subduction, with these terranes conveyed to the continental margin while the oceanic Farallon plate subducted under it. Yet purely Andean-style subduction under North America is questionable as a terrane delivery mechanism, since no comparable accretion sequence took place along the South American margin, and since North American terranes are of very varied provenance. We consider this geological question directly related to a geodynamical one: Why has it been so difficult to reconcile - even on the largest scale - the geometries and locations of slabs in the lower-mantle, as imaged by seismic tomography, with Cretaceous plate reconstructions of the North American west coast (unless anomalous mantle rheology or ad hoc shifts of absolute reference frame are invoked)? This problem was recognized soon after the discovery of the massive, lower-mantle "Farallon slabs" by Grand (1994), but has recently been aggravated by the discovery of additional, more westerly deep slabs (Sigloch et al. 2008), thanks to USArray. Not all of these slabs can be Farallon, unless very non-vertical and/or uneven slab sinking behavior is allowed for. As a joint solution, we offer a radical reinterpretation of paleogeography and test it quantitatively: The seas west of Cretaceous North America must have resembled today's western Pacific. The Farallon and two more plates subducted into the intra-oceanic trenches of a vast archipelago in the eastern Panthalassa (proto-Pacific) ocean, both from the east and the west. The trenches remained stationary throughout much of Jurassic and Cretaceous times, depositing the massive, near-vertical slab walls imaged in the lower mantle today. On their overriding plates, island arcs and subduction complexes

  14. A unique manganese (II) complex of 4-methoxy-pyridine-2-carboxylate: Synthesis, crystal structure, FT-IR and UV-Vis spectra and DFT calculations

    Science.gov (United States)

    Tamer, Ömer

    2017-09-01

    The first metal complex of 4-Methoxy-pyridine-2-carboxylic acid, [Mn(4-mpic)2(H2O)2], has been synthesized, and its crystal structure has been determined by X-Ray diffraction method. The FT-IR spectrum for [Mn(4-mpic)2(H2O)2] complex has been presented in this paper, as compared with that of single 4-mpic ligand. The electronic absorption spectrum recorded in DMSO solvent revealed that the ligand metal charge transfer (LMCT) interactions occur in Mn(II) complex. In order to support experimental results, density functional theory (DFT) calculations have been also carried out with the hybrid B3LYP functional. The coordination sphere of central Mn(II) ion has been evaluated by using the hyperconjugative interactions between the lone pair electrons of metal and donor atoms (N and O). The natural charge of Mn(II) ion demonstrated that the electronic transitions from metal ion to 4-mpic are higher than those in reverse direction. The carboxylate group has been determined as the most reactive side of Mn(II) complex in chemical reactions. A comparison among Mulliken, NBO and APT charges has been carried out for Mn(II) complex system. The first static hyperpolarizability parameter for Mn(II) complex has been also investigated by using B3LYP level.

  15. The Interdependence of Plate Coupling Processes, Subduction Rate, and Asthenospheric Pressure Drop across Subducting Slabs

    Science.gov (United States)

    Royden, L.; Holt, A.; Becker, T. W.

    2015-12-01

    One advantage of analytical models, in which analytic expressions are used for the various components of the subduction system, is the efficient exploration of parameter space and identification of the physical mechanisms controlling a wide breadth of slab kinematics. We show that, despite subtle differences in how plate interfaces and boundary conditions are implemented, results for single subduction from a 3-D semi-analytical model for subduction FAST (Royden & Husson, 2006; Jagoutz et al., 2015) and from the numerical finite-element model CitcomCU (Moresi & Gurnis, 1996, Zhong et al., 2006) are in excellent agreement when plate coupling (via shear stress on the plate interface) takes place in the FAST without the development of topographic relief at the plate boundary. Results from the two models are consistent across a variety of geometries, with fixed upper plate, fixed lower plate, and stress-free plate ends. When the analytical model is modified to include the development of topography above the subduction boundary, subduction rates are greatly increased, indicating a strong sensitivity of subduction to the mode of plate coupling. Rates of subduction also correlate strongly with the asthenospheric pressure drop across the subducting slab, which drives toroidal flow of the asthenosphere around the slab. When the lower plate is fixed, subduction is relatively slow and the pressure drop from below to above the slab is large, inhibiting subduction and slab roll-back. When the upper plate is fixed and when the plate ends are stress-free, subduction rates are approximately 50% faster and the corresponding asthenospheric pressure drop from below to above the slab is small, facilitating rapid subduction. This qualitative correlation between plate coupling processes, asthenospheric pressure drop, and rates of subduction can be extended to systems with more than one subduction zone (Holt et al., 2015 AGU Fall Abstract). Jagoutz, O., Royden, L., Holt, A. & Becker, T. W

  16. Genesis of Mariana shoshonites: Contribution of the subduction component

    Science.gov (United States)

    Sun, Chih-Hsien; Stern, Robert J.

    2001-01-01

    The Izu-Bonin-Mariana arc contains a unique group of shoshonitic volcanoes from along the magmatic front of this intraoceanic arc. Shoshonites are greatly enriched in incompatible elements compared to lavas typically found in primitive arc settings but have fractionations of lithophile (LIL) and high-field strength (HFSE) incompatible elements characteristic of convergent margin magmas and thus are characterized by an unusually large "subduction component." New geochemical and isotopic data for Izu-Bonin-Mariana shoshonites and related rocks are presented and interpreted to examine the origin of these enrichments. Enrichments are associated with distinctive isotopic compositions, including the most radiogenic Pb (206Pb/204Pb ˜ 19.47) and least radiogenic Nd (ɛNd ˜ 5.6) from along the magmatic front of the arc. Despite highly elevated concentrations of fluid-mobile lithophile elements in the lavas, the similarity of diagnostic element ratios (e.g., Ba/La, Pb/Ce, and U/Th) to those in mid-ocean ridge basalts and ocean island basalts indicates little role for fluid-induced elemental fractionation in the generation of these shoshonites. Modeling isotopic data allows up to 6% subducted sediments to be involved, but oxygen isotopic evidence limits this to <3%. Low-P fractionation explains most of the chemical variations observed in these shoshonites. Removal of <2% Ti-rich phases could fractionate HFSE from LIL, indicating an important role for low-P fractionation. Although many features of these shoshonites are consistent with a greater role for subducted sediments, such a role is not accompanied by an unequivocal and universal signal in both isotopic compositions and trace element abundances and fractionations. This signifies a large role for both equilibration of these melts with mantle and for low-pressure fractionation.

  17. Subduction obliquity as a prime indicator for geotherm in subduction zone

    Science.gov (United States)

    Plunder, Alexis; Thieulot, Cédric; van Hinsbergen, Douwe

    2016-04-01

    The geotherm of a subduction zone is thought to vary as a function of subduction rate and the age of the subducting lithosphere. Along a single subduction zone the rate of subduction can strongly vary due to changes in the angle between the trench and the plate convergence vector, namely the subduction obliquity. This phenomenon is observed all around the Pacific (i.e., Marianna, South America, Aleutian…). However due to observed differences in subducting lithosphere age or lateral convergence rate in nature, the quantification of temperature variation due to obliquity is not obvious. In order to investigate this effect, 3D generic numerical models were carried out using the finite element code ELEFANT. We designed a simplified setup to avoid interaction with other parameters. An ocean/ocean subduction setting was chosen and the domain is represented by a 800 × 300 × 200 km Cartesian box. The trench geometry is prescribed by means of a simple arc-tangent function. Velocity of the subducting lithosphere is prescribed using the analytical solution for corner flow and only the energy conservation equation is solved in the domain. Results are analysed after steady state is reached. First results show that the effect of the trench curvature on the geotherm with respect to the convergence direction is not negligible. A small obliquity yields isotherms which are very slightly deflected upwards where the obliquity is maximum. With an angle of ˜30°, the isotherms are deflected upwards of about 10 kilometres. Strong obliquity (i.e., angles from 60° to almost 90°) reveal extreme effects of the position of the isotherms. Further model will include other parameter as the dip of the slab and convergence rate to highlight their relative influence on the geotherm of subduction zone.

  18. 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.

  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

    2017-04-25

    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.

  20. Synthesis of antitumor azolato-bridged dinuclear platinum(ii) complexes with in vivo antitumor efficacy and unique in vitro cytotoxicity profiles.

    Science.gov (United States)

    Komeda, Seiji; Takayama, Hiroshi; Suzuki, Toshihiro; Odani, Akira; Yamori, Takao; Chikuma, Masahiko

    2013-05-01

    We synthesised four tetrazolato-bridged dinuclear Pt(ii) complexes, [{cis-Pt(NH3)2}2(μ-OH)(μ-5-R-tetrazolato-N2,N3)](n+), where R is CH3 (1), C6H5 (2), CH2COOC2H5 (3), or CH2COO(-) (4) and n = 2 (1-3) or 1 (4). Their structures were characterised by (1)H, (13)C, and (195)Pt NMR spectroscopy, mass spectrometry, and elemental analysis, and the crystal structure of 1 was determined by X-ray crystallography. The cytotoxicities of the complexes to human non-small-cell lung cancer (NSCLC) cell lines sensitive and resistant to cisplatin were assayed. Complex 1 was more cytotoxic than cisplatin in both PC-9 and PC-14 NSCLC cell lines, and cross-resistance to 1 in the cisplatin-resistant cells was largely circumvented. Complex 3 was moderately cytotoxic, whereas 2 and 4 were only marginally cytotoxic. We also determined the growth inhibitory activities of 1 and 3, as well as prototype azolato-bridged complexes [{cis-Pt(NH3)2}2(μ-OH)(μ-pyrazolato)](2+) (AMPZ), [{cis-Pt(NH3)2}2(μ-OH)(μ-1,2,3-triazolato-N1,N2)](2+) (AMTA), [{cis-Pt(NH3)2}2(μ-OH)(μ-tetrazolato-N1,N2)](2+) (5-H-X), and [{cis-Pt(NH3)2}2(μ-OH)(μ-tetrazolato-N2,N3)](2+) (5-H-Y), against a panel of 39 human cancer cell lines (JFCR39). The average 50% growth inhibition concentrations of the complexes against the JFCR39 cell lines ranged from 0.933 to 23.4 μM. The cytotoxicity fingerprints of the complexes based on the JFCR39 cytotoxicity data were similar to one another but completely different from the fingerprints of clinical platinum-based anticancer drugs. Complex 3 exhibited marked antitumor efficiency when tested in vivo on xenografts of PANC-1 pancreatic cancer in nude mice. The high potency of 3 confirmed that the tetrazolato-bridged structure exhibits high in vivo antitumor efficacy.

  1. The effect of a realistic thermal diffusivity on numerical model of a subducting slab

    Science.gov (United States)

    Maierova, P.; Steinle-Neumann, G.; Cadek, O.

    2010-12-01

    A number of numerical studies of subducting slab assume simplified (constant or only depth-dependent) models of thermal conductivity. The available mineral physics data indicate, however, that thermal diffusivity is strongly temperature- and pressure-dependent and may also vary among different mantle materials. In the present study, we examine the influence of realistic thermal properties of mantle materials on the thermal state of the upper mantle and the dynamics of subducting slabs. On the basis of the data published in mineral physics literature we compile analytical relationships that approximate the pressure and temperature dependence of thermal diffusivity for major mineral phases of the mantle (olivine, wadsleyite, ringwoodite, garnet, clinopyroxenes, stishovite and perovskite). We propose a simplified composition of mineral assemblages predominating in the subducting slab and the surrounding mantle (pyrolite, mid-ocean ridge basalt, harzburgite) and we estimate their thermal diffusivity using the Hashin-Shtrikman bounds. The resulting complex formula for the diffusivity of each aggregate is then approximated by a simpler analytical relationship that is used in our numerical model as an input parameter. For the numerical modeling we use the Elmer software (open source finite element software for multiphysical problems, see http://www.csc.fi/english/pages/elmer). We set up a 2D Cartesian thermo-mechanical steady-state model of a subducting slab. The model is partly kinematic as the flow is driven by a boundary condition on velocity that is prescribed on the top of the subducting lithospheric plate. Reology of the material is non-linear and is coupled with the thermal equation. Using the realistic relationship for thermal diffusivity of mantle materials, we compute the thermal and flow fields for different input velocity and age of the subducting plate and we compare the results against the models assuming a constant thermal diffusivity. The importance of the

  2. An Examination of Seismicity Linking the Solomon Islands and Vanuatu Subduction Zones

    Science.gov (United States)

    Neely, J. S.; Furlong, K. P.

    2015-12-01

    The Solomon Islands-Vanuatu composite subduction zone represents a tectonically complex region along the Pacific-Australia plate boundary in the southwest Pacific Ocean. Here the Australia plate subducts under the Pacific plate in two segments: the South Solomon Trench and the Vanuatu Trench. The two subducting sections are offset by a 200 km long, transform fault - the San Cristobal Trough (SCT) - which acts as a Subduction-Transform Edge Propagator (STEP) fault. The subducting segments have experienced much more frequent and larger seismic events than the STEP fault. The northern Vanuatu trench hosted a M8.0 earthquake in 2013. In 2014, at the juncture of the western terminus of the SCT and the southern South Solomon Trench, two earthquakes (M7.4 and M7.6) occurred with disparate mechanisms (dominantly thrust and strike-slip respectively), which we interpret to indicate the tearing of the Australia plate as its northern section subducts and southern section translates along the SCT. During the 2013-2014 timeframe, little seismic activity occurred along the STEP fault. However, in May 2015, three M6.8-6.9 strike-slip events occurred in rapid succession as the STEP fault ruptured east to west. These recent events share similarities with a 1993 strike-slip STEP sequence on the SCT. Analysis of the 1993 and 2015 STEP earthquake sequences provides constraints on the plate boundary geometry of this major transform fault. Preliminary research suggests that plate motion along the STEP fault is partitioned between larger east-west oriented strike-slip events and smaller north-south thrust earthquakes. Additionally, the differences in seismic activity between the subducting slabs and the STEP fault can provide insights into how stress is transferred along the plate boundary and the mechanisms by which that stress is released.

  3. High efficiency light harvesting by carotenoids in the LH2 complex from photosynthetic bacteria: unique adaptation to growth under low-light conditions.

    Science.gov (United States)

    Magdaong, Nikki M; LaFountain, Amy M; Greco, Jordan A; Gardiner, Alastair T; Carey, Anne-Marie; Cogdell, Richard J; Gibson, George N; Birge, Robert R; Frank, Harry A

    2014-09-25

    Rhodopin, rhodopinal, and their glucoside derivatives are carotenoids that accumulate in different amounts in the photosynthetic bacterium, Rhodoblastus (Rbl.) acidophilus strain 7050, depending on the intensity of the light under which the organism is grown. The different growth conditions also have a profound effect on the spectra of the bacteriochlorophyll (BChl) pigments that assemble in the major LH2 light-harvesting pigment-protein complex. Under high-light conditions the well-characterized B800-850 LH2 complex is formed and accumulates rhodopin and rhodopin glucoside as the primary carotenoids. Under low-light conditions, a variant LH2, denoted B800-820, is formed, and rhodopinal and rhodopinal glucoside are the most abundant carotenoids. The present investigation compares and contrasts the spectral properties and dynamics of the excited states of rhodopin and rhodopinal in solution. In addition, the systematic differences in pigment composition and structure of the chromophores in the LH2 complexes provide an opportunity to explore the effect of these factors on the rate and efficiency of carotenoid-to-BChl energy transfer. It is found that the enzymatic conversion of rhodopin to rhodopinal by Rbl. acidophilus 7050 grown under low-light conditions results in nearly 100% carotenoid-to-BChl energy transfer efficiency in the LH2 complex. This comparative analysis provides insight into how photosynthetic systems are able to adapt and survive under challenging environmental conditions.

  4. 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. B

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

    NARCIS (Netherlands)

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

    2016-01-01

    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. Typica

  6. Predicting the Isotopic Composition of Subduction-Filtered Subducted Oceanic Crust and Sediment

    Science.gov (United States)

    White, W. M.

    2010-12-01

    The chemical and isotopic character of mantle plumes, which produce oceanic island volcanoes, are widely thought to reflect the presence of recycled oceanic crust and sediment. Isotopic systematics suggest the “cycle time” for this process is 1 Ga or longer, but it should be possible to use a simple mass balance approach to discern how the presently operating subduction zone filter affects the ratios of radioactive parent to radiogenic daughter isotopes. Simple uniformitarian assumptions can then be used to predict the present isotopic composition of anciently subducted lithosphere. Our underlying assumption in deciphering the subduction zone filter is that the flux of an element into the deep mantle is simply equal to the flux of element into the subduction zone less the flux of that element into subduction zone magmas. The former is readily calculated from published data. The latter can be calculated by estimating parental magma compositions, arc accretion rates, and the assumption that arc magma compositions differ from MORB only because of material derived from subducting crust and sediment. Using this approach for 8 intra-oceanic subduction zones, we find 73% of Th and Pb, 79% of U, 80% of Rb and Sr, 93% of Nd and 98% of Sm survive the subduction zone filter. The subduction zone filter systematically increases Sm/Nd ratios in all subduction zones, but the effect is small, with a weighted mean increase of 1.5%. The effect of subduction is to decrease the Sm/Nd of the mantle, but only slightly. The effect of subduction is to increase the Rb/Sr of the mantle, but the subduction zone filter does not have a systematic effect on Rb/Sr ratios: it significantly increases in Rb/Sr in 3 subduction zones and significantly decreases it in one; the weighted mean shows no significant change. The effect of the subduction zone filter on U/Pb is also not systematic. U/Pb ratios in the mantle fluxes are bimodal, with values equal to or lower than the bulk Earth value in 4

  7. A model for the unique role of factor Va A2 domain extension in the human ternary thrombin-generating complex.

    Science.gov (United States)

    Shim, Joong-Youn; Lee, Chang Jun; Wu, Sangwook; Pedersen, Lee G

    2015-04-01

    An all-atom human ternary model for the prothrombinase-prothrombin complex, including metal ions and post-translationally modified residues, was constructed from existing X-ray crystal structures. The factor Xa-prothrombin interface was taken from an existing ternary model, which locates the active site of factor Xa in the vicinity of prothrombin cleavage positions. The three sulfotyrosine residues at the C-terminal sequence of factor Va A2 domain are accommodated by modelling rational interactions with positively charged patches on the surface of prothrombin. The entire model is then solvent-equilibrated with molecular dynamics. This ternary model for the thrombin-generating complex provides an estimate as to the role of the C-terminus of the factor Va A2 domain: to establish an interface between FXa and prothrombin and to stabilize the orientation of this interface. Copyright © 2015 Elsevier B.V. All rights reserved.

  8. Mapping mantle flow during retreating subduction: Laboratory models analyzed by feature tracking

    Science.gov (United States)

    Funiciello, F.; Moroni, M.; Piromallo, C.; Faccenna, C.; Cenedese, A.; Bui, H. A.

    2006-03-01

    Three-dimensional dynamically consistent laboratory models are carried out to model the large-scale mantle circulation induced by subduction of a laterally migrating slab. A laboratory analogue of a slab-upper mantle system is set up with two linearly viscous layers of silicone putty and glucose syrup in a tank. The circulation pattern is continuously monitored and quantitatively estimated using a feature tracking image analysis technique. The effects of plate width and mantle viscosity/density on mantle circulation are systematically considered. The experiments show that rollback subduction generates a complex three-dimensional time-dependent mantle circulation pattern characterized by the presence of two distinct components: the poloidal and the toroidal circulation. The poloidal component is the answer to the viscous coupling between the slab motion and the mantle, while the toroidal one is produced by lateral slab migration. Spatial and temporal features of mantle circulation are carefully analyzed. These models show that (1) poloidal and toroidal mantle circulation are both active since the beginning of the subduction process, (2) mantle circulation is intermittent, (3) plate width affects the velocity and the dimension of subduction induced mantle circulation area, and (4) mantle flow in subduction zones cannot be correctly described by models assuming a two-dimensional steady state process. We show that the intermittent toroidal component of mantle circulation, missed in those models, plays a crucial role in modifying the geometry and the efficiency of the poloidal component.

  9. 15 Years Of Ecuadorian-French Research Along The Ecuadorian Subduction Zone

    Science.gov (United States)

    Charvis, P.

    2015-12-01

    The Ecuadorian segment of the Nazca/South America subduction zone is an outstanding laboratory to study the seismic cycle. Central Ecuador where the Carnegie ridge enters the subduction marks a transition between a highly coupled segment that hosted one of the largest seismic sequence during the 20thcentury and a ~1200-km long weakly coupled segment encompassing southern Ecuador and northern Peru. A shallow dipping subduction interface and a short trench-coast line distance ranging from 45 to 80 km, together with La Plata Island located only 33 km from the trench axis, allow to document subduction processes in the near field with an exceptional resolution. Since 2000, a close cooperation between the Institute of Geophysics (Quito), INOCAR (Oceanographic Institute of the Ecuadorian Navy) with French groups allowed us to conduct up to 6 marine geophysics cruises to survey the convergent margin and jointly develop dense GPS and seismological networks. This fruitful collaboration now takes place in the framework of an International Joint Laboratory "Earthquakes and Volcanoes in the Northern Andes" (LMI SVAN), which eases coordinating research projects and exchanges of Ecuadorian and French scientists and students. This long-term investigation has already provided a unique view on the structure of the margin, which exhibits a highly variable subduction channel along strike. It allowed us to evidence the contrast between creeping and coupled segments of subduction at various scale, and the existence of large continental slivers whose motion accommodates the obliquity of the Nazca/South America convergence. Finally, we could evidence the first Slow Slip Events (SSE) that oppositely to most SSE documented so far, are accompanied with intense micro-seismicity. The recent support of the French National Research Agency and the Ecuadorian Agency for Sciences and Technology (Senescyt) will enable us to integrate the already obtained results, in an attempt to develop an

  10. Formation of a unique zinc carbamate by CO2 fixation: implications for the reactivity of tetra-azamacrocycle ligated Zn(II) complexes.

    Science.gov (United States)

    Notni, Johannes; Schenk, Stephan; Görls, Helmar; Breitzke, Hergen; Anders, Ernst

    2008-02-18

    The macrocyclic ligand [13]aneN 4 ( L1, 1,4,7,10-tetra-azacyclotridecane) was reacted with Zn(II) perchlorate and CO 2 in an alkaline methanol solution. It was found that, by means of subtle changes in reaction conditions, two types of complexes can be obtained: (a) the mu 3 carbonate complex 1, {[Zn( L1)] 3(mu 3-CO 3)}(ClO 4) 4, rhombohedral crystals, space group R3 c, with pentacoordinate zinc in a trigonal bipyramidal enviroment, and (b) an unprecedenced dimeric Zn(II) carbamate structure, 2, [Zn( L2)] 2(ClO 4) 2, monoclinic crystals, space group P2 1/ n. The ligand L2 (4-carboxyl-1,4,7,10-tetra-azacyclotridecane) is a carbamate derivative of L1, obtained by transformation of a hydrogen atom of one of the NH moieties into carbamate by means of CO 2 uptake. In compound 2, the distorted tetrahedral Zn(II) coordinates to the carbamate moiety in a monodentate manner. Most notably, carbamate formation can occur upon reaction of CO 2 with the [Zn L1] (2+) complex, which implicates that a Zn-N linkage is cleaved upon attack of CO 2. Since complexes of tetra-azamacrocycles and Zn(II) are routinely applied for enzyme model studies, this finding implies that the Zn-azamacrocycle moiety generally should no longer be considered to play always only an innocent role in reactions. Rather, its reactivity has to be taken into account in respective investigations. In the presence of water, 2 is transformed readily into carbonate 1. Both compounds have been additionally characterized by solid-state NMR and infrared spectroscopy. A thorough comparison of 1 with related azamacrocycle ligated zinc(II) carbonates as well as a discussion of plausible reaction paths for the formation of 2 are given. Furthermore, the infrared absorptions of the carbamate moiety have been assigned by calculating the vibrational modes of the carbamate complex using DFT methods and the vibrational spectroscopy calculation program package SNF.

  11. Tomographically-imaged subducted slabs and magmatic history of Caribbean and Pacific subduction beneath Colombia

    Science.gov (United States)

    Bernal-Olaya, R.; Mann, P.; Vargas, C. A.; Koulakov, I.

    2013-12-01

    We define the length and geometry of eastward and southeastward-subducting slabs beneath northwestern South America in Colombia using ~100,000 earthquake events recorded by the Colombian National Seismic Network from 1993 to 2012. Methods include: hypocenter relocation, compilation of focal mechanisms, and P and S wave tomographic calculations performed using LOTOS and Seisan. The margins of Colombia include four distinct subduction zones based on slab dip: 1) in northern Colombia, 12-16-km-thick oceanic crust subducts at a modern GPS rate of 20 mm/yr in a direction of 110 degrees at a shallow angle of 8 degrees; as a result of its low dip, Pliocene-Pleistocene volcanic rocks are present 400 km from the frontal thrust; magmatic arc migration to the east records 800 km of subduction since 58 Ma ago (Paleocene) with shallow subduction of the Caribbean oceanic plateau starting ~24-33 Ma (Miocene); at depths of 90-150 km, the slab exhibits a negative velocity anomaly we associate with pervasive fracturing; 2) in the central Colombia-Panama area, we define an area of 30-km-thick crust of the Panama arc colliding/subducting at a modern 30/mm in a direction of 95 degrees; the length of this slab shows subduction/collision initiated after 20 Ma (Middle Miocene); we call this feature the Panama indenter since it has produced a V-shaped indentation of the Colombian margin and responsible for widespread crustal deformation and topographic uplift in Colombia; an incipient subduction area is forming near the Panama border with intermediate earthquakes at an eastward dip of 70 degrees to depths of ~150 km; this zone is not visible on tomographic images; 3) a 250-km-wide zone of Miocene oceanic crust of the Nazca plate flanking the Panama indenter subducts at a rate of 25 mm/yr in a direction of 55 degrees and at a normal dip of 40 degrees; the length of this slab suggests subduction began at ~5 Ma; 4) the Caldas tear defines a major dip change to the south where a 35 degrees

  12. Two-dimensional Numerical Modeling Research on Continent Subduction Dynamics

    Institute of Scientific and Technical Information of China (English)

    WANG Zhimin; XU Bei; ZHOU Yaoqi; XU Hehua; HUANG Shaoying

    2004-01-01

    Continent subduction is one of the hot research problems in geoscience. New models presented here have been set up and two-dimensional numerical modeling research on the possibility of continental subduction has been made with the finite element software, ANSYS, based on documentary evidence and reasonable assumptions that the subduction of oceanic crust has occurred, the subduction of continental crust can take place and the process can be simplified to a discontinuous plane strain theory model. The modeling results show that it is completely possible for continental crust to be subducted to a depth of 120 km under certain circumstances and conditions. At the same time, the simulations of continental subduction under a single dynamical factor have also been made, including the pull force of the subducted oceanic lithosphere, the drag force connected with mantle convection and the push force of the mid-ocean ridge. These experiments show that the drag force connected with mantle convection is critical for continent subduction.

  13. Subduction and exhumation of continental crust: insights from laboratory models

    Science.gov (United States)

    Bialas, Robert W.; Funiciello, Francesca; Faccenna, Claudio

    2011-01-01

    When slivers of continental crust and sediment overlying oceanic lithosphere enter a subduction zone, they may be scraped off at shallow levels, subducted to depths of up to 100-200 km and then exhumed as high pressure (HP) and ultra-high pressure (UHP) rocks, or subducted and recycled in the mantle. To investigate the factors that influence the behaviour of subducting slivers of continental material, we use 3-D dynamically consistent laboratory models. A laboratory analogue of a slab-upper mantle system is set up with two linearly viscous layers of silicone putty and glucose syrup in a tank. A sliver of continental material, also composed of silicone putty, overlies the subducting lithosphere, separated by a syrup detachment. The density of the sliver, viscosity of the detachment, geometry of the subducting system (attached plate versus free ridge) and dimensions of the sliver are varied in 34 experiments. By varying the density of the sliver and viscosity of the detachment, we can reproduce a range of sliver behaviour, including subduction, subduction and exhumation from various depths and offscraping. Sliver subduction and exhumation requires sufficient sliver buoyancy and a detachment that is strong enough to hold the sliver during initial subduction, but weak enough to allow adequate sliver displacement or detachment for exhumation. Changes to the system geometry alter the slab dip, subduction velocity, pattern of mantle flow and amount of rollback. Shallower slab dips with more trench rollback produce a mantle flow pattern that aids exhumation. Steeper slab dips allow more buoyancy force to be directed in the up-dip direction of the plane of the plate, and aide exhumation of subducted slivers. Slower subduction can also aide exhumation, but if slab dip is too steep or subduction too slow, the sliver will subduct to only shallow levels and not exhume. Smaller slivers are most easily subducted and exhumed and influenced by the mantle flow.

  14. A Geodynamical Perspective on the Subduction of Cocos and Rivera plates beneath Mexico and Central America

    Science.gov (United States)

    Constantin Manea, Vlad; Manea, Marina; Ferrari, Luca

    2013-04-01

    The Middle America subduction zone (MASZ) is one of the world most complex convergent margins as it involves the subduction of the Rivera and Cocos young oceanic plates beneath the North American and Caribbean plates and is bounded by the Gulf of California rift and the Panama slab window. Characterized by contorted and unusual slab geometry, irregularly distributed seismicity and volcanism, exceptionally large slow slip events (SSE) and non-volcanic tremors (NVT), this subduction system represents a great natural laboratory for better understanding geodynamic processes at a fundamental level. Based on a solid observational foundation, and incorporating the latest experimental results into a coherent geodynamical framework, we shed light on the main processes controlling the subduction system evolution in this region. The tectonics, volcanism, slab geometry and segmentation along the margin are reviewed from a geodynamical perspective. We proposed and discussed a series of evolutionary scenarios for the Mexican and Central American subduction zones, providing a coherent starting base for future geodynamical modeling studies tailored to this active margin. We discuss comparatively the recently discovered SSEs and NVTs along the MASZ, and try to differentiate among the proposed mechanisms responsible for these observations. Finally we discuss the recent seismic anisotropy observations in a geodynamic context, offering an integrated view of mantle flow pattern along the entire active margin. Although the MASZ as a whole may be considered a fairly complicated region with many unusual features and sometimes controversial interpretations, its complexity and unusual characteristics can improve our knowledge about the linkage between deep and surface processes associated with subduction zone dynamics.

  15. Crystal structure of Lymnaea stagnalis AChBP complexed with the potent nAChR antagonist DHβE suggests a unique mode of antagonism.

    Directory of Open Access Journals (Sweden)

    Azadeh Shahsavar

    Full Text Available Nicotinic acetylcholine receptors (nAChRs are pentameric ligand-gated ion channels that belong to the Cys-loop receptor superfamily. These receptors are allosteric proteins that exist in different conformational states, including resting (closed, activated (open, and desensitized (closed states. The acetylcholine binding protein (AChBP is a structural homologue of the extracellular ligand-binding domain of nAChRs. In previous studies, the degree of the C-loop radial extension of AChBP has been assigned to different conformational states of nAChRs. It has been suggested that a closed C-loop is preferred for the active conformation of nAChRs in complex with agonists whereas an open C-loop reflects an antagonist-bound (closed state. In this work, we have determined the crystal structure of AChBP from the water snail Lymnaea stagnalis (Ls in complex with dihydro-β-erythroidine (DHβE, which is a potent competitive antagonist of nAChRs. The structure reveals that binding of DHβE to AChBP imposes closure of the C-loop as agonists, but also a shift perpendicular to previously observed C-loop movements. These observations suggest that DHβE may antagonize the receptor via a different mechanism compared to prototypical antagonists and toxins.

  16. Development of seismic anisotropy during subduction-induced 3D mantle flow

    Science.gov (United States)

    Faccenda, M.; capitanio, F. A.

    2012-12-01

    Subduction zones are convergent margins where the rigid lithosphere sinks into the Earth's mantle inducing complex 3D flow patterns. Seismic anisotropy generated by strain-induced lattice/crystal preferred orientation (LPO/CPO) of intrinsically anisotropic minerals is commonly used to study flow in the mantle and its relations with plate motions. As the development of seismic anisotropy due to upper and lower plate motions occurs at depths and timescales such that it is not directly observable, numerical modelling provides a useful tool to investigate these processes. We computed the seismic anisotropy of dry olivine-enstatite aggregates due to strain-induced LPO in 3D mechanical models of dynamic subduction by using, respectively, D-Rex and Underworld. Subsequently, FSTRACK was used to compute seismogram synthetics and SKS splitting patterns. We found that for relatively narrow subducting plates, retreat motions are maximized producing strong subslab trench-parallel anisotropy. Here, synthetic data reproduce quite well the observations in analogous subduction systems like Calabria and South Sandwich, where the fast azimuths orients parallel to the trench in the forearc and follow the toroidal flow patterns on the slab edges. Furthermore, we found that the amount of anisotropy is proportional to the amount of subduction, while it does not depend on the rate at which the plate subducts. On the other hand, larger subducting plates subducts mainly by plate advance, favoring poloidal motions and trench-perpendicular anisotropy. Additional Earth-like plate geometries involving along-trench variation of the subducting plate age that induces differential slab retreat motions are considered. We also tested different olivine fabrics (A, B, C, E type), yielding distinct SKS splitting patterns that may help to constrain the composition of the upper mantle. Although more sophisticated numerical modelling taking into account temperature-dependent mantle rock rheologies and P

  17. SusG: A Unique Cell-Membrane-Associated [alpha]-Amylase from a Prominent Human Gut Symbiont Targets Complex Starch Molecules

    Energy Technology Data Exchange (ETDEWEB)

    Koropatkin, Nicole M.; Smith, Thomas J. (Danforth)

    2010-09-21

    SusG is an {alpha}-amylase and part of a large protein complex on the outer surface of the bacterial cell and plays a major role in carbohydrate acquisition by the animal gut microbiota. Presented here, the atomic structure of SusG has an unusual extended, bilobed structure composed of amylase at one end and an unprecedented internal carbohydrate-binding motif at the other. Structural studies further demonstrate that the carbohydrate-binding motif binds maltooligosaccharide distal to, and on the opposite side of, the amylase catalytic site. SusG has an additional starch-binding site on the amylase domain immediately adjacent to the active cleft. Mutagenesis analysis demonstrates that these two additional starch-binding sites appear to play a role in catabolism of insoluble starch. However, elimination of these sites has only a limited effect, suggesting that they may have a more important role in product exchange with other Sus components.

  18. Imaging of subducted lithosphere beneath South America

    NARCIS (Netherlands)

    Engdahl, E.R.; Hilst, R.D. van der; Berrocal, J.

    1995-01-01

    Tomographic images are produced for the deep structure of the Andean subduction zone beneath western South America. The data used in the imaging are the delay times of P, pP and pwP phases from relocated teleseismic earthquakes in the region. Regionally, structural features larger than about 150 km

  19. 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 gradie......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...

  20. 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.

  1. The role of viscoelasticity in subducting plates

    Science.gov (United States)

    Farrington, R. J.; Moresi, L.-N.; Capitanio, F. A.

    2014-11-01

    of tectonic plates into Earth's mantle occurs when one plate bends beneath another at convergent plate boundaries. The characteristic time of deformation at these convergent boundaries approximates the Maxwell relaxation time for olivine at lithospheric temperatures and pressures, it is therefore by definition a viscoelastic process. While this is widely acknowledged, the large-scale features of subduction can, and have been, successfully reproduced assuming the plate deforms by a viscous mechanism alone. However, the energy rates and stress profile within convergent margins are influenced by viscoelastic deformation. In this study, viscoelastic stresses have been systematically introduced into numerical models of free subduction, using both the viscosity and shear modulus to control the Maxwell relaxation time. The introduction of an elastic deformation mechanism into subduction models produces deviations in both the stress profile and energy rates within the subduction hinge when compared to viscous only models. These variations result in an apparent viscosity that is variable throughout the length of the plate, decreasing upon approach and increasing upon leaving the hinge. At realistic Earth parameters, we show that viscoelastic stresses have a minor effect on morphology yet are less dissipative at depth and result in an energy transfer between the energy stored during bending and the energy released during unbending. We conclude that elasticity is important during both bending and unbending within the slab hinge with the resulting stress loading and energy profile indicating that slabs maintain larger deformation rates at smaller stresses during bending and retain their strength during unbending at depth.

  2. A numerical reference model for themomechanical subduction

    DEFF Research Database (Denmark)

    Quinquis, Matthieu; Chemia, Zurab; Tosi, Nicola

    2010-01-01

    . Our reference model represents ocean-ocean convergence and describes initial geometries and lithological stratification for a three-layered subducting slab and overriding plate along with their respective flow laws and chemical composition. It also includes kinematic and thermal boundary conditions...

  3. 25 years of continental deep subduction

    Institute of Scientific and Technical Information of China (English)

    ZHENG YongFei

    2009-01-01

    @@ This year marks the 25th anniversary of the discovery of coesite in metamorphic rocks of supracrustal origin.This initiated a revolution of the plate tectonics theory due to intensive studies of ultrahigh pressure metamorphism and continental deep subduction.The occurrence of coesite was first reported in 1984 by two French scientists,C.Chopin and D.C.Smith,respectively.

  4. Archean Subduction or Not? The Archean Volcanic Record Re-assessed.

    Science.gov (United States)

    Pearce, Julian; Peate, David; Smithies, Hugh

    2013-04-01

    Methods of identification of volcanic arc lavas may utilize: (1) the selective enrichment of the mantle wedge by 'subduction-mobile' elements; (2) the distinctive preconditioning of mantle along its flow path to the arc front; (3) the distinctive combination of fluid-flux and decompression melting; and (4) the effects of fluids on crystallization of the resulting magma. It should then be a simple matter uniquely to recognise volcanic arc lavas in the Geological Record and so document past subduction zones. Essentially, this is generally true in the oceans, but generally not on the continents. Even in recent, fresh lavas and with a full battery of element and isotope tools at our disposal, there can be debate over whether an arc-like geochemical signature results from active subduction, an older, inherited subduction component in the lithosphere, or crustal contamination. In the Archean, metamorphism, deformation, a different thermal regime and potential non-uniformitarian tectonic scenarios make the fingerprinting of arc lavas particularly problematic. Not least, the complicating factor of crustal contamination is likely to be much greater given the higher magma and crustal temperatures and higher magma fluxes prevailing. Here, we apply new, high-resolution immobile element fingerprinting methods, based primarily on Th-Nb fractionation, to Archean lavas. In the Pilbara, for example, where there is a volcanic record extending for over >500 m.y., we note that lavas with high Th/Nb (negative Nb anomalies) are common throughout the lava sequence. Many older formations also follow a basalt-andesite-dacite-rhyolite (BADR) sequence resembling present-day arcs. However, back-extrapolation of their compositions to their primitive magmas demonstrates that these were almost certainly crustally-contaminated plume-derived lavas. By contrast, this is not the case in the uppermst part of the sequence where even the most primitive magmas have significant Nb anomalies. The

  5. Observations at convergent margins concerning sediment subduction, subduction erosion, and the growth of continental crust

    Science.gov (United States)

    Von Huene, R.; Scholl, D. W.

    1991-01-01

    At ocean margins where two plates converge, the oceanic plate sinks or is subducted beneath an upper one topped by a layer of terrestrial crust. This crust is constructed of continental or island arc material. The subduction process either builds juvenile masses of terrestrial crust through arc volcanism or new areas of crust through the piling up of accretionary masses (prisms) of sedimentary deposits and fragments of thicker crustal bodies scraped off the subducting lower plate. At convergent margins, terrestrial material can also bypass the accretionary prism as a result of sediment subduction, and terrestrial matter can be removed from the upper plate by processes of subduction erosion. Sediment subduction occurs where sediment remains attached to the subducting oceanic plate and underthrusts the seaward position of the upper plate's resistive buttress (backstop) of consolidated sediment and rock. Sediment subduction occurs at two types of convergent margins: type 1 margins where accretionary prisms form and type 2 margins where little net accretion takes place. At type 2 margins (???19,000 km in global length), effectively all incoming sediment is subducted beneath the massif of basement or framework rocks forming the landward trench slope. At accreting or type 1 margins, sediment subduction begins at the seaward position of an active buttress of consolidated accretionary material that accumulated in front of a starting or core buttress of framework rocks. Where small-to-mediumsized prisms have formed (???16,300 km), approximately 20% of the incoming sediment is skimmed off a detachment surface or decollement and frontally accreted to the active buttress. The remaining 80% subducts beneath the buttress and may either underplate older parts of the frontal body or bypass the prism entirely and underthrust the leading edge of the margin's rock framework. At margins bordered by large prisms (???8,200 km), roughly 70% of the incoming trench floor section is

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

    NARCIS (Netherlands)

    Maffione, Marco; Thieulot, Cedric; van Hinsbergen, Douwe J.J.; Morris, Antony; Plümper, Oliver; Spakman, Wim

    2015-01-01

    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 recen

  7. 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.; 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

  8. Mitochondrial DNA variants of respiratory complex I that uniquely characterize haplogroup T2 are associated with increased risk of age-related macular degeneration.

    Directory of Open Access Journals (Sweden)

    John Paul SanGiovanni

    Full Text Available BACKGROUND: Age-related macular degeneration (AMD, a chronic neurodegenerative and neovascular retinal disease, is the leading cause of blindness in elderly people of western European origin. While structural and functional alterations in mitochondria (mt and their metabolites have been implicated in the pathogenesis of chronic neurodegenerative and vascular diseases, the relationship of inherited variants in the mitochondrial genome and mt haplogroup subtypes with advanced AMD has not been reported in large prospective cohorts. METHODOLOGY/PRINICIPAL FINDINGS: We examined the relationship of inherited mtDNA variants with advanced AMD in 1168 people using a three-stage design on samples from 12-year and 10-year prospective studies on the natural history of age-related eye disease. In Stage I we resequenced the entire genome in 99 elderly AMD-free controls and 215 people with advanced AMD from the 12-year study. A consistent association with AMD in 14 of 17 SNPs characterizing the mtDNA T haplogroup emerged. Further analysis revealed these associations were driven entirely by the T2 haplogroup, and characterized by two variants in Complex I genes (A11812G of MT-ND4 and A14233G of MT-ND6. We genotyped T haplogroups in an independent sample of 490 cases and 61 controls from the same study (Stage II and in 56 cases and 246 controls from the 10-year study (Stage III. People in the T2 haplogroup were approximately 2.5 times more likely to have advanced AMD than their peers (odds ratio [OR] = 2.54, 95%CI 1.36-4.80, PComplex I are reasonable targets for novel functional analyses and therapeutic research in AMD.

  9. Links between fluid circulation, temperature, and metamorphism in subducting slabs

    Science.gov (United States)

    Spinelli, G.A.; Wang, K.

    2009-01-01

    The location and timing of metamorphic reactions in subducting lithosph??re are influenced by thermal effects of fluid circulation in the ocean crust aquifer. Fluid circulation in subducting crust extracts heat from the Nankai subduction zone, causing the crust to pass through cooler metamorphic faci??s than if no fluid circulation occurs. This fluid circulation shifts the basalt-to-eclogite transition and the associated slab dehydration 14 km deeper (35 km farther landward) than would be predicted with no fluid flow. For most subduction zones, hydrothermal cooling of the subducting slab will delay eclogitization relative to estimates made without considering fluid circulation. Copyright 2009 by the American Geophysical Union.

  10. Analog Modeling of Continental Lithosphere Subduction

    Science.gov (United States)

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

    2012-12-01

    Lithospheric-scale analog modeling sheds light on the consequences of decoupling within the continental lithosphere and along plate interfaces during continental collision. The model results provide valuable information in terms of strain localization, deformation of the subducting slab and the evolution and architecture of the overlying mountain belt and its topography. A weak layer has been implemented in three-layer models to simulate decoupling along the plate interface and at different levels of the lithosphere (brittle-ductile transition, entire lower crust, crust-mantle boundary). Additionally, varying the strength of the mantle lithosphere of both the upper as well as the lower plate regulated the degree of plate coupling. Plate boundaries were orthogonal to the convergence direction. All models emphasize that strong decoupling at the plate interface is a pre-requisite for the subduction of continental lithosphere. In addition, deformation of the subducting slab was found to be sensitive to the strength contrast between the subduction zone and the mantle lithosphere of the downgoing as well as the upper plate. As such, a low strength contrast between the plate interface and the lower plate leads to deformation of the subducting slab by thickening and the development of a shallow slab. Conversely, when the strength contrast is high, deep slabs evolve which undergo relatively less deformation. Furthermore, the level of decoupling in the downgoing plate governs how much continental crust is subducted together with the mantle lithosphere. Shallow decoupling, at the brittle-ductile transition, results in subduction of the lower crust whereas small amounts of lower crust are subducted when decoupling occurs at the level of the Moho. Weak plate coupling and a weak lower crust of the lower plate steer the evolution of mountain belts such that deformation propagates outward, in the direction of the incoming plate, by successive imbrication of upper crustal thrust

  11. Developing the plate tectonics from oceanic subduction to continental collision

    Institute of Scientific and Technical Information of China (English)

    ZHENG YongFei; YE Kai; ZHANG LiFei

    2009-01-01

    The studies of continental deep subduction and ultrahigh-pressure metamorphism have not only promoted the development of solid earth science in China,but also provided an excellent opportunity to advance the plate tectonics theory.In view of the nature of subducted crust,two types of subduction and collision have been respectively recognized in nature.On one hand,the crustal subduction occurs due to underflow of either oceanic crust (Pacific type) or continental crust (Alpine type).On the other hand,the continental collision proceeds by arc-continent collision (Himalaya-Tibet type) or continent-continent collision (Dabie-Sulu type).The key issues in the future study of continental dynamics are the chemical changes and differential exhumation in continental deep subduction zones,and the temporal-spatial transition from oceanic subduction to continental subduction.

  12. Insights on the Subduction Process from High-Resolution 3D Models

    Science.gov (United States)

    Jadamec, Margarete

    2015-04-01

    This is an exciting time in geodynamics as the use of unprecedented high-resolution 3D modeling allows us to ask new questions that were previously unattainable. It is now relatively straightforward to run 3D numerical simulations, with local mesh refinement to ~1 km, input data mapped onto over 100 million finite element nodes, and using tens of thousands of compute hours per model, e.g. Jadamec et al. [2012]. With the additional computational resources, comes a new approach to modeling the tectonic problem. For example, mapping tectonic plates onto a high-resolution 3D geodynamic model grid forces the modeler to ask questions much as a field geologist would ask when constructing a geologic map. In this process of moving from textbook models of subduction to using models based on observation, the modeler is forced to explain the more complicated geometries and features in the Earth, allowing for the new computational approaches to be powerful tools for scientific discovery. Subduction modeling of this kind has expanded the classical view of two-dimensional corner flow, e.g. McKenzie [1969], to a slab driven flow that can be quite complex with predictions for upper mantle flow rates that can be over ten times surface plate motions, e.g. Jadamec et al. [2010] and others. In this talk, I will investigate the role of the third-dimension and non-linearity in plate boundary deformation. I will present high-resolution 3D numerical models that examine the effect of observationally based slab geometry, multiple subducting plates, non-linear rheology, and variations in overriding plate thickness on the subduction related deformation of plate margins. Specific examples include the Alaska and Central America subduction systems. In addition, I will highlight future directions in subduction modeling, and how these can be advanced by the increased incorporation of observational data, high-performance computing, focused numerical algorithms, and 3D interactive data visualization.

  13. Large Influence of Subduction Geometry on Extreme Exhumation in Orogen Syntaxes

    Science.gov (United States)

    Ehlers, T. A.; Bendick, R. O.

    2014-12-01

    Some of the highest and most localized rates of lithospheric deformation in the world are observed at the transition between adjacent plate boundary subduction segments (syntaxes). The initiating perturbation of this deformation has long been attributed to vigorous, climate driven, erosional processes as observed at Nanga Parbat and Namche Barwa in the Himalaya and at Mt. St. Elias in Alaska. However, an erosion-dominated mechanism ignores the 3D geometry of curved subducting plates and changes in paleoclimate. Here we present an alternative explanation for rapid exhumation at these locations based on the 3D thermo-mechanical evolution of collisions between plates with nonplanar geometries. A set of numerical solutions and thermochronometer observations are presented for the interaction between a rigid indenter between subduction segments with an overriding viscous material. The model setup is intentionally simplified to identify how the 3D geometry of a subducting plate influences upper plate deformation, and therefore omits many of the complexities of collision interfaces, such as the transfer of mass between the downgoing and overriding plates. Temperatures are calculated using the 3D advection diffusion equation with radiogenic heat production and shear heating. The thermal and Stokes flow solutions are fully coupled and evolve throughout the simulation. Model predicted cooling ages are compared to observed cooling ages from published bedrock and detrital thermochronometer studies by calculating cooling rate dependent thermochronometer ages. Comparison of model predictions with existing thermochronometer data reproduces the defining characteristics of these mountains such as a localized "bulls-eye" pattern of rapid exhumation and young cooling ages above the rigid indenter between subduction segments. These results demonstrate a 'bottom up' tectonic rather than 'top down' erosional initiation of feedbacks between erosion and tectonic deformation. While the role

  14. Numerical modeling of mantle wedge processes and exhumation of UHP mantle in subduction zones

    Science.gov (United States)

    Gorczyk, W.; Gerya, T. V.; Guillot, S.; Connolly, J. A.; Yuen, D.

    2007-12-01

    The upwelling of subduction generated partially molten rocks is potentially a mechanism for the exhumation of UHP rocks through the mantle wedge. We investigated this processes using a 2-D coupled petrological- thermomechanical model that incorporates slab dehydration and water transport as well as partial melting of mantle and crustal rocks. This approach allows us to study the dynamics of mantle wedge processes including evolution of partially molten plumes and their interaction with surrounding dry mantle. To study the internal structure of the plumes we used ultra-high resolution numerical simulations with 10 billion active markers to detail the internal structure of natural plumes originating from the slab. The plumes consist of partially molten hydrated peridotite, dry solid mantle and subducted oceanic crust, which may comprise up to 12 volume % of the plume. As the plumes grow and mature these materials mix chaotically resulting in attenuation and duplication of the original layering on scales of 1-1000 m. Comparison of numerical results with geological observations from the Horoman ultramafic complex in Japan suggests that mixing and differentiation processes related to development of partially molten plumes above slabs may be responsible for strongly layered lithologically mixed (marble cake) structure of asthenospheric mantle wedges. The recent discovery of garnet bearing peridotites in the subduction zone of the Great Antilles in Hispaniola has raised questions about the process that leads to their exhumation. To evaluate whether upwelling plumes are a plausible exhumation mechanism we investigated the dynamics of subduction of slow spreading ridges. The results show that subduction of strongly serpentinized oceanic plate causes strong dehydration of the slab and leads to a rheological weakening of the interface between subducting and overriding plate. This weakening triggers trench retreat and massive asthenospheric upwelling into the gap between the

  15. A geophysical potential field study to image the Makran subduction zone in SE of Iran

    Science.gov (United States)

    Abedi, Maysam; Bahroudi, Abbas

    2016-10-01

    The Makran subduction wedge as one of the largest subduction complexes has been forming due to the Arabian oceanic lithosphere subducting beneath the Lut and the Afghan rigid block microplates. To better visualize the subducting oceanic crust in this region, a geophysical model of magnetic susceptibility from an airborne magnetic survey (line spacing about 7.5 km) over the Makran zone located at southeast of Iran is created to image various structural units in Iran plate. The constructed geophysical model from the 3D inverse modeling of the airborne magnetic data indicates a thin subducting slab to the north of the Makran structural zone. It is demonstrated that the thickness of sedimentary units varies approximately at an interval of 7.5-11 km from north to south of this zone in the Iranian plate, meanwhile the curie depth is also estimated approximately < 26 km. It is also shown the Jazmurian depression zone adjacent to the north of the Makran indicates high intensity magnetic anomalies due to being underlain by an ophiolite oceanic basement, while such intensity reduces over the Makran. The directional derivatives of the magnetic field data have subtle changes in the Makran, but strongly increase in the Jazmurian by enhancing and separating different structural boundaries in this region. In addition, the density variations of the subsurface geological layers were determined by 3D inversion of the ground-based gravity data over the whole study area, where the constructed density model was in good agreement with the magnetic one. According to the outputs of the magnetic susceptibility and the density contrast, the Arabian plate subducts to the north under the Eurasia with a very low dip angle in the Makran structural zone.

  16. Formulation and Application of a Physically-Based Rupture Probability Model for Large Earthquakes on Subduction Zones: A Case Study of Earthquakes on Nazca Plate

    Science.gov (United States)

    Mahdyiar, M.; Galgana, G.; Shen-Tu, B.; Klein, E.; Pontbriand, C. W.

    2014-12-01

    Most time dependent rupture probability (TDRP) models are basically designed for a single-mode rupture, i.e. a single characteristic earthquake on a fault. However, most subduction zones rupture in complex patterns that create overlapping earthquakes of different magnitudes. Additionally, the limited historic earthquake data does not provide sufficient information to estimate reliable mean recurrence intervals for earthquakes. This makes it difficult to identify a single characteristic earthquake for TDRP analysis. Physical models based on geodetic data have been successfully used to obtain information on the state of coupling and slip deficit rates for subduction zones. Coupling information provides valuable insight into the complexity of subduction zone rupture processes. In this study we present a TDRP model that is formulated based on subduction zone slip deficit rate distribution. A subduction zone is represented by an integrated network of cells. Each cell ruptures multiple times from numerous earthquakes that have overlapping rupture areas. The rate of rupture for each cell is calculated using a moment balance concept that is calibrated based on historic earthquake data. The information in conjunction with estimates of coseismic slip from past earthquakes is used to formulate time dependent rupture probability models for cells. Earthquakes on the subduction zone and their rupture probabilities are calculated by integrating different combinations of cells. The resulting rupture probability estimates are fully consistent with the state of coupling of the subduction zone and the regional and local earthquake history as the model takes into account the impact of all large (M>7.5) earthquakes on the subduction zone. The granular rupture model as developed in this study allows estimating rupture probabilities for large earthquakes other than just a single characteristic magnitude earthquake. This provides a general framework for formulating physically

  17. Observations of large earthquakes in the Mexican subduction zone over 110 years

    Science.gov (United States)

    Hjörleifsdóttir, Vala; Krishna Singh, Shri; Martínez-Peláez, Liliana; Garza-Girón, Ricardo; Lund, Björn; Ji, Chen

    2016-04-01

    Fault slip during an earthquake is observed to be highly heterogeneous, with areas of large slip interspersed with areas of smaller or even no slip. The cause of the heterogeneity is debated. One hypothesis is that the frictional properties on the fault are heterogeneous. The parts of the rupture surface that have large slip during earthquakes are coupled more strongly, whereas the areas in between and around creep continuously or episodically. The continuously or episodically creeping areas can partly release strain energy through aseismic slip during the interseismic period, resulting in relatively lower prestress than on the coupled areas. This would lead to subsequent earthquakes having large slip in the same place, or persistent asperities. A second hypothesis is that in the absence of creeping sections, the prestress is governed mainly by the accumulative stress change associated with previous earthquakes. Assuming homogeneous frictional properties on the fault, a larger prestress results in larger slip, i.e. the next earthquake may have large slip where there was little or no slip in the previous earthquake, which translates to non-persistent asperities. The study of earthquake cycles are hampered by short time period for which high quality, broadband seismological and accelerographic records, needed for detailed studies of slip distributions, are available. The earthquake cycle in the Mexican subduction zone is relatively short, with about 30 years between large events in many places. We are therefore entering a period for which we have good records for two subsequent events occurring in the same segment of the subduction zone. In this study we compare seismograms recorded either at the Wiechert seismograph or on a modern broadband seismometer located in Uppsala, Sweden for subsequent earthquakes in the Mexican subduction zone rupturing the same patch. The Wiechert seismograph is unique in the sense that it recorded continuously for more than 80 years

  18. Subduction zones seen by GOCE gravity gradients

    DEFF Research Database (Denmark)

    Švarc, Mario; Herceg, Matija; Cammarano, Fabio

    and used as starting point for analysis based on image processing. On obtained maps, locations of known subduction zones were represented with characteristic elongated patterns and cross-sections. Cross sections of well-known subduction zones were used as input patterns for pattern recognition method....... Few pattern recognition methods were tested on all 6 gravity gradient tensor components represented as global scale maps with resolution of 100km (corresponds to the resolution of the GOCE satellite data). By adjusting pattern recognition methods’ features and optimizing various input patterns......, the best method was applied. That is a combination of methods based on SURF (Speeded Up Robust Features) and MSER (Maximally Stable Extremal Regions) algorithms provided in MATLAB’s Computer Vision System Toolbox. Based on 6 gravity gradient components, the global gradient anomaly maps were produced...

  19. 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.

  20. Nonvolcanic tremors in the Mexican subduction zone

    Science.gov (United States)

    Payero, J. S.; Kostoglodov, V.; Mikumo, T.; Perez-Campos, X.; Iglesias, A.; Clayton, R.

    2007-05-01

    Nonvolcanic low frequency tremors (NVT) have been discovered and studied recently in Japan and Cascadia subduction zones and deep beneath the San Andreas Fault. The tremors activity is increasing during so-called silent earthquakes (SQ) in Japan and Cascadia. NVT clusters also migrate following the propagation of the SQ. The origin of the NVT is still unclear. The studies of NVT and SQ in different subduction zones are required to understand the cause for these phenomena. We discovered a number of NVT from daily spectrograms of continuous broad band records at seismic stations of Servicio Seismológico Nacional (SSN) an MASE project. The analyzed data cover a period of 2001-2004 (SSN) when in 2002 a large SQ has occurred in the Guerrero- Oaxaca region, and a steady-state interseismic epoch of 2005 and a new large SQ in 2006 (MASE). NVT occurred in the central part of the Mexican subduction zone (Guerrero) at approximately 200 km from the coast. We can not accurately localize the tremors because of sparse station coverage in 2001-2004. The MASE data of 2005-2006 show that NVT records in Mexico are very similar to those obtained in Cascadia subduction zone. The tremors duration is of 10-60 min, and they appear to travel at S-wave velocities. More than 100 strong NVT were recorded by most of the MASE stations with the epicenters clustered in the narrow band of ~40x150 km to the south of Iguala city and parallel to the coast line. NVT depths are poorly constrained but seem to be less than 40 km deep. We noticed a some increase of NVT activity during the 2001-2002 and 2006 SQs compared with an NVT activity for the "SQ quiet" period of 2003-2004 nevertheless. A lack of NVT for the period of 2-3 months after the SQ is apparent in 2002 and 2006.

  1. Deflection rheoevolution of lithosphere under subduction

    Institute of Scientific and Technical Information of China (English)

    韩玉英; 王维襄

    1997-01-01

    Along the continental margin, the tectonic system consisting of trench, island arc, back arc basin and outer rise is often known as a convergent transitional belt between the oceanic lithosphere and the continental litho-sphere. The occurrence, development and activity of trench and outer rise bear closely on the underthrusting process of the oceanic lithosphere. A generalized analytical theory of deflection rheoevolution of lithosphere under subduction is established, and solutions with universal significance have been obtained.

  2. Nazca plate subduction, mantle flow and Cordilleras formation

    Science.gov (United States)

    Capitanio, Fabio A.

    2013-04-01

    The Nazca-South America convergence represents a unique natural laboratory to probe our understanding of subduction, mantle flow and stress coupling at Andean-type margins. Here, it is shown that the most fundamental balance of forces associated with the downgoing slab, the upper plates and the mantle can account for the Nazca plate motions, although it does not adequately explain the variations of the Cordilleran tectonics found along the ~6000 km wide margin. Using three-dimensional numerical models it is shown that trench-parallel gradients in both the driving and resisting forces are an essential component of the force balance, and necessary to reproduce the macroscopic features observed. When along-trench buoyancy variations similar to the Nazca plate's are included, the slab dips and upper plate deformations observed in the Nazca slab, in the Cordilleras and South American continent interiors can be reproduced. The models show that gradients in the resisting shear force along the trench can be as relevant, as they modulate the trench retreat to form the concave Bolivian Orocline. Pressure gradients in the mantle follow the Nazca buoyancy gradients, and effectively rearrange the flow introducing a trench-parallel component, similar to what suggested by seismic anisotropy in this area. Although they introduce only secondary variations to the primary subduction and mantle flow dynamics, the regional features of the Nazca and South American plates exert a primary control at the margin-local scale. This suggests that far-field forces, e.g. from spreading Atlantic or large-scale convection, should play a minor role in the formation of the Cordilleras.

  3. 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...

  4. Earth Sphericity Effects on Subduction Morphology

    Science.gov (United States)

    Morra, G.; Chatelain, P.; Tackley, P.; Koumoutsakos, P.

    2007-12-01

    We present here the first application in Geodynamics of a Multipole accelerated Boundary Element Method (FMM- BEM) for Stokes Flow. The approach offers the advantage of a reduced number of computational elements and linear scaling with the problem size. We show that this numerical mehod can be fruitfully applied to the simulation of several geodynamic systems at the planetary scale in spheical coordinates and we suggest a general appraoch for modeling combined mantle convection and plate tectonics. The potentialities of the approach are shown investigating the effect played by Earth sphericity on the subduction of a very wide oceanic lithosphere , comparing the morphology of the subducted lithosphere in a spherical and in flat setting. The results show a striking difference between the two models: while the slab on a "flat Earth" shows slight undulation, the same subducting plate on a spherical Earth-like setting presents a distinct folding below the trench far from the edges, with wavelength of (1000km-2000km) as Pacific trenches.

  5. 3-D numerical modeling of plume-induced subduction initiation

    Science.gov (United States)

    Baes, Marzieh; Gerya, taras; Sobolev, Stephan

    2016-04-01

    Investigation of mechanisms involved in formation of a new subduction zone can help us to better understand plate tectonics. Despite numerous previous studies, it is still unclear how and where an old oceanic plate starts to subduct beneath the other plate. One of the proposed scenarios for nucleation of subduction is plume-induced subduction initiation, which was investigated in detail, using 2-D models, by Ueda et al. (2008). Recently. Gerya et al. (2015), using 3D numerical models, proposed that plume-lithosphere interaction in the Archean led to the subduction initiation and onset of plate tectonic. In this study, we aim to pursue work of Ueda et al. (2008) by incorporation of 3-D thermo-mechanical models to investigate conditions leading to oceanic subduction initiation as a result of thermal-chemical mantle plume-lithosphere interaction in the modern earth. Results of our experiments show four different deformation regimes in response to plume-lithosphere interaction, that are a) self-sustaining subduction initiation where subduction becomes self-sustained, b) freezing subduction initiation where subduction stops at shallow depths, c) slab break-off where subducting circular slab breaks off soon after formation and d) plume underplating where plume does not pass through the lithosphere but spreads beneath it (failed subduction initiation). These different regimes depend on several parameters such as plume's size, composition and temperature, lithospheric brittle/plastic strength, age of the oceanic lithosphere and presence/absence of lithospheric heterogeneities. Results show that subduction initiates and becomes self-sustained when lithosphere is older than 10 Myr and non-dimensional ratio of the plume buoyancy force and lithospheric strength above the plume is higher than 2.

  6. The complex and unique ATLAS Toroid family

    CERN Multimedia

    2002-01-01

    Big parts for the toroid magnets that will be used in the ATLAS experiment have been continuously arriving at CERN since March. These structures will create the largest superconducting toroid magnet ever.

  7. Magnesium Isotopic Composition of Subducting Marine Sediments

    Science.gov (United States)

    Hu, Y.; Teng, F. Z.; Plank, T. A.; Huang, K. J.

    2015-12-01

    Subducted marine sediments have recently been called upon to explain the heterogeneous Mg isotopic composition (δ26Mg, ‰) found in mantle wehrlites (-0.39 to +0.09 [1]) in the context of a homogeneous mantle (-0.25 ± 0.07 [2]). However, no systematic measurements of δ26Mg on marine sediments are currently available to provide direct support to this model. To characterize the Mg inputs to global subduction zones, we measured δ26Mg data for a total of 90 marine sediments collected from 12 drill sites outboard of the world's major subduction zones. These sediments span a 1.73‰ range in δ26Mg. The detritus-dominated sediments have δ26Mg (-0.59 to +0.53) comparable to those of weathered materials on continents (e.g. -0.52 to +0.92 [3]), while the calcareous oozes yield δ26Mg (as light as -1.20) more similar to the seawater value (-0.83 [4]). The negative correlation between δ26Mg and CaO/Al2O3 in these sediments indicates the primary control of mineralogy over the Mg isotopic distribution among different sediment types, as carbonates are enriched in light Mg isotopes (-5.10 to -0.40 [5]) whereas clay-rich weathering residues generally have heavier δ26Mg (e.g. up to +0.65 in saprolite [6]). In addition, chemical weathering and grain-size sorting drive sediments to a heavier δ26Mg, as indicated by the broad positive trends between δ26Mg with CIA (Chemical Index of Alteration [7]) and Al2O3/SiO2, respectively. Collectively, the arc systems sampled in this study represent ~30% of global arc length and the extrapolated global Mg flux of subducting marine sediments accounts for ~9% of the yearly Mg riverine input with a flux-weighted average δ26Mg at -0.26. Subduction of these heterogeneous sediments may not cause significant mantle heterogeneity on a global scale, but the highly variable Mg fluxes and δ26Mg of sediments delivered to different trenches are capable of producing local mantle variations. Volcanic rocks sourced from these mantle domains are thus

  8. 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.

  9. Upper and mid mantle fabric developing during subduction-induced mantle flow

    Science.gov (United States)

    Faccenda, Manuele

    2013-04-01

    Subduction zones are convergent margins where the rigid lithosphere sinks into the Earth's mantle inducing complex 3D flow patterns. Seismic anisotropy generated by strain-induced lattice/crystal preferred orientation (LPO/CPO) of intrinsically anisotropic minerals is commonly used to study flow in the mantle and its relations with plate motions. We computed the seismic anisotropy of the upper and mid mantle due to strain-induced LPO in 3D mechanical models of dynamic subduction by using, respectively, D-Rex and Underworld. Subsequently, FSTRACK was used to compute seismogram synthetics and SKS splitting patterns. Strong anisotropy develops in the upper mantle, while weak or null seismic anisotropy is formed in the upper transition zone/lower mantle and lower transition zone, respectively. The distribution of the fabric in the mantle depends on the distribution and amount of the deformation, and not on the rate at which the slab subducts. The SKS splitting patterns are controlled by the anisotropy in the upper mantle because SKS waves are more sensitive to the anisotropy in the shallowest layers. Horizontally propagating shear waves in the mid mantle originating from local earthquakes are characterized by significant splitting that is mostly due to the fabric in the uppermost lower mantle. We discuss the implications of our results for real subduction settings like Tonga, where a discrete amount of observations have been collected in the past 10 years on the anisotropy in the upper and mid mantle.

  10. 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

    2015-04-01

    Although of paramount importance for understanding the nature of mechanical coupling in subduction zones, the portions downdip of the locked segments of subduction interfaces remain poorly understood. These deep transition zones often are sites of megathrust earthquake nucleation and concentrated postseismic afterslip, as well as the focus sites of episodic tremor and slip features, recently discovered at several plate boundaries. The extensive, exhumed remnants of the former Alpine subduction zone found in the Swiss Alps allow analyzing fluid and deformation processes at the original depths of 30-40 km, typical for the depth range of such transition zones. We identify the shear zone at the base of the Dent Blanche complex (Dent Blanche Thrust, DBT) as a lower blueschist-facies, fossilized subduction interface where granitic mylonites overlie a metamorphosed ophiolite. We report field observations from the DBT region where a complex, discontinuous network of meter- to tens of meters-thick foliated cataclasites is interlayered with the basal DBT mylonites. Petrological results indicate that cataclasis took place at near peak metamorphic conditions (450-500°C, c. 1.2 GPa) during subduction of the Tethyan seafloor in Eocene times (42-48 Ma). Despite some tectonic reactivation during exhumation, these networks exhibit mutual cross-cutting relationships between mylonites, foliated cataclasites and vein systems indicating multiple switching between brittle deformation and ductile creep. Whole-rock chemical compositions, in situ 40Ar-39Ar age data of newly formed phengite, and strontium isotopic signatures reveal that these rocks also underwent multiple hydrofracturing events via infiltration of fluids mainly derived from the ophiolitic metasediments underneath the DBT. From the rock fabrics we infer strain rate fluctuations of several orders of magnitude beyond subduction strain rates (c. 10-12s-1) accompanied by fluctuation of near-lithostatic fluid pressures (1>λ>0

  11. Subduction Zone Science - Examples of Seismic Images of the Central Andes and Subducting Nazca Slab

    Science.gov (United States)

    Beck, S. L.; Zandt, G.; Scire, A. C.; Ward, K. M.; Portner, D. E.; Bishop, B.; Ryan, J. C.; Wagner, L. S.; Long, M. D.

    2015-12-01

    Subduction has shaped large regions of the Earth and constitute over 55,000 km of convergent plate margin today. The subducting slabs descend from the surface into the lower mantle and impacts earthquake occurrence, surface uplift, arc volcanism and mantle convection as well as many other processes. The subduction of the Nazca plate beneath the South America plate is one example and constitutes the largest present day ocean-continent convergent margin system and has built the Andes, one of the largest actively growing mountain ranges on Earth. This active margin is characterized by along-strike variations in arc magmatism, upper crustal shortening, crustal thickness, and slab geometry that make it an ideal region to study the relationship between the subducting slab, the mantle wedge, and the overriding plate. After 20 years of portable seismic deployments in the Central Andes seismologists have combined data sets and used multiple techniques to generate seismic images spanning ~3000 km of the South American subduction zone to ~800 km depth with unprecedented resolution. For example, using teleseismic P- waves we have imaged the Nazca slab penetrating through the mantle transition zone (MTZ) and into the uppermost lower mantle. Our tomographic images show that there is significant along-strike variation in the morphology of the Nazca slab in the upper mantle, MTZ, and the lower mantle, including possible tears, folding, and internal deformation. Receiver function studies and surface wave tomography have revealed major changes in lithospheric properties in the Andes. Improved seismic images allow us to more completely evaluate tectonic processes in the formation and uplift of the Andes including: (1) overthickened continental crust driven by crustal shortening, (2) changes in slab dip and coupling with the overlying plate (3) localized lithospheric foundering, and (4) large-scale mantle and crustal melting leading to magmatic addition and/or crustal flow. Although

  12. 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

  13. Unique Path Partitions

    DEFF Research Database (Denmark)

    Bessenrodt, Christine; Olsson, Jørn Børling; Sellers, James A.

    2013-01-01

    We give a complete classification of the unique path partitions and study congruence properties of the function which enumerates such partitions.......We give a complete classification of the unique path partitions and study congruence properties of the function which enumerates such partitions....

  14. Structural, geochronological, magnetic and magmatic constraints of a ridge collision/ridge subduction-related ophiolite

    Science.gov (United States)

    Anma, Ryo

    2013-04-01

    A mid-oceanic ridge system subducts underneath South American plate at latitude 46S off Chilean coast, forming a ridge-trench-trench type triple junction. At ~ 6 Ma, a short segment of the Chile ridge system subducted in south of the present triple junction. This ridge subduction event resulted in emplacement of a young ophiolite (5. 6 to 5. 2 Ma) and rapid crustal uplift (partly emerged after 4.9 Ma), and synchronous magmatism. This ophiolite, namely the Taitao ophiolite, provides criteria for the recognition of ridge collision/ridge subduction-related ophiolites. Aiming to establish recognition criteria, we studied distribution of structures, magnetic properties, geochemical characteristics, and radiometric ages of the Taitao ophiolite and related igneous rocks. The Taitao ophiolite exhibits a classic Penrose-type stratigraphy: ultramafic rocks and gabbros (collectively referred as plutonic section hereafter) in the south, and sheeted dike complex (SDC) and volcanic sequences in the north. Composite foliations developed in the plutonic section, which were folded. SDC were exposed in two isolated blocks having orthogonal strikes of dike margins. Geochemically, gabbros have an N-MORB composition whereas basalts of the volcanic sequence have an E-MORB composition. U-Pb ages of zircons separated from gabbros, SDC and sediments interbeded with billow lavas implied that the center of magmatic activities migrated from the plutonic section to volcanic section during ~5.6 Ma and ~5.2 Ma. Zircon fission track ages of gabbros coincide with U-Pb ages within error range, implying rapid cooling. Demagnetization paths for SDC and lavas form a straight line, whereas those from the plutonic section are Z-shaped and divisble into two components: low coercivity and high coercivity. Restored orientation of gabbro structures imply that the magnetization acquired while gabbroic structures were folding. Thus, magma genesis and emplacement of the plutonic section of ophiolite took place

  15. 2D Numerical simulations of intraoceanic subduction: the case study of the Ligurian Alps.

    Science.gov (United States)

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

    2010-05-01

    Intraoceanic subduction is an important part of the present and past subduction systems, and some features of such process are not yet fully understood. We therefore studied intraoceanic subduction zones with the help of 2D numerical models, analyzing the parameters influencing their evolution in time and space. We applied the finite differences method on a rectangular grid, to calculate properties such as pressure, temperatures and velocities inside the models solving a set of equations. The latter comprise the Stokes equation of motion, the continuity equation and the heat transport equation. Temperature and velocities are computed on the nodes of the grid whereas pressures are calculated for the geometrical centers of the cells. We defined material properties such as density or viscosity on marker points, initially positioned on a regular rectangular grid. The markers and therefore the material properties are moved through the mesh according to the velocity field using the forth order Runge-Kutta method (Gerya et al. 2002). Subduction is forced to begin at a weak zone in the lithospheric mantle within an oceanic basin of prescribed width. The effect of different arrangements of rock bodies inside the subducting lithosphere on the evolution of the process was carefully analyzed. In particular we reproduced two distinct structures of the oceanic lithosphere: i) the layered oceanic crust made up of a stratified succession typical of fast-spreading ridges and ii) the oceanic lithosphere typical of slow and ultra-slow spreading centers, where an incomplete sequence is observable. The latter structure lacks a sheeted dike complex, has a low volume of gabbros and basalts and gabbros form discrete intrusions in variably serpentinized peridotites (Lagabrielle et al., 1997; Mével, 2003). Such an "heterogeneous" structure is characteristic of the Alpine and Appennine ophiolites that characterized the Mesozoic Ligurian Tethys located between Europe and Adria. The depth of

  16. Crystal structure of the complex between Pseudomonas effector AvrPtoB and the tomato Pto kinase reveals both a shared and a unique interface compared with AvrPto-Pto.

    Science.gov (United States)

    Dong, Jing; Xiao, Fangming; Fan, Fenxia; Gu, Lichuan; Cang, Huaixing; Martin, Gregory B; Chai, Jijie

    2009-06-01

    Resistance to bacterial speck disease in tomato (Solanum lycopersicum) is activated upon recognition by the host Pto kinase of either one of two sequence-unrelated effector proteins, AvrPto or AvrPtoB, from Pseudomonas syringae pv tomato (Pst). Pto induces Pst immunity by acting in concert with the Prf protein. The recently reported structure of the AvrPto-Pto complex revealed that interaction of AvrPto with Pto appears to relieve an inhibitory effect of Pto, allowing Pto to activate Prf. Here, we present the crystal structure of the Pto binding domain of AvrPtoB (residues 121 to 205) at a resolution of 1.9A and of the AvrPtoB(121-205)-Pto complex at a resolution of 3.3 A. AvrPtoB(121-205) exhibits a tertiary fold that is completely different from that of AvrPto, and its conformation remains largely unchanged upon binding to Pto. In common with AvrPto-Pto, the AvrPtoB-Pto complex relies on two interfaces. One of these interfaces is similar in both complexes, although the primary amino acid sequences from the two effector proteins are very different. Amino acid substitutions in Pto at the other interface disrupt the interaction of AvrPtoB-Pto but not that of AvrPto-Pto. Interestingly, substitutions in Pto affecting this unique interface also cause Pto to induce Prf-dependent host cell death independently of either effector protein.

  17. Segmentation of Makran Subduction Zone and its consequences on tsunami hazard estimations

    Science.gov (United States)

    Mokhtari, M.

    2009-04-01

    In a plate tectonic setting like that of the Makran Accretionary Complex of Oman Sea, a fairly high earthquake activity would be expected, as in many of the other major Accretionary complexes/subduction zones around the world. But this region which is located between the Zendan-Minab Fault System and Oranch Fault Zone shows relatively low seismicity in comparison with the surrounding region. Better documented tsunami events in the Makran subduction zones are 3, including two events of seismic origin, and one of unknown origin. The latest event is the major earthquake generated tsunami of 1945 in eastern Makran that ruptured approximately one-fifth the length of the subduction zone. It is important to note that, the epicenter of this event is also close to the Sonne Fault which has created segments on the Makran Subduction Zone. The crossing points between Makran Subduction Zone and these oblique fault zones can be a location for occurrence of major earthquake activities. However, more studies are required for further clarification. In contrast to the east, the plate boundary in western Makran has no clear record of historically as well as instrumental great events. The large changes in seismicity between eastern and western Makran suggest segmentation of the subduction zone. This is being supported by Kukowski et al., (2000) where they introduce a new boundary coinciding very well with the Sonne strike-slip fault. As mentioned the western part is characterized by the absence of events. East of the Sonne fault and west of long 64°E is the only region with a clustering of events within the submarine and southernmost onshore part of the Accretionary Wedge, also including the Mw 8.1 event of 1945 (Byrne et al., 1992). Most events in the wedge appear to be pure-thrust earthquakes and are interpreted as plate boundary events (Quittmeyer and Kafka, 1984; Byrne et al., 1992). The earthquake of August 12, 1963, a few tens of kilometers east of the Sonne fault, had a large

  18. Flat-slab subduction, topography, and mantle dynamics in southwestern Mexico

    Science.gov (United States)

    Gérault, Mélanie; Husson, Laurent; Miller, Meghan S.; Humphreys, Eugene D.

    2015-09-01

    Topography above subduction zones arises from the isostatic contribution of crustal and lithospheric buoyancy, as well as the dynamic contribution from slab-driven mantle flow. We evaluate those effects in southwestern Mexico, where a segment of the Cocos slab subducts horizontally. The eastern part of the volcanic arc—the Trans-Mexican Volcanic Belt—stands at an average elevation of 2.3 km, nearly 1.3 km above the fore-arc. Lateral changes in bulk crustal density are relatively small, and seismic imaging shows that there is little variation in crustal thickness between these two regions. Thus, the elevation difference between the arc and the fore-arc should arise from differences in mantle properties. We present finite element models of flat-slab subduction that provide a simultaneous match to topography, plate velocities, and stress state in the overriding plate. We find that the dynamic effects are primarily controlled by the amount of coupling at the subduction interface and in the mantle wedge, the lack of slab anchoring into the lower mantle, and the absence of continental mantle lithosphere. With a mantle wedge and a subduction interface that are, respectively, 2 and 4 orders of magnitude weaker than the asthenosphere, the flat slab exerts a downward pull that can explain most of the elevation difference between the fore-arc and the arc. We infer that lateral viscosity variations play a significant role in shaping dynamic topography in complex tectonic settings and that sublithospheric dynamics can influence the topography at wavelengths that are significantly shorter than previously recognized.

  19. Strain localization in a fossilized subduction channel: Insights from the Cycladic Blueschist Unit (Syros, Greece)

    Science.gov (United States)

    Laurent, Valentin; Jolivet, Laurent; Roche, Vincent; Augier, Romain; Scaillet, Stéphane; Cardello, Giovanni Luca

    2016-03-01

    Syros Island is worldwide known for its preservation of HP-LT parageneses in the Cycladic Blueschist Unit (CBU) providing one of the best case-studies to understand the tectonometamorphic evolution of a subduction channel. Conflicting structural interpretations have been proposed to explain the geological architecture of Syros, in part reflecting a lack of consensus about the tectonic structure of the CBU. In this study, the geological and tectonometamorphic maps of Syros have been entirely redrawn in order to decipher the structure of a fossilized subduction channel. Based on structural and petrological observations, the CBU has been subdivided into three subunits separated by major ductile shear zones. New observations of the Vari Unit confirm that it rests on top of the CBU through a detachment or exhumation fault. While retrograde top-to-the E/NE shearing overprinting prograde deformation is widespread across the island, the prograde deformation has been only locally preserved within the less retrograded units. We show that after the prograde top-to-the S/SW shearing deformation, the CBU was exhumed by an overall top-to-the E/NE shearing from the depth of the eclogite-facies all the way to the depth of the greenschist-facies and finally, to the brittle crust. The exhumation process encompassed the syn-orogenic stage (contemporaneous of subduction, within the subduction channel - Eocene) to the post-orogenic stage (contemporaneous with the formation of the Aegean Sea - Oligocene to Miocene). From syn-orogenic to post-orogenic exhumation, deformation progressively localized toward the base of the CBU, along large-scale ductile shear zones, allowing the preservation of earlier HP-LT structures and HP-LT metamorphic parageneses. Finally, this study brings new insights on the tectonometamorphic evolution of a subduction channel showing how strain localizes during the history of an accretionary complex, both during the prograde and retrograde history.

  20. Subduction of Serpentinized and Weathered Ultramafic Rocks in the Puerto Rico Trench: Preliminary Results

    Science.gov (United States)

    Horning, G.; Klein, F.

    2012-12-01

    Exposure of mantle peridotite and its interactions with seawater to form serpentinite are integral parts of seafloor spreading, and play a key role in affecting the rheology, chemistry, and microbial habitability of the oceanic lithosphere at slow- and ultra-slow spreading ridges. Away from the spreading centers, within subduction zones, the formation and dehydration of serpentinized peridotite impacts seismicity, element cycling, and melt generation. Here we present preliminary results of a petrographic and spectroscopic study of altered rocks recovered from the from the north wall of the trench Puerto Rico Trench (PRT). In fact, the PRT represents one of two subduction zones worldwide where slow spreading oceanic lithosphere is presently subducted, and where serpentinized peridotite has been directly evidenced by seafloor sampling {Bowin, 1966}. Thin section petrography, XRF analysis, scanning electron microscopy, and confocal Raman spectroscopy reveal that the peridotite, which in all likelihood originated at the Mid-Atlantic Ridge during the early Cretaceous, was virtually completely serpentinized under static conditions (as it is evidenced by the preserved mesh texture after olivine and bastite after orthopyroxene), and underwent subsequent seafloor weathering. While it is questionable where exactly serpentinization and subsequent seafloor weathering took place, our preliminary results strongly suggest that the material presently subducted in the PRT is not simply composed of serpentine, magnetite, and brucite; it is rather a complex disequilibrium assemblage of minerals including serpentine, brucite, chlorite, talc, magnetite, hematite, goethite, sulfur-rich sulfides and various clay minerals. Furthermore, our results imply that serpentinite and its weathering products influence the loci of dehydration and mineral replacement reactions, as well as the water input and element recycling in subduction zones.

  1. 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.

  2. Subducting an old subduction zone sideways provides insights into what controls plate coupling

    Science.gov (United States)

    Reyners, Martin; Eberhart-Phillips, Donna; Bannister, Stephen

    2017-05-01

    The Hikurangi Plateau has had two episodes of subduction beneath New Zealand - firstly at ca. 100 Ma during north-south convergence with Gondwana, and currently during east-west convergence between the Pacific and Australian plates. As a result of this ninety-degree change in convergence direction, an old subduction zone is now being subducted sideways, and the tectonic history of the subducted plate varies dramatically along the strike of the Hikurangi Margin. Here we identify the location of the underplated Hikurangi Plateau along the shallow part of the Hikurangi Margin, using results from both relocated seismicity and seismic tomography. Next we decipher the tectonic history of the plateau along strike, particularly in terms of the hydration state of the plateau, and the nature of any sedimentary rock units capping the plateau. We then use this information to understand plate coupling at two scales: on the large scale, the southward transition from typical subduction in the North Island to continental collision in the South Island; and at a smaller scale, the strong lateral change from a high deficit in slip rate at the plate interface in the southern North Island to a low deficit in slip rate in the northeastern North Island. We find that the southward transition from subduction to continental collision is controlled by the plateau being more dehydrated to the south, as a result of being more deeply subducted at the Gondwana margin. The southward transition from localized slip at the plate interface to distributed upper plate deformation with no active plate interface occurs in Cook Strait and is relatively sharp. The high deficit in slip rate at the plate interface in the southern North Island is likely due to a relatively smooth plate interface from sedimentary rocks capping the Hikurangi Plateau, an impermeable terrane in the overlying plate, and the hydrated plateau acting in concert to produce an interseismically sealed plate interface. Further northeast

  3. The role of elastic compressibility in dynamic subduction models

    Science.gov (United States)

    Austmann, Walter; Govers, Rob; Burov, Evgenii

    2014-05-01

    Recent advances in geodynamic numerical models show a trend towards more realistic rheologies. The Earth is no longer modeled as a purely viscous fluid, but the effects of, for example, elasticity and plasticity are also included. However, by making such improvements, it is essential to include these more complex rheologies in a consistent way. Specifically, compressibility needs also to be included, an effect that is commonly neglected in numerical models. Recently, we showed that the effect of elastic compressibility is significant. This was done for a gravity driven cylinder in a homogeneous Maxwell fluid bounded by closed boundaries. For a fluid with a realistic compressibility (Poisson ratio equals 0.3), the settling velocity showed a discrepancy with the semi-analytical steady state incompressible solution of approximately 40%. The motion of the fluid was no longer restricted by a small region around the cylinder, but the motion of the cylinder compressed also the fluid near the bottom boundary. This compression decreased the resistance on the cylinder and resulted in a larger settling velocity. Here, we examine the influence of elastic compressibility in an oceanic subduction setting. The slab is driven by slab pull and a far field prescribed plate motion. Preliminary results indicate that elastic compressibility has a significant effect on the fluid motion. Differences with respect to nearly incompressible solution are most significant near material boundaries. In line with our earlier findings, the flow is increased in regions of confined flow, such as the mantle wedge or the subduction channel. As a consequence, an increasing compressibility results in a larger slab velocity. We seek to identify surface observables, such as topography and plate motion, that allow us to distinguish the compressible and incompressible behavior.

  4. Subduction Stability: Lithospheric Strength and Roll-back

    Science.gov (United States)

    Patel, P. I.; Lavier, L.; Grand, S.

    2007-12-01

    In exploring the issue of subduction zone stability, we ran a series of simulations representing subduction systems consisting of simple 2D representations of oceanic lithosphere subducting beneath continental lithosphere. Our modelling software utilizes temperature dependent visco-elasto-plastic rheologies as well as a few proxies for significant chemical processes such as ecologitization and hydration. With externally imposed convergence rates, these models evolve from a contrived subduction initiation state to "normal-looking" subduction within approximately 10 million years. The simulations are then allowed to continue to evolve for up to 30 million more years. From our early results, we note that while most systems start with similar subduction geometries, they may deviate from each other over time. Notably, subduction initiated at "cooler" (and therefore stronger) junctures tend to form very stable subduction zones which maintain normal-looking geometries throughout the life of the simulation. However, subduction initiated at warmer margins tend to result in slab rollback relatively quickly. Systems with junctures of intermediate temperature also tend to subduct stably for a substantial amount of time, yet they too eventually result in rollback as the subducting slab entrains and removes some of the cooler lithosphere near the juncture, allowing hotter asthenospheric material into the contact region between the plates. The hot, low-viscosity material sharply reduces the fluid-dynamically derived suction force that partially supports the stable subduction geometry, facilitating the retreat of the subducting slab as well as the rifting of the over-riding slab. These simulations incorporate a variety of approximations and assumptions which may not reflect the actual conditions within the Earth. However, they do offer a chance to observe how a system that at least appears geometrically similar to observed Earth systems may behave when subjected to varying

  5. Fluid migration in continental subduction: The Northern Apennines case study

    Science.gov (United States)

    Agostinetti, Nicola Piana; Bianchi, Irene; Amato, Alessandro; Chiarabba, Claudio

    2011-02-01

    Subduction zones are the place in the world where fluids are transported from the foredeep to the mantle and back-to-the-surface in the back-arc. The subduction of an oceanic plate implies the transportation of the oceanic crust to depth and its methamorphization. Oceanic sediments release water in the (relatively) shallower part of the subduction zone, while dehydration of the subducted basaltic crust allows fluid circulation at larger depths. While the water budget in oceanic subduction has been deeply investigated, less attention has been given to the fluids implied in the subduction of a continental margin (i.e. in continental subduction). In this study, we use teleseismic receiver function (RF) analysis to image the process of water migration at depth, from the subducting plate to the mantle wedge, under the Northern Apennines (NAP, Italy). Harmonic decomposition of the RF data-set is used to constrain both isotropic and anisotropic structures. Isotropic structures highlight the subduction of the Adriatic lower crust under the NAP orogens, from 35-40 km to 65 km depth, as a dipping low S-velocity layer. Anisotropic structures indicate the presence of a broad anisotropic zone (anisotropy as high as 7%). This zone develops in the subducted Adriatic lower crust and mantle wedge, between 45 and 65 km depth, directly beneath the orogens and the more recent back-arc extensional basin. The anisotropy is related to the metamorphism of the Adriatic lower crust (gabbro to blueschists) and its consequent eclogitization (blueschists to eclogite). The second metamorphic phase releases water directly in the mantle wedge, hydrating the back-arc upper mantle. The fluid migration process imaged in this study below the northern Apennines could be a proxy for understanding other regions of ongoing continental subduction.

  6. Complexity

    CERN Document Server

    Gershenson, Carlos

    2011-01-01

    The term complexity derives etymologically from the Latin plexus, which means interwoven. Intuitively, this implies that something complex is composed by elements that are difficult to separate. This difficulty arises from the relevant interactions that take place between components. This lack of separability is at odds with the classical scientific method - which has been used since the times of Galileo, Newton, Descartes, and Laplace - and has also influenced philosophy and engineering. In recent decades, the scientific study of complexity and complex systems has proposed a paradigm shift in science and philosophy, proposing novel methods that take into account relevant interactions.

  7. 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.

  8. Earthquake nucleation in weak subducted carbonates

    Science.gov (United States)

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

    2016-09-01

    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 performed on simulated fault gouges prepared from ocean-floor carbonates and clays, cored during IODP drilling offshore Costa Rica. Clay-rich gouges show internal friction coefficients (that is, the slope of linearized shear stress versus normal stress data) of μint = 0.44 - 0.56, irrespective of temperature and pore-fluid pressure (Pf). By contrast, μint for the carbonate gouge strongly depends on temperature and pore-fluid pressure, with μint decreasing dramatically from 0.84 at room temperature and Pf = 20 MPa to 0.27 at T = 140 °C and Pf = 120 MPa. This effect provides a fundamental mechanism of shear localization and earthquake generation in subduction zones, and makes carbonates likely nucleation sites for plate-boundary earthquakes. Our results imply that rupture nucleation is prompted by a combination of temperature-controlled frictional instability and temperature- and pore-pressure-dependent weakening of calcareous fault gouges.

  9. Kinematic Subduction Rate of Labrador Sea Water

    Science.gov (United States)

    Courtois, P.; Garcia, Y.; Hu, X.; Myers, P. G.

    2016-02-01

    The Labrador Sea (LS) is one of few places where the atmosphere has a direct impact on the deep ocean. During strong winters, the heat loss at the surface of Labrador Sea preconditions the cooling process, disrupts the stratified water column, producing a uniformly denser water mass. This process is called deep convection and is characterized by the production of Labrador Sea Water(LSW), which in turn contributes, from a larger scale, to the lower limb of the Meridional Overturning Circulation (MOC). Due to higher anthropogenic activities, resulting in a warmer environment, freshwater input (e.g. Greenland runoff, sea­ice melting, etc.) in the LS has increased in the past decades. This has a strong impact on the ocean ventilation as it restratifies the water column and prevents the convection process.The mixed layer at the surface of the ocean is often considered as an interface between the atmosphere and the deep ocean. In the LS, the depth of the mixed layer (MLD) is greatly affected by the seasonal cycle, the freshwater input, and local processes such as the deep convection. A way to study the ventilation process in the LS is to use a kinematic approach to calculate the subduction rate, which is the vertical transport of a water mass from the mixed layer into the permanent thermocline.In this study, we present our results on the subduction rate for a different range of LSW, using the Nucleus for European Modelling of the Ocean (NEMO) numerical model.

  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. The Sulfur Cycle at Subduction Zones

    Science.gov (United States)

    de Moor, M. J.; Fischer, T. P.; Sharp, Z. D.

    2013-12-01

    We present sulfur (S) isotope data for magmatic gases emitted along the Central American (CA) Arc (oxidizing conditions ΔQFM ~+ 1.5) and at the East African Rift (reduced conditions ΔQFM ~0). The results are interpreted through mass balance calculations to characterize the S cycle through subduction zones with implications for the redox conditions of arc magmas. Voluminous gas emissions from Masaya, an open vent basaltic volcano in Nicaragua, represent >20% of the SO2 flux from the CA arc [1]. Samples from the Masaya plume have S isotope compositions of + 4.8 × 0.4 ‰ [2]. Degassing fractionation modeling and assessment of differentiation processes in this oxidized volcano suggest that this value is close to that of the source composition. High T gas samples from other CA volcanoes (Momotombo, Cerro Negro, Poas, Turrialba) range from + 3 ‰ (Cerro Negro) to + 7 ‰ (Poas; [3]). The high δ34S values are attributed to recycling of subducted oxidized sulfur (sulfate ~ + 20 ‰) through the CA arc. The δ34S values of the more reduced samples from East African Rift volcanoes, Erta Ale - 0.5 × 0.6 ‰ [3] and Oldoinyo Lengai -0.7 ‰ to + 1.2 ‰) are far lower and are probably sourced directly from ambient mantle. The subduction of oxidized material at arcs presents a likely explanation for the oxidized nature of arc magmas relative to magmas from spreading centers. We observe no distinguishable change in melt fO2 with S degassing and attribute these differences to tectonic setting. Monte Carlo modeling suggests that subducted crust (sediments, altered oceanic crust, and serpentinized lithospheric mantle) delivers ~7.7 × 2.2 x 1010 mols of S with δ34S of -1.5 × 2.3‰ per year into the subduction zone. The total S output from the arc is estimated to be 3.4 × 1.1 x 1010 mols/yr with a δ34S value similar to that of Masaya gas (+5 × 0.5 ‰). Considering δ34S values for ambient upper mantle (0 ‰ [4]) and slab-derived fluids (+14 ‰ [5]) allows calculation

  12. Effects of Two Subducting Slabs on the Temperature Distribution Along the Subduction Faults in the Kanto Region, Japan

    Science.gov (United States)

    Wada, I.; He, J.

    2015-12-01

    In this study, we investigate the thermal effects of subduction of two oceanic plates in the Kanto region of Japan, using a 3-D numerical thermal model. The Kanto region lies in the forearc of a subduction system, where the Pacific (PAC) plate and the Philippine Sea (PHS) plate subduct beneath the North American (NA) plate. In a typical subduction setting with one subducting slab, the motion of the slab drives solid-state mantle flow in the overlying mantle wedge, and the flow brings in hot mantle from the backarc towards the forearc. In the Kanto region, however, the presence of the PHS plate between the overlying NA plate and the subducting PAC plate prevents a typical mantle flow pattern. We developed a 3-D thermal model for the Kanto region to simulate the pattern of mantle wedge flow and to quantify its effect on the thermal structure. The model incorporates realistic slab geometries that were delineated from seismological studies. Mantle wedge flow between the PHS slab and the overlying NA plate is expected to be subdued due to the small space and the relatively slow subduction of the PHS slab. We simplify the model by incorporating the results of a 2-D thermal modeling for the subduction of the PHS slab as part of boundary conditions in the 3-D model to approximate the effect of the subdued mantle wedge flow and the subduction of the PHS slab. We use geophysical observations as constraints for the 3-D thermal model and estimate the temperature distributions along the subduction plate interfaces. The model predicts a particularly cold condition in the central part of the Kanto region where the PAC and PHS slabs are in contact with one another, consistent with the observed deeper extent of seismicity along the subduction faults compared to the neighboring regions.

  13. 3-D simulation for the tectonic evolution around the Kanto Region of Japan using the kinematic plate subduction model

    Science.gov (United States)

    Hashima, A.; Sato, T.; Ito, T.; Miyauchi, T.; Kameo, K.; Yamamoto, S.

    2011-12-01

    In the Kanto region of Japan, we can observe one of the most active crustal deformations on the earth. In the southern part of the Boso peninsula to the south, the uplift rate is estimated to be 5 mm/yr from the height of marine terraces. From geological evidence, the Kanto mountains to the west are considered to uplift at 1mm/yr. In contrast, the center part of the Kanto region is stable or subsiding, covered by the Holocene sediments. The depth of the basement reaches 3 km at the deepest. Vertical deformation in the timescale of 1 Myr is being revealed by the analysis of the recent seismic reflection experiments compared with the heights of the dated sediment layers exposed on land. These crustal deformation occurs in a highly complex tectonic setting with four plates interacting with each other: beneath Kanto, situated on the Eurasian and North American plates, the Philippine sea plate subducts and the Pacific plate further descends beneath the North American and Philippine sea plates, forming the unique trench-trench-trench triple junction on the earth. In addition, the Izu-Bonin (Ogasawara) arc on the Philippine sea plate is colliding with the Japan islands due to the buoyancy of the arc crust. At the plate boundaries near the Izu-Bonin arc, large interplate earthquakes occurred at the Sagami trough in 1703 and 1923 (Kanto earthquake) and at the Nankai trough in 1707, 1854 and 1944. To reveal the crustal deformation under these plate-to-plate interactions, we use the kinematic plate subduction model based on the elastic dislocation theory. This model is based on the idea that mechanical interaction between plates can rationally be represented by the increase of the displacement discontinuity (dislocation) across plate interfaces. Given the 3-D geometry of plate interfaces, the distribution of slip rate vectors for simple plate subduction can be obtained directly from relative plate velocities. In collision zones, the plate with arc crust cannot easily descend

  14. Seamount, ridge, and transform subduction in southern Central America

    Science.gov (United States)

    Morell, Kristin D.

    2016-02-01

    Understanding the factors that control subduction zone processes is a first-order goal in the study of convergent margins. In southern Central America, a growing body of research reveals strong links between the character of the subducting slab and the mechanics of important processes that include subduction erosion, fluid flow, deformation, and seismogenesis. In this paper, I evaluate the role that seamount, ridge, and transform subduction have in the development of upper plate deformation and volcanism by summarizing previous work across a >500 km long region of Central America where each of these three scenarios are present along strike. The data show that the subduction of short-wavelength bathymetry (e.g., seamounts and faults on the seafloor) produces short-wavelength deformation that persists for relatively short timescales (104-105 years), whereas the subduction of longer-wavelength bathymetry (e.g., the aseismic Cocos Ridge) results in longer-wavelength deformation that endures over a longer time scale (106 years). The timing and distribution of upper plate deformation are consistent with subhorizontal Cocos Ridge subduction driving upper plate deformation, and the increased crustal thickness (>20 km) of the subducting Cocos Ridge is likely one of the most important factors in the production of upper plate contraction and crustal thickening. The data illustrate a fundamental connection between lower plate properties and upper plate deformation and highlight the profound influence that bathymetry and crustal thickness have in the localization and kinematics of upper plate strain and volcanism in Middle America.

  15. Global correlation of lower mantle structure and past subduction

    NARCIS (Netherlands)

    Domeier, M.; Doubrovine, Pavel V.; Torsvik, Trond H.; Spakman, W.|info:eu-repo/dai/nl/074103164; Bull, A.L.

    2016-01-01

    Advances in global seismic tomography have increasingly motivated identification of subducted lithosphere in Earth's deep mantle, creating novel opportunities to link plate tectonics and mantle evolution. Chief among those is the quest for a robust subduction reference frame, wherein the mantle asse

  16. 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.

  17. 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.

  18. Buckling instabilities of subducted lithosphere beneath the transition zone

    NARCIS (Netherlands)

    Ribe, N.M.; Stutzmann, E.; Ren, Y.; Hilst, R.D. van der

    2007-01-01

    A sheet of viscous fluid poured onto a surface buckles periodically to generate a pile of regular folds. Recent tomographic images beneath subduction zones, together with quantitative fluid mechanical scaling laws, suggest that a similar instability can occur when slabs of subducted oceanic

  19. Recycling of subducted crustal components into carbonatite melts revealed by boron isotopes

    Science.gov (United States)

    Hulett, Samuel R. W.; Simonetti, Antonio; Rasbury, E. Troy; Hemming, N. Gary

    2016-12-01

    The global boron geochemical cycle is closely linked to recycling of geologic material via subduction processes that have occurred over billions of years of Earth’s history. The origin of carbonatites, unique melts derived from carbon-rich and carbonate-rich regions of the upper mantle, has been linked to a variety of mantle-related processes, including subduction and plume-lithosphere interaction. Here we present boron isotope (δ11B) compositions for carbonatites from locations worldwide that span a wide range of emplacement ages (between ~40 and ~2,600 Ma). Hence, they provide insight into the temporal evolution of their mantle sources for ~2.6 billion years of Earth’s history. Boron isotope values are highly variable and range between -8.6‰ and +5.5‰, with all of the young (-4.0‰), whereas most of the older carbonatite samples record lower B isotope values. Given the δ11B value for asthenospheric mantle of -7 +/- 1‰, the B isotope compositions for young carbonatites require the involvement of an enriched (crustal) component. Recycled crustal components may be sampled by carbonatite melts associated with mantle plume activity coincident with major tectonic events, and linked to past episodes of significant subduction associated with supercontinent formation.

  20. 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.

  1. Depth-varying azimuthal anisotropy in the Tohoku subduction channel

    Science.gov (United States)

    Liu, Xin; Zhao, Dapeng

    2017-09-01

    We determine a detailed 3-D model of azimuthal anisotropy tomography of the Tohoku subduction zone from the Japan Trench outer-rise to the back-arc near the Japan Sea coast, using a large number of high-quality P and S wave arrival-time data of local earthquakes recorded by the dense seismic network on the Japan Islands. Depth-varying seismic azimuthal anisotropy is revealed in the Tohoku subduction channel. The shallow portion of the Tohoku megathrust zone (plate mainly exhibits trench-parallel FVDs, except for the top portion of the subducting Pacific slab where visible trench-normal FVDs are revealed. A qualitative tectonic model is proposed to interpret such anisotropic features, suggesting transposition of earlier fabrics in the oceanic lithosphere into subduction-induced new structures in the subduction channel.

  2. Global correlation of lower mantle structure and past subduction

    Science.gov (United States)

    Domeier, Mathew; Doubrovine, Pavel V.; Torsvik, Trond H.; Spakman, Wim; Bull, Abigail L.

    2016-05-01

    Advances in global seismic tomography have increasingly motivated identification of subducted lithosphere in Earth's deep mantle, creating novel opportunities to link plate tectonics and mantle evolution. Chief among those is the quest for a robust subduction reference frame, wherein the mantle assemblage of subducted lithosphere is used to reconstruct past surface tectonics in an absolute framework anchored in the deep Earth. However, the associations heretofore drawn between lower mantle structure and past subduction have been qualitative and conflicting, so the very assumption of a correlation has yet to be quantitatively corroborated. Here we show that a significant, time-depth progressive correlation can be drawn between reconstructed subduction zones of the last 130 Myr and positive S wave velocity anomalies at 600-2300 km depth, but that further correlation between greater times and depths is not presently demonstrable. This correlation suggests that lower mantle slab sinking rates average between 1.1 and 1.9 cm yr-1.

  3. 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

  4. Bayesian geodynamic inversion to constrain the rheology of the flat subduction system in southwestern Mexico

    Science.gov (United States)

    Gérault, Mélanie; Bodin, Thomas

    2016-04-01

    The flat slab in southwestern Mexico differs from others at the present-day because (1) it is associated with abundant arc volcanism, (2) it is associated with extension in the arc and a neutral state of stress in the fore-arc, (3) it generates relatively low seismic activity, (4) the continental mantle lithosphere is very thin or nonexistent, (5) it is not directly caused by the subduction of thickened oceanic crust, and (6) there is no nearby cratonic keel. In a recent study, we showed that the topography in the area is controlled by both isostatic and dynamic contributions. The Trans-Mexican Volcanic Belt is either isostatically supported or slightly buoyed up by a low-density mantle wedge. To the contrary, the forearc is pulled downward by the flat slab, resulting in about 1 km of subsidence. Using a two-dimensional instantaneous Stokes flow finite-elements model, we found a combination of slab, mantle, and subduction interface properties that can predict the observed topography, plate velocities, and stress state in the continent. However, this solution is not unique, and there are trade-offs between these properties such that several combinations can provide a similarly good fit to the data. In this work, we present a geodynamic inversion to further investigate what viscosities and densities are required in different zones of the subduction system to explain the observations collected at the surface. The inverse problem is cast in a Bayesian framework, where model parameters (e.g. the viscosity in the mantle wedge and along the subduction interface) can be reconstructed in a probabilistic sense, and where trade-offs and uncertainties can be quantitatively constrained. We use a direct parameter search approach based on a Markov chain Monte Carlo (McMC) scheme to test a large number of potential scenarios.

  5. Cascadia Seismicity Related to Seamount Subduction as detected by the Cascadia Initiative Amphibious Data

    Science.gov (United States)

    Morton, E.; Bilek, S. L.; Rowe, C. A.

    2016-12-01

    Unlike other subduction zones, the Cascadia subduction zone (CSZ) is notable for the absence of detected and located small and moderate magnitude interplate earthquakes, despite the presence of recurring episodic tremor and slip (ETS) downdip and evidence of pre-historic great earthquakes. Thermal and geodetic models indicate that the seismogenic zone exists primarily, if not entirely, offshore; therefore the perceived unusual seismic quiescence may be a consequence of seismic source location in relation to land based seismometers. The Cascadia Initiative (CI) amphibious community seismic experiment includes ocean bottom seismometers (OBS) deployed directly above the presumed locked seismogenic zone. We use the CI dataset to search for small magnitude interplate earthquakes previously undetected using the on-land sensors alone. We implement subspace detection to search for small earthquakes. We build our subspace with template events from existing earthquake catalogs that appear to have occurred on the plate interface, windowing waveforms on CI OBS and land seismometers. Although our efforts will target the entire CSZ margin and full 4-year CI deployment, here we focus on a previously identified cluster off the coast of Oregon, related to a subducting seamount. During the first year of CI deployment, this target area yields 293 unique detections with 86 well-located events. Thirty-two of these events occurred within the seamount cluster, and 13 events were located in another cluster to the northwest of the seamount. Events within the seamount cluster are separated into those whose depths place them on the plate interface, and a shallower set ( 5 km depth). These separate event groups track together temporally, and seem to agree with a model of seamount subduction that creates extensive fracturing around the seamount, rather than stress concentrated at the seamount-plate boundary. During CI year 2, this target area yields >1000 additional event detections.

  6. Relative impact of mantle densification and eclogitization of slabs on subduction dynamics: A numerical thermodynamic/thermokinematic investigation of metamorphic density evolution

    Science.gov (United States)

    Duesterhoeft, Erik; Quinteros, Javier; Oberhänsli, Roland; Bousquet, Romain; de Capitani, Christian

    2014-12-01

    Understanding the relationships between density and spatio-thermal variations at convergent plate boundaries is important for deciphering the present-day dynamics and evolution of subduction zones. In particular, the interaction between densification due to mineralogical phase transitions and slab pull forces is subject to ongoing investigations. We have developed a two-dimensional subduction zone model that is based on thermodynamic equilibrium assemblage calculations and includes the effects of melting processes on the density distribution in the lithosphere. Our model calculates the 'metamorphic density' of rocks as a function of pressure, temperature and chemical composition in a subduction zone down to 250 km. We have used this model to show how the hydration, dehydration, partial melting and fractionation processes of rocks all influence the metamorphic density and greatly depend on the temperature field within the subduction system. These processes are largely neglected by other approaches that reproduce the density distribution within this complex tectonic setting. Our model demonstrates that the initiation of eclogitization (i.e., when crustal rocks reach higher densities than the ambient mantle) of the slab is not the only significant process that makes the descending slab denser and generates the slab pull force. Instead, the densification of the lithospheric mantle of the sinking slab starts earlier than eclogitization and contributes significantly to slab pull in the early stages of subduction. Accordingly, the complex metamorphic structure of the slab and the mantle wedge has an important impact on the development of subduction zones.

  7. Inside the subduction factory: Modeling fluid mobile element enrichment in the mantle wedge above a subduction zone

    Science.gov (United States)

    Shervais, John W.; Jean, Marlon M.

    2012-10-01

    Enrichment of the mantle wedge above subduction zones with fluid mobile elements is thought to represent a fundamental process in the origin of arc magmas. This "subduction factory" is typically modeled as a mass balance of inputs (from the subducted slab) and outputs (arc volcanics). We present here a new method to model fluid mobile elements, based on the composition of peridotites associated with supra-subduction ophiolites, which form by melt extraction and fluid enrichment in the mantle wedge above nascent subduction zones. The Coast Range ophiolite (CRO), California, is a Jurassic supra-subduction zone ophiolite that preserves mantle lithologies formed in response to hydrous melting. We use high-precision laser ablation ICP-MS analyses of relic pyroxenes from these peridotites to document fluid-mobile element (FME) concentrations, along with a suite of non-fluid mobile elements that includes rare earth and high-field strength elements. In the CRO, fluid-mobile elements are enriched by factors of up to 100× DMM, whereas fluid immobile elements are progressively depleted by melt extraction. The high concentrations of fluid mobile elements in supra-subduction peridotite pyroxene can be attributed to a flux of aqueous fluid or fluid-rich melt phase derived from the subducting slab. To model this enrichment, we derive a new algorithm that calculates the concentration of fluid mobile elements added to the source: C=[C/[[D/(D-PF)]∗[1-(PF/D)

  8. Complex

    African Journals Online (AJOL)

    CLEMENT O BEWAJI

    Schiff bases and their complex compounds have been studied for their .... establishing coordination of the N–(2 – hydroxybenzyl) - L - α - valine Schiff base ..... (1967); “Spectrophotometric Identification of Organic Compounds”, Willey, New.

  9. Geochemical evidence for subduction in the early Archaean from quartz-carbonate-fuchsite mineralization, Isua Supracrustal Belt, West Greenland

    DEFF Research Database (Denmark)

    Pope, Emily Catherine; Rosing, Minik Thorleif; Bird, Dennis K.

    with Phanerozoic orogenic deposits and that this type of metasomatism is a unique result of subduction-related processes. Fuchsite from the ISB has a δ18O and δD of 7.7 to 17.9‰ and -115 to -61‰, respectively. δ18O of quartz from the same rocks is between 10.3 and 18.6‰. Muscovite-quartz oxygen isotope thermometry...

  10. Early Cretaceous subduction of continental crust at the Diego de Almagro archipelago, southern Chile

    Institute of Scientific and Technical Information of China (English)

    FranciscoHervé; C.MarkFanning

    2003-01-01

    In the Diego de Almagro archipelago of southern Chile, a quartz rich mica schist and a mylonitized granite contain Late Jurassic zircons of ca 166 and 170 Ma respectively. These rocks were metamorphosed during the Cretaceous in a subduction zone environment, which developed blueschist assemblages in metabasalts interleaved with the mica schist. The dated rocks were probably part of the acid large igneous province developed in southwestern Gondwanaland during the extensional phase which preceded the dismembering of the supercontinent. They constitute evidence that tectonic erosion of the margin occurred, as these siliceous igneous rocks, formed in the South American upper plate, were transported in the subduction zone to some 20 km depth prior to their exhumation. These rocks are in tectonic contact through the Seno Arcabuz shear zone, with late Permian turbidites of the Duque de York complex, which did not undergo blueschist metamorphism.

  11. Mapping Yakutat Subduction with Tectonic Tremor

    Science.gov (United States)

    Wech, A.

    2015-12-01

    Subduction of the Yakutat microplate (YAK) in south-central Alaska may be responsible for regional high topography, large slip during the 1964 earthquake, and the anomalous gap in arc volcanism, but the exact geodynamics and its relationship with the underlying Pacific Plate (PP) are not fully understood. Refraction data support distinct subducting layers, and both GPS and body wave tomography suggest the YAK extends from the Cook Inlet volcanoes in the west to the Wrangell volcanic field in the east. Earthquakes, however, are limited to normal faulting within the PP with an abrupt eastern boundary 80 km west of the inferred YAK edge, and more recent active source seismic data suggest subduction of one homogenous thickened oceanic plateau. Here, I perform a search for tectonic tremor to investigate the role of tremor and slow slip in the system. I scan continuous waveforms from 2007-2015 using all available data from permanent and campaign seismic stations in south-central Alaska. Using envelope cross-correlation, I detect and locate ~9,000 tectonic tremor epicenters, providing a map of the transition zone downdip of the 1964 earthquake. Tremor epicenters occur downdip of discrete slow slip events, and tremor rates do not correlate temporally with slow slip behavior. Depth resolution is poor, but horizontal locations are well constrained and spatially correlate with the velocity images of the YAK. Likewise, tremor extends 80 km further east than intraslab seismicity. Tremor swarms occur intermittently and manifest as ambient tremor. I interpret tremor to mark slow, semi-continuous slip occurring at the boundary between the YAK and North American plates, whose interface continues beyond the eastern edge of the PP. In this model, the YAK is welded to the underlying PP in the west, but extends past the eastern terminus of the PP. This geometry explains the correlation between tremor and the YAK, the discrepancy between deep seismicity and tremor, and the paucity of

  12. Unique Access to Learning

    Science.gov (United States)

    Goble, Don

    2009-01-01

    This article describes the many learning opportunities that broadcast technology students at Ladue Horton Watkins High School in St. Louis, Missouri, experience because of their unique access to technology and methods of learning. Through scaffolding, stepladder techniques, and trial by fire, students learn to produce multiple television programs,…

  13. Comparison of earthquake source parameters and interseismic plate coupling variations in global subduction zones (Invited)

    Science.gov (United States)

    Bilek, S. L.; Moyer, P. A.; Stankova-Pursley, J.

    2010-12-01

    Geodetically determined interseismic coupling variations have been found in subduction zones worldwide. These coupling variations have been linked to heterogeneities in interplate fault frictional conditions. These connections to fault friction imply that observed coupling variations are also important in influencing details in earthquake rupture behavior. Because of the wealth of newly available geodetic models along many subduction zones, it is now possible to examine detailed variations in coupling and compare to seismicity characteristics. Here we use a large catalog of earthquake source time functions and slip models for moderate to large magnitude earthquakes to explore these connections, comparing earthquake source parameters with available models of geodetic coupling along segments of the Japan, Kurile, Kamchatka, Peru, Chile, and Alaska subduction zones. In addition, we use published geodetic results along the Costa Rica margin to compare with source parameters of small magnitude earthquakes recorded with an onshore-offshore network of seismometers. For the moderate to large magnitude earthquakes, preliminary results suggest a complex relationship between earthquake parameters and estimates of strongly and weakly coupled segments of the plate interface. For example, along the Kamchatka subduction zone, these earthquakes occur primarily along the transition between strong and weak coupling, with significant heterogeneity in the pattern of moment scaled duration with respect to the coupling estimates. The longest scaled duration event in this catalog occurred in a region of strong coupling. Earthquakes along the transition between strong and weakly coupled exhibited the most complexity in the source time functions. Use of small magnitude (0.5 Osa Peninsula relative to the Nicoya Peninsula, mimicking the along-strike variations in calculated interplate coupling.

  14. Serpent: Magnetic signatures of serpentinized mantle and mesoscale oceanic variability along the Alaska/Aleutian subduction zone

    Science.gov (United States)

    Purucker, Michael; Serpent Team

    2010-05-01

    NASA recently solicited suborbital missions as a part of its new Earth Venture program element. These missions are designed as complete PI-led investigations to conduct innovative, integrated, hypothesis or scientific question driven approaches to pressing questions in Earth System science. The missions should require sustained observations (5 years) and significant resources (team led by Raytheon's Photon Research Associates, propose to carry out a suborbital magnetic survey of the Aleutian subduction zone using NASA's Global Hawk to test the magnetic serpentinite hypothesis. This hypothesis states that dewatering of the descending slab within subduction zones produces an observable static magnetic signature through the formation of serpentinite in the overriding mantle. This signature may serve as a predictor of the location of large megathrust earthquakes and their associated tsunamis. Magnetic field measurements from 20 km (sub-orbital) altitude are essential to the testing of this hypothesis; analysis shows orbital and/or near-surface measurements are not likely to provide sufficient sensitivity and uniform calibration to confirm or reject the hypothesis, nor to consistently map its presence around the world. Static and dynamic magnetic signatures from the motion of seawater in the earth's magnetic field have the potential to confound an evaluation of the magnetic serpentinite hypothesis. Through a combination of modeling and exact repeat surveys over the subduction zone, spaced weeks to as much as six months apart, we can study the magnetic signature of the motion that characterizes the mesoscale oceanic circulation in order to develop the best possible corrections for lithospheric imaging, and elucidating the intrinsic and unique oceanic information content in the magnetic fields for the first time ever. The role of water in subduction zones, and in the overlying ocean, can be traced by sustained suborbital observations of the magnetic field. At critical

  15. Seismic Structure Related to the Philippine Sea Plate Subduction beneath the Nansei-Shoto (Ryukyu) Trench

    Science.gov (United States)

    Nishizawa, A.; Kaneda, K.; Oikawa, M.; Horiuchi, D.; Fujioka, Y.; Okada, C.

    2016-12-01

    The Philippine Sea plate (PHS) subduction develops a trench-arc-backarc system at the Nansei-Shoto island arc, southwest of Japan. Its backarc basin, the Okinawa Trough, is the only area around Japan where rifting has been observed at present. In the north of the Nansei-Shoto island arc, the PHS with large bathymetric highs (e.g. the Amami Plateau and the Daito Ridge) subducts approximately perpendicularly to the trench axis. In the southwest, the PHS obliquely subducts with linear seafloor topographies such as the Okinawa-Luzon fracture zone and the Gagua Ridge. We conducted multichannel seismic reflection and wide-angle seismic surveys to obtain inhomogeneous crustal structures related to such complex features of the plate subduction. The seismic lines that we shot across the Nansei-Shoto arc, consisted of two lines in the north and five lines in the southwest. We also shot two along-arc lines in the island arc and forearc areas in the southwest. Since we could not constrain the crustal structure deeper than 10 km precisely by a tomographic inversion of first arrival traveltimes, we carried out two-dimensional forward modeling using several reflection signals from the inner crust and Moho discontinuity. As a result, a middle crust with P wave velocity (Vp) of 5.9-6.5 km/s was detected between an upper and lower crust beneath the arc for all the seismic lines. However, the inner crustal structure largely differs depending on the survey lines. Distribution of low Vp forearc accretionary wedge also varies regionally along the trench axis. High Vp of 4-5 km/s within 2 km below the seafloor and Vp larger than 6 km/s just on the subducting plate boundary characterize the forearc at 125-127 E in the southwest region, which corresponds distinctive high free-air gravity anomaly. We could also obtain clear seismic images of the subducting bathymetric highs in the north and the Okinawa-Luzon fracture zone in the southwest.

  16. Carbonate dissolution and transport in aqueous fluids from subducting oceanic lithosphere

    Science.gov (United States)

    Frezzotti, M.; Huizenga, J.; Selverstone, J.; Compagnoni, R.; Sharp, Z. D.

    2012-12-01

    Subduction zones modulate the long-term carbon cycle. However, the mechanisms for the transfer of carbon from the subducting slab and sediments into the overlying mantle wedge are not well understood. Decarbonation reactions, releasing molecular CO2, were thought to be the primary mechanism. Yet, thermodynamic models show that decarbonation occurs at much greater pressures and temperatures than those found in typical subduction zones (Connolly, 2005. Earth Planet. Sci. Lett. 236, 524-541; Poli, 2009. Earth Planet. Sci. Lett. 278, 350-360). Carbon should therefore be retained in the slab and transported to great depths in the mantle, rather than supply the arc volcanoes. Diamond-bearing fluid inclusions in garnet in oceanic metasedimentary graphite-free rocks from Lago di Cignana (western Alps, Italy) represent the first occurrence of diamond from a low-temperature subduction complex of clearly oceanic origin (T ≤600°C; P ≥3.2 GPa; Groppo et al., 2009. J. Metam. Geol. 27, 207-231). The presence of diamonds in and associated with fluid inclusions provides clear evidence of carbon transport by fluids at depths that are directly relevant to sub-arc slab-mantle fluid transfer during subduction (Frezzotti et al. 2011. Nature G,4, 703-706 ). At room temperature, the fluid inclusions contain liquid water, a vapor bubble, and multiple solid daughter crystals. Daughter crystals include ubiquitous Mg-calcite/calcite and rutile, less common diamond, quartz, paragonite, hydrous/hydrated carbonates, and minor sulfates. The aqueous liquid phase further contains ≥ 0.2 wt%, HCO3-, CO32-, and SO42- ions, along with Si(OH)4(aq) and deprotonated hydrous silica monomers (e.g., SiO(OH)3-(aq), and SiO2(OH)22-(aq)). Fluid inclusions do not contain any detectable molecular CO2 in the vapor phase. This constrains XCO2 in the fluid phase to be arc depths (> 100 km) mainly through dissolution, not decarbonation. Models on the long-term carbon cycle in the Earth compute mass balances

  17. 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.

  18. Relamination of mafic subducting crust throughout Earth's history

    Science.gov (United States)

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

    2016-09-01

    Earth has likely cooled by several hundred degrees over its history, which has probably affected subduction dynamics and associated magmatism. Today, the process of compositional buoyancy driven upwelling, and subsequent underplating, of subducted materials (commonly referred to as ;relamination;) is thought to play a role in the formation of continental crust. Given that Archean continental crust formation is best explained by the involvement of mafic material, we investigate the feasibility of mafic crust relamination under a wide range of conditions applicable to modern and early Earth subduction zones, to assess if such a process might have been viable in an early Earth setting. Our numerical parametric study illustrates that the hotter, thicker-crust conditions of the early Earth favour the upward relamination of mafic subducting crust. The amount of relaminating subducting crust is observed to vary significantly, with subduction convergence rate having the strongest control on the volume of relaminated material. Indeed, removal of the entire mafic crust from the subducting slab is possible for slow subduction (∼2 cm/yr) under Archean conditions. We also observe great variability in the depth at which this separation occurs (80-120 km), with events corresponding to shallower detachment being more voluminous, and that relaminating material has to remain metastably buoyant until this separation depth, which is supported by geological, geophysical and geodynamical observations. Furthermore, this relamination behaviour is commonly episodic with a typical repeat time of approximately 10 Myrs, similar to timescales of episodicity observed in the Archean rock record. We demonstrate that this relamination process can result in the heating of considerable quantities of mafic material (to temperatures in excess of 900 °C), which is then emplaced below the over-riding lithosphere. As such, our results have implications for Archean subduction zone magmatism, for

  19. 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 o

  20. A recent phase of accretion along the southern Costa Rican subduction zone

    Science.gov (United States)

    Bangs, Nathan L.; McIntosh, Kirk D.; Silver, Eli A.; Kluesner, Jared W.; Ranero, César R.

    2016-06-01

    In 2011 we acquired a 3D seismic reflection volume across the Costa Rica margin NW of the Osa Peninsula to investigate the complex structure and the development of the seismogenic zone within the Costa Rican subduction zone in the vicinity of recent International Ocean Drilling Program (IODP) drilling. In contrast to previous interpretations, these newly acquired seismic images show that the margin wedge is composed of a layered fabric that is consistent with clastic sediments, similar to materials recovered from IODP drilling, that have been thrust and thickened into thrust-bounded folded sequences. These structures are consistent with a balanced sequence that has been frontally accreted in the context of an accretionary model. We interpret these sequences as sediment originally deposited on the subducting crust in a trench basin created by the southward migration of the Cocos-Nazca-Caribbean triple junction, and accreted during recent margin subduction that also accelerated with passage of the triple junction. The margin is composed of relatively rapidly accreted sediment that was added to the margin during a phase of accretion within the last ∼5 Ma that was probably preceded throughout the Neogene by periods of non-accretion or erosion.

  1. 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

    2017-01-01

    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. PMID:28295018

  2. 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.

  3. 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

    2017-03-01

    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.

  4. Incorporation of island-arc rocks into a Caribbean subduction channel: Geochemical constraints from eclogite boulders and greenschist rocks, Guajira region, Colombia

    Science.gov (United States)

    Weber, M.; Cardona, A.; Altenberger, U.; Garcia-Casco, A.; Valencia, V.; Tobón, M.; Zapata, S.

    2009-12-01

    Characterization of the protoliths of a subduction-accretion complex can provide major insights into the dynamics of the subduction channel. Geochemistry of eclogites found as boulders in a Tertiary conglomerate from the Guajira Peninsula, Colombia, indicate that these rocks are mainly metamorphosed basalts. A negative Nb-anomaly and flat to enriched REE patterns suggest that the eclogite protoliths evolved in a subduction related tectonic setting, with island arc affinities. The geochemical characteristics are similar to low-grade greenschists from the nearby Etpana Formation, which is interpreted as part of a Cretaceous intra-oceanic arc. This further supports evidence that the deposition and metamorphism of these units record the ongoing Late Cretaceous continental subduction of the South American margin beneath the advancing Caribbean arc. This gave way to an arc-continent collision between the Caribbean and the South American plates. Arc-rocks were incorporated into the subduction channel and the accretionary wedge, either though influx of tectonically eroded arc material (subduction erosion) or incorporation into the accretionary wedge during arc-continent collision.

  5. The role of subducting bathymetric highs on the oceanic crust to deformation of accretionary wedge and earthquake segmentation in the Java forearc

    Science.gov (United States)

    Singh, S. C.; Mukti, M.; Deighton, I.

    2014-12-01

    Stratigraphic and structural observations of newly acquired seismic reflection data along the offshore south Java reveal the structural style of deformation along the forearc and the role of subducting bathymetric highs to the morphology of the forearc region. The forearc region can be divided in to two major structural units: accretionary wedge and forearc and forearc basin where a backthrust marks the boundary between the accretionary wedge and the forearc basin sediments. The continuous compression in the subduction zone has induced younger landward-vergent folds and thrusts within the seaward margin of the forearc basin sediments, which together with the backthrust is referred as the Offshore South Java Fault Zone (OSJFZ), representing the growth of the accretionary wedge farther landward. Seaward-vergent imbricated thrusts have deformed the sediments in the accretionary wedge younging seaward, and have developed fold-thrust belts in the accretionary wedge toward trench. Together with the backthrusts, these seaward-vergent thrusts characterize the growth of accretionary wedge in South of Java trench. Based on these new results, we suggest that accretionary wedge mechanic is not the first order factor in shaping the morphology of the accretionary wedge complex. Instead the subducting bathymetric highs play the main role in shaping the forearc that are manifested in the uplift of the forearc high and intense deformation along the OSJFZ. These subducting highs also induce compression within the accretionary sediments, evident from landward deflection of the subduction front at the trench and inner part of accretionary wedge in the seaward margin of the forearc basin. Intense deformation is also observed on the seaward portion of the accretionary wedge area where the bathymetric highs subducted. We suggest that these subducted bathymetric features define the segment boundaries for megathrust earthquakes, and hence reducing the maximum size of the earthquakes in the

  6. Reducing risk where tectonic plates collide—U.S. Geological Survey subduction zone science plan

    Science.gov (United States)

    Gomberg, Joan S.; Ludwig, Kristin A.; Bekins, Barbara; Brocher, Thomas M.; Brock, John C.; Brothers, Daniel; Chaytor, Jason D.; Frankel, Arthur; Geist, Eric L.; Haney, Matt; Hickman, Stephen H.; Leith, William S.; Roeloffs, Evelyn A.; Schulz, William H.; Sisson, Thomas W.; Wallace, Kristi; Watt, Janet; Wein, Anne

    2017-06-19

    The U.S. Geological Survey (USGS) serves the Nation by providing reliable scientific information and tools to build resilience in communities exposed to subduction zone earthquakes, tsunamis, landslides, and volcanic eruptions. Improving the application of USGS science to successfully reduce risk from these events relies on whole community efforts, with continuing partnerships among scientists and stakeholders, including researchers from universities, other government labs and private industry, land-use planners, engineers, policy-makers, emergency managers and responders, business owners, insurance providers, the media, and the general public.Motivated by recent technological advances and increased awareness of our growing vulnerability to subduction-zone hazards, the USGS is uniquely positioned to take a major step forward in the science it conducts and products it provides, building on its tradition of using long-term monitoring and research to develop effective products for hazard mitigation. This science plan provides a blueprint both for prioritizing USGS science activities and for delineating USGS interests and potential participation in subduction zone science supported by its partners.The activities in this plan address many USGS stakeholder needs:High-fidelity tools and user-tailored information that facilitate increasingly more targeted, neighborhood-scale decisions to mitigate risks more cost-effectively and ensure post-event operability. Such tools may include maps, tables, and simulated earthquake ground-motion records conveying shaking intensity and frequency. These facilitate the prioritization of retrofitting of vulnerable infrastructure;Information to guide local land-use and response planning to minimize development in likely hazardous zones (for example, databases, maps, and scenario documents to guide evacuation route planning in communities near volcanoes, along coastlines vulnerable to tsunamis, and built on landslide-prone terrain);New tools

  7. Slab2 - Providing updated subduction zone geometries and modeling tools to the community

    Science.gov (United States)

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

    2015-12-01

    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 to reproduce the models it described. Currently underway, Slab2 will update and replace Slab1.0 by: (1) extending modeled slab geometries to all global subduction zones; (2) incorporating regional data sets that may describe slab geometry in finer detail 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) migrating the slab modeling code base to a more universally distributable language, Python; and (6) 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 describe our vision for Slab2, and the first results of this modeling process.

  8. NASA's unique networking environment

    Science.gov (United States)

    Johnson, Marjory J.

    1988-01-01

    Networking is an infrastructure technology; it is a tool for NASA to support its space and aeronautics missions. Some of NASA's networking problems are shared by the commercial and/or military communities, and can be solved by working with these communities. However, some of NASA's networking problems are unique and will not be addressed by these other communities. Individual characteristics of NASA's space-mission networking enviroment are examined, the combination of all these characteristics that distinguish NASA's networking systems from either commercial or military systems is explained, and some research areas that are important for NASA to pursue are outlined.

  9. Effects of the metamorphic changes on the subducting processes

    Science.gov (United States)

    Bousquet, R.; de Capitani, C.; Arcay, D.

    2005-12-01

    During the subduction-collision processes, the Earth's crust is squeezed, thickened and uplifted. Therefore rocks will be exposed to changing temperature, pressures and stress regimes and they may undergo metamorphism or partial melting. Meanwhile less attention has been paid to other important aspects of the metamorphic processes. The formation of different kind of rocks (amphibolites, eclogites, granulites) can lead to dramatic changes in petrophysical properties. When reacting rocks expand and contract, the volume changes will set up in the surrounding material. Modeling several cases of subduction for different types of rocks (granites, sediments, mafic and ultramafic rocks), we explore implications 1) on the dynamic of the subduction. Hence computing changes of physical properties of rocks as well quantity of released fluids by dynamic modeling of metamorphic reactions, we will show that some subductions are more propitious to exhume (U)HP rocks and thus to obstruct the subduction dynamic the while others are more propitious to produce heavier rocks and self-sustained subduction. 2) on the localization of earthquakes into the subducting slab. As shown by several authors, intermediate-depth earthquakes mainly occur where hydrous minerals are predicted to be present, implying a causal link between dehydration reactions and seismicity. We investigate petrophysical changes related to dehydration and their implications for generating an earthquake? 3) on the dynamic of the mantle wedge. In many subductions, the upper plate thinning seems to be controlled by the dehydration reactions. We test influence of bulk composition of the lithosphere to estimate the back-arc dynamic. Preliminary results suggest that the appearance of amphiboles within the lithosphere favors local convection and formation of back-arc basin. We conclude that changes associated with metamorphism as an alternative to changes attributed solely to compositional differences.

  10. Subduction of oceanic asthenosphere: A critical appraisal in central Alaska

    Science.gov (United States)

    Song, Teh-Ru Alex; Kawakatsu, Hitoshi

    2013-04-01

    Song and Kawakatsu (2012) have shown that the sub-slab fast splitting pattern observed in most subduction zones can be a direct consequence of subduction of the oceanic asthenosphere that has strong radial anisotropy. This model not only explains the non-intuitive trench-parallel splitting pattern in most of subduction zones, but also predicts the trench-normal behavior (fast polarization direction sub-parallel to the absolute plate motion of the incoming plate) observed in several shallow subduction zones. The general validity of such a scenario is crucial to fundamental understandings of the development of mantle anisotropy in sub-lithosphere or/and sub-slab conditions, the nature and formation of oceanic asthenosphere as well as the flow pattern and mass transport near subduction zones. To validate this scenario, we examine SKS splitting patterns observed across the fore-arc in central Alaska. Here the fast splitting direction varies from plate motion sub-parallel near the trench to mostly trench-parallel beyond the 100 km slab-isodepth contour, while being strongly variable in between. After taking into account the rotation of anisotropy symmetry in the oceanic asthenosphere with respect to the local plate motion obliquity and down-dip variations in the slab dip, we reproduce a general 90-degree switch in fast splitting direction as well as the back azimuth dependent splitting pattern across the entire fore-arc. The current validation further augments the idea that, apart from anisotropy in the mantle wedge and the subducting slab, subduction of the oceanic asthenosphere is likely to be the dominant source of seismic anisotropy in central Alaska and potentially in many subduction zones. Furthermore, this result also provides alternative views to models of seismic anisotropy in the mantle wedge and on the length scale in which the 3D mantle flow may be important.

  11. Trench curvature and deformation of the subducting lithosphere

    Science.gov (United States)

    Schettino, Antonio; Tassi, Luca

    2012-01-01

    The subduction of oceanic lithosphere is generally accompanied by downdip and lateral deformation. The downdip component of strain is associated with external forces that are applied to the slab during its sinking, namely the gravitational force and the mantle resistance to penetration. Here, we present theoretical arguments showing that a tectonic plate is also subject to a predictable amount of lateral deformation as a consequence of its bending along an arcuate trench zone, independently from the long-term physical processes that have determined the actual curvature of the subduction zone. In particular, we show that the state of lateral strain and the lateral strain rate of a subducting slab depend from geometric and kinematic parameters, such as trench curvature, dip function and subduction velocity. We also demonstrate that the relationship between the state of lateral strain in a subducting slab and the geometry of bending at the corresponding active margin implies a small component of lateral shortening at shallow depths, and may include large extensional lateral deformation at intermediate depths, whereas a state of lateral mechanical equilibrium can only represent a localized exception. Our formulation overcomes the flaws of the classic 'ping-pong ball' model for the bending of the lithosphere at subduction zones, which lead to severe discrepancies with the observed geometry and style of deformation of the modern subducting slabs. A study of the geometry and seismicity of eight modern subduction zones is performed, to assess the validity of the theoretical relationship between trench curvature, slab dip function, and lateral strain rate. The strain pattern within the eight present-day slabs, which is reconstructed through an analysis of Harvard CMT solutions, shows that tectonic plates cannot be considered as flexible-inextensible spherical caps, whereas the lateral intraslab deformation which is accommodated through seismic slip can be explained in terms

  12. Evidence for subduction-related magmatism during the Cretaceous and Cenozoic in Myanmar

    Science.gov (United States)

    Sevastjanova, Inga; Sagi, David Adam; Webb, Peter; Masterton, Sheona; Hill, Catherine; Davies, Clare

    2017-04-01

    Myanmar's complex geological history, numerous controversies around its tectonic evolution and the presence of prospective hydrocarbon basins make it a key area of interest for geologists. Understanding whether a passive or an active margin existed in the region during the Cenozoic is particularly important for the production of accurate basin models; active Cenozoic subduction would imply that hydrocarbon basins in the forearc experienced extension due to slab rollback. The geology of Myanmar was influenced by the regional tectonics associated with the Cretaceous and Cenozoic closure of the Neotethys Ocean. During this time, India travelled rapidly from Gondwana to Asia at speeds up to 20 cm/yr. To accommodate the north-eastward motion of India, the Neotethys Ocean was consumed at the subduction zone along the southern margin of Eurasia. Based on our Global Plate Model, this subduction zone can reasonably be expected to extend for the entire width of the Neotethys Ocean as far as Myanmar and Southeast Asia at their eastern extent. Moreover, a) Cretaceous volcanism onshore Myanmar, b) the middle Cenozoic arc-related extension in the Present Day eastern Andaman Sea and c) the late Cenozoic uplift of the Indo-Burman Ranges are all contemporaneous with the subduction ages predicted by the global plate motions. However, because of the geological complexity of the area, additional evidence would augment interpretations that are based on structural data. In an attempt to reduce the uncertainty in the existing interpretations, we have compiled published zircon geochronological data from detrital and igneous rocks in the region. We have used published zircon U-Pb ages and, where available, published Hf isotope data and CL images (core/rim) in order to distinguish 'juvenile' mantle-derived zircons from those of reworked crustal origin. The compilation shows that Upper Cretaceous and Cenozoic zircons, which are interpreted to have a volcanic provenance, are common across the

  13. Subduction to Continental Delamination: Insights From Laboratory Experiments

    Science.gov (United States)

    Gogus, O. H.; Corbi, F.; Faccenna, C.; Pysklywec, R. N.

    2009-05-01

    The evolution of the lithosphere through subduction-collision and delamination and its surface/crustal response (topography/deformation) is investigated in this work. We present a series of lithosphere scale two dimensional (2-D) and three dimensional (3-D) laboratory experiments to better understand such processes. In these experiments, an idealized viscously deforming crust-mantle lithosphere-mantle system is configured with silicone putty (representing lithospheric mantle and upper crust) and glucose syrup (representing the upper mantle and lower crust). The initial focus was to investigate the physical development of delamination versus continental subduction without plate convergence. Experiments show that the delamination or continental subduction is strongly dependent on the density of the crust (both crust and mantle lithosphere subducts when crust has a higher density, instead of delamination), while in the investigated range, the viscosity of the weak layer does not have much influence on the process. In all the experiments, the topography is asymmetric with subsidence above the delaminating hinge due to the dynamic vertical pulling driven by the delaminating slab, and uplift above the delaminated region due to the buoyancy of asthenosphere. Our investigation on the oceanic subduction with a convergence rate of ~ 3cm/year plate velocity suggests that subduction -collision - delamination is well defined and at the end, the delaminating crust from the lithosphere is overthrusted on top of the overriding plate. Our results provide integrated insights on the Alpine-Himalayan type orogenies, in particular the neotectonic evolution of Eastern Anatolian plateau.

  14. The Cascadia Subduction Zone: two contrasting models of lithospheric structure

    Science.gov (United States)

    Romanyuk, T.V.; Blakely, R.; Mooney, W.D.

    1998-01-01

    The Pacific margin of North America is one of the most complicated regions in the world in terms of its structure and present day geodynamic regime. The aim of this work is to develop a better understanding of lithospheric structure of the Pacific Northwest, in particular the Cascadia subduction zone of Southwest Canada and Northwest USA. The goal is to compare and contrast the lithospheric density structure along two profiles across the subduction zone and to interpet the differences in terms of active processes. The subduction of the Juan de Fuca plate beneath North America changes markedly along the length of the subduction zone, notably in the angle of subduction, distribution of earthquakes and volcanism, goelogic and seismic structure of the upper plate, and regional horizontal stress. To investigate these characteristics, we conducted detailed density modeling of the crust and mantle along two transects across the Cascadia subduction zone. One crosses Vancouver Island and the Canadian margin, the other crosses the margin of central Oregon.

  15. Crystal Structure of the Human Cytomegalovirus pUL50-pUL53 Core Nuclear Egress Complex Provides Insight into a Unique Assembly Scaffold for Virus-Host Protein Interactions.

    Science.gov (United States)

    Walzer, Sascha A; Egerer-Sieber, Claudia; Sticht, Heinrich; Sevvana, Madhumati; Hohl, Katharina; Milbradt, Jens; Muller, Yves A; Marschall, Manfred

    2015-11-13

    Nuclear replication of cytomegalovirus relies on elaborate mechanisms of nucleocytoplasmic egress of viral particles. Thus, the role of two essential and conserved viral nuclear egress proteins, pUL50 and pUL53, is pivotal. pUL50 and pUL53 heterodimerize and form a core nuclear egress complex (NEC), which is anchored to the inner nuclear membrane and provides a scaffold for the assembly of a multimeric viral-cellular NEC. Here, we report the crystal structure of the pUL50-pUL53 heterodimer (amino acids 1-175 and 50-292, respectively) at 2.44 Å resolution. Both proteins adopt a globular fold with mixed α and β secondary structure elements. pUL53-specific features include a zinc-binding site and a hook-like N-terminal extension, the latter representing a hallmark element of the pUL50-pUL53 interaction. The hook-like extension (amino acids 59-87) embraces pUL50 and contributes 1510 Å(2) to the total interface area (1880 Å(2)). The pUL50 structure overall resembles the recently published NMR structure of the murine cytomegalovirus homolog pM50 but reveals a considerable repositioning of the very C-terminal α-helix of pUL50 upon pUL53 binding. pUL53 shows structural resemblance with the GHKL domain of bacterial sensory histidine kinases. A close examination of the crystal structure indicates partial assembly of pUL50-pUL53 heterodimers to hexameric ring-like structures possibly providing additional scaffolding opportunities for NEC. In combination, the structural information on pUL50-pUL53 considerably improves our understanding of the mechanism of HCMV nuclear egress. It may also accelerate the validation of the NEC as a unique target for developing a novel type of antiviral drug and improved options of broad-spectrum antiherpesviral therapy.

  16. Mantle flow influence on the evolution of subduction systems.

    Science.gov (United States)

    Chertova, Maria; Spakman, Wim; Steinberger, Bernhard

    2016-04-01

    Evolution of the subducting slab has been widely investigated in the past two decades be means of numerical and laboratory modeling, including analysis of the factors controlling its behavior. However, until present, relatively little attention has been paid to the influence of the mantle flow. While for large subduction zones, due to the high slab buoyancy force, this effect might be small, mantle flow might be a primary factor controlling the evolution of a regional subduction zone. Here we investigate the impact of prescribed mantle flow on the evolution of both generic and real-Earth subduction models by means of 3D thermo-mechanical numerical modeling. The generic setup consists of a laterally symmetric subduction model using a 3000×2000×1000 km modeling domain with a lateral slab width varying from 500 to 1500 km. Non-linear rheology is implemented including diffusion, dislocation creep and a viscosity-limiter. To satisfy mass conservation, while implementing mantle inflow on some side boundaries, we keep other sides open (Chertova et al. 2012). To test the mantle flow influence on the dynamics of real-Earth subduction zone we adopt the numerical model from Chertova et al. (2014) for the evolution of the western Mediterranean subduction since 35 Ma. First, this model was tested with the arbitrary mantle flow prescribed on one of the four side boundaries or for the combination of two boundaries. In the last set of experiments, for side boundary conditions we use time-dependent estimates of actual mantle flow in the region based on Steinberger (2015) given for every 1 My. We demonstrate that for the western-Mediterranean subduction, the surrounding mantle flow is of second-order compared to slab buoyancy in controlling the dynamics of the subducting slab. Introducing mantle flow on the side boundaries might, however, improve the fit between the modeled and real slab imaged by tomography, although this may also trade-off with varying rheological parameters of

  17. Three Dimensional Simulations of Strong Motions for Great Earthquakes on the Cascadia Subduction Zone

    Science.gov (United States)

    Delorey, A. A.; Frankel, A. D.; Stephenson, W. J.; Liu, P.

    2011-12-01

    Using a finite-fault rupture model, we ran a finite difference code to simulate a variety of Mw 8 and larger events on the Cascadia subduction zone using a 3D regional velocity model and two different 3D velocity models for the Seattle basin. Our results reveal the magnitude and duration of shaking that should be expected in the built environment for a megathrust event with a rupture length less than the entire length of the subduction zone. In the next step we will consider events that rupture the entire length of the subduction zone, similar in scope to the 1700 event, and compare our results to those considered for the national seismic hazard maps. In order to make predictions on the strength and duration of shaking in Cascadia due to a large megathrust event, we developed a kinematic fault rupture model based on a k-2 decay in final slip spectrum that has a scale-dependent rise time. This produces a ω-2 decay in the radiated displacement spectrum above the corner frequency, which is then modified by rupture directivity. In order to produce a k-2 decay in the final slip spectrum, we modeled the final slip as the sum of asperities with various wave numbers produced by calculating normal modes for a membrane, then shifting the phase of the standing waves to randomize the pattern. In this way, slip naturally decays towards the edges of the rupture without having to use a taper, we can produce a final slip model with any spectrum we choose, and each wave number can be assigned a unique rise time. The slip on each individual asperity initiates in time according to its closest distance to the hypocenter and the rupture velocity. The Cascadia subduction zone off the coast of northwestern United States and southwestern Canada is capable of producing megathrust earthquakes with magnitudes up to Mw 9.0 for margin-wide events and magnitudes greater than Mw 8.0 if only part of the subduction zone ruptures. The average recurrence interval for margin-wide megathrust

  18. Carboniferous granites on the northern margin of Gondwana, Anatolide-Tauride Block, Turkey - Evidence for southward subduction of Paleotethys

    Science.gov (United States)

    Candan, O.; Akal, C.; Koralay, O. E.; Okay, A. I.; Oberhänsli, R.; Prelević, D.; Mertz-Kraus, R.

    2016-06-01

    Carboniferous metagranites with U-Pb zircon crystallization ages of 331-315 Ma crop out in the Afyon zone in the northern margin of the Anatolide-Tauride Block, which is commonly regarded as part of Gondwana during the Late Palaeozoic. They are peraluminous, calc-alkaline and are characterized by increase in Rb and Ba, decrease in Nb-Ta, and enrichment in Sr and high LILE/HFSE ratios compatible with a continental arc setting. The metagranites intrude a metasedimentary sequence of phyllite, metaquartzite and marble; both the Carboniferous metagranites and metasedimentary rocks are overlain unconformably by Lower Triassic metaconglomerates, metavolcanics and Upper Triassic to Cretaceous recrystallized limestones. The low-grade metamorphism and deformation occurred at the Cretaceous-Tertiary boundary. There is no evidence for Carboniferous deformation and metamorphism in the region. Carboniferous arc-type granites and previously described Carboniferous subduction-accretion complexes on the northern margin of the Anatolide-Tauride Block suggest southward subduction of Paleotethys under Gondwana during the Carboniferous. Considering the Variscan-related arc granites in Pelagonian and Sakarya zones on the active southern margin of Laurasia, a dual subduction of Paleotethys can be envisaged between Early Carboniferous and Late Permian. However, the southward subduction was short-lived and by the Late Permian the Gondwana margin became passive.

  19. Subduction-zone cycling of nitrogen in serpentinized mantle rocks

    Science.gov (United States)

    Halama, R.; Bebout, G. E.; John, T.; Scambelluri, M.

    2010-12-01

    Nitrogen (N) has shown great potential as a geochemical tracer of volatiles recycling, in part because of large differences in the N isotope composition of the various Earth reservoirs. The subduction flux of N in serpentinized oceanic mantle could be as important as N input flux in oceanic crust and even sediment because, although its N concentrations are lower, its volume is potentially far greater than that of the crust/sediment. However, recycling of oceanic mantle rocks is still poorly constrained for the N cycle, and N isotope data for subduction-related ultramafic rocks are scarce [1]. The primary goal of this study is to characterize the subduction flux of N in subducting altered oceanic mantle by documenting concentrations and isotopic compositions of N in mantle rocks that reflect different stages of the metamorphic subduction zone cycle. The results are crucial to assess the composition of N recycled into the mantle, to determine the extent to which N can be retained in subducted mantle rocks to depths approaching those beneath arcs, and to balance N subduction-zone inputs with outputs in arc volcanic gases. Moreover, information has been gained regarding the redistribution and isotope fractionation of N via ultramafic dehydration and metamorphic fluid-rock interaction. The samples analyzed in this study are ultramafic rocks from shallow oceanic environments to increasing P-T conditions up to depths of ~70 km. Three distinct metamorphic grades, reflecting seafloor fluid uptake, water release due to brucite breakdown and the final antigorite breakdown, were investigated: 1. Pre-subduction serpentinized mantle peridotite from non-subducted ophiolite sequences from the Northern Apennines, Italy (Monte Nero). 2. Eclogite-facies antigorite serpentinites from the Ligurian Alps, Italy (Erro Tobbio). 3. Eclogite-facies chlorite harzburgites derived from dehydration of serpentinites from the Betic Cordillera, Spain (Cerro de Almirez). The pre-subduction

  20. 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

  1. High-resolution Imaging of the Philippine Sea Plate subducting beneath Central Japan

    Science.gov (United States)

    Padhy, S.; Furumura, T.

    2016-12-01

    Thermal models predict that the oceanic crust of the young (PHP) is more prone to melting. Deriving a high-resolution image of the PHP, including slab melting and other features of the subduction zone, is a key to understand the basics of earthquake occurrence and origin of magma in complex subduction zone like central Japan, where both the PHP and Pacific (PAC) Plates subduct. To this purpose, we analyzed high-resolution waveforms of moderate sized (M 4-6), intermediate-to-deep (>150 km) PAC earthquakes occurring in central Japan and conducted numerical simulation to derive a fine-scale PHP model, which is not constrained in earlier studies. Observations show spindle-shaped seismograms with strong converted phases and extended coda with very slow decay from a group of PAC events occurring in northern part of central Japan and recorded by high-sensitivity seismograph network (Hi-net) stations in the region. We investigate the mechanism of propagation of these anomalous waveforms using the finite difference method (FDM) simulation of wave propagation through the subduction zone. We examine the effects on waveform changes of major subduction zone features, such as the melting of oceanic crust in PHP, serpentinized mantle wedge, hydrated layer on the PAC due to slab dehydration, and anomaly in upper mantle between the PAC and PHP. Simulation results show that the waveform anomaly is primarily explained by strong scattering and absorption of high-frequency energy by the low-velocity anomalous mantle structure, with a strong coda excitation yielding spindle-shaped waveforms. The data are secondarily explained by melting of PHP in the basaltic crust. The location of the mantle anomaly is tightly constrained by the observation and evidence of PAC thinning in the region; these localized low-velocity structures aid in ascending the slab-derived fluids around the slab thinning. We expect that the results of this study will enhance our present understanding on the mechanism

  2. Postseismic deformation after Maule earthquake and the mechanical properties of the asthenosphere and subduction interface

    Science.gov (United States)

    Klein, Emilie; Fleitout, Luce; Vigny, Christophe

    2015-04-01

    The interseismic and postseismic deformations preceding and following the large subduction earthquake of Maule (Chile, Mw8.8, 2010) have been closely monitored with GPS from 70 km up to 2000 km away from the trench. Post-seismic deformations exhibit a behavior generally similar to that already observed after the Aceh and Tohoku-Oki earthquakes: vertical uplift is observed on the oceanward side of the volcanic arc. A moderate large scale subsidence is associated with sizeable horizontal deformation in the far-field (500-2000km from the trench). In addition, near-field data (70-200km from the trench) feature a rather complex deformation pattern. A 3D FE code (Zebulon Zset) is used to relate these deformations to the mechanical properties of the mantle and of the subduction interface. The mesh features a spherical shell-portion from the core-mantle boundary to the Earth's surface, extending over more than 60 degrees in latitude and longitude. The overridding and subducting plates are elastic, and the asthenosphere is viscoelastic. We test the presence and shape of two low viscosity areas in the mantle : a low viscosity wedge (LVW) above the subducting plate extending beneath the volcanic arc, and a narrow low viscosity channel (LVCh) along the lower part of the subduction interface, and potentially deeper. All the viscoelastic regions feature a Burgers rheology and we invert for their mechanical properties and geometrical characteristics. Our best fitting models present, (i) an asthenosphere extending down to 270km, with a 'long-term' viscosity of the order of 3.1018Pa.s; (ii) a LVCh along the plate interface extending from depths of 50 to 150 km with viscosities slightly below 1018 Pa.s; (iii) a LVW restricted to the base of the lithosphere below the volcanic arc, with viscosities of a few 1018 Pa.s. Increased horizontal velocities are due to relaxation in both the asthenosphere and the LVCh. A deep channel is necessary to produce enough uplift in the middle

  3. The 2014 Mw6.2 Eketahuna earthquake, Hikurangi subduction zone - normal faulting in the subducted Pacific Plate crust

    Science.gov (United States)

    Abercrombie, R. E.; Bannister, S. C.; Francois-Holden, C.; Hamling, I. J.; Ristau, J. P.

    2014-12-01

    The 2014 January 20th M6.2 Eketahuna earthquake occurred in the subducted crust of the Pacific plate at the Hikurangi subduction zone, beneath North Island, New Zealand. Moment tensor analysis together with aftershock relocations show that this event was an oblique-normal faulting intraplate event, with hypocentre depth ca.30 km, and with rupture on a northwest-dipping fault extending through the subducted crust up to the subduction megathrust at ca.18-20 km depth. More than 3500 aftershocks were subsequently recorded by the New Zealand GeoNet network, with only minor migration of the aftershocks away from the inferred mainshock rupture, and with very few aftershocks within +/- 1 km of the subduction megathrust. The megathrust in this particular region is inferred to be interseismically locked with no seismic or aseismic slip, although slow slip is occurring ca.15-30 km down-dip (Wallace et al, 2013). Similar oblique-normal faulting events have previously occurred along the Hikurangi subduction margin, including in 1985 (ML5.7) and 1990 (Mw6.2). Earlier earthquakes in 1942 (Mw6.8) and 1921 (Mw6.8) are also inferred to have occurred at a similar depth within the subducted crust. The 1990 earthquake sequence occurred ~40 km along-strike from the 2014 Eketahuna event, and involved a Mw6.2 oblique-normal faulting event in the subducted crust, which was quickly followed by a Mw6.4 event in the overlying crust, with both thrust and dextral strike-slip components, possibly responding to deeper aseismic slip. Deeper earthquakes of similar type at other subduction margins are thought to be high stress drop. We calculate the stress drops of the mainshock and larger aftershocks, using a direct wave, empirical Green's function (EGF) approach that includes measurement uncertainties and objective criteria for assessing the quality of each spectral ratio (Abercrombie, 2013). We compare the results to those for earthquakes in other tectonic regions of New Zealand, calculated using

  4. Slab Detachment, Flat Subduction and Slab Rollback in Central Mexico: Fitting the Neogene Evolution of the Trans-Mexican Volcanic Belt into the History and Dynamics of Subduction

    Science.gov (United States)

    Ferrari, L.

    2001-12-01

    I present a comparative analysis of the volcanic record of the Trans-Mexican Volcanic Belt (TMVB) and the plate tectonic history since 16 Ma in central Mexico that has important implications for the dynamic of the Cocos-Rivera subduction system. The TMVB volcanism has occurred in episodes characterized by across-arc and along strike variation and/or migration. In its first stage (16 to 10 Ma) the TMVB consisted of a broad andesitic arc emplaced between Long. 102° and 97° 30' (central Mexico). During this period volcanism was absent in the western and eastern TMVB. Between 11 and 6 Ma a voluminous mafic volcanism was emplaced to the northof the previous arc with ages progressively younger from west (Tepic-Guadalajara) to east (Queretaro-Hidalgo). Large calderas and silicic dome complexes developed in latest Miocene and early Pliocene (7.5 to 3.5 Ma) west of the Taxco-San Miguel de Allende fault system (TSMA). East of the TSMA a volcanic gap is clearly observed between ~9 and 3.5 Ma. In the western TMVB small amount of lavas with an intra-plate affinity started to be emplaced since 5 Ma. At the same time the volcanic front migrated to the south by about 70 km. East of the TSMA volcanism resumed at about 3.5 Ma in the Mexico City region and at the end of Pliocene in the eastern TMVB (excluding the Palma Sola area). In the Toluca - Mexico City area the volcanic front migrated trenchward in the Quaternary. No southward migration of the volcanic front is observed in the eastern TMVB. The Middle Miocene volcanism represent a "normal" volcanic arc developed after a gap of ~15 Ma following the formation of the Acapulco trench. I propose that the following unusual volcanic evolution was controlled by the detachment of the deeper part of the Cocos slab and the resulting variation in slab inclination. Slab must have detached after 12.5 following the end of subduction off Baja California. This is a kinematic-dynamic requirement, also supported by the fact that the present

  5. Constraints from Li isotope systematics on subduction recycling, arc magmatism, and continent growth: An overview

    Science.gov (United States)

    Leeman, W. P.; Lee, C. A.; Chan, L. H.

    2008-12-01

    Great expectations that Li isotopic systematics can uniquely constrain many fluid-mitigated geologic processes have met with mixed success for a variety of reasons. On a local scale (some volcanic arc segments) Li composition can be highly correlated with other geochemical tracers of subduction fluids whereas, globally, such correlations tend to be disappointingly poor. The utility of Li isotopes as a tracer is limited in part by extensive overlap between mantle and subduction inputs, by limited understanding of equilibrium isotopic fractionation effects, and by apparent departures from equilibrium behavior. On the other hand, Li elemental systematics provide important constraints on global recycling processes because major litho-tectonic reservoirs have distinctive enrichments or depletions with respect to Nb or other HFSEs. Such chemical fractionations can be understood in terms of differential solubility of these elements in aqueous fluids vs. silicate melts, as well as the roles of weathering, dehydration, metamorphic or melting processes. For example, arc lavas are are systematically enriched in Li compared to those from other settings and typically have Li/Nb greater than BSE (consistent with addition of Li-rich fluids to their sources). In contrast, bulk continental crust and orogenic granitoids tend to have lower Li/Nb than BSE or arc lavas. Moreover, mass balance implies that the residual mantle (DM) produced by segregation of crust has higher Li/Nb than BSE. However, if continental crust is ultimately derived by subduction related magmatism, high Li/Nb would be expected for the crust and low Li/Nb for the upper mantle. This interesting conundrum is easiest explained in terms of selective Li removal from crustal protolith rocks via chemical weathering and erosion, which also is consistent with Li isotopic compositions of crust, mantle and seawater reservoirs. Thus, Li elemental and isotopic systematics (and relevant proxies) provide complementary

  6. 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

  7. Role of the subduction filter in mantle recycling

    Science.gov (United States)

    Kimura, J. I.; Skora, S. E.; Gill, J.; Van Keken, P. E.

    2015-12-01

    Subduction modifies the descending basaltic and sedimentary oceanic crust and generates felsic arc materials and continental crust. Studies of element mass balances in the subduction zone therefore reveal the evolution of the Earth's two major geochemical reservoirs: the continent crust and mantle. We use the Arc Basalt Simulator ver.4 (ABS4) to model the geochemical mass balance during dehydration by prograde metamorphism and melting of the slab followed by subsequent flux melting of the wedge mantle caused by the addition of slab-derived liquids. The geochemistry of high-Mg andesite or adakite formed in a hot subduction zone is akin to the present-day bulk continental crust and to the Archean (>2 Ga) Tonalite-Trondjhemite-Granodiorite composition. Therefore, the residual slab and the metasomatized mantle wedge at hot subduction zones should be the most plausible sources for materials recycled back into the deep mantle. Model calculations of isotopic growth in the residual slab and mantle formed in hot subduction zones reproduce fairly well the EM1-FOZO-HIMU isotope arrays found in ocean island basalts (OIBs) of deep mantle plume origin, although FOZO with high 3He/4He is not generated by this slab recycling process. The recycled materials are bulk igneous ocean crust for HIMU and metasomatized mantle wedge peridotite for EM1. In contrast, the EM2-FOZO array can be generated in a cold subduction zone with igneous oceanic crust for FOZO and sediment for EM2 sources. Necessary residence time are ~2 Ga to form HIMU-FOZO-EM1 and ~1 Ga to form EM2-FOZO. The subducted oceanic crust (forming HIMU) and mantle wedge peridotite (forming EM1) may have travelled in the mantle together. They then melted together in an upwelling mantle plume to form the EM1-FOZO-HIMU isotopic variations found frequently in OIBs. In contrast, the less frequent EM2-FOZO array suggests a separate source and recycling path. These recycling ages are consistent with the change in the mantle potential

  8. Curie depth vs. flat subduction in Central Mexico

    Science.gov (United States)

    Manea, Marina; Constantin Manea, Vlad

    2010-05-01

    Forearcs located above active subduction zones are generally characterized by low heat flow values, and this is considered a consequence of the subduction of cold slabs beneath continental plates. In the case of Central Mexico, the geometry of the subducting Cocos plate is quite unusual, the slab runs flat for several hundreds of kilometers before plunging into the asthenosphere. This particular geometry has a strong influence on the temperature distribution of the overriding plate where very low heatflow values are recorded (15-30 mW/m2). In this paper we use the aeromagnetic map of Mexico in order to infer the maximum depth of magnetic source, regarded as Curie depth and corresponding to a temperature of 575-600C°. Our spectral analysis revealed the existence of a deep magnetic source (30-40 km). We compare these results with the thermal structure associated with flat slab subduction in the area. We obtained a good agreement between the two estimates and we conclude that flat slab subduction in Central Mexico controls the maximum depth of magnetic sources in the overriding plate.

  9. 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.

  10. Structural controls on fluid escape from the subduction interface

    Science.gov (United States)

    Reynard, Bruno; Tauzin, Benoit; Bodin, Thomas; Perrillat, Jean-Philippe; Debayle, Eric

    2017-04-01

    Seismic activity and non-volcanic tremors are often associated with fluid circulation resulting from the dehydration of subducting plates. Tremors in the overriding continental crust of several subduction zones suggest fluid circulation at shallower depths, but potential fluid pathways are still poorly documented. Fluids are also released at different depths in hot and cold subduction zones, which may result in different schemes of fluid escape. We document potential fluid pathways in Cascadia, one of the hottest subduction zone, using receiver function analysis. We provide evidence for a seismic discontinuity near 15 km depth in the crust of the overriding North American plate. This interface is segmented, and its interruptions are spatially correlated with conductive regions of the forearc and shallow swarms of seismicity and non-volcanic tremors. The comparison of seismological and electrical conductivity profiles suggests that fluid escape is controlled by fault zones between blocks of accreted terranes in the overriding plate. These zones constitute fluid escape routes that may influence the seismic cycle by releasing fluid pressure from the megathrust. Results on Cascadia are compared to fluid escape routes suggested by former geophysical observations in NE Japan, one of the coldest subduction zones. Links between fluid escape, permeability and fluid-rock reactions at or above the plate interface are discussed.

  11. Plume head - trench interaction: impact on subduction dynamics

    Science.gov (United States)

    Betts, P. G.; Moresi, L. N.; Mason, W. G.; Willis, D.

    2013-12-01

    The geologic record provides numerous examples where plumes and their associated buoyancy swell have disrupted convergent plate margins. These interactions have produced a variety of responses in the overriding plate including transient episodes of arc amagmatism, transient episodes of crustal shortening followed by plume-related magmatism in the overriding plate. The latter observation implies the plume must have transitioned from the subducting plate to the overriding plate. We present several 3D Underworld numerical models of plume heads of variable dimension and buoyancy interacting with a subduction trench. The models indicate that plume heads impact enormously on trench geometry. Arcuate trenches are created as the trench retreats around the edges of the plume head, whereas trench advance occurs in front of the plume resulting in transient crustal shortening in the overriding plate. Stalling of subduction when the plume head impacts the trench causes slab windowing. The size of the slab window is dependent on the size and buoyancy of the plume. The creation of the slab window provides a potential conduit for plume migration to the overriding plate. Alternatively, the plume head may be transferred to the overriding plate as subduction is re-established behind the plume. Models with "strong" slabs, characterized by high yield strengths, display different behavior. Plume-heads are entrained in the slab and are subducted without the development of a slab window.

  12. Rock uplift at the transition from flat-slab to normal subduction: The Kenai Mountains, Southeast Alaska

    Science.gov (United States)

    Valentino, Joshua D.; Spotila, James A.; Owen, Lewis A.; Buscher, Jamie T.

    2016-03-01

    The process of flat-slab subduction results in complex deformation of overlying forearcs, yet how this deformation decays with distance away from the zone of underthrusting is not well understood. In south central Alaska, flat-slab subduction of the Yakutat microplate drives shortening and rock uplift in a broad coastal orogenic belt. Defined limits of the zone of underthrusting allow testing how orogenesis responds to the transition from flat-slab to normal subduction. To better understand forearc deformation across this transition, apatite (U-Th)/He low temperature thermochronometry is used to quantify the exhumation history of the Kenai Mountains that are within this transition zone. Measured ages in the northern Kenai Mountains vary from 10-20 Ma and merge with the exhumation pattern in the Chugach Mountains to the northeast, where high exhumation occurs due to flat-slab-related deformation. In the southern Kenai Mountains, however, ages increase to 30-50 Ma across a transition near Seward, Alaska, above the zone from flat-slab to normal subduction. These ages are relatively old in comparison to ages determined in other studies in southern Alaska and suggest minimal exhumation. Furthermore, transitions in topographic expression of the coastal orogen also occur at the margin of Yakutat underthrusting. These observations suggest that either deformation associated with flat-slab subduction requires tens of kilometers to decay with distance away from the zone of underthrusting, or that orogenesis in the Kenai Mountains is driven by a distinct tectonic cause. A potential driver of deformation is underplating of thick sediments, specifically the Surveyor Submarine Fan, along the Aleutian Megathrust, analogous to the tectonic mechanism responsible for the emergence of the Kodiak Island forearc. If correct, this may represent a recent tectonic transition in the region, given the minimal exhumation of the rugged Kenai Mountains despite the presence of an erosion

  13. Crustal Structure of the Caribbean-South American Diffuse Plate Boundary: Subduction Zone Migration and Polarity Reversal Along BOLIVAR Profile 64W

    Science.gov (United States)

    Clark, S. A.; Levander, A.; Magnani, M.; Zelt, C. A.; Sawyer, D. S.; Ave Lallemant, H. G.

    2005-12-01

    The BOLIVAR (Broadband Ocean-Land Investigation of Venezuela and the Antilles arc Region) project is an NSF funded, collaborative seismic experiment in the southeast Caribbean region. The purpose of the project is to understand the diffuse plate boundary created by the oblique collision between the Caribbean and South American plates. Profile 64W of the BOLIVAR experiment, a 450 km-long, N-S transect onshore and offshore Venezuela located at ~64°W longitude, images the deep crustal structures formed by this collision. The active source components of profile 64W include 300 km of MCS reflection data, 33 coincident OBSs, and 344 land seismic stations which recorded 7500 offshore airgun shots and 2 explosive land shots. Results from the reflection and refraction seismic data along 64W show complex crustal structure across the entire span of the diffuse plate boundary. The onshore portion of 64W crosses the fold and thrust belt of the Serrania del Interior, which formed at ~16 Ma by collision of the Caribbean forearc with the northern South American passive margin. Underlying the Serrania del Interior is a south-vergent, remnant Lesser Antillean subduction zone. As this Lesser Antilles subduction impinged on continental crust, it caused a polarity reversal and jump offshore to the north. Convergence was initially localized in the closure and inversion of the Grenada Basin. However, subduction could not develop because of the ~20-km-thick crust of the Aves Ridge; instead, north-vergent subduction initiated further to the north, where ~12-km-thick Caribbean oceanic crust of the Venezuela Basin began to subduct beneath the Aves Ridge in the Pliocene (~4 Ma) and appears to continue subducting today. Between the remnant subduction zone and the modern one, the El Pilar and Coche dextral strike-slip faults accommodate most of the transform motion of the plate boundary. From the Serrania del Interior to the Aves Ridge, ~260 km of accreted orogenic float comprises the diffuse

  14. Carbonation of subduction-zone serpentinite (high-pressure ophicarbonate; Ligurian Western Alps) and implications for the deep carbon cycling

    Science.gov (United States)

    Scambelluri, Marco; Bebout, Gray E.; Belmonte, Donato; Gilio, Mattia; Campomenosi, Nicola; Collins, Nathan; Crispini, Laura

    2016-05-01

    Much of the long-term carbon cycle in solid earth occurs in subduction zones, where processes of devolatilization, partial melting of carbonated rocks, and dissolution of carbonate minerals lead to the return of CO2 to the atmosphere via volcanic degassing. Release of COH fluids from hydrous and carbonate minerals influences C 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. Several lines of evidence indicate mobility of C, of uncertain magnitude, in forearcs. A poorly constrained fraction of the 40-115 Mt/yr of C initially subducted is released into fluids (by decarbonation and/or carbonate dissolution) and 18-43 Mt/yr is returned at arc volcanoes. Current estimates suggest the amount of C released into subduction fluids is greater than that degassed at arc volcanoes: the imbalance could reflect C subduction into the deeper mantle, beyond subarc regions, or storage of C in forearc/subarc reservoirs. We examine the fate of C in plate-interface ultramafic rocks, and by analogy serpentinized mantle wedge, via study of fluid-rock evolution of marble and variably carbonated serpentinite in the Ligurian Alps. Based on petrography, major and trace element concentrations, and carbonate 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 and that the interaction of these COH fluids with serpentinite led to the formation of high-P carbonated ultramafic-rock domains (high-P ophicarbonates). We estimate that this could result in the retention of ∼0.5-2.0 Mt C/yr in such rocks along subduction interfaces. As another means of C storage, 1 to 3 km-thick layers of serpentinized forearc mantle wedge containing 50 modal % dolomite could sequester 1.62 to

  15. Tectonometamorphic record in a fossilized subduction channel: insights from the Cycladic Blueschist Unit (Cyclades, Greece)

    Science.gov (United States)

    Laurent, Valentin; Roche, Vincent; Jolivet, Laurent; Lanari, Pierre; Augier, Romain; Scaillet, Stéphane

    2016-04-01

    structure of a fossilized subduction channel. Based on structural and petrological observations, the CBU has been subdivided into subunits separated by major ductile shear zones. The Vari Detachment, interpreted as the Eocene subduction channel roof, separates these HP subunits from the overlying Vari Unit that has not seen HP-LT conditions. We show that after the prograde top-to-the S/SW shearing deformation, the CBU was exhumed by an overall top-to-the E/NE shearing from the depth of eclogites all the way to the depth of the greenschist-facies. Finally, considering geochronologic data from the literature, we propose a possible P-T-t-d evolution scenario of the CBU in the context of the Hellenic subduction by reconstructing step-by-step north-south cross-sections of the Aegean domain from Late Paleocene (~55 Ma) to the present-day geometry. This tectonometamorphic evolution shows how strain localizes during the history of an accretionary complex, both during the prograde and retrograde paths.

  16. Segmented Coastal Uplift Along an Erosional Subduction Margin, Northern Hikurangi Fore Arc, North Island, New Zealand

    Science.gov (United States)

    Marshall, J. S.; Litchfield, N. J.; Berryman, K. R.; Clark, K.; Cochran, U. A.

    2013-12-01

    Bay and Hawke's Bay), a prominent flight of Holocene and late Pleistocene marine terraces (OIS 1-7) record outer forearc uplift at 1.0-2.5 m/ky above the upper-plate Lachlan thrust (Berryman, 1993). Five steps of discrete age within the Holocene terrace are interpreted as coseismic uplift events ranging in age from 250 - 4500 ybp. At Cape Kidnappers (south of Hawke's Bay), at least three late Pleistocene marine terraces were observed in this study at 50-120 m above msl. Preliminary correlation with OIS 5a-e sea level high stands indicates net uplift at 0.8-1.0 m/ky along the Kidnappers anticline. Adjacent Holocene shore deposits overlie a 6 m high uplifted wavecut platform that records coseismic uplift circa 2300 ybp (Hull, 1987). Tectonic uplift along the northern Hikurangi margin is the net result of a complex interaction between megathrust slip at depth and localized upper-plate contraction on steeply-dipping imbricate thrust faults. The segmented uplift pattern may reflect the focused impact of subducting seamounts and consequent variations in subduction erosion and downdip underplating of sediments and eroded debris.

  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. Relationship Between Subduction Erosion, Seamount Subduction, Fluid Venting and Mound Formation on the Slope of the Costa Rican Continental Margin

    Science.gov (United States)

    Petersen, C.; Klaucke, I.; Weinrebe, W.

    2006-12-01

    The oceanic crust off central Costa Rica northwest of the Cocos Ridge is dominated by chains of seamounts rising 1-2 km above the seafloor with diameters of up to 20 km. The subduction of these seamounts leads to strong indentations, scars and slides on the continental margin. A smoother segment of about 80 km width is located offshore Nicoya peninsula. The segment ends at a fracture zone which marks the transition of oceanic crust created at the Cocos-Nazca spreading center (CNS) and at the East Pacific Rise (EPR). Offshore Nicaragua the incoming EPR crust is dominated by bending related faults. To investigate the relationship between subduction erosion, fluid venting and mound formation, multibeam bathymetry and high-resolution deep-tow sidescan sonar and sediment echosounder data were acquired during R/V Sonne cruises SO163 and SO173 (2002/2003). The deep-tow system consisted of a dual-frequency 75/410 kHz sidescan sonar and a 2-12 kHz chirp sub-bottom profiler. The connection of the observed seafloor features to deeper subduction related processes is obtained by analysis of multi-channel streamer (MCS) data acquired during cruises SO81 (1992) and BGR99 (1999). Data examples and interpretations for different settings along the margin are presented. Near the Fisher seamount the large Nicoya slump failed over the flank of a huge subducted seamount. The sidescan and echosounder data permit a detailed characterization of fault patterns and fluid escape structures around the headwall of the slump. Where the fracture zone separating CNS and EPR crust subducts, the Hongo mound field was mapped in detail. Several mounds of up to 100 m height are located in line with a scar possibly created by a subducting ridge of the fracture zone. MCS data image a topographic high on the subducting oceanic crust beneath the mound field which lead to uplift and possibly enabled ascent of fluids from the subducting plate. The combined analysis of geoacoustic and seismic MCS data

  19. Uniqueness is Important in Competition

    Institute of Scientific and Technical Information of China (English)

    FENG Ai-Xia; XV Xiu-Lian; HE Da-Ren

    2009-01-01

    We propose a quantitative network description on the function of uniqueness in a competition system. Two statistical parameters, competition ability and uniqueness are defined, and their relationship in ordinary cases is analytically discussed. The competition between Chinese regional universities is taken as an example. The empirical investigation results show that the uniqueness of a university is really important in competition. Also,uniqueness is very helpful in the promotion of the university overall quality.

  20. Extreme localized exhumation at syntaxes initiated by subduction geometry

    Science.gov (United States)

    Bendick, Rebecca; Ehlers, Todd A.

    2014-08-01

    Some of the highest and most localized rates of lithospheric deformation in the world are observed at the transition between adjacent plate boundary subduction segments. The initiating perturbation of this deformation has long been attributed to vigorous erosional processes as observed at Nanga Parbat and Namche Barwa in the Himalaya and at Mount St. Elias in Alaska. However, an erosion-dominated mechanism ignores the 3-D geometry of curved subducting plates. Here we present an alternative explanation for rapid exhumation at these locations based on the 3-D thermomechanical evolution of collisions between plates with nonplanar geometries. Comparison of model predictions with existing data reproduces the defining characteristics of these mountains and offers an explanation for their spatial correlation with arc termini. These results demonstrate a "bottom-up" tectonic rather than "top-down" erosional initiation of feedbacks between erosion and tectonic deformation; hence, the importance of 3-D subduction geometry.

  1. Subduction and recycling of nitrogen along the Central American margin.

    Science.gov (United States)

    Fischer, Tobias P; Hilton, David R; Zimmer, Mindy M; Shaw, Alison M; Sharp, Zachary D; Walker, James A

    2002-08-16

    We report N and He isotopic and relative abundance characteristics of volatiles emitted from two segments of the Central American volcanic arc. In Guatemala, delta15N values are positive (i.e., greater than air) and N2/He ratios are high (up to 25,000). In contrast, Costa Rican N2/He ratios are low (maximum 1483) and delta15N values are negative (minimum -3.0 per mil). The results identify shallow hemipelagic sediments, subducted into the Guatemalan mantle, as the transport medium for the heavy N. Mass balance arguments indicate that the subducted N is efficiently cycled to the atmosphere by arc volcanism. Therefore, the subduction zone acts as a "barrier" to input of sedimentary N to the deeper mantle.

  2. Interferometric imaging of the underside of a subducting crust

    Science.gov (United States)

    Poliannikov, Oleg V.; Rondenay, Stéphane; Chen, Ling

    2012-04-01

    Seismic interferometry provides tools for redatuming physical data to a new source location. Turning a source, located close to a structure of interest, into a virtual receiver has the potential benefit of improving the quality of imaging by increasing the effective aperture and mitigating the effect of velocity uncertainty in the overburden. Here, we consider the problem of estimating the Green's function between two earthquakes located inside a subducting slab using earthquake data recorded at the surface. Our primary focus is to obtain an accurate time-image of the subducting interface. We propose a novel two-step kinematically correct redatuming procedure that first redatums the data from earthquakes below the subducting interface to the surface via classical interferometry, and then utilizes source-receiver wavefield interferometry to redatum virtual surface seismic data to the location of a particular earthquake event.

  3. On Uniqueness of coalitional equilibria

    NARCIS (Netherlands)

    Finus, M.; Mouche, van P.H.M.; Rundshagen, B.

    2014-01-01

    For the so-called "new approach" of coalitio formation it is important that coalitional equilibria are unique. Uniqueness comes down to existene and to semi-uniqueness, i.e.\\\\that there exists at most one equilibrium. Although conditions for existence are not problematic, conditions for semi-uniquen

  4. Physical characteristics of subduction-type seismogenic zones revisited

    Science.gov (United States)

    Heuret, A.; Lallemand, S.; Piromallo, C.; Funiciello, F.

    2009-12-01

    Based on both the Centennial earthquake catalog, the revised 1964-2007 EHB hypocenters and the 1976-2007 CMT Harvard catalog, we have extracted the hypocenters, nodal planes and seismic moments of worldwide subduction earthquakes for the period 1900-2007. For the period 1976-2007, we use the focal solutions provided by Harvard and the revised hypocenters from Engdahl et al. (1998). Older events are extracted from the Centennial catalogue (Engdahl and Villasenor, 2002) and they are used for the estimate of the cumulated seismic moment only. The criteria used to select the subduction earthquakes are similar to those used by Mc Caffrey (1994), i.e., we test if the focal mechanisms are consistent with 1/ shallow thrust events (positive slips, at least one nodal plane get dip 70 km), and, 2/ the plate interface local geometry and orientation (one nodal plane is oriented toward the volcanic arc, the azimut of this nodal plane is ± 45° with respect to the trench one, its dip is ± 20° with respect to the slab one and the epicenter is located seaward of the volcanic arc). Our study concerns segments of subduction zones that fit with estimated paleoruptures associated with major events (M > 8). We assume that the seismogenic zone coincides with the distribution of 5.5 laws obtained for example by Kanamori (1986) in light of a more complete, more detailed, more accurate and more uniform description of the subduction interplate seismogenic zone. Since the subduction earthquakes result from stress accumulation along the interplate and that stress depends on plates kinematics, subduction zone geometry, thermal state and seismic coupling, we aim to isolate some correlations between parameters.

  5. Fluid activity during exhumation of deep-subducted continental plate

    Institute of Scientific and Technical Information of China (English)

    ZHENG Yongfei

    2004-01-01

    It is well known that a great deal of fluid was released during subduction of oceanic crust, resulting in arc magmatism, quartz veining and metamorphic mineralization of syn-subduction. In contrast, the process of continental subduction is characterized by the relative lack of fluid and thus no arc magmatism has been found so far. During exhumation of deep-subducted continental crust, nevertheless,significant amounts of aqueous fluid became available from the decomposition of hydrous minerals, the decrepitation of primary fluid inclusions, and the exsolution of structural hydroxyls. This kind of metamorphic fluid has recently attracted widespread interests and thus been one of the most important targets in deciphering the geological processes concerning metamorphism, magmatism and mineralization in collisional orogens. A large number of studies involving stable isotopes, fluid inclusions and petrological phase relationships have been accomplished in past a few years with respect to the mobility and amount of metamorphic fluid in UHP metamorphic rocks from the Dabie-Sulu orogenic belt.The results demonstrate that the fluid activity during the exhumation of deep-subducted continental crust has the following effects: (1) amphibolite-facies retrogression due to pervasive fluid flow; (2) formation of HP quartz veins within eclogites due to channelized fluid flow; and (3) partial melting of overlying crustal rocks due to focused fluid flow, producing syn-exhumation magmatism within the orogenic belt.In particular, the aqueous fluid released by decompression exsolution of hydroxyl from UHP minerals is characterized by low salinity and is capable of resulting in pervasive and channellized flow. Therefore, the intensive study of fluid activity during exhumation of UHP metamorphic rocks can not only provide insight into geodynamic processes that occurred in continental collisional belts, but also shed light on understanding of crust-mantle recycling and relevant magmatism in

  6. Did growth of high Andes slow down Nazca plate subduction?

    Science.gov (United States)

    Quinteros, J.; Sobolev, S. V.

    2010-12-01

    The convergence velocity rate of the Nazca and South-American plate and its variations during the last 100 My are quite well-known from the global plate reconstructions. The key observation is that the rate of Nazca plate subduction has decreased by about 2 times during last 20 Myr and particularly since 10 Ma. During the same time the Central Andes have grown to its present 3-4 km height. Based on the thin-shell model, coupled with mantle convection, it was suggested that slowing down of Nazca plate resulted from the additional load exerted by the Andes. However, the thin-shell model, that integrates stresses and velocities vertically and therefore has no vertical resolution, is not an optimal tool to model a subduction zone. More appropriate would be modeling it with full thermomechanical formulation and self-consistent subduction. We performed a set of experiments to estimate the influence that an orogen like the Andes could have on an ongoing subduction. We used an enhanced 2D version of the SLIM-3D code suitable to simulate the evolution of a subducting slab in a self-consistent manner (gravity driven) at vertical crossections through upper mantle, transition zone and shallower lower mantle. The model utilizes non-linear temperature- and stress-dependant visco-elasto-plastic rheology and phase transitions at 410 and 660 km depth. We started from a reference case with a similar configuration as both Nazca and South-America plates. After some Mys of slow kinematicaly imposed subduction, to develop a coherent thermo-mechanical state, subduction was totally dynamic. On the other cases, the crust was slowly thickened artificially during 10 My to generate the Andean topography. Although our first results show no substantial changes on the velocity pattern of the subduction, we, however, consider this result as preliminary. At the meeting we plan to report completed and verified modeling results and discuss other possible cases of the late Cenozoic slowing down of

  7. Geochemical Evidence for Subduction in the Early Archaean from Quartz-Carbonate-Fuchsite Mineralization, Isua Supracrustal Belt, West Greenland

    Science.gov (United States)

    Pope, E. C.; Rosing, M. T.; Bird, D. K.

    2011-12-01

    Quartz, carbonate and fuchsite (chromian muscovite) is a common metasomatic assemblage observed in orogenic gold systems, both in Phanerozoic convergent margin settings, and within supracrustal and greenstone belts of Precambrian rocks. Geologic and geochemical observations in younger orogenic systems suggest that ore-forming metasomatic fluids are derived from subduction-related devolitilization reactions, implying that orogenic Au-deposits in Archaean and Proterozoic supracrustal rock suites are related to subduction-style plate tectonics beginning early in Earth history. Justification of this metasomatic-tectonic relationship requires that 1) Phanerozoic orogenic Au-deposits form in subduction-zone environments, and 2) the geochemical similarity of Precambrian orogenic deposits to their younger counterparts is the result of having the same petro-genetic origin. Hydrogen and oxygen isotope compositions of fuchsite and quartz from auriferous mineralization in the ca. 3.8 Ga Isua Supracrustal Belt (ISB) in West Greenland, in conjunction with elevated concentrations of CO2, Cr, Al, K and silica relative to protolith assemblages, suggest that this mineralization shares a common petro-tectonic origin with Phanerozoic orogenic deposits and that this type of metasomatism is a unique result of subduction-related processes. Fuchsite from the ISB has a δ18O and δD of +7.7 to +17.9% and -115 to -61%, respectively. δ18O of quartz from the same rocks is between +10.3 and +18.6%. Muscovite-quartz oxygen isotope thermometry indicates that the mineralization occurred at 560 ± 90oC, from fluids with a δD of -73 to -49% and δ18O of +8.8 to +17.2%. Calculation of isotopic fractionation during fluid-rock reactions along hypothetical fluid pathways demonstrates that these values, as well as those in younger orogenic deposits, are the result of seawater-derived fluids liberated from subducting lithosphere interacting with ultramafic rocks in the mantle wedge and lower crust

  8. Post subduction thermal regime of the western North America and effects on the Great Valley, Sierra Nevada and northern Baja California provinces

    Science.gov (United States)

    Erkan, Kamil

    Tectonic evolution of the transform margin of western North America has attracted great interest. This boundary formed as the fault-fault-trench type Mendocino triple junction has moved north. The tectonic transition is expected to have a significant thermal signature because the subduction zones are quite distinct from any other plate boundary zones with their depressed heat flow in the outer arc regions. There is a significant amount of heat flow data in most of California covering the Great Valley and Sierra Nevada regions where were part of the outer arc of the Farallon subduction was located. The heat flow in a very large area covering all over the Great Valley and western Sierra Nevada shows the consistent pattern of a recent subduction. The unique pattern of the heat flow distribution indicates the tectonic origin of the data which has a potential to reveal the nature of the tectonic transition after the cessation of subduction 30 Ma. In this collection, the first two papers deal with the interpretation of heat flow data using forward thermal models of the lithosphere. The two proposed tectonic scenarios, namely the slab window and the stalled slab models, were compared in terms of the thermal consequences. The low heat flow in the Great Valley and the narrow transition zone toward the Coast Ranges rules out opening of a slab window in a conventional sense and is therefore indicative of a stalled slab type transition. Therefore, the high heat flow in the Coast Ranges must be explained by a mechanism other than opening of a slab window beneath the Coast Ranges. The low (reduced) heat flow in the Western Sierra Nevada which extends to the south end of the region where the subduction ceased more than 15 My ago is important in understating the thermal history of the lithosphere after the cessation of subduction. The thermal data are also in close agreement with the seismic cut-out depth where sufficient seismic activity is present. The numerical thermal model of

  9. Revisiting the physical characterisitics of the subduction interplate seismogenic zones

    Science.gov (United States)

    Heuret, Arnauld; Lallemand, Serge; Funiciello, Francesca; Piromallo, Claudia

    2010-05-01

    Based on the Centennial earthquake catalog, the revised 1964-2007 EHB hypocenters catalog and the 1976-2007 CMT Harvard catalog, we have extracted the hypocenters, nodal planes and seismic moments of worldwide subduction earthquakes for the 1900-2007 period. For the 1976-2007 period, we combine the focal solutions provided by Harvard and the revised hypocenters from Engdahl et al. (1998). Older events are extracted from the Centennial catalogue (Engdahl and Villasenor, 2002) and they are used to estimate the cumulated seismic moment only. The selection criteria for the subduction earthquakes are similar to those used by Mc Caffrey (1994), i.e., we test if the focal mechanisms are consistent with 1/ shallow thrust events (depth > 70 km, positive slips, and at least one nodal plane gets dip 8). We assume that the seismogenic zone coincides with the distribution of 5.5 laws obtained for example by Ruff and Kanamori (1980) in light of a more complete, detailed, accurate and uniform description of the subduction interplate seismogenic zone. Since subduction earthquakes result from stress accumulation along the interplate and stress depends on plates kinematics, subduction zone geometry, thermal state and seismic coupling, we aim to isolate some correlations between parameters. The statistical analysis reveals that: 1- vs, the subduction velocity is the first order controlling parameter of seismogenic zone variability, both in term of geometry and seismic behaviour; 2- steep dip, large vertical extent and narrow horizontal extent of the seismogenic zone are associated to fast subductions, and cold slabs, the opposite holding for slow subductions and warm slabs; the seismogenic zone usually ends in the fore-arc mantle rather than at the upper plate Moho depth; 3- seismic rate () variability is coherent with the geometry of the seismogenic zone:  increases with the dip and with the vertical extent of the seismogenic zone, and it fits with vs and with the subducting

  10. Numerical Modelling of Subduction Zones: a New Beginning

    Science.gov (United States)

    Ficini, Eleonora; Dal Zilio, Luca; Doglioni, Carlo; Gerya, Taras V.

    2016-04-01

    Subduction zones are one of the most studied although still controversial geodynamic process. Is it a passive or an active mechanism in the frame of plate tectonics? How subduction initiates? What controls the differences among the slabs and related orogens and accretionary wedges? The geometry and kinematics at plate boundaries point to a "westerly" polarized flow of plates, which implies a relative opposed flow of the underlying Earth's mantle, being the decoupling located at about 100-200 km depth in the low-velocity zone or LVZ (Doglioni and Panza, 2015 and references therein). This flow is the simplest explanation for determining the asymmetric pattern of subduction zones; in fact "westerly" directed slabs are steeper and deeper with respect to the "easterly or northeasterly" directed ones, that are less steep and shallower, and two end members of orogens associated to the downgoing slabs can be distinguished in terms of topography, type of rocks, magmatism, backarc spreading or not, foredeep subsidence rate, etc.. The classic asymmetry comparing the western Pacific slabs and orogens (low topography and backarc spreading in the upper plate) and the eastern Pacific subduction zones (high topography and deep rocks involved in the upper plate) cannot be ascribed to the age of the subducting lithosphere. In fact, the same asymmetry can be recognized all over the world regardless the type and age of the subducting lithosphere, being rather controlled by the geographic polarity of the subduction. All plate boundaries move "west". Present numerical modelling set of subduction zones is based on the idea that a subducting slab is primarily controlled by its negative buoyancy. However, there are several counterarguments against this assumption, which is not able to explain the global asymmetric aforementioned signatures. Moreover, petrological reconstructions of the lithospheric and underlying mantle composition, point for a much smaller negative buoyancy than predicted

  11. Niobium-tantalum Fractionation During Slab Subduction:Implications for the Formation of Continental Crust

    Institute of Scientific and Technical Information of China (English)

    Yilin Xiao; Weidong Sun; Jochen Hoefs; Klaus Simon; Zeming Zhang; Shuguang Li; Albrecht W. Hofmann

    2007-01-01

    @@ Compared with the oceanic crust, knowledge about the formation of the continental crust (CC) is relatively poor. Although melting of subducted slabs in the early history of the Earth has been considered as the major way that shaped the chemical characteristics of the CC by most geologists, as the CC shares many characteristics with modern adakites, some geologists argued that Archean TTG was formed in the same way as modern arcs rather than slab melting, whereas others proposed that melting at the bottom of the thickened oceanic crust was more important. Recently,the debate is mainly focused on the unique subchondritic Nb/Ta value of the CC, and particularly, how Nb and Ta fractionated from each other and consequently how, in detail, the CC was built.

  12. Modeling fluid- and trace element-fluxes in subducted slabs utilising two-dimensional thermodynamic and trace element models

    Science.gov (United States)

    Konrad-Schmolke, M.; Jahn, S.

    2012-12-01

    The subduction of oceanic lithosphere induces one of the major element cycles on Earth. Devolatilisation reactions in the subducted plate, the associated major and trace element transport as well as fluid-rock interaction within the slab and the mantle wedge control the flux of matter from the down-going plate into the upper plate and the atmosphere. Prediction and quantification of these fluxes is therefore a fundamental task in geosciences. The amount and composition of liberated fluids in a subducted slab is controlled by thermodynamic constraints, the fluid-rock element distribution as well as reaction kinetics in the affected rocks. Consequently, prediction of the element transfer within the slab and into the overlying rocks must consider these processes and their complex interactions. In this contribution we focus on the thermodynamic constraints on devolatilisation reactions in slab-crust and -mantle, the associated fluid migration and the chemical aspect of fluid-rock interaction within a hydrated subducted plate. Based on numerically modeled isotherm patterns of contrasting subduction settings we calculate phase relations in different layers of the subducted slabs. We use incremental Gibbs energy minimisation models and consider upward migration of liberated fluids during subduction. Moreover, modeled phase relations, fluid amounts and trace element partition coefficients, are used to calculate mass balanced distribution of fluid-mobile trace elements among the stable phases within the slab. Trace element transport occurs within the migrating fluid phase that equilibrates with the wall rock during ascent. This process controls element depletion and/or enrichment of fluid and wall rock and enables detailed prediction of the trace element transfer along the slab mantle interface. Our results show that fluid fluxes at the slab surface are clearly bimodal: at fore-arc depths water is continuously released predominantly from the MORB layer whereas at sub- and

  13. Subduction-related oceanic crust in the Khantaishir ophiolite (western Mongolia).

    Science.gov (United States)

    Gianola, O.; Schmidt, M. W.; Jagoutz, O. E.

    2014-12-01

    Most of the oceanic crust is generated at mid oceanic ridges and only a minor portion results from magmatism related to subduction zones (i.e. back-arc basins or in incipient arcs). However it has been observed that several ophiolites preserve an oceanic crust displaying a subduction zone signature. Such a signature is also found in the Khantaishir ophiolite located in western Mongolia. This ~570 m.y. old ophiolite is ~480 km2 in size and displays a complete sequence, tectonically slightly dismembered during the emplacement process. The ophiolite exposes ~130 km2 of highly refractory harzburgitic mantle with local dunite channels and lenses. Towards its top the mantle is replaced by sub-horizontal km-wide discrete zones of pyroxenites situated either in the mantle or forming a crust-mantle transition zone overlain by gabbros. The crust is then composed of various gabbros and minor gabbronorite (both in part replaced by pyroxenites and/or cut by intermediate dykes), by a dyke/sill-complex and by pillow lavas. The entire ophiolite is re-equilibrated at lower greenschist facies conditions. Major and trace elements of the crustal rocks of the Khantaishir ophiolite show trends similar to those observed for the Izu-Bonin-Mariana subduction system. Mafic dykes/sills and pillow lavas of the Khantaishir ophiolite have overall basaltic-andesite compositions, resembling high-Mg andesites with an average SiO2 of 57 wt%. Their low TiO2 (high-Mg andesites and boninites from modern island arcs. This evidence suggests that the Kantaishir crust might represent the submarine initial stage of an incipient arc, probably when the preexisting oceanic crust is spread and incipient island arc crust is formed.

  14. MARGINS mini-lessons: A tour of the Mariana Subduction System (Invited)

    Science.gov (United States)

    Goodliffe, A. M.; Oakley, A.

    2009-12-01

    MARGINS mini-lessons provide an efficient way to quickly move cutting edge MARGINS research into the university classroom. Instructors who are not necessarily familiar with the MARGINS program can easily use mini-lessons in a variety of educational settings. The mini-lesson described herein is centered on bathymetric and multi-channel seismic data collected during a 2003 NSF-MARGINS funded marine geophysical survey in the Mariana Basin. Designed as an approximately sixty minute lecture segment, the lesson covers both the techniques used to collect marine geophysical data and a description of the geology of the system. All geological provinces are included, from the subducting Pacific Plate in the east to the remnant arc in the west. Representative seismic lines and bathymetric images are presented for each province, along with a description of key processes including deformation of the subducting plate, serpentinite mud volcanism, forearc faulting, potentially tsunamigenic landslides, arc volcanism, and backarc spreading. The Mariana subduction system mini-lesson requires a computer with an internet connection, powerpoint, Google Earth, and a web-browser. Questions are embedded in the powerpoint presentation that can be adapted to a specific interactive response system as needed. Optimally the lesson should be used in parallel with a GeoWall. A 3-dimensional ArcScene visualization of the Mariana system is available for download through the MARGINS mini-lessons web site. Such visualizations are particularly effective in helping students understand complex three-dimensional systems. If presented in a computer lab students will benefit from being able to explore the Mariana system using tools such as GeoMapApp.

  15. Linking the kinematics of the interplate and the offshore morphology along the Chilean subduction margin

    Science.gov (United States)

    Urrutia, Isabel; Moreno, Marcos; Oncken, Onno

    2016-04-01

    Morphological features at subduction zones are undoubtedly influenced by the complex interplay between the subducting slab and the overriding plate. Several studies suggest that the subduction dynamics is strongly dependent on the geometry and rheology of the margin (including gravity/density anomalies, viscous mantle flow and roughness of the slab, among others). However, it is not clear how the geomorphological variation of the forearc along strike can be used as a proxy for better understanding the mechanics on the interface and seismotectonic segmentation. Here we investigate the links between the kinematics of the plate interface and the morphology of the overriding plate along the Chilean margin by combining morphometrical and statistical analysis. We constructed swath profiles subtracting the averaged topography and performed gradient analysis to characterize variations of morphological features, and we compared these results with the locking degree distribution derived from the inversion of GPS data. On the coastal area the bathymetry and topography analysis shows a planar feature, gently dipping ocean-wards and backed by a cliff, which exhibits spatial variations in its width, height and extension along-strike. This morphology suggests a quiescence process or a "stable tectonic condition", at least since the late Quaternary (over multiple seismic cycles). The results indicate that this planar feature spatially correlates with the rupture size of recent great earthquakes and locking degree areas, suggesting that earthquake cycle deformation has an imprint on the offshore morphology, which can be used to study the transfer of stresses among adjacent seismotectonic segments and the periodicity and location of large earthquakes. In addition, the longevity of this correlation between topography, earthquake rupture and geodetic locking that likely integrates over a time window of several 103 to several 105 years indicates that the instrumentally inferred locking

  16. P wave anisotropic tomography of the Nankai subduction zone in Southwest Japan

    Science.gov (United States)

    Wang, Jian; Zhao, Dapeng

    2012-05-01

    The active subduction of the young Philippine Sea (PHS) plate and the old Pacific plate has resulted in significant seismic heterogeneity and anisotropy in Southwest (SW) Japan. In this work we determined a detailed 3-D P wave anisotropic tomography of the crust and upper mantle beneath SW Japan using ˜540,000 P wave arrival times from 5,249 local earthquakes recorded by 1095 stations. The PHS slab is imaged clearly as a high-velocity (high-V) anomaly which exhibits considerable lateral variations. Significant low-velocity (low-V) anomalies are revealed above and below the PHS slab. The low-V anomalies above the PHS slab may reflect the upwelling flow in the mantle wedge and the PHS slab dehydration, and they form the source zone of the arc volcanoes in SW Japan. The low-V zones under the PHS slab may reflect the upwelling flow in the big mantle wedge above the Pacific slab. The anisotropy in the crust and upper mantle is complex. In Kyushu, the P wave fast velocity direction (FVD) is generally trench-normal in the mantle wedge under the back-arc, which is consistent with the corner flow driven by the PHS slab subduction. The FVD is trench-parallel in the subducting PHS slab under Kyushu. We think that the intraslab seismicity is a potential indicator to the slab anisotropy. That is, the PHS slab with seismicity has kept its original fossil anisotropy formed at the mid-ocean ridge, while the aseismic PHS slab has reproduced the anisotropy according to its current deformation.

  17. Storage of fluids and melts at subduction zones detectable by seismic tomography

    Science.gov (United States)

    Luehr, B. G.; Koulakov, I.; Rabbel, W.; Brotopuspito, K. S.; Surono, S.

    2015-12-01

    During the last decades investigations at active continental margins discovered the link between the subduction of fluid saturated oceanic plates and the process of ascent of these fluids and partial melts forming a magmatic system that leads to volcanism at the earth surface. For this purpose the geophysical structure of the mantle and crustal range above the down going slap has been imaged. Information is required about the slap, the ascent paths, as well as the reservoires of fluids and partial melts in the mantle and the crust up to the volcanoes at the surface. Statistically the distance between the volcanoes of volcanic arcs down to their Wadati Benioff zone results of approximately 100 kilometers in mean value. Surprisingly, this depth range shows pronounced seismicity at most of all subduction zones. Additionally, mineralogical laboratory investigations have shown that dehydration of the diving plate has a maximum at temperature and pressure conditions we find at around 100 km depth. The ascent of the fluids and the appearance of partial melts as well as the distribution of these materials in the crust can be resolved by seismic tomographic methods using records of local natural seismicity. With these methods these areas are corresponding to lowered seismic velocities, high Vp/Vs ratios, as well as increased attenuation of seismic shear waves. The anomalies and their time dependence are controlled by the fluids. The seismic velocity anomalies detected so far are within a range of a few per cent to more than 30% reduction. But, to explore plate boundaries large and complex amphibious experiments are required, in which active and passive seismic investigations should be combined to achieve best results. The seismic station distribution should cover an area from before the trench up to far behind the volcanic chain, to provide under favorable conditions information down to 150 km depth. Findings of different subduction zones will be compared and discussed.

  18. Paleomagnetic results from IODP Expedition 344 Site U1381 and implications for the initial subduction of the Cocos Ridge

    Science.gov (United States)

    Li, Yong-Xiang; Zhao, Xixi; Jovane, Luigi; Petronotis, Katerina; Gong, Zheng; Xie, Siyi

    2016-04-01

    Understanding the processes that govern the strength, nature, and distribution of slip along subduction zones is a fundamental and societally relevant goal of modern earth science. The Costa Rica Seismogenesis Project (CRISP) is specially designed to understand the processes that control nucleation and seismic rupture of large earthquakes at erosional subduction zones. Drilling directly on the Cocos Ridge (CR) during International Ocean Drilling Program (IODP) Expedition 344 discovered a sedimentary hiatus in Site U1381 cores. In this study, we conducted a magnetostratigraphic and rock magnetic study on the Cenozoic sedimentary sequences of site U1381. Anisotropy of magnetic susceptibility data from sediments above and below the hiatus show oblate fabrcis, but the Kmin axes of the AMS data from sediments below the hiatus are more dispersed than those from sediments above the hiatus, implying that formation of hiatus may have affected AMS. Paleomagnetic results of the U1381 core, together with available Ar-Ar dates of ash layers from sediments below the hiatus, allow us to establish a geomagnetic polarity timescale that brackets the hiatus between ca. 9.61 and 1.52 Ma. Analyses of sedimentary records from ODP/IODP cores in the vicinity reveal that the hiatus appears to be regional, spanning the northeastern end of the CR. Also, the hiatus appears to occur only at certain locations. Its regional occurrence at unique locations implies a link to the initial shallow subduction of the Cocos Ridge. The hiatus was probably produced by either bottom current erosion or the CR buckling upon its initial collision with the Middle American trench (MAT). Thus, the initial subduction of the CR must have taken place on or before 1.52 Ma.

  19. Subduction beneath Eurasia in connection with the Mesozoic Tethys

    NARCIS (Netherlands)

    Spakman, W.

    2007-01-01

    In this paper we present new results concerning the existence and subduction of Meso-Tethyan oceanic lithosphere in the upper mantle beneath Europe, the Mediterranean and the Middle-East. The results arise from a large scale body wave tomographic analysis of the upper mantle in this region. It is sh

  20. Preface: Serpentinites from mid-oceanic ridges to subduction

    OpenAIRE

    Reynard, Bruno; Godard, Marguerite; Guillot, Stéphane

    2013-01-01

    Serpentine minerals and serpentinites have been recognized as essential in the dynamics of planet Earth, with a major role in plate tectonics from plate accretion to subduction, volatile cycling into the deep Earth, arc volcanism, seismic cycle and deep seismicity, and as primary sites for abiotic hydrocarbon production and the emergence of life.

  1. 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.

  2. 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.

  3. 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

  4. 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

  5. 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

  6. 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 initiation

  7. Influence of paired subduction zones: insight into Central Mediterranean tectonics

    Science.gov (United States)

    Miller, Meghan Samantha; Moresi, Louis; Faccenna, Claudio; Funiciello, Francesca

    2015-04-01

    The Hellenic and Calabrian slabs are subducting the last remnant of the Ionian oceanic lithosphere into the deep mantle beneath the Central Mediterranean. Seismic tomography studies have provided clear images of the present day morphology of the subducted lithosphere [1]. Tectonic studies have shown that the Calabrian slab has rolled back into its current geometry with episodes of back-arc spreading that have now ceased [2]. Conversely, GPS observations along with tectonic reconstructions show that the Hellenic slab is currently rolling back and appears to have accelerated in the past ~15 My [3], which has resulted in the only region of backarc spreading still active in the Mediterranean. Observations of seismic anisotropy from SKS splitting [4] indicate toroidal flow patterns at the edges of the subducted slabs, which lead to interpretations of mantle convection and flow. Rollback in a confined setting has allowed the two slabs to become a plate-tectonic pushmi-pullyu [5]. The evolution of each slab is necessarily dependent on the other as they are both subducting the same lithosphere in opposite directions and are sufficiently close together that their induced mantle flow patterns must interact strongly. Although this seems to be an oddity in the classical picture of plate tectonics, we note that rollback-dominated subduction is more likely to be important in the highly-confined setting of a closing ocean where the oceanic lithosphere is not always able to develop into a freely-moving plate. Under such conditions, back-to-back pairings of subducting slabs are potentially more common. To investigate this setting, we present preliminary numerical models of paired subduction zones that we have developed using Underworld. We include variations in the strength and buoyancy of the surrounding (over-riding) plates and account for the presence of continentally-derived basement in the Adriatic sea. The geodynamic models allow for exploration into the timing, mechanics

  8. Assessing the Seismic Potential Hazard of the Makran Subduction Zone

    Science.gov (United States)

    Frohling, E.; Szeliga, W. M.; Melbourne, T. I.; Abolghasem, A.; Lodi, S. H.

    2013-12-01

    Long quiescent subduction zones like the Makran, Sunda, and Cascadia, which have long recurrence intervals for large (> Mw 8) earthquakes, often have poorly known seismic histories and are particularly vulnerable and often ill-prepared. The Makran subduction zone has not been studied extensively, but the 1945 Mw 8.1 earthquake and subsequent tsunami, as well as more recent mid magnitude, intermediate depth (50-100 km) seismicity, demonstrates the active seismic nature of the region. Recent increases in regional GPS and seismic monitoring now permit the modeling of strain accumulations and seismic potential of the Makran subduction zone. Subduction zone seismicity indicates that the eastern half of the Makran is presently more active than the western half. It has been hypothesized that the relative quiescence of the western half is due to aseismic behavior. However, based on GPS evidence, the entire subduction zone generally appears to be coupled and has been accumulating stress that could be released in another > 8.0 Mw earthquake. To assess the degree of coupling, we utilize existing GPS data to create a fault coupling model for the Makran using a preliminary 2-D fault geometry derived from ISC hypocenters. Our 2-D modeling is done using the backslip approach and defines the parameters in our coupling model; we forego the generation of a 3-D model due to the low spatial density of available GPS data. We compare the use of both NUVEL-1A plate motions and modern Arabian plate motions derived from GPS station velocities in Oman to drive subduction for our fault coupling model. To avoid non-physical inversion results, we impose second order smoothing to eliminate steep strain gradients. The fit of the modeled inter-seismic deformation vectors are assessed against the observed strain from the GPS data. Initial observations indicate that the entire subduction zone is currently locked and accumulating strain, with no identifiable gaps in the interseismic locking

  9. 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)

  10. 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.

  11. Andean subduction orogeny: feedbacks between tectonics, relief evolution and global climate

    Science.gov (United States)

    Lacassin, Robin; Armijo, Rolando; Coudurier-Curveur, Aurélie; Carrizo, Daniel

    2016-04-01

    The Andean subduction margin, largest tectonic relief on the Earth (13 km vertically from the trench to the Altiplano) has a stepped morphology, which results of the evolution over the past 50 Myr of two parallel flat-ramp thrust systems, at the - previously unidentified - West Andean Thrust (WAT), and at the subduction interface. The evolution of those thrusts appears concomitant with increasing aridity in the Atacama Desert, which keeps a large-scale record of interplaying tectonics and Cenozoic climate change. The coastal morphology is dominated by the Atacama Bench, a giant uplifted terrace at 1-2km asl. Geomorphic and climatic data, numerical experiments of drainage formation are consistent with the development of a flat Atacama morphology close to sea level, interrupted at ≤10 Ma by tectonic uplift prevailing to the present. This suggests recent trench-ward relief growth by incorporation of the coastal Atacama Bench to the Andes reliefs. Thrust splay structures and other complexities above the subduction interface may explain this relief growth, as well as the distribution of asperities under the oceanward forearc, and the down-dip segmentation of coupling and seismicity on the megathrust. Combining those results with geological knowledge at the scale of the whole Central Andes, we show that the Andean orogeny results from protracted processes of bivergent crustal shortening in a wide region squeezed between the rigid Marginal Block and the S America Plate. The overall growth curve of Andean orogeny over the past 50 Myr appears synchronous with the onset of the "ramp-shaped" temperature decrease since the Early Eocene climatic optimum. Andean growth and global cooling may have operated under the same forcing mechanism at plate-scale, involving viscous flow in the mantle. But Andean growth appears modulated by climatic feedbacks causative of stepwise reductions of erosive power over the Andean margin. The first of such events is coeval with Late Eocene

  12. Subduction Tectonic Erosion, Sediment Accretion and Arc Collisions in maintaining the Continental Crust

    Science.gov (United States)

    Clift, P.; Vannucchi, P.; Schouten, H.

    2007-12-01

    Estimates of modern continental crustal recycling in subduction zones can be made from plate convergence velocities, the thicknesses of trench sediments, volumes and ages of accretionary complexes together with rates of trench retreat. Plate convergence rates appear to be the primary control on crustal subduction, with convergence >7.5 cm/yr associated with tectonic erosion. Collision of aseismic ridges with trenches drives around two thirds of forearc tectonic erosion over periods >10 m.y.. Globally material subduction at least as deep as the magmatic roots of arc systems is around 3.0 Armstrong Units (1 AU = 1 km3/yr), of which 1.65 AU comprises subducted sediments, with 1.33 AU of eroded forearc crust. Recycling rates along a single margin may show strong temporal variation over 1 m.y. periods. Isotopic variations in Costa Rican tephra suggest that sediment accretion is the most common mode of tectonism, but this is separated by short periods of dramatic erosion that cause net crustal loss. Even where erosion is continuous this can operate in a fast steady-state mode or a slower temporary style. On the Central Andean margin tectonic erosion since 20 Ma has caused trench retreat, but slow subsidence under the coastal zone implies steepening of the forearc taper rather than large scale retreat. The Neogene mass loss rate of 13 km3/m.y./km is 5-10 times lower than the long-term average. Since 2 Ma this rate has slowed further due to underplating under the coastal zone. A climatic role in driving continental erosion and moving the margin into a more accretionary state has been suggested but is hard to demonstrate. Average global mass loss requires that Cenozoic arc productivity lies close to 75 km3/m.y./km if the volume of the continental crust is to be maintained. Efficient accretion of oceanic arc crust is essential in maintaining the total crustal volume. In the classic Taiwan-Luzon example local crustal mass balancing implies that ~90% of the igneous arc crust

  13. Role of iron content on serpentinite dehydration depth in subduction zones: Experiments and thermodynamic modeling

    Science.gov (United States)

    Merkulova, Margarita; Muñoz, Manuel; Vidal, Olivier; Brunet, Fabrice

    2016-11-01

    A series of dehydration experiments in the piston-cylinder apparatus was carried out at 2 GPa and 550-850 °C on a natural antigorite sample mixed with 5 wt.% of magnetite. Chemical analyses of experimental products show a progressive decrease of the Mg# in antigorite and clinopyroxene between 550 and 675 °C, whereas the Mg# of olivine increases. The observed behavior of Mg# signifies Fe-Mg exchange between coexisting minerals. At higher temperatures, between 700 and 850 °C, compositions remain stable for all minerals in experimental assemblages. Thermodynamic parameters of the ferrous antigorite end-member were refined with the use of Holland and Powell (1998) data set and added to the antigorite solid solution. Good agreement between theoretical calculations performed for the studied bulk composition and experimental results confirms extrapolated thermodynamic data for Fe-antigorite. Constrained parameters allowed to calculate phase relationships for various serpentinite compositions. First, we assessed the effect of bulk iron content, from 0 to 10 wt.% FeO, on the stability field of antigorite. The results show significant decrease of the antigorite thermal stability with increasing bulk Fe content. Second, we demonstrated the influence of bulk iron content on dehydration reactions in subduction zones along typical thermal gradients. Dehydration observed in pure MSH (MgO-SiO2-H2O) systems comprised of antigorite appears as a univariant reaction, which happens at 710 °C/3.7 GPa and 640 °C/6 GPa in "hot" and "cold" subduction, respectively. In contrast, more complex in composition Fe-bearing serpentinites show spread dehydration profiles through divariant reactions from ~ 300 °C/0.8 GPa to 700 °C/3.6 GPa and from 450 °C/4 GPa to 650 °C/7.4 GPa for "hot" and "cold" thermal gradients respectively. A comparison between depths of "water-release events" and "earthquake occurrence" in the South Chile slab ("hot" subduction) highlights a clear correlation between

  14. Deformation and topography above the lateral transition from continental to oceanic subduction in three-dimensional laboratory models: what can we learn on the Hellenic subduction?

    Science.gov (United States)

    Guillaume, B.; Funiciello, F.; Faccenna, C.; Husson, L.; Royden, L. H.

    2012-04-01

    We use three-dimensional dynamically self-consistent laboratory models to analyze relationships between surface evolution and deep dynamics at convergent margins. Our models are setup with a viscous plate of silicone (lithosphere) subducting under negative buoyancy in a viscous layer of glucose syrup (upper mantle). We focus on the subduction of a laterally heterogeneous lithosphere characterized by an abrupt transition of density using negatively and positively buoyant silicone to reproduce oceanic and continental subduction, respectively. We quantify and establish relationships between the subduction dynamics and resulting slab geometry, trench kinematics and pattern of horizontal/vertical deformation for both the overriding plate and the upper mantle. Assuming that our modeling results can be representative of the natural behavior of subduction zones, we compare them to the Neogene to Quaternary evolution of the Hellenic subduction zone. We more particularly focus on the deformation and topography of the Hellenic upper plate, which may have been influenced by the difference in subduction dynamics north and south of the Kephalonia Transform Zone, with a slowly subducting Adriatic continental lithosphere in the north and a rapidly subducting Ionian oceanic lithosphere in the south.

  15. Fifteen Years of Slow Slip and Tremor Observations at the Northern Costa Rica Subduction Zone

    Science.gov (United States)

    Schwartz, S. Y.; Dixon, T. H.; Protti, M.; González, V. M.

    2015-12-01

    Coordinated long-term geophysical observations at the northern Costa Rica seismogenic zone, facilitated by NSF's MARGINS program, have greatly expanded our understanding of its megathrust behavior. Here we review fifteen years of seismic, geodetic, ocean bottom fluid flow and pressure sensor data collected on or near the Nicoya Peninsula, above the shallow thrust interface that document a variety of slow slip behaviors. These include relatively deep (~30-40 km), large slow slip events that occur about every 2 years, smaller events that locate at more intermediate depth (10-15 km) and occur more frequently (~1 per year), and very shallow events at the toe of the margin wedge that produce no discernible GPS signal on land but are detected on seafloor pressure sensors. Most of these slow slip events at the toe are accompanied by seismic tremor. Short-term, GPS only observations might have detected a few of these slow slip events; however, the longer more diverse instrument deployment was necessary to reveal their greater complexity. This demonstrates the need for a sustained, multi-instrument deployment and off-shore instrumentation at several different subduction zones, like that proposed for the Subduction Zone Observatory (SZO), to significantly advance our understanding of slow slip at convergent boundaries. Similar instrumentation to what exists in Nicoya is presently being established in the Osa-Burica region of southern Costa Rica to capture earthquake cycle deformation there. These two installations can provide a good nucleus for a larger circum-Pacific SZO effort.

  16. Mineralogy and fluid content of sediments entering the Costa Rica subduction zone - Results from Site U1414, IODP Expedition 344

    Science.gov (United States)

    Charpentier, D.; Buatier, M.; Kutterolf, S.; Straub, S. M.; Nascimento, D.; Millan, C.

    2013-12-01

    Subduction zones are characterized by the largest thrust earthquakes, as quantified by both rupture area and seismic moment release. Offshore Costa Rica, the oceanic Cocos Plate subducts under the Caribbean plate forming the southern end of the Middle America trench. A high convergence rate and almost complete subduction of incoming sediments make the Costa Rica convergent margin an extremely dynamic environment. The Costa Rica Seismogenesis Project (CRISP) is designed to understand the processes that control nucleation and seismic rupture of large earthquakes at erosional subduction zones. Site U1414 of IODP Exp.344 was drilled to investigate the material from the incoming Cocos Plate. A key parameter of incoming plate is fluid content and release because it impacts deformation within the subduction complex. The deposition, compaction and diagenesis of sedimentary rocks control the distribution of fluids, fluid pressures and fluid flow patterns within subduction zones. We therefore decided to characterize sediment composition and quantify the different types of water at Site U1414. Mineralogical investigations were performed using optical and electronic microscope observations, X Ray Diffraction (on bulk and clay fractions), Cation Exchange Capacity measurements, carbon analyses (to determine carbonate contents), and sequenced extractions in NaOH (to quantify the biogenic opal content). Fluid characteristics were approached by thermal gravimetric analyses. The entire sedimentary sequence was recovered at Site U1414 and can be divided into three major sedimentary units. The first one is a hemipelagic silty clay to clay with a gradual increase of calcareous nannofossils. The dominant mineral is smectite associated in the clay fractions with kaolinite and zeolites. Small amounts of biogenic opal have been analyzed. Other minerals like quartz, feldspar and calcite are also present. The second unit is composed of nannofossil-rich calcareous ooze. The proportion of

  17. Preseismic, Postseismic and Slow Faulting in Subduction Zones

    Science.gov (United States)

    Melbourne, T. I.; Webb, F. H.; Miller, M. M.

    2002-12-01

    The last several years have witnessed a broad reappraisal of our understanding of the energy budgets of subduction zones. Due primarily to the deployment of continuous geodetic instrumentation along convergent margins worldwide, we now recognize that fault rupture commonly occurs over rates ranging from kilometers per second to millimeters per day. Along with transient postseismic slip, both isolated and episodic slow slip events have now been recorded along convergent margins offshore Japan, Alaska, Mexico, Cascadia and Peru, and thus would appear to constitute a fundamental mode of strain release only observable through geodetic methods. In many instances, postseismic creep along the deeper plate interface is triggered by seismogenic rupture up-dip. Continuous GPS measurements from three earthquakes in México (Mw=8.0,1995), Peru (Mw=8.4,2001) and Japan (Mw=7.7, 1994) show that deep postseismic creep was triggered by local Coulomb stress increases of the order of one half bar produced by their mainshock ruptures. For these three events, afterslip along their primary coseismic asperities is significantly less important than triggered deep creep. Deeper slow faulting does not have to be triggered by adjacent seismogenic rupture. In Cascadia, eight episodic slow slip events since 1991 have been recognized to have an astonishingly regular 14.5-month onset period, the most recent of which began in February of 2002. For these events, time dependent inversion of GPS data map the propagation of creep fronts and show they released moment with magnitudes in excess of Mw=6.5. If they occur throughout the Cascadia interseismic period, then cumulatively they rival the moment release of the infrequent Mw=9.0 megathrust events. Most recently, an 18-hour precursor to an Mw=7.6 aftershock of the 2001 Mw=8.4 Peru earthquake was detected at Arequipa, Peru. This precursor appears as a ~3 cm departure from a continuous time series broken only by the coseismic displacements of the

  18. GEODYNAMICS OF NAZCA RIDGE’S OBLIQUE SUBDUCTION AND MIGRATION - IMPLICATIONS FOR TSUNAMI GENERATION ALONG CENTRAL AND SOUTHERN PERU: Earthquake and Tsunami of 23 June 2001

    Directory of Open Access Journals (Sweden)

    George Pararas-Carayannis

    2012-01-01

    Full Text Available Peru is in a region of considerable geologic and seismic complexity. Thrust faulting along the boundary where the Nazca plate subducts beneath the South American continent has created three distinct seismic zones. The angle of subduction of the Nazca oceanic plate beneath the South American plate is not uniform along the entire segment of the Peru-Chile Trench. Furthermore, subduction is affected by buoyancy forces of the bounding oceanic ridges and fractures - such as the Mendana Fracture Zone (MFZ to the North and the Nazca Ridge to the South. This narrow zone is characterized by shallow earthquakes that can generate destructive tsunamis of varied intensities. The present study examines the significance of Nazca Ridge’s oblique subduction and migration to the seismicity of Central/Southern Peru and to tsunami generation. The large tsunamigenic earthquake of 23 June 2001 is presented as a case study. This event generated a destructive, local tsunami that struck Peru’s southern coasts with waves ranging from 3 to 4.6 meters (10-15 feet and inland inundation that ranged from 1 to 3 km. In order to understand the near and far-field tsunamigenic efficiency of events along Central/Southern Peru and the significance of Nazca Ridge’s oblique subduction, the present study examines further the geologic structure of the region and this quake’s moment tensor analysis, energy release, fault rupture and the spatial distribution of aftershocks. Tsunami source mechanism characteristics for this event are presented, as inferred from seismic intensities, energy releases, fault plane solutions and the use of empirical relationships. The study concludes that the segment of subduction and faulting paralleling the Peru-Chile Trench from about 150 to 180 South, as well as the obliquity of convergent tectonic plate collision in this region, may be the reason for shorter rupture lengths of major earthquakes and the generation of only local destructive tsunamis.

  19. Deciphering the structure of isomeric oligosaccharides in a complex mixture by tandem mass spectrometry: Photon activation with vacuum ultra-violet brings unique information and enables definitive structure assignment

    Energy Technology Data Exchange (ETDEWEB)

    Ropartz, David, E-mail: David.Ropartz@nantes.inra.fr [INRA, UR1268 Biopolymers Interactions Assemblies, F-44316 Nantes (France); Lemoine, Jérôme [Institut des Sciences Analytiques, UMR 5280, Université Lyon 1-CNRS, Université de Lyon, F-69622 Villeurbanne cedex (France); Giuliani, Alexandre [Synchrotron SOLEIL, L’Orme des Merisiers, F-91190 Gif-sur-Yvette (France); UAR 1008 CEPIA, INRA, F-44316 Nantes (France); Bittebière, Yann [INRA, UR1268 Biopolymers Interactions Assemblies, F-44316 Nantes (France); Enjalbert, Quentin [Institut des Sciences Analytiques, UMR 5280, Université Lyon 1-CNRS, Université de Lyon, F-69622 Villeurbanne cedex (France); Institut Lumière Matière, UMR5306, Université Lyon 1-CNRS, Université de Lyon, F-69622 Villeurbanne cedex (France); Antoine, Rodolphe; Dugourd, Philippe [Institut Lumière Matière, UMR5306, Université Lyon 1-CNRS, Université de Lyon, F-69622 Villeurbanne cedex (France); Ralet, Marie-Christine; Rogniaux, Hélène [INRA, UR1268 Biopolymers Interactions Assemblies, F-44316 Nantes (France)

    2014-01-07

    Graphical abstract: -- Highlights: •A complex mixture of methylated oligogalacturonans was fractionated by IP-RP-UHPLC. •Synchrotron-radiation in VUV range was used as an activation process for tandem MS. •VUV activation brought rich structural information compared to LE-CAD. •Resolution of more than 35 structures, including isomers, was successfully completed. -- Abstract: Carbohydrates have a wide variety of structures whose complexity and heterogeneity challenge the field of analytical chemistry. Tandem mass spectrometry, with its remarkable sensitivity and high information content, provides key advantages to addressing the structural elucidation of polysaccharides. Yet, classical fragmentation by collision-activated dissociation (CAD) in many cases fails to reach a comprehensive structural determination, especially when isomers have to be differentiated. In this work, for the first time, vacuum ultra-violet (VUV) synchrotron radiation is used as the activation process in tandem mass spectrometry of large oligosaccharides. Compared to low energy CAD (LE-CAD), photon activated dissociation brought more straightforward and valuable structural information. The outstanding feature was that complete series of informative ions were produced, with only minor neutral losses. Moreover, systematic fragmentation rules could be drawn thus facilitating the definitive assignments of fragment identities. As a result, most of the structures present in a complex mixture of oligogalacturonans could be comprehensively resolved, including many isomers differing in the position of methyl groups along the galacturonic acid backbone.

  20. Synthesis, X-Ray crystal structure, photophysical characterization and nonlinear optical properties of the unique manganese complex with picolinate and 1,10 phenantroline: toward the designing of new high NLO response crystal

    Science.gov (United States)

    Tamer, Ömer; Avcı, Davut; Atalay, Yusuf

    2016-12-01

    The first manganese complex of picolinic acid (also known as 2-pyridinecarboxylic acid) and 1,10 phenantroline has been synthesized, and its structure has been fully characterized by means of X-Ray diffraction method as well as FT-IR, Raman and UV-vis spectroscopies. In order to provide a deep understanding about the relation among the nonlinear optical properties, structural, spectroscopic and electronic behaviors, density functional theory (DFT) calculations have been performed by using hybrid B3LYP level. The intensive interactions between the bonding orbitals of donor O/N atoms and antibonding orbitals of Mn(II) lone pairs confirm the X-Ray diffraction results. Each of the conditions such as small energy gap between HOMO and LUMO, high energy second order perturbation interaction, elongation of conjugated π system and high spin Mn(II) ion induce the first static hyperpolarizability (β) parameter of investigated complex. The β parameter for [Mn(pic)2(phen)]·H2O complex has been found to be approximately 22 times higher than p-nitroaniline.

  1. 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

  2. Comparing the Gibraltar and Calabrian subduction zones (central western Mediterranean) based on seismic tomography

    Science.gov (United States)

    Argnani, Andrea; Battista Cimini, Giovanni; Frugoni, Francesco; Monna, Stephen; Montuori, Caterina

    2016-04-01

    The Central Western Mediterranean (CWM) was shaped by a complex tectonic and geodynamic evolution. Deep seismicity and tomographic studies point to the existence, under the Alboran and Tyrrhenian Seas, of lithospheric slabs extending down to the bottom of the mantle transition zone, at 660 km depth. Two narrow arcs correspond to the two slabs, the Gibraltar and Calabrian Arcs (e.g., Monna et al., 2013; Montuori et al., 2007). Similarities in the tectonic and mantle structure of the two areas have been explained by a common subduction and roll-back mechanism for the opening of the CWM, in which the two arcs are symmetrical end products. In spite of this unifying model, a wide amount of literature from different disciplines shows that many aspects of the two areas are still controversial. We present a new 3-D tomographic model at mantle scale for the Calabrian Arc and compare it with a recently published 3-D tomographic model for the Gibraltar Arc by Monna et al (2013). The two models are based on non-linear inversion of teleseismic phase arrivals, and have scale and parametrization that allow for a direct comparison. Unlike previous studies the tomographic models here presented include Ocean Bottom Seismometer broadband data, which improved the resolution of the mantle structures in the marine areas surrounding the arcs. We focus on key features of the two models that constrain reconstructions of the geodynamic evolution of the CWM (e.g., Monna et al., 2015). At Tortonian time the opening of the Tyrrhenian basin was in its initial stage, and the Calabrian arc formed subsequently; on the contrary, the Gibraltar arc was almost completely defined. We hypothesize that the complexity of the continental margin approaching the subduction zone played a key role during the final stages of the arc formation. References Monna, S., G. B. Cimini, C. Montuori, L. Matias, W. H. Geissler, and P. Favali (2013), New insights from seismic tomography on the complex geodynamic evolution

  3. Shear wave reflectivity imaging of the Nazca-South America subduction zone: Stagnant slab in the mantle transition zone?

    Science.gov (United States)

    Contenti, Sean; Gu, Yu Jeffrey; Ökeler, Ahmet; Sacchi, Mauricio D.

    2012-01-01

    In this study we utilize over 5000 SS waveforms to investigate the high-resolution mantle reflectivity structure down to 1200 km beneath the South American convergent margin. Our results indicate that the dynamics of the Nazca subduction are more complex than previously suggested. The 410- and 660-km seismic discontinuities beneath the Pacific Ocean and Amazonian Shield exhibit limited lateral depth variations, but their depths vary substantially in the vicinity of the subducting Nazca plate. The reflection amplitude of the 410-km discontinuity is greatly diminished in a ˜1300-km wide region in the back-arc of the subducting plate, which is likely associated with a compositional heterogeneity on top of the upper mantle transition zone. The underlying 660-km discontinuity is strongly depressed, showing localized depth and amplitude variations both within and to the east of the Wadati-Benioff zone. The width of this anomalous zone (˜1000 km) far exceeds that of the high-velocity slab structure and suggesting significant slab deformation within the transition zone. The shape of the 660-km discontinuity and the presence of lower mantle reflectivity imply both stagnation and penetration are possible as the descending Nazca slab impinges upon the base of the upper mantle.

  4. Multiple plates subducting beneath Colombia, as illuminated by seismicity and velocity from the joint inversion of seismic and gravity data

    Science.gov (United States)

    Syracuse, Ellen M.; Maceira, Monica; Prieto, Germán A.; Zhang, Haijiang; Ammon, Charles J.

    2016-06-01

    Subduction beneath the northernmost Andes in Colombia is complex. Based on seismicity distributions, multiple segments of slab appear to be subducting, and arc volcanism ceases north of 5° N. Here, we illuminate the subduction system through hypocentral relocations and Vp and Vs models resulting from the joint inversion of local body wave arrivals, surface wave dispersion measurements, and gravity data. The simultaneous use of multiple data types takes advantage of the differing sensitivities of each data type, resulting in velocity models that have improved resolution at both shallower and deeper depths than would result from traditional travel time tomography alone. The relocated earthquake dataset and velocity model clearly indicate a tear in the Nazca slab at 5° N, corresponding to a 250-km shift in slab seismicity and the termination of arc volcanism. North of this tear, the slab is flat, and it comprises slabs of two sources: the Nazca and Caribbean plates. The Bucaramanga nest, a small region of among the most intense intermediate-depth seismicity globally, is associated with the boundary between these two plates and possibly with a zone of melting or elevated water content, based on reduced Vp and increased Vp/Vs. We also use relocated seismicity to identify two new faults in the South American plate, one related to plate convergence and one highlighted by induced seismicity.

  5. Redox-variability and controls in subduction zones from an iron-isotope perspective

    Science.gov (United States)

    Nebel, O.; Sossi, P. A.; Bénard, A.; Wille, M.; Vroon, P. Z.; Arculus, R. J.

    2015-12-01

    An ongoing controversy in mantle geochemistry concerns the oxidation state of the sources of island arc lavas (IAL). Three key factors control oxidation-reduction (redox) of IAL sources: (i) metasomatism of the mantle wedge by fluids and/or melts, liberated from the underlying subducted slab; (ii) the oxidation state of the wedge prior to melting and metasomatism; and (iii) the loss of melt from IAL sources. Subsequently, magmatic differentiation by fractional crystallisation, possible crustal contamination and degassing of melts en route to and at the surface can further modify the redox states of IAL. The remote nature of sub-arc processes and the complex interplay between them render direct investigations difficult. However, a possible gauge for redox-controlled, high-temperature pre-eruptive differentiation conditions is variations in stable Fe isotope compositions (expressed here as δ57Fe) in erupting IAL because Fe isotopes can preserve a record of sub-surface mass transfer reactions involving the major element Fe. Here we report Fe isotope compositions of bulk IAL along the active Banda arc, Indonesia, which is well known for a prominent subducted sediment input. In conjunction with other arc rocks, δ57Fe in erupted Banda IAL indicates that fractional crystallisation and possibly crustal contamination primarily control their Fe isotope signatures. When corrected for fractional crystallisation and filtered for contamination, arc magmas that had variable sediment melt contributions in their sources show no resolvable co-variation of δ57Fe with radiogenic isotope tracers. This indicates that crustal recycling in the form of subducted sediment does not alter the Fe isotope character of arc lavas, in agreement with mass balance estimates. Primitive sources of IAL, however, are clearly isotopically lighter than those sourced beneath mid-ocean ridges, indicating either preferential Fe3+-depletion in the mantle wedge by prior, δ57Fe-heavy melt extraction, and

  6. 整函数及其差分分担有限集的唯一性%On the Uniqueness of Shared Set with Finite Complex Numbers of Differences of Entire Functions

    Institute of Scientific and Technical Information of China (English)

    胡祎; 易才凤; 徐洪焱

    2011-01-01

    In this paper, we study the uniqueness problems of sharing sets of difference polynomials of entire functions and obtain the following result. Let n(> 5),m(≥ 2) be two positive integers, c ∈ C - {0}, and Sm = {1,ω, ··· ,ωm-1}, where ω = cos(2π/m) + I sin(2π/m). If two nonconstant entire functions f(z),g(z) satisfy E(Sm, f(z)n(f(z) - 1)f(z + c)) = E(Sm,9(z)n(g(z) - l))g(z + c)), then f(z) = g(z).%研究了整函数及其差分多项式分担有限复数集的唯一性,得到了如下结果:设Sm={1,ω,…,ωm-1},其中ω=cos(2π/m)+isin(2π/m),c为非零有限复数,n(>5),m(≥2)均为正整数.如果f(z),g(z)为有限级整函数,满足E(Sm,f(z)n(f(z)-1)f(z+c))=E(Sm,g(z)n(g(z)-1))g(z+c)),那么f(z)(三)g(z).

  7. Density structure and geometry of the Costa Rican subduction zone from 3-D gravity modeling and local earthquake data

    Science.gov (United States)

    Lücke, O. H.; Arroyo, I. G.

    2015-10-01

    The eastern part of the oceanic Cocos Plate presents a heterogeneous crustal structure due to diverse origins and ages as well as plate-hot spot interactions which originated the Cocos Ridge, a structure that converges with the Caribbean Plate in southeastern Costa Rica. The complex structure of the oceanic plate directly influences the dynamics and geometry of the subduction zone along the Middle American Trench. In this paper an integrated interpretation of the slab geometry in Costa Rica is presented based on 3-D density modeling of combined satellite and surface gravity data, constrained by available geophysical and geological data and seismological information obtained from local networks. The results show the continuation of steep subduction geometry from the Nicaraguan margin into northwestern Costa Rica, followed by a moderate dipping slab under the Central Cordillera toward the end of the Central American Volcanic Arc. Contrary to commonly assumed, to the southeast end of the volcanic arc, our preferred model shows a steep, coherent slab that extends up to the landward projection of the Panama Fracture Zone. Overall, a gradual change in the depth of the intraplate seismicity is observed, reaching 220 km in the northwestern part, and becoming progressively shallower toward the southeast, where it reaches a maximum depth of 75 km. The changes in the terminal depth of the observed seismicity correlate with the increased density in the modeled slab. The absence of intermediate depth (> 75 km) intraplate seismicity in the southeastern section and the higher densities for the subducted slab in this area, support a model in which dehydration reactions in the subducted slab cease at a shallower depth, originating an anhydrous and thus aseismic slab.

  8. Uniqueness property for quasiharmonic functions

    Directory of Open Access Journals (Sweden)

    Sevdiyor A. Imomkulov

    2014-10-01

    Full Text Available In this paper we consider a class of continuous functions, called quasiaharmonic functions, admitting best approximations by harmonic polynomials. In this class we prove a uniqueness theorem by analogy with the analytic functions.

  9. Diabetes: Unique to Older Adults

    Science.gov (United States)

    ... Stroke Urinary Incontinence Related Documents PDF Choosing Wisely: Diabetes Tests and Treatments Download Related Video Join our e-newsletter! Aging & Health A to Z Diabetes Unique to Older Adults This section provides information ...

  10. Osteoporosis: Unique to Older Adults

    Science.gov (United States)

    ... our e-newsletter! Aging & Health A to Z Osteoporosis Unique to Older Adults This section provides information ... and widely-prescribed medications for the treatment of osteoporosis. Some serious side effects of these medication have ...

  11. Nutrition: Unique to Older Adults

    Science.gov (United States)

    ... our e-newsletter! Aging & Health A to Z Nutrition Unique to Older Adults This section provides information ... teeth that are needed for grinding up food, nutrition suffers. If you are unable to chew and ...

  12. Melting of subducted basalt at the core-mantle boundary.

    Science.gov (United States)

    Andrault, Denis; Pesce, Giacomo; Bouhifd, Mohamed Ali; Bolfan-Casanova, Nathalie; Hénot, Jean-Marc; Mezouar, Mohamed

    2014-05-23

    The geological materials in Earth's lowermost mantle control the characteristics and interpretation of seismic ultra-low velocity zones at the base of the core-mantle boundary. Partial melting of the bulk lower mantle is often advocated as the cause, but this does not explain the nonubiquitous character of these regional seismic features. We explored the melting properties of mid-oceanic ridge basalt (MORB), which can reach the lowermost mantle after subduction of oceanic crust. At a pressure representative of the core-mantle boundary (135 gigapascals), the onset of melting occurs at ~3800 kelvin, which is ~350 kelvin below the mantle solidus. The SiO2-rich liquid generated either remains trapped in the MORB material or solidifies after reacting with the surrounding MgO-rich mantle, remixing subducted MORB with the lowermost mantle.

  13. Can slabs melt beneath forearcs in hot subduction zones?

    Science.gov (United States)

    Ribeiro, J.; Maury, R.; Gregoire, M.

    2015-12-01

    At subduction zones, thermal modeling predict that the shallow part of the downgoing oceanic crust (test the hypothesis that adakites are pristine slab melts. We find that adakites from Baja California and Philippines formed by two distinct petrogenetic scenarios. In Baja California, hydrous mantle melts mixed/mingled with high-pressure (HP) adakite-type, slab melts within a lower crustal (~30 km depth) magma storage region before stalling into the upper arc crust (~7-15 km depth). In contrast, in the Philippines, primitive mantle melts stalled and crystallized within lower and upper crustal magma storage regions to produce silica-rich melts with an adakitic signature. Thereby, slab melting is not required to produce an adakitic geochemical fingerprint in hot subduction zones. However, our results also suggest that the downgoing crust potentially melted beneath Baja California.

  14. The Trobriand Subduction System in the Western Solomon Sea

    Science.gov (United States)

    Lock, J.; Davies, H. L.; Tiffin, D. L.; Murakami, F.; Kisimoto, K.

    1987-09-01

    A south-dipping Subduction system which underlies the Trobriand Trough and 149° Embayment, on the southern margin of the Solomon Sea, is active or was recently active. Oceanic basement is overlain by 2.5 s, two-way travel time (TWTT), of sediment that shows at least two stages of deformation: early thrusts (inner wall) and normal faults (outer wall), and later normal faults that have elevated the outer trench margin. Thrust anticlines and slope basins are developed on the inner wall. The floor of the Solomon Sea Basin arches upward between the Trobriand Trough and the New Britain Trench to form isolated peaks and ridges in the east (152° Peaks) and an east-west Central Ridge in the west. Structures in the subduction system, and in the Solomon Sea Basin, plunge westward towards the point of collision with the New Britain Trench.

  15. Reaction-induced rheological weakening enables oceanic plate subduction

    Science.gov (United States)

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

    2016-08-01

    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 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.

  16. 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

  17. Watching dehydration: transient vein-shaped porosity in the oceanic mantle of the subducting Nazca slab

    Science.gov (United States)

    Bloch, Wasja; John, Timm; Kummerow, Jörn; Wigger, Peter; Salazar, Pablo; Shapiro, Serge

    2016-04-01

    Subduction zones around the world show the common pattern of a Double Seismicity Zone, where seismicity is organized in the form of two sub-parallel planes, one at the plate contact and the other one, 10 to 30 km below, in the mantle of the oceanic lithosphere (Lower Seismicity Zone, LSZ). A commonly held hypothesis states that dehydration processes and the associated mineral reactions promote the earthquakes of the LSZ. Fluids filling a porespace strongly alter the petropyhsical properties of a rock. Especially the seismic P- to S-wave velocity ratio (Vp/Vs) has been shown to be sensitive to the presence of fluid-filled porosity. It transforms uniquely to Poisson's ratio. To test the mineral-dehydration-hypothesis, we use local earthquake data to measure Vp/Vs in the oceanic mantle of the subducting Nazca slab at 21°S. We determine it as the slope of the de-meaned differential P- vs. S-wave arrivaltimes of a dense seismicity cluster in the LSZ. This measurement yields a value for Vp/Vs of 2.10 ± 0.09, i.e. a Poisson's ratio of ˜0.35. This value clearly exceeds the range of Vp/Vs values expected for oceanic mantle rocks in their purely solid form at ˜50km depth. We follow a poroelastic approach to model the rock's elastic properties, including Vp/Vs, as a function of porosity and porespace-geometry. This results in a porespace model for the target volume having a vein-like porosity occupying only a minor volume fraction. Porosity is in the order of 0.1%. These findings are in very good agreement with field surveys and laboratory experiments of mantle dehydration. The pore-geometry is close to the geometrical percolation threshold, where long-ranged interconnectivity statistically emerges, suggesting good draining capabilities. Indeed, porosity is soft so that the amount of porosity and, consequently, permeability is very sensitive to local fluid pressure. We conclude that in the oceanic mantle of the subducting Nazca slab, mineral dehydration reactions are

  18. The Relationships of Upper Plate Ridge-Trench-Trench and Ridge-Trench-Transform Triple Junction Evolution to Arc Lengthening, Subduction Zone initiation and Ophiolitic Forearc Obduction

    Science.gov (United States)

    Casey, J.; Dewey, J. F.

    2013-12-01

    The principal enigma of large obducted ophiolite slabs is that they clearly must have been generated by some form of organized sea-floor spreading/plate-accretion, such as may be envisioned for the oceanic ridges, yet the volcanics commonly have arc affinity (Miyashiro) with boninites (high-temperature/low-pressure, high Mg and Si andesites), which are suggestive of a forearc origin. PT conditions under which boninites and metamorphic soles form and observations of modern forearc systems lead us to the conclusion that ophiolite formation is associated with overriding plate spreading centers that intersect the trench to form ridge-trench-trench of ridge-trench-tranform triple junctions. The spreading centers extend and lengthen the forearc parallel to the trench and by definition are in supra-subduction zone (SSZ) settings. Many ophiolites likewise have complexly-deformed associated mafic-ultramafic assemblages that suggest fracture zone/transform along their frontal edges, which in turn has led to models involving the nucleation of subduction zones on fracture zones or transpressional transforms. Hitherto, arc-related sea-floor-spreading has been considered to be either pre-arc (fore-arc boninites) or post-arc (classic Karig-style back arc basins that trench-parallel split arcs). Syn-arc boninites and forearc oceanic spreading centers that involve a stable ridge/trench/trench triple or a ridge-trench-transform triple junction, the ridge being between the two upper plates, are consistent with large slab ophiolite formation in an obduction-ready settting. The direction of subduction must be oblique with a different sense in the two subduction zones and the oblique subduction cannot be partitioned into trench orthogonal and parallel strike-slip components. As the ridge spreads, new oceanic lithosphere is created within the forearc, the arc and fore-arc lengthen significantly, and a syn-arc ophiolite forearc complex is generated by this mechanism. The ophiolite ages

  19. Controls on Earthquake Rupture and Triggering Mechanisms in Subduction Zones

    Science.gov (United States)

    2010-06-01

    of stressing rate variations in space and time from seismicity data can be used in tectonic settings besides subduction zones and has other...2004), Pre- and post- seismic slow slip on the plate boundary off Sanriku, NE Japan associated with three interplate earthquakes as estimated from...observed deformation transients in various tectonic environments. We find that stressing rate transients increase the background seismicity rate without

  20. Origin of geochemical mantle components: Role of subduction filter

    Science.gov (United States)

    Kimura, Jun-Ichi; Gill, James B.; Skora, Susanne; van Keken, Peter E.; Kawabata, Hiroshi

    2016-08-01

    We quantitatively explore element redistribution at subduction zones using numerical mass balance models to evaluate the roles of the subduction zone filter in the Earth's geochemical cycle. Our models of slab residues after arc magma genesis differ from previous ones by being internally consistent with geodynamic models of modern arcs that successfully explain arc magma genesis and include element fluxes from the dehydration/melting of each underlying slab component. We assume that the mantle potential temperature (Tp) was 1400-1650°C at 3.5-1.7 Ga and gradually decreased to 1300-1350°C today. Hot subduction zones with Tp ˜1650°C have a thermal structure like modern SW Japan where high-Mg andesite is formed which is chemically like continental crust. After 2.5-1.7 Gyr of storage in the mantle, the residual igneous oceanic crust from hot subduction zones can evolve isotopically to the HIMU mantle component, the residual base of the mantle wedge to EMI, the residual sediment becomes an essential part of EMII, and the residual top of the mantle wedge can become the subcontinental lithosphere component. The Common or Focal Zone component is a stable mixture of the first three residues occasionally mixed with early depleted mantle. Slab residues that recycled earlier (˜2.5 Ga) form the DUPAL anomaly in the southern hemisphere, whereas residues of more recent recycling (˜1.7 Ga) underlie the northern hemisphere. These ages correspond to major continental crust forming events. The east-west heterogeneity of the depleted upper mantle involves subcontinental mantle except in the Pacific.

  1. Unraveling topography around subduction zones from laboratory models

    Science.gov (United States)

    Husson, Laurent; Guillaume, Benjamin; Funiciello, Francesca; Faccenna, Claudio; Royden, Leigh H.

    2012-03-01

    The relief around subduction zones results from the interplay of dynamic processes that may locally exceed the (iso)static contributions. The viscous dissipation of the energy in and around subduction zones is capable of generating kilometer scale vertical ground movements. In order to evaluate dynamic topography in a self-consistent subduction system, we carried out a set of laboratory experiments, wherein the lithosphere and mantle are simulated by means of Newtonian viscous materials, namely silicone putty and glucose syrup. Models are kept in their most simple form and are made of negative buoyancy plates, of variable width and thickness, freely plunging into the syrup. The surface of the model and the top of the slab are scanned in three dimensions. A forebulge systematically emerges from the bending of the viscous plate, adjacent to the trench. With a large wavelength, dynamic pressure offsets the foreside and backside of the slab by ~ 500 m on average. The suction, that accompanies the vertical descent of the slab depresses the surface on both sides. At a distance equal to the half-width of the slab, the topographic depression amounts to ~ 500 m on average and becomes negligible at a distance that equals the width of the slab. In order to explore the impact of slab rollback on the topography, the trailing edge of the plates is alternatively fixed to (fixed mode) and freed from (free mode) the end wall of the tank. Both the pressure and suction components of the topography are ~ 30% lower in the free mode, indicating that slab rollback fosters the dynamic subsidence of upper plates. Our models are compatible with first order observations of the topography around the East Scotia, Tonga, Kermadec and Banda subduction zones, which exhibit anomalous depths of nearly 1 km as compared to adjacent sea floor of comparable age.

  2. A slow slip event along the northern Ecuadorian subduction zone

    Science.gov (United States)

    Nocquet, J.; Mothes, P. A.; Vallee, M.; Regnier, M.

    2009-12-01

    Rapid subduction of the Nazca plate beneath the Ecuador-Colombia margin (~58 mm/yr) has produced one of the largest megathrust earthquake sequence during the last century. The 500-km-long rupture zone of the 1906 (Mw = 8.8) event was partially reactivated by three thrust events; in 1942 (Mw = 7.8), 1958 (Mw = 7.7), and 1979 (Mw = 8.2), whose rupture zones abut one another. New continuously-recording GPS stations installed along the Ecuadorian coast, together with campaign sites observed since 1994 indicate that the current velocities results from the superimposition of a NNE motion the crustal North Andean Block occurring at ~8 mm/yr in Ecuador and the elastic deformation involved by partial locking of the subduction interface. We first estimate the long-term kinematics of the North Andean block in a joint inversion including GPS data, earthquake slip vectors and quaternary slip rates on major faults. The inversion provides a Euler pole located at long. -107.8°E, lat. 36.2°N, 0.091°/Ma and indicates little internal deformation of the North Andean Block (wrms=1.3 mm/yr). Residual velocities with respect to the North Andean Block are then modeled in terms of elastic locking along the subduction interface. Models indicate that the subduction interface is partially locked (50%) up to a depth of 40 km. Finally, we report a transient event that occurred in early 2008 near the Ecuador-Colombia border. The magnitude of the trenchward displacement is 13 mm, with uplift of similar magnitude. While the total duration of the slip event is 5 months, the horizontal time series clearly shows two sub-phases of slip with approximatively similar magnitud of displacement and duration, separated by 6 weeks. Modelling indicates that the slip occurs at 40 km depth, immediately below downdip extension of the locked zone.

  3. 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.

  4. Water and the Oxidation State of Subduction Zone Magmas

    Energy Technology Data Exchange (ETDEWEB)

    Kelley, K.; Cottrell, E

    2009-01-01

    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 (Fe{sup 3+}/{Sigma}Fe), determined with Fe K-edge micro-x-ray absorption near-edge structure spectroscopy, and pre-eruptive magmatic H{sub 2}O contents of a global sampling of primitive undegassed basaltic glasses and melt inclusions covering a range of plate tectonic settings. Magmatic Fe{sup 3+}/{Sigma}Fe 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 H{sub 2}O 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.

  5. An investigation of deformation and fluid flow at subduction zones using newly developed instrumentation and finite element modeling

    Science.gov (United States)

    Labonte, Alison Louise

    electronic flow meter that can measure flow rates of 0.1 to >500 m/yr at a temporal resolution of 30 minutes to 0.5 minutes, respectively. Test deployments of the OTIS at cold seeps in the transpressional Monterey Bay demonstrated the OTIS functionality over this range of flow environments. Although no deformation events were detected during these test deployments, the OTIS's temporally accurate measurements at the vigorously flowing Monterey Bay cold seep rendered valuable insight into the plumbing of the seep system. In addition to the capability to detect transient flow events, a primary functional requirement of the OTIS was the ability to communicate and transfer data for long-term real-time monitoring deployments. Real-time data transfer from the OTIS to the desktop was successful during a test deployment of the Nootka Observatory, an acoustically-linked moored-buoy system. A small array of CAT meters was also deployed at the Nootka transform-Cascadia subduction zone triple junction. Four anomalous flow rate events were observed across all four meters during the yearlong deployment. Although the records have low temporal accuracy, a preliminary explanation for the regional changes in flow rate is made through comparison between flow rate records and seismic records. The flow events are thought to be a result of a tectonic deformation event, possibly with an aseismic component. Further constraints are not feasible given the unknown structure of faulting near the triple junction. In a final proof of concept study, I find that use these hydrologic instruments, which capture unique aseismic flow rate patterns, is a valuable method for extracting information about deformation events on the decollement in the offshore subduction zone margin. Transient flow events observed in the frontal prism during a 1999--2000 deployment of CAT meters on the Costa Rica Pacific margin suggest episodic slow-slip deformation events may be occurring in the shallow subduction zone. The FEM

  6. Continental Subduction and Subduction Initiation Leading to Extensional Exhumation of Ultra-High Pressure Rocks During Ongoing Plate Convergence in Papua New Guinea

    Science.gov (United States)

    Buck, W. R.; Petersen, K. D.

    2014-12-01

    Subduction of continental rocks is necessary to produce ultra-high pressure (UHP) rocks but the mechanism bringing them to the surface is disputed. A major question is whether this involves fairly small diapirs of crust that move up through the mantle or it involves an entire subducted plate that undergoes coherent 'reverse subduction' (sometimes called 'eduction'). Both mechanisms have been invoked to explain the only known region of on-going exhumation of UHP rocks, on the D'Entrecasteaux Islands of Papua New Guinea. Ductile flow fabrics in the island rocks have been used to argue for a diapiric model while constraints on the plate kinematics of the region require relatively large (>100 km) amounts of recent (>6 Myr) extension, supporting eduction as a primary mechanism. A self-consistent thermo-mechanical model of continental subduction shows that eduction can be accompanied by some ductile flow within the crust. Also we show, that subduction and stacking of continental crust can cause a subduction zone to lock up and lead to subduction initiation elsewhere. When this happens the region of earlier continental subduction can reverse direction causing exhumation of rocks from depth of ~100 km followed by localized extension and plate spreading. This can occur even if a region is in overall convergence. Applied to New Guinea our results are consistent with earlier suggestions that extension of the Woodlark Basin was caused by the initiation of the New Britain Trench, as indicated on the attached figure. We suggest that this subduction initiation event triggered eduction that led to exposure of the D'Entrcasteaux Islands and exhumation of the UHP rocks there. Our numerical results are broadly consistent with the recently refined seismic structure of the region around the islands. The model implies that the present-day basement of the ~70 km wide Goodenough Bay, south of the islands, was subducted then exhumed. This can be tested by drilling.

  7. Collapse of the northern Jalisco continental slope:Subduction erosion, forearc slivering, or subduction beneath the Tres Marias escarpment?

    Science.gov (United States)

    Bandy, W. L.; Mortera-Gutierrez, C. A.; Ortiz-Zamora, G.; Ortega-Ramirez, J.; Galindo Dominguez, R. E.; Ponce-Núñez, F.; Pérez-Calderón, D.; Rufino-Contreras, I.; Valle-Hernández, S.; Pérez-González, E.

    2010-12-01

    The Jalisco subduction zone exhibits several interesting characteristics. Among these is that convergence between the Rivera and North American plate is highly oblique, especially north of 20N, the obliquity progressively increasing to the NW. By analogy to other better studied subduction zones, this distribution of forces should produce a NW-SE extension in the overriding plate, especially north of 20N. This has led to the proposal that the trench perpendicular Bahia de Banderas is an expression of this extension [Kostoglodov and Bandy, JGR, vol. 100, 1995]. To further investigate this proposal, multibeam bathymetric data and seafloor backscatter images, seismic reflection sub-bottom profiles and marine magnetic data were collected during the MORTIC08 campaign of the B.O. EL PUMA in March 2009. The bathymetric data provides for 100% coverage (20 to 200 meter spacing of the actual measured depth value depending on the water depth) of the continental slope and trench areas north of 20N. These data indicate that a marked change occurs in the morphology of the continental slope at 20N. To the north the slope consists of a broad, fairly flat plain lying between a steep lower inner trench slope to the west and a steep, concave seaward, escarpment to the east. In contrast, to the south the continental slope exhibits a more gradual deepening until the steep lower inner trench slope. A prominent submarine canyon deeply incises the continental slope between these two morphotectonic domains. This canyon appears to represent the boundary between two NW-SE diverging forearc blocks or slivers, consistent with the presence of oblique convergence. In contrast, the broad, fairly flat plain is better explained by subsidence induced by subduction erosion (i.e. erosion of the base of the overriding plate underneath the continental slope area). The shoaling of the trench axis northward towards the Puerto Vallarta Graben and subsequent deepening may be related to subduction of the

  8. a New Animation of Subduction Processes for Undergraduates

    Science.gov (United States)

    Stern, R. J.; Lieu, W. K.; Mantey, A.; Ward, A.; Todd, F.; Farrar, E.; Sean, M.; Windler, J.

    2015-12-01

    The subduction of oceanic lithosphere beneath convergent plate margins is a fundamental plate tectonic concept and an important Earth process. It is responsible for some of Earth's most dangerous natural hazards including earthquakes and volcanic eruptions but also produced the continental crust and important mineral deposits. A range of geoscientific efforts including NSF MARGINS and GeoPRISMS initiatives have advanced our understanding of subduction zone processes. In spite the importance of subduction zones and our advancing understanding of how these function, there are few animations that clearly explain the subduction process to non-expert audiences. This deficiency reflects the disparate expertises between geoscientists who know the science but have weak animation skills and digital artists and animators who have strong skills in showing objects in motion but are not experts in natural processes like plate tectonics. This transdisciplinary gap can and should be bridged. With a small grant from NSF (DUE-1444954) we set about to generate a realistic subduction zone animation aimed at the university undergraduate audience by first working within our university to rough out a draft animation and then contract a professional to use this to construct the final version. UTD Geosciences faculty (Stern) and graduate student (Lieu) teamed up with faculty from UTD School of Arts, Technology, and Emerging Communication (ATEC)(Farrar, Fechter, and McComber) to identify and recruit talented ATEC undergraduate students (Mantey, Ward) to work on the project. Geoscientists assembled a storyboard and met weekly with ATEC undergraduates to generate a first draft of the animation, which guided development of an accompanying narrative. The draft animation with voice-over was then handed off to professional animator Windler (Archistration CG) to generate the final animation. We plan to show both the student-generated draft version and the final animation during our presentation

  9. Probable Maximum Earthquake Magnitudes for the Cascadia Subduction

    Science.gov (United States)

    Rong, Y.; Jackson, D. D.; Magistrale, H.; Goldfinger, C.

    2013-12-01

    The concept of maximum earthquake magnitude (mx) is widely used in seismic hazard and risk analysis. However, absolute mx lacks a precise definition and cannot be determined from a finite earthquake history. The surprising magnitudes of the 2004 Sumatra and the 2011 Tohoku earthquakes showed that most methods for estimating mx underestimate the true maximum if it exists. Thus, we introduced the alternate concept of mp(T), probable maximum magnitude within a time interval T. The mp(T) can be solved using theoretical magnitude-frequency distributions such as Tapered Gutenberg-Richter (TGR) distribution. The two TGR parameters, β-value (which equals 2/3 b-value in the GR distribution) and corner magnitude (mc), can be obtained by applying maximum likelihood method to earthquake catalogs with additional constraint from tectonic moment rate. Here, we integrate the paleoseismic data in the Cascadia subduction zone to estimate mp. The Cascadia subduction zone has been seismically quiescent since at least 1900. Fortunately, turbidite studies have unearthed a 10,000 year record of great earthquakes along the subduction zone. We thoroughly investigate the earthquake magnitude-frequency distribution of the region by combining instrumental and paleoseismic data, and using the tectonic moment rate information. To use the paleoseismic data, we first estimate event magnitudes, which we achieve by using the time interval between events, rupture extent of the events, and turbidite thickness. We estimate three sets of TGR parameters: for the first two sets, we consider a geographically large Cascadia region that includes the subduction zone, and the Explorer, Juan de Fuca, and Gorda plates; for the third set, we consider a narrow geographic region straddling the subduction zone. In the first set, the β-value is derived using the GCMT catalog. In the second and third sets, the β-value is derived using both the GCMT and paleoseismic data. Next, we calculate the corresponding mc

  10. Thermal Evolution of Juvenile Subduction Zones ' New Constraints from Lu-Hf Geochronology on HP oceanic rocks (Halilbaǧi, Central Anatolia)

    Science.gov (United States)

    Pourteau, Amaury; Scherer, Erik; Schmidt, Alexander; Bast, Rebecca

    2015-04-01

    The thermal structure of subduction zones plays a key role on mechanical and chemical processes taking place along the slab-mantle interface. Until now, changes through time of this thermal structure have been explored mostly by the means of numerical simulations. However, both "warm" (i.e., epidote-bearing), and "cold" (i.e., lawsonite-bearing) HP oceanic rocks have been reported in some fossil subduction complexes exposed at the Earth's surface (e.g., Franciscan Complex, California; Rio San Juan Complex, Hispañola; Halilbağı Unit, Central Anatolia). These a-priori "incompatible" rocks witness different thermal stages of ancient subduction zones and their study might provide complementary constraints to numerical models. To decipher the meaning of these contrasting metamorphic rocks in the Halilbağı Unit, we are carrying out Lu-Hf geochronology on garnet (grt) and lws from a variety of HP oceanic rocks, as well as the metamorphic sole of the overlying ophiolite. We selected five samples that are representative of the variety of metamorphic evolutions (i.e. peak conditions and P-T paths) encountered in this area. Preliminary analyses yielded 110 Ma (grt-hbl isochron) for a sub-ophiolitic grt amphibolite; 92 Ma (grt-omp) for an eclogite with prograde and retrograde ep; 90 Ma (grt-omp) for an eclogitic metabasite with prograde ep and retrograde ep+lws; 87 Ma (grt-gln) for a lws eclogite with prograde ep; and 86 Ma (grt-gln) for a blueschist with prograde and retrograde lws. These ages are mainly two-point isochrons. Further-refined data will be presented at the EGU General Assembly 2015, in Vienna. The consistent younging trend from "warm" to "cold" metamorphic rocks revealed by these first-order results points to metamorphic-sole formation during the initiation of intra-oceanic subduction at ~110 Ma, and subsequent cooling of the slab-mantle interface between 92 and 86 Ma. Therefore, the contrasting metamorphic evolutions encountered in the Halilbağı Unit

  11. Three dimensional structure of the MqsR:MqsA complex: a novel TA pair comprised of a toxin homologous to RelE and an antitoxin with unique properties.

    Directory of Open Access Journals (Sweden)

    Breann L Brown

    2009-12-01

    Full Text Available One mechanism by which bacteria survive environmental stress is through the formation of bacterial persisters, a sub-population of genetically identical quiescent cells that exhibit multidrug tolerance and are highly enriched in bacterial toxins. Recently, the Escherichia coli gene mqsR (b3022 was identified as the gene most highly upregulated in persisters. Here, we report multiple individual and complex three-dimensional structures of MqsR and its antitoxin MqsA (B3021, which reveal that MqsR:MqsA form a novel toxin:antitoxin (TA pair. MqsR adopts an alpha/beta fold that is homologous with the RelE/YoeB family of bacterial ribonuclease toxins. MqsA is an elongated dimer that neutralizes MqsR toxicity. As expected for a TA pair, MqsA binds its own promoter. Unexpectedly, it also binds the promoters of genes important for E. coli physiology (e.g., mcbR, spy. Unlike canonical antitoxins, MqsA is also structured throughout its entire sequence, binds zinc and coordinates DNA via its C- and not N-terminal domain. These studies reveal that TA systems, especially the antitoxins, are significantly more diverse than previously recognized and provide new insights into the role of toxins in maintaining the persister state.

  12. 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

  13. 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.

  14. Background seismicity rate at subduction zones linked to slab-bending-related hydration

    Science.gov (United States)

    Nishikawa, Tomoaki; Ide, Satoshi

    2015-09-01

    Tectonic properties strongly control variations in seismicity among subduction zones. In particular, fluid distribution in subduction zones influences earthquake occurrence, and it varies among subduction zones due to variations in fluid sources such as hydrated oceanic plates. However, the relationship between variations in fluid distribution and variations in seismicity among subduction zones is unclear. Here we divide Earth's subduction zones into 111 regions and estimate background seismicity rates using the epidemic type aftershock sequence model. We demonstrate that background seismicity rate correlates to the amount of bending of the incoming oceanic plate, which in turn is related to the hydration of oceanic plates via slab-bending-related faults. Regions with large bending may have high-seismicity rates because a strongly hydrated oceanic plate causes high pore fluid pressure and reduces the strength of the plate interface. We suggest that variations in fluid distribution can also cause variations in seismicity in subduction zones.

  15. Are diamond-bearing Cretaceous kimberlites related to low-angle subduction beneath western North America?

    Science.gov (United States)

    Currie, Claire A.; Beaumont, Christopher

    2011-02-01

    Diamond-bearing Cretaceous kimberlites of western North America were emplaced 1000-1500 km inboard of the Farallon plate subduction margin and overlap with the development of the Western Interior Seaway, shut-down of the Sierra Nevada arc, and the Laramide orogeny. These events are consistent with a decrease in subduction angle along much of the margin, which placed the subducted Farallon plate in close proximity to the continental interior at the time of kimberlite magmatism. Our numerical models demonstrate that low-angle subduction can result from high plate convergence velocities and enhanced westward motion of North America. Further, rapid subduction allows hydrous minerals to remain stable within the cool interior of the subducting plate to more than 1200 km from the trench. Destabilization of these minerals provides a fluid source that can infiltrate the overlying material, potentially triggering partial melting and kimberlite/lamproite magmatism.

  16. Thermal regime along the Antilles subduction zone: Influence of the oceanic lithosphere materials subducted in the oceanic crust

    Science.gov (United States)

    Biari, Youssef; Marcaillou, Boris; Klingelhoefer, Frauke; Francis, Lucazeau; Fréderique, Rolandone; Arnauld, Heuret; Thibaud, Pichot; Hélène, Bouquerel

    2017-04-01

    Heat-flow measurements acquired during the Antithesis Cruise in the Northern Lesser Antilles reveal an atypical heat-flow trend, from the trench to the margin forearc, where the subducting crust consists of exhumed and serpentinized mantle rocks (see Marcaillou et al. same session). We investigate the thermal structure of the Lesser Antilles subduction zone along two transects perpendicular to the margin located off Antigua and Martinique Islands. We perform 2-D steady-state finite elements thermal modelling constrained by newly-recorded and existing data: heat flow measurements, deep multichannel reflection and wide angle seismic data as well as earthquake hypocenters location at depth. Along the Martinique profile, the heat-flow decreases from the trench (45 mW.m-2) to minimum in the outer fore-arc (30 mW.m-2) and increases to a plateau (50 mW.m-2) toward the back-arc area. These trend and values are typical for the subduction of a steep 80-MYr old oceanic plate beneath an oceanic margin. As a result, the 150°-350°C temperature range along the interplate contact, commonly associated to the thermally-defined seismogenic zone, is estimated to be located between 200 - 350km from the trench. In contrast, along the Antigua profile, the heat-flow shows an atypical "flat" trend at 40 ± 15 mW.m-2 from the trench to the inner forearc. Purely conductive thermal models fail at fitting both the measured values and the flat trend. We propose that the subducting crust made of serpentinized exhumed mantle rock strongly affecting the heat-flow at the surface and the margin thermal structure. The geothermal gradient in the 5-km-thick serpentinized layer is expected to be low compared to "normal" oceanic crust because of cold water percolation and peridotite alteration. Moreover, from 50km depth, serpentine dehydration reactions provide significant amounts of hot water expelled toward the upper plate, generated heat beneath the forearc. As a result, in our preferred model: 1/ A

  17. Subducting slab ultra-slow velocity layer coincident with silent earthquakes in southern Mexico

    OpenAIRE

    Song, Teh-Ru Alex; Helmberger, Donald V.; Brudzinski, Michael R.; Clayton, Robert W.; Davis, Paul; Pérez-Campos, Xyoli; Singh, Shri K.

    2009-01-01

    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...

  18. Effect of aseismic ridge subduction on slab geometry and overriding plate deformation: Insights from analogue modeling

    OpenAIRE

    Martinod, Joseph; Guillaume, Benjamin; Espurt, Nicolas; Faccenna, Claudio; Funiciello, Francesca; Regard, Vincent

    2013-01-01

    International audience; We present analogue models simulating the subduction of a buoyant ridge beneath an advancing overriding plate whose velocity is imposed by lateral boundary conditions. We analyze the 3D geometry of the slab, the deformation and topography of the overriding plate. Ridge subduction diminishes the dip of the slab, eventually leading to the appearance of a horizontal slab segment. This result contrasts with that obtained in free subduction experiments, in which ridge subdu...

  19. Styles of continental subduction and collision and their effect on formation and exhumation of UHP rocks

    Science.gov (United States)

    Warren, C. J.; Beaumont, C.; Jamieson, R. A.

    2006-12-01

    Ultra-high pressure (UHP) metamorphic rocks are exposed in many Phanerozoic mountain belts. It is now widely accepted that they represent continental margin rocks that were subducted to ≥100km during the transition from oceanic subduction to continental collision. A range of subduction-collision mechanisms have been proposed to account for UHP formation and exhumation. A series of upper-mantle-scale geodynamic models is used to test the sensitivity of a subset of these mechanisms to variations in lithosphere density, radioactive heat production, and crustal strength. The subducting crust includes an oceanic domain, a continental margin domain with variable width, thickness, strength, and heat production, and a strong internal continental domain. The models involve dynamic subduction, constant convergence velocity, density changes that accompany the main phase changes during burial, and surface erosion in the collision zone. Results show that continental subduction without retro-continent deformation is favored by relatively dense mantle lithosphere. Subduction of the retro-continent (forearc subduction) is associated with shallow-dipping, low- density mantle lithosphere. Back-thrusting of retro-lithosphere is favored by relatively weak retro-continental crust. UHP material can be exhumed in all 3 model styles, depending on the evolving geometry of the subduction-accretion zone and the degree of decoupling between subducting upper and lower continental crust in this zone. Weaker and/or hotter margins decouple and accrete, and their subsequent exhumation is driven by bulk density contrast (buoyancy) and/or forced expulsion in response to advection of strong continental material into the subduction zone (plunger effect). Stronger and/or colder continental margin material is subducted without decoupling and is then transported laterally, underplating the retro-mantle lithosphere. Model results are compatible with observed geometries and PTt paths from some UHP

  20. Geothermal structure of the Miura-Boso plate subduction margin, central Japan

    Science.gov (United States)

    Yamamoto, Yuzuru; Hamada, Yohei; Kamiya, Nana; Ojima, Takanori; Chiyonobu, Shun; Saito, Saneatsu

    2017-07-01

    We have constrained the geothermal structure of the Miura-Boso plate subduction margin, located in central Japan, using maximum paleo-temperature data derived from vitrinite reflectance measurements. We established that higher maximum paleo-temperatures are restricted to the western part of the early Miocene Hota accretionary complex (Hota and Hayama groups), indicating a spatial difference in the amount of slip upon the out-of-sequence thrust potentially associated with the Izu-Bonin Island Arc collision. The weakly deformed sedimentary sequences overlying the highly deformed Hota Group strata have much lower vitrinite reflectance values than the latter. This variation indicates that the sedimentary sequences of the trench slope experienced a markedly lower maximum burial depth than the relatively deep-buried and uplifted Hota accretionary complex. Conversely, maximum paleo-temperatures obtained for tectonic blocks hosted by the neighboring Mineoka ophiolite complex are very high: ca. 140 °C for the large, early Miocene Haccho Formation blocks, and 65-90 °C for the other blocks. This result suggests that the individual tectonic blocks enclosed in the ophiolite complex were subjected exhumation from depths of 3-5 km.

  1. Effects of Prolonged Flat Subduction on the Miocene Magmatic Record of the Central Trans-Mexican Volcanic Belt

    Science.gov (United States)

    Mori, L.; Gomez-Tuena, A.; Goldstein, S. L.

    2006-12-01

    Temporal modifications in the chemical compositions of middle to late Miocene rocks from the central Trans- Mexican Volcanic Belt elucidate how a process of prolonged flat subduction influences arc magmatism. These are recorded in the Palo Huerfano-La Joya-Zamorano Volcanic Complex (PH-LJ-Z; 16-9 Ma), a group of andesitic to dacitic stratovolcanoes located at ~500 km from the current trench, and in the Queretaro Volcanic Succession (QVS; 9-6 Ma), a basaltic to basaltic-andesitic plateau which stratigraphically overlies the stratovolcanoes. The two rock groups have typical arc-like trace element patterns, but the PH-LJ-Z suite has higher Sr/Y and LREE(MREE)/HREE ratios with MORB-like Sr, Nd and Pb isotopic compositions; geochemical features that are typical of experimental and natural slab melts. In contrast, rocks from the QVS have an overall weaker subduction signature, do not show slab melt signals, and have higher FeO^{tot} and MgO contents at equivalent Na2O and Mg# (40-70) than the PH-LJ-Z suite. Since Fe in arc magmas is a sensitive proxy of melting pressure and/or water contents (Gaetani &Grove, CMP, 1998), and Na could be either sensitive to slab melt additions (Kelemen et al., Tr. Geoch., 2003) or to the thickness of the mantle column that controls the extent of melting (Plank &Langmuir, EPSL, 1998), the overall chemical differences of both rock suites can only be reconciled if they equilibrated with the mantle wedge at the same pressures but with different amounts of dissolved water. The geochemical evidence thus indicates that the compositional differences between the two magmatic episodes are mainly related to different mechanisms of element recycling that occurred without major changes in the local tectonic configuration. The slab melt features of PH- LJ-Z rocks, and their emplacement at a large distance from the trench, are consistent with a sub-horizontal subduction geometry which favors slab melting at relatively low pressures (Gutscher et al

  2. Rufus Choate: A Unique Orator.

    Science.gov (United States)

    Markham, Reed

    Rufus Choate, a Massachusetts lawyer and orator, has been described as a "unique and romantic phenomenon" in America's history. Born in 1799 in Essex, Massachusetts, Choate graduated from Dartmouth College and attended Harvard Law School. Choate's goal was to be the top in his profession. Daniel Webster was Choate's hero. Choate became well…

  3. Uniqueness of PL Minimal Surfaces

    Institute of Scientific and Technical Information of China (English)

    Yi NI

    2007-01-01

    Using a standard fact in hyperbolic geometry, we give a simple proof of the uniqueness of PL minimal surfaces, thus filling in a gap in the original proof of Jaco and Rubinstein. Moreover, in order to clarify some ambiguity, we sharpen the definition of PL minimal surfaces, and prove a technical lemma on the Plateau problem in the hyperbolic space.

  4. On the Nagumo uniqueness theorem

    OpenAIRE

    Octavian G. Mustafa; O'Regan, Donal

    2011-01-01

    By a convenient reparametrisation of the integral curves of a nonlinear ordinary differential equation (ODE), we are able to improve the conclusions of the recent contribution [A. Constantin, Proc. Japan Acad. {\\bf 86(A)} (2010), 41--44]. In this way, we establish a flexible uniqueness criterion for ODEs without Lipschitz-like nonlinearities.

  5. The Lasso Problem and Uniqueness

    CERN Document Server

    Tibshirani, Ryan J

    2012-01-01

    The lasso is a popular tool for sparse linear regression, especially for problems in which the number of variables p exceeds the number of observations n. But when p>n, the lasso criterion is not strictly convex, and hence it may not have a unique minimum. An important question is: when is the lasso solution well-defined (unique)? We review results from the literature, which show that if the predictor variables are drawn from a continuous probability distribution, then there is a unique lasso solution with probability one, regardless of the sizes of n and p. We also show that this result extends easily to $\\ell_1$ penalized minimization problems over a wide range of loss functions. A second important question is: how can we deal with the case of non-uniqueness in lasso solutions? In light of the aforementioned result, this case really only arises when some of the predictor variables are discrete, or when some post-processing has been performed on continuous predictor measurements. Though we certainly cannot c...

  6. How does the Nazca Ridge subduction influence the modern Amazonian foreland basin?

    Science.gov (United States)

    Espurt, N.; Baby, P.; Brusset, S.; Roddaz, M.; Hermoza, W.; Regard, V.; Antoine, P.-O.; Salas-Gismondi, R.; Bolaños, R.

    2007-06-01

    The subduction of an aseismic ridge has important consequences on the dynamics of the overriding upper plate. In the central Andes, the Nazca Ridge subduction imprint can be tracked on the eastern side of the Andes. The Fitzcarrald arch is the long-wavelength topography response of the Nazca Ridge flat subduction, 750 km inboard of the trench. This uplift is responsible for the atypical three-dimensional shape of the Amazonian foreland basin. The Fitzcarrald arch uplift is no older than Pliocene as constrained by the study of Neogene sediments and geomorphic markers, according to the kinematics of the Nazca Ridge subduction.

  7. Active Subduction on Both Coasts of Costa Rica Does not Represent an Important Tsunami Hazard

    Science.gov (United States)

    Protti, M.; Gonzalez, V.

    2007-05-01

    Costa Rica, on the southern terminus of the Middle American Trench is being affected by active subduction on both, along the Pacific coast as well as on its Caribbean coast. Three main subduction segments can be recognized along the Pacific coast: 1) under northwestern Costa Rica, off Papagayo Gulf and Nicoya peninsula, the Cocos plate is subducting under the Caribbean plate; 2) under southern Costa Rica (Osa and Burica peninsulas) the Cocos plate subducts under the Panama Block and 3) in the central Pacific coast (between Nicoya and Osa peninsulas) the Cocos plate subducts under a shear zone that marks the transition between the Caribbean and the Cocos plate. Along the Caribbean coast, south of Puerto Limon, the Caribbean plate subducts under the Panama block. Large subduction earthquakes occur under the Nicoya peninsula, Osa peninsula and south of Limon. Most of the rupture area of these large events lies below land so the deformation of the ocean floor is minimal and therefore the tsunamis they generate are small. No large subduction earthquakes occur under the central Pacific coast of Costa Rica due to the subduction of small sea mounts that act as small asperities without potential to accumulate large amounts of slip. For this reason the region between Nicoya and Osa peninsulas is not an important tsunamigenic zone.

  8. 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.

  9. The truncated Second Main Theorem and uniqueness theorems

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    In this paper, we first establish a truncated Second Main Theorem for algebraically nondegenerate holomorphic mappings from the complex plane into a complex projective variety V intersecting hypersurfaces. We then prove some uniqueness results for meromorphic mappings. The result of Demailly about a partial solution to the Fujita’s conjecture is used.

  10. The fate of carbon and CO2 - fluid-rock interaction during subduction metamorphism of serpentinites

    Science.gov (United States)

    Menzel, Manuel D.; Garrido, Carlos J.; López Sánchez-Vizcaíno, Vicente; Marchesi, Claudio; Hidas, Károly

    2016-04-01

    Given to its large relevance for present and past climate studies, the deep carbon cycle received increasing attention recently. However, there are still many open questions concerning total mass fluxes and transport processes between the different carbon reservoirs in the Earth's interior. One key issue is the carbon transfer from the subducting slab into fluids and rocks in the slab and mantle wedge. This transfer is controlled by the amount and speciation of stable carbon-bearing phases, which have a strong impact on the pH, redox conditions and trace-element budget of slab fluids. As recent experiments and thermodynamic modeling have shown, water released from dehydrating serpentinites has a great potential to produce CO2-enriched slab fluids by dissolution of carbonate minerals. To constrain the fate of carbon and CO2-fluid-rock interactions during subduction metamorphism of serpentinites, we have studied carbonate-bearing serpentinites recording different prograde evolutions from antigorite schists to Chl-harzburgites in high-P massifs of the Nevado-Filabride Complex (Betic Cordillera, S. Spain). Our results indicate that dissolution of dolomite in marbles in contact with dehydrating serpentinites is spatially limited during prograde metamorphism of carbonate-bearing serpentinites, but it can lead to the formation of silicate-rich zones in marbles close to the contacts. In lower grade serpentinite massifs (1.0-1.5 GPa / 550 °C), the presence of marble lenses in contact with antigorite schists appears to promote local dehydration of serpentinite coupled with carbonation of antigorite, forming Cpx-Tr-Chl-bearing high grade ophicarbonate zones. At the Cerro del Almirez ultramafic massif, where a dehydration front from antigorite-serpentinite to prograde Chl-harzburgite is preserved (1.9 GPa / 680 °C), a significant amount of carbon is retained in prograde Chl-harzburgites and Tr-Dol-marble lenses. This observation is at odds with thermodynamic models that

  11. Spatial and temporal patterns of nonvolcanic tremor along the southern Cascadia subduction zone

    Science.gov (United States)

    Boyarko, Devin C.; Brudzinski, Michael R.

    2010-08-01

    Episodic tremor and slip (ETS), the spatial and temporal correlation of slow slip events monitored via GPS surface displacements and nonvolcanic tremor (NVT) monitored via seismic signals, is a newly discovered mode of deformation thought to be occurring downdip from the seismogenic zone along several subduction zone megathrusts. To provide overall constraints on the distribution and migration behavior of NVT in southern Cascadia, we apply a semiautomated location algorithm to seismic data available during the EarthScope Transportable Array deployment to detect the most prominent pulses of NVT and invert analyst-refined relative arrival times for source locations. In the processing, we also detect distinct and isolated bursts of energy within the tremor similar to observations of low-frequency earthquakes in southwest Japan. We investigate in detail eight NVT episodes between November 2005 and August 2007 with source locations extending over a 650 km along-strike region from northern California to northern Oregon. We find complex tremor migration patterns with periods of steady migration (4-10 km/d), halting, and frequent along-strike jumps (30-400 km) in activity. The initiation and termination points of laterally continuous tremor activity appear to be repeatable features between NVT episodes which support the hypothesis of segmentation within the ETS zone. The overall distribution of NVT epicenters occur within a narrow band primarily confined by the surface projections of the 30 and 40 km contours of the subducting plate interface. We find as much as 50 km spatial offset from the updip edge of the tremor source zone to the downdip edge of the thermally and geodetically defined transition zone, which may inhibit ETS from triggering earthquakes further updip. Intriguingly, NVT activity is spatially anticorrelated with local seismicity, suggesting the two processes are mutually exclusive. We propose that the transition in frictional behavior coupled with high pore

  12. Apparent stress, fault maturity and seismic hazard for normal-fault earthquakes at subduction zones

    Science.gov (United States)

    Choy, G.L.; Kirby, S.H.

    2004-01-01

    The behavior of apparent stress for normal-fault earthquakes at subduction zones is derived by examining the apparent stress (?? a = ??Es/Mo, where E s is radiated energy and Mo is seismic moment) of all globally distributed shallow (depth, ?? 1 MPa) are also generally intraslab, but occur where the lithosphere has just begun subduction beneath the overriding plate. They usually occur in cold slabs near trenches where the direction of plate motion across the trench is oblique to the trench axis, or where there are local contortions or geometrical complexities of the plate boundary. Lower ??a (tectonic regime suggests that the level of ?? a is related to fault maturity. Lower stress drops are needed to rupture mature faults such as those found at plate interfaces that have been smoothed by large cumulative displacements (from hundreds to thousands of kilometres). In contrast, immature faults, such as those on which intraslab-normal-fault earthquakes generally occur, are found in cold and intact lithosphere in which total fault displacement has been much less (from hundreds of metres to a few kilometres). Also, faults on which high ??a oceanic strike-slip earthquakes occur are predominantly intraplate or at evolving ends of transforms. At subduction zones, earthquakes occurring on immature faults are likely to be more hazardous as they tend to generate higher amounts of radiated energy per unit of moment than earthquakes occurring on mature faults. We have identified earthquake pairs in which an interplate-thrust and an intraslab-normal earthquake occurred remarkably close in space and time. The intraslab-normal member of each pair radiated anomalously high amounts of energy compared to its thrust-fault counterpart. These intraslab earthquakes probably ruptured intact slab mantle and are dramatic examples in which Mc (an energy magnitude) is shown to be a far better estimate of the potential for earthquake damage than Mw. This discovery may help explain why loss of

  13. Anisotropy above and below the subducting Nazca lithosphere

    Science.gov (United States)

    MacDougall, J. G.; Fischer, K. M.; Anderson, M. L.; Kincaid, C. R.

    2011-12-01

    The goal of this study is to constrain mantle flow above and below the subducting Nazca plate at latitudes of 30°-41° S. In this segment of the South American subduction zone, slab dip varies from flat slab subduction in the north to a dip of ~40° in the south, where the segment ends at a slab gap associated with Chile Ridge. We measured shear-wave splitting in over 280 S arrivals from local earthquakes recorded by the 2010 Chile RAMP IRIS/PASSCAL array (aftershock locations from Lange et al., 2010), the 2000-2002 CHARGE IRIS/PASSCAL array, and permanent stations PLCA (USGS/GTSN) and PEL (Geoscope). We also resolved splitting in 17 SK(K)S phases at PLCA and permanent station TRQA (IRIS/GSN). Splitting parameters for a subset of phases were determined using a range of filters; most were stable as a function of frequency. The results reported below correspond to a 0.05-2 Hz bandpass filter. Local S lag times range from 0.1-0.9 seconds. For back-arc stations above the area of steep subduction, lag times correlate with path length in the mantle wedge, indicating that wedge anisotropy dominates. Lag times from the Chile RAMP stations, which are located in the forearc between 33°S and 39°S and in general correspond to shorter paths, span a narrower range (0.1-0.4 seconds). Splitting fast polarizations at back-arc stations show a coherent variation with latitude. Fast polarizations vary from NE at 40°-41°S, to N (roughly slab-strike parallel) at 35°-36°S, to NE-ESE at 30°-33°S, curving as the slab flattens. Modeling of these local S splitting results reveals that the fast symmetry axis of anisotropy is sub-parallel to the overall trend of fast polarization directions at each station, and that the strength of anisotropy is equivalent to 10-30% of single crystal olivine anisotropy. At forearc stations, we observe roughly trench-parallel fast polarization directions (largely N-NE) with the exception of two areas of localized, yet robust trench-normal trends (E

  14. 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

  15. 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

  16. 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

  17. Mantle plumes in the vicinity of subduction zones

    Science.gov (United States)

    Mériaux, C. A.; Mériaux, A.-S.; Schellart, W. P.; Duarte, J. C.; Duarte, S. S.; Chen, Z.

    2016-11-01

    We present three-dimensional deep-mantle laboratory models of a compositional plume within the vicinity of a buoyancy-driven subducting plate with a fixed trailing edge. We modelled front plumes (in the mantle wedge), rear plumes (beneath the subducting plate) and side plumes with slab/plume systems of buoyancy flux ratio spanning a range from 2 to 100 that overlaps the ratios in nature of 0.2-100. This study shows that 1) rising side and front plumes can be dragged over thousands of kilometres into the mantle wedge, 2) flattening of rear plumes in the trench-normal direction can be initiated 700 km away from the trench, and a plume material layer of lesser density and viscosity can ultimately almost entirely underlay a retreating slab after slab/plume impact, 3) while side and rear plumes are not tilted until they reach ∼600 km depth, front plumes can be tilted at increasing depths as their plume buoyancy is lessened, and rise at a slower rate when subjected to a slab-induced downwelling, 4) rear plumes whose buoyancy flux is close to that of a slab, can retard subduction until the slab is 600 km long, and 5) slab-plume interaction can lead to a diversity of spatial plume material distributions into the mantle wedge. We discuss natural slab/plume systems of the Cascadia/Bowie-Cobb, and Nazca/San Felix-Juan Fernandez systems on the basis of our experiments and each geodynamic context and assess the influence of slab downwelling at depths for the starting plumes of Java, Coral Sea and East Solomon. Overall, this study shows how slab/plume interactions can result in a variety of geological, geophysical and geochemical signatures.

  18. Large earthquake processes in the northern Vanuatu subduction zone

    Science.gov (United States)

    Cleveland, K. Michael; Ammon, Charles J.; Lay, Thorne

    2014-12-01

    The northern Vanuatu (formerly New Hebrides) subduction zone (11°S to 14°S) has experienced large shallow thrust earthquakes with Mw > 7 in 1966 (MS 7.9, 7.3), 1980 (Mw 7.5, 7.7), 1997 (Mw 7.7), 2009 (Mw 7.7, 7.8, 7.4), and 2013 (Mw 8.0). We analyze seismic data from the latter four earthquake sequences to quantify the rupture processes of these large earthquakes. The 7 October 2009 earthquakes occurred in close spatial proximity over about 1 h in the same region as the July 1980 doublet. Both sequences activated widespread seismicity along the northern Vanuatu subduction zone. The focal mechanisms indicate interplate thrusting, but there are differences in waveforms that establish that the events are not exact repeats. With an epicenter near the 1980 and 2009 events, the 1997 earthquake appears to have been a shallow intraslab rupture below the megathrust, with strong southward directivity favoring a steeply dipping plane. Some triggered interplate thrusting events occurred as part of this sequence. The 1966 doublet ruptured north of the 1980 and 2009 events and also produced widespread aftershock activity. The 2013 earthquake rupture propagated southward from the northern corner of the trench with shallow slip that generated a substantial tsunami. The repeated occurrence of large earthquake doublets along the northern Vanuatu subduction zone is remarkable considering the doublets likely involved overlapping, yet different combinations of asperities. The frequent occurrence of large doublet events and rapid aftershock expansion in this region indicate the presence of small, irregularly spaced asperities along the plate interface.

  19. Detection of earthquake swarms in subduction zones around Japan

    Science.gov (United States)

    Nishikawa, T.; Ide, S.

    2015-12-01

    Earthquake swarms in subduction zones are likely to be related with slow slip events (SSEs) and locking on the plate interface. In the Boso-Oki region in central Japan, swarms repeatedly occur accompanying SSEs (e.g, Hirose et al., 2012). It is pointed out that ruptures of great earthquakes tend to terminate in regions with recurring swarm activity because of reduced and heterogeneous locking there (Holtkamp and Brudzinsiki, 2014). Given these observations, we may be able to infer aseismic slips and spatial variations in locking on the plate interface by investigating swarm activity in subduction zones. It is known that swarms do not follow Omori's law and have much higher seismicity rates than predicted by the ETAS model (e.g., Llenos et al., 2009). Here, we devised a statistical method to detect unexpectedly frequent earthquakes using the space-time ETAS model (Zhuang et al., 2002). We applied this method to subduction zones around Japan (Tohoku, Ibaraki-Boso-oki, Hokkaido, Izu, Tonankai, Nankai, and Kyushu) and detected swarms in JMA catalog (M ≥ 3) from 2001 to 2010. We detected recurring swarm activities as expected in the Boso-Oki region and also in the Ibaraki-Oki region (see Figures), where intensive foreshock activity was found by Maeda and Hirose (2011). In Tohoku, regions with intensive foreshock activity also appear to roughly correspond to regions with recurring swarm activity. Given that both foreshocks and swarms are triggered by SSEs (e.g., Bouchon et al., 2013), these results suggest that the regions with foreshock activity and swarm activity such as the Ibaraki-Oki region are characterized by extensive occurrences of SSEs just like the Boso-Oki region. Besides Ibaraki-Oki and Boso-Oki, we detected many swarms in Tohoku, Hokkaido, Izu, and Kyushu. On the other hand, swarms are rare in the rupture areas of the 1944 Tonankai and 1946 Nankai earthquakes. These variations in swarm activity may reflect variations in SSE activity among subduction zones

  20. Experimental constraints on phase relations in subducted continental crust

    Science.gov (United States)

    Hermann, Jörg

    2002-01-01

    Synthesis piston cylinder experiments were carried out in the range 2.0-4.5 GPa and 680-1,050 °C to investigate phase relations in subducted continental crust. A model composition (KCMASH) has been used because all major ultrahigh-pressure (UHP) minerals of the whole range of rock types typical for continental crust can be reproduced within this system. The combination of experimental results with phase petrologic constraints permits construction of a UHP petrogenetic grid. The phase relations demonstrate that the most important UHP paragenesis consists of coesite, kyanite, phengite, clinopyroxene, and garnet in subducted continental crust. Below 700 °C talc is stable instead of garnet. As most of these minerals are also stable at much lower pressure and temperature conditions it is thus not easy to recognize UHP metamorphism in subducted crust. A general feature, however, is the absence of feldspars at H2O-saturated conditions. Plagioclase is never stable at UHP conditions, but K-feldspar can occur in H2O-undersaturated rocks. Mineral compositions in the experiments are fully buffered by coexisting phases. The Si content of phengite and biotite increase with increasing pressure. At 4.0 GPa, 780 °C, biotite contains 3.28 Si per formula unit, which is most probably caused by solid solution of biotite with talc. Above 800 °C, the CaAl2SiO6 component in clinopyroxene buffered with kyanite, coesite and a Mg-phase increases with increasing temperature, providing a tool to distinguish between 'cold' and 'hot' eclogites. Up to 10% Ca-eskolaite (Ca0.5[]0.5AlSi2O6) in clinopyroxene has been found at the highest temperature and pressure investigated (>900 °C, 4.5 GPa). Garnet buffered with coesite, kyanite and clinopyroxene displays an increase of grossular component with increasing pressure for a given temperature. Although the investigated system represents a simplification with respect to natural rocks, it helps to constrain general features of subducted continental

  1. 2012 Haida Gwaii Quake: Insight Into Cascadia's Subduction Extent

    Science.gov (United States)

    Szeliga, Walter

    2013-02-01

    The limits of Cascadia were first defined to contain nearly the entire margin of the Pacific Northwest, from Cape Mendocino through the Alaska Panhandle [Schuchert, 1910; Schuchert and Barrell, 1914]. Since that time, the boundary of Cascadia has shrunk to become essentially synonymous with the region where the Juan de Fuca plate subducts beneath the North American plate. As a consequence, seismic hazard assessments in the Pacific Northwest have conventionally focused on the potential for large megathrust earthquakes along the interface of the Juan de Fuca and North American plates.

  2. A Review on Forearc Ophiolite Obduction, Adakite-Like Generation, and Slab Window Development at the Chile Triple Junction Area: Uniformitarian Framework for Spreading-Ridge Subduction

    Science.gov (United States)

    Bourgois, Jacques; Lagabrielle, Yves; Martin, Hervé; Dyment, Jérôme; Frutos, Jose; Cisternas, Maria Eugenia

    2016-10-01

    This paper aggregates the main basic data acquired along the Chile Triple Junction (CTJ) area (45°-48°S), where an active spreading center is presently subducting beneath the Andean continental margin. Updated sea-floor kinematics associated with a comprehensive review of geologic, geochemical, and geophysical data provide new constraints on the geodynamics of this puzzling area. We discuss: (1) the emplacement mode for the Pleistocene Taitao Ridge and the Pliocene Taitao Peninsula ophiolite bodies. (2) The occurrence of these ophiolitic complexes in association with five adakite-like plutonic and volcanic centers of similar ages at the same restricted locations. (3) The inferences from the co-occurrence of these sub-coeval rocks originating from the same subducting oceanic lithosphere evolving through drastically different temperature-pressure ( P- T) path: low-grade greenschist facies overprint and amphibolite-eclogite transition, respectively. (4) The evidences that document ridge-jump events and associated microplate individualization during subduction of the SCR1 and SCR-1 segments: the Chonos and Cabo Elena microplates, respectively. The ridge-jump process associated with the occurrence of several closely spaced transform faults entering subduction is controlling slab fragmentation, ophiolite emplacement, and adakite-like production and location in the CTJ area. Kinematic inconsistencies in the development of the Patagonia slab window document an 11- km westward jump for the SCR-1 spreading segment at ~6.5-to-6.8 Ma. The SCR-1 spreading center is relocated beneath the North Patagonia Icefield (NPI). We argue that the deep-seated difference in the dynamically sustained origin of the high reliefs of the North and South Patagonia Icefield (NPI and SPI) is asthenospheric convection and slab melting, respectively. The Chile Triple Junction area provides the basic constraints to define the basic signatures for spreading-ridge subduction beneath an Andean

  3. A Review on Forearc Ophiolite Obduction, Adakite-Like Generation, and Slab Window Development at the Chile Triple Junction Area: Uniformitarian Framework for Spreading-Ridge Subduction

    Science.gov (United States)

    Bourgois, Jacques; Lagabrielle, Yves; Martin, Hervé; Dyment, Jérôme; Frutos, Jose; Cisternas, Maria Eugenia

    2016-05-01

    This paper aggregates the main basic data acquired along the Chile Triple Junction (CTJ) area (45°-48°S), where an active spreading center is presently subducting beneath the Andean continental margin. Updated sea-floor kinematics associated with a comprehensive review of geologic, geochemical, and geophysical data provide new constraints on the geodynamics of this puzzling area. We discuss: (1) the emplacement mode for the Pleistocene Taitao Ridge and the Pliocene Taitao Peninsula ophiolite bodies. (2) The occurrence of these ophiolitic complexes in association with five adakite-like plutonic and volcanic centers of similar ages at the same restricted locations. (3) The inferences from the co-occurrence of these sub-coeval rocks originating from the same subducting oceanic lithosphere evolving through drastically different temperature-pressure (P-T) path: low-grade greenschist facies overprint and amphibolite-eclogite transition, respectively. (4) The evidences that document ridge-jump events and associated microplate individualization during subduction of the SCR1 and SCR-1 segments: the Chonos and Cabo Elena microplates, respectively. The ridge-jump process associated with the occurrence of several closely spaced transform faults entering subduction is controlling slab fragmentation, ophiolite emplacement, and adakite-like production and location in the CTJ area. Kinematic inconsistencies in the development of the Patagonia slab window document an 11- km westward jump for the SCR-1 spreading segment at ~6.5-to-6.8 Ma. The SCR-1 spreading center is relocated beneath the North Patagonia Icefield (NPI). We argue that the deep-seated difference in the dynamically sustained origin of the high reliefs of the North and South Patagonia Icefield (NPI and SPI) is asthenospheric convection and slab melting, respectively. The Chile Triple Junction area provides the basic constraints to define the basic signatures for spreading-ridge subduction beneath an Andean

  4. Nazca-South America Subduction Zone Reflectivity from P'P' Precursors

    Science.gov (United States)

    Gu, Y. J.; Schultz, R.

    2012-12-01

    Much of what is known about mantle owes to the interpretation of its reflectivity structure. On the global scale mantle stratifications have been attributed to mineralogical phase changes of olivine; two widely observed examples are the 410 and 660 km discontinuities. Among the various seismological tools, results from longer-period SS/PP precursors and high frequency receiver functions are routinely compared to increase the confidence of the recovered mantle stratifications. The former are lower frequency approaches with complex Fresnel zones, while constraints on receiver distribution hinder analysis in oceanic regions for the latter. P'P' precursors are a promising high frequency alternative, capable of resolving small-scale structures (resolution of ~5 km vertically, 200 km laterally) in the mantle, owing to its short-period nature (~1Hz), shallow angle of incidence and nearly symmetric Fresnel zone. However, P'P' precursors are known for several complications: phase triplication (PKiKPPKiKP, PKIKPPKIKP, PKPPKPab and PKPPKPbc) and the maximum-phase Fresnel zones result in strong scattering and asymmetric arrivals. Much of these concerns are alleviated through revamped processing techniques involving stacking, deconvolution, Radon transform and migration. We utilize P'P' precursors to constrain the mantle structure and layering beneath the Nazca-South America subduction zone. Our migration profiles reveal both olivine (e.g., 410, 520, 660) and garnet related transitions in the mantle, with constraints on the sharpness of these transitions. Observations of a depressed 660 are attributed to thermal variations, showing the spatial extent of the impinging Nazca slab. Prominent 520 arrivals near subducted slab material suggest this transition is sharpened to a thickness resonant with P'P' (~10km). The possibility of chemical heterogeneity is evidenced near the top of the mantle transition zone through complicated 410 amplitudes. The existence, depth, sharpness and

  5. Uniqueness theorems in linear elasticity

    CERN Document Server

    Knops, Robin John

    1971-01-01

    The classical result for uniqueness in elasticity theory is due to Kirchhoff. It states that the standard mixed boundary value problem for a homogeneous isotropic linear elastic material in equilibrium and occupying a bounded three-dimensional region of space possesses at most one solution in the classical sense, provided the Lame and shear moduli, A and J1 respectively, obey the inequalities (3 A + 2 J1) > 0 and J1>O. In linear elastodynamics the analogous result, due to Neumann, is that the initial-mixed boundary value problem possesses at most one solution provided the elastic moduli satisfy the same set of inequalities as in Kirchhoffs theorem. Most standard textbooks on the linear theory of elasticity mention only these two classical criteria for uniqueness and neglect altogether the abundant literature which has appeared since the original publications of Kirchhoff. To remedy this deficiency it seems appropriate to attempt a coherent description ofthe various contributions made to the study of uniquenes...

  6. Insights from Pb and O isotopes into along-arc variations in subduction inputs and crustal assimilation for volcanic rocks in Java, Sunda arc, Indonesia

    Science.gov (United States)

    Handley, Heather K.; Blichert-Toft, Janne; Gertisser, Ralf; Macpherson, Colin G.; Turner, Simon P.; Zaennudin, Akhmad; Abdurrachman, Mirzam

    2014-08-01

    New Pb isotope data are presented for Gede Volcanic Complex, Salak and Galunggung volcanoes in West Java, Merbabu and Merapi volcanoes in Central Java and Ijen Volcanic Complex in East Java of the Sunda arc, Indonesia. New O isotope data for Merbabu and new geochemical and radiogenic isotope data (Sr-Nd-Hf-Pb) for three West Javanese, upper crustal, Tertiary sedimentary rocks are also presented. The data are combined with published geochemical and isotopic data to constrain the relative importance of crustal assimilation and subducted input of crustal material in petrogenesis in Java. Also discussed are the significance of limestone assimilation in controlling the geochemical and isotopic characteristics of erupted Javanese rocks and the geochemical impact upon central and eastern Javanese arc rocks due to the subduction of Roo Rise between 105 and 109°E. The negative correlation between Pb isotopes and SiO2, combined with mantle-like δ18O values in Gede Volcanic Complex rocks, West Java, are most likely explained by assimilation of more isotopically-primitive arc rocks and/or ophiolitic crust known to outcrop in West Java. The negative Pb isotope-SiO2 trend cannot be explained by assimilation of the known compositions of the upper crustal rocks. A peak in δ18O whole-rock and mineral values in Central Javanese volcanic rocks (Merbabu and Merapi) combined with along-arc trends in Sr isotope ratios suggest that a different or additional crustal assimilant exerts control on the isotopic composition of Central Javanese volcanic rocks. This assimilant (likely carbonate material) is characterised by high δ18O and high Sr isotope ratio but is not particularly elevated in its Pb isotopic ratio. Once the effects of crustal assimilation are accounted for, strong East to West Java regional variations in Ba concentration, Ba/Hf ratio and Pb isotopic composition are evident. These differences are attributed to heterogeneity in the subducted source input component along the

  7. The role of the Hikurangi Plateau in the dynamics of the Hikurangi Subduction Margin

    Science.gov (United States)

    Willis, David; Moresi, Louis; Betts, Peter; Ailleres, Laurent

    2015-04-01

    The collision of the Hikurangi Plateau with the Hikurangi Subduction Zone coincides with a change from extension to shortening in the overriding Australian Plate. The 15km thick oceanic Hikurangi Plateau is juxtaposed with Chatham Rise at the southern edge of the subduction margin, possibly extending an unknown distance beneath the Chatham Rise. We explore the influence of the Hikurangi Plateau and its size on subduction dynamics using a series of 3D visco-elastic Underworld models with free slip boundary conditions. The models rely on negative slab buoyancy to drive subduction, with the buoyant oceanic plateau altering the dynamics. The models are benchmarked against New Zealand GPS velocities, paleomagnetic rotations, and fault zones. Both the overriding and subducting plates have undergone significant rotation since 23Ma with ~90° clockwise rotation of the overriding plate relative to the subducting plate. Distinctive fault zones have also been created with the Marlborough Fault Zone facilitating escape tectonics around the Chatham Rise; the North Island Dextral Fault Belt allowing lateral movement between the fore and back-arcs; extension in Taupo Volcanic Zone assisting back-arc extension; and active N-S extension in the Chatham Rise adjacent to the Hikurangi Plateau. In a model without an oceanic plateau, the subduction zone undergoes roll-back along its entire margin. Extension occurs along the overriding plate adjacent to subduction, with shortening limited to the collision of the Chatham Rise. Rotation rates adjacent to the Chatham Rise are extremely high, and decrease rapidly northward and there is no rotation of the subducting plate. When an oceanic plateau is included in the model, shortening occurs at the southern margin of the subduction zone as subduction shallows with the entry of the bouyant plateau. Rotation starts in the subducting plate as the plateau enters the subduction zone. This rotation is attributed to a decrease in slab pull southward

  8. 3-D thermo-mechanical modeling of plume-induced subduction initiation

    Science.gov (United States)

    Baes, M.; Gerya, T.; Sobolev, S. V.

    2016-11-01

    Here, we study the 3-D subduction initiation process induced by the interaction between a hot thermo-chemical mantle plume and oceanic lithosphere using thermo-mechanical viscoplastic finite difference marker-in-cell models. Our numerical modeling results show that self-sustaining subduction is induced by plume-lithosphere interaction when the plume is sufficiently buoyant, the oceanic lithosphere is sufficiently old and the plate is weak enough to allow the buoyant plume to pass through it. Subduction initiation occurs following penetration of the lithosphere by the hot plume and the downward displacement of broken, nearly circular segments of lithosphere (proto-slabs) as a result of partially molten plume rocks overriding the proto-slabs. Our experiments show four different deformation regimes in response to plume-lithosphere interaction: a) self-sustaining subduction initiation, in which subduction becomes self-sustaining; b) frozen subduction initiation, in which subduction stops at shallow depths; c) slab break-off, in which the subducting circular slab breaks off soon after formation; and d) plume underplating, in which the plume does not pass through the lithosphere and instead spreads beneath it (i.e., failed subduction initiation). These regimes depend on several parameters, such as the size, composition, and temperature of the plume, the brittle/plastic strength and age of the oceanic lithosphere, and the presence/absence of lithospheric heterogeneities. The results show that subduction initiates and becomes self-sustaining when the lithosphere is older than 10 Myr and the non-dimensional ratio of the plume buoyancy force and lithospheric strength above the plume is higher than approximately 2. The outcomes of our numerical experiments are applicable for subduction initiation in the modern and Precambrian Earth and for the origin of plume-related corona structures on Venus.

  9. Uniqueness and Non-uniqueness in the Einstein Constraints

    CERN Document Server

    Pfeiffer, H P; Pfeiffer, Harald P.; York, James W.

    2005-01-01

    We examine numerically a sequence of free data for the conformal thin sandwich (CTS) equations representing non-linearly perturbed Minkowski spacetimes. We find only one solution for the standard (four) CTS equations; however, we find {\\em two} distinct solutions for the same free data when the lapse is determined by a fifth elliptic equation arising from specification of the time derivative of the mean curvature. For a given {\\em physical} (conformally scaled) amplitude of the perturbation, the solution for the physical data $g_{ij}, K_{ij}$ nevertheless appears to be unique.

  10. Geochemistry of ultrapotassic volcanic rocks in Xiaogulihe NE China: Implications for the role of ancient subducted sediments

    Science.gov (United States)

    Sun, Yang; Ying, Jifeng; Zhou, Xinhua; Shao, Ji'an; Chu, Zhuyin; Su, Benxun

    2014-11-01

    The unique eruptions of ultrapotassic volcanic rocks in eastern China reported so far took place in the Xiaogulihe area of western Heilongjiang Province, NE China. These ultrapotassic rocks are characterized by extremely high K2O contents (> 7 wt.%), abnormally unradiogenic Pb isotopic compositions (206Pb/204Pb = 16.44-16.55; 207Pb/204Pb = 15.39-15.46; 208Pb/204Pb = 36.35-36.61), and moderately high 87Sr/86Sr ratios (0.7053-0.7057), which can be basically correlated with those of ultrapotassic igneous rocks distributed widely in northwestern America and Aldan Shield. The positive correlation between 187Os/188Os and 1/Os argues that these ultrapotassic rocks have probably experienced negligible lower continental crust addition (less than 1%) during magma ascent. The high contents of K2O and negative correlation between 87Sr/86Sr and 206Pb/204Pb of these ultrapotassic rocks indicate the presence of a potassic phase, mostly phlogopite, in their mantle source. Their strong fractionation of rare earth elements and lack of Nd-Hf isotopic decoupling reveal a low-degree partial melting of garnet-bearing source rocks. In addition, the low CaO and Al2O3 contents of whole-rock compositions and low Fe/Mn ratios of olivine phenocryst chemistries suggest peridotites rather than pyroxenites as dominant source rocks for the Xiaogulihe ultrapotassic rocks. Based on these distinctive geochemical characteristics, we thus propose that the ultimate mantle source of the Xiaogulihe ultrapotassic volcanic rocks is phlogopite-bearing garnet peridotite within the lower part of the sub-continental lithospheric mantle (SCLM) that had been metasomatized by potassium-rich silicate melts. Combined with the unradiogenic Pb compositions, the most likely source of these potassium-rich silicate melts is the ancient subducted continental-derived sediments (> 1.5 Ga). These ancient subducted sediments, possessing relatively low initial Pb isotopic compositions, had experienced large U/Pb fractionation

  11. Implications of the serpentine phase transition on the behaviour of beryllium and lithium-boron of subducted ultramafic rocks

    Science.gov (United States)

    Vils, Flurin; Müntener, Othmar; Kalt, Angelika; Ludwig, Thomas

    2011-03-01

    The Totalp-Platta-Malenco ophiolites in the Eastern Central Alps offer a unique opportunity to study the behaviour of Li, Be and B in ultramafic rocks in response to serpentinization and to progressive Alpine metamorphism. These units represent the remnants of a former ocean-continent transition that was intensely serpentinized during exposure on the Jurassic seafloor of the Ligurian Tethys. From north to the south, three isograd reactions ( lizardite⇒antigorite+brucite;lizardite+talc⇒antigorite;lizardite+tremolite⇒antigorite+diopside) have been used to quantify the evolution of the light element content of metamorphic minerals. We determined the Li, Be and B concentrations in major silicate minerals from the ultramafic bodies of Totalp, Platta and Malenco by secondary ion mass spectrometry. Mantle minerals have Be concentrations (e.g. <0.001-0.009 μg/g in olivine) similar to the metamorphic minerals that replace them (e.g. <0.001-0.016 μg/g in serpentine). The mantle signature of Be is thus neither erased during seafloor alteration nor by progressive metamorphism from prehnite-pumpellyite to epidote-amphibolite facies. In contrast, the Li and B inventories of metamorphic minerals are related to the lizardite-to-antigorite transition. Both elements display higher concentrations in the low-temperature serpentine polymorph lizardite (max. 156 μg/g Li, max. 318 μg/g B) than in antigorite (max. 0.11 μg/g Li, max. 12 μg/g B). Calculated average B/Li ratios for lizardite (˜1395) and antigorite (˜115) indicate that Li fractionates from B during the lizardite-to-antigorite transition during prograde metamorphism in ultramafic rocks. In subduction zones, this signature is likely to be recorded in the B-rich nature of forearc fluids. Relative to oceanic mantle the Be content of mantle clinopyroxene is much higher, but similar to Be values from mantle xenoliths and subduction-related peridotite massifs. These data support previous hypothesis that the mantle

  12. 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.

  13. Observations of seasonal subduction at the Iceland-Faroe Front

    Science.gov (United States)

    Beaird, N. L.; Rhines, P. B.; Eriksen, C. C.

    2016-06-01

    The polar front in the North Atlantic is bound to the ridge between Iceland and the Faroe Islands, where about one-half of the northward transport of warm Atlantic Water into the Nordic Seas occurs, as well as about one sixth of the equatorward dense overflow. We find a low salinity water mass at the surface of the Iceland-Faroe Front (IFF), which in wintertime subducts along outcropping isopycnals and is found in much modified form on the Atlantic side of the Iceland-Faroe Ridge (IFR) crest. The features found on the Atlantic side of the crest at depth have temperature and salinity characteristics which are clearly traceable to the surface outcrop of the IFF. The presence of coherent low salinity layers on the Atlantic side of the IFR crest has not been previously reported. Warm waters above the IFR primarily feed the Faroe Current, and injection of a low salinity water mass may play an early role in the water mass transformation taking place in the Nordic Seas. The seasonality of the intrusive features suggests a link between winter convection, mixed layer instability and deep frontal subduction. These low salinity anomalies (as well as a low oxygen water mass from the Iceland Basin) can be used as tracers of the intermediate circulation over the IFR.

  14. Using glacial morphology to constrain the impact of the Chile active spreading ridge subduction in Central Patagonia

    Science.gov (United States)

    Scalabrino, B.; Ritz, J. F.; Lagabrielle, Y.

    2009-04-01

    The Central Patagonian Cordillera is a unique laboratory to study interaction between oceanic and continental lithospheres during the subduction of an active spreading ridge beneath a continent. The subduction of the South Chile spreading Ridge, which separates the Nazca plate from the Antarctic plate, started ca. 15-14 Ma at the southern tip of Patagonia (55°S latitude). The northwards migration of the Chile Triple Junction induces the subduction of several segments especially around 46°S latitude. There, three segments subducted at ca. 6, 3 and 0.3 Ma, leading to the formation of a large asthenospheric slab-window beneath Central Patagonia. Contemporaneously, the Central Patagonia reliefs are undergoing major glacial events since at least 7 Ma. These events are evidenced to the east of the Central Patagonian morphotectonic front within perched relict surfaces. Inset in these perched glacial surfaces are found mid-Pleistocene glacial valleys, as the Lake General Carrera-Buenos Aires amphitheatre (LGCBA), which formed between 1.1 Ma and 16 ka. We used the relationships between the glacial valleys and the volcanism associated with the asthenospheric slab-window to better constraints the structural evolution of the Patagonian Cordillera related to the subduction of the Chili active spreading Ridge. The present work focused within two well-preserved perched flat surfaces named Meseta del Lago Buenos Aires and Meseta del Cerro Galera: (i) The meseta del Lago Buenos Aires defines a plateau made of interbedded units of tills and lavas dated between 12 Ma and 3 Ma. The top surface of the meseta, ˜2000 meters high is dated at 3 Ma, and is shaped by four NE-SW trending glacial lobes characterized with kettles, lineations and moraines. The glacial valleys are beheaded westwards and define perched valleys 200 to 400 meters higher than the western Cordillera. This suggests recent vertical movement along N160 extensive/transtensive corridor located between the morphotectonic

  15. Subduction of Fracture Zones control mantle melting and geochemical signature above slabs

    Science.gov (United States)

    Constantin Manea, Vlad; Leeman, William; Gerya, Taras; Manea, Marina; Zhu, Guizhi

    2014-05-01

    The geochemistry of arc volcanics proximal to oceanic fracture zones (FZs) is consistent with higher than normal fluid inputs to arc magma sources. Here, enrichment of boron (B/Zr) in volcanic arc lavas is used 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 FZs in the relatively cool Aleutian and Andean subduction zones, but not in the relatively warm Cascadia and Mexican subduction zones, suggesting that FZ subduction locally enhances fluid introduction beneath volcanic arcs, and retention of fluids to sub-arc depths diminishes with subduction zone thermal gradient. Geodynamic treatments of lateral inhomogeneities in subducting plates have not previously considered how FZs may influence the melt and fluid distribution above the slab. Using high-resolution three-dimensional coupled petrological-thermomechanical numerical simulations of subduction, we show that fluids, including melts and water, concentrate in areas where fracture zones are subducted, resulting in along-arc variability in magma source compositions and processes.

  16. Geometry and brittle deformation of the subducting Nazca Plate, Central Chile and Argentina

    Science.gov (United States)

    Anderson, Megan; Alvarado, Patricia; Zandt, George; Beck, Susan

    2007-10-01

    We use data from the Chile Argentina Geophysical Experiment (CHARGE) broad-band seismic deployment to refine past observations of the geometry and deformation within the subducting slab in the South American subduction zone between 30°S and 36°S. This region contains a zone of flat slab subduction where the subducting Nazca Plate flattens at a depth of ~100 km and extends ~300 km eastward before continuing its descent into the mantle. We use a grid-search multiple-event earthquake relocation technique to relocate 1098 events within the subducting slab and generate contours of the Wadati-Benioff zone. These contours reflect slab geometries from previous studies of intermediate-depth seismicity in this region with some small but important deviations. Our hypocentres indicate that the shallowest portion of the flat slab is associated with the inferred location of the subducting Juan Fernández Ridge at 31°S and that the slab deepens both to the south and the north of this region. We have also determined first motion focal mechanisms for ~180 of the slab earthquakes. The subhorizontal T-axis solutions for these events are almost entirely consistent with a slab pull interpretation, especially when compared to our newly inferred slab geometry. Deviations of T-axes from the direction of slab dip may be explained with a gap within the subducting slab below 150 km in the vicinity of the transition from flat to normal subducting geometry around 33°S.

  17. Internal deformation of the subducted Nazca slab inferred from seismic anisotropy

    Science.gov (United States)

    Eakin, Caroline M.; Long, Maureen D.; Scire, Alissa; Beck, Susan L.; Wagner, Lara S.; Zandt, George; Tavera, Hernando

    2016-01-01

    Within oceanic lithosphere a fossilized fabric is often preserved originating from the time of plate formation. Such fabric is thought to form at the mid-ocean ridge when olivine crystals align with the direction of plate spreading. It is unclear, however, whether this fossil fabric is preserved within slabs during subduction or overprinted by subduction-induced deformation. The alignment of olivine crystals, such as within fossil fabrics, can generate anisotropy that is sensed by passing seismic waves. Seismic anisotropy is therefore a useful tool for investigating the dynamics of subduction zones, but it has so far proved difficult to observe the anisotropic properties of the subducted slab itself. Here we analyse seismic anisotropy in the subducted Nazca slab beneath Peru and find that the fast direction of seismic wave propagation aligns with the contours of the slab. We use numerical modelling to simulate the olivine fabric created at the mid-ocean ridge, but find it is inconsistent with our observations of seismic anisotropy in the subducted Nazca slab. Instead we find that an orientation of the olivine crystal fast axes aligned parallel to the strike of the slab provides the best fit, consistent with along-strike extension induced by flattening of the slab during subduction (A. Kumar et al., manuscript in preparation). We conclude that the fossil fabric has been overprinted during subduction and that the Nazca slab must therefore be sufficiently weak to undergo internal deformation.

  18. Quantifying potential tsunami hazard in the Puysegur subduction zone, south of New Zealand

    Science.gov (United States)

    Hayes, G.P.; Furlong, K.P.

    2010-01-01

    Studies of subduction zone seismogenesis and tsunami potential, particularly of large subduction zones, have recently seen a resurgence after the great 2004 earthquake and tsunami offshore of Sumatra, yet these global studies have generally neglected the tsunami potential of small subduction zones such as the Puysegur subduction zone, south of New Zealand. Here, we study one such relatively small subduction zone by analysing the historical seismicity over the entire plate boundary region south of New Zealand, using these data to determine the seismic moment deficit of the subduction zone over the past ~100 yr. Our calculations indicate unreleased moment equivalent to a magnitude Mw 8.3 earthquake, suggesting this subduction zone has the potential to host a great, tsunamigenic event. We model this tsunami hazard and find that a tsunami caused by a great earthquake on the Puysegur subduction zone would pose threats to the coasts of southern and western South Island, New Zealand, Tasmania and southeastern Australia, nearly 2000 km distant. No claim to original US government works Geophysical Journal International ?? 2010 RAS.

  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. Constraining Cretaceous subduction polarity in eastern Pacific from seismic tomography and geodynamic modeling

    Science.gov (United States)

    Liu, Lijun

    2014-11-01

    Interpretation of recent mantle seismic images below the America ignited a debate on the Cretaceous subduction polarity in the eastern Pacific Ocean. The traditional view is that the massive vertical slab wall under eastern North America resulted from an eastward Farallon subduction. An alternative interpretation attributes this prominent seismic structure to a westward subduction of the North American Plate against a stationary intraoceanic trench. Here I design quantitative subduction models to test these two scenarios, using their implied plate kinematics as velocity boundary conditions. Modeling results suggest that the westward subduction scenario could not produce enough slab volume as seismic images reveal, as is due to the overall slow subduction rate (~2.5 cm/yr). The results favor the continuous eastward Farallon subduction scenario, which, with an average convergence rate of >10 cm/yr prior to the Eocene, can properly generate both the volume and the geometry of the imaged lower mantle slab pile. The eastward subduction model is also consistent with most Cretaceous geological records along the west coast of North America.

  1. 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

  2. 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

  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. Geochemical evidence for the melting of subducting oceanic lithosphere at plate edges.

    Science.gov (United States)

    Yogodzinski, G M; Lees, J M; Churikova, T G; Dorendorf, F; Wöerner, G; Volynets, O N

    2001-01-25

    Most island-arc magmatism appears to result from the lowering of the melting point of peridotite within the wedge of mantle above subducting slabs owing to the introduction of fluids from the dehydration of subducting oceanic crust. Volcanic rocks interpreted to contain a component of melt (not just a fluid) from the subducting slab itself are uncommon, but possible examples have been recognized in the Aleutian islands, Baja California, Patagonia and elsewhere. The geochemically distinctive rocks from these areas, termed 'adakites, are often associated with subducting plates that are young and warm, and therefore thought to be more prone to melting. But the subducting lithosphere in some adakite locations (such as the Aleutian islands) appears to be too old and hence too cold to melt. This implies either that our interpretation of adakite geochemistry is incorrect, or that our understanding of the tectonic context of adakites is incomplete. Here we present geochemical data from the Kamchatka peninsula and the Aleutian islands that reaffirms the slab-melt interpretation of adakites, but in the tectonic context of the exposure to mantle flow around the edge of a torn subducting plate. We conclude that adakites are likely to form whenever the edge of a subducting plate is warmed or ablated by mantle flow. The use of adakites as tracers for such plate geometry may improve our understanding of magma genesis and thermal structure in a variety of subduction-zone environments.

  5. A review of the geodynamic evolution of flat slab subduction in Mexico, Peru, and Chile

    Science.gov (United States)

    Manea, V. C.; Manea, M.; Ferrari, L.; Orozco-Esquivel, T.; Valenzuela, R. W.; Husker, A.; Kostoglodov, V.

    2017-01-01

    Subducting plates around the globe display a large variability in terms of slab geometry, including regions where smooth and little variation in subduction parameters is observed. While the vast majority of subduction slabs plunge into the mantle at different, but positive dip angles, the end-member case of flat-slab subduction seems to strongly defy this rule and move horizontally several hundreds of kilometers before diving into the surrounding hotter mantle. By employing a comparative assessment for the Mexican, Peruvian and Chilean flat-slab subduction zones we find a series of parameters that apparently facilitate slab flattening. Among them, trench roll-back, as well as strong variations and discontinuities in the structure of oceanic and overriding plates seem to be the most important. However, we were not able to find the necessary and sufficient conditions that provide an explanation for the formation of flat slabs in all three subduction zones. In order to unravel the origin of flat-slab subduction, it is probably necessary a numerical approach that considers also the influence of surrounding plates, and their corresponding geometries, on 3D subduction dynamics.

  6. 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 c

  7. 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 zo

  8. 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 c

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

    NARCIS (Netherlands)

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

    2001-01-01

    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 mechanis

  10. Rheological properties of deep subducted oceanic lithosphere and their geodynamic implications

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    According to the experimental studies on the rheology of two important mantle rocks (eclogite and harzburgite), the rheological properties of the deep subducted oceanic lithosphere are investigated by assuming a simplified harzburgite type slab model with moderate thickness of basaltic layer. When the mantle convergence rate is small or the subducting slab has been trapped in the mantle for an enough long time, the strength profile of the slab is characterized by a strong subducting crustal component lying on a weak subducting upper mantle. However, if the convergence rate is large enough, the subducting slab will be featured only by a rigid cold center. Our study suggests that the detachment of the subducting crust component from the underlying upper mantle is only likely to happen in hot slow subducting slabs, but not the cold fast subducting lithosphere. Rheological properties of the harzburgitic and the eclogitic upper mantle vary with depths. The eclogitic upper mantle is stronger than the peridotitic upper mantle across the upper mantle. Transition zone is the high strength and high viscosity layer in the upper mantle except the lithosphere.

  11. Rapid pulses of uplift, subsidence, and subduction erosion offshore Central America: Implications for building the rock record of convergent margins

    Digital Repository Service at National Institute of Oceanography (India)

    Vannucchi, P.; Sak, P.B.; Morgan, J.P.; Ohkushi, K.; Ujiie, K.; IODP Expedition 334 Shipboard Scientists; Yatheesh, V.

    Integrated Ocean Drilling Program (IODP) Expedition 334 to southern Costa Rica, Central America, documented unprecedented subduction erosion in an area of active seismic slip. Widespread subduction erosion of the upper plate initiated when the Cocos...

  12. Lithium nephropathy: unique sonographic findings.

    Science.gov (United States)

    Di Salvo, Donald N; Park, Joseph; Laing, Faye C

    2012-04-01

    This case series describes a unique sonographic appearance consisting of numerous microcysts and punctate echogenic foci seen on renal sonograms of 10 adult patients receiving chronic lithium therapy. Clinically, chronic renal insufficiency was present in 6 and nephrogenic diabetes insipidus in 2. Sonography showed numerous microcysts and punctate echogenic foci. Computed tomography in 5 patients confirmed microcysts and microcalcifications, which were fewer in number than on sonography. Magnetic resonance imaging in 2 patients confirmed microcysts in each case. Renal biopsy in 1 patient showed chronic interstitial nephritis, microcysts, and tubular dilatation. The diagnosis of lithium nephropathy should be considered when sonography shows these findings.

  13. Mucormycosis in India: unique features.

    Science.gov (United States)

    Chakrabarti, Arunaloke; Singh, Rachna

    2014-12-01

    Mucormycosis remains a devastating invasive fungal infection, with high mortality rates even after active management. The disease is being reported at an alarming frequency over the past decades from India. Indian mucormycosis has certain unique features. Rhino-orbito-cerebral presentation associated with uncontrolled diabetes is the predominant characteristic. Isolated renal mucormycosis has emerged as a new clinical entity. Apophysomyces elegans and Rhizopus homothallicus are emerging species in this region and uncommon agents such as Mucor irregularis and Thamnostylum lucknowense are also being reported. This review focuses on these distinct features of mucormycosis observed in India.

  14. UNIQUE ORAL DRUG DELIVERY SYSTEM

    Institute of Scientific and Technical Information of China (English)

    Raphael M. Ottenbrite; ZHAO Ruifeng; Sam Milstein

    1995-01-01

    An oral drug delivery system using proteinoid microspheres is discussed with respect to its unique dependence on pH. It has been found that certain drugs such as insulin and heparin can be encapsulated in proteinoid spheres at stomach pH's (1-3). These spheres also dissemble at intestinal pH's (6-7) releasing the drug for absorption. Using this technique low molecular weight heparin and human growth hormone have been orally delivered successfully to several animal species. Future work has been proposed to study the interaction and binding of the specific drugs with synthesized oligopeptides.

  15. Analysis of unique beta transitions

    DEFF Research Database (Denmark)

    Eman, B.; Krmpotic, F.; Tadic, D;

    1967-01-01

    The Heidelberg group measurements [For abstr. see Phys. Rev. Nucl. Sci. Vol. 15 (1965)] of unique forbidden transitions have been analysed. It has been found that experimental shape factors can be reproduced only with the induced pseudoscalar form factor d ...-non-conserving tensor form factor b > 0. In the former case they contradict Daniel's results [See abstr. 1966A10720] for 0- rarr 0+ transitions, whereas in the latter they are in disagreement with other known analyses of mu-meson capture, allowed and forbidden transitions. The conclusion appears to be independent...

  16. Mantle flow and deformation of subducting slab at the junction of Tohoku-Kurile arc

    Science.gov (United States)

    Morishige, M.; Honda, S.

    2012-12-01

    Geophysical studies of the plate junction reveal possible evidence of the presence of 3D mantle flow and deformation of subducting slabs. The junction of the Tohoku-Kurile is one of the best studied junctions in the world. The Pacific plate subducts under the North American plate in a direction almost perpendicular to Japan trench, while it subducts obliquely along the Kurile arc. Analysis of seismic anisotropy in this region shows the trench-normal fast polarization direction of S-wave splitting in the back arc even where the oblique subduction occurs. The angle of subduction varies along the strike of the trench, that is, it is smallest near the plate junction and becomes large beneath Kurile arc. There is also an important distinction in the slab behavior. The slab beneath Tohoku stagnates in the transition zone, whereas the slab beneath the Kurile arc penetrates into the lower mantle. In this presentation, we show the dynamic effects of the junction using a numerical model of mantle convection with a realistic curved shape of the trench in spherical geometry. The model is set so that it becomes similar to the geometry of the surface plate boundary in the Tohoku-Kurile arc. In order to enable one-sided subduction, the velocities are imposed both on the surface and in the small 3D boundary region around the trench. We obtain 3D flow in the mantle wedge which is consistent with the observation of seismic anisotropy including the oblique subduction zone. The flow and hence the fast polarization direction in the subslab mantle is almost 2D. We also find that the angle of subduction varies along-strike, which agrees with the observations. This variation can be explained by a torque balance acting on subducting slabs in the case of oblique subduction. This along-arc variation of the angle of subduction partly contributes to the different behavior of slab stagnation in the Tohoku-Kurile arc. Our results show that the shape of the trench is an important factor which

  17. Modification of Thickened Orogenic Crust by a Subducting Ridge: Disruption of the Andean Lower Crust of Southern Peru by the Subducting Aseismic Nazca Ridge

    Science.gov (United States)

    Bishop, B.; Beck, S. L.; Zandt, G.; Wagner, L. S.; Long, M. D.; Tavera, H.

    2015-12-01

    The subduction of oceanic plateaus or aseismic ridges represent significant perturbations to the long term development of subduction systems and associated orogenies, the consequences of which are variable and determined by the physical characteristics of both the overriding and subducting plates. Flat subduction of the ~18 km oceanic crust of the aseismic Nazca Ridge under the 50 km to 65 km continental crust of the Peruvian Andes provides an opportunity to investigate these consequences. Through analysis of 2233 teleseismic P-wave receiver functions from 55 broadband seismometers deployed in southern Peru for the PULSE, CAUGHT and PeruSE seismic experiments we have identified the South American continental Moho and subducted Nazca oceanic Moho to a higher degree of detail than previously possible in the region.We find that the continental Moho beneath the Western and Eastern Cordilleras of the Peruvian Andes is at a depth >60 km to the north and south of the subducted Nazca Ridge but at 500 km from the trench.

  18. Subduction processes off chile (SPOC) - results from The amphibious wide-angle seismic experiment across The chilean subduction zone

    Science.gov (United States)

    Lueth, S.; Spoc Resaerch Group

    2003-04-01

    One component of the onshore-offshore, active-passive seismic experiment SPOC (Krawczyk et al., Stiller et al., this vol.) was a 2-D wide-angle seismic experiment covering the Chilean subduction zone from the Nazca Plate to the Magmatic Arc in the main cordillera. Three W-E-profiles of 52 stations each and up to 240 km long were deployed between 36° and 39° S. These profiles recorded chemical shots at their ends and, in order to extend the onshore profiles, the airgun pulses from RV SONNE cruising simultaneously on offshore profiles. On the southernmost of the three profiles OBHs/OBSs were deployed offshore, thus providing continuous wide-angle seismic data from the Nazca Plate to the South-American continent. Data examples, correlations, and velocity models along the three transects will be presented. The Moho of the subducted oceanic crust can be constrained by PmP-reflections down to 45 km depth under the coastal cordillera. The P-wave velocity field of the crust of the upper plate is characterized by gradually increasing P-wave velocities from East to West. Low seismic velocities (Vp ~6.5 km/s below 10 km depth) are observed at the eastern margin of the investigated area.

  19. 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.

  20. Effects of water transportation on subduction dynamics: Roles of viscosity and density reduction

    Science.gov (United States)

    Nakao, Atsushi; Iwamori, Hikaru; Nakakuki, Tomoeki

    2016-11-01

    The effects of water on subduction dynamics, e.g., plate migration rate, slab geometry, stress field, and back-arc spreading, are investigated by using a 2-D self-consistent model for lithosphere subduction and whole mantle convection. We solve water transportation coupled with hydrous mineral phase changes. Mantle flows and water transportation are interactive through constitutive and state equations for hydrous rocks. Our model has successfully reproduced the water distribution in a mantle wedge and along the slab with sufficient resolution comparable to that of previous models that focus on the mantle wedge structure. As a result, low density owing to hydration reduces subduction rates, back-arc spreading, and slab stagnation on the phase boundary at 660-km depth, whereas low viscosity owing to hydration enhances rapid subduction, trench migration, and slab stagnation. We attribute these results to mechanisms that cause the hydrous buoyancy of subducting plates to reduce the slab pull force and the accompanying tensile stress on overlying lithosphere. In addition, hydrous weakening diminishes the mechanical coupling of the subducted slab with the wedge mantle and overriding lithosphere. Thus, water is capable of generating two opposite situations in the stress field of the overlying lithosphere and the subduction rate. Water is therefore expected to be an important mechanism for generating broad styles of the subduction structure and kinematics, as observed in actual subduction zones such as Tonga and Mariana. Such observed variation in the subduction mode can be caused by variation in buoyancy corresponding to the water content from relatively dry to several thousands of parts per million for the wedge mantle and slab surface, whereas the extremely buoyant case does not appear to occur in nature. Water in the mantle is thus key to better understand the whole-mantle-scale slab dynamics as well as island arc volcanic processes.

  1. 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.

  2. The Impact of the Subduction Modeling Beneath Calabria on Seismic Hazard

    Science.gov (United States)

    Morasca, P.; Johnson, W. J.; Del Giudice, T.; Poggi, P.; Traverso, C.; Parker, E. J.

    2014-12-01

    The aim of this work is to better understand the influence of subduction beneath Calabria on seismic hazard, as very little is known about present-day kinematics and the seismogenic potential of the slab interface in the Calabrian Arc region. This evaluation is significant because, depending on stress conditions, subduction zones can vary from being fully coupled to almost entirely decoupled with important consequences in the seismic hazard assessment. Although the debate is still open about the current kinematics of the plates and microplates lying in the region and the degree of coupling of Ionian lithosphere beneath Calabria, GPS data suggest that this subduction is locked in its interface sector. Also the lack of instrumentally recorded thrust earthquakes suggests this zone is locked. The current seismotectonic model developed for the Italian National territory is simplified in this area and does not reflect the possibility of locked subduction beneath the Calabria that could produce infrequent, but very large earthquakes associated with the subduction interface. Because of this we have conducted an independent seismic source analysis to take into account the influence of subduction as part of a regional seismic hazard analysis. Our final model includes two separate provinces for the subduction beneath the Calabria: inslab and interface. From a geometrical point of view the interface province is modeled with a depth between 20-50 km and a dip of 20°, while the inslab one dips 70° between 50 -100 km. Following recent interpretations we take into account that the interface subduction is possibly locked and, in such a case, large events could occur as characteristic earthquakes. The results of the PSHA analysis show that the subduction beneath the Calabrian region has an influence in the total hazard for this region, especially for long return periods. Regional seismotectonic models for this region should account for subduction.

  3. Mineral inclusions in sublithospheric diamonds from Collier 4 kimberlite pipe, Juina, Brazil: subducted protoliths, carbonated melts and primary kimberlite magmatism

    Science.gov (United States)

    Bulanova, Galina P.; Walter, Michael J.; Smith, Chris B.; Kohn, Simon C.; Armstrong, Lora S.; Blundy, Jon; Gobbo, Luiz

    2010-10-01

    We report on a suite of diamonds from the Cretaceous Collier 4 kimberlite pipe, Juina, Brazil, that are predominantly nitrogen-free type II crystals showing complex internal growth structures. Syngenetic mineral inclusions comprise calcium- and titanium-rich phases with perovskite stoichiometry, Ca-rich majoritic-garnet, clinopyroxene, olivine, TAPP phase, minerals with stoichiometries of CAS and K-hollandite phases, SiO2, FeO, native iron, low-Ni sulfides, and Ca-Mg-carbonate. We divide the diamonds into three groups on the basis of the carbon isotope compositions (δ13C) of diamond core zones. Group 1 diamonds have heavy, mantle-like δ13C (-5 to -10‰) with mineral inclusions indicating a transition zone origin from mafic protoliths. Group 2 diamonds have intermediate δ13C (-12 to -15‰), with inclusion compositions indicating crystallization from near-primary and differentiated carbonated melts derived from oceanic crust in the deep upper mantle or transition zone. A 206Pb/238U age of 101 ± 7 Ma on a CaTiSi-perovskite inclusion (Group 2) is close to the kimberlite emplacement time (93.1 ± 1.5 Ma). Group 3 diamonds have extremely light δ13C (-25‰), and host inclusions have compositions akin to high-pressure-temperature phases expected to be stable in pelagic sediments subducted to transition zone depths. Collectively, the Collier 4 diamonds and their inclusions indicate multi-stage, polybaric growth histories in dynamically changing chemical environments. The young inclusion age, the ubiquitous chemical and isotopic characteristics indicative of subducted materials, and the regional tectonic history, suggest a model in which generation of sublithospheric diamonds and their inclusions, and the proto-kimberlite magmas, are related genetically, temporally and geographically to the interaction of subducted lithosphere and a Cretaceous plume.

  4. S-Local-Wave Seismic Anisotropy in the Forearc Above the Subducted Nazca Plate Between 33°S and 34.5°S

    Science.gov (United States)

    Nacif, Silvina; Triep, Enrique G.

    2016-04-01

    S-wave splitting from local earthquakes within the Nazca plate that are deeper than the interplate seismogenic zone enabled the determination of the fast velocity direction, Φ, and the lag time, δt, in the forearc of the overriding plate. Data were collected from 20 seismic stations, most of which were temporary, deployed between ~33.5°S and ~34.5°S and included part of the normal subduction section to the south and part of the transitional section to flat subduction to the north. The fast velocity direction has a complex pattern with three predominant directions northwest-southeast, north-south and northeast-southwest and relatively high δt. A quality evaluation of the highest measurements enabled us to identify possible cycle skipping in some of the measurements, which could be responsible for the large observed lag time. We consider that most of the anisotropy that was observed in the forearc is probably located in the mantle wedge, and a minor part is located in the crust. The complex pattern of splitting parameters when the anisotropy is associated at the mantle wedge could be the result of three-dimensional variations in the subducting Nazca plate at these latitudes. Also, similarities between the splitting parameters and the principal compressional stress direction from Pliocene and Quaternary rocks suggest that the anisotropy in the crust could originate by tectonic local stress.

  5. Contamination of the Convecting Mantle in Eastern Tethyan 'Subduction Factories'

    Science.gov (United States)

    Flower, M. F.; Nguyen, T. H.

    2003-04-01

    As subduction gives way to collision at the end of a Wilson Cycle the associated magmatic activity becomes increasingly enriched in potassium and other large-ion lithophile elements. This is usually attributed to the addition of continental crust-derived material to the convecting mantle wedge. Corresponding depletions in high-field strength elements (Ti and Nb) are more commonly explained in terms of accessory phase buffering or protracted reaction of melts with mantle wallrock. It is increasingly apparent that mantle wedge magmatic sources range from 'fertile' (lherzolitic) to 'refractory' (harzburgitic) although the extent to which this corresponds to the LILE and HFSE variation is unclear. Mantle wedge mass balances clearly hold clues to enrichment-depletion histories of the convecting asthenosphere with respect to both the overriding and subducting plates. With a view to better understanding these effects we have used the MELTS algorithm to calculate hypothetical partial melt compositions as a function of source fertility and H2O content, in the pressure range, 0-1.0 GPa as a basis comparison for natural partial melts. Primitive magmas characterizing the Mariana (western Pacific) and Sunda-Banda (Indonesia) arcs, and the northeastern syntaxis of the India-Asia collision suture (Yunnan) appear to resemble calculated equilibrium melts of refractory (basalt-depleted) peridotite, variably enriched in lithophile and light rare earth elements. These comparisons lead to three observations. 1) HFSE and Fe abundances in primitive MORB, calcalkaline, and boninite magmas, and their respective high-potassium variants are consistent with those implied by phase equilibria associated with partial melting and fractionation, suggesting accessory phases, wall-rock reaction, and slab contamination are probably not important as causes of HFSE depletions. 2) Magmatic sources at convergent and colliding margins are typically refractory (basalt-depleted) compared to those yielding

  6. 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

  7. 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

  8. Transdimensional imaging of random velocity inhomogeneities in Nankai subduction zone

    Science.gov (United States)

    Takahashi, T.; Obana, K.; Yamamoto, Y.; Kaiho, Y.; Nakanishi, A.; Kodaira, S.; Kaneda, Y.

    2014-12-01

    The Nankai trough in southwestern Japan is a convergent margin where the Philippine Sea plate is subducting beneath the Eurasian plate. We have conducted five seismic observations with ocean bottom seismograms (OBSs) from 2008 to 2012 to elucidate detailed seismic structures and its relations with fault segments of large earthquakes. These observations covered the entire area of the Nankai trough, but quantity and quality of data are not spatially uniform because of different observing lengths and various noises. Waveform data of OBSs suggests variously-sized anomalies of random velocity inhomogeneity (i.e., scattering strength) in this subduction zone. To clarify details of random inhomogeneity structures, we conducted a transdimensional imaging of random inhomogeneities by means of the reversible jump Markov Chain Monte Carlo (rjMCMC) without assuming smooth spatial distributions of unknown parameters. We applied the rjMCMC for the inversion of peak delay times of S-wave envelopes at 4-8, 8-16, and 16-32 Hz, where the peak delay time is defined as the time lag from the S-wave onset to its maximal amplitude arrival. This delay time mainly reflects the accumulated multiple forward scattering effect due to random inhomogeneities. We assumed the von Karman type power spectral density function (PSDF) for random velocity fluctuation, and estimated two parameters related with the PSDF at large wavenumber. Study area is partitioned by discrete Voronoi cells of which number and spatial sizes are variable. Estimated random inhomogeneities show clear lateral variations along the Nankai trough. The strongest inhomogeneity on the Nankai trough was found near the subducted Kyushu-Palau ridge that is located at the western margin of the fault segments. We also find a horizontal variation of inhomogeneity along the non-volcanic tremor zone. Relatively strong inhomogeneities in this tremor zone were imaged beneath west Shikoku and Kii-Peninsula. These anomalies were not clearly

  9. Modeling of Slow Slip Events at the Hikurangi Subduction Margin

    Science.gov (United States)

    Williams, C. A.; Wallace, L. M.; Beavan, R. J.; Lohman, R. B.; Ellis, S. M.; Marson-Pidgeon, K.; Eberhart-Phillips, D. M.; Reyners, M.; Henrys, S. A.; Bell, R. E.

    2011-12-01

    Slow slip events (SSEs) occur along nearly the entire Hikurangi subduction margin adjacent to the North Island, New Zealand. Long duration (1-2 years), deep (40- 60 km depth), large events (equivalent to Mw ~7.0) occur at the southern Hikurangi margin, while shallow (10-15 km depth), short (1-2 weeks), smaller events (equivalent to Mw ~6.5) occur at the northern and central Hikurangi margin. A recently-initiated shallow event (Castle Point) lies further to the south than previous shallow events and appears to be rupturing a portion of the plate interface that was previously thought to be locked. Since 2000, three major slow slip events have been identified at the southern Hikurangi margin; the 2003 Kapiti SSE, the 2004/2005 Manawatu SSE, and the 2007/2008 Kapiti SSE (which ended in early 2009). A repeat of the 2004/2005 Manawatu event is presently underway. In some cases, these SSEs may have triggered moderate seismicity within the subducting Pacific plate (e.g., Reyners and Bannister, 2007). To date, all of the inferred slip distributions for the SSEs have been obtained using elastic half-space dislocation models. Numerous recent studies of coseismic displacement fields have shown that variations in elastic properties and surface topography can influence the predicted deformation. In our initial work, we used a finite element model to evaluate the influence of material property variations on the predicted surface deformation field. Elastic properties were assigned based on a seismic velocity model, and slip distributions inferred from an elastic half-space model were applied. When compared to the elastic half- space model, we found that the heterogeneous models generally predict larger amounts of surface deformation, indicating that the half-space models may be overestimating the amount of slip. As the next phase in our study, we are using finite element models that include material property variations and topography to generate Green's functions for use in an

  10. Tsunamigenic potential of Mediterranean fault systems and active subduction zones

    Science.gov (United States)

    Petricca, Patrizio; Babeyko, Andrey

    2016-04-01

    Since the North East Atlantic and Mediterranean Tsunami Warning System (NEAMTWS) is under development by the European scientific community, it becomes necessary to define guidelines for the characterization of the numerous parameters must be taken into account in a fair assessment of the risk. Definition of possible tectonic sources and evaluation of their potential is one of the principal issues. In this study we systematically evaluate tsunamigenic potential of up-to-now known real fault systems and active subduction interfaces in the NEAMTWS region. The task is accomplished by means of numerical modeling of tsunami generation and propagation. We have simulated all possible uniform-slip ruptures populating fault and subduction interfaces with magnitudes ranging from 6.5 up to expected Mmax. A total of 15810 individual ruptures were processed. For each rupture, a tsunami propagation scenario was computed in linear shallow-water approximation on 1-arc minute bathymetric grid (Gebco_08) implying normal reflection boundary conditions. Maximum wave heights at coastal positions (totally - 23236 points of interest) were recorded for four hours of simulation and then classified according to currently adopted warning level thresholds. The resulting dataset allowed us to classify the sources in terms of their tsunamigenic potential as well as to estimate their minimum tsunamigenic magnitude. Our analysis shows that almost every source in the Mediterranean Sea is capable to produce local tsunami at the advisory level (i.e., wave height > 20 cm) starting from magnitude values of Mw=6.6. In respect to the watch level (wave height > 50 cm), the picture is less homogeneous: crustal sources in south-west Mediterranean as well as East-Hellenic arc need larger magnitudes (around Mw=7.0) to trigger watch levels even at the nearby coasts. In the context of the regional warning (i.e., source-to-coast distance > 100 km) faults also behave more heterogeneously in respect to the minimum

  11. Unmanned Aerial Vehicles unique cost estimating requirements

    Science.gov (United States)

    Malone, P.; Apgar, H.; Stukes, S.; Sterk, S.

    Unmanned Aerial Vehicles (UAVs), also referred to as drones, are aerial platforms that fly without a human pilot onboard. UAVs are controlled autonomously by a computer in the vehicle or under the remote control of a pilot stationed at a fixed ground location. There are a wide variety of drone shapes, sizes, configurations, complexities, and characteristics. Use of these devices by the Department of Defense (DoD), NASA, civil and commercial organizations continues to grow. UAVs are commonly used for intelligence, surveillance, reconnaissance (ISR). They are also use for combat operations, and civil applications, such as firefighting, non-military security work, surveillance of infrastructure (e.g. pipelines, power lines and country borders). UAVs are often preferred for missions that require sustained persistence (over 4 hours in duration), or are “ too dangerous, dull or dirty” for manned aircraft. Moreover, they can offer significant acquisition and operations cost savings over traditional manned aircraft. Because of these unique characteristics and missions, UAV estimates require some unique estimating methods. This paper describes a framework for estimating UAV systems total ownership cost including hardware components, software design, and operations. The challenge of collecting data, testing the sensitivities of cost drivers, and creating cost estimating relationships (CERs) for each key work breakdown structure (WBS) element is discussed. The autonomous operation of UAVs is especially challenging from a software perspective.

  12. Developing innovative programs for unique student populations.

    Science.gov (United States)

    Heath, D A; Caruso, J; Chauncey, D M

    1994-12-01

    Optometric education has been faced with ever-increasing expectations. These include the ability to educate students and practitioners to care for new patient populations, deal with more diverse and complex clinical problems, to be significant participants in the research community and to fulfill leadership positions within the profession. To fulfill this expectation, schools and colleges need to diversify their program offerings to attract and educate unique student populations who come from diverse backgrounds and bring a range of pre-existing knowledge and skills. This paper provides an overview of The New England College of Optometry's efforts in this area and two programs, the "Advanced Standing International Program" and the "Accelerated Doctor of Optometry Degree Program," are examined in detail. An emphasis is placed on outcomes assessment to ensure the programs are fulfilling their purpose and the results of a retrospective analysis of the two programs is provided.

  13. Unique Features of Mobile Commerce

    Institute of Scientific and Technical Information of China (English)

    DING Xiaojun; IIJIMA Junichi; HO Sho

    2004-01-01

    While the market potentials and impacts of web-based e-commerce are still in the ascendant, the advances in wireless technologies and mobile networks have brought about a new business opportunity and research attention, what is termed mobile commerce. Commonly, mobile commerce is considered to be another new application of existing web-based e-commerce onto wireless networks, but as an independent business area, mobile commerce has its own advantages and challenges as opposed to traditional e-commerce applications. This paper focuses on exploring the unique features of mobile commerce as. Compared with traditional e-commerce. Also, there are still some limitations arisen in m-commerce in contrast to web-based e-commerce. Finally, current state of mobile commerce in Japan is presented in brief, with an introduction of several cases involving mobile commerce applications in today 's marketplace.

  14. Unique features of space reactors

    Science.gov (United States)

    Buden, David

    Space reactors are designed to meet a unique set of requirements; they must be sufficiently compact to be launched in a rocket to their operational location, operate for many years without maintenance and servicing, operate in extreme environments, and reject heat by radiation to space. To meet these restrictions, operating temperatures are much greater than in terrestrial power plants, and the reactors tend to have a fast neutron spectrum. Currently, a new generation of space reactor power plants is being developed. The major effort is in the SP-100 program, where the power plant is being designed for seven years of full power, and no maintenance operation at a reactor outlet operating temperature of 1350 K.

  15. The probabilities of unique events.

    Directory of Open Access Journals (Sweden)

    Sangeet S Khemlani

    Full Text Available Many theorists argue that the probabilities of unique events, even real possibilities such as President Obama's re-election, are meaningless. As a consequence, psychologists have seldom investigated them. We propose a new theory (implemented in a computer program in which such estimates depend on an intuitive non-numerical system capable only of simple procedures, and a deliberative system that maps intuitions into numbers. The theory predicts that estimates of the probabilities of conjunctions should often tend to split the difference between the probabilities of the two conjuncts. We report two experiments showing that individuals commit such violations of the probability calculus, and corroborating other predictions of the theory, e.g., individuals err in the same way even when they make non-numerical verbal estimates, such as that an event is highly improbable.

  16. The Evolution of Human Uniqueness.

    Science.gov (United States)

    Boyd, Robert

    2017-01-09

    The human species is an outlier in the natural world. Two million years ago our ancestors were a slightly odd apes. Now we occupy the largest ecological and geographical range of any species, have larger biomass, and process more energy. Usually, this transformation is explained in terms of cognitive ability-people are just smarter than all the rest. In this paper I argue that culture, our ability to learn from each other, and cooperation, our ability to make common cause with large groups of unrelated individuals are the real roots of human uniqueness, and sketch an evolutionary account of how these crucial abilities co-evolved with each other and with other features of our life histories.

  17. Subducted slabs beneath the eastern Indonesia-Tonga region: insights from tomography

    Science.gov (United States)

    Hall, Robert; Spakman, Wim

    2002-07-01

    Tomographic images of mantle structure beneath the region north and northeast of Australia show a number of anomalously fast regions. These are interpreted using a recent plate tectonic reconstruction in terms of current and former subduction systems. Several strong anomalies are related to current subduction. The inferred slab lengths and positions are consistent with Neogene subduction beneath the New Britain and Halmahera arcs, and at the Tonga and the New Hebrides trenches where there has been rapid rollback of subduction hinges since about 10 Ma. There are several deeper flat-lying anomalies which are not related to present subduction and we interpret them as former subduction zones overridden by Australia since 25 Ma. Beneath the Bird's Head and Arafura Sea is an anomaly interpreted to be due to north-dipping subduction beneath the Philippines-Halmahera arc between 45 and 25 Ma. A very large anomaly extending from the Papuan peninsula to the New Hebrides, and from the Solomon Islands to the east Australian margin, is interpreted to be the remnant of south-dipping subduction beneath the Melanesian arc between 45 and 25 Ma. This interpretation implies that a flat-lying slab can survive for many tens of millions of years at the bottom of the upper mantle. In the lower mantle there is a huge anomaly beneath the Gulf of Carpentaria and east Papua New Guinea. This is located above the position where the tectonic model interprets a change in polarity of subduction from north-dipping to south-dipping between 45 and 25 Ma. We suggest this deep anomaly may be a slab subducted beneath eastern Australian during the Cretaceous, or subducted north of Australia during the Cenozoic before 45 Ma. The tomography also supports the tectonic interpretation which suggests little Neogene subduction beneath western New Guinea since no slab is imaged south of the New Guinea trench. However, one subduction zone in the tectonic model and many others, that associated with the Trobriand

  18. Do magnitudes of great subduction earthquakes depend on strength of mechanical coupling between the plates?

    Science.gov (United States)

    Sobolev, Stephan; Muldashev, Iskander

    2017-04-01

    The common thinking is that the magnitude of a great subduction earthquake correlates with the strength of mechanical coupling between slab and overriding plate. Based on this idea, Ruff and Kanamori (1980) suggested that maximum earthquake's magnitude is controlled by two parameters: age of subducting plate and plate convergence rate, when the youngest and the fastest slabs generate the largest earthquakes. This view was supported by many researches since then. However, since 1980 a number of great earthquakes, and particularly two largest earthquakes of the last 12 years, i.e. Great Sumatra/Andaman 2004 Earthquake and Tohoku 2011 earthquake, have violated the suggested correlation. We address the relation between strength of mechanical coupling and earthquake magnitude directly by cross-scale geodynamic modeling of seismic cycles of great subduction earthquakes. This modeling technique employs elasticity, non-linear transient viscous rheology, and rate-and-state friction at slab interface. It generates spontaneous earthquake sequences, and, by using an adaptive time-step algorithm, recreates the deformation process as observed naturally over single and multiple seismic cycles. We model seismic cycles for the great subduction earthquakes with different geometries of subducting plates, different static friction coefficients in subduction channels and different subduction velocities. Under the assumption that rupture length scales with the rupture width, our models demonstrate that maximum magnitudes of the earthquakes are exclusively controlled by the factors that increase rupture width. These factors are: low slab's dipping angle (the largest effect), low friction coefficient in subduction channel (smaller effect) and high subduction velocity (the smallest effect). Models suggest that maximum magnitudes of earthquakes do not correlate significantly with the magnitudes of normal and shear stresses at subduction interface. In agreement with observations, our models

  19. Waveform effects of a metastable olivine tongue in subducting slabs

    Science.gov (United States)

    Vidale, John E.; Williams, Quentin; Houston, Heidi

    1991-01-01

    Velocity models of subducting slabs with a kinetically-depressed olivine to beta- and gamma-spinel transition are constructed, and the effect that such structures would have on teleseismic P waveforms are examined using a full-wave finite-difference method. These 2D calculations yielded waveforms at a range of distances in the downdip direction. The slab models included a wedge-shaped, low-velocity metastable olivine tongue (MOTO) to a depth of 670 km, as well as a plausible thermal anomaly; one model further included a 10-km-thick fast layer on the surface of the slab. The principal effect of MOTO is to produce grazing reflections at wide angles off the phase boundary, generating a secondary arrival 0 to 4 seconds after the initial arrival depending on the take-off angle. The amplitude and timing of this feature vary with the lateral location of the seismic source within the slab cross-section.

  20. 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.

  1. Waveform effects of a metastable olivine tongue in subducting slabs

    Science.gov (United States)

    Vidale, John E.; Williams, Quentin; Houston, Heidi

    1991-01-01

    Velocity models of subducting slabs with a kinetically-depressed olivine to beta- and gamma-spinel transition are constructed, and the effect that such structures would have on teleseismic P waveforms are examined using a full-wave finite-difference method. These 2D calculations yielded waveforms at a range of distances in the downdip direction. The slab models included a wedge-shaped, low-velocity metastable olivine tongue (MOTO) to a depth of 670 km, as well as a plausible thermal anomaly; one model further included a 10-km-thick fast layer on the surface of the slab. The principal effect of MOTO is to produce grazing reflections at wide angles off the phase boundary, generating a secondary arrival 0 to 4 seconds after the initial arrival depending on the take-off angle. The amplitude and timing of this feature vary with the lateral location of the seismic source within the slab cross-section.

  2. GEOMETRIC MODEL OF THE NAZCA PLATE SUBDUCTION IN SOUTHWEST COLOMBIA

    Directory of Open Access Journals (Sweden)

    Monsalve J Hugo

    2007-12-01

    Full Text Available A geometric model for the subduction of the Nazca plate beneath the South American plate in southwestern of Colombia is proposed based on the relocation of hypocenters of local and distant
    earthquakes. By means of the simultaneous inversion of teleseismic P and SH body waves, the depths of the 15 events with Mw ≥ 5.8 were constrained, and the hypocenters of the 250 earthquakes recorded
    between 1990 and 2005 by the International Seismological Centre (ISC and U.S. Geological Survey, National Earthquake Information Center (NEIC were constrained and relocated. A model is proposed
    for the hypocentral sections taking into account the trench along of the Earth and Colombia-Ecuador.
    Three different possible shapes of subduction of the Nazca plate in the Colombia-Ecuador trench were obtained: The first configuration, in the Cali A segment, the dip angle changes from17º to 45º down to a maximum depth of 100km; the second configuration, in the Popayán B and Nariño C segments, the dip angle holds approximately constant at 30º down to a maximum depth of 200 km; and the third configuration, in the Quito D segment, the dip angle changes of 9º to 50º to a maximum depth 220 km. The maximum depth of seismicity along the Colombia-Ecuador trench shows two increases, the first between latitudes 4.5ºN-5ºN and the second between the latitudes 1ºS-2ºS, which suggest that the presence of the Malpelo and Carnegie Ridges may generate a differential blockage at the Pacific Colombia-Ecuador basin.

  3. Subduction of Fukushima accident derived radiocaesium in the Pacific Ocean

    Energy Technology Data Exchange (ETDEWEB)

    Aoyama, M. [Meteorological Res. Inst. (Japan); Hamajima, Y. [LLRL, Kanazawa University (Japan)

    2014-07-01

    The oceans are important sinks of anthropogenic pollutants, such as radionuclides, heavy metals and organic compounds, that are mainly atmospherically derived and/or directly discharged, but there is little information on their overall transport process during several decades after their injection. The bulk of the anthropogenic radionuclide {sup 137}Cs present in the oceans today was injected about five decades ago from atmospheric nuclear weapons tests and total inventory of {sup 137}Cs in the North Pacific Ocean was 69 PBq just before the TEPCO Fukushima Dai-ichi Nuclear Power Plant (FNPP1) accident. FNPP1 accident occurred on 11 March 2011, {sup 134}Cs and {sup 137}Cs were released into the air and ocean from three cores of FNPP1 and about 15 PBq of {sup 137}Cs were injected in the North Pacific Ocean. Until the end of 2012, a main body of Fukushima derived radiocaesium was located at around 40 deg. N and between 160 deg. E and 170 deg. W and not to reach western coast of American continent. We also found subsurface maximum of Fukushima derived {sup 134}Cs and {sup 137}Cs at about 400 meters depth due to subduction in 2012. Regarding with {sup 137}Cs activity in surface water at the center of the North Pacific Ocean, it is already close to pre-Fukushima level, a few Bq m{sup -3}, while 80 % of total water column inventory of {sup 137}Cs was already below 200 meters depth at the region of subduction. Document available in abstract form only. (authors)

  4. 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.

  5. 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.

  6. Geodetic Constraints From The Volcanic Arc Of The Andaman - Nicobar Subduction Zone

    Science.gov (United States)

    Earnest, A.; Krishnan, R.; Mayandi, S.; Sringeri, S. T.; Jade, S.

    2012-12-01

    We report first ever GPS derived surface deformation rates in the Barren and Narcondum volcanic islands east of Andaman-Nicobar archipelago which lies in the Bay of Bengal, a zone that generates frequent earthquakes, and coincides with the eastern plate boundary of India. The tectonics of this region is predominantly driven by the subduction of the Indian plate under the Burma plate. Andaman sea region hosts few volcanoes which lies on the inner arc extending between Sumatra and Myanmar with the sub-aerial expressions at Barren and Narcondum Islands. Barren Island, about 135 km ENE of Port Blair, is presently active with frequent eruptive histories whereas Narcondum is believed to be dormant. We initiated precise geodetic campaign mode measurements at Barren Island between 2007 to 2012 and one year (2011-2012) continuous measurements at Narcondum island. Preliminary results from this study forms a unique data set, being the first geodetic estimate from the volcanic arc of this subducting margin. Our analysis indicates horizontal convergence of the Barren benchmark to south-westward (SW) direction towards the Andaman accretionary fore-arc wedge where as the Narcondum benchmark recorded northeast (NE) motion. West of the Andaman fore-arc there is NE oriented subduction of the Indian plate which is moving at the rate of ~5 cm/yr. Convergence rates for the Indian plate from the Nuvel 1A model also show oblique convergence towards N23°E at 5.4 cm/yr. GPS derived inter seismic motion of Andaman islands prior to 2004 Sumatra earthquake is ~4.5 cm/yr NE. The marginal sea basin east of Barren Island at the Andaman spreading ridge has a NNW orienting opening of the sea-floor at 3.6 cm/yr. However the recent post seismic measurements of Andaman islands indicate rotation of displacement vectors from SW to NNE during 2005 to 2012. In this tectonic backdrop, the estimated rate of displacement of the volcanic islands probably represents a composite signal of tectonic as well as

  7. Insights into Shallow Anisotropic Structure in the Forearc Hikurangi Subduction Zone, New Zealand via Splitting of Teleseisms

    Science.gov (United States)

    Karalliyadda, S.; Savage, M. K.

    2013-12-01

    We use a recent transect that consists of 10 broadband stations across the northeast of Wellington region to explore the anisotropic structure of the forearc of the Hikurangi subduction zone in the southern North Island (NI), New Zealand from shear-wave splitting of SKS, ScS and teleseismic S phases. These measurements are then integrated with the previous splitting measurements in northwest of the transect. Splitting parameters from teleseismic S-phases revealed an abrupt lateral variation in the anisotropic structure. The general trend of splitting agrees well with the previous studies around this area, with NE-SW trench-parallel fast direction (φ). The range of delay times ( 0.5 - 3.0 s) and slightly varying SKS φ across the southeast of NI sugg