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Sample records for arc plutons beneath

  1. Petrology and Geochemistry of Neoproterozoic Arc Plutons Beneath the Atlantic Coastal Plain, SRS, SC

    Energy Technology Data Exchange (ETDEWEB)

    Maryak, M.

    1998-10-21

    In this report is presented first a brief review of the regional geologic setting of the Savannah River Site, descriptions of the plutonic rock units sampled here, whole rock geochemical data on the plutonic igneous rocks, and finally, a discussion of how the crystalline basement rocks of the Savannah River Site formed and how they may correlate with other terranes exposed in the Piedmont of the Carolinas, Georgia, and Virginia.

  2. Active Subduction Beneath The Gibraltar Arc

    Science.gov (United States)

    Gutscher, M.-A.; Malod, J.; Rehault, J.-P.; Contrucci, I.; Klingelhoefer, F.; Spakman, W.; Sismar Scientific Team

    The Gibraltar region features the arcuate Betic - Rif mountain belt with outward di- rected thrusting, surrounding a zone of strong Neogene subsidence and crustal thin- ning in the Western Alboran Sea. Until now its geodynamic interpretation has re- mained controversial. The Gibraltar Arc is located at the eastern end of the Azores- Gibraltar transform, a diffuse transpressional plate boundary between the Iberian and African Plates. Attention has recently been focussed on this plate boundary, while seeking the likely source of the destructive Lisbon great earthquake (M 8.5 - 9) and tsunami of 1755. The SISMAR marine seismic survey conducted in April 2001 ac- quired over 3000 km of 360-channel seismic data with a 4.5 km long streamer and 1000 km of wide-angle data recorded by ocean bottom seismometers (OBS), com- pletely spanning the actively deforming region between the margins of Portugal and northwest Morocco. Results from this seismic survey reveal a thick chaotic sedimen- tary mass west of Gibraltar to be an actively deforming accretionary wedge, with east dipping thrust faults disrupting the seafloor and soleing out to an east dipping decolle- ment. New travel-time tomographic results image a continuous east dipping body with high seismic velocities (i.e. a cold slab of oceanic lithosphere) descending from the Atlantic domain of the Gulf of Cadiz, passing through intermediate depth (60 - 120 km) seismicity beneath the Gibraltar Arc and Western Alboran Sea, and merging with a region of deep focus earthquakes 600 - 660 km below Granada Spain. Together these provide compelling evidence for an active east dipping subduction zone. Slab rollback towards the west provides a plausible mechanism for extension and subsidence in the Alboran Sea, while the associated westward advance of the Gibraltar Arc drives com- pressional deformation in the accretionary wedge where active mud volcanoes have recently been discovered.

  3. Magmatic arc construction: Constraints from the structure of the Coast plutonic complex

    Science.gov (United States)

    Andronicos, C. L.

    2007-12-01

    The Coast plutonic complex of British Columbia exposes the middle crust of a vigorous magmatic arc formed in the late Cretaceous and early Cenozoic. The arc is divided into two parts by the crustal scale Coast shear zone. West of the Coast shear zone between Prince Rupert and Douglas Channel plutons were emplaced at pressures between 500 and 850 MPa, are elongate with steeply dipping contacts and have tadpole shaped terminations. The steeply dipping sides of the plutons are concordant with country rock foliations that grade into mylonitic foliations in the cores of transpressive shear zones which strike NW parallel to the arc axis. Field relationships demonstrate that pluton emplacement occurred during displacement on the shear zones, folding of adjacent country rocks and pluton enhanced anatexis of host rocks. Pressure differences in single plutons and across shear zones attests to major vertical displacements during pluton construction. The data indicate that the plutons record emplacement during major transpressive deformation and crustal thickening. The tabular shape of the plutons, their steep dips and concordance with country rock fabric show that pluton emplacement and plate scale deformation were synchronous between ~120 and 85 Ma. East of plutons that intrude the Coast shear zone a sequence of upper amphibolite to granulite facies gneiss and migmatite (central gneiss complex) occurs that host gently dipping tonalite and granodiorite sills. Mineral assemblages in country rocks of the sills track uplift and exhumation from pressures of ~800 MPa to 200 MPa during sill emplacement between ~75 and 50 Ma. The gently to moderately dipping fabrics that host the sills are the result of transposition of an earlier steeply dipping foliation. Sill emplacement occurred during both contractional and extensional deformation as indicated by a reversal in shear from reverse to normal sense observed at a regional scale. The sills are concordant with host rock foliations and

  4. A comparative study of two rear-arc plutons and implications for the Fuegian Andes tectonic evolution: Mount Kranck Pluton and Jeu-Jepén Monzonite, Argentina

    Science.gov (United States)

    González-Guillot, M.; Prezzi, C.; Acevedo, R. D.; Escayola, M.

    2012-10-01

    A petrologic, geochemical and geophysical study of two Late Cretaceous plutons of the Fuegian Andes is carried out: the Jeu-Jepén Monzonite (JJM) and the Mt. Kranck Pluton (MKP). The plutons show a wide lithological spectrum from ultramafic lithologies (clinopyroxenites and hornblendites), gabbros, diorites to late stage K-feldspar syenite veins. They represent the top of magmatic chambers exposed at or close to the roof level. Mode and chemistry indicate a monzonitic-mildly alkaline trend with high K2O content, equivalent to shoshonitic series. Trace element composition is typical of arc magmas. These features plus their high LILE content (Ba 320-1600 ppm, Sr 475-1560 ppm), high LILE/HFSE ratio (Rb/Zr 0.6-1.6) and age confirm they belong to a rear-arc, monzonitic to mildly alkaline suite (the Fuegian Potassic Magmatism). Therefore, they represent the farthest-from-the-trench plutons in the suite. The petrographical and chemical characteristics of the plutons suggest the lithological spectrum is the result of magmatic differentiation. The process involved crystal accumulation and magma mingling at the early stages, favored either by injections of fresh magma from deeper reservoirs and/or the action of convective currents within the chamber. Country rock assimilation also took part simultaneously with crystallization. The JJM and MKP lie along the trace of a Cenozoic left-lateral strike-slip fault (Magallanes-Fagnano fault system), on opposite blocks. However, lithological, chemical and geophysical subtle differences between these two plutons suggest they evolved in individual magmatic chambers and therefore the distance between them cannot be used as an estimation of total offset along the fault, as was indicated in previous studies.

  5. Slab melting and magma formation beneath the southern Cascade arc

    Science.gov (United States)

    Walowski, K. J.; Wallace, P. J.; Clynne, M. A.; Rasmussen, D. J.; Weis, D.

    2016-07-01

    The processes that drive magma formation beneath the Cascade arc and other warm-slab subduction zones have been debated because young oceanic crust is predicted to largely dehydrate beneath the forearc during subduction. In addition, geochemical variability along strike in the Cascades has led to contrasting interpretations about the role of volatiles in magma generation. Here, we focus on the Lassen segment of the Cascade arc, where previous work has demonstrated across-arc geochemical variations related to subduction enrichment, and H-isotope data suggest that H2O in basaltic magmas is derived from the final breakdown of chlorite in the mantle portion of the slab. We use naturally glassy, olivine-hosted melt inclusions (MI) from the tephra deposits of eight primitive (MgO > 7 wt%) basaltic cinder cones to quantify the pre-eruptive volatile contents of mantle-derived melts in this region. The melt inclusions have B concentrations and isotope ratios that are similar to mid-ocean ridge basalt (MORB), suggesting extensive dehydration of the downgoing plate prior to reaching sub-arc depths and little input of slab-derived B into the mantle wedge. However, correlations of volatile and trace element ratios (H2O/Ce, Cl/Nb, Sr/Nd) in the melt inclusions demonstrate that geochemical variability is the result of variable addition of a hydrous subduction component to the mantle wedge. Furthermore, correlations between subduction component tracers and radiogenic isotope ratios show that the subduction component has less radiogenic Sr and Pb than the Lassen sub-arc mantle, which can be explained by melting of subducted Gorda MORB beneath the arc. Agreement between pMELTS melting models and melt inclusion volatile, major, and trace element data suggests that hydrous slab melt addition to the mantle wedge can produce the range in primitive compositions erupted in the Lassen region. Our results provide further evidence that chlorite-derived fluids from the mantle portion of the

  6. Slab melting and magma generation beneath the southern Cascade Arc

    Science.gov (United States)

    Walowski, K. J.; Wallace, P. J.; Clynne, M. A.

    2014-12-01

    Magma formation in subduction zones is interpreted to be caused by flux melting of the mantle wedge by fluids derived from dehydration of the downgoing oceanic lithosphere. In the Cascade Arc and other hot-slab subduction zones, however, most dehydration reactions occur beneath the forearc, necessitating a closer investigation of magma generation processes in this setting. Recent work combining 2-D steady state thermal models and the hydrogen isotope composition of olivine-hosted melt inclusions from the Lassen segment of the Cascades (Walowski et al., 2014; in review) has shown that partial melting of the subducted basaltic crust may be a key part of the subduction component in hot arcs. In this model, fluids from the slab interior (hydrated upper mantle) rise through the slab and cause flux-melting of the already dehydrated MORB volcanics in the upper oceanic crust. In the Shasta and Lassen segments of the southern Cascades, support for this interpretation comes from primitive magmas that have MORB-like Sr isotope compositions that correlate with subduction component tracers (H2O/Ce, Sr/P) (Grove et al. 2002, Borg et al. 2002). In addition, mass balance calculations of the composition of subduction components show ratios of trace elements to H2O that are at the high end of the global arc array (Ruscitto et al. 2012), consistent with the role of a slab-derived melt. Melting of the subducted basaltic crust should contribute a hydrous dacitic or rhyolitic melt (e.g. Jego and Dasgupta, 2013) to the mantle wedge rather than an H2O-rich aqueous fluid. We are using pHMELTS and pMELTS to model the reaction of hydrous slab melts with mantle peridotite as the melts rise through the inverted thermal gradient in the mantle wedge. The results of the modeling will be useful for understanding magma generation processes in arcs that are associated with subduction of relatively young oceanic lithosphere.

  7. Distinctly different parental magmas for calc-alkaline plutons and tholeiitic lavas in the central and eastern Aleutian arc

    Science.gov (United States)

    Cai, Yue; Rioux, Matthew; Kelemen, Peter B.; Goldstein, Steven L.; Bolge, Louise; Kylander-Clark, Andrew R. C.

    2015-12-01

    Cenozoic calc-alkaline plutons that comprise the middle crust of the central and eastern Aleutians have distinct isotopic and elemental compositions compared to Holocene tholeiitic lavas in the same region, including those from the same islands. Therefore the Holocene lavas are not representative of the net magmatic transfer from the mantle into the arc crust. Compared to the lavas, the Eocene to Miocene (9-39 Ma) intermediate to felsic plutonic rocks show higher SiO2 at a given Fe/Mg ratio, and have higher εNd-εHf values and lower Pb-Sr isotope ratios. However, the plutonic rocks strongly resemble calc-alkaline Holocene volcanics with more "depleted" isotope ratios in the western Aleutians, whose composition has been attributed to significant contributions from partial melting of subducted basaltic oceanic crust. These data could reflect a temporal variation of central and eastern Aleutian magma source compositions, from predominantly calc-alkaline compositions with more "depleted" isotope ratios in the Paleogene, to tholeiitic compositions with more "enriched" isotopes more recently. Alternatively, the differences between central Aleutian plutonic and volcanic rocks may reflect different transport and emplacement processes for the magmas that form plutons versus lavas. Calc-alkaline parental magmas, with higher SiO2 and high viscosity, are likely to form plutons after extensive mid-crustal degassing of initially high water contents. This conclusion has overarching importance because the plutonic rocks are chemically similar to bulk continental crust. Formation of similar plutonic rocks worldwide may play a key role in the genesis and evolution of continental crust.

  8. Time span of plutonism, fabric development, and cooling in a Neoproterozoic magmatic arc segment: U Pb age constraints from syn-tectonic plutons, Sark, Channel Islands, UK

    Science.gov (United States)

    Miller, Brent V.; Samson, Scott D.; D'Lemos, Richard S.

    1999-10-01

    New U-Pb zircon and titanite dates from syn-tectonic plutons on the British Channel Island of Sark constrain the time span of plutonism, fabric development, and cooling in this part of the Neoproterozoic Cadomian magmatic arc. The Tintageu leucogneiss is a mylonitic unit that was dated previously at 615.6 +4.2-2.3 Ma. The Port du Moulin quartz diorite, which intruded the Tintageu unit, contains a high-strain solid-state deformation fabric that is less intense than, but parallel to, fabrics in the leucogneiss and yields a U-Pb zircon date of 613.5 +2.3-1.5 Ma. The Little Sark quartz diorite also displays solid-state deformation fabrics in addition to relict magmatic textures, and yields a U-Pb zircon date of 611.4 +2.1-1.3 Ma. The North Sark granodiorite is largely penetratively undeformed, exhibits mainly magmatic fabrics and textures and has a U-Pb zircon date of 608.7 +1.1-1.0 Ma. Two fractions of titanite from each intrusion are essentially concordant and are identical within error, with mean dates of 606.5±0.4 Ma (Port du Moulin quartz diorite), 606.2±0.6 Ma (Little Sark quartz diorite), 606.4±0.6 Ma (North Sark granodiorite). The new U-Pb data, in combination with previous U-Pb and 40Ar/ 39Ar data and previous field studies, confirm the syn-tectonic nature of the Sark plutons and quantify the time span (ca. 7 m.y.) required for intrusion and sufficient crystallization of each body to record incremental strain during waning deformation. Titanite U-Pb and hornblende 40Ar/ 39Ar dates mark final cooling about 2 m.y. after intrusion of the last pluton.

  9. Mantle Melting as a Function of Water Content beneath the Mariana Arc

    OpenAIRE

    Kelley, Katherine A.; Plank, Terry; Newman, Sally; Stolper, Edward M.; Grove, Timothy L.; Parman, Stephen; Erik H. Hauri

    2010-01-01

    Subduction zone magmas are characterized by high concentrations of pre-eruptive H_2O, presumably as a result of an H_2Oflux originating from the dehydrating, subducting slab. The extent of mantle melting increases as a function of increasing water content beneath back-arc basins and is predicted to increase in a similar manner beneath arc volcanoes. Here, we present new data for olivine-hosted, basaltic melt inclusions from the Mariana arc that reveal pre-eruptive H_2O c...

  10. The Fazenda Gavião granodiorite and associated potassic plutons as evidence for Palaeoproterozoic arc-continent collision in the Rio Itapicuru greenstone belt, Brazil

    Science.gov (United States)

    Costa, Felipe G.; Oliveira, Elson P.; McNaughton, Neal J.

    2011-08-01

    Several granitic plutons have intruded the Palaeoproterozoic Rio Itapicuru greenstone belt, São Francisco craton, Brazil, in the time interval 2163-2080 Ma, but their tectonic significance is poorly understood. The Fazenda Gavião granodiorite (FGG) is one of a set of plutons emplaced along the western boundary of the greenstone belt with Archaean migmatite-gneiss basement. The pluton is mostly composed of hornblende granodiorite, occasionally crosscut by syn-plutonic mafic dykes. The FGG is metaluminous, medium- to high-K calc-alkaline with relatively constant silica abundances (SiO2 ˜ 63-66 wt%), high Sr (900-800 ppm) and high Ba (1000-1500 ppm). The associated mafic dykes are ultrapotassic, with high abundances of Ba, Sr, MgO, Ni, Cr, and light rare earth elements, suggesting derivation from partial melts of an enriched mantle source. The FGG originated probably by fractional crystallization from a primitive K-rich mafic magma that interacted with crustal melts. Its zircon U-Pb SHRIMP age of 2106 ± 6 Ma indicates that the FGG is younger than the early (2163-2127 Ma) tonalite-trondhjemite-granodiorite (TTG) and calc-alkaline arc plutons of the greenstone belt, and is closely related in time and space with potassic to ultrapotassic plutons (ca. 2110-2105 Ma). The negative ɛNd(t) of FGG and coeval K-rich plutons of the Rio Itapicuru greenstone belt contrasts markedly with the positive ɛNd(t) of the older arc plutons, indicating a major change of isotope signatures in granites of the Rio Itapicuru greenstone belt with time. This isotope shift may be related to magma contamination with older continental material and/or derivation of the parental potassic magma from enriched lithospheric mantle sources. We suggest that the K-rich plutons were emplaced during or shortly after Palaeoproterozoic arc-continent collision.

  11. Slab detachment of subducted Indo-Australian plate beneath Sunda arc, Indonesia

    Indian Academy of Sciences (India)

    Bhaskar Kundu; V K Gahalaut

    2011-04-01

    Necking, tearing, slab detachment and subsequently slab loss complicate the subduction zone processes and slab architecture. Based on evidences which include patterns of seismicity, seismic tomography and geochemistry of arc volcanoes, we have identified a horizontal slab tear in the subducted Indo-Australian slab beneath the Sunda arc. It strongly reflects on trench migration, and causes along-strike variations in vertical motion and geochemically distinct subduction-related arc magmatism. We also propose a model for the geodynamic evolution of slab detachment.

  12. Evolution and geochemistry of the Tertiary calc-alkaline plutons in the Adak Island region of the central Aleutian oceanic island arc

    Science.gov (United States)

    Kay, Suzanne; Citron, Gary P.; Kay, Robert W.; Jicha, Brian; Tibbetts, Ashley

    2014-05-01

    Calc-alkaline plutons are major crustal building blocks of continental margin mountain belts like the Mesozoic to Tertiary Andes and the Sierra Nevada, but are rare in oceanic island arcs. Some of the most calc-alkaline I-type island arc plutons are in the Central Aleutians with the most extreme signatures, as indicated by FeO/MgO ratios of stages of volcanism as the magmatic arc front was displaced to the north, possibly in response to accelerated periods of forearc subduction erosion. The gabbroic to leucogranodioritic units evolved in the lower to mid-crust with more silicic magmas rising buoyantly to higher levels where final crystallization and segregation of aplites occurred. Most gabbro and all mafic diorite units are largely crystal cumulates; one gabbro approaches the melt composition of a high Al basalt. The volumetrically dominant silicic diorites and granodiorites (58-63% SiO2) show the most zoning in their mineral phases and approach melt compositions. The leucogranodiorite (67-70% SiO2)unit was the last to crystallize. The silicic units are considered to be deep-crustal differentiates of high-Al basalt magmas, although partial melting of older magmatic rocks may play a role. Mafic dikes in the pluton represent the basic magmas under the dying arc front as the front moved northward.

  13. Thorium isotope evidence for melting of the mafic oceanic crust beneath the Izu arc

    Science.gov (United States)

    Freymuth, Heye; Ivko, Ben; Gill, James B.; Tamura, Yoshihiko; Elliott, Tim

    2016-08-01

    We address the question of whether melting of the mafic oceanic crust occurs beneath ordinary volcanic arcs using constraints from U-Series (238U/232Th, 230Th/232Th and 226Ra/230Th) measurements. Alteration of the top few hundred meters of the mafic crust leads to strong U enrichment. Via decay of 238U to 230Th, this results in elevated (230Th/232Th) (where brackets indicate activity ratios) over time-scales of ∼350 ka. This process leads to the high (230Th/232Th), between 2.6 and 11.0 in the mafic altered oceanic crust (AOC) sampled at ODP Sites 801 and 1149 near the Izu-Bonin-Mariana arc. Th activity ratios in the Izu arc lavas range from (230Th/232Th) = 1.2-2.0. These values are substantially higher than those in bulk sediment subducting at the Izu trench and also extend to higher values than in mid-ocean ridge basalts and the Mariana arc. We show that the range in Th isotope ratios in the Izu arc lavas is consistent with the presence of a slab melt from a mixed source consisting of AOC and subducted sediments with an AOC mass fraction of up to approximately 80 wt.% in the component added to the arc lava source. The oceanic plate subducting at the Izu arc is comparatively cold which therefore indicates that temperatures high enough for fluid-saturated melting of the AOC are commonly achieved beneath volcanic arcs. The high ratio of AOC/sediments of the slab melt component suggested for the Izu arc lavas requires preferential melting of the AOC. This can be achieved when fluid-saturated melting of the slab is triggered by fluids derived from underlying subducted serpentinites. Dehydration of serpentinites and migration of the fluid into the overlying crust causes melting to start within the AOC. The absence of a significant sediment melt component suggests there was insufficient water to flux both AOC and overlying sediments.

  14. Petrochemistry and petrology of I-type granitoids in an arc setting: the composite Torul pluton, Eastern Pontides, NE Turkey

    Science.gov (United States)

    Kaygusuz, Abdullah; Siebel, Wolfgang; Şen, Cüneyt; Satir, Muharrem

    2008-07-01

    The Upper Cretaceous Torul pluton, located in the Eastern Pontides, is of sub-alkaline affinity and displays features typical of volcanic arc granitoids. It is a composite pluton consisting of granodiorite, biotite hornblende monzogranite, quartz monzodiorite, quartz monzonite and hornblende biotite monzogranite. The oldest syenogranite (77.9 ± 0.3 Ma) and the youngest quartz diorite form small stocks within the pluton. Samples from the granodiorites, biotite hornblende monzogranites, quartz monzodiorites, quartz monzonites and hornblende biotite monzogranites have SiO2 between 57 and 68 wt% and display high-K calc-alkaline, metaluminous to peraluminous characteristics. Chondrite-normalized REE patterns are fractionated (Lacn/Lucn = 6.0-14.2) with pronounced negative Eu anomalies (Eu/Eu* = 0.59-0.84). Initial ɛNd(i) values vary between -3.1 and -4.1, initial 87Sr/86Sr values between 0.7058 and 0.7072, and δ18O values between +4.4 and +7.3‰. The quartz diorites are characterized by relatively high Mg-number of 36-38, low contents of Na2O (2.3-2.5 wt%) and SiO2 (52-55 wt%) and medium-K calc-alkaline, metaluminous composition. Chondrite-normalized REE patterns are relatively flat [(La/Yb)cn = 2.8-3.3; (Tb/Yb)cn = 1.2] and show small negative Eu anomalies (Eu/Eu* = 0.74-0.76). Compared to the other rock types, radiogenic isotope signatures of the quartz diorites show higher 87Sr/86Sr (0.7075-0.7079) and lower ɛNd(i) (-4.5 to -5.3). The syenogranites have high SiO2 (70-74 wt%) and display high-K calc-alkaline, peraluminous characteristics. Their REE patterns are characterized by higher Lacn/Lucn (12.9) and Eu/Eu* (0.76-0.77) values compared to the quartz diorites. Isotopic signatures of these rocks [ɛNd(i) = -4.0 to -3.3; 87Sr/86Sr(i) = 0.7034-0.7060; δ18 O = + 4.9 to + 8.2] are largely similar to the other rock types but differ from that of the quartz diorites. Fractionation of plagioclase, hornblende, pyroxene and Fe-Ti oxides played an important role in the

  15. Arc petrogenesis in southern Ireland and the Isle of Man: Implications for Ordovician accretionary history and constraints from Late Caledonian plutonism

    Science.gov (United States)

    Fritschle, Tobias; Daly, J. Stephen; Whitehouse, Martin J.; McConnell, Brian; Buhre, Stephan

    2016-04-01

    Peri-Laurentian and peri-Gondwanan magmatic arcs and microcontinents, and their attendant sedimentary basins were assembled during the Caledonian Orogeny (c. 490 - 400 Ma) to form the Irish and British lithosphere. Accretion of these terranes to Laurentia and subsequent closure of the Iapetus Ocean initiated the generation of widespread Late Caledonian plutons (c. 425 - 400 Ma). Petrogenetic investigation of Ordovician arc-related rocks aims to test possible terrane affinities, using geochemical data from the arcs and related rocks as well as isotopic signatures preserved within Late Caledonian granites. SIMS zircon U-Pb geochronology has provided middle to early Ordovician ages for volcanic rocks with arc affinities from Avoca (Ireland, c. 463 Ma) and a newly discovered volcanic sequence from Port-e-Vullen (Isle of Man, c. 473 Ma). Granitic rocks from Leinster (Ireland), interpreted as arc plutons, yielded late to middle Ordovician ages of c. 457 - 454 Ma (Croghan Kinshelagh) and c. 462 - 459 Ma (Graiguenamanagh), similar to the c. 457 Ma age of the Dhoon Granite (Isle of Man). Oxygen isotopic compositions of zircons from the Ordovician volcanic and plutonic rocks are close to or slightly heavier than mantle values (δ18O generally < 7 ‰). Lu-Hf zircon compositions suggest different terrane affinities: relatively juvenile ɛHfT values (c. +8.5 - +5.3) for the Avoca volcanics are similar to those of the older unit of the Croghan Kinshelagh Granite, whereas the Port-e-Vullen volcanics and the Graiguenamanagh Granite have less radiogenic ɛHfT values (c. +4.4 - +1.3). The present-day geographic distribution of these rocks and petrogenetic inferences from their North American correlatives invite comparison with the Avalonian and the Ganderian microcontinent, respectively[1]. These constraints are supported by inherited zircons and corresponding isotopic analyses. ɛHfT values (c. +11.5 - +1.5) from magmatic zircons of the Dhoon Granite and the younger unit of the

  16. Along-arc variation in water distribution in the upper mantle beneath Kyushu, Japan, as derived from receiver function analyses

    Science.gov (United States)

    Abe, Y.; Ohkura, T.; Hirahara, K.; Shibutani, T.

    2013-12-01

    The Kyushu district, Japan, under which the Philippine Sea (PHS) plate is subducting in a WNW direction, has several active volcanoes. On the volcanic front in Kyushu, a 110 km long gap in volcanism exists in the central part of Kyushu and volcanic rocks with various degrees of contamination by slab-derived fluid are distributed. To reveal the causes of the gap in volcanism and the chemical properties of volcanic rocks and to understand the process of magma genesis and water transportation, we should reveal along-arc variation in water distribution beneath Kyushu. We investigated the seismic velocity discontinuities in the upper mantle beneath Kyushu, with seismic waveform data from 65 stations of Hi-net, which are established by National Research Institute for Earth Science and Disaster Prevention, and 55 stations of the J-array, which are established by Japan Meteorological Agency, Kyushu University, Kagoshima University and Kyoto University. We used receiver function analyses developed especially for discontinuities with high dipping angles (Abe et al., 2011, GJI). We obtained the geometry and velocity contrasts of the continental Moho, the oceanic Moho, and the upper boundary of the PHS slab. From the geometry of these discontinuities and contrast in S wave velocities, we interpreted that the oceanic crust of the PHS slab has a low S wave velocity and is hydrated to a depth of 70 km beneath south Kyushu, to a depth of 80-90 km beneath central Kyushu, and to a depth of no more than 50 km beneath north Kyushu. We also interpreted that the fore-arc mantle beneath central Kyushu has a low velocity region (Vs < 3.2 km/s) that can contain hydrated materials and free aqueous fluid. Such a low velocity fore-arc mantle does not exist beneath north and south Kyushu. Beneath north Kyushu, the oceanic crust does not appear to convey much water in the mantle wedge. Beneath south Kyushu, water dehydrated from the slab could move to the back-arc side and cause arc volcanism

  17. Complex structure of the lithospheric slab beneath the Banda arc, eastern Indonesia depicted by a seismic tomographic model

    Directory of Open Access Journals (Sweden)

    Sri Widiyantoro

    2011-10-01

    Full Text Available Seismic tomography with a non-linear approach has been successfully applied to image the P-wave velocity structure beneath the Banda arc in detail. Nearly one million compressional phases including the surfacereflected depth phases pP and pwP from events within the Indonesian region have been used. The depth phases have been incorporated in order to improve the sampling of the uppermantle structure, particularly below the Banda Sea in the back-arc regions. For the model parameterization, we have combined a highresolution regional inversion with a low-resolution global inversion to allow detailed images of slab structures within the study region and to minimize the mapping of distant aspherical mantle structure into the volume under study. In this paper, we focus our discussion on the upper mantle and transition zone structure beneath the curved Banda arc. The tomographic images confirm previous observations of the twisting of the slab in the upper mantle, forming a spoon-shaped structure beneath the Banda arc. A slab lying flat on the 660 km discontinuity beneath the Banda Sea is also well imaged. Further interpretations of the resulting tomograms and seismicity data support the scenario of the Banda arc subduction rollback.

  18. Wide-angle seismic reflections as direct indictors of partial melt beneath an andesite arc

    Science.gov (United States)

    Stern, T. A.; Benson, A.; Stratford, W. R.; Gamble, J. A.

    2011-12-01

    Quasi-linear arcs of andesite volcanoes that erupt above 120 ± 40 km deep Waditi-Benioff zones are one of the most striking surface manifestations of plate tectonics. The prevailing view is that andesite magma that feed these arcs are an end-product of fluid-assisted melting in the mantle wedge1. Two key questions remain unresolved: why is the line of an active arc so sharply defined? and where do parental mantle-derived melts pool and differentiate into mafic restite and more felsic magma components that are so distinctive of continental magmatic arc systems ? Here we present seismic evidence from the MORC (mantle or crust?) project for a focused zone of melt below the andesite arc within northern New Zealand. Nine ~ 0.4 - 1.3 tonne dynamite shots were recorded on ~ 700 seismographs spaced along a 120 km long array across, and normal to the axis of the Taupo Volcanic Zone (TVZ). Two important features of the ray tracing solution are: (i) a lower-crustal, 10 km thick, "rift-pillow" of rocks where the P-wave seismic velocities (Vp) are ~ 6.8-7.1 km/s. Seismic reflections from top and bottom of the pillow are termed R1 and R2 respectively. (ii) Strong seismic reflections (termed R3 reflector) are recorded from a relatively short (12 -18 km-long) reflector at a depth of ~ 32 ± 2 km. An analysis of interval velocities between the R2 and R3 reflectors show a P-wave speed of 7.6 +/- 0.2 km/s, which is interpreted as anomalous upper mantle. Thus R3 is regarded as being a reflector within the upper mantle. Ray-tracing locates R3 beneath the eastern margin of the TVZ and directly beneath the active volcanic (andesite) front and geothermal fields. A causal relationship between the R3 reflector and the andesite arc is therefore implied. The amplitude ratio of the R3/R2 reflections along common traces is as high as 4-6 for incidence angles of reflection of 45-60 degrees. These data suggest R3 is best explained with numerical methods by an interface across which there is a

  19. Petrological and geochemical constraints on the origin of mafic dykes intruding the composite Kaçkar Pluton from the eastern Blacksea magmatic arc, NE Turkey

    Science.gov (United States)

    Aydin, Faruk; Oguz, Simge; Baser, Rasim; Uysal, Ibrahim; Sen, Cüneyt; Karsli, Orhan; Kandemir, Raif

    2015-04-01

    Geological, petrographical and geochemical data of mafic dykes intruding the composite Kaçkar Pluton from the eastern Blacksea magmatic arc (EBMA), NE Turkey, provide new insights into the nature of the metasomatizing agents in subcontinental lithospheric mantle beneath the region during the late Mesozoic-early Tertiary. Mafic dykes from the Çaykara and Hayrat (Trabzon), and also Ikizdere (Rize) areas from the northern margin of the EBMA consist of basalts, dolerites, lamprophyres (basic member) and lesser basaltic andesites and trachyandesites (evolved member). All dykes have no deformation and metamorphism. The outcrops of these dykes vary, with thickness from 0.2 to 10 m. and visible length from 3 to 20 m. In general, the mafic dykes dip steeply and cut directly across the Kaçkar Pluton, and show NW- and NE-trending, roughly parallel to the orientations of the EBMA main faults. Most of the dyke samples display subaphyric to porphyritic texture with phenocrysts of plagioclase (up to 10%), clinopyroxene (5-20%), amphibole (5-15%), and some contain variable amount of biotite (5-20%), lesser quartz (1-2%), and minor euhedral zircon, apatite and Fe-Ti oxides. The basic members of the mafic dykes have SiO2 of 44.1-51.9%, MgO of 4.5-12.1%, and TiO2 >mostly 0.8% (up to 2.3%) with K2O+Na2O of 1.3-6.6% with mostly subalkaline character. They are relatively high in mg-number (0.45-0.73) and transition metals (V=171-376 ppm, Co=22-45 ppm, Ni=3-148 ppm, and Sc=21-49 ppm). The evolved members of the dykes exhibit relatively higher SiO2 (57.1-60.2%) and K2O+Na2O (5.6-9.0%), and lower MgO (2.2-5.9%) and TiO2 (0.5-0.8%) contents than those from the basic dykes. Also, these samples have slightly low mg-number (0.41-0.65) and transition metals (V=99-172 ppm, Co=9-22 ppm, Ni=1-43 ppm, and Sc=9-20 ppm). In the Harker diagrams, all samples of the mafic dykes form a continuous array, and exhibit similar geochemical characteristics. In general, SiO2 inversely correlates with MgO, Fe

  20. Results from NICLAKES Survey of Active Faulting Beneath Lake Managua,Central American Volcanic arc

    Science.gov (United States)

    McIntosh, K.; Funk, J.; Mann, P.; Perez, P.; Strauch, W.

    2006-12-01

    Lake Managua covers an area of 1,035 km2 of the Central American volcanic arc and is enclosed by three major stratovolcanoes: Momotombo to the northwest was last active in AD 1905, Apoyeque in the center on the Chiltepe Peninsula was last active ca. 4600 years BP, and Masaya to the southeast was last active in AD 2003. A much smaller volcano in the lake (Momotombito) is thought to have been active <4500 yrs B.P. In May of 2006, we used a chartered barge to collect 330 km of 3.5 kHz profiler data along with coincident 274 km of sidescan sonar and 27 km of seismic reflection data. These data identify three zones of faulting on the lake floor: 1) A zone of north-northeast-striking faults in the shallow (2.5-7.5 m deep) eastern part of the lake that extends from the capital city of Managua, which was severely damaged by shallow, left-lateral strike-slip displacements on two of these faults in 1931 (M 5.6) and 1972 (M 6.2): these faults exhibit a horst and graben character and include possible offsets on drowned river valleys 2) a semicircular rift zone that is 1 km wide and can be traced over a distance of 30 km in the central part of the lake; the rift structure defines the deepest parts of the lake ranging from 12 to 18 m deep and is concentric about the Apoyeque stratocone/Chiltepe Peninsula; and 3) a zone of fault scarps defining the northwestern lake shore that may correlate to the northwestern extension of the Mateare fault zone, a major scarp-forming fault that separates the Managua lowlands from the highlands south and west of the city. Following previous workers, we interpret the northeast- trending group of faults in the eastern part of the lake as part of a 15-km-long discontinuity where the trend of the volcanic arc is offset in a right-lateral sense. The semi-circular pattern of the rift zone that is centered on Chiltepe Peninsula appears to have formed as a distal effect of either magma intrusion or withdrawal from beneath this volcanic complex. The

  1. Results From NICLAKES Survey of Active Faulting Beneath Lake Nicaragua, Central American Volcanic Arc

    Science.gov (United States)

    Funk, J.; Mann, P.; McIntosh, K.; Wulf, S.; Dull, R.; Perez, P.; Strauch, W.

    2006-12-01

    In May of 2006 we used a chartered ferry boat to collect 520 km of seismic data, 886 km of 3.5 kHz subbottom profiler data, and 35 cores from Lake Nicaragua. The lake covers an area of 7700 km2 within the active Central American volcanic arc, forms the largest lake in Central America, ranks as the twentieth largest freshwater lake in the world, and has never been previously surveyed or cored in a systematic manner. Two large stratovolcanoes occupy the central part of the lake: Concepcion is presently active, Maderas was last active less than 2000 years ago. Four zones of active faulting and doming of the lake floor were mapped with seismic and 3.5 kHz subbottom profiling. Two of the zones consist of 3-5-km-wide, 20-30-km-long asymmetric rift structures that trend towards the inactive cone of Maderas Volcano in a radial manner. The northeastern rift forms a 20-27-m deep depression on the lake bottom that is controlled by a north-dipping normal fault. The southwestern rift forms a 25-35-m deep depression controlled by a northeast-dipping normal fault. Both depressions contain mound-like features inferred to be hydrothermal deposits. Two zones of active faulting are associated with the active Concepcion stratovolcano. A 600-m-wide and 6-km-long fault bounded horst block extends westward beneath the lake from a promontory on the west side of the volcano. Like the two radial rift features of Maderas, the horst points roughly towards the active caldera of Concepcion. A second north-south zone of active faulting, which also forms a high, extends off the north coast of Concepcion and corresponds to a localized zone of folding and faulting mapped by previous workers and inferred by them to have formed by gravitational spreading of the flank of the volcano. The close spatial relation of these faults to the two volcanic cones in the lake suggests that the mechanism for faulting is a result of either crustal movements related to magma intrusion or gravitational sliding and is

  2. Crustal structure beneath two seismic stations in the Sunda-Banda arc transition zone derived from receiver function analysis

    Energy Technology Data Exchange (ETDEWEB)

    Syuhada, E-mail: hadda9@gmail.com [Graduate Research on Earthquake and Active Tectonics (GREAT), Bandung Institute of Technology, Jalan Ganesha 10, Bandung 40132 (Indonesia); Research Centre for Physics - Indonesian Institute of Sciences (LIPI), Kompleks Puspiptek Serpong, Tangsel 15314, Banten Indonesia (Indonesia); Hananto, Nugroho D.; Handayani, Lina [Research Centre for Geotechnology - Indonesian Institute of Sciences (LIPI), Jl. Sangkuriang (Kompleks LIPI) Bandung 40135 (Indonesia); Puspito, Nanang T; Yudistira, Tedi [Faculty of Mining and Petroleum Engineering ITB, Jalan Ganesha 10, Bandung 40132 (Indonesia); Anggono, Titi [Research Centre for Physics - Indonesian Institute of Sciences (LIPI), Kompleks Puspiptek Serpong, Tangsel 15314, Banten Indonesia (Indonesia)

    2015-04-24

    We analyzed receiver functions to estimate the crustal thickness and velocity structure beneath two stations of Geofon (GE) network in the Sunda-Banda arc transition zone. The stations are located in two different tectonic regimes: Sumbawa Island (station PLAI) and Timor Island (station SOEI) representing the oceanic and continental characters, respectively. We analyzed teleseismic events of 80 earthquakes to calculate the receiver functions using the time-domain iterative deconvolution technique. We employed 2D grid search (H-κ) algorithm based on the Moho interaction phases to estimate crustal thickness and Vp/Vs ratio. We also derived the S-wave velocity variation with depth beneath both stations by inverting the receiver functions. We obtained that beneath station PLAI the crustal thickness is about 27.8 km with Vp/Vs ratio 2.01. As station SOEI is covered by very thick low-velocity sediment causing unstable solution for the inversion, we modified the initial velocity model by adding the sediment thickness estimated using high frequency content of receiver functions in H-κ stacking process. We obtained the crustal thickness is about 37 km with VP/Vs ratio 2.2 beneath station SOEI. We suggest that the high Vp/Vs in station PLAI may indicate the presence of fluid ascending from the subducted plate to the volcanic arc, whereas the high Vp/Vs in station SOEI could be due to the presence of sediment and rich mafic composition in the upper crust and possibly related to the serpentinization process in the lower crust. We also suggest that the difference in velocity models and crustal thicknesses between stations PLAI and SOEI are consistent with their contrasting tectonic environments.

  3. Mantle wedge anisotropy beneath the Japan and Ryukyu arcs from teleseismic receiver functions - Implications for mantle flow and wedge hydration

    Science.gov (United States)

    Wirth, E. A.; Long, M. D.; Mccormack, K. A.

    2012-12-01

    Many fundamental aspects of the mantle wedge above subducting slabs, such as the dynamics of mantle flow and the transport of water and melt, have yet to be fully understood. A complete characterization of seismic anisotropy can yield powerful constraints on mantle flow and the degree of mantle wedge hydration. In this study, we characterize the geometry and strength of anisotropy in the mantle wedges beneath northeast Japan and the Ryukyu arc, which overlie the subducting Pacific and Philippine Sea plates, respectively. We compute radial and transverse component P-to-S receiver functions from 15 stations of the F-net array using the multitaper correlation receiver function estimator (Park and Levin, 2000). In both regions, we observe P-to-SV converted energy on radial component receiver functions that are consistent with conversions originating at the subducting oceanic Moho and the top of the subducting oceanic crust. We also observe P-to-SH conversions on the transverse component receiver functions that are consistent with the presence of multiple anisotropic and/or dipping layers. We compute synthetic receiver functions using a forward modeling scheme to create models for the depths, thicknesses, and strengths of the anisotropic layers beneath both northeast Japan and Ryukyu. Beneath Ryukyu, we detect evidence for a layer of strong anisotropy and high Vp/Vs ratio directly above the slab, consistent with the presence of serpentinite. We see no evidence of this signature in receiver functions from northeast Japan; instead, we see evidence for relatively modest anisotropy due to olivine fabric. We also detect a low-velocity region in the mantle wedge beneath northeast Japan, which may be consistent with the presence of partial melt. Since the presence of serpentinite indicates significant hydration of the wedge, the contrast in anisotropic structure between Ryukyu and northeast Japan has important implications for our understanding of slab hydration and how water

  4. The South Tibetan Tadpole Zone: Ongoing density sorting at the Moho beneath the Indus-Tsangpo suture zone (and beneath volcanic arcs?)

    Science.gov (United States)

    Kelemen, Peter; Hacker, Bradley

    2016-04-01

    at less than 700°C (e.g. Jackson 02). We build on earlier studies (LePichon et al 92, 97; Schulte-Pelkum et al 05; Monsalve et al 08) to develop the hypothesis that there is rapid growth of garnet at 80 km and 1000°C within subducting Indian crust, causing increased rock densities. Dense eclogites founder into the mantle, while relatively buoyant lithologies accumulate in thickening lower crust. Mantle return flow plus radioactive heating in thick, felsic crust maintains high temperature, facilitating formation of hybrid magmas and pyroxenites. The crustal volume grows at 760 cubic m/yr/m of strike length. Moho-depth earthquakes may be due to localized deformation and thermal runaway in weak layers and along the margins of dense, foundering diapirs (e.g., Larsen & Yuen 97; Braeck & Podladchikov 07; Kelemen & Hirth 07; Lister et al 08; Kufner et al 16). A similar process may take place at some convergent margins, where forearc crust is thrust beneath hot, magmatic arc crust, leading to extensive, Moho-depth density sorting and hybrid crust-mantle magmatism in Arc Tadpole Zones.

  5. Locations and focal mechanisms of deep long period events beneath Aleutian Arc volcanoes using back projection methods

    Science.gov (United States)

    Lough, A. C.; Roman, D. C.; Haney, M. M.

    2015-12-01

    Deep long period (DLP) earthquakes are commonly observed in volcanic settings such as the Aleutian Arc in Alaska. DLPs are poorly understood but are thought to be associated with movements of fluids, such as magma or hydrothermal fluids, deep in the volcanic plumbing system. These events have been recognized for several decades but few studies have gone beyond their identification and location. All long period events are more difficult to identify and locate than volcano-tectonic (VT) earthquakes because traditional detection schemes focus on high frequency (short period) energy. In addition, DLPs present analytical challenges because they tend to be emergent and so it is difficult to accurately pick the onset of arriving body waves. We now expect to find DLPs at most volcanic centers, the challenge lies in identification and location. We aim to reduce the element of human error in location by applying back projection to better constrain the depth and horizontal position of these events. Power et al. (2004) provided the first compilation of DLP activity in the Aleutian Arc. This study focuses on the reanalysis of 162 cataloged DLPs beneath 11 volcanoes in the Aleutian arc (we expect to ultimately identify and reanalyze more DLPs). We are currently adapting the approach of Haney (2014) for volcanic tremor to use back projection over a 4D grid to determine position and origin time of DLPs. This method holds great potential in that it will allow automated, high-accuracy picking of arrival times and could reduce the number of arrival time picks necessary for traditional location schemes to well constrain event origins. Back projection can also calculate a relative focal mechanism (difficult with traditional methods due to the emergent nature of DLPs) allowing the first in depth analysis of source properties. Our event catalog (spanning over 25 years and volcanoes) is one of the longest and largest and enables us to investigate spatial and temporal variation in DLPs.

  6. Crust-mantle interaction beneath the Luxi Block, eastern North China Craton: Evidence from coexisting mantle- and crust-derived enclaves in a quartz monzonite pluton

    Science.gov (United States)

    Lan, Ting-Guang; Fan, Hong-Rui; Santosh, M.; Hu, Fang-Fang; Yang, Kui-Feng; Yang, Yue-Heng; Liu, Yongsheng

    2013-09-01

    The Laiwu quartz monzonite in the Luxi Block of eastern North China Craton (NCC) is characterized by the presence of abundant plagioclase amphibolite and gabbro-diorite enclaves. Here we present LA-ICPMS zircon U-Pb ages which show that the host quartz monzonite was emplaced at 129.8 ± 1.0 Ma, whereas the protolith of the plagioclase amphibolite enclaves formed during early Paleoproterozoic. The gabbro-diorite enclaves were produced simultaneously with or slightly earlier than the formation of the host quartz monzonite. Combined with the Archean and Paleoproterozoic zircons as well as the low εNd(0) values (- 18.4 to - 18.0) in the plagioclase amphibolite enclaves, the equilibrium temperature and pressure conditions (645-670 °C and 4.8-6.5 Kb) suggest that the plagioclase amphibolite enclaves are fragments of the middle crust. The gabbro-diorite enclaves mainly originated from an enriched lithospheric mantle metasomatized by melts/fluids derived from the continental crust, as indicated by their low SiO2 (54.4-54.7 wt.%) and high MgO (10.9-11.1 wt.%) contents as well as the negative εNd(t) values (- 13.5 to - 10.7) and enrichment of LILEs (e.g., Ba and Sr) and depletion of HFSEs (e.g., Nb, Ta, P and Ti). Compared with the ancient crustal rocks and the mafic plutons considered to have been derived from lithospheric mantle in the Luxi Block, the moderate εNd(t) (- 15.7 to - 15.1) and εHf(t) (- 20.7 to - 13.0) values of the quartz monzonite in our study suggest that both mantle- and crust-derived melts were involved in the magma generation. Thus we propose a model involving magma mixing between mantle- and crust-derived melts for the formation of the quartz monzonite. Since significant crust-mantle interaction is recorded not only in the quartz monzonite and its enclaves in the Luxi Block but also in the other granitoids widespread in the NCC, it is considered that large-scale crust-mantle interaction and magmatic underplating were associated with the Mesozoic

  7. Seismic evidence for tearing in the subducting Indian slab beneath the Andaman arc

    Science.gov (United States)

    Kumar, Prakash; Srijayanthi, G.; Ravi Kumar, M.

    2016-05-01

    Segmentation of a subduction zone through tearing is envisaged as an inevitable consequence of the differential rate of slab rollback along the strike of convergent plate boundaries. It is a key feature that controls plate tectonics and seismogenesis in a subduction setting. Globally, lithospheric tears are mostly recognized by seismic tomography and seismicity trends. However, such an intriguing feature has never been imaged with high resolution. Here we present seismological evidence for tearing of the Indian oceanic plate at shallow depths along the Andaman arc. Our image of the subducted plate using the shear-wave receiver function technique reveals three distinct plate segments. The middle lithospheric chunk has an abrupt offset of ~20 km relative to the northern and southern segments along the entire stretch of Andaman-Nicobar Islands. We interpret that this abrupt offset in the base of the lithosphere is caused by the tearing of the subducted oceanic plate. For the plate age of ~80 to 60 Myr, the lithospheric thickness varies from ~40 to 70 km.

  8. Seismic structure of subducted Philippine Sea plate beneath the southern Ryukyu arc by receiver function and local earthquakes tomography

    Science.gov (United States)

    Nakamura, M.

    2012-12-01

    Seismic coupling of the Ryukyu subduction zone is assumed to be weak from the lack of historical interplate large earthquakes. However, recent investigation of repeating slow slip events (Heki & Kataoka, 2008), shallow low frequency earthquakes (Ando et al., 2012), and source of 1771 Yaeyama mega-tsunami (Nakamura, 2009), showed that the interplate coupling is not weak in the south of Ryukyu Trench. The biannually repeating SSEs (Mw=6.5) occur at the depth of 20-40 km on the upper interface of the subducted Philippine Sea plate beneath Yaeyama region, where earthquake swarm occurred on 1991 and 1992. To reveal the relation among the crustal structure, earthquake swarms, and occurrence of slow slip events (SSE), local earthquake tomography and receiver function (RF) analysis was computed in the southwestern Ryukyu arc. A tomographic inversion was used to determine P and S wave structures beneath Iriomote Island in the southwestern Ryukyu region for comparison with the locations of the SSE. The seismic tomography (Thurber & Eberhart-Phillips, 1999) was employed. The P- and S- wave arrival time data picked manually by Japan Meteorological Agency (JMA) are used. The 6750 earthquakes from January 2000 to July 2012 were used. For the calculation of the receiver function, the 212 earthquakes whose magnitudes are over 6.0 and epicentral distances are between 30 and 90 degrees were selected. The teleseicmic waveforms observed at two short-period seismometers of the JMA, and one broadband seismometer of F-net of National Research Institute for Earth Science and Disaster Prevention were used. The water level method (the water level is 0.01) is applied to original waveforms. Assuming that each later phase in a RF is the wave converted from P to S at a depth, I transformed the time domain RF into the depth domain one along each ray path in a reference velocity model. The JMA2001 velocity model is used in this study. The results of tomography show that the low Vp and high Vp

  9. 40Ar/39Ar geochronology of subaerial lava flows of Barren Island volcano and the deep crust beneath the Andaman Island Arc, Burma Microplate

    Science.gov (United States)

    Ray, Jyotiranjan S.; Pande, Kanchan; Bhutani, Rajneesh

    2015-06-01

    Little was known about the nature and origin of the deep crust beneath the Andaman Island Arc in spite of the fact that it formed part of the highly active Indonesian volcanic arc system, one of the important continental crust forming regions in Southeast Asia. This arc, formed as a result of subduction of the Indian Plate beneath the Burma Microplate (a sliver of the Eurasian Plate), contains only one active subaerial magmatic center, Barren Island volcano, whose evolutional timeline had remained uncertain. In this work, we present results of the first successful attempt to date crustal xenoliths and their host lava flows from the island, by incremental heating 40Ar/39Ar method, in an attempt to understand the evolutionary histories of the volcano and its basement. Based on concordant plateau and isochron ages, we establish that the oldest subaerial lava flows of the volcano are 1.58 ± 0.04 (2σ) Ma, and some of the plagioclase xenocrysts have been derived from crustal rocks of 106 ± 3 (2σ) Ma. Mineralogy (anorthite + Cr-rich diopside + minor olivine) and isotopic compositions (87Sr/86Sr 7.0) of xenoliths not only indicate their derivation from a lower (oceanic) crustal olivine gabbro but also suggest a genetic relationship between the arc crust and the ophiolitic basement of the Andaman accretionary prism. We speculate that the basements of the forearc and volcanic arc of the Andaman subduction zone belong to a single continuous unit that was once attached to the western margin of the Eurasian Plate.

  10. Is there a geochemical link between volcanic and plutonic rocks in the Organ Mountains caldera?

    Science.gov (United States)

    Memeti, V.; Davidson, J.

    2013-12-01

    Results from separate volcanic and plutonic studies have led to inconsistent conclusions regarding the origins and thus links between volcanic and plutonic systems in continental arcs and the magmatic processes and time scales responsible for their compositional variations. Some have suggested that there is a geochemical and geochronological disconnect between volcanic and plutonic rocks and hence have questioned the existence of magma mush columns beneath active volcanoes. Investigating contemporary volcanic and plutonic rocks that are spatially connected is thus critical in exploring these issues. The ca. 36 Ma Organ Mountains caldera in New Mexico, USA, represents such a system exposing contemporaneous volcanic and plutonic rocks juxtaposed at the surface due to tilting during extensional tectonics along the Rio Grande Rift. Detailed geologic and structural mapping [1] and 40Ar/39Ar ages of both volcanics and plutons [2] demonstrate the spatial and temporal connection of both rock types with active magmatism over >2.5 myr. Three caldera-forming ignimbrites erupted within 600 kyr [2] from this system with a total erupted volume of 500-1,000 km3 as well as less voluminous pre- and post-caldera trachyte and andesite lavas. The ignimbrite sequence ranges from a crystal-poor, high-SiO2 rhyolite at the base to a more crystal-rich, low-SiO2 rhyolite at the top. Compositional zoning with quartz-monzonite at the base grading to syenite and alaskite at the top is also found in the Organ Needle pluton, the main intrusion, which is interpreted to be the source for the ignimbrites [1]. Other contemporaneous and slightly younger plutons have dioritic to leucogranitic compositions. We examined both volcanic and plutonic rocks with petrography and their textural variations with color cathodoluminescence, and used whole rock element and Sr, Nd and Pb isotope geochemistry to constrain magma compositions and origins. Electron microprobe analyses on feldspars have been completed to

  11. Distinct S wave reflector in the midcrust beneath Nikko-Shirane volcano in the northeastern Japan arc

    Energy Technology Data Exchange (ETDEWEB)

    Matsumoto, Satoshi; Hasegawa, Akira [Tohoku Univ., Sendai (Japan)

    1996-02-10

    This paper investigates the geometry and the features of the midcrustal s wave reflector beneath Nikko-Shirane valcano in detail based on data acquired through seismic observations with a dense station network. The geometry and internal structure of the reflector is discribed.

  12. Shear wave splitting from local events beneath the Ryukyu arc : Trench-parallel anisotropy in the mantle wedge

    NARCIS (Netherlands)

    Long, Maureen D.; Hilst, R.D. van der

    2006-01-01

    We present shear wave splitting measurements from local slab earthquakes at eight seismic stations of the Japanese F-net array located in the Ryukyu arc. We obtained high-quality splitting measurements for 70 event-station pairs and found that the majority of the measured fast directions were parall

  13. Evolution of Ataúro Island: Temporal constraints on subduction processes beneath the Wetar zone, Banda Arc

    Science.gov (United States)

    Ely, Kim S.; Sandiford, Mike; Hawke, Margaret L.; Phillips, David; Quigley, Mark; Reis, Joao Edmundo dos

    2011-06-01

    Ataúro is a key to understanding the late stage volcanic and subduction history of the Banda Arc to the north of Timor. A volcanic history of bi-modal subaqueous volcanism has been established and new whole rock and trace element geochemical data show two compositional groups, basaltic andesite and dacite-rhyolite. 40Ar/ 39Ar geochronology of hornblende from rhyo-dacitic lavas confirms that volcanism continued until 3.3 Ma. Following the cessation of volcanism, coral reef marine terraces have been uplifted to elevations of 700 m above sea level. Continuity of the terraces at constant elevations around the island reflects regional-scale uplift most likely linked to sublithospheric processes such as slab detachment. Local scale landscape features of the eastern parts of Ataúro are strongly controlled by normal faults. The continuation of arc-related volcanism on Ataúro until at least 3.3 Ma suggests that subduction of Australian lithosphere continued until near this time. This data is consistent with findings from the earthquake record where the extent of the Wetar seismic gap to a depth of 350 km suggests slab breakoff, as a result of collision, commenced at ˜4 Ma, leading to subsequent regional uplift recorded in elevated terraces on Ataúro and neighbouring islands.

  14. 鄂东南地区存在古元古代-太古宙基底--来自铜鼓山岩体锆石U-Pb-Hf同位素的证据%Paleoproterozoic-Archean Basement Beneath Southeast Hubei Province:Evidence from U-Pb-Hf Isotopes in Zircons from the Tonggushan Pluton

    Institute of Scientific and Technical Information of China (English)

    夏金龙; 黄圭成; 丁丽雪; 吴昌雄; 祝敬明; 金尚刚

    2013-01-01

    This paper has reported the integrated study of zircon U-Pb age and Lu-Hf isotope composition in zircons from the Tonggushan pluton, southeast Hubei Province. Tonggushan pluton is composed of quartz diorite porphyry. The 206Pb/238U mean age of magmatic zircon is (147±2.6) Ma, indicating that Tonggushan pluton was formed in the Late Jurassic-Early Cretaceous, which is consistent with the formation time of other plutons in this area. A large number of inherited zircons, formed in 1798~2888 Ma, exist in Tonggushan pluton. The Paleoproterozoic zircons are of magmatic origin and have similar 176Hf/177Hf and 176Lu/177Hf ratios, suggesting that they were probably derived from the same igneous basement rock. The Paleoproterozoic zircons have low Hf-isotope compositions and characteristics of crustal source. Hf model ages of these zircons and the presence of older inherited cores within them suggest that the source of Paleoproterozoic magma was Neoarchaean crust, implying the existence of an unexposed old basement beneath southeast Hubei Province and the whole Yangtze block. These data supply new clue to the study of the Precambrian basement evolution of Yangtze block. The Paleoproterozoic-Archean basement of the Yangtze Block most likely spreads from the Sichuan Basin through western Huebei Province to southeastern Hubei Province.%对鄂东南地区位于毛铺-两剑桥断裂带上的铜鼓山岩体进行了野外地质及镜下显微研究及岩石化学分析,重点分析了其中锆石U-Pb年龄和Hf同位素组成。结果表明铜鼓山岩体为石英闪长玢岩,岩体形成于(147±2.6) Ma,属晚侏罗世-早白垩世,与鄂东南地区其它岩体年龄具有一致性。铜鼓山岩体中存在的大量继承锆石。分析的4个继承锆石形成于古元古代晚期1798~1888 Ma。继承锆石具有高的Th/U比值和极其相似的Lu-Hf同位素组成,表明它们捕获于同一火成岩。这表明鄂东南地区存在古元古代基底。这些古元古代

  15. Tectonomagmatism in continental arcs: evidence from the Sark arc complex

    Science.gov (United States)

    Gibbons, Wes; Moreno, Teresa

    2002-07-01

    The island of Sark (Channel Islands, UK) exposes syntectonic plutons and country rock gneisses within a Precambrian (Cadomian) continental arc. This Sark arc complex records sequential pulses of magmatism over a period of 7 Ma (ca. 616-609 Ma). The earliest intrusion (ca. 616 Ma) was a composite sill that shows an ultramafic base overlain by a magma-mingled net vein complex subsequently deformed at near-solidus temperatures into the amphibolitic and tonalitic Tintageu banded gneisses. The deformation was synchronous with D 2 deformation of the paragneissic envelope, with both intrusion and country rock showing flat, top-to-the-south LS fabrics. Later plutonism injected three homogeneous quartz diorite-granodiorite sheets: the Creux-Moulin pluton (150-250 m; ca. 614 Ma), the Little Sark pluton (>700 m; 611 Ma), and the Northern pluton (>500 m; 609 Ma). Similar but thinner sheets in the south (Derrible-Hogsback-Dixcart) and west (Port es Saies-Brecqhou) are interpreted as offshoots from the Creux-Moulin pluton and Little Sark pluton, respectively. All these plutons show the same LS fabric seen in the older gneisses, with rare magmatic fabrics and common solid state fabrics recording syntectonic crystallisation and cooling. The cooling rate increased rapidly with decreasing crystallisation age: >9 Ma for the oldest intrusion to cool to lower amphibolite conditions, 7-8 Ma for the Creux Moulin pluton, 5-6 Ma for the Little Sark pluton, and 10 -14 s -1) that focussed extensional deformation into the Sark area. The increased rates of extension allowed ingress of the subsequent quartz diorite-granodiorite sheets, although strain rate slowly declined as the whole complex cooled during exhumation. The regional architecture of syntectonic Cadomian arc complexes includes flat-lying "Sark-type" and steep "Guernsey-type" domains produced synchronously in shear zone networks induced by oblique subduction: a pattern seen in other continental arcs such as that running from Alaska

  16. LA-ICP MS zircon dating, whole-rock and Sr-Nd-Pb-O isotope geochemistry of the Camiboğazı pluton, Eastern Pontides, NE Turkey: Implications for lithospheric mantle and lower crustal sources in arc-related I-type magmatism

    Science.gov (United States)

    Kaygusuz, Abdullah; Arslan, Mehmet; Siebel, Wolfgang; Sipahi, Ferkan; İlbeyli, Nurdane; Temizel, İrfan

    2014-04-01

    Late Cretaceous I-type plutons are widespread in the Eastern Pontides, NE Turkey. The studied Camiboğazı pluton is a composite pluton consisting of diorite, tonalite, monzodiorite, monzonite, quartz monzonite, granite, and mafic microgranular enclaves (MMEs). Laser ablation ICP-MS U-Pb dating of zircon yielded crystallization ages of 76.21 ± 0.79 Ma, 75.65 ± 0.50 Ma, 75.04 ± 0.83 Ma, and 74.73 ± 0.86 Ma for diorite, monzodiorite, monzonite, and granite, respectively. The rocks of the pluton have I-type, high-K to shoshonitic and metaluminous character, displaying whole-rock geochemical features of arc-related granites. They are enriched in large-ion lithophile and light rare-earth elements, and depleted in high-field-strength elements. Major element variations can be attributed to fractionation of plagioclase, clinopyroxene, hornblende, and Fe-Ti oxides. The rocks show considerable variation in 87Sr/86Sr(i) (0.70498 to 0.70622), ɛNd(i) (- 2.79 to - 0.36), δ18O values (+ 6.3 to + 11.4) and Nd model ages (TDM) (0.81 Ga to 1.26 Ga). Besides, they have (206Pb/204Pb) = 18.44-19.09, (207Pb/204Pb) = 15.64-15.69, and (208Pb/204Pb) = 38.37-38.89. Although isotope signatures of the mafic microgranular enclaves (MMEs) (87Sr/86Sr(i) = 0.70551 to 0.70622; ɛNd(i) = - 2.9 to - 1.23; δ18O = + 8.3 to + 9.7) are largely similar to the host rocks, MMEs are characterized by relatively high Mg-numbers (32-36), low contents of SiO2 (52-56 wt.%) and low ASI (0.7-0.9). Estimated crystallization temperatures for the rocks of the pluton range from 735 ± 58 °C to 844 ± 24 °C and a shallow intrusion depth (< 10 km) is estimated from Al-in-hornblende thermobarometry. Whole-rock geochemical and isotopic data suggest magma generation by dehydration melting of an amphibolite-type lower crustal component with additional input of a subcontinental lithospheric mantle component. Furthermore, Sr-Nd isotope mixing model reveals ~ 30% to 40% lower crustal magma contribution to the mantle

  17. 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

  18. SHRIMP U-Pb zircon age, geochemistry and Nd isotope of the Guandaoshan pluton in SW Sichuan: Petrogenesis and tectonic significance

    Institute of Scientific and Technical Information of China (English)

    LI; Xianhua(李献华); LI; Zhengxiang(李正祥); ZHOU; Hanwen(周汉文); LIU; Ying(刘颖); LIANG; Xirong(梁细荣); LI; Wuxian(李武显)

    2003-01-01

    SHRIMP U-Pb zircon age, geochemical and Nd isotopic data are reported for the Neoproterozoic Guandaoshan pluton in the Yanbian region, SW Sichuan. This pluton is of typical I-type granite and emplaced at (857±13) Ma. Geochemical and Nd isotopic characters suggest that the pluton was generated by partial melting of pre-existing, young (late Mesoproterozoic to early Neoproterozoic) low-K tholeiitic protolith within an intraplate anorogenic setting. The Guandaoshan pluton probably records the earliest magmatism induced by the proposed ca. 860-750 Ma mantle superplume beneath the supercontinent Rodinia.

  19. Anatomy of Intra-Oceanic Arc Systems

    Science.gov (United States)

    Stern, R. J.

    2007-12-01

    involves anatexis of amphibolite and mafic melt fractionation to form nests of felsic plutons, accompanied by drip-delamination of pyroxene-rich residues and cumulates back into the mantle. Active IOASs thus have mass transfer in both directions across the crust-mantle boundary beneath the magmatic arc, leading to small P-wave velocity differences between gabbroic lower crust and pyroxenitic upper mantle. Forearcs, in contrast, are underlain by serpentinized harzburgite. Intra-oceanic arc systems are rarely associated with accretionary prisms; because most are far-removed from continental sources of sediment, they subduct oceanic lithosphere with thin sediments and have naked forearcs subjected to tectonic erosion. These aspects of IOASs should be revealed in accreted ancient arcs: 1) Ancient IOAs should be large, both wide and thick; and 2) Ancient IOASs should be asymmetric. Scraps of IOASs could be smaller slivers of crust, brought into place by strike-slip faulting, but a true accreted arc should be as obvious to a geologist as a beached whale is to a beachcomber.

  20. Epithermal gold-siver deposits in the western United States: time-space products of evolving plutonic, volcanic and tectonic environments

    Science.gov (United States)

    Berger, B.R.; Bonham, H.F.

    1990-01-01

    The western United States has been the locus of considerable subaerial volcanic and plutonic igneous activity since the mid-Mesozoic. After the destruction of the Jurassic-Cretaceous magmatic arc-trench system, subduction was re-established in the Late Mesozoic with low-angle underthrusting of the oceanic plate beneath western North America. This resulted in crustal shortening during the Late Cretaceous to Early Tertiary and removal of the mantle lithosphere west of the Rocky Mountains. Commencing in the Eocene, flat subduction ceased, the volcanic arc began to re-establish itself along the continental margin, and the hingeline along the steepening subducting plate migrated from east to west. The crust east of the migrating hingeline was exposed to hot asthenosphere, and widespread tectonics and volcanic activity resulted. Hydrothermal activity accompanied the volcanism resulting in numerous epithermal gold-silver deposits. The temporal and spatial distributions of epithermal deposits in the region are therefore systematic and can be subdivided into discrete time intervals which are related to widespread changes in magmatic activity. Time intervals selected for discussion are Pre-Cenozoic, 66-55 Ma, 54-43 Ma, 42-34 Ma, 33-24 Ma, 23-17 Ma, and tectonic context of the western United States provides a unified framework in which to understand and explore for epithermal type deposits. ?? 1990.

  1. Origin of adakite-like plutons in southern Korea

    Science.gov (United States)

    Oh, Jeong-Im; Choi, Sung Hi; Yi, Keewook

    2016-10-01

    We present Sr-Nd-Pb isotopic compositions for two adakite-like intrusions in southern Korea (Jindong and Bongnae), including major and trace element concentrations, and the sensitive high-resolution ion microprobe (SHRIMP) zircon U-Pb age. Our aim is to constrain the origin and tectonomagmatic processes that gave rise to the plutons. A SHRIMP U-Pb zircon age of 88.7 ± 0.7 Ma was obtained from a Jindong granodiorite sample. The Jindong plutons belong to the medium-K calc-alkaline series, and have an overall enrichment in large ion lithophile elements (LILE), such as K, Rb, Ba, and Pb, and a relative depletion in high field strength elements, such as Nb, Ta, and Ti, compared with the neighboring elements in the primitive mantle-normalized multi-trace element variation diagram. It was found that (87Sr/86Sr)i = 0.70475-0.70596, (143Nd/144Nd)i = 0.512547-0.512604, [(εNd)i = + 0.4 to 2.2], and (206Pb/204Pb)i = 18.19-18.37, which fall within the field of the arc-type Cretaceous to Tertiary Bulguksa intrusive rocks in the Sr-Nd and Pb-Pb isotopic correlation diagrams. The elevated Sr/Y (17-40), but low La/Yb (3.7-8.8) ratios of the Jindong plutons, together with their coherent geochemical trends and U-shaped rare earth element (REE) patterns, indicate that they were not formed by slab melting, but by amphibole-dominated fractional crystallization of the Bulguksa-like arc magma. A SHRIMP U-Pb zircon age of 226.5 ± 2.5 Ma was obtained from a Bongnae tonalite sample. The Bongnae plutons belong to the shoshonitic series. Their trace element patterns resemble the Jindong samples, but are characterized by significantly negative U anomalies in mafic rocks. They also have elevated MgO, Ni, Co, Cr, Rb, Ba, Sr, and low Al2O3 and Na2O contents at a given SiO2 concentration compared with the Jindong plutons, and are typified by highly radiogenic Sr and unradiogenic Nd and Pb isotopic compositions: [(87Sr/86Sr)i = 0.71096-0.71290, (143Nd/144Nd)i = 0.511641-0.511681, (εNd)i = - 13

  2. Mixing and mingling in the evolution of andesite dacite magmas; evidence from co-magmatic plutonic enclaves, Taupo Volcanic Zone, New Zealand

    Science.gov (United States)

    Cole, J. W.; Gamble, J. A.; Burt, R. M.; Carroll, L. D.; Shelley, D.

    2001-10-01

    within the magma chambers beneath a typical volcanic arc.

  3. Petrology and radiogeology of the Stripa pluton

    Energy Technology Data Exchange (ETDEWEB)

    Wollenberg, H.; Flexser, S.; Andersson, L.

    1980-12-01

    Both the quartz monzonite and the metavolcanic leptite which it intruded are strongly fractured. Two stages of fracture filling are evident; an earlier stage encompassing quartz, sericite, feldspar, epidote, and chlorite, and a later stage dominated by carbonate minerals. The Stripa quartz monozite is chemically and mineralogically distinct from other plutons in the region. Muscovite is the predominant mica in the quartz monzonite; biotite has been altered to chlorite, hornblende is absent, and accessory minerals are scarce. In contrast, in other plutons in the Stripa region, biotite and hornblende are prominent mafic minerals and accessory minerals are abundant. The Stripa quartz monzonite is also considerably more radioactive than the the leptite and other plutons in the region. Uranium and thorium abundances are both approx. 30 ppM, considerably higher than in normal granitic rocks where the thorium-to-uranium ratio generally exceeds 2. Potassium-argon dating of muscovite from the Stripa quartz monzonite indicates that this rock may be older, at 1691 million years than granitic rock of the neighboring Gusselby and Kloten massifs, whose ages, based on K-Ar dating of biotite, are respectively 1604 and 1640 m.y. Heat flow and heat productivity considerations show that although Stripa quartz monzonite contains high abundances of radioelements, the pluton has little efect on the regional heat flow. If it occurs in a layered plutonic setting, it is not more than 1.5 km thick; otherwise it may comprise a stock, dike, or border phase that is relatively small compared with the large granitic plutons exposed in the region.

  4. Petrology and radiogeology of the Stripa pluton

    International Nuclear Information System (INIS)

    Both the quartz monzonite and the metavolcanic leptite which it intruded are strongly fractured. Two stages of fracture filling are evident; an earlier stage encompassing quartz, sericite, feldspar, epidote, and chlorite, and a later stage dominated by carbonate minerals. The Stripa quartz monozite is chemically and mineralogically distinct from other plutons in the region. Muscovite is the predominant mica in the quartz monzonite; biotite has been altered to chlorite, hornblende is absent, and accessory minerals are scarce. In contrast, in other plutons in the Stripa region, biotite and hornblende are prominent mafic minerals and accessory minerals are abundant. The Stripa quartz monzonite is also considerably more radioactive than the the leptite and other plutons in the region. Uranium and thorium abundances are both approx. 30 ppM, considerably higher than in normal granitic rocks where the thorium-to-uranium ratio generally exceeds 2. Potassium-argon dating of muscovite from the Stripa quartz monzonite indicates that this rock may be older, at 1691 million years than granitic rock of the neighboring Gusselby and Kloten massifs, whose ages, based on K-Ar dating of biotite, are respectively 1604 and 1640 m.y. Heat flow and heat productivity considerations show that although Stripa quartz monzonite contains high abundances of radioelements, the pluton has little efect on the regional heat flow. If it occurs in a layered plutonic setting, it is not more than 1.5 km thick; otherwise it may comprise a stock, dike, or border phase that is relatively small compared with the large granitic plutons exposed in the region

  5. A dearth of intermediate melts at subduction zone volcanoes and the petrogenesis of arc andesites.

    Science.gov (United States)

    Reubi, Olivier; Blundy, Jon

    2009-10-29

    Andesites represent a large proportion of the magmas erupted at continental arc volcanoes and are regarded as a major component in the formation of continental crust. Andesite petrogenesis is therefore fundamental in terms of both volcanic hazard and differentiation of the Earth. Andesites typically contain a significant proportion of crystals showing disequilibrium petrographic characteristics indicative of mixing or mingling between silicic and mafic magmas, which fuels a long-standing debate regarding the significance of these processes in andesite petrogenesis and ultimately questions the abundance of true liquids with andesitic composition. Central to this debate is the distinction between liquids (or melts) and magmas, mixtures of liquids with crystals, which may or may not be co-genetic. With this distinction comes the realization that bulk-rock chemical analyses of petrologically complex andesites can lead to a blurred picture of the fundamental processes behind arc magmatism. Here we present an alternative view of andesite petrogenesis, based on a review of quenched glassy melt inclusions trapped in phenocrysts, whole-rock chemistry, and high-pressure and high-temperature experiments. We argue that true liquids of intermediate composition (59 to 66 wt% SiO(2)) are far less common in the sub-volcanic reservoirs of arc volcanoes than is suggested by the abundance of erupted magma within this compositional range. Effective mingling within upper crustal magmatic reservoirs obscures a compositional bimodality of melts ascending from the lower crust, and masks the fundamental role of silicic melts (>/=66 wt% SiO(2)) beneath intermediate arc volcanoes. This alternative view resolves several puzzling aspects of arc volcanism and provides important clues to the integration of plutonic and volcanic records.

  6. Multiphase groundwater flow near cooling plutons

    Science.gov (United States)

    Hayba, D.O.; Ingebritsen, S.E.

    1997-01-01

    We investigate groundwater flow near cooling plutons with a computer program that can model multiphase flow, temperatures up to 1200??C, thermal pressurization, and temperature-dependent rock properties. A series of experiments examines the effects of host-rock permeability, size and depth of pluton emplacement, single versus multiple intrusions, the influence of a caprock, and the impact of topographically driven groundwater flow. We also reproduce and evaluate some of the pioneering numerical experiments on flow around plutons. Host-rock permeability is the principal factor influencing fluid circulation and heat transfer in hydrothermal systems. The hottest and most steam-rich systems develop where permeability is of the order of 10-15 m2. Temperatures and life spans of systems decrease with increasing permeability. Conduction-dominated systems, in which permeabilities are ???10-16m2, persist longer but exhibit relatively modest increases in near-surface temperatures relative to ambient conditions. Pluton size, emplacement depth, and initial thermal conditions have less influence on hydrothermal circulation patterns but affect the extent of boiling and duration of hydrothermal systems. Topographically driven groundwater flow can significantly alter hydrothermal circulation; however, a low-permeability caprock effectively decouples the topographically and density-driven systems and stabilizes the mixing interface between them thereby defining a likely ore-forming environment.

  7. Petrology and radiogeology of the Stripa pluton

    Energy Technology Data Exchange (ETDEWEB)

    Wollenberg, Harold; Flexser, Steve; Andersson, Lennart

    1980-12-01

    To better define the character of the rock encompassing the thermomechanical and hydrological experiments at the Stripa mine in central Sweden, and to help determine the size of the Stripa pluton, detailed studies were conducted of the petrology and radiogeology of the quartz monzonite and adjacent rocks. Petrologic studies emphasized optical petrography, with supplementary X-ray diffraction, X-ray fluorescence and microprobe analyses. Radiogeologic investigations were based primarily on surface and underground gamma-ray spectrometric measurements of uranium, thorium and potassium, supplemented by laboratory gamma spectrometric analyses and fission-track radiographic determinations of the locations and abundance of uranium in the rock matrix. Both the quartz monzonite and the metavolcanic leptite which it intruded are strongly fractured. Two stages of fracture filling are evident; an earlier stage encompassing quartz, sericite, feldspar, epidote, and chlorite, and a later stage dominated by carbonate minerals. The Stripa quartz monzonite is chemically and mineralogically distinct from other plutons in the region. Muscovite is the predominant mica in the quartz monzonite; biotite has been altered to chlorite, hornblende is absent, and accessory minerals are scarce. In contrast, in other plutons in the Stripa region biotite and hornblende are prominent mafic minerals and accessory minerals are abundant. The Stripa quartz monzonite is also considerably more radioactive than the leptite and other plutons in the region. Uranium and thorium abundances are both- 30 ppm, considerably higher than in "normal" granitic rocks where the thorium-to-uranium ratio generally exceeds 2. Potassium-argon dating of muscovite from the Stripa quartz monzonite indicates that this rock may be older, at 1691 million years than granitic rock of the neighboring Gusselby and Kloten massifs, whose ages, based on K-Ar dating of biotite, are respectively 1604 and 1640 m.y. Heat flow and heat

  8. Correct nomenclature for the Angadimogar pluton, Kerala, southwestern India

    Indian Academy of Sciences (India)

    H M Rajesh

    2006-04-01

    The proper usage of modal composition and geochemical classification of granitoids is discussed for assigning a proper nomenclature for the Angadimogar pluton,Kerala,southwestern India.This discussion is mainly aimed at addressing questions concerning the nomenclature of Angadimogar pluton (syenite vs. granite).Modal composition and whole-rock XRD data clearly show that the pluton exposed near Angadimogar is a quartz-syenite and its geochemistry is typical of a ferroan, metaluminous,alkali (A-type)granitoid.

  9. Petrological studies of plutonic rocks of Ecuador

    International Nuclear Information System (INIS)

    The feldspars of many tonalitic plutonic rocks in the coastal regions and West Andean regions are zoned. This leads to the conclusion that they are relatively flat intrusions and to some extent transition rocks in the subvulcanite direction. This is in accordance with the genetic and chronological relationship between plutonites and the surrounding vulcanites of the Basic Igreous Complex (BIC). The composition of representative minerals, e.g. alkali feldspar, plagioclase feldspar, biotite, chlorite, and amphibole has been determined as well as the age of plutonite samples by the K/Ar dating method. (DG)

  10. Petrología del magmatismo de arco pre-deformacional en el cordón de El Realito y la zona norte del plutón La Escalerilla. Sierra de San Luis Petrology of the pre-deformational arc magmatism in the Cordón de El Realito and in the northern zone of the La Escalerilla pluton, Sierra de San Luis

    Directory of Open Access Journals (Sweden)

    N. Brogioni

    2005-09-01

    Escalerilla pluton are the most extensive. High-K calcalkaline magmas intrude low- to medium-grade metasedimentary rocks in both areas. The oldest event is represented by arc-type, metaluminous Pl+Bt+Ep±Hbl±Kf granodiorites, tonalites and scarce diorites, carrying numerous enclaves of gabbroic to monzodioritic composition. Chemical abundances and evolutionary trends of these rocks correlate well with those of the metaluminous arcsequence of Sierras de Chepes and Los Llanos in La Rioja province. The youngest event consists of peraluminous and collisionrelated Kf+Pl+Ms±Bt±Grt, leucocratic monzogranites, intruding the arc-sequence. The monzogranites do not appear to be generated as a result of differentiation from the metaluminous sequence, although both magmatic suites are part of the Famatinian subductionrelated arc. The peraluminous magmatism displays the typical vertical evolutionary trend of felsic peraluminous granitoids and is interpreted as derived mainly from partial melting of Ms-metapelites and greywackes. Some geochemical abundances and HREE patterns of the La Escalerilla stock are probably controlled by differences in the source. The Famatinian regional metamorphism and shearing strongly modified the arc-sequence rocks fabrics. However, the magmatic rocks preserved their whole chemical signatures except for the most basic members of the series which display spreading in evolutionary trends and increased peraluminosity. The pre-deformational peraluminous melts in both areas are clearly distinct from those of some syn-kinematic Ms±Bt±Grt leucogranitoids which crop out in the Eastern Basement Complex of the Sierra.

  11. A statistical approach to the volcanic-plutonic connection

    Science.gov (United States)

    Schoene, B.; Keller, C.; Samperton, K. M.; Barboni, M.; Husson, J. M.

    2013-12-01

    The geochemical relationship between volcanic and plutonic rocks - whether the two are geochemically identical, or if the choice between eruption or intrusion is correlated with magma chemistry - represents a major unanswered question in igneous petrology. In one endmember scenario, felsic to intermediate plutons represent the unerupted residue from which crystal-poor eruptible melts are extracted. At the other end of the spectrum, it is argued that a nearly the entire volume of magma is evacuated during eruption, and that the probability of eruption versus intrusion is instead largely a function of magma flux. In the first scenario, parental magmas originating at depth experience substantial fractionation during volcanic melt extraction, leading to complementary volcanic and plutonic reservoirs. In the second endmember scenario, volcanic/plutonic fractionation in the middle to upper crust is negligible, predicting no geochemical difference between volcanic and plutonic rocks. A third endmember scenario that is not exclusive from the other two predicts differences between volcanic and plutonic rocks if geochemical characteristics are correlated with the eventual eruptibility of magma. Deciphering the relative importance of each of these models is important for understanding both the long-term geochemical balance of the crust and mantle due to increased erosion and recycling of volcanic rocks and also for understanding magma transport dynamics. We have compared the geochemistry of ~500,000 volcanic and plutonic rocks from a range of tectonic settings by Monte Carlo bootstrap analysis in order to produce maximally representative average compositions. The results indicate that while volcanic and plutonic rocks in general show remarkably similar major element trends, intermediate to felsic plutonic rocks, for a given silica content, display clear enrichments in Sr and Ba and depletions in Zr, Hf, and HREEs relative to their volcanic equivalents. More subtly

  12. Late Cretaceous ARC to MORB compositional switch in the Quebradagrande Complex, Colombian Andes: understanding the long term tectonic evolution of a magmatic arc.

    Science.gov (United States)

    Jaramillo, J. S.; Cardona, A.; Zapata, S.; Valencia, V.

    2014-12-01

    The spatial and compositional characters of arc rocks are sensible markers of the tectonic changes experienced by convergent margins and therefore provide a fundamental view to the continuous tectonic evolution of active margins. The Early to Late Cretaceous tectonic evolution of the Northern Andes have been related to the growth and accretion of different continental and oceanic arc systems that were juxtaposed at the beginning of the Andean Orogeny in the Late Cretaceous. The Quebradagrande Complex is a tectonostratigraphic unit made of mafic to intermediate plutonic rocks, basic to intermediate volcanic flows and associated marine sedimentary rocks that have been related to a single Albian arc or back-arc environment that discontinuously outcrops along the western margin of the Central Cordillera of Colombia. New field, geochronological and geochemical data from the plutonic and volcanic rocks of the Quebradagrande complex shows that the pre-90-80 Ma volcanic arc rocks are intruded by ca. 90 Ma pyroxene gabbroic and hornblende dioritic plutons with medium to pegmatitic grain size characterized by a contrasting MORB-type signature. We related the compositional change to a transient modification of the convergent margin system, where and extensional roll-back related configuration or the subduction of an oceanic ridge allows the flux of the astenospheric mantle. This continental magmatic arc was subsequently deformed due to the collision and accretion of an allocthonous oceanic arc that migrate from the southeast Pacific at the beginning of the Andean orogeny.

  13. Bulk arc strain, crustal thickening, magma emplacement, and mass balances in the Mesozoic Sierra Nevada arc

    Science.gov (United States)

    Cao, Wenrong; Paterson, Scott; Saleeby, Jason; Zalunardo, Sean

    2016-03-01

    Quantifying crustal deformation is important for evaluating mass balance, material transfer, and the interplay between tectonism and magmatism in continental arcs. We present a dataset of >650 finite strain analyses compiled from published works and our own studies with associated structural, geochronologic, and geobarometric information in central and southern Sierra Nevada, California, to quantify the arc crust deformation. Our results show that Mesozoic tectonism results in 65% arc-perpendicular bulk crust shortening under a more or less plane strain condition. Mesozoic arc magmatism replaced ∼80% of this actively deforming arc crust with plutons requiring significantly greater crustal thickening. We suggest that by ∼85 Ma, the arc crust thickness was ∼80 km with a 30-km-thick arc root, resulting in a ∼5 km elevation. Most tectonic shortening and magma emplacement must be accommodated by downward displacements of crustal materials into growing crustal roots at the estimated downward transfer rate of 2-13 km/Myr. The downward transfer of crustal materials must occur in active magma channels, or in "escape channels" in between solidified plutons that decrease in size with time and depth resulting in an increase in the intensity of constrictional strain with depth. We argue that both tectonism and magmatism control the thickness of the crust and surface elevation with slight modification by surface erosion. The downward transported crustal materials initially fertilize the MASH zone thus enhancing to the generation of additional magmas. As the crustal root grows it may potentially pinch out and cool the mantle wedge and thus cause reduction of arc magmatism.

  14. Evidence for Active Subduction Beneath Gibraltar

    Science.gov (United States)

    Gutscher, M.; Malod, J. A.; Rehault, J.; Contrucci, I. M.; Klingelhoefer, F.; Victor, L. M.; Spakman, W.

    2002-12-01

    The Gibraltar arc encompasses the Betic - Rif mountain belts with outward directed thrusting, surrounding a zone of strong Neogene subsidence and crustal thinning in the Western Alboran Sea. The SISMAR marine seismic survey conducted in April 2001 acquired over 3000 km of 360-channel seismic data with a 4.5 km long streamer and 1000 km of wide-angle data recorded by ocean bottom seismometers (OBS), completely spanning the actively deforming region between the margins of Portugal and northwest Morocco. We report on results from this seismic survey which reveal a thick chaotic sedimentary mass west of Gibraltar to be an actively deforming accretionary wedge, with east dipping thrust faults disrupting the seafloor and soleing out to an east dipping decollement. New travel-time tomographic results image a continuous east dipping body with high seismic velocities (i.e. a cold slab of oceanic lithosphere) descending from the Atlantic domain of the Gulf of Cadiz, passing through intermediate depth (60 - 120 km) seismicity beneath the Gibraltar Arc and Western Alboran Sea, and merging with a region of deep focus earthquakes 600 - 660 km below Granada Spain. Together these provide compelling evidence for an active east dipping subduction zone. Slab rollback towards the west provides a plausible mechanism for extension and subsidence in the Alboran Sea, while the associated westward advance of the Gibraltar Arc drives compressional deformation in the accretionary wedge where active mud volcanoes have recently been discovered. Active subduction beneath Gibraltar should be considered as a possible candidate for the source of the destructive Lisbon great earthquake (M 8.5-9) and tsunami of 1755 which ravaged the coast of the Gulf of Cadiz.

  15. Geophysical modeling and structure of Ushuaia Pluton, Fuegian Andes, Argentina

    Science.gov (United States)

    Peroni, Javier Ignacio; Tassone, Alejandro Alberto; Menichetti, Marco; Cerredo, María Elena

    2009-10-01

    Within the area of Ushuaia Bay (Tierra del Fuego, southernmost South America) the deformed Lower Cretaceous sedimentary rocks of Yahgán Formation host the Ushuaia Pluton. The intrusive body is oval in map view; it is compositionally varied with rocks ranging from the ultrabasic to the mesosiliceous realm. The emplacement time is constrained within the Albian-Cenomanian span by new amphibole K/Ar data. Meso- and microstructures of Ushuaia Pluton and its host indicate a synkinematic emplacement with a dominant extensional component. A set of transcurrent and normal faults related to the sinistral strike-slip Beagle Channel Fault System affects the pluton and its host. On the basis of aeromagnetic data combined with field information, a new model is presented for the Ushuaia Pluton. Modeling results fit well with a laccolithic body with an estimated volume of around 111 km 3. The model pluton cross-section displays a central zone with an average thickness of 2000 m which progressively thins toward the margins (˜ 500 m) and a southern root which reaches 5000 m deep. The combined structural and geophysical model supports a transtensive scenario for the Ushuaia Pluton emplacement at Early-Late Cretaceous boundary.

  16. Temporal and Spatial Fluctuations in Ancestral Northern Cascade Arc Magmatism from New LA-ICP-MS U-Pb Zircon Dating

    Science.gov (United States)

    McCallum, I. S.; Mullen, E.; Jean-Louis, P.; Tepper, J. H.

    2015-12-01

    Mt. Baker and the adjacent Chilliwack batholith (MBC focus) in NW Washington preserve the longest magmatic record in the Cascade Arc, providing an excellent natural laboratory for examining the spatial, temporal and geochemical evolution of Cascade magmatism and links to tectonic processes. We present new U-Pb zircon LA-ICP-MS ages for 14 samples from MBC and neighboring regions of the north Cascades. The new results are up to 8 Myr different from previous K-Ar ages, illustrating the need for new age determinations in the Cascades. A maximum age of 34.74±0.24 Ma (2σ) (Post Creek stock) is consistent with 35-40 Ma ages for arc inception in the southern Cascades. The most voluminous MBC plutons cluster at 32-29 Ma, consistent with an early flare-up that also coincides with intrusion of the Index batholith farther south (2 samples at 33.26±0.19, 33.53±0.15 Ma). This flare-up is absent in the northernmost Cascades where the oldest pluton (Fall Creek stock) is 6.646±0.046 Ma, 4 Myr younger than previously cited. Earliest Cascade magmatism is progressively younger to the north of MBC, possibly tracing the northerly passage of the slab edge. MBC activity was continuous to 22.75±0.17 Ma (Whatcom Arm), marking the initiation of an 11 Myr hiatus. Magmatism resumed at 11.33±0.08 Ma (Indian Creek) and continued to the modern Mt. Baker cone, defining a pattern of southwesterly migration over ~55 km that may be attributable to slab rollback and arc rotation (e.g. Wells & McCaffrey 2013). Uniformity of the rate and direction of migration implies that rollback and rotation began at least 11 Myr ago. Post-hiatus magmas show distinct geochemical and petrologic characteristics including a major Pb isotopic shift. The 2.430±0.016 Ma Lake Ann stock contains 4.2 Ma zircon antecrysts, recording prolonged activity in that area. The 1.165±0.013 Ma Kulshan caldera ignimbrite contains ~200 Ma inherited zircons that may provide the first direct record of Wrangellian basement beneath

  17. Determinism beneath Quantum Mechanics

    CERN Document Server

    Hooft, G

    2002-01-01

    Contrary to common belief, it is not difficult to construct deterministic models where stochastic behavior is correctly described by quantum mechanical amplitudes, in precise accordance with the Copenhagen-Bohr-Bohm doctrine. What is difficult however is to obtain a Hamiltonian that is bounded from below, and whose ground state is a vacuum that exhibits complicated vacuum fluctuations, as in the real world. Beneath Quantum Mechanics, there may be a deterministic theory with (local) information loss. This may lead to a sufficiently complex vacuum state, and to an apparent non-locality in the relation between the deterministic ("ontological") states and the quantum states, of the kind needed to explain away the Bell inequalities. Theories of this kind would not only be appealing from a philosophical point of view, but may also be essential for understanding causality at Planckian distance scales.

  18. Adakitic-like magmatism in western Ossa-Morena Zone (Portugal): Geochemical and isotopic constraints of the Pavia pluton

    Science.gov (United States)

    Lima, S. M.; Neiva, A. M. R.; Ramos, J. M. F.

    2013-02-01

    Granitic rocks are a major component of the Earth's continental crust and occur in a wide variety of tectonic settings. Their chemical and isotopic characterization is crucial to the recognition of the potential sources and mechanisms involved in their generation. In this study, we present the first whole rock chemical and isotopic (Sr-Nd-O) data for the Pavia pluton (328-317 Ma), located near the western border of the Ossa-Morena Zone (Évora Massif, Portugal). Major and trace element geochemistry suggests that the different granitic phases composing this intrusive body (enclaves, granites (s.l.) and crosscutting dikes) represent independent magma pulses and the majority is similar to TTGs and adakites. The little Sr-Nd-O isotopic variation, with (87Sr/86Sr)328 = 0.70428-0.70560, ɛNd328 ranging between - 3.4 and + 0.4 and δ18O varying from + 5.6‰ to + 8.4‰ implies an isotopically similar protolith for all phases. The most viable mechanism for the generation of the Pavia pluton adakitic-like magmatism is assimilation-fractional crystallization of a mantle-derived magma. This mechanism was also invoked to explain the genesis of other plutons within the Évora Massif but they have a distinct chemistry (typical arc calc-alkaline rocks). The chemical differences between them and the Pavia pluton granitic rocks are interpreted as the result of lower degrees of crustal assimilation and higher degrees of contamination of mantle-derived magmas by the sinking slab (after subduction blocking and subsequent slab break-off).

  19. Arc Statistics

    CERN Document Server

    Meneghetti, M; Dahle, H; Limousin, M

    2013-01-01

    The existence of an arc statistics problem was at the center of a strong debate in the last fifteen years. With the aim to clarify if the optical depth for giant gravitational arcs by galaxy clusters in the so called concordance model is compatible with observations, several studies were carried out which helped to significantly improve our knowledge of strong lensing clusters, unveiling their extremely complex internal structure. In particular, the abundance and the frequency of strong lensing events like gravitational arcs turned out to be a potentially very powerful tool to trace the structure formation. However, given the limited size of observational and theoretical data-sets, the power of arc statistics as a cosmological tool has been only minimally exploited so far. On the other hand, the last years were characterized by significant advancements in the field, and several cluster surveys that are ongoing or planned for the near future seem to have the potential to make arc statistics a competitive cosmo...

  20. Modeling Arcs

    CERN Document Server

    Insepov, Zeke; Veitzer, Seth; Mahalingam, Sudhakar

    2011-01-01

    Although vacuum arcs were first identified over 110 years ago, they are not yet well understood. We have since developed a model of breakdown and gradient limits that tries to explain, in a self-consistent way: arc triggering, plasma initiation, plasma evolution, surface damage and gra- dient limits. We use simple PIC codes for modeling plasmas, molecular dynamics for modeling surface breakdown, and surface damage, and mesoscale surface thermodynamics and finite element electrostatic codes for to evaluate surface properties. Since any given experiment seems to have more variables than data points, we have tried to consider a wide variety of arcing (rf structures, e beam welding, laser ablation, etc.) to help constrain the problem, and concentrate on common mechanisms. While the mechanisms can be comparatively simple, modeling can be challenging.

  1. Metamorphism and plutonism in the Quetico Belt, Superior Province, N.W. Ontario

    Science.gov (United States)

    Percival, J. A.

    1986-01-01

    The Quetico Belt lies between the metavolcanic Wawa-Shebandowan and Wabigoon Belts. It consists of marginal metasedimentary rocks and central pelitic, gneissic and plutonic rocks. Metamorphism is Barrovian, at depths less than 10 km, and grade increases from margins to core of the belt: the outermost pelites are at chlorite-muscovite grade; inward a garnet-andalusite zone formed throughout the inner margin; and the central zone ranges form garnet-andalusite in the west and garnet-sillimanite-muscovite to garnet-sillimanite-cordierite and rare kyanite 6 to 150 km to the east. This increase is correlated with granitic intrusives. Migmatites in the core have intrusive leucosomes in the west and locally derived ones in the east. Isograd surfaces are steep where the belt is narrow and dip gently where it is wide. The Quetico Park intrusive complex of the central region of the Quetico Belt shows a zonation across it 20 to 50 km width from older, medium grained biotite composition to younger, coarse to pegmatitic granitic composition. Sediment of the Quetico basin had its source in the bordering metavolcanic belts and was deposited ca. 2.75 to 2.70 Ga ago. Boundaries of the belt dip inward, so it essentially is a graben of inter-arc or back-arc type.

  2. Shear Wave Splitting Observations Beneath Uturuncu Volcano, Bolivia

    Science.gov (United States)

    Sims, N. E.; Christensen, D. H.; Moore-Driskell, M. M.

    2015-12-01

    Anisotropy in the upper mantle is often associated with mantle flow direction through the lattice preferred orientation of anisotropic minerals such as olivine in the upper mantle material. The flow of the mantle around subduction zones can be particularly complex, and thus difficult to explain. Because of its relationship to anisotropy, analysis of shear wave splitting measurements can help to answer questions regarding the upper mantle flow that surrounds subducting slabs. Here we present SK(K)S shear wave splitting measurements from a temporary broadband network (PLUTONS) of 33 stations deployed from April 2009 to October 2012 on the Altiplano plateau around Uturuncu volcano in Bolivia. The stations are spaced 10-20 km apart, providing a high spatial resolution of the region of the mantle directly below Uturuncu volcano. Despite the lack of numerous splitting results to analyze, preliminary measurements indicate a relatively consistent pattern of fast-polarization directions in a NW-SE orientation of about N80ºW. We think that it is likely that these observations come from anisotropy in the mantle wedge above the subducting Nazca plate indicating a direction of flow in the mantle wedge that is sub-parallel to the subduction direction of the Nazca plate. Although W-E flow beneath the subducting Nazca plate cannot be completely ruled out, these results appear to be consistent with the simple model of two-dimensional corner flow in the mantle wedge and slab-entrained mantle flow beneath the slab.

  3. Seismological constraints and speculations on Banda arc tectonics

    Science.gov (United States)

    McCaffrey, Robert

    Fault plane solutions of shallow earthquakes show that the collision of the Australian continent with the Banda Arc shortens the overriding Indonesian plate in the north-south direction and elongates it in the east-west direction by a combination of strike-slip and thrust faulting. The shallow tectonics and the distribution of deep earthquakes beneath the Banda Basin both indicate that two plates subduct beneath the Banda Arc; the Australia-Indian Ocean plate northward beneath the Java Trench, Timor Trough, and Aru Troughs, and the Bird's Head southwestward beneath the Seram Trough. The slab of the Indian Ocean plate forms a westward plunging synform beneath the Banda Basin. Its unusual shape in interpreted to have been caused by subduction beneath the westward moving Pacific plate which transported slivers of New Guinea into the back arc. The lithosphere of the Bird's Head was subducted beneath the Seram Trough and now reaches 300 km depth. At the surface decoupling between Australian and the Bird's Head probably occurs by left-lateral strike slip at the Tarera-Aiduna fault zone in western Irian Jaya and by convergence in the New Guinea fold-and-thrust belt. Seismic quiescence occurs at depths of 50 to 380 km beneath both Timor and the inactive volcanic arc to its north but the efficient propagation of S-waves through the same volume suggests that the lithospheric slab is continuous there. The lack of seismic and volcanic activity may result from removal of part of the Australian continental crust prior to subduction of the lower part of the lithosphere. This crust was stacked up to form the island of Timor.

  4. Geochemical and Sr-Nd-Pb-O isotope composition of granitoids of the Early Cretaceous Copiapó plutonic complex (27°30'S), Chile

    Science.gov (United States)

    Marschik, Robert; Fontignie, Denis; Chiaradia, Massimo; Voldet, Pia

    2003-10-01

    Early Cretaceous plutonic rocks exposed south of Copiapó form part of the Coastal Batholith of northern Chile. These rocks intrude arc-derived volcanic and volcaniclastic rocks and marine limestones that were deposited in the Early Cretaceous Atacama backarc basin. The Copiapó plutonic complex consists mainly of calc-alkaline, medium- to coarse-grained diorite, granodiorite, tonalite, monzodiorite, and quartz monzonite. The plutonic rocks are subalkaline to alkaline, metaluminous, magnetite-series, volcanic arc, I-type granitoids. Batholithic magmas are a heat, potential fluid, metal, and sulphur source for the hydrothermal iron oxide-rich Cu-Au mineralization in the Candelaria-Punta del Cobre district. Ore-related hydrothermal alteration affected large portions of the Copiapó complex. The least altered batholithic rocks have initial 87Sr/ 86Sr of 0.703070-0.703231; initial 143Nd/ 144Nd of 0.512733-0.512781; and 206Pb/ 204Pb, 207Pb/ 204Pb, and 208Pb/ 204Pb of 18.428-18.772, 15.550-15.603, and 38.127-38.401, respectively. The δ18O values for these rocks range from +6.9 to +8.6‰. Isotope signatures and trace element distributions suggest that the magmas are mantle derived. A subduction fluid-modified mantle source may explain the geochemical characteristics of the Copiapó complex. The ascent of magmas occurred along deep-rooted structures without significant crustal contamination, though minor contamination by relatively young (e.g. Jurassic) igneous rocks during ascent is possible. Intrusive rocks with high-K to shoshonitic characteristics probably represent residual liquids of less evolved magmas. The regional geologic context suggests that the plutons of the Copiapó complex were emplaced at a relatively shallow crustal level of 2-3 km.

  5. Mid-Neoproterozoic ridge subduction and magmatic evolution in the northeastern margin of the Indochina block: Evidence from geochronology and geochemistry of calc-alkaline plutons

    Science.gov (United States)

    Qi, Xuexiang; Santosh, M.; Zhao, Yuhao; Hu, Zhaocuo; Zhang, Chao; Ji, Fengbao; Wei, Cheng

    2016-04-01

    The mid-Neoproterozoic medium- to high-K calc-alkaline magmatic rocks in the northeastern margin of the Indochina block, SW China, provide important insights into the relationship of the Indochina block with the Gondwana supercontinent. Here we report zircon LA-ICP-MS U-Pb data from the early and late stage plutons which yield weighted mean 206Pb/238U ages of 765 Ma and 732-739 Ma suggesting mid-Neoproterozoic emplacement. The zircon εHf(t) values show a range of - 3.2 to + 2.4 (average + 0.1 ± 0.9) with TDMC of 1510 to 1870 Ma for the early plutons, and - 5.4 to + 5.1 (average + 2.1 to - 3.9) with TDMC of 1366 to 1985 Ma for late plutons. Both groups show similar geochemical characteristics including high Mg#, enrichment of LILE and LREE, slight negative Eu anomalies, and strongly negative Nb, Ta and Ti anomalies, with all the samples falling within the continental/island arc field in tectonic discrimination diagrams. These features suggest that the early and late stage magmas were produced by the mixing of mantle-derived magma and crust-derived magma in different proportion within an active continental margin, in subduction-related continental-arc tectonic setting. The linear zoning and roughly parallel distribution of the two generations of intrusions with a hiatus of 20 Ma might suggest an episode of ridge subduction with asthenosphere upwelling through the slab window that generated the second phase of plutons.

  6. SHRIMP U-Pb dating and geochemistry of the Cretaceous plutonic rocks in the Korean Peninsula: A new tectonic model of the Cretaceous Korean Peninsula

    Science.gov (United States)

    Kim, Sung Won; Kwon, Sanghoon; Park, Seung-Ik; Lee, Changyeol; Cho, Deung-Lyong; Lee, Hong-Jin; Ko, Kyoungtae; Kim, Sook Ju

    2016-10-01

    The Cretaceous tectonomagmatism of the Korean Peninsula was examined based on geochemical and geochronological data of the Cretaceous plutonic rocks, along with distribution of volcano-sedimentary nonmarine N- to NE-trending fault bounded sedimentary basins. We conducted sensitive high-resolution ion microprobe (SHRIMP) zircon U-Pb ages and whole-rock geochemical compositions of 21 Cretaceous plutonic rocks, together with previously published data, from the central to southern Korean Peninsula. Four age groups of plutonic rocks were identified: Group I (ca. 119-106 Ma) in the northern to central area, Group II (ca. 99-87 Ma) in the central southern area, Group III (ca. 85-82 Ma) in the central to southern area, and Group IV (ca. 76-67 Ma) in the southernmost area. These results indicate a sporadic trenchward-younging trend of the Cretaceous magmatism in the Korean Peninsula. The Group I, II, and III rocks are dominated by high-K calc-alkaline I-type rocks with rift-related A-type granitoids. In contrast, the Group IV rocks are high-K calc-alkaline I-type plutonic rocks with no A-type rocks. The geochemical signatures of the entire groups indicated LREEs (light rare earth elements) enrichments and negative Nb, Ta, and Ti anomalies, indicating normal arc magmatism. A new tectonic model of the Cretaceous Korean Peninsula was proposed based on temporal and spatial distribution of the Cretaceous plutons represented by four age groups; 1) magmatic quiescence throughout the Korean Peninsula from ca. 160 to 120 Ma, 2) intrusions of the I- and A-type granitoids in the northern and central Korean Peninsula (Group I plutonic rocks from ca. 120 to 100 Ma) resulted from the partial melting of the lower continental crust due to the rollback of the Izanagi plate expressed as the conversion from flat-lying subduction to normal subduction. The Gyeongsang nonmarine sedimentary rift basin in the Korean Peninsula and adakite magmatism preserved in the present-day Japanese Islands

  7. Geochronology and Geochemical Characteristics of the Early Mesozoic Tangquan Pluton in Southwestern Fujian and Its Tectonic Implications

    Institute of Scientific and Technical Information of China (English)

    MAO Jianren; HU Qing; XU Naizheng; XIE Fanggui; TAO Kuiyuan

    2003-01-01

    The Tangquan granodioritic pluton in Datian County, southwestern Fujian, China, which extends in a NE direction with an exposed area of about 130 km2, used to be considered a product of Early Cretaceous magmatism. The present study suggests for the first time that the pluton was formed in the Early Jurassic by using multiple methods for isotopic dating, which give zircon U-Pb ages of 186.8 Ma and 179.0 Ma, Rb-Sr isochron age of 162.02(4.5 Ma, and biotite 40Ar/39Ar plateau age of 158.1(0.7 Ma. The cooling rate for the pluton was relatively low (4.76°C/Ma) during the early stage (183(162 Ma) because of the compressional environment. It was emplaced in a higher cooling rate (50°C/Ma) in an extensional environment during the later stage (162(158 Ma). The granodiorites are metaluminous(peraluminous, relatively enriched in Na2O and depleted in K2O, and characteristic of I-type granites of crust-mantle mixed sources. They are moderately enriched in Rb, Th, Hf and LREE, and depleted in Ti, Nb, Ta and Sr, and have geochemical features of cal-alkaline rocks of an island arc or active continental margin. Their (87Sr/86Sr)i ratio varies from 0.70769 to 0.70822, εNd(t) from -9.68 to -10.07 and TDM from 1.52 to 1.55 Ga. They were formed by mixing of mantle-derived mafic magma with the granitic magma resulting from partial melting of crust-derived materials in an upwelling of the asthenospheric mantle in South China during the Early Mesozoic.

  8. Towards Understanding the Sunda and Banda Arcs

    Science.gov (United States)

    Hall, R.

    2014-12-01

    The present change from oceanic subduction beneath the Sunda Arc to arc-continent collision east of Sumba is merely the latest stage in a complex collision history that began more than 20 million years ago. Understanding present-day tectonics requires restoring the pre-collisional margins and unravelling the history of the entire Sunda-Banda Arc, not just a segment centred on Sumba. Seismic tomography displays a single folded slab beneath the Banda Arc around which mantle has flowed. Above this is a wide actively deforming zone of complex geology. Australian crust was first added to the Sunda margin in the Cretaceous. Early Miocene closure of the oceanic gap north of Australia led to further additions of continental crust during collision of the Sula Spur. Few microcontinental fragments were sliced from New Guinea as commonly interpreted. Most are parts of the Sula Spur fragmented by extension and strike-slip faulting during development of subduction zones and rollback into the Banda embayment. Many metamorphic 'basement' rocks are significantly younger than expected. They were metamorphosed during multiple episodes of extension which also exhumed the sub-lithospheric mantle, melted the deep continental crust, created new ocean basins, and dispersed continental crust throughout the inner and outer arc, and forearc, so that in places Australian crust is colliding with Australian crust. Thus, many of the arc volcanoes are built on continental not oceanic crust, and sediment eroded from recently emergent islands is compositionally different to subducted sediment that contributed to arc magmas. The published literature is inadequate. New fieldwork and data are required, particularly in remote areas, with integration of information from a variety of sources (e.g. industry seismic and multibeam bathymetry, remotely acquired imagery) and sub-disciplines (e.g. geochronology, geochemistry, seismology, modelling). No single methodology can provide a complete solution.

  9. Petrographical and geochemical characterization and deformation conditions of the San Cristobal pluton, Sierra de Velasco, La Rioja, Argentina; Caracterizacion petrografica y geoquimica y condiciones de deformacion del pluton San Cristobal, Sierra de Velasco, La Rioja, Argentina

    Energy Technology Data Exchange (ETDEWEB)

    Bellos, L.I.; Toselli, A.J.; Rossi, J.N.; Grosse, P.; Rosa, J.D. de la; Castro, A.

    2010-07-01

    The San Cristobal pluton is a 35 km2 granitic body that outcrops at the southestern tip of the Sierra de Velasco, located west of La Rioja city, Argentina. It is formed by monzogranites and syenogranites, together with scarce granodiorites, with medium to fine-grained, equigranular to slightly porphyritic textures. Their mineral assemblage consists of quartz + microcline + plagioclase + biotite {+-} muscovite + zircon + apatite + magnetite. The granite contains dioritic to tonalitic mafic enclaves. The central and eastern parts of the granite have been deformed by the NNW-SSE trending South Mylonitic shear zone formed by mylonitic rocks. The metamorphic host-rock is represented by scarce greenschist facies xenoliths and hornfels with the high T/P assemblage K-feldspar - cordierite - biotite {+-} sillimanite. The granites are calc-alkaline, weak- to moderately peraluminous, and formed as part of a continental magmatic arc developed along the active margin of western Gondwana during the Early Paleozoic. The depth of emplacement of the San Cristobal pluton is estimated at {approx}12 km. (Author).

  10. Thermophysical properties of americium-containing barium plutonate

    International Nuclear Information System (INIS)

    Polycrystalline specimens of americium-containing barium plutonate have been prepared by mixing the appropriate amounts of (Pu0.91Am0.09)O2 and BaCO3 powders followed by reacting and sintering at 1600 K under the flowing gas atmosphere of dry-air. The sintered specimens had a single phase of orthorhombic perovskite structure and were crack-free. Elastic moduli were determined from longitudinal and shear sound velocities. Debye temperature was also determined from sound velocities and lattice parameter measurements. Thermal conductivity was calculated from measured density at room temperature, literature values of heat capacity and thermal diffusivity measured by laser flash method in vacuum. Thermal conductivity of americium-containing barium plutonate was roughly independent of temperature and registered almost the same magnitude as that of BaPuO3 and BaUO3. (author)

  11. Indoor - soil gas radon relationshipin the Central Bohemian Plutonic Complex

    OpenAIRE

    I. Fojtíková; J. Miksová; I. Barnet

    2005-01-01

    The relationship of indoor radon measurements and radon in bedrock was studied in the granitoid Central Bohemian Plutonic Complex (CBPC). The indoor data were linked to vectorised geological and radon risk maps using the coordinates of particular dwellings. For each geological unit and rock type it was possible to calculate the statistical characteristics of indoor radon measurements. A clear relationship between indoor radon values and radon in bedrock was confirmed in al...

  12. Arc saw development report

    International Nuclear Information System (INIS)

    The arc saw is one of the key components of the Contaminated Equipment Volume Reduction (CEVR) Program. This report describes the progress of the arc saw from its inception to its current developmental status. History of the arc saw and early contributors are discussed. Particular features of the arc saw and their advantages for CEVR are detailed. Development of the arc saw including theory of operation, pertinent experimental results, plans for the large arc saw and advanced control systems are covered. Associated topics such as potential applications for the arc saw and other arc saw installations in the world is also touched upon

  13. The mafic dikes from the Panticosa pluton (Pyrenean Axial Zone): petrology and mineral chemistry

    OpenAIRE

    Tierz, Pablo; Lago San José, Marceliano; Galé, Carlos; Arranz, Enrique; Ubide, Teresa; Larrea, Patricia; Sanz, Tomás

    2012-01-01

    The Panticosa pluton is one of multiple granitic plutons cropping out in the Pyrenean Axial Zone, which corresponds to the Palaeozoic core of the Pyrenees. Mafic dikes cut both the Panticosa pluton and its Devonian metasedimentary country rocks. According to their mineralogy and mineral composition, these dikes can be classified into two different groups, with little textural variations: a calc-alkaline group and an alkaline group. The calcalkaline rocks (spessartites and ca...

  14. The Early Andean Magmatic Province (EAMP): 40Ar/ 39Ar dating on Mesozoic volcanic and plutonic rocks from the Coastal Cordillera, northern Chile

    Science.gov (United States)

    Oliveros, Verónica; Féraud, Gilbert; Aguirre, Luis; Fornari, Michel; Morata, Diego

    2006-10-01

    The Early Andean Magmatic Province (EAMP), consists of about 150 000 km 3 of volcanic and plutonic units in the Coastal Cordillera of northern Chile and southern Peru and represents a major magmatic Mesozoic event in the world, for which the precise age of the thick volcanic series was unknown. Thirty 40Ar/ 39Ar analyses were carried out on primary mineral phases of volcanic and plutonic rocks from northern Chile (18°30'-24°S). Reliable plateau and "mini plateau" ages were obtained on plagioclase, amphibole and biotite from volcanic and plutonic rocks, despite widespread strong alteration degree. In the Arica, Tocopilla and Antofagasta (700 km apart) regions, the ages obtained on lava flows constrain the volcanic activity between 164 and 150 Ma and no N-S migration of volcanism is observed. The uppermost lava flows of the volcanic sequence at the type locality of the La Negra Formation extruded at ca. 153-150 Ma, suggesting the end of the volcanic activity of the arc at that time. The oldest volcanic activity occurred probably at ca. 175-170 Ma in the Iquique area, although no plateau age could be obtained. The plutonic bodies of the same regions were dated between ca. 160 and 142 Ma, indicating that they were partly contemporaneous with the volcanic activity. At least one volcanic pulse around 160 Ma is evidenced over the entire investigated reach of the EAMP, according to the ages found in Arica, Tocopilla, Michilla and Mantos Blancos regions. The episodic emplacement of huge amounts of subduction related volcanism is observed throughout the whole Andean history and particularly during the Jurassic (southern Peru, northern Chile and southern Argentina). These events probably correspond to periodic extensional geodynamic episodes, as a consequence of particular subduction conditions, such as change of obliquity of the convergence, change in the subduction angle, slab roll back effect or lower convergence rate, that remain to be precisely defined.

  15. Evidence of an upper mantle seismic anomaly opposing the Cocos slab beneath the Isthmus of Tehuantepec, Mexico

    OpenAIRE

    Kim, YoungHee; Lim, Hobin; Miller, Meghan S.; Pearce, Fred; Clayton, Robert W.

    2014-01-01

    Subduction of the Cocos plate beneath southern Mexico is characterized by several unusual features, such as a discontinuous volcanic arc, unusual arc chemistry, and anomalously low topography of Tehuantepec Isthmus. Recent seismic images from both receiver functions and seismic tomography suggest that there may be an additional, opposing structure dipping to the southwest from the Gulf of Mexico, and these images have been previously explained by a southwest-dipping slab. However, standard mo...

  16. 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

  17. Mechanisms and Processes Leading to Reverse Zoning in the Andong Granitoid Pluton, Andong Batholith, Korea

    Institute of Scientific and Technical Information of China (English)

    Sang Koo HWANG

    2002-01-01

    The Andong pluton consists of comagmatic granitoid rocks which constitute outstanding examples of reversely zoned granitoids. The pluton has three lithofacies: hornblende biotite tonalite, biotite granodiorite and porphyritic biotite granite. The zoned pattern forms by locating a tonalite core containing high-temperature mafic assemblages in central part,granodiorite rims in marginal part, and a porphyritic granite cap containing more felsic assemblages in topside of the pluton.Mineral abundances as well as bulk compositions of the granitoids indicate that the interior is enriched in mafic minerals and that it shows higher contents of oxides than the margin and topside. The compositional gradients change gradually with continuity between the lithofacies. The regular compositional variations within the pluton support the argument that the pluton behaved as an individual petrochemical system. Model abundances of the granitoids are in agreement with the bulk compositional gradients, suggesting that no significant interaction with country rocks occurred. Remobilization (resurgence) of deeper parts of the system into the more felsic magmas of the chamber explains the reverse zoning. Fractional crystallization was of importance and probably accounts for the selective removal of the settling phases. The Andong pluton is an example of reversely zoned plutons related by remobilization of more mafic but consanguineous magmas. Large-scale upwelling occurred in the pluton leading to the present arrangement of three lithofacies. It is conceivable that remnants of the reverse zoning become more difficult to discern as the plutonic rocks reach the latest stages of their evolution. In this case, the Andong pluton represents an earlier stage in the evolution of a felsic system that is usually represented by the final stages in normally zoned plutons.

  18. Sheeted and bulbous pluton intrusion mechanisms of a small granitoid from southeastern Australia: implications for dyke-to-pluton transformation during emplacement

    Science.gov (United States)

    Fowler, T. J.

    1994-06-01

    The small late syn-tectonic Carboniferous Davys Creek Granite (DCG) of southeastern Australia consists of microgranitic intrusive bodies of diverse geometry and structure. These bodies include: (1) subvertical concordant sheets; (2) bulbous peneconcordant plutons with apophyses and discordant lobes; and (3) subvertical dykes and stocks. The sequence of changing intrusive style is broadly 1-2-3. Transition from 1 to 2 was probably a response to rising magma pressures or declining tectonic stresses. The λ parameter of Emerman and Marrett (1990), which discriminates between stable sheet-like and potential stock/pluton/batholith emplacement modes, adequately predicts the transitions between sheet and pluton emplacements for the DCG. Ductile dyking along actively forming foliations appears to have been an important early intrusive mechanism. A transition from sheet to bulbous pluton intrusion style is suggested to have been in response to magma pressure increases.

  19. Geochemical characteristics of the Kuh-e Dom intrusion, Urumieh-Dokhtar Magmatic Arc (Iran): Implications for source regions and magmatic evolution

    Science.gov (United States)

    Kananian, Ali; Sarjoughian, Fatemeh; Nadimi, Alireza; Ahmadian, Jamshid; Ling, Wenli

    2014-08-01

    The Kuh-e Dom Pluton is located along the central northeastern margin of the Urumieh-Dokhtar Magmatic Arc, spanning a wide range of compositions from felsic rocks, including granite, granodiorite, and quartz monzonite, through to intermediate-mafic rocks comprising monzonite, monzodiorite, diorite, monzogabbro, and gabbro. The Urumieh-Dokhtar Magmatic Arc forms a distinct linear magmatic complex that is aligned parallel with the orogenic suture of the Zagros fold-thrust belt. Most samples display characteristics of metaluminous, high-K calc-alkaline, I-type granitoids. The initial isotopic signatures range from εNd (47 Ma) = -4.77 to -5.89 and 87Sr/86Sr(i) = 0.7069 to 0.7074 for felsic rocks and εNd (47 Ma) = -3.04 to -4.06 and 87Sr/86Sr(i) = 0.7063 to 0.7067 for intermediate to mafic rocks. This geochemical and isotopic evidence support a mixed origin for the Kuh-e Dom hybrid granitoid with a range of contributions of both the crust and mantle, most probably by the interaction between lower crust- and mantle-derived magmas. It is seem, the felsic rocks incorporate about 56-74% lower crust-derived magma and about 26-44% of the enriched mantle-derived mafic magma. In contrast, 66-84% of the enriched mantle-derived mafic magma incorporates 16-34% of lower crust-derived magma to generate the intermediate-mafic rocks. According to the differences in chemical composition, the felsic rocks contain a higher proportion of crustal material than the intermediate to mafic ones. Enrichment in LILEs and depletion in HFSEs with marked negative Nb, Ba, and Ti anomalies are consistent with subduction-related magmatism in an active continental margin arc environment. This suggestion is consistent with the interpretation of the Urumieh-Dokhtar Magmatic Arc as an active continental margin during subduction of the Neotethys oceanic crust beneath the Central Iranian microcontinent.

  20. Gas arc constriction for plasma arc welding

    Science.gov (United States)

    McGee, William F. (Inventor); Rybicki, Daniel J. (Inventor)

    1994-01-01

    A welding torch for plasma arc welding apparatus has an inert gas applied circumferentially about the arc column externally of the constricting nozzle so as to apply a constricting force on the arc after it has exited the nozzle orifice and downstream of the auxiliary shielding gas. The constricting inert gas is supplied to a plenum chamber about the body of the torch and exits through a series of circumferentially disposed orifices in an annular wall forming a closure at the forward end of the constricting gas plenum chamber. The constricting force of the circumferential gas flow about the arc concentrates and focuses the arc column into a more narrow and dense column of energy after exiting the nozzle orifice so that the arc better retains its energy density prior to contacting the workpiece.

  1. Reappraisal of the Arc-Arc Collision in Taiwan

    Directory of Open Access Journals (Sweden)

    Tetsuzo Seno and Yoshiaki Kawanishi

    2009-01-01

    Full Text Available Al though it is evident that Taiwan has been formed by the collision of the west-facing Luzon arc with the Eurasian continental mar gin, _ main a lot of enigmas in this collision. The major ones are: (1 a trans form fault presently connecting the Manila and Ryukyu Trenches in the Philippine Sea _ Eurasia relative motion direction is missing, and in stead, the Ryukyu Trench ex tends near off shore E. Tai wan, (2 the western edge of the intermediate-depth seismicity associated with We pro pose a new model of the collision in Tai wan to re solve these enigmas, assuming that the southern Ryukyu forearc was mi grating to the south west with respect to Eurasia for the past several m.y. and the Luzon arc has been colliding with this actively migrating Ryukyu forearc. The northern most Luzon arc is divided into two parts by the NNW line directing along the Philippine Sea - Ryukyu forearc motion from its initial intersection point with the Ryukyu Trench; the part west of this line has been obducted on the Ryukyu forearc-Eurasian mar gin, producing the collision orogen in Taiwan, and the part east of it has been subducted beneath the Ryukyu forearc. This evolutionary scenario resolves enigmas (1 and (2 kinematically. This model also predicts that the South China Sea slab has to be torn by the west ward component of the motion of the subducting Philippine Sea slab to Eurasia. This would have brought large lateral compression in the shallow portion of the Philippine Sea slab at its western border, which might lead to buck ling of the slab causing the ob served undulated gravity anomaly.

  2. Magma Emplacement and Mafic-Felsic Magma Hybridisation: Structural, Microstructural and Geochemical Evidences From the Pan-African Negash Pluton, Northern Ethiopia

    Science.gov (United States)

    ASRAT, A.; BARBEY, P.; GLEIZES, G.; LUDDEN, J.

    2002-05-01

    The Negash pluton (50 sq. km) consists of late Pan-African, high-K, calc-alkaline granitoids intruded into low-grade metavolcanics and metasediments. This almost circular massif consists of monzogranites, granodiorites, monzodiorites, monzogabbros, and hybrid quartz monzodiorites. The rocks are enriched in LIL-elements, depleted in HFS-elements, have fractionated REE patterns, low 87Sr/86Sri (0.702344 - 0.703553) and 143Nd/144Ndi (0.512031 - 0.512133) ratios, positive ɛ Nd values (3.46 to 5.40), and Pan-African model Nd ages (0.83 to 1.08 Ga). These data, along with single zircon U-Pb dating, show that the pluton was emplaced at 608 Ma from primitive source (underplated material or juvenile island arc crust) with contamination by the country rocks. The pluton shows widespread mafic-felsic magma interactions of two types: (i) homogeneous and heterogeneous hybrid monzodiorites at the northwestern part; and (ii) mingled interfaces at the diorite-granodiorite contact zones in the Eastern and Southeastern parts. Detailed structural (using the method of the anisotropy of magnetic susceptibility) and microstructural studies have been applied to understand how these interactions occurred with respect to pluton construction. The monzodiorites constituting the northwestern part of the pluton, which are composed of complexly zoned plagioclases or unzoned plagioclase laths, euhedral hornblende with biotite cores and acicular apatites, are characterized by abundant net veining, synplutonic dikes, microgranitoid enclaves, and juxtaposed series of discrete mafic-felsic pulses of hybrid nature with vertical syn-emplacement structures. The mingled interfaces between the diorites and granodiorites, on the other hand, are characterized by lobate contacts with interfingering of diorites into granodiorites at the decametric scale, abundant inclined to horizontal granitic pipes, breccia dykes and veins, which are strongly enriched in megacrysts of K-feldspars, and numerous swarms of

  3. Melt segregation evidence from a young pluton, Takidani Granodiorite (Japan)

    Science.gov (United States)

    Hartung, Eva; Caricchi, Luca; Floess, David; Wallis, Simon; Harayama, Satoru; Chiaradia, Massimo; Kouzmanov, Kalin

    2016-04-01

    We are presenting new petrological data from one of the youngest exposed plutons in the world, the Takidani Granodiorite (Japan), which has been suggested as a source for large volume ignimbrites (> 300km3). Takidani Granodiorite (1.54 Ma ± 0.23 Ma) is located within the active Norikura Volcanic Chain in the Northen Japan Alps and has been previously linked to large andesitic (1.76 Ma ± 0.17 Ma) and rhyolitic eruptions (1.75 Ma ± 0.17 Ma). The pluton is vertically zoned and consists of granites (67 to 68 wt.% SiO2) in the lower section, granodiorites (65 to 66 wt.% SiO2) in the middle section, a chemically more evolved fine-grained porphyritic unit (67 to 71 wt.% SiO2) near the roof and a marginal granodiorite at the roof (67 to 68 wt.% SiO2). The porphyritic texture of the more evolved unit near the roof indicates rapid crystallisation, which could be the result of the late intrusion of this unit at the roof of the magmatic system. However, no sharp contact is found between the underlying granodiorite and the porphyritic unit. Instead, a gradual change in rock fabric, whole-rock chemistry and mineralogy is observed suggesting that melt was extracted from the granodiorite. Electron microprobe analyses of plagioclases show three main crystal populations (Type I, II and III) with distinct anorthite and Fe contents. Type I plagioclase (An30‑40) occurs dominantly within the marginal granodiorite at the roof. Type II plagioclase (An40‑45) are common in the granodiorite and porphyritic unit. Type III plagioclase (An45‑50) is predominantly present in the granite. All plagioclase populations share a common sodic rim (An22) across the different units. Takidani Granodiorite rocks are compared to crystallisation experiments from similar magmatic suites. Emplacement conditions of the Takidani Granodiorite are obtained from the latter as well as barometry, thermometry and hygrometry indicating that magmas were ultimately emplaced at around 200 MPa, 850° C to 875° C

  4. Crustal thickening prior to 220 Ma in the East Kunlun Orogenic Belt: Insights from the Late Triassic granitoids in the Xiao-Nuomuhong pluton

    Science.gov (United States)

    Xia, Rui; Wang, Changming; Deng, Jun; Carranza, Emmanuel John M.; Li, Wenliang; Qing, Min

    2014-10-01

    The East Kunlun Orogenic Belt (EKOB) played an important role in plate tectonics, magma generation, and crustal evolution. Late Triassic granodiorites and their mafic micro-granular enclaves (MMEs) from Xiao-Nuomuhong in the EKOB were studied for geochemistry and geochronology to constrain their petrogenesis. Zircon LA-ICP-MS dating indicates that the Xiao-Nuomuhong granodiorites are coeval with their MMEs (∼222 Ma). The granodiorites are high-K calc-alkaline rocks that are enriched in Rb, Th, U and LREE, and depleted in Cr, Ni and HFSE, with high Sr/Y ratios (82.2-85.3) and geochemically resemble the lower crust-derived adakites. The MMEs are also high-K calc-alkaline rocks, with high Al2O3 (16.8-18.8 wt.%), low Mg# (30-40), Nb, Zr and Hf, with weak negative Eu anomalies (Eu/Eu# = 0.8-0.9). We suggest the MMEs are mafic magmatic globules that were injected into the felsic host magma. The adakitic rocks from the Xiao-Nuomuhong pluton were generated by partial melting of thickened crust, while the primitive compositions of the MMEs were most likely from the lithospheric mantle beneath the EKOB. The Late Triassic Xiao-Nuomuhong pluton is important evidence that crustal thickening in the EKOB occurred prior to 220 Ma. The pluton is interpreted as the result of mixing between thickened lower crust-derived melts and lithospheric mantle-derived mafic melts and the protracted magmatic response to the break-off of the Paleo-Tethys oceanic slab at ∼232 Ma.

  5. Isotopic and trace element variations in the Ruby Batholith, Alaska, and the nature of the deep crust beneath the Ruby and Angayucham Terranes

    Science.gov (United States)

    Arth, Joseph G.; Zmuda, Clara C.; Foley, Nora K.; Criss, Robert E.; Patton, W.W., Jr.; Miller, T.P.

    1989-01-01

    Thirty-six samples from plutons of the Ruby batholith of central Alaska were collected and analyzed for 22 trace elements, and many were analyzed for the isotopic compositions of Sr, Nd, O, and Pb in order to delimit the processes that produced the diversity of granodioritic to granitic compositions, to deduce the nature of the source of magmas at about 110 Ma, and to characterize the deep crust beneath the Ruby and Angayucham terranes. Plutons of the batholith show a substantial range in initial 87Sr/86Sr (SIR) of 0.7055–0.7235 and a general decrease from southwest to northeast. Initial 143Nd/144Nd (NIR) have a range of 0.51150–0.51232 and generally increase from southwest to northeast. The δ18O values for most whole rocks have a range of +8.4 to +11.8 and an average of +10.3‰. Rb, Cs, U, and Th show large ranges of concentration, generally increase as SiO2 increases, and are higher in southwest than in northeast plutons. Sr, Ba, Zr, Hf, Ta, Sc, Cr, Co, and Zr show large ranges of concentration and generally decrease as SiO2 increases. Rare earth elements (REE) show fractionated patterns and negative Eu anomalies. REE concentrations and anomalies are larger in the southwest than in the northeast plutons. Uniformity of SIR and NIR in Sithylemenkat and Jim River plutons suggests a strong role for fractional crystallization or melting of uniform magma sources at depth. Isotopic variability in Melozitna, Ray Mountains, Hot Springs, and Kanuti plutons suggests complex magmatic processes such as magma mixing and assimilation, probably combined with fractional crystallization, or melting of a complex source at depth. The large variations in SIR and NIR in the batholith require a variation in source materials at depth. The southwestern plutons probably had dominantly siliceous sources composed of metamorphosed Proterozoic and Paleozoic upper crustal rocks. The northeastern plutons probably had Paleozoic sources that were mixtures of siliceous and intermediate

  6. Rb-Sr isochronous age of Vepor pluton granitoids

    International Nuclear Information System (INIS)

    The result are presented of geochronological investigations of the Vepor pluton granitoids by the Rb-Sr isochronous method. The results prove the Variscan age of granodiorite magmatism of the Sihla type (387±27 m.y.) and the Early Variscan age of leucocratic granitoids of the Vepor and the Ipel types (284±22 m.y.). Since the initial ratio of 87Sr/86Sr in granitoids of the Sihla type is 0.7054 and of the Vepor type 0.7060, it can be assumed that during the formation of the granitoids of veporides there was an increased supply of matter from the main source affecting genesis of granitoids. The results prove a polyphase character of the Variscan granitoids of Veporicum. (author)

  7. Why are plutons dry? Outgassing mechanisms of crustal magmatic bodies

    Science.gov (United States)

    parmigiani, andrea; Huber, Christian; Bachmann, Olivier; Leclaire, Sébastien

    2016-04-01

    Magma bodies crystallizing to completion within the crust (i.e., forming plutons) typically undergo significant amounts of second boiling (i.e. cooling and crystallization of dominantly anhydrous minerals lead to volatile saturation and bubble nucleation/growth). The low water content ( 6 wt % H2O for evolved compositions in subduction zones), testify that outgassing from crystalline mushy reservoirs must be an efficient and widespread process. Understanding this outgassing mechanism is key to understand how volatiles are transferred from mantle depths to the surface. From the hydrodynamics point of view, the mass balance of exsolved volatiles in these plutonic bodies is controlled by the difference between the rate of degassing (formation of bubbles by 2nd boiling) and outgassing (transport of gas out of the magma body). In this study, we use pore-scale multiphase modeling to constrain these rates as function of the crystal and volatile contents in the magma. Because second boiling is a slow process, one can consider equilibrium degassing as a valid assumption. Outgassing, on the other end, is controlled by the competition between buoyancy, capillary and viscous forces. Our numerical simulations are used to determine the most efficient setting for gas to escape its magmatic trap. The high viscosity of interstitial melts and capillary forces (due to the non-wetting nature of the gas phase with most of the mineral phases in magmatic systems) strongly limits gas transport until vertically extensive gas channels are generated. We show that channels can readily form in volatile-rich coarse-grained mush zones in the upper crust, and allow efficient outgassing at crystallinities around 50-75 vol%, when millimetric bubbles can still win capillary resistive forces.

  8. Growth of plutons by incremental emplacement of sheets in crystal-rich host: Evidence from Miocene intrusions of the Colorado River region, Nevada, USA

    Science.gov (United States)

    Miller, C.F.; Furbish, D.J.; Walker, B.A.; Claiborne, L.L.; Koteas, G.C.; Bleick, H.A.; Miller, J.S.

    2011-01-01

    crystal-laden host is important in pluton construction. The dominant granite unit of the Spirit Mountain batholith displays only subtle internal contacts. However, ages and elemental zoning in zircons demonstrate a protracted history of almost 2 million years, major fluctuations in T and host melt chemistry, and mixing of strongly contrasting populations of magmatic zircon in single samples. We interpret this to reflect reactivation of rigid sponge and mush and entrainment of earlier-formed crystals, and we infer that this was in response to granitic replenishment. Much of the smaller Aztec Wash pluton comprises interlayered cumulate-textured quartz monzonite and mafic sheets. The latest phase of pluton emplacement is marked by numerous thick, fine-grained granite "sills" that intruded the subhorizontal quartz monzonite sheets. Contacts between granite and quartz monzonite are "soft," highly irregular on cm-dm scale with coarse xenocrysts from the quartz monzonite entrained in the fine-grained granite. We interpret the granite replenishments to have spread laterally within crystal-rich, melt-bearing quartz monzonite beneath rigid mafic sheets. In this case, clear evidence for the emplacement process is fortuitously preserved because the granite was emplaced in the waning stage of the thermal lifetime of the pluton, and because the mafic sheets enhance the strength contrast and make the geometry more visible. Similar "sills" of fine-grained granite were also preserved during the late stages of the history of the Spirit Mountain batholith. ?? 2009 Elsevier B.V.

  9. Rotating arc spark plug

    Science.gov (United States)

    Whealton, John H.; Tsai, Chin-Chi

    2003-05-27

    A spark plug device includes a structure for modification of an arc, the modification including arc rotation. The spark plug can be used in a combustion engine to reduce emissions and/or improve fuel economy. A method for operating a spark plug and a combustion engine having the spark plug device includes the step of modifying an arc, the modifying including rotating the arc.

  10. 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.

  11. Cretaceous plutonic rocks in the Donner Lake-Cisco Grove area, northern Sierra Nevada, California

    Science.gov (United States)

    Kulow, Matthew J.; Hanson, Richard E.; Girty, Gary H.; Girty, Melissa S.; Harwood, David S.

    1998-01-01

    The northernmost occurrences of extensive, glaciated exposures of the Sierra Nevada batholith occur in the Donner Lake-Cisco Grove area of the northern Sierra Nevada. The plutonic rocks in this area, which are termed here the Castle Valley plutonic assemblage, crop out over an area of 225 km2 and for the most part are shown as a single undifferentiated mass on previously published geological maps. In the present work, the plutonic assemblage is divided into eight separate intrusive units or lithodemes, two of which each consist of two separate plutons. Compositions are dominantly granodiorite and tonalite, but diorite and granite form small plutons in places. Spectacular examples of comb layering and orbicular texture occur in the diorites. U-Pb zircon ages have been obtained for all but one of the main units and range from ~120 to 114 Ma, indicating that the entire assemblage was emplaced in a narrow time frame in the Early Cretaceous. This is consistent with abundant field evidence that many of the individual phases were intruded penecontemporaneously. The timing of emplacement correlates with onset of major Cretaceous plutonism in the main part of the Sierra Nevada batholith farther south. The emplacement ages also are similar to isotopic ages for gold-quartz mineralization in the Sierran foothills west of the study area, suggesting a direct genetic relationship between the voluminous Early Cretaceous plutonism and hydrothermal gold mineralization.

  12. An Archean Geomagnetic Reversal in the Kaap Valley Pluton, South Africa

    Science.gov (United States)

    Layer; Kroner; McWilliams

    1996-08-16

    The Kaap Valley pluton in South Africa is a tonalite intrusion associated with the Archean Barberton Greenstone Belt. Antipodal paleomagnetic directions determined from the central and marginal parts of the pluton record a geomagnetic reversal that occurred as the pluton cooled. The age of the reversal is constrained by an 40Ar/39Ar plateau age from hornblende at 3214 +/- 4 million years, making it the oldest known reversal. The data presented here suggest that Earth has had a reversing, perhaps dipolar, magnetic field since at least 3.2 billion years ago. PMID:8688075

  13. Three-dimensional attenuation structure beneath North Island, New Zealand

    Science.gov (United States)

    Satake, Kenji; Hashida, Toshihiko

    1989-03-01

    Three-dimensional attenuation structure beneath North Island, New Zealand is determined by inversion of seismic intensity data. The method developed by Hashida and Shimazaki is used; the seismic intensity is converted to the maximum acceleration of the S-wave to obtain the acceleration at a point source and the attenuation structure. Because seismic intensity data have been accumulated on a uniform scale in New Zealand since the 1950's, we were able to use more than 2000 seismic intensity data from 26 earthquakes. The results show a remarkable contrast in the attenuation structure. In the top crustal layer, a low-Q area corresponding to the Central Volcanic Region is found. This low-Q area becomes wider to the northeast of North Island, suggesting that the Central Volcanic Region continues to the Havre Trough, a young back-arc basin. The southeastern part of the upper mantle beneath North Island shows high Q while the northwestern part shows low Q. The cross section shows that the high-Q region is dipping to the northwest, with a large amount of dip in the northeast and a smaller dip in the southwestern part of North Island. A comparison of the attenuation structure with microearthquake distribution indicates that this high-Q zone is the obliquely subducting Pacific plate. A zone of abnormally low Q which has cut the high-Q slab is found at a depth range of 130 to 230 km beneath the active volcanoes in the Taupo Volcanic Zone. A tear in the Pacific plate is suggested by this discontinuity in the attenuation structure. (1984).

  14. Forceful Emplacement of Granitic Plutons in an Extensional Tectonic Setting: Syn-kinematic Plutons in the Yagan-Onch Hayrhan Metamorphic Core Complex

    Institute of Scientific and Technical Information of China (English)

    王涛; 郑亚东; 李天兵; 高永军; 马铭波

    2002-01-01

    It is generally considered that granitic plutons are forcefully emplaced in a compressional setting and permissively emplaced in an extensional setting. This paper, however, shows that syn-kinematic (extensional) elliptic granitic plutons in the Yagan-Onch Hayrhan metamorphic core complex (MCC) have relatively strong forceful emplacement, which are indicated by (1) concentric distribution of the rock units, (2) a strain pattern with strong strains on the margins and low strains at the centre of a pluton, and particularly (3) syn-emplacement shortening of the host rocks within the aureole. The strain analysis for the host rocks shows that the host-rock ductile shortening, I.e. Forceful emplacement, provides about 16?24% of the emplacement space for the present plutons. All these suggest that forceful emplacement occurs not only in a compressional tectonic setting, but also in an extensional setting. This study further demonstrates the significance of the multiple emplacement of granitic plutons and provides new information about the causality between granitic magmatism and the formation of the MCC and its dynamics.

  15. Geochemical and geochronologic analysis of the plutonic basement of the Tacaná Volcano Complex, Chiapas México.

    Science.gov (United States)

    Paul William, L.

    2006-12-01

    The Tacana Volcano Complex (TVC) is located on the border between the State of Chiapas, southern Mexico, and Guatemala. This volcanic complex has been described as the last volcano in the northwest part of the Central American Volcanic Arc (CAVA). The region where the TVC was emplaced is influenced by the transpressional boundary formed by the shear movement between the North American and Caribbean Plates and the compressive stress by the subduction of the Cocos Plate under the North American Plate. The most recently study about TVC was by García-Palomo et al. (2004), who summarized the chronology of the TVC from basement formation to its recent activity and report that the active TVC lies on igneous basement rocks that were formed by two magmatic processes during the Mesozoic and Cenozoic. In this work, we present the results of detailed petrographic, geochemical and geochronologic analyses obtained from plutonic rocks in the basement of the TVC zone. The results show that t this basement (granites: SiO2 of 64.64 to 65.29 wt%, granodiorites: SiO2 of 60.18 wt%, and gabbros: SiO2 of 51.67 wt%) belongs to the suite of plutonic rocks of an orogenic environment. The granites are classified as both S-type peraluminosus granites derived form partial melting of continental crust, characterized by minerals such as quartz, k-feldspar, biotite, hornblende and some Fe-Ti oxides and I-type metaluminous granites derived from subduction processes with the main mineral phases being quartz, k-feldspar, hornblende, biotite and Fe-Ti oxides. The ages thus far obtained (K- Ma to 12.65 +/- 0.08 Ma) suggest that there were at least nine periods of magmatic activity that produced granitic and mafic magmas. Reference: Garcia-Palomo, A., Macias, J.L., Arce, J.L., Mora, J.C., Hughes, S., Saucedo, R., Espindola, J.M., Escobar, R., and Layer, P., (2004). GSA Special Paper 412, p 39-57.

  16. Mesoproterozoic Continental Arc Type Granite in the Central Tianshan Mountains: Zircon SHRIMP U-Pb Dating and Geochemical Analyses

    Institute of Scientific and Technical Information of China (English)

    YANG Tiannan; LI Jinyi; SUN Guihua; WANG Yanbin

    2008-01-01

    The Central Tianshan belt in northwestern China is a small Precambrian block located in the southern part of the Central Asia Orogenic Belt (CAOB), which is considered as "the most voluminous block of young continental crust in the world" that comprises numerous small continental blocks separated by Paleozoic magmatic arcs. The Precambrian basement of the central Tianshan Mountains is composed of volcanic rocks and associated volcano-sedimentary rocks that were intruded by granitic plutons. Geochemical analyses demonstrate that the granitic plutons and volcanic rocks were generated in the Andean-type active continental arc environment like today's Chile, and the zircon U-Pb SHRIMP dating indicates that they were developed at about 956 Ma, possibly corresponding to the subduction of the inferred Mozambique Ocean under the Baltic-African super-continent.

  17. Ridge Subduction Beneath the Americas: Synthesis and New Research on Anomalous Tectonism and Magmatism

    Science.gov (United States)

    Thorkelson, D. J.; Madsen, J. K.; Breitsprecher, K.; Groome, W. G.; Sluggett, C.

    2006-12-01

    The west coast of the Americas has been repeatedly affected by ridge-trench interactions from Mesozoic to Recent time. Beneath North America, subduction of the Kula-Farallon, Kula-Resurrection and Farallon- Resurrection spreading ridges resulted in anomalous and time-transgressive forearc to backarc magmatism and related tectonism from the Late Cretaceous to the Eocene. Following consumption and redistribution of the Kula and Resurrection plates, the Neogene Farallon-Pacific ridge system intersected the North American trench in two locations - western Canada and northwestern Mexico / southwestern United States - causing pronounced magmatic and tectonic effects that continue to the present. Beneath Central America, divergent subduction of the Nazca and Cocos plates led to development of a slab window, with a present location beneath Panama and a probable pre-Pliocene position beneath Columbia or Ecuador. Patagonia has been the site of localized ridge subduction from the Eocene to the Recent, with the Phoenix-Farallon ridge subducting from the Eocene to the early Miocene, and the Nazca-Antarctic ridge from the Miocene to the present. Antarctica experienced diverging Antarctic-Phoenix plate subduction from the Eocene to the Pliocene. In all cases, normal arc magmatism was interrupted or eliminated by anomalous igneous activity ranging in signature from adakitic to intraplate. Our current research involves geochemical, tectonic, and thermal modeling of slab window environments. A new geochemical analysis on the effects of Miocene to Recent subduction of the northern segment of the Farallon (Juan de Fuca)-Pacific ridge is underway. A symmetrical arc-intraplate-arc geochemical pattern is evident in a transect from the northern Cascade Arc, through the volcanic fields of British Columbia, Yukon and eastern Alaska, and into the Aleutian Arc. This pattern can be explained by Neogene displacement of the arc-metasomatized mantle wedge caused by upwelling oceanic

  18. Pn anisotropic tomography and mantle dynamics beneath China

    Science.gov (United States)

    Zhou, Zhigang; Lei, Jianshe

    2016-08-01

    We present a new high-resolution Pn anisotropic tomographic model of the uppermost mantle beneath China inferred from 52,061 Pn arrival-time data manually picked from seismograms recorded at provincial seismic stations in China and temporary stations in Tibet and the Tienshan orogenic belt. Significant features well correlated with surface geology are revealed and provide new insights into the deep dynamics beneath China. Prominent high Pn velocities are visible under the stable cratonic blocks (e.g., the Tarim, Junngar, and Sichuan basins, and the Ordos block), whereas remarkable low Pn velocities are observed in the tectonically active areas (e.g., Pamir, the Tienshan orogenic belt, central Tibet and the Qilian fold belt). A distinct N-S trending low Pn velocity zone around 86°E is revealed under the rift running from the Himalayan block through the Lhasa block to the Qiangtang block, which indicates the hot material upwelling due to the breaking-off of the subducting Indian slab. Two N-S trending low Pn velocity belts with an approximate N-S Pn fast direction along the faults around the Chuan-Dian diamond block suggest that these faults may serve as channels of mantle flow from Tibet. The fast Pn direction changes from N-S in the north across 27°N to E-W in the south, which may reflect different types of mantle deformation. The anisotropy in the south could be caused by the asthenospheric flow resulted from the eastward subduction of the Indian plate down to the mantle transition zone beneath the Burma arc. Across the Talas-Fergana fault in the Tienshan orogenic belt, an obvious difference in velocity and anisotropy is revealed. To the west, high Pn velocities and an arc-shaped fast Pn direction are observed, implying the Indo-Asian collision, whereas to the east low Pn velocities and a range-parallel Pn fast direction are imaged, reflecting the northward underthrusting of the Tarim lithosphere and the southward underthrusting of the Kazakh lithosphere. In

  19. Iron variation within a granitic pluton as determined by near-infrared reflectance

    Science.gov (United States)

    Baird, A. K.

    1984-01-01

    One-hundred fifty-one previously chemically analyzed samples of tonalite from the Lakeview Mountains pluton, southern California batholith, were analyzed for their iron content using near-infrared spectrophotometry. Compared to the earlier analyses of the same sample set by X-ray fluorescence spectrography, the infrared data have higher analytical variance but clearly define patterns of compositional zonation in the pluton which are closely similar to those patterns obtained from X-ray data; petrogenetic interpretations for the pluton would be the same from either data set. Infrared spectral data can be obtained directly in the field with relatively simple instruments and field measurements can be made to average local heterogeneities that often mask significant plutonic variations.

  20. Chronology and cooling history of the Tianmenshan pluton in South Jiangxi Province and their geological significance

    Institute of Scientific and Technical Information of China (English)

    ZENG Qingtao; MAO Jianren; HU Qing; ZHAO Xilin; YE Haimin

    2008-01-01

    Geochronological studies on the crust-derived Tianmenshan pluton were undertaken by SHRIMP zircon U-Pb dating and Ar-Ar dating of biotite, muscovite and K-feldspar, giving a petrogenetic age of 167 Ma. Owing to the closure systems in different minerals, the cooling history of the pluton can be determined with an age-temperature diagram. The late hydrothermal event has been recognized, which is related probably with mineralization. In terms of the comparative geochronological and petrologic records, it is concluded that there are some constrains on tectonic evolution and that the formation of the Tianmenshan pluton proceeded in a transition period from lndosinian post-orogeny extension to strong compressive tectonics. And the timing of the hydrothermal event matches the compressive climax of the Yanshanian orogeny. The temporal gap between granite emplacement and wolframite mineralization could last 10-20 Ma owing to the low cooling rate of the pluton.

  1. Forearc structure beneath southwestern British Columbia: A three-dimensional tomographic velocity model

    Science.gov (United States)

    Ramachandran, K.; Dosso, S.E.; Spence, G.D.; Hyndman, R.D.; Brocher, T.M.

    2005-01-01

    This paper presents a three-dimensional compressional wave velocity model of the forearc crust and upper mantle and the subducting Juan de Fuca plate beneath southwestern British Columbia and the adjoining straits of Georgia and Juan de Fuca. The velocity model was constructed through joint tomographic inversion of 50,000 first-arrival times from earthquakes and active seismic sources. Wrangellia rocks of the accreted Paleozoic and Mesozoic island arc assemblage underlying southern Vancouver Island in the Cascadia forearc are imaged at some locations with higher than average lower crustal velocities of 6.5-7.2 km/s, similar to observations at other island arc terranes. The mafic Eocene Crescent terrane, thrust landward beneath southern Vancouver Island, exhibits crustal velocities in the range of 6.0-6.7 km/s and is inferred to extend to a depth of more than 20 km. The Cenozoic Olympic Subduction Complex, an accretionary prism thrust beneath the Crescent terrane in the Olympic Peninsula, is imaged as a low-velocity wedge to depths of at least 20 km. Three zones with velocities of 7.0-7.5 km/s, inferred to be mafic and/or ultramafic units, lie above the subducting Juan de Fuca plate at depths of 25-35 km. The forearc upper mantle wedge beneath southeastern Vancouver Island and the Strait of Georgia exhibits low velocities of 7.2-7.5 km/s, inferred to correspond to ???20% serpentinization of mantle peridotites, and consistent with similar observations in other warm subduction zones. Estimated dip of the Juan de Fuca plate beneath southern Vancouver Island is ???11??, 16??, and 27?? at depths of 30, 40, and 50 km, respectively. Copyright 2005 by the American Geophysical Union.

  2. Continent-arc collision in the Banda Arc imaged by ambient noise tomography

    Science.gov (United States)

    Porritt, Robert W.; Miller, Meghan S.; O'Driscoll, Leland J.; Harris, Cooper W.; Roosmawati, Nova; Teofilo da Costa, Luis

    2016-09-01

    The tectonic configuration of the Banda region in southeast Asia captures the spatial transition from subduction of Indian Ocean lithosphere to subduction and collision of the Australian continental lithosphere beneath the Banda Arc. An ongoing broadband seismic deployment funded by NSF is aimed at better understanding the mantle and lithospheric structure in the region and the relationship of the arc-continent collision to orogenesis. Here, we present results from ambient noise tomography in the region utilizing this temporary deployment of 30 broadband instruments and 39 permanent stations in Indonesia, Timor Leste, and Australia. We measure dispersion curves for over 21,000 inter-station paths resulting in good recovery of the velocity structure of the crust and upper mantle beneath the Savu Sea, Timor Leste, and the Nusa Tenggara Timur (NTT) region of Indonesia. The resulting three dimensional model indicates up to ∼25% variation in shear velocity throughout the plate boundary region; first-order velocity anomalies are associated with the subducting oceanic lithosphere, subducted Australian continental lithosphere, obducted oceanic sediments forming the core of the island of Timor, and high velocity anomalies in the Savu Sea and Sumba. The structure in Sumba and the Savu Sea is consistent with an uplifting forearc sliver. Beneath the island of Timor, we confirm earlier inferences of pervasive crustal duplexing from surface mapping, and establish a link to underlying structural features in the lowermost crust and uppermost mantle that drive upper crustal shortening. Finally, our images of the volcanic arc under Flores, Wetar, and Alor show high velocity structures of the Banda Terrane, but also a clear low velocity anomaly at the transition between subduction of oceanic and continental lithosphere. Given that the footprint of the Banda Terrane has previously been poorly defined, this model provides important constraints on tectonic reconstructions that

  3. Growth of a Large Composite Magma System: the EJB Pluton, Eastern California.

    Science.gov (United States)

    Matty, D. J.; Vervoort, J.; Dufrane, A.; Hart, G.; Student, J.; Morgan, S.

    2008-12-01

    the BCG, but taken as absolute, the ages tantalizingly decrease from NW to SE within the exposed area of the BCG. No such pattern is suggested within the JFQM. Collectively, these new LA-ICP-MS zircon age data support the observed field relationships and suggest that the EJB magma system was periodically active for as long as 10-12 million years. This time scale agrees well with current models of incremental growth of plutons and has important implications for strain accumulation in mid-crustal arc environments.

  4. Investigation of the deep crustal structure and magmatic activity at the NW Hellenic Volcanic Arc with 3-D aeromagnetic inversion and seimotectonic analysis.

    Science.gov (United States)

    Efstathiou, Angeliki; Tzanis, Andreas; Chailas, Stylianos; Stamatakis, Michael

    2013-04-01

    We report the results of a joint analysis of geophysical (aeromagnetic) and seismotectonic data, applied to the investigation of the deep structure, magmatic activity and geothermal potential of the north-western stretches of the Hellenic Volcanic Arc (HVA). The HVA is usually considered to be a single arcuate entity stretching from Sousaki (near Corinth) at the NW, to Nisyros Island at the SE. However, different types of and their ages indicate the presence of two different volcanic groups. Our study focuses on the northern part of the west (older) volcanic group and includes the Crommyonian (Sousaki) volcanic field at the west end of Megaris peninsula (east margin on the contemporary Corinth Rift), the Aegina and Methana volcanic complex at the Saronic Gulf, where typical Quaternary calc-alkaline volcanics predominate, and the Argolid peninsula to the south and south-west. In addition to the rocks associated with Quaternary volcanism, the study area includes a series of Mesozoic ultramafic (ophiolitic) outcrops at the Megaris peninsula, to the north and north-east of the Crommyonian volcanic field, as well as throughout the Argolid. A major deep structural and tectonic feature of the study area, and one with profound influence on crustal deformation and the evolution of rapidly deforming extensional structures like the Corinth Rift and the Saronic Gulf, is the local geometry and dynamics of the African oceanic crust subducting beneath the Aegean plate. Locally, the subducting slab has a NNW strike and ENE plunge, with the dip angle changing rapidly (steepening) approx. beneath the Argolid. The aeromagnetic data was extracted from the recently (re)compiled aeromagnetic map of Greece (Chailas et al, 2010) and was inverted with the UBC-GIF magnetic inversion suite (Li and Oldenburg, 1996). The inversion included rigorous geological constraints introduced by means of numerous in-situ magnetic susceptibility measurements. The inversion has imaged several isolated

  5. Peek Arc Consistency

    CERN Document Server

    Bodirsky, Manuel

    2008-01-01

    This paper studies peek arc consistency, a reasoning technique that extends the well-known arc consistency technique for constraint satisfaction. In contrast to other more costly extensions of arc consistency that have been studied in the literature, peek arc consistency requires only linear space and quadratic time and can be parallelized in a straightforward way such that it runs in linear time with a linear number of processors. We demonstrate that for various constraint languages, peek arc consistency gives a polynomial-time decision procedure for the constraint satisfaction problem. We also present an algebraic characterization of those constraint languages that can be solved by peek arc consistency, and study the robustness of the algorithm.

  6. Wire + Arc Additive Manufacturing

    OpenAIRE

    Williams, Stewart W.; Martina, Filomeno; Addison, Adrian C.; Ding, Jialuo; Pardal, Goncalo; Colegrove, Paul A.

    2016-01-01

    Depositing large components (>10 kg) in titanium, aluminium, steel and other metals is possible using Wire + Arc Additive Manufacturing. This technology adopts arc welding tools and wire as feedstock for additive manufacturing purposes. High deposition rates, low material and equipment costs, and good structural integrity make Wire+Arc Additive Manufacturing a suitable candidate for replacing the current method of manufacturing from solid billets or large forgings, especially with regards to ...

  7. Source of magma for Elet-Ozero pluton (NE Baltic Shield) - subduction or plume-related material?

    Science.gov (United States)

    Ryabchikov, Igor; Kogarko, Liya

    2016-04-01

    Eletozero pluton is located in the northeastern part of the Karelian Craton, it covers an area of about 100 km2 and cuts through Archaean granite-gneisses. The complex has a concentric zoned structure, the peripheral part being composed of a layered gabbro series; the central area is occupied by nepheline syenites. Mafic and ultramafic rocks in this intrusion often contain potassium feldspar (olivine monzonites and monzonites). Gabbroids are characterized by rhythmic layering expressed in the alternation of leucocratic layers predominantly composed of plagioclase and melanocratic layers with pyroxenes, olivine, titanomagnetite and ilmenite. The rocks of the pluton are enriched in highly incompatible elements by comparison with moderately incompatible elements: average primitive mantle normalized La/Lu ratio is 18.3. At the same time, all the rocks from Elet-Ozero massif including the most primitive ones (high Mg-numbers and high Ni contents) exhibit distinct positive Ba anomaly: mean chondrite normalized Ba/Th ratio is 15.3 (both elements have similar incompatibility-[1]). Enrichment of parent magma in Ba is also confirmed by the presence of high-Ba feldspars and micas in some samples of gabbroids. The most Ba-rich feldspar contains 75% of celsian component: K0.09Na0.04Ca0.008Sr0.04Ba0.75Al1.73Fe0.14Si2.20O8. Ba is a fluid mobile incompatible lithophile element that is probably the most sensitive indicator of subduction fluid addition to the mantle wedge. Thus, positive Ba anomaly suggests input of subduction related component into the source of Elet-Ozero magma. The presence of subduction related material in the lithosphere of Karelian craton has been proposed on the basis of Os isotope studies of mantle xenoliths from Finnish kimberlites [2]. The age of this subduction event is similar to the age of Elet-Ozero pluton. On the other hand, there are certain arguments in favor of connection of Elet-Ozero intrusive complex with mantle plume activity. In particular it

  8. Welding arc plasma physics

    Science.gov (United States)

    Cain, Bruce L.

    1990-01-01

    The problems of weld quality control and weld process dependability continue to be relevant issues in modern metal welding technology. These become especially important for NASA missions which may require the assembly or repair of larger orbiting platforms using automatic welding techniques. To extend present welding technologies for such applications, NASA/MSFC's Materials and Processes Lab is developing physical models of the arc welding process with the goal of providing both a basis for improved design of weld control systems, and a better understanding of how arc welding variables influence final weld properties. The physics of the plasma arc discharge is reasonably well established in terms of transport processes occurring in the arc column itself, although recourse to sophisticated numerical treatments is normally required to obtain quantitative results. Unfortunately the rigor of these numerical computations often obscures the physics of the underlying model due to its inherent complexity. In contrast, this work has focused on a relatively simple physical model of the arc discharge to describe the gross features observed in welding arcs. Emphasis was placed of deriving analytic expressions for the voltage along the arc axis as a function of known or measurable arc parameters. The model retains the essential physics for a straight polarity, diffusion dominated free burning arc in argon, with major simplifications of collisionless sheaths and simple energy balances at the electrodes.

  9. The Ediacaran Rio Doce magmatic arc revisited (Araçuaí-Ribeira orogenic system, SE Brazil)

    Science.gov (United States)

    Tedeschi, Mahyra; Novo, Tiago; Pedrosa-Soares, Antônio; Dussin, Ivo; Tassinari, Colombo; Silva, Luiz Carlos; Gonçalves, Leonardo; Alkmim, Fernando; Lana, Cristiano; Figueiredo, Célia; Dantas, Elton; Medeiros, Sílvia; De Campos, Cristina; Corrales, Felipe; Heilbron, Mônica

    2016-07-01

    Described half a century ago, the Galiléia tonalite represents a milestone in the discovery of plate margin magmatic arcs in the Araçuaí-Ribeira orogenic system (southeastern Brazil). In the 1990's, analytical studies on the Galiléia tonalite finally revealed the existence of a Late Neoproterozoic calc-alkaline magmatic arc in the Araçuaí orogen. Meanwhile, the name Rio Doce magmatic arc was applied to calc-alkaline plutons found in the Araçuaí-Ribeira boundary. After those pioneer studies, the calc-alkaline plutons showing a pre-collisional volcanic arc signature and age between 630 Ma and 585 Ma have been grouped in the G1 supersuite, corresponding to the Rio Doce arc infrastructure. Here, we revisit the Rio Doce arc with our solid field knowledge of the region and a robust analytical database (277 lithochemical analyses, and 47 U-Pb, 53 Sm-Nd, 25 87Sr/86Sr and 7 Lu-Hf datasets). The G1 supersuite consists of regionally deformed, tonalitic to granodioritic batholiths and stocks, generally rich in melanocratic to mesocratic enclaves and minor gabbroic to dioritic plutons. Gabbroic to dioritic enclaves show evidence of magma mixing processes. The lithochemical and isotopic signatures clearly reveal a volcanic arc formed on a continental margin setting. Melts from a Rhyacian basement form the bulk of the magma produced, whilst gabbroic plutons and enclaves record involvement of mantle magmas in the arc development. Tonalitic stocks (U-Pb age: 618-575 Ma, εNd(t): -5.7 to -7.8, Nd TDM ages: 1.28-1.68 Ga, 87Sr/86Sr(t): 0.7059-0.7118, and εHf(t): -5.2 to -11.7) form the northernmost segment of the Rio Doce arc, which dies out in the ensialic sector of the Araçuaí orogen. At arc eastern and central zones, several batholiths (e.g., Alto Capim, Baixo Guandu, Galiléia, Muniz Freire, São Vítor) record a long-lasting magmatic history (632-580 Ma; εNd(t): -5.6 to -13.3; Nd TDM age: 1.35-1.80 Ga; 87Sr/86Sr(t): 0.7091-0.7123). At arc western border, the magmatic

  10. Petrogenetic evolution of the Early Miocene Alaçamdağ volcano-plutonic complex, northwestern Turkey: implications for the geodynamic framework of the Aegean region

    Science.gov (United States)

    Erkül, Sibel Tatar

    2012-01-01

    Extensional-tectonic processes have generated extensive magmatic activity that produced volcanic/plutonic rocks along an E-W-trending belt across north-western Turkey; this belt includes granites and coeval volcanic rocks of the Alaçamdağ volcano-plutonic complex. The petrogenesis of the Early Miocene Alaçamdağ granitic and volcanic rocks are here investigated by means of whole-rock Sr-Nd isotopic data along with field, petrographic and whole-rock geochemical studies. Geological and geochemical data indicate two distinct granite facies having similar mineral assemblages, their major distinguishing characteristic being the presence or absence of porphyritic texture as defined by K-feldspar megacrysts. I-type Alaçamdağ granitic stocks have monzogranitic-granodioritic compositions and contain a number of mafic microgranular enclaves of monzonitic, monzodioritic/monzogabbroic composition. Volcanic rocks occur as intrusions, domes, lava flows, dykes and volcanogenic sedimentary rocks having (first episode) andesitic and dacitic-trachyandesitic, and (second episode) dacitic, rhyolitic and trachytic-trachydacitic compositions. These granitic and volcanic rocks are metaluminous, high-K, and calc-alkaline in character. Chondrite-normalised rare earth element patterns vary only slightly such that all of the igneous rocks of the Alaçamdağ have similar REE patterns. Primitive-mantle-normalised multi-element diagrams show that these granitic and volcanic rocks are strongly enriched in LILE and LREE pattern, high (87Sr/86Sr)i and low ɛ Nd( t) ratios suggesting Alaçamdağ volcano-plutonic rocks to have been derived from hybrid magma that originated mixing of co-eval lower crustal-derived more felsic magma and enriched subcontinental lithospheric mantle-derived more mafic magmas during extensional processes, and the crustal material was more dominant than the mantle contribution. The Alaçamdağ volcano-plutonic complex rocks may form by retreat of the Hellenic

  11. Characterizing fractured plutonic rocks of the Canadian shield for deep geological disposal of Canada`s radioactive wastes

    Energy Technology Data Exchange (ETDEWEB)

    Lodha, G.S.; Davison, C.C.; Gascoyne, M. [Atomic Energy of Canada Ltd. , Pinawa, MB (Canada). Whiteshell Labs.

    1998-09-01

    Since 1978 AECL has been investigating plutonic rocks of the Canadian Shield as a potential medium for the disposal of Canada`s nuclear fuel waste. During the last two years this study has been continued as part of Ontario Hydro`s used fuel disposal program. Methods have been developed for characterizing the geotechnical conditions at the regional scale of the Canadian Shield as well as for characterizing conditions at the site scale and the very near-field scale needed for locating and designing disposal vault rooms and waste emplacement areas. The Whiteshell Research Area (WRA) and the Underground Research Laboratory (URL) in southeastern Manitoba have been extensively used to develop and demonstrate the different scales of characterization methods. At the regional scale, airborne magnetic and electromagnetic surveys combined with LANDSAT 5 and surface gravity survey data have been helpful in identifying boundaries of the plutonic rocks , overburden thicknesses, major lineaments that might be geological structures, lithological contacts and depths of the batholiths. Surface geological mapping of exposed rock outcrops, combined with surface VLF/EM, radar and seismic reflection surveys were useful in identifying the orientation and depth continuity of low-dipping fracture zones beneath rock outcrops to a depth of 500 to 1000 m. The surface time-domain EM method has provided encouraging results for identifying the depth of highly saline pore waters. The regional site scale investigations at the WRA included the drilling of twenty deep boreholes (> 500 m) at seven separate study areas. Geological core logging combined with borehole geophysical logging, TV/ATV logging, flowmeter logging and full waveform sonic logging in these boreholes helped to confirm the location of hydro geologically important fractures, orient cores and infer the relative permeability of some fracture zones. Single-hole radar and crosshole seismic tomography surveys were useful to establish the

  12. Granite intrusion by externally induced growth and deformation of the magma reservoir, the example of the Plasenzuela pluton, Spain

    Science.gov (United States)

    Castro, Antonio; Fernández, Carlos

    1998-09-01

    The Plasenzuela pluton in the Central Extremadura batholith in the southern Iberian Massif, is an example of permissive emplacement in relation to the tectonic development of extensional fractures in the upper continental crust. Paradoxically, this pluton has a concordant structural pattern which is classically attributed to diapirism or ballooning. This pattern consists of the following elements: (a) nearly elliptical shape in the horizontal section; (b) conformity of the pre-existing aureole structures to the shape of the pluton contacts; and (c) development of a crenulation cleavage, parallel to the contacts, in the vicinity of the pluton walls. All these features have been interpreted in many plutons as resulting from the pushing-aside of the country rock structures due to the expansion of the pluton. However, the detailed structural relationships in the aureole do not favour a forceful emplacement mechanism. By contrast, these relationships constitute prime evidence of permissive intrusion in extensional fractures. According to this interpretation, the concordant shape of the pluton was acquired by syn-plutonic opening of a mixed tensional-shear fracture, parallel to the main foliation in the host rocks, and by folding of the fracture walls together with the previous anisotropy of the country rocks. This is a growth-deformation process that can operate at local conditions in the upper continental crust giving rise to concordant syn-tectonic plutons.

  13. Depth variations of P-wave azimuthal anisotropy beneath Mainland China.

    Science.gov (United States)

    Wei, Wei; Zhao, Dapeng; Xu, Jiandong; Zhou, Bengang; Shi, Yaolin

    2016-01-01

    A high-resolution model of P-wave anisotropic tomography beneath Mainland China and surrounding regions is determined using a large number of arrival-time data recorded by the China seismic network, the International Seismological Centre (ISC) and temporary seismic arrays deployed on the Tibetan Plateau. Our results provide important new insights into the subducted Indian plate and mantle dynamics in East Asia. Our tomographic images show that the northern limit of the subducting Indian plate has reached the Jinsha River suture in eastern Tibet. A striking variation of P-wave azimuthal anisotropy is revealed in the Indian lithosphere: the fast velocity direction (FVD) is NE-SW beneath the Indian continent, whereas the FVD is arc parallel beneath the Himalaya and Tibetan Plateau, which may reflect re-orientation of minerals due to lithospheric extension, in response to the India-Eurasia collision. There are multiple anisotropic layers with variable FVDs in some parts of the Tibetan Plateau, which may be the cause of the dominant null splitting measurements in these regions. A circular pattern of FVDs is revealed around the Philippine Sea slab beneath SE China, which reflects asthenospheric strain caused by toroidal mantle flow around the edge of the subducting slab. PMID:27432744

  14. Depth variations of P-wave azimuthal anisotropy beneath Mainland China.

    Science.gov (United States)

    Wei, Wei; Zhao, Dapeng; Xu, Jiandong; Zhou, Bengang; Shi, Yaolin

    2016-07-19

    A high-resolution model of P-wave anisotropic tomography beneath Mainland China and surrounding regions is determined using a large number of arrival-time data recorded by the China seismic network, the International Seismological Centre (ISC) and temporary seismic arrays deployed on the Tibetan Plateau. Our results provide important new insights into the subducted Indian plate and mantle dynamics in East Asia. Our tomographic images show that the northern limit of the subducting Indian plate has reached the Jinsha River suture in eastern Tibet. A striking variation of P-wave azimuthal anisotropy is revealed in the Indian lithosphere: the fast velocity direction (FVD) is NE-SW beneath the Indian continent, whereas the FVD is arc parallel beneath the Himalaya and Tibetan Plateau, which may reflect re-orientation of minerals due to lithospheric extension, in response to the India-Eurasia collision. There are multiple anisotropic layers with variable FVDs in some parts of the Tibetan Plateau, which may be the cause of the dominant null splitting measurements in these regions. A circular pattern of FVDs is revealed around the Philippine Sea slab beneath SE China, which reflects asthenospheric strain caused by toroidal mantle flow around the edge of the subducting slab.

  15. Geophysical imaging of buried volcanic structures within a continental back-arc basin

    DEFF Research Database (Denmark)

    Stratford, Wanda Rose; Stern, T.A.

    2008-01-01

    Hidden beneath the ~2 km thick low-velocity volcaniclastics on the western margin of the Central Volcanic Region, North Island, New Zealand, are two structures that represent the early history of volcanic activity in a continental back-arc. These ~20×20 km structures, at Tokoroa and Mangakino, fo...

  16. Microstructure and magnetic fabric in the Shuanghe pluton: A synkinematic granite in Eastern Dabie Mountains, China

    Institute of Scientific and Technical Information of China (English)

    YANG; Kunguang; LIU; Qiang; LIU; Yuyan; MA; Changqian; XU

    2004-01-01

    Strain analyses for the Shuanghe pluton show that the main strain planes suffered distinct deformation. The main strain value (XZ) is up to 1.59-2.18, and the value of Flinn index (K) ranges from 0.11 to 0.82. Anisotropy of magnetic susceptibility (AMS) measurements reveal that the orientations of the magnetic foliation and lineation gently dip SE, consistent with the macroscopic foliation of the pluton. The value of anisotropy degree (P) ranges from 1.109 to 1.639, and the shape parameter (7) from 0.079 to 0.534. These studies prove that the pluton was deformed under strong compression. Quartz c-axis textures, defined by monoclinic or triclinic asymmetry, usually developed the high maxima paralleling the b-axis, which is defined by the developed in the high-ultrahigh pressure rocks (UHP) which were captured in the pluton or country rocks. It is concluded that the Shuanghe pluton emplaced under regional compression slightly after the formation of UHP, and it is characterized by synkinematic granitic deformation.

  17. Arc deflection model and arc direction control for DC arc furnace

    Institute of Scientific and Technical Information of China (English)

    Liping Wei; Huang Zhou; Huade Li; Yuanhang Zhou

    2004-01-01

    Based on the analysis of three-dimensional power conductor for DC arc furnace, the electric arc deflection model was set up and the control system of the arc direction was configured. According to the bus bar distribution at the bottom electrodes cooled by water, the arc direction control principle and its configuration were described. The simulation results show that the control system can restrain the electric arc deflection and control the arc direction.

  18. Crustal structure and fluid distribution beneath the southern part of the Hidaka collision zone revealed by 3-D electrical resistivity modeling

    Science.gov (United States)

    Ichihara, Hiroshi; Mogi, Toru; Tanimoto, Kengo; Yamaya, Yusuke; Hashimoto, Takeshi; Uyeshima, Makoto; Ogawa, Yasuo

    2016-04-01

    The Hidaka collision zone, where the Kurile and northeastern (NE) Japan arcs collide, provides a useful study area for elucidating the processes of arc-continent evolution and inland earthquakes. To produce an image of the collision structure and elucidate the mechanisms of anomalously deep inland earthquakes such as the 1970 Hidaka earthquake (M6.7), we conducted magnetotelluric observations and generated a three-dimensional resistivity distribution in the southern part of the Hidaka collision zone. The modeled resistivity was characterized by a high resistivity area in the upper crust of the Kurile arc corresponding to metamorphic rocks. The model also showed conductive zones beneath the center of the collision zone. The boundary between the resistive and conductive areas corresponds geometrically to the Hidaka main thrust, which is regarded as the arc-arc boundary. The correspondence supports the collision model that the upper-middle part of crust in the Kurile arc is obducting over the NE Japan arc. The conductive areas were interpreted as fluid-filled zones associated with collision processes and upwelling of dehydrated fluid from the subducting Pacific slab. The fluid flow possibly contributes to over-pressurized conduction that produces deep inland earthquakes. We also observed a significant conductive anomaly beneath the area of Horoman peridotite, which may be related to the uplift of mantle materials to the surface.

  19. Tokamak ARC damage

    International Nuclear Information System (INIS)

    Tokamak fusion reactors will have large plasma currents of approximately 10 MA with hundreds of megajoules stored in the magnetic fields. When a major plasma instability occurs, the disruption of the plasma current induces voltage in the adjacent conducting structures, giving rise to large transient currents. The induced voltages may be sufficiently high to cause arcing across sector gaps or from one protruding component to another. This report reviews a tokamak arcing scenario and provides guidelines for designing tokamaks to minimize the possibility of arc damage

  20. Episodic continental arc volcanism, tectonism and erosion recorded in stratigraphy and detrital zircon geochronology

    Science.gov (United States)

    Cao, W.; Paterson, S. R.

    2015-12-01

    Stratigraphic studies and detrital zircon geochronology of metamorphic host rock pendants of the Mesozoic Sierra Nevada arc in California show temporal correlations with episodic arc volcanism and tectonism, and have implications for our understanding of sources and sinks of recycled volcanic and sedimentary materials, as well as the paleo-geography and erosion history of an ancient continental arc. The Middle Triassic to Early Cretaceous stratigraphy of the metamorphic pendants shows alternating volcanic and sedimentary beds. The latter varies from rocks formed in high-energy terrestrial to low-energy shallow marine environments. Sedimentary textures also vary from poorly sorted volcanic-clast/breccia-rich to well-sorted fine-grained rocks and carbonates. We interpret these variations in stratigraphic records to reflect the waning and waxing of arc volcanism and tectonism, which controls erosion of source rocks, as well as elevation changes through isostastic balance. These in turn control the paleo-geography and depositional environments. Detrital zircon geochronology confirms our hypothesis. Detrital zircon ages of sedimentary rocks closely track the ages of volcanic/plutonic rocks formed immediately earlier and also include age signals of older igneous rocks and pre-arc basement, suggesting the erosion of igneous rocks of higher elevation during the magmatic flare-ups and deposition of these clasts afterwards. We conclude that episodic arc volcanism and tectonism play important roles on processes of surface erosion and sedimentation.

  1. Receiver Function Analysis of the Lithospheric Structure Beneath the Western Great Plains

    Science.gov (United States)

    Thurner, S.; Zhai, Y.; Levander, A.

    2010-12-01

    The lithosphere in the western Great Plain region of the Southwestern U.S. has been subject to tectonic deformation from the Proterozoic to present day. Proterozoic island arc terranes accreted onto the North American continent between 1.8 and 1.1 Ga, forming the original continent, and there is evidence for Proterozoic continental extension which formed basement penetrating faults between 1.5 and .6 Ga . This was followed by the uplift of the Ancestral Rockies and, most recently, the subduction of the Farallon plate beneath North America. Extension has occurred throughout the Basin and Range and formed the Rio Grand Rift (RGR). However, the relative impact that large scale tectonic forces, regional asthenospheric upwelling, and preexisting structural weaknesses have on the extension of the RGR is still undetermined. This study seeks to better understand the current tectonic system east of the Colorado Plateau beneath the RGR and western Great Plains. We use teleseismic receiver functions to investigate the nature of extension in the RGR as well as its connection to the small-scale convection thought to be occurring beneath the Colorado Plateau-RGR-Great Plains region. Our receiver function images were generated from 85 earthquake events recorded at 187 USArray Transportable Array seismic stations located throughout the western Great Plains (Latitude: 28-48, Longitude: -105-100). Previous studies have indicated crustal thickness between 39 km and 50 km beneath the Great Plains and as thin as 35 km beneath the RGR (Wilson et.al, 2005). Tomography results have shown high velocity anomalies on both sides of the RGR, extending to 600 km depth beneath the western Great Plains, and a low velocity anomaly directly beneath the RGR (Gok et. al, 2003, Wilson et. al, 2005, Gao et. al, Song and Helmberger, 2007). The western Great Plains high velocity anomaly has been interpreted to be part of the downwelling portion of an edge driven convection system induced by a lateral

  2. Lithospheric structure beneath the Caribbean- South American plate boundary from S receiver functions

    Science.gov (United States)

    Masy, J.; Levander, A.; Niu, F.

    2010-12-01

    We have analyzed teleseismic S-wave data recorded by the permanent national seismic network of Venezuela and the BOLIVAR broadband array (Broadband Onshore-offshore Lithospheric Investigation of Venezuela and the Antilles arc Region) deployed from 2003 to 2005. A total of 28 events with Mw > 5.7 occurring at epicentral distances from 55° to 85° were used. We made Sp receiver functions to estimate the rapid variations of lithospheric structure in the southern Caribbean plate boundary region to try to better understand the complicated tectonic history of the region. Estimated Moho depth ranges from ~20 km beneath the Caribbean Large Igneous Provinces to ~50 km beneath the Mérida Andes in western Venezuela and the Sierra del Interior in northeastern Venezuela. These results are consistent with previous receiver functions studies (Niu et al., 2007) and active source profiles (Schmitz et al., 2001; Bezada et al., 2007; Clark et al., 2008; Guedez, 2008; Magnani et al., 2009). Beneath the Maracaibo Block we observe a signal at a depth of 100 km dipping ~24° towards the continent, which we interpret as the top of the oceanic Caribbean slab that is subducting beneath South America from the west. The deeper part of the slab was previously imaged using P-wave tomography (Bezada et al, 2010), and the upper part inferred from intermediate depth seismicity (Malavé and Suarez, 1995). These studies indicate flat slab subduction beneath northern Colombia and northwestern Venezuela with the slab dipping between 20° - 30° beneath Lake Maracaibo. Like others we attribute the flat slab subduction to the uplift of the Mérida Andes (for example Kellogg and Bonini, 1982). In eastern Venezuela beneath the Sierra del Interior we also observe a deep signal that we interpret as deep South American lithosphere that is detaching from the overriding plate as the Atlantic subducts and tears away from SA (Bezada et al., 2010; Clark et al, 2008). The lithosphere-asthenosphere boundary (LAB

  3. Rates, Mechanisms, and Implications of Crustal Assimilation in Continental Arcs

    Science.gov (United States)

    Dungan, M.; Davidson, J.

    2002-12-01

    chemical consequences for whole-rock compositions of arc basalts at the Tatara-San Pedro complex (TSPC), Chilean Andes. This occurrence, although thermally challenged according to the traditional paradigm, demonstrates that significant modifications of trace element abundances and ratios need not shift the host magma composition outside the basaltic range. In fact, the retention of micro-xenolithic clots rich in olivine and augite has produced positive correlations between incompatible and compatible elements in some magmas, and 87Sr/86Sr decreases from 0.7041 to 0.7039 with increasing Rb (8-27 ppm). Hornblende and phlogopite in mafic arc plutonic xenoliths promote rapid digestion by lowering solidus temperatures and such melts amplify the chemical overprint in contaminated magmas, but partially melted gabbroic and troctolitic xenoliths lacking hydrous minerals are widespread at the TSPC, and many mafic magmas contain micro-xenolithic plutonic crystal clots derived from such lithologies that volumetrically rival the true phenocryst assemblage. Among the implications of these observations is that long-lived arc volcanoes may extensively recycle their own plutonic roots. [1] Huppert HH and Sparks RSJ (1985) E.P.S.Lett., 74, 371-386. [2] Dungan et al. (1986) J. Geophys. Res., 91, 5999-6028. [3] Philpotts AR and Asher PM (1993) J. Petrol., 34, 1029-1058. [4] Heliker C (1995) J. Volc. Geoth. Res., 6, 115-135. [5] Reiners et al. (1995) Geology, 23, 563-566. [6] Spera FJ and Bohrson WA (2001) J. Petrol., 42, 999-1018. [7] Grove et al. (1988) Contrib. Min. Petrol., 99, 320-343. [8] Dungan et al. (2001) J. Petrol., 42, 555-626.

  4. Uptaking of plagioclase xenocryst into H2O-rich rear-arc basaltic magma

    Science.gov (United States)

    Hamada, M.

    2015-12-01

    Kuritani et al. (2013, Mineral. Petrol.) and Kuritani et al. (2014, Contrib. Mineral. Petrol.) estimated genetic conditions of primary arc magmas beneath the Iwate volcano (a frontal arc volcano in the northeast Japan arc) and the Sannome-gata volcano (a rear-arc volcano in the northeast Japan arc) based on analyses of volcanic rocks and numerical simulation. They estimated that H2O concentrations of primary melts are 4-5 wt.% beneath the Iwate volcano and 6-7 wt.% beneath the Sannnome-gata volcano, respectively. Their arguments mean that primary melts beneath frontal-arc volcanoes and rear-arc volcanoes are both H2O-rich, yet there has been no direct evidence to support their arguments at the Sannnome-gata volcano because volcanic rocks are either almost aphyric and/or almost no melt inclusions were found. Hydrogen concentration in nominally anhydrous minerals serves as a hygrometer of arc basaltic melts (e.g., Hamada et al. 2013, Earth Planet. Sci. Lett.). In this study, hydrogen concentration of plagioclase as a crustal xenocryst was analyzed to estimate H2O concentration of basaltic melt coexisted with plagioclase before the eruption. Plagioclase xenocrists were separated from crushed scoria which erupted from the Sannome-gata volcano 20,000-24,000 years ago. Composition of the plagioclase core is homogeneous and ranges from An30 through An35. The rim is 150 to 200-μm-thick dusty zone whose composition is around An60, suggesting that the rim crystallized rapidly from degassed basaltic melt. The profiles of infrared absorption area per unit thickness across the plagioclase core were obtained using Fourier Transform InfraRed spectrometer (FTIR). The inner core contains hydrogen of about 60 wt. ppm H2O, and hydrogen concentration elevates at outer core. Hydrogen concentration at the outermost core of plagioclase is >200 wt. ppm H2O, suggesting that plagioclase xenocrists were taken by hydrous melt (H2O>5 wt.%; Hamada et al. 2014, Earth Planet. Sci. Lett.) and

  5. Imaging the seismic structure beneath oceanic spreading centers using ocean bottom geophysical techniques

    Science.gov (United States)

    Zha, Yang

    This dissertation focuses on imaging the crustal and upper mantle seismic velocity structure beneath oceanic spreading centers. The goals are to provide a better understanding of the crustal magmatic system and the relationship between mantle melting processes, crustal architecture and ridge characteristics. To address these questions I have analyzed ocean bottom geophysical data collected from the fast-spreading East Pacific Rise and the back-arc Eastern Lau Spreading Center using a combination of ambient noise tomography and seafloor compliance analysis. To characterize the crustal melt distribution at fast spreading ridges, I analyze seafloor compliance - the deformation under long period ocean wave forcing - measured during multiple expeditions between 1994 and 2007 at the East Pacific Rise 9º - 10ºN segment. A 3D numerical modeling technique is developed and used to estimate the effects of low shear velocity zones on compliance measurements. The forward modeling suggests strong variations of lower crustal shear velocity along the ridge axis, with zones of possible high melt fractions beneath certain segments. Analysis of repeated compliance measurements at 9º48'N indicates a decrease of crustal melt fraction following the 2005 - 2006 eruption. This temporal variability provides direct evidence for short-term variations of the magmatic system at a fast spreading ridge. To understand the relationship between mantle melting processes and crustal properties, I apply ambient noise tomography of ocean bottom seismograph (OBS) data to image the upper mantle seismic structure beneath the Eastern Lau Spreading Center (ELSC). The seismic images reveal an asymmetric upper mantle low velocity zone (LVZ) beneath the ELSC, representing a zone of partial melt. As the ridge migrates away from the volcanic arc, the LVZ becomes increasingly offset and separated from the sub-arc low velocity zone. The separation of the ridge and arc low velocity zones is spatially coincident

  6. ALICE - ARC integration

    OpenAIRE

    Anderlik, Csaba; Gregersen, Anders Rhod; Kleist, Josva; Peters, Andreas; Siaz, Pablo

    2007-01-01

    AliEn or Alice Environment is the Gridware developed and used within the ALICE collaboration for storing and processing data in a distributed manner. ARC (Advanced Resource Connector) is the Grid middleware deployed across the Nordic countries and gluing together the resources within the Nordic Data Grid Facility (NDGF). In this paper we will present our approach to integrate AliEn and ARC, in the sense that ALICE data management and job processing can be carried out on the NDGF infrastructur...

  7. 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.

  8. 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

  9. Contrasting sedimentary processes along a convergent margin: the Lesser Antilles arc system

    Science.gov (United States)

    Picard, Michel; Schneider, Jean-Luc; Boudon, Georges

    2006-12-01

    Sedimentation processes occurring in an active convergent setting are well illustrated in the Lesser Antilles island arc. The margin is related to westward subduction of the North and/or the South America plates beneath the Caribbean plate. From east to west, the arc can be subdivided into several tectono-sedimentary depositional domains: the accretionary prism, the fore-arc basin, the arc platform and inter-arc basin, and the Grenada back-arc basin. The Grenada back-arc basin, the fore-arc basin (Tobago Trough) and the accretionary prism on the east side of the volcanic arc constitute traps for particles derived from the arc platform and the South American continent. The arc is volcanically active, and provides large volumes of volcaniclastic sediments which accumulate mainly in the Grenada basin by volcaniclastic gravity flows (volcanic debris avalanches, debris flows, turbiditic flows) and minor amounts by fallout. By contrast, the eastern side of the margin is fed by ash fallout and minor volcaniclastic turbidites. In this area, the dominant component of the sediments is pelagic in origin, or derived from South America (siliciclastic turbidites). Insular shelves are the locations of carbonate sedimentation, such as large platforms which develop in the Limestone Caribbees in the northern part of the margin. Reworking of carbonate material by turbidity currents also delivers lesser amounts to eastern basins of the margin. This contrasting sedimentation on both sides of the arc platform along the margin is controlled by several interacting factors including basin morphology, volcanic productivity, wind and deep-sea current patterns, and sea-level changes. Basin morphology appears to be the most dominant factor. The western slopes of the arc platform are steeper than the eastern ones, thus favouring gravity flow processes.

  10. Seismic response to slab rupture and variation in lithospheric structure beneath the Savu Sea, Indonesia

    Science.gov (United States)

    Ely, Kim S.; Sandiford, Mike

    2010-03-01

    Variations in seismic moment release and stress state across the transition from subduction of oceanic crust to arc-continent collision in the Banda Arc are constrained by focal mechanism solutions from the CMT earthquake catalogue. In particular the slab under the western Savu Sea is unusual in that intermediate depth (70-300 km) events indicate that at this depth range the slab is largely in down-dip compression. This contrasts with the intermediate depth, down-dip tension that typifies the Sunda slab to the west and the far eastern Banda slab to the east. Down-dip compression beneath the Savu Sea reflects subduction of transitional crust of the Scott Plateau, more buoyant than the Indian Ocean crust subducting further west. In this region, enhanced magma flux is indicated by unusually narrow volcano spacing in the overlying arc, and suggests that down-dip compression reflects not only more buoyant transitional crust but also a reduction in slab-wedge coupling induced by enhanced magma flux. East of the Savu Sea, the near complete absence of intermediate depth seismicity is attributed to a slab window that has opened where Australian continental crust has collided with the arc. Differences in seismic moment release around this slab window indicate asymmetric rupture, propagating to the east at a much faster rate than to the west.

  11. Imaging Magma Plumbing Beneath Askja Volcano, Iceland

    Science.gov (United States)

    Greenfield, T. S.; White, R. S.

    2015-12-01

    Using a dense seismic network we have imaged the plumbing system beneath Askja, a large central volcano in the Northern Volcanic Zone, Iceland. Local and regional earthquakes have been used as sources to solve for the velocity structure beneath the volcano. We find a pronounced low-velocity anomaly beneath the caldera at a depth of ~7 km around the depth of the brittle-ductile transition. The anomaly is ~10% slower than the initial best fitting 1D model and has a Vp/Vs ratio higher than the surrounding crust, suggesting the presence of increased temperature or partial melt. We use relationships between mineralogy and seismic velocities to estimate that this region contains ~10% partial melt, similar to observations made at other volcanoes such as Kilauea. This low-velocity body is deeper than the depth range suggested by geodetic studies of a deflating source beneath Askja. Beneath the large low-velocity zone a region of reduced velocities extends into the lower crust and is coincident with seismicity in the lower crust. This is suggestive of a high temperature channel into the lower crust which could be the pathway for melt rising from the mantle. This melt either intrudes into the lower crust or stalls at the brittle-ductile boundary in the imaged body. Above this, melt can travel into the fissure swarm through large dikes or erupt within the Askja caldera itself.We generate travel time tables using a finite difference technique and the residuals used to simultaneously solve for both the earthquake locations and velocity structure. The 2014-15 Bárðarbunga dike intrusion has provided a 45 km long, distributed source of large earthquakes which are well located and provide accurate arrival time picks. Together with long-term background seismicity these provide excellent illumination of the Askja volcano from all directions.hhhh

  12. Reconstruction of mid-crustal pluton assembly and evolution using trace elements in augite: Sausfjellet pluton, Bindal batholith, north-central Norway.

    Science.gov (United States)

    Coint, Nolwenn; Barnes, Calvin; Yoshinobu, Aaron; Prestvik, Tore; Barnes, Melanie

    2013-04-01

    The Sausfjellet pluton is a 445 Ma gabbroic to monzonitic body of 7 Km in diameter emplaced in two stages at ~700 MPa pressure. Stage 1 is a coarse pyroxene hornblende gabbro. Stage 2 intrudes a steep contact between marbles on the east and pelitic migmatites on the west. Stage 2 displays a gradational transition from hornblende biotite two-pyroxene diorite to hornblende biotite three-pyroxene quartz monzonite. This transition is accompanied by a decrease in the An content of normally-zoned plagioclase from An61 to An27. Much of the pluton consists of cumulate rocks, as illustrated by the presence of anorthosite and pyroxene-rich layers. In the western part of the intrusion, hosted by metapelitic rocks, incompatible element concentrations and bulk-rock ^18O increase to levels that cannot be explained by fractional crystallization. These increases were originally explained by AFC processes, but because of the cumulative nature of the rocks, it is difficult to assess magmatic processes using bulk rock compositions. Therefore, we analyzed trace element contents and core-to-rim zoning in augite as a proxy to track changes in melt composition. Augite is normally zoned, with lower incompatible element abundances in the cores than in the rims, consistent with evolution of the melt by fractional crystallization. However, instead of plotting along a single differentiation trend, augite compositions define two trends, which is inconsistent with a closed system. The most mafic rocks define a trend with lower REE contents and smaller (negative) Eu anomalies compared to those from the more evolved part of the pluton, although the two trends overlap in Zr content. The two trends correspond to the central, more mafic zone that intrudes marble and the western, more evolved zone that intrudes metapelites. The trend associated with the western zone consists of the same samples that show bulk-rock ^18O enrichment, and is best explained as resulting from assimilation of the host

  13. Modeling of Arc Force in Plasma Arc Welding

    Institute of Scientific and Technical Information of China (English)

    GAO Zhonglin; HU Shengsun; YIN Fengliang; WANG Rui

    2008-01-01

    A three. dimensional mathematical model for the transferred-type argon arc was developed to describe arc force on the anode surface. The software ANSYS was employed to solve the model. The model includes a part of torch and tungsten electrode to achieve m ore reasonable results. The arc temperature and flow fields were derived. And the influences of welding parameters on arc force were also studied. The simulated results show that arc pressure at the anode are dependent on the welding current, plasma gas flow rate and electrode neck-in, while not sensitive to arc length.

  14. Using micro-scale evidence to understand regional-scale hydrothermal alteration of plutonic rocks

    NARCIS (Netherlands)

    Plümper, O.; King, H. E.; Putnis, A.

    2009-01-01

    Subsolidus re-equilibration of plutonic feldspars induced by hydrothermal fluids provides a valuable record of fluid-rock interactions that affect large volumes of the Earth's continental crust (Taylor, 1977). The effect of hydrothermal fluids has important implications for the interpretation of the

  15. Geochronology and geochemistry of granite plutons from east Khasi hills, Meghalaya

    International Nuclear Information System (INIS)

    Discordant granite plutons at Kyrdem, Nongpoh and South Khasi intrude the basement gneisses and the overlying Shillong Group of metasediments in the Meghalaya Plateau. Porphyritic granitoids ranging in composition from quartz monazonite to granite represent the dominant component in all the three plutons. Common characteristics of these granitoids are spatial association with homblende dioritic rocks, dominantly potassic and metaluminous nature. A positive correlation of SiO2, Na2O+K2O, Rb, Rb/Sr and negative correlation of CaO, MgO, FeO(T), Sr, TiO2 with Differentiation Index in the Kyrdem pluton point to fractional crystallisation processes. Rb-Sr whole rock isochron data of the plutons yield ages in the range 480-690 Ma with initial 87Sr/86Sr ratios ranging from 0.70948-0.71482. Absence of post emplacement tectonothermal event is suggested by near concordant K-Ar biotite ages. A protracted thermal event during late proterozoic-early paleozoic (500-700 Ma), possibly related to mantle upwelling, possibly triggered the generation of these granitoids. (author). 14 refs., 9 figs. , 6 tabs

  16. Tectonic rotations and internal structure of Eocene plutons in Chuquicamata, northern Chile

    Science.gov (United States)

    Somoza, R.; Tomlinson, A. J.; Zaffarana, C. B.; Singer, S. E.; Puigdomenech Negre, C. G.; Raposo, M. I. B.; Dilles, J. H.

    2015-07-01

    A paleomagnetic and AMS study on Eocene plutonic complexes in the Calama area, northern Chile, reveals high-temperature, high-coercivity magnetizations of dominantly thermoremanent origin and magnetic fabrics controlled by magnetite. The paleomagnetic results indicate that ~ 43 Ma plutons underwent clockwise tectonic rotation, whereas adjacent ~ 39 Ma plutons did not undergo discernible rotation. This points to a middle Eocene age for the younger tectonic rotations associated with the Central Andean Rotation Pattern in the Chuquicamata-Calama area. The petrofabric in these rocks formed under conditions ranging from purely magmatic (i.e. before full crystallization) to low-temperature solid-state deformation. AMS and paleomagnetism suggest that the plutonic bodies were formed by progressive amalgamation of subvertical magma sheets spanning multiple magnetic polarity chrons. The parallelism between magmatic and tectonic foliations suggests that regional tectonic stress controlled ascent, emplacement and rock deformation during cooling. In this context, we suggest that magma ascent and emplacement in the upper crust likely exploited Mesozoic structures which were locally reactivated in the Eocene.

  17. The geochemistry, age, and origin of groundwater in a mafic pluton, East Bull Lake, Ontario, Canada

    International Nuclear Information System (INIS)

    Atomic Energy of Canada Ltd. (AECL) is conducting geoscience investigations of several plutons in Canada's Precambrian Shield as part of the Canadian Nuclear Fuel Waste Management Program, to determine whether such rock masses are suitable for the safe disposal of nuclear fuel waste. The East Bull Lake (EBL) gabbro-anorthosite layered complex is unique in this program as it is the only mafic pluton in which hydrogeological and hydrogeochemical studies have been conducted. These results can be compared with those of similar studies of granitic rocks which have been investigated more extensively. During the period, 1983-85, hydrogeological testing and hydrochemical sampling were conducted by the National Hydrology Research Institute of Environment Canada and AECL in boreholes drilled to depths of up to 850 m into the EBL pluton (Raven et al., 1987). This paper discusses the hydrogeochemistry of the pluton and identifies the major rock-water interactions controlling the chemistry. The spatial variability in chemistry will be shown to be related to the nature of the groundwater flow systems present at this site. The ages and origins of the groundwaters and their solutes are inferred from isotopic analyses

  18. Thermal modification of hematite-ilmenite intergrowths in the Ecstall pluton, British Columbia, Canada

    DEFF Research Database (Denmark)

    Brownlee, S.J.; Feinberg, J.M.; Harrison, R.J.;

    2010-01-01

    . Higher temperatures also enhanced oxidation in ilmenite. The formation of magnetite altered the bulk magnetic properties of these samples, increasing NRM intensity. This study underscores the need to consider a pluton's post-emplacement thermal history before making tectonic interpretations based...

  19. Insights Into the Formation of Rhyolite From the Searchlight Pluton: Evidence from Oriented Quartz Clusters

    Science.gov (United States)

    Froemming, N.; Deering, C. D.; Beane, R. J.; Bachmann, O.

    2012-12-01

    The Miocene Searchlight pluton (SLP) in the Colorado River extensional corridor of southern Nevada, is well-exposed and tilted near-vertical for exceptional cross-sectional study of magma reservoir dynamics and crystal fractionation of a mid- to upper-crustal pluton (3 to 13 km depth). The upper quartz monzonite section is dominated by minerals in apparent random orientation with a medium- to fine-grained texture due to direct contact with the cold host rock. The middle granitic section is dominated by coarse-grained quartz and feldspar, and interpreted to be a zone of extracted liquid from an intermediate magma. The lower monzonite section is composed of coarse-grained plagioclase and potassium feldspar. We used the crystallographic orientations of quartz clusters, as determined by Electron Backscatter Diffraction (EBSD), to test for crystal accumulation in the SLP. Clusters of quartz crystals with matched dipyramidal faces (parallel or Esterel twin orientation) may indicate a period of crystal accumulation. By analyzing representative samples from each section of the pluton, we found that the lower section (intermediate cumulate) and upper section (crystallization front) do not have quartz clusters with matched dipyramidal faces. Although plagioclase grains are aligned in the lower section, the late crystallization of quartz appears to have prevented aligned or preferred growth orientations. In contrast, the middle section has a high percentage of quartz clusters with matched dipyramidal faces - similar to that found in granite porphyry of the Vinalhaven pluton, Maine. The aligned grains may have formed by fractional crystallization, compaction and synneusis of the early forming quartz in this granitic section. We interpret the middle section of the Searchlight pluton as being similar to shallow, upper crustal plutons (3-8 km depth) such as Vinalhaven pluton. The deep vertical exposure of the SLP, shows that the middle section was formed from periodic episodes of

  20. Magnetic fabrics and their relationship with the emplacement of the Piracaia pluton, SE Brazil

    Science.gov (United States)

    Raposo, M. Irene B.; Pressi, Leonardo Frederico; de Assis Janasi, Valdecir

    2012-04-01

    Magnetic fabric and rock-magnetism studies were performed on the four units of the 578 ± 3-Ma-old Piracaia pluton (NW of São Paulo State, southern Brazil). This intrusion is roughly elliptical (~32 km2), composed of (i) coarse-grained monzodiorite (MZD-c), (ii) fine-grained monzodiorite (MZD-f), which is predominant in the pluton, (iii) monzonite heterogeneous (MZN-het), and (iv) quartz syenite (Qz-Sy). Magnetic fabrics were determined by applying both anisotropy of low-field magnetic susceptibility (AMS) and anisotropy of anhysteretic remanent magnetization (AARM). The two fabrics are coaxial. The parallelism between AMS and AARM tensors excludes the presence of a single domain (SD) effect on the AMS fabric of the units. Several rock-magnetism experiments performed in one specimen from each sampled units show that for all of them, the magnetic susceptibility and magnetic fabrics are carried by magnetite grains, which was also observed in the thin sections. Foliations and lineations in the units were successfully determined by applying magnetic methods. Most of the magnetic foliations are steeply dipping or vertical in all units and are roughly parallel to the foliation measured in the field and in the country rocks. In contrast, the magnetic lineations present mostly low plunges for the whole pluton. However, for eight sites, they are steep up to vertical. Thin-section analyses show that rocks from the Piracaia pluton were affected by the regional strain during and after emplacement since magmatic foliation evolves to solid-state fabric in the north of the pluton, indicating that magnetic fabrics in this area of the pluton are related to this strain. Otherwise, the lack of solid-state deformation at outcrop scale and in thin sections precludes deformation in the SW of the pluton. This evidence allows us to interpret the observed magnetic fabrics as primary in origin (magmatic) acquired when the rocks were solidified as a result of magma flow, in which steeply

  1. Study of the Emplacement Mechanism of the Fenghuangshan Granite Pluton and Related Cu-Au Mineralization in Tongling, Anhui Province

    Institute of Scientific and Technical Information of China (English)

    WU Ganguo; ZHANG Da; LI Dongxu; ZHANG Xiangxin; SHAO Yongjun; ZANG Wenshuan; WANG Qunfeng

    2004-01-01

    The Fenghuangshan Pluton is located in the Tongling polymineral-cluster district in the middle-lower section of the Yangtze metallogenic belt. In tectonic terms, it is in the middle of the Guichi-Fanchang faulted fold bundle of the lower Yangtze Platform fold belt between the Dabie Orogenic Belt and the Jiangnan Massif. Analyses of the structural deformation characteristics of both the contact zone and the interior of the pluton are used to explain its emplacement mechanism. The foliation and lineation of the pluton, consisting of the oriented distribution of dark minerals and xenoliths, mainly concentrate along the margin of the pluton. Toward the center of the pluton, the foliation structure becomes weak, showing intense compression formation at the margin, and reflecting the conformable intrusion of the pluton. The relatively gentle lineation is evidence of a rotatory emplacement mechanism. Relatively steep marginal foliation reflects compression expanding. Affected by the thermal power of the pluton, the metamorphism of the contact zone has zonation. Both the strike of the axial plane of fold at the contact zone and that of the flow cleavage of the ductile shear zone are consistent with the boundary of the pluton, which reflects the speciality of conformable intrusion. The hinges of the folds are mostly inclined and erect, reflecting both the rotation of the pluton and its upward spiraling emplacement mechanism. Boudins developed in both the contact zone and the steep strata indicate the emplacement characteristic of the ballon expanding. The surrounding rock of the contact zone shortens horizontally. The average percentage of shortening is 39.7%, which further proves the mechanism of the pluton expanding, and the space occupied by the active expanding intrusion was provided by the shortening of the surrounding rock. The left-lateral shear shown by the ductile shear zone and the rheomorphic fold reveals that the pluton emplacement and the deformation of

  2. ALICE-ARC integration

    International Nuclear Information System (INIS)

    AliEn or Alice Environment is the Grid middleware developed and used within the ALICE collaboration for storing and processing data in a distributed manner. ARC (Advanced Resource Connector) is the Grid middleware deployed across the Nordic countries and gluing together the resources within the Nordic Data Grid Facility (NDGF). In this paper we will present our approach to integrate AliEn and ARC, in the sense that ALICE data management and job processing can be carried out on the NDGF infrastructure, using the client tools available in AliEn. The inter-operation has two aspects, one is the data management part and the second the job management aspect. The first aspect was solved by using dCache across NDGF to handle data. Therefore, we will concentrate on the second part. Solving it, was somewhat cumbersome, mainly due to the different computing models employed by AliEn and ARC. AliEN uses an Agent based pull model while ARC handles jobs through the more 'traditional' push model. The solution comes as a module implementing the functionalities necessary to achieve AliEn job submission and management to ARC enabled sites

  3. MODELING PARAMETERS OF ARC OF ELECTRIC ARC FURNACE

    Directory of Open Access Journals (Sweden)

    R.N. Khrestin

    2015-08-01

    Full Text Available Purpose. The aim is to build a mathematical model of the electric arc of arc furnace (EAF. The model should clearly show the relationship between the main parameters of the arc. These parameters determine the properties of the arc and the possibility of optimization of melting mode. Methodology. We have built a fairly simple model of the arc, which satisfies the above requirements. The model is designed for the analysis of electromagnetic processes arc of varying length. We have compared the results obtained when testing the model with the results obtained on actual furnaces. Results. During melting in real chipboard under the influence of changes in temperature changes its properties arc plasma. The proposed model takes into account these changes. Adjusting the length of the arc is the main way to regulate the mode of smelting chipboard. The arc length is controlled by the movement of the drive electrode. The model reflects the dynamic changes in the parameters of the arc when changing her length. We got the dynamic current-voltage characteristics (CVC of the arc for the different stages of melting. We got the arc voltage waveform and identified criteria by which possible identified stage of smelting. Originality. In contrast to the previously known models, this model clearly shows the relationship between the main parameters of the arc EAF: arc voltage Ud, amperage arc id and length arc d. Comparison of the simulation results and experimental data obtained from real particleboard showed the adequacy of the constructed model. It was found that character of change of magnitude Md, helps determine the stage of melting. Practical value. It turned out that the model can be used to simulate smelting in EAF any capacity. Thus, when designing the system of control mechanism for moving the electrode, the model takes into account changes in the parameters of the arc and it can significantly reduce electrode material consumption and energy consumption

  4. Magma Plumbing beneath Askja Volcano, Iceland

    Science.gov (United States)

    Greenfield, T. S.; White, R. S.

    2013-12-01

    Through a combination of accurate earthquake locations and tomography we have imaged the melt feeding network beneath Askja, a large central volcano, in the Northern Volcanic Zone, Iceland. We have deployed and operated a dense network of 3-component, broadband seismometers around the volcano since 2006 and have recorded a large number of events (on the order of 150 a day). The majority of these are due to an extensive geothermal area within the caldera and tectonically induced earthquakes to the northeast which are not related to the magma plumbing system. More intriguing are the less numerous deeper earthquakes situated in three distinct areas within the volcanic system. These have a lower frequency content to the shallower events which may be the result of highly attenuating lower crust. The deep earthquakes extend from 12-25 km depth, significantly below a well defined brittle-ductile boundary at 8-9 km. These earthquakes indicate the presence of melt moving or degassing at depth as only high strain rates or increased pore fluid pressures would cause brittle fracture in what is normally an aseismic region in the ductile zone. To image the structure beneath Askja, local and regional earthquakes have been used as sources to solve for the velocity structure beneath the volcano. Travel-time tables were created using a finite difference technique and the residuals were used to solve simultaneously for both the earthquake locations and velocity structure. Results showed a pronounced low-velocity anomaly beneath the caldera at a depth of ~5 km. The anomaly is ~10% slower than the initial best fitting 1D model and has a Vp/Vs ratio higher than the surrounding crust, suggesting the presence of increased temperature or partial melt. The body is unlikely to be entirely melt as S-waves are still detected at stations directly above the anomaly. This low-velocity body is slightly deeper than the depth range suggested by InSAR and GPS studies of a deflating source beneath

  5. Early Paleozoic subduction processes of the Paleo-Asian Ocean: Insights from geochronology and geochemistry of Paleozoic plutons in the Alxa Terrane

    Science.gov (United States)

    Liu, Qian; Zhao, Guochun; Sun, Min; Han, Yigui; Eizenhöfer, Paul R.; Hou, Wenzhu; Zhang, Xiaoran; Zhu, Yanlin; Wang, Bo; Liu, Dongxing; Xu, Bing

    2016-10-01

    The Alxa Terrane is situated in a key area between the North China and Tarim cratons. Paleozoic magmatic records in this terrane place important constraints on the subduction processes of the southern Paleo-Asian Ocean. New data of zircon U-Pb ages and whole-rock elemental and isotopic data reveal two groups of intermediate to felsic plutons in the Alxa Terrane. One group consists of diorites and granitoids that were emplaced at ca. 460-440 Ma and characterized by lower Al2O3/TiO2 ratios and higher TiO2 contents, implying high temperature-low pressure crystallization conditions and a shallow source region. The second group is dominated by granitoids aged at ca. 420-407 Ma and displays high Sr and Ba, low Y and high rare earth elements, with very high Sr/Y ratios and mostly positive Eu anomalies. These characteristics imply low temperature-high pressure crystallization conditions and source regions at deep crustal levels where garnet is stable in the residual phase. Both of the two groups are mostly calc-alkaline to high-K calc-alkaline, depleted in Nb, Ta and Ti and enriched in Ba, K and Sr, indicative of an arc affinity most likely related to the southward subduction of the Paleo-Asian Ocean. Zircon εHf(t) and whole-rock εNd(t) values of these magmatic rocks decrease from 458 Ma to 440 Ma and increase from 417 Ma to 407 Ma, whereas whole-rock initial 87Sr/86Sr ratios display an opposite trend. Such an isotopic change suggests a tectonic switch from an advancing to a retreating subduction regime at ~ 407 Ma. Synthesized data from this and previous studies suggest that the 460-400 Ma magmatic arc in the Alxa Terrane represented the western extension of the Paleozoic arc belt on the northern margin of the North China Craton.

  6. Arc Plasma Torch Modeling

    CERN Document Server

    Trelles, J P; Vardelle, A; Heberlein, J V R

    2013-01-01

    Arc plasma torches are the primary components of various industrial thermal plasma processes involving plasma spraying, metal cutting and welding, thermal plasma CVD, metal melting and remelting, waste treatment and gas production. They are relatively simple devices whose operation implies intricate thermal, chemical, electrical, and fluid dynamics phenomena. Modeling may be used as a means to better understand the physical processes involved in their operation. This paper presents an overview of the main aspects involved in the modeling of DC arc plasma torches: the mathematical models including thermodynamic and chemical non-equilibrium models, turbulent and radiative transport, thermodynamic and transport property calculation, boundary conditions and arc reattachment models. It focuses on the conventional plasma torches used for plasma spraying that include a hot-cathode and a nozzle anode.

  7. Seismic attenuation beneath Europe and the North Atlantic: Implications for water in the mantle

    Science.gov (United States)

    Zhu, Hejun; Bozdağ, Ebru; Duffy, Thomas S.; Tromp, Jeroen

    2013-11-01

    It is well known that anelasticity has significant effects on the propagation of seismic waves, as manifested by physical dispersion and dissipation. Investigations of anelasticity provide complementary constraints on the physical properties of Earth materials, but — contrary to imaging with elastic waves — progress in mapping Earth's anelasticity has been relatively slow, and there is only limited agreement between different studies or methodologies. Here, within the framework of adjoint tomography, we use frequency-dependent phase and amplitude anomalies between observed and simulated seismograms to simultaneously constrain upper mantle wavespeeds and attenuation beneath the European continent and the North Atlantic Ocean. In the sea-floor spreading environment beneath the North Atlantic, we find enhanced attenuation in the asthenosphere and within the mantle transition zone (MTZ). In subduction zone settings, for example beneath the Hellenic arc, elevated attenuation is observed along the top of the subducting slab down to the MTZ. No prominent reductions in wavespeeds are correlated with these distinct attenuation features, suggesting that non-thermal effects may play an important role in these environments. A plausible explanation invokes the transport of water into the deep Earth by relatively cold subducting slabs, leading to a hydrated MTZ, as previously suggested by mineral physics and geodynamics studies.

  8. Attenuation structure beneath the volcanic front in northeastern Japan from broad-band seismograms

    Science.gov (United States)

    Takanami, Tetsuo; Selwyn Sacks, I.; Hasegawa, Akira

    2000-10-01

    Anelastic structure in the asthenosphere beneath the volcanic front in northeastern Japan arc is estimated by using the spectral amplitude ratio data of P and S waves from about 100 events which occurred in the subducting Pacific slab below Japan. These earthquakes occurred within a 90 km radius centered about the station Sawauchi (SWU), with focal depths ranging from 60 to 200 km. Waveforms were recorded by the Carnegie broad-band three-component seismograph and were corrected for instrument responses, crustal reverberations, corner frequencies, and superimposed noise. Ray paths and travel times of P and S waves are calculated using a three-dimensional velocity model [Zhao, D., Hasegawa, A., Horiuchi, S., 1992. J. Geophys. Res. 97, 19909-19928]. We find a low- Q region ( QS˜70) extending down to 55 km depth from the lower crust beneath the volcanic front. Using Q-temperature laboratory results [Sato, H., Sacks, I.S., Murase, T., Muncill, G., Fukushima, H., 1989. J. Geophys. Res. 94, 10647-10661], this implies a temperature of about 130°C higher than the eastern forearc region and about 30°C higher than the western backarc region, in good agreement with the tomographic results of Zhao et al. [Zhao, D., Hasegawa, A., Horiuchi, S., 1992. J. Geophys. Res. 97, 19909-19928]. This suggests that low velocities in the crust and uppermost mantle beneath SWU may be explained by a subsolidus temperature increase without partial melting.

  9. Subducting slab structure below the eastern Sunda arc inferred from non-linear seismic tomographic imaging

    Science.gov (United States)

    Widiyantoro, S.; Pesicek, J. D.; Thurber, C. H.

    2011-12-01

    Detailed P-wave speed velocity structure beneath the Sunda arc has been successfully imaged by applying a non-linear approach to seismic tomography. Nearly one million compressional phases from events within the Indonesian region have been used. These include the surface-reflected depth phases pP and pwP in order to improve the sampling of the uppermantle structure, particularly below the back-arc regions. We have combined a high-resolution regional inversion with a low-resolution global inversion to minimize the mapping of distant aspherical mantle structure into the study region. In this paper, we focus our discussion on the upper mantle structure beneath the eastern part of the Sunda arc. The tomographic images confirm previous observations of a hole in the subducted slab in the upper mantle beneath eastern Java. The images also suggest that a tear in the slab exists below the easternmost part of the Sunda arc, where the down-going slab is deflected in the mantle transition zone. In good agreement with previous studies, the properties of the deflected slab show a strong bulk-sound signature.

  10. Oceanographic conditions beneath Fimbul Ice Shelf, Antarctica

    OpenAIRE

    Abrahamsen, Einar Povl

    2012-01-01

    Antarctic ice shelves play a key role in the global climate system, acting as important sites for the cooling of shelf waters, thereby facilitating deep and bottom water formation. Many of the processes that take place under large ice shelves can be observed more conveniently beneath smaller ice shelves such as Fimbul Ice Shelf, an ice shelf in the eastern Weddell Sea. Fimbul Ice Shelf and nearby ice shelves might also play a significant regional role: although no bottom water is produced in ...

  11. Numerical modeling of forceful pluton emplacement and associated deformation at different crustal levels - instantaneous, continuous or episodic intrusion?

    Science.gov (United States)

    Chen, Y.; Nabelek, P. I.

    2015-12-01

    The Papoose Flat pluton in the White-Inyo Range, California, is one of the best examples of forceful magma emplacement at mid-crustal levels that is revealed by a highly strained aureole. A thermo-rheological 2-D model of the pluton and its aureole is proposed. We explored how the frequency of magma input, from instantaneous to continuous to the bottom of the laccolith, affects the ductile width of the aureole and the crystallinity of the pluton, which has implications for eruption of magma. We modeled these aspects at mid- and upper-crustal levels. The pluton was assumed to be 5 km thick in the middle and 13 km wide. Except for instantaneous growth, pluton was assumed to grow over 5 m.y. The aureole was assumed to have power-law rheology of quartz with dependence on H2O fugacity, which was calculated using the CORK equation (Holland & Powell, 1991) Our result shows that the bottom of the Papoose Flat pluton was emplaced at the brittle-ductile transition zone of the crust. The crustal rheology profile assisted the softening of rocks around the pluton. The simulated temperature and strength profiles confirm that ductile deformation was related to thermal weakening (Saint-Blanquat et al., 2001). Results of incremental growth calculations show that the pluton remains hot and only partially crystalline for millions of years when it grows by frequent input of small batches of liquid. At the mid-crustal level, the ductile region around the pluton is much wider and exists longer than at the shallow crustal level. Brittle rheology is dominant during the late stage growth at the shallow depth. When the pluton grows instantly or by only few episodes of large batches of input, the mobile part of the pluton is thin and the ductile aureole is narrower. High-frequency incremental growth by smaller magma batches produces a large volume of mobile magma that has the potential to induce internal magmatic layering that may be reflected in aligned acquired magnetic susceptibility (AMS

  12. Magnetic properties of ilmenite-hematite single crystals from the Ecstall pluton near Prince Rupert, British Columbia

    DEFF Research Database (Denmark)

    Brownlee, Sarah J.; Feinberg, Joshua M.; Kasama, Takeshi;

    2011-01-01

    and hematite, the primary paleomagnetic recorder in the Ecstall pluton. Measurements of hysteresis properties, low-temperature remanence, and room temperature isothermal remanent magnetization acquisition and observations from magnetic force microscopy and off-axis electron holography indicate that samples...... to an increase in coercivity and magnetization, as well as to development of mixed phase hysteresis. These results indicate that shallow paleomagnetic directions from the western Ecstall pluton are not affected by reheating and are therefore likely to record original field conditions at the time of pluton...

  13. Formation of heterogeneous magmatic series beneath North Santorini, South Aegean island arc

    DEFF Research Database (Denmark)

    Bailey, John C; Jensen, E.S.; Hansen, A.;

    2008-01-01

    The geochemistry of basaltic to dacitic lavas and dykes in the volcanic centres of NorthSantorini (Greece) has been investigated using elemental and Sr-Nd-Pb isotopic data andthree main magmatic series with sub-parallel trace element patterns for basalts can bedistinguished. The basalts have Sr...... and Nd isotopic values consistent with varying levels of incompatible-element mantle depletion. A fourth magma group with only two basalt samples has a trace element pattern with even lower contents of incompatible elements, especially Th, and with lower 87Sr/86Sr but higher 206Pb/ 204Pb. Heterogeneous...

  14. Evidence for pressure-release melting beneath magmatic arcs from basalt at Galunggung, Indonesia

    Science.gov (United States)

    Sisson, T.W.; Bronto, S.

    1998-01-01

    The melting of peridotite in the mantle wedge above subduction zones is generally believed to involve hydrous fluids derived from the subducting slab. But if mantle peridotite is upwelling within the wedge, melting due to pressure release could also contribute to magma production. Here we present measurements of the volatile content of primitive magmas from Galunggung volcano in the Indonesian are which indicate that these magmas were derived from the pressure-release melting of hot mantle peridotite. The samples that we have analysed consist of mafic glass inclusions in high-magnesium basalts. The inclusions contain uniformly low H2O concentrations (0.21-0.38 wt%), yet relatively high levels of CO2 (up to 750 p.p.m.) indicating that the low H2O concentrations are primary and not due to degassing of the magma. Results from previous anhydrous melting experiments on a chemically similar Aleutian basalts indicate that the Galunggung high-magnesium basalts were last in equilibrium with peridotite at ~1,320 ??C and 1.2 GPa. These high temperatures at shallow sub-crustal levels (about 300-600 ??C hotter than predicted by geodynamic models), combined with the production of nearly H2O- free basaltic melts, provide strong evidence that pressure-release melting due to upwelling in the sub-are mantle has taken place. Regional low- potassium and low-H2O (ref. 5) basalts found in the Cascade are indicate that such upwelling-induced melting can be widespread.

  15. Experimental Evidence for Polybaric Intracrustal Differentiation of Primitive Arc Basalt beneath St. Vincent, Lesser Antilles

    Science.gov (United States)

    Blundy, Jon; Melekhova, Lena; Robertson, Richard

    2014-05-01

    We present experimental phase equilibria for a primitive, high-Mg basalt from St. Vincent, Lesser Antilles. Experimental details were presented in Melekhova et al (Nature Geosci, 2013); the objective here is to compare experimental phase compositions to those of erupted lavas and cumulates from St. Vincent. Starting material with 4.5 wt% H2O is multiply-saturated with a lherzolite assemblage at 1.3 GPa and 1180 ° C, consistent with mantle wedge derivation. Experimental glasses from our study, in addition to those of Pichavant et al (GCA, 2002) and Pichavant & Macdonald (CMP 2007) on a similar high-Mg basalt, encompass a compositional range from high-magnesian basalt to dacite, with a systematic dependence on H2O content, temperature and pressure. We are able to match the glasses from individual experiments to different lava types, so as to constrain the differentiation depths at which these magmas could be generated from a high-Mg parent, as follows: Composition wt% H2OP (GPa) T (° C) High-Mg basalt 3.9-4.8 1.45-1.751180-1200 Low-Mg basalt 2.3-4.5 1.0-1.3 1065-1150 High alumina basalt 3.0-4.5 0.4 1050-1080 Basaltic andesite 0.6-4.5 0.7-1.0 1050-1130 Andesite 0.6 1.0 1060-1080 The fact that St. Vincent andesites (and some basaltic andesites) appear to derive from a low-H2O (0.6 wt%) parent suggest that they are products of partial melting of older, high-Mg gabbroic rocks, as 0.6 wt% H2O is approximately the amount that can be stored in amphibole-bearing gabbros. The higher H2O contents of parents for the other lava compositions is consistent with derivation by crystallization of basalts with H2O contents that accord with those of olivine-hosted melt inclusions from St. Vincent (Bouvier et al, J Petrol, 2008). The generation of evolved melts both by basalt crystallization and gabbro melting is consistent with the hot zone concept of Annen et al (J Petrol, 2006) wherein repeated intrusion of mantle-derived basalt simultaneously crystallize by cooling and melt country rocks composed of ancestral, solidified basalt. Isotopic data for St. Vincent (Heath et al, J Petrol, 1998) rule out any involvement of much older sialic crust. Although our experimental glasses provide a very good match to erupted lavas, the compositions of residual minerals do not match those of cumulate xenoliths (Tollan et al, CMP, 2012), which are abundant on St. Vincent. Therefore cumulates are not entrained fragments of the source region, but shallow accumulations of crystals generated by cooling of magmas on their journey through the crust. Thus melt compositions are a consequence of high pressure, H2O-understaurated phase relations, whereas cumulates are a consequence of low pressure, typically H2O-saturated, phase relations. We integrate these findings into a simple polybaric model of magma differentiation on St. Vincent involving a single, high-Mg, mantle-derived parental basalt.

  16. Calc-alkaline rear-arc magmatism in the Fuegian Andes: Implications for the mid-cretaceous tectonomagmatic evolution of southernmost South America

    Science.gov (United States)

    Guillot, Mauricio González; Escayola, Mónica; Acevedo, Rogelio

    2011-02-01

    The magmatic arc of the Fuegian Andes is composed mostly of Upper Mesozoic to Cenozoic calc-alkaline plutons and subordinated lavas. To the rear arc, however, isolated mid-Cretaceous monzonitic plutons and small calc-alkaline dykes and sills crop out. This calc-alkaline unit (the Ushuaia Peninsula Andesites, UPA) includes hornblende-rich, porphyritic quartz meladiorites, granodiorites, andesites, dacites and lamprophyres. Radiometric dating and cross-cutting relationships indicate that UPA is younger than the monzonitic suite. The geochemistry of UPA is medium to high K, with high LILE (Ba 500-2000 ppm, Sr 800-1400 ppm), HFSE (Th 7-23 ppm, Nb 7-13 ppm, Ta 0.5-1.1 ppm) and LREE (La 16-51 ppm) contents, along with relatively low HREE (Yb 1.7-1.3 ppm) and Y (9-19 ppm). The similar mineralogy and geochemistry of all UPA rocks suggest they evolved from a common parental magma, by low pressure crystal fractionation, without significant crustal assimilation. A pure Rayleigh fractionation model indicates that 60-65% of crystal fractionation of 60% hornblende + 34% plagioclase + 4% clinopyroxene + 1% Fe-Ti oxide, apatite and sphene (a paragenesis similar of UPA mafic rocks) can explain evolution from lamprophyres to dacites. The UPA has higher LILE, HFSE and LREE, and lower HREE and Y than the calc-alkaline plutons and lavas of the volcanic front. The HREE and Y are lower than in the potassic plutons as well. High concentrations of Th, Nb, Ta, Zr, Hf, LREE and Ce/Pb, and low U/Th, Ba/Th ratios in UPA, even in the least differentiated samples, suggest contributions from subducted sediments to the mantle source. On the other hand, relatively low HREE and Y, high LREE/HREE (La/Yb 11-38) ratios and Nb-Ta contents can be interpreted as mantle metasomatism by partial melts of either subducted garnetiferous oceanic sediment or basalt as well. Additionally, high LILE content in UPA, similar to the potassic plutons, suggests also a mantle wedge previously metasomatized by potassic

  17. Thermal Arc Spray Overview

    Science.gov (United States)

    Hafiz Abd Malek, Muhamad; Hayati Saad, Nor; Kiyai Abas, Sunhaji; Mohd Shah, Noriyati

    2013-06-01

    Usage of protective coating for corrosion protection was on highly demand during the past decade; and thermal spray coating played a major part during that time. In recent years, the thermal arc spray coating becomes a popular coating. Many big players in oil and gas such as PETRONAS, EXXON MOBIL and SHELL in Malaysia tend to use the coating on steel structure as a corrosion protection. Further developments in coating processes, the devices, and raw materials have led to expansion of functional coatings and applications scope from conventional coating to specialized industries. It is widely used because of its ability to withstand high process temperature, offer advantages in efficiency, lower cost and acts as a corrosion protection. Previous research also indicated that the thermal arc spray offers better coating properties compared to other methods of spray. This paper reviews some critical area of thermal spray coating by discussing the process/parameter of thermal arc spray technology and quality control of coating. Coating performance against corrosion, wear and special characteristic of coating are also described. The field application of arc spray technology are demonstrated and reviewed.

  18. ALICE: ARC integration

    CERN Document Server

    Anderlik, C; Kleist, J; Peters, A; Saiz, P

    2008-01-01

    AliEn or Alice Environment is the Grid middleware developed and used within the ALICE collaboration for storing and processing data in a distributed manner. ARC (Advanced Resource Connector) is the Grid middleware deployed across the Nordic countries and gluing together the resources within the Nordic Data Grid Facility (NDGF). In this paper we will present our approach to integrate AliEn and ARC, in the sense that ALICE data management and job processing can be carried out on the NDGF infrastructure, using the client tools available in AliEn. The inter-operation has two aspects, one is the data management part and the second the job management aspect. The first aspect was solved by using dCache across NDGF to handle data. Therefore, we will concentrate on the second part. Solving it, was somewhat cumbersome, mainly due to the different computing models employed by AliEn and ARC. AliEN uses an Agent based pull model while ARC handles jobs through the more 'traditional' push model. The solution comes as a modu...

  19. The rapakivi granite plutons of Bodom and Obbnäs, southern Finland: petrography and geochemistry

    Directory of Open Access Journals (Sweden)

    Kosunen, P.

    1999-12-01

    Full Text Available The Obbnäs and Bodom granite plutons of southernmost Finland show the typical petrographic and geochemical features of the Proterozoic rapakivi granites in Finland and elsewhere: they cut sharply across the 1900 Ma Svecofennian metamorphic bedrock and have the geochemical characteristics of subalkaline A-type granites. The Bodom pluton is composed of porphyritic granites (hornblende-, hornblende-biotite-, and biotite-bearing varieties and an even-grained granite that probably represent two separate intrusive phases. This lithologic variation does not occur in the Obbnäs pluton, which is almost entirely composed of porphyritic hornblende-biotite granite that gradually becomes more mafic to the southwest. Three types of hybrid granitoids resulting from magma mingling and mixing occur on the southwestern tip of the Obbnäs peninsula. The Bodom granites are syenogranites, whereas the composition of the Obbnäs granite varies from syeno- to monzogranite. The main silicates of both the Bodom and Obbnäs granites are quartz, microcline, plagioclase (An1541, biotite (siderophyllite, and generally also amphibole (ferropargasite or hastingsite. Plagioclase-mantled alkali feldspar megacrysts are absent or rare. The accessory minerals are fluorite, allanite, zircon, apatite, and iron-titanium oxides; the Obbnäs granite also contains titanite. The Bodom and Obbnäs granites are metaluminous to weakly peraluminous, with average A/CNK of 1.00 and 1.05, respectively, have high Fe/Mg (average FeOtot/[FeOtot+MgO] is 0.94 for the Bodom and 0.87 for the Obbnäs granites, and high Ga/Al (3.78 to 5.22 in Bodom and 2.46 to 4.18 in Obbnäs. The REE contents are high with LREE-enriched chondrite-normalized patterns and moderate (Obbnäs to relatively strong (Bodom negative Eu-anomalies. The Obbnäs granite is enriched in CaO, TiO2, MgO, and FeO, and depleted in SiO2 and K2O compared to the Bodom granites. Also, there are differences in the Ba, Rb, and Sr contents of

  20. Origin of the late Early Cretaceous granodiorite and associated dioritic dikes in the Hongqilafu pluton, northwestern Tibetan Plateau: A case for crust-mantle interaction

    Science.gov (United States)

    Li, Jiyong; Niu, Yaoling; Hu, Yan; Chen, Shuo; Zhang, Yu; Duan, Meng; Sun, Pu

    2016-09-01

    We present a detailed study of geochronology, mineral chemistries, bulk-rock major and trace element abundances, and Sr-Nd-Hf isotope compositions of the granodiorite and associated dioritic dikes in the Hongqilafu pluton at the northwestern margin of the Tibetan Plateau. The granodiorite and dioritic dikes yielded zircon U-Pb ages of ~ 104 Ma and ~ 100 Ma, respectively. The dioritic dikes comprise varying lithologies of gabbroic diorite, diorite porphyry and granodiorite porphyry, exhibiting a compositional spectrum from intermediate to felsic rocks. Their mineral compositions display disequilibrium features such as large major element compositional variations of plagioclase, clinopyroxene and amphibole crystals. These dioritic dikes are enriched in incompatible elements (Ba, Rb, Th, U, K) and Sr-Nd-Hf isotopes (87Sr/86Sri: 0.7066 to 0.7071, εNd(t): - 5.3 to - 7.4, εHf(t): - 3.6 to - 6.2). We suggest that the dioritic dikes were most likely derived from partial melting of mantle wedge metasomatized by the subducted/subducting seafloor with a sediment component, followed by AFC processes with fractional crystallization of clinopyroxene, amphibole and plagioclase and assimilation of lower continental crust. The mantle-wedge derived magma parental to the dioritic dikes underplated and induced the lower continental crust to melt, forming the felsic crustal magma parental to the granodiorite with mantle melt signatures and having more enriched isotope compositions (87Sr/86Sri: 0.7087 to 0.7125, εNd(t): - 9.5 to - 11.6, εHf(t): - 10.3 to - 14.1) than those of the dioritic dikes. The Hongqilafu pluton is thus the product of mantle-crust interaction at an active continental margin subduction setting over the period of several million years. This understanding further indicates that the closure timing of the Shyok back-arc basin and the collision between the Kohistan-Ladakh Arc and the Karakoram Terrane may have taken place later than ~ 100 Ma.

  1. Apatite trace element and halogen compositions as petrogenetic-metallogenic indicators: Examples from four granite plutons in the Sanjiang region, SW China

    Science.gov (United States)

    Pan, Li-Chuan; Hu, Rui-Zhong; Wang, Xin-Song; Bi, Xian-Wu; Zhu, Jing-Jing; Li, Chusi

    2016-06-01

    The abundances of trace elements including Sr, Ga and rare earth elements (REE) and halogens in apatite crystals from four intermediate-felsic plutons in the Zhongdian terrane in the Sanjiang region have been determined using electron microprobe and laser ablation inductively coupled plasma mass spectrometry to evaluate the potential of apatite as a petrogenic-metallogenic indicator. The selected plutons include one that is not mineralized (the Triassic Xiuwacu pluton, or the TXWC pluton), one that hosts a porphyry-type Cu deposit (the Pulang pluton, or the PL pluton), one that hosts a porphyry-type Mo deposit (the Tongchanggou pluton, or the TCG pluton), and one that hosts a vein-type Mo deposit (the Cretaceous Xiuwacu pluton, or the CXWC pluton). Except for the CXWC pluton, the other three plutons have adakite-like trace element signatures in whole rocks. The results from this study show that REE, Sr and halogens in apatite can be used to track magma compositions, oxidation states and crystallization history. Apatite crystals from the adakite-like plutons are characterized by much higher Sr/Y and δEu than the non-adakite-type pluton. This means that apatite, which is not susceptible to alteration, is a useful tool for identifying the adakite-like plutons that no longer preserve the initial Sr/Y ratios in whole rocks due to weathering and hydrothermal alteration. Based on apatite Ga contents and δEu values, it is inferred that the parental magmas for the two adakite-like plutons containing porphyry-type Cu and Mo mineralization are more oxidized than that for the non-adakite-type pluton containing vein-type Mo mineralization. Apatite crystals from the vein-type Mo deposit have much lower Cl/F ratios than those from the porphyry-type Cu and Mo deposits. Apatite crystals from the adakite-like pluton without Cu or Mo mineralization is characterized by much lower Cl/F ratios than those from the adakite-like plutons that host the porphyry-type Cu and Mo deposits. The

  2. Complexity of In-situ zircon U-Pb-Hf isotope systematics during arc magma genesis at the roots of a Cretaceous arc, Fiordland, New Zealand

    Science.gov (United States)

    Milan, L. A.; Daczko, N. R.; Clarke, G. L.; Allibone, A. H.

    2016-11-01

    Zircons from seventeen samples of Western Fiordland Orthogneiss (WFO) diorites and three samples of country rock (two schists and one Darran Suite diorite) from the lowermost exposed sections of the Median Batholith, Fiordland, New Zealand, were analysed for in-situ U-Pb and Hf-isotopes. The WFO represents the deeper levels of Early Cretaceous continental arc magmatism on the Pacific margin of Gondwana, marking the final stage of long-lived arc magmatism on the margin spanning the Palaeozoic. The WFO plutons were emplaced at high-P (mid to deep crust at c. 8-12 kbar) between 124 and 114 Ma. Minor very high-P (c. 18 kbar) WFO eclogite and omphacite granulite facies orthogneiss (Breaksea Orthogneiss) are inferred to have crystallised in the base of thickened crust at c. 124 Ma. Zircons from the Breaksea Orthogneiss are considered to be variably affected by Pb-loss due to emplacement of the adjacent (Malaspina) Pluton at c. 114 Ma. By identifying Pb-loss, magmatic ages were able to be inferred in respect to apparent Pb-loss ages. Hf isotope data for the WFO define an excursion to less radiogenic Hf isotope ratios with time, reflecting increased recycling of an old source component. Peaks at c. 555, 770 and 2480 Ma, determine the age spectra of inherited populations of zircons within the WFO. This contrasts with detrital zircon patterns in country rocks of the Takaka terrane, which include peaks at c. 465 Ma, and 1250-900 Ma that are absent in the WFO inheritance pattern. These results indicate a previously unrecognised Precambrian lower crustal component of New Zealand. Recycling of this lower crust became increasingly important as a source for the final stage or Mesozoic arc magmatism along this segment of the palaeo-Pacific margin of Gondwana.

  3. Neogene kinematic history of Nazca-Antarctic-Phoenix slab windows beneath Patagonia and the Antarctic Peninsula

    Science.gov (United States)

    Breitsprecher, Katrin; Thorkelson, Derek J.

    2009-01-01

    The Patagonian slab window is a subsurface tectonic feature resulting from subduction of the Nazca-Antarctic spreading-ridge system (Chile Rise) beneath southern South America. The geometry of the slab window had not been rigorously defined, in part because of the complex nature of the history of ridge subduction in the southeast Pacific region, which includes four interrelated spreading-ridge systems since 20 Ma: first, the Nazca-Phoenix ridge beneath South America, then simultaneous subduction of the Nazca-Antarctic and the northern Phoenix-Antarctic spreading-ridge systems beneath South America, and the southern Phoenix-Antarctic spreading-ridge system beneath Antarctica. Spreading-ridge paleo-geographies and rotation poles for all relevant plate pairs (Nazca, Phoenix, Antarctic, South America) are available from 20 Ma onward, and form the mathematical basis of our kinematic reconstruction of the geometry of the Patagonia and Antarctic slab windows through Neogene time. At approximately 18 Ma, the Nazca-Phoenix-Antarctic oceanic (ridge-ridge-ridge) triple junction enters the South American trench; we recognize this condition as an unstable quadruple junction. Heat flow at this junction and for some distance beneath the forearc would be considerably higher than is generally recognized in cases of ridge subduction. From 16 Ma onward, the geometry of the Patagonia slab window developed from the subduction of the trailing arms of the former oceanic triple junction. The majority of the slab window's areal extent and geometry is controlled by the highly oblique (near-parallel) subduction angle of the Nazca-Antarctic ridge system, and by the high contrast in relative convergence rates between these two plates relative to South America. The very slow convergence rate of the Antarctic slab is manifested by the shallow levels achieved by the slab edge (< 45 km); thus no point on the Antarctic slab is sufficiently deep to generate "normal" mantle-derived arc-type magmas

  4. Map showing the distribution and characteristics of plutonic rocks in the Tonopah 1 degree by 2 degrees Quadrangle, central Nevada

    Science.gov (United States)

    John, D.A.

    1987-01-01

    Plutonic rocks, mostly granite and granodiorite, are widely distributed in the west two-thirds of the Tonopah 1 degree by 2 degree quadrangle, Nevada. These rocks were systematically studied as part of the Tonopah CUSMAP project. Studies included field mapping, petrographic and modal analyses, geochemical studies of both fresh and altered plutonic rocks and altered wallrocks, and K-Ar and Rb-Sr radiometric dating. Data collected during this study were combined with previously published data to produce a 1:250,000-scale map of the Tonopah quadrangle showing the distribution of individual plutons and an accompanying table summarizing composition, texture, age, and any noted hydrothermal alteration and mineralization effects for each pluton.

  5. Analysis of groundwater flow beneath ice sheets

    Energy Technology Data Exchange (ETDEWEB)

    Boulton, G. S.; Zatsepin, S.; Maillot, B. [Univ. of Edinburgh (United Kingdom). Dept. of Geology and Geophysics

    2001-03-01

    The large-scale pattern of subglacial groundwater flow beneath European ice sheets was analysed in a previous report. It was based on a two-dimensional flowline model. In this report, the analysis is extended to three dimensions by exploring the interactions between groundwater and tunnel flow. A theory is developed which suggests that the large-scale geometry of the hydraulic system beneath an ice sheet is a coupled, self-organising system. In this system the pressure distribution along tunnels is a function of discharge derived from basal meltwater delivered to tunnels by groundwater flow, and the pressure along tunnels itself sets the base pressure which determines the geometry of catchments and flow towards the tunnel. The large-scale geometry of tunnel distribution is a product of the pattern of basal meltwater production and the transmissive properties of the bed. The tunnel discharge from the ice margin of the glacier, its seasonal fluctuation and the sedimentary characteristics of eskers are largely determined by the discharge of surface meltwater which penetrates to the bed in the terminal zone. The theory explains many of the characteristics of esker systems and can account for tunnel valleys. It is concluded that the large-scale hydraulic regime beneath ice sheets is largely a consequence of groundwater/tunnel flow interactions and that it is essential similar to non-glacial hydraulic regimes. Experimental data from an Icelandic glacier, which demonstrates measured relationships between subglacial tunnel flow and groundwater flow during the transition from summer to winter seasons for a modern glacier, and which support the general conclusions of the theory is summarised in an appendix.

  6. Semicircular Rashba arc spin polarizer

    Energy Technology Data Exchange (ETDEWEB)

    Bin Siu, Zhuo, E-mail: a0018876@nus.edu.sg [NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore, Singapore 117456 (Singapore); Advanced Concepts and Nanotechnology, Data Storage Institute, DSI Building, 5 Engineering Drive 1 (Off Kent Ridge Crescent, NUS), Singapore 117608 (Singapore); Jalil, Mansoor B. A. [NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore, Singapore 117456 (Singapore); Ghee Tan, Seng [Advanced Concepts and Nanotechnology, Data Storage Institute, DSI Building, 5 Engineering Drive 1 (Off Kent Ridge Crescent, NUS), Singapore 117608 (Singapore)

    2014-05-07

    In this work, we study the generation of spin polarized currents using curved arcs of finite widths, in which the Rashba spin orbit interaction (RSOI) is present. Compared to the 1-dimensional RSOI arcs with zero widths studied previously, the finite width presents charge carriers with another degree of freedom along the transverse width of the arc, in addition to the longitudinal degree of freedom along the circumference of the arc. The asymmetry in the transverse direction due to the difference in the inner and outer radii of the arc breaks the antisymmetry of the longitudinal spin z current in a straight RSOI segment. This property can be exploited to generate spin z polarized current output from the RSOI arc by a spin unpolarized current input. The sign of the spin current can be manipulated by varying the arc dimensions.

  7. Progressive enrichment of arc magmas caused by the subduction of seamounts under Nishinoshima volcano, Izu-Bonin Arc, Japan

    Science.gov (United States)

    Sano, Takashi; Shirao, Motomaro; Tani, Kenichiro; Tsutsumi, Yukiyasu; Kiyokawa, Shoichi; Fujii, Toshitsugu

    2016-06-01

    The chemical composition of intraplate seamounts is distinct from normal seafloor material, meaning that the subduction of seamounts at a convergent margin can cause a change in the chemistry of the mantle wedge and associated arc magmas. Nishinoshima, a volcanic island in the Izu-Bonin Arc of Japan, has been erupting continuously over the past 2 years, providing an ideal opportunity to examine the effect of seamount subduction on the chemistry of arc magmas. Our research is based on the whole-rock geochemistry and the chemistry of minerals within lavas and air-fall scoria from Nishinoshima that were erupted before 1702, in 1973-1974, and in 2014. The mineral phases within the analyzed samples crystallized under hydrous conditions (H2O = 3-4 wt.%) at temperatures of 970 °C-990 °C in a shallow (3-6 km depth) magma chamber. Trace element data indicate that the recently erupted Nishinoshima volcanics are much less depleted in the high field strength elements (Nb, Ta, Zr, Hf) than other volcanics within the Izu-Bonin Arc. In addition, the level of enrichment in the Nishinoshima magmas has increased in recent years, probably due to the addition of material from HIMU-enriched (i.e., high Nb/Zr and Ta/Hf) seamounts on the Pacific Plate, which is being subducted westwards beneath the Philippine Sea Plate. This suggests that the chemistry of scoria from Nishinoshima volcano records the progressive addition of components derived from subducted seamounts.

  8. Iron mineralization and associated skarn development around southern contact of the Eğrigöz pluton (northern Menderes Massif-Turkey)

    Science.gov (United States)

    Uǧurcan, Okşan Gökçen; Oyman, Tolga

    2016-11-01

    The Eğrigöz pluton is located in the northern portion of the Menderes Massif, which is the largest known metamorphic core complex that is also characterized by large-scale extension. Kalkan and Karaağıl skarn deposits are located on the southern border of the Eğrigöz Pluton, whereas Katrandağ mineralization developed along the roof pendant. Skarnization in these three areas is associated with the peraluminous, I-type, calc-alkaline, high-K calc-alkaline Eğrigöz Pluton. Geochemical characteristics of the pluton indicate that it was generated in a continental arc setting. Kalkan, Karaağıl, and Katrandağ skarns are hosted in marble bands in two-mica gneiss of the Kalkan Formation, a locally dolomitic and clay-bearing limestone of the Arıkaya Formation and locally dolomitised limestone of the Balıkbaşı Formation, respectively. Skarn development occurred sequentially in two stages, prograde and retrograde. In Kalkan skarn, prograde stage is characterized by clinopyroxene (Di56-73 Hd26-43 Joh1-2), garnet (Adr45-69 Grs30-52 Alm0-1.4 Sps0.7-2.3), amphibole, and magnetite, whereas retrograde stage is dominated by epidote, amphibole, chlorite, quartz, and calcite. In Karaağıl, both calcic and magnesian skarn association occurred as a result of local variations in dolomite content in Arıkaya Formation. The prograde assemblage of magnesian skarn is composed chiefly of spinel, amphibole and olivine. These mineral assemblages were, partially or fully, altered to serpentine, talc, and chlorite during retrograde alteration. Mesh textures of the serpentine indicates that the serpentine was altered from olivine. Olivine was completely destroyed during retrograde alteration without relict grains remaining. Calcic skarn paragenesis include garnet (Grs36-80Adr20-62Alm0-2.2Sps0.2-2.6), clinopyroxene (Di81-92 Hd7-19 Jo0-1), and plagioclase, that belongs to the earlier stage, and amphibole of the retrograde stage. High grossular end member of the garnet probably

  9. Two stages of isotopic exchanges experienced by the Ertaibei granite pluton, northern Xinjiang, China

    Institute of Scientific and Technical Information of China (English)

    刘伟

    2000-01-01

    18O/16O and D/H of coexisting feldspar, quartz, and biotite separates of twenty samples collected from the Ertaibei granite pluton, northern Xinjiang, China are determined. It is shown that the Ertaibei pluton experienced two stages of isotopic exchanges. The second stage of 18O/16O and D/H exchanges with meteoric water brought about a marked decrease in the δ18O values of feldspar and biotite from the second group of samples. The D/H of biotite exhibits a higher sensitivity to the meteoric water alteration than its 18O/16O. However, the first stage of 18O/16O exchange with the 18O-rich aqueous fluid derived from the dehydration within the deep crust caused the Δ18OQuariz-Feidspar reversal. It is inferred that the dehydration-melting may have been an important mechanism for anatexis. It is shown that the deep fluid encircled the Ertaibei pluton like an envelope which serves as an effective screen to the surface waters.

  10. Two stages of isotopic exchanges experienced by the Ertaibei granite pluton, northern Xinjiang, China

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    18O/16O and D/H of coexisting feldspar, quartz, and biotite separates of twenty samples collected from the Ertaibei granite pluton, northern Xinjiang, China are determined. It is shown that the Ertaibei pluton experienced two stages of isotopic exchanges. The second stage of 18O/16O and D/H exchanges with meteoric water brought about a marked decrease in the δ18O values of feldspar and biotite from the second group of samples. The D/H of biotite exhibits a higher sensitivity to the meteoric water alteration than its 18O/16O. However, the first stage of 18O/16O exchange with the 18O-rich aqueous fluid derived from the dehydration within the deep crust caused the δ18OQuartz-Feldspar reversal. It is inferred that the dehydration-melting may have been an important mechanism for anatexis. It is shown that the deep fluid encircled the Ertaibei pluton like an envelope which serves as an effective screen to the surface waters.

  11. Zircon LA-ICPMS study and petrogenesis simulation of Dahuabei pluton in the Wulashan area,Inner Mongolia

    Institute of Scientific and Technical Information of China (English)

    Dapeng Li; Yuelong Chen; Liemeng Chen; Zhong Wang; Jinbao Liu

    2009-01-01

    Dahuabei pluton in the Wulashan area,Inner Mongolia,is an alkaline and peraluminous granitic pluton.LA-ICPMS U-Pb dating of zircons indicates that this pluton crystallized at 330±10 Myr.The pluton did not experience apparent zircon fractionation.The consistent temperatures between Zr saturation (765℃) and the average zircon-rutile Ti equilibrium (780℃),together with zircon ages and their CL images,indicated that there were no inherited zircons in this pluton.Through the simulation of the dry-system crystallization process of magma cooling at 200 MPa and 1100-709℃,the phase diagram and composition evolution tendency of different phases were obtained.The magma reached its liquidus at 1069℃.Sanidine was the first crystallized phase;at 709℃ the residual magma was less than 4%,and the range of 1069-719℃ should be the most suitable approach to the real condition.It is shown that at least some part of the pluton underwent such isobaric equilibrium crystallization processes during its crystallization.

  12. ALICE-ARC integration

    DEFF Research Database (Denmark)

    Anderlik, Csaba; Gregersen, Anders Rhod; Kleist, Josva;

    2008-01-01

    Data Grid Facility (NDGF). In this paper we will present our approach to integrate AliEn and ARC, in the sense that ALICE data management and job processing can be carried out on the NDGF infrastructure, using the client tools available in AliEn. The interoperation has two aspects, one is the data......AliEn or Alice Environment is the Gridware developed and used within the ALICE collaboration for storing and processing data in a distributed manner. ARC (Advanced Resource Connector) is the Grid middleware deployed across the Nordic countries and gluing together the resources within the Nordic...... management part and the second the job management aspect. The first aspect was solved by using dCache across NDGF to handle data. dCache provides support for several data management tools (among them for xrootd the tools used by AliEn) using the so called "doors". Therefore, we will concentrate on the second...

  13. ALICE - ARC integration

    DEFF Research Database (Denmark)

    Anderlik, Csaba; Gregersen, Anders Rhod; Kleist, Josva;

    Data Grid Facility (NDGF). In this paper we will present our approach to integrate AliEn and ARC, in the sense that ALICE data management and job processing can be carried out on the NDGF infrastructure, using the client tools available in AliEn. The interoperation has two aspects, one is the data......AliEn or Alice Environment is the Gridware developed and used within the ALICE collaboration for storing and processing data in a distributed manner. ARC (Advanced Resource Connector) is the Grid middleware deployed across the Nordic countries and gluing together the resources within the Nordic...... management part and the second the job management aspect. The first aspect was solved by using dCache across NDGF to handle data. dCache provides support for several data management tools (among them for xrootd the tools used by AliEn) using the so called "doors". Therefore, we will concentrate on the second...

  14. Vacuum Arc Ion Sources

    OpenAIRE

    Brown, I.

    2014-01-01

    The vacuum arc ion source has evolved into a more or less standard laboratory tool for the production of high-current beams of metal ions, and is now used in a number of different embodiments at many laboratories around the world. Applications include primarily ion implantation for material surface modification research, and good performance has been obtained for the injection of high-current beams of heavy-metal ions, in particular uranium, into particle accelerators. As the use of the sourc...

  15. Circular arc structures

    KAUST Repository

    Bo, Pengbo

    2011-07-01

    The most important guiding principle in computational methods for freeform architecture is the balance between cost efficiency on the one hand, and adherence to the design intent on the other. Key issues are the simplicity of supporting and connecting elements as well as repetition of costly parts. This paper proposes so-called circular arc structures as a means to faithfully realize freeform designs without giving up smooth appearance. In contrast to non-smooth meshes with straight edges where geometric complexity is concentrated in the nodes, we stay with smooth surfaces and rather distribute complexity in a uniform way by allowing edges in the shape of circular arcs. We are able to achieve the simplest possible shape of nodes without interfering with known panel optimization algorithms. We study remarkable special cases of circular arc structures which possess simple supporting elements or repetitive edges, we present the first global approximation method for principal patches, and we show an extension to volumetric structures for truly threedimensional designs. © 2011 ACM.

  16. Life Beneath Glacial Ice - Earth(!) Mars(?) Europa(?)

    Science.gov (United States)

    Allen, Carlton C.; Grasby, Stephen E.; Longazo, Teresa G.; Lisle, John T.; Beauchamp, Benoit

    2002-01-01

    We are investigating a set of cold springs that deposit sulfur and carbonate minerals on the surface of a Canadian arctic glacier. The spring waters and mineral deposits contain microorganisms, as well as clear evidence that biological processes mediate subglacial chemistry, mineralogy, and isotope fractionation . The formation of native sulphur and associated deposits are related to bacterially mediated reduction and oxidation of sulphur below the glacier. A non-volcanic, topography driven geothermal system, harboring a microbiological community, operates in an extremely cold environment and discharges through solid ice. Microbial life can thus exist in isolated geothermal refuges despite long-term subfreezing surface conditions. Earth history includes several periods of essentially total glaciation. lee in the near subsurface of Mars may have discharged liquid water in the recent past Cracks in the ice crust of Europa have apparently allowed the release of water to the surface. Chemolithotrophic bacteria, such as those in the Canadian springs, could have survived beneath the ice of "Snowball Earth", and life forms with similar characteristics might exist beneath the ice of Mars or Europa. Discharges of water from such refuges may have brought to the surface living microbes, as well as longlasting chemical, mineralogical, and isotopic indications of subsurface life.

  17. Giant magmatic water reservoir beneath Uturuncu volcano and Altiplano-Puna region (Central Andes)

    Science.gov (United States)

    Laumonier, Mickael; Gaillard, Fabrice; Muir, Duncan; Blundy, Jon; Unsworth, Martyn

    2016-04-01

    Volcanism at continental arcs is the surface manifestation of long-lived crustal magmatic processes whereby mantle-derived hydrous basalt magma differentiates to more silica-rich magmas by a combination of crystallization and crustal melting. What erupts is just a fraction of the total volume of magma produced by these processes; the unerupted, plutonic residues solidify and are inaccessible to direct study until millions of years of uplift and erosion bring them to the surface. In contrast, geophysical surveys, using electromagnetic and seismic waves, can provide real-time images of subduction zone magmatic systems. Several such studies have revealed that arc volcanoes are underlain by large partially molten regions at depths of >10 km, the largest known example being the Altiplano-Puna magma body (APMB) in central Andes. Interpreting such geophysical images in terms of amount, composition and distribution of partial melts is limited by our lack of knowledge of the physical properties of silicate melts at elevated pressures and temperatures. Here we present high-pressure, in situ experimental data showing that the electrical conductivity of andesitic melts is primarily controlled by their dissolved water contents. Linking our new measurements to petrological constraints from andesites erupted on the Altiplano, we show that the APMB is composed of 10-20% of an andesitic melt containing 8-10 wt% dissolved water. This implies that the APMB is a giant water anomaly in the global subduction system, with a total mass of dissolved magmatic water about half of the water contained within the Adriatic Sea. In addition to the controls on the physical properties of the melts, the abundance of dissolved water governs the structural levels of magma ponding, equivalent to the depth of water saturation, where degassing and crystallisation promote partial melting and weakening of the upper crust. Unexpectedly, very high concentrations of water in andesite magmas shall impede their

  18. Natural radioactivity and radiation index of the major plutonic bodies in Greece

    International Nuclear Information System (INIS)

    The natural radioactivity of the major plutonic bodies in Greece, as well as the assessment of any potential health hazard due to their usage as decorative building materials is studied. One hundred and twenty one samples from every major plutonic body in Greece, including various rock-types from gabbro to granite, have been measured for their natural radioactivity using γ-spectrometry methodology. According to the experimental results, the natural radioactivity levels were ranged up to 315 Bq kg−1 for 226Ra, up to 376 Bq kg−1 for 232Th and up to 1632 Bq kg−1 for 40K, with arithmetic mean values and standard deviations of 74 (±51), 85 (±54) and 881 (±331) Bq kg−1 respectively, which are below the international representative mean values for granite stones. The excess on the effective dose received annually indoors due to granite tiles usage is estimated considering a standard room model where granite tiles with 1.5 cm in thickness cover only the floor of the room. The increment on the external γ-radiation effective dose rate shows a Gaussian distribution well dispersed below 0.3 mSv y−1, presenting a mean value of 0.14 (±0.06) mSv y−1. In case of the internal α-radiation a log-normal distribution is appeared scattering below 0.5 mSv y−1 with a mean value 0.19 (±0.13) mSv y−1, for a well-ventilated living environment. In case of a poor-ventilated room the increment on internal effective dose rate is estimated with a mean value 0.27 (±0.19) mSv y−1 scattering below 0.8 mSv y−1. The majority of the samples increase the external as well as the internal dose less than 30% of the maximum permitted limit of the effective dose rate. Therefore, at least from radiological point of view, the plutonic rocks of Greece could be safely used as decorative building materials. -- Highlights: • Data upon natural radioactivity of all the major plutons of Greece are presented. • The samples from Pelagonian zone present the lower excess of the total

  19. From Migmatites to Plutons: Power Law Relationships in the Evolution of Magmatic Bodies

    Science.gov (United States)

    Soesoo, Alvar; Bons, Paul D.

    2015-07-01

    Magma is generated by partial melting from micrometre-scale droplets at the source and may accumulate to form >100 km-scale plutons. Magma accumulation thus spans well over ten orders of magnitude in scale. Here we provide measurements of migmatitic leucosomes and granitic veins in drill cores from the Estonian Proterozoic basement and outcrops at Masku in SW Finland and Montemor-o-Novo, central Portugal. Despite the differences in size and number of measured leucosomes and magmatic veins, differences in host rock types and metamorphic grades, the cumulative width distribution of the studied magmatic leucosomes/veins follows a power law with exponents usually between 0.7 and 1.8. Published maps of the SE Australian Lachlan Fold Belt were used to investigate the distribution of granitoid pluton sizes. The granites occupy ca. 22 % of the 2.6 × 105 km2 area. The cumulative pluton area distributions show good power law distributions with exponents between 0.6 and 0.8 depending on pluton area group. Using the self-affine nature of pluton shapes, it is possible to estimate the total volume of magma that was expelled from the source in the 2.6 × 105 km2 map area, giving an estimated 0.8 km3 of magma per km2. It has been suggested in the literature that magma batches in the source merge to form ever-bigger batches in a self-organized way. This leads to a power law for the cumulative distribution of magma volumes, with an exponent m V between 1 for inefficient melt extraction, and 2/3 for maximum accumulation efficiency as most of the volume resides in the largest batches that can escape from the source. If m V ≥ 1, the mass of the magma is dominated by small batches; in case m = 2/3, about 50 % of all magma in the system is placed in a single largest batch. Our observations support the model that the crust develops a self-organized critical state during magma generation. In this state, magma batches accumulate in a non-continuous, step-wise manner to form ever

  20. Imaging magma plumbing beneath Askja volcano, Iceland

    Science.gov (United States)

    Greenfield, Tim; White, Robert S.

    2015-04-01

    Volcanoes during repose periods are not commonly monitored by dense instrumentation networks and so activity during periods of unrest is difficult to put in context. We have operated a dense seismic network of 3-component, broadband instruments around Askja, a large central volcano in the Northern Volcanic Zone, Iceland, since 2006. Askja last erupted in 1961, with a relatively small basaltic lava flow. Since 1975 the central caldera has been subsiding and there has been no indication of volcanic activity. Despite this, Askja has been one of the more seismically active volcanoes in Iceland. The majority of these events are due to an extensive geothermal area within the caldera and tectonically induced earthquakes to the northeast which are not related to the magma plumbing system. More intriguing are the less numerous deeper earthquakes at 12-24km depth, situated in three distinct areas within the volcanic system. These earthquakes often show a frequency content which is lower than the shallower activity, but they still show strong P and S wave arrivals indicative of brittle failure, despite their location being well below the brittle-ductile boundary, which, in Askja is ~7km bsl. These earthquakes indicate the presence of melt moving or degassing at depth while the volcano is not inflating, as only high strain rates or increased pore fluid pressures would cause brittle fracture in what is normally an aseismic region in the ductile zone. The lower frequency content must be the result of a slower source time function as earthquakes which are both high frequency and low frequency come from the same cluster, thereby discounting a highly attenuating lower crust. To image the plumbing system beneath Askja, local and regional earthquakes have been used as sources to solve for the velocity structure beneath the volcano. Travel-time tables were created using a finite difference technique and the residuals were used to solve simultaneously for both the earthquake locations

  1. Arc-preserving subsequences of arc-annotated sequences

    CERN Document Server

    Popov, Vladimir Yu

    2011-01-01

    Arc-annotated sequences are useful in representing the structural information of RNA and protein sequences. The longest arc-preserving common subsequence problem has been introduced as a framework for studying the similarity of arc-annotated sequences. In this paper, we consider arc-annotated sequences with various arc structures. We consider the longest arc preserving common subsequence problem. In particular, we show that the decision version of the 1-{\\sc fragment LAPCS(crossing,chain)} and the decision version of the 0-{\\sc diagonal LAPCS(crossing,chain)} are {\\bf NP}-complete for some fixed alphabet $\\Sigma$ such that $|\\Sigma| = 2$. Also we show that if $|\\Sigma| = 1$, then the decision version of the 1-{\\sc fragment LAPCS(unlimited, plain)} and the decision version of the 0-{\\sc diagonal LAPCS(unlimited, plain)} are {\\bf NP}-complete.

  2. Development of modal layering in granites: a case study from the Carna Pluton, Connemara, Ireland

    Science.gov (United States)

    McKenzie, Kirsty; McCarthy, William; Hunt, Emma

    2016-04-01

    Modal layering in igneous rocks uniquely record dynamic processes operating in magma chambers and also host a large proportion of Earth's strategic mineral deposits. This research investigates the origin of biotite modal layering and primary pseudo-sedimentary structures in felsic magmas, by using a combination of Crystal Size Distribution (CSD) analysis and Electron Probe Microanalysis (EPMA) to determine the mechanisms responsible for the development of these structures in the Carna Pluton, Connemara, Ireland. The Carna Pluton is a composite granodiorite intrusion and is one of five plutons comprising the Galway Granite Complex (425 - 380 Ma). Prominent 30 cm thick modal layers are defined by sharp basal contacts to a biotite-rich (20%) granite, which grades upward over 10 cm into biotite-poor, alkali-feldspar megacrystic granite. The layering strikes parallel to, and dips 30-60° N toward the external pluton contact. Pseudo-sedimentary structures (cross-bedding, flame structures, slumping and crystal graded bedding) are observed within these layers. Petrographic observations indicate the layers contain euhedral biotite and fresh undeformed quartz and feldspar. Throughout the pluton, alkali-feldspar phenocrysts define a foliation that is sub-parallel to the strike of biotite modal layers. Together these observations indicate that the intrusion's concentric foliation, biotite layers and associated structures formed in the magmatic state and due to a complex interaction between magma flow and crystallisation processes. Biotite CSDs (>250 crystals per sample) were determined for nine samples across three biotite-rich layers in a single unit. Preliminary CSD results suggest biotite within basal contacts accumulated via fractional crystallisation within an upward-growing crystal pile, likely reflecting the yield strength of the magma as a limiting factor to gravitational settling of biotite. This is supported by the abrupt decrease in mean biotite crystal size across

  3. Intrusive rocks of the Holden and Lucerne quadrangles, Washington; the relation of depth zones, composition, textures, and emplacement of plutons

    Science.gov (United States)

    Cater, Fred W.

    1982-01-01

    The core of the northern Cascade Range in Washington consists of Precambrian and upper Paleozoic metamorphic rocks cut by numerous plutons, ranging in age from early Triassic to Miocene. The older plutons have been eroded to catazonal depths, whereas subvolcanic rocks are exposed in the youngest plutons. The Holden and Lucerne quadrangles span a -sizeable and representative part of this core. The oldest of the formations mapped in these quadrangles is the Swakane Biotite Gneiss, which was shown on the quadrangle maps as Cretaceous and older in age. The Swakane has yielded a middle Paleozoic metamorphic age, and also contains evidence of zircon inherited from some parent material more than 1,650 m.y. old. In this report, the Swakane is assigned an early Paleozoic or older age. It consists mostly of biotite gneiss, but interlayered with it are scattered layers and lenses of hornblende schist and gneiss, clinozoisite-epidote gneiss, and quartzite. Thickness of the Swakane is many thousands of meters, and the base is not exposed. The biotite gneiss is probably derived from a pile of siliceous volcanic rocks containing scattered sedimentary beds and basalt flows. Overlying the Swakane is a thick sequence of eugeosynclinal upper Paleozoic rocks metamorphosed to amphibolite grade. The sequence includes quartzite and thin layers of marble, hornblende schist and gneiss, graphitic schist, and smaller amounts of schist and gneiss of widely varying compositions. The layers have been tightly and complexly folded, and, in places, probably had been thrust over the overlying Swakane prior to metamorphism. Youngest of the supracrustal rocks in the area are shale, arkosic sandstone, and conglomerate of the Paleocene Swauk Formation. These rocks are preserved in the Chiwaukum graben, a major structural element of the region. Of uncertain age, but possibly as old as any of the intrusive rocks in the area, are small masses of ultramafic rocks, now almost completely altered to

  4. Trans-lithospheric scheme of arc magma transfer and evolution (Invited)

    Science.gov (United States)

    Bouilhol, P.; Schmidt, M. W.; Connolly, J. A.; Burg, J.

    2013-12-01

    Understanding the formation of magmatic arcs requires not only conceiving the formation of primitive arc melts, but also their evolution during migration from the mantle source to the arc. Indeed, the chemical characteristics of arc-melts are acquired during a complex process involving the slab input, the mantle wedge, and transfer of the melt at the base of and in the crust. Because the retrograde thermal regime in the upper portion of the mantle wedge is hostile to melt transport, the dominant mechanism by which melts ascend from their source through the mantle remains uncertain and mainly based on theoretical and exported models from MOR settings because of the scarcity of observations available. Within the lower crust, melts must be efficiently transferred toward higher structural levels to feed plutons and volcanoes but such melt highways are elusive and not always recognized as such. Petro-geochemical and structural analyses conducted on a mantle and lower crust section of the Kohistan Paleo-Island Arc (The Sapat Complex, Pakistan) unravel some aspects of the transfer and evolution of arc-magmas. The dominantly harzburgitic mantle shows a continuum of transport mechanisms ranging from pervasive to fully segregated melt flow, related to the formation of dunitic conduits associated with clinopyroxene-rich zones. Structural observations, linked to rock chemistry and numerical simulations show that primitive melts where transferred via porosity waves within the mantle. This efficient way of forming mantle conduit will drain the primitive mantle source region until melting cease. During this transfer, a competitive series of reaction-crystallization marks the staggering of melt evolution. The crustal section, fed with the same primitive melt, is predominantly composed of meta-plutonics that host kilometer-scale pyroxenite bodies. Within the bodies, sub-vertical magmatic and reactional structures indicate vertical magma percolation accompanied by massive cumulate

  5. Hybrid laser-arc welding

    DEFF Research Database (Denmark)

    Hybrid laser-arc welding (HLAW) is a combination of laser welding with arc welding that overcomes many of the shortfalls of both processes. This important book gives a comprehensive account of hybrid laser-arc welding technology and applications. The first part of the book reviews...... the characteristics of the process, including the properties of joints produced by hybrid laser-arc welding and ways of assessing weld quality. Part II discusses applications of the process to such metals as magnesium alloys, aluminium and steel as well as the use of hybrid laser-arc welding in such sectors as ship...... building and the automotive industry. With its distinguished editor and international team of contributors, Hybrid laser-arc welding, will be a valuable source of reference for all those using this important welding technology. Professor Flemming Ove Olsen works in the Department of Manufacturing...

  6. Consistent magmatic and magnetic anisotropy data in La Gloria Pluton, central Chile: Implications for the magma flow record in a shallow pluton

    Science.gov (United States)

    Payacan, I.; Gutierrez, F. J.; Bachmann, O.; Parada, M.

    2012-12-01

    The magmatic origin of the anisotropy of magnetic susceptibility (AMS) is examined in comparison with magmatic anisotropy data in a small, shallow, silicic magma reservoir in the upper crust. La Gloria Pluton (LGP) is a 10 Ma granodiorite/quartz monzonite of about 250 km3 located in the southern Andes, central Chile. LGP represents a particularly simple case of a silicic intrusion which was assembled in a few pulses and cooled over a short time interval. Hornblende, biotite and minor magnetite are ubiquitous mafic phases. The AMS tensor indicates that magnetic fabric has an oblate shape (i.e. magnetic foliation is higher than magnetic lineation). Lineations are weak (values up to 1.05), have a N-NW trend with a nearly horizontal dip and represent axisymmetric convection parallel to the main pluton elongation. Foliations are more pronounced (values up to 1.14), having NW trends and dips that vary gradually from vertical at the walls, to horizontal at the center and near the roof of the chamber. We interpret this to represent shear localization near the magma locking point along solidification fronts. Magmatic anisotropy data were obtained by measuring mineral length, width and orientation in the three main planes of the AMS tensor. We define the planes Pmax, Pint, and Pmin as orthogonal to the maximum, intermediate, and minimum axes of the AMS tensor, respectively. Mineral data were collected for plagioclase and amphibole + bitotite independently. For each site, the Bingham distribution with 95% of confidence is used to determine the mean mineral orientation and their angle difference with the AMS axes. Preliminary results indicate that mean crystal orientations are well defined for Pmax and Pint for all analyzed minerals, but Pmin is only well constrained for amphibole + bitotite and poorly constrained for plagioclase. Angle differences generally decrease with magnetic anisotropy but are independent of the size and aspect ratio of the crystals. Mean values of

  7. Definition of magmatic suites in ediacaran bodies of the NE Province Borborema (State of Rio Grande do Norte: Pitombeira, Taipu and Gameleira Plutons

    Directory of Open Access Journals (Sweden)

    Maria Tatiany Duarte de Oliveira

    2014-12-01

    Full Text Available The Pitombeira, Taipu and Gameleira plutons, located in the northeasternmost portion of the São José do Campestre Domain within the Borborema Province (NE, Brazil, are subjects of lithogeochemical studies in the present work. The Pitombeira Pluton comprises a monzo- to syenogranitic facies defined by K-feldspar phenocrysts, and a quartz-dioritic to tonalitic facies, mainly as enclaves, with laths of plagioclase showing compositional zoning and chilled rims. The Taipu Pluton is made of equigranular, locally porphyritic, monzo- to syenogranites, whereas the Gamaleira Pluton encompasses tonalitic and grano- dioritic rocks with porphyritic textures and compositionally zoned plagioclase crystals. Geochemical discriminant diagrams reveal that the rocks forming the Gameleira Pluton are metaluminous, with a calc-alkaline signature and magnesian character, contrasting with the subalkaline (high-K calc-alkaline signature and ferroan character of the Taipu and Pitombeira Plutons, where the former is highly peraluminous and the latter is metaluminous to slightly peraluminous. Rare Earth Elements patterns are similar to all plutons and register negative Eu anomalies and a relative enrichment of LREE over HREE, with LaN/YbN ratios between 9.38 to 16.20 (Gamaleira Pluton, 17.99 to 31.39 (granitic facies of the Pitombeira Pluton, 14.15 to 21.81 (dioritic facies of the Pitombeira Pluton and 15.17 to 175.41 (Taipu Pluton. Based on the combined investigation of structural, textural and geochemical data, a late- to post-collisional tectonic environment is suggested for the plutons here studied.

  8. Fabric and microstructural analysis of the Loch Borralan pluton, Northwest Highlands, Scotland

    Science.gov (United States)

    Calhoun, Justin

    The Loch Borralan pluton was emplaced within the Assynt Region of the Moine Thrust zone during the Scandian event (ca. 435-425 Ma) of the Caledonian Orogeny (478-425 Ma). It consists of two major magma suites, the syenitic early suite (431.1 +/- 1.2 Ma), and the quartz syenitic later suite (429.2 +/- 0.5 Ma). The region is characterized by a series of in-sequence thrust faults that strike NE-SW and dip approximately 20° to the SE, including (from lower to upper): the Sole Thrust, the Borralan Thrust (hypothesized, but not exposed), the Ben More Thrust, and the Moine Thrust. A series of imbricate thrusts between the Sole and Borralan Thrusts juxtapose repeated Cambrian and Ordovician strata. The Loch Borralan pluton intruded between the Sole and Ben More thrust faults, and may be bounded below by a hypothesized Borralan Thrust fault. Based on the overlap in pluton crystallization age and orogenic activity, the combination of macroscopic field lineation and foliation measurements, anisotropy of magnetic susceptibility (AMS) lineation and foliations measurements, mineral shape preferred orientation (SPO) analysis, and petrographic deformation microstructure analysis will be used to determine if the pluton expresses deformation features and fabrics corresponding to thrust fault tectonics. The dominant magnetic mineralogy as determined by thermomagnetic data and hysteresis plots was determined to be magnetite and titanomagnetite. Some paramagnetic components were seen in the early suite, and can be attributed to biotite. Both minerals contributed to the AMS signal that was used to interpret pluton fabrics. The pluton contains S>L (foliation stronger than lineation) fabrics throughout, defined by alignment of alkali feldspar grains. The foliation strike of both the early and late suites are subparallel to the thrust faults, providing evidence that the fabrics are related to deformation. The early suite is only well exposed in the southeast at the top of the Borralan

  9. PRESSURE FLUCTUATIONS BENEATH SPATIAL HYDRAULIC JUMPS

    Institute of Scientific and Technical Information of China (English)

    YAN Zhong-min; ZHOU Chun-tian; LU Shi-qiang

    2006-01-01

    This article deals with statistical analysis of pressure fluctuations at the bottom of spatial hydraulic jumps with abrupt lateral expansions. The effects of the channel expansion ratio and inflow condition on the power spectral and dominant frequency were examined. Pressure data were recorded for different Froude numbers ranging from 3.52 to 6.86 and channel expansion ratios ranging from 1.5 to 3.0. A sampling frequency of 100 Hz was selected. The measurements were conducted in the bed of a glass-walled laboratory flume by means of pressure transducers and data acquisition systems. Power spectra as well as dominant frequency and some other statistical characteristics of fluctuating pressure beneath hydraulic jumps were obtained. Test results were compared with those of classical jump, which indicates that the peak frequencies and intensity coefficients of pressure fluctuations are higher than those of the corresponding classical jumps.

  10. Seismic tomography reveals the upper-mantle structure beneath the Carpathian-Pannonian system

    Science.gov (United States)

    Dando, B. D.; Houseman, G.; Stuart, G. W.; Hegedus, E.; Kovacs, A.; Brueckl, E. P.; Hausmann, H.; Radovanovic, S.

    2009-12-01

    The Carpathian Basins Project (CBP) aims to understand the formation of the Miocene-age extensional basins contained within the convergent arc of the Alpine-Carpathian system. To test competing models for the recent geological evolution of the Carpathian-Pannonian lithosphere and upper mantle, we present a new tomographic determination of P-wave velocity structure to depths of 700 km beneath this region. This model is based on inversion of seismic travel-time residuals from 97 broadband seismic stations. We include CBP data from a 15-month deployment of a high resolution network of 46 stations deployed NW-SE across the Vienna and western Pannonian basins through Austria, Hungary and Serbia, together with 10 broadband stations spread across the Pannonian basin and a further 41 permanent broadband stations. We use P-wave arrival times from 232 teleseismic events. To avoid contamination of our inversion results from crustal velocity variations, deterministic corrections are applied to our travel-time residuals using crustal velocity models obtained from controlled source experiments and sediment thickness maps. Our 3-D velocity model images the fast velocity structure of the eastern Alps down to ~350 km. Beneath the Pannonian basin the velocity variation at 300 km depth is dominated by a fast region which extends eastward from the Alpine anomaly and reaches down into the mantle transition zone (MTZ). This fast structure is limited on the North side by slow material beneath the North Carpathians. At depths greater than 450 km, below the eastern Pannonian basin, a slow anomaly extends to the base of the model. Beneath the same region Hetenyi et al. (submitted to GRL), used receiver functions from the CBP dataset, to show a localised depression of the 660 km discontinuity of up to ~40 km. We aim to address how the depression of the 660 km discontinuity and its associated density and velocity variations affect our tomographic images. Our results will help to provide

  11. Major disruption of D″ beneath Alaska

    Science.gov (United States)

    Sun, Daoyuan; Helmberger, Don; Miller, Meghan S.; Jackson, Jennifer M.

    2016-05-01

    D″ represents one of the most dramatic thermal and compositional layers within our planet. In particular, global tomographic models display relatively fast patches at the base of the mantle along the circum-Pacific which are generally attributed to slab debris. Such distinct patches interact with the bridgmanite (Br) to post-bridgmanite (PBr) phase boundary to generate particularly strong heterogeneity at their edges. Most seismic observations for the D″ come from the lower mantle S wave triplication (Scd). Here we exploit the USArray waveform data to examine one of these sharp transitions in structure beneath Alaska. From west to east beneath Alaska, we observed three different characteristics in D″: (1) the western region with a strong Scd, requiring a sharp δVs = 2.5% increase; (2) the middle region with no clear Scd phases, indicating a lack of D″ (or thin Br-PBr layer); and (3) the eastern region with strong Scd phase, requiring a gradient increase in δVs. To explain such strong lateral variation in the velocity structure, chemical variations must be involved. We suggest that the western region represents relatively normal mantle. In contrast, the eastern region is influenced by a relic slab that has subducted down to the lowermost mantle. In the middle region, we infer an upwelling structure that disrupts the Br-PBr phase boundary. Such an interpretation is based upon a distinct pattern of travel time delays, waveform distortions, and amplitude patterns that reveal a circular-shaped anomaly about 5° across which can be modeled synthetically as a plume-like structure rising about 400 km high with a shear velocity reduction of ~5%, similar to geodynamic modeling predictions of upwellings.

  12. Evidence for a large-scale remnant of subducted lithosphere beneath Fiji.

    Science.gov (United States)

    Chen, W P; Brudzinski, M R

    2001-06-29

    We combine spatial variations of P- and S-wave speeds, 1000 fault plane solutions, and 6600 well-determined hypocenters to investigate the nature of subducted lithosphere and deep earthquakes beneath the Tonga back-arc. We show that perplexing patterns in seismicity and fault plane solutions can be accounted for by the juxtaposition of a steep-dipping Wadati-Benioff zone and a subhorizontal remnant of slab that is no longer attached to the actively subducting lithosphere. The detached slab may be from a previous episode of subduction along the fossil Vitiaz trench about 5 to 8 million years ago. The juxtaposition of slabs retains a large amount of subducted material in the transition zone of the mantle. Such a configuration, if common in the past, would allow the preservation of a primordial component in the lower mantle.

  13. Melting features along the Ryukyu slab tear, beneath the southwestern Okinawa Trough

    Science.gov (United States)

    Lin, Jing-Yi; Hsu, Shu-Kun; Sibuet, Jean-Claude

    2004-10-01

    The present-day active volcanic front associated with the Ryukyu subduction zone extends from Japan to the Ilan plain (northern Taiwan) and is located within the Okinawa Trough, 80-100 km above the Ryukyu slab. An abnormal amount of arc volcanism, which consists of basalt, andesite and rhyolite occurs within the southwestern Okinawa Trough, above a slab tear of the Ryukyu subduction zone (CBVT). The power spectrum analysis of magnetic data shows the occurrence of a thin crust above the slab tear and a thick crust beneath this volcanic area. We suggest that an excess of H2O-rich fluid might occur at the slab tear and might increase the melt flux. Both are conveyed obliquely to the uppermost mantle and lower crust CBVT magmas. After interactions, basaltic magmas would rise up, accounting for the contrast of magnetization between this volcanic body and the adjacent OT crust.

  14. Late Cenozoic Magmatic and Tectonic Evolution of the Ancestral Cascade Arc in the Bodie Hills, California and Nevada: Insights from Integrated Geologic, Geophysical, Geochemical and Geochronologic Studies

    Science.gov (United States)

    John, D. A.; du Bray, E. A.; Box, S. E.; Blakely, R. J.; Fleck, R. J.; Vikre, P. G.; Cousens, B.; Moring, B. C.

    2012-12-01

    Geologic mapping integrated with new geophysical, geochemical, and geochronologic data characterize the evolution of Bodie Hills volcanic field (BHVF), a long-lived eruptive center in the southern part of the ancestral Cascade arc. The ~700 km2 field was a locus of magmatic activity from ~15 to 8 Ma. It includes >25 basaltic andesite to trachyandesite stratovolcanoes and silicic trachyandesite to rhyolite dome complexes. The southeastern part of the BHVF is overlain by the ~3.9 to 0.1 Ma, post-arc Aurora Volcanic Field. Long-lived BHVF magmatism was localized by crustal-scale tectonic features, including the Precambrian continental margin, the Walker Lane, the Basin and Range Province, and the Mina deflection. BHVF eruptive activity occurred primarily during 3 stages: 1) dominantly trachyandesite stratovolcanoes (~15.0 to 12.9 Ma), 2) coalesced trachydacite and rhyolite lava domes and trachyandesite stratovolcanoes (~11.6 to 9.7 Ma), and 3) dominantly silicic trachyandesite to dacite lava dome complexes (~9.2 to 8.0 Ma). Small rhyolite domes were emplaced at ~6 Ma. Relatively mafic stratovolcanoes surrounded by debris flow aprons lie on the margins of the BHVF, whereas more silicic dome fields occupy its center. Detailed gravity and aeromagnetic data suggest the presence of unexposed cogenetic granitic plutons beneath the center of the BHVF. Isotopic compositions of BHVF rocks are generally more radiogenic with decreasing age (e.g., initial Sr isotope values increase from ~0.7049 to 0.7061), which suggests progressively greater magma contamination by crustal components during evolution of the BHVF. Approximately circular, polygenetic volcanoes and scarcity of dikes suggest a low differential horizontal stress field during BHVF formation. Extensive alluvial gravel deposits that grade laterally into fluvial gravels and finer grained lacustrine sediments and the westerly sourced Eureka Valley Tuff (EVT; ~9.4 Ma) blanket large parts of the BHVF. The earliest sediments

  15. Microstructure and magnetic fabric in the Shuanghe pluton:A synkinematic granite in Eastern Dabie Mountains, China

    Institute of Scientific and Technical Information of China (English)

    YANG Kunguang; LIU Qiang; LIU Yuyan; MA Changqian; XU Yajun; YANG Kuifeng

    2004-01-01

    Strain analyses for the Shuanghe pluton show that the main strain planes suffered distinct deformation. The main strain value (XZ) is up to 1.59-2.18, and the value of Flinn index (K) ranges from 0.11 to 0.82. Anisotropy of magnetic susceptibility (AMS) measurements reveal that the orientations of the magnetic foliation and lineation gently dip SE, consistent with the macroscopic foliation of the pluton. The value of anisotropy degree (P) ranges from 1.109 to 1.639, and the shape parameter (7) from 0.079 to 0.534. These studies prove that the pluton was deformed under strong compression. Quartz c-axis textures, defined by monoclinic or triclinic asymmetry, usually developed the high maxima paralleling the b-axis, which is defined by the developed in the high-ultrahigh pressure rocks (UHP) which were captured in the pluton or country rocks. It is concluded that the Shuanghe pluton emplaced under regional compression slightly after the formation of UHP, and it is characterized by synkinematic granitic deformation.

  16. Ductile strain rate recorded in the Symvolon syn-extensional plutonic body (Rhodope core complex, Greece)

    Science.gov (United States)

    Cirrincione, Rosolino; Fazio, Eugenio; Ortolano, Gaetano; Fiannacca, Patrizia; Kern, Hartmut; Mengel, Kurt; Pezzino, Antonino; Punturo, Rosalda

    2016-04-01

    The present contribution deals with quantitative microstructural analysis, which was performed on granodiorites of the syn-tectonic Symvolon pluton (Punturo et al., 2014) at the south-western boundary of the Rhodope Core Complex (Greece). Our purpose is the quantification of ductile strain rate achieved across the pluton, by considering its cooling gradient from the centre to the periphery, using the combination of a paleopiezometer (Shimizu, 2008) and a quartz flow law (Hirth et al., 2001). Obtained results, associated with a detailed cooling history (Dinter et al., 1995), allowed us to reconstruct the joined cooling and strain gradient evolution of the pluton from its emplacement during early Miocene (ca. 700°C at 22 Ma) to its following cooling stage (ca. 500-300°C at 15 Ma). Shearing temperature values were constrained by means of a thermodynamic approach based on the recognition of syn-shear assemblages at incremental strain; to this aim, statistical handling of mineral chemistry X-Ray maps was carried out on microdomains detected at the tails of porphyroclasts. Results indicate that the strain/cooling gradients evolve "arm in arm" across the pluton, as also testified by the progressive development of mylonitic fabric over the magmatic microstructures approaching the host rock. References • Dinter, D. A., Macfarlane, A., Hames, W., Isachsen, C., Bowring, S., and Royden, L. (1995). U-Pb and 40Ar/39Ar geochronology of the Symvolon granodiorite: Implications for the thermal and structural evolution of the Rhodope metamorphic core complex, northeastern Greece. Tectonics, 14 (4), 886-908. • Shimizu, I. (2008). Theories and applicability of grain size piezometers: The role of dynamic recrystallization mechanisms. Journal of Structural Geology, 30 (7), 899-917. • Hirth, G., Teyssier, C., and Dunlap, J. W. (2001). An evaluation of quartzite flow laws based on comparisons between experimentally and naturally deformed rocks. International Journal of Earth

  17. Petrology of upper Eocene-Oligocene plutonic rocks of Moalleman Damghan area

    Science.gov (United States)

    Kohansal, Reza; Zolfaghari, Seddigheh; Hashem Emami, Mohammad

    2010-05-01

    The plutonic rocks of this area include cryptodoms, hypoabyssal plutonic bodies and dikes which intruded in to the late Lutetian- late Eocene rocks. The hypoabyssal plutonic rocks in Moalleman are classified in to two main groups: - Acidic rocks, including microgranite to microgranodiorite. - Intermediate rocks, including microquartzmonzodiorite to microquartzdiorite of hypoabyssal type. Presence of fine-grained mafic xenoliths with abundant biotite, amphibole and pyroxene in the intermediate rocks may be considered as an evidence of the role of mantle melting occurrence in the formation of these rocks. Occurrence of a felsitic texture, showing a high differentiation coefficient and existence of large quarts which are embayed, rounded and infiltered by material, and finally turmalinization in the acidic rocks due to Boron metasomatism suggest the role of crust in the formation of afore mentioned rocks as well. In some acidic rocks plagioclases show oscillatory zoning. This phenomenon along with the fact that biotite granites in these rocks crystallized before crystallization of quarts and after crystallization of alkali feldspar suggest that the crystallization of these rocks accomplished in the presence of 2 percent water, pertitic texture in some feldspars of the intermediate rocks this conclusion. Supports on the basis of the geochemical studies most of the hypoabyssal rocks of Moalleman area fall in subalkaline- calcoalkaline fields. Variation of immobile incompatible trace elements versus differentiation coefficient and the situation of samples in winkler diagram show the role of crustal- melting in the formation of acidic rocks. Trace element content of some rocks (e.g. Cu and Sm) with in this group show mantle specification, while some other rocks (e.g. Zr, Th, Hf) show crustal specification. The intermediate rocks of the study area therefore, indicate a hybridization of magmas from both the mantle and crust. Study of the temperature and water vapour

  18. Broadband Seismic Investigations of the Upper Mantle Beneath the Vienna and Pannonian Basins

    Science.gov (United States)

    Dando, B. D.; Stuart, G. W.; Houseman, G. A.; Team, C.

    2008-12-01

    The Carpathian Basins Project (CBP) aims to understand the origin of the Miocene-age extensional basins contained within the compressional arc of the Alpine-Carpathian system. To test competing models for the recent geological evolution of the Carpathian-Pannonian lithosphere and upper mantle, we present a new determination of P-wave velocity structure to depths of 700 km beneath this region. This model is based on inversion of seismic travel-time residuals from 97 broadband seismic stations. We include CBP data from a 15-month deployment of a high resolution network of 46 stations deployed NW-SE across the Vienna and western Pannonian basins through Austria, Hungary and Serbia, together with 10 broadband stations spread across the Pannonian basin and a further 41 permanent broadband stations. We use P-wave arrival times from approximately 341 teleseismic events. The 3-D velocity variation obtained by tomographic inversion of the P-wave travel-time residuals shows an approximately linear belt of fast material of width about 100 km, orientated WNW-ESE beneath the western Pannonian Basin at sub-lithospheric depths. This feature is apparently continuous with structure beneath the Eastern Alps, but becomes more diffuse into the transition zone. Our initial interpretation of these fast velocities is in terms of mantle downwelling related to the early collision of Adria and Europe. We use receiver functions to assess crustal structure variations. We also determine SKS anisotropy; regionally SKS varies systematically in direction, with a delay time of about 1.0s. E-W fast directions above the fast tomographic anomaly change to NW-SE across the Great Hungarian Plane and the Vienna Basin.

  19. Layered anisotropy within the crust and lithospheric mantle beneath the Sea of Japan

    Science.gov (United States)

    Legendre, C. P.; Zhao, L.; Deschamps, F.; Chen, Q.-F.

    2016-10-01

    Continental rifting during the Oligocene to mid-Miocene caused the opening of the Sea of Japan and the separation between the Japanese Islands and the Eurasian Plate. The tectonic evolution in the Sea of Japan is important for understanding the evolution of back-arc regions in active convergent margins. Here, we use data from the seismic stations surrounding the Sea of Japan to map the Rayleigh-wave azimuthal anisotropy in the crust and lithospheric mantle beneath the Sea of Japan. We explore the variations of Rayleigh-wave phase-velocity beneath the Sea of Japan in a broad period range (30-80 s). Rayleigh-wave dispersion curves are measured by the two-station technique for a total of 231 interstation paths using vertical-component broad-band waveforms at 22 seismic stations around the Sea of Japan from 1411 global earthquakes. The resulting maps of Rayleigh-wave phase velocity and azimuthal anisotropy allow the examination of azimuthal anisotropy at specific periods. They exhibit several regions with different isotropic and anisotropic patterns: the Japan Basin displays fast velocities at shorter periods (30 and 40 s) with NNE-SSW anisotropy, whereas at 60 s and longer, the velocities become slow even if the anisotropy remains NE-SW; the East China Sea shows fast velocities at all periods (30-80 s) with constant NW-SE anisotropy. Trench-normal anisotropy beneath the Japanese Islands is found at short periods (30-40 s) and become trench-parallel at periods of 60 s and longer. Overall, our model resolves two layers of anisotropy, the shallowest and deepest layers being potentially related to frozen deformation due to recent geodynamic events, and asthenospheric flow, respectively.

  20. Revisiting the Baja-British Columbia hypothesis: Argon-argon geochronology and paleomagnetism of the Ecstall, Butedale, and Smith Island plutons, British Columbia, Canada

    Science.gov (United States)

    Brownlee, Sarah Jo

    The controversy concerning terrane displacements in western British Columbia, otherwise known as the Baja-BC hypothesis, is revisited using paleomagnetism, rock magnetism, and 40Ar/39Ar geochronology and thermal modeling. We studied three plutons in northwest British Columbia, the Ecstall, Butedale, and Smith Island plutons. The Ecstall pluton is the focus of this research as it has been the subject of considerable debate over the cause of systematic variations in paleomagnetic direction across the ˜25 km wide pluton. Hollister et al. (2004) proposed that magnetization carried by lamellar magnetism in ilmenite-hematite was variably reset during reheating by emplacement of the younger Quottoon plutonic complex on the eastern margin of the Ecstall pluton, thus causing the systematic variations in paleomagnetic direction. To test this hypothesis we conducted a number of studies on samples from the Ecstall pluton. First, a detailed mineralogic study using scanning electron microscopy, and transmission electron microscopy found evidence of microstructural and mineralogic changes to the magnetic oxides of the Ecstall pluton as a function of distance from the Quottoon plutonic complex. Second, rock magnetic experiments on single crystals of Fe-Ti oxides confirm changes to the magnetic properties of single crystals that are related to both microstructure and distance from the Quottoon plutonic complex. Third, spatial trends in 40Ar/39Ar cooling ages from hornblende and biotite were found to be consistent with reheating by the Quottoon plutonic complex. In addition to reheating by the Quottoon plutonic complex, thermal modeling suggests that spatial trends in 40Ar/39Ar cooling ages are most consistent with a thermal history that also includes northeast side up tilt of the Ecstall. The Smith Island and Butedale plutons do not show evidence for tilting in their 40Ar/39Ar cooling age trends, and paleomagnetic directions from these plutons are approximately concordant with the

  1. Source variation for Mesozoic granitoid plutons in the White-Inyo Range, California, and implications for changes in the lithospheric structure

    Science.gov (United States)

    Gammel, E.; Nabelek, P. I.; Phillips, E. H. W.; Scott, S. R.; Sims, K. W. W.

    2015-12-01

    The White-Inyo Range (WIR) of eastern California lies to the east of Owen's Valley and the Sierra Nevada batholith (SNB). Over twenty recognized Mesozoic, granitic to gabbroic plutons intruded into Precambrian and Cambrian sedimentary units that were previously metamorphosed to the greenschist facies. These plutons represent intrusive equivalents of volcanics erupted during two magmatic events at ca. 180-167 Ma and 102-86 Ma (Coleman et al, 2003). The motivation of this study is to understand changes in magma sources over this time period. We propose there is a time-transgressive change in source material in the WIR. Preliminary trace element data suggest that Jurassic plutons were sourced from deep crustal material, whereas later Cretaceous plutons may have had a shallower origin. This is supported by high Sr/Y ratios in the Jurassic plutons (up to 300) and relatively lower ratios in Cretaceous plutons (down to 14). Chiaradia (2015) suggests elevated Sr/Y ratios are directly linked to increasing crustal thickness, therefore the WIR plutons may record the period of crustal thinning in this region or maturation of the crust that allowed shallower melting in the Cretaceous. The highest values also suggest possible adakitic source material. REE patterns suggest that the youngest plutons (e.g. Sage Hen Flat) are more similar to samples collected from the eastern Sierra Nevada batholith than older plutons with higher La/Yb ratios. Relatively flat patterns REE patterns of Tertiary basalts and a late diabase dike in the WIR are also similar to SNB samples. Another goal of this study is to determine the degree of mixing as a function of time during the emplacement of plutons in the range. Field and petrographic analyses suggest that older plutons represent more mafic materials and younger plutons are more granitic with mafic enclaves. We propose either (1) older plutons represent initial lower lithosphere melting, and with time, there is an increase of incorporation of

  2. Investigating Late Cenozoic Mantle Dynamics beneath Yellowstone

    Science.gov (United States)

    Zhou, Q.; Liu, L.

    2015-12-01

    Recent tomography models (Sigloch, 2011; Schmandt & Lin, 2014) reveal unprecedented details of the mantle structure beneath the United States (U.S.). Prominent slow seismic anomalies below Yellowstone, traditionally interpreted as due to a mantle plume, are restricted to depths either shallower than 200 km or between 500 and 1000 km, but a continuation to greater depth is missing. Compared to fast seismic anomalies, which are usually interpreted as slabs or delaminated lithosphere, origin of deep slow seismic anomalies, especially those in the vicinity of subduction zones, is more enigmatic. As a consequence, both the dynamics and evolution of these slow anomalies remain poorly understood. To investigate the origin and evolution of the Yellowstone slow anomaly during the past 20 Myr, we construct a 4D inverse mantle convection model with a hybrid data assimilation scheme. On the one hand, we use the adjoint method to recover the past evolution of mantle seismic structures beyond the subduction zones. On the other hand, we use a high-resolution forward model to simulate the subduction of the oceanic (i.e., Farallon) plate. During the adjoint iterations, features from these two approaches are blended together at a depth of ~200 km below the subduction zone. In practice, we convert fast and slow seismic anomalies to effective positive and negative density heterogeneities. Our preliminary results indicate that at 20 Ma, the present-day shallow slow anomalies beneath the western U.S. were located inside the oceanic asthenosphere, which subsequently entered the mantle wedge, through the segmented Farallon slab. The eastward encroachment of the slow anomaly largely followed the Yellowstone hotspot track migration. The present deep mantle Yellowstone slow anomaly originated at shallower depths (i.e. transition zone), and was then translated down to the lower mantle accompanying the sinking fast anomalies. The temporal evolution of the slow anomalies suggests that the deep

  3. Geomorphologic Indices for Transition from Subduction to Arc-Continent Collision in Sumba Island, Indonesia

    Science.gov (United States)

    Authemayou, C.; Delcaillau, B.; Brocard, G. Y.; Molliex, S.; Nexer, M.; Pedoja, K.

    2014-12-01

    The Sumba Island lies in a key area to study the eastern Indonesia geodynamics. It is located in the Sunda-Banda fore-arc in the area of transition from subduction of the Indian oceanic lithosphere (W) beneath the Sunda-Banda arc to arc-continent collision between the Australian continental margin and the Sunda-Banda arc (E). East of the Sumba Island, the western boundary of the Savu basin originated during Middle Miocene by the southeastward slab retreat below the Sunda-Banda arc (Rigg and Hall, 2001). Previous studies has detected a global uplift of the island accommodating the Australian plate - South West Banda Arc convergence (Fleury et al., 2009). This uplift is associated with northeastward tilting and gravitational collapse to the South. Analyses of various geomorphic markers (perched low relief landscapes, rockyshore platform, coral reef terraces, drainages) and of morphometric indices allowed us to localise new structures (faults and folds), to determine the chronology of their activation and to better constraint the uplift history of Sumba Island. These results aim to understand the evolution of the deformation in Sumba Island in regard with its geodynamic context from Middle Miocene to present-day.

  4. Pluton accommodation at high strain rates in the upper continental crust. The example of the Central Extremadura batholith, Spain

    Science.gov (United States)

    Fernández, Carlos; Castro, Antonio

    1999-08-01

    Emplacement in the tensional bridge of a stepped dextral shear zone system is proposed for the Central Extremadura batholith (Spain). The country rocks show a pervasive anisotropy that conditioned the style of the structures developed as a consequence of the transference of displacement from the stepped shear zones to the releasing area. The kinematic evolution of the resulting megakink fold provided the volume increase necessary for the granite emplacement. Thermal and kinematic models suggest that the growth of individual plutons took place in periods of no more than several hundred to a few thousand years. Fast strain rates (10 -10-10 -11 s -1) must concentrate in local structures (e.g. initiation of kink folds) even in zones deforming as a whole under typical strain rates (10 -14±1 s -1). Granite plutons might be used as strain-rate gauges for syn-plutonic structures.

  5. Probing the volcanic-plutonic connection and the genesis of crystal-rich rhyolite in a deeply dissected supervolcano in the Nevada Great Basin: Source of the late Eocene Caetano Tuff

    Science.gov (United States)

    Watts, Kathryn E.; John, David A.; Colgan, Joseph P.; Henry, Christopher D.; Bindeman, Ilya N.; Schmitt, Axel K.

    2016-01-01

    ignimbrite eruption and caldera collapse. Thus, the Caetano Tuff contradicts models for the mutually exclusive origins of voluminous volcanic and plutonic magmas in the upper crust. Crystal-scale O isotope data indicate that the Caetano Tuff is one of the most 18O-enriched rhyolites in the Great Basin (δ18Omagma = 10·2 ± 0·2‰), supporting anatexis of local metasedimentary basement crust. Metapelite xenoliths in the Carico Lake pluton and ubiquitous xenocrystic zircons in the Caetano Tuff provide constraints for the anatexis process; these data point to shallow (<15 km) dehydration melting of a protolith similar to the Proterozoic McCoy Creek Group siliciclastic sediments in eastern Nevada, projected beneath Caetano in fault-stacked shelf sediments that were thickened during Mesozoic crustal shortening. Mean zircon U–Pb ages for different stratigraphic levels of the intra-caldera Caetano Tuff are 34·2–34·5 Ma, 0·2–0·5 Myr older than the caldera sanidine 40Ar/39Ar age of 34·00 ± 0·03 Ma, documenting protracted duration of assembly and homogenization of isotopically diverse upper crustal melts, followed by crystallization and zonation to generate the Caetano Tuff magma chamber. Sanidine rims in the least evolved Caetano Tuff and in the Carico Lake pluton and Redrock Canyon porphyry have sharply zoned Ba domains that point to crystal growth during magmatic recharge events. The recharge magma is inferred to have been compositionally similar to the Caetano Tuff magma, with increased Ba resulting from remelting of Ba-rich sanidine cumulates. Mush reactivation to generate the Caetano Tuff eruption was sufficiently rapid to preserve compositional gradients in the intracaldera ignimbrite, calling into question models that predict homogeneity as a prerequisite for remobilizing crystal-rich ignimbrite magmas.

  6. Of Eggs and Arcs

    Science.gov (United States)

    Burns, Joseph A.; Thomas, P. C.; Helfenstein, P.; Tiscareno, M. S.; Hedman, M. M.; Agarwal, M.

    2012-10-01

    New scenarios for the origins of Saturn’s rings/interior moons have directed scientific attention to the region just exterior to Saturn’s main rings. Four satellites (Aegaeon = Ae; Anthe = An; Methone = Me; Pallene = Pa) discovered by the Cassini mission on either side of Mimas’s orbit perhaps comprise a distinct class of ring-moon. They are tiny (R = 0.3-2.5 km); three (AeAnMe) are trapped in co-rotation resonances with Mimas and reside within ring-arcs; and at least two (MePa) have remarkably regular shapes. Images with pixel scales as fine as 27 m taken in May 2012 reveal Methone to be ovoid within 10 m (from sub-pixel limb detection) and devoid of any craters (>130 m) across its 9 km2 of surface; Pallene and even tiny Aegaeon have similar appearances in lesser-quality images. Numerical simulations demonstrate that particles comprising the surrounding ring-arcs populate the same resonances as their embedded moons; escape speeds from the moons are bodies. In this environment, the moons’ shapes are smooth equipotentials; electrostatic effects may also determine how grains settle to surfaces. Considering these shapes to represent equipotential surfaces for rotating, tidally distorted, homogeneous bodies, we infer mean satellite densities of 250+/-60 (Pa), 310+/-30 (Me), and 540+/-120 (Ae) kg m-3. About half of Methone’s leading hemisphere is covered by a sharply bounded, lemon-shaped, relatively dark region, having a form reminiscent of Mimas’s thermal anomaly (Howett et al. 2011). Its (601 nm) albedo is 13% lower than the bounding brighter material. An irregularly shaped, even-darker (by 4%) blotch straddles the apex of the moon’s motion. Impacts with circum-planetary meteoroids and plasma are likely responsible for these features.

  7. U-Pb geochronology and geochemistry of Eocene and Oligocene plutons in southeast Iran: Implication for closure of the South Sistan Suture Zone

    Science.gov (United States)

    Burg, Jean-Pierre; Mohammadi, Ali; Ruh, Jonas; Bouilhol, Pierre

    2016-04-01

    The N-S trending Sistan Suture Zone in eastern Iran is a splay of the Tethys sutures. It represents an oceanic embayment that separated the Central Iran from the Afghan continental blocks. Structural, tectonic and petrological/geochemical evidence define eastward subduction beneath the Afghan continental block of the Sistan inlet of the Mesozoic Tethys Ocean. Mapping of the area allowed reaching and sampling intermediate to granitic intrusions stretched along the southern segment of this collisional suture zone. U-Pb zircon crystallization ages combined with major and trace element analyses, dated the series of granite-granodiorite-rhyolite at ca 40.5-44.3 Ma and ca 28.9-30.9 Ma. Isotopic geochemistry, including Sr-Nd isotopes and Hf isotope analyses, and petrological modelling suggest that the 40.5-44.3 Ma plutons crystallized from melts largely derived from the turbidites of the host accretionary wedge. Melting of the deep wedge was induced by the intrusion of mantle magmas interacting with the crustal turbiditic melts, which is responsible for the wide range of compositions. Most of the 28.9-30.9 Ma magmas were generated from mantle melting, with assimilation of the surrounding turbidites. The rare setting of within-wedge intrusions is attributed to mantle upwelling reaching wedge sediments at the inception of delamination processes, which sign the end of subduction-related deformational and thermal events in the Sistan Suture Zone. Numerical modelling of subduction - magma production - intrusion and melting of wedge sediments further constrains this collisional to post-collisional scenario.

  8. Crustal structure variations along the Lesser Antilles Arc

    Science.gov (United States)

    Schlaphorst, D.; Kendall, J. M.; Melekhova, E.; Blundy, J.; Baptie, B.; Latchman, J. L.

    2013-12-01

    Continental crust is predominantly formed along subduction zones. Therefore, an investigation of the crustal and mantle structure variation of these areas is crucial for understanding the growth of continental crust. This work deals with the seismological characteristics along the Lesser Antilles Arc, an island arc system built by the relatively slow subduction (~2cm/yr) of the North and South American plates beneath the Caribbean plate. The amount of subducted sediments changes significantly from sediment-rich subduction in the South to sediment-poor subduction in the North. The abundance of broadband seismic stations on the Lesser Antilles islands enables a range of seismic methods to be used to study arc processes. Furthermore, the abundance of cumulate samples allows for a detailed petrological analysis, which can be related to the seismological patterns. We use data from three component broadband stations located on the individual islands along the arc. From the island of Grenada in the South to the Virgin Islands in the North significant variations in sediment load, petrology and volcanism are observed along the arc. In this work, we investigate crustal structure using receiver functions to determine Moho depth and Vp/Vs ratio. The ratio gives an idea about the material of the subsurface as well as its water and its melt contents. The receiver functions are computed using the extended-time multitaper frequency domain cross-correlation receiver-function (ETMTRF) by Helffrich (2006). This method has the advantage of resistance to noise, which is helpful since most of the data around the arc will have been collected by stations close to the ocean, thus containing a large amount of noise. Our results show clear variations in these measurements. There are also regions where the Moho is not very sharp due to a low velocity contrast. The real data results were then compared to synthetic receiver functions from subsurface models. We compute a range of synthetic

  9. Les granitoïdes néoprotérozoïques de Khzama, Anti-Atlas central, Maroc: marqueurs de l'évolution d'un magmatisme d'arc à un magmatisme alcalineNeoproterozoic granitoids from Khzama, central Anti-Atlas, Morocco: evolution markers from arc magmatism to alkaline magmatism

    Science.gov (United States)

    El-Khanchaoui, T.; Lahmam, M.; El-Boukhari, A.; El-Beraaouz, H.

    2001-05-01

    Petrological study and zircon typology provide important information that is related to the classification and genesis of Neoproterozoic granitoids in the Khzama area (northeast Siroua). The Pan-African granitoids show a transition from island-arc magmatism to alkaline magmatism. A space and time zonation of magmatism from the north to the south is evident. Early Pan-African granitoids were generated from various magma sources through different petrogenetic mechanisms. The first association corresponds to the low-K calc-alkaline plutons of Ait Nebdas, the second one correponds to high-K calc-alkaline post-collisional granites (Tamassirte-Tiferatine and Ifouachguel). Finally, shoshonitic magmatism (Irhiri) ends the magmatic evolution of the region. Thus, the late Pan-African granitic plutonism began with calc-alkaline associations and ended with K-alkaline magmatism in a transtensional setting, heralding the onset of the Moroccan Palæozoic cycle.

  10. Investigation of the mineral potential of the Clipper Gap, Lone Mountain-Weepah, and Pipe Spring plutons, Nevada

    International Nuclear Information System (INIS)

    The Clipper Gap pluton, composed mostly of quartz monzonite with minor granite, granodiorite, and crosscutting alaskite dikes, intrudes Paleozoic western facies strata. A narrow zone of contact metamorphism is present at the intrusive-sediment contact. No mineral production has been recorded from Clipper Gap, but quartz veins containing gold-silver-copper mineral occurrences have been prospected there from the late 1800's to the present. Areas of the Lone Mountain-Weepah plutons that were studied are located in Esmeralda County about 14 km west of Tonopah, Nevada. At Lone Mountain, a Cretaceous intrusive cuts folded Precambrian and Cambrian sediments. Lead-zinc ores have been mined from small replacement ore bodies in the Alpine district, west of Lone Mountain. Copper and molybdenum occurrences have been found along the east flank of Lone Mountain, and altered areas were noted in intrusive outcrops around the south end of Lone Mountain. Mineral occurrences are widespread and varied with mining activity dating back to the 1860's. The Pipe Spring pluton study area is flanked by two important mining districts, Manhattan to the north and Belmont to the northeast. Mining activity at Belmont dates from 1865. Activity at Manhattan was mainly between 1907 and 1947, but the district is active at the present time (1979). Four smaller mining areas, Monarch, Spanish Springs, Baxter Spring, and Willow Springs, are within the general boundary of the area. The Pipe Spring pluton study area contains numerous prospects along the northern contact zone of the pluton. Tungsten-bearing veins occur within the pluton near Spanish Springs, with potential for gold-tungsten placer in the Ralston Valley. Nickel and associated metals occur at Willow Spring and Monarch Ranch, where prospects may be associated with the margin of the Big Ten Peak Caldera

  11. Mantle transition zone beneath northeast China from P-receiver function

    Science.gov (United States)

    Zhang, R.; Wu, Q.

    2015-12-01

    We used receiver functions to examine lateral topographical variations on the 410- and 660-km beneath northeast China and particularly the Kuril-Japan arc junctions. Compared to other receiver functions studies, our analysis was based on greater station coverage of higher density by combining all recent seismic arrays so far deployed in northeast China. Our image shows that the 410-km is featured by a ~10-20 km uplift extending in the NNE direction beneath some areas of the Quaternary basaltic rocks distributed at Abaga and at Wudalianchi. The Clapeyron slope of the olivine phase transiton at 410-km suggests that the uplift is compatible with a negative thermal anomaly. We also confirm a significant depression of the 660 from the Changbai volcanism in the north to Korea in the south along the NW-SE direction. The depression is also accompanied by an uplift of the 660 to the west. The shallow 660-km discontinuity is also particularly detected beneath the Kuril-Japan arc junctions, while it was not detected before. The thermal anomaly at 410 km depth is most likely a remnant of a detached mantle lithosphere that recently sank to depth, thus providing robust evidence for the source and evolution of these basalts. The depression of the 660-km discontinuity may support that the subducting Pacific slab bends sharply and becomes stagnant when it meets strong resistance at a depth of about 670 km. After accumulation to a great extent the stagnant slab finally penetrates into the lower mantle. Combined with the previous triplicated studies, the shallow 660-km may suggest that descending Pacific slab at its leading and junction edges might be accommodated by a tearing near a depth of 660 km. Acknowledgements. Two liner seismic arrays were deployed by the Institute of Geophysics, China Earthquake Administration. The data of the permanent stations were provided by the Data Management Centre of China, National Seismic Network at the Institute of Geophysics, China Earthquake

  12. Channelization of plumes beneath ice shelves

    KAUST Repository

    Dallaston, M. C.

    2015-11-11

    © 2015 Cambridge University Press. We study a simplified model of ice-ocean interaction beneath a floating ice shelf, and investigate the possibility for channels to form in the ice shelf base due to spatial variations in conditions at the grounding line. The model combines an extensional thin-film description of viscous ice flow in the shelf, with melting at its base driven by a turbulent ocean plume. Small transverse perturbations to the one-dimensional steady state are considered, driven either by ice thickness or subglacial discharge variations across the grounding line. Either forcing leads to the growth of channels downstream, with melting driven by locally enhanced ocean velocities, and thus heat transfer. Narrow channels are smoothed out due to turbulent mixing in the ocean plume, leading to a preferred wavelength for channel growth. In the absence of perturbations at the grounding line, linear stability analysis suggests that the one-dimensional state is stable to initial perturbations, chiefly due to the background ice advection.

  13. Turbulence beneath finite amplitude water waves

    Energy Technology Data Exchange (ETDEWEB)

    Beya, J.F. [Universidad de Valparaiso, Escuela de Ingenieria Civil Oceanica, Facultad de Ingenieria, Valparaiso (Chile); The University of New South Wales, Water Research Laboratory, School of Civil and Environmental Engineering, Sydney, NSW (Australia); Peirson, W.L. [The University of New South Wales, Water Research Laboratory, School of Civil and Environmental Engineering, Sydney, NSW (Australia); Banner, M.L. [The University of New South Wales, School of Mathematics and Statistics, Sydney, NSW (Australia)

    2012-05-15

    Babanin and Haus (J Phys Oceanogr 39:2675-2679, 2009) recently presented evidence of near-surface turbulence generated below steep non-breaking deep-water waves. They proposed a threshold wave parameter a {sup 2}{omega}/{nu} = 3,000 for the spontaneous occurrence of turbulence beneath surface waves. This is in contrast to conventional understanding that irrotational wave theories provide a good approximation of non-wind-forced wave behaviour as validated by classical experiments. Many laboratory wave experiments were carried out in the early 1960s (e.g. Wiegel 1964). In those experiments, no evidence of turbulence was reported, and steep waves behaved as predicted by the high-order irrotational wave theories within the accuracy of the theories and experimental techniques at the time. This contribution describes flow visualisation experiments for steep non-breaking waves using conventional dye techniques in the wave boundary layer extending above the wave trough level. The measurements showed no evidence of turbulent mixing up to a value of a {sup 2}{omega}/{nu} = 7,000 at which breaking commenced in these experiments. These present findings are in accord with the conventional understandings of wave behaviour. (orig.)

  14. The Precambrian/Lower Cambrian pluton from Vila Nova (Central Portugal)

    Energy Technology Data Exchange (ETDEWEB)

    Reis, A. I. M.; Silva, M. M. V. G.; Antunes, I. M. H. R.

    2010-07-01

    The Vila Nova pluton is a small, Pre-Variscan granitic body that intruded rocks of the Central Iberian Zone near the contact with the Ossa Morena Zone and is affected by several shear zones and faults. Its contact metamorphic aureole is constituted by micaschist with porphyroblasts in the outer zone and hornfels in the inner zone. Small mainstreamed xenoliths are dispersed all over the body. The pluton has a great mineralogical heterogeneity with pronounced variations in muscovite/biotite and plagioclase/ microcline contents and is classified as granite, granodiorite or tonalite. It is a leuco granite, highly peraluminous (A/CN K = 1.31 - 1.64), magnesian and calc-alkaline to alkaline-calcic. The variation diagrams show curvilinear trends with silica. Eu/Eu* = 0.47 - 0.77 and there is a slight enrichment in LREE relative to HREE. The normalized diagrams indicated dominantly crustal granite, related to subduction. U-Pb isotopic data of zircon and monazite gives 540-542 Ma age. (Author) 19 refs.

  15. The gabbro (shoshonitic)-monzonite-granodiorite association of Khankandi pluton, Alborz Mountains, NW Iran

    Science.gov (United States)

    Aghazadeh, Mehraj; Castro, Antonio; Omran, Nematallah Rashidnejad; Emami, Mohamad Hashem; Moinvaziri, Hossien; Badrzadeh, Zahra

    2010-05-01

    The Khankandi pluton forms part of a group of gabbro-granodiorite intrusions in the Alborz Mountains of NW Iran. A petrographical and geochemical study of this plutonic association reveals the existence of several magmatic cycles with different origins and slight differences in age. The oldest cycle (C1) is represented by granodiorites. A second cycle (C2) is formed by a gabbro-monzonite association, with a clear shoshonitic affinity, that dominates most of the intrusive volume. Gabbros and monzonites form a co-magmatic association. Zircons from the monzonites were analyzed by LA-ICP-MS for U-Pb dating. An average age of 28.9 Ma, ranging from 23.7 to 33.6 Ma was obtained. Gabbros, monzonites and granodiorites share a nearly common isotopic ratio for Sr and Nd. Both initial Sr and Nd ratios are clustered within a narrow range from 0.7045 to 0.7047 for the 87Sr/ 86Sr ratio and ɛNd from 1.46 to 1.89. Comparison with experimental studies, together with mantle-like isotopic ratios and comparisons of REE patterns, points to an origin by variable melting rates from a common metasomatised mantle source for gabbros and monzonites. Melting of a subducted mélange is suggested for the granodiorite magmas predating the gabbro-monzonite intrusion. The two sources, a metasomatised mantle and ascending silicic plumes, are direct consequence of subduction.

  16. Arc Interference Behavior during Twin Wire Gas Metal Arc Welding Process

    Directory of Open Access Journals (Sweden)

    Dingjian Ye

    2013-01-01

    Full Text Available In order to study arc interference behavior during twin wire gas metal arc welding process, the synchronous acquisition system has been established to acquire instantaneous information of arc profile including dynamic arc length variation as well as relative voltage and current signals. The results show that after trailing arc (T-arc is added to the middle arc (M-arc in a stable welding process, the current of M arc remains unchanged while the agitation increases; the voltage of M arc has an obvious increase; the shape of M arc changes, with increasing width, length, and area; the transfer frequency of M arc droplet increases and the droplet itself becomes smaller. The wire extension length of twin arc turns out to be shorter than that of single arc welding.

  17. Progress on the seismic anisotropy knowledge beneath Iberia and northern Morocco: the contribution of the second Topoiberia-Iberarray deployment

    Science.gov (United States)

    Diaz Cusí, J.; Gallart, J.

    2012-04-01

    In summer 2009 the dense Iberarray broad-band seismic network deployed in the framework of the large-scale TopoIberia project moved to its second footprint. Up to 55 stations covered the central part of the Iberian Peninsula for roughly 18 months, distributed in a regular grid with a nominal spacing of 60 km. 19 additional stations, active since late 2007 in the Northern part of Morocco, were moved southwards during the summer 2010 to the High Atlas, thus extending the investigated area. Continuous data from all the permanent broad-band networks covering the region have also been gathered to produce a complete database. We focus here in the results constraining the presence of anisotropy as evidenced from the analysis of splitted teleseismic phases. Few anisotropic results in the area covered by this IberArray deployment have been published till now, all of them coming from a scarce number of permanent stations. The results here presented extend the anisotropic map obtained from the first TopoIberia-Iberarray deployment in the Betics-Alboran zone (Díaz et al, 2010). The inferred fast polarization directions (FPD) clearly document a spectacular rotation along the Gibraltar arc, following the curvature of the Rif-Betic chain, from roughly N65E beneath the Betics to close to N65W beneath the Rif chain. The stations beneath the Central Iberian Massif present a small amount of anisotropy, oriented roughly E-W. Beneath SW Iberia, within the Variscan Ossa-Morena zone, the dominant orientation changes to NNE-SSW, the induced time delays are smaller and a number of good quality measurements show no evidences for anisotropy. Beneath Eastern Iberia, the NE-SW and E-W FPD observed respectively in the Betics and Central Iberia seems to converge, without any indication of an abrupt change similar to that evidenced in the southern part of the Gibraltar arc. The preliminary data of the stations located in the High Atlas show a small degree of anisotropy, with rather unconstrained

  18. Seismotectonics of New Guinea: a Model for Arc Reversal Following Arc-Continent Collision

    Science.gov (United States)

    Cooper, Patricia; Taylor, Brian

    1987-02-01

    The structure and evolution of the northern New Guinea collision zone is deduced from International Seismological Center (ISC) seismicity (1964-1985), new and previously published focal mechanisms and a reexamination of pertinent geological data. A tectonic model for the New Guinea margin is derived which illustrates the sequential stages in the collision and suturing of the Bewani-Toricelli-Adelbert-Finisterre-Huon-New Britain arc to central New Guinea followed by subduction polarity reversal in the west. East of 149°E, the Solomon plate is being subducted both to the north and south; bringing the New Britain and Trobriand forearcs toward collision. West of 149°E the forearcs have collided, and together they override a fold in the doubly subducted Solomon plate lithosphere, which has an axis that is parallel to the strike of the Ramu-Markham suture and that plunges westward at an angle of 5° beneath the coast ranges of northern New Guinea. Active volcanism off the north coast of New Guinea is related to subduction of the Solomon plate beneath the Bismarck plate. Active volcanism of the Papuan peninsula and Quaternary volcanism of the New Guinea highlands are related to slow subduction of the Solomon plate beneath the Indo-Australian plate along the Trobriand Trough and the trough's former extension to the west, respectively. From 144°-148°E, seismicity and focal mechanisms reveal that convergence between the sutured Bismarck and Indo-Australian plates is accommodated by thrusting within the Finisterre and Adelbert ranges and compression of the New Guinea orogenic belt, together with basement-involved foreland folding and thrusting to the south. The Finisterre block overthrusts the New Guinea orogenic belt, whereas the Adelbert block is sutured to New Guinea and overthrusts the oceanic lithosphere of the Bismarck Sea. Along the New Guinea Trench, west of 144°E, seismicity defines a southward dipping Wadati-Benioif zone, and focal mechanisms indicate oblique

  19. On arc efficiency in gas tungsten arc welding

    Directory of Open Access Journals (Sweden)

    Nils Stenbacka

    2013-12-01

    Full Text Available The aim of this study was to review the literature on published arc efficiency values for GTAW and, if possible, propose a narrower band. Articles between the years 1955 - 2011 have been found. Published arc efficiency values for GTAW DCEN show to lie on a wide range, between 0.36 to 0.90. Only a few studies covered DCEP - direct current electrode positive and AC current. Specific information about the reproducibility in calorimetric studies as well as in modeling and simulation studies (considering that both random and systematic errors are small was scarce. An estimate of the average arc efficiency value for GTAW DCEN indicates that it should be about 0.77. It indicates anyway that the GTAW process with DCEN is an efficient welding method. The arc efficiency is reduced when the arc length is increased. On the other hand, there are conflicting results in the literature as to the influence of arc current and travel speed.

  20. Groundwater Mounding Beneath Stormwater Infiltration Basins

    Science.gov (United States)

    Nimmer, M.; Thompson, A. M.; Misra, D.

    2007-12-01

    An accurate understanding of groundwater mound formation is important in the proper design of stormwater infiltration basins since these basins are often required to recharge a portion of pre-development infiltration volume. Mound formation due to localized recharge may reduce the infiltration rate of the basin and the ability of the soil to filter pollutants. The goal of this research was to understand groundwater mounding and the potential for contaminant transport resulting from recharge beneath stormwater infiltration basins. A 0.10 ha infiltration basin serving a 9.4 ha residential subdivision in Oconomowoc, Wisconsin was used in this study. Subsurface conditions included sand and gravel material and a groundwater table at 2.3 m below grade. Three storm events, 4.9 cm, 2.8 cm, and 4.3 cm, between August 2006 and April 2007 were modeled using the two-dimensional numerical model HYDRUS. The calibrated model was used to evaluate hypothetical basin operation scenarios for various basin sizes, soil types, ponding depths, and water table depths. The groundwater mound intersected the basin floor in most scenarios with loamy sand and sandy loam soils, an unsaturated thickness of 1.52 m, and a ponding depth of 0.61 m. No groundwater table response was observed with ponding depths less than 0.31 m with an unsaturated zone thickness of 6.09 m. The mound height was most sensitive to hydraulic conductivity and unsaturated zone thickness. A 7.6 cm sediment layer delayed the time to reach maximum mound height, but had a minimal effect on the magnitude of the mound. Mound heights increased as infiltration basin size increased.

  1. Mantle Structure Beneath Central South America

    Science.gov (United States)

    Vandecar, J. C.; Silver, P. G.; James, D. E.; Assumpcao, M.; Schimmel, M.; Zandt, G.

    2003-12-01

    Making use of 60 digital broadband seismic stations that have operated across central South America in recent years, we have undertaken an inversion for the upper- and uppermost lower-mantle P- and S-wave velocity structures beneath the region. We have combined data from four portable PASSCAL-type experiments as well as the 3 GTSN permanent stations (LPAZ, BDFB and CPUP) and 1 Geoscope station (SPB) located in the region. The portable data were deployed at various times between 1992 and 1999 and include: 28 sites from the Brazilian Lithosphere Seismic Project (BLSP: Carnegie Institution of Washington and Universidade de Sao Paulo), 16 sites from the Broadband ANdean JOint experiment (BANJO: Carnegie Institution of Washington and University of Arizona), 8 sites from the Seismic Exploration of the Deep Altiplano project (SEDA: Lawrence Livermore National Laboratory) and 4 sites from the University of Brasilia. The P- and S-wave relative delay times are independently obtained via a multi-channel cross correlation of band-passed waveforms for each teleseismic event. These data are then inverted using an iterative, robust, non-linear scheme which parameterizes the 3-D velocity variations as splines under tension constrained at over 120,000 nodes across South America between latitudes of 15 and 30 degrees South. Amongst other features, we robustly image the high-velocity subducting Nazca plate penetrating into the lower mantle and the high-velocity root of the ~3.2 Gyr old Sao Francisco Craton extending to depths of 200-300 km. We will discuss the consistency between our tomographic models and predictions of dynamic mantle models based on plate tectonic reconstructions of subduction.

  2. Miocene through Holocene Arc and Post-arc Volcanism in the Northern Sierra Nevada and Western Nevada

    Science.gov (United States)

    Cousens, B.; Henry, C. D.; Timmermans, A.; Sylvester, A.; Wise, W.; Prytulak, J.; Stoffers, A. J.; Gupta, V.

    2009-12-01

    , Upsal Hogback and Soda Lake maars, and the Buffalo Valley field. The lavas are poorly-phyric alkalic basalt, trachybasalt, basaltic trachyandesite, and porphyritic rhyolite. Trace element and isotope geochemistry varies from west to east, from post-arc-like compositions to “OIB”-like compositions typical of young Mojave Desert or Lunar Craters volcanic rocks. This gradient probably reflects the dominance of two mantle sources, “Sierran” to the west (arc and post-arc lavas) and “Great Basin” to the east. We suggest that the Sierran source is primarily metasomatized lithospheric mantle, whereas the Great Basin source is in the asthenosphere. In the wake of the westward-migrating slab hinge through the Tertiary, the lithospheric mantle was largely exhausted of fusible components, so that later melting beneath the central Great Basin occurred only in the asthenosphere.

  3. Arc of opportunity.

    Science.gov (United States)

    Delaney, Adam Vai

    2011-07-01

    Born in Port Moresby, Papua New Guinea, the author had a 20 year career in diplomacy, political affairs, and development policy analysis at the Pacific Islands Forum, the United Nations in New York; the Prime Minister's Department in Papua New Guinea (PNG) and in the Foreign Ministry of PNG. He has also been involved in theatre for over a decade in PNG, and participated in a three-month program at the Eugene O'Neill Theatre Center in Connecticut, USA. He is currently the Business Development Manager at the Torres Strait Regional Authority (Commonwealth) on Thursday Island. Since 1975 the Australian government's overseas development policy has supported various sectoral programs in its neighbouring countries, in particular Papua New Guinea and the Solomon Islands. The "creative" field has not been prominent in this strategy. While natural resources and the sports sectors have gained much greater attention, in terms of being viable international commercial enterprises, the arts, have remained stagnant. In this paper the need for joint programs genuinely supporting "wellbeing" and promoting social enterprise throughout the "arc of opportunity" is described to harness Melanesian creativity to compete successfully in world-markets, starting with penetration of the largest economy at its door-step: Australia.

  4. STUDY ON THE PRESSURE IN PLASMA ARC

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    The axial pressure in plasma arc is measured under different conditions. The effects of the parameters, such as welding current, plasma gas flow rate, electrode setback and arc length, on the pressure in plasma arc are investigated and quantitative analyzed to explain the relationship between the quality of weld and the matching of parameters in plasma arc welding process.

  5. Large capacity cnergy from Geo- Plutonic formation for power plants with zero CO2 emissions

    Directory of Open Access Journals (Sweden)

    R.H. Kozłowski

    2010-12-01

    Full Text Available Purpose: The publication presented is a realistic, one of the practicable idea for a substitute to system power plants, consisting in the construction of combined heat and power plants using renewable resources of geo-plutonic energy.Design/methodology/approach: There are various methods of obtaining geothermal energy and various uses for it. The proposed GEO-PLUTONIC ENERGY represents an endless, renewable source of energy coming from nuclear reaction in the Earth’s nucleus, where the temperature reaches 6,000 Centigrade. Mass production of electricity from the Earth’s heat, possible in Iceland due to the volcanic nature of these resources and the shallow depth at which they occur, was difficult in other countries due to the high cost of drilling to greater depths. This barrier has been overcome by us through using a special horizontal drilling technique.Findings: In order to extract and collect the accumulated energy from the area of a large thermal field, a modified shaft/drilling system (called a Super Daisy System equipped with a 3D grate of directional bore-holes called Jet-Stingers fitted with multi-functional heat exchangers is used. The emission-free concept of Geo-Plutonic Energy with the temperature of only over 250ºC, from which we can obtain about 30 MPa of pressure on the turbine. With increased the depth the temperature and heat transmissibility will be raised significantly, which can resulted the yield even to 7-10 MWe (of electricity from one deep heat exchanger.Research limitations/implications: From the rock mass we can collect renewable resources of ,,dry” ascending energy from the paleo heat flow coming from the great atomic furnace – the magma.Originality/value: We are experienced in using the appropriate hydro-thermodynamic theory and its applications which allows us to almost precisely forecast and control the quantity of heat not exceeding 20% of the 100% regeneration capability in the same time range.

  6. Mantle structure beneath the western edge of the Colorado Plateau

    Science.gov (United States)

    Sine, C.R.; Wilson, D.; Gao, W.; Grand, S.P.; Aster, R.; Ni, J.; Baldridge, W.S.

    2008-01-01

    Teleseismic traveltime data are inverted for mantle Vp and Vs variations beneath a 1400 km long line of broadband seismometers extending from eastern New Mexico to western Utah. The model spans 600 km beneath the moho with resolution of ???50 km. Inversions show a sharp, large-magnitude velocity contrast across the Colorado Plateau-Great Basin transition extending ???200 km below the crust. Also imaged is a fast anomaly 300 to 600 km beneath the NW portion of the array. Very slow velocities beneath the Great Basin imply partial melting and/or anomalously wet mantle. We propose that the sharp contrast in mantle velocities across the western edge of the Plateau corresponds to differential lithospheric modification, during and following Farallon subduction, across a boundary defining the western extent of unmodified Proterozoic mantle lithosphere. The deep fast anomaly corresponds to thickened Farallon plate or detached continental lithosphere at transition zone depths. Copyright 2008 by the American Geophysical Union.

  7. High-K calc-alkaline magmatism at the Archaean-Proterozoic boundary: implications for mantle metasomatism and continental crust petrogenesis. Example of the Bulai pluton (Central Limpopo Belt, South Africa)

    Science.gov (United States)

    Laurent, Oscar; Martin, Hervé; Doucelance, Régis; Moyen, Jean-François; Paquette, Jean-Louis

    2010-05-01

    The Neoarchaean Bulai pluton, intrusive within the supracrustal granulites of the Central Limpopo Belt (Limpopo Province, South Africa) is made up of large volumes of porphyritic granodiorites with subordinate enclaves and dykes which have monzodioritic and charno-enderbitic compositions. New U-Pb LA-ICP-MS dating on separated zircons yielded pluton emplacement ages ranging between 2.60 and 2.63 Ga, which are slightly older than previous proposed ages (~ 2.57-2.61 Ga). The whole-rock major- and trace-element composition of the Bulai pluton evidences unequivocal affinities with "high-Ti" late-Archaean sanukitoids. It belongs to a high-K calc-alkaline differentiation suite, with metaluminous affinities (0.7 affinities, such as eNd ranging between -0.5 and 0.5, and in addition, are very rich in all incompatible trace elements, which is particularly obvious in monzodioritic enclaves and enderbites where primitive mantle-normalized LILE and LREE contents are up to 300. These characteristics point to an enriched mantle source for the Bulai batholith. Chondrite normalized, REE patterns are strongly fractionated ([La/Yb]N ~ 25-80), mainly due to high LREE contents (LaN ~ 250-630), and chiefly high HFSE contents (Nb ~ 15-45 ppm ; up to 770 ppm Zr) indicate that the metasomatic agent is a silicic melt rather than a hydrous fluid. Moreover, based on high Nb/Ta, Th/Rb, La/Rb and low Sr/Nd and Ba/La, we suggest that the metasomatic agent is a granitic melt generated by melting of terrigenous sediments. Interactions of this melt with mantle peridotites implies that sediments are located under a mantle slice; geometry which is easily achieved in subduction zone settings. This conclusion is supported by the fact that Bulai trace element patterns are very similar to those of sub-actual potassic magmas generated in magmatic arc environments by interactions between mantle and terrigenous sediments (e.g. Sunda arc). Geochemical modeling indicates that the mafic facies of the Bulai

  8. Foundering lithosphere imaged beneath the southern Sierra Nevada, California, USA.

    Science.gov (United States)

    Boyd, Oliver S; Jones, Craig H; Sheehan, Anne F

    2004-07-30

    Seismic tomography reveals garnet-rich crust and mantle lithosphere descending into the upper mantle beneath the southeastern Sierra Nevada. The descending lithosphere consists of two layers: an iron-rich eclogite above a magnesium-rich garnet peridotite. These results place descending eclogite above and east of high P wave speed material previously imaged beneath the southern Great Valley, suggesting a previously unsuspected coherence in the lithospheric removal process.

  9. Transpressional granite-emplacement model: Structural and magnetic study of the Pan-African Bandja granitic pluton (West Cameroon)

    Science.gov (United States)

    Sandjo, A. F. Yakeu; Njanko, T.; Njonfang, E.; Errami, E.; Rochette, P.; Fozing, E.

    2016-02-01

    The Pan-African NE-SW elongated Bandja granitic pluton, located at the western part of the Pan-African belt in Cameroon, is a K-feldspar megacryst granite. It is emplaced in banded gneiss and its NW border underwent mylonitization. The magmatic foliation shows NE-SW and NNE-SSW strike directions with moderate to strong dip respectively in its northern and central parts. This mostly, ferromagnetic granite displays magnetic fabrics carried by magnetite and characterized by (i) magnetic foliation with best poles at 295/34, 283/33 and 35/59 respectively in its northern, central and southern parts and (ii) a subhorizontal magnetic lineation with best line at 37/8, 191/9 and 267/22 respectively in the northern, central and southern parts. Magnetic lineation shows an `S' shape trend that allows to (1) consider the complete emplacement and deformation of the pluton during the Pan-African D 2 and D 3 events which occurred in the Pan-African belt in Cameroon and (2) reorganize Pan-African ages from Nguiessi Tchakam et al. (1997) compared with those of the other granitic plutons in the belt as: 686 ±17 Ma (Rb/Sr) for D 1 age of metamorphism recorded in gneiss; and the period between 604-557 Ma for D 2-D 3 emplacement and deformation age of the granitic pluton in a dextral ENE-WSW shear movement.

  10. Magmatic epidote, hornblende barometric estimates, and emplacement of the Conceicao das Creoulas pluton, Alto Pajeu Terrane, NE Brazil

    International Nuclear Information System (INIS)

    The Brasiliano-age magmatic epidote-bearing Conceicao das Creoulas batholith, in the Transversal Zone superterrane in northeastern Brazil, intruded migmatites and metagranitoids of the Riacho do Forno/Recanto Formations. This pluton is composed of porphyritic granodiorite and porphyritic monzogranite. Hornblendes in this pluton solidified between 6-7 Kbar in mafic enclaves and around 8 Kbar for porphyritic granodiorite as estimated by its Al contents. Temperatures for zircon saturation are in the 790-830 deg C range for the mafic enclaves and 800-850 deg C for the porphyritic granodiorite, whereas hornblende-plagioclase pairs yielded temperatures in the 670-690 de C range. In this pluton, epidote, undoubtedly of magmatic origin, with or without allanite cores, included in plagioclase, is rimmed by biotite or is partially resorpted by the magma. Sometimes, patches of hornblende and biotite are present inside epidote. Magmatic epidote compositions vary in the interval 20-25% mole of pistacite, and always exhibit Ti O2 < 0.20% by weight. This compositional range suggested crystallization along the NNO buffer. High initial ratio suggest a significant crustal component in the magma genesis. The magma probably was transported upward by diking and inflated outwards near or at its final site of emplacement, giving to the pluton a diapiric appearance. (author)

  11. Crustal structure of Guadeloupe Islands and the Lesser Antilles Arc from a new gravity and magnetic synthesis

    OpenAIRE

    Gailler, Lydie; Bouchot, Vincent; Martelet, Guillaume; Thinon, Isabelle; Lebrun, Jean-Frédéric; Münch, Philippe

    2012-01-01

    Guadeloupe Island (West French Indies) is one of the twenty islands that compose the Lesser Antilles Arc, which results from the subduction of the Atlantic Ocean plate beneath the Caribbean one. The island lies in a complex volcano-tectonic system and the need to understand its geological context has led to numerous on- and offshore geophysical investigations. This work presents the compilation and processing of available, on-land, airborne and marine, gravity and magnetic data acquired durin...

  12. Post-collisional adakitic biotite plagiogranites from Guangtoushan pluton (Mianxian, central China): Petrogenesis and tectonic implication

    Institute of Scientific and Technical Information of China (English)

    QIN Jiangfeng; LAI Shaocong; LI Yongfei

    2007-01-01

    The post-collisional Guangtoushan pluton intruded into the Mianlue suture, Central China. Geochemi-cally, the Guangtoushan biotite plagiogranites show many close compositional similarities to high-silica adakites from the supra-subduction zone setting, but tend to have a higher concentration of K2O (3.22%-3.84%). Chondrite-normalized rare earth element pattems are characterized by high ratios of (La/Yb)N, concave-upward shapes of the heavy rare earth element (HREE), and a lack of significant Eu anomalies. In conjunction with high abundances of Ba and Sr, as well as low abundances of Y and HREE, these pattems suggest a feldspar-poor, garnet±amohibole-rich fractionation mineral assemblage. Coupled with previous studies, we suggest that the Guangtoushan biotite plagiogranites were likely to be caused by subducting slab break-off during the late orogenic stage in the West Qinling orogenic belt.

  13. Neo-tectonic fracturing after emplacement of quaternary granitic pluton in the Kakkonda geothermal field, Japan

    Energy Technology Data Exchange (ETDEWEB)

    Doi, N.; Kato, O. [JMC Goethermal Eng. Co., Ltd., Iwate-ken (Japan); Kanisawa, S.; Ishikawa, K. [Tohoku Univ., Sendai (Japan)

    1995-12-31

    The fracture which occurs in the Kakkonda geothermal system was formed by neo-tectonic stress after the emplacement of the neo-granite (Quaternary Kakkonda Granite) at middle Pleistocene to recent. The characteristic contrast in permeability at ca.1.5 km is strongly controlled by the contact metamorphic zone, especially cordierite and higher grade metamorphic zones, in which the high temperature (320{degrees}C<) and low permeable deep reservoir was created. The five geothermal wells 2.5-3.0 km deep have clarified that a microearthquake zone below -1.0 km shows high permeability especially at the margin of the Kakkonda Granite, and low permeability outside of a microearthquake zone. The Kakkonda Granite is a composite pluton which has very few fractures inside of it. Thus, neo-tectonic fracturing has developed in the non-metamorphosed Tertiary formations and the margin of the Kakkonda Granite.

  14. Exploring the plutonic crust at a fast-spreading ridge:new drilling at Hess Deep

    Energy Technology Data Exchange (ETDEWEB)

    Gillis, Kathryn M. [Univ. of Victoria, BC (Canada). School of Earth and Ocean Sciences; Snow, Jonathan E. [Univ. of Houston, Houston, TX (United States). Earth & Atmospheric Sciences; Klaus, Adam [Texas A & M Univ., College Station, TX (United States). Integrated Ocean Drilling Program (IODP). United States Implementing Organization.; Guerin, Gilles [Lamont-Doherty Earth Observatory of Columbia Univ., Palisades, NY (United States). Borehole Research Group; Abe, Natsue [Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka (Japan). Inst. for Research on Earth Evolution (IFREE); Akizawa, Norikatsu [Kanazawa Univ. (Japan). Dept. of Earth Sciences; Ceuleneer, Georges [Univ. Paul Sabatier, Toulouse (France). Observatoire Midi-Pyrenees (UMS 831), CNRS; Cheadle, Michael J. [Univ. of Wyoming, Laramie, WY (United States). Dept. of Geology and Geophysics; Adriao, Alden de Brito [Federal Univ. of Rio Grande do Sul, Porto Alegre (Brazil). Geology Inst. (IGEO); Faak, Kathrin [Ruhr Univ., Bochum (Germany). Geological Inst.; Falloon, Trevor J. [Univ. of Tasmania, Hobart, TAS (Australia). Inst. for Marine and Antarctic Studies; Friedman, Sarah A. [Southern Illinois Univ., Carbondale, IL (United States). Dept. of Geology; Godard, Marguerite M. [Univ. Montpellier II (France). Geosciences Montpellier-UMR 5243; Harigane, Yumiko [National Inst. of Advanced Industrial Science and Technology (AIST), Tsukuba (Japan). Marine Geology Dept.; Horst, Andrew J. [Syracuse Univ., NY (United States). Dept. of Earth Science; Hoshide, Takashi [Tohoku Univ., Sendai (Japan). Graduate School of Science; Ildefonse, Benoit [Univ. Montpellier II (France). Lab. de Tectonophysique; Jean, Marlon M. [Northern Illinois Univ., DeKalb, IL (United States). Dept. of Geology and Environmental Geosciences; John, Barbara E. [Univ. of Wyoming, Laramie, WY (United States). Dept. of Geology and Geophysics; Koepke, Juergen H. [Univ. of Hannover (Germany). Inst. of Mineralogy; Machi, Sumiaki [Kanazawa Univ. (Japan). Dept. of Earth Sciences; Maeda, Jinichiro [Hokkaido Univ., Sapporo (Japan). Dept. of Natural History Sciences; Marks, Naomi E. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). Chemistry and Material Sciences Dept.; McCaig, Andrew M. [Univ. of Leeds (United Kingdom). School of Earth and Environment; Meyer, Romain [Univ. of Bergen (Norway). Dept. of Earth Science and Centre for Geobiology; Morris, Antony [Univ. of Plymouth (United Kingdom). School of Earth, Ocean & Environmental Sciences; Nozaka, Toshio [Okayama Univ. (Japan). Dept. of Earth Sciences; Python, Marie [Hokkaido Univ., Sapporo (Japan). Dept. of Earth and Planetary Sciences; Saha, Abhishek [Indian Inst. of Science (IISC), Bangalore (India). Centre for Earth Sciences; Wintsch, Robert P. [Indiana Univ., Bloomington, IN (United States). Dept. of Geological Sciences

    2013-02-28

    Integrated Ocean Drilling Program (IODP) Hess Deep Expedition 345 was designed to sample lower crustal primitive gabbroic rocks that formed at the fast-spreading East Pacific Rise (EPR) in order to test models of magmatic accretion and the intensity of hydrothermal cooling at depth. The Hess Deep Rift was selected to exploit tectonic exposures of young EPR plutonic crust, building upon results from ODP Leg 147 as well as more recent submersible, remotely operated vehicle, and near-bottom surveys. The primary goal was to acquire the observations required to test end-member crustal accretion models that were in large part based on relationships from ophiolites, in combination with mid-ocean ridge geophysical studies. This goal was achieved with the recovery of primitive layered olivine gabbros and troctolites with many unexpected mineralogical and textural relationships, such as the abundance of orthopyroxene and the preservation of delicate skeletal olivine textures.

  15. Magma intrusion and accumulation in the southern Altiplano: Structural observations from the PLUTONS project

    Science.gov (United States)

    West, M. E.; Christensen, D. H.; Pritchard, M. E.; Del Potro, R.; Gottsmann, J.; Unsworth, M.; Minaya, E.; Sunagua, M.; McNutt, S. R.; Yu, Q.; Farrell, A. K.

    2012-12-01

    The PLUTONS project is attempting to capture the process of magma intrusion and pluton formation, in situ, through multi-disciplinary study of known magmatic inflation centers. With support from the NSF Continental Dynamics program, and a sister project in the UK funded by NERC, two such centers are receiving focused study. Uturuncu volcano in the Altiplano of southern Bolivia is being investigated with combined seismics, magnetotellurics, geodesy, microgravity, geomorphology, petrology, geochemistry, historical studies and modeling. 350 km to the south, comparable investigations are targeting the Lastarria-Cordon del Azufre complex. Field studies are ongoing into 2013. In this presentation we highlight results from Uturuncu that bear on the crustal magmatic process. Seismic tomography, gravity and magnetotellurics indicate a complex structure in the upper 20 km with some evidence for partial melt. Seismic receiver functions indicate a layer of very low velocities across the region at 15-25 km depth that is almost certainly melt-rich. High conductivities corroborate the interpretation of a partial melt component to this layer. In addition to the throughgoing melt layer, seismic velocities and attenuation indicate shallow features above the melt body extending upward toward the surface. It is not clear whether these features are associated with recent uplift or are remnants from a previous period of activity. Uturuncu is seismically active with hundreds of locatable earthquakes each year. Seismic lineations and swarm behavior suggest that the seismicity reflects regional stress patterns. While there is little evidence that these earthquakes are the direct result of magmatic intrusion, the resulting high heat flow may be hastening existing strains.

  16. U-Pb geochronology of Gangdese (Transhimalaya) plutonism in the Lhasa-Xigaze region, Tibet

    International Nuclear Information System (INIS)

    A series of different plutons from the Lhasa-Xigaze segment of the Gangdese (Transhimalaya) belt has been studied by high-resolution U-Pb analyses of zircon (using zircon fractions of 5-100 grains each, selected upon specific grain characteristics). For two diorites, located east of Xigaze (Dazhuka), the zircons yield concordant ages of 93.4 +- 1.0 and 94.2 +- 1.0 m.y., respectively. Also concordant ages of 41.1 +- 0.4 and 41.7 +- 0.4 m.y. have been obtained for two granodiorites, collected southwest of Lhasa (Qushui). The precision on the ages of two granites from the Xigaze and Lhasa area, is limited by two factors: the presence of inherited radiogenic lead and the occurrence of subsequent lead loss. However, some concordant zircons, detected in both granites, define approximate ages of about 67 and 53 m.y., respectively. The inherited lead components show the melting of Precambrian material was involved in magma genesis. The U-Pb ages substantiate a magmatic activity lasting from mid-Cretaceous (Cenomanian) to Eocene (Lutetian) time. Such a period of plutonism at the southern margin of Eurasia, as well as the occurrence of magma generation from continental crust, suggest that the Gangdese range results from the subduction of Tethys oceanic lithosphere (Indian plate) underneath Eurasia (Eurasian plate). If this model is true, the collision of India with Eurasia (Along the Lhasa-Xigaze sector) postdates the emplacement of the 41 m.y. old Gangdese granodiorites, i.e. the collision occurred after Lutetian time. (orig.)

  17. Structural evolution of the Rieserferner Pluton: insight into the localization of deformation and regional tectonics implications

    Science.gov (United States)

    Ceccato, Alberto; Pennacchioni, Giorgio

    2016-04-01

    The Rieserferner pluton (RFP, Eastern Alps, 32.2±0.4 Ma, Romer et al. 2003) represents a relatively deep intrusion (12-15 km; Cesare, 1994) among Periadriatic plutons. The central portion of the RFP consists of dominant tonalites and granodiorites that show a sequence of solid-state deformation structures developed during pluton cooling and exhumation. This sequence includes: (1) quartz veins, filling two set of steeply-dipping joints trending respectively E-W and NW-SE, commonly showing a millimetric grain size and associated with strike-slip displacement. (2) Quartz- and locally epidote-filled shallowly E-dipping joint set, commonly exploited as discrete derived from both the quartz veins and the host tonalite. These mylonites show a composite sense of shear with a first stage of left-lateral strike-slip followed by a top-to-E dip-slip (normal) movement. The synmylonitic assemblage includes biotite + plagioclase + white mica + epidote ± sphene ± garnet. (3) Set of N-S-trending steeply-dipping joints. These joints are concentrated in zones 1-2 m wide, separated by otherwise un-jointed domains a few tens to hundred meters wide, and are commonly exploited as brittle-ductile faults with dominant dip-slip (normal) kinematics. The mineral assemblage of fault rocks includes white mica + calcite ± chlorite ± quartz. The joints/faults are locally involved in folding. (4) Mafic dikes, dated at 26.3±3 Ma (Steenken et al., 2000), locally injecting the N-S trending set of joints. (5) Cataclasite- and pseudotachylyte-bearing faults also forming a set of steeply-dipping N-S-trending structures. These faults are commonly associated with epidote veins surrounded by bleaching haloes. (6) Zeolite-bearing faults marked by whitish cataclasites, fault gouges and mirror-like surfaces. These faults have a complex oblique- to strike-slip kinematics with an overall N-S trending lineation. As observed in other plutons (e.g. Adamello; Pennacchioni et al., 2006), the network of

  18. Philippine Sea Slab and South-Ryukyu Arc Sliver Accommodation of Arc-Continent Collision East of Taiwan

    Science.gov (United States)

    Lallemand, S.; Theunissen, T.; Font, Y.; Schnurle, P.; Lee, C.; Liu, C.

    2011-12-01

    The southern termination of the Ryukyu arc-trench system underwent a complex polyphased and extremely rapid tectonic evolution during the last 5 to 8 My. At first, the relative motion of the Philippine Sea plate (PSP) has changed about 5 My ago from a northward to a northwestward motion relative to Eurasia. Secondly, the Ryukyu trench has propagated from east to west during the same time period resulting in a tectonic inversion along the former passive margin of the South China Sea into the active margin of the S-Ryukyu trench. Thirdly, the convergence rate along the neo-formed S-Ryukyu trench dramatically increased from 8 to 13 cm/yr since at least 2 My when the Southern Okinawa Trough (SOT) started to rift. At the same time, the oceanic subduction of the South China Sea beneath the northern Manila arc progressively evolved into a continental subduction of the Chinese platform at the origin of the Taiwan orogen. The timing of these various kinematic and tectonic events should have been recorded in the deformed sedimentary basins and fold-and-thrust belts in the region. Unfortunately, a large part is now below the sea-level and no or a few age constraints are available. The recent joint project between Taiwan-USA & France (TAIGER & ACTS) gave us the opportunity to considerably increase the resolution of the seismic imagery around the island and especially in the most highly deformed area east of Taiwan along the S-Ryukyu forearc. We already knew that the seismic activity focussed in this region but we ignored how the converging plates deformed. We can now argue that the PSP strongly deforms in the vicinity of its deep interaction with the root of the Taiwan orogen. The north-dipping PSP slab buckles and tears along two diverging directions with a down-faulted part subducting beneath the SOT.

  19. Petrologic perspectives on tectonic evolution of a nascent basin (Okinawa Trough) behind Ryukyu Arc:A review

    Institute of Scientific and Technical Information of China (English)

    YAN Quanshu; SHI Xuefa

    2014-01-01

    Okinawa Trough is a back-arc, initial marginal sea basin, located behind the Ryukyu Arc-Trench System. The formation and evolution of the Okinawa Trough is intimately related to the subduction process of the Philippine Sea Plate beneath the Eurasian Plate since the late Miocene. The tectonic evolution of the trough is similar to other active back-arcs, such as the Mariana Trough and southern Lau Basin, all of which are experiencing the initial rifting and subsequent spreading process. This study reviews all petrologic and geochemical data of mafic volcanic lavas from the Okinawa Trough, Ryukyu Arc, and Philippine Sea Plate, combined with geophysical data to indicate the relationship between the subduction sources (input) and arc or back-arc magmas (output) in the Philippine Sea Plate-Ryukyu Arc-Okinawa Trough system (PROS). The results obtained showed that several components were variably involved in the petrogenesis of the Oki-nawa Trough lavas:sub-continental lithospheric mantle underlying the Eurasian Plate, Indian mid-oceanic ridge basalt (MORB)-type mantle, and Pacific MORB-type mantle. The addition of shallow aqueous fluids and deep hydrous melts from subducted components with the characteristics of Indian MORB-type mantle into the mantle source of lavas variably modifies the primitive mantle wedge beneath the Ryukyu and sub-continental lithospheric mantle (SCLM) beneath the Okinawa Trough. In the northeastern end of the trough and arc, instead of Indian MORB-type mantle, Pacific MORB-type mantle dominates the magma source. Along the strike of the Ryukyu Arc and Okinawa Trough, the systematic variations in trace element ratios and isotopic compositions reflect the first-order effect of variable subduction input on the magma source. In general, petrologic data, combined with geophysical data, imply that the Okinawa Trough is experiencing the“seafloor spreading”process in the southwest segment,“rift propagation”process in the middle seg-ment, and

  20. Heterogeneous stress state of island arc crust in northeastern Japan affected by hot mantle fingers

    Science.gov (United States)

    Shibazaki, Bunichiro; Okada, Tomomi; Muto, Jun; Matsumoto, Takumi; Yoshida, Takeyoshi; Yoshida, Keisuke

    2016-04-01

    By considering a thermal structure based on dense geothermal observations, we model the stress state of the crust beneath the northeastern Japan island arc under a compressional tectonic regime using a finite element method with viscoelasticity and elastoplasticity. We consider a three-layer structure (upper crust, lower crust, and uppermost mantle) to define flow properties. Numerical results show that the brittle-viscous transition becomes shallower beneath the Ou Backbone Range compared with areas near the margins of the Pacific Ocean and the Japan Sea. Moreover, several elongate regions with a shallow brittle-viscous transition are oriented transverse to the arc, and these regions correspond to hot fingers (i.e., high-temperature regions in the mantle wedge). The stress level is low in these regions due to viscous deformation. Areas of seismicity roughly correspond to zones of stress accumulation where many intraplate earthquakes occur. Our model produces regions with high uplift rates that largely coincide with regions of high elevation (e.g., the Ou Backbone Range). The stress state, fault development, and uplift around the Ou Backbone Range can all be explained by our model. The results also suggest the existence of low-viscosity regions corresponding to hot fingers in the island arc crust. These low-viscosity regions have possibly affected viscous relaxation processes following the 2011 Tohoku-oki earthquake.

  1. Late Jurassic Crustal Thickening in the Mesozoic Arc of Ecuador and Colombia: Implications on the Evolution of Continental Arcs.

    Science.gov (United States)

    Vanegas, J.; Cardona, A.; Blanco-Quintero, I.; Valencia, V.

    2014-12-01

    The tectonic evolution of South America during the Jurassic is related to the subduction of the Farallon plate and the formation of a series of continental arcs. In the northern Andes such arcs have been considered as controlled by extensional dominated tectonics. Paleomagnetic constraints have also suggested that between the Early and Late Jurassic several crustal domains were translate along the continental margin in association with strain partitioning in the convergent margin. A review of the character of the Salado terrane in the Cordillera Real of Ecuador indicates that it includes extensively deformed and metamorphosed volcano-sedimentary rocks that have achieved a greenschist to amphibolite facies event with chloritoid and garnet. This rocks are tightly associated with a ca. 143 Ma syn-tectonic granodiorite to monzogranite batholith that is also extensively milonitized.A similar Late Jurassic crustal thickening event that apparently affected volcano-sedimentary rocks have been also recently suspected in the Central Cordillera of the Colombian Andes in association with Jurassic plutonic rocks (Blanco-Quintero et al., 2013) It is therefore suggested that during the Late Jurassic the Northern Andes experienced significant contractional tectonics. Such crustal thickening may be related to either the active subduction setting were the crustal slivers formed in relation to oblique convergence are transfered and re-accreted to the margin and triggered the deformational event or to a collisional event associated to the arrival of an allocthonous terrane. New geochronological constraints on the metamorphic evolution and precise understanding on the relations between magmatism and deformation are going to be obtain in the Salado Terrane to appropriately test this hypothesis and contribute to the understanding of the extensional to compressional tectonic switching in continental arcs. Blanco-Quintero, I. F., García-Casco, A., Ruíz, E. C., Toro, L. M., Moreno, M

  2. High pressure neon arc lamp

    Science.gov (United States)

    Sze, Robert C.; Bigio, Irving J.

    2003-07-15

    A high pressure neon arc lamp and method of using the same for photodynamic therapies is provided. The high pressure neon arc lamp includes a housing that encloses a quantity of neon gas pressurized to about 500 Torr to about 22,000 Torr. At each end of the housing the lamp is connected by electrodes and wires to a pulse generator. The pulse generator generates an initial pulse voltage to breakdown the impedance of the neon gas. Then the pulse generator delivers a current through the neon gas to create an electrical arc that emits light having wavelengths from about 620 nanometers to about 645 nanometers. A method for activating a photosensitizer is provided. Initially, a photosensitizer is administered to a patient and allowed time to be absorbed into target cells. Then the high pressure neon arc lamp is used to illuminate the target cells with red light having wavelengths from about 620 nanometers to about 645 nanometers. The red light activates the photosensitizers to start a chain reaction that may involve oxygen free radicals to destroy the target cells. In this manner, a high pressure neon arc lamp that is inexpensive and efficiently generates red light useful in photodynamic therapy is provided.

  3. The Banda Arc subduction enigma

    Science.gov (United States)

    Spakman, Wim; Hall, Robert

    2010-05-01

    The spectacularly curved Banda arc comprises young oceanic crust enclosed by a volcanic inner arc, outer arc islands, and a trough parallel to the Australian continental margin. Seismicity defines a spoon-shaped lithospheric fold in the upper mantle for which there are two contrasting explanations: deformation of a single subducted slab, or two different slabs subducted from north and south. We show that the Banda arc resulted from subduction of a single slab. Based on geology and seismic tomography, we argue that the arc formed since 15 Ma by subduction of a Jurassic oceanic embayment within the Australian plate. Viewed in an Atlantic-Indian hotspot reference frame, the stationary E-W striking Java trench propagated ESE into the Banda embayment by hinge rollback. Extension of the upper plate formed oceanic crust in the present Banda Sea between stretched continental crust of Australian origin. Slab morphology depends primarily on the geometry of the continental margin enclosing the embayment. Our model explains the first order tectonic development of the Banda region and links slab deformation to absolute plate motion.

  4. Mohorovicic discontinuity depth analysis beneath North Patagonian Massif

    Science.gov (United States)

    Gómez Dacal, M. L.; Tocho, C.; Aragón, E.

    2013-05-01

    The North Patagonian Massif is a 100000 km2, sub-rectangular plateau that stands out 500 to 700 m higher in altitude than the surrounding topography. The creation of this plateau took place during the Oligocene through a sudden uplift without noticeable internal deformation. This quite different mechanical response between the massif and the surrounding back arc, the short time in which this process took place and a regional negative Bouguer anomaly in the massif area, raise the question about the isostatic compensation state of the previously mentioned massif. In the present work, a comparison between different results about the depth of the Mohorovicic discontinuity beneath the North Patagonian Massif and a later analysis is made. It has the objective to analyze the crustal thickness in the area to contribute in the determination of the isostatic balance and the better understanding of the Cenozoic evolution of the mentioned area. The comparison is made between four models; two of these were created with seismic information (Feng et al., 2006 and Bassin et al., 2000), another model with gravity information (Barzaghi et al., 2011) and the last one with a combination of both techniques (Tassara y Etchaurren, 2011). The latter was the result of the adaptation to the work area of a three-dimensional density model made with some additional information, mainly seismic, that constrain the surfaces. The work of restriction and adaptation of this model, the later analysis and comparison with the other three models and the combination of both seismic models to cover the lack of resolution in some areas, is presented here. According the different models, the crustal thickness of the study zone would be between 36 and 45 Km. and thicker than the surrounding areas. These results talk us about a crust thicker than normal and that could behave as a rigid and independent block. Moreover, it can be observed that there are noticeable differences between gravimetric and seismic

  5. Transient crustal movement in the northern Izu-Bonin arc starting in 2004: A large slow slip event or a slow back-arc rifting event?

    Science.gov (United States)

    Arisa, Deasy; Heki, Kosuke

    2016-07-01

    The Izu-Bonin arc lies along the convergent boundary where the Pacific Plate subducts beneath the Philippine Sea Plate. Horizontal velocities of continuous Global Navigation Satellite System stations on the Izu Islands move eastward by up to ~ 1 cm/year relative to the stable part of the Philippine Sea Plate suggesting active back-arc rifting behind the northern part of the arc. Here, we report that such eastward movements transiently accelerated in the middle of 2004 resulting in ~ 3 cm extra movements in 3 years. We compare three different mechanisms possibly responsible for this transient movement, i.e. (1) postseismic movement of the 2004 September earthquake sequence off the Kii Peninsula far to the west, (2) a temporary activation of the back-arc rifting to the west dynamically triggered by seismic waves from a nearby earthquake, and (3) a large slow slip event in the Izu-Bonin Trench to the east. By comparing crustal movements in different regions, the first possibility can be shown unlikely. It is difficult to rule out the second possibility, but current evidence support the third possibility, i.e. a large slow slip event with moment magnitude of ~ 7.5 may have occurred there.

  6. Progress on the Seismic Anisotropy Parameters Knowledge Beneath Iberia and Morocco: New Results from the Second Topoiberia-Iberarray Deployment

    Science.gov (United States)

    Diaz, J.; Gallart, J.; TopoIberia Seismic Working Group

    2011-12-01

    In summer 2009 the dense Iberarray broad-band seismic network deployed in the framework of the large-scale TopoIberia project moved to its second footprint. Up to 55 stations covered the central part of the Iberian Peninsula until end 2010, distributed in a regular grid with a nominal spacing of 60 km. Up to 19 additional stations, active since late 2007, have remained operative in the Northern part of Morocco till summer 2010 and then moved southwards, to cover the Atlas belt. Continuous data from permanent broad-band stations have also been gathered to produce a complete database. We focus here in the results constraining the presence of anisotropy as evidenced from the analysis of splitted teleseismic phases. Few anisotropic results in the area covered by this IberArray deployment have been published till now, all of them coming from a scarce number of permanent stations. Beneath Iberia, this second deployment encompasses mainly the Variscan units of the Central Iberian Massif. To the East, the investigated area includes also the southern part of the Celtiberian Chain and reaches the Valencia Gulf, affected by a significant extensional episode in Neogene times. Beneath Morocco, the newly installed stations cover the Atlas belt, and area that seems to be associated with a significant lithospheric thinning, even if its geodynamic features are still poorly constrained. The results would extend the anisotropic map obtained from the first TopoIberia-Iberarray deployment in the Betics-Alboran zone (Díaz et al, 2010). The inferred fast polarization directions (FPD) have clearly documented a spectacular rotation along the Gibraltar arc, following the curvature of the Rif-Betic chain, from roughly N65E beneath the Betics to close to N65W beneath the Rif chain. The stations of that first deployment located in the Iberian Massif tent to present a relatively small amount of anisotropy and suggested complex anisotropy features, probably including two anisotropic layers. The

  7. Kinematic variables and water transport control the formation and location of arc volcanoes.

    Science.gov (United States)

    Grove, T L; Till, C B; Lev, E; Chatterjee, N; Médard, E

    2009-06-01

    The processes that give rise to arc magmas at convergent plate margins have long been a subject of scientific research and debate. A consensus has developed that the mantle wedge overlying the subducting slab and fluids and/or melts from the subducting slab itself are involved in the melting process. However, the role of kinematic variables such as slab dip and convergence rate in the formation of arc magmas is still unclear. The depth to the top of the subducting slab beneath volcanic arcs, usually approximately 110 +/- 20 km, was previously thought to be constant among arcs. Recent studies revealed that the depth of intermediate-depth earthquakes underneath volcanic arcs, presumably marking the slab-wedge interface, varies systematically between approximately 60 and 173 km and correlates with slab dip and convergence rate. Water-rich magmas (over 4-6 wt% H(2)O) are found in subduction zones with very different subduction parameters, including those with a shallow-dipping slab (north Japan), or steeply dipping slab (Marianas). Here we propose a simple model to address how kinematic parameters of plate subduction relate to the location of mantle melting at subduction zones. We demonstrate that the location of arc volcanoes is controlled by a combination of conditions: melting in the wedge is induced at the overlap of regions in the wedge that are hotter than the melting curve (solidus) of vapour-saturated peridotite and regions where hydrous minerals both in the wedge and in the subducting slab break down. These two limits for melt generation, when combined with the kinematic parameters of slab dip and convergence rate, provide independent constraints on the thermal structure of the wedge and accurately predict the location of mantle wedge melting and the position of arc volcanoes.

  8. Estimation of the Crustal Bulk Properties Beneath Mainland Portugal from P-Wave Teleseismic Receiver Functions

    Science.gov (United States)

    Dündar, Süleyman; Dias, Nuno A.; Silveira, Graça; Kind, Rainer; Vinnik, Lev; Matias, Luís; Bianchi, Marcelo

    2016-06-01

    In this work, we present results from teleseismic P-wave receiver functions (PRFs) obtained in Portugal, Western Iberia. A dense seismic station deployment conducted between 2010 and 2012, in the scope of the WILAS project and covering the entire country, allowed the most spatially extensive probing on the bulk crustal seismic properties of Portugal up to date. The application of the H- κ stacking algorithm to the PRFs enabled us to estimate the crustal thickness ( H) and the average crustal ratio of the P- and S-waves velocities V p/ V s ( κ) for the region. Observations of Moho conversions indicate that this interface is relatively smooth with the crustal thickness ranging between 24 and 34 km, with an average of 30 km. The highest V p/ V s values are found on the Mesozoic-Cenozoic crust beneath the western and southern coastal domain of Portugal, whereas the lowest values correspond to Palaeozoic crust underlying the remaining part of the subject area. An average V p/ V s is found to be 1.72, ranging 1.63-1.86 across the study area, indicating a predominantly felsic composition. Overall, we systematically observe a decrease of V p/ V s with increasing crustal thickness. Taken as a whole, our results indicate a clear distinction between the geological zones of the Variscan Iberian Massif in Portugal, the overall shape of the anomalies conditioned by the shape of the Ibero-Armorican Arc, and associated Late Paleozoic suture zones, and the Meso-Cenozoic basin associated with Atlantic rifting stages. Thickened crust (30-34 km) across the studied region may be inherited from continental collision during the Paleozoic Variscan orogeny. An anomalous crustal thinning to around 28 km is observed beneath the central part of the Central Iberian Zone and the eastern part of South Portuguese Zone.

  9. Seismic images of the mantle transition zone beneath Northeast China and the Sino-Korean craton from P-wave receiver functions

    Science.gov (United States)

    Zhang, Ruiqing; Gao, Zhanyong; Wu, Qingju; Xie, Zhenxing; Zhang, Guangcheng

    2016-04-01

    Seismic data from northeast (NE) China and the Sino-Korean craton were combined to image the upper mantle discontinuities at 410 and 660 km. Fine-scale topographic variations on these two discontinuities provide important clues for both delineating geometry of the subducting Pacific slab particularly at arc-arc junction and interpreting regional Cenozoic intraplate volcanism. We used over 90,000 receiver functions from 1916 teleseismic earthquakes recorded by 584 broadband seismic stations, primary those of temporary seismic arrays. We found the average depths of the two discontinuities to be 410 km and 672 km, respectively, beneath the study area. Results show that the 660-km discontinuity is strongly depressed by about 20-30 km in a narrow region beneath and around the Changbaishan volcano, consistent with the results of previous receiver function studies. In contrast, much of the Sino-Korean craton exhibits typical transition zone thickness (~ 260 km) and thus offers no evidence of a stagnated Pacific slab. Our results also reveal an elevated 660-km discontinuity and a thinner transition zone both to the west of the observed depression region and beneath the Kuril-Japan arc junction. This feature is most likely due to a tearing of the descending Pacific plate at both its leading and junction edges. An additional elevated 660-km discontinuity together with a thinner transition zone appears in the vicinity of the Dariganga lava field, supporting interpretations of a deep-rooted mantle plume. Our observations of an elevated 410-km discontinuity and a thicker transition zone correlate spatially with the diffuse distribution of volcanism around Hannuoba, Aershan and Wudalianchi. This correlation may suggest lithospheric removal as a mechanism for these magmatic activities.

  10. Minor arcs for Goldbach's problem

    OpenAIRE

    Helfgott, H. A.

    2012-01-01

    The ternary Goldbach conjecture states that every odd number n>=7 is the sum of three primes. The estimation of sums of the form \\sum_{p\\leq x} e(\\alpha p), \\alpha = a/q + O(1/q^2), has been a central part of the main approach to the conjecture since (Vinogradov, 1937). Previous work required q or x to be too large to make a proof of the conjecture for all n feasible. The present paper gives new bounds on minor arcs and the tails of major arcs. This is part of the author's proof of the ternar...

  11. Unzipping of the volcano arc, Japan

    Science.gov (United States)

    Stern, R.J.; Smoot, N.C.; Rubin, M.

    1984-01-01

    A working hypothesis for the recent evolution of the southern Volcano Arc, Japan, is presented which calls upon a northward-progressing sundering of the arc in response to a northward-propagating back-arc basin extensional regime. This model appears to explain several localized and recent changes in the tectonic and magrnatic evolution of the Volcano Arc. Most important among these changes is the unusual composition of Iwo Jima volcanic rocks. This contrasts with normal arc tholeiites typical of the rest of the Izu-Volcano-Mariana and other primitive arcs in having alkaline tendencies, high concentrations of light REE and other incompatible elements, and relatively high silica contents. In spite of such fractionated characteristics, these lavas appear to be very early manifestations of a new volcanic and tectonic cycle in the southern Volcano Arc. These alkaline characteristics and indications of strong regional uplift are consistent with the recent development of an early stage of inter-arc basin rifting in the southern Volcano Arc. New bathymetric data are presented in support of this model which indicate: 1. (1) structural elements of the Mariana Trough extend north to the southern Volcano Arc. 2. (2) both the Mariana Trough and frontal arc shoal rapidly northwards as the Volcano Arc is approached. 3. (3) rugged bathymetry associated with the rifted Mariana Trough is replaced just south of Iwo Jima by the development of a huge dome (50-75 km diameter) centered around Iwo Jima. Such uplifted domes are the immediate precursors of rifts in other environments, and it appears that a similar situation may now exist in the southern Volcano Arc. The present distribution of unrifted Volcano Arc to the north and rifted Mariana Arc to the south is interpreted not as a stable tectonic configuration but as representing a tectonic "snapshot" of an arc in the process of being rifted to form a back-arc basin. ?? 1984.

  12. Mantle discontinuities beneath Izu-Bonin and the implications

    Institute of Scientific and Technical Information of China (English)

    臧绍先; 周元泽; 蒋志勇

    2003-01-01

    The SdP, pdP and sdP phases are picked up with the Nth root slant stack method from the digital waveform data recorded by the networks and arrays in USA, Germany and Switzerland for the earthquakes occurring beneath Izu-Bonin and Japan Sea. The mantle discontinuities and the effects of subducting slab on the 660 km and 410 km discontinuities are studied. It is found that there are mantle discontinuities existing at the depths of 170, 220, 300, 410, 660, 850 and 1150 km. Beneath Izu-Bonin, the 410 km discontinuity is elevated, while the 660 km discontinuity is depressed; for both discontinuities, there are regionalized differences. Beneath Japan Sea, however, there is no depth variation of the 410 km discontinuity, and the 660 km discontinuity is depressed without obvious effect of the subducting slab.

  13. Initiation of liquid-solid contact beneath an impacting drop

    Science.gov (United States)

    Rubinstein, Shmuel; Kolinski, John

    2015-11-01

    Before an impacting drop contacts the solid surface it must first drain the air beneath it. As a prelude to wetting, before any contact occurs, the impinging liquid confines the intervening air into a nanometers-thin film. Once liquid-solid contact initiates by the spontaneous formation of a liquid bridge, the fluid rapidly wicks through the thin film of air, permanently binding the drop to the surface. Here, we experimentally examine these initial stages in the formation of the liquid solid contact beneath the impacting drop. Fast TIR microscopy enables unprecedented spatial and temporal resolution of the wetting process beneath the impacting drop and permits 3-dimensional imaging of the real contact line as well as nanometer-resolution of the thin film of air separating the liquid from the solid.

  14. Geochronology of and Nd—Sr—Pb Isotopic Evidence for Mantle Source in the Ancient Subduction Zone beneath Sanshui Basin,Guangdong Province,China

    Institute of Scientific and Technical Information of China (English)

    朱炳泉; 蒲志平; 等

    1989-01-01

    The available petrochemical data indicate that volcanic rocks in the Sanshui basin of Guangdong Prov-ince are characteristic of the island-arc tholeiite-calc-alkaline series.Their K-Ar ages range from 43 to 64 Ma,corresponding to Early Tertiary.The Nd-Sr-Pb isotopic correlations give two binary mixing trends,indicating a mixed source of Leiqiong depleted mantle,seawater and altered sediments pertaining to subduction.Our studies have confirmed the existence of an ancient subduction zone beneath the South Chi-na continent,which is considered to have resulted from the suturing of various terrains in southern China.

  15. Geochemical and Sr-Nd-Hf isotopic constraints on the origin of Late Triassic granitoids from the Qinling orogen, central China: Implications for a continental arc to continent-continent collision

    Science.gov (United States)

    Jiang, Yao-Hui; Jin, Guo-Dong; Liao, Shi-Yong; Zhou, Qing; Zhao, Peng

    2010-06-01

    The Qinling-Dabie-Sulu orogen marks the junction between the North and South China Blocks. However, the exact timing of the final coalescence of the North and South China Blocks in the Qinling orogen is poorly constrained. This paper presents new SHRIMP zircon U-Pb chronology, major and trace elements, and Sr-Nd-Hf isotope data for five early Mesozoic granitic plutons across the Qinling orogen. SHRIMP zircon U-Pb dating shows that four plutons were emplaced in the Carnian (227-218 Ma) of Late Triassic with a southward-younging trend and one pluton was emplaced in the Norian (˜ 211 Ma) of Late Triassic. The Carnian plutons consist of high-K calc-alkaline granitoids (quartz monzodiorite, quartz monzonite, granodiorite and monzogranite) and calc-alkaline diorite. These rocks are mainly metaluminous and are characterized by high Sr and low Y and Yb contents, with high Sr/Y and La/Yb ratios, and by high Mg#, higher than pure crustal melts. The Norian pluton is composed of high-K calc-alkaline two-mica granites, which are peraluminous. These granites have low Sr and high Y and Yb contents and show similar Mg# to pure crustal melts. Detailed elemental and isotopic data suggest that the Carnian plutons were emplaced in a continental arc setting coupled with the northward subduction of the Paleo-Tethyan oceanic crust. Partial melting of subducted sediments triggered by dehydration of the underlying igneous oceanic crust, with subsequent melts interacting with the overlying mantle wedge, formed the high-K calc-alkaline granitic magmas. Partial melting of the hybridized peridotitic mantle wedge induced by slab melts generated the calc-alkaline dioritic magma. The Norian pluton was emplaced during continental collision between the South Qinling terrane and South China Block, which marks the final integration of the North and South China Blocks. Partial melting of subducted sediments at a shallow depth (origin of the Norian peraluminous granites. Our new data suggest that the

  16. Imaging of seismic scatterers beneath the Gauribidanur (GBA) array

    International Nuclear Information System (INIS)

    A study has been conducted to image seismic scatterers beneath the Gauribidanur (GBA) array in the Precambrian shield of south India. Short period digital data from teleseisms and regional events recorded over the 20 station L shaped array was used to image seismic scatterers beneath the array employing semblance technique. The results indicate a zone of dominant scattering encompassing the crust in a region west of GBA. The inferred zone of scattering coincides with a large N-S elongated granitic intrusion believed to be Precambrian suture zone between the East and West Dharwar craton. (author). 16 refs, 7 figs, 1 tab

  17. Seismic imaging of the downwelling Indian lithosphere beneath central Tibet.

    Science.gov (United States)

    Tilmann, Frederik; Ni, James

    2003-05-30

    A tomographic image of the upper mantle beneath central Tibet from INDEPTH data has revealed a subvertical high-velocity zone from approximately 100- to approximately 400-kilometers depth, located approximately south of the Bangong-Nujiang Suture. We interpret this zone to be downwelling Indian mantle lithosphere. This additional lithosphere would account for the total amount of shortening in the Himalayas and Tibet. A consequence of this downwelling would be a deficit of asthenosphere, which should be balanced by an upwelling counterflow, and thus could explain the presence of warm mantle beneath north-central Tibet.

  18. Hooded arc ion-source

    CERN Multimedia

    1972-01-01

    The positioning system for the hooded arc ion-source, shown prior to mounting, consists of four excentric shafts to locate the ion-source and central electrodes. It will be placed on the axis of the SC and introduced into the vacuum tank via the air locks visible in the foreground.

  19. Craniospinal irradiation using Rapid Arc

    Energy Technology Data Exchange (ETDEWEB)

    Fandino, J. M.; Silva, M. C.; Marino, A.; Candal, A.; Diaz, I.; Fernandez, C.; Gesto, C.; Izquierdo, P.; Losada, C.; Poncet, M.; Soto, M.; Triana, G.

    2013-07-01

    Cranio-Spinal Irradiation is technically very challenging, historically field edge matching is needed because of the mechanical limitations of standard linear accelerators. The purpose of this study is to assess the Volumetric Arc Therapy as a competitive technique for Cranio-Spinal Irradiation compared to the conventional 3D Conformal Radiotherapy technique. (Author)

  20. The Ajo Mining District, Pima County, Arizona--Evidence for Middle Cenozoic Detachment Faulting, Plutonism, Volcanism, and Hydrothermal Alteration

    Science.gov (United States)

    Cox, Dennis P.; Force, Eric R.; Wilkinson, William H.; More, Syver W.; Rivera, John S.; Wooden, Joseph L.

    2006-01-01

    Introduction: The Ajo porphyry copper deposit and surrounding Upper Cretaceous rocks have been separated from their plutonic source and rotated by detachment faulting. Overlying middle Cenozoic sedimentary and volcanic rocks have been tilted and show evidence for two periods of rotation. Following these rotations, a granitic stock (23.7?0.2 Ma) intruded basement rocks west of the Ajo deposit. This stock was uplifted 2.5 km to expose deep-seated Na-Ca alteration.

  1. Ion-adsorption REEs in regolith of the Liberty Hill pluton, South Carolina, USA: An effect of hydrothermal alteration

    Science.gov (United States)

    Bern, Carleton R.; Yesavage, Tiffany; Foley, Nora K.

    2017-01-01

    Ion-adsorbed rare earth element (REE) deposits supply the majority of world heavy REE production and substantial light REE production, but relatively little is known of their occurrence outside Southeast Asia. We examined the distribution and forms of REEs on a North American pluton located in the highly weathered and slowly eroding South Carolina Piedmont. The Hercynian Liberty Hill pluton experiences a modern climate that includes ~ 1500 mm annual rainfall and a mean annual temperature of 17 °C. The pluton is medium- to coarse-grained biotite-amphibole granite with minor biotite granite facies. REE-bearing phases are diverse and include monazite, zircon, titanite, allanite, apatite and bastnäsite. Weathered profiles were sampled up to 7 m-deep across the ~ 400 km2pluton. In one profile, ion-adsorbed REEs plus yttrium (REE + Y) ranged up to 581 mg/kg and accounted for up to 77% of total REE + Y in saprolite. In other profiles, ion-adsorbed REE + Y ranged 12–194 mg/kg and only accounted for 3–37% of totals. The profile most enriched in ion-adsorbed REEs was located along the mapped boundary of two granite facies and contained trioctahedral smectite in the saprolite, evidence suggestive of hydrothermal alteration of biotite at that location. Post-emplacement deuteric alteration can generate easily weathered REE phases, particularly fluorocarbonates. In the case of Liberty Hill, hydrothermal alteration may have converted less soluble to more soluble REE minerals. Additionally, regolith P content was inversely correlated with the fraction ion-adsorbed REEs, and weathering related secondary REE-phosphates were found in some regolith profiles. Both patterns illustrate how low P content aids in the accumulation of ion-adsorbed REEs. The localized occurrence at Liberty Hill sheds light on conditions and processes that generate ion-adsorbed REEs.

  2. Petrogenesis of the Dengzhazi A-type pluton from the Taihang-Yanshan Mesozoic orogenic belts, North China Craton

    Science.gov (United States)

    Xiaolu, Niu; Bin, Chen; Xu, Ma

    2011-05-01

    The voluminous Mesozoic monzonitic to monzogranitic rocks in the north China craton (NCC) mostly show high-K calc-alkaline and I-type granitoids features. The Dengzhazi granitic pluton, however, shows features typical of A-type granites. The A-type pluton was emplaced in the Taihang-Yanshan orogenic belts of the northern margin of the NCC, with zircon U-Pb ages of around 140 Ma. The Dengzhazi A-type granites are characterized by high SiO 2 (70.2-77.7 wt.%), K 2O + Na 2O, Zr, Nb, Ga, Zn, and Y contents as well as high Ga/Al ratios, and extremely low CaO, Ba, Sr. In addition, they show high zircon saturation temperatures (870-950 °C), low water and low oxygen fugacity. All these features are consistent with the A-type affinity of the pluton. In situ Hf isotopic analyses for the dated zircons show relatively small range of ɛHf( t) (-13 to -17). They also have homogeneous initial Nd isotopic compositions with ɛNd( t) ranging from -15.1 to -16.3. The Hf and Nd isotopic data suggest that the Dengzhazi A-type granites originated from a homogeneous crustal source, probably the Archean mafic-intermediate granulites. Taking into account the high temperatures, the low H 2O and fO 2 of the magma system, we believe that partial melting of the granulites should have been triggered by underplating of mantle-derived magmas at the base of the mafic lower crust in an extensional regime. The Dengzhazi A-type granite is the oldest pluton of the Taihang-Yanshan Mesozoic magma belts, signifying the commencement of extensive underplating of mafic magmas, and thus of lithospheric thinning in the northern NCC.

  3. STRUVE arc and EUPOS® stations

    Science.gov (United States)

    Lasmane, Ieva; Kaminskis, Janis; Balodis, Janis; Haritonova, Diana

    2013-04-01

    The Struve Geodetic Arc was developed in Years 1816 to 1855, 200 years ago. Historic information on the points of the Struve Geodetic Arc are included in the UNESCO World Heritage list in 2005. Nevertheless, the sites of many points are still not identified nor included in the data bases nowadays. Originally STRUVE arc consisted of 258 main triangles with 265 triangulation points. Currently 34 of the original station points are identified and included in the in the UNESCO World Heritage list. identified original measurement points of the Meridian Arc are located in Sweden (7 points), Norway (15), Finland (83), Russia (1), Estonia (22), Latvia (16), Lithuania (18), Belorussia (28), Ukraine (59) and Moldova (27). In Year 2002 was initiated another large coverage project - European Position Determination System "EUPOS®". Currently there are about 400 continuously operating GNSS (Global Navigation Satellite Systems) stations covering EU countries Estonia, Latvia, Lithuania, Poland, Czech Republic, Slovakia, Hungary, Bulgaria, Romania and East European countries Ukraine and Moldavia. EUPOS® network is a ground based GNSS augmentation system widely used for geodesy, land surveying, geophysics and navigation. It gives the opportunity for fast and accurate position determination never available before. It is an honorable task to use the EUPOS® system for research of the Struve triangulation former sites. Projects with Struve arc can popularize geodesy, geo-information and its meaning in nowadays GIS and GNSS systems. Struve Arc and its points is unique cooperation cross-border object which deserve special attention because of their natural beauty and historical value for mankind. GNSS in geodesy discovers a powerful tool for the verification and validation of the height values of geodetic leveling benchmarks established historically almost 200 years ago. The differential GNSS and RTK methods appear very useful to identify vertical displacement of landscape by means of

  4. Making Conductive Polymers By Arc Tracking

    Science.gov (United States)

    Daech, Alfred F.

    1992-01-01

    Experimental technique for fabrication of electrically conductive polymeric filaments based on arc tracking, in which electrical arc creates conductive carbon track in material that initially was insulator. Electrically conductive polymeric structures made by arc tracking aligned along wire on which formed. Alignment particularly suited to high conductivity and desirable in materials intended for testing as candidate superconductors.

  5. Fate of an Oceanic Island-arc at the Collision Zone: Insight From a Modern Case at the Izu Collision Zone, Central Japan

    Science.gov (United States)

    Aoike, K.

    2003-12-01

    the lower crust delamination is occurring beneath the Tanzawa Terrane and the major part of the central ICZ. As a consequence, survival rate of an arc crust in an orthogonal arc-arc collision zone like the ICZ can be estimated at about 70 % of the active arc and 30 % of the whole crust. Furthermore, taking a preexisting 6 km thick oceanic crust into account, the survival rate of arc magmatic products in this pattern of collision can be calculated at about 50 %.

  6. Fission Track Geochronology of Xiaonanchuan Pluton and the Morphotectonic Evolution of Eastern Kunlun since Late Miocene

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    Apatite fission track (AFT) thermochronology of seven samples from the Xiaonanchuan(小南川) pluton in the Kunlun (昆仑) pass area was carried out, for the purpose of determining the timing of cooling and the relation between the exhumation and the morphotectonic processes. The AFT ages yield low denudation rates of 0.020-0.035 mm/ a during the late Miocene, which correspond to a stable geomorphic and weak tectonic uplifting environment. The low denudation rates can be considered as the approximate tectonic uplifting rates. The AFT geochronology shows paroxysmally rapid cooling since the Pliocene and an apparent material unroofing of more than 3 km in the Xiaonanchuan area. This was not the result of simple denudation. The rapid cooling was coupled with the intensive orogeny since the Pliocene, which was driven by tectonic uplifting. The accelerated relief building was accompanied by a series of faulting, which caused the basin and the valley formation and sinking. The space pattern of the AFT ages also shows differential uplifting, which decreases northwardly. This trend is supported by the regional AFT data, which indicate that the exhumation decreases northwardly in eastern Kunlun. This trend also exists in east-west orientation from the western Kunlun range to the eastern. The uplifting trend is also supported by geomorphic characteristics including the elevation and the relief differences as well as the distribution of the Late Cenozoic volcanism.

  7. The intrusive complexof the Island of Giglio: geomagnetic characteristics of plutonic facies with low susceptibility contrast

    Directory of Open Access Journals (Sweden)

    R. Cavallini

    1998-06-01

    Full Text Available Two main plutonic facies characterize the intrusive complex of the Island of Giglio, and the trend of their contact at depth has been modelled using a 2D½ analysis based on a detailed geomagnetic survey in order to verify the geological hypothesis of the subsurface geometry of this contact. The magnetic anomaly connected with the discontinuity is quite low, due to the small difference between the magnetic susceptibilities of the two granitic facies. Development of this model of inversion of the magnetic field, which is in good agreement with the geological interpretation, was made possible by: 1 accurate control of the geomagnetic time variations and consequent temporal reduction, 2 a very low level of the artificial magnetic noise, 3 high density of the magnetic survey, 4 detailed knowledge of the mapped geologic contact between facies and of their petrologic characteristics, and 5 direct local measurements of the magnetic susceptibilities of the key lithologies. The model shows the trends of the geological contact, as projected in three E-W sections, that dips eastward in the range between 210 and 540, supporting the geologic hypothesis that the Pietrabona facies represents an external shell of the shallowly emplaced Giglio monzogranite intrusion.

  8. Deep long-period earthquakes beneath Washington and Oregon volcanoes

    Science.gov (United States)

    Nichols, M.L.; Malone, S.D.; Moran, S.C.; Thelen, W.A.; Vidale, J.E.

    2011-01-01

    Deep long-period (DLP) earthquakes are an enigmatic type of seismicity occurring near or beneath volcanoes. They are commonly associated with the presence of magma, and found in some cases to correlate with eruptive activity. To more thoroughly understand and characterize DLP occurrence near volcanoes in Washington and Oregon, we systematically searched the Pacific Northwest Seismic Network (PNSN) triggered earthquake catalog for DLPs occurring between 1980 (when PNSN began collecting digital data) and October 2009. Through our analysis we identified 60 DLPs beneath six Cascade volcanic centers. No DLPs were associated with volcanic activity, including the 1980-1986 and 2004-2008 eruptions at Mount St. Helens. More than half of the events occurred near Mount Baker, where the background flux of magmatic gases is greatest among Washington and Oregon volcanoes. The six volcanoes with DLPs (counts in parentheses) are Mount Baker (31), Glacier Peak (9), Mount Rainier (9), Mount St. Helens (9), Three Sisters (1), and Crater Lake (1). No DLPs were identified beneath Mount Adams, Mount Hood, Mount Jefferson, or Newberry Volcano, although (except at Hood) that may be due in part to poorer network coverage. In cases where the DLPs do not occur directly beneath the volcanic edifice, the locations coincide with large structural faults that extend into the deep crust. Our observations suggest the occurrence of DLPs in these areas could represent fluid and/or magma transport along pre-existing tectonic structures in the middle crust. ?? 2010 Elsevier B.V.

  9. Subduction of the Indian Lithospheric Slab Beneath Tibet

    Science.gov (United States)

    Zhou, H.; Murphy, M. A.

    2001-12-01

    In order to characterize the dynamics of continent-continent collisions, it is essential to define its present geometry and physical state. We report the results of a seismic tomography study of the Tibet-Himalayan collision zone, using a global data set, which indicates that the Indian lithospheric slab has been subducted subhorizontally beneath nearly the entire Tibetan plateau to depths of 165-260 km. Tibetan velocity structure is low in the crust and high in mantle lithosphere at depths between 75-120 km. An asthenospheric layer overlies the subducted Indian slab at depths between 120-165 km beneath the Tibetan plateau. There is a large low-velocity anomaly north of the Indus-Yalu suture zone between 85ºE and 93ºE that extends from the crust down to at least 310 km depth beneath the plateau. This low-velocity anomaly is indicative of mantle upwelling through a weakened zone of the subducted slab. The extent to which India has subducted beneath Tibet, as revealed by these seismic images, is comparable to estimates of crustal shortening across the Himalaya. Moreover, we hypothesize that the buoyancy due to heating of the subducted Indian slab and the existence of the asthenospheric layer contribute to the elevation and flatness of the Tibetan plateau.

  10. Arc-oblique fault systems: their role in the Cenozoic structural evolution and metallogenesis of the Andes of central Chile

    Science.gov (United States)

    Piquer, Jose; Berry, Ron F.; Scott, Robert J.; Cooke, David R.

    2016-08-01

    The evolution of the Main Cordillera of Central Chile is characterized by the formation and subsequent inversion of an intra-arc volcano-tectonic basin. The world's largest porphyry Cu-Mo deposits were emplaced during basin inversion. Statistically, the area is dominated by NE- and NW-striking faults, oblique to the N-striking inverted basin-margin faults and to the axis of Cenozoic magmatism. This structural pattern is interpreted to reflect the architecture of the pre-Andean basement. Stratigraphic correlations, syn-extensional deposits and kinematic criteria on fault surfaces show several arc-oblique structures were active as normal faults at different stages of basin evolution. The geometry of syn-tectonic hydrothermal mineral fibers, in turn, demonstrates that most of these structures were reactivated as strike-slip ± reverse faults during the middle Miocene - early Pliocene. Fault reactivation age is constrained by 40Ar/39Ar dating of hydrothermal minerals deposited during fault slip. The abundance and distribution of these minerals indicates fault-controlled hydrothermal fluid flow was widespread during basin inversion. Fault reactivation occurred under a transpressive regime with E- to ENE-directed shortening, and was concentrated around major plutons and hydrothermal centers. At the margins of the former intra-arc basin, deformation was largely accommodated by reverse faulting, whereas in its central part strike-slip faulting was predominant.

  11. Stratigraphic and Petrological Constraints of Cretaceous Subduction Initiation and Arc-Continent Collision in the Northern Andes

    Science.gov (United States)

    Leon, S.; Cardona, A.; Mejia, D.; Parra, M.

    2014-12-01

    Middle to Late-Cretaceous orogenic events in the northern Andes have been commonly reconstructed from the analysis of inland basins or the integration of regional scale thermochronological, geochronological and geochemical datasets from the accreted blocks. In contrast, limited studies have been developed on the stratigraphic and deformational record of magmatic and sedimentary sequences exposed near the suture zones. New field and petrologic data are used to characterize an ophiolite type sequence that outcrops in the western flank from the northwestern segment of the Central Cordillera of Colombia. Stratigraphic analysis indicate the existence of Albian-Aptian deep marine pelitic sequence interbedded with minor chert and thin quartz sandstone beds that apparently change to a volcanic dominate stratigraphy. Deformed ophiolite-like mafic and ultramafic plutonic rocks and isolated pillow lavas are also exposed to the east in fault contact with the pelitic sequence. The pelitic and interlayered volcanic rocks represent the growth of an extensional Early-Cretaceous basin that followed a Late-Jurassic magmatic quiescence in the Northern Andes. The volcano-sedimentary record is probably related to the growth of a fore-arc basin in a new subduction zone that extends until the Late Cretaceous. The deformation and obduction of the ophiolitic association and the fore-arc basin were probably triggered by the Late Cretaceous collision with an allocthonous plateau-arc associated to the migration of the Caribbean plate.

  12. Left-lateral transtension along the Tierra Colorada deformation zone, northern margin of the Xolapa magmatic arc of southern Mexico

    Science.gov (United States)

    Riller, U.; Ratschbacher, L.; Frisch, W.

    1992-05-01

    Structural analysis of steeply NNW-dipping tectonites along the northern margin of the Xolapa magmatic arc, southern Mexico, reveals progressive deformation involving ductile and brittle deformation mechanisms. Ductile deformation detached Cretaceous cover rocks from the Xolapa basement along a crustal-scale mylonite zone with normal fault geometry. Normal faults dissected the mylonite zone into blocks which rotated a minimum of 35° to the north. Stress tensors calculated from fault-striae data show subhorizontal, roughly N/S-trending principal extension. Deformation resulted from differential uplift of the Xolapa magmatic arc with respect to its northern hinterland (Mixteca terrane). The oblique normal fault geometry of the mylonites conforms with strike-slip and dip-slip movements along the faults. Left-lateral transtension commenced ductilely between 90 Ma (age of deformed cover rocks) and 34 Ma (U/Pb zircon age of an undeformed pluton cutting the mylonite zone) and continued brittlely into the late Tertiary (tilted Miocene volcanic rocks). We argue that deformation resulted from the interaction of a left-lateral strike-slip regime established during formation of the Caribbean, and an extensional collapse of the Xolapa magmatic arc resulting from a change in steady-state plate-boundary conditions in the early Tertiary.

  13. The Central Metasedimentary Belt (Grenville Province) as a failed back-arc rift zone: Nd isotope evidence

    Science.gov (United States)

    Dickin, A. P.; McNutt, R. H.

    2007-07-01

    Nd isotope data are presented for granitoid orthogneisses from the Central Metasedimentary Belt (CMB) of the Grenville Province in order to map the extent of juvenile Grenvillian-age crust within this orogenic belt that is composed mostly of older crustal terranes. The data reveal a 150 km-wide belt of juvenile crust in Ontario, but this belt contains a block of pre-Grenvillian crust (containing the Elzevir pluton) which yields an estimated crustal formation age of 1.5 Ga. The recognition of an older block within the CMB has profound implications for its structure and tectonic evolution, because it implies that juvenile Grenvillian crust, apparently forming a wide NE-SW belt, is in fact distributed in two narrower segments with approximately N-S strike. We suggest that the CMB comprises an en echelon series of ensimatic rift segments, created by back-arc spreading behind a continental margin arc. These rift segments extend southwards (in the subsurface) into the northeastern Unites States. The rift segments contain abundant marble outcrops, consistent with marine incursion into the rift zone, and these deposits also continue northwards into a 'Marble domain' of the CMB in Quebec. However, crustal formation ages in the latter domain are largely pre-Grenvillian, implying that the Quebec rift segment was ensialic. Hence, we interpret the CMB in Ontario and Quebec as the northern termination of a failed back-arc rift zone.

  14. 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

  15. Geochemical features of the mantle source beneath Irazú and Turrialba volcanoes, Costa Rica

    Science.gov (United States)

    Rizzo, A. L.; Di Piazza, A.; Alvarado-Induni, G.; Carapezza, M. L.; de Moor, M. J.; Martinez, M.

    2015-12-01

    Irazú and Turrialba are active arc volcanoes located at the southeastern terminus of the Central American Volcanic Arc (CAVA). These volcanoes have been considered in literature as "twin volcanoes" or as a linked volcanic system. Effectively their proximity may lead to the assumption that they share a common plumbing system, but geochemical data on rocks and fluids reveal a more complicated framework. In this study, we analyzed the rock chemistry of a selected suite of eruptive products emitted in the last 50ka from Irazú volcano, including products from the 1963-1965 eruption. We also analyzed He-Ne-Ar isotopes in fluid inclusions hosted in olivines and pyroxenes hand-picked from these products, and we compared our results with those available for Irazú and the neighboring Turrialba. Rock samples from Irazú are basalts to andesites with MgO content ranging between 3 and 8 wt%, with a variability that follows typical trends of fractional crystallization. The pattern of trace elements is subduction-related with an OIB-like component, testified by an unusual enrichment (e.g., K, REE; e.g., Benjamin et al., 2007 and references therein), associated with the subduction of the Galapagos seamounts. In addition, Turrialba volcano shows the presence of andesites with adakite-like affinity (Di Piazza et al., 2015) which is not observed in rocks from Irazú . The 3He/4He ratio measured in olivine crystals from Irazú varies from 7.1 to 7.5 Ra, overlapping the measurements performed in surface gases (7.2 Ra; Fischer et al., 2002). This range is also comprised in the measurements carried out in gases and rocks from Turrialba (7.0-8.1 Ra; Di Piazza et al., 2015), which showed the presence of a MORB- and OIB-like component at the mantle source. Based on these evidences, we propose that the mantle beneath Irazú reflects an intermediate composition respect to the extreme components recognized at Turrialba. Irazú shows more typical arc-like geochemical signatures, whereas

  16. Velocity structure of uppermost mantle beneath China continent from Pn tomography

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    39473 Pn travel times are inverted to tomographically image both lateral variation and anisotropy of uppermost mantle velocities beneath China continent. The result indicates that the overall average Pn velocity of uppermost mantle in the studied region is 8.0 km/s and the regional velocity fluctuation varies from -0.30 km/s to +0.35 km/s. Pn velocities higher than 8.2 km/s are found in the regions surrounding Qingzang Plateau, such as Junggar Basin, Tarim Basin, Qaidam Basin and Sichun Basin. Pn velocities slightly lower than the average are found in western Sichuan and Yunnan, Shanxi Graben and Bohai Bay region. A Pn velocity as low as 7.8 km/s may exist in the region striding the boundary between Guangxi and Guangdong provinces. In general, Pn velocity in tectonically stable region like cratonic platform tends to be high, while that in tectonically active region tends to be low. The regions in compressive setting usually show higher Pn velocity, while extensional basins or grabens generally display lower one. Anisotropy of Pn velocity is seen in some regions. In the southeastern region of Qingzang Plateau the directions of fastest Pn velocity show a rotation pattern, which may be related to southeastward escape of the plateau material due to the collision and compression of Indian Plate to Asia along Himalaya arc. Notable anisotropy also exists around Bohai Bay region, likely indicating crustal extending and possible magma activity therein.

  17. Implications of topographic relief on the brittle-to-plastic boundary beneath the southern Central Range, Taiwan

    Science.gov (United States)

    Cavallotti, C. J.; Lewis, J. C.

    2015-12-01

    The result of the ongoing arc-continent collision between the Eurasian (EU) and Philippine Sea (PSP) plates, Taiwan is an important tool in understanding the real time mechanics of the mountain building process. We show an apparent gap in seismicity beneath Taiwan's Southern Central Range that may represent the presence of a volume of rock lacking the shear strength required to record brittle processes. A spatially accurate 3D map was created, utilizing data recorded for over 8000 seismic events beneath Taiwan and the surrounding area, and shows an elongate aseismic volume trending northeast southwest generally parallel to the topographic grain of the island. Published P-wave data shows an area nearly coincident with the aseismic zone with lower velocities at depths of 7.5km in the west to nearly 40km in the east which suggests a difference in density (and rheology) from the surrounding, seismically active, areas. Strain inversions assuming a micropolar model for crustal deformation suggest systematic changes in strain tensor geometry from east to west across the hypothesized density boundary. Preliminary results indicate that seismogenic strain along the western margin of the aseismic zone accommodates crustal thinning with stretching oblique to the orogen. In contrast, on the east side of the aseismic zone we see crustal thickening with minimum stretching (shortening) subparallel to PSP-EU motion. The profound change in strain geometry suggests that the asiesmic zone is a partially ductile volume of rock caused by interactions of the EU and PSP beneath Taiwan. We hypothesize that if the rheology contrast is sufficient, higher spatial resolution inversions may reveal that events near the seismic/aseismic interface exhibit Andersonian-like behavior wherein one principal strain axis would lie orthogonal at any given point to a surface mapped to this boundary. Alternatively, if the contrast is smaller the inverted strain geometries may vary systematically and provide

  18. Simulation of Magnetically Dispersed Arc Plasma

    Institute of Scientific and Technical Information of China (English)

    白冰; 查俊; 张晓宁; 王城; 夏维东

    2012-01-01

    Magnetically dispersed arc plasma exhibits typically dispersed uniform arc column as well as diffusive cathode root and diffusive anode root. In this paper magnetically dispersed arc plasma coupled with solid cathode is numerically simulated by the simplified cathode sheath model of LOWKE . The numerical simulation results in argon show that the maximum value of arc root current density on the cathode surface is 3.5×10^7 A/m^2), and the maximum value of energy flux on the cathode surface is 3× 10^7 J/m^2, both values are less than the average values of a contracted arc, respectively.

  19. A dual doubly vergent orogen in the Banda Arc continent-arc collision zone as observed on deep seismic reflection profiles

    Science.gov (United States)

    Snyder, D. B.; Prasetyo, H.; Blundell, D. J.; Pigram, C. J.; Barber, A. J.; Richardson, A.; Tjokosaproetro, S.

    1996-02-01

    New deep seismic reflection profiles across the Banda Arc of Indonesia reveal reflectors in the uppermost 50 km of the lithosphere. Combined with existing earthquake hypocenter locations and focal mechanisms, the new structural geometries inferred from the reflectors yield a more complete analysis of deformation during the past 10 m.y. and provide insights into how strain is partitioned across an orogenic belt in which volcanic arcs and continents converge. A clearly defined Wadati-Benioff zone, and recent deformation of shelf sediments observed on older shallow seismic profiles, indicated to previous workers that substantial convergence occurred at the Timor Trough. A few focal mechanisms, seafloor escarpments, and recent geodetic surveying indicate that convergence at ˜7 cm yr-1 currently (last 200 kyr?) occurs at the northern margin of the now inactive volcanic arc, the Wetar Thrust zone. Reflectors on the new seismic profiles are interpreted as thrust faults and folds that occur throughout the crust and within the uppermost mantle between the Timor Trough and Wetar Thrust. Specifically, basement reflectors beneath the toe of the accretionary complex have reverse-sense offsets that imply blind thrusts. The whole crust is horizontally shortened, not only the sedimentary cover rocks that previously deformed into duplexes above a decollément. Reflectors dipping away from both margins of the forearc basin and at the northern margin of the volcanic arc are interpreted as evidence of thrusting. Thus each arc represents a doubly vergent fold-and-thrust belt, but only the northern one is currently active. Crustal thicknesses inferred from seismic velocities, reflectors, and gravity anomalies are consistent with the merging of a thinned continental shelf margin with oceanic lithosphere to form an orogenic belt with at present 3-4 km of topographic relief in the region of eastern Timor.

  20. A mechanism that triggers double arcing during plasma arc cutting

    Energy Technology Data Exchange (ETDEWEB)

    Nemchinsky, Valerian, E-mail: nemchinsky@bellsouth.ne [Keiser University, Fort Lauderdale, FL 33309 (United States)

    2009-10-21

    Double arcing (DA) is a phenomenon when a transferred arc, flowing inside an electrically insulated nozzle, breaks into two separate arcs: one that connects the cathode and the nozzle and another that connects the nozzle and a work-piece. It is a commonly accepted opinion that the reason for DA is high voltage drop in the plasma inside the nozzle. However, the specific mechanism that triggers the DA development is not clear. In this paper, we propose such a mechanism. Dielectric films deposited inside the nozzle's orifice play the key role in this mechanism. These films are charged by ion current from plasma. A strong electric field is created inside the film and at the boundary of the film and clean metal of the nozzle. This gives rise to a thermo-field electron emission from the clean metal that borders the film. Emitted electrons are accelerated at the voltage drop between the nozzle and plasma. These electrons produce extra ions, which in turn move back to the film and additionally charge it. This sequence of events leads to explosive instability if the voltage drop inside the nozzle is high enough. Experiments to check the proposed mechanism are suggested.

  1. Modelling the Crust beneath the Kashmir valley in Northwestern Himalaya

    Science.gov (United States)

    Mir, R. R.; Parvez, I. A.; Gaur, V. K.; A.; Chandra, R.; Romshoo, S. A.

    2015-12-01

    We investigate the crustal structure beneath five broadband seismic stations in the NW-SE trendingoval shaped Kashmir valley sandwiched between the Zanskar and the Pir Panjal ranges of thenorthwestern Himalaya. Three of these sites were located along the southwestern edge of the valley andthe other two adjoined the southeastern. Receiver Functions (RFs) at these sites were calculated usingthe iterative time domain deconvolution method and jointly inverted with surface wave dispersiondata to estimate the shear wave velocity structure beneath each station. To further test the results ofinversion, we applied forward modelling by dividing the crust beneath each station into 4-6homogeneous, isotropic layers. Moho depths were separately calculated at different piercing pointsfrom the inversion of only a few stacked receiver functions of high quality around each piercing point.These uncertainties were further reduced to ±2 km by trial forward modelling as Moho depths werevaried over a range of ±6 km in steps of 2 km and the synthetic receiver functions matched with theinverted ones. The final values were also found to be close to those independently estimated using theH-K stacks. The Moho depths on the eastern edge of the valley and at piercing points in itssouthwestern half are close to 55 km, but increase to about 58 km on the eastern edge, suggesting thathere, as in the central and Nepal Himalaya, the Indian plate dips northeastwards beneath the Himalaya.We also calculated the Vp/Vs ratio beneath these 5 stations which were found to lie between 1.7 and1.76, yielding a Poisson's ratio of ~0.25 which is characteristic of a felsic composition.

  2. Crustal structure beneath northeast India inferred from receiver function modeling

    Science.gov (United States)

    Borah, Kajaljyoti; Bora, Dipok K.; Goyal, Ayush; Kumar, Raju

    2016-09-01

    We estimated crustal shear velocity structure beneath ten broadband seismic stations of northeast India, by using H-Vp/Vs stacking method and a non-linear direct search approach, Neighbourhood Algorithm (NA) technique followed by joint inversion of Rayleigh wave group velocity and receiver function, calculated from teleseismic earthquakes data. Results show significant variations of thickness, shear velocities (Vs) and Vp/Vs ratio in the crust of the study region. The inverted shear wave velocity models show crustal thickness variations of 32-36 km in Shillong Plateau (North), 36-40 in Assam Valley and ∼44 km in Lesser Himalaya (South). Average Vp/Vs ratio in Shillong Plateau is less (1.73-1.77) compared to Assam Valley and Lesser Himalaya (∼1.80). Average crustal shear velocity beneath the study region varies from 3.4 to 3.5 km/s. Sediment structure beneath Shillong Plateau and Assam Valley shows 1-2 km thick sediment layer with low Vs (2.5-2.9 km/s) and high Vp/Vs ratio (1.8-2.1), while it is observed to be of greater thickness (4 km) with similar Vs and high Vp/Vs (∼2.5) in RUP (Lesser Himalaya). Both Shillong Plateau and Assam Valley show thick upper and middle crust (10-20 km), and thin (4-9 km) lower crust. Average Vp/Vs ratio in Assam Valley and Shillong Plateau suggest that the crust is felsic-to-intermediate and intermediate-to-mafic beneath Shillong Plateau and Assam Valley, respectively. Results show that lower crust rocks beneath the Shillong Plateau and Assam Valley lies between mafic granulite and mafic garnet granulite.

  3. Hot mantle upwelling across the 660 beneath Yellowstone

    Science.gov (United States)

    Schmandt, Brandon; Dueker, Kenneth; Humphreys, Eugene; Hansen, Steven

    2012-05-01

    P-to-s receiver functions mapped to depth through P and S body-wave tomography models image continuous 410 and 660 km discontinuities beneath the area covered by USArray prior to the year 2011. Mean depths to the 410 and 660 km discontinuities of 410 and 656 km imply a mantle transition zone that is about 4 km thicker than the global average and hence has a slightly cooler mean temperature and/or enhanced water content. Compared to the mean 660 depth beneath this ~ 2000 km wide area, the 660 beneath the Yellowstone hotspot is deflected upward by 12-18 km over an area about 200 km wide. This is the most anomalous shallowing of the 660 imaged and its horizontal extent is similar to the area where P and S tomography image low-velocity mantle extending from the top of the transition zone to about 900 km depth. Together, these results indicate a high-temperature, plume-like upwelling extending across the 660. The depth of 410 km discontinuity beneath the Yellowstone region is within 5 km of the mean depth implying that the plume is vertically heterogeneous and possibly discontinuous. Tomography indicates a similar vertically heterogeneous thermal plume. The irregular plume structure may be intrinsic to the dynamics of upwelling through the transition zone, or distortion may be caused by subduction-induced mantle flow. Topography of the 410 and 660 confirms that subducted slabs beneath the western U.S. are highly segmented, as inferred from recent tomography studies. We find no evidence of regionally pervasive velocity discontinuities between 750 and 1400 km depth. The plume's depth of origin within the lower mantle remains uncertain.

  4. Origin of back-arc basins and effects of western Pacific subduction systems on eastern China geology

    Science.gov (United States)

    Niu, Y.

    2013-12-01

    Assuming that subduction initiation is a consequence of lateral compositional buoyancy contrast within the lithosphere [1], and recognizing that subduction initiation within normal oceanic lithosphere is unlikely [1], we can assert that passive continental margins that are locations of the largest compositional buoyancy contrast within the lithosphere are the loci of future subduction zones [1]. We hypothesize that western Pacific back-arc basins were developed as and evolved from rifting at passive continental margins in response to initiation and continuation of subduction zones. This hypothesis can be tested by demonstrating that intra-oceanic island arcs must have basement of continental origin. The geology of the Islands of Japan supports this. The highly depleted forearc peridotites (sub-continental lithosphere material) from Tonga and Mariana offer independent lines of evidence for the hypothesis [1]. The origin and evolution of the Okinawa Trough (back-arc basin) and Ryukyu Arc/Trench systems represents the modern example of subduction initiation and back-arc basin formation along a (Chinese) continental margin. The observation why back-arc basins exit behind some subduction zones (e.g., western Pacific) but not others (e.g., in South America) depends on how the overlying plate responds to subduction, slab-rollback and trench retreat. In the western Pacific, trench retreat towards east results in the development of extension in the upper Eurasian plate and formation of back-arc basins. In the case of South America, where no back-arc basins form because trench retreat related extension is focused at the 'weakest' South Mid-Atlantic Ridge. It is thus conceptually correct that the South Atlantic is equivalent to a huge 'back-arc basin' although its origin may be different. Given the negative Clayperon slope of the Perovskite-ringwoodite phase transition at the 660 km mantle seismic discontinuity (660-D), slab penetration across the 660-D is difficult and

  5. Four flavours of orogenic plateau magmatism: what's melting beneath the Turkish-Iranian Plateau?

    Science.gov (United States)

    Neill, Iain; Allen, Mark; Kheirkhah, Monireh; Meliksetian, Khachatur; Kaislaniemi, Lars; van Hunen, Jeroen

    2014-05-01

    in (1) is plausibly caused by asthenospheric upwelling following slab breakoff, whereas magmatism in (2) is dominated by melting of the base of the still-present lithospheric mantle during convective removal or asthenospheric upwelling. Magmatism in (3) is probably triggered by decomposition of hydrous phases within the lithosphere, whereas those in (4) have various triggers: OIB-like magmas may relate to local delamination or thin-spots, more arc-like magmas may be due to lithospheric thickening in the Alborz and Greater Caucasus. Geochemical and geodynamic modelling suggest that at ~500 km distance from the suture there is a cut-off, at which asthenosphere stirring (due to slab break-off) ceases to be an effective cause of decompression melting, small-scale lithospheric delamination and convection. The relative scarcity of magmatism in Western and Central Iran is good evidence that the mantle beneath this region is not being stirred by delamination processes: there is otherwise little difference in the previous Tethyan subduction histories of Iran and Eastern Turkey. Overall, there is no single trigger or source of magmatism beneath the TIP, but two processes appear to dominate: melting due to dehydration of the lithosphere as it is thickened or convectively removed, and decompression melting of upwelling asthenosphere.

  6. Zircon Recycling in Arc Intrusions

    Science.gov (United States)

    Miller, J.; Barth, A.; Matzel, J.; Wooden, J.; Burgess, S.

    2008-12-01

    Recycling of zircon has been well established in arc intrusions and arc volcanoes, but a better understanding of where and how zircons are recycled can help illuminate how arc magma systems are constructed. To that end, we are conducting age, trace element (including Ti-in-zircon temperatures; TzrnTi) and isotopic studies of zircons from the Late Cretaceous (95-85 Ma) Tuolumne Intrusive Suite (TIS) in the Sierra Nevada Batholith (CA). Within the TIS zircons inherited from ancient basement sources and/or distinctly older host rocks are uncommon, but recycled zircon antecrysts from earlier periods of TIS-related magmatism are common and conspicuous in the inner and two most voluminous units of the TIS, the Half Dome and Cathedral Peak Granodiorites. All TIS units have low bulk Zr ([Zr]825°C), [Zr] in the TIS is a factor of 2 to 3 lower than saturation values. Low [Zr] in TIS rocks might be attributed to a very limited supply of zircon in the source, by disequilibrium melting and rapid melt extraction [1], by melting reactions involving formation of other phases that can incorporate appreciable Zr [2], or by removal of zircon at an earlier stage of magma evolution. Based on a preliminary compilation of literature data, low [Zr] is common to Late Cretaceous N.A. Cordilleran granodioritic/tonalitic intrusions (typically Tzrnsat [3]. A corollary is that slightly older zircon antecrysts that are common in the inner units of the TIS could be considered inherited if they are derived from remelting of slightly older intrusions. Remelting at such low temperatures in the arc would require a source of external water. Refs: [1] Sawyer, J.Pet 32:701-738; [2] Fraser et al, Geology 25:607-610; [3] Harrison et al, Geology 35:635- 638

  7. Minor arcs for Goldbach's problem

    CERN Document Server

    Helfgott, H A

    2012-01-01

    The ternary Goldbach conjecture states that every odd number $n\\geq 7$ is the sum of three primes. The estimation of sums of the form $\\sum_{p\\leq x} e(\\alpha p)$, $\\alpha = a/q + O(1/q^2)$, has been a central part of the main approach to the conjecture since (Vinogradov, 1937). Previous work required $q$ or $x$ to be too large to make a proof of the conjecture for all $n$ feasible. The present paper gives new bounds on minor arcs and the tails of major arcs. For $q\\geq 4\\cdot 10^6$, these bounds are of the strength needed to solve the ternary Goldbach conjecture. Only the range $q\\in \\lbrack 10^5, 4\\cdot 10^6\\rbrack$ remains to be checked, possibly by brute force, before the conjecture is proven for all $n$. The new bounds are due to several qualitative improvements. In particular, this paper presents a general method for reducing the cost of Vaughan's identity, as well as a way to exploit the tails of minor arcs in the context of the large sieve.

  8. Multi-sensor geophysical constraints on crustal melt in the central Andes: the PLUTONS project

    Science.gov (United States)

    Pritchard, M. E.; Comeau, M. J.; West, M. E.; Christensen, D. H.; Mcfarlin, H. L.; Farrell, A. K.; Del Potro, R.; Gottsmann, J.; McNutt, S. R.; Michelfelder, G.; Diez, M.; Elliott, J.; Henderson, S. T.; Keyson, L.; Delgado, F.; Unsworth, M. J.

    2015-12-01

    The central Andes is a key global location to quantify storage, transport, and volumes of magma in the Earth's crust as it is home to the world's largest zone of partial melt (the Altiplano-Puna Magma or Mush Body, APMB) as well as the more recently documented Southern Puna Magma Body (SPMB). We describe results from the recently completed international PLUTONS project that focused inter-disciplinary study on two sites of large-scale surface uplift that presumably represent ongoing magmatic intrusions in the mid to upper crust - Uturuncu, Bolivia (in the center of the APMB) and Lazufre on the Chile-Argentina border (on the edge of the SPMB). In particular, a suite of geophysical techniques (seismology, gravity, surface deformation, and electro-magnetic methods) have been used to infer the current subsurface distribution and quantity of partial melts in combination with geochemical and lab studies on samples from the area. Both Uturuncu and Lazufre show separate geophysical anomalies in the upper and mid/lower crust (e.g., low seismic velocity, low resistivity, etc.) indicating multiple distinct reservoirs of magma and/or hydrothermal fluids with different properties. The characteristics of the geophysical anomalies differ somewhat depending on the technique used - reflecting the different sensitivity of each method to subsurface melt of different compositions, connectivity, and volatile content. For example, the depth to the top of the APMB is shallower in a joint ambient noise tomography and receiver function analysis compared to a 3D magnetotelluric inversion. One possibility is that the seismic methods are detecting brines above the APMB that do not have a large electromagnetic signature. Comparison of the geophysical measurements with laboratory experiments at the APMB indicate a minimum of 4-25% melt averaged over the region is needed -- higher melt volumes are permitted by the gravity and MT data and may exist in small regions. However, bulk melt values above

  9. Geologic and hydrologic controls on the economic potential of hydrothermal systems associated with upper crustal plutons

    Science.gov (United States)

    Weis, Philipp; Driesner, Thomas; Scott, Samuel; Lecumberri-Sanchez, Pilar

    2016-04-01

    Heat and mass transport in hydrothermal systems associated with upper crustal magmatic intrusions can result in resources with large economic potential (Kesler, 1994). Active hydrothermal systems can form high-enthalpy geothermal reservoirs with the possibility for renewable energy production. Fossil continental or submarine hydrothermal systems may have formed ore deposits at variable crustal depths, which can be mined near today's surface with an economic profit. In both cases, only the right combination of first-order geologic and hydrologic controls may lead to the formation of a significant resource. To foster exploration for these hydrothermal georesources, we need to improve our understanding of subsurface fluxes of mass and energy by combining numerical process modelling, observations at both active and fossil systems, as well as knowledge of fluid and rock properties and their interactions in natural systems. The presentation will highlight the role of non-linear fluid properties, phase separation, salt precipitation, fluid mixing, permeability structure, hydraulic fracturing and the transition from brittle to ductile rock behavior as major geologic and hydrologic controls on the formation of high-enthalpy and supercritical geothermal resources (Scott et al., 2015), and magmatic-hydrothermal mineral resources, such as porphyry copper, massive sulfide and epithermal gold deposits (Lecumberri-Sanchez et al., 2015; Weis, 2015). References: Kesler, S. E., 1994: Mineral Resources, economics and the environment, New York, McMillan, 391. Lecumberri-Sanchez, P., Steele-MacInnis, M., Weis, P., Driesner, T., Bodnar, R.J. (2015): Salt precipitation in magmatic-hydrothermal systems associated with upper crustal plutons. Geology, v. 43, p. 1063-1066, doi:10.1130/G37163.1 Scott, S., Driesner, T., Weis, P. (2015): Geologic controls on supercritical geothermal resources above magmatic intrusions. Nature Communications, 6:7837 doi: 10.1038/ncomms8837 Weis, P. (2015): The

  10. 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.

  11. Evidence of an upper mantle seismic anomaly opposing the Cocos slab beneath the Isthmus of Tehuantepec, Mexico

    Science.gov (United States)

    Kim, YoungHee; Lim, Hobin; Miller, Meghan S.; Pearce, Fred; Clayton, Robert W.

    2014-07-01

    of the Cocos plate beneath southern Mexico is characterized by several unusual features, such as a discontinuous volcanic arc, unusual arc chemistry, and anomalously low topography of Tehuantepec Isthmus. Recent seismic images from both receiver functions and seismic tomography suggest that there may be an additional, opposing structure dipping to the southwest from the Gulf of Mexico, and these images have been previously explained by a southwest-dipping slab. However, standard models of the Caribbean tectonic history do not support this interpretation. To better define the Cocos slab's structure and the possible existence of a structure dipping in the opposite direction, dense seismic data across southern Mexico are used to form high-resolution seismic images, based on the 2-D generalized radon transform method, and to relocate regional earthquakes. Our images show the Cocos plate dipping at 30° to the northeast encounters the anomaly that is dipping in the opposite sense at ˜150 km depth. Relocated seismicity clearly delineates a Wadati-Benioff zone that marks the subducting Cocos plate. A cluster of seismicity also appears at ˜150 km depth which may be related to the subduction of the Tehuantepec ridge and/or to the imaged seismic structure with opposite polarity.

  12. Arc Root Attachment on the Anode Surface of Arc Plasma Torch Observed with a Novel Method

    Institute of Scientific and Technical Information of China (English)

    PAN Wen-Xia; LI Teng; MENG Xian; CHEN Xi; WU Cheng-Kang

    2005-01-01

    @@ The arc-root attachment on the anode surface of a dc non-transferred arc plasma torch has been successfullyobserved using a novel approach. A specially designed copper mirror with a boron nitride film coated on itssurface central-region is employed to avoid the effect of intensive light emitted from the arc column upon theobservation of weakly luminous arc root. It is found that the arc-root attachment is diffusive on the anode surfaceof the argon plasma torch, while constricted arc roots often occur when hydrogen or nitrogen is added into argonas the plasma-forming gas.

  13. 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.

  14. Lithospheric thinning beneath rifted regions of Southern California.

    Science.gov (United States)

    Lekic, Vedran; French, Scott W; Fischer, Karen M

    2011-11-11

    The stretching and break-up of tectonic plates by rifting control the evolution of continents and oceans, but the processes by which lithosphere deforms and accommodates strain during rifting remain enigmatic. Using scattering of teleseismic shear waves beneath rifted zones and adjacent areas in Southern California, we resolve the lithosphere-asthenosphere boundary and lithospheric thickness variations to directly constrain this deformation. Substantial and laterally abrupt lithospheric thinning beneath rifted regions suggests efficient strain localization. In the Salton Trough, either the mantle lithosphere has experienced more thinning than the crust, or large volumes of new lithosphere have been created. Lack of a systematic offset between surface and deep lithospheric deformation rules out simple shear along throughgoing unidirectional shallow-dipping shear zones, but is consistent with symmetric extension of the lithosphere.

  15. Simulation of Wave-Plus-Current Scour beneath Submarine Pipelines

    DEFF Research Database (Denmark)

    Eltard-Larsen, Bjarke; Fuhrman, David R.; Sumer, B. Mutlu

    2016-01-01

    A fully coupled hydrodynamic and morphologic numerical model was utilized for the simulation of wave-plus-current scour beneath submarine pipelines. The model was based on incompressible Reynolds-averaged Navier–Stokes equations, coupled with k-ω turbulence closure, with additional bed and suspen......A fully coupled hydrodynamic and morphologic numerical model was utilized for the simulation of wave-plus-current scour beneath submarine pipelines. The model was based on incompressible Reynolds-averaged Navier–Stokes equations, coupled with k-ω turbulence closure, with additional bed....... This validation complements previously demonstrated accuracy for the same model in simulating pipeline scour processes in pure-wave environments. The model was subsequently utilized to simulate combined wave-plus-current scour over a wide range of combined Keulegan–Carpenter numbers and relative current strengths...

  16. How does recycling of sediment components in arc magmatism really work?

    Science.gov (United States)

    Kelemen, P.; Hacker, B.; Austin, N.

    2007-12-01

    Past work indicates substantial recycling of a sediment component rich in LILE, Th, Sr, Pb and LREE in arcs. For example, in the relatively well-constrained case of Central America, Plank et al (Geology 02) estimate that 80% of subducted, sedimentary Th is recycled in arc magmas. To understand how such a component is transferred from subducted sediment to arc lava, we examined trace-element variation in (a) mid-crustal (0.4 GPa) contact metamorphic rocks (Austin & Kelemen, Fall 06 AGU) and (b) ultrahigh-pressure (UHP, > 3 GPa) metasediments. Most UHP samples were metamorphosed along subduction-zone geotherms (Hacker, Int Geol Rev 06), but some record substantially higher T (e.g., Erzgebirge & Kokchetav, Massone EPSL 03). Unmelted, mid-crustal metapelites are indistinguishable from pelitic sediments for the entire suite of elements analyzed by ICP-MS at WSU. Melt extraction from the mid-crustal metapelites led to systematic depletion of incompatible elements in high-grade hornfels. Depletion increases with decreasing distance to the contact with a mafic pluton, most clearly at peak T > 750°C. In contrast, although many UHP metapelites record PT above the aqueous fluid-saturated solidus, and have fluid inclusions and/or hydrous phases, compared to pelites they show no detectable depletion of "fluid-mobile" elements such as LILE (Cs, Rb, Ba, U, K), Sr and Pb, no depletion of "fluid-immobile, incompatible" elements such as Th and LREE, and no systematic change in key soluble/insoluble ratios such as Ba/Th or K/Zr up to ~1000 C. Mobility of incompatible elements is evident for T > 1000 C, well above PT for subduction-zone geotherms. Presumably, trace phases rich in LILE, Th and LREE persist to ~1050 C in metapelites at UHP conditions.How can our observations be reconciled with the recycled sediment component in arc lavas? Our preferred hypothesis is that low-density metasediments rise into the mantle wedge when heating yields viscosities low enough for density

  17. The oldest island arc and ophiolite complexes of the Russian Arctic (Taimyr Peninsula)

    Science.gov (United States)

    Vernikovskaya, Antonina E.; Vernikovsky, Valery A.; Metelkin, Dmitriy V.; Matushkin, Nikolay Y.; Romanova, Irina V.

    2015-04-01

    in the mouths of Krasnaya River and Kabachkovaya Hill. The Kabachkovaya ophiolites form near E-W elongated narrow zones of ultramafic rocks and small plutons of fine and medium grained gabbros and diabases among flows of tholeitic basalts forming pillow lavas and tuffs. Ar/Ar dating of amphiboles from metagabbros in the Krasnaya R. mouth yielded an age of 1029 Ma. In conclusion, these data indicate the existence of Meso-Neoproterozoic ophiolites and island arcs in the Russian Arctic, which, with available paleomagnetic data, allows composing more correct plate tectonic reconstructions for the early stages of the evolution of this region.

  18. Chemical Variation and Origin of Pleistocene Silicic Pyroclastic Flows from Central American Volcanic Arc

    Science.gov (United States)

    Patino, L. C.; Vogel, T. A.; Alvarado, G. E.; Rose, W. I.; Viray, E. L.

    2003-12-01

    Silicic pyroclastic flows have occurred along the Central American volcanic arc during the Pleistocene. The volcanic products from these eruptions range in composition have SiO{2} mode of 70 wt.%. In the latest part of the Pleistocene (Costa Rica. Phenocryst phases of the silicic pyroclastic flows along Central America are generally very similar. Plagioclase dominates as phenocryst and in the groundmass. Sub-calcic augite, hypersthene are common in dacites. Amphibole as well as biotite are common in the rhyolites and rhyodacites in Guatemala and El Salvador, but these minerals are absent from all units in Nicaragua, and from the youngest unit in Costa Rica. In addition, Ti-oxides, apatite, quartz, are common. It is worth noting that the silicic rocks from Central America contain very little alkali feldspar. There are some chemical variations in the composition of ash-flow tuffs along the arc. The most primitive materials in ignimbrites from Guatemala and Costa Rica are basaltic andesites and andesites; but in Nicaragua and El Salvador, basaltic scorias are present. The ignimbrites from Central Costa Rica have higher alkali content, than the rest of the Pleistocene ash-flow tuffs from Central America, a pattern similar to that observed in lavas. Furthermore, some trace element and trace element ratios also vary along the arc in a pattern similar to that observed in the lavas. The ignimbrites from Nicaragua tend to have the lowest concentrations of Zr (200 ppm); Ba/Th, U/Th are highest and La/Yb is the lowest in Nicaragua.Fractional crystallization has played a role in the evolution of ash-flow sheets in the Central American volcanic arc. Some samples from Guatemala and El Salvador have Eu/Eu*Caribbean large igneous province in the south, are not possible sources for the Pleistocene silicic pyroclastic flows. Based on the similar key trace-element ratios of the ignimbrites and the arc lavas, we concluded that remelting of the calc-alkaline plutons, emplaced at depth

  19. Kelvin-Helmholtz wave generation beneath hovercraft skirts

    Science.gov (United States)

    Sullivan, P. A.; Walsh, C.; Hinchey, M. J.

    1993-05-01

    When a hovercraft is hovering over water, the air flow beneath its skirts can interact with the water surface and generate waves. These, in turn, can cause the hovercraft to undergo violent self-excited heave motions. This note shows that the wave generation is due to the classical Kelvin-Helmholtz mechanism where, beyond a certain air flow rate, small waves at the air water interface extract energy from the air stream and grow.

  20. New interpretation of the deep mantle structure beneath eastern China

    Science.gov (United States)

    Ma, Pengfei; Liu, Shaofeng; Lin, Chengfa; Yao, Xiang

    2016-04-01

    Recent study of high resolution seismic tomography presents a large mass of high velocity abnormality beneath eastern China near the phase change depth, expanding more than 1600km-wide in East-west cross-section across the North China plate. This structure high is generally believed to be the subducted slab of Pacific plate beneath the Eurasia continent, while its origin and dynamic effect on the Cenozoic tectonic evolution of eastern China remain to be controversial. We developed a subduction-driven geodynamic mantle convection model that honors a set of global plate reconstruction data since 230Ma to help understand the formation and evolution of mantle structure beneath eastern China. The assimilation of plate kinematics, continuous evolving plate margin, asymmetric subduction zone, and paleo seafloor age data enables the spatial and temporal consistency between the geologic data and the mantle convection model, and guarantees the conservation of the buoyancy flux across the lithosphere and subducted slabs. Our model achieved a first order approximation between predictions and the observed data. Interestingly, the model suggests that the slab material stagnated above discontinuity didn't form until 15Ma, much later than previous expected, and the fast abnormality in the mid-mantle further west in the tomographic image is interpreted to be the remnants of the Mesozoic Izanagi subduction. Moreover, detailed analysis suggests that the accelerated subduction of Philippine Sea plate beneath Eurasia plate along the Ryukyu Trench and Nankai Trough since 15Ma may largely contribute to extending feature above 670km discontinuity. The long distance expansion of the slab material in the East-west direction may be an illusion caused by the approximate spatial perpendicularity between the cross-section and the subduction direction of the Philippine Sea plate. Our model emphasizes the necessity of the re-examination on the geophysical observation and its tectonic and

  1. On Irrotational Flows Beneath Periodic Traveling Equatorial Waves

    Science.gov (United States)

    Quirchmayr, Ronald

    2016-08-01

    We discuss some aspects of the velocity field and particle trajectories beneath periodic traveling equatorial surface waves over a flat bed in a flow with uniform underlying currents. The system under study consists of the governing equations for equatorial ocean waves within a non-inertial frame of reference, where Euler's equation of motion has to be suitably adjusted, in order to account for the influence of the earth's rotation.

  2. The Dumbarton Oaks Tlazolteotl: looking beneath the surface

    OpenAIRE

    MacLaren Walsh, Jane

    2014-01-01

    The Dumbarton Oaks Tlazolteotl: looking beneath the surface. Some of the earliest and most revered pre-Columbian artifacts in the world’s major museum and private collections were collected prior to the advent of systematic, scientific archaeological excavation, and have little or no reliable provenience data. They have consistently posed problems for researchers due to anomalies of theme, material, size, technical virtuosity and iconography. This paper offers a historical and scientific appr...

  3. Convective upwelling in the mantle beneath the Gulf of California.

    Science.gov (United States)

    Wang, Yun; Forsyth, Donald W; Savage, Brian

    2009-11-26

    In the past six million years, Baja California has rifted obliquely apart from North America, opening up the Gulf of California. Between transform faults, seafloor spreading and rifting is well established in several basins. Other than hotspot-dominated Iceland, the Gulf of California is the only part of the world's seafloor-spreading system that has been surrounded by enough seismometers to provide horizontal resolution of upper-mantle structure at a scale of 100 kilometres over a distance great enough to include several spreading segments. Such resolution is needed to address the long-standing debate about the relative importance of dynamic and passive upwelling in the shallow mantle beneath spreading centres. Here we use Rayleigh-wave tomography to image the shear velocity in the upper 200 kilometres or so of the mantle. Low shear velocities similar to those beneath the East Pacific Rise oceanic spreading centre underlie the entire length of the Gulf, but there are three concentrated locations of anomalously low velocities spaced about 250 kilometres apart. These anomalies are 40 to 90 kilometres beneath the surface, at which depths petrological studies indicate that extensive melting of passively upwelling mantle should begin. We interpret these seismic velocity anomalies as indicating that partial melting triggers dynamic upwelling driven by either the buoyancy of retained melt or by the reduced density of depleted mantle. PMID:19940924

  4. Flow separation and resuspension beneath shoaling nonlinear internal waves

    Science.gov (United States)

    Boegman, Leon; Ivey, Gregory N.

    2009-02-01

    Laboratory observations are presented showing the structure and dynamics of the turbulent bottom boundary layer beneath nonlinear internal waves (NLIWs) of depression shoaling upon sloping topography. The adverse pressure gradient beneath the shoaling waves causes the rear face to steepen, flow separation to occur, and wave-induced near-bottom vortices to suspend bed material. The resuspension is directly attributed to the near-bed viscous stress and to near-bed patches of elevated positive Reynolds stress generated by the vortical structures. These results are consistent with published field observations of resuspension events beneath shoaling NLIWs. Elevated near-bed viscous stresses are found throughout the domain at locations that are not correlated to the resuspension events. Near-bed viscous stress is thus required for incipient sediment motion but is not necessarily a precursor for resuspension. Resuspension is dependent on the vertical velocity field associated with positive Reynolds stress and is also found to occur where the mean (wave-averaged) vertical velocity is directed away from the bed. The results are interpreted by analogy to the eddy-stress and turbulent bursting resuspension models developed for turbulent channel flows.

  5. Recovery of datable charcoal beneath young lavas: lessons from Hawaii.

    Science.gov (United States)

    Lockwood, J.P.; Lipman, P.W.

    1980-01-01

    Field studies in Hawaii aimed at providing a radiocarbon-based chronology of prehistoric eruptive activity have led to a good understanding of the processes that govern the formation and preservation of charcoal beneath basaltic lava flows. Charcoal formation is a rate-dependent process controlled primarily by temperature and duration of heating, as well as by moisture content, density, and size of original woody material. Charcoal will form wherever wood buried by lava is raised to sufficiently high temperatures, but owing to the availability of oxygen it is commonly burned to ash soon after formation. Wherever oxygen circulation is sufficiently restricted, charcoal will be preserved, but where atmospheric oxygen circulates freely, charcoal will only be preserved at a lower temperature, below that required for charcoal ignition or catalytic oxidation. These factors cause carbonized wood, especially that derived from living roots, to be commonly preserved beneath all parts of pahoehoe flows (where oxygen circulation is restricted), but only under margins of aa. Practical guidelines are given for the recovery of datable charcoal beneath pahoehoe and aa. Although based on Hawaiian basaltic flows, the guidelines should be applicable to other areas. -Authors

  6. Transuranic distribution beneath a retired underground disposal facility, Hanford Site

    International Nuclear Information System (INIS)

    Past liquid waste disposal practices at the Hanford Site included the discharge of solutions containing low-level concentrations of transuranics directly to the ground via structures collectively termed cribs. A study was conducted to determine the present spatial distribution of plutonium and americium beneath the retired 216-Z-1A Crib, which contains one of the highest cumulative plutonium inventories, 57 kilograms. Sixteen shallow wells were drilled in the unsaturated sediments underlying the facility using specialized, totally contained drilling techniques. Samples from each well were analyzed to obtain profiles of both sediment type and plutonium and americium concentrations as a function of depth beneath the facility. The results of the study show that the highest concentration of plutonium (>104 nCi/g of sediment) occurs within the first 3 meters of sediment beneath the central distribution pipe. The high activity at this position is tentatively attributed to the removal of solid particles from the waste stream by sediment filtration. The distributions of plutonium and americium in the sediments are similar. Peak transuranic activity in the sediment profile is generally associated with silt lenses or with major sedimentary unit interfaces (ie, sand to gravel). The maximum vertical extent of transuranic activity found is approximately 30 meters below the bottom of the crib or approximately 25 meters above the regional water table. No contamination greater than the instrumental limit of detection of 10-5 nCi/g of sediment was found from a depth of 30 to 40 meters, the maximum depth of sampling

  7. P, S velocity and VP/VS ratio beneath the Toba caldera complex (Northern Sumatra) from local earthquake tomography

    Science.gov (United States)

    Koulakov, Ivan; Yudistira, Tedi; Luehr, Birger-G.; Wandono

    2009-06-01

    In this paper, we investigate the crustal and uppermost mantle structure beneath Toba caldera, which is known as the location of one of the largest Cenozoic eruptions on Earth. The most recent event occurred 74000 yr BP, and had a significant global impact on climate and the biosphere. In this study, we revise data on local seismicity in the Toba area recorded by a temporary PASSCAL network in 1995. We applied the newest version of the LOTOS-07 algorithm, which includes absolute source location, optimization of the starting 1-D velocity model, and iterative tomographic inversion for 3-D seismic P, S (or the VP/VS ratio) and source parameters. Special attention is paid to verification of the obtained results. Beneath the Toba caldera and other volcanoes of the arc, we observe relatively moderate (for volcanic areas) negative P- and S-velocity anomalies that reach 18 per cent in the uppermost layer, 10-12 per cent in the lower crust and about 7 per cent in the uppermost mantle. Much stronger contrasts are observed for the VP/VS ratio that is a possible indicator of dominant effect of melting in origin of seismic anomalies. At a depth of 5 km beneath active volcanoes, we observe small patterns (7-15 km size) with a high VP/VS ratio that might be an image of actual magmatic chambers filled with partially molten material feeding the volcanoes. In the mantle wedge, we observe a vertical anomaly with low P and S velocities and a high VP/VS ratio that link the cluster of events at 120-140 km depth with Toba caldera. This may be an image of ascending fluids and melts released from the subducted slab due to phase transitions. However, taking into account poor vertical resolution, these results should be interpreted with prudence. Although the results show clear signatures that are quite typical for volcanic areas (low velocity and high VP/VS ratio beneath volcanoes), we do not observe any specific features in seismic structure that could characterize Toba as a super volcano.

  8. Magnification Bias in Gravitational Arc Statistics

    CERN Document Server

    Caminha, G B; Makler, M; Mollerach, S; Roulet, E

    2013-01-01

    The statistics of arcs in galaxy clusters is a powerful probe of the inner parts of cluster structure and may provide complementary cosmological constraints. Although progresses involving simulations at the image level have improved the agreement among modelling and observations of arc abundance, there are still discrepancies regarding the redshift distribution of strong lensing clusters. Besides, fast "semi-analytic" methods still have to incorporate the success obtained with simulations. In this paper we discuss the contribution of magnification in gravitational arc statistics. Although lensing conserves surface brightness, the magnification (\\mu) increases the signal-to-noise ratio of the arcs in the images, enhancing their detectability. We present an approach to include this and other observational effects in semi-analytic calculations for arc statistics. The cross section for arc formation (\\sigma) is computed through a semi-analytic method based on the eigenvalue ratio of the magnification tensor. Usin...

  9. Internal fabrics in magmatic plutons emplaced in extended brittle crust - insight from analogue models with AMS (Anisotropy of Magnetic Susceptibility)

    Science.gov (United States)

    Mirzaei, Masoud; Zavada, Prokop; Machek, Matej; Roxerova, Zuzana

    2016-04-01

    Magma emplacement in extended brittle crust was simulated by injecting plaster of Paris (magma) into a large sandbox with central deformable rubber sheet. Analog magma is during the experiments injected through small circular inlet cut in the center of the elastic sheet. Injection force oscillation during the steadily evacuating analog magma was recorded during the experiments and regularly showed 3-4 increases followed by a quick drop. The recorded oscillation amplitude is largest for static injection without extension of the sandbox, which formed a columnar body with concentric and zonal internal fabric. Experiments including normal or oblique 20% extension resulted in along rift axis elongated oblate ellipsoidal pluton with rift parallel ridges in the top part of the pluton. Inspection of horizontal profiles show bone-shaped internal zoning patterns limited by conjugate sets of shear zones. Orientation of these internal shear zones is correlated with the sand-clock fault pattern developed in the overburden sand pack. Another set of shear zones parallel with the long axes of the plutons (rift axis) are associated with successive emplacement of distinct plaster pulses during the buildup of the entire body. The innermost lastly emplaced pulses of plaster display weak vertical magnetic fabrics with vertical lineations, while the outer shells of already emplaced plaster reveal stronger and margin parallel oblate magnetic fabrics with subhorizontal lineations. We interpret the vertical innermost fabrics as a result of active ascent of plaster from the injection inlet, while the fabrics in the outer zones likely reflect push due to inflation of the inner domain reflected in the reworking of the magnetic fabric.

  10. Integrating ArcGIS Online with GEOSS Data Access Broker

    Science.gov (United States)

    Lucchi, Roberto; Hogeweg, Marten

    2014-05-01

    The Global Earth Observation System of Systems (GEOSS) seeks to address 9 societal benefit areas for Earth observations to address: disasters, health, energy, climate, agriculture, ecosystems, biodiversity, water, and weather. As governments and their partners continue to monitor the face of the Earth, the collection, storage, analysis, and sharing of these observations remain fragmented, incomplete, or redundant. Major observational gaps also remain (particularly as we seek to look beneath the surface of the land and the water). As such, GEO's credo is that "decision makers need a global, coordinated, comprehensive, and sustained system of observing systems." Not surprisingly, one of the largest block of issues facing GEOSS is in the area of data: the access to data (including the building services to make the data more accessible), inadequate data integration and interoperability, error and uncertainty of observations, spatial and temporal gaps in observations, and the related issues of user involvement and capacity building. This is especially for people who stand to gain the most benefit from the datasets, but don't have the resources or knowledge to use them. Esri has millions of GIS and imagery users in hundreds of thousands of organizations around the world that work in the aforementioned 9 GEO societal benefit areas. Esri is therefore proud to have entered into a partnership with GEOSS, more specifically by way of a Memorandum of Understanding (MOU) between Esri and the Earth and Space Science Informatics (ESSI) Laboratory of Prof. Stefano Nativi at the CNR (National Research Council of Italy) Institute of Atmospheric Pollution Research. Esri is working with the ESSI Lab to integrate ArcGIS Online by way of the ArcGIS Online API into the GEOSS Data Access Broker (DAB), resulting in the discoverability of all public content from ArcGIS Online through many of the search portals that participate in this network (e.g., DataOne, CEOS, CUAHSI, OneGeology, IOOS

  11. Structural characterization of the Misajé granitic pluton (NW Cameroon): constraints from magnetic and field observations

    Science.gov (United States)

    Fozing, Eric Martial; Njanko, Théophile; Naba, Séta; Kwékam, Maurice; Njonfang, Emmanuel; Rochette, Pierre

    2015-12-01

    The Misajé granitic pluton, emplaced between 569 and 560 Ma in an amphibolitic and gneissic host rock, comprises four petrographic units namely biotite-hornblende granite (BHG), granodiorite (Gd), biotite granite (BG), and leucocratic granite (LG). Four major tectonic events have been described in the studied area: a D1-early tectonic event, responsible of the E-W flat foliation which has been progressively transposed by a D2 tectonic event. A D2 event has developed heterogeneous simple shear in a dextral transpressive context with moderate to strong dipping NE-SW striking foliation; a D3 tectonic event has lead to a sinistral N-S ductile shear characterized by N- to ENE-striking foliation and E-W strike-slip shear corridors and a D4 tectonic event that developed N-S dextral ductile strike-slip deformation. The magnetic study of the pluton, based on the AMS parameters, reveals the coexistence of both paramagnetic (dominated by iron-bearing silicates; 54 % of sites) and ferromagnetic (due to the occurrence of PSD and MD grains of magnetite or other ferromagnetic minerals; 46 % of sites) behaviors. Magnetic foliation shows best poles at 55/82 for the whole pluton, 95/32 in BHG, and 273/83 in BG, and the magnetic lineation trends are mostly NNE-SSW with best lines at 210/8, 198/19, and 36/3, respectively. The trend of the magnetic lineation in BG indicates an S-shape trajectory, suggesting a sinistral sense of shear motion along discrete E-W corridors situated at the northern and southern ends. Kinematic indicators in BG point to a sinistral sense of shear, suggesting its emplacement during the D3 event. The close relationship between K 1 and K 3 points to a syn-kinematic emplacement and crystallization of the Misajé granitic pluton during the Pan-African event, and the tectonic evolution of the study area is considered to be coeval with the tectonic evolution of the trans-Saharan Pan-African belt of eastern Nigeria.

  12. The use of borehole geophysical logs and hydrologic tests to characterize plutonic rock for nuclear fuel waste disposal

    International Nuclear Information System (INIS)

    The selection of an igneous rock body for the disposal of nuclear fuel waste will likely require the drilling and testing of a number of deep investigative boreholes in the rock body. Although coring of at least one hole at each Research Area will be essential, methods for making in situ geophysical and hydrological measurements can substitute for widespread coring and result in significant savings in time and money. A number of borehole methods have been applied to the investigation of plutonic rocks at Whiteshell Nuclear Research Establishment and Chalk River Nuclear Laboratories in Canada

  13. FASTER MUSE CSP ARC CONSISTENCY ALGORITHMS

    OpenAIRE

    Harper, Mary P.; White, Christopher M.; Helzerman, Randall A.; Hockema, Stephen A.

    1997-01-01

    MUSE CSP (Multiply SEgmented Constraint Satisfaction Problem) [5, 61 is an extension to the constraint satisfaction problem (CSP) which is especially useful for problems that segment into riultiple instances of CSP that share variables. In Belzerman and Harper [6], the concepts of MUSE node, arc, and path consistency were defined and algorithms for MUSE arc consistency, MUSE AC-1, and MUSE path consistency were developed. MUSE AC-1 is similar to the CSP arc consistency algorithm AC-4 [ l j ] ...

  14. Programming ArcGIS with Python cookbook

    CERN Document Server

    Pimpler, Eric

    2015-01-01

    Programming ArcGIS with Python Cookbook, Second Edition, is written for GIS professionals who wish to revolutionize their ArcGIS workflow with Python. Whether you are new to ArcGIS or a seasoned professional, you almost certainly spend time each day performing various geoprocessing tasks. This book will teach you how to use the Python programming language to automate these geoprocessing tasks and make you a more efficient and effective GIS professional.

  15. Geochemistry and Nd-Sr Isotopic Signatures of the Pensamiento Granitoid Complex, Rondonian-San Ignacio Province, Eastern Precambrian Shield of Bolivia: Petrogenetic Constraints for a Mesoproterozoic Magmatic Arc Setting

    Directory of Open Access Journals (Sweden)

    Ramiro Matos

    2009-06-01

    Full Text Available The Pensamiento Granitoid Complex (PGC, located in the northern part of the eastern Precambrian shield of Bolivia, istectonically assigned to the Rondonian-San Ignacio Province (1.55 - 1.30 Ga of the Amazonian Craton that is made up byArchean and Proterozoic provinces. The Proterozoic ones result from accretionary orogens that become successively youngersouthwestwards, such as the Rondonian/San Ignacio (1.37 - 1.32 Ga and the Sunsás orogenies (1.20 - 1.00 Ga. The PGCcrops out mainly on the “Paragua craton” bounded to the south by the Sunsás belt, and composed of granites and subvolcanicterms, and subordinately of syenites, granodiorites, tonalites, trondhjemites and diorites as orogenic representatives of theRondonian/San Ignacio Orogeny, intrusive into the Lomas Maneches (ca. 1.68 Ga and Chiquitania (ca. 1.7 Ga complexes.Thirteen whole rock chemical analyses for major, trace and REE elements were performed for the La Junta, San Martín, Diamantina,Porvernir, San Cristobal, Piso Firme plutons of the PGC. The negative trends of MgO, Al2O3 and CaO contents withincreasing SiO2 suggest that fractional crystallization played an important role in the petrogenesis of the investigated rocks.The data also indicate a mainly peraluminous, sub-alkaline to high-K calc-alkaline composition, and fractionated LREE/HREE patterns are consistent with a magmatic arc character for these plutons. SHRIMP U-Pb zircon ages of the La Junta andSan Martín syn- to late-kinematic plutons are 1347 ± 21 Ma and 1373 ± 20 Ma respectively, and the Sm-Nd TDM model agesare between 1.9 to 2.0 Ga, while εNd(1330 values range from +1.8 to -4.3, respectively. In addition, the late- to post-kinematicDiamantina pluton yields SHRIMP U-Pb zircon age of 1340 ± 20 Ma, and variable Sm-Nd TDM model ages (1.6 to 1.9 Ga andεNd(1330 values (+0.4 to -1.2 that are comparable with previous results found for other coeval plutons. The Porvenir, San Cristobaland Piso Firme plutons show ε

  16. Effect of Gravity on Arc Shape in GTA Welding-for Low Electric Arc Current

    Institute of Scientific and Technical Information of China (English)

    Hidetoshi FUJII; Yosuke SUMI; Manabu TANAKA; Kiyoshi NOGI

    2003-01-01

    Gas tungsten arc (GTA) welding was performed both in a microgravity environment and in a terrestrial environment,and the arc shapes in both environments were compared. A microgravity condition was obtained using the free fallsystem at the Japan Microgravi

  17. Diffuse and spot mode of cathode arc attachments in an atmospheric magnetically rotating argon arc

    International Nuclear Information System (INIS)

    A model including the cathode, near-cathode region, and arc column was constructed. Specifically, a thermal perturbation layer at the arc fringe was calculated in order to couple sheath/presheath modelling with typical arc column modelling. Comparative investigation of two modes of attachment of a dc (100, 150, 200 A) atmospheric-pressure arc in argon to a thermionic cathode made of pure tungsten was conducted. Computational data revealed that there exists two modes of arc discharge: the spot mode, which has an obvious cathode surface temperature peak in the arc attachment centre; and the diffuse mode, which has a flat cathode surface temperature distribution and a larger arc attachment area. The modelling results of the arc attachment agree with previous experimental observations for the diffuse mode. A further 3D simulation is obviously needed to investigate the non-axisymmetrical features, especially for the spot mode. (paper)

  18. Subduction Controls of Hf and Nd Isotopes in Lavas of the Aleutian Island Arc

    Energy Technology Data Exchange (ETDEWEB)

    Yogodzinski, Gene; Vervoort, Jeffery; Brown, Shaun Tyler; Gerseny, Megan

    2010-08-29

    trench east of the Amlia Fracture Zone, which is being subducting beneath the arc at Seguam Island. Mixing trends between mantle wedge and sediment end members become flatter in Hf-Nd isotope space at locations further west along the arc, indicating that the sediment end member in the west has either higher Nd/Hf or is more radiogenic in Hf compared to Nd. This pattern is interpreted to reflect an increase in pelagic clay relative to the terrigenous subducted sedimentary component westward along the arc. Results of this study imply that Hf does not behave as a conservative element in the Aleutian subduction system, as has been proposed for some other arcs.

  19. Major arcs for Goldbach's problem

    OpenAIRE

    Helfgott, H. A.

    2013-01-01

    The ternary Goldbach conjecture states that every odd number $n\\geq 7$ is the sum of three primes. The estimation of the Fourier series $\\sum_{p\\leq x} e(\\alpha p)$ and related sums has been central to the study of the problem since Hardy and Littlewood (1923). Here we show how to estimate such Fourier series for $\\alpha$ in the so-called major arcs, i.e., for $\\alpha$ close to a rational of small denominator. This is part of the author's proof of the ternary Goldbach conjecture. In contrast ...

  20. Understanding the nature of mantle upwelling beneath East-Africa

    Science.gov (United States)

    Civiero, Chiara; Hammond, James; Goes, Saskia; Ahmed, Abdulhakim; Ayele, Atalay; Doubre, Cecile; Goitom, Berhe; Keir, Derek; Kendall, Mike; Leroy, Sylvie; Ogubazghi, Ghebrebrhan; Rumpker, Georg; Stuart, Graham

    2014-05-01

    The concept of hot upwelling material - otherwise known as mantle plumes - has long been accepted as a possible mechanism to explain hotspots occurring at Earth's surface and it is recognized as a way of removing heat from the deep Earth. Nevertheless, this theory remains controversial since no one has definitively imaged a plume and over the last decades several other potential mechanisms that do not require a deep mantle source have been invoked to explain this phenomenon, for example small-scale convection at rifted margins, meteorite impacts or lithospheric delamination. One of the best locations to study the potential connection between hotspot volcanism at the surface and deep mantle plumes on land is the East African Rift (EAR). We image seismic velocity structure of the mantle below EAR with higher resolution than has been available to date by including seismic data recorded by stations from many regional networks ranging from Saudi Arabia to Tanzania. We use relative travel-time tomography to produce P- velocity models from the surface down into the lower mantle incorporating 9250 ray-paths in our model from 495 events and 402 stations. We add smaller earthquakes (4.5 poorly sampled regions in order to have a more uniform data coverage. The tomographic results allow us to image structures of ~ 100-km length scales to ~ 1000 km depth beneath the northern East-Africa rift (Ethiopia, Eritrea, Djibouti, Yemen) with good resolution also in the transition zone and uppermost lower mantle. Our observations provide evidence that the shallow mantle slow seismic velocities continue trough the transition zone and into the lower mantle. In particular, the relatively slow velocity anomaly beneath the Afar Depression extends up to depths of at least 1000 km depth while another low-velocity anomaly beneath the Main Ethiopian Rift seems to be present in the upper mantle only. These features in the lower mantle are isolated with a diameter of about 400 km indicating deep

  1. Generalized hyperfocused arcs in $PG(2,p)$

    OpenAIRE

    Blokhuis, A Aart; Marino, G.; Mazzocca, F.

    2013-01-01

    A {\\em generalized hyperfocused arc} $\\mathcal H $ in $PG(2,q)$ is an arc of size $k$ with the property that the $k(k-1)/2$ secants can be blocked by a set of $k-1$ points not belonging to the arc. We show that if $q$ is a prime and $\\mathcal H$ is a generalized hyperfocused arc of size $k$, then $k=1,2$ or 4. Interestingly, this problem is also related to the (strong) cylinder conjecture [Ball S.: The polynomial method in Galois geometries, in Current research topics in Galois geometry, Chap...

  2. Electrode Evaporation Effects on Air Arc Behavior

    Institute of Scientific and Technical Information of China (English)

    LI Xingwen; CHEN Degui; LI Rui; WU Yi; NIU Chunping

    2008-01-01

    A numerical study of the effects of copper and silver vapours on the air arc behavior is performed. The commercial software FLUENT is adapted and modified to develop a two-dimensional magneto-hydrodynamic (MHD) models of arc with the thermodynamic properties and transport coefficients, net emission coefficient for the radiation model of 99% ai-1% Cu, 99% air-1% Ag, and pure air, respectively. The simulation result demonstrates that vaporization of the electrode material may cool the arc center region and reduce the arc velocity. The effects of Ag vapour are stronger compared to those of Cu vapour.

  3. Stability of alternating current gliding arcs

    DEFF Research Database (Denmark)

    Kusano, Yukihiro; Salewski, Mirko; Leipold, Frank;

    2014-01-01

    A gliding arc is a quenched plasma that can be operated as a non-thermal plasma at atmospheric pressure and that is thus suitable for large-scale plasma surface treatment. For its practical industrial use the discharge should be extended stably in ambient air. A simple analytical calculation based...... on Ohm’s law indicates that the critical length of alternating current (AC) gliding arc discharge columns can be larger than that of a corresponding direct current (DC) gliding arc. This finding is supported by previously published images of AC and DC gliding arcs. Furthermore, the analysis shows...

  4. The Abundance of Large Arcs From CLASH

    Science.gov (United States)

    Xu, Bingxiao; Postman, Marc; Meneghetti, Massimo; Coe, Dan A.; Clash Team

    2015-01-01

    We have developed an automated arc-finding algorithm to perform a rigorous comparison of the observed and simulated abundance of large lensed background galaxies (a.k.a arcs). We use images from the CLASH program to derive our observed arc abundance. Simulated CLASH images are created by performing ray tracing through mock clusters generated by the N-body simulation calibrated tool -- MOKA, and N-body/hydrodynamic simulations -- MUSIC, over the same mass and redshift range as the CLASH X-ray selected sample. We derive a lensing efficiency of 15 ± 3 arcs per cluster for the X-ray selected CLASH sample and 4 ± 2 arcs per cluster for the simulated sample. The marginally significant difference (3.0 σ) between the results for the observations and the simulations can be explained by the systematically smaller area with magnification larger than 3 (by a factor of ˜4) in both MOKA and MUSIC mass models relative to those derived from the CLASH data. Accounting for this difference brings the observed and simulated arc statistics into full agreement. We find that the source redshift distribution does not have big impact on the arc abundance but the arc abundance is very sensitive to the concentration of the dark matter halos. Our results suggest that the solution to the "arc statistics problem" lies primarily in matching the cluster dark matter distribution.

  5. Metals purification by improved vacuum arc remelting

    Science.gov (United States)

    Zanner, Frank J.; Williamson, Rodney L.; Smith, Mark F.

    1994-12-13

    The invention relates to improved apparatuses and methods for remelting metal alloys in furnaces, particularly consumable electrode vacuum arc furnaces. Excited reactive gas is injected into a stationary furnace arc zone, thus accelerating the reduction reactions which purify the metal being melted. Additionally, a cooled condensation surface is disposed within the furnace to reduce the partial pressure of water in the furnace, which also fosters the reduction reactions which result in a purer produced ingot. Methods and means are provided for maintaining the stationary arc zone, thereby reducing the opportunity for contaminants evaporated from the arc zone to be reintroduced into the produced ingot.

  6. New U-Pb ages and lithochemical attributes of the Ediacaran Rio Doce magmatic arc, Araçuaí confined orogen, southeastern Brazil

    Science.gov (United States)

    Gonçalves, Leonardo; Farina, Federico; Lana, Cristiano; Pedrosa-Soares, Antônio C.; Alkmim, Fernando; Nalini, Hermínio A.

    2014-07-01

    The Araçuaí orogen of southeastern Brazil, together with its counterpart located in Africa, the West Congo belt, formed through closure of a gulf connected to the Adamastor Ocean by the end of the Ediacaran and beginning of the Cambrian. Convergence of the margins of the gulf led to the development of the Rio Doce magmatic arc between 630 Ma and 580 Ma on a continental basement mostly composed of Rhyacian orthogneisses. The Rio Doce arc mainly consists of tonalite-granodiorite batholiths, generally crowded with mafic to dioritic enclaves, and minor gabbronorite-enderbite-charnockite plutons, suggesting mixing processes involving crustal and mantle sources. We investigate the basement, magma sources and emplacement ages of the Rio Doce arc. Our data suggest the arc comprises three main granitic rock groups: i) Opx-bearing rocks mostly of enderbite to charnockite composition; ii) enclave-rich tonalite-granodiorite (ETG); and iii) enclave-poor granite-granodiorite with minor tonalite (GT). The Opx-bearing rocks are magnesian, calc-alkalic to alkali-calcic and metaluminous. Together, the ETG and GT rock groups range in composition from tonalite to granite, are metaluminous to slightly peraluminous, show a predominantly medium- to high-K, expanded calc-alkaline signature, and other geochemical and isotopic attributes typical of a pre-collisional volcanic arc formed on a continental margin setting. Mineralogical, chemical, and geochronological data suggest the involvement of HT-melting of granulitic (H2O-depleted) sources of Rhyacian age for the generation of Opx-bearing granitic rocks, additionally to magma mixing and fractional crystallization processes. In conclusion, the studied rock groups of the Rio Doce arc were likely formed by interactions of mantle and crustal processes, in an active continental margin setting. These processes involved ascent of mantle magmas that induced partial melting on the continental basement represented by the Rhyacian gneisses.

  7. Unstable behavior of anodic arc discharge for synthesis of nanomaterials

    Science.gov (United States)

    Gershman, Sophia; Raitses, Yevgeny

    2016-09-01

    A short carbon arc operating with a high ablation rate of the graphite anode exhibits a combined motion of the arc and the arc attachment to the anode. A characteristic time scale of this motion is in a 10‑3 s range. The arc exhibits a negative differential resistance before the arc motion occurs. Thermal processes in the arc plasma region interacting with the ablating anode are considered as possible causes of this unstable arc behavior. It is also hypothesized that the arc motion could potentially cause mixing of the various nanoparticles synthesized in the arc in the high ablation regime.

  8. A comparison of the seismic structure of oceanic island arc crust and continental accreted arc terranes

    Science.gov (United States)

    Calvert, A. J.

    2015-12-01

    Amalgamation of island arcs and their accretion to pre-existing continents is considered to have been one of the primary mechanisms of continental growth over the last 3 Ga, with arc terranes identified within Late Archean, Proterozoic, and Phanerozoic continental crust. Crustal-scale seismic refraction surveys can provide P wave velocity models that can be used as a proxy for crustal composition, and although they indicate some velocity variation in accreted arcs, these terranes have significantly lower velocities, and are hence significantly more felsic, than modern island arcs. Modern oceanic arcs exhibit significant variations in crustal thickness, from as little as 10 km in the Bonin arc to 35 km in the Aleutian and northern Izu arcs. Although globally island arcs appear to have a mafic composition, intermediate composition crust is inferred in central America and parts of the Izu arc. The absence of a sharp velocity contrast at the Moho appears to be a first order characteristic of island arc crust, and indicates the existence of a broad crust-mantle transition zone. Multichannel seismic reflection surveys complement refraction surveys by revealing structures associated with variations in density and seismic velocity at the scale of a few hundred meters or less to depths of 60 km or more. Surveys from the Mariana and Aleutian arcs show that modern middle and lower arc crust is mostly non-reflective, but reflections are observed from depths 5-25 km below the refraction Moho suggesting the localized presence of arc roots that may comprise gabbro, garnet gabbro, and pyroxenite within a broad transition from mafic lower crust to ultramafic mantle. Such reflective, high velocity roots are likely separated from the overlying arc crust prior to, or during arc-continent collision, and seismic reflections within accreted arc crust document the collisional process and final crustal architecture.

  9. Micro-arcing and arc erosion minimization using a DC hybrid switching device

    OpenAIRE

    Swingler, J.; McBride, J. W.

    2008-01-01

    Hybrid switching devices utilize the advantages of both conventional electrical contacts and solid state electronics to minimize arcing during opening and closing operations. This can result in higher reliability and reduces the need for high cost specialist contact materials. The hybrid switch does not eliminate arcing completely, due to the inductive nature of circuits; micro-arcing is known to occur. An experimental dc hybrid switching device is introduced which minimizes arcing for 42 ...

  10. Chronological and geochemical studies of granite and enclave in Baimashan pluton, Hunan, South China

    Institute of Scientific and Technical Information of China (English)

    CHEN; WeiFeng; CHEN; PeiRong; HUANG; HongYe; DING; Xing; SUN; Tao

    2007-01-01

    Zircon LA-ICP-MS U-Pb dating reveals that the Baimashan Pluton is composed mainly of late Indosinian (204.5±2.8 Ma-209.2±3.8 Ma) biotite granodiorites/monzonitic granites (LIGs) and early Yanshanian (176.7±1.7 Ma) two-micas monzonitic granites (EYGs),and the coeval (203.2±4.5 Ma-205.1±3.9 Ma) mafic microgranular enclaves (MMEs) are generally found in the former.In addition,the ages of cores within zircons from LIGs and MMEs ranging from 221.4±4.0 Ma to 226.5±4.1Ma provide evidence of multistage magma intrusion during Indosinian in the study area.Measured 3010±20.6 Ma of inherited zircon age suggests that there may be recycling Archaean curstal material in existence in this area.LIGs and EYGs share some similar geochemical features: subalkaline and peraluminous granites,enrichment of Th,U,K,Ta,Zr,Hf and LREE but depletion of Ba,Nb,P,Ti and Eu,low εNd(t) values but high (87Sr/86Sr)i ratios,and old T2DM (ca.1.9-2.0 Ga).The behaviors of incompatible elements and REE are mainly dominated by fractional crystallization of plagioclase,K-feldspar,ilmenite and apatite,but that of Sr isotope mainly controlled by EC-AFC.They are crust-sourced and derived from partial melting of paleo-Proterozoic metagreywackes and related to biotite dehydration melting.LIGs are formed in post-collisional tectonic setting as crustal local extension and thinning during late Indosinian.But EYGs may be evolved products of congeneric granitic magma with LIGs formed in late Indoinian,which were emplaced again when crust underwent extensive thinning and extension in post-orogenic tectonic setting during Yanshanian in SC after undergoing EC-AFC.MMEs should be cognate enclaves and derived from liquid immiscibility of host magma.

  11. Feedback Linearization Based Arc Length Control for Gas Metal Arc Welding

    DEFF Research Database (Denmark)

    Thomsen, Jesper Sandberg

    2005-01-01

    In this paper a feedback linearization based arc length controller for gas metal arc welding (GMAW) is described. A nonlinear model describing the dynamic arc length is transformed into a system where nonlinearities can be cancelled by a nonlinear state feedback control part, and thus, leaving only...

  12. Isotopic characteristics (Nd and Sr) of the intrusive plutonism at the northwestern Amazonian Craton, Venezuela, and implications for the Paleoproterozoic evolution

    International Nuclear Information System (INIS)

    Nd and Sr analyses were performed on selected granitoid plutons that intrude Archean and Paleoproterozoic domains of the Guyana shield (Venezuela). The isotopic signatures of these plutons together with the geochronologic background of the country rocks are used to constrain their magma genesis and tectonic setting within the Paleoproterozoic evolutions of mobile belts (Maroni-Itacaiunas and Ventuari-Tapajos provinces) of the Amazonian Craton. The Encrucijada Suite (2187 +- 94 Ma), which intrudes Archean rocks of the Imataca Complex, originated predominantly from partial melt of this crust, as supported by negative epsilonNd(2.1Ga) values (-2.2 to - 4.9) and TDM ages between 2.82 and 2.49 Ga. Conversely, the plutons from the Supamo Complex (2230 - 2050 Ma) and Cuchivero Group (1980 - 1830 Ma), occurring within the adjoining Paleoproterozoic provinces, are juvenile in nature (derived from roughly contemporary protoliths). These bodies display TDM ages between 2.13 and 2.22 Ga, as well as positive epsilonNd(2.1Ga) values (+0.74 to + 3.05). Isotopic correlation diagrams 143 Nd/144 Nd vs. 147 Sm/144 Nd and 143 Nd/144 Nd vs. time) plotted together with the plutonic rocks and Imataca Complex rocks were evaluated taking into account the geologic background of the NW part of the Amazonian Craton. Interpretation of these isotopic data supports the idea of tectonic juxtaposition between the Imataca Complex and the Maroni-Itacaiunas province during the Transamazonian orogeny (2.25 - 2.05 Ga). On the other hand, the Cuchivero Group plutons have a contrasting isotopic signature compared to the other Paleoproterozoic plutonic rocks. This is consistent with the existence of a tectonic boundary between the Maroni-Itacaiunas and the Ventuari-Tapajos province in the late Paleoproterozoic. (author)

  13. Geology and metallogeny of the Ar Rayn terrane, eastern Arabian shield: Evolution of a Neoproterozoic continental-margin arc during assembly of Gondwana within the East African orogen

    Science.gov (United States)

    Doebrich, J.L.; Al-Jehani, A. M.; Siddiqui, A.A.; Hayes, T.S.; Wooden, J.L.; Johnson, P.R.

    2007-01-01

    The Neoproterozoic Ar Rayn terrane is exposed along the eastern margin of the Arabian shield. The terrane is bounded on the west by the Ad Dawadimi terrane across the Al Amar fault zone (AAF), and is nonconformably overlain on the east by Phanerozoic sedimentary rocks. The terrane is composed of a magmatic arc complex and syn- to post-orogenic intrusions. The layered rocks of the arc, the Al Amar group (>689 Ma to ???625 Ma), consist of tholeiitic to calc-alkaline basaltic to rhyolitic volcanic and volcaniclastic rocks with subordinate tuffaceous sedimentary rocks and carbonates, and are divided into an eastern and western sequence. Plutonic rocks of the terrane form three distinct lithogeochemical groups: (1) low-Al trondhjemite-tonalite-granodiorite (TTG) of arc affinity (632-616 Ma) in the western part of the terrane, (2) high-Al TTG/adakite of arc affinity (689-617 Ma) in the central and eastern part of the terrane, and (3) syn- to post-orogenic alkali granite (607-583 Ma). West-dipping subduction along a trench east of the terrane is inferred from high-Al TTG/adakite emplaced east of low-Al TTG. The Ar Rayn terrane contains significant resources in epithermal Au-Ag-Zn-Cu-barite, enigmatic stratiform volcanic-hosted Khnaiguiyah-type Zn-Cu-Fe-Mn, and orogenic Au vein deposits, and the potential for significant resources in Fe-oxide Cu-Au (IOCG), and porphyry Cu deposits. Khnaiguiyah-type deposits formed before or during early deformation of the Al Amar group eastern sequence. Epithermal and porphyry deposits formed proximal to volcanic centers in Al Amar group western sequence. IOCG deposits are largely structurally controlled and hosted by group-1 intrusions and Al Amar group volcanic rocks in the western part of the terrane. Orogenic gold veins are largely associated with north-striking faults, particularly in and near the AAF, and are presumably related to amalgamation of the Ar Rayn and Ad Dawadimi terranes. Geologic, structural, and metallogenic

  14. Increasing the arc efficiency by the removal of arc electromagnetic blowing in electric arc furnaces: I. Effect of electromagnetic blowing and the slag height on the arc efficiency in an electric arc furnace

    Science.gov (United States)

    Makarov, A. N.; Sokolov, A. Yu.; Lugovoi, Yu. A.

    2012-06-01

    The effect of electromagnetic blowing and the slag layer height on the arc efficiency is analytically studied. An arc is blown from under an electrode toward the furnace walls under an electromagnetic force. The arc efficiency of a 100-t high-power electric arc furnace changes from 0.47 to 0.76 when the slag height increases from 0 to 550 mm.

  15. Geochemistry and petrogenesis of anorogenic basic volcanic-plutonic rocks of the Kundal area, Malani Igneous Suite, western Rajasthan, India

    Indian Academy of Sciences (India)

    A Krishnakanta Singh; G Vallinayagam

    2004-12-01

    The Kundal area of Malani Igneous Suite consists of volcano-plutonic rocks. Basalt flows and gabbro intrusives are associated with rhyolite. Both the basic rocks consist of similar mineralogy of plagioclase, clinopyroxene as essential and Fe-Ti oxides as accessories. Basalt displays sub-ophitic and glomeroporphyritic textures whereas gabbro exhibits sub-ophitic, porphyritic and intergrannu- lar textures. They show comparable chemistry and are enriched in Fe, Ti and incompatible ele- ments as compared to MORB/CFB. Samples are enriched in LREE and slightly depleted HREE patterns with least significant positive Eu anomalies. Petrographical study and petrogenetic mod- eling of [Mg]-[Fe], trace and REE suggest cogenetic origin of these basic rocks and they probably derived from Fe-enriched source with higher Fe/Mg ratio than primitive mantle source. Thus, it is concluded that the basic volcano-plutonic rocks of Kundal area are the result of a low to moderate degree (> 30%) partial melting of source similar to picrite/komatiitic composition. Within plate, anorogenic setting for the basic rocks of Kundal area is suggested, which is in conformity with the similar setting for Malani Igneous Suite.

  16. Modeling of the Climax Stock and Related Plutons Based on the Inversion of Magnetic Data, Southwest Nevada

    Science.gov (United States)

    Phelps, Geoffrey A.; Jachens, Robert C.; Moring, Barry C.; Roberts, Carter W.

    2004-01-01

    Two models of the Climax and Gold Meadows stocks were generated using a new method of magnetic inversion modeling based on the pseudogravity anomaly. The first model examined the shape of the two stocks and their connection at depth, concluding that the stocks are connected -4000 m below the ground surface. The second model re-examined the shape and depth of the Climax stock using a two-layer model and new magnetic data collected from drill hole ER-8-1. Existing and new magnetic data support a model of a zoned pluton with increasing magnetization with depth. A model of a zoned pluton was generated and adjusted to fit the magnetic anomaly measured over the stock. The model has an upper layer that extends to a depth of 1,700 m and is magnetized at 0.06 A/m, and a lower layer that extends to a maximum depth of 7,600 m and is magnetized at 0.17 A/m. The model matches the outcrop data, but was unable to match the intercept of the Climax stock from drill hole ER-8-1.

  17. Metamorphic evolution of the contact aureole of the Jhirgadandi pluton, Sonbhadra district,Mahakoshal mobile belt, central India

    Indian Academy of Sciences (India)

    S P Singh; Anand K Srivastava; Gopendra Kumar; S B Dwivedi

    2013-06-01

    The metamorphic evolution of the contact aureole around the Late Paleoproterozoic Jhirgadandi pluton in the eastern part of Parsoi Formation of Mahakoshal terrain, central India represents three distinct metamorphic zones, characterized by definite mineral assemblages. The contact-metamorphic event produced the peak-metamorphic mineral assemblages Bt + Qtz + Alb + Sil ± Cd ± Grt ± Mus ± Kfs in the metapelites of inner aureole, Bt + Qtz + And + Mus + Kfs + Plag ± Cd ± Chl in middle aureole and Chl + Mus + Bt ± And + Alb + Qtz ± Ep + Mt ± tourmaline in the outer aureole. The estimated P–T conditions based on detailed geothermobarometric calculations in the thermal metamorphosed rocks are 690°C/3.4 kbar, 580 ± 15°C and 487 ± 30°C in inner aureole, middle aureole and outer aureole, respectively. The variation in metamorphic condition suggests that the shallow crustal level emplacement of Jhirgadandi pluton is responsible for the overprinting of contact metamorphic assemblages (M2) in the low grade metapelites (regional metamorphism M1) of Mahakoshal Group.

  18. Geochemistry of the Bonin Fore-arc Volcanic Sequence: Results from IODP Expedition 352

    Science.gov (United States)

    Godard, M.; Ryan, J. G.; Shervais, J. W.; Whattam, S. A.; Sakuyama, T.; Kirchenbaur, M.; Li, H.; Nelson, W. R.; Prytulak, J.; Pearce, J. A.; Reagan, M. K.

    2015-12-01

    The Izu-Bonin-Mariana intraoceanic arc system, in the western Pacific, results from ~52 My of subduction of the Pacific plate beneath the eastern margin of the Philippine Sea plate. Four sites were drilled south of the Bonin Islands during IODP Expedition 352 and 1.22 km of igneous basement was cored upslope to the west of the trough. These stratigraphically controlled igneous suites allow study of the earliest stages of arc development from seafloor spreading to convergence. We present the preliminary results of a detailed major and trace element (ICPMS) study on 128 igneous rocks drilled during Expedition 352. Mainly basalts and basaltic andesites were recovered at the two deeper water sites (U1440 and U1441) and boninites at the two westernmost sites (U1439 and U1442). Sites U1440 and U1441 basaltic suites are trace element depleted (e.g. Yb 4-6 x PM); they have fractionated REE patterns (LREE/HREE = 0.2-0.4 x C1-chondrites) compared to mid-ocean ridge basalts. They have compositions overlapping that of previously sampled Fore-Arc Basalts (FAB) series. They are characterized also by an increase in LILE contents relative to neighboring elements up-section (e.g. Rb/La ranging from FAB generation into their mantle source.

  19. Deep Magma Transport beneath Soufriere Hills Volcano, Montserrat, WI: 1995-2007

    Science.gov (United States)

    Elsworth, D.; Mattioli, G.; Taron, J.; Voight, B.; Herd, R.; Foroozan, R.

    2009-04-01

    Magma melting and transport produces a complex architecture of connected magmatic systems present beneath many arc volcanoes. Although melt supplied by subduction may be considered constant over very long timescales (>Ma), rates of magma transport and eruptive episodes are episodic at timescales encompassing millennia and centuries to hours. A variety of mechanisms act at these various timescales; in general longer periodicities imply controlling processes rooted at greater depth and involving reservoirs of increasing volumes. Here we use histories of magma efflux and surface deformation to quantitatively constrain magma transfer into and within the deep (>12 km) crustal plumbing of the Soufrière Hills volcano over a 12-year eruptive cycle of active effusion punctuated by discrete pauses. For three cycles of effusion followed by pause, with a periodicity of 4-6 years, deep supply to the system is continuous and never drops below ~0.5-1 m3/s; this minimum supply is similar in magnitude to both the mean measured eruptive efflux (including pauses) (~0.7 m3/s) and the mass accumulation due to crustal convergence (~0.6 m3/s). Deep fluxes rise synchronously from this background magnitude in times of active eruption (~1-5 m3/s), are augmented by deflation (~1-2 m3/s) of a reservoir centered at ~12 km, and pass through an upper magmatic reservoir. An eruptive pause is marked by a decrease in supply from the deep crust, fully accommodated as the deep reservoir switches to reinflate, and with no resulting supply to the shallow crust. For a two-reservoir model, these observations implicate the deep system in controlling short-term (~3-5 yr) eruptive periodicity. They are consistent with a model involving the continuous supply of magma from the deep crust/mantle into a voluminous and compliant deep reservoir, episodically-valved below the shallow reservoir.

  20. P wave tomography and anisotropy beneath Southeast Asia: Insight into mantle dynamics

    Science.gov (United States)

    Huang, Zhouchuan; Zhao, Dapeng; Wang, Liangshu

    2015-07-01

    Southeast Asia is surrounded by subduction zones resulting from the interactions of several lithospheric plates. Its evolution has been also influenced by active tectonics due to the Indo-Asian collision in the Cenozoic. In this study, we use a large number of arrival-time data of local and regional earthquakes to determine 3-D P wave tomography and azimuthal anisotropy in the mantle beneath SE Asia. High-velocity (high-V) anomalies representing the subducting slabs are clearly visible in the upper mantle and the mantle transition zone (MTZ). Low-velocity (low-V) zones with trench-normal anisotropy are revealed in the uppermost mantle, which indicate back-arc spreading or secondary mantle-wedge flow induced by the slab subduction. In contrast, trench-parallel anisotropy dominates in the deep upper mantle and reflects structures either in the subducting slab or in the upper mantle surrounding the slab. The trench-parallel anisotropy is also significant in the lower MTZ, which may contribute to shear wave splitting observations. A low-V body extending down to the lower mantle is visible under the Hainan volcano far away from the plate boundaries, suggesting that Hainan is a hot spot fed by a lower-mantle plume. The low-V body under Hainan is connected with low-V zones in the upper mantle under SE Tibet and Vietnam. Our P wave anisotropy results reflect significant mantle flow existing in the asthenosphere from SE Tibet to Hainan and further southwestward to Vietnam. The present study, especially the 3-D P wave anisotropy results, provides important new insight into mantle dynamics in SE Asia.

  1. Risk assessment of metal vapor arcing

    Science.gov (United States)

    Hill, Monika C. (Inventor); Leidecker, Henning W. (Inventor)

    2009-01-01

    A method for assessing metal vapor arcing risk for a component is provided. The method comprises acquiring a current variable value associated with an operation of the component; comparing the current variable value with a threshold value for the variable; evaluating compared variable data to determine the metal vapor arcing risk in the component; and generating a risk assessment status for the component.

  2. Characterization of Micro-arc Oxidized Titanium

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    The observation of the sparkling discharges during the micro-arc oxidation process in KOH aqueous electrolyte was achieved. The change of surface morphology was progressively observed and a plausible pore formation mechanism is proposed. Cell proliferation and ALP activity of micro-arc oxidized titanium was evaluated by human body derived osteoblasts and slightly better than those of blasted surface.

  3. The next-generation ARC middleware

    DEFF Research Database (Denmark)

    Appleton, O.; Cameron, D.; Cernak, J.;

    2010-01-01

    The Advanced Resource Connector (ARC) is a light-weight, non-intrusive, simple yet powerful Grid middleware capable of connecting highly heterogeneous computing and storage resources. ARC aims at providing general purpose, flexible, collaborative computing environments suitable for a range of use...

  4. Plasma Arc Augmented CO2 laser welding

    DEFF Research Database (Denmark)

    Bagger, Claus; Andersen, Mikkel; Frederiksen, Niels;

    2001-01-01

    In order to reduce the hardness of laser beam welded 2.13 mm medium strength steel CMn 250, a plasma arc has been used simultaneously with a 2.6 kW CO2 laser source. In a number of systematic laboratory tests, the plasma arc current, plasma gas flow and distance to the laser source were varied wi...

  5. Implementing RapidArc into clinical routine

    DEFF Research Database (Denmark)

    Van Esch, Ann; Huyskens, Dominique P; Behrens, Claus F;

    2011-01-01

    With the increased commercial availability of intensity modulated arc therapy (IMAT) comes the need for comprehensive QA programs, covering the different aspects of this newly available technology. This manuscript proposes such a program for the RapidArc (RA) (Varian Medical Systems, Palo Alto) I...

  6. Evidence for dike emplacement beneath Iliamna Volcano, Alaska in 1996

    Science.gov (United States)

    Roman, D.C.; Power, J.A.; Moran, S.C.; Cashman, K.V.; Doukas, M.P.; Neal, C.A.; Gerlach, T.M.

    2004-01-01

    Two earthquake swarms, comprising 88 and 2833 locatable events, occurred beneath Iliamna Volcano, Alaska, in May and August of 1996. Swarm earthquakes ranged in magnitude from -0.9 to 3.3. Increases in SO2 and CO2 emissions detected during the fall of 1996 were coincident with the second swarm. No other physical changes were observed in or around the volcano during this time period. No eruption occurred, and seismicity and measured gas emissions have remained at background levels since mid-1997. Earthquake hypocenters recorded during the swarms form a cluster in a previously aseismic volume of crust located to the south of Iliamna's summit at a depth of -1 to 4 km below sea level. This cluster is elongated to the NNW-SSE, parallel to the trend of the summit and southern vents at Iliamna and to the regional axis of maximum compressive stress determined through inversion of fault-plane solutions for regional earthquakes. Fault-plane solutions calculated for 24 swarm earthquakes located at the top of the new cluster suggest a heterogeneous stress field acting during the second swarm, characterized by normal faulting and strike-slip faulting with p-axes parallel to the axis of regional maximum compressive stress. The increase in earthquake rates, the appearance of a new seismic volume, and the elevated gas emissions at Iliamna Volcano indicate that new magma intruded beneath the volcano in 1996. The elongation of the 1996-1997 earthquake cluster parallel to the direction of regional maximum compressive stress and the accelerated occurrence of both normal and strike-slip faulting in a small volume of crust at the top of the new seismic volume may be explained by the emplacement and inflation of a subvertical planar dike beneath the summit of Iliamna and its southern satellite vents. ?? 2003 Elsevier B.V. All rights reserved.

  7. A magmatic probe of dynamic topography beneath western North America

    Science.gov (United States)

    Klöcking, M.; White, N. J.; Maclennan, J.

    2014-12-01

    A region centered on the Yellowstone hotspot and encompassing the Colorado Plateau sits at an elevation 2 km higher than the cratonic North America. This difference broadly coincides with tomographically observed variations in lithospheric thickness: ~120 km beneath western North America, ~240 km beneath the craton. Thermochronology of the Grand Canyon area, sedimentary flux to the Gulf of Mexico, and river profile inversion all suggest that regional uplift occurred in at least two separate stages. High resolution seismic tomographic models, using USArray data, have identified a ring of low velocity material beneath the edges of the Colorado Plateau. Magmatism coincides with these low velocity zones and shows distinct phases: an overall increase in volume around 40 Ma and a change from lithospheric to asthenospheric signatures around 5 Ma. Volcanism is also observed to migrate north-east with time. Here, we attempt to integrate these different observations with lithospheric thickness. A dynamic topography model of progressive lithospheric erosion over a hot mantle plume might account for uplift as well as the temporal and spatial distribution of magmatism across western North America. Thinning of the lithosphere around the edges of the Colorado Plateau in combination with the hotter mantle potential temperature of a plume could create isostatic and dynamic uplift as well as allowing for melt production. To test this model, we have analysed around 100 samples from volcanic centers across western North America by ICP-MS for rare earth elements (REE). Most of the samples are younger than 5 Ma, and all of them have previously been analysed by XRF. Using trace element ratios such as La/Yb and Nb/Y we assess depth of melting and melt fraction, respectively. In addition, we use REE inversion modelling to estimate melt fractions as a function of depth and temperature of melting. The results are compared to existing constraints on lithospheric thickness and mantle potential

  8. Microearthquake seismicity and fault plane solutions related to arc-continent collision in the Eastern Sunda Arc, Indonesia

    Science.gov (United States)

    McCaffrey, Robert; Molnar, Peter; Roecker, Steven W.; Joyodiwiryo, Yoko S.

    1985-05-01

    The collision of Australia with the eastern Sunda and Banda arcs of Indonesia represents a modern example of the early stages of arc-continent collision. In order to obtain a more detailed view of the tectonics of the collision zone, a microearthquake survey was conducted around the Savu Sea, the region that encompasses the transition from subduction of Indian Ocean lithosphere on the west to collision or subduction of Australian continental lithosphere on the east. Intermediate depth earthquakes were concentrated near Pantar Island, the easternmost active volcano of the Sunda arc, and outline a northwest dipping zone that strikes N65°E from 70 to 150 km depth. The seismic zone probably marks the western edge of the collision zone and its more northerly strike, and the orientations of nodal planes from fault plane solutions indicate a 25° bend in the subducted slab to a depth of at least 150 km. Because the convergence rate and the timing of collision from geologic observations on Timor suggest that the part of the slab now at 150 km depth was at the trench when Australia first collided with Timor, we infer that continental crust (or at least rifted continental margin crust) caused the bend in the convergent margin and has been subducted to 150 km depth. Fault plane solutions of several events show nearly vertical nodal planes that trend parallel to the strike of the seismic zone, along which a northwest-side-down sense of displacement is indicated: these events are concentrated at the southern (top) side of the seismic zone and suggest that the subducted lithosphere is presently detaching in the 50-100 km depth range beneath the eastern Savu Sea. Fault plane solutions for earthquakes within the upper part of the detaching slab (70-100 km depth) have P and T axes whose trends lie parallel to the strike of the seismic zone and horizontal, southeast trending B axes. These earthquakes are interpreted as due to stresses caused by the bend in the subducting plate.

  9. Zircon U–Pb geochronology and geochemistry of rhyolitic tuff, granite porphyry and syenogranite in the Lengshuikeng ore district, SE China: Implications for a continental arc to intra-arc rift setting

    Indian Academy of Sciences (India)

    Changming Wang; Da Zhang; Ganguo Wu; Yigan Xu; Emmanuel John M Carranza; Yaoyao Zhang; Huaikun Li; Jianzhen Geng

    2013-06-01

    SE China is well known for its Mesozoic large-scale granitoid plutons and associated ore deposits. Here, zircon U–Pb geochronological and geochemical data have been used to better constrain the petrogenesis of the igneous rocks associated with porphyry Ag–Pb–Zn deposits in the Lengshuikeng ore district, SE China. The Lengshuikeng rhyolitic tuff, granite porphyry and syenogranite yielded zircon U–Pb ages of 161, 155 and 138 Ma, respectively. The Lengshuikeng granite porphyries belong to calc-alkaline series and show fractionated I-type affinities. The rhyolitic tuffs show almost similar characteristics as the granite porphyries. The engshuikeng syenogranites are all alkali-rich and show A-type affinities. The syenogranites have high contents of high field strength elements such as Nb, Ta, Zr, Hf; with Zr + Nb + Ce + Y contents of < 350 ppm. Chondrite-normalized REE patterns show relative enrichment of LREEs and strong negative Eu anomalies. The Lengshuikeng granite porphyries, syenogranites and tuffs were probably derived from partial melting of underlying Proterozoic metasedimentary rocks with minor addition of mantle-derived magmas, accompanied by fractional crystallization. Detailed petrologic and geochemical data for the Jurassic igneous rocks from the Lengshuikeng ore district imply that during the Late Jurassic, SE China on the southeast of the Shi-Hang zone was a continental arc associated with the subduction of the Palaeo-Pacific plate and that since the beginning of the Early Cretaceous an intra-arc rift has been formed along the Shi-Hang zone.

  10. Numerical Study on Arc Plasma Behavior During Arc Commutation Process in Direct Current Circuit Breaker

    Institute of Scientific and Technical Information of China (English)

    杨飞; 马瑞光; 吴翊; 孙昊; 纽春萍; 荣命哲

    2012-01-01

    This paper focuses on the numerical investigation of arc plasma behavior during arc commutation process in a medium-voltage direct current circuit breaker (DCCB) contact system. A three-dimensional magneto-hydrodynamic (MHD) model of air arc plasma in the contact system of a DCCB is developed, based on commercial software FLUENT. Coupled electromagnetic and gas dynamic interactions are considered as usual, and a thin layer of nonlinear electrical resistance elements is used to represent the voltage drop of plasma sheath and the formation of new arc root. The distributions of pressure, temperature, gas flow and current density of arc plasma in arc region are calculated. The simulation results indicate that the pressure distribution related to the contact system has a strong effect on the arc commutation process, arising from the change of electrical conductivity in the arc root region. In DCCB contact system, the pressure of arc root region will be concentrated and higher if the space above the moving contact is enclosed, which is not good for arc root commutation. However, when the region is opened, the pressure distribution would be lower and more evenly, which is favorable for the arc root commutation.

  11. Sensor Control of Robot Arc Welding

    Science.gov (United States)

    Sias, F. R., Jr.

    1983-01-01

    The potential for using computer vision as sensory feedback for robot gas-tungsten arc welding is investigated. The basic parameters that must be controlled while directing the movement of an arc welding torch are defined. The actions of a human welder are examined to aid in determining the sensory information that would permit a robot to make reproducible high strength welds. Special constraints imposed by both robot hardware and software are considered. Several sensory modalities that would potentially improve weld quality are examined. Special emphasis is directed to the use of computer vision for controlling gas-tungsten arc welding. Vendors of available automated seam tracking arc welding systems and of computer vision systems are surveyed. An assessment is made of the state of the art and the problems that must be solved in order to apply computer vision to robot controlled arc welding on the Space Shuttle Main Engine.

  12. Arc flash hazard analysis and mitigation

    CERN Document Server

    Das, J C

    2012-01-01

    "All the aspects of arc flash hazard calculations and their mitigation have been covered. Knowledge of electrical power systems up to undergraduate level is assumed. The calculations of short-circuits, protective relaying and varied electrical system configurations in industrial power systems are addressed. Protection systems address differential relays, arc flash sensing relays, protective relaying coordination, current transformer operation and saturation and applications to major electrical equipments from the arc flash considerations. Current technologies and strategies for arc flash mitigation have been covered. A new algorithm for the calculation of arc flash hazard accounting for the decaying nature of the short-circuit currents is included. There are many practical examples and study cases. Review questions and references follow each chapter"--

  13. The flow beneath a periodic travelling surface water wave

    International Nuclear Information System (INIS)

    We discuss some recent results on the behaviour of the velocity field, pressure and particle trajectories beneath a periodic travelling wave propagating at the surface of water with a flat bed, in a flow without underlying currents. By analysing the governing equations we avoid approximations, thus ensuring the validity of the results without restrictions on the wave amplitude. In particular, the presented approach applies to waves of large amplitude. We also formulate some open problems, venturing into the relatively unexplored field of wave–current interactions. (topical review)

  14. The ionospheric heating beneath the magnetospheric cleft revisited

    Directory of Open Access Journals (Sweden)

    G. W. Prölss

    2005-03-01

    Full Text Available A prominent peak in the electron temperature of the topside ionosphere is observed beneath the magnetospheric cleft. The present study uses DE-2 data obtained in the Northern Winter Hemisphere to investigate this phenomenon. First, the dependence of the location and magnitude of the temperature peak on the magnetic activity is determined. Next, using a superposed epoch analysis, the mean latitudinal profile of the temperature enhancement is derived. The results of the present study are compared primarily with those obtained by Titheridge (1976, but also with more recent observations and theoretical predictions.

  15. On the Turbulence Beneath Finite Amplitude Water Waves

    CERN Document Server

    Babanin, Alexander V

    2015-01-01

    The paper by Beya et al. (2012, hereinafter BPB) has a general title of Turbulence Beneath Finite Amplitude Water Waves, but is solely dedicated to discussing the experiment by Babanin and Haus (2009, hereinafter BH) who conducted measurements of wave-induced non-breaking turbulence by particle image velocimetry (PIV). The authors of BPB conclude that their observations contradict those of BH. Here we argue that the outcomes of BPB do not contradict BH. In addition, although the main conclusion of BPB is that there is no turbulence observed in their experiment, it actually is observed.

  16. Crustal structure beneath China from receiver function analysis

    Science.gov (United States)

    Chen, Youlin; Niu, Fenglin; Liu, Ruifeng; Huang, Zhibin; TkalčIć, Hrvoje; Sun, Li; Chan, Winston

    2010-03-01

    We collected and processed a large amount of high-quality broadband teleseismic waveform data recorded by the 48 Chinese National Digital Seismic Network stations to estimate large-scale lateral variations of crustal thickness and Vp/Vs ratio (hence Poisson's ratio) beneath China. A statistical method was used to select mutually coherent receiver functions at each station, which yielded over 200 traces for most of the stations. With the conventional H-κ (the crustal thickness and Vp/Vs ratio) approach, there is a large trade-off between H and κ. Consequently, multiple maxima are frequently observed in the H-κ domain. We introduced a weight function that measures the coherence between the P-to-S conversion and the reverberation phases at each H-κ grid to reduce the trade-off. A 4th-root stacking method was further applied to reduce uncorrelated noise relative to the linear stack. These modifications turned out to be very effective in reducing the H-κ trade-off and yielded reliable estimates of crustal thickness and Vp/Vs ratio. The crust beneath eastern China is as thin as 31-33 km and the underlying Moho is relatively flat and sharp. In the western part of China, the crust is considerably thicker and shows large variations. The Moho is observed at about 51 km depth along the Tian Shan fold system and about 84 km deep beneath the central part of the Tibetan Plateau. The transition occurs at the so-called N-S belt between about 100° and 110°E, which is featured by unusually high seismicity and large gravity anomalies. The average Vp/Vs ratio over the mainland China crust is about 1.730 (σ = 0.249), significantly lower than the global average 1.78 (σ = 0.27) of the continental crust. This lower Vp/Vs ratio may suggest a general absence of mafic lowermost crustal layer beneath China.

  17. Computer simulation to arc spraying

    Institute of Scientific and Technical Information of China (English)

    梁志芳; 李午申; 王迎娜

    2004-01-01

    The arc spraying process is divided into two stages: the first stage is atomization-spraying stream (ASS) and the second one is spraying deposition (SD). Then study status is described of both stages' physical model and corresponding controlling-equation. Based on the analysis of study status, the conclusion as follows is got. The heat and mass transfer models with two or three dimensions in ASS stage should be established to far deeply analyses the dynamical and thermal behavior of the overheat droplet. The statistics law of overheated droplets should be further studied by connecting simulation with experiments. More proper validation experiments should be designed for flattening simulation to modify the models in SD stage.

  18. ATLAS DDM integration in ARC

    DEFF Research Database (Denmark)

    Behrmann, Gerd; Cameron, David; Ellert, Mattias;

    The Nordic Data Grid Facility (NDGF) consists of Grid resources running ARC middleware in Scandinavia and other countries. These resources serve many virtual organisations and contribute a large fraction of total worldwide resources for the ATLAS experiment, whose data is distributed and managed...... by the DQ2 software. Managing ATLAS data within NDGF and between NDGF and other Grids used by ATLAS (the LHC Computing Grid and the Open Science Grid) presents a unique challenge for several reasons. Firstly, the entry point for data, the Tier 1 centre, is physically distributed among heterogeneous...... resources in several countries and yet must present a single access point for all data stored within the centre. The middleware framework used in NDGF differs significantly from other Grids, specifically in the way that all data movement and registration is performed by services outside the worker node...

  19. ATLAS DDM integration in ARC

    DEFF Research Database (Denmark)

    Behrmann, Gerd; Cameron, David; Ellert, Mattias;

    2008-01-01

    The Nordic Data Grid Facility (NDGF) consists of Grid resources running ARC middleware in Denmark, Finland, Norway and Sweden. These resources serve many virtual organisations and contribute a large fraction of total worldwide resources for the ATLAS experiment, whose data is distributed...... and managed by the DQ2 software. Managing ATLAS data within NDGF and between NDGF and other Grids used by ATLAS (the Enabling Grids for E-sciencE Grid and the Open Science Grid) presents a unique challenge for several reasons. Firstly, the entry point for data, the Tier 1 centre, is physically distributed...... among heterogeneous resources in several countries and yet must present a single access point for all data stored within the centre. The middleware framework used in NDGF differs significantly from other Grids, specifically in the way that all data movement and registration is performed by services...

  20. Plasma arc welding weld imaging

    Science.gov (United States)

    Rybicki, Daniel J. (Inventor); Mcgee, William F. (Inventor)

    1994-01-01

    A welding torch for plasma arc welding apparatus has a transparent shield cup disposed about the constricting nozzle, the cup including a small outwardly extending polished lip. A guide tube extends externally of the torch and has a free end adjacent to the lip. First and second optical fiber bundle assemblies are supported within the guide tube. Light from a strobe light is transmitted along one of the assemblies to the free end and through the lip onto the weld site. A lens is positioned in the guide tube adjacent to the second assembly and focuses images of the weld site onto the end of the fiber bundle of the second assembly and these images are transmitted along the second assembly to a video camera so that the weld site may be viewed continuously for monitoring the welding process.

  1. INTERPOLATION WITH RESTRICTED ARC LENGTH

    Institute of Scientific and Technical Information of China (English)

    Petar Petrov

    2003-01-01

    For given data (ti,yi), I= 0,1,…,n,0 = t0 <t1 <…<tn = 1we study constrained interpolation problem of Favard type inf{‖f"‖∞|f∈W2∞[0,1],f(ti)=yi,i=0,…,n,l(f;[0,1])≤l0}, wherel(f";[0,1])=∫1 0 / 1+f'2(x)dx is the arc length off in [0,1]. We prove the existence of a solution f* of the above problem, that is a quadratic spline with a second derivative f"* , which coincides with one of the constants - ‖f"*‖∞,0,‖f"*‖∞ between every two consecutive knots. Thus, we extend a result ofKarlin concerning Favard problem, to the case of restricted length interpolation.

  2. The 1590-1520 Ma Cachoeirinha magmatic arc and its tectonic implications for the Mesoproterozoic SW Amazonian craton crustal evolution

    Directory of Open Access Journals (Sweden)

    Ruiz Amarildo S.

    2004-01-01

    Full Text Available Isotopic and chemical data of rocks from the Cachoeirinha suite provide new insights on the Proterozoic evolution of the Rio Negro/Juruena Province in SW Amazonian craton. Six U-Pb and Sm-Nd analyses in granitoid rocks of the Cachoeirinha suite yielded ages of 1587-1522 Ma and T DM model ages of 1.88-1.75 Ga (EpsilonNd values of -0.8 to +1.0. In addition, three post-tectonic plutonic rocks yielded U-Pb ages from 1485-1389 Ma (T DM of 1.77-1.74 Ga and EpsilonNd values from -1.3 to +1.7. Variations in major and trace elements of the Cachoeirinha suite rocks indicate fractional crystallization process and magmatic arc geologic setting. These results suggest the following interpretations: (1 The interval of 1590-1520 Ma represents an important magmatic activity in SW Amazonian craton. (2 T DM and arc-related chemical affinity supportthe hypothesis that the rocks are genetically associated with an east-dipping subduction zone under the older (1.79-1.74 Ga continental margin. (3 The 1590-1520 Ma age of intrusive rocks adjacent to an older crust represents similar geological framework along the southern margin of Baltica, corroborating the hypothesis of tectonic relationship at that time.

  3. A Fresh Plutonic Igneous Angrite Containing Grain Boundary Glass From Tamassint, Northwest Africa

    Science.gov (United States)

    Irving, A. J.; Kuehner, S. M.; Rumble, D.

    2006-12-01

    Tamassint Angrite: A small fragmented stone found in June 2006 south of Tamassint oasis in the Morocco-Algeria border region represents a new type of angrite lithology, unlike the coarse grained metamorphic or fine grained "basaltic" to quench-textured examples known previously. This extremely fresh, fusion-crusted specimen has a coarse grained (0.6-12 mm) plutonic igneous cumulate texture, and is composed of Al-Ti-rich clinopyroxene (33.4%), pure anorthite (28.6%), Ca-rich olivine (18.7%) with prominent exsolution lamellae (10-50 μm wide) of kirschsteinite, ulvöspinel (18.5%), and accessory glass, troilite and metal. Subhedral anorthite grains are partially enclosed within larger ulvöspinel grains. Mineral compositions are as follows: clinopyroxene (Fs20.8-33.3Wo53-54.9, Al2O3 = 5.7 to 9.4 wt.%, TiO2 = 0.9 to 2.9 wt.%, FeO/MnO = 85-278), olivine (Fa72.6-74.7Ln3.5-3.6, CaO = 2.1 wt.%, FeO/MnO = 70-87), kirschsteinite (Fa44.7-45.4Ln46-47.2, FeO/MnO = 73-82), ulvöspinel (TiO2 = 27.6 wt.%, Al2O3 = 5.5 wt.%). Reintegration of the kirschsteinite lamellae gives a pre-exsolution olivine composition of Fa68.1Ln12.2 with 7.3 wt.% CaO. Present along grain boundaries (notably between anorthite and ulvöspinel) are narrow (5-20 μm) curvilinear zones of glass associated with secondary kirschteinite, clinopyroxene and olivine (which show similar curvilinear morphology and truncate kirschsteinite lamellae). Glass compositions plot close to a mixing line between anorthite and ulvöspinel. Replicate oxygen isotopic analyses of acid-washed minerals by laser fluorination gave δ18O = 3.881, 3.845, δ17O = 1.967, 1.927, Δ17O = -0.0745, -0.0956 per mil (for TFL slope = 0.526). Comparison With NWA 2999: We previously showed [1] that angrite Northwest Africa 2999 is a metamorphically annealed breccia with distinctive symplectites and coronas representing forward and reverse versions of the same solid state reaction. We suggested that these disequilibrium textures required burial

  4. Sr-Nd-Hf-Pb isotopic constraints on the origin of silicic lavas in the northern Cascade Arc

    Science.gov (United States)

    Martindale, M.; Mullen, E.; Weis, D.

    2015-12-01

    The Cascade Arc is the type-locality for a 'hot' subduction zone, where the downgoing slab is young and subduction is relatively slow; a unique setting for studying the controls on silicic (>56 wt% SiO2) magma genesis [1,2]. We present high precision Sr-Nd-Hf-Pb isotopic and trace element data for silicic lavas and country rocks from the major centres of the Garibaldi Volcanic Belt (GVB) in British Columbia, which are hosted by the Mesozoic Coast Plutonic Complex and accreted Coast Belt terranes. In isotopic plots, the silicic GVB lavas define mixing curves between northern Cascadia Basin sediment [3] and Juan de Fuca MORB. The silicic GVB lavas have lower ɛNd, and higher ɛHf, 87Sr/86Sr, 208Pb/204Pb and 207Pb/204Pb for a given 206Pb/204Pb than co-existing alkalic mafic lavas [2,4] which define a separate isotopic cluster. The alkalic mafic lavas have OIB-like trace element compositions [2,4], but the silicic lavas are calc-alkaline with a typical 'arc' trace element signature. Geochemical systematics suggest that a mafic, isotopically 'depleted' contaminant may be affecting the composition of GVB silicic lavas. However, modelling indicates that slab melts do not constitute a major component of the lavas despite high slab temperatures. Geochemical models also rule out the accreted Coast Belt terranes as an assimilant. However, AFC modelling using 147 Ma Cloudburst quartz diorite [5] as the assimilant can explain both the trace element and isotopic compositional range displayed by GVB silicic magmas, consistent with the Coast Plutonic Complex as a major component of the deep crust in this region. Crustal assimilation would have partially overprinted any alkalic mantle-derived signature of parental magmas, while imparting a calc-alkaline arc signature to resulting silicic magmas. [1] Green & Harry (1999) EPSL, 171; [2] Mullen & Weis (2013) G3, 14; [3] Carpentier et al. (2014) Chem Geol, 382; [4] Mullen & Weis (2015) EPSL, 414; [5] Friedman & Armstrong (1995) GSA

  5. Analysis of arc emission spectra of stainless steel electric arc furnace slag affected by fluctuating arc voltage.

    Science.gov (United States)

    Aula, Matti; Mäkinen, Ari; Fabritius, Timo

    2014-01-01

    Control of chromium oxidation in the electric arc furnace (EAF) is a significant problem in stainless steel production due to variations of the chemical compositions in the EAF charge. One potential method to control chromium oxidation is to analyze the emission spectrum of the electric arc in order to find indicators of rising chromium content in slag. The purpose of this study was to determine if slag composition can be gained by utilizing electric arc emission spectra in the laboratory environment, despite electric arc voltage fluctuations and varying slag composition. The purpose of inducing voltage fluctuation was to simulate changes in the industrial EAF process. The slag samples were obtained from Outokumpu Stainless Oy Tornio Works, and three different arc currents were used. The correlation analysis showed that the emission spectra offer numerous peak ratios with high correlations to the X-ray fluorescence-measured slag CrO(x)/FeO(x) and MnO/SiO2 ratios. These ratios are useful in determining if the reduction agents have been depleted in the EAF. The results suggest that analysis of laboratory-scale electric arc emission spectra is suitable for indicating the high CrO(x) or MnO content of the slag despite the arc fluctuations. Reliable analysis of other slag components was not successful.

  6. Multiparameter adjoint tomography of the crust and upper mantle beneath East Asia: 1. Model construction and comparisons

    Science.gov (United States)

    Chen, Min; Niu, Fenglin; Liu, Qinya; Tromp, Jeroen; Zheng, Xiufen

    2015-03-01

    We present a 3-D radially anisotropic model of the crust and mantle beneath East Asia down to 900 km depth. Adjoint tomography based on a spectral element method is applied to a phenomenal data set comprising 1.7 million frequency-dependent traveltime measurements from waveforms of 227 earthquakes recorded by 1869 stations. Compressional wave speeds are independently constrained and simultaneously inverted along with shear wave speeds (VSH and VSV) using the same waveform data set with comparable resolution. After 20 iterations, the new model (named EARA2014) exhibits sharp and detailed wave speed anomalies with improved correlations with surface tectonic units compared to previous models. In the upper 100 km, high wave speed (high-V) anomalies correlate very well with the Junggar and Tarim Basins, the Ordos Block, and the Yangtze Platform, while strong low wave speed (low-V) anomalies coincide with the Qiangtang Block, the Songpan Ganzi Fold Belt, the Chuandian Block, the Altay-Sayan Mountain Range, and the back-arc basins along the Pacific and Philippine Sea Plate margins. At greater depths, narrow high-V anomalies correspond to major subduction zones and broad high-V anomalies to cratonic roots in the upper mantle and fragmented slabs in the mantle transition zone. In particular, EARA2014 reveals a strong high-V structure beneath Tibet, appearing below 100 km depth and extending to the bottom of the mantle transition zone, and laterally spanning across the Lhasa and Qiangtang Blocks. In this paper we emphasize technical aspects of the model construction and provide a general discussion through comparisons.

  7. Isotopic discontinuities in ground water beneath Yucca Mountain, Nevada

    International Nuclear Information System (INIS)

    Analytical data for stable isotopes in ground water from beneath Yucca Mountain, when examined in map view, show areal patterns of heterogeneity that can be interpreted in terms of mixing of at least three end members. One end member must be isotopically heavy in terms of hydrogen and oxygen and have a young apparent 14C age such as water found at the north end of Yucca Mountain beneath Fortymile Wash. A second end member must contain isotopically heavy carbon and have an old apparent 14C age such as water from the Paleozoic aquifer. The third end member cannot be tightly defined. It must be isotopically lighter than the first with respect of hydrogen and oxygen and be intermediate to the first and second end members with respect to both apparent 14C age and δ13C. The variable isotopic compositions of hydrogen and oxygen indicate that two of the end members are waters, but the variable carbon isotopic composition could represent either a third water end member or reaction of water with a carbon-bearing solids such as calcite. 15 refs., 4 figs., 1 tab

  8. Shear wave anisotropy in D" region beneath the western Pacific

    Institute of Scientific and Technical Information of China (English)

    DAI Zhi-yang; LIU Bin; WANG Xiao-xiang; ZHA Xian-jie; ZHANG Hu; YANG Feng-qin

    2007-01-01

    Using seismic shear phases from 47 Tonga-Fiji and its adjacent region events recorded by the CENC and IRIS, and from 26 northeast Asia and north Pacific events recorded by IRIS, we studied the shear wave anisotropy in D" region beneath the western Pacific utilizing the ScS-S differential travel time method and obtained the splitting time values between the radial and transverse components of each ScS wave corresponding to each core-mantle boundary (CMB) reflection point. We found that most shear waves involved horizontally polarized shear wave components traveling faster than vertically polarized shear wave components through the D" region. The splitting time values of ScS wave range from (0.91 s to 3.21 s with an average value of 1.1 s. The strength of anisotropy varies from (0.45% to 1.56% with an average value of 0.52%. The observations and analyses show that in the D" region beneath the western Pacific the lateral flow is expected to be dominant and the vertical transverse isotropy may be the main anisotropic structure. This structure feature may be explained by the shape preferred orientation of the CMB chemical reaction products or partial melt and the lattice preferred orientation of the lower mantle materials caused by the lateral flow at lowermost mantle.

  9. Erosion of the continental lithosphere at the cusps of the Calabrian arc: Evidence from S receiver functions analysis

    Science.gov (United States)

    Miller, Meghan S.; Piana Agostinetti, Nicola

    2011-12-01

    Mediterranean tectonics has been characterized by an irregular, complex temporal evolution with episodic rollback and retreat of the subducted plate followed by period of slow trench-migration. To provide insight into the geodynamics of the Calabrian arc, we image the characteristics and lithospheric structure of the convergent, Apulian and Hyblean forelands at the cusps of the arc. Specifically we investigate the crustal and lithospheric thicknesses using teleseismic S-to-p converted phases, applied to the Adria-Africa plate margin for the first time. We find that the Moho in the Apulian foreland is nearly flat at ˜30 km depth, consistent with previous P receiver functions results, and that the Hyblean crustal thickness is more complex, which can be understood in terms of the nature of the individual pieces of carbonate platform and pelagic sediments that make up the Hyblean platform. The lithospheric thicknesses range between 70-120 km beneath Apulia and 70-90 km beneath Sicily. The lithosphere of the forelands at each end of the Calabrian arc are continental in nature, buoyant compared to the subducting oceanic lithosphere and have previously been interpreted as mostly undeformed carbonate platforms. Our receiver function images also show evidence of lithospheric erosion and thinning close to Mt. Etna and Mt. Vulture, two volcanoes which have been associated with asthenospheric upwelling and mantle flow around of the sides the slab. We suggest that as the continental lithosphere resists being subducted it is being thermo-mechanically modified by toroidal flow around the edges of the subducting oceanic lithosphere of the Calabrian arc.

  10. 1.3-0.9 Ga Oaxaquia (Mexico): Remnant of an arc/backarc on the northern margin of Amazonia

    Science.gov (United States)

    Keppie, J. Duncan; Ortega-Gutiérrez, Fernando

    2010-01-01

    Rocks with ages of ca. 1 Ga occur in central and southern Mexico as inliers surrounded by ubiquitous Mesozoic and Cenozoic rocks. They appear to share a common history consisting of: (i) ca. 1300-1200 Ma arc magmatism and deposition of sediments including evaporites; (ii) ca.1160-1100 Ma intrusion of syenite, granite and anorthosite, the later part of which is synchronous with migmatization; (iii) intrusion of a ca. 1035-1010 Ma anorthosite-gabbro-charnockite-granite (AMCG) suite; (iv) a 1000-980 Ma granulite facies tectonothermal event with a stretching axis parallel to the long axis of Oaxaquia; (v) gradual exhumation at 750 and/or 545 Ma; and (vi) 517 Ma intrusion of an isolated calcalkaline granitoid pluton. The common Precambrian geological record of these outcrops suggests that they belonged to a single terrane (Oaxaquia) and formed a juvenile arc/backarc bordering a continent that underwent collision with, and overthrusting of, the Avalonian arc at 1000-980 Ma. This buried Oaxaquia to 25-30 km and was followed by further supra-subduction zone magmatism at ca. 917 Ma. These Precambrian rocks are unconformably overlain by uppermost Cambrian and Silurian platform rocks containing Gondwanan fauna and ca. 1 detrital zircons of Oaxacan provenance. The neighbouring Mixteca terrane includes lower Paleozoic, rift-passive margin sedimentary rocks that also contain 900-750 Ma detrital zircons probably derived from the Goiás arc in eastern Amazonia. The arc-backarc tectonic setting inferred for the 1300-900 Ma rocks also suggests that Oaxaquia lay on an active periphery of Amazonia until ca. 900 Ma, well after the amalgamation of Rodinia. This precludes a location for Oaxaquia off southern and western Amazonia that are inferred to have been juxtaposed against eastern Laurentia; contiguity with eastern Amazonia is also unlikely given the absence of the 900-750 Ma convergent tectonics in the Goiás arc. This leaves northern Amazonia as the most likely position, a

  11. Geochemistry and Nd-Sr isotopic signatures of the Pensamiento Granitoid Complex, Rondonian-San Ignacio Province, eastern precambrian shield of Bolivia: petrogenetic constraints for a mesoproterozoic magmatic arc setting;Geoquimica e assinaturas Nd-Sr do Complexo Granitoide Pensamiento, provincia Rondoniana-San Ignacio, pre-cambriano de Bolivia Oriental: caracterizacao petrogenetica de um arco magmatico no mesoproterozoico

    Energy Technology Data Exchange (ETDEWEB)

    Matos, Ramiro, E-mail: rmatoss@igc.usp.b [Universidad Mayor de San Andre (UMSA), La Paz (Bolivia, Plurinational State of). Inst. de Investigaciones Geologicas y del Medio Ambiente; Teixeira, Wilson; Bettencourt, Jorge Silva, E-mail: wteixeir@usp.b, E-mail: jsbetten@usp.b [Universidade de Sao Paulo (IGC/USP), SP (Brazil). Inst. de Geociencias. Dept. de Mineralogia e Geotectonica; Geraldes, Mauro Cesar, E-mail: geraldes@uerj.b [Universidade do Estado do Rio de Janeiro (FG/UERJ), RJ (Brazil). Faculdade de Geologia

    2009-07-01

    The Pensamiento Granitoid Complex (PGC), located in the northern part of the eastern Precambrian shield of Bolivia, is tectonically assigned to the Rondonian-San Ignacio Province (1.55 - 1.30 Ga) of the Amazonian Craton that is made up by Archean and Proterozoic provinces. The Proterozoic ones result from accretionary orogens that become successively younger south westwards, such as the Rondonian/San Ignacio (1.37 - 1.32 Ga) and the Sunsas orogenies (1.20 - 1.00 Ga). The PGC crops out mainly on the 'Paragua craton' bounded to the south by the Sunsas belt, and composed of granites and subvolcanic terms, and subordinately of syenites, granodiorites, tonalites, trondhjemites and diorites as orogenic representatives of the Rondonian/San Ignacio Orogeny, intrusive into the Lomas Maneches (ca. 1.68 Ga) and Chiquitania (ca. 1.7 Ga) complexes. Thirteen whole rock chemical analyses for major, trace and REE elements were performed for the La Junta, San Martin, Diamantina, Porvernir, San Cristobal, Piso Firme plutons of the PGC. The negative trends of MgO, Al{sub 2}O{sub 3} and CaO contents with increasing SiO{sub 2} suggest that fractional crystallization played an important role in the petrogenesis of the investigated rocks. The data also indicate a mainly peraluminous, sub-alkaline to high-K calc-alkaline composition, and fractionated LREE/HREE patterns are consistent with a magmatic arc character for these plutons. SHRIMP U-Pb zircon ages of the La Junta and San Martin syn- to late-kinematic plutons are 1347 {+-} 21 Ma and 1373 {+-} 20 Ma respectively, and the Sm-Nd T{sub DM} model ages are between 1.9 to 2.0 Ga, while {epsilon}{sub Nd(1330)} values range from +1.8 to -4.3, respectively. In addition, the late- to post-kinematic Diamantina pluton yields SHRIMP U-Pb zircon age of 1340 {+-} 20 Ma, and variable Sm-Nd T{sub DM} model ages (1.6 to 1.9 Ga) and {epsilon}{sub Nd(1330)} values (+0.4 to -1.2) that are comparable with previous results found for other coeval

  12. Polytopic Vector Analysis (PVA) modelling of whole-rock and apatite chemistry from the Karkonosze composite pluton (Poland, Czech Republic)

    Science.gov (United States)

    Lisowiec, Katarzyna; Słaby, Ewa; Förster, Hans-Jürgen

    2015-08-01

    This study presents a novel approach for analysing the magma evolution path in composite plutons, applying the so-termed Polytopic Vector Analysis (PVA) to whole-rock and apatite chemistry. As an example of a multiphase magmatic body the Karkonosze granitoid pluton was chosen, which formed by a combination of magma mixing and fractional crystallization of two distinct melts - granitic crust-derived and lamprophyric mantle-derived. The goal was to model end-member magma compositions recorded by apatite and to estimate to what extent these end-members interacted with each other. Although using single minerals as proxies to magma compositions is tricky, the studied apatite well reflects the compositional trends within the magma (e.g., decreasing LREE/Y ratios, varying halogen content, increasing Mn and Na concentrations). The results of PVA simulations for whole-rock geochemistry demonstrate a model similar to that constrained from previous studies. Apart from the main trend of mixing between a felsic (~ 80 wt.% SiO2) and a mafic (~ 53 wt.% SiO2) end-member (EM), an additional process has been recognized, representing most probably the continuous evolution of the mafic end-member, responsible for the compositional diversity of some rocks. One felsic (REE-poor, Mn-F-rich) and one mafic (Cl-Sr-Si-REE-rich) apatite end-members were recognized, whereas the third one represents most probably a fluid component (enriched in Si, Y, Ce and Nd), present at all magmatic stages, however, most prominent during the late stage. The widest range of EM proportions and the highest contribution of the mafic EM are displayed by apatites from the early stage. During the middle and late stages, the apatites present a narrow range of EM proportions, with almost all apatites bearing a felsic signature. This pattern reflects the progressive homogenization of the system. Although the PVA method applied to mineral chemistry poses some limitations, it may provide a more detailed image of the

  13. Constraining the magma flow record based on magmatic and magnetic data in La Gloria Pluton, central Chile

    Science.gov (United States)

    Gutierrez, F. J.; Payacán, I.; Gelman, S. E.; Bachmann, O.; Creative Physical Petrology Team

    2013-05-01

    The magmatic origin of the anisotropy of magnetic susceptibility (AMS) is examined in comparison with magmatic anisotropy data in a small, shallow, silicic magma reservoir in the upper crust. La Gloria Pluton (LGP) is a 10 Ma granodiorite/quartz monzonite of about 250 km3 located in the southern Andes, central Chile. LGP represents a particularly simple case of a silicic intrusion that was assembled in only a few pulses and cooled over a short time interval. Hornblende, biotite and minor magnetite are ubiquitous mafic phases. The AMS tensor indicates that magnetic fabric has an oblate shape (i.e. magnetic foliation is higher than magnetic lineation). Lineations are weak (values up to 1.05), have a N-NW trend with a nearly horizontal dip and are interpreted to represent axisymmetric convection parallel to the main pluton elongation. Foliations are more pronounced (values up to 1.14), having NW trends and dips that vary gradually from vertical at the walls, to horizontal at the center and near the roof of the chamber. We selected 12 samples from AMS sites to obtain petrographic data (well-distributed throughout the pluton, containing samples from the walls, the center and the roof of LGP), and then, determine the magmatic fabric (anisotropy, lineation, foliation). We made 3 oriented thin sections per sample oriented with the AMS. Magmatic anisotropy data were obtained by measuring mineral length, width and orientation in photomicrographs of the three main planes of the AMS tensor, producing 3-D mineral data which were collected for plagioclase and amphibole + bitotite independently. For each site, a Bingham distribution with 95% of confidence is used to determine the mean mineral orientations and their angle difference with the AMS axes. Magmatic anisotropy tensor and rotations with respect to the AMS tensor are determined using both eigenvalues and minimization algorithms. Preliminary results indicate that crystals are coherently oriented in both mineral groups, and

  14. Acoustic characteristics of electric arc furnaces

    Science.gov (United States)

    Cherednichenko, V. S.; Bikeev, R. A.; Cherednichenko, A. V.; Ognev, A. M.

    2016-06-01

    A mathematical model is constructed to describe the appearance and development of the noise characteristics of superpower electric arc furnaces. The noise formation is shown to be related to the pulsation of the axial plasma flows in arc discharges because of the electrodynamic pressure oscillations caused by the interaction of the self-magnetic field with the current passing in an arc. The pressure in the arc axis changes at a frequency of 100 Hz at the maximum operating pressure of 66 kPa for an arc current of 80 kA. The main ac arc sound frequencies are multiples of 100 Hz, which is supported in the practice of operation of electric arc furnaces. The sound intensity in the furnace laboratory reaches 160 dB and is decreased to 115-120 dB in the working furnace area due to shielding by the furnace jacket, the molten metal, and the molten slag. The appropriateness of increasing the hermetic sealing of electric furnaces and creating furnaces operating at low currents and high transformer voltages is corroborated.

  15. Reconstruction of Late Cretaceous Magmatic Arcs in the Northern Andes: Single Versus Multiple Arc Systems

    Science.gov (United States)

    Cardona, A.; Jaramillo, J. S.; Leon, S.; Hincapie, S.; Mejia, D.; Patino, A. M.; Vanegas, J.; Zapata, S.; Valencia, V.; Jimenez, G.; Monsalve, G.

    2014-12-01

    Although magmatic rocks are major tracers of the geological evolution of convergent margins, pre-collisional events such as subduction erosion, collisional thrusting or late collisional strike slip segmentation may difficult the recognizing of multiple arc systems and therefore the existence of paleogeographic scenarios with multiple subduction systems. New field, U-Pb geochronology and whole rock geochemistry constraints from the northwestern segment of the Central Cordillera in the states of Antioquia and Caldas (Colombia) are used to understand the nature of the Late Cretaceous arc magmatism and evaluate the existence of single or multiple Pacific and Caribbean arc systems in the growth of the Northwestern Andes. The new results integrated with additional field and published information is used to suggest the existence of at least three different magmatic arcs. (1) An Eastern Continental arc built within a well defined Permian to Triassic continental crust that record a protracted 90-70 Ma magmatic evolution, (2) a 90-80 arc formed within attenuated continental crust and associated oceanic crust, (3) 90-88 Ma arc formed over a Late Cretaceous plateau crust. The eastern arcs were formed as part of double eastern vergent subduction system, where the most outboard arc represent a fringing arc formed over detached fragments of continental crust, whereas the easternmost continental arc growth by the closure an subduction of and older and broad Triassic to Early Jurassic back-arc ocean. Its closure also end up in ophiolite emplacement. The third allochtonous oceanic arc was formed over the Caribbean plateau crust and was accreted to the continental margin in the Late Cretaceous. Ongoing paleomagnetic, deformational, gravimetric and basin analysis will be integrate to test this model and understand the complex Late Cretaceous tectonic evolution of the Northern Andes.

  16. Time-scales of assembly and thermal history of a composite felsic pluton: constraints from the Emerald Lake area, northern Canadian Cordillera, Yukon

    Science.gov (United States)

    Coulson, Ian M.; Villeneuve, Mike E.; Dipple, Gregory M.; Duncan, Robert A.; Russell, James K.; Mortensen, James K.

    2002-05-01

    Knowledge of the time-scales of emplacement and thermal history during assembly of composite felsic plutons in the shallow crust are critical to deciphering the processes of crustal growth and magma chamber development. Detailed petrological and chemical study of the mid-Cretaceous, composite Emerald Lake pluton, from the northern Canadian Cordillera, Yukon Territory, coupled with U-Pb and 40Ar/ 39Ar geochronology, indicates that this pluton was intruded as a series of magmatic pulses. Intrusion of these pulses produced a strong petrological zonation from augite syenite, hornblende quartz syenite and monzonite, to biotite granite. Our data further indicate that multiple phases were emplaced and cooled to below the mineral closure temperatures over a time-scale on the order of the resolution of the 40Ar/ 39Ar technique (˜1 Myr), and that emplacement occurred at 94.3 Ma. Simple thermal modelling and heat conduction calculations were used to further constrain the temporal relationships within the intrusion. These calculations are consistent with the geochronology and show that emplacement and cooling were complete in less than 100 kyr and probably 70±5 kyr. These results demonstrate that production, transport and emplacement of the different phases of the Emerald Lake pluton occurred essentially simultaneously, and that these processes must also have been closely related in time and space. By analogy, these results provide insights into the assembly and petrogenesis of other complex intrusions and ultimately lead to an understanding of the processes involved in crustal development.

  17. Modeling Multi-Arc Spraying Systems

    Science.gov (United States)

    Bobzin, K.; Öte, M.

    2016-06-01

    The use of plasma as energy source in thermal spraying enables among others the processing of feed stock materials with very high melting temperatures as coating materials. New generation multi-arc plasma spraying systems are widely spread and promise several advantages in comparison to the conventional single-arc systems. Numerical modeling of multi-arc plasma spraying offers the possibility to increase the understanding about this process. This study focuses on the numerical modeling of three-cathode spraying systems, introducing the recent activities in this field and discussing the numerical aspects which influence the prediction power of the models.

  18. Formation of the G-ring arc

    Science.gov (United States)

    Araujo, N. C. S.; Vieira Neto, E.; Foryta, D. W.

    2016-09-01

    Since 2004, the images obtained by the Cassini spacecraft's on-board cameras have revealed the existence of several small satellites in the Saturn system. Some of these small satellites are embedded in arcs of particles. While these satellites and their arcs are known to be in corotation resonances with Mimas, their origin remains unknown. This work investigates one possible process for capturing bodies into a corotation resonance, which involves increasing the eccentricity of a perturbing body. Therefore, through numerical simulations and analytical studies, we show a scenario in which the excitation of Mimas's eccentricity could capture particles in a corotation resonance. This is a possible explanation for the origin of the arcs.

  19. Formation of the G-ring arc

    CERN Document Server

    Araujo, N C S; Foryta, D W

    2016-01-01

    Since 2004, the images obtained by Cassini spacecraft's on-board cameras have revealed the existence of several small satellites in the Saturn system. Some of these small satellites are embedded in arcs of particles. While these satellites and their arcs are known to be in corotation resonances with Mimas, their origin remains unknown. This work investigates one possible process for capturing bodies into a corotation resonance, which involves raising the eccentricity of a perturbing body. Therefore, through numerical simulations and analytical studies, we show a scenario that the excitation of Mimas' eccentricity could capture particles in a corotation resonance and given a possible explanation for the origin for the arcs.

  20. Arc saw and its application to decommissioning

    International Nuclear Information System (INIS)

    The arc saw is a toothless, circular saw that cuts by arc erosion. A model was built to study the arc saw's usefulness in cutting up radioactively contaminated metal scrap. It was chosen because it cuts with very little contact to the work piece and because cutting is not affected by material hardness. After installation of several improvements it was found it could cut almost any combination of metals and that clamping or fixturing requirements were minimum. Cutting proceeds rapidly and efficiently. 10 figures

  1. Petrogenesis of the Neoproterozoic Ngondo Plutonic complex (Cameroon, west central Africa): a case of late-collisional ferro-potassic magmatism

    Science.gov (United States)

    Tagne-Kamga, Gabriel

    2003-04-01

    The Ngondo complex is a late-collisional pluton, which was emplaced around 600 Ma along a N030° E strike-slip shear zone in the southwestern part of the Neoproterozoic Fold Belt of Cameroon. It comprises three successively emplaced plutonic groups of rocks: (i) mafic to felsic intrusive rocks (MFR), (ii) fine-grained granites (FGG) and (iii) coarse-grained granites (CGG). Late aplitic and pegmatite dykes were emplaced along brittle fractures in these plutons. The complex is metaluminous to weakly peraluminous, high-K, calc-alkaline to " trans-alkaline" ferro-potassic, with mineralogical and geochemical characteristic of I-type granites. The plutonic rocks are characterised by high Ba, Sr, Rb and ∑REE concentrations and low Ni and Cr contents in the mafic members. They also display chondrite-normalised REE patterns characterised by variable LREE enrichment, moderate to minor HREE fractionation with moderate to pronounced negative Eu anomalies (Eu/Eu∗: 0.6-0.9 (MFR), 0.2-0.5 (FGG), 0.3-0.7 (CGG)). Trace element distribution patterns for the three plutonic groups are similar with a distinctive depletion in Nb, Sr and Ti relative to other trace elements and a greater enrichment in LILE compared to HFSE. These plutonic groups present distinct evolutionary trends precluding their origin from differentiation of a single parental magma. The geochemical and isotopic data indicate that they derived from partial melting of heterogeneous (meta)-igneous mafic lower crustal materials, having possibly the composition of amphibolitised high-K calc-alkaline basaltic andesites and andesitic metagreywackes. Petrographic evidences such as the presence of quartz-ocelli, xenocrysts of feldspar, fragments of country rocks (migmatitic gneisses) strongly indicate that crustal contamination may have played an important role in the genesis of the plutonic rocks. This contamination process is further supported by the variation of major and trace elements together with Sr-Nd isotopic data

  2. Geochemistry and Geochronology of Eocene Plutons in Northeastern Washington: A Test of Farallon Slab Rollback as a Cause of the Challis Event

    Science.gov (United States)

    Caulfield, L.; Tepper, J. H.

    2015-12-01

    The causes of widespread magmatism and extension that affected the Pacific Northwest during the Eocene "Challis Event" are poorly understood. Two models that have been advanced to explain this activity are passage of a slab window (e.g., Haeussler et al., 2011) and rollback of the subducting Farallon slab following accretion of Siletzia (Schmandt and Humphreys, 2011). Both scenarios would have resulted in widespread magmatism but with different temporal patterns. Based on reconstructed plate motion vectors magmatism related to a slab window should produce a younging-to-the-NW pattern whereas magmatism associated with slab rollback should young to the S or SW. Existing dates on Eocene igneous units in NE Washington appear to show an overall younging to the SW, consistent with the slab rollback model. However, many of these dates (mainly K-Ar) have large uncertainties so we are conducting a U-Pb dating and geochemical survey of Eocene plutons across the region. An initial set of zircon U-Pb ages (by LA-MC-ICP-MS) from five intrusions in east-central WA range from 50.7 - 46.7 Ma and young to the SW, a trend similar to that observed among Eocene rocks in the Idaho Batholith (Gaschnig et al., 2013). To further investigate this pattern we are dating an additional ten plutonic units that define a ~100 km SW-NE transect through NE WA. From NE to SW the units in this transect are (with dates from WA DNR mapping) as follows: Sheppard granite (undated), Herron Creek intrusion (51.4 +/- 1.9 Ma), Mt. Bonaparte pluton (52.8 +/- 2.6 Ma), Daisy Trail granite (49.9 +/- 0.3 Ma), Swimptkin Creek pluton (48.2 +/- 1.2 Ma), Moses pluton (48.6 +/- 1.2 Ma), Keller Butte granite (52.9 +/- 0.4 Ma), Johnny George plutonic complex (49.9 +/- 0.45 Ma), Manilla Creek (undated), and Swawilla Basin pluton (58.8 +/- 2.2 Ma). Results of this study should lead to a better understanding of the cause(s) of Challis magmatism and specifically its relationship to the ~50-48 Ma accretion of Siletzia.

  3. Linear volcanic segments in the Sunda Arc, Indonesia: Implications for arc lithosphere control upon volcano distribution

    Science.gov (United States)

    Macpherson, C. G.; Pacey, A.; McCaffrey, K. J.

    2012-12-01

    The overall curvature of many subduction zones is immediately apparent and the term island arc betrays the common assumption that subduction zone magmatism occurs in curved zones. This assumption can be expressed by approximating island arcs as segments of small circles on the surface of a sphere. Such treatments predict that the location of arc volcanoes is related to their vertical separation from the slab (in fact, the depth to seismicity in the slab) and require that the primary control on the locus of magmatism lies either within the subducted slab or the mantle wedge that separates the subducted and overriding lithospheric plates. The concept of curved arcs ignores longstanding observations that magmatism in many subduction systems occurs as segments of linearly arranged volcanic centres. Further evidence for this distribution comes from the close relationship between magmatism and large scale, arc-parallel fabrics in some arcs. Similarly, exposures of deep arc crust or mantle often reveal elongation of magmatic intrusions sub-parallel to the inferred trend of the arc. The Sunda Arc forms the Indonesian islands from Sumatra to Alor and provides an important test for models of volcano distribution for several reasons. First, Sunda has hosted abundant historic volcanic activity. Second, with the notable exception of Krakatau, every volcano in the arc is subaerial from base to cone and, therefore, can be readily identified where there is a suitable extent of local mapping that can be used to ground-truth satellite imagery. Third, there are significant changes in the stress regime along the length of the arc, allowing the influence of the upper plate to be evaluated by comparison of different arc segments. Finally, much of the Sunda Arc has proved difficult to accommodate in models that try to relate volcano distribution to the depth to the subducted slab. We apply an objective line-fitting protocol; the Hough Transform, to explore the distribution of volcanoes

  4. On the link between orogenic shortening and back-arc extensional collapse in low topography orogens

    Science.gov (United States)

    Matenco, L. C.

    2012-04-01

    Classical models of orogenic evolution assume that back arc basins form in the hinterland of orogens, collapsing the upper plate above oceanic subduction zones. This is a common characteristic commonly thought to apply to all low-topography orogens of Mediterranean type driven by the fast roll-back of subducted slabs, or other analogues such as the Miocene to recent evolution of the SE Asia subduction zones. This extension may take place far at the interior of the upper plate, as is the case in various segments of the Carpathians or in the core of the SE Asian domain, but in most cases of the Dinarides, Apennines or Hellenides it take place superposed or far into the foreland of oceanic suture zones. Therefore, the term back-arc extension in many cases is misleading, as exhumation along major detachment zones takes place in the core of the orogen (Rif, Betics), in the accreted crustal material of the lower plate (Apennines, Dinarides) or even in a presumed former fore-arc (Aegean, Sunda-Banda arc). In all these subduction zones, collision has largely duplicated crustal blocks from the lower plate and has gradually shifted subduction zone far towards the lower plate. As a result, crustal thickening takes place in the foreland of the orogen, in contrast with the typical crustal roots of the high convergence orogens, such as the Alps or Himalaya. This demonstrate an active shift of the main subduction zone, the position of slabs detected by teleseismic mantle tomography is displaced to the foreland and cannot be connected with the position of the lower plate crust beneath the orogen. This shift is associated with large scale magmatism with unusual large crustal signatures, atypical for subduction related magmas. These observations demonstrate the need for an active reconsideration of existing orogenic models which should include displacements of subduction zones during orogenic shortening and an active investigation of the role of continental subduction and associated

  5. New petrographic, geochemical and geochronological data for the Reguengos de Monsaraz pluton (Ossa Morena Zone, SW Iberian Massif, Portugal)

    Energy Technology Data Exchange (ETDEWEB)

    Antunes, A.; Santos, J. F.; Azevedo, M. R.; Mendez, M. H.; Ribeiro, S.

    2010-07-01

    The Reguengos de Monsaraz pluton is a late to post-tectonic Variscan intrusion occurring in the Ossa Morena Zone (Iberian Variscan Chain). The dominant lithological types are tonalites and granodiorites, but the internal area of the massif is composed of gabbro-dioritic rocks. Field evidence shows that the intrusion is heterogeneous at mesoscopic scale suggesting that the emplacement of mafic and felsic magmas was contemporaneous. Petrographic and geochemical studies reveal that the different lithologic types define a continuous sequence with compositions varying from metaluminous to slightly peraluminous and a typical calc-alkaline signature. In Harker variation diagrams, it is possible to observe systematic rectilinear correlations pointing to the involvement of magma mingling/mixing processes in the petrogenesis of this sequence. Rb-Sr isotopic data, using a mineral-mineral pair from a granodiorite sample, yielded an age of 298 Ma, interpreted as a cooling age after igneous crystallization. (Author) 13 refs.

  6. Imaging Transition Zone Thickness Beneath South America from SS Precursors

    Science.gov (United States)

    Schmerr, N.; Garnero, E.

    2006-12-01

    We image detailed upper mantle discontinuity structure beneath a number of geologically active regions, including the South American subduction zone, the Scotia plate subduction zone, and several volcanic hotspots (e.g., the Galapagos Islands), in a region ~10,000 km by 10,000 km wide, spanning 70° S to 20° N and 20° W to 110° W. Precursors to the seismic phase SS are analyzed, which form as a result of underside reflections off seismic discontinuities beneath the midpoint of the SS path and are highly sensitive to discontinuity depth and sharpness. Our SS dataset consists of over 15,000 high-quality transverse component broadband displacement seismograms collected from the Incorporated Research Institutions for Seismology (IRIS), the Canadian National Seismic Network (CNSN), as well as data from EarthScope seismic stations, and from the Canadian Northwest Experiment (CANOE) temporary broadband array deployment. This dataset densely samples several regions in our study area and significantly improves the sampling for this area compared to previous precursor studies. Data with common central SS bouncepoints are stacked to enhance precursory phases. Solution discontinuity structure depends on a number of factors, including dominant seismic period, crustal correction, signal-to-noise ratio threshold, and tomography model used for mantle heterogeneity correction. We exclude precursor data predicted to interfere with other seismic phases, such as topside reflections (e.g., s670sS), which have been demonstrated to contaminate final stacks. Solution transition zone thickness is at least 20 km thicker than global average estimates of 242 km along the northwestern portion of the South American subduction complex (Peru, Ecuador, and Columbia); this thickening extends 1000-1500 km to the east beneath the continent, but does not appear to continue south of -20° latitude along the convergent margin. A minimum of 10 km of thickening is imaged to the west of the Scotia

  7. Sr and Pb isotopic geochemistry of feldspars and implications for the growth of megacrysts in plutonic settings.

    Science.gov (United States)

    Munnikhuis, J.; Glazner, A. F.; Coleman, D. S.; Mills, R. D.

    2015-12-01

    Why megacrystic textures develop in silicic igneous rocks is still unknown. One hypothesis is that these crystals nucleate early in a magma chamber with a high liquid content. A supportive observation of this hypothesis is areas in plutons with high concentrations of megacrysts suggesting flow sorting. Another group of hypotheses suggest megacrystic textures form during protracted late-stage coarsening in a low-melt, interlocked matrix due to either thermal oscillations from incremental pluton emplacement, or Ostwald ripening. Isotopic analyses of large, euhedral K-feldspar megacrysts from the Cretaceous intrusive suites of the Sierra Nevada batholith (SNB) provide new insight into their origin. Megacrysts from the SNB reach the decimeter scale, are Or rich (85-90%), are perthitic, and host mineral inclusions of nearly all phases in the host rock. In-situ micro-drilling of transects, from core to rim, of the alkali feldspars provides material for Sr and Pb isotopic analyses by thermal ionization mass spectrometry (TIMS). Preliminary 87Sr/86Sr(i) isotopic data from samples from the Cathedral Peak Granodiorite, of the Tuolumne Intrusive Suite range from 0.706337 to 0.706452 (~1.6ɛSr) near the cores, whereas a sawtooth pattern with larger variability, 0.706179 to 0.706533 (~5ɛSr), occurs nears the rims. We interpret these preliminary data to indicate that the late portion of growth (i.e. crystal rim) was dominated by either cannibalism of small K-feldspar crystals with isotopic variability, or by addition of isotopically diverse late components to the magma. By comparing the Sr and Pb isotopic stratigraphy of megacrysts from a variety of rock matrices and different granitoids in the SNB isotopic trends can be evaluated to determine if crystals sizes are dependent on disequilibrium processes or grow at a steady state.

  8. PLUTON: Three-group neutronic code for burnup analysis of isotope generation and depletion in highly irradiated LWR fuel rods

    International Nuclear Information System (INIS)

    PLUTON is a three-group neutronic code analyzing, as functions of time and burnup, the change of radial profiles, together with average values, of power density, burnup, concentration of trans-uranium elements, plutonium buildup, depletion of fissile elements, and fission product generation in water reactor fuel rod with standard UO2, UO2-Gd2O3, inhomogeneous MOX, and UO2-ThO2. The PLUTON code, which has been designed to be run on Windows PC, has adopted a theoretical shape function of neutron attenuation in pellet, which enables users to perform a very fast and accurate calculation easily. The present code includes the irradiation conditions of the Halden Reactor which gives verification data for the code. The total list of trans-uranium elements included in the calculations consists of 92U233-239, 93Np237-239, 94Pu238-243, 95Am241-244 (including isomers), and 96Cm242-245. Poisoning fission products are represented by 54Xe131,133,135, 48Cd113, 62Sm149,151,152, 64Gd154-160, 63Eu153,155, 36Kr83,85, 42Mo95, 43Tc99, 45Rh103, 47Ag109, 53I127,129,131, 55Cs133, 57La139, 59Pr141, 60Nd143-150, 61Pm147. Fission gases and volatiles included in the code are 36Kr83-86, 54Xe129-136, 52Te125-130, 53I127-131, 55Cs133-137, and 56Ba135-140. Verification has been performed up to 83 GWd/tU, and a satisfactory agreement has been obtained. (author)

  9. Magmatic and solid state structures of the Abu Ziran pluton: Deciphering transition from thrusting to extension in the Eastern Desert of Egypt

    Science.gov (United States)

    Fritz, Harald; Loizenbauer, Jürgen; Wallbrecher, Eckart

    2014-11-01

    The 606 Ma old Abu Ziran granite of the Eastern Desert of Egypt intruded the southern margin of the Meatiq dome in a sinistral shear extensional setting. Its emplacement was enabled by a system of NW-trending sinistral shears, related Riedel shears and N-S extensional shear zones and faults. Magmatic flow was east-directed and controlled by Riedel shears that progressively rotated to an orientation favourable for extension. Strain markers that document magmatic flow show eastward decreasing strain together with strain increase from pluton centre to margins. This is explained by Newtonian flow between non-parallel plates and differences in flow velocities across the pluton. Solid state fabrics including shear fabrics, orientation of late magmatic dykes and quartz tension gashes, together with quartz C-axes distributions, document southward extensional shear within the solidified pluton and adjacent host rocks. Extensional shear is correlated with exhumation of the Meatiq dome coeval and soon after pluton solidification (585 Ma). Pressure temperature evolutionary paths, derived from fluid inclusions, show a clockwise path with exhumation by isothermal decompression in the Meatiq dome. By contrast, the overlying volcanosedimentary nappes experienced an anti-clockwise path released by temperature rise due to pluton emplacement followed by isobaric cooling. Quartz fabrics indicate high-temperature coaxial N-S flow in the northern Meatiq dome and lower-temperature, non-coaxial southward flow within the overlaying superficial nappe. This is explained by the exhumation process itself that progressively localised into simple shear domains when rocks approached higher crustal levels. Late extension at ca. 580 Ma was pure shear dominated and resulted in reversal of shear, now dextral, in the western Meatiq shear zone.

  10. Paleomagnetism and magnetic fabric of Miocene plutons of the Tonalá shearz zone, Chiapas, Mexico: evidence of rotation of the remanence vector

    Science.gov (United States)

    Molina-Garza, Roberto S.; Geissman, John W.

    2016-04-01

    The Late Miocene plutons of coastal Chiapas are elongated parallel to the Tonalá mylonite belt, and some plutons show asymmetric outcrop patterns with sheared tails that trail behind the intrusions. Plutons were emplaced within a transpressional sinistral shear zone. Magnetic fabrics in the plutons are well-developed, and are subparallel to the structural trend of the Tonalá mylonitic belt, but locally magmatic fabrics are preserved. Magnetic fabrics in undeformed granites with igneous textures are also subparallel to the shear zone axis. Strongly deformed plutons have Ṕvalues as high as 1.7. Fabric ellipsoids are predominantly oblate, but they are triaxial in sites with igneous textures. Characteristic magnetizations reside in a cubic phase, such as low-Ti magnetite, but abundant particles in the MD range prevent isolating a stable magnetization in many of the sites. Site means are NW to NE directed, and of moderate positive inclination (or its antipodal), but locally they are very discordant in declination. The overall mean, discarding highly discordant sites is of D= 359.5 and I=41.9 (k=14.2, alpha95=8.1), which is nearly concordant with the NA reference direction indicating gentle northward tilt of less than about 10°. We explain the highly discordant directions as caused by continuing, progressive, deformation in the transpressive shear zone of a thermochemical remanence acquired during deformation. Deformation resulted in rotations, both in a clockwise and an anticlockwise sense. These results are interpreted as paleomagnetic vectors affected by distortional strain, which based on AMS exceed 40% shortening and accommodate shape and volume change in the rock.

  11. Zircon U-Pb geochronology, Sr-Nd-Hf isotopic composition and geological significance of the Late Triassic Baijiazhuang and Lvjing granitic plutons in West Qinling Orogen

    Science.gov (United States)

    Duan, Meng; Niu, Yaoling; Kong, Juanjuan; Sun, Pu; Hu, Yan; Zhang, Yu; Chen, Shuo; Li, Jiyong

    2016-09-01

    The Qinling Orogen was a consequence of continental collision of the South China Craton with the North China Craton in the Triassic and caused widespread granitoid magmatism. However, the petrogenesis of these granitoids remains controversial. In this paper, we choose the Baijiazhuang (BJZ) and Lvjing (LJ) plutons in the West Qinling Orogen for a combined study of the zircon U-Pb geochronology, whole-rock major and trace element compositions and Sr-Nd-Hf isotopic characteristics. We obtained zircon crystallization ages of ~ 216 Ma and ~ 212 Ma for the BJZ and the LJ plutons, respectively. The granitoid samples from both plutons have high K2O metaluminous to peraluminous compositions. They are enriched in large ion lithophile elements (LILEs), light rare earth elements (LREEs) and depleted in high field-strength elements (HFSEs) with significant negative Eu anomalies. The BJZ samples have initial Sr isotopic ratios of 0.7032 to 0.7078, εNd(t) of - 10.99 to - 8.54 and εHf (t) of - 10.22 to - 6.41. The LJ granitoids have initial Sr isotopic ratios of 0.7070 to 0.7080, εNd(t) of - 5.37 to - 4.58 and εHf(t) of - 3.64 to - 1.78. The enriched isotopic characteristics of the two plutons are consistent with their source being dominated by ancient continental crust. However, two BJZ samples show depleted Sr isotope compositions, which may infer possible involvement of mantle materials. Mantle-derived melt, which formed from partial melting of mantle wedge peridotite facilitated by dehydration of the subducted/subducting Mianlue ocean crust, provide the required heat for the crustal melting while also contributing to the compositions of these granitoids. That is, the two granitic plutons are magmatic responses to the closure of the Mianlue ocean basin and the continental collision between the Yangtze and South Qinling crustal terranes.

  12. Numerical investigations of arc behaviour in gas metal arc welding using ANSYS CFX

    Science.gov (United States)

    Schnick, M.; Fuessel, U.; Hertel, M.; Spille-Kohoff, A.; Murphy, A. B.

    2011-06-01

    Current numerical models of gas metal arc welding (GMAW) are trying to combine magnetohydrodynamics (MHD) models of the arc and volume of fluid (VoF) models of metal transfer. They neglect vaporization and assume an argon atmosphere for the arc region, as it is common practice for models of gas tungsten arc welding. These models predict temperatures above 20 000 K and a temperature distribution similar to tungsten inert gas (TIG) arcs. However, current spectroscopic temperature measurements in GMAW arcs demonstrate much lower arc temperatures. In contrast to TIG arcs they found a central local minimum of the radial temperature distribution. The paper presents a GMAW arc model that considers metal vapour and which is in a very good agreement with experimentally observed temperatures. Furthermore, the model is able to predict the local central minimum in the radial temperature and the radial electric current density distributions for the first time. The axially symmetric model of the welding torch, the work piece, the wire and the arc (fluid domain) implements MHD as well as turbulent mixing and thermal demixing of metal vapour in argon. The mass fraction of iron vapour obtained from the simulation shows an accumulation in the arc core and another accumulation on the fringes of the arc at 2000 to 5000 K. The demixing effects lead to very low concentrations of iron between these two regions. Sensitive analyses demonstrate the influence of the transport and radiation properties of metal vapour, and the evaporation rate relative to the wire feed. Finally the model predictions are compared with the measuring results of Zielińska et al.

  13. Prostate treatments, 1MRT o RapidArc; Tratamiento de prostata, IMART o RapidArc?

    Energy Technology Data Exchange (ETDEWEB)

    Castro novais, J.; Ruiz Maqueda, S.; Pardo Perez, E.; Molina Lopez, M. Y.; Cerro Penalver, E.

    2015-07-01

    Techniques that modulate the dose (as IMRT or RapidArcTM) improve dose homogeneity within the target volume decreasing the dose in healthy organs. The aim of this work is to study the dosimetric differences in prostate radiotherapy treatments with IMRT and RapidArcTM. The results of the 109 patients studied show that plans to RapidArcTM have better coverage, compliance and dose gradient outside the target volume. (Author)

  14. Stretched arc discharge in produced water.

    Science.gov (United States)

    Cho, Y I; Wright, K C; Kim, H S; Cho, D J; Rabinovich, A; Fridman, A

    2015-01-01

    The objective of the present study was to investigate the feasibility of stretching an arc discharge in produced water to increase the volume of produced water treated by plasma. Produced water is the wastewater generated by hydraulic fracturing of shale during the production phase in shale-oil or shale-gas exploration. The electric conductivity of produced water is in the range of 50-200 mS/cm, which provides both a challenge and opportunity for the application of plasmas. Stretching of an arc discharge in produced water was accomplished using a ground electrode and two high-voltage electrodes: one positioned close to the ground electrode and the other positioned farther away from the ground. The benefit of stretching the arc is that the contact between the arc and water is significantly increased, resulting in more efficient plasma treatment in both performance and energy cost. PMID:25638080

  15. Observation of gliding arc surface treatment

    DEFF Research Database (Denmark)

    Kusano, Yukihiro; Zhu, Jiajian; Ehn, A.;

    2015-01-01

    . Water contact angle measurements indicate that the treatment uniformity improves significantly when the AC gliding arc is tilted to the polymer surface. Thickness reduction of the gas boundary layer, explaining the improvement of surface treatment, by the ultrasonic irradiation was directly observed for......An alternating current (AC) gliding arc can be conveniently operated at atmospheric pressure and efficiently elongated into the ambient air by an air flow and thus is useful for surface modification. A high speed camera was used to capture dynamics of the AC gliding arc in the presence of polymer...... surfaces. A gap was observed between the polymer surface and the luminous region of the plasma column, indicating the existence of a gas boundary layer. The thickness of the gas boundary layer is smaller at higher gas flow-rates or with ultrasonic irradiation to the AC gliding arc and the polymer surface...

  16. Sitka, Alaska 1 arc-second DEM

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The Sitka, Alaska Elevation Grid provides bathymetric data in ASCII raster format of 1 arc-second resolution in geographic coordinates. This grid is strictly for...

  17. Seward, Alaska 1 arc-second DEM

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The 1 arc-second Seward Alaska Elevation Grid provides bathymetric data in ASCII raster format of .89-second resolution in geographic coordinates. This grid is...

  18. Ocean mixing beneath Pine Island Glacier Ice Shelf

    Science.gov (United States)

    Kimura, Satoshi; Dutrieux, Pierre; Jenkins, Adrian; Forryan, Alexander; Naveira Garabato, Alberto; Firing, Yvonne

    2016-04-01

    Ice shelves around Antarctica are vulnerable to increase in ocean-driven melting, with the melt rate depending on ocean temperature and strength of sub-ice-shelf-cavity circulations. We present repeated measurements of velocity, temperature, salinity, turbulent kinetic energy dissipation rate and thermal variance dissipation rate beneath Pine Island Glacier Ice Shelf, collected by CTD, ADCP and turbulence sensors mounted on an Autonomous Underwater Vehicle (AUV). The turbulence quantities measured by the AUV outside the ice shelf are in good agreement with ship-based measurements. The highest rate of turbulent kinetic energy dissipation is found near the grounding line, while its temporal fluctuation over seabed ridge within the cavity corresponds to the tidal fluctuation predicted in the Pine Island Bay to the west. The highest thermal variance dissipation rate is found when the AUV was 0.5 m away from the ice, and the thermal variance dissipation generally increases with decreasing distance between the AUV and ice.

  19. Similarity law of fluctuating pressure spectrum beneath hydraulic jump

    Institute of Scientific and Technical Information of China (English)

    LIAN JiJian; WANG JiMin; GU JinDe

    2008-01-01

    Similarity law is the conversion rule between model and prototype, on which a lot of research works have been done, with no agreement reached referring to the similarity law of fluctuating pressure fre-quency spectrum. Experimental data of peak frequency and dominant frequency range of fluctuating pressure spectrum beneath hydraulic jump obtained from serial models of scales 1:1, 1:2 and 1:5 are compared. As a result, similarity law of fluctuating pressure spectrum in the strongly rolling area agrees with the gravity law. As peak frequency and dominant frequencies of fluctuating pressures in hydraulic normalized spectrums of fluctuating pressures show that the similarity nearly agrees with the gravity law.

  20. Multicomponent seismic forward modeling of gas hydrates beneath the seafloor

    Institute of Scientific and Technical Information of China (English)

    Yang Jia-Jia; He Bing-Shou; Zhang Jian-Zhong

    2014-01-01

    We investigated the effect of microscopic distribution modes of hydrates in porous sediments, and the saturation of hydrates and free gas on the elastic properties of saturated sediments. We simulated the propagation of seismic waves in gas hydrate-bearing sediments beneath the seafloor, and obtained the common receiver gathers of compressional waves (P-waves) and shear waves (S-waves). The numerical results suggest that the interface between sediments containing gas hydrates and free gas produces a large-amplitude bottom-simulating reflector. The analysis of multicomponent common receiver data suggests that ocean-bottom seismometers receive the converted waves of upgoing P-and S-waves, which increases the complexity of the wavefield record.

  1. Effect of arc on radiation thermometry in welding process

    Institute of Scientific and Technical Information of China (English)

    李亮玉; 王燕; 武宝林

    2002-01-01

    The effect of arc on radiation thermometry is analyzed in a field close to the arc during the welding process, and the ratio of signal to noise and other factors are obtained for a small current arc .The method of the temperature measurement is feasible when the arc current is decreased to a smaller value in the welding process.

  2. 49 CFR 195.226 - Welding: Arc burns.

    Science.gov (United States)

    2010-10-01

    ... 49 Transportation 3 2010-10-01 2010-10-01 false Welding: Arc burns. 195.226 Section 195.226 Transportation Other Regulations Relating to Transportation (Continued) PIPELINE AND HAZARDOUS MATERIALS SAFETY... PIPELINE Construction § 195.226 Welding: Arc burns. (a) Each arc burn must be repaired. (b) An arc burn...

  3. 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

  4. Arc distribution during the vacuum arc remelting of Ti-6Al-4V

    Energy Technology Data Exchange (ETDEWEB)

    Woodside, Charles Rigel [U.S. DOE; King, Paul E. [U.S. DOE; Nordlund, Chris [ATI Albany Operations

    2013-01-01

    Currently, the temporal distribution of electric arcs across the ingot during vacuum arc remelting (VAR) is not a known or monitored process parameter. Previous studies indicate that the distribution of arcs can be neither diffuse nor axisymmetric about the center of the furnace. Correct accounting for the heat flux, electric current flux, and mass flux into the ingot is critical to achieving realistic solidification models of the VAR process. The National Energy Technology Laboratory has developed an arc position measurement system capable of locating arcs and determining the arc distribution within an industrial VAR furnace. The system is based on noninvasive magnetic field measurements and a VAR specific form of the Biot–Savart law. The system was installed on a coaxial industrial VAR furnace at ATI Albany Operations in Albany, OR. This article reports on the different arc distributions observed during production of Ti-6Al-4V. It is shown that several characteristic arc distribution modes can develop. This behavior is not apparent in the existing signals used to control the furnace, indicating the measurement system is providing new information. It is also shown that the different arc distribution modes observed may impact local solidification times, particularly at the side wall.

  5. Influence of metal vapour on arc temperatures in gas-metal arc welding: convection versus radiation

    Science.gov (United States)

    Murphy, Anthony B.

    2013-06-01

    The presence of metal vapour in gas-metal arc welding has been shown to have two strong effects on the arc plasma: a decrease in temperature throughout the arc, and the formation of a local temperature minimum near the arc axis. These effects have been attributed, on the basis of different computational models, to either the increased radiative emission associated with the presence of metal vapour in the arc plasma, or the influence of the metal vapour influx on convective flow in the arc. This question is investigated using a three-dimensional computational model in which the production and the transport of metal vapour are taken into account self-consistently. Parameters relevant to welding of thin sheets of aluminum are examined. For these conditions, it is found that the first effect (the decrease in temperature throughout the arc) is due to both the increased radiative emission and the influence of the metal vapour influx on flow. The second effect (the local temperature minimum, which in this case occurs just below the wire electrode) is a consequence of the influence of aluminum vapour produced from the wire electrode on flow in the arc. By examining published results and the energy balance in the plasma, it is shown that for welding of steel with higher arc currents, the increased radiative emission can lead to a local temperature minimum at a greater distance from the wire electrode.

  6. Heat flow in the Lesser Antilles island arc and adjacent back arc Grenada basin

    OpenAIRE

    Manga, Michael; Hornbach, Matthew J.; Friant, Anne Le; Ishizuka, Osamu; Stroncik, Nicole; Adachi, Tatsuya; Aljahdali, Mohammed; Boudon, Georges; Breitkreuz, Christoph; Fraass, Andrew; Fujinawa, Akihiko; Hatfield, Robert; Jutzeler, Martin; Kataoka, Kyoko; Lafuerza, Sara

    2012-01-01

    Using temperature gradients measured in 10 holes at 6 sites, we generate the first high fidelity heat flow measurements from Integrated Ocean Drilling Program drill holes across the northern and central Lesser Antilles arc and back arc Grenada basin. The implied heat flow, after correcting for bathymetry and sedimentation effects, ranges from about 0.1 W/m2 on the crest of the arc, midway between the volcanic islands of Montserrat and Guadeloupe, to 15 km from the crest in the back arc direct...

  7. Spectral characteristics of arc plasma during laser-arc double-sided welding for aluminum alloy

    Institute of Scientific and Technical Information of China (English)

    Kezhao Zhang; Zhenglong Lei; Xianglong Wang; Yanbin Chen; Yaobang Zhao

    2015-01-01

    In laser-arc double-sided welding,the spectral characteristics of the arc plasma are calculated and analyzed by spectroscopic diagnosis.The results show that,compared with conventional tungsten inert gas (TIG) welding,the introduction of a laser changes the physical characteristics of the arc plasma regardless of whether laser plasma penetration takes place,and that the influence of the laser mainly affects the near-anode region of the arc.When the laser power is relatively low,the arc column tends to compress,and the arc spectral characteristics show no significant difference.When the arc root constricts,compared with pure TIG arc,the electron density increases by ~2.7 times and the electron temperature decreases by ~3000 K.When the arc column expands,the intensities of spectral lines of both the metal and Ar atoms are the strongest.But it is also observed that the electron density reduces,whereas there is no obvious decrease of electron temperature.

  8. Chemical transport beneath a uranium mill tailings pile, Riverton, Wyoming

    International Nuclear Information System (INIS)

    A detailed geochemical study at the Riverton site was undertaken in order to define the nature of chemical transport between an inactive tailings pile and the relationship between the underlying shallow groundwater system. Isotopic measurements of oxygen, deuterium, and tritium showed that although both the shallow alluvial aquifer and a deeper aquifer in the Wind River Formation were derived from a similar source, the nearby river, recharge from the tailings pile is occurring only in the shallow alluvium. 34S/32S ratios are used as a conservative tracer in defining zones of tailings water contamination. Offsite, drilling has revealed the existence of a chemical plume in which calcium and sulfate concentrations are an order of magnitude or more above background. The plume is also characterized by high dissolved molybdenum concentrations. Pore waters in the tailings exhibit extremely high concentrations of Al, Fe and SO4 and low pH. The dissolution of calcite occurs in the alluvium beneath the pile which is characterized by high partial pressures of CO/sub 2(g)/ in the tailings while serving to neutralize pH. The groundwater, however remains saturated with CaCO3, suggesting that a buffering capacity is active. Beneath and downgradient from the tailings, the groundwater becomes saturated with gypsum. The chemical speciation code, PHREEQE, was used to model mixing reactions, assuming a hydrologically static system. Reaction path simulations were fit to observed trends of pH that were depressed in the contaminated groundwater. The simulations estimate one percent mixing of tailings-pore water with groundwater from the shallow alluvial aquifer

  9. Crustal and uppermost mantle structure beneath the United States

    Science.gov (United States)

    Shen, Weisen; Ritzwoller, Michael H.

    2016-06-01

    This paper presents a new model of the shear velocity structure of the crust and uppermost mantle beneath the contiguous U.S. The model is based on more than a decade of USArray Transportable Array (TA) data across the U.S. and derives from a joint Bayesian Monte Carlo inversion of Rayleigh wave group and phase speeds determined from ambient noise and earthquakes, receiver functions, and Rayleigh wave ellipticity (H/V) measurements. Within the Bayesian inverse theoretic framework, a prior distribution of models is posited and a posterior distribution is inferred beneath all of the more than 1800 TA stations across the U.S. The resulting mean and standard deviation of the mean of the posterior distribution at each station summarize the inversion results, which are then interpolated onto a regular 0.25°×0.25° grid across the U.S. to define the final 3-D model. We present arguments that show that the standard deviation of the posterior distribution overestimates the effect of nonsystematic errors in the final model by a factor of 4-5 and identify uncertainties in density and mantle Q as primary potential sources of remaining systematic error in the final model. The model presents a great many newly resolved structural features across the U.S. that require further analysis and dedicated explication. We highlight here low-velocity anomalies in the upper mantle that underlie the Appalachians with centers of anomalies in northern Georgia, western Virginia, and, most prominently, New England.

  10. Magma heating by decompression-driven crystallization beneath andesite volcanoes.

    Science.gov (United States)

    Blundy, Jon; Cashman, Kathy; Humphreys, Madeleine

    2006-09-01

    Explosive volcanic eruptions are driven by exsolution of H2O-rich vapour from silicic magma. Eruption dynamics involve a complex interplay between nucleation and growth of vapour bubbles and crystallization, generating highly nonlinear variation in the physical properties of magma as it ascends beneath a volcano. This makes explosive volcanism difficult to model and, ultimately, to predict. A key unknown is the temperature variation in magma rising through the sub-volcanic system, as it loses gas and crystallizes en route. Thermodynamic modelling of magma that degasses, but does not crystallize, indicates that both cooling and heating are possible. Hitherto it has not been possible to evaluate such alternatives because of the difficulty of tracking temperature variations in moving magma several kilometres below the surface. Here we extend recent work on glassy melt inclusions trapped in plagioclase crystals to develop a method for tracking pressure-temperature-crystallinity paths in magma beneath two active andesite volcanoes. We use dissolved H2O in melt inclusions to constrain the pressure of H2O at the time an inclusion became sealed, incompatible trace element concentrations to calculate the corresponding magma crystallinity and plagioclase-melt geothermometry to determine the temperature. These data are allied to ilmenite-magnetite geothermometry to show that the temperature of ascending magma increases by up to 100 degrees C, owing to the release of latent heat of crystallization. This heating can account for several common textural features of andesitic magmas, which might otherwise be erroneously attributed to pre-eruptive magma mixing.

  11. Overtwisted open books from sobering arcs

    OpenAIRE

    Goodman, Noah

    2004-01-01

    We study open books on three manifolds which are compatible with an overtwisted contact structure. We show that the existence of certain arcs, called sobering arcs, is a sufficient condition for an open book to be overtwisted, and is necessary up to stabilization by positive Hopf-bands. Using these techniques we prove that some open books arising as the boundary of symplectic configurations are overtwisted, answering a question of Gay in Algebr. Geom. Topol. 3 (2003) 569--586.

  12. Hybrid Laser-Arc Welding Tanks Steels

    Science.gov (United States)

    Turichin, G.; Tsibulskiy, I.; Kuznetsov, M.; Akhmetov, A.; Klimova-Korsmik, O.

    2016-04-01

    The results investigate hybrid laser-arc welding of high strength steels using design responsible metallic construction and the highest strength body of vehicles. Welds from modern high strength steels grade Hardox 400, Hardox 450, Armox 600T and AB were created. High power fiber laser LS-15 with output 15 kW and arc rectifier VDU - 1500 DC were used in the experiment. Results of the metallographic research and mechanical tests are presented.

  13. Multi-color detection of gravitational arcs

    OpenAIRE

    Maturi, Matteo; Mizera, Sebastian; Seidel, Gregor

    2013-01-01

    Strong gravitational lensing provides fundamental insights into the understanding of the dark matter distribution in massive galaxies, galaxy clusters and the background cosmology. Despite their importance, the number of gravitational arcs discovered so far is small. The urge for more complete, large samples and unbiased methods of selecting candidates is rising. A number of methods for the automatic detection of arcs have been proposed in the literature, but large amounts of spurious detecti...

  14. Electric arc furnace models for flicker study

    Directory of Open Access Journals (Sweden)

    Catalina González Castaño

    2016-06-01

    Full Text Available Objective: The aim of this paper is to evaluate voltage fluctuations or flicker of two electric arc furnace models through comparison with real data.Method: The first proposed model is founded on the energy conservation principle, which generates a non-linear differential equation modelling the electric arc voltage – current characteristics. Voltage fluctuations are generated using a chaotic circuit that modulates the amplitude of arc voltage. The second model is based on the empirical relationship between the arc diameter or length as well as voltage and electrical current on the arc. Voltage fluctuations are considered adding a random signal in the arc length. Both models are implemented in PSCADTM.Results: The results of both models are compared with real data taken at the most critical stage of the operation of the furnace, and they show that the model based on energy conservation has a lower average mean square error in the voltages and currents 5.6 V and 1.7 kA against 27,2 V y 3.38 kA obtained with the second model.Conclusions: Both models consider the nonlinearity and random behavior present in this type of load, validating their inclusion in computer models of electric power systems.

  15. Recent ARC developments: Through modularity to interoperability

    Energy Technology Data Exchange (ETDEWEB)

    Smirnova, O; Cameron, D; Ellert, M; Groenager, M; Johansson, D; Kleist, J [NDGF, Kastruplundsgade 22, DK-2770 Kastrup (Denmark); Dobe, P; Joenemo, J; Konya, B [Lund University, Experimental High Energy Physics, Institute of Physics, Box 118, SE-22100 Lund (Sweden); Fraagaat, T; Konstantinov, A; Nilsen, J K; Saada, F Ould; Qiang, W; Read, A [University of Oslo, Department of Physics, P. O. Box 1048, Blindern, N-0316 Oslo (Norway); Kocan, M [Pavol Jozef Safarik University, Faculty of Science, Jesenna 5, SK-04000 Kosice (Slovakia); Marton, I; Nagy, Zs [NIIF/HUNGARNET, Victor Hugo 18-22, H-1132 Budapest (Hungary); Moeller, S [University of Luebeck, Inst. Of Neuro- and Bioinformatics, Ratzeburger Allee 160, D-23538 Luebeck (Germany); Mohn, B, E-mail: oxana.smirnova@hep.lu.s [Uppsala University, Department of Physics and Astronomy, Div. of Nuclear and Particle Physics, Box 535, SE-75121 Uppsala (Sweden)

    2010-04-01

    The Advanced Resource Connector (ARC) middleware introduced by NorduGrid is one of the basic Grid solutions used by scientists worldwide. While being well-proven in daily use by a wide variety of scientific applications at large-scale infrastructures like the Nordic DataGrid Facility (NDGF) and smaller scale projects, production ARC of today is still largely based on conventional Grid technologies and custom interfaces introduced a decade ago. In order to guarantee sustainability, true cross-system portability and standards-compliance based interoperability, the ARC community undertakes a massive effort of implementing modular Web Service (WS) approach into the middleware. With support from the EU KnowARC project, new components were introduced and the existing key ARC services got extended with WS technology based standard-compliant interfaces following a service-oriented architecture. Such components include the hosting environment framework, the resource-coupled execution service, the re-engineered client library, the self-healing storage solution and the peer-to-peer information system, to name a few. Gradual introduction of these new services and client tools into the production middleware releases is carried out together with NDGF and thus ensures a smooth transition to the next generation Grid middleware. Standard interfaces and modularity of the new component design are essential for ARC contributions to the planned Universal Middleware Distribution of the European Grid Initiative.

  16. Recent ARC developments: Through modularity to interoperability

    International Nuclear Information System (INIS)

    The Advanced Resource Connector (ARC) middleware introduced by NorduGrid is one of the basic Grid solutions used by scientists worldwide. While being well-proven in daily use by a wide variety of scientific applications at large-scale infrastructures like the Nordic DataGrid Facility (NDGF) and smaller scale projects, production ARC of today is still largely based on conventional Grid technologies and custom interfaces introduced a decade ago. In order to guarantee sustainability, true cross-system portability and standards-compliance based interoperability, the ARC community undertakes a massive effort of implementing modular Web Service (WS) approach into the middleware. With support from the EU KnowARC project, new components were introduced and the existing key ARC services got extended with WS technology based standard-compliant interfaces following a service-oriented architecture. Such components include the hosting environment framework, the resource-coupled execution service, the re-engineered client library, the self-healing storage solution and the peer-to-peer information system, to name a few. Gradual introduction of these new services and client tools into the production middleware releases is carried out together with NDGF and thus ensures a smooth transition to the next generation Grid middleware. Standard interfaces and modularity of the new component design are essential for ARC contributions to the planned Universal Middleware Distribution of the European Grid Initiative.

  17. New method for capturing arc of moving on switching apparatus

    Institute of Scientific and Technical Information of China (English)

    LIU Jiao-min; WANG Jing-hong

    2007-01-01

    The switching arc that occurs in contact gap when contact of low voltage apparatus closes or breaks in electric circuit is harmful to the contacts, insulation, and reliability of electrical gear because of its very high temperature. As arcing time is very short in switching gear, it is very difficult to observe arc phenomena directly for researchers. Therefore, visualization of switching arc is important for understanding arc phenomena, to analyze the arc features, and to improve the design and reliability of switching gear. Based on analyzing the visualization methods proposed by researchers, a new switching arc capturing approach is introduced in this paper. Arc image acquisition, and image processing techniques were studied. A switching arc image acquisition and visual simulation software based on high speed CCD camera hard ware system was designed and implemented to yield enhanced arc image with good visual effect.

  18. Kinematics, crustal structure and seismotectonics of the subducting northernmost Luzon arc in eastern Taiwan

    Science.gov (United States)

    Lee, Jian-Cheng; Chen, Chia-Yu; Chen, Rou-Fei; Chen, Yue-Gau; Chen, Horng-Yue

    2015-04-01

    arc system with significant volume. Instead subducting toward the NW, we tend to interpret that the fore-arc basement has been squeezed beneath the plate suture whereas the arc itself, including volcanic arc and fore-arc deposits (i.e., the Coastal Range), detached and were thrust over the Central Range of the Eurasian plate. Recent studies of seismic tomography allowed us interpreting the fore-arc basement is in contact with the Eurasian crust under the northern Coastal Range, characterized by a high-angle W-dipping seismicity zone. We also argue that recent two moderate earthquakes, including the 2013 M=6.3 Ruishui earthquake and the 2014 M=5.9 Fenglin earthquake, resulted from rupturing of the interface of Eurasian plate and Luzon fore-arc basement.

  19. Episodic intrusion, internal differentiation, and hydrothermal alteration of the miocene tatoosh intrusive suite south of Mount Rainier, Washington

    Science.gov (United States)

    du Bray, E.A.; Bacon, C.R.; John, D.A.; Wooden, J.L.; Mazdab, F.K.

    2011-01-01

    The Miocene Tatoosh intrusive suite south of Mount Rainier is composed of three broadly granodioritic plutons that are manifestations of ancestral Cascades arc magmatism. Tatoosh intrusive suite plutons have individually diagnostic characteristics, including texture, mineralogy, and geochemistry, and apparently lack internal contacts. New ion-microprobe U-Pb zircon ages indicate crystallization of the Stevens pluton ca. 19.2 Ma, Reflection-Pyramid pluton ca. 18.5 Ma, and Nisqually pluton ca. 17.5 Ma. The Stevens pluton includes rare, statistically distinct ca. 20.1 Ma zircon antecrysts. Wide-ranging zircon rare earth element (REE), Hf, U, and Th concentrations suggest late crystallization from variably evolved residual liquids. Zircon Eu/Eu*-Hf covariation is distinct for each of the Reflection-Pyramid, Nisqually, and Stevens plutons. Although most Tatoosh intrusive suite rocks have been affected by weak hydrothermal alteration, and sparse mineralized veins cut some of these rocks, significant base or precious metal mineralization is absent. At the time of shallow emplacement, each of these magma bodies was largely homogeneous in bulk composition and petrographic features, but, prior to final solidification, each of the Tatoosh intrusive suite plutons developed internal compositional variation. Geochemical and petrographic trends within each pluton are most consistent with differential loss of residual melt, possibly represented by late aplite dikes or erupted as rhyolite, from crystal-rich magma. Crystal-rich magma that formed each pluton evidently accumulated in reservoirs below the present level of exposure and then intruded to a shallow depth. Assembled by episodic intrusion, the Tatoosh intrusive suite may be representative of midsized composite plutonic complexes beneath arc volcanoes. ?? 2011 Geological Society of America.

  20. Vacuum arc under axial magnetic fields: experimental and simulation research

    International Nuclear Information System (INIS)

    Axial magnetic field (AMF) technology is a most important control method of vacuum arc, particularly for high-current vacuum arcs in vacuum interrupters. In this paper, a review of the state of current research on vacuum arcs under AMF is presented. The major aspects of vacuum arc in an AMF such as arc voltage, the motion of cathode spots, and anode activities are discussed, and the most recent progress both of experimental and simulation research is presented. (topical review)

  1. Direct probing of anode arc root dynamics and voltage instability in a dc non-transferred arc plasma jet

    Science.gov (United States)

    Ghorui, S.; Tiwari, N.; Meher, K. C.; Jan, A.; Bhat, A.; Sahasrabudhe, S. N.

    2015-12-01

    The transient dynamics of the anode arc root in a dc non-transferred arc plasma torch is captured through fast photography and directly correlated with the associated voltage instability for the first time. The coexistence of multiple arc roots, the transition to a single arc root, root formation and extinction are investigated for the steady, takeover and re-strike modes of the arc. Contrary to the usual concept, the emerging plasma jet of a dc non-transferred arc plasma torch is found to carry current. An unusually long self-propelled arc plasma jet, a consequence of the phenomenon, is demonstrated.

  2. Carboniferous magmatism in the Evora Massif (southwest Portugal, Ossa-Morena Zone): from typical arc calc-alkaline to adakitic-like magmatism

    Science.gov (United States)

    Lima, Selma M.; Neiva, Ana M. R.; Ramos, Joao M. F.

    2014-05-01

    the PP and the neighboring plutons are observed. First, the PP has the most primitive Sr-Nd isotopic signature; second, several chemical features (like high Na2O [3.86-5.87 %], Sr [278-939 ppm] and Sr/Y [12.4-192.5], low Y [2.4-19.5 ppm] and K2O/Na2O [0.19-0.75], strongly fractionated REE patterns [LaCN/YbCN = 18-43] and lack of pronounced Eu anomaly) suggest that the PP is chemically distinct from typical calc-alkaline arc rocks and is more similar to Archean TTGs and modern adakites. Using the compositional criteria of [6], an evolution towards 'slab-melts' compositions is observed within the PP, whereas the other Evora Massif plutons clearly represent 'non-slab melts'. Given their close spatial and temporal relation, we believe that the link between these granitic bodies deserves further investigation. [1] Silva and Pereira (2004) Geologische Rundschau 93, 886-896; [2] Moita et al. (2005) Geogaceta 37, 55-58; [3] Antunes et al. (2011) Estudios Geologicos 66, 25-34; [4] Antunes et al. (2011) Hutton Symposium Abstracts 9-10; [5] Lima et al. (2012) Journal of Petrology 53, 1887-1911; [6] Defant and Drummond (1990) Nature 347, 662-665.

  3. Upper crust response to geodynamic processes beneath Isparta Angle, SW Turkey: Revealed by CMT solutions of earthquakes

    Science.gov (United States)

    Över, Semir; Özden, Süha; Kamacı, Züheyr; Yılmaz, Hüseyin; Ünlügenç, Ulvi Can; Pınar, Ali

    2016-09-01

    The Isparta Angle is an important area of SW Anatolia where extensions in all directions (N-S, NE-SW, NW-SE and E-W) meet. These extensions were determined by normal faulting structures as well as by shallow earthquakes. All extensions, except the E-W one, were attributed to the deviatoric stresses in relation to slab forces and/or extrusion of Anatolia. The moment tensor inversion of 40 shallow earthquakes which occurred in the inner part of the Isparta Angle give focal mechanisms mostly indicating normal faulting. Inversion of all focal mechanisms of the earthquakes obtained from the moment tensor inversion yields normal faulting characterized by an approximately E-W (N268°E) σ3 axis. The calculated stress ratio R is 0.6944 indicating a triaxial stress state. Commonly accepted geodynamic models for the eastern Mediterranean region do not include plate boundary forces acting in the east or west direction. Our hypothesis is that the cause of the E-W extension is the combined forces of Gravitational Potential Energy and the hot asthenosphere upwelling through a tear fault in the subducted African plate between the Hellenic and Cyprus arcs beneath the Isparta Angle.

  4. Neotectonic development of the El Salvador Fault Zone and implications for deformation in the Central America Volcanic Arc: Insights from 4-D analog modeling experiments

    Science.gov (United States)

    Alonso-Henar, Jorge; Schreurs, Guido; Martinez-Díaz, José Jesús; Álvarez-Gómez, José Antonio; Villamor, Pilar

    2015-01-01

    The El Salvador Fault Zone (ESFZ) is an active, approximately 150 km long and 20 km wide, segmented, dextral strike-slip fault zone within the Central American Volcanic Arc striking N100°E. Although several studies have investigated the surface expression of the ESFZ, little is known about its structure at depth and its kinematic evolution. Structural field data and mapping suggest a phase of extension, at some stage during the evolution of the ESFZ. This phase would explain dip-slip movements on structures that are currently associated with the active, dominantly strike slip and that do not fit with the current tectonic regime. Field observations suggest trenchward migration of the arc. Such an extension and trenchward migration of the volcanic arc could be related to slab rollback of the Cocos plate beneath the Chortis Block during the Miocene/Pliocene. We carried out 4-D analog model experiments to test whether an early phase of extension is required to form the present-day fault pattern in the ESFZ. Our experiments suggest that a two-phase tectonic evolution best explains the ESFZ: an early pure extensional phase linked to a segmented volcanic arc is necessary to form the main structures. This extensional phase is followed by a strike-slip dominated regime, which results in intersegment areas with local transtension and segments with almost pure strike-slip motion. The results of our experiments combined with field data along the Central American Volcanic Arc indicate that the slab rollback intensity beneath the Chortis Block is greater in Nicaragua and decreases westward to Guatemala.

  5. Electrical conductivity anomaly beneath Mare Serenitatis detected by Lunokhod 2 and Apollo 16 magnetometers

    Science.gov (United States)

    Vanian, L. L.; Vnuchkova, T. A.; Egorov, I. V.; Basilevskii, A. T.; Eroshenko, E. G.; Fainberg, E. B.; Dyal, P.; Daily, W. D.

    1979-01-01

    Magnetic fluctuations measured by the Lunokhod 2 magnetometer in the Bay Le Monnier are distinctly anisotropic when compared to simultaneous Apollo 16 magnetometer data measured 1100 km away in the Descartes highlands. This anisotropy can be explained by an anomalous electrical conductivity of the upper mantle beneath Mare Serenitatis. A model is presented of anomalously lower electrical conductivity beneath Serenitatis and the simultaneous magnetic data from the Lunokhod 2 site at the mare edge and the Apollo 16 site are compared to the numerically calculated model solutions. This comparison indicates that the anisotropic fluctuations can be modeled by a nonconducting layer in the lunar lithosphere which is 150 km thick beneath the highlands and 300 km thick beneath Mare Serenitatis. A decreased electrical conductivity in the upper mantle beneath the mare may be due to a lower temperature resulting from heat carried out the magma source regions to the surface during mare flooding.

  6. Emplacement mechanism of the Middle-Late Jurassic Qitianling pluton and its implications on the Mesozoic tectonics of South China Block

    Science.gov (United States)

    Liu, Hongsheng; Chen, Yan; Faure, Michel; Scaillet, Bruno; Wang, Bo; Martelet, Guillaume; Huang, Fangfang; Zhu, Jinchu; Wang, Rucheng; Erdmann, Saskia

    2016-04-01

    The widespread Mesozoic magmatism that extends about 1500km along the NE-SW strike and 800km wide in the southeastern part of the South China Block is a remarkable feature that has attracted the attention of geoscientists since 1940's. Numerous studies have been carried out, and consequently, several geodynamic models related to the emplacement mechanism have been proposed, based essentially on petrology, geochronology, and (isotopic) geochemistry. Recently, a general consensus is apparently achieved within the geosciences community on the tectonic contexts of the South China Block during the Triassic (compressive) and Cretaceous (extensive) periods, however the tectonic setting of the Jurassic is still in debate, moreover the Jurassic magmatism is closely related to abundant mineralization of rare metal elements. Due to the similarities in age, rock type and major geochemical feature of Jurassic granite, the Qitianling granitic pluton, situated in the Nanling area and dated at ca. 157 Ma, was chosen as the target of this study among 41 visited plutons. Previous studies divide the Qitianling pluton into three petrographic facies, namely: i) Bt + Qtz + Fsd + Amp, ii) Bt + Qtz + Fsd + (Amp) , iii) Bt + Qtz + Fsd. Zircon U-Pb dating indicate the age peak of these different facies at 161Ma, 157-156Ma and 149Ma, respectively. The field observation shows that: 1) the granite is isotropic without visible preferred mineral orientation or deformation; 2) the contact between the granite and country rocks is sharp, with a 1-10m narrow thermal aureole, but without any visible deformation. The microscopic observation on the thin sections of wall rocks and granite doesn't show any mineral preferred orientation consisting to the field observation. Therefore, a total of 53 sampling sites and 318 oriented cores were collected from the Qitianling pluton for an Anisotropy of Magnetic Susceptibility (AMS) study. The investigation on rock magnetism shows the pseudo

  7. Magnetic anisotropy of the Redenção granite, eastern Amazonian craton (Brazil): Implications for the emplacement of A-type plutons

    Science.gov (United States)

    de Oliveira, Davis Carvalho; Neves, Sérgio Pacheco; Trindade, Ricardo I. F.; Dall'Agnol, Roberto; Mariano, Gorki; Correia, Paulo Barros

    2010-10-01

    A magnetic fabric study was performed on the Redenção pluton in an attempt to understand its emplacement history. The Redenção pluton is part of the 1.88 Ga, anorogenic, A-type Jamon suite that intruded 2.97-2.86 Ga-old Archean granitoids of the Rio Maria Granite-Greenstone Terrane in the eastern Amazonian craton (northern Brazil). Previous gravity survey indicates that the pluton is a 6 km-thick, tabular intrusion. It is characterized by a concentric distribution of facies, with rings of seriated and porphyritic granite that cut across the main facies of even-grained monzogranites. The whole set is intruded by leucogranites that occupy the center of the pluton. Petrographic examination, magnetic susceptibilities, coercivity-spectra and thermomagnetic curves indicate that the magnetic fabric is primarily carried by coarse-grained multidomain magnetite. This is reinforced by the coincidence of magnetic susceptibility and remanence anisotropy principal axes. The absence of solid-state deformation features and the low anisotropy degrees indicate that the magnetic fabric is magmatic in origin. The magnetic fabric displays a systematic pattern, with all facies, including the rings of porphyritic granite, being characterized by concentric, gently dipping foliations associated with gently plunging lineations. Only the central leucogranitic facies shows a slightly discordant pattern with steeply dipping fabrics at its northeastern sector. An emplacement model by vertical stacking of successive magma batches is proposed for the construction of the Redenção pluton, which reconciles the tabular shape of the intrusion, the petrographic and geochemical zoning, and the magnetic fabric pattern. Initially, two magma batches were emplaced as sills. First the even-grained monzogranite, then the seriated and porphyritic granites, which formed by mingling of a leucogranitic melt with the host biotite-monzogranitic magma as attested by geochemical data and field evidence. The

  8. Episodicity in back-arc tectonic regimes

    Science.gov (United States)

    Clark, Stuart R.; Stegman, Dave; Müller, R. Dietmar

    2008-12-01

    The evolution of back-arc basins is tied to the development of the dynamics of the subduction system they are a part of. We present a study of back-arc basins and model their development by implementing 3D time-dependant computer models of subduction including an overriding plate. We define three types of episodicity: pseudo-, quasi- and hyper-episodicity, and find evidence of these in nature. Observations of back-arc basin ages, histories of spreading, quiescence and compression in the overriding plate give us an understanding of the time-development of these subduction zones and back-arc basins. Across the globe today, a number of trenches are advancing—the Izu-Bonin Trench, the Mariana Trench, the Japan Trench, the Java-Sunda Trench and the central portion of the Peru-Chile Trench (the Andes subduction zone). The Izu-Bonin, Mariana and Japan all have established back-arc basins, while the others have documented episodes of spreading, quiescence, compression or a combination of these. The combination of advancing and retreating trench motion places these subduction zones in the category of hyper-episodicity. Quasi-episodicity, in which the back-arc shifts between phases of rifting, spreading and quiescence, is the dominant form of episodic back-arc development in the present. We find this type of episodicity in models for which the system is dynamically consistent—that we have allowed the subducting plate's velocity to be determined by the sinking slabs' buoyancy. Quasi- and hyper-episodicity are only found in subduction zones with relatively high subducting plate velocities, between 6 and 9 cm/year. Finally, those subduction zones for which the subducting plate is moving slowly, such as in the Mediterranean or the Scotia Sea, experience only pseudo-episodicity, where the spreading moves linearly towards the trench but often does so in discrete ridge-jump events.

  9. arcControlTower: the System for Atlas Production and Analysis on ARC

    Science.gov (United States)

    Filipčič, Andrej; ATLAS Collaboration

    2011-12-01

    PanDA, the Atlas management and distribution system for production and analysis jobs on EGEE and OSG clusters, is based on pilot jobs to increase the throughput and stability of the job execution on grid. The ARC middleware uses a specific approach which tightly connects the job requirements with cluster capabilities like resource usage, software availability and caching of input files. The pilot concept renders the ARC features useless. The arcControlTower is the job submission system which merges the pilot benefits and ARC advantages. It takes the pilot payload from the panda server and submits the jobs to the Nordugrid ARC clusters as regular jobs, with all the job resources known in advance. All the pilot communication with the PanDA server is done by the arcControlTower, so it plays the role of a pilot factory and the pilot itself. There are several advantages to this approach: no grid middleware is needed on the worker nodes, the fair-share between the production and user jobs is tuned with the arcControlTower load parameters, the jobs can be controlled by ARC client tools. The system could be extended to other submission systems using central distribution.

  10. arcControlTower: the System for Atlas Production and Analysis on ARC

    International Nuclear Information System (INIS)

    PanDA, the Atlas management and distribution system for production and analysis jobs on EGEE and OSG clusters, is based on pilot jobs to increase the throughput and stability of the job execution on grid. The ARC middleware uses a specific approach which tightly connects the job requirements with cluster capabilities like resource usage, software availability and caching of input files. The pilot concept renders the ARC features useless. The arcControlTower is the job submission system which merges the pilot benefits and ARC advantages. It takes the pilot payload from the panda server and submits the jobs to the Nordugrid ARC clusters as regular jobs, with all the job resources known in advance. All the pilot communication with the PanDA server is done by the arcControlTower, so it plays the role of a pilot factory and the pilot itself. There are several advantages to this approach: no grid middleware is needed on the worker nodes, the fair-share between the production and user jobs is tuned with the arcControlTower load parameters, the jobs can be controlled by ARC client tools. The system could be extended to other submission systems using central distribution.

  11. Effect of acoustic field parameters on arc acoustic binding during ultrasonic wave-assisted arc welding.

    Science.gov (United States)

    Xie, Weifeng; Fan, Chenglei; Yang, Chunli; Lin, Sanbao

    2016-03-01

    As a newly developed arc welding method, power ultrasound has been successfully introduced into arc and weld pool during ultrasonic wave-assisted arc welding process. The advanced process for molten metals can be realized by utilizing additional ultrasonic field. Under the action of the acoustic wave, the plasma arc as weld heat source is regulated and its characteristics make an obvious change. Compared with the conventional arc, the ultrasonic wave-assisted arc plasma is bound significantly and becomes brighter. To reveal the dependence of the acoustic binding force on acoustic field parameters, a two-dimensional acoustic field model for ultrasonic wave-assisted arc welding device is established. The influences of the radiator height, the central pore radius, the radiator radius, and curvature radius or depth of concave radiator surface are discussed using the boundary element method. Then the authors analyze the resonant mode by this relationship curve between acoustic radiation power and radiator height. Furthermore, the best acoustic binding ability is obtained by optimizing the geometric parameters of acoustic radiator. In addition, three concave radiator surfaces including spherical cap surface, paraboloid of revolution, and rotating single curved surface are investigated systematically. Finally, both the calculation and experiment suggest that, to obtain the best acoustic binding ability, the ultrasonic wave-assisted arc welding setup should be operated under the first resonant mode using a radiator with a spherical cap surface, a small central pore, a large section radius and an appropriate curvature radius. PMID:26558995

  12. Effect of arc distance on temperature field and weld shape during double-sided arc welding

    Institute of Scientific and Technical Information of China (English)

    ZHANG Guangjun; ZHANG Huajun; GAO Hongming; WU Lin

    2009-01-01

    A new high efficiency welding method, double-sided double arc welding with double powers (DSAW-D), is developed for thick plate of low alloy high strength steel in this study. It is well known that the thermal cycles have an important influence on the microstructure, shape, stress, distortion and mechanical property. The DSA W-D method can control the tempernture field on a wide range by regulating the distance between two arcs, improve the rnicrostructure and prevent hot and cold cracking of high strength steel. But at present, the effect of arc distance on the temperature field and shape is not clear. Therefore, the paper researches the effect of arc distance on the temperature field and weld pool during DSA W-D using finite element method. The transient temperature field of different arc distance in DSAW-D is calculated.To verify the numerical results, the temperature is measured by the thermo-couple and the calculated results agree approximately with experimental data. Farther, the thermal property and mutual effect of double-sided arcs are investigated. The temperature distributions and weld pool profile at different arc distances are obtained. The results show that arc distance is a very important factor to affect the heat process.

  13. Effect of acoustic field parameters on arc acoustic binding during ultrasonic wave-assisted arc welding.

    Science.gov (United States)

    Xie, Weifeng; Fan, Chenglei; Yang, Chunli; Lin, Sanbao

    2016-03-01

    As a newly developed arc welding method, power ultrasound has been successfully introduced into arc and weld pool during ultrasonic wave-assisted arc welding process. The advanced process for molten metals can be realized by utilizing additional ultrasonic field. Under the action of the acoustic wave, the plasma arc as weld heat source is regulated and its characteristics make an obvious change. Compared with the conventional arc, the ultrasonic wave-assisted arc plasma is bound significantly and becomes brighter. To reveal the dependence of the acoustic binding force on acoustic field parameters, a two-dimensional acoustic field model for ultrasonic wave-assisted arc welding device is established. The influences of the radiator height, the central pore radius, the radiator radius, and curvature radius or depth of concave radiator surface are discussed using the boundary element method. Then the authors analyze the resonant mode by this relationship curve between acoustic radiation power and radiator height. Furthermore, the best acoustic binding ability is obtained by optimizing the geometric parameters of acoustic radiator. In addition, three concave radiator surfaces including spherical cap surface, paraboloid of revolution, and rotating single curved surface are investigated systematically. Finally, both the calculation and experiment suggest that, to obtain the best acoustic binding ability, the ultrasonic wave-assisted arc welding setup should be operated under the first resonant mode using a radiator with a spherical cap surface, a small central pore, a large section radius and an appropriate curvature radius.

  14. Effects of process parameters on arc shape and penetration in twin-wire indirect arc welding

    Institute of Scientific and Technical Information of China (English)

    Shun-shan ZHANG; Mei-qing CAO; Dong-ting WU; Zeng-da ZOU

    2009-01-01

    In this study, the effects of variable parameters on arc shape and depth of penetration in twin-wire indirect arc gas shielded welding were investigated. The variation of arc shape caused by changes of the parameters was recorded by a high-speed camera,and the depths of penetration of specimen were measured after bead welding by an optical microscope. Experiments indicated that proper parameters give birth to a concentrated and compressed welcimg arc, which Would increase the depth of penetration as the incensement of the arc foice Several pnncipal parameters including toe distance ot twin wires intersecting point to base metal,the included angle,and the content of shielding gas were determined. The arc turned more concentrated and the depth of penetration increased obviously as the welding current increased,the arc turned brighter while unobvlous change of penetration occurred as the arc voltage increased,and the deepest penetration was obtained when the welding speed was 10.5 mm/s..

  15. Does the Nazca Slab Beneath Central Argentina Influence the Water Content of the Adjacent Transition Zone?

    Science.gov (United States)

    Booker, J. R.; Pomposiello, M. C.; Favetto, A.; Burd, A.

    2008-12-01

    When the Nazca flat-slab rolls over and plunges into the transition zone under Argentina, it appears to separate an electrically resistive transition zone to the west from an electrically conductive transition zone to the east. The simplest explanation for this is that the water content of the transition zone is much lower to the west than the east. The low conductivity to the west can be explained if anhydrous upper mantle mantle is being carried down into the transition zone by slab motion. The much higher conductivity to the east is beneath the Rio de la Plata Craton whose root almost certainly inhibits vertical motion east of the slab. Thus water injected by the descending slab is likely to accumulate in the transition zone. This idea was first presented in a Nature paper in 2004. Since then, we have collected more magnetotelluric data to the south where the slab dip is normal, but voluminous back-arc basaltic volcanism occurs and in the region where the slab is said to be flexing continuously between the two geometries. A goal of this work is to test whether the slab has a similar relation to transition zone conductivity along strike. The new data, originally collected along linear profiles perpendicular to the expected strike of the slab in the mantle clearly indicated that 2-D interpretation would be problematic. Indeed, analysis of new data in the flexure region using 2-D methods reveals a narrow, roughly east-west, near vertical resistive structure extending down to the top of a conductive transition zone. A possible, but controversial interpretation of this structure is that it is the signature of a slab tear rather than the widely-accepted continuous flexure geometry. If a tear is indeed correct, then there is an opportunity to test how the slab is influencing the transition zone conductivity and by inference the water content by looking at the southern edge of the plunging 'flat- slab' as it enters the transition zone. Since the original data were

  16. Geodynamic evolution of the lithosphere beneath the Eastern Anatolia region: Constraints from geodynamic modeling

    Science.gov (United States)

    Memis, Caner; Hakan Gogus, Oguz; Pysklywec, Russell; Keskin, Mehmet; Celal Sengor, A. M.; Topuz, Gultekin

    2016-04-01

    The east Anatolian orogenic plateau is characterized by an average elevation of 2 km, and is delimited by the Bitlis-Zagros collision zone to the south and the Pontide arc to the north. Stratigraphic evidence suggests that the high plateau attained its current elevation since the Serravallian (about 12 million years ago), but probably did not reach its present height until at least the latest Pliocene. While the crustal shortening following the Arabia-Eurasia collision in the south enabled its relatively rapid rise and regional tectonic evolution, the presumed removal of the downgoing slab beneath east Anatolia has potentially played a significant role in this geodynamic configuration. According to the proposed scenario, the northward subducting slab of Neo-Tethys peels away from the overlying crust similar to the lithospheric delamination model. In this work, we performed a series of lithospheric removal models by varying rheological, physical and mechanical properties by using 2D numerical geodynamic experiments, (e.g. plate convergence rate, crustal thickness, mantle lithosphere yield-stress). Our model results show that the average amount of delamination hinge motion is maximum (18 km/my) when the lower crustal rheology is felsic granulite. The slab break-off only occurs at lower convergence rates (≤ 2 cm/yr), and is imposed on the margin of delaminating mantle lithosphere. The surface uplift takes place above the asthenospheric column (or plateau gap) through isostatic and thermal support of asthenospheric upwelling, and varies dependent on the width of the asthenospheric column. However; with higher plate convergence rates (≥3 cm/yr), the asthenospheric column does not widen enough and the continental collision occurs rather than delamination/peeling away. In this case, the average uplift appears in the central section of the crust, and this exceeds a surface elevation of 3 km. All model results are consistent with the observations from the Eastern

  17. Overview of ArcGIS Engine Controls%ArcGIS Engine控件综述

    Institute of Scientific and Technical Information of China (English)

    刘磊

    2010-01-01

    ArcGIS Engine是ESRI公司发布的嵌入式地理信息系统软件开发包.基于ArcGIS Engine开发的应用程序一般有3类:独立非可视化应用程序、独立可视化应用程序和嵌入式应用程序,由于ArcGIS Engine提供了一套可复用、跨平台、设计良好的ArcGIS控件,因此利用控件开发可视化的GIS应用程序是一种常用的开发方式.重点探讨了ArcGIS Engine自带控件的功能、使用方法以及与伙伴控件之间的联系机制.

  18. Method to reduce arc blow during DC arc welding of pipelines

    Energy Technology Data Exchange (ETDEWEB)

    Espina-Hernandez, J. H.; Rueda-Morales, G.L.; Caleyo, F.; Hallen, J. M. [Instituto Politecnico Nacional, Mexico, (Mexico); Lopez-Montenegro, A.; Perz-Baruch, E. [Pemex Exploracion y Produccion, Tabasco, (Mexico)

    2010-07-01

    Steel pipelines are huge ferromagnetic structures and can be easily subjected to arc blow during the DC arc welding process. The development of methods to avoid arc blow during pipeline DC arc welding is a major objective in the pipeline industry. This study developed a simple procedure to compensate the residual magnetic field in the groove during DC arc welding. A Gaussmeter was used to perform magnetic flux density measurements in pipelines in southern Mexico. These data were used to perform magnetic finite element simulations using FEMM. Different variables were studied such as the residual magnetic field in the groove or the position of the coil with respect to the groove. An empirical predictive equation was developed from these trials to compensate for the residual magnetic field. A new method of compensating for the residual magnetic field in the groove by selecting the number of coil turns and the position of the coil with respect to the groove was established.

  19. Critical Length Criterion and the Arc Chain Model for Calculating the Arcing Time of the Secondary Arc Related to AC Transmission Lines

    Science.gov (United States)

    Cong, Haoxi; Li, Qingmin; Xing, Jinyuan; Li, Jinsong; Chen, Qiang

    2015-06-01

    The prompt extinction of the secondary arc is critical to the single-phase reclosing of AC transmission lines, including half-wavelength power transmission lines. In this paper, a low-voltage physical experimental platform was established and the motion process of the secondary arc was recorded by a high-speed camera. It was found that the arcing time of the secondary arc rendered a close relationship with its arc length. Through the input and output power energy analysis of the secondary arc, a new critical length criterion for the arcing time was proposed. The arc chain model was then adopted to calculate the arcing time with both the traditional and the proposed critical length criteria, and the simulation results were compared with the experimental data. The study showed that the arcing time calculated from the new critical length criterion gave more accurate results, which can provide a reliable criterion in term of arcing time for modeling and simulation of the secondary arc related with power transmission lines. supported by National Natural Science Foundation of China (Nos. 51277061 and 51420105011)

  20. Thermal-rheological structure of the lithosphere beneath Jiyang Depression: Its implications for geodynamics

    Institute of Scientific and Technical Information of China (English)

    LIU Shaowen; WANG Liangshu; GONG Yuling; LI Cheng; LI Hua; HAN Yongbing

    2005-01-01

    Jiyang Depression, located in the southeast Bohai Bay Basin, has the geomorphologic framework of multiple uplifts intervening with sags. Combined the abundant geo-temperature data and thermo-physical parameters of rock samples derived from oil and gas exploration during the past years, with geothermal approaches, here we investigate the lithospheric thermal regime of this depression. Consequently, based on the obtained thermal structure of the lithosphere, along with rheological modeling, the lithospheric rheological profiles of Jiyang Depression are then determined. Our results show that the temperature at the bottom of sedimentary cover within depression varies from 129℃ to 298℃, accompanied with the basement heat flow ranging between 54.3 and 60.5 mW/m2; and 406℃-436℃ for temperature at the bottom of the upper crust, along with heat flow varying from 47.7 to 52.6 mW/m2; while the temperature at the bottom of the middle crust is between 537℃ and 572℃, as well as heat flow ranging from 41.3 to 56.3 mW/m2. The temperature at Moho ranges from 669℃ to 721℃, the heat flow derived from mantle is between 38.1 and 43.1 mW/m2, and calculated thickness of the thermal lithosphere beneath depression varies from 71 to 90 km. Lithospheric thermal regime is a close correlation with such factors as crustal thickness and surface heat flow, etc. Usually, the larger the surface heat flow, the larger the deep temperature and heat flow within lithosphere, and the thinner the thermal lithospheric thickness. This high thermal regime of the lithosphere in Jiyang Depression is thought to be related to Cenozoic back-arc spreading during the western Pacific plate subduction into Eurasian continent. Lithospheric rheological modeling shows that the lithosphere in Jiyang Depression is characterized by its distinct rheological stratification as follows: The upper and most part of the middle crust are of brittle, while the lower crust and the lower part of middle crust are all

  1. The geochemistry and petrogenesis of the Paleoproterozoic Green Mountain arc: A composite(?), bimodal, oceanic, fringing arc

    Science.gov (United States)

    Jones, D.S.; Barnes, C.G.; Premo, W.R.; Snoke, A.W.

    2011-01-01

    The inferred subduction affinity of the ~1780-Ma Green Mountain arc, a dominantly bimodal igneous terrane (together with immature marine and volcaniclastic sedimentary rocks) accreted to the southern margin of the Wyoming province, is integral to arc-accretion models of the Paleoproterozoic growth of southern Laurentia. Conversely, the dominantly bimodal nature of many putative arc-related igneous suites throughout southern Laurentia, including the Green Mountain arc, has also been used to support models of growth by extension of pre-existing crust. We report new geochemical and isotopic data from ~1780-Ma gabbroic and granodioritic to tonalitic rocks of the Big Creek Gneiss, interpreted as consanguineous with previously studied metavolcanic rocks of the Green Mountain Formation.The ~1780-Ma Big Creek Gneiss mafic rocks show clear geochemical signatures of a subduction origin and provide no supporting evidence for extensional tectonism. The ~1780-Ma Big Creek Gneiss felsic rocks are attributed to partial melting of mafic and/or mixed lower-crustal material. The bimodal nature of the suite results from the combination of arc basalts and felsic crustal melts. The lack of andesite is consistent with the observed tholeiitic differentiation trend of the mafic magmas. The lower e{open}Nd(1780Ma) values for the felsic rocks vs. the mafic rocks suggest that the unexposed lower crust of the arc may be older than the arc and that Trans-Hudson- or Penokean-aged rocks possibly form the substratum of the arc. Our results reinforce previous interpretations that arc-related magmatism played a key role in the Paleoproterozoic crustal growth of southern Laurentia, but also support the possibility of unexposed older crust as basement to the arcs. ?? 2011 Elsevier B.V.

  2. BASIC THEORY AND METHOD OF WELDING ARC SPECTRAL INFORMATION

    Institute of Scientific and Technical Information of China (English)

    Li Junyue; Li Zhiyong; Li Huan; Xue Haitao

    2004-01-01

    Arc spectral information is a rising information source which can solve many problems that can not be done with arc electric information and other arc information.It is of important significance to develop automatic control technique of welding process.The basic theory and methods on it play an important role in expounding and applying arc spectral information.Using concerned equation in plasma physics and spectrum theory,a system of equations including 12 equations which serve as basic theory of arc spectral information is set up.Through analyzing of the 12 equations,a basic view that arc spectral information is the reflection of arc state and state variation,and is the most abundant information resource reflecting welding arc process is drawn.Furthermore,based on the basic theory,the basic methods of test and control of arc spectral information and points out some applications of it are discussesed.

  3. Aeolus or Pluton?; Eole ou pluton?

    Energy Technology Data Exchange (ETDEWEB)

    Anon.

    2003-07-01

    In the next years the french government will have to take great decisions in matter of energy and specifically electric power. This report aims to give an estimation of wind power channel in France supposing financial possibilities equivalent to those implemented for the EPR (European Pressurized Reactor) channel. After a presentation of the electric power industry in France, the two channels are compared. (A.L.B.)

  4. Ti Mobility in Quartzite from the Eureka Valley-Joshua Flat-Beer Creek Pluton (EJB) Aureole in California, USA.

    Science.gov (United States)

    Student, J. J.; Morgan, S.

    2015-12-01

    The EJB pluton intruded into Paleozoic sandstone during the Jurassic leaving a well-exposed aureole. Quartzite was collected from the contact outward to investigate the response of Ti in sedimentary quartz to varying grades of metamorphism using EPMA and CL imaging. TitaniQ and Zr in rutile thermobarometers were applied to rutile bearing quartzite at 225, 500, and 1540 meters from the contact. Comparison CL images, including those of Harkless sandstone collected 15 km away and Harkless quartzite in the aureole reveal significant Ti mobility and a general smoothing of the Ti distribution in the quartzite. The CL images also reveal that the redistribution of Ti in the quartzite was incomplete. Discounting this, TitaniQ was applied using a Ti activity of 1.0 and a pressure of 2.75 kbars based on previous studies. In an effort to establish possible peak conditions, Ti was measured in the brightest CL quartz grain interiors, and the Zr was measured in surrounding rutile grains. The temperature calculations are inconsistent. At 225 meters, the Zr in rutile resulted in a temperature range from 662-762 °C (n=31) compared to a maximum temperature of 595 °C based on Ti in quartz. At 500 meters, rutile resulted in a range from 635-720 °C (n=44) compared to quartz at 525 °C. At 1540 meters, the rutile ranged from 650-710 °C (n=55) compared to quartz at 547 °C. The thermometric results may suggest that the aureole was extensively heated to above 500 °C even at 1.5 km from the pluton contact. This is supported by previous studies using other thermometers, thermal modeling, quartz deformation fabrics, and evidence of partial melting-type textures. In all likelihood though, the thermometric results in this study reflect components of inheritance of the original grains, lack of complete Ti re-equilibration due to sluggish diffusion of Ti during metamorphism, and the varying effects of water availability as related to the formation of distinct deformation textures.

  5. Late Pleistocene pluton formation during the waning stages of the Altiplano-Puna ignimbrite flare-up

    Science.gov (United States)

    Tierney, C. R.; Schmitt, A. K.; Lovera, O. M.; de Silva, S. L.

    2015-12-01

    least 600 km3 of plutons underpinning each dome. The combined intrusive volume of 3,000 km3 results in a high intrusive to extrusive ratio of 75:1. This suggests that plutonic addition to the uppermost crust can be significant during the waning stages of high-flux events, although volcanic output is diminished.

  6. Mid-Miocene Rhyolite Sequence, Highland Range, NV: Record of Magma Evolution and Eruption From the Searchlight Pluton Magma Chamber

    Science.gov (United States)

    Colombini, L. L.; Gualda, G. A.; Miller, C. F.; Faulds, J.; Miller, J.; Wooden, J.; Mazdab, F.

    2008-12-01

    The Highland Range in southern Nevada contains a ~3 km-thick sequence of pre- to synextensional volcanic rock that records both large-magnitude Miocene extension and the evolution of large magma system. The volcanic sequence and probable source pluton are both well-exposed in a steeply W-tilted fault block (Faulds et al. 2002). A km-thick sequence of rhyolite in the southeast part of the range was emplaced above a thick section of trachyandesite and trachydacite at 16.2-16.0 Ma (SHRIMP zircon U-Pb, biotite Ar/Ar; Faulds et al 2002, J Miller et al 2007, new data). The lower half of the sequence comprises low-SiO2 rhyolite lavas (plag + biotite + cpx phenocrysts), which abruptly give way to tuffs and inter-fingered lavas (qtz + san + plag + bio + cpx + sphene) that mark a transition to a more explosive period of eruption of more evolved rhyolite plus active mafic input. Throughout the rhyolite sequence, mafic enclaves are abundant, changing from brittle fragments (lithics) in the lower lavas to quenched, crenulate-bordered magmatic enclaves in upper lavas and tuffs. Xenocrysts of reacted olivine, pyroxene, and plagioclase are evident in some rhyolites. The uppermost unit of the sequence is a quartz + sanidine-bearing lava that is heavily contaminated on all scales by mafic enclaves, lithics, and xenocrysts. Basaltic trachyandesite overlies this upper rhyolite. SHRIMP analysis of Ti and other trace elements in zircon from two samples near the top of the sequence documents strongly fluctuating T (720-920 C) and evolution of melt compositions; for the most part, rims grew at lower T from more evolved melt. Zr-in-sphene thermometry indicates that these phenocrysts grew at the lower temperatures recorded by the zircon rims. The rhyolite sequence appears to have erupted from the middle granite zone of the nearby Searchlight pluton, which is the same age and similarly evolved toward highly silicic compositions, records co-injection of mafic magma, and overlies slightly

  7. PLUTON: Three-group neutronic code for burnup analysis of isotope generation and depletion in highly irradiated LWR fuel rods

    Energy Technology Data Exchange (ETDEWEB)

    Lemehov, Sergei E; Suzuki, Motoe [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment

    2001-08-01

    PLUTON is a three-group neutronic code analyzing, as functions of time and burnup, the change of radial profiles, together with average values, of power density, burnup, concentration of trans-uranium elements, plutonium buildup, depletion of fissile elements, and fission product generation in water reactor fuel rod with standard UO{sub 2}, UO{sub 2}-Gd{sub 2}O{sub 3}, inhomogeneous MOX, and UO{sub 2}-ThO{sub 2}. The PLUTON code, which has been designed to be run on Windows PC, has adopted a theoretical shape function of neutron attenuation in pellet, which enables users to perform a very fast and accurate calculation easily. The present code includes the irradiation conditions of the Halden Reactor which gives verification data for the code. The total list of trans-uranium elements included in the calculations consists of {sub 92}U{sup 233-239}, {sub 93}Np{sup 237-239}, {sub 94}Pu{sup 238-243}, {sub 95}Am{sup 241-244} (including isomers), and {sub 96}Cm{sup 242-245}. Poisoning fission products are represented by {sub 54}Xe{sup 131,133,135}, {sub 48}Cd{sup 113}, {sub 62}Sm{sup 149,151,152}, {sub 64}Gd{sup 154-160}, {sub 63}Eu{sup 153,155}, {sub 36}Kr{sup 83,85}, {sub 42}Mo{sup 95}, {sub 43}Tc{sup 99}, {sub 45}Rh{sup 103}, {sub 47}Ag{sup 109}, {sub 53}I{sup 127,129,131}, {sub 55}Cs{sup 133}, {sub 57}La{sup 139}, {sub 59}Pr{sup 141}, {sub 60}Nd{sup 143-150}, {sub 61}Pm{sup 147}. Fission gases and volatiles included in the code are {sub 36}Kr{sup 83-86}, {sub 54}Xe{sup 129-136}, {sub 52}Te{sup 125-130}, {sub 53}I{sup 127-131}, {sub 55}Cs{sup 133-137}, and {sub 56}Ba{sup 135-140}. Verification has been performed up to 83 GWd/tU, and a satisfactory agreement has been obtained. (author)

  8. World's youngest exposed granite pluton. ; Geological features, ages, and cooling model for Takidani granodiorite. Sekaiichi wakai roshutsu kakogan pluton. ; Takidani kako senryokugan no chishitsu nendai to reikyaku model

    Energy Technology Data Exchange (ETDEWEB)

    Harayama, S.

    1992-12-01

    This paper describes the Takidani granodiorite mainly on its dating results. The granodiorite is exposed over an area of 21 km[sup 2] In an axial area in the mountain range south to the Japanese North Alps. Its lithofacies changes from a granodiorite in a deep phase to a granite in an upper phase. Any of the lithofacies is very fresh not having been subjected to alterations, and bears no evidence of having been reheated. Four test pieces were sampled from this grandiorite, and were dated using the K-Ar method and the Pb-Sr method. The result showed a minimum value of 1.09 [plus minus] 0.03 Ma, and a maximum value of 1.93 [plus minus] 0.16 Ma. This granodiorite pluton age is the youngest among those having been reported from various parts of the world. The solidification age for this granodiorite at its shallow zone is estimated at 2.2 [plus minus] 0.3 Ma with reference to the age of pyroclastic flow deposits (about 2.4 Ma) which is assumed to have close spatial and chronological relation with the granodiorite in question. 46 refs., 3 figs., 4 tabs.

  9. The Chahnaly low sulfidation epithermal gold deposit, western Makran volcanic arc, southeastern Iran

    Science.gov (United States)

    Sholeh, Ali; Rastad, Ebrahim; Huston, David L.; Gemmell, J. Bruce; Taylor, Ryan D.

    2016-01-01

    The Chahnaly low-sulfidation epithermal Au deposit and nearby Au prospects are located northwest of the intermittently active Bazman stratovolcano on the western end of the Makran volcanic arc, which formed as the result of subduction of the remnant Neo-Tethyan oceanic crust beneath the Lut block. The arc hosts the Siah Jangal epithermal and Kharestan porphyry prospects, near Taftan volcano, as well as the Saindak Cu-Au porphyry deposit and world-class Reko Diq Cu-Au porphyry deposit, near Koh-i-Sultan volcano to the east-northeast in Pakistan. The host rocks for the Chahnaly deposit include early Miocene andesite and andesitic volcaniclastic rocks that are intruded by younger dacitic domes. Unaltered late Miocene dacitic ignimbrites overlie these rocks. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U-Pb zircon geochronology data yield ages between 21.8 and 9.9 Ma for the acidic-intermediate regional volcanism. The most recent volcanic activity of the Bazman stratovolcano involved extrusion of an olivine basalt during Pliocene to Quaternary times. Interpretation of geochemical data indicate that the volcanic rocks are synsubduction and calc-alkaline to subalkaline. The lack of a significant negative Eu anomaly, a listric-shaped rare earth element pattern, and moderate La/Yb ratios of host suites indicate a high water content of the source magma.

  10. The link between volcanism and plutonism in epizonal magma systems; high-precision U–Pb zircon geochronology from the Organ Mountains caldera and batholith, New Mexico

    Science.gov (United States)

    Rioux, Matthew; Farmer, Lang; Bowring, Samuel; Wooton, Kathleen M.; Amato, Jeffrey M.; Coleman, Drew S.; Verplanck, Philip L.

    2016-01-01

    The Organ Mountains caldera and batholith expose the volcanic and epizonal plutonic record of an Eocene caldera complex. The caldera and batholith are well exposed, and extensive previous mapping and geochemical analyses have suggested a clear link between the volcanic and plutonic sections, making this an ideal location to study magmatic processes associated with caldera volcanism. Here we present high-precision thermal ionization mass spectrometry U–Pb zircon dates from throughout the caldera and batholith, and use these dates to test and improve existing petrogenetic models. The new dates indicate that Eocene volcanic and plutonic rocks in the Organ Mountains formed from ~44 to 34 Ma. The three largest caldera-related tuff units yielded weighted mean 206Pb/238U dates of 36.441 ± 0.020 Ma (Cueva Tuff), 36.259 ± 0.016 Ma (Achenback Park tuff), and 36.215 ± 0.016 Ma (Squaw Mountain tuff). An alkali feldspar granite, which is chemically similar to the erupted tuffs, yielded a synchronous weighted mean 206Pb/238U date of 36.259 ± 0.021 Ma. Weighted mean 206Pb/238U dates from the larger volume syenitic phase of the underlying Organ Needle pluton range from 36.130 ± 0.031 to 36.071 ± 0.012 Ma, and the youngest sample is 144 ± 20 to 188 ± 20 ka younger than the Squaw Mountain and Achenback Park tuffs, respectively. Younger plutonism in the batholith continued through at least 34.051 ± 0.029 Ma. We propose that the Achenback Park tuff, Squaw Mountain tuff, alkali feldspar granite and Organ Needle pluton formed from a single, long-lived magma chamber/mush zone. Early silicic magmas generated by partial melting of the lower crust rose to form an epizonal magma chamber. Underplating of the resulting mush zone led to partial melting and generation of a high-silica alkali feldspar granite cap, which erupted to form the tuffs. The deeper parts of the chamber underwent continued recharge and crystallization for 144 ± 20 ka after the

  11. Lead isotope compositions of Late Cretaceous and early Tertiary igneous rocks and sulfide minerals in Arizona: Implications for the sources of plutons and metals in porphyry copper deposits

    Science.gov (United States)

    Bouse, R.M.; Ruiz, J.; Titley, S.R.; Tosdal, R.M.; Wooden, J.L.

    1999-01-01

    Porphyry copper deposits in Arizona are genetically associated with Late Cretaceous and early Tertiary igneous complexes that consist of older intermediate volcanic rocks and younger intermediate to felsic intrusions. The igneous complexes and their associated porphyry copper deposits were emplaced into an Early Proterozoic basement characterized by different rocks, geologic histories, and isotopic compositions. Lead isotope compositions of the Proterozoic basement rocks define, from northwest to southeast, the Mojave, central Arizona, and southeastern Arizona provinces. Porphyry copper deposits are present in each Pb isotope province. Lead isotope compositions of Late Cretaceous and early Tertiary plutons, together with those of sulfide minerals in porphyry copper deposits and of Proterozoic country rocks, place important constraints on genesis of the magmatic suites and the porphyry copper deposits themselves. The range of age-corrected Pb isotope compositions of plutons in 12 Late Cretaceous and early Tertiary igneous complexes is 206Pb/204Pb = 17.34 to 22.66, 207Pb/204Pb = 15.43 to 15.96, and 208Pb/204Pb = 37.19 to 40.33. These Pb isotope compositions and calculated model Th/U are similar to those of the Proterozoic rocks in which the plutons were emplaced, thereby indicating that Pb in the younger rocks and ore deposits was inherited from the basement rocks and their sources. No Pb isotope differences distinguish Late Cretaceous and early Tertiary igneous complexes that contain large economic porphyry copper deposits from less rich or smaller deposits that have not been considered economic for mining. Lead isotope compositions of Late Cretaceous and early Tertiary plutons and sulfide minerals from 30 metallic mineral districts, furthermore, require that the southeastern Arizona Pb province be divided into two subprovinces. The northern subprovince has generally lower 206Pb/204Pb and higher model Th/U, and the southern subprovince has higher 206Pb/204Pb and

  12. Geophysical investigation of seepage beneath an earthen dam.

    Science.gov (United States)

    Ikard, S J; Rittgers, J; Revil, A; Mooney, M A

    2015-01-01

    A hydrogeophysical survey is performed at small earthen dam that overlies a confined aquifer. The structure of the dam has not shown evidence of anomalous seepage internally or through the foundation prior to the survey. However, the surface topography is mounded in a localized zone 150 m downstream, and groundwater discharges from this zone periodically when the reservoir storage is maximum. We use self-potential and electrical resistivity tomography surveys with seismic refraction tomography to (1) determine what underlying hydrogeologic factors, if any, have contributed to the successful long-term operation of the dam without apparent indicators of anomalous seepage through its core and foundation; and (2) investigate the hydraulic connection between the reservoir and the seepage zone to determine whether there exists a potential for this success to be undermined. Geophysical data are informed by hydraulic and geotechnical borehole data. Seismic refraction tomography is performed to determine the geometry of the phreatic surface. The hydro-stratigraphy is mapped with the resistivity data and groundwater flow patterns are determined with self-potential data. A self-potential model is constructed to represent a perpendicular profile extending out from the maximum cross-section of the dam, and self-potential data are inverted to recover the groundwater velocity field. The groundwater flow pattern through the aquifer is controlled by the bedrock topography and a preferential flow pathway exists beneath the dam. It corresponds to a sandy-gravel layer connecting the reservoir to the downstream seepage zone.

  13. Investigation of upper crustal structure beneath eastern Java

    Science.gov (United States)

    Martha, Agustya Adi; Widiyantoro, Sri; Cummnins, Phil; Saygin, Erdinc; Masturyono

    2016-05-01

    The complexity of geology structure in eastern Java causes this region has many potential resources as much as the disasters. Therefore, the East Java province represents an interesting area to be explored, especially regarding its upper crustal structure. To investigate this structure, we employ the Ambient Noise Tomography (ANT) method. We have used seismic waveform data from 25 Meteorological, Climatological and Geophysical Agency (BMKG) stationary seismographic stations and 26 portable seismographs installed for 2 to 8 weeks. Inter-station cross-correlation produces more than 800 Rayleigh wave components, which depict the structure beneath eastern Java. Based on the checkerboard resolution test, we found that the optimal grid size is 0.25ox0.25o. Our inversion results for the periods of 1 to 10 s indicate a good agreement with geological and Bouguer anomaly maps. Rembang high depression, most of the southern mountains zone, the northern part of Rembang zone and the central part of the Madura Island, the area of high gravity anomaly and areas dominated with igneous rocks are associated with high velocity zones. On the other hand, Kendeng zone and most of the basin in the Rembang zone are associated with low velocity zones.

  14. PN velocity beneath Western New Mexico and Eastern Arizona

    Science.gov (United States)

    Jaksha, L. H.

    1985-01-01

    The experiment involved observing Pn arrivals on an areal array of 7 seismic stations located in the transition zone and along the Jemez lineament. Explosions in coal and copper mines in New Mexico and Arizona were used as energy sources as well as military detonations at White Sands Missile Range, New Mexico, Yuma, Arizona, and the Nevada Test Site. Very preliminary results suggest a Pn velocity of 7.94 km/s (with a fairly large uncertainty) beneath the study area. The Pn delay times, which can be converted to estimates of crustal thickness given knowledge of the velocity structure of the crust increase both to the north and east of Springerville, Arizona. As a constraint on the velocity of Pn, researchers analyzed the reversed refraction line GNOME-HARDHAT which passes through Springerville oriented NW to SE. This analysis resulted in a Pn velocity of 7.9-8.0 km/s for the transition zone. These preliminary results suggest that a normal Pn velocity might persist even though the crust thins (from north to south) by 15 km along the length of the Arizona-New Mexico border. If the upper mantle is currently hot anywhere in western New Mexico or eastern Arizona then the dimensions of the heat source (or sources) might be small compared to the intra-station distances of the seismic arrays used to estimate the velocity of Pn.

  15. Crawling beneath the free surface: Water snail locomotion

    CERN Document Server

    Lee, Sungyon; Hosoi, A E; Lauga, Eric

    2008-01-01

    Land snails move via adhesive locomotion. Through muscular contraction and expansion of their foot, they transmit waves of shear stress through a thin layer of mucus onto a solid substrate. Since a free surface cannot support shear stress, adhesive locomotion is not a viable propulsion mechanism for water snails that travel inverted beneath the free surface. Nevertheless, the motion of the freshwater snail, Sorbeoconcha physidae, is reminiscent of that of its terrestrial counterparts, being generated by the undulation of the snail foot that is separated from the free surface by a thin layer of mucus. Here, a lubrication model is used to describe the mucus flow in the limit of small amplitude interfacial deformations. By assuming the shape of the snail foot to be a traveling sine wave and the mucus to be Newtonian, an evolution equation for the interface shape is obtained and the resulting propulsive force on the snail is calculated. This propulsive force is found to be non-zero for moderate values of Capillar...

  16. Zircon U-Pb age, Lu-Hf isotope, mineral chemistry and geochemistry of Sundamalai peralkaline pluton from the Salem Block, southern India: Implications for Cryogenian adakite-like magmatism in an aborted-rift

    Science.gov (United States)

    Renjith, M. L.; Santosh, M.; Li, Tang; Satyanarayanan, M.; Korakoppa, M. M.; Tsunogae, T.; Subba Rao, D. V.; Kesav Krishna, A.; Nirmal Charan, S.

    2016-01-01

    The Sundamalai peralkaline pluton is one among the Cryogenian alkaline plutons occurring in the Dharmapuri Rift Zone (DRZ) of the Salem Block in the Southern Granulite Terrane (SGT) of India. Here we present zircon U-Pb age and Lu-Hf isotopic composition, mineral chemistry and geochemistry of the pluton to explore the petrogenesis and geodynamic implications. Systematic modal variation of orthoclase, Na-plagioclase, Ca-amphibole (ferro-edenite and hastingsite) and quartz developed quartz-monzonite and granite litho units in the Sundamalai pluton. Thermometry based on amphibole-plagioclase pair suggests that the pluton was emplaced and solidified at around 4.6 kbar pressure with crystallization of the major phases between 748 and 661 °C. Estimated saturation temperature of zircon (712-698 °C) is also well within this range. However, apatite saturation occurred at higher temperatures between 835 and 870 °C, in contrast with monazite saturation (718-613 °C) that continued up to the late stage of crystallization. Estimated oxygen fugacity values (log fO2: -14 to -17) indicate high oxidation state for the magma that stabilized titanite and magnetite. The magmatic zircons from Sundamalai pluton yielded a weighted mean 206Pb/238U age of 832.6 ± 3.2 Ma. Geochemically, the Sundamalai rocks are high-K to shoshonitic, persodic (Na2O/K2O ratio > 1), silica-saturated (SiO2:65-72 wt.%), and peralkaline in composition (aluminum saturation index, ASI aborted rifting along the DRZ generating the magma that crystallized the Sundamalai rocks. Age of this pluton is comparable with that of the other Cryogenian felsic alkaline plutons from Salem Block suggesting extensive rift-related magmatism at this time in the SGT.

  17. Circular arc snakes and kinematic surface generation

    KAUST Repository

    Barton, Michael

    2013-05-01

    We discuss the theory, discretization, and numerics of curves which are evolving such that part of their shape, or at least their curvature as a function of arc length, remains unchanged. The discretization of a curve as a smooth sequence of circular arcs is well suited for such purposes, and allows us to reduce evolution of curves to the evolution of a control point collection in a certain finite-dimensional shape space. We approach this evolution by a 2-step process: linearized evolution via optimized velocity fields, followed by optimization in order to exactly fulfill all geometric side conditions. We give applications to freeform architecture, including "rationalization" of a surface by congruent arcs, form finding and, most interestingly, non-static architecture. © 2013 The Author(s) Computer Graphics Forum © 2013 The Eurographics Association and Blackwell Publishing Ltd.

  18. Geophysical exploration of disseminated and stockwork deposits associated with plutonic intrusive rock: a case study on the eastern flank of colombia’s western cordillera

    OpenAIRE

    Hernández Pardo Orlando; Gretta C; Alexander E; Iraida M; Pintor B

    2012-01-01

    Disseminated deposits are low-grade, large tonnage deposits which are mainly mined for gold, copper, molybdenum and tin. These deposits are normally associated with intermediate to acid plutonic intrusive rocks and all are characterized by intense, extensive hydrothermal alteration of host rocks. Disseminated deposit exploration in the tropics suffers from difficult geological mapping due to dense vegetation, lack of rock outcrops and extensive but variable saprolytic weathering. Geo...

  19. Seismic discontinuities beneath the southwestern United States from S receiver functions

    Science.gov (United States)

    Akanbi, Olufemi; Li, Aibing

    2016-05-01

    S-receiver functions along the Colorado Plateau-Rio Grande Rift-Great Plains Transect known as LA RISTRA in the southwestern United States have been utilized to map seismic discontinuities beneath this tectonically active region. Individual receiver functions were stacked according to ray piercing points with moveout corrections in order to improve the signal-to-noise ratio of the converted S-to-P phases. A mantle discontinuity, which is interpreted as the lithosphere-asthenosphere boundary (LAB), is observed along the profile with depth ranging from 80 km beneath the Rio Grande Rift (RGR) to 100 km beneath the Great Plains (GP) and 120-180 km beneath the Colorado Plateau (CP). The shallow LAB beneath the Rio Grande Rift is indicative of lithosphere extension and asthenosphere upwarp. The LAB deepens sharply at the RGR-CP and RGR-GP boundaries, providing evidence for edge-driven, small-scale mantle convection beneath LA RISTRA. Two local discontinuities beneath the southeastern Colorado Plateau are imaged at ~ 250 km and ~ 300 km and could be the top and base of the eroded lithosphere, respectively. The S receiver function images suggest that edge-driven, small-scale convection is probably the mantle source for recent extension and uplift in the Rio Grande Rift and the Colorado Plateau.

  20. Magnesium isotope geochemistry in arc volcanism.

    Science.gov (United States)

    Teng, Fang-Zhen; Hu, Yan; Chauvel, Catherine

    2016-06-28

    Incorporation of subducted slab in arc volcanism plays an important role in producing the geochemical and isotopic variations in arc lavas. The mechanism and process by which the slab materials are incorporated, however, are still uncertain. Here, we report, to our knowledge, the first set of Mg isotopic data for a suite of arc lava samples from Martinique Island in the Lesser Antilles arc, which displays one of the most extreme geochemical and isotopic ranges, although the origin of this variability is still highly debated. We find the δ(26)Mg of the Martinique Island lavas varies from -0.25 to -0.10, in contrast to the narrow range that characterizes the mantle (-0.25 ± 0.04, 2 SD). These high δ(26)Mg values suggest the incorporation of isotopically heavy Mg from the subducted slab. The large contrast in MgO content between peridotite, basalt, and sediment makes direct mixing between sediment and peridotite, or assimilation by arc crust sediment, unlikely to be the main mechanism to modify Mg isotopes. Instead, the heavy Mg isotopic signature of the Martinique arc lavas requires that the overall composition of the mantle wedge is buffered and modified by the preferential addition of heavy Mg isotopes from fluids released from the altered subducted slab during fluid-mantle interaction. This, in turn, suggests transfer of a large amount of fluid-mobile elements from the subducting slab to the mantle wedge and makes Mg isotopes an excellent tracer of deep fluid migration. PMID:27303032

  1. Magnesium isotope geochemistry in arc volcanism

    Science.gov (United States)

    Teng, Fang-Zhen; Hu, Yan

    2016-01-01

    Incorporation of subducted slab in arc volcanism plays an important role in producing the geochemical and isotopic variations in arc lavas. The mechanism and process by which the slab materials are incorporated, however, are still uncertain. Here, we report, to our knowledge, the first set of Mg isotopic data for a suite of arc lava samples from Martinique Island in the Lesser Antilles arc, which displays one of the most extreme geochemical and isotopic ranges, although the origin of this variability is still highly debated. We find the δ26Mg of the Martinique Island lavas varies from −0.25 to −0.10, in contrast to the narrow range that characterizes the mantle (−0.25 ± 0.04, 2 SD). These high δ26Mg values suggest the incorporation of isotopically heavy Mg from the subducted slab. The large contrast in MgO content between peridotite, basalt, and sediment makes direct mixing between sediment and peridotite, or assimilation by arc crust sediment, unlikely to be the main mechanism to modify Mg isotopes. Instead, the heavy Mg isotopic signature of the Martinique arc lavas requires that the overall composition of the mantle wedge is buffered and modified by the preferential addition of heavy Mg isotopes from fluids released from the altered subducted slab during fluid−mantle interaction. This, in turn, suggests transfer of a large amount of fluid-mobile elements from the subducting slab to the mantle wedge and makes Mg isotopes an excellent tracer of deep fluid migration. PMID:27303032

  2. On the Trail of Joan of Arc

    Directory of Open Access Journals (Sweden)

    Linda Joyce Forristal

    2013-12-01

    Full Text Available The year 2012 marked the 600th anniversary of the birthday of Joan of Arc (Fr., Jeanne d’Arc (1412–1431. Tributes to this national heroine can be found all over France. There are literally countless statues, streets and restaurants named after her and many sites dedicated to her life. However, despite widespread social and mechanical reproduction and cultural naming in relation to the Maid of Orléans, there is no official network or integrated signage in France to promote cultural heritage tourism to the numerous Joan of Arc sites and festivals, even though her life and death, by any measure, were seminal events in the country’s history. Unfortunately, the pilgrim who wants to follow or intersect with Joan of Arc’s trail through France, for cultural, historical or religious reasons, must do so without much help. Using Actor Network Theory and Site Sacralization Theory as framing devices, this paper explores human actors and tangible and intangible non-human factors that may have contributed to the lack of a unified tourism product despite the existence of an adequate Joan of Arc tourismscape. Insights gleaned from this research include Joan’s conflicted status as both/either saint and/or patriot, the existence of no cooperation or linkage between Joan of Arc sites, and cautious French tourism development policies. Several possible scenarios are suggested as suitable means to help implement or foster the creation of an on-the-ground or virtual Joan of Arc trail or tour.

  3. arcControlTower: the System for Atlas Production and Analysis on ARC

    CERN Document Server

    Filipcic, A; The ATLAS collaboration

    2011-01-01

    PanDA, the Atlas management and distribution system for production and analysis jobs on EGEE and OSG clusters, is based on pilot jobs to increase the throughput and stability of the job execution on grid. The ARC middleware uses specific approach which tightly connects the job requirements with cluster capabilities like resource usage, software availability and caching of input files. The pilot concept renders the ARC features useless. The arcControlTower is the job submission system which merges the pilot benefits and ARC advantages. It takes the pilot payload from the panda server and submits the jobs to the Nordugrid ARC clusters as regular jobs, with all the job resources known in advance. All the pilot communication with the PanDA server is done by the arcControlTower, so it plays the role of a pilot factory and the pilot itself. There are several advantages to this approach: no grid middleware is needed on the worker nodes, the fair-share between the production and user jobs is tuned with the arcControl...

  4. A numerical simulation of ablation controlled arcs

    Energy Technology Data Exchange (ETDEWEB)

    Godin, D.; Trepanier, J.Y. [Ecole Polytechnique, Dept. of Mechanical Engineering, Montreal, PQ (Canada); Eby, S.D. [Ecole Polytechnique, Centre de Recherche en Calcul Applique, Montreal, PQ (Canada); Robin-Jouan, P. [GEC-Alsthom T and D, Villeurbanne, (France)

    1998-09-01

    An approach to model the ablation phenomenon of ablation controlled arcs using computational fluid dynamics was presented. Ablation controlled arcs are found in high voltage electrical equipment such as fuses and circuit-breakers. A qualitative prediction of the ablation level is critical from an industrial point of view because deliberate use of ablation is made to increase the pressure in a circuit-breaker chamber to allow for an efficient extinction when the current returns to zero. The numerical model was validated by comparing results of published experimental data. 7 refs., 10 figs.

  5. ArcAid interactive archery assistant

    OpenAIRE

    Jeroen Vervaeke; Jente Ameye; Sievert van Esch; Jelle Saldien; Steven Verstockt

    2015-01-01

    This paper describes the design process of a bow aiming system, called ArcAid, which is an interactive archery assistant. The main goal of ArcAid is to introduce a way for beginner Robin Hoods to learn the art of archery to its fullest. In order to achieve this goal, our smartphone-based design focuses on a fun and interactive learning process that gives constant feedback to the user on how to hit a certain goal. A SPIKE high- end laser sensor is used for the distance measurement and the smar...

  6. Electric-arc steam plasma generator

    Science.gov (United States)

    Anshakov, A. S.; Urbakh, E. K.; Radko, S. I.; Urbakh, A. E.; Faleev, V. A.

    2015-01-01

    Investigation results on the arc plasmatorch for water-steam heating are presented. The construction arrangement of steam plasma generator with copper electrodes of the stepped geometry was firstly implemented. The energy characteristics of plasmatorch and erosion of electrodes reflect the features of their behavior at arc glow in the plasma-forming environment of steam. The results of numerical study of the thermal state of the composite copper-steel electrodes had a significant influence on optimization of anode water-cooling aimed at improvement of its operation life.

  7. Architectural Surfaces and Structures from Circular Arcs

    KAUST Repository

    Shi, Ling

    2013-12-01

    In recent decades, the popularity of freeform shapes in contemporary architecture poses new challenges to digital design. One of them is the process of rationalization, i.e. to make freeform skins or structures affordable to manufacture, which draws the most attention from geometry researchers. In this thesis, we aim to realize this process with simple geometric primitives, circular arcs. We investigate architectural surfaces and structures consisting of circular arcs. Our focus is lying on how to employ them nicely and repetitively in architectural design, in order to decrease the cost in manufacturing. Firstly, we study Darboux cyclides, which are algebraic surfaces of order ≤ 4. We provide a computational tool to identify all families of circles on a given cyclide based on the spherical model of M ̈obius geometry. Practical ways to design cyclide patches that pass through certain inputs are presented. In particular, certain triples of circle families on Darboux cyclides may be suitably arranged as 3-webs. We provide a complete classification of all possible 3-webs of circles on Darboux cyclides. We then investigate the circular arc snakes, which are smooth sequences of circu- lar arcs. We evolve the snakes such that their curvature, as a function of arc length, remains unchanged. The evolution of snakes is utilized to approximate given surfaces by circular arcs or to generated freeform shapes, and it is realized by a 2-step pro- cess. More interestingly, certain 6-arc snake with boundary constraints can produce a smooth self motion, which can be employed to build flexible structures. Another challenging topic is approximating smooth freeform skins with simple panels. We contribute to this problem area by approximating a negatively-curved 5 surface with a smooth union of rational bilinear patches. We provide a proof for vertex consistency of hyperbolic nets using the CAGD approach of the rational B ́ezier form. Moreover, we use Darboux transformations for the

  8. Dynamic Arc-Flags in Road Networks

    OpenAIRE

    D 'angelo, Gianlorenzo; Frigioni, Daniele; Vitale, Camillo

    2011-01-01

    International audience In this work we introduce a new data structure, named Road-Signs, which allows us to efficiently update the Arc-Flags of a graph in a dynamic scenario. Road-Signs can be used to compute Arc-Flags, can be efficiently updated and do not require large space consumption for many real-world graphs like, e.g., graphs arising from road networks. In detail, we define an algorithm to preprocess Road-Signs and an algorithm to update them each time that a weight increase operat...

  9. Plasma distribution of cathodic ARC deposition system

    Energy Technology Data Exchange (ETDEWEB)

    Anders, S.; Raoux, S.; Krishnan, K.; MacGill, R.A.; Brown, I.G. [Lawrence Berkeley National Lab., CA (United States)

    1996-08-01

    The plasma distribution using a cathodic arc plasma source with and without magnetic macroparticle filter has been determined by depositing on a transparent plastic substrate and measuring the film absorption. It was found that the width of the distribution depends on the arc current, and it also depends on the cathode material which leads to a spatial separation of the elements when an alloy cathode is used. By applying a magnetic multicusp field near the exit of the magnetic filter, it was possible to modify the plasma distribution and obtain a flat plasma profile with a constant and homogeneous elemental distribution.

  10. Small Universal Petri Nets with Inhibitor Arcs

    OpenAIRE

    Ivanov, Sergiu; Pelz, Elisabeth; Verlan, Sergey

    2013-01-01

    We investigate the problem of construction of small-size universal Petri nets with inhibitor arcs. We consider four descriptional complexity parameters: the number of places, transitions, inhibitor arcs, and the maximal degree of a transition, each of which we try to minimize. We give six constructions having the following values of parameters (listed in the above order): $(30,34,13,3)$, $(14, 31, 51, 8)$, $(11, 31, 79, 11)$, $(21,25,13,5)$, $(67, 64, 8, 3)$, $(58, 55, 8, 5)$ that improve the...

  11. The impact of geology on the migration of fluorides in mineral waters of the Bukulja and Brajkovac pluton area, Serbia

    Directory of Open Access Journals (Sweden)

    Papić Petar

    2012-01-01

    Full Text Available One of the hydrogeochemical parameters that classify groundwater as mineral water is the content of fluoride ions. Their concentration is both important and limited for bottled mineral waters. Hydrochemical research of mineral waters in the surrounding area of Bukulja and Brajkovac pluton, in central Serbia, was conducted in order to define the chemical composition and genesis of these waters. They are carbonated waters, with content of fluoride ranging from 0.2 up to 6.6 mg/L. Since hydrochemical analyses showed variations in the major water chemistry, it was obvious that, apart from hydrochemical research, some explorations of the structure of the regional terrain would be inevitable. For these purposes, some additional geological research was performed, creating an adequate basis for the interpretation of the genesis of these carbonated mineral waters. The results confirmed the significance of the application of hydrochemical methods in the research of mineral waters. The work tended to emphasize that “technological treatment” for decreasing the concentration of fluoride in mineral waters occurs in nature, indicating the existence of natural defluoridization. [Projekat Ministarstva nauke Republike Srbije, br. 43004

  12. Neutron activation and other analytical data for plutonic rocks from North America and Africa. National Uranium Resource Evaluation

    International Nuclear Information System (INIS)

    The objective of this report is to retrieve the elements of an analytical study of granites and associated other plutonic rocks which was begun as a part of the U.S. Department of Energy's National Uranium Resource Evaluation (NURE) program. A discussion of the Savannah River Laboratory (SRL) neutron activation analysis system is given so that a user will understand the linmitations of the data. Enough information is given so that an experienced geochemist can clean up the data set to the extent required by any project. The data are generally good as they are presented. It is intended that the data be read from a magnetic tape written to accompany this report. Microfiche tables of the data follow the text. These tables were prepared from data on the tape, and programs which will read the tape are presented in the section THE DATA TAPE. It is our intent to write a later paper which will include a thoroughly scrubbed data set and a technical discussion of results of the study. 1 figure

  13. Interaction between two contrasting magmas in the Albtal pluton (Schwarzwald, SW Germany): textural and mineral-chemical evidence

    Science.gov (United States)

    Michel, Lorenz; Wenzel, Thomas; Markl, Gregor

    2016-07-01

    The magmatic evolution of the Variscan Albtal pluton, Schwarzwald, SW Germany, is explored using detailed textural observations and the chemical composition of plagioclase and biotite in both granite and its mafic magmatic enclaves (MMEs). MMEs probably formed in a two-step process. First, mafic magma intruded a granitic magma chamber and created a boundary layer, which received thermal and compositional input from the mafic magma. This is indicated by corroded "granitic" quartz crystals and by large "granitic" plagioclase xenocrysts, which contain zones of higher anorthite and partly crystallized from a melt of higher Sr content. Texturally, different plagioclase types (e.g. zoned and inclusion-rich types) correspond to different degrees of overprint most likely caused by a thermal and compositional gradient in the boundary layer. The intrusion of a second mafic magma batch into the boundary layer is recorded by a thin An50 zone along plagioclase rims that crystallized from a melt enriched in Sr. Most probably, the second mafic intrusion caused disruption of the boundary layer, dispersal of the hybrid magma in the granite magma and formation of the enclaves. Rapid thermal quenching of the MMEs in the granite magma is manifested by An30 overgrowths on large plagioclase grains that contain needle apatites. Our results demonstrate the importance of microtextural investigations for the reconstruction of possible mixing end members in the formation of granites.

  14. P-wave tomography of the Calabrian Arc region (South Italy) using a new 'a priori

    Science.gov (United States)

    Orecchio, Barbara; Presti, Debora; Totaro, Cristina; Guerra, Ignazio; Neri, Giancarlo

    2010-05-01

    A recently published tomographic investigation of the Calabrian Arc, South Italy (Neri et al., SRL, 2009) has shown that the Ionian subducting slab appears in-depth continuous only beneath the central part of the Arc (southern Calabria), while it has already undergone detachment at the edges of the arcuate structure (northern Calabria and northeastern Sicily). Starting from this result we tried to better define the features of the slab by performing a new tomographic inversion of crust and upper lithosphere in the Calabrian Arc region. The starting velocity model was derived from the integration of a new crustal velocity model obtained applying the method proposed by Waldhauser et al. (GJI, 1998 and 2002) and a deep model used by Neri et al. (SRL, 2009). We merged these two models into an averaged regional one, ranging between the surface and 300km depth. Then we used it to perform a new P-wave tomographic inversion of shallow and deep earthquakes occurred between 1981 and 2008 in Southern Italy. We selected all the events with a minimum of 12P+S and 8 P+S readings for shallow and deep earthquakes respectively. The quality of the readings was, in the majority of cases, checked directly on the recordings. The final inversion dataset consists of 75141 P and 40118 S arrival times relative to 7050 earthquakes recorded at a total of 591 stations. All the data available from the national and local networks, including the CAT-SCAN and UniCal network, have been used for inversion. This new model reduced significantly the RMS parameter and allowed us to enlarge the inversion zone. The investigation, together with a detailed analysis of seismicity, allows us to propose an improved and more complete view of the subduction system with respect to the previous works, including Neri et al. (SRL, 2009).

  15. Arcing Model of a Disconnector and its Effect on VFTO

    International Nuclear Information System (INIS)

    In the computational process of very fast transient over-voltage (VFTO), it is essential to find an accurate model for a gas insulated substation. The arcing model of the disconnector is particularly important. The general arcing model is not able to give a good description of the arc development process. In this paper, based on the physical process of arcing and existing arc models (the exponential time-varying resistance model and the segmental arcing models), a dynamic arcing model is proposed, which is divided into two stages before and after the zero crossing. The dynamic arcing model combines hyperbola time-varying resistance and the Mayr model to describe the dynamic process of arcing. The present paper creates an arc model blockset upon the Matlab/Simulink software platform. Moreover for a specific 1100 kV station, VFTO is simulated in detail based on different arcing models. It is demonstrated that the dynamic arcing model can describe the physical arc process precisely and is useful for improving the accuracy of VFTO simulations

  16. Magnetic Signatures and Curie Surface Trend Across an Arc-Continent Collision Zone: An Example from Central Philippines

    Science.gov (United States)

    Manalo, Pearlyn C.; Dimalanta, Carla B.; Ramos, Noelynna T.; Faustino-Eslava, Decibel V.; Queaño, Karlo L.; Yumul, Graciano P.

    2016-05-01

    Ground and aeromagnetic data are combined to characterize the onshore and offshore magnetic properties of the central Philippines, whose tectonic setting is complicated by opposing subduction zones, large-scale strike-slip faulting and arc-continent collision. The striking difference between the magnetic signatures of the islands with established continental affinity and those of the islands belonging to the island arc terrane is observed. Negative magnetic anomalies are registered over the continental terrane, while positive magnetic anomalies are observed over the Philippine Mobile Belt. Several linear features in the magnetic anomaly map coincide with the trace of the Philippine Fault and its splays. Power spectral analysis of the magnetic data reveals that the Curie depth across the central Philippines varies. The deepest point of the magnetic crust is beneath Mindoro Island at 32 km. The Curie surface shallows toward the east: the Curie surface is 21 km deep between the islands of Sibuyan and Masbate, and 18 km deep at the junction of Buruanga Peninsula and Panay Island. The shallowest Curie surface (18 km) coincides with the boundary of the arc-continent collision, signifying the obduction of mantle rocks over the continental basement. Comparison of the calculated Curie depth with recent crustal thickness models reveals the same eastwards thinning trend and range of depths. The coincidence of the magnetic boundary and the density boundary may support the existence of a compositional boundary that reflects the crust-mantle interface.

  17. Simulation of Snow Processes Beneath a Boreal Scots Pine Canopy

    Institute of Scientific and Technical Information of China (English)

    LI Weiping; LUO Yong; XIA Kun; LIU Xin

    2008-01-01

    A physically-based multi-layer snow model Snow-Atmosphere-Soil-Transfer scheme (SAST) and a land surface model Biosphere-Atmosphere Transfer Scheme (BATS) were employed to investigate how boreal forests influence snow accumulation and ablation under the canopy. Mass balance and energetics of snow beneath a Scots pine canopy in Finland at different stages of the 2003-2004 and 2004-2005 snow seasons are analyzed. For the fairly dense Scots pine forest, drop-off of the canopy-intercepted snow contributes, in some cases, twice as much to the underlying snowpack as the direct throughfall of snow. During early winter snow melting, downward turbulent sensible and condensation heat fluxes play a dominant role together with downward net longwave radiation. In the final stage of snow ablation in middle spring, downward net all-wave radiation dominates the snow melting. Although the downward sensible heat flux is comparable to the net solar radiation during this period, evaporative cooling of the melting snow surface makes the turbulent heat flux weaker than net radiation. Sensitivities of snow processes to leaf area index (LAI) indicate that a denser canopy speeds up early winter snowmelt, but also suppresses melting later in the snow season. Higher LAI increases the interception of snowfall, therefore reduces snow accumulation under the canopy during the snow season; this effect and the enhancement of downward longwave radiation by denser foliage outweighs the increased attenuation of solar radiation, resulting in earlier snow ablation under a denser canopy. The difference in sensitivities to LAI in two snow seasons implies that the impact of canopy density on the underlying snowpack is modulated by interannual variations of climate regimes.

  18. Determination of the Basin Structure Beneath European Side of Istanbul

    Science.gov (United States)

    Karabulut, Savas; Cengiz Cinku, Mulla; Thomas, Michael; Lamontagne, Maurice

    2016-04-01

    Istanbul (near North Anatolian Fault Zone:NAFZ, Turkey) is located in northern part of Sea of Marmara, an area that has been influenced by possible Marmara Earthquakes. The general geology of Istanbul divided into two stratigraphic unit such as sedimentary (from Oligocene to Quaternary Deposits) and bedrock (Paleozoic and Eocene). The bedrock units consists of sand stone, clay stone to Paleozoic age and limestone to Eocene age and sedimentary unit consist of sand, clay, mil and gravel from Oligocene to Quaternary age. Earthquake disaster mitigation studies divided into two important phases, too. Firstly, earthquake, soil and engineering structure problems identify for investigation area, later on strategic emergency plan can prepare for these problems. Soil amplification play important role the disaster mitigation and the site effect analysis and basin structure is also a key parameter for determining of site effect. Some geophysical, geological and geotechnical measurements are requeired to defined this relationship. Istanbul Megacity has been waiting possible Marmara Earthquake and their related results. In order to defined to possible damage potential related to site effect, gravity measurements carried out for determining to geological structure, basin geometry and faults in Istanbul. Gravity data were collected at 640 sites by using a Scientrex CG-5 Autogravity meter Standard corrections applied to the gravity data include those for instrumental drift, Earth tides and latitude, and the free-air and Bouguer corrections. The corrected gravity data were imported into a Geosoft database to create a grid and map of the Bouguer gravity anomaly (grid cell size of 200 m). As a previously results, we determined some lineminants, faults and basins beneath Istanbul City. Especially, orientation of faults were NW-SE direction and some basin structures determined on between Buyukcekmece and Kucukcekmece Lake.

  19. Fine structure of Pn velocity beneath Sichuan-Yunnan region

    Institute of Scientific and Technical Information of China (English)

    黄金莉; 宋晓东; 汪素云

    2003-01-01

    We use 23298 Pn arrival-time data from Chinese national and provincial earthquake bulletins to invert fine structure of Pn velocity and anisotropy at the top of the mantle beneath the Sichuan-Yunnan and its adjacent region. The results suggest that the Pn velocity in this region shows significant lateral variation; the Pn velocity varies from 7.7 to 8.3 km/s. The Pn-velocity variation correlates well with the tectonic activity and heat flow of the region. Low Pn velocity is observed in southwest Yunnan , Tengchong volcano area, and the Panxi tectonic area. These areas have very active seismicity and tectonic activity with high surface heat flow. On the other hand, high Pn velocity is observed in some stable regions, such as the central region of the Yangtze Platform; the most pronounced high velocity area is located in the Sichuan Basin, south of Chengdu. Pn anisotropy shows a complex pattern of regional deformation. The Pn fast direction shows a