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Sample records for aceh forearc basin

  1. Tectonic wedging in the forearc basin - Accretionary prism transition, Lesser Antilles forearc

    NASA Technical Reports Server (NTRS)

    Torrini, Rudolph, Jr.; Speed, Robert C.

    1989-01-01

    This paper describes regional structure of the inner forearc of the southern Lesser Antilles, which contains an extensive 50-70 km wide inner forearc deformation belt (IFDB) developed above crystalline basement of the undeformed forearc basin (FAB), close to and perhaps above its probable subduction trace with Atlantic lithosphere. The IFDB is analyzed, with emphasis placed on five transects across the belt, using mainly migrated seismic sections and balanced model cross sections. The IFDB features and its evolution are discussed, with special attention given to the major structures divided by early and late stages of development, paleobathymetric history, event timing, displacement and strain, and alternative tectonic explanations.

  2. Tectonic evolution of the Tobago Trough forearc basin

    NASA Technical Reports Server (NTRS)

    Speed, R.; Torrini, R., Jr.; Smith, P. L.

    1989-01-01

    The histories of configurational changes and sedimentation in the Tobago Trough, which is a modern bathymetric forearc basin of the Lesser Antilles island arc, were investigated using marine seismic data from the Tobago Trough. Special attention is given to two tectonic problems. The first is the evolution of the southeastern corner of the Caribbean as related to the finding that the early forearc basins had substantially different configurations from that of the modern forearc basin. The second is the interaction between the forearc basin and the accretionary prism within the Lesser Antilles system. It is pointed out that Miocene and younger features of the Tobago Trough might reflect a superposition of tectonism associated with the development of the Neogene Lesser Antilles arc on an older arc system.

  3. Evolution of the Izu-Bonin forearc basin

    SciTech Connect

    Cooper, P.A. )

    1990-06-01

    Three sites within the Izu-Bonin intra-oceanic forearc were drilled during Leg 126; two penetrated basement. The 7 km wide forearc basin, defined by thick (1.5-4 km) sequences of relatively undeformed coarse-grained volcaniclastic and fine-grained hemipelagic strata, occupies a long belt between the Izu-Bonin frontal arc to the west and the outer-arc high to the east. Based on correlations of logging, physical properties measurements, and lithostratigraphic data to regional multichannel seismic surveys, four major seismostratigraphic sequences, representing four major developmental phases, are recognized: (1) Initial mid-Eocene to early Oligocene tholeiitic and boninitic volcanism formed a basement with highly variable acoustic characteristics - basement near the frontal arc high is well defined and lacks coherent reflectors, while nearer the outer-arc high, basement is often seismically stratified and cut by dipping reflectors. (2) Mid-Oligocene rifting of the forearc and late Oligocene volcanism; the lowermost sedimentary units lap out onto basement to the east. Chaotic, subparallel reflectors are capped by strong, continuous reflectors, parallel and conformable to the underlying units, representing coarse, volcaniclastic turbiditic basin in-fill. The entire late Oligocene sequence is extensively faulted. (3) Miocene spreading in Shikoku basin; a volcanic minimum in the forearc region (27- 13 Ma) resulted in dominantly nannofossil-rich hemipelagic sedimentation. (4) Pliocene-Quaternary volcanism, increasing to present maximum; this upper sequence thickens and is downfaulted towards the arc. It consists of many thin packets of strong reflectors, repeatedly interrupted by canyon cutting and filling.

  4. Earthquake Nonconcordancies in the Aceh-Nias and Mentawai Forearcs: Implications for the Energetics of Earthquakes and Tsunamis

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    The identification and characterization of nonconcordant events, by virtue of their strong influence on rupture geometry and extent, will be valuable for estimating seismic and tsunami potential. We classify thrust earthquakes at the subduction zone as nonconcordant if (1) their depths are unequivocally off the slab interface; (2) neither nodal plane of their focal mechanisms is compatible with the dip of the slab interface; or (3) their radiated energies are anomalously high (having taua > 1 MPa, where taua is apparent stress mu ES/M_O). We find that about 12% of large (M > 5.5) thrust earthquakes in the subduction zone occur off the slab interface. Other earthquakes with hypocenters that are not distinguishable from the slab interface have nonconcordant focal mechanisms. Another subset of earthquakes is characterized by high apparent stress. This is an indicator of nonconcordancy because high energy radiation is associated with immature faults. [In contrast, the subducting-plate interface is a mature fault on which thrust events radiate generally low energy (Choy and Kirby, 2004)]. The environments in which nonconcordant high-energy events typically occur are intraslab or regions of plate reorganization. On the other hand, nonconcordant mid-energy events (taua < 1 MPa) often correlate with subducted topography or splay faults. Transoceanic tsunamis are often associated with slow earthquakes which are characterized by an anomalous depletion of high frequency energy. However, some recent large earthquakes in the Aceh-Nias and Mentawai forearcs show (1) that tsunamis generated by mid- and high-energy earthquakes are possible, and (2) that regional tsunami wave heights can be associated with intraslab and intracrustal earthquakes. Furthermore, epicenters of nonconcordant earthquakes in the Sunda arc can help define the rupture zone of large earthquakes as they tend to be located on the periphery of the rupture zones. Clusters of high-energy nonconcordant events

  5. Shallow shear-wave reflection seismics in the tsunami struck Krueng Aceh River Basin, Sumatra

    NASA Astrophysics Data System (ADS)

    Polom, U.; Arsyad, I.; Kümpel, H.-J.

    2008-01-01

    As part of the project "Management of Georisk" (MANGEONAD) of the Federal Institute for Geosciences and Natural Resources (BGR), Hanover, high resolution shallow shear-wave reflection seismics was applied in the Indonesian province Nanggroe Aceh Darussalam, North Sumatra in cooperation with the Government of Indonesia, local counterparts, and the Leibniz Institute for Applied Geosciences, Hanover. The investigations were expected to support classification of earthquake site effects for the reconstruction of buildings and infrastructure as well as for groundwater exploration. The study focussed on the city of Banda Aceh and the surroundings of Aceh Besar. The shear-wave seismic surveys were done parallel to standard geoengineering investigations like cone penetrometer tests to support subsequent site specific statistical calibration. They were also partly supplemented by shallow p-wave seismics for the identification of (a) elastic subsurface parameters and (b) zones with abundance of groundwater. Evaluation of seismic site effects based on shallow reflection seismics has in fact been found to be a highly useful method in Aceh province. In particular, use of a vibratory seismic source was essential for successful application of shear-wave seismics in the city of Banda Aceh and in areas with compacted ground like on farm tracks in the surroundings, presenting mostly agricultural land use areas. We thus were able to explore the mechanical stiffness of the subsurface down to 100 m depth, occasionally even deeper, with remarkably high resolution. The results were transferred into geotechnical site classification in terms of the International Building Code (IBC, 2003). The seismic images give also insights into the history of the basin sedimentation processes of the Krueng Aceh River delta, which is relevant for the exploration of new areas for construction of safe foundations of buildings and for identification of fresh water aquifers in the tsunami flooded region.

  6. Geodynamics of the Sivas Basin (Turkey): from a forearc basin to a retroarc foreland basin

    NASA Astrophysics Data System (ADS)

    Legeay, Etienne; Ringenbach, Jean-Claude; Kergaravat, Charlie; Callot, Jean-Paul; Mohn, Geoffroy; Kavak, Kaan

    2016-04-01

    Anatolia records the consumption of several oceanic basins, from the Northern Neotethys domain, by north-dipping subduction until the end of Mesozoic. The associated obduction event occurred during Campanian, from North to South and from Greece to Oman, leading to the emplacement of ophiolite thrust sheets and associated ophiolitic mélange. In particular, the Sivas Basin in Eastern Anatolia is located at the boundary between the Kırsehir block to the East, Pontide arc to the North and Tauride Platform to the South, sutured by ophiolitic belts. The Sivas Basin formed a Tertiary fold-and-thrust belt, which exhibits mainly north verging thrust in Paleogene deposits, and South verging thrust in oligo-miocene sequence. To understand the northern verging thrust above south verging obduction, it is necessary to zoom out of the basin, and include a set of processes that affect the eastern Anatolia. This study aims to characterize the structural and sedimentary evolution of the Sivas Basin, based on a fieldwork approach, coupled to the interpretation of subsurface data, thermochronology and biostratigraphy. The Sivas Basin was initiated in a forearc setting relatively to the subduction of the Inner-Tauride Ocean while the associated ophiolites are obducted onto the northern passive margin of the Tauride margin. Early Maastrichtian to Paleocene deposits are represented by carbonate platforms located on ophiolitic highs, passing to turbidites and olistostomes toward the North. The early Eocene sediments, mainly composed of ophiolitic clasts, are deposited on a regional unconformity marked along the southern margin of the basin by incisions in response to the emergence of north-verging thrust. The middle Eocene sediments, intensively folded by northward thrusting, are mostly represented by flysch type deposits (olistostromes, mass-flows and turbidites). The onset of the compression is related to the initiation of the Taurus shortening in a retroarc situation, in response to

  7. Basin Evolution of the Cretaceous-Early Eocene Xigaze Forearc, Southern Tibet

    NASA Astrophysics Data System (ADS)

    Orme, D. A.; Carrapa, B.; Kapp, P. A.; Gehrels, G. E.; Reiners, P. W.

    2013-12-01

    An understanding of the processes which control the evolution of forearc basins is important for deciphering the tectonic development of a convergent margin prior to continent-continent suturing. This study presents sedimentologic, modal petrographic and geo-thermochronologic data from the Xigaze forearc basin, preserved along ~ 600 km of the Indus-Yarlung Suture Zone in southern Tibet. From late Cretaceous to early Cenozoic time, subduction of Neo-Tethyan oceanic crust beneath the southern margin of Asia accommodated the northward motion of the Indian craton and formed the Xigaze forearc basin. Following collision with India in the early Cenozoic, the basin transitioned from predominantly marine to non-marine sedimentation and was subsequently uplifted to a mean elevation of 5000 m. Thus, the sedimentary record in the Xigaze forearc preserves information regarding the tectonic evolution of the Indo-Asia continental margin prior to and following collision. We present new measured sections and geo-thermochronologic data from Early Cretaceous to Early Eocene clastic and carbonate sedimentary rocks, preserved in two previously unexplored regions of the forearc, (1) at its western most extent, northwest of Saga, and (2) north of Lhatse. In turn, we compare our results with previously published data in order to synthesize our current understanding of forearc evolution. Strata preserved in the Lhaste region record an initial shallow marine phase of forearc sedimentation (Aptian), but quickly transition to deep marine slope and distal fan turbidite facies (Albian-Campanian). In contrast, facies preserved in the Saga region record a younger shoaling upward marine sequence (Maastrichtian-Ypresian), with the uppermost ~ 400 m consisting of fluvial channel sandstones and red-green paleosols. Facies and depositional environments in the Saga region are highly variable along strike, with turbidites, shelf limestones, estuarine siliciclastics and thick paleosols sequences all

  8. Shallow-water limestones within the Paleogene forearc basin of California: Unique paleogeographic indicators

    SciTech Connect

    Whidden, K.J.; Bottjer, D.J.; Lund, S.P. . Dept. of Geological Sciences)

    1992-01-01

    A number of shallow-water limestones have recently been documented in late Mesozoic/Paleogene forearc strata of the Cordilleran continental arc. These limestones occur on two different tectonic blocks which were both developed within the forearc basin and subsequently moved relative to one another due to oblique convergence since Late Cretaceous time. Faunal evidence suggests that these limestones were deposited within the photic zone, at shelfal depths. Each limestone represents part or all of the basal Paleogene sequence; they are intercalated with or overlain by deeper-water strata. One region of outcrops in the western Santa Monica Mountains is latest Paleocene in age, while the other region, in the eastern Santa Ynez Mountains and Wheeler Gorge area, is early Eocene in age. These shallow-water limestones may be used as paleogeographic indicators, as they represent relative topographic highs within the basin. The microplate tectonic reconstruction of Hornafius (1985) suggests that the limestones occur on opposite sides of a north-south trending trough within the overall forearc basin. The Paleocene limestones, which occur along the eastern margin of the trough, are intercalated with marine shales and may represent small fluctuations in relative sea level and/or sediment supply on a topographic high. The Eocene limestones, which occur along the western side of the trough, are always the basal Paleogene unit deposited on tilted Cretaceous strata or Franciscan rocks and overlain by deeper-water shales. The occurrence of Franciscan as basement for limestone deposition implies localized tectonic uplift within the forearc. Each of these limestones probably represents initiation of a single period of relative sea level rise, as the basal shallow-water carbonates were eventually overwhelmed by deeper-water shales. Thus two episodes of carbonate deposition allow for the delineation of two topographic highs within the Paleogene forearc basin.

  9. Tectonics and sedimentary evolution of the Sandino forearc basin off Nicaragua, Central America

    NASA Astrophysics Data System (ADS)

    Costa Pisani, P.; Silver, E.; McIntosh, K.; Ahmed, I.; Ranero, C. R.; Taylor, B.

    2003-04-01

    The Sandino basin is the Nicaragua sector of the Central American forearc, where the Cocos plate subducts beneath the Middle America trench. Recently, Ranero et al. have interpreted a seismic section across the margin and proposed a history of formation of the forearc which is constrained by industry drilling in the basin. They suggested a late Cretaceous to Paleocene accretion event, followed by later subduction erosion processes. The margin wedge consists of the ophiolitic Nicoya complex. The seismic units, unconformities and tectonic features record a rich history of both local and regional vertical movements occurring since the Middle Eocene, which are linked to the evolution of the Pacific convergent margin. During June, 2000, 2800 kms of multichannel seismic reflection data were collected on the R/V Ewing off Nicaragua. Analysis of the 240 channels dataset indicates rapid changes along strike in the Sandino basin. The basin is relatively thin in the southern part, thinning quite rapidly southward against the Nicoya complex of the Santa Elena peninsula of Costa Rica. The forearc sediments thickness approaches and locally exceeds 10 kms in the central and northern parts of the Sandino basin. The oldest units (Upper Cretaceous-Middle Eocene) are very thick off northern Nicaragua, with relatively thin middle to late Cenozoic deposits. However, off central Nicaragua the latter units (Middle-Upper Miocene) attain great thicknesses and the older units appear to thin. This pattern suggests a history of successive deepening of the basin from north to south, after the convergent system evolved from accretion to subduction erosion processes. Present efforts are devoted to quantifying this change in development and using it to understand the dynamics of forearc basin evolution offshore of Central America.

  10. Tectonic erosion of the Peruvian forearc, Lima Basin, by subduction and Nazca Ridge collision

    NASA Astrophysics Data System (ADS)

    Clift, Peter D.; Pecher, Ingo; Kukowski, Nina; Hampel, Andrea

    2003-06-01

    Subsidence of Lima Basin, part of the Peruvian forearc, is controlled by tectonic erosion by the subducting Nazca plate. Multichannel seismic reflection data coupled with age and paleowater depth constraints derived from Ocean Drilling Program (ODP) coring now allow the rates of erosion to be reconstructed through time. In trenchward locations the forearc has experienced limited recent relative uplift (700-850 m) likely due to preferential basal erosion under the center of Lima Basin. Long-term subsidence driven by basal tectonic erosion dominates and is fastest closest to the trench. Since 47 Ma (Eocene) up to 148 km of the plate margin have been lost at an average rate of up to 3.1 km myr-1. Appoximately 110 km of that total appears to be lost since 11 Ma, implying much faster average rates of trench retreat (10 km myr-1) since collision of the Nazca Ridge with the Lima Basin at 11 Ma. Although there is no clear subsidence event at ODP Site 679 during the time at which Nazca Ridge was subducting beneath this part of the forearc (4-11 Ma), the more trenchward ODP Sites 682 and 688 show significant deepening after 11 Ma indicating that subduction of the ridge accelerates tectonic erosion. Long-term rates of crustal erosion in the region of Lima Basin are greater than estimates of regional arc magmatic productivity, implying that such margins are net sinks of continental crust.

  11. Deformation of the Bellingham Basin in the Northern Cascadia Forearc as Inferred from Potential Field Data

    NASA Astrophysics Data System (ADS)

    Taylor, J.; Wolf, L. W.; Blakely, R. J.; Sherrod, B. L.; Brown, J.

    2013-12-01

    The Bellingham basin, spanning onshore and offshore regions of northwestern Washington state and southwestern British Columbia, is deforming under north-south shortening in the north Cascadia forearc. Accommodating the regional strain are Holocene-active faults within the basin that have been traced both offshore and onshore on the basis of gravity, aeromagnetic, and limited seismic data. In this study, we add 160 new gravity measurements to an existing database to better define the geometry of the Bellingham basin and its relation to recently discovered NW-trending faults. The new gravity data, spaced at ~ 1 km in the study area, were collected to address gaps in the irregular spatial distribution of existing data and extrapolate deformation recorded in coastal areas eastward into the basin. Regional-residual separation methods and derivative maps suggest that the Bellingham basin is segmented into three smaller basins. The southeast-trending Birch Bay fault extends 30 km into the basin, in agreement with previous work. The Sandy Point fault to the south of Birch Bay and the Drayton Harbor fault to the north appear as pronounced NW-SE trending lineations in magnetic data but are not as apparent as the Birch Bay fault in the new gravity data. The new data indicate that the northern margin of the Bellingham basin follows an arcuate path, southeastward from Birch Bay, then curving northeastward to connect with the Boulder Creek Fault. Two cross-sectional 2.5D models crossing the Bellingham basin show that the Birch Bay fault is steeply dipping and closely associated with a NW-SE trending anticlinal structure involving the underlying Chuckanut Formation and older rocks. An industry seismic line located ~2 km north of the Birch Bay fault shows an anticline involving Quaternary strata, consistent with the cross-sectional models. Results from the study suggest that the Bellingham basin contains evidence of Holocene-active faulting that, like other forearc basins to the

  12. Tertiary tectonics and sedimentation in the Salin (fore-arc) basin, Myanmar

    SciTech Connect

    Trevena, A.S.; Varga, R.J. ); Collins, I.D.; Nu, U. )

    1991-03-01

    Salin basin of central Myanmar is a tertiary fore-arc basin that extends over 10,000 mi{sup 2} and contains 30,000+ ft of siliciclastic rocks. In the western Salin basin, Tertiary deltaic and fluvial formations contain thousands of feet of lithic sandstones that alternate with transgressive shallow marine shales. Facies and paleocurrent studies indicate deposition by north-to-south prograding tidal deltas and associated fluvial systems in a semi-restricted basin. Presence of serpentinite and volcanic clasts in Tertiary sandstones may imply that the basin was bounded to the east by the volcanic arc and to the west by a fore-arc accretionary ridge throughout much of the Cenozoic. Salin basin is currently defined by a regional north/south-trending syncline with uplifts along the eastern and western margins. Elongate folds along the eastern basin margin verge to the east and lie above the reverse faults that dip west; much of Myanmar's present hydrocarbon production is from these structures. Analogous structures occur along the western margin, but verge to the west and are associated with numerous hydrocarbon seeps and hand-dug wells. These basin-bounding structures are the result of fault-propagation folding. In the western Salin basin, major detachments occur within the shaly Tabyin and Laungshe formations. Fault ramps propagated through steep forelimbs on the western sides of the folds, resulting in highly asymmetric footwall synclines. Stratigraphic and apatite fission track data are consistent with dominantly Plio-Pleistocene uplift, with limited uplift beginning approximately 10 Ma. Paleostress analysis of fault/slickenside data indicates that fold and thrust structures formed during regional east/west compression and are not related in any simple way to regional transpression as suggested by plate kinematics.

  13. Holocene faulting in the Bellingham forearc basin: upper-plate deformation at the northern end of the Cascadia subduction zone

    USGS Publications Warehouse

    Kelsey, Harvey M.; Sherrod, Brian L.; Blakely, Richard J.; Haugerud, Ralph A.

    2013-01-01

    The northern Cascadia forearc takes up most of the strain transmitted northward via the Oregon Coast block from the northward-migrating Sierra Nevada block. The north-south contractional strain in the forearc manifests in upper-plate faults active during the Holocene, the northern-most components of which are faults within the Bellingham Basin. The Bellingham Basin is the northern of four basins of the actively deforming northern Cascadia forearc. A set of Holocene faults, Drayton Harbor, Birch Bay, and Sandy Point faults, occur within the Bellingham Basin and can be traced from onshore to offshore using a combination of aeromagnetic lineaments, paleoseismic investigations and scarps identified using LiDAR imagery. With the recognition of such Holocene faults, the northernmost margin of the actively deforming Cascadia forearc extends 60 km north of the previously recognized limit of Holocene forearc deformation. Although to date no Holocene faults are recognized at the northern boundary of the Bellingham Basin, which is 15 km north of the international border, there is no compelling tectonic reason to expect that Holocene faults are limited to south of the international border.

  14. Basin Evolution and Exhumation of the Xigaze Forearc, Southern Tibet: Insight from Sedimentology, Stratigraphy, and Geo-Thermochronology

    NASA Astrophysics Data System (ADS)

    Orme, D. A.; Carrapa, B.; Abbey, A. L.; Kapp, P. A.; Ding, L.

    2012-12-01

    Forearc basins are important data archives for understanding continental dynamics because they preserve the tectono-erosional record of continental margins before collision. This study focuses on the Cretaceous-Eocene Xigaze forearc basin in southern Tibet, which is exposed along ~600 km of the Indus-Yarlung Suture Zone between the Indian craton to the south and the Asian Lhasa terrane to the north. From late Cretaceous to early Cenozoic time, subduction of Neo-Tethyan oceanic crust beneath the southern margin of Asia accommodated the northward motion of the Indian craton and formed the Xigaze forearc basin. Following collision with India in the early Cenozoic, the basin transitioned from predominantly marine to non-marine sedimentation and was subsequently uplifted to a mean elevation of 5000 m. How this transition occurred remains unresolved. This study's overall objective is to decipher forearc-basin and Indo-Asia continental-margin development from field sedimentology and stratigraphy, and detrital geo-thermochronology. We present new stratigraphic sections, totaling 8 km thick, from a previously unexplored ~60 km segment of the Xigaze forearc, ~50 km north-northwest of Saga. These sections are quite different from those known farther east. Sedimentary facies of mid-Cretaceous to early Eocene deposits indicate a shoaling-upward trend consistent with other ancient forearc basins (e.g., Great Valley forearc, California). Middle to late Cretaceous deposits indicate a variety of facies and depositional environments along strike in the study area. Facies include distal marine turbidites, shelf limestones, estuarine siliciclastics, and brown paleosols. In contrast, Eocene depositional environments are transitional from nearshore marine to pericontinental. Facies consist of dirty limestones, packstones, and wackestones, interbedded with terrigenous conglomerates and red-green paleosols. Eocene fauna include abundant foraminifera such as Nummulites-Discocyclina and

  15. Structure and Stratigraphy of the Barbados Accretionary Prism and the Tobago Forearc Basin

    NASA Astrophysics Data System (ADS)

    Chaderton, N. A.; Wood, L. J.; Mann, P.

    2004-12-01

    The relationship between the Lesser Antilles island arc, the Tobago forearc basin, and the Barbados accretionary prism shows classic convergent margin geometry. Barbados is the only emergent part of the accretionary prism with 80% of the island's land area being covered by Pleistocene limestone. Erosion of the limestone cap in the northeastern part of the island exposes older rocks of the prism. A 450-km2 2-D seismic data volume allows extension of these stratigraphic units offshore and definition of a regional structural framework. The relationship between the unit identified onshore as the Early Eocene to Middle Miocene Oceanic Formation and the basal unit, the intensively folded and faulted Eocene prism rocks of the Scotland Group, has long been debated. Previous proposals claim that the Oceanic Formation, consisting of pelagic clays with some ash beds, is allochthonous and has been thrusted into its present position above accreted sediments of the Scotland Group. However, seismic data show no evidence of nappes-the basis for the overthrusting hypothesis. Seismic interpretation presented here supports the opposing view that the Oceanic Formation and its offshore equivalent in the offshore Tobago forearc basin was deposited in situ and onlap the older, more highly deformed rocks of the accretionary prism. Previous workers proposed that the region's extensive mud diapirism (identified onshore as the Joes River Formation) has caused the emergence of Barbados, which continues to rise 0.44 mm/yr. However, seismic lines suggest that the island's emergence and present-day uplift is related to footwall uplift along a large, NE-striking normal fault off the east coast of the island.

  16. A review of tectonics and sedimentation in a forearc setting: Hellenic Thrace Basin, North Aegean Sea and Northern Greece

    NASA Astrophysics Data System (ADS)

    Maravelis, A. G.; Boutelier, D.; Catuneanu, O.; Seymour, K. St.; Zelilidis, A.

    2016-04-01

    Exposure of the forearc region of the North Aegean Sea, Greece, offers insight into evolving convergent margins. The sedimentary fill of the Thrace Basin during the Late Eocene to Oligocene time provides a record of subduction-driven processes, such as growth of magmatic arcs and construction of accretionary complexes. This large sediment repository received sediment from two sources. The southern (outboard) basin margin reflects the active influence of the exhumed accretionary prism (e.g. Pindic Cordillera or Biga peninsula), while the northern (inboard) margin records the effect of the magmatic arc in the Rhodope region. The forearc basin sedimentary fills shoal upward into shallow-marine strata but are dominated mainly by deep-marine facies. The depositional trend and stacking pattern are dominated by progradational patterns. This trend, which is observed in both basin margins, is related to tectonic deformation rather than sea-level fluctuations. Additional evidence for this tectonic uplift comes from the backstripping analysis. The accretionary complex provided material into the forearc basin. This material was transported northeast and formed a sand-rich turbidity system that evolved upslope into shallow-marine deposits. Stratigraphic data indicate that this turbidity system exhibits a successive landward (inboard) migration of the depocenter. Provenance data utilizing sandstone petrography, conglomerate clast composition, and bulk-rock geochemistry suggest that this system reflects an increased influx of mafic material into the basin. Volcanic arc-derived material was transported south and east and accumulated in deep-marine settings. Both stratigraphic and provenance data indicate a seaward (outboard) migration of the basin depocenter and a significant increase in felsic detritus into the forearc.

  17. Influence of the Amlia fracture zone on the evolution of the Aleutian Terrace forearc basin, central Aleutian subduction zone

    USGS Publications Warehouse

    Ryan, Holly F.; Draut, Amy E.; Keranen, Katie M.; Scholl, David W.

    2012-01-01

    During Pliocene to Quaternary time, the central Aleutian forearc basin evolved in response to a combination of tectonic and climatic factors. Initially, along-trench transport of sediment and accretion of a frontal prism created the accommodation space to allow forearc basin deposition. Transport of sufficient sediment to overtop the bathymetrically high Amlia fracture zone and reach the central Aleutian arc began with glaciation of continental Alaska in the Pliocene. As the obliquely subducting Amlia fracture zone swept along the central Aleutian arc, it further affected the structural evolution of the forearc basins. The subduction of the Amlia fracture zone resulted in basin inversion and loss of accommodation space east of the migrating fracture zone. Conversely, west of Amlia fracture zone, accommodation space increased arcward of a large outer-arc high that formed, in part, by a thickening of arc basement. This difference in deformation is interpreted to be the result of a variation in interplate coupling across the Amlia fracture zone that was facilitated by increasing subduction obliquity, a change in orientation of the subducting Amlia fracture zone, and late Quaternary intensification of glaciation. The change in coupling is manifested by a possible tear in the subducting slab along the Amlia fracture zone. Differences in coupling across the Amlia fracture zone have important implications for the location of maximum slip during future great earthquakes. In addition, shaking during a great earthquake could trigger large mass failures of the summit platform, as evidenced by the presence of thick mass transport deposits of primarily Quaternary age that are found in the forearc basin west of the Amlia fracture zone.

  18. Impact of structural and autocyclic basin-floor topography on the depositional evolution of the deep-water Valparaiso forearc basin, central Chile

    USGS Publications Warehouse

    Laursen, J.; Normark, W.R.

    2003-01-01

    The Valparaiso Basin constitutes a unique and prominent deep-water forearc basin underlying a 40-km by 60-km mid-slope terrace at 2.5-km water depth on the central Chile margin. Seismic-reflection data, collected as part of the CONDOR investigation, image a 3-3.5-km thick sediment succession that fills a smoothly sagged, margin-parallel, elongated trough at the base of the upper slope. In response to underthrusting of the Juan Ferna??ndez Ridge on the Nazca plate, the basin fill is increasingly deformed in the seaward direction above seaward-vergent outer forearc compressional highs. Syn-depositional growth of a large, margin-parallel monoclinal high in conjunction with sagging of the inner trough of the basin created stratal geometries similar to those observed in forearc basins bordered by large accretionary prisms. Margin-parallel compressional ridges diverted turbidity currents along the basin axis and exerted a direct control on sediment depositional processes. As structural depressions became buried, transverse input from point sources on the adjacent upper slope formed complex fan systems with sediment waves characterising the overbank environment, common on many Pleistocene turbidite systems. Mass failure as a result of local topographic inversion formed a prominent mass-flow deposit, and ultimately resulted in canyon formation and hence a new focused point source feeding the basin. The Valparaiso Basin is presently filled to the spill point of the outer forearc highs, causing headward erosion of incipient canyons into the basin fill and allowing bypass of sediment to the Chile Trench. Age estimates that are constrained by subduction-related syn-depositional deformation of the upper 700-800m of the basin fill suggest that glacio-eustatic sea-level lowstands, in conjunction with accelerated denudation rates, within the past 350 ka may have contributed to the increase in simultaneously active point sources along the upper slope as well as an increased

  19. Episodic Deep Fluid Expulsion at Mud Volcanoes in the Kumano Forearc Basin, SE Offshore Japan

    NASA Astrophysics Data System (ADS)

    Hammerschmidt, S.; Kopf, A.

    2014-12-01

    Compressional forces at convergent margins govern a variety of processes, most prominently earthquakes, landslides and mud volcanoes in the forearc. Although all seem related to fluid pressure changes, mud volcanoes are not only characterized by expulsion of fluids, but also fluidized mud and clasts that got ripped-up during mud ascension. They hence provide information regarding mobilization depth, diagenetic overprint, and geodynamic pathways. At the Nankai Trough subduction zone, SE offshore Japan, mud volcanism id common and supposed to be related to seismogenic processes. During MARUM Expedition SO-222 with R/V SONNE, mud volcanoes in the Kumano forearc basin were mapped, cored and sampled. By extending the Integrated Ocean Drilling Program (IODP) Kumano transect landwards, 5 new mud volcanoes were identified by multibeam mapping. Cores revealed mud breccia with semi-consolidated silt- to claystone clasts and gaseous fluid escape structures, while the hemipelagic background sediments are characterized by intercalations of turbidites, ash layers and calcareous fossils. Clasts were subject to thin-section analyses, and the cores were sampled for XRD analyses and radiocarbon dating. Clasts showed prominent deformation structures, neomorphism and pores and fractures filled with polycrystalline quartz and/or calcite cement, probably formed during deep burial and early metamorphosis. Illite crystallinity based on XRD measurements varies between 0.24 and 0.38, which implies that the material originates from the Anchizone at depths ≥ 4 km. Radiocarbon dating revealed ages between 4450 and 30300 yr cal. BP, with age reversals occurring not earlier than 17000 yr cal. BP. Radiocarbon dating beneath turbidites and ash layers found at mud volcano #9 points to an episodic occurrence of these earthquake-related features in intervals of ca. 620 yr, while the mud volcano itself remained inactive. In summary, the preliminary results suggest that the mud volcanoes are nurtured

  20. Using Satellite Gravity to Map and Model Forearc Basins and Thickness of Trench Sediment Worldwide: Implications for Great Earthquakes

    NASA Astrophysics Data System (ADS)

    Blakely, R. J.; Scholl, D. W.; Wells, R. E.; von Huene, R.; Barckhausen, U.

    2006-12-01

    There is growing evidence that historic great earthquakes (M>8) favor segments of subduction zones that exhibit key geologic factors, such as high sediment influx into the trench (e.g., Ruff, 1989), the presence of young accretionary prisms (von Huene and Scholl, 1991), the presence of trench-slope forearc basins (Wells et al., 2003; Song and Simons, 2003), and the mineralogical structure of the upper plate. The USGS Tsunami Sources Working Group (http://walrus.wr.usgs.gov/tsunami/workshop/index.html) recently described and quantified these factors for all eastern Pacific subduction margins. Although the level of knowledge of subduction zones world-wide is highly uneven, free-air gravity anomalies observed at satellite altitudes provide a consistent measure of some of these geologic factors. Satellite gravity demonstrates, for example, that regions of greatest slip during past megathrust earthquakes around the circum-Pacific spatially correlate with forearc basins and their associated deep-sea terrace gravity lows, with amplitudes typically >20 mGal. Basins may evolve because interseismic subsidence, possibly linked to basal erosion of the forearc by the subducting plate, does not fully recover after earthquakes. By inference, therefore, forearc basin gravity lows should be predictors of the location of large moment release during future great earthquakes. Moreover, great earthquakes have a statistical propensity to occur at trenches with excess sediments, in contrast to trenches dominated by horst-and-graben bathymetry. After removing the effects of bathymetric depth, low densities associated with trench fill are evident in satellite gravity anomalies and thus permit identification of trench segments with high sediment influx. Additional studies using satellite gravity anomalies may lead to new avenues in understanding the geologic processes that accompany great megathrust earthquakes, but we must confirm the ability of satellite gravity data to serve as a

  1. Structural Evolution of the Crotone Basin: Successive Shortening and Extension Episodes Parallel to the Calabrian Forearc (South Italy)

    NASA Astrophysics Data System (ADS)

    Reitz, M.; Seeber, L.

    2008-12-01

    At 10-12 Ma, the continental fragment of Calabria separated from Sardinia and became the crystalline core of a forearc in a NW-directed subduction system that is being consuming the Mesozoic (Neo-Tethys) oceanic lithosphere. The southeastward rollback of this arc has left in its wake the Tyrrhenian Sea by back-arc spreading. This system is confined between the continental margins of Africa and its Apulian promontory and created matching oblique-collision orogens (Sicilian Maghrebides and Apennines, respectively) along the margins. These progressive collisions shortened the arc because the gap between the margins narrowed to the SE. However, the arc is now lengthening after passing the point of closest approach of Sicily and Apulia, probably in the Quaternary. We seek evidence of this and other neotectonic episodes in the evolution of the forearc in the Crotone basin, which is situated on the accretionary E side of Calabria. A widespread unconformity correlated with the onset of rollback marks a regional foundering controlled by multidirectional extensional growth faults. These faults are consistently capped by the Messinian evaporite sequence. This sequence ends with a widespread unconformity that marks the final desiccation of the Ionian Sea ~5Ma. Mechanical changes due to drop in pore pressure and backward tilting of the accretionary wedge due to flexural unloading may be responsible for the landward emplacement of an accretionary mélange on the NE side of the Crotone Basin and the deposition of a characteristic conglomerate that locally caps the evaporites. After a well known mid-Pliocene basin-forming extensional event, we find evidence for a basin- wide contraction affecting the entire Neogene sequence up to the mid-to-late Pliocene. Vergence ranges from N to NW from east to west across the basin and is consistent with longitudinal shortening of the forearc. The shortening structures are cut or reactivated(?) by extensional faulting which we associate with

  2. Cretaceous stratigraphic sequences of north-central California suggest a discontinuity in the Late Cretaceous forearc basin

    SciTech Connect

    Haggart, J.W.

    1986-10-01

    The Cretaceous sedimentary succession preserved east of Redding, at the northern end of California's Great Valley, indicates that marine deposition was widespread in the region for only two periods during the Late Cretaceous. If it is assumed that there was minimal Cenozoic offset between the northern Sierra Nevada and eastern Klamath Mountains terranes, Cretaceous sedimentation in this region was most likely restricted to a narrow trough and was not a continuation of the wide, Cretaceous forearc basin of central California. The dissimilar depositional histories of the Redding basin and the Hornbrook basin of north-central California suggest that the basins were not linked continuously during the Late Cretaceous. A thick section of Cretaceous strata beneath the southwestern Modoc Plateau is considered unlikely.

  3. Formation of forearc basins by collision between seamounts and accretionary wedges: an example from the New Hebrides subduction zone

    USGS Publications Warehouse

    Collot, J.-Y.; Fisher, M.A.

    1989-01-01

    Seabeam data reveal two deep subcircular reentrants in the lower arc slope of the New Hebrides island arc that may illustrate two stages in the development of a novel type of forearc basin. The Malekula reentrant lies just south of the partly subducted Bougainville seamount. This proximity, as well as the similarity in morphology between the reentrant and an indentation in the lower arc slope off Japan, suggests that the Malekula reentrant formed by the collision of a seamount with the arc. An arcuate fold-thrust belt has formed across the mouth of the reentrant, forming the toe of a new accretionary wedge. The Efate reentrant may show the next stage in basin development. This reentrant lies landward of a lower-slope ridge that may have begun to form as an arcuate fold-thrust belt across the mouth of a reentrant. This belt may have grown by continued accretion at the toe of the wedge, by underplating beneath the reentrant, and by trapping of sediment shed from the island arc. These processes could result in a roughly circular forearc basin. Basins that may have formed by seamount collision lie within the accretionary wedge adjacent to the Aleutian trenches. -Authors

  4. Upper Paleogene shallow-water events in the Sandino Forearc Basin, Nicaragua-Costa Rica - response to tectonic uplift

    NASA Astrophysics Data System (ADS)

    Andjic, Goran; Baumgartner-Mora, Claudia; Baumgartner, Peter O.

    2016-04-01

    The Upper Cretaceous-Neogene Sandino Forearc Basin is exposed in the southeastern Nicaraguan Isthmus and in the northwestern corner of Costa Rica. It consists of an elongated, slightly folded belt (160 km long/30 km wide). During Campanian to Oligocene, the predominantly deep-water pelagic, hemipelagic and turbiditic sequences were successively replaced by shelf siliciclastics and carbonates at different steps of the basin evolution. We have made an inventory of Tertiary shallow-water limestones in several areas of Nicaragua and northern Costa Rica. They always appear as isolated rock bodies, generally having an unconformable stratigraphic contact with the underlying detrital sequences. The presence of these short-lived carbonate shoals can be attributed to local or regional tectonic uplift in the forearc area. The best-preserved exposure of such a carbonate buildup is located on the small Isla Juanilla (0.15 km2, Junquillal Bay, NW Costa Rica). The whole island is made of reef carbonates, displaying corals in growth position, associated with coralline red algae (Juanilla Formation). Beds rich in Larger Benthic Foraminifera such as Lepidocyclina undosa -favosa group permit to date this reef as late Oligocene. A first uplift event affected the Nicaraguan Isthmus, that rose from deep-water to shelfal settings in the latest Eocene-earliest Oligocene. The upper Oligocene Juanilla Formation formed on an anticline that developed during the early Oligocene, contemporaneously with other folds observed in the offshore Sandino Forearc Basin. During the early Oligocene, a period of global sea-level fall, the folded tectonic high underwent deep erosion. During the late Oligocene, a time of overall stable eustatic sea level, tectonic uplift gave way to moderate subsidence, creating accommodation space for reef growth. A 4th or 5th order (Milankovic-type) glacio-eustatic sea level rise, could also have triggered reef growth, but its preservation implies at least moderate

  5. Evolution of subsidence styles in forearc basin: example from Cretaceous of southern Vizcaino Peninsula, Baja California, Mexico

    SciTech Connect

    Busby-Spera, C.J.; Boles, J.R.

    1986-04-01

    Late Jurassic to Early Cretaceous arc magmatism is represented by volcaniclastic rocks of the Eugenia Formation in the northern Vizcaino Peninsula and by the metamorphosed Cedros-San Andres volcanoplutonic complex, with a dismembered ophiolitic basement, in the southern peninsula. The Vizcaino Peninsula became the site of forearc sedimentation by the Aptian-Albian (late Early Cretaceous), when arc magmatism moved abruptly eastward to the present-day Peninsular Range. On the southern Vizcaino Peninsula, a conformable stratigraphic section, complicated by later faulting, records a gradual transition from a ridged forearc, broken by basement uplifts and grabens (the Aptian-Albian Asunction Formation), to a broadly subsiding, deep marine forearc basin (the Cenomanian Valle Formation). The basal contact of the Asunction formation has irregular relief caused by brecciated basement rocks and talus accumulated along fault zones. An upward-fining sequence several hundred meters thick records abrupt uplift and gradual denudation of adjacent metamorphic basement. Contemporaneous andesite arc volcanism to the east supplied ash and fresh volcanic detritus to the grabens. Angular sand to boulder-size detritus of the Asunction Formation was derived locally, and includes basic to intermediate meta-igneous rock fragments, with epidote, actinolite, and chlorite, as well as serpentine. Abundant calcareous fossils are commonly unbroken, suggesting local sources for these as well. Angular to subrounded, sand to cobble-sized, intermediate to mafic volcanic rock fragments were derived from a more distant island arc to the east, which occasionally provided intermediate to felsic tuffs to the basin. This source is probably represented by the Aptian-Albian Alisitos Group, which forms much of the western wall of the Late Cretaceous Peninsular Range batholith.

  6. Hydrocarbon seep-carbonates of a Miocene forearc (East Coast Basin), North Island, New Zealand

    NASA Astrophysics Data System (ADS)

    Campbell, Kathleen A.; Francis, David A.; Collins, Mike; Gregory, Murray R.; Nelson, Campbell S.; Greinert, Jens; Aharon, Paul

    2008-02-01

    An ancient hydrocarbon seep province of 14 isolated, authigenic carbonate deposits has been identified in fine-grained, deep-marine siliciclastic strata of the Miocene East Coast Basin, North Island, New Zealand. These forearc sediments have been uplifted and complexly deformed into accretionary ridges, adjacent to the still-active Hikurangi convergent margin. Older active and passive margin strata (mid-Cretaceous to Oligocene in age) underlie the Neogene sequence, and contain oil- and gas-prone source rocks. Older Mesozoic meta-sedimentary rocks constitute the backstop against which the current phase of subduction-related sedimentation has accumulated (~ 24 Ma-present). The seep-carbonates (up to 10 m thick, 200 m across) archive methane signatures in their depleted carbon isotopes (to δ13C -51.7‰ PDB), and contain chemosynthesis-based paleocommunities (e.g. worm tubes, bathymodioline mussels, and vesicomyid, lucinid and thyasirid bivalves) typical of other Cenozoic and modern seeps. Northern and southern sites are geographically separated, and exhibit distinct lithological and faunal differences. Structural settings are variable. Seep-associated lithologies also are varied, and suggest carbonate development in sub-seafloor, seafloor and physically reworked (diapiric expansion, gas explosion, gravity slide or debris flow) settings, similar to Italian Apennine seep deposits of overlapping ages. Peculiar attributes of the New Zealand Miocene seep deposits are several, including digitate thrombolites of clotted microbial micrite encased in thick, isopachous horizons and botryoids of aragonite. Seep plumbing features are also well-exposed at some sites, displaying probable gas-explosion breccias filled with aragonite, tubular concretions (fluid conduits), and carbonate-cemented, thin sandstone beds and burrows within otherwise impermeable mudstones. A few seeps were large enough to develop talus-debris piles on their flanks, which were populated by lucinid bivalves

  7. Forearc Basin Structure in the Andaman-Nicobar Segment of the Sumatra-Andaman Subduction Zone: Insight from High-Resolution Seismic Reflection Data

    NASA Astrophysics Data System (ADS)

    Moeremans, R. E.; Singh, S. C.

    2014-12-01

    The Andaman-Nicobar subduction is the northernmost segment of the Sumatra-Andaman subduction zone and marks the western boundary of the Andaman Sea, which is a complex backarc extensional basin. We present the interpretation of a new set of deep seismic reflection data acquired across the Andaman-Nicobar forearc basin, from 8°N to 11°N, to understand the structure and evolution of the forearc basin, focusing on how the obliquity of convergence affects deformation in the forearc, as well as on the Diligent (DF) and Eastern Margin Faults (EMF). Constraining the evolution of this basin, which is strongly related to the collision of India and Eurasia, can help shed light onto present-day deformation processes along this segment of the subduction zone, where convergence is highly oblique and little data is available. We find that he DF is a backthrust and corresponds to the Mentawai (MFZ) and West Andaman Fault (WAF) systems further south, offshore Sumatra. The DF is expressed as a series of mostly landward verging folds and faults, deforming the early to late Miocene sediments. The DF seems to root from the boundary between the accretionary complex and the continental backstop, where it meets the EMF. The EMF marks the western boundary of the forearc basin; it is associated with subsidence and is expressed as a deep piggyback basin, associated with recent Pliocene to Pleistocene subsidence at the western edge of the forearc basin. The eastern edge of the forearc basin is marked by the Invisible Bank (IB), which is thought to be tilted and uplifted continental crustal block. Subsidence along the EMF and uplift and tilting of the IB seem to be related to different opening phases in the Andaman Sea. The sliver Andaman-Nicobar Fault (ANF), which is the active northward extension of the Great Sumatra sliver Fault (GSF), lies to the east of the IB, and marks the boundary between continental crust underlying the forearc basin and crust accreted at the Andaman Sea Spreading

  8. In situ stress and pore pressure in the Kumano Forearc Basin, offshore SW Honshu from downhole measurements during riser drilling

    NASA Astrophysics Data System (ADS)

    Saffer, D. M.; Flemings, P. B.; Boutt, D.; Doan, M.-L.; Ito, T.; McNeill, L.; Byrne, T.; Conin, M.; Lin, W.; Kano, Y.; Araki, E.; Eguchi, N.; Toczko, S.

    2013-05-01

    situ stress and pore pressure are key parameters governing rock deformation, yet direct measurements of these quantities are rare. During Integrated Ocean Drilling Program (IODP) Expedition #319, we drilled through a forearc basin at the Nankai subduction zone and into the underlying accretionary prism. We used the Modular Formation Dynamics Tester tool (MDT) for the first time in IODP to measure in situ minimum stress, pore pressure, and permeability at 11 depths between 729.9 and 1533.9 mbsf. Leak-off testing at 708.6 mbsf conducted as part of drilling operations provided a second measurement of minimum stress. The MDT campaign included nine single-probe (SP) tests to measure permeability and in situ pore pressure and two dual-packer (DP) tests to measure minimum principal stress. Permeabilities defined from the SP tests range from 6.53 × 10-17 to 4.23 × 10-14 m2. Pore fluid pressures are near hydrostatic throughout the section despite rapid sedimentation. This is consistent with the measured hydraulic diffusivity of the sediments and suggests that the forearc basin should not trap overpressures within the upper plate of the subduction zone. Minimum principal stresses are consistently lower than the vertical stress. We estimate the maximum horizontal stress from wellbore failures at the leak-off test and shallow MDT DP test depths. The results indicate a normal or strike-slip stress regime, consistent with the observation of abundant active normal faults in the seaward-most part of the basin, and a general decrease in fault activity in the vicinity of Site C0009.

  9. Distribution and structure of active strike-slip faults in the Enshu forearc basin of the eastern Nankai subduction zone

    NASA Astrophysics Data System (ADS)

    Ojima, T.; Ashi, J.; Nakamura, Y.

    2010-12-01

    Accretionary prisms and forearc basins are developed in the Nankai Trough, SW Japan. Many active faults are recognized and classified into five fault systems in the eastern Nankai Trough. The Enshu Faults System, the most landward one, runs over 200 km along the northern edge of the Tokai, Enshu and Kumano forearc basins. Swath bathymetry and side-scan sonar surveys indicate a general fault trend of ENE-WSW and dextral displacement of submarine canyons across the landward-most fault. Seismic reflection profiles partly exhibit landward dipping fault planes and flower structures suggesting that the Enshu fault system is affected by oblique subduction of the Philippines Sea Plate. Structural investigation of this area is important for earthquake disaster mitigation as well as understanding of oblique subduction tectonics. However, activity of faults has not been clarified. Japan Oil, Gas and Metal National Corporation (JOGMEC) conducted dense seismic reflection survey at the Tokai-Kumano area in 2001. Seismic reflection profiles clearly show depositional sequences and deformation structures such as faults and folds. This study examined deformation styles and fault activities based on detailed interpretation of seismic reflection profiles. Sediment thickness mapped from seismic profiles clearly changes with age. Sediment thickness is almost homogeneous from the acoustic basement (probably Paleogene Shimanto Complex) to a Pliocene horizon in the survey area. In contrast, thickness between a Pliocene horizon and present seafloor shows large variations from east to west. It is suggested that sedimentary environments change drastically at this period. There are also small-scale variations in sediment thickness for all horizons. Some distinct changes are distributed along linear boundaries. It seems that they correspond to the faults recognized as lineaments on the sidescan sonar images. We estimated activities of faulting based on such sediment thickness changes and their

  10. Cenozoic stratigraphic development in the north Chilean forearc: Implications for basin development and uplift history of the Central Andean margin

    NASA Astrophysics Data System (ADS)

    Hartley, Adrian J.; Evenstar, Laura

    2010-11-01

    Analysis of the Cenozoic stratigraphic development of the forearc of northern Chile between 18°S and 23°30'S, allows constraints to be placed on the timing and nature of basin formation and the uplift history of the Central Andes. Chronostratigraphic charts have been constructed from 20 lithostratigraphic sections distributed throughout the forearc. Sections were taken from the Longitudinal Valley, Central Depression, Calama Basin, Salar de Atacama, Precordillera and the western flank of the Western Cordillera. Correlation and timing of events is largely based on the presence of dated volcanic horizons in all the studied sections. Three chronostratigraphic units are defined based upon the presence of regional unconformities. Deposition of the Late Eocene to Early Miocene chronostratigraphic unit (38-19 Ma) commenced across an irregular unconformity surface between ˜ 38 and 30 Ma with alluvial fan and fluvial sediments derived from the east interbedded with rhyolitic ignimbrites. Aggradation after 25 Ma resulted in development of a large broad basin over much of northern Chile that expanded eastwards through onlap onto basement. Deposition terminated around 19 Ma with the development of an angular unconformity over much, but not all of the study area. During deposition of the Early to Late Miocene chronostratigraphic unit (18-10 Ma) emergent volcanic source areas to the east provided catchments for large fluvial systems that drained westwards into endorheic ephemeral lacustrine basins. Fold growth affected sedimentation restricting accommodation space to small intra-thrust basins in the Precordillera and localised disruption and unconformity development in the Longitudinal Valley. The Late Miocene to present day chronostratigraphic unit (10-0 Ma) followed the development of a regional angular unconformity at 10 Ma. Sedimentation was restricted to a series of thrust-bounded endorheic basins in both the Central Depression and the Precordillera sourced from the east

  11. Miocene fluvial-tidal sedimentation in a residual forearc basin of the Northeastern Pacific Rim: Cook Inlet, Alaska case study

    SciTech Connect

    Stricker, G.D.; Flores, R.M. )

    1996-01-01

    Cook Inlet in southern Alaska represents a Cenozoic residual forearc basin in a convergent continental margin, where the Pacific Plate is being subducted beneath the North American Plate. This basin accumulated the >6,700-m-thick, mainly nonmarine, Eocene-Pliocene Kenai Group. These rocks contain biogenic coal-bed methane estimated to be as high as 245 TCF. Lignites to subbituminous coals with subsurface R[sub o] ranging from 0.38 to 0.73 percent and the stage of clay-mineral diagenesis and expandibility indicate a thermally [open quotes]cool[close quotes] basin. Miocene Tyonek and Beluga Formations compose 65 percent (>4,300 m thick) of the Kenai Group. The Tyonek includes conglomeratic sandstones, siltstones, mudstones, coals, and carbonaceous shales, interpreted as braided- stream deposits. These fluvial deposits are interbecided with burrowed, lenticular, and flaser-bedded sandstones, siltstones, and mudstones, interpreted as tidal deposits. Tyonek framework conglomerates formed in wet alluvial fans incised on paleovalleys of the Chugach terrane. Coal-forming mires are well developed on abandoned braided-stream deposits. Tyonek drainages formed in high-gradient alluvial plains inundated by tides similar to environments in the modern upper Cook Inlet. The upper Miocene Beluga consists of sandstones, siltstones, mudstones, carbonaceous shales, and coals deposited in meandering (low sinuosity) and anastomosed fluvial systems. These fluvial deposits alternated vertically with deposits of coal-forming mires. The Beluga drainages formed in low-gradient alluvial plains. The high-gradient Tyonek alluvial plain was probably controlled by provenance uplift and eustatic change, whereas the low-gradient Beluga alluvial plain was influenced by subdued provenance uplift and rapid basin subsidence. Rapid sedimentation on both these low- and high-gradient alluvial plains, which kept up with subsidence, produced a thermally [open quotes]cool[close quotes] basin.

  12. Miocene fluvial-tidal sedimentation in a residual forearc basin of the Northeastern Pacific Rim: Cook Inlet, Alaska case study

    SciTech Connect

    Stricker, G.D.; Flores, R.M.

    1996-12-31

    Cook Inlet in southern Alaska represents a Cenozoic residual forearc basin in a convergent continental margin, where the Pacific Plate is being subducted beneath the North American Plate. This basin accumulated the >6,700-m-thick, mainly nonmarine, Eocene-Pliocene Kenai Group. These rocks contain biogenic coal-bed methane estimated to be as high as 245 TCF. Lignites to subbituminous coals with subsurface R{sub o} ranging from 0.38 to 0.73 percent and the stage of clay-mineral diagenesis and expandibility indicate a thermally {open_quotes}cool{close_quotes} basin. Miocene Tyonek and Beluga Formations compose 65 percent (>4,300 m thick) of the Kenai Group. The Tyonek includes conglomeratic sandstones, siltstones, mudstones, coals, and carbonaceous shales, interpreted as braided- stream deposits. These fluvial deposits are interbecided with burrowed, lenticular, and flaser-bedded sandstones, siltstones, and mudstones, interpreted as tidal deposits. Tyonek framework conglomerates formed in wet alluvial fans incised on paleovalleys of the Chugach terrane. Coal-forming mires are well developed on abandoned braided-stream deposits. Tyonek drainages formed in high-gradient alluvial plains inundated by tides similar to environments in the modern upper Cook Inlet. The upper Miocene Beluga consists of sandstones, siltstones, mudstones, carbonaceous shales, and coals deposited in meandering (low sinuosity) and anastomosed fluvial systems. These fluvial deposits alternated vertically with deposits of coal-forming mires. The Beluga drainages formed in low-gradient alluvial plains. The high-gradient Tyonek alluvial plain was probably controlled by provenance uplift and eustatic change, whereas the low-gradient Beluga alluvial plain was influenced by subdued provenance uplift and rapid basin subsidence. Rapid sedimentation on both these low- and high-gradient alluvial plains, which kept up with subsidence, produced a thermally {open_quotes}cool{close_quotes} basin.

  13. Field and experimental evidence for coseismic ruptures along shallow creeping faults in forearc sediments of the Crotone Basin, South Italy

    NASA Astrophysics Data System (ADS)

    Balsamo, Fabrizio; Aldega, Luca; De Paola, Nicola; Faoro, Igor; Storti, Fabrizio

    2014-05-01

    Large seismic slip occurring along shallow creeping faults in tectonically active areas represents an unsolved paradox, which is largely due to our poor understanding of the mechanics governing creeping faults, and to the lack of documented geological evidence showing how coseismic rupturing overprints creep in near-surface conditions. In this contribution we integrate field, petrophysical, mineralogical and friction data to characterize the signature of coseismic ruptures propagating along shallow creeping faults affecting unconsolidated forearc sediments of the seismically active Crotone Basin, in South Italy. Field observations of fault zones show widespread foliated cataclasites in fault cores, locally overprinted by sharp slip surfaces decorated by thin (0.5-1.5 cm) black gouge layers. Compared to foliated cataclasites, black gouges have much lower grain size, porosity and permeability, which may have facilitated slip weakening by thermal fluid pressurization. Moreover, black gouges are characterized by distinct mineralogical assemblages compatible with high temperatures (180-200°C) due to frictional heating during seismic slip. Foliated cataclasites and black gouges were also produced by laboratory friction experiments performed on host sediments at sub-seismic (≤ 0.1 m/s) and seismic (1 m/s) slip rates, respectively. Black gouges display low friction coefficients (0.3) and velocity-weakening behaviours, as opposed to high friction coefficients (0.65) and velocity-strengthening behaviours shown by the foliated cataclasites. Our results show that narrow black gouges developed within foliated cataclasites represent a potential diagnostic marker for episodic seismic activity in shallow creeping faults. These findings can help understanding the time-space partitioning between aseismic and seismic slip of faults at shallow crustal levels, impacting on seismic hazard evaluation of subduction zones and forearc regions affected by destructive earthquakes and

  14. Unmetamorphosed sedimentary mélange with high-pressure metamorphic blocks in a nascent forearc basin setting

    NASA Astrophysics Data System (ADS)

    Hitz, Brian; Wakabayashi, John

    2012-09-01

    Mélanges crop out within unmetamorphosed basal Great Valley Group (GVG) forearc basin strata and between GVG and the underlying Coast Range Ophiolite (CRO) in the San Francisco Bay region of coastal California. These mélanges include high-pressure (HP) metamorphic blocks of the Franciscan subduction complex that structurally underlies the unmetamorphosed CRO as well as blocks of GVG and CRO. The matrix consists of foliated shale and serpentinite, locally interleaved at centimeter scale. The mélanges strike and dip parallel to bounding GVG sandstones and conglomerates. The matrix locally consists of sedimentary breccia and conglomerate made up of clasts of serpentinite and shale. GVG sandstones within and bounding the mélanges have detrital serpentinite clasts. The field relationships indicate a sedimentary origin of the mélanges as olistostromal deposits within latest Jurassic to earliest Cretaceous basal GVG. The mélanges correlate to units along the eastern margin of the northern Coast Ranges, about 250 km to the north with restoration of post-subduction dextral faulting, and differ from the latter in the higher proportion of shale, stronger matrix foliation, and common occurrence of HP blocks. Similar units may have mistakenly been assigned to the Franciscan owing to the foliated nature of the matrix and occurrence of HP blocks. This and the broad distribution of localities indicate that these deposits are more widespread than previously believed. Exhumation rates of coarse-grained HP mélange blocks may have been 2 to 10 mm/yr or higher based on the ages of similar blocks in the Coast Ranges, burial depth of the blocks, and depositional age of the enclosing strata. Exhumation and deposition of Franciscan blocks in these GVG mélanges predates preserved accretion of similar materials in the adjacent Franciscan by at least 30 m.y., suggesting subduction erosion of previously accreted material, or exhumation of the blocks in forearc serpentinite

  15. Sedimentation in forearc basins, trenches, and collision zones of the western Pacific: A summary of results from the Ocean Drilling Program

    NASA Astrophysics Data System (ADS)

    Underwood, Michael B.; Ballance, Peter F.; Clift, Peter D.; Hiscott, Richard N.; Marsaglia, Kathleen M.; Pickering, Kevin T.; Reid, R. Pamela

    The comprehensive strategy pursued by the Ocean Drilling Program in the western Pacific Ocean resulted in significant improvements in our understanding of arc-related geologic processes and products. Many types of depositional environments were examined, including intraoceanic forearc basins, backarc basins, trenches, and ridge-trench collision zones. Most of the ODP sites were chosen to address tectonic, geochemical, or hydrologic objectives, but a wealth of new sedimentologic information was generated at the same time. We now have a better appreciation of how intraoceanic forearcs are affected by diverse depositional processes (e.g., debris flows, turbidity currents, and vertical settling of tephra, hemipelagic mud, and pelagic ooze). Detailed turbidite stratigraphy deduced from FMS borehole imagery shows that the Izu-Bonin forearc basin is characterized by a noncyclic basin-plain style of sedimentation, rather than a channelized submarine fan or a channelized slope apron. Detrital modes for volcaniclastic sands in the Izu-Bonin forearc are consistent with an undissected-arc provenance; subdivisions of volcanic texture and glass type provide additional details and support the idea of extensive subaerial production and mixing of epiclastic detritus. Evolution of the Tonga forearc has been affected by a complicated interplay of tectonic subsidence, eustacy, and arc volcanism. Stratigraphic evolution of the Nankai accretionary prism produced a classic upward-coarsening and upward-thickening mega-cycle representative of transition from abyssal hemipelagites to trench turbidites. Turbidite sands within the outer trench-wedge facies display indicators of northwest-directed paleoflow; those flows probably experienced a phase of upslope movement onto the outer wall and deflection back toward the Nankai trench axis. Sand petrography and clay mineralogy collectively support a mixed detrital provenance for the Nankai trench wedge; the main source area is located in the Izu

  16. Hydrocarbon seepage and its sources at mud volcanoes of the Kumano forearc basin, Nankai Trough subduction zone

    NASA Astrophysics Data System (ADS)

    Pape, Thomas; Geprägs, Patrizia; Hammerschmidt, Sebastian; Wintersteller, Paul; Wei, Jiangong; Fleischmann, Timo; Bohrmann, Gerhard; Kopf, Achim J.

    2014-06-01

    submarine mud volcanoes (MV) in the Kumano forearc basin within the Nankai Trough subduction zone were investigated for hydrocarbon origins and fluid dynamics. Gas hydrates diagnostic for methane concentrations exceeding solubilities were recovered from MVs 2, 4, 5, and 10. Molecular ratios (C1/C2 < 250) and stable carbon isotopic compositions (δ13C-CH4 >-40‰ V-PDB) indicate that hydrate-bound hydrocarbons (HCs) at MVs 2, 4, and 10 are derived from thermal cracking of organic matter. Considering thermal gradients at the nearby IODP Sites C0009 and C0002, the likely formation depth of such HCs ranges between 2300 and 4300 m below seafloor (mbsf). With respect to basin sediment thickness and the minimum distance to the top of the plate boundary thrust we propose that the majority of HCs fueling the MVs is derived from sediments of the Cretaceous to Tertiary Shimanto belt below Pliocene/Pleistocene to recent basin sediments. Considering their sizes and appearances hydrates are suggested to be relicts of higher MV activity in the past, although the sporadic presence of vesicomyid clams at MV 2 showed that fluid migration is sufficient to nourish chemosynthesis-based organisms in places. Distributions of dissolved methane at MVs 3, 4, 5, and 8 pointed at fluid supply through one or few MV conduits and effective methane oxidation in the immediate subsurface. The aged nature of the hydrates suggests that the major portion of methane immediately below the top of the methane-containing sediment interval is fueled by current hydrate dissolution rather than active migration from greater depth.

  17. Forced sea-level change in a forearc basin related to subduction of a spreading ridge: the Fossil Bluff Group (Jurassic-Cretaceous), Alexander Island, Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Macdonald, David

    2015-04-01

    During the Mesozoic, the Antarctic Peninsula was the site of an active volcanic arc related to the eastwards subduction of proto-Pacific oceanic crust. Alexander Island is the largest of the many islands that lie on the western (fore-arc) side of the Antarctic Peninsula; it forms one of the best-exposed ancient fore-arcs in the world. The pre-Tertiary rocks can be divided into two main units. The LeMay Group (Jurassic-Tertiary) forms the structural basement to Alexander Island and comprises greenschist-facies metasedimentary rocks. It is interpreted as a Mesozoic accretionary prism. The Fossil Bluff Group unconformably overlies and is faulted against the LeMay Group; it represents the sedimentary fill of a coeval fore-arc basin. Subduction ceased due to a series of Cenozoic ridge-trench collisions which began off Alexander Island at 50 Ma and got progressively younger to the north. However, the approach of the ridge can be inferred from the Mesozoic deposits of the Fossil Bluff Group (Jurassic-Cretaceous) in Alexander Island. In this paper, I will show that the ocean floor being subducted became progressively shallower through Jurassic and Cretaceous time (by at least 1,000 m). The result in the forearc basin was a sudden shallowing in water depths from at least 1,000 m at 125 Ma, to emergent at 100 Ma. This forced shallowing ended sedimentation in the basin and resulted in considerable topography on Alexander Island that persists to the present day.

  18. Ophiolitic basement to a forearc basin and implications for continental growth: The Coast Range/Great Valley ophiolite, California

    NASA Astrophysics Data System (ADS)

    Godfrey, Nicola J.; Klemperer, Simon L.

    1998-08-01

    We present a compilation of 18 published models from the length of the Great Valley forearc basin, California, based on seismic reflection, borehole, seismic refraction, gravity, and aeromagnetic data to address long-standing questions about the nature of the basement to the Great Valley, its origin, its tectonic history, and it's mechanism of incorporation into the North American continental margin. The geophysical models permit a 700-km-long, 70-km-wide, complete ophiolite sequence beneath the entire Great Valley. In the northern Great Valley, the ophiolite is overlain by ophiolitic breccia, the ophiolite crust is 7-8 km thick, and the mantle section is mostly unserpentinized. Beneath the southern Great Valley, there is no ophiolitic breccia, the crust may be up to 10 - 12 km thick, and the mantle section, if present at all, is serpentinized to such a degree that it cannot be distinguished from Sierran basement or mafic ophiolite members on the basis of velocity or density data. Geochemical, petrological, and paleomagnetic data support suprasubduction zone ophiolite formation at North American paleolatitudes, and geological data and geophysical models are consistent with ophiolite formation by back arc spreading behind an east facing arc. In the north, this was apparently followed by obduction of back arc crust onto older continental basement during the Late Jurassic Nevadan orogeny. In the south, the newly formed intraoceanic arc and back arc apparently collided with the continental margin during the Nevadan orogeny but were not obducted onto it. Instead, the arc and back arc "docked" with the continental margin leaving the arc itself to become the basement to the Great Valley basin. Cretaceous Sierran magmatism then intruded plutons beneath the docked ophiolite and mafic arc. Irrespective of the detailed accretionary history, our cross sections show a rapid pulse of continental growth by ophiolite accretion of more than 500 km³ km-1 in less than 10 Myr.

  19. Sedimentologic evolution of a submarine canyon in a forearc basin, Upper Cretaceous Rosario Formation, San Carlos, Mexico

    SciTech Connect

    Morris, W.R.; Busby-Spera, C.J.

    1988-06-01

    The walls, floor, and fill of a submarine canyon are well-exposed near San Carlos, Mexico, in forecarc strata of the Upper Cretaceous Rosario Formation. The submarine canyon is about 7 km wide and at least 230 m deep and has eroded a minimum of 150 m into underlying fluvial red beds. It is unclear whether subaerial or submarine processes initiated the canyon cutting; however, marine processes, especially debris flows, modified the morphology of the submarine canyon. The submarine canyon fill and overlying slope deposits form two major fining-upward sequences. The first includes a 120 m thick lower conglomerate-sandstone unit (LCSU) at the base of the canyon fill overlain by a 50-110 m thick middle mudstone-sandstone unit (MMSU). The MMSU consists predominantly of mudstone and thin-bedded sandstone, but includes a channel filled with sandstone beds that form a fining- and thinning-upward sequence. This sequence is overlain by the second major sequence, a 0-60 m thick upper conglomerate-sandstone unit (UCSU), which is confined to three channels within the submarine canyon and passes gradationally upward into slope mudstone. Each of the two major fining-upward sequences records a gradual decrease in supply of coarse-grained sediment to the submarine canyon head. The first fining-upward sequence may correspond to a lowstand and subsequent rise in global sea level or, alternatively, may have resulted from local downdropping of the basin. The second fining-upward sequence does not correspond to global sea level fluctuations but is age-correlative with a drop then rise in relative sea level recognized by other workers 300-400 km to the north in the San Diego-Ensenada area. This sea level drop is inferred to have been a regional-scale tectonic event that affect the forearc basin along its length. 18 figures, 2 tables.

  20. Paleomagnetic and geochronological study of Carboniferous forearc basin rocks in the Southern New England Orogen (Eastern Australia)

    NASA Astrophysics Data System (ADS)

    Pisarevsky, Sergei A.; Rosenbaum, Gideon; Shaanan, Uri; Hoy, Derek; Speranza, Fabio; Mochales, Tania

    2016-06-01

    We present results of a paleomagnetic study from Carboniferous forearc basin rocks that occur at both limbs of the Texas Orocline (New England Orogen, eastern Australia). Using thermal and alternating field demagnetizations, two remanence components have been isolated from rocks sampled from the Emu Creek terrane, in the eastern limb of the orocline. A middle-temperature Component M is post-folding and was likely acquired during low-temperature oxidation at 65-35 Ma. A high-temperature Component H is pre-folding, but its comparison with the paleomagnetic data from coeval rocks in the northern Tamworth terrane on the other limb of Texas Orocline does not indicate rotations around a vertical axis, as expected from geological data. A likely explanation for this apparent discrepancy is that Component H postdates the oroclinal bending, but predates folding in late stages of the 265-230 Ma Hunter Bowen Orogeny. The post-Kiaman age of Component H is supported by the presence of an alternating paleomagnetic polarity in the studied rocks. A paleomagnetic study of volcanic and volcaniclastic rocks in the Boomi Creek area (northern Tamworth terrane) revealed a stable high-temperature pre-folding characteristic remanence, which is dated to c. 318 Ma using U-Pb zircon geochronology. The new paleopole (37.8°S, 182.7°E, A95 = 16.2°) is consistent with previously published poles from coeval rocks from the northern Tamworth terrane. The combination of our new paleomagnetic and geochronological data with previously published results allows us to develop a revised kinematic model of the New England Orogen from 340 Ma to 270 Ma, which compared to the previous model, incorporates a different orientation of the northern Tamworth terrane at 340 Ma.

  1. Anaerobic Oxidation of Methane at a Marine Methane Seep in a Forearc Sediment Basin off Sumatra, Indian Ocean

    PubMed Central

    Siegert, Michael; Krüger, Martin; Teichert, Barbara; Wiedicke, Michael; Schippers, Axel

    2011-01-01

    A cold methane seep was discovered in a forearc sediment basin off the island Sumatra, exhibiting a methane-seep adapted microbial community. A defined seep center of activity, like in mud volcanoes, was not discovered. The seep area was rather characterized by a patchy distribution of active spots. The relevance of anaerobic oxidation of methane (AOM) was reflected by 13C-depleted isotopic signatures of dissolved inorganic carbon. The anaerobic conversion of methane to CO2 was confirmed in a 13C-labeling experiment. Methane fueled a vital microbial community with cell numbers of up to 4 × 109 cells cm−3 sediment. The microbial community was analyzed by total cell counting, catalyzed reporter deposition–fluorescence in situ hybridization (CARD–FISH), quantitative real-time PCR (qPCR), and denaturing gradient gel electrophoresis (DGGE). CARD–FISH cell counts and qPCR measurements showed the presence of Bacteria and Archaea, but only small numbers of Eukarya. The archaeal community comprised largely members of ANME-1 and ANME-2. Furthermore, members of the Crenarchaeota were frequently detected in the DGGE analysis. Three major bacterial phylogenetic groups (δ-Proteobacteria, candidate division OP9, and Anaerolineaceae) were abundant across the study area. Several of these sequences were closely related to the genus Desulfococcus of the family Desulfobacteraceae, which is in good agreement with previously described AOM sites. In conclusion, the majority of the microbial community at the seep consisted of AOM-related microorganisms, while the relevance of higher hydrocarbons as microbial substrates was negligible. PMID:22207865

  2. 3D seismic geomorphology and geologic controls on gas hydrate accumulation mechanism in the Miyazaki-oki forearc basin, Japan

    NASA Astrophysics Data System (ADS)

    Komatsu, Y.; Kobayashi, T.; Fujii, T.

    2015-12-01

    The stratigraphy of the Miyazaki-oki forearc basin along the Southwest Japan Arc comprises the early Miocene to early Pleistocene Miyazaki Group and the Hyuganada Group. These groups comprise sediments (up to 5000 m) deposited in deep marine to shallow marine environments. Based on characteristics of well data outside seismic exploration area and stratigraphy of land areas, the Miyazaki Group was divided into four seismic units and the Hyuganada Group was divided into two seismic units. In this area, bottom-simulating reflectors (BSRs) have been widely observed and considered as representing lower boundaries of methane-hydrate-bearing deposits. However, the gas hydrate accumulation mechanism for this area is not yet well understood. We show the relation between sandy sediment distribution identified from the 3D seismic geomorphological analysis and methane hydrate occurrence to identify the accumulation mechanism. A submarine fan system was subdivided into four seismic facies: Submarine canyon complexes; Leveed channel complexes; Submarine fan complexes; Mass transport complexes (MTD). Depositional systems of target layers are characterized by a transition from submarine fan deposits (Miyazaki Group) to channel-levee deposits and MTD (Hyuganada Group). This transition of depositional environments is strongly influenced by global tectonics since early Miocene in the Southwest Japan Arc. A part of channel-fill located around structural wing and middle fan deposits above the BSR is inferred as sediments intercalated with sandy layers. We consider that these deposits contain methane hydrate because the sandy sediment distribution approximately coincides with a high-velocity zone as an indicator of gas hydrate. The comparison of the areal extent of the seismic facies and the mapped structural configuration, suggest that the gas hydrate accumulation represent combination structural-stratigraphic trap.

  3. Apparent overconsolidation of mudstones in the Kumano Basin of southwest Japan: Implications for fluid pressure and fluid flow within a forearc setting

    NASA Astrophysics Data System (ADS)

    Guo, Junhua; Underwood, Michael B.; Likos, William J.; Saffer, Demian M.

    2013-04-01

    The Kumano Basin is located in the Nankai Trough subduction zone of southwest Japan. During the past 1.6 million years, approximately 800 meters of sandy turbidites and hemipelagic mud were deposited near the distal edge of the forearc basin, at Site C0002 of the Integrated Ocean Drilling Program. Constant-rate-of-strain consolidation tests yield estimates of in situ permeability that range from 2.6 × 10-17 m2 to 2.5 × 10-18 m2; overconsolidation ratios range from 1.7 to 2.6, and values of the compression index range from 0.39 to 0.78. Several processes contributed to the apparent overconsolidation. Strata dip toward land, and pore fluids probably migrate up-dip and vent along a bathymetric notch near the seaward edge of the basin. Efficient lateral drainage through sandy turbidites has kept pore pressures within interbeds of mudstone at (or close to) hydrostatic. In addition, alteration of dispersed volcanic glass, precipitation of authigenic clay minerals, and collapse of random grain fabric has probably strengthened the bonding among grains. Cementation is particularly likely within the lower basin (unit III), where values of porosity remain anomalously high. If fluid overpressures (and underconsolidation) exist anywhere within the basin, the most likely loci are where sandy turbidites terminate against impermeable mudstones along landward-dipping on-lap surfaces. Those types of on-lap geometries, in addition to structural closures, might provide promising targets for oil/gas accumulation in other forearc basins, particularly where petroleum source rocks have been buried to the optimal depths of catagenesis.

  4. Extension of Hellenic forearc shear zones in SW Turkey: the Pliocene-Quaternary deformation of the Eşen Çay Basin

    NASA Astrophysics Data System (ADS)

    ten Veen, Johan H.

    2004-03-01

    The Pliocene-Quaternary Eşen Çay Basin in southwestern Turkey has a key position in the southern Aegean to gain insight into both lateral and temporal changes in stresses exerted by plate convergence at the Hellenic-Cyprus arc junction. A tectonosedimentary study of the basin development in combination with a structural analysis helped to reveal internal basin deformation and adjacent basement kinematics in order to delineate 3D strain through time. In the Pliocene the basin originated as a fluviolacustrine basin situated in a depression related to a ramp-fold geometry in the Lycian nappe stack. During the late Pliocene, E-W extension caused the development of N-S normal faults, displacement along which caused the differentiation of the relief and deposition of local alluvial fan systems. The Pleistocene is also marked by widespread alluvial-fluvial sedimentation that is triggered by activity at 020° faults. This fault system resulted from WNW-ESE extension and caused disruption of the former basin floor by uplift and tilting of intrabasinal areas, which initiated development of new source areas for the fan sedimentation. The Holocene-Recent period is characterized by a complex combination of faults of which 070° sinistral strike-slip faults are the most important. Fault-slip analysis reveals that deformation occurred in transtension, explained by the addition of a sinistral shear component. This implies that stresses evolved from simple tensional to transtensional over the Pliocene-Quaternary period. The initial extension phase is explained by the kinematic effects of outward growth of the Hellenic forearc, comparable with observations from the island of Rhodes and the eastern Anaximander Mountains. The time-transgressive addition of a sinistral shear component was likely produced by the northeastward propagating transcurrent motions of forearc slivers sheared from the expanding forearc as has been previously inferred for Crete and Rhodes. The latter process

  5. Quantification of Free Gas in the Kumano Forearc Basin detected from Borehole Physical Properties: IODP NanTroSEIZE drilling Site C0009

    NASA Astrophysics Data System (ADS)

    Doan, M.; Conin, M.; Henry, P.; Wiersberg, T.; Scientific Team Of Iodp Drilling Leg 319, .

    2010-12-01

    Free gas is easily detected from seismic reflection data. However its quantification is a difficult task in soft sedimentary basins, as S-waves velocities are difficult to extract from sonic data. We used high quality borehole sonic data from IODP NantroSEIZE Site C0009, not only to quantify free gas distribution, but also to discriminate the effects of clay porosity and mineralogy. The Kumano forearc basin, formed by the subduction of the Philippine Sea plate below the Eurasian plate, overlays the Nankai accretionary prism, offshore the Kii peninsula, SW Honshu, Japan. Seismic surveys and boreholes within the framework of the NanTroSEIZE project (Nankai Trough SEIsmogenic Zone Experiment) show evidence of gas hydrates and free gas within the basin. Among the multiple breakthroughs performed while drilliong the IODP Site C0009 with riser technology, is the use of the Schlumberger's SonicScanner sonic too. It provides high quality borehole sonic data, giving even S-wave velocities for poorly consolidated clayish sediments. We use the Brie theory to quantify the gas content. The sonic parameters used in this model are calibrated from laboratory measurements on drill cores. First, we show that sonic data are mainly sensitive to the fluid phase filling the intergranular pores (effective porosity), rather than to the total porosity, which includes water bound to clay minerals. The effective porosity is then compared to lithodensity-derived porosity that constitutes a proxy for total porosity. The combination of the two datasets also provides information to assess the clay mineralogy of the sediments. Second, free gas saturation has been computed. A gas-rich interval lies within a lithological unit characterized by a high abundance of wood fragments and lignite. This unit, at the base of the forearc basin, is a source of gas that should be taken into account in models explaining the gas distribution and the formation of the Bottom Simulating Reflector (BSR) within the

  6. Origin and Dynamics of Depositionary Forearc Margins

    NASA Astrophysics Data System (ADS)

    Vannucchi, Paola; Morgan, Jason

    2015-04-01

    Depositionary forearcs are built by terrigenous sediments that never reach the axis of a trench. It has been usually thought that at subduction zones, terrigenous sediments shed from the continent drape the upper plate slope, accumulate in aprons or forearc basins, and can easily reach the trench as turbidites or mass slope deposits. Here we propose a new framework for forearc evolution that focuses on the potential feedbacks between subduction tectonics, sedimentation and geomorphology that take place during an extreme event of subduction erosion, such as the onset of subduction of a major aseismic ridge. There subduction erosion has the potential to rapidly remove the upper plate basement, and replace it from above by rapidly redeposited sediments. This feedback can lead to the creation of "depositionary forearcs", a forearc structure that extends the traditional division of forearcs into accretionary vs. erosive subduction margins, and which emphasizes the dynamic evolution processes at these margins. We need to further recognize that subduction forearcs are usually shaped by interactions between slow long term processes and severe punctuated events reflecting the sudden influences of large-scale morphological variations in the incoming plate. Both types of processes contribute to the large-scale morphology of the forearc, with sudden events associated with a replacive depositionary mode that can suddenly create a sub-section of a typical forearc margin.

  7. Sedimentary fills of Izu-Bonin fore-arc and back-arc rift basins south of Japan, ODP Leg 126

    SciTech Connect

    Rodolfo, K.S. ); Colella, A. ); Hiscott, R.N. ); Janecek, T.; Firth, J. ); Marsaglia, K. ); Nishimura, A. ); Tazaki, K. ); Gill, J.B. ); Kaiho, K. ); Fujioka, K. ); Taylor, B. )

    1990-05-01

    From April to June 1989, Leg 126 of the Ocean Drilling Program successfully drilled the Izu-Bonin intraoceanic arc: Sites 787, 792, and 793 in the eastern, western, and central portions of a 40-70-km-wide fore-arc basin; Sites 790 and 791 on the 2-km-deep floor of the Sumizu back-arc rift; and Site 788 on the eastern rift footwall. Basaltic andesite and andesite basement of the fore-arc basin, initially 4-5 km deep, was produced by rifting or spreading that started 31-34 Ma (middle Oligocene) and has since been uplifted 1-2 km. Volcanism and erosion of surrounding highs provided debris flows and turbidites that began to fill the basin 250-300 m/m.y. Sharply declining volcanism and epiclastic supply are recorded in slowly accumulated Oligocene-Miocene (24-13 Ma) hemipelagic sediments. Regional explosive volcanism, renewed after 13 Ma, has left more than 200 thin ash layers in the uppermost (late Pliocene-Holocene) sediments. Total basin fill is 1.5-4 km thick. The Sumisu began to form 3.56-1.1 Ma. Prerift and present-day volcanism has been dominated by rhyolitic pumice eruptions. The eastern rift footwall, now 1.1 km below sea level, has been uplifted 0.2-1.7 km. Basaltic and arc-pyroclastic rift basement was 2 km deep prior to 1.1 Ma. From 1.1 to 0.235 Ma, 100-400 m of predominantly hemipelagic sediment were deposited, although intrarift basaltic eruptions and rhyolitic eruptions were fairly common. Explosive arc volcanism increased dramatically 250 Ka, leaving 165-428 m of fine to coarse pumiceous sediments in layers that are each 30-50 m thick at Site 790.

  8. Does the Great Valley Group contain Jurassic strata? Reevaluation of the age and early evolution of a classic forearc basin

    USGS Publications Warehouse

    Surpless, K.D.; Graham, S.A.; Covault, J.A.; Wooden, J.L.

    2006-01-01

    The presence of Cretaceous detrital zircon in Upper Jurassic strata of the Great Valley Group may require revision of the lower Great Valley Group chronostratigraphy, with significant implications for the Late Jurassic-Cretaceous evolution of the continental margin. Samples (n = 7) collected from 100 km along strike in the purported Tithonian strata of the Great Valley Group contain 20 Cretaceous detrital zircon grains, based on sensitive high-resolution ion microprobe age determinations. These results suggest that Great Valley Group deposition was largely Cretaceous, creating a discrepancy between biostratigraphy based on Buchia zones and chronostratigraphy based on radiometric age dates. These results extend the duration of the Great Valley Group basal unconformity, providing temporal separation between Great Valley forearc deposition and creation of the Coast Range Ophiolite. If Great Valley forearc deposition began in Cretaceous time, then sediment by passed the developing forearc in the Late Jurassic, or the Franciscan subduction system did not fully develop until Cretaceous time. In addition to these constraints on the timing of deposition, pre-Mesozoic detrital zircon age signatures indicate that the Great Valley Group was linked to North America from its inception. ?? 2006 Geological Society of America.

  9. Estimation of maximum burial depth of Neogene-Quaternary fore-arc basin formation based on laboratory porosity measurements under pressure

    NASA Astrophysics Data System (ADS)

    Uehara, Shin-ichi; Tamura, Yukie; Marumo, Haruna; Mitsuhashi, Shunsuke

    2016-05-01

    Estimating the maximum effective stress that rocks have experienced, Pe,max, or the maximum burial depth for sedimentary rocks, Dmax, is important for many types of research, ranging from engineering applications to estimation of tectonic evolution. We estimated Pe,max and Dmax for the Kazusa fore-arc basin formations (the Kazusa Group) in the Boso Peninsula of Japan using a laboratory-based method. We carried out measurements of porosity n with siltstone specimens from the Kazusa Group formations (the Umegase, Otadai, Kiwada, Ohara, and Katsuura formations) under various effective pressure Pe conditions and estimated Pe,max from the inflection points of the log Pe-log n curve on the Pe increasing path. Except for the specimens from the Ohara Formation, estimated values of Pe,max ranged from approximately 13-24 MPa. This range corresponded to approximately 1.3-3.2 km of Dmax. Differences in Dmax among the specimens were at least four times smaller than distances normal to bedding planes among the sampling locations. This suggests that the formations were not deposited horizontally, but that deposition proceeded as the subsidence center of the fore-arc basin moved in a northwestward (NW) direction, and that formations were then uplifted almost horizontally. The Pe,max of the specimens from the Ohara Formation were 6-10 MPa smaller than the others. Thus, it is possible that pore pressure at the sampling location was more than 6 MPa larger than the hydrostatic condition when the sediments were deposited and lithified. Previous studies reported the center of a high-porosity zone at the Ohara Formation, and this high-porosity zone probably developed due to Pp over-pressurization. These results support the applicability of this method to estimation of tectonic evolution of sedimentary basins and magnitude of over-pressurization.

  10. Why the Sacramento Delta area differs from other parts of the great valley: Numerical modeling of thermal structure and thermal subsidence of forearc basins

    NASA Astrophysics Data System (ADS)

    Mikhailov, V. O.; Parsons, T.; Simpson, R. W.; Timoshkina, E. P.; Williams, C.

    2007-01-01

    Data on present-day heat flow, subsidence history, and paleotemperature for the Sacramento Delta region, California, have been employed to constrain a numerical model of tectonic subsidence and thermal evolution of forearc basins. The model assumes an oceanic basement with an initial thermal profile dependent on its age subjected to refrigeration caused by a subducting slab. Subsidence in the Sacramento Delta region appears to be close to that expected for a forearc basin underlain by normal oceanic lithosphere of age 150 Ma, demonstrating that effects from both the initial thermal profile and the subduction process are necessary and sufficient. Subsidence at the eastern and northern borders of the Sacramento Valley is considerably less, approximating subsidence expected from the dynamics of the subduction zone alone. These results, together with other geophysical data, show that Sacramento Delta lithosphere, being thinner and having undergone deeper subsidence, must differ from lithosphere of the transitional type under other parts of the Sacramento Valley. Thermal modeling allows evaluation of the rheological properties of the lithosphere. Strength diagrams based on our thermal model show that, even under relatively slow deformation (10-17 s-1), the upper part of the delta crystalline crust (down to 20-22 km) can fail in brittle fashion, which is in agreement with deeper earthquake occurrence. Hypocentral depths of earthquakes under the Sacramento Delta region extend to nearly 20 km, whereas, in the Coast Ranges to the west, depths are typically less than 12-15 km. The greater width of the seismogenic zone in this area raises the possibility that, for fault segments of comparable length, earthquakes of somewhat greater magnitude might occur than in the Coast Ranges to the west.

  11. Why the sacramento delta area differs from other parts of the great valley: numerical modeling of thermal structure and thermal subsidence of forearc basins

    USGS Publications Warehouse

    Mikhailov, V.O.; Parsons, T.; Simpson, R.W.; Timoshkina, E.P.; Williams, C.

    2007-01-01

    Data on present-day heat flow, subsidence history, and paleotemperature for the Sacramento Delta region, California, have been employed to constrain a numerical model of tectonic subsidence and thermal evolution of forearc basins. The model assumes an oceanic basement with an initial thermal profile dependent on its age subjected to refrigeration caused by a subducting slab. Subsidence in the Sacramento Delta region appears to be close to that expected for a forearc basin underlain by normal oceanic lithosphere of age 150 Ma, demonstrating that effects from both the initial thermal profile and the subduction process are necessary and sufficient. Subsidence at the eastern and northern borders of the Sacramento Valley is considerably less, approximating subsidence expected from the dynamics of the subduction zone alone. These results, together with other geophysical data, show that Sacramento Delta lithosphere, being thinner and having undergone deeper subsidence, must differ from lithosphere of the transitional type under other parts of the Sacramento Valley. Thermal modeling allows evaluation of the rheological properties of the lithosphere. Strength diagrams based on our thermal model show that, even under relatively slow deformation (10−17 s−1), the upper part of the delta crystalline crust (down to 20–22 km) can fail in brittle fashion, which is in agreement with deeper earthquake occurrence. Hypocentral depths of earthquakes under the Sacramento Delta region extend to nearly 20 km, whereas, in the Coast Ranges to the west, depths are typically less than 12–15 km. The greater width of the seismogenic zone in this area raises the possibility that, for fault segments of comparable length, earthquakes of somewhat greater magnitude might occur than in the Coast Ranges to the west.

  12. Part I: Neoacadian to Alleghanian foreland basin development and provenance in the central appalachian orogen, pine mountain thrust sheet Part II: Structural configuration of a modified Mesozoic to Cenozoic forearc basin system, south-central Alaska

    NASA Astrophysics Data System (ADS)

    Robertson, Peter Benjamin

    Foreland and forearc basins are large sediment repositories that form in response to tectonic loading and lithospheric flexure during orogenesis along convergent plate boundaries. In addition to their numerous valuable natural resources, these systems preserve important geologic information regarding the timing and intensity of deformation, uplift and erosion history, and subsidence history along collisional margins, and, in ancient systems, may provide more macroscopic information regarding climate, plate motion, and eustatic sea level fluctuations. This thesis presents two studies focused in the Paleozoic Appalachian foreland basin system along the eastern United States and in the Mesozoic to Cenozoic Matanuska forearc basin system in south-central Alaska. Strata of the Appalachian foreland basin system preserve the dynamic history of orogenesis and sediment dispersal along the east Laurentian margin, recording multiple episodes of deformation and basin development during Paleozoic time. A well-exposed, >600 m thick measured stratigraphic section of the Pine Mountain thrust sheet at Pound Gap, Kentucky affords one of the most complete exposures of Upper Devonian through Middle Pennsylvanian strata in the basin. These strata provide a window into which the foreland basin's development during two major collisional events known as the Acadian-Neoacadian and the Alleghanian orogenies can be observed. Lithofacies analysis of four major sedimentary successions observed in hanging wall strata record the upward transition from (1) a submarine deltaic fan complex developed on a distal to proximal prodelta in Late Devonian to Middle Mississippian time, to (2) a Middle to Late Mississippian carbonate bank system developed on a slowly subsiding, distal foreland ramp, which was drowned by (3) Late Mississippian renewed clastic influx to a tidally influenced, coastal deltaic complex to fluvial delta plain system unconformably overlain by (4) a fluvial braided river complex

  13. Magnetic fabric of Plio-Pleistocene sediments from the Crotone fore-arc basin: Insights on the recent tectonic evolution of the Calabrian Arc (Italy)

    NASA Astrophysics Data System (ADS)

    Macrì, Patrizia; Speranza, Fabio; Capraro, Luca

    2014-11-01

    Low-field anisotropy of magnetic susceptibility (AMS) analyses were performed on 532 samples collected in 36 (mostly lower Pliocene to lower Pleistocene) marine clay sites from the Crotone basin, a fore-arc basin located on top of the external Calabrian accretionary wedge. The Crotone basin formed since mid-late Miocene under a predominant extensional tectonic regime, but it was influenced thereafter by complex interactions with NW-SE left-lateral strike-faults bounding the basin, which also yielded post-1.2 Ma ∼30° counterclockwise block rotations. The basin is filled by continental to marine sediments yielding one of the thickest and best-exposed Neogene succession available worldwide. The deep-marine facies - represented by blue-grey marly clays gave the best results, as they both preserved a clear magnetic fabric, and provided accurate chronology based on previously published magnetostratigraphy and calcareous plankton (i.e. foraminifers and nannofossils) biostratigraphy. Magnetic susceptibility range and rock magnetic analyses both indicate that AMS reflects paramagnetic clay matrix crystal arrangement. The fabric is predominantly oblate to triaxial, the anisotropy degree low (<1.06), and the magnetic foliation mostly subparallel to bedding. Magnetic lineation is defined in 30 out of 36 sites (where the e12 angle is <35°). By also considering local structural analysis data, we find that magnetic fabric was generally acquired during the first tectonic phases occurring after sediment deposition, thus validating its use as temporally dependent strain proxy. Although most of the magnetic lineations trend NW-SE and are orthogonal to normal faults (as observed elsewhere in Calabria), few NE-SW compressive lineations show that the Neogene extensional regime of the Crotone basin was punctuated by compressive episodes. Finally, compressive lineations (prolate magnetic fabric) documented along the strike-slip fault bounding the basin to the south support the

  14. Structural geology of cuttings and cores recovered from below the Kumano forearc basin, Nankai accretionary margin of Japan: Expedition 319 of the Integrated Ocean Drilling Program (IODP)

    NASA Astrophysics Data System (ADS)

    Hayman, N. W.; Byrne, T. B.; Huftile, G.; McNeill, L. C.; Kanamatsu, T.; Saffer, D.; Araki, E.; Eguchi, N. O.; Toczko, S.; Takahashi, K.; Scientists, E.

    2009-12-01

    The geologic materials below the Kumano Basin provide critical information for understanding the geologic evolution of Japan’s Nankai margin and its earthquake hazards. Riser-based drilling at IODP Site C0009 recovered these geologic materials in cuttings from 704-1604 mbsf, and in ~70 m of core from 1510-1594 mbsf. The >4-mm size fraction of cuttings from 1332-1482 mbsf contains abundant vein structures in moderately consolidated, coarse-siltstones. Vein structures are <1 mm-wide granular rearrangements, possibly paleoseismites, and are mostly restricted to the late Miocene section below a significant unconformity at ~1300 mbsf. At Site C0002, close to the southeastern edge of the forearc basin, vein structures were also localized to a narrow depth interval in a slightly younger (Pliocene age) section. The cored interval at Site C0009 is from below a prominent unconformity at ~1360 mbsf and comprises finely (~10 cm-scale) interbedded, unmetamorphosed, and moderately cohesive silt- and sandstone. Bedding in the cored interval generally dips NNW in logging data and increases in dip from ~20° to ~ 60° with depth in both the FMI and the core data. A set of dominantly thrust-sense shear zones cuts and locally imbricates bedding, with dips <20° to >40°. The shear zones are 1-2 cm-wide, exhibit granular rather than cataclastic (fracture-dominated) microstructures, and though dark in appearance and bright in tomographic images (and thus likely higher density than the surrounding core), they are mineralogically similar to the surrounding material. The shear zones may have formed during tectonically induced dewatering and consolidation. In many places the shear zones define the center of a gradient in stretched and folded sedimentary structures. Younger faults also appear dark relative to the surrounding core, but are <1-mm wide, with a range of geometries and cross cutting relationships; there are likely at least two generations of these thin faults. The youngest

  15. Out-of-sequence thrusting in experimental Coulomb wedges: Implications for the structural development of mega-splay faults and forearc basins

    NASA Astrophysics Data System (ADS)

    Haq, Saad S. B.

    2012-10-01

    We have investigated how an arc-ward increase in bulk mechanical strength in an experimental accretionary prism influences the development, timing, and duration of slip on out-of-sequence thrusts. We have monitored the structural development and kinematics, in side-view, during the development of a frontally accreting Coulomb wedge growing out in front of a critically tapered and mechanically stronger inner wedge. The inner-wedge initially behaved as classic backstop to deformation with the most actively slipping thrust occurring near the deformation front on the forward most thrust structures. With continued growth, however, significant out-of-sequence slip on reactivated fore-thrusts occurred in conjunction with slip on newly formed back-thrusts in the inner-wedge. This out-of-sequence deformation resulted in punctuated, rapid uplift of the model forearc basin and a noticeable break in topographic slope in the outer pro-wedge. Cyclical out-of-sequence fore- and back-thrusting, driven by ongoing frontal thrust imbrication, continued with periodic recovery of taper and was followed by additional out-of-sequence faulting and associated basin uplift.

  16. Out-Of-Sequence Thrusting In Coulomb Wedges: Implications For The Structural Development Of Mega-Splay Faults And Forearc Basins

    NASA Astrophysics Data System (ADS)

    Haq, S. S.

    2012-12-01

    By quantifying deformation in frictional analog models we have investigated how an arc-ward increase in bulk mechanical strength in an accretionary prism influences the development, timing, and duration of slip on out-of-sequence thrusts. We have monitored the structural development and kinematics, in side-view, during the development of a frontally accreting Coulomb wedge growing out in front of a critically tapered and mechanically stronger inner wedge. The inner-wedge initially behaved as classic backstop to deformation with the most actively slipping thrust occurring near the deformation front on the forward most thrust structures. With continued growth, however, significant out-of-sequence slip on reactivated fore-thrusts occurred in conjunction with slip on newly formed back-thrusts in the inner-wedge. This out-of-sequence deformation resulted in punctuated, rapid uplift of the model forearc basin and a noticeable break in topographic slope in the outer pro-wedge. Cyclical out-of-sequence fore- and back-thrusting, driven by ongoing frontal thrust imbrication, continued with periodic recovery of taper and was followed by additional out-of-sequence faulting and associated basin uplift.

  17. Composition and spatial evolution of mantle and fluids released beneath the active Southeast Mariana Forearc Rift: do they have arc or backarc basin signatures?

    NASA Astrophysics Data System (ADS)

    Ribeiro, J. M.; Stern, R. J.; Kelley, K. A.; Ishizuka, O.; Anthony, E. Y.; Ren, M.; Manton, W. I.; Ohara, Y.; Reagan, M. K.; Bloomer, S. H.

    2010-12-01

    Fluids of progressively changing composition are released from the subducting slab. Whereas the composition and effects of deep fluids are understood from studying arcs and backarc basin (BAB) lavas, those released at shallower depths beneath forearcs are less well known. Forearc rifts give us a unique opportunity to study the composition of ultra-shallow subduction-related fluids. At the southern end of the Mariana arc, the S.E. Mariana Forearc Rift (SEMFR), was discovered by HMR-1 sonar swath mapping (Martinez et al. 2000, JGR), and investigated in July 2008 by the manned submersible Shinkai 6500. The rift extends from the trench to the BAB spreading axis, where a magma chamber was recently documented (Becker et al., 2010, G-cubed). SEMFR is opening due to continued widening of the Mariana Trough BAB. Two suites of tholeiitic pillow lavas were recovered from the N.E. flank of the rift (dive 1096; slab depth ~ 30 ± 5 km), indicating recent magmatic activity. Dive 1096 lavas consist of upper primitive basalts (Mg# ≥ 60) and lower fractionated, basaltic andesites (Mg# < 60), separated by a thin sediment layer. Geochemical and isotopic studies show that these lavas were produced by extensive hydrous melting (≥ 15%) of a common depleted MORB-like mantle (Nb/Yb ~ 1, ɛNd ~ 9.3), likely S. Mariana BAB mantle, that interacted with < 3% metasomatic fluids. Thermobarometry constraints (Lee et al., 2009, EPSL) suggest that the primary melts equilibrated with the mantle at ~ 28 km, just above the slab, with a mean temperature ~1230°C. The fluid was enriched in fluid-mobile elements (Rb, Ba, K, U, Sr, Pb, Cs), mobilized from the ultra-shallow slab at low temperature, as well as melt-mobile elements (e.g. Th, LREE), released deeper and hotter. These fluids contribute 100% Cs, 97% Rb, 99% Ba, 69% Th, 74% U, 80% K, 83% Pb, 71% Sr, 45% La, 33% Ce, 20% Nd and 11% Sm to the magma. SEMFR lavas acquired BAB-like deep subduction component as well as arc-like ultra

  18. Part I: Neoacadian to Alleghanian foreland basin development and provenance in the central appalachian orogen, pine mountain thrust sheet Part II: Structural configuration of a modified Mesozoic to Cenozoic forearc basin system, south-central Alaska

    NASA Astrophysics Data System (ADS)

    Robertson, Peter Benjamin

    Foreland and forearc basins are large sediment repositories that form in response to tectonic loading and lithospheric flexure during orogenesis along convergent plate boundaries. In addition to their numerous valuable natural resources, these systems preserve important geologic information regarding the timing and intensity of deformation, uplift and erosion history, and subsidence history along collisional margins, and, in ancient systems, may provide more macroscopic information regarding climate, plate motion, and eustatic sea level fluctuations. This thesis presents two studies focused in the Paleozoic Appalachian foreland basin system along the eastern United States and in the Mesozoic to Cenozoic Matanuska forearc basin system in south-central Alaska. Strata of the Appalachian foreland basin system preserve the dynamic history of orogenesis and sediment dispersal along the east Laurentian margin, recording multiple episodes of deformation and basin development during Paleozoic time. A well-exposed, >600 m thick measured stratigraphic section of the Pine Mountain thrust sheet at Pound Gap, Kentucky affords one of the most complete exposures of Upper Devonian through Middle Pennsylvanian strata in the basin. These strata provide a window into which the foreland basin's development during two major collisional events known as the Acadian-Neoacadian and the Alleghanian orogenies can be observed. Lithofacies analysis of four major sedimentary successions observed in hanging wall strata record the upward transition from (1) a submarine deltaic fan complex developed on a distal to proximal prodelta in Late Devonian to Middle Mississippian time, to (2) a Middle to Late Mississippian carbonate bank system developed on a slowly subsiding, distal foreland ramp, which was drowned by (3) Late Mississippian renewed clastic influx to a tidally influenced, coastal deltaic complex to fluvial delta plain system unconformably overlain by (4) a fluvial braided river complex

  19. In situ gas concentrations in the Kumano forearc basin from drilling mud gas monitoring and sonic velocity data (IODP NanTroSEIZE Exp. 319 Site C0009)

    NASA Astrophysics Data System (ADS)

    Wiersberg, T.; Doan, M.-L.; Schleicher, A. M.; Horiguchi, K.; Eguchi, N.; Erzinger, J.

    2012-04-01

    Conventional IODP shipboard methods of gas investigations comprise gas sampling from core voids and headspace gas sampling followed by shipboard gas analysis. These methods possibly underestimate the in situ gas concentration due to core degassing during retrieval and handling on deck. In few cases, a Pressure Core Sampler (PCS) was used in the past to overcome this problem, providing gas concentrations one or two order of magnitude higher than headspace gas analysis from corresponding depths. Here, we describe two new techniques applied during IODP NanTroSEIZE Exp. 319 Site C0009 riser drilling in the Kumano forearc basin to estimate in situ gas concentrations without drill core recovery. During riser drilling of site C0009 between 703 to 1594 mbsf, gas was continuously extracted from returing drilling mud and analysed in real-time (drill mud gas monitoring). This method results in information on the gas composition and gas concentration at depth. The chemical (C1-C3) and isotope (δ13C, H/D) composition of hydrocarbons, the only formation-derived gases identified in drill mud, demonstrate a microbial hydrocarbon gas source mixing with small but increasing amounts of thermogenic gas at greater depth. Methane content in drilling mud semi-quantitatively correlates with visible allochtonous material (wood, lignite) in drilling cuttings. In situ gas concentration determination from drill mud gas monitoring based on the assumption that gas is either liberated from the rock into the drilling mud during drilling and ascent with the mud column or remains in the pore space of the drilling cuttings. Drilling mud gas data were calibrated with a defined amount of C2H2 (175 l [STP]) from a carbide test and result in methane concentrations reaching up to 24 lgas/lsediment, in good agreement with findings from other IODP Legs using the PCS. Hydrocarbon gas concentrations in drilling cuttings from C0009 are significantly lower, indicating cuttings outgassing during ascent of the

  20. Pre-and post-Missoula flood geomorphology of the Pre-Holocene ancestral Columbia River Valley in the Portland forearc basin, Oregon and Washington, USA

    NASA Astrophysics Data System (ADS)

    Peterson, Curt D.; Minor, Rick; Peterson, Gary L.; Gates, Edward B.

    2011-06-01

    Geomorphic landscape development in the pre-Holocene ancestral Columbia River Valley (1-5 km width) in the Portland forearc basin (~ 50 km length) is established from depositional sequences, which pre-date and post-date the glacial Lake Missoula floods. The sequences are observed from selected borehole logs (150 in number) and intact terrace soil profiles (56 in number) in backhoe trenches. Four sequences are widespread, including (1) a vertically aggraded Pleistocene alluvial plain, (2) a steep sided valley that is incised (125-150 m) into the Pleistocene gravel plain, (3) Missoula flood terraces (19-13 ka) abandoned on the sides of the ancestral valley, and (4) Holocene flooding surfaces (11-8 ka) buried at 70-30 m depth in the axial Columbia River Valley. Weathering rims and cementation are used for relative dating of incised Pleistocene gravel units. Soil development on the abandoned Missoula flood terraces is directly related to terrace deposit lithology, including thin Bw horizons in gravel, irregular podzols in sand, and multiple Bw horizons in thicker loess-capping layers. Radiocarbon dating of sand and mud alluvium in the submerged axial valley ties Holocene flooding surfaces to a local sea level curve and establishes Holocene sedimentation rates of 1.5 cm year- 1 during 11-9 ka and 0.3 cm year- 1 during 9-0 ka. The sequences of Pleistocene gravel aggradation, river valley incision, cataclysmic Missoula flooding, and Holocene submergence yield complex geomorphic landscapes in the ancestral lower Columbia River Valley.

  1. From foreland rift to forearc basin: Tectono-thermal controls on subsidence and stratigraphic development in the Mesozoic-Recent Salar de Atacama basin, Chilean Andes

    SciTech Connect

    Flint, S. ); Turner, P. ); Hartley, A. ); Jolley, E. )

    1991-03-01

    The Salar de Atacama and westerly adjacent Domeyko basins originated as Permian foreland rifts, containing some 2 km of Triassic synrift red beds. Continued extension and volcanic are establishment resulted in deposition of important Jurassic marine source rocks in the Domeyko basin. Rift basin subsidence was controlled by extension, followed by thermal sagging. Middle Cretaceous contraction (opening of the south Atlantic) inverted the Domeyko back-arc basin as a thrustbelt. To the east, the Salar basin subsequently accommodated 4 km of Late Cretaceous-Palaeocene continental detritus. Accommodation space reflected the interplay between limited flexural loading and thermal effects related to a 150 km eastward jump of the Andean volcanic arc to the margin of the arc-related, foreland-style basin. Late Eocene transpression (high rate of oblique convergence between the Farallon and South American plates) inverted the western basin margin, sourcing a 2 km thick Oligocene intra-arc basin-fill component. Accommodation space was controlled by thermal sagging associated with a further 100 km eastward arc jump. The Salar de Atacama basin thus provides a model for the evolution of complex, mixed origin basins associated with a migrating volcanic arc and varying crustal stress regime. The complex interplay between variable tectonic style and thermal processes in controlling subsidence and resultant stratigraphic development is not yet adequately constrained. However, simple, single stage tectono-sedimentary models commonly used in play definition may not be appropriate in complex, arc-related basin settings.

  2. Gas in Place Resource Assessment for Concentrated Hydrate Deposits in the Kumano Forearc Basin, Offshore Japan, from NanTroSEIZE and 3D Seismic Data

    NASA Astrophysics Data System (ADS)

    Taladay, K.; Boston, B.

    2015-12-01

    Natural gas hydrates (NGHs) are crystalline inclusion compounds that form within the pore spaces of marine sediments along continental margins worldwide. It has been proposed that these NGH deposits are the largest dynamic reservoir of organic carbon on this planet, yet global estimates for the amount of gas in place (GIP) range across several orders of magnitude. Thus there is a tremendous need for climate scientists and countries seeking energy security to better constrain the amount of GIP locked up in NGHs through the development of rigorous exploration strategies and standardized reservoir characterization methods. This research utilizes NanTroSEIZE drilling data from International Ocean Drilling Program (IODP) Sites C0002 and C0009 to constrain 3D seismic interpretations of the gas hydrate petroleum system in the Kumano Forearc Basin. We investigate the gas source, fluid migration mechanisms and pathways, and the 3D distribution of prospective HCZs. There is empirical and interpretive evidence that deeply sourced fluids charge concentrated NGH deposits just above the base of gas hydrate stability (BGHS) appearing in the seismic data as continuous bottoms simulating reflections (BSRs). These HCZs cover an area of 11 by 18 km, range in thickness between 10 - 80 m with an average thickness of 40 m, and are analogous to the confirmed HCZs at Daini Atsumi Knoll in the eastern Nankai Trough where the first offshore NGH production trial was conducted in 2013. For consistency, we calculated a volumetric GIP estimate using the same method employed by Japan Oil, Gas and Metals National Corporation (JOGMEC) to estimate GIP in the eastern Nankai Trough. Double BSRs are also common throughout the basin, and BGHS modeling along with drilling indicators for gas hydrates beneath the primary BSRs provides compelling evidence that the double BSRs reflect a BGHS for structure-II methane-ethane hydrates beneath a structure-I methane hydrate phase boundary. Additional drilling

  3. Fore-arc mantle peridotites and back-arc basin basalts from the Izu-Bonin-Mariana subduction factory (ODP LEGs 125 and 195): a modern analogue for Mediterranean ophiolites

    NASA Astrophysics Data System (ADS)

    Zanetti, A.; D'Antonio, M.; Vannucci, R.; Raffone, N.; Spadea, P.

    2009-04-01

    occurring in all IBM forearc peridotites (e.g. crystallisation of late cpx, embayment of opx porphyroclasts), and likely marks the accretion of the mantle sequence to the thermal boundary layer. It was accompanied by the devolopment of transient geochemical gradients in the migrating liquids mainly governed by chromatographic-type chemical exchange with the peridotite. The West Philippine Basin (WPB) is a back-arc basin that opened in the Philippine Sea Plate (PSP) between the current position of the Palau-Kyushu Ridge (PKR) and the margin of East Asia. Spreading occurred at the Central Basin Fault (CBF) from 54 to 30 Ma. The PKR was active since ~48 to 35 Ma constituting a single volcanic arc with the Izu-Bonin-Mariana Arc. ODP Leg 195 Site 1201 is located in the WPB, ~100 km west of the PKR, on 49 Ma basaltic crust formed by NE-SW spreading at the CBF. From ~35 to 30 Ma, pelagic sedimentation at Site 1201 was followed by turbidite sedimentation, fed mostly by early Mariana Arc (PKR)-derived volcanic clasts. These volcanics are calc-alkaline, whereas PKR rocks from literature have mostly boninitic and arc tholeiitic affinity; the WPB basement basalts have MORB to arc-like affinity, as expected for a back-arc basin. Sr, Nd, Pb and Hf isotope data highlight the Indian Ocean MORB-like character of WPB basement basalts, suggesting an upper mantle domain distinct from that underlying the Pacific Plate. The geochemical and isotopic features of PKR volcanics reflect higher amounts of subduction-derived components, added mostly as siliceous melts, in the source of arc magmas relative to that of basement basalts. In that respect, Site 1201 PKR volcanics resemble calc-alkaline volcanics of the currently active Mariana Arc. In addition, their calc-alkaline affinity, unradiogenic neodymium, and inferred Middle Oligocene age, suggest they might represent an evolved stage of arc volcanism at Palau-Kyushu Ridge, perhaps shortly before the end of its activity.

  4. Clastic Intrusions and Chemosynthetic Paleocommunities in the Cretaceous-Paleocene Great Valley Forearc Basin, Panoche Hills, CA: Geochemistry of Carbonates Suggests Biogenic and Thermogenic Input During Early Tertiary Subduction

    NASA Astrophysics Data System (ADS)

    Sample, J.; Moore, C.; Weberling, K.; Schwartz, H.; Vrolijk, P.

    2001-12-01

    A Paleocene seep system is remarkably well preserved in the Panoche Hills of central California. The seep horizons lie within a 45-m-thick interval in the Dos Palos Shale Member of the Moreno Formation, which contains chemosynthetic fauna. Extensive sandstone dikes in the underlying Cretaceous to Paleocene units presumably acted as conduits to replenish the seep organisms with the methane-enriched fluids required for chemoynthesis. We investigated the geochemistry of the carbonate cements and veins within the seep horizons and sandstone dikes to determine the nature of the fluid sources. Carbonate occurs as pore-filling cement, infill of tubes, shell material, veins, and possible replacement of tubeworm walls. The preserved carbonate textures, including fibrous, syntaxial vein minerals and radial, fibrous fills of tubes (fluid pipes?), indicate that many of the samples have not undergone extensive recrystallization during diagenesis. Isotopic values of 33 seep samples are δ 13CPDB = -42.56‰ to 0.55‰ and δ 18OPDB = -5.81‰ to 3.78‰ . These carbon isotope values are consistent with a fluid source during seep formation containing a mixture of oxidized thermogenic methane from marine organic matter, seawater bicarbonate, and a component of biogenic methane. Three dike samples have carbonate with δ 13CPDB = -21.12‰ to -5.54‰ , and δ 18OPDB = -8.45‰ to -6.26‰ . The low dike oxygen values suggest that fluids retained some of the elevated temperature of the source region during migration, or later diagenesis recrystallized the cement. Given that the source of sandstone dikes was at most a few hundred metres below the seeps at the time of their formation, a significant component of thermogenic methane preserved in the carbonates requires some westward lateral migration of fluids from beneath the Great Valley forearc basin before expulsion at the Paleocene seafloor. The migration pathways probably developed as a consequence of early Tertiary subduction and

  5. The origin and internal structures of submarine-slide deposits in a lower Pleistocene outer-fan succession in the Kazusa forearc basin on the Boso Peninsula of Japan

    NASA Astrophysics Data System (ADS)

    Fukuda, Kayo; Suzuki, Masahiro; Ito, Makoto

    2015-05-01

    This study investigates the internal geometry and formation processes of submarine-slide deposits in a lower Pleistocene outer-fan succession in the Kazusa forearc basin on the Boso Peninsula of Japan. The submarine-slide deposits are ~ 40 m thick, with a minimum length of ~ 900 m and a width of ~ 700 m. Both the submarine-slide deposits and host deposits comprise siltstones intercalated with very thin- to medium-bedded, sheet-like turbidites and volcanic ash beds. Based on the sequence-stratigraphic framework of the submarine-fan succession, we conclude that the submarine-slide deposits formed during a glacioeustatic sea-level lowstand at about 1.16 Ma. The submarine-slide deposits are characterized by thrust sequences with a ramp anticline in the frontal part. A basal slide plane in the lower part of the deposits is developed at a horizon located 2-4 cm below the base of a coarse volcanic ash bed and is associated with sheared deposits. Slide planes are sealed in the upper part of the submarine-slide deposits in association with drag folds and chaotic deposits. Finally, the submarine-slide deposits are transitionally overlain by ~ 3-m-thick chaotic muddy deposits, and are finally overlain by siltstones intercalated with very thin- to medium-bedded, sheet-like turbidites and volcanic ash beds, which show lithofacies features similar to those of the submarine-slide deposits. The variations in the deformation styles indicate that sliding occurred as a synsedimentary process in the outer-fan environment, and the basal slide plane formed when the porosity of the muddy deposits was reduced to ~ 55% or less. Based on the empirical relationship between the submarine-fan length and lower-fan slopes from modern examples, the gradient of the outer-fan is estimated at 0.31°-0.46°, which is lower than the threshold gradient of 1.2° for a 40-m-thick submarine slide with the estimated basal porosity. Based on the distribution of deformed deposits within the lower-fan host

  6. Results of ODP Leg 125 drilling in the Mariana/Izu-Bonin forearcs

    SciTech Connect

    Fryer, P. ); Pearce, J.A. ); Stokking, L. )

    1990-06-01

    ODP Leg 125 drilled a total of nine sites in the Mariana and Izu-Bonin forearcs, the regions between the active volcanic arc and the trench axis. Six sites were located on or adjacent to serpentine seamounts, four of these (Sites 778-781) on Conical Seamount in the Mariana forearc, and two others (783 and 784) on the Torishima Forearc Seamount in the Izu-Bonin forearc. The remaining sites (Sites 782, 785, and 786) were drilled into volcanic sequences along the eastern edge of the Izu-Bonin forearc basin. The principal results of the drilling were to achieve (1) the recovery of the first evidence for Pliocene or younger magmatic activity in an extant intraoceanic forearc terrain; (2) the first deep penetration of the Eocene basement of the Izu-Bonin outer-arc high to recover 650 m of boninite flows and hyaloclastite, andesite-dacite flows, breccias, sills, and dikes; (3) the confirmation that some forearc serpentine seamounts can form by flows of clast-bearing serpentine mud from a central conduit, as do mud volcanoes; (4) the discovery of mafic clasts within the serpentine mud flows that have both IAT and MORB affinities, that are metamorphosed in the low to moderate temperature/pressure regimes; (5) the confirmation of high-pH, low-chlorinity fluids at shallow levels near the summit of the seamount which probably originated beneath the forearc and are subduction-related; (6) the recovery of complex hydrocarbon-rich gases also of probable subduction related origin within the Mariana serpentine seamount; and (7) the identification of numerous ash layers within the Izu-Bonin forearc basin that indicate peaks of volcanic activity in the Eocene-Oligocene and from the late Miocene to the Holocene.

  7. Continental margin tectonics - Forearc processes

    SciTech Connect

    Lundberg, N.; Reed, D.L. )

    1991-01-01

    Recent studies of convergent plate margins and the structural development of forearc terranes are summarized in a critical review of U.S. research from the period 1987-1990. Topics addressed include the geometry of accretionary prisms (Coulomb wedge taper and vertical motion in response to tectonic processes), offscraping vs underplating or subduction, the response to oblique convergence, fluids in forearc settings, the thermal framework and the effects of fluid advection, and serpentinite seamounts. Also included is a comprehensive bibliography for the period.

  8. The Peru continental margin: High petroleum potential in a modern fore-arc setting

    SciTech Connect

    Crouch, J.K.; Bachman, S.B.; Zucker, C.L. )

    1990-05-01

    Strata within modern fore-arc basins commonly are characterized as (1) containing little or no oil-prone source rocks and poor, volcaniclastic-rich reservoir rocks and (2) being submature due to low geothermal gradients. Hence, many explorationists may view modern fore-arc basin settings as having little oil potential or, at best as only marginally prospective. The Talara fore-arc basin of Peru is a striking exception to this generally held belief. Situated along the northwestern part of Peru's active convergent margin, it extends offshore to within 50 km of the Peru-Chile Trench. Unlike the typical modern fore arc, the Talara basin is a prolific oil producer. From onshore and offshore fields, it has already produced over 1.3 billion bbl of oil averaging 38{degree} API gravity. Moreover, the lightly explored offshore, which constitutes more than half of the Talara basin, probably holds an additional 2 billion bbl of undiscovered recoverable reserves. The Talara basin encloses an area of about 17,000 km{sup 2} yet 70% of the production (> 900 million bbl) has come from coastal onshore fields that encompass an area about one-tenth this total size (1,750 km{sup 2}). Production has come chiefly from Paleocene and Eocene sandstones enclosed within a thick (composite thickness of 10,000 m) lower Tertiary marine clastic section. Pervasive normal block faulting has persisted across this and other fore-arc basins situated along the Peru margin from the Late Cretaceous through much of the Tertiary. This distinctive structural style, along with younger detachment faults, provides numerous structural traps whose complexities will, no doubt, challenge explorationists for years to come. A number of other Peru fore-arc basins. which are both geomorphically and structurally on trend with the Talata basin, also contain thick lower Tertiary sections and exhibit similar extensional histories.

  9. Advanced Colloids Experiment (ACE-H-2)

    NASA Technical Reports Server (NTRS)

    Meyer, William V.; Sicker, Ron; Chmiel, Alan J.; Eustace, John; LaBarbera, Melissa

    2015-01-01

    Increment 43 - 44 Science Symposium presentation of Advanced Colloids Experiment (ACE-H-2) to RPO. The purpose of this event is for Principal Investigators to present their science objectives, testing approach, and measurement methods to agency scientists, managers, and other investigators.

  10. Geological structure of the offshore Sumatra forearc region estimated from high-resolution MCS reflection survey

    NASA Astrophysics Data System (ADS)

    Misawa, Ayanori; Hirata, Kenji; Seeber, Leonard; Arai, Kohsaku; Nakamura, Yasuyuki; Rahardiawan, Riza; Udrekh; Fujiwara, Toshiya; Kinoshita, Masataka; Baba, Hisatoshi; Kameo, Katsura; Adachi, Keita; Sarukawa, Hiroshi; Tokuyama, Hidekazu; Permana, Haryadi; Djajadihardja, Yusuf S.; Ashi, Juichiro

    2014-01-01

    To investigate detailed fault distributions and shallow geological structure offshore northwestern Sumatra, we obtained high-resolution Multi-Channel Seismic (MCS) reflection data around the Sunda Trench, trench slope, and forearc high regions offshore northwestern Sumatra. In general, trench-parallel anticlinal ridges are distributed from trench slope region to forearc high region. Two kinds of different vergence systems are characterized in the Sumatra forearc region; landward vergence is dominant in the lower trench slope region, and seaward vergence is dominant in the forearc high region. Moreover, piggyback or slope basins are recognized between anticlinal ridges. Deformation in the uppermost part of these basins, that is referred to ‘recent’ deformation in this paper, can be identified not only along major thrusts but also between major thrusts and the lower trench slope, suggesting these are related to recently active faulting. Several but the largest number of such deformation are distributed along a major thrust located in the middle of the forearc high region, whereas few are done along other major thrusts.

  11. Management of hospitals in Aceh during the tsunami.

    PubMed

    Kartowisastro, Hermansyur

    2005-01-01

    On December 26th, 2004, Aceh and its vicinity was hit by two natural forces consecutively, an earthquake and a tsunami. Hundreds of thousands of people perished, leaving the remaining of about the same number to become refugees. The writer was assigned by the Ministry of Health to Aceh on duty on the second and third week after the catastrophe, to help the management of Zainoel Abidin General Hospital in Banda Aceh, the province's biggest hospital, revive its operation. PMID:16300161

  12. Testing Spatial Correlation of Subduction Interplate Coupling and Forearc Morpho-Tectonics

    NASA Technical Reports Server (NTRS)

    Goldfinger, Chris; Meigs, Andrew; Meigs, Andrew; Kaye, Grant D.; VanLaningham, Sam

    2005-01-01

    Subduction zones that are capable of generating great (Mw greater than 8) earthquakes appear to have a common assemblage of forearc morphologic elements. Although details vary, each have (from the trench landward), an accretionary prism, outer arc high, outer forearc basin, an inner forean: basin, and volcanic arc. This pattern is common in spite of great variation in forearc architecture. Because interseismic strain is known to be associated with a locked seismogenic plate interface, we infer that this common forearc morphology is related, in an unknown way, to the process of interseismic Strain accumulation and release in great earthquakes. To date, however, no clear relationship between the subduction process and the common elements of upper plate form has emerged. Whereas certain elements of the system, i.e. the outer arc high, are reasonably well- understood in a structural context, there is little understanding of the structural or topographic evolution of the other key elements like the inner arc and inner forearc basin, particularly with respect to the coupled zone of earthquake generation. This project developed a model of the seismologic, topographic, and uplift/denudation linkages between forearc topography and the subduction system by: 1) comparing geophysical, geodetic, and topographic data from subduction margins that generate large earthquakes; 2) using existing GPS, seismicity, and other data to model the relationship between seismic cycles involving a locked interface and upper-plate topographic development; and 3) using new GPS data and a range-scale topographic, uplift, and denudation analysis of the presently aseismic Cascadia margin to constrain topographic/plate coupling relationships at this poorly understood margin.

  13. April 2012 intra-oceanic seismicity off Sumatra boosted by the Banda-Aceh megathrust.

    PubMed

    Delescluse, Matthias; Chamot-Rooke, Nicolas; Cattin, Rodolphe; Fleitout, Luce; Trubienko, Olga; Vigny, Christophe

    2012-10-11

    Large earthquakes nucleate at tectonic plate boundaries, and their occurrence within a plate's interior remains rare and poorly documented, especially offshore. The two large earthquakes that struck the northeastern Indian Ocean on 11 April 2012 are an exception: they are the largest strike-slip events reported in historical times and triggered large aftershocks worldwide. Yet they occurred within an intra-oceanic setting along the fossil fabric of the extinct Wharton basin, rather than on a discrete plate boundary. Here we show that the 11 April 2012 twin earthquakes are part of a continuing boost of the intraplate deformation between India and Australia that followed the Aceh 2004 and Nias 2005 megathrust earthquakes, subsequent to a stress transfer process recognized at other subduction zones. Using Coulomb stress change calculations, we show that the coseismic slips of the Aceh and Nias earthquakes can promote oceanic left-lateral strike-slip earthquakes on pre-existing meridian-aligned fault planes. We further show that persistent viscous relaxation in the asthenospheric mantle several years after the Aceh megathrust explains the time lag between the 2004 megathrust and the 2012 intraplate events. On a short timescale, the 2012 events provide new evidence for the interplay between megathrusts at the subduction interface and intraplate deformation offshore. On a longer geological timescale, the Australian plate, driven by slab-pull forces at the Sunda trench, is detaching from the Indian plate, which is subjected to resisting forces at the Himalayan front. PMID:23023134

  14. Conflict nightmares and trauma in Aceh.

    PubMed

    Grayman, Jesse Hession; Good, Mary-Jo Delvecchio; Good, Byron J

    2009-06-01

    In both the Acehnese and Indonesian languages, there is no single lexical term for "nightmare." And yet findings from a large field research project in Aceh that examined post traumatic experience during Aceh's nearly 30-year rebellion against the Indonesian state and current mental distress revealed a rich variety of dream narratives that connect directly and indirectly to respondents' past traumatic experiences. The results reported below suggest that even in a society that has a very different cultural ideology about dreams, where "nightmares" as such are not considered dreams but rather the work of mischievous spirits called jin, they are still a significant part of the trauma process. We argue that it is productive to distinguish between terrifying and repetitive dreams that recreate the traumatic moment and the more ordinary varieties of dreams that Acehnese reported to their interviewers. Nightmares that refer back to conflict events do not appear as an elaborated feature of trauma as the condition is understood by people in Aceh, but when asked further about their dreams, respondents who reported symptoms suggestive of PTSD were more likely to report PTSD-like dreams, memory intrusions that repeat the political violence of the past. PMID:19283458

  15. Crustal architecture of the cascadia forearc

    USGS Publications Warehouse

    Trehu, A.M.; Asudeh, I.; Brocher, T.M.; Luetgert, J.H.; Mooney, W.D.; Nabelek, J.L.; Nakamura, Y.

    1994-01-01

    Seismic profiling data indicate that the thickness of an accreted oceanic terrane of Paleocene and early Eocene age, which forms the basement of much of the forearc beneath western Oregon and Washington, varies by approximately a factor of 4 along the strike of the Cascadia subduction zone. Beneath the Oregon Coast Range, the accreted terrane is 25 to 35 kilometers thick, whereas offshore Vancouver Island it is about 6 kilometers thick. These variations are correlated with variations in arc magmatism, forearc seismicity, and long-term forearc deformation. It is suggested that the strength of the forearc crust increases as the thickness of the accreted terrane increases and that the geometry of the seaward edge of this terrane influences deformation within the subduction complex and controls the amount of sediment that is deeply subducted.

  16. Crustal architecture of the cascadia forearc.

    PubMed

    Trehu, A M; Asudeh, I; Brocher, T M; Luetgert, J H; Mooney, W D; Nabelek, J L; Nakamura, Y

    1994-10-14

    Seismic profiling data indicate that the thickness of an accreted oceanic terrane of Paleocene and early Eocene age, which forms the basement of much of the forearc beneath western Oregon and Washington, varies by approximately a factor of 4 along the strike of the Cascadia subduction zone. Beneath the Oregon Coast Range, the accreted terrane is 25 to 35 kilometers thick, whereas offshore Vancouver Island it is about 6 kilometers thick. These variations are correlated with variations in arc magmatism, forearc seismicity, and long-term forearc deformation. It is suggested that the strength of the forearc crust increases as the thickness of the accreted terrane increases and that the geometry of the seaward edge of this terrane influences deformation within the subduction complex and controls the amount of sediment that is deeply subducted. PMID:17771442

  17. Forearc tectonic evolution of the South Shetland Margin, Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Maldonado, A.; Larter, R. D.; Aldaya, F.

    1994-12-01

    The main provinces of the South Shetland margin, Antarctic Peninsula characterized on the basis of multichannel seismic, long-range side scan sonar and swath bathymetry data, include from northwest to southeast (1) the oceanic crust of the former Phoenix Plate, flexed down toward the margin and affected by normal faulting in the upper crust; (2) a narrow trench, with a horizontally layered sediment fill which onlaps the thin sedimentary cover on the oceanic crust and shows incipient deformation near its landward edge; (3) an accretionary prism with a complex internal structure, the toe of which is overthrust above the youngest trench deposits; (4) a midslope forearc basin, with an asymmetric synformal structure; and (5) the continental shelf, which includes two distinct tectonic provinces. Calculations of the late Cenozoic convergence history at the trench indicate a rapid decrease in convergence rate after 6.7 Ma from about 60 mm/yr, resulting from the slowing and eventual cessation of spreading on the Antarctic-Phoenix ridge. Once spreading had completely ceased (3.5-2.4 Ma), the convergence rate at the trench equalled the rate of extension in Bransfield Strait, which was probably less than 10 mm/yr at first but may have increased since 1.3 Ma, and this, in turn, would imply a corresponding increase in convergence rate. Above the basal detachment the toe of the accretionary prism is composed of a stack of thrust fault bounded wedges, laterally and vertically segmented by normal faults. Most of the trench fill sediments are overthrust by the toe of the accretionary prism and subducted beneath it for as far as they can be traced on the seismic profiles. This suggests that there may be tectonic erosion of the forearc since a large part of the trench sediment appears to be derived from erosion on the forearc slope. The forearc basin records a long history of subsidence, during which the depocenter migrated landward, paralleling retrogradational erosion of the distal

  18. The Role of Upper Plate Slivering in Burial of the Luzon Forearc in Taiwan

    NASA Astrophysics Data System (ADS)

    Lewis, J. C.; O'Hara, D.; Rau, R.

    2013-12-01

    Seismogenic strain across the subduction-to-collision transition in Taiwan reveals a forearc sliver that explains an array of existing geologic and geophysical data. South of the collision the Luzon forearc experiences partitioning of oblique Eurasia-Philippine Sea plate motion into a western domain of arc-normal backthrusting, and an eastern domain of arc-parallel sinistral shearing. The forearc is therefore partially detached from the Philippine Sea plate by strike-slip motion at the same time that it is inverting in response to E-W shortening. North of ~22° N backthrusting and strike-slip motion become spatially comingled, and north of ~22° 45' N, collision-related deformation prevails, marked by oblique slip on reactivated steeply NW- and SW-dipping faults. Strike-slip motion appears to be localized on the western flank of the Luzon arc and the linkage between this motion and the collision zone is accomplished via a km-scale releasing left step. The linkage is marked by an offshore pull-apart basin south of the collided volcanic arc exposed in the Coastal Range. South of the pull-apart basin the N-S trending Huatung ridge represents a forearc basement uplift. Northward translation of the forearc into the collision zone is therefore accompanied by localized extension and deposition, and these processes conspire to bury the forearc. A protracted history of such processes is suggested by seismic tomography that reveals a gently N-plunging sliver of material with a high Poisson's ratio and inferred to be mafic in composition. This body might thus comprise forearc basement that was initially buried by pull-apart basin formation and further buried beneath the suture zone as collision progressed. Within the Coastal Range a well-documented unconformity separating volcanic arc basement and its cover from collision-derived clastics serves as a possible record of similar tectonic basins from Miocene-Pliocene time. Small collisional pull-apart basins of this type also

  19. The Ophiolite - Oceanic Fore-Arc Connection

    NASA Astrophysics Data System (ADS)

    Reagan, M. K.; Pearce, J. A.; Stern, R. J.; Ishizuka, O.; Petronotis, K. E.

    2014-12-01

    Miyashiro (1973, EPSL) put forward the hypothesis that many ophiolites are generated in subduction zone settings. More recently, ophiolitic sequences including MORB-like basalts underlying boninites or other subduction-related rock types have been linked to near-trench spreading during subduction infancy (e.g., Stern and Bloomer, 1992, GSA Bull.; Shervais, 2001, G-cubed; Stern et al., 2012, Lithos.). These contentions were given strong support by the results of Shinkai 6500 diving in the Izu-Bonin-Mariana (IBM) fore-arc (e.g., Reagan et al., 2010, G-cubed; Ishizuka et al., 2011, EPSL; Reagan et al., 2013, EPSL). Based on widely spaced dives and grab sampling at disbursed dive stops, these studies concluded that the most abundant and most submerged volcanic rocks in the IBM fore-arc are MORB-like basalts (fore-arc basalts or FAB), and that these basalts appear to be part of a crustal sequence of gabbro, dolerite, FAB, boninite, and normal arc lavas overlying depleted peridotite. This ophiolitic sequence was further postulated to make up most or all of the IBM fore-arc from Guam to Japan, with similar magmatic ages (52 Ma FAB to 45 Ma arc) north to south, reflecting a western-Pacific wide subduction initiation event. At the time of this writing, IODP Expedition 352 is about to set sail, with a principal goal of drilling the entire volcanic sequence in the Bonin fore-arc. This drilling will define the compositional gradients through the volcanic sequence associated with subduction initiation and arc infancy, and test the hypothesized oceanic fore-arc - ophiolite genetic relationship. A primary goal of this expedition is to illustrate how mantle compositions and melting processes evolved during decompression melting of asthenosphere during subduction initiation to later flux melting of depleted mantle. These insights will provide important empirical constraints for geodynamic models of subduction initiation and early arc development.

  20. North Chilean forearc tectonics and cenozoic plate kinematics

    NASA Astrophysics Data System (ADS)

    Buddin, Tim S.; Stimpson, Ian G.; Williams, Graham D.

    1993-04-01

    The continental forearc of northern Chile has been subjected to contemporaneous extension and compression. Here, cross-sections constructed across the forearc are presented which show that since initial shortening, deformation of the forearc has occurred in two tectonically distinct areas. These inner and outer forearc areas are separated by the strain discontinuity of the Atacama fault system and the tectonically neutral Central Depression. The outer forearc, the Coastal Cordillera, exhibits extensional tectonics, with large (up to 300 m) normal fault scarps preserved. These faults cut the earlier thrusts responsible for the elevation of Jurassic rocks at the coast above their regional elevation. The normal faults have been re-activated, displacing Quaternary salt deposits in the Salar Grande. This re-activation of the basement faults is probably due to the subduction of anomalously thick oceanic crust, producing an isostatic imbalance in the outer forearc. In the inner forearc, cross-sections through the Sierra del Medio and Cordillera de Domeyko show that structures of the Pre-Cordillera are best explained by a thick-skinned thrust system, with localized thin-skinned tectonics controlled by evaporite detachment horizons. Current forearc deformation features indicate a strong degree of correlation between subduction zone geometry and forearc tectonics. The timing of Cenozoic tectonism also fits well with established plate motion parameters, and the spatial and temporal variation in the state of stress of the forearc shows a close relationship throughout the Cenozoic to the plate kinematics and morphology of the subducting Nazca plate.

  1. Alkaline volcanisms in the Proto-Kuril forearc

    NASA Astrophysics Data System (ADS)

    Yutani, T.; Hirano, N.

    2015-12-01

    The Nemuro Group in the northeasternmost part of Japan represents forearc basin deposits of the Proto-Kuril arc that consist of Upper Cretaceous-Paleocene sedimentary rocks with andesitic volcaniclastics and alkaline lavas. Their occurrence in this setting is unusual because such alkaline lavas and intrusions are not commonly found in forearc environments. Here, we report new petrological and geological data to discuss the nature of magmatic process involved in their petrogenesis. Pillow and massive lava flows represent subaqueous volcanic activity, and the occurrence of inter-pillow sedimentary units indicates their eruption on unconsolidated sediments of the lower Nemuro Group. Sill intrusions with layered structures and thicknesses ranging from 10 to 130 m are also common widely distributed in the Nemuro Group. Major and trace element chemistry and mineralogical data distinguish the analyzed samples as K-rich alkaline rocks with low TiO2 or Nb contents, analogous to island arc-like tholeiites. These K-rich alkaline rocks can be classified into two groups of shoshonites: shoshonites containing olivine phenocrysts and intruding into the lower Nemuro Group (Group 1), and shoshonites with no olivine and making up the middle part of the Nemuro Group (Group 2). Group 1 shoshonites have higher MgO, Cr and Ni contents than those of Group 2. The bulk-rock composition of Group 2, which has lower MgO contents, shows higher SiO2 than that of Group 1. Such compositional differences possibly represent fractional crystallization of magmas between Groups 1 and 2. Based on the limited available data, we conclude that these alkaline rocks intruding into the Nemuro Group represent arc-shoshonites, and that the Group 1 magmas underwent fractional crystallization to produce the Group 2 magmas.

  2. IODP Expedition 352 (Bonin Forearc): First Results

    NASA Astrophysics Data System (ADS)

    Pearce, J. A.; Reagan, M. K.; Stern, R. J.; Petronotis, K. E.

    2014-12-01

    IODP Expedition #352 (Testing Subduction Initiation and Ophiolite Models by Drilling the Outer Izu-Bonin-Mariana Forearc: July 30-Sept. 29, 2014) is just underway at the time of writing. It is testing the Stern-Bloomer hypothesis that subduction initiation (SI) was followed by a strongly extensional period of slab sinking and trench roll-back and then by a transitional period leading to the establishment of significant slab-parallel plate motion and hence normal subduction. The Expedition aims to carry out offset drilling at two sites near 28°30'N in the Bonin forearc. Ideally, these together will give the vertical volcanic stratigraphy needed to trace the geodynamic and petrogenetic processes associated with SI, and provide the complete reference section required for comparison with volcanic sequences of possible SI origin found on land in ophiolite complexes and elsewhere. We predict, but need to confirm, a c. 1.0-1.5km sequence with basal, MORB-like forearc basalts (known as FAB) marking the initial period of extension, boninites characterizing the transitional period, and tholeiitic and calc-alkaline lavas marking the establishment of normal arc volcanism. Study of such a sequence will enable us to understand the chemical gradients within and across these volcanic units, to reconstruct mantle flow and melting processes during the course of SI, and to test the hypothesis that fore-arc lithosphere created during SI is the birthplace of most supra-subduction zone ophiolites. Here, we present the first Expedition results, including (a) the volcanic stratigraphic record and subdivision into lava units, (b) the classifications and interpretations made possible by shipboard (portable XRF and ICP) analyses and down-hole measurements, and (c) the biostratigraphic, magnetic, mineralogical, sedimentary and structural constraints on the geological history of the SI section and the interactions between magmatic, hydrothermal and tectonic activity during its evolution.

  3. Aceh Free Pasung: Releasing the mentally ill from physical restraint

    PubMed Central

    2011-01-01

    Background Physical restraint and confinement of the mentally ill (called pasung in Indonesia) is common in Aceh. In early 2010, the local government initiated a program called Aceh Free Pasung 2010. The main goal of the program is to release the mentally ill in the province from restraint and to provide appropriate medical treatment and care. The aim of the paper is to report the findings of a preliminary investigation of the demographic and clinical characteristics of patients who have been admitted to the Banda Aceh Mental Hospital as part of the Aceh Free Pasung program. Methods This is a cross-sectional descriptive study conducted at the Banda Aceh Mental Hospital, where people who had been restrained or confined in the community are being admitted for psychiatric treatment and, where necessary, physical rehabilitation, as part of the Aceh Free Pasung program. Results Fifty-nine of former ex-pasung patients were examined. The majority (88.1%) of the patients were male, aged 18 to 68 years. The duration of pasung varied from a few days to 20 years, with a mean duration of 4.0 years. The reasons for applying pasung are many, with concerns about dangerousness being most common. The great majority (89.8%) had a diagnosis of schizophrenia. Discussion The development of a community mental health system and the introduction of a health insurance system in Aceh (together with the national health insurance scheme for the poor) has enabled access to free hospital treatment for people with severe mental disorders, including those who have been in pasung. The demographic and clinical characteristics of this group of ex-pasung patients are broadly similar to those reported in previous studies. Conclusions The Aceh Free Pasung program is an important mental health and human rights initiative that can serve to inform similar efforts in other parts of Indonesia and other low and middle-income countries where restraint and confinement of the mentally ill is receiving

  4. Tsunami damage in Aceh Province, Sumatra

    NASA Technical Reports Server (NTRS)

    2004-01-01

    The island of Sumatra suffered from both the rumblings of the submarine earthquake and the tsunamis that were generated on December 26, 2004. Within minutes of the quake, the sea surged ashore, bringing destruction to the coasts of northern Sumatra. This pair of natural-color images from Landsat 7's Enhanced Thematic Mapper Plus (ETM+) instrument shows a small area along the Sumatran coast in Aceh province where the tsunami smashed its way ashore. In this region, the wave cut a swath of near-total destruction 1.5 kilometers (roughly one mile) in most places, but penetrating farther in many others. Some of these deeper paths of destruction can be seen especially dramatically in the larger-area ETM+ images linked to above. (North is up in these larger images.) ETM+ collects data at roughly 30 meter resolution, complimenting sensors like NASA's MODIS (onboard both Terra and Aqua satellites) which observed this area at 250-meter resolution to give a wide view and ultra-high-resolution sensors like Space Imaging's IKONOS, which observed the same region at 4-meter resolution to give a detailed, smaller-area view. NASA images created by Jesse Allen, Earth Observatory, using data provided courtesy of the Landsat 7 Science Project Office

  5. The forearc extension in the Central Kuril Islands and the trench rollback

    NASA Astrophysics Data System (ADS)

    Baranov, B. V.; Lobkovsky, L. I.; Dozorova, K. A.

    2016-07-01

    On the basis of bathymetric and seismic data, obtained during cruises 37 (2005) and 41 (2006) of R/V Akademik M.A. Lavrentiev, a new structural scheme of transverse faults in the forearc of the Central Kuril Islands was compiled, the fault kinematics was studied, and a model of the extension zone in the structural pattern of the study area was proposed. According to this model, the trench rollback and development of back-arc basins resulted from the continuous supply of material into the upper mantle convection cell owing to subduction and an increase in the dynamic pressure that pushes the subducting plate, causing it to migrate toward the ocean.

  6. Field data and satellite imagery of tsunami effects in Banda Aceh.

    PubMed

    Borrero, Jose C

    2005-06-10

    After the 26 December 2004 earthquake and tsunami, field data on the extent of the inundation in Banda Aceh, Sumatra, were combined with satellite imagery to quantify the tsunami effects. Flow depths along the shores of Banda Aceh exceeded 9 meters, with inundation reaching 3 to 4 kilometers inland. To the southwest, at Lhoknga, flow depths were more than 15 meters at the shoreline and runup exceeded 25 meters. Erosion and subsidence moved the shoreline of Banda Aceh inland up to 1.5 kilometers, and 65 square kilometers of land between Banda Aceh and Lhoknga were flooded. PMID:15947180

  7. Geology and geochemistry of the Izu-Bonin fore-arc region: Results from ODP Leg 26 and the Bonin Islands

    SciTech Connect

    Taylor, R.N.; Nesbitt, R.W. )

    1990-06-01

    One of the main aims of ODP Leg 126 was to investigate the origin, composition, and evolution of the Izu-Bonin fore-arc region. To achieve this, three drill sites were targeted in the hitherto uninvestigated intraoceanic fore-arc basin. Of these, Holes 792E and 793B reached basement, the latter being the deepest DSDP or ODP hole to do so. Hole 792E was located on a frontal arc promontory and drilled through a sequence of arc lavas with calc-alkaline affinities. The deep Hole 793B drilled the center of the fore-arc basin and drilled 280 m of volcanic basement overlain by late Oligocene turbidites. The basement consists of intercalated heterolithic/hyaloclastitic breccias and basaltic andesite flows. Geochemically these lavas have boninitic affinities, with low Ti/Zr and Y/Zr ratios akin to the type locality lavas from the Bonin Islands. A comprehensive study of the boninites from Chich Jima, located on the fore-arc high, has revealed that these lavas are geochemically diverse. A wide range of trace element and isotopic compositions are recognized, which represent combinations of variably depleted mantle and incompatible element enriched component(s). It is clear from the Hole 793B basement that these ingredients of depleted source and enriched additions occurred not only in the mantle wedge closest to the trench, but also beneath the region that is now the forearc basin. In addition, the boninitic signature prevailed in the forearc region from the middle Eocene at least through to late Oligocene times.

  8. Rift basins of ocean-continent convergent margins

    SciTech Connect

    Forsythe, R.D.; Newcomb, K.R.

    1986-05-01

    Modern and ancient circum-Pacific convergent margins contain many examples of forearc basins where subsidence, occurring simultaneously with subduction of oceanic lithosphere, is controlled by rifting transverse to the margin. The elongate axes of these deep and narrow basins jut obliquely from the plate margin into the interior of the forearc. Similar to aulacogens, faulting and related subsidence appear greatest at their seaward limits and decreases inland. Examples from eastern Pacific forearcs suggest that localized rifting accommodates margin-parallel extension of forearc blocks that are kinetically linked to motions along major margin-parallel strike-slip fault systems. The most prominent examples of modern forearc rift basins are the Sanak and East Sanak basins of the western Alaska Peninsula subduction zone. In this region, the continental shelf is being rifted apart by a series of northwest- and northeast-trending faults. Basement-activated normal faults bounding the basins have listric geometries. Seismostratigraphic relationships within the basins indicate the protracted, synsedimentary, and active nature of faulting and basin subsidence. Along the Peru-Chile trench, two prominent rifted basins also occur: the Gulf of Guayaquil and the Gulf of Penas-Taitao basin of southern Chile. There, margin-parallel rifting controls subsidence in localized basins at the southern terminus to margin-parallel dextral fault systems. These and other examples suggest that strike-slip motion and transverse rifting of forearcs is a common phenomenon inadequately described by existing two-dimensional models of forearcs. Margin-parallel motions of forearc blocks can be related not only to oblique plate convergence, but also to the geometric and compositional nature of the overriding and subducted plates.

  9. Geomorphic Indices in the Assessment of Tectonic Activity in Forearc of the Active Mexican Subduction Zone

    NASA Astrophysics Data System (ADS)

    Gaidzik, K.; Ramirez-Herrera, M. T.

    2015-12-01

    Rapid development of GIS techniques and constant advancement of digital elevation models significantly improved the accuracy of extraction of information on active tectonics from landscape features. Numerous attempts were made to quantitatively evaluate recent tectonic activity using GIS and DEMs, and a set of geomorphic indices (GI), however these studies focused mainly on sub-basins or small-scale areal units. In forearc regions where crustal deformation is usually large-scale and do not concentrate only along one specific fault, an assessment of the complete basin is more accurate. We present here the first attempt to implement thirteen GI in the assessment of active tectonics of a forearc region of an active convergent margin using the entire river basins. The GIs were divided into groups: BTAI - basin geomorphic indices (reflecting areal erosion vs. tectonics) and STAI - stream geomorphic indices (reflecting vertical erosion vs. tectonics). We calculated selected indices for 9 large (> 450 km2) drainage basins. Then we categorized the obtained results of each index into three classes of relative tectonic activity: 1 - high, 2 - moderate, and 3 - low. Finally we averaged these classes for each basin to determine the tectonic activity level (TAI). The analysis for the case study area, the Guerrero sector at the Mexican subduction zone, revealed high tectonic activity in this area, particularly in its central and, to a lesser degree, eastern part. This pattern agrees with and is supported by interpretation of satellite images and DEM, and field observations. The results proved that the proposed approach indeed allows identification and recognition of areas witnessing recent tectonic deformation. Moreover, our results indicated that, even though no large earthquake has been recorded in this sector for more than 100 years, the area is highly active and may represent a seismic hazard for the region.

  10. Erosional Fluxes of the Cascadia Forearc High

    NASA Astrophysics Data System (ADS)

    Gosse, J.; Brandon, M.; Pazzaglia, F.; Antinao, J.

    2005-12-01

    Catchment-wide 10Be inventories have been used to estimate average erosion rates for drainages over timescales of ca. 10 ka along the Cascadia Forearc High. Samples comprise 150-350 micrometer sand from modern and terrace sediment. Terrace sediment ranged from a few hundred to ca. 11,000 years old and was considered to represent pre-logging inventories. The 10Be catchment-average erosion rate estimates in the Clearwater River drainage of western Olympic Peninsula range from 0.18-0.07 mm/a (2'a unc) for Miller Creek, a tributary in a low relief zone close to the coast to 0.39-0.16 mm/a for the upper reach of the mainstem with higher relief. The pattern and magnitude of erosion matches incision rates for similar time scales. That incision rates are similar to the average erosion rates for similar timescales may indicate that steady state has been achieved. The 10Be erosion rate for the entire catchment is 0.34-0.25 mm/a, similar to a modern suspended sediment load erosion rate estimate of 0.32 from the neighbouring Hoh River. Long-term cooling history derived estimates of Olympic Peninsula exhumation reveal a similar pattern (highest rates in highest relief regions) and magnitude of exhumation over long time periods. Samples collected from 6 additional catchments from Vancouver Island to southern Oregon yield erosion estimates that range from 0.52-0.05 mm/a (Myra River) to 0.12-0.01 mm/a (Umpqua River). A weak relationship between relief or slope and erosion rate can be distilled, however these erosion rates may reflect differential rates of sediment accretion along the Forearc.

  11. Structure and composition of the Southern Mariana Forearc: new observations and samples from Shinkai 6500 dive studies in 2010

    NASA Astrophysics Data System (ADS)

    Ohara, Y.; Reagan, M. K.; Ishizuka, O.; Stern, R. J.

    2010-12-01

    The 3000-km long Izu-Bonin-Mariana (IBM) Arc system is an outstanding example of an intraoceanic convergent plate margin, and has become the particular focus of Japanese and US efforts to understand the operation of the “Subduction Factory”. In 2006 and 2008, twelve DSV Shinkai 6500 dives (973-977 and 1091-1097) were performed during YK06-12 and YK08-08 Leg 2 cruises along the landward slope of the southern Mariana Trench. The goal was to sample the remaining early arc crust associated with subduction initiation in the IBM system and upper mantle exposed in the forearc in order to gain a clearer understanding of the structure and evolution of Mariana forearc crust and upper mantle. The fruitful results include the recovery of the entire suite of rocks associated with what could be termed a “supra-subduction zone ophiolite” that formed during subduction initiation. An important discovery is that MORB-like tholeiitic basalts crop out over large areas. These “fore-arc basalts” (FAB) underlie boninites and overlie diabasic and gabbroic rocks. Potential origins include eruption at a spreading center before subduction began or eruption during near-trench spreading after subduction began (Reagan et al., 2010, G3). Another important discovery is a region of active forearc rifting at the southern end of the Mariana arc, named SE Mariana Forearc Rift (SEMFR). The SEMFR was firstly mapped with HMR-1 sonar (Martinez et al., 2000, JGR). Two dives at SEMFR recovered less-depleted backarc related peridotites (at Dive 973; Michibayashi et al., 2009, G3), and fresh basalts and basaltic andesites with petrographic characteristics like backarc basin lavas (at Dive 1096; see Ribeiro et al., AGU FM 2010). Although our previous studies have produced a number of important new observations about the geology of the southern Mariana forearc, our understanding of the region is still primitive. We will be conducting another cruise (YK10-12) during late September, 2010 to tackle

  12. Out of Disaster Comes Opportunity: Initial Lessons from Teacher Mentoring in Banda Aceh, Indonesia

    ERIC Educational Resources Information Center

    Lesnick, Joy; Schultz, Katherine

    2006-01-01

    On December 26, 2004, a 9.0 magnitude earthquake--the most powerful in more than 40 years--struck deep under the Indian Ocean. It was centered about 100 miles southwest off the coast of Aceh, Indonesia, and triggered massive tsunamis across the coasts of Asia and Africa. In Aceh province, located at the northwest tip of the island of Sumatra in…

  13. Recurrence of great earthquakes and tsunamis, Aceh Province, Sumatra

    NASA Astrophysics Data System (ADS)

    Rubin, C. M.; Horton, B.; Sieh, K.; Pilarczyk, J.; Hawkes, A. D.; Daly, P.; Kelsey, H. M.; McKinnon, E.; Ismail, N.; Daryono, M. R.

    2013-12-01

    The timing and characterization of ancient earthquakes and tsunamis inferred from a variety of geologic studies in Aceh Province, Sumatra, are helping to understand predecessors of the 2004 event in the Indian Ocean region. We report results from three different depositional environments along the western and northern coast of Aceh Province, Sumatra, that illuminate the history of tsunamis through the past several millennia. Within a coastal cave along the western coast is an extraordinary sedimentary deposit that contains a 7,000-year long sequence of tsunami sands separated by bat guano. In two sea cliff exposures along the northern coast of Aceh is evidence for two closely timed predecessors of the giant 2004 tsunami that destroyed communities along the coast about 500 years ago. In addition, coastal wetlands along the western coast document land-level changes and tsunamis associated with the earthquake cycle in the early- to mid-Holocene. Together these records show a marked variability in recurrence of large tsunamis along the Acehnese coast. Time between inundations averages close to 500 years but range from a few centuries to a millennium.

  14. Rapid response: email, immediacy, and medical humanitarianism in Aceh, Indonesia.

    PubMed

    Grayman, Jesse Hession

    2014-11-01

    After more than 20 years of sporadic separatist insurgency, the Free Aceh Movement and the Indonesian government signed an internationally brokered peace agreement in August 2005, just eight months after the Indian Ocean tsunami devastated Aceh's coastal communities. This article presents a medical humanitarian case study based on ethnographic data I collected while working for a large aid agency in post-conflict Aceh from 2005 to 2007. In December 2005, the agency faced the first test of its medical and negotiation capacities to provide psychiatric care to a recently amnestied political prisoner whose erratic behavior upon returning home led to his re-arrest and detention at a district police station. I juxtapose two methodological approaches-an ethnographic content analysis of the agency's email archive and field-based participant-observation-to recount contrasting narrative versions of the event. I use this contrast to illustrate and critique the immediacy of the humanitarian imperative that characterizes the industry. Immediacy is explored as both an urgent moral impulse to assist in a crisis and a form of mediation that seemingly projects neutral and transparent transmission of content. I argue that the sense of immediacy afforded by email enacts and amplifies the humanitarian imperative at the cost of abstracting elite humanitarian actors out of local and moral context. As a result, the management and mediation of this psychiatric case by email produced a bureaucratic model of care that failed to account for complex conditions of chronic political and medical instability on the ground. PMID:24788052

  15. Uplift Patterns in the Forearc of the Middle America Trench, Costa Rica: Implications for Mass Balance and Fore-arc Kinematics

    NASA Astrophysics Data System (ADS)

    Fisher, D. M.; Gardner, T. W.; Sak, P.; Marshall, J. S.; Protti, M.

    2001-12-01

    Uplift patterns along the Pacific Coast of Costa Rica provide insight into the balance of mass in the fore arc and depict an inner forearc that thickens nonuniformly at the expense of a subsiding margin wedge. Offshore, incoming seamounts and ridges on the subducting Cocos plate result in embayment of the trench axis and scarring that reflects downdropping of fault bounded blocks in the wake of subducting seamounts. The upper slope displays a regional unconformity that records late Tertiary subsidence and arcward displacement of the trench axis. Uplifted marine wavecut benches along the coast of Costa Rica, combined with analysis of fault populations, indicate that the inner fore arc has experienced a history that is in marked contrast to the subsidence and erosion observed in the margin wedge. Regionally, the inner forearc, from Osa to Nicaragua, has experienced uplift. One way to produce this regional uplift signal is movement on an out-of-sequence fault, or an active fault arcward of the frontal thrust. The longitudinal fault that marks the front of the Fila Costena may be an example of such a fault. Wood from a raised wavecut platform along this thrust front was radiocarbon dated at 5540 yrs. A balanced cross section of the Fila Costena indicates a detachment at a depth of ~ 2 km near the contact between upper slope sediments of the Terraba basin and the underlying basement of the margin wedge. This cross section also requires a >10 km of shortening accomplished by underthrusting of the outer fore arc. Crustal thickening by this mechanism could explain the dichotomy between uplift of the mountainous Fila Costena and Talamanca Ranges and subsidence of the slope apron offshore. Superimposed on this regional uplift of the Costa Rican coast is a pattern of faster uplift within fault-bounded blocks that lie inboard of incoming seamount chains. Offshore of Nicoya, the subducting plate displays two parallel ridges: a ridge coincident with the trace of the Coc

  16. Emplacement and Growth of Serpentinite Seamounts on the Mariana Forearc

    NASA Astrophysics Data System (ADS)

    Oakley, A. J.; Taylor, B.; Moore, G. F.; Fryer, P.; Morgan, J. K.; Goodliffe, A. M.

    2004-12-01

    Seamounts comprised primarily of serpentinite muds are found on the outer forearc of the Izu-Bonin-Mariana subduction system. They represent some of the first material outputs of the recycling process that takes place in subduction zones. Therefore, understanding their evolution is necessary to correctly quantify the flux of material through the subduction system. Serpentinite seamounts have been described as mud diapirs, mud volcanoes, uplifted blocks of mantle material, and a composite of the latter two. Multi-channel seismic (MCS) data collected in 2002 from the outer Mariana forearc imaged, for the first time, the large-scale internal structure of these seamounts. These data, combined with new bathymetry, have provided insight into how the seamounts grow and deform with time and have allowed us to evaluate proposed models for their formation. The serpentinite seamounts rest on faulted and sedimented Mariana forearc basement. Flank flows of serpentinite muds downlap existing forearc substrate, leaving the underlying stratigraphy largely undisturbed. Reflections located 3.5-5 km beneath forearc basement may represent Moho, suggesting that the seamounts are built on anomalously thin forearc crust. A strong reflection at the summit of Big Blue, the largest serpentinite seamount in the Mariana Forearc, represents a collapse structure that has been partially in-filled by younger muds, supporting the idea that serpentinite seamount growth is episodic. Basal thrusts that incorporate forearc sediments at the toe of Turquoise Seamount provide evidence for seamount settling and lateral growth. We are conducting numerical simulations of seamount growth and evolution using the discrete element method (DEM), previously used to examine gravity spreading phenomena in magmatic volcanoes. Simulations employing distinctly low basal and internal friction coefficients provide a good match to the overall morphology of the serpentinite seamounts, and offer insight into their internal

  17. [Tsunami in South-East Asia--rapid response deployment in Banda Aceh].

    PubMed

    Streuli, Rolf A

    2008-01-01

    On December 26, 2004 the second largest earthquake ever seismographically registered occurred in South-East Asia. It had a magnitude of 9.3 on Richter's scale and its epicentre was located on sea ground 160 km West of Banda Aceh, the capital of the province of Aceh on the island of Sumatra. The earthquake resulted in a tsunami which almost completely destroyed the city of Banda Aceh. Its death toll on the island of Sumatra was 168,000. The Swiss Humanitarian Aid Unit was deployed within a few days after the catastrophe with an advance team, which had to evaluate the need for supplies and personal in Banda Aceh. In close collaboration with relief forces of the Australian armed forces the team was able to deliver efficient medical and technical support. The most prevalent medical problems were: (1) Tsunami associated aspiration pneumonia; (2) Infected wounds of lower extremities; (3) Open bone fractures of lower extremities; (4) Tetanus infection. PMID:18399180

  18. First results from TN273 studies of the SE Mariana Forearc rift

    NASA Astrophysics Data System (ADS)

    Ribeiro, J. M.; Stern, R. J.; Kelley, K. A.; Shaw, A. M.; Shimizu, N.; Martinez, F.; Ishii, T.; Ishizuka, O.; Manton, W. I.

    2012-12-01

    TN 273 aboard R/V Thomas Thompson (Dec. 22 2011- Jan. 22 2012) studied an unusual region of rifting affecting the southern Mariana forearc S.W. of Guam. The S.E. Mariana Forearc Rift (SEMFR) formed by diffuse tectonic and volcanic deformation (Martinez and Sleeper, this meeting) ~2.7-3.7 Ma ago to accommodate opening of the southernmost Mariana Trough backarc basin. A total of 730 km linear-track of SEMFR seafloor was surveyed with deep-towed side-scan sonar IMI-30. 14 dredges provided samples of SEMFR igneous rocks, analyzed for whole rock (WR) and glass compositions. These new results coupled with results of earlier investigations confirm that SEMFR is dominated by Miocene lavas along with minor gabbro and diabase. SEMFR lavas range in major element composition from primitive basalt to fractionated andesite (Mg# = 0.36-0.73; SiO2 = 50-57 wt%), mainly controlled by crystal fractionation. Rare Earth Element (REE) patterns range from LREE-depleted, N-MORB-like to flat patterns, reflecting different mantle processes (i.e. different sources, degree of melting …). Glassy rinds and olivine-hosted melt inclusions in these lavas contain variable volatile compositions (F = 75-358 ppm, S = 35-1126 ppm, Cl= 74-1400 ppm, CO2 = 15-520 ppm, 0.36-2.36 wt% H2O). SEMFR lavas show spider diagrams with positive anomalies in LILE and negative anomalies in HSFE. SEMFR lavas have backarc basin-like (BAB-like) chemical composition (H2O < 2.5wt%, Ba/Yb~20, Nb/Yb~1 and ɛNd~9) along with stronger enrichment in Rb and Cs than arc and BAB lavas, as demonstrated by their higher Rb/Th and Cs/Ba ratios in WR and glasses, which may reflect the role of the ultra-shallow fluids. Ultra-shallow fluids are derived from the top of the subducting slab, beneath the forearc, where most of the water and the fluid-mobile elements (Rb, Cs, Ba,) are thought to be released (Schmidt and Poli, 1998, EPSL, Savov et al., 2005, G-3). Our results suggest that i) SEMFR lavas formed by metasomatism of a BAB mantle

  19. An inverted continental Moho and serpentinization of the forearc mantle.

    PubMed

    Bostock, M G; Hyndman, R D; Rondenay, S; Peacock, S M

    2002-05-30

    Volatiles that are transported by subducting lithospheric plates to depths greater than 100 km are thought to induce partial melting in the overlying mantle wedge, resulting in arc magmatism and the addition of significant quantities of material to the overlying lithosphere. Asthenospheric flow and upwelling within the wedge produce increased lithospheric temperatures in this back-arc region, but the forearc mantle (in the corner of the wedge) is thought to be significantly cooler. Here we explore the structure of the mantle wedge in the southern Cascadia subduction zone using scattered teleseismic waves recorded on a dense portable array of broadband seismometers. We find very low shear-wave velocities in the cold forearc mantle indicated by the exceptional occurrence of an 'inverted' continental Moho, which reverts to normal polarity seaward of the Cascade arc. This observation provides compelling evidence for a highly hydrated and serpentinized forearc region, consistent with thermal and petrological models of the forearc mantle wedge. This serpentinized material is thought to have low strength and may therefore control the down-dip rupture limit of great thrust earthquakes, as well as the nature of large-scale flow in the mantle wedge. PMID:12037564

  20. Biological control of Black Pod Disease and Seedling Blight of cacao caused by Phytophthora Species using Trichoderma from Aceh Sumatra

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The cocoa tree, Theobroma cacao L., suffers large yield losses in Aceh Indonesia to the disease black pod rot, caused by Phytophthora spp. Despite having the largest area under cacao production in Sumatra, farmers in the Aceh region have low overall production because of losses to insect pests and b...

  1. Active Crustal Faults in the Forearc Region, Guerrero Sector of the Mexican Subduction Zone

    NASA Astrophysics Data System (ADS)

    Gaidzik, Krzysztof; Ramírez-Herrera, Maria Teresa; Kostoglodov, Vladimir

    2016-01-01

    This work explores the characteristics and the seismogenic potential of crustal faults on the overriding plate in an area of high seismic hazard associated with the occurrence of subduction earthquakes and shallow earthquakes of the overriding plate. We present the results of geomorphic, structural, and fault kinematic analyses conducted on the convergent margin between the Cocos plate and the forearc region of the overriding North American plate, within the Guerrero sector of the Mexican subduction zone. We aim to determine the active tectonic processes in the forearc region of the subduction zone, using the river network pattern, topography, and structural data. We suggest that in the studied forearc region, both strike-slip and normal crustal faults sub-parallel to the subduction zone show evidence of activity. The left-lateral offsets of the main stream courses of the largest river basins, GPS measurements, and obliquity of plate convergence along the Cocos subduction zone in the Guerrero sector suggest the activity of sub-latitudinal left-lateral strike-slip faults. Notably, the regional left-lateral strike-slip fault that offsets the Papagayo River near the town of La Venta named "La Venta Fault" shows evidence of recent activity, corroborated also by GPS measurements (4-5 mm/year of sinistral motion). Assuming that during a probable earthquake the whole mapped length of this fault would rupture, it would produce an event of maximum moment magnitude Mw = 7.7. Even though only a few focal mechanism solutions indicate a stress regime relevant for reactivation of these strike-slip structures, we hypothesize that these faults are active and suggest two probable explanations: (1) these faults are characterized by long recurrence period, i.e., beyond the instrumental record, or (2) they experience slow slip events and/or associated fault creep. The analysis of focal mechanism solutions of small magnitude earthquakes in the upper plate, for the period between 1995

  2. Origin of Izu-Bonin forearc submarine canyons

    SciTech Connect

    Fujioka, Kantaro ); Yoshida, Haruko )

    1990-06-01

    Submarine canyons on the Izu-Bonin forearc are morphologically divided from north to south into four types based on their morphology, long profiles, and seismic profiles: Mikura, Aogashima, Sofu, and Chichijima types, respectively. These types of canyons are genetically different from each other. Mikura group is formed by the faults related to bending of the subducting Philippine Sea Plate. Aogashima type genetically relates to the activity of large submarine calderas that supply large amounts of volcaniclastic material to the consequent forearc slope. The third, Sofu group, is thought to be formed by the large-scale mega mass wasting in relation to the recent movement of the Sofugan tectonic line. The last, Chichijima group, is formed by collision of the Uyeda Ridge and the Ogasawara Plateau on the subducting Pacific Plate with Bonin Arc. Long profiles of four types of submarine canyons also support this.

  3. Composition of the Southeast Mariana Forearc Rift pillow lavas : interaction between adiabatic decompression mantle melting and ultra-shallow slab-derived fluids

    NASA Astrophysics Data System (ADS)

    Ribeiro, J. M.; Stern, R. J.; Kelley, K. A.; Ishizuka, O.; Ren, M.; Ohara, Y.; Reagan, M. K.; Bloomer, S.; Anthony, E.

    2009-12-01

    The Mariana intraoceanic arc system is related to the subduction of the Pacific plate beneath the Philippine Sea plate. A northward-propagating forearc rift extending from the southernmost backarc basin spreading ridge to the trench, called the SE Mariana Forearc Rift (SEMFR), has been inferred by regional HMR-1 bathymetric and backscatter mapping south of Guam (see Martinez & Stern abstract). SEMFR formed by lateral stretching as a result of slab rollback and collision of the Caroline ridge with the IBM arc. This forearc rift provides an unusual opportunity to study melts generated very shallow (~ 40 km deep) above a subduction zone. Forearc rifts are extensional zones occurring in subduction settings providing the opportunity to sample rocks produced by adiabatic asthenosphere decompression and fluid-metasomatized mantle melting. During YK08-08 in July 2008, manned submersible Shinkai 6500 Dive 1096 dived in SEMFR and sampled a 663 m thick section of fresh tholeiitic pillow lavas. These lavas are composed of upper primitive basalts (Mg# = 61 - 67) and lower basaltic andesites (Mg# = 49 - 51). The upper series phenocrysts are olivine (Fo85-87), diopside, and plagioclase (An80-83) with scattered olivine xenocrysts (3 mm, Fo92) hosting Cr-spinel (Cr# = 68 - 69). Lower series lavas contain phenocrysts of olivine (Fo76-79), augite and two plagioclases (An66-71 and An80-86), perhaps indicating magma mixing. Flat REE patterns, and high Mg# ( > 60) of the upper basalts indicate generation by fractional melting of spinel peridotite. LA-ICP-MS analysis show that lower series clinopyroxenes formed in equilibrium with more REE-enriched melts than their host rock, also supporting an interpretation of magma mixing. Discrimination diagrams using Th-Ba-Nb-Yb systematics (Pearce, 2008, Lithos, v. 100; Pearce and Stern, 2006, Geophysical Monograph Series 166, AGU) show that both series lavas have composition similar to that of Mariana backarc basin but with higher Ba/Nb content

  4. Mental health in Aceh--Indonesia: A decade after the devastating tsunami 2004.

    PubMed

    Marthoenis, Marthoenis; Yessi, Sarifah; Aichberger, Marion C; Schouler-Ocak, Meryam

    2016-02-01

    The province of Aceh has suffered enormously from the perennial armed conflict and the devastating Tsunami in 2004. Despite the waves of external aid and national concern geared toward improving healthcare services as part of the reconstruction and rehabilitation efforts after the Tsunami, mental health services still require much attention. This paper aims to understand the mental healthcare system in Aceh Province, Indonesia; its main focus is on the burden, on the healthcare system, its development, service delivery and cultural issues from the devastating Tsunami in 2004 until the present. We reviewed those published and unpublished reports from the local and national government, from international instances (UN bodies, NGOs) and from the academic literature pertaining to mental health related programs conducted in Aceh. To some extent, mental health services in Aceh have been improved compared to their condition before the Tsunami. The development programs have focused on procurement of policy, improvement of human resources, and enhancing service delivery. Culture and religious beliefs shape the pathways by which people seek mental health treatment. The political system also determines the development of the mental health service in the province. The case of Aceh is a unique example where conflict and disaster serve as the catalysts toward the development of a mental healthcare system. Several factors contribute to the improvement of the mental health system, but security is a must. Whilst the Acehnese enjoy the improvements, some issues such as stigma, access to care and political fluctuations remain challenging. PMID:26957340

  5. Evaluating the influence of aseismic ridge subduction and accretion(?) on detrital modes of forearc sandstone: an example from the Kronotsky Peninsula in the Kamchatka Forearc

    NASA Astrophysics Data System (ADS)

    Marsaglia, Kathleen M.; Mann, Paul; Hyatt, Ronda J.; Olson, Hilary C.

    1999-01-01

    The Kronotsky Peninsula, in the forearc region of the Kamchatka magmatic arc, lies on trend with the Emperor Seamount chain situated on the currently subducting Pacific tectonic plate. Detrital modes of volcaniclastic sandstone interbedded with mafic Eocene(?) basement rocks and within the overlying sedimentary sequence provide insight into the late Cenozoic geologic history of this area. Eocene(?) and basal Miocene sandstones are primarily composed of variably altered mafic volcanic debris. Their detrital modes are similar to those of Emperor Seamount sandstones and Hawaiian beach sands. Although aspects of the stratigraphy and volcaniclastic sand composition are consistent with a seamount setting, there is no physical evidence for an accretion event, and the suggested Eocene age for this unit makes an Emperor Seamount origin unlikely. A seamount origin cannot be ruled out for older Kronotsky basement complexes, however. A Miocene lull in Kronotsky volcanism was followed by rapid basin subsidence and influx of arc-derived turbidites from the west. Detrital modes of these sandstones are typical of a moderately evolved continental or micro-continental arc. An anomalously high proportion of sedimentary lithic fragments is the only possible compositional fingerprint attributable to seamount or ridge subduction.

  6. Gravity anomalies, forearc morphology and seismicity in subduction zones

    NASA Astrophysics Data System (ADS)

    Bassett, D.; Watts, A. B.; Das, S.

    2012-12-01

    We apply spectral averaging techniques to isolate and remove the long-wavelength large-amplitude trench-normal topographic and free-air gravity anomaly "high" and "low" associated with subduction zones. The residual grids generated illuminate the short-wavelength structure of the forearc. Systematic analysis of all subduction boundaries on Earth has enabled a classification of these grids with particular emphasis placed on topography and gravity anomalies observed in the region above the shallow seismogenic portion of the plate interface. The isostatic compensation of these anomalies is investigated using 3D calculations of the gravitational admittance and coherence. In the shallow region of the megathrust, typically within 100 km from the trench, isolated residual anomalies with amplitudes of up to 2.5 km and 125 mGal are generally interpreted as accreted/subducting relief in the form of seamounts and other bathymetric features. While most of these anomalies, which have radii < 50km, are correlated with areas of reduced seismicity, several in regions such as Japan and Java appear to have influenced the nucleation and/or propagation of large magnitude earthquakes. Long-wavelength (500 - >1000 km) trench-parallel forearc ridges with residual anomalies of up to 1.5 km and 150 mGal are identified in approximately one-third of the subduction zones analyzed. Despite great length along strike, these ridges are less than 100 km wide and several appear uncompensated. A high proportion of arc-normal structure and the truncation/morphological transition of trench-parallel forearc ridges is explained through the identification and tracking of pre-existing structure on the over-riding and subducting plates into the seismogenic portion of the plate boundary. Spatial correlations between regions with well-defined trench-parallel forearc ridges and the occurrence of large magnitude interplate earthquakes, in addition to the uncompensated state of these ridges, suggest links

  7. The offshore basement of Perú: Evidence for different igneous and metamorphic domains in the forearc

    NASA Astrophysics Data System (ADS)

    Romero, Darwin; Valencia, Kiko; Alarcón, Pedro; Peña, Daniel; Ramos, Victor A.

    2013-03-01

    As a result of new studies carried out in the offshore of Perú during the exploration and hydrocarbon evaluation of the forearc basins, new U-Pb SHRIMP and TIMS in zircons and some Ar-Ar data were obtained in the metamorphic and igneous basement. The understanding of this basement was critical to evaluate different hypotheses that have been proposed for the tectonic evolution of pre-Andean crust of Perú. Recent research performed in the basement rocks of the Marañón Massif in northern Perú, claimed that west of this area was a basement-free region in the Paleozoic, where the arc and forearc were developed in a mafic quasi-oceanic crust. However, petrographic studies and new preliminary ages indicate, for the first time, the nature and age of this sialic basement. Reconnaissance studies were performed in several offshore islands, as the Las Hormigas de Afuera Island west of Lima, and Macabí and Lobera islands along the edge of the continental platform. These data were complemented with the studies of some cutting samples obtained in recent exploration wells in northern Perú. The results of the present work show two large crustal domains in the Peruvian offshore forearc. A northern domain contains late Paleozoic igneous rocks that appear to be the southern offshore continuation of the Amotape-Tahuin block, which is interpreted as the southernmost remnant of the Laurentia Alleghenian orogen. The central offshore domain, known as the Paracas High, corresponds to the outer shelf high of previous studies. It contains orthogneisses of Grenville-age, probably recrystallized during an Ordovician magmatic episode. The new results show that the central offshore of Perú is an extension of the Grenville-age basement affected by Famatinian, early Paleozoic magmatism, well exposed in the southern domain in the Arequipa Massif along the coast of southern Perú.

  8. Gravity anomalies, crustal structure, and seismicity at subduction zones: 2. Interrelationships between fore-arc structure and seismogenic behavior

    NASA Astrophysics Data System (ADS)

    Bassett, Dan; Watts, Anthony B.

    2015-05-01

    An ensemble-averaging technique is used to remove the long-wavelength topography and gravity field associated with subduction zones. Short-wavelength residual anomalies are attributed to the tectonic structure of subducting and overthrusting plates. A paired (positive-negative) fore-arc anomaly is observed consisting of a long (>1000 km), linear, trench-parallel ridge landward of the deep-sea-terrace basin. Ridges have amplitudes of 1500-3000 m and 160-240 mGal, wavelengths of 150-200 km, and high gravity anomaly to topography ratios (50-75 mGal km-1). The ridge crests correlate with the downdip limit of coseismic slip and strong interplate coupling and in Cascadia, the updip limit of tremor epicenters. The ridge crest may be interpreted as defining the boundary between the velocity-weakening and seismogenic region of the subduction interface and the downdip frictional transition zone. In Tonga-Kermadec, the Kuril Islands and Chile landward ridges are associated with extinct volcanic arcs. Paired anomalies are attributed to the preferential subduction erosion of the outer fore arc and a spatially varying combination of (a) lower crustal underplating beneath the inner fore arc, (b) the transformation of interseismic strain into permanent geologic strain via faulting, folding, or buckling of the inner fore arc, and (c) the relative trenchward migration of extinct volcanic arcs in regions operating with a net crustal deficit. Along-strike transitions in fore-arc morphology and seismogenic behavior are related to preexisting crustal structure of subducting and overthrusting plates. Fore arcs have the added potential of recording the time-integrated response of the upper plate to subduction processes, and fore-arc structure should be considered in tandem with seismological observations.

  9. Structural and stratigraphic evolution of Aleutian convergent-margin basins - ridge crest to trench floor

    SciTech Connect

    Scholl, D.W.; Ryan, H.F.; Geist, E.L.; Vallier, T.L.; Stevenson, A.J.; Childs, J.R. )

    1988-02-01

    The Aleutian Ridge lies along nearly 2000 km of the north Pacific's obliquely converging plate boundary with North America. Since middle Eocene time, convergent-margin basins have repeatedly formed here, typically as summit basins along the ridge crest, and as forearc basins on the landward trench slope. Summit and forearc basins formed as a consequence of plate-boundary coupling and the application of compressional and right-lateral shear stresses to the arc massif. Basins typically evolved along shear zones in response to transtensional processes, and as trailing-edge grabens behind rotating blocks of arc massif. In the late Cenozoic, high rates of trench sedimentation led to the growth of an accretionary complex that underthrust forearc basement. Wedging and improved plate coupling elevated and laterally shifted blocks of outer forearc rocks, creating much of the structural framework of the regionally extensive Aleutian Terrace forearc basin. Changes in plate-boundary conditions that affected the ridge's volcanic activity and regional elevation importantly influenced basinal sedimentation. Changes of greatest significance were a major shift in convergence direction and rate about 42 Ma (reduced volcanism), ridge underthrusting by increasingly younger ocean crust in Oligocene and Miocene time (arc elevation), and the combination of more orthogonal underthrusting and the subduction of a dead spreading center 5-10 Ma (arc subsidence).

  10. Morphology of submarine canyon system and geotechnical properties of surficial sediments across the Peru-Chile forearc

    SciTech Connect

    Bergersen, D.D.; Coulbourn, W.T.; Moberly, R.

    1989-03-01

    During August 1987, a SeaMARC II side-scan and sampling survey was conducted across the Peru-Chile forearc from 17/degrees/30'S to 19/degrees/30'S. Side-scan images reveal a complex submarine canyon system. Incised canyons meander across the Arequipa basin; their sinuosity results from erosion and cutbank slumping of the basin sediments. Lenticular packets of strata visible in reprocessed digital single-channel seismic profiles are interpreted to be buried channels. Tributary canyons coalesce into a single canyon at the structural high that deviates from its north-south course to a northeast-southwest course as a result of stream piracy. A dendritic drainage basin forming on the midslope may be the rejuvenation of an abandoned channel. Sediment properties were measured on 42 free-fall cores and 7 piston cores recovered both in and around the submarine canyon. Olive-gray (5Y 3/2) hemipelagic mud is the predominant sediment across the forearc. Most cores exhibit a small degree of bioturbation and thin laminae of sand; the number of sand laminae increases as the distance away from the canyon decreases. Shear strengths, averaged over a 1-m core length, decrease slightly with water depth. Carbonate content in all samples from this area is negligible with the exception of one piston core recovered from the upper reaches of the canyon, the bottom of which is composed of gravel- and sand-size shell fragments. Bulk mineralogy, determined from semiquantitative analysis of x-ray diffraction patterns, shows a decrease in relative feldspar percent and an increase in total clay content with increasing water depth. Preliminary analysis of core tops shows a mean grain size in the medium to very fine silt class, with increasing grain size toward the canyon. Smear slide counts generally show a surprisingly low abundance of volcanic glass and biogenic material, particularly diatoms.

  11. Variability in forearc deformation during subduction: Insight from geodynamic models and application to the Calabria subduction zone

    NASA Astrophysics Data System (ADS)

    Chen, Zhihao; Schellart, Wouter; Duarte, Joao

    2015-04-01

    In nature subducting slabs and overriding plate segments bordering subduction zones are generally embedded within larger plates. Such large plates can impose far-field boundary conditions that impact the style of subduction and overriding plate deformation. Here we present 3D dynamic analogue models of subduction, in which the far-field boundary conditions at the trailing edges of the subducting plate (SP) and overriding plate (OP) are varied. Four configurations are presented: Free (both plates free), SP-Fixed, OP-Fixed and SP-OP-Fixed. We investigate their impact on the kinematics and dynamics of subduction, with a special focus on overriding plate deformation. Our models indicate that in natural (narrow) subduction zones, assuming a homogeneous overriding plate, the formation of backarc basins (e.g., Tyrrhenian Sea, Aegean Sea, Scotia Sea) is generally expected to occur at a comparable location (300-500 km from the trench), irrespective of the boundary condition. Furthermore, our models indicate that the style of forearc deformation (shortening or extension) is determined by the mobility of the overriding plate through controlling the force normal to the subduction zone interface (trench suction). Our geodynamic model that uses the SP-OP-Fixed set-up is comparable to the Calabria subduction zone with respect to subduction kinematics, slab geometry, trench curvature and accretionary wedge configuration. Furthermore, it provides explanation for the natural observations of both backarc extension in the Tyrrhenian Sea and forearc extension in the Calabria region, which have been active since the Miocene. We explain the observations as a consequence of subduction of the narrow Calabrian slab and the immobility of the subducting African plate and overriding Eurasian plate. This setting forced subduction to be accommodated almost entirely by slab rollback (not trenchward overriding plate motion), while trench retreat was accommodated almost entirely by backarc and

  12. Active shortening of the Cascadia forearc and implications for seismic hazards of the Puget Lowland

    USGS Publications Warehouse

    Johnson, S.Y.; Blakely, R.J.; Stephenson, W.J.; Dadisman, S.V.; Fisher, M.A.

    2004-01-01

    Margin-parallel shortening of the Cascadia forearc is a consequence of oblique subduction of the Juan de Fuca plate beneath North America. Strike-slip, thrust, and oblique crustal faults beneath the densely populated Puget Lowland accommodate much of this north-south compression, resulting in large crustal earthquakes. To better understand this forearc deformation and improve earthquake hazard, assessment, we here use seismic reflection surveys, coastal exposures of Pleistocene strata, potential-field data, and airborne laser swath mapping to document and interpret a significant structural boundary near the City of Tacoma. This boundary is a complex structural zone characterized by two distinct segments. The northwest trending, eastern segment, extending from Tacoma to Carr Inlet, is formed by the broad (??? 11.5 km), southwest dipping (??? 11??-2??) Rosedale monocline. This monocline raises Crescent Formation basement about 2.5 km, resulting in a moderate gravity gradient. We interpret the Rosedale monocline as a fault-bend fold, forming above a deep thrust fault. Within the Rosedale monocline, inferred Quaternary strata thin northward and form a growth triangle that is 4.1 to 6.6 km wide at its base, suggesting ??? 2-3 mm/yr of slip on the underlying thrust. The western section of the >40-km-long, north dipping Tacoma fault, extending from Hood Canal to Carr Inlet, forms the western segment of the Tacoma basin margin. Structural relief on this portion of the basin margin may be several kilometers, resulting in steep gravity and aeromagnetic anomalies. Quaternary structural relief along the Tacoma fault is as much as 350-400 m, indicating a minimum slip rate of about 0.2 mm/yr. The inferred eastern section of the Tacoma fault (east of Carr Inlet) crosses the southern part of the Seattle uplift, has variable geometry along strike, and diminished structural relief. The Tacoma fault is regarded as a north dipping backthrust to the Seattle fault, so that slip on a

  13. Seismicity of the forearc marginal wedge (accrertionary prism)

    SciTech Connect

    Chen, A.T.; Frohlich, C.; Latham, G.V.

    1982-05-10

    Three different types of seismic data have been examined for seismic events occurring within the zone called the accreted wedge or forearc marginal wedge that underlies the inner trench wall of some arcs. These types of data are (1) teleseismically recorded earthquakes that have been reported in the literature as occurring in major arc-trench regions; these events fail to demonstrate that earthquakes occur within the accreted wedge because the uncertainty of focal depth usually exceeds the depth dimension of the accreted wedge; these data include many tsunamigenic earthquakes, (2) local earthquakes located by combined ocean bottom seismograph and land networks in the arc-trench region in the New Hebrides and the central and eastern Aleutian Trench; none of the more reliable of these hypocenters lies within the accreted wedge; (3) S-P intervals measured at stations on islands located on the outer ridge or at ocean bottom seismograph stations on the forearc marginal wedge; these data do not show the existence of events occurring within the accreted wedge; e.g., from 18 ocean bottom seismograph stations with a cumulative operation time of about 1 year, the smallest S-P time is about 2.5 s for events in the New Hebrides and about 4 s for events in the Adak and Kodiak regions. We found no S-P time smaller than 2 s from 6 years of seismograms recorded at Middleton Island, Alaska, and no S-P time smaller than 4 s from 25 years of seismograms recorded on Barbados. All of the events could have occured outside the forearc marginal wedge.

  14. Helium as a tracer for fluids released from Juan de Fuca lithosphere beneath the Cascadia forearc

    NASA Astrophysics Data System (ADS)

    McCrory, P. A.; Constantz, J. E.; Hunt, A. G.; Blair, J. L.

    2016-06-01

    Helium isotopic ratios (3He/4He) observed in 25 mineral springs and wells above the Cascadia forearc provide a marker for fluids derived from Juan de Fuca lithosphere. This exploratory study documents a significant component of mantle-derived helium within forearc springs and wells, and in turn, documents variability in helium enrichment across the Cascadia forearc. Sample sites arcward of the forearc mantle corner generally yield significantly higher ratios (˜1.2-4.0 RA) than those seaward of the corner (˜0.03-0.7 RA). 3He detected above the inner forearc mantle wedge may represent a mixture of both oceanic lithosphere and forearc mantle sources, whereas 3He detected seaward of the forearc mantle corner likely has only an oceanic source. The highest ratios in the Cascadia forearc coincide with slab depths (˜40-45 km) where metamorphic dehydration of young oceanic lithosphere is expected to release significant fluid and where tectonic tremor occurs, whereas little fluid is expected to be released from the slab depths (˜25-30 km) beneath sites seaward of the corner. These observations provide independent evidence that tremor is associated with deep fluids, and further suggest that high pore pressures associated with tremor may serve to keep fractures open for 3He migration through the ductile upper mantle and lower crust.

  15. Petrological Characteristics of Upper Mantle Peridotites from the Izu-Ogasawara-Mariana-Palau-Yap and Tonga Forearcs; Relation to Troodos and Semail Ophiolites.

    NASA Astrophysics Data System (ADS)

    ISHII, T.; SATO, H.; FUJIOKA, K.

    2001-12-01

    Many ophiolitic igneous complexes in the ocean floor have been reported along trench inner wall of the Izu-Ogasawara-Mariana-Palau-Yap and Tonga trenches. These igneous bodies from the ocean floor are called as proto-ophiolite in this paper. Serpentinite diapiric seamounts have been only reported from the forearc area of the Izu-Ogasawara-Mariana (excluding Southern Mariana) arc-trench system in the world. Petrological characteristics of mantle peridotites constituting those seamounts were summarized in comparison with other trench region peridotites. Mantle peridotites drilled from the Conical seamounts during ODP Leg 125 (Site 779) have distinctive compositions both in bulk rock chemistry and mineral chemistry. Their compositions suggest that they underwent a higher degree of partial melting (more than 30 %) that is related to island arc volcanism in the mantle wedge. Most of compositions of mantle peridotites collected by submersible dives from other serpentinite seamounts (the Pacman seamount by Alvin, the Hahajima seamount by Shinkai 2000 and the Chamorro seamount by Shinkai 6500) in the Izu-Ogasawara-Mariana forearc have also similar compositions to those from the Conical seamount. It indicates that most mantle peridotites from the seamounts are refractory residues (harzburgite and dunite) derived from partial melting in the high degree during the island-arc volcanism, including boninite and island-arc tholeiite. On the other hand, mantle peridotites recovered from the Tonga forearc exhibit wider chemistry including more fertile and intermediate peridotites as well as deplete peridotites, suggesting that the former are residues of relatively lower degrees of partial melting. It is probable that they are related to the volcanism during the formation of the back arc basin. Furthermore, although mantle peridotites of the Tonga forearc are considered to be derived from a layered sequence from the upper crust through the lower crust to the upper mantle rather than

  16. Surviving Women's Learning Experiences from the Tsunami in Aceh

    ERIC Educational Resources Information Center

    Teng, Yan Fang Jane; Yusof, Qismullah

    2014-01-01

    This study investigated surviving women's learning experiences from the 2004 tsunami in Aceh. Women were the majority of casualties and the most vulnerable after the tsunami. Almost a decade later, we used a conceptual framework of experiential learning, critical reflection, and transformative learning to understand the surviving women's…

  17. "The Fruit Caught between Two Stones": The Conflicted Position of Teachers within Aceh's Independence Struggle

    ERIC Educational Resources Information Center

    Lopes Cardozo, Mieke T.A.; Shah, Ritesh

    2016-01-01

    This paper explores the challenging situation faced by teachers as professionals and members of the community in Aceh, Indonesia during the province's civil war. It reveals how teachers' sense of agency during this period was deeply influenced by the economic/material, political and socio-cultural condition at that time -- conditions and…

  18. The role of students' activities in Indonesian realistic mathematics education in primary schools of Aceh

    NASA Astrophysics Data System (ADS)

    Zubainur, Cut Morina; Veloo, Arsaythamby; Khalid, Rozalina

    2015-05-01

    This study aims to explore the implementation of the Indonesian Realistic Mathematics Education (PMRI) in Aceh primary schools, Indonesia. This study investigates the students' mathematics activities involved in the implementation of PMRI and for this purpose; students' mathematics activities in the classroom were observed. Students were observed three times within five weeks during mathematics class, based on PMRI. A total of 25 year five students from a public school participated in this study. Observation check list was used in this study based on ten items. The observation conducted was based on two different time periods which were 105 minutes for group A and 70 minutes for group B. The observation was conducted every 5 minutes. The results show that PMRI is being practised in Aceh, but not completely. This study shows that mathematics activities for those who were taught using PMRI are higher than for those using the traditional approach. Overall, the findings showed that the number of student activities undertaken in PMRI achieved 90.56%. The higher percentage of activities suggests that the Aceh Education Office expands the implementation of PMRI in all primary schools so that learning of mathematics is more effective. This indirectly increases the mathematics achievement of students in Aceh to a higher level on par with Indonesia's national achievement.

  19. A serpentinite-hosted ecosystem in the Southern Mariana Forearc

    PubMed Central

    Ohara, Yasuhiko; Reagan, Mark K.; Fujikura, Katsunori; Watanabe, Hiromi; Michibayashi, Katsuyoshi; Ishii, Teruaki; Stern, Robert J.; Pujana, Ignacio; Martinez, Fernando; Girard, Guillaume; Ribeiro, Julia; Brounce, Maryjo; Komori, Naoaki; Kino, Masashi

    2012-01-01

    Several varieties of seafloor hydrothermal vents with widely varying fluid compositions and temperatures and vent communities occur in different tectonic settings. The discovery of the Lost City hydrothermal field in the Mid-Atlantic Ridge has stimulated interest in the role of serpentinization of peridotite in generating H2- and CH4-rich fluids and associated carbonate chimneys, as well as in the biological communities supported in highly reduced, alkaline environments. Abundant vesicomyid clam communities associated with a serpentinite-hosted hydrothermal vent system in the southern Mariana forearc were discovered during a DSV Shinkai 6500 dive in September 2010. We named this system the “Shinkai Seep Field (SSF).” The SSF appears to be a serpentinite-hosted ecosystem within a forearc (convergent margin) setting that is supported by fault-controlled fluid pathways connected to the decollement of the subducting slab. The discovery of the SSF supports the prediction that serpentinite-hosted vents may be widespread on the ocean floor. The discovery further indicates that these serpentinite-hosted low-temperature fluid vents can sustain high-biomass communities and has implications for the chemical budget of the oceans and the distribution of abyssal chemosynthetic life. PMID:22323611

  20. A serpentinite-hosted ecosystem in the Southern Mariana Forearc.

    PubMed

    Ohara, Yasuhiko; Reagan, Mark K; Fujikura, Katsunori; Watanabe, Hiromi; Michibayashi, Katsuyoshi; Ishii, Teruaki; Stern, Robert J; Pujana, Ignacio; Martinez, Fernando; Girard, Guillaume; Ribeiro, Julia; Brounce, Maryjo; Komori, Naoaki; Kino, Masashi

    2012-02-21

    Several varieties of seafloor hydrothermal vents with widely varying fluid compositions and temperatures and vent communities occur in different tectonic settings. The discovery of the Lost City hydrothermal field in the Mid-Atlantic Ridge has stimulated interest in the role of serpentinization of peridotite in generating H(2)- and CH(4)-rich fluids and associated carbonate chimneys, as well as in the biological communities supported in highly reduced, alkaline environments. Abundant vesicomyid clam communities associated with a serpentinite-hosted hydrothermal vent system in the southern Mariana forearc were discovered during a DSV Shinkai 6500 dive in September 2010. We named this system the "Shinkai Seep Field (SSF)." The SSF appears to be a serpentinite-hosted ecosystem within a forearc (convergent margin) setting that is supported by fault-controlled fluid pathways connected to the decollement of the subducting slab. The discovery of the SSF supports the prediction that serpentinite-hosted vents may be widespread on the ocean floor. The discovery further indicates that these serpentinite-hosted low-temperature fluid vents can sustain high-biomass communities and has implications for the chemical budget of the oceans and the distribution of abyssal chemosynthetic life. PMID:22323611

  1. A serpentinite-hosted ecosystem in the Southern Mariana Forearc

    NASA Astrophysics Data System (ADS)

    Ohara, Yasuhiko; Reagan, Mark K.; Fujikura, Katsunori; Watanabe, Hiromi; Michibayashi, Katsuyoshi; Ishii, Teruaki; Stern, Robert J.; Pujana, Ignacio; Martinez, Fernando; Girard, Guillaume; Ribeiro, Julia; Brounce, Maryjo; Komori, Naoaki; Kino, Masashi

    2012-02-01

    Several varieties of seafloor hydrothermal vents with widely varying fluid compositions and temperatures and vent communities occur in different tectonic settings. The discovery of the Lost City hydrothermal field in the Mid-Atlantic Ridge has stimulated interest in the role of serpentinization of peridotite in generating H2- and CH4-rich fluids and associated carbonate chimneys, as well as in the biological communities supported in highly reduced, alkaline environments. Abundant vesicomyid clam communities associated with a serpentinite-hosted hydrothermal vent system in the southern Mariana forearc were discovered during a DSV Shinkai 6500 dive in September 2010. We named this system the "Shinkai Seep Field (SSF)." The SSF appears to be a serpentinite-hosted ecosystem within a forearc (convergent margin) setting that is supported by fault-controlled fluid pathways connected to the decollement of the subducting slab. The discovery of the SSF supports the prediction that serpentinite-hosted vents may be widespread on the ocean floor. The discovery further indicates that these serpentinite-hosted low-temperature fluid vents can sustain high-biomass communities and has implications for the chemical budget of the oceans and the distribution of abyssal chemosynthetic life.

  2. Crustal Structure of the Northern Chilean Forearc from Ambient Noise Tomography

    NASA Astrophysics Data System (ADS)

    Comte, D.; Carrizo, D.; Roecker, S. W.; Peyrat, S.; Arriaza, R.; Chi, R. K.; Baeza, S.

    2015-12-01

    In addition to being an excellent venue for investigating the tectonics of the Andean margin, northern Chile is of particular interest to seismologists because of its potential for an imminent megathrust earthquake. Such events often trigger destructive seismic activity in the populated forearc, as demonstrated for example in the aftermath of the 2010 Maule event. To investigate the nature of deformation in the forearc, we generated high resolution images of the subsurface from Rayleigh wave dispersion curves derived from cross correlation of ambient noise. The ambient noise data were recorded over a period of three years by 60 stations from three different networks of broad band stations. Because of the proximity of the stations to the Pacific Ocean, we estimated the bias in the estimated Green's functions caused by the asymmetry of the noise distribution using a technique based on that described by Yao and van der Hilst (2009). Our results suggest that this bias can be as large as 5% for some station pairs. The unbiased times are then used to refine phase velocity maps, from which we derived transit times to generate a 3D image of shear wavespeed (Vs) from the surface to about 50 km depth. To first order, low-Vs anomalies correlate well with the geometry of the Atacama Bench Structure (western foreland basin) where leaching processes are related to large incisions in the Atacama Desert (north of 19ºS). In addition, high Vs anomalies correlate with the locations of fossil magmatic arcs developed as trench-parallel belts from the coast to the Altiplano. For example, high Vs correlates with the Jurassic-Cretaceous magmatic arc along the coast, the Paleocene-Oligocene magmatic arc in the central depression, and the Eocene-Oligocene magmatic arc in the Frontal Cordillera. A continuous seismic anomaly of low-Vs, located between 15 - 25 km depth, may be evidence of a weak and/or hydrated zone within the lower continental crust, related to slab-linked upper plate

  3. Magnetic and gravity constraints on forearc upper crustal structure and composition, offshore northeast Japan

    USGS Publications Warehouse

    Finn, C.

    1994-01-01

    Marine magnetic and gravity data from the northeast Japan forearc offer insight to the subsurface structure, density and magnetization from which geologic interpretations and tectonic reconstructions can be made. Positive marine magnetic anomalies, on-land geology, drill hole data, and 2-1/2-dimensional models reveal that Kitakami plutons and possibly their associated volcanic rocks constitute part of the modern forearc basement and lie 100-150 km further east than previously thought. A method to create magnetization and density contrast maps was employed to produce a three-dimensional picture of the forearc basement rock properties averaged over a 14-km thickness. -Author

  4. Fore-arc migration in Cascadia and its neotectonic significance

    NASA Astrophysics Data System (ADS)

    Wells, Ray E.; Weaver, Craig S.; Blakely, Richard J.

    1998-08-01

    Neogene deformation, paleomagnetic rotations, and sparse geodetic data suggest the Cascadia fore arc is migrating northward along the coast and breaking up into large rotating blocks. Deformation occurs mostly around the margins of a large, relatively aseismic Oregon coastal block composed of thick, accreted seamount crust. This 400-km-long block is moving slowly clockwise with respect to North America about a Euler pole in eastern Washington, thus increasing convergence rates along its leading edge near Cape Blanco, and creating an extensional volcanic arc on its trailing edge. Northward movement of the block breaks western Washington into smaller, seismically active blocks and compresses them against the Canadian Coast Mountains restraining bend. Arc-parallel transport of fore-arc blocks is calculated to be up to 9 mm/yr, sufficient to produce damaging earthquakes in a broad deformation zone along block margins.

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    At subduction zones, thermal modeling predict that the shallow part of the downgoing oceanic crust (< 80 - 100 km depth to the slab) is usually too cold to cross the water-rich solidus and melts beneath the forearc. Yet, the occasional occurrence of adakites, commonly considered as slab melts, in the forearc region challenges our understanding of the shallow subduction processes. Adakites are unusual felsic rocks commonly associated with asthenospheric slab window opening or fast subduction of young (< 25 Ma) oceanic plate that enable slab melting at shallow depths; but their genesis has remained controversial. Here, we present a new approach that provides new constraints on adakite petrogenesis in hot subduction zones (the Philippines) and above an asthenospheric window (Baja California, Mexico). We use amphibole compositions to estimate the magma storage depths and the composition of the parental melts to 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.

  6. Post-magmatic tectonic deformation of the outer Izu-Bonin-Mariana forearc system: initial results of IODP Expedition 352

    NASA Astrophysics Data System (ADS)

    Kurz, Walter; Ferré, Eric C.; Robertson, Alastair; Avery, Aaron; Christeson, Gail L.; Morgan, Sally; Kutterorf, Steffen; Sager, William W.; Carvallo, Claire; Shervais, John; Party IODP Expedition 352, Scientific

    2015-04-01

    IODP Expedition 352 was designed to drill through the entire volcanic sequence of the Bonin forearc. Four sites were drilled, two on the outer fore arc and two on the upper trench slope. Site survey seismic data, combined with borehole data, indicate that tectonic deformation in the outer IBM fore arc is mainly post-magmatic. Post-magmatic extension resulted in the formation of asymmetric sedimentary basins such as, for example, the half-grabens at sites 352-U1439 and 352-U1442 located on the upper trench slope. Along their eastern margins these basins are bounded by west-dipping normal faults. Sedimentation was mainly syn-tectonic. The lowermost sequence of the sedimentary units was tilted eastward by ~20°. These tilted bedding planes were subsequently covered by sub-horizontally deposited sedimentary beds. Based on biostratigraphic constraints, the minimum age of the oldest sediments is ~ 35 Ma; the timing of the sedimentary unconformities lies between ~ 27 and 32 Ma. At sites 352-U1440 and 352-U1441, located on the outer forearc, post-magmatic deformation resulted mainly in strike-slip faults possibly bounding the sedimentary basins. The sedimentary units within these basins were not significantly affected by post-sedimentary tectonic tilting. Biostratigraphic ages indicate that the minimum age of the basement-cover contact lies between ~29.5 and 32 Ma. Overall, the post-magmatic tectonic structures observed during Expedition 352 reveal a multiphase tectonic evolution of the outer IBM fore arc. At sites 352-U1439 and 352-U1442, shear with dominant reverse to oblique reverse displacement was localized along distinct subhorizontal cataclastic shear zones as well as steeply dipping slickensides and shear fractures. These structures, forming within a contractional tectonic regime, were either re-activated as or cross-cut by normal-faults as well as strike-slip faults. Extension was also accommodated by steeply dipping to subvertical mineralized veins and

  7. Is the Central America forearc sliver part of the North America plate?

    NASA Astrophysics Data System (ADS)

    Guzman-Speziale, M.

    2012-04-01

    The Central America Forearc sliver is located between the Central America volcanic arc and the Middle America trench. Several authors have suggested that the forearc is being displaced to the northwest with respect to the Caribbean plate; they point to right-lateral, normal-faulting earthquakes along the Central America volcanic arc as prime evidence of this displacement. Apparently, the forearc continues to the northwest into southeastern Mexico, although this portion of the forearc is not being displaced. I present evidence that suggests that the forearc indeed continues into southeastern Mexico and that it belongs to the North America plate. Physiographically, there is a continuity of the forearc into the Coastal plains of southeastern (Chiapas) Mexico, across the Motagua and Polochic faults. Offshore, cross-sections of the Middle America trench are similar along the mexican (Chiapas) segment, and the Central American segment. Furthermore, at the northwestern end of the coastal plain there are no compressive structures, which suggests that the coastal plain is not being displaced to the northwest. As a matter of fact, fault-plane solutions for shallow earthquakes show extension rather than compression. Shallow, interplate earthquakes along the trench show similar parameters along both segments. P-axes and earthquake slip vectors have consistent azimuths, which relate better with Cocos-North America convergence than with Cocos-Caribbean. Azimuth of T-axes for normal-faulting earthquakes also agree well with Cocos-North America convergence. Similarity in several parameters is thus found across both segments, the Chiapas coastal plain and the Central America forearc sliver proper. This suggests that both segments are continuous and probably one and the same, and belonging to the North America plate. Perhaps more properly, the forearc sliver extends into southeastern Mexico and is part of the zone of deformation associated to the Cocos-North America-Caribbean plates

  8. An Integrated Study of the Kinematics and Evolution of Fault Systems in the Hellenic Margin, Crete, Greece: Insight into Forearc Development above a Retreating Subduction Zone

    NASA Astrophysics Data System (ADS)

    Gallen, S. F.; Wegmann, K. W.; Bohnenstiehl, D. R.

    2012-12-01

    Accommodating ~ 36 mm/yr of convergence between the African and Eurasian tectonic plates the Hellenic Subduction zone is the largest, fastest and most seismically active subduction zone in the Mediterranean. Long-lived Cenozoic subduction of the African slab has resulted in the construction of a large south-facing subduction wedge. Rollback of the African slab likely initiated sometime in the Eocene and continues today. This geodynamic setting has given rise to a forearc characterized by a series of dramatic 2-4 km high topographic escarpments south of the Island of Crete; one of the few subaerial forearc highs along the Hellenic margin. It is generally agreed that these escarpments represent the surface expression of large intra-crust faults, yet the kinematics of faulting remains contentious in contemporary scientific literature. Different geologic and geophysical datasets have been used to argue that these structures accommodate either shortening due to continued plate convergence or extension driven by processes related to slab rollback. Resolving the debate over the kinematics of the large-scale structures embedded in the Hellenic forearc is paramount to our understanding of seismic hazards, the development of forearc basins, and the geodynamic processes operating in this region. We present results from a study of the tectonic geomorphology and structural geology of the south-central coastline of Crete that constrain the kinematics and evolution of one of the aforementioned fault systems that is related to the construction of a large forearc basin known as the Ptolemy trough. Field surveys and geochronology of marine terraces reveal the pattern of late Quaternary uplift along the south-central coastline. Two large south-dipping extensional faults, which extend offshore into the Ptolemy trough, are found to offset Pleistocene marine terraces and are inferred to be active with average slip rates of ca. 0.5 mm/yr. The hanging walls and footwalls of these faults

  9. Structural and stratigraphic evolution of Aleutian convergent-margin basins - Ridge crest to trench floor

    SciTech Connect

    Scholl, D.W.; Ryan, H.F.; Geist, E.L.; Vallier, T.L.

    1988-01-01

    The Aleutian Ridge lies along nearly 2,000 km of the north Pacific's obliquely converging plate boundary with North America. Since middle Eocene time, convergent-margin basins have repeatedly formed here, typically as summit basins along the ridge crest, and as forecarc basins on the landward trench slope. Thick (1-4 km) sequences of terrigenous, hemipelagic, and biogenic debris have accumulated in these depressions, which are mostly intra-arc structures floored by arc-basement rocks. Summit and forearc basins formed as a consequence of plate-boundary coupling and the application of compressional and right-lateral shear stresses to the arc massif. Basins typically evolved along shear zones in response to transtensional processes, and as trailing-edge grabens behind rotating blocks of arc massif. In the late Cenozoic, high rates of trench sedimentation led to the growth of an accretionary complex that underthrust forearc basement. Wedging and improved plate coupling elevated and laterally shifted blocks of outer forearc rocks, creating much of the structural framework of the regionally extensive Aleutian Terrace forearc basin. Changes in plate-boundary conditions that affected the ridge's volcanic activity and regional elevation importantly influenced basinal sedimentation. Changes of greatest significant were a major shift in convergence direction and rate about 42 Ma (reduced volcanism), ridge underthrusting by increasingly younger ocean crust in Oligocena and Miocene time (arc elevation), and the combination of more orthogonal underthrusting and the subduction of a dead spreading center 5-120 Ma (arc subsidence).

  10. Grassroots development and upwards accountabilities: tensions in the reconstruction of Aceh's fishing industry.

    PubMed

    Dixon, Rowan; McGregor, Andrew

    2011-01-01

    This article explores the tensions between aid funding and grassroots development goals in the context of post-disaster fisheries reconstruction in Aceh, Indonesia. We argue that both short- and long-term grassroots goals are distorted by upward accountability requirements which lead to unsatisfactory aid outcomes. Our analysis employs the concept of aid webs and draws on fifty-one formal interviews with stakeholders in Aceh in 2007/2008. The findings initially concentrate on the impacts of upward accountability on project cycles, with a particular focus on the problematic incorporation of private boat-building contractors and commercial values during the implementation phase. We then discuss the more subtle, long-term impacts of upward accountability on the professionalization of community institutions — in this case, the Panglima Laot Lhok. We conclude with a few observations about the hybrid institutions — combining elements of local and development cultures — that are produced within the current political economy of aid. PMID:22235491

  11. Slab roll-back and trench retreat as controlling factor for basin subsidence in southern Central America

    NASA Astrophysics Data System (ADS)

    Brandes, Christian; Winsemann, Jutta

    2015-04-01

    Slab roll-back and trench retreat are important factors for basin subsidence, magma generation and volcanism in arc-trench systems. Based on the sedimentary and tectonic record of the southern Central American island-arc we conclude that repeated phases of slab roll-back and trench retreats occurred the arc-trench system since the Late Cretaceous. These trench retreats were most probably related to the subduction of oceanic plateaus and seamounts and effected both the fore-arc and back-arc evolution. We used numerical basin modelling techniques to analyse the burial history of fore-arc and back-arc basins in Central America and combined the results with field data of the sedimentological evolution of the basin-fills. From the basin models, geohistory curves were extracted for the fore-arc and back-arc basins to derive the subsidence evolution. The Sandino Fore-arc Basin is characterized by low subsidence during the first 40 Myr. Since the Late Cretaceous the basin has a linear moderate subsidence with a phase of accelerated subsidence in the Oligocene. In the North and South Limón Back-arc Basin, subsidence started at approximately the same time as in the Sandino Fore-arc Basin. The North and South Limón Basins show a linear subsidence trend in the Paleocene and Eocene. Evidence for trench retreats is given by pulses of uplift in the outer-arc area, followed by subsidence in both the fore-arc and back-arc basins. The first slab roll-back probably occurred during the Early Paleocene. This is indicated by the collapse of carbonate platforms, and the re-deposition of large carbonate blocks into deep-water turbidites. A new pulse of uplift or decreased subsidence, respectively during the Late Eocene is attributed to subduction of rough crust. A subsequent slab detachment and the establishment of a new subduction zone further westward was described by Walther et al. (2000). Strong uplift affected the entire fore-arc area, which led to the deposition of very coarse

  12. Detrital zircon provenance analysis of the Great Valley Group, California: Evolution of an arc-forearc system

    USGS Publications Warehouse

    DeGraaff-Surpless, K.; Graham, S.A.; Wooden, J.L.; McWilliams, M.O.

    2002-01-01

    The improved resolution of sediment provenance from detrital zircon analysis of Great Valley stratigraphy enables recognition of previously undocumented arc magmatism and the evolution of regional drainage systems within the Cretaceous arc-forearc system related to uplift, magmatism, and structure in the arc. Great Valley detrital zircon age data confirm previous studies that indicate that the locus of the sediment source in the southern Sierra Nevada arc migrated east with the active volcanic front and suggest rapid rates of uplift and unroofing of the southern arc. Sacramento Valley detrital zircon age data indicate a more complex history of drainage in the northern Klamath-Sierran arc than previously documented. Detrital zircon age distributions from the Cache Creek section of the Great Valley Group broaden through time from nearly unimodal age distributions to signatures with multiple age peaks. This transition to more broadly distributed detrital zircon age spectra likely results from a combination of (1) expanding subaerial drainage systems from highly localized to more broadly distributed catchments; (2) changing shelf and submarine-canyon morphology with rising sea level and/or basin subsidence; (3) increased degree of dissection of the Klamath-Sierran arc; and (4) potential drainage capture and redirection within the arc. Sacramento Valley detrital zircon age data also record a pulse of Late Jurassic to Early Cretaceous magmatism in the northwestern Sierra Nevada arc, an age of Cordilleran magmatism and deformation represented by limited exposure in the modern Sierra Nevada. These results offer significant new insights into the evolution of a well-studied arc-forearc system.

  13. Submarine Landslides and Mass-Transport Deposition in the Nankai fore-arc

    NASA Astrophysics Data System (ADS)

    Strasser, M.; Henry, P.; Kanamatsu, T.; Moe, K.; Moore, G. F.; IODP Expedition 333 Scientists

    2011-12-01

    Multiple lines of evidence exist for a range of sediment mass movement processes within the shallow megasplay fault zone (MSFZ) area and the adjacent slope basin in the outer fore-arc of the Nankai subduction zone, Japan. Diagnostic features observed in 3-D reflection seismic data and in cores from Integrated Ocean Drilling Program (IODP) Expedition 316 document a complex mass movement history spanning at least ˜2.87 million years. Various modes and scales of sediment remobilization can be related to the different morphotectonic settings in which they occurred and allow integration of knowledge on the spatial and temporal distribution of submarine landslides into a holistic reconstruction of the tectonostratigraphic evolution. New data from the most-recent Nankai IODP Expedition 333, which drilled and cored a Pleistocene-to-Holocene succession of the slope-basin seaward of the MSFZ, provides unprecedented details on submarine landslide processes occurring over the last Million year. The slope-basin represents the depocentre for downslope sediment transport and is characterized in 3-D reflection seismic data by several mass-transport deposits (MTDs), including an up to 180 m thick MTD. Here we present D/V Chikyu shipboard results and first post cruise results from Site C0018, including litho- bio- magneto- tephra- and stable isotope-stratigraphy, X-ray computed tomography analysis and physical properties data. Six MTDs were identified from visual core description and X-ray CT-scans. The thickest MTD is also the oldest (emplaced between 0.85 and 1.05 Ma) and it coincides with a lithological transition between a sandy turbidite sequence below, and ash-bearing hemipelagites comprising several MTDs above. Deformation styles within the MTD are heterogeneous: intervals of disturbed sediments are interbedded within intervals inferred to retain original, coherent bedding. In three occurrences the base of the MTD is defined by a shear zone within fine-grained sediments

  14. Structure and tectonics of a Lower Ordovician forearc ophiolite in central western Maine

    SciTech Connect

    Stetzer, L.M.; Dilek, Y. . Dept. of Geology and Geography)

    1993-03-01

    The Lower Ordovician Boil Mountain ophiolite complex (BMO) in central western Maine occurs in the Gander tectonic zone, nearly 100 km SE of the main Appalachian ophiolite belt, and represents part of the Iapetus oceanic domain. It is exposed in an ENE trending narrow zone immediately south of the Precambrian Chain Lakes massif (CLM). The contact between the CLM and the BMO is characterized by a steeply to vertically south-dipping shear zone composed of several fault planes, which display subhorizontal slickenside lineations with sinistral sense of shearing and counterclockwise rotated porphyroclasts. The BMO consists mainly of pyroxenite, gabbro, diorite, plagiogranite, autobreccia, mafic to felsic volcanic, volcaniclastic, and hemipelagic sedimentary rocks, and contacts between these lithologic units are commonly vertical and faulted. Autobreccia outcrops containing clasts and blocks of serpentinite, diabase, pillowed basalt, and radioalarian chert in a medium-grained hemipelagic matrix indicates deposition penecontemporaneous with ocean floor tectonism during evolution of the ophiolite. Extrusive rocks include basaltic, massive to pillow-lava flows, and andesites, dacites, and rhyolites and are commonly metamorphosed up to a lower-greenschist facies. The BMO is overlain to the SE by a melange-flysch sequence composed mainly of metapelite, metagraywacke, phyllite, and slate with abundant volcanic material suggesting alternated shallow- and deep-water sedimentation in a forearc basin. These relations and the observed structures in the ophiolite indicate its development in an oceanic environment with a low magma budget and active vertical tectonism. The available geochemical data show low Ti, Zr, Y, Cr, and REE contents of volcanic rocks suggesting a depleted magma source in a suprasubduction zone tectonic setting for the ophiolite.

  15. BOLIVAR Project: A New Model for Grenada and Tobago Basin Evolution

    NASA Astrophysics Data System (ADS)

    Christeson, G. L.; Mann, P.; Escalona, A.

    2005-12-01

    The Grenada basin, located in the SE Caribbean, is bounded to the northwest by the Aves Ridge and to the southeast by the Lesser Antilles Arc and Tobago basin. Existing tectonic models for Grenada basin evolution are based on the assumption that the Grenada basin fits into the traditional backarc model, with the Grenada basin formed by rifting of the Lesser Antilles arc away from the Aves Ridge. However our analysis of new seismic reflection and refraction data, acquired during the 2004 BOLIVAR program, suggests that the Grenada and Tobago basins were connected as a single basin during the Paleogene. Uplift of the Lesser Antilles arc and associated platform initiated during early to middle Miocene; the arc formed a barrier to sedimentation between the two basins by the late Miocene. We suggest a new tectonic model for evolution of these basins: 1) Paleogene extension of at least 70 km of the preexisting forearc of the Great Arc of the Caribbean (Aves Ridge) by the mechanisms of slab rollback and flexural subsidence. 2) Flexural and thermal subsidence ceases in the middle Eocene, producing a wide, deep-marine forearc basin encompassing the present-day Grenada and Tobago basins. 3) Oblique plate convergence between the Caribbean and South American plates causes a backthrust response in the weakened and thinned crust of the Grenada/Tobago forearc basin during the late Oligocene to middle Miocene. 4) Magmatism in the Lesser Antilles arc builds a ridge on the inverted forearc that becomes a major sediment barrier between the Grenada and Tobago basins during post-middle Miocene.

  16. Tectonic accretion and underplating of mafic terranes in the Late Eocene intraoceanic fore-arc of New Caledonia (Southwest Pacific): geodynamic implications

    NASA Astrophysics Data System (ADS)

    Cluzel, Dominique; Aitchison, Jonathan C.; Picard, Christian

    2001-10-01

    This paper deals with the tectonic events that result in the accretion of mafic terranes in the fore-arc region and a close juxtaposition of ultramafic rocks, low grade and high-grade mafic terranes in many collisional orogens. The example is taken from New Caledonia where tectonic accretion, subduction, underplating and obduction of mafic terranes took place during the late Eocene in an intra-oceanic forearc setting. The late Eocene tectonic complex comprised three major terranes: an overlying ultramafic, mainly harzburgitic allochthon named the Ophiolitic Nappe, an intermediate mafic, mainly basaltic off-scraped melange, composed of kilometre-scale slices of oceanic upper crust, called the Poya Terrane, parts of which have been metamorphosed into an eclogite/blueschist facies complex, the Pouebo Terrane; and a lower, continental basement formed by the Norkolk Ridge terranes. Based upon exhaustive sampling of the mafic terranes and field surveys, our tectonic, micropaleontologic and geochemical data reveal that Poya and Pouebo terranes rocks originally formed within one single Campanian to late Paleocene oceanic basin, floored by tholeiitic basalt associated with some minor seamount-related intraplate alkali basalt. The tholeiitic basalt displays a continuous range of compositions spanning between "undepleted" and "depleted" end-members; the former being volumetrically predominant. The overall geochemical and isotopic features indicate an origin from a prominently heterogeneous mantle source during the opening of a marginal basin, the South Loyalty Basin, which almost completely disappeared during Eocene convergence. The opening of this basin originally located to the east of the Norfolk Ridge was synchronous with that of Tasman Sea basin as a consequence of oceanward migration of the west-dipping Pacific subduction zone. Establishing the origin of the ultramafic Ophiolitic Nappe is beyond the scope of this paper; however, it appears to be genetically unrelated to

  17. Cascadia subducting plate fluids channelled to fore-arc mantle corner: ETS and silica deposition

    NASA Astrophysics Data System (ADS)

    Hyndman, R. D.; McCrory, P. A.; Wech, A.; Kao, H.; Ague, J.

    2015-06-01

    In this study we first summarize the constraints that on the Cascadia subduction thrust, there is a 70 km gap downdip between the megathrust seismogenic zone and the Episodic Tremor and Slip (ETS) that lies further landward; there is not a continuous transition from unstable to conditionally stable sliding. Seismic rupture occurs mainly offshore for this hot subduction zone. ETS lies onshore. We then suggest what does control the downdip position of ETS. We conclude that fluids from dehydration of the downgoing plate, focused to rise above the fore-arc mantle corner, are responsible for ETS. There is a remarkable correspondence between the position of ETS and this corner along the whole margin. Hydrated mineral assemblages in the subducting oceanic crust and uppermost mantle are dehydrated with downdip increasing temperature, and seismic tomography data indicate that these fluids have strongly serpentinized the overlying fore-arc mantle. Laboratory data show that such fore-arc mantle serpentinite has low permeability and likely blocks vertical expulsion and restricts flow updip within the underlying permeable oceanic crust and subduction shear zone. At the fore-arc mantle corner these fluids are released upward into the more permeable overlying fore-arc crust. An indication of this fluid flux comes from low Poisson's Ratios (and Vp/Vs) found above the corner that may be explained by a concentration of quartz which has exceptionally low Poisson's Ratio. The rising fluids should be silica saturated and precipitate quartz with decreasing temperature and pressure as they rise above the corner.

  18. Serpentinization at Isua, a forearc environment identified by Zn isotopes

    NASA Astrophysics Data System (ADS)

    Pons, M.; Quitté, G.; Rosing, M.; Douchet, C.; Reynard, B.; Mills, R.; Albarede, F.

    2010-12-01

    The present study deals with the isotope compositions of Zn in the 3.8 Ga old serpentinites from the Archean complex of Isua, Greenland. The sample set includes igneous, metamorphic, and sedimentary rocks such as serpentinites, metagabbros, amphibolites, talc schists, and metagreywackes. For comparison, modern serpentines from Mexico and the Alps were also analyzed together with deep-sea clays from the Pacific, and metalliferous sediments from the East Pacific Rise and from the TAG area. The modern serpentinites show the enrichment in heavy zinc, with δ66/64Zn values from +0.21 to +0.52‰, typical of the modern igneous rocks. In contrast, the δ66/64Zn values of the Isua serpentines are conspicuously negative and range from -0.48 ‰ to +0.04 ‰ and can be clearly distinguished from other both igneous and sedimentary lithologies from the same area, in which the δ66/64Zn values range from -0.08 to 0.36‰ and overlap with the range of modern igneous rocks. Along mid-oceanic ridges, serpentinization takes place in high-temperature hydrothermal fields (typically > 250°C). The modern serpentinites analyzed seem to have formed in that way and formed by interaction between peridotites and low-pH, high-temperature, high-salinity seawater. Under such conditions, zinc is leached from rock by hydrothermal fluids as Zn2+ [1]. During this reaction, Zn from the rocks becomes depleted in light isotopes and its δ66/64Zn rises. The higher the temperature of the fluid, the lighter its isotope Zn composition becomes [2]. The remarkably low δ66/64Zn observed in Isua serpentinites indicates a different context of alteration and suggests reaction of peridotites with a low-temperature and high-pH fluid, which stabilizes Zn-sulfide complexes in solution. This is consistent with the arc subduction zone model of Isua [3]. Our δ66/64Zn data suggest that the closest equivalents of Isua serpentinites are the serpentinite mud volcanoes from the Mariana forearc [4]. This arc is

  19. Overriding plate deformation and variability of fore-arc deformation during subduction: Insight from geodynamic models and application to the Calabria subduction zone

    NASA Astrophysics Data System (ADS)

    Chen, Zhihao; Schellart, Wouter P.; Duarte, João. C.

    2015-10-01

    In nature, subducting slabs and overriding plate segments bordering subduction zones are generally embedded within larger plates. Such large plates can impose far-field boundary conditions that influence the style of subduction and overriding plate deformation. Here we present dynamic laboratory models of progressive subduction in three-dimensional space, in which the far-field boundary conditions at the trailing edges of the subducting plate (SP) and overriding plate (OP) are varied. Four configurations are presented: Free (both plates free), SP-Fixed, OP-Fixed, and SP-OP-Fixed. We investigate their impact on the kinematics and dynamics of subduction, particularly focusing on overriding plate deformation. The results indicate that the variation in far-field boundary conditions has an influence on the slab geometry, subduction partitioning, and trench migration partitioning. Our models also indicate that in natural (narrow) subduction zones, assuming a homogeneous overriding plate, the formation of back-arc basins (e.g., Tyrrhenian Sea, Aegean Sea, and Scotia Sea) is generally expected to occur at a comparable location (250-700 km from the trench), irrespective of the boundary condition. In addition, our models indicate that the style of fore-arc deformation (shortening or extension) is influenced by the mobility of the overriding plate through controlling the force normal to the subduction zone interface (trench suction). Our geodynamic model that uses the SP-OP-Fixed setup is comparable to the Calabria subduction zone with respect to subduction kinematics, slab geometry, trench curvature, and accretionary configuration. Furthermore, the model can explain back-arc and fore-arc extension at the Calabria subduction zone since the latest middle Miocene as a consequence of subduction of the narrow Calabrian slab and the immobility of the subducting African plate and overriding Eurasian plate. This setting induced strong trench suction, driving fore-arc extension, and

  20. The Structural Evolution of the Calabrian Forearc: A Multidisciplinary Approach to Investigating Time-Transgressive Deformation in a Subduction-Rollback System

    NASA Astrophysics Data System (ADS)

    Reitz, Margaret A.

    This dissertation investigates the temporal and spatial variations in deformation of the Calabrian forearc during the evolution of the subduction-rollback system. In addition to contributing new data to the area, I develop three strategies for understanding recent and active deformation by linking long-term structural data with short-term geomorphological data. First, setting a "baseline" of deformation is important when studying plate boundaries. Through the structural mapping of an uplifted forearc basin, I conclude that rapid rollback is characterized by tectonic quiescence in the Calabrian forearc when it is located far from collision (from ~12 Ma -- ~5 Ma). This "baseline" provides a framework from which I interpret younger phases of deformation. In the middle Pliocene (~5-4 Ma), an arc-parallel shortening event characterizes the first stage of forearc collision in my field area. These folded sediments are later tilted, but structural data from the field cannot constrain the age or structure responsible for this youngest phase of deformation. The Neto River dissects this tilted surface opening up the possibly of linking structural data with geomorphic data from river erosion. I collected a transect of river sediment samples for 10Be analysis to determine variation in catchment-wide erosion rates through the modern day deformation. I, then, developed a numerical model that describes changes in erosion rate through time with the structural growth of the tilted surface. The model is the first of its kind to use catchment-wide erosion rates to constrain a structural model. The model results constrain the age of the beginning of deformation to 850 ka and suggest that a fold with a migrating hinge caused tilting of the surface. The model provides the basis for my hypothesis that the forearc is experiencing an arc-perpendicular shortening strain, which contradicts conclusions from GPS data and the well-documented extension in the western part of the forearc. To

  1. Seismic evidence for widespread serpentinized forearc upper mantle along the Cascadia margin

    NASA Astrophysics Data System (ADS)

    Brocher, Thomas M.; Parsons, Tom; Tréhu, Anne M.; Snelson, Catherine M.; Fisher, Michael A.

    2003-03-01

    Petrologic models suggest that dehydration and metamorphism of subducting slabs release water that serpentinizes the overlying forearc mantle. To test these models, we use the results of controlled-source seismic surveys and earthquake tomography to map the upper mantle along the Cascadia margin forearc. We find anomalously low upper-mantle velocities and/or weak wide-angle reflections from the top of the upper mantle in a narrow region along the margin, compatible with recent teleseismic studies and indicative of a serpentinized upper mantle. The existence of a hydrated forearc upper-mantle wedge in Cascadia has important geological and geophysical implications. For example, shearing within the upper mantle, inferred from seismic reflectivity and consistent with its serpentinite rheology, may occur during aseismic slow slip events on the megathrust. In addition, progressive dehydration of the hydrated mantle wedge south of the Mendocino triple junction may enhance the effects of a slab gap during the evolution of the California margin.

  2. How do subduction processes contribute to forearc Andean uplift? Insights from numerical models

    NASA Astrophysics Data System (ADS)

    Martinod, J.; Regard, V.; Letourmy, Y.; Henry, H.; Hassani, R.; Baratchart, S.; Carretier, S.

    2016-05-01

    We present numerical models to study how changes in the process of subduction may explain the observed Quaternary uplift of the Andean forearc region. Indeed, most segments of the South American Pacific coasts between 16 and 32° S have been uplifting since the Lower Pleistocene, following a period of stability of the forearc region. Models confirm that local uplift is expected to occur above ridges, this phenomenon being predominant in central Peru where the Nazca Ridge is subducting. We investigate the effects of slab pull, interplate friction and convergence velocity on the vertical displacements of the overriding plate. We propose that the global tendency to coastal uplift is accompanying the deceleration of the Nazca-South America convergence that occurred in the Pleistocene. In contrast, forearc subsidence may accompany increasing convergence velocities, as suggested by the subsidence history of the South America active margin.

  3. Forearc deformation and great subduction earthquakes: implications for cascadia offshore earthquake potential.

    PubMed

    McCaffrey, R; Goldfinger, C

    1995-02-10

    The maximum size of thrust earthquakes at the world's subduction zones appears to be limited by anelastic deformation of the overriding plate. Anelastic strain in weak forearcs and roughness of the plate interface produced by faults cutting the forearc may limit the size of thrust earthquakes by inhibiting the buildup of elastic strain energy or slip propagation or both. Recently discovered active strike-slip faults in the submarine forearc of the Cascadia subduction zone show that the upper plate there deforms rapidly in response to arc-parallel shear. Thus, Cascadia, as a result of its weak, deforming upper plate, may be the type of subduction zone at which great (moment magnitude approximately 9) thrust earthquakes do not occur. PMID:17813913

  4. Basins in ARC-continental collisions

    USGS Publications Warehouse

    Draut, Amy E.; Clift, Peter D.

    2012-01-01

    Arc-continent collisions occur commonly in the plate-tectonic cycle and result in rapidly formed and rapidly collapsing orogens, often spanning just 5-15 My. Growth of continental masses through arc-continent collision is widely thought to be a major process governing the structural and geochemical evolution of the continental crust over geologic time. Collisions of intra-oceanic arcs with passive continental margins (a situation in which the arc, on the upper plate, faces the continent) involve a substantially different geometry than collisions of intra-oceanic arcs with active continental margins (a situation requiring more than one convergence zone and in which the arc, on the lower plate, backs into the continent), with variable preservation potential for basins in each case. Substantial differences also occur between trench and forearc evolution in tectonically erosive versus tectonically accreting margins, both before and after collision. We examine the evolution of trenches, trench-slope basins, forearc basins, intra-arc basins, and backarc basins during arc-continent collision. The preservation potential of trench-slope basins is low; in collision they are rapidly uplifted and eroded, and at erosive margins they are progressively destroyed by subduction erosion. Post-collisional preservation of trench sediment and trench-slope basins is biased toward margins that were tectonically accreting for a substantial length of time before collision. Forearc basins in erosive margins are usually floored by strong lithosphere and may survive collision with a passive margin, sometimes continuing sedimentation throughout collision and orogeny. The low flexural rigidity of intra-arc basins makes them deep and, if preserved, potentially long records of arc and collisional tectonism. Backarc basins, in contrast, are typically subducted and their sediment either lost or preserved only as fragments in melange sequences. A substantial proportion of the sediment derived from

  5. Studies of the Southern Izu-Bonin-Mariana (IBM) Forearc using Shinkai 6500: Watery Glimpses of an In Situ Forearc Ophiolite

    NASA Astrophysics Data System (ADS)

    Ohara, Y.; Reagan, M. K.; Bloomer, S. H.; Fryer, P.; Fuji, A.; Hickey-Vargas, R.; Imoto, H.; Ishii, T.; Ishizuka, O.; Johnson, J.; Michibayashi, K.; Ribiero, J.; Stern, R. J.; Uehara, S.

    2008-12-01

    Two expeditions with research submersible Shinkai 6500 and R/V Yokosuka (YK06-12 and YK08-08-2) studied the lithospheric structure of the Mariana forearc south of Guam. Igneous crustal and mantle rocks are well exposed along the inner trench wall because of the great depth of the trench, low sediment flux, and recent shearing and extension along N-S and E-W faults. A total of 12 dives studied crust between 6500 and 2000 mbsl along ~500km of the forearc. West Santa Rosa Bank Fault (WSRBF), a major N-S fault at ~144°10'E above a tear in the subducted slab, marks an important lithospheric boundary, with very thin crust to the west and thicker crust to the east. 3 of 4 dives west of WSRBF recovered peridotite and a fourth (#1096) sampled a scarp between 6100 and 5400m depth exposing multiple flows of fresh basalt. This may mark a previously unknown, N-S oriented forearc rift (W. Santa Rosa Terrane, WSRT). The zone of thin crust and shallow peridotite continues west as far as ~143°07'E, as demonstrated by the fact that 3 out of 4 Shinkai dives and 15 out of 18 total bottom samplings in this region recovered peridodite; thicker crust lies west of this. The concentration of shallow (<25km deep) seismicity between 143- 144°E further indicates a broad zone of crustal extension in the SE part of the Mariana Trough encompassing the WSRT. In contrast, peridotite was not recovered from 8 dives east of WSRBF and only recovered in 3 out of 19 total samplings; these peridotites may sample incipient serpentinite mud volcanoes forming along the disrupted outer forearc. Diabase was recovered from 3 out of 8 Shinkai dives east of the WSRBF and 4 out of 19 total samplings, indicating that dikes or sills are exposed at depths accessible to Shinkai, consistent with what is likely to be exposed for Mariana inner forearc crustal thicknesses of ~20-25 km. Gabbro and pyroxenite is reasonably common among samples from west of WSRBF (0 of 4 Shinkai dives; 7 of 26 total samples) and scarcer

  6. GPS Constraints on Lesser Antilles Forearc Motion and Rigid Caribbean Plate

    NASA Astrophysics Data System (ADS)

    López, A. M.; Stein, S.; Sella, G.; Dixon, T. H.; Calais, E.; Jansma, P. E.

    2005-05-01

    We are using a decade of Global Positioning System data to address two tectonic problems of the Caribbean (CA) plate; 1) Whether a forearc sliver exists along the Lesser Antilles forearc and if so what is its dynamics and location, and 2) Whether the Caribbean plate is deforming internally. We approach this problem by developing GPS-derived velocity vectors at sites within the CA plate and its boundaries and comparing them to four decades of earthquake data. In a number of subduction zones, misfits between slip vectors and predicted convergence azimuths from Euler vectors suggest the presence of a forearc sliver, where trench-parallel motion is accommodated along a strike-slip fault system. Such a situation may be occurring at the eastern boundary of the CA plate along the Lesser Antilles (LA) forearc, where the North America (NA) plate subducts obliquely. Comparing slip vectors of shallow (0-60 km) thrust events to the predicted motions of GPS-based Euler vectors show a systematic northerly misfit, suggesting a trench-parallel component of motion taken up by the forearc sliver. This possibility can be tested with GPS data from the forearc. In addition, we use new GPS data to constrain the internal rigidity of the plate. Previous GPS work yielded a possible upper bound on internal deformation of 4-6 mm/yr. With an expansion in the data set on critically located stations in the CA plate (SANA, ROJO, CRO1 and AVES), we have computed new sets of Euler vector pairs for the CA-NA and CA-South America plate pairs.

  7. Multi-Channel Seismic Images of the Mariana Forearc: EW0202 Initial Results

    NASA Astrophysics Data System (ADS)

    Oakley, A. J.; Goodliffe, A. M.; Taylor, B.; Moore, G. F.; Fryer, P.

    2002-12-01

    During the Spring of 2002, the Mariana Subduction Factory was surveyed using multi-channel seismics (MCS) as the first major phase of a US-Japanese collaborative NSF-MARGINS funded project. The resulting geophysical transects extend from the Pacific Plate to the West Mariana remnant arc. For details of this survey, including the results from the back-arc, refer to Taylor et al. (this session). The incoming Pacific Plate and its accompanying seamounts are deformed by plate flexure, resulting in extension of the upper crust as it enters the subduction zone. The resultant trench parallel faults dominate the bathymetry and MCS data. Beneath the forearc, in the southern transects near Saipan, the subducting slab is imaged to a distance of 50-60 km arcward. In addition to ubiquitous trench parallel normal faulting, a N-S transect of the forearc clearly shows normal faults perpendicular to the trench resulting from N-S extension. On the east side of the Mariana Ridge, thick sediment packages extend into the forearc. Directly east of Saipan and Tinian, a large, deeply scouring slide mass is imaged. Several serpentine mud volcanoes (Big Blue, Turquoise and Celestial) were imaged on the Mariana Forearc. Deep horizontal reflectors (likely original forearc crust) are imaged under the flanks of some of these seamounts. A possible "throat" reflector is resolved on multiple profiles at the summit of Big Blue, the northern-most seamount in the study area. The flanks of Turquoise seamount terminate in toe thrusts that represent uplift and rotation of surrounding sediments as the volcano grows outward. These thrusts form a basal ridge around the seamount similar to that previously noted encircling Conical Seamount. Furthermore, MCS data has revealed that some forearc highs previously thought to be fault blocks are in actuality mud volcanoes.

  8. Community Willingness to Participate in a Dengue Study in Aceh Province, Indonesia

    PubMed Central

    Anwar, Samsul; Bustaman, Aslam; Radiansyah, Arsil; Angraini, Pradiba; Fasli, Riny; Salwiyadi, Salwiyadi; Bastian, Reza Akbar; Oktiviyari, Ade; Akmal, Imaduddin; Iqbalamin, Muhammad; Adil, Jamalul; Henrizal, Fenni; Darmayanti, Darmayanti; Pratama, Rovy; Fajar, Jonny Karunia; Setiawan, Abdul Malik; Imrie, Allison; Kuch, Ulrich; Groneberg, David Alexander; Sasmono, R. Tedjo; Dhimal, Meghnath; Müller, Ruth

    2016-01-01

    Background Dengue virus infection is the most rapidly spreading vector-borne disease in the world. Essential research on dengue virus transmission and its prevention requires community participation. Therefore, it is crucial to understand the factors that are associated with the willingness of communities in high prevalence areas to participate in dengue research. The aim of this study was to explore factors associated with the willingness of healthy community members in Aceh province, Indonesia, to participate in dengue research that would require phlebotomy. Methodology/Principal Findings A community-based cross-sectional study was carried out in nine regencies and municipalities of Aceh from November 2014 to March 2015. Interviews using a set of validated questionnaires were conducted to collect data on demography, history of dengue infection, socioeconomic status, and knowledge, attitude and practice regarding dengue fever. Two-step logistic regression and Spearman’s rank correlation (rs) analysis were used to assess the influence of independent variables on dependent variables. Among 535 participants, less than 20% had a good willingness to participate in the dengue study. The factors associated with good willingness to participate were being female, working as a civil servant, private employee or entrepreneur, having a high socioeconomic status and good knowledge, attitude and practice regarding dengue. Good knowledge and attitude regarding dengue were positive independent predictors of willingness to participate (OR: 2.30 [95% CI: 1.36–3.90] and 3.73 [95% CI: 2.24–6.21], respectively). Conclusion/Significance The willingness to participate in dengue research is very low among community members in Aceh, and the two most important associated factors are knowledge and attitude regarding dengue. To increase participation rate, efforts to improve the knowledge and attitude of community members regarding dengue fever and dengue-related research is required

  9. Numerical Simulation of the 2004 Indian Ocean Tsunami: Accurate Flooding and drying in Banda Aceh

    NASA Astrophysics Data System (ADS)

    Cui, Haiyang; Pietrzak, Julie; Stelling, Guus; Androsov, Alexey; Harig, Sven

    2010-05-01

    The Indian Ocean Tsunami on December 26, 2004 caused one of the largest tsunamis in recent times and led to widespread devastation and loss of life. One of the worst hit regions was Banda Aceh, which is the capital of the Aceh province, located in the northern part of Sumatra, 150km from the source of the earthquake. A German-Indonesian Tsunami Early Warning System (GITEWS) (www.gitews.de) is currently under active development. The work presented here is carried out within the GITEWS framework. One of the aims of this project is the development of accurate models with which to simulate the propagation, flooding and drying, and run-up of a tsunami. In this context, TsunAWI has been developed by the Alfred Wegener Institute; it is an explicit, () finite element model. However, the accurate numerical simulation of flooding and drying requires the conservation of mass and momentum. This is not possible in the current version of TsunAWi. The P1NC - P1element guarantees mass conservation in a global sense, yet as we show here it is important to guarantee mass conservation at the local level, that is within each individual cell. Here an unstructured grid, finite volume ocean model is presented. It is derived from the P1NC - P1 element, and is shown to be mass and momentum conserving. Then a number of simulations are presented, including dam break problems flooding over both a wet and a dry bed. Excellent agreement is found. Then we present simulations for Banda Aceh, and compare the results to on-site survey data, as well as to results from the original TsunAWI code.

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

    NASA Astrophysics Data System (ADS)

    Reynard, Bruno

    2016-12-01

    In the forearc region, aqueous fluids are released from the subducting slab at a rate depending on its thermal state. Escaping fluids tend to rise vertically unless they meet permeability barriers such as the deformed plate interface or the Moho of the overriding plate. Channeling of fluids along the plate interface and Moho may result in fluid overpressure in the oceanic crust, precipitation of quartz from fluids, and low Poisson ratio areas associated with tremors. Above the subducting plate, the forearc mantle wedge is the place of intense reactions between dehydration fluids from the subducting slab and ultramafic rocks leading to extensive serpentinization. The plate interface is mechanically decoupled, most likely in relation to serpentinization, thereby isolating the forearc mantle wedge from convection as a cold, potentially serpentinized and buoyant, body. Geophysical studies are unique probes to the interactions between fluids and rocks in the forearc mantle, and experimental constrains on rock properties allow inferring fluid migration and fluid-rock reactions from geophysical data. Seismic velocities reveal a high degree of serpentinization of the forearc mantle in hot subduction zones, and little serpentinization in the coldest subduction zones because the warmer the subduction zone, the higher the amount of water released by dehydration of hydrothermally altered oceanic lithosphere. Interpretation of seismic data from petrophysical constrain is limited by complex effects due to anisotropy that needs to be assessed both in the analysis and interpretation of seismic data. Electrical conductivity increases with increasing fluid content and temperature of the subduction. However, the forearc mantle of Northern Cascadia, the hottest subduction zone where extensive serpentinization was first demonstrated, shows only modest electrical conductivity. Electrical conductivity may vary not only with the thermal state of the subduction zone, but also with time for

  11. Active and long-lived permanent forearc deformation driven by the subduction seismic cycle

    NASA Astrophysics Data System (ADS)

    Aron Melo, Felipe Alejandro

    I have used geological, geophysical and engineering methods to explore mechanisms of upper plate, brittle deformation at active forearc regions. My dissertation particularly addresses the permanent deformation style experienced by the forearc following great subduction ruptures, such as the 2010 M w8.8 Maule, Chile and 2011 Mw9.0 Tohoku, Japan earthquakes. These events triggered large, shallow seismicity on upper plate normal faults above the rupture reaching Mw7.0. First I present new structural data from the Chilean Coastal Cordillera over the rupture zone of the Maule earthquake. The study area contains the Pichilemu normal fault, which produced the large crustal aftershocks of the megathrust event. Normal faults are the major neotectonic structural elements but reverse faults also exist. Crustal seismicity and GPS surface displacements show that the forearc experiences pulses of rapid coseismic extension, parallel to the heave of the megathrust, and slow interseismic, convergence-parallel shortening. These cycles, over geologic time, build the forearc structural grain, reactivating structures properly-oriented respect to the deformation field of each stage of the interplate cycle. Great subduction events may play a fundamental role in constructing the crustal architecture of extensional forearc regions. Static mechanical models of coseismic and interseismic upper plate deformation are used to explore for distinct features that could result from brittle fracturing over the two stages of the interplate cycle. I show that the semi-elliptical outline of the first-order normal faults along the Coastal Cordillera may define the location of a characteristic, long-lived megathrust segment. Finally, using data from the Global CMT catalog I analyzed the seismic behavior through time of forearc regions that have experienced great subduction ruptures >Mw7.7 worldwide. Between 61% and 83% of the cases where upper plate earthquakes exhibited periods of increased seismicity

  12. Fragility of Forearc Stresses as a Consequence of Extreme Weakness of Megathrust Faults

    NASA Astrophysics Data System (ADS)

    Wang, K.; Brown, L. N.; He, J.; Sun, T.

    2015-12-01

    There is mounting evidence that subduction megathrusts are extremely weak. The weakness is based on a spatial and temporal average. Spatially, a seismogenic megathrust may host interspersed stronger and weaker patches due to variations in pore fluid pressure, gouge properties, and fault zone structure. In the 2011 M=9 Tohoku-oki earthquake, one strong patch underwent a local stress drop of several tens of MPa, although the rupture-zone average of the stress drop is less than 5 MPa on the basis of all the (> 20) published rupture models for this earthquake that we have examined. Temporally, megathrust strength fluctuates in earthquake cycles, punctuated by coseismic weakening or strengthening of different patches. Using finite element modeling, we demonstrate that the weakness of the megathrust leads to a fragile state of stress in the overlying forearc wedge, where compression due to plate coupling and tension due to gravity are in a subtle balance that can be tipped by small perturbations. Prior to the Tohoku-oki earthquake, the Japan Trench forearc was predominantly under margin-normal compression, a state that can be modeled using an effective friction coefficient of 0.032 for the megathrust. In a coseismic deformation model, an average stress drop of about 4 MPa on the megathrust changes the offshore forearc into tension. This is consistent with the observed stress reversal in this region as a result of the Tohoku-oki earthquake. The same level of coseismic stress drop would not cause the observed forearc stress reversal if the megathrust was assumed to have a higher strength such as 0.045. The state of stress in the offshore forearc is so fragile that large changes can be caused by other seemingly benign perturbing factors. For example, without the ocean water compressing the continental slope, much of the offshore forearc would no longer be in compression even if the megathrust strength were twice the value of 0.032. If the slope angle of the continental

  13. Large Clockwise Rotations In The Fore-arc of Northern Chile

    NASA Astrophysics Data System (ADS)

    Arriagada, C.; Fernandez, R.; Roperch, P.; Mpodozis, C.; Cobbold, P. R.

    Obliquely convergent plate boundaries typically exhibit wide zones of deformation characterized by block rotations and complex patterns of contractional, extensional, and strike-slip faulting. In the overriding plate the trench-parallel component of dis- placement commonly occurs on strike-slip faults that dissect the fore-arc into elongate slivers by displacements subparallel to the boundary. However, differences in the pat- tern of strain partitioning along the fore-arc, may produce complex structural zones oblique to the mean strike-slip faults. In northern Chile, the Domeyko Fault System in the Chilean Precordillera is often described as a major strike-slip system due to oblique convergence between Nazca and South America plates. In this context , we have carried out a paleomagnetic study in the fore-arc, southward of the Arica elbow (Antofagasta-Copiapo region, 22-27 degrees South). We sampled about 250 sites from Mezosoic-Paleogene units constituted mainly by volcanic and sedimentary rocks and few intrusives. The results show extensive and large clockwise tectonic rotations up to 65 degrees. Rotations are not only related to the Domeyko Fault System, but are widely observed across the fore-arc. Paleomagnetic results from Mezosoic-Paleogene rocks contrast with those obtained in sedimentary and volcanic Neogene sequences for which no or little evidence of tectonic rotation is found. We cannot discard the hypothesis that rotations in Jurassic and Cretaceous rocks of the Coastal Cordillera are older than rotations observed in Paleogene units. This interpretation would sug- gest that a long-lasting (late Cretaceous to Oligocene) tectonic mechanism inducing clockwise rotations has been acting during the eastward migration of the volcanic arc. An other interpretation is that the tectonic rotations occurred mostly during the late Paleogene across the whole fore-arc as suggested by the observation of major faults oblique to the mainly N-S Domeyko Fault System. The

  14. RESIDENTIAL WATER USE IN BANDA ACEH BEFORE AND AFTER DISASTER RECONSTRUCTION

    NASA Astrophysics Data System (ADS)

    Kuwata, Yasuko; Nagasawa, Masaharu

    This study focuses on the residential consciousness on water use in the background of disaster reconstruction of water supply system in Banda Aceh, Indonesia after the 2004 Indian Ocean earthquake and tsunami. Itwas turned out that half of residents started usingwater supply system after the earthquake and the water supply system user satisfies water quality rather than the domestic water user does. The satisfaction on water supply stability is not obtained well though there is a problem in resident's manner. Finally, the disaster countermeasure to the area where earthquake and tsunami are high potential and where the water supply system is not developed yet were discussed.

  15. Cenozoic evolution of San Joaquin basin, California

    SciTech Connect

    Bartow, J.A.

    1988-03-01

    The Neogene San Joaquin basin in the southern part of the 700-km long Great Valley of California is a successor to a late Mesozoic and earliest Tertiary forearc basin. The transition from forearc basin to the more restricted Neogene marine basin occurred principally during the Paleogene as the plate tectonic setting changed from oblique convergence to normal convergence, and finally to the initiation of tangential (transform) movement near the end of the Oligocene. Regional-scale tectonic events that affected the basin include: (1) clockwise rotation of the southernmost Sierra Nevada, and large-scale en echelon folding in the southern Diablo Range, both perhaps related to Late Cretaceous and early Tertiary right slip on the proto-San-Andreas fault; (2) regional uplift of southern California in the Oligocene that resulted from the subduction of the Pacific-Farallon spreading ridge: (3) extensional tectonism in the Basin and Range province, particularly in the Miocene; (4) wrench tectonism adjacent to the San Andreas fault in the Neogene; (5) northeastward emplacement of a wedge of the Franciscan complex at the west side of the Sierran block, with associated deep-seated thrusting in the late Cenozoic; and (6) the accelerated uplift of the Sierra Nevada beginning in the late Miocene. Neogene basin history was controlled principally by the tectonic effects of the northwestward migration of the Mendocino triple junction along the California continental margin and by the subsequent wrench tectonism associated with the San Andreas fault system. East-west compression in the basin, resulting from extension in the Basin and Range province was an important contributing factor to crustal shortening at the west side of the valley. Analysis of the sedimentary history of the basin, which was controlled to some extent by eustatic sea level change, enables reconstruction of the basin paleogeography through the Cenozoic.

  16. Determining Proportion of Exfoliative Vaginal Cell during Various Stages of Estrus Cycle Using Vaginal Cytology Techniques in Aceh Cattle

    PubMed Central

    Siregar, Tongku N.; Melia, Juli; Rohaya; Thasmi, Cut Nila; Masyitha, Dian; Wahyuni, Sri; Rosa, Juliana; Nurhafni; Panjaitan, Budianto; Herrialfian

    2016-01-01

    The aim of this study was to investigate the period of estrus cycle in aceh cattle, Indonesia, based on vaginal cytology techniques. Four healthy females of aceh cattle with average weight of 250–300 kg, age of 5–7 years, and body condition score of 3-4 were used. All cattle were subjected to ultrasonography analysis for the occurrence of corpus luteum before being synchronized using intramuscular injections of PGF2 alpha 25 mg. A vaginal swab was collected from aceh cattle, stained with Giemsa 10%, and observed microscopically. Period of estrus cycle was predicted from day 1 to day 24 after estrus synchronization was confirmed using ultrasonography analysis at the same day. The result showed that parabasal, intermediary, and superficial epithelium were found in the vaginal swabs collected from proestrus, metestrus, and diestrus aceh cattle. Proportions of these cells in the particular period of estrus cycle were 36.22, 32.62, and 31.16 (proestrus); 21.33, 32.58, and 46.09 (estrus); 40.75, 37.58, and 21.67 (metestrus); and 41.07, 37.38, and 21.67 (diestrus), respectively. In conclusion, dominant proportion of superficial cell that occurred in estrus period might be used as the base for determining optimal time for insemination. PMID:26977335

  17. Hydrocarbon habitat of the Tuz Golu basin, central Anatolia, Turkey

    SciTech Connect

    More, C.; Bird, P.R.; Clark-Lowes, D.D. )

    1988-08-01

    The Tuz Golu basin (TGB) of central Anatolia has been interpreted as a northwest-southeast-aligned terraced forearc basin that accumulated a Maastrichtian to Holocene, predominantly terrigenous, sedimentary succession. Evidence is presented from an integrated study incorporating all seismic, gravity, and well data for the following basin evolution. (1) Late Cretaceous sedimentation on the west of the Kirsehir block with a diverse assemblage of facies including terrestrial, possible sabkha, shallow marine carbonate and turbidite deposits; (2) eastward subduction of Neotethys beginning in the Maastrichtian and development of the Tuz Golu as a forearc basin; (3) deposition of a thick Paleocene to Eocene flysch succession; (4) late Eocene inversion of the thick flysch section along the central axis of the basin and development of flanking shallow basins; (5) late Eocene-Oligocene emergence with deposition of evaporites and red beds in a restricted basin, followed by suturing of continental blocks, uplift, and erosion; (6) dextral displacement along the Kochisar fault; (7) Oligocene-Miocene diapirism of Eocene salt along major faults in the western shallow basin; and (8) terrestrial and lacustrine sedimentation in the neotectonic TGB. Of the 22 wells drilled in the TGB, four contained oil or gas shows from formations of Paleocene to Miocene age. Potential shale source rocks occur in the Upper Cretaceous, Paleocene, and Eocene sections. Cretaceous rudist reefs and Paleocene/Eocene sandstones provide target reservoirs, while Eocene salt represents an ideal seal. Late Eocene deformation created the major trap-forming structures of the basin.

  18. Geoelectrical dimensionality analyses in Sumatran Fault (Aceh segment) using magnetotelluric phase tensor

    NASA Astrophysics Data System (ADS)

    Prihantoro, Rudy; Nurhasan, Sutarno, Doddy; Ogawa, Yasuo; Priahadena, Has; Fitriani, Dini

    2014-03-01

    Earth electrical / geoelectrical conductivity may vary in any direction in a complex earth model. When conductivity only varying within one direction such as depth, it is considered as an one-dimensional (1-D) structure model. Two-dimensional (2-D) and three-dimensional (3-D) structure have more degrees of conductivity variation. In magnetotelluric (MT) surveys localized heterogeneities in conductivity near the Earth's surface distort the electromagnetic (EM) response produced by the underlying or 'regional' conductivity structure under investigation. Several attempts had been done to remove this distortion effect in measured MT transfer functions (impedances tensor) by a series of techniques and general conductivity models of increasing complexity. The most common technique are Bahr's method and Groom-Bailey decompositions, that is restricted by assumption of two dimensional (2D) regional conductivity structure. MT phase tensor technique proposed by Caldwell et al. (2004) requires no assumption about the dimensionality of the regional conductivity structure and is applicable where both the heterogeneity and the regional conductivity structure are 3-D. Here, we examine the dimensionality analyses using the MT phase tensor to measured data of Sumatran Fault (SF) Aceh segment that we've collected during July 2012. A small value of phase tensor dimensionality indicator (β) was found along the profile. This result indicate a strong a two dimensionality of regional conductivity structure of SF Aceh segment.

  19. Dividing disasters in Aceh, Indonesia: separatist conflict and tsunami, human rights and humanitarianism.

    PubMed

    Zeccola, Paul

    2011-04-01

    This paper examines the interface between human rights and humanitarian action in the context of the conflict and tsunami in Aceh, Indonesia, between 1998 and 2007. It looks at the challenges international humanitarian non-governmental organisations (NGOs) faced as they engaged in human rights work in the conflict period and in conflict-related activities in the post-tsunami period. The paper argues that many large NGOs may have compromised what some would hold to be essential principles for humanitarian action because of domestic political concerns, donor restrictions and resistance among certain NGO chiefs. In contrast with the pre-tsunami period, in which NGOs worked for years amid military operations, in the post-tsunami period NGOs were decidedly apolitical, neglecting the conflict in their tsunami response--despite significant developments that permitted greater political engagement in Aceh's post-conflict transformation. The evidence suggests that NGOs are challenged in contextualising humanitarian responses and that there is a need to underscore donor flexibility and independence in humanitarian action. PMID:21054497

  20. Caribbean basin framework, 3: Southern Central America and Colombian basin

    SciTech Connect

    Kolarsky, R.A.; Mann, P. )

    1991-03-01

    The authors recognize three basin-forming periods in southern Central America (Panama, Costa Rica, southern Nicaragua) that they attempt to correlate with events in the Colombian basin (Bowland, 1984): (1) Early-Late Cretaceous island arc formation and growth of the Central American island arc and Late Cretaceous formation of the Colombian basin oceanic plateau. During latest Cretaceous time, pelagic carbonate sediments blanketed the Central American island arc in Panama and Costa Rica and elevated blocks on the Colombian basin oceanic plateau; (2) middle Eocene-middle Miocene island arc uplift and erosion. During this interval, influx of distal terrigenous turbidites in most areas of Panama, Costa Rica, and the Colombian basin marks the uplift and erosion of the Central American island arc. In the Colombian basin, turbidites fill in basement relief and accumulate to thicknesses up to 2 km in the deepest part of the basin. In Costa Rica, sedimentation was concentrated in fore-arc (Terraba) and back-arc (El Limon) basins; (3) late Miocene-Recent accelerated uplift and erosion of segments of the Central American arc. Influx of proximal terrigenous turbidites and alluvial fans in most areas of Panama, Costa Rica, and the Colombian basin marks collision of the Panama arc with the South American continent (late Miocene early Pliocene) and collision of the Cocos Ridge with the Costa Rican arc (late Pleistocene). The Cocos Ridge collision inverted the Terraba and El Limon basins. The Panama arc collision produced northeast-striking left-lateral strike-slip faults and fault-related basins throughout Panama as Panama moved northwest over the Colombian basin.

  1. Obliquely convergent plate motion and its relation with forearc sliver movement, El Salvador volcanic arc

    NASA Astrophysics Data System (ADS)

    Tikoff, B.; DeMets, C.; Garibaldi, N.; Hernandez, W.; Hernandez, D.

    2012-12-01

    The magmatic arc in El Salvador is interpreted to result from the subduction of the Cocos plate underneath the Caribbean plate along the Middle America trench. In addition, El Salvador contains a fore-arc sliver that moves 11 mm/yr westward relative to the back-arc. Well-defined strike-slip faults along the magmatic arc accommodate forearc sliver motion, but are offset at several locations by en echelon pull-apart step-overs with abundant normal faults. All basaltic-andesitic magmatic centers (San Miguel, San Vincente, San Salvador, Santa Ana) are located within these step-overs, while the two major rhyolitic calderas (Ilopango, Coatepeque) occur directly along the strike-slip faults. There are two puzzling aspects about the strike-slip tectonism. First, a silicic, shallow magma body that intrudes the San Miguel fault zone (part of the El Salvador fault system) was emplaced syn-tectonically (sigmoidal field and magnetic foliations, subhorizontally plunging magnetic lineations and dextral shear at the microscale). Within the dextrally sheared portion of the intrusion, an obsidian band with a 40Ar/39Ar age of 7.46 Ma indicates that dextral strike-slip tectonism in the Salvadoran arc has been an ongoing process for ~7.5 Ma. This casts significant doubt on whether Cocos ridge subduction (that started ~1 Ma ago) is the cause of the ongoing forearc movement. The potentially more significant problem is that the fore-arc sliver in El Salvador moves 11 mm/yr westward relative to the back-arc despite a nearly orthogonal angle of convergence (with a convergence rate of ~77 mm/yr) near El Salvador and absence of significant frictional coupling along the subduction interface. Further, GPS indicates that the Nicaraguan and Salvadoran forearcs define a semi-rigid sliver moving at nearly the same trench-parallel rates despite along-trench changes in the subduction angle. Consequently, it is tempting to attribute the movement of both forearc slivers to Cocos ridge subduction

  2. Helium As a Tracer for Fluids Released from Juan De Fuca Lithosphere Beneath the Cascadia Forearc

    NASA Astrophysics Data System (ADS)

    McCrory, P. A.; Constantz, J. E.; Hunt, A. G.; Blair, J. L.

    2014-12-01

    Helium isotope ratios in mineral springs provide an indication of the sources and pathways for magma ascending beneath volcanic arcs and are used as a tracer for fluids associated tectonic processes occurring in subduction systems. We sampled a series of mineral springs to define fluids derived from Juan de Fuca lithosphere beneath the forearc as the subducting slab dehydrates and densifies with increasing depth. Surface springs above the slab depth of 25-30 km have 3He/4He ratios of ~0.3 (R/RA); above the slab at a depth of ~40 km the ratio is ~4.0; and for springs above the slab at depths of 50-55 km the ratio ranges from ~0.7-1.6. The springs situated trenchward of the forearc mantle corner (FMC; varying from 35 to 43 km deep), yield the lowest ratios, thus indicating only a minor component of mantle-derived helium within spring waters. Springs situated arcward of the FMC yield intermediate (0.8-1.2 RC/RA ) to high (>1.2 RC/RA ) ratios, indicating a significant component of mantle-derived helium. Although helium isotopes do not allow us to differentiate between oceanic and forearc mantle sources, the lowest values are situated above the region that lacks forearc mantle, suggesting that either little slab-derived fluid is released at shallow slab depths, or that forearc mantle is the major source of 3He and acquired as the fluids rise to the surface. Sample sites range from 40 km to more than 200 km from the nearest Cascade Arc volcano. For the closer sites, we cannot rule out that 3He may be partially derived from westward migration of arc related fluids. The highest value occurs ~130 km from the nearest arc volcano, thus likely does not reflect arc related fluids. These preliminary observations provide geologic evidence that slab-derived fluids can migrate through the forearc mantle wedge to the surface even though the mantle is typically considered a sink for fluids owing to serpentinization processes. Likely pathways consist of fractures in the forearc mantle

  3. Potential Sedimentary Evidence of Two Closely Spaced Tsunamis on the West Coast of Aceh, Indonesia

    NASA Astrophysics Data System (ADS)

    Monecke, Katrin; Meilianda, Ella; Rushdy, Ibnu; Moena, Abudzar; Yolanda, Irvan P.

    2016-04-01

    Recent research in the coastal regions of Aceh, Indonesia, an area that was largely affected by the 2004 Sumatra Andaman earthquake and ensuing Indian Ocean tsunami, suggests the possibility that two closely spaced tsunamis occurred at the turn of the 14th to 15th century (Meltzner et al., 2010; Sieh et al., 2015). Here, we present evidence of two buried sand layers in the coastal marshes of West Aceh, possibly representing these penultimate predecessors of the 2004 tsunami. We discovered the sand layers in an until recently inaccessible area of a previously studied beach ridge plain about 15 km North of Meulaboh, West Aceh. Here, the 2004 tsunami left a continuous, typically a few cm thick sand sheet in the coastal hinterland in low-lying swales that accumulate organic-rich deposits and separate the sandy beach ridges. In keeping with the long-term progradation of the coastline, older deposits have to be sought after further inland. Using a hand auger, the buried sand layers were discovered in 3 cores in a flooded and highly vegetated swale in about 1 km distance to the shoreline. The pair of sand layers occurs in 70-100 cm depth and overlies 40-60 cm of dark-brown peat that rests on the basal sand of the beach ridge plain. The lower sand layer is only 1-6 cm thick, whereas the upper layer is consistently thicker, measuring 11-17 cm, with 8-14 cm of peat in between sand sheets. Both layers consist of massive, grey, medium sand and include plant fragments. They show very sharp upper and lower boundaries clearly distinguishing them from the surrounding peat and indicating an abrupt depositional event. A previously developed age model for sediments of this beach ridge plain suggest that this pair of layers could indeed correlate to a nearby buried sand sheet interpreted as tsunamigenic and deposited soon after 1290-1400AD (Monecke et al., 2008). The superb preservation at this new site allows the clear distinction of two depositional events, which, based on a first

  4. Quaternary Tectonic and Climatic Processes shaping the Central Andean hyperarid forearc (southern Peru)

    NASA Astrophysics Data System (ADS)

    Audin, Laurence; Benavente, Carlos; Zerathe, Swann; Saillard, Marianne; Hall, Sarah R.; Farber, Daniel L.

    2015-04-01

    Understanding the forearc structure and processes related to Quaternary evolution and uplift of the Western Andean Cordillera remains an outstanding scientific issue. Models of Andean Plateau evolution based on Tertiary volcanic stratigraphy since 5Ma suggest that the deformation was focused along the eastern margin of the plateau and that minimal uplift occurred along the Pacific margin. On the contrary, new tectonic data and Quaternary surface 10Be dating highlight the presence of recently active deformation, incision and alluvial processes within the upper Andean forearc together with a regional uplift of the coastal zone. Additionally, the high obliquity observed in the northern Arica Bend region makes it an ideal target to discuss whether partitioning of the oblique convergence is accommodated by the neotectonic features that dissect the Quaternary forearc. Our goals are both to decipher the Quaternary tectonic and climatic processes shaping the hyperarid forearc along strike and across strike. Finally, we aim to quantify the respective influence of these factors in the overall uplift of the Western Andes. Indeed, sequences of pediment surfaces, landslide products, paleolake deposits and marine terraces found along the oblique Peruvian margin are a unique set of datable markers that can be used to quantify the rates of Quaternary processes. In this study, we focus on the southern Peru hyperarid Atacama area where regional surfaces and tectonic markers (scarps, folds, temporary streams and paleolake levels offsets…) are well preserved for the Quaternary timescale. Numerous landsliding events align on the major fault segments and reflect Plio-Pleistocene climatic and tectonic activity together with filled and strath terraces. As the present day sea-level is one of the highest levels recorded for Quaternary time span, any emerged marine terrace is preserved by tectonic coastal uplift. In particular, the geomorphic and chronologic correlation between marine and

  5. Inner forearc response to subduction of the Panama Fracture Zone, southern Central America

    NASA Astrophysics Data System (ADS)

    Morell, Kristin D.; Fisher, Donald M.; Gardner, Thomas W.

    2008-01-01

    Subduction of the right-lateral Panama Fracture Zone, along the convergent margin of Central America creates abrupt lateral variations in convergence rate, obliquity, and subducting crustal thickness at its intersection with the Middle America Trench. This intersection, known as the Panama (CO-NZ-CA) Triple Junction, is migrating to the southeast at a rate of 55 mm/yr, and currently coincides with the lateral termination of the Fila Costeña Thrust Belt in the inner forearc of the overriding plate. Mapping in the inner forearc in the area that straddles the subducting Panama Fracture Zone reveals that Cocos-Caribbean convergence west of the triple junction leads to the development of an inner forearc thrust belt inboard of the colliding Cocos Ridge, while little deformation is evident inboard of Nazca-Caribbean convergence, east of the triple junction. This results in the lateral termination of the Fila Costeña Thrust Belt in the region of the forearc that projects over the Panama Fracture Zone, where four out of five mapped thrust faults tip out and are buried by lahars. Three new balanced cross-sections indicate a steep gradient in shortening from the center of the thrust belt to its southeastern termination. The short-term history of the inner forearc recorded in the landscape and topography of the Fila Costeña is consistent with the southeastward migration of the thrust belt and the Panama Triple Junction throughout the past ˜ 3 Ma, with evidence for the growth of a new topographic divide and reorganization of stream channel networks.

  6. Geology and Petrology of the Southeast Mariana Forearc Rift

    NASA Astrophysics Data System (ADS)

    Ribeiro, J. M.; Anthony, E. Y.; Bloomer, S. H.; Girard, G.; Ishizuka, O.; Kelley, K. A.; Manton, W. I.; Martinez, F.; Merle, S. G.; Ohara, Y.; Reagan, M. K.; Ren, M.; Stern, R. J.

    2011-12-01

    The southernmost Mariana convergent margin is tectonically and magmatically very active, with submarine arc volcanoes that are sub-parallel to the Malaguana-Gadao Ridge backarc spreading center at ~110km from the trench axis. This activity reflects widening of the S. Mariana Trough. Stretching formed 3 southeast-facing, broad rifts extending from the trench to an extinct arc volcano chain (~80km from the trench axis) that is mostly composed of outcrops and fragments of pillow lavas partially covered by sediments. The 3 rifts comprise the S.E. Mariana Forearc Rift (SEMFR) and are 50-56km long and 3600 to 8200m deep, with axial valleys that narrow near the extinct arc. We studied the SEMFR using one Shinkai 6500 dive in 2008 and two Shinkai 6500 dives and 7 deep-tows in 2010. Near the trench, the SEMFR flanks are very steep and dominated by talus slopes of lava, fine-grained gabbro, diabase and peridotite, sometimes covered by thin volcaniclastic sediments. Few outcrops of pillow lavas, lava flows and volcaniclastics are observed, strongly suggesting that SEMFR morphology is dominated by faulting and landsliding. Lava outcrops are smoother and better preserved towards the extinct arc, suggesting that magmatic activity dominates that part of the rift. 40Ar-39Ar ages of 3 SEMFR lavas are 3.0-3.7Ma, so post-magmatic rifting is younger than ~3Ma. SEMFR pillow lavas are vesicular and microporphyritic with crystallite-rich glassy rinds, indicating they erupted underwater at near-liquidus conditions. In contrast, the lava flows are more crystallized and less vesicular. SEMFR lavas exhibit similar ranges in mineral composition with 2 kinds of plagioclase (An>80% and An<80%), clinopyroxene (Mg#≥80% and Mg#<80%), olivine (Fo>90 and Fo<90), suggesting magma mixing. Gabbroic rocks are slightly altered and have olivine and clinopyroxene compositions similar to those of the lavas, but contain less anorthitic plagioclase with a wider range in composition (An20-70) than the lavas

  7. Thallium as a tracer of fluid-rock interaction in the shallow Mariana forearc

    NASA Astrophysics Data System (ADS)

    Nielsen, Sune G.; Klein, Frieder; Kading, Tristan; Blusztajn, Jerzy; Wickham, Katie

    2015-11-01

    Fluids driven off the subducting Pacific plate infiltrate the shallow Mariana forearc and lead to extensive serpentinization of mantle peridotite. However, the sources, pathways, and chemical modifications of ascending, slab-derived fluids remain poorly constrained and controversial. In this study, we use thallium (Tl) concentrations and isotopic ratios of serpentinized peridotite and rodingitized diabase from the South Chamorro and Conical Seamounts to discriminate between potential fluid sources with distinct Tl isotope compositions. Serpentinite samples from the Mariana forearc all display ε205 Tl > - 0.5 (where ε205 Tl = 10 , 000 × (205Tl /Tl203sample -205Tl /SRM 997 203Tl) / (205Tl / - 0.5 and, therefore, we interpret the heavy Tl isotope signatures as signifying that the serpentinizing fluids were derived from subducting pelagic sediments. A rodingitized diabase from Conical Seamount was found to have an ε205 Tl of 0.8, suggesting that sediment-sourced serpentinization fluids could also affect diabase and other mafic lithologies in the shallow Mariana forearc. Forearc rodingitization of diabase led to a strong depletion in Tl content and a virtually complete loss of K, Na and Rb. The chemical composition of hybrid fluids resulting from serpentinization of harzburgite with concomitant rodingitization of diabase can be highly alkaline, depleted in Si, yet enriched in Ca, Na, K, and Rb, which is consistent with the composition of fluids emanating from mud volcanoes in the Mariana forearc. Our study suggests that fluid-rock interactions between sedimentary, mafic, and

  8. Remote sensing-based neural network mapping of tsunami damage in Aceh, Indonesia.

    PubMed

    Aitkenhead, Matthew J; Lumsdon, Parivash; Miller, David R

    2007-09-01

    In addition to the loss of human life, the tsunami event of 26 December 2004 caused extensive damage to coastal areas. The scale of the disaster was such that remote sensing may be the only way to determine its effects on the landscape. This paper presents the results of a neural network-based mapping of part of the region of Aceh, Sumatra. Before-and-after satellite imagery, combined with a novel neural network methodology, enabled a characterisation of landscape change. The neural network technique used a threshold of acceptance for identification, in combination with a bootstrapped identification method for identifying problem pixels. Map analysis allowed identification of urban areas that were inaccessible by road, and which aid agencies could therefore only reach by air or sea. The methods used provide a rapid and effective mapping ability and would be a useful tool for aid agencies, insurance underwriters and environmental monitoring. PMID:17714164

  9. Intestinal and blood parasites of man in Bireuen and Takengon, Aceh Province, Sumatra, Indonesia.

    PubMed

    Stafford, E E; Joesoef, A

    1976-12-01

    A survey for blood and intestinal parasites was carried out in Aceh Province of North Sumatra, Indonesia. A total of 348 stool specimens were obtained from 167 males and 181 females ranging in age from 6 months to 70 years. Over 98% of the population sampled were found infected with at least one intestinal parasite. Ascaris lumbricoides, Trichuris trichiura, hookworm and Entamoeba coli, in that order, were the most common parasites detected. Other intestinal parasites found less frequently were Entamoeba histolytica, Iodamoeba bütschlii, Entamoeba hartmanni, Endolimax nana and Giardia lamblia, Brugia malayi microfilaraemias were detected in 2% of those examined and only in the coastal villages of Cot Ketapang and Rusip Dayah. No malaria was found. PMID:1030850

  10. Using 10Be cosmogenic surface exposure dating to determine the evolution of the Purgatorio active fault in the Andean forearc, southern Peru

    NASA Astrophysics Data System (ADS)

    Carlos, Benavente; Swann, Zerathe; Laurence, Audin; Fabrizio, Delgado; Marianne, Saillard; Sarah, Hall R.; Aster Team

    2015-04-01

    Active transpressive deformation has been occurring along the Andean hyperarid forearc for the last 3 Myrs but many of these faults are still not described even if able to produce large damaging earthquakes. Active faulting along the northern part of the Arica Bend can be recognized due to the presence of well-preserved and sharp fault scarps indicating recent surface slip. During the Mio-Pliocene, deposition within the forearc continental basins resulted in the formation of vast fan deposits and conglomerates of the Moquegua Formation, which can be considered as bedrock in this exposure study (~45-4 Ma; Tosdal et al., 1984; Sebrier et al., 1988a; Roperch et al., 2006). The typical vertical Purgatorio fault scarps offset both the Moquegua bedrock and several younger geomorphic features associated with <300kyrs climatic and 400 years old volcanic extreme events. This study focus on quantifying slip rate variations in time along a 5-meters high vertical fault scarp to understand how the fault is evolving. These results are achieved via surface exposure dating of the sampled seismically broken cobbolds of the Moquegua formation outcroping vertically along the fault scarp. These samples are well-suited to the application of in situ produced cosmogenic radionuclides for surface exposure dating, as the hyperarid region has extremely low erosion rates. We sampled the scarp away from any significant drainage so as to avoid possibly disturbed areas. The sampling did involve extracting quarzite conglomeratic material along the bedrock scarp and on the upper surrounding crests. The aim has been to measure Berylium-20 TCN (Terrestrial in situ Cosmogenic Nuclides) concentrations to determine exposure age as a function of height on the scarp. This has been successfully employed on one scarp in Italy based on Chlorine-36 TCN (Palumbo et al., 2004). However, slow faults behaviour remains unclear and more contributions are needed. Quaternary activity of the Purgatorio fault system

  11. Heterogeneous density-structure of the northern Chile marine fore-arc and its relation to the rupture of the 2014 Mw8.2 Iquique earthquake

    NASA Astrophysics Data System (ADS)

    Maksymowicz, Andrei; Ruiz, Javier; Contreras-Reyes, Eduardo

    2016-04-01

    gravity and the northern limit of the earthquake correlates with the location of a relatively high local gravity anomaly. This local gravity high corresponds to the southern border of the well developed Arica marine forearc basin. The models show that the frontal portion of the continental wedge in the studied area is formed by low density material that is interpreted as fractured rock. The location of the foreshocks suggests that the presence of this highly fractured material is related to the location of the rupture updip and the stress accommodation process after the earthquake. The results show that detailed studies of the forearc gravity signal provide information of the structures that can play a key role in the earthquakes along the current seismic gaps to the north and to the south of Iquique earthquake.

  12. Subduction-zone magnetic anomalies and implications for hydrated forearc mantle

    USGS Publications Warehouse

    Blakely, R.J.; Brocher, T.M.; Wells, R.E.

    2005-01-01

    Continental mantle in subduction zones is hydrated by release of water from the underlying oceanic plate. Magnetite is a significant byproduct of mantle hydration, and forearc mantle, cooled by subduction, should contribute to long-wavelength magnetic anomalies above subduction zones. We test this hypothesis with a quantitative model of the Cascadia convergent margin, based on gravity and aeromagnetic anomalies and constrained by seismic velocities, and find that hydrated mantle explains an important disparity in potential-field anomalies of Cascadia. A comparison with aeromagnetic data, thermal models, and earthquakes of Cascadia, Japan, and southern Alaska suggests that magnetic mantle may be common in forearc settings and thus magnetic anomalies may be useful in mapping hydrated mantle in convergent margins worldwide. ?? 2005 Geological Society of America.

  13. Geology of the Eel River basin and adjacent region: implications for late Cenozoic tectonics of the southern Cascadia subduction zone and Mendocino triple junction

    USGS Publications Warehouse

    Clarke, S.H., Jr.

    1992-01-01

    Two upper Cenozoic depositional sequences of principally marine strata about 4000m thick overlie accreted basement terranes of the Central and Coastal belts of the Franciscan Complex in the onshore-offshore Eel River basin of northwestern California. The older depositional sequence is early to middle Miocene in age and represents slope basin and slope-blanket deposition, whereas the younger sequence, late Miocene to middle Pleistocene in age, consists largely of forearc basin deposits. -from Author

  14. 16ch high-resolution seismic reflection surveys on the active fault of upper fore-arc slope off Okinawa Island, central Ryukyu Island Arc, Southwest Japan

    NASA Astrophysics Data System (ADS)

    Arai, K.; Inoue, T.; Sato, T.; Tuzino, T.

    2010-12-01

    The Ryukyu Island Arc extends from Kyushu to Taiwan, a distance of 1,200 km, along the Ryukyu Trench where the Philippine Sea Plate is subducting beneath the Eurasian Plate. The Okinawa Trough, a back arc basin has formed behind the Ryukyu Island Arc in late Pliocene to early Pleistocene. The research cruises of GH08 (from 28th July to 29th August 2008) and GH09 (from 16th July to 17th August 2009) were carried out around Okinawa Island, which is located on the central Ryukyu Island Arc. More than 4,500 miles multi channel high-resolution seismic profiles were acquired during these two cruises by the GI-gun (355cu. inch) or the Cluster-gun (30+30 cu. inch) systems with 16ch digital streamer cable. Survey area in the southeast off Okinawa Island is located on the upper fore-arc slope. Seismic reflections of the upper fore-arc slope show a distinct reflector which may represent erosional unconformable surface. The distinct reflector had tilted southeastward and was overlain by the stratified sediments. No obvious deformation such as the fold and faults parallel to the Ryukyu Trench axis was found under the upper slope. In contrast, some active faults which were perpendicular to the Ryukyu Trench axis (NW-SE direction) were observed. The most conspicuous normal fault was found on north off Okinawa Island. The fault with 70-80°dipping toward northeast has been active since the early Pleistocene inferred from seismic stratigraphy and calcareous nannofossil biochronology. The maximum displacement reaches to 0.7 s two way travel time in depth. An average of maximum vertical displace component of the normal fault may reach up to ten cm/1000 years. Seismic profiles indicate that the tilting of Ryukyu Island Arc forward to the Ryukyu Trench plays the important role of formation of the fault in a NW-SE direction.

  15. New insights into the North American Cordillera forearc: Cretaceous to Eocene tectonic evolution of the Leech River Schist, Southern Vancouver Island, Canada

    NASA Astrophysics Data System (ADS)

    Jakob, Johannes; Johnston, Stephen

    2015-04-01

    The Leech River Complex on southern Vancouver Island is a part of the Pacific Rim Terrane of the North American Cordillera and comprises a series of fault-bounded slices of mainly meta-sedimentary and meta-igneous rocks of Triassic to Cretaceous age. The tectono-metamorphic history of this unit provides important constraints on the history of terrane accretion and the paleogeographic and tectonic evolution of the western North American forearc region. Our focus is on the structures and tectonic fabrics that developed within the western most part of the Leech River Schist from ~88 Ma through ~37 Ma. Similar syn- and post-instrusive structures that developed during emplacement of the ~88 Ma Jordan River meta-granodiorite and the ~51 Ma Walker Creek Intrusions respectively, indicate a consistent stress field during >35 m.y. of northward translation of the outboard Cordilleran terranes. A regional high temperature, Staurolite-Andalusite-grade metamorphic event is recorded in the meta-sedimentary rocks. Subcretion of the Crescent terrane beneath the Leech River Schist at ~51 Ma caused folding of the metamorphic rocks, the development of a system of dextral and sinistral brittle shears, and normal faulting. Related extension to the northwest resulted in the opening of Barkley Sound and the more westerly marine Tofino basin. These multi-faceted deformational structures are most likely a direct consequence of the subcretion of the Crescent terrane and the linked development of the Southern Vancouver Island Orocline. The deposition of sandstones and conglomerates of the Sooke Formation began at ca. 37 Ma. This siliciclastic sequence unconformably overlies the Leech River Schist, records rapid subsidence of the forearc following a preceding uplift and exhumation event, and may be a record of a younger subcretion event.

  16. Deformation across the forearc of the Cascadia subduction zone at Cape Blanco, Oregon

    USGS Publications Warehouse

    Savage, J.C.; Svarc, J.L.; Prescott, W.H.; Murray, M.H.

    2000-01-01

    Over the interval 1992-1999 the U.S. Geological Survey measured the deformation of a geodetic array extending N880°E (approximate direction of plate convergence) from Cape Blanco on the Oregon coast to the volcanic arc near Newberry Crater (55 and 350 km, respectively, from the deformation front). Within about 150 km from the deformation front, the forearc is being compressed arcward (N80°E) by coupling to the subducting Juan de Fuca plate. Dislocation modeling of the observed N80°E compression suggests that the main thrust zone (the locked portion of the Juan de Fuca-forearc interface) is about 40 km wide in the downdip direction. The transverse (N10°W) velocity component of the forearc measured with respect to the fixed interior of North America decreases with distance from the deformation front at a rate of about 0.03 mm yr-1 km-1. That gradient appears to be a consequence of rigid rotation of the forearc block relative to fixed interior North America (Euler vector of 43.4°±0.1° N, 120.0°±0.4° W, and -1.67±0.17° (m.y.)-1; quoted uncertainties are standard deviations). The rotation rate is similar to the paleomagnetically measured rotation rate (-1.0±0.2° (m.y.)-1) of the 15 Ma lava flows along the Columbia River 250 km farther north. The back arc does not appear to participate in this rotation but rather is migrating at a rate of about 3.6 mm yr-1northward with respect to fixed North America. That migration could be partly an artifact of an imperfect tie of our reference coordinate system to the interior of North America.

  17. A Numerical Study of Strain Partitioning and the Development of Forearc Slivers at Obliquely Convergent Margins

    NASA Astrophysics Data System (ADS)

    Koster, K. L.; Haq, S. S.; Flesch, L. M.

    2012-12-01

    Oblique relative plate motion is common at convergent margins, often with a significant component of margin-parallel motion. At such margins, relative plate motion is often accommodated as spatially distinct margin-normal thrusting and margin-parallel shear, leading to the development of fore-arc slivers. These crustal slivers are bounded trench-ward by thrust faults and arc-ward by a well developed margin-parallel strike-slip fault and are observed in about half of all modern convergent boundaries. Some modestly oblique convergent settings are known to develop fore-arc slivers while some higher obliquity margins fail to effectively partition the margin-parallel component of plate motion in a distinct zone. Analog modeling has shown that pure frictional wedges only produce fore-arc like sliver motion at very high obliquities, however, the presence of ductile layers at depth can localize shear at lower obliquities. We have performed finite-element numerical simulations of oblique convergent wedges, over a wide range of obliquities, governed by viscous behavior at depth in which we solve force-balance equations for Stokes flow using COMSOL Multiphysics to quantify the magnitude and style of stress. Our numerical models reproduce topographic profiles and surface velocity fields of similarly parameterized analog experiments and demonstrate a progressive localization of margin-parallel shear with wedge growth. We also observe the onset and localization of shear in all wedges of non-zero obliquity, which we quantify by comparing the magnitudes of principal compressional and extensional stress tensor axes to constrain the timing of the transition between intermediate and high partitioning of strain in evolving wedges. These results suggest, in conjunction with analog models, that viscous behavior at depth and increase in topography during convergence both work to localize margin-parallel shear in obliquely convergent wedges and gives a mechanism for the development of

  18. Heterogeneous Oxidation in Supra-Subduction Settings: Evidence from Forearc Peridotites

    NASA Astrophysics Data System (ADS)

    Birner, S.; Warren, J. M.; Cottrell, E.; Davis, F. A.

    2015-12-01

    The forearc region of subduction zones record the magmatic processes associated with subduction initiation. Volcanics from these regions are well studied, but the forearc lithospheric mantle is less well understood, partly due to the limited number of locations with peridotite exposed in situ. The Tonga and Mariana trenches are non-accretionary convergent margins where peridotites have been collected from the wall of the over-riding plate. These forearc peridotites present a unique opportunity to study the processes associated with subduction initiation from an in-situ source. Forearc peridotites from both localities show distinct chemical heterogeneity. While all samples are extremely refractory, as evidenced by low modal abundances of clinopyroxene, they differ significantly in terms of mineral compositions and accessory phases. Minerals present in a subset of samples include plagioclase, amphibole, and sulfides. Samples also vary significantly in spinel Cr# and wt% TiO2. We used the spinel peridotite oxygen barometer of Bryndzia and Wood (1990) to calculate the oxygen fugacity of the samples, calculating Fe3+/ΣFe ratio in spinels using Mössbauer-calibrated electron microprobe analysis. Samples from Mariana as well as one dredge from Tonga record elevated fO2 (1-2 log units above the QFM buffer), similar to results seen from subduction xenoliths. However, three other dredges from Tonga do not show this signature of oxidation, instead trending to high Cr# at a more ridge-like oxidation state (slightly below QFM). We interpret these non-oxidized values to be representative of primary mantle at the earliest stages of subduction, suggesting that sub-arc mantle is not oxidized prior to arc initiation. Elevated oxidation signatures then develop once this primary mantle interacts with arc-like melts and fluids related to dehydration of the subducting slab.

  19. Forearc deformation and megasplay fault system of the Ryukyu subduction zone

    NASA Astrophysics Data System (ADS)

    Hsu, S.; Yeh, Y.; Sibuet, J.; Tsai, C.; Doo, W.

    2011-12-01

    A great tsunami caused by a subduction earthquake had struck south Ryukyu islands and killed ~12000 people in 1771. Here we report the existence of a megasplay fault system along the south Ryukyu forearc. Analyses of deep multi-channel seismic reflection profiles indicate that the megasplay fault system is rising from the summit of a ~1 km high mount sitting on a ~5° landward dipping subducted plate interface. The fault system has accumulated large strain as evidenced by the active and widespread normal faults in the inner wedge. The along-trench length of the megasplay fault system is estimated to be ~450 km. The origin of this south Ryukyu megasplay fault system is linked to the subduction of elevated ridges parallel to the fracture zones. In contrast, no similar splay fault system is found in the west of 125. 5°E where the oblique subduction has produced shear zones along the south Ryukyu forearc. We infer that the megasplay fault system is responsible for the 1771 south Ryukyu tsunami. Likewise, after a quiescence of ~240 years, a near-future great earthquake and tsunami is anticipated as the extensional feature is strongly widespread over the south Ryukyu forearc.

  20. Impacts of soil and groundwater salinization on tree crop performance in post-tsunami Aceh Barat, Indonesia

    NASA Astrophysics Data System (ADS)

    Marohn, C.; Distel, A.; Dercon, G.; Wahyunto; Tomlinson, R.; Noordwijk, M. v.; Cadisch, G.

    2012-09-01

    The Indian Ocean tsunami of December 2004 had far reaching consequences for agriculture in Aceh province, Indonesia, and particularly in Aceh Barat district, 150 km from the seaquake epicentre. In this study, the spatial distribution and temporal dynamics of soil and groundwater salinity and their impact on tree crops were monitored in Aceh Barat from 2006 to 2008. On 48 sampling points along ten transects, covering 40 km of coastline, soil and groundwater salinity were measured and related to mortality and yield depression of the locally most important tree crops. Given a yearly rainfall of over 3000 mm, initial groundwater salinity declined rapidly from over 10 to less than 2 mS cm-1 within two years. On the other hand, seasonal dynamics of the groundwater table in combination with intrusion of saline water into the groundwater body led to recurring elevated salinity, sufficient to affect crops. Tree mortality and yield depression in the flooded area varied considerably between tree species. Damage to coconut (65% trees damaged) was related to tsunami run-up height, while rubber (50% trees damaged) was mainly affected by groundwater salinity. Coconut yields (-35% in average) were constrained by groundwater Ca2+ and Mg2+, while rubber yields (-65% on average) were related to groundwater chloride, pH and soil sodium. These findings have implications on planting deep-rooted tree crops as growth will be constrained by ongoing oscillations of the groundwater table and salinity.

  1. Forearc hyperextension by detachment faulting and ophiolite dismemberment: examples from the Yarlung Tsangpo Suture Zone (Southern Tibet)

    NASA Astrophysics Data System (ADS)

    Maffione, M.; Van Hinsbergen, D. J. J.; Huang, W.; Koornneef, L.; Guilmette, C.; Borneman, N.; Hodges, K. V.; Kapp, P. A.; Lin, D.

    2014-12-01

    The broad deformation zone of the Himalayan belt and Tibetan plateau is largely the product of continent-continent collision between India and Eurasia plates since the Early Eocene. Ophiolites exposed along the Yarlung Tsangpo Suture Zone (southern Tibet) demonstrate that a long-lasting intra-oceanic subduction zone must have played a significant role in accommodating closure of the >7500 km wide Neotethyan Ocean before continental collision. Their study can provide key constraints on the initial history of the Neotethyan subduction systems, and the following formation and emplacement of the ophiolite. Paleomagnetic analyses of the sheeted dykes complex of ophiolites have been successfully applied in the past to reconstruct the initial geometry of the spreading system associated to the ophiolite formation. Furthermore, oceanic detachment faults, structures widely occurring in modern magma-poor (slow-spreading) mid-ocean ridges, have been recently recognized also in ophiolites (i.e., Mirdita ophiolite of Albania), and (if present) their study may provide unique insights into the geodynamics and geometry of the associated spreading system. The YZSZ ophiolites form a 2500 km long belt mainly composed of dismembered ultramafic massifs locally covered by a crustal sequence and oceanic sediments, underlying a regionally continuous clastic Xigaze sedimentary basin interpreted as the Tibetan forearc. Our study focused along a ~250 km transect within the eastern sector of the YZSZ between the Sangsang and Xigatze ophiolite. Paleomagnetic, structural geological, and geochemical analyses evidenced the presence of fossil oceanic detachment faults that locally (Sangsang) exposed the lowermost units (mantle) directly at the seafloor. Based on this evidence, and the reconstructed rotation pattern of the region we propose a tectonic evolutionary model characterized by the interplay between magmatic crustal accretion and trench-parallel and trench-perpendicular tectonic extension

  2. Long-term and Short-term Vertical Deformation Rates across the Forearc in the Central Mexican Subduction Zone

    NASA Astrophysics Data System (ADS)

    Ramirez-Herrera, M. T.; Gaidzik, K.; Forman, S. L.; Kostoglodov, V.; Burgmann, R.

    2015-12-01

    Spatial scales of the earthquake cycle, from rapid deformation associated with earthquake rupture to slow deformation associated with interseismic and transient slow-slip behavior, span from fractions of a meter to thousands of kilometers (plate boundaries). Similarly, temporal scales range from seconds during an earthquake rupture to thousands of years of strain accumulation between earthquakes. The complexity of the multiple physical processes operating over this vast range of scales and the limited coverage of observations leads most scientists to focus on a narrow space-time window to isolate just one or a few process. We discuss here preliminary results on the vertical crustal deformation associated with both slow and rapid crustal deformation along a profile across the forearc region of the central Mexican subduction zone on the Guerrero sector, where the Cocos plate underthrusts the North American plate. This sector of the subduction zone is characterized by a particular slab geometry (with zones of rapid bending-unbending of the slab), irregular distributed seismicity, exceptionally large slow slip events (SSE) and non-volcanic tremors (NVT). We used the river network and geomorphic features of the Papagayo River to assess Quaternary crustal deformation. The Papagayo drainage network is strongly controlled by Late Cenozoic tectonic, Holocene and recent earthquake cycle processes. This is particularly true for the southern section of the drainage basin; from the dam in La Venta to the river mouth, where W-E structures commonly offset the course of the main river. River terraces occur along the course of the river at different elevations. We measured the height of a series of terraces and obtained OSL ages on quartz extracts to determine long-term rates of deformation. Finally, we discuss associations of the topography and river characteristics with the Cocos slab geometry, slow earthquakes, crustal deformation, and interseismic deformation.

  3. Constraining the Fore-Arc Flux Along the Central America Margin

    NASA Astrophysics Data System (ADS)

    Hilton, D. R.; Barry, P. H.; Ramirez, C. J.; Kulongoski, J. T.; Patel, B. S.; Blackmon, K.

    2014-12-01

    The transport of carbon to the deep mantle via subduction zones is interrupted by outputs via the fore-arc, volcanic front, and back-arc regions. Whereas output fluxes for the front and back-arc locales are well constrained for Central America (CA) [1], the fore-arc flux via cold seeps and groundwaters is virtually unknown. We present new He and CO2 data for the inner fore-arc of Costa Rica and western Panama to complement our study [2] of offshore CO2fluxes on the outer-forearc. On the Nicoya Peninsula, the Costa Rica Pacific coastline (including the Oso Peninsula) and the Talamanca Mountain Range, as well as coastal seeps in Panama, coupled CO2-He studies allow recognition of mantle (3He/4He up to 6RA) and crustal inputs to the volatile inventory. We associate the crustal component with CO2 derived from limestone (L) and organic sediments (S) on the subducting slab, and see a decrease in the L/S ratio trench-ward with the lowest values akin to those of diatomaceous ooze in the uppermost sequence of the subducting sediment package. This observation is consistent with the removal of the uppermost organic-rich sediment from deep subduction by under-plating. As the input carbon fluxes of the individual sedimentary layers are well constrained [3], we can limit the potential steady-state flux of carbon loss at the subaerial fore-arc to ~ 6 × 107 gCkm-1yr-1, equivalent to ~88% of the input flux of C associated with the ooze, or <4% of the total incoming sedimentary C. This study confirms that the greatest loss of slab-derived carbon at the CA margin occurs at the volcanic front with recycling efficiencies between 12% (Costa Rica) and 29% (El Salvador) of the sedimentary input [1]. It also demonstrates the utility of the coupled He-CO2approach for mass balance studies at subduction zones. [1] De Leeuw et al., EPSL, 2007; [2] Furi et al., G-cubed, 2010; [3] Li and Bebout, JGR, 2005.

  4. Emplacement, growth, and gravitational deformation of serpentinite seamounts on the Mariana forearc

    NASA Astrophysics Data System (ADS)

    Oakley, A. J.; Taylor, B.; Fryer, P.; Moore, G. F.; Goodliffe, A. M.; Morgan, J. K.

    2007-08-01

    Serpentinite seamounts, representing some of the first material outputs of the recycling process that takes place in subduction zones, are found on the outer Mariana forearc. Multichannel seismic (MCS) and bathymetric data collected in 2002 image the large-scale structures of five seamounts, as well as the pre-seamount basement geometry and sediment stratigraphy. We present data from three edifices that provide insights into seamount growth and internal deformation processes and allow us to support the interpretation that serpentinite mud volcanoes are formed by the episodic eruption of mud flows from a central region. The presence of thrust faulting at the base of Turquoise and Big Blue Seamounts, along with the low surface slopes (5°-18°) of all the seamounts studied, lead us to infer that these edifices spread laterally and are subject to gravitational deformation as they grow. Numerical simulations using the discrete element method (DEM) were used to model their growth and the origins of features that we see in MCS sections, such as basal thrusts, inward-dipping reflections and mid-flank benches. The DEM simulations successfully reproduced many of the observed features. Simulations employing very low basal and internal friction coefficients (~0.1 and ~0.4, respectively) provide the best match to the overall morphology and structures of the serpentinite seamounts. However the simulations do not capture all of the processes involved in seamount growth, such as withdrawal of material from a central conduit leading to summit deflation; compaction, dewatering and degassing of mud flows; mass wasting in the form of sector collapse and growth upon a dipping substrate. A strong reflection beneath the summit of Big Blue, the largest serpentinite seamount on the Mariana forearc, represents the floor of a summit depression that has been partially in-filled by younger muds, supporting the idea that serpentinite seamounts grow by episodic mud volcanism. Boundaries of mud

  5. Evidence for formation of a flexural backarc basin by compression and crustal thickening in the central Alaska peninsula

    SciTech Connect

    Bond, G.C.; Lewis, S.D.; Taber, J.; Steckler, M.S.; Kominz, M.A. )

    1988-12-01

    The North Aleutian Basin is a large, Cenozoic sedimentary basin in the northern part of the central Alaska Peninsula and the southern Bering shelf. The gravity anomaly pattern, the geometry, and the structure of the basin suggest that if formed by downward flexure of the backarc lithosphere. Basin modeling suggests that the flexure was driven by the emplacement of surface and subsurface loads having densities comparable to those of oceanic crust and mantle rocks, at approximately the position of the present-day volcanic arc and forearc. The authors suggest that the inferred loads consist of tectonically thickened mafic crustal materials lying beneath the arc and forearc of the central Alaska Peninsula. The crustal thickening may have occurred within a dominantly transpressional regime resulting from oblique convergence between the North American and Pacific plates during the Cenozoic.

  6. Basin-centered asperities in great subduction zone earthquakes: A link between slip, subsidence, and subduction erosion?

    USGS Publications Warehouse

    Wells, R.E.; Blakely, R.J.; Sugiyama, Y.; Scholl, D. W.; Dinterman, P.A.

    2003-01-01

    Published areas of high coseismic slip, or asperities, for 29 of the largest Circum-Pacific megathrust earthquakes are compared to forearc structure revealed by satellite free-air gravity, bathymetry, and seismic profiling. On average, 71% of an earthquake's seismic moment and 79% of its asperity area occur beneath the prominent gravity low outlining the deep-sea terrace; 57% of an earthquake's asperity area, on average, occurs beneath the forearc basins that lie within the deep-sea terrace. In SW Japan, slip in the 1923, 1944, 1946, and 1968 earthquakes was largely centered beneath five forearc basins whose landward edge overlies the 350??C isotherm on the plate boundary, the inferred downdip limit of the locked zone. Basin-centered coseismic slip also occurred along the Aleutian, Mexico, Peru, and Chile subduction zones but was ambiguous for the great 1964 Alaska earthquake. Beneath intrabasin structural highs, seismic slip tends to be lower, possibly due to higher temperatures and fluid pressures. Kilometers of late Cenozoic subsidence and crustal thinning above some of the source zones are indicated by seismic profiling and drilling and are thought to be caused by basal subduction erosion. The deep-sea terraces and basins may evolve not just by growth of the outer arc high but also by interseismic subsidence not recovered during earthquakes. Basin-centered asperities could indicate a link between subsidence, subduction erosion, and seismogenesis. Whatever the cause, forearc basins may be useful indicators of long-term seismic moment release. The source zone for Cascadia's 1700 A.D. earthquake contains five large, basin-centered gravity lows that may indicate potential asperities at depth. The gravity gradient marking the inferred downdip limit to large coseismic slip lies offshore, except in northwestern Washington, where the low extends landward beneath the coast. Transverse gravity highs between the basins suggest that the margin is seismically segmented and

  7. Sr isotopic composition of gypsic paleosols as a proxy for Neogene forearc uplift in the South America - Nazca plate system at latitudes 19 to 22° S

    NASA Astrophysics Data System (ADS)

    Cosentino, N. J.; Jordan, T. E.

    2011-12-01

    Quantification of uplift of a continental surface relative to sea level is challenging. The study area comprises the forearc associated with the South America - Nazca plate margin in northern Chile. The Coastal Cordillera (CdlC) is a mountain range 800 to 2300 m in elevation that ends abruptly to the west at the Pacific Ocean, terminated at a 400 m to 1700 m high scarp. The CdlC is formed mainly of Jurassic - Early Cretaceous igneous rocks, the remnants of a Mesozoic magmatic arc. To the east, the Central Depression (CD) is a forearc basin filled with Cenozoic sediments derived from the arc to the east. Arid to hyperarid climate conditions dominated throughout the Neogene. Profiles from rivers draining the CD and cutting through the CdlC are strongly suggestive that at least 1 km of relative surface uplift occurred since 10 Ma. Paleogeographic reconstructions of continental deposits, marine terraces and tilted originally horizontal depositional surfaces in the CdlC constrain surface uplift histories. However, we seek quantitative information about the magnitude as well as ages of uplift, so that numerical models of forearc geodynamics can be tested against uplift history. We are testing a new paleoaltimetry proxy based on the 87Sr/86Sr ratio of gypsum-rich paleosols. Published studies show that modern pedogenic gypsum in the study area is derived from two sources of distinguishable Sr isotopic values; salts precipitate from aerosols in persistent winter marine fogs and dust comes from the weathering of Andean rocks. It has been shown for modern soils that a transect from the coast to the Andes reveals a progressive decline in 87Sr/86Sr, corresponding to the mixing of marine aerosols and weathered dust. Below 1.5 km altitude, the marine signal diminishes as altitude rises. The low mass difference between 87Sr and 86Sr leads to little fractionation by environmental processes, which is ideal for studying the primary marine vs. Andean signal. Because the Neogene strata

  8. Searching for conditions of observation of subduction seismogenic zone transients on Ocean Bottom Seismometers deployed at the Lesser Antilles submerged fore-arc

    NASA Astrophysics Data System (ADS)

    Bécel, Anne; Laigle, Mireille; Diaz, Jordi; Hirn, Alfred; Flueh, Ernst; Charvis, Philippe

    2010-05-01

    different instruments deployments, it provided diverse views, as through different glasses. This ultimately proved valuable to help extract the harder facts from their diverse appearances when seen through different instruments and in different types of sites. After analyzing the data for spurious and instrument-related peculiarities, and possible interpretation pitfalls, it remains that the noise level shows an overwhelming influence of the marine domain due to both its own sources, hydrosphere motions, and to meteorological-climatological actions. As well, the response of the laterally variable fore-arc basin on top of which measurements have to be made is much adverse to quality recording, with respect to seismological observatories on land which can be buried deep into basement rocks. The study of this noise itself may allow us to initiate a discussion of the interactions of the oceanic and atmospheric processes with the Solid Earth. Transients at depth in the subduction zone have been tentatively discussed in terms of its seismogenic evolution. If such transient events would indeed have a component over a very broad spectral range from NVT to LP and ULP events as it has been suggested very recently in Japan (Ide et al., 2008), the conditions and the best observation windows in which they can be best searched for are now documented for ocean bottom recording in the case of the Lesser Antilles subduction zone.

  9. Utilization of the Local Government Health Insurance Scheme (JKA) for Maternal Health Services Among Women Living in Underdeveloped Areas of Aceh Province, Indonesia.

    PubMed

    Kesuma, Zurnila Marli; Chongsuvivatwong, Virasakdi

    2015-04-01

    Aceh province of Indonesia created its own health coverage scheme called Jaminan Kesehatan Aceh (JKA) to cover Aceh's populations who were not registered under insurance for the poor (Jamkesmas). This study aims to compare the utilization rate of maternal health care (MHC) services and contraceptive prevalence rate (CPR) before JKA, during the transition period, and after JKA had been established. A cross-sectional household survey was conducted from June 2011 to July 2012. Utilization of MHC services and CPR during the 3 periods was assessed using a questionnaire. The Mantel-Haenszel χ(2) test was used to examine the association between period and coverage. Generalized estimating equations (GEEs) were used to examine utilization and type of service, period of service, and type of scheme. Coverage of utilization of skilled birth attendants significantly improved among the JKA holders (odds ratio = 1.84; 95% confidence interval = 1.18-2.89). JKA, thus, has shown its positive impact. PMID:24566605

  10. The Southern Mariana Forearc: An Active Subduction Initiation (SI) Analogue

    NASA Astrophysics Data System (ADS)

    Stern, R. J.; Bloomer, S. H.; Brounce, M. N.; Ishii, T.; Ishizuka, O.; Kelley, K. A.; Martinez, F.; Ohara, Y.; Pujana, I.; Reagan, M. K.; Ribeiro, J.

    2014-12-01

    It is important to understand how new subduction zones form. Some subduction zones begin spontaneously, with sinking of dense oceanic lithosphere adjacent to a lithospheric weakness. The Eocene evolution of the Izu-Bonin-Mariana convergent margin is the type example of this process, with an increasingly well-documented evolution including results from IODP 352 drilling. A lack of any active examples of spontaneous SI hinders our understanding, but our studies of the evolution of the southernmost Mariana convergent margin provides important insights. Here the Mariana Trough backarc basin terminates against the Challenger Deep trench segment, where it has opened ~250 km in the past ~4 Ma. This corresponds to GPS opening rate of ~4.5cm/y at the latitude of Guam (Kato et al., 2003). This newly formed and rapidy widening margin faces the NW-converging Pacific plate and causes it to contort and tear. Pacific plate continues to move NW but the upper plate response is illustrative of a newly formed subduction zone. Slab-related earthquakes can be identified to ~200 km deep beneath this margin; with convergence rate of 3cm/yr, this may reflect no more than 7 Ma of subduction. The usual well-defined magmatic arc is missing; its position ~100 km above the subducted slab is occupied by the magma-rich (inflated) Malaguana-Gadao Ridge (MGR), and hydrous MORB-like basalts with ~2 wt. % H2O have erupted unusually close to the trench where they overly mantle peridotites ~6 km water depth. HMR-1 sonar backscatter mapping reveals a chaotic fabric that is at a high angle to the trend of the MGR to the east but is concordant to the west. This unusual spreading fabric may have formed by chaotic upper plate extension in response to rapid rollback of the short, narrow Pacific slab in a manner similar to that thought to occur during SI. Further interdisciplinary studies are needed to understand this rapidly-evolving tectono-magmatic province and what it can teach us about SI.

  11. The Great 2006 and 2007 Kuril Earthquakes, Forearc Segmentation and Seismic Activity of the Central Kuril Islands Region

    NASA Astrophysics Data System (ADS)

    Baranov, B. V.; Ivashchenko, A. I.; Dozorova, K. A.

    2015-12-01

    We present a structural study of the Central Kuril Islands forearc region, where the great megathrust tsunamigenic earthquake ( M w 8.3) occurred on November 15, 2006. Based on new bathymetry and seismic profiles obtained during two research cruises of R/V Akademik Lavrentiev in 2005 and 2006, ten crustal segments with along-arc length ranging from 30 to 100 km, separated by NS- and NW-trending transcurrent faults were identified within the forearc region. The transcurrent faults may serve as barriers impeding stress transfer between the neighboring segments, so that stress accumulated within separate forearc segments is usually released by earthquakes of moderate-to-strong magnitudes. However, the great November 15, 2006 earthquake ruptured seven of the crustal segments probably following a 226-year gap since the last great earthquake in 1780. The geographic extent of earthquake rupture zones, aftershock areas and earthquake clusters correlate well with forearc crustal segments identified using the geophysical data. Based on segmented structure of the Central Kuril Islands forearc region, we consider and discuss three scenarios of a great earthquake occurrence within this area. Although the margin is segmented, we suggest that a rupture could occupy the entire seismic gap with a total length of about 500 km. In such a case, the earthquake magnitude M w might exceed 8.5, and such an event might generate tsunami waves significantly exceeding in height to those produced by the great 2006-2007 Kuril earthquakes.

  12. Detailed seismic velocity structure beneath the Hokkaido corner, NE Japan: Collision process of the forearc sliver

    NASA Astrophysics Data System (ADS)

    Kita, S.; Hasegawa, A.; Okada, T.; Nakajima, J.; Matsuzawa, T.; Katsumata, K.

    2010-12-01

    1. Introduction In south-eastern Hokkaido, the Kuril forearc sliver is colliding with the northeastern Japan arc due to the oblique subduction of the Pacific plate. This collision causes the formation of the Hidaka mountain range since the late Miocene (Kimura, 1986) and delamination of the lower-crust materials of the Kuril forearc sliver, which would be expected to descend into the mantle wedge below (e.g., Ito 2000; Ito and Iwasaki, 2002). In this study, we precisely investigated the three-dimensional seismic velocity structure beneath the Hokkaido corner to examine the collision of two forearcs in this area by using both of data from a dense temporary seismic network deployed in this area (Katsumata et al. [2006]) and those from the Kiban observation network, which covers the entire Japanese Islands with a station separation of 15-20 km. 2. Data and method The double-difference tomography method (Zhang and Thurber, 2003; 2006) was applied to a large number of arrival time data of 201,527 for P-waves and 150,963 for S-waves that were recorded at 125 stations from 10,971 earthquakes that occurred from 1999 to 2010. Grid intervals were set at 10 km in the along-arc direction, 12.5 km perpendicular to it, and 5-10 km in the vertical direction. 3. Results and discussion Inhomogeneous seismic velocity structure was clearly imaged in the Hokkaido corner at depths of 0-120 km. A high-velocity anomaly of P- and S- waves with a volume of 20 km x 90 km x 35km was detected just beneath the main zone of the Hidaka metamorphic belt at depths of 0-35 km. This high-velocity anomaly is continuously distributed from the depths of the mantle wedge to the surface. The western edge of the anomaly exactly corresponds to the Hidaka main thrust (HMT) at the surface. The highest velocity value in the anomaly corresponds to those of the uppermost mantle material (e.g. peridotite). The location of them at depths of 0-35km is also consistent with that of the Horoman-Peridotite belt, which

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

    USGS Publications Warehouse

    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.

  14. Stress switching in subduction forearcs: Implications for overpressure containment and strength cycling on megathrusts

    NASA Astrophysics Data System (ADS)

    Sibson, Richard H.

    2013-07-01

    Seismogenic megathrusts contained within subduction interface shear zones (SISZ) appear generally to be overpressured to near-lithostatic values (λv > 0.9) below forearc hanging-walls. Solution transfer within fine-grained material along the deeper interface (150 < T < 350 °C) contributes to hydrothermal sealing of fractures lowering bulk permeability. Down-dip variations in overpressuring likely affect the depth of the peak in frictional shear resistance which may serve as the prime asperity affecting megathrust rupture. To account for postseismic changes in the velocity structure of the fore-arc hanging-wall following the 1995 Antofagasta, Chile, Mw8.0 megathrust rupture, Husen and Kissling (2001) proposed massive trans-megathrust discharge of fluids across the interface. Such discharges are a form of 'fault-valve' action where the megathrust itself acts as a seal to overpressured fluids derived from within the SISZ and from dehydration of the descending slab. Brittle failure or fault reactivation limits fluid overpressure which is highest at low differential stress under a compressional stress regime. Over much of the forearc hanging-wall of the 2011 Mw9.0 Tohoku-Oki megathrust rupture, focal mechanisms show that the stress-state switched from compressional reverse-slip faulting prefailure to extensional normal-slip faulting postfailure. Mean stress and fault-normal stress thus changed from being greater than vertical stress prefailure, to less than vertical stress postfailure. Reductions in overpressure are expected from a combination of poroelastic effects and fluid loss through fault-fracture networks enhancing postfailure permeability in the changing stress field. Local drainage across the subduction interface increases frictional strength significantly, giving rise to a postfailure distribution of strength asperities. The amplitude of strength variations from such fluid discharge is potentially large (< hundreds of MPa). Time to the next failure is then

  15. Early Eocene uplift of southernmost San Joaquin basin, California

    SciTech Connect

    Reid, S.A.; Cox, B.F.

    1989-04-01

    Stratigraphic studies in the southern San Joaquin basin and in the El Paso Mountains of the southwestern Great Basin corroborate a hypothesized early Eocene regional uplift event. Eocene uplift and erosion of the southernmost San Joaquin basin south of Bakersfield were recently proposed because an early Paleogene fluviodeltaic sequence in the El Paso Mountains (Goler Formation) apparently had no seaward counterpart to the southwest. New microfossil data (coccoliths) indicate that marine deposits near the top of the Goler Formation are uppermost Paleocene (nannofossil zone CP8) rather than lower Eocene, as reported previously. These data (1) confirm that the oldest known Tertiary strata south of Bakersfield (Eocene Tejon Formation) are younger than the uppermost Goler Formation and (2) seem to restrict uplift to the earliest Eocene. The authors propose that the uppermost Cretaceous and Paleocene deposits were eroded and the Mushrush trough was cut and filled mainly in response to earliest Eocene uplift. The uplift was transverse to the northwest-trending forearc basin. Thus, it was distinct from late early Eocene (pre-Comengine Formation) regional tilting and uplift, which produced northwest-trending structures. Early Eocene uplift probably played only a minor role in the southward termination of pre-Maastrichtian parts of the forearc basin, which they instead attribute to massive uplift of the southernmost Sierra Nevada during the early(.) Late Cretaceous.

  16. Multi-phase Uplift of the Indo-Burman Ranges and Western Thrust Belt of Minbu Sub-basin (West Myanmar): Constraints from Apatite Fission Track Data

    NASA Astrophysics Data System (ADS)

    Zhang, P.; Qiu, H.; Mei, L.

    2015-12-01

    The forearc regions in active continental margins are important keys to analysis geodynamic processes such as oceanic crust oblique subduction, mechanism of subduction zone, and sediments recycling. The West Myanmar, interpreted as forearc silver, is the archetype example of such forearc regions subordinate to Sunda arc-trench system, and is widely debated when and how its forearc regions formed. A total of twenty-two samples were obtained from the Indo-Burman Ranges and western thrust belt of Minbu Sub-basin along Taungup-Prome Road in Southwestern Myanmar (Figure 1), and five sandstone samples of them were performed at Apatite to Zircon, Inc. Three samples (M3, M5, and M11) collected from Eocene flysch and metamorphic core at the Indo-Burman Ranges revealed apatite fission track (AFT) ages ranging from 19 to 9 Ma and 6.5 to 2 Ma. Two samples (M20 and M21) acquired from the western thrust belt of Minbu Sub-basin yielded AFT ages ranging from 28 to 13.5 Ma and 7.5 to 3.5 Ma. Time-temperature models based on AFT data suggest four major Cenozoic cooling episodes, Late Oligocene, Early to Middle Miocene, Late Miocene, and Pliocene to Pleistocene. The first to third episode, models suggest the metamorphic core of the Indo-Burman Ranges has experienced multi-phase rapidly uplifted during the early construction of the forearc regions. The latest episode, on which this study focused, indicated a fast westward growth of the Palaeogene accretionary wedge and a eastward propagation deformation of folding and thrusting of the western thrust belt of Minbu Sub-basin. We argued that above multi-phase uplifted and deformation of the forearc regions were results of India/West Burma plate's faster oblique convergence and faster sedimentation along the India/Eurasia suture zone.

  17. Geodynamic models of continental subduction and obduction of overriding plate forearc oceanic lithosphere on top of continental crust

    NASA Astrophysics Data System (ADS)

    Edwards, Sarah J.; Schellart, Wouter P.; Duarte, Joao C.

    2015-07-01

    Continental subduction takes place in the final stage of subduction when all oceanic lithosphere is consumed and continental passive margin is pulled into the mantle. When the overriding plate is oceanic, dense forearc oceanic lithosphere might be obducted onto light continental crust forming an ophiolite (Tethyan-style ophiolite obduction). Four-dimensional dynamic analog subduction models have been constructed to evaluate the mechanical feasibility of continental subduction and forearc oceanic lithosphere obduction on top of continental crust. The roles of continental crust thickness, passive margin length, subducting lithosphere thickness, and overriding plate thickness were investigated to determine the maximum continental subduction depth, maximum forearc obduction distance, and forearc deformation during continental subduction. Our buoyancy-driven experiments indicate that deep continental subduction occurs in most circumstances (down to ~560 km) and that obduction of dense oceanic forearc lithosphere on top of light continental crust is mechanically feasible. Maximum obduction distances are relatively small (~26-37 km) but are sufficient to explain obduction of short ophiolite sheets, such as observed in New Caledonia. When including the thin (5-10 km thick) accretionary wedge of off-scraped deep sea sediments, oceanic crust, and mantle, then maximum obduction distances are much larger, ~60-160 km, sufficient to account for the obducted Northland Allochthon in New Zealand. Results indicate that increasing continental crust thickness decreases continental subduction depth, whereas increasing passive margin length and subducting lithosphere thickness increases continental subduction depth. Notably, during continental subduction, backarc extension continues, while forearc deformation (shortening) increases moderately compared to the preceding phase of normal (oceanic) subduction.

  18. Forearc oceanic crust in the Izu-Bonin arc - new insights from active-source seismic survey -

    NASA Astrophysics Data System (ADS)

    Kodaira, S.; Noguchi, N.; Takahashi, N.; Ishizuka, O.; Kaneda, Y.

    2009-12-01

    Petrological studies have suggested that oceanic crust is formed in forearc areas during the initial stage of subduction. However, there is little geophysical evidence for the formation of oceanic crust in those regions. In order to examine crustal formation process associated with a subduction initiation process, we conducted an active-source seismic survey at a forearc region in the Izu-Bonin intra-oceanic arc. The resultant seismic image shows a remarkably thin crust (less than 10 km) at the northern half of the Bonin ridge (at the north of the Chichi-jima) and abrupt thickening the crust (~ 20 km thick) toward the south (at the Haha-jima). Comparison of velocity-depth profiles of the thin forearc crust of the Bonin ridge with those of typical oceanic crusts showed them to be seismologically identical. The observed structural variation also well corresponds to magmatic activities along the forearc. Boninitic magmatism is evident in the area of thin crust and tholeiitic-calcalkaline andesitic volcanism in the area of thick crust. Based on high precision dating studies of those volcanic rocks, we interpreted that the oceanic-type thin crust associated with boninitic volcanism has been created soon after the initiation of subduction (45-48 Ma) and and that the nonoceanic thick crust was created by tholeiitic-calcalkaline andesitic magmatism after the boninitic magmatism was ceased. The above seismological evidences strongly support the idea of forearc oceanic crust (or phiolite) created by forearc spreading in the initial stage of subduction along the intra-oceanic arc.

  19. Outbreak of tetanus cases following the tsunami in Aceh Province, Indonesia.

    PubMed

    2006-01-01

    Aceh Province in Indonesia was the area most severely affected by the tsunami of 26 December 2004. Extensive loss of life, property, and livelihood left a large segment of the population without basic needs and vulnerable to epidemic-prone diseases. Following the tsunami, a surveillance/early warning and response system was implemented to detect, investigate, and respond to outbreaks of communicable diseases. Fixed and mobile clinics, hospitals, and laboratories, operating all over the affected areas, reported weekly figures and daily alerts. Over 1 month following the tsunami, 106 cases of clinically diagnosed tetanus were reported. Most cases occurred among adults. The case fatality ratio was 18.9%, higher among older patients and among those with short incubation periods. No other major outbreaks occurred in the acute phase of the emergency. This series of tetanus cases was the largest cluster reported following a natural disaster or mass casualty event, overtaken only by the recent earthquake in the Kashmir (139 cases reported), and reflects the high number of injuries which occurred during the tsunami and poor prior immunization status of the population. In the context of natural disasters, preventive measures against tetanus, including wound cleaning and active and passive immunization, should be routinely conducted. Immediate disaster relief should include supplies for the management of wounds and cases of tetanus. PMID:19153905

  20. Rebuilt risk: involuntary return, voluntary migration, and socioeconomic segregation in post-tsunami Aceh

    NASA Astrophysics Data System (ADS)

    McCaughey, Jamie; Daly, Patrick; Mundzir, Ibnu; Mahdi, Saiful; Patt, Anthony

    2016-04-01

    In light of growing coastal populations and rising relative sea levels, understanding the consequences of infrequent, high-impact coastal hazards for human migration is a key ingredient for meeting the challenges of sustainable development. Using new quantitative and qualitative evidence from 1160 households and 121 village leaders, we examine longer-term migration in the city of Banda Aceh, Indonesia, following the devastating 2004 tsunami and an international aid response that offered most survivors only resettlement back in the tsunami-affected area. While many survivors wanted to return, some preferred to relocate further from the coast but did not have the chance to do so. Since that time, selective out-migration by those with the means and socioeconomic sorting of newcomers have led to a new socioeconomic segregation of the tsunami-affected parts of the city. More broadly, these findings suggest that short-distance socioeconomic sorting into and out from vulnerable areas may be an important migratory response to a newly recognized risk.

  1. Penultimate predecessors of the 2004 Indian Ocean tsunami in Aceh, Sumatra: Stratigraphic, archeological, and historical evidence

    NASA Astrophysics Data System (ADS)

    Sieh, Kerry; Daly, Patrick; Edwards McKinnon, E.; Pilarczyk, Jessica E.; Chiang, Hong-Wei; Horton, Benjamin; Rubin, Charles M.; Shen, Chuan-Chou; Ismail, Nazli; Vane, Christopher H.; Feener, R. Michael

    2015-01-01

    We present stratigraphic, archeological and historical evidence for two closely timed predecessors of the giant 2004 tsunami on the northern coast of Aceh, northern Sumatra. This is the first direct evidence that a tsunami played a role in a fifteenth century cultural hiatus along the northern Sumatran portion of the maritime silk route. One seacliff exposure on the eastern side of the Lambaro headlands reveals two beds of tsunamigenic coral rubble within a small alluvial fan. Radiocarbon and Uranium-Thorium disequilibrium dates indicate emplacement of the coral rubble after 1344 ± 3 C.E. Another seacliff exposure, on the western side of the peninsula, contains evidence of nearly continuous settlement from ~1240 C.E. to soon after 1366 ± 3 C.E., terminated by tsunami destruction. At both sites, the tsunamis are likely coincident with sudden uplift of coral reefs above the Sunda megathrust 1394 ± 2 C.E., evidence for which has been published previously. The tsunami (or tsunami pair) appears to have destroyed a vibrant port community and led to the temporary recentering of marine trade dominance to more protected locations farther east. The reestablishment of vibrant communities along the devastated coast by about 1500 CE set the stage for the 2004 disaster.

  2. Influence of coastal vegetation on the 2004 tsunami wave impact in west Aceh

    PubMed Central

    Laso Bayas, Juan Carlos; Marohn, Carsten; Dercon, Gerd; Dewi, Sonya; Piepho, Hans Peter; Joshi, Laxman; van Noordwijk, Meine; Cadisch, Georg

    2011-01-01

    In a tsunami event human casualties and infrastructure damage are determined predominantly by seaquake intensity and offshore properties. On land, wave energy is attenuated by gravitation (elevation) and friction (land cover). Tree belts have been promoted as “bioshields” against wave impact. However, given the lack of quantitative evidence of their performance in such extreme events, tree belts have been criticized for creating a false sense of security. This study used 180 transects perpendicular to over 100 km on the west coast of Aceh, Indonesia to analyze the influence of coastal vegetation, particularly cultivated trees, on the impact of the 2004 tsunami. Satellite imagery; land cover maps; land use characteristics; stem diameter, height, and planting density; and a literature review were used to develop a land cover roughness coefficient accounting for the resistance offered by different land uses to the wave advance. Applying a spatial generalized linear mixed model, we found that while distance to coast was the dominant determinant of impact (casualties and infrastructure damage), the existing coastal vegetation in front of settlements also significantly reduced casualties by an average of 5%. In contrast, dense vegetation behind villages endangered human lives and increased structural damage. Debris carried by the backwash may have contributed to these dissimilar effects of land cover. For sustainable and effective coastal risk management, location of settlements is essential, while the protective potential of coastal vegetation, as determined by its spatial arrangement, should be regarded as an important livelihood provider rather than just as a bioshield. PMID:22065751

  3. Influence of coastal vegetation on the 2004 tsunami wave impact in west Aceh.

    PubMed

    Laso Bayas, Juan Carlos; Marohn, Carsten; Dercon, Gerd; Dewi, Sonya; Piepho, Hans Peter; Joshi, Laxman; van Noordwijk, Meine; Cadisch, Georg

    2011-11-15

    In a tsunami event human casualties and infrastructure damage are determined predominantly by seaquake intensity and offshore properties. On land, wave energy is attenuated by gravitation (elevation) and friction (land cover). Tree belts have been promoted as "bioshields" against wave impact. However, given the lack of quantitative evidence of their performance in such extreme events, tree belts have been criticized for creating a false sense of security. This study used 180 transects perpendicular to over 100 km on the west coast of Aceh, Indonesia to analyze the influence of coastal vegetation, particularly cultivated trees, on the impact of the 2004 tsunami. Satellite imagery; land cover maps; land use characteristics; stem diameter, height, and planting density; and a literature review were used to develop a land cover roughness coefficient accounting for the resistance offered by different land uses to the wave advance. Applying a spatial generalized linear mixed model, we found that while distance to coast was the dominant determinant of impact (casualties and infrastructure damage), the existing coastal vegetation in front of settlements also significantly reduced casualties by an average of 5%. In contrast, dense vegetation behind villages endangered human lives and increased structural damage. Debris carried by the backwash may have contributed to these dissimilar effects of land cover. For sustainable and effective coastal risk management, location of settlements is essential, while the protective potential of coastal vegetation, as determined by its spatial arrangement, should be regarded as an important livelihood provider rather than just as a bioshield. PMID:22065751

  4. The Tonalá fault in southeastern Mexico: Evidence that the Central America forearc sliver is not being detached?

    NASA Astrophysics Data System (ADS)

    Guzman-Speziale, M.; Molina-Garza, R. S.

    2012-12-01

    The Tonalá fault is a NW-SE oriented feature that flanks the Chiapas Massif on its southwestern side. Several authors coincide that the fault originally developed as a right-lateral structure in the Jurassic, but was reactivated as a left-lateral fault in the Miocene. Seismicity along the fault is low: Only one earthquake with magnitude 5.0 or larger is reported along the Tonalá fault in the years 1964 to present. Fault-plane solutions determined by the Mexican Seismological Survey for earthquakes along the fault show left-lateral, strike-slip faulting. The Tonalá fault lies on the northwestern continuation of the Central America volcanic arc. The volcanic arc is the site of medium-sized (magnitudes up to 6.5) shallow, right-lateral, strike-slip earthquakes. This has led several workers to propose that the forearc sliver is being detached from the Caribbean plate along the arc, moving northward. GPS studies have confirmed relative motion between the Chortis block and the forearc sliver. Recent and current motion along the Tonalá fault is in contradiction with motion and detachment of the forearc sliver along the Central America volcanic arc. Left-lateral motion along it cannot accomodate northwest displacement of the forearc sliver. Motion of the Central America forearc would require NW directed compression between the continental shelf of Chiapas and the forearc itself, which is not observed. Therefore, either another fault (or faults) accomodates right-lateral motion and detachment of the forearc sliver, or the sliver is not being detached and relative motion between the forearc sliver and the Chortis block corresponds to displacement of the latter. We suggest that, as proposed by previous authors, the Tonalá fault is instead part of a fault system that runs from the state of Oaxaca (the Valle Nacional fault), forming an arc concave to the northeast, and running perpendicular to the maximum slope of subduction in the area.

  5. Heavy Oil and Natural Bitumen Resources in Geological Basins of the World

    USGS Publications Warehouse

    Meyer, Richard F.; Attanasi, E.D.; Freeman, P.A.

    2007-01-01

    Heavy oil and natural bitumen are oils set apart by their high viscosity (resistance to flow) and high density (low API gravity). These attributes reflect the invariable presence of up to 50 weight percent asphaltenes, very high molecular weight hydrocarbon molecules incorporating many heteroatoms in their lattices. Almost all heavy oil and natural bitumen are alteration products of conventional oil. Total resources of heavy oil in known accumulations are 3,396 billion barrels of original oil in place, of which 30 billion barrels are included as prospective additional oil. The total natural bitumen resource in known accumulations amounts to 5,505 billion barrels of oil originally in place, which includes 993 billion barrels as prospective additional oil. This resource is distributed in 192 basins containing heavy oil and 89 basins with natural bitumen. Of the nine basic Klemme basin types, some with subdivisions, the most prolific by far for known heavy oil and natural bitumen volumes are continental multicyclic basins, either basins on the craton margin or closed basins along convergent plate margins. The former includes 47 percent of the natural bitumen, the latter 47 percent of the heavy oil and 46 percent of the natural bitumen. Little if any heavy oil occurs in fore-arc basins, and natural bitumen does not occur in either fore-arc or delta basins.

  6. Seismotectonic implications of the Kyushu-Palau ridge subducting beneaththe westernmost Nankai forearc

    NASA Astrophysics Data System (ADS)

    Park, J.-O.; Hori, T.; Kaneda, Y.

    2009-08-01

    The Kyushu-Palau ridge, a remnant arc on the Philippine Sea Plate, subducts beneath the Eurasian Plate along the westernmost part of the Nankai Trough. A seismic reflection profile on strike line images the ˜70-km-wide Kyushu-Palau ridge where it subducts beneath the toe of the forearc accretionary wedge. The geomagnetic anomaly signature, seafloor topographic features, wide-angle refraction data, and on-land geomorphologic evidence enable us to trace the forearc extension of the subducted ridge up to the east Kyushu. The subducted Kyushu-Palau ridge with excess mass may be relatively buoyant, and thus is more likely to resist subduction upon collision with the overriding plate at depth, leading us to speculate that there is locally large tectonic stress at the contact zone between the subducted ridge and base of the overriding plate. The large stress zone is marked by historic thrust-type intermediate-class (magnitude 6 or 7) earthquakes. The flank regions of the subducted buoyant Kyushu-Palau ridge are more likely to tear and result in slab fracturing when the ridge subducts deeper. We propose that the subducted Kyushu-Palau ridge may serve not only as a seismic asperity at depth but also produce the slab fracture as a seismic barrier inhibiting the rupture propagation of the adjacent megathrust earthquakes in the Hyuga segment.

  7. Atmospheric Ar and Ne returned from mantle depths to the Earth's surface by forearc recycling.

    PubMed

    Baldwin, Suzanne L; Das, J P

    2015-11-17

    In subduction zones, sediments, hydrothermally altered lithosphere, fluids, and atmospheric gases are transported into the mantle, where ultrahigh-pressure (UHP) metamorphism takes place. However, the extent to which atmospheric noble gases are trapped in minerals crystallized during UHP metamorphism is unknown. We measured Ar and Ne trapped in phengite and omphacite from the youngest known UHP terrane on Earth to determine the composition of Ar and Ne returned from mantle depths to the surface by forearc recycling. An (40)Ar/(39)Ar age [7.93 ± 0.10 My (1σ)] for phengite is interpreted as the timing of crystallization at mantle depths and indicates that (40)Ar/(39)Ar phengite ages reliably record the timing of UHP metamorphism. Both phengite and omphacite yielded atmospheric (38)Ar/(36)Ar and (20)Ne/(22)Ne. Our study provides the first documentation, to our knowledge, of entrapment of atmospheric Ar and Ne in phengite and omphacite. Results indicate that a subduction barrier for atmospheric-derived noble gases does not exist at mantle depths associated with UHP metamorphism. We show that the crystallization age together with the isotopic composition of nonradiogenic noble gases trapped in minerals formed during subsolidus crystallization at mantle depths can be used to unambiguously assess forearc recycling of atmospheric noble gases. The flux of atmospheric noble gas entering the deep Earth through subduction and returning to the surface cannot be fully realized until the abundances of atmospheric noble gases trapped in exhumed UHP rocks are known. PMID:26542683

  8. Possible emplacement of crustal rocks into the forearc mantle of the Cascadia Subduction Zone

    USGS Publications Warehouse

    Calvert, A.J.; Fisher, M.A.; Ramachandran, K.; Trehu, A.M.

    2003-01-01

    Seismic reflection profiles shot across the Cascadia forearc show that a 5-15 km thick band of reflections, previously interpreted as a lower crustal shear zone above the subducting Juan de Fuca plate, extends into the upper mantle of the North American plate, reaching depths of at least 50 km. In the extreme western corner of the mantle wedge, these reflectors occur in rocks with P wave velocities of 6750-7000 ms-1. Elsewhere, the forearc mantle, which is probably partially serpentinized, exhibits velocities of approximately 7500 ms-1. The rocks with velocities of 6750-7000 ms-1 are anomalous with respect to the surrounding mantle, and may represent either: (1) locally high mantle serpentinization, (2) oceanic crust trapped by backstepping of the subduction zone, or (3) rocks from the lower continental crust that have been transported into the uppermost mantle by subduction erosion. The association of subparallel seismic reflectors with these anomalously low velocities favours the tectonic emplacement of crustal rocks. Copyright 2003 by the American Geophysical Union.

  9. Tectonic controls on sedimentation in Mesozoic convergent margin basin of Baja California (Mexico)

    SciTech Connect

    Busby-Spera, C.J.; Smith, D.P.; Morris, W.R. )

    1990-05-01

    Mesozoic rocks of the Baja California peninsula form one of the most extensive, best exposed, oldest (160 m.y.), and least-tectonized and metamorphosed convergent margin basin complexes in the world. Much of the fill of these basins consist of coarse-grained volcaniclastic and epiclastic sequences that directly reflect the tectonic evolution of the region. The early history of the convergent margin was dominated by sedimentation in small, steep-sided basins within oceanic island arc systems. The Triassic and Jurassic convergent margin basins probably represent proto-Pacific terranes that traveled from another area. These terranes were assembled by the Late Jurassic to Early Cretaceous, and underlie the forearc region of a medial Cretaceous oceanic island arc system. Tbis system fringed the Mesoamerican continental margin and underwent regional-scale extension during subduction of old, dense lithosphere. The latest phases of sedimentation in the convergent margin occurred in broad, relatively stable forearc basins of a mature continental arc, during the Late Cretaceous to Paleocene. Nonetheless, intrabasinal faults provided some controls on depositional systems and bathymetry. The authors speculate that these faults formed in response to oblique convergence which ultimately resulted in 10-19{degree} northward displacement of Baja California relative to the North American craton, from the latitude of Central America to northern Mexico. The fill of oceanic island arc basins in Baja California is dominated by coarse-grained marine wedges including (1) arc apron deposits, consisting of pyroclastic and/or volcanic epiclastic debris deposited in intra-arc or back-arc basins, and (2) slope apron deposits, consisting of epiclastic debris shed from local fault scarps and more distally derived arc volcaniclastics, deposited in forearc basins.

  10. Insights into Shallow Anisotropic Structure in the Forearc Hikurangi Subduction Zone, New Zealand via Splitting of Teleseisms

    NASA Astrophysics Data System (ADS)

    Karalliyadda, S.; Savage, M. K.

    2013-12-01

    We use a recent transect that consists of 10 broadband stations across the northeast of Wellington region to explore the anisotropic structure of the forearc of the Hikurangi subduction zone in the southern North Island (NI), New Zealand from shear-wave splitting of SKS, ScS and teleseismic S phases. These measurements are then integrated with the previous splitting measurements in northwest of the transect. Splitting parameters from teleseismic S-phases revealed an abrupt lateral variation in the anisotropic structure. The general trend of splitting agrees well with the previous studies around this area, with NE-SW trench-parallel fast direction (φ). The range of delay times ( 0.5 - 3.0 s) and slightly varying SKS φ across the southeast of NI suggest a laterally varying anisotropic structure. As inferred by splitting variations from long period (>7 s) phases across the profile, the upper-plate Wairarapa fault and basin area appear to be characterized by a distinct anisotropic structure that is possibly localized at crustal depths. The sharp change in delay time (δt) around this fault zone divides the region in to two distinct domains of eastern and western sides. The average δt on the eastern side (2.05 × 0.45 s) is ~0.6 s higher than that measured in the western side (1.44 × 0.24 s) of the Wairarapa fault. This change takes place between two stations that are separated by ~3 km. Clear frequency dependent splitting from ScS and teleseismic S-phases suggests that the anisotropic structure is either stratified or governed by more complex anisotropy. Multilayer models are unable to explain the observations adequately, suggesting a more complex structure. We think that this complex structure is governed in part by the laterally-varying crustal contribution of anisotropy and this lateral variation is likely associated with the multilayer anisotropy to form a more complex structure. We suggest that the subduction structure is dominated by the mantle flow in the

  11. Steep REE patterns and enriched Pb isotopes in southern Central American arc magmas: Evidence for forearc subduction erosion?

    NASA Astrophysics Data System (ADS)

    Goss, A. R.; Kay, S. M.

    2006-05-01

    The appearance of adakitic magmas with steep rare earth element (REE) patterns in southern Costa Rica and Panama at ˜4 Ma coincides with the collision of the Cocos Ridge and the inception of slab shallowing along the margin. Distinctly higher 206Pb/204Pb and 208Pb/204Pb ratios in these adakitic lavas than in older Miocene lavas suggest that components enriched in radiogenic Pb also entered the mantle magma source at ˜4 Ma. Published Pb-isotopic data for Central American arc lavas show that a similar radiogenic component is not present in lavas farther north and that maxima in post-Miocene 206Pb/204Pb and 208Pb/204Pb ratios occur in central Costa Rica and western Panama. Cretaceous and early Tertiary ophiolites in the forearc, whose origins have been linked to the Galápagos hot spot, show a similar spatial pattern in Pb isotopic ratios. The incorporation of ophiolitic forearc crust into the mantle wedge by forearc subduction erosion can explain the along-arc spatial and temporal pattern of Pb-isotopic ratios in southern Central American arc lavas. Partial melting of crust removed from the base of the forearc and subjected to high-pressure metamorphism in the subduction channel provides an explanation for the steep adakitic REE patterns in some Costa Rican and Panamanian arc lavas.

  12. Stress interaction between subduction earthquakes and forearc strike-slip faults: Modeling and application to the northern Caribbean plate boundary

    USGS Publications Warehouse

    ten Brink, U.; Lin, J.

    2004-01-01

    Strike-slip faults in the forearc region of a subduction zone often present significant seismic hazard because of their proximity to population centers. We explore the interaction between thrust events on the subduction interface and strike-slip faults within the forearc region using three-dimensional models of static Coulomb stress change. Model results reveal that subduction earthquakes with slip vectors subparallel to the trench axis enhance the Coulomb stress on strike-slip faults adjacent to the trench but reduce the stress on faults farther back in the forearc region. In contrast, subduction events with slip vectors perpendicular to the trench axis enhance the Coulomb stress on strike-slip faults farther back in the forearc, while reducing the stress adjacent to the trench. A significant contribution to Coulomb stress increase on strike-slip faults in the back region of the forearc comes from "unclamping" of the fault, i.e., reduction in normal stress due to thrust motion on the subduction interface. We argue that although Coulomb stress changes from individual subduction earthquakes are ephemeral, their cumulative effects on the pattern of lithosphere deformation in the forearc region are significant. We use the Coulomb stress models to explain the contrasting deformation pattern between two adjacent segments of the Caribbean subduction zone. Subduction earthquakes with slip vectors nearly perpendicular to the Caribbean trench axis is dominant in the Hispaniola segment, where the strike-slip faults are more than 60 km inland from the trench. In contrast, subduction slip motion is nearly parallel to the Caribbean trench axis along the Puerto Rico segment, where the strike-slip fault is less than 15 km from the trench. This observed jump from a strike-slip fault close to the trench axis in the Puerto Rico segment to the inland faults in Hispaniola is explained by different distributions of Coulomb stress in the forearc region of the two segments, as a result

  13. Design and testing of fish drier system utilizing geothermal energy resource in Ie Suum, Aceh Besar

    NASA Astrophysics Data System (ADS)

    Mubarak, Amir Zaki; Maulana, M. Ilham; Syuhada, Ahmad

    2016-03-01

    In an effort to increase the value of fish produced by the community in Krueng Raya Sub-district, it has been designed and tested a fish drier system utilizing geothermal energy resource in IeSuum Village, Krueng Raya Sub-district, Aceh Besar District. The geothermal energy is in the form of hot water with the temperature range is between 86 and 86.4 °C. Based on the design consideration, it is used a terraced rack type drier system. The drier system consists of a heat exchanger, drying chamber, and a blower to blow the air. Hot water from the geothermal source is passed into the heat exchanger to increase the air temperature outside it. The air is then blown into the drying chamber. Based on the design analysis is obtained that to dry 200 kg of fish in 24 hour, it is required a drying chamber with 1m long, 1 m width and 0.4 m high, the temperature of hot water entering the exchanger is 80 °C and the temperature of the air entering the drying chamber is maintained at 60°C. The average time required to dry fish till 10% of water level is 18-20 jam. The research is then continued by developing and testing the drying system with three layer rack to put in the fish. From the experimental result is obtained that the average water temperature flows out of the chamber is in the range of 76-78 °C and the temperature in the chamber is in the range of 57-62 °C. In addition, the weight of the fish, which initially is 20 kg, becomes12 kg in average after 18 hours drying process.

  14. The 2004 Aceh-Andaman Earthquake: Early clay dehydration controls shallow seismic rupture

    NASA Astrophysics Data System (ADS)

    Geersen, Jacob; McNeill, Lisa; Henstock, Timothy J.; Gaedicke, Christoph

    2013-09-01

    The physical state of the shallow plate-boundary fault governs the updip extent of seismic rupture during powerful subduction zone earthquakes and thus on a first order impacts on the tsunamigenic hazard of such events. During the 2004 Mw 9.2 Aceh-Andaman Earthquake seismic rupture extended unusually far seaward below the accretionary prism causing the disastrous Indian Ocean Tsunami. Here we show that the formation of a strong bulk sediment section and a high fluid-pressured predécollement, that likely enabled the 2004 rupture to reach the shallow plate-boundary, result from thermally controlled diagenetic processes in the upper oceanic basement and overlying sediments. Thickening of the sediment section to >2 km ˜160 km seaward of the subduction zone increases temperatures at the sediment basement interface and triggers mineral transformation and dehydration (e.g., smectite-illite) prior to subduction. The liberated fluids migrate into a layer that likely host high porosity and permeability and that is unique to the 2004 rupture area where they generate a distinct overpressured predécollement. Clay mineral transformation further supports processes of semilithification, induration of sediments, and coupled with compaction dewatering all amplified by the thick sediment section together strengthens the bulk sediments. Farther south, where the 2005 Sumatra Earthquake did not include similar shallow rupture, sediment thickness on the oceanic plate is significantly smaller. Therefore, similar diagenetic processes occur later and deeper in the subduction zone. Hence, we propose that shallow seismic rupture during the 2004 earthquake is primarily controlled by the thickness and composition of oceanic plate sediments.

  15. Spawning seasons of Rasbora tawarensis (Pisces: Cyprinidae) in Lake Laut Tawar, Aceh Province, Indonesia

    PubMed Central

    2010-01-01

    Background Rasbora tawarensis is an endemic freshwater fish in Lake Laut Tawar, Aceh Province, Indonesia. Unfortunately, its status is regarded as critical endangered with populations decreasing in recent years. To date no information on the spawning activities of the fish are available. Therefore, this study provides a contribution to the knowledge on reproductive biology of R. tawarensis especially on spawning seasons as well as basic information for conservation of the species. Methods Monthly sampling was conducted from April 2008 to March 2009 by using selective gillnets. The gonadosomatic index, size composition and sex ratio were assessed. The gonadal development was evaluated based on macroscopic and microscopic examinations of the gonads. Results The gonadosomatic index (GSI) varied between 6.65 to 18.16 in female and 4.94 to 8.56 for male. GSI of the female R. tawarensis was higher in March, September and December indicating the onset of reproductive seasons, the GSI and oocyte size being directly correlated with gonadal development stages. Although, a greater proportion of mature male than female was detected during the study, the sex ratio showed that the overall number of female was higher than male. The ovaries had multiple oocyte size classes at every stage of gonadal development, thus R. tawarensis can be classified as a group synchronous spawner or a fractional multiple spawner. Conclusion The spawning seasons of R. tawarensis were three times a year and September being the peak of the reproductive season and the female was the predominant sex. This species is classified as a group synchronous spawner. PMID:20482777

  16. Fluid Origins, Thermal Regimes, and Fluid and Solute Fluxes in the Forearc of Subduction Zones

    NASA Astrophysics Data System (ADS)

    Kastner, M.; Solomon, E. A.; Harris, R. N.; Torres, M. E.

    2014-12-01

    An in-depth analysis and synthesis of published and newly acquired data on the chemical and isotopic composition of forearc fluids, fluid fluxes, and the associated thermal regimes in five well-studied, representative erosional and accretionary subduction zone (SZ) forearcs will be presented. Evidence of large-scale fluid flow, primarily focused along faults, is manifested by widespread seafloor venting, associated biological communities, authigenic carbonate formation, chemical and isotopic anomalies in pore-fluid depth-profiles, and thermal anomalies. The nature of fluid venting seems to differ at the two types of SZs. At both, fluid and gas venting sites are primarily associated with faults. At accretionary SZs, the décollement and underthrust coarser-grained stratigraphic horizons are the main fluid conduits, whereas at non-accreting and erosive margins, the fluids from compaction and dehydration reactions are to a great extent partitioned between the décollement and focused conduits through the prism. The measured fluid output fluxes at seeps are high, ~15-40 times the amount that can be produced through local steady-state compaction, suggesting additional fluid sources or non-steady-state fluid flow must be involved. Recirculation of seawater must be an important component of the overall forearc output fluid flux. The most significant chemical and isotopic characteristics of the expelled fluids relative to seawater are: Cl dilution, sulfate, Ca and Mg depletions, and enrichments in Li, B, Si, Sr, alkalinity, and hydrocarbon concentrations; they often have distinctive δ18O, δD, δ7Li, δ11B, and δ37Cl values, and variable Sr isotope ratios. These characteristics provide key insights on the source of the fluid and the temperature at the source. Using our best fluid output flux estimate and considering an ocean volume of 1340 × 106 km3, the global ocean residence time in SZs is ~100 Myr. This value is five times faster than previous estimates for SZs and

  17. Snow Peak, Oregon: Latest Miocene low-K tholeiite volcanism in the Cascadia forearc

    NASA Astrophysics Data System (ADS)

    Hatfield, A. K.; Nielsen, R. L.; Kent, A. J. R.; Rowe, M. C.; Duncan, R. A.

    2015-12-01

    Snow Peak, Oregon, is a moderate size basaltic shield volcano (50-52 wt.% SiO2, > 7.4 km3) located within the forearc of the Cascadia subduction zone, ~ 50 km west of the current arc front. Herein we present new whole rock geochemistry, mineral chemistry and 11 new 40Ar/39Ar ages, together with petrologic modeling that allow us to constrain the timing and origin of volcanism. In contrast to previous K-Ar ages that suggested volcanism occurred at ~ 3 Ma, our new 40Ar/39Ar ages show that Snow Peak formed between 5.3 and 6 million years ago. The volcano lies unconformably on ~ 30 Ma volcanic rocks of the Western Cascades. Volcanism occurred over a total duration of < 0.5-1 Ma, and at eruption rates (~ 0.008-0.013 km3/ka), lower than those observed in large Cascade shield volcanoes. Snow Peak lavas derived from a single, or restricted set of primary magma compositions and evolved via crystal fractionation of olivine + pyroxene + plagioclase over a range of pressures equivalent to crustal depths of ~ 3-35 km, consistent with fractionation occurring primarily during crustal transit or residence. The most evolved Snow Peak lava can be produced by ~ 50% crystallization from a primary magma with > 14 wt.% MgO. Snow Peak lavas have trace element characteristics transitional between the calc-alkaline basalt (CAB) and low-K tholeiite (LKT) primary magma types recognized throughout the Cascade Range, but are closer to LKT and are classified as such. Estimates based on phase equilibria models and plagioclase hygrometers suggest that the primary magmas contained moderate amounts of water (1.5-2 wt.%), consistent with LILE/HFSE ratios that are greater than MORB values. Snow Peak is part of a widespread suite of LKT magmas that erupted between 5-8 Ma throughout the central Oregon Cascade Range in response to intra-arc rifting, and Snow Peak shows that LKT magmatism at this time extended well into the forearc of the central Oregon Cascade Range. Overall LKT magmas of this age occur

  18. Finite Strain in the Forearc Mantle: Testing the B-type Fabric Anisotropy Hypothesis

    NASA Astrophysics Data System (ADS)

    Kneller, E. A.; van Keken, P.; Karato, S.; Park, J.

    2005-12-01

    Seismic observations from many subduction zones show that the seismically fast direction is perpendicular to the direction of convergence. This is opposite of what is expected from models that assume flow is parallel to plate motion and the seismically fast axis of olivine [100] aligns sub-parallel to the shear direction (A-type fabric). Recent deformation experiments on olivine aggregates show that under low-temperature and high-stress conditions, the fast axis of olivine aligns sub-perpendicular to the shear direction (B-type fabric)(Jung and Karato, 2001; Katayama et al., 2004). B-type fabric has potential to explain convergence-perpendicular anisotropy in subduction zones with flow parallel to plate motion. Kneller et al. (2005) used combined data from deformation experiments on olivine aggregates and dynamical models of subduction zones to predict the distribution of B-type fabric in the mantle wedge. This study predicted that the forearc mantle has suitable thermal and stress conditions for B-type fabric and a rapid transition toward the backarc to conditions more suitable for other olivine fabrics. A vertical projection of the volcanic arc into the mantle wedge is predicted to mark the fabric transition between B-type and A-, E-, or C-type fabrics depending on water content. An important aspect not thoroughly investigated by our previous research is finite strain accumulation across the predicted fabric transition. In this study we present finite strain calculation for non-Newtonian subduction zone models with composite water-dependent rheology. This composite rheology includes experimentally based Peierls, dislocation, and diffusion creep. We predict greater than 100 % strain accumulation across 75 km for material traveling into the forearc mantle. This strain accumulation may be sufficient to produce a well developed B-type fabric. Furthermore, material enters the forearc mantle from a low-strain-rate thermal boundary layer at the base of the overriding

  19. Degree of serpentinization in the forearc mantle wedge of Kyushu subduction zone: quantitative evaluations from seismic velocity

    NASA Astrophysics Data System (ADS)

    Xia, Shaohong; Sun, Jinlong; Huang, Haibo

    2015-09-01

    Serpentinization is an important phenomenon for understanding the water cycle and geodynamics of subduction zones in the upper mantle. In this study, we evaluate quantitatively the degree of serpentinization using the seismic velocity. The results show that serpentinization mainly occurs in the forearc mantle wedge along the subducted oceanic crust, and the degree of serpentinization in the forearc mantle wedge of Kyushu is strongly heterogeneous and varies from 0 to 12 %, containing about 0-1.8 % water contents. In general, the degree of serpentinization gradually decreases with depth from 40 to 80 km and the largest degree usually occur in about 40-50 km depth. Localized high anomalies of serpentinization are revealed in the northern and southern portions of Kyushu, respectively. We suggest that in the northern portion of the forearc mantle wedge, the water contents are relatively large, which might result from the abundant fractures and cracks with more fluids in the subducting slab because of the subduction of Kyushu-Palau ridge and the sudden change in its subduction angle of Philippine Sea lithosphere. But the high degree of serpentinization in the southern portion is closely associated with the active left-lateral shear zone revealed by global positioning system site velocities and earthquake focal mechanisms. In addition, the present results also display that the low degree of serpentinization in the central domain of the forearc mantle wedge is consistent with the location of anomalous arc volcano. The distribution of water contents is closely associated with the degree of serpentinization in the forearc mantle wedge.

  20. Silurian clastic sediments in the North Qilian Shan, NW China: Chemical and isotopic constraints on their forearc provenance with implications for the Paleozoic evolution of the Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Yan, Z.; Xiao, W. J.; Windley, B. F.; Wang, Z. Q.; Li, J. L.

    2010-11-01

    The North Qilian Shan is an accretion-collision orogenic belt in the northeastern margin of the Tibetan Plateau that connects the North China plate to the north with the Tethyan orogenic assemblage to the south. Its Early Paleozoic temporal-spatial tectonic evolution has been extensively studied, but the nature and tectonic setting of its Silurian deposition is poorly understood. Our new petrological analysis suggests that the clast composition of fan conglomerates is complex. In the Danbanshan and Zhongdabanshan sections, abundant lenticular conglomerate beds contain mainly subrounded-rounded metamorphic clasts; whereas the Tongziba and Haichaoba sections contain volcanic, chert, limestone, ultramafic and granitoid clasts. However, in the Sunan area, clast types are relatively simple, dominated by basalt and granitoids, and at Tongziba gabbro and basalt clasts are subrounded and angular, indicating two different types of provenance. Ultramafic, limestone and abundant chert clasts in the Haichaoba and Tonghe conglomerates indicate an ophiolitic source, whereas subrounded-rounded quartzite and granitoid gneiss clasts were probably derived from the Central Qilian basement. Geochemical data from the volcanic and granitoid clasts suggest an arc-related source and their zircon U-Pb ages of 515-429 Ma suggest that the arc magmatism did not end in the Mid-Silurian. Sandstone petrology and detrital modes suggest that the Silurian sediments were deposited in a forearc basin. Paleogeographic reconstructions inferred from NNW-NNE paleocurrent data indicate that an island arc was present off the southern margin of the Silurian basin, and that southward subduction of oceanic crust between North China and the Qilian Shan was active or continued in the Silurian.

  1. Franciscan olistoliths in Upper Cretaceous conglomerate deposits, Western Transverse Ranges, California: Implications for basin morphology and tectonic history

    SciTech Connect

    Reed, W.E.; Campbell, M.D. . Dept. of Earth and Space Sciences)

    1993-04-01

    Compositional analyses reveal that Upper Cretaceous sediments exposed in the Western Transverse Ranges of CA were deposited in submarine fan systems in a forearc basin. Point count data suggest a magmatic arc/recycled orogen as the dominant provenance for these sediments. Paleocurrent measurements from conglomerates in these sediments yield a northerly transport direction. Removal of ca. 90[degree] of clockwise rotation and 70 km of right-lateral slip restore this section to a position west of the San Diego area. The forearc basin would have had a N-S orientation, with the bulk of sediments supplied by the Peninsular Ranges to the east. Evidence of the erosion of the accretionary wedge is provided by the presence of large, internally stratified olistoliths of Franciscan material interbedded with and surrounded by upper Cretaceous conglomerate. Petrographic, quantitative SEM, and microprobe analyses indicate the presence of diagnostic Franciscan mineralogy, including glaucophane, riebeckite, lawsonite, and serpentine. Olistoclasts of chert, jadeitic graywacke, serpentine, and blueschist are found intermixed with the conglomerates in close association with the olistoliths. This association provides strong field evidence that recirculation of melange material within the subduction zone was active and well-established by late Cretaceous time. Inferences regarding the forearc system morphology can be drawn from these observations. The occurrence of coarse, easterly-derived conglomerates surrounded by large, stratified, but sheared, westerly-derived Franciscan debris, suggests a narrow, relatively steep-sided basin. Paleocurrent measurements gave no indication of axial transport within the basin. This morphology suggests that, in late Cretaceous time, the forearc basin was youthful, with a narrow arc-trench gap. Thus, relative convergence rates between the North American and Pacific plates were possibly slower than Tertiary convergence rates.

  2. Decarbonation, Serpentinization, Abiogenic Methane, and Extreme pH beneath the Mariana Forearc

    NASA Astrophysics Data System (ADS)

    Mottl, M. J.; Wheat, C. G.; Fryer, P.

    2004-12-01

    Low-chlorinity springs sampled from ten sites on nine serpentinite mud volcanoes show systematic chemical gradients across the outer Mariana forearc that result from progressive devolatilization of the subducting Pacific plate. Sites range from 50 to 90 km from the trench axis corresponding to depths to the top of the plate of ˜15 to 29 km. Dissolved sulfate, Na/Cl, K, Rb, Cs, and B in the springs all increase regularly with distance from the trench, leached from the subducting sediment and altered basalt in response to increasing temperature at depth from ˜100-300° C. Sites nearer the trench have high Ca (up to 75 mmol/kg) and Sr, low alkalinity, and pH 10.7, whereas sites farther from the trench have almost no Ca and Sr, alkalinity (some carbonate but mostly hydroxyl) as high as 69 meq/kg, and pH 12.5. Springs with high alkalinity also have high methane (>44 mmol/kg) that feeds sulfate-reducing microbial communities in the shallow subsurface and macrofauna at the seafloor. These distal springs form chimneys and crusts of CaCO3, whereas the proximal springs form chimneys of brucite. High alkalinity at the distal sites apparently results from decarbonation at the top of the subducting plate; because serpentinization during ascent generates both high pH and H2, the resulting dissolved carbonate is reduced to methane such that carbonate alkalinity is replaced by hydroxyl alkalinity: 4H2 + CO3= = CH4 + H2O + 2OH-. This reaction can account for the much higher pH of the distal springs. Chlorinity of the springs varies from 234-546 mmol/kg and is related more to latitude N-S than to distance from the trench. Distal springs have otherwise similar compositions over this entire range of chlorinity, implying that chloride derives from depth rather than from mixing with seawater within the seamounts themselves. The range in chlorinity can readily be explained by serpentinization at reasonable water/rock mass ratios of 0.2-1.0 if 30-40% of the spring water originates as

  3. Late Cenozoic Deformation of the Coastal Cordillera, Northern Chilean Forearc, 18- 25°S

    NASA Astrophysics Data System (ADS)

    Allmendinger, R. W.; González, G.; Loveless, J. P.; Carrizo, D.

    2004-12-01

    Overlying the only part of the South American continental crust that is in direct contact with the subducting Nazca Plate, the Coastal Cordillera of northern Chile and southern Peru should provide the most complete geological record of the coupling between the two plates. This record of coupling is exquisitely preserved in the hyperarid Atacama Desert. This preservation is both one of the major advantages and major challenges of working in this region: On the positive side, exposure of geomorphic surfaces is complete and unencumbered by erosion or vegetation, and brittle saline soils preserve subtle deformation features that would quickly be obliterated in more humid environments. On the negative side, ancient geomorphic features are just as fresh as Recent one and the lack of organic material precludes radiocarbon dating, a traditional tool of paleoseismology. During the last several years, we have concentrated on documenting three fundamental characteristics of late Cenozoic forearc deformation: (1) NS shortening on reverse faults striking at a high angle to, and dextral-reverse faults striking oblique to, the continental margin; (2) N-striking normal faults of the forearc and their reactivation, locally, as reverse faults; and (3) extensive suites of tension cracks. Reverse faults striking at a high angle to the margin are present between 19 and 21.5°S, straddling the topographic symmetry plane that marks the axis of the Bolivian orocline. Limited dating of tuffs and surfaces shows that these structures have been active for at least the last 6 Ma. At least 5 of these structures -- Atajaña, Pisagua, Iquique north and south, and Barranco Alto -- cut the Pleistocene marine terraces of the coastal platform, producing 20 to 50 m of vertical offset. A forearc crustal earthquake just south of Pisagua in March 2007 demonstrates that margin parallel shortening continues to the present and that permanent deformation occurs during the interseismic part of the plate

  4. Late Cenozoic Deformation of the Coastal Cordillera, Northern Chilean Forearc, 18- 25°S

    NASA Astrophysics Data System (ADS)

    Allmendinger, R. W.; González, G.; Loveless, J. P.; Carrizo, D.

    2007-12-01

    Overlying the only part of the South American continental crust that is in direct contact with the subducting Nazca Plate, the Coastal Cordillera of northern Chile and southern Peru should provide the most complete geological record of the coupling between the two plates. This record of coupling is exquisitely preserved in the hyperarid Atacama Desert. This preservation is both one of the major advantages and major challenges of working in this region: On the positive side, exposure of geomorphic surfaces is complete and unencumbered by erosion or vegetation, and brittle saline soils preserve subtle deformation features that would quickly be obliterated in more humid environments. On the negative side, ancient geomorphic features are just as fresh as Recent one and the lack of organic material precludes radiocarbon dating, a traditional tool of paleoseismology. During the last several years, we have concentrated on documenting three fundamental characteristics of late Cenozoic forearc deformation: (1) NS shortening on reverse faults striking at a high angle to, and dextral-reverse faults striking oblique to, the continental margin; (2) N-striking normal faults of the forearc and their reactivation, locally, as reverse faults; and (3) extensive suites of tension cracks. Reverse faults striking at a high angle to the margin are present between 19 and 21.5°S, straddling the topographic symmetry plane that marks the axis of the Bolivian orocline. Limited dating of tuffs and surfaces shows that these structures have been active for at least the last 6 Ma. At least 5 of these structures -- Atajaña, Pisagua, Iquique north and south, and Barranco Alto -- cut the Pleistocene marine terraces of the coastal platform, producing 20 to 50 m of vertical offset. A forearc crustal earthquake just south of Pisagua in March 2007 demonstrates that margin parallel shortening continues to the present and that permanent deformation occurs during the interseismic part of the plate

  5. Flow rates, residence times and origin of fluids in the Hikurangi forearc, New Zealand

    NASA Astrophysics Data System (ADS)

    Reyes, A. G.

    2013-12-01

    Part of the Hikurangi forearc is subaerial in the east coast of the North Island, allowing the chemical and isotopic study of accretionary prism fluids without surface seawater contamination. More than 250 sources of saline waters (2000 to 16600 mg/kg Cl), methane-rich gases and occasional oil seeps are discharged from springs, mud volcanoes and gas vents from about -37.5 to -41.3 deg latitude along active NE-SW and N-S striking faults, 80 to 100 km from the subduction margin. Discharge areas, occupying <0.005 to 10 ha each, form a band about 500 km in length with widths ranging from 25 km in the south to 75 to 100 km in the north and centre. All fluid discharges are cold except for two isolated hot spring systems in the central and northern blocks, where 51degC (150 L/min flow rate) and 69 degC saline waters (540 L/min flow rate) are discharged. Recent measurements indicate that the total flow rate of cold saline aqueous solutions, from >100 sources, is at least 2.5 x 10^8 L/a compared to 4 x 10^8 L/a from the two hot springs. Chemical and isotopic compositions indicate that saline aqueous solutions emerging from a thick sequence of Cretaceous to Pleistocene sedimentary formations, in the Hikurangi forearc, consist of subducted waters derived mainly from clay water of hydration (<50%) and seawater that had interacted at varying degrees with organic-rich marine sediments/formations at depth and at varying temperatures. Gases and aqueous solutions along the length of the forearc have equilibrated at about 100degC +/- 20degC (median values), near the smectite-illite transition, at depths of about 5 to 6 km based on general geothermal gradients in the region. Higher temperatures may be possible at deeper levels as indicated by stable isotopic compositions of hydration water expelled from clays. Saline waters with similar origins emerge at high elevations in the axial ranges west of the forearc, albeit modified by higher temperatures, mixing with large volumes of

  6. Subduction-related cryptic metasomatism in fore-arc to nascent fore-arc Neoproterozoic mantle peridotites beneath the Eastern Desert of Egypt: mineral chemical and geochemical evidences

    NASA Astrophysics Data System (ADS)

    Hamdy, Mohamed; Salam Abu El-Ela, Abdel; Hassan, Adel; Kill, Youngwoo; Gamal El Dien, Hamed

    2013-04-01

    Mantle spinel peridotites beneath the Arabian Nubian Shield (ANS) in the Eastern Desert (ED) of Egypt were formed in arc stage in different tectonic setting. Thus they might subject to exchange with the crustal material derived from recycling subducting oceanic lithosphere. This caused metasomatism enriching the rocks in incompatible elements and forming non-residual minerals. Herein, we present mineral chemical and geochemical data of four ophiolitic mantle slice serpentinized peridotites (W. Mubarak, G. El-Maiyit, W. Um El Saneyat and W. Atalla) widely distributed in the ED. These rocks are highly serpentinized, except some samples from W. Mubarak and Um El-Saneyat, which contain primary olivine (Fo# = 90-92 mol %) and orthopyroxene (En# = 86-92 mol %) relics. They have harzburgite composition. Based on the Cr# and Mg# of the unaltered spinel cores, all rocks formed in oceanic mantle wedge in the fore-arc setting, except those from W. Atalla formed in nascent fore-arc. This implies that the polarity of the subduction during the arc stage was from the west to the east. These rocks are restites formed after partial melting between 16.58 in W. Atalla to 24 % in G-El Maiyit. Melt extraction occurred under oxidizing conditions in peridotites from W. Mubarak and W. Atalla and under reducing conditions in peridotites from G. El-Maiyit and Um El-Saneyat. Cryptic metasomatism in the studied mantle slice peridotites is evident. This includes enrichment in incompatible elements in minerals and whole rocks if compared with the primitive mantle (PM) composition and the trend of the depletion in melt. In opx the Mg# doesn't correlate with TiO2, CaO, MnO, NiO and Cr2O3concentrations. In addition, in serpentinites from W. Mubarak and W. Atalla, the TiO2spinel is positively correlated with the TiO2 whole-rock, proposing enrichment by the infiltration of Ti-rich melts, while in G. El- Maiyit and Um El-Saneyat serpentinites they are negatively correlated pointing to the reaction

  7. Sedimentary deposits of the 26 December 2004 tsunami on the northwest coast of Aceh, Indonesia

    USGS Publications Warehouse

    Moore, A.; Nishimura, Y.; Gelfenbaum, G.; Kamataki, T.; Triyono, R.

    2006-01-01

    The 2004 Sumatra-Andaman tsunami flooded coastal northern Sumatra to a depth of over 20 m, deposited a discontinuous sheet of sand up to 80 cm thick, and left mud up to 5 km inland. In most places the sand sheet is normally graded, and in some it contains complex internal stratigraphy. Structures within the sand sheet may record the passage of up to 3 individual waves. We studied the 2004 tsunami deposits in detail along a flow-parallel transect about 400 m long, 16 km southwest of Banda Aceh. Near the shore along this transect, the deposit is thin or absent. Between 50 and 400 m inland it ranges in thickness from 5 to 20 cm. The main trend in thickness is a tendency to thicken by filling low spots, most dramatically at pre-existing stream channels. Deposition generally attended inundation - along the transect, the tsunami deposited sand to within about 40 m of the inundation limit. Although the tsunami deposit contains primarily material indistinguishable from material found on the beach one month after the event, it also contains grain sizes and compositions unavailable on the current beach. Along the transect we studied, these grains become increasingly dominant both landward and upward in the deposit; possibly some landward source of sediment was exposed and exploited by the passage of the waves. The deposit also contains the unabraded shells of subtidal marine organisms, suggesting that at least part of the deposit came from offshore. Grain sizes within the deposit tend to fine upward and landward, although individual units within the deposit appear massive, or show reverse grading. Sorting becomes better landward, although the most landward sites generally become poorly sorted from the inclusion of soil clasts. These sites commonly show interlayering of sandy units and soil clast units. Deposits from the 2004 tsunami in Sumatra demonstrate the complex nature of the deposits of large tsunamis. Unlike the deposits of smaller tsunamis, internal stratigraphy is

  8. Embedded wisdom or rooted problems? Aid workers' perspectives on local social and political infrastructure in post-tsunami Aceh.

    PubMed

    Daly, Patrick

    2015-04-01

    This paper analyses the role of local social, cultural, and political institutions in post-disaster reconstruction projects. It contends that such institutions are important considerations within community-driven reconstruction initiatives, but are often viewed with ambivalence by external aid organisations. This paper draws upon in-depth qualitative interviews with aid workers involved in the post-tsunami reconstruction in Aceh, Indonesia, to establish: (i) what roles community institutions were suited to play in the reconstruction; (ii) what were the limitations of community institutions when engaging with external aid agencies; (iii) how did external aid agencies engage with local community institutions; and (iv) how did external aid agencies perceive community institutions. PMID:25442350

  9. Fast performance tool for Tsunami Flood Hazard Assessment and Early Warning, Banda Aceh (2004) and American Samoan case (2009)

    NASA Astrophysics Data System (ADS)

    Vatvani, Deepak; Kie Thio, Hong; Gelfenbaum, Guy

    2010-05-01

    Recent tsunami flood disasters in the American Samoa and in 2004 in the Indian Ocean region have shown the need for obtaining a quick estimate on the flooding extent caused by a tsunamigenic earthquakes. An overview of the flooding is crucial to help plan the first relief operation and damage estimate. An estimate of tsunami height along the coast using a relatively coarse grid numerical model and assumed tsunami source based on earthquake parameters could, theoretically, be performed shortly after an earthquake event. Inundation models, however, requires very high resolution numerical models which still needs large amount of computation time. Based on a Digital Terrain Model (DTM) and an empirical relation (derived from numerical experiments and analytical expressions from well known publications), a fast 2D tsunami flooding and run-up estimation tool has been built that can produce sufficiently accurate overall run-up and flooding estimate caused by the tsunami. The accuracy of the tool depends on the quality of the underlying DTM and tsunami heights fed to the tool. Because of its speed, this tool may even be used in near real time / early warning system to obtain a good indication of the area under threat in case of an approaching tsunami. The tool may also be used to produce flood (hazard/vulnerability) maps that may occur in future. The model has been tested for the 2004 tsunami event in Banda Aceh and 2009 tsunami event in American Samoa. The inundation and run-up maps for Banda Aceh event were compared to numerical model results (Delft3D) as well as survey data. The American Samoa event were compared to numerical model run by URS and preliminary survey data from USGS.

  10. Preliminary study on detection sediment contamination in soil affected by the Indian Ocean giant tsunami 2004 in Aceh, Indonesia using laser-induced breakdown spectroscopy (LIBS)

    NASA Astrophysics Data System (ADS)

    Idris, Nasrullah; Ramli, Muliadi; Hedwig, Rinda; Lie, Zener Sukra; Kurniawan, Koo Hendrik

    2016-03-01

    This work is intended to asses the capability of LIBS for the detection of the tsunami sediment contamination in soil. LIBS apparatus used in this work consist of a laser system and an optical multichannel analyzer (OMA) system. The soil sample was collected from in Banda Aceh City, Aceh, Indonesia, the most affected region by the giant Indian Ocean tsunami 2004. The laser beam was focused onto surface of the soil pellet using a focusing lens to produce luminous plasma. The experiment was conducted under air as surrounding gas at 1 atmosphere. The emission spectral lines from the plasma were detected by the OMA system. It was found that metal including heavy metals can surely be detected, thus implying the potent of LIBS technique as a fast screening tools of tsunami sediment contamination.

  11. How wide is the seismogenic zone of the Lesser Antilles forearc?

    NASA Astrophysics Data System (ADS)

    Gutscher, M.; Westbrook, G. K.; Marcaillou, B.; Graindorge, D.; Gailler, A.; Pichot, T.; Maury, R.

    2009-12-01

    The Lesser Antilles subduction zone has produced no recent strong thrust earthquakes, making it difficult to quantify the seismic hazard from such events. Numerical models of forearc thermal structure were constructed along six transects perpendicular to the arc in order to determine the thermally predicted width of the seismogenic zone. The geometry of each section is constrained by published seismic profiles and by earthquake hypocenters at depth. The dip of the deep slab ranges from 53° in the north to 45° in the south. The age of the subducting oceanic lithosphere is 80 Ma and the subduction velocity 2 cm/yr. The temperature beneath the volcanic arc (1100-1200°C) as well as observed surface heat flow provide some constraints on the modeled thermal structure. Modeling results indicate a systematic southward increase in the width of the seismogenic zone, more than doubling in width from north to south and corresponding to a dramatic southward increase in forearc width (trench - arc distance). The minimum width (as defined by the 150°C and 350°C isotherms) increases from about 80 km north of 16°N to 230 km at 13°N, respectively. The maximum width (as defined by the 100°C and 450°C isotherms) ranges from 150-160 km in the north to up to 320 km in the south. There is good agreement between the thermally predicted seismogenic limits and the sparse distribution of recorded thrust earthquakes, which are observed only in the northern portion of the arc. Possible scenarios for mega-thrust earthquakes are discussed. Depending on the segment length (along-strike) of the rupture plane, an event of magnitude 8-9 cannot be excluded. (left) seismicity map of the Lesser Antilles with focal mechanisms of shallow dipping thrust type earthquakes shown and the possible rupture zones of the 1839 and 1844 earthquakes (intensities X) the position of the cross section at right is indicated; (right) modeled thermal structure for a transect through Guadeloupe, with earthquake

  12. Variations in Oxygen Fugacity among Forearc Peridotites from the Tonga Trench

    NASA Astrophysics Data System (ADS)

    Birner, S.; Warren, J. M.; Cottrell, E.; Lopez, O. G.; Davis, F. A.; Falloon, T.

    2013-12-01

    The Tonga subduction zone is an extension-dominated, non-accreting convergent plate margin in the South Pacific, characterized by rapid slab rollback [1]. It is unusual among subduction zones in that forearc peridotites, thought to be pieces of lithospheric mantle originating from the overriding plate, have been dredged from the trench. These spinel peridotites appear in dredges along almost 1000 km of the trench's length, from near the Samoa hotspot in the north to the Louisville seamounts in the south, and have been dredged from 4-9 km depth. The samples are very depleted, consisting entirely of dunites and harzburgites, with no observed lherzolites. Low modal abundances of orthopyroxene and high spinel Cr# (Cr/(Cr+Al)) also indicate large degrees of melt extraction. While some samples have been variably altered by hydrothermal processes, a large fraction of them are remarkably unaltered, making them ideal targets for geochemical investigation. Oxygen fugacity is an important geochemical control on phase stability, the composition of volatiles, and the position of the mantle solidus, thus rendering it critical to the understanding of mantle processes. Previous studies have suggested that subduction zone processes result in arc magmas with increased oxygen fugacity (fO2) relative to ridge magmas [2], but few direct observations of mantle wedge fO2 are available. In order to investigate the oxygen fugacity of the Tonga peridotites, mineral major element compositions were determined via electron microprobe. Fe3+/ΣFe ratios were calculated for the spinel phase, calibrated with spinel standards of known Fe3+/ΣFe ratio provided by B.J. Wood to the Smithsonian following the procedure of Lopez et al [3]. Oxygen fugacity was calculated according to the olivine-orthopyroxene-spinel oxybarometer method of Wood et al. [4]. Results from five dredges along approximately 600 km of trench showed oxygen fugacity values of 1 log unit above the QFM buffer, compared to the global

  13. Alteration and mineralization of an oceanic forearc and the ophiolite-ocean crust analogy

    USGS Publications Warehouse

    Alt, J.C.; Teagle, D.A.H.; Brewer, T.; Shanks, Wayne C., III; Halliday, A.

    1998-01-01

    Mineralogical, chemical, and isotopic (O, C, S, and Sr) analyses were performed on minerals and bulk rocks from a forearc basement section to understand alteration processes and compare with mid-ocean ridges (MOR) and ophiolites. Ocean Drilling Program Hole 786B in the Izu-Bonin forearc penetrates 103 m of sediment and 725 m into volcanic flows, breccias, and basal dikes. The rocks comprise boninites and andesites to rhyolites. Most of the section was affected by low-temperature (<100??C) seawater alteration, with temperatures increasing downward. The rocks are partly (5-25%) altered to smectite, Fe-oxyhydroxide, calcite, and phillipsite, and exhibit gains of K, Rb, and P, loss of Ca, variable changes in Si, Na, Mg, Fe, Sr, and Y, and elevated ??18O and 87Sr/86Sr. Higher temperatures (???150??C) in the basal dikes below 750 m led to more intense alteration and formation of chlorite-smectite, corrensite, albite, K-feldspar, and quartz (??chlorite). A 5 m thick hydrothermally altered and pyritized zone at 815 m in the basal dikes reacted with mixtures of seawater and hydrothermal fluids to Mg-chlorite, albite, and pyrite, and gained Mg and S and lost Si and Ca. Focused flow of hydrothermal fluids produced sericitization halos (Na-K sericite, quartz, pyrophyllite, K-feldspar, and pyrite) along quartz veins at temperatures of 200??-250??C. High 87Sr/86Sr ratios of chloritized (???0.7055) and sericitized (???0.7065) rocks indicate involvement of seawater via mixing with hydrothermal fluids. Low ??34S of sulfide (???2 to -5.5???) and sulfate (12.5???) are consistent with input of magmatic SO2 into hydrothermal fluids and disproportionation to sulfide and sulfate. Alteration processes were generally similar to those at MORs, but the arc section is more intensively altered, in part because of the presence of abundant glassy rocks and mafic phases. The increase in alteration grade below 750 m and the mineralization in the basal dikes are analogous to changes that occur near

  14. Postseismic Deformations of the Aceh, Nias and Benkulu Earthquakes and the Viscoelastic Properties of the Mantle

    NASA Astrophysics Data System (ADS)

    Fleitout, L.; Garaud, J.; Cailletaud, G.; Vigny, C.; Simons, W. J.; Ambrosius, B. A.; Trisirisatayawong, I.; Satirapod, C.; Geotecdi Song

    2011-12-01

    The giant seism of Aceh (december 2004),followed by the Nias and Bengkulu earthquakes, broke a large portion of the boundary between the Indian ocean and the Sunda block. For the first time in history, the deformations associated with a very large earthquake can be followed by GPS, in particular by the SEAMERGE (far-field) and SUGAR (near-field) GPS networks. A 3D finite element code (Zebulon-Zset) is used to model both the cosismic and the postseismic deformations. The modeled zone is a large portion of spherical shell around Sumatra extanding over more than 60 degrees in latitude and longitude and from the Earth's surface to the core-mantle boundary. The mesh is refined close to the subduction zone. First, the inverted cosismic displacements on the subduction plane are inverted for and provide a very good fit to the GPS data for the three seisms. The observed postseismic displacements, non-dimensionalized by the cosismic displacements, present three very different patterns as function of time: For GPS stations in the far-field, the total horizontal post-seismic displacement after 4 years is as large as the cosismic displacement. The velocities vary slowly over 4 years. A large subsidence affects Thailand and Malaysia. In the near-field, the postseismic displacement reaches only some 15% of the cosismic displacement and it levels off after 2 years. In the middle-field (south-west coast of Sumatra), the postseismic displacement also levels-off with time but more slowly and it reaches more than 30% of the cosismic displacement after four years. In order to fit these three distinct displacement patterns, we need to invoke both viscoelastic deformation in the asthenosphere and a low-viscosity wedge: Neither the vertical subsidence nor the amplitude of the far-field horizontal velocities could be explained by postseismic sliding on the subduction interface. The low viscosity wedge permits to explain the large middle-field velocities. The viscoelastic properties of the

  15. Constraining porosity of the shallow forearc and plate interface offshore Nicaragua with marine electromagnetic data

    NASA Astrophysics Data System (ADS)

    Naif, S.; Key, K.; Constable, S.; Evans, R. L.

    2015-12-01

    We imaged the electrical resistivity structure of the incoming plate and outer forearc across the Middle America Trench with 2-D inversion of marine controlled-source electromagnetic data. The inverted data reveal a high conductivity channel that is congruent with the geometry of the plate interface, which we infer to be subducted sediments. We used the resistivity model to estimate the porosity of the upper plate and underthrust sediments. The sediment porosity decays exponentially as it is subducted along the plate interface, in good agreement with existing constraints from compaction studies. The plate interface is overlain by an upper plate that is one to two orders of magnitude more resistive, requiring low porosities (<15%) that are consistent with a non-accreting margin composed of crystalline basement or lithified sediments.At 18 to 23 km landward of the trench, the conductive channel diverges from the plate interface and extends 1-2 km into the overlying plate below a cluster of active seafloor seeps. The location of the anomaly at depth is synonymous with a rapid steepening of the seafloor slope. The steepened slope occurs at 15 to 25 km landward of the trench and is extensive, persisting for more than 100 km along the margin. This correlation leads us to conclude that the cause of the conductive feature is sediment underplating. The implications for the 1992 tsunami earthquake will be discussed.

  16. Distributional prediction of Pleistocene forearc minibasin turbidites in the NE Nankai Trough area (off central Japan)

    NASA Astrophysics Data System (ADS)

    Egawa, K.; Furukawa, T.; Saeki, T.; Suzuki, K.; Narita, H.

    2011-12-01

    Natural gas hydrate-related sequences commonly provide unclear seismic images due to bottom simulating reflector, a seismic indicator of the theoretical base of gas hydrate stability zone, which usually causes problems for fully analyzing the detailed sedimentary structures and seismic facies. Here we propose an alternative technique to predict the distributional pattern of gas hydrate-related deep-sea turbidites with special reference to a Pleistocene forearc minibasin in the northeastern Nankai Trough area, off central Japan, from the integrated 3D structural and sedimentologic modeling. Structural unfolding and stratigraphic backstripping successively modeled a simple horseshoe-shaped paleobathymetry of the targeted turbidite sequence. Based on best-fit matching of net-to-gross ratio (or sand fraction) between the model and wells, subsequent turbidity current modeling on the restored paleobathymetric surface during a single flow event demonstrated excellent prediction results showing the morphologically controlled turbidity current evolution and selective turbidite sand distribution within the modeled minibasin. Also, multiple turbidity current modeling indicated the stacking sheet turbidites with regression and proximal/distal onlaps in the minibasin due to reflections off an opposing slope, whose sedimentary features are coincident with the seismic interpretation. Such modeling works can help us better understand the depositional pattern of gas hydrate-related, unconsolidated turbidites and also can improve gas hydrate reservoir characterization. This study was financially supported by MH21 Research Consortium.

  17. Subduction of very rugged seafloor topography imposes stronger interplate coupling and elevated mean stress levels at the Western Solomon Islands forearc

    NASA Astrophysics Data System (ADS)

    Taylor, F. W.; Lavier, L. L.; Bevis, M. G.; Frohlich, C. A.; Grand, S.; Papabatu, A. K.

    2010-12-01

    Recent large thrusting earthquakes in the context of paleoseismicity and GPS data indicate that only ~ 50 per cent of Australian plate convergence at the Western Solomon Islands forearc is accommodated by megathrust rupture. No instrumentally recorded events larger than M ~7.0 occurred in this region until the Mw 8.1 event of April 2007 and a Mw 7.1 event in January 2010. The 2007 event apparently ruptured to the base of the seismogenic zone with typical uplift of the outer forearc and subsidence of islands located greater than 40 km from the trench. The Mw 7.1 event of 2010 occurred to the east at the adjacent segment very near the trench where the Coleman seamount is impinging on the forearc. Just arcward of the epicenter, Rendova and Tetepare Islands subsided indicating that all of the coseismic slip occurred beneath the ~15 km strip separating these islands from the trench. This movement is opposite in direction to the geologic record of episodic uplifts of these islands at mean rates up to 7-8 mm/yr. Thus both the 2007 and 2010 earthquakes may have transferred stress to the deeper seismogenic zone arcward of the 2010 earthquake. The extremely rugged and young subducting seafloor at this margin resists subduction very strongly and induces very strong interplate coupling. Thus we propose that this margin operates at an elevated stress level. Such strong coupling impedes subduction and thus megathrust rupture occurs more rarely than if coupling were weaker. Forearc deformation as well as occasional megathrust ruptures may combine to accommodate plate convergence. We propose that initiation of rapid forearc uplift marked the beginning of the current episode of very strong interplate coupling and elevated forearc stress when some combination of seamounts and ridges on the downgoing plate began to impinge more forcefully on the forearc backstop.

  18. Cenozoic subsurface stratigraphy and structure of the Salar de Atacama Basin, northern Chile

    NASA Astrophysics Data System (ADS)

    Jordan, T. E.; Mpodozis, C.; Muñoz, N.; Blanco, N.; Pananont, P.; Gardeweg, M.

    2007-02-01

    Sequence mapping of industry seismic lines and their correlation to exposed stratigraphic formations enable a description of the evolution of the nonmarine Salar de Atacama Basin. This major tectonic basin, located in the present-day forearc of the northern Chilean Andes, was first defined topographically by late Cretaceous inversion of the Jurassic-early Cretaceous extensional Tarapacá backarc Basin. Inversion led to both the uplift of the Cordillera de Domeyko and subsidence of the Salar de Atacama Basin along its eastern flank. The basin evolved from a continental backarc in the Cretaceous and Paleogene to a forearc tectonic setting during the Neogene. The principal causes of basin-scale tectonic subsidence include late Cretaceous and earliest Paleocene shortening and Oligocene-early Miocene localized extension. The basin was not completely filled by late Cretaceous (Purilactis Group, sequence G) and Paleocene (sequence H) strata, and its empty space persisted through the Cenozoic. Eocene deformation caused long-wavelength rotation of a deeply weathered surface, generating an erosional unconformity across which coarse clastic strata accumulated (sequence J). Oligocene-early Miocene normal faulting, perhaps in a transtensional environment, repositioned the western basin margin and localized hangingwall subsidence, leading to the accumulation of thousands of meters of evaporitic strata (sequence K, Paciencia Group). By the close of the early Miocene, shortening resumed, first uplifting the intrabasinal Cordillera de la Sal and later generating Pliocene blind reverse faults within the topographically lowest part of the basin. Unequal deposition and tilting across the nascent Cordillera de la Sal induced diapirism of the Paciencia Group halite. In combination, inherited accommodation space and new tectonic subsidence, plus local salt-withdrawal subsidence, shaped the distribution of Upper Miocene-Recent ignimbrites, evaporites, and clastics (sequence M and Vilama

  19. Forearc Structure and Fault Slip Near the Epicenter of the April 1, 2007, Megathrust Earthquake (Mw 8.1) and Tsunami in the Solomon Islands

    NASA Astrophysics Data System (ADS)

    Fisher, M. A.; Scholl, D. W.; Geist, E. L.; Sliter, R. W.; Wong, F. L.; Reiss, C.; Mann, D. M.

    2007-12-01

    We reprocessed three multichannel seismic-reflection (MCS) lines collected by the USGS (1982, 1984) near the epicenter of the 2007 Mw-8.1 megathrust earthquake that struck the Solomon Islands. Near the epicenter, several bathymetric and tectonic elements, including an active spreading ridge and a transform fault, are being subducted at the New Britain Trench. These subducted elements affected fault slip during the earthquake, as indicated by two finite fault models (Yagi, 2007; Ji, 2007). Slip began around the epicenter, southeast of where the spreading ridge enters the subduction zone. Slip was reduced directly over the ridge, and northwest of the ridge, slip resumed with increased, possibly maximum amplitude. Fault rupture propagated northwestward at about 1.95 km/s (Yagi, 2007). The Woodlark spreading ridge, with its irregular bathymetry and probable high heat flow, injects a strong three-dimensionality into the analysis of fault slip along the interplate thrust. MCS data show smooth reflections from the interplate decollement that can be followed for about 40 km east of the trench, and hypocenters locally recorded during 1998 (Yoneshima et al., 2005) trace the plate interface deep into the subduction zone. The downgoing plate dips ~30° northeast through the zone of highest 1998 seismic activity, which occurs below 20 km depth. Although young oceanic crust is being subducted eastward along the New Britain Trench, the subducting plate bends sharply downward and dips steeply (30° to 45°) into the mantle. Teleseismic data place the 2007 earthquake epicenter near the trench axis, close to the up-dip limit of the seismogenic zone indicated by the 1998 seismicity. Under the upper slope of the island arc south of the epicenter, strong reflections suggest a mixed volcanic and carbonate-rock framework of the island arc. Down slope of where the strong reflections end, seaward-verging thrust faults deform several small forearc basins. Deformation occurred episodically

  20. Lesser Antilles Subduction Zone Investigation by a Cluster of Large Seismic Experiments in the Forearc Region

    NASA Astrophysics Data System (ADS)

    Last, T.

    2007-12-01

    Thales LAST stands for Lesser Antilles Subduction zone Team which gathers the scientific teams of a cluster of surveys and cruises that have been carried out in 2007 and coordinated under the European Union THALES WAS RIGHT project (Coord. A. Hirn). This cluster is composed by the German cruise TRAIL with the vessel F/S Merian (PI E. Flueh and H. Kopp, IFM-GEOMAR), the French cruise SISMANTILLES 2 with the IFREMER vessel N/O Atalante (PI M. Laigle, IPG Paris and JF. Lebrun, Univ. Antilles Guyane), and French cruise OBSANTILLES with the IRD vessel N/O Antea (PI P. Charvis, Geoazur, Nice, France). During these cruises and surveys, 84 Ocean Bottom 3-components Seismometers (OBS) and 20 Hydrophones (OBHs) have been brought together from several pools (Geoazur, INSU, IPGP, IFM-GEOMAR, AWI,), with up to 30 land stations (CSIC Barcelone, IPG Paris, INSU-RLBM and -LITHOSCOPE) in addition to the permanent onshore arrays of IPGP and SRU. The deployment of all these instruments has been supported principally by ANR Catastrophes Telluriques et Tsunamis (SUBSISMANTI), by the EU SALVADOR Programme of IFM-GEOMAR, as well as by the EU project THALES WAS RIGHT on the Antilles and Hellenic active subductions to which contribute IPGP, Geoazur, IFM-GEOMAR (Germany), ETH Zurich (Switzerland), CSIC Barcelona (Spain), Univ. Trieste (Italy) and NOA Athens (Greece). The main goal of this large seismic investigation effort is the understanding of the behaviour of the seismogenic zone and location of potential source regions of mega-thrust earthquakes. Specific goals are the mapping of the subduction interplate in the range where it may be seismogenic along the Lesser Antilles Arc from Antigua to southern Martinique Islands, as a contribution to identification and localisation in advance of main rupture zones of possible future major earthquakes, and to the search for transient signals of the activity. The forearc region, commonly considered as a proxy to the seismogenic portion of the

  1. Tectonics of crystalline forearcs: insights from the southern Andes and Indentor experiments

    SciTech Connect

    Forsythe, R.D.

    1985-01-01

    South of Peru over 90% of the Andean forearc is dominated by metamorphic or plutonic rocks, the bulk of which are exposed above sea level within the coastal ranges of the western Chile. These coastal ranges are divisible into 9 elongate, semi-independent blocks, that are separated from each other by zones of oblique faulting and from the main South American lithosphere by longitudinal fault zones that parallel the magmatic arc. Most of the fault zone have had late Tertiary and Quaternary movements. Constrained by the underlying subduction zone, north and south bounding oblique faults, and eastern longitudinal faults, 6 of the 9 blocks have geometries of a doubly-tapered wedge. Transverse, principally normal, faults develop as splays to the main longitudinal faults, producing a distinctive batwing fault pattern. Strike-slip motion on longitudinal faults leads to four kinematic and two dynamic classes of block terminations. These terminations correlate with the limits of rupture zones to great earthquakes and anomalous regions of both coastal uplift and shelf subsidence. Since Nazca-South American relative motion has been almost normal to the margin for the last 25 Ma, components of oblique convergence cannot easily account for late Cenozoic block movements. Variations in the gravitational potential energy associated with the subduction of bathymetric highs along the Peru-Chile Trench should produce variations in the resolved horizontal stress acting normal to the plate boundary. This offers a dynamic alternative to kinematic models that have principally relied on oblique convergence to explain strike-slip movements on faults that parallel the arc or trench. Modified rigid indentor/plasticine experiments have been run to model collision of a bathymetric high.

  2. Local thickening of the Cascadia forearc crust and the origin of seismic reflectors in the uppermost mantle

    USGS Publications Warehouse

    Calvert, A.J.; Ramachandran, K.; Kao, H.; Fisher, M.A.

    2006-01-01

    Seismic reflection profiles from three different surveys of the Cascadia forearc are interpreted using P wave velocities and relocated hypocentres, which were both derived from the first arrival travel time inversion of wide-angle seismic data and local earthquakes. The subduction decollement, which is characterized beneath the continental shelf by a reflection of 0.5 s duration, can be traced landward into a large duplex structure in the lower forearc crust near southern Vancouver Island. Beneath Vancouver Island, the roof thrust of the duplex is revealed by a 5–12 km thick zone, identified previously as the E reflectors, and the floor thrust is defined by a short duration reflection from a − 1. We suggest that these relatively low velocities indicate the presence of either crustal rocks from the oceanic plate that have been underplated to the continent or crustal rocks from the forearc that have been transported downward by subduction erosion. The absence of seismicity from within the E reflectors implies that they are significantly weaker than the overlying crust, and the reflectors may be a zone of active ductile shear. In contrast, seismicity in parts of the D reflectors can be interpreted to mean that ductile shearing no longer occurs in the landward part of the duplex. Merging of the D and E reflectors at 42–46 km depth creates reflectivity in the uppermost mantle with a vertical thickness of at least 15 km. We suggest that pervasive reflectivity in the upper mantle elsewhere beneath Puget Sound and the Strait of Georgia arises from similar shear zones.

  3. Ultramafic clasts from the South Chamorro serpentine mud volcano reveal a polyphase serpentinization history of the Mariana forearc mantle

    NASA Astrophysics Data System (ADS)

    Kahl, Wolf-Achim; Jöns, Niels; Bach, Wolfgang; Klein, Frieder; Alt, Jeffrey C.

    2015-06-01

    Serpentine seamounts located on the outer half of the pervasively fractured Mariana forearc provide an excellent window into the forearc devolatilization processes, which can strongly influence the cycling of volatiles and trace elements in subduction zones. Serpentinized ultramafic clasts recovered from an active mud volcano in the Mariana forearc reveal microstructures, mineral assemblages and compositions that are indicative of a complex polyphase alteration history. Petrologic phase relations and oxygen isotopes suggest that ultramafic clasts were serpentinized at temperatures below 200 °C. Several successive serpentinization events represented by different vein generations with distinct trace element contents can be recognized. Measured in situ Rb/Cs ratios are fairly uniform ranging between 1 and 10, which is consistent with Cs mobilization from sediments at lower temperatures and lends further credence to the low-temperature conditions proposed in models of the thermal structure in forearc settings. Late veins show lower fluid mobile element (FME) concentrations than early veins, suggesting a decreasing influence of fluid discharge from the subducting slab on the composition of the serpentinizing fluids. The continuous microfabric and mineral chemical evolution observed in the ultramafic clasts may have implications as to the origin and nature of the serpentinizing fluids. We hypothesize that opal and smectite dehydration produce quartz-saturated fluids with high FME contents and Rb/Cs between 1 and 4 that cause the early pervasive serpentinization. The partially serpentinized material may then be eroded from the basal plane of the suprasubduction mantle wedge. Serpentinization continued but the interacting fluids did not carry a pronounced sedimentary signature, either because FMEs were no longer released from the slab, or due to an en route loss of FMEs. Late chrysotile veins that document the increased access of fluids in a now fluid-dominated regime are

  4. Forearc Sliver Translation, a Lack of Arc-Normal Strain Accumulation, and Interplate Thrust Earthquakes: GPS Geodesy in Western Nicaragua

    NASA Astrophysics Data System (ADS)

    Turner, H. L.; Mattioli, G. S.; Jansma, P. E.; Styron, R. H.

    2007-05-01

    We have been investigating the kinematics of the Nicaraguan forearc using campaign GPS measurements of our geodetic network made over the last seven years (Turner et al., 2007). We currently have interseismic velocities for 18 campaign sites and have installed 10 additional sites in the backarc to investigate the nature of the transition from forearc sliver motion to stable Caribbean Plate motion. Our work focusing on the later issue is presented elsewhere at this meeting (Styron et al., 2007). Corrections for modeled coseismic offsets from the Jan. 13, 2001 Mw7.7 earthquake off the coast of El Salvador have been applied to our campaign site velocities. Some of our time-series are also strongly affected by coseismic and postseismic effects of the Oct. 9, 2004 Mw6.9 earthquake off of the coast of Nicaragua. The geodetic effects of this event are being removed from the affected time-series for interseismic velocity analysis. We have also derived interseismic velocities for five continuous GPS sites in the region. Our GPS results confirm previous predictions of northwest transport of a forearc sliver with an average Northwest velocity of ~15 mm yr-1, but show little evidence for an arc- normal component of strain accumulation associated with locking on the subduction interface. However, the amount of seismicity along this section of the Middle America Trench, including several recent large events such as the 1992 Mw7.6 and 2004 Mw6.9 earthquakes, indicates some amount of locking is present. Several possibilities may account for the apparent contradiction between the GPS results and observed seismicity. The locked zone may be too shallow and too far offshore for the arc-normal component to show up in our network, or the arc-normal signal may be masked by post-seismic effects from the 1992 offshore earthquake. If coupling between the downgoing slab and the overriding plate is weak or limited to a small seismogenic zone, then arc-parallel motion of the forearc sliver may

  5. How much does it cost to achieve coverage targets for primary healthcare services? A costing model from Aceh, Indonesia.

    PubMed

    Abdullah, Asnawi; Hort, Krishna; Abidin, Azwar Zaenal; Amin, Fadilah M

    2012-01-01

    Despite significant investment in improving service infrastructure and training of staff, public primary healthcare services in low-income and middle-income countries tend to perform poorly in reaching coverage targets. One of the factors identified in Aceh, Indonesia was the lack of operational funds for service provision. The objective of this study was to develop a simple and transparent costing tool that enables health planners to calculate the unit costs of providing basic health services to estimate additional budgets required to deliver services in accordance with national targets. The tool was developed using a standard economic approach that linked the input activities to achieving six national priority programs at primary healthcare level: health promotion, sanitation and environment health, maternal and child health and family planning, nutrition, immunization and communicable diseases control, and treatment of common illness. Costing was focused on costs of delivery of the programs that need to be funded by local government budgets. The costing tool consisting of 16 linked Microsoft Excel worksheets was developed and tested in several districts enabled the calculation of the unit costs of delivering of the six national priority programs per coverage target of each program (such as unit costs of delivering of maternal and child health program per pregnant mother). This costing tool can be used by health planners to estimate additional money required to achieve a certain level of coverage of programs, and it can be adjusted for different costs and program delivery parameters in different settings. PMID:22887349

  6. Post Disaster Governance, Complexity and Network Theory: Evidence from Aceh, Indonesia After the Indian Ocean Tsunami 2004.

    PubMed

    Lassa, Jonatan A

    2015-01-01

    This research aims to understand the organizational network typology of large--scale disaster intervention in developing countries and to understand the complexity of post--disaster intervention, through the use of network theory based on empirical data from post--tsunami reconstruction in Aceh, Indonesia, during 2005/-2007. The findings suggest that the ' degrees of separation' (or network diameter) between any two organizations in the field is 5, thus reflecting 'small- world' realities and therefore making no significant difference with the real human networks, as found in previous experiments. There are also significant loops in the network reflecting the fact that some actors tend to not cooperate, which challenges post- disaster coordination. The findings show the landscape of humanitarian actors is not randomly distributed. Many actors were connected to each other through certain hubs, while hundreds of actors make 'scattered' single 'principal--client' links. The paper concludes that by understanding the distribution of degree, centrality, 'degrees of separation' and visualization of the network, authorities can improve their understanding of the realities of coordination, from macro to micro scales. PMID:26236562

  7. An evaluation of public, private, and mobile health clinic usage for children under age 5 in Aceh after the tsunami: implications for future disasters

    PubMed Central

    Rassekh, Bahie Mary; Shu, Winnie; Santosham, Mathuram; Burnham, Gilbert; Doocy, Shannon

    2014-01-01

    Background: Aceh, Indonesia, was the hardest-hit area in the 26 December 2004 Indian Ocean earthquake and tsunami, with more than 500,000 people displaced, 120,000 people dead, and total damages and losses estimated at $4.5 billion. The relief effort following the tsunami was also immense. Objectives: This study aimed to determine and assess utilization patterns of formal public versus private and mobile health services for children under age 5 with diarrhea, cough and difficulty breathing, fever, or skin disease and to identify determinants of care usage. Methods: A household survey of 962 households was administered to caretakers of children aged 1–5 years. A sample of clusters within Banda Aceh and Aceh Besar were selected and those caretakers within the cluster who fit the inclusion criteria were interviewed. Results: Of those caretakers who utilized formal health services as the first line of care for their sick child, 62% used a public health facility, 30% used a private health facility, and 8% used a mobile clinic. In terms of significant factors associated with public, private, and mobile care utilization, mobile clinics were at one side of the spectrum and private clinics were at the other side overall, with public care somewhere in between. This was true for several variables. Mobile clinic users reported the lowest cost of services and medicine and the highest perceived level of accessibility, and private care users reported the highest perceived level of satisfaction. Conclusions: Utilization of formal health services for children was quite high after the tsunami. The caretaker's perceived satisfaction with public health services could have been improved. Mobile clinics were an accessible source of health care and could be used in future disaster relief efforts to target those populations that seek less care for their sick children, including displaced populations, and those children whose parents have died. PMID:25750788

  8. Atmospheric Ar and Ne returned from mantle depths to the Earth’s surface by forearc recycling

    PubMed Central

    Baldwin, Suzanne L.; Das, J. P.

    2015-01-01

    In subduction zones, sediments, hydrothermally altered lithosphere, fluids, and atmospheric gases are transported into the mantle, where ultrahigh-pressure (UHP) metamorphism takes place. However, the extent to which atmospheric noble gases are trapped in minerals crystallized during UHP metamorphism is unknown. We measured Ar and Ne trapped in phengite and omphacite from the youngest known UHP terrane on Earth to determine the composition of Ar and Ne returned from mantle depths to the surface by forearc recycling. An 40Ar/39Ar age [7.93 ± 0.10 My (1σ)] for phengite is interpreted as the timing of crystallization at mantle depths and indicates that 40Ar/39Ar phengite ages reliably record the timing of UHP metamorphism. Both phengite and omphacite yielded atmospheric 38Ar/36Ar and 20Ne/22Ne. Our study provides the first documentation, to our knowledge, of entrapment of atmospheric Ar and Ne in phengite and omphacite. Results indicate that a subduction barrier for atmospheric-derived noble gases does not exist at mantle depths associated with UHP metamorphism. We show that the crystallization age together with the isotopic composition of nonradiogenic noble gases trapped in minerals formed during subsolidus crystallization at mantle depths can be used to unambiguously assess forearc recycling of atmospheric noble gases. The flux of atmospheric noble gas entering the deep Earth through subduction and returning to the surface cannot be fully realized until the abundances of atmospheric noble gases trapped in exhumed UHP rocks are known. PMID:26542683

  9. On the Rock Magnetic Properties of Some Serpentinized Peridotites in the Southern Mariana Forearc

    NASA Astrophysics Data System (ADS)

    Herrero-Bervera, E.; Martinez, F.; Fryer, P. B.; Ohara, Y.

    2014-12-01

    We have studied the magnetic properties of 12 peridotite samples recovered during the JAMSTEC Cruise of the R/V Yokosuka YK10-12 and collected on Shinkai 6500 dive 1234 in the Shinkai See Field (SSF) located in the deep (~5700 m) outer forearc (11°39.10'N, 143°02.94'E). We conducted remanence and induced experiments on the samples to determine degree of serpentinization. Stepwise alternating field (AF) and thermal demagnetization experiments from 2.5 to 70 mT and from 28 to 575°C, respectively, yield univectorial diagrams showing the removal of secondary components (e.g., VRM, IRM, CRM etc) by isolating a Characteristic Remanent Magnetization (ChRM) at low fields and temperatures. The normalized intensity of demagnetization J/Jo shows the decrease of the magnetization of the specimens where about 50% of the original magnetization is lost at about 5 mT and 100°C (i.e. Median Destructive Field). The stereograms show magnetic stability of the specimens by determining the directional behavior after 4 demagnetization steps (from 7.5-10 mT fields and low temps). Induced magnetization such as magnetic granulometry tests, sIRM's, hysteresis saturation loops and back-fields were performed. Diagnostic values of Mrs/Ms and Hrc/Hc determine the domain structure of a magnetic sample. The magnetic grain sizes were determined using the protocol of Dunlop [2002 a and b]. Most of the samples are distributed over the Pseudo-Single Domain (PSD) range with a certain degree of clustering. Curie points were obtained by measuring their low-field susceptibility vs. temperature (k-T) from 28 °C up to 700 °C in an Argon atmosphere showing a minimum of 1-4 magnetic mineral phases with temperatures ranging from ~100°C up to 640°C, which are predominantly Ti-poor and Ti-rich magnetites and magnetite. Samples recovered by the Shinkai 6500 show appreciable variation in bulk susceptibility (22.3 x 10-3 to 142 x 10-6 SI units). The samples appear to be modestly to moderately serpentinized

  10. The Xigaze ophiolite, southern Tibet: a fossil oceanic forearc generated during subduction initiation

    NASA Astrophysics Data System (ADS)

    Dai, J.; Wang, C.; Zhu, D. C.; Li, Y.

    2014-12-01

    source. Taking into account the geological and geochronological characteristics of the Xigaze ophiolite, we propose they were formed in a forearc setting through rapid slab rollback during subduction initiation between 127-122 Ma.

  11. Forearc Morphotectonics and Megathrust Earthquakes Along the Middle America Convergent Margin, Nicoya Peninsula, Costa Rica

    NASA Astrophysics Data System (ADS)

    Marshall, J. S.; Spotila, J. A.; Gardner, T.; Protti, M.; LaFromboise, E. J.; Morrish, S.; Robinson, M.; Barnhart, A.; Butcher, A.; Khaw, F.; Piestrzeniewicz, P.; Ritzinger, B.; Utick, J.; Wellington, K.

    2015-12-01

    The Nicoya Peninsula, Costa Rica forms a prominent morphologic high along the Middle America forearc where the Cocos plate subducts beneath the Caribbean plate at 8.5 cm/yr. This emergent coastal landmass lies directly above the megathrust along a seismogenic zone that produces frequent major earthquakes. Along the Nicoya coast, Quaternary marine and fluvial terraces record net uplift in a pattern that shadows the peninsula's overall topographic form. Terrace mapping, surveying, and age dating (14C, OSL, TCN) reveal uplift variations that coincide with three contrasting domains of subducting seafloor (EPR, CNS-1, CNS-2). Uplift rates vary between 0.1-0.2 m/ky inboard of older EPR crust in the north; 0.2-0.5 m/ky inboard of younger CNS-1 crust along the central coast; and 1.5-2.5 m/ky inboard of CNS-2 seamounts impacting the peninsula's southern tip. GIS digital terrain analysis reveals a deformation pattern consistent with field geomorphic and geologic observations. The two largest Nicoya earthquakes in the past century (1950 Mw7.8; 2012 Mw7.6) each generated decimeter-scale coseismic uplift along the central coast. The 2012 uplift pattern coincides with the area of pre-event locking, mainshock slip, prior 1950 rupture, and 1950 coseismic uplift. Most of the 1950 uplift was recovered by gradual interseismic subsidence during six decades of strain accumulation leading to the 2012 rupture. Paleoseismic sediment coring in Nicoya coastal wetlands reveals fragmentary stratigraphic evidence consistent with earlier Holocene earthquake induced changes in land level. While elastic strain accumulation and release produce short-term cycles of uplift and subsidence, long-term net uplift results in gradual coastal emergence and the growth of topographic relief. Net uplift along the central Nicoya segment may be the product of irrecoverable seismic cycle strain (shortening), coupled with tectonic erosion near the trench and subsequent underplating of eroded material at depth

  12. Forearc Deformation, Arc Volcanism, and Landscape Evolution near the Cocos-Nazca-Caribbean Triple Junction

    NASA Astrophysics Data System (ADS)

    Morell, K. D.; Fisher, D.; Gardner, T.; Protti, M.

    2005-12-01

    terraces suggest that these gravels were probably deposited by the Rio Chiriqui prior to the uplift of the Fila Costena, when the river channel was west of its current location. Thus, the Rio Chiriqui drainage network and its associated landscape are migrating eastward through time. These observations indicate major changes in the arc-forearc system associated with the changing subduction parameters in the wake of the migrating triple junction.

  13. Dynamic Passage of Topography Beneath the Southern Costa Rica Forearc seen with Seismic Stratigraphy

    NASA Astrophysics Data System (ADS)

    Edwards, J. H.; Kluesner, J. W.; Silver, E. A.

    2014-12-01

    3D seismic reflection data (CRISP) collected across the southern Costa Rica margin reveals that a thick, deforming sedimentary wedge underlies the younger slope sediments (Silver et al., this meeting). The older wedge material and younger slope sediments are separated by a high-amplitude regional unconformity. Seismic stratigraphy of the sedimentary strata overlying this regional unconformity reflects a dynamic deformation history of the margin. The younger slope sediments contain series of more localized unconformities, separating sedimentary units as thick as 1 km that reveal a dynamically changing set of inverted, overlapping basins. The geometry of these overlapping, inverted basins indicate sequential uplift events. The direction of basin thickening varies upsection, and these basins are cut by both thrust and normal faults and are deformed by folding. Structural development appears to be controlled by relief on the subducting plate interface, which induces uplift and subsidence and thereby controls the pattern of erosion and deposition. We interpret the evolution of these inverted stratigraphic packages as forming from subducting topography. Correlating these seismic-stratigraphic packages to recent drilling based on preliminary magnetostratigraphy from IODP site U1413 (Expedition 344 Scientists, 2013), allows us to date the passage of the subducting plate topography beginning ~2 Ma.

  14. Deep seismic structure of the Atacama basin, northern Chile

    NASA Astrophysics Data System (ADS)

    Schurr, B.; Rietbrock, A.

    2004-06-01

    The Atacama basin is a prominent morphological anomaly in the Central Andean forearc. 3D seismic structure beneath the depression and its surroundings has been determined from local earthquake tomography. Depth maps of P-wave velocity and attenuation (1/Qp) through the lithosphere reveal a rheologically strong (high Qp and vp) lithospheric block beneath the basin, surrounded by weak regions (low Qp and vp) beneath Pre- and Western Cordilleras. The anomalous lithospheric structure appears to bar hot asthenospheric mantle from penetrating trenchward, and hence causes the volcanic front to be deflected by the Salar de Atacama basin. The cold block may also influence the thermal structure of the subducted slab causing reduced Benioff seismicity and less hydration of mantle rocks evident from reduced vp/vs ratios. Seismic data are hard to reconcile with extension and lithospheric thinning as a mechanism for subsidence of the basin. Instead, high strength of the Atacama lithospheric block may contribute to basin formation by focussing deformation and uplift along the block's weak edges.

  15. Deformation of forearcs caused by subduction of aseismic ridges: The role of ridge orientation and convergence direction investigated with 3D finite-element models

    NASA Astrophysics Data System (ADS)

    Zeumann, Stefanie; Hampel, Andrea

    2015-04-01

    Subduction of aseismic oceanic ridges causes considerable deformation of the forearc region. To investigate the role of ridge orientation relative to the margin and convergence direction on the style of forearc deformation, we developed a series of 3D finite-elemente models, in which a rigid oceanic plate carrying the model ridge subducts beneath a deformable forearc wedge. Experiments were carried out for angles of 30°, 60° and 90° between the ridge axis and the trench and for different convergence directions. In the experiments, in which the ridge axis is parallel to the convergence direction, the ridge is stationary; in all other experiments, the ridge migrates along the margin and thus affects different regions of the forearc. Our results show that the ridge indents and uplifts the forearc in all models. For obliquely subducting ridges the displacement and strain fields become highly asymmetric regardless if the ridge is stationary or migrates along the forearc. Only if the ridge is stationary and oriented perpendicular to the margin, the deformation is symmetric relative to the ridge axis. Stationary ridges show uplift only above the ridge tip, whereas a migrating ridge causes a wave of uplift above the leading flank of the ridge followed by subsidence above the trailing flank. Horizontal strain components show domains of both extension and shortening, with extension occurring above the ridge tip and shortening above the ridge flanks. To compare our results with natural case studies, we computed additional models reflecting the setting of the stationary Cocos Ridge subducting beneath southern Costa Rica and of the Nazca Ridge, which migrates along the Peruvian margin. The results of these adjusted models are in good agreement with field observations. For the model of the Cocos Ridge the highest degree of shortening occurs normal to the margin, which coincides with the location of a thrust belt in the forearc of Costa Rica with its maximum shortening inboard

  16. Determining the Controlling Factors of Coastal Development along an Active Margin - A Case Study from Aceh, Indonesia

    NASA Astrophysics Data System (ADS)

    Monecke, Katrin; Meilianda, Ella; Hill, Emma; McAdoo, Brian; Qiang, Qui; Storms, Joep; Walstra, Dirk-Jan; Setiawan, Agus; Masputri, Aisha S.; Mayasari, Cut D.; Riandi, Indra; Nasir, Muhammad

    2016-04-01

    Understanding the recovery of shorelines after catastrophic events is crucial for sustainable coastal development and future hazard mitigation. Here, we present post-seismic coastal development data from West Aceh, Indonesia, an area that was severely affected by the 2004 Sumatra Andaman earthquake and ensuing Indian Ocean tsunami. Using a combined approach of spatial data analysis, field surveys and numerical modeling, we reconstruct the build-up of a new beach ridge along a 10 kilometer long stretch of the western Acehnese coast after the complete destruction of the beach in 2004. The coastline of West Aceh can be characterized as a microtidal, wave dominated environment with the wave climate being controlled by the monsoon seasons reaching a significant wave height of Hs = 1.2 m during the more energetic West Monsoon from April to September. Waves approach the shoreline at a very low angle resulting in minor and variable longshore sediment transport. The beach has an average foreshore slope of 0.07 and is composed of well sorted medium sand. Recently obtained bathymetric data indicates a steep upper shoreface with a slope of 0.03. Further offshore the slope decreases to 0.01 with 14 m water depth being reached in about 700 m distance to the shoreline. Grab samples obtained in 10 m water depth are composed of fine to medium sand but lenses of medium to coarse sand with abundant shell debris do also occur. Beach ridges can be traced up to 2 km inland and indicate long-term coastal progradation and abundant sediment supply to the littoral zone. The western Acehnese shoreline parallels the Sunda trench and subsided 50 to 100 cm during the 2004 rupture. Modeled land elevation changes as a result of afterslip and viscoelastic mantle relaxation, indicate rapid post-seismic uplift of 4.4 cm/year in the year following the earthquake, but more moderate uplift rates of 1.4 cm/year since mid-2006. In 2004, co-seismic subsidence and tsunami scouring caused the coastline to

  17. Oblique strike-slip faulting of the Cascadia submarine forearc: The Daisy Bank fault zone off central Oregon

    NASA Astrophysics Data System (ADS)

    Goldfinger, Chris; Kulm, LaVerne D.; Yeats, Robert S.; Hummon, Cheryl; Huftile, Gary J.; Niem, Alan R.; McNeill, Lisa C.

    The Cascadia submarine forearc off Oregon and Washington is deformed by numerous active WNW-trending, left-lateral strike-slip faults. The kinematics of this set of sub-parallel left-lateral faults suggests clockwise block rotation of the forearc driven by oblique subduction. One major left-lateral strike-slip fault, the 94 km-long Daisy Bank fault, located off central Oregon, was studied in detail using high-resolution AMS 150 kHz and SeaMARC-lA sidescan sonar, swath bathymetry, multichannel seismic reflection profiles and a submersible. The Daisy Bank fault zone cuts the sediments and basaltic basement of the subducting Juan de Fuca plate, and the overriding North American plate, extending from the abyssal plain to the upper slope-outer shelf region. The Daisy Bank fault, a near-vertical left-lateral fault striking 292°, is a wide structural zone with multiple scarps observed in high-resolution sidescan images. From a submersible, we observe that these scarps offset late Pleistocene gray clay and overlying olive green Holocene mud, dating fault activity as post-12 ka on the upper slope. Vertical separation along individual fault scarps ranges from a few centimeters to 130 meters. Using a retrodeformation technique with multichannel reflection records, we calculate a net slip of 2.2±0.5 km. Fault movement commenced at about 380±50 ka near the western fault tip, based upon an analysis of growth strata and correlation with deep-sea drill hole biostratigraphy. We calculate a slip rate of 5.7±2.0 mm/yr. for the Daisy Bank fault at its western end on the Juan de Fuca plate. The motion of the set of oblique faults, including the Daisy Bank fault, may accommodate a significant portion of the oblique component of plate motion along the central Cascadia margin. We propose a block rotation model by which the seawardmost part of the forearc rotates clockwise and translates northward.

  18. Toward long-term geochemical sampling of gases and deep fluids in subduction zone fore-arcs: New instrument developments

    NASA Astrophysics Data System (ADS)

    Tryon, M. D.; Labonte, A. L.; Fueri, E.; Hilton, D. R.; Brown, K. M.

    2004-12-01

    We present preliminary results of an on-going instrument development study aimed at quantifying the rate of elemental loss to the ocean/atmosphere in active fore-arc margins. Work on subduction zones to date has focused on elemental fluxes associated with magmatism at the arc front. For example, the flux of carbon output along the strike of the Central America arc is ˜ 5 x 107 mol/yr/km, or ~14% of that potentially available by input via the trench (Shaw et al., EPSL, 2003). This result indicates that carbon is (a) efficiently recycled to the (deeper) mantle, i.e. the mantle beyond the zone of arc magma generation, and/or (b) lost in the fore-arc region. There are few constraints on elemental losses at the fore-arc region; the present work, therefore, is motivated by quantifying the flux of volatiles (and other species) lost in the early stages of the subduction cycle. This will allow a qualitative assessment of the importance of deep recycling and contribute to an increased understanding of the hydrogeology of active margins. The Chemical and Aqueous Transport (CAT) meters (Tryon et al., Deep Sea Research, 2001) used in this study record a time series of flow rates by injecting a tracer at a constant known rate into the flow stream through the instrument and by sampling downstream of this point for tracer dilution. They also collect a time series of seep fluids in copper coils and maintain them at seafloor pressure during recovery. The Optical Flow Meter (OFM) measures flow by determining the time-of-flight of a tracer pulse injected into the flow stream. An osmotic pump is used to sample fluids in a manner similar to the CAT meters. A series of tests utilizing both sets of instruments has been conducted at the Extrovert Cliffs site in Monterey Bay during 2004. Sites chosen range from diffuse flow sites with output rates of 10s of cm/yr to highly focused visibly flowing sites: all localities are covered by extensive microbial mats and chemosynthetic clams. Our

  19. Megathrust Friction in the Maule Earthquake Area in Relation to Forearc Morphology and Mechanical Stability, and to Earthquake Rupture Dynamics

    NASA Astrophysics Data System (ADS)

    Cubas, N.; Avouac, J.; Lapusta, N.

    2011-12-01

    Determining the spatio-temporal variations of frictional properties is a key issue in order to advance our understanding of earthquake dynamics. This study aims to characterize these variations for the 2010 Maule Mw 8.8 earthquake area based on the analysis of the forearc morphology and dynamic earthquake simulation. Two different mechanical approaches are applied to determine static and dynamic frictions. The first one relies on the critical taper theory and allows to constrain basal and internal frictions as well as the internal pore fluid pressure. The forearc above aseismic slipping areas of the Megathrust appear to be at critical mechanical state as evidenced from its morphology and indices of active deformation. Aseismic areas updip of the Maule Earthquake rupture area, where the forearc consists of a recently accreted sedimentary prism, show a moderate basal friction (0.17 - 0.21) and an internal pore fluid pressure close to hydrostatic conditions. Aseismic areas downdip of the Maule Earthquake rupture and beneath the Arauco peninsula, known to be a recurrent barrier to earthquake propagation, have higher basal friction (0.4). By contrast the forerarc above the seismogenic zone is observed to be mechanically stable, all the deformation being accommodated by slip along the Megathrust. We use the limit analysis approach to constrain the dynamic friction of the seismogenic zone as the critical taper theory provides only limited insight in this case. We determine spatial variations of the basal friction from the position of active faults. We focus on the Santa Maria island cross-section where an active backthrust splays from the megathrust near the transition from seismic sliding to aseismic sliding. A low basal friction in the seismogenic zone (< 0.1) is required for this splay fault to be active. These frictional properties are then integrated in a three-dimensional earthquake sequence model to investigate whether the low friction in the seismogenic zone is

  20. Geological characteristics of the Shinkai Seep Field, a serpentinite-hosted ecosystem in the Southern Mariana Forearc

    NASA Astrophysics Data System (ADS)

    Ohara, Y.; Stern, R. J.; Martinez, F.; Michibayashi, K.; Reagan, M. K.; Fujikura, K.; Watanabe, H.; Ishii, T.; Kelley, K. A.

    2012-12-01

    Most hydrothermal vents along mid-ocean spreading ridges are high-temperature, sulfide-rich, and low pH (acidic environments). For this reason, the discovery of the Lost City hydrothermal field on the Mid-Atlantic Ridge has stimulated interest in the role of serpentinization of peridotite in generating H2- and CH4-rich fluids and associated carbonate chimneys, as well as in the biological communities adapted to highly reduced, alkaline environments. A new serpentinite-hosted ecosystem, the Shinkai Seep Field (SSF), was discovered by a Shinkai 6500 dive in the inner trench slope of the southern Mariana Trench, near the Challenger Deep, during YK10-12 cruise of R/V Yokosuka in September 2010. Abundant chemosynthetic biological communities, principally consisting of vesicomyid clams are associated with serpentinized peridotite in the SSF. Serpentinization beneath several hydrothermal sites on the Mid-Atlantic Ridge is controlled by interacting seawater and peridotite, variably influenced by magmatic heat. In contrast, the SSF is located in a deep inner trench slope where magmatic heat contribution is unlikely. Instead, serpentinization reactions feeding the SSF may be controlled by persistent fluid flow from the subducting slab. Slab-derived fluid flow is probably controlled by flow through fractures because no serpentinite mud volcano can be discerned along the southern Mariana forearc. Deep-towed IMI-30 sonar backscatter imaging during TN273 cruise of R/V Thomas G. Thompson in January 2012 indicates that the SSF is associated with a small, low backscatter feature that may be a small mound. There are 20 or more of these features in the imaged area, the size of which is ~200 m width and ~200 m to ~700 m long. Since the southern Mariana forearc is heavily faulted, with a deep geology that is dominated by peridotite, more SSF-type seeps are likely to exist along the forearc above the Challenger Deep. The discovery of the SSF suggests that serpentinite-hosted vents may

  1. Stable isotope compositions of serpentinite seamounts in the Mariana forearc: Serpentinization processes, fluid sources and sulfur metasomatism

    USGS Publications Warehouse

    Alt, J.C.; Shanks, Wayne C., III

    2006-01-01

    The Mariana and Izu-Bonin arcs in the western Pacific are characterized by serpentinite seamounts in the forearc that provide unique windows into the mantle wedge. We present stable isotope (O, H, S, and C) data for serpentinites from Conical seamount in the Mariana forearc and S isotope data for Torishima seamount in the Izu-Bonin forearc in order to understand the compositions of fluids and temperatures of serpentinization in the mantle wedge, and to investigate the transport of sulfur from the slab to the mantle wedge. Six serpentine mineral separates have a restricted range of ??18O (6.5-8.5???). Antigorite separates have ??D values of -29.5??? to -45.5??? that reflect serpentinization within the mantle wedge whereas chrysotile has low ??D values (-51.8??? to -84.0???) as the result of re-equilibration with fluids at low temperatures. Fractionation of oxygen isotopes between serpentine and magnetite indicate serpentinization temperatures of 300-375 ??C. Two late cross-fiber chrysotile veins have higher ??18O values of 8.9??? to 10.8??? and formed at lower temperatures (as low as ???100 ??C). Aqueous fluids in equilibrium with serpentine at 300-375 ??C had ??18O = 6.5-9??? and ??D = -4??? to -26???, consistent with sediment dehydration reactions at temperatures <200 ??C in the subducting slab rather than a basaltic slab source. Three aragonite veins in metabasalt and siltstone clasts within the serpentinite flows have ??18O = 16.7-24.5???, consistent with the serpentinizing fluids at temperatures <250 ??C. ??13C values of 0.1-2.5??? suggest a source in subducting carbonate sediments. The ??34S values of sulfide in serpentinites on Conical Seamount (-6.7??? to 9.8???) result from metasomatism through variable reduction of aqueous sulfate (??34S = 14???) derived from slab sediments. Despite sulfur metasomatism, serpentinites have low sulfur contents (generally < 164 ppm) that reflect the highly depleted nature of the mantle wedge. The serpentinites are mostly

  2. Stable isotope compositions of serpentinite seamounts in the Mariana forearc: Serpentinization processes, fluid sources and sulfur metasomatism

    NASA Astrophysics Data System (ADS)

    Alt, Jeffrey C.; Shanks, Wayne C.

    2006-02-01

    The Mariana and Izu-Bonin arcs in the western Pacific are characterized by serpentinite seamounts in the forearc that provide unique windows into the mantle wedge. We present stable isotope (O, H, S, and C) data for serpentinites from Conical seamount in the Mariana forearc and S isotope data for Torishima seamount in the Izu-Bonin forearc in order to understand the compositions of fluids and temperatures of serpentinization in the mantle wedge, and to investigate the transport of sulfur from the slab to the mantle wedge. Six serpentine mineral separates have a restricted range of δ18O (6.5-8.5‰). Antigorite separates have δD values of - 29.5‰ to - 45.5‰ that reflect serpentinization within the mantle wedge whereas chrysotile has low δD values (- 51.8‰ to - 84.0‰) as the result of re-equilibration with fluids at low temperatures. Fractionation of oxygen isotopes between serpentine and magnetite indicate serpentinization temperatures of 300-375 °C. Two late cross-fiber chrysotile veins have higher δ18O values of 8.9‰ to 10.8‰ and formed at lower temperatures (as low as ˜100 °C). Aqueous fluids in equilibrium with serpentine at 300-375 °C had δ18O = 6.5-9‰ and δD = - 4‰ to - 26‰, consistent with sediment dehydration reactions at temperatures < 200 °C in the subducting slab rather than a basaltic slab source. Three aragonite veins in metabasalt and siltstone clasts within the serpentinite flows have δ18O = 16.7-24.5‰, consistent with the serpentinizing fluids at temperatures < 250 °C. δ13C values of 0.1-2.5‰ suggest a source in subducting carbonate sediments. The δ34S values of sulfide in serpentinites on Conical Seamount (- 6.7‰ to 9.8‰) result from metasomatism through variable reduction of aqueous sulfate ( δ34S = 14‰) derived from slab sediments. Despite sulfur metasomatism, serpentinites have low sulfur contents (generally < 164 ppm) that reflect the highly depleted nature of the mantle wedge. The serpentinites are

  3. Methane Production In Forearc Sediments At The Costa Rican Convergent Margin

    NASA Astrophysics Data System (ADS)

    Cardace, D.; Morris, J. D.; Peacock, A.; White, D. C.

    2004-12-01

    Plate tectonics creates suitable habitats for deep biosphere organisms, affecting the distribution of biological communities on Earth. Subduction zones, where crustal materials return to the planetary interior through plate convergence, expose active microbial communities in subducting seafloor sediments to a fresh chemical inventory as diagenesis, metamorphic reactions, and tectonically-induced fluid flow alter sediments and surrounding porewaters. The plate interface (the decollement) experiences persistent geochemical flux of light hydrocarbon- and metal-bearing fluids from depth. This project (1) examines the habitability of the decollement zone at the Costa Rican convergent margin from a geochemical perspective, (2) uses lipid biomarkers to describe biomass distribution in sediment samples adjacent to and within the decollement, and (3) cites methanogenesis as a likely metabolic strategy employed by the resident microbial community. Sterile plugs of sediment were recovered from cores taken during Leg 205 of the Ocean Drilling Program, in the Middle America Trench off Costa Rica. Samples are from the incoming carbonate section of Site 1253 at 370-437 meters below seafloor (mbsf), in the forearc sedimentary wedge at Site 1255 at 134-145 mbsf, and around an upper fault (153-220 mbsf) and in the decollement zone (305-366 mbsf) at Site 1254. Drilling mud and fluid were sampled to monitor potential microbial contamination. Samples were immediately frozen at -80ºC. Prior to analysis, samples were freeze-dried in preparation for serial extraction of DNA and lipids. DNA was identified by fluorometry in 13 of 26 samples tested. The DNA was screened for methanogens by real time polymerase chain reaction (PCR), employing ME1 and ME2 primers that amplify a 0.75-kb region of the alpha-subunit gene for methyl coenzyme M reductase (MCR). Methanogen-specific genes were detected in DNA extracted from one Site 1253 sample (at 436.9 mbsf in the basal carbonates) and four Site

  4. Potential seismic hazards and tectonics of the upper Cook Inlet basin, Alaska, based on analysis of Pliocene and younger deformation

    USGS Publications Warehouse

    Haeussler, P.J.; Bruhn, R.L.; Pratt, T.L.

    2000-01-01

    The Cook Inlet basin is a northeast-trending forearc basin above the Aleutian subduction zone in southern Alaska. Folds in Cook Inlet are complex, discontinuous structures with variable shape and vergence that probably developed by right-transpressional deformation on oblique-slip faults extending downward into Mesozoic basement beneath the Tertiary basin. The most recent episode of deformation may have began as early as late Miocene time, but most of the deformation occurred after deposition of much of the Pliocene Sterling Formation. Deformation continued into Quaternary time, and many structures are probably still active. One structure, the Castle Mountain fault, has Holocene fault scarps, an adjacent anticline with flower structure, and historical seismicity. If other structures in Cook Inlet are active, blind faults coring fault-propagation folds may generate Mw 6-7+ earthquakes. Dextral transpression of Cook Inlet appears to have been driven by coupling between the North American and Pacific plates along the Alaska-Aleutian subduction zone, and by lateral escape of the forearc to the southwest, due to collision and indentation of the Yakutat terrane 300 km to the east of the basin.

  5. Source Evolution After Subduction Initiation as Recorded in the Izu-Bonin-Mariana Fore-arc Crust

    NASA Astrophysics Data System (ADS)

    Shervais, J. W.; Reagan, M. K.; Pearce, J. A.; Shimizu, K.

    2015-12-01

    Drilling in the Izu-Bonin-Mariana (IBM) fore-arc during IODP Expedition 352 and DSDP Leg 60 recovered consistent stratigraphic sequences of volcanic rocks reminiscent of those found in many ophiolites. The oldest lavas in these sections are "fore-arc basalts" (FAB) with ~51.5 Ma ages. Boninites began eruption approximately 2-3 m.y. later (Ishizuka et al., 2011, EPSL; Reagan et al., 2013, EPSL) and further from the trench. First results from IODP Expedition 352 and preliminary post-cruise data suggest that FAB at Sites U1440 and U1441 were generated by decompression melting during near-trench sea-floor spreading, and that fluids from the subducting slab were not involved in their genesis. Temperatures appear to have been unusually high and pressures of melting appear to have been unusually low compared to mid-ocean ridges. Spreading rates at this time appear to have been robust enough to maintain a stable melt lens. Incompatible trace element abundances are low in FAB compared to even depleted MORB. Nd and Hf Isotopic compositions published before the expedition suggest that FAB were derived from typical MORB source mantle. Thus, their extreme deletion resulted from unusually high degrees of melting immediately after subduction initiation. The oldest boninites from DSDP Site 458 and IODP Sites U1439 and U1442 have relatively high concentrations of fluid-soluble elements, low concentrations of REE, and light depleted REE patterns. Younger boninites, have even lower REE concentrations, but have U-shaped REE patterns. Our first major and trace element compositions for the FAB through boninite sequence suggests that melting pressures and temperatures decreased through time, mantle became more depleted though time, and spreading rates waned during boninite genesis. Subduction zone fluids involved in boninite genesis appear to have been derived from progressively higher temperatures and pressures over time as the subducting slab thermally matured.

  6. Searching for unconventional seismic signals on a subduction zone with a submerged forearc: OBS offshore the Lesser Antilles

    NASA Astrophysics Data System (ADS)

    Bécel, Anne; Diaz, Jordi; Laigle, Mireille; Hirn, Alfred

    2013-09-01

    Detecting unconventional seismic signals related to subduction zone processes at depth in continuous ocean bottom seismometer (OBS) records requires the analysis and identification of noise due to instrumental problems, deployment sites or sea state conditions. The temporary OBS deployment at the Lesser Antilles subduction zone provides new insights into the feasibility of detecting unconventional signals such as non volcanic tremor (NVT), long-period (LP) or ultra-long period (ULP) events. Analysis of noise at an array comprising several sites and types of instruments and comparison with recordings on land shows transients in the noise. Episodes can be identified considering the diversity of sites and instrument types and comparing the seismic signals with meteorological and oceanographic data. In order to reliably detect NVT (1-10 Hz) originating from inside the solid Earth, one must first characterize noise induced by the activity of the atmosphere and hydrosphere at the sea-bottom as well as on land. The semidiurnal modulation of noise amplitude can be shown here not to be due to that of the NVT from a seismic source at depth which is related to the subduction interplate and whose activity is modulated by the tidal stresses as inferred for other megathrusts on emerged forearcs. Here, the semidiurnal modulation is rather due to the effect of the tides themselves, such as tidal currents, since they do not affect all types and all components of the unique multi-station array of OBS that could be deployed on this submerged forearc. The short period cut-off of the strong noise due to ocean surface infragravity waves increases to longer periods with OBS depth, thereby increasing the observational window with low noise to lower frequencies, and deep OBS sites may be advantageous for detecting LP events.

  7. Terrestrial and GPS measurements of deformation across the Taupo back arc and Hikurangi forearc regions in New Zealand

    NASA Astrophysics Data System (ADS)

    Darby, Desmond J.; Meertens, Charles M.

    1995-05-01

    Geodetic measurements of deformation across the Taupo back arc and Hikurangi forearc regions of New Zealand are derived from Global Positioning System (GPS) measurements made in 1990 and 1991 and triangulation observations made in the 1920s, 1950s, and 1970s. The GPS horizontal coordinate differences have precisions of 5-6 mm and the triangulation observations have precisions of 0.7-1.2 arc sec. These different kinds of observation allow simultaneous estimation of strain parameters and single-epoch coordinates for a total of 184 stations, at 68 of which GPS observations were made. Under the assumption that no shift of the scale or orientation of the GPS reference frame is embodied in the data from 13 GPS stations within the Taupo Volcanic Zone (TVZ) common to the 1990 and 1991 surveys, the rotational, dilatational and shear components of the deformation rate tensor within the TVZ can be estimated for that 1-year interval. The principal extension rate from 1990 to 1991 is 0.21 +/- 0.09 x 10(exp -6)/yr (68% confidence) at an azimuth of 124 +/- 13 deg, corresponding to 8 +/- 4 mm/yr extension over 40 km. Neither the orthogonal principal extension rate, 0.02 +/- 0.03 x 10(exp -6)/yr, nor the rotation rate, 0.06 +/- 0.04 microrad/yr, is significant. The dilatation rate of 0.23 +/- 0.09 x 10(exp -6)/yr is therefore produced by uniaxial extension. The data from 75 stations distributed from behind the back arc region and well into the forearc region, which were surveyed in at least two of the triangulation or GPS epochs between the 1920s and 1991, allow the spatial variation of the shear components of the deformation rate tensor to be estimated.

  8. Unroofing of fore-arc ranges along the Hikurangi Margin, New Zealand: Constraints from low-temperature thermochronology

    NASA Astrophysics Data System (ADS)

    Jiao, Ruohong; Seward, Diane; Little, Timothy A.; Kohn, Barry P.

    2015-08-01

    The Axial Ranges of North Island, New Zealand, parallel the Hikurangi subduction margin. They consist of uplifted and exhumed Mesozoic meta-sedimentary basement rocks of the overriding Australian Plate, beneath which the Pacific Plate has been subducting since at least the Late Oligocene. We investigate the unroofing histories of these fore-arc mountains during the evolution of the Hikurangi Margin, based on new and previous zircon and apatite fission-track, and apatite (U-Th-Sm)/He data which we interpret based on inverse modelling. The results suggest that the exhumation of rocks in the Axial Ranges initiated in the west and migrated trench-wards towards the east. Onsets of accelerated exhumation in different parts of the ranges indicate significant eastwards thrusting on the margin-parallel Ngamatea Fault before ~ 20-17 Ma and on the Wellington-Mohaka Fault before ~ 10-7 Ma. The exhumation rate has varied significantly along-strike since the Late Miocene, lower in the central part of the Axial Ranges and significantly higher to the south. Since the Late Miocene, the increasing exhumation rate from the central to southern Axial Ranges is consistent with the clockwise vertical-axis rotation of eastern North Island relative to the Australian Plate. In the Hikurangi Margin, although underplating of subducted material at the basal upper plate may have contributed to localised rock uplift (e.g., in the Raukumara Range), we suggest that the shortening of the fore-arc upper plate was the chief driver of unroofing of the (proto-) Axial Ranges.

  9. Highly refractory peridotites in Songshugou, Qinling orogen: Insights into partial melting and melt/fluid-rock reactions in forearc mantle

    NASA Astrophysics Data System (ADS)

    Cao, Yi; Song, Shuguang; Su, Li; Jung, Haemyeong; Niu, Yaoling

    2016-05-01

    The Songshugou ultramafic massif is located in the eastern segment of the Qinling orogenic belt, central China. It is a large spinel peridotite body dominated by coarse-grained, porphyroclastic, and fine-grained dunite with minor harzburgite, olivine clinopyroxenite, and banded/podiform chromitite. The compositions of the bulk-rock dunite and harzburgite, and the constituent olivine and spinel, together with the textures and chemical characteristics of multiphase mineral inclusions, point to the highly refractory nature of these rocks with complex histories of high-temperature boninite melt generation and boninitic melt-rock reaction, probably in a young, warm, and volatile-rich forearc lithospheric mantle setting. Additionally, a subsequent low-temperature fluid-rock reaction is also recorded by TiO2-rich spinel with Ti solubility/mobility enhanced by chloride- or fluoride-rich subduction-zone fluids as advocated by Rapp et al. (2010). The olivine clinopyroxenite, on the other hand, was likely crystallized from a residual boninitic melt that had reacted with harzburgitic residues. The ubiquitous occurrences of hydrous minerals, such as anthophyllite, tremolite, Cr-chlorite, and serpentine (stable at lower P-T crustal conditions) in the matrix, suggest that further low-temperature fluid-rock reaction (or retrograde metamorphism) has affected the original volatile-poor peridotites either in a mature and cool subduction zone, or in a continental crust during their exhumation into the Qinling collisional orogeny at early Paleozoic era, or both. The prolonged and intense ductile/brittle deformation can decrease the mineral grain size through dynamic recrystallization and fracturing, and thus aid the fluid-rock reaction or retrograde metamorphism and mineral chemical re-equilibration processes. Therefore, the Songshugou peridotites present a good example for understanding the petrogenesis and evolution of the mantle wedge, with the emphasis on the complex partial

  10. Along-Strike Electrical Conductivity Variations in the Incoming Plate and Shallow Forearc of the Cascadia Subduction Zone

    NASA Astrophysics Data System (ADS)

    Key, K.; Bedrosian, P.; Egbert, G. D.; Livelybrooks, D.; Parris, B. A.; Schultz, A.

    2015-12-01

    The Magnetotelluric Observations of Cascadia using a Huge Array (MOCHA) experiment was carried out to study the nature of the seismogenic locked zone and the down-dip transition zone where episodic tremor and slip (ETS) originates. This amphibious magnetotelluric (MT) data set consists of 8 offshore and 15 onshore profiles crossing from just seaward of the trench to the western front of the Cascades, with a north-south extent spanning from central Oregon to central Washington. The 71 offshore stations and the 75 onshore stations (red triangles in the image below) fit into the broader context of the more sparsely sampled EarthScope MT transportable array (black triangles) and other previous and pending MT surveys (other symbols). These data allows us to image variations in electrical conductivity along distinct segments of the Cascadia subduction zone defined by ETS recurrence intervals. Since bulk conductivity in this setting depends primarily on porosity, fluid content and temperature, the conductivity images created from the MOCHA data offer unique insights on fluid processes in the crust and mantle, and how the distribution of fluid along the plate interface relates to observed variations in ETS behavior. This abstract explores the across- and along-strike variations in the incoming plate and the shallow offshore forearc. In particular we examine how conductivity variations, and the inferred fluid content and porosity variations, are related to tectonic segmentation, seismicity and deformation patterns, and arc magma variations along-strike. Porosity inferred in the forearc crust can be interpreted in conjunction with active and passive seismic imaging results and may provide new insights on the origin of recently observed extremely high heat flow values. A companion abstract (Parris et al.) examines the deeper conductivity structure of the locked and ETS zones along the plate interface in order to identify correlations between ETS occurrence rates and inferred

  11. Tectonosedimentary evolution of the Crotone basin, Italy: Implications for Calabrian Arc geodynamics

    SciTech Connect

    Smale, J.L. ); Rio, D. ); Thunell, R.C. )

    1990-05-01

    Analysis of outcrop, well, and offshore seismic data has allowed the Neogene tectonosedimentary evolution of an Ionian Sea satellite basin to be outlined. The Crotone basin contains a series of postorogenic sediments deposited since Serravallian time atop a complex nappe system emplaced in the early Miocene. The basin's evolution can be considered predominantly one of distension in a fore-arc setting punctuated by compressional events. The earliest sediments (middle-late Miocene) consist of conglomerates, marls, and evaporites infilling a rapidly subsiding basin. A basin-wide Messinian unconformity and associated intraformational folding mark the close of this sedimentary cycle. Reestablishment of marine conditions in the early Pliocene is documented by sediments which show a distinct color banding and apparent rhythmicity, which may represent the basin margin to lowermost Pliocene marl/limestone rhythmic couplets present in southern Calabria. A bounding unconformity surface of middle Pliocene age (3.0 Ma), which corresponds to a major northwest-southeast compressional event, closes this depositional sequence. The basin depocenter shifted markedly toward the southeast, and both chaotic and strong subparallel reflector seismic facies of wide-ranging thicknesses fill the depositional topography created during this tectonic episode. Basin subsidence decreases dramatically in the late Pliocene and cessates in response to basin margin uplift in the early Pleistocene. The chronostratigraphic hierarchy of these depositional sequences allows them to constrain the deformational history of the basin. In addition, similar depositional hierarchies in adjacent basins (i.e., Paola, Cefalu, and Tyrrhenian Sea) allow them to tie the stratigraphy and evolution of the Crotone basin to the geodynamic evolution of the Calabrian arc system.

  12. Formation temperatures of clays from the volcaniclastic series of Site 841 ODP: an oxygen isotopic record of a paleothermal flux into the Tonga forearc

    NASA Astrophysics Data System (ADS)

    Vitali, Frédéric; Blanc, Gérard; Gauthier-Lafaye, François; France-Lanord, Christian

    Oxygen isotopic compositions of clay minerals were determined on representative samples of the volcano-sedimentary series from Site 841 ODP (Tonga forearc). This isotopic study has demonstrated an abnormally high crystallisation temperature of the clay minerals with respect to temperature expected in burial diagenesis. Formation temperatures obtained using 18O reach up to 200°C in a Fe-chlorite-corrensite paragenesis found in the vicinity of basaltic andesite sills intruded into the Miocene tuffs. The paleothermal flux resulting from the cooling of the sills has produced very low grade contact metamorphism in the Miocene Tonga forearc deposits. The consequence of this was the formation of a large amount of hydrous silicates characterised near the sills by a Fe-clays-analcime mineralogical association.

  13. Deformation within the Pisco Basin sedimentary record (southern Peru): Stratabound orthogonal vein sets and their impact on fault development

    NASA Astrophysics Data System (ADS)

    Rustichelli, Andrea; Di Celma, Claudio; Tondi, Emanuele; Bianucci, Giovanni

    2016-01-01

    This outcrop-based study reports diffuse joints and veins, normal to strike-slip fault zones and minor folds that developed, from Miocene to Quaternary, within the clastic to siliceous sedimentary record of the forearc Pisco Basin of southern Peru. Patterns, orientations, dimensional parameters and other outcrop-scale characteristics of the various deformation features are illustrated and their genetic mechanisms and timing of development are inferred. These new structural data and interpretations allow a better constraint of the structural style and evolution of the Pisco Basin, and can represent useful guidelines for characterizing the outcrop-scale deformation affecting similar forearc basins along the Peruvian coast. Major results of this study are that the development of the documented deformation features, their patterns, dimensional parameters and kinematics seem influenced by local perturbations of the paleostress field by mechanic processes partly independent of plate tectonics forces. These processes include strain localization on both pre-existing and progressively forming new structural discontinuities, and cyclic switches of the horizontal, principal stress axes σ2 and σ3. In particular, we discuss how different normal fault patterns, from sub-parallel to multidirectional/polygonal, could form in a same deformation phase in response of the local σ2/σ3 magnitude ratio, as an evolution of stratabound, mutually orthogonal vein sets.

  14. Deformation and sedimentation along a developing terrane suture: Eastern Sunda forearc, Indonesia

    SciTech Connect

    Reed, D.L.; Silver, E.A.; Prasetyo, H.; Meyer, A.W.

    1986-12-01

    The collision of the eastern Sunda arc with northwest Australia has resulted in the development of a suture between the Sumba ridge and Sawu-Timor terranes along a zone of intraforearc convergence. The developing suture varies from the low-angle Sawu thrust, with attendant mud diapirs in the Sumba basin, to high-angle reverse faults near a basement high of the underthrust Sumba ridge terrane. Bottom currents, associated with the flow of Pacific Ocean deep water into the Indian Ocean, have eroded the terranes and subsequently deposited the detritus in an assemblage of contourites along the suture. This study reveals the high structural variability of a terrane suture and the oceanographic influence on the deposition of overlap assemblages.

  15. Along-strike structure of the Costa Rican convergent margin from seismic a refraction/reflection survey: Evidence for underplating beneath the inner forearc

    NASA Astrophysics Data System (ADS)

    St. Clair, J.; Holbrook, W. S.; Van Avendonk, H. J. A.; Lizarralde, D.

    2016-02-01

    The convergent margin offshore Costa Rica shows evidence of subsidence due to subduction erosion along the outer forearc and relatively high rates of uplift (˜3-6 mm/yr) along the coast. Recently erupted arc lavas exhibit a low 10Be signal, suggesting that although nearly the entire package of incoming sediments enters the subduction zone, very little of that material is carried directly with the downgoing Cocos plate to the magma generating depths of the mantle wedge. One mechanism that would explain both the low 10Be and the coastal uplift is the underplating of sediments, tectonically eroded material, and seamounts beneath the inner forearc. We present results of a 320 km long, trench-parallel seismic reflection and refraction study of the Costa Rican forearc. The primary observations are (1) margin perpendicular faulting of the basement, (2) thickening of the Cocos plate to the northwest, and (3) two weak bands of reflections in the multichannel seismic (MCS) reflection image with travel times similar to the top of the subducting Cocos plate. The modeled depths to these reflections are consistent with an ˜40 km long, 1-3 km thick region of underplated material ˜15 km beneath some of the highest observed coastal uplift rates in Costa Rica.

  16. Extensional Basins in a Convergent Margin: Oligocene-Early Miocene Salar de Atacama and Calama basins, Central Andes

    NASA Astrophysics Data System (ADS)

    Jordan, T. E.; Mpodozis, C.; Blanco, N.; Pananont, P.; Dávila, F.

    2004-12-01

    The Salar de Atacama Basin (SdAB) is the largest and most persistent sedimentary basin of northern Chile, accumulating nonmarine sediment from Cretaceous to modern times. Its northwestern neighbor, the Calama, was a Cenozoic basin. Although SdAB was in the backarc zone early in the Andean orogeny, both are now forearc basins. Others demonstrated that the basins overlie anomalously cold, strong, and dense crust and lithosphere. We focus on an extensional Oligocene basin stage. Interpretation of the basin-controlling faults is based on seismic reflection studies supported by field relations. The SdAB is limited to the west by the NNE-trending, steeply east-dipping, Paciencia Fault (PF). The PF experienced 5-7 km of down-to-the-east offset during the Oligocene-early Miocene. Syntectonic strata, an arid succession of siliciclastics and evaporites, are asymmetric, with thicknesses of 5000 m and abundant halite adjacent to the PF, and of 1000 m with fine detrital clastic strata 25 km farther east. Relations in conglomeratic growth strata that overlap the PF also demonstrate normal displacement during sediment accumulation. Seismic data reveal that a buried normal fault with 1-1.5 km down-to-the-east displacement limits the western margin of the Oligocene-Miocene Calama siliciclastic basin fill. Regionally, Oligocene-early Miocene margin-parallel strike-slip deformation dominated northwest of the basins, contributing sinistral offset (West Fissure Fault) to the northern segment of the long-lived Domeyko Fault System. The new SdAB and Calama data reveal that a 20,000 km2 domain of extensional basins existed within the dominantly strike-slip region. Even if PF and the fault in the Calama Basin were transtensional, the proportion of extension to strike-slip displacement is much greater in these basins than elsewhere in northern Chile. Further study is required to understand what combination of factors caused this kinematic distinction as well as delayed the onset of CVZ

  17. Uncovering the factors that can support and impede post-disaster EIA practice in developing countries: The case of Aceh Province, Indonesia

    SciTech Connect

    Gore, Tom; Fischer, Thomas B.

    2014-01-15

    The close relationship between environmental degradation and the occurrence and severity of disaster events has in recent years raised the profile of environmental assessment (EA) in the disaster management field. EA has been identified as a potentially supportive tool in the global effort to reduce disaster risk. As a component of this, attention has been brought specifically to the importance of the application of EA in the aftermath of disaster events in order to help prevent recurrence and promote sustainability. At the same time, however, it has also been recognised that post-disaster environments may be unfavourable to such practices. Looking at the practice of environmental impact assessment (EIA), this paper reports on a study which sought to identify more specifically the factors which can both support and hinder such practice following disaster events in a developing country context. Analysing the situation in Aceh Province, Indonesia, after the impact of two tsunamigenic earthquakes in late 2004 and early 2005, it is concluded that if EIA is to have a central role in the post-disaster period, pre-disaster preparation could be a key. -- Highlights: • Close relationship between environmental degradation and occurrence/severity of disaster events has raised profile of EA. • EA as a potentially supportive tool in the global effort to reduce disaster risk • Application of EA in the aftermath of disaster events to help prevent recurrence and promote sustainability • The paper looks at factors which can both support and hinder EA following disaster events in a developing country context. • We analyse the situation in Aceh Province, Indonesia, after the impact of two tsunamigenic earthquakes in 2004 and 2005.

  18. Tectono-stratigraphic evolution and exhumation of the Haymana basin: Unravelling the subduction and collision history of Neotethys in Turkey

    NASA Astrophysics Data System (ADS)

    Gülyüz, Erhan; Özkaptan, Murat; Lefebvre, Côme; Kaymakci, Nuretdin; Persano, Cristina; Stuart, Finlay M.

    2014-05-01

    The Haymana basin straddles the Izmir-Ankara-Erzincan Suture Zone (IAESZ) in the north and Intra-Tauride Suture Zone (ITSZ) in the south. The two suture zones developed in response to the subduction and demise of Neotethys Ocean in Turkey during the late Cretaceous to early Tertiary; the tectonic significance of the basin and its relationship with the ITSZ are still poorly constrained. In order to unravel subduction and subsequent collision history of the Neotethys in the region, we have carried out a detailed analysis of the stratigraphy and sedimentology of the Haymana basin infill and, using a combination of palaeomagnetic and thermochronometric data we have unravelled its structural evolution since its formation. The basin developed on the IAESZ and comprises fore-arc late Cretaceous to foreland Middle Eocene sedimentary sequences. The analysis of the sedimentogical facies and depositional environments indicate four Late Cretaceous to Paleogene key sequences in the basin. These sequences grade laterally and vertically into each other and are continuous from the late Cretaceous to Eocene whereas local progressive syn-sedimentary unconformities and frequent depocenter migrations are common. Late Cretaceous sequences fine upward whereas coarsening upwards sequences are common in the later units. These characteristics possibly reflect the response to local uplift and subsidence in front of south-verging thrust faults associated with the transition from fore-arc to foreland basin settings, following the terminal subduction of the Neotethys at the end of Cretaceous. About 4000 paleomagnetic and magnetostratigraphic data from the basin infill units and the Neogene cover indicate large clockwise vertical axes rotations in the NW and counter-clockwise rotations in the SE part of the basin. We suggest that these rotations are related to the northward movement and indentation of the Gondwana-derived continental blocks into Eurasia. A model of southward thrust propagation

  19. Polyphase serpentinization history of Mariana forearc mantle: observations on the microfabric of ultramafic clasts from ODP Leg 195, Site 1200

    NASA Astrophysics Data System (ADS)

    Kahl, Wolf-Achim; Jöns, Niels; Bach, Wolfgang; Klein, Frieder

    2013-04-01

    In the forearc of the Mariana subduction zone system, a number of seamounts form from extrusion of blueschist and serpentine mud. Ocean Drilling Program Leg 195 drilled the South Chamorro seamount, where ultramafic clasts occur within the mud matrix. These clasts show a complex serpentinization history, which bears the potential for tracking the alteration history during uplift and cooling of mantle wedge rocks to the seafloor. Moreover, the microfabrics of the highly serpentinized harzburgite and dunite clasts exhibit evidence for multiple fracturing events in the forearc mantle. These, in turn, lead to fluid influx and varied styles of serpentinization of harzburgite and dunite. The serpentinized ultramafic clasts exhibit a variety of microfabrics that range from virtually undeformed to strongly deformed samples. Pervasively serpentinized harzburgites feature either an equigranular fabric of serpentinized olivine and orthopyroxene crystals, or different vein generations related to multiple stages of serpentinization. Several types of fluid pathways in harzburgites are present: (i) veins containing brucite and iron oxides, developed linearly without marked conformance with the rock fabric. In places, these veins developed mm-cm wide halos with finger-shaped serpentinization fronts. Veins of type (i) are either developed as syntaxial veins from a single crack-seal event with large magnetite crystals growing from one wall to the other (as confirmed with high-resolution X-ray microtomography), or formed by multiple fluid events. (ii) serpentine veins that encompass regions of marginally serpentinized, microgranular olivine and large orthopyroxene crystals. (iii) extensional serpentine veins (known as "Frankenstein" type). In the clasts studied, their occurrence is restricted to the halo region of type (i) veins. (iv) as a late-stage feature, extensional veins documenting multiple crack-seal events can be present in the serpentinites (either in undeformed regions with

  20. Origin of Siletzia, a Large Igneous Province in the Cascadia Forearc, and the Early History of the Yellowstone Hotspot

    NASA Astrophysics Data System (ADS)

    Wells, R. E.; Bukry, D.; Friedman, R. M.; Pyle, D. G.; Duncan, R. A.; Haeussler, P. J.

    2015-12-01

    Siletzia is a Paleogene large igneous province (LIP) forming the oceanic basement of coastal OR, WA and S. BC that was accreted to North America (NAM) in the early Eocene. Crustal thickness from seismic refraction ranges from 10 to 32 km, with 16 km of pillow and subaerial basalt exposed on the Olympic Peninsula. At 1.7-2.4 x 106 km3, Siletzia is at least 10 times the volume of the Columbia River flood basalts. U-Pb and 40Ar/39Ar ages, global coccolith (CP) zones, and magnetostratigraphy allow correlation of Siletzia with the 2012 geomagnetic polarity time scale. Siletzia was erupted 56-49 Ma (Chron 25-22), and accretion was completed between 51 and 49 Ma in Oregon. Siletzia's composition, great crustal thickness, rapid eruption, and timing of accretion are consistent with formation as an oceanic plateau. Eight m.y. after accretion, margin-parallel extension and regional dike swarms accompanied the voluminous tholeiitic to highly alkalic Tillamook magmatic episode in the forearc (41.6 Ma; CP14a; Chron 19r). We examined the origin of Siletzia and the possible role of a long-lived Yellowstone hotspot (YHS) in GPlates. In most reference frames, the YHS is ~ 500km offshore S. OR, near an inferred northeast-striking Kula- Farallon and/or Resurrection-Farallon ridge 60 to 50 Ma. The YHS could have provided the 56-49 Ma source on the Farallon plate for Siletzia, which in the model accretes to NAM by 50 Ma. A sister plateau, the Eocene basalt basement of the Yakutat terrane, now in Alaska, may have formed on the adjacent Kula (or Resurrection) plate and accreted to British Columbia at about the same time. Following accretion, the leading edge of NAM overrode the YHS ca. 42 Ma. The encounter with an active YHS may explain the voluminous 42-34 Ma Tillamook episode and forearc extension. Clockwise rotation of western Oregon about a pole in the backarc has since moved the Tillamook center and underlying Siletzia northward ~250 km from the likely hotspot track on NAM.

  1. Origin of Siletzia, an Accreted Large Igneous Province in the Cascadia Forearc, and the Early History of the Yellowstone Hotspot

    NASA Astrophysics Data System (ADS)

    Wells, R. E.; Bukry, D.; Friedman, R. M.; Pyle, D. G.; Duncan, R. A.; Haeussler, P. J.; Wooden, J.

    2014-12-01

    Siletzia as named by Irving (1979) is a Paleogene large igneous province forming the oceanic basalt basement of coastal OR, WA and S. BC that was accreted to North America in the early Eocene. U-Pb (magmatic, detrital zircon) and 40Ar/39Ar ages constrained by mapping, global coccolith (CP) zones, and magnetic polarities permit correlation of basalts with the geomagnetic polarity time scale of Gradstein et al. (2012). Siletzia was rapidly erupted 56-49 Ma (Chron 25-22), and accretion was completed between 51 and 49 Ma in Oregon. Magmatism continued until ca. 46 Ma with emplacement of a basalt sill complex during or shortly after accretion. Siletzia's great crustal thickness, rapid eruption, and timing of accretion are consistent with formation as an oceanic plateau. Eight m.y. after accretion, margin-parallel extension and regional dike swarms mark the Tillamook magmatic episode in the forearc (41.6 Ma; CP zone 14a; Chron 19r). We examined the origin of Siletzia and the possible role of a long-lived Yellowstone hotspot (YHS) in an open source plate modeling program. In most reference frames, the YHS is on or near an inferred northeast-striking Kula- Farallon and/or Resurrection-Farallon ridge 60 to 50 Ma. The YHS thus could have provided a 56-49 Ma source on the Farallon plate for Siletzia, which accreted to North America by 50 Ma. A sister plateau, the Eocene basalt basement of the Yakutat terrane, now in Alaska, formed on the adjacent Kula (or Resurrection) plate and accreted to coastal British Columbia at about the same time. Following accretion of Siletzia, the leading edge of North America overrode the YHS ca. 42 Ma. The encounter with an active YHS may explain the voluminous high-Ti tholeiitic to alkalic magmatism of the 42-34 Ma Tillamook episode and extension in the forearc. Clockwise rotation of western Oregon about a pole in the backarc has since moved the Tillamook center and underlying Siletzia northward ~250 km from the probable hotspot track on North

  2. Parana basin

    SciTech Connect

    Zalan, P.V.; Wolff, S.; Conceicao, J.C.J.; Vieira, I.S.; Astolfi, M.A.; Appi, V.T.; Zanotto, O.; Neto, E.V.S.; Cerqueira, J.R.

    1987-05-01

    The Parana basin is a large intracratonic basin in South America, developed entirely on continental crust and filled with sedimentary and volcanic rocks ranging in age from Silurian to Cretaceous. It occupies the southern portion of Brazil (1,100,000 km/sup 2/ or 425,000 mi/sup 2/) and the eastern half of Paraguay (100,000 km/sup 2/ or 39,000 mi/sup 2/); its extension into Argentina and Uruguay is known as the Chaco-Parana basin. Five major depositional sequences (Silurian, Devonian, Permo-Carboniferous, Triassic, Juro-Cretaceous) constitute the stratigraphic framework of the basin. The first four are predominantly siliciclastic in nature, and the fifth contains the most voluminous basaltic lava flows of the planet. Maximum thicknesses are in the order of 6000 m (19,646 ft). The sequences are separated by basin wide unconformities related in the Paleozoic to Andean orogenic events and in the Mesozoic to the continental breakup and sea floor spreading between South America and Africa. The structural framework of the Parana basin consists of a remarkable pattern of criss-crossing linear features (faults, fault zones, arches) clustered into three major groups (N45/sup 0/-65/sup 0/W, N50/sup 0/-70/sup 0/E, E-W). The northwest- and northeast-trending faults are long-lived tectonic elements inherited from the Precambrian basement whose recurrent activity throughout the Phanerozoic strongly influenced sedimentation, facies distribution, and development of structures in the basin. Thermomechanical analyses indicate three main phases of subsidence (Silurian-Devonian, late Carboniferous-Permian, Late Jurassic-Early Cretaceous) and low geothermal gradients until the beginning of the Late Jurassic Permian oil-prone source rocks attained maturation due to extra heat originated from Juro-Cretaceous igneous intrusions. The third phase of subsidence also coincided with strong tectonic reactivation and creation of a third structural trend (east-west).

  3. Seismology in Ryukyu arc, Japan reveals the distribution and orientation of serpentine minerals suggesting convection and low viscosity of forearc mantle

    NASA Astrophysics Data System (ADS)

    Nagaya, T.; Walker, A.; Wookey, J. M.; Kendall, M.; Wallis, S.

    2014-12-01

    Refining available estimates of the amount, distribution and alignment of serpentinite in the forearc wedge is needed to develop a better understanding of the seismic anisotropy, strength and fluid transport in this region. Mantle dominantly consists of olivine. However, petrological studies and thermal modeling of convergent margins predict that olivine will be replaced by hydrous mineral phases in fluid-rich and relatively cold forearc mantle. The dominant hydrous mineral will be antigorite. Lower seismic velocities (Vp < ~8 km/s and Vs < ~4 km/s) and higher Vp/Vs values (> ~1.8) of serpentine minerals than those of olivine are commonly used as to detect the distribution of antigorite and estimate its proportion compared to olivine. However, antigorite is highly anisotropic and this anisotropy can disguise the presence of antigorite in seismic tomography; the apparent Vp/Vs ratio of antigorite can vary from 1.2-3.4 (Vp = 5.6-8.9 km/s and Vs = 2.5-5.1 km/s) depending on the propagation path of the seismic wave relative to the crystal orientation. Here, we take advantage of this anisotropy and perform an analysis of seismic anisotropy that takes into account ray path measured above the forearc mantle of the Rykuyu arc subduction zone. The measured shear wave splitting delay time above this subduction zone is very large, suggesting the presence of aligned antigorite. Comparing the results of modeling to observed shear wave splitting for both local-S and teleseismic SKS phases, we conclude that the mantle wedge consists of 65 % antigorite and that the antigorite must be aligned along the subducting slab in the deepest part of the wedge but aligned vertically at intermediate depths. This distribution of different orientations strongly suggests the presence of convective mantle flow in the forearc mantle. Physical modeling of the dynamics of the mantle wedge shows that a bulk long-term viscosity of less than 1019 Pa s is required to maintain this large-scale flow. This

  4. Evidence for shallow dehydration of the subducting plate beneath the Mariana forearc: New insights into the water cycle at subduction zones

    NASA Astrophysics Data System (ADS)

    Ribeiro, J.; Stern, R. J.; Kelley, K. A.; Shaw, A. M.; Martinez, F.; Ohara, Y.

    2014-12-01

    Water is efficiently recycled at subduction zones. It is fluxed from the surface into the mantle by the subducted plate and back to the surface or crust through explosive arc volcanism and degassing. Fluids released from dehydrating the subducting plate are transfer agents of water. Geophysical modeling [1] and the geochemistry of arc glasses [2] suggest that at cold-slab subduction zones, such as the Mariana convergent margin, the downgoing plate mostly dehydrates beneath the volcanic arc front (≥ ~ 80 -100 km depth to slab) to trigger volcanism. However, there is a gap in our understanding of the water fluxes released beneath forearcs, as examples of forearc magmatism are extremely rare. Here, we investigate the Southernmost Mariana Forearc Rift (SEMFR), where MORB-like spreading occurred unusually close to the trench, sampling slab-derived aqueous fluids released at ~ 30 to 100 km depth from the subducted plate. Examining the trace element and water contents of olivine-hosted melt inclusions and glassy rinds from the young (2 - 4 Ma) and fresh SEMFR pillowed basalts provide new insights into the global water cycle. SEMFR lavas contain ~2 wt % H2O, and the olivine-hosted melt inclusions have the highest subduction-related H2O/Ce ratios (H2O/Ce = 6000 - 19000) ever recorded in arc magmas (H2O/Ce < 10600 and global averaged H2O/Ce < 3000). Our findings show that (i) slab-derived fluids released beneath forearcs are water-rich compared to the deeper fluids released beneath the arc system; and (ii) cold downgoing plates lose most of their water at shallow depths (~ 70 - 80 km slab depth), suggesting that water is efficiently recycled beneath the forearc (≥ 90%). 1. Van Keken, P.E., et al., Subduction factory: 4. Depth-dependent flux of H2O from subducting slabs worldwide. Journal of Geophysical Research: Solid Earth, 2011. 116(B1): p. B01401, DOI: 10.1029/2010jb007922. 2. Ruscitto, D.M., et al., Global variations in H2O/Ce: 2. Relationships to arc magma

  5. Tectonic and stratigraphic evolution of the Western Alboran Sea Basin in the last 25 Myrs

    NASA Astrophysics Data System (ADS)

    Do Couto, Damien; Gorini, Christian; Jolivet, Laurent; Lebret, Noëmie; Augier, Romain; Gumiaux, Charles; d'Acremont, Elia; Ammar, Abdellah; Jabour, Haddou; Auxietre, Jean-Luc

    2016-05-01

    The Western Alboran Basin (WAB) formation has always been the subject of debate and considered either as a back-arc or a forearc basin. Stratigraphic analyses of high-resolution 2D seismic profiles mostly located offshore Morocco, enabled us to clarify the tectonic and stratigraphic history of the WAB. The thick pre-rift sequence located beneath the Miocene basin is interpreted as the topmost Malaguide/Ghomaride complex composing the Alboran domain. The structural position of this unit compared with the HP-LT exhumed Alpujarride/Sebtide metamorphic basement, leads us to link the Early Miocene subsidence of the basin with an extensional detachment. Above the Early Miocene, a thick Serravallian sequence marked by siliciclastic deposits is nearly devoid of extensional structures. Its overall landward to basinward onlap geometry indicates that the WAB has behaved as a sag basin during most of its evolution from the Serravallian to the late Tortonian. Tectonic reconstructions in map view and in cross section further suggest that the basin has always represented a strongly subsiding topographic low without internal deformation that migrated westward together with the retreating slab. We propose that the subsidence of the WAB was controlled by the pull of the dipping subducting lithosphere hence explaining the considerable thickness (10 km) of the mostly undeformed sedimentary infill.

  6. Tectonic and stratigraphic evolution of the Western Alboran Sea basin since the last 25 Myrs

    NASA Astrophysics Data System (ADS)

    Do Couto, Damien; Gorini, Christian; Jolivet, Laurent; Lebret, Noëmie; Augier, Romain; Gumiaux, Charles; D'Acremont, Elia; Ammar, Abdellah; Auxietre, Jean-Luc

    2016-04-01

    The Western Alboran Basin (WAB) formation has always been a matter of debate and was either considered as a backarc or a forearc basin. Based on stratigraphic analysis of high-resolution 2D seismic profiles mostly located offshore Morocco, the tectonic and stratigraphic history of the WAB is clarified. A thick pre-rift sequence is observed beneath the Miocene basin and interpreted as the topmost Malaguide/Ghomaride complex composing the Alboran domain. The structural position of this unit compared with the HP-LT exhumed Alpujarride/Sebtide metamorphic basement, leads us to link the Early Miocene subsidence of the basin with an extensional detachment. Above the Early Miocene, a thick Serravallian sequence marked by siliciclastic deposits is nearly devoid of extensional structures. Its overall landward to basinward onlap geometry indicates that the WAB has behaved as a sag basin during most of its evolution, from the Serravallian to the Late Tortonian. Tectonic reconstructions in map view and cross-section further suggest that the basin has always represented a strongly subsiding topographic low without internal deformation that has migrated westward together with the retreating slab. We propose that the subsidence of the WAB was controlled by the pull of the dipping subducting lithosphere explaining the large thickness (10 km) of the mostly undeformed sedimentary infill.

  7. T-waves excited by S-waves and oscillated within the ocean above the Southeastern Taiwan Forearc

    NASA Astrophysics Data System (ADS)

    Lin, Cheng-Horng

    The generation processes of T-waves were investigated from seismograms produced by a local intermediate-depth earthquake and recorded at one short-period station in Taiwan. The first group of T-phases arrived 44 seconds after the S-phases, while the following 2 groups consistently had the same travel-time difference of about 88 seconds each. Analyses of the ray paths and travel-times of these phases show that the T-waves were converted from the S-waves and oscillated within the ocean above the forearc in the southeastern Taiwan area. Further comparisons of these results with those of previous studies suggest that the generation of T-waves is probably dependent on the incidence angles of the seismic waves. The T-waves were converted from S-waves when the incidence angles of the seismic waves were near vertical, whereas they were generated from P-waves when those angles were near horizontal.

  8. Three-dimensional velocity structure of Siletzia and other accreted terranes in the Cascadia forearc of Washington

    USGS Publications Warehouse

    Parsons, T.; Wells, R.E.; Fisher, M.A.; Flueh, E.; ten Brink, U.S.

    1999-01-01

    Eocene mafic crust with high seismic velocities underlies much of the Oregon and Washington forearc and acts as a backstop for accretion of marine sedimentary rocks from the obliquely subducting Juan de Fuca slab. Arc-parallel migration of relatively strong blocks of this terrane, known as Siletzia, focuses upper crustal deformation along block boundaries, which are potential sources of earthquakes. In a three-dimensional velocity model of coastal Washington, we have combined surface geology, well data, and travel times from earthquakes and controlled source seismic experiments to resolve the major boundaries of the Siletz terrane with the adjacent accreted sedimentary prism and volcanic arc. In southern Washington and northern Oregon the Siletz terrane appears to be a thick block (???20 km) that extends west of the coastline and makes a high-angle contact with the offshore accreted sedimentary prism. On its east flank the high-velocity Siletz terrane boundary coincides with an en echelon zone of seismicity in the arc. In northern Washington the western edge of Siletzia makes a lower-angled, fault-bound contact with the accretionary prism. In addition, alternating, east-west trending uplifts and downwarps of the Siletz terrane centered on the antiformal Olympic Mountains may reflect focusing of north-south compression in the northern part of the Siletz terrane. This compressional strain may result from northward transport and clockwise rotation of the Siletz terrane into the relatively fixed Canadian Coast Mountains restraining bend along the coast.

  9. Relationship between the Cascadia fore-arc mantle wedge, nonvolcanic tremor, and the downdip limit of seismogenic rupture

    NASA Astrophysics Data System (ADS)

    McCrory, Patricia A.; Hyndman, Roy D.; Blair, J. Luke

    2014-04-01

    earthquakes anticipated on the Cascadia subduction fault can potentially rupture beyond the geodetically and thermally inferred locked zone to the depths of episodic tremor and slip (ETS) or to the even deeper fore-arc mantle corner (FMC). To evaluate these extreme rupture limits, we map the FMC from southern Vancouver Island to central Oregon by combining published seismic velocity structures with a model of the Juan de Fuca plate. These data indicate that the FMC is somewhat shallower beneath Vancouver Island (36-38 km) and Oregon (35-40 km) and deeper beneath Washington (41-43 km). The updip edge of tremor follows the same general pattern, overlying a slightly shallower Juan de Fuca plate beneath Vancouver Island and Oregon (˜30 km) and a deeper plate beneath Washington (˜35 km). Similar to the Nankai subduction zone, the best constrained FMC depths correlate with the center of the tremor band suggesting that ETS is controlled by conditions near the FMC rather than directly by temperature or pressure. Unlike Nankai, a gap as wide as 70 km exists between the downdip limit of the inferred locked zone and the FMC. This gap also encompasses a ˜50 km wide gap between the inferred locked zones and the updip limit of tremor. The separation of these features offers a natural laboratory for determining the key controls on downdip rupture limits.

  10. Mapping the Tohoku forearc: Implications for the mechanism of the 2011 East Japan earthquake (Mw 9.0)

    NASA Astrophysics Data System (ADS)

    Wang, Zhi; Huang, Wenli; Zhao, Dapeng; Pei, Shunping

    2012-02-01

    To investigate the generation mechanism of the 2011 great East Japan (GEJ) earthquake (M 9.0), we determined a three-dimensional (3-D) seismic model under the NE Japan forearc region using a large number of P and S wave arrival times from local earthquakes. Our results show that the GEJ main-shock occurred in a high-velocity (Vp, Vs) zone with higher Poisson's ratio (σ). The aftershocks relocated with a master-event location (MEL) procedure indicate that most of them are located at the corner of the mantle wedge along the upper boundary of the subducting Pacific slab, and their focal depths are slightly shallower than the background seismicity. The tomographic images and spatial distribution of the aftershocks imply strong interplate coupling (asperity) in the main-shock area and weak coupling in the surrounding areas of the megathrust zone. We think that fluids in the crust and uppermost mantle in the subduction zone could have affected the earthquake generation through the physical role of fluid pressure and a variety of chemical effects. We conclude that the 2011 GEJ earthquake initiation and the rupture processes of the aftershock sequence were influenced by fluid extrusion into the rupture zone due to the dehydration of the subducting Pacific slab. Fluid-bearing structural heterogeneities with thermal-petrologic variations in the megathrust zone played a key role in the initiation of the 2011 GEJ earthquake and its aftershocks.

  11. Characterization of gas fields by petroleum system, Sacramento Basin, California

    SciTech Connect

    Magoon, L.B.; Valin, Z.C.; Reid, R.A.

    1996-12-31

    The Sacramento Basin, a north-trending forearc basin, contains Late Jurassic to Holocene sedimentary rocks that thicken to the south. The basin fill is about 300 km long, 80 km wide, and as much as 16 km thick. Because the 157 gas fields with original reserves of 9.14 tcf (1012 ft3) cover a large area, a change in chemical composition due to migration from wet gas to pure methane is recorded. On the basis of the carbon-isotopic composition of methane and stratigraphic occurrence, two petroleum systems have been identified in the Sacramento Basin. The Dobbins-Forbes(?) gas system, which contained about 2.25 tcf of recoverable gas, underlies the Winters-Domengine(?) gas system, which contained about 6.89 tcf of recoverable gas. Gas migrated laterally to the north as far as 200 km in the Dobbins-Forbes(?) system, whereas in the Winters-Domengine(?) system, gas first migrated vertically and then crossed the Midland Fault to the east for as far as 40 km. In both systems, depth of gas production is less than 3 km. By applying the petroleum-system concept and available information about the geology and geochemistry of this province, our study provides a new testable hypothesis for the origin, migration, and accumulation of gas in the Sacramento Basin. By reinterpreting some of the natural-gas information, along with data on gas wetness, gas-oil ratio, vectors of migration, hydrocarbon volume, and thermal history, two gas systems have been identified.

  12. Characterization of gas fields by petroleum system, Sacramento Basin, California

    SciTech Connect

    Magoon, L.B.; Valin, Z.C. ); Reid, R.A. )

    1996-01-01

    The Sacramento Basin, a north-trending forearc basin, contains Late Jurassic to Holocene sedimentary rocks that thicken to the south. The basin fill is about 300 km long, 80 km wide, and as much as 16 km thick. Because the 157 gas fields with original reserves of 9.14 tcf (1012 ft3) cover a large area, a change in chemical composition due to migration from wet gas to pure methane is recorded. On the basis of the carbon-isotopic composition of methane and stratigraphic occurrence, two petroleum systems have been identified in the Sacramento Basin. The Dobbins-Forbes( ) gas system, which contained about 2.25 tcf of recoverable gas, underlies the Winters-Domengine( ) gas system, which contained about 6.89 tcf of recoverable gas. Gas migrated laterally to the north as far as 200 km in the Dobbins-Forbes( ) system, whereas in the Winters-Domengine( ) system, gas first migrated vertically and then crossed the Midland Fault to the east for as far as 40 km. In both systems, depth of gas production is less than 3 km. By applying the petroleum-system concept and available information about the geology and geochemistry of this province, our study provides a new testable hypothesis for the origin, migration, and accumulation of gas in the Sacramento Basin. By reinterpreting some of the natural-gas information, along with data on gas wetness, gas-oil ratio, vectors of migration, hydrocarbon volume, and thermal history, two gas systems have been identified.

  13. Late Cretaceous - Paleogene forearc sedimentation and accretion of oceanic plateaus and seamounts along the Middle American convergent margin (Costa Rica)

    NASA Astrophysics Data System (ADS)

    Baumgartner, Peter O.; Baumgartner-Mora, Claudia; Andjic, Goran

    2016-04-01

    The Late Cretaceous-Paleogene sedimentation pattern in space and time along the Middle American convergent margin was controlled by the accretion of Pacific plateaus and seamounts. The accretion of more voluminous plateaus must have caused the temporary extinction of the arc and tectonic uplift, resulting in short lived episodes of both pelagic and neritic biogenic sedimentation. By the Late Eocene, shallow carbonate environments became widespread on a supposed mature arc edifice, that is so far only documented in arc-derived sediments. In northern Costa Rica forearc sedimentation started during the Coniacian-Santonian on the Aptian-Turonian basement of the Manzanillo Terrane. The arrival and collision of the Nicoya Terrane (a CLIP-like, 139-83 Ma Pacific plateau) and the Santa Elena Terrane caused the extinction of the arc during late Campanian- Early Maastrichtian times, indicated by the change to pelagic limestone sedimentation (Piedras Blancas Formation) in deeper areas and shallow-water rudistid - Larger Benthic Foraminfera limestone on tectonically uplifted areas of all terranes. Arc-derived turbidite sedimentation resumed in the Late Maastrichtian and was again interrupted during the Late Paleocene - Early Eocene, perhaps due to the underplating of a yet unknown large seamount. The extinction of the arc resulted in the deposition of the siliceous pelagic Buenavista Formation, as well as the principally Thanetian Barra Honda carbonate platform on a deeply eroded structural high in the Tempisque area. In southern Costa Rica the basement is thought to be the western edge of the CLIP. It is Santonian-Campanian in age and is only exposed in the southwestern corner of Herradura. Cretaceous arc-forearc sequences are unknown, except for the Maastrichtian-Paleocene Golfito Terrane in southeastern Costa Rica. The distribution and age of shallow/pelagic carbonates vs. arc-derived detrital sediments is controlled by the history of accretion of Galápagos hot spot

  14. Structure and geologic history of late Cenozoic Eel River basin, California

    SciTech Connect

    Clarke, S.H. Jr.

    1988-03-01

    The Eel River basin formed as a late Cenozoic forearc basin floored by late Mesozoic and early Cenozoic allochthonous terranes (central and coastal belts of the Franciscan complex). Regionally, basement rocks are unconformably overlain on land by a sedimentary sequence as much as about 4200 m thick that comprises the Bear River Formation (early and middle Miocene) and the Wildcat Group (late Miocene to middle Pleistocene) and offshore by broadly coeval upper Tertiary and Quaternary deposits as much as 3300 m thick. Offshore, the southern part of the basin is typified by the seaward extensions of youthful northeast-dipping thrust and reverse faults and northwest-trending anticlines. The latest period of deformation in this part of the basin began during the middle Pleistocene and probably reflects north-northwestward migration of the Mendocino triple junction and encroachment of the Pacific plate. Farther north, the western basin margin and adjacent upper continental slope are separated from the axial part of the offshore basin by a narrow zone of north-northwest-trending, right-stepping en echelon folds. These folds indicate that northeast-southwest compression characteristic of the southern part of the basin is accompanied toward the north by right-lateral shear between the accretionary complex to the west and the basin to the east. The northeastern margin of the offshore basin is cut by north to north-northwest-trending high-angle reverse faults that vertically offset basement rocks as much as 1300 m, west side down. These faults, which may merge northward, coincide with older terrane boundaries and locally show evidence of late Cenozoic reactivation with possible right-lateral slip.

  15. Strain Accommodation Along an Oblique Subduction Zone: Integrating Paleomagnetic Data and Stress Patterns in the Central Aleutian Forearc

    NASA Astrophysics Data System (ADS)

    Krutikov, L.; Reynolds, J. R.; Stone, D. B.

    2005-12-01

    Present day motion of the Pacific plate relative to the North American plate shifts along the Aleutian arc from normal convergence in the east to transform motion in the west. Oblique subduction, partitioned into an arc-normal component and an arc-parallel component, creates a spatially complex pattern of deformation in the overriding plate. Strain partitioning results in tectonic segmentation of the forearc region, caused by increasing obliquity of plate convergence and apparently characterized by clockwise rotation and westward translation of discrete blocks in the central and western Aleutian arc [e.g., Geist et al., Tectonics 7, 327-341, 1988]. Archived cores collected from islands in the central Aleutian arc for previous paleomagnetic studies are being remeasured and reanalyzed using modern thermal demagnetization techniques that were not available at the time of collection. These new measurements indicate counterclockwise rotation or less significant clockwise rotations than those predicted by the block rotation model. Paleomagnetic results are presented for Tertiary and Quaternary volcanic rocks from Adak and Amchitka Islands in the central Aleutians. Results range from no statistically significant rotation in young intrusives, to a number of paleomagnetic vectors in the Finger Bay volcanics (~55 Ma) that suggest clockwise rotation since the time of original magnetization. Paleomagnetic results are combined with analyses of seafloor lineations in high-resolution multibeam sonar data collected in 2003 and 2004 of representative sites between 173W and 179E along the central Aleutian arc. Major fault lineations and joint patterns observed in the bathymetry data are analyzed to estimate the direction of maximum horizontal stress. Lineations in rocks of different stratigraphic ages and paleomagnetic results are being compared with 0-5Ma regional stress patterns [Scholl et al., 1989] to constrain the style and timing of deformation.

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

  17. Teleseismic constraints on the geological environment of deep episodic slow earthquakes in subduction zone forearcs: A review

    NASA Astrophysics Data System (ADS)

    Audet, Pascal; Kim, YoungHee

    2016-02-01

    More than a decade after the discovery of deep episodic slow slip and tremor, or slow earthquakes, at subduction zones, much research has been carried out to investigate the structural and seismic properties of the environment in which they occur. Slow earthquakes generally occur on the megathrust fault some distance downdip of the great earthquake seismogenic zone in the vicinity of the mantle wedge corner, where three major structural elements are in contact: the subducting oceanic crust, the overriding forearc crust and the continental mantle. In this region, thermo-petrological models predict significant fluid production from the dehydrating oceanic crust and mantle due to prograde metamorphic reactions, and their consumption by hydrating the mantle wedge. These fluids are expected to affect the dynamic stability of the megathrust fault and enable slow slip by increasing pore-fluid pressure and/or reducing friction in fault gouges. Resolving the fine-scale structure of the deep megathrust fault and the in situ distribution of fluids where slow earthquakes occur is challenging, and most advances have been made using teleseismic scattering techniques (e.g., receiver functions). In this paper we review the teleseismic structure of six well-studied subduction zones (three hot, i.e., Cascadia, southwest Japan, central Mexico, and three cool, i.e., Costa Rica, Alaska, and Hikurangi) that exhibit slow earthquake processes and discuss the evidence of structural and geological controls on the slow earthquake behavior. We conclude that changes in the mechanical properties of geological materials downdip of the seismogenic zone play a dominant role in controlling slow earthquake behavior, and that near-lithostatic pore-fluid pressures near the megathrust fault may be a necessary but insufficient condition for their occurrence.

  18. Basins and thrust belts in western Turkey: Tectonic history and hydrocarbons potential

    SciTech Connect

    Bird, P.R.; Johns, C.C.; Clark-Lowes, D.D. )

    1990-05-01

    Western Turkey consists of a number of tectonic terranes joined together by a network of suture zones. The terranes originated as microcontinental plates that rifted away from the continental margins forming the northern and southern boundaries of the Tethyan sea. These micro-continents were united by a series of collisions beginning in the Late Triassic and ending in the Miocene, with the final closure of the Tethyan sea. The sedimentary cover of the microcontinents consists of Paleozoic and Mesozoic passive margin and rift basin sequences containing numerous potential source and reservoir intervals. Most of these sequences show affinities with Gondwanaland, with the notable exception of the Istanbul nappe, which is strongly Laurasian in character. Forearc basin sequences were also deposited on the margins of the microcontinents during early Tertiary plate convergence. Ensuing continental collisions resulted in compressional deformation of sedimentary cover sequences. The intensity of deformation ranged from basin inversion producing numerous potential hydrocarbon traps, to large-scale overthrusting. Following continental suturing, continued compression in eastern Turkey has been accommodated since the Miocene by westward escape of continental lithosphere between the North and South Anatolian transform faults. Neotectonic pull-apart basins formed in response to these movements, accumulating large thicknesses of Miocene-Pliocene carbonates and clastic sediments. Potential reservoirs in the Neotectonic basins may be sourced either in situ or from underlying Paleozoic and Mesozoic source rocks that remain within the hydrocarbon generating window today.

  19. Two petroleum systems in the Sacramento Basin, California - A basis for new discoveries

    SciTech Connect

    Magoon, L.B. ); Castano, J.R. ); Lillis, P. ); Mackevett, N.H.; Naeser, N. )

    1994-04-01

    The Sacramento basin is a north-trending fore-arc basin that contains Lat Jurassic to Holocene sedimentary rocks that become thicker to the south and are overpressured at depth. The basin fill is about 300 km long, 80 km wide, and as much as 16 km thick. Two petroleum systems occur in the Sacramento basin. The Dobbins-Forbes( ) gas system, which contained about 2.25 tcf (10[sup 12]ft[sup 3]) of recoverable gas, underlies the Winters-Domingine( ) gas system, which contained about 6.89 tcf of recoverable gas. Gas migrated laterally and to the north as much as 200 km in the Dobbins-Forbes( ) system, whereas in the Winters-Domingine( ) system, gas first migrated vertically and then crossed the Midland fault to the east for up to 40 km. For both systems, depth of gas production from reservoir rocks of Lake Cretaceous to Oligocene in different trap types is less than 3 km. By applying the petroleum-system concept and information about the geology and geochemistry available for this province, this study- provides a new testable hypthesis for the origin, migration, and accumulation of gas in the Sacramento basin. By reinterpreting some of the natural gas information, gas wetness, gas-oil ratio, vectors of migration, hydrocarbon volume, and thermal history, two petroleum systems are identified. Understanding of the origin of known accumulations in this province provides a basis for new plays that should lead to discoveries with substantial reserves.

  20. Multibeam bathymetric survey of the Ipala Submarine Canyon, Jalisco, Mexico (20°N): The southern boundary of the Banderas Forearc Block?

    NASA Astrophysics Data System (ADS)

    Urías Espinosa, J.; Bandy, W. L.; Mortera Gutiérrez, C. A.; Núñez Cornú, Fco. J.; Mitchell, N. C.

    2016-03-01

    The Middle America Trench bends sharply northward at 20°N. This, along with the close proximity of the Rivera-North America Euler pole to the northern end of this trench, sharply increases the obliquity of subduction at 20°N. By analogy with other subduction zones with similar sharply changing obliquity, significant trench parallel extension is expected to exist in the forearc region near the bend. To evaluate this possibility, multibeam bathymetric, seafloor backscatter and sub-bottom seismic reflection data were collected in this area during the MORTIC08 campaign of the B.O. El Puma. These data image in detail a large submarine canyon (the Ipala Canyon) extending from the coast at 20°05‧N to the Middle America Trench at 19°50‧N. This canyon is 114 km long and is fed by sediments originating from two, possibly three, small rivers: the Ipala, Tecolotlán and Maria Garza. This canyon deeply incises (up to 600 m) the entire continental slope and at least the outer part of the shelf. Within the canyon, we observe meanders and narrow channels produced by turbidity flows indicating that the canyon is active. In the marginal areas of the canyon slumps, rills, and uplifts suggest that mass movements and fluid flow have had a major impact on the seafloor morphology. The seafloor bathymetry, backscatter images and sub-bottom reflection profiles evidence the tectonic processes occurring in this area. Of particular interest, the canyon is deflected by almost 90° at three locations, the deflections all having a similar azimuth of between 125° and 130°. Given the prominence and geometry of this canyon, along with its tectonic setting, we propose that the presence of the canyon is related to extension produced by the sharp change in the plate convergence. If so, the canyon may lie along the southeast boundary of a major forearc block (the Banderas Forearc Block).

  1. Multibeam Bathymetric Survey of the Ipala Submarine Canyon, Jalisco. Mexico (20°N): The Southern Boundary of the Banderas Forearc Block?

    NASA Astrophysics Data System (ADS)

    Urias Espinosa, J.; Bandy, W. L.; Mortera-Gutierrez, C. A.; Nuñez-Cornu, F. J.; Mitchell, N. C.

    2015-12-01

    The Middle America Trench bends sharply northward at 20°N. This, along with the close proximity of the Rivera-North America Euler pole (e.g., Suárez et al., 2103) to the northern end of the Middle American trench (the Jalisco Subduction Zone), produces a sharp increase in the obliquity of subduction at 20°N. By analogy with other subduction zones where this situation occurs,a significant trench parallel extensional stress field is expected to exist in the forearc region near the bend. Given the poor bathymetric coverage previously existing in this area, to verify that such stresses are present in the forearc area of the Jalisco Subduction Zone, multibeam bathymetric, seafloor backscatter and sub-bottom seismic reflection data were collected during the MORTIC08 campaign of the B.O. EL PUMA using the Kongsberg EM300 multibeam system and TOPAS sub-bottom profiler. Consistent with the analogy, these data image in detail a large submarine canyon extending from the coast at 20°05'N to the Middle America Trench at 19°50'N. This canyon, which we call the Ipala canyon (the canyon head lies offshore of the town of Ipala, Jalisco) is approximately 120km in length and is most likely fed by two, possibly three, small rivers, namely: the Ipala, Tecolotlán and Maria Garza rivers. . The seafloor and subbottom seismic reflection images also expose the tectonic processes that are actively influencing the present day geomorphology of the canyon region. Specifically, the new information indicates that much of the physical geography of seafloor is the result of active tectonic deformation of the plate margin, including uplift, erosion along structural lineaments and faulting. Of particular interest, the canyon is deflected by almost 90° at three locations, the deflections all having a similar azimuth of between 125° and 130°. Given the prominence and geometry of this canyon, along with its tectonic setting, we propose that this canyon is the result of extensional stresses

  2. Influence of the Density Structure of the Caribbean Plate Forearc on the Static Stress State and Asperity Distribution along the Costa Rican Seismogenic Zone

    NASA Astrophysics Data System (ADS)

    Lücke, O. H.; Gutknecht, B. D.

    2014-12-01

    Most of the forearc region along the Central American Subduction Zone shows a series of trench-parallel, positive gravity anomalies with corresponding gravity lows along the trench and toward the coast. These features extend from Guatemala to northern Nicaragua. However, the Costa Rican segment of the forearc does not follow this pattern. In this region, the along-trench gravity low is segmented, the coastal low is absent, and the forearc gravity high is located onshore at the Nicoya Peninsula which overlies the seismogenic zone. Geodetic and seismological studies along the Costa Rican Subduction Zone suggest the presence of coupled areas beneath the Nicoya Peninsula prior to the 2012, magnitude Mw 7.6 earthquake. These areas had previously been associated with asperities. Previous publications have proposed a mechanical model for the generation of asperities along the Chilean convergent margin based on the structure of the overriding plate above the seismogenic zone in which dense igneous bodies disturb the state of stress on the seismogenic zone and may influence seismogenic processes. In Costa Rica, surface geology and gravity data indicate the presence of dense basalt/gabbro crust overlying the seismogenic zone where the coupling is present. Bouguer anomaly values in this region reach up to 120×10-5 m/s2, which are the highest for Costa Rica. In this work, the state of stress on the Cocos-Caribbean plate interface is calculated based on the geometry and mass distribution of a 3D density model of the subduction zone as interpreted from gravity data from combined geopotential models. Results show a correlation between the coupled areas at the Nicoya Peninsula and the presence of stress anomalies on the plate interface. The stress anomalies are calculated for the normal component of the vertical stress on the seismogenic zone and are interpreted as being generated by the dense material which makes up the forearc in the area. The dense material of the Nicoya

  3. Fluid migration pathways, sediment subduction, and the source of fluids escaping along the forearc seafloor revealed offshore Nicaragua with marine electromagnetic data

    NASA Astrophysics Data System (ADS)

    Naif, S.; Key, K.; Constable, S.; Evans, R. L.

    2014-12-01

    The subduction of sediments and hydrated oceanic plates transports the primary flux of water into the interior of the Earth. As an oceanic plate sinks, water is progressively released by compaction and chemical dehydration reactions, a significant fraction of which is released during the initial stages of subduction. In order to map the flux of fluids at the Middle America Trench, we collected marine magnetotelluric and controlled-source electromagnetic data along a 280-km profile that spans the offshore component of the Nicaraguan margin. Fluids and volatiles present in the crust and mantle can decrease the bulk electrical resistivity by up to several orders of magnitude, making electromagnetic methods an ideal exploration tool for quantifying fluids along convergent margins. Our joint two-dimensional electrical resistivity model provides new constraints on the cycling of fluids at crustal depths. We image a variety of conductive channels that are indicative of: (1) crustal hydration along bending-induced normal faults at the outer rise, (2) the complete subduction of water-rich sediments, and (3) the vertical migration of fluids from the plate interface to the forearc seafloor. We estimate porosity from electrical resistivity using Archie's law to show that the porosity of the lower crust is increased by 115% at the outer rise compared with the abyssal plain, suggesting that more pore water is being subducted than previously thought. At the margin toe, we observe the porosity of the underthrust sediment layer to decay exponentially with increasing depth of burial to 10-km inland of the trench, which agrees well with laboratory studies of compaction driven porosity loss. At 23-km into the forearc, our data reveal an anomalous conductor that extends from the plate interface into the overlying forearc crust, terminating 1-2-km below a high density region of active fluid seeps and mud mounds that have previously been mapped. The temperature and pressure regime in the

  4. Paleogene palaeogeography and basin evolution of the Western Carpathians, Northern Pannonian domain and adjoining areas

    NASA Astrophysics Data System (ADS)

    Kováč, Michal; Plašienka, Dušan; Soták, Ján; Vojtko, Rastislav; Oszczypko, Nestor; Less, György; Ćosović, Vlasta; Fügenschuh, Bernhard; Králiková, Silvia

    2016-05-01

    The data about the Paleogene basin evolution, palaeogeography, and geodynamics of the Western Carpathian and Northern Pannonian domains are summarized, re-evaluated, supplemented, and newly interpreted. The presented concept is illustrated by a series of palinspastic and palaeotopographic maps. The Paleogene development of external Carpathian zones reflects gradual subduction of several oceanic realms (Vahic, Iňačovce-Kričevo, Szolnok, Magura, and Silesian-Krosno) and growth of the orogenic accretionary wedge (Pieniny Klippen Belt, Iňačovce-Kričevo Unit, Szolnok Belt, and Outer Carpathian Flysch Belt). Evolution of the Central Western Carpathians is characterized by the Paleocene-Early Eocene opening of several wedge-top basins at the accretionary wedge tip, controlled by changing compressional, strike-slip, and extensional tectonic regimes. During the Lutetian, the diverging translations of the northward moving Eastern Alpine and north-east to eastward shifted Western Carpathian segment generated crustal stretching at the Alpine-Carpathian junction with foundation of relatively deep basins. These basins enabled a marine connection between the Magura oceanic realm and the Northern Pannonian domain, and later also with the Dinaridic foredeep. Afterwards, the Late Eocene compression brought about uplift and exhumation of the basement complexes at the Alpine-Carpathian junction. Simultaneously, the eastern margin of the stretched Central Western Carpathians underwent disintegration, followed by opening of a fore-arc basin - the Central Carpathian Paleogene Basin. In the Northern Hungarian Paleogene retro-arc basin, turbidites covered a carbonate platform in the same time. During the Early Oligocene, the rock uplift of the Alpine-Carpathian junction area continued and the Mesozoic sequences of the Danube Basin basement were removed, along with a large part of the Eocene Hungarian Paleogene Basin fill, while the retro-arc basin depocentres migrated toward the east

  5. Ophiolitic basement to the Great Valley forearc basin, California, from seismic and gravity data: Implications for crustal growth at the North American continental margin

    USGS Publications Warehouse

    Godfrey, N.J.; Beaudoin, B.C.; Klemperer, S.L.; Levander, A.; Luetgert, J.; Meltzer, A.; Mooney, W.; Trehu, A.

    1997-01-01

    The nature of the Great Valley basement, whether oceanic or continental, has long been a source of controversy. A velocity model (derived from a 200-km-long east-west reflection-refraction profile collected south of the Mendocino triple junction, northern California, in 1993), further constrained by density and magnetic models, reveals an ophiolite underlying the Great Valley (Great Valley ophiolite), which in turn is underlain by a westward extension of lower-density continental crust (Sierran affinity material). We used an integrated modeling philosophy, first modeling the seismic-refraction data to obtain a final velocity model, and then modeling the long-wavelength features of the gravity data to obtain a final density model that is constrained in the upper crust by our velocity model. The crustal section of Great Valley ophiolite is 7-8 km thick, and the Great Valley ophiolite relict oceanic Moho is at 11-16 km depth. The Great Valley ophiolite does not extend west beneath the Coast Ranges, but only as far as the western margin of the Great Valley, where the 5-7-km-thick Great Valley ophiolite mantle section dips west into the present-day mantle. There are 16-18 km of lower-density Sierran affinity material beneath the Great Valley ophiolite mantle section, such that a second, deeper, "present-day" continental Moho is at about 34 km depth. At mid-crustal depths, the boundary between the eastern extent of the Great Valley ophiolite and the western extent of Sierran affinity material is a near-vertical velocity and density discontinuity about 80 km east of the western margin of the Great Valley. Our model has important implications for crustal growth at the North American continental margin. We suggest that a thick ophiolite sequence was obducted onto continental material, probably during the Jurassic Nevadan orogeny, so that the Great Valley basement is oceanic crust above oceanic mantle vertically stacked above continental crust and continental mantle.

  6. Record of Plio-Pleistocene extreme event in the Lesser Antilles fore-arc basin. Example of Grande-Terre (Guadeloupe, French West Indies).

    NASA Astrophysics Data System (ADS)

    Jeanlèn, L.; Philippon, M. M.; Randrianasolo, A.; Jean-Frederic, L.; Cornée, J. J.; Münch, P.

    2015-12-01

    Guadeloupe archipelago is part of the Lesser Antilles active volcanic arc and is therefore subjected to both enhanced seismic and volcanic activity related to the Lesser Antilles subduction zone, along which the Atlantic plate is subducted westward bellow the Caribbean plate. The volcanic arc is composed of several immerged volcanic islands (St Kitts, Nevis Montserrat, Basse Terre, Dominica, Martinique, St Lucia, Grenada) and submerged volcanoes (Kick em'Jenny). These volcanoes are known to be explosives and when they are entering in an eruptive cycle, debris flow could potentially initiate a tsunami and generate peculiar deposits within the sedimentary record recognized as tsunami deposits (or tsunamite). Subduction- related earthquakes might also initiate slope instabilities and trigger debris flow. Another controlling factor of slope (in-)-stabilities and debris flow is massive rainfalls. During cyclonic season (June to December), massive rainfalls are recorded in the area, which moreover is located on the trajectory of Atlantic Hurricanes that are responsible for numerous landslides. As a consequence, tsunami deposit are described and well studied in the Lesser Antilles arc as the islands shoreline and coastal plain are perpetually re-shaped by hurricanes responsible for tempestite deposits. However, the report of these deposit concern recent to actual events, for example present-day deposits consisting of large (metric) boulders, more or less aligned, located in the supralittoral fringe can be observed along Guadeloupe shore. In this study, we investigate the Plio-pleistocene sedimentary sequence of Grande Terre carbonate platform (Guadeloupe), and track the presence of such extreme-event related deposits and discuss our findings in the frame of the Lesser Antilles geological context.

  7. Analysis of rupture area of aftershocks caused by twin earthquakes (Case study: 11 April 2012 earthquakes of Aceh-North Sumatra)

    NASA Astrophysics Data System (ADS)

    Diansari, Angga Vertika; Purwana, Ibnu; Subakti, Hendri

    2015-04-01

    The 11 April 2012 earthquakes off-shore Aceh-North Sumatra are unique events for the history of Indonesian earthquake. It is unique because that they have similar magnitude, 8.5 Mw and 8.1 Mw; close to epicenter distance, similar strike-slip focal mechanism, and occuring in outer rise area. The purposes of this research are: (1) comparing area of earthquakes base on models and that of calculation, (2) fitting the shape and the area of earthquake rupture zones, (3) analyzing the relationship between rupture area and magnitude of the earthquakes. Rupture area of the earthquake fault are determined by using 4 different formulas, i.e. Utsu and Seki (1954), Wells and Coppersmith (1994), Ellsworth (2003), and Christophersen and Smith (2000). The earthquakes aftershock parameters are taken from PGN (PusatGempabumiNasional or National Earthquake Information Center) of BMKG (Indonesia Agency Meteorology Climatology and Geophysics). The aftershock epicenters are plotted by GMT's software. After that, ellipse and rectangular models of aftershock spreading are made. The results show that: (1) rupture areas were calculated using magnitude relationship which are larger than the the aftershock distributions model, (2) the best fitting model for that earthquake aftershock distribution is rectangular associated with Utsu and Seki (1954) formula, (3) the larger the magnitude of the earthquake, the larger area of the fault.

  8. Contribution of Anisotropy of Magnetic Susceptibility (AMS) to reconstruct flooding characteristics of a 4220 BP tsunami from a thick unconsolidated structureless deposit (Banda Aceh, Sumatra)

    NASA Astrophysics Data System (ADS)

    Wassmer, Patrick; Gomez, Christopher; Iskandasyah, T. Yan W. M.; Lavigne, Franck; Sartohadi, Junun

    2015-07-01

    One of the main concerns of deciphering tsunami sedimentary records along seashore is to link the emplaced layers with marine high energy events. Based on a combination of morphologic features, sedimentary figures, grain size characteristics, fossils content, microfossils assemblages, geochemical elements, heavy minerals presence; it is, in principle, possible to relate the sedimentary record to a tsunami event. However, experience shows that sometimes, in reason of a lack of any visible sedimentary features, it is hard to decide between a storm and a tsunami origin. To solve this issue, the authors have used the Anisotropy of Magnetic Susceptibility (AMS) to evidence the sediment fabric. The validity of the method for reconstructing flow direction has been proved when applied on sediments in the aftermath of a tsunami event, for which the behaviour was well documented (2004 IOT). We present herein an application of this method for a 56 cm thick paleo-deposit dated 4220 BP laying under the soil covered by the 2004 IOT, SE of Banda Aceh, North Sumatra. We analysed this homogenous deposit, lacking of any visible structure, using methods of classic sedimentology to confirm the occurrence of a high energy event. We then applied AMS technique that allowed the reconstruction of flow characteristics during sediment emplacement. We show that all the sequence was emplaced by uprush phases and that the local topography played a role on the re-orientation of a part of the uprush flow, creating strong reverse current. This particular behaviour was reported by eyewitnesses during the 2004 IOT event.

  9. Analysis of rupture area of aftershocks caused by twin earthquakes (Case study: 11 April 2012 earthquakes of Aceh-North Sumatra)

    SciTech Connect

    Diansari, Angga Vertika Purwana, Ibnu; Subakti, Hendri

    2015-04-24

    The 11 April 2012 earthquakes off-shore Aceh-North Sumatra are unique events for the history of Indonesian earthquake. It is unique because that they have similar magnitude, 8.5 Mw and 8.1 Mw; close to epicenter distance, similar strike-slip focal mechanism, and occuring in outer rise area. The purposes of this research are: (1) comparing area of earthquakes base on models and that of calculation, (2) fitting the shape and the area of earthquake rupture zones, (3) analyzing the relationship between rupture area and magnitude of the earthquakes. Rupture area of the earthquake fault are determined by using 4 different formulas, i.e. Utsu and Seki (1954), Wells and Coppersmith (1994), Ellsworth (2003), and Christophersen and Smith (2000). The earthquakes aftershock parameters are taken from PGN (PusatGempabumiNasional or National Earthquake Information Center) of BMKG (Indonesia Agency Meteorology Climatology and Geophysics). The aftershock epicenters are plotted by GMT’s software. After that, ellipse and rectangular models of aftershock spreading are made. The results show that: (1) rupture areas were calculated using magnitude relationship which are larger than the the aftershock distributions model, (2) the best fitting model for that earthquake aftershock distribution is rectangular associated with Utsu and Seki (1954) formula, (3) the larger the magnitude of the earthquake, the larger area of the fault.

  10. Efficient post-disaster patient transportation and transfer: experiences and lessons learned in emergency medical rescue in Aceh after the 2004 Asian tsunami.

    PubMed

    Li, Xiang-Hui; Zheng, Jing-Chen

    2014-08-01

    This descriptive study aimed to present experiences and lessons learned in emergency medical rescue after the 2004 Asian tsunami in terms of transportation and transfer of patients and coordination of medical rescue forces. After the tsunami, numerous rescue institutions and international organizations rushed to Aceh province to aid in the rescue work. To coordinate various aspects of medical rescue efforts, an airport-based joint patient transfer center was developed. Within the framework of the joint transport center, rescue teams, militaries, and international institutions worked together to jointly triage, rapidly treat, and transfer patients. As members of the Chinese International Search and Rescue team, we were involved in the rescue efforts in the joint patient transfer center, and treated and transferred a total of 217 injured patients, the majority of whom were triaged as level II, followed by level III, and level I. The top three diseases were trauma/wound infection, respiratory system disease, and digestive system disease. The airport-based joint patient transfer center provided an efficient mechanism for successfully coordinating various aspects of the medical rescue efforts to transfer patients. Large-scale air transport, available health resources, and effective triage criteria also played an essential role in patient transportation and transfer. PMID:25102536

  11. Petroleum systems in the Sacramento Basin, California, USA

    SciTech Connect

    Magoon, L.B.; Valin, Z.C.; Lillis, P.G.

    1996-08-01

    The Sacramento Basin, a north-trending forearc basin that contains Late Jurassic to Holocene sedimentary rocks which thicken to the south, is primarily a gas province with minor occurrences of oil, comprising four petroleum systems, two of gas and two of oil. The Dobbins-Forbes(?) gas system, which contained about 2.2 5 tcf (10{sup 12} ft{sup 3}) of recoverable gas, underlies the Winters-Domengine(?) gas system, which contained about 6.89 tcf of recoverable gas. Gas migrated laterally to the north as far as 200 km in the Dobbins-Forbes(?) system, whereas in the Winters-Domengine(?) system, gas first migrated vertically and then crossed the Midland Fault to the east for as far as 40 km. In both systems, depth of gas production is less than 3 km. On the basis of petroleum geochemistry of the oils, two unnamed oil systems have been identified. Oil recovered from cinnabar mines, a gold mine, seeps, and a few wells along the northwest flank of the basin are all similar and constitute one oil system. The provenance of this oil type is a Cretaceous source rock. The oil from the Brentwood and Livermore Oil Fields at the south end of the province, which constitute the other oil system, is thought to originate from the Kreyenhagen Formation of Eocene age. By applying the petroleum-system concept and available information about the geology and geochemistry of this province, our study provides a new testable hypothesis for the origin, migration, and accumulation of petroleum in the Sacramento Basin.

  12. S-Local-Wave Seismic Anisotropy in the Forearc Above the Subducted Nazca Plate Between 33°S and 34.5°S

    NASA Astrophysics Data System (ADS)

    Nacif, Silvina; Triep, Enrique G.

    2016-04-01

    S-wave splitting from local earthquakes within the Nazca plate that are deeper than the interplate seismogenic zone enabled the determination of the fast velocity direction, Φ, and the lag time, δt, in the forearc of the overriding plate. Data were collected from 20 seismic stations, most of which were temporary, deployed between ~33.5°S and ~34.5°S and included part of the normal subduction section to the south and part of the transitional section to flat subduction to the north. The fast velocity direction has a complex pattern with three predominant directions northwest-southeast, north-south and northeast-southwest and relatively high δt. A quality evaluation of the highest measurements enabled us to identify possible cycle skipping in some of the measurements, which could be responsible for the large observed lag time. We consider that most of the anisotropy that was observed in the forearc is probably located in the mantle wedge, and a minor part is located in the crust. The complex pattern of splitting parameters when the anisotropy is associated at the mantle wedge could be the result of three-dimensional variations in the subducting Nazca plate at these latitudes. Also, similarities between the splitting parameters and the principal compressional stress direction from Pliocene and Quaternary rocks suggest that the anisotropy in the crust could originate by tectonic local stress.

  13. Structural Geology of the Active Forearc above the Maule Megathrust: Traces of a Long-lived Subduction Segment

    NASA Astrophysics Data System (ADS)

    Aron, F. A.; Cembrano, J. M.; Allmendinger, R. W.; Astudillo, F.; Arancibia, G.

    2012-12-01

    The 2010 Mw8.8 Maule earthquake rupture in central Chile produced significant upper and lower plate normal fault aftershocks including some of the largest recorded, the Mw7.0 Pichilemu events 11 days after the main event. Our understanding of the context and significance of these events for permanent deformation of the upper plate has been hampered by poorly known regional geology overlying the northern and central parts of the Maule rupture. We present new structural data of the Coastal Cordillera from the northern end of the rupture which illuminates the relationship between coseimic and long term deformation. We show that the Neogene normal faults along the outer forearc, including the Pichilemu normal fault, can be reactivated by the coseismic stress imposed within the upper plate by great subduction ruptures. The structural style of the region overlying the northern end of the Maule rupture is dominated by kilometer-scale normal faults which have been active at least throughout the Neogene. The strikes of these main structures define three structural systems: (1) a NE and (2) a NW sets of margin-oblique faults, and (3) a ~NS, margin-parallel set. The SW-dipping Pichilemu fault, which has at least three flights of uplifted marine terraces in the footwall but only a single low terrace displaying a rollover anticline in the footwall, belongs to the second group. The first two sets characterize the northernmost part of the rupture and spatially overlap, displaying a bimodal orientation; the third set occurs farther south and appears to characterize the central part of the rupture segment. Reverse faults exist but are scarce. Using the slip model of the Maule earthquake by Vigny et al. 2011 we calculate the strikes of optimally oriented normal faults along the Coastal Cordillera from the Coulomb stress increment. Comparing these strikes to the strikes of known faults and our new data, we find that nearly half agree in orientation within 22.5°. The extensional

  14. Forearc deformation processes inferred from drowned shorelines in the Arauco Bay, Southern Chile (37°S)

    NASA Astrophysics Data System (ADS)

    Jara-Muñoz, Julius; Melnick, Daniel; Bernhardt, Anne; Argandoña, Boris; Gonzalez-Acuña, Javiera; Strecker, Manfred

    2015-04-01

    Relict drowned landscapes often constitute preserved snapshots of terrestrial environments prior to flooding episodes during the Quaternary. Forearc deformation processes are usually recorded by coastal landforms, such as paleo-shorelines or marine terraces reflecting pronounced vertical movements. Similarly, drowned coastal landscapes represent past sea-level positions that can be used as tracers of tectonic deformation and sea-level change. In this study we present hitherto unrecognized drowned Quaternary shorelines in the Arauco Bay of southern Chile. The Arauco Bay lies inland of the Santa Maria Fault and is surrounded by densely populated areas, many devastated by the tsunami following the 2010 M 8.8 Maule earthquake. The shorelines are folded, apparently as a result of slip along the Santa Maria Fault, a blind splay-fault system rooted in the Nazca-South America plate-boundary zone, documenting protracted tectonic activity. We mapped and used these drowned geomorphic markers using high-resolution bathymetry (2.5 m) to infer rates and style of deformation along the Santa Maria splay fault. For this purpose we used surface classification models, observations from a remotely operated vehicle (ROV), and sedimentology of sea-bottom samples. High roughness areas correspond to well-exposed bedrock outcrops. The enclosed patches were studied in detail and compared with LiDAR data from emerged and actively forming marine platforms from nearby areas. Three levels of drowned shorelines were identified: at ~110 m, ~40 and ~60 m depth, respectively. The shallower two shorelines are distributed as fringes parallel to the coastline of the Arauco Bay and deepen towards the trench. We selected the shallowest level as an exploratory target for a ROV dive obtaining video and still images of micromorphologic features; a sampling target was selected at 45 m where professional divers collected samples of bedrock and sediments. Chronologic correlation was performed based on global

  15. Deep sourced mounds offshore Costa Rica: A mechanism for non-magmatic forearc recycling of oceanic crust ?

    NASA Astrophysics Data System (ADS)

    Moerz, T.; Brueckmann, W.; Kopf, A.; Kreiter, S.; Wallmann, K.; Suess, E.

    2003-04-01

    supplement our study. These finds together with a large sediment-physical data set from an extensive core collection demonstrates for the first time that crustal material may be recycled in the forearc and that convergent stress from plate subduction provides ways for deep and efficient export capabilities via "cold" mud diapirs even in an erosive subduction setting that lacks a distinct accretionary wedge and high sediment accumulations on the slope.

  16. Evidence for silicic crust formation in an incipient stage of intra-oceanic subduction zone: discovery of deep crustal sections in Izu-Bonin forearc

    NASA Astrophysics Data System (ADS)

    Tani, K.; Shukuno, H.; Hirahara, Y.; Chang, Q.; Kimura, J.; Nichols, A. R.; Ishii, T.; Tatsumi, Y.; Dunkley, D. J.

    2009-12-01

    Recent research cruises surveying forearc slopes of Izu-Bonin-Mariana (IBM) arc have discovered outcrops representing the deep crustal section of the early IBM arc. Ongoing geochemcial, petrological, and geochronological studies of recovered rocks are providing new insights into the magmatism and development of arc crust during the inception of an intra-oceanic subduction system. ROV traverses, conducted at the northern Izu-Bonin forearc, discovered peridotite exposures from deep (~7000 mbsl) sections, and observed a drastic shift in lithofacies towards the upper sections (~5000 mbsl), from gabbro, through dolerite, porphyrite, tonalite, and finally volcanic breccia and sedimentary rocks. This indicates that the traverses covered a full arc crust section from uppermost mantle to upper crust. The gabbroic and doleritic rocks show geochemical signatures (e.g. LREE-depletion and low-Ba/La) similar to those of N-MORB, with minimum arc signatures (e.g. Nb-depletion and LILE-enrichment). The results from zircon and titanite U-Pb geochronology show that this MORB-like basaltic magmatism was episodically active ~52 Ma, predating the boninitic magmatism broadly exposed in the uppermost section of forearc slope, which began ~49 Ma (Ishizuka et al., 2006) and previously considered to be the first magmatism in IBM arc. The collected peridotite samples were mostly dunite and harzburgite, and show variable degrees of serpentinization. Compositions of Cr-spinel and olivine, and the calculated oxygen fugacity indicate that these peridotite samples probably coexisted with MORB-type magma rather than the boninitic or island-arc basaltic magmas. Massive outcrops of tonalitic rocks and associated dacitic-rhyolitic prophyrites were discovered in one of the surveyed area, underlain by gabbro and dolerite with MORB-like geochemical signatures. Tonalitic rocks, weakly-foliated hornblende tonalites, are continuously exposed in a ~300 m-high wall in the middle section of the forearc slope

  17. Utilization of formal health services for children aged 1–5 in Aceh after the 2004 tsunami: Which children did not receive the health care they needed? Implications for other natural disaster relief efforts

    PubMed Central

    Rassekh, Bahie Mary; Santosham, Mathuram

    2014-01-01

    Aceh, Indonesia, was the hardest-hit area in the December 26, 2004 Indian Ocean earthquake and tsunami, with more than 500,000 people displaced, 120,000 people dead, and total damages and losses estimated at $4.5 billion. The relief effort following the tsunami was also immense, with billions of dollars of aid pledged to this province alone. Since then, there have been several natural disasters, including Typhoon Haiyan, which have caused great loss of life and displacement and for which these results are applicable. This study aimed to determine and assess utilization patterns of health services for children under the age of five with diarrhea, cough and difficulty breathing, fever, or skin disease and to identify determinants of formal and non-formal healthcare usage. A household survey of 1439 households was administered to caretakers of children aged 1–5 years. A sample of clusters within Banda Aceh and Aceh Besar were selected and those caretakers within the cluster who fit the inclusion criteria were interviewed. In the two weeks prior to the survey, 78.3% of respondents utilized formal health services as the first line of care for their child's illness episode. Factors significantly associated with decreased formal healthcare usage for the sick children were if the children were living in a displaced household, if the children's mother or father were not living, and if the children's caretaker was not the mother. Although utilization of formal health services for children was quite high after the tsunami, there were certain children who received significantly less care, including those who were displaced, those who were being cared for by someone other than their mother, and those for whom one or both parents had died. Among the recommendations are suggestions to target these children to ensure that they receive the health care they need. PMID:25750772

  18. A review on earthquake and tsunami hazards of the Sumatran plate boundary: Observing expected and unexpected events after the Aceh-Andaman Mw 9.15 event

    NASA Astrophysics Data System (ADS)

    Natawidjaja, D.

    2013-12-01

    The 600-km Mentawai megathrust had produced two giant historical earthquakes generating big tsunamies in 1797 and 1833. The SuGAr (Sumatran GPS continuous Array) network, first deployed in 2002, shows that the subduction interface underlying Mentawai Islands and the neighboring Nias section in the north are fully locked, thus confirming their potential hazards. Outreach activities to warn people about earthquake and tsunamies had been started since 4 months prior to the 26 December 2004 in Aceh-Andaman earthquake (Mw 9.15). Later in March 2005, the expected megathrust earthquake (Mw 8.7) hit Nias-Simelue area and killed about 2000 people, releasing the accumulated strain since the previous 1861 event (~Mw 8.5). After then many Mw 7s and smaller events occured in Sumatra, filling areas between and around two giant ruptures and heighten seismicities in neighboring areas. In March 2007, the twin earthquake disaster (Mw 6.3 and Mw 6.4) broke two consecutive segments of the transcurrent Sumatran fault in the Singkarak lake area. Only six month later, in September 2007, the rapid-fire-failures of three consecutive megathrust patches (Mw 8.5, Mw 7.9 and Mw 7.0) ruptured a 250-km-section of the southern part of the Mentawai. It was a big surprise since this particular section is predicted as a very-low coupled section from modelling the SuGAr data, and hence, bypassing the more potential fully coupled section of the Mentawai in between the 2005 and 2007 ruptures. In September 2009, a rare unexpected event (Mw 7.6) suddenly ruptured an intracrustal fault in the subducted slab down under Padang City and killed about 500 people. Padang had been in preparation for the next tsunami but not for strong shakes from near by major earthquake. This event seems to have remotely triggered another Mw 6.7 on the Sumatran fault near kerinci Lake, a few hundred kilometers south of Padang, in less than a day. Just a year later, in November 2010, again an unexpected large slow-slip event of

  19. Evidence of Crustal Faulting and Deformation in the Muckleshoot Basin, Washington

    NASA Astrophysics Data System (ADS)

    Cox, J.; Wolf, L. W.

    2015-12-01

    The Muckleshoot basin of western Washington, sandwiched between the Seattle Uplift on the west and the Cascade Range on the east, is deforming under north-south shortening and clockwise rotation of the north Cascadia forearc. Accommodating the regional strain are crustal faults in the Puget Lowland that cluster around three azimuths: east-west, northwest-southeast, and north-northwest-south-southeast. Evidence for all three groups appears on the periphery of the Muckleshoot basin. In this study, we add gravity measurements to an existing database to better define the geometry of the Muckleshoot basin and its relation to previously mapped faults appearing on the basin margins. A northwest-trending gravity high bisects the basin into two sub-basins, a larger one to the south and a smaller one to the north. We suggest that the gravity high is associated with a deep basement structure and its orientation is consistent with northward-directed crustal shortening. Regional-residual separation methods and derivative maps show pronounced magnetic lineations that extend faults expressed along the basin margins to east-west trending faults that cross the Puget Sound. Three intersecting cross-sectional models produced for this study are consistent with the following hypotheses: (1) the northwest-trending White River and Green River faults mapped on the eastern basin margin appear as south-verging, steeply dipping reverse faults in the central basin; (2) the north-northwest trending Franklin fault, mapped previously as a strike-slip fault, projects into the basin and shows little vertical offset in the single profile it crosses, and (3) the northwest trajectory of both the White River and Green River faults appears to curve southward as the faults traverse the Muckleshoot basin, following east-west oriented gravity and magnetic anomalies that cross the Puget Sound. Results from the study suggest that the faults and folds in Muckleshoot basin are actively interacting with other

  20. Eocene extension in Idaho generated massive sediment floods into Franciscan trench and into Tyee, Great Valley, and Green River basins

    USGS Publications Warehouse

    Dumitru, Trevor A.; Ernst, W.G.; Wright, James E.; Wooden, Joseph L.; Wells, Ray E.; Farmer, Lucia P.; Kent, Adam J.R.; Graham, Stephan A.

    2013-01-01

    The Franciscan Complex accretionary prism was assembled during an ∼165-m.y.-long period of subduction of Pacific Ocean plates beneath the western margin of the North American plate. In such fossil subduction complexes, it is generally difficult to reconstruct details of the accretion of continent-derived sediments and to evaluate the factors that controlled accretion. New detrital zircon U-Pb ages indicate that much of the major Coastal belt subunit of the Franciscan Complex represents a massive, relatively brief, surge of near-trench deposition and accretion during Eocene time (ca. 53–49 Ma). Sediments were sourced mainly from the distant Idaho Batholith region rather than the nearby Sierra Nevada. Idaho detritus also fed the Great Valley forearc basin of California (ca. 53–37 Ma), the Tyee forearc basin of coastal Oregon (49 to ca. 36 Ma), and the greater Green River lake basin of Wyoming (50–47 Ma). Plutonism in the Idaho Batholith spanned 98–53 Ma in a contractional setting; it was abruptly superseded by major extension in the Bitterroot, Anaconda, Clearwater, and Priest River metamorphic core complexes (53–40 Ma) and by major volcanism in the Challis volcanic field (51–43 Ma). This extensional tectonism apparently deformed and uplifted a broad region, shedding voluminous sediments toward depocenters to the west and southeast. In the Franciscan Coastal belt, the major increase in sediment input apparently triggered a pulse of massive accretion, a pulse ultimately controlled by continental tectonism far within the interior of the North American plate, rather than by some tectonic event along the plate boundary itself.

  1. Location and extent of Tertiary structures in Cook Inlet Basin, Alaska, and mantle dynamics that focus deformation and subsidence

    USGS Publications Warehouse

    Haeussler, Peter J.; Saltus, Richard W.

    2011-01-01

    Subduction of the buoyant Yakutat microplate likely caused deformation to be focused preferentially in upper Cook Inlet. The upper Cook Inlet region has both the highest degree of shortening and the deepest part of the Neogene basin. This forearc region has a long-wavelength magnetic high, a large isostatic gravity low, high conductivity in the lower mantle, low p-wave velocity (Vp), and a high p-wave to shear-wave velocity ratio (Vp/Vs). These data suggest that fluids in the mantle wedge caused serpentinization of mafic rocks, which may, at least in part, contribute to the long-wavelength magnetic anomaly. This area lies adjacent to the subducting and buoyant Yakutat microplate slab. We suggest the buoyant Yakutat slab acts much like a squeegee to focus mantle-wedge fluid flow at the margins of the buoyant slab. Such lateral flow is consistent with observed shear-wave splitting directions. The additional fluid in the adjacent mantle wedge reduces the wedge viscosity and allows greater corner flow. This results in focused subsidence, deformation, and gravity anomalies in the forearc region.

  2. Subducting oceanic high causes compressional faulting in southernmost Ryukyu forearc as revealed by hypocentral determinations of earthquakes and reflection/refraction seismic data

    NASA Astrophysics Data System (ADS)

    Font, Yvonne; Lallemand, Serge

    2009-03-01

    Absolute earthquake hypocenter locations have been determined in the area offshore eastern Taiwan, at the Southernmost Ryukyu subduction zone. Location process is run within a 3D velocity model by combining the Taiwanese and neighboring Japanese networks and using the 3D MAXI technique. The study focuses on the most active seismic cluster in the Taiwan region that occurs in the forearc domain offshore eastern Taiwan. Earthquakes distribute mainly along 2 active planes. The first one aligns along the subduction interface and the second one, shallower affects the overriding margin. Focal mechanisms within the shallow group indicate that nodal planes are either compatible with high-angle back-thrusts or low-angle thrusts. The active seismic deformation exclusively indicates reverse faulting revealing that the forearc basement undergoes trench-perpendicular strong compression. By integrating the seismological image into the regional context, we favor the hypothesis in which the dense seismicity occurring offshore marks the activity of en-échelon high-angle reverse faults accommodating the uplift of a broken piece of Ryukyu Arc basement, called Hoping Basement Rise. The uplift is inferred to be caused by the subduction of an oceanic relief, either exotic block, seamount or oceanic crust sliver. Our favored solution satisfies the narrowness of epicenter's cluster along the Hoping Canyon, and the observation of high-angle active faults on seismic lines crossing the area. Furthermore, this solution is compatible with the active uplift of the Hoping Rise demonstrated from morphological and sedimentological data. We do not exclude the branching of the high-angle reverse faults system onto a splay fault connected with the subduction interface but further investigations are needed to map precisely the 3D distribution of active faults that break the margin.

  3. A kinematic model for the formation of the Siletz-Crescent forearc terrane by capture of coherent fragments of the Farallon and Resurrection plates

    USGS Publications Warehouse

    McCrory, Patricia A.; Wilson, Douglas S.

    2013-01-01

    The volcanic basement of the Oregon and Washington Coast ranges has been proposed to represent a pair of tracks of the Yellowstone hotspot formed at a mid-ocean ridge during the early Cenozoic. This interpretation has been questioned on many grounds, especially that the range of ages does not match the offshore spreading rates and that the presence of continental coarse clastic sediments is difficult to reconcile with fast convergence rates between the oceanic plates and North America. Updates to basement geochronology and plate motion history reveal that these objections are much less serious than when they were first raised. Forward plate kinematic modeling reveals that predicted basement ages can be consistent with the observed range of about 55–49 Ma, and that the entire basement terrane can form within about 300 km of continental sources for clastic sediments. This kinematic model indicates that there is no firm reason to reject the near-ridge hotspot hypothesis on the basis of plate motions. A novel element of the model is the Resurrection plate, previously proposed to exist between the Farallon and Kula plates. By including the defunct Resurrection plate in our reconstruction, we are able to model the Farallon hotspot track as docking against the Oregon subduction margin starting about 53 Ma, followed by docking of the Resurrection track to the north starting about 48 Ma. Accretion of the Farallon plate fragment and partial subduction of the Resurrection fragment complicates the three-dimensional structure of the modern Cascadia forearc. We interpret the so-called “E” layer beneath Vancouver Island to be part of the Resurrection fragment. Our new kinematic model of mobile terranes within the Paleogene North American plate boundary allows reinterpretation of the three-dimensional structure of the Cascadia forearc and its relationship to ongoing seismotectonic processes.

  4. Geologic Assessment of Undiscovered Oil and Gas Resources of the North Cuba Basin, Cuba

    USGS Publications Warehouse

    Schenk, Christopher J.

    2010-01-01

    Petroleum generation in the North Cuba Basin is primarily the result of thrust loading of Jurassic and Cretaceous source rocks during formation of the North Cuba fold and thrust belt in the Late Cretaceous to Paleogene. The fold and thrust belt formed as Cuban arc-forearc rocks along the leading edge of the Caribbean plate translated northward during the opening of the Yucatan Basin and collided with the passive margin of southern North America in the Paleogene. Petroleum fluids generated during thrust loading migrated vertically into complex structures in the fold and thrust belt, into structures in the foreland basin, and possibly into carbonate reservoirs along the margins of the Yucatan and Bahama carbonate platforms. The U.S. Geological Survey (USGS) defined a Jurassic-Cretaceous Composite Total Petroleum System (TPS) and three assessment units (AU)-North Cuba Fold and Thrust Belt AU, North Cuba Foreland Basin AU, and the North Cuba Platform Margin Carbonate AU-within this TPS based mainly on structure and reservoir type (fig. 1). There is considerable geologic uncertainty as to the extent of petroleum migration that might have occurred within this TPS to form potential petroleum accumulations. Taking this geologic uncertainty into account, especially in the offshore area, the mean volumes of undiscovered resources in the composite TPS of the North Cuba Basin are estimated at (1) 4.6 billion barrels of oil (BBO), with means ranging from an F95 probability of 1 BBO to an F5 probability of 9 BBO; and (2) 8.6 trillion cubic feet of of gas (TCFG), of which 8.6 TCFG is associated with oil fields, and about 1.2 TCFG is in nonassociated gas fields in the North Cuba Foreland Basin AU.

  5. Definition and kinematics of the northern of the Puerto Rico-Virgin Islands block and the Lesser Antilles forearc based on an updated and improved GPS velocity field and revised block models

    NASA Astrophysics Data System (ADS)

    Mattioli, G. S.; Jansma, P. E.; Stafford-Glenn, M.; Calais, E.

    2011-12-01

    The presence of small tectonic blocks the Greater Antilles, for example the Puerto Rico-Virgin Islands block (PRVI), which may be translating, rotating, and possibly internally deforming, has been proposed and some cases well-documented by several workers. In addition, the existence of a Lesser Antilles forearc has been proposed based on interplate earthquake slip vectors (Lopez et al. 2006). Manaker et al. (2008) used sparse GPS and earthquake slip data from the northeastern Caribbean to construct a DEFNODE block and fault model to constrain interseismic fault coupling among the microplates in the northeastern Caribbean. They concluded that the Enriquillo fault in Haiti could produce a Mw7.2, if the entire accumulated elastic strain was released in one event. On January 12, 2010, the strain was released in a Mw7.0 earthquake that left Port-au-Prince in rubble. The interseismic GPS velocity field has been updated for Hispanolia (Calais et al, 2010); in addition, new data have been collected in the northern Lesser Antilles (NLA) in 2009 as well as throughout the PRVI block in 2007 and 2011, and the existing GPS time series updated and transformed into ITRF05 (IGS05). GPS data from the NLA are consistent with a NLA forearc sliver that moves differently from the Caribbean and North American plates as originally proposed by Lopez et al. (2006). The forearc does not, however, continue as single tectonic entity across the Anegada Passage as previously suggested. Here we report revised DEFNODE models using both the original geometry and constraints of Manaker et al. (2008) with an updated GPS data set as well as new models that explicitly include a forearc block. The models may be used to explicitly define the rotation parameters of the block as well as the coupling along block bounding faults. The original model geometry (without a forearc sliver) yields a higher reduced chi-squared (2.57 vs. 2.01), when additional the GPS velocities from NLA are used to condition the

  6. A tectonically controlled basin-fill within the Valle del Cauca, West-Central Colombia

    SciTech Connect

    Rine, J.M.; Keith, J.F. Jr.; Alfonso, C.A.; Ballesteros, I.; Laverde, F.; Sacks, P.E.; Secor, D.T. Jr. ); Perez, V.E.; Bernal, I.; Cordoba, F.; Numpaque, L.E. )

    1993-02-01

    Tertiary strata of the Valle del Cauca reflect a forearc/foreland basin tectonic history spanning a period from pre-uplift of the Cordillera Central to initiation of uplift of the Cordillera Occidental. Stratigraphy of the Valle del Cauca begins with Jurassic-Cretaceous rocks of exotic and/or volcanic provenance and of oceanic origin. Unconformably overlying these are Eocene to Oligocene basal quartz-rich sandstones, shallow marine algal limestones, and fine-grained fluvial/deltaic mudstones and sandstones with coalbeds. These Eocene to Oligocene deposits represent a period of low tectonic activity. During late Oligocene to early Miocene, increased tectonic activity produced conglomeratic sediments which were transported from east to west, apparently derived from uplift of the Cordillera Central, and deposited within a fluvial to deltaic setting. East-west shortening of the Valle del Cauca basin folded the Eocene to early Miocene units, and additional uplift of the Cordillera Central during the later Miocene resulted in syn-tectonic deposition of alluvial fans. After additional fold and thrust deformation of the total Eocene-Miocene basin-fill, tectonic activity abated and Pliocene-Quaternary alluvial and lacustrine strata were deposited. Within the framework of this depositional and tectonic history of the Valle del Cauca, hydrocarbon exploration strategies can be formulated and evaluated.

  7. The impact of structural deformation in a 2D basin and petroleum system model of the East Coast Basin, New Zealand

    NASA Astrophysics Data System (ADS)

    Burgreen, B.; Graham, S. A.; Meisling, K. E.

    2013-12-01

    The East Coast Basin of New Zealand is a petroliferous forearc basin that has eluded commercial development largely because of challenges related to its complex structural and tectonic history. Basin formation is associated with three tectonic phases: 1) a Cretaceous convergent margin phase, 2) a Late Cretaceous to Paleogene rifting to passive margin phase, and 3) a Neogene to present convergent margin phase. Beginning in Neogene time, the basin underwent multiple stages of structural deformation including low angle thrust faulting, listric normal faulting, and inversion. This complex basin history provides an ideal situation to test the influence of tectonics on petroleum system development. This study focuses on offshore Hawke Bay where a regional 2D seismic line has been interpreted, palinspastically reconstructed, and incorporated into a basin and petroleum system model. In the model, several paleo-heat flow scenarios are developed to represent the tectonic evolution of the basin. Higher heat flow is modeled during the rifting to passive margin phase, and a reduction in heat flow is modeled during the Neogene phase to account for cold slab subduction. Heat flow scenarios are calibrated to temperature, apatite-fission track data, and vitrinite-intertinite reflectance and fluorescence data from the Hawke Bay-1 and Opoutama-1 wells. The palinspastic reconstructions are integrated into the basin and petroleum system model to assess the impact of different styles of deformation. Faults play a key role in the burial history/rate of burial, fluid migration, and pressure compartmentalization. The relative timing of paleo-heat flow and structural events are tested in the model to understand how they enhance and/or negate effects on petroleum generation. For example, models with early Miocene low angle thrusts (i.e. structural thickening) contemporaneous with remnant high heat flow from the passive margin phase create a scenario for mid-Miocene petroleum generation

  8. Sedimentary Signature of the 26 December 2004 Mega Tsunami on the Eastern Coast of Banda Aceh, Indonesia P. Wassmer, F. Lavigne, J. Sartohadi, Ph. Baumert, R. Paris

    NASA Astrophysics Data System (ADS)

    Wassmer, P. C.; Franck, L.; Sartohadi, J.; Baumert, P.; Paris, R.

    2007-05-01

    The eastern part of Banda Aceh was hit by a series of waves with flow depth measured up to 15 meters. In the Kajuh district, at least seven waves were observed by eyewitnesses. They emplaced sand deposits up to 80cm in thickness. We carried out a sedimentological study of these deposits along a 2km long transect oriented according to the main run up flow direction. The sedimentary signature of the tsunami moving landward shows a succession of sequences of normally graded deposit, except for the ungraded basal layer. Close to the shoreline only one or two sequences can be observed. The number of sequences increases progressively landward to reach a maximum of seven up to 2km from the former shoreline. Further inland, the thickness of the deposits is very limited. The sequences are attributed to sediment pulses related to each new wave reaching our investigation sites. Each pulsation corresponds to the arrival of a wave front. The high turbulence led to the deposit of the coarse basal material of each sequence. At the end of each pulse the decreasing of the energy allowed deposition of the finer material. The basal layer, which is undoubtedly related to the first wave, seems to have been truncated by the second and highest wave. This explains the absence of the fine material at the top of the basal layer. Close to the shoreline, the high energy of each new wave, and probably of the backwash, may explain the small amount of sedimentary sequences.The energy decreasing 2km from the shoreline allows each wave to sign his passage, emplacing a new sequence. This sedimentary record is of high interest for its exceptional number of sequences rarely observed so far. Such recording is to be related to several factors: the succession of several high waves progressing far inland, the presence on the shore of a stock of heterometric sediments easily removable, a flat topography which reduced the turbulence of the incoming flows. However, we put in light the key role played by the

  9. Evolution of the late Paleozoic accretionary complex and overlying forearc-magmatic arc, south central Chile (38°-41°S): Constraints for the tectonic setting along the southwestern margin of Gondwana

    NASA Astrophysics Data System (ADS)

    Martin, Mark W.; Kato, Terence T.; Rodriguez, Carolina; Godoy, Estanislao; Duhart, Paul; McDonough, Michael; Campos, Alberto

    1999-08-01

    lithologies from Late Triassic shallow marine to continental deposits suggests that substantial uplift also affected the inner forearc and magmatic arc region during the D2 event. We propose that dextral-oblique convergence, initiated during the middle Permian along this segment of the Gondwana margin, resulted in the transpressional uplift and juxtaposition of high pressure/temperature (P/T) Western Series against low P/T Eastern Series lithologies and culminated with deposition of Late Triassic, continental to shallow marine, coarse clastic sedimentary rocks in fault-bounded strike-slip basins adjacent to the exhumed Western Series. Large-scale dextral transpression and northward displacement of the accretionary complex during Late Permian to Late Triassic time along the Chilean margin of Gondwana are synchronous and kinematically compatible with widespread regional transpression, extension, and silicic magmatism inboard of the southern Gondwana margin at this time. We thank C. Mpodozis, M. Gardeweg, and J. Muñoz of the Servicio de Geología y Minería de Chile (SERNAGEOMIN) for their support of this work. Fruitful discussions with N. Blanco, F. Hervé, H. Moreno, C. Mpodozis, and F. Munizaga have aided in our understanding of the geology of the region. The hard work by the staff of SERNAGEOMIN's Puerto Varas office is graciously appreciated. We thank J.D. Walker and W.R. Van Schmus at the University of Kansas for allowing MWM use of their U-Pb and mass spectrometer facilities and J. Vargas and the staff of SERNAGEOMIN's geochemistry laboratory for their assistance in this project. F. Munizaga allowed us to cite an unpublished 40Ar-39Ar date. We thank G. Ya˜nez for access to aeromagnetic data. T. Kato wishes to thank W. G. Ernst. Comments by I. Dalziel, S. Kay, and V. Ramos helped clarify ideas presented in this paper and are greatly appreciated. This work is dedicated to our friend and colleague Alberto Campos C., who died in a climbing accident on Calbuco Volcano, 1996.

  10. Reserves in western basins

    SciTech Connect

    Caldwell, R.H.; Cotton, B.W.

    1992-06-01

    This project requires generation of producible tight gas sand reserve estimates for three western basins. The requirement is to perform such reserve estimates using industry accepted practices so that results will have high credibility and acceptance by the oil and gas industry. The ultimate goal of the project is to encourage development of the tight gas formation by industry through reduction of the technical and economic risks of locating, drilling and completing commercial gas wells. The three geological basins selected for study are the Greater Green River Basin, Uinta Basin and Piceance Basin, located in the Colorado, Utah and Wyoming Rocky Mountain region.

  11. Reserves in western basins

    SciTech Connect

    Caldwell, R.H.; Cotton, B.W.

    1992-01-01

    This project requires generation of producible tight gas sand reserve estimates for three western basins. The requirement is to perform such reserve estimates using industry accepted practices so that results will have high credibility and acceptance by the oil and gas industry. The ultimate goal of the project is to encourage development of the tight gas formation by industry through reduction of the technical and economic risks of locating, drilling and completing commercial gas wells. The three geological basins selected for study are the Greater Green River Basin, Uinta Basin and Piceance Basin, located in the Colorado, Utah and Wyoming Rocky Mountain region.

  12. Seismic structure and activity of the north-central Lesser Antilles subduction zone from an integrated approach: Similarities with the Tohoku forearc

    NASA Astrophysics Data System (ADS)

    Laigle, M.; Hirn, A.; Sapin, M.; Bécel, A.; Charvis, P.; Flueh, E.; Diaz, J.; Lebrun, J.-F.; Gesret, A.; Raffaele, R.; Galvé, A.; Evain, M.; Ruiz, M.; Kopp, H.; Bayrakci, G.; Weinzierl, W.; Hello, Y.; Lépine, J.-C.; Viodé, J.-P.; Sachpazi, M.; Gallart, J.; Kissling, E.; Nicolich, R.

    2013-09-01

    The 300-km-long north-central segment of the Lesser Antilles subduction zone, including Martinique and Guadeloupe islands has been the target of a specific approach to the seismic structure and activity by a cluster of active and passive offshore-onshore seismic experiments. The top of the subducting plate can be followed under the wide accretionary wedge by multichannel reflection seismics. This reveals the hidden updip limit of the contact of the upper plate crustal backstop onto the slab. Two OBS refraction seismic profiles from the volcanic arc throughout the forearc domain constrain a 26-km-large crustal thickness all along. In the common assumption that the upper plate Moho contact on the slab is a proxy of its downdip limit these new observations imply a three times larger width of the potential interplate seismogenic zone under the marine domain of the Caribbean plate with respect to a regular intra-oceanic subduction zone. Towards larger depth under the mantle corner, the top of the slab imaged from the conversions of teleseismic body-waves and the locations of earthquakes appears with kinks which increase the dip to 10-20° under the forearc domain, and then to 60° from 70 km depth. At 145 km depth under the volcanic arc just north of Martinique, the 2007 M 7.4 earthquake, largest for half a century in the region, allows to document a deep slab deformation consistent with segmentation into slab panels. In relation with this occurrence, an increased seismic activity over the whole depth range provides a new focussed image thanks to the OBS and land deployments. A double-planed dipping slab seismicity is thus now resolved, as originally discovered in Tohoku (NE Japan) and since in other subduction zones. Two other types of seismic activity uniquely observed in Tohoku, are now resolved here: "supraslab" earthquakes with normal-faulting focal mechanisms reliably located in the mantle corner and "deep flat-thrust" earthquakes at 45 km depth on the interplate

  13. Sequence stratigraphy, tectonics and hydrocarbon trap geometries of Middle Tertiary strata in the southern San Joaquin Basin, California

    SciTech Connect

    Phillips, S.; Hewlett, J.S.; Bazeley, W.J.M.

    1996-12-31

    Tectonic evolution of the southern San Joaquin basin exerted a fundamental control on Cenozoic sequence boundary development, reservoir, source and seal facies distribution, and hydrocarbon trap development. Spatial and temporal variations in Tertiary sequence architecture across the basin reflect differences in eastside versus westside basin-margin geometries and deformation histories. Deposition of Tertiary sequences initiated in a forearc basin setting, bounded on the east by a ramp-margin adjacent to the eroded Sierran arc complex and on the west by the imbricated accretionary wedge of the Coast Ranges thrust. The major stages of Cenozoic basin evolution are: (1) Episodic compressional folding and thrusting associated with oblique convergence of the Farallon and North American plates (Late Cretaceous to Oligocene), (2) localized folding and onset of basin subsidence related to Pacific Plate reorganization, microplate formation and rotation (Oligocene to Early Miocene), (3) transtensional faulting, folding basin subsidence associated with initiation of the San Andreas transform and continued microplate rotation (Micocene to Pliocene), and (4) compressional folding, extensional and strike- slip faulting related to evolution of the Pacific-North American transform boundary (Plio- Pleistocene). Complex stratigraphic relationships within Eocene to Middle Miocene rocks provide examples of tectonic influences on sequence architecture. These include development of: (1) Tectonically enhanced sequence boundaries (Early Eocene base Domengine unconformity) and local mid-sequence angular unconformities, (2) westside-derived syntectonic {open_quotes}lowstand{close_quotes} systems (Yokut/Turitella Silt wedge and Leda Sand/Cymric/Salt Creek wedge), (3) regional seals associated with subsidence-related transgressions (Round Mountain Silt), and (4) combination traps formed by structural inversion of distal lowstand delta reservoirs (e.g. Coalinga East Extension field).

  14. Sequence stratigraphy, tectonics and hydrocarbon trap geometries of Middle Tertiary strata in the southern San Joaquin Basin, California

    SciTech Connect

    Phillips, S.; Hewlett, J.S. ); Bazeley, W.J.M.

    1996-01-01

    Tectonic evolution of the southern San Joaquin basin exerted a fundamental control on Cenozoic sequence boundary development, reservoir, source and seal facies distribution, and hydrocarbon trap development. Spatial and temporal variations in Tertiary sequence architecture across the basin reflect differences in eastside versus westside basin-margin geometries and deformation histories. Deposition of Tertiary sequences initiated in a forearc basin setting, bounded on the east by a ramp-margin adjacent to the eroded Sierran arc complex and on the west by the imbricated accretionary wedge of the Coast Ranges thrust. The major stages of Cenozoic basin evolution are: (1) Episodic compressional folding and thrusting associated with oblique convergence of the Farallon and North American plates (Late Cretaceous to Oligocene), (2) localized folding and onset of basin subsidence related to Pacific Plate reorganization, microplate formation and rotation (Oligocene to Early Miocene), (3) transtensional faulting, folding basin subsidence associated with initiation of the San Andreas transform and continued microplate rotation (Micocene to Pliocene), and (4) compressional folding, extensional and strike- slip faulting related to evolution of the Pacific-North American transform boundary (Plio- Pleistocene). Complex stratigraphic relationships within Eocene to Middle Miocene rocks provide examples of tectonic influences on sequence architecture. These include development of: (1) Tectonically enhanced sequence boundaries (Early Eocene base Domengine unconformity) and local mid-sequence angular unconformities, (2) westside-derived syntectonic [open quotes]lowstand[close quotes] systems (Yokut/Turitella Silt wedge and Leda Sand/Cymric/Salt Creek wedge), (3) regional seals associated with subsidence-related transgressions (Round Mountain Silt), and (4) combination traps formed by structural inversion of distal lowstand delta reservoirs (e.g. Coalinga East Extension field).

  15. A slow-slipping active fold and thrust system at the SE corner of the Atacama basin, northern Chile

    NASA Astrophysics Data System (ADS)

    Lin, Y.; Shyu, J. H.; González, G.

    2009-12-01

    The western South American offshore is one of the major active convergent plate boundaries in the world, where the Nazca plate is subducting northeastward beneath the South American plate at a rate of about 84 mm/yr. Despite of this rapid plate convergence, the forearc region of western Andes does not seem to undergo large deformation at present. In order to understand the characteristics and mechanisms of active forearc deformation related to the plate convergence, we investigated tectono-geomorphic features in the area of Tilocalar, near the SE margin of the Atacama Basin in northern Chile, where active structures have been previously identified. To map topographic features produced by active structures, we used a combination of several remote-sensing data sets, including digital elevation models (DEM) made from Shuttle Radar Topographic Mission (SRTM), as well as higher resolution ASTER and QuickBird satellite images. Detailed geomorphic surveys using real time kinematic (RTK) GPS are carried out in the field to obtain high-resolution topographic profiles across these features. We also performed 40Ar/39Ar dating of deformed volcanic rocks in order to determine the long-term slip rates of the active structures. The hyper-aridity of the Atacama Basin results in extremely low erosion and sedimentation rates in the area. As a result, the present relief of land surface is mostly produced by neotectonic activity, and can be used as deformation marker. In the Tilocalar area, several N-S trending ridges are present. These ridges, generally several tens of meters high, are likely formed by asymmetric anticlines or monoclines with steep forelimbs facing east, and these folds are likely fault-propagation folds produced by underlying thrust faults. We suggest that these faults merge at depth to become a major active thrust system. From 40Ar/39Ar plateau ages, we found that the surface ignimbrites mostly deposited in latest Pliocene (2.3~4.3 Ma). If the structures have been

  16. Tectonic evolution of forearc nappes of the active Banda arc-continent collision: Origin, age, metamorphic history and structure of the Lolotoi Complex, East Timor

    NASA Astrophysics Data System (ADS)

    Standley, Carl E.; Harris, Ron

    2009-12-01

    An integrated multidisciplinary investigation of the Lolotoi Complex of East Timor (Timor Leste) indicates that it is part of the Banda forearc that was metamorphosed and rapidly exhumed during the Eocene and accreted to the NW Australian continental margin during Late Miocene to present arc-continent collision. Greenschist, graphitic phyllite, quartz-mica schist, amphibolite and pelitic schist dominate metamorphic rock types. Mineral, whole rock, and trace element geochemical analyses of metabasites indicate protolith compositions consistent with tholeiitic basalt and basaltic andesite with mixed MORB and oceanic arc affinities. Metapelite schist is mostly composed of metasedimentary units derived from mafic to intermediate rocks with oceanic to continental volcanic arc provenance. Thermobarometric calculations show peak metamorphic conditions of 530 °C to 680 °C for garnet-biotite pairs and amphibole, and peak pressures of 5 to 10 kbar for garnet-aluminosilicate-quartz-plagioclase assemblages. Peak metamorphism occurred at 45.36 ± 0.63 Ma, as indicated by Lu-Hf analyses of garnet. Detrital zircon grains have a U/Pb age distribution with spikes at 663, 120 and 87 Ma, which is typical of detrital zircon ages throughout the Great Indonesian Arc of Asia, but is distinct from Australian affinity units. These data indicate deposition and later metamorphism occurred after 87 Ma. Structural analyses of the metamorphic rocks and their sedimentary and volcanic cover units reveals 5-6 deformational phases of alternating shortening and extension. There is little to no evidence of strike-slip deformation. Phases 1-4 are inferred as pre-Oligocene from age determinations. Phases 5 and 6 are most likely related to latest Miocene to Pliocene nappe emplacement and Pliocene to present collisional deformation. Kinematic indicators show mostly top to the SE directed shortening and top to the south and SE extension. Structural mapping indicates that the Lolotoi Complex and some of

  17. Zircon U-Pb age of the Pescadero felsite: A late Cretaceous igneous event in the forearc, west-central California Coast Ranges

    USGS Publications Warehouse

    Ernst, W.G.; Martens, U.C.; McLaughlin, R.J.; Clark, J.C.; Moore, Diane E.

    2011-01-01

    forearc units of the Transverse Ranges. Based on zircon U-Pb ages, geologic and petrographic relations, the Pescadero felsite and a capping, sheared metaconglomerate underlie the Pigeon Point Formation. We infer that the magma formed by anatexis of Franciscan or Great Valley clastic sedimentary rocks originating from a parental Mesozoic Sierran-Mojave-Salinian calcalkaline arc. The felsite erupted during Late Cretaceous time, was metamorphosed to pumpellyite-prehnite grade within the subduction zone, and then was rapidly exhumed, weakly zeolitized, and exposed before Pigeon Point forearc deposition. Pescadero vol canism apparently reflects a previously unrecognized ca. 86-90 Ma felsic igneous event in the accretionary margin. ?? 2011 Geological Society of America.

  18. Geochemical and Tectonic Evidence for the Role of Crustal Thickening and Forearc Subduction Erosion in Miocene to Recent Andean Southern Volcanic Zone Magmas

    NASA Astrophysics Data System (ADS)

    Kay, S. M.; Godoy, E.

    2002-12-01

    Key to understanding temporal and spatial variations in Andean-type margin magmas is identifying their mantle and crustal sources in well constrained tectonic settings. A study of Andean Southern Volcanic Zone (SVZ) Early Miocene to Recent magmas in an west to east transect near 34° S points to a linked role for crustal thickening and forearc subduction erosion. The whole rock and isotopic chemistry of these magmas show a trend from Early Miocene tholeiitic sequences with low pressure pyroxene-bearing residual mineral assemblages and more depleted isotopic signatures (87Sr/^{86}Sr ~ 0.7036; ɛ Nd ~ +6 to +4; 206Pb/^{204}Pb ~ 18.5) to Pliocene/Recent high-K calc-alkaline sequences with high pressure garnet-bearing residual mineral assemblages and enriched isotopic signatures (87Sr/^{86}Sr ~ 0.7042; ɛ Nd ~ +1 to 0; 206Pb/^{204}Pb ~ 18.6). Relatively abrupt breaks in this sequence at ~ 19 to 15 Ma and ~ 7 to 4 Ma coincide with an early Miocene extensional to compressional deformational switch and major Late Miocene out-of-sequence thrusting that accompany eastward shifts of ~ 35 and ~ 50 km of the arc front and peaks in uplift history. These changes are consistent with peaks in forearc subduction erosion that introduce continental crust into subcrustal magma sources and in backarc shortening that enhance MASH processes in a thickening crust. Shifts to higher pressure chemical signatures and isotopic enrichment as frontal arc magmatism wanes in the west and migrates eastward fit with continental crust entering subcrustal magma sources. The projections of extinct arc fronts near 34° S into chemically equivalent units to the south indicate an ~ 35 km shift of the arc front north of 36.5° S at ~ 19 to 15 Ma and another ~ 50 km shift north of 34.5° S between ~ 7 to 4 Ma. These SVZ shifts coincide with major tectonic changes along the Andean margin that are best related to variations in plate convergence parameters.

  19. Divergent/passive margin basins

    SciTech Connect

    Edwards, J.D. ); Santogrossi, P.A. )

    1989-01-01

    This book discusses the detailed geology of the four divergent margin basins and establishes a set of analog scenarios which can be used for future petroleum exploration. The divergent margin basins are the Campos basin of Brazil, the Gabon basin, the Niger delta, and the basins of the northwest shelf of Australia. These four petroleum basins present a wide range of stratigraphic sequences and structural styles that represent the diverse evolution of this large and important class of world petroleum basins.

  20. Meso- and microscale vein structures in fore-arc basalts and boninites related to post-magmatic tectonic deformation in the outer Izu-Bonin-Mariana fore arc system: preliminary results from IODP Expedition 352

    NASA Astrophysics Data System (ADS)

    Quandt, Dennis; Micheuz, Peter; Kurz, Walter

    2016-04-01

    The International Ocean Discovery Program (IODP) Expedition 352 aimed to drill through the entire volcanic sequence of the Izu-Bonin-Mariana fore arc. Two drill sites are situated on the outer fore arc composed of fore arc basalts (FAB) whereas two more sites are located on the upper trench slope penetrating the younger boninites. First results from IODP Expedition 352 and preliminary post-cruise data suggest that FAB were generated by decompression melting during near-trench sea-floor spreading, and that fluids from the subducting slab were not involved in their genesis. Subduction zone fluids involved in boninite genesis appear to have been derived from progressively higher temperatures and pressures over time as the subducting slab thermally matured. Structures within the drill cores combined with borehole and site survey seismic data indicate that tectonic deformation in the outer Izu-Bonin-Mariana fore arc is mainly post-magmatic associated with the development of syn-tectonic sedimentary basins. Within the magmatic basement deformation was accommodated by shear along cataclastic fault zones and the formation of tension fractures, shear fractures and hybrid (tension and shear) fractures. Veins form by mineral filling of tension or hybrid fractures and show no or limited observable macroscale displacement along the fracture plane. (Low Mg-) Calcite and/or various types of zeolite are the major vein constituents, where the latter are considered to be alteration products of basaltic glass. Micrite contents vary significantly and are related to neptunian dikes. In boninites calcite develops mainly blocky shapes but veins with fibrous and stretched crystals also occur in places indicating antitaxial as well as ataxial growth, respectively. In FAB calcite forms consistently blocky crystals without any microscopic identifiable growth direction suggesting precipitation from a highly supersaturated fluid under dropping fluid pressure conditions. However, fluid pressure

  1. The distinct hydrogeological system of the forearc of the Middle America Trench: significance for long-term tectonics and updip limit of the interplate seismogenic zone.

    NASA Astrophysics Data System (ADS)

    Ranero, C. R.; Grevemeyer, I.; Sahling, H.; Barckhausen, U.; Hensen, C.; Wallmann, K.; Weinrebe, W.

    2008-12-01

    The distribution and flow of fluid has been widely studied at accretionary prisms, but at convergent margins where tectonic erosion affects overriding plates fluid distribution and tectonics are far less understood. Observations along the erosional subduction zone of Middle America Trench indicates a hydrogeological system distinctly different from those that have been described at accretionary prisms. The hydrogeological system has been studied by: 1) compiling an inventory of focused seepage sites at the seafloor using a multiscale mapping approach, sequentially applying methods of increasing spatial resolution during successive ship cruises, 2) mapping the relative distribution of fluid at the plate boundary with seismic data, and 3) calculating the forearc fluid budget after estimating flow rates from thermal structure and pore fluid chemistry. Most fluid originally contained at the plate boundary migrates by focused flow across a fractured overriding plate, contrasting with conceptual models of accretionary margins where the decollement has been inferred to be the main fluid flow conduit. The distribution of fluid created by the hydrogeological system influences the locus of long-term tectonic erosion determining which areas of the margin are tectonically thinned. Where fluid is more abundant along the plate boundary, the overriding plate is being actively thinned, and fractures and subsides to form the continental slope. Also, the transition with depth from aseismic to the area of nucleation of earthquakes along the plate boundary appears related to fluid distribution. Earthquakes nucleate where fluid appears to be less abundant indicating a first order control on subduction zone thrust earthquakes.

  2. Deep long-period earthquakes west of the volcanic arc in Oregon: evidence of serpentine dehydration in the fore-arc mantle wedge

    USGS Publications Warehouse

    Vidale, John E.; Schmidt, David A.; Malone, Stephen D.; Hotovec-Ellis, Alicia J.; Moran, Seth C.; Creager, Kenneth C.; Houston, Heidi

    2014-01-01

    Here we report on deep long-period earthquakes (DLPs) newly observed in four places in western Oregon. The DLPs are noteworthy for their location within the subduction fore arc: 40–80 km west of the volcanic arc, well above the slab, and near the Moho. These “offset DLPs” occur near the top of the inferred stagnant mantle wedge, which is likely to be serpentinized and cold. The lack of fore-arc DLPs elsewhere along the arc suggests that localized heating may be dehydrating the serpentinized mantle wedge at these latitudes and causing DLPs by dehydration embrittlement. Higher heat flow in this region could be introduced by anomalously hot mantle, associated with the western migration of volcanism across the High Lava Plains of eastern Oregon, entrained in the corner flow proximal to the mantle wedge. Alternatively, fluids rising from the subducting slab through the mantle wedge may be the source of offset DLPs. As far as we know, these are among the first DLPs to be observed in the fore arc of a subduction-zone system.

  3. Northwest Basin and Range tectonic deformation observed with the Global Positioning System, 1999-2003

    USGS Publications Warehouse

    Hammond, W.C.; Thatcher, W.

    2005-01-01

    We use geodetic velocities obtained with the Global Positioning System (GPS) to quantify tectonic deformation of the northwest Basin and Range province of the western United States. The results are based on GPS data collected in 1999 and 2003 across five new quasi-linear networks in northern Nevada, northeast California, and southeast Oregon. The velocities show ???3 mm/yr westward movement of northern Nevada with respect to stable North America. West of longitude 119??W the velocities increase and turn northwest, parallel to Sierra Nevada/Great Valley microplate motion, and similar to velocities previously obtained to the south. The observations are explained by a kinematic model with three domains that rotate around Euler poles in eastern Oregon and western Idaho. Northeast California experiences internal dextral shear deformation (11.2 ?? 3.6 nstrain/yr) subparallel to Pacific/North America motion. Relative motions of the domains imply 2-5 mm/yr approximately east-west extension in northwest Nevada and 1-4 mm/yr approximately north-south contraction near the California/Oregon border. The northward decreasing approximately east-west extension in northwest Nevada is consistent with the northern termination of Basin and Range deformation, faulting and characteristic topography. No significant extension is detected in the Oregon Basin and Range. The Oregon Cascade arc moves north at ???3.5 mm/yr and is possibly influenced by the approximately eastward motion of the Juan de Fuca plate. These results disagree with secular northwest trenchward motion of the Oregon forearc inferred from paleomagnetic rotations. South of latitude 43??, however, trenchward motion exists and is consistent with block rotations, approximately east-west Basin and Range extension, and northwest Sierra Nevada translation. Copyright 2005 by the American Geophysical Union.

  4. Origin of cratonic basins

    NASA Astrophysics Data System (ADS)

    Dev. Klein, George; Hsui, Albert T.

    1987-12-01

    Tectonic subsidence curves show that the Illinois, Michigan, and Williston basins formed by initial fault-controlled mechanical subsidence during rifting and by subsequent thermal subsidence. Thermal subsidence began around 525 Ma in the Illinois Basin, 520 460 Ma in the Michigan Basin, and 530 500 Ma in the Williston Basin. In the Illinois Basin, a second subsidence episode (middle Mississippian through Early Permian) was caused by flexural foreland subsidence in response to the Alleghanian-Hercynian orogeny. Resurgent Permian rifting in the Illinois Basin is inferred because of intrusion of well-dated Permian alnoites; such intrusive rocks are normally associated with rifting processes. The process of formation of these cratonic basins remains controversial. Past workers have suggested mantle phase changes at the base of the crust, mechanical subsidence in response to isostatically uncompensated excess mass following igneous intrusions, intrusion of mantle plumes into the crust, or regional thermal metamorphic events as causes of basin initiation. Cratonic basins of North America, Europe, Africa, and South America share common ages of formation (around 550 to 500 Ma), histories of sediment accumulation, temporal volume changes of sediment fills, and common dates of interregional unconformities. Their common date of formation suggests initiation of cratonic basins in response to breakup of a late Precambrian super-continent. This supercontinent acted as a heat lens that caused partial melting of the lower crust and upper mantle followed by emplacement of anorogenic granites during extensional tectonics in response to supercontinent breakup. Intrusion of anorogenic granites and other partially melted intrusive rocks weakened continental lithosphere, thus providing a zone of localized regional stretching and permitting formation of cratonic basins almost simultaneously over sites of intrusion of these anorogenic granites and other partially melted intrusive rocks.

  5. The Oquirrh basin revisited

    SciTech Connect

    Erskine, M.C.

    1997-04-01

    The upper Paleozoic succession in the Oquirrh basin in unusually thick, up to 9300 m, and consists mainly of a Pennsylvanian-middle Permian miogeocline of northwestern Utah. Previous workers have suggested a tectonic origin for the Oquirrh basin that is incompatible with the basin location in both time and space. There is no evidence for Pennsylvanian and Lower Permian tectonism in the middle of the miogeocline. Thermal evidence from the Mississippian Mission Canyon shale does no support the implied deep burial of the crustal sag models of basin formation. Stratigraphic and facies evidence indicates a growth fault origin for the basin. Regional isopach maps and facies maps are powerful tools in interpreting depositional environments and in reconstructing fold-and-thrust belts. However, the location of measured sections relative to the location of the growth fault basin. The Charleston-Nebo thrust may have essentially reversed the movement on a growth fault. Thick Oquirrh basin sedimentary rocks may not be required to balance structural sections across this thrust fault. A thin-skinned, extensional growth fault origin for the Oquirrh basin implies that the Cordilleran miogeocline did not participate in the Pennsylvanian north-vergent uplifts of the Ancestral Rocky Mountains.

  6. K Basin safety analysis

    SciTech Connect

    Porten, D.R.; Crowe, R.D.

    1994-12-16

    The purpose of this accident safety analysis is to document in detail, analyses whose results were reported in summary form in the K Basins Safety Analysis Report WHC-SD-SNF-SAR-001. The safety analysis addressed the potential for release of radioactive and non-radioactive hazardous material located in the K Basins and their supporting facilities. The safety analysis covers the hazards associated with normal K Basin fuel storage and handling operations, fuel encapsulation, sludge encapsulation, and canister clean-up and disposal. After a review of the Criticality Safety Evaluation of the K Basin activities, the following postulated events were evaluated: Crane failure and casks dropped into loadout pit; Design basis earthquake; Hypothetical loss of basin water accident analysis; Combustion of uranium fuel following dryout; Crane failure and cask dropped onto floor of transfer area; Spent ion exchange shipment for burial; Hydrogen deflagration in ion exchange modules and filters; Release of Chlorine; Power availability and reliability; and Ashfall.

  7. Interplay between regional uplift and glacio-eustasy in the Crotone Basin (Calabria, southern Italy) since 0.45 Ma: A review

    NASA Astrophysics Data System (ADS)

    Zecchin, Massimo; Caffau, Mauro; Ceramicola, Silvia

    2016-08-01

    During the last 0.45 Ma, the Crotone Basin, a forearc basin located on the Ionian side of Calabria, southern Italy, experienced a phase of uplift that persists today. The transition from subsidence to uplift occurred close to the Marine Isotope Stage (MIS) 11 (ca. 0.4 Ma). The subsequent progressive emergence of the area was punctuated by several marine transgressions linked to high-frequency, high-magnitude glacio-eustatic changes, which are recorded as coastal terraces. These high-frequency sequences show a variable stacking pattern due to the interplay between glacio-eustasy, uplift and local physiography. In particular, a progressive SE-ward migration of the shoreline is documented in the study area since MIS 11. This trend was enhanced during the MIS 5.5 to MIS 2 time interval, due to the combined effect of uplift and lowering glacio-eustatic sea level until the Last Glacial Maximum. Moreover, the regional uplift also led to a physiographic change from relatively low-gradient to high-gradient settings between MIS 7.1 and MIS 5.5. A comparison between the late Quaternary geological record of the Crotone Basin and that of other basins is crucial to improve the present knowledge on past sea levels related to MISs. This ultimately will help to better understand the Holocene sea-level history and the human contribution to sea-level change, in order to predict future scenarios.

  8. Paleomagnetic rotation pattern of the southern Chile fore-arc sliver (38°S-42°S): A new tool to evaluate plate locking along subduction zones

    NASA Astrophysics Data System (ADS)

    Hernandez-Moreno, Catalina; Speranza, Fabio; Di Chiara, Anita

    2016-02-01

    The Chile fore arc at 37°S-47°S represents the coseismic deformation zone of the 1960 Mw 9.5 Valdivia earthquake. Here we report on the paleomagnetism of 43 Oligocene-Pleistocene volcanic sites from the fore-arc sliver between 38°S and 42°S. Sites were gathered west of the 1000 km long Liquiñe-Ofqui dextral fault zone (LOFZ) that represents the eastern fore-arc sliver boundary. Nineteen reliable sites reveal that the fore arc is characterized by counterclockwise (CCW) rotations of variable magnitude, except at 40°S-41°S, where ultrafast (>50°/Myr) clockwise (CW) rotations occur within a 30 km wide zone adjacent to the LOFZ. CCW rotation variability (even at close sites) and rapidity (>10°/Myr) suggest that the observed block rotation pattern is related to NW-SE seismically active sinistral faults crosscutting the whole fore arc. According to previously published data, CW rotations up to 170° also occur east of the LOFZ and have been related to ongoing LOFZ shear. We suggest that the occurrence and width of the eastern fore-arc sliver undergoing CW rotations is a function of plate coupling along the subduction zone interface. Zones of high coupling enhance stress normal to the LOFZ, induce high LOFZ strength, and yield a wide deformation zone characterized by CW rotations. Conversely, low coupling imply a weak LOFZ, a lack of CW rotations, and a fore arc entirely dominated by CCW rotations related to sinistral fault kinematics. Our locking inferences are in good agreement with those recently derived by GPS analysis and indicate that seismotectonic segment coupling has remained virtually unchanged during the last 5 Ma.

  9. Reserves in western basins

    SciTech Connect

    Caldwell, R.H.; Cotton, B.W.

    1995-04-01

    The objective of this project is to investigate the reserves potential of tight gas reservoirs in three Rocky Mountain basins: the Greater Green River (GGRB), Uinta and Piceance basins. The basins contain vast gas resources that have been estimated in the thousands of Tcf hosted in low permeability clastic reservoirs. This study documents the productive characteristics of these tight reservoirs, requantifies gas in place resources, and characterizes the reserves potential of each basin. The purpose of this work is to promote understanding of the resource and to encourage its exploitation by private industry. At this point in time, the GGRB work has been completed and a final report published. Work is well underway in the Uinta and Piceance basins which are being handled concurrently, with reports on these basins being scheduled for the middle of this year. Since the GGRB portion of the project has been completed, this presentation win focus upon that basin. A key conclusion of this study was the subdivision of the resource, based upon economic and technological considerations, into groupings that have distinct properties with regard to potential for future producibility, economics and risk profile.

  10. Paleozoic evolution of active margin basins in the southern Central Andes (northwestern Argentina and northern Chile)

    NASA Astrophysics Data System (ADS)

    Bahlburg, H.; Breitkreuz, C.

    originated as an extensional structure at the continental margin of Gondwana. Independent lines of evidence imply that basin evolution was not connected to subduction. Thus, the basin could not have been in a fore-arc position as previously postulated. Above the folded Devonian-Early Carboniferous strata, a continental volcanic arc developed from the Late Carboniferous to the Middle Triassic. It represents the link between the Choiyoi Province in central Chile and Argentina, and the Mitu Group rift in southern Peru. The volcanic arc succession is characterized by the prevalence of silicic lavas and tuffs and volcaniclastic sedimentary rocks. During the latest Carboniferous, a thick ostracod-bearing lacustrine unit formed in an extended lake in the area of the Depresión Preandina. This lake basin originated in an intra-arc tensional setting. During the Early Permian, marine limestones were deposited on a marine platform west and east of the volcanic arc, connected to the depositional area of the Copacabana Formation in southern Peru.

  11. K Basin Hazard Analysis

    SciTech Connect

    PECH, S.H.

    2000-08-23

    This report describes the methodology used in conducting the K Basins Hazard Analysis, which provides the foundation for the K Basins Final Safety Analysis Report. This hazard analysis was performed in accordance with guidance provided by DOE-STD-3009-94, Preparation Guide for U. S. Department of Energy Nonreactor Nuclear Facility Safety Analysis Reports and implements the requirements of DOE Order 5480.23, Nuclear Safety Analysis Report.

  12. K Basins Hazard Analysis

    SciTech Connect

    WEBB, R.H.

    1999-12-29

    This report describes the methodology used in conducting the K Basins Hazard Analysis, which provides the foundation for the K Basins Safety Analysis Report (HNF-SD-WM-SAR-062, Rev.4). This hazard analysis was performed in accordance with guidance provided by DOE-STD-3009-94, Preparation Guide for U. S. Department of Energy Nonreactor Nuclear Facility Safety Analysis Reports and implements the requirements of DOE Order 5480.23, Nuclear Safety Analysis Report.

  13. Transition of magma genesis estimated by change of chemical composition of Izu-bonin arc volcanism associated with spreading of Shikoku Basin

    NASA Astrophysics Data System (ADS)

    Haraguchi, S.; Ishii, T.

    2006-12-01

    Arc volcanism in the Izu-Ogasawara arc is separated into first and latter term at the separate of Shikoku Basin. Middle to late Eocene early arc volcanism formed a vast terrane of boninites and island arc tholeiites that is unlike active arc systems. A following modern-style arc volcanism was active during the Oligocene, along which intense tholeiitic and calc-alkaline volcanism continued until 29Ma, before spreading of the back- arc basin. The recent arc volcanism in the Izu-Ogasawara arc have started in the middle Miocene, and it is assumed that arc volcanism were decline during spreading of back-arc basin. In the northern Kyushu-Palau Ridge, submarine bottom materials were dredged during the KT95-9 and KT97-8 cruise by the R/V Tansei-maru, Ocean Research Institute, university of Tokyo, and basaltic to andesitic volcanic rocks were recovered during both cruise except for Komahashi-Daini Seamount where recovered acidic plutonic rocks. Komahashi-Daini Seamount tonalite show 37.5Ma of K-Ar dating, and this age indicates early stage of normal arc volcanism. These volcanic rocks are mainly cpx basalt to andesite. Two pyroxene basalt and andesite are only found from Miyazaki Seamount, northern end of the Kyushu-Palau Ridge. Volcanic rocks show different characteristics from first term volcanism in the Izu-Ogasawara forearc rise and recent arc volcanism. The most characteristic is high content of incompatible elements, that is, these volcanics show two to three times content of incompatible elements to Komahashi-Daini Seamount tonalite and former normal arc volcanism in the Izu outer arc (ODP Leg126), and higher content than recent Izu arc volcanism. This characteristic is similar to some volcanics at the ODP Leg59 Site448 in the central Kyushu- Palau Ridge. Site448 volcanic rocks show 32-33Ma of Ar-Ar ages, which considered beginning of activity of Parece Vela Basin. It is considered that the dredged volcanic rocks are uppermost part of volcanism before spreading of

  14. Offshore double-planed shallow seismic zone in the NE Japan forearc region revealed by sP depth phases recorded by regional networks

    NASA Astrophysics Data System (ADS)

    Gamage, Shantha S. N.; Umino, Norihito; Hasegawa, Akira; Kirby, Stephen H.

    2009-07-01

    We detected the sP depth phase at small epicentral distances of about 150 km or more in the seismograms of shallow earthquakes in the NE Japan forearc region. The focal depths of 1078 M > 3 earthquakes that occurred from 2000 to 2006 were precisely determined using the time delay of the sP phase from the initial P-wave arrival. The distribution of relocated hypocentres clearly shows the configuration of a double-planed shallow seismic zone beneath the Pacific Ocean. The upper plane has a low dip angle near the Japan Trench, increasing gradually to ~30° at approximately 100 km landward of the Japan Trench. The lower plane is approximately parallel to the upper plane, and appears to be the near-trench counterpart of the lower plane of the double-planed deep seismic zone beneath the land area. The distance between the upper and lower planes is 28-32 km, which is approximately the same as or slightly smaller than that of the double-planed deep seismic zone beneath the land area. Focal mechanism solutions of the relocated earthquakes are determined from P-wave initial motion data. Although P-wave initial motion data for these offshore events are not ideally distributed on the focal sphere, we found that the upper-plane events that occur near the Japan Trench are characterized by normal faulting, whereas lower-plane events are characterized by thrust faulting. This focal mechanism distribution is the opposite to that of the double-planed deep seismic zone beneath the land area. The characteristics of these focal mechanisms for the shallow and deep doubled-planed seismic zones can be explained by a bending-unbending model of the subducting Pacific plate. Some of relocated earthquakes took place in the source area of the 1933 Mw8.4 Sanriku earthquake at depths of 10-23 km. The available focal mechanisms for these events are characterized by normal faulting. Given that the 1933 event was a large normal-fault event that occurred along a fault plane dipping landward, the

  15. Offshore double-planed shallow seismic zone in the NE Japan forearc region revealed by sP depth phases recorded by regional networks

    USGS Publications Warehouse

    Gamage, S.S.N.; Umino, N.; Hasegawa, A.; Kirby, S.H.

    2009-01-01

    We detected the sP depth phase at small epicentral distances of about 150 km or more in the seismograms of shallow earthquakes in the NE Japan forearc region. The focal depths of 1078 M > 3 earthquakes that occurred from 2000 to 2006 were precisely determined using the time delay of the sP phase from the initial P-wave arrival. The distribution of relocated hypocentres clearly shows the configuration of a double-planed shallow seismic zone beneath the Pacific Ocean. The upper plane has a low dip angle near the Japan Trench, increasing gradually to ???30?? at approximately 100 km landward of the Japan Trench. The lower plane is approximately parallel to the upper plane, and appears to be the near-trench counterpart of the lower plane of the double-planed deep seismic zone beneath the land area. The distance between the upper and lower planes is 28-32 km, which is approximately the same as or slightly smaller than that of the double-planed deep seismic zone beneath the land area. Focal mechanism solutions of the relocated earthquakes are determined from P-wave initial motion data. Although P-wave initial motion data for these offshore events are not ideally distributed on the focal sphere, we found that the upper-plane events that occur near the Japan Trench are characterized by normal faulting, whereas lower-plane events are characterized by thrust faulting. This focal mechanism distribution is the opposite to that of the double-planed deep seismic zone beneath the land area. The characteristics of these focal mechanisms for the shallow and deep doubled-planed seismic zones can be explained by a bending-unbending model of the subducting Pacific plate. Some of relocated earthquakes took place in the source area of the 1933 Mw8.4 Sanriku earthquake at depths of 10-23 km. The available focal mechanisms for these events are characterized by normal faulting. Given that the 1933 event was a large normal-fault event that occurred along a fault plane dipping landward, the

  16. Petrochemical Results for Volcanic Rocks recovered from SHINKAI 6500 diving on the Bonin Ridge (27°15'N-28°25'N): submarine extension of Ogasawara forearc volcanism

    NASA Astrophysics Data System (ADS)

    Bloomer, S. H.; Kimura, J.; Stern, R. J.; Ohara, Y.; Ishii, T.; Ishizuka, O.; Haraguchi, S.; Machida, S.; Reagan, M.; Kelley, K.; Hargrove, U.; Wortel, M.; Li, Y. B.

    2004-12-01

    Four SHINKAI 6500 submersible dives (dive #823 to #826) were performed along the Bonin Ridge escarpment west of Ogasawara (Bonin) Islands in the West Pacific during May 2004, in the hopes of finding exposures of lower crust of the IBM forearc. The Ogasawara Islands are located on the Bonin ridge, exposing 48-40 Ma boninites on Chichi-jima and depleted arc tholeiite lavas of the same age on Haha-jima. These extremely depleted lavas are believed to have been generated when subduction began beneath the Izu-Bonin-Mariana oceanic arc system. Subsequent rifting (35-30 Ma) formed the Bonin Trough and a 350 km long N-S trending eastern escarpment (Bonin Ridge), where we concentrated our dives. We observed lavas and volcaniclastic sequences by the four SHINKAI dives along the escarpment, and 16 fresh basaltic to andesitic lava samples have been recovered. The first three dives appear to have sampled volcanic constructs, of presumed Oligocene age, along the escarpment, whereas the last dive sampled exposures similar to Eocene rocks of the Bonin islands, including nummulitic limestone. The lava samples were analyzed by ICP-MS at Shimane University for 30 incompatible trace elements. All samples show arc-like chemical signatures, including elevated concentrations of LIL elements, depletions in Ta and Nb, and spikes in Pb, Sr, and Li. All samples show modest enrichments in LREE. A lava sample from the northernmost dive #824 is identical with the depleted tholeiite from Haha-jima Islands at the southernmost end of the Bonin Ridge in terms of trace element characteristics. Other lava samples from northern three dives (#823, #824, #825) have tholeiitic affinities with more elevated highly incompatible elements. This suggests derivation of the series of lavas by different degree of partial melting of a similar source mantle. Samples from southernmost dive site #826, immediately northwest of Chichi-jima Islands, are boninites with U-shaped REE patterns and relatively enriched Zr and

  17. Southward trench migration at ∼130-120 Ma caused accretion of the Neo-Tethyan forearc lithosphere in Tibetan ophiolites

    NASA Astrophysics Data System (ADS)

    Xiong, Qing; Griffin, William L.; Zheng, Jian-Ping; O'Reilly, Suzanne Y.; Pearson, Norman J.; Xu, Bo; Belousova, Elena A.

    2016-03-01

    The preservation of ultrahigh-pressure and super-reduced phases (diamond, moissanite, etc.) in the harzburgites and chromitites of the Yarlung Zangbo ophiolites (South Tibet, China) has major implications for mantle recycling and lithosphere evolution in the tectonic system related to the closing of the Neo-Tethyan Ocean. However, important aspects of the genesis of these enigmatic ophiolites and the related geodynamic evolution are still unclear. In the Zedang ophiolite of the eastern Yarlung Zangbo Suture, detailed mineral chemical data reveal that the harzburgite domain in the east [spinel Cr# (mole Cr3+/(Cr3+ + Al3+) = 0.62-0.33] is more depleted than the lherzolite domain in the west (spinel Cr# = 0.30-0.17) and shows much lower equilibration temperatures (by ∼250-150 °C) than the lherzolites. Clinopyroxene trace-element compositions indicate that the harzburgites underwent pervasive metasomatism after melt extraction, while the lherzolites did not. New zircon U-Pb ages show that the harzburgites were intruded by dolerite dykes with chilled margins at ∼130-128 Ma, consistent with the widespread mafic magmatism at ∼130-120 Ma in the Yarlung Zangbo ophiolites. Nd-Hf isotopic data indicate that the Zedang lherzolites subcreted the pre-emplaced harzburgites concurrently with the intrusion of the dolerite dykes into the harzburgites, and that the lherzolites and dolerites both were derived from upwelling asthenosphere with minor slab input. Available zircon geochronology and Hf-isotope data show that juvenile magmatism in the adjacent Gangdese Arc was almost completely interrupted from ∼130-120 Ma. We suggest that the extension of the overlying harzburgitic lithosphere, subcretion of lherzolites, intrusion of mafic dykes, and the waning of Gangdese-Arc magmatism all reflect a southward trench migration in the Neo-Tethyan subduction system from the Gangdese Arc to the oceanic forearc lithosphere. This magmatic relocation and tectonic linkage are inferred to

  18. Oceanic crust of the Grenada Basin in the Southern Lesser Antilles Arc Platform

    NASA Astrophysics Data System (ADS)

    Speed, R. C.; Walker, J. A.

    1991-03-01

    Seismic refraction data permit the southern Lesser Antilles arc and surrounding regions to be divided by the velocity of their basement. We propose that high-velocity basement of the arc platform beneath the Grenadine islands and below a part of the Tobago Trough forearc basin is oceanic and continuous and was originally connected with oceanic crust of the Grenada Basin. Low-velocity basements of the Tobago terrane and the arc platform from St. Vincent north lie south and north, respectively, of the high-velocity basement of the arc platform. An oceanic origin of this high-velocity crust in the Grenadines is argued to be more plausible than an origin as unroofed lower arc crust. The segment of probable oceanic crust in the arc platform was greatly uplifted during development of the present island arc, mainly in late Neogene time, relative to the Grenada Basin and Tobago Trough. Accepting the proposition of shallow oceanic crust in the Grenadines, early middle Eocene and possibly older pillow basalts of Mayreau, the oldest rock unit of the southern Lesser Antilles arc platform, may be an exposure of such basement. Major and minor element compositions of Mayreau Basalt are indicative of a spreading rather than arc origin. The stratigraphy of the pillow basalts indicates extrusion in an open marine environment, distant or shielded from sources of arc or continental sediment, followed by a period of pelagic sedimentation above the carbonate compensation depth. The Eocene basalt and pelagic cover formed a relatively deep floor of a marine basin in which arc-derived turbidites and pelagic sediments accumulated over the succeeding 25-30 ma. Such basalts thus indicate a probable spreading origin of the Grenada Basin and an age of cessation of spreading in the region of Mayreau in Eocene time. The configuration of the Eocene basin and the direction of spreading, however, are unknowns. Regional structural relationships imply the spreading was probably backarc, an origin also

  19. The internal structure of the southeastern margin of the South China Sea between Reed Bank and the W-Luzon basin

    NASA Astrophysics Data System (ADS)

    Steuer, S.; Franke, D.; Arfai, J.; Meresse, F.; Pubellier, M.; Mouly, B.

    2011-12-01

    might imply a volcanic/magmatic origin for the ridge. However, we observe extensional faults at the rims and also within this ridge that are not expected for volcanic intrusions. The other type is characterized by rotated fault blocks, bounded by listric normal faults that ramp down to a common detachment surface. The recent seafloor relief is smooth across this type of COT. On the northeastern side the SCS is subducted at the Manila Trench. Associated with this subduction is the formation of the forearc-basin-like W-Luzon Basin. This basin shows two peculiarities that are not well in accordance with a forearc setting: (1) The acoustic basement was affected by extensional normal faults, but extension does not affect the sediments above. (2) The relatively high heat flow (45-62 mW/sqm) is untypical for forearc basins. On the southern end of the Manila Trench a continent-continent collision takes place. As the northern boundary of the colliding continental parts is unclear we speculate that the W-Luzon Basin may be partly underlain by continental crust.

  20. Nam Con Son Basin

    SciTech Connect

    Tin, N.T.; Ty, N.D.; Hung, L.T.

    1994-07-01

    The Nam Con Son basin is the largest oil and gas bearing basin in Vietnam, and has a number of producing fields. The history of studies in the basin can be divided into four periods: Pre-1975, 1976-1980, 1981-1989, and 1990-present. A number of oil companies have carried out geological and geophysical studies and conducted drilling activities in the basin. These include ONGC, Enterprise Oil, BP, Shell, Petro-Canada, IPL, Lasmo, etc. Pre-Tertiary formations comprise quartz diorites, granodiorites, and metamorphic rocks of Mesozoic age. Cenozoic rocks include those of the Cau Formation (Oligocene and older), Dua Formation (lower Miocene), Thong-Mang Cau Formation (middle Miocene), Nam Con Son Formation (upper Miocene) and Bien Dong Formation (Pliocene-Quaternary). The basement is composed of pre-Cenozoic formations. Three fault systems are evident in the basin: north-south fault system, northeast-southwest fault system, and east-west fault system. Four tectonic zones can also be distinguished: western differentiated zone, northern differentiated zone, Dua-Natuna high zone, and eastern trough zone.

  1. SURVEY OF CROSS-BASIN BOAT TRAFFIC, ATCHAFALAYA BASIN, LOUISIANA

    EPA Science Inventory

    For flood control and for the preservation and enhancement of environmental quality of overflow swamp habitats, introduction of sediment from the Atchafalaya Basin Main Channel into backwater areas of the Atchafalaya Basin Floodway should be minimized. This introduction occurs ma...

  2. Geodynamic evolution of ophiolites from Albania and Greece (Dinaric-Hellenic belt): one, two, or more oceanic basins?

    NASA Astrophysics Data System (ADS)

    Bortolotti, Valerio; Chiari, Marco; Marroni, Michele; Pandolfi, Luca; Principi, Gianfranco; Saccani, Emilio

    2013-04-01

    All the geological constraints for an exhaustive reconstruction of the Triassic to Tertiary tectonic history of the southern Dinaric-Hellenic belt can be found in Albania and Greece. This article aims to schematically reconstruct this long tectonic evolution primarily based on a detailed analysis of the tectonic setting, the stratigraphy, the geochemistry, and the age of the ophiolites. In contrast to what was previously reported in the literature, we propose a new subdivision on a regional scale of the ophiolite complexes cropping out in Albania and Greece. This new subdivision includes six types of ophiolite occurrences, each corresponding to different tectonic units derived from a single obducted sheet. These units are represented by: (1) sub-ophiolite mélange, (2) Triassic ocean-floor ophiolites, (3) metamorphic soles, (4) Jurassic fore-arc ophiolites, (5) Jurassic intra-oceanic-arc ophiolites, and (6) Jurassic back-arc basin ophiolites. The overall features of these ophiolites are coherent with the existence of a single, though composite, oceanic basin located east of the Adria/Pelagonian continental margin. This oceanic basin was originated during the Middle Triassic and was subsequently (Early Jurassic) affected by an east-dipping intra-oceanic subduction. This subduction was responsible for the birth of intra-oceanic-arc and back-arc oceanic basins separated by a continental volcanic arc during the Early to Middle Jurassic. From the uppermost Middle Jurassic to the Early Cretaceous, an obduction developed, during which the ophiolites were thrust westwards firstly onto the neighboring oceanic lithosphere and then onto the Adria margin.

  3. River basin management

    SciTech Connect

    Newsome, D.H.; Edwards, A.M.C.

    1984-01-01

    The quality of water is of paramount importance in the management of water resources - including marine waters. A quantitative knowledge of water quality and the factors governing it is required to formulate and implement strategies requiring an inter-disciplinary approach. The overall purpose of this conference was to bring together the latest work on water quality aspects of river basin management. These proceedings are structured on the basis of five themes: problems in international river basins; the contribution of river systems to estuarial and marine pollution; the setting of standards; monitoring; and practical water quality management including use of mathematical models. They are followed by papers from the workshop on advances in the application of mathematical modelling to water quality management, which represent some of the current thinking on the problems and concepts of river basin management.

  4. Geology, exploration status of Uruguay's sedimentary basins

    SciTech Connect

    Goso, C.; Santa Ana, H. de )

    1994-02-07

    This article attempts to present the geological characteristics and tectonic and sedimentary evolution of Uruguayan basins and the extent to which they have been explored. Uruguay is on the Atlantic coast of South America. The country covers about 318,000 sq km, including offshore and onshore territories corresponding to more than 65% of the various sedimentary basins. Four basins underlie the country: the Norte basin, the Santa Lucia basin, the offshore Punta del Este basin, and the offshore-onshore Pelotas-Merin basin. The Norte basin is a Paleozoic basin while the others are Mesozoic basins. Each basin has been explored to a different extent, as this paper explains.

  5. Trinity river basin, Texas

    USGS Publications Warehouse

    Ulery, Randy L.; Van Metre, Peter C.; Crossfield, Allison S.

    1993-01-01

    In 1991 the Trinity River Basin National Water-Quality Assessment (NAWQA) will include assessments of surface-water and ground-water quality. Initial efforts have focused on identifying water-quality issues in the basin and on the environmental factors underlying those issues. Physical characteristics described include climate, geology, soils, vegetation, physiography, and hydrology. Cultural characteristics discussed include population distribution, land use and land cover, agricultural practices, water use, an reservoir operations. Major water-quality categories are identified and some of the implications of the environmental factors for water quality are presented.

  6. Water Release from Cold Serpentinized Forearc Mantle During Subduction Associated with Changes in Incoming Oceanic Plate Thermal Structure and Plate Boundary Kinematics: New Insights into Serpentinite Belts and Plate-Boundary Rheology

    NASA Astrophysics Data System (ADS)

    Kirby, Stephen

    2016-04-01

    Kirby, Wang, and Brocher (Earth Planets and Space, 2014) recently showed how the change in kinematics of the California margin from subduction motion to continental transform motion with the birth and growth of the San Andreas Fault System (SAFS) beginning at about 33 Ma BP likely led to a warming of the former forearc mantle and the release of water from serpentinized mantle by dehydration and a likely increase in fluid pressures along the SAFS. Such a mantle source of pressurized water gives insights into both the low sliding resistance for the SAFS and the mobilization and ascent of some serpentinized mantle peridotites through the crust. Thermal modeling by others has also shown that changes in the incoming plate age and subduction rate can also lead to warming of the forearc mantle during subduction. This development gives insights into the Mesozoic and Paleogene ages of emplacement of some, but not all, California serpentinites. Recent mineralogical and geochemical observations of serpentinite blocks in serpentinize mélange bodies in the San Francisco Bay Area (Uno and Kirby, 2014 AGU Meeting and Lewis and Kirby, 2015 AGU Meeting) suggest that these rocks sustained multiple stages of serpentinization that are broadly consistent with the model of Kirby et al. (2014). A new development comes from interpretation of investigations in the literature of localized late-stage silica-carbonate-water alteration of serpentinite bodies in California that this alteration occurred largely in Neogene time when the highest rates of water release from the former forearc mantle probably occurred. This presentation also suggests that the occurrence of serpentinite belts emplaced in Cenozoic time during changing plate-boundary kinematics, such as the Cenozoic closing of the Tethys Ocean bordering Eurasia by subduction and collision and arc reversal and decreasing convergence rates under the Greater Antilles and Colombia and New Guinea, may give insights into the serpentinite

  7. The Talara Basin province of northwestern Peru: cretaceous-tertiary total petroleum system

    USGS Publications Warehouse

    Higley, Debra K.

    2004-01-01

    More than 1.68 billion barrels of oil (BBO) and 340 billion cubic feet of gas (BCFG) have been produced from the Cretaceous-Tertiary Total Petroleum System in the Talara Basin province, northwestern Peru. Oil and minor gas fields are concentrated in the onshore northern third of the province. Current production is primarily oil, but there is excellent potential for offshore gas resources, which is a mostly untapped resource because of the limited local market for gas and because there are few pipelines. Estimated mean recoverable resources from undiscovered fields in the basin are 1.71 billion barrels of oil (BBO), 4.79 trillion cubic feet of gas (TCFG), and 255 million barrels of natural gas liquids (NGL). Of this total resource, 15 percent has been allocated to onshore and 85 percent to offshore; volumes are 0.26 BBO and 0.72 TCFG onshore, and 1.45 BBO and 4.08 TCFG offshore. The mean estimate of numbers of undiscovered oil and gas fields is 83 and 27, respectively. Minimum size of fields that were used in this analysis is 1 million barrels of oil equivalent and (or) 6 BCFG. The Paleocene Talara forearc basin is superimposed on a larger, Mesozoic and pre-Mesozoic basin. Producing formations, ranging in age from Pennsylvanian to Oligocene, are mainly Upper Cretaceous through Oligocene sandstones of fluvial, deltaic, and nearshore to deep-marine depositional origins. The primary reservoirs and greatest potential for future development are Eocene sandstones that include turbidites of the Talara and Salinas Groups. Additional production and undiscovered resources exist within Upper Cretaceous, Paleocene, and Oligocene formations. Pennsylvanian Amotape quartzites may be productive where fractured. Trap types in this block-faulted basin are mainly structural or a combination of structure and stratigraphy. Primary reservoir seals are interbedded and overlying marine shales. Most fields produce from multiple reservoirs, and production is reported commingled. For this

  8. 'East Basin' Panorama

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site] Click on the image for 'East Basin' Panorama (QTVR)

    NASA's Mars Exploration Rover Spirit used its panoramic camera to obtain this view of the impact feature called 'East Basin' to the northeast of 'Husband Hill.' The images combined into this mosaic were taken during Spirit's 653rd Martian day, or sol (Nov. 3, 2005), just before Spirit descended eastward onto 'Haskin Ridge.' The view is about 150 degrees wide. It is an approximately true-color rendering generated using the camera's 750-nanometer, 530-nanometer, and 480-nanometer filters.

    Dark features on the far side of the basin, just left of center in this view, are basaltic sand deposits that were emplaced on the lee sides of hills by northwesterly winds. Haskin Ridge is visible along the right margin of the image, capped by a light-toned layer of rock. Spirit investigated the light-toned rock unit after taking this image. The basaltic plains located east of the 'Columbia Hills' can be seen in the distance beyond 'East Basin.' The rim of Thira crater is just visible on the distant horizon some 15 kilometers (9.3 miles) away.

  9. Zircon U-Pb Ages of Tuffs and Volcaniclastic Sandstone of the Core Sample of IODP Exp. 322 at the Northern Part of the Shikoku Basin.

    NASA Astrophysics Data System (ADS)

    Shinjoe, H.; Nakajima, T.; Orihashi, Y.; Saito, S.; Oda, H.; Danhara, T.

    2014-12-01

    We determined U-Pb ages of zircons from core samples of IODP Exp. 322 using the laser abrasion ICP-MS (VG Plasma Quad 3 with New Wave Research UP-213). Zircon crystals were separated from four felsic tuffs from the Unit V of Site C0011, and a volcaniclastic turbidite sandstone of the lowermost horizon of the Unit V of Site C0012. Both of the drilling sites are located off the Nankai trough on the Shikoku Basin of the Philippine Sea plate, southwest Japan. Zircons from two felsic tuffs from Site C0011 are euhedral crystals, and most of their 238U-206Pb ages range 13 - 16 Ma. Weighted means of the 238U-206Pb ages of these samples are ca. 14.3 Ma. The other two felsic tuffs include zircon grains with older ages (80 - 260 Ma), however, weighted means of the 238U-206Pb ages of population with young ages ranges 14.5 - 14.7 Ma. These ages are coincide with those of the intense felsic magmatism occurred in the forearc region of southwest Japan (14 - 15 Ma) just after the opening of the Japan Sea and consequent clockwise rotation of the southwest Japan. Some of the felsic igneous bodies of the middle Miocene southwest Japan ejected large amount of felsic materials resulting caldera formation. So the provenance of felsic tuffs from the core of the Site C0011 are presumed to be one of the felsic igneous bodies of the forearc region of southwest Japan. Turbidite sandstone from Site C0012 also includes Miocene zircon grains of which their weighted mean of the 238U-206Pb ages is ca. 14.2 Ma. Moreover turbidite sandstone contains zircons with various ages (19 - 2500 Ma). One of the possible origin of such old zircon grains is reworking from sediments of the accretionary complex in the forearc of southwest Japan. If we assume the present rate of convergence of the Philippine sea plate (ca. 4 cm/y) is invariant, the turbidite including both clastic sediment and coeval felsic igneous materials traveled ca. 600 km across the trench.

  10. Bransfield Basin and Cordilleran Orogenesis

    NASA Astrophysics Data System (ADS)

    Dalziel, I. W.; Austin, J. A.; Barker, D. H.; Christensen, G. L.

    2003-12-01

    Tectonic uplift of the Andean Cordillera was initiated in the mid-Cretaceous with inversion of a composite marginal basin along 7500 km of the continental margin of South America, from Peru to Tierra del Fuego and the North Scotia Ridge. In the southernmost Andes, from 50-56 degrees S, the quasi-oceanic floor of this basin is preserved in the obducted ophiolitic rocks of the Rocas Verdes (Green Rocks) basin. We suggest that the basin beneath Bransfield Strait, 61-64 degrees S, separating the South Shetland Islands from the Antarctic Peninsula, constitutes a modern analog for the Rocas Verdes basin. Marine geophysical studies of Bransfield basin have been undertaken over the past 12 years by the Institute for Geophysics, University of Texas at Austin, under the auspices of the Ocean Sciences Division and United States Antarctic Program, National Science Foundation. These studies have elucidated the structure and evolution of Bransfield basin for comparison with the Rocas Verdes basin, with a view to eventual forward modeling of the evolution of a hypothetical cordilleran orogen by compression and inversion of the basin. These are the processes that can be observed in the tectonic transformation of the Rocas Verdes basin into the southernmost Andean cordillera, as South America moved rapidly westward in an Atlantic-Indian ocean hot-spot reference frame during the mid-Cretaceous. Multi-channel reflection seismic data from the Bransfield basin reveal an asymmetric structural architecture characterized by steeply-dipping normal faults flanking the South Shetlands island arc and gently dipping listric normal faults along the Antarctic Peninsula margin. Normal fault polarity reversals appear to be related to distributed loci of magmatic activity within the basin. This architecture is remarkably similar to that deduced from field structural studies of the Rocas Verdes basin. Notably, the oceanward-dipping, low angle normal faults along the Antarctic Peninsula margin

  11. Geology of the Eel River basin and adjacent region: Implications for late Cenozoic tectonics of the southern Cascadia subduction zone and Mendocino triple junction

    SciTech Connect

    Clarke, S.H. Jr. )

    1992-02-01

    Two upper Cenozoic depositional sequences of principally marine strata about 4,000 m thick overlie accreted basement terranes of the Central and Coastal belts of the Franciscan Complex in the onshore-offshore Eel River basin of northwestern California. The older depositional sequence is early to middle Miocene in age and represents slope basin and slope-blanket deposition, whereas the younger sequence, later Miocene to middle Pleistocene in age, consists largely of forearc basin deposits. Youthful tectonic activity related to Gorda-North American plate convergence indicates an active Cascadia subduction zone and strong partial coupling between these plates. Structures of the northeastern margin of the Eel River basin are principally north-northwest-trending, east-northeast-dipping thrust and reverse faults that form imbricate thrust fans. The Coastal belt fault, the early Tertiary accretionary suture between the Franciscan Central and Coastal belts, can be traced from Arcata Bay northward offshore to the southern Oregon border. It is tentatively extended farther northward based on aeromagnetic data to an offshore position west of Cape Blanco. Thereafter, it may coincide with the offshore Fulmar fault. The Cascadia subduction zone (CSZ) does not join the Mendocino transform fault at the commonly depicted offshore location of the Mendocino triple junction (MTJ). Instead, the CSZ extends southeastward around the southern Eel River basin and shoreward along Mendocino Canyon to join the Petrolia shear zone. Similarly, the Mendocino fault may extend shoreward via Mattole Canyon and join the Cooskie shear zone. These two shear zones intersect onshore north of the King Range, and the area of their intersection is the probable location of the MTJ.

  12. Newly Discovered Martian Impact Basins

    NASA Technical Reports Server (NTRS)

    Stam, M.

    1985-01-01

    Three previously unrecognized Martian impact basins were discovered through detailed mapping of landforms, structures and terrains near Cassini and Al Qahira basins. Al Qahira A lies on the Martian dichotomy boundary and intersects the older basin, Al Qahira. It has four rings that are expressed by a variety of landforms. Southwestward Al Qahira A is out by a younger Basin, Al Qahira B. Al Qahira B is a highly degraded basin with one identifiable ring. Its ring is expressed by a few massifs, knobs and inward-facing scarps, but is recognized by the distributions of wrinkle ridges and plains units. Cassini A lies southward of the younger Cassini Basin and is intersected by it. It probably has four rings. The importance of detailed mapping of various types of landforms and terrains to the discovery of basins on Mars are demonstrated.

  13. Natural frequency of regular basins

    NASA Astrophysics Data System (ADS)

    Tjandra, Sugih S.; Pudjaprasetya, S. R.

    2014-03-01

    Similar to the vibration of a guitar string or an elastic membrane, water waves in an enclosed basin undergo standing oscillatory waves, also known as seiches. The resonant (eigen) periods of seiches are determined by water depth and geometry of the basin. For regular basins, explicit formulas are available. Resonance occurs when the dominant frequency of external force matches the eigen frequency of the basin. In this paper, we implement the conservative finite volume scheme to 2D shallow water equation to simulate resonance in closed basins. Further, we would like to use this scheme and utilizing energy spectra of the recorded signal to extract resonant periods of arbitrary basins. But here we first test the procedure for getting resonant periods of a square closed basin. The numerical resonant periods that we obtain are comparable with those from analytical formulas.

  14. The open scars of Latin America: The Bolivian Orocline as a basament-related hinge, and the influence of accreted terranes on the paleomagnetic rotational patterns of the Chilean forearc.

    NASA Astrophysics Data System (ADS)

    Peña Gomez, M. A.; Arriagada, C.; Gómez, I.; Roperch, P. J.

    2015-12-01

    We made a paleomagnetic study in two separate zones of the Chilean forearc, between 18-22ºS and between 28-32ºS, sampling igneous and sedimentary rocks with ages ranging from Triassic to Miocene. More than 500 samples showed a stable magnetization, with hematite and magnetite being the principal carriers of magnetism. The rotation pattern obtained, added to previously published paleomagnetic data, show a continuous database for the Chilean forearc, between 19 and 35ºS, allowing us to separate distinct patterns in 4 major rotational zones: (1) Between 18-19.5ºS there is a strong anticlockwise rotational pattern, in agreement with the data known in southern Peru. (2) Between 19.5-22.5ºS, there is little to no rotation, with the southern limit being related to a major structural feature: The Antofagasta-Calama Lineament. (3) Between 22.5-29ºS there is a strong clockwise rotation pattern of nearly 30º. (4) Between 29-32ºS there is again a little to non-rotational pattern, in the area of the Pampean flat-slab. Overlapping these zones and the recognized accreted terranes boundaries shows a clear spatial relation between these and the limits of the rotated zones. We propose that the limits of this rotational domains can be linked to basament hinge-like weakness zones that helped to create the margin curvatures observed today. Under this model, the bolivian orocline would be the result of the opening of a hinge, helped by other geodynamics features like sea mountains and ridges, at the limit between the old accreted paleozoic terranes of Antofalla and Arequipa.

  15. Global analysis of intraplate basins

    NASA Astrophysics Data System (ADS)

    Heine, C.; Mueller, D. R.; Dyksterhuis, S.

    2005-12-01

    Broad intraplate sedimentary basins often show a mismatch of lithospheric extension factors compared to those inferred from sediment thickness and subsidence modelling, not conforming to the current understanding of rift basin evolution. Mostly, these basins are underlain by a very heterogeneous and structurally complex basement which has been formed as a product of Phanerozoic continent-continent or terrane/arc-continent collision and is usually referred to as being accretionary. Most likely, the basin-underlying substrate is one of the key factors controlling the style of extension. In order to investigate and model the geodynamic framework and mechanics controlling formation and evolution of these long-term depositional regions, we have been analysing a global set of more than 200 basins using various remotely sensed geophysical data sets and relational geospatial databases. We have compared elevation, crustal and sediment thickness, heatflow, crustal structure, basin ages and -geometries with computed differential beta, anomalous tectonic subsidence, and differential extension factor grids for these basins. The crust/mantle interactions in the basin regions are investigated using plate tectonic reconstructions in a mantle convection framework for the last 160 Ma. Characteristic parameters and patterns derived from this global analysis are then used to generate a classification scheme, to estimate the misfit between models derived from either crustal thinning or sediment thickness, and as input for extension models using particle-in-cell finite element codes. Basins with high differential extension values include the ``classical'' intraplate-basins, like the Michigan Basin in North America, the Zaire Basin in Africa, basins of the Arabian Penisula, and the West Siberian Basin. According to our global analysis so far, these basins show, that with increasing basin age, the amount of crustal extension vs. the extension values estimated from sediment thickness

  16. Buried-euxenic-basin model sets Tarim basin potential

    SciTech Connect

    Hsu, K.J. )

    1994-11-28

    The Tarim basin is the largest of the three large sedimentary basins of Northwest China. The North and Southwest depressions of Tarim are underlain by thick sediments and very thin crust. The maximum sediment thickness is more than 15 km. Of the several oil fields of Tarim, the three major fields were discovered during the last decade, on the north flank of the North depression and on the Central Tarim Uplift. The major targets of Tarim, according to the buried-euxenic-basin model, should be upper Paleozoic and lower Mesozoic reservoirs trapping oil and gas condensates from lower Paleozoic source beds. The paper describes the basin and gives a historical perspective of exploration activities and discoveries. It then explains how this basin can be interpreted by the buried-euxenic-basin model. The buried-euxenic-basin model postulates four stages of geologic evolution: (1) Sinian and early Paleozoic platform sedimentation on relic arcs and deep-marine sedimentation in back-arc basins in Xinjiang; (2) Late Paleozoic foreland-basin sedimentation in north Tarim; (3) Mesozoic and Paleogene continental deposition, subsidence under sedimentary load; and (4) Neogene pull-apart basin, wrench faulting and extension.

  17. Canada Basin revealed

    USGS Publications Warehouse

    Mosher, David C.; Shimeld, John; Hutchinson, Deborah R.; Chian, D; Lebedeva-Ivanova, Nina; Jackson, Ruth

    2012-01-01

    More than 15,000 line-km of new regional seismic reflection and refraction data in the western Arctic Ocean provide insights into the tectonic and sedimentologic history of Canada Basin, permitting development of new geologic understanding in one of Earth's last frontiers. These new data support a rotational opening model for southern Canada Basin. There is a central basement ridge possibly representing an extinct spreading center with oceanic crustal velocities and blocky basement morphology characteristic of spreading centre crust surrounding this ridge. Basement elevation is lower in the south, mostly due to sediment loading subsidence. The sedimentary succession is thickest in the southern Beaufort Sea region, reaching more than 15 km, and generally thins to the north and west. In the north, grabens and half-grabens are indicative of extension. Alpha-Mendeleev Ridge is a large igneous province in northern Amerasia Basin, presumably emplaced synchronously with basin formation. It overprints most of northern Canada Basin structure. The seafloor and sedimentary succession of Canada Basin is remarkably flat-lying in its central region, with little bathymetric change over most of its extent. Reflections that correlate over 100s of kms comprise most of the succession and on-lap bathymetric and basement highs. They are interpreted as representing deposits from unconfined turbidity current flows. Sediment distribution patterns reflect changing source directions during the basin’s history. Initially, probably late Cretaceous to Paleocene synrift sediments sourced from the Alaska and Mackenzie-Beaufort margins. This unit shows a progressive series of onlap unconformities with a younging trend towards Alpha and Northwind ridges, likely a response to contemporaneous subsidence. Sediment source direction appeared to shift to the Canadian Arctic Archipelago margin for the Eocene and Oligocene, likely due to uplift of Arctic islands during the Eurekan Orogeny. The final

  18. Mercury's Caloris Basin

    NASA Technical Reports Server (NTRS)

    2001-01-01

    Mercury: Computer Photomosaic of the Caloris Basin

    The largest basin on Mercury (1300 km or 800 miles across) was named Caloris (Greek for 'hot') because it is one of the two areas on the planet that face the Sun at perihelion.

    The Image Processing Lab at NASA's Jet Propulsion Laboratory produced this photomosaic using computer software and techniques developed for use in processing planetary data. The Mariner 10 spacecraft imaged the region during its initial flyby of the planet.

    The Mariner 10 spacecraft was launched in 1974. The spacecraft took images of Venus in February 1974 on the way to three encounters with Mercury in March and September 1974 and March 1975. The spacecraft took more than 7,000 images of Mercury, Venus, the Earth and the Moon during its mission.

    The Mariner 10 Mission was managed by the Jet Propulsion Laboratory for NASA's Office of Space Science in Washington, D.C.

  19. ADVANCED CHEMISTRY BASINS MODEL

    SciTech Connect

    William Goddard III; Lawrence Cathles III; Mario Blanco; Paul Manhardt; Peter Meulbroek; Yongchun Tang

    2004-05-01

    The advanced Chemistry Basin Model project has been operative for 48 months. During this period, about half the project tasks are on projected schedule. On average the project is somewhat behind schedule (90%). Unanticipated issues are causing model integration to take longer then scheduled, delaying final debugging and manual development. It is anticipated that a short extension will be required to fulfill all contract obligations.

  20. Petroleum basin studies

    SciTech Connect

    Shannon, P.M. ); Naylor, D. )

    1989-01-01

    This book reviews the tectonic setting, basin development and history of exploration of a number of selected petroleum provinces located in a variety of settings in the Middle East, North Sea, Nigeria, the Rocky Mountains, Gabon and China. This book illustrates how ideas and models developed in one area may be applied to other regions. Regional reviews and the reassessment of petroleum provinces are presented.

  1. Albuquerque Basin seismic network

    USGS Publications Warehouse

    Jaksha, Lawrence H.; Locke, Jerry; Thompson, J.B.; Garcia, Alvin

    1977-01-01

    The U.S. Geological Survey has recently completed the installation of a seismic network around the Albuquerque Basin in New Mexico. The network consists of two seismometer arrays, a thirteen-station array monitoring an area of approximately 28,000 km 2 and an eight-element array monitoring the area immediately adjacent to the Albuquerque Seismological Laboratory. This report describes the instrumentation deployed in the network.

  2. Dimension of fractal basin boundaries

    SciTech Connect

    Park, B.S.

    1988-01-01

    In many dynamical systems, multiple attractors coexist for certain parameter ranges. The set of initial conditions that asymptotically approach each attractor is its basin of attraction. These basins can be intertwined on arbitrary small scales. Basin boundary can be either smooth or fractal. Dynamical systems that have fractal basin boundary show final state sensitivity of the initial conditions. A measure of this sensitivity (uncertainty exponent {alpha}) is related to the dimension of the basin boundary d = D - {alpha}, where D is the dimension of the phase space and d is the dimension of the basin boundary. At metamorphosis values of the parameter, there might happen a conversion from smooth to fractal basin boundary (smooth-fractal metamorphosis) or a conversion from fractal to another fractal basin boundary characteristically different from the previous fractal one (fractal-fractal metamorphosis). The dimension changes continuously with the parameter except at the metamorphosis values where the dimension of the basin boundary jumps discontinuously. We chose the Henon map and the forced damped pendulum to investigate this. Scaling of the basin volumes near the metamorphosis values of the parameter is also being studied for the Henon map. Observations are explained analytically by using low dimensional model map.

  3. Advanced Chemistry Basins Model

    SciTech Connect

    William Goddard; Mario Blanco; Lawrence Cathles; Paul Manhardt; Peter Meulbroek; Yongchun Tang

    2002-11-10

    The DOE-funded Advanced Chemistry Basin model project is intended to develop a public domain, user-friendly basin modeling software under PC or low end workstation environment that predicts hydrocarbon generation, expulsion, migration and chemistry. The main features of the software are that it will: (1) afford users the most flexible way to choose or enter kinetic parameters for different maturity indicators; (2) afford users the most flexible way to choose or enter compositional kinetic parameters to predict hydrocarbon composition (e.g., gas/oil ratio (GOR), wax content, API gravity, etc.) at different kerogen maturities; (3) calculate the chemistry, fluxes and physical properties of all hydrocarbon phases (gas, liquid and solid) along the primary and secondary migration pathways of the basin and predict the location and intensity of phase fractionation, mixing, gas washing, etc.; and (4) predict the location and intensity of de-asphaltene processes. The project has be operative for 36 months, and is on schedule for a successful completion at the end of FY 2003.

  4. Great Basin Paleontological Bibliography

    USGS Publications Warehouse

    Blodgett, Robert B.; Zhang, Ning; Hofstra, Albert H.; Morrow, Jared R.

    2007-01-01

    Introduction This work was conceived as a derivative product for 'The Metallogeny of the Great Basin' project of the Mineral Resources Program of the U.S. Geological Survey. In the course of preparing a fossil database for the Great Basin that could be accessed from the Internet, it was determined that a comprehensive paleontological bibliography must first be compiled, something that had not previously been done. This bibliography includes published papers and abstracts as well as unpublished theses and dissertations on fossils and stratigraphy in Nevada and adjoining portions of California and Utah. This bibliography is broken into first-order headings by geologic age, secondary headings by taxonomic group, followed by ancillary topics of interest to both paleontologists and stratigraphers; paleoecology, stratigraphy, sedimentary petrology, paleogeography, tectonics, and petroleum potential. References were derived from usage of Georef, consultation with numerous paleontologists and geologists working in the Great Basin, and literature currently on hand with the authors. As this is a Web-accessible bibliography, we hope to periodically update it with new citations or older references that we have missed during this compilation. Hence, the authors would be grateful to receive notice of any new or old papers that the readers think should be added. As a final note, we gratefully acknowledge the helpful reviews provided by A. Elizabeth J. Crafford (Anchorage, Alaska) and William R. Page (USGS, Denver, Colorado).

  5. 26th December 2004 Great Sumatra Earthquake: first insights from the summer 2005 Marion Dufresne cruise

    NASA Astrophysics Data System (ADS)

    Sibuet, J.

    2005-12-01

    The 26th December 2004 Great Sumatra Earthquake is the second biggest earthquake (Mw=9.3) recorded during the past century. It initiated at a depth of 20-30 km, close to an indentation of the Indonesian fore-arc. The rupture propagated about 1200 km northward and terminated north of Andaman Islands. The "Sumatra Aftershocks" cruise performed on the French R/V Marion Dufresne started July 15 in Jakarta and ended August 9, 2005 in Colombo. We carried out a complete swath-bathymetric survey in a 370*75 km stripe located between northern Sumatra and the Indonesia/India boundary and from the trench to northeast of the Sumatra fault. 20 OBSs were deployed in the area and recorded about 2000 earthquakes during that period. Coring, heat-flow and piezometer measurements were also carried out. Offshore northern Sumatra, the Australia/Sundaland motion is 5 cm/yr in the N008° direction (Bock et al., J. Geophys. Res., 2003), which means that both strike-slip and normal components might occur along features parallel to the trench direction. However, focal mechanisms of the 26th December 2004 earthquake as well as co-seismic motions and 5-days post-seismic displacement field determined from GPS sites are essentially perpendicular to the trench direction (Vigny et al., Nature, 2005). There is consequently an apparent mismatch between deformations derived from plate motions and from co-seismic and immediate after-slip motions. This might suggest that long-term post-seismic motions might have also a significant component of strike-slip motion along features parallel to the trench direction. Between the trench and the backstop located southwest of the Aceh forearc basin, numerous trench parallel piggy back basins were mapped, suggesting the existence of numerous thrust faults. On the basis of morphology, coring and heat flow measurements, a major active thrust fault, which might correspond to an active splay fault, was identified southwest of the Aceh forearc basin. The

  6. Geodynamics of flat-slab subduction, sedimentary basin development, and hydrocarbon systems along the southern Alaska convergent plate margin

    NASA Astrophysics Data System (ADS)

    Finzel, Emily S.

    Combining field-based geologic studies and numerical modeling provides a robust tool for evaluating the geodynamics of convergent margins. Southern Alaska is arguably the most tectonically active part of the convergent margin of western North America. This conceptual approach has been used to interpret the modern basin dynamics, as well as key stages in the Cenozoic development of this region, including spreading-ridge and flat-slab subduction. New macrofossil, palynological, and lithostratigraphic data for the Bear Lake Formation in the Bristol Bay retroarc basin allow us to construct the first chronostratigraphic framework for this formation, and indicate deposition during Middle and Late Miocene time in a regional transgressive estuarine depositional system. In the Cook Inlet forearc basin, new detrital zircon U-Pb geochronology, rare earth element geochemistry, and clast compositional data from middle Eocene-Pliocene strata demonstrate the importance of sediment sources located in the retroarc region and along strike within the basin. The Yakutat microplate has recently been reinterpreted to represent buoyant crust that is presently subducting at a shallow angle beneath southern Alaska. Integration of stratigraphic, geochronologic, and thermochronologic data indicate that in the flat-slab region, exhumation initiated ca. 43 Ma and migrated inboard, magmatism ceased at ca. 32 Ma, and deposition in sedimentary basins ended by ca. 23 Ma. Sedimentary basins positioned along the western and northern perimeter of the flat-slab region record enhanced subsidence and sediment delivery from the flat-slab region beginning in late Oligocene and middle Miocene time respectively. The discrete contributions of unique driving forces for lithospheric deformation in western Canada and Alaska have not been quantified in detail, so their relative role in influencing deformation has remained unresolved. Using finite element models, we calculate a continuous strain rate and velocity

  7. Age, distribution, and stratigraphic relationship of rock units in the San Joaquin Basin Province, California: Chapter 5 in Petroleum systems and geologic assessment of oil and gas in the San Joaquin Basin Province, California

    USGS Publications Warehouse

    Hosford Scheirer, Allegra; Magoon, Leslie B.

    2008-01-01

    The San Joaquin Basin is a major petroleum province that forms the southern half of California’s Great Valley, a 700-km-long, asymmetrical basin that originated between a subduction zone to the west and the Sierra Nevada to the east. Sedimentary fill and tectonic structures of the San Joaquin Basin record the Mesozoic through Cenozoic geologic history of North America’s western margin. More than 25,000 feet (>7,500 meters) of sedimentary rocks overlie the basement surface and provide a nearly continuous record of sedimentation over the past ~100 m.y. Further, depositional geometries and fault structures document the tectonic evolution of the region from forearc setting to strike-slip basin to transpressional margin. Sedimentary architecture in the San Joaquin Basin is complicated because of these tectonic regimes and because of lateral changes in depositional environment and temporal changes in relative sea level. Few formations are widespread across the basin. Consequently, a careful analysis of sedimentary facies is required to unravel the basin’s depositional history on a regional scale. At least three high-quality organic source rocks formed in the San Joaquin Basin during periods of sea level transgression and anoxia. Generated on the basin’s west side, hydrocarbons migrated into nearly every facies type in the basin, from shelf and submarine fan sands to diatomite and shale to nonmarine coarse-grained rocks to schist. In 2003, the U.S. Geological Survey (USGS) completed a geologic assessment of undiscovered oil and gas resources and future additions to reserves in the San Joaquin Valley of California (USGS San Joaquin Basin Province Assessment Team, this volume, chapter 1). Several research aims supported this assessment: identifying and mapping the petroleum systems, modeling the generation, migration, and accumulation of hydrocarbons, and defining the volumes of rock to be analyzed for additional resources. To better understand the three dimensional

  8. Great Basin paleontological database

    USGS Publications Warehouse

    Zhang, N.; Blodgett, R.B.; Hofstra, A.H.

    2008-01-01

    The U.S. Geological Survey has constructed a paleontological database for the Great Basin physiographic province that can be served over the World Wide Web for data entry, queries, displays, and retrievals. It is similar to the web-database solution that we constructed for Alaskan paleontological data (www.alaskafossil.org). The first phase of this effort was to compile a paleontological bibliography for Nevada and portions of adjacent states in the Great Basin that has recently been completed. In addition, we are also compiling paleontological reports (Known as E&R reports) of the U.S. Geological Survey, which are another extensive source of l,egacy data for this region. Initial population of the database benefited from a recently published conodont data set and is otherwise focused on Devonian and Mississippian localities because strata of this age host important sedimentary exhalative (sedex) Au, Zn, and barite resources and enormons Carlin-type An deposits. In addition, these strata are the most important petroleum source rocks in the region, and record the transition from extension to contraction associated with the Antler orogeny, the Alamo meteorite impact, and biotic crises associated with global oceanic anoxic events. The finished product will provide an invaluable tool for future geologic mapping, paleontological research, and mineral resource investigations in the Great Basin, making paleontological data acquired over nearly the past 150 yr readily available over the World Wide Web. A description of the structure of the database and the web interface developed for this effort are provided herein. This database is being used ws a model for a National Paleontological Database (which we am currently developing for the U.S. Geological Survey) as well as for other paleontological databases now being developed in other parts of the globe. ?? 2008 Geological Society of America.

  9. Apollo Basin, Moon: Estimation of Impact Conditions

    NASA Astrophysics Data System (ADS)

    Echaurren, J. C.

    2015-07-01

    The Apollo Basin is a, pre-Nectarian, multi-ring basin located within the large South Pole-Aitken Basin (SPA). Multispectral data from both Galileo and Clementine showed that the composition of materials in Apollo is distinct…

  10. Advanced Chemistry Basins Model

    SciTech Connect

    Blanco, Mario; Cathles, Lawrence; Manhardt, Paul; Meulbroek, Peter; Tang, Yongchun

    2003-02-13

    The objective of this project is to: (1) Develop a database of additional and better maturity indicators for paleo-heat flow calibration; (2) Develop maturation models capable of predicting the chemical composition of hydrocarbons produced by a specific kerogen as a function of maturity, heating rate, etc.; assemble a compositional kinetic database of representative kerogens; (3) Develop a 4 phase equation of state-flash model that can define the physical properties (viscosity, density, etc.) of the products of kerogen maturation, and phase transitions that occur along secondary migration pathways; (4) Build a conventional basin model and incorporate new maturity indicators and data bases in a user-friendly way; (5) Develop an algorithm which combines the volume change and viscosities of the compositional maturation model to predict the chemistry of the hydrocarbons that will be expelled from the kerogen to the secondary migration pathways; (6) Develop an algorithm that predicts the flow of hydrocarbons along secondary migration pathways, accounts for mixing of miscible hydrocarbon components along the pathway, and calculates the phase fractionation that will occur as the hydrocarbons move upward down the geothermal and fluid pressure gradients in the basin; and (7) Integrate the above components into a functional model implemented on a PC or low cost workstation.

  11. Atlantic marginal basins of Africa

    SciTech Connect

    Moore, G.T.

    1988-02-01

    The over 10,000-km long Atlantic margin of Africa is divisible into thirty basins or segments of the margin that collectively contain over 18.6 x 10/sup 6/ km/sup 3/ of syn-breakup and post-breakup sediments. Twenty of these basins contain a sufficiently thick volume of sediments to be considered prospects. These basins lie, at least partially, within the 200 m isobath. The distribution of source rocks is broad enough to give potential to each of these basins. The sedimentation patterns, tectonics, and timing of events differ from basin to basin and are related directly to the margin's complex history. Two spreading modes exist: rift and transform. Rifting dates from Late Triassic-Early Jurassic in the northwest to Early Cretaceous south of the Niger Delta. A complex transform fault system separated these two margins. Deep-water communication between the two basins became established in the middle Cretaceous. This Mesozoic-Cenozoic cycle of rifting and seafloor spreading has segmented the margin and where observable, basins tend to be bounded by these segments.

  12. MASSACHUSETTS DRAINAGE SUB-BASINS

    EPA Science Inventory

    MassGIS has produced a statewide digital datalayer of the approximately 2300 sub-basins as defined and used by the USGS Water Resources Division and the Mass Water Resources Commission and as modified by Executive Office of Environmental Affairs (EOEA) agencies. These sub-basins...

  13. Estancia Basin dynamic water budget.

    SciTech Connect

    Thomas, Richard P.

    2004-09-01

    The Estancia Basin lies about 30 miles to the east of Albuquerque, NM. It is a closed basin in terms of surface water and is somewhat isolated in terms of groundwater. Historically, the primary natural outlet for both surface water and groundwater has been evaporation from the salt lakes in the southeastern portion of the basin. There are no significant watercourses that flow into this basin and groundwater recharge is minimal. During the 20th Century, agriculture grew to become the major user of groundwater in the basin. Significant declines in groundwater levels have accompanied this agricultural use. Domestic and municipal use of the basin groundwater is increasing as Albuquerque population continues to spill eastward into the basin, but this use is projected to be less than 1% of agricultural use well into the 21st Century. This Water Budget model keeps track of the water balance within the basin. The model considers the amount of water entering the basin and leaving the basin. Since there is no significant surface water component within this basin, the balance of water in the groundwater aquifer constitutes the primary component of this balance. Inflow is based on assumptions for recharge made by earlier researchers. Outflow from the basin is the summation of the depletion from all basin water uses. The model user can control future water use within the basin via slider bars that set values for population growth, water system per-capita use, agricultural acreage, and the types of agricultural diversion. The user can also adjust recharge and natural discharge within the limits of uncertainty for those parameters. The model runs for 100 years beginning in 1940 and ending in 2040. During the first 55 years model results can be compared to historical data and estimates of groundwater use. The last 45 years are predictive. The model was calibrated to match to New Mexico Office of State Engineer (NMOSE) estimates of aquifer storage during the historical period by

  14. Stratigraphic modeling of sedimentary basins

    SciTech Connect

    Aigner, T. ); Lawrence, D.T. )

    1990-11-01

    A two-dimensional stratigraphic forward model has been successfully applied and calibrated in clastic, carbonate, and mixed clastic/carbonate regimes. Primary input parameters are subsidence, sea level, volume of clastics, and carbonate growth potential. Program output includes sequence geometries, facies distribution lithology distribution, chronostratigraphic plots, burial history plots, thermal and maturity histories, and crossplots. The program may be used to predict reservoir distribution, to constrain interpretations of well and seismic data, to rapidly test exploration scenarios in frontier basins, and to evaluate the fundamental controls on observed basin stratigraphy. Applications to data sets from Main Pass (US Gulf Coast), Offshore Sarawak (Malaysia), Rub'al Khali basin (Oman), Paris basin (France), and Baltimore Canyon (US East Coast) demonstrate that the program can be used to simulate stratigraphy on a basin-wide scale as well as on the scale of individual prospects.

  15. The deep Ionian Basin revisited

    NASA Astrophysics Data System (ADS)

    Tugend, Julie; Chamot-Rooke, Nicolas; Arsenikos, Stavros; Frizon de Lamotte, Dominique; Blanpied, Christian

    2016-04-01

    The deep Eastern Mediterranean Basins (Ionian and Herodotus) are characterized by thick sedimentary sequences overlying an extremely thinned basement evidenced from different geophysical methods. Yet, the nature of the crust (continental or oceanic) and the timing of the extreme crustal and lithosphere thinning in the different sub-basins remain highly controversial, casting doubts on the tectonic setting related to the formation of this segment of the North Gondwana paleo-margin. We focus on the Ionian Basin located at the western termination of the Eastern Mediterranean with the aim of identifying, characterizing and mapping the deepest sedimentary sequences. We present tentative age correlations relying on calibrations and observations from the surrounding margins and basins (Malta shelf and Escarpment, Cyrenaica margin, Sirte Basin, Apulian Platform). Two-ship deep refraction seismic data (Expanding Spread Profiles from the PASIPHAE cruise) combined with reprocessed reflection data (from the ARCHIMEDE survey) enabled us to present a homogeneous seismic stratigraphy across the basin and to investigate the velocity structure of its basement. Based on our results, and on a review of geological and geophysical observations, we suggest an Upper Triassic-Early Dogger age for the formation of the deep Ionian Basin. The nature of the underlying basement remains uncertain, both highly-thinned continental and slow-spreading type oceanic crust being compatible with the available constraints. The narrow size and relatively short-lived evolution of the Ionian Basin lead us to suggest that it is more likely the remnant of an immature oceanic basin than of a stable oceanic domain. Eventually, upscaling these results at the scale of the Eastern Mediterranean Basins highlights the complex interaction observed between two propagating oceans: The Central Atlantic and Neo-Tethys.

  16. RESERVES IN WESTERN BASINS PART IV: WIND RIVER BASIN

    SciTech Connect

    Robert Caldwell

    1998-04-01

    Vast quantities of natural gas are entrapped within various tight formations in the Rocky Mountain area. This report seeks to quantify what proportion of that resource can be considered recoverable under today's technological and economic conditions and discusses factors controlling recovery. The ultimate goal of this project is to encourage development of tight gas reserves by industry through reducing the technical and economic risks of locating, drilling and completing commercial tight gas wells. This report is the fourth in a series and focuses on the Wind River Basin located in west central Wyoming. The first three reports presented analyses of the tight gas reserves and resources in the Greater Green River Basin (Scotia, 1993), Piceance Basin (Scotia, 1995) and the Uinta Basin (Scotia, 1995). Since each report is a stand-alone document, duplication of language will exist where common aspects are discussed. This study, and the previous three, describe basin-centered gas deposits (Masters, 1979) which contain vast quantities of natural gas entrapped in low permeability (tight), overpressured sandstones occupying a central basin location. Such deposits are generally continuous and are not conventionally trapped by a structural or stratigraphic seal. Rather, the tight character of the reservoirs prevents rapid migration of the gas, and where rates of gas generation exceed rates of escape, an overpressured basin-centered gas deposit results (Spencer, 1987). Since the temperature is a primary controlling factor for the onset and rate of gas generation, these deposits exist in the deeper, central parts of a basin where temperatures generally exceed 200 F and drill depths exceed 8,000 feet. The abbreviation OPT (overpressured tight) is used when referring to sandstone reservoirs that comprise the basin-centered gas deposit. Because the gas resources trapped in this setting are so large, they represent an important source of future gas supply, prompting studies to

  17. Basement blocks and basin inversion structures mapped using reprocessed Gulfrex 2D seismic data, Caribbean-South American oblique collisional zone

    NASA Astrophysics Data System (ADS)

    Escalona, A.; Sena, A.; Mann, P.

    2003-12-01

    We have reprocessed and reinterpreted more than 10,000 km of "Gulfrex" multi-channel 2D seismic reflection lines collected by Gulf Oil Corporation in 1972 along the northern margin of South America (offshore Venezuela and Trinidad). These digital data were donated to the University of Texas Institute for Geophysics and represent the largest single, digital reflection survey of the region. Reprocessing of these data included: format correction, filtering, post-stack multiple suppression, and fk migration. Reprocessed data were loaded and interpreted on a workstation. The data straddle a 2,000,000 km2 zone of Paleocene-Recent, time-transgressive, oblique collision between the Caribbean arc system and the passive continental margin of northern South America. Free-air, satellite gravity data shows the remarkable 1000-km-scale continuity of four basement ridges between the uncollided part of the Caribbean arc system (NS-trending Lesser Antilles arc) and the EW-trending collisional area north of Venezuela. The basement ridges involved in the Venezuelan collisional zone include: 1) Aruba-Bonaire-Curacao ridge that can be traced as a continuous feature to the Aves ridge remnant arc of the Lesser Antilles; 2) the partially inverted Blanquilla-Bonaire basin that can be traced into the Grenada back-arc basin; 3) Margarita-Los Testigos platform that can be traced to the Lesser Antilles volcanic arc; and 4) foreland basins and fold-thrust belts of eastern Venezuela (Serrania del Interior and Maturin basin) that can be traced to the Tobago forearc basin and Barbados accretionary prism. Gulfrex data document the progressive change of basinal fault systems from NS-striking normal faults formed in extensional, Lesser Antilles intra-arc settings to rotated and inverted, NE and EW-striking normal faults deformed in the collisional area north of Venezuela. Age of initial shortening of basinal areas and inversion of normal faults setting does not follow the simple, expected pattern of

  18. Aleutian basin oceanic crust

    USGS Publications Warehouse

    Christeson, Gail L.; Barth, Ginger A.

    2015-01-01

    We present two-dimensional P-wave velocity structure along two wide-angle ocean bottom seismometer profiles from the Aleutian basin in the Bering Sea. The basement here is commonly considered to be trapped oceanic crust, yet there is a change in orientation of magnetic lineations and gravity features within the basin that might reflect later processes. Line 1 extends ∼225 km from southwest to northeast, while Line 2 extends ∼225 km from northwest to southeast and crosses the observed change in magnetic lineation orientation. Velocities of the sediment layer increase from 2.0 km/s at the seafloor to 3.0–3.4 km/s just above basement, crustal velocities increase from 5.1–5.6 km/s at the top of basement to 7.0–7.1 km/s at the base of the crust, and upper mantle velocities are 8.1–8.2 km/s. Average sediment thickness is 3.8–3.9 km for both profiles. Crustal thickness varies from 6.2 to 9.6 km, with average thickness of 7.2 km on Line 1 and 8.8 km on Line 2. There is no clear change in crustal structure associated with a change in orientation of magnetic lineations and gravity features. The velocity structure is consistent with that of normal or thickened oceanic crust. The observed increase in crustal thickness from west to east is interpreted as reflecting an increase in melt supply during crustal formation.

  19. K-Basins design guidelines

    SciTech Connect

    Roe, N.R.; Mills, W.C.

    1995-06-01

    The purpose of the design guidelines is to enable SNF and K Basin personnel to complete fuel and sludge removal, and basin water mitigation by providing engineering guidance for equipment design for the fuel basin, facility modifications (upgrades), remote tools, and new processes. It is not intended to be a purchase order reference for vendors. The document identifies materials, methods, and components that work at K Basins; it also Provides design input and a technical review process to facilitate project interfaces with operations in K Basins. This document is intended to compliment other engineering documentation used at K Basins and throughout the Spent Nuclear Fuel Project. Significant provisions, which are incorporated, include portions of the following: General Design Criteria (DOE 1989), Standard Engineering Practices (WHC-CM-6-1), Engineering Practices Guidelines (WHC 1994b), Hanford Plant Standards (DOE-RL 1989), Safety Analysis Manual (WHC-CM-4-46), and Radiological Design Guide (WHC 1994f). Documents (requirements) essential to the engineering design projects at K Basins are referenced in the guidelines.

  20. Late Cretaceous and Early Tertiary depositional environments of the northern Sacramento basin revealed by seismic-stratigraphic analysis

    SciTech Connect

    Damuth, J.E.; Link, M.H.; Gabay, S.H. )

    1990-05-01

    Seismic-stratigraphic analysis of regional seismic data across the Willows-Beehive Bend gas field reveals a prograding shelf-slope depositional sequence, including basic submarine-fan, slope, and shelf deltaic deposits, that progressively infilled the northern Sacramento forearc basin during the Campanian. The base of the Forbes Formation and the base of the Princeton Gorge fill form the lower and upper boundaries, respectively, of this sequence. Upper Cretaceous submarine-fan and basin-plain deposit form the strata between the Sierran basement and the base of the Forbes and progressively onlap the basement from west to east. The lower to middle Forbes Formation is characterized by high-amplitude discontinuous reflections and consists of mud-rich submarine-fan deposit with laterally restricted, sand-prone channel/levee complexes and broader depositional lobes. In contrast the upper Forbes consist of mud-rich slope deposits characterized by broad, southward-dipping clinoforms. Submarine-canyon/gully fills are common and return discordant hummocky to chaotic reflections. The overlying Kione Formation consists of sand-rich, delta-front deposits that return high amplitude, gently dipping subparallel reflections and are transitional into the slope deposits of the uppermost Forbes. The Kione was partially eroded during cutting of the Princeton Gorge submarine canyon in the early Tertiary. The lower (Eocene) Princeton Gorge fill shows highly variable reflection character and seismic facies that suggest multiple episodes of submarine erosion and deposition. At least three northwest-southeast-striking fault zones, including the Willows fault, disrupt these formations and appear to have strike-slip components.

  1. Late Cretaceous and Paleogene sedimentation along east side of San Joaquin basin, California

    SciTech Connect

    Reid, S.A.

    1986-04-01

    Depositional systems of the Late Cretaceous contrast with those of the Paleogene in the subsurface along the east side of the San Joaquin basin between Bakersfield and Fresno, California. Upper Cretaceous deposits include thick fan-delta and submarine fan facies of the Moreno and Panoche Formations, whereas the paleogene contains extensive nearshore, shelf, slope, and submarine fan deposits of the Lodo, Domengine, and Kreyenhagen Formations. These sediments were deposited on a basement surface having several west-trending ridges and valleys. West-flowing streams draining an ancestral Sierra Nevada of moderate relief formed prograding fan deltas that filled the valleys with thick wedges of nonmarine channel deposits, creating a bajada along the shoreline. Detrital material moved rapidly from the shoreline through a narrow shelf, into a complex of submarine fans in the subduction trough. During the early Eocene, a low sea level stand plus an end of Sierra Nevada uplift resulted in the erosion of the range to a peneplain. Stream-fed fan deltas were replaced by a major river system, which flowed west on about the present course of the Kern River. Following a rapid sea level increase, sand from the river system was deposited on the now broad shelf along a wide belt roughly coincident with California Highway 99. The river was also the point source for sand in a submarine fan northwest of Bakersfield. Both Upper Cretaceous and Paleogene depositional systems probably continue north along the east edge of the Great Valley. This proposed scenario for the east side of the San Joaquin is analogous to forearc deposits in the San Diego area, including the Cretaceous Rosario fan-delta and submarine fan system and the Eocene La Jolla and Poway nearshore, shelf, and submarine fan systems.

  2. Ancient mantle trapped in the Mariana arc-basin system: Insights from the platinum group elements and Os isotopes

    NASA Astrophysics Data System (ADS)

    Savov, I. P.; Shirey, S. B.; Horan, M. F.; Mock, T. D.

    2006-12-01

    Serpentinized harzburgites recently drilled during ODP Leg 195 at South Chamorro Seamount in the Mariana forearc region have been studied for their platinum group element (PGE) concentrations and Os isotopic compositions. The samples allow a look at the slab fluid-modified subarc mantle immediately overlaying the actively subducting Pacific slab at depths of ~ 30 km. The average PGE (Os 2.3 ppb, Ir 1.5 ppb, Ru 5.4 ppb, Pd 1.6 ppb and Pt 16.3 ppb) and Re (60 ppt) abundances are comparable to those measured in other subarc mantle xenolith suites. The PGE and Re abundances are depleted up to 3 orders of magnitude relative to chondrites, with relative order of depletions Ru > Os > Ir> Pt> Re> Pd. The variable Pd contents (0.01-4.5 ppb) and the low Pd/Os (<2) in the Mariana forearc samples differ significantly from that of altered oceanic crust (Pd/Os~ 22), suggesting Os remained relatively unchanged during low temperature subduction-fluid additions. Serpentinitization of the harzburgites occurred in equilibrium with fluids that were both reducing and highly alkaline. Os in its original phases may be stabilized in such an environment, therefore can preserve evidence for ancient melting despite later slab interactions. Finally, the high Pt/Pd (ave. ~ 25) and low Re contents (ave.~ 60 ppt) in the Leg 195 forearc samples are complementary to those measured in boninites from the Izu-Bonin-Mariana arc-basin system, showing a genetic relationship. Our samples reveal an average 187Os/188Os of 0.123 [range = 0.119- 0.127], making them similar to abyssal peridotites from elsewhere. Radiogenic 187Os/188Os ratios would have been imparted to the serpentinites by slab fluids, so the subchondritic Os isotopic compositions implies that peridotite-slab fluid interactions did not alter the Os isotope systematics of the mantle protoliths. Low alumina abundances (<1 %) and trace element signatures (low HFSE; REE with U-shaped chondrite-normalized patterns and 2-3 times lower than

  3. Basin development and petroleum potential of offshore Otway basin, Australia

    SciTech Connect

    Williamson, P.E.; O'Brien, G.W.; Swift, M.G.; Scherl, A.S.; Marlow, M.S.; Exon, N.F.; Falvey, D.A.; Lock, J.; Lockwood, K.

    1987-05-01

    The Bass Strait region in southeastern Australia contains three sedimentary basins, which are, from east to west, the Gippsland, Bass, and Otway basins. The offshore Gippsland basin is Australia's most prolific petroleum-producing province and supplies over 90% of the country's production. In contrast, exploration has been unsuccessful in the offshore portion of the Otway basin; 17 wells have been drilled, and although shows of oil and gas have been common, no commercial discoveries have been made. Many of these wells, drilled in the 1960s and 1970s, were sited using poor-quality seismic data and, as a consequence, were frequently off structure. Seismic data quality has, however, improved significantly in recent years. The present study by the Australian Bureau of Mineral Resources (BMR) involved the collection, in the offshore Otway basin, of 3700 km of high-quality, 48-channel seismic reflection data by the BMR research vessel R/V Rig Seismic. These data have been integrated with existing industry seismic data, well data, limited dredged material, and geohistory analyses in a framework study of basin development and hydrocarbon potential in this under-explored area. The offshore Otway basin extends 500 km along the southern coastline and is typically 50 km wide in water depths of less than 200 m. It contains up to 10 km of predominantly late Mesozoic to early Cenozoic sediments, which are overlain by a thin sequence of middle to late Tertiary shelf carbonates. It has been divided into three main structural elements: the Mussel Platform in the east, the central Voluta Trough, and the Crayfish Platform in the west. The basin was initiated at the end of the Jurassic as part of the Bassian rift. Up to 6 km of Lower Cretaceous sediments were deposited prior to breakup at the end of the Early Cretaceous and the onset of sea-floor spreading between Australia and Antarctica.

  4. Martian lake basins and lacustrine plains

    NASA Astrophysics Data System (ADS)

    de Hon, R. A.

    1992-02-01

    A classification of Martian lake basins based on the location of the basin in respect to water sources is proposed. The classes are type 1: valley-head basins; type 2: intravalley basins; type 3: valley-terminal basins; and type 4: isolated basins. Martian lakes are ephemeral features. Many craters and irregular depressions impounded water only until the basins filled and overflowed. Water escaping by spillover rapidly cut crevasses in the downstream side of basins and drained the ponds. Clastic lacustrine sediments collected in the lakes as flowing water lost velocity and turbulence. Evaporitic deposits may be significant in those basins that were not rapidly drained. Sediments deposited in lake basins form smooth, featureless plains. Lacustrine plains are potentially candidate sites for Mars landings and for the search for evidence of ancient life.

  5. Tectonic framework of Turkish sedimentary basins

    SciTech Connect

    Yilmaz, P.O. )

    1988-08-01

    Turkey's exploration potential primarily exists in seven onshore (Southeast Turkey platform, Tauride platform, Pontide platform, East Anatolian platform, Interior, Trace, and Adana) basins and four offshore (Black Sea, Marmara Sea, Aegean Sea, and Mediterranean Sea) regional basins formed during the Mesozoic and Tertiary. The Mesozoic basins are the onshore basins: Southeast Turkey, Tauride, Pontide, East Anatolian, and Interior basins. Due to their common tectonic heritage, the southeast Turkey and Tauride basins have similar source rocks, structural growth, trap size, and structural styles. In the north, another Mesozoic basin, the Pontide platform, has a much more complex history and very little in common with the southerly basins. The Pontide has two distinct parts; the west has Paleozoic continental basement and the east is underlain by island-arc basement of Jurassic age. The plays are in the upper Mesozoic rocks in the west Pontide. The remaining Mesozoic basins of the onshore Interior and East Anatolian basins are poorly known and very complex. Their source, reservoir, and seal are not clearly defined. The basins formed during several orogenic phases in mesozoic and Tertiary. The Cenozoic basins are the onshore Thrace and Adana basins, and all offshore regional basins formed during Miocene extension. Further complicating the onshore basins evolution is the superposition of Cenozoic basins and Mesozoic basins. The Thrace basin in the northwest and Adana basin in the south both originate from Tertiary extension over Tethyan basement and result in a similar source, reservoir, and seal. Local strike-slip movement along the North Anatolian fault modifies the Thrace basin structures, influencing its hydrocarbon potential.

  6. Deformation History of the Haymana Basin: Structural Records of Closure-Collision and Subsequent Convergence (Indentation) Events at the North-Central Neotethys (Central Anatolia, Turkey)

    NASA Astrophysics Data System (ADS)

    Gülyüz, Erhan; Özkaptan, Murat; Kaymakcı, Nuretdin

    2016-04-01

    Gondwana- (Tauride Platfrom and Kırşehir Block) and Eurasia (Pontides) - derived continental blocks bound the Haymana basin, in the south and north, respectively. Boundaries between these blocks are signed by İzmir-Ankara-Erzincan and debatable Intra-Tauride Suture zones which are straddled by the Haymana Basin in the region. In this regard, deformation recorded in the upper Cretaceous to middle Eocene deposits of the basin is mainly controlled by the relative movements of these blocks. Therefore, understanding the structural evolution of the Haymana Basin in a spatio-temporal concept is crucial to shed some light on some debatable issues such as ; (1) timing of late stage subduction histories of various branches of Neotethys and subsequent collision events, (2) effects of post-collisional tectonic activity in the Haymana region. Fault kinematic analyses (based on 623 fault-slip data from 73 stations) indicate that the basin was subjected to initially N-S to NNE-SSW extension until middle Paleocene and then N-S- to NNE-SSW- directed continuous compression and coeval E-W to ESE-WNW extension up to middle Miocene. These different deformation phases correspond to the fore-arc (closure) and foreland (collision and further convergence) stages of the basin. Additionally, fold analyses (based on 1017 bedding attitudes) and structural mapping studies show that development of folds and major faults are coeval and they can be explained by principle stress orientations of the second deformation phase. The Haymana basin is, based on the trends of E-W- and WNW-ESE- directed structures at the south-eastern and the north-western parts of the basin, respectively, divided into two structural segments. The balanced cross-sections also indicate ~4% and ~25% shortening at the north-western and south-eastern segments, respectively. The differences in amounts of shortenings are explained by reduce in effectiveness zone of basin-bounding thrust faults towards west. On the other hand

  7. Provenance and basin evolution, Zhada basin, southwestern Tibet

    NASA Astrophysics Data System (ADS)

    Saylor, J.; Decelles, P.; Gehrels, G.; Kapp, P.

    2007-12-01

    The Zhada basin is a late Miocene - Pliocene intermontane basin situated at high elevations in the Himalayan hinterland. The fluvial and lacustrine sediments of the Zhada formation are undeformed and sit in angular unconformity above the deformed Tethyan Sedimentary Sequence (TSS). The basin sits just south of the Indus suture in a structural position occupied elsewhere in the Himalayan orogen by some of the highest mountains on earth, including Everest. The occurrence of a basin at this location demands explanation. Currently, the Sutlej River flows parallel to the structural grain of the Himalaya, westward through the basin, towards the Leo Pargil (Qusum) range. Near the range front it takes a sharp southward turn, cuts across the structural grain of the Himalaya and out into the Gangetic foreland. Palaeocurrent indicators in the lower part of the Zhada formation show that the basin originated as a northwest flowing axial river. Palaeocurrent indicators are consistently northwest oriented, even to within to within 10 km of the Leo Pargil range front in the north-western end of the basin. This implies that at the onset of sedimentation in Zhada basin the Leo Pargil range was not a barrier as it is today. In the upper part of the Zhada formation, palaeocurrent indicators are generally directed towards the centre of the basin. In the central and southern portions of the basin this indicates a transition from an axial, northwest flowing river to prograding fluvial and alluvial fans. However, in the north-western part of the basin the change between lower and upper Zhada formation involves a complete drainage reversal. This change in palaeocurrent orientation is also reflected in the detrital zircon signal from basin sediments. Low in the Zhada formation the detrital zircon signal is dominated by zircons from the Kailash (Gangdese) batholith (or associated extrusives, see below). However, higher in the sections, a local source, either from the TSS or the core of the

  8. 77 FR 45653 - Yakima River Basin Conservation Advisory Group; Yakima River Basin Water Enhancement Project...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-08-01

    ... Bureau of Reclamation Yakima River Basin Conservation Advisory Group; Yakima River Basin Water... on the structure, implementation, and oversight of the Yakima River Basin Water Conservation Program... of the Water Conservation Program, including the applicable water conservation guidelines of...

  9. Mid-Pleistocene to present stratigraphic responses in a tectonically-driven depositional setting: Eel River Basin, Northern California

    NASA Astrophysics Data System (ADS)

    Burger, Robert Lawrence

    The Eel River Basin of northern California is an actively deforming forearc basin, affected today by Gorda-North America Plate convergence, northward migration of the Mendocino Triple Junction, glacioeustatic sea-level fluctuations that periodically exposed the continental shelf, and high rates of sediment input. A high-resolution multichannel seismic reflection survey of the shelf and upper slope has been conducted as part of the Office of Naval Research STRATAFORM initiative, with the goal of understanding processes affecting sediment dispersal and preservation in this complex continental margin setting. Interpretations of the seismic images indicate that, although tectonism strongly overprints preserved sequence morphologies, glacioeustacy is of primary importance in the distribution and preservation of sediments along this margin. On the shelf, stacked sequences dominated by interpreted highstand marine sediment are separated by prominent ravinement surfaces formed during sea-level transgressions. Folding and faulting locally modify sequence morphologies. At the south end of the seismic grid, localized uplift attributed to Mendocino Triple Junction encroachment overrides the glacioeustatic stacking pattern dominant over the rest of the shelf, inducing shelf incision and preferential preservation of vertically stacked channel-fills. An abrupt shift in shelf sequence morphology ˜500 ka suggests that the triple junction began to affect the southern basin at that time, by decreasing accommodation space marginwide. On the adjacent slope, effects of tectonism and glacioeustacy can also be discerned. In the south, the Humboldt Slide is identified as a long-lived masswasting feature, likely triggered by triple junction-related uplift and associated seismicity ˜450--500 ka. However, a cyclical succession of contrasting lithologies is also apparent in the deformed slide sequences, which I attribute to glacioeustatic cyclicity. To the north, effects of regional

  10. Flexural analysis of two broken foreland basins; Late Cenozoic Bermejo basin and Early Cenozoic Green River basin

    SciTech Connect

    Flemings, P.B.; Jordan, T.E.; Reynolds, S.

    1986-05-01

    Lithospheric flexure that generates basin in a broke foreland setting (e.g., the Laramide foreland of Wyoming) is a three-dimensional system related to shortening along basin-bounding faults. The authors modeled the elastic flexure in three dimensions for two broken foreland basins: the early Cenozoic Green River basin and the analogous late Cenozoic Bermejo basin of Argentina. Each basin is located between a thrust belt and a reverse-fault-bounded basement uplift. Both basins are asymmetric toward the basement uplifts and have a central basement high: the Rock Springs uplift and the Pie de Palo uplift, respectively. The model applies loads generated by crustal thickening to an elastic lithosphere overlying a fluid mantle. Using the loading conditions of the Bermejo basin based on topography, limited drilling, and reflection and earthquake seismology, the model predicts the current Bermejo basin geometry. Similarly, flexure under the loading conditions in the Green River basin, which are constrained by stratigraphy, well logs, and seismic profiling and summed for Late Cretaceous (Lance Formation) through Eocene (Wasatch Formation), successfully models the observed geometry of the pre-Lance surface. Basin depocenters (> 4 km for the Green River basin; > 7 km for the Bermejo basin) and central uplifts are predicted to result from constructive interference of the nonparallel applied loads. Their Bermejo model implies that instantaneous basin geometry is successfully modeled by crustal loading, whereas the Green River basin analysis suggests that basin evolution can be modeled over large time steps (e.g., 20 Ma). This result links instantaneous basin geometry to overall basin evolution and is a first step in predicting stratigraphic development.

  11. Viscoelastic Relaxation of Lunar Basins

    NASA Astrophysics Data System (ADS)

    Mohit, P. S.; Phillips, R. J.

    2004-12-01

    The large lunar impact basins provide a unique glimpse into early lunar history. Here we investigate the possibility that the relief of the oldest lunar basins (with the exception of South-Pole Aitken) has decayed through viscous relaxation. We identify nine ancient multi-ring basins with very low relief and low-amplitude Bouguer and free-air gravity anomalies. The characteristics of these basins are consistent with either 1) relaxation of topographic relief by ductile flow (e.g. Solomon et al., 1982) or 2) obliteration of basin topography during crater collapse immediately following impact. Both scenarios require that the basins formed early in lunar history, when the Moon was hot. The latter possibility appears to be unlikely due to the great topographic relief of South Pole-Aitken basin (SPA), the largest and oldest impact basin on the Moon (with the possible exception of the putative Procellarum basin; Wilhelms, 1987). On the other hand, the thin crust beneath SPA may not have allowed ductile flow in its lower portions, even for a hot Moon, implying that a thicker crust is required beneath other ancient basins for the hypothesis of viscous relaxation to be tenable. Using a semi-analytic, self-gravitating viscoelastic model, we investigate the conditions necessary to produce viscous relaxation of lunar basins. We model topographic relaxation for a crustal thickness of 30 km, using a dry diabase flow law for the crust and dry olivine for the mantle. We find that the minimum temperature at the base of the crust (Tb) permitting nearly complete relaxation of topography by ductile flow on a timescale < 108 yrs is 1400 K, corresponding to a heat flow of 55mW/m2, into the crust. Ductile flow in the lower crust becomes increasingly difficult as the crustal thickness decreases. The crust beneath SPA, thinned by the impact, is only 15-20 km thick and would require Tb ≥ 1550 K for relaxation to occur. The fact that SPA has maintained high-amplitude relief suggests that

  12. Paleothermometry of the Sydney Basin

    SciTech Connect

    Middleton, M.F.; Schmidt, P.W.

    1982-07-10

    Evidence from overprinting of magnetizations of Late Permian and Mesozoic rocks and from the rank of Permian coals and Mesozoic phytoclasts (coal particles) suggests that surface rocks in the Sydney Basin, eastern Australia, have been raised to temperatures of the order of 200 /sup 0/C or higher. As vitrinite reflectance, an index of coal rank or coalification, is postulated to vary predictably with temperature and time, estimates of the paleotemperatures in the Sydney Basin based on observed vitrinite reflectance measurements can be made in conjunction with reasonable assumptions about the tectonic and thermal histories of the basin. These estimates give maximum paleotemperatures of present day surface rocks in the range 60--249 /sup 0/C, depending on factors such as location in the basin, the thickness of the sediment eroded, and the maximum paleogeothermal gradient. Higher coal rank and, consequently, larger eroded thicknesses and paleogeothermal gradients occur along the eastern edge of the basin and may be related to seafloor spreading in the Tasman Sea on the basin's eastern margin. A theory of thermal activation of magnetization entailing the dependence of magnetic viscosity on the size distribution of the magnetic grains is used to obtain an independent estimate of the maximum paleotemperatures in the Sydney Basin. This estimate places the maximum paleotemperature in the range 250--300 /sup 0/C along the coastal region. Both coalification and thermal activation of magnetization models provide strong evidence of elevated paleotemperatures, which in places exceed 200 /sup 0/C, and the loss of sediment thicknesses in excess of 1 km due to erosion.

  13. Crustal structure of the eastern Algerian continental margin and adjacent deep basin: implications for late Cenozoic geodynamic evolution of the western Mediterranean

    NASA Astrophysics Data System (ADS)

    Bouyahiaoui, B.; Sage, F.; Abtout, A.; Klingelhoefer, F.; Yelles-Chaouche, K.; Schnürle, P.; Marok, A.; Déverchère, J.; Arab, M.; Galve, A.; Collot, J. Y.

    2015-06-01

    emplacement of magmatic intrusions in both the deep basin and the continental margin. Based on the crustal structure, we propose that the eastern Algerian basin opened during the southeastward migration of the European forearc before the collision, along a NW-SE elongated spreading centre that ran perpendicular to the subduction trend. Such an atypical geometry is explained by the diverging directions of the subduction rollback during the backarc opening: eastward for the Corsica-Sardinia block, and southward for the Kabylian blocks. This geometry of the forearc can be interpreted as the surface expression of a slab tear at depth, which is responsible for atypical magmatism in the overlying backarc oceanic basin.

  14. What do Great Subduction Earthquakes tell us About Continental Deformation of the Upper Plate in the Central Andes Forearc? Insights From Seismotectonics, Continental Deformation and Coulomb Modelisation Along Southern Peru Margin

    NASA Astrophysics Data System (ADS)

    Audin, L.; Perfettini, H.; Tavera, H.

    2007-05-01

    Calientes Fault system (parallel to the trench) and a crustal depth of about 20km. Such a magnitud and crustal depth in the area correlates perfectly with the Quaternary geomorphic evidences of tectonic activity along the Sama-Calientes thrust fault in the forearc in Southern Peru. Some questions are raised by the occurrence of such continental seismicity, just after a major subduction event, as none has been registered in the area since more than 40 years. Continental fault systems constitute a key to the understanding of the forearc deformation in the Arica Elbow, where the Andes obliquity with respect to the Nazca plate convergence direction. Also these results suggest that continental deformation should give us clues to define the pattern of segmentation of the subduction zone by studying seismotectonics and its relation to the segmentation of the upper continental plate.

  15. Neogene Structural Basins Beneath Santa Rosa Plain: Strike-Slip Basins Formed in Wake of the Mendocino Triple Junction During Initiation of the Rodgers Creek-Healdsburg Fault Zone

    NASA Astrophysics Data System (ADS)

    McLaughlin, R. J.; Sarna-Wojcicki, A. M.; Fleck, R. J.; Langenheim, V. E.; McPhee, D. K.; Jachens, R. C.; Wagner, D. L.; McCabe, C. A.

    2006-12-01

    Located on the Humboldt Plate, just N of the San Francisco Bay block, the Santa Rosa Plain (SRP) is a NW- oriented dissected lowland ~60 km long by 12 km wide, underlain by fault bounded Neogene basins containing syntectonic sedimentary and volcanic fills up to 2.5 km-thick. In response to lengthening of the transform margin ~7 to 5 Ma, Neogene strata now beneath the plain were dropped into extensional basins in a SE-tapered wedge-shaped block bounded on the SW by ~N 50° W-oriented faults of a proto-Hayward fault zone, and on the NE by newly initiated ~N 35°- 40°W-oriented faults of the Rodgers Creek-Healdsburg fault zone. Comparisons of the geologic, chronostratigraphic and geophysical frameworks of SRP with well constrained datasets used for Neogene reconstructions of the northern San Andreas Fault system indicates to us that the SRP and its buried basins are firmly tied to a strike-slip basin formational setting in the wake of the Mendocino triple junction (MTJ). Onshore and offshore datasets that integrate the geology and chronostratigraphy with geophysical data show that the MTJ at ~7 to 5 Ma was situated between the present latitudes of ~38.5° and ~39° N, opposite SRP. The SRP formed the delta of a large river that flowed toward the WNW, around a proto-Hayward fault-bounded bedrock promontory, into an estuary that adjoined the adjacent near shore and shelf of the margin. The modern Eel River basin, a deformed and uplifted remnant of the Cascadia Forearc margin just north of the present position of the MTJ, lies in a setting similar to the paleogeographic setting of the SRP. Closer examination, however, reveals two important differences between the SRP and MTJ settings. First, the ~6 to 9 Ma fluvial system that flowed NW across the Hayward fault from the east San Francisco Bay region onto SRP, also flowed across the San Andreas fault into submarine canyons of the Delgada Fan on the Pacific Plate, south of the MTJ. In contrast, sediment transported by the

  16. Basin Overflow Floods on Mars

    NASA Astrophysics Data System (ADS)

    Irwin, R. P.

    2006-12-01

    On Earth, the most intense recognized historical and paleofloods have been ice dambursts or overflows of large basins, often initiated by abundant runoff or meltwater from the contributing watersheds. Many impact craters and other basins also overflowed in the Martian cratered highlands, and some of their incised outlet valleys similarly record evidence of erosive floods. Otherwise, the commonly small, enclosed watersheds on Mars contain poorly developed valley networks and relatively simple depositional landforms, which record little evidence of intense (by terrestrial standards) meteorological floods. For these reasons, basin overflows may have been disproportionately important mechanisms for incision of large valleys on Mars. Many of the Martian outflow channels head in topographic settings that favored ponding, including large canyons, impact or intercrater basins, chaotic terrain basins, and grabens. This topography may have accumulated somewhat slower groundwater discharges from the subsurface to support peak channel discharges of 106-108 m3/s. To yield a discharge of 106, 107, and 108 m3/s from a dam failure with a width/depth ratio of 5, the model predicts that a breach of ~100, 250, and 640 m, respectively, must form rapidly with respect to the decline of lake level. Terrestrial damburst floods have not exceeded ~106 m3/s for earthen dams and ~107 m3/s for ice dams, but brecciation of the Martian surface by impact cratering may have allowed larger damburst failures, whereas solid bedrock was exposed at shallower depths in the terrestrial examples. Moreover, many of the Martian basins were much larger than enclosed continental basins on Earth, so long-lived overflows may have facilitated entrenchment of deeper channels. Some large, mid-latitude basins overflowed to carve Ma'adim Vallis and the Uzboi-Ladon-Margaritifer Valles system, which are similar in scale to the terrestrial Grand Canyon but record much larger formative discharges. Models of damburst

  17. Hydrogeologic framework of sedimentary deposits in six structural basins, Yakima River basin, Washington

    USGS Publications Warehouse

    Jones, M.A.; Vaccaro, J.J.; Watkins, A.M.

    2006-01-01

    The hydrogeologic framework was delineated for the ground-water flow system of the sedimentary deposits in six structural basins in the Yakima River Basin, Washington. The six basins delineated, from north to south are: Roslyn, Kittitas, Selah, Yakima, Toppenish, and Benton. Extent and thicknesses of the hydrogeologic units and total basin sediment thickness were mapped for each basin. Interpretations were based on information from about 4,700 well records using geochemical, geophysical, geologist's or driller's logs, and from the surficial geology and previously constructed maps and well interpretations. The sedimentary deposits were thickest in the Kittitas Basin reaching a depth of greater than 2,000 ft, followed by successively thinner sedimentary deposits in the Selah basin with about 1,900 ft, Yakima Basin with about 1,800 ft, Toppenish Basin with about 1,200 ft, Benton basin with about 870 ft and Roslyn Basin with about 700 ft.

  18. Stormwater detention basin sediment removal

    SciTech Connect

    Gross, W.E.

    1995-12-31

    In the past, stormwater runoff from landfills has been treated mainly by focusing on reducing the peak storm discharge rates so as not to hydraulically impact downstream subsheds. However, with the advent of stricter water quality regulations based on the Federal Clean Water Act, and the related NPDES and SPDES programs, landfill owners and operators are now legally responsible for the water quality of the runoff once it leaves the landfill site. At the Fresh Kills Landfill in New York City, the world`s largest covering over 2000 acres, landfilling activities have been underway since 1945. With the main objective at all older landfill sites having focused on maximizing the available landfill footprint in order to obtain the most possible airspace volume, consideration was not given for the future siting of stormwater basin structures. Therefore, when SCS Engineers began developing the first comprehensive stormwater management plan for the site, the primary task was to locate potential sites for all the stormwater basins in order to comply with state regulations for peak stormwater runoff control. The basins were mostly constructed where space allowed, and were sized to be as large as possible given siting and subshed area constraints. Seventeen stormwater basins have now been designed and are being constructed to control the peak stormwater runoff for the 25-year, 24-hour storm as required by New York State. As an additional factor of safety, the basins were also designed for controlled discharge of the 100-year, 24 hour storm.

  19. Water Accounting from Ungauged Basins

    NASA Astrophysics Data System (ADS)

    Bastiaanssen, W. G.; Savenije, H.

    2014-12-01

    Water scarcity is increasing globally. This requires a more accurate management of the water resources at river basin scale and understanding of withdrawals and return flows; both naturally and man-induced. Many basins and their tributaries are, however, ungauged or poorly gauged. This hampers sound planning and monitoring processes. While certain countries have developed clear guidelines and policies on data observatories and data sharing, other countries and their basin organization still have to start on developing data democracies. Water accounting quantifies flows, fluxes, stocks and consumptive use pertaining to every land use class in a river basin. The objective is to derive a knowledge base with certain minimum information that facilitates decision making. Water Accounting Plus (WA+) is a new method for water resources assessment reporting (www.wateraccounting.org). While the PUB framework has yielded several deterministic models for flow prediction, WA+ utilizes remote sensing data of rainfall, evaporation (including soil, water, vegetation and interception evaporation), soil moisture, water levels, land use and biomass production. Examples will be demonstrated that show how remote sensing and hydrological models can be smartly integrated for generating all the required input data into WA+. A standard water accounting system for all basins in the world - with a special emphasis on data scarce regions - is under development. First results of using remote sensing measurements and hydrological modeling as an alternative to expensive field data sets, will be presented and discussed.

  20. Inversion of Extensional Sedimentary Basins

    NASA Astrophysics Data System (ADS)

    Buiter, Susanne J. H.; Pfiffner, O. Adrian

    The evolution of extensional sedimentary basins is governed by the surrounding stress field and can, therefore, be expected to be highly sensitive to variations in these stresses. Important changes in basin geometry are to be expected in the case of an even short-lived reversal from extension to compression. We investigate the evolu- tion of fold and thrust structures which form in compression after extension, when basin forming processes have come to a complete stop. To this purpose, we use a two- dimensional, viscoplastic model and start our experiments from a pre-existing exten- sional geometry. We illustrate the sensitivity of the evolving structures to inherited extensional geometry, sedimentary and erosional processes, and material properties. One series of our model experiments involves the upper- to middle crust only in order to achieve a high detail in the basin area. We find that our results agree with examples from nature and analogue studies in, among others, the uplift and rotation of syn-rift sediments, the propagation of shear zones into the post-rift sediments and, in specific cases, the development of back-thrusts or basement short-cut faults. We test the out- come of these models by performing a second series of model simulations in which basins on a continental margin are inverted through their progressive approach of a subduction zone. These latter models are on the scale of the whole upper mantle.

  1. Testing for Basins of Wada

    PubMed Central

    Daza, Alvar; Wagemakers, Alexandre; Sanjuán, Miguel A. F.; Yorke, James A.

    2015-01-01

    Nonlinear systems often give rise to fractal boundaries in phase space, hindering predictability. When a single boundary separates three or more different basins of attraction, we say that the set of basins has theWada property and initial conditions near that boundary are even more unpredictable. Many physical systems of interest with this topological property appear in the literature. However, so far the only approach to study Wada basins has been restricted to two-dimensional phase spaces. Here we report a simple algorithm whose purpose is to look for the Wada property in a given dynamical system. Another benefit of this procedure is the possibility to classify and study intermediate situations known as partially Wada boundaries. PMID:26553444

  2. Interplay between compression and extension and its impact on basins evolution along the Europe-Adria suture in the area of Belgrade, Serbia

    NASA Astrophysics Data System (ADS)

    Marinko, Toljić; Liviu, Matenco; Uroš, Stojadinović

    2015-04-01

    The segment of the suture zone between units of contrasting Adriatic and European affinities situated in Belgrade area of central Serbia is composed of a complex tectono-sedimentary setting that was amalgamated during Cretaceous to Paleogene closure of the Neothethys Ocean. We have analyzed this Cretaceous sedimentary succession in the context of broader kinematic and depositional evolution of the Europe - Adria collision zone, where the basinal evolution was governed by the enduring processes of subduction. A slice of oceanic lithosphere was obducted during the latest Jurassic times far towards the SW over the Adriatic continental margin creating an underlying ophiolitic mélange. This mélange contains radiolarites deposited over oceanic lithosphere, the youngest being of Early Tithonian in age. These radiolarites and the Cretaceous post-tectonic overlying the ophiolites cover define a Middle-Late Tithonian age of the obduction. The obduction was followed by rapid subsidence affecting the European margin during Cretaceous times, which was unconformably covered by a gradual deepening facies. The base of this overstepping sequence, generally referred as the Lower Cretaceous "para-flysch", is composed of thick layered shallow-water limestones that cemented large fragments of re-deposited Tithonian high-organic limestones. These are overlain by a turbiditic alternation of mudstones and sandstones that are laterally replaced by graded calcareous sandstones and breccias containing Lower Cretaceous microfauna and local large olistostromic fragments of re-deposited Upper Jurassic macrofauna. These deposits are overlain into a deep-water carbonatic succession containing often cherts and radiolarites replaced laterally to the S and SW by turbidites that marks the transition to the Barremian. These gradually deepening deposits with a highly lateral variation in paleo-bathimetry define an Early Cretaceous fore-arc basin system, its sediments being deposited over the European

  3. Oil in the Malvinas Basin

    SciTech Connect

    Galeazzi, J.S.

    1996-08-01

    The Malvinas Basin is petroliferous. The main source rocks are Late Jurassic and Early Cretaceous outer shelf to basinal shales known as the Pampa Rincon and Lower Inoceramus formations. Main reservoirs are fluvial and shallow-marine sandstones of the coeval Springhill Formation. On the western flank of the basin, 17 wells drilled the Cenozoic and Mesozoic column. Three of these wells discovered hydrocarbons within the Springhill Formation, and one discovered oil in Early Paleogene sandstones. Additionally, some wells recorded shows at different levels within the stratigraphic succession. A detailed overview of the drilled portion of the basin permitted the construction of a sequence stratigraphic framework, and yielded clues on a complex history of deformation. Interpretation of facies and stratal stacking and termination patterns determined that the main reservoir and source rocks were deposited in a ramp-style depositional setting. They represent the lower transgressive phase of a Late Jurassic to Early Cretaceous megasequence deposited during the early sag stage of the basin. Alternative reservoirs to the Springhill sandstones include early Paleogene glauconitic sandstones and carbonates, and Miocene deep-water turbidites. Structural trap styles include normal fault features of Jurassic to Early Cretaceous age, and compressional and inverted positive structures due to Neogene compression. Possible combination and stratigraphic traps include: little tested onlap pinchout of Late Jurassic to Early Cretaceous and Paleogene sandstones and untested erosionally truncated Paleogene sandstones; Early Paleogene carbonate buildups and Miocene deep-water turbidite mounds. The understanding of the geology of the western Malvinas Basin is the key to success of exploration in the huge frontier surrounding areas.

  4. H-Area Seepage Basins

    SciTech Connect

    Stejskal, G.

    1990-12-01

    During the third quarter of 1990 the wells which make up the H-Area Seepage Basins (H-HWMF) monitoring network were sampled. Laboratory analyses were performed to measure levels of hazardous constituents, indicator parameters, tritium, nonvolatile beta, and gross alpha. A Gas Chromatograph Mass Spectrometer (GCMS) scan was performed on all wells sampled to determine any hazardous organic constituents present in the groundwater. The primary contaminants observed at wells monitoring the H-Area Seepage Basins are tritium, nitrate, mercury, gross alpha, nonvolatile beta, trichloroethylene (TCE), tetrachloroethylene, lead, cadmium, arsenic, and total radium.

  5. Origin of the earth's ocean basins

    NASA Technical Reports Server (NTRS)

    Frey, H.

    1977-01-01

    The earth's original ocean basins are proposed to be mare-type basins produced 4 billion y.a. by the flux of asteroid-sized objects responsible for the lunar mare basins. Scaling upward from the observed number of lunar basins for the greater capture cross-section and impact velocity of the earth indicates that at least 50% of an original global crust would have been converted to basin topography. These basins were flooded by basaltic liquids in times short compared to the isostatic adjustment time for the basin. The modern crustal dichotomy (60% oceanic, 40% continental crust) was established early in the history of the earth, making possible the later onset of plate tectonic processes. These later processes have subsequently reworked, in several cycles, principally the oceanic parts of the earth's crust, changing the configuration of the continents in the process. Ocean basins (and oceans themselves) may be rare occurrences on planets in other star systems.

  6. Origin of the earth's ocean basins

    NASA Technical Reports Server (NTRS)

    Frex, H.

    1977-01-01

    The earth's original ocean basins were mare-type basins produced 4 billion years ago by the flux of asteroid-sized objects responsible for the lunar mare basins. Scaling upwards from the observed number of lunar basins for the greater capture cross-section and impact velocity of the Earth