Investigating the 3-D Subduction Initiation Processes at Transform Faults and Passive Margins

Science.gov (United States)

Peng, H.; Leng, W.

2017-12-01

Studying the processes of subduction initiation is a key for understanding the Wilson cycle and improving the theory of plate tectonics. Previous studies investigated subduction initiation with geological synthesis and geodynamic modeling methods, discovering that subduction intends to initiate at the transform faults close to oceanic arcs, and that its evolutionary processes and surface volcanic expressions are controlled by plate strength. However, these studies are mainly conducted with 2-D models, which cannot deal with lateral heterogeneities of crustal thickness and strength along the plate interfaces. Here we extend the 2-D model to a 3-D parallel subduction model with high computational efficiency. With the new model, we study the dynamic controlling factors, morphology evolutionary processes and surface expressions for subduction initiation with lateral heterogeneities of material properties along transform faults and passive margins. We find that lateral lithospheric heterogeneities control the starting point of the subduction initiation along the newly formed trenches and the propagation speed for the trench formation. New subduction tends to firstly initiate at the property changing point along the transform faults or passive margins. Such finds may be applied to explain the formation process of the Izu-Bonin-Mariana (IBM) subduction zone in the western Pacific and the Scotia subduction zone at the south end of the South America. Our results enhance our understanding for the formation of new trenches and help to provide geodynamic modeling explanations for the observed remnant slabs in the upper mantle and the surface volcanic expressions.

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

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

2017-09-01

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

Formation of mantle "lone plumes" in the global downwelling zone - A multiscale modelling of subduction-controlled plume generation beneath the South China Sea

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Zhang, Nan; Li, Zheng-Xiang

2018-01-01

It has been established that almost all known mantle plumes since the Mesozoic formed above the two lower mantle large low shear velocity provinces (LLSVPs). The Hainan plume is one of the rare exceptions in that instead of rising above the LLSVPs, it is located within the broad global mantle downwelling zone, therefore classified as a "lone plume". Here, we use the Hainan plume example to investigate the feasibility of such lone plumes being generated by subducting slabs in the mantle downwelling zone using 3D geodynamic modelling. Our geodynamic model has a high-resolution regional domain embedded in a relatively low resolution global domain, which is set up in an adaptive-mesh-refined, 3D mantle convection code ASPECT (Advanced Solver for Problems in Earth's ConvecTion). We use a recently published plate motion model to define the top mechanical boundary condition. Our modelling results suggest that cold slabs under the present-day Eurasia, formed from the Mesozoic subduction and closure of the Tethys oceans, have prevented deep mantle hot materials from moving to the South China Sea from regions north or west of the South China Sea. From the east side, the Western Pacific subduction systems started to promote the formation of a lower-mantle thermal-chemical pile in the vicinity of the future South China Sea region since 70 Ma ago. As the top of this lower-mantle thermal-chemical pile rises, it first moved to the west, and finally rested beneath the South China Sea. The presence of a thermochemical layer (possible the D″ layer) in the model helps stabilizing the plume root. Our modelling is the first implementation of multi-scale mesh in the regional model. It has been proved to be an effective way of modelling regional dynamics within a global plate motion and mantle dynamics background.

Water, oceanic fracture zones and the lubrication of subducting plate boundaries—insights from seismicity

Science.gov (United States)

Schlaphorst, David; Kendall, J.-Michael; Collier, Jenny S.; Verdon, James P.; Blundy, Jon; Baptie, Brian; Latchman, Joan L.; Massin, Frederic; Bouin, Marie-Paule

2016-03-01

We investigate the relationship between subduction processes and related seismicity for the Lesser Antilles Arc using the Gutenberg-Richter law. This power law describes the earthquake-magnitude distribution, with the gradient of the cumulative magnitude distribution being commonly known as the b-value. The Lesser Antilles Arc was chosen because of its along-strike variability in sediment subduction and the transition from subduction to strike-slip movement towards its northern and southern ends. The data are derived from the seismicity catalogues from the Seismic Research Centre of The University of the West Indies and the Observatoires Volcanologiques et Sismologiques of the Institut de Physique du Globe de Paris and consist of subcrustal events primarily from the slab interface. The b-value is found using a Kolmogorov-Smirnov test for a maximum-likelihood straight line-fitting routine. We investigate spatial variations in b-values using a grid-search with circular cells as well as an along-arc projection. Tests with different algorithms and the two independent earthquake cataloges provide confidence in the robustness of our results. We observe a strong spatial variability of the b-value that cannot be explained by the uncertainties. Rather than obtaining a simple north-south b-value distribution suggestive of the dominant control on earthquake triggering being water released from the sedimentary cover on the incoming American Plates, or a b-value distribution that correlates with on the obliquity of subduction, we obtain a series of discrete, high b-value `bull's-eyes' along strike. These bull's-eyes, which indicate stress release through a higher fraction of small earthquakes, coincide with the locations of known incoming oceanic fracture zones on the American Plates. We interpret the results in terms of water being delivered to the Lesser Antilles subduction zone in the vicinity of fracture zones providing lubrication and thus changing the character of the

Chromosomes of South American Bufonidae (Amphibia, Anura Chromosomes of South American Bufonidae (Amphibia, Anura

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Brum Zorrilla N.

1973-09-01

Full Text Available Karyotypes of eight of South American Bufonidae were studied: B.ictericus, B. spinulosus spinulosus, B. arenarum, B. g. fernandezae, B. g. d'orbignyi, B. crucifer, B. paracnemis and B. marinus. In all species 2n = 22 chromosomes were found. Neither heteromorphic pairs of chromosomes nor bivalents with characteristic morphology and behavior of sex chromosomesduring male meiosis were observed in any species.Karyotypes of eight of South American Bufonidae were studied: B.ictericus, B. spinulosus spinulosus, B. arenarum, B. g. fernandezae, B. g. d'orbignyi, B. crucifer, B. paracnemis and B. marinus. In all species 2n = 22 chromosomes were found. Neither heteromorphic pairs of chromosomes nor bivalents with characteristic morphology and behavior of sex chromosomesduring male meiosis were observed in any species.

Using thermal and compositional modeling to assess the role of water in Alaskan flat slab subduction

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Robinson, S. E.; Porter, R. C.; Hoisch, T. D.

2017-12-01

Although plate tectonic theory is well established in the geosciences, the mechanisms and details of various plate-tectonics related phenomena are not always well understood. In some ( 10%) convergent plate boundaries, subduction of downgoing oceanic plates is characterized by low angle geometries and is termed "flat slab subduction." The mechanism(s) driving this form of subduction are not well understood. The goal of this study is to explore the role that water plays in these flat slab subduction settings. This is important for a better understanding of the behavior of these systems and for assessing volcanic hazards associated with subduction and slab rollback. In southern Alaska, the Pacific Plate is subducting beneath the North American plate at a shallow angle. This low-angle subduction within the region is often attributed to the subduction of the Yakutat block, a terrane accreting to the south-central coast of Alaska. This flat slab region is bounded by the Aleution arc to the west and the strike-slip Queen Charlotte fault to the east. Temperature and compositional models for a 500-km transect across this subduction zone in Alaska were run for ten million years (the length of time that flat slab subduction has been ongoing in Alaska) and allow for interpretation of present-day conditions at depth. This allows for an evaluation of two hypotheses regarding the role of water in flat-slab regions: (1) slab hydration and dehydration help control slab buoyancy which influences whether flat slab subduction will be maintained or ended. (2) slab hydration/dehydration of the overlying lithosphere impacts deformation within the upper plate as water encourages plate deformation. Preliminary results from thermal modeling using Thermod8 show that cooling of the mantle to 500 °C is predicted down to 100 km depth at 10 million years after the onset of low-angle subduction (representing present-day). Results from compositional modeling in Perple_X show the maximum amount

Transition from strike-slip faulting to oblique subduction: active tectonics at the Puysegur Margin, South New Zealand

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Lamarche, Geoffroy; Lebrun, Jean-Frédéric

2000-01-01

South of New Zealand the Pacific-Australia (PAC-AUS) plate boundary runs along the intracontinental Alpine Fault, the Puysegur subduction front and the intraoceanic Puysegur Fault. The Puysegur Fault is located along Puysegur Ridge, which terminates at ca. 47°S against the continental Puysegur Bank in a complex zone of deformation called the Snares Zone. At Puysegur Trench, the Australian Plate subducts beneath Puysegur Bank and the Fiordland Massif. East of Fiordland and Puysegur Bank, the Moonlight Fault System (MFS) represents the Eocene strike-slip plate boundary. Interpretation of seafloor morphology and seismic reflection profiles acquired over Puysegur Bank and the Snares Zone allows study of the transition from intraoceanic strike-slip faulting along the Puysegur Ridge to oblique subduction at the Puysegur Trench and to better understand the genetic link between the Puysegur Fault and the MFS. Seafloor morphology is interpreted from a bathymetric dataset compiled from swath bathymetry data acquired during the 1993 Geodynz survey, and single beam echo soundings acquired by the NZ Royal Navy. The Snares Zone is the key transition zone from strike-slip faulting to subduction. It divides into three sectors, namely East, NW and SW sectors. A conspicuous 3600 m-deep trough (the Snares Trough) separates the NW and East sectors. The East sector is characterised by the NE termination of Puysegur Ridge into right-stepping en echelon ridges that accommodate a change of strike from the Puysegur Fault to the MFS. Between 48°S and 47°S, in the NW sector and the Snares Trough, a series of transpressional faults splay northwards from the Puysegur Fault. Between 49°50'S and 48°S, thrusts develop progressively at Puysegur Trench into a decollement. North of 48°S the Snares Trough develops between two splays of the Puysegur Fault, indicating superficial extension associated with the subsidence of Puysegur Ridge. Seismic reflection profiles and bathymetric maps show a

Barium isotope geochemistry of subduction-zone magmas

Science.gov (United States)

Yu, H.; Nan, X.; Huang, J.; Wörner, G.; Huang, F.

2017-12-01

Subduction zones are crucial tectonic setting to study material exchange between crust and mantle, mantle partial melting with fluid addition, and formation of ore-deposits1-3. The geochemical characteristics of arc lavas from subduction zones are different from magmas erupted at mid-ocean ridges4, because there are addition of fluids/melts from subducted AOC and its overlying sediments into their source regions in the sub-arc mantle4. Ba is highly incompatible during mantle melting5, and it is enriched in crust (456 ppm)6 relative to the mantle (7.0 ppm)7. The subducted sediments are also enriched in Ba (776 ppm of GLOSS)8. Moreover, because Ba is fluid soluble during subduction, it has been used to track contributions of subduction-related fluids to arc magmas9 or recycled sediments to the mantle10-11. To study the Ba isotope fractionation behavior during subduction process, we analyzed well-characterized, chemically-diverse arc lavas from Central American, Kamchatka, Central-Eastern Aleutian, and Southern Lesser Antilles. The δ137/134Ba of Central American arc lavas range from -0.13 to 0.24‰, and have larger variation than the arc samples from other locations. Except one sample from Central-Eastern Aleutian arc with obviously heavy δ137/134Ba values (0.27‰), all other samples from Kamchatka, Central-Eastern Aleutian, Southern Lesser Antilles arcs are within the range of OIB. The δ137/134Ba is not correlated with the distance to trench, partial melting degrees (Mg#), or subducting slab-derived components. The samples enriched with heavy Ba isotopes have low Ba contents, indicating that Ba isotopes can be fractionated at the beginning of dehydration process with small amount of Ba releasing to the mantle wedge. With the dehydration degree increasing, more Ba of the subducted slab can be added to the source of arc lavas, likely homogenizing the Ba isotope signatures. 1. Rudnick, R., 1995 Nature; 2. Tatsumi, Y. & Kogiso, T., 2003; 3. Sun, W., et al., 2015 Ore

Can north american fish passage tools work for South american migratory fishes?

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Claudio Rafael Mariano Baigún

Full Text Available In North America, the Numerical Fish Surrogate (NFS is used to design fish bypass systems for emigrating juvenile salmon as they migrate from hatchery outfalls and rearing habitats to adult habitat in the oceans. The NFS is constructed of three linked modules: 1 a computational fluid dynamics model describes the complex flow fields upstream of dams at a scale sufficiently resolved to analyze, understand and forecast fish movement, 2 a particle tracking model interpolates hydraulic information from the fixed nodes of the computational fluid model mesh to multiple locations relevant to migrating fish, and 3 a behavior model simulates the cognition and behavior of individual fish in response to the fluid dynamics predicted by the computational fluid dynamics model. These three modules together create a virtual reality where virtual fish exhibit realistic dam approach behaviors and can be counted at dam exits in ways similar to the real world. Once calibrated and validated with measured fish movement and passage data, the NFS can accurately predict fish passage proportions with sufficient precision to allow engineers to select one optimum alternative from among many competing structural or operational bypass alternatives. Although South American fish species are different from North American species, it is likely that the basic computational architecture and numerical methods of the NFS can be used for fish conservation in South America. Consequently, the extensive investment made in the creation of the NFS need not be duplicated in South America. However, its use in South America will require that the behavioral response of the continent's unique fishes to hydrodynamic cues must be described, codified and tested before the NFS can be used to conserve fishes by helping design efficient South American bypass systems. To this end, we identify studies that could be used to describe the movement behavior of South American fishes of sufficient detail

Mutation spectrum in South American Lynch syndrome families

DEFF Research Database (Denmark)

Dominguez-Valentin, Mev; Nilbert, Mef; Wernhoff, Patrik

2013-01-01

Genetic counselling and testing for Lynch syndrome have recently been introduced in several South American countries, though yet not available in the public health care system.......Genetic counselling and testing for Lynch syndrome have recently been introduced in several South American countries, though yet not available in the public health care system....

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

Science.gov (United States)

Garth, Tom; Rietbrock, Andreas

2017-09-01

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

Miocene-Recent sediment flux in the south-central Alaskan fore-arc basin governed by flat-slab subduction

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Finzel, Emily S.; Enkelmann, Eva

2017-04-01

The Cook Inlet in south-central Alaska contains the early Oligocene to Recent stratigraphic record of a fore-arc basin adjacent to a shallowly subducting oceanic plateau. Our new measured stratigraphic sections and detrital zircon U-Pb geochronology and Hf isotopes from Neogene strata and modern rivers illustrate the effects of flat-slab subduction on the depositional environments, provenance, and subsidence in fore-arc sedimentary systems. During the middle Miocene, fluvial systems emerged from the eastern, western, and northern margins of the basin. The axis of maximum subsidence was near the center of the basin, suggesting equal contributions from subsidence drivers on both margins. By the late Miocene, the axis of maximum subsidence had shifted westward and fluvial systems originating on the eastern margin of the basin above the flat-slab traversed the entire width of the basin. These mud-dominated systems reflect increased sediment flux from recycling of accretionary prism strata. Fluvial systems with headwaters above the flat-slab region continued to cross the basin during Pliocene time, but a change to sandstone-dominated strata with abundant volcanogenic grains signals a reactivation of the volcanic arc. The axis of maximum basin subsidence during late Miocene to Pliocene time is parallel to the strike of the subducting slab. Our data suggest that the character and strike-orientation of the down-going slab may provide a fundamental control on the nature of depositional systems, location of dominant provenance regions, and areas of maximum subsidence in fore-arc basins.

Premature mortality patterns among American Indians in South Dakota, 2000-2010.

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Christensen, Mathew; Kightlinger, Lon

2013-05-01

American Indians in South Dakota have the highest mortality rates in the nation compared to other racial and ethnic groups and American Indians in other states. Cause-related and age-specific mortality patterns among American Indians in South Dakota are identified to guide prevention planning and policy efforts designed to reduce mortality within this population, in both South Dakota and other parts of the U.S. Death certificate data from South Dakota (2000-2010), on 5738 American Indians and 70,580 whites, were used to calculate age-specific mortality rates and rate ratios. These values were examined in order to identify patterns among the leading causes of death. Analyses were completed in 2011 and 2012. Within the South Dakota population, 70% of American Indians died before reaching age 70 years, compared to 25% of whites. Fatal injuries and chronic diseases were the leading causes of premature mortality. Nine leading causes of death showed consistent patterns of mortality disparity between American Indians and whites, with American Indians having significantly higher rates of mortality at lower ages. Premature mortality among American Indians in South Dakota is a serious public health problem. Unified efforts at the federal, tribal, state, and local levels are needed to reduce premature death within this population. Copyright © 2013 American Journal of Preventive Medicine. Published by Elsevier Inc. All rights reserved.

The rigid Andean sliver hypothesis challenged : impact on interseismic coupling on the Chilean subduction zone

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Metois, M.

2017-12-01

Convergence partitioning between subduction zones and crustal active structures has been widely evidenced. For instance, the convergence between the Indian and Sunda plates is accommodated both by the Sumatra subduction zone and the Great Sumatran strike-slip fault, that defines a narrow sliver. In Cascadia, small-scale rotating rigid blocks bounded by active faults have been proposed (e.g. McCaffrey et al. 2007). Recent advances in geodetic measurements along the South-American margin especially in Ecuador, Peru and Chile and the need for precise determination of the coupling amount on the megathrust interface in particular for seismic hazard assessment, led several authors to propose the existence of large-scale Andean slivers rotating clockwise and counter-clockwise South and North of the Arica bend, respectively (e.g. Chlieh et al. 2011, Nocquet et al. 2014, Métois et al. 2013). In Chile, one single large Andean sliver bounded to the west by the subduction thrust and to the east by the subandean fold-an-thrust belt active front is used to mimic the velocities observed in the middle to far field that are misfitted by elastic coupling models on the megathrust interface alone (Métois et al. 2016). This rigid sliver is supposed to rotate clockwise around a Euler pole located in the South Atlantic ocean, consistently with long-term observed rotations detected by paleomagnetism (e.g. Arriagada et al. 2008). However, recent GPS data acquired in the Taltal area ( 26°S, Klein et al. submitted) show higher than expected middle-field eastward velocities and question the first-order assumption of a rigid Andean sliver. Mis-modeling the fore-arc deformation has a direct impact on the inverted coupling amount and distribution, and could therefore bias significantly the megathrust rupture scenarios. Correctly estimating the current-day deformation of the Andes is therefore required to properly assess for coupling on the plate interface and is challenging since crustal

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

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Horton, Brian K.

2016-04-01

-skinned basement inversion with geometrically and kinematically linked thin-skinned thrust structures at shallower levels in the eastern foreland, including well-dated late Miocene growth strata. The mid-Cenozoic hiatus potentially signifies nondeposition during passage of a flexural forebulge or nondeposition during neutral to extensional conditions possibly driven by a transient retreating-slab configuration along the western margin of South America. Similar long-lived stratigraphic gaps are commonly observed in other foreland records of continental convergent margins. It is proposed that Andean orogenesis along the South American convergent margin has long been sensitive to variations in subduction dynamics throughout Mesozoic-Cenozoic time, such that shifts in relative convergence and degree of mechanical coupling along the subduction interface (i.e., transitions between advancing versus retreating modes of subduction) have governed fluctuating contractional, extensional, and neutral conditions. Unclear is whether these various modes affected the entire convergent margin simultaneously due to continental-scale changes (e.g., temporal shifts in plate convergence, absolute motion of upper plate, or mantle wedge circulation) or whether parts of the margin behaved independently due to smaller-scale fluctuations (e.g., spatial variations in the age of the subducted plate, buoyant asperities in the downgoing slab, or asthenospheric anomalies).

South American climate during the Last Glacial Maximum: Delayed onset of the South American monsoon

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Cook, K. H.; Vizy, E. K.

2006-01-01

The climate of the Last Glacial Maximum (LGM) over South America is simulated using a regional climate model with 60-km resolution, providing a simulation that is superior to those available from global models that do not resolve the topography and regional-scale features of the South American climate realistically. LGM conditions on SST, insolation, vegetation, and reduced atmospheric CO2 on the South American climate are imposed together and individually. Remote influences are not included. Annual rainfall is 25-35% lower in the LGM than in the present day simulation throughout the Amazon basin. A primary cause is a 2-3 month delay in the onset of the rainy season, so that the dry season is about twice as long as in the present day. The delayed onset occurs because the low-level inflow from the tropical Atlantic onto the South American continent is drier than in the present day simulation due to reduced evaporation from cooler surface waters, and this slows the springtime buildup of moist static energy that is needed to initiate convection. Once the monsoon begins in the Southern Hemisphere, LGM rainfall rates are similar to those in the present day. In the Northern Hemisphere, however, rainfall is lower throughout the (shortened) rainy season. Regional-scale structure includes slight precipitation increases in the Nordeste region of Brazil and along the eastern foothills of the Andes, and a region in the center of the Amazon basin that does not experience annual drying. In the Andes Mountains, the signal is complicated, with regions of significant rainfall increases adjacent to regions with reduced precipitation.

Haemotrophic mycoplasmas in South American camelids in Switzerland

OpenAIRE

Kaufmann, C; Meli, Marina L; Robert, N; Willi, Barbara; Hofmann-Lehmann, Regina; Wengi, Nicole; Lutz, Hans; Zanolari, P

2007-01-01

The red blood cell parasite 'Candidatus Mycoplasma haemolamae', formerly Eperythrozoon, is known to be widespread in South American camelids in the USA, causing anaemia in affected animals. Up to now, haemotrophic mycoplasmas were not observed in South American camelids in Europe; however, they were known in a herd of alpacas in Switzerland and to identify them as 'Candidatus M. haemolamae'. Possible ways of transmission are discussed.

Continental crust melting induced by subduction initiation of the South Tianshan Ocean: Insight from the Latest Devonian granitic magmatism in the southern Yili Block, NW China

Science.gov (United States)

Bao, Zihe; Cai, Keda; Sun, Min; Xiao, Wenjiao; Wan, Bo; Wang, Yannan; Wang, Xiangsong; Xia, Xiaoping

2018-03-01

The Tianshan belt of the southwestern Central Asian Orogenic Belt was generated by Paleozoic multi-stage subduction and final closure of several extinct oceans, including the South Tianshan Ocean between the Kazakhstan-Yili and Tarim blocks. However, the subduction initiation and polarity of the South Tianshan Ocean remain issues of highly debated. This study presents new zircon U-Pb ages, geochemical compositions and Sr-Nd isotopes, as well as zircon Hf isotopic data of the Latest Devonian to Early Carboniferous granitic rocks in the Wusun Mountain of the Yili Paleozoic convergent margin, which, together with the spatial-temporal distributions of regional magmatic rocks, are applied to elucidate their petrogenesis and tectonic linkage to the northward subduction initiation of the South Tianshan Ocean. Our zircon U-Pb dating results reveal that these granites were emplaced at the time interval of 362.0 ± 1.2-360.3 ± 1.9 Ma, suggesting a marked partial melting event of the continental crust in the Latest Devonian to Early Carboniferous. These granites, based on their mineral compositions and textures, can be categorized as monzogranites and K-feldspar granites. Geochemically, both monzogranites and K-feldspar granites have characters of I-type granites with high K2O contents (4.64-4.83 wt.%), and the K-feldspar granites are highly fractionated I-type granites, while the monzogranites have features of unfractionated I-type granites. Whole-rock Sr-Nd isotopic modeling results suggest that ca. 20-40% mantle-derived magmas may be involved in magma mixing with continental crust partial melts to generate the parental magmas of the granites. The mantle-derived basaltic magmas was inferred not only to be a major component of magma mixture but also as an important heat source to fuse the continental crust in an extensional setting, which is evidenced by the high zircon saturation temperatures (713-727 °C and 760-782 °C) of the studied granites. The Latest Devonian to

Tearing, segmentation, and backstepping of subduction in the Aegean: New insights from seismicity

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Bocchini, G. M.; Brüstle, A.; Becker, D.; Meier, T.; van Keken, P. E.; Ruscic, M.; Papadopoulos, G. A.; Rische, M.; Friederich, W.

2018-06-01

This study revisits subduction processes at the Hellenic Subduction Zone (HSZ) including tearing, segmentation, and backstepping, by refining the geometry of the Nubian slab down to 150-180 km depth using well-located hypocentres from global and local seismicity catalogues. At the western termination of the HSZ, the Kefalonia Transform Fault marks the transition between oceanic and continental lithosphere subducting to the south and to the north of it, respectively. A discontinuity is suggested to exist between the two slabs at shallow depths. The Kefalonia Transform Fault is interpreted as an active Subduction-Transform-Edge-Propagator-fault formed as consequence of faster trench retreat induced by the subduction of oceanic lithosphere to the south of it. A model reconstructing the evolution of the subduction system in the area of Peloponnese since 34 Ma, involving the backstepping of the subduction to the back-side of Adria, provides seismological evidence that supports the single-slab model for the HSZ and suggests the correlation between the downdip limit of the seismicity to the amount of subducted oceanic lithosphere. In the area of Rhodes, earthquake hypocentres indicate the presence of a NW dipping subducting slab that rules out the presence of a NE-SW striking Subduction-Transform-Edge-Propagator-fault in the Pliny-Strabo trenches region. Earthquake hypocentres also allow refining the slab tear beneath southwestern Anatolia down to 150-180 km depth. Furthermore, the distribution of microseismicity shows a first-order slab segmentation in the region between Crete and Karpathos, with a less steep and laterally wider slab segment to the west and a steeper and narrower slab segment to the east. Thermal models indicate the presence of a colder slab beneath the southeastern Aegean that leads to deepening of the intermediate-depth seismicity. Slab segmentation affects the upper plate deformation that is stronger above the eastern slab segment and the seismicity

Stochastic strong ground motion simulations for the intermediate-depth earthquakes of the south Aegean subduction zone

Science.gov (United States)

Kkallas, Harris; Papazachos, Konstantinos; Boore, David; Margaris, Vasilis

2015-04-01

We have employed the stochastic finite-fault modelling approach of Motazedian and Atkinson (2005), as described by Boore (2009), for the simulation of Fourier spectra of the Intermediate-depth earthquakes of the south Aegean subduction zone. The stochastic finite-fault method is a practical tool for simulating ground motions of future earthquakes which requires region-specific source, path and site characterizations as input model parameters. For this reason we have used data from both acceleration-sensor and broadband velocity-sensor instruments from intermediate-depth earthquakes with magnitude of M 4.5-6.7 that occurred in the south Aegean subduction zone. Source mechanisms for intermediate-depth events of north Aegean subduction zone are either collected from published information or are constrained using the main faulting types from Kkallas et al. (2013). The attenuation parameters for simulations were adopted from Skarladoudis et al. (2013) and are based on regression analysis of a response spectra database. The site amplification functions for each soil class were adopted from Klimis et al., (1999), while the kappa values were constrained from the analysis of the EGELADOS network data from Ventouzi et al., (2013). The investigation of stress-drop values was based on simulations performed with the EXSIM code for several ranges of stress drop values and by comparing the results with the available Fourier spectra of intermediate-depth earthquakes. Significant differences regarding the strong-motion duration, which is determined from Husid plots (Husid, 1969), have been identified between the for-arc and along-arc stations due to the effect of the low-velocity/low-Q mantle wedge on the seismic wave propagation. In order to estimate appropriate values for the duration of P-waves, we have automatically picked P-S durations on the available seismograms. For the S-wave durations we have used the part of the seismograms starting from the S-arrivals and ending at the

Present coupling along the Peruvian subduction asperity that devastated Lima while breaking during the 1746 earthquake

Science.gov (United States)

Cavalié, O.; Chlieh, M.; Villegas Lanza, J. C.

2017-12-01

Subduction zone are particularly prone to generating large earthquakes due to its wide lateral extension. In order to understand where, and possibly when, large earthquakes will occur, interseismic deformation observation is a key information because it allows to map asperities that accumulate stress on the plate interface. South American subduction is one of the longest worldwide, running all along the west coast of the continent. Combined with the relatively fast convergence rate between the Nazca plate and the South American continent, Chile and Peru experience regularly M>7.5 earthquakes. In this study, we focused on the Peruvian subduction margin and more precisely on the Central segment containing Lima where the seismic risk is the highest in the country due the large population that lives in the Peruvian capital. On the Central segment (10°S and 15°S), we used over 50 GPS interseismic measurements from campaign and continuous sites, as well as InSAR data to map coupling along the subduction interface. GPS data come from the Peruvian GPS network and InSAR data are from the Envisat satellite. We selected two tracks covering the central segment (including Lima) and with enough SAR image acquisitions between 2003 and 2010 to get a robust deformation estimation. GPS and InSAR data show a consistent tectonic signal with a maximum of surface displacement by the coast: the maximum horizontal velocities from GPS is about 20 mm and InSAR finds 12-13 mm in the LOS component. In addition, InSAR reveals lateral variations along the coast: the maximum motion is measured around Lima (11°S) and fades on either side. By inverting the geodetic data, we were able to map the coupling along the segment. It results in a main asperity where interseismic stress is loading. However, compared the previous published models based on GPS only, the coupling in the central segment seems more heterogeneous. Finally, we compared the deficit of seismic moment accumulating in the

Exploring opportunities and challenges for establishing a South American Space Agency

Science.gov (United States)

Silva-Martinez, Jackelynne P.; Aguilar, Andrés D.; Sarli, Bruno V.; Pardo Spiess, Monika Johanna; Sorice, Andreia F.; Genaro, Gino; Ojeda, Oscar I.

2018-06-01

The idea of establishing a South American Space Agency (SASA) is not new. There have been many discussions about this topic for a couple of decades, including an agreement by the Union of South American Nations to create such a space agency. Roughly 10 years ago, Argentina was the first to propose this collaboration with a military orientation. As the ideas progressed, Brazil was proposed to host its headquarters. However, not much support from the South American region has been given, either financially or logistically. To this day, a South American Space Agency or a similar concept has not yet been established in the region. The Space Generation Advisory Council (SGAC) hosted the first South American Space Generation Workshop in Argentina in 2015, where one of the working groups was tasked to further investigate the feasibility, advantages and challenges of implementing SASA. This paper presents an extension of the main findings from this working group where South American students and young professionals study and present a rationale in favor of SASA, outlining possible solutions and a structure that could be taken into account for its implementation. This paper pays particular attention to the question: Is it possible for countries in South America to establish the kind of cooperation necessary to stimulate the development and application of capabilities in the space sector, which would then enable undertaking missions far beyond the scope of what any single country in South America could do on its own? The existence of SASA would allow access to a common representative agency, which would lower costs, be accessible to all participating countries, and allow engagement with other emerging and established space agencies around the world.

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

Science.gov (United States)

Charvis, P.

2015-12-01

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

Quaternary volcanism in Deception Island (Antarctica): South Shetland Trench subduction-related signature in the Bransfield Basin back arc domain

International Nuclear Information System (INIS)

Gale, C.; Ubide, T.; Lago, M.; Gil-Imaz, A.; Gil-Pena, I.; Galindo-Zaldivar, J.; Rey, J.; Maestro, A.; Lopez-Martinez, J.

2014-01-01

Deception Island shows a volcanism related to the Phoenix Plate subduction and roll-back under South Shetland Block in the present times. The development of the island is related to the evolution and collapse of a volcanic caldera, and this study is focused on the petrology, mineralogy and geochemistry of the post-caldera rocks. We have made a study of the lava flows, dikes and the youngest historic eruption in 1970. These rocks range from dacite to rhyolite and have a microporphyritic texture with olivine and minor clinopyroxene. A pre-caldera basaltic andesite has also been studied. It has a microporphyritic texture with clinopyroxene. The intermediate and acid compositions alternating in the volcanostratigraphic sequence suggest either mafic recharge events or melt extraction from different levels in the deep magmatic system. All the studied compositions share a subduction-related signature similar to other magmatics from the Bransfield Basin. However, compositional differences between pre-caldera and post-caldera rocks indicate a different magma source and depth of crystallisation. According to the geothermobarometric calculations the pre-caldera magmas started to crystallise at deeper levels (13.5-15 km) than the post-caldera magmas (6.2-7.8 km). Specifically, the postcaldera magmas indicate a smaller influence of the subducting slab in the southwestern part of the Bransfield Basin in respect to the available data from other sectors as well as the involvement of crustal contamination in the genesis of the magmas. (Author)

Neogene subduction beneath Java, Indonesia: Slab tearing and changes in magmatism

Science.gov (United States)

Cottam, Michael; Hall, Robert; Cross, Lanu; Clements, Benjamin; Spakman, Wim

2010-05-01

Java is a Neogene calc-alkaline volcanic island arc formed by the northwards subduction of the Indo-Australian Plate beneath Sundaland, the continental core of SE Asia. The island has a complex history of volcanism and displays unusual subduction characteristics. These characteristics are consistent with the subduction of a hole in the down going slab that was formed by the arrival of a buoyant oceanic plateau at the trench. Subduction beneath Java began in the Eocene. However, the position and character of the calc-alkaline arc has changed over time. An older Paleogene arc ceased activity in the Early Miocene. Volcanic activity resumed in the Late Miocene producing a younger arc to the north of the older arc, and continues to the present day. An episode of Late Miocene thrusting at about 7 Ma is observed throughout Java and appears to be linked to northward movement of the arc. Arc rocks display typical calc-alkaline characteristics and reflect melting of the mantle wedge and subducted sediments associated with high fluid fluxes. Between West Java and Bali the present arc-trench gap is unusually wide at about 300 km. Seismicity identifies subducted Indian Ocean lithosphere that dips north at about 20° between the trench and the arc and then dips more steeply at about 60-70° from 100 to 600 km depth. In East Java there is gap in seismicity between about 250 and 500 km. Seismic tomography shows that this gap is not an aseismic section of the subduction zone but a hole in the slab. East Java is also unusual in the presence of K-rich volcanoes, now inactive, to the north of the calc-alkaline volcanoes of the active arc. In contrast to the calc-alkaline volcanism of the main arc, these K-rich melts imply lower fluid fluxes and a different mantle source. We suggest that all these observations can be explained by the tearing of the subducting slab when a buoyant oceanic plateau arrived at the trench south of East Java at about 8 Ma. With the slab unable to subduct

[Endo- and ectoparasites of South American camelids and their control].

Science.gov (United States)

Schmäschke, R

2015-01-01

In a literature review, common endo- and ectoparasites of South American camelids are described, presenting morphological details and clinical signs important for diagnosis. Based on the life cycle of the parasites, possibilities for prophylaxis and therapy are indicated. The review should aid the veterinarian to diagnose and control common parasitic infections in South American camelids.

Craton Heterogeneity in the South American Lithosphere

Science.gov (United States)

Lloyd, S.; Van der Lee, S.; Assumpcao, M.; Feng, M.; Franca, G. S.

2012-04-01

We investigate structure of the lithosphere beneath South America using receiver functions, surface wave dispersion analysis, and seismic tomography. The data used include recordings from 20 temporary broadband seismic stations deployed across eastern Brazil (BLSP02) and from the Chile Ridge Subduction Project seismic array in southern Chile (CRSP). By jointly inverting Moho point constraints, Rayleigh wave group velocities, and regional S and Rayleigh wave forms we obtain a continuous map of Moho depth. The new tomographic Moho map suggests that Moho depth and Moho relief vary slightly with age within the Precambrian crust. Whether or not a correlation between crustal thickness and geologic age can be derived from the pre-interpolation point constraints depends strongly on the selected subset of receiver functions. This implies that using only pre-interpolation point constraints (receiver functions) inadequately samples the spatial variation in geologic age. We also invert for S velocity structure and estimate the depth of the lithosphere-asthenosphere boundary (LAB) in Precambrian South America. The new model reveals a relatively thin lithosphere throughout most of Precambrian South America (< 140 km). Comparing LAB depth with lithospheric age shows they are overall positively correlated, whereby the thickest lithosphere occurs in the relatively small Saõ Francisco craton (200 km). However, within the larger Amazonian craton the younger lithosphere is thicker, indicating that locally even larger cratons are not protected from erosion or reworking of the lithosphere.

Tectonic significance of changes in post-subduction Pliocene-Quaternary magmatism in the south east part of the Carpathian-Pannonian Region

Science.gov (United States)

Seghedi, Ioan; Maţenco, Liviu; Downes, Hilary; Mason, Paul R. D.; Szakács, Alexandru; Pécskay, Zoltán

2011-04-01

The south-eastern part of the Carpathian-Pannonian region records the cessation of convergence between the European platform/Moesia and the Tisza-Dacia microplate. Plio-Quaternary magmatic activity in this area, in close proximity to the 'Vrancea zone', shows a shift from normal calc-alkaline to much more diverse compositions (adakite-like calc-alkaline, K-alkalic, mafic Na-alkalic and ultrapotassic), suggesting a significant change in geodynamic processes at approximately 3 Ma. We review the tectonic setting, timing, petrology and geochemistry of the post-collisional volcanism to constrain the role of orogenic building processes such as subduction or collision on melt production and migration. The calc-alkaline volcanism (5.3-3.9 Ma) marks the end of normal subduction-related magmatism along the post-collisional Călimani-Gurghiu-Harghita volcanic chain in front of the European convergent plate margin. At ca. 3 Ma in South Harghita magma compositions changed to adakite-like calc-alkaline and continued until recent times (< 0.03 Ma) interrupted at 1.6-1.2 Ma by generation of Na and K-alkalic magmas, signifying changes in the source and melting mechanism. We attribute the changes in magma composition in front of the Moesian platform to two main geodynamic events: (1) slab-pull and steepening with opening of a tear window (adakite-like calc-alkaline magmas) and (2) renewed contraction associated with deep mantle processes such as slab steepening during post-collisional times (Na and K-alkalic magmas). Contemporaneous post-collisional volcanism at the eastern edge of the Pannonian Basin at 2.6-1.3 Ma was dominated by Na-alkalic and ultrapotassic magmas, suggesting a close relationship with thermal asthenospheric doming and strain partitioning related to the Adriatic indentation. Similar timing, magma chamber processes and volume for K-alkalic (shoshonitic) magmas in the South Apuseni Mountains (1.6 Ma) and South Harghita area at a distance of ca. 200 km imply a

Amphibious Shear Velocity Structure of the Cascadia Subduction Zone

Science.gov (United States)

Janiszewski, H. A.; Gaherty, J. B.; Abers, G. A.; Gao, H.

2017-12-01

The amphibious Cascadia Initiative crosses the coastline of the Cascadia subduction zone (CSZ) deploying seismometers from the Juan de Fuca ridge offshore to beyond the volcanic arc onshore. This allows unprecedented seismic imaging of the CSZ, enabling examination of both the evolution of the Juan de Fuca plate prior to and during subduction as well as the along strike variability of the subduction system. Here we present new results from an amphibious shear velocity model for the crust and upper mantle across the Cascadia subduction zone. The primary data used in this inversion are surface-wave phase velocities derived from ambient-noise Rayleigh-wave data in the 10 - 20 s period band, and teleseismic earthquake Rayleigh wave phase velocities in the 20 - 160 s period band. Phase velocity maps from these data reflect major tectonic structures including the transition from oceanic to continental lithosphere, Juan de Fuca lithosphere that is faster than observations in the Pacific for oceanic crust of its age, slow velocities associated with the accretionary prism, the front of the fast subducting slab, and the Cascades volcanic arc which is associated with slower velocities in the south than in the north. Crustal structures are constrained by receiver functions in the offshore forearc and onshore regions, and by active source constraints on the Juan de Fuca plate prior to subduction. The shear-wave velocities are interpreted in their relationships to temperature, presence of melt or hydrous alteration, and compositional variation of the CSZ.

The Impact of China on South American Political and Economic Development

DEFF Research Database (Denmark)

Christensen, Steen Fryba

2018-01-01

The analysis compares three typologies of South American countries in terms of the impact of China on their political and economic development.......The analysis compares three typologies of South American countries in terms of the impact of China on their political and economic development....

The upper-mantle transition zone beneath the Chile-Argentina flat subduction zone

Science.gov (United States)

Bagdo, Paula; Bonatto, Luciana; Badi, Gabriela; Piromallo, Claudia

2016-04-01

The main objective of the present work is the study of the upper mantle structure of the western margin of South America (between 26°S and 36°S) within an area known as the Chile-Argentina flat subduction zone. For this purpose, we use teleseismic records from temporary broad band seismic stations that resulted from different seismic experiments carried out in South America. This area is characterized by on-going orogenic processes and complex subduction history that have profoundly affected the underlying mantle structure. The detection and characterization of the upper mantle seismic discontinuities are useful to understand subduction processes and the dynamics of mantle convection; this is due to the fact that they mark changes in mantle composition or phase changes in mantle minerals that respond differently to the disturbances caused by mantle convection. The discontinuities at a depth of 410 km and 660 km, generally associated to phase changes in olivine, vary in width and depth as a result of compositional and temperature anomalies. As a consequence, these discontinuities are an essential tool to study the thermal and compositional structure of the mantle. Here, we analyze the upper-mantle transition zone discontinuities at a depth of 410 km and 660 km as seen from Pds seismic phases beneath the Argentina-Chile flat subduction.

Fault plane orientations of deep earthquakes in the Izu-Bonin-Marianas subduction zone system

Science.gov (United States)

Myhill, R.; Warren, L. M.

2011-12-01

We present the results of directivity analysis on 45 deep earthquakes within the Izu-Bonin-Marianas subduction zone between 1993 and 2011. The age of the subducting Pacific plate increases from north to south along the trench, from 120 Ma offshore Tokyo to over 150 Ma east of the Mariana Islands. The dip of the deep slab generally increases from north to south, and is steep to overturned beneath the southern Bonin Islands and Marianas. Between 34 and 26 degrees north, a peak in seismicity at 350-450 km depth marks a decrease in dip as the slab approaches the base of the upper mantle. We observe directivity for around 60 percent of the analysed earthquakes, and use the propagation characteristics to find the best fitting rupture vector. In 60-70 percent of cases with well constrained rupture directivity, the best fitting rupture vector allows discrimination of the fault plane and the auxiliary plane of the focal mechanism. The identified fault planes between 100 km and 500 km are predominantly near-horizontal or south-southwest dipping. Rotated into the plane of the slab, the fault plane poles form a single cluster, since the more steeply dipping fault planes are found within more steeply dipping sections of slab. The dominance of near-horizontal fault planes at intermediate depth agrees with results from previous studies of the Tonga and Middle-America subduction zones. However, the presence of a single preferred fault plane orientation for large deep-focus earthquakes has not been previously reported, and contrasts with the situation for deep-focus earthquakes in the Tonga-Kermadec subduction system. Ruptures tend to propagate away from the top surface of the slab. We discuss potential causes of preferred fault plane orientations within subducting slabs in the light of existing available data, and the implications for mechanisms of faulting at great depths within the Earth.

Quantifying the humanitarian and economic impact of earthquakes on South American capital cities (Invited)

Science.gov (United States)

Zoback, M. L.; Cabrera, C.; Pomonis, A.; Baca, A.; Brunner, I.; Cheung, G.; Chen, A.; Nagel, B.; Carrasco, S.

2009-12-01

By 2000, an estimated 80% of South America’s population lived in urban areas (Veblen et al., The Physical Geography of South America, Oxford University Press, 2007). A significant fraction of those urban dwellers resides in the capital cities which are major economic centers and act as magnets for rural poor and refugees. This population concentration includes many residents living in extreme poverty in substandard and informal housing, often on the margins of these capital cities and sometimes on steep slopes, greatly compounding the vulnerability to natural hazards. We are analyzing the humanitarian and economic risk for six of the seismically most-at-risk South American capitals along the northern and western plate boundaries of South America: Caracas, Venezuela; Bogotá, Colombia; Quito, Ecuador; Lima, Perú; La Paz, Bolivia; and Santiago, Chile. Impacts are provided in the form of expected losses for a specific “likely” scenario earthquake and in a probabilistic format using exceedance probability curves (probability of exceeding a given loss in different return periods). Impacts to be quantified include: total economic losses, potential fatalities, potential serious injuries, and the number of displaced households. Probabilistic seismic hazard was developed in collaboration with numerous South American experts and includes subduction interface, intraslab, background crustal and, where available, active fault sources. A significant challenge for this study is to accurately account for the exposure and vulnerability of populations living in the informal, shanty areas. Combining analysis of aerial imagery and on-the-ground reconnaissance, we define between 20-30 “inventory districts” of relatively uniform construction styles within each capital. Statistical distributions of the different construction types and their characteristics (height, occupancy, year built, average value) are estimated for each district. In addition, working with local graduate

Linking Late Cretaceous to Eocene Tectonostratigraphy of the San Jacinto Fold Belt of NW Colombia With Caribbean Plateau Collision and Flat Subduction

Science.gov (United States)

Mora, J. Alejandro; Oncken, Onno; Le Breton, Eline; Ibánez-Mejia, Mauricio; Faccenna, Claudio; Veloza, Gabriel; Vélez, Vickye; de Freitas, Mario; Mesa, Andrés.

2017-11-01

Collision with and subduction of an oceanic plateau is a rare and transient process that usually leaves an indirect imprint only. Through a tectonostratigraphic analysis of pre-Oligocene sequences in the San Jacinto fold belt of northern Colombia, we show the Late Cretaceous to Eocene tectonic evolution of northwestern South America upon collision and ongoing subduction with the Caribbean Plate. We linked the deposition of four fore-arc basin sequences to specific collision/subduction stages and related their bounding unconformities to major tectonic episodes. The Upper Cretaceous Cansona sequence was deposited in a marine fore-arc setting in which the Caribbean Plate was being subducted beneath northwestern South America, producing contemporaneous magmatism in the present-day Lower Magdalena Valley basin. Coeval strike-slip faulting by the Romeral wrench fault system accommodated right-lateral displacement due to oblique convergence. In latest Cretaceous times, the Caribbean Plateau collided with South America marking a change to more terrestrially influenced marine environments characteristic of the upper Paleocene to lower Eocene San Cayetano sequence, also deposited in a fore-arc setting with an active volcanic arc. A lower to middle Eocene angular unconformity at the top of the San Cayetano sequence, the termination of the activity of the Romeral Fault System, and the cessation of arc magmatism are interpreted to indicate the onset of low-angle subduction of the thick and buoyant Caribbean Plateau beneath South America, which occurred between 56 and 43 Ma. Flat subduction of the plateau has continued to the present and would be the main cause of amagmatic post-Eocene deposition.

Aldehyde dehydrogenase polymorphism in North American, South American, and Mexican Indian populations.

Science.gov (United States)

Goedde, H W; Agarwal, D P; Harada, S; Rothhammer, F; Whittaker, J O; Lisker, R

1986-01-01

While about 40% of the South American Indian populations (Atacameños, Mapuche, Shuara) were found to be deficient in aldehyde dehydrogenase isozyme I (ALDH2 or E2), preliminary investigations showed very low incidence of isozyme deficiency among North American natives (Sioux, Navajo) and Mexican Indians (mestizo). Possible implications of such trait differences on cross-cultural behavioral response to alcohol drinking are discussed. PMID:3953578

Segmentation of Slow Slip Events in South Central Alaska Possibly Controlled by a Subducted Oceanic Plateau

Science.gov (United States)

Li, Haotian; Wei, Meng; Li, Duo; Liu, Yajing; Kim, YoungHee; Zhou, Shiyong

2018-01-01

Recent GPS observations show that slow slip events in south central Alaska are segmented along strike. Here we review several mechanisms that might contribute to this segmentation and focus on two: along-strike variation of slab geometry and effective normal stress. We then test them by running numerical simulations in the framework of rate-and-state friction with a nonplanar fault geometry. Results show that the segmentation is most likely related to the along-strike variation of the effective normal stress on the fault plane caused by the Yakutat Plateau. The Yakutat Plateau could affect the effective normal stress by either lowering the pore pressure in Upper Cook Inlet due to less fluids release or increasing the normal stress due to the extra buoyancy caused by the subducted Yakutat Plateau. We prefer the latter explanation because it is consistent with the relative amplitudes of the effective normal stress in Upper and Lower Cook Inlet and there is very little along-strike variation in Vp/Vs ratio in the fault zone from receiver function analysis. However, we cannot exclude the possibility that the difference in effective normal stress results from along-strike variation of pore pressure due to the uncertainties in the Vp/Vs estimates. Our work implies that a structural anomaly can have a long-lived effect on the subduction zone slip behavior and might be a driving factor on along-strike segmentation of slow slip events.

Gender, Family, and Community Correlates of Mental Health in South Asian Americans

OpenAIRE

Masood, Nausheen; Okazaki, Sumie; Takeuchi, David T.

2009-01-01

Nationally representative data from the National Latino and Asian American Study (Alegría et al., 2004) was used to examine both disorder prevalence rates and correlates of distress for the South Asian American subgroup (n = 164). South Asian Americans generally appeared to have lower or comparable rates of lifetime and 12-month mood and anxiety disorders when compared with the overall Asian American sample. A multiple-regression model fitted to predict recent psychological distress, with 12-...

Why Archaean TTG cannot be generated by MORB melting in subduction zones

Science.gov (United States)

Martin, Hervé; Moyen, Jean-François; Guitreau, Martin; Blichert-Toft, Janne; Le Pennec, Jean-Luc

2014-06-01

produced. Consequently, internal recycling of oceanic plateaus does not appear to be a suitable process for the genesis of Archaean continental crust. A possible alternative to this scenario is the subduction of oceanic plateaus. This hypothesis is supported by a present-day analog. In Ecuador, the Carnegie ridge, which is an oceanic plateau resulting from the Galapagos hot spot activity, is being subducted beneath the South American plate. Not only are the resulting magmas adakitic (TTG-like) in composition, but the volcanic productivity is several times greater than in other parts of the Andean volcanic arc. Above the location where the plateau is subducted, the arc is wide and the quaternary volcanoes numerous (about 80 active edifices). The volcanic productivity of each individual volcano also is more intense than away from the subduction focal point with an average output rate of about 0.4-0.5 km3·ka- 1 compared with only about 0.05-0.2 km3·ka- 1 for production rates at volcanoes erupting in the rest of the arc. Consequently, we infer that occasional subduction of oceanic plateaus throughout Earth's history can account for the episodic nature of crustal growth. Additionally, the generation by this mechanism of huge volumes of TTG-like magmas would readily dominate the crustal growth record.

Afrikaans, American and British Models for South African English ...

African Journals Online (AJOL)

tions in a national and international context, by comparing the traditions and the roles of the lan- ... The changing linguistic, social, and educational situations in South Africa ... abroad, by the British and American leXicographical traditions. ... interactional styles in the South African social psychology and cross-cultural.

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

Science.gov (United States)

Fan, Jianke; Zhao, Dapeng; Dong, Dongdong

2016-02-01

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

Southward Ejection of Subcontinental Lithosphere and large-scale Asthenospheric Enrichment beneath central Chile resulting from Flat Subduction

Science.gov (United States)

Jacques, G.; Hoernle, K.; Schaefer, B. F.; Hauff, F.; Gill, J.; Holm, P. M.; Bindeman, I. N.; Folguera, A.; Lara, L.; Ramos, V. A.

2015-12-01

Flat subduction is a common process in subduction zones, causing crustal shortening and thickening and possibly subduction erosion. These processes can lead to the contamination of asthenospheric melts either by lithospheric assimilation (e.g. MASH) or by subduction erosion of lithosphere into the asthenospheric source. We present new major and trace element and Sr-Nd-Pb-Hf-O-Os isotope data for a transect of Quaternary volcanic rocks across the Northern Southern Volcanic Front (NSVZ) of Chile at ~33.5°S, just south of the area of flat subduction, extending from the volcanic front (VF) to the rear arc (RA). The newly discovered calc-alkaline to alkaline RA rocks are more mafic (MgO~4-9wt.%) than the VF rocks (MgO~2.0-4.5wt.%). Both groups have overlapping Sr-Nd-Hf isotopic compositions that are more enriched than lavas from further south in the SVZ with two RA trachybasalts displaying extreme 87Sr/86Sr (0.710), eNd (-6) and eHf (-9). The RA samples, however, have less radiogenic Pb isotopic compositions with the two extreme RA trachybasalt samples having the least radiogenic Pb. The 207Pb/204Pb vs. Nd/Pb, Ce/Pb and Nb/U form good inverse linear correlations extending from subducted sediments to a mantle-like component. Mesozoic/Paleozoic crust and Grenvillian Argentinian lower crust do not fall on or along an extension of these arrays. The ol, plag and groundmassd18O (normalized to melt) of samples covering the full range in Sr-Nd-Pb-Hf isotopic composition lie within the mantle range (5.5-5.9). High Os abundances (~330ppt) in radiogenic Os (187Os/188Os=0.18) samples are not consistent with derivation from a mantle plume or continental crust. eNd and eHf increase to the south along the VF, e.g. eHf ranges from -9 to +10, forming an excellent linear correlation (r2=0.99), indicating that the enriched component is present in the source for >1000km to at least ~43°S. We propose that flattening of the Pampean slab 1) triggered subduction erosion of enriched

Lithospheric Expressions of the Precambrian Shield, Mesozoic Rifting, and Cenozoic Subduction and Mountain Building in Venezuela

Science.gov (United States)

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

2013-05-01

The Caribbean (CAR)-South American (SA) plate boundary in Venezuela is a broad zone of faulting and diffuse deformation. GPS measurements show the CAR moving approximately 2 cm/yr relative to SA, parallel to the strike slip fault system in the east, with more oblique convergence in the west (Weber et al., 2001) causing the southern edge of the Caribbean to subduct beneath northwestern South America. The west is further complicated by the motion of the triangular Maracaibo block, which is escaping northeastward relative to SA along the Bocono and Santa Marta Faults. In central and eastern Venezuela, plate motion is accommodated by transpression and transtension along the right lateral San Sebastian- El Pilar strike-slip fault system. The strike-slip system marks the northern edge of coastal thrust belts and their associated foreland basins. The Archean-Proterozoic Guayana Shield, part of the Amazonian Craton, underlies southeastern and south-central Venezuela. We used the 87 station Venezuela-U.S. BOLIVAR array (Levander et al., 2006) to investigate lithospheric structure in northern South America. We combined finite-frequency Rayleigh wave tomography with Ps and Sp receiver functions to determine lithosphere-asthenosphere boundary (LAB) depth. We measured Rayleigh phase velocities from 45 earthquakes in the period band 20-100s. The phase velocities were inverted for 1D shear velocity structure on a 0.5 by 0.5 degree grid. Crustal thickness for the starting model was determined from active seismic experiments and receiver function analysis. The resulting 3D shear velocity model was then used to determine the depth of the LAB, and to CCP stack Ps and Sp receiver functions from ~45 earthquakes. The receiver functions were calculated in several frequency bands using iterative deconvolution and inverse filtering. Lithospheric thickness varies by more a factor of 2.5 across Venezuela. We can divide the lithosphere into several distinct provinces, with LAB depth

Incorporating Cutting Edge Scientific Results from the Margins-Geoprisms Program into the Undergraduate Curriculum: The Subduction Factory

Science.gov (United States)

Penniston-Dorland, S.; Stern, R. J.; Edwards, B. R.; Kincaid, C. R.

2014-12-01

The NSF-MARGINS Program funded a decade of research on continental margin processes. The NSF-GeoPRISMS Mini-lesson Project, funded by NSF-TUES, is designed to integrate fundamental results from the MARGINS program into open-source college-level curriculum. Three Subduction Factory (SubFac) mini-lessons were developed as part of this project. These include hands-on examinations of data sets representing 3 key components of the subduction zone system: 1) Heat transfer in the subducted slab; 2) Metamorphic processes happening at the plate interface; and 3) Typical magmatic products of arc systems above subduction zones. Module 1: "Slab Temperatures Control Melting in Subduction Zones, What Controls Slab Temperature?" allows students to work in groups using beads rolling down slopes as an analog for the mathematics of heat flow. Using this hands-on, exploration-based approach, students develop an intuition for the mathematics of heatflow and learn about heat conduction and advection in the subduction zone environment. Module 2: "Subduction zone metamorphism" introduces students to the metamorphic rocks that form as the subducted slab descends and the mineral reactions that characterize subduction-related metamorphism. This module includes a suite of metamorphic rocks available for instructors to use in a lab, and exercises in which students compare pressure-temperature estimates obtained from metamorphic rocks to predictions from thermal models. Module 3: "Central American Arc Volcanoes, Petrology and Geochemistry" introduces students to basic concepts in igneous petrology using the Central American volcanic arc, a MARGINS Subduction Factory focus site, as an example. The module relates data from two different volcanoes - basaltic Cerro Negro (Nicaragua) and andesitic Ilopango (El Salvador) including hand sample observations and major element geochemistry - to explore processes of mantle and crustal melting and differentiation in arc volcanism.

“Liting it up”: Popular Culture, Indo-Pak Basketball, and South Asian American Institutions

Directory of Open Access Journals (Sweden)

Stanley Ilango Thangaraj

2010-08-01

Full Text Available South Asian American participants of a co-ethnic basketball league, known as Indo-Pak Basketball, utilized urban basketball vernacular through the phrase “liting it up” to identify individuals scoring points in great numbers. The person “liting it up” becomes visible and receives recognition. Accordingly, I want to “lite up” the scholarship on South Asian America whereby situating South Asian American religious sites and cultural centers as key arenas for “Americanization” through US popular culture. I situate sport as a key element of popular culture through which South Asian American communities work out, struggle through, and contest notions of self. Informed by an Anthropology of Sport, ethnography of South Asian American communities in Atlanta takes place alongside an examination of the North American Indo-Pak Basketball circuit. Accordingly, my findings indicate that such community formation has also taken shape at the intersections of institutions, gender, and sexuality whereby excluding queers, women, and other communities of color.

Gender, family, and community correlates of mental health in South Asian Americans.

Science.gov (United States)

Masood, Nausheen; Okazaki, Sumie; Takeuchi, David T

2009-07-01

Nationally representative data from the National Latino and Asian American Study (Alegría et al., 2004) was used to examine both disorder prevalence rates and correlates of distress for the South Asian American subgroup (n = 164). South Asian Americans generally appeared to have lower or comparable rates of lifetime and 12-month mood and anxiety disorders when compared with the overall Asian American sample. A multiple-regression model fitted to predict recent psychological distress, with 12-month diagnosis as a covariate, found gender differences. For women, lack of extended family support was related to higher levels of distress, whereas for men, greater conflict with family culture, and a lower community social position (but higher U.S. social position) predicted higher distress scores. Findings suggest that mental health services consider a broad framework of psychological functioning for South Asian Americans that reflect their gendered, familial, and sociopolitical realities.

Gender, Family, and Community Correlates of Mental Health in South Asian Americans

Science.gov (United States)

Masood, Nausheen; Okazaki, Sumie; Takeuchi, David T.

2014-01-01

Nationally representative data from the National Latino and Asian American Study (Alegría et al., 2004) was used to examine both disorder prevalence rates and correlates of distress for the South Asian American subgroup (n = 164). South Asian Americans generally appeared to have lower or comparable rates of lifetime and 12-month mood and anxiety disorders when compared with the overall Asian American sample. A multiple-regression model fitted to predict recent psychological distress, with 12-month diagnosis as a covariate, found gender differences. For women, lack of extended family support was related to higher levels of distress, whereas for men, greater conflict with family culture, and a lower community social position (but higher U.S. social position) predicted higher distress scores. Findings suggest that mental health services consider a broad framework of psychological functioning for South Asian Americans that reflect their gendered, familial, and sociopolitical realities. PMID:19594255

Exploring Hybrid Identities: South Asian American Women Pursue a Career in Teaching

Science.gov (United States)

Shah, Amita Roy

2013-01-01

This study explores how second-generation South Asian American women negotiated their hybrid identities to pursue a career in teaching. Many South Asian Americans have not pursued a career in teaching because of various external and internal factors that have influenced their sense of identity, academic achievement, and professional career path…

Trench Advance By the Subduction of Buoyant Features - Application to the Izu-Bonin-Marianas Arc

Science.gov (United States)

Goes, S. D. B.; Fourel, L.; Morra, G.

2014-12-01

Most subduction trenches retreat, not only today but throughout the Cenozoic. However, a few trenches clearly advance during part of the evolution, including Izu-Bonin Marianas (IBM) and Kermadec. Trench retreat is well understood as a basic consequence of slab pull, but it is debated what causes trench advance. The IBM trench underwent a complex evolution: right after its initiation, it rotated clockwise, leading to very fast retreat in the north and slow retreat in the south. But since 10-15 Ma, IBM trench motions have switched to advance at the southern end, and since 5 Ma also the northern end is advancing. Based on 2-D subduction models, it has been proposed proposed that the change in age of the subducting plate at the IBM trench (from 40-70 m.y. at the initiation of the trench 45 m.y. ago to 100-140 m.y. lithosphere subducting at the trench today) and its effect on plate strength could explain the transition from trench retreat to trench advance, and that the age gradient (younger in the north and older in the south) could explain the rotation of the trench. However, with new 3-D coupled fluid-solid subduction model where we can include such lateral age gradients, we find that this does not yield the observed behaviour. Instead, we propose an alternative mechanism, involving the subduction of the buoyant Caroline Island Ridge at the southern edge of the Mariana trench and show that it can explain both trench motion history and the current morphology of the IBM slab as imaged by seismic tomography.

Ecogeographical Variation in Skull Shape of South-American Canids: Abiotic or Biotic Processes?

Science.gov (United States)

de Moura Bubadué, Jamile; Cáceres, Nilton; Dos Santos Carvalho, Renan; Meloro, Carlo

Species morphological changes can be mutually influenced by environmental or biotic factors, such as competition. South American canids represent a quite recent radiation of taxa that evolved forms very disparate in phenotype, ecology and behaviour. Today, in the central part of South America there is one dominant large species (the maned wolf, Chrysocyon brachyurus ) that directly influence sympatric smaller taxa via interspecific killing. Further south, three species of similar sized foxes ( Lycalopex spp.) share the same habitats. Such unique combination of taxa and geographic distribution makes South American dogs an ideal group to test for the simultaneous impact of climate and competition on phenotypic variation. Using geometric morphometrics, we quantified skull size and shape of 431 specimens belonging to the eight extant South American canid species: Atelocynus microtis , Cerdocyon thous , Ch. brachyurus , Lycalopex culpaeus , L. griseus , L. gymnocercus , L. vetulus and Speothos venaticus . South American canids are significantly different in both skull size and shape. The hypercarnivorous bush dog is mostly distinct in shape from all the other taxa while a degree of overlap in shape-but not size-occurs between species of the genus Lycalopex . Both climate and competition impacts interspecific morphological variation. We identified climatic adaptations as the main driving force of diversification for the South American canids. Competition has a lower degree of impact on their skull morphology although it might have played a role in the past, when canid community was richer in morphotypes.

The South American fruit fly, Anastrepha fraterculus (Wiedemann) in Brazil

International Nuclear Information System (INIS)

Zucchi, R.A.; Araujo, E.L.; Canal D, N.A.; Uchoa F, M.A.

1999-01-01

Anastrepha fraterculus, the South American fruit fly, is the most common and economically important pest for the fruit-bearing species in the Neotropical region. However, there are some species that are close to A. fraterculus and, sometimes they can be erroneously identified as A. fraterculus. The separation of A. fraterculus from A. obliqua, A. sororcula and A. zenildae, species closely related to South American fruit fly, is discussed. Also, information on the host plants and braconid parasitoids for A. fraterculus in Brazil is presented. (author)

Central and South America GPS geodesy - CASA Uno

Science.gov (United States)

Kellogg, James N.; Dixon, Timothy H.

1990-01-01

In January 1988, scientists from over 25 organizations in 13 countries and territories cooperated in the largest GPS campaign in the world to date. A total of 43 GPS receivers collected approximately 590 station-days of data in American Samoa, Australia, Canada, Colombia, Costa Rica, Ecuador, New Zealand, Norway, Panama, Sweden, United States, West Germany, and Venezuela. The experiment was entitled CASA Uno. Scientific goals of the project include measurements of strain in the northern Andes, subduction rates for the Cocos and Nazca plates beneath Central and South America, and relative motion between the Caribbean plate and South America. A second set of measurements are planned in 1991 and should provide preliminary estimates of crustal deformation and plate motion rates in the region.

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

KAUST Repository

Tan, Eh

2012-10-01

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

Modelling guided waves in the Alaskan-Aleutian subduction zone

Science.gov (United States)

Coulson, Sophie; Garth, Thomas; Reitbrock, Andreas

2016-04-01

Subduction zone guided wave arrivals from intermediate depth earthquakes (70-300 km depth) have a huge potential to tell us about the velocity structure of the subducting oceanic crust as it dehydrates at these depths. We see guided waves as the oceanic crust has a slower seismic velocity than the surrounding material, and so high frequency energy is retained and delayed in the crustal material. Lower frequency energy is not retained in this crustal waveguide and so travels at faster velocities of the surrounding material. This gives a unique observation at the surface with low frequency energy arriving before the higher frequencies. We constrain this guided wave dispersion by comparing the waveforms recorded in real subduction zones with simulated waveforms, produced using finite difference full waveform modelling techniques. This method has been used to show that hydrated minerals in the oceanic crust persist to much greater depths than accepted thermal petrological subduction zone models would suggest in Northern Japan (Garth & Rietbrock, 2014a), and South America (Garth & Rietbrock, in prep). These observations also suggest that the subducting oceanic mantle may be highly hydrated at intermediate depth by dipping normal faults (Garth & Rietbrock 2014b). We use this guided wave analysis technique to constrain the velocity structure of the down going ~45 Ma Pacific plate beneath Alaska. Dispersion analysis is primarily carried out on guided wave arrivals recorded on the Alaskan regional seismic network. Earthquake locations from global earthquake catalogues (ISC and PDE) and regional earthquake locations from the AEIC (Alaskan Earthquake Information Centre) catalogue are used to constrain the slab geometry and to identify potentially dispersive events. Dispersed arrivals are seen at stations close to the trench, with high frequency (>2 Hz) arrivals delayed by 2 - 4 seconds. This dispersion is analysed to constrain the velocity and width of the proposed waveguide

South American Youth : Regional Democracy-Building Dialogue ...

International Development Research Centre (IDRC) Digital Library (Canada)

This project will undertake a comparative analysis of South American youth in the Mercosur countries (Argentina, Brazil, Paraguay and Uruguay) and their perception of rights, democracy and regional integration. Researchers will examine the meaning that young people, adults and mediators of youth demands attribute to ...

Insight into American tourists’ experiences with weather in South Africa

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Giddy Julia K.

2017-12-01

Full Text Available Weather and climate are often important factors determining the success of a tourism destination and resultant satisfaction among tourists. This is particularly true for South Africa due the predominance of outdoor tourist attractions. Increasing numbers of international tourists have visited South Africa since the fall of apartheid, particularly those from the United States (U.S., which is an important market for South African tourism. Therefore, this paper seeks to examine a sample of American tourists’ experience with day-to-day weather and climatic conditions in South Africa. The results show that although respondents did not feel that climatic conditions were an important factor in motivations to visit the country, the day-to-day weather did often impact the enjoyment of their visit. Most notably, weather controlled their ability to participate in outdoor activities. In correlating accounts of unpleasant weather conditions with the meteorological records, a close association emerged, particularly for excessively high temperatures. This indicates that the experiences of American tourists are an accurate indication of climatic unsuitability for tourism, which poses threats to the South African outdoor tourism sector.

Sandbox Simulations of the Evolution of a Subduction Wedge following Subduction Initiation

Science.gov (United States)

Brandon, M. T.; Ma, K. F.; DeWolf, W.

2012-12-01

Subduction wedges at accreting subduction zones are bounded by a landward dipping pro-shear zone (= subduction thrust) and a seaward-dipping retro-shear zone in the overriding plate. For the Cascadia subduction zone, the surface trace of the retro-shear zone corresponds to the east side of the Coast Ranges of Oregon and Washington and the Insular Mountains of Vancouver Island. This coastal high or forearc high shows clear evidence of long-term uplift and erosion along its entire length, indicating that it is an active part of the Cascadia subduction wedge. The question addressed here is what controls the location of the retro-shear zone? In the popular double-sided wedge model of Willet et al (Geology 1993), the retro-shear zone remains pinned to the S point, which is interpreted to represent where the upper-plate Moho intersects the subduction zone. For this interpretation, the relatively strong mantle is considered to operate as a flat backstop. That model, however. is somewhat artificial in that the two plates collide in a symmetric fashion with equal crustal thicknesses on both sides. Using sandbox experiments, we explore a more realistic configuration where the upper and lower plate are separated by a gentle dipping (10 degree) pro-shear zone, to simulate the initial asymmetric geometry of the subduction thrust immediately after initiation of subduction. The entire lithosphere must fail along some plane for subduction to begin and this failure plane must dip in the direction of subduction. Thus, the initial geometry of the overriding plate is better approximated as a tapered wedge than as a layer of uniform thickness, as represented in the Willett et al models. We demonstrate this model using time-lapse movies of a sand wedge above a mylar subducting plate. We use particle image velocimetry (PIV) to show the evolution of strain and structure within the overriding plate. Material accreted to the tapered end of the overriding plate drives deformation and causes

Phylogenetic reconstruction of South American felids defined by protein electrophoresis.

Science.gov (United States)

Slattery, J P; Johnson, W E; Goldman, D; O'Brien, S J

1994-09-01

Phylogenetic associations among six closely related South American felid species were defined by changes in protein-encoding gene loci. We analyzed proteins isolated from skin fibroblasts using two-dimensional electrophoresis and allozymes extracted from blood cells. Genotypes were determined for multiple individuals of ocelot, margay, tigrina, Geoffroy's cat, kodkod, and pampas cat at 548 loci resolved by two-dimensional electrophoresis and 44 allozyme loci. Phenograms were constructed using the methods of Fitch-Margoliash and neighbor-joining on a matrix of Nei's unbiased genetic distances for all pairs of species. Results of a relative-rate test indicate changes in two-dimensional electrophoresis data are constant among all South American felids with respect to a hyena outgroup. Allelic frequencies were transformed to discrete character states for maximum parsimony analysis. Phylogenetic reconstruction indicates a major split occurred approximately 5-6 million years ago, leading to three groups within the ocelot lineage. The earliest divergence led to Leopardus tigrina, followed by a split between an ancestor of an unresolved trichotomy of three species (Oncifelis guigna, O. geoffroyi, and Lynchailuris colocolo) and a recent common ancestor of Leopardus pardalis and L. wiedii. The results suggest that modern South American felids are monophyletic and evolved rapidly after the formation of the Panama land bridge between North and South America.

Close relationship of Plasmodium sequences detected from South American pampas deer (Ozotoceros bezoarticus to Plasmodium spp. in North American white-tailed deer

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Masahito Asada

2018-04-01

Full Text Available We report, for the first time, the presence of ungulate malaria parasites in South America. We conducted PCR-based surveys of blood samples of multiple deer species and water buffalo from Brazil and detected Plasmodium sequences from pampas deer (Ozotoceros bezoarticus samples. Phylogenic analysis revealed that the obtained sequences are closely related to the Plasmodium odocoilei clade 2 sequence from North American white-tailed deer (Odocoileus virginianus. Nucleotide differences suggest that malaria parasites in South American pampas deer and North American P. odocoilei clade 2 branched more recently than the Great American Interchange. Keywords: Malaria, Pampas deer, South America, Plasmodium odocoilei, Brazil

New views on American colonization: critical tests from South America

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O'Rourke, Dennis

2007-01-01

Full Text Available The traditional view of colonization of the Americas as a migration across Beringia and subsequent dispersal southward following the last glacial maximum is being increasingly questioned. In North America, archaeological links to Siberia are tenuous and genetic data are more consistent with an earlier entry of people into the Americas, from Central rather than Northeast Siberia. An entry of populations into the Americas prior to the last glacial maximum forces a reconsideration not only of timing, but also geographic points of entry and speed of dispersal, based on ecological theory. A number of emerging alternative hypotheses on the colonization of the Americas predict early entry and dispersal of people into South America - earlier than, or coeval with, initial dispersal in North America. The study of genetic, morphological, and archaeological variation across South America is critical to testing these new, alternative hypotheses of Native American origins. I will review the evidence for emerging, alternative views of American Colonization, and suggest ways in which data from South American populations and prehistory will be crucial in testing them.

South American Field Experience: An Initiative in International Education. The Implementation Journal for the South American Field Experience.

Science.gov (United States)

Martin, William J.

A description is provided of Williamsport Area Community College's (WACC's) South American Field Experience program, a travel/study program for faculty and staff designed to provide a variety of learning experiences through a three week trip to Peru, Chile, Argentina, and Brazil. Chapter I presents an overview of the development of the project,…

Iberian (South American) Model of Judicial Review: Toward Conceptual Framework

Science.gov (United States)

Klishas, Andrey A.

2016-01-01

The paper explores Latin American countries legislation with the view to identify specific features of South American model of judicial review. The research methodology rests on comparative approach to analyzing national constitutions' provisions and experts' interpretations thereof. The constitutional provisions of Brazil, Peru, Mexico, and…

Mantle constraints on the plate tectonic evolution of the Tonga-Kermadec-Hikurangi subduction zone and the South Fiji Basin region

NARCIS (Netherlands)

Schellart, W. P.; Spakman, W.

The Tonga-Kermadec-Hikurangi subduction zone is a major plate boundary in the Southwest Pacific region, where the Pacific plate subducts westward underneath the Australian plate. Considerable controversy exists regarding the Cenozoic evolution of this subduction zone, its connection with the

Mantle constraints on the plate tectonic evolution of the Tonga-Kermadec-Hikurangi subduction zone and the South Fiji Basin region

NARCIS (Netherlands)

Schellart, W.P.; Spakman, W.

2012-01-01

The Tonga–Kermadec–Hikurangi subduction zone is a major plate boundary in the Southwest Pacific region, where the Pacific plate subducts westward underneath the Australian plate. Considerable controversy exists regarding the Cenozoic evolution of this subduction zone, its connection with

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

Science.gov (United States)

von Huene, Roland E.; Scholl, D. W.

1991-01-01

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

Desi Women on the Forty Acres: Exploring Intergenerational Issues and Identity Development of South Asian American College Students

Science.gov (United States)

Ruzicka, Smita Sundaresan

2011-01-01

South Asian Americans are one of the fastest growing sub-groups within the Asian American population in the United States today. Between 1960 and 1990, the South Asian American population witnessed an increase of approximately 900% (Leonard, 1997). This increase in population also corresponds with the increase in South Asian American students…

South American Youth and Integration : Typical Situations and Youth ...

International Development Research Centre (IDRC) Digital Library (Canada)

South American Youth and Integration : Typical Situations and Youth ... IDRC partner the World Economic Forum is building a hub for inclusive growth ... Brazil, Paraguay and Uruguay) and their perception of rights, democracy and regional.

Anthropozoonotic Endoparasites in Free-Ranging ?Urban? South American Sea Lions (Otaria flavescens)

OpenAIRE

Hermosilla, Carlos; Silva, Liliana M. R.; Navarro, Mauricio; Taubert, Anja

2016-01-01

The present study represents the first report on the gastrointestinal endoparasite fauna of a free-ranging “urban” colony of South American sea lions (Otaria flavescens) living within the city of Valdivia, Chile. A total of 40 individual faecal samples of South American sea lions were collected during the year 2012 within their natural habitat along the river Calle-Calle and in the local fish market of Valdivia. Coprological analyses applying sodium acetate acetic formalin methanol (SAF) tech...

“Liting it up”: Popular Culture, Indo-Pak Basketball, and South Asian American Institutions

OpenAIRE

Stanley Ilango Thangaraj

2010-01-01

South Asian American participants of a co-ethnic basketball league, known as Indo-Pak Basketball, utilized urban basketball vernacular through the phrase “liting it up” to identify individuals scoring points in great numbers. The person “liting it up” becomes visible and receives recognition. Accordingly, I want to “lite up” the scholarship on South Asian America whereby situating South Asian American religious sites and cultural centers as key arenas for “Americanization” through US popula...

The water economy of South American desert rodents: from integrative to molecular physiological ecology.

Science.gov (United States)

Bozinovic, Francisco; Gallardo, Pedro

2006-01-01

Rodents from arid and semi-arid habitats live under conditions where the spatial and temporal availability of free water is limited, or scarce, thus forcing these rodents to deal with the problem of water conservation. The response of rodents to unproductive desert environments and water deficits has been intensively investigated in many deserts of the world. However, current understanding of the cellular, systemic and organismal physiology of water economy relies heavily on short-term, laboratory-oriented experiments, which usually focus on responses at isolated levels of biological organization. In addition, studies in small South American mammals are scarce. Indeed xeric habitats have existed in South America for a long time and it is intriguing why present day South American desert rodents do not show the wide array of adaptive traits to desert life observed for rodents on other continents. Several authors have pointed out that South American desert rodents lack physiological and energetic specialization for energy and water conservation, hypothesizing that their success is based more on behavioral and ecological strategies. We review phenotypic flexibility and physiological diversity in water flux rate, urine osmolality, and expression of water channels in South American desert-dwelling rodents. As far as we know, this is the first review of integrative studies at cellular, systemic and organismal levels. Our main conclusion is that South American desert rodents possess structural as well as physiological systems for water conservation, which are as remarkable as those found in "classical" rodents inhabiting other desert areas of the world.

Radioactive mineral potential of carbonatites in western parts of the South American shields

International Nuclear Information System (INIS)

Premoli, C.; Kroonenberg, S.B.

1984-01-01

During the last eight years at least six carbonatites or clusters of carbonatites have been discovered in the western parts of the South American cratons. In contrast to the carbonatites of the eastern part of the South American shields, which have been well studied and placed in a tectonic context together with the West African carbonatite provinces, those of the western part of the South American cratons have received litte attention. This paper is a compilation of published and original data on these occurrences, their geology, geochemistry, structural setting and radioactive mineral potential. An exploration strategy is devised based on experiences in this rainforest-clad area and the peculiar genetic aspect of carbonatites. Some details of a possibly new uranium mineral encountered in Cerro Cora carbonatite are given. (author)

South Asian American Perspectives on Overweight, Obesity, and the Relationship Between Weight and Health

OpenAIRE

Tang, Joyce W.; Mason, Maryann; Kushner, Robert F.; Tirodkar, Manasi A.; Khurana, Neerja; Kandula, Namratha R.

2012-01-01

Introduction Compared with other racial groups, South Asian adults develop type 2 diabetes and cardiovascular disease at a lower body mass index (BMI). Perceptions of weight and the effect of weight on health can influence weight-loss attempts but are not well described in this population. The objective of this study was to examine perceptions of weight appropriateness and the effect of weight on health among South Asian Americans. Methods We recruited 75 South Asian American adults from a si...

Tenancy and African American Marriage in the Postbellum South.

Science.gov (United States)

Bloome, Deirdre; Muller, Christopher

2015-10-01

The pervasiveness of tenancy in the postbellum South had countervailing effects on marriage between African Americans. Tenancy placed severe constraints on African American women's ability to find independent agricultural work. Freedwomen confronted not only planters' reluctance to contract directly with women but also whites' refusal to sell land to African Americans. Marriage consequently became one of African American women's few viable routes into the agricultural labor market. We find that the more counties relied on tenant farming, the more common was marriage among their youngest and oldest African American residents. However, many freedwomen resented their subordinate status within tenant marriages. Thus, we find that tenancy contributed to union dissolution as well as union formation among freedpeople. Microdata tracing individuals' marital transitions are consistent with these county-level results.

STUDIES ON SOUTH AMERICAN YELLOW FEVER

Science.gov (United States)

Davis, Nelson C.; Shannon, Raymond C.

1929-01-01

Yellow fever virus from M. rhesus has been inoculated into a South American monkey (Cebus macrocephalus) by blood injection and by bites of infected mosquitoes. The Cebus does not develop the clinical or pathological signs of yellow fever. Nevertheless, the virus persists in the Cebus for a time as shown by the typical symptoms and lesions which develop when the susceptible M. rhesus is inoculated from a Cebus by direct transfer of blood or by mosquito (A. aegypti) transmission. PMID:19869607

Structure of the subducted Cocos Plate from locations of intermediate-depth earthquakes

Science.gov (United States)

Lomnitz, C.; Rodríguez-Padilla, L. D.; Castaños, H.

2013-05-01

Locations of 3,000 earthquakes of 40 to 300 km depth are used to define the 3-D structure of the subducted Cocos Plate under central and southern Mexico. Discrepancies between deep-seated lineaments and surface tectonics are described. Features of particular interest include: (1) a belt of moderate activity at 40 to 80 km depth that parallels the southern boundary of the Mexican Volcanic Plateau; (2) an offset of 150 km across the Isthmus of Tehuantepec where all seismic activity is displaced toward the northeast; (3) three nests of frequent, deep-seated events (80 to 300 km depth) under southern Veracruz, Chiapas and the coast of Mexico-Guatemala. The active subduction process is sharply delimited along a NW-SE lineament from the Yucatan Peninsula, of insignificant earthquake activity. The focal distribution of intermediate-depth earthquakes in south-central Mexico provides evidence of stepwise deepening of the subduction angle along the Trench, starting at 15 degrees under Michoacan-Guerrero to 45 degrees under NW Guatemala. Historical evidence suggests that the hazard to Mexico City from large intermediate-depth earthquakes may have been underestimated.

The ADN project : an integrated seismic monitoring of the northern Ecuadorian subduction

Science.gov (United States)

Nocquet, Jean-Mathieu; Yepes, Hugo; Vallee, Martin; Mothes, Patricia; Regnier, Marc; Segovia, Monica; Font, Yvonne; Vaca, Sandro; Bethoux, Nicole; Ramos, Cristina

2010-05-01

The subduction of the Nazca plate beneath South America has caused one of the largest megathrust earthquake sequence during the XXth century with three M>7.7 earthquakes that followed the great 1906 (Mw = 8.8) event. Better understanding the processes leading to the occurrence of large subduction earthquakes requires to monitor the ground motion over a large range of frequencies. We present a new network (ADN) developed under a collaboration between the IRD-GeoAzur (Nice, France) and the IG-EPN (Quito, Ecuador). Each station of the ADN network includes a GPS recording at 5 Hz, an accelerometer and a broadband seismometer. CGPS data will quantify the secular deformation induced by elastic locking along the subduction interface, enabling a detailed modelling of the coupling distribution. CGPS will be used to monitor any transient deformation induced by Episodic Slip Event along the subduction, together with broadband seismometers that can detect any tremors or seismic signatures that may accompany them. In case of any significant earthquake, 5 Hz GPS and accelerometer will provide near field data for earthquake source detailed study. Finally, the broadband seismometers will be used for study of the microseismicity and structure of the subduction zone. The network includes 9 stations, operating since 2008 and covering the coastal area from latitude 1.5°S to the Colombian border. In this poster, we will present preliminary assessment of the data, first hypocenters location, magnitude and focal mechanism determination, as well as results about an episodic slip event detected in winter 2008.

The evolutionary history of Lygodactylus lizards in the South American open diagonal.

Science.gov (United States)

Lanna, Flávia M; Werneck, Fernanda P; Gehara, Marcelo; Fonseca, Emanuel M; Colli, Guarino R; Sites, Jack W; Rodrigues, Miguel T; Garda, Adrian A

2018-06-12

The Pleistocenic Arc Hypothesis (PAH) posits that South American Seasonally Dry Tropical Forests (SDTF) were interconnected during Pleistocene glacial periods, enabling the expansion of species ranges that were subsequently fragmented in interglacial periods, promoting speciation. The lizard genus Lygodactylus occurs in Africa, Madagascar, and South America. Compared to the high diversity of African Lygodactylus, only two species are known to occur in South America, L. klugei and L. wetzeli, distributed in SDTFs and the Chaco, respectively. We use a phylogenetic approach based on mitochondrial (ND2) and nuclear (RAG-1) markers covering the known range of South American Lygodactylus to investigate (i) if they are monophyletic relative to their African congeners, (ii) if their divergence is congruent with the fragmentation of the PAH, and (iii) if cryptic diversity exists within currently recognized species. Maximum likelihood and Bayesian phylogenetic analyses recovered a well-supported monophyletic South American Lygodactylus, presumably resulting from a single trans-Atlantic dispersal event 29 Mya. Species delimitation analyses supported the existence of five putative species, three of them undescribed. Divergence times among L. klugei and the three putative undescribed species, all endemic to the SDTFs, are not congruent with the fragmentation of the PAH. However, fragmentation of the once broader and continuous SDTFs likely influenced the divergence of L. wetzeli in the Chaco and Lygodactylus sp. 3 (in a SDTF enclave in the Cerrado). Copyright © 2018. Published by Elsevier Inc.

Imaging megathrust zone and Yakutat/Pacific plate interface in Alaska subduction zone

Science.gov (United States)

Kim, Y.; Abers, G. A.; Li, J.; Christensen, D. H.; Calkins, J. A.

2013-05-01

We image the subducted slab underneath a 450 km long transect of the Alaska subduction zone. Dense stations in southern Alaska are set up to investigate (1) the geometry and velocity structure of the downgoing plate and their relation to slab seismicity, and (2) the interplate coupled zone where the great 1964 (magnitude 9.3) had greatest rupture. The joint teleseismic migration of two array datasets (MOOS, Multidisciplinary Observations of Onshore Subduction, and BEAAR, Broadband Experiment Across the Alaska Range) based on teleseismic receiver functions (RFs) using the MOOS data reveal a shallow-dipping prominent low-velocity layer at ~25-30 km depth in southern Alaska. Modeling of these RF amplitudes shows a thin (<6.5 km) low-velocity layer (shear wave velocity of ~3 km/s), which is ~20-30% slower than normal oceanic crustal velocities, between the subducted slab and the overriding North American plate. The observed low-velocity megathrust layer (with P-to-S velocity ratio (Vp/Vs) exceeding 2.0) may be due to a thick sediment input from the trench in combination of elevated pore fluid pressure in the channel. The subducted crust below the low-velocity channel has gabbroic velocities with a thickness of 11-12 km. Both velocities and thickness of the low-velocity channel abruptly increase as the slab bends in central Alaska, which agrees with previously published RF results. Our image also includes an unusually thick low-velocity crust subducting with a ~20 degree dip down to 130 km depth at approximately 200 km inland beneath central Alaska. The unusual nature of this subducted segment has been suggested to be due to the subduction of the Yakutat terrane. We also show a clear image of the Yakutat and Pacific plate subduction beneath the Kenai Peninsula, and the along-strike boundary between them at megathrust depths. Our imaged western edge of the Yakutat terrane, at 25-30 km depth in the central Kenai along the megathrust, aligns with the western end of the

Heterogeneous subduction structure within the Pacific plate beneath the Izu-Bonin arc

Science.gov (United States)

Gong, Wei; Xing, Junhui; Jiang, Xiaodian

2018-05-01

The Izu-Bonin subduction zone is a subduction system formed in early Eocene. The structure of the subduction zone becomes complicated with the evolution of the surrounding plate motion, and many aspects are still unkown or ambiguous. The geodynamic implications are further investigated in related to published seismic observations and geochemical characters of the Izu-Bonin subduction zone. As indicated by seismic tomography and epicentral distributions, the dip angle of the plate beneath the segment to the south of 29°-30°N (the southern Izu-Bonin) is much steeper than the northern one (the northern Izu-Bonin). Deep focus events in the southern segment extend to the depth of ∼600 km, whereas in the northern section deep events just terminate at 420-450 km. Particularly, tomographic images show an obvious boundary between the northern and southern Izu-Bonin at depths of 150-600 km neglected in the previous studies. The northern and southern segments are even separated by a wide range of low-velocity anomaly in P and S wave tomography at 380 km and 450 km depths. In this depth range, three events near 30°N are characterized by strike-slip mechanisms with slab parallel σ1 and horizontally north-south trending σ3, which differ with the typical down-dip compression mechanisms for neighboring events. These events could be attributed to an abrupt change of the morphology and movement of the slab in the transition segment between the northern and southern Izu-Bonin. Indicated by the focal mechanisms, the northern and southern Izu-Bonin exhibits an inhomogeneous stress field, which is closely related to age differences of the downgoing slab. Because of the reheating process, the thermal age of the Pacific plate entering the Izu-Bonin trench in the past 10 Ma, is only 60-90 ± 20 Ma, along with the younger plate subducting in the northern segment. The seismic anisotropy implies that mantle wedge flow orientation is between the motion direction of the Pacific plate and

Cultural Patterns of South Asian and Southeast Asian Americans.

Science.gov (United States)

Mathews, Rachel

2000-01-01

An overview of South Asian and Southeast Asian Americans is discussed to aid teachers in understanding behaviors exhibited by Asian students. Culture influences in the following areas are explored: family relationships, respect for age, social interaction, communication style, family expectations, humility, school situations, decision making, and…

2009 South American benchmarking study: natural gas transportation companies

Energy Technology Data Exchange (ETDEWEB)

Jordan, Nathalie [Gas TransBoliviano S.A. (Bolivia); Walter, Juliana S. [TRANSPETRO, Rio de Janeiro, RJ (Brazil)

2009-07-01

In the current business environment large corporations are constantly seeking to adapt their strategies. Benchmarking is an important tool for continuous improvement and decision-making. Benchmarking is a methodology that determines which aspects are the most important to be improved upon, and it proposes establishing a competitive parameter in an analysis of the best practices and processes, applying continuous improvement driven by the best organizations in their class. At the beginning of 2008, GTB (Gas TransBoliviano S.A.) contacted several South American gas transportation companies to carry out a regional benchmarking study in 2009. In this study, the key performance indicators of the South American companies, whose reality is similar, for example, in terms of prices, availability of labor, and community relations, will be compared. Within this context, a comparative study of the results, the comparative evaluation among natural gas transportation companies, is becoming an essential management instrument to help with decision-making. (author)

78 FR 50135 - CNC Development, Ltd., Exousia Advanced Materials, Inc., and South American Minerals, Inc.; Order...

Science.gov (United States)

2013-08-16

... SECURITIES AND EXCHANGE COMMISSION [File No. 500-1] CNC Development, Ltd., Exousia Advanced Materials, Inc., and South American Minerals, Inc.; Order of Suspension of Trading August 14, 2013. It... securities of South American Minerals, Inc. because it has not filed any periodic reports since it filed a...

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

NARCIS (Netherlands)

Schellart, W. P.; Rawlinson, N.

2013-01-01

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

South American collaboration in scientific publications on leishmaniasis: bibliometric analysis in SCOPUS (2000-2011).

Science.gov (United States)

Huamaní, Charles; Romaní, Franco; González-Alcaide, Gregorio; Mejia, Miluska O; Ramos, José Manuel; Espinoza, Manuel; Cabezas, César

2014-01-01

Evaluate the production and the research collaborative network on Leishmaniasis in South America. A bibliometric research was carried out using SCOPUS database. The analysis unit was original research articles published from 2000 to 2011, that dealt with leishmaniasis and that included at least one South American author. The following items were obtained for each article: journal name, language, year of publication, number of authors, institutions, countries, and others variables. 3,174 articles were published, 2,272 of them were original articles. 1,160 different institutional signatures, 58 different countries and 398 scientific journals were identified. Brazil was the country with more articles (60.7%) and Oswaldo Cruz Foundation (FIOCRUZ) had 18% of Brazilian production, which is the South American nucleus of the major scientific network in Leishmaniasis. South American scientific production on Leishmaniasis published in journals indexed in SCOPUS is focused on Brazilian research activity. It is necessary to strengthen the collaboration networks. The first step is to identify the institutions with higher production, in order to perform collaborative research according to the priorities of each country.

Are diamond-bearing Cretaceous kimberlites related to shallow-angle subduction beneath western North America?

Science.gov (United States)

Currie, C. A.; Beaumont, C.

2009-05-01

The origin of deep-seated magmatism (in particular, kimberlites and lamproites) within continental plate interiors remains enigmatic in the context of plate tectonic theory. One hypothesis proposes a relationship between kimberlite occurrence and lithospheric subduction, such that a subducting plate releases fluids below a continental craton, triggering melting of the deep lithosphere and magmatism (Sharp, 1974; McCandless, 1999). This study provides a quantitative evaluation of this hypothesis, focusing on the Late Cretaceous- Eocene (105-50 Ma) kimberlites and lamproites of western North America. These magmas were emplaced along a corridor of Archean and Proterozoic lithosphere, 1000-1500 km inboard of the plate margin separating the subducting Farallon Plate and continental North America Plate. Kimberlite-lamproite magmatism coincides with tectonic events, including the Laramide orogeny, shut-down of the Sierra Nevada arc, and eastward migration of volcanism, that are commonly attributed to a change in Farallon Plate geometry to a shallow-angle trajectory (subduction that places the Farallon Plate beneath the western edge of the cratonic interior of North America. This geometry is consistent with the observed continental dynamic subsidence that lead to the development of the Western Interior Seaway. The models also show that the subducting plate has a cool thermal structure, and subducted hydrous minerals (serpentine, phengite and phlogopite) remain stable to more than 1200 km from the trench, where they may break down and release fluids that infiltrate the overlying craton lithosphere. This is supported by geochemical studies that indicate metasomatism of the Colorado Plateau and Wyoming craton mantle lithosphere by an aqueous fluid and/or silicate melt with a subduction signature. Through Cretaceous shallow-angle subduction, the Farallon Plate was in a position to mechanically and chemically interact with North American craton lithosphere at the time of

Y-chromosome lineages in native South American population.

Science.gov (United States)

Blanco-Verea, A; Jaime, J C; Brión, M; Carracedo, A

2010-04-01

The present work tries to investigate the population structure and variation of the Amerindian indigenous populations living in Argentina. A total of 134 individuals from three ethnic groups (Kolla, Mapuche and Diaguitas) living in four different regions were collected and analysed for 26 Y-SNPs and 11 Y-STRs. Intra-population variability was analysed, looking for population substructure and neighbour populations were considered for genetic comparative analysis, in order to estimate the contribution of the Amerindian and the European pool, to the current population. We observe a high frequency of R1b1 and Q1a3a* Y-chromosome haplogroups, in the ethnic groups Mapuche, Diaguita and Kolla, characteristic of European and Native American populations, respectively. When we compare our native Argentinean population with other from the South America we also observe that frequency values for Amerindian lineages are relatively lower in our population. These results show a clear Amerindian genetic component but we observe a predominant European influence too, suggesting that typically European male lineages have given rise to the displacement of genuinely Amerindian male lineages in our South American population. Copyright 2009 Elsevier Ireland Ltd. All rights reserved.

An introduction to South American camelids

International Nuclear Information System (INIS)

Urquieta, B.; Rojas, J.R.

1990-01-01

The South American camelids - the domesticated alpaca and llama, and the wild vicuna and guanaco - which belong to the Camelidae family of the Artiodactyla order are of considerable sociological, economic and ecological importance to the native populations living in the high plateau (altiplano) of the central Andes. Owing to their biological characteristics they are able to provide meat, wool, hides and transportation without disrupting the fragile ecosystem. Increasing interest is being taken in these animals, both in their native lands of Argentina, Bolivia, Chile and Peru and in other parts of the world. (author). 55 refs, 5 figs

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

Science.gov (United States)

Abedi, Maysam; Bahroudi, Abbas

2016-10-01

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

Absolute Plate Motion Control Since the Triassic from the Cocos Slab and its Associated Subduction Record in Mexico

Science.gov (United States)

Boschman, L.; Van Hinsbergen, D. J. J.; Langereis, C. G.; Molina-Garza, R. S.; Kimbrough, D. L.; Spakman, W.

2017-12-01

A positive wave speed anomaly interpreted as the Cocos slab stretches from the uppermost mantle at the Middle America trench in the west, to the lowermost mantle below the Atlantic in the east. The length and continuity of this slab indicates long-lived, uninterrupted eastward subduction of the attached Cocos Plate and its predecessor, the Farallon Plate. The geological record of Mexico contains Triassic to present day evidence of subduction, of which the post-Late Cretaceous phase is of continental margin-style. Interpretations of the pre-Upper Cretaceous subduction-related rock assemblages are under debate, and vary from far-travelled exotic intra-oceanic island arc character to in-situ extended continental margin origin. We present new paleomagnetic data that show that Triassic, Jurassic and Cretaceous subduction-related rocks from the Vizcaíno Peninsula and the Guerrero terrane have a paleolatitudinal plate motion history that is equal to that of the North American continent. This suggests that these rock assemblages were part of the overriding plate and were perhaps only separated from the North American continent by temporal fore- or back-arc spreading. The entire Triassic-present day subduction record, and hence, reconstructed trench location, can therefore be linked to the Cocos slab, which provides control on longitudinal plate motion of North America since the time of Pangea. Compared to the latest state of the art mantle frames, in which longitudes are essentially unconstrained for pre-Cretaceous times, our reconstructed absolute position of North America requires a significant westward longitudinal shift for Mesozoic times.

The impact of the subtropical South Atlantic SST on South American precipitation

Directory of Open Access Journals (Sweden)

A. S. Taschetto

2008-11-01

Full Text Available The Community Climate Model (CCM3 from the National Center for Atmospheric Research (NCAR is used to investigate the effect of the South Atlantic sea surface temperature (SST anomalies on interannual to decadal variability of South American precipitation. Two ensembles composed of multidecadal simulations forced with monthly SST data from the Hadley Centre for the period 1949 to 2001 are analysed.

A statistical treatment based on signal-to-noise ratio and Empirical Orthogonal Functions (EOF is applied to the ensembles in order to reduce the internal variability among the integrations. The ensemble treatment shows a spatial and temporal dependence of reproducibility. High degree of reproducibility is found in the tropics while the extratropics is apparently less reproducible. Austral autumn (MAM and spring (SON precipitation appears to be more reproducible over the South America-South Atlantic region than the summer (DJF and winter (JJA rainfall. While the Inter-tropical Convergence Zone (ITCZ region is dominated by external variance, the South Atlantic Convergence Zone (SACZ over South America is predominantly determined by internal variance, which makes it a difficult phenomenon to predict. Alternatively, the SACZ over western South Atlantic appears to be more sensitive to the subtropical SST anomalies than over the continent.

An attempt is made to separate the atmospheric response forced by the South Atlantic SST anomalies from that associated with the El Niño – Southern Oscillation (ENSO. Results show that both the South Atlantic and Pacific SSTs modulate the intensity and position of the SACZ during DJF. Particularly, the subtropical South Atlantic SSTs are more important than ENSO in determining the position of the SACZ over the southeast Brazilian coast during DJF. On the other hand, the ENSO signal seems to influence the intensity of the SACZ not only in DJF but especially its oceanic branch during MAM. Both local and

The fossil record of South American short-faced bears (Ursidae, Tremarctinae)

OpenAIRE

Bond, Mariano; Tonni, Eduardo Pedro; Soibelzon, Leopoldo Héctor

2005-01-01

The present study includes a review of the geographic and stratigraphic distribution of short-faced bears (Ursidae, Tremarctinae) in South America. In addition, the authors discuss biogeographic hypotheses regarding the origin of South American tremarctines. The Tremarctinae subfamily is distributed exclusively in America, from Alaska to southern Patagonia. Its biochron comprises the temporal lapse between Late Miocene and recent times; the first record of Tremarctinae in North America corres...

New GPS velocity field in the northern Andes (Peru - Ecuador - Colombia): heterogeneous locking along the subduction, northeastwards motion of the Northern Andes

Science.gov (United States)

Nocquet, J.; Mothes, P. A.; Villegas Lanza, J.; Chlieh, M.; Jarrin, P.; Vallée, M.; Tavera, H.; Ruiz, G.; Regnier, M.; Rolandone, F.

2010-12-01

Rapid subduction of the Nazca plate beneath the northen Andes margin (~6 cm/yr) results in two different processes: (1) elastic stress is accumulating along the Nazca/South American plate interface which is responsible for one of the largest megathrust earthquake sequences during the last century. The 500-km-long rupture zone of the 1906 (Mw= 8.8) event was partially reactivated by three events from the 1942 (Mw = 7.8), 1958 (Mw = 7.7), to the 1979 (Mw = 8.2). However, south of latitude 1°S, no M>8 earthquake has been reported in the last three centuries, suggesting that this area is slipping aseismically (2) permanent deformation causes opening of the Gulf of Guayaquil, with northeastwards motion of the Northern Andean Block (NAB). We present a new GPS velocity field covering the northern Andes from south of the Gulf of Guayaquil to the Caribbean plate. Our velocity field includes new continuously-recording GPS stations installed along the Ecuadorian coast, together with campaign sites observed since 1994 in the CASA project (Kellogg et al., 1989). We first estimate the long-term kinematics of the NAB in a joint inversion including GPS data, earthquake slip vectors, and quaternary slip rates on major faults. The inversion provides an Euler pole located at long. -107.8°E, lat. 36.2°N, 0.091°/Ma and indicates little internal deformation of the NAB (wrms=1.2 mm/yr). As a consequence, 30% of the obliquity of the Nazca/South America motion is accommodated by transcurrent to transpressive motion along the eastern boundary of the NAB. Residual velocities with respect to the NAB are then modeled in terms Models indicate a patchwork of highly coupled asperities encompassed by aseismic patches over the area of rupture of the M~8.8 1906 earthquake. Very low coupling is found along the southern Ecuadorian and northern Peru subduction.

Vertical slab sinking and westward subduction offshore of Mesozoic North America

Science.gov (United States)

Sigloch, Karin; Mihalynuk, Mitchell G.

2013-04-01

Subducted slabs in the mantle, as imaged by seismic tomography, preserve a record of ancient subduction zones. Ongoing debate concerns how direct this link is. How long ago did each parcel of slab subduct, and where was the trench located relative to the imaged slab position? Resolving these questions will benefit paleogeographic reconstructions, and restrict the range of plausible rheologies for mantle convection simulations. We investigate one of the largest and best-constrained Mesozoic slab complexes, the "Farallon" in the transition zone and lower mantle beneath North America. We quantitatively integrate observations from whole-mantle P-wave tomography, global plate reconstructions, and land geological evidence from the North American Cordillera. These three data sets permit us to test the simplest conceivable hypothesis for linking slabs to paleo-trenches: that each parcel of slab sank only vertically shortly after entering the trench That is, we test whether within the limits of tomographic resolution, all slab material lies directly below the location where it subducted beneath its corresponding arc. Crucially and in contrast to previous studies, we do not accept or impose an Andean-style west coast trench (Farallon-beneath-continent subduction) since Jurassic times, as this scenario is inconsistent with many geological observations. Slab geometry alone suggests that trenches started out as intra-oceanic because tomography images massive, linear slab "walls" in the lower mantle, extending almost vertically from about 800 km to 2000+ km depth. Such steep geometries would be expected from slabs sinking vertically beneath trenches that were quasi-stationary over many tens of millions of years. Intra-oceanic trenches west of Mesozoic North America could have been stationary, whereas a coastal Farallon trench could not, because the continent moved westward continuously as the Atlantic opened. Overlap of North American west-coast positions, as reconstructed in a

Potential use of the sterile insect technique against the South American fruit fly

International Nuclear Information System (INIS)

Ortiz, G.

1999-01-01

The Latin American countries have a strong interest in increasing fruit production and quality to facilitate commercialization within and outside the region. Various fruit fly control programmes in South America and their objectives and benefits are described here. Specific priorities to improve fruit fly control and eradication technologies include strengthening of quarantine, development of pre- and post-phytosanitary measures, and harmonization of the most effective and advanced technical procedures/methodologies to control fruit flies. A subregional strategy to control fruit flies in South America would promote technical co-operation among the South American countries and strengthen the activities of less advanced fruit fly programmes. Effective use can be made of local/regional infrastructure, expertise, sterile fly production and human/technical resources. In Argentina, advanced technology related to the use of medfly genetic sexing strains for SIT programmes has been successfully introduced. Joint efforts between technicians and scientists would contribute to developing new technology to control important pests in South America. (author)

SOUTH AMERICAN COLLABORATION IN SCIENTIFIC PUBLICATIONS ON LEISHMANIASIS: BIBLIOMETRIC ANALYSIS IN SCOPUS (2000-2011

Directory of Open Access Journals (Sweden)

Charles Huamaní

2014-09-01

Full Text Available Objectives: Evaluate the production and the research collaborative network on Leishmaniasis in South America. Methods: A bibliometric research was carried out using SCOPUS database. The analysis unit was original research articles published from 2000 to 2011, that dealt with leishmaniasis and that included at least one South American author. The following items were obtained for each article: journal name, language, year of publication, number of authors, institutions, countries, and others variables. Results: 3,174 articles were published, 2,272 of them were original articles. 1,160 different institutional signatures, 58 different countries and 398 scientific journals were identified. Brazil was the country with more articles (60.7% and Oswaldo Cruz Foundation (FIOCRUZ had 18% of Brazilian production, which is the South American nucleus of the major scientific network in Leishmaniasis. Conclusions: South American scientific production on Leishmaniasis published in journals indexed in SCOPUS is focused on Brazilian research activity. It is necessary to strengthen the collaboration networks. The first step is to identify the institutions with higher production, in order to perform collaborative research according to the priorities of each country.

Perspectives of the mercosur parliament performance according to south american political organization

Directory of Open Access Journals (Sweden)

Clarissa Franzoi Dri

2007-04-01

Full Text Available The signature of the MERCOSUR Parliament Constitutive Protocol, in 2005, has opened new parliamentary perspectives to the integration process which takes place in the South Cone. The nomination “parliament”, the universal suffrage prevision and new legislative and control functions evidence possibilities for an outstanding actuation. But is it possible to consider that this new organ was created in the middle of political conditions favorable to an effective functionality? Looking for traces to an answer, the paper examines political and electoral characteristics common to the South American States. First, we study the daily relations between the Executive and Legislative Powers in South American presidential regimes. Then, we verify to what extent the proportional open-list electoral system, largely used in the election of the lower houses members in the continent, influences such relations. At the end, we discuss the new assembly perspectives of effectiveness based on the regional characteristics studied.

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

NARCIS (Netherlands)

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

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

Electricity consumption and economic growth in seven South American countries

International Nuclear Information System (INIS)

Yoo, Seung-Hoon; Kwak, So-Yoon

2010-01-01

This paper attempts to investigate the causal relationship between electricity consumption and economic growth among seven South American countries, namely Argentina, Brazil, Chile, Columbia, Ecuador, Peru, and Venezuela using widely accepted time-series techniques for the period 1975-2006. The results indicate that the causal nexus between electricity consumption and economic growth varies across countries. There is a unidirectional, short-run causality from electricity consumption to real GDP for Argentina, Brazil, Chile, Columbia, and Ecuador. This means that an increase in electricity consumption directly affects economic growth in those countries. In Venezuela, there is a bidirectional causality between electricity consumption and economic growth. This implies that an increase in electricity consumption directly affects economic growth and that economic growth also stimulates further electricity consumption in that country. However, no causal relationships exist in Peru. The documented evidence from seven South American countries can provide useful information for each government with regard to energy and growth policy.

Arc magmatism as a window to plate kinematics and subduction polarity: Example from the eastern Pontides belt, NE Turkey

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Yener Eyuboglu

2011-01-01

Full Text Available The Eastern Pontides orogenic belt in the Black Sea region of Turkey offers a critical window to plate kinematics and subduction polarity during the closure of the Paleotethys. Here we provide a brief synthesis on recent information from this belt. We infer a southward subduction for the origin of the Eastern Pontides orogenic belt and its associated late Mesozoic–Cenozoic magmatism based on clear spatial and temporal variations in Late Cretaceous and Cenozoic arc magmatism, together with the existence of a prominent south-dipping reverse fault system along the entire southern coast of the Black Sea. Our model is at variance with some recent proposals favoring a northward subduction polarity, and illustrates the importance of arc magmatism in evaluating the geodynamic milieu associated with convergent margin processes.

The American South in the Atlantic World

DEFF Research Database (Denmark)

decisively shaped the history and culture of the American South from colonial times to the modern era. The essays in this interdisciplinary volume examine a wide range of topics, including race, migration, religion, law, slavery, emancipation, literature, memoir, popular culture, and ethnography. At a time...... when there is growing emphasis on globalizing southern studies the collection both demonstrates and critiques the value of Atlantic World perspectives on the region. Equally important, the mix of case studies and state-of-the field essays combines the latest historical thinking on the South’s myriad...

Subduction zone locking, strain partitioning, intraplate deformation and their implications to Seismic Hazards in South America

Science.gov (United States)

Galgana, G. A.; Mahdyiar, M.; Shen-Tu, B.; Pontbriand, C. W.; Klein, E.; Wang, F.; Shabestari, K.; Yang, W.

2014-12-01

We analyze active crustal deformation in South America (SA) using published GPS observations and historic seismicity along the Nazca Trench and the active Ecuador-Colombia-Venezuela Plate boundary Zone. GPS-constrained kinematisc models that incorporate block and continuum techniques are used to assess patterns of regional tectonic deformation and its implications to seismic potential. We determine interplate coupling distributions, fault slip-rates, and intraplate crustal strain rates in combination with historic earthquakes within 40 seismic zones crust to provide moment rate constraints. Along the Nazca subduction zone, we resolve a series of highly coupled patches, interpreted as high-friction producing "asperities" beneath the coasts of Ecuador, Peru and Chile. These include areas responsible for the 2010 Mw 8.8 Maule Earthquake and the 2014 Mw 8.2 Iquique Earthquake. Predicted tectonic block motions and fault slip rates reveal that the northern part of South America deforms rapidly, with crustal fault slip rates as much as ~20 mm/a. Fault slip and locking patterns reveal that the Oca Ancón-Pilar-Boconó fault system plays a key role in absorbing most of the complex eastward and southward convergence patterns in northeastern Colombia and Venezuela, while the near-parallel system of faults in eastern Colombia and Ecuador absorb part of the transpressional motion due to the ~55 mm/a Nazca-SA plate convergence. These kinematic models, in combination with historic seismicity rates, provide moment deficit rates that reveal regions with high seismic potential, such as coastal Ecuador, Bucaramanga, Arica and Antofagasta. We eventually use the combined information from moment rates and fault coupling patterns to further constrain stochastic seismic hazard models of the region by implementing realistic trench rupture scenarios (see Mahdyiar et al., this volume).

Spirits of the Air: Birds and American Indians in the South

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E. N. Anderson

2010-08-01

Full Text Available Review of Spirits of the Air: Birds and American Indians in the South. Shepard Krech III. 2009. University of Georgia Press, Athens. Pp. 245, copiously illustrated. $44.95 (hardbound. ISBN-13 978-0-8203-2815-7.

Metamorphic Perspectives of Subduction Zone Volatiles Cycling

Science.gov (United States)

Bebout, G. E.

2008-12-01

Field study of HP/UHP metamorphic rocks provides "ground-truthing" for experimental and theoretical petrologic studies estimating extents of deep volatiles subduction, and provides information regarding devolatilization and deep subduction-zone fluid flow that can be used to reconcile estimates of subduction inputs and arc volcanic outputs for volatiles such as H2O, N, and C. Considerable attention has been paid to H2O subduction in various bulk compositions, and, based on calculated phase assemblages, it is thought that a large fraction of the initially structurally bound H2O is subducted to, and beyond, subarc regions in most modern subduction zones (Hacker, 2008, G-cubed). Field studies of HP/UHP mafic and sedimentary rocks demonstrate the impressive retention of volatiles (and fluid-mobile elements) to depths approaching those beneath arcs. At the slab-mantle interface, high-variance lithologies containing hydrous phases such as mica, amphibole, talc, and chlorite could further stabilize H2O to great depth. Trench hydration in sub-crustal parts of oceanic lithosphere could profoundly increase subduction inputs of particularly H2O, and massive flux of H2O-rich fluids from these regions into the slab-mantle interface could lead to extensive metasomatism. Consideration of sedimentary N concentrations and δ15N at ODP Site 1039 (Li and Bebout, 2005, JGR), together with estimates of the N concentration of subducting altered oceanic crust (AOC), indicates that ~42% of the N subducting beneath Nicaragua is returned in the corresponding volcanic arc (Elkins et al., 2006, GCA). Study of N in HP/UHP sedimentary and basaltic rocks indicates that much of the N initially subducted in these lithologies would be retained to depths approaching 100 km and thus available for addition to arcs. The more altered upper part of subducting oceanic crust most likely to contribute to arcs has sediment-like δ15NAir (0 to +10 per mil; Li et al., 2007, GCA), and study of HP/UHP eclogites

Ocean-atmosphere forcing of South American tropical paleoclimate, LGM to present

Science.gov (United States)

Baker, P. A.; Fritz, S. C.; Dwyer, G. S.; Rigsby, C. A.; Silva, C. G.; Burns, S. J.

2012-12-01

Because of many recent terrestrial paleoclimatic and marine paleoceanographic records, late Quaternary South American tropical paleoclimate is as well understood as that anywhere in the world. While lessons learned from the recent instrumental record of climate are informative, this record is too short to capture much of the lower frequency variability encountered in the paleoclimate records and much of the observed paleoclimate is without modern analogue. This paleoclimate is known to be regionally variable with significant differences both north and south of the equator and between the western high Andes and eastern lowlands of the Amazon and Nordeste Brazil. Various extrinsic forcing mechanisms affected climate throughout the period, including global concentrations of GHGs, Northern Hemisphere ice sheet forcing, seasonal insolation forcing of the South American summer monsoon (SASM), millennial-scale Atlantic forcing, and Pacific forcing of the large-scale Walker circulation. The magnitude of the climate response to these forcings varied temporally, largely because of the varying amplitude of the forcing itself. For example, during the last glacial, large-amplitude north Atlantic forcing during Heinrich 1 and the LGM itself, led to wet (dry) conditions south (north) of the equator. During the Holocene, Atlantic forcing was lower amplitude, thus seasonal insolation forcing generally predominated with a weaker-than-normal SASM during the early Holocene resulting in dry conditions in the south-western tropics and wet conditions in the eastern lowlands and Nordeste; in the late Holocene seasonal insolation reached a maximum in the southern tropics and climate conditions reversed.

A bayesian approach to genome/linguistic relationships in native South Americans.

Science.gov (United States)

Amorim, Carlos Eduardo Guerra; Bisso-Machado, Rafael; Ramallo, Virginia; Bortolini, Maria Cátira; Bonatto, Sandro Luis; Salzano, Francisco Mauro; Hünemeier, Tábita

2013-01-01

The relationship between the evolution of genes and languages has been studied for over three decades. These studies rely on the assumption that languages, as many other cultural traits, evolve in a gene-like manner, accumulating heritable diversity through time and being subjected to evolutionary mechanisms of change. In the present work we used genetic data to evaluate South American linguistic classifications. We compared discordant models of language classifications to the current Native American genome-wide variation using realistic demographic models analyzed under an Approximate Bayesian Computation (ABC) framework. Data on 381 STRs spread along the autosomes were gathered from the literature for populations representing the five main South Amerindian linguistic groups: Andean, Arawakan, Chibchan-Paezan, Macro-Jê, and Tupí. The results indicated a higher posterior probability for the classification proposed by J.H. Greenberg in 1987, although L. Campbell's 1997 classification cannot be ruled out. Based on Greenberg's classification, it was possible to date the time of Tupí-Arawakan divergence (2.8 kya), and the time of emergence of the structure between present day major language groups in South America (3.1 kya).

MT2D Inversion to Image the Gorda Plate Subduction Zone

Science.gov (United States)

Lubis, Y. K.; Niasari, S. W.; Hartantyo, E.

2018-04-01

The magnetotelluric method is applicable for studying complicated geological structures because the subsurface electrical properties are strongly influenced by the electric and magnetic fields. This research located in the Gorda subduction zone beneath the North American continental plate. Magnetotelluric 2D inversion was used to image the variation of subsurface resistivity although the phase tensor analysis shows that the majority of dimensionality data is 3D. 19 MT sites were acquired from EarthScope/USArray Project. Wepresent the image of MT 2D inversion to exhibit conductivity distribution from the middle crust to uppermost asthenosphere at a depth of 120 kilometers. Based on the inversion, the overall data misfit value is 3.89. The Gorda plate subduction appears as a high resistive zone beneath the California. Local conductive features are found in the middle crust downward Klamath Mountain, Bonneville Lake, and below the eastern of Utah. Furthermore, mid-crustal is characterized by moderately resistive. Below the extensional Basin and Range province was related to highly resistive. The middle crust to the uppermost asthenosphere becomes moderately resistive. We conclude that the electrical parameters and the dimensionality of datain the shallow depth(about 22.319 km) beneath the North American platein accordance with surface geological features.

Cretaceous to Recent Asymetrical Subsidence of South American and West African Conjugate Margins

Science.gov (United States)

Kenning, J.; Mann, P.

2017-12-01

Two divergent interpretations have been proposed for South American rifted-passive margins: the "mirror hypothesis" proposes that the rifted margins form symmetrically from pure shear of the lithosphere while upper-plate-lower plate models propose that the rifted margins form asymmetrically by simple shear. Models based on seismic reflection and refraction imaging and comparison of conjugate, rifted margins generally invoke a hybrid stretching process involving elements of both end member processes along with the effects of mantle plumes active during the rift and passive margin phases. We use subsidence histories of 14, 1-7 km-deep exploration wells located on South American and West African conjugate pairs now separated by the South Atlantic Ocean, applying long-term subsidence to reveal the symmetry or asymmetry of the underlying, conjugate, rift processes. Conjugate pairs characterize the rifted margin over a distance of 3500 km and include: Colorado-South Orange, Punta Del Este-North Orange, South Pelotas-Lüderitz and the North Pelotas-Walvis Basins. Of the four conjugate pairs, more rapid subsidence on the South American plate is consistently observed with greater initial rift and syn-rift subsidence rates of >60m/Ma (compared to 100 m/Ma are observed offshore South Africa between approximately 120-80 Ma, compatible with onset of the post-rift thermal sag phase. During this period the majority of burial is completed and rates remain low at Argentina/Uruguay displays more gradual subsidence throughout the Cretaceous, consistently averaging a moderate 15-30m/Ma. By the end of this stage there is a subsequent increase to 25-60 m/Ma within the last 20 Ma, interpreted to reflect lithospheric loading due to increased sedimentation rates during the Cenozoic. This increase in subsidence rate is not seen in the African conjugate section where the majority of sediments bypassed the highly aggraded Cretaceous shelf. Initially greater on the Brazilian margin compared to

History and evolution of Subduction in the Precambrium

Science.gov (United States)

Fischer, R.; Gerya, T.

2013-12-01

Plate tectonics is a global self-organising process driven by negative buoyancy at thermal boundary layers. Phanerozoic plate tectonics with its typical subduction and orogeny is relatively well understood and can be traced back in the geological records of the continents. Interpretations of geological, petrological and geochemical observations from Proterozoic and Archean orogenic belts however (e.g. Brown, 2006), suggest a different tectonic regime in the Precambrian. Due to higher radioactive heat production the Precambrian lithosphere shows lower internal strength and is strongly weakened by percolating melts. The fundamental difference between Precambrian and Phanerozoic subduction is therefore the upper-mantle temperature, which determines the strength of the upper mantle (Brun, 2002) and the further subduction history. 3D petrological-thermomechanical numerical modelling experiments of oceanic subduction at an active plate at different upper-mantle temperatures show these different subduction regimes. For upper-mantle temperatures 250 K above the present day value no subduction occurs any more. The whole lithosphere starts to delaminate and drip-off. But the subduction style is not only a function of upper-mantle temperature but also strongly depends on the thickness of the subducting plate. If thinner present day oceanic plates are used in the Precambrian models, no shallow underplating is observed but steep subduction can be found up to an upper-mantle temperature of 200 K above present day values. Increasing oceanic plate thickness introduces a transition from steep to flat subduction at lower temperatures of around 150 K. Thicker oceanic plates in the Precambrium also agree with results from earlier studies, e.g. Abbott (1994). References: Abbott, D., Drury, R., Smith, W.H.F., 1994. Flat to steep transition in subduction style. Geology 22, 937-940. Brown, M., 2006. Duality of thermal regimes is the distinctive characteristic of plate tectonics since the

Daily and seasonal activity patterns of free range South-American rattlesnake (Crotalus durissus).

Science.gov (United States)

Tozetti, Alexandro M; Martins, Marcio

2013-09-01

This study aimed at describing daily and seasonal variation in the activity of a population of South-American rattlesnakes (Crotalus durissus) in a savanna like habitat (Cerrado) in Southeastern Brazil. Seasonal and daily activities of snakes were evaluated by the number of captures of snakes during road surveys, accidental encounters, and relocations by radio-tracking. Our results show that climatic variables such as air temperature and rainfall have little influence on the activity pattern of rattlesnakes. Our findings indicate that rattlesnakes spend most of the day resting and most of the night in ambush posture. The South-American rattlesnake is active throughout the year with a discrete peak in activity of males during the matting season. The possibility of maintaining activity levels even during the coldest and driest season can facilitate the colonization of several habitats in South America. This possibility currently facilitates the colonization of deforested areas by rattlesnakes.

Introduction to the structures and processes of subduction zones

Science.gov (United States)

Zheng, Yong-Fei; Zhao, Zi-Fu

2017-09-01

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

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

Science.gov (United States)

Zhao, Dapeng; Fujisawa, Moeto; Toyokuni, Genti

2017-03-01

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

Array-Based Receiver Function Analysis of the Subducting Juan de Fuca Plate Beneath the Mount St. Helens Region and its Implications for Subduction Geometry and Metamorphism

Science.gov (United States)

Mann, M. E.; Abers, G. A.; Creager, K. C.; Ulberg, C. W.; Crosbie, K.

2017-12-01

Mount St. Helens (MSH) is unusual as a prolific arc volcano located 50 km towards the forearc of the main Cascade arc. The iMUSH (imaging Magma Under mount St. Helens) broadband deployment featured 70 seismometers at 10-km spacing in a 50-km radius around MSH, spanning a sufficient width for testing along-strike variation in subsurface geometry as well as deep controls on volcanism in the Cascade arc. Previous estimates of the geometry of the subducting Juan de Fuca (JdF) slab are extrapolated to MSH from several hundred km to the north and south. We analyze both P-to-S receiver functions and 2-D Born migrations of the full data set to locate the upper plate Moho and the dip and depth of the subducting slab. The strongest coherent phase off the subducting slab is the primary reverberation (Ppxs; topside P-to-S reflection) from the Moho of the subducting JdF plate, as indicated by its polarity and spatial pattern. Migration images show a dipping low velocity layer at depths less than 50 km that we interpret as the subducting JdF crust. Its disappearance beyond 50 km depth may indicate dehydration of subducting crust or disruption of high fluid pressures along the megathrust. The lower boundary of the low velocity zone, the JdF Moho, persists in the migration image to depths of at least 90 km and is imaged at 74 km beneath MSH, dipping 23 degrees. The slab surface is 68 km beneath MSH and 85 km beneath Mount Adams volcano to the east. The JdF Moho exhibits 10% velocity contrasts as deep as 85 km, an observation difficult to reconcile with simple models of crustal eclogitization. The geometry and thickness of the JdF crust and upper plate Moho is consistent with similar transects of Cascadia and does not vary along strike beneath iMUSH, indicating a continuous slab with no major disruption. The upper plate Moho is clear on the east side of the array but it disappears west of MSH, a feature we interpret as a result of both serpentinization of the mantle wedge and a

A large mantle water source for the northern San Andreas Fault System: A ghost of subduction past

Science.gov (United States)

Kirby, Stephen H.; Wang, Kelin; Brocher, Thomas M.

2014-01-01

Recent research indicates that the shallow mantle of the Cascadia subduction margin under near-coastal Pacific Northwest U.S. is cold and partially serpentinized, storing large quantities of water in this wedge-shaped region. Such a wedge probably formed to the south in California during an earlier period of subduction. We show by numerical modeling that after subduction ceased with the creation of the San Andreas Fault System (SAFS), the mantle wedge warmed, slowly releasing its water over a period of more than 25 Ma by serpentine dehydration into the crust above. This deep, long-term water source could facilitate fault slip in San Andreas System at low shear stresses by raising pore pressures in a broad region above the wedge. Moreover, the location and breadth of the water release from this model gives insights into the position and breadth of the SAFS. Such a mantle source of water also likely plays a role in the occurrence of Non-Volcanic Tremor (NVT) that has been reported along the SAFS in central California. This process of water release from mantle depths could also mobilize mantle serpentinite from the wedge above the dehydration front, permitting upward emplacement of serpentinite bodies by faulting or by diapiric ascent. Specimens of serpentinite collected from tectonically emplaced serpentinite blocks along the SAFS show mineralogical and structural evidence of high fluid pressures during ascent from depth. Serpentinite dehydration may also lead to tectonic mobility along other plate boundaries that succeed subduction, such as other continental transforms, collision zones, or along present-day subduction zones where spreading centers are subducting.

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

Directory of Open Access Journals (Sweden)

D. Arcay

2012-12-01

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

New species of Bidessonotus Régimbart, 1895 with a review of the South American species (Coleoptera, Adephaga, Dytiscidae, Hydroporinae, Bidessini

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Kelly Miller

2016-10-01

Full Text Available The South American species of the New World genus Bidessonotus Régimbart, 1895 are reviewed with descriptions of seven new species. This brings the total number of valid Bidessonotus species to 37, making it the largest Bidessini genus in the New World. The new species are B. annae sp. n. (Venezuela, B. josiahi sp. n. (Venezuela, B. palecephalus sp. n. (Venezuela, B. reductus sp. n. (Venezuela, B. septimus sp. n. (Venezuela, B. spinosus sp. n. (Venezuela, and B. valdezi sp. n. (Guyana, Suriname. New distribution records are provided for many other South American Bidessonotus species. The main diagnostic features of Bidessonotus species are in the male genitalia, and these are illustrated for all South American species. Diagnostic features, distributions (including distribution maps, and additional comments are provided for all South American species.

Geochemical and Sr-Nd-Pb-Li isotopic characteristics of volcanic rocks from the Okinawa Trough: Implications for the influence of subduction components and the contamination of crustal materials

Science.gov (United States)

Guo, Kun; Zhai, Shikui; Yu, Zenghui; Wang, Shujie; Zhang, Xia; Wang, Xiaoyuan

2018-04-01

The Okinawa Trough is an infant back-arc basin developed along the Ryukyu arc. This paper provides new major and trace element and Sr-Nd-Pb-Li isotope data of volcanic rocks in the Okinawa Trough and combines the published geochemical data to discuss the composition of magma source, the influence of subduction component, and the contamination of crustal materials, and calculate the contribution between subduction sediment and altered oceanic crust in the subduction component. The results showed that there are 97% DM and 3% EMI component in the mantle source in middle trough (MS), which have been influenced by subduction sediment. The Li-Nd isotopes indicate that the contribution of subduction sediment and altered oceanic crust in subduction component are 4 and 96%, respectively. The intermediate-acidic rocks suffer from contamination of continental crust material in shallow magma chamber during fractional crystallization. The acidic rocks in south trough have experienced more contamination of crustal material than those from the middle and north trough segments.

Daily and seasonal activity patterns of free range South-American rattlesnake (Crotalus durissus

Directory of Open Access Journals (Sweden)

ALEXANDRO M. TOZETTI

2013-09-01

Full Text Available This study aimed at describing daily and seasonal variation in the activity of a population of South-American rattlesnakes (Crotalus durissus in a savanna like habitat (Cerrado in Southeastern Brazil. Seasonal and daily activities of snakes were evaluated by the number of captures of snakes during road surveys, accidental encounters, and relocations by radio-tracking. Our results show that climatic variables such as air temperature and rainfall have little influence on the activity pattern of rattlesnakes. Our findings indicate that rattlesnakes spend most of the day resting and most of the night in ambush posture. The South-American rattlesnake is active throughout the year with a discrete peak in activity of males during the matting season. The possibility of maintaining activity levels even during the coldest and driest season can facilitate the colonization of several habitats in South America. This possibility currently facilitates the colonization of deforested areas by rattlesnakes.

Chile's seismogenic coupling zones - geophysical and neotectonic observations from the South American subduction zone prior to the Maule 2010 earthquake

Science.gov (United States)

Oncken With Tipteq, Onno; Ipoc Research Groups

2010-05-01

supported from recent findings along the exhumed, fossil seismogenic coupling zone of the European Alps. The data provide additional evidence that the degree of interseismic locking is closely mirrored by subsequent megathrust failure as evidenced by the slip and aftershock pattern of the Maule 2010 earthquake. Neogene surface deformation in Chile has been complex exhibiting tectonically uplifting areas along the coast driven by interseismically active reverse faulting. In addition, we observe coseismically subsiding domains along other parts of the coast. Moreover, the coseismic and interseismic vertical displacement identified is not coincident with long-term vertical motion that probably is superseded by slow basal underplating or tectonic erosion occurring at the downdip parts of the seismogenic zone causing discontinuous uplift. Analogue and numerical modelling lend additional support to the kinematic patterns linking slip at the seismogenic coupling zone and upper plate response. Finally we note that the characteristic peninsulas along the South American margin constitute stable rupture boundaries/barriers and appear to have done so for a protracted time as evidenced by their long-term uplift history since at least the Late Pliocene that points to anomalous properties of the plate interface affecting the mode of strain accumulation and plate interface rupture.

African American Medical Culture in the Antebellum South: As Remembered in the WPA Narratives

OpenAIRE

Barber, Daniel

2015-01-01

This project examines the oral accounts of former slaves, as recorded in the WPA narratives in the 1930s, to study the development of African American medical culture in the Antebellum South. Through an examination of these transcribed memories, my research investigates how African American praxes with medicinal flora, healing techniques, and spiritual harmony, reflected their ethnomedical and cosmological ideologies. The duality of these ideologies represents an African American medical iden...

The subduction erosion and mantle source region contamination model of Andean arc magmatism: Isotopic evidence from igneous rocks of central Chile

International Nuclear Information System (INIS)

Stern, Charles R

2001-01-01

Continental crust may be incorporated in mantle-derived Andean magmas as these magmas rise through the crust (Hildreth and Moorbath, 1988), or alternatively, crust may be tectonically transported into the mantle by subduction of trench sediments and subduction erosion of the continental margin, and then added into the mantle source region of Andean magmas (Stern, 1991). Since the mantle has relatively low Sr, Nd, and Pb concentrations compared to continental crust, differences in the isotopic compositions of magmas erupted in different region of the Andes may be produced by relatively small differences in the amount of subducted crust added to the mantle source region of these magmas. By comparison, significantly larger amounts of crust must be assimilated by mantle-derived magmas to produce isotopic differences of similar magnitude. Therefore, constraining the process by which continental crust is incorporated in Andean magmas has important implications for understanding the chemical cycling that takes place in the Andean subduction-related magma factory. Isotopic data suggest the incorporation of a greater proportion of crust in Andean magmas erupted at the northern portion of the Southern Volcanic Zone of central Chile compared to those erupted in the southern portion of the Southern Volcanic Zone of south central Chile (SSVZ) (Stern et al., 1984; Futa and Stern, 1988; Hildreth and Moorbath, 1988). The NSVZ occurs just south of the current locus of the subduction of the Juan Fernandez Ridge. The southward migration of the locus of subduction of this ridge has resulted in decreasing subduction angle below the NSVZ, the eastward migration of the volcanic front of the Andean arc, and an increase in the crustal thickness below the arc. These factors together have caused changes, since the middle Miocene, in the isotopic composition of Andean igneous rocks of central Chile. The data indicate a close chronologic relation between the southward migrations of the locus

Results from CAT/SCAN, the Calabria-Apennine-Tyrrhenian/Subduction-Accretion-Collision Network

Science.gov (United States)

Steckler, M. S.; Amato, A.; Guerra, I.; Armbruster, J.; Baccheschi, P.; Diluccio, F.; Gervasi, A.; Harabaglia, P.; Kim, W.; Lerner-Lam, A.; Margheriti, L.; Seeber, L.; Tolstoy, M.; Wilson, C. K.

2005-12-01

for the instruments that were not recovered. The experiment is determining the structure of the Calabrian subduction and southern Apennine collision systems and the structure of the transition from oceanic subduction in Calabria to continental collision in the southern Apennines. We have delineated a strong anisotropy with a fast direction following the curved arc, but weaker anisotropy beneath the Tyrrhenian Sea. Receiver function images show variations in crustal thickness throughout the region, consistent with previous conceptual models. We also image a negative polarity interface dipping to the southwest that we interpret as the main thrust ramp in the north transitioning to the subduction interface in the south. The transition from one to the other is marked by a loss of amplitude in the Moho conversion. Local seismicity is consistent with surface structure in showing extension normal and parallel to the Calabrian forearc as well as continuing southeastward motion of Calabria relative to the southern Apennines and Maghrebides.

Seismic imaging along a 600 km transect of the Alaska Subduction zone (Invited)

Science.gov (United States)

Calkins, J. A.; Abers, G. A.; Freymueller, J. T.; Rondenay, S.; Christensen, D. H.

2010-12-01

We present earthquake locations, scattered wavefield migration images, and phase velocity maps from preliminary analysis of combined seismic data from the Broadband Experiment Across the Alaska Range (BEAAR) and Multidisciplinary Observations of Onshore Subduction (MOOS) projects. Together, these PASSCAL broadband arrays sampled a 500+ km transect across a portion of the subduction zone characterized by the Yakutat terrane/Pacific plate boundary in the downgoing plate, and the Denali volcanic gap in the overriding plate. These are the first results from the MOOS experiment, a 34-station array that was deployed from 2006-2008 to fill in the gap between the TACT offshore refraction profile (south and east of the coastline of the Kenai Peninsula), and the BEAAR array (spanning the Alaska Range between Talkeetna and Fairbanks). 2-D images of the upper 150 km of the subduction zone were produced by migrating forward- and back-scattered arrivals in the coda of P waves from large teleseismic earthquakes, highlighting S-velocity perturbations from a smoothly-varying background model. The migration images reveal a shallowly north-dipping low velocity zone that is contiguous near 20 km depth on its updip end with previously obtained images of the subducting plate offshore. The low velocity zone steepens further to the north, and terminates near 120 km beneath the Alaska Range. We interpret this low velocity zone to be the crust of the downgoing plate, and the reduced seismic velocities to be indicative of hydrated gabbroic compositions. Earthquakes located using the temporary arrays and nearby stations of the Alaska Regional Seismic Network correlate spatially with the inferred subducting crust. Cross-sections taken along nearly orthogonal strike lines through the MOOS array reveal that both the dip angle and the thickness of the subducting low velocity zone change abruptly across a roughly NNW-SSE striking line drawn through the eastern Kenai Peninsula, coincident with a

First South American Agathis (Araucariaceae), Eocene of Patagonia.

Science.gov (United States)

Wilf, Peter; Escapa, Ignacio H; Cúneo, N Rubén; Kooyman, Robert M; Johnson, Kirk R; Iglesias, Ari

2014-01-01

Agathis is an iconic genus of large, ecologically important, and economically valuable conifers that range over lowland to upper montane rainforests from New Zealand to Sumatra. Exploitation of its timber and copal has greatly reduced the genus's numbers. The early fossil record of Agathis comes entirely from Australia, often presumed to be its area of origin. Agathis has no previous record from South America. We describe abundant macrofossils of Agathis vegetative and reproductive organs, from early and middle Eocene rainforest paleofloras of Patagonia, Argentina. The leaves were formerly assigned to the New World cycad genus Zamia. Agathis zamunerae sp. nov. is the first South American occurrence and the most complete representation of Agathis in the fossil record. Its morphological features are fully consistent with the living genus. The most similar living species is A. lenticula, endemic to lower montane rainforests of northern Borneo. Agathis zamunerae sp. nov. demonstrates the presence of modern-aspect Agathis by 52.2 mya and vastly increases the early range and possible areas of origin of the genus. The revision from Zamia breaks another link between the Eocene and living floras of South America. Agathis was a dominant, keystone element of the Patagonian Eocene floras, alongside numerous other plant taxa that still associate with it in Australasia and Southeast Asia. Agathis extinction in South America was an integral part of the transformation of Patagonian biomes over millions of years, but the living species are disappearing from their ranges at a far greater rate.

Mitogenomic phylogeny, diversification, and biogeography of South American spiny rats

DEFF Research Database (Denmark)

Fabre, Pierre-Henri; Upham, Nathan S.; Emmons, Louise H.

2017-01-01

Echimyidae is one of the most speciose and ecologically diverse rodent families in the world, occupying a wide range of habitats in the Neotropics. However, a resolved phylogeny at the genus-level is still lacking for these 22 genera of South American spiny rats, including the coypu (Myocastorina...... Atlantic and Amazonian Forests and (2) the Northern uplift of the Andes....

Slab Geometry and Deformation in the Northern Nazca Subduction Zone Inferred From The Relocation and Focal mechanisms of Intermediate-Depth Earthquakes

Science.gov (United States)

Chang, Y.; Warren, L. M.; Prieto, G. A.

2015-12-01

In the northern Nazca subduction zone, the Nazca plate is subducting to the east beneath the South American Plate. At ~5.6ºN, the subducting plate has a 240-km east-west offset associated with a slab tear, called the Caldas tear, that separates the northern and southern segments. Our study seeks to better define the slab geometry and deformation in the southern segment, which has a high rate of intermediate-depth earthquakes (50-300 km) between 3.6ºN and 5.2ºN in the Cauca cluster. From Jan 2010 to Mar 2014, 228 intermediate-depth earthquakes in the Cauca cluster with local magnitude Ml 2.5-4.7 were recorded by 65 seismic stations of the Colombian National Seismic Network. We review and, if necessary, adjust the catalog P and S wave arrival picks. We use the travel times to relocate the earthquakes using a double difference relocation method. For earthquakes with Ml ≥3.8, we also use waveform modeling to compute moment tensors . The distribution of earthquake relocations shows an ~15-km-thick slab dipping to the SE. The dip angle increases from 20º at the northern edge of the cluster to 38º at the southern edge. Two concentrated groups of earthquakes extend ~40 km vertically above the general downdip trend, with a 20 km quiet gap between them at ~100 km depth. The earthquakes in the general downdip seismic zone have downdip compressional axes, while earthquakes close to the quiet gap and in the concentrated groups have an oblique component. The general decrease in slab dip angle to the north may be caused by mantle flow through the Caldas tear. The seismicity gap in the slab may be associated with an active deformation zone and the concentrated groups of earthquakes with oblique focal mechanisms could be due to a slab fold.

Subduction Drive of Plate Tectonics

Science.gov (United States)

Hamilton, W. B.

2003-12-01

Don Anderson emphasizes that plate tectonics is self-organizing and is driven by subduction, which rights the density inversion generated as oceanic lithosphere forms by cooling of asthenosphere from the top. The following synthesis owes much to many discussions with him. Hinge rollback is the key to kinematics, and, like the rest of actual plate behavior, is incompatible with bottom-up convection drive. Subduction hinges (which are under, not in front of, thin leading parts of arcs and overriding plates) roll back into subducting plates. The Pacific shrinks because bounding hinges roll back into it. Colliding arcs, increasing arc curvatures, back-arc spreading, and advance of small arcs into large plates also require rollback. Forearcs of overriding plates commonly bear basins which preclude shortening of thin plate fronts throughout periods recorded by basin strata (100 Ma for Cretaceous and Paleogene California). This requires subequal rates of advance and rollback, and control of both by subduction. Convergence rate is equal to rates of rollback and advance in many systems but is greater in others. Plate-related circulation probably is closed above 650 km. Despite the popularity of concepts of plumes from, and subduction into, lower mantle, there is no convincing evidence for, and much evidence against, penetration of the 650 in either direction. That barrier not only has a crossing-inhibiting negative Clapeyron slope but also is a compositional boundary between fractionated (not "primitive"), sluggish lower mantle and fertile, mobile upper mantle. Slabs sink more steeply than they dip. Slabs older than about 60 Ma when their subduction began sink to, and lie down on and depress, the 650-km discontinuity, and are overpassed, whereas younger slabs become neutrally buoyant in mid-upper mantle, into which they are mixed as they too are overpassed. Broadside-sinking old slabs push all upper mantle, from base of oceanic lithosphere down to the 650, back under

Geochemistry of subduction zone serpentinites: A review

OpenAIRE

DESCHAMPS, Fabien; GODARD, Marguerite; GUILLOT, Stéphane; HATTORI, Kéiko

2013-01-01

Over the last decades, numerous studies have emphasized the role of serpentinites in the subduction zone geodynamics. Their presence and role in subduction environments are recognized through geophysical, geochemical and field observations of modern and ancient subduction zones and large amounts of geochemical database of serpentinites have been created. Here, we present a review of the geochemistry of serpentinites, based on the compilation of ~ 900 geochemical data of abyssal, mantle wedge ...

Tracing halogen and B cycling in subduction zones based on obducted, subducted and forearc serpentinites of the Dominican Republic.

Science.gov (United States)

Pagé, Lilianne; Hattori, Keiko

2017-12-19

Serpentinites are important reservoirs of fluid-mobile elements in subduction zones, contributing to volatiles in arc magmas and their transport into the Earth's mantle. This paper reports halogen (F, Cl, Br, I) and B abundances of serpentinites from the Dominican Republic, including obducted and subducted abyssal serpentinites and forearc mantle serpentinites. Abyssal serpentinite compositions indicate the incorporation of these elements from seawater and sediments during serpentinization on the seafloor and at slab bending. During their subduction and subsequent lizardite-antigorite transition, F and B are retained in serpentinites, whilst Cl, Br and I are expelled. Forearc mantle serpentinite compositions suggest their hydration by fluids released from subducting altered oceanic crust and abyssal serpentinites, with only minor sediment contribution. This finding is consistent with the minimal subduction of sediments in the Dominican Republic. Forearc mantle serpentinites have F/Cl and B/Cl ratios similar to arc magmas, suggesting the importance of serpentinite dehydration in the generation of arc magmatism in the mantle wedge.

South American Guidelines for Cardiovascular Disease Prevention and Rehabilitation

Directory of Open Access Journals (Sweden)

AH Herdy

2014-08-01

Full Text Available In this document, the Inter-American Committee of Cardiovascular Prevention and Rehabilitation, together with the South American Society of Cardiology, aimed to formulate strategies, measures, and actions for cardiovascular disease prevention and rehabilitation (CVDPR. In the context of the implementation of a regional and national health policy in Latin American countries, the goal is to promote cardiovascular health and thereby decrease morbidity and mortality. The study group on Cardiopulmonary and Metabolic Rehabilitation from the Department of Exercise, Ergometry, and Cardiovascular Rehabilitation of the Brazilian Society of Cardiology has created a committee of experts to review the Portuguese version of the guideline and adapt it to the national reality. The mission of this document is to help health professionals to adopt effective measures of CVDPR in the routine clinical practice. The publication of this document and its broad implementation will contribute to the goal of the World Health Organization (WHO, which is the reduction of worldwide cardiovascular mortality by 25% until 2025. The study group's priorities are the following: • Emphasize the important role of CVDPR as an instrument of secondary prevention with significant impact on cardiovascular morbidity and mortality; • Join efforts for the knowledge on CVDPR, its dissemination, and adoption in most cardiovascular centers and institutes in South America, prioritizing the adoption of cardiovascular prevention methods that are comprehensive, practical, simple and which have a good cost/benefit ratio; • Improve the education of health professionals and patients with education programs on the importance of CVDPR services, which are directly targeted at the health system, clinical staff, patients, and community leaders, with the aim of decreasing the barriers to CVDPR implementation.

Explaining and improving breast cancer information acquisition among African American women in the Deep South.

Science.gov (United States)

Anderson-Lewis, Charkarra; Ross, Levi; Johnson, Jarrett; Hastrup, Janice L; Green, B Lee; Kohler, Connie L

2012-06-01

A major challenge facing contemporary cancer educators is how to optimize the dissemination of breast cancer prevention and control information to African American women in the Deep South who are believed to be cancer free. The purpose of this research was to provide insight into the breast cancer information-acquisition experiences of African American women in Alabama and Mississippi and to make recommendations on ways to better reach members of this high-risk, underserved population. Focus group methodology was used in a repeated, cross-sectional research design with 64 African American women, 35 years old or older who lived in one of four urban or rural counties in Alabama and Mississippi. Axial-coded themes emerged around sources of cancer information, patterns of information acquisition, characteristics of preferred sources, and characteristics of least-preferred sources. It is important to invest in lay health educators to optimize the dissemination of breast cancer information to African American women who are believed to be cancer free in the Deep South.

English or Perish: How Contemporary South Korea Received, Accommodated, and Internalized English and American Modernity

Science.gov (United States)

Lee, JongHwa; Han, Min Wha; McKerrow, Raymie E.

2010-01-01

This paper discusses the positionality of English in South Korea as a form of symbolic capital that represents the discursive power of Americanism and East Asian Social Darwinism. By employing Bourdieu's and Foucault's theoretical orientations, this paper traces how South Korean linguistic policies to incorporate English loan words coincide with…

The Taitao Granites: I-type granites formed by subduction of the Chile Ridge and its implication in growth of continental crusts

Science.gov (United States)

Anma, Ryo

2016-04-01

Late Miocene to Early Pliocene granite plutons are exposed at the tip of the Taitao peninsula, the westernmost promontory of the Chilean coast, together with a contemporaneous ophiolite with a Penrose-type stratigraphy. Namely, the Taitao granites and the Taitao ohiolite, respectively, are located at ~30 km southeast of the Chile triple junction, where a spreading center of the Chile ridge system is subducting underneath the South America plate. This unique tectonic setting provides an excellent opportunity to study the generation processes of granitic magmas at a ridge subduction environment, and the complex magmatic interactions between the subducting ridge, overlying crust and sediments, and mantle. This paper reviews previous studies on the Taitao ophiolite/granite complex and use geochemical data and U-Pb age distributions of zircons separated from igneous and sedimentary rocks from the area to discuss the mechanism that formed juvenile magma of calc-alkaline I-type granites during ridge subduction. Our model implies that the magmas of the Taitao granites formed mainly due to partial melting of hot oceanic crust adjacent to the subducting mid-oceanic ridge that has been under influence of deep crustal contamination and/or metasomatized sub-arc mantle through slab window. The partial melting took place under garnet-free-amphibolite conditions. The juvenile magmas then incorporated a different amount of subducted sediments to form the I-type granites with various compositions. The Taitao granites provide an ideal case study field that shows the processes to develop continental crusts out of oceanic crusts through ridge subduction.

A proof of concept study to assess the potential of PCR testing to detect natural Mycobacterium bovis infection in South American camelids.

Science.gov (United States)

Crawshaw, Timothy R; Chanter, Jeremy I; McGoldrick, Adrian; Line, Kirsty

2014-02-07

Cases of Mycobacterium bovis infection South American camelids have been increasing in Great Britain. Current antemortem immunological tests have some limitations. Cases at post mortem examination frequently show extensive pathology. The feasibility of detecting Mycobacterium bovis DNA in clinical samples was investigated. A sensitive extraction methodology was developed and used on nasal swabs and faeces taken post-mortem to assess the potential for a PCR test to detect Mycobacterium bovis in clinical samples. The gross pathology of the studied South American camelids was scored and a significantly greater proportion of South American camelids with more severe pathology were positive in both the nasal swab and faecal PCR tests. A combination of the nasal swab and faecal PCR tests detected 63.9% of all the South American camelids with pathology that were tested. The results suggest that antemortem diagnosis of Mycobacterium bovis in South American camelids may be possible using a PCR test on clinical samples, however more work is required to determine sensitivity and specificity, and the practicalities of applying the test in the field.

Geochemistry of subduction zone serpentinites: A review

Science.gov (United States)

Deschamps, Fabien; Godard, Marguerite; Guillot, Stéphane; Hattori, Kéiko

2013-09-01

Over the last decades, numerous studies have emphasized the role of serpentinites in the subduction zone geodynamics. Their presence and role in subduction environments are recognized through geophysical, geochemical and field observations of modern and ancient subduction zones and large amounts of geochemical database of serpentinites have been created. Here, we present a review of the geochemistry of serpentinites, based on the compilation of ~ 900 geochemical data of abyssal, mantle wedge and exhumed serpentinites after subduction. The aim was to better understand the geochemical evolution of these rocks during their subduction as well as their impact in the global geochemical cycle. When studying serpentinites, it is essential to determine their protoliths and their geological history before serpentinization. The geochemical data of serpentinites shows little mobility of compatible and rare earth elements (REE) at the scale of hand-specimen during their serpentinization. Thus, REE abundance can be used to identify the protolith for serpentinites, as well as magmatic processes such as melt/rock interactions before serpentinization. In the case of subducted serpentinites, the interpretation of trace element data is difficult due to the enrichments of light REE, independent of the nature of the protolith. We propose that enrichments are probably not related to serpentinization itself, but mostly due to (sedimentary-derived) fluid/rock interactions within the subduction channel after the serpentinization. It is also possible that the enrichment reflects the geochemical signature of the mantle protolith itself which could derive from the less refractory continental lithosphere exhumed at the ocean-continent transition. Additionally, during the last ten years, numerous analyses have been carried out, notably using in situ approaches, to better constrain the behavior of fluid-mobile elements (FME; e.g. B, Li, Cl, As, Sb, U, Th, Sr) incorporated in serpentine phases

Evaluation of insulin resistance in two kinds of South American camelids: llamas and alpacas.

Science.gov (United States)

Araya, A V; Atwater, I; Navia, M A; Jeffs, S

2000-10-01

Insulin resistance was evaluated in South American camelids, llamas and alpacas, by use of the minimal model test and the insulin tolerance test. Animals were catheterized for long-term studies and tamed to minimize stress during evaluation. Results indicated a low insulin sensitivity index (SI) = 0 to 0.97, median = 0.39 x 10(-4) min/uIU x ml, about a fifth the value in other mammals and humans. The KITT was between 1.43 and 3.19 %/min, also significantly lower than that reported for humans. Glycosylated hemoglobin concentration was 6%, and HbAlc concentration was 5.5%; red blood cell lifetime, as measured by use of the 51Cr method, was 120 days, similar to the value in humans. We concluded that llamas and alpacas have naturally higher blood glucose concentration than do humans and other mammals during the glucose tolerance test. Using the same mathematical tools to evaluate glucose metabolism as those used in people, South American camelids appear to be resistant to insulin. Thus, the South American camelid may be a useful new animal model for the study of sugar metabolism and various facets of diabetes mellitus, especially protection from the deleterious effects of glycosylation.

A possible mechanism for earthquakes found in the mantle wedge of the Nazca subduction zone

Science.gov (United States)

Warren, L. M.; Chang, Y.; Prieto, G. A.

2017-12-01

Beneath Colombia, the Cauca cluster of intermediate-depth earthquakes extends for 200 km along the trench (3.5°N-5.5°N, 77.0°W-75.3°W) and, with 58 earthquakes per year with local magnitude ML >= 2.5, has a higher rate of seismicity than the subduction zone immediately to the north or south. By precisely locating 433 cluster earthquakes from 1/2010-3/2014 with data from the Colombian National Seismic Network, we found that the earthquakes are located both in a continuous Nazca plate subducting at an angle of 33°-43° and in the overlying mantle wedge. The mantle wedge earthquakes (12% of the earthquakes) form two isolated 40-km-tall columns extending perpendicular to the subducting slab. Using waveform inversion, we computed focal mechanisms for 69 of the larger earthquakes. The focal mechanisms are variable, but the intraslab earthquakes are generally consistent with an in-slab extensional stress axis oriented 25° counterclockwise from the down-dip direction. We suggest that the observed mantle wedge earthquakes are the result of hydrofracture in a relatively cool mantle wedge. This segment of the Nazca Plate is currently subducting at a normal angle, but Wagner et al. (2017) suggested that a flat slab slowly developed in the region between 9-5.9 Ma and persisted until 4 Ma. During flat slab subduction, the overlying mantle wedge typically cools because it is cut off from mantle corner flow. After hydrous minerals in the slab dehydrate, the dehydrated fluid is expelled from the slab and migrates through the mantle wedge. If a cool mantle wedge remains today, fluid dehydrated from the slab may generate earthquakes by hydrofracture, with the mantle wedge earthquakes representing fluid migration pathways. Dahm's (2000) model of water-filled fracture propagation in the mantle wedge shows hydrofractures propagating normal to the subducting slab and extending tens of km into the mantle wedge, as we observe.

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

NARCIS (Netherlands)

Schellart, Wouter P.

2005-01-01

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

Melting of subducted continental crust: Geochemical evidence from Mesozoic granitoids in the Dabie-Sulu orogenic belt, east-central China

Science.gov (United States)

Zhao, Zi-Fu; Liu, Zhi-Bin; Chen, Qi

2017-09-01

Syn-collisional and postcollisional granitoids are common in collisional orogens, and they were primarily produced by partial melting of subducted continental crust. This is exemplified by Mesozoic granitoids from the Dabie-Sulu orogenic belt in east-central China. These granitoids were emplaced in small volumes in the Late Triassic (200-206 Ma) and the Late Jurassic (146-167 Ma) but massively in the Early Cretaceous (111-143 Ma). Nevertheless, all of them exhibit arc-like trace element distribution patterns and are enriched in Sr-Nd-Hf isotope compositions, indicating their origination from the ancient continental crust. They commonly contain relict zircons with Neoproterozoic and Triassic U-Pb ages, respectively, consistent with the protolith and metamorphic ages for ultrahigh-pressure (UHP) metaigneous rocks in the Dabie-Sulu orogenic belt. Some granitoids show low zircon δ18O values, and SIMS in-situ O isotope analysis reveals that the relict zircons with Neoproterozoic and Triassic U-Pb ages also commonly exhibit low δ18O values. Neoproterozoic U-Pb ages and low δ18O values are the two diagnostic features that distinguish the subducted South China Block from the obducted North China Block. Thus, the magma source of these Mesozoic granitoids has a genetic link to the subducted continental crust of the South China Block. On the other hand, these granitoids contain relict zircons with Paleoproterozoic and Archean U-Pb ages, which are present in both the South and North China Blocks. Taken together, the Mesozoic granitoids in the Dabie-Sulu orogenic belt and its hanging wall have their magma sources that are predominated by the continental crust of the South China Block with minor contributions from the continental crust of the North China Block. The Triassic continental collision between the South and North China Blocks brought the continental crust into the thickened orogen, where they underwent the three episodes of partial melting in the Late Triassic, Late

Intestinal helminths in lowland South American Indians: some evolutionary interpretations.

Science.gov (United States)

Confalonieri, U; Ferreira, L F; Araújo, A

1991-12-01

Data on intestinal parasite infections for South American Indians in prehistoric times as revealed by coprolite analysis are being used to support transoceanic migration routes from the Old World to the New World. These same findings on modern semi-isolated aborigines, considered persisting prehistoric patterns, are also of great importance as indicators of pre-Columbian peopling of South America. This is the case for the Lengua Indians from Paraguay, studied in the 1920s, and the Yanomami and the Salumã from Brazil, studied in the 1980s. The intestinal parasitic profile of these groups can be empirically associated with culture change, but no clear correlations with the population biology of their hosts can be made at present because of scarcity of data.

Phylogenetic reconstruction of South American felids defined by protein electrophoresis

OpenAIRE

Pecon Slattery, J.; Johnson, W. E.; Goldman, D.; O'Brien, S. J.

1994-01-01

Phylogenetic associations among six closely related South American felid species were defined by changes in protein-encoding gene loci. We analyzed proteins isolated from skin fibroblasts using two-dimensional electrophoresis and allozymes extracted from blood cells. Genotypes were determined for multiple individuals of ocelot, margay, tigrina, Geoffroy's cat, kodkod, and pampas cat at 548 loci resolved by two-dimensional electrophoresis and 44 allozyme loci. Phenograms were constructed using...

Diversity and disparity of sparassodonts (Metatheria) reveal non-analogue nature of ancient South American mammalian carnivore guilds

Science.gov (United States)

Dolgushina, Tatiana; Wesley, Gina

2018-01-01

This study investigates whether terrestrial mammalian carnivore guilds of ancient South America, which developed in relative isolation, were similar to those of other continents. We do so through analyses of clade diversification, ecomorphology and guild structure in the Sparassodonta, metatherians that were the predominant mammalian carnivores of pre-Pleistocene South America. Body mass and 16 characters of the dentition are used to quantify morphological diversity (disparity) in sparassodonts and to compare them to extant marsupial and placental carnivores and extinct North American carnivoramorphans. We also compare trophic diversity of the Early Miocene terrestrial carnivore guild of Santa Cruz, Argentina to that of 14 modern and fossil guilds from other continents. We find that sparassodonts had comparatively low ecomorphological disparity throughout their history and that South American carnivore palaeoguilds, as represented by that of Santa Cruz, Argentina, were unlike modern or fossil carnivore guilds of other continents in their lack of mesocarnivores and hypocarnivores. Our results add to a growing body of evidence highlighting non-analogue aspects of extinct South American mammals and illustrate the dramatic effects that historical contingency can have on the evolution of mammalian palaeocommunities. PMID:29298933

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

DEFF Research Database (Denmark)

Brandt, Frederik Ejvang

The thesis is a contribution towards the understanding of the generation of the source mantle for magmas related to the subduction of the Nazca plate under South America with an emphasis on the geochemistry of the volatiles Cl, F, S, H2O and CO2. The study presents analytical data for tephra, min...

The tectonic setting of the Caribbean region and the K/T turnover of the South American land-mammal fauna

Energy Technology Data Exchange (ETDEWEB)

Ortiz-Jaureguizar, E.; Pascual, R.

2011-07-01

According to the fossil record, a biotic interchange of land vertebrates (e.g. booid snakes, dinosaurs and mammals) occurred between the Americas during the Late Cretaceous-Early Palaeocene. The arrival of North American immigrants (particularly marsupials and placental) during the latest Cretaceous-earliest Palaeocene had a profound influence on the composition of the South American mammal communities. During the Late Cretaceous these communities were dominated by native groups of Pangeic lineages, which represented more than 95% of the known genera, but during the Early Palaeocene 70% of South American mammals were derived from North American immigrants that had arrived during the Late Cretaceous-earliest Palaeocene, and by the Late Palaeocene all the South American mammals (with the possible exception of the xenarthrans) were descendants of these North American immigrants. In spite of the fact that no geological evidence is currently available to support the existence of a continuous land connection between the Americas during the Late Cretaceousearly Palaeocene, the fossil record is substantial enough to point to a temporary inter-American connection that permitted the beginning of a land-mammal exchange by the end of the Cretaceous. This interpretation is supported by recent geographic reconstructions of the Caribbean region. (Author)

Geodynamic models assist in determining the South Loyalty Basin's slab location and its implications for regional topography

Science.gov (United States)

Clark, Stuart R.

2010-05-01

In the Western Pacific, two competing kinematic reconstructions exist: one with wholly westward subduction of the Pacific plate at what is now the Tonga-Kermadec trench and one combining a degree of eastward subduction under what has been termed the New Caledonia trench. New seismological observations indicate that eastward subduction could explain the existence of a fast anomaly, the hyothesised South Loyalty Basin slab, below the 660km transition zone distinct from the fast anomaly aligned with the Tonga-Kermadec slab. A plate reconstruction dated from the suggested initiation of New Caledonia subduction in the Eocene has been developed. This reconstruction is then used to predict the thermal history of the region and together provide kinematic and thermal boundary conditions for a regional mantle convection model. The model-predicted location of the South Loyalty Basin slab's location will be presented along with the location's dependence on the mantle rheological parameters and the hotspot reference frame. The implications for the topography of the region will also be discussed.

Reconstruction of Northeast Asian Deformation Integrated with Western Pacific Plate Subduction since 200 Ma

Science.gov (United States)

Liu, S.; Gurnis, M.; Ma, P.; Zhang, B.

2017-12-01

The configuration and kinematics of continental deformation and its marginal plate tectonics on the Earth's surface are intrinsic manifestations of plate-mantle coupling. The complex interactions of plate boundary forces result in plate motions that are dominated by slab pull and ridge push forces and the effects of mantle drag; these interactions also result in continental deformation with a complex basin-mountain architecture and evolution. The kinematics and evolution of the western Pacific subduction and northeast Asian continental-margin deformation are a first-order tectonic process whose nature and chronology remains controversial. This paper implements a "deep-time" reconstruction of the western Pacific subduction, continental accretion or collision and basin-mountain deformation in northeast Asia since 200 Ma based on a newly revised global plate model. The results demonstrate a NW-SE-oriented shortening from 200-137 Ma, a NWW-SEE-oriented extension from 136-101 Ma, a nearly N-S-oriented extension and uplift with a short-term NWW-SEE-oriented compressional inversion in northeast China from 100-67 Ma, and a NW-SE- and nearly N-S-oriented extension from 66 Ma to the present day. The western Pacific oceanic plate subducted forward under East Asia along Mudanjiang-Honshu Island during the Jurassic, and the trenches retreated to the Sikhote-Alin, North Shimanto, and South Shimanto zones from ca. 137-128 Ma, ca. 130-90 Ma, and in ca. 60 Ma, respectively. Our time-dependent analysis of plate motion and continental deformation coupling suggests that the multi-plate convergent motion and ocean-continent convergent orogeny were induced by advance subduction during the Jurassic and earliest Cretaceous. Our analysis also indicates that the intra-continent rifting and back-arc extension were triggered by trench retreat during the Cretaceous and that the subduction of oceanic ridge and arc were triggered by trench retreat during the Cenozoic. Therefore, reconstructing

Subduction zone guided waves in Northern Chile

Science.gov (United States)

Garth, Thomas; Rietbrock, Andreas

2016-04-01

Guided wave dispersion is observed in subduction zones as high frequency energy is retained and delayed by low velocity structure in the subducting slab, while lower frequency energy is able to travel at the faster velocities associated with the surrounding mantle material. As subduction zone guided waves spend longer interacting with the low velocity structure of the slab than any other seismic phase, they have a unique capability to resolve these low velocity structures. In Northern Chile, guided wave arrivals are clearly observed on two stations in the Chilean fore-arc on permanent stations of the IPOC network. High frequency (> 5 Hz) P-wave arrivals are delayed by approximately 2 seconds compared to the low frequency (young subducting lithosphere also has the potential to carry much larger amounts of water to the mantle than has previously been appreciated.

Influence of Surface Processes over Africa on the Atlantic Marine ITCZ and South American Precipitation.

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Hagos, Samson M.; Cook, Kerry H.

2005-12-01

Previous studies show that the climatological precipitation over South America, particularly the Nordeste region, is influenced by the presence of the African continent. Here the influence of African topography and surface wetness on the Atlantic marine ITCZ (AMI) and South American precipitation are investigated.Cross-equatorial flow over the Atlantic Ocean introduced by north south asymmetry in surface conditions over Africa shifts the AMI in the direction of the flow. African topography, for example, introduces an anomalous high over the southern Atlantic Ocean and a low to the north. This results in a northward migration of the AMI and dry conditions over the Nordeste region.The implications of this process on variability are then studied by analyzing the response of the AMI to soil moisture anomalies over tropical Africa. Northerly flow induced by equatorially asymmetric perturbations in soil moisture over northern tropical Africa shifts the AMI southward, increasing the climatological precipitation over northeastern South America. Flow associated with an equatorially symmetric perturbation in soil moisture, however, has a very weak cross-equatorial component and very weak influence on the AMI and South American precipitation. The sensitivity of the AMI to soil moisture perturbations over certain regions of Africa can possibly improve the skill of prediction.

Time, Space, and National Belonging in The Namesake: Redrawing South Asian American Citizenship in the Shadow of 9/11

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Sue Brennan

2011-03-01

Full Text Available The terms of national belonging after 9/11 for South Asian Americans have taken shape through a vague and depoliticized discourse around ethnic identity, one in which the clichés of multiculturalism and melting-pot nationalism stand in for the specific socioeconomic and historical conditions that helped form the South Asian diaspora in the US. This paper explores the ways in which Jhumpa Lahiri’s novel The Namesake and its cinematic adaptation by filmmaker Mira Nair challenge the erasure of South Asian American citizenship following 9/11. Recounting the journey of a young Bengali graduate student and his wife migrating to the US in the late 1960s, each text speaks back to the erasure of South Asian American citizenship through the materialization of time in space: while Lahiri foregrounds the state itself in producing the rhythms through which immigrants are assimilated into the nation, Nair creates a narrative world in which filmic space materializes many, and often competing, histories, unifying multiple temporalities and histories through the representations of space. I argue that the cinematic adaptation of The Namesake generates a new spatiotemporal state of affairs, one in which the iconography of 9/11 both challenges post-9/11 racial logics and destabilizes the singular, progressive, and institutionalized temporality through which Lahiri writes South Asian American immigrants back into nation.

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

Science.gov (United States)

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

2018-01-01

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

Interpretation of interseismic deformations and the seismic cycle associated with large subduction earthquakes

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Trubienko, Olga; Fleitout, Luce; Garaud, Jean-Didier; Vigny, Christophe

2013-03-01

The deformations of the overriding and subducting plates during the seismic cycle associated with large subduction earthquakes are modelled using 2D and 3D finite element techniques. A particular emphasis is put on the interseismic velocities and on the impact of the rheology of the asthenosphere. The distance over which the seismic cycle perturbs significantly the velocities depends upon the ratio of the viscosity in the asthenosphere to the period of the seismic cycle and can reach several thousand km for rheological parameters deduced from the first years of deformation after the Aceh earthquake. For a same early postseismic velocity, a Burger rheology of the asthenosphere implies a smaller duration of the postseismic phase and thus smaller interseismic velocities than a Maxwell rheology. A low viscosity wedge (LVW) modifies very significantly the predicted horizontal and vertical motions in the near and middle fields. In particular, with a LVW, the peak in vertical velocity at the end of the cycle is predicted to be no longer above the deep end of the locked section of the fault but further away, above the continentward limit of the LVW. The lateral viscosity variations linked to the presence at depth of the subducting slab affect substantially the results. The north-south interseismic compression predicted by this preliminary 2D model over more than 1500 km within the Sunda block is in good agreement with the pre-2004 velocities with respect to South-China inferred from GPS observations in Thailand, Malaysia and Indonesia. In Japan, before the Tohoku earthquake, the eastern part of northern Honshu was subsiding while the western part was uplifting. This transition from subsidence to uplift so far away from the trench is well fitted by the predictions from our models involving a LVW. Most of the results obtained here in a 2D geometry are shown to provide a good estimate of the displacements for fault segments of finite lateral extent, with a 3D spherical

Human consumption of a vagrant South American Fur Seal Arctocephalus australis (Carnivora: Otariidae in Brazil

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S. Siciliano

2016-04-01

Full Text Available The South American Fur Seal Arctocephalus australis is one of the most widely distributed South American otariid species. In Brazil, during austral winter months specimens of A. australis are regularly found along the Rio Grande do Sul and Santa Catarina coasts. Occasionally, vagrants have been recorded along the southeastern coast but rarely moves north of Rio de Janeiro, at 23°S. On 01 May 2015, fishermen noticed in the surf zone an unidentified large animal in Ilhéus, Bahia, northeastern Brazil. Severely wounded, it was still alive when first spotted. Numerous shark bites were observed in the rostrum and flippers, the peduncle was severely lacerated and the intestines were protruding. The specimen was identified as an adult of South American Fur Seal based on the combination of the characteristic coloration of the pelage, head shape, body size, the relatively large eye size, and mainly due to the pronounced three cusped teeth in post canines. Fishermen decided to butcher the carcass and share the meat among their companions. The present record, however, is of special concern as human consumption South American Fur Seal seems to be unusual in Brazil. Pieces of meat were shared among fishermen. In addition, small pieces of blubber were used as bait in the local shark long-line fishery. Consumption of an injured and presumably weak marine mammal carcass points to an increasing risk of contact between potentially harmful viruses, bacteria and fungi and humans. This note represents an alert to public health specialists and wildlife authorities in Brazil. It calls the urgency of an outreach campaign advertising to the potential risks of ingesting bushmeat either from land or aquatic sources. 

Thermal structure and geodynamics of subduction zones

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Wada, Ikuko

The thermal structure of subduction zones depends on the age-controlled thermal state of the subducting slab and mantle wedge flow. Observations indicate that the shallow part of the forearc mantle wedge is stagnant and the slab-mantle interface is weakened. In this dissertation, the role of the interface strength in controlling mantle wedge flow, thermal structure, and a wide range of subduction zone processes is investigated through two-dimensional finite-element modelling and a global synthesis of geological and geophysical observations. The model reveals that the strong temperature-dependence of the mantle strength always results in full slab-mantle decoupling along the weakened part of the interface and hence complete stagnation of the overlying mantle. The interface immediately downdip of the zone of decoupling is fully coupled, and the overlying mantle is driven to flow at a rate compatible with the subduction rate. The sharpness of the transition from decoupling to coupling depends on the rheology assumed and increases with the nonlinearity of the flow system. This bimodal behaviour of the wedge flow gives rise to a strong thermal contrast between the cold stagnant and hot flowing parts of the mantle wedge. The maximum depth of decoupling (MDD) thus dictates the thermal regime of the forearc. Observed surface heat flow patterns and petrologically and geochemically estimated mantle wedge temperatures beneath the volcanic arc require an MDD of 70--80 km in most, if not all, subduction zones regardless of their thermal regime of the slab. The common MDD of 70--80 km explains the observed systematic variations of the petrologic, seismological, and volcanic processes with the thermal state of the slab and thus explains the rich diversity of subduction zones in a unified fashion. Models for warm-slab subduction zones such as Cascadia and Nankai predict shallow dehydration of the slab beneath the cold stagnant part of the mantle wedge, which provides ample fluid

Tectonothermal events of southeastern Brazil: Implications for consolidation of the South American platform

International Nuclear Information System (INIS)

Hackspacher, P.C.; Fetter, A.H; Dantas, E.L; Hadler Neto, J.C; Ribeiro, L.F.B; Tello, C.E.S

2001-01-01

The tectonothermal history of the South American Platform and it consolidation have to be analyzed considering different tectonic and stabilization stages. For that propose we have studied the Precambrian basement southwest of the city of Sao Paulo, which was consolidated and deformed during the Brasiliano Orogeny and later affected by Phanerozoic tectonics. Geological data from a northwest/southeast transect between Sao Roque and Jundiai - SP, were obtained through U/Pb, K/Ar and Ar/Ar mineral and whole rock studies. Metamorphic PT values, relation of brittle-ductile zone of felsic crustal rocks and fission track ages were also obtained. Such data were plotted on a temperature-time plot representing a preliminary overview of the geological evolution of this part of the South American platform. Recently dated highly deformed metaplutons from the Ribeira Belt suggest that convergence that preceded collision was underway by around 650 Ma. Low-grade (rarely reaching 4000 o C) metasediments and metavolcanics of the Sao Roque Group, interpreted to be a backarc basin that formed during active Brasiliano collision, yield a crystallization age of 627 Ma (Hackspacher et al., 2000). Syn-collisional granitoids with U/Pb zircon and monazite ages of 625 Ma (Janasi, 1999) provide more constraints on the timing of active collision. Temperatures of these calc-alkaline rocks can be considered around 650 o C. U/Pb zircon and monazite ages between 610 and 595 Ma obtained igneous bodies associated with transpressional tectonics place age constraints on the transition to a transpressional regime, with crystallization temperature around 580 o C. Related strike-slip shear zones in brittle-ductile transition, present K-Ar ages on biotite and hornblende between 600 and 580 Ma. The temperature interval for these greenschist grade shear zones is estimated between 450 and 300 o C. Apatite Fission Track Analysis (AFTA) near the Jundiuvira Shear Zone present a corrected Fission Track Age of 477

Helminth parasites of South American fishes: current status and characterization as a model for studies of biodiversity.

Science.gov (United States)

Luque, J L; Pereira, F B; Alves, P V; Oliva, M E; Timi, J T

2017-03-01

The South American subcontinent supports one of the world's most diverse and commercially very important ichthyofauna. In this context, the study of South American fish parasites is of increased relevance in understanding their key roles in ecosystems, regulating the abundance or density of host populations, stabilizing food webs and structuring host communities. It is hard to estimate the number of fish parasites in South America. The number of fish species studied for parasites is still low (less than 10%), although the total number of host-parasite associations (HPAs) found in the present study was 3971. Monogeneans, with 835 species (1123 HPAs, 28.5%), and trematodes, with 662 species (1127 HPAs, 30.9%), are the more diverse groups. Data gathered from the literature are useful to roughly estimate species richness of helminths from South American fish, even though there are some associated problems: the reliability of information depends on accurate species identification; the lack of knowledge about life cycles; the increasing number of discoveries of cryptic species and the geographically biased number of studies. Therefore, the closest true estimations of species diversity and distribution will rely on further studies combining both molecular and morphological approaches with ecological data such as host specificity, geographical distribution and life-cycle data. Research on biodiversity of fish parasites in South America is influenced by problems such as funding, taxonomic impediments and dispersion of research groups. Increasing collaboration, interchange and research networks in the context of globalization will enable a promising future for fish parasitology in South America.

Excerpt from The Red Land to the South: American Indian Writers and Indigenous Mexico

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James H. Cox

2013-09-01

Full Text Available Excerpted from James H. Cox, The Red Land to the South: American Indian Writers and Indigenous Mexico (Minneapolis: University of Minnesota Press, 2012.Reprinted with permission from University of Minnesota Press.

Curare: the South American arrow poison.

Science.gov (United States)

Lee, M R

2005-02-01

The history of curare is both curious and convoluted. A product of South American culture it emerged in the sixteenth century from the mists of antiquity at the same time as quinine, coca, and chocolate. Like quinine, at first came the extract but no plant, and later the plant but no chemical compound. It took more than 300 years and the efforts of many explorers and scientists to resolve the problem. These included Condamine, Humboldt, Brodie, Waterton, Bernard, Dale, Walker, and King. Finally, the pure compound d-tubocurarine was isolated from the liana Chondrodendron and synthesised. Its specific physiological action was blockade of the effect of acetylcholine at the neuro-muscular junction. Such a paralytic poison could be used to kill oneself or others. The bizarre plot to kill the Prime Minister, Lloyd George, during the First World War is described. Fortunately this nefarious plan was thwarted by the Secret Service!

Deep mantle seismic heterogeneities in Western Pacific subduction zones

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Bentham, H. L. M.; Rost, S.

2012-04-01

In recent years array seismology has been used extensively to image the small scale (~10 km) structure of the Earth. In the mantle, small scale structure likely represents chemical heterogeneity and is essential in our understanding of mantle convection and especially mantle mixing. As subduction is the main source of introducing crustal material into the Earth's mantle, it is of particular interest to track the transport of subducted crust through the mantle to resolve details of composition and deformation of the crust during the subduction process. Improved knowledge of subduction can help provide constraints on the mechanical mixing process of crustal material into the ambient mantle, as well as constraining mantle composition and convection. This study uses seismic array techniques to map seismic heterogeneities associated with Western Pacific subduction zones, where a variety of slab geometries have been previously observed. We use seismic energy arriving prior to PP, a P-wave underside reflection off the Earth's surface halfway between source and receiver, to probe the mantle for small-scale heterogeneities. PP precursors were analysed at Eielson Array (ILAR), Alaska using the recently developed Toolkit for Out-of-Plane Coherent Arrival Tracking (TOPCAT) algorithm. The approach combines the calculated optimal beampower and an independent semblance (coherency) measure, to improve the signal-to-noise ratio of coherent arrivals. 94 earthquakes with sufficient coherent precursory energy were selected and directivity information of the arrivals (i.e. slowness and backazimuth) was extracted from the data. The scattering locations for 311 out-of-plane precursors were determined by ray-tracing and minimising the slowness, backazimuth and differential travel time misfit. Initial analyses show that deep scattering (>1000 km) occurs beneath the Izu-Bonin subduction zone, suggesting that subducted crust does continue into the lower mantle in this location. Other

Splendid oddness: revisiting the curious trophic relationships of South American Pleistocene mammals and their abundance

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RICHARD A. FARIÑA

2014-03-01

Full Text Available The South American Pleistocene mammal fauna includes great-sized animals that have intrigued scientists for over two centuries. Here we intend to update the knowledge on its palaeoecology and provide new evidence regarding two approaches: energetics and population density and relative abundance of fossils per taxa. To determine whether an imbalance exists, population density models were applied to several South American fossil faunas and the results compared to those that best describe the palaeoecology of African faunas. The results on the abundance study for Uruguay and the province of Buenos Aires during the Lujanian stage/age reveal that bulk-feeding ground sloths (Lestodon and Glossotherium were more represented in the first territory, while the more selective Scelidotherium and Megatherium were more abundant in the second. Although the obtained values were corrected to avoid size-related taphonomic biases, linear regressions of abundance vs. body mass plots did not fit the expected either for first or second consumers. South American Pleistocene faunas behave differently from what models suggest they should. Changes in sea level and available area could account for these differences; the possibility of a floodplain in the area then emerged could explain seasonal changes, which would modify the calculations of energetics and abundance.

Coping with Discrimination: The Subjective Well-Being of South Asian American Women

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Liang, Christopher T. H.; Nathwani, Anisha; Ahmad, Sarah; Prince, Jessica K.

2010-01-01

The relationship between coping strategies used by South Asian American women and subjective well-being (SWB) was studied. Second-generation women were found to use more support compared with 1st-generation women. Problem-solving coping was inversely related to age. Avoidance coping was found to predict SWB when controlling for age and…

Digenetic trematodes in South American sea lions from southern Brazilian waters.

Science.gov (United States)

Pereira, E M; Müller, G; Secchi, E; Pereira, J; Valente, A L S

2013-10-01

The aim of this work was to perform a systematic study to detect and quantify the digenetic trematode infections in South American sea lions from the southern Brazilian coast. Twenty-four South American sea lions, Otaria flavescens (Carnivora: Otaridae), were found dead along the coast of Rio Grande do Sul State, Brazil, between June 2010 and September of 2011. Two trematode species were found in the intestines of O. flavescens, i.e., Stephanoprora uruguayense (Digenea: Echinostomatidae) and Ascocotyle (Phagicola) longa (Digenea: Heterophyidae). Ascocotyle (P.) longa reached a prevalence of 33.3% and mean intensity of 248,500, whereas S. uruguayense showed a prevalence of 4.2% and mean intensity of 202. The 2 trematode species infecting sea lions were likely transmitted by feeding on mullets, Mugil platanus, that commonly harbor heterophyid metacercariae. The present work is the first report of digenetic trematodes infecting O. flavescens in Brazil. The high prevalence and mean intensity values of the 2 trematode species infecting sea lions in the present study suggest caution in human consumption of mullets and other fish, which can be infected with the metacercariae of these trematodes known to have zoonotic potential.

Two decades of spatiotemporal variations in subduction zone coupling offshore Japan

Science.gov (United States)

Loveless, John P.; Meade, Brendan J.

2016-02-01

Spatial patterns of interplate coupling on global subduction zones can be used to guide seismic hazard assessment, but estimates of coupling are often constrained using a limited temporal range of geodetic data. Here we analyze ∼19 years of geodetic observations from the GEONET network to assess time-dependent variations in the spatial distribution of coupling on the subduction zones offshore Japan. We divide the position time series into five, ∼3.75-year epochs each decomposed into best-fit velocity, annual periodic signals, coseismic offsets, and postseismic effects following seven major earthquakes. Nominally interseismic velocities are interpreted in terms of a combination of tectonic block motions and earthquake cycle activity. The duration of the inferred postseismic activity covaries with the linear velocity. To address this trade-off, we assume that the nominally interseismic velocity at each station varies minimally from epoch to epoch. This approach is distinct from prior time-series analysis across the earthquake cycle in that position data are not detrended using preseismic velocity, which inherently assumes that interseismic processes are spatially stable through time, but rather the best-fit velocity at each station may vary between epochs. These velocities reveal significant consistency since 1996 in the spatial distribution of coupling on the Nankai subduction zone, with variation limited primarily to the Tokai and Bungo Channel regions, where long-term slow slip events have occurred, and persistently coupled regions coincident with areas that slipped during historic great earthquakes. On the Sagami subduction zone south of Tokyo, we also estimate relatively stable coupling through time. On the Japan-Kuril Trench, we image significant coupling variations owing to effects of the 1994 MW = 7.7 Sanriku-oki, 2003 MW = 8.2 Tokachi-oki, and 2011 MW = 9.0 Tohoku-oki earthquakes. In particular, strong coupling becomes more spatially extensive following

Stress Drops of Earthquakes on the Subducting Pacific Plate in the South-East off Hokkaido, Japan

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Saito, Y.; Yamada, T.

2013-12-01

Large earthquakes have been occurring repeatedly in the South-East of Hokkaido, Japan, where the Pacific Plate subducts beneath the Okhotsk Plate in the north-west direction. For example, the 2003 Tokachi-oki earthquake (Mw8.3 determined by USGS) took place in the region on September 26, 2003. Yamanaka and Kikuchi (2003) analyzed the slip distribution of the earthquake and concluded that the 2003 earthquake had ruptured the deeper half of the fault plane of the 1952 Tokachi-oki earthquake. Miyazaki et al. (2004) reported that a notable afterslip was observed at adjacent areas to the coseismic rupture zone of the 2003 earthquake, which suggests that there would be significant heterogeneities of strength, stress and frictional properties on the surface of the Pacific Plate in the region. In addition, some previous studies suggest that the region with a large slip in large earthquakes permanently have large difference of strength and the dynamic frictional stress level and that it would be able to predict the spatial pattern of slip in the next large earthquake by analyzing the stress drop of small earthquakes (e.g. Allmann and Shearer, 2007 and Yamada et al., 2010). We estimated stress drops of 150 earthquakes (4.2 ≤ M ≤ 5.0), using S-coda waves, or the waveforms from 4.00 to 9.11 seconds after the S wave arrivals, of Hi-net data. The 150 earthquakes were the ones that occurred from June, 2002 to December, 2010 in south-east of Hokkaido, Japan, from 40.5N to 43.5N and from 141.0E to 146.5E. First we selected waveforms of the closest earthquakes with magnitudes between 3.0 and 3.2 to individual 150 earthquakes as empirical Green's functions. We then calculated source spectral ratios of the 150 pairs of interested earthquakes and EGFs by deconvolving the individual S-coda waves. We finally estimated corner frequencies of earthquakes from the spectral ratios by assuming the omega-squared model of Boatwright (1978) and calculated stress drops of the earthquakes by

Seismic evidence for hydration of the Central American slab: Guatemala through Costa Rica

Science.gov (United States)

Syracuse, E. M.; Thurber, C. H.

2011-12-01

The Central American subduction zone exhibits a wide variability in along-arc slab hydration as indicated by geochemical studies. These studies generally show maximum slab contributions to magma beneath Nicaragua and minimum contributions beneath Costa Rica, while intermediate slab fluid contributions are found beneath El Salvador and Guatemala. Geophysical studies suggest strong slab serpentinization and fluid release beneath Nicaragua, and little serpentinization beneath Costa Rica, but the remainder of the subduction zone is poorly characterized seismically. To obtain an integrated seismic model for the Central American subduction zone, we combine 250,000 local seismic arrivals and 1,000,000 differential arrivals for 6,500 shallow and intermediate-depth earthquakes from the International Seismic Centre, the Central American Seismic Center, and the temporary PASSCAL TUCAN array. Using this dataset, we invert for Vp, Vs, and hypocenters using a variable-mesh double-difference tomography algorithm. By observing low-Vp areas within the normally high-Vp slab, we identify portions of the slab that are likely to contain serpentinized mantle, and thus contribute to higher degrees of melting and higher volatile components observable in arc lavas.

A possible connection between post-subduction arc magmatism and adakite-NEB rock association in Baja California, Mexico

Science.gov (United States)

Castillo, P. R.

2007-05-01

Late Miocene to Recent arc-related magmatism occurs in Baja California, Mexico despite the cessation of plate subduction along its western margin at ~12.5 Ma. It includes calcalkaline and K-rich andesites, tholeiitic basalts and basaltic andesites, alkalic basalts similar to many ocean island basalts (OIB), magnesian and basaltic andesites with adakitic affinity (bajaiites), adakites, and Nb-enriched basalts (NEB). A popular model for the close spatial and temporal association of adakite (plus bajaiite) and NEB in Baja California is these are due to melting of the subducted Farallon/Cocos plate, which in turn is caused by the influx of hot asthenospheric mantle through a window created in the subducted slab directly beneath the Baja California peninsula [e.g., Benoit, M. et. al. (2002) J. Geol. 110, 627-648; Calmus, T. et al. (2003) Lithos 66, 77-105]. Here I propose an alternative model for the cause of post-subduction magmatism in Baja California in particular and origin of adakite-NEB rock association in general. The complicated tectonic configuration of the subducting Farallon/Cocos plate and westward motion of the North American continent caused western Mexico to override the hot, upwelling Pacific mantle that was decoupled from the spreading centers abandoned west of Baja California. The upwelling asthenosphere is best manifested east of the peninsula, beneath the Gulf of California, and is most probably due to a tear or window in the subducted slab there. The upwelling asthenosphere is compositionally heterogeneous and sends materials westward into the mantle wedge beneath the peninsula. These materials provide sources for post-subduction tholeiitic and alkalic magmas. Portions of tholeiitic magmas directly erupted at the surface produce tholeiitic lavas, but some get ponded beneath the crust. Re-melting and/or high-pressure fractional crystallization of the ponded tholeiitic magmas generate adakitic rocks. Alkalic magmas directly erupted at the surface

How weak is the subduction zone interface?

NARCIS (Netherlands)

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

2015-01-01

Several lines of evidence suggest that subduction zones are weak and that the unique availability of water on Earth is a critical factor in the weakening process. We have evaluated the strength of subduction zone interfaces using two approaches: (i) from empirical relationships between shear stress

Prevalence and genetic diversity of haematozoa in South American waterfowl and evidence for intercontinental redistribution of parasites by migratory birds

Science.gov (United States)

Smith, Matthew M.; Ramey, Andy M.

2015-01-01

To understand the role of migratory birds in the movement and transmission of haematozoa within and between continental regions, we examined 804 blood samples collected from eleven endemic species of South American waterfowl in Peru and Argentina for infection by Haemoproteus, Plasmodium, and/or Leucocytozono blood parasites. Infections were detected in 25 individuals of six species for an overall apparent prevalence rate of 3.1%. Analysis of haematozoa mitochondrial DNA revealed twelve distinct parasite haplotypes infecting South American waterfowl, four of which were identical to lineages previously observed infecting ducks and swans sampled in North America. Analysis of parasite mitochondrial DNA sequences revealed close phylogenetic relationships between lineages originating from waterfowl samples regardless of continental affiliation. In contrast, more distant phylogenetic relationships were observed between parasite lineages from waterfowl and passerines sampled in South America for Haemoproteus and Leucocytozoon, suggesting some level of host specificity for parasites of these genera. The detection of identical parasite lineages in endemic, South American waterfowl and North American ducks and swans, paired with the close phylogenetic relationships of haematozoa infecting waterfowl on both continents, provides evidence for parasite redistribution between these regions by migratory birds.

Anthropozoonotic Endoparasites in Free-Ranging "Urban" South American Sea Lions (Otaria flavescens).

Science.gov (United States)

Hermosilla, Carlos; Silva, Liliana M R; Navarro, Mauricio; Taubert, Anja

2016-01-01

The present study represents the first report on the gastrointestinal endoparasite fauna of a free-ranging "urban" colony of South American sea lions (Otaria flavescens) living within the city of Valdivia, Chile. A total of 40 individual faecal samples of South American sea lions were collected during the year 2012 within their natural habitat along the river Calle-Calle and in the local fish market of Valdivia. Coprological analyses applying sodium acetate acetic formalin methanol (SAF) technique, carbol fuchsin-stained faecal smears and Giardia/Cryptosporidium coproantigen ELISAs, revealed infections with 8 different parasites belonging to protozoan and metazoan taxa with some of them bearing anthropozoonotic potential. Thus, five of these parasites were zoonotic (Diphyllobothriidae gen. sp., Anisakidae gen. sp., Giardia, Cryptosporidium, and Balantidium). Overall, these parasitological findings included four new parasite records for Otaria flavescens, that is, Giardia, Cryptosporidium, Balantidium, and Otostrongylus. The current data serve as a baseline for future monitoring studies on anthropozoonotic parasites circulating in these marine mammals and their potential impact on public health.

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

Energy Technology Data Exchange (ETDEWEB)

Marini, J.Ch

2004-05-15

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

Arthroscopic approach and intraarticular anatomy of the stifle in South American camelids.

Science.gov (United States)

Pentecost, Rebecca L; Niehaus, Andrew J; Santschi, Elizabeth

2012-05-01

To describe a cranial arthroscopic approach to the stifle of South American camelids and to report our clinical experience with camelid stifle arthroscopy. Experimental study and retrospective case series. (1) Cadaveric alpaca hindlimbs (n = 18; 9 alpacas); (2) 1 alpaca and 1 llama Polymethylmethacrylate joint casts (n = 2) were made to define stifle joint dimensions. Cadaveric stifle joints (n = 16) were evaluated arthroscopically to determine arthroscopic portal locations, describe the intraarticular anatomy, and report potential complications. An alpaca and a llama with stifle joint disease had diagnostic arthroscopy. Successful entry into the stifle joint was achieved in 16 cadaver limbs. Observed structures were: the suprapatellar pouch, articular surface of the patella, femoral trochlear ridges and groove, cranial aspect of the femoral condyles (n = 16); distal aspect of the cranial and proximal aspect of the caudal cruciate ligaments (14); and cranial aspects of the medial and lateral menisci (11), and cranial meniscotibial and intermeniscal ligaments (8). Stifle arthroscopy allowed for joint evaluation and removal of osteochondral fragments in 1 alpaca and 1 llama with naturally occurring stifle disease. Complications of cadaver or live procedures included minor cartilage scoring (3 stifles) and subcutaneous periarticular fluid accumulation (8 stifles). Arthroscopy provides a safe approach for diagnosis and treatment of stifle lesions in South American camelids. Copyright 2012 by The American College of Veterinary Surgeons.

Flux and genesis of CO2 degassing from volcanic-geothermal fields of Gulu-Yadong rift in the Lhasa terrane, South Tibet: Constraints on characteristics of deep carbon cycle in the India-Asia continent subduction zone

Science.gov (United States)

Zhang, Lihong; Guo, Zhengfu; Sano, Yuji; Zhang, Maoliang; Sun, Yutao; Cheng, Zhihui; Yang, Tsanyao Frank

2017-11-01

Gulu-Yadong rift (GYR) is the longest extensional, NE-SW-trending rift in the Himalayas and Lhasa terrane of South Tibet. Many volcanic-geothermal fields (VGFs), which comprise intense hot springs, steaming fissures, geysers and soil micro-seepage, are distributed in the GYR, making it ideal area for studying deep carbon emissions in the India-Asia continent subduction zone. As for the northern segment of GYR in the Lhasa terrane, its total flux and genesis of CO2 emissions are poorly understood. Following accumulation chamber method, soil CO2 flux survey has been carried out in VGFs (i.e., Jidaguo, Ningzhong, Sanglai, Tuoma and Yuzhai from south to north) of the northern segment of GYR. Total soil CO2 output of the northern GYR is about 1.50 × 107 t a-1, which is attributed to biogenic and volcanic-geothermal source. Geochemical characteristics of the volcanic-geothermal gases (including CO2 and He) of the northern GYR indicate their significant mantle-derived affinities. Combined with previous petrogeochemical and geophysical data, our He-C isotope modeling calculation results show that (1) excess mantle-derived 3He reflects degassing of volatiles related with partial melts from enriched mantle wedge induced by northward subduction of the Indian lithosphere, and (2) the crust-mantle interaction can provide continuous heat and materials for the overlying volcanic-geothermal system, in which magma-derived volatiles are inferred to experience significant crustal contamination during their migration to the surface.

Sarcoptic Mange in a South American Gray Fox (Chilla Fox; Lycalopex griseus ), Chile.

Science.gov (United States)

Verdugo, Claudio; Espinoza, Angelo; Moroni, Manuel; Valderrama, Rocio; Hernandez, Carlos

2016-07-01

Mange, a prevalent disease of dogs in Chile, is also a serious threat to wildlife. We report a case of sarcoptic mange in a South American gray fox or chilla fox ( Lycalopex griseus ). Further research is needed to understand the impact of mange in wildlife populations.

Using open sidewalls for modelling self-consistent lithosphere subduction dynamics

Directory of Open Access Journals (Sweden)

M. V. Chertova

2012-10-01

Full Text Available Subduction modelling in regional model domains, in 2-D or 3-D, is commonly performed using closed (impermeable vertical boundaries. Here we investigate the merits of using open boundaries for 2-D modelling of lithosphere subduction. Our experiments are focused on using open and closed (free slip sidewalls while comparing results for two model aspect ratios of 3:1 and 6:1. Slab buoyancy driven subduction with open boundaries and free plates immediately develops into strong rollback with high trench retreat velocities and predominantly laminar asthenospheric flow. In contrast, free-slip sidewalls prove highly restrictive on subduction rollback evolution, unless the lithosphere plates are allowed to move away from the sidewalls. This initiates return flows pushing both plates toward the subduction zone speeding up subduction. Increasing the aspect ratio to 6:1 does not change the overall flow pattern when using open sidewalls but only the flow magnitude. In contrast, for free-slip boundaries, the slab evolution does change with respect to the 3:1 aspect ratio model and slab evolution does not resemble the evolution obtained with open boundaries using 6:1 aspect ratio. For models with open side boundaries, we could develop a flow-speed scaling based on energy dissipation arguments to convert between flow fields of different model aspect ratios. We have also investigated incorporating the effect of far-field generated lithosphere stress in our open boundary models. By applying realistic normal stress conditions to the strong part of the overriding plate at the sidewalls, we can transfer intraplate stress to influence subduction dynamics varying from slab roll-back, stationary subduction, to advancing subduction. The relative independence of the flow field on model aspect ratio allows for a smaller modelling domain. Open boundaries allow for subduction to evolve freely and avoid the adverse effects (e.g. forced return flows of free-slip boundaries. We

Subduction, Extension, and a Mantle Plume in the Pacific Northwest

Science.gov (United States)

Hawley, W. B.; Allen, R. M.; Richards, M. A.

2016-12-01

Subduction zones are some of the most important systems that control the dynamics and evolution of the earth. The Cascadia Subduction Zone offers a unique natural laboratory for understanding the subduction process, and how subduction interacts with other large-scale geodynamical phenomena. The small size of the Juan de Fuca (JdF) plate and the proximity of the system to the Yellowstone Hotspot and the extensional Basin and Range province allow for detailed study of the effects these important systems have on each other. We present both a P-wave and an S-wave tomographic model of the Pacific Northwestern United States using regional seismic arrays, including the amphibious Cascadia Initiative. These models share important features, such as the Yellowstone plume, the subducting JdF slab, a gap in the subducting slab, and a low-velocity feature beneath the shallowest portions of the slab. But subtle differences in these features between the models—the size of the gap in the subducting JdF slab and the shape of the Yellowstone plume shaft above the transition zone, for example—provide physical insight into the interpretation of these models. The physics that we infer from our seismic tomography and other studies of the region will refine our understanding of subduction zones worldwide, and will help to identify targets for future amphibious seismic array studies. The discovery of a pronounced low-velocity feature beneath the JdF slab as it subducts beneath the coastal Pacific Northwest is, thus far, the most surprising result from our imaging work, and implies a heretofore unanticipated regime of dynamical interaction between the sublithospheric oceanic asthenosphere and the subduction process. Such discoveries are made possible, and rendered interpretable, by ever-increasing resolution that the Cascadia Initiative affords seismic tomography models.

Ectoparasites from the South American sea lion (Otaria flavescens from Peruvian coast

Directory of Open Access Journals (Sweden)

Luis A. Gomez-Puerta

2015-10-01

Full Text Available Two species of ectoparasites were collected from a South American sea lion (Otaria flavescens found stranded on the beaches of Chorrillos in Lima, Peru. The ectoparasites were identified as Antarctophthirus microchir (Phthiraptera and Orthohalarachne attenuata (Acari. Some morphological characteristics are described in this report. The finding of these ectoparasites is the first records in Peru.

Tomography and Dynamics of Western-Pacific Subduction Zones

Science.gov (United States)

Zhao, D.

2012-01-01

We review the significant recent results of multiscale seismic tomography of the Western-Pacific subduction zones and discuss their implications for seismotectonics, magmatism, and subduction dynamics, with an emphasis on the Japan Islands. Many important new findings are obtained due to technical advances in tomography, such as the handling of complex-shaped velocity discontinuities, the use of various later phases, the joint inversion of local and teleseismic data, tomographic imaging outside a seismic network, and P-wave anisotropy tomography. Prominent low-velocity (low-V) and high-attenuation (low-Q) zones are revealed in the crust and uppermost mantle beneath active arc and back-arc volcanoes and they extend to the deeper portion of the mantle wedge, indicating that the low-V/low-Q zones form the sources of arc magmatism and volcanism, and the arc magmatic system is related to deep processes such as convective circulation in the mantle wedge and dehydration reactions in the subducting slab. Seismic anisotropy seems to exist in all portions of the Northeast Japan subduction zone, including the upper and lower crust, the mantle wedge and the subducting Pacific slab. Multilayer anisotropies with different orientations may have caused the apparently weak shear-wave splitting observed so far, whereas recent results show a greater effect of crustal anisotropy than previously thought. Deep subduction of the Philippine Sea slab and deep dehydration of the Pacific slab are revealed beneath Southwest Japan. Significant structural heterogeneities are imaged in the source areas of large earthquakes in the crust, subducting slab and interplate megathrust zone, which may reflect fluids and/or magma originating from slab dehydration that affected the rupture nucleation of large earthquakes. These results suggest that large earthquakes do not strike anywhere, but in only anomalous areas that may be detected with geophysical methods. The occurrence of deep earthquakes under

Evolution and diversity of subduction zones controlled by slab width

NARCIS (Netherlands)

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

2007-01-01

Subducting slabs provide the main driving force for plate motion and flow in the Earth's mantle, and geodynamic, seismic and geochemical studies offer insight into slab dynamics and subduction-induced flow. Most previous geodynamic studies treat subduction zones as either infinite in trench-parallel

Noble gases recycled into the mantle through cold subduction zones

Science.gov (United States)

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

2017-08-01

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

Hafnium at subduction zones: isotopic budget of input and output fluxes

International Nuclear Information System (INIS)

Marini, J.Ch.

2004-05-01

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

The South American Mailed Catfishes of the genus Pseudoloricaria Bleeker, 1862 (Pisces, Siluriformes, Loricariidae)

NARCIS (Netherlands)

Isbrücker, I.J.H.; Nijssen, H.

1976-01-01

Two species of South American Mailed Catfishes of the genus Pseudoloricaria Bleeker, 1862 are redescribed and figured from type-specimens and additional material: Pseudoloricaria laeviuscula (Valenciennes, 1840), and Pseudoloricaria punctata (Regan, 1904). Since the provenance of the holotype of P.

Geochemistry of serpentinites in subduction zones: A review

Science.gov (United States)

Deschamps, Fabien; Godard, Marguerite; Guillot, Stéphane; Hattori, Kéiko

2013-04-01

Over the last decades, numerous studies have emphasized the role of serpentinites in the subduction zones geodynamics. Their presence and effective role in this environment is acknowledged notably by geophysical, geochemical and field observations of (paleo-) subduction zones. In this context, with the increasing amount of studies concerning serpentinites in subduction environments, a huge geochemical database was created. Here, we present a review of the geochemistry of serpentinites, based on the compilation of ~ 900 geochemical analyses of abyssal, mantle wedge and subducted serpentinites. The aim was to better understand the geochemical evolution of these rocks during their subduction history as well as their impact in the global geochemical cycle. When studying serpentinites, it is often a challenge to determine the nature of the protolith and their geological history before serpentinisation. The present-day (increasing) geochemical database for serpentinites indicates little to no mobility of incompatible elements at the scale of the hand-sample in most serpentinized peridotites. Thus, Rare Earth Elements (REE) distribution can be used to identify the initial protolith for abyssal and mantle wedge serpentinites, as well as magmatic processes such as melt/rock interactions taking place before serpentinisation. In the case of subducted serpentinites, the interpretation of trace element data is more difficult due to secondary enrichments independent of the nature of the protolith, notably in (L)REE. We propose that these enrichments reflect complex interactions probably not related to serpentinisation itself, but mostly to fluid/rock or sediment/rock interactions within the subduction channel, as well as intrinsic feature of the mantle protolith which could derive from the continental lithosphere exhumed at the ocean-continent transition. Additionally, during the last ten years, numerous studies have been carried out, notably using in situ approaches, to better

Dominant seismic sources for the cities in South Sumatra

Science.gov (United States)

Sunardi, Bambang; Sakya, Andi Eka; Masturyono, Murjaya, Jaya; Rohadi, Supriyanto; Sulastri, Putra, Ade Surya

2017-07-01

Subduction zone along west of Sumatra and Sumatran fault zone are active seismic sources. Seismotectonically, South Sumatra could be affected by earthquakes triggered by these seismic sources. This paper discussed contribution of each seismic source to earthquake hazards for cities of Palembang, Prabumulih, Banyuasin, OganIlir, Ogan Komering Ilir, South Oku, Musi Rawas and Empat Lawang. These hazards are presented in form of seismic hazard curves. The study was conducted by using Probabilistic Seismic Hazard Analysis (PSHA) of 2% probability of exceedance in 50 years. Seismic sources used in analysis included megathrust zone M2 of Sumatra and South Sumatra, background seismic sources and shallow crustal seismic sources consist of Ketaun, Musi, Manna and Kumering faults. The results of the study showed that for cities relatively far from the seismic sources, subduction / megathrust seismic source with a depth ≤ 50 km greatly contributed to the seismic hazard and the other areas showed deep background seismic sources with a depth of more than 100 km dominate to seismic hazard respectively.

A deforestation-induced tipping point for the South American monsoon system

Science.gov (United States)

Boers, Niklas; Marwan, Norbert; Barbosa, Henrique M. J.; Kurths, Jürgen

2017-01-01

The Amazon rainforest has been proposed as a tipping element of the earth system, with the possibility of a dieback of the entire ecosystem due to deforestation only of parts of the rainforest. Possible physical mechanisms behind such a transition are still subject to ongoing debates. Here, we use a specifically designed model to analyse the nonlinear couplings between the Amazon rainforest and the atmospheric moisture transport from the Atlantic to the South American continent. These couplings are associated with a westward cascade of precipitation and evapotranspiration across the Amazon. We investigate impacts of deforestation on the South American monsoonal circulation with particular focus on a previously neglected positive feedback related to condensational latent heating over the rainforest, which strongly enhances atmospheric moisture inflow from the Atlantic. Our results indicate the existence of a tipping point. In our model setup, crossing the tipping point causes precipitation reductions of up to 40% in non-deforested parts of the western Amazon and regions further downstream. The responsible mechanism is the breakdown of the aforementioned feedback, which occurs when deforestation reduces transpiration to a point where the available atmospheric moisture does not suffice anymore to release the latent heat needed to maintain the feedback.

Double subduction of continental lithosphere, a key to form wide plateau

Science.gov (United States)

Replumaz, Anne; Funiciello, Francesca; Reitano, Riccardo; Faccenna, Claudio; Balon, Marie

2016-04-01

The mechanisms involved in the creation of the high and wide topography, like the Tibetan Plateau, are still controversial. In particular, the behaviour of the indian and asian lower continental lithosphere during the collision is a matter of debate, either thickening, densifying and delaminating, or keeping its rigidity and subducting. But since several decades seismicity, seismic profiles and global tomography highlight the lithospheric structure of the Tibetan Plateau, and make the hypotheses sustaining the models more precise. In particular, in the western syntaxis, it is now clear that the indian lithosphere subducts northward beneath the Hindu Kush down to the transition zone, while the asian one subducts southward beneath Pamir (e.g. Negredo et al., 2007; Kufner et al., 2015). Such double subduction of continental lithospheres with opposite vergence has also been inferred in the early collision time. Cenozoic volcanic rocks between 50 and 30 Ma in the Qiangtang block have been interpreted as related to an asian subduction beneath Qiangtang at that time (De Celles et al., 2011; Guillot and Replumaz, 2013). We present here analogue experiments silicone/honey to explore the subduction of continental lithosphere, using a piston as analogue of far field forces. We explore the parameters that control the subductions dynamics of the 2 continental lithospheres and the thickening of the plates at the surface, and compare with the Tibetan Plateau evolution. We show that a continental lithosphere is able to subduct in a collision context, even lighter than the mantle, if the plate is rigid enough. In that case the horizontal force due to the collision context, modelled by the piston push transmitted by the indenter, is the driving force, not the slab pull which is negative. It is not a subduction driving by the weight of the slab, but a subduction induced by the collision, that we could call "collisional subduction".

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

NARCIS (Netherlands)

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

2015-01-01

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

Shear heating and metamorphism in subduction zones, 1. Thermal models

Science.gov (United States)

Kohn, M. J.; Castro, A. E.; Spear, F. S.

2017-12-01

Popular thermal-mechanical models of modern subduction systems are 100-500 °C colder at c. 50 km depth than pressure-temperature (P-T) conditions determined from exhumed metamorphic rocks. This discrepancy has been ascribed by some to profound bias in the rock record, i.e. metamorphic rocks reflect only anomalously warm subduction, not normal subduction. Accurately inferring subduction zone thermal structure, whether from models or rocks, is crucial for predicting depths of seismicity, fluid release, and sub-arc melting conditions. Here, we show that adding realistic shear stresses to thermal models implies P-T conditions quantitatively consistent with those recorded by exhumed metamorphic rocks, suggesting that metamorphic rock P-T conditions are not anomalously warm. Heat flow measurements from subduction zone fore-arcs typically indicate effective coefficients of friction (µ) ranging from 0.025 to 0.1. We included these coefficients of friction in analytical models of subduction zone interface temperatures. Using global averages of subducting plate age (50 Ma), subduction velocity (6 cm/yr), and subducting plate geometry (central Chile), temperatures at 50 km depth (1.5 GPa) increase by c. 200 °C for µ=0.025 to 700 °C for µ=0.1. However, at high temperatures, thermal softening will reduce frictional heating, and temperatures will not increase as much with depth. Including initial weakening of materials ranging from wet quartz (c. 300 °C) to diabase (c. 600 °C) in the analytical models produces concave-upward P-T distributions on P-T diagrams, with temperatures c. 100 to 500 °C higher than models with no shear heating. The absolute P-T conditions and concave-upward shape of the shear-heating + thermal softening models almost perfectly matches the distribution of P-T conditions derived from a compilation of exhumed metamorphic rocks. Numerical models of modern subduction zones that include shear heating also overlap metamorphic data. Thus, excepting the

South American energy integration: new perspectives; Novas perspectivas para a integracao energetica sul-americana

Energy Technology Data Exchange (ETDEWEB)

Silva, Jose Malhaes da [Malhaes da Silva Consultoria Ltda., Rio de Janeiro, RJ (Brazil); Salomao, Luiz Alfredo [Universidade Candido Mendes, Rio de Janeiro, RJ (Brazil). Escola de Politicas Publicas e Governo

2008-07-01

This paper analyses the South American energy integration, the advantages related to this process as well as the existing obstacles . What is the scope in terms of projects and initiatives, and the role of political and institutional barriers to be overcome. (author)

War, religion, and white supremacy in comparative perspective: South Africa and the American South

Directory of Open Access Journals (Sweden)

R M�ller

2004-10-01

Full Text Available The southern states of the United States of America and South Africa share a number of analogous historical realities. One of these, which is the main subject of� this article,� is� the way in which the memory of a lost war had fused cultural mythology and religious symbolism to provide a foundation for the formation and maintenance of attitudes of white supremacy in both contexts.� This article seeks to achieve a historical� understanding of the complex interrelationship between the development of cultural identity and Protestant Christianity by� focusing on these issues in the histories of the Afrikaner and the white American Southerner in comparative perspective.�

Earthquakes, fluid pressures and rapid subduction zone metamorphism

Science.gov (United States)

Viete, D. R.

2013-12-01

High-pressure/low-temperature (HP/LT) metamorphism is commonly incomplete, meaning that large tracts of rock can remain metastable at blueschist- and eclogite-facies conditions for timescales up to millions of years [1]. When HP/LT metamorphism does take place, it can occur over extremely short durations (the role of fluids in providing heat for metamorphism [2] or catalyzing metamorphic reactions [1]. Earthquakes in subduction zone settings can occur to depths of 100s of km. Metamorphic dehydration and the associated development of elevated pore pressures in HP/LT metamorphic rocks has been identified as a cause of earthquake activity at such great depths [3-4]. The process of fracturing/faulting significantly increases rock permeability, causing channelized fluid flow and dissipation of pore pressures [3-4]. Thus, deep subduction zone earthquakes are thought to reflect an evolution in fluid pressure, involving: (1) an initial increase in pore pressure by heating-related dehydration of subduction zone rocks, and (2) rapid relief of pore pressures by faulting and channelized flow. Models for earthquakes at depth in subduction zones have focussed on the in situ effects of dehydration and then sudden escape of fluids from the rock mass following fracturing [3-4]. On the other hand, existing models for rapid and incomplete metamorphism in subduction zones have focussed only on the effects of heating and/or hydration with the arrival of external fluids [1-2]. Significant changes in pressure over very short timescales should result in rapid mineral growth and/or disequilibrium texture development in response to overstepping of mineral reaction boundaries. The repeated process of dehydration-pore pressure development-earthquake-pore pressure relief could conceivably produce a record of episodic HP/LT metamorphism driven by rapid pressure pulses. A new hypothesis is presented for the origins of HP/LT metamorphism: that HP/LT metamorphism is driven by effective pressure

Distributional patterns of the South American species of Hyalella (Amphipoda: Hyalellidae)

OpenAIRE

De los Ríos-Escalante, Patricio; Morrone, Juan J; Rivera, Reinaldo

2012-01-01

Distributional patterns of the South American species of the freshwater amphipod genus Hyalella were analysed using a panbiogeographic approach. Five generalized tracks were found: (1) northern Andes to Lake Titicaca (H. dielaii, H. meinerti, H. dybowskii, H.jelskii, H. lubominsky, and H. pauperocavae; (2) lake Titicaca (H. armata, H. cuprea, H. latinamus, H. lucifugax, H. montforti, H. neveulemairei, H. robusta, H. tiwanaku, H. simplex simplex, and H. solida); (3) central Andes (H. fossamanc...

U.S. foreign policy, the south american integration, and the case of the military bases in Colombia

OpenAIRE

Iglesias Cavicchioli, Manuel

2010-01-01

This article analyzes the nature of the conflict generated in South America by the adoption of the new military agreement between the U.S. and Colombia. The article will evaluate the political and the geostrategic implications of this agreement, especially its repercussions for the regional integration process of South America. It will also analyze the stances of the local actors in order to consider prospective scenarios, and will assess the U.S. approach to South American int...

Time, Space, and National Belonging in The Namesake: Redrawing South Asian American Citizenship in the Shadow of 9/11

Directory of Open Access Journals (Sweden)

Sue Brennan

2011-03-01

Full Text Available

The terms of national belonging after 9/11 for South Asian Americans have taken shape through a vague and depoliticized discourse around ethnic identity, one in which the clichés of multiculturalism and melting-pot nationalism stand in for the specific socioeconomic and historical conditions that helped form the South Asian diaspora in the US. This paper explores the ways in which Jhumpa Lahiri’s novel The Namesake and its cinematic adaptation by filmmaker Mira Nair challenge the erasure of South Asian American citizenship following 9/11. Recounting the journey of a young Bengali graduate student and his wife migrating to the US in the late 1960s, each text speaks back to the erasure of South Asian American citizenship through the materialization of time in space: while Lahiri foregrounds the state itself in producing the rhythms through which immigrants are assimilated into the nation, Nair creates a narrative world in which filmic space materializes many, and often competing, histories, unifying multiple temporalities and histories through the representations of space. I argue that the cinematic adaptation of The Namesake generates a new spatiotemporal state of affairs, one in which the iconography of 9/11 both challenges post-9/11 racial logics and destabilizes the singular, progressive, and institutionalized temporality through which Lahiri writes South Asian American immigrants back into nation.

Prevalence of neurodevelopmental disorders among low-income African Americans at a clinic on Chicago's south side.

Science.gov (United States)

Bell, Carl C; Chimata, Radhika

2015-05-01

This study examined the point prevalence of neurodevelopmental disorders among predominantly low-income, African-American psychiatric patients at Jackson Park Hospital's Family Medicine Clinic on Chicago's South Side. Using active case ascertainment methodology, the authors assessed the records of 611 psychiatric patients visiting the clinic between May 23, 2013, and January 14, 2014, to identify those with DSM-5 neurodevelopmental disorders. A total of 297 patients (49%) met criteria for a neurodevelopmental disorder during childhood. Moreover, 237 (39%) had clinical profiles consistent with neurobehavioral disorder associated with prenatal alcohol exposure, and 53 (9%) had other neurodevelopmental disorders. The authors disagreed on the specific type of neurodevelopmental disorder of seven (1% of 611) of the 297 patients with neurodevelopmental disorders. A high prevalence of neurodevelopmental disorders was found among low-income predominantly African-American psychiatric patients on Chicago's South Side. If replicated, these findings should bring about substantial changes in medical practice with African-American patients.

Mantle flow influence on subduction evolution

Science.gov (United States)

Chertova, Maria V.; Spakman, Wim; Steinberger, Bernhard

2018-05-01

The impact of remotely forced mantle flow on regional subduction evolution is largely unexplored. Here we investigate this by means of 3D thermo-mechanical numerical modeling using a regional modeling domain. We start with simplified models consisting of a 600 km (or 1400 km) wide subducting plate surrounded by other plates. Mantle inflow of ∼3 cm/yr is prescribed during 25 Myr of slab evolution on a subset of the domain boundaries while the other side boundaries are open. Our experiments show that the influence of imposed mantle flow on subduction evolution is the least for trench-perpendicular mantle inflow from either the back or front of the slab leading to 10-50 km changes in slab morphology and trench position while no strong slab dip changes were observed, as compared to a reference model with no imposed mantle inflow. In experiments with trench-oblique mantle inflow we notice larger effects of slab bending and slab translation of the order of 100-200 km. Lastly, we investigate how subduction in the western Mediterranean region is influenced by remotely excited mantle flow that is computed by back-advection of a temperature and density model scaled from a global seismic tomography model. After 35 Myr of subduction evolution we find 10-50 km changes in slab position and slab morphology and a slight change in overall slab tilt. Our study shows that remotely forced mantle flow leads to secondary effects on slab evolution as compared to slab buoyancy and plate motion. Still these secondary effects occur on scales, 10-50 km, typical for the large-scale deformation of the overlying crust and thus may still be of large importance for understanding geological evolution.

Teleseismic P and S wave attenuation constraints on temperature and melt of the upper mantle in the Alaska Subduction Zone.

Science.gov (United States)

Soto Castaneda, R. A.; Abers, G. A.; Eilon, Z.; Christensen, D. H.

2017-12-01

Recent broadband deployments in Alaska provide an excellent opportunity to advance our understanding of the Alaska-Aleutians subduction system, with implications for subduction processes worldwide. Seismic attenuation, measured from teleseismic body waves, provides a strong constraint on thermal structure as well as an indirect indication of ground shaking expected from large intermediate-depth earthquakes. We measure P and S wave attenuation from pairwise amplitude and phase spectral ratios for teleseisms recorded at 204 Transportable Array, Alaska Regional, and Alaska Volcano Observatory, SALMON (Southern Alaska Lithosphere & Mantle Observation Network) and WVLF (Wrangell Volcanics & subducting Lithosphere Fate) stations in central Alaska. The spectral ratios are inverted in a least squares sense for differential t* (path-averaged attenuation operator) and travel time anomalies at every station. Our preliminary results indicate a zone of low attenuation across the forearc and strong attenuation beneath arc and backarc in the Cook Inlet-Kenai region where the Aleutian-Yakutat slab subducts, similar to other subduction zones. This attenuation differential is observed in both the volcanic Cook Inlet segment and amagmatic Denali segments of the Aleutian subduction zone. By comparison, preliminary results for the Wrangell-St. Elias region past the eastern edge of the Aleutian slab show strong attenuation beneath the Wrangell Volcanic Field, as well as much further south than in the Cook Inlet-Kenai region. This pattern of attenuation seems to indicate a short slab fragment in the east of the subduction zone, though the picture is complex. Results also suggest the slab may focus or transmit energy with minimal attenuation, adding to the complexity. To image the critical transition between the Alaska-Aleutian slab and the region to its east, we plan to incorporate new broadband data from the WVLF array, an ongoing deployment of 37 PASSCAL instruments installed in 2016

Heterogeneous coupling along Makran subduction zone

Science.gov (United States)

Zarifi, Z.; Raeesi, M.

2010-12-01

The Makran subduction zone, located in the southeast of Iran and southern Pakistan, extends for almost 900 km along the Eurasian-Arabian plate boundary. The seismic activities in the eastern and western Makran exhibit very different patterns. The eastern Makran characterized by infrequent large earthquakes and low level of seismicity. The only large instrumentally recorded earthquake in the eastern Makran, the 27 Nov. 1945 (Mw=8.1) earthquake, was followed by tsunami waves with the maximum run-up height of 13 m and disastrous effects in Pakistan, India, Iran and Oman. The western Makran, however, is apparently quiescent without strong evidence on occurrence of large earthquakes in historical times, which makes it difficult to ascertain whether the slab subducts aseismically or experiences large earthquakes separated by long periods exceeding the historical records. We used seismicity and Trench Parallel Free air and Bouguer Anomalies (TPGA and TPBA) to study the variation in coupling in the slab interface. Using a 3D mechanical Finite Element (FE) model, we show how heterogeneous coupling can influence the rate of deformation in the overriding lithosphere and the state of stress in the outer rise, overriding, and subducting plates within the shortest expected cycle of earthquake. We test the results of FE model against the observed focal mechanism of earthquakes and available GPS measurements in Makran subduction zone.

A comparative study between South African serial killers and their American counterparts

OpenAIRE

2009-01-01

M.A. This dissertation explores the similarities and differences between South African serial killers and their American counterparts. Seven male candidates, each having committed their reign of terror within the relevant time period, have been included. The candidates compared well in home environments, number of friendships, emotional maturity, abuse undergone, temperament, and anti-social behaviour. Differences were found in comparing family bonding, wealth and education. This dissertat...

Anthropozoonotic Endoparasites in Free-Ranging “Urban” South American Sea Lions (Otaria flavescens

Directory of Open Access Journals (Sweden)

Carlos Hermosilla

2016-01-01

Full Text Available The present study represents the first report on the gastrointestinal endoparasite fauna of a free-ranging “urban” colony of South American sea lions (Otaria flavescens living within the city of Valdivia, Chile. A total of 40 individual faecal samples of South American sea lions were collected during the year 2012 within their natural habitat along the river Calle-Calle and in the local fish market of Valdivia. Coprological analyses applying sodium acetate acetic formalin methanol (SAF technique, carbol fuchsin-stained faecal smears and Giardia/Cryptosporidium coproantigen ELISAs, revealed infections with 8 different parasites belonging to protozoan and metazoan taxa with some of them bearing anthropozoonotic potential. Thus, five of these parasites were zoonotic (Diphyllobothriidae gen. sp., Anisakidae gen. sp., Giardia, Cryptosporidium, and Balantidium. Overall, these parasitological findings included four new parasite records for Otaria flavescens, that is, Giardia, Cryptosporidium, Balantidium, and Otostrongylus. The current data serve as a baseline for future monitoring studies on anthropozoonotic parasites circulating in these marine mammals and their potential impact on public health.

Anthropozoonotic Endoparasites in Free-Ranging “Urban” South American Sea Lions (Otaria flavescens)

Science.gov (United States)

Silva, Liliana M. R.; Navarro, Mauricio; Taubert, Anja

2016-01-01

The present study represents the first report on the gastrointestinal endoparasite fauna of a free-ranging “urban” colony of South American sea lions (Otaria flavescens) living within the city of Valdivia, Chile. A total of 40 individual faecal samples of South American sea lions were collected during the year 2012 within their natural habitat along the river Calle-Calle and in the local fish market of Valdivia. Coprological analyses applying sodium acetate acetic formalin methanol (SAF) technique, carbol fuchsin-stained faecal smears and Giardia/Cryptosporidium coproantigen ELISAs, revealed infections with 8 different parasites belonging to protozoan and metazoan taxa with some of them bearing anthropozoonotic potential. Thus, five of these parasites were zoonotic (Diphyllobothriidae gen. sp., Anisakidae gen. sp., Giardia, Cryptosporidium, and Balantidium). Overall, these parasitological findings included four new parasite records for Otaria flavescens, that is, Giardia, Cryptosporidium, Balantidium, and Otostrongylus. The current data serve as a baseline for future monitoring studies on anthropozoonotic parasites circulating in these marine mammals and their potential impact on public health. PMID:27051860

Tensor-guided fitting of subduction slab depths

Science.gov (United States)

Bazargani, Farhad; Hayes, Gavin P.

2013-01-01

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

Cretaceous–Eocene provenance connections between the Palawan Continental Terrane and the northern South China Sea margin

NARCIS (Netherlands)

Shao, Lei; Cao, Licheng; Qiao, Peijun; Zhang, Xiangtao; Li, Qianyu; van Hinsbergen, Douwe J.J.

2017-01-01

The plate kinematic history of the South China Sea opening is key to reconstructing how the Mesozoic configuration of Panthalassa and Tethyan subduction systems evolved into today's complex Southeast Asian tectonic collage. The South China Sea is currently flanked by the Palawan Continental Terrane

Magmatic tectonic effects of high thermal regime at the site of active ridge subduction: the Chile Triple Junction model

Science.gov (United States)

Lagabrielle, Yves; Guivel, Christèle; Maury, René C.; Bourgois, Jacques; Fourcade, Serge; Martin, Hervé

2000-11-01

High thermal gradients are expected to be found at sites of subduction of very young oceanic lithosphere and more particularly at ridge-trench-trench (RTT) triple junctions, where active oceanic spreading ridges enter a subduction zone. Active tectonics, associated with the emplacement of two main types of volcanic products, (1) MORB-type magmas, and (2) calc-alkaline acidic magmas in the forearc, also characterize these plate junction domains. In this context, MORB-type magmas are generally thought to derive from the buried active spreading center subducted at shallow depths, whereas the origin of calc-alkaline acidic magmas is more problematic. One of the best constrained examples of ridge-trench interaction is the Chile Triple Junction (CTJ) located southwest of the South American plate at 46°12'S, where the active Chile spreading center enters the subduction zone. In this area, there is a clear correlation between the emplacement of magmatic products and the migration of the triple junction along the active margin. The CTJ lava population is bimodal, with mafic to intermediate lavas (48-56% SiO 2) and acidic lavas ranging from dacites to rhyolites (66-73% SiO 2). Previous models have shown that partial melting of oceanic crust plus 10-20% of sediments, leaving an amphibole- and plagioclase-rich residue, is the only process that may account for the genesis of acidic magmas. Due to special plate geometry in the CTJ area, a given section of the margin may be successively affected by the passage of several ridge segments. We emphasize that repeated passages will lead to the development of very high thermal gradients allowing melting of rocks of oceanic origin at temperatures of 800-900°C and low pressures, corresponding to depths of 10-20 km depth only. In addition, the structure of the CTJ forearc domain is dominated by horizontal displacements and tilting of crustal blocks along a network of strike-slip faults. The occurrence of such a deformed domain implies

Transfer of subduction fluids into the deforming mantle wedge during nascent subduction: Evidence from trace elements and boron isotopes (Semail ophiolite, Oman)

Science.gov (United States)

Prigent, C.; Guillot, S.; Agard, P.; Lemarchand, D.; Soret, M.; Ulrich, M.

2018-02-01

The basal part of the Semail ophiolitic mantle was (de)formed at relatively low temperature (LT) directly above the plate interface during "nascent subduction" (the prelude to ophiolite obduction). This subduction-related LT deformation was associated with progressive strain localization and cooling, resulting in the formation of porphyroclastic to ultramylonitic shear zones prior to serpentinization. Using petrological and geochemical analyses (trace elements and B isotopes), we show that these basal peridotites interacted with hydrous fluids percolating by porous flow during mylonitic deformation (from ∼850 down to 650 °C). This process resulted in 1) high-T amphibole crystallization, 2) striking enrichments of minerals in fluid mobile elements (FME; particularly B, Li and Cs with concentrations up to 400 times those of the depleted mantle) and 3) peridotites with an elevated δ11B of up to +25‰. These features indicate that the metasomatic hydrous fluids are most likely derived from the dehydration of subducting crustal amphibolitic materials (i.e., the present-day high-T sole). The rapid decrease in metasomatized peridotite δ11B with increasing distance to the contact with the HT sole (to depleted mantle isotopic values in <1 km) suggests an intense interaction between peridotites and rapid migrating fluids (∼1-25 m.y-1), erasing the initial high-δ11B subduction fluid signature within a short distance. The increase of peridotite δ11B with increasing deformation furthermore indicates that the flow of subduction fluids was progressively channelized in actively deforming shear zones parallel to the contact. Taken together, these results also suggest that the migration of subduction fluids/melts by porous flow through the subsolidus mantle wedge (i.e., above the plate interface at sub-arc depths) is unlikely to be an effective mechanism to transport slab-derived elements to the locus of partial melting in subduction zones.

The fate of carbonates along a subducting slab

Science.gov (United States)

Bouilhol, P.; Debret, B.; Inglis, E.

2017-12-01

Carbon long-term cycling is a subject of recent controversy as new mass balance calculations suggest that most carbon is transferred from the slab to the mantle wedge by fluids during subduction, limiting the efficiency of carbon recycling to the deep mantle. Here, we examine the mobility of carbon at large scale during subduction through field, petrographic and geochemical studies on exhumed portion of the alpine slab that have recorded different metamorphic conditions during subduction. We studied serpentinite samples, metasomatic horizon between serpentinites and sediments, as well as veins hosted in serpentinites. Samples are from the Western Alps (Queyras and Zermatt) and have recorded a prograde metamorphic history from low temperature blueshist to eclogite facies P-T conditions. We show that during subduction there are several stages of carbonate precipitation and dissolution at metasomatic interfaces between metasedimentary and ultramafic rocks in the slab, as well as within the serpentinites. The early stage of subduction sees carbonate precipitation from the sediment derived fluids into the serpentnites. At higher temperature, when the dehydration shift from sediment to serpentinite dominated, the carbonates are dissolved, inducing the release of CO2 rich fluids. This occurs before the eclogite facies is attained, providing strong evidence for the mobility of carbon in fluids during the early stages of subduction. These fluids are a potential metasomatic agent for the fore-arc mantle wedge, corroborating the observation of carbonate bearing veins in sub-arc mantle ultramafic rocks. In eclogite facies conditions, olivine and carbonate veins within the serpentinites witness the mobility of CO2 during serpentinite dehydration, and may provide clues about the large scale recycling of CO2 within the deep mantle, as well as secondary precipitation associated with exhumation. Trace elements, Fe and Zn isotopic composition of the different samples provides

New seismic observation on the lithosphere and slab subduction beneath the Indo-Myanmar block: Implications for continent oblique subduction and transition to oceanic slab subduction

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Jiang, M.; He, Y.; Zheng, T.; Mon, C. T.; Thant, M.; Hou, G.; Ai, Y.; Chen, Q. F.; Sein, K.

2017-12-01

The Indo-Myanmar block locates to the southern and southeastern of the Eastern Himalayan Syntax (EHS) and marks a torsional boundary of the collision between the Indian and Eurasian plates. There are two fundamental questions concerned on the tectonics of Indo-Myanmar block since the Cenozoic time. One is whether and how the oblique subduction is active in the deep; the other is where and how the transition from oceanic subduction and continental subduction operates. However, the two problems are still under heated debate mainly because the image of deep structure beneath this region is still blurring. Since June, 2016, we have executed the China-Myanmar Geophysical Survey in the Myanmar Orogen (CMGSMO) and deployed the first portable seismic array in Myanmar in cooperation with Myanmar Geosciences Society (MGS). This array contains 70 stations with a dense-deployed main profile across the Indo-Myanmar Range, Central Basin and Shan State Plateau along latitude of 22° and a 2-D network covering the Indo-Myanmar Range and the western part of the Central Basin. Based on the seismic data collected by the new array, we conducted the studies on the lithospheric structure using the routine surface wave tomography and receiver function CCP stacking. The preliminary results of surface wave tomography displayed a remarkable high seismic velocity fabric in the uppermost of mantle beneath the Indo-Myanmar Range and Central Basin, which was interpreted as the subducted slab eastward. Particularly, we found a low velocity bulk within the high-velocity slab, which was likely to be a slab window due to the slab tearing. The preliminary results of receiver function CCP stacking showed the obvious variations of the lithospheric structures from the Indo-Myanmar Range to the Central Basin and Shan State Plateau. The lithospheric structure beneath the Indo-Myanmar Range is more complex than that beneath the Central Basin and Shan State Plateau. Our resultant high-resolution images

Prosopis pod production - comparison of North American, South American, Hawaiian, and African germplasm in young plantations

Energy Technology Data Exchange (ETDEWEB)

Felker, P.; Clark, P.R.; Osborn, J.F.; Cannell, G.H.

Prosopis pod production was compared in 3 field trials in southern California, i.e., a typical orchard planting, an irrigation trial, and a heat/drought stress trial. Thirteen species representing North American, South American, Hawaiian, and African germplasm were evaluated. Hawaiian and African accessions were eliminated from the irrigation trial by a minus 5/sup 0/C temperature. The most productive pod producers were P. velutina accessions from southern Arizona. In the fifth season, 5 trees of the most productive accession, i.e. P. velutina 32 had a mean pod production of 7.2 kg/tree with a range of 3.2-12.2 kg/tree. P. chilensis and P. alba trees of the same age were much larger but had less pod production. Pod production estimates of 3000-4000 kg/ha were obtained in the dry irrigation treatment by P. velutina 20 which received 370 mm rainfall in the year preceding harvest.

Evidence for ˜80-75 Ma subduction jump during Anatolide-Tauride-Armenian block accretion and ˜48 Ma Arabia-Eurasia collision in Lesser Caucasus-East Anatolia

Science.gov (United States)

Rolland, Yann; Perincek, Dogan; Kaymakci, Nuretdin; Sosson, Marc; Barrier, Eric; Avagyan, Ara

2012-05-01

Orogens formed by a combination of subduction and accretion are featured by a short-lived collisional history. They preserve crustal geometries acquired prior to the collisional event. These geometries comprise obducted oceanic crust sequences that may propagate somewhat far away from the suture zone, preserved accretionary prism and subduction channel at the interplate boundary. The cessation of deformation is ascribed to rapid jump of the subduction zone at the passive margin rim of the opposite side of the accreted block. Geological investigation and 40Ar/39Ar dating on the main tectonic boundaries of the Anatolide-Tauride-Armenian (ATA) block in Eastern Turkey, Armenia and Georgia provide temporal constraints of subduction and accretion on both sides of this small continental block, and final collisional history of Eurasian and Arabian plates. On the northern side, 40Ar/39Ar ages give insights for the subduction and collage from the Middle to Upper Cretaceous (95-80 Ma). To the south, younger magmatic and metamorphic ages exhibit subduction of Neotethys and accretion of the Bitlis-Pütürge block during the Upper Cretaceous (74-71 Ma). These data are interpreted as a subduction jump from the northern to the southern boundary of the ATA continental block at 80-75 Ma. Similar back-arc type geochemistry of obducted ophiolites in the two subduction-accretion domains point to a similar intra-oceanic evolution prior to accretion, featured by slab steepening and roll-back as for the current Mediterranean domain. Final closure of Neotethys and initiation of collision with Arabian Plate occurred in the Middle-Upper Eocene as featured by the development of a Himalayan-type thrust sheet exhuming amphibolite facies rocks in its hanging-wall at c. 48 Ma.

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

Science.gov (United States)

Stanley, Dal; Villaseñor, Antonio; Benz, Harley

1999-01-01

buttress occurs under the North Cascades region of Washington and under southern Vancouver Island. We find that regional faults zones such as the Devils Mt. and Darrington zones follow the margin of this buttress and the Olympic-Wallowa lineament forms its southern boundary east of the Puget Lowland. Thick, high-velocity, lower-crustal rocks are interpreted to be a mafic/ultramafic wedge occuring just above the subduction thrust. This mafic wedge appears to be jointly deformed with the arch, suggesting strong coupling between the subducting plate and upper plate crust in the Puget Sound region at depths >30 km. Such tectonic coupling is possible if brittle-ductile transition temperatures for mafic/ultramafic rocks on both sides of the thrust are assumed. The deformation models show that dominant north-south compression in the coast ranges of Washington and Oregon is controlled by a highly mafic crust and low heat flow, allowing efficient transmission of margin-parallel shear from Pacific plate interaction with North America. Complex stress patterns which curve around the Puget Sound region require a concentration of northwest-directed shear in the North Cascades of Washington. The preferred model shows that greatest horizontal shortening occurs across the Devils Mt. fault zone and the east end of the Seattle fault.

Neotropics and natural ingredients for pharmaceuticals: why isn't South American biodiversity on the crest of the wave?

Science.gov (United States)

Desmarchelier, Cristian

2010-06-01

Despite the advent of biotechnology and modern methods of combinatorial chemistry and rational drug design, nature still plays a surprisingly important role as a source of new pharmaceutical compounds. These are marketed either as herbal drugs or as single active ingredients. South American tropical ecosystems (or the Neotropics) encompass one-third of the botanical biodiversity of the planet. For centuries, indigenous peoples have been using plants for healing purposes, and scientists are making considerable efforts in order to validate these uses from a pharmacological/phytochemical point of view. However, and despite the unique plant diversity in the region, very few natural pharmaceutical ingredients from this part of the world have reached the markets in industrialized countries. The present review addresses the importance of single active ingredients and herbal drugs from South American flora as natural ingredients for pharmaceuticals; it highlights the most relevant cases in terms of species of interest; and discusses the key entry barriers for these products in industrialized countries. It explores the reasons why, in spite of the region's competitive advantages, South American biodiversity has been a poor source of natural ingredients for the pharmaceutical industry. (c) 2010 John Wiley & Sons, Ltd.

Experimental infection of two South American reservoirs with four distinct strains of Trypanosoma cruzi

Science.gov (United States)

Roellig, Dawn M.; McMillan, Katherine; Ellis, Angela E.; Vandeberg, John L.; Champagne, Donald E.; Yabsley, Michael J.

2010-01-01

SUMMARY Trypanosoma cruzi (Tc), the causative agent of Chagas disease, is a diverse species with 2 primary genotypes, TcI and TcII, with TcII further subdivided into 5 subtypes (IIa–e). This study evaluated infection dynamics of 4 genetically and geographically diverse T. cruzi strains in 2 South American reservoirs, degus (Octodon degus) and grey short-tailed opossums (Monodelphis domestica). Based on prior suggestions of a genotype-host association, we hypothesized that degus (placental) would more readily become infected with TcII strains while short-tailed opossums (marsupial) would be a more competent reservoir for a TcI strain. Individuals (n = 3) of each species were intraperitoneally inoculated with T. cruzi trypomastigotes of TcIIa [North America (NA)-raccoon (Procyon lotor) origin], TcI [NA-Virginia opossum (Didelphis virginiana)], TcIIb [South America (SA)-human], TcIIe (SA-Triatoma infestans), or both TcI and TcIIa. Parasitaemias in experimentally infected degus peaked earlier (7–14 days post-inoculation (p.i.)) compared with short-tailed opossums (21–84 days p.i.). Additionally, peak parasitaemias were higher in degus; however, the duration of detectable parasitaemias for all strains, except TcIIa, was greater in short-tailed opossums. Infections established in both host species with all genotypes, except for TcIIa, which did not establish a detectable infection in short-tailed opossums. These results indicate that both South American reservoirs support infections with these isolates from North and South America; however, infection dynamics differed with host and parasite strain. PMID:20128943

The southern cape conductive belt (South Africa): Its composition, origin and tectonic significance

Science.gov (United States)

De Beer, J. H.; Van Zijl, J. S. V.; Gough, D. I.

1982-03-01

Magnetometer array studies have led to the discovery and mapping of the Southern Cape Conductive Belt (SCCB) crossing the southern tip of Africa from west to southeast coasts. The SCCB lies just south of the Namaqua-Natal Belt of cratonic rocks remobilized about 1000 m.y. B.P. It is shown that it coincides with a zone of weakness which has been exploited by three major geosynclinal accumulations over some 600 m.y. Relationships between the SCCB and the basement geochronology, geology and tectonics are considered in detail. These relationships support the view that the conductive belt was formed by an accumulation of marine sediments and oceanic lithosphere at the top of a Proterozoic subduction which stopped about 1000 to 800 m.y. B.P. Associated with this subduction we propose a Proterozoic range of Andean mountains, whose roots are now exposed in the Namaqua-Natal Belt. Later subduction further south, near the present south coast, is proposed to account for the intrusion, between the south coast and the SCCB, of the Cape Granites in the time interval 600-500 m.y. B.P. There is some evidence for a third, yet more distant, subduction episode off Permian Gondwanaland. After outlining this tectonic history, the paper turns to a closer examination of the hypothesis that the Southern Cape Conductive Belt consists of partly serpentinized basalt accumulated at the top of a Proterozoic subduction. A large static magnetic anomaly, which correlates with the SCCB over most of its length, is well fitted by a model which strongly supports this hypothesis. Bouguer gravity anomalies along western and central profiles likewise support the hypothesis. A discussion follows of the process of formation of the proposed block of serpentinized marine rocks, beginning with serpentinization of the crust near oceanic ridges by reaction of warm, porous, newly-extruded basalt with seawater convecting through it. The serpentinized basalt is stable at crustal temperatures and pressures and so

Seattle - seeking balance between the Space Needle, Starbucks, the Seahawks, and subduction

Science.gov (United States)

Vidale, J. E.

2012-12-01

Seattle has rich natural hazards. Lahars from Mount Rainier flow from the south, volcanic ash drifts from the East, the South Whidbey Island fault lies north and east, the Cascadia subduction zone dives underfoot from the west, and the Seattle fault lies just below the surface. Past and future landslides are sprinkled democratically across the surface, and Lake Washington and Puget Sound are known to seiche. All are ultimately due to subduction tectonics. As in most tectonically-exposed cities, the hazards are due mainly (1) to the buildings predating the relatively recent revelation that faulting here is active, (2) transportation corridors built long ago that are aging without a good budget for renewal, and (3) the unknown unknowns. These hazards are hard to quantify. Only the largest earthquakes on the Cascadia megathrust have a 10,000-year history, and even for them the down-dip rupture limits, stress drop and attenuation have unacceptable uncertainty. For the threatening faults closer in the upper crust, written history is short, glacial erosion and blanketing preclude many geophysical investigations, and healthy forests frustrate InSAR. On the brighter side, the direct hazard of earthquake shaking is being addressed as well as it can be. The current seismic hazard estimate is derived by methods among the most sophisticated in the world. Logic trees informed by consensus forged from a series of workshops delineate the scenarios. Finite difference calculations that include the world-class deep and soggy basins project the shaking from fault to vulnerable city. One useful cartoon synthesizing the earthquake hazard, based on Art Frankel's report, is shown below. It illustrates that important areas will be strongly shaken, and issues remain to be addressed. Fortunately, with great coffee and good perspective, we are moving toward improved disaster preparedness and resilience.

Ichthyophonus sp. (Ichthyophonae, Ichthyophonida) infection in a South American amphibian, the hylid frog Hypsiboas pulchellus.

Science.gov (United States)

Borteiro, Claudio; Verdes, José Manuel; Cruz, Juan Carlos; Sabalsagaray, María Jesús; Kolenc, Francisco; Martínez Debat, Claudio; Ubilla, Martín

2015-04-01

We report infection by Ichthyophonus sp. in a South American amphibian, the hylid frog Hypsiboas pulchellus in Uruguay. This frog had a large subcutaneous mass over the urostyle and dorsal musculature comprised of parasitic cysts with mild granulomatous inflammation but otherwise appeared healthy.

Projected inundations on the South African coast by tsunami waves ...

African Journals Online (AJOL)

Historical and recent evidence recorded along the South African coast suggests that five tsunami events have occurred since 1960. These were mostly associated with trigger mechanisms associated with sources of remote submarine seismicity along far-field subduction zones and local atmospheric disturbances ...

Climate change and American Bullfrog invasion: what could we expect in South America?

Directory of Open Access Journals (Sweden)

Javier Nori

Full Text Available BACKGROUND: Biological invasion and climate change pose challenges to biodiversity conservation in the 21(st century. Invasive species modify ecosystem structure and functioning and climatic changes are likely to produce invasive species' range shifts pushing some populations into protected areas. The American Bullfrog (Lithobates catesbeianus is one of the hundred worst invasive species in the world. Native from the southeast of USA, it has colonized more than 75% of South America where it has been reported as a highly effective predator, competitor and vector of amphibian diseases. METHODOLOGY/PRINCIPAL FINDINGS: We modeled the potential distribution of the bullfrog in its native range based on different climate models and green-house gases emission scenarios, and projected the results onto South America for the years of 2050 and 2080. We also overlaid projected models onto the South American network of protected areas. Our results indicate a slight decrease in potential suitable area for bullfrog invasion, although protected areas will become more climatically suitable. Therefore, invasion of these sites is forecasted. CONCLUSION/SIGNIFICANCE: We provide new evidence supporting the vulnerability of the Atlantic Forest Biodiversity Hotspot to bullfrog invasion and call attention to optimal future climatic conditions of the Andean-Patagonian forest, eastern Paraguay, and northwestern Bolivia, where invasive populations have not been found yet. We recommend several management and policy strategies to control bullfrog invasion and argue that these would be possible if based on appropriate articulation among government agencies, NGOs, research institutions and civil society.

Stigma of poverty. The discursive construction of ­"South" term in Latin American countries

Directory of Open Access Journals (Sweden)

GÓMEZ QUINTERO, Juan David

2014-05-01

Full Text Available This article reflects a general knowledge and a macro-paradigmatic contribution of developmentalist discourses, in particular, its modernist and Eurocentric roots. In particular we analyze the artificiality of the discursive construction of certain categories that represent geopolitical stigma of poverty, such as ­Third World® or ­South® or ­underdeveloped® adopted in the field of international relations and the development cooperation. It notes that there are not metaphors opposite (North-South in its own right, the ­South® is not the opposite of the ­North®, but its negative extension, as evidenced by the imaginarium of most Latin American countries. The metaphors that stigmatize poverty are symbolic discourse used to define in a European way the identity of the winner (rich people.

Geothermics of the Apenninic subduction

Directory of Open Access Journals (Sweden)

G. Zito

1997-06-01

Full Text Available The subduction of the Adriatic microplate is analysed from a geothermal point of view. In particular four main geodynamic units are distinguished: foreland, foredeep and slab, accretionary prism, and back-arc basin. Each of them is examined from a geothermal point of view and the related open question are discussed. The most relevant results are the determination of the undisturbed geothermal gradient in the aquifer of the foreland; the discovery of a « hot » accretionary prism; and a new model of instantaneous extension of the back-arc basins. The main conclusion is that geothermal data are consistent with a westward dipping subduction that migrated eastward producing a sequence of several episodes at the surface.

Gallbladder cancer: South American experience.

Science.gov (United States)

Arroyo, Gerardo F; Gentile, Alberto; Parada, Luis A

2016-10-01

Large differences in terms of incidence and mortality due to gallbladder cancer (GBC) have been reported worldwide. Moreover, it seems that GBC has unique characteristics in South America. We surveyed the literature looking for information about the epidemiology, basic and translational research, and clinical trials performed in South America in order to critically analyze the magnitude of this health problem in the region. Compared to other geographic areas, age-standardized mortality rates (ASMR) for GBC in women are very high, particularly in many western areas of South America. Genetic, as well as dietary and environmental factors likely contribute to the pathogenesis of this disease in the area. Compared to other regions the profile of abnormalities of key genes such as KRAS and TP53 in GBC seems to slightly differ in South America, while the clinical behavior appears to be similar with a median overall survival (OS) of 6.5 to 8 months in advanced GBC. In contrast to Europe and USA, prophylactic cholecystectomy is a common practice in western areas of South America. GBC particularly affects women in South America, and represents a significant public health problem. It appears to have peculiarities that pose an urgent need for additional research aimed to discover risk factors, molecular events associated with its development and new treatment options for this lethal disease.

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

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

2015-09-01

The initiation of tectonic plate subduction into the mantle is poorly understood. If subduction is induced by the push of a distant mid-ocean ridge or subducted slab pull, we expect compression and uplift of the overriding plate. In contrast, spontaneous subduction initiation, driven by subsidence of dense lithosphere along faults adjacent to buoyant lithosphere, would result in extension and magmatism. The rock record of subduction initiation is typically obscured by younger deposits, so evaluating these possibilities has proved elusive. Here we analyse the geochemical characteristics of igneous basement rocks and overlying sediments, sampled from the Amami Sankaku Basin in the northwest Philippine Sea. The uppermost basement rocks are areally widespread and supplied via dykes. They are similar in composition and age--as constrained by the biostratigraphy of the overlying sediments--to the 52-48-million-year-old basalts in the adjacent Izu-Bonin-Mariana fore-arc. The geochemical characteristics of the basement lavas indicate that a component of subducted lithosphere was involved in their genesis, and the lavas were derived from mantle source rocks that were more melt-depleted than those tapped at mid-ocean ridges. We propose that the basement lavas formed during the inception of Izu-Bonin-Mariana subduction in a mode consistent with the spontaneous initiation of subduction.

The new Central American seismic hazard zonation: Mutual consensus based on up to day seismotectonic framework

Science.gov (United States)

Alvarado, Guillermo E.; Benito, Belén; Staller, Alejandra; Climent, Álvaro; Camacho, Eduardo; Rojas, Wilfredo; Marroquín, Griselda; Molina, Enrique; Talavera, J. Emilio; Martínez-Cuevas, Sandra; Lindholm, Conrad

2017-11-01

Central America is one of the most active seismic zones in the World, due to the interaction of five tectonic plates (North America, Caribbean, Coco, Nazca and South America), and its internal deformation, which generates almost one destructive earthquakes (5.4 ≤ Mw ≤ 8.1) every year. A new seismological zonation for Central America is proposed based on seismotectonic framework, a geological context (tectonic and geological maps), geophysical and geodetic evidence (gravimetric maps, magnetometric, GPS observations), and previous works. As a main source of data a depurated earthquake catalog was collected covering the period from 1522 to 2015. This catalog was homogenized to a moment magnitude scale (Mw). After a careful analysis of all the integrated geological and seismological information, the seismogenic zones were established into seismic areas defined by similar patterns of faulting, seismicity, and rupture mechanism. The tectonic environment has required considering seismic zones in two particular seismological regimes: a) crustal faulting (including local faults, major fracture zones of plate boundary limits, and thrust fault of deformed belts) and b) subduction, taking into account the change in the subduction angle along the trench, and the type and location of the rupture. The seismicity in the subduction zone is divided into interplate and intraplate inslab seismicity. The regional seismic zonation proposed for the whole of Central America, include local seismic zonations, avoiding discontinuities at the national boundaries, because of a consensus between the 7 countries, based on the cooperative work of specialists on Central American seismotectonics and related topics.

Velocities of Subducted Sediments and Continents

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

2009-12-01

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

Links Between Earthquake Characteristics and Subducting Plate Heterogeneity in the 2016 Pedernales Ecuador Earthquake Rupture Zone

Science.gov (United States)

Bai, L.; Mori, J. J.

2016-12-01

The collision between the Indian and Eurasian plates formed the Himalayas, the largest orogenic belt on the Earth. The entire region accommodates shallow earthquakes, while intermediate-depth earthquakes are concentrated at the eastern and western Himalayan syntaxis. Here we investigate the focal depths, fault plane solutions, and source rupture process for three earthquake sequences, which are located at the western, central and eastern regions of the Himalayan orogenic belt. The Pamir-Hindu Kush region is located at the western Himalayan syntaxis and is characterized by extreme shortening of the upper crust and strong interaction of various layers of the lithosphere. Many shallow earthquakes occur on the Main Pamir Thrust at focal depths shallower than 20 km, while intermediate-deep earthquakes are mostly located below 75 km. Large intermediate-depth earthquakes occur frequently at the western Himalayan syntaxis about every 10 years on average. The 2015 Nepal earthquake is located in the central Himalayas. It is a typical megathrust earthquake that occurred on the shallow portion of the Main Himalayan Thrust (MHT). Many of the aftershocks are located above the MHT and illuminate faulting structures in the hanging wall with dip angles that are steeper than the MHT. These observations provide new constraints on the collision and uplift processes for the Himalaya orogenic belt. The Indo-Burma region is located south of the eastern Himalayan syntaxis, where the strike of the plate boundary suddenly changes from nearly east-west at the Himalayas to nearly north-south at the Burma Arc. The Burma arc subduction zone is a typical oblique plate convergence zone. The eastern boundary is the north-south striking dextral Sagaing fault, which hosts many shallow earthquakes with focal depth less than 25 km. In contrast, intermediate-depth earthquakes along the subduction zone reflect east-west trending reverse faulting.

Buckling instabilities of subducted lithosphere beneath the transition zone

NARCIS (Netherlands)

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

2007-01-01

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

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

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Mark Scheltens

2015-03-01

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

Understanding the Association of Type 2 Diabetes Mellitus in Breast Cancer Among African American and European American Populations in South Carolina.

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Samson, Marsha E; Adams, Swann Arp; Orekoya, Olubunmi; Hebert, James R

2016-09-01

In South Carolina, the co-occurrence of diabetes mellitus (DM) and breast cancer (BrCA) is much more prevalent among African American populations than among European American populations. The underlying relationship between diabetes and breast cancer may influence breast cancer survival. The purpose of this investigation is to examine the effect of diabetes on developing breast cancer and to reduce racial disparities in breast cancer outcomes. Study participants included women of European American (EA) and African American (AA) ethnicity from both the Medicaid ICD-9 designations and the South Carolina Central Cancer Registry (SCCCR). A historical prospective cohort design was used to determine the risk of developing breast cancer among women of different ethnicities with and without DM. The chi-square test was used to determine the significance of the association; the logistic model was used to assess the relationship between breast cancer and other factors among EA and AA women. Menopause may have protective properties for AA compared to EA women. AA women have twice the odds of not surviving from each breast cancer stage compared to EA women with respect to their breast cancer stage. Adherence to diabetes medication may contribute to lower breast cancer death in EA. This study illustrates the discrepancy between EA and AA women in terms of breast cancer survival. AA women bear a higher disease burden than EA women. To create ethnic-appropriate public health policies, it is imperative that we understand the effect of comorbidities on breast cancer and how we can prevent them from occurring.

Mitochondrial control region haplotypes of the South American sea lion Otaria flavescens (Shaw, 1800).

Science.gov (United States)

Artico, L O; Bianchini, A; Grubel, K S; Monteiro, D S; Estima, S C; Oliveira, L R de; Bonatto, S L; Marins, L F

2010-09-01

The South American sea lion, Otaria flavescens, is widely distributed along the Pacific and Atlantic coasts of South America. However, along the Brazilian coast, there are only two nonbreeding sites for the species (Refúgio de Vida Silvestre da Ilha dos Lobos and Refúgio de Vida Silvestre do Molhe Leste da Barra do Rio Grande), both in Southern Brazil. In this region, the species is continuously under the effect of anthropic activities, mainly those related to environmental contamination with organic and inorganic chemicals and fishery interactions. This paper reports, for the first time, the genetic diversity of O. flavescens found along the Southern Brazilian coast. A 287-bp fragment of the mitochondrial DNA control region (D-loop) was analyzed. Seven novel haplotypes were found in 56 individuals (OFA1-OFA7), with OFA1 being the most frequent (47.54%). Nucleotide diversity was moderate (π = 0.62%) and haplotype diversity was relatively low (67%). Furthermore, the median joining network analysis indicated that Brazilian haplotypes formed a reciprocal monophyletic clade when compared to the haplotypes from the Peruvian population on the Pacific coast. These two populations do not share haplotypes and may have become isolated some time back. Further genetic studies covering the entire species distribution are necessary to better understand the biological implications of the results reported here for the management and conservation of South American sea lions.

The dynamics of double slab subduction

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

2017-04-01

We use numerical models to investigate the dynamics of two interacting slabs with parallel trenches. Cases considered are: a single slab reference, outward dipping slabs (out-dip), inward dipping slabs (in-dip) and slabs dipping in the same direction (same-dip). Where trenches converge over time (same-dip and out-dip systems), large positive dynamic pressures in the asthenosphere are generated beneath the middle plate and large trench-normal extensional forces are transmitted through the middle plate. This results in slabs that dip away from the middle plate at depth, independent of trench geometry. The single slab, the front slab in the same-dip case and both out-dip slabs undergo trench retreat and exhibit stable subduction. However, slabs within the other double subduction systems tend to completely overturn at the base of the upper mantle, and exhibit either trench advance (rear slab in same-dip), or near-stationary trenches (in-dip). For all slabs, the net slab-normal dynamic pressure at 330 km depth is nearly equal to the slab-normal force induced by slab buoyancy. For double subduction, the net outward force on the slabs due to dynamic pressure from the asthenosphere is effectively counterbalanced by the net extensional force transmitted through the middle plate. Thus, dynamic pressure at depth, interplate coupling and lithospheric stresses are closely linked and their effects cannot be isolated. Our results provide insights into both the temporal evolution of double slab systems on Earth and, more generally, how the various components of subduction systems, from mantle flow/pressure to interplate coupling, are dynamically linked.

Mantle hydration and Cl-rich fluids in the subduction forearc

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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

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

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R. D. Müller

2012-12-01

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

Diversification in the Andes: age and origins of South American Heliotropium lineages (Heliotropiaceae, Boraginales).

Science.gov (United States)

Luebert, Federico; Hilger, Hartmut H; Weigend, Maximilian

2011-10-01

The uplift of the Andes was a major factor for plant diversification in South America and had significant effects on the climatic patterns at the continental scale. It was crucial for the formation of the arid environments in south-eastern and western South America. However, both the timing of the major stages of the Andean uplift and the onset of aridity in western South America remain controversial. In this paper we examine the hypothesis that the Andean South American groups of Heliotropium originated and diversified in response to Andean orogeny during the late Miocene and a the subsequent development of aridity. To this end, we estimate divergence times and likely biogeographical origins of the major clades in the phylogeny of Heliotropium, using both Bayesian and likelihood methods. Divergence times of all Andean clades in Heliotropium are estimated to be of late Miocene or Pliocene ages. At least three independent Andean diversification events can be recognized within Heliotropium. Timing of the diversification in the Andean lineages Heliotropium sects.Heliothamnus, Cochranea, Heliotrophytum, Hypsogenia, Plagiomeris, Platygyne clearly correspond to a rapid, late Miocene uplift of the Andes and a Pliocene development of arid environments in South America. Copyright © 2011 Elsevier Inc. All rights reserved.

Influence of lateral slab edge distance on plate velocity, trench velocity, and subduction partitioning

NARCIS (Netherlands)

Schellart, W. P.; Stegman, D. R.; Farrington, R. J.; Moresi, L.

2011-01-01

Subduction of oceanic lithosphere occurs through both trenchward subducting plate motion and trench retreat. We investigate how subducting plate velocity, trench velocity and the partitioning of these two velocity components vary for individual subduction zone segments as a function of proximity to

Second-generation bioethanol from industrial wood waste of South American species

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María E. Vallejos

2017-09-01

Full Text Available There is a global interest in replacing fossil fuels with renewable sources of energy. The present review evaluates the significance of South-American wood industrial wastes for bioethanol production. Four countries have been chosen for this review, i.e., Argentina, Brazil, Chile, and Uruguay, based on their current or potential forestry industry. It should be noted that although Brazil has a global bioethanol market share of 25%, its production is mainly first-generation bioethanol from sugarcane. The situation in the other countries is even worse, in spite of the fact that they have regulatory frameworks in place already allowing the substitution of a percentage of gasoline by ethanol. Pines and eucalyptus are the usually forested plants in these countries, and their industrial wastes, as chips and sawdust, could serve as promising raw materials to produce second-generation bioethanol in the context of a forest biorefinery. The process to convert woody biomass involves three stages: pretreatment, enzymatic saccharification, and fermentation. The operational conditions of the pretreatment method used are generally defined according to the physical and chemical characteristics of the raw materials and subsequently determine the characteristics of the treated substrates. This article also reviews and discusses the available pretreatment technologies for eucalyptus and pines applicable to South-American industrial wood wastes, their enzymatic hydrolysis yields, and the feasibility of implementing such processes in the mentioned countries in the frame of a biorefinery.

IMPROVING MASS REARING TECHNOLOGY FOR SOUTH AMERICAN FRUIT FLY (DIPTERA:TEPHRITIDAE

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Raimundo Braga Sobrinho

2006-01-01

Full Text Available Studies on availability of suitable and economic diets for adults and larvae of the South American fruit fly Anastrepha fraterculus (Wiedemann, 1830 were carried out at the Entomology Unit of the FAO/IAEA Agriculture and Biotechnology Laboratories in Seibersdorf, Austria with the aim to find the best diets to fit in a large scale mass rearing production. The best diet for adult was the combination of Hydrolysate Corn Protein + Yeast Hydrolysate Enzymatic + Sugar (3:1:3. This diet resulted in the highest numbers of egg/female/day, spermatozoid in the spermathecae, percentages of egg hatch, the lowest mortality rate of adults and the highest average mating duration compared with the standard adult diet based on Yeast Hydrolysate Enzymatic + Sugar (1:3. Among eleven larval diets tested, diets based on sugarcane and sugarbeet bagases plus 7% brewer yeast, 8% sugar, 0.2% sodium benzoate, 0.8% of hydrochloric acid and 60% water (adjusted, yielded the highest percentages of egg hatching, pupal recovery, pupal weight and adult emergence. There was no statistical difference with the standard larval diet based on wheat germ 3%, corncob 15%, corn flower 8%, brewer yeast 6%, sugar 8%, sodium benzoate 0.23%, hydrochloric acid 0.63%, nipagin 0.14% and water 59% (adjusted. The significant performance of these adult and larval diets open discussion for future researches on improvement of rearing techniques required for the establishment of sterile insect technique (SIT program focused on the South American fruit fly.

Analysis of the genetic ancestry of patients with oral clefts from South American admixed populations.

Science.gov (United States)

Vieira-Machado, Camilla D; de Carvalho, Flavia M; Santana da Silva, Luiz C; Dos Santos, Sidney E; Martins, Claudia; Poletta, Fernando A; Mereb, Juan C; Vieira, Alexandre R; Castilla, Eduardo E; Orioli, Iêda M

2016-08-01

Increased susceptibility to cleft lip, with or without cleft palate (CL±P) has been observed in South America, as related to Amerindian ancestry, using epidemiological data, uniparental markers, and blood groups. In this study, it was evaluated whether this increased risk remains when Amerindian ancestry is estimated using autosomal markers and considered in the predictive model. Ancestry was estimated through genotyping 62 insertion and deletion (INDEL) markers in sample sets of patients with CL±P, patients with cleft palate (CP), and controls, from Patagonia in southern Argentina and Belém in northern Brazil. The Amerindian ancestry in patients from Patagonia with CL±P was greater than in controls although it did not reach statistical significance. The European ancestry in patients with CL±P from Belém and in patients with CP from Belém and Patagonia was higher than in controls and statistically significant for patients with CP who were from Belém. This high contribution of European genetic ancestry among patients with CP who were from Belém has not been previously observed in American populations. Our results do not corroborate the currently accepted risks for CL±P and CP estimated by epidemiological studies in the North American populations and probably reflect the higher admixture found in South American ethnic groups when compared with the same ethnic groups from the North American populations. © 2016 Eur J Oral Sci.

Frictional behavior of carbonate-rich sediments in subduction zones

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

2016-12-01

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

Highly Structured Duets in the Song of the South American Hornero

Science.gov (United States)

Laje, Rodrigo; Mindlin, Gabriel B.

2003-12-01

The South American Hornero (Furnarius rufus) is a suboscine bird widely known for its mud-made, oven-looking nest. Beyond their architectural skills, the male and female Horneros sing in highly structured duets. The analysis of field recordings reported in this work reveals that as the male increases the note production rate the female responds by switching to different locking states: the ones predicted by the theory of nonlinear forced oscillators. This gives the duet a most appealing rhythm, and unveils the nonlinear nature of the underlying brain activity needed to generate the song.

Is the Local Seismicity in Haiti Capable of Imaging the Northern Caribbean Subduction?

Science.gov (United States)

Corbeau, J.; Clouard, V.; Rolandone, F.; Leroy, S. D.; de Lepinay, B. M.

2017-12-01

The boundary between the Caribbean (CA) and North American (NAM) plates in the Hispaniola region is the western prolongation of the NAM plate subduction evolving from a frontal subduction in the Lesser Antilles to an oblique collision against the Bahamas platform in Cuba. We analyze P-waveforms arriving at 27 broadband seismic temporary stations deployed along a 200 km-long N-S transect across Haiti, during the Trans-Haiti project. We compute teleseismic receiver functions using the ETMTRF method, and determine crustal thickness and bulk composition (Vp/Vs) using the H-k stacking method. Three distinctive crustal domains are imaged. We relate these domains to crustal terranes that have been accreted along the plate boundary during the northeastwards displacement of the CA plate. We propose a N-S crustal profile across Haiti accounting for the surface geology, shallow structural history and these new seismological constraints. Local seismicity recorded by the temporary network from April 2013 to June 2014 is used to relocate the seismicity. A total of 593 events were identified with magnitudes ranging from 1.6 to 4.5. This local seismicity, predominantly shallow (accommodation of an important part of convergence in this area.

PARTICULATE ORGANIC CARBON, cloud amount/frequency and other data from COLUMBUS ISELIN in the North American Coastline-South and South Atlantic Ocean from 1990-05-23 to 1990-06-13 (NODC Accession 9100150)

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National Oceanic and Atmospheric Administration, Department of Commerce — Data was collected from R/V COLUMBUS ISELIN in South Atlantic Ocean and North American Coast line-South during the Amazon Shelf Sediment Study (AMASSEDS) between May...

Prosopis pod production: comparison of North American, South American, Hawaiin, and African germplasm in young plantations

Energy Technology Data Exchange (ETDEWEB)

Felker, P.; Clark, P.R.; Osborn, J.F.; Cannell, G.H.

Prosopis pod production was compared in 3 field trials in southern California, i.e., a typical orchard planting, an irrigation trial, and a heat/drought stress trial. Thirteen species representing North American, South American, Hawaiian, and African germplasm were evaluated. Hawaiian and African accessions were eliminated from the irrigation trial by a minus 5/sup 0/C temperature. The most productive pod producers were P. velutina accessions from southern Arizona. In the fifth season, 5 trees of the most productive accession, i.e., P. velutina 32 had a mean pod production of 7.2 kg/tree with a range of 3.2-12.2 kg/tree. P. chilensis and P. alba trees of the same age were much larger but had less pod production. Trees in the driest irrigation treatment had the greatest pod production. Pod production estimates of 3000-4000 kg/ha were obtained in the dry irrigation treatment by P. velutina 20 which received 370 mm rainfall in the year preceding harvest. 32 references, 1 figure, 6 tables.

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

Science.gov (United States)

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

2001-01-01

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

Seismic Imaging of the Lesser Antilles Subduction Zone Using S-to-P Receiver Functions: Insights From VoiLA

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Chichester, B.; Rychert, C.; Harmon, N.; Rietbrock, A.; Collier, J.; Henstock, T.; Goes, S. D. B.; Kendall, J. M.; Krueger, F.

2017-12-01

In the Lesser Antilles subduction zone Atlantic oceanic lithosphere, expected to be highly hydrated, is being subducted beneath the Caribbean plate. Water and other volatiles from the down-going plate are released and cause the overlying mantle to melt, feeding volcanoes with magma and hence forming the volcanic island arc. However, the depths and pathways of volatiles and melt within the mantle wedge are not well known. Here, we use S-to-P receiver functions to image seismic velocity contrasts with depth within the subduction zone in order to constrain the release of volatiles and the presence of melt in the mantle wedge, as well as slab structure and arc-lithosphere structure. We use data from 55-80° epicentral distances recorded by 32 recovered broadband ocean-bottom seismometers that were deployed during the 2016-2017 Volatiles in the Lesser Antilles (VoiLA) project for 15 months on the back- and fore-arc. The S-to-P receiver functions are calculated using two methods: extended time multi-taper deconvolution followed by migration to depth to constrain 3-D discontinuity structure of the subduction zone; and simultaneous deconvolution to determine structure beneath single stations. In the south of the island arc, we image a velocity increase with depth associated with the Moho at depths of 32-40 ± 4 km on the fore- and back-arc, consistent with various previous studies. At depths of 65-80 ± 4 km beneath the fore-arc we image a strong velocity decrease with depth that is west-dipping. At 96-120 ± 5 km beneath the fore-arc, we image a velocity increase with depth that is also west-dipping. The dipping negative-positive phase could represent velocity contrasts related to the top of the down-going plate, a feature commonly imaged in subduction zone receiver function studies. The negative phase is strong, so there may also be contributions to the negative velocity discontinuity from slab dehydration and/or mantle wedge serpentinization in the fore-arc.

Subduction on Venus and Implications for Volatile Cycling, Early Earth and Exoplanets

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Smrekar, S. E.; Davaille, A.; Mueller, N. T.; Dyar, M. D.; Helbert, J.; Barnes, H.

2017-12-01

Plate tectonics plays a key role in long-term climate evolution by cycling volatiles between the interior, surface and atmosphere. Subduction is a critical process. It is the first step in transitioning between a stagnant and a mobile lid, a means for conveying volatiles into the mantle, and a mechanism for creating felsic crust. Laboratory experiments using realistic rheology illuminate the deformation produced by plume-induced subduction (Davaille abstract). Characteristics include internal rifting and volcanism, external rift branches, with a partial arc of subduction creating a trench on the margins of the plume head, and an exterior flexural bulge with small strain extension perpendicular to the trench. These characteristics, along with a consistent gravity signature, occur at the two largest coronae (quasi-circular volcano-tectonic features) on Venus (Davaille et al. Nature Geos. 2017). This interpretation resolves a long-standing debate about the dual plume and subduction characteristics of these features. Numerous coronae also show signs of plume-induced subduction. At Astkhik Planum, subduction appears to have migrated beyond the margins of Selu Corona to create a 1600 km-long, linear subduction zone, along Vaidilute Rupes. The fractures that define Selu Corona merge with the trench to the north and a rift zone to the east, consistent with plume-induced subduction migrating outward from the corona. The lithosphere and crust are much thinner here than in other potential subduction zones. Subduction appears to have generated massive volcanism which could explain the 400 m elevation of the plateau. Within the plateau there are low-viscosity flow sets nearly 1000 km that may be associated with near infrared low emissivity in VIRTIS data. Unusual lava compositions might be indicative of recycling of CO2 or other volatiles into the lithosphere. Little evidence exists to illustrate how plate tectonics initiated on Earth, but Venus' high surface temperature makes

Revisiting the physical characterisitics of the subduction interplate seismogenic zones

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

2010-05-01

Based on the Centennial earthquake catalog, the revised 1964-2007 EHB hypocenters catalog and the 1976-2007 CMT Harvard catalog, we have extracted the hypocenters, nodal planes and seismic moments of worldwide subduction earthquakes for the 1900-2007 period. For the 1976-2007 period, we combine the focal solutions provided by Harvard and the revised hypocenters from Engdahl et al. (1998). Older events are extracted from the Centennial catalogue (Engdahl and Villasenor, 2002) and they are used to estimate the cumulated seismic moment only. The selection criteria for the subduction earthquakes are similar to those used by Mc Caffrey (1994), i.e., we test if the focal mechanisms are consistent with 1/ shallow thrust events (depth > 70 km, positive slips, and at least one nodal plane gets dip 8). We assume that the seismogenic zone coincides with the distribution of 5.5 statistical study done by Pacheco et al. (1993) and test some empirical laws obtained for example by Ruff and Kanamori (1980) in light of a more complete, detailed, accurate and uniform description of the subduction interplate seismogenic zone. Since subduction earthquakes result from stress accumulation along the interplate and stress depends on plates kinematics, subduction zone geometry, thermal state and seismic coupling, we aim to isolate some correlations between parameters. The statistical analysis reveals that: 1- vs, the subduction velocity is the first order controlling parameter of seismogenic zone variability, both in term of geometry and seismic behaviour; 2- steep dip, large vertical extent and narrow horizontal extent of the seismogenic zone are associated to fast subductions, and cold slabs, the opposite holding for slow subductions and warm slabs; the seismogenic zone usually ends in the fore-arc mantle rather than at the upper plate Moho depth; 3- seismic rate () variability is coherent with the geometry of the seismogenic zone:  increases with the dip and with the vertical

Three new South American mailed catfishes of the genera Rineloricaria and Loricariichthys (Pisces, Siluriformes, Loricariide)

NARCIS (Netherlands)

Isbrücker, I.J.H.; Nijssen, H.

1979-01-01

Three new species belonging to two different genera of South American mailed catfishes of the subfamily Loricariinae are described and figured. A discussion of and comparative notes on related species are added. Rineloricaria formosa n. sp. is described from the Río Inírida/Río Orinoco drainage in

Native South American genetic structure and prehistory inferred from hierarchical modeling of mtDNA.

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Lewis, Cecil M; Long, Jeffrey C

2008-03-01

Genetic diversity in Native South Americans forms a complex pattern at both the continental and local levels. In comparing the West to the East, there is more variation within groups and smaller genetic distances between groups. From this pattern, researchers have proposed that there is more variation in the West and that a larger, more genetically diverse, founding population entered the West than the East. Here, we question this characterization of South American genetic variation and its interpretation. Our concern arises because others have inferred regional variation from the mean variation within local populations without taking into account the variation among local populations within the same region. This failure produces a biased view of the actual variation in the East. In this study, we analyze the mitochondrial DNA sequence between positions 16040 and 16322 of the Cambridge reference sequence. Our sample represents a total of 886 people from 27 indigenous populations from South (22), Central (3), and North America (2). The basic unit of our analyses is nucleotide identity by descent, which is easily modeled and proportional to nucleotide diversity. We use a forward modeling strategy to fit a series of nested models to identity by descent within and between all pairs of local populations. This method provides estimates of identity by descent at different levels of population hierarchy without assuming homogeneity within populations, regions, or continents. Our main discovery is that Eastern South America harbors more genetic variation than has been recognized. We find no evidence that there is increased identity by descent in the East relative to the total for South America. By contrast, we discovered that populations in the Western region, as a group, harbor more identity by descent than has been previously recognized, despite the fact that average identity by descent within groups is lower. In this light, there is no need to postulate separate founding

Length Scales and Types of Heterogeneities Along the Deep Subduction Interface: Insights From an Exhumed Subduction Complex on Syros Island, Greece

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Kotowski, A. J.; Behr, W. M.; Tong, X.; Lavier, L.

2017-12-01

The rheology of the deep subduction interface strongly influences the occurrence, recurrence, and migration of episodic tremor and slow slip (ETS) events. To better understand the environment of deep ETS, we characterize the length scales and types of rheological heterogeneities that decorate the deep interface using an exhumed subduction complex. The Cycladic Blueschist Unit on Syros, Greece, records Eocene subduction to 60 km, partial exhumation along the top of the slab, and final exhumation along Miocene detachment faults. The CBU reached 450-580˚C and 14-16 kbar, PT conditions similar to where ETS occurs in several modern subduction zones. Rheological heterogeneity is preserved in a range of rock types on Syros, with the most prominent type being brittle pods embedded within a viscous matrix. Prograde, blueschist-facies metabasalts show strong deformation fabrics characteristic of viscous flow; cm- to m-scale eclogitic lenses are embedded within them as massive, veined pods, foliated pods rotated with respect to the blueschist fabric, and attenuated, foliation-parallel lenses. Similar relationships are observed in blueschist-facies metasediments interpreted to have deformed during early exhumation. In these rocks, metabasalts form lenses ranging in size from m- to 10s of m and are distributed at the m-scale throughout the metasedimentary matrix. Several of the metamafic lenses, and the matrix rocks immediately adjacent to them, preserve multiple generations of dilational veins and shear fractures filled with quartz and high pressure minerals. These observations suggest that coupled brittle-viscous deformation under high fluid pressures may characterize the subduction interface in the deep tremor source region. To test this further, we modeled the behavior of an elasto-plastic pod in a viscous shear zone under high fluid pressures. Our models show that local stress concentrations around the pod are large enough to generate transient dilational shear at seismic

Initiation of Extension in South China Continental Margin during the Active-Passive Margin Transition: Thermochronological and Kinematic Constraints

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Zuo, X.; Chan, L. S.

2015-12-01

The South China continental margin is characterized by a widespread magmatic belt, prominent NE-striking faults and numerous rifted basins filled by Cretaceous-Eocene sediments. The geology denotes a transition from active to passive margin, which led to rapid modifications of crustal stress configuration and reactivation of older faults in this area. Our zircon fission-track data in this region show two episodes of exhumation: The first episode, occurring during 170-120Ma, affected local parts of the Nanling Range. The second episode, a more regional exhumation event, occurred during 115-70Ma, including the Yunkai Terrane and the Nanling Range. Numerical geodynamic modeling was conducted to simulate the subduction between the paleo-Pacific plate and the South China Block. The modeling results could explain the fact that exhumation of the granite-dominant Nanling Range occurred earlier than that of the gneiss-dominant Yunkai Terrane. In addition to the difference in rock types, the heat from Jurassic-Early Cretaceous magmatism in Nanling may have softened the upper crust, causing the area to exhume more readily than Yunkai. Numerical modeling results also indicate that (1) high lithospheric geothermal gradient, high slab dip angle and low convergence velocity favor the reversal of crustal stress state from compression to extension in the upper continental plate; (2) late Mesozoic magmatism in South China was probably caused by a slab roll-back; and (3) crustal extension could have occurred prior to the cessation of plate subduction. The inversion of stress regime in the continental crust from compression to crustal extension imply that the Late Cretaceous-early Paleogene red-bed basins in South China could have formed during the late stage of the subduction, accounting for the occurrence of volcanic events in some sedimentary basins. We propose that the rifting started as early as Late Cretaceous, probably before the cessation of subduction process.

Highly oxidising fluids generated during serpentinite breakdown in subduction zones.

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Debret, B; Sverjensky, D A

2017-09-04

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

Mitochondrial control region haplotypes of the South American sea lion Otaria flavescens (Shaw, 1800

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L.O. Artico

2010-09-01

Full Text Available The South American sea lion, Otaria flavescens, is widely distributed along the Pacific and Atlantic coasts of South America. However, along the Brazilian coast, there are only two nonbreeding sites for the species (Refúgio de Vida Silvestre da Ilha dos Lobos and Refúgio de Vida Silvestre do Molhe Leste da Barra do Rio Grande, both in Southern Brazil. In this region, the species is continuously under the effect of anthropic activities, mainly those related to environmental contamination with organic and inorganic chemicals and fishery interactions. This paper reports, for the first time, the genetic diversity of O. flavescens found along the Southern Brazilian coast. A 287-bp fragment of the mitochondrial DNA control region (D-loop was analyzed. Seven novel haplotypes were found in 56 individuals (OFA1-OFA7, with OFA1 being the most frequent (47.54%. Nucleotide diversity was moderate (π = 0.62% and haplotype diversity was relatively low (67%. Furthermore, the median joining network analysis indicated that Brazilian haplotypes formed a reciprocal monophyletic clade when compared to the haplotypes from the Peruvian population on the Pacific coast. These two populations do not share haplotypes and may have become isolated some time back. Further genetic studies covering the entire species distribution are necessary to better understand the biological implications of the results reported here for the management and conservation of South American sea lions.

Porphyry copper deposits distribution along the western Tethyan and Andean subductions: insights from a paleogeographic approach

Science.gov (United States)

Bertrand, G.

2012-12-01

The genesis of many types of mineral deposits is closely linked to tectonic and petrographic conditions resulting from specific geodynamic contexts. Porphyry deposits, for instance, are associated to calc-alkaline magmatism of subduction zones. In order to better understand the relationships between ore deposit distribution and their tectonic context, and help identifying geodynamic-related criteria of favorability that would, in turn, help mineral exploration, we propose a paleogeographic approach. Paleogeographic reconstructions, based on global or regional plate tectonic models, are crucial tools to assess tectonic and kinematic contexts of the past. We use this approach to study the distribution of porphyry copper deposits along the western Tethyan and Andean subductions since Lower Cretaceous and Paleocene, respectively. For both convergent contexts, databases of porphyry copper deposits, including, among other data, their age and location, were compiled. Spatial and temporal distribution of the deposits is not random and show that they were emplaced in distinct clusters. Five clusters are identified along the western Tethyan suture, from Lower Cretaceous to Pleistocene, and at least three along the Andes, from Paleocene to Miocene. Two clusters in the Aegean-Balkan-Carpathian area, that were emplaced in Upper Cretaceous and Oligo-Miocene, and two others in the Andes, that were emplaced in late Eocene and Miocene, are studied in details and correlated with the past kinematics of the Africa-Eurasia and Nazca-South America plate convergences, respectively. All these clusters are associated with a similar polyphased kinematic context that is closely related to the dynamics of the subductions. This context is characterized by 1) a relatively fast convergence rate, shortly followed by 2) a drastic decrease of this rate. To explain these results, we propose a polyphased genetic model for porphyry copper deposits with 1) a first stage of rapid subduction rate

South American regional ionospheric maps computed by GESA: A pilot service in the framework of SIRGAS

Science.gov (United States)

Brunini, C.; Meza, A.; Gende, M.; Azpilicueta, F.

2008-08-01

SIRGAS (Geocentric Reference Frame for the Americas) is an international enterprise of the geodetic community that aims to realize the Terrestrial Reference Frame in the America's countries. In order to fulfill this commitment, SIRGAS manages a network of continuously operational GNSS receivers totalling around one hundred sites in the Caribbean, Central, and South American region. Although the network was not planed for ionospheric studies, its potential to be used for such a purpose was recently recognized and SIRGAS started a pilot experiment devoted to establish a regular service for computing and releasing regional vertical TEC (vTEC) maps based on GNSS data. Since July, 2005, the GESA (Geodesia Espacial y Aeronomía) laboratory belonging to the Facultad de Ciencias Astronómicas y Geofísicas of the Universidad Nacional de La Plata computes hourly maps of vertical Total Electron Content (vTEC) in the framework of the SIRGAS pilot experiment. These maps exploit all the GNSS data available in the South American region and are computed with the LPIM (La Plata Ionospheric Model). LPIM implements a de-biasing procedure that improves data calibration in relation to other procedures commonly used for such purposes. After calibration, slant TEC measurements are converted to vertical and mapped using local-time and modip latitude. The use of modip latitude smoothed the spatial variability of vTEC, especially in the South American low latitude region and hence allows for a better vTEC interpolation. This contribution summarizes the results obtained by GESA in the framework of the SIRGAS pilot experiment.

Genetic Differentiation within the Puccinia triticina Population in South America and Comparison with the North American Population Suggests Common Ancestry and Intercontinental Migration

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Leaf rust, caused by Puccinia triticina is the most prevalent and widespread disease of wheat in South America. The objective of this study was to determine the number of genetically differentiated groups of P. triticina that are currently present in South America, and to compare the South American ...

Seismic Evidence of Ancient Westward Residual Slab Subduction Beneath Southern Taiwan

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Cheng-Horng Lin

2015-01-01

Full Text Available The northeastern convergence of the Philippine Sea plate toward the Eurasian plate causes the major western Philippine Sea plate boundary to subduct toward the northwest or west directions. However, this phenomenon is not clearly observed along the plate boundary between Luzon and Taiwan. Careful examination of deep seismicity in the southern Taiwan area from the earthquake catalog reported by the Central Weather Bureau shows two seismic zones dipping toward the opposing directions. The first dips toward the east from the surface down to 150 km in depth, while the second dips westward at depths between 150 and 200 km. These two seismic zones are confirmed further by seismogram observation and modeling results generated by two deep faults in the southern Taiwan area. The eastward seismic zone clearly results from the Eurasia plate subduction along the Manila trench, while a small section of the westward seismic zone might likely be a residual slab from the ancient subducted Philippine Sea plate. Based on the subduction speed obtained from GPS observations and the subducted Eurasian plate geometry, we can further estimate the eastward Eurasian plate subduction started at least 3.35 million years ago. This result is roughly consistent with the volcanic ages (3 - 4 Ma observed in the arc between Luzon and Taiwan.

Dynamics of subduction, accretion, exhumation and slab roll-back: Mediterranean scenarios

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Tirel, C.; Brun, J.; Burov, E. B.; Wortel, M. J.; Lebedev, S.

2010-12-01

A dynamic orogen reveals various tectonic processes brought about by subduction: accretion of oceanic and continental crust, exhumation of UHP-HP rocks, and often, back-arc extension. In the Mediterranean, orogeny is strongly affected by slab retreat, as in the Aegean and Tyrrhenian Seas. In order to examine the different dynamic processes in a self-consistent manner, we perform a parametric study using the fully coupled thermo-mechanical numerical code PARAFLAM. The experiments reproduce a subduction zone in a slab pull mode, with accretion of one (the Tyrrhenian case) and two continental blocks (the Aegean case) that undergo, in sequence, thrusting, burial and exhumation. The modeling shows that despite differences in structure between the two cases, the deformation mechanisms are fundamentally similar and can be described as follows. The accretion of a continental block at the trench beneath the suture zone begins with its burial to UHP-HP conditions and thrusting. Then the continental block is delaminated from its subducting lithosphere. During the subduction-accretion process, the angle of the subducting slab increases due to the buoyancy of the continental block. When the oceanic subduction resumes, the angle of the slab decreases to reach a steady-state position. The Aegean and Tyrrhenian scenarios diverge at this stage, due naturally to the differences of their accretion history. When continental accretion is followed by oceanic subduction only, the continental block that has been accreted and detached stays at close to the trench and does not undergo further deformation, despite the continuing rollback. The extensional deformation is located further within the overriding plate, resulting in continental breakup and the development of an oceanic basin, as in the Tyrrhenian domain. When the continental accretion is followed first by oceanic subduction and then by accretion of another continental block, however, the evolution of the subduction zone is

Subduction zone forearc serpentinites as incubators for deep microbial life

NARCIS (Netherlands)

Plümper, Oliver|info:eu-repo/dai/nl/37155960X; King, Helen E.|info:eu-repo/dai/nl/411261088; Geisler, Thorsten; Liu, Yang|info:eu-repo/dai/nl/411298119; Pabst, Sonja; Savov, Ivan P.; Rost, Detlef; Zack, Thomas

2017-01-01

Serpentinization-fueled systems in the cool, hydrated forearc mantle of subduction zones may provide an environment that supports deep chemolithoautotrophic life. Here, we examine serpentinite clasts expelled from mud volcanoes above the Izu–Bonin–Mariana subduction zone forearc (Pacific Ocean) that

Seismic evidence for deep fluid circulation in the overriding plate of subduction zones

Science.gov (United States)

Tauzin, B.; Reynard, B.; Bodin, T.; Perrillat, J. P.; Debayle, E.

2015-12-01

In subduction zones, non-volcanic tremors are associated with fluid circulations (Obara, 2002). Their sources are often located on the interplate boundary (Rogers and Dragert, 2003; Shelly et al, 2006; La Rocca, 2009), consistent with fluids released by the dehydration of subducted plates (Hacker et al., 2003). Reports of tremors in the overriding continental crust of several subduction zones in the world (Kao et al., 2005; Payero et al., 2008; Ide, 2012) suggest fluid circulation at shallower depths but potential fluid paths are poorly documented. Here we obtained seismic observations from receiver functions that evidence the close association between the shallow tremor zone, electrical conductivity, and tectonic features of the Cascadia overriding plate. A seismic discontinuity near 15 km depth in the crust of the overriding North American plate is attributed to the Conrad discontinuity. This interface is segmented, and its interruption is spatially correlated with conductive regions and shallow swarms of seismicity and non-volcanic tremors. These observations suggest that shallow fluid circulation, tremors and seismicity are controlled by fault zones limiting blocks of accreted terranes in the overriding plate (Brudzinski and Allen, 2007). These zones constitute fluid "escape" routes that may contribute unloading fluid pressure on the megathrust. Obara, K. (2002). Science, 296, 1679-1681. Rogers, G., & Dragert, H. (2003). Science, 300, 1942-1943. Shelly, D. R., et al. (2006). Nature, 442, 188-191. La Rocca, M., et al. (2009). Science, 323, 620-623. Kao, H., et al. (2005). Nature, 436, 841-844. Payero, J. S., et al. (2008). Geophysical Research Letters, 35. Ide, S. (2012). Journal of Geophysical Research: Solid Earth, 117. Brudzinski, M. R., & Allen, R. M. (2007). Geology, 35, 907-910.

Fission-track dating of South American natural glasses: an overview

Energy Technology Data Exchange (ETDEWEB)

Bigazzi, G. [Istituto di Geoscienze e Georisorse, C.N.R., Via G. Moruzzi, 1, 56124 Pisa (Italy)]. E-mail: g.bigazzi@igg.cnr.it; Hadler Neto, J.C. [Instituto de Fisica Gleb Wataghin, Universidade Estadual de Campinas, UNICAMP, 13083-970 Campinas SP (Brazil); Iunes, P.J. [Instituto de Fisica Gleb Wataghin, Universidade Estadual de Campinas, UNICAMP, 13083-970 Campinas SP (Brazil); Osorio Araya, A.M. [Departamento de Fisica, Quimica e Biologia, Universidade do Estado de Sao Paulo, UNESP, 19060-900 Presidente Prudente SP (Brazil)

2005-12-01

Although many glass-bearing horizons can be found in South American volcanic complexes or sedimentary series, only a relatively few tephra and obsidian-bearing volcanic fields have been studied using the fission-track (FT) dating method. Among them, the volcanics located in the Sierra de Guamani (east of Quito, Ecuador) were studied by several authors. Based upon their ages, obsidians group into three clusters: (1) very young obsidians, {approx}0.2Ma old (2) intermediate-age obsidians, {approx}0.4-{approx}0.8Ma old, and (3) older obsidians, {approx}1.4-{approx}1.6Ma old. The FT method is also an efficient alternative technique for identification of the sources of prehistoric obsidian artefacts. Provenance studies carried out in South America have shown that the Sierra de Guamani obsidian occurrences were important sources of raw material for tool making during pre-Columbian times. Glasses originated from these sources were identified in sites distributed over relatively wide areas of Ecuador and Colombia. Only a few systematic studies on obsidians in other sectors were carried out. Nevertheless, very singular glasses have been recognised in South America, such as Macusanite (Peru) and obsidian Quiron (Argentina), which are being proposed as additional reference materials for FT dating. Analyses of tephra beds interstratified with sedimentary deposits revealed the performance of FT dating in tephrochronological studies. A remarkable example is the famous deposit outcropping at Farola Monte Hermoso, near Bahia Blanca (Buenos Aires Province), described for the first time by the middle of the 19th century by Charles Darwin. Considering the large number of volcanic glasses that were recognised in volcanic complexes and in sedimentary series, South America is a very promising region for the application of FT dating. The examples given above show that this technique may yield important results in different disciplinary fields.

Fission-track dating of South American natural glasses: an overview

International Nuclear Information System (INIS)

Bigazzi, G.; Hadler Neto, J.C.; Iunes, P.J.; Osorio Araya, A.M.

2005-01-01

Although many glass-bearing horizons can be found in South American volcanic complexes or sedimentary series, only a relatively few tephra and obsidian-bearing volcanic fields have been studied using the fission-track (FT) dating method. Among them, the volcanics located in the Sierra de Guamani (east of Quito, Ecuador) were studied by several authors. Based upon their ages, obsidians group into three clusters: (1) very young obsidians, ∼0.2Ma old (2) intermediate-age obsidians, ∼0.4-∼0.8Ma old, and (3) older obsidians, ∼1.4-∼1.6Ma old. The FT method is also an efficient alternative technique for identification of the sources of prehistoric obsidian artefacts. Provenance studies carried out in South America have shown that the Sierra de Guamani obsidian occurrences were important sources of raw material for tool making during pre-Columbian times. Glasses originated from these sources were identified in sites distributed over relatively wide areas of Ecuador and Colombia. Only a few systematic studies on obsidians in other sectors were carried out. Nevertheless, very singular glasses have been recognised in South America, such as Macusanite (Peru) and obsidian Quiron (Argentina), which are being proposed as additional reference materials for FT dating. Analyses of tephra beds interstratified with sedimentary deposits revealed the performance of FT dating in tephrochronological studies. A remarkable example is the famous deposit outcropping at Farola Monte Hermoso, near Bahia Blanca (Buenos Aires Province), described for the first time by the middle of the 19th century by Charles Darwin. Considering the large number of volcanic glasses that were recognised in volcanic complexes and in sedimentary series, South America is a very promising region for the application of FT dating. The examples given above show that this technique may yield important results in different disciplinary fields

Interactions between strike-slip earthquakes and the subduction interface near the Mendocino Triple Junction

Science.gov (United States)

Gong, Jianhua; McGuire, Jeffrey J.

2018-01-01

The interactions between the North American, Pacific, and Gorda plates at the Mendocino Triple Junction (MTJ) create one of the most seismically active regions in North America. The earthquakes rupture all three plate boundaries but also include considerable intraplate seismicity reflecting the strong internal deformation of the Gorda plate. Understanding the stress levels that drive these ruptures and estimating the locking state of the subduction interface are especially important topics for regional earthquake hazard assessment. However owing to the lack of offshore seismic and geodetic instruments, the rupture process of only a few large earthquakes near the MTJ have been studied in detail and the locking state of the subduction interface is not well constrained. In this paper, first, we use the second moments inversion method to study the rupture process of the January 28, 2015 Mw 5.7 earthquake on the Mendocino transform fault that was unusually well recorded by both onshore and offshore strong motion instruments. We estimate the rupture dimension to be approximately 6 km by 3 km corresponding to a stress drop of ∼4 MPa for a crack model. Next we investigate the frictional state of the subduction interface by simulating the afterslip that would be expected there as a result of the stress changes from the 2015 earthquake and a 2010 Mw 6.5 intraplate earthquake within the subducted Gorda plate. We simulate afterslip scenarios for a range of depths of the downdip end of the locked zone defined as the transition to velocity strengthening friction and calculate the corresponding surface deformation expected at onshore GPS monuments. We can rule out a very shallow downdip limit owing to the lack of a detectable signal at onshore GPS stations following the 2010 earthquake. Our simulations indicate that the locking depth on the slab surface is at least 14 km, which suggests that the next M8 earthquake rupture will likely reach the coastline and strong shaking

Great earthquake potential in Oregon and Washington: An overview of recent coastal geologic studies and possible segmentation of the central Cascadia subduction zone

International Nuclear Information System (INIS)

Nelson, A.R.; Personius, S.F.

1990-01-01

Fundamental questions in earthquake hazards research in the Pacific Northwest concern the magnitude and recurrence of great earthquakes in the Cascadia subduction zone in Oregon and Washington. Geologic work of the last few years has produced convincing evidence for coseismic subsidence along the Washington and Oregon coasts. Regional subsidence recorded by estuarine deposits suggests that plate-interface earthquakes of at least M w 8 (>100-km-long ruptures) occurred during the late Holocene in northern Oregon and southern Washington. Differences in the types of coastal marsh sequences between northern and south-central Oregon, however, suggest that regional coastal subsidence does not extend south of about 45.5 degrees N along the Oregon coast. North of this latitude, the coast may intersect the seaward edge of a zone of coseismic subsidence that continues southward onshore. Alternatively, the Cascadia subduction zone is segmented near 44-45 degrees N; a segment boundary at this location would suggest that plate-interface events near M w 8 along the central CSZ would be more frequent than larger (M w 9) events. South of this boundary in the Coos Bay region, the tectonic framework developed through mapping and dating of marine and fluvial terraces indicates that many episodes of abrupt marsh burial in south-central Oregon are best interpreted as the product of deformation on local structures. Some of the local deformation could be associated with moderate earthquakes (M s <6). At most sites in south-central Oregon, however, it is still unclear whether coseismic events were responses to local faulting or folding, to regional deformation during great plate-interface earthquakes, or to both. This study has potential implications for risk assessments for light water reactors in North America

Thermal-Chemical Model Of Subduction: Results And Tests

Science.gov (United States)

Gorczyk, W.; Gerya, T. V.; Connolly, J. A.; Yuen, D. A.; Rudolph, M.

2005-12-01

Seismic structures with strong positive and negative velocity anomalies in the mantle wedge above subduction zones have been interpreted as thermally and/or chemically induced phenomena. We have developed a thermal-chemical model of subduction, which constrains the dynamics of seismic velocity structure beneath volcanic arcs. Our simulations have been calculated over a finite-difference grid with (201×101) to (201×401) regularly spaced Eulerian points, using 0.5 million to 10 billion markers. The model couples numerical thermo-mechanical solution with Gibbs energy minimization to investigate the dynamic behavior of partially molten upwellings from slabs (cold plumes) and structures associated with their development. The model demonstrates two chemically distinct types of plumes (mixed and unmixed), and various rigid body rotation phenomena in the wedge (subduction wheel, fore-arc spin, wedge pin-ball). These thermal-chemical features strongly perturb seismic structure. Their occurrence is dependent on the age of subducting slab and the rate of subduction.The model has been validated through a series of test cases and its results are consistent with a variety of geological and geophysical data. In contrast to models that attribute a purely thermal origin for mantle wedge seismic anomalies, the thermal-chemical model is able to simulate the strong variations of seismic velocity existing beneath volcanic arcs which are associated with development of cold plumes. In particular, molten regions that form beneath volcanic arcs as a consequence of vigorous cold wet plumes are manifest by > 20% variations in the local Poisson ratio, as compared to variations of ~ 2% expected as a consequence of temperature variation within the mantle wedge.

IAEA Helps Remove Highly Radioactive Material from Five South American Countries

International Nuclear Information System (INIS)

2018-01-01

The International Atomic Energy Agency (IAEA) has helped remove 27 disused highly radioactive sources from five South American countries in a significant step forward for nuclear safety and security in the region. It was the largest such project ever facilitated by the IAEA. The material, mainly used for medical purposes such as treating cancer and sterilizing instruments, was transported to Germany and the United States for recycling. Canada, where some of the sources were manufactured, funded the project upon requests for IAEA support from Bolivia, Ecuador, Paraguay, Peru and Uruguay. The sealed Cobalt-60 and Caesium-137 sources pose safety and security risks when no longer in use, according to Raja Adnan, Director of the IAEA’s Division of Nuclear Security. “The removal of this large number of radioactive sources has significantly reduced those risks in the five countries,” Adnan said. In recent years, the IAEA has assisted Bosnia and Herzegovina, Cameroon, Costa Rica, Honduras, Lebanon, Morocco, Tunisia and Uzbekistan in the removal of disused sources. The South American operation was the largest the IAEA has so far coordinated in terms of both the number of highly radioactive sources and countries involved. While nuclear safety and security are national responsibilities, the IAEA helps Member States upon request to meet these responsibilities through training, technical advice, peer reviews and other advisory services. Such efforts may include support for Member States in implementing the safe and cost-effective recovery, conditioning, storage, disposal or transportation of disused sealed radioactive sources (DSRS).

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

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

2015-01-01

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

Grandparent caregiving among rural African Americans in a community in the American South: challenges to health and wellbeing.

Science.gov (United States)

Clottey, Emmanuel N; Scott, Alison J; Alfonso, Moya L

2015-01-01

An increasing number of grandparents in rural USA are serving as primary caregivers for their grandchildren because of parental incarceration, addiction, joblessness, or illness. Low-income, African American women from the South are overrepresented in this growing population. There is a paucity of research exploring the challenges faced by rural grandparent caregivers, and past studies have not explicitly addressed the potential consequences of rural grandparent caregiving for health. The purpose of this qualitative study was to explore grandparent caregiving among rural, low-income, African American grandmothers in a community in the American South, and to identify challenges to health that arose in that context. McLeroy's social ecological model (SEM) was used to examine these challenges at multiple levels of influence. This qualitative interview-based study was conducted in a high-poverty community in rural Georgia. In-depth interviews were conducted with African American grandparent caregivers and key informants from local community-based organizations. A key informant assisted in identifying initial interview participants, and then snowball sampling was used to recruit additional participants. Interview questions were grouped under five domains (intrapersonal, interpersonal, community, organizational, and policy), according to the levels of the SEM. Iterative content analysis of interview transcripts was utilized. Transcripts were coded to identify text segments related to each domain of the SEM, which were grouped together for analysis by domain. Reflexive memo-writing aided in development of themes, and data quality was assessed using Lincoln and Guba's trustworthiness criteria. Rural African American grandparent caregivers faced a range of challenges to health. Direct physical challenges included chronic pain that interfered with sleep and daily functioning, mobility issues exacerbated by child care, and the pressure of managing their own medical conditions

Disparities in Birth Weight and Gestational Age by Ethnic Ancestry in South American countries

Science.gov (United States)

Wehby, George L.; Gili, Juan A.; Pawluk, Mariela; Castilla, Eduardo E.; López-Camelo, Jorge S.

2015-01-01

Objective We examine disparities in birth weight and gestational age by ethnic ancestry in 2000–2011 in eight South American countries. Methods The sample included 60480 singleton live-births. Regression models were estimated to evaluate differences in birth outcomes by ethnic ancestry controlling for time trends. Results Significant disparities were found in seven countries. In four countries – Brazil, Ecuador, Uruguay, and Venezuela – we found significant disparities in both low birth weight and preterm birth. Disparities in preterm birth alone were observed in Argentina, Bolivia, and Colombia. Several differences in continuous birth weight, gestational age, and fetal growth rate were also observed. There were no systematic patterns of disparities between the evaluated ethnic ancestry groups across the study countries, in that no racial/ethnic group consistently had the best or worst outcomes in all countries. Conclusions Racial/ethnic disparities in infant health are common in several South American countries. Differences across countries suggest that racial/ethnic disparities are driven by social and economic mechanisms. Researchers and policymakers should acknowledge these disparities and develop research and policy programs to effectively target them. PMID:25542227

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

NARCIS (Netherlands)

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

2013-01-01

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

Change in the foraging strategy of female South American sea lions (Carnivora: Pinnipedia after parturition

Directory of Open Access Journals (Sweden)

Massimiliano Drago

2010-08-01

Full Text Available This study tests the hypothesis that female South American sea lions shift from off-shore, pelagic prey to coastal, benthic prey after parturition in order to reduce the foraging trip duration and hence the time pups remain unattended on the beach during early lactation. The δ13C and δ15N values of the serum and blood cells of 26 South American sea lion suckling pups from northern Patagonia were used to track the dietary changes of their mothers from late pregnancy to early lactation, after correction for differential isotopic fractionation between tissues. Primary producers and potential prey species were also analysed to establish a baseline for interpreting the stable isotope concentration of serum and blood cells. Isotopic ratios revealed a generalized increase in the consumption of coastal-benthic prey after parturition. Such a generalized post-partum shift will allow females to spend more time on land and look after their pups. The effects of this foraging strategy on the nutritional quality of the female’s diet are discussed.

Gravity and Magnetic Anomaly Interpretations and 2.5D Cross-Section Models over the Border Ranges Fault System and Aleutian Subduction Zone, Alaska

Science.gov (United States)

Mankhemthong, N.; Doser, D. I.; Baker, M. R.; Kaip, G.; Jones, S.; Eslick, B. E.; Budhathoki, P.

2011-12-01

Quaternary glacial covers and lack of dense geophysical data on the Kenai Peninsula cause a location and geometry of the Border Ranges fault system (BRFS) within a recent forearc-accretionary boundary of Aleutian subduction zone in southern Alaska are unclear. Using new ~1,300 gravity collections within the Anchorage and Kenai Peninsula regions complied with prior 1997 gravity and aeromagnetic data help us better imaging these fault and the subduction structures. Cook Inlet forearc basin is corresponded by deep gravity anomaly lows; basin boundaries are characterized by a strong gravity gradient, where are considered to be traces of Border Ranges fault system on the east and Castle Mountain and Bruin Bay fault system on the west and northwest of the forearc basin respectively. Gravity anomaly highs over accreted rocks generally increase southeastward to the Aleutian trench, but show a gravity depression over the Kenai Mountains region. The lineament between gravity high and low in the same terrenes over the Kenai Peninsula is may be another evidence to determine the Southern Edge of the Yakutat Microplate (SEY) as inferred by Eberhart-Phillips et al. (2006). Our 2.5-D models illustrate the main fault of the BRFS dips steeply toward the west with a downslip displacement. Gravity and Magnetic anomaly highs, on the east of the BRFS, probably present a slice of the ultramafic complex emplaced by faults along the boundary of the forearc basin and accretionary wedge terranes. Another magnetic high beneath the basin in the southern forearc basin support a serpentiznied body inferred by Saltus et al. (2001), with a decreasing size toward the north. Regional density-gravity models show the Pacific subducting slab beneath the foreacre-arc teranes with a gentle and flatted dip where the subducting plate is located in north of SEY and dips more steeply where it is located on the south of SEY. The gravity depression over the accreted terrene can be explained by a density low

The South American fruit fly, Anastrepha fraterculus (Wied.); advances in artificial rearing, taxonomic status and biological studies. Proceedings of a workshop

Energy Technology Data Exchange (ETDEWEB)

1999-01-01

One of the fruit flies of major concern, because of its economic and quarantine importance in the Americas, is the exotic Mediterranean fruit fly, Ceratitis capitata, which is established throughout the Central and South American countries, excluding Chile. Chile, Mexico and the USA have conducted multi-million dollar campaigns to prevent the establishment of this and other exotic fruit flies in their respective territories, in support of the development of important fruit production and export industries. Other important fruit fly species, which are native to the American continent, are those of the genus Anastrepha. In this group, of most economic importance are A. obliqua and A. ludens for Mexico and some Central American countries and A. fraterculus and A. obliqua for South America. In this publication, attention is focused on A. fraterculus, the South American fruit fly. This species, as it is presently recognized, occurs from Mexico to Argentina and is reported from approximately 80 host plants, including commercial fruits of economic importance, such as mango, citrus, guava, apple and coffee. As A. fraterculus if considered to be of high economic and quarantine importance in many countries in South America, it is justifiable to recommend and promote the implementation of activities to strengthen knowledge of the species and develop techniques for its control and/or eradication. The development of sterile insect technique (SIT) and other biological control methods are very encouraging alternatives, as can be seen from examples in Mexico and the USA, where these approaches are in use against A. ludens and A. obliqua Refs, figs, tabs

The South American fruit fly, Anastrepha fraterculus (Wied.); advances in artificial rearing, taxonomic status and biological studies. Proceedings of a workshop

International Nuclear Information System (INIS)

1999-01-01

One of the fruit flies of major concern, because of its economic and quarantine importance in the Americas, is the exotic Mediterranean fruit fly, Ceratitis capitata, which is established throughout the Central and South American countries, excluding Chile. Chile, Mexico and the USA have conducted multi-million dollar campaigns to prevent the establishment of this and other exotic fruit flies in their respective territories, in support of the development of important fruit production and export industries. Other important fruit fly species, which are native to the American continent, are those of the genus Anastrepha. In this group, of most economic importance are A. obliqua and A. ludens for Mexico and some Central American countries and A. fraterculus and A. obliqua for South America. In this publication, attention is focused on A. fraterculus, the South American fruit fly. This species, as it is presently recognized, occurs from Mexico to Argentina and is reported from approximately 80 host plants, including commercial fruits of economic importance, such as mango, citrus, guava, apple and coffee. As A. fraterculus if considered to be of high economic and quarantine importance in many countries in South America, it is justifiable to recommend and promote the implementation of activities to strengthen knowledge of the species and develop techniques for its control and/or eradication. The development of sterile insect technique (SIT) and other biological control methods are very encouraging alternatives, as can be seen from examples in Mexico and the USA, where these approaches are in use against A. ludens and A. obliqua

The Fairway-Aotea Basin and the New Caledonia Trough, witnesses of the Pacific-Australian plate boundary evolution : from mid-Cretaceous cessation of subduction to Eocene subduction renewal

Science.gov (United States)

Collot, J.; Geli, L. B.; Lafoy, Y.; Sutherland, R.; Herzer, R. H.; Roest, W. R.

2009-12-01

The geodynamical history of the SW Pacific is controlled since the Mesozoic by the evolution of peri-Pacific subduction zones, in a trench retreat by slab roll-back process, which successively occurred along the Eastern Gondwana margin. In this context, most basins which formed after 45 Ma reached a stage of seafloor spreading, have recorded the inversions of the earth's magnetic field and present typical oceanic crust morphologies. By contrast, the New Caledonia and Fairway basins, which are narrower and present thick sedimentary covers have a less known and more controversial origin. Based on a regional geological synthesis and on interpretation of multichannel seismic reflection and refraction data, combined with drill hole data off New Zealand and a compilation of regional potential data, we distinguish 2 phases of the evolution of the Fairway-Aotea Basin (FAB) and the New Caledonia Trough (NCT), which reflect the evolution of the Gondwana-Pacific plate boundary: Phase 1: Mid Cretaceous formation of the FAB in a continental intra- or back- arc position of the Pacific-Gondwana subduction system. The formation of this shallow basin reflects the onset of continental breakup of the Eastern Gondwana margin during Cenomanian which was most probably caused by a dynamic change of the subduction zone through a « verticalization » of the slab. This event may be the result of the 99 Ma kinematic plate reorganization which probably led to subduction cessation along the Gondwana-Pacific plate boundary. A tectonic escape mechanism, in relation with the locking of the subduction zone by the Hikurangi Plateau, could also be responsible of the trench retreat leading to backarc extension. Phase 2: Regional Eocene-Oligocene uplift followed by rapid subsidence (3-4 km) of the system « Lord Howe Rise - FAB - Norfolk Ridge ». The structural style of this deformation leads us to suggest that detachment of the lower crust is the cause of subsidence. We therefore propose a model in

Structure of the Cascadia Subduction Zone Imaged Using Surface Wave Tomography

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Schaeffer, A. J.; Audet, P.

2017-12-01

Studies of the complete structure of the Cascadia subduction zone from the ridge to the arc have historically been limited by the lack of offshore ocean bottom seismograph (OBS) infrastructure. On land, numerous dense seismic deployments have illuminated detailed structures and dynamics associated with the interaction between the subducting oceanic plate and the overriding continental plate, including cycling of fluids, serpentinization of the overlying forearc mantle wedge, and the location of the upper surface of the Juan de Fuca plate as it subducts beneath the Pacific Northwest. In the last half-decade, the Cascadia Initiative (CI), along with Neptune (ONC) and several other OBS initiatives, have instrumented both the continental shelf and abyssal plains off shore of the Cascadia subduction zone, facilitating the construction of a complete picture of the subduction zone from ridge to trench and volcanic arc. In this study, we present a preliminary azimuthally anisotropic surface-wave phase-velocity based model of the complete system, capturing both the young, unaltered Juan de Fuca plate from the ridge, to its alteration as it enters the subduction zone, in addition to the overlying continent. This model is constructed from a combination of ambient noise cross-correlations and teleseismic two station interferometry, and combines together concurrently running offshore OBS and onshore stations. We furthermore perform a number of representative 1D depth inversions for shear velocity to categorize the pristine oceanic, subducted oceanic, and continental crust and lithospheric structure. In the future the dispersion dataset will be jointly inverted with receiver functions to constrain a 3D shear-velocity model of the complete region.

Using open sidewalls for modelling self-consistent lithosphere subduction dynamics

NARCIS (Netherlands)

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

2012-01-01

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

Migration Imaging of the Java Subduction Zones

Science.gov (United States)

Dokht, Ramin M. H.; Gu, Yu Jeffrey; Sacchi, Mauricio D.

2018-02-01

Imaging of tectonically complex regions can greatly benefit from dense network data and resolution enhancement techniques. Conventional methods in the analysis of SS precursors stack the waveforms to obtain an average discontinuity depth, but smearing due to large Fresnel zones can degrade the fine-scale topography on the discontinuity. To provide a partial solution, we introduce a depth migration algorithm based on the common scattering point method while considering nonspecular diffractions from mantle transition zone discontinuities. Our analysis indicates that, beneath the Sunda arc, the depth of the 410 km discontinuity (the 410) is elevated by 30 km and the 660 km discontinuity (the 660) is depressed by 20-40 km; the region of the strongest anticorrelation is correlated with the morphology of the subducting Indo-Australian slab. In eastern Java, a "flat" 410 coincides with a documented slab gap, showing length scales greater than 400 km laterally and 200 km vertically. This observation could be explained by the arrival of a buoyant oceanic plateau at the Java trench at approximately 8 Ma ago, which may have caused a temporary cessation of subduction and formed a tear in the subducting slab. Our results highlight contrasting depths of the 410 and 660 along the shallow-dipping slab below the Banda trench. The 660, however, becomes significantly uplifted beneath the Banda Sea, which is accompanied by enhanced reflection amplitudes. We interpret these observations as evidence for a subslab low-velocity zone, possibly related to the lower mantle upwelling beneath the subducting slab.

Brightness of venous blood in South American camelids: implications for jugular catheterization.

Science.gov (United States)

Grint, Nicola; Dugdale, Alexandra

2009-01-01

To compare the brightness of South American camelid venous blood to that of Equidae. Prospective clinical evaluation. Twelve South American camelids (eight llamas, four alpacas), eight horses and ponies (control group). Appropriately sized catheters were placed in the jugular vein of each animal under local anaesthesia. The blood spilt before the catheter was capped was caught on a white tile. A sample of blood was drawn for blood-gas analysis. The brightness of the blood (both on the tile and in the syringe) was matched to a colour chart (1 = darkest red, 8 = brightest red) by a single observer under bright light conditions. Packed cell volume (PCV) and partial pressure of oxygen (PvO(2)) in the blood were also measured on the syringe blood. Normally distributed data were compared using a two tailed t-test, and non-normally distributed data were compared using a Mann-Whitney U-test. Significance was set at p Camelid venous blood was significantly brighter red than that of horses and ponies both on the white tile (p = 0.0003) and in the syringe (p = 0.0001). PCV was significantly lower in camelids (32 +/- 4%) compared with horses (37 +/- 5%). Partial pressure of oxygen values were similar between groups. Jugular venous blood in alpacas and llamas is significantly brighter red than that of horses. Colour should not be used as a sole determinant of venous or arterial catheterization in this species.

Seismicity and stress state in the South China Sea, Indochina and their vicinity

Science.gov (United States)

Zang, Shaoxian; Wu, Zhongliang; Li, Aibing

1992-02-01

The distribution of earthquakes from 1973 to 1982 in the South China Sea, Indochina and their vicinity was studied using the data from I. S. C. It was found that the earthquakes are mainly concentrated along the boundaries of plates. Beside, some of shallow eartqhuakes are distributed in west part of Burma and the boundary between Burma and China, a few of earthquakes occurred in South China Sea. The features of Benioff zone along the boundaries between India plate, Philippine Sea plate and Eurasia plate were studied. The plate do not coupled well under the Java trench and the Philippine trench. The subducted India plate under Burmese range, Andaman—Nicobar arc moves NNE. The fault plane solutions of earthquakes were studied using the first motions of P wave. The stress state on subduction zones and within the area were deduced from the fault plane solutions and the fault movement. It was found that the direction of principal compression axis of stress is in the NNE in west part of Burma, in S—N in south and middle part of Bruma and Thailand, and in NNE or S—N in the South China Sea. It was also found that the stress state has close relation with the interaction of plates.

American Indian Parents’ Assessment of and Concern About Their Kindergarten Child’s Weight Status, South Dakota, 2005-2006

OpenAIRE

Arcan, Chrisa; Hannan, Peter J.; Himes, John H.; Fulkerson, Jayne A.; Holy Rock, Bonnie; Smyth, Mary; Story, Mary

2012-01-01

Introduction Obesity is highly prevalent among American Indians, and effective prevention efforts require caregiver involvement. We examined American Indian (AI) parents' assessment of and level of concern about their kindergarten child's weight status. Methods We collected baseline data (fall of 2005 and fall of 2006) on children and their parents or caregivers for a school-based obesity prevention trial (Bright Start) on an AI reservation in South Dakota. The current study uses 413 parent-c...

Subduction and vertical coastal motions in the eastern Mediterranean

Science.gov (United States)

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

2017-10-01

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

Cefazolin high-inoculum effect in methicillin-susceptible Staphylococcus aureus from South American hospitals.

Science.gov (United States)

Rincón, Sandra; Reyes, Jinnethe; Carvajal, Lina Paola; Rojas, Natalia; Cortés, Fabián; Panesso, Diana; Guzmán, Manuel; Zurita, Jeannete; Adachi, Javier A; Murray, Barbara E; Nannini, Esteban C; Arias, Cesar A

2013-12-01

Clinical failures with cefazolin have been described in high-inoculum infections caused by methicillin-susceptible Staphylococcus aureus (MSSA) producing type A β-lactamase. We investigated the prevalence of the cefazolin inoculum effect (InE) in MSSA from South American hospitals, since cefazolin is used routinely against MSSA due to concerns about the in vivo efficacy of isoxazolyl penicillins. MSSA isolates were recovered from bloodstream (n = 296) and osteomyelitis (n = 68) infections in two different multicentre surveillance studies performed in 2001-02 and 2006-08 in South American hospitals. We determined standard-inoculum (10(5)cfu/mL) and high-inoculum (10(7) cfu/mL) cefazolin MICs. PFGE was performed on all isolates that exhibited a cefazolin InE. Multilocus sequence typing (MLST) and sequencing of part of blaZ were performed on representative isolates. The overall prevalence of the cefazolin InE was 36% (131 isolates). A high proportion (50%) of MSSA isolates recovered from osteomyelitis infections exhibited the InE, whereas it was observed in 33% of MSSA recovered from bloodstream infections. Interestingly, Ecuador had the highest prevalence of the InE (45%). Strikingly, 63% of MSSA isolates recovered from osteomyelitis infections in Colombia exhibited the InE. MLST revealed that MSSA isolates exhibiting the InE belonged to diverse genetic backgrounds, including ST5, ST8, ST30 and ST45, which correlated with the prevalent methicillin-resistant S. aureus clones circulating in South America. Types A (66%) and C (31%) were the most prevalent β-lactamases. Our results show a high prevalence of the cefazolin InE associated with type A β-lactamase in MSSA isolates from Colombia and Ecuador, suggesting that treatment of deep-seated infections with cefazolin in those countries may be compromised.

Magmatic dyke swarms of the south shetland islands volcanic arc, west-antarctica - tracers of geodynamic history

Science.gov (United States)

Kraus, St.; Miller, H.

2003-04-01

Magmatic dykes are essential components of volcanic arcs, following joint systems and fracture zones. This work aims to reconstruct the deformational and intrusive history of the northern part of the Antarctic Peninsula by combining structural information with the geochemistry, isotopy and age of the dykes. On the South Shetland Islands volcanic activity began about 130 Ma ago. From Mid to Late Eocene (49-34 Ma) the northern Antarctic Peninsula and southern South America underwent extensional tectonics, which led to sea-floor spreading in the Drake Passage 28 Ma ago. Subsequent slab-rollback caused arc-extension and the opening of the Bransfield Rift as a backarc-basin between 4 and 1.3 Ma ago. Very slow subduction (1mm/a) at the South Shetland trench continues until the present day. Several changes of subduction direction caused crucial variations regarding the tectonic regime in the overlying South Shetland block, being the reason for the shifting strike of the dykes. Several dyke systems were mapped in areas of up to 100000m2, with the outcrop situation being good enough to observe plenty of relative age relationships. ICP-MS geochemical analysis on 132 dykes shows, as expected, that the majority of them correspond to a typical subduction-related calcalcalic suite, ranging from basalts to rhyolites. Nevertheless, some dykes show shoshonitic characteristics and are maybe related to an early stage extensional crustal regime. This is supported by the relative ages observed in the field, indicating, that these dykes belong to the oldest ones outcropping in the investigated area. In one case, the geochemical behaviour of the dyke corresponds clearly to adacitic conditions, being a hint on partially molten subducted oceanic crust. In several areas (e.g. Potter Peninsula, King George Island, and Hurd Peninsula, Livingston Island) a strong correlation between chemism and strike of the dykes - and therefore the tectonic regime at the time of intrusion - is observed. Ce

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

Science.gov (United States)

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

2016-11-01

The chemistry of aqueous fluids controls the transport and exchange—the cycles—of metals and volatile elements on Earth. Subduction zones, where oceanic plates sink into the Earth’s interior, are the most important geodynamic setting for this fluid-mediated chemical exchange. Characterizing the ionic speciation and pH of fluids equilibrated with rocks at subduction zone conditions has long been a major challenge in Earth science. Here we report thermodynamic predictions of fluid-rock equilibria that tie together models of the thermal structure, mineralogy and fluid speciation of subduction zones. We find that the pH of fluids in subducted crustal lithologies is confined to a mildly alkaline range, modulated by rock volatile and chlorine contents. Cold subduction typical of the Phanerozoic eon favours the preservation of oxidized carbon in subducting slabs. In contrast, the pH of mantle wedge fluids is very sensitive to minor variations in rock composition. These variations may be caused by intramantle differentiation, or by infiltration of fluids enriched in alkali components extracted from the subducted crust. The sensitivity of pH to soluble elements in low abundance in the host rocks, such as carbon, alkali metals and halogens, illustrates a feedback between the chemistry of the Earth’s atmosphere-ocean system and the speciation of subduction zone fluids via the composition of the seawater-altered oceanic lithosphere. Our findings provide a perspective on the controlling reactions that have coupled metal and volatile cycles in subduction zones for more than 3 billion years7.

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

NARCIS (Netherlands)

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

2017-01-01

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

Fluid and mass transfer at subduction interfaces-The field metamorphic record

Science.gov (United States)

Bebout, Gray E.; Penniston-Dorland, Sarah C.

2016-01-01

The interface between subducting oceanic slabs and the hanging wall is a structurally and lithologically complex region. Chemically disparate lithologies (sedimentary, mafic and ultramafic rocks) and mechanical mixtures thereof show heterogeneous deformation. These lithologies are tectonically juxtaposed at mm to km scales, particularly in more intensely sheared regions (mélange zones, which act as fluid channelways). This juxtaposition, commonly in the presence of a mobile fluid phase, offers up huge potential for mass transfer and related metasomatic alteration. Fluids in this setting appear capable of transporting mass over scales of kms, along flow paths with widely varying geometries and P-T trajectories. Current models of arc magmatism require km-scale migration of fluids from the interface into mantle wedge magma source regions and implicit in these models is the transport of any fluids generated in the subducting slab along and ultimately through the subduction interface. Field and geochemical studies of high- and ultrahigh-pressure metamorphic rocks elucidate the sources and compositions of fluids in subduction interfaces and the interplay between deformation and fluid and mass transfer in this region. Recent geophysical studies of the subduction interface - its thickness, mineralogy, density, and H2O content - indicate that its rheology greatly influences the ways in which the subducting plate is coupled with the hanging wall. Field investigation of the magnitude and styles of fluid-rock interaction in metamorphic rocks representing "seismogenic zone" depths (and greater) yields insight regarding the roles of fluids and elevated fluid pore pressure in the weakening of plate interface rocks and the deformation leading to seismic events. From a geochemical perspective, the plate interface contributes to shaping the "slab signature" observed in studies of the composition of arc volcanic rocks. Understanding the production of fluids with hybridized chemical

Adhesive and invasive capacities of Edwarsiella tarda isolated from South American sea lion

OpenAIRE

Fernández, Araceli; Paz Villanueva, María; González, Mario; Fernández, Fabiola; Latif, Fadua; Flores, Sandra Nonier; Fernández, Heriberto

2014-01-01

Edwarsiella tarda is a zoonotic bacterium that can be isolated from humans, animals and the environment. Although E. tarda is primarily considered a fish pathogen, it is the only species of its genus considered to be pathogenic for humans as well. A survey of zoonotic intestinal bacteria in fresh feces from South American sea lions (SASL) Otaria flavescens, reported E. tarda as the most frequently isolated species. In this study, we used HEp-2 cells to establish in vitro the adherence and inv...

Imaging subducted slabs using seismic arrays in the Western Pacific

Science.gov (United States)

Bentham, H. L.; Rost, S.

2010-12-01

In recent years array seismology has been used extensively to image the small scale structure of the Earth. Such structure likely represents chemical heterogeneity and is therefore essential in our understanding of mantle convection and the composition of the Earth’s deep interior. As subduction is the main source of (re)introducing slab material into the Earth, it is of particular interest to track these heterogeneities. Resolving details of the composition and deformation of subducted lithosphere can help provide constraints on the subduction process, the composition of the mantle and mantle convection. This study uses seismic array techniques to map seismic heterogeneities associated with western Pacfic subduction zones, where a variety of slab geometries have been previously observed. Seismic energy arriving prior to the PP arrival was analysed at Eielson Array (ILAR), Alaska. More than 200 earthquakes were selected with Mw ≥ 6 and with epicentral distances of 90-110deg, giving a good coverage of the PP precursor (P*P) wavefield. Initial findings indicate that the observed P*P arrive out of plane and are likely a result of scattering. These scatterers are linked to the subduction of the Pacific Plate under the Philippine Sea in the Izu-Bonin and Mariana subduction zones. To enable efficient processing of large datasets, a robust automatic coherent (but unpredicted) arrival detector algorithm has been developed to select suitable precursors. Slowness and backazimuth were calculated for each precursor and were used in conjunction with P*P arrival times to back-raytrace the energy from the array to the scatterer location. Processing of the full dataset will help refine models regarding slab deformation as they descend into the mantle as well as unveiling the depth of their descent.

Building a risk-targeted regional seismic hazard model for South-East Asia

Science.gov (United States)

Woessner, J.; Nyst, M.; Seyhan, E.

2015-12-01

The last decade has tragically shown the social and economic vulnerability of countries in South-East Asia to earthquake hazard and risk. While many disaster mitigation programs and initiatives to improve societal earthquake resilience are under way with the focus on saving lives and livelihoods, the risk management sector is challenged to develop appropriate models to cope with the economic consequences and impact on the insurance business. We present the source model and ground motions model components suitable for a South-East Asia earthquake risk model covering Indonesia, Malaysia, the Philippines and Indochine countries. The source model builds upon refined modelling approaches to characterize 1) seismic activity from geologic and geodetic data on crustal faults and 2) along the interface of subduction zones and within the slabs and 3) earthquakes not occurring on mapped fault structures. We elaborate on building a self-consistent rate model for the hazardous crustal fault systems (e.g. Sumatra fault zone, Philippine fault zone) as well as the subduction zones, showcase some characteristics and sensitivities due to existing uncertainties in the rate and hazard space using a well selected suite of ground motion prediction equations. Finally, we analyze the source model by quantifying the contribution by source type (e.g., subduction zone, crustal fault) to typical risk metrics (e.g.,return period losses, average annual loss) and reviewing their relative impact on various lines of businesses.

The Tetramerium lineage (Acanthaceae: Justicieae) does not support the Pleistocene Arc hypothesis for South American seasonally dry forests.

Science.gov (United States)

Côrtes, Ana Luiza A; Rapini, Alessandro; Daniel, Thomas F

2015-06-01

The Tetramerium lineage (Acanthaceae) presents a striking ecological structuring in South America, with groups concentrated in moist forests or in seasonally dry forests. In this study, we investigate the circumscription and relationships of the South American genera as a basis for better understanding historic interactions between dry and moist biomes in the Neotropics. We dated the ancestral distribution of the Tetramerium lineage based on one nuclear and four plastid DNA regions. Maximum parsimony, maximum likelihood, and Bayesian inference analyses were performed for this study using 104 terminals. Phylogenetic divergences were dated using a relaxed molecular clock approach and ancestral distributions obtained from dispersal-vicariance analyses. The genera Pachystachys, Schaueria, and Thyrsacanthus are nonmonophyletic. A dry forest lineage dispersed from North America to South America and reached the southwestern part of the continent between the end of the Miocene and beginning of the Pleistocene. This period coincides with the segregation between Amazonian and Atlantic moist forests that established the geographic structure currently found in the group. The South American genera Pachystachys, Schaueria, and Thyrsacanthus need to be recircumscribed. The congruence among biogeographical events found for the Tetramerium lineage suggests that the dry forest centers currently dispersed throughout South America are relatively old remnants, probably isolated since the Neogene, much earlier than the Last Glacial Maximum postulated by the Pleistocene Arc hypothesis. In addition to exploring the Pleistocene Arc hypothesis, this research also informs evolution in a lineage with numerous geographically restricted and threatened species. © 2015 Botanical Society of America, Inc.

The Lithosphere-asthenosphere Boundary beneath the South Island of New Zealand

Science.gov (United States)

Hua, J.; Fischer, K. M.; Savage, M. K.

2017-12-01

Lithosphere-asthenosphere boundary (LAB) properties beneath the South Island of New Zealand have been imaged by Sp receiver function common-conversion point stacking. In this transpressional boundary between the Australian and Pacific plates, dextral offset on the Alpine fault and convergence have occurred for the past 20 My, with the Alpine fault now bounded by Australian plate subduction to the south and Pacific plate subduction to the north. This study takes advantage of the long-duration and high-density seismometer networks deployed on or near the South Island, especially 29 broadband stations of the New Zealand permanent seismic network (GeoNet). We obtained 24,980 individual receiver functions by extended-time multi-taper deconvolution, mapping to three-dimensional space using a Fresnel zone approximation. Pervasive strong positive Sp phases are observed in the LAB depth range indicated by surface wave tomography (Ball et al., 2015) and geochemical studies. These phases are interpreted as conversions from a velocity decrease across the LAB. In the central South Island, the LAB is observed to be deeper and broader to the west of the Alpine fault. The deeper LAB to the west of the Alpine fault is consistent with oceanic lithosphere attached to the Australian plate that was partially subducted while also translating parallel to the Alpine fault (e.g. Sutherland, 2000). However, models in which the Pacific lithosphere has been underthrust to the west past the Alpine fault cannot be ruled out. Further north, a zone of thin lithosphere with a strong and vertically localized LAB velocity gradient occurs to the west of the fault, juxtaposed against a region of anomalously weak LAB conversions to the east of the fault. This structure, similar to results of Sp imaging beneath the central segment of the San Andreas fault (Ford et al., 2014), also suggests that lithospheric blocks with contrasting LAB properties meet beneath the Alpine fault. The observed variations in

Diamond Growth in the Subduction Factory

Science.gov (United States)

Bureau, H.; Frost, D. J.; Bolfan-Casanova, N.; Leroy, C.; Estève, I.

2014-12-01

Natural diamonds are fabulous probes of the deep Earth Interior. They are the evidence of the deep storage of volatile elements, carbon at first, but also hydrogen and chlorine trapped as hydrous fluids in inclusions. The study of diamond growth processes in the lithosphere and mantle helps for our understanding of volatile elements cycling between deep reservoirs. We know now that inclusion-bearing diamonds similar to diamonds found in nature (i.e. polycrystalline, fibrous and coated diamonds) can grow in hydrous fluids or melts (Bureau et al., GCA 77, 202-214, 2012). Therefore, we propose that the best environment to promote such diamonds is the subduction factory, where highly hydrous fluids or melts are present. When oceanic plates are subducted in the lithosphere, they carry an oceanic crust soaked with seawater. While the slabs are traveling en route to the mantle, dehydration processes generate saline fluids highly concentrated in NaCl. In the present study we have experimentally shown that diamonds can grow from the saline fluids (up to 30 g/l NaCl in water) generated in subducted slabs. We have performed multi-anvil press experiments at 6-7 GPa and from 1300 to 1400°C during 6:00 hours to 30:00 hours. We observed large areas of new diamond grown in epitaxy on pure diamond seeds in salty hydrous carbonated melts, forming coated gems. The new rims are containing multi-component primary inclusions. Detailed characterizations of the diamonds and their inclusions have been performed and will be presented. These experimental results suggest that multi-component salty fluids of supercritical nature migrate with the slabs, down to the deep mantle. Such fluids may insure the first stage of the deep Earth's volatiles cycling (C, H, halogen elements) en route to the transition zone and the lower mantle. We suggest that the subduction factory may also be a diamond factory.

Subduction factory 1. Theoretical mineralogy, densities, seismic wave speeds, and H2O contents

Science.gov (United States)

Hacker, Bradley R.; Abers, Geoffrey A.; Peacock, Simon M.

2003-01-01

We present a new compilation of physical properties of minerals relevant to subduction zones and new phase diagrams for mid-ocean ridge basalt, lherzolite, depleted lherzolite, harzburgite, and serpentinite. We use these data to calculate H2O content, density and seismic wave speeds of subduction zone rocks. These calculations provide a new basis for evaluating the subduction factory, including (1) the presence of hydrous phases and the distribution of H2O within a subduction zone; (2) the densification of the subducting slab and resultant effects on measured gravity and slab shape; and (3) the variations in seismic wave speeds resulting from thermal and metamorphic processes at depth. In considering specific examples, we find that for ocean basins worldwide the lower oceanic crust is partially hydrated (measurements. Subducted hydrous crust in cold slabs can persist to several gigapascals at seismic velocities that are several percent slower than the surrounding mantle. Seismic velocities and VP/VS ratios indicate that mantle wedges locally reach 60-80% hydration.

Time-reversibility in seismic sequences: Application to the seismicity of Mexican subduction zone

Science.gov (United States)

Telesca, L.; Flores-Márquez, E. L.; Ramírez-Rojas, A.

2018-02-01

In this paper we investigate the time-reversibility of series associated with the seismicity of five seismic areas of the subduction zone beneath the Southwest Pacific Mexican coast, applying the horizontal visibility graph method to the series of earthquake magnitudes, interevent times, interdistances and magnitude increments. We applied the Kullback-Leibler divergence D that is a metric for quantifying the degree of time-irreversibility in time series. Our findings suggest that among the five seismic areas, Jalisco-Colima is characterized by time-reversibility in all the four seismic series. Our results are consistent with the peculiar seismo-tectonic characteristics of Jalisco-Colima, which is the closest to the Middle American Trench and belongs to the Mexican volcanic arc.

GPS-derived coupling estimates for the Central America subduction zone and volcanic arc faults: El Salvador, Honduras and Nicaragua

Science.gov (United States)

Correa-Mora, F.; DeMets, C.; Alvarado, D.; Turner, H. L.; Mattioli, G.; Hernandez, D.; Pullinger, C.; Rodriguez, M.; Tenorio, C.

2009-12-01

We invert GPS velocities from 32 sites in El Salvador, Honduras and Nicaragua to estimate the rate of long-term forearc motion and distributions of interseismic coupling across the Middle America subduction zone offshore from these countries and faults in the Salvadoran and Nicaraguan volcanic arcs. A 3-D finite element model is used to approximate the geometries of the subduction interface and strike-slip faults in the volcanic arc and determine the elastic response to coupling across these faults. The GPS velocities are best fit by a model in which the forearc moves 14-16 mmyr-1 and has coupling of 85-100 per cent across faults in the volcanic arc, in agreement with the high level of historic and recent earthquake activity in the volcanic arc. Our velocity inversion indicates that coupling across the potentially seismogenic areas of the subduction interface is remarkably weak, averaging no more than 3 per cent of the plate convergence rate and with only two poorly resolved patches where coupling might be higher along the 550-km-long segment we modelled. Our geodetic evidence for weak subduction coupling disagrees with a seismically derived coupling estimate of 60 +/- 10 per cent from a published analysis of earthquake damage back to 1690, but agrees with three other seismologic studies that infer weak subduction coupling from 20th century earthquakes. Most large historical earthquakes offshore from El Salvador and western Nicaragua may therefore have been intraslab normal faulting events similar to the Mw 7.3 1982 and Mw 7.7 2001 earthquakes offshore from El Salvador. Alternatively, the degree of coupling might vary with time. The evidence for weak coupling indirectly supports a recently published hypothesis that much of the Middle American forearc is escaping to the west or northwest away from the Cocos Ridge collision zone in Costa Rica. Such a hypothesis is particularly attractive for El Salvador, where there is little or no convergence obliquity to drive the

How long-term dynamics of sediment subduction controls short-term dynamics of seismicity

Science.gov (United States)

Brizzi, S.; van Zelst, I.; van Dinther, Y.; Funiciello, F.; Corbi, F.

2017-12-01

Most of the world's greatest earthquakes occur along the subduction megathrust. Weak and porous sediments have been suggested to homogenize the plate interface and thereby promote lateral rupture propagation and great earthquakes. However, the importance of sediment thickness, let alone their physical role, is not yet unequivocally established. Based on a multivariate statistical analysis of a global database of 62 subduction segments, we confirm that sediment thickness is one of the key parameters controlling the maximum magnitude a megathrust can generate. Moreover, Monte Carlo simulations highlighted that the occurrence of great earthquakes on sediment-rich subduction segments is very unlikely (p-value≪0.05) related to pure chance. To understand how sediments in the subduction channel regulate earthquake size, this study extends and demystifies multivariate, spatiotemporally limited data through numerical modeling. We use the 2D Seismo-Thermo-Mechanical modeling approach to simulate both the long- and short-term dynamics of subduction and related seismogenesis (van Dinther et al., JGR, 2013). These models solve for the conservation of mass, momentum and energy using a visco-elasto-plastic rheology with rate-dependent friction. Results show that subducted sediments have a strong influence on the long-term evolution of the convergent margin. Increasing the sediment thickness on the incoming plate from 0 to 6 km causes a decrease of slab dip from 23° to 10°. This, in addition to increased radiogenic heating, extends isotherms, thereby widening the seismogenic portion of the megathrust from 80 to 150 km. Consequently, over tens of thousands of years, we observe that the maximum moment magnitude of megathrust earthquakes increases from 8.2 to 9.2 for these shallower and warmer interfaces. In addition, we observe more and larger splay faults, which could enhance vertical seafloor displacements. These results highlight the primary role of subducted sediments in

Seismic evidence for overpressured subducted oceanic crust and megathrust fault sealing.

Science.gov (United States)

Audet, Pascal; Bostock, Michael G; Christensen, Nikolas I; Peacock, Simon M

2009-01-01

Water and hydrous minerals play a key part in geodynamic processes at subduction zones by weakening the plate boundary, aiding slip and permitting subduction-and indeed plate tectonics-to occur. The seismological signature of water within the forearc mantle wedge is evident in anomalies with low seismic shear velocity marking serpentinization. However, seismological observations bearing on the presence of water within the subducting plate itself are less well documented. Here we use converted teleseismic waves to obtain observations of anomalously high Poisson's ratios within the subducted oceanic crust from the Cascadia continental margin to its intersection with forearc mantle. On the basis of pressure, temperature and compositional considerations, the elevated Poisson's ratios indicate that water is pervasively present in fluid form at pore pressures near lithostatic values. Combined with observations of a strong negative velocity contrast at the top of the oceanic crust, our results imply that the megathrust is a low-permeability boundary. The transition from a low- to high-permeability plate interface downdip into the mantle wedge is explained by hydrofracturing of the seal by volume changes across the interface caused by the onset of crustal eclogitization and mantle serpentinization. These results may have important implications for our understanding of seismogenesis, subduction zone structure and the mechanism of episodic tremor and slip.

a New Animation of Subduction Processes for Undergraduates

Science.gov (United States)

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

2015-12-01

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

Natural Infection of the South American Tapir ( Tapirus terrestris ) by Theileria equi.

Science.gov (United States)

Da Silveira, Alexandre Welzel; De Oliveira, Gustavo Gomes; Menezes Santos, Leandro; da Silva Azuaga, Lucas Bezerra; Macedo Coutinho, Claudia Regina; Echeverria, Jessica Teles; Antunes, Tamires Ramborger; do Nascimento Ramos, Carlos Alberto; Izabel de Souza, Alda

2017-04-01

Theileria equi is a tick-borne piroplasm considered endemic in equines in Brazil. The cohabitation of domestic and wild animals in areas of extensive cattle breeding favors the close contact between different species and the sharing of vectors and, consequently, pathogens. We report the natural infection of a young South American tapir ( Tapirus terrestris ) by T. equi in Mato Grosso do Sul, Brazil. Although it was not possible to associate the clinical and hematologic status of the animal with the infection by the protozoan parasite, our report represents an alert on the sharing of pathogens between domestic and wild animals.

Scattering beneath Western Pacific subduction zones: evidence for oceanic crust in the mid-mantle

Science.gov (United States)

Bentham, H. L. M.; Rost, S.

2014-06-01

Small-scale heterogeneities in the mantle can give important insight into the dynamics and composition of the Earth's interior. Here, we analyse seismic energy found as precursors to PP, which is scattered off small-scale heterogeneities related to subduction zones in the upper and mid-mantle. We use data from shallow earthquakes (less than 100 km depth) in the epicentral distance range of 90°-110° and use array methods to study a 100 s window prior to the PP arrival. Our analysis focuses on energy arriving off the great circle path between source and receiver. We select coherent arrivals automatically, based on a semblance weighted beampower spectrum, maximizing the selection of weak amplitude arrivals. Assuming single P-to-P scattering and using the directivity information from array processing, we locate the scattering origin by ray tracing through a 1-D velocity model. Using data from the small-aperture Eielson Array (ILAR) in Alaska, we are able to image structure related to heterogeneities in western Pacific subduction zones. We find evidence for ˜300 small-scale heterogeneities in the region around the present-day Japan, Izu-Bonin, Mariana and West Philippine subduction zones. Most of the detected heterogeneities are located in the crust and upper mantle, but 6 per cent of scatterers are located deeper than 600 km. Scatterers in the transition zone correlate well with edges of fast features in tomographic images and subducted slab contours derived from slab seismicity. We locate deeper scatterers beneath the Izu-Bonin/Mariana subduction zones, which outline a steeply dipping pseudo-planar feature to 1480 km depth, and beneath the ancient (84-144 Ma) Indonesian subduction trench down to 1880 km depth. We image the remnants of subducted crustal material, likely the underside reflection of the subducted Moho. The presence of deep scatterers related to past and present subduction provides evidence that the subducted crust does descend into the lower mantle at

AIRSAR South American deployment: Operation plan, version 3.0

Science.gov (United States)

Kobrick, M.

1993-01-01

The United States National Aeronautics and Space Administration (NASA) and the Brazilian Commission for Space Activities (COBAE) are undertaking a joint experiment involving NASA's DC-8 research aircraft and the Airborne Synthetic Aperture Radar (AIRSAR) system during late May and June 1993. The research areas motivating these activities are: (1) fundamental research in the role of soils, vegetation, and hydrology in the global carbon cycle; and (2) in cooperation with South American scientists, airborne remote sensing research for the upcoming NASA Spaceborne Imaging Radar (SIR)-C/X-SAR flights on the Space Shuttle. A flight schedule and plans for the deployment that were developed are included. Maps of the site locations and schematic indications of flight routes and dates, plots showing swath locations derived from the flight requests and generated by flight planning software, and, most importantly, a calendar showing which sites will be imaged each day are included.

Sources of Magmatic Volatiles Discharging from Subduction Zone Volcanoes

Science.gov (United States)

Fischer, T.

2001-05-01

Subduction zones are locations of extensive element transfer from the Earth's mantle to the atmosphere and hydrosphere. This element transfer is significant because it can, in some fashion, instigate melt production in the mantle wedge. Aqueous fluids are thought to be the major agent of element transfer during the subduction zone process. Volatile discharges from passively degassing subduction zone volcanoes should in principle, provide some information on the ultimate source of magmatic volatiles in terms of the mantle, the crust and the subducting slab. The overall flux of volatiles from degassing volcanoes should be balanced by the amount of volatiles released from the mantle wedge, the slab and the crust. Kudryavy Volcano, Kurile Islands, has been passively degassing at 900C fumarole temperatures for at least 40 years. Extensive gas sampling at this basaltic andesite cone and application of CO2/3He, N2/3He systematics in combination with C and N- isotopes indicates that 80% of the CO2 and approximately 60% of the N 2 are contributed from a sedimentary source. The mantle wedge contribution for both volatiles is, with 12% and 17% less significant. Direct volatile flux measurements from the volcano using the COSPEC technique in combination with direct gas sampling allows for the calculation of the 3He flux from the volcano. Since 3He is mainly released from the astenospheric mantle, the amount of mantle supplying the 3He flux can be determined if initial He concentrations of the mantle melts are known. The non-mantle flux of CO2 and N2 can be calculated in similar fashion. The amount of non-mantle CO2 and N2 discharging from Kudryavy is balanced by the amount of CO2 and N2 subducted below Kudryavy assuming a zone of melting constrained by the average spacing of the volcanoes along the Kurile arc. The volatile budget for Kudryavy is balanced because the volatile flux from the volcano is relatively small (75 t/day (416 Mmol/a) SO2, 360 Mmol/a of non-mantle CO2 and

Coalescent Simulation and Paleodistribution Modeling for Tabebuia rosealba Do Not Support South American Dry Forest Refugia Hypothesis.

Directory of Open Access Journals (Sweden)

Warita Alves de Melo

Full Text Available Studies based on contemporary plant occurrences and pollen fossil records have proposed that the current disjunct distribution of seasonally dry tropical forests (SDTFs across South America is the result of fragmentation of a formerly widespread and continuously distributed dry forest during the arid climatic conditions associated with the Last Glacial Maximum (LGM, which is known as the modern-day dry forest refugia hypothesis. We studied the demographic history of Tabebuia rosealba (Bignoniaceae to understand the disjunct geographic distribution of South American SDTFs based on statistical phylogeography and ecological niche modeling (ENM. We specifically tested the dry forest refugia hypothesis; i.e., if the multiple and isolated patches of SDTFs are current climatic relicts of a widespread and continuously distributed dry forest during the LGM. We sampled 235 individuals across 18 populations in Central Brazil and analyzed the polymorphisms at chloroplast (trnS-trnG, psbA-trnH and ycf6-trnC intergenic spacers and nuclear (ITS nrDNA genomes. We performed coalescence simulations of alternative hypotheses under demographic expectations from two a priori biogeographic hypotheses (1. the Pleistocene Arc hypothesis and, 2. a range shift to Amazon Basin and other two demographic expectances predicted by ENMs (3. expansion throughout the Neotropical South America, including Amazon Basin, and 4. retraction during the LGM. Phylogenetic analyses based on median-joining network showed haplotype sharing among populations with evidence of incomplete lineage sorting. Coalescent analyses showed smaller effective population sizes for T. roseoalba during the LGM compared to the present-day. Simulations and ENM also showed that its current spatial pattern of genetic diversity is most likely due to a scenario of range retraction during the LGM instead of the fragmentation from a once extensive and largely contiguous SDTF across South America, not supporting the

Coalescent Simulation and Paleodistribution Modeling for Tabebuia rosealba Do Not Support South American Dry Forest Refugia Hypothesis.

Science.gov (United States)

de Melo, Warita Alves; Lima-Ribeiro, Matheus S; Terribile, Levi Carina; Collevatti, Rosane G

2016-01-01

Studies based on contemporary plant occurrences and pollen fossil records have proposed that the current disjunct distribution of seasonally dry tropical forests (SDTFs) across South America is the result of fragmentation of a formerly widespread and continuously distributed dry forest during the arid climatic conditions associated with the Last Glacial Maximum (LGM), which is known as the modern-day dry forest refugia hypothesis. We studied the demographic history of Tabebuia rosealba (Bignoniaceae) to understand the disjunct geographic distribution of South American SDTFs based on statistical phylogeography and ecological niche modeling (ENM). We specifically tested the dry forest refugia hypothesis; i.e., if the multiple and isolated patches of SDTFs are current climatic relicts of a widespread and continuously distributed dry forest during the LGM. We sampled 235 individuals across 18 populations in Central Brazil and analyzed the polymorphisms at chloroplast (trnS-trnG, psbA-trnH and ycf6-trnC intergenic spacers) and nuclear (ITS nrDNA) genomes. We performed coalescence simulations of alternative hypotheses under demographic expectations from two a priori biogeographic hypotheses (1. the Pleistocene Arc hypothesis and, 2. a range shift to Amazon Basin) and other two demographic expectances predicted by ENMs (3. expansion throughout the Neotropical South America, including Amazon Basin, and 4. retraction during the LGM). Phylogenetic analyses based on median-joining network showed haplotype sharing among populations with evidence of incomplete lineage sorting. Coalescent analyses showed smaller effective population sizes for T. roseoalba during the LGM compared to the present-day. Simulations and ENM also showed that its current spatial pattern of genetic diversity is most likely due to a scenario of range retraction during the LGM instead of the fragmentation from a once extensive and largely contiguous SDTF across South America, not supporting the South

Antiviral activity of some South American medicinal plants.

Science.gov (United States)

Abad, M J; Bermejo, P; Sanchez Palomino, S; Chiriboga, X; Carrasco, L

1999-03-01

Folk medicinal plants are potential sources of useful therapeutic compounds including some with antiviral activities. Extracts prepared from 10 South American medicinal plants (Baccharis trinervis, Baccharis teindalensis, Eupatorium articulatum, Eupatorium glutinosum, Tagetes pusilla, Neurolaena lobata, Conyza floribunda, Phytolacca bogotensis, Phytolacca rivinoides and Heisteria acuminata) were screened for in vitro antiviral activity against herpes simplex type I (HSV-1), vesicular stomatitis virus (VSV) and poliovirus type 1. The most potent inhibition was observed with an aqueous extract of B. trinervis, which inhibited HSV-1 replication by 100% at 50-200 micrograms/mL, without showing cytotoxic effects. Good activities were also found with the ethanol extract of H. acuminata and the aqueous extract of E. articulatum, which exhibited antiviral effects against both DNA and RNA viruses (HSV-1 and VSV, respectively) at 125-250 micrograms/mL. The aqueous extracts of T. pusilla (100-250 micrograms/mL), B. teindalensis (50-125 micrograms/mL) and E. glutinosum (50-125 micrograms/mL) also inhibited the replication of VSV, but none of the extracts tested had any effect on poliovirus replication.

Hot subduction: Magmatism along the Hunter Ridge, SW Pacific

International Nuclear Information System (INIS)

Crawford, A.J.; Verbeeten, A.; Danyushevsky, L.V.; Sigurdsson, I.A.; Maillet, P.; Monzier, M.

1997-01-01

The Hunter 'fracture zone' is generally regarded as a transform plate boundary linking the oppositely dipping Tongan and Vanuatu subduction systems. Dredging along the Hunter Ridge and sampling of its northernmost extent, exposed as the island of Kadavu in Fiji, has yielded a diversity of magmatic suites, including arc tholeiites and high-Ca boninites, high-Mg lavas with some affinities to boninites and some affinities to adakites, and true adakitic lavas associated with remarkable low-Fe, high-Na basalts with 8-16 ppm Nb (herein high-Nb basalts). Lavas which show clear evidence of slab melt involvement in their petrogenesis occur at either end of the Hunter Ridge, whereas the arc tholeiites and high-Ca boninites appear to be restricted to the south central part of the ridge. Mineralogical and whole rock geochemical data for each of these suites are summarized, and a tectono-magmatic model for their genesis and distribution is suggested. Trace element features and radiogenic isotope data for the Hunter Ridge lavas indicate compositions analogue to Pacific MORB-like mantle

Observations of the F-region ionospheric irregularities in the South American sector during the October 2003 "Halloween Storms"

Directory of Open Access Journals (Sweden)

Y. Sahai

2009-12-01

Full Text Available The response of the ionospheric F-region in the South American sector during the super geomagnetic storms on 29 and 30 October 2003 is studied in the present investigation. In this paper, we present ionospheric sounding observations during the period 29–31 October 2003 obtained at Palmas (a near equatorial location and Sao Jose dos Campos (a location under the southern crest of the equatorial ionospheric anomaly, Brazil, along with observations during the period 27–31 October 2003 from a chain of GPS stations covering the South American sector from Imperatriz, Brazil, to Rio Grande, Argentina. Also, complementary observations that include sequences of all-sky images of the OI 777.4 and 630.0 nm emissions observed at El Leoncito, Argentina, on the nights of 28–29 (geomagnetically quiet night and 29–30 (geomagnetically disturbed night October 2003, and ion densities observed in the South American sector by the DMSP F13, F14 and F15 satellites orbiting at about 800 km on 29 and 30 October 2003 are presented. In addition, global TEC maps derived from GPS observations collected from the global GPS network of International GPS Service (IGS are presented, showing widespread and drastic TEC changes during the different phases of the geomagnetic disturbances. The observations indicate that the equatorial ionospheric irregularities or plasma bubbles extend to the Argentinean station Rawson (geom. Lat. 33.1° S and map at the magnetic equator at an altitude of about 2500 km.

Factors Associated with Toothache among African American Adolescents Living in Rural South Carolina

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Wiegand, Ryan E.; Hill, Elizabeth G.; Magruder, Kathryn M.; Slate, Elizabeth H.; Salinas, Carlos F.; London, Steven D.

2012-01-01

Objective The aim of this study is to explore behavioral factors associated with toothache among African American adolescents living in rural South Carolina. Methods Using a self-administered questionnaire, data were collected on toothache experience in the past 12 months, oral hygiene behavior, dental care utilization, and cariogenic snack and non-diet soft drink consumption in a convenience sample of 156 African American adolescents aged 10-18 years old living in rural South Carolina. Univariable and multivariable logistic regression analyses were used to assess the associations between reported toothache experience and socio-demographic variables, oral health behavior, and snack consumption. Results Thirty-four percent of adolescents reported having toothache in the past 12 months. In univariable modeling, age, dental visit in the last two years, quantity and frequency of cariogenic snack consumption, and quantity of non-diet soft drink consumption were each significantly associated with experiencing toothache in the past 12 months (all p-values cariogenic snacks, and number of cans of non-diet soft drink consumed during the weekend significantly increased the odds of experiencing toothache in the past 12 months (all p-values ≤ 0.01). Conclusion Findings indicate age, frequent consumption of cariogenic snacks and number of cans of non-diet soft drinks are related to toothache in this group. Public policy implications related to selling cariogenic snacks and soft drink that targeting children and adolescents especially those from low income families are discussed. PMID:22085328

Initiation of extension in South China continental margin during the active-passive margin transition: kinematic and thermochronological constraints

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ZUO, Xuran; CHAN, Lung

2015-04-01

The southern South China Block is characterized by a widespread magmatic belt, prominent NE-striking fault zones and numerous rifted basins filled by Cretaceous-Eocene sediments. The geology denotes a transition from an active to a passive margin, which led to rapid modifications of crustal stress configuration and reactivation of older faults in this area. In this study, we used zircon fission-track dating (ZFT) and numerical modeling to examine the timing and kinematics of the active-passive margin transition. Our ZFT results on granitic plutons in the SW Cathaysia Block show two episodes of exhumation of the granitic plutons. The first episode, occurring during 170 Ma - 120 Ma, affected local parts of the Nanling Range. The second episode, a more regional exhumation event, occurred during 115 Ma - 70 Ma. Numerical geodynamic modeling was conducted to simulate the subduction between the paleo-Pacific plate and the South China Block. The modeling results could explain the observation based on ZFT data that exhumation of the granite-dominant Nanling Range occurred at an earlier time than the gneiss-dominant Yunkai Terrane. In addition to the difference in geology between Yunkai and Nanling, the heating from Jurassic-Early Cretaceous magmatism in the Nanling Range may have softened the upper crust, causing the area to exhume more readily. Numerical modeling results also indicate that (1) high slab dip angle, high geothermal gradient of lithosphere and low convergence velocity favor the subduction process and the reversal of crustal stress state from compression to extension in the upper plate; (2) the late Mesozoic magmatism in South China was probably caused by a slab roll-back; and (3) crustal extension could have occurred prior to the cessation of plate subduction. The inversion of stress regime in the continental crust from compression to crustal extension has shed light on the geological condition producing the red bed basins during Late Cretaceous

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

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

2013-12-01

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

Nonlinear viscoplasticity in ASPECT: benchmarking and applications to subduction

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Glerum, Anne; Thieulot, Cedric; Fraters, Menno; Blom, Constantijn; Spakman, Wim

2018-03-01

ASPECT (Advanced Solver for Problems in Earth's ConvecTion) is a massively parallel finite element code originally designed for modeling thermal convection in the mantle with a Newtonian rheology. The code is characterized by modern numerical methods, high-performance parallelism and extensibility. This last characteristic is illustrated in this work: we have extended the use of ASPECT from global thermal convection modeling to upper-mantle-scale applications of subduction.Subduction modeling generally requires the tracking of multiple materials with different properties and with nonlinear viscous and viscoplastic rheologies. To this end, we implemented a frictional plasticity criterion that is combined with a viscous diffusion and dislocation creep rheology. Because ASPECT uses compositional fields to represent different materials, all material parameters are made dependent on a user-specified number of fields.The goal of this paper is primarily to describe and verify our implementations of complex, multi-material rheology by reproducing the results of four well-known two-dimensional benchmarks: the indentor benchmark, the brick experiment, the sandbox experiment and the slab detachment benchmark. Furthermore, we aim to provide hands-on examples for prospective users by demonstrating the use of multi-material viscoplasticity with three-dimensional, thermomechanical models of oceanic subduction, putting ASPECT on the map as a community code for high-resolution, nonlinear rheology subduction modeling.

Central plane of the ring current responsible for geomagnetic disturbance in the South-American region

International Nuclear Information System (INIS)

Kane, R.P.; Trivedi, N.B.

1981-01-01

Using hourly values of H, D, Z from a network of South American stations, operative during the IGY-IGC, the latitude dependence of storm effects was studied. It was found that whereas there were considerable distortions due to conductivity anomalies under the Andes, there was also evidence of latitudinal excursions of overhead current system, not only from storm to storm but even during the course of the same storm

Seismic attenuation structure beneath Nazca Plate subduction zone in southern Peru

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Jang, H.; Kim, Y.; Clayton, R. W.

2017-12-01

We estimate seismic attenuation in terms of quality factors, QP and QS using P and S phases, respectively, beneath Nazca Plate subduction zone between 10°S and 18.5°S latitude in southern Peru. We first relocate 298 earthquakes with magnitude ranges of 4.0-6.5 and depth ranges of 20-280 km. We measure t*, which is an integrated attenuation through the seismic raypath between the regional earthquakes and stations. The measured t* are inverted to construct three-dimensional attenuation structures of southern Peru. Checkerboard test results for both QP and QS structures ensure good resolution in the slab-dip transition zone between flat and normal slab subduction down to a depth of 200 km. Both QP and QS results show higher attenuation continued down to a depth of 50 km beneath volcanic arc and also beneath the Quimsachata volcano, the northernmost young volcano, located far east of the main volcanic front. We also observe high attenuation in mantle wedge especially beneath the normal subduction region in both QP and QS (100-130 in QP and 100-125 in QS) and slightly higher QP and QS beneath the flat-subduction and slab-dip transition regions. We plan to relate measured attenuation in the mantle wedge to material properties such as viscosity to understand the subduction zone dynamics.

Study of changes in the lineament structure, caused by earthquakes in South America by applying the lineament analysis to the Aster (Terra) satellite data

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Arellano-Baeza, A. A.; Zverev, A. T.; Malinnikov, V. A.

The region between Southern Peru and Northern Chile is one of the most seismically and volcanically active regions in South America. This is caused by a constant subduction of the South American Plate, converging with the Nazca Plate in the extreme North of Chile. We used the 15 and 30 m resolution satellite images, provided by the ASTER (VNIR and SWIR) instrument onboard the Terra satellite to study changes in the geological faults close to earthquake epicenters in southern Peru. Visible and infrared spectral bands were analysed using “The Lineament Extraction and Stripes Statistic Analysis” (LESSA) software package to examine changes in the lineament features and stripe density fields caused by seismic activity. We used the satellite images 128 and 48 days before and 73 days after a 5.2 Richter scale magnitude earthquake. The fact that the seasonal variations in the South of Peru and North of Chile are very small, and the vegetation is very limited, allowed us to establish substantial changes in the lineament and the stripe density field features. We develop a methodology that allows to evaluate the seismic risk in this region for the future.

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

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

2017-04-01

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

On the use of the South-American neutron monitors

Energy Technology Data Exchange (ETDEWEB)

Cordaro, E. G. [Santiago de Chile Univ., Santiago de Chile (Chile). Facultad de Ciencias Fisicas y Matematicas, Dept. de Fisica, Lewis Research Center; Storini, M. [Consiglio Nazionale delle Ricerche, Istituto di Fisica dello Spazio Interplanetario, Rome (Italy); Rome Univ. Tre, Rome (Italy). Dipt. di Fisica, Raggi Cosmici

2001-10-01

Cosmic ray scientific community deserves special attention to the Chacaltaya site for its over 5 km altitude. In this site, a neutron monitor of the IGY type operated from 1960 to 1969, and the one of the NM-64 type since 1966 (16.31{sup 0}S, 291.85{sup 0}E, height: about 5200 m a.s.l.). It was discussed the relevance of such kind of detector when it is integrated with the other South-American neutron monitors: a) LARC (62.20{sup 0}S, 301.04{sup 0}E, height: 40 m a.s.l., King George Island, Antarctica; operating since 1991); b) Los Cerrillos (33.45{sup 0}S, 289.40{sup 0}E, height: 570 m a. s. l., Santiago, Chile; to be installed in the near future); c) Huancayo (12.03{sup 0}S, 284.67{sup 0}E, height: 3400 m a.s.l., Huancayo, Peru; hoping to recover its acquired data).

Dinosaur speed demon: the caudal musculature of Carnotaurus sastrei and implications for the evolution of South American abelisaurids.

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W Scott Persons

Full Text Available In the South American abelisaurids Carnotaurus sastrei, Aucasaurus garridoi, and, to a lesser extent Skorpiovenator bustingorryi, the anterior caudal ribs project at a high dorsolateral inclination and have interlocking lateral tips. This unique morphology facilitated the expansion of the caudal hypaxial musculature at the expense of the epaxial musculature. Distinct ridges on the ventrolateral surfaces of the caudal ribs of Aucasaurus garridoi are interpreted as attachment scars from the intra caudofemoralis/ilio-ischiocaudalis septa, and confirm that the M. caudofemoralis of advanced South American abelisaurids originated from a portion of the caudal ribs. Digital muscle models indicate that, relative to its overall body size, Carnotaurus sastrei had a substantially larger M. caudofemoralis than any other theropod yet studied. In most non-avian theropods, as in many extant sauropsids, the M. caudofemoralis served as the primary femoral retractor muscle during the locomotive power stroke. This large investment in the M. caudofemoralis suggests that Carnotaurus sastrei had the potential for great cursorial abilities, particularly short-burst sprinting. However, the tightly interlocking morphology of the anterior caudal vertebrae implies a reduced ability to make tight turns. Examination of these vertebral traits in evolutionary context reveals a progressive sequence of increasing caudofemoral mass and tail rigidity among the Abelisauridae of South America.

Magnetotelluric Investigation of the South Aegean Volcanic Arc, Greece

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Kalisperi, Despina; Romano, Gerardo; Smirnov, Maxim; Kouli, Maria; Perrone, Angela; Makris, John P.; Vallianatos, Filippos

2014-05-01

The South Aegean Volcanic Arc (SAVA) is a chain of volcanic islands in the South Aegean resulting from the subduction of the African tectonic plate beneath the Eurasian plate. It extends from Methana, northwest, to the Island of Nisyros southeast (450 km total length). SAVA comprises a series of dormant and historically active volcanoes, with the most prominent to be Aegina, Methana, Milos, Santorini, Kolumbo, Kos and Nisyros. The aim of the ongoing research project "MagnetoTellurics in studying Geodynamics of the hEllenic ARc (MT-GEAR)" is to contribute to the investigation of the geoelectric structure of Southern Aegean, and particularly to attempt to image the Hellenic Subduction Zone. In this context, onshore magnetotelluric (MT) measurements were recently carried out on the central and eastern part of SAVA (Milos, Santorini, Nisyros and Kos Islands). Data were collected using two MT systems running simultaneously plus a remote reference station installed in Omalos plateau (Western Crete). Robust MT data analysis of the broad-band MT soundings and the resulting model of the conductivity structure of the South Aegean Volcanic Arc is presented. The research is co-funded by the European Social Fund (ESF) and National Resources under the Operational Programme 'Education and Lifelong Learning (EdLL) within the context of the Action 'Supporting Postdoctoral Researchers' in the framework of the project title "MagnetoTellurics in studying Geodynamics of the hEllenic ARc (MT-GEAR)".

Source and fractionation controls on subduction-related plutons and dike swarms in southern Patagonia (Torres del Paine area) and the low Nb/Ta of upper crustal igneous rocks

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Müntener, Othmar; Ewing, Tanya; Baumgartner, Lukas P.; Manzini, Mélina; Roux, Thibaud; Pellaud, Pierre; Allemann, Luc

2018-05-01

The subduction system in southern Patagonia provides direct evidence for the variability of the position of an active continental arc with respect to the subducting plate through time, but the consequences on the arc magmatic record are less well studied. Here we present a geochemical and geochronological study on small plutons and dykes from the upper crust of the southern Patagonian Andes at 51°S, which formed as a result of the subduction of the Nazca and Antarctic plates beneath the South American continent. In situ U-Pb geochronology on zircons and bulk rock geochemical data of plutonic and dyke rocks are used to constrain the magmatic evolution of the retro-arc over the last 30 Ma. We demonstrate that these combined U-Pb and geochemical data for magmatic rocks track the temporal and spatial migration of the active arc, and associated retro-arc magmatism. Our dataset indicates that the rear-arc area is characterized by small volumes of alkaline basaltic magmas at 29-30 Ma that are characterized by low La/Nb and Th/Nb ratios with negligible arc signatures. Subsequent progressive eastward migration of the active arc culminated with the emplacement of calc-alkaline plutons and dikes 17-16 Ma with elevated La/Nb and Th/Nb ratios and typical subduction signatures constraining the easternmost position of the southern Patagonian batholith at that time. Geochemical data on the post-16 Ma igneous rocks including the Torres del Paine laccolith indicate an evolution to transitional K-rich calc-alkaline magmatism at 12.5 ± 0.2 Ma. We show that trace element ratios such as Nb/Ta and Dy/Yb systematically decrease with increasing SiO2, for both the 17-16 Ma calc-alkaline and the 12-13 Ma K-rich transitional magmatism. In contrast, Th/Nb and La/Nb monitor the changes in the source composition of these magmas. We suggest that the transition from the common calc-alkaline to K-rich transitional magmatism involves a change in the source component, while the trace element ratios

Imaging Shear Strength Along Subduction Faults

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Bletery, Quentin; Thomas, Amanda M.; Rempel, Alan W.; Hardebeck, Jeanne L.

2017-11-01

Subduction faults accumulate stress during long periods of time and release this stress suddenly, during earthquakes, when it reaches a threshold. This threshold, the shear strength, controls the occurrence and magnitude of earthquakes. We consider a 3-D model to derive an analytical expression for how the shear strength depends on the fault geometry, the convergence obliquity, frictional properties, and the stress field orientation. We then use estimates of these different parameters in Japan to infer the distribution of shear strength along a subduction fault. We show that the 2011 Mw9.0 Tohoku earthquake ruptured a fault portion characterized by unusually small variations in static shear strength. This observation is consistent with the hypothesis that large earthquakes preferentially rupture regions with relatively homogeneous shear strength. With increasing constraints on the different parameters at play, our approach could, in the future, help identify favorable locations for large earthquakes.

Imaging shear strength along subduction faults

Science.gov (United States)

Bletery, Quentin; Thomas, Amanda M.; Rempel, Alan W.; Hardebeck, Jeanne L.

2017-01-01

Subduction faults accumulate stress during long periods of time and release this stress suddenly, during earthquakes, when it reaches a threshold. This threshold, the shear strength, controls the occurrence and magnitude of earthquakes. We consider a 3-D model to derive an analytical expression for how the shear strength depends on the fault geometry, the convergence obliquity, frictional properties, and the stress field orientation. We then use estimates of these different parameters in Japan to infer the distribution of shear strength along a subduction fault. We show that the 2011 Mw9.0 Tohoku earthquake ruptured a fault portion characterized by unusually small variations in static shear strength. This observation is consistent with the hypothesis that large earthquakes preferentially rupture regions with relatively homogeneous shear strength. With increasing constraints on the different parameters at play, our approach could, in the future, help identify favorable locations for large earthquakes.

Subduction in the Subtropical Gyre: Seasoar Cruises Data Report

Science.gov (United States)

1995-09-01

Julie Pallant , Frank Bahr, Terrence Joyce, Jerome Dean, James R. Luyten & Performing Organization Rept No. WHOI-95- 13 IL Performing Organization Name...AD-A28 6 861 WHOI-95-13 Woods Hole x Oceanc grapbic Ifliotitutionf de Subduction in the Subtropical Gyre: Seasoar Cruises Data Report by Julie S. •P...unlimiled. =Tfl QUALuTr =S) ij Ai Si 4 ;•IIII.. " - II •r * 9 9 * 11S 0 WIHOI-95-13 Subduction in the Subtropical Gyre: Seasoar Cruises Data Report by 0 Julie

Evolution of naturally occurring 5'non-coding region variants of Hepatitis C virus in human populations of the South American region

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García-Aguirre Laura

2007-08-01

Full Text Available Abstract Background Hepatitis C virus (HCV has been the subject of intense research and clinical investigation as its major role in human disease has emerged. Previous and recent studies have suggested a diversification of type 1 HCV in the South American region. The degree of genetic variation among HCV strains circulating in Bolivia and Colombia is currently unknown. In order to get insight into these matters, we performed a phylogenetic analysis of HCV 5' non-coding region (5'NCR sequences from strains isolated in Bolivia, Colombia and Uruguay, as well as available comparable sequences of HCV strains isolated in South America. Methods Phylogenetic tree analysis was performed using the neighbor-joining method under a matrix of genetic distances established under the Kimura-two parameter model. Signature pattern analysis, which identifies particular sites in nucleic acid alignments of variable sequences that are distinctly representative relative to a background set, was performed using the method of Korber & Myers, as implemented in the VESPA program. Prediction of RNA secondary structures was done by the method of Zuker & Turner, as implemented in the mfold program. Results Phylogenetic tree analysis of HCV strains isolated in the South American region revealed the presence of a distinct genetic lineage inside genotype 1. Signature pattern analysis revealed that the presence of this lineage is consistent with the presence of a sequence signature in the 5'NCR of HCV strains isolated in South America. Comparisons of these results with the ones found for Europe or North America revealed that this sequence signature is characteristic of the South American region. Conclusion Phylogentic analysis revealed the presence of a sequence signature in the 5'NCR of type 1 HCV strains isolated in South America. This signature is frequent enough in type 1 HCV populations circulating South America to be detected in a phylogenetic tree analysis as a distinct

The distribution and uranium content characteristics of Indosinian granite in South China

International Nuclear Information System (INIS)

Sun Wenliang; Zhang Zhuo; Chen Wenwen; Chen Lulu; Xu Wenzheng

2014-01-01

In recent years, more and more Indosinian granite plutons has been found in South China, so some new ideas about the granity were proposed by scholars. The Indosinian granite in South China distributed in lineshape, and is controlled by some regional faults. Its formation was mainly related to geodynamic setting which began in the late Permian (about 256 Ma) by the subduction of the ancient Pacific Plate to the Eurasia. The average uranium content of Indosinian granite is 10.34ppm, much higher than the average value of world's acid rock. There occurs some couplings between the distribution of the Indosinian granite plutons and uranium mineralization belt in South China. So the Indosinian granite in South China may act as important uranium sources for the mineralization. (authors)

What controls intermediate depth seismicity in subduction zones?

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Florez, M. A.; Prieto, G. A.

2017-12-01

Intermediate depth earthquakes seem to cluster in two distinct planes of seismicity along the subducting slab, known as Double Seismic Zones (DSZ). Precise double difference relocations in Tohoku, Japan and northern Chile confirm this pattern with striking accuracy. Furthermore, past studies have used statistical tests on the EHB global seismicity catalog to suggest that DSZs might be a dominant global feature. However, typical uncertainties associated with hypocentral depth prevent us from drawing meaningful conclusions about the detailed structure of intermediate depth seismicity and its relationship to the physical and chemical environment of most subduction zones. We have recently proposed a relative earthquake relocation algorithm based on the precise picking of the P and pP phase arrivals using array processing techniques [Florez and Prieto, 2017]. We use it to relocate seismicity in 24 carefully constructed slab segments that sample every subduction zone in the world. In all of the segments we are able to precisely delineate the structure of the double seismic zone. Our results indicate that whenever the lower plane of seismicity is active enough the width of the DSZ decreases in the down dip direction; the two planes merge at depths between 140 km and 300 km. We develop a method to unambiguously pick the depth of this merging point, the end of the DSZ, which appears to be correlated with the slab thermal parameter. We also confirm that the width of the DSZ increases with plate age. Finally, we estimate b-values for the upper and lower planes of seismicity and explore their relationships to the physical parameters that control slab subduction.

Oxygen isotopes in garnet and accessory minerals to constrain fluids in subducted crust

Science.gov (United States)

Rubatto, Daniela; Gauthiez-Putallaz, Laure; Regis, Daniele; Rosa Scicchitano, Maria; Vho, Alice; Williams, Morgan

2017-04-01

Fluids are considered a fundamental agent for chemical exchanges between different rock types in the subduction system. Constraints on the sources and pathways of subduction fluids thus provide crucial information to reconstruct subduction processes. Garnet and U-Pb accessory minerals constitute some of the most robust and ubiquitous minerals in subducted crust and can preserve multiple growth zones that track the metamorphic evolution of the sample they are hosted in. Microbeam investigation of the chemical (major and trace elements) and isotopic composition (oxygen and U-Pb) of garnet and accessory minerals is used to track significant fluid-rock interaction at different stages of the subduction system. This approach requires consideration of the diffusivity of oxygen isotopes particularly in garnet, which has been investigated experimentally. The nature of the protolith and ocean floor alteration is preserved in relict accessory phases within eclogites that have been fully modified at HP conditions (e.g. Monviso and Dora Maira units in the Western Alps). Minerals in the lawsonite-blueschists of the Tavsanli zone in Turkey record pervasive fluid exchange between mafic and sedimentary blocks at the early stage of subduction. High pressure shear zones and lithological boundaries show evidence of intense fluid metasomatism at depth along discontinuities in Monviso and Corsica. In the UHP oceanic crust of the Zermatt-Saas Zone, garnet oxygen isotopes and tourmaline boron isotopes indicate multistage fluid infiltration during prograde metamorphism. Localized exchanges of aqueous fluids are also observed in the subducted continental crust of the Sesia-Lanzo Zone. In most cases analyses of distinct mineral zones enable identification of multiple pulses of fluids during the rock evolution.

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

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

2017-04-01

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

Mantle Noble Gas Contents Controlled by Subduction of Serpentinite

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Krantz, J. A.; Parman, S. W.; Kelley, S. P.; Smye, A.; Jackson, C.

2017-12-01

Geochemical analyses of exhumed subduction zone material1, well gases2, MORB, and OIBs3 indicate that noble gases are being recycled from the surface of the earth into the mantle. However, the path taken by these noble gases is unclear. To estimate the distribution and quantity of Ar, Kr, and Xe in subducting slabs, a model consisting of layers of sediments, altered oceanic crust (AOC), and serpentinite (hydrously altered mantle) has been developed. The noble gas contents of sediments and AOC were calculated using the least air-like and most gas-rich analyses from natural systems4,5, while serpentinite was modelled using both data from natural systems1 and experimentally determined solubilities. Layer thicknesses were assessed over a range of values: 1 to 12 km of sediments, 5 to 9 km of AOC, and 1 to 30 km of serpentinite. In all cases, the serpentinite layer contains at least an order of magnitude more Ar and Kr than the other layers. For realistic layer thicknesses (1 km of sediments, 6 km of AOC, and 3 km of serpentinite), Xe is distributed roughly equally between the three layers. By incorporating global subduction rates6, fluxes of the heavy noble gases into the mantle have been calculated as 4 · 1012 mol/Ma for 36Ar, 6 · 1011 mol/Ma for 84Kr, and 8 · 109 mol/Ma for 130Xe. These fluxes are equivalent to the total 84Kr and 130Xe contents of the depleted and bulk mantle over 1 and 10 Ma7. Similarly, the flux of 36Ar is equivalent over 1 and 100 Ma. Since the Kr and Xe have not been completely overprinted by recycling, the large majority of subducted noble gases must escape in the subduction zone. However, even the small amounts that are subducted deeper have affected the mantle as measured in both MORB and OIBs. 1. Kendrick, M.A. et al., Nature Geoscience, 4, 807-812, 2011 2. Holland, G. and Ballentine, C.J., Nature, 441, 186-191, 2006 3. Parai, R. and Mukhopadhyay, S., G3, 16, 719-735, 2015 4. Matsuda, J. and Nagao, K., Geochemical Journal, 20, 71-80, 1986

ISOSTATICALLY DISTURBED TERRAIN OF NORTHWESTERN ANDES MOUNTAINS FROM SPECTRALLY CORRELATED FREE-AIR AND GRAVITY TERRAIN DATA

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Hernández P Orlando

2006-12-01

Full Text Available Recently revised models on global tectonics describe the convergence of the North Andes, Nazca, Caribbean and South American Plates and their seismicity, volcanism, active faulting and extreme
topography. The current plate boundaries of the area are mainly interpreted from volcanic and seismic datasets with variable confidence levels. New insights on the isostatic state and plate boundaries of
the northwestern Andes Mountains can be obtained from the spectral analysis of recently available gravity and topography data.
Isostatically disturbed terrain produces free-air anomalies that are highly correlated with the gravity effects of the terrain. The terrain gravity effects (TGE and free air gravity anomalies (FAGA of the
Andes mountains spectral correlation data confirms that these mountains are isostatically disturbed. Strong negative terrain-correlated FAGA along western South America and the Greater and Lesser Antilles are consistent with anomalously deepened mantle displaced by subducting oceanic plates.

Inversion of the compensated terrain gravity effects (CTGE reveals plate subduction systems with alternating shallower and steeper subduction angles. The gravity modeling highlights crustal
deformation from plate collision and subduction and other constraints on the tectonism of the plate boundary zones for the region.

Investigating subduction reversal in Papua New Guinea from automatic analysis of seismicity recorded on a temporary local network

Science.gov (United States)

Hicks, S. P.; Harmon, N.; Rychert, C.; Tharimena, S.; Bogiatzis, P.; Savage, B.; Shen, Y.; Baillard, C.

2017-12-01

The area of Papua New Guinea is one of the most seismically active regions on the planet. Seismicity in the region results from oblique convergence between the Pacific and India-Australia plates, with deformation occurring across a broad region involving several microplates. The region gives an excellent natural laboratory to test geodynamic models of subduction polarity reversal, microplate interaction, and to delineate the structure of subducting plates and relic structures at depth. However, a lack of permanent seismic stations means that routine earthquake locations for small to intermediate sized earthquakes have significant location errors. In 2014, we deployed a temporary network of eight broadband stations on islands in eastern Papua New Guinea to record ongoing seismic deformation. The network straddles a complex region where subduction of the Solomon plate occurs to the south and possible subduction of the Ontong-Java plateau occurs to the north. The stations were installed for 27 months. During the deployment period, there were 13 M>6.5 earthquakes in the area, including M7.5 doublet events in 2015, giving a rich seismic dataset. A high-quality catalogue of local events was formed by a multi-step process. Using the scanloc module of SeisComp3, we first detect P-onsets using a STA/LTA detection. Once clusters of P onsets are found, S-wave picks are incorporated based on a pre-defined window length of maximum S-P time. Groups of onsets are then associated to events, giving us a starting catalogue of 269 events (1765 P-onsets) with minimum magnitude of M 3.5. In a second step, we refine onset times using a Kurtosis picker to improve location accuracy. To form robust hypocentral locations using an appropriate structural model for the area and to constrain crust and mantle structure in the region, we derive a minimum 1-D velocity model using the VELEST program. We use a starting model from Abers et al. (1991) and we restrict our catalogue to events with an

The Rise of Oxygen in the Earth's Atmosphere Controlled by the Efficient Subduction of Organic Carbon

Science.gov (United States)

Duncan, M. S.; Dasgupta, R.

2017-12-01

Carbon cycling between the Earth's surface environment, i.e., the ocean-atmosphere system, and the Earth's interior is critical for differentiation, redox evolution, and long-term habitability of the planet. This carbon cycle is influenced heavily by the extent of carbon subduction. While the fate of carbonates during subduction has been discussed in numerous studies [e.g., 1], little is known how organic carbon is quantitatively transferred from the Earth's surface to the interior. Efficient subduction of organic carbon would remove reduced carbon from the surface environment over the long-term (≥100s Myrs) while release at subduction zone arc volcanoes would result in degassing of CO2. Here we conducted high pressure-temperature experiments to determine the carbon carrying capacity of slab derived, rhyolitic melts under graphite-saturated conditions over a range of P (1.5-3.0 GPa) and T (1100-1400 °C) at a fixed melt H2O content (2 wt.%) [2]. Based on our experimental data, we developed a thermodynamic model of CO2 dissolution in C-saturated slab melts, that allows us to quantify the extent of organic carbon mobility as a function of slab P, T, and fO2 during subduction through time. Our experimental data and thermodynamic model suggest that the subduction of graphitized organic C, and graphite/diamond formed by reduction of carbonates with depth [e.g., 3], remained efficient even in ancient, hotter subduction zones - conditions at which subduction of carbonates likely remained limited [1]. Considering the efficiency the subduction of organic C and potential conditions for ancient subduction, we suggest that the lack of remobilization in subduction zones and deep sequestration of organic C in the mantle facilitated the rise and maintenance atmospheric oxygen in the Paleoproterozoic and is causally linked to the Great Oxidation Event (GOE). Our modeling shows that episodic subduction and organic C sequestration pre-GOE may also explain occasional whiffs of

Fossil intermediate-depth earthquakes in subducting slabs linked to differential stress release

Science.gov (United States)

Scambelluri, Marco; Pennacchioni, Giorgio; Gilio, Mattia; Bestmann, Michel; Plümper, Oliver; Nestola, Fabrizio

2017-12-01

The cause of intermediate-depth (50-300 km) seismicity in subduction zones is uncertain. It is typically attributed either to rock embrittlement associated with fluid pressurization, or to thermal runaway instabilities. Here we document glassy pseudotachylyte fault rocks—the products of frictional melting during coseismic faulting—in the Lanzo Massif ophiolite in the Italian Western Alps. These pseudotachylytes formed at subduction-zone depths of 60-70 km in poorly hydrated to dry oceanic gabbro and mantle peridotite. This rock suite is a fossil analogue to an oceanic lithospheric mantle that undergoes present-day subduction. The pseudotachylytes locally preserve high-pressure minerals that indicate an intermediate-depth seismic environment. These pseudotachylytes are important because they are hosted in a near-anhydrous lithosphere free of coeval ductile deformation, which excludes an origin by dehydration embrittlement or thermal runaway processes. Instead, our observations indicate that seismicity in cold subducting slabs can be explained by the release of differential stresses accumulated in strong dry metastable rocks.

Phylogeny of Amazona barbadensis and the Yellow-headed Amazon complex (Aves: Psittacidae): a new look at South American parrot evolution.

Science.gov (United States)

Urantówka, Adam Dawid; Mackiewicz, Paweł; Strzała, Tomasz

2014-01-01

The Yellow-shouldered Amazon (Amazona barbadensis) is the sole parrot of the genus Amazona that inhabits only dry forests. Its population has been dropping; therefore it has been the topic of many studies and conservation efforts. However, the phylogenetic relationship of this species to potential relatives classified within the Yellow-Headed Amazon (YHA) complex are still not clear. Therefore, we used more extensive data sets, including the newly sequenced mitochondrial genome of A. barbadensis, to conduct phylogenetic analyses. Various combinations of genes and many phylogenetic approaches showed that A. barbadensis clustered significantly with A. ochrocephala ochrocephala from Colombia and Venezuela, which created the Northern South American (NSA) lineage, clearly separated from two other lineages within the YHA complex, the Central (CA) and South American (SA). Tree topology tests and exclusion of rapidly evolving sites provided support for a NSA+SA grouping. We propose an evolutionary scenario for the YHA complex and its colonization of the American mainland. The NSA lineage likely represents the most ancestral lineage, which derived from Lesser Antillean Amazons and colonized the northern coast of Venezuela about a million years ago. Then, Central America was colonized through the Isthmus of Panama, which led to the emergence of the CA lineage. The southward expansion to South America and the origin of the SA lineage happened almost simultaneously. However, more intensive or prolonged gene flow or migrations have led to much weaker geographic differentiation of genetic markers in the SA than in the CA lineage.

Slab1.0: A three-dimensional model of global subduction zone geometries

Science.gov (United States)

Hayes, Gavin P.; Wald, David J.; Johnson, Rebecca L.

2012-01-01

We describe and present a new model of global subduction zone geometries, called Slab1.0. An extension of previous efforts to constrain the two-dimensional non-planar geometry of subduction zones around the focus of large earthquakes, Slab1.0 describes the detailed, non-planar, three-dimensional geometry of approximately 85% of subduction zones worldwide. While the model focuses on the detailed form of each slab from their trenches through the seismogenic zone, where it combines data sets from active source and passive seismology, it also continues to the limits of their seismic extent in the upper-mid mantle, providing a uniform approach to the definition of the entire seismically active slab geometry. Examples are shown for two well-constrained global locations; models for many other regions are available and can be freely downloaded in several formats from our new Slab1.0 website, http://on.doi.gov/d9ARbS. We describe improvements in our two-dimensional geometry constraint inversion, including the use of ‘average’ active source seismic data profiles in the shallow trench regions where data are otherwise lacking, derived from the interpolation between other active source seismic data along-strike in the same subduction zone. We include several analyses of the uncertainty and robustness of our three-dimensional interpolation methods. In addition, we use the filtered, subduction-related earthquake data sets compiled to build Slab1.0 in a reassessment of previous analyses of the deep limit of the thrust interface seismogenic zone for all subduction zones included in our global model thus far, concluding that the width of these seismogenic zones is on average 30% larger than previous studies have suggested.

The energy geopolitics interests: the Initiative for South American Regional Integration - ISARI; Os interesses da geopolitica energetica: a Iniciativa para Integracao Regional Sul Americana - IIRSA

Energy Technology Data Exchange (ETDEWEB)

Jeronymo, Alexandre; Roig, Carla de Almeida; Guerra, Sinclair Mallet Guy [Universidade Federal do ABC (UFABC), Santo Andre, SP (Brazil). Programa de Pos-Graduacao em Energia], e-mail: alexandre.jeronymo@ufabc.edu.br, e-mail: carla.roig@ufabc.edu.br, e-mail: sguerra@ufabc.edu.br

2008-07-01

This work adds itself to the debates on the project Integration of South America Regional Infrastructure - ISARI. Its focus is related with Energy Geopolitics and the South America integration under the world system of commodities production. The ISARI, as a project oriented to the viability of low value aggregated which should be transported from the south american continent for consumption at the world market.

A numerical reference model for themomechanical subduction

DEFF Research Database (Denmark)

Quinquis, Matthieu; Chemia, Zurab; Tosi, Nicola

2010-01-01

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

Resveratrol, phenolic antioxidants, and saccharides in South American red wines

Directory of Open Access Journals (Sweden)

Osorio-Macías DE

2018-01-01

Full Text Available Daniel E Osorio-Macías,1,2 Pamela Vásquez,3 Cristhian Carrasco,3 Bjorn Bergenstahl,1 J Mauricio Peñarrieta2 1Department of Food Technology, Faculty of Engineering LTH, Lund University, Lund, Sweden; 2School of Chemistry, Faculty of Pure and Natural Sciences, 3Institute of Research and Development of Chemical Processes, Department of Chemical Engineering, Faculty of Engineering, Universidad Mayor de San Andrés (UMSA, La Paz, Bolivia Abstract: Wine is an important beverage with a long tradition, and its moderate consumption may be considered beneficial for human health. Although there are many studies regarding phenolic compounds in wines, there is a lack of information about antioxidants and phenolic content in South American wines. In this study, 35 South American red wines from four different countries, vintages 2004–2013, purchased at retail stores in La Paz, Bolivia, were studied. Resveratrol content, total antioxidant capacity (TAC by the 2,2′-azino-bis(3-ethylbenzotiazoline-6-sulfonic acid (ABTS and ferric-reducing antioxidant power (FRAP methods, total phenolic content (TPH, total flavonoids (TF, and main saccharides were assessed using the well-established spectrophotometric and high-performance liquid chromatography methods. The results ranged from 4 to 24 mmol/L for TAC determined by ABTS method and 14 to 43 mmol/L for TAC determined by FRAP method, 1600 to 3500 mg gallic acid equivalents/L for TPH, and 2 to 6 mmol catechin equivalents /L for TF. The resveratrol content ranged from 0.1 to 8 mg/L. Saccharides, glucose, and fructose content ranged from 0.4 to 10 g/L, 1.4 to 8.6 g/L, and 0.2 to 12 g/L, respectively. There was a high correlation among the different methods. The results showed that some wines growing at high altitude (>1500 meters above the sea level have higher amounts of TAC and phenolic content, including resveratrol, while non-varietal wines showed the lowest values. It was also observed that the saccharose

"No Unfavorable Comments from Any Quarter": Teaching Black History to White Students in the American South, 1928-1943

Science.gov (United States)

Woyshner, Christine

2012-01-01

Background/Context: The history curriculum is often used to help reach the goal of racial tolerance and understanding by teaching about the nation's diversity. Many educators believe that teaching about diverse peoples in schools will bring about greater equity in society. This historical study looks at the segregated American South from 1928 to…

Genetic diversity of neotropical Myotis (chiroptera: vespertilionidae with an emphasis on South American species.

Directory of Open Access Journals (Sweden)

Roxanne J Larsen

Full Text Available BACKGROUND: Cryptic morphological variation in the Chiropteran genus Myotis limits the understanding of species boundaries and species richness within the genus. Several authors have suggested that it is likely there are unrecognized species-level lineages of Myotis in the Neotropics. This study provides an assessment of the diversity in New World Myotis by analyzing cytochrome-b gene variation from an expansive sample ranging throughout North, Central, and South America. We provide baseline genetic data for researchers investigating phylogeographic and phylogenetic patterns of Myotis in these regions, with an emphasis on South America. METHODOLOGY AND PRINCIPAL FINDINGS: Cytochrome-b sequences were generated and phylogenetically analyzed from 215 specimens, providing DNA sequence data for the most species of New World Myotis to date. Based on genetic data in our sample, and on comparisons with available DNA sequence data from GenBank, we estimate the number of species-level genetic lineages in South America alone to be at least 18, rather than the 15 species currently recognized. CONCLUSIONS: Our findings provide evidence that the perception of lower species richness in South American Myotis is largely due to a combination of cryptic morphological variation and insufficient sampling coverage in genetic-based systematic studies. A more accurate assessment of the level of diversity and species richness in New World Myotis is not only helpful for delimiting species boundaries, but also for understanding evolutionary processes within this globally distributed bat genus.

The Eocene South American metatherian Zeusdelphys complicatus is not a protodidelphidid but a hatcheriform: Paleobiogeographic implications

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Leonardo M. Carneiro

2017-09-01

Full Text Available Zeusdelphys complicatus is one of the most enigmatic metatherians from the Itaboraí Basin. The type and only known specimen was previously regarded as the upper dentition of Eobrasilia; an M4 of a new taxon; an M3 of a Kollpaniidae (now regarded as a group of “condylarths”; a probable M1 of an incertae sedis taxon; and as an M1 of a Protodidelphidae. Herein, we present a morphological review of the dental structures of Zeusdelphys complicatus, presenting new interpretations and comparing it with other North and South American taxa. We also perform a phylogenetic analysis in order to test the affinities of Zeusdelphys and the validity of most studied characters. The results recovered Zeusdelphys complicatus as more closely related to Hatcheritherium alpha than to any other metatherian. Glasbiidae were recovered as the sister lineage of Protodidelphidae within Didelphimorphia, as true marsupials. Ectocentrocristus was recovered as the sister taxon of Zeusdelphys + Hatcheritherium, as a Hatcheriformes. The analysis recovered this suborder as an independent lineage from Polydolopimorphia, being more closely related to “Alphadontidae”. The affinities with Protodidelphidae are a result of convergent evolution, as Zeusdelphys is more closely related to Hatcheritherium alpha from the Late Cretaceous of North America. The results support a North American origin for Hatcheriformes. The presence of strong sea-level lowstands and islands in the Caribbean Plate during the Late Cretaceous provide valid data to support a faunal interchange between Americas during the latest Late Cretaceous. Based on the results, Zeusdelphys represents a South American early Eocene surviving Hatcheriformes.

Invasion of South American suckermouth armoured catfishes Pterygoplichthys spp. (Loricariidae) in Kerala, India - a case study

OpenAIRE

A. Bijukumar; R. Smrithy; U. Sureshkumar; S. George

2015-01-01

This paper documents the occurrence of the exotic South American suckermouth armoured catfishes (Loricariidae) of the genus Pterygoplichthys spp. in the drainages of Thiruvananthapuram City, Kerala.  The morphological taxonomy revealed that the specimens are closely related to Pterygoplichthys disjunctivus (Weber, 1991) and P. pardalis (Castelnau, 1855), in addition to intermediary forms of unknown identity.  DNA barcoding using the mitochondrial DNA cytochrome c oxidase 1 (CO1) also failed t...

76 FR 18419 - Movement of Hass Avocados From Areas Where Mediterranean Fruit Fly or South American Fruit Fly Exist

Science.gov (United States)

2011-04-04

... where the infested avocados were grown will immediately be suspended from the export program until an... Avocados From Areas Where Mediterranean Fruit Fly or South American Fruit Fly Exist AGENCY: Animal and... certain restrictions regarding the movement of fresh Hass variety avocados. Specifically, we are proposing...

75 FR 41237 - Public Land Order No. 7746; Withdrawal of Public Lands, South Fork of the American River; California

Science.gov (United States)

2010-07-15

... DEPARTMENT OF THE INTERIOR Bureau of Land Management [LLCAC08000-L1430000-ET0000; CACA 41334] Public Land Order No. 7746; Withdrawal of Public Lands, South Fork of the American River; California AGENCY: Bureau of Land Management, Interior. ACTION: Public Land Order. SUMMARY: This order withdraws 2...

Current meter and bathythermograph data from moored current meter and xbt casts in the North American Coastline-South as part of the Outer Continental Shelf - South Atlantic (OCS-South Atlantic) project from 1982-02-16 to 1985-07-01 (NODC Accession 8600124)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Current direction and bathythermograph (xbt) data were collected using moored current meter casts and other instruments in the North American Coastline-South from...

Depositional history of sedimentary linear alkylbenzenes (LABs) in a large South American industrial coastal area (Santos Estuary, Southeastern Brazil)

International Nuclear Information System (INIS)

Martins, Cesar C.; Bicego, Marcia C.; Mahiques, Michel M.; Figueira, Rubens C.L.; Tessler, Moyses G.; Montone, Rosalinda C.

2010-01-01

This paper reports the reconstruction of the contamination history of a large South American industrial coastal area (Santos Estuary, Brazil) using linear alkylbenzenes (LABs). Three sediment cores were dated by 137 Cs. Concentrations in surficial layers were comparable to the midrange concentrations reported for coastal sediments worldwide. LAB concentrations increased towards the surface, indicating increased waste discharges into the estuary in recent decades. The highest concentration values occurred in the early 1970s, a time of intense industrial activity and marked population growth. The decreased LAB concentration, in the late 1970s was assumed to be the result of the world oil crisis. Treatment of industrial effluents, which began in 1984, was represented by decreased LAB levels. Microbial degradation of LABs may be more intense in the industrial area sediments. The results show that industrial and domestic waste discharges are a historical problem in the area. - The contamination history of a large South American industrial coastal area indicated by molecular indicator of sewage input.

Ancient female philopatry, asymmetric male gene flow, and synchronous population expansion support the influence of climatic oscillations on the evolution of South American sea lion (Otaria flavescens.

Directory of Open Access Journals (Sweden)

Larissa Rosa de Oliveira

Full Text Available The South American sea lion (Otaria flavescens is widely distributed along the southern Atlantic and Pacific coasts of South America with a history of significant commercial exploitation. We aimed to evaluate the population genetic structure and the evolutionary history of South American sea lion along its distribution by analyses of mitochondrial DNA (mtDNA and 10 nuclear microsatellites loci. We analyzed 147 sequences of mtDNA control region and genotyped 111 individuals of South American sea lion for 10 microsatellite loci, representing six populations (Peru, Northern Chile, Southern Chile, Uruguay (Brazil, Argentina and Falkland (Malvinas Islands and covering the entire distribution of the species. The mtDNA phylogeny shows that haplotypes from the two oceans comprise two very divergent clades as observed in previous studies, suggesting a long period (>1 million years of low inter-oceanic female gene flow. Bayesian analysis of bi-parental genetic diversity supports significant (but less pronounced than mitochondrial genetic structure between Pacific and Atlantic populations, although also suggested some inter-oceanic gene flow mediated by males. Higher male migration rates were found in the intra-oceanic population comparisons, supporting very high female philopatry in the species. Demographic analyses showed that populations from both oceans went through a large population expansion ~10,000 years ago, suggesting a very similar influence of historical environmental factors, such as the last glacial cycle, on both regions. Our results support the proposition that the Pacific and Atlantic populations of the South American sea lion should be considered distinct evolutionarily significant units, with at least two managements units in each ocean.

Ancient female philopatry, asymmetric male gene flow, and synchronous population expansion support the influence of climatic oscillations on the evolution of South American sea lion (Otaria flavescens)

Science.gov (United States)

Gehara, Marcelo C. M.; Fraga, Lúcia D.; Lopes, Fernando; Túnez, Juan Ignacio; Cassini, Marcelo H.; Majluf, Patricia; Cárdenas-Alayza, Susana; Pavés, Héctor J.; Crespo, Enrique Alberto; García, Nestor; Loizaga de Castro, Rocío; Hoelzel, A. Rus; Sepúlveda, Maritza; Olavarría, Carlos; Valiati, Victor Hugo; Quiñones, Renato; Pérez-Alvarez, Maria Jose; Ott, Paulo Henrique

2017-01-01

The South American sea lion (Otaria flavescens) is widely distributed along the southern Atlantic and Pacific coasts of South America with a history of significant commercial exploitation. We aimed to evaluate the population genetic structure and the evolutionary history of South American sea lion along its distribution by analyses of mitochondrial DNA (mtDNA) and 10 nuclear microsatellites loci. We analyzed 147 sequences of mtDNA control region and genotyped 111 individuals of South American sea lion for 10 microsatellite loci, representing six populations (Peru, Northern Chile, Southern Chile, Uruguay (Brazil), Argentina and Falkland (Malvinas) Islands) and covering the entire distribution of the species. The mtDNA phylogeny shows that haplotypes from the two oceans comprise two very divergent clades as observed in previous studies, suggesting a long period (>1 million years) of low inter-oceanic female gene flow. Bayesian analysis of bi-parental genetic diversity supports significant (but less pronounced than mitochondrial) genetic structure between Pacific and Atlantic populations, although also suggested some inter-oceanic gene flow mediated by males. Higher male migration rates were found in the intra-oceanic population comparisons, supporting very high female philopatry in the species. Demographic analyses showed that populations from both oceans went through a large population expansion ~10,000 years ago, suggesting a very similar influence of historical environmental factors, such as the last glacial cycle, on both regions. Our results support the proposition that the Pacific and Atlantic populations of the South American sea lion should be considered distinct evolutionarily significant units, with at least two managements units in each ocean. PMID:28654647

Knowledge and screening of head and neck cancer among American Indians in South Dakota.

Science.gov (United States)

Dwojak, Sunshine; Deschler, Daniel; Sargent, Michele; Emerick, Kevin; Guadagnolo, B Ashleigh; Petereit, Daniel

2015-06-01

We established the level of awareness of risk factors and early symptoms of head and neck cancer among American Indians in South Dakota and determined whether head and neck cancer screening detected clinical findings in this population. We used the European About Face survey. We added questions about human papillomavirus, a risk factor for head and neck cancer, and demographics. Surveys were administered at 2 public events in 2011. Participants could partake in a head and neck cancer screening at the time of survey administration. Of the 205 American Indians who completed the survey, 114 participated in the screening. Mean head and neck cancer knowledge scores were 26 out of 44. Level of education was the only factor that predicted higher head and neck cancer knowledge (b = 0.90; P = .01). Nine (8%) people had positive head and neck cancer screening examination results. All abnormal clinical findings were in current or past smokers (P = .06). There are gaps in American Indian knowledge of head and neck cancer risk factors and symptoms. Community-based head and neck cancer screening in this population is feasible and may be a way to identify early abnormal clinical findings in smokers.

[South American camelids in Switzerland. II. Reference values for blood parameters].

Science.gov (United States)

Hengrave Burri, I; Tschudi, P; Martig, J; Liesegang, A; Meylan, M

2005-08-01

In order to establish reference values for blood parameters of South American camelids in Switzerland, 273 blood samples were collected from 141 llamas and 132 alpacas. These animals were classified in three categories (young animals blood cell count, white blood cell count, electrolytes, metabolites and enzymes). Significant differences between llamas and alpacas were evident for 26 parameters. This study also showed that differences between young animals, females and males must be taken into consideration. A comparison of blood values with the results of fecal analysis for parasite eggs showed that an infestation with Dicrocoelium dendriticum was associated with elevated activity of two liver enzymes (GLDH and gamma-GT) in the serum. In contrast, no differences were found in the results of blood analyses between animals shedding eggs of gastrointestinal strongyles or not.

Two brittle ductile transitions in subduction wedges, as revealed by topography

Science.gov (United States)

Thissen, C.; Brandon, M. T.

2013-12-01

Subduction wedges contain two brittle ductile transitions. One transition occurs within the wedge interior, and a second transition occurs along the decollement. The decollement typically has faster strain rates, which suggests that the brittle ductile transition along the decollement will be more rearward (deeper) than the transition within the interior. However, the presence of distinct rheologies or other factors such as pore fluid pressure along the decollement may reverse the order of the brittle-ductile transitions. We adopt a solution by Williams et al., (1994) to invert for these brittle ductile transitions using the wedge surface topography. At present, this model does not include an s point or sediment loading atop the wedge. The Hellenic wedge, however, as exposed in Crete presents an ideal setting to test these ideas. We find that the broad high of the Mediterranean ridge represents the coulomb frictional part of the Hellenic wedge. The rollover in topography north of the ridge results from curvature of the down going plate, creating a negative alpha depression in the vicinity of the Strabo, Pliny, and Ionian 'troughs' south of Crete. A steep topographic rise out of these troughs and subsequent flattening reflects the brittle ductile transition at depth in both the decollement and the wedge interior. Crete exposes the high-pressure viscous core of the wedge, and pressure solution textures provide additional evidence for viscous deformation in the rearward part of the wedge. The location of the decollement brittle ductile transition has been previously poorly constrained, and Crete has never experienced a subduction zone earthquake in recorded history. Williams, C. A., et al., (1994). Effect of the brittle ductile transition on the topography of compressive mountain belts on Earth and Venus. Journal of Geophysical Research Solid Earth

Hematozoa of forest birds in American Samoa - Evidence for a diverse, indigenous parasite fauna from the South Pacific

Science.gov (United States)

Atkinson, C.T.; Utzurrum, R.C.; Seamon, J.O.; Savage, Amy F.; Lapointe, D.A.

2006-01-01

Introduced avian diseases pose a significant threat to forest birds on isolated island archipelagos, especially where most passerines are endemic and many groups of blood-sucking arthropods are either absent or only recently introduced. We conducted a blood parasite survey of forest birds from the main islands of American Samoa to obtain baseline information about the identity, distribution and prevalence of hematozoan parasites in this island group. We examined Giemsa-stained blood smears from 857 individual birds representing 20 species on Tutuila, Ofu, Olosega, and Ta'u islands. Four hematozoan parasites were identified - Plasmodium circumflexum (1%, 12/857), Trypanosoma avium (4%, 32/857), microfilaria (9%, 76/857), and an Atoxoplasma sp. (parasite infections. Given the central location of American Samoa in the South Pacific, it is likely that avian malaria and other hematozoan parasites are indigenous and widespread at least as far as the central South Pacific. Their natural occurrence may provide some immunological protection to indigenous birds in the event that other closely related parasites are accidentally introduced to the region.

Rollback of an intraoceanic subduction system and termination against a continental margin

Science.gov (United States)

Campbell, S. M.; Simmons, N. A.; Moucha, R.

2017-12-01

The Southeast Indian Slab (SEIS) seismic anomaly has been suggested to represent a Tethyan intraoceanic subduction system which operated during the Jurassic until its termination at or near the margin of East Gondwana (Simmons et al., 2015). As plate reconstructions suggest the downgoing plate remained coupled to the continental margin, this long-lived system likely experienced a significant amount of slab rollback and trench migration (up to 6000 km). Using a 2D thermomechanical numerical code that includes the effects of phase transitions, we test this interpretation by modeling the long-term subduction, transition zone stagnation, and rollback of an intraoceanic subduction system in which the downgoing plate remains coupled to a continental margin. In addition, we also investigate the termination style of such a system, with a particular focus on the potential for some continental subduction beneath an overriding oceanic plate. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS-735738

Uncinaria hamiltoni (Nematoda: Ancylostomatidae) in South American Sea Lions, Otaria flavescens, From Northern Patagonia, Argentina

OpenAIRE

Berón-Vera, B.; Crespo, Enrique Alberto; Raga Esteve, Juan Antonio; Pedraza, S. N.

2004-01-01

Thirty-one South American sea lion pups (Otaria flavescens) found dead in Punta León, Argentina, during the summer of 2002, were examined for hookworms (Uncinaria hamiltoni). Parasite parameters were analyzed in 2 locations of the rookery, i.e., a traditional, well-structured breeding area and an expanding area with juveniles and a lax social structure. Prevalence of hookworms was 50% in both localities, and no difference was observed in prevalence between pup sexes (P > 0.05). Hookworms were...

Whole-genome characterization of Uruguayan strains of avian infectious bronchitis virus reveals extensive recombination between the two major South American lineages.

Science.gov (United States)

Marandino, Ana; Tomás, Gonzalo; Panzera, Yanina; Greif, Gonzalo; Parodi-Talice, Adriana; Hernández, Martín; Techera, Claudia; Hernández, Diego; Pérez, Ruben

2017-10-01

Infectious bronchitis virus (Gammacoronavirus, Coronaviridae) is a genetically variable RNA virus that causes one of the most persistent respiratory diseases in poultry. The virus is classified in genotypes and lineages with different epidemiological relevance. Two lineages of the GI genotype (11 and 16) have been widely circulating for decades in South America. GI-11 is an exclusive South American lineage while the GI-16 lineage is distributed in Asia, Europe and South America. Here, we obtained the whole genome of two Uruguayan strains of the GI-11 and GI-16 lineages using Illumina high-throughput sequencing. The strains here sequenced are the first obtained in South America for the infectious bronchitis virus and provide new insights into the origin, spreading and evolution of viral variants. The complete genome of the GI-11 and GI-16 strains have 27,621 and 27,638 nucleotides, respectively, and possess the same genomic organization. Phylogenetic incongruence analysis reveals that both strains have a mosaic genome that arose by recombination between Euro Asiatic strains of the GI-16 lineage and ancestral South American GI-11 viruses. The recombination occurred in South America and produced two viral variants that have retained the full-length S1 sequences of the parental lineages but are extremely similar in the rest of their genomes. These recombinant virus have been extraordinary successful, persisting in the continent for several years with a notorious wide geographic distribution. Our findings reveal a singular viral dynamics and emphasize the importance of complete genomic characterization to understand the emergence and evolutionary history of viral variants. Copyright © 2017 Elsevier B.V. All rights reserved.

Antarctica: Arena for South American Cooperation or Conflict.

Science.gov (United States)

Child, Jack

A number of converging circumstances suggest that Antarctica may be a major object of geopolitical attention in South America in the decade to come. The Malvinas/Falklands crisis focused geopolitical attention on the South Atlantic and the chain of Southern (Austral) Islands which link the southern tip of South America to the Antarctic Peninsula.…

H2O and CO2 devolatilization in subduction zones: implications for the global water and carbon cycles (Invited)

Science.gov (United States)

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

2010-12-01

Subduction of sediments and altered oceanic crust functions as a major carbon sink. Upon subduction the carbon may be released by progressive metamorphic reactions, which can be strongly enhanced by free fluids. Quantification of the CO2 release from subducting slabs is important to determine the provenance of CO2 that is released by the volcanic arc and to constrain the flux of carbon to the deeper mantle. In recent work we used a global set of high resolution thermal models of subduction zones to predict the flux of H2O from the subducting slab (van Keken, Hacker, Syracuse, Abers, Subduction factory 4: Depth-dependent flux of H2O from subducting slabs worldwide, J. Geophys. Res., under review) which provides a new estimate of the dehydration efficiency of the global subducting system. It was found that mineralogically bound water can pass efficiently through old and fast subduction zones (such as in the western Pacific) but that warm subduction zones (such as Cascadia) see nearly complete dehydration of the subducting slab. The top of the slab is sufficiently hot in all subduction zones that the upper crust dehydrates significantly. The degree and depth of dehydration is highly diverse and strongly depends on (p,T) and bulk rock composition. On average about one third of subducted H2O reaches 240 km depth, carried principally and roughly equally in the gabbro and peridotite sections. The present-day global flux of H2O to the deep mantle translates to an addition of about one ocean mass over the age of the Earth. We extend the slab devolatilization work to carbon by providing an update to Gorman et al. (Geochem. Geophys. Geosyst, 2006), who quantified the effects of free fluids on CO2 release. The thermal conditions were based on three end-member subduction zones with linear interpolation to provide a global CO2 flux. We use the new high resolution and global set of models to provide higher resolution predictions for the provenance and pathways of CO2 release to

The Dual Role a Buddhist Monk Played in the American South: The Balance between Heritage and Citizenship in the Refugee Community

OpenAIRE

Daniel Rhodes

2016-01-01

Buddhist Monks in Vietnam struggle with cultural preservation differently from a monk in the U.S. where the forces of acculturation for new arrivals, often refugees, are extraordinarily overwhelming. The author provides a case study examining how Buddhist leaders engage in cultural preservation and community building in the American South. Fusing ideas of Engaged Buddhism and community building, the author will demonstrate how a Buddhist monk is able to navigate the broader American culture a...

The role of SST on the South American atmospheric circulation during January, February and March 2001

Science.gov (United States)

Drumond, Anita Rodrigues De Moraes; Ambrizzi, Tércio

2005-06-01

Precipitation deficits were observed over southeastern, northeastern and Central Brazil during the 2001 Austral Summer. They contributed to the worsening of the energy crisis that was occurring in the country. A low-level anomalous anticyclonic circulation observed over eastern Brazil enhanced the deviation of moisture transport that usually occurs from the Amazon Basin to southeastern Brazil and inhibited the occurrence of South Atlantic Convergence Zone events in that period. However, an anomalous low-level northerly moisture flux was observed over the La Plata Basin, and positive precipitation anomalies occurred over Bolivia, Paraguay, northeastern Argentina and southern Brazil. Using the ensemble technique, a numerical study was carried out to investigate the role of different sea surface temperature (SST) forcings observed over this anomalous South American atmospheric circulation. Reynolds SST monthly means were used as boundary conditions to study the influence of South Atlantic, South Indian, South Pacific and Equatorial Pacific oceans. The simulations were run from September 2000 to April 2001 using the Community Climate Model version 3.6 General Circulation Model. Ten integrations using different initial conditions were done to each experiment. Numerical experiments suggested that the combined influence of South Pacific and Equatorial Pacific oceans could be responsible for the drought observed over Central Brazil. These experiments simulated the low-level anticyclonic anomaly observed over eastern Brazil. However, both experiments have poorly reproduced the intensity of the anomalous low-level northerly moisture flux observed over the La Plata Basin. Therefore, the intensity of the simulated precipitation anomalies over the subtropical regions was much weaker than observed.

Precipitation changes in the South American Altiplano since 1300 AD reconstructed by tree-rings

Directory of Open Access Journals (Sweden)

M. S. Morales

2012-03-01

Full Text Available Throughout the second half of the 20th century, the Central Andes has experienced significant climatic and environmental changes characterized by a persistent warming trend, an increase in elevation of the 0 °C isotherm, and sustained glacier shrinkage. These changes have occurred in conjunction with a steadily growing demand for water resources. Given the short span of instrumental hydroclimatic records in this region, longer time span records are needed to understand the nature of climate variability and to improve the predictability of precipitation, a key factor modulating the socio-economic development in the South American Altiplano and adjacent arid lowlands. In this study we present the first quasi-millennial, tree-ring based precipitation reconstruction for the South American Altiplano. This annual (November–October precipitation reconstruction is based on the Polylepis tarapacana tree-ring width series and represents the closest dendroclimatological record to the Equator in South America. This high-resolution reconstruction covers the past 707 yr and provides a unique record characterizing the occurrence of extreme events and consistent oscillations in precipitation. It also allows an assessment of the spatial and temporal stabilities of the teleconnections between rainfall in the Altiplano and hemispheric forcings such as El Niño-Southern Oscillation. Since the 1930s to present, a persistent negative trend in precipitation has been recorded in the reconstruction, with the three driest years since 1300 AD occurring in the last 70 yr. Throughout the 707 yr, the reconstruction contains a clear ENSO-like pattern at interannual to multidecadal time scales, which determines inter-hemispheric linkages between our reconstruction and other precipitation sensitive records modulated by ENSO in North America. Our reconstruction points out that century-scale dry periods are a recurrent feature in the Altiplano climate, and that the

[Pathology of South American Camelids: a retrospective study of necropsies at the Institute of Veterinary Pathology, University of Leipzig, Germany].

Science.gov (United States)

Theuß, T; Goerigk, D; Rasenberger, S; Starke, A; Schoon, H-A

2014-01-01

The number of South American Camelids (New World Camelids) housed in Germany has increased in the recent years. While these species were formerly kept solely in zoological gardens, ever more private and commercial livestock is being established. Compared to indigenous livestock animals, they bear some distinctive differences, particularly in terms of digestive tract anatomy and physiology. Therefore, it is of considerable interest for veterinarians working with South American Camelids to obtain knowledge about the distinguishing features of these animals and the typical diseases affecting them in Germany. For this purpose, the necropsy reports, including the anamnestic data, and their diagnostic usefulness, from 1995 to 2012 were studied retrospectively. Du- ring this period, a total of 233 New World Camelids were examined (195 alpacas and 38 llamas). Anamnestic data of diagnostic usefulness regarding the cause of disease were only submitted in a limited number of cases, because most of the animals died without specific symptoms. The following were the most frequent pathological findings: enteritis (n = 91), gastritis (n = 76), cachexia (n = 73), pneumonia (n = 30), stomatitis (n = 27), azotaemia (n = 22) and anaemia (n = 9). An endoparasitosis occurred in 107 cases and was considered the predominant cause of enteritis. As with indigenous ruminants, llamas and alpacas primarily suffered from diseases of the digestive and respiratory tracts. Other organ systems were affected to a lesser extent. Even in cases with severe alterations in the affected organs, South American Camelids do not show or show too late diagnostically indicative clinical symptoms. Therefore, a detailed clinical examination of these animals is important.

Crustal Gravitational Potential Energy Change and Subduction Earthquakes

Science.gov (United States)

Zhu, P. P.

2017-05-01

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

Carbon Retention and Isotopic Evolution in Deeply Subducted Sediments: Evidence from the Italian Alps

Science.gov (United States)

Cook-Kollars, J.; Bebout, G. E.; Agard, P.; Angiboust, S.

2012-12-01

Subduction-zone metamorphism of oceanic crust and carbonate-rich seafloor sediments plays an important regulatory role in the global C cycle by controlling the fraction of subducting C entering long-term storage in the mantle and the fraction of subducting C emitted into the atmosphere in arc volcanic gases. Modeling studies suggest that the extent of decarbonation of subducting sediments could be strongly affected by extents of infiltration by external H2O-rich fluids and that, in cool subduction zones, the dehydration of subducting oceanic slabs may not release sufficient H2O to cause significant decarbonation of overlying sediments [Gorman et al. (2006), G-cubed; Hacker (2008), G-cubed]. Metasedimentary suites in the Western Alps (sampled from the Schistes Lustres, Zermatt-Saas ophiolite, and at Lago di Cignana) were subducted to depths corresponding to 1.5-3.2 GPa, over a range of peak temperatures of 350-600°C, and are associated with HP/UHP-metamorphosed Jurassic ophiolitic rocks [Agard et al. (2001), Bull. soc. geol. France; Frezzotti et al. (2011), Nature Geoscience]. These metasedimentary suites are composed of interlayered metapelites and metacarbonates and represent a range of peak P-T conditions experienced in modern, relatively cool subduction zones. Integrated petrologic and isotopic study of these rocks allows an analysis of decarbonation and isotopic exchange among oxidized and reduced C reservoirs along prograde subduction-zone P-T paths. Petrographic work on Schistes Lustres metacarbonates indicates only minor occurrences of calc-silicate phases, consistent with the rocks having experienced only very minor decarbonation during prograde metamorphism. Carbonate δ13CVPDB values (-1.5 to 1‰) are similar to values typical of marine carbonates. Higher grade, UHP-metamorphosed carbonates at Cignana show mineralogic evidence of decarbonation; however, the δ13C of the calcite in these samples remains similar to that of marine carbonate. With

Upper mantle beneath foothills of the western Himalaya: subducted lithospheric slab or a keel of the Indian shield?

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Vinnik, L.; Singh, A.; Kiselev, S.; Kumar, M. Ravi

2007-12-01

The fate of the mantle lithosphere of the Indian Plate in the India-Eurasia collision zone is not well understood. Tomographic studies reveal high P velocity in the uppermost mantle to the south of the western Himalaya, and these high velocities are sometimes interpreted as an image of subducting Indian lithosphere. We suggest that these high velocities are unrelated to the ongoing subduction but correspond to a near-horizontal mantle keel of the Indian shield. In the south of the Indian shield upper-mantle velocities are anomalously low, and relatively high velocities may signify a recovery of the normal shield structure in the north. Our analysis is based on the recordings of seismograph station NIL in the foothills of the western Himalaya. The T component of the P receiver functions is weak relative to the Q component, which is indicative of a subhorizontally layered structure. Joint inversion of the P and S receiver functions favours high uppermost mantle velocities, typical of the lithosphere of Archean cratons. The arrival of the Ps converted phase from 410 km discontinuity at NIL is 2.2 s earlier than in IASP91 global model. This can be an effect of remnants of Tethys subduction in the mantle transition zone and of high velocities in the keel of the Indian shield. Joint inversion of SKS particle motions and P receiver functions reveals a change in the fast direction of seismic azimuthal anisotropy from 60° at 80-160 km depths to 150° at 160-220 km. The fast direction in the lower layer is parallel to the trend of the Himalaya. The change of deformation regimes at a depth of 160 km suggests that this is the base of the lithosphere of the Indian shield. A similar boundary was found with similar techniques in central Europe and the Tien Shan region, but the base of the lithosphere in these regions is relatively shallow, in agreement with the higher upper-mantle temperatures. The ongoing continental collision is expressed in crustal structure: the crust

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

Science.gov (United States)

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

2017-05-01

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

Intra-continental subduction and contemporaneous lateral extrusion of the upper plate: insights into Alps-Adria interactions

Science.gov (United States)

van Gelder, Inge; Willingshofer, Ernst; Sokoutis, Dimitrios; Cloetingh, Sierd

2017-04-01

A series of physical analogue experiments were performed to simulate intra-continental subduction contemporaneous with lateral extrusion of the upper plate to study the interferences between these two processes at crustal levels and in the lithospheric mantle. The lithospheric-scale models are specifically designed to represent the collision of the Adriatic microplate with the Eastern Alps, simulated by an intra-continental weak zone to initiate subduction and a weak confined margin perpendicular to the direction of convergence in order to allow for extrusion of the lithosphere. The weak confined margin is the analog for the opening of the Pannonian back-arc basin adjacent to the Eastern Alps with the direction of extension perpendicular to the strike of the orogen. The models show that intra-continental subduction and coeval lateral extrusion of the upper plate are compatible processes. The obtained deformation structures within the extruding region are similar compared to the classical setup where lateral extrusion is provoked by lithosphere-scale indentation. In the models a strong coupling across the subduction boundary allows for the transfer of abundant stresses to the upper plate, leading to laterally varying strain regimes that are characterized by crustal thickening near a confined margin and dominated by lateral displacement of material near a weak lateral confinement. During ongoing convergence the strain regimes propagate laterally, thereby creating an area of overlap characterized by transpression. In models with oblique subduction, with respect to the convergence direction, less deformation of the upper plate is observed and as a consequence the amount of lateral extrusion decreases. Additionally, strain is partitioned along the oblique plate boundary leading to less subduction in expense of right lateral displacement close to the weak lateral confinement. Both oblique and orthogonal subduction models have a strong resemblance to lateral extrusion

A comparison of seismicity in world's subduction zones: Implication by the difference of b-values

Science.gov (United States)

Nishikawa, T.; Ide, S.

2013-12-01

Since the pioneering study of Uyeda and Kanamori (1979), it has been thought that world's subduction zones can be classified into two types: Chile and Mariana types. Ruff and Kanamori (1980) suggested that the maximum earthquake size within each subduction zone correlates with convergence rate and age of subducting lithosphere. Subduction zones with younger lithosphere and larger convergence rates are associated with great earthquakes (Chile), while subduction zones with older lithosphere and smaller convergence rates have low seismicity (Mariana). However, these correlations are obscured after the 2004 Sumatra earthquake and the 2009 Tohoku earthquake. Furthermore, McCaffrey (2008) pointed out that the history of observation is much shorter than the recurrence times of very large earthquakes, suggesting a possibility that any subduction zone may produce earthquakes larger than magnitude 9. In the present study, we compare world's subduction zones in terms of b-values in the Gutenberg-Richer relation. We divided world's subduction zones into 146 regions, each of which is bordered by a trench section of about 500 km and extends for 200 km from the trench section in the direction of relative plate motion. In each region, earthquakes equal to or larger than M4.5 occurring during 1988-2009 were extracted from ISC catalog. We find a positive correlation between b-values and ages of subducting lithosphere, which is one of the two important variables discussed in Ruff and Kanamori (1980). Subduction zones with younger lithosphere are associated with high b-values and vice versa, while we cannot find a correlation between b-values and convergence rates. We used the ages determined by Müller et al. (2008) and convergence rate calculated using PB2002 (Bird, 2003) for convergence rate. We also found a negative correlation between b-values and the estimates of seismic coupling, which is defined as the ratio of the observed seismic moment release rate to the rate calculated

Multivariate statistical analysis to investigate the subduction zone parameters favoring the occurrence of giant megathrust earthquakes

Science.gov (United States)

Brizzi, S.; Sandri, L.; Funiciello, F.; Corbi, F.; Piromallo, C.; Heuret, A.

2018-03-01

The observed maximum magnitude of subduction megathrust earthquakes is highly variable worldwide. One key question is which conditions, if any, favor the occurrence of giant earthquakes (Mw ≥ 8.5). Here we carry out a multivariate statistical study in order to investigate the factors affecting the maximum magnitude of subduction megathrust earthquakes. We find that the trench-parallel extent of subduction zones and the thickness of trench sediments provide the largest discriminating capability between subduction zones that have experienced giant earthquakes and those having significantly lower maximum magnitude. Monte Carlo simulations show that the observed spatial distribution of giant earthquakes cannot be explained by pure chance to a statistically significant level. We suggest that the combination of a long subduction zone with thick trench sediments likely promotes a great lateral rupture propagation, characteristic of almost all giant earthquakes.

Tasman frontier subduction initiation and paleogene climate

NARCIS (Netherlands)

Sutherland, Rupert; Dickens, Gerald R.; Blum, Peter; Agnini, Claudia; Alegret, Laia; Bhattacharya, Joyeeta; Bordenave, Aurelien; Chang, Liao; Collot, Julien; Cramwinckel, Margot J.; Dallanave, Edoardo; Drake, Michelle K.; Etienne, Samuel J.G.; Giorgioni, Martino; Gurnis, Michael; Harper, Dustin T.; Huang, Huai Hsuan May; Keller, Allison L.; Lam, Adriane R.; Li, He; Matsui, Hiroki; Newsam, Cherry; Park, Yu Hyeon; Pascher, Kristina M.; Pekar, Stephen F.; Penman, Donald E.; Saito, Saneatsu; Stratford, Wanda R.; Westerhold, Thomas; Zhou, Xiaoli

International Ocean Discovery Program (IODP) Expedition 371 drilled six sites in the Tasman Sea of the southwest Pacific between 27 July and 26 September 2017. The primary goal was to understand Tonga-Kermadec subduction initiation through recovery of Paleogene sediment records. Secondary goals

Diapir versus along-channel ascent of crustal material during plate convergence: constrained by the thermal structure of subduction zones

Science.gov (United States)

Liu, M. Q.; Li, Z. H.

2017-12-01

Crustal rocks can be subducted to mantle depths, interact with the mantle wedge, and then exhume to the crustal depth again, which is generally considered as the mechanism for the formation of ultrahigh-pressure metamorphic rocks in nature. The crustal rocks undergo dehydration and melting at subarc depths, giving rise to fluids that metasomatize and weaken the overlying mantle wedge. There are generally two ways for the material ascent from subarc depths: one is along subduction channel; the other is through the mantle wedge by diapir. In order to study the conditions and dynamics of these contrasting material ascent modes, systematic petrological-thermo-mechanical numerical models are constructed with variable thicknesses of the overriding and subducting continental plates, ages of the subducting oceanic plate, as well as the plate convergence rates. The model results suggest that the thermal structures of subduction zones control the thermal condition and fluid/melt activity at the slab-mantle interface in subcontinental subduction channels, which further strongly affect the material transportation and ascent mode. Thick overriding continental plate and low-angle subduction style induced by young subducting oceanic plate both contribute to the formation of relatively cold subduction channels with strong overriding mantle wedge, where the along-channel exhumation occurs exclusively to result in the exhumation of HP-UHP metamorphic rocks. In contrast, thin overriding lithosphere and steep subduction style induced by old subducting oceanic plate are the favorable conditions for hot subduction channels, which lead to significant hydration and metasomatism, melting and weakening of the overriding mantle wedge and thus cause the ascent of mantle wedge-derived melts by diapir through the mantle wedge. This may corresponds to the origination of continental arc volcanism from mafic to ultramafic metasomatites in the bottom of the mantle wedge. In addition, the plate

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

Science.gov (United States)

Schaefer, Andreas; Wenzel, Friedemann

2017-04-01

Subduction zones are generally the sources of the earthquakes with the highest magnitudes. Not only in Japan or Chile, but also in Pakistan, the Solomon Islands or for the Lesser Antilles, subduction zones pose a significant hazard for the people. To understand the behavior of subduction zones, especially to identify their capabilities to produce maximum magnitude earthquakes, various physical models have been developed leading to a large number of various datasets, e.g. from geodesy, geomagnetics, structural geology, etc. There have been various studies to utilize this data for the compilation of a subduction zone parameters database, but mostly concentrating on only the major zones. Here, we compile the largest dataset of subduction zone parameters both in parameter diversity but also in the number of considered subduction zones. In total, more than 70 individual sources have been assessed and the aforementioned parametric data have been combined with seismological data and many more sources have been compiled leading to more than 60 individual parameters. Not all parameters have been resolved for each zone, since the data completeness depends on the data availability and quality for each source. In addition, the 3D down-dip geometry of a majority of the subduction zones has been resolved using historical earthquake hypocenter data and centroid moment tensors where available and additionally compared and verified with results from previous studies. With such a database, a statistical study has been undertaken to identify not only correlations between those parameters to estimate a parametric driven way to identify potentials for maximum possible magnitudes, but also to identify similarities between the sources themselves. This identification of similarities leads to a classification system for subduction zones. Here, it could be expected if two sources share enough common characteristics, other characteristics of interest may be similar as well. This concept

Interaction between two subducting plates under Tokyo and its possible effects on seismic hazards

Science.gov (United States)

Wu, Francis; Okaya, David; Sato, Hiroshi; Hirata, Naoshi

2007-09-01

Underneath metropolitan Tokyo the Philippine Sea plate (PHS) subducts to the north on top of the westward subducting Pacific plate (PAC). New, relatively high-resolution tomography images the PHS as a well-defined subduction zone under western Kanto Plain. As PAC shoals under eastern Kanto, the PHS lithosphere is being thrusted into an increasingly tighter space of the PAC-Eurasian mantle wedge. As a result, zones of enhanced seismicity appear under eastern Kanto at the top of PHS, internal to PHS and also at its contact with PAC. These zones are located at depths greater than the causative fault of the disastrous 1923 Great Tokyo ``megathrust'' earthquake, in the vicinity of several well-located historical, damaging (M6 and M7) earthquakes. Thus a rather unique interaction between subducting plates under Tokyo may account for additional seismic hazards in metropolitan Tokyo.

Strategies to Improve Teacher Retention in American Overseas Schools in the Near East South Asia Region: A Qualitative Analysis

Science.gov (United States)

Mancuso, Steven V.; Roberts, Laura; White, George P.; Yoshida, Roland K.; Weston, David

2011-01-01

Using a qualitative analysis and drawing from sociological theory, this study examined reasons for teacher turnover and retention from a representative sample of 248 teachers in American overseas schools in the Near East South Asia region. Results suggested that the most important reasons to stay or move pertained to supportive leadership,…

Out-of-plane reflections - are they evidence for deep subducted lithosphere?

Science.gov (United States)

Schumacher, Lina; Thomas, Christine

2015-04-01

Subduction zones form dominant tectonic features on the Earth and have complex three-dimensional structures. Tomographic inversions for P- and S-wave seismic velocities in the Earth's mantle give impressive images of slabs descending into the deep Earth. However, direct observations of deep slabs are scarce but necessary to make statements concerning physical parameters, structural differences within the slab and its behavior with depth. The main objective of this study is to investigate the geometry, physical parameters and structural differences of subducted lithosphere by investigating seismic P-wave arrivals that reflect off the base of the slab using seismic array techniques. The great circle paths of the source-receiver combinations used do not intersect the slab and serve as reference. We focus on the North pacific region by using earthquakes from Japan, the Philippines and the Hindukush recorded at North American networks (e.g. USArray, Alaska and Canada). The data cover a period from 2000-2012 with a minimum magnitude of 5.6 Mw and depths below 100 km. We are looking for reflections from the slab region that would arrive at the stations with deviating backazimuths. Information on slowness, backazimuth and travel time of the observed out-of-plane arrivals is used to backtrace the wave to its scattering location and to map seismic heterogeneities associated with subduction zones. The reflection points give an idea for the 3D structures within the mantle. Assuming only single scattering in the backtracing algorithm, most out-of-plane signals have to travel as P*P and only a few as S*P phases, due to their timing. Taking into account the radiation pattern of each event in direction of the great circle path and towards the calculated reflection point, it is possible to compare the polarities of the out-of-plane signals with P and/or PP. Furthermore, we analyze the out-of-plane waveforms in the beam trace of the observed slowness and backazimuth by cross

Continental Subduction: Mass Fluxes and Interactions with the Wider Earth System

Science.gov (United States)

Cuthbert, S. J.

2011-12-01

Substantial parts of ultra-high pressure (UHP) terrains probably represent subducted passive continental margins (PCM). This contribution reviews and synthesises research on processes operating in such systems and their implication for the wider Earth system. PCM sediments are large repositories of volatiles including hydrates, nitrogen species, carbonates and hydrocarbons. Sediments and upper/ mid-crustal basement are rich in incompatible elements and are fertile for melting. Lower crust may be more mafic and refractory. Juvenile rift-related mafic rocks also have the potential to generate substantial volumes of granitoid melts, especially if they have been hydrated. Exposed UHP terrains demonstrate the return of continental crust from mantle depths, show evidence for substantial fluxes of aqueous fluid, anatexis and, in entrained orogenic peridotites, metasomatism of mantle rocks by crust- derived C-O-H fluids. However, substantial bodies of continental material may never return to the surface as coherent masses of rock, but remain sequestered in the mantle where they melt or become entrained in the deeper mantle circulation. Hence during subduction, PCM's become partitioned by a range of mechanisms. Mechanical partitioning strips away weaker sediment and middle/upper crust, which circulate back up the subduction channel, while denser, stronger transitional pro-crust and lower crust may "stall" near the base of the lithosphere or be irreversibly subducted to join the global mantle circulation. Under certain conditions sediment and upper crustal basement may reach depths for UHPM. Further partitioning takes place by anatexis, which either aids stripping and exhumation of the more melt-prone rock-masses through mechanical softening, or separates melt from residuum so that melt escapes and is accreted to the upper plate leading to "undercrusting", late-orogenic magmatism and further refinement of the crust. Melt that traverses sections of mantle will interact with

Hierarchical modeling of genome-wide Short Tandem Repeat (STR) markers infers native American prehistory.

Science.gov (United States)

Lewis, Cecil M

2010-02-01

This study examines a genome-wide dataset of 678 Short Tandem Repeat loci characterized in 444 individuals representing 29 Native American populations as well as the Tundra Netsi and Yakut populations from Siberia. Using these data, the study tests four current hypotheses regarding the hierarchical distribution of neutral genetic variation in native South American populations: (1) the western region of South America harbors more variation than the eastern region of South America, (2) Central American and western South American populations cluster exclusively, (3) populations speaking the Chibchan-Paezan and Equatorial-Tucanoan language stock emerge as a group within an otherwise South American clade, (4) Chibchan-Paezan populations in Central America emerge together at the tips of the Chibchan-Paezan cluster. This study finds that hierarchical models with the best fit place Central American populations, and populations speaking the Chibchan-Paezan language stock, at a basal position or separated from the South American group, which is more consistent with a serial founder effect into South America than that previously described. Western (Andean) South America is found to harbor similar levels of variation as eastern (Equatorial-Tucanoan and Ge-Pano-Carib) South America, which is inconsistent with an initial west coast migration into South America. Moreover, in all relevant models, the estimates of genetic diversity within geographic regions suggest a major bottleneck or founder effect occurring within the North American subcontinent, before the peopling of Central and South America. 2009 Wiley-Liss, Inc.

Quaternary volcanism in Deception Island (Antarctica): South Shetland Trench subduction-related signature in the Bransfield Basin back arc domain; Vulcanismo cuaternario de la Isla Decepcion (Antartida): una signatura relacionada con la subduccion de la Fosa de las Shetland del Sur en el dominio de tras-arco de la Cuenca de Bransfield

Energy Technology Data Exchange (ETDEWEB)

Gale, C.; Ubide, T.; Lago, M.; Gil-Imaz, A.; Gil-Pena, I.; Galindo-Zaldivar, J.; Rey, J.; Maestro, A.; Lopez-Martinez, J.

2014-06-01

Deception Island shows a volcanism related to the Phoenix Plate subduction and roll-back under South Shetland Block in the present times. The development of the island is related to the evolution and collapse of a volcanic caldera, and this study is focused on the petrology, mineralogy and geochemistry of the post-caldera rocks. We have made a study of the lava flows, dikes and the youngest historic eruption in 1970. These rocks range from dacite to rhyolite and have a microporphyritic texture with olivine and minor clinopyroxene. A pre-caldera basaltic andesite has also been studied. It has a microporphyritic texture with clinopyroxene. The intermediate and acid compositions alternating in the volcanostratigraphic sequence suggest either mafic recharge events or melt extraction from different levels in the deep magmatic system. All the studied compositions share a subduction-related signature similar to other magmatics from the Bransfield Basin. However, compositional differences between pre-caldera and post-caldera rocks indicate a different magma source and depth of crystallisation. According to the geothermobarometric calculations the pre-caldera magmas started to crystallise at deeper levels (13.5-15 km) than the post-caldera magmas (6.2-7.8 km). Specifically, the postcaldera magmas indicate a smaller influence of the subducting slab in the southwestern part of the Bransfield Basin in respect to the available data from other sectors as well as the involvement of crustal contamination in the genesis of the magmas. (Author)

Subduction zones seen by GOCE gravity gradients

DEFF Research Database (Denmark)

Švarc, Mario; Herceg, Matija; Cammarano, Fabio

In this study, the GOCE (Gravity field and steady state Ocean Circulation Explorer) gradiometry data were used to study geologic structures and mass variations within the lithosphere in areas of known subduction zones. The advantage of gravity gradiometry over other gravity methods is that gradie...

Upper Mantle Discontinuities Underneath Central and Southern Mexico

Science.gov (United States)

Perez-Campos, X.; Clayton, R. W.

2011-12-01

Central and southern Mexico are affected by the subduction of Cocos plate beneath North American plate. The MesoAmerican Subduction Experiment (MASE) and the Veracruz-Oaxaca (VEOX) project have mapped the geometry of the Cocos slab. It is characterized in central Mexico by a shallow horizontal geometry up to ~300 km from the trench, then it dives steeply (70°) into the mantle, to its apparent end at 500 km depth. In contrast, some 400 km to the south, the slab subducts smoothly, with a dip angle of ~26° to a depth of 150 km. We use receiver functions from teleseismic events, recorded at stations from MASE, VEOX, and the Servicio Sismológico Nacional (SSN, Mexican National Seismological Service) to map the upper mantle discontinuities and properties of the transition zone in central and southern Mexico. We also use data from the Mapping the Rivera Subduction Zone (MARS) Experiment to get a complete picture of the subduction regime in central Mexico and compare the mantle transition zone in a slab tear regime. The 410 discontinuity shows significant variation in topography in central Mexico, particularly where the slab is expected to reach such depth. The 660 discontinuity shows a smoother topography, indicating that the slab does not penetrate this far down. The results will be compared with a ridge regime in the Gulf of California.

3D absolute hypocentral determination - 13 years of seismicity in Ecuadorian subduction zone

Science.gov (United States)

Font, Yvonne; Segovia, Monica; Theunissen, Thomas

2010-05-01

of azimuthal coverage, record frequency and signal quality. Then, we define 5 domains: Offshore/coast, North-Andean margin, Volcanic chain, Southern Ecuador, and a domain deeper than 50 km. We process earthquake location only if at least 3 proximal stations exist in the event's domain. This data selection allows providing consistent quality location. The third step consists in improving the 3D MAXI technique that is well adapted to perform absolute earthquake location in velocity model presenting strong lateral Vp heterogeneities. The resulting catalogue allows specifying the deformation in the subduction system. All seismicity previously detected before trench occurs indeed between the trench and the coastal range. South of 0°, facing the subducting Carnegie Ridge, the seismicity aligns along the interplate seismogenic zone between an updip limit shallower than ~8 km and a downdip limit that reaches up to 50 km depth. The active seismogenic zone is interrupted by a gap that extends right beneath the coastal range. At these latitudes, a diffuse intraplate deformation also affects the subducting plate, probably induced by the locally thickened lithosphere flexure. Between the trench and the coast, earthquake distribution clearly defines a gap, which size is comparable to the 1942 M7.9 asperity (ellipse of axes ~55/35 km). A slab is clearly defines and dips around 25 to 30°. The slab seismicity is systematically interrupted between 100-170 km, approximately beneath the volcanic chain. North of 0°, i.e. in the megathrust earthquake domain, the interseismic activity is clearly reduced. The interplate distribution seems to gather along alignments perpendicular to the trench attesting probably of the margin segmentation. The North Andean overriding margin is undergoing active deformation, especially at the location where the Andean Chain strike changes of direction. At these latitudes, no earthquake occurs deeper than 100 km depth.

Normalized difference vegetation index for the South American continent used as a climatic variability indicator

International Nuclear Information System (INIS)

Liu, W.T.; Massambani, O.; Festa, M.

1992-01-01

The NOAA AVHRR GAC data set was used to produce Normalized Difference Vegetation Index (NDVI) maps for the South American Continent covering the period from August 1, 1981 to June 30, 1987. A 15-day maximum value composite procedure was used to partially eliminate the cloud contamination and atmospheric attenuation. Monthly evolution of NDVI for a dry and a wet year within the period studied was used to estimate the area covered by NDVI value less than 0.223, This value was used as an indicator of the drought area and the delineation of the Low rainfall areas in the continent. It was observed a well defined regional dependence of the drought area variability for the Northeast, Southwest and Northwest continent and also for the Amazon region. It is shown a relative estimation of the area coverage with NDVI less than 0.223 for the years 1982/83 and 1984/85. The dynamics of the drought area evolution in the continent is discussed. It is also presented a diagnosis of regional variability of the continental distribution of drought area from 1981 to 1987 for the months of May and September. This information is also used to discuss its relationship with the EL-Nino-Southern Oscillation (ENSO) and the South American Precipitation patterns during this period. It is suggested that the use of NDVI image to identify the dynamics of the drought induced by low rainfall may provide us valuable information to study the large scale climatic variation

Circum-Pacific accretion of oceanic terranes to continental blocks: accretion of the Early Permian Dun Mountain ophiolite to the E Gondwana continental margin, South Island, New Zealand

Science.gov (United States)

Robertson, Alastair

2016-04-01

Accretionary orogens, in part, grow as a result of the accretion of oceanic terranes to pre-existing continental blocks, as in the circum-Pacific and central Asian regions. However, the accretionary processes involved remain poorly understood. Here, we consider settings in which oceanic crust formed in a supra-subduction zone setting and later accreted to continental terranes (some, themselves of accretionary origin). Good examples include some Late Cretaceous ophiolites in SE Turkey, the Jurassic Coast Range ophiolite, W USA and the Early Permian Dun Mountain ophiolite of South Island, New Zealand. In the last two cases, the ophiolites are depositionally overlain by coarse clastic sedimentary rocks (e.g. Permian Upukerora Formation of South Island, NZ) that then pass upwards into very thick continental margin fore-arc basin sequences (Great Valley sequence, California; Matai sequence, South Island, NZ). Field observations, together with petrographical and geochemical studies in South Island, NZ, summarised here, provide evidence of terrane accretion processes. In a proposed tectonic model, the Early Permian Dun Mountain ophiolite was created by supra-subduction zone spreading above a W-dipping subduction zone (comparable to the present-day Izu-Bonin arc and fore arc, W Pacific). The SSZ oceanic crust in the New Zealand example is inferred to have included an intra-oceanic magmatic arc, which is no longer exposed (other than within a melange unit in Southland), but which is documented by petrographic and geochemical evidence. An additional subduction zone is likely to have dipped westwards beneath the E Gondwana margin during the Permian. As a result, relatively buoyant Early Permian supra-subduction zone oceanic crust was able to dock with the E Gondwana continental margin, terminating intra-oceanic subduction (although the exact timing is debatable). The amalgamation ('soft collision') was accompanied by crustal extension of the newly accreted oceanic slab, and

Multi-stage mixing in subduction zone: Application to Merapi volcano, Indonesia

Science.gov (United States)

Debaille, V.; Doucelance, R.; Weis, D.; Schiano, P.

2003-04-01

Basalts sampling subduction zone volcanism (IAB) often show binary mixing relationship in classical Sr-Nd, Pb-Pb, Sr-Pb isotopic diagrams, generally interpreted as reflecting the involvement of two components in their source. However, several authors have highlighted the presence of minimum three components in such a geodynamical context: mantle wedge, subducted and altered oceanic crust and subducted sediments. The overlying continental crust can also contribute by contamination and assimilation in magma chambers and/or during magma ascent. Here we present a multi-stage model to obtain a two end-member mixing from three components (mantle wedge, altered oceanic crust and sediments). The first stage of the model considers the metasomatism of the mantle wedge by fluids and/or melts released by subducted materials (altered oceanic crust and associated sediments), considering mobility and partition coefficient of trace elements in hydrated fluids and silicate melts. This results in the generation of two distinct end-members, reducing the number of components (mantle wedge, oceanic crust, sediments) from three to two. The second stage of the model concerns the binary mixing of the two end-members thus defined: mantle wedge metasomatized by slab-derived fluids and mantle wedge metasomatized by sediment-derived fluids. This model has been applied on a new isotopic data set (Sr, Nd and Pb, analyzed by TIMS and MC-ICP-MS) of Merapi volcano (Java island, Indonesia). Previous studies have suggested three distinct components in the source of indonesian lavas: mantle wedge, subducted sediments and altered oceanic crust. Moreover, it has been shown that crustal contamination does not significantly affect isotopic ratios of lavas. The multi-stage model proposed here is able to reproduce the binary mixing observed in lavas of Merapi, and a set of numerical values of bulk partition coefficient is given that accounts for the genesis of lavas.

Resistivity Image from 2D Inversion of Magnetotelluric Data in the Northern Cascadia Subduction Zone (United States)

Science.gov (United States)

Gultom, F. B.; Niasari, S. W.; Hartantyo, E.

2018-04-01

Cascadia Subduction Zone (CSZ) lies between Pacific margin and North America plate. The purpose of this research is to identify the CSZ along Oregon, Idaho, Wyoming from conductivity (σ) contrast in the subsurface by using the magnetotelluric (MT) method. MT is an electromagnetic method that use frequency between 10-4 Hz and 104 Hz. We obtained the MT data from the EarthScope USArray in the form of EDI-File (five components of the electromagnetic field). We analyzed the MT data using phase tensor and modeled the data using 2D inversion. From the phase tensor analysis, the 3D data dominated the eastern regions. Global data misfit is 6,88, where WYI18 (close to Yellowstone) contributes misfit of 29,3. This means that the model response does not fit the data, which implies the data is not fully 2D. The 2D inversion results are found high resistivity anomalies (more than 500 ohm.m) at shallow depth beneath Oregon and Wyoming, which coresspond to high density anomalies. This high resistivity anomalies might correspond to the north American plate. Thus, it can be concluded that 2D inversion model can be used for most 3D MT data to illustrate the resistivity distribution in the Cascadia Subduction Zone.

Trench Parallel Bouguer Anomaly (TPBA): A robust measure for statically detecting asperities along the forearc of subduction zones

Science.gov (United States)

Raeesi, M.

2009-05-01

generate tsunami earthquakes. It gives a logical dimension to the foreshock and aftershock distributions. Using the TPBA, we can derive the scenarios for the early 20th century great earthquakes for which limited data is available. We present cases from Aleutian and South America subduction zones. The TPBA explains why there should be no great earthquake in the down-dip of Shumagin, but that there should be a major tsunami earthquake for its up-dip. Our evidences suggest that the process has already started. We give numerous examples for South America, Aleutian-Alaska, and Kurile-Kamchatka subduction zones and we also look at Cascadia. Despite the possible various applications of the new measure, here we draw the attention to its most important application - the detection of critical asperities. Supplied with this new measure, in addition to the available seismological data, seismologists should be able to detect the critical asperities and follow the evolving rupture process. This paves the way for revealing systematically the great interplate earthquakes.

Beginning the Modern Regime of Subduction Tectonics in Neoproterozoic time: Inferences from Ophiolites of the Arabian-Nubian Shield

Science.gov (United States)

Stern, R.

2003-04-01

It is now clear that the motive force for plate tectonics is provided by the sinking of dense lithosphere in subduction zones. Correspondingly, the modern tectonic regime is more aptly called ``subduction tectonics" than plate tectonics, which only describes the way Earth's thermal boundary layer adjusts to subduction. The absence of subduction tectonics on Mars and Venus implies that special circumstances are required for subduction to occur on a silicate planet. This begs the question: When did Earth's oceanic lithosphere cool sufficiently for subduction to began? This must be inferred from indirect lines of evidence; the focus here is on the temporal distribution of ophiolites. Well-preserved ophiolites with ``supra-subduction zone" (SSZ) affinities are increasingly regarded as forming when subduction initiates as a result of lithospheric collapse (± a nudge to get it started), and the formation of ophiolitic lithosphere in evolving forearcs favors their emplacement and preservation. The question now is what percentage of ophiolites with ``supra-subduction zone" (SSZ) chemical signatures formed in forearcs during subduction initiation events? Most of the large, well-preserved ophiolites (e.g., Oman, Cyprus, California, Newfoundland) may have this origin. If so, the distribution in space and time of such ophiolites can be used to identify ``subduction initiation" events, which are important events in the evolution of plate tectonics. Such events first occurred at the end of the Archean (˜2.5Ga) and again in the Paleoproterozoic (˜1.8 Ga), but ophiolites become uncommon after this. Well-preserved ophiolites become abundant in Neoproterozoic time, at about 800±50 Ma. Ophiolites of this age are common and well-preserved in the Arabian-Nubian Shield (ANS) of Egypt, Sudan, Ethiopia, Eritrea, and Saudi Arabia. ANS ophiolites mostly contain spinels with high Cr#, indicating SSZ affinities. Limited trace element data on pillowed lavas supports this interpretation

Probable Maximum Earthquake Magnitudes for the Cascadia Subduction

Science.gov (United States)

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

2013-12-01

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

Review of the South American characiform fish genus Chilodus, with description of a new species, C. gracilis (Pisces, Characiformes, Chilodontidae)

NARCIS (Netherlands)

Isbrücker, I.J.H.; Nijssen, H.

1988-01-01

Examination of 291 specimens of Chilodus, a genus of South American fresh water fishes, yielded the presence of three species, viz.: C. punctatus, C. zunevei, and C. gracilis. Of the first species the lectotype is designated. The type material of C. zunevei is lost; new material enabled a

Widespread pollution of the South American atmosphere predates the industrial revolution by 240 years

Science.gov (United States)

Uglietti, Chiara; Gabrielli, Paolo; Cooke, Colin; Vallelonga, Paul; Thompson, Lonnie

2015-04-01

In the Southern Hemisphere, evidence for preindustrial atmospheric pollution is restricted to a few geological archives of low temporal resolution that record trace element deposition originating from past mining and metallurgical operations in South America. Therefore the timing and the spatial impact of these activities on the past atmosphere remain poorly constrained. Here we present an annually resolved ice-core record (793-1989 AD) from the high altitude drilling site of Quelccaya (Peru) that archives preindustrial and industrial variations in trace elements. During the pre-colonial period (i.e., pre-1532 AD), the deposition of trace elements was mainly dominated by the fallout of aeolian dust and of ash from occasional volcanic eruptions indicating that metallurgic production during the Inca Empire (1438-1532 AD) had a negligible impact on the South American atmosphere. In contrast, a widespread anthropogenic signal is evident after 1540 AD, which corresponds with the beginning of colonial mining and metallurgy in Peru and Bolivia, 240 years prior to the Industrial Revolution. This shift was due to a major technological transition for silver extraction in South America (1572 AD), from lead-based smelting to mercury amalgamation, which precipitated a massive increase in mining activities. However, deposition of toxic trace metals during the Colonial era was still several factors lower than 20th century pollution that was unprecedented over the entirety of human history.

Widespread pollution of the South American atmosphere predates the industrial revolution by 240 y.

Science.gov (United States)

Uglietti, Chiara; Gabrielli, Paolo; Cooke, Colin A; Vallelonga, Paul; Thompson, Lonnie G

2015-02-24

In the Southern Hemisphere, evidence for preindustrial atmospheric pollution is restricted to a few geological archives of low temporal resolution that record trace element deposition originating from past mining and metallurgical operations in South America. Therefore, the timing and the spatial impact of these activities on the past atmosphere remain poorly constrained. Here we present an annually resolved ice core record (A.D. 793-1989) from the high-altitude drilling site of Quelccaya (Peru) that archives preindustrial and industrial variations in trace elements. During the precolonial period (i.e., pre-A.D. 1532), the deposition of trace elements was mainly dominated by the fallout of aeolian dust and of ash from occasional volcanic eruptions, indicating that metallurgic production during the Inca Empire (A.D. 1438-1532) had a negligible impact on the South American atmosphere. In contrast, a widespread anthropogenic signal is evident after around A.D. 1540, which corresponds with the beginning of colonial mining and metallurgy in Peru and Bolivia, ∼240 y before the Industrial Revolution. This shift was due to a major technological transition for silver extraction in South America (A.D. 1572), from lead-based smelting to mercury amalgamation, which precipitated a massive increase in mining activities. However, deposition of toxic trace metals during the Colonial era was still several factors lower than 20th century pollution that was unprecedented over the entirety of human history.

Food Insecurity, Not Stress is Associated with Three Measures of Obesity in Low-Income, Mexican-American Women in South Texas.

Science.gov (United States)

Salinas, Jennifer J; Shropshire, William; Nino, Ana; Parra-Medina, Deborah

2016-01-01

To determine the relationship between obesity, food insecurity and perceived stress in very low income Mexican American women. Cross-sectional baseline data analysis of a randomized clinical trial. Texas-Mexico border region of South Texas. Very Low Income Mexican American Women. The relationship between obesity and food insecurity in a sample of very low income Hispanic women living in South Texas depends on the measure of obesity and the dimension of food insecurity. The only measure of food insecurity associated with all measures of obesity was often not having enough money to afford to eat balanced meals. Waist circumference was associated with the most dimensions of food insecurity, while BMI had the least associations. Finally, perceived stress was not significantly associated with BMI, waist circumference or percent body fat when adjusted for other covariates. We have found a strong and significant relationship between food insecurity related to having enough resources to eat a balanced diet and BMI, waist circumference, and percent body fat in low-income Mexican American women. While behavioural change is an important strategy for reducing obesity, consideration may need to be made as to how food access with high nutritional value, may be in and of itself a contributing factor in obesity in low income populations.

Separate zones of sulfate and sulfide release from subducted mafic oceanic crust

Science.gov (United States)

Tomkins, Andrew G.; Evans, Katy A.

2015-10-01

Liberation of fluids during subduction of oceanic crust is thought to transfer sulfur into the overlying sub-arc mantle. However, despite the importance of sulfur cycling through magmatic arcs to climate change, magma oxidation and ore formation, there has been little investigation of the metamorphic reactions responsible for sulfur release from subducting slabs. Here, we investigate the relative stability of anhydrite (CaSO4) and pyrite (FeS2) in subducted basaltic oceanic crust, the largest contributor to the subducted sulfur budget, to place constraints on the processes controlling sulfur release. Our analysis of anhydrite stability at high pressures suggests that this mineral should dominantly dissolve into metamorphic fluids released across the transition from blueschist to eclogite facies (∼450-650 °C), disappearing at lower temperatures on colder geothermal trajectories. In contrast, we suggest that sulfur release via conversion of pyrite to pyrrhotite occurs at temperatures above 750 °C. This higher temperature stability is indicated by the preservation of pyrite-bornite inclusions in coesite-bearing eclogites from the Sulu Belt in China, which reached temperatures of at least 750 °C. Thus, sulfur may be released from subducting slabs in two separate pulses; (1) varying proportions of SO2, HSO4- and H2S are released via anhydrite breakdown at the blueschist-eclogite transition, promoting oxidation of remaining silicates in some domains, and (2) H2S is released via pyrite breakdown well into the eclogite facies, which may in some circumstances coincide with slab melting or supercritical liquid generation driven by influx of serpentinite-derived fluids. These results imply that the metallogenic potential in the sub-arc mantle above the subducting slab varies as a function of subduction depth, having the greatest potential above the blueschist-eclogite transition given the association between oxidised magmas and porphyry Cu(-Au-Mo) deposits. We speculate

Phylodynamic analysis of avian infectious bronchitis virus in South America.

Science.gov (United States)

Marandino, Ana; Pereda, Ariel; Tomás, Gonzalo; Hernández, Martín; Iraola, Gregorio; Craig, María Isabel; Hernández, Diego; Banda, Alejandro; Villegas, Pedro; Panzera, Yanina; Pérez, Ruben

2015-06-01

Infectious bronchitis virus (IBV) is a coronavirus of chickens that causes great economic losses to the global poultry industry. The present study focuses on South American IBVs and their genetic relationships with global strains. We obtained full-length sequences of the S1 coding region and N gene of IBV field isolates from Uruguay and Argentina, and performed Phylodynamic analysis to characterize the strains and estimate the time of the most recent common ancestor. We identified two major South American genotypes, which were here denoted South America I (SAI) and Asia/South America II (A/SAII). The SAI genotype is an exclusive South American lineage that emerged in the 1960s. The A/SAII genotype may have emerged in Asia in approximately 1995 before being introduced into South America. Both SAI and A/SAII genotype strains clearly differ from the Massachusetts strains that are included in the vaccine formulations being used in most South American countries. © 2015 The Authors.

The interplay between subduction and lateral extrusion: A case study for the European Eastern Alps based on analogue models

Science.gov (United States)

van Gelder, I. E.; Willingshofer, E.; Sokoutis, D.; Cloetingh, S. A. P. L.

2017-08-01

A series of analogue experiments simulating intra-continental subduction contemporaneous with lateral extrusion of the upper plate are performed to study the interference between these two processes at crustal levels and in the lithospheric mantle. The models demonstrate that intra-continental subduction and coeval lateral extrusion of the upper plate are compatible processes leading to similar deformation structures within the extruding region as compared to the classical setup, lithosphere-scale indentation. Strong coupling across the subduction boundary allows for the transfer of stresses to the upper plate, where strain regimes are characterized by crustal thickening near a confined margin and dominated by lateral displacement of material near a weak lateral confinement. The strain regimes propagate laterally during ongoing convergence creating an area of overlap characterized by transpression. When subduction is oblique to the convergence direction, the upper plate is less deformed and as a consequence the amount of lateral extrusion decreases. In addition, strain is partitioned along the oblique plate boundary resulting in less subduction in expense of right lateral displacement close to the weak lateral confinement. Both oblique and orthogonal subduction models have a strong resemblance to lateral extrusion tectonics of the Eastern Alps (Europe), where subduction of the adjacent Adriatic plate beneath the Eastern Alps is debated. Our results imply that subduction of Adria is a valid mechanisms to induce extrusion-type deformation within the Eastern Alps lithosphere. Furthermore, our findings suggest that the Oligocene to Late Miocene structural evolution of the Eastern Alps reflects a phase of oblique subduction followed by a later stage of orthogonal subduction conform a Miocene shift in the plate motion of Adria. Oblique subduction also provides a viable mechanism to explain the rapid decrease in slab length of the Adriatic plate beneath the Eastern Alps

Bimodal volcanism in northeast Puerto Rico and the Virgin Islands (Greater Antilles Island Arc): Genetic links with Cretaceous subduction of the mid-Atlantic ridge Caribbean spur

Science.gov (United States)

Jolly, Wayne T.; Lidiak, Edward G.; Dickin, Alan P.

2008-07-01

Bimodal extrusive volcanic rocks in the northeast Greater Antilles Arc consist of two interlayered suites, including (1) a predominantly basaltic suite, dominated by island arc basalts with small proportions of andesite, and (2) a silicic suite, similar in composition to small volume intrusive veins of oceanic plagiogranite commonly recognized in oceanic crustal sequences. The basaltic suite is geochemically characterized by variable enrichment in the more incompatible elements and negative chondrite-normalized HFSE anomalies. Trace element melting and mixing models indicate the magnitude of the subducted sediment component in Antilles arc basalts is highly variable and decreases dramatically from east to west along the arc. In the Virgin Islands, the sediment component ranges between 4% during the Cenomanian-Campanian interval. The silicic suite, consisting predominantly of rhyolites, is characterized by depleted Al 2O 3 (average Virgin Islands on the east, rhyolites comprise up to 80% of Lower Albian strata (112 to 105 Ma), and about 20% in post-Albian strata (105 to 100 Ma). Farther west, in Puerto Rico, more limited proportions (Atlantic Ridge, which was located approximately midway between North and South America until Campanian times. Within this hypothetical setting the centrally positioned Virgin Islands terrain remained approximately fixed above the subducting ridge as the Antilles arc platform swept northeastward into the slot between the Americas. Accordingly, heat flow in the Virgin Islands was elevated throughout the Cretaceous, giving rise to widespread crustal melting, whereas the subducted sediment flux was limited. Conversely, toward the west in central Puerto Rico, which was consistently more remote from the subducting ridge, heat flow was relatively low and produced limited crustal melting, while the sediment flux was comparatively elevated.

Plateau subduction, intraslab seismicity, and the Denali (Alaska) volcanic gap

Science.gov (United States)

Chuang, Lindsay Yuling; Bostock, Michael; Wech, Aaron; Plourde, Alexandre

2018-01-01

Tectonic tremors in Alaska (USA) are associated with subduction of the Yakutat plateau, but their origins are unclear due to lack of depth constraints. We have processed tremor recordings to extract low-frequency earthquakes (LFEs), and generated a set of six LFE waveform templates via iterative network matched filtering and stacking. The timing of impulsive P (compressional) wave and S (shear) wave arrivals on template waveforms places LFEs at 40–58 km depth, near the upper envelope of intraslab seismicity and immediately updip of increased levels of intraslab seismicity. S waves at near-epicentral distances display polarities consistent with shear slip on the plate boundary. We compare characteristics of LFEs, seismicity, and tectonic structures in central Alaska with those in warm subduction zones, and propose a new model for the region’s unusual intraslab seismicity and the enigmatic Denali volcanic gap (i.e., an area of no volcanism where expected). We argue that fluids in the Yakutat plate are confined to its upper crust, and that shallow subduction leads to hydromechanical conditions at the slab interface in central Alaska akin to those in warm subduction zones where similar LFEs and tremor occur. These conditions lead to fluid expulsion at shallow depths, explaining strike-parallel alignment of tremor occurrence with the Denali volcanic gap. Moreover, the lack of double seismic zone and restriction of deep intraslab seismicity to a persistent low-velocity zone are simple consequences of anhydrous conditions prevailing in the lower crust and upper mantle of the Yakutat plate.

Vizualization Challenges of a Subduction Simulation Using One Billion Markers

Science.gov (United States)

Rudolph, M. L.; Gerya, T. V.; Yuen, D. A.

2004-12-01

Recent advances in supercomputing technology have permitted us to study the multiscale, multicomponent fluid dynamics of subduction zones at unprecedented resolutions down to about the length of a football field. We have performed numerical simulations using one billion tracers over a grid of about 80 thousand points in two dimensions. These runs have been performed using a thermal-chemical simulation that accounts for hydration and partial melting in the thermal, mechanical, petrological, and rheological domains. From these runs, we have observed several geophysically interesting phenomena including the development of plumes with unmixed mantle composition as well as plumes with mixed mantle/crust components. Unmixed plumes form at depths greater than 100km (5-10 km above the upper interface of subducting slab) and consist of partially molten wet peridotite. Mixed plumes form at lesser depth directly from the subducting slab and contain partially molten hydrated oceanic crust and sediments. These high resolution simulations have also spurred the development of new visualization methods. We have created a new web-based interface to data from our subduction simulation and other high-resolution 2D data that uses an hierarchical data format to achieve response times of less than one second when accessing data files on the order of 3GB. This interface, WEB-IS4, uses a Javascript and HTML frontend coupled with a C and PHP backend and allows the user to perform region of interest zooming, real-time colormap selection, and can return relevant statistics relating to the data in the region of interest.

The Role of a Weak Layer at the Base of an Oceanic Plate on Subduction Dynamics

Science.gov (United States)

Carluccio, R.; Moresi, L. N.; Kaus, B. J. P.

2017-12-01

Plate tectonics relies on the concept of an effectively rigid lithospheric lid moving over a weaker asthenosphere. In this model, the lithosphere asthenosphere boundary (LAB) is a first-order discontinuity that accommodates differential motion between tectonic plates and the underlying mantle. Recent seismic studies have revealed the existence of a low velocity and high electrical conductivity layer at the base of subducting tectonic plates. This thin layer has been interpreted as being weak and slightly buoyant and it has the potential to influence the dynamics of subducting plates. However, geodynamically, the role of a weak layer at the base of the lithosphere remains poorly studied, especially at subduction zones. Here, we use numerical models to investigate the first-order effects of a weak buoyant layer at the LAB on subduction dynamics. We employ both 2-D and 3-D models in which the slab and the mantle are either linear viscous or have a more realistic temperature-dependent, visco-elastic-plastic rheology and we vary the properties of the layer at the base of the oceanic lithosphere. Our results show that the presence of a weak layer affects the dynamics of plates, primarily by increasing the subduction speed and also influences the morphology of subducting slab. For moderate viscosity contrasts (1000), it can also change the morphology of the subduction itself and for thinner and more buoyant layers, the overall effect is reduced. The overall impact of this effects may depend on the effective contrast between the properties of the slab and the weak layer + mantle systems, and so, by the layer characteristics modelled such as its viscosity, density, thickness and rheology. In this study, we show and summarise this impact consistently with the recent seismological constraints and observations, for example, a pile-up of weak material in the bending zone of the subducting plate.

A detailed map of the 660-kilometer discontinuity beneath the izu-bonin subduction zone.

Science.gov (United States)

Wicks, C W; Richards, M A

1993-09-10

Dynamical processes in the Earth's mantle, such as cold downwelling at subduction zones, cause deformations of the solid-state phase change that produces a seismic discontinuity near a depth of 660 kilometers. Observations of short-period, shear-to-compressional wave conversions produced at the discontinuity yield a detailed map of deformation beneath the Izu-Bonin subduction zone. The discontinuity is depressed by about 60 kilometers beneath the coldest part of the subducted slab, with a deformation profile consistent with the expected thermal signature of the slab, the experimentally determined Clapeyron slope of the phase transition, and the regional tectonic history.

Mycobacterium pinnipedii: Transmission from South American sea lion (Otaria byronia) to Bactrian camel (Camelus bactrianus bactrianus) and Malayan tapirs (Tapirus indicus)

NARCIS (Netherlands)

Moser, I.; Prodinger, W.M.; Hotzel, H.; Greenwald, R.; Lyashchenko, K.P.; Bakker, D.; Gomis, D.; Seidler, T.; Ellenberger, C.; Hetzel, U.; Wuennemann, K.; Moisson, P.

2008-01-01

Tuberculosis infections caused by Mycobacterium (M.) pinnipedii in a South American sea lion, Bactrian camel, and Malayan tapirs kept in two zoological gardens spanning a time period of 5 years are reported. The zoos were linked by the transfer of one tapir. Conventional bacteriological and

Glacial refugia and the prediction of future habitat coverage of the South American lichen species Ochrolechia austroamericana

OpenAIRE

Martin Kukwa; Marta Kolanowska

2016-01-01

The biogeographic history of lichenized fungi remains unrevealed because those organisms rarely fossilize due to their delicate, often tiny and quickly rotting thalli. Also the ecology and factors limiting occurrence of numerous taxa, especially those restricted in their distribution to tropical areas are poorly recognized. The aim of this study was to determine localization of glacial refugia of South American Ochrolechia austroamericana and to estimate the future changes in the coverage of ...

Permian arc evolution associated with Panthalassa subduction along the eastern margin of the South China block, based on sandstone provenance and U-Pb detrital zircon ages of the Kurosegawa belt, Southwest Japan

Science.gov (United States)

Hara, Hidetoshi; Hirano, Miho; Kurihara, Toshiyuki; Takahashi, Toshiro; Ueda, Hayato

2018-01-01

We have studied the petrography, geochemistry, and detrital zircon U-Pb ages of sandstones from shallow-marine forearc sediments, accretionary complexes (ACs), and metamorphosed accretionary complexes (Meta-ACs) within the Kurosegawa belt of Southwest Japan. Those rocks formed in a forearc region of a Permian island arc associated with subduction of the Panthalassa oceanic crust along the eastern margin of the South China block (Yangtze block). The provenance of the shallow-marine sediments was dominated by basaltic to andesitic volcanic rocks and minor granitic rocks during the late Middle to Late Permian. The ACs were derived from felsic to andesitic volcanic rocks during the Late Permian. The provenance of Meta-ACs was dominated by andesitic volcanic rocks in the Middle Permian. The provenance, source rock compositions, and zircon age distribution for the forearc sediments, ACs and Meta-ACs have allowed us to reconstruct the geological history of the Permian arc system of the Kurosegawa belt. During the Middle Permian, the ACs were accreted along the eastern margin of the South China block. The Middle Permian arc was an immature oceanic island arc consisting of andesitic volcanic rocks. During the Late Permian, the ACs formed in a mature arc, producing voluminous felsic to andesitic volcanic rocks. A forearc basin developed during the late Middle to Late Permian. Subsequently, the Middle Permian ACs and part of the Late Permian AC underwent low-grade metamorphism in the Late to Early Jurassic, presenting the Meta-ACs.

The thermal effects of steady-state slab-driven mantle flow above a subducting plate: the Cascadia subduction zone and backarc

Science.gov (United States)

Currie, C. A.; Wang, K.; Hyndman, Roy D.; He, Jiangheng

2004-06-01

At subduction zones, geophysical and geochemical observations indicate that the arc and backarc regions are hot, in spite of the cooling effects of a subducting plate. At the well-studied Cascadia subduction zone, high mantle temperatures persist for over 500 km into the backarc, with little lateral variation. These high temperatures are even more surprising due to the juxtaposition of the hot Cascadia backarc against the thick, cold North America craton lithosphere. Given that local heat sources appear to be negligible, mantle flow is required to transport heat into the wedge and backarc. We have examined the thermal effects of mantle flow induced by traction along the top of the subducting plate. Through systematic tests of the backarc model boundary, we have shown that the model thermal structure of the wedge is primarily determined by the assumed temperatures along this boundary. To get high temperatures in the wedge, it is necessary for flow to mine heat from depth, either by using a temperature-dependent rheology, or by introducing a deep cold boundary through a thick adjacent lithosphere, consistent with the presence of a craton. Regardless of the thermal conditions along the backarc boundary, flow within an isoviscous wedge is too slow to transport a significant amount of heat into the wedge corner. With a more realistic stress- and temperature-dependent wedge rheology, flow is focused into the wedge corner, resulting in rapid flow upward toward the corner and enhanced temperatures below the arc, compatible with temperatures required for arc magma generation. However, this strong flow focusing produces a nearly stagnant region further landward in the shallow backarc mantle, where model temperatures and heat flow are much lower than observed. Observations of high backarc temperatures, particularly in areas that have not undergone recent extension, provide an important constraint on wedge dynamics. None of the models of simple traction-driven flow were able

Dry Juan de Fuca slab revealed by quantification of water entering Cascadia subduction zone

Science.gov (United States)

Canales, J. P.; Carbotte, S. M.; Nedimovic, M. R.; Carton, H. D.

2017-12-01

Water is carried by subducting slabs as a pore fluid and in structurally bound minerals, yet no comprehensive quantification of water content and how it is stored and distributed at depth within incoming plates exists for any segment of the global subduction system. Here we use controlled-source seismic data collected in 2012 as part of the Ridge-to-Trench seismic experiment to quantify the amount of pore and structurally bound water in the Juan de Fuca plate entering the Cascadia subduction zone. We use wide-angle OBS seismic data along a 400-km-long margin-parallel profile 10-15 km seaward from the Cascadia deformation front to obtain P-wave tomography models of the sediments, crust, and uppermost mantle, and effective medium theory combined with a stochastic description of crustal properties (e.g., temperature, alteration assemblages, porosity, pore aspect ratio), to analyze the pore fluid and structurally bound water reservoirs in the sediments, crust and lithospheric mantle, and their variations along the Cascadia margin. Our results demonstrate that the Juan de Fuca lower crust and mantle are much drier than at any other subducting plate, with most of the water stored in the sediments and upper crust. Previously documented, variable but limited bend faulting along the margin, which correlates with degree of plate locking, limits slab access to water, and a warm thermal structure resulting from a thick sediment cover and young plate age prevents significant serpentinization of the mantle. Our results have important implications for a number of subduction processes at Cascadia, such as: (1) the dryness of the lower crust and mantle indicates that fluids that facilitate episodic tremor and slip must be sourced from the subducted upper crust; (2) decompression rather than hydrous melting must dominate arc magmatism in northern-central Cascadia; and (3) dry subducted lower crust and mantle can explain the low levels of intermediate-depth seismicity in the Juan de

Reconstructing the paleogeography and subduction geodynamics of Greater India: how to apply Ockham's Razor?

Science.gov (United States)

Van Hinsbergen, D. J. J.; Li, S.; Lippert, P. C.; Huang, W.; Advokaat, E. L.; Spakman, W.

2017-12-01

Key in understanding the geodynamics governing subduction and orogeny is reconstructing the paleogeography of `Greater India', the Indian plate lithosphere that subducted since Tibetan Himalayan continental crustal collision with Asia. Here, we discuss how the principle of Ockham's Razor, favoring the simplest scenario as the most likely, may apply to three perspectives on Greater India's paleogeography. We follow recent constraints suggesting a 58 Ma initial collision and update the kinematic restoration of intra-Asian shortening with a recently proposed Indochina extrusion model that reconciles long-debated large and small estimates of Indochina extrusion. The reconstruction is tested against Tibetan paleomagnetic rotation data, and against seismic tomographic constraints on paleo-subduction zone locations. The resulting restoration shows 1000-1200 km of post-collisional intra-Asian shortening, leaving a 2600-3400 km wide Greater India. Ockham's Razor from a paleogeographic, sediment provenance perspective would prefer a fully continental Greater India, although these sediments may also source from the Paleocene-Eocene west Indian orogen unrelated to the India-Asia collision. Ockham's Razor applied from a kinematic, paleomagnetic perspective, prefers major Cretaceous extension and `Greater India Basin' opening within Greater India, but data uncertainty may speculatively allow for minimal extension. Finally, from a geodynamic perspective, assuming a fully continental Greater India would require that the highest subduction rates recorded in the Phanerozoic would have been driven by a subduction of a lithosphere-crust assemblage more buoyant than the mantle, which seems physically improbable. Ockhams Razor thereby isolates the Greater India Basin hypothesis as the only scenario sustainable from all perspectives. Finally, we infer that the old pre-collisional lithosphere rapidly entered the lower mantle sustaining high subduction rates, whilst post

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

Science.gov (United States)

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

2010-12-01

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

Earthquake nucleation in weak subducted carbonates

Science.gov (United States)

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

2016-09-01

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

Subducted bathymetric features linked to variations in earthquake apparent stress along the northern Japan Trench

Science.gov (United States)

Moyer, P. A.; Bilek, S. L.; Phillips, W. S.

2010-12-01

Ocean floor bathymetric features such as seamounts and ridges are thought to influence the earthquake rupture process when they enter the subduction zone by causing changes in frictional conditions along the megathrust contact between the subducting and overriding plates. Once subducted, these features have been described as localized areas of heterogeneous plate coupling, with some controversy over whether these features cause an increase or decrease in interplate coupling. Along the northern Japan Trench, a number of bathymetric features, such as horst and graben structures and seamounts, enter the subduction zone where they may vary earthquake behavior. Using seismic coda waves, scattered energy following the direct wave arrivals, we compute apparent stress (a measure of stress drop proportional to radiated seismic energy that has been tied to the strength of the fault interface contact) for 329 intermediate magnitude (3.2 earthquake spectra for path and site effects and compute apparent stress using the seismic moment and corner frequency determined from the spectra. Preliminary results indicate apparent stress values between 0.3 - 22.6 MPa for events over a depth range of 2 - 55 km, similar to those found in other studies of the region although within a different depth range, with variations both along-strike and downdip. Off the Sanriku Coast, horst and graben structures enter the Japan Trench in an area where a large number of earthquakes occur at shallow (< 30 km) depth. These shallow events have a mean apparent stress of 1.2 MPa (range 0.3 - 3.8 MPa) which is approximately 2 times lower then the mean apparent stress for other events along the northern portion of this margin in the same shallow depth range. The relatively low apparent stress for events related to subducting horst and graben structures suggests weak interplate coupling between the subducting and overriding plates due to small, irregular contact zones with these features at depth. This is in

Crustal evolution of South American Platform based on Sm-Nd isotope geochemistry

International Nuclear Information System (INIS)

Sato, Kei

1998-01-01

Sm-Nd isotopic systematics is relevant to the topics of origin and evolution the of continental crust, where model ages refer to the time when crustal material was differentiated from the upper mantle. Alternative interpretations are due to a lack of adequate information on crustal processes and the variable composition of the mantle sources. The Sm-Nd methods are presented, and applied on rock materials from the South American Platform. The main conclusions indicate juvenile accretion with higher growth rates (peaks), around 3.7-3.5 Ga (∼ 0.5% in volume), 3.1 - 2.9 Ga (∼16%), 2.7 - 2.6 (∼ 9%), 2.2 - 1.9 (35%) and 1.3-1.0 (7%). The continental growth curve indicates that about 35 % of the crust was formed by 2.5 Ga, 88% by 1.8 Ga and 99% by 1.0 Ga, and the remaining ∼ 1 % was added in the Phanerozoic. Rapid crustal growth occurred between 2.2 and 1.9 Ga. The main period of continental crust formation occurred during the Paleoproterozoic, corresponding to 54 % in volume. Sm-Nd model ages, when compared with the crystallisation ages of granitoid rocks, furnish a rough estimate of juvenile vs. reworked material. Within the South American Platform about 45% of juvenile continental crust is still preserved within tectonic provinces of different ages. The remainder represents continental crust reworked in younger tectono-thermal events. In particular crustal reworking was predominating over juvenile accretion during Meso-Neoproterozoic. The Transbrasiliano Lineament is a megasuture, active in the Neoproterozoic, which separates a large northwestern mass, including the Amazonian and Sao Luis Cratons, from a southeastern mass, formed by a collage of cratonic fragments, of which the Sao Francisco and Rio de La Plata are the largest. The crustal evolutions of these two large continental masses are considered individually, and can be resumed following form: I - Old Archean rocks (>3.4 Ga) are found only within the south-eastern part (Gaviao Block, Contendas

Lithospheric electrical structure of the middle Lhasa terrane in the south Tibetan plateau

Science.gov (United States)

Liang, Hongda; Jin, Sheng; Wei, Wenbo; Gao, Rui; Ye, Gaofeng; Zhang, Letian; Yin, Yaotian; Lu, Zhanwu

2018-04-01

The Lhasa terrane in southern Tibetan plateau is a huge tectono-magmatic belt and an important metallogenic belt. Its formation evolution process and mineralization are affected by the subduction of oceanic plate and subsequent continental collision. However, the evolution of Lhasa terrane has been a subject of much debate for a long time. The Lithospheric structure records the deep processes of the subduction of oceanic plate and continental collision. The magnetotelluric (MT) method can probe the sub-surface electrical conductivity, newly dense broadband and long period magnetotelluric data were collected along a south-north trending profile that across the Lhasa terrane at 88°-89°E. Dimensionality analyses demonstrated that the MT data can be interpreted using two-dimensional approaches, and the regional strike direction was determined as N110°E.Based on data analysis results, a two-dimensional (2-D) resistivity model of crust and upper mantle was derived from inversion of the transverse electric mode, transverse magnetic mode and vertical magnetic field data. Inversion model shows a large north-dipping resistor that extended from the upper crust to upper mantle beneath the Himalaya and the south of Lhasa Terrane, which may represent the subducting Indian continental lithosphere. The 31°N may be an important boundary in the Lhasa Terrane, the south performs a prominent high-conductivity anomaly from the lower crust to upper mantle which indicates the existence of asthenosphere upwelling, while the north performs a higher resistivity and may have a reworking ancient basement. The formation of the ore deposits in the study area may be related to the upwelling of the mantle material triggered by slab tearing and/or breaking off of the Indian lithosphere, and the mantle material input also contributed the total thickness of the present-day Tibetan crust. The results provide helpful constrains to understand the mechanism of the continent-continent collision and

Accessory minerals and subduction zone metasomatism: a geochemical comparison of two mélanges (Washington and California, U.S.A.)

Science.gov (United States)

Sorensen, Sorena S.; Grossman, Jeffrey N.

1993-01-01

The ability of a subducted slab or subducted sediment to contribute many incompatible trace elements to arc source regions may depend on the stabilities of accessory minerals within these rocks, which can only be studied indirectly. In contrast, the role of accessory minerals in lower-T and -P metasomatic processes within paleo-subduction zones can be studied directly in subduction-zone metamorphic terranes.

American marsupials chromosomes: why study them?

Directory of Open Access Journals (Sweden)

Marta Svartman

2009-01-01

Full Text Available Marsupials, one of the three main groups of mammals, are only found in Australia and in the American continent. Studies performed in Australian marsupials have demonstrated the great potential provided by the group for the understanding of basic genetic mechanisms and chromosome evolution in mammals. Genetic studies in American marsupials are relatively scarce and cytogenetic data of most species are restricted to karyotype descriptions, usually without banding patterns. Nevertheless, the first marsupial genome sequenced was that of Monodelphis domestica, a South American species. The knowledge about mammalian genome evolution and function that resulted from studies on M. domestica is in sharp contrast with the lack of genetic data on most American marsupial species. Here, we present an overview of the chromosome studies performed in marsupials with emphasis on the South American species.

Fate of Subducting Organic Carbon: Evidence from HP/UHP Metasedimentary Suites

Science.gov (United States)

Kraft, K.; Bebout, G. E.

2017-12-01

Community interest in deep-Earth C cycling has focused attention on extents of C release from subducting oceanic lithosphere and sediment and the fate of this released C. Many have suggested that, based on isotopic and other arguments, 20% of the C subducted into the deeper mantle is in reduced form (organic); however, individual margins show large variation in carbonate to organic C ratios. Despite the size of the potentially deeply subducted organic C reservoir, its fate in subducting sections remains largely unexplored, with most attention paid to release of carbonate C. To characterize the forearc behavior of organic C, metamorphosed to P-T as high as that beneath volcanic fronts, we evaluated records of reduced C (RC) contents and isotope compositions in HP/UHP metasediments: 1) Schistes Lustres/Cignana (SLC) suite (Alps; Cook-Kollars et al., 2014, Chem Geol) with abundant carbonate and resembling sediment entering the East Sunda trench; and (2) Franciscan Complex (FC), W. Baja Terrain (WBT), Catalina Schist (CS) metasediments (Sadofsky and Bebout, 2003, G3), largely sandstone-shale sequences containing very little carbonate. In general, more Al-rich samples (shaley) in the terrigenous metasedimentary suites have higher concentrations of RC, which in low-grade units preserves δ13C of its organic protoliths. Carbonate-poor rocks in the SLC suite, and at ODP Site 765, show correlated major element (Al, Mg, Mn, Ti, P) and RC contents (up to 1.2 wt.%) reflecting sandstone-shale mixture. In the FC, WBT, and CS, the more Al-rich samples contain up to 2 wt. % RC. In high-grade Catalina Schist, RC has elevated δ13C due to C loss in CH4 and high-grade Alps rocks show reduced RC wt. % normalized to Al content. We consider processes that could alter contents and isotopic compositions of RC in sediment, e.g., devolatilization, closed-system exchange with carbonate, redox reactions, isotopic exchange with C in externally-derived fluids. It appears that, on modern Earth

Tomographic Imaging of the Lesser Antilles Subducted Slab and its Significance for Estimating the Age and Amount of Eastward Motion of the Overriding Caribbean Plate

Science.gov (United States)

Mann, P.; Chen, Y. W.; Wu, J.; Suppe, J.

2017-12-01

The idea of a Pacific-derived and eastward-transported Caribbean and Scotia plates was first proposed by J. Tuzo Wilson in 1966. Wilson proposed that the motion of these two, small plates was analogous to "ice rafting" observed on frozen lakes and oceans when a narrow ( 50 m) strip of ice is forced over a lower plate of ice. In the Caribbean the upper plate corresponds to the 750 km-long, north-south length of the Lesser Antilles volcanic arc ranging in thickness from 20-30 km while its subducting plate is Atlantic Cretaceous oceanic crust of 8-10 km thickness and subducting at an angle of 45º to a depth of 300 km into the mantle. We estimated the length of the Lesser Antilles slab from MIT P-wave global tomography (MITP08; Li et al., 2008) and compared to published transects from Utrecht UUP-07 global tomography (van Bentham et al., 2013). The measured slab lengths vary from 1550 km (Utrecht) to 1250 km (MIT). We then unfolded both slabs to the Earth's surface, and used GPlates to restore the leading edge of the Caribbean plate at the time of the Lesser Antilles slab's initial subduction. The Middle Eocene (49 Ma) reconstruction realigns the proto-Lesser Antilles arc and leading edge of the Caribbean plate in a continuous arc with older arc rocks in Cuba. During this Middle Eocene period of abrupt tectonic transition, the Cuban arc segment was terminated on its northeastward path by collision with the Bahama carbonate platform with subsequent reorientation onto its present, east-west path into the central Atlantic Ocean from 49-0 Ma. This collision/plate reorientation event is independently recorded by: 1) a poorly defined Greater Antilles slab seen on tomography that is aligned with the Cuban arc; 2) identical initiation ages of 49 Ma for the Cayman trough pull-apart and the Lesser Antilles slab; and 3) similarity in lengths for the length of the subducted, Lesser Antilles slab ( 1250-1550 km) and the length of the Cayman trough pull-apart basin ( 1100 km). East

Optimizing Surveillance for South American Origin Influenza A Viruses Along the United States Gulf Coast Through Genomic Characterization of Isolates from Blue-winged Teal (Anas discors).

Science.gov (United States)

Ramey, A M; Walther, P; Link, P; Poulson, R L; Wilcox, B R; Newsome, G; Spackman, E; Brown, J D; Stallknecht, D E

2016-04-01

Relative to research focused on inter-continental viral exchange between Eurasia and North America, less attention has been directed towards understanding the redistribution of influenza A viruses (IAVs) by wild birds between North America and South America. In this study, we genomically characterized 45 viruses isolated from blue-winged teal (Anas discors) along the Texas and Louisiana Gulf Coast during March of 2012 and 2013, coincident with northward migration of this species from Neotropical wintering areas to breeding grounds in the United States and Canada. No evidence of South American lineage genes was detected in IAVs isolated from blue-winged teal supporting restricted viral gene flow between the United States and southern South America. However, it is plausible that blue-winged teal redistribute IAVs between North American breeding grounds and wintering areas throughout the Neotropics, including northern South America, and that viral gene flow is limited by geographical barriers further south (e.g., the Amazon Basin). Surveillance for the introduction of IAVs from Central America and northern South America into the United States may be further optimized through genomic characterization of viruses resulting from coordinated, concurrent sampling efforts targeting blue-winged teal and sympatric species throughout the Neotropics and along the United States Gulf Coast. © Published 2014. This article is a US Government work and is in the public domain in the USA.

Remnants of Eoarchean continental crust derived from a subducted proto-arc.

Science.gov (United States)

Ge, Rongfeng; Zhu, Wenbin; Wilde, Simon A; Wu, Hailin

2018-02-01

Eoarchean [3.6 to 4.0 billion years ago (Ga)] tonalite-trondhjemite-granodiorite (TTG) is the major component of Earth's oldest remnant continental crust, thereby holding the key to understanding how continental crust originated and when plate tectonics started in the early Earth. TTGs are mostly generated by partial melting of hydrated mafic rocks at different depths, but whether this requires subduction remains enigmatic. Recent studies show that most Archean TTGs formed at relatively low pressures (≤1.5 GPa) and do not require subduction. We report a suite of newly discovered Eoarchean tonalitic gneisses dated at ~3.7 Ga from the Tarim Craton, northwestern China. These rocks are probably the oldest high-pressure TTGs so far documented worldwide. Thermodynamic and trace element modeling demonstrates that the parent magma may have been generated by water-fluxed partial melting of moderately enriched arc-like basalts at 1.8 to 1.9 GPa and 800° to 830°C, indicating an apparent geothermal gradient (400° to 450°C GPa -1 ) typical for hot subduction zones. They also locally record geochemical evidence for magma interaction with a mantle wedge. Accordingly, we propose that these high-pressure TTGs were generated by partial melting of a subducted proto-arc during arc accretion. Our model implies that modern-style plate tectonics was operative, at least locally, at ~3.7 Ga and was responsible for generating some of the oldest continental nuclei.

Semen preservation and artificial insemination in domesticated South American camelids.

Science.gov (United States)

Bravo, P Walter; Alarcon, V; Baca, L; Cuba, Y; Ordoñez, C; Salinas, J; Tito, F

2013-01-10

Semen preservation and artificial insemination in South American camelids are reviewed giving emphasis to work done in Peru and by the authors. Reports on semen evaluation and the preservation process indicate that semen of alpacas and llamas can be manipulated by making it liquid first. Collagenase appears to be the best enzyme to eliminate viscosity. Tris buffer solution maintains a higher motility than egg-yolk citrate, phosphate buffered saline (PBS), Triladyl, and Merck-I extenders. Cooling of semen took 1h after collected, and equilibrated with 7% glycerol presented a better motility and spermatozoa survival at 1, 7, 15 and 30days after being slowly frozen in 0.25mL plastic straws. Trials of artificial insemination with freshly diluted semen and frozen-thawed semen are encouraging and needs to be tested extensively under field conditions. Recently, fertility rates varied from 3 to 67%. Semen preservation and most important, artificial insemination appear to be a reality, and could be used to improve the genetic quality of alpacas and llamas. Copyright © 2012 Elsevier B.V. All rights reserved.

Subduction of the Rivera plate beneath the Jalisco block as imaged by magnetotelluric data

OpenAIRE

Corbo-Camargo, Fernando; Arzate-Flores, Jorge Arturo; Álvarez-Béjar, Román; Aranda-Gómez, José Jorge; Yutsis, Vsevolod

2013-01-01

Two magnetotelluric (MT) profiles perpendicular to the trench provide information on the subduction of the Rivera plate under the Jalisco block (JB). The geometry of the subducting slab is inferred by the anomalous conductor on the top of the profile in the central part of the JB. High conductivity zones (

Social Identity Integration, Parental Response, and Psychological Outcomes among Lesbian, Gay, Bisexual, and Queer South Asian Americans

OpenAIRE

Kishore, Saanjh Aakash

2015-01-01

The goal of this study is to understand how social identities are integrated across domains of identity. Focusing on a population in which cultural norms dictate sexuality behaviors as a condition of ethnic membership, the study examines how South Asian LGBQ Americans integrate their ethnic and sexual orientation identities, and also examines the role of this dual social identity integration in the relationship between the distal stress of parental responses to LGBQ identity, the proximal str...

Review of South American mines

International Nuclear Information System (INIS)

Anon.

1984-01-01

A general overview is presented of the mining activity and plans for South America. The countries which are presented are Columbia, Argentina, Brazil, Venezuela, Chile, Peru, and Bolivia. The products of the mines include coal, bauxite, gold, iron, uranium, copper and numerous other minor materials. A discussion of current production, support and processing facilities, and mining strategies is also given

Carbonation by fluid-rock interactions at high-pressure conditions: Implications for carbon cycling in subduction zones

Science.gov (United States)

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

2016-07-01

Carbonate-bearing lithologies are the main carbon carrier into subduction zones. Their evolution during metamorphism largely controls the fate of carbon, regulating its fluxes between shallow and deep reservoirs. Recent estimates predict that almost all subducted carbon is transferred into the crust and lithospheric mantle during subduction metamorphism via decarbonation and dissolution reactions at high-pressure conditions. Here we report the occurrence of eclogite-facies marbles associated with metasomatic systems in Alpine Corsica (France). The occurrence of these marbles along major fluid-conduits as well as textural, geochemical and isotopic data indicating fluid-mineral reactions are compelling evidence for the precipitation of these carbonate-rich assemblages from carbonic fluids during metamorphism. The discovery of metasomatic marbles brings new insights into the fate of carbonic fluids formed in subducting slabs. We infer that rock carbonation can occur at high-pressure conditions by either vein-injection or chemical replacement mechanisms. This indicates that carbonic fluids produced by decarbonation reactions and carbonate dissolution may not be directly transferred to the mantle wedge, but can interact with slab and mantle-forming rocks. Rock-carbonation by fluid-rock interactions may have an important impact on the residence time of carbon and oxygen in subduction zones and lithospheric mantle reservoirs as well as carbonate isotopic signatures in subduction zones. Furthermore, carbonation may modulate the emission of CO2 at volcanic arcs over geological time scales.

South American camelid illegal traffic detection by means of molecular markers.

Science.gov (United States)

Di Rocco, F; Posik, D M; Ripoli, M V; Díaz, S; Maté, M L; Giovambattista, G; Vidal-Rioja, L

2011-11-01

South American camelids comprise the wild species guanaco and vicuña and their respective domestic relatives llama and alpaca. The aim of the present study was to determine by DNA analysis to which of these species belong a herd of camelids confiscated from a llama breeder but alleged to be alpacas by the prosecution, and to evaluate the usefulness of mitochondrial and autosomal DNA markers to solve judicial cases involving camelid taxa. Cytochrome b and cytochrome oxidase I mitochondrial genes and 7 STR were analyzed in 25 confiscated samples. Mitochondrial results were inconclusive because 18 of the sequestered samples presented haplotypes that corresponded to the guanaco haplogroup and the remaining seven belonged to a vicuña linage. Microsatellite data of casework samples and llama reference samples revealed different genetic profiles by the presence of private alleles at two microsatellites suggesting that the confiscated animals could be alpaca, or at least alpaca hybrids instead of pure llama. Copyright © 2011 Elsevier Ireland Ltd. All rights reserved.

Rheological Properties of Natural Subduction Zone Interface: Insights from "Digital" Griggs Experiments

Science.gov (United States)

Ioannidi, P. I.; Le Pourhiet, L.; Moreno, M.; Agard, P.; Oncken, O.; Angiboust, S.

2017-12-01

The physical nature of plate locking and its relation to surface deformation patterns at different time scales (e.g. GPS displacements during the seismic cycle) can be better understood by determining the rheological parameters of the subduction interface. However, since direct rheological measurements are not possible, finite element modelling helps to determine the effective rheological parameters of the subduction interface. We used the open source finite element code pTatin to create 2D models, starting with a homogeneous medium representing shearing at the subduction interface. We tested several boundary conditions that mimic simple shear and opted for the one that best describes the Grigg's type simple shear experiments. After examining different parameters, such as shearing velocity, temperature and viscosity, we added complexity to the geometry by including a second phase. This arises from field observations, where shear zone outcrops are often composites of multiple phases: stronger crustal blocks embedded within a sedimentary and/or serpentinized matrix have been reported for several exhumed subduction zones. We implemented a simplified model to simulate simple shearing of a two-phase medium in order to quantify the effect of heterogeneous rheology on stress and strain localization. Preliminary results show different strength in the models depending on the block-to-matrix ratio. We applied our method to outcrop scale block-in-matrix geometries and by sampling at different depths along exhumed former subduction interfaces, we expect to be able to provide effective friction and viscosity of a natural interface. In a next step, these effective parameters will be used as input into seismic cycle deformation models in an attempt to assess the possible signature of field geometries on the slip behaviour of the plate interface.

Distribution and depth of bottom-simulating reflectors in the Nankai subduction margin

Science.gov (United States)

Ohde, Akihiro; Otsuka, Hironori; Kioka, Arata; Ashi, Juichiro

2018-04-01

Surface heat flow has been observed to be highly variable in the Nankai subduction margin. This study presents an investigation of local anomalies in surface heat flows on the undulating seafloor in the Nankai subduction margin. We estimate the heat flows from bottom-simulating reflectors (BSRs) marking the lower boundaries of the methane hydrate stability zone and evaluate topographic effects on heat flow via two-dimensional thermal modeling. BSRs have been used to estimate heat flows based on the known stability characteristics of methane hydrates under low-temperature and high-pressure conditions. First, we generate an extensive map of the distribution and subseafloor depths of the BSRs in the Nankai subduction margin. We confirm that BSRs exist at the toe of the accretionary prism and the trough floor of the offshore Tokai region, where BSRs had previously been thought to be absent. Second, we calculate the BSR-derived heat flow and evaluate the associated errors. We conclude that the total uncertainty of the BSR-derived heat flow should be within 25%, considering allowable ranges in the P-wave velocity, which influences the time-to-depth conversion of the BSR position in seismic images, the resultant geothermal gradient, and thermal resistance. Finally, we model a two-dimensional thermal structure by comparing the temperatures at the observed BSR depths with the calculated temperatures at the same depths. The thermal modeling reveals that most local variations in BSR depth over the undulating seafloor can be explained by topographic effects. Those areas that cannot be explained by topographic effects can be mainly attributed to advective fluid flow, regional rapid sedimentation, or erosion. Our spatial distribution of heat flow data provides indispensable basic data for numerical studies of subduction zone modeling to evaluate margin parallel age dependencies of subducting plates.[Figure not available: see fulltext.

Eastern Mediterranean geothermal resources and subduction dynamics

Science.gov (United States)

Roche, Vincent; Sternai, Pietro; Guillou-Frottier, Laurent; Jolivet, Laurent; Gerya, Taras

2017-04-01

The Aegean-Anatolian retreating subduction and collision zones have been investigated through 3D numerical geodynamic models involving slab rollback/tearing/breakoff constrained by, for instance, seismic tomography or anisotropy and geochemical proxies. Here, we integrate these investigations by using the well documented geothermal anomalies geothermal anomalies. First, we use 3D high-resolution thermo-mechanical numerical models to quantify the potential contribution of the past Aegean-Anatolian subduction dynamics to such present-day measured thermal anomalies. Results suggest an efficient control of subduction-related asthenospheric return flow on the regional distribution of thermal anomalies. Our quantification shows that the slab-induced shear heating at the base of the crust could partly explain the high heat flow values above the slab tear (i.e. in the Menderes Massif, Western Turkey). Second, the associated thermal signature at the base of the continental crust is used as basal thermal boundary condition for 2D crustal-scale models dedicated to the understanding of heat transfer from the abnormally hot mantle to the shallow geothermal reservoir. These models couple heat transfer and fluid flow equations with appropriate fluid and rock physical properties. Results suggest that permeable low-angle normal faults (detachments) in the back-arc region can control the bulk of the heat transport and fluid circulation patterns. We suggest that detachments can drain crustal and/or mantellic fluids up to several kilometers depths. At the basin-scale, we show that the permeability of detachments may control the reservoirs location. Temperatures at the base of detachments may be subject to protracted increase (due to anomalously high basal heat flow) through time, thereby generating dome-shaped thermal structures. These structures, usually with 20km characteristic wavelength, may reach the Moho involving lateral rheological contrasts and possibly crustal

The population genetics of Quechuas, the largest native South American group: autosomal sequences, SNPs, and microsatellites evidence high level of diversity.