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Sample records for plateaus volcanic arcs

  1. Submarine volcanoes along the Aegean volcanic arc

    Science.gov (United States)

    Nomikou, Paraskevi; Papanikolaou, Dimitrios; Alexandri, Matina; Sakellariou, Dimitris; Rousakis, Grigoris

    2013-06-01

    The Aegean volcanic arc has been investigated along its offshore areas and several submarine volcanic outcrops have been discovered in the last 25 years of research. The basic data including swath bathymetric maps, air-gun profiles, underwater photos and samples analysis have been presented along the four main volcanic groups of the arc. The description concerns: (i) Paphsanias submarine volcano in the Methana group, (ii) three volcanic domes to the east of Antimilos Volcano and hydrothermal activity in southeast Milos in the Milos group, (iii) three volcanic domes east of Christiana and a chain of about twenty volcanic domes and craters in the Kolumbo zone northeast of Santorini in the Santorini group and (iv) several volcanic domes and a volcanic caldera together with very deep slopes of several volcanic islands in the Nisyros group. The tectonic structure of the volcanic centers is described and related to the geometry of the arc and the neotectonic graben structures that usually host them. The NE-SW direction is dominant in the Santorini and Nisyros volcanic groups, located at the eastern part of the arc, where strike-slip is also present, whereas NW-SE direction dominates in Milos and Methana at the western part, where co-existence of E-W disrupting normal faults is observed. The volcanic relief reaches 1100-1200 m in most cases. This is produced from the outcrops of the volcanic centers emerging usually at 400-600 m depth and ending either below sea level or at high altitudes of 600-700 m on the islands. Hydrothermal activity at relatively high temperatures observed in Kolumbo is remarkable whereas low temperature phenomena have been detected in the Santorini caldera around Kameni islands and in the area southeast of Milos. In Methana and Nisyros, hydrothermal activity seems to be limited in the coastal areas without other offshore manifestations.

  2. Future accreted terranes: a compilation of island arcs, oceanic plateaus, submarine ridges, seamounts, and continental fragments

    Directory of Open Access Journals (Sweden)

    J. L. Tetreault

    2014-07-01

    Full Text Available Allochthonous accreted terranes are exotic geologic units that originated from anomalous crustal regions on a subducting oceanic plate and were transferred to the overriding plate during subduction by accretionary processes. The geographical regions that eventually become accreted allochthonous terranes include island arcs, oceanic plateaus, submarine ridges, seamounts, continental fragments, and microcontinents. These future allochthonous terranes (FATs contribute to continental crustal growth, subduction dynamics, and crustal recycling in the mantle. We present a review of modern FATs and their accreted counterparts based on available geological, seismic, and gravity studies and discuss their crustal structure, geological origin, and bulk crustal density. Island arcs have an average crustal thickness of 26 km, average bulk crustal density of 2.79 g cm−3, and have 3 distinct crustal units overlying a crust-mantle transition zone. Oceanic plateaus and submarine ridges have an average crustal thickness of 21 km and average bulk crustal density of 2.84 g cm−3. Continental fragments presently on the ocean floor have an average crustal thickness of 25 km and bulk crustal density of 2.81 g cm−3. Accreted allochthonous terranes can be compared to these crustal compilations to better understand which units of crust are accreted or subducted. In general, most accreted terranes are thin crustal units sheared off of FATs and added onto the accretionary prism, with thicknesses on the order of hundreds of meters to a few kilometers. In addition many island arcs, oceanic plateaus, and submarine ridges were sheared off in the subduction interface and underplated onto the overlying continent. And other times we find evidence of collision leaving behind accreted terranes 25 to 40 km thick. We posit that rheologically weak crustal layers or shear zones that were formed when the FATs were produced can be activated as detachments during subduction, allowing

  3. Progressive Landslides in Uplifted Volcanic Plateaus: Persistent Loci of Channel Perturbation

    Science.gov (United States)

    Safran, E. B.; Anderson, S. W.; Mills-Novoa, M.; Othus, S.; Ely, L.; House, P. K.; O'Connor, J. E.; Grant, G.; Fenton, C.; Beebee, R. A.

    2007-12-01

    The semi-arid uplifted volcanic plateaus of the southern interior Columbia River basin contain over 300 large landslides or landslide complexes, ranging in area from several tenths of a km2 to several tens of km2. The distribution of these landslides is dominated by the outcropping of key stratigraphic contacts between coherent, volcanic cap rock atop weak sedimentary or volcaniclastic units in areas of >100 m local relief. The morphologies of many of these landslide complexes suggest a progressive mode of mass movement, with rubble-capped failure slices arrayed downslope at intervals of 10s to 100s of meters and deep tension cracks separating incipient failure blocks from the intact headscarp. Field evidence from the Owyhee River in southeastern Oregon indicates that individual landslide complexes can persist for millions of years. In one reach, for example, remnants of a 1.9 million year old intracanyon lava flow are inset against ancient landslide blocks. In the same location, cosmogenic isotope dating of boulders on a likely dam-burst flood deposit reveal a channel-blocking mass movement that may be as young as Holocene in age. The persistence of these landslide complexes has important implications for channel evolution, as it suggests that, in some environments, sediment supply may be chronically elevated at point sources. On the basis of GIS-based mapping of regional landslides and on field study of individual landslide complexes, we hypothesize that: 1) this sediment supply becomes increasingly dominated by fine-grained material as channels progressively incise into the weak units underlying coherent lava caps; and 2) the mass movements that impinge on the channels become correspondingly more earthflow-like. Loci of persistent landsliding are also subject to episodic variations in channel width due to physical constrictions caused by impinging failure masses. The discrete localization of large landslide complexes by particular stratigraphic and topographic

  4. Magnesium isotope geochemistry in arc volcanism

    Science.gov (United States)

    Teng, Fang-Zhen; Hu, Yan; Chauvel, Catherine

    2016-06-01

    Incorporation of subducted slab in arc volcanism plays an important role in producing the geochemical and isotopic variations in arc lavas. The mechanism and process by which the slab materials are incorporated, however, are still uncertain. Here, we report, to our knowledge, the first set of Mg isotopic data for a suite of arc lava samples from Martinique Island in the Lesser Antilles arc, which displays one of the most extreme geochemical and isotopic ranges, although the origin of this variability is still highly debated. We find the δ26Mg of the Martinique Island lavas varies from -0.25 to -0.10, in contrast to the narrow range that characterizes the mantle (-0.25 ± 0.04, 2 SD). These high δ26Mg values suggest the incorporation of isotopically heavy Mg from the subducted slab. The large contrast in MgO content between peridotite, basalt, and sediment makes direct mixing between sediment and peridotite, or assimilation by arc crust sediment, unlikely to be the main mechanism to modify Mg isotopes. Instead, the heavy Mg isotopic signature of the Martinique arc lavas requires that the overall composition of the mantle wedge is buffered and modified by the preferential addition of heavy Mg isotopes from fluids released from the altered subducted slab during fluid-mantle interaction. This, in turn, suggests transfer of a large amount of fluid-mobile elements from the subducting slab to the mantle wedge and makes Mg isotopes an excellent tracer of deep fluid migration.

  5. Magnesium isotope geochemistry in arc volcanism.

    Science.gov (United States)

    Teng, Fang-Zhen; Hu, Yan; Chauvel, Catherine

    2016-06-28

    Incorporation of subducted slab in arc volcanism plays an important role in producing the geochemical and isotopic variations in arc lavas. The mechanism and process by which the slab materials are incorporated, however, are still uncertain. Here, we report, to our knowledge, the first set of Mg isotopic data for a suite of arc lava samples from Martinique Island in the Lesser Antilles arc, which displays one of the most extreme geochemical and isotopic ranges, although the origin of this variability is still highly debated. We find the δ(26)Mg of the Martinique Island lavas varies from -0.25 to -0.10, in contrast to the narrow range that characterizes the mantle (-0.25 ± 0.04, 2 SD). These high δ(26)Mg values suggest the incorporation of isotopically heavy Mg from the subducted slab. The large contrast in MgO content between peridotite, basalt, and sediment makes direct mixing between sediment and peridotite, or assimilation by arc crust sediment, unlikely to be the main mechanism to modify Mg isotopes. Instead, the heavy Mg isotopic signature of the Martinique arc lavas requires that the overall composition of the mantle wedge is buffered and modified by the preferential addition of heavy Mg isotopes from fluids released from the altered subducted slab during fluid-mantle interaction. This, in turn, suggests transfer of a large amount of fluid-mobile elements from the subducting slab to the mantle wedge and makes Mg isotopes an excellent tracer of deep fluid migration.

  6. Magnesium isotope geochemistry in arc volcanism

    Science.gov (United States)

    Teng, Fang-Zhen; Hu, Yan

    2016-01-01

    Incorporation of subducted slab in arc volcanism plays an important role in producing the geochemical and isotopic variations in arc lavas. The mechanism and process by which the slab materials are incorporated, however, are still uncertain. Here, we report, to our knowledge, the first set of Mg isotopic data for a suite of arc lava samples from Martinique Island in the Lesser Antilles arc, which displays one of the most extreme geochemical and isotopic ranges, although the origin of this variability is still highly debated. We find the δ26Mg of the Martinique Island lavas varies from −0.25 to −0.10, in contrast to the narrow range that characterizes the mantle (−0.25 ± 0.04, 2 SD). These high δ26Mg values suggest the incorporation of isotopically heavy Mg from the subducted slab. The large contrast in MgO content between peridotite, basalt, and sediment makes direct mixing between sediment and peridotite, or assimilation by arc crust sediment, unlikely to be the main mechanism to modify Mg isotopes. Instead, the heavy Mg isotopic signature of the Martinique arc lavas requires that the overall composition of the mantle wedge is buffered and modified by the preferential addition of heavy Mg isotopes from fluids released from the altered subducted slab during fluid−mantle interaction. This, in turn, suggests transfer of a large amount of fluid-mobile elements from the subducting slab to the mantle wedge and makes Mg isotopes an excellent tracer of deep fluid migration. PMID:27303032

  7. Numerical modeling of volcanic arc development

    Science.gov (United States)

    Gerya, T.; Gorczyk, W.; Nikolaeva, K.

    2007-05-01

    We have created a new coupled geochemical-petrological-thermomechanical numerical model of subduction associated with volcanic arc development. The model includes spontaneous slab bending, subducted crust dehydration, aqueous fluid transport, mantle wedge melting and melt extraction resulting in crustal growth. Two major volcanic arc settings are modeled so far: active continental margins, and intraoceanic subduction. In case of Pacific-type continental margin two fundamentally different regimes of melt productivity are observed in numerical experiments which are in line with natural observations: (1) During continuous convergence with coupled plates highest amounts of melts are formed immediately after the initiation of subduction and then decrease rapidly with time due to the steepening of the slab inclination angle precluding formation of partially molten mantle wedge plumes; (2) During subduction associated with slab delamination and trench retreat resulting in the formation of a pronounced back arc basin with a spreading center in the middle melt production increases with time due to shallowing/stabilization of slab inclination associated with upward asthenospheric mantle flow toward the extension region facilitating propagation of hydrous partially molten plumes from the slab. In case of spontaneous nucleation of retreating oceanic subduction two scenarios of tecono-magmatic evolution are distinguished: (1) decay and, ultimately, the cessation of subduction and related magmatic activity, (2) increase in subduction rate (to up to ~12 cm/yr) and stabilization of subduction and magmatic arc growth. In the first case the duration of subduction correlates positively with the intensity of melt extraction: the period of continued subduction increases from 15,4 Myrs to 47,6 Myrs with the increase of melt extraction threshold from 1% to 9%. In scenario (1) the magmatic arc crust includes large amounts of rocks formed by melting of subducted crust atop the thermally

  8. Magma genesis of the acidic volcanism in the intra-arc rift zone of the Izu volcanic arc, Japan

    Science.gov (United States)

    Haraguchi, S.; Tokuyama, H.; Ishii, T.

    2010-12-01

    The Izu volcanic arc extends over 550 km from the Izu Peninsula, Japan, to the Nishinoshima Trough or Sofugan tectonic line. It is the northernmost segment of the Izu-Bonin-Mariana arc system, which is located at the eastern side of the Philippine Sea Plate. The recent magmatism of the Izu arc is bimodal and characterized by basalt and rhyolite (e.g. Tamura and Tatsumi 2002). In the southern Izu arc, volcanic front from the Aogashima to the Torishima islands is characterized by submarine calderas and acidic volcanisms. The intra-arc rifting, characterized by back-arc depressions, small volcanic knolls and ridges, is active in this region. Volcanic rocks were obtained in 1995 during a research cruise of the R/V MOANA WAVE (Hawaii University, cruise MW9507). Geochemical variation of volcanic rocks and magma genesis was studied by Hochstaedter et al. (2000, 2001), Machida et al (2008), etc. These studies focused magma and mantle dynamics of basaltic volcanism in the wedge mantle. Acidic volcanic rocks were also dredged during the curies MW9507. However, studies of these acidic volcanics were rare. Herein, we present petrographical and chemical analyses of these acidic rocks, and compare these results with those of other acidic rocks in the Izu arc and lab experiments, and propose a model of magma genesis in a context of acidic volcanism. Dredge sites by the cruise MW9507 are 120, and about 50 sites are in the rift zone. Recovered rocks are dominated by the bimodal assemblage of basalt-basaltic andesite and dacite-rhyolite. The most abundant phase is olivine basalt, less than 50 wt% SiO2. Andesites are minor in volume and compositional gap from 56 to 65 wt% SiO2 exists. The across-arc variation of the HFSE contents and ratios, such as Zr/Y and Nb/Zr of rhyolites exhibit depleted in the volcanic front side and enriched in reararc side. This characteristic is similar to basaltic volcanism pointed out by Hochstaedter et al (2000). The petrographical features of rhyolites

  9. Current perspectives on energy and mass fluxes in volcanic arcs

    Science.gov (United States)

    Leeman, William; Davidson, Jon; Fischer, Tobias; Grunder, Anita; Reagan, Mark; Streck, Martin

    Volcanoes of the Pacific Ring of Fire and other convergent margins worldwide are familiar manifestations of nature's energy, account for about 25% of global volcanic outputs, dominate volcanic gas emissions to the atmosphere, and pose significant physical threats to a large human population. Yet the processes behind this prolific activity remain poorly understood.An international “State of the Arc” (SOTA) conference was held in August on the slopes of Mt. Hood, Oregon, to address current views on the energy and mass fluxes in volcanic arcs. This meeting brought together some 90 leading experts and students of subduction zones and their related magmatism.

  10. The Fina Nagu volcanic complex: Unusual submarine arc volcanism in the rapidly deforming southern Mariana margin

    Science.gov (United States)

    Brounce, Maryjo; Kelley, Katherine A.; Stern, Robert; Martinez, Fernando; Cottrell, Elizabeth

    2016-10-01

    In the Mariana convergent margin, large arc volcanoes disappear south of Guam even though the Pacific plate continues to subduct and instead, small cones scatter on the seafloor. These small cones could form either due to decompression melting accompanying back-arc extension or flux melting, as expected for arc volcanoes, or as a result of both processes. Here, we report the major, trace, and volatile element compositions, as well as the oxidation state of Fe, in recently dredged, fresh pillow lavas from the Fina Nagu volcanic chain, an unusual alignment of small, closely spaced submarine calderas and cones southwest of Guam. We show that Fina Nagu magmas are the consequence of mantle melting due to infiltrating aqueous fluids and sediment melts sourced from the subducting Pacific plate into a depleted mantle wedge, similar in extent of melting to accepted models for arc melts. Fina Nagu magmas are not as oxidized as magmas elsewhere along the Mariana arc, suggesting that the subduction component responsible for producing arc magmas is either different or not present in the zone of melt generation for Fina Nagu, and that amphibole or serpentine mineral destabilization reactions are key in producing oxidized arc magmas. Individual Fina Nagu volcanic structures are smaller in volume than Mariana arc volcanoes, although the estimated cumulative volume of the volcanic chain is similar to nearby submarine arc volcanoes. We conclude that melt generation under the Fina Nagu chain occurs by similar mechanisms as under Mariana arc volcanoes, but that complex lithospheric deformation in the region distributes the melts among several small edifices that get younger to the northeast.

  11. Preliminary geochemical characterization of volcanic and geothermal fluids discharged from the Ecuadorian volcanic arc.

    OpenAIRE

    Inguaggiato, S.; Hidalgo, S.; Beate, B.; Bourquin, J.

    2009-01-01

    In Ecuador, magmatism results from the subduction of the Nazca Plate beneath the North Western part of South America (Pennington, 1981; Kellogg and Vega, 1995; Witt et al., 2006). North of 2.5°S, the Ecuadorian Quaternary volcanic arc is characterized by about 60 volcanoes distributed in three different parallel chains. Many of these volcanoes are potentially active or currently in activity and display associated geothermal fields. South of this latitude, no active arc is present in Ecuador. ...

  12. Linear volcanic segments in the Sunda Arc, Indonesia: Implications for arc lithosphere control upon volcano distribution

    Science.gov (United States)

    Macpherson, C. G.; Pacey, A.; McCaffrey, K. J.

    2012-12-01

    The overall curvature of many subduction zones is immediately apparent and the term island arc betrays the common assumption that subduction zone magmatism occurs in curved zones. This assumption can be expressed by approximating island arcs as segments of small circles on the surface of a sphere. Such treatments predict that the location of arc volcanoes is related to their vertical separation from the slab (in fact, the depth to seismicity in the slab) and require that the primary control on the locus of magmatism lies either within the subducted slab or the mantle wedge that separates the subducted and overriding lithospheric plates. The concept of curved arcs ignores longstanding observations that magmatism in many subduction systems occurs as segments of linearly arranged volcanic centres. Further evidence for this distribution comes from the close relationship between magmatism and large scale, arc-parallel fabrics in some arcs. Similarly, exposures of deep arc crust or mantle often reveal elongation of magmatic intrusions sub-parallel to the inferred trend of the arc. The Sunda Arc forms the Indonesian islands from Sumatra to Alor and provides an important test for models of volcano distribution for several reasons. First, Sunda has hosted abundant historic volcanic activity. Second, with the notable exception of Krakatau, every volcano in the arc is subaerial from base to cone and, therefore, can be readily identified where there is a suitable extent of local mapping that can be used to ground-truth satellite imagery. Third, there are significant changes in the stress regime along the length of the arc, allowing the influence of the upper plate to be evaluated by comparison of different arc segments. Finally, much of the Sunda Arc has proved difficult to accommodate in models that try to relate volcano distribution to the depth to the subducted slab. We apply an objective line-fitting protocol; the Hough Transform, to explore the distribution of volcanoes

  13. Detailed Seismic Reflection Images of the Central American Volcanic Arc

    Science.gov (United States)

    McIntosh, K. D.; Fulthorpe, C. S.

    2005-12-01

    New high-resolution seismic reflection profiles across the Central American volcanic arc (CAVA) reveal an asymmetric deformation pattern with large-scale folding and uplift of basinal strata in the forearc contrasted by intrusive bodies, normal faults, and possible strikes-slip faults in the backarc. Since Miocene times the CAVA has migrated seaward, apparently impinging on the Sandino forearc basin and creating or modifying the low-lying Nicaragua depression, which contains the backarc and much of the arc. However the structural nature of the depression and its possible relationship to forearc sliver movement is poorly known. In November-December 2004 we recorded a large, high-resolution, seismic reflection dataset largely on the Pacific shelf (forearc) area of Central America, extending from NW Costa Rica to the SE edge of El Salvador's territorial waters. We seized an opportunity to study the nature of the CAVA by recording data into the Gulf of Fonseca, a large embayment at the intersection of Nicaragua, Honduras, and El Salvador. With 3 GI airguns and a 2100 m streamer we recorded data with typical penetration of 2-3 seconds in the Sandino basin and frequency content of ~10-250 Hz (at shallow levels). Penetration was limited over the arc summit with high velocity volcanic rocks encountered at depths as shallow as a few hundred meters. To the NE the edge of the Nicaragua depression occurs abruptly; our data show a well-developed sedimentary basin 1.5-3 km thick separated by numerous steeply-dipping faults. The broadband signal and good penetration of this dataset will help us determine the chronology of arc development in this position and the styles of deformation in the forearc, arc, and backarc areas. In turn, this will help us understand the regional tectonic and stratigraphic development of this margin due to the profound affects of the arc.

  14. Stress fields of the overriding plate at convergent margins and beneath active volcanic arcs.

    Science.gov (United States)

    Apperson, K D

    1991-11-01

    Tectonic stress fields in the overriding plate at convergent plate margins are complex and vary on local to regional scales. Volcanic arcs are a common element of overriding plates. Stress fields in the volcanic arc region are related to deformation generated by subduction and to magma generation and ascent processes. Analysis of moment tensors of shallow and intermediate depth earthquakes in volcanic arcs indicates that the seismic strain field in the arc region of many convergent margins is subhorizontal extension oriented nearly perpendicular to the arc. A process capable of generating such a globally consistent strain field is induced asthenospheric corner flow below the arc region.

  15. Gravitational removal of volcanic arc roots in Cordilleran orogens

    Science.gov (United States)

    Currie, C. A.; Ducea, M. N.; DeCelles, P. G.; Beaumont, C.

    2013-12-01

    Cordilleran orogens, such as the central Andes, form above subduction zones and their evolution depends on processes associated with oceanic plate subduction and continental plate shortening. Such orogens are characterized by abundant arc volcanism and the formation of thick (>30 km) granitoid batholiths. The magma composition is consistent with a multi-stage model, in which parental mantle-derived basaltic magmas stagnate within the continental lithosphere and then undergo differentiation. Felsic partial melts rise through the crust, leaving a high-density garnet pyroxenite root in the deep lithosphere. Here, we study the dynamics of gravitational removal of this root using regional two-dimensional thermal-mechanical models of subduction below a continent. In the models, the volcanic arc location is determined dynamically based on subduction zone thermal structure, and formation of the batholith-root complex is simulated by changing the density of the volcanic arc lithosphere over time. For the lithosphere structure used in our models, arc roots that undergo even a small density increase are readily removed through gravitational foundering for a wide range of root strengths and subduction rates. The dynamics of removal depend on the relative rates of downward gravitational growth and horizontal shearing by subduction-induced mantle flow. Gravitational growth dominates for high root densification rates, high root viscosities and low subduction rates, leading to drip-like removal of the root as a single downwelling over 1-3 Myr. At lower growth rates, the root is removed over ~6 Myr through shear entrainment, as it is carried sideways by mantle flow and then subducted on top of the oceanic plate. In all models, >80% of the root is removed, making this an effective way to thin mantle lithosphere in the volcanic arc region. This can help resolve the mass problem in the central Andes, where observations indicate a thin mantle lithosphere, despite significant crustal

  16. Magmatic control along a strike-slip volcanic arc: The central Aeolian arc (Italy)

    KAUST Repository

    Ruch, Joel

    2016-01-23

    The regional stress field in volcanic areas may be overprinted by that produced by magmatic activity, promoting volcanism and faulting. In particular, in strike-slip settings, the definition of the relationships between the regional stress field and magmatic activity remains elusive. To better understand these relationships, we collected stratigraphic, volcanic and structural field data along the strike-slip Central Aeolian arc (Italy): here the islands of Lipari and Vulcano separate the extensional portion of the arc (to the east) from the contractional one (to the west). We collected >500 measurements of faults, extension fractures and dikes at 40 sites. Most structures are NNE-SSW to NNW-SSE oriented, eastward dipping, and show almost pure dip-slip motion; consistent with an E-W extension direction, with minor dextral and sinistral shear. Our data highlight six eruptive periods during the last 55 ka, which allow considering both islands as a single magmatic system, in which tectonic and magmatic activity steadily migrated eastward and currently focus on a 10 km long x 2 km wide active segment. Faulting appears to mostly occur in temporal and spatial relation with magmatic events, supporting that most of the observable deformation derives from transient magmatic activity (shorter-term, days to months), rather than from steady longer-term regional tectonics (102-104 years). More in general, the Central Aeolian case shows how magmatic activity may affect the structure and evolution of volcanic arcs, overprinting any strike-slip motion with magma-induced extension at the surface.

  17. Magmatic control along a strike-slip volcanic arc: The central Aeolian arc (Italy)

    Science.gov (United States)

    Ruch, J.; Vezzoli, L.; De Rosa, R.; Di Lorenzo, R.; Acocella, V.

    2016-02-01

    The regional stress field in volcanic areas may be overprinted by that produced by magmatic activity, promoting volcanism and faulting. In particular, in strike-slip settings, the definition of the relationships between the regional stress field and magmatic activity remains elusive. To better understand these relationships, we collected stratigraphic, volcanic, and structural field data along the strike-slip central Aeolian arc (Italy): here the islands of Lipari and Vulcano separate the extensional portion of the arc (to the east) from the contractional one (to the west). We collected >500 measurements of faults, extension fractures, and dikes at 40 sites. Most structures are NNE-SSW to NNW-SSE oriented, eastward dipping, and show almost pure dip-slip motion, consistent with an E-W extension direction, with minor dextral and sinistral shear. Our data highlight six eruptive periods during the last 55 ka, which allow considering both islands as a single magmatic system, in which tectonic and magmatic activities steadily migrated eastward and currently focus on a 10 km long × 2 km wide active segment. Faulting appears to mostly occur in temporal and spatial relation with magmatic events, supporting that most of the observable deformation derives from transient magmatic activity (shorter term, days to months), rather than from steady longer-term regional tectonics (102-104 years). More in general, the central Aeolian case shows how magmatic activity may affect the structure and evolution of volcanic arcs, overprinting any strike-slip motion with magma-induced extension at the surface.

  18. Submarine Arc Volcanism in the Southern Mariana Arc: Results of Recent ROV studies

    Science.gov (United States)

    Nichols, A. R.; Tamura, Y.; Stern, R. J.; Embley, R. W.; Hein, J. R.; Jordan, E.; Ribeiro, J. M.; Sica, N.; Kohut, E. J.; Whattam, S. A.; Hirahara, Y.; Senda, R.; Nunokawa, A.

    2009-12-01

    The submarine Diamante cross-arc volcanoes (~16°N) and the Sarigan-Zealandia Bank Multi-Volcano Complex (SZBMVC; ~16°45’N), north and south, respectively, of Anatahan Island in the southern Mariana Arc, were studied during several dives in June 2009 using the ROV Hyper-Dolphin, cruise NT09-08 (R/V Natsushima); neither has been studied in detail before. The data collected provide a new perspective on how the subduction factory operates to complement previous studies on other cross-arc volcanic chains in the Izu-Bonin-Mariana Arc. The Diamante complex consists of three major edifices, two cones (West and Central Diamante) and a more complex caldera-like edifice at the volcanic front (East Diamante). West and Central Diamante are basaltic volcanoes but East Diamante has a more complex history. Our studies indicate initial construction of a basaltic volcano. Magmatic evolution led to a violent caldera-forming and quieter dome-building events. Post-caldera quiescence allowed a carbonate platform to grow, now preserved on the eastern caldera wall. Felsic magma or hot rock provides a heat source for an active hydrothermal field associated with felsic domes in the caldera, which NOAA investigators discovered in 2004. A new type of hydrothermal deposit was discovered in the hydrothermal field, consisting of large sulfide-sulfate mounds topped by bulbous constructions of low-temperature Fe and Mn oxides. Vents on the mounds were observed to emit shimmering water. The SZBMVC consists of six closely spaced edifices whose loci are aligned along two parallel trends, one along the volcanic front (Zealandia Bank, Sarigan and South Sarigan), and one about 15 km west towards the rear-arc (Northwest Zealandia, West Zealandia and West Sarigan). Zealandia Bank dives revealed that, as with East Diamante, initial activity was basaltic and became more evolved with time. The western half of Zealandia Bank is dominated by felsic lavas centered on a small (~2 km diameter) caldera and

  19. Oceanic ecosystem dynamics during gigantic volcanic episodes: the Ontong Java and Manihiki Plateaus recorded by calcareous nannoplankton. (Invited)

    Science.gov (United States)

    Erba, E.

    2010-12-01

    Earth's volcanic activity introduces environmental stress that biota are forced to survive. There is a general consensus on the role of volcanogenic carbon dioxide increases, and implicit tectonic-igneous events, triggering major climate changes and profound variations in chemical, physical and trophic characteristics of the oceans through the Phanerozoic. Cretaceous geological records indicate conditions of excess atmCO2 (up to 2000-3000 ppm) derived from construction of Large Igneous Provinces (LIPs). In such “high CO2 world” and greenhouse conditions, the deep ocean became depleted of oxygen promoting the accumulation and burial of massive amounts of organic matter; such episodes are recognized as Oceanic Anoxic Events (OAEs) and their geological records merit careful examination of how the Earth system, and Life in particular, can overcome extreme experiments of global change. The Early Aptian (˜ 120 million years ago) OAE1a is a complex example of volcanicCO2-induced environmental stress. There is a general consensus on the causes of this case-history, namely excess CO2 derived from the construction of the Ontong Java-Manihiki LIP. Multi- and inter-disciplinary studies of the OAE1a have pointed out C, O, Os, Sr isotopic anomalies, a biocalcification crisis in pelagic and neritic settings, enhanced fertility and primary productivity, as well as ocean acidification. Available cyclochronology allows high-resolution dating of biotic and environmental fluctuations, providing the precision necessary for understanding the role of volcanogenic CO2 on nannoplankton biocalcification, adaptations, evolutionary innovation and/or extinctions. The reconstructed sequence of volcanogenic CO2 pulses, and perhaps some clathrate melting, triggered a climate change to supergreenhouse conditions, anoxia and ocean acidification. The demise of heavily calcified nannoconids and reduced calcite paleofluxes marks beginning of the pre-OAE1a calcification crisis. Ephemeral coccolith

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

    DEFF Research Database (Denmark)

    Stratford, Wanda Rose; Stern, T.A.

    2008-01-01

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

  1. Geothermal systems in volcanic arcs: Volcanic characteristics and surface manifestations as indicators of geothermal potential and favorability worldwide

    Science.gov (United States)

    Stelling, P.; Shevenell, L.; Hinz, N.; Coolbaugh, M.; Melosh, G.; Cumming, W.

    2016-09-01

    This paper brings a global perspective to volcanic arc geothermal assessments by evaluating trends and correlations of volcanic characteristic and surface manifestation data from world power production sites in subduction zone volcanic settings. The focus of the work was to evaluate volcanic centers individually and as a group in these arcs by correlating various geologic characteristics with known potential to host electricity grade geothermal systems at the volcanic centers. A database was developed that describes key geologic factors expected to be indicative of productive geothermal systems in a global training set, which includes all 74 subduction zone volcanic centers world-wide with current or proven power production capability. Importantly, this data set only contains data from subduction zone volcanoes and contains no negative cases, limiting the populations of any statistical groups. Regardless, this is the most robust geothermal benchmark training set for magmatic-heated systems to date that has been made public. The work reported here is part of a larger project that included data collection, evaluation, correlations and weightings, fairway and favorability modeling and mapping, prediction of blind systems, and uncertainty analysis to estimate errors associated with model predictions. This first paper describes volcano characteristics, compositions and eruption ages and trends along with surface manifestation observations and temperatures as they relate to known power producing systems. Our findings show a strong correlation between the presence and size of active flank fumarole areas and installed power production. Additionally, the majority of volcanic characteristics, including long-held anecdotal correlations related to magmatic composition or size, have limited to no correlation with power production potential. Notable exceptions are correlations between greater power yield from geothermal systems associated with older (Pleistocene) caldera systems

  2. Landscape evolution within a retreating volcanic arc, Costa Rica, Central America

    Science.gov (United States)

    Marshall, Jeffrey S.; Idleman, Bruce D.; Gardner, Thomas W.; Fisher, Donald M.

    2003-05-01

    Subduction of hotspot-thickened seafloor profoundly affects convergent margin tectonics, strongly affecting upper plate structure, volcanism, and landscape evolution. In southern Central America, low-angle subduction of the Cocos Ridge and seamount domain largely controls landscape evolution in the volcanic arc. Field mapping, stratigraphic correlation, and 40Ar/39Ar geochronology for late Cenozoic volcanic rocks of central Costa Rica provide new insights into the geomorphic response of volcanic arc landscapes to changes in subduction parameters (slab thickness, roughness, dip). Late Neogene volcanism was focused primarily along the now-extinct Cordillera de Aguacate. Quaternary migration of the magmatic front shifted volcanism northeastward to the Caribbean slope, creating a new topographic divide and forming the Valle Central basin. Stream capture across the paleo Aguacate divide led to drainage reversal toward the Pacific slope and deep incision of reorganized fluvial networks. Pleistocene caldera activity generated silicic ash flows that buried the Valle Central and descended the Tárcoles gorge to the Orotina debris fan at the coast. Growth of the modern Cordillera Central accentuated relief along the new divide, establishing the Valle Central as a Pacific slope drainage basin. Arc migration, relocation of the Pacific-Caribbean drainage divide, and formation of the Valle Central basin resulted from slab shallowing as irregular, hotspot-thickened crust entered the subduction zone. The geomorphic evolution of volcanic arc landscapes is thus highly sensitive to changes in subducting plate character.

  3. The trace-element characteristics of Aegean and Aeolian volcanic arc marine tephra

    Science.gov (United States)

    Clift, Peter; Blusztajn, Jerzy

    1999-10-01

    High-silica volcanic ashes are found within deep-sea sediments throughout the Eastern Mediterranean. Although coring by Ocean Drilling Program has penetrated Lower Pliocene (˜4 Ma) sediments, few ashes older than 400 k.y. have been recovered, suggesting a young initiation to subaerial Aegean Arc volcanism. Ashes derived from the Aegean volcanic front were cored south and east of the arc, and are typified by medium-K, calc-alkaline major-element compositions, contrasting with high-K ashes from the Aeolian Arc found in the Ionian Sea and as far east as Crete. Ion microprobe analysis of individual glass shards shows that all the ashes have a light rare earth element (LREE)-enriched pattern after normalizing against a chondrite standard. Aeolian Arc-derived ashes show greater enrichment than those from the Aegean area. Within the latter set, two groups are discernible, a mildly enriched set similar to the volcanoes of the arc volcanic front, and a more enriched group corresponding to lavas from the backarc region or possible from western Anatolia. Multi-element `spider diagrams' also show a bimodal division of enriched and depleted Aegean ashes, possibly caused by source depletion due to melt extraction in the Aegean backarc followed by remelting under the volcanic front. Relative Nb depletion, a characteristic of arc volcanism, is seen to be modest in Aegean and non-existent in Aeolian ashes. Using B/Be as a proxy for the flux of material from the subducting slab, this influence is seen to be low in the Aeolian Arc but higher than at Vesuvius. B/Be is higher again in the Aegean Arc. These differences may reflect the rate of subduction in each system. Data suggest caution is required when correlating ashes solely on the basis of major elements, as alkaline ashes from the central part of the study may be derived from Italy or from the Aegean backarc.

  4. The Relationship Between the Signature of Subducted Sediments in Volcanic Gases and Volatile Flux along the Central American Volcanic Arc

    Science.gov (United States)

    Fischer, T. P.; Zimmer, M. M.; Hilton, D. R.; Shaw, A. M.; Cameron, B. I.; Walker, J. A.; Molina C., E.

    2002-05-01

    Volcanic arcs are locations where elements are recycled from the Earth's surface into the mantle. Fluxes of volcanic volatile emissions can vary significantly along a single arc and a fundamental aim of arc-related studies is to quantify these variations and compare them to subduction zone parameters. As part of the Central American arc study, we report N2, He and Ar abundance relationships and N-isotope ratios for 7 volcanic centers in Guatemala to complement on-going studies in Costa Rica. In Guatemala, the arc crust is thicker and older than in Costa Rica and the entire sediment sequence on the down-going plate is likely to contribute to the slab flux. Sulfur dioxide fluxes vary significantly along the arc (2001 measurements): in the Guatemala segment, Fuego and Pacaya emit a total of ~1500 t/day whereas in Costa Rica, Arenal and Poas are emitting only ~190 t/day. The Guatemalan volcanic centers of Amatitlan-Pacaya, Fuego, Moyuta, Tecuamburro, Amatitlan, Zunil and San Marcos have N2/He ratios ranging from 2200 - 8100, typical for arc-related fluids. N2/Ar ratios (40-500) and the high N2/He indicate addition of N2 from subducted sediments or arc crust to a mantle derived component (N2/He Guatemala are in contrast to typical mantle-derived N2/He ratios (160 - 600) measured at Poas and Turialba, Costa Rica. Nitrogen isotope ratios for the Guatemalan volcanic centers range from δ 15N = + 1.0‰ for San Marcos to + 5.8‰ for Fuego (δ 15N air = 0.0‰ ), indicating a sedimentary nitrogen component. The mantle-derived N2/He ratios for Poas (- 3.0‰ ) are consistent with a more mantle-like δ 15N. In Guatemala, the highest 3He/4He ratios (7.6 for Pacaya and 7.3 Ra for Fuego) correlate with the lowest N2/He ratios (1500 and 2100) and high δ 15N values (+3.8‰ and +5.8‰ ). Mixing relationships (3He/4He and δ 15N) suggest that at Fuego and Pacaya up to 20% of the nitrogen is of subducted sedimentary origin, contrary to Poas and Turialba where the slab derived

  5. Continental arc volcanism as the principal driver of icehouse-greenhouse variability

    Science.gov (United States)

    McKenzie, N. Ryan; Horton, Brian K.; Loomis, Shannon E.; Stockli, Daniel F.; Planavsky, Noah J.; Lee, Cin-Ty A.

    2016-04-01

    Variations in continental volcanic arc emissions have the potential to control atmospheric carbon dioxide (CO2) levels and climate change on multimillion-year time scales. Here we present a compilation of ~120,000 detrital zircon uranium-lead (U-Pb) ages from global sedimentary deposits as a proxy to track the spatial distribution of continental magmatic arc systems from the Cryogenian period to the present. These data demonstrate a direct relationship between global arc activity and major climate shifts: Widespread continental arcs correspond with prominent early Paleozoic and Mesozoic greenhouse climates, whereas reduced continental arc activity corresponds with icehouse climates of the Cryogenian, Late Ordovician, late Paleozoic, and Cenozoic. This persistent coupled behavior provides evidence that continental volcanic outgassing drove long-term shifts in atmospheric CO2 levels over the past ~720 million years.

  6. Along-arc geochemical and isotopic variations in Javanese volcanic rocks: 'crustal' versus 'source' contamination at the Sunda arc, Indonesia

    Science.gov (United States)

    Handley, H.; Blichert-Toft, J.; Turner, S.; Macpherson, C. G.

    2012-12-01

    Understanding the genesis of volcanic rocks in subduction zone settings is complicated by the multitude of differentiation processes and source components that exert control on lava geochemistry. Magma genesis and evolution at the Sunda arc is controlled and influenced by 1) along arc changes in the composition and thickness of the overriding Eurasian plate, 2) the variable age of the subducting oceanic crust and, 3) changes in the type and amount of sediment deposited on the subducting plate. Along-arc changes in geochemistry have long been recognised in the Sunda arc (Whitford, 1975), but debate still prevails over the cause of such variations and the relative importance of shallow (crustal) versus deep (subduction) contamination at the Sunda arc, Indonesia. Detailed study of individual Sunda arc volcanic centres is, therefore, a prerequisite in order to establish the relative importance and contributions of various potential source components and composition modifying differentiation processes at individual volcanoes, prior to an along arc comparative petrogenetic investigation. We present new radiogenic isotope data for Javanese volcanoes, which is combined with our recently published (Handley et al., 2007; Handley et al., 2008, Handley et al., 2010; Handley et al., 2011) geochemical and isotopic data of Javanese volcanic rocks along with data from other detailed geochemical studies to establish whether variable contributions from the subducting slab, or a change in crustal architecture of the overriding plate, best explain along-arc variations in isotope ratios and trace element characteristics. In West and Central Java Sr isotope ratios of the volcanic rocks broadly correlate with inferred lithospheric thickness implicating a shallow level control on isotopic composition. However, key trace element ratios combined with Hf isotope data indicate that the subducted slab and slab thermal regime also exert major control on the composition of the erupted Javanese

  7. The Dras arc: two successive volcanic events on eroded oceanic crust

    Science.gov (United States)

    Reuber, Ingrid

    1989-04-01

    The Dras arc is recognized as a volcanic arc system in the western part of the Indus suture zone and it constitutes the link between the Ladakh batholith and the Kohistan arc. This study is based on detailed mapping of the area between Dras, Kargil and Sanku which revealed the following: (1) The ultramafics of Dras and Thasgam can be followed across the Suru Dras ridge and are not intrusive into the arc volcanics, but instead constitute the most probably oceanic substratum of these volcanics. (2) Successive volcanic events are distinguished: (a) Dras I is a variable volcaniclastic series rich in slates and carbonates, which can probably be assigned to the Albo-Cenomanian, as dated by orbitolines. This series is intruded by gabbro, diorite and granite and is deformed, essentially in the northern part. It is unconformably overlain by (b) the Dras II pyroclastics which grade southward into volcanic breccia and thus enable the location of the centres of volcanic activity during this younger period.

  8. Geology and geochemistry characteristics of the Chiapanecan Volcanic Arc (Central Area), Chiapas Mexico

    Science.gov (United States)

    Mora, J. C.; Jaimes-Viera, M. C.; Garduño-Monroy, V. H.; Layer, P. W.; Pompa-Mera, V.; Godinez, M. L.

    2007-04-01

    The Chiapanecan Volcanic Arc (CVA), located in the central portion of the State of Chiapas, is a 150 km stretch of volcanoes irregularly aligned in the northwest direction between two great volcanic features: the Trans-Mexican Volcanic Belt to the northwest and the Central American Volcanic Arc to the southeast. The CVA is located in a complex zone marking the interaction of the North American, Caribbean and Cocos plates, near the Motagua-Polochic fault system, the boundary between North American and Caribbean plates. The central part of the CVA is composed of an irregular northwest alignment of at least 10 volcanic structures generally lying along NNW-SSE-trending faults splayed from the Motagua-Polochic system. Among the structures there are seven volcanic domes (Huitepec, Amahuitz, La Iglesia, Mispía, La Lanza, Venustiano Carranza and Santotón), one explosion crater (Navenchauc), one collapse structure (Apas), and one dome complex (Tzontehuitz). In the majority of the structures there is a clear resurgence with the formation of several domes in the same structure, with the destruction of previous domes (Navenchauc) or with the formation of new explosion craters or collapse structures (Apas). The volcanic activity in the CVA was mainly effusive accompanied by explosive and phreatomagmatic events and is characterized by volcanic domes accompanied by block-and-ash-flows, ash flows with accretionary lapilli, falls, and pumice flows. The volcanic structures and deposits are calcalkaline in composition with a medium to high content of potassium. CVA volcanic rocks vary from andesite to dacite with SiO 2 between 57 and 66 wt.%, show low concentrations of Ti, P, Nb and Ta, are enriched in Light Rare Earths, depleted in Heavy Rare Earths, and show a small Eu anomaly; all indicative of arc-related volcanism associated with subduction of the Cocos plate under the North American plate, but complicated by the geometry of the plate boundary fault system.

  9. The volcanic response to deglaciation: Evidence from glaciated arcs and a reassessment of global eruption records

    Science.gov (United States)

    Watt, Sebastian F. L.; Pyle, David M.; Mather, Tamsin A.

    Several lines of evidence have previously been used to suggest that ice retreat after the last glacial maximum (LGM) resulted in regionally-increased levels of volcanic activity. It has been proposed that this increase in volcanism was globally significant, forming a substantial component of the post-glacial rise in atmospheric CO2, and thereby contributing to climatic warming. However, as yet there has been no detailed investigation of activity in glaciated volcanic arcs following the LGM. Arc volcanism accounts for 90% of present-day subaerial volcanic eruptions. It is therefore important to constrain the impact of deglaciation on arc volcanoes, to understand fully the nature and magnitude of global-scale relationships between volcanism and glaciation. The first part of this paper examines the post-glacial explosive eruption history of the Andean southern volcanic zone (SVZ), a typical arc system, with additional data from the Kamchatka and Cascade arcs. In all cases, eruption rates in the early post-glacial period do not exceed those at later times at a statistically significant level. In part, the recognition and quantification of what may be small (i.e. less than a factor of two) increases in eruption rate is hindered by the size of our datasets. These datasets are limited to eruptions larger than 0.1 km3, because deviations from power-law magnitude-frequency relationships indicate strong relative under-sampling at smaller eruption volumes. In the southern SVZ, where ice unloading was greatest, eruption frequency in the early post-glacial period is approximately twice that of the mid post-glacial period (although frequency increases again in the late post-glacial). A comparable pattern occurs in Kamchatka, but is not observed in the Cascade arc. The early post-glacial period also coincides with a small number of very large explosive eruptions from the most active volcanoes in the southern and central SVZ, consistent with enhanced ponding of magma during

  10. Ages and geochemical comparison of coeval plutons and volcanics from the central and eastern Aleutian arc

    Science.gov (United States)

    Cai, Y.; Kelemen, P. B.; Goldstein, S. L.; Yogodzinski, G. M.; Hemming, S. R.; Rioux, M. E.; Cooperdock, E. H. G.

    2016-12-01

    On average, arc volcanics are compositionally different from the bulk continental crust. The relatively little known plutonic part of intra-oceanic arcs is more similar to continental crust, and may play a significant role for understanding continental crust formation. Our pilot study [1] demonstrated that in the central and eastern Aleutian islands, predominantly tholeiitic Quaternary volcanic rocks have statistically different Pb-Nd-Sr-Hf isotopic signatures than predominantly calc-alkaline Miocene and older plutonic rocks, showing that these plutonics and volcanics were derived from compositionally different sources. However, studies of older volcanics are needed to determine whether (1) there was a change in magma chemistry in the central and eastern Aleutian arc between the Miocene and the present-day, or (2) coeval plutonics and volcanics are compositionally different, and formed by different processes. For example, silica- and water-rich calc-alkaline magmas may preferentially stall and form plutons after extensive degassing and rapid viscosity increase in the mid-crust, while silica- and water-poor tholeiitic magmas tend to erupt at the surface. Here we report new geochronological and geochemical results on samples collected during the 2015 GeoPRISMS shared logistics field campaign. We collected more than 500 volcanic and plutonic samples from Unalaska, Umnak and Atka islands, including pillow lavas, sills, and larger plutons. A subset of 50 samples has been analyzed for major and trace element chemistry, Pb-Nd-Sr-Hf isotopes, and Ar-Ar geochronology. So far,40Ar/39Ar cooling dates measured for the volcanics span a wide range, from zero to 35 Ma, which is comparable to the age distribution of the plutons ( 9 Ma to 39 Ma) from these islands. The forthcoming, combined geochronology and geochemistry of coeval plutonics and volcanics will contribute to our understanding of the connections between arc magmatism and continental crust formation. [1] Cai et al

  11. Geochemical variations in the Quaternary Andean back-arc volcanism, southern Mendoza, Argentina

    Science.gov (United States)

    Espanon, Venera R.; Chivas, Allan R.; Kinsley, Leslie P. J.; Dosseto, Anthony

    2014-11-01

    The Payenia Basaltic Province (PBP) is located 450 km east of the Chile-Peru trench in central west Argentina, behind the Andean arc front, constituting the back-arc. In order to evaluate the influence of the subducting slab as well as the magmatic source of this region, two volcanic fields located at comparable distance to the trench, having abundant basaltic products and similar eruptive timeframes were chosen. The Llancanelo (LLVF) and the Payún Matrú (PMVF) volcanic fields are part of the PBP and exhibit abundant basaltic activity during the Pleistocene. The geochemical data suggest that the LLVF has some arc signatures which have been described as weak as they are not as pronounced as in the Andean arc. The weak arc signature is not derived from slab dehydration as high Th enrichment relative to U cannot be explained by this process. We relate the Th enrichment as well as the lack of large residual garnet signatures, to slab sediments in the source. In the case of the PMVF, no arc signature has been inferred despite being only 30 km south of the LLVF. However the PMVF has a composition similar to that of the local intraplate end member, represented by the Rio Colorado volcanic field. The two volcanic fields, LLVF and PMVF, show indications of lower crustal assimilation as they trend towards the lower continental crust end member in Nb/U vs Ce/Pb and Nb/Yb vs Th/Yb diagrams. The geochemical differences between the LLVF and the PMVF as well as between several volcanic fields are illustrated using spatial distribution maps of geochemical ratios. Using this new approach, the decrease in arc signature can be traced in the back-arc and the higher enrichment in high field strength elements (HFSE) relative to large ion lithophile elements (LILE) in the PMVF compared to the LLVF is explicitly shown. These geospatial maps provide a graphical manner to illustrate the presence of two distinct types of volcanism (OIB-like and arc-like) occurring in the same Quaternary

  12. Characteristics of Mineralized Volcanic Centers in Javanese Sunda Island Arc, Indonesia

    Science.gov (United States)

    Setijadji, L. D.; Imai, A.; Watanabe, K.

    2007-05-01

    The subduction-related arc magmatism in Java island, Sunda Arc, Indonesia might have started in earliest Tertiary period, but the distinctively recognizable volcanic belts related with Java trench subduction occurred since the Oligocene. We compiled geoinformation on volcanic centers of different epochs, distribution of metallic mineral deposits, petrochemistry of volcanic rocks, geologic structures, and regional gravity image in order to elucidate characteristics of the known mineralized volcanic centers. Metallic deposits are present in various styles from porphyry-related, high-sulfidation, and low-sulfidation epithermal systems; all related with subaerial volcanism and subvolcanic plutonism. Only few and small occurrences of volcanigenic massive sulfides deposits suggest that some mineralization also occurred in a submarine environment. Most locations of mineral deposits can be related with location of Tertiary volcanic centers along the volcanic arcs (i.e. volcanoes whose genetic link with subduction is clear). On the other side there is no mineralization has been identified to occur associated with backarc magmatism whose genetic link with subduction is under debate. There is strong evidence that major metallic deposit districts are located within compressive tectonic regime and bound by coupling major, deep, and old crustal structures (strike-slip faults) that are recognizable from regional gravity anomaly map. So far the most economical deposits and the only existing mines at major industry scale are high-grade epithermal gold deposits which are young (Upper Miocene to Upper Pliocene), concentrated in Bayah dome complex in west Java, and are associated with alkalic magmatism-volcanism. On the other hand, known porphyry Cu-Au deposits are associated with old (Oligocene to Upper Miocene) stocks, and except for one case, all deposits are located in east Java. Petrochemical data suggest a genetic relationship between porphyry mineralization with low- to

  13. Spatial distribution of helium isotopes in volcanic gases and thermal waters along the Vanuatu (New Hebrides) volcanic arc

    Science.gov (United States)

    Jean-Baptiste, P.; Allard, P.; Fourré, E.; Bani, P.; Calabrese, S.; Aiuppa, A.; Gauthier, P. J.; Parello, F.; Pelletier, B.; Garaebiti, E.

    2016-08-01

    We report the first helium isotope survey of volcanic gases, hot springs and some olivine phenocrysts along the Vanuatu island arc, from Tanna in the south to Vanua Lava in the north. Low CO2 content and low 3He/4He ratios in thermal fluids of Epi (4.0 ± 0.1 Ra), Efate (4.5 ± 0.1 Ra) and Pentecost (5.3 ± 0.5 Ra) islands coherently indicate reduced mantle gas leakage and crustal contamination by radiogenic helium on these extinct volcanic systems of the former (Pliocene) arc. Instead, presently active Vanuatu volcanoes display 3He/4He and C/3He ratios typical of subduction-related volcanic arcs: 3He/4He ratios range from 6.4 ± 0.5 Ra in southernmost Tanna and 7.23 ± 0.09 Ra in northernmost Vanua Lava to typical MORB values in the central islands of Gaua (7.68 ± 0.06 Ra), Ambrym (7.6 ± 0.8 Ra) and Ambae (7 ± 2 Ra in groundwaters, 7.9 ± 1.4 Ra in olivine phenocrysts, and 8.0 ± 0.1 Ra in summit fumaroles of Aoba volcano). On Ambrym, however, we discover that hydrothermal manifestations separated by only 10-15 km on both sides of a major E-W transverse fault zone crossing the island are fed by two distinct helium sources, with different 3He/4He signatures: while fluids in southwest Ambrym (Baiap and Sesivi areas) have typical arc ratios (7.6 ± 0.8 Ra), fluids on the northwest coast (Buama Bay area) display both higher 3He/4He ratios (9.8 ± 0.2 Ra in waters to 10.21 ± 0.08 Ra in bubbling gases) and lower C/3He ratios that evidence a hotspot influence. We thus infer that the influx of Indian MORB mantle beneath the central Vanuatu arc, from which Ambrym magmas originate, also involves a 3He-rich hotspot component, possibly linked to a westward influx of Samoan hotspot material or another yet unknown local source. This duality in magmatic He source at Ambrym fits with the bimodal composition and geochemistry of the erupted basalts, implying two distinct magma sources and feeding systems. More broadly, the wide He isotopic variations detected along the Vanuatu

  14. Geology and Geochronology of the Central Part of Chiapanecan Volcanic Arc, Mexico.

    Science.gov (United States)

    Layer, P. W.

    2006-12-01

    The Chiapanecan Volcanic Arc (CVA) is a 150 km stretch of volcanoes irregularly aligned in a northwest direction, including El Chichón volcano located in the central portion of the State of Chiapas, southern Mexico. It lies between two great volcanic features: the Trans-Mexican Volcanic Arc to the northwest, and the Central American Volcanic Arc to the southeast, in a complex zone of the interaction of the North American, Caribbean and Cocos Plates. The central part of the CVA is composed of an irregular northwest alignment of at least 12 volcanic structures located 80 km to the southeast of El Chichón (the only currently active volcano in the CVA). These structures include one explosion crater (Navenchauc), one collapse structure (Apas), one dome complex (Tzontehuitz) and nine volcanic domes (Navenchauc, Huitepec, Amahuitz, La Iglesia, Mispía, La Lanza, Venustiano Carranza, Miguel Hidalgo and Santotón) with associated pyroclastic flow deposits. The juvenile lithics from these deposits have a porphyritic texture with phenocrysts of plagioclase (±), amphibole (±), clinopyroxene (±), orthopyroxene (±) and Fe-Ti oxides surrounded by a matrix composed by microlites of plagioclase and glass. The chemical results obtained from representative samples from the deposits and structures indicate that these belong to the series of subalkaline rocks, and fall into the calcalkaline field with medium to high contents of potassium. They vary in their composition from andesite to dacite with an interval of silica between a 56 to a 66% (wt.). The ages reported in the literature and obtained in this study by means of the K-Ar and the 40Ar/39Ar methods, respectively, indicated that volcanism was episodic and spanned a time from 2100 ky ago (Tzontehuitz) to 225 ky ago (Venustiano Carranza).

  15. Significance of an Active Volcanic Front in the Far Western Aleutian Arc

    Science.gov (United States)

    Yogodzinski, G. M.; Kelemen, P. B.; Hoernle, K.

    2015-12-01

    Discovery of a volcanic front west of Buldir Volcano, the western-most emergent Aleutian volcano, demonstrates that the surface expression of Aleutian volcanism falls below sea level just west of 175.9° E longitude, but is otherwise continuous from mainland Alaska to Kamchatka. The newly discovered sites of western Aleutian seafloor volcanism are the Ingenstrem Depression, a 60 km-long structural depression just west of Buldir, and an unnamed area 300 km further west, referred to as the Western Cones. These locations fall along a volcanic front that stretches from Buldir to Piip Seamount near the Komandorsky Islands. Western Aleutian seafloor volcanic rocks include large quantities of high-silica andesite and dacite, which define a highly calc-alkaline igneous series and carry trace element signatures that are unmistakably subduction-related. This indicates that subducting oceanic lithosphere is present beneath the westernmost Aleutian arc. The rarity of earthquakes below depths of 200 km indicates that the subducting plate is unusually hot. Some seafloor volcanoes are 6-8 km wide at the base, and so are as large as many emergent Aleutian volcanoes. The seafloor volcanoes are submerged in water depths >3000 m because they sit on oceanic lithosphere of the Bering Sea. The volcanic front is thus displaced to the north of the ridge of arc crust that underlies the western Aleutian Islands. This displacement, which developed since approximately 6 Ma when volcanism was last active on the islands, must be a consequence of oblique convergence in a system where the subducting plate and large blocks of arc crust are both moving primarily in an arc-parallel sense. The result is a hot-slab system where low subduction rates probably limit advection of hot mantle to the subarc, and produce a relatively cool and perhaps stagnant mantle wedge. The oceanic setting and highly oblique subduction geometry also severely limit rates of sediment subduction, so the volcanic rocks, which

  16. Systematic Osmium Isotope Binary Mixing Arrays in Arc Volcanism

    Science.gov (United States)

    Alves, S.; Alves, S.; Schiano, P.; Capmas, F.; Allegre, C. J.

    2001-12-01

    Isotopic and geochemical studies on subduction-related lavas aim at constraining the nature of their mantle sources and the respective roles of source heterogeneity and petrogenetic processes in their compositions. Many components are potentially involved in producing the geochemical signatures of arc lavas: depleted mantle, subducted oceanic crust and sediments, and the overlying continental or oceanic crust. A further complication in characterizing mantle sources of arc lavas is complex mixing of some component parts via derivative fluids or melts released from the slab. Os isotope ratios are potential tracers of slab contribution in arc lavas because 1) subducted sediments are very radiogenic in Os compared to the upper mantle, and 2) Re behaves as a moderately incompatible element during mantle partial melting, whereas Os is highly compatible. Therefore, MORB have much higher Re/Os ratios than peridotites. Consequently, old oceanic crust is likely to be extremely more radiogenic than the depleted upper mantle so that recycled basaltic components should be identified by their elevated 187Os/188Os ratios. Os isotope ratios and Os and Re concentrations have been measured in 55 lavas coming from 10 different subduction zones. Samples span a large range of major element concentrations (from basalts to dacites) and Mg# (from 0.32 to 0.81). The 10 subduction zones, namely the Lesser Antilles, Java, Papua-New Guinea, the Philippines, Izu-Bonin, Kamchatka, the Aleutians, Mexico, Colombia and Peru-Chile, have a range of basement nature and thickness, as well as a range of age and sediment cover of the subducting plate. Measured 187Os/188Os ratios range from 0.130 to 1.524 and Os concentrations range from 0.048 to 46 ppt. Re concentrations range from 37 to 915 ppt. Os initial isotope ratios are systematically positively and linearly correlated with the inverse of Os concentrations in arc lavas from a given volcano, indicating that the Os isotopic compositions always

  17. The arc arises: The links between volcanic output, arc evolution and melt composition

    Science.gov (United States)

    Brandl, Philipp A.; Hamada, Morihisa; Arculus, Richard J.; Johnson, Kyle; Marsaglia, Kathleen M.; Savov, Ivan P.; Ishizuka, Osamu; Li, He

    2017-03-01

    Subduction initiation is a key process for global plate tectonics. Individual lithologies developed during subduction initiation and arc inception have been identified in the trench wall of the Izu-Bonin-Mariana (IBM) island arc but a continuous record of this process has not previously been described. Here, we present results from International Ocean Discovery Program Expedition 351 that drilled a single site west of the Kyushu-Palau Ridge (KPR), a chain of extinct stratovolcanoes that represents the proto-IBM island arc, active for ∼25 Ma following subduction initiation. Site U1438 recovered 150 m of oceanic igneous basement and ∼1450 m of overlying sediments. The lower 1300 m of these sediments comprise volcaniclastic gravity-flow deposits shed from the evolving KPR arc front. We separated fresh magmatic minerals from Site U1438 sediments, and analyzed 304 glass (formerly melt) inclusions, hosted by clinopyroxene and plagioclase. Compositions of glass inclusions preserve a temporal magmatic record of the juvenile island arc, complementary to the predominant mid-Miocene to recent activity determined from tephra layers recovered by drilling in the IBM forearc. The glass inclusions record the progressive transition of melt compositions dominated by an early 'calc-alkalic', high-Mg andesitic stage to a younger tholeiitic stage over a time period of 11 Ma. High-precision trace element analytical data record a simultaneously increasing influence of a deep subduction component (e.g., increase in Th vs. Nb, light rare earth element enrichment) and a more fertile mantle source (reflected in increased high field strength element abundances). This compositional change is accompanied by increased deposition rates of volcaniclastic sediments reflecting magmatic output and maturity of the arc. We conclude the 'calc-alkalic' stage of arc evolution may endure as long as mantle wedge sources are not mostly advected away from the zones of arc magma generation, or the rate of

  18. Gas venting rates from submarine hydrothermal areas around the island of Milos, Hellenic Volcanic Arc

    Science.gov (United States)

    Dando, P. R.; Hughes, J. A.; Leahy, Y.; Niven, S. J.; Taylor, L. J.; Smith, C.

    1995-07-01

    Gas seeps were located, by echo sounding, SCUBA divers and ROV observations, at hydrothermal sites around the island of Milos, in the Hellenic Volcanic Arc. Samples were collected by SCUBA divers and by a ROV from water depths between 3 and 110 m. Fifty-six flow rates from 39 individual seeps were measured and these ranged from 0.2 to 18.51 h -1 at the depth of collection. The major component, 54.9-91.9% of the gas, was carbon dioxide. Hydrogen (≤3%), methane (≤9.7%) and hydrogen sulphide (≤8.1%) were also measured. Hydrothermal free gas fluxes from the submarine hydrothermal areas around Milos were estimated to be greater than 10 10 moles y -1. It was concluded that submarine gas seeps along volcanic island arcs may be an important carbon dioxide source.

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

    Science.gov (United States)

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

    2005-12-01

    New geologic mapping in SE Costa Rica and SW Panama reveals a system of structures and landscape features that are actively propagating with the Cocos-Nazca-Caribbean Triple Junction. The triple junction migrates to the SE at ~50 km/my, so the upper plate inboard of the Nazca plate experiences a rapid change from steep, slow subduction of the Nazca plate to shallow, rapid subduction of the Cocos plate. High plate boundary coupling for ~100 km NW of the triple junction has led to the development of the Fila Costena Thrust Belt. Balanced cross-sections indicate that shortening rates are highest near the center of the thrust belt, and decrease to the SE nearest the triple junction, where the thrust belt abruptly terminates. Right lateral tear faults cut the thrusts of the Fila Costena and allow for a sharp gradient in upper plate shortening above the subducted projection of the Panama Fracture Zone (PFZ), or the Cocos-Nazca boundary. East of the triple junction, a ridge exposes a fault-related anticline that may represent the incipient propagation of the Fila Costena into Panama. The volcanic arc is active just to the east of the onland projection of the subducting PFZ (e.g., Volcan Baru), with the extinct Talamanca arc lying to the west of this projection. Lahar fans on the slopes of the active Volcan Baru are analogous to the backtilted lahars now restricted to the rear of the Fila Costena. The spatial and temporal distribution of arc volcanism is consistent with a mantle wedge restricted to the east of the PFZ that migrates eastward with the triple junction. The Rio Chiriqui drainage system is currently the only river that carries arc volcanics to the eastern thrust front. The river skirts the southeast edge of the thrust belt and is inset into lahar fans on the slopes of Volcan Baru. Uplifted Quaternary fluvial terraces, located several kilometers west from the current drainage system, are offset at the thrust front by about 100-150 m. Andesite clasts in these

  20. The Chahnaly low sulfidation epithermal gold deposit, western Makran volcanic arc, southeastern Iran

    Science.gov (United States)

    Sholeh, Ali; Rastad, Ebrahim; Huston, David L.; Gemmell, J. Bruce; Taylor, Ryan D.

    2016-01-01

    The Chahnaly low-sulfidation epithermal Au deposit and nearby Au prospects are located northwest of the intermittently active Bazman stratovolcano on the western end of the Makran volcanic arc, which formed as the result of subduction of the remnant Neo-Tethyan oceanic crust beneath the Lut block. The arc hosts the Siah Jangal epithermal and Kharestan porphyry prospects, near Taftan volcano, as well as the Saindak Cu-Au porphyry deposit and world-class Reko Diq Cu-Au porphyry deposit, near Koh-i-Sultan volcano to the east-northeast in Pakistan. The host rocks for the Chahnaly deposit include early Miocene andesite and andesitic volcaniclastic rocks that are intruded by younger dacitic domes. Unaltered late Miocene dacitic ignimbrites overlie these rocks. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U-Pb zircon geochronology data yield ages between 21.8 and 9.9 Ma for the acidic-intermediate regional volcanism. The most recent volcanic activity of the Bazman stratovolcano involved extrusion of an olivine basalt during Pliocene to Quaternary times. Interpretation of geochemical data indicate that the volcanic rocks are synsubduction and calc-alkaline to subalkaline. The lack of a significant negative Eu anomaly, a listric-shaped rare earth element pattern, and moderate La/Yb ratios of host suites indicate a high water content of the source magma.

  1. Constraints on the origin and evolution of magmas in the Payún Matrú Volcanic Field, Quaternary Andean Back-arc of Western Argentina

    NARCIS (Netherlands)

    Hernando, I.R.; Aragón, E.; Frei, R.; González, P.D.; Spakman, W.

    2014-01-01

    The Payún Matrú Volcanic Field (Pleistocene–Holocene) is located in the Andean back-arc of the Southern Volcanic Zone, western Argentina, and is contemporaneous with the Andean volcanic arc at the same latitude. It includes two polygenetic, mostly trachytic volcanoes: Payún Matrú (with a summit cald

  2. Temporal and geochemical evolution of Miocene volcanism in the Andean back-arc between 36°S and 38°S and U-series analyses of young volcanic centers in the arc and back-arc, Argentina

    DEFF Research Database (Denmark)

    Dyhr, Charlotte Thorup

    New 40Ar/39Ar, major and trace element, and Sr, Nd and Pb isotopic data for the c. 24-7 Ma volcanic rocks from the Andean back-arc (35°S – 38°S) in the Mendoza and Neuquén (Argentina) regions shed light on the Miocene evolution of the back-arc of the Southern Volcanic Zone. Incipient shallowing...... lasting from ~17 to ~9 Ma. The reoccurrence of extensive magmatism in the Sierra de Palaoco provides evidence for a retreat of the shallow subduction zone towards the west during the Late Miocene. Evidence for the ending of the time of flat subduction comes from major- and trace element chemistry and Nd...

  3. Tectonic shortening and coeval volcanism during the Quaternary, Northeast Japan arc

    Indian Academy of Sciences (India)

    Koji Umeda; Masao Ban; Shintaro Hayashi; Tomohiro Kusano

    2013-02-01

    The Northeast Japan arc, a mature volcanic arc with a back-arc marginal basin (Japan Sea), is located on a convergent plate boundary along the subducting Pacific plate and the overriding North American plate. From a compilation and analysis of stratigraphy, radiometric age and data on erupted magma volumes, 176 eruptive episodes identified from 69 volcanoes so far, indicate that notable changes in eruption style, magma discharge rates and distribution of eruptive centres occurred around 1.0 Ma. Before ca.1.0 Ma, large-volume felsic eruptions were dominant, forming large calderas in the frontal arc, a region of low crustal strain rate. After ca. 1.0 Ma to the present, the calc-alkaline andesite magma eruptions in the frontal and rear arcs, synchronous with crustal shortening characterized by reverse faulting, resulted in stratovolcano development along narrow uplifted zones. Although, it is widely assumed that magma cannot rise easily in a compressional setting, some of the magma stored within basal sills could be extruded where N–S-trending uplifted mountains bounded by reverse faults formed since about ca.1.0 Ma.

  4. Arc-rift transition volcanism in the Volcanic Hills, Jacumba and Coyote Mountains, San Diego and Imperial Counties, california

    Science.gov (United States)

    Fisch, Gregory Zane

    Neogene volcanism associated with the subduction of the Farallon-Pacific spreading center and the transition from a subduction zone to a rift zone has been studied extensively in Baja, California, Mexico. One of the main goals of these studies was to find a geochemical correlation with slab windows that may have formed during that complicated transition. While workers have been able to find distinct geochemical signatures in samples from Baja California, none have shown statistically significant correlation with samples from southern California that are thought to be related to the same arc-rift transition events. All of the basaltic samples from this study of southern California rocks have prominent Nb depletions typical of island-arc subduction-related volcanism, in contrast to the chemistry of Baja California volcanics that have trace element patterns typical of synrift related volcanism. The work done by previous investigators has been additionally complicated due to each investigator's choice of important ratios or patterns, which bears little, if any, correlation with work done by others working in the same area. For example, Martin-Barajas et al. (1995) use K/Rb ratios in their study of the Puertocitos Volcanic Province, while Castillo (2008) argues that Sr/Y vs. Y is a better indicator of petrogenetic processes. Little petrologic work has been done on Neogene volcanic rocks in the Imperial Valley and eastern San Diego County region of Southern California. This thesis combines new research with that of previous workers and attempts to establish a better understanding of the processes involved with the transition volcanism. Prior work documents significant differences in the geochemistry between some of these areas, especially those in close proximity to each other (e.g. the Volcanic Hills and Coyote Mountains). These differences were thought to be largely the result different magmatic sources. The potential of finding two differing magma types in close

  5. Geochemical characteristics of island-arc volcanic rocks in the Nan-Nam Pat-Phetchabun zone, northern Thailand

    Institute of Scientific and Technical Information of China (English)

    SHEN Shangyue; FENG Qinglai; YANG Wenqiang; ZHANG Zhibin; Chongpom Chonglakmani

    2010-01-01

    Late Permian-Early Triassic (P2-T1) volcanic rocks distributed on the eastern side of ocean-ridge and oceanic-island basalts in the Nan-Uttaradit zone were analyzed from aspects of petrographic characteristics, rock assemblage, REE, trace elements, geotectonic setting, etc., indicating that those volcanic rocks possess the characteristic features of island-arc volcanic rocks. The volcanic rock assemblage is basalt-basaltic andesite-andesite. The volcanic rocks are sub-alkaline, dominated by calc-alkaline series, with tholeiite series coming next. The chemical composition of the volcanic rocks is characterized by low TiO2 and K2O and high Al2O3 and Na2O. Their REE patterns are of the flat, weak LREE-enrichment right-inclined type. The trace elements are characterized by the enrichment of large cation elements such as K, Rb and Ba, common enrichment of U and Th, and depletion of Nb, Ta, Zr and Hf. The petrochemical plot falls within the field of volcanic rocks, in consistency with the plot of island-arc volcanic rocks in the Jinsha River zone of China. This island-arc volcanic zone, together with the ocean-ridge/oceanic island type volcanic rocks in the Nan-Uttaradit zone, constitutes the ocean-ridge volcanic rock-island-arc magmatic rock zones which are distributed in pairs, indicating that the oceanic crust of the Nan-Uttaradit zone once was of eastward subduction. This work is of great significance in exploring the evolution of paleo-Tethys in the Nan-Uttaradit zone.

  6. Transition of magma genesis estimated by change of chemical composition of Izu-bonin arc volcanism associated with spreading of Shikoku Basin

    Science.gov (United States)

    Haraguchi, S.; Ishii, T.

    2006-12-01

    Arc volcanism in the Izu-Ogasawara arc is separated into first and latter term at the separate of Shikoku Basin. Middle to late Eocene early arc volcanism formed a vast terrane of boninites and island arc tholeiites that is unlike active arc systems. A following modern-style arc volcanism was active during the Oligocene, along which intense tholeiitic and calc-alkaline volcanism continued until 29Ma, before spreading of the back- arc basin. The recent arc volcanism in the Izu-Ogasawara arc have started in the middle Miocene, and it is assumed that arc volcanism were decline during spreading of back-arc basin. In the northern Kyushu-Palau Ridge, submarine bottom materials were dredged during the KT95-9 and KT97-8 cruise by the R/V Tansei-maru, Ocean Research Institute, university of Tokyo, and basaltic to andesitic volcanic rocks were recovered during both cruise except for Komahashi-Daini Seamount where recovered acidic plutonic rocks. Komahashi-Daini Seamount tonalite show 37.5Ma of K-Ar dating, and this age indicates early stage of normal arc volcanism. These volcanic rocks are mainly cpx basalt to andesite. Two pyroxene basalt and andesite are only found from Miyazaki Seamount, northern end of the Kyushu-Palau Ridge. Volcanic rocks show different characteristics from first term volcanism in the Izu-Ogasawara forearc rise and recent arc volcanism. The most characteristic is high content of incompatible elements, that is, these volcanics show two to three times content of incompatible elements to Komahashi-Daini Seamount tonalite and former normal arc volcanism in the Izu outer arc (ODP Leg126), and higher content than recent Izu arc volcanism. This characteristic is similar to some volcanics at the ODP Leg59 Site448 in the central Kyushu- Palau Ridge. Site448 volcanic rocks show 32-33Ma of Ar-Ar ages, which considered beginning of activity of Parece Vela Basin. It is considered that the dredged volcanic rocks are uppermost part of volcanism before spreading of

  7. The Galapagos-OIB signature of the central Costa Rican volcanic front: arc-hotspot interaction

    Science.gov (United States)

    Gazel, E.; Carr, M. J.; Hoernle, K.; Feigenson, M. D.; Hauff, F.; Szymanski, D.; van den Bogaard, P.

    2008-12-01

    Although most Central American magmas have a typical arc geochemical signature, magmas in southern Central America have isotopic and trace element compositions with an OIB affinity, similar to the Galapagos hotspot lavas. Our new data for Costa Rica suggest that this signature, unusual for a convergent margin, has a relatively recent origin (Late Miocene-Pliocene ca. 6 Ma). We also show that there was a transition from typical arc magmas (analogous to the modern Nicaraguan volcanic front) to OIB-like magmas. The geographic distribution of the Galapagos signature in recent lavas from southern Central America is present landward from the subduction of the Galapagos hotspot tracks (the Seamount Province and the Cocos/Coiba Ridges) at the Middle American Trench. The higher Pb isotopic ratios, relatively low Nd isotopic ratios and enriched geochemical signature of central Costa Rican magmas can be explained by arc-hotspot interaction. The isotopic ratios of central Costa Rican lavas require the subducting Seamount Province (Northern Galapagos Domain) component, whereas the isotopic ratios of the adakites and alkaline basalts from southern Costa Rica and Panama are in the geochemical range of the subducting Cocos/Coiba Ridges (Central Galapagos Domain). Geological, geochemical, and isotopic evidence collectively indicate that the relatively recent Galapagos-OIB signature in southern Central America represents a geochemical signal from subducting Galapagos hotspot tracks, which started to collide with the margin ~8 Ma ago. The Galapagos hotspot contribution decreases systematically along the volcanic front from central Costa Rica to NW Nicaragua.

  8. Geodetic Constraints From The Volcanic Arc Of The Andaman - Nicobar Subduction Zone

    Science.gov (United States)

    Earnest, A.; Krishnan, R.; Mayandi, S.; Sringeri, S. T.; Jade, S.

    2012-12-01

    We report first ever GPS derived surface deformation rates in the Barren and Narcondum volcanic islands east of Andaman-Nicobar archipelago which lies in the Bay of Bengal, a zone that generates frequent earthquakes, and coincides with the eastern plate boundary of India. The tectonics of this region is predominantly driven by the subduction of the Indian plate under the Burma plate. Andaman sea region hosts few volcanoes which lies on the inner arc extending between Sumatra and Myanmar with the sub-aerial expressions at Barren and Narcondum Islands. Barren Island, about 135 km ENE of Port Blair, is presently active with frequent eruptive histories whereas Narcondum is believed to be dormant. We initiated precise geodetic campaign mode measurements at Barren Island between 2007 to 2012 and one year (2011-2012) continuous measurements at Narcondum island. Preliminary results from this study forms a unique data set, being the first geodetic estimate from the volcanic arc of this subducting margin. Our analysis indicates horizontal convergence of the Barren benchmark to south-westward (SW) direction towards the Andaman accretionary fore-arc wedge where as the Narcondum benchmark recorded northeast (NE) motion. West of the Andaman fore-arc there is NE oriented subduction of the Indian plate which is moving at the rate of ~5 cm/yr. Convergence rates for the Indian plate from the Nuvel 1A model also show oblique convergence towards N23°E at 5.4 cm/yr. GPS derived inter seismic motion of Andaman islands prior to 2004 Sumatra earthquake is ~4.5 cm/yr NE. The marginal sea basin east of Barren Island at the Andaman spreading ridge has a NNW orienting opening of the sea-floor at 3.6 cm/yr. However the recent post seismic measurements of Andaman islands indicate rotation of displacement vectors from SW to NNE during 2005 to 2012. In this tectonic backdrop, the estimated rate of displacement of the volcanic islands probably represents a composite signal of tectonic as well as

  9. A distinct source and differentiation history for Kolumbo submarine volcano, Santorini volcanic field, Aegean arc.

    Science.gov (United States)

    Klaver, Martijn; Carey, Steven; Nomikou, Paraskevi; Smet, Ingrid; Godelitsas, Athanasios; Vroon, Pieter

    2016-08-01

    This study reports the first detailed geochemical characterization of Kolumbo submarine volcano in order to investigate the role of source heterogeneity in controlling geochemical variability within the Santorini volcanic field in the central Aegean arc. Kolumbo, situated 15 km to the northeast of Santorini, last erupted in 1650 AD and is thus closely associated with the Santorini volcanic system in space and time. Samples taken by remotely-operated vehicle that were analyzed for major element, trace element and Sr-Nd-Hf-Pb isotope composition include the 1650 AD and underlying K2 rhyolitic, enclave-bearing pumices that are nearly identical in composition (73 wt.% SiO2, 4.2 wt.% K2O). Lava bodies exposed in the crater and enclaves are basalts to andesites (52-60 wt.% SiO2). Biotite and amphibole are common phenocryst phases, in contrast with the typically anhydrous mineral assemblages of Santorini. The strong geochemical signature of amphibole fractionation and the assimilation of lower crustal basement in the petrogenesis of the Kolumbo magmas indicates that Kolumbo and Santorini underwent different crustal differentiation histories and that their crustal magmatic systems are unrelated. Moreover, the Kolumbo samples are derived from a distinct, more enriched mantle source that is characterized by high Nb/Yb (>3) and low (206)Pb/(204)Pb (<18.82) that has not been recognized in the Santorini volcanic products. The strong dissimilarity in both petrogenesis and inferred mantle sources between Kolumbo and Santorini suggests that pronounced source variations can be manifested in arc magmas that are closely associated in space and time within a single volcanic field.

  10. Geomorphic and exhumational response of the Central American Volcanic Arc to Cocos Ridge subduction

    Science.gov (United States)

    Morell, Kristin D.; Kirby, Eric; Fisher, Donald M.; van Soest, Matthijs

    2012-04-01

    The timing of collision of the Cocos Ridge at the Middle America Trench remains one of the outstanding questions in the tectonic evolution of the Central American convergent margin. New analyses of the tectonic geomorphology of the Cordillera de Talamanca, the extinct volcanic arc inboard of the Cocos Ridge, coupled with low temperature thermochronometry data, provide insight into the cooling and erosional history of the arc from late Miocene to present. We identify a low-relief surface at high elevation along the northeastern flanks of the range, which represents a relict erosional landscape cut across shallow plutonic rocks of the arc edifice. Longitudinal profiles of rivers on this surface are isolated from steep downstream sections by prominent knickzones that are interpreted to reflect a migrating wave of transient incision generated during differential rock uplift of the range. Reconstruction of pre-incision profiles suggests that rock uplift during the growth of the Cordillera de Talamanca is no greater than ˜2 km. This inference is corroborated by results from our apatite (U-Th)/He and apatite fission track analyses along an elevation transect on Mt. Chirripó, the highest mountain in the Cordillera de Talamanca. Low-temperature cooling ages overlap significantly with published high-temperature40Ar/39Ar ages; the combined results imply that rapid cooling in the late Miocene was related to secular cooling of a shallow pluton, rather than exhumation. Our results imply that rapid incision along downstream channel segments, differential rock uplift, and growth of the Talamanca as a bivergent orogenic wedge associated with the onset of Cocos Ridge subduction are relatively young characteristics of the range. A review of previously published radiometric ages and revised plate reconstructions for the late Miocene further suggest that the cessation of arc volcanism in both the Cordillera de Talamanca and the Cordillera Central of western Panama was coeval with the

  11. NOAA Deepwater Exploration of the Marianas 2016: Volcanic arc and Backarc Basin

    Science.gov (United States)

    Stern, R. J.; Brounce, M. N.; Chadwick, B.; Fryer, P. B.; Glickson, D.; Merle, S. G.

    2016-12-01

    Legs 1 and 3 of NOAA Okeanos Explorer EX1605 devoted a total of 17 ROV dives to exploring the Mariana magmatic arc and backarc basin (BAB). Dives were carried out on 11 submarine arc volcanoes, the submerged slopes of two volcanic islands, and at 3 BAB sites along 1000 km of the Mariana arc system. Four of the studied arc volcanoes are extinct, three are dormant, and six are active. All BAB dives were on the spreading ridge between 15-17°N, which is volcanically active. Geologic highpoints of these dives include: 1) discovery of an extinct hydrothermal chimney ( 15m tall) in Fina Nagu A (Leg 1, Dive 7; L1D7); 2) observations of very fresh (<3 years old) BAB pillow basalts (L1D9); 3) discovery of a very active BAB hydrothermal field (T 340°C, active chimneys up to 30m tall; L1D11); 4) examination of Esmeralda Bank crater floor (active venting but too murky to find vents; L1D19); 5) discovery of hydrothermal vents with vent fauna on Chamorro volcano (L3D7; T 30°C, active chimneys 2m tall); and 6) examination of active venting and S degassing at 500-350 m depth on Daikoku volcano (L3D9). Video clips of some of the most exciting discoveries and examinations will be presented. We plan to compare previous bathymetry over the active volcanoes with what was collected during EX1605 to quantify how these edifices have changed since when these were previously mapped, over the past 13 years or less. These dives also provided visual evidence in support of the hypothesis that individual edifices of the Fina Nagu Volcanic Complex increase in age from NE to SW, interpreted as due to the motion of actively-extending lithosphere of the southern Mariana BAB to the SW over a relatively fixed source of arc magma above the subducting Pacific plate (Brounce et al. G3 2016). Continuous interaction between biologists and geologists on EX1605 allowed us to identify regions of high faunal density on hard substrates around some active volcanoes, for example Esmeralda Bank, presumably

  12. Late Miocene volcanism and intra-arc tectonics during the early development of the Trans-Mexican Volcanic Belt

    Science.gov (United States)

    Ferrari, Luca; Conticelli, Sandro; Vaggelli, Gloria; Petrone, Chiara M.; Manetti, Piero

    2000-03-01

    The early stage of the Trans-Mexican Volcanic Belt (hereafter TMVB) is marked by widespread, mafic to intermediate, volcanism emplaced between 11 and 7 Ma from the Pacific coast to the longitude of Mexico City, to the north of the modern volcanic arc. Petrological and geochronological data support the hypothesis that this volcanism made up a unique late Miocenic central Mexican comagmatic province. Mafic lavas at the mouth of the Gulf of California and along the northwestern sector of the TMVB made up the Nayarit district, which includes calc-alkaline to transitional varieties. The central sector of the TMVB is characterized by two basaltic districts: the Jalisco-Guanajuato and the Queretaro-Hidalgo, which are distinguished from the westernmost ones by their lower Nb/La and generally lower HFSE/LILE values, as well as by spider diagrams characterized by larger negative spikes at Th, Ta, Nb, and Ti. The surface occurrence of the late Miocene basalts appears to be controlled by pre-existing zones of crustal weakness that channeled the mafic magmas. Field observations suggest that these structures have been reactivated in a transtensional fashion induced by differential tectonic motion of crustal blocks to the south and to the north of the TMVB. Starting from ˜12 Ma the TMVB separates a northern tectonic domain, subject to the developing divergent Pacific-North America plate boundary, from a southern tectonic domain, characterized by oblique subduction of the Rivera and Cocos plates. Apparently, far field stresses related to these complex plate boundaries reactivated older suture zones, allowing rapid uprise of mantle-derived magmas. The subduction-related signature shown by Miocene mafic lavas of the Jalisco-Guanajuato district argues against the existence of mantle plumes beneath this sector of the North America plate. On the other hand, the occurrence in the western TMVB and in the Guadalajara region of a large volume of mafic magmas, which sometimes show

  13. Primitive magmas at five Cascade volcanic fields: Melts from hot, heterogeneous sub-arc mantle

    Science.gov (United States)

    Bacon, C.R.; Bruggman, P.E.; Christiansen, R.L.; Clynne, M.A.; Donnelly-Nolan, J. M.; Hildreth, W.

    1997-01-01

    Major and trace element concentrations, including REE by isotope dilution, and Sr, Nd, Pb, and O isotope ratios have been determined for 38 mafic lavas from the Mount Adams, Crater Lake, Mount Shasta, Medicine Lake, and Lassen volcanic fields, in the Cascade arc, northwestern part of the United States. Many of the samples have a high Mg# [100Mg/(Mg + FeT) > 60] and Ni content (>140 ppm) such that we consider them to be primitive. We recognize three end-member primitive magma groups in the Cascades, characterized mainly by their trace-element and alkali-metal abundances: (1) High-alumina olivine tholeiite (HAOT) has trace element abundances similar to N-MORB, except for slightly elevated LILE, and has Eu/Eu* > 1. (2) Arc basalt and basaltic andesite have notably higher LILE contents, generally have higher SiO2 contents, are more oxidized, and have higher Cr for a given Ni abundance than HAOT. These lavas show relative depletion in HFSE, have lower HREE and higher LREE than HAOT, and have smaller Eu/Eu* (0.94-1.06). (3) Alkali basalt from the Simcoe volcanic field east of Mount Adams represents the third end-member, which contributes an intraplate geochemical signature to magma compositions. Notable geochemical features among the volcanic fields are: (1) Mount Adams rocks are richest in Fe and most incompatible elements including HFSE; (2) the most incompatible-element depleted lavas occur at Medicine Lake; (3) all centers have relatively primitive lavas with high LILE/HFSE ratios but only the Mount Adams, Lassen, and Medicine Lake volcanic fields also have relatively primitive rocks with an intraplate geochemical signature; (4) there is a tendency for increasing 87Sr/86Sr, 207Pb/204Pb, and ??18O and decreasing 206Pb/204Pb and 143Nd/144Nd from north to south. The three end-member Cascade magma types reflect contributions from three mantle components: depleted sub-arc mantle modestly enriched in LILE during ancient subduction; a modern, hydrous subduction component

  14. An Early Cretaceous volcanic arc/marginal basin transition zone, Peninsula hardy, southernmost Chile

    Science.gov (United States)

    Miller, Christopher A.; Barton, Michael; Hanson, Richard E.; Fleming, Thomas H.

    1994-10-01

    The Hardy Formation represents a latest Jurassic-Early Cretaceous volcanic arc that was located along the Pacific margin of southern South America. It was separated from the continent by a marginal basin floored by portions of an ophiolite sequence (the Rocas Verdes ophiolites). The transition between the arc and marginal basin occurs on Peninsula Hardy, southernmost Chile, where there is a lateral facies transition from arc deposits of the Hardy Formation into proximal marginal basin fill of the Yahgan Formation. Interfingering of arc and marginal basin sequences demonstrates that subduction-related arc magmatism was concurrent with marginal basin formation. The lateral facies transition is reflected in the geochemistry of volcanic rocks from the Hardy and Yahgan formations. Basalts, andesites and dacites of the arc sequence follow a calc-alkaline differentiation trend whereas basalts from the marginal basin follow a tholeiitic differentiation trend. Estimates of temperature and oxygen fugacity for crystallization of the arc andesites are similar to values reported for other calc-alkaline andesites. It is suggested that water activity influenced the early or late crystallization of Ti-magnetite and this controlled the style of differentiation of the magmas erupted on Peninsula Hardy. Magmas with high water contents evolved along the calc-alkaline differentiation trend whereas those with low water contents evolved along the tholeiitic differentiation trend. Some rhyolites are differentiated from the calc-alkaline andesites and dacites, but most appear to be the products of crustal anatexis on the basis of trace-element evidence. The arc basalts and some marginal basin basalts show relative enrichment in LILE, relative depletion in HFSE, and enrichment in LREE. Other marginal basin basalts are LREE depleted and show small relative depletions in HFSE. Basalts with both calc-alkaline and tholeiitic affinities can also be recognized in the Rocas Verdes ophiolites

  15. Geochemistry and Petrogenesis of Volcanic Rocks in the Yeba Formation on the Gangdise Magmatic Arc, Tibet

    Institute of Scientific and Technical Information of China (English)

    Geng Quanru; Pan Guitang; Jin Zhenmin; Wang Liquan; Liao Zhongli

    2005-01-01

    The Early Jurassic bimodal volcanic rocks in the Yeba Formation, situated between Lhasa, Dagzê and Maizhokunggar, composed of metabasalt, basaltic ignimbrite, dacite, silicic tuff and volcanic breccia, are an important volcanic suite for the study of the tectonic evolution of the Gangdise magmatic arc and the Mesozoic Tethys. Based on systematic field investigations, we carried out geochemical studies on representative rock samples. Major and trace element compositions were analyzed for these rock samples by XRF and ICP-MS respectively, and an isotope analysis of Rb-Sr and Sm-Nd was carried out by a MAT 262 mass spectrograph. The results show that the SiO2 contents in lava rocks are 41 %-50.4 % and 64 %-69 %, belonging to calc-alkaline basalt and dacite. One notable feature of the basalt is its low TiO2 content, 0.66 %-1.01 %, much lower than those of continental tholeiite. The ΣREE contents of basalt and dacite are 60.3-135 μg/g and 126.4-167.9 μg/g respectively. Both rocks have similar REE and other trace element characteristics, with enriched LREE and LILE relative to HREE and HFS, similar REE patterns without Eu anomaly. The basalts have depleted Ti, Ta and Nb and slightly negative Nb and Ta anomalies, with Nb*=0.54-1.17 averaging 0.84. The dacites have depleted P and Ti and also slightly negative Nb and Ta anomalies, with Nb*=0.74-1.06 averaging 0.86. Major and trace elemental and isotopic studies suggest that both basalt and dacite originated from the partial melting of the mantle wedge at different degrees above the subduction zone. The spinal lherzolite in the upper mantle is likely to be their source rocks, which might have been affected by the selective metasomatism of fluids with crustal geochemistry. The LILE contents of both rocks were affected by metamorphism at later stages. The Yeba bimodal volcanic rocks formed in a temporal extensional situation in a mature island arc resulting from the Indosinian Gangdise magmatic arc.

  16. The record of magma chamber processes in plagioclase phenocrysts at Thera Volcano, Aegean Volcanic Arc, Greece

    Science.gov (United States)

    Stamatelopoulou-Seymour, Karen; Vlassopoulos, Dimitrios; Pearce, Thomas H.; Rice, Craig

    1990-01-01

    Lavas and pyroclastic rocks throughout the volcanic stratigraphy of the Tertiary-Quaternary volcanic complex of Thera in the Aegean island arc display inhomogenous plagioclase populations and phenocryst resorption textures, interpreted as indicative of magma mixing. Plagioclase zoning characteristics studied by Nomarski and laser interferometry techniques establish three main categories of plagioclase: (i) inherited plagioclase (nucleated in endmember prior to initial mixing event) (ii) in situ plagioclase (nucleated in mixed or hybrid magma) and (iii) xenocrystic plagioclase. Nomarski contrast images and linearized compositional zoning profiles reveal striking differences between calcic and sodic plagioclases, depending on the composition of the lava in which they are hosted. These differences reflect the contrasting effects of changes in physical-chemical parameters in basic vis-a-vis more acidic melts during magma mixing and/or influx of new magma into the subvolcanic magma chamber, as well as the influence of magma chamber dynamics on plagioclase equilibration. Variations in bulk major and trace element abundances of Thera volcanic products reflect the dominant overprint of crystal fractionation, but decoupling between major and trace element fractionation models and variations in incompatible trace element distributions are all indicative of magma mixing processes, consistent with compositional and textural zoning in plagioclases.

  17. Metagenomic investigation of the geologically unique Hellenic Volcanic Arc reveals a distinctive ecosystem with unexpected physiology.

    Science.gov (United States)

    Oulas, Anastasis; Polymenakou, Paraskevi N; Seshadri, Rekha; Tripp, H James; Mandalakis, Manolis; Paez-Espino, A David; Pati, Amrita; Chain, Patrick; Nomikou, Paraskevi; Carey, Steven; Kilias, Stephanos; Christakis, Christos; Kotoulas, Georgios; Magoulas, Antonios; Ivanova, Natalia N; Kyrpides, Nikos C

    2016-04-01

    Hydrothermal vents represent a deep, hot, aphotic biosphere where chemosynthetic primary producers, fuelled by chemicals from Earth's subsurface, form the basis of life. In this study, we examined microbial mats from two distinct volcanic sites within the Hellenic Volcanic Arc (HVA). The HVA is geologically and ecologically unique, with reported emissions of CO2 -saturated fluids at temperatures up to 220°C and a notable absence of macrofauna. Metagenomic data reveals highly complex prokaryotic communities composed of chemolithoautotrophs, some methanotrophs, and to our surprise, heterotrophs capable of anaerobic degradation of aromatic hydrocarbons. Our data suggest that aromatic hydrocarbons may indeed be a significant source of carbon in these sites, and instigate additional research into the nature and origin of these compounds in the HVA. Novel physiology was assigned to several uncultured prokaryotic lineages; most notably, a SAR406 representative is attributed with a role in anaerobic hydrocarbon degradation. This dataset, the largest to date from submarine volcanic ecosystems, constitutes a significant resource of novel genes and pathways with potential biotechnological applications.

  18. Andesite petrogenesis in a hybrid arc-rift setting: the Western Trans-Mexican Volcanic Belt

    Science.gov (United States)

    Gómez-Tuena, A.; Vázquez-Duarte, A.; Díaz-Bravo, B.; Mori, L.

    2011-12-01

    The western sector of the Mexican subduction zone is characterized by the steep subduction of one of the youngest slabs on the planet (Rivera plate), and by the existence of a continental rift at ~230 km to the north from the trench (the so-called Tepic-Zacoalco rift, TZR), under which the subducted slab is either extremely deep or even absent (>250 km). The volcanic front is located at ~170 km from the trench and contains abundant potassic-alkaline lamprophyres with strong subduction (Ba/Ta= 1600-6000) and garnet signatures (Gd/Yb= 2-8), that have been recently interpreted as influenced by deep K2O-rich slab melts or supercritical fluids (Gómez-Tuena et al., 2011, GCA). In contrast, the most mafic rocks within the TZR are high-Nb, intraplate-like basalts that appear to derive from low extents of melting of a dryer (Ba/Ta= 800-60) and shallower (Gd/Yb= 2-2.5) mantle source. Even though a simple transition from an arc environment to an extensional tectonic regime is apparent when only the most primitive volcanic rocks are taken into account, the scenario becomes more complicated since at least five stratovolcanoes have been erupting typical arc andesites within the TZR over the last million years (San Juan, Sanganguey, Tepetiltic, Ceboruco and Tequila). Surprisingly, true calc-alkaline basalts that could be parental to andesites have not been found, indicating that andesites may have a direct mantle origin. Indeed, mayor and trace element compositions of volcanic rocks from western Mexico arrange in discrete suites with linear trends that are indicative of mixing, but they form sub-parallel arrays that do not converge to a common primitive basaltic melt, and often follow diverging trends in trace element-ratio plots. Melt-crust interactions likely occurred during magma ascent, since the volcanic rocks frequently include xenoliths and disequilibrium textures, but correlations among isotopic compositions and indexes of fractionation are not clearly observed in the

  19. Modeling Central American Volcanic Front Primitive Lavas with the Arc Basalt Simulator (abs 4.0)

    Science.gov (United States)

    Feigenson, M.; Carr, M. J.; Gazel, E.

    2012-12-01

    We have used the Arc Basalt Simulator (ABS), developed by J-I Kimura, to explore the conditions and components of melting beneath the Central American volcanic front. ABS is a comprehensive forward model that incorporates slab dehydration and melting and mantle wedge fluxing and melting using realistic P-T conditions and experimentally determined phase relations and partition coefficients. We have applied ABS version 4.00, which includes melting/dehydration relations in eight distinct subducting layers, to model representative magma types along the Central American volcanic front. These magmas are first projected to primary melt compositions by the addition of olivine until they reach Fo90. Then, using a wide range of input parameters including variations in slab components, extent of peridotite depletion, depth of slab dehydration and wedge fluxing and degree of peridotite melting, successful model fits are generated (based on trace element and isotope matching). The solution space is probed using a Monte Carlo technique to cover the enormous range of parameter values. Nicaragua and Costa Rica represent geochemical and geophysical end members of the volcanic front, differing greatly in volcano volume, slab dip beneath the volcano, isotopic composition and incompatible element enrichment. Using appropriate input compositions for ABS 4.0, we find through millions of simulations that the Cerro Negro primary magma (Nicaragua) requires high degrees of source melting (22-27%) and large amounts of slab-derived water (3-5%). In contrast, the Irazu primary magma (central Costa Rica) is generated from more enriched sources with only a small amount of water (less than 0.5%) and at low degrees of partial melting (less than 5%). Other Central American lavas with intermediate geochemical characteristics are produced from conditions within the Nicaragua-Costa Rica range. By reproducing the lava geochemistry with ABS 4.0, it becomes possible to extract constraints on source input

  20. Structure and petrology of newly discovered volcanic centers in the northern Kermadec-southern Tofua arc, South Pacific Ocean

    Science.gov (United States)

    Graham, Ian J.; Reyes, Agnes G.; Wright, Ian C.; Peckett, Kimberley M.; Smith, Ian E. M.; Arculus, Richard J.

    2008-08-01

    The NZAPLUME III expedition of September-October 2004 to the northern Kermadec-southern Tofua (NKST) arc, between 28°52'S and 25°07'S, resulted in the discovery of at least seven new submarine volcanic centers and a substantial caldera complex adjacent to the previously known Monowai Seamount. The volcanic centers form a sublinear chain that coincides with the Kermadec Ridge crest in the south (Hinetapeka) and diverges ˜45 km westward of the ridge crest in the north ("V") just to the south of where the Louisville Ridge intersects with the arc. All of the centers contain calderas or caldera-like structures, as well as multiple cones, domes, fissure ridges, and vent fields. All show signs of recent eruptive and current hydrothermal activity. There are strong structural controls on edifice location, with cones and fissure ridges typically associated with faulting parallel to the regional ˜12° strike of the arc front. Several of the calderas are ellipsoidal, orientated northwest-southeast in the general direction of least compressive stress. Sampled volcanic rocks, representing the most recently erupted lavas, are all low-K tholeiites. Two of the centers, Gamble and Rakahore, yielded only high-silica dacite to rhyolite (69-74 wt% silica), whereas two others, Monowai and "V," yielded only basalt to andesite (48-63 wt% silica). Mineral assemblages are plagioclase-pyroxene dominated, with accessory Fe-Ti oxides, apatite, olivine, and quartz/tridymite/cristobalite, typical of dry volcanic arc systems. Hornblende occurs only in a felsitic rhyolite from Hinepuia volcanic center, and zircon is absent. Glass contents range to 57% in basalts-andesites (mean 20%), and 97% in andesites-rhyolites (mean 59%) and other quench textures, including swallow-tailed, plumose, or dendritic crystal forms and crystallites, are common. Most lavas are highly vesicular (≤63%; mean 28%) and have low volatile contents (mostly cristobalite, indicates explosive eruption and rapid cooling

  1. Late cenozoic vertical movements of non-volcanic islands in the Banda Arc area

    Science.gov (United States)

    De Smet, M. E. M.; Fortuin, A. R.; Tjokrosapoetro, S.; Van Hinte, J. E.

    During onshore campaigns of the Snellius-II Expedition late Cenozoic sections were recorded and systematically sampled on the non-volcanic outer Banda Arc Islands of Timor, Buton, Buru, Seram and Kai. Microfaunal studies provided age and palaeobathymetric data to construct geohistory diagrams. Geohistory analysis of field and laboratory data allows to calculate rates of vertical movements of the island basements. The vertical movements were intermittent and differed widely from place to place in the arc; short periods of uplift alternated with longer periods of tectonic rest or subsidence and lateral variations in timing and magnitude seem to be more the rule than the exception. Movements affected larger segments of the arc at about the same time, especially since the late Pliocene, when widespread vertical movements started, which led to the present configuration of the arc. Rates of uplift or subsidence differed within each segment. On an intermediate scale, deformation has the character of tilting or doming of whole islands or parts of islands. On a local scale, various types of deformation occur. Calculated duration of uplift pulses is in the order of a million years where less than 50 cm·ka -1 of vertical movements are involved. Sections, however, with a high time stratigraphic resolutions show pulses of uplift with a duration of only some hundreds of thousands of years and rates of more than 500 cm·ka -1. The duration of such pulses therefore is comparable to that of eustatic third order sea level changes. But because their amplitude is an order of magnitude larger, this implies that in tectonically active areas eustatic signals, preserved in the sedimentary record, will be overprinted by tectonics, i.e. will be difficult to disentangle from the tectonic signal.

  2. Late Cretaceous volcanic arc system in Southwest Korea: Occurrence, lithological characteristics, SHRIMP zircon U-Pb age, and tectonic implications

    Science.gov (United States)

    Koh, Hee Jae; Kwon, Chang Woo

    2017-04-01

    In the southwest region of the Korean Peninsula, four large volcanoes, the Buan, Seonunsan, Wido, and Beopseongpo, with a maximum diameter of ca 20 km, form a distinct topographic undulation along the NE-SW-trending Hamyeol Fault. These volcanics comprise various types of pyroclastic, sedimentary, and lava/intrusive rocks, and are interpreted as remnants of calderas resulting from various volcanic eruptions, indicating that Hamyeol Fault, together with crustal extension, played an important role in volcano formation in this region. SHRIMP U-Pb ages of zircon isolated from each volcanics are as follows. For Buan Volcanics, Cheonmasan Tuff 87.23 ±0.92 Ma, Udongje Tuff 86.79 ±0.71 Ma, Seokpo Tuff 87.30 ±0.99 Ma and Yujeongje Tuff 86.66 ±0.93 Ma. For Seonunsan Volcanics, Gyeongsusan Tuff 84.9 ±1.1 Ma and Yeongije Tuff 86.61 ±0.67 Ma. These ages indicate that the four volcanics were formed in the Late Cretaceous. The ages are comparable to those of the volcanic rocks of the Aioi and Arima groups in Southwestern Japan, suggesting that the Late Cretaceous volcanic arc systems developed in a NE-SW direction from the Japanese Islands to the southwestern part of the Korean Peninsula caused by regional magmatism together with crustal deformation as reflected by occurrence of the volcanic rocks along the Hamyeol Fault.

  3. Halogen content in Lesser Antilles arc volcanic rocks : exploring subduction recycling

    Science.gov (United States)

    Thierry, Pauline; Villemant, Benoit; Caron, Benoit

    2016-04-01

    Halogens (F, Cl, Br and I) are strongly reactive volatile elements which can be used as tracers of igneous processes, through mantle melting, magma differentiation and degassing or crustal material recycling into mantle at subduction zones. Cl, Br and I are higly incompatible during partial melting or fractional cristallization and strongly depleted in melts by H2O degassing, which means that no Cl-Br-I fractionation is expected through magmatic differenciation [current thesis]. Thus, Cl/Br/I ratios in lavas reflect the halogen content of their mantle sources. Whereas these ratios seemed quite constant (e.g. Cl/Br =300 as seawater), recent works suggest significant variations in arc volcanism [1,2]. In this work we provide high-precision halogen measurements in volcanic rocks from the recent activity of the Lesser Antilles arc (Montserrat, Martinique, Guadeloupe, Dominique). Halogen contents of powdered samples were determined through extraction in solution by pyrohydrolysis and analysed by Ion Chromatography for F and Cl and high performance ICP-MS (Agilent 8800 Tripe Quad) for Cl, Br and I [3,4]. We show that lavas - and mantle sources - display significant vraiations in Cl/Br/I ratios along the Lesser Antilles arc. These variations are compared with Pb, Nd and Sr isotopes and fluid-mobile elements (Ba, U, Sr, Pb etc.) compositions which vary along the arc from a nothern ordinary arc compositions to a southern 'crustal-like' composition [5,6]. These characteristics are attributed to subducted sediments recycling into the mantle wedge, whose contribution vary along the arc from north to south [7,8]. The proportion of added sediments is also related to the distance to the trench as sediment melting and slab dehydration may occur depending on the slab depth [9]. Further Cl-Br-I in situ measurements by LA-ICP-MS in Lesser Antilles arc lavas melt inclusions will be performed, in order to provide better constraints on the deep halogen recycling cycle from crust to

  4. Multidisciplinary exploratory study of a geothermal resource in the active volcanic arc of Basse-Terre (Guadeloupe, Lesser Antilles)

    Science.gov (United States)

    Navelot, Vivien; Favier, Alexiane; Géraud, Yves; Diraison, Marc; Corsini, Michel; Verati, Chrystèle; Lardeaux, Jean-Marc; Mercier de Lépinay, Jeanne; Munschy, Marc

    2017-04-01

    The GEOTREF project (high enthalpy geothermal energy in fractured reservoirs), supported by the French government program, "Investissements d'avenir" develops a sustainable geothermal resource in the Vieux Habitants area, 8-km south of the currently exploited Bouillante geothermal field. The Basse Terre Island is a recent volcanic arc (geothermal gradient of 70 ˚ C/km.

  5. Deep long-period earthquakes west of the volcanic arc in Oregon: evidence of serpentine dehydration in the fore-arc mantle wedge

    Science.gov (United States)

    Vidale, John E.; Schmidt, David A.; Malone, Stephen D.; Hotovec-Ellis, Alicia J.; Moran, Seth C.; Creager, Kenneth C.; Houston, Heidi

    2014-01-01

    Here we report on deep long-period earthquakes (DLPs) newly observed in four places in western Oregon. The DLPs are noteworthy for their location within the subduction fore arc: 40–80 km west of the volcanic arc, well above the slab, and near the Moho. These “offset DLPs” occur near the top of the inferred stagnant mantle wedge, which is likely to be serpentinized and cold. The lack of fore-arc DLPs elsewhere along the arc suggests that localized heating may be dehydrating the serpentinized mantle wedge at these latitudes and causing DLPs by dehydration embrittlement. Higher heat flow in this region could be introduced by anomalously hot mantle, associated with the western migration of volcanism across the High Lava Plains of eastern Oregon, entrained in the corner flow proximal to the mantle wedge. Alternatively, fluids rising from the subducting slab through the mantle wedge may be the source of offset DLPs. As far as we know, these are among the first DLPs to be observed in the fore arc of a subduction-zone system.

  6. The tectonic emplacement of Sumba in the Sunda-Banda Arc: paleomagnetic and geochemical evidence from the early Miocene Jawila volcanics

    NARCIS (Netherlands)

    Wensink, H.; Bergen, M.J. van

    1995-01-01

    The island of Sumba is a continental fragment in the fore-arc region near the transition between the Sunda Arc and Banda Arc in southeastern Indonesia. Paleomagnetic and geochemical evidence from the early Miocene volcanics of the Jawila Formation in western Sumba constrain the final drift stage

  7. Oligocene and Miocene arc volcanism in northeastern California: evidence for post-Eocene segmentation of the subducting Farallon plate

    Science.gov (United States)

    Colgan, J.P.; Egger, A.E.; John, D.A.; Cousens, B.; Fleck, R.J.; Henry, C.D.

    2011-01-01

    The Warner Range in northeastern California exposes a section of Tertiary rocks over 3 km thick, offering a unique opportunity to study the long-term history of Cascade arc volcanism in an area otherwise covered by younger volcanic rocks. The oldest locally sourced volcanic rocks in the Warner Range are Oligocene (28–24 Ma) and include a sequence of basalt and basaltic andesite lava flows overlain by hornblende and pyroxene andesite pyroclastic flows and minor lava flows. Both sequences vary in thickness (0–2 km) along strike and are inferred to be the erosional remnants of one or more large, partly overlapping composite volcanoes. No volcanic rocks were erupted in the Warner Range between ca. 24 and 16 Ma, although minor distally sourced silicic tuffs were deposited during this time. Arc volcanism resumed ca. 16 Ma with eruption of basalt and basaltic andesite lavas sourced from eruptive centers 5–10 km south of the relict Oligocene centers. Post–16 Ma arc volcanism continued until ca. 8 Ma, forming numerous eroded but well-preserved shield volcanoes to the south of the Warner Range. Oligocene to Late Miocene volcanic rocks in and around the Warner Range are calc-alkaline basalts to andesites (48%–61% SiO2) that display negative Ti, Nb, and Ta anomalies in trace element spider diagrams, consistent with an arc setting. Middle Miocene lavas in the Warner Range are distinctly different in age, composition, and eruptive style from the nearby Steens Basalt, with which they were previously correlated. Middle to Late Miocene shield volcanoes south of the Warner Range consist of homogeneous basaltic andesites (53%–57% SiO2) that are compositionally similar to Oligocene rocks in the Warner Range. They are distinctly different from younger (Late Miocene to Pliocene) high-Al, low-K olivine tholeiites, which are more mafic (46%–49% SiO2), did not build large edifices, and are thought to be related to backarc extension. The Warner Range is ∼100 km east of the

  8. Drilling of Submarine Shallow-water Hydrothermal Systems in Volcanic Arcs of the Tyrrhenian Sea, Italy

    Science.gov (United States)

    Petersen, S.; Augustin, N.; de Benedetti, A.; Esposito, A.; Gaertner, A.; Gemmell, B.; Gibson, H.; He, G.; Huegler, M.; Kleeberg, R.; Kuever, J.; Kummer, N. A.; Lackschewitz, K.; Lappe, F.; Monecke, T.; Perrin, K.; Peters, M.; Sharpe, R.; Simpson, K.; Smith, D.; Wan, B.

    2007-12-01

    Seafloor hydrothermal systems related to volcanic arcs are known from several localities in the Tyrrhenian Sea in water depths ranging from 650 m (Palinuro Seamount) to less than 50 m (Panarea). At Palinuro Seamount 13 holes (Metal enrichment at the top of the deposit is evident in some cores with polymetallic (Zn, Pb, Ag) sulfides overlying more massive and dense pyritic ore. The massive sulfide mineralization at Palinuro Seamount contains a number of unusual minerals, including enargite, tennantite, luzonite, and Ag-sulfosalts, that are not commonly encountered in mid-ocean ridge massive sulfides. In analogy to epithermal deposits forming on land, the occurrence of these minerals suggests a high sulfidation state of the hydrothermal fluids during deposition implying that the mineralizing fluids were acidic and oxidizing rather than near-neutral and reducing as those forming typical base metal rich massive sulfides along mid-ocean ridges. Oxidizing conditions during sulfide deposition can probably be related to the presence of magmatic volatiles in the mineralizing fluids that may be derived from a degassing magma chamber. Elevated temperatures within sediment cores and TV-grab stations (up to 60°C) indicate present day hydrothermal fluid flow. This is also indicated by the presence of small tube-worm bushes present on top the sediment. A number of drill holes were placed around the known phreatic gas-rich vents of Panarea and recovered intense clay-alteration in some holes as well as abundant massive anhydrite/gypsum with only trace sulfides along a structural depression suggesting the presence of an anhydrite seal to a larger hydrothermal system at depth. The aim of this study is to understand the role that magmatic volatiles and phase separation play in the formation of these precious and trace element-rich shallow water (hydrothermal systems in the volcanic arcs of the Tyrrhenian Sea.

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

    Science.gov (United States)

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

    2016-04-01

    -derived plateaus and seamounts. Scarce redeposited remnants of Campanian-Maastrichtian and Late Paleocene-Early Eocene shallow water limestones are associated either with shoals on oceanic seamounts such as the Tulín and Quepos Terranes, or on accreted and uplifted plateaus, such as the Inner Osa Igneous Complex. The latter was probably accreted during the Early Paleocene and partly uplifted and maintained in the photic zone during the Late Paleocene - Late Eocene, as indicated by shallow water material both in place (Burica Peninsula, western Panama) and resedimented in deep water hemipelagic series. The Paleocene-Middle Eocene period is punctuated by the accretion of large pieces of plateaus and oceanic islands that may have temporarily extinguished the arc in southern Costa Rica. Only distal (airborne and suspension) volcanic material is known from that time. By Late Eocene, arc-volcanic activity resumed. The accretion of small seamounts and mass wasting of earlier accreted material from the hanging wall created the Osa Mélange. It contains scarce remnants of the insular shallow water carbonates along with a big volume of arc-derived detritals, including upper Eocene shallow water resediments.

  10. Generation of porphyry copper deposits by gas-brine reaction in volcanic arcs

    Science.gov (United States)

    Blundy, Jon; Mavrogenes, John; Tattitch, Brian; Sparks, Steve; Gilmer, Amy

    2014-05-01

    Porphyry copper deposits (PCDs) are characterised by a close spatial and temporal association with small, hypabyssal intrusions of silicic magmas in volcanic arcs. PCD formation requires elevated chlorine and water to concentrate copper in magmatic hypersaline liquids (or brines), and elevated sulphur to precipitate copper-rich sulphides. These twin requirements are hard to reconcile with experimental and petrological evidence that voluminous chlorine-rich, hydrous silicic magmas, of the variety favourable to copper enrichment, lack sufficient sulphur to precipitate directly the requisite quantities of sulphides. These features are, however, consistent with observations of active volcanic arcs whereby PCDs can be viewed as roots of dome volcanoes above shallow reservoirs where silicic magmas accumulate over long time spans. During protracted periods of dormancy metal-enriched dense brines accumulate in and above the silicic reservoir through slow, low-pressure degassing. Meanwhile cogenetic volatile-rich mafic magmas and their exsolved, sulphur and CO2-rich fluids accumulate in deeper reservoirs. Periodic destabilisation of these reservoirs leads to short-lived bursts of volcanism liberating sulphurous gases, which react with the shallow-stored brines to form copper-rich sulphides and acidic vapours. We test this hypothesis with a novel set of 'porphyry in a capsule' experiments designed to simulate low-pressure (1-2 kbar) interaction of basalt-derived, sulphur-rich gases with brine-saturated, copper-bearing, but sulphur-free, granite. Experiments were run at 720-850 ° C in cold-seal apparatus with basaltic andesite, loaded with H2O and S, situated below dacite, loaded with H2O, Cl and Cu. At run conditions both compositions are substantially degassed and crystallized. S-rich gas from the basaltic andesite ascends to react with Cu-rich brines exsolved from the dacite, Our experiments reveal the direct precipitation of copper-sulphide minerals, in vugs and veins

  11. Age and chemical constraints of Volcán Tunupa: Implications for behind arc volcanism in the Bolivian central Andes

    Science.gov (United States)

    salisbury, M. J.; Kent, A. J.; Jiménez, N.; Jicha, B. R.

    2011-12-01

    New 40Ar/39Ar age determinations of groundmass separates and whole-rock geochemical data constrain the Pleistocene eruptive history of Volcán Tunupa, a glacially-dissected composite volcano (~50 km3) situated between the Salar de Uyuni and Salar de Coipasa. Tunupa erupted ~110 km east of the arc front of the Western Cordillera of the central Andes near the eastern edge of the Intersalar Volcanic Field, an arc-perpendicular expression of volcanism that extends to the central Altiplano basin of Bolivia. 40Ar/39Ar age determinations indicate that the edifice was constructed between ~1.40 and 1.55 Ma, whereas nearby Cerro Huayrana lavas erupted ~ 11 Ma. Published ages from the Western Cordillera that are concordant with both Tunupa and Huayrana lavas demonstrate that the central Altiplano lavas are a long-lived expression of behind arc volcanism. The Tunupa lavas define a calc-alkaline trend from trachyandesite to trachydacite (wt.% SiO2 = 60.6 - 63.6; wt.% K2O + Na2O = 7.5 - 8.3) and are overlain by younger, more silicic (wt.% SiO2 = 66) trachydacitic domes. Major element compositions of Tunupa and Huayrana are enriched in FeO and TiO2 compared to the arc front. These lavas are also enriched in high field strength elements, notably Nb and Ta, and are characterized by considerably lower Ba/Nb and La/Ta ratios than arc front lavas in northern Chile. The geochemical and spatiotemporal patterns of the behind arc Tunupa and Huayrana lavas suggest different petrogenetic histories from typical central Andean arc lavas.

  12. Backarc tectonism, volcanism, and mass wasting shape seafloor morphology in the Santorini-Christiana-Amorgos region of the Hellenic Volcanic Arc

    Science.gov (United States)

    Hooft, Emilie E. E.; Nomikou, Paraskevi; Toomey, Douglas R.; Lampridou, Danai; Getz, Claire; Christopoulou, Maria-Eleni; O'Hara, Daniel; Arnoux, Gillean M.; Bodmer, Miles; Gray, Melissa; Heath, Benjamin A.; VanderBeek, Brandon P.

    2017-08-01

    In subduction zone backarcs, extensional deformation and arc volcanism interact and these processes, together with mass wasting, shape the seafloor morphology. We present a new bathymetric map of the Santorini-Christiana-Amorgos backarc region of the Hellenic subduction zone by merging high-resolution multibeam swath data from the R/V Langseth PROTEUS seismic experiment with existing maps. The map together with Knudsen subbottom echosounding profiles reveal that recent tectonism, volcanism, and mass wasting are more prevalent in the Santorini-Amorgos region on the east side of Santorini than in the Christiana Basin on the west side. In the Santorini-Amorgos region, large normal faults form the Anydros and Anafi Basins. Where normal fault segments overlap, two nearby accommodation zones generate a relay ramp and the adjoining Anydros synclinal horst with associated complex faulting and elevated seismicity. The ongoing normal faulting in the Santorini-Amorgos region is accompanied by potentially tsunamigenic submarine landsliding; we identified a large submarine landslide along the Santorini-Amorgos Fault and a smaller landslide with an overlying debris chute along the Amorgos Fault. Volcanic activity is also focused in this eastern region along the Kolumbo lineament within the Anydros Basin. Within the Christiana Basin we discovered the Proteus Knoll and adjacent buried edifice. We suggest that this is an older volcanic edifice formed along the Hellenic Volcanic Arc between Santorini and Milos. Around Santorini itself, features formed during, and immediately after, the Late Bronze Age eruption dominate the seafloor morphology such as the northern strait and wrinkled seafloor pyroclastic flow deposits. This topography is continually reshaped at a smaller scale by ongoing mass wasting. We infer that the earthquake, volcanic, and tsunami activity of the Santorini-Amorgos region is a consequence of focused northwest-southeast extension as the southeastern Aegean moves

  13. Seismotectonic pattern and the source region of volcanism in the central part of Sunda Arc

    Science.gov (United States)

    Špičák, Aleš; Hanuš, Václav; Vaněk, Jiří

    2005-07-01

    The seismotectonic pattern in the central part of the Sunda Arc (Java, Nusa Tenggara) was studied in relation to the distribution of active calc-alkaline volcanoes, using global seismological data. Hypocentral determinations of the International Seismological Centre from the period 1964-1999, as relocated by Engdahl, and Harvard Centroid Moment Tensor Solutions from the period 1976-2003 were used. The following phenomena, which could assist the location of the source region of primary magma for island arc calc-alkaline volcanism, were observed: (1) An aseismic gap without any strong teleseismically recorded earthquakes was found in the Wadati-Benioff zone of the subducting slab along the whole investigated region of the Sunda Arc, forming a continuous strip of laterally variable depth and shape, at depths between 100 and 200 km. The absence of strong earthquakes (with mb>4.0) indicates a significant change in the mechanical properties of the subducting slab at intermediate depths. All active calc-alkaline volcanoes in the Sunda Arc are located above this gap. (2) The majority of earthquakes occurring in the lithospheric wedge of the Eurasian Plate above the subducted slab could be attributed to several deep-rooted seismically active fracture zones of regional extent. All delineated active fracture zones display a thrust tectonic regime as shown by the available fault plane solutions. (3) Clusters of earthquakes were found beneath active volcanoes of western Java, Bali and Nusa Tenggara in the lithospheric wedge above the slab and identified as seismically active columns. These clusters occur only beneath the volcanoes that are located at the outcrops of seismically active fracture zones. We interpret the earthquakes in these clusters beneath volcanoes as events induced by magma transport through the medium of the lithospheric wedge that has been subcritically pre-stressed by the process of plate convergence. (4) Beneath the volcanoes of central Java no seismically

  14. From northern Gondwana passive margin to arc dismantling: a geochemical discrimination of Ordovician volcanisms (Sardinia, Italy)

    Science.gov (United States)

    Gaggero, L.; Oggiano, G.; Buzzi, L.; Funedda, A.

    2009-04-01

    In Sardinia, one of the southernmost remain of the European Variscan belt, a crustal section through northern Gondwanan paleodomains is largely preserved. It bears significant evidence of igneous activity, recently detailed in field relationships and radiometric dating (Oggiano et al., submitted). A Cambro - Ordovician (491.7 ± 3.5 Ma ÷ 479.9 ± 2.1 Ma, LA-ICP-MS U-Pb zircon age) bimodal volcanic suite occurs with continuity in external and inner Variscan nappes of Sardinia below the so-called Sardic unconformity. The igneous suite represents an intraplate volcanic activity developed through subsequent episodes: i) an intermediate explosive and effusive volcanism, i.e. pyroclastic fall deposits and lava flows, embedded into epicontinental clastic sediments, culminating in silicic ignimbrite eruptions, and ii) mafic effusives. Geochemical data document a transitional, within-plate signature, e.g. the average Th/Ta (4.5) and La/Nb (2.7) overlap the upper continental crust values. The volcanites are characterized by slight fractionation of LREEs, nearly flat HREE abundance. The negative Eu anomaly increases towards evolved compositions. Some prominent HREE depletion (GdCN/YbCN = 13.8), and the high Nb/Y suggest a garnet-bearing source. The high 87Sr radiogenic content (87Sr/86Sr 490 Ma = 0.71169) and the epsilon Nd 490 Ma value of -6.54 for one dacite sample, imply a time integrated LREE-enriched source with a high Rb/Sr, such as a metasedimentary source. The stratigraphy of the succession and the geochemical composition of igneous members suggest a volcanic passive margin along the northern Gondwana at the early Ordovician. The bimodal Mid-Ordovician arc volcanism (465.4 ± 1.4 Ma, U-Pb zircon age; Oggiano et al., submitted) is developed in the external nappes (e.g. in Sarrabus and Sarcidano) and in the foreland occurs as clasts at the base of the Hirnantian succession (Leone et al. 1991). The Mid Ordovician sub-alkalic volcanic suite has reliable stratigraphic and

  15. Transient magmatic control in a tectonic domain: the central Aeolian volcanic arc (South Italy)

    KAUST Repository

    Ruch, Joel

    2015-04-01

    The background stress field in volcanic areas may be overprinted by that produced by transient magmatic intrusions, generating local faulting. These events are rarely monitored and thus not fully understood, generating debate about the role of magma and tectonics in any geodynamic setting. Here we carried out a field structural analysis on the NNW-SSE strike-slip system of the central Aeolian Arc, Italy (Lipari and Vulcano islands) with ages constrained by stratigraphy to better capture the tectonic and magmatic evolution at the local and regional scales. We consider both islands as a single magmatic system and define 5 principal stratigraphic units based on magmatic and tectonic activity. We collected >500 measurements of faults, extension fractures and dikes at 40 sites, mostly NNE-SSW to NNW-SSE oriented with a dominant NS orientation. These structures are governed quasi exclusively by pure dip-slip motion, consistent with an E-W extension direction, with minor dextral and sinistral slip, the latter being mostly related to old deposits (>50 ka). We further reconstructed the evolution of the Vulcano-Lipari system during the last ~20 ka and find that it consists of an overall half-graben-like structure, with faults with predominant eastward dips. Field evidence suggests that faulting occurs often in temporal and spatial relation with magmatic events, suggesting that most of the observable deformation derived from transient magmatic activity, rather than from steady regional tectonics. To explain the dominant magmatic and episodic extension in a tectonic dominant domain, we propose a model where the regional N-S trending maximum horizontal stress, responsible for strike-slip activity, locally rotates to vertical in response to transient pressurization of the magmatic system and magma rise below Lipari and Vulcano. This has possibly generated the propagation of N-S trending dikes in the past 1 ka along a 10 km long by 1 km wide crustal corridor, with important

  16. Off-axis magmatism along a subaerial back-arc rift: Observations from the Taupo Volcanic Zone, New Zealand.

    Science.gov (United States)

    Hamling, Ian J; Hreinsdóttir, Sigrun; Bannister, Stephen; Palmer, Neville

    2016-06-01

    Continental rifting and seafloor spreading play a fundamental role in the generation of new crust. However, the distribution of magma and its relationship with tectonics and volcanism remain poorly understood, particularly in back-arc settings. We show evidence for a large, long-lived, off-axis magmatic intrusion located on the margin of the Taupo Volcanic Zone, New Zealand. Geodetic data acquired since the 1950s show evidence for uplift outside of the region of active extension, consistent with the inflation of a magmatic body at a depth of ~9.5 km. Satellite radar interferometry and Global Positioning System data suggest that there was an increase in the inflation rate from 2003 to 2011, which correlates with intense earthquake activity in the region. Our results suggest that the continued growth of a large magmatic body may represent the birth of a new magma chamber on the margins of a back-arc rift system.

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

    Science.gov (United States)

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

    2014-08-01

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

  18. Investigations of the geochemical controls on anomalous arsenic enrichment in the Santiago Peak Volcanics of Southern California: implications for arsenic distribution in volcanic arc systems

    Science.gov (United States)

    Johnston, E. C.; Pollock, M.; Cathcart, E. M.; AlBashaireh, A.; O'shea, B. M.

    2016-12-01

    The Santiago Peak Volcanics (SPV) of Southern CA and Northern Baja CA, Mexico are remnants of a Cretaceous subaerial volcanic arc system that underwent greenschist facies metamorphism contemporaneous with volcanism. Observed SPV exposed at the surface of Black Mountain Open Space Park (San Diego, CA) exhibit anomalous arsenic (As) enrichment (100 - 480,000 ppm) up to five orders of magnitude greater than average for igneous rocks (1.5 ppm). We hypothesize that these rocks underwent localized syn-volcanic hydrothermal alteration along a highly fractured zone that today trends between N10°W and N20°W, leading to anomalous As enrichment on the spatial scale of tens of meters. We suspect that such As has been further mobilized by modern water-rock interactions. Using standard geochemical techniques (e.g. XRD, XRF, EDX) and mass balance analyses, we aim to (1) summarize the extent of As enrichment in altered SPV, and (2) present an integrated view of the interactions between ancient hydrothermal volcanic arc processes, surficial weathering, and observed As anomalies. Alteration textures of samples range from partially altered phenocrysts (i.e. minimally altered) to massive hydrothermal replacement, in which virtually all primary phases are altered to new hydrothermal minerals such as epidote, Fe-rich chlorite, and sericite (i.e. highly altered). Highly altered rocks contain average As concentrations (mean = 37,680 +/- 15,396 ppm, n = 23) >10,000 times that of minimally altered SPV (mean = 26 +/- 6 ppm As, n = 19). In some rocks, As-rich iron oxide and gypsum containing up to 900 ppm As are present as surficial rinds, suggesting modern day remobilization of As from hydrothermal host minerals, like arsenopyrite. These findings indicate that such As is highly soluble and, therefore, may be further mobilized by physical and chemical weathering. No other trace metals (e.g. Pb, Cu, Ag, Au) are consistently enriched above upper-crustal averages, and As does not always occur

  19. Stratigraphic and geochemical evolution of an oceanic arc upper crustal section: The Jurassic Talkeetna Volcanic Formation, south-central Alaska

    Science.gov (United States)

    Clift, P.D.; Draut, A.E.; Kelemen, P.B.; Blusztajn, J.; Greene, A.

    2005-01-01

    The Early Jurassic Talkeetna Volcanic Formation forms the upper stratigraphic level of an oceanic volcanic arc complex within the Peninsular Terrane of south-central Alaska. The section comprises a series of lavas, tuffs, and volcaniclastic debris-How and flow turbidite deposits, showing significant lateral facies variability. There is a general trend toward more volcaniclastic sediment at the top of the section and more lavas and tuff breccias toward the base. Evidence for dominant submarine, mostly mid-bathyal or deeper (>500 m) emplacement is seen throughout the section, which totals ???7 km in thickness, similar to modern western Pacific arcs, and far more than any other known exposed section. Subaerial sedimentation was rare but occurred over short intervals in the middle of the section. The Talkeetna Volcanic Formation is dominantly calc-alkatine and shows no clear trend to increasing SiO2 up-section. An oceanic subduction petrogenesis is shown by trace element and Nd isotope data. Rocks at the base of the section show no relative enrichment of light rare earth elements (LREEs) versus heavy rare earth elements (REES) or in melt-incompatible versus compatible high field strength elements (HFSEs). Relative enrichment of LREEs and HFSEs increases slightly up-section. The Talkeetna Volcanic Formation is typically more REE depleted than average continental crust, although small volumes of light REE-enriched and heavy REE-depleted mafic lavas are recognized low in the stratigraphy. The Talkeetna Volcanic Formation was formed in an intraoceanic arc above a north-dipping subduction zone and contains no preserved record of its subsequent collisions with Wrangellia or North America. ?? 2005 Geological Society of America.

  20. Zircon U-Pb Age Determination of Volcanic Eruptions in Lutao and Lanyu in the Northern Luzon Magmatic Arc

    Directory of Open Access Journals (Sweden)

    Wen-Yu Shao

    2014-01-01

    Full Text Available This paper reports for the first time zircon U-Pb ages of volcanic rocks and sands from Lutao and Lanyu, two islets off SE Taiwan in the north Luzon arc. The samples include (1 seven andesites from four volcanic units and three river/beach sands from Lutao and (2 five basaltic andesites from four volcanic units and two river/beach sands from Lanyu. The Lutao andesites contain abundant magmatic zircons, aging from ~1.54 to ~1.24 Ma for individual sample, which yielded an overall mean 206Pb/238U age of 1.31 ±± 0.03 Ma (n = 190, MSWD = 2.6. This is slightly older than, or broadly coincident with, a mean 206Pb/238U age of 1.23 ±± 0.03 Ma (n = 103, MSWD = 1.9 given by detrital zircons from the three sands. The Lanyu volcanics appear to have less abundant magmatic zircons, aging from ~2.72 to ~2.35 Ma for individual sample, which yielded an overall mean 206Pb/238U age of 2.61 ±± 0.13 Ma (n = 11, MSWD = 1.8. This accords with a mean 206Pb/238U age of 2.69 ±± 0.11 Ma (n = 34, MSWD = 4.7 obtained by detrital zircons from the two sands. The age data suggest that in Lutao and Lanyu the major volcanic eruptions occurred at ~1.3 and ~2.6 Ma, respectively. Moreover, volcanic samples from both islets contain various amounts of older inherited zircons, ~11% in Lutao and up to ~82% in Lanyu, which together with detrital zircons from the sands show main age peaks at ~150 Ma and ~1.9 and ~2.5 Ga, consistent with the notion for a _ continental crust involved in the genesis of the northern Luzon magmatic arc.

  1. Age and duration of intra-oceanic arc volcanism built on a suprasubduction zone type oceanic crust in southern Neotethys, SE Anatolia

    Directory of Open Access Journals (Sweden)

    Fatih Karaoğlan

    2013-07-01

    Full Text Available The southeastern Anatolia comprises numbers of tectono-magmatic/stratigraphic units such as the metamorphic massifs, the ophiolites, the volcanic arc units and the granitoid rocks. All of them play important role for the late Cretaceous evolution of the southern Neotethys. The spatial and temporal relations of these units suggest the progressive development of coeval magmatism and thrusting during the late Cretaceous northward subduction/accretion. Our new U-Pb zircon data from the rhyolitic rocks of the wide-spread volcanic arc unit show ages of (83.1 ± 2.2–(74.6 ± 4.4 Ma. Comparison of the ophiolites, the volcanic arc units and the granitoids suggest following late Cretaceous geological evolution. The ophiolites formed in a suprasubduction zone (SSZ setting as a result of northward intra-oceanic subduction. A wide-spread island-arc tholeiitic volcanic unit developed on the top of the SSZ-type crust during 83–75 Ma. Related to regional plate convergence, northward under-thrusting of SSZ-type ophiolites and volcanic arc units was initiated beneath the Tauride platform (Malatya-Keban and followed by the intrusion of I-type calc-alkaline volcanic arc granitoids during 84–82 Ma. New U-Pb ages from the arc-related volcanic-sedimentary unit and granitoids indicate that under-thrusting of ophiolites together with the arc-related units beneath the Malatya-Keban platform took place soon after the initiation of the volcanic arc on the top of the SSZ-type crust. Then the arc-related volcanic-sedimentary unit continued its development and lasted at ∼75 Ma until the deposition of the late Campanian–Maastrichtian shallow marine limestone. The subduction trench eventually collided with the Bitlis-Pütürge massif giving rise to HP-LT metamorphism of the Bitlis massif. Although the development of the volcanic arc units and the granitoids were coeval at the initial stage of the subduction/accretion both tectono-magmatic units were

  2. Geochemical variability of hydrothermal emissions between three Pacific volcanic arc systems: Alaskan-Aleutian and Cascadian, North America and Taupo Volcanic Zone, New Zealand

    Science.gov (United States)

    Blackstock, J. M.; Horton, T. W.; Gravley, D. M.; Deering, C. D.

    2013-12-01

    Knowledge of the source, transport, and fate of hydrothermal fluids in the upper crust informs our understanding and interpretation of ore-forming processes, volcanogenic hazards, geothermal resources, and volatile cycling. Co-variation between fluid inclusion CO2/CH4 and N2/Ar ratios is an established tracer of magmatic, meteoric, and crustal fluid end-members. Yet, this tracer has had limited application to macroscopic fluid reservoirs accessible via geothermal wells and hydrothermal features (e.g. pools). In this study, we compared the covariance CO2/CH4 and N2/Ar ratios of gases collected throughout the Taupo Volcanic Zone, New Zealand (TVZ), the Alaska-Aleutian Volcanic Arc, USA (AAVA), and the Cascadian Volcanic Arc, USA (CVA) with corresponding δ13C and 3He/4He values. Our findings show that there is good agreement between these proxies for different end-member contributions at coarse scales. However, some samples classified as meteoric water according to the CO2/CH4 and N2/Ar ratios also show more positive δ13C values (~ -7.0 per mil) and relatively higher 3He/4He ratios indicative of magmatic input from primarily mantle sources. This unexpected result may be related to magmatic fluids, CO2 in particular, mixing with predominantly meteoric derived waters. The potential to identify magmatic CO2 in groundwater samples overlying geothermal systems in differing volcanic arc settings using simple and cost-effective gas ratios is a promising step forward in the search for ';surface blind' but developable geothermal systems and volcanic monitoring. 3He/4He anomalies also support this inference and underscore the potential decoupling of thermal anomalies and magmatic-derived fluids in the Earth's crust. The general agreement between the co-variation of CO2/CH4 and N2/Ar ratios with other isotope and geochemical proxies for magmatic, meteoric, and crustal end-members is encouraging to employ expanded use of these ratios for both the exploration and monitoring of

  3. The role of crystallization-driven exsolution on the sulfur mass balance in volcanic arc magmas

    Science.gov (United States)

    Su, Y.; Huber, Christian; Bachmann, Olivier; Zajacz, Zoltán.; Wright, Heather; Vazquez, Jorge

    2016-08-01

    The release of large amounts of sulfur to the stratosphere during explosive eruptions affects the radiative balance in the atmosphere and consequentially impacts climate for up to several years after the event. Quantitative estimations of the processes that control the mass balance of sulfur between melt, crystals, and vapor bubbles is needed to better understand the potential sulfur yield of individual eruption events and the conditions that favor large sulfur outputs to the atmosphere. The processes that control sulfur partitioning in magmas are (1) exsolution of volatiles (dominantly H2O) during decompression (first boiling) and during isobaric crystallization (second boiling), (2) the crystallization and breakdown of sulfide or sulfate phases in the magma, and (3) the transport of sulfur-rich vapor (gas influx) from deeper unerupted regions of the magma reservoir. Vapor exsolution and the formation/breakdown of sulfur-rich phases can all be considered as closed-system processes where mass balance arguments are generally easier to constrain, whereas the contribution of sulfur by vapor transport (open system process) is more difficult to quantify. The ubiquitous "excess sulfur" problem, which refers to the much higher sulfur mass released during eruptions than what can be accounted for by amount of sulfur originally dissolved in erupted melt, as estimated from melt inclusion sulfur concentrations (the "petrologic estimate"), reflects the challenges in closing the sulfur mass balance between crystals, melt, and vapor before and during a volcanic eruption. In this work, we try to quantify the relative importance of closed- and open-system processes for silicic arc volcanoes using kinetic models of sulfur partitioning during exsolution. Our calculations show that crystallization-induced exsolution (second boiling) can generate a significant fraction of the excess sulfur observed in crystal-rich arc magmas. This result does not negate the important role of vapor

  4. The role of crystallization-driven exsolution on the sulfur mass balance in volcanic arc magmas

    Science.gov (United States)

    Su, Yanqing; Huber, Christian; Bachmann, Olivier; Zajacz, Zoltán; Wright, Heather M.; Vazquez, Jorge A.

    2016-01-01

    The release of large amounts of sulfur to the stratosphere during explosive eruptions affects the radiative balance in the atmosphere and consequentially impacts climate for up to several years after the event. Quantitative estimations of the processes that control the mass balance of sulfur between melt, crystals, and vapor bubbles is needed to better understand the potential sulfur yield of individual eruption events and the conditions that favor large sulfur outputs to the atmosphere. The processes that control sulfur partitioning in magmas are (1) exsolution of volatiles (dominantly H2O) during decompression (first boiling) and during isobaric crystallization (second boiling), (2) the crystallization and breakdown of sulfide or sulfate phases in the magma, and (3) the transport of sulfur-rich vapor (gas influx) from deeper unerupted regions of the magma reservoir. Vapor exsolution and the formation/breakdown of sulfur-rich phases can all be considered as closed-system processes where mass balance arguments are generally easier to constrain, whereas the contribution of sulfur by vapor transport (open system process) is more difficult to quantify. The ubiquitous “excess sulfur” problem, which refers to the much higher sulfur mass released during eruptions than what can be accounted for by amount of sulfur originally dissolved in erupted melt, as estimated from melt inclusion sulfur concentrations (the “petrologic estimate”), reflects the challenges in closing the sulfur mass balance between crystals, melt, and vapor before and during a volcanic eruption. In this work, we try to quantify the relative importance of closed- and open-system processes for silicic arc volcanoes using kinetic models of sulfur partitioning during exsolution. Our calculations show that crystallization-induced exsolution (second boiling) can generate a significant fraction of the excess sulfur observed in crystal-rich arc magmas. This result does not negate the important role of

  5. Late Cenozoic tephrostratigraphy offshore the southern Central American Volcanic Arc: 2. Implications for magma production rates and subduction erosion

    Science.gov (United States)

    Schindlbeck, J. C.; Kutterolf, S.; Freundt, A.; Straub, S. M.; Vannucchi, P.; Alvarado, G. E.

    2016-11-01

    Pacific drill sites offshore Central America provide the unique opportunity to study the evolution of large explosive volcanism and the geotectonic evolution of the continental margin back into the Neogene. The temporal distribution of tephra layers established by tephrochonostratigraphy in Part 1 indicates a nearly continuous highly explosive eruption record for the Costa Rican and the Nicaraguan volcanic arc within the last 8 Myr. The widely distributed marine tephra layers comprise the major fraction of the respective erupted tephra volumes and masses thus providing insights into regional and temporal variations of large-magnitude explosive eruptions along the southern Central American Volcanic Arc (CAVA). We observe three pulses of enhanced explosive volcanism between 0 and 1 Ma at the Cordillera Central, between 1 and 2 Ma at the Guanacaste and at >3 Ma at the Western Nicaragua segments. Averaged over the long-term the minimum erupted magma flux (per unit arc length) is ˜0.017 g/ms. Tephra ages, constrained by Ar-Ar dating and by correlation with dated terrestrial tephras, yield time-variable accumulation rates of the intercalated pelagic sediments with four prominent phases of peak sedimentation rates that relate to tectonic processes of subduction erosion. The peak rate at >2.3 Ma near Osa particularly relates to initial Cocos Ridge subduction which began at 2.91 ± 0.23 Ma as inferred by the 1.5 Myr delayed appearance of the OIB geochemical signal in tephras from Barva volcano at 1.42 Ma. Subsequent tectonic re-arrangements probably involved crustal extension on the Guanacaste segment that favored the 2-1 Ma period of unusually massive rhyolite production.

  6. Segmentation of the Cascade Arc Based on Compositional and Sr and Nd Isotopic Variations in Primitive Volcanic Rocks

    Science.gov (United States)

    Schmidt, M. E.; Grunder, A. L.

    2006-12-01

    We define four segments in the Cascade Volcanic Arc based on 87Sr/86Sr and 143Nd/144Nd of primitive volcanic rocks: 1) The North segment extends 450 km from Mt. Meager to Glacier Peak; 2) the 350-km Columbia segment includes volcanoes from Mt. Rainier to Mt. Jefferson; 3) the 250 km Central segment comprises the portion of the arc between the Three Sisters and Crater Lake; and 4) the 350-km South segment includes Mt. Shasta to Mt. Lassen. Isotopic data were compiled for primitive bulk composition (MgO concentrations >8 wt.% MgO) as a fingerprint mantle sources. The North segment has a range in 87Sr/86Sr of 0.7030-0.7037 and is distinguished by the predominance of calcalkaline basalts (CAB) and few low K tholeiites (LKT). The North segment lies on the North Cascade craton where convergence is near orthogonal. Oblique subduction occurs beneath the Columbia, Central, and South segments. The Columbia segment (87Sr/86Sr of 0.7028-0.7037) has both LKT and CABs as well as enriched ocean island-like basalts (OIB) that are found both on the arc axis and, especially at the Simcoe Volcanic Field, behind the arc. This segment lies primarily on the accreted Tertiary oceanic plateau terrane of the Columbia Embayment. The Central segment is dominated by LKT with lesser CAB and has the most restricted Sr isotopic range (0.7034- 0.7038). Like the South segment, the Central segment mainly overlies accreted terranes stitched by Mesozoic plutons and has Basin and Range (B&R) extension behind as well as locally within the arc. Medicine Lake Volcano, on the margin of the B&R behind Mt. Shasta is also dominated by LKT and has a narrow isotopic range like the Central segment. This suggests that the LKT's are related to extension in the arc. The South segment is distinguished by the widest Sr isotopic range (0.7028-0.7042) and the presence of high Mg basaltic andesite and andesite compositions in addition to LKT and CABs. These arc segments broadly correspond to physical segments that were

  7. Submarine record of volcanic island construction and collapse in the Lesser Antilles arc: First scientific drilling of submarine volcanic island landslides by IODP Expedition 340

    Science.gov (United States)

    Le Friant, A.; Ishizuka, O.; Boudon, G.; Palmer, M. R.; Talling, P. J.; Villemant, B.; Adachi, T.; Aljahdali, M.; Breitkreuz, C.; Brunet, M.; Caron, B.; Coussens, M.; Deplus, C.; Endo, D.; Feuillet, N.; Fraas, A. J.; Fujinawa, A.; Hart, M. B.; Hatfield, R. G.; Hornbach, M.; Jutzeler, M.; Kataoka, K. S.; Komorowski, J.-C.; Lebas, E.; Lafuerza, S.; Maeno, F.; Manga, M.; Martínez-Colón, M.; McCanta, M.; Morgan, S.; Saito, T.; Slagle, A.; Sparks, S.; Stinton, A.; Stroncik, N.; Subramanyam, K. S. V.; Tamura, Y.; Trofimovs, J.; Voight, B.; Wall-Palmer, D.; Wang, F.; Watt, S. F. L.

    2015-02-01

    IODP Expedition 340 successfully drilled a series of sites offshore Montserrat, Martinique and Dominica in the Lesser Antilles from March to April 2012. These are among the few drill sites gathered around volcanic islands, and the first scientific drilling of large and likely tsunamigenic volcanic island-arc landslide deposits. These cores provide evidence and tests of previous hypotheses for the composition and origin of those deposits. Sites U1394, U1399, and U1400 that penetrated landslide deposits recovered exclusively seafloor sediment, comprising mainly turbidites and hemipelagic deposits, and lacked debris avalanche deposits. This supports the concepts that i/ volcanic debris avalanches tend to stop at the slope break, and ii/ widespread and voluminous failures of preexisting low-gradient seafloor sediment can be triggered by initial emplacement of material from the volcano. Offshore Martinique (U1399 and 1400), the landslide deposits comprised blocks of parallel strata that were tilted or microfaulted, sometimes separated by intervals of homogenized sediment (intense shearing), while Site U1394 offshore Montserrat penetrated a flat-lying block of intact strata. The most likely mechanism for generating these large-scale seafloor sediment failures appears to be propagation of a decollement from proximal areas loaded and incised by a volcanic debris avalanche. These results have implications for the magnitude of tsunami generation. Under some conditions, volcanic island landslide deposits composed of mainly seafloor sediment will tend to form smaller magnitude tsunamis than equivalent volumes of subaerial block-rich mass flows rapidly entering water. Expedition 340 also successfully drilled sites to access the undisturbed record of eruption fallout layers intercalated with marine sediment which provide an outstanding high-resolution data set to analyze eruption and landslides cycles, improve understanding of magmatic evolution as well as offshore sedimentation

  8. A new view into the Cascadia subduction zone and volcanic arc: Implications for earthquake hazards along the Washington margin

    Science.gov (United States)

    Parsons, T.; Trehu, A.M.; Luetgert, J.H.; Miller, K.; Kilbride, F.; Wells, R.E.; Fisher, M.A.; Flueh, E.; ten Brink, U.S.; Christensen, N.I.

    1998-01-01

    In light of suggestions that the Cascadia subduction margin may pose a significant seismic hazard for the highly populated Pacific Northwest region of the United States, the U.S. Geological Survey (USGS), the Research Center for Marine Geosciences (GEOMAR), and university collaborators collected and interpreted a 530-km-long wide-angle onshore-offshore seismic transect across the subduction zone and volcanic arc to study the major structures that contribute to seismogenic deformation. We observed (1) an increase in the dip of the Juan de Fuca slab from 2??-7?? to 12?? where it encounters a 20-km-thick block of the Siletz terrane or other accreted oceanic crust, (2) a distinct transition from Siletz crust into Cascade arc crust that coincides with the Mount St. Helens seismic zone, supporting the idea that the mafic Siletz block focuses seismic deformation at its edges, and (3) a crustal root (35-45 km deep) beneath the Cascade Range, with thinner crust (30-35 km) east of the volcanic arc beneath the Columbia Plateau flood basalt province. From the measured crustal structure and subduction geometry, we identify two zones that may concentrate future seismic activity: (1) a broad (because of the shallow dip), possibly locked part of the interplate contact that extends from ???25 km depth beneath the coastline to perhaps as far west as the deformation front ???120 km offshore and (2) a crustal zone at the eastern boundary between the Siletz terrane and the Cascade Range.

  9. Evolving volcanism at the tip of a propagating arc: The earliest high-Mg andesites in northern New Zealand

    Science.gov (United States)

    Booden, Mathijs A.; Smith, Ian E. M.; Mauk, Jeffrey L.; Black, Philippa M.

    2010-08-01

    A NNW-striking string of isolated volcanic centers, the Kiwitahi chain, erupted between 15 and 5.5 Ma in northern New Zealand. Prior to 6.2 Ma, the erupted rocks were plagioclase- and hornblende-dominated andesites, which are geochemically comparable to coeval andesites erupted in the nearby, much larger Coromandel Volcanic Zone (CVZ). Compared to CVZ andesites, however, the Kiwitahi andesites show more subdued incompatible element enrichments, and they generally have relatively unradiogenic Sr isotope compositions. These features, and the small eruption volumes involved, suggest that the Kiwitahi centers formed over the edge of a magmatic system that was centered on the CVZ. The Kiwitahi centers progressively become younger towards the SSE representing the migration over the time of the edge of this magmatic system. Between 6.2 and 5.5 Ma, four centers at the southern end of the chain erupted pyroxene-dominated, high-magnesium andesites that are geochemically unlike coeval andesites in the CVZ, but similar to Quaternary high-Mg andesites erupted along the western edge of the Taupo Volcanic Zone. These are the earliest known high-Mg andesites in northern New Zealand; their appearance may mark the inception of the current configuration where high-Mg andesite eruptions precede regular andesitic volcanism at the leading edge of the arc.

  10. Intraplate volcanism controlled by back-arc and continental structures in NE Asia inferred from transdimensional Bayesian ambient noise tomography

    Science.gov (United States)

    Kim, Seongryong; Tkalčić, Hrvoje; Rhie, Junkee; Chen, Youlin

    2016-08-01

    Intraplate volcanism adjacent to active continental margins is not simply explained by plate tectonics or plume interaction. Recent volcanoes in northeast (NE) Asia, including NE China and the Korean Peninsula, are characterized by heterogeneous tectonic structures and geochemical compositions. Here we apply a transdimensional Bayesian tomography to estimate high-resolution images of group and phase velocity variations (with periods between 8 and 70 s). The method provides robust estimations of velocity maps, and the reliability of results is tested through carefully designed synthetic recovery experiments. Our maps reveal two sublithospheric low-velocity anomalies that connect back-arc regions (in Japan and Ryukyu Trench) with current margins of continental lithosphere where the volcanoes are distributed. Combined with evidences from previous geochemical and geophysical studies, we argue that the volcanoes are related to the low-velocity structures associated with back-arc processes and preexisting continental lithosphere.

  11. 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

  12. Bromine release during Plinian eruptions along the Central American Volcanic Arc

    Science.gov (United States)

    Hansteen, T. H.; Kutterolf, S.; Appel, K.; Freundt, A.; Perez-Fernandez, W.; Wehrmann, H.

    2010-12-01

    Volcanoes of the Central American Volcanic Arc (CAVA) have produced at least 72 highly explosive eruptions within the last 200 ka. The eruption columns of all these “Plinian” eruptions reached well into the stratosphere such that their released volatiles may have influenced atmospheric chemistry and climate. While previous research has focussed on the sulfur and chlorine emissions during such large eruptions, we here present measurements of the heavy halogen bromine by means of synchrotron radiation induced micro-XRF microanalysis (SR-XRF) with typical detection limits at 0.3 ppm (in Fe rich standard basalt ML3B glass). Spot analyses of pre-eruptive glass inclusions trapped in minerals formed in magma reservoirs were compared with those in matrix glasses of the tephras, which represent the post-eruptive, degassed concentrations. The concentration difference between inclusions and matrix glasses, multiplied by erupted magma mass determined by extensive field mapping, yields estimates of the degassed mass of bromine. Br is probably hundreds of times more effective in destroying ozone than Cl, and can accumulate in the stratosphere over significant time scales. Melt inclusions representing deposits of 22 large eruptions along the CAVA have Br contents between 0.5 and 13 ppm. Br concentrations in matrix glasses are nearly constant at 0.4 to 1.5 ppm. However, Br concentrations and Cl/Br ratios vary along the CAVA. The highest values of Br contents (>8 ppm) and lowest Cl/Br ratios (170 to 600) in melt inclusions occur across central Nicaragua and southern El Salvador, and correlate with bulk-rock compositions of high Ba/La > 85 as well as low La/Yb discharged 700 kilotons of Br. On average, each of the remaining 21 CAVA eruptions studied have discharged c.100 kilotons of bromine. During the past 200 ka, CAVA volcanoes have emitted a cumulative mass of 3.2 Mt of Br through highly explosive eruptions. There are six periods in the past (c. 2ka, 6ka, 25ka, 40ka, 60ka, 75

  13. The Dras arc Complex: lithofacies and reconstruction of a Late Cretaceous oceanic volcanic arc in the Indus Suture Zone, Ladakh Himalaya

    Science.gov (United States)

    Robertson, Alastair; Degnan, Paul

    1994-08-01

    The purpose of this paper is to give an integrated description and interpretation of mainly volcaniclastic sediments related to excellently exposed oceanic volcanic arc successions in the Ladakh Himalayas. The mainly Late Cretaceous (Aptian—Paleocene?) Dras arc Complex in the Indus Suture Zone (N. India) is reconstructed as an oceanic arc, passing southwards into a proximal to distal forearc apron. The arc complex comprises three structural units. From west to east these are the Suru unit, the Naktul unit and the Nindam Formation. The Suru unit and the Naktul unit are unconformably underlain by dissected Late Jurassic? oceanic crust and mantle. The Suru unit preserves the interior of the arc and is divided into Dras 1 and Dras 2 sub-units. The Dras 1 Sub-unit, of mid-Late Cretaceous age, was intruded by arc plutonics, deformed, then unconformably overlain by the poorly dated Dras 2 Sub-unit (Lower Tertiary). The Dras 1 Sub-unit comprises arc extrusives, volcaniclastic and tuffaceous sedimentary rocks, and mainly redeposited shallow-water limestones. The Dras 2 Sub-unit is dominated by coarse volcaniclastics and lava flows, passing up into rhythmically layered acidic extrusives, with interbedded turbiditic siltstones and siliceous pelagic limestones. Further east, the Naktul unit is mainly clastic, with large volumes of massive volcaniclastic talus, thick-bedded debris flows, volcaniclastic turbidites and reworked shallow-water carbonates. Pillowed extrusives and ribbon radiolarites are present, mainly low in the succession in some areas, while pelagic carbonates are abundant near the top. The Naktul unit is interpreted as a proximal forearc apron. The Nindam Formation in the east is dominated by deep-water volcaniclastic turbidites, tuffaceous sediments and pelagic carbonates, with subordinate debris flows and is interpreted as a distal deep-water forearc succession. Cyclical alternations of mainly volcaniclastics and pelagic carbonates in the Nindam Formation

  14. A study on the geochemical characteristics of Upper Permian continental marginal arc volcanic rocks in the northern segment of South Lancangjiang Belt

    Institute of Scientific and Technical Information of China (English)

    SHEN Shangyue; FENG Qinglai; WEI Qirong; ZHANG Zhibin; ZHANG Hu

    2006-01-01

    Geochemical characteristics of the Upper Permian ( P2 ) continental marginal arc volcanic rocks are described, which have been found recently around the areas of Xiaodingxi and Zangli on the eastern side of the Yunxian-Lincang granite, in terms of rock assemblage, petrochemistry, REE, trace elements, Pb isotopes, geotectonic environment and so on. The volcanic rock assemblage is dominated by basalt-andesite-dacite, with minor trachyte andecite-trachyte; the volcanic rock series is predominated by the calc-alkaline series, with minor tholleiite series and alkaline series rocks; the volcanic rocks are characterized by high Al2O3 and low TiO2 , with K2O contents showing extremely strong polarity; the REE distribution patterns are characterized by LREE enrichment and right-inclined type; trace elements and large cation elements are highly enriched, Ti and Cr are depleted, and P and Nb are partially depleted; the Pb composition is of the Gondwana type; the petrochemical points mostly fall within the field of island-arc volcanic rocks, in consistency with the projection of data points of continental marginal volcanic rocks in the southern segment of the South Lancangjiang Belt and the North Lancangjiang Belt. This continental marginal arc volcanic rock belt, together with the ocean-ridge and ocean-island volcanic rocks and ophiolites in the Changning-Menglian Belt, constitute the ocean-ridge volcanic rock, ophiolite-arc rock-magmatic rock belts which are distributed in pairs, indicating that the Lancangjiang oceanic crust subducted eastwards. This result is of great importance in constraining the evolution of the paleo-Tethys in the Lancangjiang Belt.

  15. Geothermal Potential of the Cascade and Aleutian Arcs, with Ranking of Individual Volcanic Centers for their Potential to Host Electricity-Grade Reservoirs

    Energy Technology Data Exchange (ETDEWEB)

    Shevenell, Lisa [ATLAS Geosciences, Inc., Reno, NV (United States); Coolbaugh, Mark [ATLAS Geosciences, Inc., Reno, NV (United States); Hinz, Nick [Univ. of Nevada, Reno, NV (United States); Stelling, Pete [Western Washington Univ., Bellingham, WA (United States); Melosh, Glenn [GEODE, Santa Rosa, CA (United States); Cumming, William [Cumming Geoscience, Santa Rosa, CA (United States)

    2015-10-16

    This project brings a global perspective to volcanic arc geothermal play fairway analysis by developing statistics for the occurrence of geothermal reservoirs and their geoscience context worldwide in order to rank U.S. prospects. The focus of the work was to develop play fairways for the Cascade and Aleutian arcs to rank the individual volcanic centers in these arcs by their potential to host electricity grade geothermal systems. The Fairway models were developed by describing key geologic factors expected to be indicative of productive geothermal systems in a global training set, which includes 74 volcanic centers world-wide with current power production. To our knowledge, this is the most robust geothermal benchmark training set for magmatic systems to date that will be made public.

  16. The temporal evolution of back-arc magmas from the Auca Mahuida shield volcano (Payenia Volcanic Province, Argentina)

    Science.gov (United States)

    Pallares, Carlos; Quidelleur, Xavier; Gillot, Pierre-Yves; Kluska, Jean-Michel; Tchilinguirian, Paul; Sarda, Philippe

    2016-09-01

    In order to better constrain the temporal volcanic activity of the back-arc context in Payenia Volcanic Province (PVP, Argentina), we present new K-Ar dating, petrographic data, major and trace elements from 23 samples collected on the Auca Mahuida shield volcano. Our new data, coupled with published data, show that this volcano was built from about 1.8 to 1.0 Ma during five volcanic phases, and that Auca Mahuida magmas were extracted from, at least, two slightly different OIB-type mantle sources with a low partial melting rate. The first one, containing more garnet, was located deeper in the mantle, while the second contains more spinel and was thus shallower. The high-MgO basalts (or primitive basalts) and the low-MgO basalts (or evolved basalts), produced from the deeper and shallower lherzolite mantle sources, respectively, are found within each volcanic phase, suggesting that both magmatic reservoirs were sampled during the 1 Myr lifetime of the Auca Mahuida volcano. However, a slight increase of the proportion of low-MgO basalts, as well as of magmas sampled from the shallowest source, can be observed through time. Similar overall petrological characteristics found in the Pleistocene-Holocene basaltic rocks from Los Volcanes and Auca Mahuida volcano suggest that they originated from the same magmatic source. Consequently, it can be proposed that the thermal asthenospheric anomaly is probably still present beneath the PVP. Finally, our data further support the hypothesis that the injection of hot asthenosphere with an OIB mantle source signature, which was triggered by the steepening of the Nazca subducting plate, induced the production of a large volume of lavas within the PVP since 2 Ma.

  17. Stratigraphy, petrology, and geochemistry of the Spurr Volcanic Complex, eastern Aleutian Arc, Alaska. [(Appendix for geothermal fluid chemistry)

    Energy Technology Data Exchange (ETDEWEB)

    Nye, C.J.

    1987-12-01

    The Spurr Volcanic Complex (SVC) is a calcalkaline, medium-K, sequence of andesites erupted over the last quarter of a million years by the easternmost currently active volcanic center in the Aleutian Arc. The ancestral Mt. Spurr was built mostly of andesites of uniform composition (58 to 60% SiO/sub 2/), although andesite production was episodically interrupted by the introduction of new batches of more mafic magma. Near the end of the Pleistocene the ancestral Mt. Spurr underwent Bezyianny-type avalanche caldera formation, resulting in the production of a volcanic debris avalanche with overlying ashflows. Immediately afterward, a large dome (the present Mt. Spurr) was emplaced in the caldera. Both the ashflows and dome are made of acid andesite more silicic than any analyzed lavas from the ancestral Mt. Spurr (60 to 63% SiO/sub 2/), yet contain olivine and amphibole xenocrysts derived from more mafic magma. The mafic magma (53 to 57% SiO/sub 2/) erupted during and after dome emplacement, forming proto-Crater Peak and Crater Peak. Hybrid pyroclastic flows and lavas were also produced. Proto-Crater Peak underwent glacial dissection prior to the formation of Crater Peak in approximately the same location. Appendices II through VIII contain a summary of mineral compositions; Appendix I contains geochemical data. Appendix IX by R.J. Motyka and C.J. Nye describes the chemistry of geothermal fluids. 78 refs., 16 figs., 3 tabs.

  18. Evidence for voluminous bimodal pyroclastic volcanism during rifting of a Paleoproterozoic arc at Snow Lake, Manitoba

    National Research Council Canada - National Science Library

    Lafrance, Bruno; Rubingh, Kate E; Gibson, Harold L

    2017-01-01

    ...) assemblage of the Flin Flon belt. Stratigraphic correlation of volcanic strata of the MB sequence with strata of the thrust-bounded Chisel sequence indicates that distinctive, submarine, eruption-fed, pyroclastic flow deposits...

  19. The 10 April 2014 Nicaraguan Crustal Earthquake: Evidence of Complex Deformation of the Central American Volcanic Arc

    Science.gov (United States)

    Suárez, Gerardo; Muñoz, Angélica; Farraz, Isaac A.; Talavera, Emilio; Tenorio, Virginia; Novelo-Casanova, David A.; Sánchez, Antonio

    2016-10-01

    On 10 April 2014, an M w 6.1 earthquake struck central Nicaragua. The main event and the aftershocks were clearly recorded by the Nicaraguan national seismic network and other regional seismic stations. These crustal earthquakes were strongly felt in central Nicaragua but caused relatively little damage. This is in sharp contrast to the destructive effects of the 1972 earthquake in the capital city of Managua. The differences in damage stem from the fact that the 1972 earthquake occurred on a fault beneath the city; in contrast, the 2014 event lies offshore, under Lake Managua. The distribution of aftershocks of the 2014 event shows two clusters of seismic activity. In the northwestern part of Lake Managua, an alignment of aftershocks suggests a northwest to southeast striking fault, parallel to the volcanic arc. The source mechanism agrees with this right-lateral, strike-slip motion on a plane with the same orientation as the aftershock sequence. For an earthquake of this magnitude, seismic scaling relations between fault length and magnitude predict a sub-surface fault length of approximately 16 km. This length is in good agreement with the extent of the fault defined by the aftershock sequence. A second cluster of aftershocks beneath Apoyeque volcano occurred simultaneously, but spatially separated from the first. There is no clear alignment of the epicenters in this cluster. Nevertheless, the decay of the number of earthquakes beneath Apoyeque as a function of time shows the typical behavior of an aftershock sequence and not of a volcanic swarm. The northeast-southwest striking Tiscapa/Ciudad Jardín and Estadio faults that broke during the 1972 and 1931 Managua earthquakes are orthogonal to the fault where the 10 April earthquake occurred. These orthogonal faults in close geographic proximity show that Central Nicaragua is being deformed in a complex tectonic setting. The Nicaraguan forearc sliver, between the trench and the volcanic arc, moves to the

  20. The 10 April 2014 Nicaraguan Crustal Earthquake: Evidence of Complex Deformation of the Central American Volcanic Arc

    Science.gov (United States)

    Suárez, Gerardo; Muñoz, Angélica; Farraz, Isaac A.; Talavera, Emilio; Tenorio, Virginia; Novelo-Casanova, David A.; Sánchez, Antonio

    2015-11-01

    On 10 April 2014, an M w 6.1 earthquake struck central Nicaragua. The main event and the aftershocks were clearly recorded by the Nicaraguan national seismic network and other regional seismic stations. These crustal earthquakes were strongly felt in central Nicaragua but caused relatively little damage. This is in sharp contrast to the destructive effects of the 1972 earthquake in the capital city of Managua. The differences in damage stem from the fact that the 1972 earthquake occurred on a fault beneath the city; in contrast, the 2014 event lies offshore, under Lake Managua. The distribution of aftershocks of the 2014 event shows two clusters of seismic activity. In the northwestern part of Lake Managua, an alignment of aftershocks suggests a northwest to southeast striking fault, parallel to the volcanic arc. The source mechanism agrees with this right-lateral, strike-slip motion on a plane with the same orientation as the aftershock sequence. For an earthquake of this magnitude, seismic scaling relations between fault length and magnitude predict a sub-surface fault length of approximately 16 km. This length is in good agreement with the extent of the fault defined by the aftershock sequence. A second cluster of aftershocks beneath Apoyeque volcano occurred simultaneously, but spatially separated from the first. There is no clear alignment of the epicenters in this cluster. Nevertheless, the decay of the number of earthquakes beneath Apoyeque as a function of time shows the typical behavior of an aftershock sequence and not of a volcanic swarm. The northeast-southwest striking Tiscapa/Ciudad Jardín and Estadio faults that broke during the 1972 and 1931 Managua earthquakes are orthogonal to the fault where the 10 April earthquake occurred. These orthogonal faults in close geographic proximity show that Central Nicaragua is being deformed in a complex tectonic setting. The Nicaraguan forearc sliver, between the trench and the volcanic arc, moves to the

  1. Newly developed evidence for the original Tethysan island-arc volcanic rocks in the southern segment of the South Lancangjiang Belt

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    This paper re-describes the characteristics of pre-Ordovician (Pt3) metamorphic volcanic rocks in the Huimin-Manlai region of Yunnan Province from the aspects of petrographic characteristics, rock assemblage, petrochemistry, REE, trace elements, lead isotopes and geotectonic setting. The metamorphic volcanic rocks maintain blasto-intergranular and blasto-andesitic textures; the volcanic rocks are characterized by a basalt-andesite-dacite assemblage; the volcanic rocks are basic-intermediate-intermediate-acid in chemical composition, belonging to semi-alkaline rocks, with calc-alkaline series and tholeiite series coexisting, and they are characterized by low TiO2 contents; their REE distribution patterns are of the LREE-enrichment right-inclined type; the volcanic rocks are enriched in large cation elements and commonly enriched in Th and partly depleted in Ti, Cr and P, belonging to the Gondwana type as viewed from their Pb isotopic composition; petrochemically the data points fall mostly within the field of island-arc volcanic rocks. All these characteristics provided new evidence for the existence of original Tethysan island-arc volcanic rocks in the region studied.

  2. Late-Pleistocene to precolumbian behind-the-arc mafic volcanism in the eastern Mexican Volcanic Belt; implications for future hazards

    Science.gov (United States)

    Siebert, Lee; Carrasco-Núñez, Gerardo

    2002-06-01

    An area of widespread alkaline-to-subalkaline volcanism lies at the northern end of the Cofre de Perote-Citlaltépetl (Pico de Orizaba) volcanic chain in the eastern Mexican Volcanic Belt (MVB). Two principal areas were active. About a dozen latest-Pleistocene to precolumbian vents form the 11-km-wide, E-W-trending Cofre de Perote vent cluster (CPVC) at 2300-2800 m elevation on the flank of the largely Pleistocene Cofre de Perote shield volcano and produced an extensive lava field that covers >100 km 2. More widely dispersed vents form the Naolinco volcanic field (NVF) in the Sierra de Chiconquiaco north of the city of Jalapa (Xalapa). Three generations of flows are delineated by cone and lava-flow morphology, degree of vegetation and cultivation, and radiocarbon dating. The flows lie in the behind-the-arc portion of the northeastern part of the MVB and show major- and trace-element chemical patterns transitional between intraplate and subduction zone environments. Flows of the oldest group originated from La Joya cinder cone (radiocarbon ages ˜42 000 yr BP) at the eastern end of the CPVC. This cone fed an olivine-basaltic flow field of ˜20 km 2 that extends about 14 km southeast to underlie the heavily populated northern outskirts of Jalapa, the capital city of the state of Veracruz. The Central Cone Group (CCG), of intermediate age, consists of four morphologically youthful cinder cones and associated vents that were the source of a lava field>27 km 2 of late-Pleistocene or Holocene age. The youngest group includes the westernmost flow, from Cerro Colorado, and a lava flow ˜2980 BP from the Rincón de Chapultepec scoria cone of the NVF. The latest eruption, from the compound El Volcancillo scoria cone, occurred about 870 radiocarbon years ago and produced two chemically and rheologically diverse lava flows that are among the youngest precolumbian flows in México and resemble paired aa-pahoehoe flows from Mauna Loa volcano. The El Volcancillo eruption

  3. Receiver function images from the Moho and the slab beneath the Altiplano and Puna plateaus in the Central Andes

    Science.gov (United States)

    Wölbern, I.; Heit, B.; Yuan, X.; Asch, G.; Kind, R.; Viramonte, J.; Tawackoli, S.; Wilke, H.

    2009-04-01

    Teleseismic data recorded during one and a half years are investigated with the receiver function technique to determine the crustal and upper-mantle structures underneath the highly elevated Altiplano and Puna plateaus in the central Andes. A series of converting interfaces are determined along two profiles at 21°S and 25.5°S, respectively, with a station spacing of approximately 10 km. The data provide the highest resolution gained from a passive project in this area, so far. The oceanic Nazca plate is detected down to 120 km beneath the Altiplano whereas beneath the Puna, the slab can unexpectedly be traced down to 200 km depth at longer periods. A shallow crustal low-velocity zone is determined beneath both plateaus exhibiting segmentation. In the case of the Altiplano, the segments present vertical offsets and are separated by inclined interfaces, which coincide with major fault systems at the surface. An average depth to Moho of about 70 km is determined for the Altiplano plateau. A strong negative velocity anomaly located directly below the Moho along with local crustal thinning is interpreted beneath the volcanic arc of the Altiplano plateau between 67°W and 68.5°W. A deep section of the Puna profile reveals thinning of the mantle transition zone. Although poorly resolved, the detected anomaly may suggest the presence of a mantle plume, which may constitute the origin of the anomalous temperatures at the depth of the upper-mantle discontinuities.

  4. Palaeoproterozoic Volcanic Massive Sulphides (VMS) in the Lithuanian crystalline basement: evidences for a back-arc tectonic setting

    Science.gov (United States)

    Skridlaite, Grazina; Siliauskas, Laurynas

    2014-05-01

    In the southwestern part of the East European Craton (EEC), several events of Palaeoproterozoic volcanic arc magmatic activity were recognized in the concealed crystalline basement. In Lithuania, the TTG suites of 1.89 Ga and 1.86-1.84 Ga were later metamorphosed in amphibolite and granulite facies conditions. Remnants of a volcano-sedimentary sequence metamorphosed in green schist and amphibolite facies conditions were discovered in central and southern Lithuania. In southern Lithuania, the upper part of the Lazdijai 13 (Lz13) drilling (at c. 493 m depth) consists of exhalitic quartz chlorite cherts mixed with andesitic rocks. The rocks are impregnated with magnetite in some places replacing calcite. Most of the magnetite grains are overgrown by a dendritic kovelite, which may have formed while magnetite was still in aqueous surrounding. Other accessory minerals are xenotime, zircon, apatite, Sr-Ba sulphates etc. The cherts are underlain by a metaandesite which volcanic structures were obscured by hydrothermal alteration, i.e. the idiomorphic magnetite crystals and porphyritic plagioclase grains were replaced by clay minerals and quartz or muscovite in many places. Thin metamorphosed mudstone layers turned into garnet, biotite (+/-staurolite) and chlorite schists. The rocks were affected by silicification, chloritization, argilitization and carbonatization. Taking into account the rock composition, micro and macro scale alteration zones and absence of breccia, the whole package resembles an outer part of the VMS stockwork. The lower boundary at 526 m is sharp, marked by a quartz vein, below which lies quartz, biotite (+/- chlorite) bearing schist with minor tremolite (former sandstone). It was intensely affected by silicification, and was enriched in Na, K and Ca. Accessory minerals are monazite, xenotime, apatite and detrital zircon. The schist exhibits fine mineral foliation, and is fine-grained. A 4 m thick granitic vein cuts the rock at 654 m depth, below

  5. Behavior of volatiles in arc volcanism : geochemical and petrologic evidence from active volcanoes in Indonesia

    NARCIS (Netherlands)

    Hoog, J.C.M. de

    2001-01-01

    Large amounts of material are recycled along subduction zones by uprising magmas, of which volcanoes are the surface expression. This thesis focuses on the behavior of volatiles elements (S, Cl, H) during these recycling processes. The study area is the Indonesian arc system, which hosts

  6. Behavior of volatiles in arc volcanism : geochemical and petrologic evidence from active volcanoes in Indonesia

    NARCIS (Netherlands)

    Hoog, J.C.M. de

    2001-01-01

    Large amounts of material are recycled along subduction zones by uprising magmas, of which volcanoes are the surface expression. This thesis focuses on the behavior of volatiles elements (S, Cl, H) during these recycling processes. The study area is the Indonesian arc system, which hosts

  7. Localised magmatic constraints on continental back-arc volcanism in southern Mendoza, Argentina: the Santa Maria Volcano

    Science.gov (United States)

    Espanon, Venera R.; Chivas, Allan R.; Turner, Simon P.; Kinsley, Leslie P. J.; Dosseto, Anthony

    2016-11-01

    The Payún Matrú Volcanic Field constitutes part of the continental back-arc in Argentina. This volcanic field has been the focus of several regional investigations; however, geochemical analysis of recent volcanoes (<8 ka) at the scale of an individual volcano has not been conducted. We present a morphological description for the Santa Maria Volcano in addition to results from major and trace element analysis and 238U-230Th-226Ra disequilibria. The trace element evidence suggests that the Santa Maria magmatic source has a composition similar to that of the local intraplate end member (resembling an ocean island basalt-like source), with a slight contribution from subduction-related material. The U-series analyses suggest a high 226Ra excess over 230Th for this volcano, which is not derived from a shallow process such as hydrothermal alteration or upper crustal contamination. Furthermore, intermediate-depth processes such as fractional crystallisation have been inferred for the Santa Maria Volcano, but they are not capable of producing the 226Ra excess measured. The 226Ra excess is explained by deep processes like partial melting of mantle lithologies with some influence from subducted Chilean trench sediments. Due to the short half-life of 226Ra (1600 years), we infer that fast magma ascent rates are required to preserve the high 226Ra excess.

  8. Postcaldera volcanism and hydrothermal activity revealed by autonomous underwater vehicle surveys in Myojin Knoll caldera, Izu-Ogasawara arc

    Science.gov (United States)

    Honsho, Chie; Ura, Tamaki; Kim, Kangsoo; Asada, Akira

    2016-06-01

    Myojin Knoll caldera, one of the submarine silicic calderas lying on the volcanic front of the northern Izu-Ogasawara arc, has attracted increasing attention since the discovery of a large hydrothermal field called the Sunrise deposit. Although numerous submersible surveys have been conducted in Myojin Knoll caldera, they have not sufficiently explored areas to produce a complete picture of the caldera and understand the origin of the Sunrise deposit. We conducted comprehensive deep-sea surveys using an autonomous underwater vehicle and obtained high-resolution bathymetric and magnetic data and sonar images from ~70% of the caldera. The detailed bathymetric map revealed that faulting and magma eruptions, possibly associated with an inflation-deflation cycle of the magma reservoir during postcaldera volcanism, had generally occurred in the caldera wall. The main dome of the central cone was covered with lava flows and exhibits exogenous growth, which is unusual for rhyolitic domes. The magnetization distribution in the central cone indicates preferential magma intrusion along a NW-SE direction. It is presumed that magma migrated along this direction and formed a rhyolite dome at the foot of the southeastern caldera wall, where the Sunrise deposit occurs. The Sunrise deposit is composed mainly of three ridges extending in slope directions and covers ~400 × ~400 m. Magnetization reduction in the deposit area is small, indicating that the alteration zone beneath the Sunrise deposit is slanting rather than vertical. It is presumed that several slanting and near-vertical volcanic vents serve as pathways of hydrothermal fluid in Myojin Knoll caldera.

  9. The tectonic emplacement of Sumba in the Sunda-Banda Arc: paleomagnetic and geochemical evidence from the early Miocene Jawila volcanics

    Science.gov (United States)

    Wensink, Hans; van Bergen, Manfred J.

    1995-11-01

    The island of Sumba is a continental fragment in the fore-arc region near the transition between the Sunda Arc and Banda Arc in southeastern Indonesia. Paleomagnetic and geochemical evidence from the early Miocene volcanics of the Jawila Formation in western Sumba constrain the final drift stage and tectonic emplacement of the island. The lavas range from predominantly andesites to dacites, and display textural evidence for a weak metamorphism. Rock magnetic and mineral chemical data point to pseudo-single- to multi-domain (titano)magnetite (Fe 2.5-3Ti 0.5-0O 3), with grain sizes up to 10 μm, as the main carrier of remanence. The Jawila Formation reveals a ChRM direction with declination = 4.6°, inclination = - 19.2°, α95 = 9.9° and a paleolatitude of 9.9°S, which corroborates earlier results (Chamalaun and Sunata, 1982). Taking paleomagnetic evidence from other formations on the island into account, we conclude that the Sumba fragment has occupied approximately its present position since the Miocene. The calc-alkaline affinity and trace-element signatures of the lavas point to an origin in an arc environment. This occurrence of subduction-related volcanic activity in the early Miocene on Sumba implies that a volcanic arc existed south of the present-day East Sunda Arc, or that the island was located within the latter arc between Sumbawa and eastern Flores, and still had a minor southward drift to cover.

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

    Science.gov (United States)

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

    2015-12-01

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

  11. Temporal and geochemical evolution of Miocene volcanism in the Andean back-arc between 36°S and 38°S and U-series analyses of young volcanic centers in the arc and back-arc, Argentina

    DEFF Research Database (Denmark)

    Dyhr, Charlotte Thorup

    of the subducting slab at ca. 20 Ma is inferred. The eruption of 24-20 Ma alkali olivine basalt up to 500 km east of the trench marks the beginning of a long-lasting magmatic episode with widespread volcanism north of the Cortaderas lineament following a regional magmatic hiatus lasting from 39 Ma to 26 Ma...

  12. Basalt-Limestone and Andesite-Limestone Interaction in the Arc Crust - Implications for Volcanic Degassing of CO2

    Science.gov (United States)

    Carter, L. B.; Dasgupta, R.

    2014-12-01

    Volcanically emitted CO2 is generally mantle-derived, but high degassing rates at some arcs (e.g. Merapi [1] and Colli Albani Volcanic District [2]) are thought to be affected by magma-carbonate interaction in the upper plate. However, the effects of depth, temperature, and composition on this process are poorly known. We experimentally simulated magma (50%)-limestone (50%) wallrock interactions at 0.5-1.0 GPa, 1100-1200 °C using pure calcite and a hydrous (~3-5 wt.% H2O) melt (basalt, andesite, or dacite). At 1.0 GPa, 1200 °C starting melts are superliquidus, whereas in the presence of calcite, Ca-rich cpx ± Ca-scapolite are produced. With increasing T, basalt-calcite interaction causes the melt, on a volatile-free basis, to become silica-poor and Ca-rich with alumina decreasing as cpx becomes more CaTs-rich. The same trend is seen with all starting melt compositions as P decreases at a constant T (1200 °C), producing melts similar to ultracalcic (CaO/Al2O3>>1) melt inclusions found in arc settings. Shifting from basalt to andesite has little effect on SiO2 and CaO of the reacted melt (e.g. 37 wt.% SiO2, 42 wt.% CaO at 0.5 GPa, 1200 °C), whereas Al2O3 of andesite-derived reacted melt is lower, likely a result of lower alumina in the starting andesite. Wall-rock calcite consumption is observed to increase with increasing T, decreasing P, and increasing melt XSiO2. At 0.5 GPa between 1100 and 1200 °C, our basalt experiments yield carbonate assimilation from 22 to 48 wt.%. This decreases to 20 wt.% at 1.0 GPa, 1200 °C, whereas an andesitic composition assimilates 59 to 52 wt.% from 0.5 to 1.0 GPa at 1200 °C. The higher assimilation in andesite-added runs at high-T is because of lower silicate liquidus as evidenced by lower modal proportion or absence of cpx ± scapolite. Using a magma flux rate estimated for Mt. Vesuvius [3], we obtain a CO2 outflux for a single such volcano experiencing arc magma-calcite reaction [4] of at least 2-4% of the present

  13. Neotectonic development of the El Salvador Fault Zone and implications for deformation in the Central America Volcanic Arc: Insights from 4-D analog modeling experiments

    Science.gov (United States)

    Alonso-Henar, Jorge; Schreurs, Guido; Martinez-Díaz, José Jesús; Álvarez-Gómez, José Antonio; Villamor, Pilar

    2015-01-01

    The El Salvador Fault Zone (ESFZ) is an active, approximately 150 km long and 20 km wide, segmented, dextral strike-slip fault zone within the Central American Volcanic Arc striking N100°E. Although several studies have investigated the surface expression of the ESFZ, little is known about its structure at depth and its kinematic evolution. Structural field data and mapping suggest a phase of extension, at some stage during the evolution of the ESFZ. This phase would explain dip-slip movements on structures that are currently associated with the active, dominantly strike slip and that do not fit with the current tectonic regime. Field observations suggest trenchward migration of the arc. Such an extension and trenchward migration of the volcanic arc could be related to slab rollback of the Cocos plate beneath the Chortis Block during the Miocene/Pliocene. We carried out 4-D analog model experiments to test whether an early phase of extension is required to form the present-day fault pattern in the ESFZ. Our experiments suggest that a two-phase tectonic evolution best explains the ESFZ: an early pure extensional phase linked to a segmented volcanic arc is necessary to form the main structures. This extensional phase is followed by a strike-slip dominated regime, which results in intersegment areas with local transtension and segments with almost pure strike-slip motion. The results of our experiments combined with field data along the Central American Volcanic Arc indicate that the slab rollback intensity beneath the Chortis Block is greater in Nicaragua and decreases westward to Guatemala.

  14. Early Permian arc-related volcanism and sedimentation at the western margin of Gondwana:Insight from the Choiyoi Group lower section

    Institute of Scientific and Technical Information of China (English)

    Leonardo Strazzere; Daniel A. Gregori; Leonardo Benedini

    2016-01-01

    Permian sedimentary and basic to intermediate volcanic rocks assigned to the Conglomerado del Río Blanco and Portezuelo del Cenizo Formation, lower part of the Choiyoi Group, crop out between the Cordon del Plata, Cordillera Frontal and Precordillera of Mendoza Province, Argentina. The sedimentary rocks are represented by six lithofacies grouped in three facies associations. They were deposited by mantled and gravitational flows modified by high-energy fluvial currents that evolved to low-energy fluvial and lacustrine environments. They constitute the Conglomerado del Río Blanco, which cover unconformably marine Carboniferous sequences. Five volcanic and volcaniclastic facies make up the beginning of volcanic activity. The first volcanic event in the Portezuelo del Cenizo is basaltic to andesitic lava-flows emplaced in the flanks of volcanoes. Lava collapse produced thick block and ash flows. Interbedding in the intermediate volcanic rocks, there are dacites of different geochemical signature, which indicate that the development of acidic volcanism was coetaneous with the first volcanic activity. The geochemistry of these rocks induces to consider that the Choiyoi Group Lower section belongs to a magmatic arc on continental crust. The age of this section is assigned to the lower Permian (277 ? 3.0 Ma, Kungurian age).

  15. Sandstone provenance and U-Pb ages of detrital zircons from Permian-Triassic forearc sediments within the Sukhothai Arc, northern Thailand: Record of volcanic-arc evolution in response to Paleo-Tethys subduction

    Science.gov (United States)

    Hara, Hidetoshi; Kunii, Miyuki; Miyake, Yoshihiro; Hisada, Ken-ichiro; Kamata, Yoshihito; Ueno, Katsumi; Kon, Yoshiaki; Kurihara, Toshiyuki; Ueda, Hayato; Assavapatchara, San; Treerotchananon, Anuwat; Charoentitirat, Thasinee; Charusiri, Punya

    2017-09-01

    Provenance analysis and U-Pb dating of detrital zircons in Permian-Triassic forearc sediments from the Sukhothai Arc in northern Thailand clarify the evolution of a missing arc system associated with Paleo-Tethys subduction. The turbidite-dominant formations within the forearc sediments include the Permian Ngao Group (Kiu Lom, Pha Huat, and Huai Thak formations), the Early to earliest Late Triassic Lampang Group (Phra That and Hong Hoi formations), and the Late Triassic Song Group (Pha Daeng and Wang Chin formations). The sandstones are quartzose in the Pha Huat, Huai Thak, and Wang Chin formations, and lithic wacke in the Kiu Lom, Phra That, Hong Hoi and Pha Daeng formations. The quartzose sandstones contain abundant quartz, felsic volcanic and plutonic fragments, whereas the lithic sandstones contain mainly basaltic to felsic volcanic fragments. The youngest single-grain (YSG) zircon U-Pb age generally approximates the depositional age in the study area, but in the case of the limestone-dominant Pha Huat Formation the YSG age is clearly older. On the other hand, the youngest cluster U-Pb age (YC1σ) represents the peak of igneous activity in the source area. Geological evidence, geochemical signatures, and the YC1σ ages of the sandstones have allowed us to reconstruct the Sukhothai arc evolution. The initial Sukhothai Arc (Late Carboniferous-Early Permian) developed as a continental island arc. Subsequently, there was general magmatic quiescence with minor I-type granitic activity during the Middle to early Late Permian. In the latest Permian to early Late Triassic, the Sukhothai Arc developed in tandem with Early to Middle Triassic I-type granitic activity, Middle to Late Triassic volcanism, evolution of an accretionary complex, and an abundant supply of sediments from the volcanic rocks to the trench through a forearc basin. Subsequently, the Sukhothai Arc became quiescent as the Paleo-Tethys closed after the Late Triassic. In addition, parts of sediments of

  16. Oxygen isotope geochemistry of the lassen volcanic center, California: Resolving crustal and mantle contributions to continental Arc magmatism

    Science.gov (United States)

    Feeley, T.C.; Clynne, M.A.; Winer, G.S.; Grice, W.C.

    2008-01-01

    This study reports oxygen isotope ratios determined by laser fluorination of mineral separates (mainly plagioclase) from basaltic andesitic to rhyolitic composition volcanic rocks erupted from the Lassen Volcanic Center (LVC), northern California. Plagioclase separates from nearly all rocks have ??18O values (6.1-8.4%) higher than expected for production of the magmas by partial melting of little evolved basaltic lavas erupted in the arc front and back-arc regions of the southernmost Cascades during the late Cenozoic. Most LVC magmas must therefore contain high 18O crustal material. In this regard, the ??18O values of the volcanic rocks show strong spatial patterns, particularly for young rhyodacitic rocks that best represent unmodified partial melts of the continental crust. Rhyodacitic magmas erupted from vents located within 3.5 km of the inferred center of the LVC have consistently lower ??18 O values (average 6.3% ?? 0.1%) at given SiO2 contents relative to rocks erupted from distal vents (>7.0 km; average 7.1% ?? 0.1%). Further, magmas erupted from vents situated at transitional distances have intermediate values and span a larger range (average 6.8% ?? 0.2%). Basaltic andesitic to andesitic composition rocks show similar spatial variations, although as a group the ??18O values of these rocks are more variable and extend to higher values than the rhyodacitic rocks. These features are interpreted to reflect assimilation of heterogeneous lower continental crust by mafic magmas, followed by mixing or mingling with silicic magmas formed by partial melting of initially high 18O continental crust (??? 9.0%) increasingly hybridized by lower ??18O (???6.0%) mantle-derived basaltic magmas toward the center of the system. Mixing calculations using estimated endmember source ??18O values imply that LVC magmas contain on a molar oxygen basis approximately 42 to 4% isotopically heavy continental crust, with proportions declining in a broadly regular fashion toward the

  17. Submarine Hydrothermal Sites in Arc Volcanic-Back Arc Environment: Insight from Recent Marine Geophysical Investigations in the Southern Tyrrhenian Sea.

    Science.gov (United States)

    Cocchi, L.; Ligi, M.; Bortoluzzi, G.; Petersen, S.; Plunkett, S.; Muccini, F.; Canese, S.; Caratori Tontini, F.; Carmisciano, C.

    2014-12-01

    Hydrothermal alteration processes involve mineralogical and chemical changes, which are reflected in a major modification of potential field patterns observed over hydrothermal areas. Basalt-hosted hydrothermal sites exhibit characteristic responses with magnetic lows and minima of the gravity field. Near bottom AUV (Autonomous Underwater Vehicle) based potential field surveys have become a very effective technique in deep sea exploration. Here we present results of recent ship-borne and near seafloor magnetic and gravity investigations at deep (Marsili and Palinuro seamounts) and shallow (Panarea, Basiluzzo and Secca del Capo) hydrothermal sites in the Southern Tyrrhenian Sea including multibeam bathymetry, seafloor reflectivity and seismic profiles. At Marsili seamount, a large Fe-Mn-oxyhydroxides-rich chimney field is located at the summit (500 m depth). This site is correlated with pronounced magnetic and gravity lows (0 A/m and 2.0 g/cm3). Deep tow magnetic survey (Cruise MAVA11) revealed strong association between the complicated magnetization pattern and the main volcano-tectonic features of the ridge. Hydrothermal manifestations at Palinuro seamount occur mainly on the western sector within the rim of a caldera structure at depth of 600m. Recent AUV based magnetic surveys (Cruise POS442, 2012 using AUV "Abyss") detailed a magnetization low interpreted to represent the local distribution of subseafloor hydrothermal alteration (potentially massive sulfide deposits), and also mapped previously undiscovered inactive chimney fields. Hydrothermal sites observed at the arc-related volcanic islands (Panarea, Basiluzzo, Eolo and Secca del Capo) are confined to shallow depths (less then 300m) and associated with large ochreaceous mounds, vents and chimney fields such as those observed E of Basiluzzo Island. At this site a recent magnetic survey (Cruise PANA13_ASTREA) combined with Remote Operated Vehicle (ROV) investigations revealed that the submarine geothermal

  18. Textural and chemical variation in phenocrysts from the early eruptions of Lutao volcanic island, the northern Luzon arc

    Science.gov (United States)

    Liu, Y.; Iizuka, Y.; Huang, K.

    2012-12-01

    The Lutao volcanic island at the northern end of Luzon arc was formed by the subduction of South China Sea Plate beneath the Philippine Sea plate. Three edifices on the island were built up by pyroclastic deposits from different eruption stages. In this study, the textural and chemical zonings in phenocrysts are used to characterize the subvolcanic magma chamber for the earliest eruption stage (1.4-2.0 Ma). The high 143Nd/144Nd and 176Hf/177Hf ratios of six volcanic breccias collected from the lowermost layer indicate that they were derived from a common depleted mantle source. However, their compositional variations cannot be explained by simple fractional crystallization. The textures and compositions of the phenocrysts reveal the complication in the magma chamber processes. Compared to the average primitive arc basalts, two basaltic andesites have similar major element compositions with higher incompatible trace element abundances. The un-zoned or normally zoned olivine, plagioclase, and pyroxenes indicate the relatively undisturbed processes (961-1011°C and 2.8-5.5 kb) at the earlier crystallization stage. The peritectic olivine and abundance melt inclusions accompanied by abrupt XAn increase at the rims of plagioclase inferred recharge of H2O-rich mafic melt at later stage, which also triggered rapid eruption. The cryptic magma mixing had limited effect on isotopic signatures and major element variations, but had great chance to modify the bulk trace element abundances. In contrast, plagioclase phenocrysts in four low-mg# basaltic samples contain An-rich dissolved or resorbed cores with abundant melt inclusions, which were formed from rapid decompression of volatile-rich magma at H2O-undersaturated conditions. The calcic plagioclase and minor Mg-rich olivine formed at greater depth were rapidly brought to magma chamber to crystallized sodic plagioclase rim, clinopyroxene, and minor orthopyroxene (954-994°C and 2.1-4.1 kb). The normally zoned clinopyroxene

  19. On-and offshore tephrostratigraphy and -chronology of the southern Central American Volcanic Arc (CAVA)

    Science.gov (United States)

    Schindlbeck, J. C.; Kutterolf, S.; Hemming, S. R.; Wang, K. L.

    2015-12-01

    Including the recently drilled CRISP sites (IODP Exp. 334&344) the deep sea drilling programs have produced 69 drill holes at 29 Sites during 9 Legs at the Central American convergent margin, where the Cocos plate subducts beneath the Caribbean plate. The CAVA produced numerous plinian eruptions in the past. Although abundant in the marine sediments, information and data regarding large late Cenozoic explosive eruptions from Costa Rica, Nicaragua, Honduras, El Salvador, and Guatemala remain very sparse and discontinuous on land. We have established a tephrostratigraphy from recent through Miocene times from the unique archive of ODP/IODP sites offshore Central America in which we identify tephra source regions by geochemical fingerprinting using major and trace element glass shard compositions. Here we present first order correlations of ­~500 tephra layers between multiple holes at a single site as well as between multiple sites. We identified ashes supporting Costa Rican (~130), Nicaraguan (17) and Guatemalan (27) sources as well as ~150 tephra layers from the Galápagos hotspot. Within our marine record we also identified well-known marker beds such as the Los Chocoyos tephra from Atitlán Caldera in Guatemala and the Tiribi Tuff from Costa Rica but also correlations to 15 distinct deposits from known Costa Rican and Nicaraguan eruptions within the last 4.1 Ma. These correlations, together with new radiometric age dates, provide the base for an improved tephrochronostratigraphy in this region. Finally, the new marine record of explosive volcanism offshore southern CAVA provides insights into the eruptive history of long-living volcanic complexes (e.g., Barva, Costa Rica) and into the distribution and frequency of large explosive eruptions from the Galápagos hotspot. The integrated approach of Ar/Ar age dating, correlations with on land deposits from CAVA, biostratigraphic ages and sediment accumulation rates improved the age models for the drilling sites.

  20. Investigation of the thermal regime and geologic history of the Cascade volcanic arc: First phase of a program for scientific drilling in the Cascade Range

    Energy Technology Data Exchange (ETDEWEB)

    Priest, G.R.

    1987-01-01

    A phased, multihole drilling program with associated science is proposed as a means of furthering our understanding of the thermal regime and geologic history of the Cascade Range of Washington, Oregon, and northern California. The information obtained from drilling and ancillary geological and geophysical investigations will contribute to our knowledge in the following general areas: (1) the magnitude of the regional background heat flow of parts of the Quaternary volcanic belt dominated by the most abundant volcanic rock types, basalt and basaltic andesite; (2) the nature of the heat source responsible for the regional heat-flow anomaly; (3) the characteristics of the regional hydrothermal and cold-water circulation; the rates of volcanism for comparison with models for the rate and direction of plate convergence of the Cascades; (5) the history of deformation and volcanism in the volcanic arc that can be related to subduction; (6) the present-day stress regime of the volcanic arc and the relation of these stresses to plate interactions and possible large earthquakes; and the current geometry of the subducted oceanic plate below the Cascade Range and the relationship of the plate to the distribution of heat flow, Quaternary volcanism, and Quaternary deformation. Phase I research will be directed toward a detailed investigation of the Santiam Pass segment. In concert with the Santiam Pass research, a detailed study of the nearby Breitenbush Hot Springs area is also recommended as a component of Phase I. The object of the Breitenbush research is to study one of the hottest known Cascade hydrothermal systems, which coincidentally also has a good geological and geophysical data base. A coordinated program of drilling, sampling, subsurface measurements, and surface surveys will be associated with the drilling of several holes.

  1. A structural outline of the Yenkahe volcanic resurgent dome (Tanna Island, Vanuatu Arc, South Pacific)

    Science.gov (United States)

    Merle, O.; Brothelande, E.; Lénat, J.-F.; Bachèlery, P.; Garaébiti, E.

    2013-12-01

    A structural study has been conducted on the resurgent Yenkahe dome (5 km long by 3 km wide) located in the heart of the Siwi caldera of Tanna Island (Vanuatu arc, south Pacific). This spectacular resurgent dome hosts a small caldera and a very active strombolian cinder cone - the Yasur volcano - in the west and exhibits an intriguing graben in its central part. Detailed mapping and structural observations make it possible to unravel the volcano-tectonic history of the dome. It is shown that, following the early formation of a resurgent dome in the west, a complex collapse (caldera plus graben) occurred and this was associated with the recent uplift of the eastern part of the present dome. Eastward migration of the underlying magma related to regional tectonics is proposed to explain this evolution.

  2. Middle Jurassic Topawa group, Baboquivari Mountains, south-central Arizona: Volcanic and sedimentary record of deep basins within the Jurassic magmatic arc

    Science.gov (United States)

    Haxel, G.B.; Wright, J.E.; Riggs, N.R.; Tosdal, R.M.; May, D.J.

    2005-01-01

    Among supracrustal sequences of the Jurassic magmatic arc of the southwestern Cordillera, the Middle Jurassic Topawa Group, Baboquivari Mountains, south-central Arizona, is remarkable for its lithologic diversity and substantial stratigraphic thickness, ???8 km. The Topawa Group comprises four units (in order of decreasing age): (1) Ali Molina Formation-largely pyroclastic rhyolite with interlayered eolian and fluvial arenite, and overlying conglomerate and sandstone; (2) Pitoikam Formation-conglomerate, sedimentary breccia, and sandstone overlain by interbedded silt- stone and sandstone; (3) Mulberry Wash Formation-rhyolite lava flows, flow breccias, and mass-flow breccias, with intercalated intraformational conglomerate, sedimentary breccia, and sandstone, plus sparse within-plate alkali basalt and comendite in the upper part; and (4) Tinaja Spring Porphyry-intrusive rhyolite. The Mulberry Wash alkali basalt and comendite are genetically unrelated to the dominant calcalkaline rhyolite. U-Pb isotopic analyses of zircon from volcanic and intrusive rocks indicate the Topawa Group, despite its considerable thickness, represents only several million years of Middle Jurassic time, between approximately 170 and 165 Ma. Sedimentary rocks of the Topawa Group record mixing of detritus from a minimum of three sources: a dominant local source of porphyritic silicic volcanic and subvolcanic rocks, identical or similar to those of the Topawa Group itself; Meso- proterozoic or Cambrian conglomerates in central or southeast Arizona, which contributed well-rounded, highly durable, polycyclic quartzite pebbles; and eolian sand fields, related to Middle Jurassic ergs that lay to the north of the magmatic arc and are now preserved on the Colorado Plateau. As the Topawa Group evidently represents only a relatively short interval of time, it does not record long-term evolution of the Jurassic magmatic arc, but rather represents a Middle Jurassic "stratigraphic snapshot" of the arc

  3. Generation of porphyry copper deposits by gas-brine reaction in volcanic arcs

    Science.gov (United States)

    Blundy, J.; Mavrogenes, J.; Tattitch, B.; Sparks, S.; Gilmer, A.

    2015-03-01

    Porphyry copper deposits, that is, copper ore associated with hydrothermal fluids rising from a magma chamber, supply 75% of the world's copper. They are typically associated with intrusions of magma in the crust above subduction zones, indicating a primary role for magmatism in driving mineralization. However, it is not clear that a single, copper-rich magmatic fluid could trigger both copper enrichment and the subsequent precipitation of sulphide ore minerals within a zone of hydrothermally altered rock. Here we draw on observations of modern subduction zone volcanism to propose an alternative process for porphyry copper formation. We suggest that copper enrichment initially involves metalliferous, magmatic hyper-saline liquids, or brines, that exsolve from large, magmatic intrusions assembled in the shallow crust over tens to hundreds of thousands of years. In a subsequent step, sulphide ore precipitation is triggered by the interaction of the accumulated brines with sulphur-rich gases, liberated in short-lived bursts from the underlying mafic magmas. We use high-temperature and high-pressure laboratory experiments to simulate such gas-brine interactions. The experiments yield copper-iron sulphide minerals and hydrogen chloride gas at magmatic temperatures of 700-800 °C, with textural and chemical characteristics that resemble those in porphyry copper deposits. We therefore conclude that porphyry copper ore forms in a two-stage process of brine enrichment followed by gas-induced precipitation.

  4. A 36,000-Year-Old Volcanic Eruption Depicted in the Chauvet-Pont d'Arc Cave (Ardèche, France)?

    Science.gov (United States)

    Nomade, Sébastien; Genty, Dominique; Sasco, Romain; Scao, Vincent; Féruglio, Valérie; Baffier, Dominique; Guillou, Hervé; Bourdier, Camille; Valladas, Hélène; Reigner, Edouard; Debard, Evelyne; Pastre, Jean-François; Geneste, Jean-Michel

    2016-01-01

    Among the paintings and engravings found in the Chauvet-Pont d'Arc cave (Ardèche, France), several peculiar spray-shape signs have been previously described in the Megaloceros Gallery. Here we document the occurrence of strombolian volcanic activity located 35 km northwest of the cave, and visible from the hills above the cave entrance. The volcanic eruptions were dated, using 40Ar/39Ar, between 29 ± 10 ka and 35 ± 8 ka (2σ), which overlaps with the 14C AMS and thermoluminescence ages of the first Aurignacian occupations of the cave in the Megaloceros Gallery. Our work provides the first evidence of an intense volcanic activity between 40 and 30 ka in the Bas-Vivarais region, and it is very likely that Humans living in the Ardèche river area witnessed one or several eruptions. We propose that the spray-shape signs found in the Chauvet-Pont d'Arc cave could be the oldest known depiction of a volcanic eruption, predating by more than 34 ka the description by Pliny the Younger of the Vesuvius eruption (AD 79) and by 28 ka the Çatalhöyük mural discovered in central Turkey.

  5. Age, geochemical and isotopic variations in volcanic rocks from the Coastal Range of Taiwan: Implications for magma generation in the Northern Luzon Arc

    Science.gov (United States)

    Lai, Yu-Ming; Song, Sheng-Rong; Lo, Ching-Hua; Lin, Te-Hsien; Chu, Mei-Fei; Chung, Sun-Lin

    2017-02-01

    This paper reports the first systematic analysis of age and geochemical variations in volcanic rocks from the Coastal Range of Taiwan, the Northern Luzon Arc. The rocks, recovered from four main volcanoes, vary from low-K tholeiitic to medium-K calc-alkaline basalts to dacites. The rocks are typical of arc magmatic products, exhibiting enrichment in the large ion lithophile elements and depletion in the high field strength elements. Our new 40Ar/39Ar age data constrain the youngest eruption time in each of the four volcanoes, i.e., from north to south, at 7.2 Ma (Yuemei), 4.2 Ma (Chimei), 6.2 Ma (Chengkuang'ao) and 8.5 Ma (Tuluanshan), respectively. These data indicate that volcanism in the Northern Luzon Arc did not cease progressively from north to south, as previously alleged. The high and broadly uniform Nd isotope ratios [εNd = + 10.1 to + 8.8] and trace element characteristics of the rocks suggest a principal magma source from the depleted mantle wedge. Their overall geochemical variations are ascribed to magma chamber processes. The effects of magmatic differentiation and crustal contamination differ among each volcano, most likely owing to the discrepancy of residence time in individual magma chambers. Consequently, we propose a binary mixing model for the magma generation that involves arc magmas sourced from the depleted mantle wedge and up to 5% crustal contamination with a continental fragment split off from the Eurasian margin.

  6. Back arc extension, tectonic inheritance, and volcanism in the Ligurian Sea, Western Mediterranean

    Science.gov (United States)

    Rollet, Nadège; Déverchère, Jacques; Beslier, Marie-Odile; Guennoc, Pol; Réhault, Jean-Pierre; Sosson, Marc; Truffert, Catherine

    2002-06-01

    The Ligurian basin, western Mediterranean Sea, has opened from late Oligocene to early Miocene times, behind the Apulian subduction zone and partly within the western Alpine belt. We analyze the deep structures of the basin and its conjugate margins in order to describe the tectonic styles of opening and to investigate the possible contributions of forces responsible for the basin formation, especially the pulling force induced by the retreating subduction hinge and the gravitational body force from the Alpine wedge. To undertake this analysis, we combine new multichannel seismic reflection data (Malis cruise, 1995) with other geophysical data (previous multichannel and monochannel seismic sections, magnetic anomalies) and constrain them by geological sampling from two recent cruises (dredges from Marco cruise, 1995, and submersible dives from Cylice cruise, 1997). From an analysis of basement morphology and seismic facies, we refine the extent of the different domains in the Ligurian Sea: (1) the continental thinned margins, with strong changes in width and structure along strike and on both sides of the ocean; (2) the transitional domain to the basin; and (3) a narrow, atypical oceanic domain. Margin structures are characterized by few tilted blocks along the narrow margins, where inherited structures seem to control synrift sedimentation and margin segmentation. On the NW Corsican margin, extension is distributed over more than 120 km, including offshore Alpine Corsica, and several oceanward faults sole on a relatively flat reflector. We interpret them as previous Alpine thrusts reactivated during rifting as normal faults soling on a normal ductile shear zone. Using correlations between magnetic data, seismic facies, and sampling, we propose a new map of the distribution of magmatism. The oceanic domain depicts narrow, isolated magnetic anomalies and is interpreted as tholeitic volcanics settled within an unroofed upper mantle, whereas calcalkaline volcanism

  7. Chlorine Stable Isotopes to reveal contribution of magmatic chlorine in subduction zones: the case of the Kamchatka-Kuril and the Lesser Antilles Volcanic Arcs

    Science.gov (United States)

    Agrinier, Pierre; Shilobreeva, Svetlana; Bardoux, Gerard; Michel, Agnes; Maximov, Alexandr; Kalatcheva, Elena; Ryabinin, Gennady; Bonifacie, Magali

    2015-04-01

    By using the stable isotopes of chlorine (δ 37Cl), we have shown that magmatic chlorine (δ 37Cl ≤ -0.6 ‰ [1]) is different from surface chlorine (δ 37Cl ≈ 0 ‰ [1]) in hydrothermal system of Soufrière and Montagne Pelé from the young arc volcanic system of Lesser Antilles. First measurements on condensed chlorides from volcanic gases (e.g. [2], [3]) did not permitted to get sensible δ 37Cl values on degassed chlorine likely because chlorine isotopes are fractionated during the HClgas - chloride equilibrium in the fumaroles or during sampling artifacts. Therefore we have developed an alternative strategy based on the analysis of chloride in thermal springs, streams, sout{f}lowing on the flanks of the volcanoes. Due to the highly hydrophilic behavior of Cl, we hypothesize that thermal springs incorporate chlorine without fractionation of chlorine isotopes and might reflect the chlorine isotopic composition degassed by magmas [1]. Indeed Thermal spring with low δ 37Cl chlorides (≤ -0.6 perthousand{}) are linked with magmatic volatiles characters (3He ratio at 5 Ra at and δ 13C CO2 quad ≈ -3 perthousand{}). To go further in the potentiality of using the Chlorine isotopes to reveal contribution of magmatic chlorine in volcanic systems, we have started the survey of thermal springs and wells waters in the Kamchatka-Kuril volcanic mature Arc (on sites Mutnovsky, Paratunka, Nalychevsky, Khodutkinsky, Paramushir Island, identified by Taran, 2009 [4] for concentrations of chloride). Preliminary results show δ 37Cl values ranging from 0.5 to -0.2 ‰ and generally higher chloride concentrations. The δ 37Cl values are higher than the value recorded for the young arc volcanic system of lesser Antilles. At present moment very few negative δ 37Cl have been measured in the Kamchatka-Kuril volcanic mature Arc. [1] Li et al., 2015 EPSL in press. [2] Sharp et al. 2010 GCA. [3] Rizzo et al., 2013, EPSL, 371, 134. [4] Taran, 2009, GCA, 73, 1067

  8. Fluid-melt partitioning of sulfur in differentiated arc magmas and the sulfur yield of explosive volcanic eruptions

    Science.gov (United States)

    Masotta, M.; Keppler, H.; Chaudhari, A.

    2016-03-01

    The fluid-melt partitioning of sulfur (DSfluid/melt) in differentiated arc magmas has been experimentally investigated under oxidizing conditions (Re-ReO2 buffer) from 800 to 950 °C at 200 MPa. The starting glasses ranged in composition from trachyte to rhyolite and were synthesized targeting the composition of the residual melt formed after 10-60% crystallization of originally trachy-andesitic, dacitic and rhyodacitic magmas (Masotta and Keppler, 2015). Fluid compositions were determined both by mass balance and by Raman spectroscopy of fluid inclusions. DSfluid/melt increases exponentially with increasing melt differentiation, ranging from 2 to 15 in the trachytic melt, from 20 to 100 in the dacitic and rhyodacitic melts and from 100 to 120 in the rhyolitic melt. The variation of the DSfluid/melt is entirely controlled by the compositional variation of the silicate melt, with temperature having at most a minor effect within the range investigated. Experiments from this study were used together with data from the literature to calibrate the following model that allows predicting DSfluid/melt for oxidized arc magmas: where nbo/t is the non-bridging oxygen atoms per tetrahedron, ASI is the alumina saturation index, Al# and Ca# are two empirical compositional parameters calculated in molar units (Al # = XAl2O3/XSiO2 +XTiO2 +XAl2O3 and Ca # = XCaO/XNa2O +XK2O). The interplay between fluid-melt partitioning and anhydrite solubility determines the sulfur distribution among anhydrite, melt and fluid. At increasing melt polymerization, the exponential increase of the partition coefficient and the decrease of anhydrite solubility favor the accumulation of sulfur either in the fluid phase or as anhydrite. On the other hand, the higher anhydrite solubility and lower partition coefficient for less polymerized melts favor the retention of sulfur in the melt. At equilibrium conditions, these effects yield a maximum of the sulfur fraction in the fluid phase for slightly

  9. Geochronology and geochemistry of the Early Jurassic Yeba Formation volcanic rocks in southern Tibet: Initiation of back-arc rifting and crustal accretion in the southern Lhasa Terrane

    Science.gov (United States)

    Wei, Youqing; Zhao, Zhidan; Niu, Yaoling; Zhu, Di-Cheng; Liu, Dong; Wang, Qing; Hou, Zengqian; Mo, Xuanxue; Wei, Jiuchuan

    2017-05-01

    Understanding the geological history of the Lhasa Terrane prior to the India-Asia collision ( 55 ± 10 Ma) is essential for improved models of syn-collisional and post-collisional processes in the southern Lhasa Terrane. The Miocene ( 18-10 Ma) adakitic magmatism with economically significant porphyry-type mineralization has been interpreted as resulting from partial melting of the Jurassic juvenile crust, but how this juvenile crust was accreted remains poorly known. For this reason, we carried out a detailed study on the volcanic rocks of the Yeba Formation (YF) with the results offering insights into the ways in which the juvenile crust may be accreted in the southern Lhasa Terrane in the Jurassic. The YF volcanic rocks are compositionally bimodal, comprising basalt/basaltic andesite and dacite/rhyolite dated at 183-174 Ma. All these rocks have an arc-like signature with enriched large ion lithophile elements (LILEs; e.g., Rb, Ba and U) and light rare earth elements (LREEs) and depleted high field strength elements (HFSEs; e.g., Nb, Ta, Ti). They also have depleted whole-rock Sr-Nd and zircon Hf isotopic compositions, pointing to significant mantle isotopic contributions. Modeling results of trace elements and isotopes are most consistent with the basalts being derived from a mantle source metasomatized by varying enrichment of subduction components. The silicic volcanic rocks show the characteristics of transitional I-S type granites, and are best interpreted as resulting from re-melting of a mixed source of juvenile amphibole-rich lower crust with reworked crustal materials resembling metagraywackes. Importantly, our results indicate northward Neo-Tethyan seafloor subduction beneath the Lhasa Terrane with the YF volcanism being caused by the initiation of back-arc rifting. The back-arc setting is a likely site for juvenile crustal accretion in the southern Lhasa Terrane.

  10. Fracture development within a stratovolcano: The Karaha-Telaga Bodas geothermal field, Java volcanic arc

    Science.gov (United States)

    Nemcok, M.; Moore, J.N.; Allis, R.; McCulloch, J.

    2004-01-01

    Karaha-Telaga Bodas, a vapour-dominated geothermal system located in an active volcano in western Java, is penetrated by more than two dozen deep geothermal wells reaching depths of 3 km. Detailed paragenetic and fluid-inclusion studies from over 1000 natural fractures define the liquid-dominated, transitional and vapour-dominated stages in the evolution of this system. The liquid-dominated stage was initiated by ashallow magma intrusion into the base of the volcanic cone. Lava and pyroclastic flows capped a geothermal system. The uppermost andesite flows were only weakly fractured due to the insulating effect of the intervening altered pyroclastics, which absorbed the deformation. Shear and tensile fractures that developed were filled with carbonates at shallow depths, and by quartz, epidote and actinolite at depths and temperatures over 1 km and 300??C. The system underwent numerous cycles of overpressuring, documented by subhorizontal tensile fractures, anastomosing tensile fracture patterns and implosion breccias. The development of the liquidsystem was interrupted by a catastrophic drop in fluid pressures. As the fluids boiled in response to this pressure drop, chalcedony and quartz were selectively deposited in fractures that had the largest apertures and steep dips. The orientations of these fractures indicate that the escaping overpressured fluids used the shortest possible paths to the surface. Vapour-dominated conditions were initiated at this time within a vertical chimney overlying the still hot intrusion. As pressures declined, these conditions spread outward to form the marginal vapour-dominated region encountered in the drill holes. Downward migration of the chimney, accompanied by growth of the marginal vapour-dominated regime, occurred as the intrusion cooled and the brittle-ductile transition migrated to greater depths. As the liquids boiled off, condensate that formed at the top of the vapour-dominated zone percolated downward and low

  11. Paleoproterozoic arc basalt-boninite-high magnesian andesite-Nb enriched basalt association from the Malangtoli volcanic suite, Singhbhum Craton, eastern India: Geochemical record for subduction initiation to arc maturation continuum

    Science.gov (United States)

    Rajanikanta Singh, M.; Manikyamba, C.; Ganguly, Sohini; Ray, Jyotisankar; Santosh, M.; Dhanakumar Singh, Th.; Chandan Kumar, B.

    2017-02-01

    The Singhbhum Craton of eastern India preserves distinct signatures of ultramafic-mafic-intermediate-felsic magmatism of diverse geodynamic affiliations spanning from Paleo-Mesoarchean to Proterozoic. Here we investigate the 2.25 Ga Malangtoli volcanic rocks that are predominantly clinopyroxene- and plagioclase-phyric, calc-alkaline in nature, display basalt-basaltic andesite compositions, and preserve geochemical signatures of subduction zone magmatism. Major, trace and rare earth element characteristics classify the Malangtoli volcanic rocks as arc basalts, boninites, high magnesian andesites (HMA) and Nb enriched basalts (NEB). The typical LILE enriched-HFSE depleted geochemical attributes of the arc basalts corroborate a subduction-related origin. The boninitic rocks have high Mg# (0.8), MgO (>25 wt.%), Ni and Cr contents, high Al2O3/TiO2 (>20), Zr/Hf and (La/Sm)N (>1) ratios with low (Gd/Yb)N (54 wt.%), MgO (>6 wt.%), Mg# (0.47) with elevated Cr, Co, Ni and Th contents, depleted (Nb/Th)N, (Nb/La)N, high (Th/La)N and La/Yb (<9) ratio, moderate depletion in HREE and Y with low Sr/Y. The NEBs have higher Nb contents (6.3-24 ppm), lower magnitude of negative Nb anomalies with high (Nb/Th)pm = 0.28-0.59 and (Nb/La)pm = 0.40-0.69 and Nb/U = 2.8-34.4 compared to normal arc basalts [Nb = <2 ppm; (Nb/Th)pm = 0.10-1.19; (Nb/La)pm 0.17-0.99 and Nb/U = 2.2-44 respectively] and HMA. Arc basalts and boninites are interpreted to be the products of juvenile subduction processes involving shallow level partial melting of mantle wedge under hydrous conditions triggered by slab-dehydrated fluid flux. The HMA resulted through partial melting of mantle wedge metasomatized by slab-dehydrated fluids and sediments during the intermediate stage of subduction. Slab-melting and mantle wedge hybridization processes at matured stages of subduction account for the generation of NEB. Thus, the arc basalt-boninite-HMA-NEB association from Malangtoli volcanic suite in Singhbhum Craton

  12. The geochemistry of lithium-bearing geothermal water, Taupo Volcanic Zone, and shallow fluid processes in a very active silicic volcanic arc

    Science.gov (United States)

    Dean, A. S.; Hoskin, P. W.; Rudnick, R. L.; Liu, X.; Boseley, C.

    2011-12-01

    The Li abundances and isotopic systematics of Taupo Volcanic Zone (TVZ) geothermal fluids preserves a record of processes occurring within shallow portions of geothermal reservoirs as well as deeper portions of the arc crust. Understanding Li cycling and isotopic fractionation in TVZ geothermal systems contributes to a more refined understanding of physicochemical processes affecting New Zealand's geothermal resources. A comprehensive dataset of 73 samples was compiled, with samples collected from geothermal surface features (springs, spouters, geysers, etc.) and electric-power industry production wells, collectively representing18 geothermal fields across the breadth and width the TVZ. No comparable dataset of fluid analyses exists. Ion chromatography, AAS, and quadrupole ICP-MS analyses were done for Li, Cl-, SiO2, SO42- K, Na, Ca, Mg, B, Sr and Pb concentrations. Lithium abundance in geothermal fluids from the TVZ have a dataset-wide average of 5.9 mg/L and range 4 μg/L to 29 mg/L. The Li abundance and Li/Cl ratios for geothermal water and steam condensates vary systematically as a result of boiling, mixing, and water/rock reaction. Lithium abundance and Li/Cl ratios are, therefore, indicators of shallow (above 2.5 km) and locally variable reservoir processes. δ7Li analysis of 63 samples was performed at the University of Maryland, College Park. Data quality was controlled by measurement of L-SVEC as a calibration standard and by multiple analysis of selected samples. The average δ7Li value for TVZ geothermal fluids is -0.8%. Most δ7Li values for geothermal water fall within a small range of about -3% to+2% indicating similar processes are causing similar isotopic fractionation throughout the region. Considered together, Li aundances and δ7Li values, in combination with numerical models, indicate possible evolution pathways and water/rock reactions in TVZ geothermal systems. Models based on rocks and surface water analysis indicate that Li cycles and

  13. Geochemistry of Volcanic Rocks from International Ocean Discovery Program (IODP) Site 1438, Amami Sankaku Basin: Implications for Izu-Bonin-Mariana (IBM) Arc Initiation

    Science.gov (United States)

    Hickey-Vargas, R.; Ishizuka, O.; Yogodzinski, G. M.; Bizimis, M.; Savov, I. P.; McCarthy, A. J.; Arculus, R. J.; Bogus, K.

    2015-12-01

    IODP Expedition 351 drilled 150 m of volcanic basement overlain by 1461 m of sedimentary material at Site 1438 in the Amami Sankaku basin, just west of the Kyushu Palau Ridge, the locus of IBM arc initiation. Age interpretations based on biostratigraphy (Arculus et al., Nat. Geosci., in-press) determined that the age of the basement section is between 64 and 51 Ma, encompassing the age of the earliest volcanic products of the IBM arc. The Site 1438 volcanic basement consists of multiple flows of aphyric microcrystalline to finely crystalline basalts containing plagioclase and clinopyroxene with rare olivine pseudomorphs. New XRF major and ICPMS trace element data confirm findings of shipboard analysis that the basalts are moderately differentiated (6-14 % MgO; Mg# = 51-83; 73-490 ppm Cr and 58-350 ppm Ni) with downcore variations related to flow units. Ti/V and Ti/Sc ratios are 16-27 and 75-152, respectively, with lowest values at the base of the core. One prominent characteristic of the basalts is their depletion of immobile highly incompatible elements compared with MORB. Basalts have MORB-normalized La/Nd of 0.5 to 0.9, and most have Th/La andesites from three sills in the lowermost sedimentary unit have arc-like trace element patterns with La/Nb > 3 and primitive mantle normalized La/Yb > 1. Our results suggest that mantle melting at the onset of subduction involved exceptionally depleted sources. Enrichment over time may be related to increasing subduction inputs and/or other processes, such as entrainment of fertile asthenosphere during extension of the overriding plate.

  14. Probabilities of future VEI ≥ 2 eruptions at the Central American Volcanic Arc: a statistical perspective based on the past centuries' eruption record

    Science.gov (United States)

    Dzierma, Yvonne; Wehrmann, Heidi

    2014-10-01

    A probabilistic eruption forecast is provided for seven historically active volcanoes along the Central American Volcanic Arc (CAVA), as a pivotal empirical contribution to multi-disciplinary volcanic hazards assessment. The eruption probabilities are determined with a Kaplan-Meier estimator of survival functions, and parametric time series models are applied to describe the historical eruption records. Aside from the volcanoes that are currently in a state of eruptive activity (Santa María, Fuego, and Arenal), the highest probabilities for eruptions of VEI ≥ 2 occur at Concepción and Cerro Negro in Nicaragua, which are likely to erupt to 70-85 % within the next 10 years. Poás and Irazú in Costa Rica show a medium to high eruption probability, followed by San Miguel (El Salvador), Rincón de la Vieja (Costa Rica), and Izalco (El Salvador; 24 % within the next 10 years).

  15. Petrogenesis of meta-volcanic rocks from the Maimón Formation (Dominican Republic): Geochemical record of the nascent Greater Antilles paleo-arc

    Science.gov (United States)

    Torró, Lisard; Proenza, Joaquín A.; Marchesi, Claudio; Garcia-Casco, Antonio; Lewis, John F.

    2017-05-01

    Metamorphosed basalts, basaltic andesites, andesites and plagiorhyolites of the Early Cretaceous, probably pre-Albian, Maimón Formation, located in the Cordillera Central of the Dominican Republic, are some of the earliest products of the Greater Antilles arc magmatism. In this article, new whole-rock element and Nd-Pb radiogenic isotope data are used to give new insights into the petrogenesis of the Maimón meta-volcanic rocks and constrain the early evolution of the Greater Antilles paleo-arc system. Three different groups of mafic volcanic rocks are recognized on the basis of their immobile element contents. Group 1 comprises basalts with compositions similar to low-Ti island arc tholeiites (IAT), which are depleted in light rare earth elements (LREE) and resemble the forearc basalts (FAB) and transitional FAB-boninitic basalts of the Izu-Bonin-Mariana forearc. Group 2 rocks have boninite-like compositions relatively rich in Cr and poor in TiO2. Group 3 comprises low-Ti island arc tholeiitic basalts with near-flat chondrite-normalized REE patterns. Plagiorhyolites and rare andesites present near-flat to subtly LREE-depleted chondrite normalized patterns typical of tholeiitic affinity. Nd and Pb isotopic ratios of plagiorhyolites, which are similar to those of Groups 1 and 3 basalts, support that these felsic lavas formed by anatexis of the arc lower crust. Geochemical modelling points that the parental basic magmas of the Maimón meta-volcanic rocks formed by hydrous melting of a heterogeneous spinel-facies mantle source, similar to depleted MORB mantle (DMM) or depleted DMM (D-DMM), fluxed by fluids from subducted oceanic crust and Atlantic Cretaceous pelagic sediments. Variations of subduction-sensitive element concentrations and ratios from Group 1 to the younger rocks of Groups 2 and 3 generally match the geochemical progression from FAB-like to boninite and IAT lavas described in subduction-initiation ophiolites. Group 1 basalts likely formed at magmatic

  16. 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 betweenCampanian strata. In comparison, sediment proportions in central Puerto Rico range between 0.5 to 1.5% in the Albian to 2 to > 4% during the Cenomanian-Campanian interval. The silicic suite, consisting predominantly of rhyolites, is characterized by depleted Al 2O 3 (average arc-like Sr, Nd, and Pb isotope signatures, and by the presence of plagioclase. All of these features are consistent with an anatexic origin in gabbroic sources, of both oceanic and arc-related origin, within the sub-arc basement. The abundance of silicic lavas varies widely along the length of the arc platform. In the 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 (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

  17. Comprehensive study of the seismotectonics of the easter Aleutian arc and associated volcanic systems. Annual progress report, March 1, 1978--February 28, 1979

    Energy Technology Data Exchange (ETDEWEB)

    Jacob, K.H.; Davies, J.N.; Beavan, J.; Johnson, D.; House, L.; Krause, J.; Hickman, S.; Winslow, M.; Hauptman, J.; Mori, J.; Sykes, L.R.

    1979-01-01

    Based on the historic seismic record and accurate hypocenter data obtained from the eastern Aleutian seismic network, a relationship between the subduction-zone seismicity, volcano-trench separation, and the occurrence of great thrust earthquakes has been established for the Aleutian arc. On the basis of strong-motion accelerometer data it was found that high stress drops (540 t 650 bars) were associated with two moderate-size earthquakes (m/sub b/ = 6.0 and 5.8) within the Shumagin Islands seismic gap. This indicates that near the down-dip end of the major thrust zone, at depths of about 40 km, high tectonic stresses have accumulated within the gap segment of the arc. That such accumulation of stress is presently an ongoing process is corroborated by results from geodetic precision leveling on Unga Island. The leveling data indicate tilt rates of about 1 microradian/year. The tilting is directed down towards the trench and up towards the volcanic arc. Whether the recent activity of Pavlof, Shishaldin and Westdahl volcanoes indicates transmission of high tectonic stresses from the major thrust zone to the volcanic arc is unresolved. The search for a shallow magma chamber beneath the seismically monitored Pavlof volcano is still inconclusive although large amounts of recently acquired data remain to be analyzed. A geologic reconnaissance of the Shumagin Islands and the Adjacent Alaska Peninsula revealed Quaternary uplifted marine terraces and evidence for Holocene faulting. Both findings have severe implications for long-term tectonic activity and seismic hazards in the region of this seismic gap, portions of which are presently considered for off-shore hydrocarbon exploration and development. A critical analysis of th presently operating seimic data acquisition system reveals that a major change in remote sensing and central recording equipment is urgently needed for the Pavlof, Cold Bay, and Shumagin sections of the seismic array.

  18. Geoid height versus topography for oceanic plateaus and swells

    Science.gov (United States)

    Sandwell, David T.; Mackenzie, Kevin R.

    1989-01-01

    Gridded geoid height data (Marsh et al.l, 1986) and gridded bathymetry data (Van Wykhouse, 1973) are used to estimate the average compensation depths of 53 oceanic swells and plateaus. The relationship between geoid height and topography is examined using Airy and thermal compensation models. It is shown that geoid height is linearly related to topography between wavelengths of 400 and 4000 m as predicted by isostatic compensation models. The geoid/topography ratio is dependent on the average depth of compensation. The intermediate geoid/topography ratios of most thermal swells are interpreted as a linear combination of the decaying thermal swell signature and that of the persisting Airy-compensated volcanic edifice.

  19. Deep-crustal magma reservoirs beneath the Nicaraguan volcanic arc, revealed by 2-D and semi 3-D inversion of magnetotelluric data

    Science.gov (United States)

    Brasse, Heinrich; Schäfer, Anja; Díaz, Daniel; Alvarado, Guillermo E.; Muñoz, Angélica; Mütschard, Lutz

    2015-11-01

    A long-period magnetotelluric (MT) experiment was conducted in early 2009 in western Nicaragua to study the electrical resistivity and thus fluid/melt distribution at the Central American continental margin where the Cocos plate subducts beneath the Caribbean plate. Strike analysis yields a preference direction perpendicular to the profile, with moderate deviation from two-dimensionality, however. Two-dimensional modeling maps the sediments of the Nicaraguan Depression and a high-conductivity zone in the mid-crust, slightly offset from the arc. Further conductors are modeled in the backarc. However, these features are probably artifacts when a 2-D program is applied to data which show moderate 3-D characteristics. 3-D inversion clarifies the situation, and the major remaining conductive structure is now quasi directly beneath the volcanic chain and interpreted as a deep-seated magma deposit. Conductivity in the backarc is also relatively high and may either be caused by still existing partial melts beneath the Paleocene to Miocene volcanic arcs or by related metallic deposits in the aureoles of hydrothermal alteration.

  20. Early Devonian back-arc extension in the eastern Central Asian Orogenic Belt: Evidence from a bimodal volcanic sequence from Xilinhot, central Inner Mongolia (North China)

    Science.gov (United States)

    Liao, Wen; Xu, Bei; Wang, Yanyang; Zhao, Pan; Li, Qunsheng

    2017-08-01

    The Early Devonian bimodal volcanic sequence is firstly recognized in the Xilinhot area, central Inner Mongolia (North China). Zircon U-Pb dating of rhyolitic sample gives crystallization age of 407 ± 2 Ma, which is interpreted as the extrusive age of this bimodal volcanic sequence. Basaltic samples belong to tholeiite series whereas rhyolitic samples are peraluminous. Basaltic rocks show typical N-MORB-like REE and trace elemental patterns, with depletion of LREEs and negligible anomalies of Eu (δEu = 0.83-1.00). They have initial 87Sr/86Sr ratios ranging from 0.7077 to 0.7086, and positive εNd(t) values from +7.5to +9.0. By contrast, rhyolitic rocks show enrichment in LREEs and LILEs but depletion in HFSEs, with negative Eu anomalies (δEu = 0.58-0.68). They have negative εNd(t) values from -6.7 to -7.7 and TDM2 (Nd) values from 1695 to 1771 Ma. These elemental and isotopic data indicate that basaltic rocks were derived from a depleted mantle source with input of slab-derived fluids, whereas rhyolitic rocks might have been derived from remelting of Paleoproterozoic crustal materials. From our data and previous geological studies in this region, a back-arc setting was proposed for the Early Devonian bimodal volcanic rocks in the Xilinhot region. Subduction of the Paleo-Asian oceanic lithosphere caused opening of this back-arc basin and upwelling of mantle caused the formation of basalts and provided heat for remelting of crustal materials and formation of rhyolite.the

  1. Role of the Alboran Sea volcanic arc choking the Mediterranean to the Messinian salinity crisis and foundering biota diversification in North Africa and Southeast Iberia

    Science.gov (United States)

    Booth-Rea, Guillermo; Ranero, Cesar R.; Grevemer, Ingo

    2016-04-01

    The Mediterranean Sea desiccated ~5.96 million years ago when it became isolated from the world oceans during the Messinian salinity crisis. This event permitted the exchange of terrestrial biota between Africa and Iberia contributing to the present rich biodiversity of the Mediterranean region. The cause chocking the Mediterranean has been proposed to be tectonic uplift and dynamic topography but the driving mechanism still remains debated. We present a new wide-angle seismic profile that provides a detailed image of the thickness and seismic velocity distribution of the crust in the eastern Alboran basin. The velocity model shows a characteristic structure of a subduction-related volcanic arc with a high-velocity lower crust and a 16-18 km total-thickness igneous crust that magmatic accreted mostly between ~10-6 Ma across the eastern Alboran basin. Estimation of the isostatically corrected depth of the arc crust taking into account the original thermal structure and sediment-loading subsidence since 6 Ma places a large area of the eastern Alboran basin above sea level at the time. This estimation is supported by geophysical data showing subaereal erosional unconformities for that time. This model may explain several up-to-now-disputed features of the Messinian salinity crisis, including: the progressive isolation of the Mediterranean since 7.1 Ma with the disappearance of open marine taxa, the existence of evaporites mostly to the east of the volcanic arc, the evidence that the Gibraltar straits were not a land bridge offered by continuous Messinian open marine sediments at ODP site 976 in the western Alboran basin, the importance of southeastern Iberia and North Africa as centres of biota diversification since before the salinity crisis, and patterns of speciation irradiating from SE Iberia and the eastern Rif in some taxons.

  2. Geochemistry of the Ophiolite and Island-Arc Volcanic Rocks in the Mianxian-Lueyang Suture Zone,Southern Qinling and Their Tectonic Significance

    Institute of Scientific and Technical Information of China (English)

    1999-01-01

    Ultrabasic rocks in the Mianxian-Lueyang ophiolitic melange zone include harzburgite and dunite which exhibit LREE depletion with remarkable positive Eu anomaly.The diabase dike swarm shows LREE enrichment but slightly negative Eu anomaly.Metamorphosed volcanic rocks can be divided into two groups in terms of their REE geochemistry and trace element ratios of Ti/V,Th/Ta,Th/Yb and Ta/Yb.One is ths MORB-type basalt with LREE depletion,representing the fragments of oceanic crust and implying an association of the MORB-type ophiolite and an ancient ocean basin between the Qinling and Yangtze plates during the Middle Paleozoic-Early Mesozoic era.The oter comprises the island-arc volcanic rocks including tholeiitic basalt and a large amount of calc-alkaline intermediate-acic volcanic rock,which could not be the component of the ancient oceanic crust but the result of magmatism at the continental margin.This indicates that the Mianxian-Lueyang limited ocean basin had undergone a whole process of development,evolution and vanishing from Devonian-Cretaceous to Permian.And the Qinling area had becone an independent lithospheric microplate,on the southern side of which there were exhibited the tectonic characteristics of active continental margins during the Late Paleozoic-Early Mesozoic.That is to say.the Qinling cannot be simply considered as a result of collision between the Yangtze and North China plates.

  3. The Alboran volcanic arc archipelago isolated the Mediterranean during the Messinian salinity crisis forming the land bridge for biota dispersal across the western Mediterranean

    Science.gov (United States)

    Booth-Rea, Guillermo; Ranero, Cesar R.; Grevemeyer, Ingo

    2017-04-01

    The Mediterranean Sea desiccation during isolation from the world oceans created the well-known Messinian salinity crisis but also landbridges that permitted the exchange of terrestrial biota between Africa and Iberia contributing to the present biodiversity of the Mediterranean region. The hypotheses for the cause chocking the Mediterranean have typically sought to explain geological features, particularly the giant salt deposits, but the implications of the faunal changes occurring around that time remain inadequately integrated by current geological models. We present wide-angle seismic data that constrain for the first time the 16-18 km thick crust structure of a volcanic arc formed mostly between 10 to 6 Ma across the eastern region of the Alboran basin. The crustal structure supports that the arc created an archipelago forming a land bridge across the basin that largely isolated the Mediterranean. After the cessation of volcanic activity, the archipelago progressively submerged by thermal subsidence and accompanying sediment loading, having emerged islands that persisted into the Pleistocene time and shallow straits forming sills during the early Pliocene. The presence of an archipelago in the eastern region of the basin may explain a number of puzzling observations previously inexplicable by the proposed barriers closing the Gibraltar arc west of Alboran. The progressive volcanic build up of the archipelago together with the closure of the Betic and Rifean marine corridors would explain the initial isolation of the Mediterranean since 7.1 Ma and the exchange of terrestrial biota since 6.2 Ma, i.e. before desiccation, which diversified radiating from SE Iberia and the opposite segment of the eastern Rif. In addition, an eastern barrier agrees with the continuous Messinian-age open marine sediments drilled at ODP site 976 in the western Alboran basin, which may have been the refuge of typical Mediterranean taxa that rapidly repopulated the Mediterranean in the

  4. Recording the transition from flare-up to steady-state arc magmatism at the Purico-Chascon volcanic complex, northern Chile

    Science.gov (United States)

    Burns, Dale H.; de Silva, Shanaka L.; Tepley, Frank; Schmitt, Axel K.; Loewen, Matthew W.

    2015-07-01

    The long-term evolution of continental magmatic arcs is episodic, where a few transient events of high magmatic flux or flare-ups punctuate the low-flux magmatism or "steady state" that makes up most of the arc history. How this duality manifests in terms of differences in crustal architecture, magma dynamics and chemistry, and the time scale over which transitions occur is poorly known. Herein we use multiscale geochemical and isotopic characteristics coupled with geothermobarometry at the Purico-Chascon Volcanic Complex (PCVC) in the Central Andes to identify a transition from flare-up to steady state arc magmatism over ∼800 kyr during which significant changes in upper crustal magmatic dynamics are recorded. The PCVC is one of the youngest volcanic centers related to a 10-1 Ma ignimbrite flare-up in the Altiplano-Puna Volcanic Complex of the Central Andes. Activity at the PCVC initiated 0.98 ± 0.03 Ma with the eruption of a large 80-100 km3 crystal-rich dacite ignimbrite. High, restricted 87Sr/86Sr isotope ratios between 0.7085 and 0.7090 in the bulk rock and plagioclase crystals from the Purico ignimbrite, combined with mineral chemistry and phase relationships indicate the dacite magma accumulated and evolved at relatively low temperatures around 800-850 °C in the upper crust at 4-8 km depth. Minor andesite pumice erupted late in the ignimbrite sequence records a second higher temperature (965 °C), higher pressure environment (17-20 km), but with similar restricted radiogenic bulk rock 87Sr/86Sr = 0.7089-0.7091 to the dacites. The compositional and isotopic characteristics of the Purico ignimbrite implicate an extensive zone of upper crustal mixing, assimilation, storage and homogenization (MASH) between ∼30 and 4 km beneath the PCVC ∼1 Ma. The final eruptions at the PCVC environments; an upper crustal environment identical to that recorded in the Purico ignimbrite, and a second deeper, ∼15-20 km depth, higher temperature (∼922-1001

  5. Characterization of geothermal paleosystem in the Lesser Antilles volcanic arc: structural, petrographic, thermodynamic and petrophysics analysis of Terre-de-Haut (Les Saintes archipelago, Lesser Antilles)

    Science.gov (United States)

    Favier, Alexiane; Navelot, Vivien; Verati, Chrystèle; Lardeaux, Jean-Marc; Corsini, Michel; Diraison, Marc; Géraud, Yves; Mercier de Lépinay, Jeanne; Munschy, Marc

    2017-04-01

    This survey takes part in the GEOTREF project (high enthalpy geothermal energy in fractured reservoirs), supported by the French government program "Investments for the future". The program focuses on the exploration of geothermal resource in the Lesser Antilles volcanic arc. An exclusive license has been issued in the Vieux-Habitants area (Basse-Terre, Guadeloupe) to carry on the development of high-temperature geothermal energy in this active volcanic region. The deep geothermal reservoir on the Basse-Terre island could be characterized in exhumed paleosystems. The reference paleosystem in the Guadeloupe archipelago is located in Terre-de-Haut. Four major fault directions have been highlighted N000-N020, N050-N070, N090-N110 and N130-N140. Field observations emphasize three major cleavage directions overlaying the fault systems: N035-N060, N080-N110, N145-N165. Volcanic rocks affected by cleavage display several metamorphic transformation grades. The more transformed calc-alkaline rocks are located at the intersection of several cleavage directions. Mineralogical transformations due to metamorphism and surimposed fractures are also responsible for strong changes of petrophysical properties. In comparison with the reference protolith of andesitic lava flows outcropping in Vieux-Habitants, which have porosity and permeability lower than 5 % and 10-15 m2, andesites of Terre-de-Haut have better reservoir properties with connected porosity and permeability higher than 15 % and 10-14-10-15 m2 respectively. Thermodynamic modelling based on petrography and chemical composition of the most transformed rocks highlights a steady state mineral assemblage between 0.25 - 1.5 kbar and 350 - 450 ˚ C. It corresponds to a geothermal gradient higher than 120 to 150˚ C/km. This is consistent with temperatures measured in Bouillante wells. However, this geothermal gradient is notably higher to a usual volcanic arc conductive gradient estimated to 70-100˚ C/km. It can be explained

  6. Remelting of Neoproterozoic relict volcanic arcs in the Middle Jurassic: Implication for the formation of the Dexing porphyry copper deposit, Southeastern China

    Science.gov (United States)

    Liu, Xuan; Fan, Hong-Rui; Santosh, M.; Hu, Fang-Fang; Yang, Kui-Feng; Li, Qiu-Li; Yang, Yue-Heng; Liu, Yongsheng

    2012-10-01

    The Dexing copper deposit in southeastern China is a typical non-arc porphyry deposit, the origin of which has been a topic of debate for several decades. Here we present new results from U-Pb geochronology, whole-rock chemistry and Sr-Nd-Hf-O isotopic investigations on the ore-forming granodioritic porphyry. LA-ICPMS zircon U-Pb data suggest that the granodioritic porphyry was formed in the Middle Jurassic (ca. 172.5 Ma) probably associated with lithospheric thinning driven by either sub-continental lithospheric mantle delamination or asthenospheric upwelling. The porphyry displays both arc-like and adakitic trace element signatures. The adakitic features suggest that HREE (heavy rare earth elements)-rich minerals such as garnet and hornblende, in the absence of plagioclase resided in the source region. The arc-like signatures are broadly comparable with those of the proximal Neoproterozoic island arc rocks including the keratophyre from Shuangxiwu Group and associated granitoids indicating a potential genetic relationship. The porphyry has chondritic ɛNd(t) of - 0.28 to 0.25 and radiogenic ɛHf(t) of 2 to 7, and correspondingly, uniform two stage depleted mantle Nd model ages of 940-980 Ma and Hf model ages of 800-1100 Ma (mean ~ 920 Ma). On Nd and Hf isotopic evolution diagrams, these values are markedly similar to those of the adjacent Neoproterozoic arc rocks when calculated forward to the Mid-Jurassic. Zircons of the porphyry show mantle-like oxygen isotope characters with δ18O values clustering in the range of 4.7-5.9‰, similar to the values for the Neoproterozoic arc rocks mentioned above. The geochemical and isotopic features recorded in our study suggest mantle-derived magmas with no significant supracrustal input for the source of the porphyry. With regard to the source of the Cu ore, we consider a model involving the remelting of sulfide-bearing arc-related lower crustal source. Furthermore, the occurrence of a Neoproterozoic VMS (volcanic massive

  7. Geochemistry and zircon U-Pb-Hf isotopes of Early Paleozoic arc-related volcanic rocks in Sonid Zuoqi, Inner Mongolia: Implications for the tectonic evolution of the southeastern Central Asian Orogenic Belt

    Science.gov (United States)

    Chen, Yan; Zhang, Zhicheng; Li, Ke; Yu, Haifei; Wu, Tairan

    2016-11-01

    An Early Paleozoic acid volcanic sequence has been recently detected southeast of Sonid Zuoqi in central Inner Mongolia to constrain the tectonic evolution of the Central Asian Orogenic Belt in this area. First, the volcanic rocks have zircon U-Pb ages of 439-445 Ma. They are characterized by (a) a high silica content, moderate alkali content and low iron content; (b) enrichment in light rare earth elements, depletion of heavy rare earth elements, and negative Eu anomalies; and (c) negative Nb, Ta, and Ti anomalies. Finally, the volcanic samples yield εHf(t) values of - 4.7 to + 9.2 with TDM2 ages of 835-1724 Ma. For petrogenesis, they were possibly arc derived, from predominant juvenile materials with subordinate ancient continental crust. Combined with previous studies, the Early Paleozoic Sonid Zuoqi arc magmatism can be divided into three stages: a primitive arc stage represented by 464-490 Ma low-K, calcic granitoids; a normal continental arc stage represented by 439-445 Ma medium-K, calcic to calcic-alkalic plutons and volcanic rocks and a syn-collisional stage represented by 423-424 Ma high-K granites. Furthermore, the timing and tectonic settings of the above magmatic rocks show similarities to those in Xilinhot and other areas of the northern Early to Mid-Paleozoic orogenic belt (NOB), although the rock assemblies and their proportions vary more or less in different areas. Accordingly, the NOB that formed on this arc was probably attributed to the northward subduction of the Paleo-Asian Ocean beginning at 500 Ma, which experienced this type of arc development and was terminated by a soft collision before the Late Devonian.

  8. Volcanic rock-hosted gold and base-metal mineralization associated with neoproterozoic-early Paleozoic back-arc extension in the Carolina terrane, southern Appalachian Piedmont

    Energy Technology Data Exchange (ETDEWEB)

    Feiss, P.G. (Univ. of North Carolina, Chapel Hill (United States)); Vance, R.K. (Georgia Southern Univ., Statesboro (United States)); Wesolowski, D.J. (Oak Ridge National Lab., TN (United States))

    1993-05-01

    Volcanogenic mineral deposits in the Carolina terrane, southern Appalachian Piedmont, include Kuroko-type polymetallic massive sulfide deposits and disseminated gold-pyrite deposits associated with propylitic, silicic, argillic, and advanced argillic alteration. Host rocks are metavolcaniclastic and metaepiclastic rocks of a Neoproterozoic-Early Cambrian magmatic arc. The favorable gold horizon is the transition from a lower succession of andesitic and rhyolitic pyroelastic rocks with basal mafic lavas to an upper sequence of epiclastic sedimentary units and minor lava and ash flows. Kuroko-type deposits are associated with mafic to bimodal volcanic rocks in the upper sequence. Whole-rock oxygen isotope analyses indicate that gold mineralization is associated with a transition from hydrothermal systems dominated by isotopically relatively light ([delta][sup 18]O = -6% to -10%) waters, typical of high-latitude subaerial systems, to seawater ([delta][sup 18]O = 0%). Plots of [delta][sup 18]O vs. SiO[sub 2] of the host rocks show a compositional gap associated with mineralization at the subaerial to submarine transition. Values of [delta][sup 18]O for the hydrothermal waters, lithostratigraphic analyses, and tectonic models of the Carolina terrane demonstrate that mineralization coincided with extension in a rifted arc. 34 refs., 3 figs.

  9. Recognizing subtle evidence for silicic magma derivation from petrochemically-similar arc crust: Isotopic and chemical evidence for the bimodal volcanic series of Gorely Volcanic Center, Kamchatka, Russia

    Science.gov (United States)

    Seligman, A. N.; Bindeman, I. N.; Ellis, B. S.; Ponomareva, V.; Leonov, V.

    2012-12-01

    The Kamchatka Peninsula is home to some of the most prolific subduction related volcanic activity in the world. Gorely caldera and its central volcano are located in the rear of its currently active Eastern Volcanic Front. Recent work determined the presence of explosive ignimbrite eruptions sourced from Gorely volcano during the Pleistocene. We studied 32 eruptive units, including tephrochronologically-dated Holocene tephra, stratigraphically-arranged ignimbrites, as well as pre- and post-caldera lavas. We analyzed oxygen isotope ratios of pyroxene and plagioclase grains by laser fluorination, and major and trace element compositions of whole rocks. In addition, we determined 87Sr/86Sr and 143Nd/144Nd ratios of caldera-forming ignimbrite eruptions. Chemical compositions show that Gorely eruptive units range from basalt to basaltic andesite in the "Pra-Gorely" stages prior to caldera formation and the modern Gorely stages forming its current edifice. In contrast, eruptive material from earlier ignimbrites exposed at Opasny Ravine consists primarily of dacite. Whole rock analyses for Gorely indicate that silicic rocks and ignimbrites volumetrically dominate all other products, forming separate bimodal peaks in our SiO2-frequency diagram. In addition, trace element concentrations and ratios define two trends, one for more silicic and another for more mafic material. δ18Omelt values range from a low of 4.85 up to 6.22‰, where the lowest value was found in the last caldera forming eruption, suggesting incorporation of hydrothermally-altered material from earlier eruptions. 87Sr/86Sr and 143Nd/144Nd ratios range from 0.70328 to 0.70351 and from 0.51303 to 0.51309 respectively, with higher and more diverse values being characteristic of earlier ignimbrite units; again suggesting incorporation of surrounding crustal material. In contrast to these results, MELTS modeling using a variety of likely primitive basalts from Gorely shows it is possible to obtain silicic

  10. The pre-Kos Plateau Tuff Volcanic Rocks on Kefalos Peninsula (Kos Island, Dodecanese, Greece): Crescendo to the Largest Eruption of the Modern Aegean Arc

    Science.gov (United States)

    Bachmann, O.; Schnyder, C.

    2006-12-01

    Young volcanic rocks (K-Ar ages of 3 to 0.5 Ma) from the Kefalos Peninsula (Kos Island, Dodecanese, Greece) erupted prior to the voluminous (>60 km\\ 3) Kos Plateau Tuff (KPT; Ar-Ar age of 0.16 Ma) were studied in order to better define the conditions that led to the paroxysmal eruption of the modern Aegean Arc. Two different whole-rock compositions were sampled on Kefalos peninsula; dacites (63-65 wt% SiO2) and rhyolites (75-77 wt% SiO2). Kefalos dacites are crystal-rich (>40% crystals), show high Sr-Ba contents compared to other continental arcs, and have "adakitic" Sr/Y ratios (>40). Kefalos rhyolites are typical high- SiO2 arc magmas, similar in composition and mineralogy to the KPT, but displaying lower crystallinities (30% in most of the KPT). The high Sr/Y ratios of the dacites is surprising in an area where the subducting slab is not particularly hot and the continental crust relatively thin (~30 km). If the low Y and high Sr-Ba contents result from the fact that magma formed deep enough to supress plagioclase and have garnet present, dacite magma generation must have occurred in the mantle. There is geochemical and mineralogical evidence for the Kefalos and KPT rhyolites being generated by fractional crystallization from magmas similar to the Kefalos dacites. However, the few distinctions between KPT and Kefalos rhyolites (KPT is more voluminous, contains more crystals, has lower whole-rock U and Th contents, and lower MgO-SiO2, but higher Al2O3-FeOtot in biotite) suggest slightly different conditions in the magma chambers. These observations, together with increasing explosivity of the volcanic products from ~3 Ma to 0.16 Ma, may indicate that the build-up to the large KPT eruption could be the result of an increase in magmatic water input in the system through time.

  11. Backarc rifting, constructional volcanism and nascent disorganised spreading in the southern Havre Trough backarc rifts (SW Pacific)

    Science.gov (United States)

    Wysoczanski, R. J.; Todd, E.; Wright, I. C.; Leybourne, M. I.; Hergt, J. M.; Adam, C.; Mackay, K.

    2010-02-01

    High resolution multibeam (EM300 and SEABEAM) data of the Southern Havre Trough (SHT), combined with observations and sample collections from the submersible Shinkai6500 and deep-tow camera, are used to develop a model for the evolution and magmatism of this backarc system. The Havre Trough and the associated Kermadec Arc are the product of westward subduction at the Pacific-Australian plate boundary. Detailed studies focus on newly discovered features including a seamount (Saito Seamount) and a deep graben (Ngatoroirangi Rift, > 4000 m water depth floored with a constructional axial volcanic ridge > 5 km in length and in excess of 200 m high), both of which are characterised by pillow and lobate flows estimated at Mass balance modelling indicates a maximum crustal thickness of ~ 11 km to magmatism within deep SHT rifts, we propose that the SHT is in an incipient phase of distributed and "disorganised" oceanic crustal accretion in multiple, ephemeral, and short but deep (> 4000 m) spreading systems. These discontinuous spreading systems are characterised by failed rifts, rift segmentation, and propagation. Successive episodes of magmatic intrusion into thinned faulted arc basement results in defocused asymmetrical accretion. Cross-arc volcanic chains, isolated volcanoes and underlying basement plateaus are interpreted to represent a "cap" of recent extrusives. However, they may also be composed entirely of newly accreted crust and the spatially extensive basement fabric of elongated volcanic ridges may be the surface expression of pervasive dike intrusion that has thoroughly penetrated and essentially replaced the original arc crust with newly accreted intrusives.

  12. Late Cretaceous Arc Initiation on the Edge of an Oceanic Plateau (Southern Central America)

    Science.gov (United States)

    Buchs, D. M.; Baumgartner, P. O.; Arculus, R.

    2007-12-01

    The Caribbean Plate comprises one or several late Cretaceous oceanic plateaus imbricated between the Northern and Southern Americas. Uplifted portions of plateau(s) along plate boundaries have been recognized in many sites, including that underlying the south Central American Volcanic Arc. We provide new constraints for the role of the plateau in the evolution of this arc obtained by mapping of the uplifted forearc area between southern Costa Rica and western Panama. An oceanic plateau, accreted seamounts and arc rocks were identified, and a new tectono-stratigraphy defined. The arc basement is composed of a Coniacian oceanic plateau. In the outer margin, late Cretaceous-Eocene accreted seamounts are in contact with the plateau along tectonic mélanges and active faults. Campanian-Maastrichtian primitive arc rocks are found 40-110 km to the trench on the top of -or as dykes within- the plateau. The location of these rocks correlates to previous observations and indicates that the arc front migrated away from the trench during the late Cretaceous, potentially in response to subduction erosion or slab flattening [Lissinna et al., EGU 2006]. The first island arc lavas were deposited under sea level, over a broad area. They were quickly followed by more evolved intrusives and lavas, which were emplaced along a volcanic front during the late Cretaceous-Paleocene. Detrital and volcanic records along the Central American isthmus indicate that a continuous volcanic arc extended between eastern Panama and northern Costa Rica in this time. In southern Costa Rica (Golfito complex) and western Panama (Sona-Azuero-Coiba complex), the oceanic plateau consists mainly of pillowed and massive low Fe (tholeiitic) basalts. These rocks have a highly consistent geochemistry characterized by flat, primitive upper mantle-normalized incompatible element patterns with low Pb and high Nb-Ti contents. Primitive arc igneous samples are low-medium Fe basalts to trachyandesites found as pillow

  13. 天山石炭纪火山岩系中含有富Nb岛弧玄武岩吗?%Do the Tianshan Carboniferous volcanic successions contain Nb-enriched arc basalts?

    Institute of Scientific and Technical Information of China (English)

    夏林圻; 夏祖春; 徐学义; 李向民; 马中平

    2009-01-01

    中国西北部天山石炭纪-早二叠世裂谷火山作用代表了一个新近被认可的大火成岩省.有人认为,在天山石炭纪火山岩系中发育有富Nb岛弧玄武岩、埃达克岩和高镁安山岩组合.然而,该岩石组合具有与典型富Nb岛弧玄武岩、埃达克岩和高镁安山岩不同的化学和同位素特点,表明其并非是岛弧岩石组合.这一推断的岛弧岩石组合实际上是大陆板内火山岩组合,由未遭受地壳混染、受到地壳轻微混染和遭受地壳强烈混染的大陆火山岩组成.%The Tianshan Carboniferous-Early Permian rift-related volcanism in northwestern China represents a newly recognized large igneous province. It has been deemed that an assemblage of Nb-enriched arc basalt, adakite and high-Mg andesite occurred in the Tianshan Carboniferous volcanic successions. Divergent chemical and isotopic characteristics between this rock assemblage and the typical Nb-enriched arc basalts, adakites and high-Mg andesites reveal that the former is not arc related. This postulated arc-related assemblage is indeed an intracontinental volcanic assemblage that consists of crustally uncontaminated, less-contaminated and strongly contaminated continental volcanic rocks.

  14. Periodicities in sediment temperature time-series at a marine shallow water hydrothermal vent in Milos Island (Aegean Volcanic arc, Eastern Mediterranean)

    Science.gov (United States)

    Aliani, Stefano; Meloni, Roberto; Dando, Paul R.

    2004-05-01

    Time-series data sets of total bottom pressure (tidal plus atmospheric), seawater temperature and sediment temperature from a marine shallow hydrothermal vent (Milos, Hellenic Volcanic Arc, Aegean Sea) were studied to determine factors influencing periodicity at the vents. Bottom pressure and vent temperature were mainly opposite in phase, with the main fluctuations of vent temperature occurring at tidal frequencies. Although the fluctuations in atmospheric pressure were of the same order as those due to tidal pressure, the contribution of atmospheric pressure was considerably weaker at diurnal frequencies. Some sudden discontinuities in sediment temperature were recorded, at least one of these may have been caused by seismic events. Seawater temperature changes were not reflected in the sediment temperature record. Transient loadings, such as tidal loadings, barometric pressure and earth tides, may affect the pore pressure in sediments, influencing fluid expulsion and sediment temperature as a consequence. Most of the contribution to the fluctuations in sediment temperature depends on tidal loadings. Gravitational forces, in the form of earth tides, can also be involved and barometric pressure is probably responsible for long period temperature oscillations.

  15. Constraints on the origin and evolution of magmas in the Payún Matrú Volcanic Field, Quaternary Andean back-arc of western Argentina

    DEFF Research Database (Denmark)

    Hernadno, I R; Aragón, E; Frei, Robert

    2014-01-01

    and Sr–Nd isotopic compositions of the basaltic lavas and Payún Matrú rocks indicate that the trachytes of Payún Matrú are the result of fractional crystallization of basaltic parent magmas without significant upper crustal contamination, and that the basalts have a geochemical similarity to ocean island...... basalt (La/Nb = 0·8–1·5, La/Ba = 0·05–0·08). The Sr–Nd isotopic compositions of the basaltic to trachytic rocks range between 0·703813 and 0·703841 (87Sr/86Sr) and 0·512743 and 0·512834 (143Nd/144Nd). Mass-balance and Rayleigh fractionation models support the proposed origin of the trachytes...... that the basaltic lavas originated in the asthenospheric mantle, probably within the spinel stability field and beneath an attenuated continental lithosphere in the back-arc area. The lack of a slab-fluid signature in the Payún Matrú Volcanic Field rocks, along with unpublished and published geophysical results...

  16. High resolution seismic data coupled to Multibeam bathymetry of Stromboli island collected in the frame of the Stromboli geophysical experiment: implications with the marine geophysics and volcanology of the Aeolian Arc volcanic complex (Sicily, Southern Tyrrhenian sea, Italy).

    Science.gov (United States)

    Aiello, Gemma; Di Fiore, Vincenzo; Marsella, Ennio; Passaro, Salvatore

    2014-01-01

    New high resolution seismic data (Subbottom Chirp) coupled to high resolution Multibeam bathymetry collected in the frame of the Stromboli geophysical experiment aimed at recording active seismic data and tomography of the Stromboli Island are here presented. The Stromboli geophysical experiment has been already carried out based on onshore and offshore data acquisition in order to investigate the deep structure and the location of the magma chambers of the Stromboli volcano. A new detailed swath bathymetry of Stromboli Island is here shown and discussed to reconstruct an up-to-date morpho-bathymetry and marine geology of the area compared to the volcanologic setting of the Aeolian Arc volcanic complex. Due to its high resolution the new Digital Terrain Model of the Stromboli Island gives interesting information about the submerged structure of the volcano, particularly about the volcano-tectonic and gravitational processes involving the submarine flanks of the edifice. Several seismic units have been identified based on the geologic interpretation of Subbottom Chirp profiles recorded around the volcanic edifice and interpreted as volcanic acoustic basement pertaining to the volcano and overlying slide chaotic bodies emplaced during its complex volcano-tectonic evolution. They are related to the eruptive activity of Stromboli, mainly poliphasic and to regional geological processes involving the intriguing geology of the Aeolian Arc, a volcanic area still in activity and needing improved research interest.

  17. Subduction controls on Miocene back-arc lavas from Sierra de Huantraico and La Matancilla and new 40Ar/39Ar dating from the Mendoza Region, Argentina

    Science.gov (United States)

    Dyhr, Charlotte T.; Holm, Paul M.; Llambías, Eduardo J.; Scherstén, Anders

    2013-10-01

    Back-arc volcanism in the western Argentinian provinces of Mendoza and Neuquén has been widespread from the Miocene to historic times. We present a detailed investigation of profiles through two of the major Miocene volcanic areas of the region, the neighboring Huantraico and La Matancilla plateaus, including new 40Ar/39Ar age results of major and trace elements as well as Nd, Sr and Pb isotopic data. Four million years of eruptions from 24.4 ± 0.3 Ma (2σ) of alkali olivine basalts with OIB-type incompatible trace element enrichments at La Matancilla (~ 36.50°S) provide evidence for the presence of back-arc mantle devoid of subduction-related components. In contrast, the lower Huantraico lavas (~ 37.30°S) require an atypical back-arc mantle, almost devoid of arc-like components (e.g. low La/Ta = 15-18 and Ba/La = 12-18), but with a more depleted isotopic signature (e.g. 87Sr/86Sr, 0.7033-0.7037) than observed elsewhere in the Andean back-arc. The Lower to Upper Series development in the Huantraico sequence represents a gradual change from basaltic to trachyandesitic back-arc lavas with a weak but temporally increasing arc geochemical signature (e.g. La/Ta = 15-21; Ba/La = 12-45), which is accompanied by Sr, Nd and Pb isotopic compositions approaching present day values of the Andes arc. The compositional change is accompanied by a gradually decreasing role for garnet in the mantle source, a decreasing degree of melting, but also simultaneously increasing influence from subducted fluids, probably as the slab geometry changes through time. The volcanism at Huantraico ceased when a flat slab was established around 15 Ma.

  18. From oceanic plateaus to allochthonous terranes: Numerical modelling

    NARCIS (Netherlands)

    Vogt, Katharina; Gerya, Taras

    2014-01-01

    Large segments of the continental crust are known to have formed through the amalgamation of oceanic plateaus and continental fragments. However, mechanisms responsible for terrane accretion remain poorly understood. We have therefore analysed the interactions of oceanic plateaus with the leading ed

  19. Hydrous basalt-limestone interaction at crustal conditions: Implications for generation of ultracalcic melts and outflux of CO2 at volcanic arcs

    Science.gov (United States)

    Carter, Laura B.; Dasgupta, Rajdeep

    2015-10-01

    High degassing rates for some volcanoes, typically in continental arcs, (e.g., Colli Albani Volcanic District, Etna, Vesuvius, Italy; Merapi, Indonesia; Popocatepetl, Mexico) are thought to be influenced by magma-carbonate interaction in the crust. In order to constrain the nature of reaction and extent of carbonate breakdown, we simulated basalt-limestone wall-rock interactions at 0.5-1.0 GPa, 1100-1200 °C using a piston cylinder and equal mass fractions of calcite (CaCO3) and a hydrous (∼4 wt.% H2O) basalt in a layered geometry contained in AuPd capsules. All experiments produce melt + fluid + calcite ± clinopyroxene ± plagioclase ± calcic-scapolite ± spinel. With increasing T, plagioclase is progressively replaced by scapolite, clinopyroxene becomes CaTs-rich, and fluid proportion, as inferred from vesicle population, increases. At 1.0 GPa, 1200 °C our hydrous basalt is superliquidus, whereas in the presence of calcite, the experiment produces calcite + clinopyroxene + scapolite + melt. With the consumption of calcite with increasing T and decreasing P, melt, on a volatile-free basis, becomes silica-poor (58.1 wt.% at 1.0 GPa, 1100 °C to 34.9 wt.% at 0.5 GPa, 1200 °C) and CaO-rich (6.7 wt.% at 1.0 GPa, 1100 °C to 43.7 wt.% at 0.5 GPa, 1200 °C), whereas Al2O3 drops (e.g., 19.7 at 1100 °C to 12.8 wt.% at 1200 °C at 1.0 GPa) as clinopyroxene becomes more CaTs-rich. High T or low P melt compositions are 'ultracalcic,' potentially presenting a new hypothesis for the origin of ultracalcic melt inclusions in arc lava olivines. Wall-rock calcite consumption is observed to increase with increasing T and decreasing P. At 0.5 GPa, our experiments yield carbonate assimilation from 21.6 to 47.6% between 1100 and 1200 °C. Using measured CO2 outflux rates for Mts. Vesuvius, Merapi, Etna and Popocatepetl over a T variation of 1100 to 1200 °C at 0.5 GPa, we calculate 6-92% of magmatic input estimates undergo this extent of assimilation, suggesting that up to ∼3

  20. Felsic Magmatism through Intracrustal Melting of Previously Formed Volcanic-Arc Crust: Implications for Differentiation and Secular Evolution of the Continental Crust

    Science.gov (United States)

    G R, R. K.; C, S.

    2015-12-01

    The fundamental challenge in understanding the origin and evolution of the continental crust is to recognize how primary mantle source, and oceanic crust, which are essentially mafic to ultramafic in composition, could differentiate into a more or less felsic compositions. It is possible to understand growth and differentiation of the continental crust by constraining the interplay of magmatism, deformation, and high-grade metamorphism in the lower crust. Here, we apply this knowledge on the lower crustal granitoids of southern India and speculate on the variations in geochemistry as a consequence of differentiation and secular evolution of the continental crust.The major groups of granitoids of southern India are classified as metatonalites, comparable to typical Archaean TTGs with pronounced calc-alkaline affinity, and metagranites which are magmatic fractionation produced by reworking of early crust. Metatonalites are sodic-trondhjemites with slightly magnesian, moderate LREE (average LaN = 103) and low HREE (average YbN = 2) characerestics, where as metagranites are calc-alkaline ferroan types with enriched LREE (average LaN = 427) and HREE (average YbN = 23). Petrogenetic characteristics of granitoids illustrate continuous evolution of a primary crust into diverse magmatic units by multiple stages of intracrustal differentiation processes attributed to following tectonic scenarios: (1) formation of tonalitic magma by low- to moderate-degree partial melting of hydrated basaltic crust at pressures high enough to stabilize garnet-amphibole residue and (2) genesis of granite in a continental arc-accretion setting by an episode of crustal remelting of the tonalitic crust, within plagioclase stability field. The first-stage formed in a flat-subduction setting of an volcanic-arc, leading to the formation of tonalites. The heat budget required is ascribed to the upwelling of the mantle and/or basaltic underplating. Progressive decline in mantle potential temperature

  1. Recent crustal foundering in the Northern Volcanic Zone of the Andean arc: Petrological insights from the roots of a modern subduction zone

    Science.gov (United States)

    Bloch, Elias; Ibañez-Mejia, Mauricio; Murray, Kendra; Vervoort, Jeffrey; Müntener, Othmar

    2017-10-01

    Periodic loss of the lower lithosphere into the convecting mantle due to gravitational instability is postulated to be a major mechanism for lithosphere recycling in orogenic zones, but unequivocal petrologic evidence of this process is elusive. The Granatifera Tuff, located in the Mercaderes-Rio Mayo area of the southern Colombian Andes, contains a wide variety of crustal and mantle xenoliths. Here we focus on the thermobarometry and Lu-Hf isotope systematics of crustal garnet clinopyroxenite xenoliths, the results of which offer the first evidence of recent, and likely active, crustal foundering in the Northern Volcanic Zone of the Andean arc. We find that most of these xenoliths equilibrated between 60-80 km depths, ∼7-27 km below the seismically determined Moho in this region, and that at least one crustal garnet clinopyroxenite re-equilibrated at depths exceeding 95 km. A second garnet clinopyroxenite equilibrated at ∼150 km depths, and is either foundered lithospheric material or the product of reaction between peridotite and a mobile component (either silicic melt or fluids) at >4 GPa. All of the investigated garnet clinopyroxenites are negatively buoyant relative to the upper mantle asthenosphere. The presence of minor amounts of secondary amphibole and orthopyroxene, coupled with the lack of major-element retrograde zonation in primary phases within these xenoliths, indicates that these rocks were rapidly transported to, and briefly resided at, shallow depths before eruption. Lu-Hf ages from two garnet clinopyroxenites and one garnet-clinopyroxene hornblendite are material, which the Mercaderes xenoliths document, without catastrophic removal of the crustal root.

  2. Evidence for Slab Melt Contributions to the Mexican Volcanic Belt and Other Young Hot Slab Arcs from Lu-Hf Isotopes

    Science.gov (United States)

    Goldstein, S. L.; Cai, Y. M.; Langmuir, C. H.; Lagatta, A.; Straub, S. M.; Gomez-Tuena, A.; Martin Del Pozzo, A.

    2007-12-01

    Despite major advances in delineating the processes that govern magma generation at convergent margins, the problem persists of distinguishing slab, mantle wedge, and crustal contributions. A corrollary question is whether there is significant melting of subducted ocean crust. Especially in thick crust regions, the importance of crustal versus mantle contributions to lavas represents a long-standing fundamental issue in arc magma geochemistry. We show that frontal arc magmas from the Central Mexican Volcanic Belt (CMVB), including the large andesitic stratovolcanoes Popocatepetl and Nevado de Toluca, display negligible crustal contamination, and contain substantial contributions from melting of subducted Pacific ocean crust. Despite ca. 50 km thick continental crust, the CMVB erupts near primitive lavas including "high-Nb" alkaline basalts that show negligible "subduction signatures" in their trace element patterns. These "high-Nb" basalts define the regional mantle wedge composition in isotope-trace element space. The "normal" calcalkaline lavas form a negative correlation between Hf isotopes and Lu/Hf. One endmember is like the high Nb basalts representing the regional mantle wedge. The other endmember has higher Hf isotopes (approaching values of Pacific MORB) and very low Lu/Hf of less than 0.04 (e.g. compared to typical values of ca. 0.2 in Pacific MORB). The low Lu/Hf values require low degree partial melting of a source rich in garnet. The high Hf isotopes require a depleted mantle source with isotopes like Pacific MORB. Together the Lu-Hf data indicate a substantial component derived from melting of eclogitic Pacific ocean crust. A key feature of the data is that the stratovolcano lavas showing the largest slab melt signature also show the highest Hf isotope ratios and thus are more "depleted mantle-like" than the regional mantle wedge. Thus, the integrated data allow us to clearly distinguish between mantle and crustal sources in the CMVB and point to

  3. Evolution of Eocene to Oligocene arc-related volcanism in the North Patagonian Andes (39-41°S), prior to the break-up of the Farallon plate

    Science.gov (United States)

    Iannelli, Sofía B.; Litvak, Vanesa D.; Fernández Paz, Lucía; Folguera, Andrés; Ramos, Miguel E.; Ramos, Víctor A.

    2017-01-01

    Voluminous Paleogene magmatic rocks (44 to 29 Ma) are found in a retroarc position in the Northern Patagonian to Southern Central Andes ( 39-42°S), whose origin remains controversial. Geochemical data in these Eocene to Oligocene volcanic associations are herein used to unravel their origin and understand changes in subduction parameters. Geochemical signatures indicate arc-related associations and reflect changing geodynamic boundary conditions of the Andean margin through time. In particular, Eocene magmatism ( 44 Ma; Pilcaniyeu Belt) shows an alkaline-like signature and limited slab influence. Reported contemporaneous within-plate magmatism ( 47-43 Ma) in an easternmost position reflects a more typical enriched source. Oligocene arc-like volcanism ( 29 Ma; El Maitén Belt), which developed in an extensional retroarc setting, shows a higher contribution from slab-derived fluids and a calc-alkaline source. A comparison with younger arc-related magmas from the region ( 26-20 Ma), emplaced in an intra- to retroarc position (Cura Mallín and Abanico basins), indicates a progressive increase in slab-signature, associated with a tholeiitic magma source. We propose that these compositional variations could be directly related to changes in plate configuration before and after the Farallon plate break-up and the initiation of a more orthogonal convergence typical of the present Andean-type subduction zone.

  4. New Insights Into Volcanic Hazards in Western Mexico: Multiple Cone-Building Episodes at Arc Stratovolcanoes Revealed by 40Ar/39Ar Geochronology

    Science.gov (United States)

    Frey, H. M.; Lewis-Kenedi, K.; Lange, R. A.; Hall, C. M.; Delgado-Granados, H.

    2003-12-01

    The detailed eruptive histories of two andesitic stratocones, Volcáns Ceboruco and Tequila, in the western Mexican arc have been documented using 40Ar/39Ar geochronology. The volumes of these volcanoes were obtained with mapping, airphotos, and digital elevation models. The age and volume data constrain the rate and duration of major cone-building events, which bears on the longevity of the underlying upper-crustal magma chambers that fed the eruptions. The results indicate that at each stratovolcano there were two discrete cone-building events, separated by a hiatus. At V. Tequila, six samples from the edifice yielded dates (196 +/- 8, 196 +/- 19, 178 +/- 8, 191 +/- 13, 216 +/- 11, and 198 +/- 11 ka; errors are 1 sigma) with a mean eruption age of 196 +/- 12 ka. Thus the bulk of the main edifice ( ˜31 km3) erupted within 24 kyrs (at the 2 sigma level), leading to a cone-building rate of > 1.3 km3/kyr. After a hiatus of ˜110 kyrs, ˜14 km3 of andesite erupted along the NW and SE flanks of V. Tequila at 90 +/- 19 ka. The last activity at V. Tequila produced a ˜2 km3 parasitic cone at ˜60 ka. Since an eruption has not occurred in the last 60 kyrs, V. Tequila is often considered an extinct volcano. This may be the view held by the > 75,000 inhabitants of the town of Tequila located on the northern flanks. A similar history of two discrete cone-building events is found at V. Ceboruco, ˜75 km to the NW. Seven samples taken from various parts of the edifice, including the inner caldera wall, indicate an initial cone-building event at ˜45 ka in which ˜37 km3 of andesite erupted. After a hiatus of nearly 44 kyrs, a second eruptive period began ˜1000 years ago. The first eruption to occur after the hiatus was Plinian and released 3-4 km3 of dacite. In the last 1 kyr, 9.5 km3 of andesite and dacite erupted effusively, culminating in the historic 1870 flow. The sobering conclusion, in terms of volcanic hazards assessment, is that the only Plinian eruption to occur

  5. Discovery of an active shallow submarine silicic volcano in the northern Izu-Bonin Arc: volcanic structure and potential hazards of Oomurodashi Volcano (Invited)

    Science.gov (United States)

    Tani, K.; Ishizuka, O.; Nichols, A. R.; Hirahara, Y.; Carey, R.; McIntosh, I. M.; Masaki, Y.; Kondo, R.; Miyairi, Y.

    2013-12-01

    Oomurodashi is a bathymetric high located ~20 km south of Izu-Oshima, an active volcanic island of the northern Izu-Bonin Arc. Using the 200 m bathymetric contour to define its summit dimensions, the diameter of Oomurodashi is ~20 km. Oomurodashi has been regarded as inactive, largely because it has a vast flat-topped summit at 100 - 150 meters below sea level (mbsl). During cruise NT07-15 of R/V Natsushima in 2007, we conducted a dive survey in a small crater, Oomuro Hole, located in the center of the flat-topped summit, using the remotely-operated vehicle (ROV) Hyper-Dolphin. The only heat flow measurement conducted on the floor of Oomuro Hole during the dive recorded an extremely high value of 4,200 mW/m2. Furthermore, ROV observations revealed that the southwestern wall of Oomuro Hole consists of fresh rhyolitic lavas. These findings suggest that Oomurodashi is in fact an active silicic submarine volcano. To confirm this hypothesis, we conducted detailed geological and geophysical ROV Hyper-Dolphin (cruise NT12-19). In addition to further ROV surveys, we carried out single-channel seismic (SCS) surveys across Oomurodashi in order to examine the shallow structures beneath the current edifice. The ROV surveys revealed numerous active hydrothermal vents on the floor of Oomuro Hole, at ~200 mbsl, with maximum water temperature measured at the hydrothermal vents reaching 194°C. We also conducted a much more detailed set of heat flow measurements across the floor of Oomuro Hole, detecting very high heat flows of up to 29,000 mW/m2. ROV observations revealed that the area surrounding Oomuro Hole on the flat-topped summit of Oomurodashi is covered by extensive fresh rhyolitic lava and pumice clasts with minimum biogenetic or manganese cover, suggesting recent eruption(s). These findings strongly indicate that Oomurodashi is an active silicic submarine volcano, with recent eruption(s) occurring from Oomuro Hole. Since the summit of Oomurodashi is in shallow water, it

  6. Subduction of continental material in the Banda Arc, Eastern Indonesia : Sr-Nd-Pb isotope and trace-element evidence from volcanics and sediments

    NARCIS (Netherlands)

    Vroon, Pieter Z.

    1992-01-01

    This thesis presents the results of a geochemical study of the Banda Arc (East Indonesia) where magma genesis is influenced by subducted source components that are controlled by an active arc-continent collision. The main objective of this study is to investigate the role of subducted continental

  7. The geochemistry and petrogenesis of volcanics and sheeted dikes from the Hatay (Kizildag) Ophiolite, southern Turkey: Possible formation with the Troodos Ophiolite, Cyprus, along fore-arc spreading centers

    Science.gov (United States)

    Lytwyn, J. N.; Casey, J. F.

    1993-08-01

    Geochemical and petrological investigations of the Hatay (Kizildag) Ophiolite, southern Turkey, indicate that the volcanics and sheeted dikes compositionally range from island-arc tholeiites and basaltic andesites to transitional boninitictype lavas formed within a supra-subduction zone environment. Geochemical modeling indicates that the compositional trends within both the sheeted dike and pillow basalt sections of Hatay cannot be related through fractional crystallization alone but require multiple parental magmas of differing compositions within each unit. The more refractory liquids (higher MgO, Ni and Cr coupled with lower concentrations of Ti, Zr, Y and REE) formed at lower pressures (shallower depths) through greater degrees of partial melting of a more depleted mantle source relative to less-refractory magmas which formed at higher pressures and possibly lower degrees of melting. The Hatay volcanics and dikes span the compositional range of Lower Pillow Lavas (LPLs) and Upper Pillow Lavas (UPLs) from the Troodos Complex, Cyprus, suggesting, along with other evidence, that the two ophiolites may be petrogenetically and tectonically related. Formation of the Hatay and Troodos ophiolites was possibly associated with extension within a fore-arc environment following compression and detachment along an intra-oceanic ridge system and development of a subduction zone. The range of parental liquid compositions for volcanics and dikes may reflect variable mixing of geochemically diverse melt increments generated within a polybaric melting column in the mantle wedge. The melting column may have additionally received contributions of LREE-enriched melts from deeper, more juvenile (fertile) sources. Formation of parental liquids through variable mixing of melt increments appears to be common to both the Hatay and Troodos ophiolites.

  8. Comprehensive study of the seismotectonics of the eastern Aleutian arc and associated volcanic systems. Annual progress report, March 1, 1980-February 28, 1981

    Energy Technology Data Exchange (ETDEWEB)

    Jacob, K.H.; Davies, J.N.; House, L.

    1981-01-01

    Refined hypocenter locations beneath the Shumagin Islands seismic network of the eastern Aleutian arc, Alaska, provide for the first time conclusive evidence for a double-sheeted dipping seismic (Benioff) zone in this arc. This refined seismicity structure was obtained in the arc section centered on the Shumagin seismic gap. A thorough review of three seismic gaps in the eastern Aleutian arc shows a high potential for great earthquakes within the next one to two decades in the Shumagin and Yakataga seismic gaps, and a less certain potential for a large or great earthquake in the possible Unalaska gap. A tilt reversal was geodetically observed to have occurred in 1978/79 in the forearc region of the Shumagin gap and could indicate the onset of a precursory strain relief episode prior to a great quake. A comparative study of the Pavlof volcano seismicity with that of other recently active volcanoes (i.e., Mt. St. Helens) indicates that island-arc (explosive-type) volcanoes respond to small ambient, periodic stress changes (i.e., tides). Stress drop measurements from earthquakes on the main thrust zone indicate high stress drops within the seismic gap regions of the Aleutian arc and low stress drops outside the gap region.

  9. Rhizomes and plateaus: A study of digital communities of practice in University College English Teaching

    DEFF Research Database (Denmark)

    Kjærgaard, Thomas

    2017-01-01

    Rhizomes and plateaus: A study of digital communities of practice in University College English Teaching......Rhizomes and plateaus: A study of digital communities of practice in University College English Teaching...

  10. Petrology and geochemistry of volcanic rocks from the island of Panarea: implications for mantle evolution beneath the Aeolian island arc (southern Tyrrhenian sea)

    Science.gov (United States)

    Calanchi, N.; Peccerillo, A.; Tranne, C. A.; Lucchini, F.; Rossi, P. L.; Kempton, P.; Barbieri, M.; Wu, T. W.

    2002-06-01

    Major, trace element and radiogenic isotope (Sr, Nd, Pb) data are reported for a suite of rocks from the Panarea volcano, a large structure that is largely hidden below sea level and outcrops only as a group of small islands between Lipari-Vulcano and Stromboli in the eastern Aeolian arc. The exposed rocks mostly consist of high-potassium calc-alkaline (HKCA) andesites, dacites and some rhyolites; shoshonitic basalts have been collected from submarine centres; mafic calc-alkaline (CA) rocks occur as thin layers of late-erupted strombolian scoriae. Major and trace element data are scattered, but define generally linear trends on inter-element diagrams; Sr-isotope ratios do not display significant increase with evolution, although rough positive trends of 87Sr/ 86Sr versus SiO 2 and Rb/Sr can be recognised within some units. The mafic rocks display varying enrichment in potassium, from CA to shoshonitic compositions, and are characterised by variable abundances of incompatible trace elements, which increase with potassium. There is an increase of 87Sr/ 86Sr ratios and a decrease of 143Nd/ 144Nd and 206Pb/ 204Pb ratios from CA to HKCA and shoshonitic mafic rocks. The scattered and incomplete nature of the outcrops make it difficult to constrain magmatic evolution at Panarea; geochemical and isotopic data suggest that AFC and mixing were important evolutionary processes. However, geochemical modelling does not support the possibility that the first-order compositional variations observed in the mafic rocks are the result of these processes, and suggests a genesis in a heterogeneous mantle source. Recent studies have highlighted strong differences in terms of incompatible trace element ratios and isotopic signatures, between the western-central and the eastern Aeolian arc. Rocks from the western islands (Alicudi, Filicudi, Salina, Vulcano) have typical magmatic arc geochemical signatures and relatively unradiogenic Sr-isotope compositions. By contrast, the eastern

  11. Efusiones subácueas del arco volcánico ordovícico en el norte del sistema de Famatina Subaqueous eruptions in the Ordovician volcanic arc in the northern Famatina System

    Directory of Open Access Journals (Sweden)

    Clara Eugenia Cisterna

    2010-03-01

    Full Text Available La sucesión volcánica - sedimentaria analizada, ubicada entre los 27°47`00" - 27°49`18" S y 68°04`52" - 68°02`27" O en la sierra de Las Planchadas, norte del Sistema de Famatina, registra la evolución de un arco volcánico ordovícico. Sus representantes volcánicos mayoritarios, lavas basálticas y en menor medida dacíticas, fragmentadas, autoclásticas e hialoclastitas indican el predominio de un volcanismo efusivo subácueo. Mientras tanto el elevado volumen de depósitos volcaniclásticos asociados, especialmente en los tramos superiores, generados por flujos gravitacionales en masa, ya sea por corrientes de turbidez, como por flujos de detritos y vinculados con episodios de sedimentación sin-volcánicos, evidencian la eficiencia de los procesos de fragmentación y de la erosión recurrente durante la evolución de esta cuenca ordovícica. El contenido fosilífero en las facies volcanogénicas y las asociaciones de limolitas, fangolitas y psamitas finas con abundante material de origen piroclástico y lapilli acrecional, atestiguan en favor de un ambiente somero para su depositación. Las características de los depósitos volcanogénicos, su proveniencia prácticamente única, la variación de sus facies, junto a las características geoquímicas de sus representantes magmáticos apoyan la idea para la región de un volcanismo de arco ligado a la evolución de la cuenca, mientras tenía lugar un intermitente aporte de sedimentos intracuencales, debidos a la inestabilidad de la misma.The volcanic - sedimentary sequence studied, exposed along the 27°47`00" - 27°49`18" S and 68°04`52" - 68°02`27" Win the sierra de Las Planchadas, northern Famatina System, records the evolution of an Ordovician volcanic arc. The main volcanic members are basaltic and dacitic lavas and significant volumes of lava-derived clastic aggregates that are produced by quench fragmentation and gravitational collapse. Fragmented lavas, autobreccias and

  12. Eastern Dharwar Craton, India: Continental lithosphere growth by accretion of diverse plume and arc terranes

    Directory of Open Access Journals (Sweden)

    C. Manikyamba

    2012-05-01

    Archean lithospheric mantle, distinctive in being thick, refractory, and buoyant, formed complementary to the accreted plume and convergent margin terranes, as migrating arcs captured thick plume-plateaus, and the refractory, low density, residue of plume melting coupled with accreted imbricated plume-arc crust.

  13. Warm storage for arc magmas.

    Science.gov (United States)

    Barboni, Mélanie; Boehnke, Patrick; Schmitt, Axel K; Harrison, T Mark; Shane, Phil; Bouvier, Anne-Sophie; Baumgartner, Lukas

    2016-12-06

    Felsic magmatic systems represent the vast majority of volcanic activity that poses a threat to human life. The tempo and magnitude of these eruptions depends on the physical conditions under which magmas are retained within the crust. Recently the case has been made that volcanic reservoirs are rarely molten and only capable of eruption for durations as brief as 1,000 years following magma recharge. If the "cold storage" model is generally applicable, then geophysical detection of melt beneath volcanoes is likely a sign of imminent eruption. However, some arc volcanic centers have been active for tens of thousands of years and show evidence for the continual presence of melt. To address this seeming paradox, zircon geochronology and geochemistry from both the frozen lava and the cogenetic enclaves they host from the Soufrière Volcanic Center (SVC), a long-lived volcanic complex in the Lesser Antilles arc, were integrated to track the preeruptive thermal and chemical history of the magma reservoir. Our results show that the SVC reservoir was likely eruptible for periods of several tens of thousands of years or more with punctuated eruptions during these periods. These conclusions are consistent with results from other arc volcanic reservoirs and suggest that arc magmas are generally stored warm. Thus, the presence of intracrustal melt alone is insufficient as an indicator of imminent eruption, but instead represents the normal state of magma storage underneath dormant volcanoes.

  14. PALEOMAGNETISM OF SILURIAN AND DEVONIAN VOLCANICS FROM THE CHINGIZ ISLAND ARC, KAZAKHSTAN, AND ITS BEARING ON TECTONIC EVOLUTION OF THE URAL-MONGOL BELT

    Directory of Open Access Journals (Sweden)

    Natalia M. Levashova

    2015-09-01

    Full Text Available The tectonic and paleogeographic evolution of the Ural-Mongol belt between the cratons of Baltica, Siberia, and Tarim is the key to the formation of the Eurasian supercontinent during Paleozoic time, but the views on this complicated process remain very disparate and sometimes controversial. Three volcanic formations of the Middle Silurian, LowertoMiddle Devonian and Middle Devonian age from the southwestern boundary of the Chingiz Range (NE Kazakhstan yields what are interpreted as primary paleomagnetic directions that help clarify the evolution of the belt. A singlepolarity characteristic component in midSilurian andesites yields a positive intraformational conglomerate test, whereas dualpolarity prefolding components are isolated from the two Devonian collections. These new data were evaluated together with previously published paleomagnetic results from Paleozoic rocks in the Chingiz Range, and allow us to establish with confidence the hemisphere in which the area was located at a given time. We conclude that NE Kazakhstan was steadily moving northward crossing the equator in Silurian time. These new paleomagnetic data from the Chingiz range also agree with and reinforce the hypothesis that the strongly curved volcanic belts of Kazakhstan underwent oroclinal bending between Middle Devonian and Late Carboniferous time. A comparison of the Chingiz paleolatitudes with those of Siberia shows similarities between the northward motion and rotational history of the Chingiz unit and those of Siberia, which imposes important constraints on the evolving paleogeography of the Ural-Mongol belt.

  15. Sr and O isotopes in western Aleutian seafloor lavas: Implications for the source of fluids and trace element character of arc volcanic rocks

    Science.gov (United States)

    Yogodzinski, Gene M.; Kelemen, Peter B.; Hoernle, Kaj; Brown, Shaun T.; Bindeman, Ilya; Vervoort, Jeffrey D.; Sims, Kenneth W. W.; Portnyagin, Maxim; Werner, Reinhard

    2017-10-01

    High Mg# andesites and dacites (Mg# = molar Mg/Mg + Fe) from western Aleutian seafloor volcanoes carry high concentrations of Sr (>1000 ppm) that is unradiogenic (87Sr/86Sr 0.7030). Data patterns in plots of 87Sr/86Sr vs Y/Sr and Nd/Sr imply the existence of an eclogite-melt source component - formed by partial melting of MORB eclogite in the subducting Pacific Plate - which is most clearly expressed in the compositions of western Aleutian andesites and dacites (Nd/Sr and Y/Sr viewed in combination with inversely correlated εNd and 87Sr/86Sr, these patterns rule out aqueous fluids as an important source of Sr because mixtures of fluids from altered oceanic crust with depleted mantle and sediment produce compositions with 87Sr/86Sr higher than in common Aleutian rocks. The unradiogenic nature of Sr in the western Aleutian andesite-dacite end-member may be understood if H2O required to drive melting of the subducting oceanic crust is transported in fluids containing little Sr. Mass balance demonstrates that such fluids may be produced by dewatering of serpentinite in the mantle section of the subducting plate. If the eclogite-melt source component is present throughout the Aleutian arc, melting of the subducting plate must extend into minimally altered parts of the sheeted dike section or upper gabbros, at depths >2 km below the paleo-seafloor. Oxygen isotopes in western Aleutian seafloor lavas, which fall within a narrow range of MORB-like values (δ18 O = 5.1- 5.7), are also consistent with this model. These results indicate that the subducting Pacific lithosphere beneath the Aleutian arc is significantly hotter than indicated my most thermal models.

  16. Geological and geochemical studies of the Sierra del Morro-Oeste (San Luis Province, Argentina): Meta-sediments and meta-volcanics from a probable back-arc setting

    Science.gov (United States)

    Delakowitz, B.; Höll, R.; Hack, M.; de Brodtkorb, M. K.; Stärk, H.

    The Sierra del Morro-Oeste covers an area of some 40 km 2 in the northeastern part of San Luis Province, Argentina. This area is an integral part of the scheelite- and wolframite-bearing crystalline basement of the Sierras Pampeanas. A "characteristic rock sequence"—several tens of meters thick—is concordantly embedded between uniform country rocks (quartz-oligoclase/andesine micaschists and gneises); it includes layered alternations of banded amphibolites, hornblende-epidote schists, scheelite-bearing calc-silicate rocks, lenses of barren marble, and, locally, tourmaline-bearing micaschists. Chemical analyses of amphibolite samples allow these metamorphic rocks to be interpreted as derivatives of a tholeiite-basaltic volcanism. The amphibolites are subdivided into two groups (A and B) because of significant differences in their chemical composition. These differences are related to hydrothermal seafloor alteration. This sea-water alteration has been most effective in the youngest tholeiite-basaltic lava extrusions. The derivatives of the submarine altered tholeiite-basaltic lavas (amphibolites of Group B) can therefore be interpreted as younger in comparison with the primary lavas of the non-altered amphibolites of Group A. The extrusion of the tholeiite-basaltic lavas obviously took place during an initial stage of back-arc basin rifting on continental crust.

  17. LA-ICP-MS Pb-U Dating of Young Zircons from the Kos-Nisyros Volcanic Centre, SE Aegean Arc (Greece)

    Science.gov (United States)

    Guillong, M.; Von Quadt, A.; Peytcheva, I.; Bachmann, O.

    2014-12-01

    Zircon Pb-U dating has become a key technique for answering many important questions in geosciences. This paper describes a new LA-ICP-MS approach. We show, using previously dated samples of a large quaternary rhyolitic eruption in the Kos-Nisyros volcanic centre (the 161 ka Kos Plateau Tuff), that the precision of our LA-ICP-MS method is as good as via SHRIMP, while ID-TIMS measurements confirm the accuracy. Gradational age distribution over >140 ka of the Kos zircons and the near-absence of inherited cores indicate near-continuous crystallisation in a growing magma reservoir with little input from wall rocks. Previously undated silicic eruptions from Nisyros volcano (Lower Pumice, Nikia Flow, Upper Pumice), which are stratigraphically constrained to have happened after the Kos Plateau Tuff, are dated to be younger than respectively 124 ± 35 ka, 111 ± 42 ka and 70 ± 24 ka. Samples younger than 1 Ma were corrected for initial thorium disequilibrium using a new formula that also accounts for disequilibrium in 230Th decay. Guillong, M. et al., 2014, JAAS, 29, p. 963-967; doi: 10.1039/c4ja00009a.

  18. H_2O and CO_2 in magmas from the Mariana arc and back arc systems

    OpenAIRE

    Newman, Sally; Stolper, Edward; STERN, Robert

    2000-01-01

    We examined the H2O and CO2 contents of glasses from lavas and xenoliths from the Mariana arc system, an intraoceanic convergent margin in the western Pacific, which contains an active volcanic arc, an actively spreading back arc basin, and active behind-the-arc cross-chain volcanoes. Samples include (1) glass rims from Mariana arc, Mariana trough, and cross-chain submarine lavas; (2) glass inclusions in arc and trough phenocrysts; and (3) glass inclusions from a gabbro + anorthosite xenolith...

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

    Science.gov (United States)

    Kelemen, Peter; Hacker, Bradley

    2016-04-01

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

  20. Hydrogeology and hydrologic conditions of the Ozark Plateaus aquifer system

    Science.gov (United States)

    Hays, Phillip D.; Knierim, Katherine J.; Breaker, Brian K.; Westerman, Drew A.; Clark, Brian R.

    2016-11-23

    The hydrogeology and hydrologic characteristics of the Ozark Plateaus aquifer system were characterized as part of ongoing U.S. Geological Survey efforts to assess groundwater availability across the Nation. The need for such a study in the Ozark Plateaus physiographic province (Ozark Plateaus) is highlighted by increasing demand on groundwater resources by the 5.3 million people of the Ozark Plateaus, water-level declines in some areas, and potential impacts of climate change on groundwater availability. The subject study integrates knowledge gained through local investigation within a regional perspective to develop a regional conceptual model of groundwater flow in the Ozark Plateaus aquifer system (Ozark system), a key phase of groundwater availability assessment. The Ozark system extends across much of southern Missouri and northwestern and north-central Arkansas and smaller areas of southeastern Kansas and northeastern Oklahoma. The region is one of the major karst landscapes in the United States, and karst aquifers are predominant in the Ozark system. Groundwater flow is ultimately controlled by aquifer and confining unit lithologies and stratigraphic relations, geologic structure, karst development, and the character of surficial lithologies and regolith mantle. The regolith mantle is a defining element of Ozark Plateaus karst, affecting recharge, karst development, and vulnerability to surface-derived contaminants. Karst development is more advanced—as evidenced by larger springs, hydraulic characteristics, and higher well yields—in the Salem Plateau and in the northern part of the Springfield Plateau (generally north of the Arkansas-Missouri border) as compared with the southern part of the Springfield Plateau in Arkansas, largely due to thinner, less extensive regolith and purer carbonate lithology.Precipitation is the ultimate source of all water to the Ozark system, and the hydrologic budget for the Ozark system includes inputs from recharge

  1. Episodic Volcanism and Geochemistry in Western Nicaragua

    Science.gov (United States)

    Saginor, I.; Carr, M. J.; Gazel, E.; Swisher, C.; Turrin, B.

    2007-12-01

    The active volcanic arc in western Nicaragua is separated from the Miocene arc by a temporal gap in the volcanic record, during which little volcanic material was erupted. Previous work suggested that this gap lasted from 7 to 1.6 Ma, during which volcanic production in Nicaragua was limited or nonexistent. Because the precise timing and duration of this gap has been poorly constrained, recent fieldwork has focused on locating samples that may have erupted close to or even during this apparent hiatus in activity. Recent 40Ar/39Ar dates reveal pulses of low- level episodic volcanism at 7 Ma and 1 Ma between the active and Miocene arcs with current volcanism beginning ~350 ka. In addition, sampling from an inactive area between Coseguina and San Cristobal yielded two distinct groupings of ages; one of Tamarindo age (13 Ma) and the other around 3.5 Ma-the only samples of that age collected on-strike with the active arc. This raises the possibility the bases of the other active volcanoes contain lavas that are older than expected, but have been covered by subsequent eruptions. The Miocene arc differs from the active arc in Central America in several ways, with the latter having higher Ba/La and U/Th values due to increased slab input and changes in subducted sediment composition. Analysis of sample C-51 and others taken from the same area may shed light on the timing of this shift from high to low Ba/La and U/Th values. More importantly, it may help explain why the arc experienced such a dramatic downturn in volcanic production during this time. We also report 25 new major and trace element analyses that shed some light on the origins of these minor episodes of Nicaraguan volcanism. These samples are currently awaiting Sr and Nd isotopic analyses.

  2. Contrasting records from mantle to surface of Holocene lavas of two nearby arc volcanic complexes: Caburgua-Huelemolle Small Eruptive Centers and Villarrica Volcano, Southern Chile

    Science.gov (United States)

    Morgado, E.; Parada, M. A.; Contreras, C.; Castruccio, A.; Gutiérrez, F.; McGee, L. E.

    2015-11-01

    Most of the small eruptive centers of the Andean Southern Volcanic Zone are built over the Liquiñe-Ofqui Fault Zone (LOFZ), a NS strike-slip (> 1000 km length) major structure, and close to large stratovolcanoes. This contribution compares textural features, compositional parameters, and pre- and syn-eruptive P,T conditions, between basaltic lavas of the Caburgua-Huelemolle Small Eruptive Centers (CHSEC) and the 1971 basaltic andesite lava of the Villarrica Volcano located 10 km south of the CHSEC. Olivines and clinopyroxenes occur as phenocrysts and forming crystal clots of the studied lavas. They do not markedly show compositional differences, except for the more scattered composition of the CHSEC clinopyroxenes. Plagioclase in CHSEC lavas mainly occur as phenocrysts or as microlites in a glass-free matrix. Two groups of plagioclase phenocrysts were identified in the 1971 Villarrica lava based on crystal size, disequilibrium features and zonation patterns. Most of the CHSEC samples exhibit higher LaN/YbN and more scattered Sr-Nd values than 1971 Villarrica lava samples, which are clustered at higher 143Nd/144Nd values. Pre-eruptive temperatures of the CHSEC-type reservoir between 1162 and 1165 ± 6 °C and pressures between 10.8 and 11.4 ± 1.7 kb consistent with a deep-seated reservoir were obtained from olivine-augite phenocrysts. Conversely, olivine-augite phenocrysts of 1971 Villarrica lava samples record pre-eruptive conditions of two stages or pauses in the magma ascent to the surface: 1208 ± 6 °C and 6.3-8.1 kb ± 1.7 kb (deep-seated reservoir) and 1164-1175 ± 6 °C and ≤ 1.4 kb (shallow reservoir). At shallow reservoir conditions a magma heating prior to the 1971 Villarrica eruption is recorded in plagioclase phenocrysts. Syn-eruptive temperatures of 1081-1133 ± 6 °C and 1123-1148 ± 6 °C were obtained in CHSEC and 1971 Villarrica lava, respectively using equilibrium olivine-augite microlite pairs. The LOFZ could facilitate a direct transport to

  3. Quaternary Basanitic Rocks within the Eastern Anatolian Volcanism (Turkey): Petrological and Geochemical Constrains

    Science.gov (United States)

    Özdemir, Yavuz; Mercan, Çaǧrı; Oyan, Vural; Atakul-Özdemir, Ayşe

    2017-04-01

    The Eastern Anatolian Cenozoic continental intraplate volcanism was initiated in Middle Miocene as a result of the convergence between the Arabian and Anatolian plates. The origin of Eastern Anatolian volcanism has been the focus of many petrological studies that have aimed to resolve the relative contributions of asthenospheric mantle and/or lithospheric mantle with/without subduction component in the genesis of magmas that compositionally have many affinities to ocean island basalts (OIB) and volcanic arcs. Volcanism in the region characterized by mainly stratovolcanoes, basaltic lava plateaus and are dominantly spread at the northern parts of Bitlis Pötürge Massif (BPM). Our study focuses on a small scale Quaternary basaltic system that firstly observed within the BPM. The volcanic rocks of our study located 50 km to the south of Lake Van and are basanitic in composition. They exposed along K-G striking tensional fissures and crosscut the Upper unit of the Bitlis Massif. Initial products of the volcanism are scoria fall deposits. Thick basanitic lava flows overly the pyroclastics and formed columnar structures. The basanites are generally fine-grained with phenocrysts of olivine+clinopyroxene. The groundmass is typically of clinopyroxene, olivine and Ti magnetite and Cr spinel with interstitial nepheline. The olivine phenocrysts are typically euhedral to subhedral with Forsterite contents of Fo73-83. Clinopyroxenes are highly calcic and show modest variations in Wo47-52-En34-42-Fs10-15 and are weakly zoned with mg# 89-87 at cores to 86-84 at rims. Nephelines occur as minor minerals within the networks of other groundmass minerals. Ti rich and Fe-Cr spinels occur as inclusions in olivine and clinopyroxenes as well as within the groundmass. LILE and LREE enrichments over HFSE and HREE suggest similarities with magmas generated from enriched mantle sources. EC-AFC modeling of trace element and isotope compositions indicates that assimilation of crustal

  4. Catastrophic volcanism

    Science.gov (United States)

    Lipman, Peter W.

    1988-01-01

    Since primitive times, catastrophes due to volcanic activity have been vivid in the mind of man, who knew that his activities in many parts of the world were threatened by lava flows, mudflows, and ash falls. Within the present century, increasingly complex interactions between volcanism and the environment, on scales not previously experienced historically, have been detected or suspected from geologic observations. These include enormous hot pyroclastic flows associated with collapse at source calderas and fed by eruption columns that reached the stratosphere, relations between huge flood basalt eruptions at hotspots and the rifting of continents, devastating laterally-directed volcanic blasts and pyroclastic surges, great volcanic-generated tsunamis, climate modification from volcanic release of ash and sulfur aerosols into the upper atmosphere, modification of ocean circulation by volcanic constructs and attendent climatic implications, global pulsations in intensity of volcanic activity, and perhaps triggering of some intense terrestrial volcanism by planetary impacts. Complex feedback between volcanic activity and additional seemingly unrelated terrestrial processes likely remains unrecognized. Only recently has it become possible to begin to evaluate the degree to which such large-scale volcanic processes may have been important in triggering or modulating the tempo of faunal extinctions and other evolutionary events. In this overview, such processes are examined from the viewpoint of a field volcanologist, rather than as a previous participant in controversies concerning the interrelations between extinctions, impacts, and volcanism.

  5. The presence of rapidly degrading permafrost plateaus in southcentral Alaska

    Science.gov (United States)

    Jones, Benjamin M.; Baughman, Carson; Romanovsky, V.adimir E; Parsekian, Andrew D.; Babcock, Esther; Jones, Miriam C.; Grosse, Guido; Berg, Edward E

    2016-01-01

    Permafrost presence is determined by a complex interaction of climatic, topographic, and ecological conditions operating over long time scales. In particular, vegetation and organic layer characteristics may act to protect permafrost in regions with a mean annual air temperature (MAAT) above 0°C. In this study, we document the presence of residual permafrost plateaus on the western Kenai Peninsula lowlands of southcentral Alaska, a region with a MAAT of 1.5 ± 1°C (1981 to 2010). Continuous ground temperature measurements between 16 September 2012 and 15 September 2015, using calibrated thermistor strings, documented the presence of warm permafrost (−0.04 to −0.08°C). Field measurements (probing) on several plateau features during the fall of 2015 showed that the depth to the permafrost table averaged 1.48 m but was as shallow as 0.53 m. Late winter surveys (drilling, coring, and GPR) in 2016 showed that the average seasonally frozen ground thickness was 0.45 m, overlying a talik above the permafrost table. Measured permafrost thickness ranged from 0.33 to >6.90 m. Manual interpretation of historic aerial photography acquired in 1950 indicates that residual permafrost plateaus covered 920 ha as mapped across portions of four wetland complexes encompassing 4810 ha. However, between 1950 and ca. 2010, permafrost plateau extent decreased by 60%, with lateral feature degradation accounting for 85% of the reduction in area. Permafrost loss on the Kenai Peninsula is likely associated with a warming climate, wildfires that remove the protective forest and organic layer cover, groundwater flow at depth, and lateral heat transfer from wetland surface waters in the summer. Better understanding the resilience and vulnerability of ecosystem-protected permafrost is critical for mapping and predicting future permafrost extent and degradation across all permafrost regions that are currently warming. Further work should focus on reconstructing permafrost history in

  6. Karst morphology and groundwater vulnerability of high alpine karst plateaus

    Science.gov (United States)

    Plan, Lukas; Decker, Kurt; Faber, Robert; Wagreich, Michael; Grasemann, Bernhard

    2009-07-01

    High alpine karst plateaus are recharge areas for major drinking water resources in the Alps and many other regions. Well-established methods for the vulnerability mapping of groundwater to contamination have not been applied to such areas yet. The paper characterises this karst type and shows that two common vulnerability assessment methods (COP and PI) classify most of the areas with high vulnerability classes. In the test site on the Hochschwab plateau (Northern Calcareous Alps, Austria), overlying layers are mostly absent, not protective or even enhance point recharge, where they have aquiclude character. The COP method classifies 82% of the area as highly or extremely vulnerable. The resulting maps are reasonable, but do not differentiate vulnerabilities to the extent that the results can be used for protective measures. An extension for the upper end of the vulnerability scale is presented that allows identifying ultra vulnerable areas. The proposed enhancement of the conventional approach points out that infiltration conditions are of key importance for vulnerability. The method accounts for karst genetical and hydrologic processes using qualitative and quantitative properties of karst depressions and sinking streams including parameters calculated from digital elevations models. The method is tested on the Hochschwab plateau where 1.7% of the area is delineated as ultra vulnerable. This differentiation could not be reached by the COP and PI methods. The resulting vulnerability map highlights spots of maximum vulnerability and the combination with a hazard map enables protective measures for a manageable area and number of sites.

  7. Strong degradation of palsas and peat plateaus in northern Norway during the last 60 years

    Science.gov (United States)

    Borge, Amund F.; Westermann, Sebastian; Solheim, Ingvild; Etzelmüller, Bernd

    2017-01-01

    Palsas and peat plateaus are permafrost landforms occurring in subarctic mires which constitute sensitive ecosystems with strong significance for vegetation, wildlife, hydrology and carbon cycle. Firstly, we have systematically mapped the occurrence of palsas and peat plateaus in the northernmost county of Norway (Finnmark, ˜ 50 000 km2) by manual interpretation of aerial images from 2005 to 2014 at a spatial resolution of 250 m. At this resolution, mires and wetlands with palsas or peat plateaus occur in about 850 km2 of Finnmark, with the actual palsas and peat plateaus underlain by permafrost covering a surface area of approximately 110 km2. Secondly, we have quantified the lateral changes of the extent of palsas and peat plateaus for four study areas located along a NW-SE transect through Finnmark by utilizing repeat aerial imagery from the 1950s to the 2010s. The results of the lateral changes reveal a total decrease of 33-71 % in the areal extent of palsas and peat plateaus during the study period, with the largest lateral change rates observed in the last decade. However, the results indicate that degradation of palsas and peat plateaus in northern Norway has been a consistent process during the second half of the 20th century and possibly even earlier. Significant rates of areal change are observed in all investigated time periods since the 1950s, and thermokarst landforms observed on aerial images from the 1950s suggest that lateral degradation was already an ongoing process at this time. The results of this study show that lateral erosion of palsas and peat plateaus is an important pathway for permafrost degradation in the sporadic permafrost zone in northern Scandinavia. While the environmental factors governing the rate of erosion are not yet fully understood, we note a moderate increase in air temperature, precipitation and snow depth during the last few decades in the region.

  8. Cathodic arcs

    Energy Technology Data Exchange (ETDEWEB)

    Anders, Andre

    2003-10-29

    Cathodic arc plasma deposition has become the technology of choice for hard, wear and corrosion resistant coatings for a variety of applications. The history, basic physics of cathodic arc operation, the infamous macroparticle problem and common filter solutions, and emerging high-tech applications are briefly reviewed. Cathodic arc plasmas standout due to their high degree of ionization, with important consequences for film nucleation, growth, and efficient utilization of substrate bias. Industrial processes often use cathodic arc plasma in reactive mode. In contrast, the science of arcs has focused on the case of vacuum arcs. Future research directions include closing the knowledge gap for reactive mode, large area coating, linear sources and filters, metal plasma immersion process, with application in high-tech and biomedical fields.

  9. Cathodic arcs

    OpenAIRE

    Anders, Andre

    2003-01-01

    Cathodic arc plasma deposition has become the technology of choice for hard, wear and corrosion resistant coatings for a variety of applications. The history, basic physics of cathodic arc operation, the infamous macroparticle problem and common filter solutions, and emerging high-tech applications are briefly reviewed. Cathodic arc plasmas stand out due to their high degree of ionization, with important consequences for film nucleation, growth, and efficient utilization of substrate bia...

  10. The Records of the Tectonic Evolution From the Volcanics in Qiangtang Basin, Tibet

    Institute of Scientific and Technical Information of China (English)

    He Zhonghua; Yang Deming; Li Cai; Pu Zhongyu

    2000-01-01

    The volcanism in Qiangtang Basin is very frequent due to the divergence and subduction of the various plates. The study indicates that these volcanics are formed in different tectonic settings: 1 )Hercynian volcanics are mainly basalts and are formed in the intraplate and intercontinental rift. 2 ) Indosinian volcanics markedly vary in the distribution and composition and reflect transitional MORB and island are environments respectively. 3) Yanshanian volcanics consist predominantly of basalts, andesites, dacites and rhyolites and are characterized by calc- alkaline volcanic suite, indicating island arc setting. 4)Himalayan volcanics are complicated and associated with intraplate orogency. The volcanism provides important tectonic information for recognizing the evolution of Qiangtang Basin.

  11. Quaternary basaltic volcanism in the Payenia volcanic province, Argentina

    DEFF Research Database (Denmark)

    Søager, Nina

    primitive basalts and trachybasalts but also more evolved samples from the retroarc region and the larger volcanoes Payún Matrú and Payún Liso are presented. The samples cover a broad range of compositions from intraplate lavas similar to ocean island basalts to arc andesites. A common feature found...... Pleistocene times. These basalts mark the end of a period of shallow subduction of the Nazca slab beneath the Payenia province and volcanism in the Nevado volcanic field apparently followed the downwarping slab in a north-northwest direction ending in the Northern Segment. The northern Payenia basalts...... the literature. The Nevado basalts have been modelled by 4-10 % melting of a primitive mantle added 1-5 % upper continental crust. In the southern Payenia province, intraplate basalts dominate. The samples from the Payún Matrú and Río Colorado volcanic fields are apparently unaffected by the subducting slab...

  12. Plateaus, Dips, and Leaps: Where to Look for Inventions and Discoveries During Skilled Performance.

    Science.gov (United States)

    Gray, Wayne D; Lindstedt, John K

    2016-10-20

    The framework of plateaus, dips, and leaps shines light on periods when individuals may be inventing new methods of skilled performance. We begin with a review of the role performance plateaus have played in (a) experimental psychology, (b) human-computer interaction, and (c) cognitive science. We then reanalyze two classic studies of individual performance to show plateaus and dips which resulted in performance leaps. For a third study, we show how the statistical methods of Changepoint Analysis plus a few simple heuristics may direct our focus to periods of performance change for individuals. For the researcher, dips become the marker of exploration where performance suffers as new methods are invented and tested. Leaps mark the implementation of a successful new method and an incremental jump above the path plotted by smooth and steady log-log performance increments. The methods developed during these dips and leaps are the key to surpassing one's teachers and acquiring extreme expertise.

  13. Pressure dependence of the magnetization plateaus of SrCu2(BO3)2

    Science.gov (United States)

    Schneider, David A.; Coester, Kris; Mila, Frédéric; Schmidt, Kai Phillip

    2016-06-01

    We show that the critical fields of the magnetization plateaus of the Shastry-Sutherland model decrease significantly upon increasing the ratio of inter- to intradimer coupling and accordingly that the magnetization plateaus of SrCu2(BO3)2 shift to lower field under pressure, making the first two plateaus at 1 /8 and 2 /15 potentially accessible to neutron scattering experiments. These conclusions are based on the derivation of an effective classical model of interacting pinwheel-shaped spin-2 bound states using a combination of perturbative and graph-based continuous unitary transformations, showing that pinwheel crystals are indeed the lowest-energy plateau structures at low magnetization and that a simple model of intermediate-range two-body repulsion between pinwheels is able to account quantitatively for the plateau sequence.

  14. VOLCANIC TSUNAMI GENERATING SOURCE MECHANISMS IN THE EASTERN CARIBBEAN REGION

    OpenAIRE

    2004-01-01

    Earthquakes, volcanic eruptions, volcanic island flank failures and underwater slides have generated numerous destructive tsunamis in the Caribbean region. Convergent, compressional and collisional tectonic activity caused primarily from the eastward movement of the Caribbean Plate in relation to the North American, Atlantic and South American Plates, is responsible for zones of subduction in the region, the formation of island arcs and the evolution of particular volcanic centers on the over...

  15. Spontaneous otoacoustic emissions are generated by active oscillators clustered in frequency plateaus

    DEFF Research Database (Denmark)

    Epp, Bastian; Wit, Hero; van Dijk, Pim

    It is commonly assumed that the active process linked to hair-cell motility is an important factor contributing to SOAEs. A chain of coupled, active and nonlinear oscillators with tonotopic organization can be used to account for key aspects of cochlear processing, including SOAEs and related......, 918–926] that a linear array of active oscillators with nearest neighbour coupling produces clusters of oscillators with a common oscillation frequency (frequency plateaus) and a preferred frequency separation. The frequency plateaus can also be entrained to the frequency of an external tone. Both...

  16. Hydrologic budget and conditions of Permian, Pennsylvanian, and Mississippian aquifers in the Appalachian Plateaus physiographic province

    Science.gov (United States)

    McCoy, Kurt J.; Yager, Richard M.; Nelms, David L.; Ladd, David E.; Monti,, Jack; Kozar, Mark D.

    2015-08-13

    In response to challenges to groundwater availability posed by historic land-use practices, expanding development of hydrocarbon resources, and drought, the U.S. Geological Survey Groundwater Resources Program began a regional assessment of the Appalachian Plateaus aquifers in 2013 that incorporated a hydrologic landscape approach to estimate all components of the hydrologic system: surface runoff, base flow from groundwater, and interaction with atmospheric water (precipitation and evapotranspiration). This assessment was intended to complement other Federal and State investigations and provide foundational groundwater-related datasets in the Appalachian Plateaus.

  17. Volcanism and associated hazards: the Andean perspective

    Science.gov (United States)

    Tilling, R. I.

    2009-12-01

    Andean volcanism occurs within the Andean Volcanic Arc (AVA), which is the product of subduction of the Nazca Plate and Antarctica Plates beneath the South America Plate. The AVA is Earth's longest but discontinuous continental-margin volcanic arc, which consists of four distinct segments: Northern Volcanic Zone, Central Volcanic Zone, Southern Volcanic Zone, and Austral Volcanic Zone. These segments are separated by volcanically inactive gaps that are inferred to indicate regions where the dips of the subducting plates are too shallow to favor the magma generation needed to sustain volcanism. The Andes host more volcanoes that have been active during the Holocene (past 10 000 years) than any other volcanic region in the world, as well as giant caldera systems that have produced 6 of the 47 largest explosive eruptions (so-called "super eruptions") recognized worldwide that have occurred from the Ordovician to the Pleistocene. The Andean region's most powerful historical explosive eruption occurred in 1600 at Huaynaputina Volcano (Peru). The impacts of this event, whose eruptive volume exceeded 11 km3, were widespread, with distal ashfall reported at distances >1000 km away. Despite the huge size of the Huaynaputina eruption, human fatalities from hazardous processes (pyroclastic flows, ashfalls, volcanogenic earthquakes, and lahars) were comparatively small owing to the low population density at the time. In contrast, lahars generated by a much smaller eruption (indecisiveness by government officials, rather than any major deficiencies in scientific data. Ruiz's disastrous outcome, however, together with responses to subsequent hazardous eruptions in Chile, Colombia, Ecuador, and Peru has spurred significant improvements in reducing volcano risk in the Andean region. But much remains to be done.

  18. Volcanism and associated hazards: The Andean perspective

    Science.gov (United States)

    Tilling, R.I.

    2009-01-01

    Andean volcanism occurs within the Andean Volcanic Arc (AVA), which is the product of subduction of the Nazca Plate and Antarctica Plates beneath the South America Plate. The AVA is Earth's longest but discontinuous continental-margin volcanic arc, which consists of four distinct segments: Northern Volcanic Zone, Central Volcanic Zone, Southern Volcanic Zone, and Austral Volcanic Zone. These segments are separated by volcanically inactive gaps that are inferred to indicate regions where the dips of the subducting plates are too shallow to favor the magma generation needed to sustain volcanism. The Andes host more volcanoes that have been active during the Holocene (past 10 000 years) than any other volcanic region in the world, as well as giant caldera systems that have produced 6 of the 47 largest explosive eruptions (so-called "super eruptions") recognized worldwide that have occurred from the Ordovician to the Pleistocene. The Andean region's most powerful historical explosive eruption occurred in 1600 at Huaynaputina Volcano (Peru). The impacts of this event, whose eruptive volume exceeded 11 km3, were widespread, with distal ashfall reported at distances >1000 km away. Despite the huge size of the Huaynaputina eruption, human fatalities from hazardous processes (pyroclastic flows, ashfalls, volcanogenic earthquakes, and lahars) were comparatively small owing to the low population density at the time. In contrast, lahars generated by a much smaller eruption (indecisiveness by government officials, rather than any major deficiencies in scientific data. Ruiz's disastrous outcome, however, together with responses to subsequent hazardous eruptions in Chile, Colombia, Ecuador, and Peru has spurred significant improvements in reducing volcano risk in the Andean region. But much remains to be done.

  19. Arc Statistics

    CERN Document Server

    Meneghetti, M; Dahle, H; Limousin, M

    2013-01-01

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

  20. Modeling Arcs

    CERN Document Server

    Insepov, Zeke; Veitzer, Seth; Mahalingam, Sudhakar

    2011-01-01

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

  1. Peaks, plateaus, canyons, and craters: The complex geometry of simple mid-domain effect models

    DEFF Research Database (Denmark)

    Colwell, Robert K.; Gotelli, Nicholas J.; Rahbek, Carsten

    2009-01-01

    Background: Geographic ranges, randomly located within a bounded geographical domain, Geographic ranges, randomly located within a bounded geographical domain, produce a central hump of species richness (the mid-domain effect, MDE). The hump arises from geometric constraints on the location of ra...... of a uniform size generate more complex patterns, including peaks, plateaus, canyons, and craters of species richness....

  2. Crustal and tectonic controls on large-explosive volcanic eruptions

    Science.gov (United States)

    Sheldrake, Tom; Caricchi, Luca

    2017-04-01

    Quantifying the frequency-Magnitude (f-M) relationship for volcanic eruptions is important to estimate volcanic hazard. Furthermore, understanding how this relationship varies between different groups of volcanoes can provide insights into the processes that control the size and rate of volcanic events. Using a Bayesian framework, which allows us to conceptualise the volcanic record as a series of individual and unique time series, associated by a common group behaviour, we identify variations in the size and rate of volcanism in different volcanic arcs. These variations in behaviour are linked to key parameters that include the motion of subduction, rate of subduction, age of the slab and thickness of the crust. The effects of these parameters on volcanism are interpreted in terms of variations in mantle productivity and the thermal efficiency of magma transfer in arc crustal systems. Understanding the link between subduction architecture, heat content of magmatic systems, and volcanic activity will serve to improve our capacity to quantify volcanic hazard in regions with limited geological and historical records of volcanic activity.

  3. Volcanic gas

    Science.gov (United States)

    McGee, Kenneth A.; Gerlach, Terrance M.

    1995-01-01

    In Roman mythology, Vulcan, the god of fire, was said to have made tools and weapons for the other gods in his workshop at Olympus. Throughout history, volcanoes have frequently been identified with Vulcan and other mythological figures. Scientists now know that the “smoke" from volcanoes, once attributed by poets to be from Vulcan’s forge, is actually volcanic gas naturally released from both active and many inactive volcanoes. The molten rock, or magma, that lies beneath volcanoes and fuels eruptions, contains abundant gases that are released to the surface before, during, and after eruptions. These gases range from relatively benign low-temperature steam to thick hot clouds of choking sulfurous fume jetting from the earth. Water vapor is typically the most abundant volcanic gas, followed by carbon dioxide and sulfur dioxide. Other volcanic gases are hydrogen sulfide, hydrochloric acid, hydrogen, carbon monoxide, hydrofluoric acid, and other trace gases and volatile metals. The concentrations of these gas species can vary considerably from one volcano to the next.

  4. Distribution and characteristics of volcanic reservoirs in China

    Institute of Scientific and Technical Information of China (English)

    HUANG Yulong; WANG Pujun; CHEN Shuming

    2009-01-01

    About forty productive oil/gas fields hosted in volcanic reservoirs have been found since 1957 in fourteen basins of China. They can be simply subdivided into two groups, the east and the west. Reservoir volcanic rocks of the east group are predominantly composed of Late Jurassic to Early Cretaceous rhyolite and Tertiary basalt, preferred being considered as rift type volcanics developed in the circum-Pacific tectonic regime. Those of the west are Permo-Carboniferous intermediate/basic volcanic rocks, being island-arc type ones developed in paleo-Asian Ocean tectonic regime.

  5. Venus volcanism: initial analysis from magellan data.

    Science.gov (United States)

    Head, J W; Campbell, D B; Elachi, C; Guest, J E; McKenzie, D P; Saunders, R S; Schaber, G G; Schubert, G

    1991-04-12

    Magellan images confirm that volcanism is widespread and has been fimdamentally important in the formation and evolution of the crust of Venus. High-resolution imaging data reveal evidence for intrusion (dike formation and cryptodomes) and extrusion (a wide range of lava flows). Also observed are thousands of small shield volcanoes, larger edifices up to several hundred kilometers in diameter, massive outpourings of lavas, and local pyroclastic deposits. Although most features are consistent with basaltic compositions, a number of large pancake-like domes are morphologically similar to rhyolite-dacite domes on Earth. Flows and sinuous channels with lengths of many hundreds of kilometers suggest that extremely high effusion rates or very fluid magmas (perhaps komatiites) may be present. Volcanism is evident in various tectonic settings (coronae, linear extensional and compressional zones, mountain belts, upland rises, highland plateaus, and tesserae). Volcanic resurfacing rates appear to be low (less than 2 Km(3)/yr) but the significance of dike formation and intrusions, and the mode of crustal formation and loss remain to be established.

  6. Venus volcanism: Initial analysis from Magellan data

    Science.gov (United States)

    Head, J.W.; Campbell, D.B.; Elachi, C.; Guest, J.E.; Mckenzie, D.P.; Saunders, R.S.; Schaber, G.G.; Schubert, G.

    1991-01-01

    Magellan images confirm that volcanism is widespread and has been fundamentally important in the formation and evolution of the crust of Venus. High-resolution imaging data reveal evidence for intrusion (dike formation and cryptodomes) and extrusion (a wide range of lava flows). Also observed are thousands of small shield volcanoes, larger edifices up to several hundred kilometers in diameter, massive outpourings of lavas, and local pyroclastic deposits. Although most features are consistent with basaltic compositions, a number of large pancake-like domes are morphologically similar to rhyolite-dacite domes on Earth. Flows and sinuous channels with lengths of many hundreds of kilometers suggest that extremely high effusion rates or very fluid magmas (perhaps komatiites) may be present. Volcanism is evident in various tectonic settings (coronae, linear extensional and compressional zones, mountain belts, upland rises, highland plateaus, and tesserae). Volcanic resurfacing rates appear to be low (less than 2 km3/yr) but the significance of dike formation and intrusions, and the mode of crustal formation and loss remain to be established.

  7. Volcanic Catastrophes

    Science.gov (United States)

    Eichelberger, J. C.

    2003-12-01

    The big news from 20th century geophysics may not be plate tectonics but rather the surprise return of catastrophism, following its apparent 19th century defeat to uniformitarianism. Divine miracles and plagues had yielded to the logic of integrating observations of everyday change over time. Yet the brilliant interpretation of the Cretaceous-Tertiary Boundary iridium anomaly introduced an empirically based catastrophism. Undoubtedly, decades of contemplating our own nuclear self-destruction played a role in this. Concepts of nuclear winter, volcanic winter, and meteor impact winter are closely allied. And once the veil of threat of all-out nuclear exchange began to lift, we could begin to imagine slower routes to destruction as "global change". As a way to end our world, fire is a good one. Three-dimensional magma chambers do not have as severe a magnitude limitation as essentially two-dimensional faults. Thus, while we have experienced earthquakes that are as big as they get, we have not experienced volcanic eruptions nearly as great as those preserved in the geologic record. The range extends to events almost three orders of magnitude greater than any eruptions of the 20th century. Such a calamity now would at the very least bring society to a temporary halt globally, and cause death and destruction on a continental scale. At maximum, there is the possibility of hindering photosynthesis and threatening life more generally. It has even been speculated that the relative genetic homogeneity of humankind derives from an evolutionary "bottleneck" from near-extinction in a volcanic cataclysm. This is somewhat more palatable to contemplate than a return to a form of Original Sin, in which we arrived at homogeneity by a sort of "ethnic cleansing". Lacking a written record of truly great eruptions, our sense of human impact must necessarily be aided by archeological and anthropological investigations. For example, there is much to be learned about the influence of

  8. Voltage plateaus on V( I) curves of long quasi-one-dimensional superconducting wires (without microwave irradiation)

    Science.gov (United States)

    Kuznetsov, V. I.; Firsov, A. A.

    2016-11-01

    Segments of an almost constant voltage (plateaus) on the V( I) curves of long quasi-one-dimensional superconducting aluminum wires placed in a magnetic field are found slightly below T c, which are unexpected at the parameters and geometry considered in this work. These plateaus are assumingly attributed to subharmonics of the superconducting gap and are due to multiple Andreev reflection and strong quasiparticle heating, which occur in the nonequilibrium region of a wire. The plateaus indicate the coexistence of superconductivity and dissipation in these wires. These results cannot be described by the existing theories.

  9. Making and breaking an Island arc: a new perspective from the Oligocene Kyushu-Palau arc

    Science.gov (United States)

    Ishizuka, O.; Taylor, R. N.; Yuasa, M.; Ohara, Y.

    2010-12-01

    The Kyushu-Palau Ridge (KPR) is a 2000km long remnant island arc that is separated from the active Izu-Bonin-Mariana (IBM) arc system by a series of spreading and rift basins. In this study we present 40Ar/39Ar ages and geochemical data for new samples taken from the entire length of the Kyushu-Palau arc. As such, this data provides the first comprehensive evaluation of temporal and spatial changes that are present in an Eocene-Oligocene island arc. Kyushu-Palau arc geochemistry is evaluated alongside new data from the conjugate arc which is stranded within the IBM fore-arc. Boninitic magmatism gave way to transitional arc suites including high-Mg andesites at c. 45 Ma (Ishizuka et al., 2006). After the transitional 45-41 Ma period, a mature arc system developed through the Eocene-Oligocene time: This volcanism is now preserved as the KPR. Dating results from 33 sites indicate that the KPR was active between 25 and 43 Ma, but the majority of the exposed volcanism occurred in the final phase of this arc, between 25 and 27 Ma. Unlike the IBM, the KPR has only limited systematic along-arc trends and does not include any of the strongly HIMU lavas found to the south of Izu-Bonin. Two components found along the KPR are found to have geochemistry that suggests an origin in the supra-subduction mantle rather than from the descending ocean crust. Firstly, in the south of the arc, EM-2-like lavas are present where the West Philippine Basin was in the final stages of spreading. Secondly, EM-1-like lavas are present in a restricted section of the arc, suggesting a localised heterogeneity. Subduction flux beneath the KPR generally imparted a Pb isotope vector towards low Δ8/4 (19). This is a similar trend to the Eocene/Oligocene lavas found on the eastern side of the basins which split the arc at 25Ma. Another geochemical heterogeneity is found at the KPR-Daito Ridge intersection where arc magmatism occurred on pre-existing Daito Ridge crust: a Cretaceous remnant arc

  10. Crustal thinning between the Ethiopian and East African Plateaus from modeling Rayleigh wave dispersion

    Energy Technology Data Exchange (ETDEWEB)

    Benoit, M H; Nyblade, A A; Pasyanos, M E

    2006-01-17

    The East African and Ethiopian Plateaus have long been recognized to be part of a much larger topographic anomaly on the African Plate called the African Superswell. One of the few places within the African Superswell that exhibit elevations of less than 1 km is southeastern Sudan and northern Kenya, an area containing both Mesozoic and Cenozoic rift basins. Crustal structure and uppermost mantle velocities are investigated in this area by modeling Rayleigh wave dispersion. Modeling results indicate an average crustal thickness of 25 {+-} 5 km, some 10-15 km thinner than the crust beneath the adjacent East African and Ethiopian Plateaus. The low elevations can therefore be readily attributed to an isostatic response from crustal thinning. Low Sn velocities of 4.1-4.3 km/s also characterize this region.

  11. Comparison of the renal disease at the Tibetan plateaus and plain based on renal biopsy data

    Institute of Scientific and Technical Information of China (English)

    周岩

    2014-01-01

    Objective To compare the characteristics of renal disease based on renal biopsy data between the Tibetan plateaus and the plain.Methods 160 chronic kidney diseases patients underwent renal biopsy from the plain and80 cases from Tibet plateau were compared in a parallel controlled manner.The relationship of renal pathology and clinical signs were also compared.Results(1)The male to female ratio was quite different between Tibet

  12. Retired flies, hidden plateaus, and the evolution of senescence in Drosophila melanogaster.

    Science.gov (United States)

    Curtsinger, James W

    2016-06-01

    Late-life plateaus in age-specific mortality have been an evolutionary and biodemographic puzzle for decades. Although classic theory on the evolution of senescence predicts late-life walls of death, observations in experimental organisms document the opposite trend: a slowing in the rate of increase of mortality at advanced ages. Here, I analyze published life-history data on individual Drosophila melanogaster females and argue for a fundamental change in our understanding of mortality in this important model system. Mortality plateaus are not, as widely assumed, exclusive to late life, and are not explained by population heterogeneity-they are intimately connected to individual fecundity. Female flies begin adult life in the working stage, a period of active oviposition and low but accelerating mortality. Later they transition to the retired stage, a terminal period characterized by limited fecundity and relatively constant mortality. Because ages of transition differ between flies, age-synchronized cohorts contain a mix of working and retired flies. Early- and mid-life plateaus are obscured by the presence of working flies, but can be detected when cohorts are stratified by retirement status. Stage-specificity may be an important component of Drosophila life-history evolution.

  13. Volcanism and associated hazards: the Andean perspective

    Directory of Open Access Journals (Sweden)

    R. I. Tilling

    2009-12-01

    Full Text Available Andean volcanism occurs within the Andean Volcanic Arc (AVA, which is the product of subduction of the Nazca Plate and Antarctica Plates beneath the South America Plate. The AVA is Earth's longest but discontinuous continental-margin volcanic arc, which consists of four distinct segments: Northern Volcanic Zone, Central Volcanic Zone, Southern Volcanic Zone, and Austral Volcanic Zone. These segments are separated by volcanically inactive gaps that are inferred to indicate regions where the dips of the subducting plates are too shallow to favor the magma generation needed to sustain volcanism. The Andes host more volcanoes that have been active during the Holocene (past 10 000 years than any other volcanic region in the world, as well as giant caldera systems that have produced 6 of the 47 largest explosive eruptions (so-called "super eruptions" recognized worldwide that have occurred from the Ordovician to the Pleistocene.

    The Andean region's most powerful historical explosive eruption occurred in 1600 at Huaynaputina Volcano (Peru. The impacts of this event, whose eruptive volume exceeded 11 km3, were widespread, with distal ashfall reported at distances >1000 km away. Despite the huge size of the Huaynaputina eruption, human fatalities from hazardous processes (pyroclastic flows, ashfalls, volcanogenic earthquakes, and lahars were comparatively small owing to the low population density at the time. In contrast, lahars generated by a much smaller eruption (<0.05 km3 in 1985 of Nevado del Ruiz (Colombia killed about 25 000 people – the worst volcanic disaster in the Andean region as well as the second worst in the world in the 20th century. The Ruiz tragedy has been attributed largely to ineffective communications of hazards information and indecisiveness by government officials, rather than any major deficiencies in scientific data. Ruiz's disastrous outcome, however, together with responses to subsequent

  14. Geochemical constraints on the relationship between the Miocene-Pliocene volcanism and tectonics in the Palaoco and Fortunoso volcanic fields, Mendoza Region, Argentina

    DEFF Research Database (Denmark)

    Dyhr, Charlotte Thorup; Holm, Paul Martin; Llambias, Eduardo J.

    2013-01-01

    New 40Ar/39Ar analyses constrain the formation of the volcanic succession of Sierra de Palaoco in the present back-arc of the Andean Southern Volcanic Zone (SVZ), near 36°S, to the Late Miocene and assigns them to the Huincán II Formation. The composition of major and trace elements, Sr, Nd and Pb...

  15. The Zuni-Bandera Volcanic Field, NM: An Analog for Exploring Planetary Volcanic Terrains

    Science.gov (United States)

    Bleacher, J. E.; Garry, W. B.; Zimbelman, J. R.; Crumpler, L. S.; Aubele, J. C.

    2010-12-01

    The Zuni-Bandera volcanic field, near Grants, New Mexico, is comprised of volcanic deposits from several basaltic eruptions during the last million years. This vent field exhibits a diverse group of coalesced lava flows and displays well-preserved volcanic features including a’a and pahoehoe flows, collapsed lava tubes, cinder cones and low shields. The McCartys flow is a 48-km long inflated basalt flow and is the youngest in the field at around 3000 years old. Over the last three years we have used the Zuni-Bandera volcanic field, and the McCartys flow in particular, as a terrestrial analog for exploring planetary volcanic fields, and understanding the role of lava sheet inflation in flow field development. We have conducted three different styles of analog tests, 1) basic field science focused on understanding lava sheet inflation, 2) mission operations tests related to EVA design and real-time modification of traverse plans, and 3) science enabling technology tests. The Zuni-Bandera field is an ideal location for each style of analog test because it provides easy access to a diverse set of volcanic features with variable quality of preservation. However, many limitations must also be considered in order to maximize lessons learned. The McCartys flow displays well-preserved inflation plateaus that rise up to 15 m above the surrounding field. The preservation state enables textures and morphologies indicative of this process to be characterized. However, the pristine nature of the flow does not compare well with the much older and heavily modified inflated flows of Mars and the Moon. Older flows west of McCartys add value to this aspect of analog work because of their degraded surfaces, development of soil horizons, loose float, and limited exposure of outcrops, similar to what might be observed on the Moon or Mars. EVA design tests and science enabling technology tests at the Zuni-Bandera field provide the opportunity to document and interpret the relationships

  16. Recent seismicity detection increase in the Santorini volcanic island complex

    OpenAIRE

    G. Chouliaras; Drakatos, G.; Makropoulos, K.; Melis, N. S.

    2012-01-01

    Santorini is the most active volcanic complex in the South Aegean Volcanic Arc. To improve the seismological network detectability of the seismicity in this region, the Institute of Geodynamics of the National Observatory of Athens (NOA) recently installed 4 portable seismological stations supplementary to the 3 permanent stations operating in the region. The addition of these stations has significantly improved the detectability and reporting of the local seismic activity in the NOA instrume...

  17. Neogene volcanism in Gutai Mts. (Eastern Carpathains: a review

    Directory of Open Access Journals (Sweden)

    Marinel Kovacs

    2003-04-01

    Full Text Available Two types of volcanism developed in Gutâi Mts. (inner volcanic chain of Eastern Carpathians: a felsic, extensional/“back-arc” type and an intermediate, arc type. The felsic volcanism of explosive origin, consisting of caldera-related rhyolitic ignimbrites and resedimented volcaniclastics, had taken place during Early-Middle Badenian and Early Sarmatian. The intermediate volcanism, consisting of extrusive (effusive and explosive and intrusive activity, had developed during Sarmatian and Pannonian (13.4-7.0 Ma. It is represented by typical calc-alkaline series, from basalts to rhyolites. Lava flows of basaltic andesites and andesites are predominant, often emplaced in subaqueous environment. Extrusive domes, mainly composed of dacites, are associated to the andesitic volcanic structures. The intermediate volcanism, consisting of extrusive (effusive and explosive and intrusive activity, had developed during Sarmatian and Pannonian (13.4-7.0 Ma. It is represented by typical calc-alkaline series, from basalts to rhyolites. Lava flows of basaltic andesites and andesites are predominant, often emplaced in subaqueous environment. Extrusive domes, mainly composed of dacites, are associated to the andesitic volcanic structures. The geochemical study on the volcanic rocks shows the calc-alkaline character of both felsic and intermediate volcanism and typical subduction zones geochemical signatures for the intermediate one. The felsic volcanism shows affinities with subduction-related rocks as well. The main petrogenetic process in Gutâi Mts. was crustal assimilation, strongly constrained by trace element and isotope geochemistry.

  18. Volcanic hazard management in dispersed volcanism areas

    Science.gov (United States)

    Marrero, Jose Manuel; Garcia, Alicia; Ortiz, Ramon

    2014-05-01

    Traditional volcanic hazard methodologies were developed mainly to deal with the big stratovolcanoes. In such type of volcanoes, the hazard map is an important tool for decision-makers not only during a volcanic crisis but also for territorial planning. According to the past and recent eruptions of a volcano, all possible volcanic hazards are modelled and included in the hazard map. Combining the hazard map with the Event Tree the impact area can be zoned and defining the likely eruptive scenarios that will be used during a real volcanic crisis. But in areas of disperse volcanism is very complex to apply the same volcanic hazard methodologies. The event tree do not take into account unknown vents, because the spatial concepts included in it are only related with the distance reached by volcanic hazards. The volcanic hazard simulation is also difficult because the vent scatter modifies the results. The volcanic susceptibility try to solve this problem, calculating the most likely areas to have an eruption, but the differences between low and large values obtained are often very small. In these conditions the traditional hazard map effectiveness could be questioned, making necessary a change in the concept of hazard map. Instead to delimit the potential impact areas, the hazard map should show the expected behaviour of the volcanic activity and how the differences in the landscape and internal geo-structures could condition such behaviour. This approach has been carried out in La Palma (Canary Islands), combining the concept of long-term hazard map with the short-term volcanic scenario to show the expected volcanic activity behaviour. The objective is the decision-makers understand how a volcanic crisis could be and what kind of mitigation measurement and strategy could be used.

  19. VOLCANIC TSUNAMI GENERATING SOURCE MECHANISMS IN THE EASTERN CARIBBEAN REGION

    Directory of Open Access Journals (Sweden)

    George Pararas-Carayannis

    2004-01-01

    Full Text Available Earthquakes, volcanic eruptions, volcanic island flank failures and underwater slides have generated numerous destructive tsunamis in the Caribbean region. Convergent, compressional and collisional tectonic activity caused primarily from the eastward movement of the Caribbean Plate in relation to the North American, Atlantic and South American Plates, is responsible for zones of subduction in the region, the formation of island arcs and the evolution of particular volcanic centers on the overlying plate. The inter-plate tectonic interaction and deformation along these marginal boundaries result in moderate seismic and volcanic events that can generate tsunamis by a number of different mechanisms. The active geo-dynamic processes have created the Lesser Antilles, an arc of small islands with volcanoes characterized by both effusive and explosive activity. Eruption mechanisms of these Caribbean volcanoes are complex and often anomalous. Collapses of lava domes often precede major eruptions, which may vary in intensity from Strombolian to Plinian. Locally catastrophic, short-period tsunami-like waves can be generated directly by lateral, direct or channelized volcanic blast episodes, or in combination with collateral air pressure perturbations, nuéss ardentes, pyroclastic flows, lahars, or cascading debris avalanches. Submarine volcanic caldera collapses can also generate locally destructive tsunami waves. Volcanoes in the Eastern Caribbean Region have unstable flanks. Destructive local tsunamis may be generated from aerial and submarine volcanic edifice mass edifice flank failures, which may be triggered by volcanic episodes, lava dome collapses, or simply by gravitational instabilities. The present report evaluates volcanic mechanisms, resulting flank failure processes and their potential for tsunami generation. More specifically, the report evaluates recent volcanic eruption mechanisms of the Soufriere Hills volcano on Montserrat, of Mt. Pel

  20. On the gauge invariant and topological nature of the localization determining the Quantum Hall Effect plateaus

    CERN Document Server

    Cabo-Montes de Oca, Alejandro

    2002-01-01

    It is shown how the electromagnetic response of 2DEG under Quantum Hall Effect regime, characterized by the Chern-Simons topological action, transforms the sample impurities and defects in charge-reservoirs that stabilize the Hall conductivity plateaus. The results determine the basic dynamical origin of the singular properties of localization under the occurrence of the Quantum Hall Effect obtained in the pioneering works of Laughlin and of Joynt and Prange, by means of a gauge invariance argument and a purely electronic analysis, respectively. The common intuitive picture of electrons moving along the equipotential lines gets an analytical realization through the Chern-Simons current and charge densities.

  1. Observations on Phallocryptus Spinosa (Branchiopoda, Anostraca) Populations from the high Plateaus of Northeastern Algeria

    OpenAIRE

    Mounia Amarouayache

    2014-01-01

    Phallocryptus spinosa (Thamnocephalidae) is a small primitive crustacean which lives in temporary saline pools of the Palaearctic region called Chott, Sebkha, Garâa or Daya in North Africa. Data on its biology and life history are very scarce despite its ecological importance in wetlands. Four populations living in the Northeastern High Plateaus of Algeria, Garâas Guellif, El-Tarf, Ank Djemel and Sebkha Ez-Zemoul, have been studied in point of view of their morphmetry (13 parameters) and thei...

  2. Doping-dependent magnetization plateaus of a coupled spin-electron chain: exact results

    Science.gov (United States)

    Strečka, Jozef; Čisárová, Jana

    2016-10-01

    A coupled spin-electron chain composed of localized Ising spins and mobile electrons is exactly solved in an external magnetic field within the transfer-matrix method. The ground-state phase diagram involves in total seven different ground states, which differ in the number of mobile electrons per unit cell and the respective spin arrangements. A rigorous analysis of the low-temperature magnetization process reveals doping-dependent magnetization plateaus, which may be tuned through the density of mobile electrons. It is demonstrated that the fractional value of the electron density is responsible for an enhanced magnetocaloric effect due to an annealed bond disorder of the mobile electrons.

  3. Temporal variation of the stress field during the construction of the central Andes: Constrains from the volcanic arc region (22-26°S), Western Cordillera, Chile, during the last 20 Ma

    Science.gov (United States)

    Giambiagi, Laura; Alvarez, Pamela; Spagnotto, Silvana

    2016-09-01

    In order to understand the response of the stress field state to intrinsic processes during the construction of the Andes, such as thickening of the continental crust, lithospheric delamination, and/or thermal weakening, we investigate the stress field evolution of the arc region since the last 20 Myr, in the central Andes (22-26.5°S). The 43 reduced paleostress tensors derived from inversion of 682 fault slip data reveal a complex pattern of stress states during the last episode of orogenic construction and topographic uplift. We identify two geodynamic stages: the first stage corresponds to the construction of the Altiplano/Puna plateau and the second one to its gravitational collapse. Four stress states that have prevailed in the Altiplano/Puna plateau since middle Miocene times characterize the transition from one stage to the other. Along the study latitudes, a spatiotemporal change in stress state is clearly observed, which led to an understanding that a change in the stress field may be related not only to the boundary conditions but also to intrinsic factors associated with the construction of the Andean orogeny. Our results suggest that approximately at 13-10 Ma and approximately 8-5 Ma, in the southern Altiplano and northern Puna, and in the southern Puna, respectively, regional elevation and crustal thicknesses reached threshold values necessary to generate the orogenic collapse.

  4. Volcanic hazard assessment in monogenetic volcanic fields

    OpenAIRE

    Bartolini, Stefania

    2014-01-01

    [eng] One of the most important tasks of modern volcanology, which represents a significant socio-economic implication, is to conduct hazard assessment in active volcanic systems. These volcanological studies are aimed at hazard that allows to constructing hazard maps and simulating different eruptive scenarios, and are mainly addressed to contribute to territorial planning, definition of emergency plans or managing volcanic crisis. The impact of a natural event, as a volcanic eruption, can s...

  5. The Boring Volcanic Field of the Portland-Vancouver area, Oregon and Washington: tectonically anomalous forearc volcanism in an urban setting

    Science.gov (United States)

    Evarts, Russell C.; Conrey, Richard M.; Fleck, Robert J.; Hagstrum, Jonathan T.; O'Connor, Jim; Dorsey, Rebecca; Madin, Ian P.

    2009-01-01

    More than 80 small volcanoes are scattered throughout the Portland-Vancouver metropolitan area of northwestern Oregon and southwestern Washington. These volcanoes constitute the Boring Volcanic Field, which is centered in the Neogene Portland Basin and merges to the east with coeval volcanic centers of the High Cascade volcanic arc. Although the character of volcanic activity is typical of many monogenetic volcanic fields, its tectonic setting is not, being located in the forearc of the Cascadia subduction system well trenchward of the volcanic-arc axis. The history and petrology of this anomalous volcanic field have been elucidated by a comprehensive program of geologic mapping, geochemistry, 40Ar/39Ar geochronology, and paleomag-netic studies. Volcanism began at 2.6 Ma with eruption of low-K tholeiite and related lavas in the southern part of the Portland Basin. At 1.6 Ma, following a hiatus of ~0.8 m.y., similar lavas erupted a few kilometers to the north, after which volcanism became widely dispersed, compositionally variable, and more or less continuous, with an average recurrence interval of 15,000 yr. The youngest centers, 50–130 ka, are found in the northern part of the field. Boring centers are generally monogenetic and mafic but a few larger edifices, ranging from basalt to low-SiO2 andesite, were also constructed. Low-K to high-K calc-alkaline compositions similar to those of the nearby volcanic arc dominate the field, but many centers erupted magmas that exhibit little influence of fluids derived from the subducting slab. The timing and compositional characteristics of Boring volcanism suggest a genetic relationship with late Neogene intra-arc rifting.

  6. The importance of shallow hydrothermal island arc systems in ocean biogeochemistry

    NARCIS (Netherlands)

    Hawkes, J.A.; Connelly, D.P.; Rijkenberg, M.J.A.; Achterberg, E.P.

    2014-01-01

    Hydrothermal venting often occurs at submarine volcanic calderas on island arc chains, typically at shallower depths than mid-ocean ridges. The effect of these systems on ocean biogeochemistry has been under-investigated to date. Here we show that hydrothermal effluent from an island arc caldera was

  7. Colorado Plateaus Ecoregion: Chapter 21 in Status and trends of land change in the Western United States--1973 to 2000

    Science.gov (United States)

    Stier, Michael P.

    2012-01-01

    The Colorado Plateaus Ecoregion covers approximately 129,617 km2 (50,045 mi2) within southern and eastern Utah, western Colorado, and the extreme northern part of Arizona (fig. 1). The terrain of this ecoregion is characterized by broad plateaus, ancient volcanoes, and deeply dissected canyons (Booth and others, 1999; fig. 2). The ecoregion is bounded on the east by the Wyoming Basin and Southern Rockies Ecoregions in Colorado and on the northwest by the Wasatch and Uinta Mountains Ecoregion in northern and central Utah. To the south, the ecoregion borders the Arizona/New Mexico Plateau Ecoregion, which has a higher elevation and more grasslands than the Colorado Plateaus Ecoregion (Omernik, 1987; U.S. Environmental Protection Agency, 1997).

  8. Peaks, plateaus, numerical instabilities, and achievable accuracy in Galerkin and norm minimizing procedures for solving Ax=b

    Energy Technology Data Exchange (ETDEWEB)

    Cullum, J. [IBM T.J. Watson Research Center, Yorktown Heights, NY (United States)

    1994-12-31

    Plots of the residual norms generated by Galerkin procedures for solving Ax = b often exhibit strings of irregular peaks. At seemingly erratic stages in the iterations, peaks appear in the residual norm plot, intervals of iterations over which the norms initially increase and then decrease. Plots of the residual norms generated by related norm minimizing procedures often exhibit long plateaus, sequences of iterations over which reductions in the size of the residual norm are unacceptably small. In an earlier paper the author discussed and derived relationships between such peaks and plateaus within corresponding Galerkin/Norm Minimizing pairs of such methods. In this paper, through a set of numerical experiments, the author examines connections between peaks, plateaus, numerical instabilities, and the achievable accuracy for such pairs of iterative methods. Three pairs of methods, GMRES/Arnoldi, QMR/BCG, and two bidiagonalization methods are studied.

  9. Gas arc constriction for plasma arc welding

    Science.gov (United States)

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

    1994-01-01

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

  10. The Global Array of Primitve Arc Melts

    Science.gov (United States)

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

    2015-12-01

    A longstanding question concerns the nature of the melts forming in the subarc mantle and giving rise to arc magmatism. The global array of primitive arc melts (1180 volcanic rocks in 25 arcs extracted from the georoc database, calculated to be in equilibrium with mantle olivine) yields five principal melt types: calc-alkaline basalts and high-Mg andesites, tholeiitic basalts and high-Mg andesites, and shoshonitic or alkaline arc melts; many arcs have more than one type. Primitive calc-alkaline basalts occur in 11 arcs but most strikingly, 8 continental arcs (incl. Aleutians, Cascades, Japan, Mexico, Kamtschatka) have a continuous range of calc-alkaline basalts to high-Mg andesites with mostly 48-58 wt% SiO2. In each arc, these are spatially congruent, trace element patterns overlap, and major elements form a continuum. Their Ca-Mg-Si systematics suggests saturation in olivine+opx+cpx. We hence interpret the large majority of high-Mg andesites as derived from primitive calc-alkaline basalts through fractionation and reaction in the shallower mantle. Removal of anhydrous mantle phases at lower pressures increases SiO2 and H2O-contents while Mg# and Ni remain buffered to mantle values. Primitive tholeiitic basalts (Cascades, Kermadec, Marianas, Izu-Bonin, Japan, Palau, Sunda) have a much lesser subduction signal (e.g. in LILE) than the calc-alkaline suite. These tholeiites have been interpreted to form through decompression melting, but also characterize young intraoceanic arcs. In the two continental arcs with both tholeiitic and calc-alkaline primitive basalts (clearly distinct in trace patterns), there is no clear spatial segregation (Casacades, Japan). Three intraoceanic arcs (Marianas, Izu-Bonin, Tonga) have primitive tholeiitic, highly depleted high-Mg andesites (boninites) with HFSE and HREE slightly above primitive mantle values. These deviate in majors from the array formed by the basalts and calc-alkaline andesites suggesting that only these formed from a

  11. Petrogenesis of Late Cretaceous lava flows from a Ceno-Tethyan island arc: The Raskoh arc, Balochistan, Pakistan

    Science.gov (United States)

    Siddiqui, Rehanul Haq; Qasim Jan, M.; Asif Khan, M.

    2012-10-01

    The Raskoh arc is about 250 km long, 40 km wide and trends in an ENE direction. The oldest rock unit in the Raskoh arc is an accretionary complex (Early to Late Jurassic), which is followed in age by Kuchakki Volcanic Group, the most wide spread unit of the Raskoh arc. The Volcanic Group is mainly composed of basaltic to andesitic lava flows and volcaniclastics, including agglomerate, volcanic conglomerate, breccia and tuff, with subordinate shale, sandstone, limestone and chert. The flows generally form 3-15 m thick lenticular bodies but rarely reach up to 300 m. They are mainly basaltic-andesites with minor basalts and andesites. The main textures exhibited by these rocks are hypocrystalline porphyritic, subcumulophyric and intergranular. The phenocrysts comprise mainly plagioclase (An30-54 in Nok Chah and An56-64 in Bunap). They are embedded in a micro-cryptocrystalline groundmass having the same minerals. Apatite, magnetite, titanomagnetite and hematite occur as accessory minerals. Major, trace and rare earth elements suggest that the volcanics are oceanic island arc tholeiites. Their low Mg # (42-56) and higher FeO (total)/MgO (1.24-2.67) ratios indicate that the parent magma of these rocks was not directly derived from a mantle source but fractionated in an upper level magma chamber. The trace element patterns show enrichment in LILE and depletion in HFSE relative to N-MORB. Their primordial mantle-normalized trace element patterns show marked negative Nb anomalies with positive spikes on K, Ba and Sr which confirm their island arc signatures. Slightly depleted LREE to flat chondrite normalized REE patterns further support this interpretation. The Zr versus Zr/Y and Cr versus Y studies show that their parent magma was generated by 20-30% melting of a depleted mantle source. The trace elements ratios including Zr/Y (1.73-3.10), Ti/Zr (81.59-101.83), Ti/V (12.39-30.34), La/YbN (0.74-2.69), Ta/Yb (0.02-0.05) and Th/Yb (0.11-0.75) of the volcanics are more

  12. Cross-arc Variations in Lava Chemistry in the Tonga Arc-Lau Back Arc System, 19- 23°S

    Science.gov (United States)

    Michael, P. J.; Bezos, A.; Langmuir, C. H.; Escrig, S.; Matzen, A. K.; Asimow, P.; Arculus, R.

    2007-12-01

    The Tonga arc system from 19°-23°S consists of the active Tofua arc, the Eastern Lau Spreading Center (ELSC; a back arc spreading center), and numerous seamounts between them. We use the excellent sampling of ELSC and 34 nearby seamounts, along with sparser published analyses of Tofua arc, to examine the spatial relations of chemistry and melting in this subduction system. The spatial constraints can be used to better understand the nature and mechanism of enrichment that is caused by subduction. Geochemistry along the axis of ELSC is related to its distance to the Tofua arc, which decreases continuously from 100 km in the north to 40 km in the south. The subduction influence (e.g., fluid mobile elements) along ELSC increases in several sharp gradients towards the south as ELSC gets closer to the arc. The six different tectonic segments of ELSC display mixing relationships in trace element ratio-ratio diagrams (e.g., Ba/La vs Th/La) in which one end member is a subduction component that is distinctive for each segment (Escrig et al., this meeting). We explore whether the distinctive subduction components of each ELSC segment are reflected by the Tofua arc that is adjacent to that segment, and by the intervening seamounts. Relationships between the arc, back arc and seamounts are different in the north and the south. In the south where the arc-back arc distance is smaller, the Tofua arc volcanic rocks share the distinctive trace element characteristics of their corresponding ELSC segment, and extend the mixing trajectories to higher, more arc-like values. Seamounts that are located between Tofua arc and ELSC also share the distinctive trace element characteristics of the local arc + back-arc, and are intermediate in their trace element ratios. These observations are consistent with the model of Langmuir et al., (2006) in which magmas of back arc spreading centers form from two components: a dry side similar to mid-ocean ridges and a wet (trenchward) side that

  13. Petrogenesis of Cenozoic Volcanic Rocks in Tengchong Region of Western Yunnan Province,China

    Institute of Scientific and Technical Information of China (English)

    从柏林; 陈秋媛; 张儒瑷; 吴根耀; 徐平

    1994-01-01

    The Tengchong Cenozoic volcanic rocks belong to the high-K calc-alkaline rock series.They are strongly depleted in high field strength (HFS) elements and enriched in large-ion lithophile(LIL) elements and LREE.The generation of Tengchong volcanic rocks has been considered to be relatedto the evolution of the Neo-Tethys.The Indian Plate was subducted beneath the southeastern Asia conti-nent,which resulted in the formation of Indo-Burman Arc in the Late Cretaeeous-Palaeocene time.Thecollision between the Indian continent and Indo-Burman Arc started in Eocene and lasted to the present.The Andaman Sea and the Inner Burman Tertiary Basin are a back-arc basin that has been extended sincethe Late Miocene.A distinct characteristic of Tengchong volcanics is that they show a chemical affinityrelated to island arc but their generation postdated the subduetion of the ocean plate.

  14. Partition function zeros and magnetization plateaus of the spin-1 Ising-Heisenberg diamond chain

    Science.gov (United States)

    Hovhannisyan, V. V.; Ananikian, N. S.; Kenna, R.

    2016-07-01

    We study the properties of the generalized spin-1 Ising-Heisenberg model on a diamond chain, which can be considered as a theoretical model for the homometallic magnetic complex [Ni3(C4H2O4)2 -(μ3 - OH) 2(H2O)4 ] n ṡ(2H2 O) n. The model possesses a large variety of ground-state phases due to the presence of biquadratic and single-ion anisotropy parameters. Magnetization and quadrupole moment plateaus are observed at one- and two-thirds of the saturation value. The distributions of Yang-Lee and Fisher zeros are studied numerically for a variety of values of the model parameters. The usual value σ = -1/2 alongside an unusual value σ = -2/3 ​is determined for the Yang-Lee edge singularity exponents.

  15. DO CHILDREN WITH FRAGILE X SYNDROME SHOW DECLINES OR PLATEAUS IN ADAPTIVE BEHAVIOR?

    Science.gov (United States)

    Hahn, Laura J.; Brady, Nancy C.; Warren, Steven F.; Fleming, Kandace K.

    2014-01-01

    This study explores if children with fragile X syndrome (FXS) show advances, declines, or plateaus in adaptive behavior over time and the relationship of nonverbal cognitive abilities and autistic behavior on these trajectories. Parents of 55 children with FXS completed the Vineland Adaptive Behavior Scales between 3 and 6 times from 2 to 10 years of age. Using raw scores, results indicate that about half of the sample showed advances in adaptive behavior, while the other half showed declines, indicating a regression in skills. Children who were more cognitively advanced and had less autistic behaviors had higher trajectories. Understanding the developmental course of adaptive behavior in FXS has implications for educational planning and intervention, especially for those children showing declines. PMID:26322389

  16. 2D Seismic Data Processing for Straight Lines in the Loess Plateaus in Fuxian of Shanbei

    Institute of Scientific and Technical Information of China (English)

    LiMinjie; ChenYequan; ZhangHai; PangShangming; DengGuozhen

    2005-01-01

    The crooked seismic lines along valleys were irregular previously in Fuxian of Shanbei,showing an irregular branch in plane, and hard to complete close grids. Therefore, it's difficult to conduct reservoir inversion of 2D seismic data. In 2001, Zhongyuan Oilfield Company carried out the study on field acquisition methods and seismic processing technology in Fuxian. Straight lines were passing through plateaus and formed seismic grids by using flexible geometry with variable linear bins.Data processing involved model-inversion based refraction static correction, surface consistent amplitude compensation, deconvolution, and pre-stack noise attenuation. As the result, seismic data with a high fidelity was provided for the subsequent reservoir predictions, small-amplitude structure interpretation and integrative geologic study. Because all lines were jointed to form grids, comprehensive interpretation of reservoir inversion could be finally implemented by using the pseudo logging method to control lines without wells.

  17. Brucellosis in nomadic pastoralists and their goats in two provinces of the eastern Algerian high plateaus.

    Science.gov (United States)

    Gabli, Abdelhafid; Agabou, Amir; Gabli, Zahra

    2015-08-01

    A 31-months study was conducted to elucidate the prevalence of brucellosis in nomadic pastoralists and their goats in two provinces of the eastern Algerian high plateaus. Five hundred eight human and 4955 animal sera were screened with the Rose Bengal plate test and the complement fixation test for confirmation. Uterine fluids from aborting goats were subjected to microbiological analyses to determine the biovars responsible for abortions. The overall seroprevalence was 0.98% among animals and 15.84% among herds. A significant correlation was recorded between occurrence of brucellosis and herd size (r = 0.4046, P Brucella melitensis biovar 3 was the only aetiology of brucellosis-associated abortion in goats of the studied region.

  18. Carboniferous rifted arcs leading to an archipelago of multiple arcs in the Beishan-Tianshan orogenic collages (NW China)

    Science.gov (United States)

    Tian, Zhonghua; Xiao, Wenjiao; Windley, Brian F.; Zhang, Ji'en; Zhang, Zhiyong; Song, Dongfang

    2016-12-01

    The Beishan and East Tianshan Orogenic Collages in the southernmost Central Asian Orogenic Belt (CAOB) record the final stages of evolution of the Paleo-Asian Ocean. These collages and their constituent arcs have an important significance for resolving current controversies regarding their tectonic setting and age, consequent accretionary history of the southern CAOB, and the closure time of the Paleo-Asian Ocean. In this paper, we present our work on the southern Mazongshan arc and the northern Hongyanjing Basin in the Beishan Orogenic Collage (BOC), and our comparison with the Bogda arc and associated basins in the East Tianshan Orogenic Collage. Field relationships indicate that the Pochengshan fault defines the boundary between the arc and basin in the BOC. Volcanic rocks including basalts and rhyolites in the Mazongshan arc have bimodal calc-alkaline characteristics, an enrichment in large ion lithophile elements such as Rb, Ba, and Pb and depletion in high field-strength elements (e.g., Nb and Ta), which were probably developed in a subduction-related tectonic setting. We suggest that these bimodal calc-alkaline volcanic rocks formed in rifted arcs instead of post-orogenic rifts with mantle plume inputs. By making detailed geochemical comparisons between the Mazongshan arc and the Bogda arc to the west, we further propose that they are similar and both formed in arc rifts, and helped generate a Carboniferous archipelago of multiple arcs in the southern Paleo-Asian Ocean. These data and ideas enable us to postulate a new model for the tectonic evolution of the southern CAOB.

  19. Current forest conditions of older stands of the mixed mesophytic forest region on the Appalachian Plateaus Province of eastern Kentucky

    Science.gov (United States)

    James F. Jr. Rosson

    2008-01-01

    E. Lucy Braun coined the term "mixed mesophytic forest" in 1916. These forests are structurally complex and occur extensively across the Appalachian Plateaus Province. This region is considered the epicenter of highest development of the eastern deciduous forest. I used U.S. Forest Service, Forest Inventory and Analysis (FIA) data to study current forest...

  20. Magnetization plateaus and ground-state phase diagrams of the S=1 Ising model on the Shastry Sutherland lattice

    Science.gov (United States)

    Deviren, Seyma Akkaya

    2017-02-01

    In this research, we have investigated the magnetic properties of the spin-1 Ising model on the Shastry Sutherland lattice with the crystal field interaction by using the effective-field theory with correlations. The effects of the applied field on the magnetization are examined in detail in order to obtain the magnetization plateaus, thus different types of magnetization plateaus, such as 1/4, 1/3, 1/2, 3/5, 2/3 and 7/9 of the saturation, are obtained for strong enough magnetic fields (h). Magnetization plateaus exhibit single, triple, quintuplet and sextuple forms according to the interaction parameters, hence the magnetization plateaus originate from the competition between the crystal field (D) and exchange interaction parameters (J, J‧). The ground-state phase diagrams of the system are presented in three varied planes, namely (h/J, J‧/J), (h/J, D/J) and (D/J, J‧/J) planes. These phase diagrams display the Néel (N), collinear (C) and ferromagnetic (F) phases for certain values of the model parameters. The obtained results are in good agreement with some theoretical and experimental studies.

  1. Recent seismicity detection increase in the Santorini volcanic island complex

    Science.gov (United States)

    Chouliaras, G.; Drakatos, G.; Makropoulos, K.; Melis, N. S.

    2012-04-01

    Santorini is the most active volcanic complex in the South Aegean Volcanic Arc. To improve the seismological network detectability of the seismicity in this region, the Institute of Geodynamics of the National Observatory of Athens (NOA) recently installed 4 portable seismological stations supplementary to the 3 permanent stations operating in the region. The addition of these stations has significantly improved the detectability and reporting of the local seismic activity in the NOA instrumental seismicity catalogue. In this study we analyze quantitatively the seismicity of the Santorini volcanic complex. The results indicate a recent significant reporting increase mainly for events of small magnitude and an increase in the seismicity rate by more than 100%. The mapping of the statistical significance of the rate change with the z-value method reveals that the rate increase exists primarily in the active fault zone perpendicular to the extensional tectonic stress regime that characterizes this region. The spatial distribution of the b-value around the volcanic complex indicates a low b-value distribution parallel to the extensional stress field, while the b-value cross section of the volcanic complex indicates relatively high b-values under the caldera and a significant b-value decrease with depth. These results are found to be in general agreement with the results from other volcanic regions and they encourage further investigations concerning the seismic and volcanic hazard and risk estimates for the Santorini volcanic complex using the NOA earthquake catalogue.

  2. Structural significance of the south Tyrrhenian volcanism

    Science.gov (United States)

    Gaudiosi, G.; Musacchio, G.; Ventura, G.; de Astis, G.

    2003-04-01

    The southern part of the Tyrrhenian Sea represents a transition from ocenic- (the Tyrrhenian Sea) to continental-domain (the Calabrian Arc) and is affected by active calkalkaline to potassic volcanism (the Eolian Islands). Active extensional tectonics, coupled with the general upwelling of northern Sicily and Calabria continental crust, coexists with active subduction of the Ionian Plate beneath the Calabrian Arc. This has been interpreted as the result of the detachment of the slab beneath the Calbrian Arc. Present-day tectonics is characterized by NE-SW normal faults and NNW- SSE dextral oblique-slip faults. The normal faults form the major peri- Tyrrhenian basins. Refraction and high resolution onshore-offshore wide-angle-reflection profiles, as well as potential field modeling, provide a 3D image of the Moho. Short wave-length undulations characterize the Moho beneath the Aeolian Arch. The major upraise is about 6 km, beneath the Aeolian active volcanic area, and affects all the crustal boundaries. Another sharp crustal thinning is observed beneath the gulf of Patti at the south-eastern edge of the Tyrrhenian basin. We suggest that the graben-like structure, occurring along the Salina-Lipari-Vulcano islands and oriented at high angles to the trench, is lithospheric and can be followed down to Moho depths. NNW-SSE dextral oblique-slip faults, like the Tindari Letojanni fault system, control the Salina-Lipari-Vulcano portion of the Aeolian volcanism and connect the oceanic crust of the Marsili Basin to the Malta Escarpment, through the Etna volcano. Across this lineament seismicity changes from mostly shallow to the west, to deep intra- slab to the east.

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

    Science.gov (United States)

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

    2014-12-01

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

  4. Groundwater withdrawal rates from the Ozark Plateaus aquifer system, 1900 to 2010

    Science.gov (United States)

    Knierim, Katherine J.; Nottmeier, Anna M.; Worland, Scott C.; Westerman, Drew A.; Clark, Brian R.

    2016-01-01

    Groundwater is an often overlooked freshwater resource compared to surface water, but groundwater is used widely across the United States, especially during periods of drought. If groundwater models can successfully simulate past conditions, they may be used to evaluate potential future pumping scenarios or climate conditions, thus providing a valuable planning tool for water-resource managers. Quantifying the groundwater-use component for a groundwater model is a vital but often challenging endeavor. This dataset includes groundwater withdrawal rates modeled for the Ozark Plateaus aquifer system (Ozark system) from 1900 to 2010 by groundwater model cell (2.6 square kilometers) for five water-use divisions—agriculture (including irrigation and aquaculture), livestock, public supply (including municipal and rural water districts), and non-agriculture (including thermoelectric power generation, mining, commercial, and industrial)—and by country for domestic (self-supplied) use. Two child items are included with the dataset: “Domestic groundwater withdrawal rates from the Ozark Plateaus aquifer system, 1900 to 2010” and “Public supply, non-agriculture, livestock, and agriculture groundwater withdrawal rates from the Ozark Plateaus aquifer system, 1900 to 2010”. The Ozark system is located in the central United States and is composed of interbedded Cambrian to Pennsylvanian clastic and carbonate lithologies. In stratigraphic order, the Ozark system includes the Basement confining unit, St. Francois aquifer, St. Francois confining unit, Ozark aquifer, Ozark confining unit, Springfield Plateau aquifer, and Western Interior Plains confining system. Generally, the lower portion of the Ozark aquifer is the primary source of groundwater across much of Missouri and the Springfield Plateau aquifer is used across northern Arkansas. A full description of the methods used to model groundwater withdrawal rates from the Ozark system are available in Knierim et al., IN

  5. Presence of rapidly degrading permafrost plateaus in south-central Alaska

    Science.gov (United States)

    Jones, Benjamin M.; Baughman, Carson A.; Romanovsky, Vladimir E.; Parsekian, Andrew D.; Babcock, Esther L.; Stephani, Eva; Jones, Miriam C.; Grosse, Guido; Berg, Edward E.

    2016-11-01

    Permafrost presence is determined by a complex interaction of climatic, topographic, and ecological conditions operating over long time scales. In particular, vegetation and organic layer characteristics may act to protect permafrost in regions with a mean annual air temperature (MAAT) above 0 °C. In this study, we document the presence of residual permafrost plateaus in the western Kenai Peninsula lowlands of south-central Alaska, a region with a MAAT of 1.5 ± 1 °C (1981-2010). Continuous ground temperature measurements between 16 September 2012 and 15 September 2015, using calibrated thermistor strings, documented the presence of warm permafrost (-0.04 to -0.08 °C). Field measurements (probing) on several plateau features during the fall of 2015 showed that the depth to the permafrost table averaged 1.48 m but at some locations was as shallow as 0.53 m. Late winter surveys (augering, coring, and GPR) in 2016 showed that the average seasonally frozen ground thickness was 0.45 m, overlying a talik above the permafrost table. Measured permafrost thickness ranged from 0.33 to > 6.90 m. Manual interpretation of historic aerial photography acquired in 1950 indicates that residual permafrost plateaus covered 920 ha as mapped across portions of four wetland complexes encompassing 4810 ha. However, between 1950 and ca. 2010, permafrost plateau extent decreased by 60.0 %, with lateral feature degradation accounting for 85.0 % of the reduction in area. Permafrost loss on the Kenai Peninsula is likely associated with a warming climate, wildfires that remove the protective forest and organic layer cover, groundwater flow at depth, and lateral heat transfer from wetland surface waters in the summer. Better understanding the resilience and vulnerability of ecosystem-protected permafrost is critical for mapping and predicting future permafrost extent and degradation across all permafrost regions that are currently warming. Further work should focus on reconstructing

  6. Submarine Volcanic Morphology of Santorini Caldera, Greece

    Science.gov (United States)

    Nomikou, P.; Croff Bell, K.; Carey, S.; Bejelou, K.; Parks, M.; Antoniou, V.

    2012-04-01

    Santorini volcanic group form the central part of the modern Aegean volcanic arc, developed within the Hellenic arc and trench system, because of the ongoing subduction of the African plate beneath the European margin throughout Cenozoic. It comprises three distinct volcanic structures occurring along a NE-SW direction: Christianna form the southwestern part of the group, Santorini occupies the middle part and Koloumbo volcanic rift zone extends towards the northeastern part. The geology of the Santorini volcano has been described by a large number of researchers with petrological as well as geochronological data. The offshore area of the Santorini volcanic field has only recently been investigated with emphasis mainly inside the Santorini caldera and the submarine volcano of Kolumbo. In September 2011, cruise NA-014 on the E/V Nautilus carried out new surveys on the submarine volcanism of the study area, investigating the seafloor morphology with high-definition video imaging. Submarine hydrothermal vents were found on the seafloor of the northern basin of the Santorini caldera with no evidence of high temperature fluid discharges or massive sulphide formations, but only low temperature seeps characterized by meter-high mounds of bacteria-rich sediment. This vent field is located in line with the normal fault system of the Kolumbo rift, and also near the margin of a shallow intrusion that occurs within the sediments of the North Basin. Push cores have been collected and they will provide insights for their geochemical characteristics and their relationship to the active vents of the Kolumbo underwater volcano. Similar vent mounds occur in the South Basin, at shallow depths around the islets of Nea and Palaia Kameni. ROV exploration at the northern slopes of Nea Kameni revealed a fascinating underwater landscape of lava flows, lava spines and fractured lava blocks that have been formed as a result of 1707-1711 and 1925-1928 AD eruptions. A hummocky topography at

  7. Observations on Phallocryptus Spinosa (Branchiopoda, Anostraca Populations from the high Plateaus of Northeastern Algeria

    Directory of Open Access Journals (Sweden)

    Mounia Amarouayache

    2014-12-01

    Full Text Available Phallocryptus spinosa (Thamnocephalidae is a small primitive crustacean which lives in temporary saline pools of the Palaearctic region called Chott, Sebkha, Garâa or Daya in North Africa. Data on its biology and life history are very scarce despite its ecological importance in wetlands. Four populations living in the Northeastern High Plateaus of Algeria, Garâas Guellif, El-Tarf, Ank Djemel and Sebkha Ez-Zemoul, have been studied in point of view of their morphmetry (13 parameters and their reproduction. The population of Sebkha Ez-Zemoul, living in higher salinities and in sympatry with Artemia salina was different from the 3 other populations that are close together. Its adults are the largest (21.77 ± 2.34 mm and 23.65 ± 2.36 mm for males and females respectively and produce more cysts 771.47±8.45 cysts/brood of 293.11±10.41 µm diameter. Associated carcinological fauna and some behavioral traits are also approached.

  8. Potentiometric surface and water quality in the Principal Aquifer, Mississippian Plateaus region, Kentucky

    Science.gov (United States)

    Plebuch, R.O.; Faust, R.J.; Townsend, M.A.

    1985-01-01

    The Mississippian Plateaus region is the outcrop area of rocks of Mississippian age which extends as a broad arcuate band around the Western Coal Field in westcentral Kentucky. Much of the area is characterized by plains of low relief containing numerous sinkholes, subsurface drainage, and a low density of surface streams. The principal aquifer consists of a thick sequence of limestones extending downward stratigraphically from the base of the Chesterian Series to the black shales at the top of the Devonian rocks. Well yields range from several gallons per minute to as much as 500 gallons per minute in some karst areas where secondary openings are well developed. The potentiometric map indicates that ground-water movement generally conforms to the surface drainage pattern. The actual direction of movement varies from river basin to river basin. Most water from the principal aquifer is a calcium magnesium bicarbonate type and is generally good relative to current drinking water standards. The lower St Louis Limestone, in places, yields a calcium magnesium sulfate water that is corrosive and has a strong hydrogen sulfide odor. The karst areas of the principal aquifer are vulnerable to contamination because of the well-developed subsurface drainage. Urban areas, industries, and agriculture are sources of contaminants that can be easily flushed into the ground-water system. (USGS)

  9. Optical afterglows of Gamma-Ray Bursts: peaks, plateaus, and possibilities

    CERN Document Server

    Panaitescu, A

    2010-01-01

    The optical light-curves of GRB afterglows display either peaks or plateaus. We identify 15 afterglows of the former type and 20 of the latter. Their optical energy release is similar and is correlated to the GRB output, the correlation being stronger for peaky afterglows. That suggests that the prompt (burst) and delayed emissions of peaky afterglows are from the same relativistic ejecta and that the optical emission of plateau afterglows arises more often from ejecta that did not produce the burst emission. Consequently, we propose that peaky optical afterglows are from impulsive ejecta releases and that plateau optical afterglows originate from long-lived engines, the break in the optical light-curve (peak or plateau end) marking the onset of the entire outflow deceleration. In the peak luminosity--peak time plane, the distribution of peaky afterglows displays an edge with L_p propto t_p^{-3}, which is more likely to arise from variations (among afterglows) in the ambient medium density. The fluxes and epo...

  10. Magnetization plateaus of an easy-axis kagome antiferromagnet with extended interactions

    Science.gov (United States)

    Plat, X.; Alet, F.; Capponi, S.; Totsuka, K.

    2015-11-01

    We investigate the properties in finite magnetic field of an extended anisotropic X X Z spin-1/2 model on the kagome lattice, originally introduced by Balents, Fisher, and Girvin [Phys. Rev. B 65, 224412 (2002), 10.1103/PhysRevB.65.224412]. The magnetization curve displays plateaus at magnetization m =1 /6 and 1 /3 when the anisotropy is large. Using low-energy effective constrained models (quantum loop and quantum dimer models), we discuss the nature of the plateau phases, found to be crystals that break discrete rotation and/or translation symmetries. Large-scale quantum Monte Carlo simulations were carried out in particular for the m =1 /6 plateau. We first map out the phase diagram of the effective quantum loop model with an additional loop-loop interaction to find stripe order around the point relevant for the original model as well as a topological Z2 spin liquid. The existence of a stripe crystalline phase is further evidenced by measuring both standard structure factor and entanglement entropy of the original microscopic model.

  11. Quantum vs Classical Magnetization Plateaus of S=1/2 Frustrated Heisenberg Chains

    Science.gov (United States)

    Hida, Kazuo; Affleck, Ian

    2005-06-01

    The competition between quantum and classical magnetization plateaus of S=1/2 frustrated Heisenberg chains with modified exchange couplings is investigated. The conventional S=1/2 frustrated Heisenberg chain is known to exhibit a 3-fold degenerate \\uparrow\\downarrow\\uparrow-type classical plateau at 1/3 of the saturation magnetization accompanied by the spontaneous Z3 translational symmetry breakdown. The stability of this plateau phase against period 3 exchange modulation which favors the \\bullet\\hskip -1pt-\\hskip -1pt\\bullet \\uparrow-type quantum plateau state (\\bullet\\hskip -1pt-\\hskip -1pt\\bullet = singlet dimer) is studied by bosonization, renormalization group and numerical diagonalization methods. The ground state phase diagram and the spin configuration in each phase are numerically determined. The translationally invariant Valence Bond Solid-type model with 4-spin and third neighbor interactions, which has the exact \\bullet\\hskip -1pt-\\hskip -1pt\\bullet \\uparrow-type quantum plateau state, is also presented. The phase transition to the classical \\uparrow\\downarrow\\uparrow-type ground state is also observed by varying the strength of 4-spin and third neighbor interactions. The relation between these two types of models with quantum plateau states is discussed.

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

    Science.gov (United States)

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

    2016-06-01

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

  13. Wire + Arc Additive Manufacturing

    OpenAIRE

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

    2016-01-01

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

  14. Welding arc plasma physics

    Science.gov (United States)

    Cain, Bruce L.

    1990-01-01

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

  15. Geodynamical evolution of Central Andes at 24°S as inferred by magma composition along the Calama-Olacapato-El Toro transversal volcanic belt

    Science.gov (United States)

    Matteini, M.; Mazzuoli, R.; Omarini, R.; Cas, R.; Maas, R.

    2002-11-01

    Miocene to Recent volcanism on the Puna plateau (Central Andes) developed in three geological settings: (a) volcanic arc in the Western Cordillera (Miocene-Recent); (b) trans-arc along the main NW-SE transverse fault systems (Miocene); and (c) back-arc, mainly monogenic volcanic centres (Pliocene-Quaternary). We have studied the evolution of the arc-trans-arc volcanism along one of the most extensive transverse structures of Central Andes, the Calama-Olacapato-El Toro, at 24°S. Compositional variations from arc to trans-arc volcanism provide insights into petrogenesis and magma source regions. Puntas Negras and Rincon volcanic centres are arc-type and have typical calc-alkaline geochemical and Sr-Nd-Pb isotopic characteristics. East of the arc, lavas of the Tul-Tul, Del Medio and Pocitos complexes (TUMEPO) are heavy rare earth element-depleted and could be derived from 20-30% of partial melting of a lower crustal garnet-bearing metabasite. These liquids could be variably mixed with arc magmas at the base of the crust (MASH). This suggests important contributions from lower crustal sources to TUMEPO centres. Products at the Quevar and Aguas Calientes volcanic complexes to the east of TUMEPO show a prominent upper crustal signature (high 86Sr/ 87Sr, low 143Nd/ 144Nd) and could represent mixtures of 20-30% TUMEPO-type liquids with up to 70-80% of upper crustal melts. We propose a geodynamic model to explain geochemical variations for the arc-trans-arc transverse volcanism from the Upper Miocene to Recent. In our model, arc volcanism is linked to dehydration of the subducting Nazca plate, which produces typical calc-alkaline compositions. During the Upper Miocene (10-5 Ma), lithospheric evolution in the Puna plateau was dominated by thickening of ductile lower crust and thinning of the lithosphere. Lower crustal melting was promoted by concomitant asthenospheric upwelling and water release from the amphibolite-eclogite transformation, yielding TUMEPO magmas with lower

  16. Age specificity of inbreeding load in Drosophila melanogaster and implications for the evolution of late-life mortality plateaus.

    Science.gov (United States)

    Reynolds, Rose M; Temiyasathit, Sara; Reedy, Melissa M; Ruedi, Elizabeth A; Drnevich, Jenny M; Leips, Jeff; Hughes, Kimberly A

    2007-09-01

    Current evolutionary theories explain the origin of aging as a byproduct of the decline in the force of natural selection with age. These theories seem inconsistent with the well-documented occurrence of late-life mortality plateaus, since under traditional evolutionary models mortality rates should increase monotonically after sexual maturity. However, the equilibrium frequencies of deleterious alleles affecting late life are lower than predicted under traditional models, and thus evolutionary models can accommodate mortality plateaus if deleterious alleles are allowed to have effects spanning a range of neighboring age classes. Here we test the degree of age specificity of segregating alleles affecting fitness in Drosophila melanogaster. We assessed age specificity by measuring the homozygous fitness effects of segregating alleles across the adult life span and calculated genetic correlations of these effects across age classes. For both males and females, we found that allelic effects are age specific with effects extending over 1-2 weeks across all age classes, consistent with modified mutation-accumulation theory. These results indicate that a modified mutation-accumulation theory can both explain the origin of senescence and predict late-life mortality plateaus.

  17. Altitudes and thicknesses of hydrogeologic units of the Ozark Plateaus aquifer system in Arkansas, Kansas, Missouri, and Oklahoma

    Science.gov (United States)

    Westerman, Drew A.; Gillip, Jonathan A.; Richards, Joseph M.; Hays, Phillip D.; Clark, Brian R.

    2016-09-29

    A hydrogeologic framework was constructed to represent the altitudes and thicknesses of hydrogeologic units within the Ozark Plateaus aquifer system as part of a regional groundwater-flow model supported by the U.S. Geological Survey Water Availability and Use Science Program. The Ozark Plateaus aquifer system study area is nearly 70,000 square miles and includes parts of Arkansas, Kansas, Missouri, and Oklahoma. Nine hydrogeologic units were selected for delineation within the aquifer system and include the Western Interior Plains confining system, the Springfield Plateau aquifer, the Ozark confining unit, the Ozark aquifer, which was divided into the upper, middle, and lower Ozark aquifers to better capture the spatial variation in the hydrologic properties, the St. Francois confining unit, the St. Francois aquifer, and the basement confining unit. Geophysical and well-cutting logs, along with lithologic descriptions by well drillers, were compiled and interpreted to create hydrologic altitudes for each unit. The final compiled dataset included more than 23,000 individual altitude points (excluding synthetic points) representing the nine hydrogeologic units within the Ozark Plateaus aquifer system.

  18. Volcanic signals in oceans

    KAUST Repository

    Stenchikov, Georgiy L.

    2009-08-22

    Sulfate aerosols resulting from strong volcanic explosions last for 2–3 years in the lower stratosphere. Therefore it was traditionally believed that volcanic impacts produce mainly short-term, transient climate perturbations. However, the ocean integrates volcanic radiative cooling and responds over a wide range of time scales. The associated processes, especially ocean heat uptake, play a key role in ongoing climate change. However, they are not well constrained by observations, and attempts to simulate them in current climate models used for climate predictions yield a range of uncertainty. Volcanic impacts on the ocean provide an independent means of assessing these processes. This study focuses on quantification of the seasonal to multidecadal time scale response of the ocean to explosive volcanism. It employs the coupled climate model CM2.1, developed recently at the National Oceanic and Atmospheric Administration\\'s Geophysical Fluid Dynamics Laboratory, to simulate the response to the 1991 Pinatubo and the 1815 Tambora eruptions, which were the largest in the 20th and 19th centuries, respectively. The simulated climate perturbations compare well with available observations for the Pinatubo period. The stronger Tambora forcing produces responses with higher signal-to-noise ratio. Volcanic cooling tends to strengthen the Atlantic meridional overturning circulation. Sea ice extent appears to be sensitive to volcanic forcing, especially during the warm season. Because of the extremely long relaxation time of ocean subsurface temperature and sea level, the perturbations caused by the Tambora eruption could have lasted well into the 20th century.

  19. Hydrogeologic framework bottom elevations and thicknesses of Permian, Upper Pennsylvanian, Lower Pennsylvanian, and Mississippian units in the Appalachian Plateaus Physiographic Province

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — As part of the U.S. Geological Survey Water Availability and Use Science Program study of Appalachian Plateaus aquifers, bottom elevations and thicknesses were...

  20. Mean-annual and mean-seasonal water-budget estimates from a Soil-Water-Balance model of the Appalachian Plateaus, 1980 through 2011

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — As part of the U.S. Geological Survey Groundwater Resources Program study of Appalachian Plateaus aquifers, mean-annual and mean-seasonal water-budget estimates for...

  1. Provenance of the Walash-Naopurdan back-arc-arc clastic sequences in the Iraqi Zagros Suture Zone

    Science.gov (United States)

    Ali, Sarmad A.; Sleabi, Rajaa S.; Talabani, Mohammad J. A.; Jones, Brian G.

    2017-01-01

    Marine clastic rocks occurring in the Walash and Naopurdan Groups in the Hasanbag and Qalander areas, Kurdistan region, Iraqi Zagros Suture Zone, are lithic arenites with high proportions of volcanic rock fragments. Geochemical classification of the Eocene Walash and Oligocene Naopurdan clastic rocks indicates that they were mainly derived from associated sub-alkaline basalt and andesitic basalt in back-arc and island arc tectonic settings. Major and trace element geochemical data reveal that the Naopurdan samples are chemically less mature than the Walash samples and both were subjected to moderate weathering. The seaway in the southern Neotethys Ocean was shallow during both Eocene and Oligocene permitting mixing of sediment from the volcanic arcs with sediment derived from the Arabian continental margin. The Walash and Naopurdan clastic rocks enhance an earlier tectonic model of the Zagros Suture Zone with their deposition occurring during the Eocene Walash calc-alkaline back-arc magmatism and Early Oligocene Naopurdan island arc magmatism in the final stages of intra-oceanic subduction before the Miocene closure and obduction of the Neotethys basin.

  2. WSTF electrical arc projects

    Science.gov (United States)

    Linley, Larry

    1994-09-01

    The objectives of these projects include the following: validate method used to screen wire insulation with arc tracking characteristics; determine damage resistance to arc as a function of source voltage and insulation thickness; investigate propagation characteristics of Kapton at low voltages; and investigate pyrolytic properties of polyimide insulated (Kapton) wire for low voltage (less than 35 VDC) applications. Supporting diagrams and tables are presented.

  3. H2O and CO2 in magmas from the Mariana arc and back arc systems

    Science.gov (United States)

    Newman, Sally; Stolper, Edward; Stern, Robert

    2000-05-01

    We examined the H2O and CO2 contents of glasses from lavas and xenoliths from the Mariana arc system, an intraoceanic convergent margin in the western Pacific, which contains an active volcanic arc, an actively spreading back arc basin, and active behind-the-arc cross-chain volcanoes. Samples include (1) glass rims from Mariana arc, Mariana trough, and cross-chain submarine lavas; (2) glass inclusions in arc and trough phenocrysts; and (3) glass inclusions from a gabbro + anorthosite xenolith from Agrigan (Mariana arc). Glass rims of submarine arc lavas contain 0.3-1.9 wt % H2O, and CO2 is below detection limits. Where they could be compared, glass inclusions in arc phenocrysts contain more H2O than their host glasses; most arc glasses and phenocryst inclusions contain no detectable CO2, with the exception of those from a North Hiyoshi shoshonite, which contains 400-600 ppm. The glass inclusions from the Agrigan xenolith contain 4-6% H2O, and CO2 is below the detection limit. Glasses from the cross-chain lavas are similar to those from the arc: H2O contents are 1.4-1.7 wt %, and CO2 is below detection limits. Volatile contents in Mariana trough lava glass rims are variable: 0.2-2.8 wt % H2O and 0-300 ppm CO2. Glass inclusions from trough phenocrysts have water contents similar to the host glass, but they can contain up to 875 ppm CO2. Volatile contents of melt inclusions from trough and arc lavas and from the xenolith imply minimum depths of crystallization of ~1-8 km. H2O and CO2 contents of Mariana trough glasses are negatively correlated, indicating saturation of the erupting magma with a CO2-H2O vapor at the pressure of eruption (~400 bars for these samples), with the vapor ranging from nearly pure CO2 at the CO2-rich end of the glass array to nearly pure H2O at the H2O-rich end. Degassing of these magmas on ascent and eruption leads to significant loss of CO2 (thereby masking preeruptive CO2 contents) but minimal disturbance of preeruptive H2O contents. For

  4. The Pelona-Pico Duarte basalts Formation, Central Hispaniola: an on-land section of Late Cretaceous volcanism related to the Caribbean large igneous province

    National Research Council Canada - National Science Library

    Escuder Viruete, J; Perez-Estaun, A; Joubert, Marc; Weis, D

    2011-01-01

    .... The Pelona-Pico Duarte basalts Fm. was emplaced onto Turonian-Lower Campanian island-arc volcanic and sedimentary sequences, and is overlain by Maastrichtian platformal carbonates. Two (40)Ar/(39...

  5. Pliocene Basaltic Volcanism in The East Anatolia Region (EAR), Turkey

    Science.gov (United States)

    Oyan, Vural; Özdemir, Yavuz; Keskin, Mehmet

    2016-04-01

    East Anatolia Region (EAR) is one of the high Plateau which is occurred with north-south compressional regime formed depending on continent-continent collision between Eurasia and Arabia plates (Şengör and Kidd, 1979). Recent studies have revealed that last oceanic lithosphere in the EAR have completely depleted to 20 million years ago based on fission track ages (Okay et al. 2010). Our initial studies suggest that extensively volcanic activity in the EAR peaked in the Pliocene and continued in the same productivity throughout Quaternary. Voluminous basaltic lava plateaus and basaltic lavas from local eruption centers occurred as a result of high production level of volcanism during the Pliocene time interval. In order to better understand the spatial and temporal variations in Pliocene basaltic volcanism and to reveal isotopic composition, age and petrologic evolution of the basaltic volcanism, we have started to study basaltic volcanism in the East Anatolia within the framework of a TUBITAK project (project number:113Y406). Petrologic and geochemical studies carried out on the Pliocene basaltic lavas indicate the presence of subduction component in the mantle source, changing the character of basaltic volcanism from alkaline to subalkaline and increasing the amount of spinel peridotitic melts (contributions of lithospheric mantle?) in the mantle source between 5.5-3.5 Ma. FC, AFC and EC-AFC modelings reveal that the while basaltic lavas were no or slightly influenced by crustal contamination and fractional crystallization, to more evolved lavas such as bazaltictrachyandesite, basalticandesite, trachybasalt might have been important processes. Results of our melting models and isotopic analysis data (Sr, Nd, Pb, Hf, 18O) indicate that the Pliocene basaltic rocks were derived from both shallow and deep mantle sources with different melting degrees ranging between 0.1 - 4 %. The percentage of spinel seems to have increased in the mantle source of the basaltic

  6. Volcanic Rocks and Features

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Volcanoes have contributed significantly to the formation of the surface of our planet. Volcanism produced the crust we live on and most of the air we breathe. The...

  7. Volcano geodesy in the Cascade arc, USA

    Science.gov (United States)

    Poland, Michael P.; Lisowski, Michael; Dzurisin, Daniel; Kramer, Rebecca; McLay, Megan; Pauk, Ben

    2017-08-01

    Experience during historical time throughout the Cascade arc and the lack of deep-seated deformation prior to the two most recent eruptions of Mount St. Helens might lead one to infer that Cascade volcanoes are generally quiescent and, specifically, show no signs of geodetic change until they are about to erupt. Several decades of geodetic data, however, tell a different story. Ground- and space-based deformation studies have identified surface displacements at five of the 13 major Cascade arc volcanoes that lie in the USA (Mount Baker, Mount St. Helens, South Sister, Medicine Lake, and Lassen volcanic center). No deformation has been detected at five volcanoes (Mount Rainier, Mount Hood, Newberry Volcano, Crater Lake, and Mount Shasta), and there are not sufficient data at the remaining three (Glacier Peak, Mount Adams, and Mount Jefferson) for a rigorous assessment. In addition, gravity change has been measured at two of the three locations where surveys have been repeated (Mount St. Helens and Mount Baker show changes, while South Sister does not). Broad deformation patterns associated with heavily forested and ice-clad Cascade volcanoes are generally characterized by low displacement rates, in the range of millimeters to a few centimeters per year, and are overprinted by larger tectonic motions of several centimeters per year. Continuous GPS is therefore the best means of tracking temporal changes in deformation of Cascade volcanoes and also for characterizing tectonic signals so that they may be distinguished from volcanic sources. Better spatial resolution of volcano deformation can be obtained through the use of campaign GPS, semipermanent GPS, and interferometric synthetic aperture radar observations, which leverage the accumulation of displacements over time to improve signal to noise. Deformation source mechanisms in the Cascades are diverse and include magma accumulation and withdrawal, post-emplacement cooling of recent volcanic deposits, magmatic

  8. Volcano geodesy in the Cascade arc, USA

    Science.gov (United States)

    Poland, Michael; Lisowski, Michael; Dzurisin, Daniel; Kramer, Rebecca; McLay, Megan; Pauk, Benjamin

    2017-01-01

    Experience during historical time throughout the Cascade arc and the lack of deep-seated deformation prior to the two most recent eruptions of Mount St. Helens might lead one to infer that Cascade volcanoes are generally quiescent and, specifically, show no signs of geodetic change until they are about to erupt. Several decades of geodetic data, however, tell a different story. Ground- and space-based deformation studies have identified surface displacements at five of the 13 major Cascade arc volcanoes that lie in the USA (Mount Baker, Mount St. Helens, South Sister, Medicine Lake, and Lassen volcanic center). No deformation has been detected at five volcanoes (Mount Rainier, Mount Hood, Newberry Volcano, Crater Lake, and Mount Shasta), and there are not sufficient data at the remaining three (Glacier Peak, Mount Adams, and Mount Jefferson) for a rigorous assessment. In addition, gravity change has been measured at two of the three locations where surveys have been repeated (Mount St. Helens and Mount Baker show changes, while South Sister does not). Broad deformation patterns associated with heavily forested and ice-clad Cascade volcanoes are generally characterized by low displacement rates, in the range of millimeters to a few centimeters per year, and are overprinted by larger tectonic motions of several centimeters per year. Continuous GPS is therefore the best means of tracking temporal changes in deformation of Cascade volcanoes and also for characterizing tectonic signals so that they may be distinguished from volcanic sources. Better spatial resolution of volcano deformation can be obtained through the use of campaign GPS, semipermanent GPS, and interferometric synthetic aperture radar observations, which leverage the accumulation of displacements over time to improve signal to noise. Deformation source mechanisms in the Cascades are diverse and include magma accumulation and withdrawal, post-emplacement cooling of recent volcanic deposits, magmatic

  9. Self-potential anomalies in some Italian volcanic areas

    Directory of Open Access Journals (Sweden)

    C. Silenziario

    1996-06-01

    Full Text Available The study of Self-Potential (SP space and time variations in volcanic areas may provide useful information on both the geometrical structure of the volcanic apparatuses and the dynamical behaviour of the feeding and uprising systems. In this paper, the results obtained on the islands of Vulcano (Eolian arc and Ponza (Pontine archipelago and on the Mt. Somma-Vesuvius complex are shown. On the island of Vulcano and on the Mt. Somma-Vesuvius apparatus areal SP surveys were performed with the aim of evidencing anomalies closely associated to the zones of major volcanic activity. On the island of Vulcano a profile across the fumaroles along the crater rim of the Fossa Cone was also carried out in order to have a direct relationship between fumarolic fracture migration and flow rate and SP anomaly space and time variations. The areal survey on the island of Ponza, which is considered an inactive area, is assumed as a reference test with which to compare the amplitude and pattern of the anomalies in the active areas. A tentative interpretation of the SP anomalies in volcanic areas is suggested in terms of electrokinetic phenomena, related to the movement of fluids of both volcanic and non-volcanic origin.

  10. Cenozoic back-arc magmatism of the southern extra-Andean Patagonia (44° 30' - 52° S: A review of geochemical data and geodynamic interpretations

    Directory of Open Access Journals (Sweden)

    M. D'Orazio

    2004-12-01

    Full Text Available Huge amounts of basaltic s.l. lavas were persistently erupted along the eastern side of the Andean Cordillera, throughout Cenozoic time, forming extensive plateaus, hundreds of monogenetic scoria cones and other volcanic structures in a continental back-arc setting. The igneous products exposed in the southern sector of the extra-Andean Patagonia (44° 30' - 52° S are dominantly mafic with minor slightly evolved compositions and rare highly differentiated products. The many published chemical analyses of these rocks, indicate that the mafic lavas range from strongly silica - undersaturated basanites to oversaturated basaltic andesites, and that most of the lavas have a typical within-plate geochemical signature. However, a number of lavas, generally erupted in the western-central sectors of Patagonia, are characterized by different distributions of the incompatible elements with high LILE/HFSE and LREE/HFSE ratios. The REE distribution modelling suggests a low degree of melting of a deep (> 70 km garnet-bearing source for the alkaline magmas, and a higher degree of melting of the same source, or an even higher degree of melting of an enriched source, for the subalkaline magmas. The available Sr-Nd-Pb isotope compositions clearly attest to a major geographic variation: the southernmost lavas have lower 87Sr/86Sr and higher 143Nd/144Nd and 206Pb/204Pb ratios with respect to those erupted to the north. On the whole, the Sr-Nd-Pb isotope compositions of the southern Patagonia lavas fall within the typical range of within-plate continental magmas; in addition the Pb isotope ratios fall in the range of the Southern Hemisphere Dupal Pb isotope anomaly. The geochemical variations of the southern Patagonia lavas are discussed in terms of different geochemical components: depleted and enriched sub-slab asthenosphere, enriched continental lithospheric mantle, continental crust and subducted materials. The geodynamic significance is interpreted with in the

  11. Circular-Arc Cartograms

    CERN Document Server

    Kämper, Jan-Hinrich; Nöllenburg, Martin

    2011-01-01

    We present a new circular-arc cartogram model in which countries are drawn with circular arcs instead of straight-line segments. Given a geographic map and values associated with each country in the map, the cartogram is a new map in which the areas of the countries represent the corresponding values. In the circular-arc cartogram model straight-line segments can be replaced with circular arcs in order to achieve the desired areas, while the corners of the polygons defining each country remain fixed. The countries in circular-arc cartograms have the aesthetically pleasing appearance of clouds or snowflakes, depending on whether their edges are bent outwards or inwards. This makes is easy to determine whether a country has grown or shrunk, just by its overall shape. We show that determining whether a given map and area-values can be realized with a circular-arc cartogram is an NP-hard problem. Next we describe a heuristic method for constructing circular-arc cartograms, which uses a max-flow computation on the...

  12. Formation of lower continental crust by relamination of buoyant arc lavas and plutons

    Science.gov (United States)

    Kelemen, Peter B.; Behn, Mark D.

    2016-03-01

    The formation of the Earth's continents is enigmatic. Volcanic arc magmas generated above subduction zones have geochemical compositions that are similar to continental crust, implying that arc magmatic processes played a central role in generating continental crust. Yet the deep crust within volcanic arcs has a very different composition from crust at similar depths beneath the continents. It is therefore unclear how arc crust is transformed into continental crust. The densest parts of arc lower crust may delaminate and become recycled into the underlying mantle. Here we show, however, that even after delamination, arc lower crust still has significantly different trace element contents from continental lower crust. We suggest that it is not delamination that determines the composition of continental crust, but relamination. In our conceptual model, buoyant magmatic rocks generated at arcs are subducted. Then, upon heating at depth, they ascend and are relaminated at the base of the overlying crust. A review of the average compositions of buoyant magmatic rocks -- lavas and plutons -- sampled from the Aleutians, Izu-Bonin-Marianas, Kohistan and Talkeetna arcs reveals that they fall within the range of estimated major and trace elements in lower continental crust. Relamination may thus provide an efficient process for generating lower continental crust.

  13. Carbon cycling in the mantled karst of the Ozark Plateaus, central United States

    Science.gov (United States)

    Knierim, Katherine; Pollock, Erik D.; Covington, Matthew D.; Hays, Phillip D.; Brye, Kristofor R.

    2017-01-01

    The nature of carbon (C) cycling in the unsaturated zone where groundwater is in contact with abundant gas-filled voids is poorly understood. The objective of this study was to trace inorganic-C cycling in a karst landscape using stable-C isotopes, with emphasis on a shallow groundwater flow path through the soil, to an underlying cave, and to the spring outlet of a cave stream in the Ozark Plateaus of northwestern Arkansas. Carbon dioxide (CO2) concentration and isotopic composition (δ13C-CO2) in gas and dissolved inorganic carbon (DIC) concentration and isotopic composition (δ13C-DIC) in water were measured in samples collected from two suction-cup soil samplers above the cave, three sites in the cave, and at the spring outlet of the cave stream. Soil-gas CO2 concentration (median 2,578 ppm) and δ13C-CO2 (median − 21.5‰) were seasonally variable, reflecting the effects of surface temperature changes on soil-CO2 production via respiration and organic-matter decomposition. Cave-air CO2 (median 1,026 ppm) was sourced from the soil zone and the surface atmosphere, with seasonally changing proportions of each source controlled by surface temperature-driven air density gradients. Soil-DIC concentration (median 1.7 mg L− 1) was lower and soil-δ13C-DIC (median − 19.5‰) was lighter compared to the cave (median 23.3 mg L− 1 and − 14.3‰, respectively) because carbonate-bedrock dissolution provided an inorganic source of C to the cave. Carbon species in the soil had a unique, light stable-C isotopic signature compared to the cave. Discrimination of soil-C sources to karst groundwater was achieved, which is critical for developing hydrologic budgets using environmental tracers such as C.

  14. Parental arc magma compositions dominantly controlled by mantle-wedge thermal structure

    Science.gov (United States)

    Turner, Stephen J.; Langmuir, Charles H.; Katz, Richard F.; Dungan, Michael A.; Escrig, Stéphane

    2016-10-01

    The processes that lead to the fourfold variation in arc-averaged compositions of mafic arc lavas remain controversial. Control by the mantle-wedge thermal structure is supported by chemical correlations with the thickness of the underlying arc crust, which affects the thermal state of the wedge. Control by down-going slab temperature is supported by correlations with the slab thermal parameter. The Chilean Southern Volcanic Zone provides a test of these hypotheses. Here we use chemical data to demonstrate that the Southern Volcanic Zone and global arc averages define the same chemical trends, both among elements and between elements and crustal thickness. But in contrast to the global arc system, the Southern Volcanic Zone is built on crust of variable thickness with a constant slab thermal parameter. This natural experiment, along with a set of numerical simulations, shows that global arc compositional variability is dominated by different extents of melting that are controlled by the thermal structure of the mantle wedge. Slab temperatures play a subordinate role. Variations in the subducting slab's fluid flux and sediment compositions, as well as mantle-wedge heterogeneities, produce second-order effects that are manifested as distinctive trace element and isotopic signatures; these can be more clearly elucidated once the importance of wedge thermal structure is recognized.

  15. Pulsed plasma arc cladding

    Institute of Scientific and Technical Information of China (English)

    龙; 白钢; 李振民; 张赋升; 杨思乾

    2004-01-01

    A prototype of Pulsed Plasma Arc Cladding system was developed, in which single power source supplies both transferred plasma arc (TPA) and non-transferred plasma arc (N-TPA). Both plasmas work in turn in a high frequency controlled by an IGBT connecting nozzle and workpiece. The working frequency of IGBT ranges from 50 ~ 7000Hz, in which the plasmas can work in turn smoothly. Higher than 500 Hz of working frequency is suggested for promotion of cladding quality and protection of IGBT. Drag phenomenon of TPA intensifies as the frequency goes up, which tends to increase the current proportion of TPA and suppress N-TPA. The occupation ratio of IGBT can be regulated from 5% ~ 95%, which balances the power supplies of both plasmas. An occupation ratio higher than 50% gives adequate proportion of arc current for N-TPA to preheat powder.

  16. Filtered cathodic arc source

    Science.gov (United States)

    Falabella, Steven; Sanders, David M.

    1994-01-01

    A continuous, cathodic arc ion source coupled to a macro-particle filter capable of separation or elimination of macro-particles from the ion flux produced by cathodic arc discharge. The ion source employs an axial magnetic field on a cathode (target) having tapered sides to confine the arc, thereby providing high target material utilization. A bent magnetic field is used to guide the metal ions from the target to the part to be coated. The macro-particle filter consists of two straight solenoids, end to end, but placed at 45.degree. to one another, which prevents line-of-sight from the arc spot on the target to the parts to be coated, yet provides a path for ions and electrons to flow, and includes a series of baffles for trapping the macro-particles.

  17. Recent seismicity detection increase in the Santorini volcanic island complex

    Directory of Open Access Journals (Sweden)

    G. Chouliaras

    2012-04-01

    Full Text Available Santorini is the most active volcanic complex in the South Aegean Volcanic Arc. To improve the seismological network detectability of the seismicity in this region, the Institute of Geodynamics of the National Observatory of Athens (NOA recently installed 4 portable seismological stations supplementary to the 3 permanent stations operating in the region. The addition of these stations has significantly improved the detectability and reporting of the local seismic activity in the NOA instrumental seismicity catalogue.

    In this study we analyze quantitatively the seismicity of the Santorini volcanic complex. The results indicate a recent significant reporting increase mainly for events of small magnitude and an increase in the seismicity rate by more than 100%. The mapping of the statistical significance of the rate change with the z-value method reveals that the rate increase exists primarily in the active fault zone perpendicular to the extensional tectonic stress regime that characterizes this region.

    The spatial distribution of the b-value around the volcanic complex indicates a low b-value distribution parallel to the extensional stress field, while the b-value cross section of the volcanic complex indicates relatively high b-values under the caldera and a significant b-value decrease with depth.

    These results are found to be in general agreement with the results from other volcanic regions and they encourage further investigations concerning the seismic and volcanic hazard and risk estimates for the Santorini volcanic complex using the NOA earthquake catalogue.

  18. Volcanic hazards to airports

    Science.gov (United States)

    Guffanti, M.; Mayberry, G.C.; Casadevall, T.J.; Wunderman, R.

    2009-01-01

    Volcanic activity has caused significant hazards to numerous airports worldwide, with local to far-ranging effects on travelers and commerce. Analysis of a new compilation of incidents of airports impacted by volcanic activity from 1944 through 2006 reveals that, at a minimum, 101 airports in 28 countries were affected on 171 occasions by eruptions at 46 volcanoes. Since 1980, five airports per year on average have been affected by volcanic activity, which indicates that volcanic hazards to airports are not rare on a worldwide basis. The main hazard to airports is ashfall, with accumulations of only a few millimeters sufficient to force temporary closures of some airports. A substantial portion of incidents has been caused by ash in airspace in the vicinity of airports, without accumulation of ash on the ground. On a few occasions, airports have been impacted by hazards other than ash (pyroclastic flow, lava flow, gas emission, and phreatic explosion). Several airports have been affected repeatedly by volcanic hazards. Four airports have been affected the most often and likely will continue to be among the most vulnerable owing to continued nearby volcanic activity: Fontanarossa International Airport in Catania, Italy; Ted Stevens Anchorage International Airport in Alaska, USA; Mariscal Sucre International Airport in Quito, Ecuador; and Tokua Airport in Kokopo, Papua New Guinea. The USA has the most airports affected by volcanic activity (17) on the most occasions (33) and hosts the second highest number of volcanoes that have caused the disruptions (5, after Indonesia with 7). One-fifth of the affected airports are within 30 km of the source volcanoes, approximately half are located within 150 km of the source volcanoes, and about three-quarters are within 300 km; nearly one-fifth are located more than 500 km away from the source volcanoes. The volcanoes that have caused the most impacts are Soufriere Hills on the island of Montserrat in the British West Indies

  19. Numerical study of magnetization plateaus in the spin-1/2 Heisenberg antiferromagnet on the checkerboard lattice

    Science.gov (United States)

    Capponi, Sylvain

    2017-01-01

    We present numerical evidence that the spin-1/2 Heisenberg model on the two-dimensional checkerboard lattice exhibits several magnetization plateaus for m =0 , 1 /4 , 1 /2 , and 3 /4 , where m is the magnetization normalized by its saturation value. These incompressible states correspond to somewhat similar valence-bond crystal phases that break lattice symmetries, though they are different from the already established plaquette phase for m =0 . Our results are based on exact diagonalization as well as density-matrix renormalization-group large-scale simulations and interpreted in terms of simple parameter-free trial wave functions.

  20. The geochemistry of volcanic, plutonic and turbiditic rocks from Sumba, Indonesia

    Science.gov (United States)

    Lytwyn, J.; Rutherford, E.; Burke, K.; Xia, C.

    2001-06-01

    Rocks that reveal the geology of Sumba for times before the Later Miocene (˜16 Ma) are relatively few and are not particularly well exposed. This has led to uncertainty about the nature of the basement rocks of the island and especially about whether Sumba originated as a fragment of Australia, or of that part of southeastern Eurasia which many authors have called Sundaland. A third possibility is that Sumba is underlain by arc material generated on the ocean floor and is not a fragment of either continent. We have studied the geochemistry of volcanic, plutonic and turbiditic rocks collected from Sumba in an attempt to provide additional insight into the island's origin and history between Late Cretaceous (˜86 Ma) and Early Miocene (˜16 Ma) times. Late Cretaceous to Early Oligocene (˜31 Ma) volcanic rocks on Sumba range compositionally from basalts to andesites, and are of typical oceanic island-arc affinity, exhibiting geochemical characteristics similar to those of high-Al basalts and their derivatives. Compositions indicate evolution along both calc-alkaline and tholeiitic trends. Some samples show indications of possible modifications by slab-derived melts and/or related fluids and also of contamination by turbiditic sediments. Gabbros and diorites collected from the Paleocene Tanadaro intrusion are compositionally similar to the associated volcanic rocks and, we consider, represent the plutonic equivalents of high-Al basalt. The geochemistry of Cretaceous turbiditic sedimentary rocks on Sumba indicates close proximity to an intra-oceanic island-arc environment. These results are consistent with the geochemical, sedimentological, stratigraphic, paleontological and paleomagnetic results of other investigators which together indicate that: (1) Late Cretaceous to Early Oligocene volcanic, plutonic and volcaniclastic rocks of Sumba are island-arc- and forearc-related; (2) the arc involved appears to have been what we refer to as the Great Indonesian Volcanic

  1. Geochemical Characteristics of Danfeng Meta-Volcanic Rocks in Shangzhou Area,Shaanxi Province

    Institute of Scientific and Technical Information of China (English)

    1995-01-01

    The Danfeng meta-volcanics in the Shangzhou area, Shaanxi Province are characterized by oceanic island arc volcanic geochemistry. They are a suite of low-K tholeiitic series and calc-alkaline series meta-volcanic rocks derived from different sources respectively.These meta-volcanics have high Th/Ta ratios and low contents of Ni,Ta,Ti,Y and Yb, suggesting that they were influenced by the subduction zone components.Many lines of evidence show that the Danfeng meta-volcanics were produced in an oceanic island are setting of the supra-subduction zone at the southern margin of the North China Block during the Early Paleozoic.

  2. Precambrian Lunar Volcanic Protolife

    Directory of Open Access Journals (Sweden)

    Jack Green

    2009-06-01

    Full Text Available Five representative terrestrial analogs of lunar craters are detailed relevant to Precambrian fumarolic activity. Fumarolic fluids contain the ingredients for protolife. Energy sources to derive formaldehyde, amino acids and related compounds could be by flow charging, charge separation and volcanic shock. With no photodecomposition in shadow, most fumarolic fluids at 40 K would persist over geologically long time periods. Relatively abundant tungsten would permit creation of critical enzymes, Fischer-Tropsch reactions could form polycyclic aromatic hydrocarbons and soluble volcanic polyphosphates would enable assembly of nucleic acids. Fumarolic stimuli factors are described. Orbital and lander sensors specific to protolife exploration including combined Raman/laser-induced breakdown spectrocsopy are evaluated.

  3. The Sierra de Mil Cumbres, Michoacán, México: Transitional volcanism between the Sierra Madre Occidental and the Trans-Mexican Volcanic Belt

    Science.gov (United States)

    Gómez-Vasconcelos, Martha Gabriela; Garduño-Monroy, Víctor Hugo; Macías, José Luis; Layer, Paul W.; Benowitz, Jeff A.

    2015-08-01

    The Sierra de Mil Cumbres is a Miocene volcanic range located in central México, in the north-eastern part of the State of Michoacán, near the city of Morelia. Structurally it is a ENE-trending horst that covers an area of 1022 km2 (approximately 20 km wide × 60 km long) and contains exposures of chemically-bimodal volcanism in the form of ignimbrites, lava domes, lava flows, cinder cones, and related deposits. The main volcanic manifestations of this range are the La Escalera Caldera (16.3-23 Ma), the Garnica Volcanic Complex (18.3-17.9 Ma), the Atécuaro Caldera (16.3-19.4 Ma), and the Indaparapeo Volcanic Complex (14.1-17.5 Ma). The Sierra de Mil Cumbres stands in space and time at the intersection between the Miocene-Recent Trans-Mexican Volcanic Belt and the Late Cretaceous-Early Miocene Sierra Madre Occidental, and so provides new insights into the geological evolution of central México. Arc volcanism in the Sierra de Mil Cumbres was initiated by a massive NNW-SSE extension, probably during the counterclockwise rotation of the Sierra Madre Occidental. New geological mapping, stratigraphic analysis, detailed geochemistry and 40Ar/39Ar geochronology demonstrates that this intra-plate volcanism was emplaced between 14 and 23 Ma.

  4. Lung problems and volcanic smog

    Science.gov (United States)

    ... releases gases into the atmosphere. Volcanic smog can irritate the lungs and make existing lung problems worse. ... deep into the lungs. Breathing in volcanic smog irritates the lungs and mucus membranes. It can affect ...

  5. Modeling of Arc Force in Plasma Arc Welding

    Institute of Scientific and Technical Information of China (English)

    GAO Zhonglin; HU Shengsun; YIN Fengliang; WANG Rui

    2008-01-01

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

  6. The Upper- to Middle-Crustal Section of the Alisitos Oceanic Arc, (Baja, Mexico): an Analog of the Izu-Bonin-Marianas (IBM) Arc

    Science.gov (United States)

    Medynski, S.; Busby, C.; DeBari, S. M.; Morris, R.; Andrews, G. D.; Brown, S. R.; Schmitt, A. K.

    2016-12-01

    The Rosario segment of the Cretaceous Alisitos arc in Baja California is an outstanding field analog for the Izu-Bonin-Mariana (IBM) arc, because it is structurally intact, unmetamorphosed, and has superior three-dimensional exposures of an upper- to middle-crustal section through an extensional oceanic arc. Previous work1, done in the pre-digital era, used geologic mapping to define two phases of arc evolution, with normal faulting in both phases: (1) extensional oceanic arc, with silicic calderas, and (2) oceanic arc rifting, with widespread diking and dominantly mafic effusions. Our new geochemical data match the extensional zone immediately behind the Izu arc front, and is different from the arc front and rear arc, consistent with geologic relations. Our study is developing a 3D oceanic arc crustal model, with geologic maps draped on Google Earth images, and GPS-located outcrop information linked to new geochemical, geochronological and petrographic data, with the goal of detailing the relationships between plutonic, hypabyssal, and volcanic rocks. This model will be used by scientists as a reference model for past (IBM-1, 2, 3) and proposed IBM (IBM-4) drilling activities. New single-crystal zircon analysis by TIMS supports the interpretation, based on batch SIMS analysis of chemically-abraded zircon1, that the entire upper-middle crustal section accumulated in about 1.5 Myr. Like the IBM, volcanic zircons are very sparse, but zircon chemistry on the plutonic rocks shows trace element compositions that overlap to those measured in IBM volcanic zircons by A. Schmitt (unpublished data). Zircons have U-Pb ages up to 20 Myr older than the eruptive age, suggesting remelting of older parts of the arc, similar to that proposed for IBM (using different evidence). Like IBM, some very old zircons are also present, indicating the presence of old crustal fragments, or sediments derived from them, in the basement. However, our geochemical data show that the magmas are

  7. Multiple magnetization plateaus and magnetic structures in the S =1/2 Heisenberg model on the checkerboard lattice

    Science.gov (United States)

    Morita, Katsuhiro; Shibata, Naokazu

    2016-10-01

    We study the ground state of the S =1/2 Heisenberg model on the checkerboard lattice in a magnetic field by the density matrix renormalization group method with the sine-square deformation. We obtain magnetization plateaus at M /Msat=0 ,1/4 ,3/8 ,1/2 , and 3/4 , where Msat is the saturated magnetization. The obtained 3/4 plateau state is consistent with the exact result, and the 1/2 plateau is found to have a four-spin resonating loop structure similar to the six-spin loop structure of the 1/3 plateau of the kagome lattice. Different four-spin loop structures are obtained in the 1/4 and 3/8 plateaus but no corresponding states exist in the kagome lattice. The 3/8 plateau has a unique magnetic structure of three types of four-spin local quantum states in a 4 √{2 }×2 √{2 } magnetic unit cell with a 16-fold degeneracy.

  8. Ground states, magnetization plateaus and bipartite entanglement of frustrated spin-1/2 Ising-Heisenberg and Heisenberg triangular tubes

    Science.gov (United States)

    Alécio, Raphael C.; Lyra, Marcelo L.; Strečka, Jozef

    2016-11-01

    The ground-state phase diagram, magnetization process and bipartite entanglement of the frustrated spin-1/2 Ising-Heisenberg and Heisenberg triangular tube (three-leg ladder) are investigated in a non-zero external magnetic field. The exact ground-state phase diagram of the spin-1/2 Ising-Heisenberg tube with Heisenberg intra-rung and Ising inter-rung couplings consists of six distinct gapped phases, which manifest themselves in a magnetization curve as intermediate plateaus at zero, one-third and two-thirds of the saturation magnetization. Four out of six available ground states exhibit quantum entanglement between two spins from the same triangular unit evidenced by a non-zero concurrence. Density-matrix renormalization group calculations are used in order to construct the ground-state phase diagram of the analogous but purely quantum spin-1/2 Heisenberg tube with Heisenberg intra- and inter-rung couplings, which consists of four gapped and three gapless phases. The Heisenberg tube shows a continuous change of the magnetization instead of a plateau at zero magnetization, while the intermediate one-third and two-thirds plateaus may be present or not in the zero-temperature magnetization curve.

  9. Quantification of subaerial and episodic subglacial erosion rates on high latitude upland plateaus: Cumberland Peninsula, Baffin Island, Arctic Canada

    Science.gov (United States)

    Margreth, Annina; Gosse, John C.; Dyke, Arthur S.

    2016-02-01

    Long-term rates of subaerial and episodic subglacial erosion by predominately cold-based ice cover are determined for tors on weathered plateaus on Cumberland Peninsula. By measuring terrestrial cosmogenic nuclide concentrations in differentially weathered surfaces on a given tor, we reconstruct the complex exposure and erosion history involving recurring cold-based ice cover. The style and rate of subaerial and subglacial erosion at multiple tor sites on Cumberland Peninsula are assessed with a Monte Carlo approach that computes plausible exposure histories based on a proxy record of global ice volume. Constant subaerial erosion rates by weathering are low (tors located on coastal ridge crests that have likely never been glaciated. Summit plateaus intermittently covered by cold-based ice throughout the Quaternary have experienced episodic subglacial erosion by plucking of fractured bedrock with rates between 1 and 16 mm ka-1. Variation of episodic erosion rates is associated with topographic position of the sampled tors and bedrock fracture density. Most of the tors were last glacially plucked in pre-ultimate glaciations, not during the Wisconsinan glaciation. Furthermore, the new approach provides evidence for the extent of ice coverage during the late Wisconsinan, which is significant if no erratics are available for exposure dating. Despite late Pleistocene intervals of ice cover and glacial plucking, tor-studded landscapes of Cumberland Peninsula are of considerable antiquity.

  10. Study of climatic drought in Algerian high plateaus using standardized precipitation index and observations from moderate resolution imaging spectroradiometer

    Science.gov (United States)

    Mega, Nabil; Medjerab, Abderrahmane

    2016-10-01

    The high plateaus of Algeria is a critical region to policymakers in terms of social, economic, and infrastructure development. The main goal of the present work was to monitor the climatic drought and its impact on vegetation health across the Algerian high plateaus using remote sensing techniques. Vegetation health index (VHI) showed a clear drought in the western region of the study area. The results show practically three periods of drought were evident: October to December 2006, November to December 2009, and December 2012. Agreeable correlations among the obtained results using standard precipitation index for 3 months (SPI-3) and other satellite indicators such as temperature vegetation dryness index (TVDI) and VHI were obtained. TVDI and VHI agreed well with the ground-based observations from SPI-3; thus, these may serve as key and easily accessible indicators of drought. The research shows motivating results that decision makers can use to take timely corrective measures to minimize the reduction in agricultural production in drought prone areas.

  11. Volcanism and Oil & Gas In Northeast China

    Institute of Scientific and Technical Information of China (English)

    Shan Xuanlong

    2000-01-01

    Based on study on the relation with volcanic rock and oil & gas in Songliao Basin and Liaohe Basin in northeast China, author proposes that material from deep by volcanism enrichs the resources in basins, that heat by volcanism promotes organic matter transforming to oil and gas, that volcanic reservoir is fracture, vesicular, solution pore, intercrystal pore.Lava facies and pyroclastic facies are favourable reservoir. Mesozoic volcanic reservoir is majority of intermediate, acid rock,but Cenozoic volcanic reservoir is majority of basalt. Types of oil and gas pool relating to volcanic rock include volcanic fracture pool, volcanic unconformity pool, volcanic rock - screened pool, volcanic darpe structural pool.

  12. Anatomy of Intra-Oceanic Arc Systems

    Science.gov (United States)

    Stern, R. J.

    2007-12-01

    Intra-oceanic arc systems (IOAS) are ultimately embedded in orogenic belts and added to the continental crust. Reconstructing fossil IOASs in collision zones requires understanding the salient features of a typical IOAS. IOASs have the relative dimensions of tagliatelle (flat) pasta: much wider (~250 km) than thick (10-30 km), much longer (1000's of km) than wide. IOASs begin to form when subduction begins, either spontaneously (SNSZ) or by forced convergence (INSZ). For SNSZ, IOASs start as broad zones of seafloor spreading associated with subsidence of the adjacent lithosphere, whereas INSZ IOASs are built on trapped crust. IOAS magmatism manifests the evolution of its subduction zone and indirectly the breadth of the subducted ocean. Two stages in SNSZ IOAS magmato-tectonic evolution exist: infancy and maturity. Infancy lasts 5-10 Ma and results in broad zones of seafloor spreading of tholeiite/boninite; this becomes forearc for the mature IOAS and is emplaced as ophiolite during collision (subduction zone failure). Arc maturity begins with true subduction, as the subducted slab reaches depths ~130 km, focusing magmatism to begin building the magmatic arc ~200km away from the trench and allowing the forearc to cool and hydrate. Mature magmatic arcs mostly yield low-K tholeiitic and medium-K calc-alkaline magmas. Magmatic focusing begins crustal thickening beneath the magmatic arc, at ~500m/Ma for the Izu-Bonin-Mariana IOAS. No systematic compositional evolution to more LIL-enriched primitive magmas occurs once IOAS maturity is reached, except when upper plate stress regime (BAB formation, strike- slip faulting) or the nature of subducted material (more/different sediments, young oceanic crust) changes. Thickening is accompanied by processing of crust beneath the magmatic arc, with progressive differentiation into upper volcanic, middle tonalitic, and lower mafic layers, producing an increasingly effective density filter for magma ascent. Crustal layer formation

  13. MODELING PARAMETERS OF ARC OF ELECTRIC ARC FURNACE

    Directory of Open Access Journals (Sweden)

    R.N. Khrestin

    2015-08-01

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

  14. Modeling volcanic ash dispersal

    CERN Document Server

    CERN. Geneva

    2010-01-01

    The assessment of volcanic fallout hazard is an important scientific, economic, and political issue, especially in densely populated areas. From a scientific point of view, considerable progress has been made during the last two decades through the use of increasingly powerful computational models and capabilities. Nowadays, models are used to quantify hazard...

  15. Geochemical constraints on the relationship between the Miocene-Pliocene volcanism and tectonics in the Palaoco and Fortunoso volcanic fields, Mendoza Region, Argentina: New insights from 40Ar/39Ar dating, Sr-Nd-Pb isotopes and trace elements

    Science.gov (United States)

    Dyhr, Charlotte T.; Holm, Paul M.; Llambías, Eduardo J.

    2013-10-01

    New 40Ar/39Ar analyses constrain the formation of the volcanic succession of Sierra de Palaoco in the present back-arc of the Andean Southern Volcanic Zone (SVZ), near 36°S, to the Late Miocene and assigns them to the Huincán II Formation. The composition of major and trace elements, Sr, Nd and Pb isotopes of the Palaoco and nearby Río Grande rocks require a strong arc-like component in the mantle that is absent or weak in both Early Miocene (Fortunoso Group) and Pleistocene alkaline lavas (Llancanelo Group) erupted in the same area. We evaluate the relative roles of varying mantle source compositions and crustal contamination in the generation of geochemically very different lavas from the Palaoco, Fortunoso and Río Grande volcanic fields, north of the Payún Matrú Volcano. The source for the Early Miocene Fortunoso(I) basalts was a OIB-type mantle devoid of subduction zone input. This type of OIB-like volcanic activity terminated due to a change from an extensional to a compressional tectonic regime. Towards the end of the Miocene renewed alkaline volcanism at Fortunoso (II) display a transition to arc-type incompatible element enrichment. Shortly after the calc-alkaline Palaoco volcanism started with a very strong geochemical arc-signature including Ba/La ≈ 60 and La/Nb = 2-3. After a quiesence of 1 Ma the major part of the voluminous Late Palaoco basalts were erupted around 7.5 Ma over a few hundred ka. These are less enriched in Ba and Sr and have compositions like many Holocene rocks of the Southern Volcanic Zone. Isotopically the Fortunoso I and Palaoco rocks are distinct. Regional volcanism of the Charilehue, Huincán I and II mostly has a moderate arc-type enrichment indicating incipient arc developments. However, Palaoco and La Brea at (c. 35°S) show full geochemical arc-signature, and we infer that a frontal arc was established. The subsequent development in the Palaoco-Río Grande area encompasses renewed late Pliocene calc-alkaline low volume

  16. X-ray and optical plateaus following the main bursts in GRBs and SNe Ⅱ-P: a hint about similar late injection behaviors?

    Institute of Scientific and Technical Information of China (English)

    Xiao-Hong Cui; Ren-Xin Xu

    2013-01-01

    We analyze the emission plateaus in the X-ray afterglow light curves of gamma-ray bursts (GRBs) and those in the optical light curves of type Ⅱ plateau supernovae (SNe Ⅱ-P) in order to study whether they have similar late energy injection behaviors.We show that correlations of bolometric energies (or luminosities) between the prompt explosions and the plateaus for the two phenomena are similar.The energy emitted by SNe Ⅱ-P are at the lower end of the range of possible energies for GRBs.The bolometric energies (or luminosities) in the prompt phase Eexpl (or Lexpl) and in the plateau phase Eplateau (or Lplateau) share relations of Eexpl ∝ E0.73±0.14plateau and Lexpl ∝ L~0.70plateau These results may indicate a similar late energy injection behavior that produces the observed plateaus in these two phenomena.

  17. Morphometric characterization of monogenetic volcanic cones of the Chichinautzin and Michoacán-Guanajuato monogenetic volcanic fields in Mexico

    Science.gov (United States)

    Zarazua-Carbajal, Maria Cristina; De la Cruz-Reyna, Servando; Mendoza-Rosas, Ana Teresa

    2014-05-01

    Morphometric characterization of volcanic edifices is one of the main approaches providing information about a volcano eruptive history, whether it has one or more eruptive vents or if it had any sector collapses. It also provides essential information about the physical processes that modify their shapes during periods of quietness, and quite significantly, about the volcanoes' ages. In the case of monogenetic activity, a volcanic field can be characterized by the size and slope distributions, and other cone's morphometric parameter distributions that may provide valuable information about the temporal evolution of the volcanic field. The increasingly available high-resolution digital elevation models and the continuously developing computer tools have allowed a faster development and more detailed morphometric characterization techniques. We present here a methodology to readily obtain diverse volcanic cone shape parameters from the contour curves such as mean slope, slope distribution, dimensions of the cone and crater, crater location within the cone, orientation of the cone's principal axis, eccentricity, and other morphological features using an analysis algorithm that we developed, programmed in Python and ArcPy. Preliminary results from the implementation of this methodology to the Chichinautzin and Michoacán-Guanajuato monogenetic volcanic fields in Mexico have permitted a preliminary estimation of the age distribution of some of the cones with an acceptable correlation with the available radiometric ages. A large part of the Chichinautzin region DEM was obtained from a LIDAR survey by the Mexican National Institute of Statistics and Geography (INEGI).

  18. Arc Plasma Torch Modeling

    CERN Document Server

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

    2013-01-01

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

  19. Evolution of Geochemical Variations Along the Central American Volcanic Front

    Science.gov (United States)

    Saginor, I. S.; Gazel, E.; Condie, C.; Carr, M. J.

    2014-12-01

    New geochemical analyses of volcanic rocks in El Salvador add to existing data from Nicaragua and Costa Rica to create a comprehensive set of geochemical data for Central American volcanics. These data coupled with previously published 40Ar/39Ar ages covering the past 30 Ma shows that Costa Rica and Nicaragua had similar U/Th and Ba/La values until 10 Ma when the region developed the distinctive along arc variations that made this margin famous. U/Th values increased in Nicaragua since the Miocene, while remaining unchanged along the rest of the volcanic front. This coincides temporally with the Carbonate Crash, which caused a transition in Cocos plate sediments from low-U carbonates to high-U, organic rich hemipelagic muds. Increases in uranium are not observed in Costa Rica because its lower slab dip produces a more diffuse zone of partial melting and because of the contribution from Galapagos-derived tracks dilutes this signal. Ba/La has been used as a geochemical proxy for contributions from the subducting slab, however our analyses indicate that the Ba concentrations do not vary significantly along strike either in the subducting sediment or the volcanic front. Along-arc variation is controlled by changes in La, an indicator of the degree of partial melting or source enrichment. Trace element models of five segments of the volcanic front suggest that a subducting sediment component is more important to magmas produced in El Salvador and Nicaragua than in Costa Rica, where the geochemistry is controlled by recent (<10 Ma) recycling of Galapagos tracks.

  20. SO2 flux and the thermal power of volcanic eruptions

    Science.gov (United States)

    Henley, Richard W.; Hughes, Graham O.

    2016-09-01

    A description of the dynamics, chemistry and energetics governing a volcanic system can be greatly simplified if the expansion of magmatic gas can be assumed to be adiabatic as it rises towards the surface. The conditions under which this assumption is valid are clarified by analysis of the transfer of thermal energy into the low conductivity wallrocks traversed by fractures and vents from a gas phase expanding over a range of mass flux rates. Adiabatic behavior is predicted to be approached typically within a month after perturbations in the release of source gas have stabilized, this timescale being dependent upon only the characteristic length scale on which the host rock is fractured and the thermal diffusivity of the rock. This analysis then enables the thermal energy transport due to gas release from volcanoes to be evaluated using observations of SO2 flux with reference values for the H2O:SO2 ratio of volcanic gas mixtures discharging through high temperature fumaroles in arc and mantle-related volcanic systems. Thermal power estimates for gas discharge are 101.8 to 104.1 MWH during quiescent, continuous degassing of arc volcanoes and 103.7 to 107.3 MWH for their eruptive stages, the higher value being the Plinean Pinatubo eruption in 1991. Fewer data are available for quiescent stage mantle-related volcanoes (Kilauea 102.1 MWH) but for eruptive events power estimates range from 102.8 MWH to 105.5 MWH. These estimates of thermal power and mass of gas discharges are commensurate with power estimates based on the total mass of gas ejected during eruptions. The sustained discharge of volcanic gas during quiescent and short-lived eruptive stages can be related to the hydrodynamic structure of volcanic systems with large scale gaseous mass transfer from deep in the crust coupled with episodes of high level intrusive activity and gas release.

  1. Magmatism of the troughs behind the New Hebrides island arc (RV Jean Charcot SEAPSO 2 cruise): K-Ar geochronology and petrology

    Science.gov (United States)

    Monjaret, M. C.; Bellon, H.; Maillet, P.

    1991-06-01

    The chronological, petrological and geochemical studies of lavas dredged from the New Hebrides back-arc troughs allow a new interpretation of the origin of these troughs. In every area, volcanism from the troughs precedes that of the adjacent islands. Four main periods of volcanic activity have been defined: 6.5 to 4.8, 4.1 to 2, 2 to 1 and 1 to 0 Ma. The volcanic affinity is generally orogenic. But some variation exists and two geochemical types (Mg-IAT basalts and hyper-K acid lavas) seem to mark the trough structuration. The succession of the different geochemical types reveals a polyphased and diachronous formation of the troughs from south to north on an arc substratum. Only the Vanikoro area (the most northern one) shows basalts with geochemical characteristics intermediate between MORB and island-arc tholeiites and acid lavas near primitive island-arc lavas, which illustrate the initiation of the arc in this area. So, the New Hebrides back-arc troughs must be considered as intra-arc troughs and are back-arc structures only because of their location at the rear of the active emerging arc.

  2. Aurorae and Volcanic Eruptions

    Science.gov (United States)

    2001-06-01

    Thermal-IR Observations of Jupiter and Io with ISAAC at the VLT Summary Impressive thermal-infrared images have been obtained of the giant planet Jupiter during tests of a new detector in the ISAAC instrument on the ESO Very Large Telescope (VLT) at the Paranal Observatory (Chile). . They show in particular the full extent of the northern auroral ring and part of the southern aurora. A volcanic eruption was also imaged on Io , the very active inner Jovian moon. Although these observations are of an experimental nature, they demonstrate a great potential for regular monitoring of the Jovian magnetosphere by ground-based telescopes together with space-based facilities. They also provide the added benefit of direct comparison with the terrestrial magnetosphere. PR Photo 21a/01 : ISAAC image of Jupiter (L-band: 3.5-4.0 µm) . PR Photo 21b/01 : ISAAC image of Jupiter (Narrow-band 4.07 µm) . PR Photo 21c/01 : ISAAC image of Jupiter (Narrow-band 3.28 µm) . PR Photo 21d/01 : ISAAC image of Jupiter (Narrow-band 3.21 µm) . PR Photo 21e/01 : ISAAC image of the Jovian aurorae (false-colour). PR Photo 21f/01 : ISAAC image of volcanic activity on Io . Addendum : The Jovian aurorae and polar haze. Aladdin Meets Jupiter Thermal-infrared images of Jupiter and its volcanic moon Io have been obtained during a series of system tests with the new Aladdin detector in the Infrared Spectrometer And Array Camera (ISAAC) , in combination with an upgrade of the ESO-developed detector control electronics IRACE. This state-of-the-art instrument is attached to the 8.2-m VLT ANTU telescope at the ESO Paranal Observatory. The observations were made on November 14, 2000, through various filters that isolate selected wavebands in the thermal-infrared spectral region [1]. They include a broad-band L-filter (wavelength interval 3.5 - 4.0 µm) as well as several narrow-band filters (3.21, 3.28 and 4.07 µm). The filters allow to record the light from different components of the Jovian atmosphere

  3. Generation of continental crust in intra-oceanic arcs

    Science.gov (United States)

    Gazel, E.; Hayes, J. L.; Kelemen, P. B.; Everson, E. D.; Holbrook, W. S.; Vance, E.

    2014-12-01

    The origin of continental crust is still an unsolved mystery in the evolution of our planet. Although the best candidates to produce juvenile continental crust are intra-oceanic arcs these systems are dominated by basaltic lavas, and when silicic magmas are produced, the incompatible-element compositions are generally too depleted to be a good match for continental crust estimates. Others, such as the W. Aleutians, are dominated by andesitic melts with trace element compositions similar to average continental crust. In order to evaluate which intra-oceanic arcs produced modern continental crust, we developed a geochemical continental index (CI) through a statistical analysis that compared all available data from modern intra-oceanic arcs with global estimates of continental crust. Our results suggest that magmas from Costa Rica (100 have the least continent-like geochemical signatures. In these arcs the subducting plate is old (>100 Ma), not overprinted by enriched intraplate volcanism and the geochemistry may be dominated by slab-derived, aqueous fluids. We also found a strong correlation between the CI and average crustal P-wave velocity, validating the geochemical index with the available seismic data for intra-oceanic arcs. In conclusion, the production of young continental crust with compositions similar to Archean continental crust is an unusual process, limited to locations where there are especially voluminous partial melts of oceanic crust.

  4. Early History of Island Arcs - Evidence from the Mariana Trench

    Science.gov (United States)

    Hawkins, J. W.

    2004-12-01

    Among the many problems concerning the initiation and early history of island arcs is the question - what underlies arc plutonic and volcanic series ? Conventional wisdom is that arcs are built on older ocean crust. Their deep roots should include high-Mg eruptions, crystal cumulates complementry to higher-level differentiated lavas, plutonic rocks compositionally equivalent to lavas, and depleted mantle residue complementary to extracted arc magmas. If built on older ocean crust, the "roots" should overlie seafloor sediments, pillows, dikes, etc. (i.e., ophiolites). Probable exposures of deep roots of arcs are rare; exposures such as Tonsina Complex, Alaska and Zambales Range, Luzon are notable for a lack of evidence for subjacent ocean crust. The Zambales shows unmistakeable evidence for continuity from depleted harzburgite/dunite to a thick layered cumulate series of wehrlite,dunite, pyroxenite; these are overlain by norite, gabbro and arc tholeiite basalt. Much of the cumulate series and norite-gabbro has blasto-mylonite texture. These petrologic features suggest upwelling of parental peridotite mantle into a realm of oceanic lithosphere extension. The nascent arc has replaced former ocean crust rather than being built on it. The extensional regime, owing to subduction and seaward trench roll-back, has driven opening of back arc basins, caused forearc rifting, and provided a rift setting for initiation of arc magmatism. Rocks dredged from the Mariana Trench (14 to 18 N) from depths of 9000 to 3000 m, display evidence for near-solidus penetrative deformation that developed higher amphibolite facies mylonites and blasto-mylonites. Rocks include depleted peridotite, pyroxenite, wehrlite, cumulate amphibolite, norite/gabbro, tonalite. High-T metamorphism is shown by equilibrium assemblages of labradorite-bytownite, AL-hornblende, ortho- and clino- pyroxene. Highly deformed homogeneous calcic plagioclase has cross-cutting veins of xenoblastic plagioclase and rare

  5. Plateaus and sinuous ridges as the fingerprints of lava flow inflation in the Eastern Tharsis Plains of Mars

    Science.gov (United States)

    Bleacher, Jacob E.; Orr, Tim; de Wet, Andrew P.; Zimbelman, James R.; Hamilton, Christopher W.; Garry, W. Brent; Crumpler, Larry S.; Williams, David A.

    2017-01-01

    The Tharsis Montes rift aprons are composed of outpourings of lava from chaotic terrains to the northeast and southwest flank of each volcano. Sinuous and branching channel networks that are present on the rift aprons suggest the possibility of fluvial processes in their development, or erosion by rapidly emplaced lavas, but the style of lava flow emplacement throughout rift apron development is not clearly understood. To better characterize the style of lava emplacement and role of fluvial processes in rift apron development, we conducted morphological mapping of the Pavonis Mons southwest rift apron and the eastern Tharsis plains using images from the High Resolution Imaging Science Experiment (HiRISE), Mars Orbiter Camera (MOC), Context Camera (CTX), Thermal Emission Imaging System (THEMIS), and High Resolution Stereo Camera (HRSC) along with the Mars Orbiter Laser Altimeter (MOLA) Precision Experiment Data Records (PEDRs) and gridded data. Our approach was to: (1) search for depositional fans at the slope break between the rift apron and adjacent low slope plains; (2) determine if there is evidence that previously formed deposits might have been buried by plains units; (3) characterize the Tharsis plains morphologies east of Pavonis Mons; and (4) assess their relationship to the rift apron units. We have not identified topographically significant depositional fans, nor did we observe evidence to suggest that plains units have buried older rift apron units. Flow features associated with the rift apron are observed to continue across the slope break onto the plains. In this area, the plains are composed of a variety of small fissures and low shield vents around which broad channel-fed and tube-fed flows have been identified. We also find broad, flat-topped plateaus and sinuous ridges mixed among the channels, tubes and vents. Flat-topped plateaus and sinuous ridges are morphologies that are analogous to those observed on the coastal plain of Hawai‘i, where lava

  6. Arc Heated Scramjet Test Facility

    Data.gov (United States)

    Federal Laboratory Consortium — The Arc Heated Scramjet Test Facility is an arc heated facility which simulates the true enthalpy of flight over the Mach number range of about 4.7 to 8 for free-jet...

  7. ARc Welding (Industrial Processing Series).

    Science.gov (United States)

    ARC WELDING , *BIBLIOGRAPHIES), (*ARC WELDS, BIBLIOGRAPHIES), ALUMINUM ALLOYS, TITANIUM ALLOYS, CHROMIUM ALLOYS, METAL PLATES, SPOT WELDING , STEEL...INERT GAS WELDING , MARAGING STEELS, MICROSTRUCTURE, HEAT RESISTANT ALLOYS, HEAT RESISTANT METALS, WELDABILITY, MECHANICAL PROPERTIES, MOLYBDENUM ALLOYS, NICKEL ALLOYS, RESISTANCE WELDING

  8. Historical land-use changes and potential effects on stream disturbance in the Ozark Plateaus, Missouri

    Science.gov (United States)

    Jacobson, Robert B.; Primm, Alexander T.

    1997-01-01

    Land-use changes have been blamed for creating disturbance in the morphology of streams in the Ozark Plateaus, Missouri (hereafter referred to as the "Ozarks"). Historical evidence and stratigraphic observations document that streams have been aggraded by substantial quantities of gravel beginning sometime at or near the time of European settlement of the Ozarks. Before European settlement, streams were depositing a mixed sediment load of gravel bedload and silty overbank sediment. Observations of early explorers conspicuously lack descriptions of extensive gravel bars; observations of geologists working during the middle to late 1800's before significant landuse disturbance, however, include descriptions of large quantities of gravel in stream banks and beds.The first change in land cover as settlement progressed from the early 1800's to approximately 1880 was replacement of valley-bottom forest with cultivated fields and pastures. At the same time, suppression of wildfires in the uplands caused an increase of woodland with woody understory at the expense of grassland and oak savannah. Valley-bottom clearing probably initiated some direct disturbance of stream channels, but fire suppression would have decreased runoff and sediment yield from uplands.Beginning sometime from 1870 to 1880 and continuing until 1920, commercial timber companies began large operations in the Ozarks to harvest shortleaf pine for sawlogs and oak for railroad ties. Selective cutting of large timber, use of livestock for skidding logs from the forest, and avoidance of the steeper slopes minimized the effect of this phase of logging on runoff and sediment supply of uplands and valley-side slopes. Continued decreases in the erosional resistance of valley bottoms through clearing and road building and the incidence of extreme regional floods from 1895 to 1915 probably caused initiation of moderate stream disturbance. This hypothesis is supported by historical and oral-historical observations

  9. Quaternary continetal back-arc evolution from southern Mendoza, Argentina

    Science.gov (United States)

    Espanon, Venera; Chivas, Allan; Dosseto, Anthony; Honda, Masahiko; Phillips, David; Matchan, Erin; Price, David

    2016-04-01

    The Quaternary evolution of the Payenia Basaltic Province (PBP) in southern Mendoza, Argentina has been investigated using a multi-dating approach in combination with pre-exiting geochemical data. This basaltic province covers an area of approximately 40000 km2 and is mainly characterised by backarc volcanism. In the current investigation nine new radiometric ages obtained using surface exposure, 40Ar/39Ar and thermoluminescence dating are presented. Six ages correspond to the late Pleistocene and three to the Holocene. The surface exposure ages obtained using cosmogenic 3He and 21Ne are in good agreement with previous publications and confidently suggest that part of this basaltic province was active at least 4000 years ago (taking a conservative approach). In addition, we combined the available geochronological and geochemical data to reconstruct the Quaternary evolution of this basaltic province. This approach was used to create maps of geospatial distribution of trace-element ratios to determine geochemical changes during the Pleistocene. Employing this method it is evident that two geochemical distinct types of magma were erupting at the same time interval within the PBP. In the north eastern part (Nevado volcanic field) of the PBP an arc-like signature is evident, while in the southern part (Río Colorado volcanic field) of the same basaltic province an Ocean Island Basalt (OIB) signature is evident. The arc-like signature in the north eastern part of the PBP, decreased during the Pleistocene in a north-west direction indicated by a reduction in Ba/La and La/Ta in the Nevado and Llancanelo volcanic field. The Holocene volcanism is restricted to the western side of the Payún Matrú volcanic field and is dominated by OIB-like signatures such as high Ta/Hf and low Ba/La and La/Ta. This contribution presents new geochronology for the PBP and confirms that two different types of volcanism occurred simultaneously during the Pleistocene, while the Holocene

  10. Variable polarity arc welding

    Science.gov (United States)

    Bayless, E. O., Jr.

    1991-01-01

    Technological advances generate within themselves dissatisfactions that lead to further advances in a process. A series of advances in welding technology which culminated in the Variable Polarity Plasma Arc (VPPA) Welding Process and an advance instituted to overcome the latest dissatisfactions with the process: automated VPPA welding are described briefly.

  11. Thermal Arc Spray Overview

    Science.gov (United States)

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

    2013-06-01

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

  12. ALICE: ARC integration

    CERN Document Server

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

    2008-01-01

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

  13. ALICE-ARC integration

    DEFF Research Database (Denmark)

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

    2008-01-01

    Data Grid Facility (NDGF). In this paper we will present our approach to integrate AliEn and ARC, in the sense that ALICE data management and job processing can be carried out on the NDGF infrastructure, using the client tools available in AliEn. The interoperation has two aspects, one is the data...

  14. Gas tungsten arc welder

    Science.gov (United States)

    Christiansen, D.W.; Brown, W.F.

    A welder for automated closure of fuel pins by a gas tungsten arc process in which a rotating length of cladding is positioned adjacent a welding electrode in a sealed enclosure. An independently movable axial grinder is provided in the enclosure for refurbishing the used electrode between welds.

  15. Exploring Hawaiian Volcanism

    Science.gov (United States)

    Poland, Michael P.; Okubo, Paul G.; Hon, Ken

    2013-02-01

    In 1912 the Hawaiian Volcano Observatory (HVO) was established by Massachusetts Institute of Technology professor Thomas A. Jaggar Jr. on the island of Hawaii. Driven by the devastation he observed while investigating the volcanic disasters of 1902 at Montagne Pelée in the Caribbean, Jaggar conducted a worldwide search and decided that Hawai`i provided an excellent natural laboratory for systematic study of earthquake and volcano processes toward better understanding of seismic and volcanic hazards. In the 100 years since HVO's founding, surveillance and investigation of Hawaiian volcanoes have spurred advances in volcano and seismic monitoring techniques, extended scientists' understanding of eruptive activity and processes, and contributed to development of global theories about hot spots and mantle plumes.

  16. Exploring Hawaiian volcanism

    Science.gov (United States)

    Poland, Michael P.; Okubo, Paul G.; Hon, Ken

    2013-01-01

    In 1912 the Hawaiian Volcano Observatory (HVO) was established by Massachusetts Institute of Technology professor Thomas A. Jaggar Jr. on the island of Hawaii. Driven by the devastation he observed while investigating the volcanic disasters of 1902 at Montagne Pelée in the Caribbean, Jaggar conducted a worldwide search and decided that Hawai‘i provided an excellent natural laboratory for systematic study of earthquake and volcano processes toward better understanding of seismic and volcanic hazards. In the 100 years since HVO’s founding, surveillance and investigation of Hawaiian volcanoes have spurred advances in volcano and seismic monitoring techniques, extended scientists’ understanding of eruptive activity and processes, and contributed to development of global theories about hot spots and mantle plumes.

  17. A Cambrian Arc Built on the Neoproterozoic Rifted Margin of Gondwana

    Science.gov (United States)

    Musgrave, R. J.

    2009-12-01

    Cambrian convergence along the northeastern side of the Curnamona Craton, the Gondwana margin in southeastern Australia, resulted in the development of the Delamerian Orogen. A Neoproterozoic rifted margin, marked by the alkalic Mount Arrowsmith Volcanics, forms the substrate on which is built a NE-facing Cambrian arc, complete with a clearly delineated inner imbricate accretionary prism (the Wonnaminta Zone) and outer thin-skinned wedge (the Kayrunnera Zone). Arc volcanism, represented by the calc-alkaline Mount Wright Volcanics, exhibits mixed arc-rift geochemistry. Interpretation and modelling of magnetic data reveals a chain of volcanic edifices of the Mount Wright Arc, now below 3 to 7 km of Devonian sandstones in the Bancannia Trough. Remarkably, a simple rotation around an Euler pole reconstructs the Wonnaminta Zone against the craton, and aligns structural elements on the two sides of the trough. Arc volcanism evidently occupied a rift in marginal continental crust, and the geometry, geochemistry and geophysical properties of the Mount Wright Arc are closely analogous to the Taupo Zone of New Zealand. Rifting of the arc divided Delamerian structures, indicating that at least part of the Delamerian deformation developed in a subduction accretion setting, rather than in some terminal collision. Below the Wonnaminta Zone a 3 to 5 km thick body can be traced as a large magnetic source along the length of the zone. Overridden by the thrust stack of the accretionary prism, this body is mostly planar and dips towards the east, although it is deformed into a broad antiform in the central part of the zone. Physical properties suggest that this body may be a thick rift-volcanic pile equivalent to the Mount Arrowsmith Volcanics. In the southern part of the belt a re-entrant in the Wonnaminta Zone faces a large magnetic anomaly sourced in the basement of the Kayrunnera Zone. The geometry of the re-entrant, and the development of Silurian and Devonian basins over the

  18. First time evidence of pronounced plateaus right above the Coulomb barrier in 8Li + 4He fusion

    Directory of Open Access Journals (Sweden)

    A. Del Zoppo

    2016-02-01

    Full Text Available We investigate unprecedented experimental information on the fusion reaction induced by the radioactive projectile 8Li on a 4He gas target, at center-of-mass energies between 0.6 and 5 MeV. The main issue is the tendency of the dimensionless fusion cross section σfπƛ2 to form well visible plateaus alternated to steep rises. This finding is likely to be the most genuine consequence of the discrete nature of the intervening angular momenta observed so far in fusion reactions right above the Coulomb barrier. A partial-wave analysis, exclusively based on a pure quantal penetration fusion model and sensitive to the interaction potential, identifies a remarkably low-height barrier.

  19. Motion of polar cap arcs

    Science.gov (United States)

    Hosokawa, K.; Moen, J. I.; Shiokawa, K.; Otsuka, Y.

    2011-01-01

    A statistics of motion of polar cap arcs is conducted by using 5 years of optical data from an all-sky imager at Resolute Bay, Canada (74.73°N, 265.07°E). We identified 743 arcs by using an automated arc detection algorithm and statistically examined their moving velocities as estimated by the method of Hosokawa et al. (2006). The number of the arcs studied is about 5 times larger than that in the previous statistics of polar cap arcs by Valladares et al. (1994); thus, we could expect to obtain more statistically significant results. Polar cap arcs are found to fall into two distinct categories: the By-dependent and By-independent arcs. The motion of the former arcs follows the rule reported by Valladares et al. (1994), who showed that stable polar cap arcs move in the direction of the interplanetary magnetic field (IMF) By. About two thirds of the arcs during northward IMF conditions belong to this category. The latter arcs always move poleward irrespective of the sign of the IMF By, which possibly correspond to the poleward moving arcs in the morning side reported by Shiokawa et al. (1997). At least one third of the arcs belong to this category. The By-dependent arcs tend to move faster when the magnitude of the IMF By is larger, suggesting that the transport of open flux by lobe reconnection from one polar cap compartment to the other controls their motion. In contrast, the speed of the By-independent arcs does not correlate with the magnitude of the By. The motions of both the By-dependent and By-independent arcs are most probably caused by the magnetospheric convection. Convection in the region of By-dependent arcs is affected by the IMF By, which indicates that their sources may be on open field lines or in the closed magnetosphere adjacent to the open-closed boundary, whereas By-independent arcs seem to be well on closed field lines. Hence, the magnetospheric source of the two types of arc may be different. This implies that the mechanisms causing the

  20. Subdiffusion of volcanic earthquakes

    CERN Document Server

    Abe, Sumiyoshi

    2016-01-01

    A comparative study is performed on volcanic seismicities at Mt.Eyjafjallajokull in Iceland and Mt. Etna in Sicily, Italy, from the viewpoint of science of complex systems, and the discovery of remarkable similarities between them regarding their exotic spatio-temporal properties is reported. In both of the volcanic seismicities as point processes, the jump probability distributions of earthquakes are found to obey the exponential law, whereas the waiting-time distributions follow the power law. In particular, a careful analysis is made about the finite size effects on the waiting-time distributions, and accordingly, the previously reported results for Mt. Etna [S. Abe and N. Suzuki, EPL 110, 59001 (2015)] are reinterpreted. It is shown that spreads of the volcanic earthquakes are subdiffusive at both of the volcanoes. The aging phenomenon is observed in the "event-time-averaged" mean-squared displacements of the hypocenters. A comment is also made on presence/absence of long term memories in the context of t...

  1. Geochemical Relationships between Middle- to Upper-Crustal Exposures of the Alisitos Oceanic Arc (Baja California, Mexico): An Outstanding Field Analog to Active Extensional Oceanic Arcs

    Science.gov (United States)

    Morris, R.; DeBari, S. M.; Busby, C.; Medynski, S.

    2016-12-01

    The southern volcano-bounded basin of the Rosario segment of the Cretaceous Alisitos oceanic arc provides outstanding 3-D exposures of an extensional arc, where crustal generation processes are recorded in the upper-crustal volcanic units and underlying middle-crustal plutonic rocks. Geochemical linkages between exposed crustal levels provide an analog for extensional arc systems such as the Izu-Bonin-Mariana (IBM) Arc. Upper-crustal units comprise a 3-5 km thick volcanic-volcaniclastic stratigraphy with hypabyssal intrusions. Deep-seated plutonic rocks intrude these units over a transition of overlap. The most mafic compositions occur in upper-crustal hypabyssal units, and as amphibole cumulates in the plutonic rocks ( 51% SiO2). The most felsic compositions occur in welded ignimbrites and a tonalite pluton ( 71% SiO2). All units are low K with flat REE patterns, and show LILE enrichment and HFSE depletion. Trace element ratios show limited variation throughout the crustal section. Zr/Y and Nb/Y ratios are similar to the Izu active ( 3 Ma to present) zone of extension immediately behind the arc front, suggesting comparable mantle melt % during extension. Th/Zr ratios are more enriched in Alisitos compared to Izu, suggesting greater subducted sediment input. The Alisitos crustal section shows a limited range in ɛNd (5.7-7.1), but a wider range in 87Sr/86Sr (0.7035-0.7055) and 206Pb/204Pb (18.12-19.12); the latter is likely alteration effects. Arc magmas were derived from a subduction-modified MORB mantle source, less depleted than Izu arc front and less enriched than the rear arc, but is a good match with the zone of extension that lies between. Differentiation occurred in a closed system (i.e., fractional crystallization/self-melting with back mixing), producing the entire crustal section in <3 Ma.

  2. Detection and Classification of Volcanic Earthquakes/Tremors in Central Anatolian Volcanic Province

    Science.gov (United States)

    Kahraman, Metin; Arda Özacar, A.; Bülent Tank, S.; Uslular, Göksu; Kuşcu, Gonca; Türkelli, Niyazi

    2017-04-01

    Central Anatolia has been characterized by active volcanism since 10 Ma which created the so called Central Anatolia Volcanic Province (CAVP) where a series of volcanoes are located along the NE-SW trend. The petrological investigations reveal that the magma source in the CAVP has both subduction and asthenospheric signature possibly due to tearing of ongoing northward subduction of African plate along Aegean and Cyprus arcs. Recently, a temporary seismic array was deployed within the scope of Continental Dynamics: Central Anatolian Tectonics (CD-CAT) project and provided a unique opportunity to study the deep seismic signature of the CAVP. Passive seismic imaging efforts and magnetotellurics (MT) observations revealed low velocity and high conductivity zones supporting the presence of localized partial melt bodies beneath the CAVP at varying depths, especially around Mt. Hasan which exhibits both geological and archeological evidences for its eruption around 7500 B.C. In Central Anatolia, local seismicity detected by the CD-CAT array coincides well with the active faults zones. However, active or potentially active volcanoes within CAVP are characterized by the lack of seismic activity. In this study, seismic data recorded by permanent stations of Regional Earthquake-Tsunami Monitoring Center were combined with temporary seismic data collected by the CD-CAT array to improve sampling density across the CAVP. Later, the continuous seismic waveforms of randomly selected time intervals were manually analyzed to identify initially undetected seismic sources which have signal characters matching to volcanic earthquakes/tremors. For candidate events, frequency spectrums are constructed to classify the sources according to their physical mechanisms. Preliminary results support the presence of both volcano-tectonic (VT) and low-period (LT) events within the CAVP. In the next stage, the spectral and polarization analyses techniques will be utilized to the entire seismic

  3. Long-term eruptive activity at a submarine arc volcano.

    Science.gov (United States)

    Embley, Robert W; Chadwick, William W; Baker, Edward T; Butterfield, David A; Resing, Joseph A; de Ronde, Cornel E J; Tunnicliffe, Verena; Lupton, John E; Juniper, S Kim; Rubin, Kenneth H; Stern, Robert J; Lebon, Geoffrey T; Nakamura, Ko-ichi; Merle, Susan G; Hein, James R; Wiens, Douglas A; Tamura, Yoshihiko

    2006-05-25

    Three-quarters of the Earth's volcanic activity is submarine, located mostly along the mid-ocean ridges, with the remainder along intraoceanic arcs and hotspots at depths varying from greater than 4,000 m to near the sea surface. Most observations and sampling of submarine eruptions have been indirect, made from surface vessels or made after the fact. We describe here direct observations and sampling of an eruption at a submarine arc volcano named NW Rota-1, located 60 km northwest of the island of Rota (Commonwealth of the Northern Mariana Islands). We observed a pulsating plume permeated with droplets of molten sulphur disgorging volcanic ash and lapilli from a 15-m diameter pit in March 2004 and again in October 2005 near the summit of the volcano at a water depth of 555 m (depth in 2004). A turbid layer found on the flanks of the volcano (in 2004) at depths from 700 m to more than 1,400 m was probably formed by mass-wasting events related to the eruption. Long-term eruptive activity has produced an unusual chemical environment and a very unstable benthic habitat exploited by only a few mobile decapod species. Such conditions are perhaps distinctive of active arc and hotspot volcanoes.

  4. Controls on the location of arc volcanoes: an Andean study

    Science.gov (United States)

    Scott, Erin; Allen, Mark B.; McCaffrey, Kenneth J. W.; Macpherson, Colin G.; Davidson, Jon P.; Saville, Christopher

    2016-04-01

    Depth corrected data of earthquake hypocentres from South America are used to generate new models of depth to the subducting Nazca slab. This new slab model shows a general correlation between the 100 km depth to the slab, the western edge of the Altiplano-Puna Plateau (defined by the 3500 m elevation contour) and the frontal volcanic arc. Across the entire Altiplano-Puna Plateau, volcanic centres are found to be either at or above the 3500 m critical elevation contour, which also defines the cut off for seismogenic thrusting. Normal faults are only found above this critical elevation contour, suggesting that there may be a change in the stress regime associated with high elevations in the plateau. The Salar de Atacama basin (23-24oS) defines a major break in topography on the west side of the Puna Plateau. Here, the volcanism deviates around the eastern edge of the basin, approximately 80 km inland from the general trend of the arc, remaining above the 3500 m elevation contour. The volcanoes bordering the Salar de Atacama have a depth to slab approximately 30 km deeper than those in the adjacent arc segment 200 km to the north of the basin. Across this distance there is no significant difference in subduction parameters such as the slab dip, subduction rate and age of the oceanic plate entering the trench. It is likely, therefore, that melt forms at the same depth in both locations, as the factors affecting the melt source are constant. However, in the case of the Salar de Atacama region, magma is diverted to the east due to preferential emplacement under the higher elevations of the plateau. We suggest that although mantle and subduction processes have a primary control on the location of arc volcanoes, shaping the general trend of the arc, they cannot explain anomalies from the trend. Such anomalies, such as the arc deviation around the Atacama basin, can be explained by the influence of structures and stress regime within the overriding plate.

  5. Average Estimates of Water-Budget Components Based on Hydrograph Separation and PRISM Precipitation for Gaged Basins in the Appalachian Plateaus Region, 1900-2011

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — As part of the U.S. Geological Survey’s Groundwater Resources Program study of the Appalachian Plateaus aquifers, estimates of annual water-budget components were...

  6. Annual Estimates of Water-Budget Components Based on Hydrograph Separation and PRISM Precipitation for Gaged Basins in the Appalachian Plateaus Region, 1900-2011

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — As part of the U.S. Geological Survey’s Groundwater Resources Program study of the Appalachian Plateaus aquifers, estimates of annual water-budget components were...

  7. Overview for geologic field-trip guides to volcanoes of the Cascades Arc in northern California

    Science.gov (United States)

    Muffler, L. J. Patrick; Donnelly-Nolan, Julie M.; Grove, Timothy L.; Clynne, Michael A.; Christiansen, Robert L.; Calvert, Andrew T.; Ryan-Davis, Juliet

    2017-08-15

    The California Cascades field trip is a loop beginning and ending in Portland, Oregon. The route of day 1 goes eastward across the Cascades just south of Mount Hood, travels south along the east side of the Cascades for an overview of the central Oregon volcanoes (including Three Sisters and Newberry Volcano), and ends at Klamath Falls, Oregon. Day 2 and much of day 3 focus on Medicine Lake Volcano. The latter part of day 3 consists of a drive south across the Pit River into the Hat Creek Valley and then clockwise around Lassen Volcanic Center to the town of Chester, California. Day 4 goes from south to north across Lassen Volcanic Center, ending at Burney, California. Day 5 and the first part of day 6 follow a clockwise route around Mount Shasta. The trip returns to Portland on the latter part of day 6, west of the Cascades through the Klamath Mountains and the Willamette Valley. Each of the three sections of this guidebook addresses one of the major volcanic regions: Lassen Volcanic Center (a volcanic field that spans the volcanic arc), Mount Shasta (a fore-arc stratocone), and Medicine Lake Volcano (a rear-arc, shield-shaped edifice). Each section of the guide provides (1) an overview of the extensive field and laboratory studies, (2) an introduction to the literature, and (3) directions to the most important and accessible field localities. The field-trip sections contain far more stops than can possibly be visited in the actual 6-day 2017 IAVCEI excursion from Portland. We have included extra stops in order to provide a field-trip guide that will have lasting utility for those who may have more time or may want to emphasize one particular volcanic area.

  8. The Guerrero suspect terrane (western Mexico) and coeval arc terranes (the Greater Antilles and the Western Cordillera of Colombia): a late Mesozoic intra-oceanic arc accreted to cratonal America during the Cretaceous

    Science.gov (United States)

    Tardy, M.; Lapierre, H.; Freydier, C.; Coulon, C.; Gill, J.-B.; de Lepinay, B. Mercier; Beck, C.; Martinez R., J.; O. Talavera, M.; E. Ortiz, H.; Stein, G.; Bourdier, J.-L.; Yta, M.

    1994-02-01

    The Guerrero suspect terrane, composed of Late Jurassic-Early Cretaceous sequences, extends from Baja California to Acapulco and is considered to be coeval with the late Mesozoic igneous and sedimentary arc sequences of the Greater Antilles, the West Indies, Venezuela and the Western Cordillera of Colombia. These sequences represent the remnants of an arc which accreted to the North American and northern South American cratons at the end of the Cretaceous. In western Mexico, the arc sequences built on continental crust consist of high-K calc-alkaline basalts, andesites and rhyolites enriched in LREE with abundant siliceous pyroclastic rocks interbedded either with Aptian-Albian reefal limestones or red beds. They do not show magmatic changes during the arc development. In contrast, the arc sequences built on oceanic crust show an evolution with time. Arc activity began with the development of depleted low K-tholeiitic mafic suite (Guanajuato igneous sequence), followed first by mature tholeiitic basalts and then by calc-alkaline olivine basalts interbedded with micritic limestones and radiolarian oozes of Early Cretaceous age. At the end of the arc growth, during Aptian-Albian times, calc-alkaline pillow basalts and and esites poured out in the volcanic front while shoshonitic olivine basalts extruded in the back arc. The tholeiitic and shoshonitic mafic rocks as well as the calc-alkaline lavas are mildly enriched in LREE, Y and Nb and show high ɛNd ratios, typical of oceanic arcs. In contrast, the calc-alkaline mafic suite enriched in LREE, Y and Nb exhibits lower ɛNd ratios suggesting that it was derived by the partial melting of a mantle source contaminated either by Paleozoic subducted sediments or old source enrichments (OIB). The Cretaceous arc rocks of the Greater Antilles, interbedded with and/or capped by Aptian-Albian limestones, the Cretaceous andesites of northern Colombia, the Cretaceous tholeiitic and calc-alkaline volcanic rocks of Venezuela, and

  9. Evidence of persistent seismo-volcanic activity at Marsili seamount

    Directory of Open Access Journals (Sweden)

    Antonino D'Alessandro

    2012-06-01

    Full Text Available The Marsili submarine volcano is the largest European volcano, and it can be considered as the key to our understanding of the dynamics of the spreading and back-arc lithosphere formation in the Tyrrhenian sector [Marani et al. 2004, and references therein]. Despite its size, it is very difficult to monitor due to its geographical position [D'Alessandro et al. 2011], and it still remains little known. In 2006, the Centro Nazionale Terremoti (National Earthquake Centre of the Istituto Nazionale di Geofisica e Vulcanologia (INGV deployed a broadband ocean-bottom seismometer with hydrophone (OBS/H [Mangano et al. 2011] on the flat top of Marsili volcano, at a depth of ca. 790 m. In only nine days, the instrument recorded ca. 800 seismo-volcanic events [D'Alessandro et al. 2009]. This revealed the intense seismo-volcanic activity of Marsili volcano for the first time. […] 

  10. Volcanism on Mars. Chapter 41

    Science.gov (United States)

    Zimbelman, J. R.; Garry, W. B.; Bleacher, J. E.; Crown, D. A.

    2015-01-01

    Spacecraft exploration has revealed abundant evidence that Mars possesses some of the most dramatic volcanic landforms found anywhere within the solar system. How did a planet half the size of Earth produce volcanoes like Olympus Mons, which is several times the size of the largest volcanoes on Earth? This question is an example of the kinds of issues currently being investigated as part of the space-age scientific endeavor called "comparative planetology." This chapter summarizes the basic information currently known about volcanism on Mars. The volcanoes on Mars appear to be broadly similar in overall morphology (although, often quite different in scale) to volcanic features on Earth, which suggests that Martian eruptive processes are not significantly different from the volcanic styles and processes on Earth. Martian volcanoes are found on terrains of different age, and Martian volcanic rocks are estimated to comprise more than 50% of the Martian surface. This is in contrast to volcanism on smaller bodies such as Earth's Moon, where volcanic activity was mainly confined to the first half of lunar history (see "Volcanism on the Moon"). Comparative planetology supports the concept that volcanism is the primary mechanism for a planetary body to get rid of its internal heat; smaller bodies tend to lose their internal heat more rapidly than larger bodies (although, Jupiter's moon Io appears to contradict this trend; Io's intense volcanic activity is powered by unique gravitational tidal forces within the Jovian system; see "Volcanism on Io"), so that volcanic activity on Mars would be expected to differ considerably from that found on Earth and the Moon.

  11. The lateral extent of volcanic interactions during unrest and eruption

    Science.gov (United States)

    Biggs, Juliet; Robertson, Elspeth; Cashman, Katharine

    2016-04-01

    Volcanic eruptions often occur simultaneously or tap multiple magma reservoirs. Such lateral interactions between magmatic systems are attributed to stress changes or hydraulic connections but the precise conditions under which coupled eruptions occur have yet to be quantified. Here we use interferometric synthetic aperture radar satellite data to analyse the surface deformation generated by volcanic unrest in the Kenyan Rift. We identify several magma sources located at depths of 2-5 km importantly, sources that are spaced less than about 10 km apart interact, whereas those spaced more than about 25 km apart do not. However, volcanoes up to 25 km apart have interacted in the geologic past. Thus, volcanic coupling is not simply controlled by the distance between the magma reservoirs. We then consider different tectonic settings globally, including intraplate volcanoes such as Hawaii and Yellowstone, arc volcanism in Alaska and Chile, and other rift settings, such as New Zealand, Iceland and Afar. We find that the most closely spaced magmatic interactions are controlled by the extent of a shallow crystal mush layer, stress changes can couple large eruptions over distances of about 20-40 km, and only large dyke intrusions or subduction earthquakes could generate coupled eruptions over distances of about 50-100 km.

  12. Applications of Terrestrial Remote Sensing to Volcanic Rock Masses

    Science.gov (United States)

    Dewit, M.; Williams-Jones, G.; Stead, D.; Kremsater, R.; So, M.; Francioni, M.

    2015-12-01

    Remote sensing methods are widely used in geological applications today. The physical properties of rock such as composition, texture and structure have previously been difficult to accurately quantify through remote sensing, however, new research in the fields of terrestrial LiDAR and infrared thermography has proven useful in the differentiation of lithology in sedimentary outcrops. This study focuses on the application of these methods, in conjunction with digital photogrammetry, to a number of volcanic rock masses in the Garibaldi Volcanic Belt (GVB) and Chilcotin Group (CG) of British Columbia. The GVB is a chain of volcanoes and related features extending through southwestern British Columbia and is the northern extension of the Cascade Volcanic Arc. The CG is an assemblage of Neogene-aged lavas covering nearly 36,500 km2 in central British Columbia. We integrate infrared chronothermography, which enables the characterization of temporal change in the thermal signature, laser waveform attributes such as amplitude and intensity, and digital photogrammetry, in order to distinguish between a range of rock types, lithologies and structures. This data is compared to laboratory experiments on field samples and ground-truth information collected by classical geological and geotechnical methods. Our research clearly shows that it is possible to remotely map, in 3D, otherwise inaccessible volcanic rock masses.

  13. Modeling rf breakdown arcs

    CERN Document Server

    Insepov, Zeke; Huang, Dazhang; Mahalingam, Sudhakar; Veitzer, Seth

    2010-01-01

    We describe breakdown in 805 MHz rf accelerator cavities in terms of a number of mechanisms. We devide the breakdown process into three stages: (1) we model surface failure using molecular dynamics of fracture caused by electrostatic tensile stress, (2) we model the ionization of neutrals responsible for plasma initiation and plasma growth using a particle in cell code, and (3) we model surface damage by assuming a process similar to unipolar arcing. Although unipolar arcs are strictly defined with equipotential boundaries, we find that the cold, dense plasma in contact with the surface produces very small Debye lengths and very high electric fields over a large area. These high fields produce strong erosion mechanisms, primarily self sputtering, compatible with the crater formation that we see. Results from the plasma simulation are included as a guide to experimental verification of this model.

  14. ALICE - ARC integration

    DEFF Research Database (Denmark)

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

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

  15. The role of amphibole in the evolution of arc magmas and crust: the case from the Jurassic Bonanza arc section, Vancouver Island, Canada

    Science.gov (United States)

    Larocque, Jeff; Canil, Dante

    2010-04-01

    The Jurassic Bonanza arc, on Vancouver Island, British Columbia, represents an exhumed island arc crustal section of broadly diorite composition. We studied bodies of mafic and ultramafic cumulates within deeper levels of the arc to constrain the conditions and fractionation pathways leading from high-Mg basalt to andesite and dacite. Major element trends coupled with textural information show the intercumulus crystallization of amphibole, as large oikocrysts enclosing olivine in primitive cumulates controls the compositions of liquids until the onset of plagioclase crystallization. This process is cryptic, occurring only in the plutonic section, and explains the paucity of amphibole in mafic arc volcanics and the change in the Dy/Yb ratios in many arc suites with differentiation. The correlation of octahedral Al in hornblende with pressure in liquidus experiments on high-Mg basalts is applied as an empirical barometer to hornblendes from the Bonanza arc. It shows that crystallization took place at 470-880 MPa in H2O-saturated primitive basaltic magmas. There are no magmatic equivalents to bulk continental crust in the Bonanza arc; no amount of delamination of ultramafic cumulates will shift the bulk arc composition to the high-Mg# andesite composition of bulk continental crust. Garnet removal from wet magmas appears to be the key factor in producing continental crust, requiring high pressures and thick crust. Because oceanic island arcs are built on thinner crust, the long-term process generating the bulk continental crust is the accretion of island arcs to continental margins with attendant tectonic thickening.

  16. Volcanic Ash Nephelometer Probe Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Advanced dropsondes that could effectively be guided through atmospheric regions of interest such as volcanic plumes may enable unprecedented observations of...

  17. The ARCS radial collimator

    OpenAIRE

    Stone M.B.; Niedziela J.L.; Overbay M.A.; Abernathy D.L.

    2015-01-01

    We have designed, installed, and commissioned a scattered beam radial collimator for use at the ARCS Wide Angular Range Chopper Spectrometer at the Spallation Neutron Source. The collimator has been designed to work effectively for thermal and epithermal neutrons and with a range of sample environments. Other design considerations include the accommodation of working within a high vacuum environment and having the ability to quickly install and remove the collimator from the scattered beam. W...

  18. Modelling of the thermal structure of the Mexican Volcanic Belt for geothermal energy

    Science.gov (United States)

    Bonté, Damien; María Prol-Ledesma, Rosa; Smit, Jeroen; Limberger, Jon; van Wees, Jan-Diederik

    2017-04-01

    Mexico is a major geothermal energy player in the world with an installed capacity of over 900 MW for electricity production, positioning Mexico at the 6th position. The installed capacity is supported by 4 geothermal location: Cerro Prieto, Los Azufres, Los Humeros, and Las Tres Virgenes. Two of these sites are in Trans-Mexican Volcanic Belt (TMVB) a volcanic arc structure that is the result of the subduction of the Cocos Plate underneath the North American plate. The interesting feature of this onshore volcanic arc is the combination of magmatism with the extentional stress field within the arc with a shear component as a result of the oblique subduction. As a result of this combination, is a very favourable regional setup for the development of geothermal energy. The core of the work is the establishment of a thermal model at present day at the scale of TMVB. The elements considered in the thermal-tectonic model are the composition of the lithosphere, the volcanic evidences, and temperature measurements available. The newly developed b3t software at Utrecht University and TNO will perform the modelling, which allow the identification of thermal variation in the lithosphere at present-day with the data integration. The result of the thermal-tectonic modelling is a thermal model of the TMVB lithosphere that is considered according to the general geological and geodynamical context. The variation of temperature are intricately related to the magmatic centres and the lithological composition of the TMVB.

  19. Volcanic Eruptions and Climate

    Science.gov (United States)

    Robock, A.

    2012-12-01

    Large volcanic eruptions inject sulfur gases into the stratosphere, which convert to sulfate aerosols with an e-folding residence time of about one year. The radiative and chemical effects of these aerosol clouds produce responses in the climate system. Observations and numerical models of the climate system show that volcanic eruptions produce global cooling and were the dominant natural cause of climate change for the past millennium, on timescales from annual to century. Major tropical eruptions produce winter warming of Northern Hemisphere continents for one or two years, while high latitude eruptions in the Northern Hemisphere weaken the Asian and African summer monsoon. The Toba supereruption 74,000 years ago caused very large climate changes, affecting human evolution. However, the effects did not last long enough to produce widespread glaciation. An episode of four large decadally-spaced eruptions at the end of the 13th century C.E. started the Little Ice Age. Since the Mt. Pinatubo eruption in the Philippines in 1991, there have been no large eruptions that affected climate, but the cumulative effects of small eruptions over the past decade had a small effect on global temperature trends. The June 13, 2011 Nabro eruption in Eritrea produced the largest stratospheric aerosol cloud since Pinatubo, and the most of the sulfur entered the stratosphere not by direct injection, but by slow lofting in the Asian summer monsoon circulation. Volcanic eruptions warn us that while stratospheric geoengineering could cool the surface, reducing ice melt and sea level rise, producing pretty sunsets, and increasing the CO2 sink, it could also reduce summer monsoon precipitation, destroy ozone, allowing more harmful UV at the surface, produce rapid warming when stopped, make the sky white, reduce solar power, perturb the ecology with more diffuse radiation, damage airplanes flying in the stratosphere, degrade astronomical observations, affect remote sensing, and affect

  20. Late Cretaceous - Eocene evolution of the Kronotsk arc

    Science.gov (United States)

    Shapiro, M. N.; Khotin, M. Y.

    2004-12-01

    Eastern peninsulas of Kamchatka and probably Komandorskiy Islands form Kronotsk paleoarc. Main components uniting these blocks in a single structure are Paleocene-Eocene subduction-related volcanics. The lowest part of this formation on the Kronotsk peninsula was dated as the Late Senonian. Paleomagnetic data show that, 60-40 Myr ago, Kronotsk arc undergo large northern drift after a nearly equal period of southern drift. The southern part of the Kamchatskiy Mys peninsula, Africa block, is interpreted as a fragment of the accretionary prism of the Kronotsk arc, related to period of the southern drift. There are five main parts of this prism: Olenegorsk gabbro (50-70 Ma); Smaginsk Fm (Albian-Senomanian, 110-95 Ma): hot-spot basaltes and pelagic sediments; Pickezh Fm (Campanian - Maastrichtian, 85-65 Ma): tuffites in the lower part and subarcosic sandstones in the upper; and Soldatsk ultramafics. These parts of the prism are mostly separated by the large thrusts, but locally we saw the konglobrechia with gabbroic and diabasic clasts in the lowest parts of the Smaginsk and Pickezh sequences. The transition from the Pickezh Fm to Pickezh sanstones was always described as gradual. Six published paleomagnetic determinations (from Campanian to Bartonian, 80-40 Ma) of Kronotsk arc volcanics, kinematics of the large plates in the Northern Pacific, and some geological data allow us to reconstruct the drift of the Kronotsk arc at the end of Cretaceous and the first half of Paleogene. 80-60 Myr ago, Kronotsk arc marked a southern margin of the North American Plate (or a little plate with the very similar kinematics) when the Kula plate was consumed in the Kronotsk while the Kula-Pacific Ridge and Hawaiian hot spot were placed to the south. The apron of tuffs and tuffites overlapped the slopes of the newly arc and neighboring oceanic structures. One of the latter, Smaginsk oceanic plateau on the Kula plate was partly separated from this plate and attached to the Kronotsk

  1. Circular arc structures

    KAUST Repository

    Bo, Pengbo

    2011-07-01

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

  2. Field-trip guides to selected volcanoes and volcanic landscapes of the western United States

    Science.gov (United States)

    ,

    2017-06-23

    The North American Cordillera is home to a greater diversity of volcanic provinces than any comparably sized region in the world. The interplay between changing plate-margin interactions, tectonic complexity, intra-crustal magma differentiation, and mantle melting have resulted in a wealth of volcanic landscapes.  Field trips in this guide book collection (published as USGS Scientific Investigations Report 2017–5022) visit many of these landscapes, including (1) active subduction-related arc volcanoes in the Cascade Range; (2) flood basalts of the Columbia Plateau; (3) bimodal volcanism of the Snake River Plain-Yellowstone volcanic system; (4) some of the world’s largest known ignimbrites from southern Utah, central Colorado, and northern Nevada; (5) extension-related volcanism in the Rio Grande Rift and Basin and Range Province; and (6) the eastern Sierra Nevada featuring Long Valley Caldera and the iconic Bishop Tuff.  Some of the field trips focus on volcanic eruptive and emplacement processes, calling attention to the fact that the western United States provides opportunities to examine a wide range of volcanological phenomena at many scales.The 2017 Scientific Assembly of the International Association of Volcanology and Chemistry of the Earth’s Interior (IAVCEI) in Portland, Oregon, was the impetus to update field guides for many of the volcanoes in the Cascades Arc, as well as publish new guides for numerous volcanic provinces and features of the North American Cordillera. This collection of guidebooks summarizes decades of advances in understanding of magmatic and tectonic processes of volcanic western North America. These field guides are intended for future generations of scientists and the general public as introductions to these fascinating areas; the hope is that the general public will be enticed toward further exploration and that scientists will pursue further field-based research.

  3. System of Volcanic activity

    Directory of Open Access Journals (Sweden)

    P. HÉDERVARI

    1972-06-01

    Full Text Available A comparison is made among the systems of B. G.
    Escher (3, of R. W. van Bemmelen (1 and that of the author (4. In this
    connection, on the basis of Esclier's classification, the terms of "constructiv
    e " and "destructive" eruptions are introduced into the author's system and
    at the same time Escher's concept on the possible relation between the depth
    of magma-chamber and the measure of the gas-pressure is discussed briefly.
    Three complementary remarks to the first paper (4 011 the subject of system
    of volcanic activity are added.

  4. Water-quality assessment of the Ozark Plateaus study unit, Arkansas, Kansas, Missouri, and Oklahoma- fish communities in streams of the Ozark Plateaus and their relations to selected environmental factors

    Science.gov (United States)

    Petersen, James C.

    1998-01-01

    Fish communities from 22 reaches at 18 stations in the Ozark Plateaus were sampled in 1993, 1994, and 1995. The 18 stations were chosen to represent selected combinations of major environmental factors (geology/physiographic area, land use, and basin size). Additional physical, chemical, and biological factors also were measured for each of the 22 reaches and the influence of these factors upon the fish communities was investigated. Fish community samples collected at the 22 reaches identified differences in these communities that can be attributed to differences in land use and related water-quality and habitat characteristics. Communities from agriculture reaches tended to have more species, increased relative abundance of stonerollers and members of the sucker family, and decreased relative abundance of members of the sunfish and darter families. Several groups of environmental factors (concentrations of nutrients, organic carbon, suspended sediment, and dissolved oxygen; measures related to ionic strength; measures related to riparian vegetation; measures related to substrate; and measures related to stream size) appear to be related to land-use differences and fish community differences. Three multivariate analysis techniques (two ordination techniques and a classification technique) yielded similar results when applied to the fish community data. Fish communities from reaches with more similar land use in their basins and with similar drainage areas generally were grouped closer together in the analysis. Water quality, substrate, stream morphology, and riparian measures appear to be affecting fish communities at these reaches. The relations between land use, stream size, and fish communities have implications for waterquality assessments of Ozark streams. Compared to other parts of the United States, many fish species live in the Ozark Plateaus. At least 19 of these species are endemic to the Ozarks area. Many of these species are intolerant of habitat or

  5. Arc-preserving subsequences of arc-annotated sequences

    CERN Document Server

    Popov, Vladimir Yu

    2011-01-01

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

  6. Volcanic Lightning in the Laboratory: The Effect of Ultra-Rapid Melting on Ash Particles

    Science.gov (United States)

    Mueller, S.; Keller, F.; Helo, C.; Buhre, S.; Castro, J. M.

    2016-12-01

    Lightning discharge is a common process occurring at explosive volcanic eruptions. During the formation of ash plumes, the dynamical interaction of ash particles creates charges which can, given a sufficiently large charge gradient, cause lightning discharges within the plume (`plume lightning') or from ground to plume (`near-vent lightning'), respectively. Given the extreme heat release during the short duration of a discharge (potentially > 30.000 K), it is likely that the ash particles suspended in a plume are, in any form, affected by volcanic lightning. Genareau et al. (2015) found evidence of glass spherules and glass aggregates in ash deposits of two explosive eruptions (Eyjafjallajökull, Mt. Redoubt), and linked them to short-term melting processes induced by volcanic lightning (analogue to fulgurites). In order to systematically investigate the potential impact of lightning on air-suspended ash we have designed a new experimental setup. An electric arc between two electrodes is generated by a 400 Amp arc welding device. Ash-sized sample material is then blown into the established lightning arc, and a certain proportion of the injected silicate glasses and/or minerals is melted due to the high temperatures in and around the plasma channel. In a first set of experiments, we have used natural volcanic ash from Laacher See Tephra (Eifel, Germany) in distinct size fractions between 36 and 250 microns, in order to qualitatively investigate melting and amalgamation features. Spherule and aggregate textures similar to those reported by Genareau et al. (2015) were successfully reproduced during these experiments. In a second set of experiments, homogenized phonolitic glass fragments, in different size fractions, were subjected to the electric arc and subsequently analyzed under the EMP, in order to investigate effects of "flash melting" on major element glass chemistry. Genareau K, Wardman JB, Wilson TM, McNutt SR, Izbekov P (2015): Lightning-induced volcanic

  7. S-wave attenuation structure beneath the northern Izu-Bonin arc

    Science.gov (United States)

    Takahashi, Tsutomu; Obana, Koichiro; Kodaira, Shuichi

    2016-04-01

    To understand temperature structure or magma distribution in the crust and uppermost mantle, it is essential to know their attenuation structure. This study estimated the 3-D S-wave attenuation structure in the crust and uppermost mantle at the northern Izu-Bonin arc, taking into account the apparent attenuation due to multiple forward scattering. In the uppermost mantle, two areas of high seismic attenuation (high Q -1) imaged beneath the volcanic front were mostly colocated with low-velocity anomalies. This coincidence suggests that these high- Q -1 areas in low-velocity zones are the most likely candidates for high-temperature regions beneath volcanoes. The distribution of random inhomogeneities indicated the presence of three anomalies beneath the volcanic front: Two were in high- Q -1 areas but the third was in a moderate- Q -1 area, indicating a low correlation between random inhomogeneities and Q -1. All three anomalies of random inhomogeneities were rich in short-wavelength spectra. The most probable interpretation of such spectra is the presence of volcanic rock, which would be related to accumulated magma intrusion during episodes of volcanic activity. Therefore, the different distributions of Q -1 and random inhomogeneities imply that the positions of hot regions in the uppermost mantle beneath this arc have changed temporally; therefore, they may provide important constraints on the evolutionary processes of arc crust and volcanoes.

  8. Eocene to Miocene back-arc basin basalts and associated island arc tholeiites from northern Sulawesi (Indonesia): Implications for the geodynamic evolution of the Celebes basin; Basaltes de bassin arriere-arc de l`Eocene-Miocene et tholeiites d`arc insulaire associees du nord Sulawesi (Indonesie): implications pour l`evolution geodynamique du bassin des Celebes

    Energy Technology Data Exchange (ETDEWEB)

    Rangin, C. [Centre National de la Recherche Scientifique (CNRS), 75 - Paris (France); Maury, R.C.; Bellon, H.; Cotten, J. [Universite de Bretagne Occidentale, 29 - Brest (France); Polve, M. [Universite Paul Sabatier, 31 - Toulouse (France); Priadi, B.; Soeria-Atmadja, R. [Department of Geology, ITB, Bandung (Indonesia); Joron, J.L. [CEA Centre d`Etudes de Saclay, 91 - Gif-sur-Yvette (France). Dept. de Recherche sur l`Etat Condense, les Atomes et les Molecules

    1997-12-31

    Eocene BABB basalts intruded by tholeiitic and calk-alkalic island arc magmatic rocks are reported from the north arm of Sulawesi (Indonesia). Age and geochemical similarities between these basalts and those drilled in the Celebes Sea indicate this North Sulawesi volcanic arc was built on the same oceanic crust. The 25 deg late Neogene clockwise rotation of the north arm of Sulawesi following its collision with fragments of Australia (Sula, Buton) is not sufficient to explain the asymmetrical magnetic anomalies in the Celebes basin. The North Sulawesi island arc could be interpreted as having progressively retreated northward on its own Celebes sea back arc basin, during an episode of Palaeogene-early Neogene tectonic erosion along the trench. (authors) 37 refs.

  9. Volcan Reventador's Unusual Umbrella

    Science.gov (United States)

    Chakraborty, P.; Gioia, G.; Kieffer, S. W.

    2005-12-01

    In the past two decades, field observations of the deposits of volcanoes have been supplemented by systemmatic, and sometimes, opportunistic photographic documentation. Two photographs of the umbrella of the December 3, 2002 eruption of Volcan Reventador, Ecuador, reveal a prominently scalloped umbrella that is unlike any umbrella previously documented on a volcanic column. The material in the umbrella was being swept off a descending pyroclastic flow, and was, therefore, a co-ignimbrite cloud. We propose that the scallops are the result of a turbulent Rayleigh-Taylor (RT) instability with no precedents in volcanology. We ascribe the rare loss of buoyancy that drives this instability to the fact that the Reventador column fed on a cool co-ignimbrite cloud. On the basis of the observed wavelength of the scallops, we estimate a value for the eddy viscosity of the umbrella of 4000 ~m2/s. This value is consistent with a previously obtained lower bound (200 ~m2/s, K. Wohletz, priv. comm., 2005). We do not know the fate of the material in the umbrella subsequent to the photos. The analysis suggests that the umbrella was negatively buoyant. Field work on the co-ignimbrite deposits might reveal whether or not the material reimpacted, and if so, where and whether or not this material was involved in the hazardous flows that affected the main oil pipeline across Ecuador.

  10. Uranium series, volcanic rocks

    Science.gov (United States)

    Vazquez, Jorge A.

    2014-01-01

    Application of U-series dating to volcanic rocks provides unique and valuable information about the absolute timing of crystallization and differentiation of magmas prior to eruption. The 238U–230Th and 230Th-226Ra methods are the most commonly employed for dating the crystallization of mafic to silicic magmas that erupt at volcanoes. Dates derived from the U–Th and Ra–Th methods reflect crystallization because diffusion of these elements at magmatic temperatures is sluggish (Cherniak 2010) and diffusive re-equilibration is insignificant over the timescales (less than or equal to 10^5 years) typically associated with pre-eruptive storage of nearly all magma compositions (Cooper and Reid 2008). Other dating methods based on elements that diffuse rapidly at magmatic temperatures, such as the 40Ar/39Ar and (U–Th)/He methods, yield dates for the cooling of magma at the time of eruption. Disequilibrium of some short-lived daughters of the uranium series such as 210Po may be fractionated by saturation of a volatile phase and can be employed to date magmatic gas loss that is synchronous with volcanic eruption (e.g., Rubin et al. 1994).

  11. Volcanic Eruptions and Climate

    Science.gov (United States)

    LeGrande, Allegra N.; Anchukaitis, Kevin J.

    2015-01-01

    Volcanic eruptions represent some of the most climatically important and societally disruptive short-term events in human history. Large eruptions inject ash, dust, sulfurous gases (e.g. SO2, H2S), halogens (e.g. Hcl and Hbr), and water vapor into the Earth's atmosphere. Sulfurous emissions principally interact with the climate by converting into sulfate aerosols that reduce incoming solar radiation, warming the stratosphere and altering ozone creation, reducing global mean surface temperature, and suppressing the hydrological cycle. In this issue, we focus on the history, processes, and consequences of these large eruptions that inject enough material into the stratosphere to significantly affect the climate system. In terms of the changes wrought on the energy balance of the Earth System, these transient events can temporarily have a radiative forcing magnitude larger than the range of solar, greenhouse gas, and land use variability over the last millennium. In simulations as well as modern and paleoclimate observations, volcanic eruptions cause large inter-annual to decadal-scale changes in climate. Active debates persist concerning their role in longer-term (multi-decadal to centennial) modification of the Earth System, however.

  12. Igniting flare-up events in Cordilleran arcs

    Science.gov (United States)

    Ducea, Mihai N.; Barton, Mark D.

    2007-11-01

    High-flux pulses of magmatism that make up most of the exposed North American Cordilleran arcs are derived primarily from upper plate lithospheric source materials, and not the mantle wedge as most models would predict, based on a compilation of thousands of previously published Sr, Nd, and O isotopic data. Mass balance calculations show that no more than 50% of that mass can be mantle-derived. Flare-ups must have fundamentally developed simultaneously with crustal/lithospheric thickening, thus implying a connection. Subduction erosion from the trench side, and retroarc shortening from the foreland side are the main tectonic shortening processes that operate in conjunction with high flux magmatism during subduction, and therefore are likely triggers for flare-up events in arc. These arcs represent the sites of crustal differentiation, and thus contribute to net continental growth, only if dense residual lower crust was returned to the convective mantle. Isotopic data shown here suggest that if convective removal of batholithic roots takes place, it must be a consequence and not a cause of episodic flare-ups. The Altiplano-Puna Volcanic Complex in South America may be the most recent continental arc segment in flare-up mode.

  13. Spatial Compilation of Holocene Volcanic Vents in the Western Conterminous United States

    Science.gov (United States)

    Ramsey, D. W.; Siebert, L.

    2015-12-01

    A spatial compilation of all known Holocene volcanic vents in the western conterminous United States has been assembled. This compilation records volcanic vent location (latitude/longitude coordinates), vent type (cinder cone, dome, etc.), geologic map unit description, rock type, age, numeric age and reference (if dated), geographic feature name, mapping source, and, where available, spatial database source. Primary data sources include: USGS geologic maps, USGS Data Series, the Smithsonian Global Volcanism Program (GVP) catalog, and published journal articles. A total of 726 volcanic vents have been identified from 45 volcanoes or volcanic fields spanning ten states. These vents are found along the length of the Cascade arc in the Pacific Northwest, widely around the Basin and Range province, and at the southern margin of the Colorado Plateau into New Mexico. The U.S. Geological Survey (USGS) National Volcano Early Warning System (NVEWS) identifies 28 volcanoes and volcanic centers in the western conterminous U.S. that pose moderate, high, or very high threats to surrounding communities based on their recent eruptive histories and their proximity to vulnerable people, property, and infrastructure. This compilation enhances the understanding of volcano hazards that could threaten people and property by providing the context of where Holocene eruptions have occurred and where future eruptions may occur. Locations in this compilation can be spatially compared to located earthquakes, used as generation points for numerical hazard models or hazard zonation buffering, and analyzed for recent trends in regional volcanism and localized eruptive activity.

  14. Caribbean island-arc rifting and back-arc basin development in the Late Cretaceous: Geochemical, isotopic and geochronological evidence from Central Hispaniola

    Science.gov (United States)

    Escuder Viruete, J.; Joubert, M.; Urien, P.; Friedman, R.; Weis, D.; Ullrich, T.; Pérez-Estaún, A.

    2008-08-01

    We present new regional petrologic, geochemical, Sr-Nd isotopic, and U-Pb geochronological data on the Turonian-Campanian mafic igneous rocks of Central Hispaniola that provide important clues on the development of the Caribbean island-arc. Central Hispaniola is made up of three main tectonic blocks—Jicomé, Jarabacoa and Bonao—that include four broad geochemical groups of Late Cretaceous mafic igneous rocks: group I, tholeiitic to calc-alkaline basalts and andesites; group II, low-Ti high-Mg andesites and basalts; group III, tholeiitic basalts and gabbros/dolerites; and group IV, tholeiitic to transitional and alkalic basalts. These igneous rocks show significant differences in time and space, from arc-like to non-arc-like characteristics, suggesting that they were derived from different mantle sources. We interpret these groups as the record of Caribbean arc-rifting and back-arc basin development in the Late Cretaceous. The> 90 Ma group I volcanic rocks and associated cumulate complexes preserved in the Jicomé and Jarabacoa blocks represent the Albian to Cenomanian Caribbean island-arc material. The arc rift stage magmatism in these blocks took place during the deposition of the Restauración Formation from the Turonian-Coniacian transition (~ 90 Ma) to Santonian/Lower Campanian, particularly in its lower part with extrusion at 90-88 Ma of group II low-Ti, high-Mg andesites/basalts. During this time or slightly afterwards adakitic rhyolites erupted in the Jarabacoa block. Group III tholeiitic lavas represent the initiation of Coniacian-Lower Campanian back-arc spreading. In the Bonao block, this stage is represented by back-arc basin-like basalts, gabbros and dolerite/diorite dykes intruded into the Loma Caribe peridotite, as well as the Peralvillo Sur Formation basalts, capped by tuffs, shales and Campanian cherts. This dismembered ophiolitic stratigraphy indicates that the Bonao block is a fragment of an ensimatic back-arc basin. In the Jicomé and

  15. Hybrid laser-arc welding

    DEFF Research Database (Denmark)

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

  16. The magmatic and eruptive response of arc volcanoes to deglaciation: insights from southern Chile

    Science.gov (United States)

    Rawson, Harriet; Mather, Tamsin A.; Pyle, David M.; Smith, Victoria C.; Fontijn, Karen; Lachowycz, Stefan; Naranjo, José A.; Watt, Sebastian F. L.

    2016-04-01

    Volcanism exerts a major influence on Earth's atmosphere and surface environments. Understanding feedbacks between climate and long-term changes in rates or styles of volcanism is important, but unresolved. For example, it has been proposed that a pulse of activity at once-glaciated volcanoes contributed to increasing atmospheric carbon dioxide accelerating early Holocene climate change. In plate-tectonic settings where magmatism is driven by decompression melting there is convincing evidence that activity is modulated by changes in ice- or water-loading across glacial/interglacial cycles. The response of subduction-related volcanoes, where the crust is typically thicker and mantle melting is dominated by flux melting, remains unclear. Since arc volcanoes account for 90% of subaerial eruptions, they are the most significant sources of volcanic gases and tephra directly to the atmosphere. Testing the response of arc volcanoes to deglaciation requires careful work to piece together eruption archives. Records of effusive eruptions from long-lived, arc stratovolcanoes are challenging to obtain and date; while deposits from the explosive eruptions, which dominate arc records, are prone to erosion and reworking. Our new high-resolution post-glacial (Phase 3), eruptive fluxes have been elevated, and dominated by explosive eruptions of intermediate magmas. We propose that this time-varying behaviour reflects changes in crustal plumbing systems, and magma storage timescales. During glaciations, magmas stall in the crust and differentiate to form large, evolved melt reservoirs. After the ice load is removed, much of this stored magma erupts (Phase 1). Subsequently, less-differentiated melts infiltrate the shallow crust (Phase 2). Then, as storage timescales increase, volcanism returns towards more evolved compositions (Phase 3). We suggest that on these short timescales, these observed variations are unlikely to reflect changes in mantle melt flux. Instead, the phenomena are

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

    Science.gov (United States)

    Reubi, Olivier; Blundy, Jon

    2009-10-29

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

  18. Petrogenesis of volcanic rocks that host the world-class Agsbnd Pb Navidad District, North Patagonian Massif: Comparison with the Jurassic Chon Aike Volcanic Province of Patagonia, Argentina

    Science.gov (United States)

    Bouhier, Verónica E.; Franchini, Marta B.; Caffe, Pablo J.; Maydagán, Laura; Rapela, Carlos W.; Paolini, Marcelo

    2017-05-01

    We present the first study of the volcanic rocks of the Cañadón Asfalto Formation that host the Navidad world-class Ag + Pb epithermal district located in the North Patagonian Massif, Patagonia, Argentina. These volcanic and sedimentary rocks were deposited in a lacustrine environment during an extensional tectonic regime associated with the breakup of Gondwana and represent the mafic to intermediate counterparts of the mainly silicic Jurassic Chon Aike Volcanic Province. Lava flows surrounded by autobrecciated carapace were extruded in subaerial conditions, whereas hyaloclastite and peperite facies suggest contemporaneous subaqueous volcanism and sedimentation. LA-ICPMS Usbnd Pb ages of zircon crystals from the volcanic units yielded Middle Jurassic ages of 173.9 ± 1.9 Ma and 170.8 ± 3 Ma. In the Navidad district, volcanic rocks of the Cañadón Asfalto Formation show arc-like signatures including high-K basaltic-andesite to high-K dacite compositions, Rb, Ba and Th enrichment relative to the less mobile HFS elements (Nb, Ta), enrichment in light rare earth elements (LREE), Ysbnd Ti depletion, and high Zr contents. These characteristics could be explained by assimilation of crustal rocks in the Jurassic magmas, which is also supported by the presence of zircon xenocrysts with Permian and Middle-Upper Triassic ages (281.3 Ma, 246.5, 218.1, and 201.3 Ma) and quartz xenocrysts recognized in these volcanic units. Furthermore, Sr and Nd isotope compositions suggest a contribution of crustal components in these Middle Jurassic magmas. High-K basaltic andesite has initial 87Sr/86Sr ratios of 0.70416-0.70658 and ξNd(t) values of -5.3 and -4. High-K dacite and andesite have initial 87Sr/86Sr compositions of 0.70584-0.70601 and ξNd(t) values of -4,1 and -3,2. The range of Pb isotope values (206Pb/204Pb = 18.28-18.37, 207Pb/204Pb = 15.61-15.62, and 208Pb/204Pb = 38.26-38.43) of Navidad volcanic rocks and ore minerals suggest mixing Pb sources with contributions of

  19. A Petrographic and Mineralogical Study of Volcanic Rocks from the Mayaxueshan Area, North Qilian Fold Belt, NW China

    Institute of Scientific and Technical Information of China (English)

    徐达伟; 萧炎宏

    2002-01-01

    The Ordovician volcanic rocks in the Mayaxueshan area have been pervasively altered or metamorphosedand contain abundant secondary minerals such as albite, chlorite, epidote, prehnite, pumpellyite, actinolite, titanite, quartz,and/or calcite. They were denoted as spilites or spilitic rocks in terms of their petrographic features and mineral assem-blages. The metamorphic grades of the volcanic rocks are equivalent to that of the intercalated metaclastic rocks. Thisindicates that both the spilitic volcanic rocks and metaclastic rocks in the Mayaxueshan area have formed as a result ofCaledonian regional metamorphism. We suggest that the previously denoted spilitic rocks or altered volcanic rocks shouldbe re-denoted as metabasalts or metabasaltic rocks. The metamorphic grade of the volcanic rocks increases with their age:prehnite-pumpellyite facies for the upper part of the Middle Ordovician volcanic rocks, prehnite-pumpellyite to lowergreenschist facies for the lower part of the Middle Ordovician volcanic rocks, and lower greenschist facies for the LowerOrdovician volcanic rocks. The P-T conditions are estimated as T = 240 - 290C and P = 1.5 - 4.5 kbar for the lower partof the Middle Ordovician rocks, and T = ~ 300~C for the Lower Ordovician rocks. The variations of mineral assemblagesoccurring at different domains of the volcanic rocks were controlled by the variations of the effective bulk composition inthose domains during metamorphism. The geochemical characteristics of Mg-Al chromite in the Mayaxueshan volcanicrocks are consistent with an origin of island arc environment.

  20. 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)

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

    Science.gov (United States)

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

    2016-06-01

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

  2. Recent seismicity detection increase at Santorini' s volcanic islands

    Science.gov (United States)

    Chouliaras, G.; Drakatos, G.; Makropoulos, K.; Melis, N. S.

    2012-04-01

    Santorini is the most active volcano in the southern Aegean volcanic arc. To improve the seismological network detectability of the Santorini seismicity, the Institute of Geodynamics of the National Observatory of Athens (NOA) installed 6 new seismological stations. The addition of these stations which begun in the year 2010 has significantly improved the detectability and reporting of the local seismic activity in NOA's instrumental seismicity catalog. Anomalous spatial and temporal changes in the b-value of the frequency-magnitude relationship and changes in the seismicity rate have been reported for many active volcanoes and have been used for the mapping of active magma chambers. In this study we present the results from a quantitative analysis of the seismicity in the Santorini volcanic complex using the seismicity catalog of NOA. From these results we observe a significant detection increase after the year 2010 mainly for events of small magnitudes and an increase in the seismicity rate by more than 100%. The statistical significance of this rate change is determined and mapped with the z-value method and it is found that the seismicity rate increases significantly within the two main active fault zones of the volcanic complex, in a zone perpendicular to the extensive tectonic regime that characterizes this region. Temporal variations in the b-value for different time periods indicate a rather homogeneous behaviour of the frequency-magnitude curves. The spatial distribution of the b-value is shown to vary around the volcanic complex exhibiting low b-values in the two main regions of seismic activity. A b-value cross section of the volcanic complex indicates relatively high b-values under the caldera and a significant b-value decrease with depth. The results from this study are found to be in general agreement with the results from other volcanic regions and they encourage further investigations concerning the seismic and volcanic hazard and risk estimates for

  3. Correlation methods in cutting arcs

    Energy Technology Data Exchange (ETDEWEB)

    Prevosto, L; Kelly, H, E-mail: prevosto@waycom.com.ar [Grupo de Descargas Electricas, Departamento Ing. Electromecanica, Universidad Tecnologica Nacional, Regional Venado Tuerto, Laprida 651, Venado Tuerto (2600), Santa Fe (Argentina)

    2011-05-01

    The present work applies similarity theory to the plasma emanating from transferred arc, gas-vortex stabilized plasma cutting torches, to analyze the existing correlation between the arc temperature and the physical parameters of such torches. It has been found that the enthalpy number significantly influence the temperature of the electric arc. The obtained correlation shows an average deviation of 3% from the temperature data points. Such correlation can be used, for instance, to predict changes in the peak value of the arc temperature at the nozzle exit of a geometrically similar cutting torch due to changes in its operation parameters.

  4. Friction in volcanic environments

    Science.gov (United States)

    Kendrick, Jackie E.; Lavallée, Yan

    2016-04-01

    Volcanic landscapes are amongst the most dynamic on Earth and, as such, are particularly susceptible to failure and frictional processes. In rocks, damage accumulation is frequently accompanied by the release of seismic energy, which has been shown to accelerate in the approach to failure on both a field and laboratory scale. The point at which failure occurs is highly dependent upon strain-rate, which also dictates the slip-zone properties that pertain beyond failure, in scenarios such as sector collapse and pyroclastic flows as well as the ascent of viscous magma. High-velocity rotary shear (HVR) experiments have provided new opportunities to overcome the grand challenge of understanding faulting processes during volcanic phenomena. Work on granular ash material demonstrates that at ambient temperatures, ash gouge behaves according to Byerlee's rule at low slip velocities, but is slip-weakening, becoming increasingly lubricating as slip ensues. In absence of ash along a slip plane, rock-rock friction induces cataclasis and heating which, if sufficient, may induce melting (producing pseudotachylyte) and importantly, vesiculation. The viscosity of the melt, so generated, controls the subsequent lubrication or resistance to slip along the fault plane thanks to non-Newtonian suspension rheology. The shear-thinning behaviour and viscoelasticity of frictional melts yield a tendency for extremely unstable slip, and occurrence of frictional melt fragmentation. This velocity-dependence acts as an important feedback mechanism on the slip plane, in addition to the bulk composition, mineralogy and glass content of the magma, that all influence frictional behaviour. During sector collapse events and in pyroclastic density currents it is the frictional properties of the rocks and ash that, in-part, control the run-out distance and associated risk. In addition, friction plays an important role in the eruption of viscous magmas: In the conduit, the rheology of magma is integral

  5. Joan of Arc.

    Science.gov (United States)

    Foote-Smith, E; Bayne, L

    1991-01-01

    For centuries, romantics have praised and historians and scientists debated the mystery of Joan of Arc's exceptional achievements. How could an uneducated farmer's daughter, raised in harsh isolation in a remote village in medieval France, have found the strength and resolution to alter the course of history? Hypotheses have ranged from miraculous intervention to creative psychopathy. We suggest, based on her own words and the contemporary descriptions of observers, that the source of her visions and convictions was in part ecstatic epileptic auras and that she joins the host of creative religious thinkers suspected or known to have epilepsy, from St. Paul and Mohammed to Dostoevsky, who have changed western civilization.

  6. The ARCS radial collimator

    Directory of Open Access Journals (Sweden)

    Stone M.B.

    2015-01-01

    Full Text Available We have designed, installed, and commissioned a scattered beam radial collimator for use at the ARCS Wide Angular Range Chopper Spectrometer at the Spallation Neutron Source. The collimator has been designed to work effectively for thermal and epithermal neutrons and with a range of sample environments. Other design considerations include the accommodation of working within a high vacuum environment and having the ability to quickly install and remove the collimator from the scattered beam. We present here characterization of the collimator's performance and methodologies for its effective use.

  7. The ARCS radial collimator

    Science.gov (United States)

    Stone, M. B.; Niedziela, J. L.; Overbay, M. A.; Abernathy, D. L.

    2015-01-01

    We have designed, installed, and commissioned a scattered beam radial collimator for use at the ARCS Wide Angular Range Chopper Spectrometer at the Spallation Neutron Source. The collimator has been designed to work effectively for thermal and epithermal neutrons and with a range of sample environments. Other design considerations include the accommodation of working within a high vacuum environment and having the ability to quickly install and remove the collimator from the scattered beam. We present here characterization of the collimator's performance and methodologies for its effective use.

  8. Processes of runoff generation operating during the spring and autumn seasons in a permafrost catchment on semi-arid plateaus

    Science.gov (United States)

    Genxu, Wang; Tianxu, Mao; Juan, Chang; Chunlin, Song; Kewei, Huang

    2017-07-01

    There is a lack of knowledge about how to quantify runoff generation and the hydrological processes operating in permafrost catchments on semi-arid plateaus. To understand how freeze-thaw cycles affect runoff generation processes in permafrost catchments, a typical headwater catchment with continuous permafrost on the Tibetan Plateau was measured. A new approach is presented in this study to account for runoff processes on the spring thawing period and autumn freezing period, when runoff generation clearly differs from that of non-permafrost catchments. This approach introduces a soil temperature-based water saturation function and modifies the soil water storage curve with a soil temperature threshold. The results show that surface soil thawing induced saturation excess runoff and subsurface interflow account for approximately 66-86% and 14-34% of total spring runoff, respectively, and the soil temperature significantly affects the runoff generation pattern, the runoff composition and the runoff coefficient with the enlargement of the active layer. The suprapermafrost groundwater discharge decreases exponentially with active layer frozen processes during autumn runoff recession, whereas the ratio of groundwater discharge to total runoff and the direct surface runoff coefficient simultaneously increase. The bidirectional freezing of the active layer controls and changes the autumn runoff processes and runoff composition. The new approach could be used to further develop hydrological models of cold regions dominated by permafrost.

  9. Volcanic studies at Katmai

    Energy Technology Data Exchange (ETDEWEB)

    1989-12-31

    The Continental Scientific Drilling Program (CSDP) is a national effort supported by the Department of Energy, the US Geological Survey, and the National Science Foundation. One of the projects proposed for the CSDP consists of drilling a series of holes in Katmai National Park in Alaska to give a third dimension to the model of the 1912 eruption of Novarupta, and to investigate the processes of explosive volcanism and hydrothermal transport of metals (Eichelberger et al., 1988). The proposal for research drilling at Katmai states that ``the size, youth, elevated temperature, and simplicity of the Novarupta vent make it a truly unique scientific target.`` The National Park Service (NPS), which has jurisdiction, is sympathetic to aims of the study. However, NPS wishes to know whether Katmai is indeed uniquely suited to the research, and has asked the Interagency Coordinating Group to support an independent assessment of this claim. NPS suggested the National Academy of Sciences as an appropriate organization to conduct the assessment. In response, the National Research Council -- the working arm of the Academy -- established, under the aegis of its US Geodynamics Committee, a panel whose specific charge states: ``The proposed investigation at Katmai has been extensively reviewed for scientific merit by the three sponsoring and participating agencies. Thus, the scientific merit of the proposed drilling at Katmai is not at issue. The panel will review the proposal for scientific drilling at Katmai and prepare a short report addressing the specific question of the degree to which it is essential that the drilling be conducted at Katmai as opposed to volcanic areas elsewhere in the world.``

  10. Quaternary basaltic volcanism in the Payenia volcanic province, Argentina

    DEFF Research Database (Denmark)

    Søager, Nina

    The extensive Quaternary volcanism in the Payenia volcanic province, Mendoza, Argentina, is investigated in this study by major and trace element analyses, Sr, Nd, Hf and Pb-isotopic analyses and Zr-Hf isotope dilution data on samples from almost the entire province. The samples are mainly...... in basalts from all the studied volcanic fields in Payenia is signs of lower crustal contamination indicating assimilation of, in some cases, large amounts of trace element depleted, mafic, plagioclase-bearing rocks. The northern Payenia is dominated by backarc basalts erupted between late Pliocene to late...

  11. A kinematic model for the Plio-Quaternary evolution of the Tyrrhenian Apenninic system: implications for rifting processes and volcanism

    Science.gov (United States)

    Turco, E.; Zuppetta, A.

    1998-06-01

    During the frontal accretion due to the Late Miocene-Quaternary thrusting, the interior of the Apenninic chain underwent large-scale extension which produced the opening of the Tyrrhenian Oceanic Basin, a back-arc basin in respect to the late Cenozoic Apenninic chain, and the onset of the Quaternary volcanic activity in the Campanian Plain and more generally in the Tyrrhenian area. To outline the space/time distribution and the geotectonic setting of the Tyrrhenian volcanics we approached the problem from a kinematic point of view. A synthesis of the available geological and geophysical data leads us to suggest that the progressive migration of the Apenninic Arcs is responsible for the extension phenomena which took place during the last 5 Ma. At first, the extension resulted from the kinematic interaction between the Northern Apenninic Arc and the Southern Apenninic Arc during the Late Pliocene. Then, from the Early Pleistocene the extension was controlled by the SE migration of the Southern arc only, and therefore it can be regarded as part of the general Southern Tyrrhenian extension phenomenon. Due to the intense thinning, the isotherms migrated upward very rapidly within the Toscana, Latium and Campania lithosphere where the melting point was reached, giving rise to the onset of volcanic activity at the end of the Early Pleistocene.

  12. Frequent underwater volcanism in the central Aegean Sea

    Science.gov (United States)

    Huebscher, C.; Ruhnau, M.; Dehghani, G. A.

    2012-04-01

    The extinction of the Minoan culture in the mid second millennium BCE is a well known consequence of the Plinian eruption of Thera volcano (Santorini Island). Santorini is a member of the South Aegean arc forming a chain from the Gulf of Saronikos (Susaki, Egina, Poros, Methana) at West, to an area close to the Anatolian coast at East (Kos, Nisyros and minor islands), through the central part (Milos and Santorini island groups). Underwater volcanic activity was manifested historically only once. During 1649-1650 CE the Kolumbo underwater volcano evolved about 8 km northeast of Santorini. As a consequence of this eruption volcanic ash covered the entire Aegean area and a hazardous tsunami was triggered. Here we show by means of reflection seismic and magnetic data that underwater volcanism occurred more frequently in the central Aegean Sea than previously assumed. Seismic data show that Kolumbo constitutes of five vertically stacked cones of pyroclastic sediment plus at least four smaller cones on the flank of the volcano. The formation of Kolumbo started synchronous with Santorini Island. The entire volume of the Kolumbo pyroclastic cones is estimated to more than 15 cubic-kilometers. Several small-scale cones have been detected in the Anyhdros Basin some km north-east of Kolumbo, being previously interpreted as mud volcanoes by other authors. However, the similarity of seismic and magnetic signatures of these cones and Kolumbo strongly suggest that these cones were also created by underwater volcanism. Volcanic cones, Kolumbo and Santorini are situated along a NE-SW striking graben system that evolved during five extensional tectonic pulses in the Pliocene.

  13. 0- and 2/3-magnetization plateaus in three-leg antiferromagnetic Heisenberg spin-1/2 ladders with leg-dimerization

    Energy Technology Data Exchange (ETDEWEB)

    Li, Rui-Xue; Wang, Shu-Ling; Ni, Yun [School of Physics and Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology, Wuhan 430074 (China); Yao, Kai-Lun, E-mail: klyao@mail.hust.edu.cn [School of Physics and Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology, Wuhan 430074 (China); International Center of Materials Physics, Chinese Academy of Sciences, Shenyang 110015 (China); Fu, Hua-Hua [School of Physics and Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology, Wuhan 430074 (China)

    2014-02-01

    Magnetic properties of three-leg antiferromagnetic Heisenberg spin-1/2 ladders with different dimerization patterns have been studied using the bond mean-field theory. Our results show that rung-columnar ladders are thermodynamically stable states for large rung-to-leg coupling ratios. Magnetization curves of leg-columnar and leg-staggered ladders always exhibit 0- and 2/3-magnetization plateaus, which do not appear in rung-columnar and rung-staggered ladders. In leg-dimerized ladders, the formation of spin dimers in the three legs results in the appearance of the 0- and 2/3-magnetization plateaus. Spin configuration in the 2/3-magnetization plateau can be understood from the mean-field bond parameters.

  14. Submarine volcanoes of the Kolumbo volcanic zone NE of Santorini Caldera, Greece

    Science.gov (United States)

    Nomikou, P.; Carey, S.; Papanikolaou, D.; Croff Bell, K.; Sakellariou, D.; Alexandri, M.; Bejelou, K.

    2012-06-01

    The seafloor northeast of Santorini volcano in Greece consists of a small, elongated rifted basin that has been the site of recent submarine volcanism. This area lies within the Cyclades back-arc region of the present Hellenic subduction zone where the seafloor of the eastern Mediterranean Sea is descending beneath the Aegean microplate. The Cycladic region and the Aegean Sea as a whole are known to be regions of north-south back-arc extension and thinning of continental crust. Nineteen submarine volcanic cones occur within this small rift zone, the largest of these being Kolumbo which last erupted explosively in 1650 AD, causing significant damage and fatalities on the nearby island of Santorini. Previous SEABEAM mapping and seismic studies from HCMR indicate that many of the smaller v'olcanic cones have been built above the present seafloor, while others are partly buried, indicating a range of ages for the activity along this volcanic line. None of the cones to the northeast of Kolumbo had been explored in detail prior to a cruise of the E/V Nautilus (NA007) in August 2010. The ROV Hercules was used to explore the slopes, summits and craters of 17 of the 19 centers identified on multibeam maps of the area. Water depths of the submarine volcano's summits ranged from 18 to 450 m. In general, the domes/craters northeast of Kolumbo were sediment covered and showed little evidence of recent volcanic activity. Outcrops of volcanic rock were found in the crater walls and slopes of some of the cones but they typically consisted of volcanic fragments of pumice and lava that have been cemented together by biological activity, indicative of the lack of recent eruptions. Geochemical analysis of samples collected on the northeast cones showed evidence of low temperature hydrothermal circulation on the summit and upper flanks in the form of stream-like manganese precipitates emanating from pits and fractures.

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

    Science.gov (United States)

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

    2016-09-01

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

  16. Alternating-Polarity Arc Welding

    Science.gov (United States)

    Schwinghamer, R. J.

    1987-01-01

    Brief reversing polarity of welding current greatly improves quality of welds. NASA technical memorandum recounts progress in art of variable-polarity plasma-arc (VPPA) welding, with emphasis on welding of aluminum-alloy tanks. VPPA welders offer important advantages over conventional single-polarity gas/tungsten arc welders.

  17. Western Alborz Volcanic Rocks, a new Geochemical Viewpoint

    Science.gov (United States)

    Ghorbani, M.

    2001-12-01

    Volcanic and pyroclastic rocks of Eocene age comprise vast outcrops of Alborz Mountain Range, a fold-thrusted structural unit extending across northern Iran for 2000 km in a curvilinear pattern. In his account of structural evolution of Iranian plateau, Berberian (1983; p. 55) ascribed these rocks to a subduction-type magmatism. Based on a tectonostratigraphic study, these rocks are attributed to an arc-type magmatism (Alavi; 1996, p. 29). Recently a new data set of major and trace element (including REE) analyses of volcanic rocks from western Alborz, some 50 km west of city of Qazvin, has been made available (Asiabanha, 2001). Careful examination of the data (i.e., those of basic-intermediate rocks) in present study revealed, for the first time, some geochemical characteristics which have important implications on the geodynamic synthesis of this structural unit. The rocks contain 50-60 wt% SiO2. They lie in the midalkaline-to-subalkaline domain of TAS diagram (Middlemost, 1997; p.216) and fall in the calcalkaline field of AFM diagram. The volcanic rocks display two distinct chondrite-normalized REE patterns, one is MREE-depleted while the other is a rather smooth uniform M-HREE pattern. These are called MREE-depleted and smooth M-HREE series. Basic rocks from the latter contain higher silica than the former (>53 vs. >50 wt%), yet they show lower incompatible elements (e.g., K and Rb) and HFSE contents. These features can not be explained by differentiation and might be interpreted as implying the involvement of two source regions. Chondrite-normalized trace element patterns of the MREE-depleted series is more akin to the island arc calcalkaline (IACA) basic rocks than the basic rocks from any other tectonic settings. However, island arc products, known for being depleted in HFSE relative to other incompatible elements, differ from the MREE-depleted series which is rich in both HFSE and incompatible elements. One may advocate the role of OIB-type mantle

  18. Io. [theories concerning volcanic activity

    Science.gov (United States)

    Johnson, T. V.; Soderblom, L. A.

    1983-01-01

    A report on the continuing investigation of Io is presented. Gravitational resonance is discussed as the cause of Io's volcanism, and the volcanic activity is explained in terms of sulfur chemistry. Theories concerning the reasons for the two main types of volcanic eruptions on Io are advanced and correlated with geographical features of the satellite. The sulfur and silicate models of the calderas are presented, citing the strengths and weaknesses of each. Problems of the gravitational resonance theory of Io's heat source are then described. Finally, observations of Io planned for the Galileo mission are summarized.

  19. Anhydrite solubility in differentiated arc magmas

    Science.gov (United States)

    Masotta, M.; Keppler, H.

    2015-06-01

    The solubility of anhydrite in differentiated arc magmas was experimentally studied at 200 MPa and 800-1000 °C over a range of oxygen fugacities, from 0.5 log units above the Ni-NiO buffer to the hematite-magnetite buffer. Anhydrite is stable only at oxidizing conditions (fO2 ⩾ Re-ReO2), whereas sulfides only form under reducing conditions. The solubility of anhydrite in the melt ultimately regulates the amount of sulfur available to partition between melt and fluid phase during the eruption. At oxidizing conditions, the solubility product of anhydrite increases with temperature, nbo/t and melt water content. We provide a new calibration of the anhydrite solubility product (KSP = XCaO * XSO3), which reproduces all available experimental data with greatly improved accuracy: In this equation, the molar fractions XCaO and XSO3 in the melt as well as the number of non-bridging oxygen atoms per tetrahedron (nbo/t) are calculated on an anhydrous basis (H2O refers to the melt water content, T is temperature in Kelvin). We apply our model to estimate the sulfur yield of some recent volcanic eruptions and we show that the sulfur yield of the 1991 Mt. Pinatubo dacite eruption was unusually large, because only a small fraction of the sulfur was locked up in anhydrite. In general, high sulfur yields are expected when anhydrite solubility in the melt is high, i.e. for somewhat depolymerized melts. For rhyolitic systems, most of the available sulfur will be locked up in anhydrite, so that even very large eruptions may only have a small effect on global surface temperatures. Our model therefore allows improved predictions of the environmental impact of explosive volcanic eruptions.

  20. Characteristics of Arcs Between Porous Carbon Electrodes

    OpenAIRE

    Carvou, Erwann; Le Garrec, Jean-Luc; Mitchell, Brian

    2013-01-01

    International audience; Arcs between carbon electrodes present some specific differences compared with metallic arcs. The arc voltage is higher, but does not attain a stable value displaying large fluctuations. Indeed, the arcs are produced by the direct sublimation of the electrodes, without passing through a molten phase. The arc production is also facilitated by both circuit breaking and electric field breakdown. In this paper, arcing has been examined under various conditions (voltage, cu...

  1. Adakites related to subduc- tion in the northern margin of Junggar arc for the Late Paleozoic: Products of slab melting

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Volcanic rocks with adakitic compositional signature have been recognized in the northern margin of ancient Junggar island arc for the Late Paleozoic. These adakites for the early Devonian from the Tuoranggekudouke Group (D1t) are characteristic of high Sr, Sr/Y and (La/Yb)N but low Y, Yb and HREE. Their compositional characteristics are much similar to those of the typical adakites in the world but distinct from those of the normal arc volcanic rocks from the same Group. We conclude that these adakitic volcanic rocks were produced by slab melting during the early period of Paleoasia-ocean lithosphere subduction. This infers that the Paleoasia Ocean in the north Junggar area began a new subduction process in the early Devonian.

  2. Formation of volcanic edifices in response to changes in magma budget at intermediate spreading rate ridges

    Science.gov (United States)

    Howell, J.; White, S. M.; Bohnenstiehl, D. R.; Bizimis, M.

    2010-12-01

    The spatial and abundance distributions of volcanic edifices along mid-ocean ridges have a well known correlation with spreading rate. Along slow spreading centers, volcanic edifices are normally distributed about the segment center. Volcanic edifices along fast spreading centers have the opposing trend, i.e. edifices form primarily at the ends of segments. However, in ridges affected by plumes and at back arc basins, the spatial and abundance distributions of volcanic edifices differ from that observed at normal ridges of the same spreading rate. This suggests that magma supply rate may control the spatial and abundance distribution of volcanic edifices. Recent geophysical and geochemical studies along the Galapagos Spreading Centers (GSC), Juan de Fuca Ridge (JdFR), Southeast Indian Ridge (SEIR) and the Valu Fa (VF) and Eastern Lau Spreading Centers (ELSC) put tight constraints on crustal thickness, making it possible investigate the effect of magma budget and axial morphology on the formation of volcanic edifices. Volcanic edifices are described according to their volume, shape (their height to basal radius ratio) and their location relative to the end or center of a segment (abundance distribution). For the GSC, the shape and distribution of volcanic edifices correlate with changes in crustal thickness and axial morphology, consistent with a magma supply control on their formation in this region. This relationship is not apparent along the SEIR or JdFR, where edifices show little variation with changes in axial morphology at relatively constant spreading rates. Results for VF and ELSC are what we expect for changes in spreading rate, not axial morphology. Our study suggests that the formation of volcanic edifices at intermediate spreading rate ridges are influenced by magma budget but only when it is above a certain threshold.

  3. Volcano collapse along the Aleutian Ridge (western Aleutian Arc

    Directory of Open Access Journals (Sweden)

    C. Montanaro

    2011-03-01

    Full Text Available The Aleutian Ridge, in the western part of the Aleutian Arc, consists of a chain of volcanic islands perched atop the crest of a submarine ridge with most of the active Quaternary stratocones or caldera-like volcanoes being located on the northern margins of the Aleutian Islands. Integrated analysis of marine and terrestrial data resulted in the identification and characterization of 17 extensive submarine debris avalanche deposits from 11 volcanoes. Two morphological types of deposits are recognizable, elongate and lobate, with primary controls on the size and distribution of the volcanic debris being the volume and nature of material involved, proportion of fine grained material, depth of emplacement and the paleo-bathymetry. Volume calculations show the amount of material deposited in debris avalanches is as much as three times larger than the amount of material initially involved in the collapse, suggesting the incorporation of large amounts of submarine material during transport. The orientation of the collapse events is influenced by regional fault systems underling the volcanoes. The western Aleutian Arc has a significant tsunamigenic potential and communities within the Aleutian Islands and surrounding areas of the North Pacific as well as shipping and fishing fleets that cross the North Pacific may be at risk during future eruptions in this area.

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

    Science.gov (United States)

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

    2009-06-01

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

  5. Crustal structure and tectonic history of the Kermadec arc inferred from MANGO seismic refraction profiles

    Science.gov (United States)

    Bassett, D.; Kopp, H.; Sutherland, R.; Henrys, S.; Watts, A. B.; Timm, C.; Scherwath, M.; Grevemeyer, I.; de Ronde, C. E. J.

    2016-12-01

    We have analyzed three wide-angle seismic reflection and refraction profiles and applied spectral averaging techniques to regional grids of bathymetry and free-air gravity anomaly to place the first regional constraints on the crustal structure of the Kermadec arc. These observations are used to test contrasting tectonic models for an along-strike transition in margin structure, across which, 1) the remnant Lau-Colville and active Kermadec arc ridges narrow by >50%; 2) the backarc and forearc deepen by 1 km, and 3) the active volcanic arc is deflected west into the deepest known backarc basin. We use residual bathymetric anomalies to constrain the geometry of this boundary and propose the name Central Kermadec Discontinuity (CKD). North of the CKD, the buried Tonga Ridge occupies the forearc with VP 6.5-7.3 km s-1 and residual free-air gravity anomalies constrain its latitudinal extent (north of 30.5°S), width (110±20 km) and strike ( 005° south of 25°S). South of the CKD the forearc is structurally homogeneous down-dip with VP 5.7-7.3 km s-1. Lower crustal velocities are similar to the northern Kermadec forearc, but there is no seismic or gravimetric evidence for an extinct arc ridge within the forearc. In the Havre Trough backarc, crustal thickness south of the CKD is 8-9 km, which is up-to 4 km thinner than the northern Havre Trough and at least 1 km thinner than the southern Havre Trough. The northern Kermadec/Tonga arc preserves a substrate of the Eocene arc, the southern Kermadec forearc preserves Mesozoic forearc rocks accreted at the Gondwana margin, and the central Kermadec arc may have fomed in the Kupe Abyssal Plain. The oldest arc related rocks recovered north and south of the CKD are 52 Ma and 16.7 Ma respectively, and plate tectonic reconstruction suggest the Eocene arc was originally conjoined with the Three Kings Ridge. The separation of these ridges during the early Oligocene likely formed the CKD. In contrast to previous interpretations, we

  6. Volcanism and Subduction: The Kamchatka Region

    Science.gov (United States)

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

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

  7. The interplay between tectonics and volcanism: a key to unravel the nature of Andean geothermal systems

    Science.gov (United States)

    Cembrano, J. M.

    2013-05-01

    Field mapping combined with seismic data document the interplay between tectonics and volcanism in the Andes. In the Central Volcanic Zone (CVZ) of northern Chile (22-24°S), Pleistocene east-west shortening and a thick crust (50-70 km) are associated with major composite dacitic-andesitic volcanoes and a few monogenetic basaltic eruptive centers. CVZ stratovolcanoes are devoided of flank vents; clusters of minor eruptive centers are uncommon. Composite volcanoes and minor eruptive centers are coeval with a NS-striking system of reverse faults and fault-propagation folds. Although dextral strike-slip crustal seismicity is recorded between 18 and 21°S, evidence for long-term, margin-parallel strike-slip deformation is absent. In contrast, volcanoes of the Southern Volcanic Zone (SVZ), between 38 and 46°S are built on a much thinner crust (30-40 km) during intra-arc dextral transpression. Crustal seismicity shows dextral strike-slip focal mechanisms. There, a wide variety of volcanic forms and compositions coexist along the same volcanic arc. Volcanoes range from single monogenetic cones lying on master faults to major composite volcanoes organized into either NE- or NW-trending chains, oblique to the continental margin. Flank vents and elongated clusters of minor eruptive centers are common. Compositions range from primitive basalts at minor eruptive centers, to highly evolved magmas at mature stratovolcanoes. I hypothesize that the kinematics of fault-fracture networks under which magma is transported through the crust is one fundamental factor controlling the wide variety of volcanic forms, volcanic alignment patterns and rock compositions along a single volcanic arc. As a first approximation, a thicker crust favors magma differentiation processes whereas a thinner crust prevents it. Likewise, whereas bulk intra-arc compression (vertical σ3) enhances longer residence times of magmas in the CVZ, strike-slip deformation (horizontal σ3) in SVZ provides

  8. Volcanic eruptions observed with infrasound

    Science.gov (United States)

    Johnson, Jeffrey B.; Aster, Richard C.; Kyle, Philip R.

    2004-07-01

    Infrasonic airwaves produced by active volcanoes provide valuable insight into the eruption dynamics. Because the infrasonic pressure field may be directly associated with the flux rate of gas released at a volcanic vent, infrasound also enhances the efficacy of volcanic hazard monitoring and continuous studies of conduit processes. Here we present new results from Erebus, Fuego, and Villarrica volcanoes highlighting uses of infrasound for constraining quantitative eruption parameters, such as eruption duration, source mechanism, and explosive gas flux.

  9. Los volcanes y los hombres

    OpenAIRE

    García, Carmen

    2007-01-01

    Desde las entrañas de la tierra, los volcanes han creado la atmósfera, el agua de los océanos, y esculpido los relieves del planeta: son, pues, los zahoríes de la vida. Existen volcanes que los hombres explotan o cultivan, y otros sobre los cuales se han construido observatorios en los que se llevan a cabo avanzadas investigaciones científicas.

  10. Volcanic hazards and aviation safety

    Science.gov (United States)

    Casadevall, Thomas J.; Thompson, Theodore B.; Ewert, John W.; ,

    1996-01-01

    An aeronautical chart was developed to determine the relative proximity of volcanoes or ash clouds to the airports and flight corridors that may be affected by volcanic debris. The map aims to inform and increase awareness about the close spatial relationship between volcanoes and aviation operations. It shows the locations of the active volcanoes together with selected aeronautical navigation aids and great-circle routes. The map mitigates the threat that volcanic hazards pose to aircraft and improves aviation safety.

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

    Directory of Open Access Journals (Sweden)

    Dingjian Ye

    2013-01-01

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

  12. Volcanic Zone, New Zealand

    Directory of Open Access Journals (Sweden)

    Graham J. Weir

    2001-01-01

    Full Text Available A conceptual model of the Taupo Volcanic Zone (TVZ is developed, to a depth of 25 km, formed from three constant density layers. The upper layer is formed from eruption products. A constant rate of eruption is assumed, which eventually implies a constant rate of extension, and a constant rate of volumetric creation in the middle and bottom layers. Tectonic extension creates volume which can accomodate magmatic intrusions. Spreading models assume this volume is distributed throughout the whole region, perhaps in vertical dykes, whereas rifting models assume the upper crust is thinned and the volume created lies under this upper crust. Bounds on the heat flow from such magmatic intrusions are calculated. Heat flow calculations are performed and some examples are provided which match the present total heat output from the TVZ of about 4200 MW, but these either have extension rates greater than the low values of about 8 ± 4 mm/a being reported from GPS measurements, or else consider extension rates in the TVZ to have varied over time.

  13. Extracting dynamic topography from river profiles and cosmogenic nuclide geochronology in the Middle Atlas and the High Plateaus of Morocco

    Science.gov (United States)

    Pastor, Alvar; Babault, Julien; Owen, Lewis A.; Teixell, Antonio; Arboleya, María-Luisa

    2015-11-01

    The Moulouya river system has intensely eroded the Arhbalou, Missour, and Guercif Neogene foreland basins in northeastern Morocco, having changed from net aggradation during the Miocene-early Pliocene to net incision punctuated by alluvial fan deposition at late Pliocene or early Quaternary time. This region as a whole has experienced mantle-driven, surface uplift (dynamic topography) since the late Cenozoic, being locally affected by uplift due to crustal shortening and thickening of the Middle Atlas too. Knickpoints located along the major streams of the Moulouya fluvial network, appear on both the undeformed margins of the Missour and Guercif foreland basins (High Plateaus), as well as along the thrust mountain front of the southern Middle Atlas, where they reach heights of 800-1000 m. 500-550 m of the knickpoint vertical incision might be explained by long-wavelength mantle-driven dynamic surface uplift, whereas the remaining 450-500 m in the southern Middle Atlas front and 200-300 m in the northeastern Middle Atlas front seem to be thrust-related uplift of the Jebel Bou Naceur. Be-10 terrestrial cosmogenic nuclides have been used to date two Quaternary river terraces in the Chegg Ard valley at 62 ± 14 ka and 411 ± 55 ka. The dated terraces allow the incision rates associated with the frontal structures of the Middle Atlas to be estimated at ~ 0.3 mm yr- 1. Furthermore, these ages have served to evaluate mantle-driven regional surface uplift since the middle Pleistocene in the central Missour basin, yielding values of ~ 0.1-0.2 mm yr- 1.

  14. Evolution and genesis of volcanic rocks from Mutnovsky Volcano, Kamchatka

    Science.gov (United States)

    Simon, A.; Yogodzinski, G. M.; Robertson, K.; Smith, E.; Selyangin, O.; Kiryukhin, A.; Mulcahy, S. R.; Walker, J. D.

    2014-10-01

    This study presents new geochemical data for Mutnovsky Volcano, located on the volcanic front of the southern portion of the Kamchatka arc. Field relationships show that Mutnovsky Volcano is comprised of four distinct stratocones, which have grown over that past 80 ka. The youngest center, Mutnovsky IV, has produced basalts and basaltic andesites only. The three older centers (Mutnovsky I, II, III) are dominated by basalt and basaltic andesite (60-80% by volume), but each has also produced small volumes of andesite and dacite. Across centers of all ages, Mutnovsky lavas define a tholeiitic igneous series, from 48-70% SiO2. Basalts and basaltic andesites have relatively low K2O and Na2O, and high FeO* and Al2O3 compared to volcanic rocks throughout Kamchatka. The mafic lavas are also depleted in the light rare earth elements (REEs), with chondrite-normalized La/Sm arc volcanic rocks worldwide. Radiogenic isotope ratios (Sr, Nd, Pb, Hf) are similar for samples from all four eruptive centers, and indicate that all samples were produced by melting of a similar source mixture. No clear age-progressive changes are evident in the compositions of Mutnovsky lavas. Mass balance and assimilation-fractional crystallization (AFC) modeling of major and rare earth elements (REEs) indicate that basaltic andesites were produced by FC of plagioclase, clinopyroxene and olivine from a parental basalt, combined with assimilation of a melt composition similar to dacite lavas present at Mutnovsky. This modeling also indicates that andesites were produced by FC of plagioclase from basaltic andesite, combined with assimilation of dacite. Dacites erupted from Mutnovsky I and II have low abundances of REEs, and do not appear to be related to mafic magmas by FC or AFC processes. These dacites are modeled as the products of dehydration partial melting at mid-crustal levels of a garnet-free, amphibole-bearing basaltic rock, which itself formed in the mid-crust by emplacement of magma that

  15. Arc/Forearc Lengthening at Plate Triple Junctions and the Formation of Ophiolitic Soles

    Science.gov (United States)

    Casey, John; Dewey, John

    2013-04-01

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

  16. Tectonic geomorphology of the Ryukyu Trench-Arc-Backarc System:geological-geophysical exploration and mapping

    Institute of Scientific and Technical Information of China (English)

    FU Mingzuo; LIU Lejun; ZHENG Yanpeng; LIU Baohua; WU Jinlong; XU Xiaowei

    2004-01-01

    Based on an analysis of full-cover multi-beam bathymetric data, seismic and sub-bottom profiling data, and other geological-geophysical data sets, the geomorphologic features of the Ryukyu trench-arc-backarc (T-A-BA) system are delineated, and a geomorphologic map of the system is compiled. The results show that the evolution and spatial distribution patterns of the geomorphologic types of the Ryukyu T-A-BA system are controlled mainly by tectonic movements. The tectonic geomorphologic characteristics of the Ryukyu Arc (RA) differ distinctly from those of the East China Sea (ECS) continental shelf and slope. In term of geological structures, RA consists of the Tokara volcanic ridge,the Ryukyu folded ridge, the fore-arc accretion-wedge ridge and the Amami Depression and the fore-arc depressions between the ridges, which is composed of a complex of alternating island-slope ridges and fault basins. The slope of the ECS is a passive continental margin with stepwise faults. The Okinawa Trough (OT) is a backarc rift in which tectonic movements are intensive, with active volcanic and hydrothermal eruptions and sea floor spreading. The development of geomorphic features of the OT is controlled by the central en echelon spreading axes, the faults along the ECS slope and the marginal faults to the west of the Tokara volcanic ridge.The geomorphic complex of the OT is arranged in the following pattern: the en echelon grabens and volcanic chains formed by rifting and spreading lie in the central part of the trough, the turbidite plains inclining eastwards-southeastwards from the slope foot of the ECS lie in the western-northwestern parts of the OT, and the volcaniclastic deposit plains inclining westward-northwestwards from the western slope foot of the RA lie in the eastern-southeastern parts of the OT. In term of tectonic geomorphology, the OT forms a natural division between the shelf of the ECS and the RA.

  17. Geophysical characteristics of the Ninetyeast Ridge–Andaman island arc/trench convergent zone

    Digital Repository Service at National Institute of Oceanography (India)

    Subrahmanyam, C.; Gireesh, R.; Chand, S.; KameshRaju, K.A.; Rao, D.G.

    of subduction is oblique. Thick buoyant roots underlying the basement highs tend to flatten the subducting plate and thereby inhibit the subducting process. Subduction of such bathymetric highs may also have its own effect in the spreading processes... are Bengal fan sediments, Ninetyeast Ridge, Andaman Nicobar Ridge, a sharp bathymetric depression forming the Nicobar deep east of the Andaman Nicobar Ridge, forearc basin, inner volcanic arc and the Andaman backarc basin (see Fig.1). NER is a major...

  18. Geochemical Signature of Mesozoic Volcanic and Granitic Rocks in Madina Regency Area, North Sumatra, Indonesia, and its Tectonic Implication

    Directory of Open Access Journals (Sweden)

    Iskandar Zulkarnain

    2014-06-01

    Full Text Available http://dx.doi.org/10.17014/ijog.vol4no2.20094Five samples consisting of two Permian-Triassic basalts, two Triassic-Jurassic granitic rocks, and a Miocene andesite were collected from the Madina Regency area in North Sumatra that is regionally situated on the West Sumatra Block. Previous authors have proposed three different scenarios for the geological setting of West Sumatra Permian Plutonic-Volcanic Belt, namely an island-arc, subduction related continental margin arc, and continental break-up. Petrographic analysis of the Mesozoic basaltic samples indicates that they are island-arcs in origin; however their trace element spider diagram patterns (Rock/MORB ratio also show the character of back-arc marginal basin, besides the island-arc. Furthermore, their REE spider diagram patterns (Rock/ Chondrite ratio clearly reveal that they were actually generated in a back-arc marginal basin tectonic setting. Meanwhile, the two Mesozoic granitic rocks and the Miocene andesite reflect the character of an active continental margin. Their spider diagram patterns show a significant enrichment on incompat- ible elements, usually derived from fluids of the subducted slab beneath the subduction zone. The high enrichment on Th makes their plots on Ta/Yb versus Th/Yb diagram are shifted to outside the active continental margin field. Although the volcanic-plutonic products represent different ages, their La/Ce ratio leads to a probability that they have been derived from the same magma sources. This study offers another different scenario for the geological setting of West Sumatra Permian Plutonic-Volcanic Belt, where the magmatic activities started in a back-arc marginal basin tectonic setting during the Permian-Triassic time and changed to an active continental margin during Triassic to Miocene. The data are collected through petrographic and chemical analyses for major, trace, and REE includ- ing literature studies.  

  19. Geochemical Signature of Mesozoic Volcanic and Granitic Rocks in Madina Regency Area, North Sumatra, Indonesia, and its Tectonic Implication

    Directory of Open Access Journals (Sweden)

    Iskandar Zulkarnain

    2014-06-01

    Full Text Available http://dx.doi.org/10.17014/ijog.vol4no2.20094Five samples consisting of two Permian-Triassic basalts, two Triassic-Jurassic granitic rocks, and a Miocene andesite were collected from the Madina Regency area in North Sumatra that is regionally situated on the West Sumatra Block. Previous authors have proposed three different scenarios for the geological setting of West Sumatra Permian Plutonic-Volcanic Belt, namely an island-arc, subduction related continental margin arc, and continental break-up. Petrographic analysis of the Mesozoic basaltic samples indicates that they are island-arcs in origin; however their trace element spider diagram patterns (Rock/MORB ratio also show the character of back-arc marginal basin, besides the island-arc. Furthermore, their REE spider diagram patterns (Rock/ Chondrite ratio clearly reveal that they were actually generated in a back-arc marginal basin tectonic setting. Meanwhile, the two Mesozoic granitic rocks and the Miocene andesite reflect the character of an active continental margin. Their spider diagram patterns show a significant enrichment on incompat- ible elements, usually derived from fluids of the subducted slab beneath the subduction zone. The high enrichment on Th makes their plots on Ta/Yb versus Th/Yb diagram are shifted to outside the active continental margin field. Although the volcanic-plutonic products represent different ages, their La/Ce ratio leads to a probability that they have been derived from the same magma sources. This study offers another different scenario for the geological setting of West Sumatra Permian Plutonic-Volcanic Belt, where the magmatic activities started in a back-arc marginal basin tectonic setting during the Permian-Triassic time and changed to an active continental margin during Triassic to Miocene. The data are collected through petrographic and chemical analyses for major, trace, and REE includ- ing literature studies.  

  20. Magmatic relationships and ages between adakites, magnesian andesites and Nb-enriched basalt-andesites from Hispaniola: Record of a major change in the Caribbean island arc magma sources

    Science.gov (United States)

    Escuder Viruete, J.; Contreras, F.; Stein, G.; Urien, P.; Joubert, M.; Pérez-Estaún, A.; Friedman, R.; Ullrich, T.

    2007-12-01

    Located in the Cordillera Central of the Dominican Republic, the Late Cretaceous Tireo Fm (TF) records a major change of the magma sources in the Caribbean island arc. It comprises a > 3 km thick sequence of arc-related volcanic and volcano-sedimentary rocks with variable geochemical characteristics. Combined detailed mapping, stratigraphy, geochemistry and U-Pb/Ar-Ar geochronology show that the volcanic rocks of the Tireo Fm include two main volcanic sequences. The lower volcanic sequence is dominated by monotonous submarine vitric-lithic tuffs and volcanic breccias of andesite to basaltic andesite, with minor interbedded flows of basalts and andesites. Fossil and (U-Pb and 40Ar- 39Ar) geochronological data show that arc magmatism in the lower sequence began to accumulate before ˜ 90 Ma, from the Aptian to Turonian. These rocks constitute an island arc tholeiitic suite, derived from melting by fluxing of a mantle wedge with subduction-related hydrous fluids. The upper volcanic sequence is characterized by a spatial and temporal association of adakites, high-Mg andesites, and Nb-enriched basalts, which collectivelly define a shift in the composition of the subduction-related erupted lavas. A dacitic to rhyolitic explosive volcanism with subaerial and episodic aerial eruptions, and sub-volcanic emplacements of domes, characterize mainly this stratigraphic interval. The onset of this volcanism took place at Turonian-Coniacian boundary and continued in the Santonian to Lower Campanian, with minor events in the Late Campanian. Adakites represent melts of the subducting slab, magnesian andesites the product of hybridization of adakite liquids with mantle peridotite, and Nb-enriched basalts melts of the residue from hybridization. We propose a model of oblique ridge subduction at ˜ 90 Ma and possibly subsequent slab window formation, as principal cause of magmatic variations recorded in the Caribbean island arc, above a southwestern-dipping subduction zone.

  1. Controllability of arc jet from arc horns with slits. Slit tsuki arc horn no arc jet seigyo tokusei

    Energy Technology Data Exchange (ETDEWEB)

    Sunabe, K.; Inaba, T.; Fukagawa, H. (Central Research Institute of Electric Power Industry, Tokyo (Japan)); Kito, Y. (Nagoya University, Nagoya (Japan))

    1993-09-20

    To improve the corona discharge characteristics, test preparation was made of hollow rod form horns with slits for the overhead power transmission line use. Two types of horn electrode were prepared. The first horn electrode is of a hollow hemisphere fitted with and divided by slits on its tip. The second horn electrode is the first one which is further fitted with rod form electrode at the center of its tip. In experiment, relation was obtained between the deflection angle of arc jet and arc current, electrode diameter, etc., through an observation of arc jet by high speed camera. Melting loss of electrode was also made clear. The following knowledge was obtained: For the first horn electrode, the deflection angle can be limited to a narrow range by a division with slits, e.g., within 30 degrees under the condition of 5kA in arc current, 4 in number of sectors and 200mm in diameter. For the second horn electrode, the deflection angle can be limited to within 20 degrees under the condition of 5kA in arc current and 4 in number of sectors. The arc current is also limited to below 5kA by an addition of 50mm diameter central electrode. As a conclusion for the first electrode, the arc jet control characteristics excels in the stronger arc current range than 5kA, while for the second electrode, they are effective in the weaker arc current range than 5kA. 6 refs., 19 figs., 1 tab.

  2. Convergent evolution of the arginine deiminase pathway: the ArcD and ArcE arginine/ornithine exchangers.

    Science.gov (United States)

    Noens, Elke E E; Lolkema, Juke S

    2017-02-01

    The arginine deiminase (ADI) pathway converts L-arginine into L-ornithine and yields 1 mol of ATP per mol of L-arginine consumed. The L-arginine/L-ornithine exchanger in the pathway takes up L-arginine and excretes L-ornithine from the cytoplasm. Analysis of the genomes of 1281 bacterial species revealed the presence of 124 arc gene clusters encoding the pathway. About half of the clusters contained the gene encoding the well-studied L-arginine/L-ornithine exchanger ArcD, while the other half contained a gene, termed here arcE, encoding a membrane protein that is not a homolog of ArcD. The arcE gene product of Streptococcus pneumoniae was shown to take up L-arginine and L-ornithine with affinities of 0.6 and 1 μmol/L, respectively, and to catalyze metabolic energy-independent, electroneutral exchange. ArcE of S. pneumoniae could replace ArcD in the ADI pathway of Lactococcus lactis and provided the cells with a growth advantage. In contrast to ArcD, ArcE catalyzed translocation of the pathway intermediate L-citrulline with high efficiency. A short version of the ADI pathway is proposed for L-citrulline catabolism and the presence of the evolutionary unrelated arcD and arcE genes in different organisms is discussed in the context of the evolution of the ADI pathway.

  3. Eruptive Productivity of the Ceboruco-San Pedro Volcanic Field, Nayarit, Mexico

    Science.gov (United States)

    Frey, H. M.; Lange, R. A.; Hall, C. M.; Delgado-Granados, H.

    2002-12-01

    High-precision 40Ar/39Ar geochronology coupled with GIS spatial analysis provides constraints on magma eruption rates over the past 1 Myr of the Ceboruco-San Pedro volcanic field (1870 km2), located in the Tepic-Zacoalco rift in western Mexico. The volcanic field is part of the Trans Mexican Volcanic arc and is dominated by the andesitic-dacitic stratocone of Volcan Ceboruco and includes peripheral fissure-fed flows, domes, and monogenetic cinder cones. The ages of these volcanic features were determined using 40Ar/39Ar laser step-heating techniques on groundmass or mineral separates, with 78% of the 52 analyses yielding plateau ages with a 2 sigma error < 50 kyrs. The volumes were determined using high resolution (1:50,000) digital elevation models, orthophotos, and GIS software, which allowed for the delineation of individual volcanic features, reconstruction of the pre-eruptive topography, and volume calculations by linear interpolation. The relative proportions of the 80 km3 erupted over the past 1 Myr are 14.5% basaltic andesite, 64.5% andesite, 20% dacite, and 1% rhyolite, demonstrating the dominance of intermediate magma types (in terms of silica content). Overall, there appears to be no systematic progression in the eruption of different magma types (e.g., basalt, andesite, dacite, etc.) with time. However, more than 75% of the total volume of lava within the Ceboruco-San Pedro volcanic field erupted in the last 100 kyrs. This reflects the youthfulness of Volcan Ceboruco, which was constructed during the last 50 kyrs and has a present day volume of 50 +/- 2.5 km3, accounting for 81% of the andesite and 50% of the dacite within the volcanic field. Eleven cinder cones, ranging from the Holocene to 0.37 Ma, display a narrow compositional range, with 52-58 wt% SiO2, 3-5.5 wt% MgO, and relatively high TiO2 concentrations (0.9-1.8 wt%). The total volume of the cinder cones is 0.83 km3. No lavas with < 51 wt% SiO2 have erupted in the past 1 Myr. Peripheral

  4. Arc spot grouping: An entanglement of arc spot cells

    Energy Technology Data Exchange (ETDEWEB)

    Kajita, Shin, E-mail: kajita.shin@nagoya-u.jp [EcoTopia Science Institute, Nagoya University, Nagoya 464-8603 (Japan); Hwangbo, Dogyun; Ohno, Noriyasu [Graduate School of Engineering, Nagoya University, Nagoya 464-8603 (Japan); Tsventoukh, Mikhail M. [Lebedev Physical Institute, Russian Academy of Sciences, Moscow 119991 (Russian Federation); Barengolts, Sergey A. [Prokhorov General Physics Institute, Russian Academy of Sciences, Moscow 119991 (Russian Federation)

    2014-12-21

    In recent experiments, clear transitions in velocity and trail width of an arc spot initiated on nanostructured tungsten were observed on the boundary of the thick and thin nanostructured layer regions. The velocity of arc spot was significantly decreased on the thick nanostructured region. It was suggested that the grouping decreased the velocity of arc spot. In this study, we try to explain the phenomena using a simple random walk model that has properties of directionality and self-avoidance. And grouping feature was added by installing an attractive force between spot cells with dealing with multi-spots. It was revealed that an entanglement of arc spot cells decreased the spot velocity, and spot cells tend to stamp at the same location many times.

  5. Lateral variation of H2O contents in Quaternary Magma of central Northeastern Japan arc

    Science.gov (United States)

    Miyagi, I.; Matsu'ura, T.; Itoh, J.; Morishita, Y.

    2011-12-01

    Water plays a key role in the genesis and eruptive mechanisms of subduction zone volcanoes. We estimated bulk rock water content of both frontal and back arc volcanoes from Northeastern Japan arc in order to understand the lateral variation of magmatic H2O contents in the island arc magma. Our analytical targets are the Adachi volcano located near the volcanic front and the Hijiori volcano located on back arc side. In this study, the bulk magmatic H2O content is estimated by a simple mass balance calculation of the chemistry of bulk rock and melt inclusions in phenocrysts; the melt H2O contents of melt inclusions analyzed by SIMS or EPMA are corrected according to the difference in K2O content between melt inclusions and bulk rock. The bulk magmatic H2O we obtained is 8 wt. % or even more for Adachi and is 2-3 wt. % for Hijiori. Thus, the frontal volcano has higher H2O than the back arc volcano. Although our data are opposed to the previous estimation on the lateral variation of H2O contents in Quaternary volcanoes of Northeastern Japan arc (e.g., Sakuyama, 1979), thermodynamic computations using MELTS (Ghiorso and Sack, 1995) suggest that the amount of bulk magmatic H2O we estimated is consistent with petrographical observations. Our data imply a regional characteristics in the type of eruption that the H2O rich frontal volcanoes will erupt explosively and those H2O poor back arc ones will be effusive, which implication is consistent with actual geological observations that volcanoes located on back arc side of the Northeastern Japan arc generally comprise lava flow (e.g., Iwaki, Kanpu, Chokai, Gassan), in contrast to the frontal ones that produced voluminous tephra (e.g., Osorezan, Towada, Narugo, Adachi). This research project has been conducted under the research contract with Nuclear and Industrial Safety Agency (NISA).

  6. The role of continental arc magmatism in driving long-term climate change

    Science.gov (United States)

    McKenzie, R.; Planavsky, N.; Penman, D. E.; Horton, B. K.; Loomis, S. E.; Stockli, D. F.; Lee, C. T.

    2015-12-01

    Earth's long-term climate states - icehouses and greenhouses - are largely governed by shifts in the concentration of atmospheric CO2. Silicate weathering and the burial of organic matter are primary sinks for CO2 and metamorphic and volcanic degassing are the primary sources. Continental magmatic arcs, in particular, have the ability produce large CO2 fluxes by liberating C preserved in continental bedrock. Assessment of a large compilation of detrital zircon U-Pb age data demonstrates systematic shifts in global zircon production that correspond with major shifts in icehouse-greenhouse climates: zircon generation is highest during greenhouses and lowest during icehouses. As zircon is predominantly produced in felsic melts in continental arc systems, these data demonstrate a first-order relationship between spatiotemporal variation in continental magmatism and major transitions in climate state. Since no clear consistent relationship can be discerned between long-term climate shifts and the paleogeographic location of continents or the global extent of uplift with regard to silicate weathering, it appears that the volcanic CO2 flux exerts a dominant control on shifts in baseline climate. The most prominent lulls in arc magmatism coincide with dramatic glaciations (e.g, Proterozoic Snowball Earth events), whereas extensive global volcanism and magmatic flare-ups correspond with intervals of documented environmental stress and mass extinctions, illustrating the fundamental influence of plate tectonic processes on Earth's surface environment and the evolution of the biosphere. In addition, the carbon cycle model LOSCAR is used to quantify the potential leverage of varying volcanic CO2 flux on equilibrium atmospheric CO2 under varying strengths and formulations of the silicate weathering feedback, which demonstrates the importance of the volcanic flux on baseline atmospheric CO2.

  7. Hybrid laser-arc welding

    DEFF Research Database (Denmark)

    the characteristics of the process, including the properties of joints produced by hybrid laser-arc welding and ways of assessing weld quality. Part II discusses applications of the process to such metals as magnesium alloys, aluminium and steel as well as the use of hybrid laser-arc welding in such sectors as ship...... building and the automotive industry. With its distinguished editor and international team of contributors, Hybrid laser-arc welding, will be a valuable source of reference for all those using this important welding technology. Professor Flemming Ove Olsen works in the Department of Manufacturing...

  8. The ancestral cascades arc: Cenozoic evolution of the central Sierra Nevada (California) and the birth of the new plate boundary

    Science.gov (United States)

    Busby, C.J.; Hagan, J.C.; Putirka, K.; Pluhar, C.J.; Gans, P.B.; Wagner, D.L.; Rood, D.; DeOreo, S.B.; Skilling, I.

    2008-01-01

    We integrate new stratigraphic, structural, geochemical, geochronological, and magnetostratigraphic data on Cenozoic volcanic rocks in the central Sierra Nevada to arrive at closely inter-related new models for: (1) the paleogeography of the ancestral Cascades arc, (2) the stratigraphic record of uplift events in the Sierra Nevada, (3) the tectonic controls on volcanic styles and compositions in the arc, and (4) the birth of a new plate margin. Previous workers have assumed that the ancestral Cascades arc consisted of stratovolcanoes, similar to the modern Cascades arc, but we suggest that the arc was composed largely of numerous, very small centers, where magmas frequently leaked up strands of the Sierran frontal fault zone. These small centers erupted to produce andesite lava domes that collapsed to produce block-and-ash flows, which were reworked into paleocanyons as volcanic debris flows and streamflow deposits. Where intrusions rose up through water-saturated paleocanyon fill, they formed peperite complexes that were commonly destabilized to form debris flows. Paleocanyons that were cut into Cretaceous bedrock and filled with Oligocene to late Miocene strata not only provide a stratigraphic record of the ancestral Cascades arc volcanism, but also deep unconformities within them record tectonic events. Preliminary correlation of newly mapped unconformities and new geochronological, magnetostratigraphic, and structural data allow us to propose three episodes of Cenozoic uplift that may correspond to (1) early Miocene onset of arc magmatism (ca. 15 Ma), (2) middle Miocene onset of Basin and Range faulting (ca. 10 Ma), and (3) late Miocene arrival of the triple junction (ca. 6 Ma), perhaps coinciding with a second episode of rapid extension on the range front. Oligocene ignimbrites, which erupted from calderas in central Nevada and filled Sierran paleocanyons, were deeply eroded during the early Miocene uplift event. The middle Miocene event is recorded by growth

  9. On arc efficiency in gas tungsten arc welding

    Directory of Open Access Journals (Sweden)

    Nils Stenbacka

    2013-12-01

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

  10. Hydrothermal exploration of the Mariana Back Arc Basin: Chemical Characterization

    Science.gov (United States)

    Resing, J. A.; Chadwick, B.; Baker, E. T.; Butterfield, D. A.; Baumberger, T.; Buck, N. J.; Walker, S. L.; Merle, S. G.; Michael, S.

    2016-12-01

    In November and December 2015, we visited the Southern Mariana back-arc on R/V Falkor (cruise FK151121) to explore for hydrothermal and volcanic activity. We conducted our study using the SENTRY AUV, a CTD rosette designed to do tows and vertical casts into the deep back-arc, and a trace metal CTD-package for the upper 1000m of the water column to examine transport form the nearby arc. We conducted 7 SENTRY dives, 12 tow-yos, 7 vertical casts, and 14 trace metal casts. We also mapped 24,050 km2 of the seafloor using the Falkor EM 302 multibeam. We discovered four new hydrothermal vent sites, and at one of them we found that some of the venting was coming from recently erupted lava flows. That lava flow is the deepest contemporary eruption yet discovered (at 4100-4450 m), and the first to be documented on a slow-spreading ridge. In addition, we were able to map the previously known Alice Springs hydrothermal site in unprecedented detail with AUV Sentry. The distribution of hydrothermal activity as well as chemistry of the plumes above them will be discussed. Plume chemistry data will include , Fe, Mn, CH4, H2, and 3He. The ship time for this project was provided by the Schmidt Ocean Institute with science funding provided by NOAA-Ocean Exploration.

  11. Geochemistry of Mesoproterozoic Volcanic Rocks in the Western Kunlun Mountains:Evidence for Plate Tectonic Evolution

    Institute of Scientific and Technical Information of China (English)

    ZHANG Chuanlin; DONG Yongguan; ZHAO Yu; WANG Aiguo; GUO Kunyi

    2003-01-01

    Mesoproterozoic volcanic rocks occurring in the north of the western Kunlun Mountains can be divided into two groups. The first group (north belt) is an reversely-evolved bimodal series. Petrochemistry shows that the alkalinity of the rocks decreases from early to late: alkaline→calc-alkaline→tholeiite, and geochemistry proves that the volcanic rocks were formed in rifting tectonic systems. The sedimentary facies shows characteristics of back-arc basins. The second (south belt) group, which occurs to the south of Yutian-Minfeng-Cele, is composed of calc-alkaline island arc (basaltic) andesite and minor rhyolite. The space distribution, age and geochemistry of the two volcanite groups indicate that they were formed in a back-arc basin (the first group) and an island arc (the second group) respectively and indicate the plate evolution during the Mesoproterozoic. The orogeny took place at ~1.05 Ga, which was coeval with the Grenville orogeny. This study has provided important geological data for exploring the position of the Paleo-Tarim plate in the Rodinia super-continent.

  12. Plateaus of confusion

    DEFF Research Database (Denmark)

    Kofoed, Jette

    of 'getting lost' at the limits of representation and her ideas about dwelling at the researcher's 'stuck place'. From this vantage point the paper presents a chosen stuck place in the research project Cyber@bullying : This stuck place can be described as a discrepancy between a theoretical informed...

  13. Plateaus of confusion

    DEFF Research Database (Denmark)

    Kofoed, Jette

    Cell phones and youth chat sites such as MySpace and Arto (the most used Danish youth chat) have become influential non-human actors in cyber bullying as it is practiced among children and teenagers. This paper combines Gilles Deleuze's concepts of rhizome and plateau with Patti Lathers concept...... of 'getting lost' at the limits of representation and her ideas about dwelling at the researcher's 'stuck place'. From this vantage point the paper presents a chosen stuck place in the research project Cyber@bullying : This stuck place can be described as a discrepancy between a theoretical informed...... when (human and non-human) actors in a claimed case of cyber bullying report their perspectives. A widely acknowledged theoretical expectation of asymmetrical power relations in bullying is challenged by such cases. How come that the female actors involved seem to enact incompatible and incomplete...

  14. STUDY ON THE PRESSURE IN PLASMA ARC

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

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

  15. The radiation of surface wave energy: Implications for volcanic tremor

    Science.gov (United States)

    Haney, M. M.; Denolle, M.; Lyons, J. J.; Nakahara, H.

    2015-12-01

    The seismic energy radiated by active volcanism is one common measurement of eruption size. For example, the magnitudes of individual earthquakes in volcano-tectonic (VT) swarms can be summed and expressed in terms of cumulative magnitude, energy, or moment release. However, discrepancies exist in current practice when treating the radiated energy of volcano seismicity dominated by surface waves. This has implications for volcanic tremor, since eruption tremor typically originates at shallow depth and is made up of surface waves. In the absence of a method to compute surface wave energy, estimates of eruption energy partitioning between acoustic and seismic waves typically assume seismic energy is composed of body waves. Furthermore, without the proper treatment of surface wave energy, it is unclear how much volcanic tremor contributes to the overall seismic energy budget during volcanic unrest. To address this issue, we derive, from first principles, the expression of surface wave radiated energy. In contrast with body waves, the surface wave energy equation is naturally expressed in the frequency domain instead of the time domain. We validate our result by reproducing an analytical solution for the radiated power of a vertical force source acting on a free surface. We further show that the surface wave energy equation leads to an explicit relationship between energy and the imaginary part of the surface wave Green's tensor at the source location, a fundamental property recognized within the field of seismic interferometry. With the new surface wave energy equation, we make clear connections to reduced displacement and propose an improved formula for the calculation of surface wave reduced displacement involving integration over the frequency band of tremor. As an alternative to reduced displacement, we show that reduced particle velocity squared is also a valid physical measure of tremor size, one based on seismic energy rate instead of seismic moment rate. These

  16. Late Cenozoic volcanism in the western Woodlark Basin area, SW Pacific: the sources of marine volcanic ash layers based on their elemental and Sr-Nd isotope compositions

    Science.gov (United States)

    Lackschewitz, K. S.; Mertz, D. F.; Devey, C. W.; Garbe-Schönberg, C.-D.

    2002-12-01

    Tephra fallout layers and volcaniclastic deposits, derived from volcanic sources around and on the Papuan Peninsula, form a substantial part of the Woodlark Basin marine sedimentary succession. Sampling by the Ocean Drilling Program Leg 180 in the western Woodlark Basin provides the opportunity to document the distribution of the volcanically-derived components as well as to evaluate their chronology, chemistry, and isotope compositions in order to gain information on the volcanic sources and original magmatic systems. Glass shards selected from 57 volcanogenic layers within the sampled Pliocene-Pleistocene sedimentary sequence show predominantly rhyolitic compositions, with subordinate basaltic andesites, basaltic trachy-andesites, andesites, trachy-andesites, dacites, and phonolites. It was possible to correlate only a few of the volcanogenic layers between sites using geochemical and age information apparently because of the formation of strongly compartmentalised sedimentary realms on this actively rifting margin. In many cases it was possible to correlate Leg 180 volcanic components with their eruption source areas based on chemical and isotope compositions. Likely sources for a considerable number of the volcanogenic deposits are Moresby and Dawson Strait volcanoes (D'Entrecasteaux Islands region) for high-K calc-alkaline glasses. The Dawson Strait volcanoes appear to represent the source for five peralkaline tephra layers. One basaltic andesitic volcaniclastic layer shows affinities to basaltic andesites from the Woodlark spreading tip and Cheshire Seamount. For other layers, a clear identification of the sources proved impossible, although their isotope and chemical signatures suggest similarities to south-west Pacific subduction volcanism, e.g. New Britain and Tonga-Kermadec island arcs. Volcanic islands in the Trobriand Arc (for example, Woodlark Island Amphlett Islands and/or Egum Atoll) are probable sources for several volcaniclastic layers with ages

  17. Arc of opportunity.

    Science.gov (United States)

    Delaney, Adam Vai

    2011-07-01

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

  18. Distinctly different parental magmas for plutons and lavas in the central Aleutian arc

    Science.gov (United States)

    Cai, Y.; Rioux, M. E.; Kelemen, P. B.; Goldstein, S. L.; Bolge, L.; Kylander-Clark, A. R.

    2014-12-01

    While it is generally agreed that continental crust is generated by arc magmatism, average arc lavas are basaltic while the bulk continental crust is andesitic, and this has led to many models for secondary reprocessing of the arc crust in order to form continental crust. We report new data on calc-alkaline plutons in the central Aleutians showing that they have distinctly different sources compared to Holocene tholeiitic lavas. Therefore the lavas are not representative of the net magmatic transfer from the mantle into the arc crust. Eocene to Miocene (9-39 Ma) intermediate to felsic plutonic rocks from the central Aleutian arc show higher SiO2 at a given Mg#, higher ɛNd- and ɛHf-values, and lower Pb isotope ratios than Holocene volcanic rocks from the same region. Instead, the plutonic rocks resemble volcanics from the western Aleutians isotopically, and have chemical compositions similar to bulk continental crust. These data could reflect temporal variation of Aleutian magma source compositions, from Eocene-Miocene "isotopically depleted" and predominantly calc-alkaline to Holocene "isotopically enriched" and predominantly tholeiitic. Alternatively, they may reflect different transport and emplacement processes for the magmas that form plutons and lavas: calc-alkaline magmas with higher Si content and high viscosity may preferentially form plutons, perhaps after extensive mid-crustal degassing of initially high water contents. The latter case implies that the upper and middle arc crust is more like the calc-alkaline bulk composition of the continental crust than the lavas alone. Crustal reprocessing mechanisms that preserve upper and middle arc crust, while removing lower arc crust, can account for the genesis and evolution of continental crust. Since gabbroic lower arc crust extends from ca 20-40 km depth, and is density stable over most of this depth range, "delamination" of dense lithologies [1] may not be sufficient to accomplish this. Alternatively

  19. Assimilation of sediments embedded in the oceanic arc crust: myth or reality?

    Science.gov (United States)

    Bezard, Rachel; Davidson, Jon P.; Turner, Simon; Macpherson, Colin G.; Lindsay, Jan M.; Boyce, Adrian J.

    2014-06-01

    Arc magmas are commonly assumed to form by melting of sub-arc mantle that has been variably enriched by a component from the subducted slab. Although most magmas that reach the surface are not primitive, the impact of assimilation of the arc crust is often ignored with the consequence that trace element and isotopic compositions are commonly attributed only to varying contributions from different components present in the mantle. This jeopardises the integrity of mass balance recycling calculations. Here we use Sr and O isotope data in minerals from a suite of volcanic rocks from St Lucia, Lesser Antilles arc, to show that assimilation of oceanic arc basement can be significant. Analysis of 87Sr/86Sr in single plagioclase phenocrysts from four Soufrière Volcanic Complex (SVC; St Lucia) hand samples with similar composition (87Sr/86Sr = 0.7089-0.7091) reveals crystal isotopic heterogeneity among hand samples ranging from 0.7083 to 0.7094 with up to 0.0008 difference within a single hand sample. δO18 measurements in the SVC crystals show extreme variation beyond the mantle range with +7.5 to +11.1‰ for plagioclase (n=19), +10.6 to +11.8‰ for quartz (n=10), +9.4 to +9.8‰ for amphibole (n=2) and +9 to +9.5‰ for pyroxene (n=3) while older lavas (Pre-Soufriere Volcanic Complex), with less radiogenic whole rock Sr composition (87Sr/86Sr = 0.7041-0.7062) display values closer to mantle range: +6.4 to +7.9‰ for plagioclase (n=4) and +6 to +6.8‰ for pyroxene (n=5). We argue that the 87Sr/86Sr isotope disequilibrium and extreme δO18 values provide compelling evidence for assimilation of material located within the arc crust. Positive correlations between mineral δO18 and whole rock 87Sr/86Sr, 143Nd/144Nd and 206,207,208Pb/204Pb shows that assimilation seems to be responsible not only for the isotopic heterogeneity observed in St Lucia but also in the whole Lesser Antilles since St Lucia encompasses almost the whole-arc range of isotopic compositions. This

  20. Plate flexure and volcanism: Late Cenozoic tectonics of the Tabar-Lihir-Tanga-Feni alkalic province, New Ireland Basin, Papua New Guinea

    Science.gov (United States)

    Lindley, I. D.

    2016-05-01

    Late Cenozoic Tabar-Lihir-Tanga-Feni (TLTF) alkaline volcanism, New Ireland Basin, PNG, is associated with extensional cracks along the crests of flexed ridges developed on the New Ireland Microplate (New name). The tectonic alignment of the TLTF volcanic arc is essentially perpendicular to the flexed ridges, suggesting that fractures parallel to the direction of maximum horizontal compression facilitated the rapid ascent of alkaline magmas from the mantle region, perhaps 60-70 km depth. The mainly Pliocene to Pleistocene volcanoes were localized at the intersection of ridge-parallel Kabang structures and arc-parallel Niffin structures, suggesting that the Kabang-Niffin structural intersections underlying each of the TLTF island groups provided a well developed, clustered network of open conduits which tapped the mantle source region. Periodic post-Miocene locking and unlocking along the strike-slip Kilinailau Fault (New name) are thought to have functioned as a valve, turning on (Pliocene) and then turning off (Pleistocene) volcanic activity, respectively. Partial locking of the Kilinailau Fault during the Pliocene resulted in the accumulation of intraplate stresses within the New Ireland Microplate, and caused plate flexure and ridge development, plate-cracking along ridge crests and the development of arc-parallel regional fractures parallel to the direction of maximum compression. Unlocking of the Kilinailau Fault in the Pleistocene resulted in the release of intraplate stresses in the New Ireland Microplate and a cessation of volcanic activity across most of the TLTF arc. The style and scale of plate flexure and cracking, accompanied by within-plate alkaline volcanism from equally spaced ridge-top eruptive centers confined to a narrow, linear volcanic arc are unknown from any other tectonic province.

  1. Atmospheric chemistry in volcanic plumes.

    Science.gov (United States)

    von Glasow, Roland

    2010-04-13

    Recent field observations have shown that the atmospheric plumes of quiescently degassing volcanoes are chemically very active, pointing to the role of chemical cycles involving halogen species and heterogeneous reactions on aerosol particles that have previously been unexplored for this type of volcanic plumes. Key features of these measurements can be reproduced by numerical models such as the one employed in this study. The model shows sustained high levels of reactive bromine in the plume, leading to extensive ozone destruction, that, depending on plume dispersal, can be maintained for several days. The very high concentrations of sulfur dioxide in the volcanic plume reduces the lifetime of the OH radical drastically, so that it is virtually absent in the volcanic plume. This would imply an increased lifetime of methane in volcanic plumes, unless reactive chlorine chemistry in the plume is strong enough to offset the lack of OH chemistry. A further effect of bromine chemistry in addition to ozone destruction shown by the model studies presented here, is the oxidation of mercury. This relates to mercury that has been coemitted with bromine from the volcano but also to background atmospheric mercury. The rapid oxidation of mercury implies a drastically reduced atmospheric lifetime of mercury so that the contribution of volcanic mercury to the atmospheric background might be less than previously thought. However, the implications, especially health and environmental effects due to deposition, might be substantial and warrant further studies, especially field measurements to test this hypothesis.

  2. Climatic impact of volcanic eruptions

    Science.gov (United States)

    Rampino, Michael R.

    1991-01-01

    Studies have attempted to 'isolate' the volcanic signal in noisy temperature data. This assumes that it is possible to isolate a distinct volcanic signal in a record that may have a combination of forcings (ENSO, solar variability, random fluctuations, volcanism) that all interact. The key to discovering the greatest effects of volcanoes on short-term climate may be to concentrate on temperatures in regions where the effects of aerosol clouds may be amplified by perturbed atmospheric circulation patterns. This is especially true in subpolar and midlatitude areas affected by changes in the position of the polar front. Such climatic perturbation can be detected in proxy evidence such as decrease in tree-ring widths and frost rings, changes in the treeline, weather anomalies, severity of sea-ice in polar and subpolar regions, and poor grain yields and crop failures. In low latitudes, sudden temperature drops were correlated with the passage overhead of the volcanic dust cloud (Stothers, 1984). For some eruptions, such as Tambora, 1815, these kinds of proxy and anectdotal information were summarized in great detail in a number of papers and books (e.g., Post, 1978; Stothers, 1984; Stommel and Stommel, 1986; C. R. Harrington, in press). These studies lead to the general conclusion that regional effects on climate, sometimes quite severe, may be the major impact of large historical volcanic aerosol clouds.

  3. Post-Eocene volcanics of the Abazar district, Qazvin, Iran: Mineralogical and geochemical evidence for a complex magmatic evolution

    Science.gov (United States)

    Asiabanha, A.; Bardintzeff, J. M.; Kananian, A.; Rahimi, G.

    2012-02-01

    The style of volcanism of post-Eocene volcanism in the Alborz zone of northern Iran is different to that of Eocene volcanism (Karaj Formation). Indeed, the volcanic succession of the Abazar district, located in a narrow volcanic strip within the Alborz magmatic assemblage, is characterized by distinct mineralogical and chemical compositions linked to a complex magmatic evolution. The succession was produced by explosive eruptions followed by effusive eruptions. Two main volcanic events are recognized: (1) a thin rhyolitic ignimbritic sheet underlain by a thicker lithic breccia, and (2) lava flows including shoshonite, latite, and andesite that overlie the first event across a reddish soil horizon. Plagioclase in shoshonite (An 48-92) shows normal zoning, whereas plagioclase in latite and andesite (An 48-75) has a similar composition but shows reverse and oscillatory zoning. QUILF temperature calculations for shoshonites and andesites yield temperatures of 1035 °C and 1029 °C, respectively. The geothermometers proposed by Ridolfi et al. (2010) and Holland and Blundy (1994) yield temperatures of 960 °C and 944 °C for latitic lava, respectively. The samples of volcanic rock show a typical geochemical signature of the continental arc regime, but the andesites clearly differ from the shoshonites, the latites and the rhyolites. The mineralogical and chemical characteristics of these rocks are explained by the following petrogenesis: (1) intrusion of a hot, mantle-depth mafic (shoshonitic) magma, which differentiated in the magma chamber to produce a latitic and then a rhyolitic liquid; (2) rhyolitic ignimbritic eruptions from the top of the magma chamber, following by shoshonitic and then latitic extrusions; (3) magma mingling between the latitic and andesitic magmas, as indicated by the occurrence of andesite clasts within the latite; and (4) andesitic effusions. The youngest volcanic events in the Alborz zone show a close chemical relationship with continental arc

  4. Xenolitos ultramáficos en el cerro De la Laguna, volcanismo basáltico de retroarco en el sureste de la provincia de Mendoza, Argentina Ultramafic xenoliths in De la Laguna hill, retro-arc basaltic volcanism in the southeast of Mendoza Province, Argentina

    Directory of Open Access Journals (Sweden)

    G. W. Bertotto

    2002-12-01

    Full Text Available Se describen por primera vez xenolitos ultramáficos incluidos en basaltos de retroarco cenozoicos, en el sector extraandino de la provincia de Mendoza. El basalto portador tiene estructura masiva y textura porfírica con asociaciones de fenocristales de olivino-clinopiroxeno y olivino-plagioclasa. Todos los xenolitos ultramáficos son peridotitas en facies de espinela, se reconocieron lherzolitas, wehrlitas y dunitas, en orden de abundancia. Presentan una asociación mineral compuesta por olivino, ortopiroxeno, clinopiroxeno y espinela. Las texturas identificadas son porfiroclástica de Tipo I y porfiroclástica a equigranular de Tipo I. Estos xenolitos tienen zonas de reacción microscópicas mayormente desarrolladas en los ortopiroxenos y clinopiroxenos en el contacto con el basalto. La presencia de reacción indica al menos un evento de desequilibrio. Estas peridotitas representan fragmentos del manto superior situado debajo de la zona estudiada.Ultramafic xenoliths in Cenozoic retro-arc basalts of the extra-Andean sector of Mendoza province are described here for the first time. The host basalt has a massive structure and porphyritic texture with phenocryst assemblages of olivine-clinopyroxene and olivine-plagioclase. All the ultramafic xenoliths are spinel-bearing peridotites; lherzolite, wehrlite and dunite, in order of abundance, have been recognized. The mineral assemblage is olivine-orthopyroxene-clinopyroxene-spinel. Textures are porphyroclastic Type I and porphyroclastic to equigranular Type I. The xenoliths contain microscopic reaction areas, mainly developed in orthopyroxene and clinopyroxene in the contact with basalt. The reaction indicates at least one disequilibrium event. The peridotites are fragments of the upper mantle situated beneath the study area.

  5. The development of topographic plateaus in an India-Asia-like collision zone using 3D numerical simulations

    Science.gov (United States)

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

    2014-05-01

    . We also address the question of how large topographic plateaus, such as the Tibetan Plateau, can form in an integrated lithospheric and upper-mantle scale model. Acknowledgements: Funding was provided by the European Research Council under the European Community's Seventh Framework Program (FP7/2007-2013) / ERC Grant agreement #258830. Numerical computations have been performed on MOGON (ZDV Mainz computing center) and JUQUEEN (Jülich high-performance computing center).

  6. Geopulsation, Volcanism and Astronomical Periods

    Institute of Scientific and Technical Information of China (English)

    Yang Xuexiang; Chen Dianyou; Yang Xiaoying; Yang Shuchen

    2000-01-01

    Volcanism is mainly controlled by the intermittent release of energy in the earth. As far as the differential rotation of the earth's inner core is concerned, the Galactic Year may change the gravitational constant G, the solar radiative quantity and the moving speed of the solar system and affect the exchange of angular momentum between core and mantle as well as the energy exchange between crust and mantle. As a result, this leads to eruptions of superplumes and magma, and controls the energy flow from core - mantle boundary (CMB) to crust. When the earth' s speed decreases, it will release a huge amount of energy. They are the reason of the correspondence of the volcanic cycles one by one with the astronomical periods one by one. According to the astronomical periods, volcanic eruptions may possibly be predicted in the future.

  7. Volcanic eruptions and solar activity

    Science.gov (United States)

    Stothers, Richard B.

    1989-01-01

    The historical record of large volcanic eruptions from 1500 to 1980 is subjected to detailed time series analysis. In two weak but probably statistically significant periodicities of about 11 and 80 yr, the frequency of volcanic eruptions increases (decreases) slightly around the times of solar minimum (maximum). Time series analysis of the volcanogenic acidities in a deep ice core from Greenland reveals several very long periods ranging from about 80 to about 350 yr which are similar to the very slow solar cycles previously detected in auroral and C-14 records. Solar flares may cause changes in atmospheric circulation patterns that abruptly alter the earth's spin. The resulting jolt probably triggers small earthquakes which affect volcanism.

  8. Geochemical study for volcanic surveillance

    Energy Technology Data Exchange (ETDEWEB)

    Panichi, C.; La Ruffa, G. [Consiglio Nazionale delle Ricerche, International Institute for Geothermal Research Ghezzano, PI (Italy)

    2000-07-01

    For years, geologists have been striving to reconstruct volcanic eruptions from the analysis of pyroclastic deposits and lava flows on the surface of the earth and in the oceans. This effort has produced valuable information on volcanic petrology and magma generation, separation, mixing, crystallisation, and interaction with water in phreatomagmatic and submarine eruptions. The volcanological process are tied to the dynamics of the earth's crust and lithosphere. The mantle, subducted oceanic crust, and continental crust contain different rock types and are sources of different magmas. Magmas consist primarily of completely or partially molten silicates containing volatile materials either dissolved in the melt or as bubbles of gas. The silicate and volatile portions affect the physical properties of magma and, therefore, the nature of a volcanic eruption.

  9. Models of volcanic eruption hazards

    Energy Technology Data Exchange (ETDEWEB)

    Wohletz, K.H.

    1992-01-01

    Volcanic eruptions pose an ever present but poorly constrained hazard to life and property for geothermal installations in volcanic areas. Because eruptions occur sporadically and may limit field access, quantitative and systematic field studies of eruptions are difficult to complete. Circumventing this difficulty, laboratory models and numerical simulations are pivotal in building our understanding of eruptions. For example, the results of fuel-coolant interaction experiments show that magma-water interaction controls many eruption styles. Applying these results, increasing numbers of field studies now document and interpret the role of external water eruptions. Similarly, numerical simulations solve the fundamental physics of high-speed fluid flow and give quantitative predictions that elucidate the complexities of pyroclastic flows and surges. A primary goal of these models is to guide geologists in searching for critical field relationships and making their interpretations. Coupled with field work, modeling is beginning to allow more quantitative and predictive volcanic hazard assessments.

  10. Volcano-sedimentary processes operating on a marginal continental arc: the Archean Raquette Lake Formation, Slave Province, Canada

    Science.gov (United States)

    Mueller, W. U.; Corcoran, P. L.

    2001-06-01

    The 200-m thick, volcano-sedimentary Raquette Lake Formation, located in the south-central Archean Slave Province, represents a remnant arc segment floored by continental crust. The formation overlies the gneissic Sleepy Dragon Complex unconformably, is laterally interstratified with subaqueous mafic basalts of the Cameron River volcanic belt, and is considered the proximal equivalent of the turbidite-dominated Burwash Formation. A continuum of events associated with volcanism and sedimentation, and controlled by extensional tectonics, is advocated. A complex stratigraphy with three volcanic and three sedimentary lithofacies constitute the volcano-sedimentary succession. The volcanic lithofacies include: (1) a mafic volcanic lithofacies composed of subaqueous pillow-pillow breccia, and subaerial massive to blocky flows, (2) a felsic volcanic lithofacies representing felsic flows that were deposited in a subaerial environment, and (3) a felsic volcanic sandstone lithofacies interpreted as shallow-water, wave- and storm-reworked pyroclastic debris derived from explosive eruptions. The sedimentary lithofacies are represented by: (1) a conglomerate-sandstone lithofacies consistent with unconfined debris flow, hyperconcentrated flood flow and talus scree deposits, as well as minor high-energy stream flow conglomerates that formed coalescing, steep-sloped, coarse-clastic fan deltas, (2) a sandstone lithofacies, interpreted as hyperconcentrated flood flow deposits that accumulated at the subaerial-subaqueous interface, and (3) a mudstone lithofacies consistent with suspension sedimentation in a small restricted lagoon-type setting. The Raquette Lake Formation is interpreted as a fringing continental arc that displays both high-energy clastic sedimentation and contemporaneous effusive and explosive mafic and felsic volcanism. Modern analogues that develop along active plate margins in which continental crust plays a significant role include Japan and the Baja California

  11. Geochemical Variation of Subducting Pacific Crust Along the Izu-Bonin Arc System and its Implications on the Generation of Arc Magmas

    Science.gov (United States)

    Durkin, K.; Castillo, P.; Abe, N.; Kaneko, R.; Straub, S. M.; Garcia, E. S. M.; Yan, Q.; Tamura, Y.

    2015-12-01

    Subduction zone magmatism primarily occurs due to flux melting of the mantle wedge that has been metasomatized by the slab component. The latter is enriched in volatiles and fluid-mobile elements and derived mainly from subducted sediments and altered oceanic crust (AOC). Subduction input has been linked to arc output in many studies, but this relationship is especially well documented in sedimented arc-trench systems. However, the Izu-Bonin system is sediment-poor, therefore the compositional and latitudinal variations (especially in Pb isotopes) of its arc magmas must be sourced from the subduction component originating primarily from the AOC. Pb is a very good tracer of recycled AOC that may contribute 50% or more of arc magma Pb. Izu-Bonin arc chemistry suggests a subduction influx of Indian-type crust, but the subducting crust sampled at ODP Site 1149 is Pacific-type. The discrepancy between subduction input and arc output calls into question the importance of the AOC as a source of the subduction component, and raises major concerns with our understanding of slab input. During the R/V Revelle 1412 cruise in late 2014, we successfully dredged vertical fault scarps at several sites from 27.5 N to 34.5 N, spanning a range of crustal ages that include a suggested compositional change at ~125 Ma. Major element data show an alkali enrichment towards the north of the study transect. Preliminary incompatible trace element data (e.g. Ba, Zr and Sr) data support this enrichment trend. Detailed mass balance calculations supported by Sr, Nd, Hf and especially Pb isotope analyses will be performed to evaluate whether the AOC controls the Pb isotope chemistry of the Izu-Bonin volcanic arc.

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

    Science.gov (United States)

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

    2014-12-01

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

  13. Petrogenesis and tectonic implication of the Late Triassic post-collisional volcanic rocks in Chiang Khong, NW Thailand

    Science.gov (United States)

    Qian, Xin; Wang, Yuejun; Feng, Qinglai; Zi, Jian-Wei; Zhang, Yuzhi; Chonglakmani, Chongpan

    2016-04-01

    The volcanic rocks exposed within the Chiang Khong-Lampang-Tak igneous zone in NW Thailand provide important constraints on the tectonic evolution of the eastern Paleotethys ocean. An andesite sample from the Chiang Khong area yields a zircon U-Pb age of 229 ± 4 Ma, significantly younger than the continental-arc and syn-collisional volcanic rocks (ca. 238-241 Ma). The Chiang Khong volcanic rocks are characterized by low MgO (1.71-6.72 wt.%) and high Al2O3 (15.03-17.76 wt.%). They are enriched in LILEs and LREEs and depleted in HFSEs, and have 87Sr/86Sr (i) ratios of 0.7050-0.7065, εNd (t) of - 0.32 to - 1.92, zircon εHf (t) and δ18O values of 3.5 to - 11.7 and 4.30-9.80 ‰, respectively. The geochemical data for the volcanic rocks are consistent with an origin from the enriched lithospheric mantle that had been modified by slab-derived fluid and recycled sediments. Based on available geochronological and geochemical evidences, we propose that the Late Triassic Chiang Khong volcanic rocks are equivalent to the contemporaneous volcanic rocks in the Lancangjiang igneous zone in SW China. The formation of these volcanic rocks was possibly related to the upwelling of the asthenospheric mantle during the Late Triassic, shortly after slab detachment, which induced the melting of the metasomatized mantle wedge.

  14. New Pliocene-Pleistocene 40Ar/ 39Ar ages fill in temporal gaps in the Nicaraguan volcanic record

    Science.gov (United States)

    Saginor, Ian; Gazel, Esteban; Carr, Michael J.; Swisher, Carl C., III; Turrin, Brent

    2011-04-01

    The volcanic record of western Nicaragua documents a significant lull in volcanic activity that has persisted from the late Miocene (~ 7 Ma) to the formation of the modern volcanic front around 350 ka. This study fills this gap for the first time with samples collected in Northwest Nicaragua between Cosigüina and San Cristóbal volcanoes and with samples collected from the Nicaraguan Depression. We found two previously unknown volcanic units ranging from 3.6 to 1.3 Ma and the improved volcanic record allows us to reconstruct the geochemical evolution of the Nicaraguan arc. U/Th values increased by nearly threefold since the Miocene following the "carbonate crash" at 10 Ma, when dominantly carbonate sediment deposition shifted toward hemipelagic sediment deposition. This transition was thought to be abrupt, however our new data show that it took place gradually over the last 7 Ma. Northwest Nicaragua is a particularly interesting case study because it contains Middle Miocene volcanism on either side of the Nicaraguan Depression, the Coyol Formation (25-7 Ma) to the East and the Tamarindo Formation (14.7-11.7 Ma) to the West. The presence of Mid Miocene volcanism on either side of the Nicaraguan Depression has led to the hypothesis that the two coeval units, currently separated by ~ 100 km, were once connected and have since been separated by extension. Here, we present data suggesting that the Tamarindo and Coyol are geochemically distinct and therefore cannot be considered part of the same unit.

  15. Recurrence models of volcanic events: Applications to volcanic risk assessment

    Energy Technology Data Exchange (ETDEWEB)

    Crowe, B.M. [Los Alamos National Lab., Las Vegas, NV (United States); Picard, R.; Valentine, G. [Los Alamos National Lab., NM (United States); Perry, F.V. [New Mexico Univ., Albuquerque, NM (United States)

    1992-03-01

    An assessment of the risk of future volcanism has been conducted for isolation of high-level radioactive waste at the potential Yucca Mountain site in southern Nevada. Risk used in this context refers to a combined assessment of the probability and consequences of future volcanic activity. Past studies established bounds on the probability of magmatic disruption of a repository. These bounds were revised as additional data were gathered from site characterization studies. The probability of direct intersection of a potential repository located in an eight km{sup 2} area of Yucca Mountain by ascending basalt magma was bounded by the range of 10{sup {minus}8} to 10{sup {minus}10} yr{sup {minus}1 2}. The consequences of magmatic disruption of a repository were estimated in previous studies to be limited. The exact releases from such an event are dependent on the strike of an intruding basalt dike relative to the repository geometry, the timing of the basaltic event relative to the age of the radioactive waste and the mechanisms of release and dispersal of the waste radionuclides in the accessible environment. The combined low probability of repository disruption and the limited releases associated with this event established the basis for the judgement that the risk of future volcanism was relatively low. It was reasoned that that risk of future volcanism was not likely to result in disqualification of the potential Yucca Mountain site.

  16. Short-lived tectonic switch mechanism for long-term pulses of volcanic activity after mega-thrust earthquakes

    Directory of Open Access Journals (Sweden)

    M. Lupi

    2013-06-01

    Full Text Available Eruptive rates in volcanic arcs increase significantly after mega-thrust earthquakes in subduction zones. Over short to intermediate time periods the link between mega-thrust earthquakes and arc response can be attributed to dynamic triggering processes or static stress changes, but a fundamental mechanism that controls long-term pulses of volcanic activity after mega-thrust earthquakes has not been proposed yet. Using geomechanical, geological, and geophysical arguments, we propose that increased eruption rates over longer timescales are due to the relaxation of the compressional regime that accompanies mega-thrust subduction zone earthquakes. More specifically, the reduction of the horizontal stress σh promotes the occurrence of short-lived strike-slip kinematics rather than reverse faulting in the volcanic arc. The relaxation of the pre-earthquake compressional regime facilitates magma mobilization by providing a short-circuit pathway to shallow depths by significantly increasing the hydraulic properties of the system. The timescale for the onset of strike-slip faulting depends on the degree of shear stress accumulated in the arc during inter-seismic periods, which in turn is connected to the degree of strain-partitioning at convergent margins. We performed Coulomb stress transfer analysis to determine the order of magnitude of the stress perturbations in present-day volcanic arcs in response to five actual mega-thrust earthquakes; the 2005 M8.6, 2007 M8.5, and 2007 M7.9 Sumatra earthquakes; the 2010 M8.8 Maule, Chile earthquake; and the 2011 M9.0 Tohoku, Japan earthquake. We find that all, but one, the shallow earthquakes that occurred in the arcs of Sumatra, Chile and Japan show a marked lateral component. Our hypothesis suggests that the long-term response of volcanic arcs to subduction zone mega-thrust earthquakes will be manifested as predominantly strike-slip seismic events, and that these future earthquakes will be followed closely by

  17. Crustal structure of the Kermadec arc from MANGO seismic refraction profiles

    Science.gov (United States)

    Bassett, Dan; Kopp, Heidrun; Sutherland, Rupert; Henrys, Stuart; Watts, Anthony B.; Timm, Christian; Scherwath, Martin; Grevemeyer, Ingo; de Ronde, Cornel E. J.

    2016-10-01

    Three active-source seismic refraction profiles are integrated with morphological and potential field data to place the first regional constraints on the structure of the Kermadec subduction zone. These observations are used to test contrasting tectonic models for an along-strike transition in margin structure previously known as the 32°S boundary. We use residual bathymetry to constrain the geometry of this boundary and propose the name Central Kermadec Discontinuity (CKD). North of the CKD, the buried Tonga Ridge occupies the fore-arc with VP 6.5-7.3 km s-1 and residual free-air gravity anomalies constrain its latitudinal extent (north of 30.5°S), width (110 ± 20 km), and strike ( 005° south of 25°S). South of the CKD the fore-arc is structurally homogeneous downdip with VP 5.7-7.3 km s-1. In the Havre Trough back-arc, crustal thickness south of the CKD is 8-9 km, which is up to 4 km thinner than the northern Havre Trough and at least 1 km thinner than the southern Havre Trough. We suggest that the Eocene arc did not extend along the current length of the Tonga-Kermadec trench. The Eocene arc was originally connected to the Three Kings Ridge, and the CKD was likely formed during separation and easterly translation of an Eocene arc substrate during the early Oligocene. We suggest that the first-order crustal thickness variations along the Kermadec arc were inherited from before the Neogene and reflect Mesozoic crustal structure, the Cenozoic evolution of the Tonga-Kermadec-Hikurangi margin and along-strike variations in the duration of arc volcanism.

  18. 3-D electrical resistivity structure based on geomagnetic transfer functions exploring the features of arc magmatism beneath Kyushu, Southwest Japan Arc

    Science.gov (United States)

    Hata, Maki; Uyeshima, Makoto; Handa, Shun; Shimoizumi, Masashi; Tanaka, Yoshikazu; Hashimoto, Takeshi; Kagiyama, Tsuneomi; Utada, Hisashi; Munekane, Hiroshi; Ichiki, Masahiro; Fuji-ta, Kiyoshi

    2017-01-01

    Our 3-D electrical resistivity model clearly detects particular subsurface features for magmatism associated with subduction of the Philippine Sea Plate (PSP) in three regions: a southern and a northern volcanic region, and a nonvolcanic region on the island of Kyushu. We apply 3-D inversion analyses for geomagnetic transfer function data of a short-period band, in combination with results of a previous 3-D model that was determined by using Network-Magnetotelluric response function data of a longer-period band as an initial model in the present inversion to improve resolution at shallow depths; specifically, a two-stage inversion is used instead of a joint inversion. In contrast to the previous model, the presented model clearly reveals a conductive block on the back-arc side of Kirishima volcano at shallow depths of 50 km; the block is associated with hydrothermal fluids and hydrothermal alteration zones related to the formation of epithermal gold deposits. A second feature revealed by the model is another conductive block regarded as upwelling fluids, extending from the upper surface of the PSP in the mantle under Kirishima volcano in the southern volcanic region. Third, a resistive crustal layer, which confines the conductive block in the mantle, is distributed beneath the nonvolcanic region. Fourth, our model reveals a significant resistive block, which extends below the continental Moho at the fore-arc side of the volcanic front and extends into the nonvolcanic region in central Kyushu.

  19. Controls on volcanism at intraplate basaltic volcanic fields

    Science.gov (United States)

    van den Hove, Jackson C.; Van Otterloo, Jozua; Betts, Peter G.; Ailleres, Laurent; Cas, Ray A. F.

    2017-02-01

    A broad range of controlling mechanisms is described for intraplate basaltic volcanic fields (IBVFs) in the literature. These correspond with those relating to shallow tectonic processes and to deep mantle plumes. Accurate measurement of the physical parameters of intraplate volcanism is fundamental to gain an understanding of the controlling factors that influence the scale and location of a specific IBVF. Detailed volume and geochronology data are required for this; however, these are not available for many IBVFs. In this study the primary controls on magma genesis and transportation are established for the Pliocene-Recent Newer Volcanics Province (NVP) of south-eastern Australia as a case-study for one of such IBVF. The NVP is a large and spatio-temporally complex IBVF that has been described as either being related to a deep mantle plume, or upper mantle and crustal processes. We use innovative high resolution aeromagnetic and 3D modelling analysis, constrained by well-log data, to calculate its dimensions, volume and long-term eruptive flux. Our estimates suggest volcanic deposits cover an area of 23,100 ± 530 km2 and have a preserved dense rock equivalent of erupted volcanics of least 680 km3, and may have been as large as 900 km3. The long-term mean eruptive flux of the NVP is estimated between 0.15 and 0.20 km3/ka, which is relatively high compared with other IBVFs. Our comparison with other IBVFs shows eruptive fluxes vary up to two orders of magnitude within individual fields. Most examples where a range of eruptive flux is available for an IBVF show a correlation between eruptive flux and the rate of local tectonic processes, suggesting tectonic control. Limited age dating of the NVP has been used to suggest there were pulses in its eruptive flux, which are not resolvable using current data. These changes in eruptive flux are not directly relatable to the rate of any interpreted tectonic driver such as edge-driven convection. However, the NVP and other

  20. The Caucasian-Arabian segment of the Alpine-Himalayan collisional belt: Geology,