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Sample records for aleutian island arc

  1. Paleomagnetic Evidence for Significant Rotations Within the Aleutian Island Arc.

    NASA Astrophysics Data System (ADS)

    Stone, D. B.; Krutikov, L.

    2006-12-01

    Present-day motion of the Pacific plate relative to the North American plate changes along the Aleutian arc from normal convergence in the east to transform motion in the west. It was postulated by Geist et al. (Tectonics 7, 327-341, 1988) that strain partitioning could result in tectonic segmentation of the lithosphere, caused by increasing obliquity of plate convergence and characterized by clockwise rotation and westward translation of discrete blocks. Their analysis of the present day morphology and tectonic setting of the western half of the arc suggests the presence of rotated blocks, and implies that the rotation is ongoing. Published high-quality paleomagnetic data from the far western end of the arc show rotations that are compatible with this model. This result is based on rocks of Eocene (Bering and Medny Islands) and Miocene (Shemya Island) age, thus the magnetically observed rotations could have occurred at any time since their origin. New paleomagnetic and geochronologic data from Miocene age volcanic rocks on Amchitka Island also indicate clockwise rotation at some time since the rocks were formed (13.8+/-0.2 Ma). However, two other high-quality paleomagnetic data sets from Eocene/Oligocene aged sediments from the eastern part of the arc (Atka and Umnak Islands) are significantly rotated in the same clockwise sense as the western end. Since plate convergence at these two eastern sites has been roughly normal since mid-Eocene time, strain partitioning related to oblique convergence is unlikely to be the cause of the rotation. Models involving rotation of the entire island arc to explain the similarity in magnitude and sense of the rotations seen in the paleomagnetic data require large relative latitude changes between the two ends of the arc. Though possible, such a model would put serious constraints on scenarios for the tectonic development of the Bering Sea Plate required to accommodate the degree of rotation suggested by the data. The answer may

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

    SciTech Connect

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

    2010-08-29

    The Hf and Nd isotopic compositions of 71 Quaternary lavas collected from locations along the full length of the Aleutian island arc are used to constrain the sources of Aleutian magmas and to provide insight into the geochemical behavior of Nd and Hf and related elements in the Aleutian subduction-magmatic system. Isotopic compositions of Aleutian lavas fall approximately at the center of, and form a trend parallel to, the terrestrial Hf-Nd isotopic array with {var_epsilon}{sub Hf} of +12.0 to +15.5 and {var_epsilon}{sub Nd} of +6.5 to +10.5. Basalts, andesites, and dacites within volcanic centers or in nearby volcanoes generally all have similar isotopic compositions, indicating that there is little measurable effect of crustal or other lithospheric assimilation within the volcanic plumbing systems of Aleutian volcanoes. Hafnium isotopic compositions have a clear pattern of along-arc increase that is continuous from the eastern-most locations near Cold Bay to Piip Seamount in the western-most part of the arc. This pattern is interpreted to reflect a westward decrease in the subducted sediment component present in Aleutian lavas, reflecting progressively lower rates of subduction westward as well as decreasing availability of trench sediment. Binary bulk mixing models (sediment + peridotite) demonstrate that 1-2% of the Hf in Aleutian lavas is derived from subducted sediment, indicating that Hf is mobilized out of the subducted sediment with an efficiency that is similar to that of Sr, Pb and Nd. Low published solubility for Hf and Nd in aqueous subduction fluids lead us to conclude that these elements are mobilized out of the subducted component and transferred to the mantle wedge as bulk sediment or as a silicate melt. Neodymium isotopes also generally increase from east to west, but the pattern is absent in the eastern third of the arc, where the sediment flux is high and increases from east to west, due to the presence of abundant terrigenous sediment in the

  3. Eocene to Pleistocene magmatic evolution of the Delarof Islands, Aleutian Arc

    NASA Astrophysics Data System (ADS)

    Schaen, Allen J.; Jicha, Brian R.; Kay, Suzanne M.; Singer, Brad S.; Tibbetts, Ashley

    2016-03-01

    The Delarof Islands in the Aleutian Arc near 179º W record ˜37 million years of discontinuous arc magmatism along a SW-NE cross-arc transect from near the trench to the active volcanic front. Geochemical and geochronologic data from the pre-Pleistocene volcanic record in this region are limited and the 40Ar/39Ar, isotopic, and trace element data presented here are the first from units older than the Pleistocene-Holocene volcanoes (Tanaga, Gareloi). Twenty-two new 40Ar/39Ar ages establish a temporal framework for geochemical data and reveal that magmatism in the Delarof region was coincident with two arc-wide magmatic flare ups in the late Eocene/early Oligocene and latest Miocene/Pliocene. Mafic lavas and plutons in the southern Delarofs give 40Ar/39Ar plateau ages ranging from 36.8 ± 0.2 to 26.9 ± 0.6 Ma on Amatignak Island and 37.0 ± 0.2 to 29.3 ± 1.0 Ma on Ulak Island. To the north 25 km, 40Ar/39Ar ages from the central Delarof Islands, Kavalga, Ogliuga, and Skagul are late Miocene (6.28 ± 0.04 Ma) to Pliocene (4.77 ± 0.18 Ma) with younger ages to the northeast. A significant transition in arc chemistry occurs in the Pleistocene where lavas from active volcanoes Gareloi and Tanaga exhibit higher sediment and hydrous fluid signatures (Th/La, Cs/Ta, La/Sm, LILE abundances) and lower 143Nd/144Nd than older Delarof Island units closer to the trench. Similar findings from Eocene-Miocene lavas from Amchitka to Adak suggest that a previously minor sediment melt component became more pronounced in the Quaternary.

  4. Crustal recycling and the aleutian arc

    SciTech Connect

    Kay, R.W.; Kay, S.M. )

    1988-06-01

    Two types of crustal recycling transfer continental crust back into its mantle source. The first of these, upper crustal recycling, involves elements that have been fractionated by the hydrosphere-sediment system, and are subducted as a part of the oceanic crust. The subduction process (S-process) then fractionates these elements, and those not removed at shallow tectonic levels and as excess components of arc magmas are returned to the mantle. Newly determined trace element composition of Pacific oceanic sedimants are variable and mixing is necessary during the S-process, if sediment is to provide excess element in the ratios observed in Aleutian arc magmas. Only a small fraction of the total sediment subducted at the Aleutian trench is required to furnish the excess elements in Aleutian arc magmas. Ba and {sub 10}Be data indicate that this small fraction includes a contribution from the youngest subducted sediment. The second type of recycling, lower crustal recycling, involves crystal cumulates of both arc and oceanic crustal origin, and residues from crustal melting within arc crust. Unlike the silicic sediments, recycled lower crust is mafic to ultramafic in composition. Trace element analyses of xenoliths representing Aleutian arc lower crust are presented. Recycling by delamination of lower crust and attached mantle lithosphere may occur following basalt eclogite phase transformations that are facilitated by terrane suturing events that weld oceanic island arcs to the continents. The relative importance of upper and lower crustal recycling exerts a primary control on continental crustal composition.

  5. Displacement Partitioning, Boundary-Parallel Terrane Migration, and Arc-Parallel Extension in the Aleutian Islands Based on Structural Analysis and GPS Geodesy

    NASA Astrophysics Data System (ADS)

    Ave Lallemant, H. G.; Oldow, J. S.; Lewis, D. S.

    2001-12-01

    Structural analysis of the deformed rocks on several Aleutian Islands (Attu, Adak, Atka, and Unalaska) combined with published bathymetric and seismic reflection data support the existence of displacement partitioning along the Aleutian arc. Brittle structures are remarkably consistent among all islands studied and record arc-normal contraction, arc-parallel transcurrent motion, and arc-parallel extension. This process is still active as shown by earthquake-focal mechanisms and a GPS velocity field determined from five Aleutian Islands (Attu, Shemya, Adak, Atka, and Unalaska). GPS site velocities determined from campaigns in 1996, 1998, 1999, and 2000 increase from east to west along the island arc. Primary GPS sites on five islands were occupied for three-weeks each during two to four campaigns. In a North American reference frame the sites show a systematic increase in arc-parallel motion from Unalaska (4 mm/yr) in the east to Shemya (25 mm/yr) and Attu (31 mm/yr) in the west. Velocities for Adak and Atka near the center of the Aleutian arc are 10 mm/yr and 7 mm/yr, respectively and show a greater component of arc-normal displacement than sites at the eastern and western ends of the island chain. Secondary sites occupied for several days during alternating campaigns on Attu, Adak, and Unalaska have velocities consistent with the primary GPS sites for each island. On Atka, secondary site velocities record a significant divergence from the velocity of the primary site and indicate either transtensional deformation within the island or contamination of the primary site velocity by local strain accumulation. These results indicate that convergence between the North American and Pacific plates is partitioned into arc-normal and arc-parallel components. The arc-normal component causes shortening (thrusting and folding) along an axis oriented at a high-angle to the plate boundary and the arc-parallel component causes displacements along several arc

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

    Calc-alkaline plutons are major crustal building blocks of continental margin mountain belts like the Mesozoic to Tertiary Andes and the Sierra Nevada, but are rare in oceanic island arcs. Some of the most calc-alkaline I-type island arc plutons are in the Central Aleutians with the most extreme signatures, as indicated by FeO/MgO ratios of < ~2 at 48-70% wt. % SiO2, in the ~10 km wide Oligocene Hidden Bay pluton on southern Adak Island and the 10 km wide Miocene Kagalaska pluton to the north on eastern Adak and the adjacent Kagalaska Island. Although small compared to most continental plutons, similarities in intrusive units, mineralogy and chemistry suggest common formation processes. The Aleutian calc-alkaline plutonic rocks mainly differ from continental plutons in having more oceanic like isotopic (87Sr/86Sr = 0.703-0.7033; Epsilon Nd = 9-7.8) and LIL (e.g., higher K/Rb) ratios. The Adak region plutons differ from Tertiary plutons on Unalaska Island further east in being more K-rich and in having a more oxidized and lower-temperature mineralogy. From a regional perspective, the Adak area plutons intrude Eocene/Oligocene Finger Bay Formation mafic volcanic and sedimentary rocks and postdate the small ~38 Ma tholeiitic Finger Bay pluton. The chemistry of these older magmatic rocks is basically similar to that of young Central Aleutian magmatic rocks with boninites and arc tholeiitic magmas seemingly being absent. The formation of the calc-alkaline plutons seems to require a sufficient crustal thickness, fluid concentration and contractional stress such that magma chambers can stabilize significant amounts of pargasitic hornblende. Seismic receiver function analyses (Janiszewski et al., 2013) indicate the modern Adak crust is ~ 37 km thick. Existing and new hornblende, plagioclase and biotite Ar/Ar ages from 16 Hidden Bay pluton and Gannet Lake stock gabbro, porphyritic diorite, diorite, granodiorite, leucogranodiorite and aplite samples range from 34.6 to 30

  7. Along-strike trace element and isotopic variation in Aleutian Island arc basalt: Subduction melts sediments and dehydrates serpentine

    NASA Astrophysics Data System (ADS)

    Singer, Brad S.; Jicha, Brian R.; Leeman, William P.; Rogers, Nick W.; Thirlwall, Matthew F.; Ryan, Jeff; Nicolaysen, Kirsten E.

    2007-06-01

    Trace element and Sr-Nd-Pb isotope compositions of basaltic lavas from 11 volcanoes spanning 1300 km of the Aleutian Island arc provide new constraints on the recycling of elements in melts and fluids derived from subducted oceanic crust and sediment. Despite a nearly twofold variation in the flux of sediment subducted along the Aleutians, proxies indicating the presence of sediment melt in the magma source, including Th/La and Th/Nd, do not vary systematically along strike. In contrast, ratios including B/La, B/Nb, B/Be, Cs/La, Pb/Ce, and Li/Y suggest that the quantity or composition of fluid transferred from the slab into the mantle wedge varies an order of magnitude along strike and is apparently correlated with sediment flux. However, the most distinctive fluid addition corresponds spatially with subduction of the Amlia Fracture Zone (AFZ), a likely repository for H2O-rich serpentinite. Sr, Nd, and Pb isotope ratios, together with Th/Nd and B/La ratios, show that the majority of these basalts reflect a common baseline metasomatism of the mantle that accumulated, perhaps over millions of years, via small additions of both slab fluids and partially melted sediment. The paradox of requiring slab surface temperatures high enough to melt a layer of sediment, while lower-temperature dehydration reactions that supply water occur sufficiently deep to flux melting >80 km beneath the volcanoes is reconciled in a four-stage model: (1) as sediment and altered ocean crust is carried to ˜60 km depth and temperatures increase to ˜650°C, metamorphic dehydration reactions release most of the fluid and B to the shallow mantle wedge beneath the fore arc, but some of this mantle is metasomatized and flows downward; (2) the uppermost layer of sediment begins to melt at ˜750°C and >60 km depth; this small volume of melt physically mingles with the overlying metasomatized mantle wedge as it flows further downdip; (3) below the sediment veneer, the uppermost 1 km of ocean crust

  8. Massive edifice failure at Aleutian arc volcanoes

    USGS Publications Warehouse

    Coombs, M.L.; White, S.M.; Scholl, D. W.

    2007-01-01

    Along the 450-km-long stretch of the Aleutian volcanic arc from Great Sitkin to Kiska Islands, edifice failure and submarine debris-avalanche deposition have occurred at seven of ten Quaternary volcanic centers. Reconnaissance geologic studies have identified subaerial evidence for large-scale prehistoric collapse events at five of the centers (Great Sitkin, Kanaga, Tanaga, Gareloi, and Segula). Side-scan sonar data collected in the 1980s by GLORIA surveys reveal a hummocky seafloor fabric north of several islands, notably Great Sitkin, Kanaga, Bobrof, Gareloi, Segula, and Kiska, suggestive of landslide debris. Simrad EM300 multibeam sonar data, acquired in 2005, show that these areas consist of discrete large blocks strewn across the seafloor, supporting the landslide interpretation from the GLORIA data. A debris-avalanche deposit north of Kiska Island (177.6?? E, 52.1?? N) was fully mapped by EM300 multibeam revealing a hummocky surface that extends 40??km from the north flank of the volcano and covers an area of ??? 380??km2. A 24-channel seismic reflection profile across the longitudinal axis of the deposit reveals a several hundred-meter-thick chaotic unit that appears to have incised into well-bedded sediment, with only a few tens of meters of surface relief. Edifice failures include thin-skinned, narrow, Stromboli-style collapse as well as Bezymianny-style collapse accompanied by an explosive eruption, but many of the events appear to have been deep-seated, removing much of an edifice and depositing huge amounts of debris on the sea floor. Based on the absence of large pyroclastic sheets on the islands, this latter type of collapse was not accompanied by large eruptions, and may have been driven by gravity failure instead of magmatic injection. Young volcanoes in the central and western portions of the arc (177?? E to 175?? W) are located atop the northern edge of the ??? 4000-m-high Aleutian ridge. The position of the Quaternary stratocones relative to the

  9. Observations of Seafloor Outcrops in the Oblique Subduction Setting of Adak Canyon: Implications for Understanding the Early History of the Aleutian Island Arc

    NASA Astrophysics Data System (ADS)

    Yogodzinski, G.; Scholl, D.; Jicha, B.; Wyatt, C.; Singer, B.; Kelemen, P.

    2004-12-01

    Submarine canyons in the western Aleutians (west of 177°W) are formed by oblique subduction, which has broken crustal blocks away from the arc massif and rotated them in clockwise sense, resulting in the formation of triangular-shaped summit basins and deep, structurally controlled submarine canyons (Geist et al., Tectonics v7, p327, 1988). A series of dives with the ROV Jason II on July 28-30, 2004 on Adak Canyon has provided the first-ever view of seafloor outcrops in an Aleutian canyon formed by this process. Two dives on the canyon's steep eastern wall revealed extensive exposures of blocky outcrops of volcanic rock at depths of 2900-1500 m. Samples of these units collected by the Jason II are a mixture of dark, pyroxene and plagioclase-phyric lavas and volcaniclastics. Degree of weathering/alteration is highly variable but some samples appear fresh. We anticipate that these rocks are offshore-equivalents of the Finger Bay Volcanics, which represent the earliest phase of Aleutian volcanism exposed on nearby Adak Island (e.g., Coats, 1956, USGS Bull. 1028-C). Exposures of granitic rock in Adak Canyon form low ledges of exfoliating outcrop interspersed with spheroidally weathered, bouldery sub-crop, in the depth range of 1800-1600 meters. Obtaining in-situ samples from these massive and subrounded exposures was not possible with the Jason II, but recovery of large, sub-angular slabs that litter the surface included samples of fresh diorite, fine-grained felsic intrusives and hydrothermally altered volcanic country rock. The stratigraphically highest exposures observed in Adak Canyon are gently dipping, poorly lithified `Middle Series' sedimentary rocks of probable Miocene-Oligocene age. All outcrop surfaces in Adak Canyon are covered with a uniformly dark brown, opaque coating of Mn oxide less than 1mm thick. Well-rounded cobbles and boulders interpreted to be glacial drift are largely free of Mn oxide coatings. Thick pavements of Mn-oxide were not observed

  10. From birth to death of arc magmatism: The igneous evolution of Komandorsky Islands recorded tectonic changes during 50 Ma of westernmost Aleutian history

    NASA Astrophysics Data System (ADS)

    Höfig, T. W.; Portnyagin, M.; Hoernle, K.; Hauff, F. F.; van den Bogaard, P.; Garbe-Schoenberg, C.

    2013-12-01

    The Komandorsky Islands form the westernmost end of the Aleutian Island Arc. Four igneous complexes, spanning almost 50 Ma of magmatism, have previously been identified (Ivaschenko et al., 1984: Far East Scientific Centre, Vladivostok, 192 pp.). The petrogenesis of this protracted magmatic record and accurate absolute ages of events, however, remain poorly constrained. Our study investigates the relationship between magma composition and tectonic setting. The Komandorsky igneous basement formed in subduction zone setting. It hosts some of the oldest igneous rocks of the entire Aleutian Arc with the onset of magmatism occurring at 47 Ma. This early stage was characterized by classic fluid-dominated arc volcanism, which produced two coeval but likely genetically unrelated magmatic series of tholeiitic mafic and tholeiitic to calc-alkaline felsic rocks. To date, no boninites have been found and therefore arc initiation is different at the Aleutians than at Izu-Bonin-Marianas or the oldest rocks in the Aleutians have yet to be discovered. The prolonged production of the contrasting basalt-rhyolite association on Komandorsky Islands had lasted ~25 Ma and ceased around the Oligocene-Miocene boundary. Concurrently to this long-lasting activity, a gradual transition to a different mode of arc magmatism took place reflected by newly discovered Sr-enriched, HREE-depleted calc-alkaline basaltic andesitic lavas of mid-upper Eocene age spanning a time of at least ~7 Ma. This so-called Transition Series displays a moderate garnet signature marking the increased contribution of a slab-melt component to the magma sources of the Komandorsky Islands. Slab-melt contribution increased with decreasing age leading to strongly adakitic magmatism as early as ~33 Ma (Lower Oligocene), reflected by eruption of high-Sr (up to 2,500 ppm), highly HREE-depleted Adak-type magnesian basaltic andesites and andesites. These remarkable magmas became predominant during the Lower Miocene. They were

  11. Parsing Aleutian Arc Magma Compositions

    NASA Astrophysics Data System (ADS)

    Nye, C. J.

    2011-12-01

    The first-order subdivision of Aleutian arc magma compositions is based on SiO2, and the second-order subdivision is usually based on the change of FeOt/MgO as a function of SiO2, resulting in the additional twofold subdivision into (TH) and calcalkaline (CA) magmas. However, additional robust compositional variations exist. The two most important of these are (1) variation of the calcium number [Ca#; Ca/(Na+Ca)] as a function of SiO2, and (2) the Rate of Incompatible Trace-element Enrichment (RITE) at individual volcanic centers. Additionally, the data show that the low FeOt/MgO of CA andesite and dacite is more controlled by MgO excess than FeOt depletion. The Ca# of andesites and dacites is strongly bimodal. The low-Ca# group is "calc-alkalic", while the high-Ca# group is "calcic", using Peacock (1931) criteria. A continuum of Ca#s exists, but lavas intermediate between high-Ca# and low-Ca# are much less abundant. Ca#s merge below about 55% SiO2, and have a simple normal distribution. RITE, with rare but important exceptions, is generally constant at the temporal and spatial scale of a single volcano. Among high-RITE magmas LILE, LREE, HFSE, and Th increase ~3.5-fold, and HREE increase ~2.5-fold from basalt or basaltic-andesite through andesite to dacite. There is no strong indication that RITE is silica-dependant. High-RITE magmas develop a strong negative Eu anomaly, and are qualitatively compatible with an origin primarily involving fractionation of plagioclase-dominated mineral assemblages. Low-RITE magmas, in contrast, have nearly invariant REE and HFSE, and LILE and Th increase merely 1.5-fold over the same silica range. Low-RITE magmas are not compatible with fractionation of a plagioclase-dominant mineral assemblage. Alternative qualitatively plausible explanations (needing rigorous evaluation) include fractionation of an ultramafic mineral assemblage (Alaskan-type mafic-ultramafic bodies may be a model; see USGS Prof Paper 1564); that low-RITE basaltic

  12. Tsunami recurrence in the eastern Alaska-Aleutian arc: A Holocene stratigraphic record from Chirikof Island, Alaska

    USGS Publications Warehouse

    Nelson, Alan R.; Briggs, Richard; Dura, Tina; Engelhart, Simon E.; Gelfenbaum, Guy; Bradley, Lee-Ann; Forman, S.L.; Vane, Christopher H.; Kelley, K.A.

    2015-01-01

    cannot estimate source earthquake locations or magnitudes for most tsunami-deposited beds. We infer that no more than 3 of the 23 possible tsunamis beds at both sites were deposited following upper plate faulting or submarine landslides independent of megathrust earthquakes. If so, the Semidi segment of the Alaska-Aleutian megathrust near Chirikof Island probably sent high tsunamis southward every 180–270 yr for at least the past 3500 yr.                   

  13. Alaska Open-file Report 144 Assessment of Thermal Springs Sites Aleutian Arc, Atka Island to Becherof Lake -- Preliminary Results and Evaluation

    SciTech Connect

    Motyka, R.J.; Moorman, M.A.; Liss, S.A.

    1981-12-01

    Twenty of more than 30 thermal spring areas reported to exist in the Aleutian arc extending from Atka Island to Becherof Lake were investigated during July and August, 1980. Thermal activity of three of these sites had diminished substantially or no longer existed. At least seven more sites where thermal-spring activity is probable or certain were not visited because of their remoteness or because of time constraints. The existence of several other reported thermal spring sites could not be verified; these sites are considered questionable. On the basis of geothermometry, subsurface reservoir temperatures in excess of 150 C are estimated for 10 of the thermal spring sites investigated. These sites all occur in or near regions of Recent volcanism. Five of the sites are characterized by fumaroles and steaming ground, indicating the presence of at least a shallow vapor-dominated zone. Two, the Makushin Valley and Glacier Valley thermal areas, occur on the flanks of active Mukushin Volcano located on Unalaska Island, and may be connected to a common source of heat. Gas geothermometry suggests that the reservoir feeding the Kliuchef thermal field, located on the flanks of Kliuchef volcano of northeast Atka Island, may be as high as 239 C.

  14. Lithium Isotopic Composition of Aleutian Arc Magmas

    NASA Astrophysics Data System (ADS)

    Rudnick, R. L.; Park, Y.; Liu, X.; Kay, S. M.; Kay, R. W.

    2012-12-01

    The lithium isotopic compositions of inputs to subduction zones can be highly variable. For example, altered oceanic crust is isotopically heavy (δ7Li = 4 to 22, Chan et al., 1996; Bouman et al., 2004) due to uptake of seawater Li (32). Sea floor sediments can have highly variable compositions, ranging from isotopically heavy pelagic sediments (6 to 14) to isotopically light terrigneous clays (-1.5 to 5), derived from highly weathered continental crust (Chan et al., 2006). Despite this variability in inputs, arc outputs (magmatic rocks) typically have mantle-like δ7Li (e.g., 2 to 6; Tomascak et al., 2002; Walker et al., 2009). To explore the behavior of lithium and its isotopes in arcs, we have analyzed [Li] and δ7Li in 48 lavas and plutons from the Aleutian island arc, which span the temporal (0 to 38 Ma), geographical (165-184oW) and compositional variations (SiO2 = 46-70 wt.%) seen in this arc. Previous studies have indicated a systematic geographic change in lava chemistry related to changing sediment composition along the arc (terrigneous in the east, pelagic in the west, e.g., Kay and Kay, 1994; Yogodinski et al., 2010), as well as temporal changes that may also reflect changes in sedimentary input (Kay and Kay, 1994), and we wished to determine if Li isotopes also reflect such changes. Lithium concentration [Li] shows a generally positive correlation with SiO2, consistent with the expected incompatible behavior of Li during magmatic differentiation. Intrusive rocks (all from the Adak region) show more scatter than lavas on this plot, suggesting the influence of cumulate processes. The δ7Li of the rocks span an immense range from -1 to +29, well outside the values considered typical for the MORB-source mantle (e.g., 2-6). However, the majority of the samples (28 out of 48) have δ7Li falling within the range of typical mantle values. There is a general tendency for the lavas (all but one are <2 Ma) to have slightly lower δ7Li than intrusions (which range

  15. Investigation of the Influence of the Amlia Fracture Zone on the Islands of Four Mountains Region of the Aleutian Arc, AK

    NASA Astrophysics Data System (ADS)

    Nicolaysen, K. P.; Myers, J. D.; Weis, D.

    2013-12-01

    Regional isotopic and trace element investigations of the magmatic source characteristics of the Aleutian arc have attributed regional patterns to variations in the contribution of eclogite through slab melting, to increased proportions of sediment melts, and to variation in the amount of fluid derived by progressive metamorphism of the downgoing slab. Currently the Amlia Fracture Zone (AFZ) is located between the islands of Atka and Seguam and marks a prominent boundary between subduction of large quantities of trench sediments to the east versus sediment impoverished subduction to the west of the AFZ. This boundary is not stationary through time. Instead oblique subduction of the Pacific plate moves the AFZ westward along the arc front, causing sequential subduction beneath the islands of Chuginadak, Yunaska and Seguam circa 5, 2.5 and 1 million years ago, respectively. Lavas from Atka Island, which has not yet received the sediment and fluid spike from the AFZ, act as reference compositions. Comparison of bulk rock trace element ratios and Sr, Nd, Hf, and Pb isotopic compositions for lavas from these islands relative to Atka show that contributions from melted subducted sediment are important in the genesis of Holocene and Pleistocene lavas erupted in the Islands of Four Mountains region of the arc. Sr and Pb isotopic compositions for Yunaska and Chuginadak lavas are as high or higher than Seguam values and trend in the direction of sediment values. La/Nb ratios similarly indicate sediment melting is important for all these lavas. Comparison of values for Holocene relative to Pleistocene values indicate that once sediments are introduced to the magma source, they persist in affecting magma compositions. Comparison of higher Mg# lavas (molar Mg#>50) shows that a group of the oldest sampled lavas on Chuginadak have much lower 208Pb/204Pb, 206Pb/204Pb, and 87Sr/86Sr and higher 143Nd/144Nd, Zr/Y and Zn/Mn relative to all sampled Holocene and Pleistocene lavas from

  16. Specification of Tectonic Tsunami Sources Along the Eastern Aleutian Island Arc and Alaska Peninsula for Inundation Mapping and Hazard Assessment

    NASA Astrophysics Data System (ADS)

    Suleimani, E.; Nicolsky, D.; Freymueller, J. T.; Koehler, R.

    2013-12-01

    The Alaska Earthquake Information Center conducts tsunami inundation mapping for coastal communities in Alaska along several segments of the Aleutian Megathrust, each having a unique seismic history and tsunami generation potential. Accurate identification and characterization of potential tsunami sources is a critical component of our project. As demonstrated by the 2011 Tohoku-oki tsunami, correct estimation of the maximum size event for a given segment of the subduction zone is particularly important. In that event, unexpectedly large slip occurred approximately updip of the epicenter of the main shock, based on seafloor GPS and seafloor pressure gage observations, generating a much larger tsunami than anticipated. This emphasizes the importance of the detailed knowledge of the region-specific subduction processes, and using the most up-to-date geophysical data and research models that define the magnitude range of possible future tsunami events. Our study area extends from the eastern half of the 1957 rupture zone to Kodiak Island, covering the 1946 and 1938 rupture areas, the Shumagin gap, and the western part of the 1964 rupture area. We propose a strategy for generating worst-case credible tsunami scenarios for locations that have a short or nonexistent paleoseismic/paleotsunami record, and in some cases lack modern seismic and GPS data. The potential tsunami scenarios are built based on a discretized plate interface model fit to the Slab 1.0 model geometry. We employ estimates of slip deficit along the Aleutian Megathrust from GPS campaign surveys, the Slab 1.0 interface surface, empirical magnitude-slip relationships, and a numerical code that distributes slip among the subfault elements, calculates coseismic deformations and solves the shallow water equations of tsunami propagation and runup. We define hypothetical asperities along the megathrust and in down-dip direction, and perform a set of sensitivity model runs to identify coseismic deformation

  17. Seismicity of the Earth 1900-2010 Aleutian arc and vicinity

    USGS Publications Warehouse

    Benz, Harley M.; Herman, Matthew; Tarr, Arthur C.; Hayes, Gavin P.; Furlong, Kevin P.; Villaseñor, Antonio; Dart, Richard L.; Rhea, Susan

    2011-01-01

    This map shows details of the Aleutian arc not visible in an earlier publication. The Aleutian arc extends about 3,000 km from the Gulf of Alaska to the Kamchatka Peninsula. It marks the region where the Pacific plate subducts into the mantle beneath the North America plate. This subduction is responsible for the generation of the Aleutian Islands and the deep offshore Aleutian Trench. Relative to a fixed North America plate, the Pacific plate is moving northwest at a rate that increases from about 55 mm per year at the arc's eastern edge to 75 mm per year near its western terminus. In the east, the convergence of the plates is nearly perpendicular to the plate boundary. However, because of the boundary's curvature, as one travels westward along the arc, the subduction becomes more and more oblique to the boundary until the relative plate motion becomes parallel to the arc at the Near Islands near its western edge. Subduction zones such as the Aleutian arc are geologically complex and produce numerous earthquakes from multiple sources. Deformation of the overriding North America plate generates shallow crustal earthquakes, whereas slip at the interface of the plates generates interplate earthquakes that extend from near the base of the trench to depths of 40 to 60 km. At greater depths, Aleutian arc earthquakes occur within the subducting Pacific plate and can reach depths of 300 km. Since 1900, six great earthquakes have occurred along the Aleutian Trench, Alaska Peninsula, and Gulf of Alaska: M8.4 1906 Rat Islands; M8.6 1938 Shumagin Islands; M8.6 1946 Unimak Island; M8.6 1957 Andreanof Islands; M9.2 1964 Prince William Sound; and M8.7 1965 Rat Islands. Several relevant tectonic elements (plate boundaries and active volcanoes) provide a context for the seismicity presented on the main map panel. The plate boundaries are most accurate along the axis of the Aleutian Trench and more diffuse or speculative in extreme northeastern Russia. The active volcanoes parallel

  18. Tracking along-arc sediment inputs to the Aleutian arc using thallium isotopes

    NASA Astrophysics Data System (ADS)

    Nielsen, Sune G.; Yogodzinski, Gene; Prytulak, Julie; Plank, Terry; Kay, Suzanne M.; Kay, Robert W.; Blusztajn, Jerzy; Owens, Jeremy D.; Auro, Maureen; Kading, Tristan

    2016-05-01

    Sediment transport from the subducted slab to the mantle wedge is an important process in understanding the chemical and physical conditions of arc magma generation. The Aleutian arc offers an excellent opportunity to study sediment transport processes because the subducted sediment flux varies systematically along strike (Kelemen et al., 2003) and many lavas exhibit unambiguous signatures of sediment addition to the sub-arc mantle (Morris et al., 1990). However, the exact sediment contribution to Aleutian lavas and how these sediments are transported from the slab to the surface are still debated. Thallium (Tl) isotope ratios have great potential to distinguish sediment fluxes in subduction zones because pelagic sediments and low-temperature altered oceanic crust are highly enriched in Tl and display heavy and light Tl isotope compositions, respectively, compared with the upper mantle and continental crust. Here, we investigate the Tl isotope composition of lavas covering almost the entire Aleutian arc a well as sediments outboard of both the eastern (DSDP Sites 178 and 183) and central (ODP Hole 886C) portions of the arc. Sediment Tl isotope compositions change systematically from lighter in the Eastern to heavier in the Central Aleutians reflecting a larger proportion of pelagic sediments when distal from the North American continent. Lavas in the Eastern and Central Aleutians mirror this systematic change to heavier Tl isotope compositions to the west, which shows that the subducted sediment composition is directly translated to the arc east of Kanaga Island. Moreover, quantitative mixing models of Tl and Pb, Sr and Nd isotopes reveal that bulk sediment transfer of ∼0.6-1.0% by weight in the Eastern Aleutians and ∼0.2-0.6% by weight in the Central Aleutians can account for all four isotope systems. Bulk mixing models, however, require that fractionation of trace element ratios like Ce/Pb, Cs/Tl, and Sr/Nd in the Central and Eastern Aleutians occurs after

  19. Case study: Bioremediation in the Aleutian Islands

    SciTech Connect

    Steward, K.J.; Laford, H.D.

    1995-12-31

    This case study describes the design, construction, and operation of a bioremediation pile on Adak Island, which is located in the Aleutian Island chain. Approximately 1,900 m{sup 3} of petroleum-contaminated soil were placed in the bioremediation pile. The natural bioremediation process was enhanced by an oxygen and nutrient addition system to stimulate microbial activity. Despite the harsh weather on the island, after the first 6 months of operation, laboratory analyses of soil samples indicated a significant (80%) reduction in diesel concentrations.

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

    NASA Astrophysics Data System (ADS)

    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

  1. Oxygen isotope constraints on the petrogenesis of Aleutian arc magmas

    SciTech Connect

    Singer, B.S.; O'Neil, J.R. ); Brophy, J.G. )

    1992-04-01

    The first measurement of {sup 18}O/{sup 16}O ratios of plagioclase, clinopyroxene, orthopyroxene, and titanomagnetite phenocrysts from modern Aleutian island-arc lavas provides new insight and independent constraints on magma sources and intracrustal processes. Basalts are heterogeneous on the scale of the entire arc and individual volcanic centers. Combined with Sr isotope and trace element data {delta}{sup 18}O{sub plag} values suggest a variable magma source characterized by differences in the mantle wedge or the subducted sediment component along the volcanic front. Seven tholeiitic basalt to rhyodacite lavas from the Seguam volcanic center have nearly identical {delta}{sup 18}O{sub plag} values of 6.0{per thousand} {plus minus} 0.2{per thousand}, reflecting extensive closed-system plagioclase-dominated crystal fractionation. Oxygen isotope thermometry and pyroxene and oxide equilibria indicate that differentiation occurred between 1,150 {plus minus} 100C (basalt) and 950 {plus minus} 100C (rhyodacite). In contrast, {delta}{sup 18}O{sub plag} values of 12 calc-alkalic basaltic andesites and andesites from the smaller Kanaga volcanic center span a broader range of 5.9{per thousand}-6.6{per thousand}, and consist of mostly higher values. Isotopic disequilibrium in the Kanaga system is manifest in two ways: two types of basaltic inclusions with contrasting {delta}{sup 18}O values occur in one andesite, and in two other andesites plagioclase-titanomagnetite and clinopyroxene-titanomagnetite oxygen isotope temperatures are inconsistent.

  2. Criconematina (nematoda: tylenchida) from the Aleutian Islands

    SciTech Connect

    Bernard, E.C.

    1982-01-01

    A new genus (Cerchnotocriconema) and three new species (C. psephinum, Hemicycliophora anchitkaensis, and Paratylenchus amundseni) are described from Adak and Amchitka Islands in the Aleutian chain. The new genus differs from all other criconematid genera in having irregular, convex sculpturing consisting of small, oval plates on the anterior and posterior regions of each annule, with the mid-annular region minutely punctate or dentate. H. amchitkaensis n. sp. resembles H. sinilis Thorne and H. zuckermani Brzeski, but has only one head annule, instead of two. P. amundseni n. sp., which has a stylet 17 to 19 ..mu..m long, is similar to P. tatea Wu and Townsend and P. labiosus Anderson and Kimpinski, but differs by the presence of males and the possession of conoid-truncate lip region, functional spermatheca, and long male tail (c = 8.5 to 9.5). Seriespinula seymouri Wu (Mehta and Raski), Nothocriconema longulum (Gunhold) De Grisse and Loof, and Macroposthonia xenoplax (Raski) De Grisse and Loof are also reported from the islands.

  3. Geologic implications of great interplate earthquakes along the Aleutian arc

    SciTech Connect

    Ryan, H.F.; Scholl, D.W.

    1993-12-01

    We present new marine geophysical observations and synthesize previous geologic interpretations of the Aleutian arc to show that the epicenters of these great thrust-type earthquakes coincide with upper plate segments of the arc characterized by a coherent forearc structural fabric. We propose that variations in upper plate structural strength and mobility affect the mechanical properties of the interplate thrust zone and need to be considered in localizing interplate asperities. Forearc tectonic segmentaion associated with the partitioning of strike-slip and thrust motions may exert long-term controls on the rates of seismic moment release.

  4. 76 FR 3089 - Proposed Information Collection; Comment Request; Alaska Region Bering Sea & Aleutian Islands...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-01-19

    ... Region Bering Sea & Aleutian Islands Crab Permits AGENCY: National Oceanic and Atmospheric Administration... of a currently approved collection. The Crab Rationalization Program allocates Bering Sea and Aleutian Islands (BSAI) crab resources among harvesters, processors, and coastal communities through...

  5. 50 CFR 600.1103 - Bering Sea and Aleutian Islands (BSAI) Crab species program.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 50 Wildlife and Fisheries 12 2013-10-01 2013-10-01 false Bering Sea and Aleutian Islands (BSAI... Aleutian Islands (BSAI) Crab species program. (a) Purpose. This section's purpose is to implement the... Fishery Management Plan for the Bering Sea/Aleutian Islands King and Tanner Crabs pursuant to § 679.2...

  6. Shaded Relief Mosaic of Umnak Island, Aleutian Islands, Alaska

    NASA Technical Reports Server (NTRS)

    2001-01-01

    This image is a shaded relief mosaic of Umnak Island in Alaska's Aleutian Islands.

    It was created with Airsar data that was geocoded and combined into this mosaic as part of a NASA-funded Alaska Digital Elevation Model Project at the Alaska Synthetic Aperture Radar Facility (ASF) at the University of Alaska Geophysical Institute in Fairbanks, Alaska.

    Airsar collected the Alaska data as part of its PacRim 2000 Mission, which took the instrument to French Polynesia, American and Western Samoa, Fiji, New Zealand, Australia, New Guinea, Indonesia, Malaysia, Cambodia, Philippines, Taiwan, South Korea, Japan, Northern Marianas, Guam, Palau, Hawaii and Alaska. Airsar, part of NASA's Airborne Science Program, is managed for NASA's Earth Science Enterprise by JPL. JPL is a division of the California Institute of Technology in Pasadena.

  7. Pacific Basin tsunami hazards associated with mass flows in the Aleutian arc of Alaska

    USGS Publications Warehouse

    Waythomas, Christopher F.; Watts, Philip; Shi, Fengyan; Kirby, James T.

    2009-01-01

    We analyze mass-flow tsunami generation for selected areas within the Aleutian arc of Alaska using results from numerical simulation of hypothetical but plausible mass-flow sources such as submarine landslides and volcanic debris avalanches. The Aleutian arc consists of a chain of volcanic mountains, volcanic islands, and submarine canyons, surrounded by a low-relief continental shelf above about 1000–2000 m water depth. Parts of the arc are fragmented into a series of fault-bounded blocks, tens to hundreds of kilometers in length, and separated from one another by distinctive fault-controlled canyons that are roughly normal to the arc axis. The canyons are natural regions for the accumulation and conveyance of sediment derived from glacial and volcanic processes. The volcanic islands in the region include a number of historically active volcanoes and some possess geological evidence for large-scale sector collapse into the sea. Large scale mass-flow deposits have not been mapped on the seafloor south of the Aleutian Islands, in part because most of the area has never been examined at the resolution required to identify such features, and in part because of the complex nature of erosional and depositional processes. Extensive submarine landslide deposits and debris flows are known on the north side of the arc and are common in similar settings elsewhere and thus they likely exist on the trench slope south of the Aleutian Islands. Because the Aleutian arc is surrounded by deep, open ocean, mass flows of unconsolidated debris that originate either as submarine landslides or as volcanic debris avalanches entering the sea may be potential tsunami sources. To test this hypothesis we present a series of numerical simulations of submarine mass-flow initiated tsunamis from eight different source areas. We consider four submarine mass flows originating in submarine canyons and four flows that evolve from submarine landslides on the trench slope. The flows have lengths

  8. Aleutian Pribilof Islands Wind Energy Feasibility Study

    SciTech Connect

    Bruce A. Wright

    2012-03-27

    Under this project, the Aleutian Pribilof Islands Association (APIA) conducted wind feasibility studies for Adak, False Pass, Nikolski, Sand Point and St. George. The DOE funds were also be used to continue APIA's role as project coordinator, to expand the communication network quality between all participants and with other wind interest groups in the state and to provide continued education and training opportunities for regional participants. This DOE project began 09/01/2005. We completed the economic and technical feasibility studies for Adak. These were funded by the Alaska Energy Authority. Both wind and hydro appear to be viable renewable energy options for Adak. In False Pass the wind resource is generally good but the site has high turbulence. This would require special care with turbine selection and operations. False Pass may be more suitable for a tidal project. APIA is funded to complete a False Pass tidal feasibility study in 2012. Nikolski has superb potential for wind power development with Class 7 wind power density, moderate wind shear, bi-directional winds and low turbulence. APIA secured nearly $1M from the United States Department of Agriculture Rural Utilities Service Assistance to Rural Communities with Extremely High Energy Costs to install a 65kW wind turbine. The measured average power density and wind speed at Sand Point measured at 20m (66ft), are 424 W/m2 and 6.7 m/s (14.9 mph) respectively. Two 500kW Vestas turbines were installed and when fully integrated in 2012 are expected to provide a cost effective and clean source of electricity, reduce overall diesel fuel consumption estimated at 130,000 gallons/year and decrease air emissions associated with the consumption of diesel fuel. St. George Island has a Class 7 wind resource, which is superior for wind power development. The current strategy, led by Alaska Energy Authority, is to upgrade the St. George electrical distribution system and power plant. Avian studies in Nikolski and

  9. Aleutian terranes from Nd isotopes

    NASA Technical Reports Server (NTRS)

    Kay, R. W.; Kay, S. M.; Rubenstone, J. L.

    1986-01-01

    Nd isotope ratios substantiate the identification of oceanic crustal terranes within the continental crustal basement of the Aleutian island arc. The oceanic terranes are exposed in the westernmost Aleutians, but to the east, they are completely buried by isotopically distinct arc-volcanic rocks. Analogous oceanic terranes may be important components of the terrane collages that comprise the continents.

  10. Amphibious Magnetotelluric Investigation of the Aleutian Arc: Mantle Melt Generation and Migration beneath Okmok Caldera

    NASA Astrophysics Data System (ADS)

    Zelenak, G.; Key, K.; Bennington, N. L.; Bedrosian, P.

    2015-12-01

    Understanding the factors controlling the release of volatiles from the downgoing slab, the subsequent generation of melt in the overlying mantle wedge, the migration of melt to the crust, and its evolution and emplacement within the crust are important for advancing our understanding of arc magmatism and crustal genesis. Because melt and aqueous fluids are a few orders of magnitude more electrically conductive than unmelted peridotite, the conductivity-mapping magnetotelluric (MT) method is well-suited to imaging fluids and melt beneath arc volcanoes. Here we present conductivity results from an amphibious MT profile crossing Okmok volcano in the central Aleutian arc. The Aleutian arc is one of the most volcanically active regions in North America, making it an ideal location for studying arc magnetism. Okmok volcano, located on the northeastern portion of Umnak Island, is among the most active volcanoes in the Aleutian chain. In addition to two caldera-forming events in the Holocene, numerous eruptions in the past century indicate a robust magmatic supply. Previous coarse resolution seismic studies have inferred a crustal magma reservoir. In order to investigate the role fluids play in melting the mantle wedge, how melts ascend through the corner flow regime of the mantle wedge, how melt migrates and is stored within the upper mantle and crust, and how this impacts explosive caldera forming eruptions, we carried out an amphibious geophysical survey across the arc in June-July 2015. Twenty-nine onshore MT stations and 10 offshore stations were collected in a 3D array covering Okmok, and 43 additional offshore MT stations completed a 300 km amphibious profile starting at the trench, crossing the forearc, arc and backarc. Thirteen onshore passive seismic stations were also installed and will remain in place for one year to supplement the twelve permanent stations on the island. Data collected by this project will be used to map seismic velocity and electrical

  11. Review of crustal seismicity in the Aleutian Arc and implications for arc deformation

    NASA Astrophysics Data System (ADS)

    Ruppert, Natalia A.; Kozyreva, Natalia P.; Hansen, Roger A.

    2012-02-01

    Central and eastern Aleutian Arc is characterized by oblique convergence between the subducting Pacific and overriding Bering Plates. This results in westward arc translation and formation of rotating crustal blocks in the forearc. In 2006-2010 several moderate, shallow crustal earthquakes (up to magnitude 6.7) occurred in the region. These events are located about 150 km away from the trench, on the volcanic axis, and have either strike-slip (west of 174°W) or normal (east of 174°W) faulting mechanisms. We improve aftershock locations by applying precise relocation methods to aid in identifying preferred fault planes. We also review similar earthquakes that occurred prior to 2006. For the central Aleutian Arc we conclude that, while some of these events occurred along the boundaries of the rotating blocks, the majority are left-lateral strike-slip events on NW- to N-oriented fault planes in the unrotated Bering massif. These manifest Riedel shearing in response slip partitioning due to the oblique convergence. Normal faulting events in eastern Aleutian Arc reflect along-arc extension.

  12. Cranial suture biology of the Aleutian Island inhabitants.

    PubMed

    Cray, James; Mooney, Mark P; Siegel, Michael I

    2011-04-01

    Research on cranial suture biology suggests there is biological and taxonomic information to be garnered from the heritable pattern of suture synostosis. Suture synostosis along with brain growth patterns, diet, and biomechanical forces influence phenotypic variability in cranial vault morphology. This study was designed to determine the pattern of ectocranial suture synostosis in skeletal populations from the Aleutian Islands. We address the hypothesis that ectocranial suture synostosis pattern will differ according to cranial vault shape. Ales Hrdlicka identified two phenotypes in remains excavated from the Aleutian Island. The Paleo-Aleutians, exhibiting a dolichocranic phenotype with little prognathism linked to artifacts distinguished from later inhabitants, Aleutians, who exhibited a brachycranic phenotype with a greater amount of prognathism. A total of 212 crania representing Paleo-Aleuts and Aleutian as defined by Hrdlicka were investigated for suture synostosis pattern following standard methodologies. Comparisons were performed using Guttmann analyses. Results revealed similar suture fusion patterns for the Paleo-Aleut and Aleutian, a strong anterior to posterior pattern of suture fusion for the lateral-anterior suture sites, and a pattern of early termination at the sagittal suture sites for the vault. These patterns were found to differ from that reported in the literature. Because these two populations with distinct cranial shapes exhibit similar patterns of suture synostosis it appears pattern is independent of cranial shape in these populations of Homo sapiens. These findings suggest that suture fusion patterns may be population dependent and that a standardized methodology, using suture fusion to determine age-at-death, may not be applicable to all populations. PMID:21328563

  13. Earthquake location in island arcs

    USGS Publications Warehouse

    Engdahl, E.R.; Dewey, J.W.; Fujita, K.

    1982-01-01

    A comprehensive data set of selected teleseismic P-wave arrivals and local-network P- and S-wave arrivals from large earthquakes occurring at all depths within a small section of the central Aleutians is used to examine the general problem of earthquake location in island arcs. Reference hypocenters for this special data set are determined for shallow earthquakes from local-network data and for deep earthquakes from combined local and teleseismic data by joint inversion for structure and location. The high-velocity lithospheric slab beneath the central Aleutians may displace hypocenters that are located using spherically symmetric Earth models; the amount of displacement depends on the position of the earthquakes with respect to the slab and on whether local or teleseismic data are used to locate the earthquakes. Hypocenters for trench and intermediate-depth events appear to be minimally biased by the effects of slab structure on rays to teleseismic stations. However, locations of intermediate-depth events based on only local data are systematically displaced southwards, the magnitude of the displacement being proportional to depth. Shallow-focus events along the main thrust zone, although well located using only local-network data, are severely shifted northwards and deeper, with displacements as large as 50 km, by slab effects on teleseismic travel times. Hypocenters determined by a method that utilizes seismic ray tracing through a three-dimensional velocity model of the subduction zone, derived by thermal modeling, are compared to results obtained by the method of joint hypocenter determination (JHD) that formally assumes a laterally homogeneous velocity model over the source region and treats all raypath anomalies as constant station corrections to the travel-time curve. The ray-tracing method has the theoretical advantage that it accounts for variations in travel-time anomalies within a group of events distributed over a sizable region of a dipping, high

  14. Satellite magnetic anomalies over subduction zones - The Aleutian Arc anomaly

    NASA Technical Reports Server (NTRS)

    Clark, S. C.; Frey, H.; Thomas, H. H.

    1985-01-01

    Positive magnetic anomalies seen in MAGSAT average scalar anomaly data overlying some subduction zones can be explained in terms of the magnetization contrast between the cold subducted oceanic slab and the surrounding hotter, nonmagnetic mantle. Three-dimensional modeling studies show that peak anomaly amplitude and location depend on slab length and dip. A model for the Aleutian Arc anomaly matches the general trend of the observed MAGSAT anomaly if a slab thickness of 7 km and a relatively high (induced plus viscous) magnetization contrast of 4 A/m are used. A second source body along the present day continental margin is required to match the observed anomaly in detail, and may be modeled as a relic slab from subduction prior to 60 m.y. ago.

  15. Transpressional Strain Partitioning and the Compatibility of GPS Velocities and Earthquakes Focal Mechanisms in the Aleutian Arc

    NASA Astrophysics Data System (ADS)

    Apel, E. V.; Oldow, J. S.; Lewis, D. S.; Hans, A.

    2002-12-01

    Oblique plate convergence is commonly partitioned into boundary normal and parallel components resulting in displacement of the frontal portion of the overriding plate with respect to the backarc region along arc-parallel strike-slip faults. In the Aleutian Islands, the east to west increase in relative plate motion between the North American and Pacific plates from 65 mm/yr to 75 mm/yr is accompanied by a change from normal convergence to boundary parallel displacement. The convergence obliquity increases from near zero to ~80 degrees along strike together with an observed increase in velocities based on GPS measurements from 1996, 1998, 1999, and 2000. GPS velocities have a strong arc-parallel orientation and systematically increase around the curved arc from 4 mm/yr in the east (Unalaska), to 7-10 mm/yr in the center (Atka and Adak), and 25-31 mm/yr in the west (Shemya and Attu). In all cases, GPS velocities record a small arc-normal component of displacement. The orientation of the incremental shortening axis derived from earthquake focal mechanisms on the Aleutian megathrust has an obliquity that varies systematically from zero (normal to the plate boundary) in the east to ~35 degrees in the west. The variation in incremental shortening axes, however, does not document displacement field partitioning but rather is a consequence of transpressional nonplane strain. Existence of displacement partitioning can only be assessed by direct measurement. Unfortunately, GPS velocities record permanent and recoverable strain, necessitating determination of the elastic strain component in the velocity field. The incremental shortening axis related to megathrust deformation constrains the azimuth of the elastic component of the GPS velocity field and yields minimum arc-parallel displacement components of 4 mm/yr in the east, 5-6 mm/yr in the central Aleutian chain, and 22-27 mm/yr in the west. GPS velocities along the Aleutian chain record a lateral variation in

  16. 46 CFR 7.170 - Alaska Peninsula, AK to Aleutian Islands, AK.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 46 Shipping 1 2014-10-01 2014-10-01 false Alaska Peninsula, AK to Aleutian Islands, AK. 7.170... BOUNDARY LINES Alaska § 7.170 Alaska Peninsula, AK to Aleutian Islands, AK. (a) A line drawn from the southernmost extremity of Cape Kumlium to the westernmost extremity of Nakchamik Island; thence to...

  17. 46 CFR 7.170 - Alaska Peninsula, AK to Aleutian Islands, AK.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 46 Shipping 1 2012-10-01 2012-10-01 false Alaska Peninsula, AK to Aleutian Islands, AK. 7.170... BOUNDARY LINES Alaska § 7.170 Alaska Peninsula, AK to Aleutian Islands, AK. (a) A line drawn from the southernmost extremity of Cape Kumlium to the westernmost extremity of Nakchamik Island; thence to...

  18. 46 CFR 7.170 - Alaska Peninsula, AK to Aleutian Islands, AK.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 46 Shipping 1 2010-10-01 2010-10-01 false Alaska Peninsula, AK to Aleutian Islands, AK. 7.170... BOUNDARY LINES Alaska § 7.170 Alaska Peninsula, AK to Aleutian Islands, AK. (a) A line drawn from the southernmost extremity of Cape Kumlium to the westernmost extremity of Nakchamik Island; thence to...

  19. 46 CFR 7.170 - Alaska Peninsula, AK to Aleutian Islands, AK.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 46 Shipping 1 2011-10-01 2011-10-01 false Alaska Peninsula, AK to Aleutian Islands, AK. 7.170... BOUNDARY LINES Alaska § 7.170 Alaska Peninsula, AK to Aleutian Islands, AK. (a) A line drawn from the southernmost extremity of Cape Kumlium to the westernmost extremity of Nakchamik Island; thence to...

  20. 46 CFR 7.170 - Alaska Peninsula, AK to Aleutian Islands, AK.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 46 Shipping 1 2013-10-01 2013-10-01 false Alaska Peninsula, AK to Aleutian Islands, AK. 7.170... BOUNDARY LINES Alaska § 7.170 Alaska Peninsula, AK to Aleutian Islands, AK. (a) A line drawn from the southernmost extremity of Cape Kumlium to the westernmost extremity of Nakchamik Island; thence to...

  1. Mercury concentrations of a resident freshwater forage fish at Adak Island, Aleutian Archipelago, Alaska.

    PubMed

    Kenney, Leah A; von Hippel, Frank A; Willacker, James J; O'Hara, Todd M

    2012-11-01

    The Aleutian Archipelago is an isolated arc of over 300 volcanic islands stretching 1,600 km across the interface of the Bering Sea and North Pacific Ocean. Although remote, some Aleutian Islands were heavily impacted by military activities from World War II until recently and were exposed to anthropogenic contaminants, including mercury (Hg). Mercury is also delivered to these islands via global atmospheric transport, prevailing ocean currents, and biotransport by migratory species. Mercury contamination of freshwater ecosystems is poorly understood in this region. Total Hg (THg) concentrations were measured in threespine stickleback fish (Gasterosteus aculeatus) collected from eight lakes at Adak Island, an island in the center of the archipelago with a long military history. Mean THg concentrations for fish whole-body homogenates for all lakes ranged from 0.314 to 0.560 mg/kg dry weight. Stickleback collected from seabird-associated lakes had significantly higher concentrations of THg compared to non-seabird lakes, including all military lakes. The δ(13)C stable isotope ratios of stickleback collected from seabird lakes suggest an input of marine-derived nutrients and/or marine-derived Hg. PMID:22912068

  2. MERCURY CONCENTRATIONS OF A RESIDENT FRESHWATER FORAGE FISH AT ADAK ISLAND, ALEUTIAN ARCHIPELAGO, ALASKA

    PubMed Central

    Kenney, Leah A.; von Hippel, Frank A.; Willacker, James J.; O’Hara, Todd M.

    2015-01-01

    The Aleutian Archipelago is an isolated arc of over 300 volcanic islands stretching 1,600 km across the interface of the Bering Sea and North Pacific Ocean. Although remote, some Aleutian Islands were heavily impacted by military activities from World War II until recently and were exposed to anthropogenic contaminants, including mercury (Hg). Mercury is also delivered to these islands via global atmospheric transport, prevailing ocean currents, and biotransport by migratory species. Mercury contamination of freshwater ecosystems is poorly understood in this region. Total Hg (THg) concentrations were measured in threespine stickleback fish (Gasterosteus aculeatus) collected from eight lakes at Adak Island, an island in the center of the archipelago with a long military history. Mean THg concentrations for fish whole-body homogenates for all lakes ranged from 0.314 to 0.560 mg/kg dry weight. Stickleback collected from seabird-associated lakes had significantly higher concentrations of THg compared to non-seabird lakes, including all military lakes. The δ13C stable isotope ratios of stickleback collected from seabird lakes suggest an input of marine-derived nutrients and/or marine-derived Hg. PMID:22912068

  3. August 2008 eruption of Kasatochi volcano, Aleutian Islands, Alaska-resetting an Island Landscape

    USGS Publications Warehouse

    Scott, W.E.; Nye, C.J.; Waythomas, C.F.; Neal, C.A.

    2010-01-01

    Kasatochi Island, the subaerial portion of a small volcano in the western Aleutian volcanic arc, erupted on 7-8 August 2008. Pyroclastic flows and surges swept the island repeatedly and buried most of it and the near-shore zone in decimeters to tens of meters of deposits. Several key seabird rookeries in taluses were rendered useless. The eruption lasted for about 24 hours and included two initial explosive pulses and pauses over a 6-hr period that produced ash-poor eruption clouds, a 10-hr period of continuous ash-rich emissions initiated by an explosive pulse and punctuated by two others, and a final 8-hr period of waning ash emissions. The deposits of the eruption include a basal muddy tephra that probably reflects initial eruptions through the shallow crater lake, a sequence of pumiceous and lithic-rich pyroclastic deposits produced by flow, surge, and fall processes during a period of energetic explosive eruption, and a fine-grained upper mantle of pyroclastic-fall and -surge deposits that probably reflects the waning eruptive stage as lake and ground water again gained access to the erupting magma. An eruption with similar impact on the island's environment had not occurred for at least several centuries. Since the 2008 eruption, the volcano has remained quiet other than emission of volcanic gases. Erosion and deposition are rapidly altering slopes and beaches. ?? 2010 Regents of the University of Colorado.

  4. Evolution and petroleum geology of Amlia and Amukta intra-arc summit basins, Aleutian Ridge

    USGS Publications Warehouse

    Geist, E.L.; Childs, J. R.; Scholl, D. W.

    1987-01-01

    Amlia and Amukta Basins are the largest of many intra-arc basins formed in late Cenozoic time along the crest of the Aleutian Arc. Both basins are grabens filled with 2-5 km of arc-derived sediment. A complex system of normal faults deformed the basinal strata. Although initial deposits of late Micocene age may be non-marine in origin, by early Pliocene time, most of the basinfill consisted of pelagic and hemipelagic debris and terrigenous turbidite deposits derived from wavebase and subaerial erosion of the arc's crestal areas. Late Cenozoic volcanism along the arc commenced during or shortly after initial subsidence and greatly contributed to active deposition in Amlia and Amukta Basins. Two groups of normal faults occur: major boundary faults common to both basins and 'intra-basin' faults that arise primarily from arc-parallel extension of the arc. The most significant boundary fault, Amlia-Amukta fault, is a south-dipping growth fault striking parallel to the trend of the arc. Displacement across this fault forms a large half-graben that is separated into the two depocentres of Amlia and Amukta Basins by the formation of a late Cenozoic volcanic centre, Seguam Island. Faults of the second group reflect regional deformation of the arc and offset the basement floor as well as the overlying basinal section. Intra-basin faults in Amlia Basin are predominantly aligned normal to the trend of the arc, thereby indicating arc-parallel extension. Those in Amukta basin are aligned in multiple orientations and probably indicate a more complex mechanism of faulting. Displacement across intra-basin faults is attributed to tectonic subsidence of the massif, aided by depositional loading within the basins. In addition, most intra-basin faults are listric and are associated with high growth rates. Although, the hydrocarbon potential of Amlia and Amukta Basins is difficult to assess based on existing data, regional considerations imply that an adequate thermal history conducive

  5. 75 FR 59687 - Proposed Information Collection; Comment Request; Alaska Region Bering Sea & Aleutian Islands...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-09-28

    ... Region Bering Sea & Aleutian Islands (BSAI) Crab Economic Data Reports AGENCY: National Oceanic and... Fisheries Service (NMFS) manages the crab fisheries in the waters off the coast of Alaska under the Fishery Management Plan (FMP) for the Bering Sea and Aleutian Islands (BSAI) Crab. The Magnuson-Stevens...

  6. 50 CFR Figure 8 to Part 679 - Aleutian Islands Chinook Salmon Savings Area

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 50 Wildlife and Fisheries 13 2014-10-01 2014-10-01 false Aleutian Islands Chinook Salmon Savings Area 8 Figure 8 to Part 679 Wildlife and Fisheries FISHERY CONSERVATION AND MANAGEMENT, NATIONAL... ECONOMIC ZONE OFF ALASKA Pt. 679, Fig. 8 Figure 8 to Part 679—Aleutian Islands Chinook Salmon Savings...

  7. 50 CFR Figure 8 to Part 679 - Aleutian Islands Chinook Salmon Savings Area

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 50 Wildlife and Fisheries 13 2012-10-01 2012-10-01 false Aleutian Islands Chinook Salmon Savings Area 8 Figure 8 to Part 679 Wildlife and Fisheries FISHERY CONSERVATION AND MANAGEMENT, NATIONAL... ECONOMIC ZONE OFF ALASKA Pt. 679, Fig. 8 Figure 8 to Part 679—Aleutian Islands Chinook Salmon Savings...

  8. 50 CFR Figure 8 to Part 679 - Aleutian Islands Chinook Salmon Savings Area

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 50 Wildlife and Fisheries 9 2010-10-01 2010-10-01 false Aleutian Islands Chinook Salmon Savings Area 8 Figure 8 to Part 679 Wildlife and Fisheries FISHERY CONSERVATION AND MANAGEMENT, NATIONAL... ECONOMIC ZONE OFF ALASKA Pt. 679, Fig. 8 Figure 8 to Part 679—Aleutian Islands Chinook Salmon Savings...

  9. 50 CFR Figure 8 to Part 679 - Aleutian Islands Chinook Salmon Savings Area

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 50 Wildlife and Fisheries 13 2013-10-01 2013-10-01 false Aleutian Islands Chinook Salmon Savings Area 8 Figure 8 to Part 679 Wildlife and Fisheries FISHERY CONSERVATION AND MANAGEMENT, NATIONAL... ECONOMIC ZONE OFF ALASKA Pt. 679, Fig. 8 Figure 8 to Part 679—Aleutian Islands Chinook Salmon Savings...

  10. 50 CFR Figure 8 to Part 679 - Aleutian Islands Chinook Salmon Savings Area

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 50 Wildlife and Fisheries 11 2011-10-01 2011-10-01 false Aleutian Islands Chinook Salmon Savings Area 8 Figure 8 to Part 679 Wildlife and Fisheries FISHERY CONSERVATION AND MANAGEMENT, NATIONAL... ECONOMIC ZONE OFF ALASKA Pt. 679, Fig. 8 Figure 8 to Part 679—Aleutian Islands Chinook Salmon Savings...

  11. 50 CFR Table 23 to Part 679 - Aleutian Islands Coral Habitat Protection Areas

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 50 Wildlife and Fisheries 11 2011-10-01 2011-10-01 false Aleutian Islands Coral Habitat Protection Areas 23 Table 23 to Part 679 Wildlife and Fisheries FISHERY CONSERVATION AND MANAGEMENT, NATIONAL... ECONOMIC ZONE OFF ALASKA Pt. 679, Table 23 Table 23 to Part 679—Aleutian Islands Coral Habitat...

  12. 50 CFR Table 23 to Part 679 - Aleutian Islands Coral Habitat Protection Areas

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 50 Wildlife and Fisheries 9 2010-10-01 2010-10-01 false Aleutian Islands Coral Habitat Protection Areas 23 Table 23 to Part 679 Wildlife and Fisheries FISHERY CONSERVATION AND MANAGEMENT, NATIONAL... ECONOMIC ZONE OFF ALASKA Pt. 679, Table 23 Table 23 to Part 679—Aleutian Islands Coral Habitat...

  13. 50 CFR Table 23 to Part 679 - Aleutian Islands Coral Habitat Protection Areas

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 50 Wildlife and Fisheries 13 2012-10-01 2012-10-01 false Aleutian Islands Coral Habitat Protection Areas 23 Table 23 to Part 679 Wildlife and Fisheries FISHERY CONSERVATION AND MANAGEMENT, NATIONAL... ECONOMIC ZONE OFF ALASKA Pt. 679, Table 23 Table 23 to Part 679—Aleutian Islands Coral Habitat...

  14. 50 CFR Table 23 to Part 679 - Aleutian Islands Coral Habitat Protection Areas

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 50 Wildlife and Fisheries 13 2013-10-01 2013-10-01 false Aleutian Islands Coral Habitat Protection Areas 23 Table 23 to Part 679 Wildlife and Fisheries FISHERY CONSERVATION AND MANAGEMENT, NATIONAL... ECONOMIC ZONE OFF ALASKA Pt. 679, Table 23 Table 23 to Part 679—Aleutian Islands Coral Habitat...

  15. 50 CFR Table 23 to Part 679 - Aleutian Islands Coral Habitat Protection Areas

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 50 Wildlife and Fisheries 13 2014-10-01 2014-10-01 false Aleutian Islands Coral Habitat Protection Areas 23 Table 23 to Part 679 Wildlife and Fisheries FISHERY CONSERVATION AND MANAGEMENT, NATIONAL... ECONOMIC ZONE OFF ALASKA Pt. 679, Table 23 Table 23 to Part 679—Aleutian Islands Coral Habitat...

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

    SciTech Connect

    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.

  17. A burial cave in the western Aleutian Islands, Alaska.

    PubMed

    West, Dixie; Lefèvre, Christine; Corbett, Debra; Crockford, Susan

    2003-01-01

    During the 1998 field season, the Western Aleutians Archaeological and Paleobiological Project (WAAPP) team located a cave in the Near Islands, Alaska. Near the entrance of the cave, the team identified work areas and sleeping/sitting areas surrounded by cultural debris and animal bones. Human burials were found in the cave interior. In 2000, with permission from The Aleut Corporation, archaeologists revisited the site. Current research suggests three distinct occupations or uses for this cave. Aleuts buried their dead in shallow graves at the rear of the cave circa 1,200 to 800 years ago. Aleuts used the front of the cave as a temporary hunting camp as early as 390 years ago. Finally, Japanese and American military debris and graffiti reveal that the cave was visited during and after World War II. Russian trappers may have also taken shelter there 150 to 200 years ago. This is the first report of Aleut cave burials west of the Delarof Islands in the central Aleutians. PMID:21755641

  18. 50 CFR Figure 1 to Part 679 - Bering Sea and Aleutian Islands Statistical and Reporting Areas

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 50 Wildlife and Fisheries 13 2012-10-01 2012-10-01 false Bering Sea and Aleutian Islands... Islands Statistical and Reporting Areas ER15NO99.000 b. Coordinates Code Description 300 Russian waters... Islands and straight lines between the islands connecting the following coordinates in the order...

  19. 76 FR 3090 - Proposed Information Collection; Comment Request; Alaska Region; Bering Sea and Aleutian Islands...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-01-19

    ... Region; Bering Sea and Aleutian Islands Crab Arbitration AGENCY: National Oceanic and Atmospheric... for Gulf of Alaska groundfish fisheries, arbitration system, monitoring, economic data collection, and cost recovery fee collection. The Crab Rationalization Program Arbitration System is established by...

  20. Origins of linguistic diversity in the Aleutian Islands.

    PubMed

    Berge, Anna

    2010-12-01

    The Aleut language, currently spoken along the Aleutian chain and the Pribilof and Commander islands, is the only language in its branch of the Eskimo-Aleut language family, and traditional methods of linguistic reconstruction have neither satisfactorily explained its relationship with languages on the Asian continent nor its development from Proto-Eskimo-Aleut. Linguistic reconstruction has always been important in understanding the prehistory and history of the Aleuts, and new approaches in comparative linguistics, more comprehensive information on typological features of neighboring languages, and continuing language documentation allow us to propose a rich and continuous history of contact with various groups of people. I evaluate evidence that the Aleut language may have been shaped by contact with neighbors in Asia and Alaska, eventually giving rise to its differentiation from the Eskimo languages. I look at dialect differentiation along the Aleutian chain and what this differentiation reveals about the migration trends of the Aleut along the chain. I look at the colonial expansion of the Aleut-speaking area and resulting additional varieties of Aleut in the historical period. Finally, I review the effects of the Russian and American colonial periods on the Aleut language and the severe endangerment that the language faces today as a result. I conclude that there is evidence of possible Aleut contact with both neighboring peoples; however, much of this evidence has not yet been subjected to systematic comparative reconstructions. Linguistic evidence supports theories of at least two westward expansions of Aleuts along the island chain, but it is not yet clear what motivated the dialect differentiations. Finally, I offer some thoughts on directions for future dialect studies and the continuing documentation of Aleut. PMID:21417884

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  2. Gabbroic and Peridotitic Enclaves from the 2008 Kasatochi Eruption, Aleutian Islands, Alaska

    NASA Astrophysics Data System (ADS)

    Kentner, A.; Nadin, E. S.; Izbekov, P. E.; Nye, C. J.; Neill, O. K.

    2012-12-01

    Kasatochi volcano of the Andreanof Islands in the western Aleutian Arc violently erupted over a two day period from August 7-8, 2008. The eruption involved multiple explosive events generating pyroclastic flows, which included abundant mafic and ultramafic enclaves that have since weathered out and accumulated in talus along the coast. These and other mafic enclaves sampled by modern island arc lavas provide insight into subduction magmatism because they emerge from a section of the subduction system that is less likely than shallower zones to be modified by magmatic processes such as mixing, assimilation, or fractionation. We present new whole rock, clinopyroxene, amphibole, plagioclase, and melt compositions from Kasatochi enclaves of the 2008 eruption. The highly crystalline (~40 vol. % phenocryst content), medium-K basaltic andesite host rock contains ~52-55 wt. % SiO2 and 0.6-0.9 wt. % K2O, and is composed of plagioclase, ortho- and clinopyroxene, amphibole, and Ti-magnetite in a microlite-rich groundmass. Upon eruption, this magma sampled two distinct enclave populations: gabbro and peridotite. The gabbro has abundant amphibole (mostly magnesio-hastingsite) and plagioclase with minor clinopyroxene, olivine, and magnetite, while the peridotite is composed of olivine with minor amounts of clinopyroxene and orthopyroxene. There is little textural variation amongst the peridotitic samples collected, but the gabbroic samples vary from layered to massive and cover a range in grain size from fine-grained to pegmatitic. The layered gabbros display centimeter-scale bands of alternating plagioclase- and amphibole-rich layers, with a strong preferential alignment of the amphibole grains. The coarser-grained samples are very friable, with ~10% pore space; disaggregation of these upon host-magma ascent likely formed the amphibole and plagioclase xenocrysts in the andesitic host. Based on the textural and compositional differences, we divide the enclaves into four groups

  3. Modeling potential tsunami sources for deposits near Unalaska Island, Aleutian Islands

    NASA Astrophysics Data System (ADS)

    La Selle, S.; Gelfenbaum, G. R.

    2013-12-01

    In regions with little seismic data and short historical records of earthquakes, we can use preserved tsunami deposits and tsunami modeling to infer if, when and where tsunamigenic earthquakes have occurred. The Aleutian-Alaska subduction zone in the region offshore of Unalaska Island is one such region where the historical and paleo-seismicity is poorly understood. This section of the subduction zone is not thought to have ruptured historically in a large earthquake, leading some to designate the region as a seismic gap. By modeling various historical and synthetic earthquake sources, we investigate whether or not tsunamis that left deposits near Unalaska Island were generated by earthquakes rupturing through Unalaska Gap. Preliminary field investigations near the eastern end of Unalaska Island have identified paleotsunami deposits well above sea level, suggesting that multiple tsunamis in the last 5,000 years have flooded low-lying areas over 1 km inland. Other indicators of tsunami inundation, such as a breached cobble beach berm and driftwood logs stranded far inland, were tentatively attributed to the March 9, 1957 tsunami, which had reported runup of 13 to 22 meters on Umnak and Unimak Islands, to the west and east of Unalaska. In order to determine if tsunami inundation could have reached the runup markers observed on Unalaska, we modeled the 1957 tsunami using GeoCLAW, a numerical model that simulates tsunami generation, propagation, and inundation. The published rupture orientation and slip distribution for the MW 8.6, 1957 earthquake (Johnson et al., 1994) was used as the tsunami source, which delineates a 1200 km long rupture zone along the Aleutian trench from Delarof Island to Unimak Island. Model results indicate that runup and inundation from this particular source are too low to account for the runup markers observed in the field, because slip is concentrated in the western half of the rupture zone, far from Unalaska. To ascertain if any realistic

  4. Distinctly different parental magmas for plutons and lavas in the central Aleutian arc

    NASA Astrophysics Data System (ADS)

    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

  5. Three new species of heteroderoidea (nematoda) from the Aleutian Islands

    SciTech Connect

    Bernard, E.C.

    1981-10-01

    Three new species of Heteroderoidea are described from Adak and Amchitka Islands in the Aleutian chain. Second-stage juveniles of Thecavermiculatus crassicrustata, n. sp., differ from those of T. gracililancea Robbins by having longer stylets (40 to 50 ..mu..m vs 19 to 22 ..mu..m). The female of T. crassicrustata has a longer neck, a more posterior excretory pore, and lacks a posterior protuberance. Meloidodera eurytyla, n. sp., differs from other Meloidodera spp. in that second-stage juveniles have longer stylets (32 to 35 ..mu..m) and much more massive styletknobs, while males have a longitudinally striated basal head annule. Meloidogyne subarctica, n. sp., can be separated from other Meloidogyne spp. by combinations of the following characteristics: perineal pattern with large oval areas in the tail region devoid of striae, arch with few unbroken striae; female excretory pore 1.5 to 2.5 x the stylet length from the anterior end; haploid chromosome number = 18; the spermatheca filled with sperm; stylet length of second-stage juveniles 13.5 to 15.4 ..mu..m.

  6. Hair methylmercury levels of mummies of the Aleutian Islands, Alaska

    SciTech Connect

    Egeland, G.M. Ponce, Rafael Bloom, Nicolas S. Knecht, Rick Loring, Stephen Middaugh, John P.

    2009-04-15

    Ancient human hair specimens can shed light on the extent of pre-historic exposures to methylmercury and provide valuable comparison data with current-day exposures, particularly for Indigenous Peoples who continue to rely upon local traditional food resources. Human hair from ancient Aleutian Island Native remains were tested for total and methylmercury (Hg, MeHg) and were radiocarbon dated. The remains were approximately 500 years old (1450 A.D.). For four adults, the mean and median total hair mercury concentration was 5.8 ppm (SD=0.9). In contrast, MeHg concentrations were lower with a mean of 1.2 ppm (SD=1.8) and a median of 0.54 ppm (0.12-3.86). For the five infants, the mean and median MeHg level was 1.2 ppm (SD=1.8) and 0.20 ppm (0.007-4.61), respectively. Segmental analyses showed variations in MeHg concentrations in 1-cm segments, consistent with fluctuations in naturally occurring exposure to mercury through dietary sources. The levels are comparable to or lower than those found in fish and marine mammal-eating populations today who rely far less on subsistence food than pre-historic humans. The findings are, therefore, compatible with increased anthropogenic release of trace metals during the past several centuries.

  7. Petrogenesis of Mafic and Ultramafic Enclaves from the Central Aleutian Arc, and Implications for the Formation of New Crust

    NASA Astrophysics Data System (ADS)

    Nadin, E. S.; Kentner, A. E.; Nye, C. J.; Izbekov, P. E.

    2014-12-01

    Mafic and ultramafic enclaves from the 2008 eruption of Kasatochi volcano, central Aleutians, provide insight into the sub-arc structure in this section of the subduction zone. Textural, mineralogical, and chemical similarities between these enclaves and those from neighboring Adak Island volcanoes suggest that sub-arc conditions are similar enough to form the same igneous "strata" in this part of the arc. Kasatochi gabbroic enclaves are undeformed cumulates of 0.1-11 cm euhedral plagioclase and pargasitic hornblende crystals, with minor clinopyroxene and magnetite and cryptocrystalline interstitial glass. Adak gabbro inclusions also contain plagioclase, pargasitic hornblende, clinopyroxene, and magnetite. Gabbroic enclaves from both volcanic islands typically have elongate and aligned minerals, in contrast with the granular textures of the ultramafic suite. Kasatochi ultramafic samples include wehrlite, clinopyroxenite, and olivine clinopyroxenite with Fo83-84 olivine, Mg- and Ca- rich clinopyroxene, and spinel, and pargasitic hornblende present only as a secondary, interstitial phase. Similarly, wehrlite and clinopyroxenite samples from Adak also contain forsteritic olivine, clinopyroxene, spinel, and interstitial pargasitic hornblende. The presence of hornblende and the lack of deformation textures in the cumulate gabbros from both islands suggest that these rocks were stored under similar pressure, temperature, and host-magma conditions prior to eruption. Kasatochi gabbro enclaves are compositionally related to their host basaltic andesite, as suggested by fractionation trends. There is no apparent chemical relationship between the ultramafic enclaves and the 2008 basaltic andesite, nor are these samples ever found within their host rock. Based on compositional similarities to ultramafic xenoliths from Adak Island, the Kasatochi ultramafic suite could have formed by the fractionation of spinel-lherzolite in the upper mantle. Whole-rock REE analyses show

  8. Bayesian probabilities for Mw 9.0+ earthquakes in the Aleutian Islands from a regionally scaled global rate

    NASA Astrophysics Data System (ADS)

    Butler, Rhett; Frazer, L. Neil; Templeton, William J.

    2016-05-01

    We use the global rate of Mw ≥ 9.0 earthquakes, and standard Bayesian procedures, to estimate the probability of such mega events in the Aleutian Islands, where they pose a significant risk to Hawaii. We find that the probability of such an earthquake along the Aleutians island arc is 6.5% to 12% over the next 50 years (50% credibility interval) and that the annualized risk to Hawai'i is about $30 M. Our method (the regionally scaled global rate method or RSGR) is to scale the global rate of Mw 9.0+ events in proportion to the fraction of global subduction (units of area per year) that takes place in the Aleutians. The RSGR method assumes that Mw 9.0+ events are a Poisson process with a rate that is both globally and regionally stationary on the time scale of centuries, and it follows the principle of Burbidge et al. (2008) who used the product of fault length and convergence rate, i.e., the area being subducted per annum, to scale the Poisson rate for the GSS to sections of the Indonesian subduction zone. Before applying RSGR to the Aleutians, we first apply it to five other regions of the global subduction system where its rate predictions can be compared with those from paleotsunami, paleoseismic, and geoarcheology data. To obtain regional rates from paleodata, we give a closed-form solution for the probability density function of the Poisson rate when event count and observation time are both uncertain.

  9. 76 FR 43658 - Fisheries of the Exclusive Economic Zone Off Alaska; Bering Sea and Aleutian Islands Crab...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-07-21

    ... Alaska; Bering Sea and Aleutian Islands Crab Rationalization Cost Recovery Program AGENCY: National... under the Bering Sea and Aleutian Islands Crab Rationalization Program. This action is intended to provide holders of crab allocations with the fee percentage for the 2011/2012 crab fishing year so...

  10. 76 FR 44297 - Fisheries of the Exclusive Economic Zone Off Alaska; Allocating Bering Sea and Aleutian Islands...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-07-25

    ... Economic Zone Off Alaska; Allocating Bering Sea and Aleutian Islands King and Tanner Crab Fishery Resources.... SUMMARY: The Bering Sea/Aleutian Islands (BSAI) Crab Rationalization Program (CR Program) allocates BSAI crab resources among harvesters, processors, and coastal communities. Amendment 30 would amend...

  11. 75 FR 43147 - Fisheries of the Exclusive Economic Zone Off Alaska; Bering Sea and Aleutian Islands Crab...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-07-23

    ... Alaska; Bering Sea and Aleutian Islands Crab Rationalization Cost Recovery Program AGENCY: National... under the Bering Sea and Aleutian Islands Crab Rationalization Program. This action is intended to provide holders of crab allocations with the fee percentage for the 2010/2011 crab fishing year so...

  12. 77 FR 44216 - Fisheries of the Exclusive Economic Zone Off Alaska; Bering Sea and Aleutian Islands Crab...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-07-27

    ... Alaska; Bering Sea and Aleutian Islands Crab Rationalization Cost Recovery Program AGENCY: National... recovery under the Bering Sea and Aleutian Islands Crab Rationalization Program. This action is intended to provide holders of crab allocations with the fee percentage for the 2012/2013 crab fishing year....

  13. 78 FR 46577 - Fisheries of the Exclusive Economic Zone Off Alaska; Bering Sea and Aleutian Islands Crab...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-08-01

    ... Alaska; Bering Sea and Aleutian Islands Crab Rationalization Cost Recovery Program AGENCY: National... under the Bering Sea and Aleutian Islands Crab Rationalization Program. This action is intended to provide holders of crab allocations with the fee percentage for the 2013/2014 crab fishing year so...

  14. 78 FR 24362 - Fisheries of the Exclusive Economic Zone Off Alaska; Greenland Turbot in the Aleutian Islands...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-04-25

    ... the final 2013 and 2014 harvest specifications for groundfish in the BSAI (78 FR 13813, March 1, 2013... Economic Zone Off Alaska; Greenland Turbot in the Aleutian Islands Subarea of the Bering Sea and Aleutian Islands Management Area AGENCY: National Marine Fisheries Service (NMFS), National Oceanic and...

  15. 50 CFR Figure 6 to Subpart E of... - Alaska Peninsula and Aleutian Islands Rural and Non-Rural Areas

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 50 Wildlife and Fisheries 7 2010-10-01 2010-10-01 false Alaska Peninsula and Aleutian Islands Rural and Non-Rural Areas 6 Figure 6 to Subpart E of Part 300 Wildlife and Fisheries INTERNATIONAL..., Subpt. E, Fig. 6 Figure 6 to Subpart E of Part 300—Alaska Peninsula and Aleutian Islands Rural and...

  16. 76 FR 49417 - Fisheries of the Exclusive Economic Zone Off Alaska; Bering Sea and Aleutian Islands Management...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-08-10

    ...NMFS proposes regulations that would implement Amendment 93 to the Fishery Management Plan for Groundfish of the Bering Sea and Aleutian Islands Management Area (FMP). This proposed rule would amend the Bering Sea and Aleutian Islands Amendment 80 Program to modify the criteria for forming and participating in a harvesting cooperative. This action is necessary to encourage greater......

  17. 50 CFR 600.1106 - Longline catcher processor subsector Bering Sea and Aleutian Islands (BSAI) non-pollock...

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... Bering Sea and Aleutian Islands (BSAI) non-pollock groundfish species fee payment and collection system... Bering Sea and Aleutian Islands (BSAI) non-pollock groundfish species fee payment and collection system... chapter defined as groundfish area/species endorsements. (c) Reduction loan amount. The reduction...

  18. 50 CFR 600.1106 - Longline catcher processor subsector Bering Sea and Aleutian Islands (BSAI) non-pollock...

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... Bering Sea and Aleutian Islands (BSAI) non-pollock groundfish species fee payment and collection system... Bering Sea and Aleutian Islands (BSAI) non-pollock groundfish species fee payment and collection system... chapter defined as groundfish area/species endorsements. (c) Reduction loan amount. The reduction...

  19. 50 CFR 600.1106 - Longline catcher processor subsector Bering Sea and Aleutian Islands (BSAI) non-pollock...

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... Bering Sea and Aleutian Islands (BSAI) non-pollock groundfish species fee payment and collection system... Bering Sea and Aleutian Islands (BSAI) non-pollock groundfish species fee payment and collection system... chapter defined as groundfish area/species endorsements. (c) Reduction loan amount. The reduction...

  20. 50 CFR 600.1106 - Longline catcher processor subsector Bering Sea and Aleutian Islands (BSAI) non-pollock...

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... Bering Sea and Aleutian Islands (BSAI) non-pollock groundfish species fee payment and collection system... Bering Sea and Aleutian Islands (BSAI) non-pollock groundfish species fee payment and collection system... chapter defined as groundfish area/species endorsements. (c) Reduction loan amount. The reduction...

  1. Spawning phenology and geography of Aleutian Islands and eastern Bering Sea Pacific cod (Gadus macrocephalus)

    NASA Astrophysics Data System (ADS)

    Neidetcher, Sandra K.; Hurst, Thomas P.; Ciannelli, Lorenzo; Logerwell, Elizabeth A.

    2014-11-01

    Pacific cod (Gadus macrocephalus) is an economically and ecologically important species in the southeastern Bering Sea and Aleutian Islands, yet little is known about the spawning dynamics of Pacific cod in these regions. To address this knowledge gap, we applied a gross anatomical maturity key for Pacific cod to describe temporal and spatial patterns of reproductive status over three winter spawning seasons: 2005, 2006, and 2007. Maturity status of female Pacific cod was assessed by fishery observers during sampling of commercial catches and used to construct maps showing spawning activity in the Bering Sea and Aleutian Islands. Most spawning activity was observed on the Bering Sea shelf and Aleutian Island plateaus between 100 and 200 m depth. Data for those days when a high percentage of spawning stage fish were observed were used to identify areas with concentrations of spawning fish. Spawning concentrations were identified north of Unimak Island, in the vicinity of the Pribilof Islands, at the shelf break near Zhemchug Canyon, and adjacent to islands in the central and western Aleutian Islands along the continental shelf. The spawning season was found to begin in the last days of February or early March and extend through early to mid-April. Variation in spawning time (averaging ~10 days between years) may have been associated with a change from warm (2005) to cold (2007) climate conditions during the study period. Our information on Pacific cod spawning patterns will help inform fishery management decisions, models of spawning and larval dispersal and the spatial structure of the stock.

  2. Avian mortality associated with a volcanic gas seep at Kiska Island, Aleutian Islands, Alaska

    USGS Publications Warehouse

    Bond, Alexander L.; Evans, William C.; Jones, Ian L.

    2012-01-01

    We identified natural pits associated with avian mortality at the base of Kiska Volcano in the western Aleutian Islands, Alaska in 2007. Living, moribund, and dead birds were regularly found at low spots in a canyon between two lava flows during 2001–2006, but the phenomenon was attributed to natural trapping and starvation of fledgling seabirds (mostly Least Auklets, Aethia pusilla) at a colony site with >1 million birds present. However, 302 birds of eight species, including passerines, were found dead at the site during 2007–2010, suggesting additional factors were involved. Most carcasses showed no signs of injury and concentrations of dead birds had accumulated in a few distinctive low pits in the canyon. Gas samples from these locations showed elevated CO2 concentrations in late 2010. Analysis of carcasses indicated no evidence of blunt trauma or internal bleeding. Volcanic gases accumulating at these poorly ventilated sites may have caused the observed mortality, but are temporally variable. Most auklets breeding in the Aleutian Islands do so in recent lava flows that provide breeding habitat; our study documents a cost of this unusual habitat selection.

  3. Double Glacier Volcano, a 'new' Quaternary volcano in the eastern Aleutian volcanic arc

    USGS Publications Warehouse

    Reed, B.L.; Lanphere, M.A.; Miller, T.P.

    1992-01-01

    The Double Glacier Volcano (DGV) is a small dome complex of porphyritic hornblende andesite and dacite that is part of the Cook Inlet segment of Quaternary volcanoes of the eastern Aleutian arc. Its discovery reduces the previously described large volcano gap in Cook Inlet segment to a distance similar to that between other volcanoes in the area. DGV lavas are medium-K, calcalkaline andesites and dacites with concentrations of major and minor elements similar to the other Quaternary volcanoes of the Cook Inlet segment. Available K-Ar ages indicate that DGV was active 600-900 ka. ?? 1992 Springer-Verlag.

  4. 76 FR 68161 - Proposed Information Collection; Comment Request; Aleutian Islands Pollock Fishery Requirements

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-11-03

    ... signed into law on January 23, 2004. Section 803 of this law allocates the Aleutian Islands (AI) directed... Aleut Corporation to authorize one or more agents for activities necessary for conducting the AI directed pollock fishery. Management provisions for the AI directed pollock fishery include:...

  5. 50 CFR 600.1103 - Bering Sea and Aleutian Islands (BSAI) Crab species program.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... Sound blue king crab. NVDC means the U.S. Coast Guard's National Vessel Documentation Center located in...) Crab species program. 600.1103 Section 600.1103 Wildlife and Fisheries FISHERY CONSERVATION AND... Aleutian Islands (BSAI) Crab species program. (a) Purpose. This section's purpose is to implement...

  6. 50 CFR 600.1103 - Bering Sea and Aleutian Islands (BSAI) Crab species program.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 50 Wildlife and Fisheries 12 2014-10-01 2014-10-01 false Bering Sea and Aleutian Islands (BSAI) Crab species program. 600.1103 Section 600.1103 Wildlife and Fisheries FISHERY CONSERVATION AND MANAGEMENT, NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION, DEPARTMENT OF COMMERCE MAGNUSON-STEVENS ACT PROVISIONS Specific Fishery or Program...

  7. 50 CFR 600.1103 - Bering Sea and Aleutian Islands (BSAI) Crab species program.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 50 Wildlife and Fisheries 12 2012-10-01 2012-10-01 false Bering Sea and Aleutian Islands (BSAI) Crab species program. 600.1103 Section 600.1103 Wildlife and Fisheries FISHERY CONSERVATION AND MANAGEMENT, NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION, DEPARTMENT OF COMMERCE MAGNUSON-STEVENS ACT PROVISIONS Specific Fishery or Program...

  8. Observations of deep long-period (DLP) seismic events beneath Aleutian arc volcanoes; 1989-2002

    USGS Publications Warehouse

    Power, J.A.; Stihler, S.D.; White, R.A.; Moran, S.C.

    2004-01-01

    Between October 12, 1989 and December 31, 2002, the Alaska Volcano Observatory (AVO) located 162 deep long-period (DLP) events beneath 11 volcanic centers in the Aleutian arc. These events generally occur at mid- to lower-crustal depths (10-45 km) and are characterized by emergent phases, extended codas, and a strong spectral peak between 1.0 and 3.0 Hz. Observed wave velocities and particle motions indicate that the dominant phases are P- and S-waves. DLP epicenters often extend over broad areas (5-20 km) surrounding the active volcanoes. The average reduced displacement of Aleutian DLPs is 26.5 cm2 and the largest event has a reduced displacement of 589 cm2 (or ML 2.5). Aleutian DLP events occur both as solitary events and as sequences of events with several occurring over a period of 1-30 min. Within the sequences, individual DLPs are often separated by lower-amplitude volcanic tremor with a similar spectral character. Occasionally, volcano-tectonic earthquakes that locate at similar depths are contained within the DLP sequences. At most, Aleutian volcanoes DLPs appear to loosely surround the main volcanic vent and occur as part of background seismicity. A likely explanation is that they reflect a relatively steady-state process of magma ascent over broad areas in the lower and middle portions of the crust. At Mount Spurr, DLP seismicity was initiated by the 1992 eruptions and then slowly declined until 1997. At Shishaldin Volcano, a short-lived increase in DLP seismicity occurred about 10 months prior to the April 19, 1999 eruption. These observations suggest a link between eruptive activity and magma flux in the mid- to lower-crust and uppermost mantle.

  9. Condition of groundfish resources of the eastern Bering Sea and Aleutian Islands region in 1982

    SciTech Connect

    Bakkala, R.G.; Low, L.; Ito, D.H.; Narita, R.E.; Ronholt, L.L.

    1983-03-01

    This report contains an assessment of the condition of groundfish and squid in the eastern Bering Sea and Aleutian Islands region through 1982. The assessments are based on species-by-species analyses of the data collected from the commercial fishery and research vessel surveys. Most of the resources in the Bering Sea-Aleutians management region are in good condition, including walleye pollock, Pacific cod, the flatfishes, and Atka mackerel. Pacific cod and yellowfin sole are in excellent condition and at historic high levels of abundance.

  10. InSAR imaging of volcanic deformation over cloud-prone areas - Aleutian islands

    USGS Publications Warehouse

    Lu, Zhong

    2007-01-01

    Interferometric synthetic aperture radar (INSAR) is capable of measuring ground-surface deformation with centimeter-tosubcentimeter precision and spatial resolution of tens-of meters over a relatively large region. With its global coverage and all-weather imaging capability, INSAR is an important technique for measuring ground-surface deformation of volcanoes over cloud-prone and rainy regions such as the Aleutian Islands, where only less than 5 percent of optical imagery is usable due to inclement weather conditions. The spatial distribution of surface deformation data, derived from INSAR images, enables the construction of detailed mechanical models to enhance the study of magmatic processes. This paper reviews the basics of INSAR for volcanic deformation mapping and the INSAR studies of ten Aleutian volcanoes associated with both eruptive and noneruptive activity. These studies demonstrate that all-weather INSAR imaging can improve our understanding of how the Aleutian volcanoes work and enhance our capability to predict future eruptions and associated hazards.

  11. SURFACE REMEDIATION IN THE ALEUTIAN ISLANDS: A CASE STUDY OF AMCHITKA ISLAND, ALASKA

    SciTech Connect

    Giblin, M. O.; Stahl, D. C.; Bechtel, J. A.

    2002-02-25

    Amchitka Island, Alaska, was at one time an integral player in the nation's defense program. Located in the North Pacific Ocean in the Aleutian Island archipelago, the island was intermittently inhabited by several key government agencies, including the U.S. Army, the U.S. Atomic Energy Commission (predecessor agency to the U.S. Department of Energy), and the U.S. Navy. Since 1993, the U.S. Department of Energy (DOE) has conducted extensive investigations on Amchitka to determine the nature and extent of contamination resulting from historic nuclear testing. The uninhabited island was the site of three high-yield nuclear tests from 1965 to 1971. These test locations are now part of the DOE's National Nuclear Security Administration Nevada Operations Office's Environmental Management Program. In the summer of 2001, the DOE launched a large-scale remediation effort on Amchitka to perform agreed-upon corrective actions to the surface of the island. Due to the lack of resources available on Amchitka and logistical difficulties with conducting work at such a remote location, the DOE partnered with the Navy and U.S. Army Corps of Engineers (USACE) to share certain specified costs and resources. Attempting to negotiate the partnerships while organizing and implementing the surface remediation on Amchitka proved to be a challenging endeavor. The DOE was faced with unexpected changes in Navy and USACE scope of work, accelerations in schedules, and risks associated with construction costs at such a remote location. Unfavorable weather conditions also proved to be a constant factor, often slowing the progress of work. The Amchitka Island remediation project experience has allowed the DOE to gain valuable insights into how to anticipate and mitigate potential problems associated with future remediation projects. These lessons learned will help the DOE in conducting future work more efficiently, and can also serve as a guide for other agencies performing similar work.

  12. Abundance, trends and distribution of baleen whales off Western Alaska and the central Aleutian Islands

    NASA Astrophysics Data System (ADS)

    Zerbini, Alexandre N.; Waite, Janice M.; Laake, Jeffrey L.; Wade, Paul R.

    2006-11-01

    Large whales were extensively hunted in coastal waters off Alaska, but current distribution, population sizes and trends are poorly known. Line transect surveys were conducted in coastal waters of the Aleutian Islands and the Alaska Peninsula in the summer of 2001-2003. Abundances of three species were estimated by conventional and multiple covariate distance sampling (MCDS) methods. Time series of abundance estimates were used to derive rates of increase for fin whales ( Balaenoptera physalus) and humpback whales ( Megaptera novaeangliae). Fin whales occurred primarily from the Kenai Peninsula to the Shumagin Islands, but were abundant only near the Semidi Islands and Kodiak. Humpback whales were found from the Kenai Peninsula to Umnak Island and were more abundant near Kodiak, the Shumagin Islands and north of Unimak Pass. Minke whales ( B. acutorostrata) occurred primarily in the Aleutian Islands, with a few sightings south of the Alaska Peninsula and near Kodiak Island. Humpback whales were observed in large numbers in their former whaling grounds. In contrast, high densities of fin whales were not observed around the eastern Aleutian Islands, where whaling occurred. Average abundance estimates (95% CI) for fin, humpback and minke whales were 1652 (1142-2389), 2644 (1899-3680), and 1233 (656-2315), respectively. Annual rates of increase were estimated at 4.8% (95% CI=4.1-5.4%) for fin and 6.6% (5.2-8.6%) for humpback whales. This study provides the first estimate of the rate of increase of fin whales in the North Pacific Ocean. The estimated trends are consistent with those of other recovering baleen whales. There were no sightings of blue or North Pacific right whales, indicating the continued depleted status of these species.

  13. A new population of Aleutian shield fern (Polystichum aleuticum C. Christens.) on Adak Island, Alaska

    USGS Publications Warehouse

    Talbot, S.L.; Talbot, S. S.

    2002-01-01

    We report and describe a new population of the endangered Aleutian shield fern (Polystichum aleuticum C. Christens.) discovered on Mount Reed, Adak Island, Alaska. The new population is located at a lower elevation than the other known populations, placing the species' known elevational range between 338 m and 525 m. The discovery of this population is significant because it increases the total number of known populations and individuals for the species.

  14. Four new species of Haplosclerida (Porifera, Demospongiae) from the Aleutian Islands, Alaska.

    PubMed

    Lehnert, Helmut; Stone, Robert P

    2013-01-01

    Four new species of Haplosclerida are described from the Aleutian Islands, Alaska: Callyspongia mucosa n.sp., Cladocroce infundibulum n. sp., Cladocroce attu n. sp. and Cladocroce kiska n. sp. The new species are described and compared to congeners of the region. This is the northernmost record of the genus Callyspongia and the first record of the subgenus Callyspongia from the North Pacific Ocean. To accommodate Cladocroce kiska in its genus the definition has to be broadened to allow sigmas. PMID:26106744

  15. Geology and geochemistry of the Geyser Bight Geothermal Area, Umnak Island, Aleutian Islands, Alaska

    SciTech Connect

    Nye, C.J. . Geophysical Inst. Alaska Dept. of Natural Resources, Fairbanks, AK . Div. of Geological and Geophysical Surveys); Motyka, R.J. . Div. of Geological and Geophysical Surveys); Turner, D.L. . Geophysical Inst.); Liss, S.A. (Alaska Dept. of Natural Resources, Fairba

    1990-10-01

    The Geyser Bight geothermal area is located on Umnak Island in the central Aleutian Islands. It contains one of the hottest and most extensive areas of thermal springs and fumaroles in Alaska, and is only documented site in Alaska with geysers. The zone of hot springs and fumaroles lies at the head of Geyser Creek, 5 km up a broad, flat, alluvial valley from Geyser Bight. At present central Umnak is remote and undeveloped. This report describes results of a combined program of geologic mapping, K-Ar dating, detailed description of hot springs, petrology and geochemistry of volcanic and plutonic rock units, and chemistry of geothermal fluids. Our mapping documents the presence of plutonic rock much closer to the area of hotsprings and fumaroles than previously known, thus increasing the probability that plutonic rock may host the geothermal system. K-Ar dating of 23 samples provides a time framework for the eruptive history of volcanic rocks as well as a plutonic cooling age.

  16. Geology and 40Ar/39Ar Geochronology of Akutan Volcano, Eastern Aleutian Islands

    NASA Astrophysics Data System (ADS)

    Coombs, M. L.; Jicha, B. R.

    2013-12-01

    40Ar/39Ar dating and new whole-rock geochemical analyses are used to establish an eruptive chronology for Akutan volcano, Akutan Island, in the eastern Aleutian island arc. Akutan Island (166° W, 54.1° N) is the site of long-lived volcanism and the entire island comprises volcanic rocks as old as 3.3 Ma (Richter et al., 1998, USGS Open-File 98-135). Our current focus is on the 225 km2 western half of the island, which is home to the Holocene active cone, Holocene to latest Pleistocene satellite vents, and underlying middle Pleistocene volcanic basement rocks. Eruptive products span the tholeiitic-calc-alkaline boundary, are medium-K, and range from basalt to dacite. Furnace incremental heating experiments on groundmass separates of 38 samples resulted in 29 40Ar/39Ar ages. The remainder did not yield radiogenic 40Ar contents and are likely Holocene in age. The oldest ages (1251×10 and 1385×12 ka) are from a wedge of flat-lying dissected lavas north of the Holocene cone; these likely represent the upper part of the volcanic basement that underlies the entire island. Above a major unconformity lie basaltic andesite to dacite lavas that range from 765× 4 to 522×8 ka. The eroded remnants of the source volcano for these flows appears to crop out as a series of variably hydrothermally altered breccias and domes 5 km east-northeast of the current summit. A 625 m-tall eroded basaltic center, Lava Peak, sits 6 km northwest of the summit; its deeply incised western flank exposes lava flows and a plug. Two flows are dated at 598×16 and 602×15 ka. A high ridge 1.5 km south of the summit is made of oxidized, mostly andesitic lavas 284-249 ka old; these are presumably the remnants of an eruptive center located near the current cone. Flat Top Peak, 3.5 km southwest of the summit, produced almost exclusively basalts and six dated lavas range from 155×8 to 98×18 ka. Lavas from Flat Top (1065 m asl) are deeply eroded suggesting extensive ice cover during marine isotope

  17. 77 FR 74161 - Fisheries of the Exclusive Economic Zone Off Alaska; Allocating Bering Sea and Aleutian Islands...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-12-13

    ... Program. Regulations implementing these amendments were published on March 2, 2005 (70 FR 10174), and are... blue king crab, and Pribilof Islands red and blue king crab. The North Region is north of 54 20' N... Economic Zone Off Alaska; Allocating Bering Sea and Aleutian Islands King and Tanner Crab Fishery...

  18. Dispersal and behavior of pacific halibut hippoglossus stenolepis in the bering sea and Aleutian islands region

    USGS Publications Warehouse

    Seitz, A.C.; Loher, T.; Norcross, B.L.; Nielsen, J.L.

    2011-01-01

    Currently, it is assumed that eastern Pacific halibut Hippoglossus stenolepis belong to a single, fully mixed population extending from California through the Bering Sea, in which adult halibut disperse randomly throughout their range during their lifetime. However, we hypothesize that hali but dispersal is more complex than currently assumed and is not spatially random. To test this hypo thesis, we studied the seasonal dispersal and behavior of Pacific halibut in the Bering Sea and Aleutian Islands (BSAI). Pop-up Archival Transmitting tags attached to halibut (82 to 154 cm fork length) during the summer provided no evidence that individuals moved out of the Bering Sea and Aleutian Islands region into the Gulf of Alaska during the mid-winter spawning season, supporting the concept that this region contains a separate spawning group of adult halibut. There was evidence for geographically localized groups of halibut along the Aleutian Island chain, as all of the individuals tagged there displayed residency, with their movements possibly impeded by tidal currents in the passes between islands. Mid-winter aggregation areas of halibut are assumed to be spawning grounds, of which 2 were previously unidentified and extend the species' presumed spawning range ~1000 km west and ~600 km north of the nearest documented spawning area. If there are indeed independent spawning groups of Pacific halibut in the BSAI, their dynamics may vary sufficiently from those of the Gulf of Alaska, so that specifically accounting for their relative segregation and unique dynamics within the larger population model will be necessary for correctly predicting how these components may respond to fishing pressure and changing environmental conditions.?? Inter-Research 2011.

  19. 50 CFR Table 24 to Part 679 - Except as Noted, Locations in the Aleutian Islands Habitat Conservation Area Open to Nonpelagic...

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 50 Wildlife and Fisheries 9 2010-10-01 2010-10-01 false Except as Noted, Locations in the Aleutian Islands Habitat Conservation Area Open to Nonpelagic Trawl Fishing 24 Table 24 to Part 679 Wildlife and... 24 to Part 679—Except as Noted, Locations in the Aleutian Islands Habitat Conservation Area Open...

  20. 50 CFR Table 24 to Part 679 - Except as Noted, Locations in the Aleutian Islands Habitat Conservation Area Open to Nonpelagic...

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 50 Wildlife and Fisheries 11 2011-10-01 2011-10-01 false Except as Noted, Locations in the Aleutian Islands Habitat Conservation Area Open to Nonpelagic Trawl Fishing 24 Table 24 to Part 679... Table 24 to Part 679—Except as Noted, Locations in the Aleutian Islands Habitat Conservation Area...

  1. 50 CFR Table 24 to Part 679 - Except as Noted, Locations in the Aleutian Islands Habitat Conservation Area Open to Nonpelagic...

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 50 Wildlife and Fisheries 13 2012-10-01 2012-10-01 false Except as Noted, Locations in the Aleutian Islands Habitat Conservation Area Open to Nonpelagic Trawl Fishing 24 Table 24 to Part 679... Table 24 to Part 679—Except as Noted, Locations in the Aleutian Islands Habitat Conservation Area...

  2. 50 CFR Table 24 to Part 679 - Except as Noted, Locations in the Aleutian Islands Habitat Conservation Area Open to Nonpelagic...

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 50 Wildlife and Fisheries 13 2014-10-01 2014-10-01 false Except as Noted, Locations in the Aleutian Islands Habitat Conservation Area Open to Nonpelagic Trawl Fishing 24 Table 24 to Part 679... Table 24 to Part 679—Except as Noted, Locations in the Aleutian Islands Habitat Conservation Area...

  3. 50 CFR Table 24 to Part 679 - Except as Noted, Locations in the Aleutian Islands Habitat Conservation Area Open to Nonpelagic...

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 50 Wildlife and Fisheries 13 2013-10-01 2013-10-01 false Except as Noted, Locations in the Aleutian Islands Habitat Conservation Area Open to Nonpelagic Trawl Fishing 24 Table 24 to Part 679... Table 24 to Part 679—Except as Noted, Locations in the Aleutian Islands Habitat Conservation Area...

  4. Genetic structure of the Common Eider in the western Aleutian Islands prior to fox eradication

    USGS Publications Warehouse

    Sonsthagen, Sarah A.; Talbot, Sandra L.; Wilson, Robert E.; Petersen, Margaret R.; Williams, Jeffrey C.; Byrd, G. Vernon; McCracken, Kevin G.

    2013-01-01

    Since the late 18th century bird populations residing in the Aleutian Archipelago have been greatly reduced by introduced arctic foxes (Alopex lagopus). We analyzed data from microsatellite, nuclear intron, and mitochondrial (mtDNA) loci to examine the spatial genetic structure, demography, and gene flow among four Aleutian Island populations of the Common Eider (Somateria mollissima) much reduced by introduced foxes. In mtDNA, we found high levels of genetic structure within and between island groups (ΦST = 0.643), but we found no population subdivision in microsatellites or nuclear introns. Differences in genetic structure between the mitochondrial and nuclear genomes are consistent with the Common Eider's breeding and winter biology, as females are highly philopatric and males disperse. Nevertheless, significant differences between islands in the mtDNA of males and marginal significance (P =0.07) in the Z-linked locus Smo 1 suggest that males may also have some level of fidelity to island groups. Severe reduction of populations by the fox, coupled with females' high philopatry, may have left the genetic signature of a bottleneck effect, resulting in the high levels of genetic differentiation observed in mtDNA (ΦST = 0.460–0.807) between islands only 440 km apart. Reestablishment of the Common Eider following the fox's eradication was likely through recruitment from within the islands and bolstered by dispersal from neighboring islands, as suggested by the lack of genetic structure and asymmetry in gene flow between Attu and the other Near Islands.

  5. An introduced predator alters Aleutian Island plant communities by thwarting nutrient subsidies

    USGS Publications Warehouse

    Maron, J.L.; Estes, J.A.; Croll, D.A.; Danner, E.M.; Elmendorf, S.C.; Buckelew, S.L.

    2006-01-01

    The ramifying effects of top predators on food webs traditionally have been studied within the framework of trophic cascades. Trophic cascades are compelling because they embody powerful indirect effects of predators on primary production. Although less studied, indirect effects of predators may occur via routes that are not exclusively trophic. We quantified how the introduction of foxes onto the Aleutian Islands transformed plant communities by reducing abundant seabird populations, thereby disrupting nutrient subsidies vectored by seabirds from sea to land. We compared soil and plant fertility, plant biomass and community composition, and stable isotopes of nitrogen in soil, plants, and other organisms on nine fox-infested and nine historically fox-free islands across the Aleutians. Additionally, we experimentally augmented nutrients on a fox-infested island to test whether differences in plant productivity and composition between fox-infested and fox-free islands could have arisen from differences in nutrient inputs between island types. Islands with historical fox infestations had soils low in phosphorus and nitrogen and plants low in tissue nitrogen. Soils, plants, slugs, flies, spiders, and bird droppings on these islands had low d15N values indicating that these organisms obtained nitrogen from internally derived sources. In contrast, soils, plants, and higher trophic level organisms on fox-free islands had elevated d15N signatures indicating that they utilized nutrients derived from the marine environment. Furthermore, soil phosphorus (but not nitrogen) and plant tissue nitrogen were higher on fox-free than fox-infested islands. Nutrient subsidized fox-free islands supported lush, high biomass plant communities dominated by graminoids. Fox-infested islands were less graminoid dominated and had higher cover and biomass of low-lying forbs and dwarf shrubs. While d15N profiles of soils and plants and graminoid biomass varied with island size and distance from

  6. Neotectonics and recent uplift at Kamchatka and Aleutian arc junction, Kamchatka Cape area, NE Russia

    NASA Astrophysics Data System (ADS)

    Pflanz, Dorthe; Gaedicke, Christoph; Freitag, Ralf; Krbetschek, Matthias; Tsukanov, Nikolay; Baranov, Boris

    2013-04-01

    The tectonic position of the Kamchatka Cape Peninsula at the junction of the active Kuril-Kamchatka and Aleutian arcs exposes the coastline of the peninsula to strong neotectonic activities. Fracture zones have variable influence on uplift of the Kamchatka Cape Peninsula. Relevant morphologic indicators of neotectonic activity are multilevel, highly uplifted marine terraces and terraces displaced along active faults. Recent uplift rates of coastal sediments are determined by remote sensing via ASTER and SRTM DEM combined with optically stimulated luminescence dating (OSL). On the Kamchatka Cape Peninsula, terraces from the same generation are mapped at different elevations by remote sensing methods. After defining different areas of uplifted terraces, four neotectonic blocks are identified. According to apatite fission track data, the mean differential exhumation rates range from 0.2 to 1.2 mm year-1 across the blocks since Late Miocene. The OSL data presented point to significant higher uplift rates of up to 3 ± 0.5 and 4.3 ± 1 mm year-1, which indicates an acceleration of the vertical movement along the coast of Kamchatka Cape Peninsula in Upper Pleistocene and Holocene times.

  7. Status and distribution of the Kittlitz's Murrelet Brachyramphus brevirostris along the Alaska Peninsula and Kodiak and Aleutian Islands, Alaska

    USGS Publications Warehouse

    Madison, Erica N.; Piatt, John F.; Arimitsu, Mayumi L.; Romano, Marc D.; van Pelt, Thomas I.; Nelson, S. Kim; Williams, Jeffrey C.; DeGange, Anthony R.

    2011-01-01

    The Kittlitz's Murrelet Brachyramphus brevirostris is adapted for life in glacial-marine ecosystems, being concentrated in the belt of glaciated fjords in the northern Gulf of Alaska from Glacier Bay to Cook Inlet. Most of the remaining birds are scattered along coasts of the Alaska Peninsula and Aleutian Islands, where they reside in protected bays and inlets, often in proximity to remnant glaciers or recently deglaciated landscapes. We summarize existing information on Kittlitz's Murrelet in this mainly unglaciated region, extending from Kodiak Island in the east to the Near Islands in the west. From recent surveys, we estimated that ~2400 Kittlitz's Murrelets were found in several large embayments along the Alaska Peninsula, where adjacent ice fields feed silt-laden water into the bays. On Kodiak Island, where only remnants of ice remain today, observations of Kittlitz's Murrelets at sea were uncommon. The species has been observed historically around the entire Kodiak Archipelago, however, and dozens of nest sites were found in recent years. We found Kittlitz's Murrelets at only a few islands in the Aleutian chain, notably those with long complex shorelines, high mountains and remnant glaciers. The largest population (~1600 birds) of Kittlitz's Murrelet outside the Gulf of Alaska was found at Unalaska Island, which also supports the greatest concentration of glacial ice in the Aleutian Islands. Significant populations were found at Atka (~1100 birds), Attu (~800) and Adak (~200) islands. Smaller numbers have been reported from Unimak, Umnak, Amlia, Kanaga, Tanaga, Kiska islands, and Agattu Island, where dozens of nest sites have been located in recent years. Most of those islands have not been thoroughly surveyed, and significant pockets of Kittlitz's Murrelets may yet be discovered. Our estimate of ~6000 Kittlitz's Murrelets along the Alaska Peninsula and Aleutian Islands is also likely to be conservative because of the survey protocols we employed (i.e. early

  8. Non-volcanic tremor in the Aleutian Islands captured by a mini-seismic array

    NASA Astrophysics Data System (ADS)

    Ghosh, A.; Prejean, S. G.

    2013-12-01

    The Aleutian Islands are an interesting place to study because of the presence of abundant seismicity, both subduction and volcano related. In addition to regular earthquakes, the Islands host both volcanic and non-volcanic tremor. To capture this rich variety of seismicity, we designed and installed a mini-seismic array on Akutan Island in 2012. Akutan is located in the eastern Aleutians just off the tip of the Alaska Peninsula, near the eastern edge of the 1957 Mw8.6 earthquake rupture zone. A mini-seismic array is particularly useful in this logistically challenging environment where land cover is limited. We recorded and analyzed about 2 months of data, and found both volcanic and non-volcanic events. Here we focus on non-volcanic tremor and its characteristics as captured by the Akutan array. Akutan Island and the surrounding area turn out to be prolific producers of tremor. An automatic beam-backprojection algorithm [Ghosh et al., 2009] detects almost daily tremor activity with durations ranging from several minutes to more than 3.5 hours. On average, beam-backprojection detects 1.3 hours of tremor activity per day and in total, it detects about 5 times more duration of tremor activity compared to a visual check for tremor signal using the existing seismic network. We observe tremor sources both west and east of the Akutan array. Western sources are the most active ones and their slowness parameters are consistent with the locations of low-frequency earthquakes detected by Brown et al., 2013. The eastern source area has not been identified previously and appears to be active for only a few times during this study, but shows continuous activity for several hours. In addition, we observe temporal evolution of slowness parameters consistent with steady tremor migration. Moreover, low frequency earthquakes with impulsive body wave phases are identified within the tremor signal. They show S-minus-P times consistent with their being located at the model plate

  9. Roles of magmatic oxygen fugacity and water content in generating signatures of continental crust in the Alaska-Aleutian arc

    NASA Astrophysics Data System (ADS)

    Kelley, K. A.; Cottrell, E.; Brounce, M. N.; Gentes, Z.

    2014-12-01

    Early depletion of Fe during magmatic differentiation is a characteristic of many arc magmas, and this may drive them towards the bulk composition of continental crust. In the Alaska-Aleutian arc, magmas are strongly Fe-depleted both in the east, where the arc sits atop pre-existing continental crust, and in the west, where the system is oceanic but convergence is highly oblique. Primary basaltic arc magmas may achieve early Fe depletion through a combination of high magmatic H2O, which delays silicate saturation, and high oxygen fugacity (fO2), which promotes early onset of Fe-oxide crystallization. Alternatively, low-Fe, high Mg# magmas may emerge directly from the arc mantle, possibly due to slab melting, driving mixing with Fe-rich basaltic magmas. Yet, the relative importance of H2O, fO2, and magmatic bulk composition in generating Fe-depletion is not clearly resolved. Here, we present new measurements of the oxidation state of Fe (Fe3+/∑Fe ratio; a proxy for magmatic fO2), in combination with major element and volatile data, of olivine-hosted melt inclusions from four Alaska-Aleutian arc volcanoes (Okmok, Seguam, Korovin, Augustine), acquired using XANES spectroscopy. We use the Tholeiitic Index (THI) of Zimmer et al., 2010 to quantify the behavior of Fe in each volcano magma series (<1 is Fe-depleted, >1 is Fe-enriched). These volcanoes span a range of THI, from 0.9-0.65. The Fe3+/∑Fe ratios of Aleutian basalts, corrected for fractional crystallization to 6 wt.% MgO (i.e., Fe3+/∑Fe6.0) range from 0.22-0.31 and correlate strongly with THI (r2>0.99), such that more Fe-depleted magmas contain a greater proportion of oxidized Fe. The maximum dissolved H2O contents of basaltic melt inclusions from these volcanoes also strongly correlate with THI (r2>0.96), and with measured Fe3+/∑Fe ratios (although H2O is not the direct cause of oxidation). These links point to a slab-derived origin of both H2O and oxidation and thus relate slab fluxes to the Fe

  10. 76 FR 55276 - Fisheries of the Exclusive Economic Zone Off Alaska; Octopus in the Bering Sea and Aleutian Islands

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-09-07

    ... of the BSAI (76 FR 11139, March 1, 2011) and an apportionment from the non-specified reserve of groundfish (76 FR 17360, March 29, 2011). In accordance with Sec. 679.20(d)(2), the Administrator, Alaska... Economic Zone Off Alaska; Octopus in the Bering Sea and Aleutian Islands AGENCY: National Marine...

  11. 50 CFR Figure 6 to Subpart E of... - Alaska Peninsula and Aleutian Islands Rural and Non-Rural Areas

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 50 Wildlife and Fisheries 9 2011-10-01 2011-10-01 false Alaska Peninsula and Aleutian Islands Rural and Non-Rural Areas 6 Figure 6 to Subpart E of Part 300 Wildlife and Fisheries INTERNATIONAL FISHING AND RELATED ACTIVITIES INTERNATIONAL FISHERIES REGULATIONS Pacific Halibut Fisheries Pt. 300, Subpt. E, Fig. 6 Figure 6 to Subpart E of Part...

  12. 50 CFR Figure 6 to Subpart E of... - Alaska Peninsula and Aleutian Islands Rural and Non-Rural Areas

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 50 Wildlife and Fisheries 11 2013-10-01 2013-10-01 false Alaska Peninsula and Aleutian Islands Rural and Non-Rural Areas 6 Figure 6 to Subpart E of Part 300 Wildlife and Fisheries INTERNATIONAL FISHING AND RELATED ACTIVITIES INTERNATIONAL FISHERIES REGULATIONS Pacific Halibut Fisheries Pt. 300, Subpt. E, Fig. 6 Figure 6 to Subpart E of Part...

  13. 50 CFR Figure 6 to Subpart E of... - Alaska Peninsula and Aleutian Islands Rural and Non-Rural Areas

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 50 Wildlife and Fisheries 11 2012-10-01 2012-10-01 false Alaska Peninsula and Aleutian Islands Rural and Non-Rural Areas 6 Figure 6 to Subpart E of Part 300 Wildlife and Fisheries INTERNATIONAL FISHING AND RELATED ACTIVITIES INTERNATIONAL FISHERIES REGULATIONS Pacific Halibut Fisheries Pt. 300, Subpt. E, Fig. 6 Figure 6 to Subpart E of Part...

  14. 50 CFR Figure 6 to Subpart E of... - Alaska Peninsula and Aleutian Islands Rural and Non-Rural Areas

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 50 Wildlife and Fisheries 11 2014-10-01 2014-10-01 false Alaska Peninsula and Aleutian Islands Rural and Non-Rural Areas 6 Figure 6 to Subpart E of Part 300 Wildlife and Fisheries INTERNATIONAL FISHING AND RELATED ACTIVITIES INTERNATIONAL FISHERIES REGULATIONS Pacific Halibut Fisheries Pt. 300, Subpt. E, Fig. 6 Figure 6 to Subpart E of Part...

  15. 76 FR 47155 - Fisheries of the Exclusive Economic Zone Off Alaska; Bering Sea and Aleutian Islands Crab...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-08-04

    ...NMFS has requested the Center for Independent Experts (CIE) to conduct a peer review of the agency's economic data collection program for the Bering Sea/Aleutian Islands crab fisheries managed under the BSAI Crab Rationalization program. The CIE, operated by Northern Taiga Ventures, Inc., provides independent peer reviews of NMFS's fisheries stock assessments and other science products. The......

  16. 50 CFR 600.1104 - Bering Sea and Aleutian Islands (BSAI) crab species fee payment and collection system.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 50 Wildlife and Fisheries 12 2014-10-01 2014-10-01 false Bering Sea and Aleutian Islands (BSAI) crab species fee payment and collection system. 600.1104 Section 600.1104 Wildlife and Fisheries FISHERY CONSERVATION AND MANAGEMENT, NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION, DEPARTMENT OF COMMERCE MAGNUSON-STEVENS ACT PROVISIONS...

  17. 50 CFR 600.1104 - Bering Sea and Aleutian Islands (BSAI) crab species fee payment and collection system.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 50 Wildlife and Fisheries 12 2012-10-01 2012-10-01 false Bering Sea and Aleutian Islands (BSAI) crab species fee payment and collection system. 600.1104 Section 600.1104 Wildlife and Fisheries FISHERY CONSERVATION AND MANAGEMENT, NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION, DEPARTMENT OF COMMERCE MAGNUSON-STEVENS ACT PROVISIONS...

  18. 50 CFR 600.1104 - Bering Sea and Aleutian Islands (BSAI) crab species fee payment and collection system.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... Pribilof blue king (the corresponding crab rationalization fishery is Pribilof red king and blue king crab), and (6) St. Matthew blue king (the corresponding crab rationalization fishery is also St. Matthew blue... Aleutian Islands red king, $237,588.04; (5) For Pribilof red king and Pribilof blue king,...

  19. 78 FR 16195 - Fisheries of the Exclusive Economic Zone Off Alaska; Bering Sea and Aleutian Islands; 2013 and...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-03-14

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration 50 CFR Part 679 RIN 0648-XC311 Fisheries of the Exclusive Economic Zone Off Alaska; Bering Sea and Aleutian Islands; 2013 and 2014 Harvest Specifications...

  20. 75 FR 11778 - Fisheries of the Exclusive Economic Zone Off Alaska; Bering Sea and Aleutian Islands; Final 2010...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-03-12

    ...NMFS announces final 2010 and 2011 harvest specifications and prohibited species catch allowances for the groundfish fishery of the Bering Sea and Aleutian Islands management area (BSAI). This action is necessary to establish harvest limits for groundfish during the 2010 and 2011 fishing years, and to accomplish the goals and objectives of the Fishery Management Plan for Groundfish of the BSAI......

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  2. Feasibility of Tidal and Ocean Current Energy in False Pass, Aleutian Islands, Alaska final report

    SciTech Connect

    Wright, Bruce Albert

    2014-05-07

    The Aleutian Pribilof Islands Association was awarded a U.S. Department of Energy Tribal Energy Program grant (DE-EE0005624) for the Feasibility of Tidal and Ocean Current Energy in False Pass, Aleutian Islands, Alaska (Project). The goal of the Project was to perform a feasibility study to determine if a tidal energy project would be a viable means to generate electricity and heat to meet long-term fossil fuel use reduction goals, specifically to produce at least 30% of the electrical and heating needs of the tribally-owned buildings in False Pass. The Project Team included the Aleut Region organizations comprised of the Aleutian Pribilof Island Association (APIA), and Aleutian Pribilof Island Community Development Association (APICDA); the University of Alaska Anchorage, ORPC Alaska a wholly-owned subsidiary of Ocean Renewable Power Company (ORPC), City of False Pass, Benthic GeoScience, and the National Renewable Energy Laboratory (NREL). The following Project objectives were completed: collected existing bathymetric, tidal, and ocean current data to develop a basic model of current circulation at False Pass, measured current velocities at two sites for a full lunar cycle to establish the viability of the current resource, collected data on transmission infrastructure, electrical loads, and electrical generation at False Pass, performed economic analysis based on current costs of energy and amount of energy anticipated from and costs associated with the tidal energy project conceptual design and scoped environmental issues. Utilizing circulation modeling, the Project Team identified two target sites with strong potential for robust tidal energy resources in Isanotski Strait and another nearer the City of False Pass. In addition, the Project Team completed a survey of the electrical infrastructure, which identified likely sites of interconnection and clarified required transmission distances from the tidal energy resources. Based on resource and electrical data

  3. Chemical versus temporal controls on the evolution of tholeiitic and calc-alkaline magmas at two volcanoes in the Alaska-Aleutian arc

    USGS Publications Warehouse

    George, R.; Turner, S.; Hawkesworth, C.; Bacon, C.R.; Nye, C.; Stelling, P.; Dreher, S.

    2004-01-01

    The Alaska-Aleutian island arc is well known for erupting both tholeiitic and calc-alkaline magmas. To investigate the relative roles of chemical and temporal controls in generating these contrasting liquid lines of descent we have undertaken a detailed study of tholeiitic lavas from Akutan volcano in the oceanic A1eutian arc and calc-alkaline products from Aniakchak volcano on the continental A1askan Peninsula. The differences do not appear to be linked to parental magma composition. The Akutan lavas can be explained by closed-system magmatic evolution, whereas curvilinear trace element trends and a large range in 87 Sr/86 Sr isotope ratios in the Aniakchak data appear to require the combined effects of fractional crystallization, assimilation and magma mixing. Both magmatic suites preserve a similar range in 226 Ra-230 Th disequilibria, which suggests that the time scale of crustal residence of magmas beneath both these volcanoes was similar, and of the order of several thousand years. This is consistent with numerical estimates of the time scales for crystallization caused by cooling in convecting crustal magma chambers. During that time interval the tholeiitic Akutan magmas underwent restricted, closed-system, compositional evolution. In contrast, the calc-alkaline magmas beneath Aniakchak volcano underwent significant open-system compositional evolution. Combining these results with data from other studies we suggest that differentiation is faster in calc-alkaline and potassic magma series than in tholeiitic series, owing to a combination of greater extents of assimilation, magma mixing and cooling.

  4. Eruption of Alkaline Basalts Prior to the Calc-alkaline Lavas of Mt. Cleveland Volcano, Aleutian Arc, Alaska

    NASA Astrophysics Data System (ADS)

    Bridges, D. L.; Nicolaysen, K. P.

    2005-12-01

    Mt. Cleveland is a 1,730 m stratovolcano, located on Chuginadak Island, that has erupted at least 23 times historically, with the latest occurring in August 2005. Major, trace, and REE analyses of 63 samples from Mt. Cleveland, including 8 from proximal cinder cones and 4 from andesitic domes on the lower flanks, identify two distinct lava suites. Modern Cleveland (MC) basalts to dacites (50.5-66.7 wt.% SiO2) exhibit a calc-alkaline differentiation trend. Major element trends suggest crystal fractionation of plagioclase +/- ortho- and clinopyroxene in MC lavas and olivine in cinder cone deposits. Resorption textures on plagioclase and olivine phenocrysts and multiple populations of plagioclase predominate throughout the MC suite suggesting magma mixing is a major process at Cleveland. Frothy white xenoliths of plagioclase + quartz + biotite are encased in glass and erupted as small pumiceous fragments in 2001. The partial resorption of the xenocrysts indicates assimilation is also an active crustal process at Cleveland. MC trace element spider diagrams exhibit a typical arc pattern in which HFS elements including Nb are depleted, and Pb and LIL elements are enriched. Th/La, Sm/La, and Sr, Nd, Pb, and Hf isotopic ratios indicate both a North Pacific MORB and a sediment component in the source of modern Cleveland lavas, consistent with sediment flux estimates of 90 to 95 m3/m/yr and an updip sediment thickness of 1300 to 1400 meters. Average 206Pb/204Pb, 207Pb/204Pb, 87Sr/86Sr, and 143Nd/144Nd values for the calc-alkaline suite are 18.93, 15.58, 0.70345, and 0.51303 respectively. The second suite consists of 3 olivine-rich, mildly alkaline basalts (48.5-49.4 wt.% SiO2), of older stratigraphic position than MC lavas representing deposits from an older phase of activity (ancestral Cleveland, AC). La/Yb, Sr/Y, and Th/Nb ratios indicate lower degrees of partial melting, relative to MC lavas, and suggests presence of garnet in the source region. The AC lavas, however, are

  5. Scrubbing masks magmatic degassing during repose at Cascade-Range and Aleutian-Arc volcanoes

    USGS Publications Warehouse

    Symonds, Robert B.; Janik, C.J.; Evans, William C.; Ritchie, B.E.; Counce, Dale; Poreda, R.J.; Iven, Mark

    2003-01-01

    Between 1992 and 1998, we sampled gas discharges from ≤173°C fumaroles and springs at 12 quiescent but potentially restless volcanoes in the Cascade Range and Aleutian Arc (CRAA) including Mount Shasta, Mount Hood, Mount St. Helens, Mount Rainier, Mount Baker, Augustine Volcano, Mount Griggs, Trident, Mount Mageik, Aniakchak Crater, Akutan, and Makushin. For each site, we collected and analyzed samples to characterize the chemical (H2O, CO2, H2S, N2, CH4, H2, HCl, HF, NH3, Ar, O2, He) and isotopic (δ13C of CO2, 3He/4He, 40Ar/36Ar, δ34S, δ13C of CH4, δ15N, and δD and δ18O of water) compositions of the gas discharges, and to create baseline data for comparison during future unrest. The chemical and isotopic data show that these gases contain a magmatic component that is heavily modified from scrubbing by deep hydrothermal (150° - 350°C) water (primary scrubbing) and shallow meteoric water (secondary scrubbing). The impact of scrubbing is most pronounced in gas discharges from bubbling springs; gases from boiling-point fumaroles and superheated vents show progressively less impact from scrubbing. The most effective strategies for detecting gas precursors to future CRAA eruptions are to measure periodically the emission rates of CO2 and SO2, which have low and high respective solubilities in water, and to monitor continuously CO2 concentrations in soils around volcanic vents. Timely resampling of fumaroles can augment the geochemical surveillance program by watching for chemical changes associated with drying of fumarolic pathways (all CRAA sites), increases in gas geothermometry temperatures (Mount Mageik, Trident, Mount Baker, Mount Shasta), changes in δ13C of CO2 affiliated with magma movement (all CRAA site), and increases in 3He/4He coupled with intrusion of new magma (Mount Rainier, Augustine Volcano, Makushin, Mount Shasta). Repose magmatic degassing may discharge substantial amounts of S and Cl into the edifices of Mount Baker and several other CRAA

  6. Climate program "stone soup": Assessing climate change vulnerabilities in the Aleutian and Bering Sea Islands of Alaska

    NASA Astrophysics Data System (ADS)

    Littell, J. S.; Poe, A.; van Pelt, T.

    2015-12-01

    Climate change is already affecting the Bering Sea and Aleutian Island region of Alaska. Past and present marine research across a broad spectrum of disciplines is shedding light on what sectors of the ecosystem and the human dimension will be most impacted. In a grassroots approach to extend existing research efforts, leveraging recently completed downscaled climate projections for the Bering Sea and Aleutian Islands region, we convened a team of 30 researchers-- with expertise ranging from anthropology to zooplankton to marine mammals-- to assess climate projections in the context of their expertise. This Aleutian-Bering Climate Vulnerability Assessment (ABCVA) began with researchers working in five teams to evaluate the vulnerabilities of key species and ecosystem services relative to projected changes in climate. Each team identified initial vulnerabilities for their focal species or services, and made recommendations for further research and information needs that would help managers and communities better understand the implications of the changing climate in this region. Those draft recommendations were shared during two focused, public sessions held within two hub communities for the Bering and Aleutian region: Unalaska and St. Paul. Qualitative insights about local concerns and observations relative to climate change were collected during these sessions, to be compared to the recommendations being made by the ABCVA team of researchers. Finally, we used a Structured Decision Making process to prioritize the recommendations of participating scientists, and integrate the insights shared during our community sessions. This work brought together residents, stakeholders, scientists, and natural resource managers to collaboratively identify priorities for addressing current and expected future impacts of climate change. Recommendations from this project will be incorporated into future research efforts of the Aleutian and Bering Sea Islands Landscape Conservation

  7. Genetic differentiation of the Kittlitz's Murrelet Brachyramphus brevirostris in the Aleutian Islands and Gulf of Alaska

    USGS Publications Warehouse

    Birt, T.P.; Mackinnon, D.; Piatt, J.F.; Friesen, V.L.

    2011-01-01

    Information about the distribution of genetic variation within and among local populations of the Kittlitz's Murrelet Brachyramphus brevirostris is needed for effective conservation of this rare and declining species. We compared variation in a 429 base pair fragment of the mitochondrial control region and 11 microsatellite loci among 53 Kittlitz's Murrelets from three sites in the western Aleutian Islands (Attu Island) and Gulf of Alaska (Glacier Bay and Kachemak Bay). We found that birds in these two regions differ genetically in three assessments: (1) global and pairwise indices of genetic differentiation were significantly greater than zero, (2) mitochondrial haplotypes differed by a minimum of nine substitutions, and (3) molecular assignments indicated little gene flow between regions. The data suggest that birds in these regions have been genetically isolated for an extended period. We conclude that Kittlitz's Murrelets from Attu Island and from the Gulf of Alaska represent separate evolutionarily significant units, and should be treated as such for conservation. Genetic data for Kittlitz's Murrelets from the remainder of the breeding range are urgently needed.

  8. The magmatic evolution of young island arc crust observed in gabbroic to tonalitic xenoliths from Raoul Island, Kermadec Island Arc

    NASA Astrophysics Data System (ADS)

    Haase, Karsten M.; Lima, Selma; Krumm, Stefan; Garbe-Schönberg, Dieter

    2014-12-01

    We provide new geochemical and O isotope data for minerals and whole rocks of a suite of gabbroic to tonalitic xenoliths from Raoul Island in the Kermadec island arc. The plagioclase, olivine and clinopyroxene compositions are similar to those observed in the Raoul Island lavas supporting a close relationship of the plutonic and volcanic rocks by crystal fractionation. Plagioclase in gabbros is significantly more An-rich than in similar rocks from oceanic spreading axes reflecting higher water contents in the island arc magmas. Incompatible element and O isotope data suggest that the gabbroic rocks formed from accumulation of minerals of the ascending magmas whereas the tonalites represent highly evolved magmas after extreme fractional crystallization. Temperatures of the magmas calculated from O isotope equilibria and pyroxene thermometers range from about 1200 °C in the mafic to 800 °C in felsic rocks. Barometry of the rocks suggests that gabbros formed between 12 and 18 km depth and tonalites shallower which is in agreement with seismic models of island arc crustal layering. The xenolith data from Raoul Island support seismic studies indicating that some portions of the Tonga-Kermadec island arc show similar layering of felsic and mafic rocks to the Izu-Bonin and the fossil Talkeetna island arcs.

  9. The 7-8 August 2008 eruption of Kasatochi Volcano, central Aleutian Islands, Alaska

    NASA Astrophysics Data System (ADS)

    Waythomas, Christopher F.; Scott, William E.; Prejean, Stephanie G.; Schneider, David J.; Izbekov, Pavel; Nye, Christopher J.

    2010-12-01

    Kasatochi volcano in the central Aleutian Islands erupted unexpectedly on 7-8 August 2008. Kasatochi has received little study by volcanologists and has had no confirmed historical eruptions. The island is an important nesting area for seabirds and a long-term biological study site of the U.S. Fish and Wildlife Service. After a notably energetic preeruptive earthquake swarm, the volcano erupted violently in a series of explosive events beginning in the early afternoon of 7 August. Each event produced ash-gas plumes that reached 14-18 km above sea level. The volcanic plume contained large amounts of SO2 and was tracked around the globe by satellite observations. The cumulative volcanic cloud interfered with air travel across the North Pacific, causing many flight cancelations that affected thousands of travelers. Visits to the volcano in 2008-2009 indicated that the eruption generated pyroclastic flows and surges that swept all flanks of the island, accumulated several tens of meters of pyroclastic debris, and increased the diameter of the island by about 800 m. Pyroclastic flow deposits contain abundant accidental lithic debris derived from the inner walls of the Kasatochi crater. Juvenile material is crystal-rich silicic andesite that ranges from slightly pumiceous to frothy pumice. Fine-grained pyroclastic surge and fall deposits with accretionary lapilli cover the lithic-rich pyroclastic flow deposits and mark a change in eruptive style from episodic explosive activity to more continuous ash emission with smaller intermittent explosions. Pyroclastic deposits completely cover the island, but wave erosion and gully development on the flanks have begun to modify the surface mantle of volcanic deposits.

  10. Late Holocene coastal stratigraphy of Sitkinak Island reveals Aleutian-Alaska megathrust earthquakes and tsunamis southwest of Kodiak Island

    NASA Astrophysics Data System (ADS)

    Nelson, A. R.; Briggs, R. W.; Kemp, A.; Haeussler, P. J.; Engelhart, S. E.; Dura, T.; Angster, S. J.; Bradley, L.

    2012-12-01

    Uncertainty in earthquake and tsunami prehistory of the Aleutian-Alaska megathrust westward of central Kodiak Island limit assessments of southern Alaska's earthquake hazard and forecasts of potentially damaging tsunamis along much of North America's west coast. Sitkinak Island, one of the Trinity Islands off the southwest tip of Kodiak Island, lies at the western end of the rupture zone of the 1964 Mw9.2 earthquake. Plafker reports that a rancher on the north coast of Sitkinak Island observed ~0.6 m of shoreline uplift immediately following the 1964 earthquake, and the island is now subsiding at about 3 mm/yr (PBO GPS). Although a high tsunami in 1788 caused the relocation of the first Russian settlement on southwestern Kodiak Island, the eastern extent of the megathrust rupture accompanying the tsunami is uncertain. Interpretation of GPS observations from the Shumagin Islands, 380 km southwest of Kodiak Island, suggests an entirely to partially creeping megathrust in that region. Here we report the first stratigraphic evidence of tsunami inundation and land-level change during prehistoric earthquakes west of central Kodiak Island. Beneath tidal and freshwater marshes around a lagoon on the south coast of Sitkinak Island, 27 cores and tidal outcrops reveal the deposits of four to six tsunamis in 2200 years and two to four abrupt changes in lithology that may correspond with coseismic uplift and subsidence over the past millennia. A 2- to 45-mm-thick bed of clean to peaty sand in sequences of tidal sediment and freshwater peat, identified in more than one-half the cores as far inland as 1.5 km, was probably deposited by the 1788 tsunami. A 14C age on Scirpus seeds, double 137Cs peaks at 2 cm and 7 cm depths (Chernobyl and 1963?), a consistent decline in 210Pb values, and our assumption of an exponential compaction rate for freshwater peat, point to a late 18th century age for the sand bed. Initial 14C ages suggest that two similar extensive sandy beds, identified

  11. Science, policy, and stakeholders: developing a consensus science plan for Amchitka Island, Aleutians, Alaska.

    PubMed

    Burger, Joanna; Gochfeld, Michael; Kosson, David S; Powers, Charles W; Friedlander, Barry; Eichelberger, John; Barnes, David; Duffy, Lawrence K; Jewett, Stephen C; Volz, Conrad D

    2005-05-01

    With the ending of the Cold War, the US Department of Energy is responsible for the remediation of radioactive waste and disposal of land no longer needed for nuclear material production or related national security missions. The task of characterizing the hazards and risks from radionuclides is necessary for assuring the protection of health of humans and the environment. This is a particularly daunting task for those sites that had underground testing of nuclear weapons, where the radioactive contamination is currently inaccessible. Herein we report on the development of a Science Plan to characterize the physical and biological marine environment around Amchitka Island in the Aleutian chain of Alaska, where three underground nuclear tests were conducted (1965-1971). Information on the ecology, geology, and current radionuclide levels in biota, water, and sediment is necessary for evaluating possible current contamination and to serve as a baseline for developing a plan to ensure human and ecosystem health in perpetuity. Other information required includes identifying the location of the salt water/fresh water interface where migration to the ocean might occur in the future and determining groundwater recharge balances, as well as assessing other physical/geological features of Amchitka near the test sites. The Science Plan is needed to address the confusing and conflicting information available to the public about radionuclide risks from underground nuclear blasts in the late 1960s and early 1970s, as well as the potential for volcanic or seismic activity to disrupt shot cavities or accelerate migration of radionuclides into the sea. Developing a Science Plan involved agreement among regulators and other stakeholders, assignment of the task to the Consortium for Risk Evaluation with Stakeholder Participation, and development of a consensus Science Plan that dealt with contentious scientific issues. Involvement of the regulators (State of Alaska), resource

  12. Dome growth at Mount Cleveland, Aleutian Arc, quantified by time-series TerraSAR-X imagery

    USGS Publications Warehouse

    Wang, Teng; Poland, Michael; Lu, Zhong

    2016-01-01

    Synthetic aperture radar imagery is widely used to study surface deformation induced by volcanic activity; however, it is rarely applied to quantify the evolution of lava domes, which is important for understanding hazards and magmatic system characteristics. We studied dome formation associated with eruptive activity at Mount Cleveland, Aleutian Volcanic Arc, in 2011–2012 using TerraSAR-X imagery. Interferometry and offset tracking show no consistent deformation and only motion of the crater rim, suggesting that ascending magma may pass through a preexisting conduit system without causing appreciable surface deformation. Amplitude imagery has proven useful for quantifying rates of vertical and areal growth of the lava dome within the crater from formation to removal by explosive activity to rebirth. We expect that this approach can be applied at other volcanoes that host growing lava domes and where hazards are highly dependent on dome geometry and growth rates.

  13. Organochlorine contaminants in fishes from coastal waters west of Amukta Pass, Aleutian Islands, Alaska, USA.

    PubMed

    Miles, A Keith; Ricca, Mark A; Anthony, Robert G; Estes, James A

    2009-08-01

    Organochlorines were examined in liver and stable isotopes in muscle of fishes from the western Aleutian Islands, Alaska, in relation to islands or locations affected by military occupation. Pacific cod (Gadus macrocephalus), Pacific halibut (Hippoglossus stenolepis), and rock greenling (Hexagrammos lagocephalus) were collected from nearshore waters at contemporary (decommissioned) and historical (World War II) military locations, as well as at reference locations. Total (Sigma) polychlorinated biphenyls (PCBs) dominated the suite of organochlorine groups (SigmaDDTs, Sigmachlordane cyclodienes, Sigmaother cyclodienes, and Sigmachlorinated benzenes and cyclohexanes) detected in fishes at all locations, followed by SigmaDDTs and Sigmachlordanes; dichlorodiphenyldichloroethylene (p,p'DDE) composed 52 to 66% of SigmaDDTs by species. Organochlorine concentrations were higher or similar in cod compared to halibut and lowest in greenling; they were among the highest for fishes in Arctic or near Arctic waters. Organochlorine group concentrations varied among species and locations, but SigmaPCB concentrations in all species were consistently higher at military locations than at reference locations. Moreover, all organochlorine group concentrations were higher in halibut from military locations than those from reference locations. A wide range of molecular weight organochlorines was detected at all locations, which implied regional or long-range transport and deposition, as well as local point-source contamination. Furthermore, a preponderance of higher-chlorinated PCB congeners in fishes from contemporary military islands implied recent exposure. Concentrations in all organochlorine groups increased with delta15N enrichment in fishes, and analyses of residual variation provided further evidence of different sources of SigmaPCBs and p,p'DDE among species and locations. PMID:19374473

  14. Detection and location of earthquakes in the central Aleutian subduction zone using island and ocean bottom seismograph stations

    SciTech Connect

    Frohlich, C.; Billington, S.; Engdahl, E.R.; Malahoff, A.

    1982-08-10

    A network of eight University of Texas ocean bottom seismographs (OBS) operated for 6 weeks in 1978 about 50 km offshore of Adak Island, Alaska, and nearly islands. In 1979 a similar network of nine instruments was deployed for 7 weeks farther offshore within and up to 100 km seaward of the Aleutian trench. For shallow earthquakes on the outer trench slope, for shallow earthquakes in the thrust zone, and for intermediate-depth events we have analyzed the OBS and island-based network data and evaluated the island network's capabilities for earthquake detection and location and for focal mechanism determination. Our three major conclusions are presented. The first concerns shallow earthquakes on the outer trench slope. In 1979 about 30 earthquakes occurred within the Aleutian trench and up to 60 km seaward of the trench axis. The island network located none of these events and detected P phases for only three of them. Ray tracing shows that the islands lie in a geometric shadow zone for events on the outer trench slope. The best located events are shallower than 20 km and exhibit first motions consistent with normal faulting. Several authors have suggested that these events are caused by bending of the oceanic lithosphere at the outer rise prior to subduction. If so, then the event locations reported here show that the bending stresses exceed the strength of lithosphere only in a narrow zone extending about 10 km landward and 60 km seaward of the trench axis. The second conclusion concerns shallow earthquakes in the thrust zone. Epicenters determined by island stations alone are virtually identical to epicenters determined using data from both island and OBS stations. The third conclusion concerns earthquakes deeper than 70 km. Epicenters determined using island network stations alone lie 10 to 80 km south of those determined using OBS and island stations, with the differences between epicenters depending both on event depth and on the velocity model used.

  15. Mercury concentrations in breast feathers of three upper trophic level marine predators from the western Aleutian Islands, Alaska.

    PubMed

    Kaler, Robb S A; Kenney, Leah A; Bond, Alexander L; Eagles-Smith, Collin A

    2014-05-15

    Mercury (Hg) is a toxic element distributed globally through atmospheric transport. Agattu Island, located in the western Aleutian Islands, Alaska, has no history of point-sources of Hg contamination. We provide baseline levels of total mercury (THg) concentrations in breast feathers of three birds that breed on the island. Geometric mean THg concentrations in feathers of fork-tailed storm-petrels (Oceanodroma furcata; 6703 ± 1635, ng/g fresh weight [fw]) were higher than all other species, including snowy owl (Bubo scandiacus; 2105 ± 1631, ng/g fw), a raptor with a diet composed largely of storm-petrels at Agattu Island. There were no significant differences in mean THg concentrations of breast feathers among adult Kittlitz's murrelet (Brachyramphus brevirostris; 1658 ± 1276, ng/g fw) and chicks (1475 ± 671, ng/g fw) and snowy owls. The observed THg concentrations in fork-tailed storm-petrel feathers emphasizes the need for further study of Hg pollution in the western Aleutian Islands. PMID:24656750

  16. Mercury concentrations in breast feathers of three upper trophic level marine predators from the western Aleutian Islands, Alaska

    USGS Publications Warehouse

    Kaler, Robb S.A.; Kenney, Leah A.; Bond, Alexander L.; Eagles-Smith, Collin A.

    2014-01-01

    Mercury (Hg) is a toxic element distributed globally through atmospheric transport. Agattu Island, located in the western Aleutian Islands, Alaska, has no history of point-sources of Hg contamination. We provide baseline levels of total mercury (THg) concentrations in breast feathers of three birds that breed on the island. Geometric mean THg concentrations in feathers of fork-tailed storm-petrels (Oceanodroma furcata; 6703 ± 1635, ng/g fresh weight [fw]) were higher than all other species, including snowy owl (Bubo scandiacus; 2105 ± 1631, ng/g fw), a raptor with a diet composed largely of storm-petrels at Agattu Island. There were no significant differences in mean THg concentrations of breast feathers among adult Kittlitz’s murrelet (Brachyramphus brevirostris; 1658 ± 1276, ng/g fw) and chicks (1475 ± 671, ng/g fw) and snowy owls. The observed THg concentrations in fork-tailed storm-petrel feathers emphasizes the need for further study of Hg pollution in the western Aleutian Islands.

  17. New species of sponges (Porifera, Demospongiae) from the Aleutian Islands and Gulf of Alaska.

    PubMed

    Lehnert, Helmut; Stone, Robert P

    2015-01-01

    Ten new species of demosponges, assigned to the orders Poecilosclerida, Axinellida and Dictyoceratida, discovered in the Gulf of Alaska and along the Aleutian Island Archipelago are described and compared to relevant congeners. Poecilosclerida include Cornulum globosum n. sp., Megaciella lobata n. sp., M. triangulata n. sp., Artemisina clavata n. sp., A. flabellata n. sp., Coelosphaera (Histodermion) kigushimkada n. sp., Stelodoryx mucosa n. sp. and S. siphofuscus n. sp. Axinellida is represented by Raspailia (Hymeraphiopsis) fruticosa n. sp. and Dictyoceratida is represented by Dysidea kenkriegeri n. sp. The genus Cornulum is modified to allow for smooth tylotes. We report several noteworthy biogeographical observations. We describe only the third species within the subgenus Histodermion and the first from the Indo-Pacific Region. Additionally, the subgenus Hymerhaphiopsis was previously represented by only a single species from Antarctica. We also report the first record of a dictyoceratid species from Alaska. The new collections further highlight the richness of the sponge fauna from the region, particularly for the Poecilosclerida. PMID:26624419

  18. Near-field survey of the 1946 Aleutian tsunami on Unimak and Sanak Islands

    USGS Publications Warehouse

    Okal, E.A.; Plafker, G.; Synolakis, C.E.; Borrero, J.C.

    2003-01-01

    The 1946 Aleutian earthquake stands out among tsunamigenic events because it generated both very high run-up near the earthquake source region and a destructive trans-Pacific tsunami. We obtained new data on the distribution of its tsunami in the near field along south-facing coasts between Unimak Pass on the west and Sanak Island on the east by measuring the height of driftwood and beach materials that were deposited by the tsunami above the extreme storm tide level. Our data indicate that (1) the highest measured run-up, which is at the Scotch Cap lighthouse, was 42 m above tide level or about 37 m above present storm tide elevation; (2) run-up along the rugged coast from Scotch Cap for 12 km northwest to Sennett Point is 12-18 m, and for 30 km east of Scotch Cap to Cape Lutke it is 24-42 m; (3) run-up along the broad lowlands bordering Unimak Bight is 10-20 m, and in-undation is locally more than 2 km; (5) run-up diminishes to 8 m or less at the southeast corner of Unimak Island; (6) no evidence was found for run-up above present storm tides (about 4-5 m above MLLW) on the Ikatan Peninsula or areas along the coast to the west; and (7) run-up above storm tide level in the Sanak Island group is restricted to southwest-facing coasts of Sanak, Long, and Clifford Islands, where it is continuous and locally up to 24 m high. Generation of the tsunami by one or more major earthquake-triggered submarine landslides near the shelf edge south of Unimak Island seems to be the only viable mechanism to account for the data on wave arrival time, run-up heights, and distribution, as well as for unconfirmed anecdotal reports of local postquake increases in water depth and diminished bottom-fisheries productivity. A preliminary hydrodynamic simulation of the local tsunami propagation and run-up using a dipolar model of a possible landslide off Davidson Bank provides an acceptable fit to the characteristics of the distribution of local run-up, with a value at 34 m at the Scotch Cap

  19. The 2008 Eruption of Kasatochi Volcano, Central Aleutian Islands, Alaska: Reconnaissance Observations and Preliminary Physical Volcanology

    NASA Astrophysics Data System (ADS)

    Waythomas, C. F.; Schneider, D. J.; Prejean, S. G.

    2008-12-01

    The August 7, 2008 eruption of Kasatochi volcano was the first documented historical eruption of this small (3 x 3 km) island volcano with a 1 km2 lake filled crater in the central Aleutian Islands of Alaska. Reports of previous Kasatochi eruptions are unconfirmed and lacking in detail and little is known about the eruptive history. Three explosively-generated ash plumes reaching altitudes of 15 to 20 km were observed in satellite data and were preceded by some of the most intense seismicity yet recorded by the Alaska Volcano Observatory (AVO) seismic network. Eruptive products on Kasatochi Island observed on August 22 and 23 consist of pumice-bearing, lithic-rich pyroclastic-flow deposits overlain by a 1-2 m thick sequence of fine- grained pyroclastic-surge, and -fall deposits all exposed at the coastline. These deposits completely blanket Kasatochi Island to a depth of many meters. Pyroclastic flows entered the sea and extended the coastline 300-400 m beyond prominent wave cut cliffs and sea stacks. Tide gauge data from Adak Island, 80 km to the west, indicate a small tsunami with maximum water amplitude of 20 cm, was initiated during the eruption. Kasatochi volcano lacks a real-time seismic monitoring network. Seismic activity was detected by AVO instruments on Great Sitkin Island 40 km to the west, and thus the timing of eruptive events is approximate. The eruption began explosively at 2201 UTC on August 7, and was followed by at least two additional strong eruptive bursts at 0150 UTC and 0435 UTC, August 8. Satellite data show a significant ash cloud associated with the 0435 UTC event followed by at least 14 hours of continuous ash emission. The lack of a strong ash signature in satellite data suggest that the first two plumes were ash poor. Satellite data also show a large emission of SO2 that entered the stratosphere. Correlation of eruptive periods with deposits on the island is not yet possible, but it appears that pyroclastic flows were emplaced during

  20. Preliminary geology of the Tanaga Island volcanic cluster, western Aleutians (Alaska)

    NASA Astrophysics Data System (ADS)

    Coombs, M. L.; Browne, B. L.; Larsen, J. F.

    2004-12-01

    During 2003, the northwestern portion of Tanaga Island (178° W) was mapped in detail for the first time during fieldwork by Alaska Volcano Observatory geologists in conjunction with the installation of a volcano monitoring seismic network. The northern half of the island is approximately 20 km across and comprises four discrete volcanic centers, from west to east: Sajaka (area = 22 km2), Tanaga (20 km2), East Tanaga (15 km2), and Takawangha (54 km2). The three western centers are steep-sided cones of Holocene age, and have grown in the scar formed by a catastrophic Pleistocene sector collapse directed to the northwest. To the east, a >300 m-thick sequence of volcanic and volcaniclastic rocks (Pre-Tanaga unit) underlies Takawangha, which has been active throughout the Pleistocene and Holocene. Holocene eruptive products from all four centers are predominantly lava flows, with minor explosive activity recorded in tephra sections. Additionally, Sajaka experienced a relatively young (mid-Holocene?) sector collapse of its west flank, accompanied by eruption of laterally-directed pyroclastic flows. A morphologically young cone of scoria and thin basalt flows has grown in the collapse scar. Whole-rock geochemical data on 130 samples of lava and scoria from the four centers and the Pre-Tanaga unit are basalts through low-SiO2 andesites. All but ten lavas have molar Mg# between 0.35 and 0.5 and the remainder are between 0.5 and 0.61; no primitive lavas were discovered on Tanaga Island. Lava flows of Holocene age from Tanaga and East Tanaga follow medium-K trends, all lavas from Takawangha are high-K, and Sajaka and Pre-Tanaga lavas fall along both trends. High-K lavas are enriched in other LILE (Rb, Ba, Pb) as well, and fall near or above the high end of published Aleutian lavas for these elements. The lavas exhibit petrographic as well as compositional diversity: mafic phases in Tanaga lavas are olivine, two pyroxenes, and amphibole, at East Tanaga lavas contain two

  1. Diverse lavas from closely spaced volcanoes drawing from a common parent: Emmons Lake Volcanic Center, Eastern Aleutian Arc

    USGS Publications Warehouse

    Mangan, M.; Miller, T.; Waythomas, C.; Trusdell, F.; Calvert, A.; Layer, P.

    2009-01-01

    Emmons Lake Volcanic Center (ELVC) on the lower Alaskan Peninsula is one of the largest and most diverse volcanic centers in the Aleutian Arc. Since the Middle Pleistocene, eruption of ~ 350 km3 of basalt through rhyolite has produced a 30 km, arc front chain of nested calderas and overlapping stratovolcanoes. ELVC has experienced as many as five major caldera-forming eruptions, the most recent, at ~ 27 ka, produced ~ 50 km3 of rhyolitic ignimbrite and ash fall. These violent silicic events were interspersed with less energetic, but prodigious, outpourings of basalt through dacite. Holocene eruptions are mostly basaltic andesite to andesite and historically recorded activity includes over 40 eruptions within the last 200 yr, all from Pavlof volcano, the most active site in the Aleutian Arc. Geochemical and geophysical observations suggest that although all ELVC eruptions derive from a common clinopyroxene + spinel + plagioclase fractionating high-aluminum basalt parent in the lower crust, magma follows one of two closely spaced, but distinct paths to the surface. Under the eastern end of the chain, magma moves rapidly and cleanly through a relatively young (~ 28 ka), hydraulically connected dike plexus. Steady supply, short magma residence times, and limited interaction with crustal rocks preserve the geochemistry of deep crustal processes. Below the western part of the chain, magma moves haltingly through a long-lived (~ 500 ka) and complex intrusive column in which many generations of basaltic to andesitic melts have mingled and fractionated. Buoyant, silicic melts periodically separate from the lower parts of the column to feed voluminous eruptions of dacite and rhyolite. Mafic lavas record a complicated passage through cumulate zones and hydrous silicic residues as manifested by disequilibrium phenocryst textures, incompatible element enrichments, and decoupling of REEs and HFSEs ratios. Such features are absent in mafic lavas from the younger part of the chain

  2. Long-range Receiver Function Profile of Crustal and Mantle Discontinuities From the Aleutian Arc to Tierra del Fuego

    NASA Astrophysics Data System (ADS)

    Spieker, Kathrin; Rondenay, Stéphane; Sawade, Lucas

    2016-04-01

    The Circum-Pacific belt, also called the Pacific Ring of Fire, is the most seismically active region on Earth. Multiple plate boundaries form a zone characterized by frequent volcanic eruptions and seismicity. While convergent plate boundaries such as the Peru-Chile trench dominate the Circum-Pacific belt, divergent and transform boundaries are present as well. The eastern section of the Circum-Pacific belt extends from the Aleutian arc, through the Cascadia subduction zone, San Andreas Fault, middle America trench and the Andean margin down to Tierra del Fuego. Due to the significant hazards posed by this tectonic activity, the region has been densely instrumented by thousands of seismic stations deployed across fifteen countries, over a distance of more than 15000 km. Various seismological studies, including receiver function analyses, have been carried out to investigate the crustal and mantle structure beneath local segments of the eastern Circum-Pacific belt (i.e., at ~100-500 km scale). However, to the best of our knowledge, no study to date has ever attempted to combine all available seismic data from the eastern Circum-Pacific belt to generate a continuous profile of seismic discontinuities extending from the Aleutians to Tierra del Fuego. Here, we use results from the "Global Imaging using Earthquake Records" (GLImER) P-wave receiver function database to create a long-range profile of crustal and upper mantle discontinuities across the entire eastern portion of the Circum-Pacific belt. We image intermittent crustal and mantle discontinuities along the profile, and examine them with regard to their behaviour and properties across transitions between different tectonic regimes.

  3. Barrier island arcs along abandoned Mississippi River deltas

    USGS Publications Warehouse

    Penland, S.; Suter, J.R.; Boyd, Ron

    1985-01-01

    Generation of transgressive barrier island arcs along the Mississippi River delta plain and preservation of barrier shoreline facies in their retreat paths on the inner shelf is controlled by: (1) shoreface translation; (2) age of the transgression; and (3) the thickness of the barrier island arc sediment package. Barrier island arcs experience an average relative sea level rise of 0.50-1.00 cm yr-1 and shoreface retreat rates range from 5-15 m yr-1. Young barrier island arc sediment packages (Isles Dernieres) are thin and have experienced limited landward retreat of the shoreface. Older barrier island arcs (Chandeleur Islands) are thicker and have experienced significant landward movement of the shoreface because of the greater time available for retreat. If the transgressed barrier shoreline sediment package lies above the advancing ravinement surface, the entire sequence is truncated. A thin reworked sand sheet marks the shoreface retreat path. The base of the transgressive sediment package can lie below the ravinement surface in older barrier shorelines. In this setting, the superstructure of the barrier shoreline is truncated, leaving the basal portion of the transgressive sequence preserved on the inner shelf. A variety of transgressive stratigraphic sequences from sand sheets to truncated barrier islands to sand-filled tidal inlet scars have been identified by high resolution seismic profiling across the shoreface retreat paths of Mississippi delta barrier island arcs. One of these examples, the Isles Dernieres, represents a recently detached barrier island arc in the early stages of transgression. An older example, the Chandeleur Islands, represents a barrier island arc experiencing long-term shoreface retreat. This paper describes the stratigraphic character and preserved transgressive facies for the Isles Dernieres and Chandeleur Islands. ?? 1985.

  4. Surface wind characteristics of some Aleutian Islands. [for selection of windpowered machine sites

    NASA Technical Reports Server (NTRS)

    Wentink, T., Jr.

    1973-01-01

    The wind power potential of Alaska is assessed in order to determine promising windpower sites for construction of wind machines and for shipment of wind derived energy. Analyses of near surface wind data from promising Aleutian sites accessible by ocean transport indicate probable velocity regimes and also present deficiencies in available data. It is shown that winds for some degree of power generation are available 77 percent of the time in the Aleutians with peak velocities depending on location.

  5. Data on Holocene Tephra (Volcanic Ash) Deposits in the Alaska Peninsula and Lower Cook Inlet Region of the Aleutian Volcanic Arc, Alaska

    USGS Publications Warehouse

    Riehle, J.R.; Meyer, C.E.; Miyaoka, Ronny T.

    1999-01-01

    Introduction This site provides information about the number, thickness, and grainsize of Holocene volcanic ash deposits at 50 localities in the eastern Aleutian volcanic arc. In addition, the major-element compositions of the glasses separated from more than 350 samples of tephra from these localities, determined by electron microprobe, are presented as a basis for correlating samples. Where known with reasonable certainty, the source of an analyzed sample is also identified for use in comparative studies of magma chemistry.

  6. Detection and characterization of transient forcing episodes affecting earthquake activity in the Aleutian Arc system

    NASA Astrophysics Data System (ADS)

    Reverso, T.; Marsan, D.; Helmstetter, A.

    2015-02-01

    Crustal, slow deformation transients can be caused by fluid or magmatic intrusions, and by slow slip on faults. They can affect earthquake dynamics, if they occur close to or within seismically active zones. We here further develop, and test, a statistical method for detecting and characterizing seismicity anomalies that is only based on earthquake occurrence times and locations. We make use of this method to analyze the 2004-2013 seismicity at mc = 3.5 in the Aleutian subduction system, to find six statistically significant anomalies, with typical 1 day duration and 30 to 50 km size, that are likely related to slow deformation transients. They tend to be located in zones characterized by intermediate seismic coupling, and to mark the termination of past large to mega-thrust earthquakes. These anomalies account for a non-negligible (9%) part of the total activity, proving that non-stationary aseismic loading plays an important role in the dynamics of crustal deformation.

  7. New glass sponges (Porifera: Hexactinellida) from deep waters of the central Aleutian Islands, Alaska.

    PubMed

    Reiswig, Henry M; Stone, Robert P

    2013-01-01

    Hexactinellida from deep-water communities of the central Aleutian Islands, Alaska, are described. They were mostly collected by the remotely operated vehicle 'Jason II' from 494–2311 m depths during a 2004 RV 'Roger Revelle' expedition, but one shallow-water species collected with a shrimp trawl from 155 m in the same area is included. The excellent condition of the ROV-collected specimens enabled valuable redescription of some species previously known only from badly damaged specimens. New taxa include one new genus and eight new species in five families. Farreidae consist of two new species, Farrea aleutiana and F. aspondyla. Euretidae consists of only Pinulasma fistulosum n. gen., n. sp. Tretodictyidae include only Tretodictyum amchitkensis n. sp. Euplectellidae consists of only the widespread species Regadrella okinoseana Ijima, reported here over 3,700 km from its closest previously known occurrence. The most diverse family, Rossellidae, consists of Aulosaccus ijimai (Schulze), Aulosaccus schulzei Ijima, Bathydorus sp. (young stage not determinable to species), Caulophacus (Caulophacus) adakensis n. sp., Acanthascus koltuni n. sp., Staurocalyptus psilosus n. sp., Staurocalyptus tylotus n. sp. and Rhabdocalyptus mirabilis Schulze. We present argument for reinstatement of the abolished rossellid subfamily Acanthascinae and return of the subgenera  Staurocalyptus Ijima and Rhabdocalyptus Schulze to their previous generic status. These fauna provides important complexity to the hard substrate communities that likely serve as nursery areas for the young stages of commercially important fish and crab species, refuge from predation for both young and adult stages, and also as a focal source of prey for juvenile and adult stages of those same species. PMID:25325089

  8. Mantle and Crustal Sources of Carbon, Nitrogen, and Noble gases in Cascade-Range and Aleutian-Arc Volcanic gases

    USGS Publications Warehouse

    Symonds, Robert B.; Poreda, Robert J.; Evans, William C.; Janik, Cathy J.; Ritchie, Beatrice E.

    2003-01-01

    Here we report anhydrous chemical (CO2, H2S, N2, H2, CH4, O2, Ar, He, Ne) and isotopic (3He/4He, 40Ar/36Ar, δ13C of CO2, δ13C of CH4, δ15N) compositions of virtually airfree gas samples collected between 1994 and 1998 from 12 quiescent but potentially restless volcanoes in the Cascade Range and Aleutian Arc (CRAA). Sample sites include ≤173°C fumaroles and springs at Mount Shasta, Mount Hood, Mount St. Helens, Mount Rainier, Mount Baker, Augustine Volcano, Mount Griggs, Trident, Mount Mageik, Aniakchak Crater, Akutan, and Makushin. The chemical and isotopic data generally point to magmatic (CO2, Ar, He), shallow crustal sedimentary (hereafter, SCS) (CO2, N2, CH4), crustal (He), and meteoric (N2, Ar) sources of volatiles. CH4 clearly comes from SCS rocks in the subvolcanic systems because CH4 cannot survive the higher temperatures of deeper potential sources. Further evidence for a SCS source for CH4 as well as for non-mantle CO2 and non-meteoric N2 comes from isotopic data that show wide variations between volcanoes that are spatially very close and similar isotopic signatures from volcanoes from very disparate areas. Our results are in direct opposition to many recent studies on other volcanic arcs (Kita and others, 1993; Sano and Marty, 1995; Fischer and others, 1998), in that they point to a dearth of subducted components of CO2 and N2 in the CRAA discharges. Either the CRAA volcanoes are fundamentally different from volcanoes in other arcs or we need to reevaluate the significance of subducted C and N recycling in convergent-plate volcanoes.

  9. SAR-based Estimation of Glacial Extent and Velocity Fields on Isanotski Volcano, Aleutian Islands, Alaska

    NASA Astrophysics Data System (ADS)

    Sousa, D.; Lee, A.; Parker, O. P.; Pressler, Y.; Guo, S.; Osmanoglu, B.; Schmidt, C.

    2012-12-01

    Global studies show that Earth's glaciers are losing mass at increasing rates, creating a challenge for communities that rely on them as natural resources. Field observation of glacial environments is limited by cost and inaccessibility. Optical remote sensing is often precluded by cloud cover and seasonal darkness. Synthetic aperture radar (SAR) overcomes these obstacles by using microwave-frequency electromagnetic radiation to provide high resolution information on large spatial scales and in remote, atmospherically obscured environments. SAR is capable of penetrating clouds, operating in darkness, and discriminating between targets with ambiguous spectral signatures. This study evaluated the efficacy of two SAR Earth observation methods on small (< 7 km2) glaciers in rugged topography. The glaciers chosen for this study lie on Isanotski Volcano in Unimak Island, Aleutian Archipelago, USA. The local community on the island, the City of False Pass, relies on glacial melt for drinking water and hydropower. Two methods were used: (1) velocity field estimation based on Repeat Image Feature Tracking (RIFT) and (2) glacial boundary delineation based on interferometric coherence mapping. NASA Uninhabited Aerial Vehicle SAR (UAVSAR) single-polarized power images and JAXA Advanced Land Observing Satellite Phased Array type L-band SAR (ALOS PALSAR) single-look complex images were analyzed over the period 2008-2011. UAVSAR image pairs were coregistered to sub-pixel accuracy and processed with the Coregistration of Optically Sensed Images and Correlation (COSI-Corr) feature tracking module to derive glacial velocity field estimates. Maximum glacier velocities ranged from 28.9 meters/year to 58.3 meters/year. Glacial boundaries were determined from interferometric coherence of ALOS PALSAR data and subsequently refined with masking operations based on terrain slope and segment size. Accuracy was assessed against hand-digitized outlines from high resolution UAVSAR power images

  10. Insights Into Aleutian Volcanism from Insar Observations

    NASA Astrophysics Data System (ADS)

    Lu, Z.; Dzurisin, D.

    2013-12-01

    With its global coverage and all-weather imaging capability, interferometric synthetic aperture radar (InSAR) has become an increasingly important technique for studying magma dynamics at volcanoes in remote regions, such as the Aleutian Islands. The spatial distribution of surface deformation derived from InSAR data enables the construction of detailed mechanical models to enhance the study of magmatic processes. To study Aleutian volcanism, we processed nearly 12,000 SAR images acquired by ERS-1, JERS-1, ERS-2, Radarsat-1, Envisat, ALOS, and TerraSAR-X from the early 1990s to 2010. We combined these SAR images to produce about 25,000 interferograms, which we analyzed for evidence of surface deformation at most of the arc's Holocene volcanoes. Where surface displacements were sufficiently strong, we used analytical models to estimate the location, shape, and volume change of deformation sources. This paper summarizes deformation processes at Aleutian volcanoes observed with InSAR, including: (1) time-variant volcanic inflation and magmatic intrusion, (2) deformation preceding and accompanying seismic swarms , (3) persistent volcano-wide subsidence at calderas that last erupted tens of years ago, (4) episodic magma intrusion and associated tectonic stress release, (5) subsidence caused by a decrease in pore fluid pressure in active hydrothermal systems, (6) subsidence of surface lava and pyroclastic flows, and (7) a lack of deformation at some volcanoes with recent eruptions, where deformation might be expected. Among the inferred mechanisms are magma accumulation in and withdrawal from crustal magma reservoirs, pressurization/depressurization of hydrothermal systems, and thermo-elastic contraction of young lava flows. Our work demonstrates that deformation patterns and associated magma supply mechanisms at Aleutian volcanoes are diverse and vary in both space and time. By combining InSAR results with information from the geologic record, accounts of historical

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

    SciTech Connect

    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.

  12. Pyroxenite is a possible cause of enriched magmas in island arc settings: Gorely volcano (Kamchatka)

    NASA Astrophysics Data System (ADS)

    Gavrilenko, M.; Carr, M. J.; Herzberg, C. T.; Ozerov, A.

    2013-12-01

    Kamchatka peninsula (Russia) is an island-arc with a complex geological history and structure. It has three distinct volcanic fronts, whose origins are still debated. Moreover, a junction with the Aleutian Arc (at ~56oN) complicates the understanding of geodynamics at the region. The process of magma generation in Kamchatka involves several components: N-MORB mantle wedge (variably depleted), slab fluids and melts, and enriched mantle [Churikova et al. 2001, 2007; Yogodzinsky et al. 2001; Volynets et al. 2010]. Two of these end members (mantle wedge, slab fluids) are well studied [Portnyagin et al. 2007; Duggen et al. 2007]. However, the nature/genesis of the enriched magmas is unclear. In the standard model of arc volcanism depleted mantle peridotite in the mantle wedge partially melts to form parental basalts. However, evidence for pyroxenite melting in the arc environment was reported for the Mexican Volcanic Belt [Straub et al, 2008; Straub et al, 2013] and for Kamchatka [Portnyagin, 2009; Portnyagin, 2011; Bryant et al., 2011; Gavrilenko, 2012]. High precision Ni, Ca, and Mn contents of olivines from Gorely volcano confirm the existence of pyroxenite source in the mantle wedge [Gavrilenko, 2013]. Our forward modeling using Arc Basalt Simulator 4.0 (ABS) by [Kimura et al. 2011]) shows that we have primitive mantle as a source for Gorely volcano, a mantle more enriched than the DMM in the standard model for arc magmatism) REE inverse modeling [after Feigenson et al, 1983] agrees with the ABS forward model, returning the same REE pattern for the source. In contrast, ABS modeling for Mutnovsky volcano (next to Gorely, but closer to the trench) shows standard DMM as the source for the volcano. We conclude that DMM is the composition for the mantle wedge rocks beneath Gorely volcano, but the enrichment of the parental melts at Gorely volcano is caused by reaction of DMM peridotite with slab melts/fluids to produce pyroxenite.

  13. Coral habitat in the Aleutian Islands of Alaska: depth distribution, fine-scale species associations, and fisheries interactions

    NASA Astrophysics Data System (ADS)

    Stone, R. P.

    2006-05-01

    The first in situ exploration of Aleutian Island coral habitat was completed in 2002 to determine the distribution of corals, to examine fine-scale associations between targeted fish species and corals, and to investigate the interaction between the areas’ diverse fisheries and coral habitat. Corals, mostly gorgonians and hydrocorals, were present on all 25 seafloor transects and at depths between 27 and 363 m, but were most abundant between 100 and 200 m depth. Mean coral abundance (1.23 colonies m-2) far exceeded that reported for other high-latitude ecosystems and high-density coral gardens (3.85 colonies m-2) were observed at seven locations. Slope and offshore pinnacle habitats characterized by exposed bedrock, boulders, and cobbles generally supported the highest abundances of coral and fish. Overall, 85% of the economically important fish species observed on transects were associated with corals and other emergent epifauna. Disturbance to the seafloor from bottom-contact fishing gear was evident on 88% of the transects, and approximately 39% of the total area of the seafloor observed had been disturbed. Since cold-water corals appear to be a ubiquitous feature of seafloor habitats in the Aleutian Islands, fisheries managers face clear challenges integrating coral conservation into an ecosystem approach to fisheries management.

  14. Patterns of seismogenesis for giant plate-boundary earthquakes in island-arc-type subduction systems

    NASA Astrophysics Data System (ADS)

    Kirby, S. H.

    2006-12-01

    island arcs with steeper slab dips. Finally, this subduction system receives a large sediment influx from the giant Irrawadi and Ganges River delta systems to the north that drain the active collisional mountain belts further north. High sediment influx and trench sediment acumulation are factors that are present in 12 of the 14 subduction zones that have hosted the giant interplate thrust earthquakes mentioned earlier. This influx appears to be important in the development of a subduction channel of granular material in the plate boundary that may enable ruptures to run to great lengths by smoothing out barriers to earthquake slip. Several island-arc subduction systems (the Manus, SW Ryukyu, W Aleutians, and possibly the South Shetlands systems) have attributes similar to the Nicobar/Andaman segment of the SAE rupture. Moreover, arc volcanic activity is weak or absent and convergence also tends to be slow in all of these island-arc systems. Research done in collaboration with the USGS Tsunami Source Working Group (Steve Kirby and Eric Geist (Co-Chairs) David Scholl, Roland von Huene, Rick Blakely, Ray Wells, and Willie Lee (Secretary))

  15. Exploring Paleoclimatic and -Oceanographic Consequences for Arctic Beringia by the Eocene Formation and Progressive E-W Lengthening of the Aleutian Ridge (arc) Across the North Pacific Basin

    NASA Astrophysics Data System (ADS)

    Scholl, D. W.

    2013-12-01

    INTRODUCTION: During the past ~50 Myr, magmatic growth of the offshore Aleutian Ridge (AR) or arc and its progressive tectonic lengthening to the west cordoned off the NW corner of the Pacific Basin to formed the deep water (3000-4000 m), marginal sea of the Bering Sea Basin (BSB). Cordoning continuously altered the paths, depths, and locations of water-exchange passes controlling the circulation of waters between the north Pacific and the Bering Sea (BS), and, via the fixed Bering Strait, that entering the Pacific sector of the Arctic Basin. PRESENT PATTERN OF PACIFIC-BERING-ARCTIC WATER EXCHANGE: Cool, low salinity water of the Alaska Stream flowing west along the Pacific side of the AR crosses northward into the BS via tectonically controlled, inter-island passes. The largest volume (~9 SV) enters near the western end of the AR via Near Pass. Flow turns back to the east and CCW northward over the BSB. Surface water exits southward around the western end of the AR through the far western, deep-water (~4000 m) pass of Kamchatka Strait. Because water salinity is low, vertical thermohaline circulation (THC) does not occur over the BSB. However, the deposition of the larger Meiji Drift body, which is charged with Bering-sourced, detritus, on the Pacific side of Kamchatka Strait implies THC may have occurred in the past. Deep-water circulation is presently linked to the inflow of Pacific abyssal water via Kamchatka Strait. A small volume (~0.8 SV) of cool, low salinity water entering the BS mainly through eastern, shallow-silled passes continues northward across the broad Beringian shelf to enter the Arctic Ocean via the Bering Strait. EVOLUTION OF ALEUTIAN RIDGE: At it's inception, the arc massif of the AR likely extended only about 1200 km west of Alaska. Because convergence is increasingly oblique to the west, plate-boundary-driven, right-lateral strike-slip faulting extensionally fragmented the AR and progressively rotated and transported blocks and slivers

  16. Oceanic, island arc, and back-arc remnants into eastern Kamchatka accretionary complexes

    SciTech Connect

    Fedorchuk, A.V.; Vishnevskaya, V.S.; Izvekov, I.N. )

    1990-06-01

    The Kamchatsky Mts. accretionary complex in the Eastern Kamchatka orogenic belt was studied for identification of the oceanic and suprasubduction components into accretionary wedges. That complex is divided into two tectonic units. The Lower unit is formed sedimentary and tectonic melanges containing arc-related components (Late Senonian volcaniclastics and boninitic gabbro) and oceanic fragments (Fe-Ti-tholeiites, ocean island basalts, and pelagic sediments of Valanginian to Turonian age). The Upper unit consists of ductile deformed oceanic cumulates from troctolites to Fe-Ti-gabbro, 151 to 172 Ma, which are intruded MORB-like diabases with suprasubduction characteristics, 122 to 141 Ma, and are overlain by basalts similar to latter. The Lower and Upper units are separated by a SW-dipping thrust, which is related by an ophiolitoclastic olistostrome of Late Campanian to Early Maestrichtian age. Both units are covered by Paleocene authoclastic deposits. They are all thrusted over the early Neogene island arc complex, 16 to 20 Ma. The Lower unit of the Kamchatsky Mys accretionary complex was originated in a shear zone between a Late Cretaceous island arc and an Early Cretaceous oceanic plate. The Upper unit represents a Jurassic oceanic remnant that formed a basement of Early Cretaceous back-arc or fore-arc basin. Both units were superposed in the latest Cretaceous. The Kamchatsky Mys accretionary complex was emplaced into the Eastern Kamchatka orogenic belt during late Neogene by collision of the early Neogene island arc.

  17. Adakitic volcanism in the eastern Aleutian arc: Petrology and geochemistry of Hayes volcano, Cook Inlet, Alaska

    NASA Astrophysics Data System (ADS)

    McHugh, K.; Hart, W. K.; Coombs, M. L.

    2012-12-01

    are the result of partial melting of this slab where thermal erosion and weakening of the crust occurs along the Pacific plate-Yakutat terrane transition. Additionally, flat slab subduction may be responsible for producing adakitic magmas by equilibration of the hydrous slab with ambient mantle temperatures. In contrast, it is possible that the adakitic signature at Hayes is from underplated mafic lower crust that melted as the result of pooling mantle melt at depth. Two volcanoes within the WVF, Mt. Drum and Mt. Churchill, are adakitic with an abundance of biotite and amphibole similar to Hayes volcano and have been suggested to have slab melt origins. Mt. Drum lavas have less radiogenic 87Sr/86Sr but overlapping 206Pb/204Pb signatures while Mt. Churchill, which approximately overlies the eastern edge of the Yakutat terrane, has similar 87Sr/86Sr compositions, but more radiogenic 206Pb/204Pb than Hayes. Mt. Spurr, the nearest CIV to Hayes volcano (90 km south), does not share its adakitic signature but exhibits overlapping, more heterogeneous isotopic compositions. Thus, understanding the petrogenetic history of Hayes volcano is essential not only to explain the development of an adakitic volcanic system but how this relates to regional, arc-wide volcanism.

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

    NASA Astrophysics Data System (ADS)

    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 (<15) and moderate 206Pb/204Pb (>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

  19. Geologic Map and Eruptive History of Veniaminof Volcano Record Aleutian Arc Processing of Mantle-Derived Melts

    NASA Astrophysics Data System (ADS)

    Bacon, C. R.; Sisson, T. W.; Calvert, A. T.; Nye, C. J.

    2009-12-01

    Mount Veniaminof, one of the largest volcanoes in the Aleutian arc, has a basal diameter of ~40 km, a volume of ~350 km3, an 8-km-diameter ice-filled caldera, and an active intracaldera cone. The geology of this tholeiitic basalt-to-dacite volcano has been mapped at 1:50,000 scale. Over 100 Quaternary volcanic map units are characterized by 600 chemical analyses of rocks and nearly 100 40Ar/39Ar and K-Ar ages. Throughout its history, lava flows from Veniaminof recorded alternately ice/melt-water chilling or ice-free conditions that are consistent with independent paleoclimatic records. Exposures from deep glacial valleys to the caldera rim reveal a long history dominated by basalt and basaltic andesite from ≥260 ka to 150 ka that includes compositions as primitive as 9.4% MgO and 130 ppm Ni at 50% SiO2. Basaltic andesite, common throughout Veniaminof's history, has low compatible-element contents that indicate an origin by fractionation of basaltic magma. Repeated eruption of more differentiated melts from a shallow intrusive complex, represented by granodiorite (crystallized dacitic magma) and cumulate gabbro and diorite xenoliths in pyroclastic deposits, has featured virtually aphyric andesite since 150 ka and dacite (to 69.5% SiO2) beginning ~110 ka. These variably differentiated liquids segregated from crystal mush, possibly by gas-driven filter pressing, and commonly vented but also solidified at depth. A large composite cone was present at least as early as 200 ka. Although asymmetric edifice morphology hints at early sector collapse to the southeast, coeval vents on northwest and southeast flanks and the distribution of extensive lava units indicate that a large cone (again) was present by 120 ka. Flank eruption of a wide variety of Veniaminof magmas was common from plate-convergence-parallel northwest-trending fissures from at least as early as ca. 80 ka. At 56 ka and at 46 ka, voluminous dacite lava erupted on both northwest and southeast flanks. A

  20. The Detection, Characterization and Tracking of Recent Aleutian Island Volcanic Ash Plumes and the Assessment of Their Impact on Aviation

    NASA Technical Reports Server (NTRS)

    Murray, John J.; Hudnall, L. A.; Matus, A.; Krueger, A. J.; Trepte, C. r.

    2010-01-01

    The Aleutian Islands of Alaska are home to a number of major volcanoes which periodically present a significant hazard to aviation. During summer of 2008, the Okmok and Kasatochi volcanoes experienced moderate eruptive events. These were followed a dramatic, major eruption of Mount Redoubt in late March 2009. The Redoubt case is extensively covered in this paper. Volcanic ash and SO2 from each of these eruptions dispersed throughout the atmosphere. This created the potential for major problems for air traffic near the ash dispersions and at significant distances downwind. The NASA Applied Sciences Weather Program implements a wide variety of research projects to develop volcanic ash detection, characterization and tracking applications for NASA Earth Observing System and NOAA GOES and POES satellites. Chemistry applications using NASA AURA satellite Ozone Monitoring System (OMI) retrievals produced SO2 measurements to trace the dispersion of volcanic aerosol. This work was complimented by advanced multi-channel imager applications for the discrimination and height assignment of volcanic ash using NASA MODIS and NOAA GOES and POES imager data. Instruments similar to MODIS and OMI are scheduled for operational deployment on NPOESS. In addition, the NASA Calipso satellite provided highly accurate measurements of aerosol height and dispersion for the calibration and validation of these algorithms and for corroborative research studies. All of this work shortens the lead time for transition to operations and ensures that research satellite data and applications are operationally relevant and utilized quickly after the deployment of operational satellite systems. Introduction

  1. Final Report: Weatherization and Energy Conservation Education and Home Energy and Safety Review in the Aleutian Islands

    SciTech Connect

    Bruce Wright

    2011-08-30

    Aleutian/Pribilof Islands Association, Inc. (APIA) hired three part-time local community members that desire to be Energy Technicians. The energy technicians were trained in methods of weatherization assistance, energy conservation and home safety. They developed a listing of homes in the region that required weatherization, and conducted on-site weatherization and energy conservation education and a home energy and safety reviews in the communities of Akutan, False Pass, King Cove and Nelson Lagoon. Priority was given to these smaller communities as they tend to have the residences most in need of weatherization and energy conservation measures. Local residents were trained to provide all three aspects of the project: weatherization, energy conservation education and a home energy and safety review. If the total energy saved by installing these products is a 25% reduction (electrical and heating, both of which are usually produced by combustion of diesel fuel), and the average Alaska home produces 32,000 pounds of CO2 each year, so we have saved about: 66 homes x 16 tons of CO2 each year x .25 = 264 tons of CO2 each year.

  2. MORPHOLOGY AND MOLECULAR PHYLOGENY OF AUREOPHYCUS ALEUTICUS GEN. ET SP. NOV. (LAMINARIALES, PHAEOPHYCEAE) FROM THE ALEUTIAN ISLANDS(1).

    PubMed

    Kawai, Hiroshi; Hanyuda, Takeaki; Lindeberg, Mandy; Lindstrom, Sandra C

    2008-08-01

    A previously unknown species of kelp was collected on Kagamil Island, Aleutian Islands. The species can be easily distinguished from any known laminarialean alga: the erect sporophytic thallus is composed of a thin lanceolate blade attaining ∼2 m in height and ∼0.50 m in width, without midrib, and the edge of the blade at the transition zone is thickened to form a V-shape; the stipe is solid and flattened, slightly translucent, attaining ∼1 m in length; the holdfast is semidiscoidal and up to 0.15 m in diameter. Anatomically, the blade has the typical trumpet-shaped hyphae characteristic of the Chordaceae and derived foliose laminarialean species (i.e., Alariaceae/Laminariaceae/Lessoniaceae). No hair pits or mucilaginous structures were observed on the blade or stipe. No fertile sporophytes were collected, but abundant juvenile sporophytes were observed in the field. In the molecular phylogenetic analyses using chloroplast rbcL gene, nuclear ITS1-5.8S-ITS2 rDNA, and mitochondria nad6 DNA sequences, the new species (Aureophycus aleuticus gen. et sp. nov.) showed a closer relationship with Alariaceae of conventional taxonomy, or the "Group 1" clade of Lane et al. (2006) including Alaria and related taxa than with other groups, although the species was not clearly included in the group. Aureophycus may be a key species in elucidating the evolution of the Alariaceae within the Laminariales. Because of the lack of information on reproductive organs and insufficient resolution of the molecular analyses, we refrain from assigning the new species to a family, but we place the new species in a new genus in the Laminariales. PMID:27041620

  3. Arc segmentation and seismicity in the Solomon Islands arc, SW Pacific

    NASA Astrophysics Data System (ADS)

    Chen, Ming-Chu; Frohlich, Cliff; Taylor, Frederick W.; Burr, George; van Ufford, Andrew Quarles

    2011-07-01

    This paper evaluates neotectonic segmentation in the Solomon Islands forearc, and considers how it relates to regional tectonic evolution and the extent of ruptures of large megathrust earthquakes. We first consider regional geomorphology and Quaternary vertical displacements, especially uplifted coral reef terraces. Then we consider geographic seismicity patterns, aftershock areas and vertical displacements for large earthquakes, focal mechanisms, and along-arc variations in seismic moment release to evaluate the relationship between neotectonically defined segments and seismicity. Notably, one major limitation of using seismicity to evaluate arc segmentation is the matter of accurately defining earthquake rupture zones. For example, shoreline uplifts associated with the 1 April 2007 M w 8.1 Western Solomons earthquake indicate that the along-arc extent of rupture was about 50 km smaller than the aftershock area. Thus if we had relied on aftershocks alone to identify the 2007 rupture zone, as we do for most historical earthquakes, we would have missed the rupture's relationship to a major morphologic feature. In many cases, the imprecision of defining rupture zones without surface deformation data may be largely responsible for the poor mismatches to neotectonic boundaries. However, when a precise paleoseismic vertical deformation history is absent, aftershocks are often the best available tool for inferring rupture geometries. Altogether we identify 16 segments in the Solomon Islands. These comprise three major tectonic regimes or supersegments that correspond respectively to the forearc areas of Guadalcanal-Makira, the New Georgia island group, and Bougainville Islands. Subduction of the young and relatively shallow and buoyant Woodlark Basin and spreading system distinguishes the central New Georgia supersegment from the two neighboring supersegments. The physiographic expression of the San Cristobal trench is largely absent, but bathymetric mapping of the

  4. 50 CFR Figure 1 to Part 679 - Bering Sea and Aleutian Islands Statistical and Reporting Areas

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... Statistical and Reporting Areas 1 Figure 1 to Part 679 Wildlife and Fisheries FISHERY CONSERVATION AND... Islands Statistical and Reporting Areas ER15NO99.000 b. Coordinates Code Description 300 Russian waters... statistical area is the part of a reporting area contained in the EEZ....

  5. 50 CFR Figure 1 to Part 679 - Bering Sea and Aleutian Islands Statistical and Reporting Areas

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... Statistical and Reporting Areas 1 Figure 1 to Part 679 Wildlife and Fisheries FISHERY CONSERVATION AND... Islands Statistical and Reporting Areas ER15NO99.000 b. Coordinates Code Description 300 Russian waters... statistical area is the part of a reporting area contained in the EEZ....

  6. 50 CFR Figure 1 to Part 679 - Bering Sea and Aleutian Islands Statistical and Reporting Areas

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... Statistical and Reporting Areas 1 Figure 1 to Part 679 Wildlife and Fisheries FISHERY CONSERVATION AND... Islands Statistical and Reporting Areas ER15NO99.000 b. Coordinates Code Description 300 Russian waters... statistical area is the part of a reporting area contained in the EEZ....

  7. 50 CFR Figure 1 to Part 679 - Bering Sea and Aleutian Islands Statistical and Reporting Areas

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... Statistical and Reporting Areas 1 Figure 1 to Part 679 Wildlife and Fisheries FISHERY CONSERVATION AND... Islands Statistical and Reporting Areas ER15NO99.000 b. Coordinates Code Description 300 Russian waters... statistical area is the part of a reporting area contained in the EEZ....

  8. Petrologic Evolution of Palau; A Nascent Island Arc

    NASA Astrophysics Data System (ADS)

    Hawkins, J. W.; Ishizuka, O.

    2008-12-01

    Initiation of subduction in intra-oceanic settings requires relative differences in plate thickness and density (i.e., age difference); a major zone of weakness separating the plates, e.g., a fracture zone; and a change in relative vectors of movement to cause convergence. These factors help explain the origin of the southern- most part of the > 2500 km long Kyushu - Palau Ridge (KPR). Palau Islands, at 7 deg 30 ' N, are the only significant emergent feature on KPR. Small islands are mainly uplifted Pliocene and younger reef carbonate. Large islands are mainly volcanic comprising rare boninite; major basalt, basaltic andesite and andesite; and minor dacite. Polymict breccia is abundant; sills, flows, dikes are common; pillows are rare. The same rock types, as well as high-Mg basalt, were dredged from the Palau Trench. Volcanism on Palau began in late Eocene and ended by early Miocene. Rocks are low-K primitive island arc- tholeiite series. None are MORB. REE and HFSE require a depleted mantle source. Zr* and Ti* suggest that melts interacted with OL-PX rocks of upper mantle or deep crust cumulates. Moderate enrichment of LILE and LREE indicate influx of "dehydration fluid." Ce/Ce* and Eu/Eu* show no evidence for subducted sediments or recycling of arc- derived clastics yet there is no accreted sedimentary prism. This paradox may be owing to lack of arc or terrigenous clastics on seafloor formed in open ocean "sterile" equatorial latitudes. Plate reconstructions and paleomagnetic data suggest that the "arc" probably formed on the trace of a transform fault that has migrated northward and rotated clockwise up to 90 deg. since Oligocene time. Episodes of transtension allowed upwelling of relatively fertile hot mantle into depleted mantle and sheared, altered, rocks of the transform. Episodes of transpression may have initiated subduction of seafloor having a thin cover of pelagic sediments (calcareous and radiolarian ooze, chert, chalk, limestone) deposited far from

  9. A model for selecting bioindicators to monitor radionuclide concentrations using Amchitka Island in the Aleutians as a case study.

    PubMed

    Burger, Joanna

    2007-11-01

    World War II and the Cold War have left the Unites States, and other Nations, with massive cleanup and remediation tasks for radioactive and other legacy hazardous wastes. While some sites can be cleaned up to acceptable residential risk levels, others will continue to hold hazardous wastes, which must be contained and monitored to protect human health and the environment. While media (soil, sediment, groundwater) monitoring is the usual norm at many radiological waste sites, for some situations (both biological and societal), biomonitoring may provide the necessary information to assure greater peace of mind for local and regional residents, and to protect ecologically valuable buffer lands or waters. In most cases, indicators are selected using scientific expertise and a literature review, but not all selected indicators will seem relevant to stakeholders. In this paper, I provide a model for the inclusion of stakeholders in the development of bioindicators for assessing radionuclide levels of biota in the marine environment around Amchitka Island, in the Aleutian Chain of Alaska. Amchitka was the site of three underground nuclear tests from 1965 to 1971. The process was stakeholder-initiated, stakeholder-driven, and included stakeholders during each phase. Phases included conceptualization, initial selection of biota and radionuclides, refinement of biota and radionuclide target lists, collection of biota, selection of biota and radionuclides for analysis, and selection of biota, tissues, and radionuclides for bioindicators. The process produced site-specific information on biota availability and on radionuclide levels that led to selection of site-appropriate bioindicators. I suggest that the lengthy, iterative, stakeholder-driven process described in this paper results in selection of bioindicators that are accepted by biologists, public health personnel, public-policy makers, resource agencies, regulatory agencies, subsistence hunters/fishers, and a wide

  10. Modeling the impacts of bottom trawling and the subsequent recovery rates of sponges and corals in the Aleutian Islands, Alaska

    NASA Astrophysics Data System (ADS)

    Rooper, Christopher N.; Wilkins, Mark E.; Rose, Craig S.; Coon, Catherine

    2011-11-01

    The abundance of some marine fish species are correlated to the abundance of habitat-forming benthic organisms such as sponges and corals. A concern for fisheries management agencies is the recovery of these benthic invertebrates from removal or mortality from bottom trawling and other commercial fisheries activities. Using a logistic model, observations of available substrate and data from bottom trawl surveys of the Aleutian Islands, Alaska, we estimated recovery rates of sponges and corals following removal. The model predicted the observed sponge and coral catch in bottom trawl surveys relatively accurately ( R2=0.38 and 0.46). For sponges, the results show that intrinsic growth rates were slow ( r=0.107 yr -1). Results show that intrinsic growth rates of corals were also slow ( r=0.062 yr -1). The best models for corals and sponges were models that did not include the impacts of commercial fishing removals. Subsequent recovery times for both taxa were also predicted to be slow. Mortality of 67% of the initial sponge biomass would recover to 80% of the original biomass after 20 years, while mortality of 67% of the coral biomass would recover to 80% of the original biomass after 34 years. The modeled recovery times were consistent with previous studies in estimating that recovery times were of the order of decades, however improved data from directed studies would no doubt improve parameter estimates and reduce the uncertainty in the model results. Given their role as a major ecosystem component and potential habitat for marine fish, damage and removal of sponges and corals must be considered when estimating the impacts of commercial bottom trawling on the seafloor.

  11. Levels of Polychlorinated Biphenyls (PCBs) and Three Organochlorine Pesticides in Fish from the Aleutian Islands of Alaska

    PubMed Central

    Hardell, Sara; Tilander, Hanna; Welfinger-Smith, Gretchen; Burger, Joanna; Carpenter, David O.

    2010-01-01

    Background Persistent organic pollutants (POPs), including polychlorinated biphenyls (PCBs) and chlorinated pesticides, have been shown to have many adverse human health effects. These contaminants therefore may pose a risk to Alaska Natives that follow a traditional diet high in marine mammals and fish, in which POPs bioaccumulate. Methods and Findings This study examined the levels of PCBs and three pesticides [p, p′-DDE, mirex, and hexachlorobenzene (HCB)] in muscle tissue from nine fish species from several locations around the Aleutian Islands of Alaska. The highest median PCB level was found in rock sole (Lepidopsetta bilineata, 285 ppb, wet weight), while the lowest level was found in rock greenling (Hexagrammos lagocephalus, 104 ppb, wet weight). Lipid adjusted PCB values were also calculated and significant interspecies differences were found. Again, rock sole had the highest level (68,536 ppb, lipid weight). Concerning the PCB congener patterns, the more highly chlorinated congeners were most common as would be expected due to their greater persistence. Among the pesticides, p, p′-DDE generally dominated, and the highest level was found in sockeye salmon (Oncorhynchus nerka, 6.9 ppb, wet weight). The methodology developed by U.S. Environmental Protection Agency (USEPA) was used to calculate risk-based consumption limits for the analyzed fish species. For cancer health endpoints for PCBs, all species would trigger strict advisories of between two and six meals per year, depending upon species. For noncancer effects by PCBs, advisories of between seven and twenty-two meals per year were triggered. None of the pesticides triggered consumption limits. Conclusion The fish analyzed, mainly from Adak, contain significant concentrations of POPs, in particular PCBs, which raises the question whether these fish are safe to eat, particularly for sensitive populations. However when assessing any risk of the traditional diet, one must also consider the many health

  12. A model for selecting bioindicators to monitor radionuclide concentrations using Amchitka Island in the Aleutians as a case study

    SciTech Connect

    Burger, Joanna

    2007-11-15

    World War II and the Cold War have left the Unites States, and other Nations, with massive cleanup and remediation tasks for radioactive and other legacy hazardous wastes. While some sites can be cleaned up to acceptable residential risk levels, others will continue to hold hazardous wastes, which must be contained and monitored to protect human health and the environment. While media (soil, sediment, groundwater) monitoring is the usual norm at many radiological waste sites, for some situations (both biological and societal), biomonitoring may provide the necessary information to assure greater peace of mind for local and regional residents, and to protect ecologically valuable buffer lands or waters. In most cases, indicators are selected using scientific expertise and a literature review, but not all selected indicators will seem relevant to stakeholders. In this paper, I provide a model for the inclusion of stakeholders in the development of bioindicators for assessing radionuclide levels of biota in the marine environment around Amchitka Island, in the Aleutian Chain of Alaska. Amchitka was the site of three underground nuclear tests from 1965 to 1971. The process was stakeholder-initiated, stakeholder-driven, and included stakeholders during each phase. Phases included conceptualization, initial selection of biota and radionuclides, refinement of biota and radionuclide target lists, collection of biota, selection of biota and radionuclides for analysis, and selection of biota, tissues, and radionuclides for bioindicators. The process produced site-specific information on biota availability and on radionuclide levels that led to selection of site-appropriate bioindicators. I suggest that the lengthy, iterative, stakeholder-driven process described in this paper results in selection of bioindicators that are accepted by biologists, public health personnel, public-policy makers, resource agencies, regulatory agencies, subsistence hunters/fishers, and a wide

  13. Signs of continental rifting in the southwestern Japanese Island Arc

    NASA Astrophysics Data System (ADS)

    Chernysheva, E. A.; Eroshenko, D. V.

    2016-03-01

    The southwestern margin of the Japan Arc evolved in the geodynamic regime of continental rifting during the Miocene-Pleistocene. This has been verified by broad manifestations of metasomatosis of mantle peridotites that underlie the lithosphere of the Japan Islands and by episodes of deep magmatism (kimberlites and melilitites) in the region. The high enrichment of deep melts in incompatible rare and rare earth elements is partially preserved in melts of regional basalts from smaller depths. In contrast, spreading basalts of the Sea of Japan and subduction basalts from the Nankai trench at the boundary with the Philippine Plate are extremely depleted in rare elements.

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

    NASA Astrophysics Data System (ADS)

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

    2005-12-01

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

  15. Testing the nutritional-limitation, predator-avoidance, and storm-avoidance hypotheses for restricted sea otter habitat use in the Aleutian Islands, Alaska.

    PubMed

    Stewart, Nathan L; Konar, Brenda; Tinker, M Tim

    2015-03-01

    Sea otters (Enhydra lutris) inhabiting the Aleutian Islands have stabilized at low abundance levels following a decline and currently exhibit restricted habitat-utilization patterns. Possible explanations for restricted habitat use by sea otters can be classified into two fundamentally different processes, bottom-up and top-down forcing. Bottom-up hypotheses argue that changes in the availability or nutritional quality of prey resources have led to the selective use of habitats that support the highest quality prey. In contrast, top-down hypotheses argue that increases in predation pressure from killer whales have led to the selective use of habitats that provide the most effective refuge from killer whale predation. A third hypothesis suggests that current restricted habitat use is based on a need for protection from storms. We tested all three hypotheses for restricted habitat use by comparing currently used and historically used sea otter foraging locations for: (1) prey availability and quality, (2) structural habitat complexity, and (3) exposure to prevailing storms. Our findings suggest that current use is based on physical habitat complexity and not on prey availability, prey quality, or protection from storms, providing further evidence for killer whale predation as a cause for restricted sea otter habitat use in the Aleutian Islands. PMID:25416538

  16. Magma genesis in the lesser Antilles island arc

    NASA Astrophysics Data System (ADS)

    Hawkesworth, C. J.; Powell, M.

    1980-12-01

    143Nd/ 144Nd, 87Sr/ 86Sr and REE results are reported on volcanic rocks from the islands of Dominica and St. Kitts in the Lesser Antilles. Particular attention is given to the lavas and xenoliths of the Foundland (basalt-andesite) and the Plat Pays (andesite-dacite) volcanic centres on Dominica. Combined major and trace element [ 2] and isotope results suggest that the bulk of the andesites and dacites on Dominica, and by analogy in the rest of the arc, are produced by fractional crystallisation of basaltic magma. The differences in the erupted products of the two volcanoes do not appear to be related to any significant differences in the source rocks of the magmas. Along the arc 87Sr/ 86Sr ratios range from 0.7037 on St. Kitts, to 0.7041-0.7047 on Dominica, and 0.7039-0.7058 on Grenada [ 5], and these are accompanied by a parallel increase in K, Sr, Ba and the light REE's. Moreover, compared with LIL-element-enriched and -depleted rocks from MOR and intraplate environments, the basic rocks from the Lesser Antilles are preferentially enriched in alkaline elements (K, Ba, Rb, Sr) relative to less mobile elements such as the rare earths. 143Nd/ 144Nd varies from 0.51308 on St. Kitts, to 0.51286 on Dominica, and 0.51264-0.51308 on Grenada [ 5], and all these samples have relatively high 87Sr/ 86Sr ratios compared with the main trend of Nd and Sr isotopes for most mantle-derived volcanic rocks. Alkaline elements and 87Sr appear to have been introduced from the subducted ocean crust, but the results on other, less mobile elements are more ambiguous — island arc tholeiites (as on St. Kitts) do not appear to contain significant amounts of REE's, Zr, Y, etc., from the subducted oceanic crust, but such a contribution may be present in more LIL-element-enriched calc-alkaline rock types.

  17. Altimetry data over trenches and island-arcs and convection in the mantle

    NASA Technical Reports Server (NTRS)

    1980-01-01

    Transfer function techniques were developed to calculate the isostatic component of the geoid signal over trench/island arc/back arc systems. Removal of this isostatic component from geoid profiles determined by GEOS 3 radar altimetry leaves a residual geoid that can be attributed to the effect of mass inhomogeneities below the depth of compensation. Efforts are underway to extend the analysis to all the major trench/island arc systems of the world in order to provide more detailed understanding of the dynamic processes occurring beneath island arcs.

  18. A Detailed Geochemical Study of Island Arc Crust: The Talkeetna Arc Section, South-central Alaska

    NASA Astrophysics Data System (ADS)

    Greene, A. R.; Debari, S. M.; Kelemen, P. B.; Clift, P. D.; Blusztajn, J.

    2002-12-01

    The Talkeetna arc section in south-central Alaska is recognized as the exposed upper mantle and crust of an accreted, Late Triassic to Middle Jurassic island arc. Detailed geochemical studies of layered gabbronorite from the middle and lower crust of this arc and a diverse suite of volcanic and plutonic rocks from the middle and upper crust provide crucial data for understanding arc magma evolution. We also present new data on parental magma compositions for the arc. The deepest level of the arc section consists of residual mantle and ultramafic cumulates adjacent to garnet gabbro and basal gabbronorite interlayered with pyroxenite. The middle crust is primarily layered gabbronorite, ranging from anorthosite to pyroxenite in composition, and is the most widespread plutonic lithology. The upper mid crust is a heterogenous assemblage of dioritic to tonalitic rocks mixed with gabbro and intruded by abundant mafic dikes and chilled pillows. The upper crust of the arc is comprised of volcanic rocks of the Talkeetna Formation ranging from basalt to rhyolite. Most of these volcanic rocks have evolved compositions (<5% MgO, Mg# <60) and overlap the composition of intermediate to felsic plutonic rocks (<3.5% MgO, Mg# <45). However, several chilled mafic rocks and one basalt have primitive characteristics (>8% MgO, Mg# >60). Ion microprobe analyses of clinopyroxene in mid-crustal layered gabbronorites have parallel REE patterns with positive-sloping LREE segments (La/Sm(N)=0.05-0.17; mean 0.11) and flat HREE segments (5-25xchondrite; mean 10xchondrite). Liquids in REE equilibrium with the clinopyroxene in these gabbronorite cumulates were calculated in order to constrain parental magmas. These calculated liquids(La/Sm(N)=0.77-1.83; mean 1.26) all fall within the range of dike and volcanic rock(La/Sm(N)=0.78-2.12; mean 1.23) compositions. However, three lavas out of the 44 we have analyzed show strong HREE depletion, which is not observed in any of the liquid compositions

  19. Oxygen isotope constraints on the origin of island arc granitoids

    NASA Astrophysics Data System (ADS)

    Perez, R. J.; Cavosie, A. J.; Valley, J. W.

    2007-12-01

    Granitic intrusions in island arcs constitute additions of juvenile crust from oceanic environs that ultimately get accreted to continents. The genesis of island arc granitoids is thus important to studies of the growth of oceanic and continental crust. Puerto Rico (USA) is a composite island arc terrane that preserves a record of plutonism from 85 Ma to 38 Ma (Cavosie et al., 2007 AGU). Mid-crustal granitoid plutons are exposed (~1 to 500 km2), but their origins are unknown, as no suspected parental magmas associated with the plutons (e.g., gabbro) are exposed. This study uses petrography, WR major elements, and oxygen isotopes of WR and zircon from granitoids and xenoliths to place better constraints on the origin of granitoid in the Greater Antilles island arc. WR δ18O analyses were made with laser fluorination by IRMS at the Univ. of Wisconsin (uncertainties = 0.10 to 0.20‰, 2sd). The main plutons (Caguas, Rio Blanco, San Lorenzo, Utuado, Vieques) yield primitive δ18O(WR) values, ranging from 6.24 to 7.72‰ over a range of wt.% SiO2= 58.03 to 66.54. Smaller stocks (<20 km2) yield higher δ18O(WR) values, ranging from 7.47 to 10.27‰. Qualitative petrographic analysis reveals that granitoids with δ18O(WR) >~7.5‰ are partially to pervasively altered. Zircon preserves magmatic δ18O and is used here to quantitatively evaluate the measured δ18O(WR) values. If δ18O(Zrc) and wt.% SiO2 are known, a comparison of measured vs. predicted δ18O(WR) can be made (Valley et al., 2005, CMP). The measured δ18O(WR) values record variable amounts of alteration, ranging from virtually undetectable, to WR δ18O elevations of ~4‰, indicative of low-T subsolidus alteration. The Δ18O (WR-Zrc) values using calculated δ18O(WR) yield the following fractionations: -1.57 to 1.00‰ for granodiorites (wt.% SiO2=66 to 57); -0.85‰ for diorite (wt.% SiO2=55); and -0.56‰ for the only gabbro analyzed (wt.% SiO2=50). Mafic xenoliths (53-57 wt.% SiO2) from 4 granitoids yield

  20. Mercury, arsenic, cadmium, chromium lead, and selenium in feathers of pigeon guillemots (Cepphus columba) from Prince William Sound and the Aleutian Islands of Alaska.

    PubMed

    Burger, Joanna; Gochfeld, Michael; Sullivan, Kelsey; Irons, David

    2007-11-15

    Arsenic, cadmium, chromium, lead, manganese, mercury and selenium were analyzed in the feathers of pigeon guillemots (Cepphus columba) from breeding colonies in Prince William Sound and in the Aleutian Islands (Amchitka, Kiska) to test the null hypothesis that there were no differences in metal levels as a function of location, gender, or whether the birds were from oiled or unoiled areas in Prince William Sound. Birds from locations with oil from the Exxon Valdez Oil Spill in the environment had higher levels of cadmium and lead than those from unoiled places in Prince William Sound, but otherwise there were no differences in metal levels in feathers. The feathers of pigeon guillemots from Prince William Sound had significantly higher levels of cadmium and manganese, but significantly lower levels of mercury than those from Amchitka or Kiska in the Aleutians. Amchitka had the lowest levels of chromium, and Kiska had the highest levels of selenium. There were few gender-related differences, although females had higher levels of mercury and selenium in their feathers than did males. The levels of most metals are below the known effects levels, except for mercury and selenium, which are high enough to potentially pose a risk to pigeon guillemots and to their predators. PMID:17765292

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

    NASA Astrophysics Data System (ADS)

    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

  2. 16ch high-resolution seismic reflection surveys on the active fault of upper fore-arc slope off Okinawa Island, central Ryukyu Island Arc, Southwest Japan

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

  3. Petrology and tectonics of Phanerozoic continent formation: From island arcs to accretion and continental arc magmatism

    USGS Publications Warehouse

    Lee, C.-T.A.; Morton, D.M.; Kistler, R.W.; Baird, A.K.

    2007-01-01

    Mesozoic continental arcs in the North American Cordillera were examined here to establish a baseline model for Phanerozoic continent formation. We combine new trace-element data on lower crustal xenoliths from the Mesozoic Sierra Nevada Batholith with an extensive grid-based geochemical map of the Peninsular Ranges Batholith, the southern equivalent of the Sierras. Collectively, these observations give a three-dimensional view of the crust, which permits the petrogenesis and tectonics of Phanerozoic crust formation to be linked in space and time. Subduction of the Farallon plate beneath North America during the Triassic to early Cretaceous was characterized by trench retreat and slab rollback because old and cold oceanic lithosphere was being subducted. This generated an extensional subduction zone, which created fringing island arcs just off the Paleozoic continental margin. However, as the age of the Farallon plate at the time of subduction decreased, the extensional environment waned, allowing the fringing island arc to accrete onto the continental margin. With continued subduction, a continental arc was born and a progressively more compressional environment developed as the age of subducting slab continued to young. Refinement into a felsic crust occurred after accretion, that is, during the continental arc stage, wherein a thickened crustal and lithospheric column permitted a longer differentiation column. New basaltic arc magmas underplate and intrude the accreted terrane, suture, and former continental margin. Interaction of these basaltic magmas with pre-existing crust and lithospheric mantle created garnet pyroxenitic mafic cumulates by fractional crystallization at depth as well as gabbroic and garnet pyroxenitic restites at shallower levels by melting of pre-existing lower crust. The complementary felsic plutons formed by these deep-seated differentiation processes rose into the upper crust, stitching together the accreted terrane, suture and former

  4. Island-arc magmatic processes beneath South Pagan Volcano, Northern Mariana Islands

    NASA Astrophysics Data System (ADS)

    Marske, J. P.; Trusdell, F. A.; Garcia, M. O.; Pietruszka, A. J.

    2007-12-01

    The island-arc volcanoes that make up the Northern Mariana Islands are among the most historically active stratovolcanoes along the Pacific plate, yet they have been poorly studied due to their remote location and difficult accessibility. One of the least studied areas in the Northern Mariana Islands is Pagan Island, located near the center of the Mariana ridge. Pagan Island consists of two Holocene stratovolcanoes, Mount Pagan and South Pagan. Remarkably little is known about South Pagan including its eruptive history, potential volcanic hazards, and geochemical evolution due to a small population of inhabitants, a short and intermittent recorded history, and few geological studies. There is abundant evidence that eruption of South Pagan could pose significant hazards to both residents of the Northern Mariana Islands and to aircraft flying in the western Pacific. For example, following Mount Pagan's most recent explosive eruption (VEI = 4) in 1981, destructive rain-triggered volcanic debris flows buried large tracts of land, including the site of a village that contained a school, dispensary, church, and power generating buildings. Preliminary field studies in May 2006 by the USGS showed that a full spectrum of hazardous phenomena originated from South Pagan in the past, including pyroclastic flows and surges, caldera collapses, and volcanic debris flows. Two previously unrecognized active fumaroles near the summit of South Pagan were discovered suggesting that potential volcanic hazards currently exist in this area. A majority of the new lava samples are vesicular, clinopyroxene-plagioclase basalts with minor plagioclase xenocrysts and gabbroic xenoliths. The purpose of this study is to understand the compositional history of South Pagan and how it relates to the crustal and mantle magmatic processes beneath the central Northern Mariana Islands. Pb, Sr and Nd isotope ratios, major and trace element abundances, and mineral chemistry were determined and will be

  5. Erosion and deterioration of Isles Dernieres Barrier Island arc, Louisiana: 1842-1988

    SciTech Connect

    McBride, R.A.; Westphal, K.; Penland, S. ); Jaffe, B. ) ); Williams, S.J. )

    1989-09-01

    The Isles Dernieres barrier island arc is the most rapidly eroding coastline in the US. Located on the Mississippi River delta plain in Terrebonne Parish, Louisiana, the Isles Dernieres consists of four smaller islands in a 32-km long chain. From west to east, these islands are known as Raccoon Island, Whiskey Island, Trinity Island, and East Island. The barrier island arc is separated from the mainland by Caillou Bay, Boca Caillou, and Lake Pelto lagoonal systems. The abandonment and transgression of the Bayou Petit Caillou delta (part of the larger Lafourche delta complex) over the last 600 years, along with sea level rise, repeated storm impacts, and rapid shoreface erosion, have led to the formation of the Isles Dernieres. Continued transgressive submergence combined with a diminishing sediment supply are driving the extreme coastal erosion found in the Isles Dernieres.

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

    NASA Astrophysics Data System (ADS)

    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

  7. Making and breaking an island arc: A new perspective from the Oligocene Kyushu-Palau arc, Philippine Sea

    NASA Astrophysics Data System (ADS)

    Ishizuka, Osamu; Taylor, Rex N.; Yuasa, Makoto; Ohara, Yasuhiko

    2011-05-01

    The Kyushu-Palau Ridge (KPR) is a 2600 km long remnant island arc that is separated from the active Izu-Bonin-Mariana (IBM) arc by a series of spreading and rift basins. We present 40Ar/39Ar ages and geochemical data for the entire length of the Kyushu-Palau arc as well as for the conjugate arc which is stranded within the IBM fore arc. New 40Ar/39Ar ages indicate that the KPR was active between 25 and 48 Ma, but the majority of the exposed volcanism occurred in the final phase, between 25 and 28 Ma. Rifting of the Kyushu-Palau arc to form the Shikoku and Parece Vela basins occurred simultaneously along the length of the arc (circa 25 Ma), and at a similar distance from the trench. Unlike the IBM, the KPR has only limited systematic along-arc geochemical trends. Two geochemical components within the KPR indicate an origin in the suprasubduction mantle. First, EM-1-like lavas are identified in a restricted section of the arc, suggesting a localized heterogeneity. Second, EM-2-like arc volcanoes formed on juvenile West Philippine Basin crust, potentially reflecting ingress of mantle from the then active EM-2 province which lies in the west. Another geochemical heterogeneity is found at the KPR-Daito Ridge intersection where the arc developed on preexisting Cretaceous Daito Ridge crust. The geochemical characteristics at this intersection likely result from the involvement of sub-Daito Ridge lithospheric mantle. Subduction flux beneath the KPR generally matches post-45 Ma Eocene/Oligocene lavas in the IBM fore arc, involving fluids and melts derived from altered igneous crust.

  8. Oceanic island arc stratigraphy in the Caribbean region: don't take it for granite

    NASA Astrophysics Data System (ADS)

    Larue, D. K.; Smith, A. L.; Schellekens, J. H.

    1991-11-01

    A popular misconception of island arcs is that they consist mostly of intrusive rocks belonging to the granite family, and volcanic rocks. Study of exhumed Caribbean island arcs indicates that they are composed mostly of sedimentary rocks such as epiclastic volcanic materials, and true plutonic and volcanic rocks are relatively minor. A simple model for the stratigraphic development of oceanic island arcs is proposed based on observations in the Caribbean region and intuitive reasoning. The lowermost part of the model arc is oceanic crust (oceanic arc depositional system 1, or OADS I). Built atop of the oceanic crust is the arc sequence, including volcaniclastic strata, lava flows with feeder dikes and plutons. Oceanic arc strata consist of a lower pyroclastic-absent volcanic unit (OADS II) formed by submarine volcanism, and an upper unit (OADS III) bearing volcanic, pyroclastic and epiclastic rocks (referred to here as the pyroclastic-present association or unit). Both OADS II and III may contain intercalated pelagic and/or biogenic sediments such as limestones and cherts. Submarine volcanic rocks include pillowed and sheet lava flows, lithic and hyaloclastic breccias and resedimented lithic and hyaloclastic debris. OADS III can be recognized by the presence of shallow-water fossils, stream- or beach-worn volcanic clasts and other epiclastic materials even in deep-water environments where such materials are resedimented. Shallow-water materials and epiclastic strata are never found in OADS II. Thickness of the units vary in accordance with initial water depth of oceanic crust prior to arc formation, amount of thermally induced uplift during early arc rifting, subsidence due to loading, and differential basinal subsidence or rates of volcanic aggradation. Examples of arc sequences from Aruba, Bonaire, Curaçao, Grenada, Martinique, the Virgin Islands and Puerto Rico show significant variability. Aruba and Curaçao show incomplete sequences of arc growth and may

  9. The Quaternary adakite distribution of Kyushu Island, Ryukyu Arc, Japan

    NASA Astrophysics Data System (ADS)

    Shibata, T.; Yoshikawa, M.; Takemura, K.

    2011-12-01

    The Quaternary volcanoes are widely distributed in Kyusu Island, Japan. Philippine Sea plate is subducting beneath Kyushu. Clear distribution of deep seismic foci is observed below the Quaternary volcanoes in southern area, but not in northern area. Notsu et al. (1990, JVGR) examined the contribution of subduction to the magma source, and emphasized that no slab derived material is observed in northern area from Sr isotopic compositions. Volcanic activity similar to the within-plate type volcanism has been also emphasized for the magma genesis of this area (e.g. Kita et al, 2001, JVGR). However, we found adakitic rocks, which show high Sr/Y ratios and low Y concentrations (e.g. Defant and Drummond, 1990, Nature) from some Quaternary volcanoes in north Kyushu on the basis of published data (Otha et al, 1990, GANKO; Itoh, 1990, GANKO). Therefore, the magma genesis is still controversial. We studied lateral variations of Sr, Nd and Pb isotopic and trace element compositions for Quaternary volcanics from Kyushu to investigate the magma genesis. From the results, a clear variation of Sr/Y ratio, decreasing from north to south, is observed along the volcanic front. Some of the Sr/Y ratio of the most northern part of Kyusu shows the value >100. The all analyzed Pb isotope compositions show a single liner trend in 208Pb/204Pb v.s. 206Pb/204Pb diagram. The liner trend of Pb isotope ratios can be explained by the binary mixing of the Shikoku Basin basalt and tereginious sediment which might be a constituent of the subducting slab. The similar binary mixing relationships are found in Sr and Nd isotopic systematics. The isotopic characteristics of the Quaternary magma in Kyushu can be explained by the magma generation process of island arc, in spite of the lack of deep seismic foci in northern area. It is considered that high and low Sr/Y ratios suggest the contributions of partial melt in the north and aqueous fluid derived from subducting slab in the south, respectively. If

  10. Cyclicity in Silurian island-arc carbonates, Alexander terrane, Alaska

    SciTech Connect

    Kittredge, L.E.; Soja, C.M. . Dept. of Geology)

    1993-03-01

    Silurian carbonates from Alaska (Alexander terrane) record the evolution of a submarine platform during waning volcanism in an island arc. A detailed stratigraphic analysis of a 47 meter-thick sequence revealed the existence of cyclically repeated limestones: coral-stromatoporoid wackestones alternate with oncoid packstones and bioturbated, silty lime mudstones. The coral-stromatoporoid deposits are characterized by a low-diversity assemblage of dendroid corals, massive stromatoporoids, Atrypoidea brachiopods, and rare occurrences of biostromes associated with Solenopora, high-spired gastropods, and crinoids. Oncoids typically are 2-6 mm in diameter and form massive, meter-thick units. Coated grains are symmetrically developed, have a shell or algal nucleus, and are also a minor component of coral-stromatoporoid beds. These lithologic units form seven, shallowing-upwards cycles (parasequences) that range in thickness from 3-9 meters. Coral-stomatoporoid wackestones form the base of each cycle and grade upwards into oncoid packstones with silty, lime mudstones at the top. This succession of lithofacies within each cycle reflects an increase in energy levels from relatively deeper water environments to relatively shallower ones. The lack of abrasion in the corals and stromatoporoids suggests predominantly quiet-water conditions in shallow subtidal areas affected by periodic turbulence. Comparison with correlative sections in Alaska and lack of correspondence with global sea level curves suggest that the primary cause of cyclicity was tectonic perturbations with secondary eustatic effects. Cyclic deposition in peri/subtidal sites was terminated by rapid drowning of the carbonate platform during late Silurian orogenesis.

  11. Studies of Aleutian volcanoes based on two decades of SAR imagery

    NASA Astrophysics Data System (ADS)

    Lu, Z.; Dzurisin, D.

    2015-12-01

    With its global coverage and all-weather imaging capability, interferometric synthetic aperture radar (InSAR) has become an increasingly important technique for studying magma dynamics at volcanoes in remote regions, such as the Aleutian Islands. The spatial distribution of surface deformation derived from InSAR data enables the construction of detailed mechanical models to aid the investigation of magmatic processes. We processed nearly 12,000 SAR images of Aleutian volcanoes acquired by ERS-1, JERS-1, ERS-2, Radarsat-1, Envisat, ALOS, and TerraSAR-X from the early 1990s to 2010. We combined these SAR images to produce about 25,000 interferograms, which we analyzed for evidence of surface deformation at most of the arc's Holocene volcanoes. This talk summarizes deformation processes at Aleutian volcanoes observed with InSAR, including: (1) time-varying volcanic inflation and magmatic intrusion, (2) deformation preceding and accompanying seismic swarms , (3) persistent volcano-wide subsidence at calderas that last erupted tens of years ago, (4) episodic magma intrusion and associated tectonic stress release, (5) subsidence caused by a decrease in pore fluid pressure in active hydrothermal systems, (6) subsidence of surface lava and pyroclastic flows, and (7) a lack of deformation at some volcanoes with recent eruptions, where deformation might be expected. Our work demonstrates that deformation patterns and associated magma supply mechanisms at Aleutian volcanoes are diverse and vary in both space and time. By combining InSAR results with information from the geologic record, accounts of historical eruptions, and data from seismology, petrology, gas geochemistry, and other sources, we have developed conceptual models for the magma plumbing systems and behaviors of many volcanoes in the Aleutian arc. We realize that these models are simplistic, but it is our hope that they will serve as foundations that will be refined as additional information becomes available.

  12. Cycling of sulfur in subduction zones: The geochemistry of sulfur in the Mariana Island Arc and back-arc trough

    USGS Publications Warehouse

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

    1993-01-01

    The sulfur contents and sulfur isotopic compositions of 24 glassy submarine volcanics from the Mariana Island Arc and back-arc Mariana Trough were determined in order to investigate the hypothesis that subducted seawater sulfur (??34S = 21???) is recycled through arc volcanism. Our results for sulfur are similar to those for subaerial arc volcanics: Mariana Arc glasses are enriched in 34S (??34S = up to 10.3???, mean = 3.8???) and depleted in S (20-290 ppm, mean = 100 ppm) relative to MORB (850 ppm S, ??34S = 0.1 ?? 0.5???). The back-arc trough basalts contain 200-930 ppm S and have ??34S values of 1.1 ?? 0.5???, which overlap those for the arc and MORB. The low sulfur contents of the arc and some of the trough glasses are attributed to (1) early loss of small amounts of sulfur through separation of immiscible sulfide and (2) later vapor-melt equilibrium control of sulfur contents and loss of sulfur in a vapor phase from sulfide-undersaturated melts near the minimum in sulfur solubility at f{hook}O2 ??? NNO (nickel-nickel oxide). Although these processes removed sulfur from the melts their effects on the sulfur isotopic compositions of the melts were minimal. Positive trends of ??34S with 87Sr 86Sr, LILE and LREE contents of the arc volcanics are consistent with a metasomatic seawater sulfur component in the depleted sub-arc mantle source. The lack of a 34S-rich slab signature in the trough lavas may be attributed to equilibration of metasomatic fluid with mantle material along the longer pathway from the slab to the source of the trough volcanics. Sulfur is likely to have been transported into the mantle wedge by metasomatic fluid derived from subducted sediments and pore fluids. Gases extracted from vesicles in arc and back-arc samples are predominantly H2O, with minor CO2 and traces of H2S and SO2. CO2 in the arc and back-arc rocks has ??13C values of -2.1 to -13.1???, similar to MORB. These data suggest that degassing of CO2 could explain the slightly lower

  13. Seismic Reflection Image Across the Izu-Bonin Island Arc System

    NASA Astrophysics Data System (ADS)

    Park, J.; Tsuru, T.; Takahashi, N.; Kodaira, S.; Kaneda, Y.

    2002-12-01

    The Izu-Bonin island arc system occupies almost a northern half of the Izu-Bonin-Island (IBM) arc system extending 2500 km south from near Tokyo, which is one of the largest convergent margins on earth. This Izu-Bonin island arc system is a typical intra-oceanic island arc system involving trench-arc-backarc basin system, i.e., the Izu-Bonin trench, the Izu-Bonin arc, and the backarc Shikoku basin. In order to figure out the past 50 m.y. development history of the entire Izu-Bonin intra-oceanic island arc system, we collected marine multichannel seismic (MCS) reflection data across the island arc system on board the R/V Kairei of the Japan Marine Science and Technology Center (JAMSTEC) in May 2002. We used a ~5-km, 204-channel streamer and a 12,000 cubic inch (~200 L) air-guns array. Receiver spacing was 25-m, yielding 51-fold coverage at 12.5-m CDP spacing. We acquired the MCS data on two different lines: ~560-km-long Line 1 and ~1140-km-long Line 3. The MCS data were migrated in depth domain. Velocity-depth models for the depth migration were iteratively constructed by prestack depth migration velocity analysis. Wide-angle data guided the velocity analysis. In this paper, we show the two MCS profiles and discuss the development process of the Izu-Bonin island arc system from viewpoints of seismic stratigraphy and structure. We identify a clear seismic reflector of the subducting Pacific plate with several horst-and-graben structures, which can be observed beneath the arc more than 60 km landward from the trench axis. Forearc basin is characterized by several buried normal faults and vigorous intra-oceanic sedimentation. In the arc rifting zone, we observe many seismic hyperbolic signatures indicative of active volcanic intrusions, which are related to active magmatism. The topmost sedimentary cover sequences are obviously tilted and cut by many normal faults. It is noticeable that reflectors of the middle crust in the arc-backarc transition zone appear to pinch

  14. 75 FR 4491 - Fisheries of the Exclusive Economic Zone Off Alaska; Atka Mackerel in the Bering Sea and Aleutian...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-01-28

    ... Economic Zone Off Alaska; Atka Mackerel in the Bering Sea and Aleutian Islands Management Area AGENCY... mackerel in the Eastern Aleutian District and the Bering Sea subarea of the Bering Sea and Aleutian Islands... necessary to fully use the 2010 A season total allowable catch (TAC) of Atka mackerel in these...

  15. 78 FR 42023 - Fisheries of the Exclusive Economic Zone Off Alaska; Atka Mackerel in the Bering Sea and Aleutian...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-07-15

    ... under Sec. 679.2(d)(1)(iii) on June 11, 2013 (78 FR 35771, June 14, 2013). As of July 8, 2013, NMFS has... Economic Zone Off Alaska; Atka Mackerel in the Bering Sea and Aleutian Islands Management Area AGENCY... mackerel in the Central Aleutian district (CAI) of the Bering Sea and Aleutian Islands Management...

  16. Island-arc carbonates: characterization and recognition in the ancient geologic record

    NASA Astrophysics Data System (ADS)

    Soja, C. M.

    1996-10-01

    Carbonates of island-arc origin that are preserved in Paleozoic-Mesozoic terranes of the North American Cordillera exhibit a distinctive suite of paleontologic and lithologic features and share a fundamental similarity with limestones forming in modern volcanic arcs. This study provides the first detailed synthesis of carbonate depositional systems in island arcs and documents primary sedimentary constituents based on facies relationships and faunal communities. Models are developed that show patterns in the long-term evolution of shallow marine organisms and the construction, evolution, and demise of carbonate platforms in island arcs. A suite of criteria is identified that may be used to differentiate island-arc carbonates from limestones that accumulated in other platform settings. Biogeographic isolation, prolonged subsidence, steep submarine slopes and tectonic instability of volcanic edifices contribute to the development of relatively high levels of species endemism, impoverished normal marine faunas, complex provincial affinities, and relict biotas in limestones that are characterized by exceptionally thick platform and periplatform sequences, fringing and barrier reefs at the shelf margin, extensive lagoonal deposits and rapid lateral and vertical facies changes. Although destructive tectonic and geologic processes in island arcs may hinder determining the original size and extent of the carbonate platform, and particular facies types may not be represented (e.g., fringing and barrier reefs may be replaced by sand shoals at the platform, margin), many characteristics have potential value for identifying carbonates of island-arc origin in the ancient rock record. Apart from being associated with calc-alkaline volcanic and volcaniclastic assemblages, the most valuable suite of features for recognizing island-arc carbonates is marine biotas that exhibit elevated levels of endemism and mixed paleobiogeographic affinities, extraordinary thicknesses of platform

  17. Shallow submarine volcano group in the early stage of island arc development: Geology and petrology of small islands south off Hahajima main island, the Ogasawara Islands

    NASA Astrophysics Data System (ADS)

    Kanayama, Kyoko; Umino, Susumu; Ishizuka, Osamu

    2014-05-01

    Small Islands south off Hahajima, the southernmost of the Ogasawara Archipelago, consist of primitive basalts (<12 wt.% MgO) to dacite erupted during the transitional stage immediately following boninite volcanism on the incipient arc to sustained typical oceanic arc. Strombolian to Hawaiian fissure eruptions occurring on independent volcanic centers for the individual islands under a shallow sea produced magnesian basalt to dacite fall-out tephras, hyaloclastite and a small volume of pillow lava, which were intruded by NE-trending dikes. These volcanic strata are correlated to the upper part (<40 Ma) of the Hahajima main island. Volcanic rock samples have slightly lower FeO*/MgO ratios than the present volcanic front lavas, and are divided into three types with high, medium and low La/Yb ratios. Basalt to dacite of high- and medium-La/Yb types show both tholeiitic (TH) and calc-alkaline (CA) differentiation trends. Low-La/Yb type belongs only to TH basalt. The multiple magma types are coexistence on the each island. TH basalts have phenocrysts of olivine, clinopyroxene and plagioclase, while CA basalts are free from plagioclase phenocrysts.

  18. Lode Gold Deposits and Archean Mantle Plume-Island Arc Interaction, Abitibi Subprovince, Canada.

    PubMed

    Wyman; Kerrich; Groves

    1999-11-01

    In combination with seismic interpretations and geochronological constraints, the association of juvenile arc-type low-Ti tholeiitic basalts with komatiites in the southeastern Abitibi subprovince, Canada, supports a history of subduction step back following Late Archean mantle plume-island arc interaction. The resulting paired collision zones preserved abundant komatiites and numerous massive sulphide deposits and established the critical metallogenic features to concentrate the majority of Canada's Precambrian gold resources in a small area of the southern Abitibi subprovince. PMID:10517886

  19. The petrogenesis of sodic island arc magmas at Savo volcano, Solomon Islands

    NASA Astrophysics Data System (ADS)

    Smith, D. J.; Petterson, M. G.; Saunders, A. D.; Millar, I. L.; Jenkin, G. R. T.; Toba, T.; Naden, J.; Cook, J. M.

    2009-12-01

    Savo, Solomon Islands, is a historically active volcano dominated by sodic, alkaline lavas, and pyroclastic rocks with up to 7.5 wt% Na2O, and high Sr, arc-like trace element chemistry. The suite is dominated by mugearites (plagioclase-clinopyroxene-magnetite ± amphibole ± olivine) and trachytes (plagioclase-amphibole-magnetite ± biotite). The presence of hydrous minerals (amphibole, biotite) indicates relatively wet magmas. In such melts, plagioclase is relatively unstable relative to iron oxides and ferromagnesian silicates; it is the latter minerals (particularly hornblende) that dominate cumulate nodules at Savo and drive the chemical differentiation of the suite, with a limited role for plagioclase. This is potentially occurring in a crustal “hot zone”, with major chemical differentiation occurring at depth. Batches of magma ascend periodically, where they are subject to decompression, water saturation and further cooling, resulting in closed-system crystallisation of plagioclase, and ultimately the production of sodic, crystal and feldspar-rich, high-Sr rocks. The sodic and hydrous nature of the parental magmas is interpreted to be the result of partial melting of metasomatised mantle, but radiogenic isotope data (Pb, Sr, Nd) cannot uniquely identify the source of the metasomatic agent.

  20. Bivergent thrust wedges surrounding oceanic island arcs: Insight from observations and sandbox models of the northeastern caribbean plate

    USGS Publications Warehouse

    ten Brink, U.S.; Marshak, S.; Granja, Bruna J. L.

    2009-01-01

    At several localities around the world, thrust belts have developed on both sides of oceanic island arcs (e.g., Java-Timor, Panama, Vanuatu, and the northeastern Caribbean). In these localities, the overall vergence of the backarc thrust belt is opposite to that of the forearc thrust belt. For example, in the northeastern Caribbean, a north-verging accretionary prism lies to the north of the Eastern Greater Antilles arc (Hispaniola and Puerto Rico), whereas a south-verging thrust belt called the Muertos thrust belt lies to the south. Researchers have attributed such bivergent geometry to several processes, including: reversal of subduction polarity; subduction-driven mantle flow; stress transmission across the arc; gravitational spreading of the arc; and magmatic inflation within the arc. New observations of deformational features in the Muertos thrust belt and of fault geometries produced in sandbox kinematic models, along with examination of published studies of island arcs, lead to the conclusion that the bivergence of thrusting in island arcs can develop without reversal of subduction polarity, without subarc mantle flow, and without magmatic inflation. We suggest that the Eastern Greater Antilles arc and comparable arcs are simply crustalscale bivergent (or "doubly vergent") thrust wedges formed during unidirectional subduction. Sandbox kinematic modeling suggests, in addition, that a broad retrowedge containing an imbricate fan of thrusts develops only where the arc behaves relatively rigidly. In such cases, the arc acts as a backstop that transmits compressive stress into the backarc region. Further, modeling shows that when arcs behave as rigid blocks, the strike-slip component of oblique convergence is accommodated entirely within the prowedge and the arc-the retrowedge hosts only dip-slip faulting ("frontal thrusting"). The existence of large retrowedges and the distribution of faulting in an island arc may, therefore, be evidence that the arc is

  1. Hazard communication by the Alaska Volcano Observatory Concerning the 2008 Eruptions of Okmok and Kasatochi Volcanoes, Aleutian Islands, Alaska

    NASA Astrophysics Data System (ADS)

    Adleman, J. N.; Cameron, C. E.; Neal, T. A.; Shipman, J. S.

    2008-12-01

    Augustine volcano in Cook Inlet, Alaska, the number of calls to Ops, emails to the webmaster, and the amount of data served via the AVO website greatly increased during elevated volcanic activity designated by the USGS aviation color code and volcano alert level. Lessons learned include, Ops staffing requirements during periods of high call volume, the need for ash fall hazard information in multiple languages, and the value of real-time observations of remote Aleutian eruptions made by local mariners. An important theme of public inquiries concerned the amount and potential climate impacts of the significant sulfur dioxide gas and ash plumes emitted by Okmok and Kasatochi, including specific questions on the amount of sulfur dioxide discharged during each eruption. The significant plumes produced at the onset of the Okmok and Kasatochi eruptions also had lengthy national and international aviation impacts and yet-to-be resolved hemispherical or possible global, climactic effects.

  2. Island arc picrites from the solomon islands - origin by mantle matrix collapse

    NASA Astrophysics Data System (ADS)

    Rohrbach, A.; Schuth, S.; Münker, C.; Ballhaus, C.

    2003-04-01

    The MgO enrichment in picrites is commonly explained by accumulation of liquidus olivine in a convecting magma chamber. Here we report results from subduction related picrites from the New Georgia archipelago (Solomon Islands) that were examined to derive the parental melt composition and to understand the wide range in MgO contents (13 to 30 wt.%). The New Georgia picrites cannot be explained by a simple cumulate assimilation model. The samples contain up to 40 vol.% olivine, calcic cpx, and chrome spinel as phenocrysts, set in a microcrystalline groundmass. There are two distinct populations of olivine, one with <0.12 wt.% CaO (low--Ca) and one with 0.18 to 0.34 wt.% CaO (high--Ca). The high--Ca olivines (Fo84-92) are considered to be the equilibrium olivine phenocrysts of a basaltic to picritic melt. The low--Ca olivines (Fo90-93.4) zone towards high--Ca compositions towards the rims and were obviously not in equilibrium with the melt at the time of crystal incorporation. Oxygen fugacities of the picrites calculated from Fe3+ in chrome spinel are around FMQ+3.35. At this relative fO_2 the MgO content of the parent melt is constrained to 14.85 wt.% assuming Kolv-liqDFe-Mg equilibrium (0.3) with the high--Ca olivines. The liquidus temperature of the melt [1] based on this MgO content is 1323^oC, 60^oC above the olivine--cpx Ca--exchange temperature [2]. The depth of melting is constrained to less than 60 km by the seismic depth of the Benioff zone. This is also supported by geochemistry [3] and the highly oxidized nature of the parent melt that favour the mantle wedge as the exclusive mantle source. The presence of picrites in the Solomon Islands is confined to the region above the active Woodlark spreading centre that is subducted beneath the arc. This extra heat source caused extensive melting and an eventual collapse of the mantle matrix, represented by the assimilated low--Ca olivines. The range in bulk MgO is almost entirely controlled by assimilation of

  3. Effect of underlayer on coalescence of silver islands grown byfiltered cathodic arc deposition

    SciTech Connect

    Byon, Eungsun; Anders, Andre

    2003-03-01

    For low-emissivity application on window glass, coalescenceof thin film silver islands is crucial for high transmittance in thevisible andhigh reflectance in the infrared. It is well known that theenergy of ions arriving at the substrate (kinetics) as wells as the typeof underlayer (thermodynamics) affect the nucleation and growth mode.Little is known about coalescence of silver islands synthesized byenergetic condensation, e.g., by filtered cathodic vacuum arc deposition.In this work, the effect of the underlayer on nucleation and growth ofsilver films deposited by filtered cathodic vacuum arc was investigatedby transmission electron microscopy (TEM) and atomic force microscopy(AFM). The results are compared with data obtained on magnetron sputteredfilms. It was found that uncoated and titanium-oxide-coated glass requiremore silver to achieve the same low value of sheet resistance than silveron zinc-oxide-coated glass. This can be associated with the energy ofinteraction between surface and silver atoms. Silver films made bycathodic arc deposition show an earlier onset of island coalescence andformation of short links. It was found that silver islands in energeticdeposition exhibit a reduced aspect ratio compared to evaporation andsputtering. A nominal 0.1 nm niobium underlayer increases the nucleationdensity and promotes coalescence of silver islands, however, a 0.2 nmlayer did not show these features, indicating the need for furtherstudies.

  4. Bathymetric gradients within a Paleozoic Island Arc, southeastern Alaska (Alexander Terrane)

    SciTech Connect

    Soja, C.M. )

    1990-05-01

    Early to Late Silurian (Wenlock-Ludlow) limestones belonging to the Heceta Formation reflect bathymetric gradients within the ancient island arc exposed in the Alexander terrane of southeastern Alaska. These rocks record the earliest occurrence of widespread carbonate deposition in the region and represent the earliest foundation for shallow-water platform development within the arc. The excellent preservation of platform, platform margin, and slope deposits contrasts with the poor preservation of many marine sediments that originated within other island arcs. Hence, these limestones provide important insights into the styles, processes, and bathymetry of carbonate deposition in island arcs. Carbonate depositional sites within the arc extended laterally from nearshore intertidal and relatively shallow subtidal zones of a marine platform, to the seaward margins of a rimmed shelf, and into deeper subtidal areas of a slope environment. Fossiliferous deposits that originated on the platform comprise a diversity of shelly benthos, including corals and stromatoporoids in growth position. Dasycladacean algae, oncoids, and Amphipora also indicate shallow-water conditions. Organic buildups and reefs were constructed by cyanobacteria, massive stromatoporoids, corals, and algae at the platform margin. Deposition beyond the seaward edge of the shelf is evident from the carbonate turbidites that consist of skeletal debris of shallow-water derivation and an absence of coarse siliciclastic detritus. Sedimentation and resedimentation along a bathymetric gradient within the arc is especially well illustrated by the carbonate breccias that are enclosed within these deep subtidal sediments. They comprise detached stromatolites and clasts of shallow-water origin that were derived from the platform and its margin during periodic slumping of the shelf edge.

  5. Coccidia of Aleutian Canada geese

    USGS Publications Warehouse

    Greiner, E.C.; Forrester, Donald J.; Carpenter, J.W.; Yparraguirre, D.R.

    1981-01-01

    Fecal samples from 122 captive and 130 free-ranging Aleutian Canada geese (Branta canadensis leucopareia) were examined for oocysts of coccidia. Freeranging geese sampled on the spring staging ground near Crescent City, California were infected with Eimeria hermani, E. truncata, E. magnalabia, E. fulva, E. clarkei and Tyzzeria parvula. Except for E. clarkei, the same species of coccidia were found in geese on their breeding grounds in Alaska. Most of the coccidial infections in captive geese from Amchitka Island, Alaska and Patuxent Wildlife Research Center, Maryland, consisted of Tyzzeria.

  6. Seismic velocity variations under island arcs: Examples from the Philippines and Montserrat (Lesser antilles)

    NASA Astrophysics Data System (ADS)

    Sevilla, Winchelle Ian

    Island arcs are geologically active and important structures. From a short-term perspective, they are a major source of seismic and volcanic hazards. From a longer-term perspective, arc processes are most likely a key component in the production of continental lithosphere. They are also the focus of numerous Geoscience investigations. In this thesis I investigate the seismic structure of island arcs at a regional (hundreds of kilometer) and a local (10's of km) scale. My goal in this work is to contribute to our efforts to understand the origin and evolution of these geologically important structures. I focus seismic imaging methods on two regions, the Philippine Island region and the northern Lesser Antilles island of Montserrat. The Philippine Island Arc (PIA) is commonly regarded as a complex structure in which subduction zones border its sides and the intra-arc, sinistral Philippine Fault System transects throughout its length. The arc is seismically active and volcanic activity spans almost the entire arc. While several studies provide a wealth of information on the tectonic and the geodynamic settings of PIA, few have looked carefully into the subsurface because they were limited by the availability of digital seismic data. For this reason, important data gaps exist, in particular the details of the subsurface seismic velocity structure. The recent deployments of relatively dense digital seismic stations offer an opportunity to conduct a detailed study on the arc's velocity structure. Data from this new seismic network are used to determine the three-dimensional (3--D) velocity structure of the PIA by applying the P--wave travel time tomography. A broad distribution of source depths and the arc-wide distribution of seismic stations allow tomographic imaging of structures down to 450 km depth with spatial resolution of about ˜50 km resolution. The prominent features of the tomographic images include the low velocity zones correlating with the overlying

  7. The preliminary results of new submarine caldera on the west of Kume-jima island, Central Ryukyu Arc, Japan

    NASA Astrophysics Data System (ADS)

    Harigane, Y.; Ishizuka, O.; Shimoda, G.; Sato, T.

    2014-12-01

    The Ryukyu Arc occurs between the islands of Kyushu and Taiwan with approximately 1200 km in the full length. This volcanic arc is caused by subduction of the Philippine Sea plate beneath the Eurasia Plate along the Ryukyu trench, and is composed of forearc islands, chains of arc volcanoes, and a back-arc rift called Okinawa Trough. The Ryukyu Arc is commonly divided into three segments (northern, central and southern) that bounded by the Tokara Strait and the Kerama Gap, respectively (e.g., Konishi 1965; Kato et al., 1982). Sato et al. (2014) mentioned that there is no active subaerial volcano in the southwest of Iotori-shima in the Central Ryukyu Arc whereas the Northern Ryukyu Arc (i.e., the Tokara Islands) has active frontal arc volcanoes. Therefore, the existence of volcanoes and volcanotectonic history of active volcanic front in the southwestern part of the Central Ryukyu Arc are still ambiguous. Detailed geophysical and geological survey was mainly conducted using R/V Kaiyou-maru No.7 during GK12 cruise operated by the Geological Survey of Japan/National Institute of Advanced Industrial Science and Technology, Japan. As a result, we have found a new submarine volcanic caldera on the west of Kume-jima island, where located the southwestern part of Central Ryukyu Arc. Here, we present (1) the bathymetrical feature of this new submarine caldera for the first time and (2) the microstructural and petrological observations of volcanic rocks (20 volcanic samples in 13 dredge sites) sampled from the small volcanic cones of this caldera volcano. The dredged samples from the caldera consist of mainly rhyolite pumice with minor andesites, Mn oxides-crust and hydrothermally altered rocks. Andesite has plagioclase, olivine and pyroxene phenocrysts. Key words: volcanic rock, caldera, arc volcanism, active volcanic front, Kume-jima island, Ryukyu Arc

  8. Volcano-Hydrothermal Systems of the Central and Northern Kuril Island Arc - a Review

    NASA Astrophysics Data System (ADS)

    Kalacheva, E.; Taran, Y.; Voloshina, E.; Ptashinsky, L.

    2015-12-01

    More than 20 active volcanoes with historical eruptions are known on 17 islands composing the Central and Northern part of the Kurilian Arc. Six islands - Paramushir, Shiashkotan, Rasshua, Ushishir, Ketoy and Simushir - are characterized by hydrothermal activity, complementary to the fumarolic activity in their craters. There are several types of volcano-hydrothermal systems on the islands. At Paramushir, Shiashkotan and Ketoy the thermal manifestations are acidic to ultra-acidic water discharges associated with hydrothermal aquifers inside volcano edifices and formed as the result of the absorption of magmatic gases by ground waters. A closest known analogue of such activity is Satsuma-Iwojima volcano-island at the Ryukyu Arc. Another type of hydrothermal activity are wide spread coastal hot springs (Shiashkotan, Rasshua), situated as a rule within tide zones and formed by mixing of the heated seawater with cold groundwater or, in opposite, by mixing of the steam- or conductively heated groundwater with seawater. This type of thermal manifestation is similar to that reported for other volcanic islands of the world (Satsuma Iwojima, Monserrat, Ischia, Socorro). Ushishir volcano-hydrothermal system is formed by the absorption of magmatic gases by seawater. Only Ketoy Island hosts a permanent acidic crater lake. At Ebeko volcano (Paramushir) rapidly disappearing small acidic lakes (formed after phreatic eruptions) have been reported. The main hydrothermal manifestation of Simushir is the Zavaritsky caldera lake with numerous coastal thermal springs and weak steam vents. The last time measured temperatures of fumaroles at the islands are: >500ºC at Pallas Peak (Ketoy), 480ºC at Kuntamintar volcano (Shiashkotan), variable and fast changing temperatures from 120º C to 500ºC at Ebeko volcano (Paramushir), 150ºC in the Rasshua crater, and > 300ºC in the Chirpoy crater (Black Brothers islands). The magmatic and rock-forming solute output by the Kurilian volcano

  9. Seismological, Geological and Geomorphic Aspects of Arc Segmentation and Their Relation to Subducting Bathymetric Features in the Solomon Island Arc, SW Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Chen, M.; Frohlich, C.; Taylor, F. W.

    2006-12-01

    Arc segmentation partitions forearcs into multiple blocks so that the forearc behaves like a "keyboard on a piano" as each segment potentially interacts with the downgoing plate in a different tectonic style. For example, parts of the forearc of the Solomon Islands arc has undergone hundreds of meters of rapid subsidence and uplift during late Quaternary time. Other parts have undergone only minor late Quaternary movements. We use seismology, geology, and geomorphology to identify arc segments in order to evaluate how bathymetric features on the subducting plate influence seismicity and active tectonics and cause overriding plate segmentation. Seismic rupture areas for large earthquakes, seismicity patterns, seismicity cross sections, focal mechanisms, and seismic moment calculations all reveal that the central arc being underthrust by the Woodlark Basin system of active sea-floor spreading is very different from the northwest and southeast parts of the arc. Woodlark subduction is characterized by sparse seismicity, gentle subduction angle, and thrust faulting with some normal and strike-slip components. Observations from geologic maps, coastal geomorphology, and emerged coral reefs show that the arc segments are undergoing varying amounts and rates of uplift and submergence. Larger islands such as Guadalcanal and San Cristobal have both drowning and emerging coastlines. This information indicates the individual segments have dramatically different histories of vertical tectonics. We identify three supersegments: Bougainville, New Georgia, and Guadalcanal-San Cristobal. Smaller segments subdivide each supersegment. Thus we identify nine major boundaries, seven minor boundaries, and six possible boundaries. The classification of each boundary depends on the strength of evidence supporting its existence and the amount of change in tectonic behavior across the boundary. We speculate that subduction of the young Woodlark Spreading Center with seamounts and ridges on

  10. The Halmahera Island Arc, Molucca Sea collision zone, Indonesia: A geochemical survey

    NASA Astrophysics Data System (ADS)

    Morris, J. D.; Jezek, P. A.; Hart, S. R.; Hill, J. B.

    The Halmahera island arc, northeastern Indonesia, is the east flank of the Molucca Sea collision zone which is the site of an active arc-arc collision. One unique aspect of the arc is the vast thickness of marine sediments outboard of the trench, a result of ˜1000-1500 km of closure in the Molucca Sea basin. The Halmahera arc is underlain by a 45° east dipping Benioff zone, which is present to depths of 230 km. The volcanoes form a single front which lies ˜100 km above the top of the slab. The arc can be separated into three regions, on the basis of tectonic setting and chemistry. Most volcanoes are part of the normal calc-alkaline oceanic arc segment. Lavas here are basalts through dacites, with basaltic andesites and andesites dominant. Suites are medium-K and show little to moderate Fe enrichment. Abundances of Al2O3, the alkali elements, compatible elements, and the high field strength elements are typical of calc-alkaline island arc lavas. 87Sr/86Sr ratios are 0.70357-0.70438 the average value for all volcanic centers is almost the same, but most centers show a large range of real variation around that average. Pb isotopic compositions are 206Pb/204Pb = 18.55-18.62, 207Pb/204 = Pb 15.55-15.63, 208Pb/204Pb = 38.48-38.67. On a Pb-Pb diagram, they form a linear cluster of steep slope, between oceanic sediments and the less radiogenic end of the mantle array. Pb and Sr isotopic compositions for the oceanic segment can be used to test models for the origin of arc lavas. Both isotope systems can be satisfied by a three-component mixing model where normal oceanic island basalt-type magma is mixed with MORB and contaminated by heterogeneous sediments. A two-component model, where OIB-type magmas (which are heterogeneous with respect to both Sr contents and 87Sr/86Sr ratios) are contaminated with sediments, can also explain the data. This generates isotopically heterogeneous suites, and much of this heterogeneity is preserved through the eruption process. A

  11. Deformation of island-arc lithosphere due to steady plate subduction

    NASA Astrophysics Data System (ADS)

    Fukahata, Yukitoshi; Matsu'ura, Mitsuhiro

    2016-02-01

    Steady plate subduction elastically brings about permanent lithospheric deformation in island arcs, though this effect has been neglected in most studies based on elastic dislocation theory. We investigate the characteristics of the permanent lithospheric deformation using a kinematic model, in which steady slip motion is given along a plate interface in the elastic lithosphere overlying the viscoelastic asthenosphere under gravity. As a rule of thumb, long-term lithospheric deformation can be understood as a bending of an elastic plate floating on non-viscous fluid, because the asthenosphere behaves like water on the long term. The steady slip below the lithosphere-asthenosphere boundary does not contribute to long-term lithospheric deformation. Hence, the key parameters that control the lithospheric deformation are only the thickness of the lithosphere and the geometry of the plate interface. Slip on a plate interface generally causes substantial vertical displacement, and gravity always tries to retrieve the original gravitational equilibrium. For a curved plate interface gravity causes convex upward bending of the island-arc lithosphere, while for a planar plate interface gravity causes convex downward bending. Larger curvature and thicker lithosphere generally results in larger deformation. When the curvature changes along the plate interface, internal deformation is also involved intrinsically, which modifies the deformation field due to gravity. Because the plate interface generally has some curvature, at least near the trench, convex upward bending of the island-arc lithosphere, which involves uplift of island-arc and subsidence around the trench, is always realized. On the other hand, the deformation field of the island-arc lithosphere sensitively depends on lithospheric thickness and plate interface geometry. These characteristics obtained by the numerical simulation are consistent with observed topography and free-air gravity anomalies in subduction

  12. Tracing the evolution of island-arc volcanism in the Tanna-Futuna transect (New Hebrides)

    NASA Astrophysics Data System (ADS)

    Lima, S. M.; Haase, K. M.; Beier, C.

    2014-12-01

    The New Hebrides island arc, located in the southwestern Pacific, is associated with the fast subduction of the Australian Plate under the North Fiji Basin. It extends over 1500 km including the entire Vanuatu archipelago. Several studies dealing with the geochemistry of the most important islands interpret the chemical variability to originate from the heterogeneities in the sub-arc mantle wedge1 and variable addition of the subduction component along the arc2. In order to trace the differences between the source(s) of New Hebrides volcanic arc and back-arc magmatism, five submarine cones (4 of them aligned NE-SW), located in the Futuna Through, were sampled. The lavas range from basalt to andesite with fractionation of olivine being the main magma evolution mechanism until MgO ≈ 6 wt.%. The most primitive lavas have similar fractionation-corrected TiO2 (0.90-1.18 wt.%) and Na2O (2.89-3.41 wt.%) contents suggesting comparable degrees of partial melting. The comparison with published data from adjacent islands shows a more important contribution of the slab closer to the trench (Tanna) where the erupted basalts, basaltic trachyandesites and trachyandesites have considerably higher U/Nb and Ba/Nb ratios. Yet, these lavas display significant negative Sr anomalies (PM-normalized). This could provide evidence of input of continental derived sediments or could reflect the role of plagioclase in the source / evolution of these magmas. The first hypothesis is not supported by published data from the Vanuatu trench3 and the second is not supported by the decoupled behavior of Sr and Eu in normalized-diagrams. On the other hand, island crust samples collected along the northern flank of Futuna Island display strong positive anomalies of Sr and, although more modest, the submarine cones show a similar behavior. Based on source chemical tracers, an increasing depletion of the source is observed from east to west, consistent with progressive mantle flow towards the arc front

  13. Fundamental structure model of island arcs and subducted plates in and around Japan

    NASA Astrophysics Data System (ADS)

    Iwasaki, T.; Sato, H.; Ishiyama, T.; Shinohara, M.; Hashima, A.

    2015-12-01

    The eastern margin of the Asian continent is a well-known subduction zone, where the Pacific (PAC) and Philippine Sea (PHS) plates are being subducted. In this region, several island arcs (Kuril, Northeast Japan, Southwest Japan, Izu-Bonin and Ryukyu arcs) meet one another to form a very complicated tectonic environment. At 2014, we started to construct fundamental structure models for island arcs and subducted plates in and around Japan. Our research is composed of 6 items of (1) topography, (2) plate geometry, (3) fault models, (4) the Moho and brittle-ductile transition zone, (5) the lithosphere-asthenosphere boundary, and (6) petrological/rheological models. Such information is basic but inevitably important in qualitative understanding not only for short-term crustal activities in the subduction zone (particularly caused by megathrust earthquakes) but also for long-term cumulative deformation of the arcs as a result of strong plate-arc/arc-arc interactions. This paper is the first presentation of our research, mainly presenting the results of items (1) and (2). The area of our modelling is 12o-54o N and 118o-164o E to cover almost the entire part of Japanese Islands together with Kuril, Ryukyu and Izu-Bonin trenches. The topography model was constructed from the 500-m mesh data provided from GSJ, JODC, GINA and Alaska University. Plate geometry models are being constructed through the two steps. In the first step, we modelled very smooth plate boundaries of the Pacific and Philippine Sea plates in our whole model area using 42,000 earthquake data from JMA, USGS and ISC. For 7,800 cross sections taken with several directions to the trench axes, 2D plate boundaries were defined by fitting to the earthquake distribution (the Wadati-Benioff zone), from which we obtained equi-depth points of the plate boundary. These equi-depth points were then approximated by spline interpolation technique to eliminate shorter wave length undulation (<50-100 km). The obtained

  14. Material culture across the Aleutian archipelago.

    PubMed

    Hatfield, Virginia L

    2010-12-01

    The material evidence from sites across the Aleutian Islands reflects colonization events, subsequent adaptations, and influxes of ideas and/or people from the east. The occurrence in the eastern Aleutians of bifacial technology around 7000 BP, of artifacts similar to the Arctic Small Tool tradition between 4000 and 3500 BP, and of slate and jet objects around 1000 BP reflects repeated surges of influence or movement of peoples from further east into the eastern end of the chain. In the central and western Aleutians, influence or perhaps colonization from east of the Aleutians is also marked by the occurrence of bifacial technology about 6500 BP and the appearance of slate artifacts after 1000 BP, suggesting the movement of ideas or people from further east. Basic trends across the archipelago include a decrease in formal chipped-stone tools, an increase in the use and the complexity of bone technology, and the increase in use and variety of ground-stone tools. In addition, increasing village site sizes and denser midden deposits are seen later in time throughout the archipelago. The similarity in sites and assemblages, albeit with regional variations, reflects trends that are seen across the chain and indicates that these island communities were not isolated from one another or from mainland Alaska. PMID:21417883

  15. Ancient oceanic crust in island arc lower crust: Evidence from oxygen isotopes in zircons from the Tanzawa Tonalitic Pluton

    NASA Astrophysics Data System (ADS)

    Suzuki, Kazue; Kitajima, Kouki; Sawaki, Yusuke; Hattori, Kentaro; Hirata, Takafumi; Maruyama, Shigenori

    2015-07-01

    Knowledge of the lithological variability and genesis of island arc crust is important for understanding continental growth. Although the volcanic architecture of island arcs is comparatively well known, the nature of island arc middle- and lower-crust remains uncertain owing to limited exposure. One of the best targets for deciphering the evolution of an island arc system is the Tanzawa Tonalites (4-9 Ma), in the intra-oceanic Izu-Bonin-Mariana arc. These tonalities which occupied a mid-crustal position were generated by partial melting of lower crust. To constrain protoliths of the plutonic rocks in the island arc lower crust, in-situ O-isotopic analysis using an IMS-1280 Secondary Ion Mass Spectrometer was carried out on 202 zircon grains separated from 4 plutons in the Tanzawa Tonalite. δ18O value of the zircons ranges from 4.1‰ to 5.5‰ and some zircons have δ18O slightly lower than the mantle range. The low zircon δ18O values from the Tanzawa Tonalite suggest that their protoliths involved materials with lower δ18O values than those of the mantle. Hydrothermally altered gabbros in the lower oceanic crust often have lower δ18O values than mantle and can be primary components of arc lower crust. The Tanzawa Tonalite is interpreted to have been formed by partial melting of island arc lower crust. Thus the low δ18O values in zircons from the Tanzawa Tonalites may originate by melting of the hydrothermally altered gabbro. Ancient oceanic crustal material was likely present in the Izu-Bonin-Mariana arc lower crust, at the time of formation of the Tanzawa Tonalites.

  16. Progressive enrichment of island arc mantle by melt-peridotite interaction inferred from Kamchatka xenoliths

    NASA Astrophysics Data System (ADS)

    Kepezhinskas, Pavel; Defant, Marc J.; Drummond, Mark S.

    1996-04-01

    The Pliocene (7 Ma) Nb-enriched arc basalts of the Valovayam Volcanic Field (VVF) in the northern segment of Kamchatka arc (Russia) host abundant xenoliths of spinel peridotites and pyroxenites. Textural and microstructural evidence for the high-temperature, multistage creep-related deformations in spinel peridotites supports a sub-arc mantle derivation. Pyroxenites show re-equilibrated mosaic textures, indicating recrystallization during cooling under the ambient thermal conditions. Three textural groups of clinopyroxenes exhibit progressive enrichment in Na, Al, Sr, La, and Ce accompanied by increase in Sr/Y, La/Yb, and Zr/Sm. Trace elements in various mineral phases and from felsic veins obtained through ion microprobe analysis suggest that the xenoliths have interacted with a siliceous (dacitic) melt completely unlike the host basalt. The suite of xenoliths grade from examples that display little evidence of metasomatic reaction to those containing an assemblage of minerals that have been reproduced experimentally from the reaction of a felsic melt with ultramafic rock, e.g., pargasitic amphibole, albite-rich plagioclase, Al-rich augite, and garnet. The dacitic veins within spinel lherzolite display a strong enrichment in Sr and depletion in Y and the heavy rare earth elements (e.g., Yb). The dacites are comparable to adakites (melts derived from subducted metabasalt), and not typical arc melts. We believe that these potential slab melts were introduced into the mantle beneath this portion of Kamchatka subsequent to partial melting of a relatively young (and hot) subducted crust. Island arc metasomatism by peridotite-slab melt interaction is an important mantle hybridization process responsible for arc-related alkaline magma generation from a veined sub-arc mantle.

  17. Formation of Garnet Granulite in the Lower Crust of a paleo-Island Arc

    NASA Astrophysics Data System (ADS)

    Garrido, Carlos J.; Padrón-Navarta, José Alberto; López Sánchez-Vizcaíno, Vicente; Bodinier, Jean-Louis; Bosch, Delphine; Marchesi, Claudio; Hidas, Károly

    2016-04-01

    The Jijal complex (Kohistan paleo-island arc complex, NW Pakistan) is a unique occurrence of high-pressure (HP), mafic, opx-free, garnet granulite formed in the lower crust of an island arc. The upper part of the Jijal Granulitic Gabbro Unit (GGU) records the arrested transformation of hornblende gabbronorite to garnet granulite, involving the coeval breakdown of amphibole and orthopyroxene, and the formation of garnet and quartz. Close to the transformation front (2-3 cm), clinopyroxene from the granulite displays a strong Ca-tschermak zoning with lower Al-contents at rims. REE zoning of clinopyroxene and pseudosection diagrams indicate that only clinopyroxene rims reflect chemical equilibrium with garnet in the reaction front (P = 1.1 ± 0.1 GPa, T = 800 ± 50 °C), whereas the cores retained high-Al contents inherited from precursor gabbronorite clinopyroxene and remained in chemical disequilibrium within a few centimeters of the garnet granulite assemblage. Clinopyroxene of garnet granulites from the Jijal lower GGU are completely re-equilibrated with garnet (P = 1.5 ± 0.1 GPa, T = 800 ± 50 °C). If ferric iron corrections are disregarded, equilibration pressure and temperature are highly overestimated yielding exceedingly high pressures for an island arc setting. The pressure difference between the upper and lower Jijal GGU granulites (~0.4 GPa) and its current thickness (<5 km) implies delamination of the denser parts of Jijal crust. Thermodynamically computed phase diagram sections for upper GGU bulk compositions show that, at the equilibration conditions of Jijal garnet granulite, the equilibrium assemblage is orthopyroxene-free and amphibole-free garnet granulite coexisting with melt or a fluid phase, depending on the water activity at the onset of amphibole breakdown. Pseudosections indicate that hornblende gabbronorite assemblages are highly metastable at lower arc crust depths. The transformation to garnet granulite was therefore substantially

  18. Early Proterozoic Bell Island group: initiation of, and extension within, a continental magmatic arc

    SciTech Connect

    Reichenbach, I.G.

    1985-01-01

    The Bell Island Group is the oldest sequence of supracrustal rocks of the Great Bear Magmatic Zone (GBMZ), western Wopmay Orogen, northwestern Canadian Shield. These rocks lie unconformably on a penetratively deformed and metamorphosed sialic basement complex and are unconformably beneath the calc-alkaline LaBine Group, which is interpreted as continental magmatic arc. The supracrustal rocks of the GBMZ are broadly folded about gently plunging, northwest trending axes and cut by transcurrent faults. The lower part of the Bell Island Group comprises 1.5-2 km of poorly sorted arkose and fanglomerate, aphyric mafic to intermediate lavas, block-and-ash flows, a mineralogically zone cooling unit of rhyolite ash-flow tuff, and aphyric to porphyritic rhyolite flows and domes. Structures and lithologies of the sedimentary rocks, as well as physical characteristics of the volcanics, suggest subaerial deposition. Chemical analyses of lavas and ash-flow tuff indicate a predominantly calc-alkaline suite, although minor tholeiitic lavas are present. Conformably overlying the lower subaerial succession is at least 3.5 km of tholeiitic pillow basalts, intercalated sedimentary rocks and breccias, and tholeiitic gabbro sills. The subaerial to subaqueous transition in rocks of the Bell Island Group suggests 2-3.5 km of syn-volcanic subsidence which may have begun during early subaerial volcanism, but if so, continued during the extrusion of the thick tholeiitic pillow basalt pile. Subaerial conditions resumed during eruption and deposition of the overlying calc-alkaline LaBine Group. Therefore, rocks of the Bell Island Group may represent initiation of calc-alkaline magmatism in a continental arc, followed by tholeiitic magmatism related to intra-arc extension.

  19. Evidence for a Great Aleutian Paleotsunami on Kaua`i

    NASA Astrophysics Data System (ADS)

    Butler, R.; Bai, Y.; Burney, D. A.; Cheung, K.; Yamazaki, Y.

    2013-12-01

    The Hawaiian Islands location amid the Pacific Ocean is threatened by tsunamis from great earthquakes in nearly all directions. Historical great earthquakes Mw>8.5 in the last 100 years have produced large inundations and loss of life in the Islands, but have not accounted for a substantial (>100 m^3) paleotsunami deposit in the Makauwahi sinkhole at Maha`ulepu on the Island of Kaua`i. High-resolution, digital elevation models of bathymetry and topography have been used in conjunction with a non-linear, hydrostatic tsunami model to simulate inundations from giant earthquakes in the Aleutian Islands and elsewhere to estimate the extent of tsunami threats to the State of Hawaii. We model the inundation of the sinkhole by an earthquake with a minimum moment-magnitude of Mw 9.2 located within the eastern Aleutians, where the tsunami energy is focused toward Hawaii. An alternative hypothesis wherein the deposit entered through a small cave entrance is not consistent with fine speleothems, intact in the cave, that pre-date the deposit. The results indicate that a giant earthquake in the eastern Aleutian Islands circa 1425-1665 AD, located between the source regions of the 1946 and 1957 great tsunamigenic earthquakes, generated a tsunami in Hawaii much larger than the historical record. A tsunami deposit in the Aleutians dated circa ~1550 AD is consistent with this eastern Aleutian source region.

  20. Seismicity of the Earth 1900-2007, Kuril-Kamchatka Arc and Vicinity

    USGS Publications Warehouse

    Rhea, Susan; Tarr, Arthur C.; Hayes, Gavin P.; Villaseñor, Antonio; Furlong, Kevin P.; Benz, Harley

    2010-01-01

    This map shows details of the Kuril-Kamchatka arc not visible in an earlier publication, U.S. Geological Survey Scientific Investigations Map 3064. The arc extends about 2,100 km from Hokkaido, Japan, along the Kuril Islands and the pacific coast of the Kamchatka, Russia, peninsula to its intersection with the Aleutian arc near the Commander Islands, Russia. It marks the region where the Pacific plate subducts into the mantle beneath the Okhotsk microplate, a part of the larger North America plate. This subduction is responsible for the generation of the Kuril Islands chain and the deep offshore Kuril-Kamchatka trench. Relative to a fixed North America plate, the Pacific plate is moving northwest at a rate that decreases from 83 mm per year at the arc's southern end to 75 mm per year near its northern edge.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  2. Insights into Magma Evolution in the Islands of the Four Mountains, Alaska

    NASA Astrophysics Data System (ADS)

    Fulton, A. A.; Izbekov, P. E.; Nicolaysen, K. P.

    2015-12-01

    The Islands of the Four Mountains (IFM) is a group of small volcanoes in the central region of Alaska's Aleutian island arc. There are few studies of this remote group of islands despite their rich archeological history and diverse eruptive histories. This study focuses on silicic deposits from the IFM to shed light on the area's history of large explosive eruptions and the IFM's chemical relationship to the rest of the central Aleutian Islands. This study applies whole rock geochemistry, detailed petrographic analysis, and electron microprobe analysis to samples of volcanic deposits from Tana, Cleveland, Carlisle, and Herbert volcanoes, including the first documented ignimbrite deposit in the IFM, found on northern Tana. The IFM lavas range from basaltic to dacitic and follow typical island arc and calc-alkaline chemical trends, providing evidence of high aqueous fluid input to the mantle wedge, as well as varying levels of influence from subducted sediments. Tana, the largest (~12 km2) and most siliceous of the IFM volcanoes, expresses anomalies in K and Rb concentrations that may aid in the refinement of the continental-oceanic crust boundary location along the Aleutian arc. Plagioclase phenocryst disequilibrium textures and compositions provide evidence of mixing and recharge in the IFM magma chambers. Multiple plagioclase phenocryst populations, euhedral pyroxene crystals in disequilibrium with the melt, and angular xenolithic clasts in the Tana ignimbrite suggest a rapid mixing and heating event that triggered its large explosive eruption during the Pleistocene.

  3. Trace elements and isotopic variation along Java Island, Sunda Arc: an evaluation of slab-derived fluid contribution to arc magmas

    NASA Astrophysics Data System (ADS)

    Handini, E.; Hasenaka, T.; Wibowo, H.; Shibata, T.; Mori, Y.; Harijoko, A.

    2012-12-01

    A compilation of geochemical dataset of lavas from Java island is presented, with the purpose of estimating slab-derived fluid contribution to arc magmas along Java island. Based on volcano distribution and tectonics, we grouped the island into western, central and eastern sections. Along-arc variation of subduction slab influence including both sediment (SED) and altered oceanic crust (AOC) is evaluated by ratios of fluid-mobile elements to high field strength elements/HFSE (e.g. B/Nb, B/Zr, Ba/La). In addition, Sr-Nd-Pb isotopes were determined to estimate contribution of SED and AOC to the source mantle along the island. Typical lava from Java island is characterized by elevated LILE and LREE values, as well as negative anomalies of Nb and Ti. The ratios of Nb/HFSE (e.g. Nb/Ta, Nb/Zr) imply Nb depletion along the island, a characteristic of arc magmas. These Nb/HFSE ratios are uniformly low at volcanic front all along the island. However, they increase from volcanic front toward back arc in central and eastern sections, and evenly low across the western section. The decreasing ratios of B/HFSE and Ba/HFSE from volcanic front toward back arc are observed in the central and eastern sections. However, these ratios only subtly decrease in the western section. The comparison among different sections of the island shows the highest ratios of these trace elements observed in central section. Isotopic ratios of lavas from all sections generally shifted from Indian Ocean MORB field toward higher 87 Sr/86 Sr and lower 143 Nd/144 Nd ratios. The lowest 87 Sr/86 Sr ratios along the island are shown by back-arc lavas from central section, which overlap with mantle array. In contrast, the volcanic front samples of this section overlap with composition of Indian Ocean sediment. Pb isotope ratios show that lavas from all sections are plotted within the Indian Ocean sediment and OIB fields, except Muria samples of central section. The collected lavas from this island indicate

  4. Island arc tectonics of New Zealand manifested in helium isotope ratios

    SciTech Connect

    Sano, Y.; Wakita, H.; Giggenbach, W.F.

    1987-07-01

    Thirty gas samples of various types - volcanic gas, geothermal gas, CH/sub 4/-rich natural gas, and petroleum gas - were collected in and around the North Island, New Zealand. /sup 3/He//sup 4/He and /sup 4/He//sup 20/Ne ratios were measured using a mass spectrometer. The observed /sup 3/He//sup 4/He and /sup 4/He//sup 20/Ne ratios of the samples varied from 0.08 x 10/sup -6/ to 8.75 x 10/sup -6/ and from 4.8 to 2100, respectively. Based on a /sup 3/He//sup 4/He-/sup 4/He//sup 20/Ne diagram, He in the samples can be explained by mixing of a subduction-type magmatic, a radiogenic, and an air component. The geographical distribution of /sup 3/He//sup 4/He ratios over the island indicates a clear contrast between forearc and volcanic arc regions: high in the former and low in the latter. A He boundary can be drawn from the Taupo Volcanic Zone to Egmont Volcano in terms of the /sup 3/He//sup 4/He profile. This boundary agrees well with that of high Q/low Q in the upper mantle as well as with the geographical distribution of terrestrial heat flow values. The high /sup 3/He//sup 4/He ratios in the volcanic arc region are attributed to subduction-type He associated with an uprising magma from the upper mantle and the lower ratios in the forearc region to radiogenic He derived from U and Th in basement and sedimentary rocks. This tendency is very similar to that found in northeast Japan and is understood to be a general signature of the He isotope ratio in an island arc system.

  5. Bivergent thrust wedges surrounding island arcs: Insights from observations and sandbox models of the northeastern Caribbean plate

    NASA Astrophysics Data System (ADS)

    ten Brink, U. S.; Marshak, S.; Granja Bruna, J.

    2008-12-01

    Thrust belts develop on both sides of island arcs at several localities around the world, such as southern Indonesia, Vanuatu, Panama, and the northeastern Caribbean. In all cases, the overall vergence of the backarc thrust belt is opposite to that of the forearc thrust belt. For example, in the northeastern Caribbean, an inactive arc (Hispaniola and Puerto Rico) is bordered by a north-verging accretionary prism and the Puerto Rico trench on the north, and by the south-verging Muertos thrust belt and the Muertos trough on the south. There are three models to explain such bivergent thrusting: (1) Bivergent thrusting develops where a reversal of the polarity of subduction is underway and the backarc thrust system overlies an incipient subduction zone; (2) Compression of the backarc region due to trenchward traction, applied at the base of the overriding plate by the subduction process; and (3) The arc and both thrust systems constitute a bivergent thrust wedge, whose development is driven entirely by crustal-level forces applied at a single subduction zone. The third model implies that island arc bivergent thrusting is analogous to that which develops during continent-continent collisions. Observations of deformational features from the Muertos thrust belt together with inferences from regional geometry of island arcs and simple sandbox kinematic models, lead to the conclusion that such island arcs are best explained as crustal bivergent thrust wedges. Modeling suggests, in particular, that an imbricate thrust wedge in the backarc region develops only if the arc behaves as a relatively rigid block that can transmit compressive stresses to the backarc region. In such circumstances, the strike-slip component of oblique convergence is accommodated entirely in the forearc and arc, and the backarc is a frontal (dip-slip) thrust system. The rigid block behavior of the arc may be explained by its mafic composition.

  6. Geochemistry of southern Pagan Island lavas, Mariana arc: The role of subduction zone processes

    USGS Publications Warehouse

    Marske, J.P.; Pietruszka, A.J.; Trusdell, F.A.; Garcia, M.O.

    2011-01-01

    New major and trace element abundances, and Pb, Sr, and Nd isotopic ratios of Quaternary lavas from two adjacent volcanoes (South Pagan and the Central Volcanic Region, or CVR) located on Pagan Island allow us to investigate the mantle source (i.e., slab components) and melting dynamics within the Mariana intra-oceanic arc. Geologic mapping reveals a pre-caldera (780-9.4ka) and post-caldera (<9.4ka) eruptive stage for South Pagan, whereas the eruptive history of the older CVR is poorly constrained. Crystal fractionation and magma mixing were important crustal processes for lavas from both volcanoes. Geochemical and isotopic variations indicate that South Pagan and CVR lavas, and lavas from the northern volcano on the island, Mt. Pagan, originated from compositionally distinct parental magmas due to variations in slab contributions (sediment and aqueous fluid) to the mantle wedge and the extent of mantle partial melting. A mixing model based on Pb and Nd isotopic ratios suggests that the average amount of sediment in the source of CVR (~2.1%) and South Pagan (~1.8%) lavas is slightly higher than Mt. Pagan (~1.4%) lavas. These estimates span the range of sediment-poor Guguan (~1.3%) and sediment-rich Agrigan (~2.0%) lavas for the Mariana arc. Melt modeling demonstrates that the saucer-shaped normalized rare earth element (REE) patterns observed in Pagan lavas can arise from partial melting of a mixed source of depleted mantle and enriched sediment, and do not require amphibole interaction or fractionation to depress the middle REE abundances of the lavas. The modeled degree of mantle partial melting for Agrigan (2-5%), Pagan (3-7%), and Guguan (9-15%) lavas correlates with indicators of fluid addition (e.g., Ba/Th). This relationship suggests that the fluid flux to the mantle wedge is the dominant control on the extent of partial melting beneath Mariana arc volcanoes. A decrease in the amount of fluid addition (lower Ba/Th) and extent of melting (higher Sm/Yb), and

  7. Geochemistry of southern Pagan Island lavas, Mariana arc: the role of subduction zone processes

    NASA Astrophysics Data System (ADS)

    Marske, Jared P.; Pietruszka, Aaron J.; Trusdell, Frank A.; Garcia, Michael O.

    2011-08-01

    New major and trace element abundances, and Pb, Sr, and Nd isotopic ratios of Quaternary lavas from two adjacent volcanoes (South Pagan and the Central Volcanic Region, or CVR) located on Pagan Island allow us to investigate the mantle source (i.e., slab components) and melting dynamics within the Mariana intra-oceanic arc. Geologic mapping reveals a pre-caldera (780-9.4 ka) and post-caldera (<9.4 ka) eruptive stage for South Pagan, whereas the eruptive history of the older CVR is poorly constrained. Crystal fractionation and magma mixing were important crustal processes for lavas from both volcanoes. Geochemical and isotopic variations indicate that South Pagan and CVR lavas, and lavas from the northern volcano on the island, Mt. Pagan, originated from compositionally distinct parental magmas due to variations in slab contributions (sediment and aqueous fluid) to the mantle wedge and the extent of mantle partial melting. A mixing model based on Pb and Nd isotopic ratios suggests that the average amount of sediment in the source of CVR (~2.1%) and South Pagan (~1.8%) lavas is slightly higher than Mt. Pagan (~1.4%) lavas. These estimates span the range of sediment-poor Guguan (~1.3%) and sediment-rich Agrigan (~2.0%) lavas for the Mariana arc. Melt modeling demonstrates that the saucer-shaped normalized rare earth element (REE) patterns observed in Pagan lavas can arise from partial melting of a mixed source of depleted mantle and enriched sediment, and do not require amphibole interaction or fractionation to depress the middle REE abundances of the lavas. The modeled degree of mantle partial melting for Agrigan (2-5%), Pagan (3-7%), and Guguan (9-15%) lavas correlates with indicators of fluid addition (e.g., Ba/Th). This relationship suggests that the fluid flux to the mantle wedge is the dominant control on the extent of partial melting beneath Mariana arc volcanoes. A decrease in the amount of fluid addition (lower Ba/Th) and extent of melting (higher Sm/Yb), and

  8. The Fundamental Importance of the ''Hidden'' Source of Chemical Erosion in Island Arcs : Guadeloupe and Martinique

    NASA Astrophysics Data System (ADS)

    Rad, S.; Louvat, P.; Allegre, C.

    2005-12-01

    The chemical erosion of island arcs is of fundamental importance for the erosion regime of the earth and fixing the chemical and isotopic composition of the ocean. In previous work, specially Louvat et Allegre (1997, 1998) it has been shown that erosion of basalt and andesit are in the average 10 to 20 times more efficient than granitic type one. In a comprehensive study Dessert et al.(2003) concluded that basalt erosion contributes to 30 to 35 % of the atmospheric CO2 consumed by worldwide weathering. However since this time our group has surmised that island arcs contribution as estimated by the river weathering has been greatly underestimated. The source of error is supposed to be the contribution of water that circulates in island arc underground and goes directly to the ocean. We have then studied two islands of Lesser Antilles: Guadeloupe and Martinique. Guadeloupe and Martinique are characterised by a uniform andesitic lithology. They are located in a tropical climate with high temperature (24 to 28 ° C), high precipitation (they can reach 14000 mm/year), very dense vegetation, sharp relief and very thick soils. On parts of these islands, especially in Martinique, pyroclastic formations are dominant, creating a very porous surface. This allows water transfer through infiltration in more important proportions than through runoff. The proportion of this infiltrated water is 30% to 90% of the precipitation (Folio, 2001) in Reunion, which has a similar torrential regime. From hydrological budget and the chemical composition of underground waters we calculate the chemical weathering rates of infiltrated water: 280 t/km2/year for Guadeloupe and 190 t/km2/year for Martinique. Those values are much higher than the one calculated from the runoff and corrected TDS of different rivers: 120 t/km2/year in Guadeloupe and 100 t/km2/year in Martinique. This could mean that an important part of the chemical weathering process takes place in sub-surface and is not taken into

  9. Comprehensive study of the seismotectonics of the eastern Aleutian ARC and associated volcanic systems. Annual progress report, March 1, 1981-February 28, 1982

    SciTech Connect

    Jacob, K. H.; Hauksson, E.; Sykes, L. R.

    1981-01-01

    Assessment of the seismic potential for occurrence of great earthquakes in three seismic gaps (Shumagin Islands, Unalaska Island, and Yakataga-Kayak regions) has been completed. In the best-instrumented seismic gap in the Shumagin Islands region, the likelihood for a great earthquake within the next two decades is high. Analysis of earthquake data collected from a telemetered network operated in the Shumagin seismic gap shows near-quiescence in the shallow portion of the main thrust zone. Installation of digital recording equipment at the central station of the Shumagin network, combined with interactive computer analysis at Lamont-Doherty of either digitally recorded or digitized analog seismic data has provided new research possibilities for studying seismic source properties, wave propagation in a laterally heterogeneous velocity structure of the subduction zone, and for seismically screening the root-zone and volcanic pile of Pavlof volcano. High time-resolution data (0.01 sec), and wider frequency band-pass data (0.5 to 30 Hz) are now being collected. Seismic data for two eruptive sequences of Pavlof-volcano have been obtained.

  10. Arc lavas on both sides of a trench: Slab window effects at the Solomon Islands triple junction, SW Pacific

    NASA Astrophysics Data System (ADS)

    Chadwick, John; Perfit, Michael; McInnes, Brent; Kamenov, George; Plank, Terry; Jonasson, Ian; Chadwick, Claire

    2009-03-01

    The Woodlark Spreading Center (WSC) is subducted at the San Cristobal trench, forming a triple junction at the New Georgia Group (NGG) arc in the Solomon Islands. WSC lavas are N-MORB at > 100 km from the trench, but with decreasing distance they have increasingly arc-like Sr-Nd-Pb isotopic ratios, enrichments in Rb > K > Pb > Sr, and depletions in HFSE and Y. Within 50 km of the trench on the Simbo and Ghizo Ridges, many recovered samples are island arc tholeiites to medium-K calc-alkaline andesites and dacites, and many have the same or similar major and trace element and isotopic characteristics as true arc lavas in the NGG on the other side of the trench. Previous investigations have concluded that these WSC lavas are the result of relic back arc mantle enrichments resulting from subduction of the Pacific plate prior to the late Miocene at the North Solomon trench, > 200 km to the north. However, the high-silica WSC lavas are more arc-like than those recovered from other distal back arcs, and are more voluminous, forming large submarine ridges and stratovolcanoes. We suggest that true arc mantle migrates across the plate boundary from the adjacent NGG arc through slab windows created by the subduction of the WSC. This leads to variable mixing between NGG arc and WSC N-MORB end-members, forming the transitional lavas recovered from the WSC. Lavas with similar arc-like characteristics have previously been recovered on the Chile Rise near where it is subducted at the Chile Trench, raising the possibility that such mantle transfer is a common phenomenon where active spreading centers are subducted. The presence of slab windows may also be responsible for the unusual forearc volcanism in the NGG, and melting of slab window margins may account for the presence of high-silica adakite-like lavas on the WSC.

  11. Cascades/Aleutian Play Fairway Analysis: Data and Map Files

    SciTech Connect

    Lisa Shevenell

    2015-11-15

    Contains Excel data files used to quantifiably rank the geothermal potential of each of the young volcanic centers of the Cascade and Aleutian Arcs using world power production volcanic centers as benchmarks. Also contains shapefiles used in play fairway analysis with power plant, volcano, geochemistry and structural data.

  12. Island-Arc Collision Dominates Japan's Sediment Flux to the Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Codilean, A. T.; Korup, O.; Hayakawa, Y. S.; Matsushi, Y.; Saito, H.; Matsuzaki, H.

    2013-12-01

    Quantifying volumes and rates of delivery of terrestrial sediment to subduction zones is indispensable for refining estimates of the thickness of trench fills that may eventually control the location and timing of submarine landslides and tsunami-generating mega-earthquakes. Despite these motivating insights, knowledge about the rates of erosion and sediment export from the Japanese islands to their Pacific subduction zones has somewhat stagnated despite the increasing availability of highly resolved data on surface deformation, climate, geology, and topography. Traditionally, natural erosion rates across the island arc have been estimated from catchment topographic predictors of reservoir sedimentation rates that were recorded over several years to decades. We correct for a systematic bias in these predictions, and present new estimates of decadal to millennial-scale erosion rates of the Japanese terrestrial inner forearc, drawing on several unprecedented inventories of mass wasting, reservoir sedimentation, and concentrations of cosmogenic 10Be in river sands. Our data reveal that catchments draining Japan's eastern seaboard have distinctly different tectonic, lithological, topographic, and climatic characteristics, underscored by a marked asymmetric pattern of erosion rates along and across the island arc. Erosion rates are highest in the Japanese Alps that mark the collision of two subduction zones, where high topographic relief, hillslope and bedrock-channel steepness foster rapid denudation by mass wasting. Comparable, if slightly lower, rates characterize southwest Japan, most likely due to higher typhoon-driven rainfall totals and variability rather than the similarly high relief and contemporary uplift rates that are linked to subduction earthquake cycles, and outpace long-term Quaternary uplift. In contrast, our estimated erosion and flux rates are lowest in the inner forearc catchments that feed sediment into the Japan Trench. We conclude that

  13. Structure of the collision zone between Bougainville guyot and the accretionary wedge of the New Hebrides island arc, southwest Pacific

    USGS Publications Warehouse

    Fisher, M.A.; Collot, J.-Y.; Geist, E.L.

    1991-01-01

    Multichannel seismic reflection data show the structure that develops within an island arc-guyot collision zone. The contact zone between the arc and the north and east sides of the guyot is marked by discontinuous antiforms. The extent of collision deformation to the arc and guyot depends in part on the contrast in compressibility and viscosity between these features. We propose that the high-drag, subcircular guyot evolves during collision into a more streamlined shape. We draw an analogy between some features of glacial origin and the subducted part of a guyot. -from Authors

  14. 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

    NASA Astrophysics Data System (ADS)

    Jolly, Wayne T.; Lidiak, Edward G.; Dickin, Alan P.

    2008-07-01

    Bimodal extrusive volcanic rocks in the northeast Greater Antilles Arc consist of two interlayered suites, including (1) a predominantly basaltic suite, dominated by island arc basalts with small proportions of andesite, and (2) a silicic suite, similar in composition to small volume intrusive veins of oceanic plagiogranite commonly recognized in oceanic crustal sequences. The basaltic suite is geochemically characterized by variable enrichment in the more incompatible elements and negative chondrite-normalized HFSE anomalies. Trace element melting and mixing models indicate the magnitude of the subducted sediment component in Antilles arc basalts is highly variable and decreases dramatically from east to west along the arc. In the Virgin Islands, the sediment component ranges between< 0.5 to ˜ 1% in Albian rocks, and between ˜ 1 and 2% in succeeding Cenomanian to Campanian 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 < 16%), low Mg-number (molar Mg/Mg + Fe < 0.5), TiO 2 (< 1.0%), and Sr/Y (< 10), oceanic or 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 (< 20%) of silicic lavas were erupted. The systematic variation of both sediment flux and abundance of crustally derived silicic lavas are consistent with current tectonic models of Caribbean evolution involving approximately

  15. Microearthquake seismicity in relation to double convergence around the Solomon Islands arc by ocean-bottom seismometer observation

    NASA Astrophysics Data System (ADS)

    Shinohara, Masanao; Suyehiro, Kiyoshi; Murayama, Takayuki

    2003-06-01

    The Solomon Islands arc area is a complex plate convergence zone. At the North Solomon Trench on the northern side of the arc, it is believed that the Pacific Plate was subducting before coming into collision with the Ontong Java Plateau, the world's largest oceanic plateau. After the collision about 5 Ma, northeastward subduction initiated along the southern side of the arc at the San Cristobal Trench, another trench on the south side. GPS observations and crustal seismic structure surveys confirm that convergence occurs at both trenches. Without detailed and accurate seismicity, it is difficult to characterize the plate subduction to reveal the tectonics of such a complex zone where a key mechanism of continental growth may also exist. In 1994, an ocean-bottom seismometer (OBS) experiment was carried out for the first time in the area around the Solomon Islands arc to locate microearthquakes. Observations started in late August and continued until early September. Five digital recording OBSs were deployed around the Russell Islands west of Guadalcanal Island. OBS spacing was about 20 km. All the OBSs were recovered and yielded data with a good signal-to-noise ratio. 40 earthquakes, with magnitudes in the range 1.5-4.4 were located over 8 days. The seismicity clearly images the two subducting plates. Though the seismicity beneath the arc side slope of the San Cristobal Trench is relatively high, we can see the seismicity which is related to the subducting Pacific Plate beneath Santa Isabel Island. In addition, earthquakes occur within the crust beneath the southern part of the New Georgia Basin and the Russell Islands. An aseismic area extending 40 km inward from the San Cristobal trench axis implies initial aseismic slip of the India-Australia Plate at a small dip angle.

  16. Foundering of lower island-arc crust as an explanation for the origin of the continental Moho.

    PubMed

    Jagoutz, Oliver; Behn, Mark D

    2013-12-01

    A long-standing theory for the genesis of continental crust is that it is formed in subduction zones. However, the observed seismic properties of lower crust and upper mantle in oceanic island arcs differ significantly from those in the continental crust. Accordingly, significant modifications of lower arc crust must occur, if continental crust is indeed formed from island arcs. Here we investigate how the seismic characteristics of arc crust are transformed into those of the continental crust by calculating the density and seismic structure of two exposed sections of island arc (Kohistan and Talkeetna). The Kohistan crustal section is negatively buoyant with respect to the underlying depleted upper mantle at depths exceeding 40 kilometres and is characterized by a steady increase in seismic velocity similar to that observed in active arcs. In contrast, the lower Talkeetna crust is density sorted, preserving only relicts (about ten to a hundred metres thick) of rock with density exceeding that of the underlying mantle. Specifically, the foundering of the lower Talkeetna crust resulted in the replacement of dense mafic and ultramafic cumulates by residual upper mantle, producing a sharp seismic discontinuity at depths of around 38 to 42 kilometres, characteristic of the continental Mohorovičić discontinuity (the Moho). Dynamic calculations indicate that foundering is an episodic process that occurs in most arcs with a periodicity of half a million to five million years. Moreover, because foundering will continue after arc magmatism ceases, this process ultimately results in the formation of the continental Moho. PMID:24305163

  17. Barren Island Volcano (NE Indian Ocean): Island-arc high-alumina basalts produced by troctolite contamination

    NASA Astrophysics Data System (ADS)

    Luhr, James F.; Haldar, Dhanapati

    2006-01-01

    Barren Island (BI) is a subduction-related volcanic island lying in the northeastern Indian Ocean, about 750 km north of the northern tip of Sumatra. Rising from a depth of ˜2300 m on the Andaman Sea floor, BI has a submarine volume estimated at ˜400 km 3, but the island is just 3 km across, reaches a maximum elevation of 355 m, and has a subaerial volume of only ˜1.3 km 3. The first historical eruption began in 1787 when a cinder cone grew in the center of a pre-historical caldera 2-km in diameter and sent lava flows westward to reach the sea; activity continued intermittently until 1832. Two subsequent eruptions modified the central cone and also sent lava flows westward to reach the sea in 1991 and 1994-1995. A suite of 28 lava, scoria, and ash samples were investigated from various stages of the subaerial eruptive history of BI. Most are basalts (including all 10 samples from the 1994-1995 eruption) and basaltic andesites (including 7 of 8 samples from the 1991 eruption), but 2 pre-1787 andesites were also studied. On multi-element spider diagrams the BI suite shows subparallel trends for most elements that reflect an important role for fractional crystallization, along with the characteristic depletions of Nb-Ta and enrichments of K-Rb-Pb found in other subduction-related island-arc suites. The typical relative enrichment of Ba is not present, likely because the subducted sediments in the Andaman arc are not Ba-rich. Wide compositional ranges for Cs, Th, Rb, U, and Pb may trace different degrees of scavenging from the underlying volcanic pile. BI basalts and basaltic andesites have variable abundances of phenocrystic-microphenocrystic olivine plus Cr-Al-Mg spinel inclusions, plagioclase, and clinopyroxene, embedded in a matrix of glass, the same minerals, and titanomagnetite (mostly exsolved). The most remarkable mineralogical feature of certain BI basalts and basaltic andesites is the presence of abundant (to 40 vol.%) and large (to 5 mm) crystals of

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

    NASA Astrophysics Data System (ADS)

    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.

  19. On the time-scales of magmatism at island-arc volcanoes.

    PubMed

    Turner, S P

    2002-12-15

    Precise information on time-scales and rates of change is fundamental to an understanding of natural processes and the development of quantitative physical models in the Earth sciences. U-series isotope studies are revolutionizing this field by providing time information in the range 10(2)-10(4) years, which is similar to that of many modern Earth processes. I review how the application of U-series isotopes has been used to constrain the time-scales of magma formation, ascent and storage beneath island-arc volcanoes. Different elements are distilled-off the subducting plate at different times and in different places. Contributions from subducted sediments to island-arc lava sources appear to occur some 350 kyr to 4 Myr prior to eruption. Fluid release from the subducting oceanic crust into the mantle wedge may be a multi-stage process and occurs over a period ranging from a few hundred kyr to less than one kyr prior to eruption. This implies that dehydration commences prior to the initiation of partial melting within the mantle wedge, which is consistent with recent evidence that the onset of melting is controlled by an isotherm and thus the thermal structure within the wedge. U-Pa disequilibria appear to require a component of decompression melting, possibly due to the development of gravitational instabilities. The preservation of large (226)Ra disequilibria permits only a short period of time between fluid addition and eruption. This requires rapid melt segregation, magma ascent by channelled flow and minimal residence time within the lithosphere. The evolution from basalt to basaltic andesite probably occurs rapidly during ascent or in magma reservoirs inferred from some geophysical data to lie within the lithospheric mantle. The flux across the Moho is broadly andesitic, and some magmas subsequently stall in more shallow crustal-level magma chambers, where they evolve to more differentiated compositions on time-scales of a few thousand years or less. PMID

  20. Towards Crustal Structure of Java Island (Sunda Arc) from Ambient Seismic Noise Tomography

    NASA Astrophysics Data System (ADS)

    Widiyantoro, Sri; Zulhan, Zulfakriza; Martha, Agustya; Saygin, Erdinc; Cummins, Phil

    2015-04-01

    In our previous studies, P- and S-wave velocity structures beneath the Sunda Arc were successfully imaged using a global data set and a nested regional-global tomographic method was employed. To obtain more detailed P- and S-wave velocity structures beneath Java, in the central part of the Sunda Arc, we then used local data sets, i.e. newline from the MErapi AMphibious EXperiment (MERAMEX) and the Meteorological, Climatological and Geophysical Agency (MCGA), as well as employed a double-difference technique for tomographic imaging. The results of the imaging show e.g. that P- and S-wave velocities are significantly reduced in the uppermost mantle beneath central Java. In order to obtain detailed crustal structure information beneath Java, the Ambient Noise Tomography (ANT) method was used. The application of this method to the MERAMEX data has produced a good crustal model beneath central Java. We continue our experiment to image crustal structure of eastern Java. We have used seismic waveform data recorded by 22 MCGA stationary seismographic stations and 25 portable seismographs installed for 2 to 8 weeks. The data were processed to obtain waveforms of cross-correlated noise between pairs of seismographic stations. Our preliminary results presented here indicate that the Kendeng zone, an area of low gravity anomaly, is associated with a low velocity zone. On the other hand, the southern mountain range, which has a high gravity anomaly, is related to a high velocity anomaly (as shown by our tomographic images). In future work we will install more seismographic stations in eastern Java as well as in western Java to conduct ANT imaging for the whole of Java Island. The expected result combined with the mantle velocity models resulting from our body wave tomography will allow for accurate location of earthquake hypocenters and determination of regional tectonic structures. Both of these are valuable for understanding seismic hazard in Java, the most densely populated

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

    NASA Astrophysics Data System (ADS)

    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

  2. Deformational History and Rotation of the Leeward Antilles Island Arc: Results of the BOLIVAR Project

    NASA Astrophysics Data System (ADS)

    Beardsley, A. G.; Avé Lallemant, H. G.

    2005-12-01

    The Leeward Antilles island arc is located offshore northern Venezuela and includes Aruba, Curaçao, and Bonaire (ABCs). The ABCs trend WNW-ESE parallel to the obliquely convergent Caribbean-South American plate boundary zone. Field work on the ABCs has provided new structural data supporting a minimum of 90° clockwise rotation of the islands within the diffuse plate boundary zone. Analysis of faulting, bedding, and cleavages suggest three phases of deformation (D1-D3). The oldest phase of deformation, D1, is characterized by northeast trending normal faults, northwest trending fold axes and cleavages, and northeast striking dextral strike-slip faults. East striking sinstral strike-slip faults are rare. The second phase of deformation, D2, is represented by west-northwest trending thrust faults, north-northeast striking normal faults, northwest trending dextral strike-slip faults, and northeast striking sinstral strike-slip faults. Finally, the youngest phase of deformation, D3, is characterized by northeast striking thrust faults, northwest striking normal faults, east-west dextral strike-slip faults, and north-northwest sinstral strike-slip faults. Quartz and calcite veins were also studied on the ABCs. Cross-cutting relationships in outcrop suggest three phases of veining (V1-V3). The oldest veins, V1, trend northeastward; V2 veins trend northward; and the youngest veins, V3, trend northwestward. Additionally, joints were measured on the ABCs. On Bonaire and Curaçao, joints trend approximately northeast while joints on Aruba are almost random with a slight preference for west-northwest. Fluid inclusion analysis of quartz and calcite veins provides additional information about the pressure and temperature conditions of the deformation phases. Preliminary results from the earliest veins (V1) show a single deformational event on Aruba and Bonaire. On Bonaire, they exhibit both hydrostatic and lithostatic pressure conditions. This new data supports three stages of

  3. Morphostructural analysis and Cenozoic evolution of Elephant Island, Southern Scotia Arc, Antarctica

    NASA Astrophysics Data System (ADS)

    Mink, S.; Maestro, A.; López-Martínez, J.; Schmid, T.; Galindo-Zaldívar, J.; Trouw, R. A. J.

    2015-04-01

    Elephant Island, located in the vicinity of the present-day active boundary of the South Shetland Block and the Antarctic and Scotia plates, is a region of particular interest for understanding the past and present geodynamic evolution of the southern Scotia Arc. Lineament from different data sources, field-measured fractures and geomorphological evidences have been analysed in this context. The lineaments extracted from aerial photographs (1,624), from a DEM (348) and from RADARSAT-2 satellite data (1,365) indicate four dominant lineament sets with NE-SW, NW-SE, N-S and W-E strikes. All data sources identified similar lineament families, but differences in the frequency distributions and subsequently on the dominant orientations were observed. The measurements direct of fractures were obtained from 23 sites in the field at which 278 planes were measured. Fracture planes indicate main modes trending in the NNE-SSW and NNW-SSE directions and a secondary mode in the E-W. The major trends of the fracture measurements and the lineaments display a good correlation in the E-W direction. However, there is an angular variation in the azimuth values of the NNE-SSE and NNW-SSE fractures with respect to the N-S, NE-SW and NW-SE orientations of the lineaments of approximately 20°. This trend deviation may be due to the fact that mapped lineaments are composed of small fracture sets that may be related to shear fractures that cannot be distinguished at the aerial photograph or radar satellite data scales. Submerged sea-floor morphological feature orientations match the studied morphostructures on the island and the main tectonic structures in this part of the Scotia Arc. A linkage of the main lineament families to the tectonic stages from the Oligocene to the present has been proposed, taking into account the information of the orientation and sense of movement of the fractures and stresses in the Elephant Island region.

  4. Fabric characterization associated with asthenospheric upwelling in the uppermost mantle, back-arc region of the southwest Japan arc: Evidence from peridotite xenoliths, Oki-Dogo Island

    NASA Astrophysics Data System (ADS)

    Satsukawa, Takako; Michibayashi, Katsuyoshi

    2010-05-01

    Oki-Dogo Island is an important site in terms of xenoliths because it makes the most continent ward occurrence of mantle peridotite xenoliths in the back-arc region of the southwest Japan arc. We describe the microstructure of peridotite xenoliths obtained from Oki-Dogo Island with aim of understanding the evolution of the uppermost mantle beneath the back-arc side of the Japan arc. Basement on the island consists of gneissic metamorphic complex. The alkaline basalts that contain the xenoliths were erupted during the Pliocene-Pleistocene after the opening of the Japan Sea which is thought to have occurred during the Oligocene-Miocene as a consequence of back-arc spreading. Peridotite xenoliths found on Oki-Dogo Island are up to 10 cm in size, show granular texture, and are mainly spinel lherzolites, with some harzburgites. Large xenoliths (> 3 cm) contain a foliation defined by compositional banding and aligned spinel grains, and a lineation defined by the long axes of spinel grains. All spinel lherzolites contain spinel with a low Cr# (=Cr/Fr+Al) (< 0.45); this feature, combined with their mineral assemblages and high NiO content in olivine, suggests that they are of residual origin. The Mg# (=Mg/Mg+Fe) of silicate minerals in some spinel lherzolites is lower (e.g. down to Fo86) than that in typical residual peridotites of the upper mantle, indicating that the observed Fe enrichment occurred in mantle rocks during metasomatism. We have measured crystallographic preferred orientations (CPOs) of olivine grains from highly polished thin sections using a scanning electron microscope equipped with an electron backscatter diffraction system. The dominant slip system in olivine, as determined from kink bands and CPO data, was {0kl}[100] slip. Moreover, peridotites with low olivine Mg# tend to show a AG-type ([010]-fiber) CPO pattern. This finding suggests that the peridotites were deformed in the presence of melt and represent various degrees of rock-melt interaction as

  5. Crustal thickness variation from a continental to an island arc terrane: Clues from the gravity signatures of the Central Philippines

    NASA Astrophysics Data System (ADS)

    Manalo, Pearlyn C.; Dimalanta, Carla B.; Faustino-Eslava, Decibel V.; Ramos, Noelynna T.; Queaño, Karlo L.; Yumul, Graciano P.

    2015-05-01

    Offshore and ground gravity data were utilized to estimate crustal thickness across the Central Philippines where a transition from continental to island arc terrane occurs. Significant differences in gravity anomalies were observed between the Palawan Microcontinental Block (PCB) and the Philippine Mobile Belt (PMB), two major terranes that came together through arc-continent collision. Islands of the PCB (Mindoro, Tablas, Romblon, Sibuyan and western Panay), made up of an assortment of continent-derived sedimentary and igneous rocks and slivers of ophiolitic bodies, register lower Bouguer anomalies compared to that displayed by Masbate Island in the PMB. The calculated crustal thickness of this region exhibits a complex Moho topography of non-uniform depth across the collision zone with the thickest parts (∼32 km) corresponding with ophiolitic units emplaced consequent to arc-continent collision. On the other hand, relatively thinner crust (∼21 km) within the collision zone coincides with areas surmised to have undergone attenuation following intra-arc rifting. The same characteristics are observed offshore of western Mindoro and within the Marinduque Basin, areas known to have experienced crustal thinning following regional tectonic rearrangements that triggered riftings and intra-basin openings.

  6. Erosion and deterioration of the Isles Dernieres Barrier Island Arc, Louisiana, U.S.A.: 1853 to 1988

    USGS Publications Warehouse

    McBride, Randolph A.; Penland, Shea; Jaffe, Bruce E.; Williams, S. Jeffress; Sallenger, Asbury H., Jr.; Westphal, Karen A.

    1989-01-01

    Using cartographic and aerial photography data from the years 1853, 1890, 1934, 1956, 1978, 1984, and 1988, shoreline change maps of the Isles Dernieres barrier island arc were constructed. These data were accurately superimposed, using a computer mapping system, which removed projection, datum, scale, and other cartographic inconsistencies. Linear, areal, and perimeter measurements indicate that the Isles Dernieres are suffering rapid rates of coastal erosion, land loss, and breakup. Bayside and gulfside erosion, in combination with sediment shortage and subsidence, have caused the Isles Dernieres to narrow through time. In addition, the core of the barrier island arc does not migrate landward and instead, breaks up in place as a result of inlet breaching and development. This is in contrast to other models of landward barrier island migration during transgression. If these trends continue, the Isles Dernieres will likely evolve into a subaqueous inner-shelf shoal by the early 21st century. Loss of the Isles Dernieres barrier island arc will severely impact the Terrebonne parish estuary, resulting in decreased environmental quality and increased public risk from storms and hurricanes.

  7. The Permian Dongfanghong island-arc gabbro of the Wandashan Orogen, NE China: Implications for Paleo-Pacific subduction

    NASA Astrophysics Data System (ADS)

    Sun, Ming-Dao; Xu, Yi-Gang; Wilde, Simon A.; Chen, Han-Lin; Yang, Shu-Feng

    2015-09-01

    The Dongfanghong hornblende gabbro is located in the western part of the Wandashan Orogen and to the east of the Jiamusi Block in NE China. It was emplaced into Early Paleozoic oceanic crust (i.e. Dongfanghong ophiolite) at ~ 275 Ma and both later collided with the eastern margin of the Jiamusi Block. The Dongfanghong gabbro is sub-alkaline with high Na2O contents and is characterized by enrichment in light rare earth elements (LREE), large ion lithosphile elements (LILE), Sr, Eu, and Ba, and depletion in high field strength elements (HFSE). The enriched isotopic signatures (87Sr/86Sri = ~ 0.7065, εNd(t) = ~- 0.5, 208Pb/204Pbi = ~ 38.05, 207Pb/204Pbi = ~ 15.56, 206Pb/204Pbi = ~ 18.20 and zircon εHf(t) = ~+ 5.8) indicate an enriched mantle (EM2) source, with some addition of continental material. It has arc geochemical affinities similar to Permian arc igneous rocks in the eastern margin of the Jiamusi Block, the Yakuno Ophiolite in SW Japan, arc rocks along the western margin of the North America Craton, and also the Gympie Group in eastern Australia. All these features, together with information from tectonic discrimination diagrams, suggest that the Dongfanghong gabbro formed in an immature island arc. The spatial configuration of ~ 290 Ma immature continental arc rocks in the eastern part of the Jiamusi Block and the ~ 275 Ma immature island arc Dongfanghong gabbro in the Wandashan Orogen to the east is best explained by eastward arc retreat and slab roll-back of the Paleo-Pacific Plate. This model is also supported by the Carboniferous-Permian stratigraphic transition in the Jiamusi Block from oceanic carbonate rocks to coal-bearing terrestrial clastic rocks and andesites. We thus suggest that both Paleo-Pacific subduction and roll-back occurred in the Early Permian along the eastern margin of Asia.

  8. 40Ar/39Ar geochronology of subaerial lava flows of Barren Island volcano and the deep crust beneath the Andaman Island Arc, Burma Microplate

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

    Little was known about the nature and origin of the deep crust beneath the Andaman Island Arc in spite of the fact that it formed part of the highly active Indonesian volcanic arc system, one of the important continental crust forming regions in Southeast Asia. This arc, formed as a result of subduction of the Indian Plate beneath the Burma Microplate (a sliver of the Eurasian Plate), contains only one active subaerial magmatic center, Barren Island volcano, whose evolutional timeline had remained uncertain. In this work, we present results of the first successful attempt to date crustal xenoliths and their host lava flows from the island, by incremental heating 40Ar/39Ar method, in an attempt to understand the evolutionary histories of the volcano and its basement. Based on concordant plateau and isochron ages, we establish that the oldest subaerial lava flows of the volcano are 1.58 ± 0.04 (2σ) Ma, and some of the plagioclase xenocrysts have been derived from crustal rocks of 106 ± 3 (2σ) Ma. Mineralogy (anorthite + Cr-rich diopside + minor olivine) and isotopic compositions (87Sr/86Sr < 0.7040; ɛNd > 7.0) of xenoliths not only indicate their derivation from a lower (oceanic) crustal olivine gabbro but also suggest a genetic relationship between the arc crust and the ophiolitic basement of the Andaman accretionary prism. We speculate that the basements of the forearc and volcanic arc of the Andaman subduction zone belong to a single continuous unit that was once attached to the western margin of the Eurasian Plate.

  9. Diverse deformation patterns of Aleutian volcanoes from InSAR

    USGS Publications Warehouse

    Lu, Zhiming; Dzurisin, D.; Wicks, C., Jr.; Power, J.

    2008-01-01

    Interferometric synthetic aperture radar (InSAR) is capable of measuring ground-surface deformation with centimeter-to-subcentimeter precision at a spatial resolution of tens of meters over an area of hundreds to thousands of square kilometers. With its global coverage and all-weather imaging capability, InSAR has become an increasingly important measurement technique for constraining magma dynamics of volcanoes over remote regions such as the Aleutian Islands. The spatial pattern of surface deformation data derived from InSAR images enables the construction of detailed mechanical models to enhance the study of magmatic processes. This paper summarizes the diverse deformation patterns of the Aleutian volcanoes observed with InSAR and demonstrates that deformation patterns and associated magma supply mechanisms in the Aleutians are diverse and vary between volcanoes. These findings provide a basis for improved models and better understanding of magmatic plumbing systems.

  10. Interplay between active and past tectonics in the Hellenic Arc (Greece): Geological and geomorphic evidences from Kythira Island

    NASA Astrophysics Data System (ADS)

    Fernández-Blanco, David; de Gelder, Gino; Delorme, Arthur; Lacassin, Robin; Armijo, Rolando

    2016-04-01

    The Hellenic Arc undergoes the largest convergence velocity and highest seismic activity among Mediterranean subduction systems. The outer-arc high islands of the Hellenic Arc are thus key to understand the mode of deformation of the crust during subduction and the mechanisms behind vertical motions at the front of overriding plates, here and elsewhere. Kythira Island, located between SW Peloponnese and NE Crete, provides an exceptional opportunity to understand the interaction between past and active tectonics in the Hellenic Arc. The recent uplift of the Kythira Island is marked in its landscape as paleosurfaces, marine terraces, abandon valleys and gorges. Together with the sedimentary record of the island and its geologic structures, we attempt to reconstruct its tectonic evolution since the latest Miocene. Here, we present exceptionally detailed geological and geomorphological maps of the Kythira Island based on fieldwork, Pleiades satellite imagery and 2-m resolution DEM, as well as the analyses of marine terraces and river network morphometrics. Pliocene or younger infill sequences rest atop of Palaeocene or older rocks in several marine basins in the island. In the largest marine basin, we found a stratigraphic sequence with a (tilted) continental conglomerate at the base, passing upwards to a disconformal subhorizontal conglomerate, calcarenites and fine sands, and terminating with a marine conglomerate. This marine conglomerate acts as a "cap rock" that marks the topography and shapes the highermost, and most extensive, low-relief surface. Overall, the infill sequence onlaps basement with the exception of the western margin where normal faults partly controlled the deposition of its lower sector. These faults reactivated older Hellenic fold-and-thrust structures, parallel to the subduction trench, and were not active during the maximum marine transgression that led to the deposition of the subhorizontal part of the infill sequence, including the topmost

  11. Nd- and Sr-isotopic compositions of lavas from the northern Mariana and southern Volcano arcs: implications for the origin of island arc melts

    NASA Astrophysics Data System (ADS)

    Lin, P. N.; Stern, R. J.; Morris, J.; Bloomer, S. H.

    1990-09-01

    Nd- and Sr-isotopic data are reported for lavas from 23 submarine and 3 subaerial volcanoes in the northern Mariana and southern Volcano arcs. Values of ɛNd range from +2.4 to +9.5 whereas 87Sr/86Sr ranges from 0.70319 to 0.70392; these vary systematically between and sometimes within arc segments. The Nd-and Sr-isotopic compositions fall in the field of ocean island basalt (OIB) and extend along the mantle array. Lavas from the Volcano arc, Mariana Central Island Province and the southern part of the Northern Seamount Province have ɛNd to +10 and 87Sr/86Sr=0.7032 to 0.7039. These are often slightly displaced toward higher 87Sr/86Sr at similar ɛNd. In contrast, those lavas from the northern part of the Mariana Northern Seamount Province as far north as Iwo Jima show OIB isotopic characteristics, with ɛNd and 87Sr/86Sr=0.7035 to 0.7039. Plots of 87Sr/86Sr and ɛNd versus Ba/La and (La/Yb)n support a model in which melts from the Mariana and Volcano arcs are derived by mixing of OIB-type mantle (or melts therefrom) and a metasomatized MORB-type mantle (or melts therefrom). An alternate interpretation is that anomalous trends on the plots of Nd- and Sr-isotopic composition versus incompatible-element ratios, found in some S-NSP lavas, suggest that the addition of a sedimentary component may be locally superimposed on the two-component mixing of mantle end-members.

  12. The dykes and structural setting of the volcanic front in the Lesser Antilles island arc

    NASA Astrophysics Data System (ADS)

    Wadge, G.

    1986-12-01

    The orientations of dykes from many of the islands of the Lesser Antilles island arc have been mapped. Most of these dykes can be interpreted in terms of local or regional swarms derived from specific volcanoes of known age, with distinct preferred orientations. Dykes are known from all Cenozoic epochs except the Palaeocene, but are most common in Pliocene, Miocene and Oligocene rocks. A majority of the sampled dykes are basaltic, intrude volcaniclastic host rocks and show a preference for widths of 1 1.25 m. Locally, dyke swarms dilate their hosts by up to 9% over hundreds of metres and up to 2% over distances of kilometres. The azimuths of dykes of all ages show a general NE-SW preferred orientation with a second NW-SE mode particularly in the Miocene rocks of Martinique. The regional setting for these minor intrusions is a volcanic front above a subduction zone composed of three segments: Saba-Montserrat, Guadeloupe-Martinique, St. Lucia-Grenada. The spacing of volcanic centres along this front is interpreted in terms of rising plumes of basaltic magma spaced about 30 km apart. This magma is normally intercepted at crustal depths by dioritic plutons and andesitic/dacitic magma generated there. Plumes which intersect transverse fracture systems or which migrate along the front can avoid these crustal traps. Throughout its history the volcanic front as a whole has migrated, episodically, towards the backarc at an average velocity of about 1 km/Ma. The local direction of plate convergence is negatively correlated with the local preferred orientation of dykes. The dominant NE-SW azimuth mode corresponds closely to the direction of faulting in the sedimentary cover of the backarc and the inferred tectonic fabric of the oceanic crust on which the arc is founded. A generalised model of the regional stress field that controls dyke intrusion outside of the immediate vicinity of central volcanic vents is proposed, in which the maximum horizontal stress parallels the

  13. Petrogenesis of dacite in an oceanic subduction environment: Raoul Island, Kermadec arc

    NASA Astrophysics Data System (ADS)

    Smith, Ian E. M.; Worthington, Timothy J.; Price, Richard C.; Stewart, Robert B.; Maas, R.

    2006-09-01

    Raoul Volcano in the northern Kermadec arc is typical of volcanoes in oceanic subduction systems in that it is composed mainly of low-K high-Al basalts and basaltic andesite. However, during the last 4 ka Raoul Volcano has produced mainly dacite magma in pyroclastic eruptions associated with caldera formation. The rocks produced in these episodes are almost aphyric containing only sparse crystals of plagioclase, clinopyroxene, orthopyroxene and magnetite. These apparent phenocrysts have chemical compositions that suggest that they did not crystallise from melts with the chemical composition of their host rocks. Rather they are xenocrysts and only their rims show evidence for crystallisation from their host melt. Chemical compositions of samples of the dacites show that each eruption has tapped a distinct magma batch. Compositional variations through the analysed suite cannot be accommodated in any reasonable model of fractional crystallisation from likely parental magma compositions. The hypothesis that best fits the petrology of Raoul Island dacites is one of crustal anatexis. This model requires heating of the lower crust by a magma flux to the point where dehydration melting associated with amphibole breakdown produces magma from a preconditioned source. It is suggested that Raoul is passing through an adolescent stage of development in which siliceous melts are part of an open system in which felsic and mafic magmas coexist.

  14. Geodynamic models of terrane accretion: Testing the fate of island arcs, oceanic plateaus, and continental fragments in subduction zones

    NASA Astrophysics Data System (ADS)

    Tetreault, J. L.; Buiter, S. J. H.

    2012-08-01

    Crustal growth at convergent margins can occur by the accretion of future allochthonous terranes (FATs), such as island arcs, oceanic plateaus, submarine ridges, and continental fragments. Using geodynamic numerical experiments, we demonstrate how crustal properties of FATs impact the amount of FAT crust that is accreted or subducted, the type of accretionary process, and the style of deformation on the overriding plate. Our results show that (1) accretion of crustal units occurs when there is a weak detachment layer within the FAT, (2) the depth of detachment controls the amount of crust accreted onto the overriding plate, and (3) lithospheric buoyancy does not prevent FAT subduction during constant convergence. Island arcs, oceanic plateaus, and continental fragments will completely subduct, despite having buoyant lithospheric densities, if they have rheologically strong crusts. Weak basal layers, representing pre-existing weaknesses or detachment layers, will either lead to underplating of faulted blocks of FAT crust to the overriding plate or collision and suturing of an unbroken FAT crust. Our experiments show that the weak, ultramafic layer found at the base of island arcs and oceanic plateaus plays a significant role in terrane accretion. The different types of accretionary processes also affect deformation and uplift patterns in the overriding plate, trench migration and jumping, and the dip of the plate interface. The resulting accreted terranes produced from our numerical experiments resemble observed accreted terranes, such as the Wrangellia Terrane and Klamath Mountain terranes in the North American Cordilleran Belt.

  15. Ce isotope systematics of island arc lavas from the Lesser Antilles

    NASA Astrophysics Data System (ADS)

    Bellot, Nina; Boyet, Maud; Doucelance, Régis; Pin, Christian; Chauvel, Catherine; Auclair, Delphine

    2015-11-01

    The La-Ce systematics has one of the longest half-lifes (T1/2 = 292.5 Ga) of radioactive decay systems used in isotope geochemistry. Variations of the 138Ce/142Ce ratio are expected to be small and the use of Ce as isotopic tracer requires a very precise measurement. Compared to Sm-Nd studies, the La-Ce decay system can provide additional information about the nature of sediments recycled in subduction zones, because unusually large Ce anomalies relative to the neighboring rare earth elements exist in marine sediments such as fish teeth or hydrothermal deposits. Here, we present a chemical purification technique for Ce, and mass spectrometric technique to perform accurate and reproducible analyses of Ce isotopes of natural samples. We report a large set of Ce isotope data including analysis of 2 Ce reference material solutions (AMES and JMC-304), 2 rock standards (BCR-2 and BHVO-2), 2 chondrites (the carbonaceous chondrite Allende and the enstatite chondrite Sahara 97072), 4 mid-ocean ridge basalts, 30 arc lavas from the Martinique Island and 5 oceanic sediments from DSDP-site 144 drilled on the Demerara rise. The long-term, external precision obtained on the AMES reference material is 80 ppm (2 s.d., 138Ce/142Ce = 0.0225732 ± 18, n = 89). However, we note an evolution of isotopic ratios measured in static mode over the duration of this study (33 months). When the reproducibility is calculated from the AMES reference material measured during the same analytical session, it averages 40 ppm. All the 138Ce/142Ce ratios have been normalized to the AMES value of 0.0225746 (measured in session 7, 2 s.d. = 14 ppm, n = 8), a session during which the chondritic value has been defined and the peak tailing was negligible. The 138Ce/142Ce ratio measured for the JMC-304 Ce reference reagent is 0.0225706 ± 9 (2 s.d. = 38 ppm, n = 10). The analytical precision on natural samples is improved by a factor of about 4 in relation to previous studies on island arcs (Tanaka et al

  16. Identifying potential habitat for the endangered Aleutian shield fern using topographical characteristics

    USGS Publications Warehouse

    Duarte, Adam; Wolcott, Daniel M.; Chow, T. Edwin, Ricca, Mark A.

    2012-01-01

    The Aleutian shield fern Polystichum aleuticum is endemic to the Aleutian archipelago of Alaska and is listed as endangered pursuant to the U.S. Endangered Species Act. Despite numerous efforts to discover new populations of this species, only four known populations are documented to date, and information is needed to prioritize locations for future surveys. Therefore, we incorporated topographical habitat characteristics (elevation, slope, aspect, distance from coastline, and anthropogenic footprint) found at known Aleutian shield fern locations into a Geographical Information System (GIS) model to create a habitat suitability map for the entirety of the Andreaonof Islands. A total of 18 islands contained 489.26 km2 of highly suitable and moderately suitable habitat when weighting each factor equally. This study reports a habitat suitability map for the endangered Aleutian shield fern using topographical characteristics, which can be used to assist current and future recovery efforts for the species.

  17. Teleseismically recorded seismicity before and after the May 7, 1986, Andreanof Islands, Alaska, earthquake

    USGS Publications Warehouse

    Engdahl, E.R.; Billington, S.; Kisslinger, C.

    1989-01-01

    The Andreanof Islands earthquake (Mw 8.0) is the largest event to have occurred in that section of the Aleutian arc since the March 9, 1957, Aleutian Islands earthquake (Mw 8.6). Teleseismically well-recorded earthquakes in the region of the 1986 earthquake are relocated with a plate model and with careful attention to the focal depths. The data set is nearly complete for mb???4.7 between longitudes 172??W and 179??W for the period 1964 through April 1987 and provides a detailed description of the space-time history of moderate-size earthquakes in the region for that period. Additional insight is provided by source parameters which have been systematically determined for Mw???5 earthquakes that occurred in the region since 1977 and by a modeling study of the spatial distribution of moment release on the mainshock fault plane. -from Authors

  18. Metamorphism of an obducted island arc: Example of the Kohistan sequence (Pakistan) in the Himalayan collided range

    NASA Astrophysics Data System (ADS)

    Bard, Jean Pierre

    1983-10-01

    In northern Pakistan, the extraordinary 40-km-thick Kohistan sequence of metamorphosed mafic, ultramafic and calc-alkaline layered plutonic and volcanic (mainly andesitic to rhyodacitic) rocks has been recently reinterpreted as the only complete vertical section of an intra-oceanic island arc presently exposed anywhere in the world. Plate scale-models have been suggested to explain the origin and the tectonic evolution of this arc in the Himalayan collision range. Despite some noticeable differences in the models, there is general agreement that the Kohistan sequence represents the crust of an arc obducted onto the northern edge of the Indian plate before the Oligocene collision of India against Asia. New data on the tectonometamorphic evolution of the Kohistan sequence have led to the conclusion that a first major D 1 event developed with increasing metamorphic grades oriented downward the Kohistan pile but also toward "ensandwiched" basic-ultrabasic granulitic rocks. Rare geochronological data and petrological evidence indicate that the latter granulites (pyriclasites and various plagiopyrigarnites, pyrigarnites, metatroctolites, metawebsterites, metadunites, etc.) were parts of enormous Lower to Middle Cretaceous layered calc-alkaline plutons emplaced during the arc-building stages. As the D 1 metamorphic event is correlated with the Upper Cretaceous obduction process of the Kohistan onto India, it is proposed that the D 1 thermal structure was strongly controlled by remnant magmatic heat source(s) within the obducted arc. This interpretation fits nicely with recent theoretical thermal models since the obduction of the arc was probably shortly after (10-20 Ma) the emplacement of the former plutonic arc rocks. A blueschist "tectonic mélange" underlying the obducted arc was possibly synchronous to the obduction and not clearly linked to the older subductive process. The Oligocene collision of India against Asia was associated with a Barrovian overprinting

  19. Fluid flow, element migration, and petrotectonic evolution of the Early Mesozoic central Klamath Island arc, northwesternmost California. Progress report

    SciTech Connect

    Ernst, W.G.

    1992-12-11

    Investigations in the central Klamath Mountains (KM) have documented the presence of a polymetamorphosed suite of highly magnesian basaltic rocks, the Yellow Dog greenstones, in the Sawyers Bar (SB) terrane of the western Triassic and Paleozoic belt. The assemblage was laid down, altered and metasomatized during the hypothesized collapse of a Phillipine Sea-type back-arc basin which brought the westerly SB oceanic arc terrane into juxtaposition with the inboard, pre-existing Stuart Fork subduction complex, and more easterly KM terranes in an immature island arc setting. Supporting research has concentrated on elucidating the areal extent and structural/stratigraphic relations of these mafic/ultramafic Yellow Dog metavolcanic units, and has documented the insignificant degree of crustal contamination of the melts by associated terrigenous metasediments. The thermal structure and its evolution in the central KM evidently reflects surfaceward advective transport of magmatic energy derived from the partly fused downgoing oceanic slab, as well as hydrothermal fluid circulation. Clarification of the thermal evolution of this crust-constructional event in the immature basaltic island arc are the goals of the research now underway, emptying both field and geochemical methods. Continuing work is documenting the flow and P-T history of aqueous fluids through the evolving KM arc, utilizing electron microprobe and oxygen isotopic data. The authors have nearly finished a regional reconnaissance map showing the distribution of the lavas throughout the California part of the KM. Application of the terrane concept to the central KM has also been reevaluated in the light of regional petrotectonic relationships. Investigations of the regional and contact metamorphism/metasomatism of the SB metasedimentary pile are in progress.

  20. Geochemistry of oceanic igneous rocks - Ridges, islands, and arcs - With emphasis on manganese, scandium, and vanadium

    USGS Publications Warehouse

    Doe, B.R.

    1997-01-01

    increasing Mn is an indication of titanomagnetite removal. Dual compatible and incompatible trends with differentiation are found chiefly for Cu, Sc, and Sr. Distinguishing mid-ocean ridge basalts (MORB), oceanic-island volcanic rocks (OIV), and island-arc volcanic rocks (IAV) may be accomplished by plots of Ce/Yb versus Ba/Ce, where OIV plot to higher values of Ce/Yb than do MORB, and IAV data plot to higher values of Ba/Ce than do those of MORB. These ratios do not seem to be significantly affected by submarine weathering.

  1. Magnetization strucrure of thermal vent on island arc from vector magnetic anomlies using AUV

    NASA Astrophysics Data System (ADS)

    Isezaki, N.; Matsuo, J.; Sayanagi, K.

    2012-04-01

    The geomagnetic anomaly measured by a scalar magnetometer,such as a proton precession magnetometer cannot be defined its direction, then it does not satisfy the Laplace's equation. Therefore physical formula describing the relation between magnetic field and magnetization cannot be established.Because the difference between results obtained from scalar data and from vector data is very significant, we must use vector magnetic field data for magnetization analyses to get the more reliable and exact solutions. The development program of fundamental tools for exploration of deep seabed resources started with the financial support of the Ministry of Education, Culture, Sports, Science & Technology (MEXT) in 2008 and will end in 2012. In this project, we are developing magnetic exploration tools for seabed resources using AUV (Autonomous Underwater Vehicle) and other deep-towed vehicles to measure not the scalar magnetic field but the vector magnetic field in order to estimate magnetization structure below the sea-floor exactly and precisely. We conducted AUV magnetic survey in 2010 at the thermal area called Hakurei deposit in the Bayonnaise submarine caldera at the southern end of Izu island arc, about 400km south of Tokyo. We analyzed the observed vector magnetic fields to get the vector magnetic anomaly Fields using the method of Isezaki(1984). We inverted these vector magnetic anomaly fields to magnetization structure. CONCLUSIONS 1.The scalar magnetic field TIA (Total Intensity Anomaly) has no physical formula describing the relation between M (Magnetization) and TIA because TIA does not satisfy the Laplace's equation. Then it is impossible to estimate M from TIA. 2.Anlyses of M using TIA have been done so far under assumption TIA=PTA (Projected Total Anomay on MF (Main Geomagnetic Field)), however, which caused the analysis error due to ɛT= TIA - PTA . 3.We succeeded to measure the vector magnetic anomaly fields using AUV despite the severe magnetic noises

  2. Thrust belt Formation followed by Back-Arc Extension: Mantle Dynamics from central North Island, New Zealand.

    NASA Astrophysics Data System (ADS)

    Stern, T.; Stratford, W.; Salmon, M.; Pulford, A.

    2008-12-01

    In central North Island a useful geological and geophysical data exists to examine the evolution from retro-arc compression to back-arc extension in the Neogene. We show that the switch from compression to extensional deformation is related in space and time with an event that rapidly removed much of the mantle lithosphere beneath central and western North Island at about 5 Ma. The geophysical smoking gun for this removal process is in two parts: a regional surface uplift at about 5 Ma, and a sharp east-west, lithospheric boundary across which there is a 7 km jump in Moho as determined by a common conversion point stack of receiver functions. Also associated with the boundary is sharp change in mantle properties such as seismic P-wave attenuation, isostatic gravity and Pn wave speeds. A cluster of earthquakes in the depth range 20-35 km tightly correlates with the Moho step. Thickening then removal of mantle lithosphere within central and western North Island is consistent with its geological history. About 20 my of compression and fold and thrust development within western North Island built much of the Taranaki (foreland) basin during the Miocene. This 600 km long and 200 km wide basin is now the principal source of hydrocarbons for New Zealand. Up to 100 km of shortening in both crust and mantle is estimated from deep seismic reflection profiling, subsidence curves and plate reconstructions. At the close of the Miocene thrusting ceased and a rapid (post 5 Ma) and regional (400 km wide) exhumation event began. Based on mudstone porosity data, a maximum 2.5 km of rock uplift (1 km of surface uplift) occurred and this gave shape to much of the North Island land mass as we see today. The edge of the foreland basin was exhumed by up to 1.5 km and oil wells drilled in the margin date this event as starting at 5 Ma. After 5 Ma a switch to extension occurred with present day back-arc extension occurring at rates between 8-20 mm/y. This extension is accompanied by

  3. History of earthquakes and tsunamis along the eastern Aleutian-Alaska megathrust, with implications for tsunami hazards in the California Continental Borderland

    USGS Publications Warehouse

    Ryan, Holly F.; von Huene, Roland; Wells, Ray E.; Scholl, David W.; Kirby, Stephen; Draut, Amy E.

    2012-01-01

    During the past several years, devastating tsunamis were generated along subduction zones in Indonesia, Chile, and most recently Japan. Both the Chile and Japan tsunamis traveled across the Pacific Ocean and caused localized damage at several coastal areas in California. The question remains as to whether coastal California, in particular the California Continental Borderland, is vulnerable to more extensive damage from a far-field tsunami sourced along a Pacific subduction zone. Assuming that the coast of California is at risk from a far-field tsunami, its coastline is most exposed to a trans-Pacific tsunami generated along the eastern Aleutian-Alaska subduction zone. We present the background geologic constraints that could control a possible giant (Mw ~9) earthquake sourced along the eastern Aleutian-Alaska megathrust. Previous great earthquakes (Mw ~8) in 1788, 1938, and 1946 ruptured single segments of the eastern Aleutian-Alaska megathrust. However, in order to generate a giant earthquake, it is necessary to rupture through multiple segments of the megathrust. Potential barriers to a throughgoing rupture, such as high-relief fracture zones or ridges, are absent on the subducting Pacific Plate between the Fox and Semidi Islands. Possible asperities (areas on the megathrust that are locked and therefore subject to infrequent but large slip) are identified by patches of high moment release observed in the historical earthquake record, geodetic studies, and the location of forearc basin gravity lows. Global Positioning System (GPS) data indicate that some areas of the eastern Aleutian-Alaska megathrust, such as that beneath Sanak Island, are weakly coupled. We suggest that although these areas will have reduced slip during a giant earthquake, they are not really large enough to form a barrier to rupture. A key aspect in defining an earthquake source for tsunami generation is determining the possibility of significant slip on the updip end of the megathrust near

  4. Petroleum potential of volcanogenic and volcano-sedimentary rocks in ancient and recent island arcs: Caucasus, Komandorskie, and Kuril islands, eastern Kamchatka

    SciTech Connect

    Levin, L.E. )

    1993-09-01

    In the Late Cretaceous-Eocene, subduction of the Tethys oceanic plate under the island arc of the lesser Caucasus contributed to the appearance of the special conditions favorable for petroleum occurrence: (1) tectono-magmatic destruction of the crust of the Transcaucasus median massif and formation of hydrocarbon traps of different types and origins, and (2) high heat flow lasting until the recent epoch. These led flow-intensive generation of hydrocarbons in the shallow-water sediments of the paleoshelf of the Transcaucasus massif and accumulation of hydrocarbons not only in the sedimentary but also in the volcanogenic and volcano-sedimentary reservoirs (Samgori-Patardzeuli, Muradhanly fields, etc.). At the end of the Oligocene, the geodynamic setting in the northwestern margins of the Pacific Ocean was mainly similar to that within the Transcaucasus median massif. At the end of Oligocene-Miocene, such conditions determined the tectono-magmatic destruction of the continental crust and formation of the series of interarc rifts. The main fields of Japan, with accumulations in the volcanogenic and volcano-sedimentary rocks, are concentrated here. Its analog is the rift located in the southern part of a single east Kuril basin, where petroleum occurrence is only inferred. In the separate troughs, the thickness of the volcano-sedimentary cover is 4-6 km. The stratigraphic section of the cover contains the volcanic and volcano-sedimentary sediments of the Neogene-Pleistocene. The studies of the sections of the Komandorskie islands, eastern Kamchatka, Kuril Islands, and western Sakhalin indicate that distribution of reservoirs depends on the stage of evolution of the rifts and adjacent island arcs.

  5. Sedimentation in the central segment of the Aleutian Trench: Sources, transport, and depositional style

    SciTech Connect

    Stevenson, A.J.; Scholl, D.W.; Vallier, T.L. ); Underwood, M.B. )

    1990-05-01

    The central segment of the Aleutian Trench (162{degree}W to 175{degree}E) is an intraoceanic subduction zone that contains an anomalously thick sedimentary fill (4 km maximum). The fill is an arcward-thickening and slightly tilted wedge of sediment characterized acoustically by laterally continuous, closely spaced, parallel reflectors. These relations are indicative of turbidite deposition. The trench floor and reflection horizons are planar, showing no evidence of an axial channel or any transverse fan bodies. Cores of surface sediment recover turbidite layers, implying that sediment transport and deposition occur via diffuse, sheetlike, fine-grained turbidite flows that occupy the full width of the trench. The mineralogy of Holocene trench sediments document a mixture of island-arc (dominant) and continental source terranes. GLORIA side-scan sonar images reveal a westward-flowing axial trench channel that conducts sediment to the eastern margin of the central segment, where channelized flow cases. Much of the sediment transported in this channel is derived from glaciated drainages surrounding the Gulf of Alaska which empty into the eastern trench segment via deep-sea channel systems (Surveyor and others) and submarine canyons (Hinchinbrook and others). Insular sediment transport is more difficult to define. GLORIA images show the efficiency with which the actively growing accretionary wedge impounds sediment that manages to cross a broad fore-arc terrace. It is likely that island-arc sediment reaches the trench either directly via air fall, via recycling of the accretionary prism, or via overtopping of the accretionary ridges by the upper parts of thick turbidite flows.

  6. Seasonal and distributional patterns of seabirds along the Aleutian Archipelago

    USGS Publications Warehouse

    Renner, M.; Hunt, G.L., Jr.; Piatt, J.F.; Byrd, G.V.

    2008-01-01

    The Aleutian Archipelago is of global importance to seabirds during the northern summer, but little is known about seabird use of these waters during winter. We compare summer and winter abundances of seabirds around 3 islands: Buldir in the western, Kasatochi in the central, and Aiktak in the eastern Aleutians. The density of combined seabird biomass in nearshore marine waters was higher in summer than in winter at Buldir and Kasatochi, but was higher in winter at Aiktak, despite the departure of abundant migratory species. Comparing foraging guilds, we found that only piscivores increased at the western and central sites in winter, whereas at the eastern site several planktivorous species increased as well. The only planktivore remaining in winter at the central and western sites in densities comparable to summer densities was whiskered auklet Aethia pygmaea. Crested auklet Aethia cristatella and thick-billed murre Uria lomvia showed the greatest proportional winter increase at the eastern site. The seasonal patterns of the seabird communities suggest a winter breakdown of the copepod-based food web in the central and western parts of the archipelago, and a system that remains rich in euphausiids in the eastern Aleutians. We suggest that in winter crested auklets take the trophic role that short-tailed shearwaters Puffinus tenuirostris occupy during summer. We hypothesize that advection of euphausiids in the Aleutian North Slope Current is important for supporting the high biomass of planktivores that occupy the Unimak Pass region on a year-round basis. ?? Inter-Research 2008.

  7. Boron isotopic composition of fumarolic condensates from some volcanoes in Japanese island arcs

    NASA Astrophysics Data System (ADS)

    Nomura, Masao; Kanzaki, Tadao; Ozawa, Takejiro; Okamoto, Makoto; Kakihana, Hidetake

    1982-11-01

    Boron samples from 40 fumarolic condensates from volcanoes in the Ryukyu arc (Satsuma Iwo-jima and Shiratori Iwo-yama) and the North-east Japan arc (Usu-shinzan, Showa-shinzan, Esan and Issaikyo-yama) all have 11B /10B ratios close to 4.07. Higher values, from 4.09 to 4.13, were only observed in condensates from volcanoes in the southernmost end of the North-east Japan arc (Nasu-dake), the northern part of the Izu-Bonin arc (Hakone), and the North Mariana arc (Ogasawara Iwo-jima). These higher values suggest geological interaction of the magmas with sea-water enriched in 11B.

  8. Environmental contaminants in bald eagle eggs from the Aleutian archipelago.

    PubMed

    Anthony, Robert G; Miles, A Keith; Ricca, Mark A; Estes, James A

    2007-09-01

    We collected 136 fresh and unhatched eggs from bald eagle (Haliaeetus leucocephalus) nests and assessed productivity on eight islands in the Aleutian archipelago, 2000 to 2002. Egg contents were analyzed for a broad spectrum of organochlorine (OC) contaminants, mercury (Hg), and stable isotopes of carbon (delta13C) and nitrogen (delta15N). Concentrations of polychlorinated biphenyls (SigmaPCBs), p,p'-dichlorodiphenyldichloroethylene (DDE), and Hg in bald eagle eggs were elevated throughout the archipelago, but the patterns of distribution differed among the various contaminants. Total PCBs were highest in areas of past military activities on Adak and Amchitka Islands, indicating local point sources of these compounds. Concentrations of DDE and Hg were higher on Amchitka Island, which was subjected to much military activity during World War II and the middle of the 20th century. Concentrations of SigmaPCBs also were elevated on islands with little history of military activity (e.g., Amlia, Tanaga, Buldir), suggesting non-point sources of PCBs in addition to point sources. Concentrations of DDE and Hg were highest in eagle eggs from the most western Aleutian Islands (e.g., Buldir, Kiska) and decreased eastward along the Aleutian chain. This east-to-west increase suggested a Eurasian source of contamination, possibly through global transport and atmospheric distillation and/or from migratory seabirds. Eggshell thickness and productivity of bald eagles were normal and indicative of healthy populations because concentrations of most contaminants were below threshold levels for effects on reproduction. Contrary to our predictions, contaminant concentrations were not correlated with stable isotopes of carbon (delta13C) or nitrogen (delta15N) in eggs. These latter findings indicate that contaminant concentrations were influenced more by point sources and geographic location than trophic status of eagles among the different islands. PMID:17702538

  9. Environmental contaminants in bald eagle eggs from the Aleutian archipelago

    USGS Publications Warehouse

    Anthony, R.G.; Miles, A.K.; Ricca, M.A.; Estes, J.A.

    2007-01-01

    We collected 136 fresh and unhatched eggs from bald eagle (Haliaeetus leucocephalus) nests and assessed productivity on eight islands in the Aleutian archipelago, 2000 to 2002. Egg contents were analyzed for a broad spectrum of organochlorine (OC) contaminants, mercury (Hg), and stable isotopes of carbon (??13C) and nitrogen (??15N). Concentrations of polychlorinated biphenyls (??PCBs), p,p???- dichlorodiphenyldichloroethylene (DDE), and Hg in bald eagle eggs were elevated throughout the archipelago, but the patterns of distribution differed among the various contaminants. Total PCBs were highest in areas of past military activities on Adak and Amchitka Islands, indicating local point sources of these compounds. Concentrations of DDE and Hg were higher on Amchitka Island, which was subjected to much military activity during World War II and the middle of the 20th century. Concentrations of ??PCBs also were elevated on islands with little history of military activity (e.g., Amlia, Tanaga, Buldir), suggesting non-point sources of PCBs in addition to point sources. Concentrations of DDE and Hg were highest in eagle eggs from the most western Aleutian Islands (e.g., Buldir, Kiska) and decreased eastward along the Aleutian chain. This east-to-west increase suggested a Eurasian source of contamination, possibly through global transport and atmospheric distillation and/or from migratory seabirds. Eggshell thickness and productivity of bald eagles were normal and indicative of healthy populations because concentrations of most contaminants were below threshold levels for effects on reproduction. Contrary to our predictions, contaminant concentrations were not correlated with stable isotopes of carbon (??13C) or nitrogen (??15N) in eggs. These latter findings indicate that contaminant concentrations were influenced more by point sources and geographic location than trophic status of eagles among the different islands. ?? 2007 SETAC.

  10. Middle Jurassic strata link Wallowa, Olds Ferry, and Izee terranes in the accreted Blue Mountains island arc, northeastern Oregon

    SciTech Connect

    White, J.D.L. ); Vallier, T. ); Stanley, G.D. Jr. ); Ash, S.R. ); White, D.L.

    1992-08-01

    Middle Jurassic strata atop the Wallowa terrane in northeastern Oregon link the Wallowa, Izee, and Olds Ferry terranes as related elements of a single long-lived and complex oceanic feature, the Blue Mountains island arc. Middle Jurassic strata in the Wallowa terrane include a dacitic ash-flow deposit and contain fossil corals and bivalves of North American affinity. Plant fossils in fluvial sandstones support a Jurassic age and indicate a seasonal temperate climate. Corals in a transgressive sequence traditionally overlying the fluvial units are of Bajocian age and are closely related to endemic varieties of the Western Interior embayment. They are unlike Middle Jurassic corals in other Cordilleran terranes; their presence suggests that the Blue Mountains island arc first approached the North American craton at high paleolatitudes in Middle Jurassic time. The authors consider the Bajocian marine strata and underlying fluvial volcaniclastic units to be a basin-margin equivalent of the Izee terrane, a largely Middle Jurassic (Bajocian) succession of basinal volcaniclastic and volcanic rocks known to overlie the Olds Ferry and Baker terranes.

  11. Transition of Mount Etna lavas from a mantle-plume to an island-arc magmatic source.

    PubMed

    Schiano, P; Clocchiatti, R; Ottolini, L; Busà, T

    2001-08-30

    Mount Etna lies near the boundary between two regions that exhibit significantly different types of volcanism. To the north, volcanism in the Aeolian island arc is thought to be related to subduction of the Ionian lithosphere. On Sicily itself, however, no chemical or seismological evidence of subduction-related volcanism exists, and so it is thought that the volcanism-including that on Mount Etna itself-stems from the upwelling of mantle material, associated with various surface tectonic processes. But the paucity of geological evidence regarding the primary composition of magma from Mount Etna means that its source characteristics remain controversial. Here we characterize the trace-element composition of a series of lavas emitted by Mount Etna over the past 500 kyr and preserved as melt inclusions inside olivine phenocrysts. We show that the compositional change in primary magmas from Mount Etna reflects a progressive transition from a predominantly mantle-plume source to one with a greater contribution from island-arc (subduction-related) basalts. We suggest that this is associated with southward migration of the Ionian slab, which is becoming juxtaposed with a mantle plume beneath Sicily. This implies that the volcanism of Mount Etna has become more calc-alkaline, and hence more explosive, during its evolution. PMID:11528476

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

    NASA Astrophysics Data System (ADS)

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

    2011-06-01

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

  13. Differential timing of vertical-axis block rotations in the northern Ryukyu Arc: Paleomagnetic evidence from the Koshikijima Islands, Japan

    NASA Astrophysics Data System (ADS)

    Tonai, Satoshi; Suganuma, Yusuke; Ashi, Juichiro; Itaya, Tetsumaru; Oiwane, Hisashi; Kiyokawa, Shoichi

    2011-01-01

    Over 300 samples for paleomagnetic analysis and K-Ar dating were collected from 27 sites at NW-SE and NE-SW trending dike swarms (herein, NW dikes and NE dikes, respectively) in the Koshikijima Islands, northern Ryukyu Arc. The NW dikes are Middle Miocene in age and have directions (D = - 37.7 ∘, I = 51.8 ∘, α95 = 9.6 ∘, and κ = 40.8) that are deflected westward relative to the stable eastern Asian continent. Conversely, the NE dikes, of Late Miocene age, have directions (D = 16.1 ∘, I = 57.7 ∘, α95 = 7.1 ∘, and κ = 41.9) that show no such deflection. These differences are interpreted as indicating that the Koshikijima Islands underwent approximately 40 ∘ of counter-clockwise rotation during the Middle to Late Miocene. A synthesis of the paleomagnetic and structural data suggests a three-stage history of extensional deformation: (1) displacement upon normal faults (F 1 faults) without vertical-axis block rotation, (2) strike-slip reactivation of F 1 faults and oblique-normal displacement on NE-SW-trending faults (F 2 faults) with vertical-axis block rotation, and (3) oblique-normal displacement on F 2 faults without vertical-axis block rotation. Regional differences in the timing and amount of counter-clockwise vertical-axis block rotations indicate that the northern Ryukyu Arc rotated as several distinct rigid blocks.

  14. The Island Arcs as a Major Source of Mantellic Sr to the Ocean: Tectonic Control over Seawater Chemistry and Climate

    NASA Astrophysics Data System (ADS)

    Louvat, P.; Allegre, C. J.; Meynadier, L.

    2005-12-01

    The evolution of 87Sr/86Sr in the Cenozoic ocean has been the subject of famous and vivid controversies between the BLAG model1 and Raymo's one2. No clear winner! Recently the question has been worsened because recent estimates of the hydrothermal flux at ridge crest3, 4, 5 and of the low-temperature oceanic crust weathering flux6 have shown that these fluxes are not enough to balance the continental radiogenic input to give 0.70917 (present-day seawater 87Sr/86Sr). We have re-examined this problem using both Sr and Nd isotopic budgets. Seawater 143Nd/144Nd isotopic ratio varies from one ocean to another as a consequence of its short residence time. For each ocean we can calculate the Nd contributions from continental (rivers) and mantellic sources. Since ridge crests cannot be the mantle-like source for Nd, this source is identified as the island arc and OIB weathering, in agreement with the observation by Goldstein and Hemming7. This approach leads us to examine the possibility of the same island arc origin for the missing mantle-like seawater Sr. The classical approach to the budget of water entering the ocean is to consider the river water fluxes as established by hydrological survey statistics. But these fluxes are too small, as they do not include the underground water flows, which are particularly important for volcanic terrains8. A budget calculation based on mean surface area, mean water fluxes and mean Sr concentrations in rivers and springs demonstrates island arc and OIB weathering is a sufficient source of mantellic Sr to the ocean to match the seawater 87Sr/86Sr budget. This result has a fundamental consequence on the explanation of the seawater 87Sr/86Sr evolution during the Cenozoic. Indeed, when a continental collision occurs a large portion of island arcs is eliminated. Thus the increase in the contribution of radiogenic 87Sr/86Sr from continental weathering and the decrease of the mantle contribution via island arc weathering are tectonically and

  15. Lithospheric-folding-based understanding on the origin of the back-arc basaltic magmatism beneath Jeju volcanic island, Korea

    NASA Astrophysics Data System (ADS)

    Yun, S.; Shin, Y.; CHOI, K.; Koh, J.; Nakamura, E.; Na, S.

    2012-12-01

    Jeju Island is an intraplate volcanic island located at the eastern margin on the East Asia behind the Ryukyu Trench, the collisional/subduction boundary between the Eurasian plate and Philippine Sea plate. It is a symmetrical shield volcano, having numerous monogenetic cinder cones, over 365, on the Mt. Halla volcanic edifice. The basement rock mainly consists of Precambrian gneiss, Mesozoic granite and volcanic rocks. Unconsolidated sedimentary rock is found between basement rock and surface lava. The lava plateau is composed of voluminous basaltic lava flows, which extend to the coast region with a gentle slope. Based on the evidence obtained from volcanic stratigraphy, paleontology, and geochronology, the age of the Jeju basalts ranges from the early Pleistocene to Holocene(Historic). The alkaline and tholeiitic basalts exhibits OIB composition from intraplate volcanism which is not associated with plate subduction, while the basement xenolith contained in the volcanic rock indicates that there were volcanic activities associated with the Mesozoic plate subduction. The Geochemical characteristics have been explained with the plume model, lithospheric mantle origin, and melting of shallow asthenosphere by the rapid change of stress regimes between the collision of the India-Eurasia plates and subduction of the Pacific plate, while there has not been any geophysical investigation to disclose it. Compression near collisional plate boundaries causes lithospheric folding which results in the decrease of pressure beneath the ridge of the fold while the pressure increases beneath trough. The decompression beneath lithosphere is likely to accelerate basaltic magmatism along and below the ridge. We investigate the subsurface structure beneath Jeju volcanic island, South Korea and its vicinity and propose an alternative hypothesis that the basaltic magma beneath the island could be caused by episodic lithospheric folding. Unlike the prevailing hypothesis of the

  16. Petrology and Sm-Nd dating of the Genina Gharbia Alaskan-type complex (Egypt): Insights into deep levels of Neoproterozoic island arcs

    NASA Astrophysics Data System (ADS)

    Helmy, Hassan M.; Abd El-Rahman, Yasser M.; Yoshikawa, Masako; Shibata, Tomoyuki; Arai, Shoji; Tamura, Akihiro; Kagami, Hiroo

    2014-06-01

    The deep levels of Neoproterozoic island arcs are poorly known due to limited accessibility. The Genina Gharbia Alaskan-type complex (south Eastern Desert, Egypt) is the remains of a magma chamber that crystallized at the base (crust-mantle boundary) of a mature Neoproterozoic island arc. The rock assemblage comprises hornblende-bearing harzburgite, lherzolite, pyroxenite, norite and gabbro. All lithologies show cumulus texture with evidence of extensive cumulus mineral-melt interactions. Clinopyroxenes from all lithologies have similar rare earth element (REE) patterns with slight medium-rare earth element (MREE) enrichment. Hornblendes are slightly enriched in MREE and light rare earth elements (LREE). Island arc signatures are indicated by high contents of large ion-lithophile elements and low concentration of high field-strength elements. Positive initial εNd (+ 5.7 to + 7.0) and Nd model ages (963 ± 81 Ma) are consistent with the Genina Gharbia magma being extracted from a depleted mantle source. Modeling of estimated parental magma indicates 10% partial melting of a 90% depleted mantle source with a 10% (MORB + sediments)-derived fluid, commencing in the spinel stability field (< 85 km). Relative to Phanerozoic arcs, the Neoproterozoic arcs were more hydrous, had low oxidation states and probably lasted shorter time to build-up. The hydrous nature of the sub-Arabian-Nubian Shield mantle and the long-life of the arcs are among reasons responsible for the vast crustal growth during the Pan-African Orogeny throughout the Gondwana.

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

    USGS Publications Warehouse

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

    2012-01-01

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

  18. Morphostructure at the junction between the Beata ridge and the Greater Antilles island arc (offshore Hispaniola southern slope)

    NASA Astrophysics Data System (ADS)

    Granja Bruña, J. L.; Carbó-Gorosabel, A.; Llanes Estrada, P.; Muñoz-Martín, A.; ten Brink, U. S.; Gómez Ballesteros, M.; Druet, M.; Pazos, A.

    2014-03-01

    Oblique convergence between the Caribbean plate's interior and the inactive Greater Antilles island arc has resulted in the collision and impingement of the thickened crust of the Beata ridge into southern Hispaniola Island. Deformation resulting from this convergence changes from a low-angle southward-verging thrust south of eastern Hispaniola, to collision and uplift in south-central Hispaniola, and to left-lateral transpression along the Southern peninsula of Haiti in western Hispaniola. Using new swath bathymetry and a dense seismic reflection grid, we mapped the morphological, structural and sedimentological elements of offshore southern Hispaniola. We have identified four morphotectonic provinces: the Dominican sub-basin, the Muertos margin, the Beata ridge and the Haiti sub-basin. The lower slope of the Muertos margin is occupied by the active Muertos thrust belt, which includes several active out-of-sequence thrust faults that, were they to rupture along their entire length, could generate large-magnitude earthquakes. The interaction of the thrust belt with the Beata ridge yields a huge recess and the imbricate system disappears. The upper slope of the Muertos margin shows thick slope deposits where the extensional tectonics and slumping processes predominate. The northern Beata ridge consists of an asymmetrically uplifted and faulted block of oceanic crust. Our results suggest that the shallower structure and morphology of the northern Beata ridge can be mainly explained by a mechanism of extensional unloading from the Upper Cretaceous onward that is still active residually along the summit of the ridge. The tectonic models for the northern Beata ridge involving active reverse strike-slip faults and transpression caused by the oblique convergence between the Beata ridge and the island arc are not supported by the structural interpretation. The eastern Bahoruco slope an old normal fault that acts as a passive tear fault accommodating the sharp along

  19. Hydrothermal mineralization at Kick'em Jenny submarine volcano in the Lesser Antilles island arc

    NASA Astrophysics Data System (ADS)

    Olsen, R.; Carey, S.; Sigurdsson, H.; Cornell, W. C.

    2011-12-01

    Kick 'em Jenny (KeJ) is an active submarine volcano located in the Lesser Antilles island arc, ~7.5 km northwest of Grenada. Of the twelve eruptions detected since 1939, most have been explosive as evidenced by eyewitness accounts in 1939, 1974, and 1988 and the dominance of explosive eruption products recovered by dredging. In 2003, vigorous hydrothermal activity was observed in the crater of KeJ. Video footage taken by a remotely operated vehicle (ROV) during the cruise RB-03-03 of the R/V Ronald Brown documented the venting of a vapor phase in the form of bubbles that ascended through the water column and a clear fluid phase in the form of shimmering water. The shimmering water generally ascended through the water column but can also been seen flowing down gradient from a fissure at the top of a fine-grained sediment mound. These fine-grained sediment mounds are the only structure associated with hydrothermal venting; spire or chimney structures were not observed. Hydrothermal venting was also observed coming from patches of coarse-grained volcaniclastic sediment on the crater floor and from talus slopes around the perimeter of the crater. Samples were collected from these areas and from areas void of hydrothermal activity. XRD and ICPMS analyses of bulk sediment were carried out to investigate the geochemical relationships between sediment types. Sediment samples from the hydrothermal mound structures are comprised of the same components (plagioclase, amphibole, pyroxene, and scoria) as sediment samples from areas void of hydrothermal activity (primary volcaniclastic sediment) in the 500-63 μm size range. High resolution grain size analyses show that >78% of sediment in the hydrothermal mound samples are between 63-2 μm with 6-20% clay sized (<2 μm) whereas <40% of the primary volcaniclastic sediment is between 63-2 μm with ~2% clay sized. The presence of clay minerals (smectite, illite, talc, and I/S mixed layer) in the hydrothermal mound samples was

  20. Aleutian basin oceanic crust

    USGS Publications Warehouse

    Christeson, Gail L.; Barth, Ginger A.

    2015-01-01

    We present two-dimensional P-wave velocity structure along two wide-angle ocean bottom seismometer profiles from the Aleutian basin in the Bering Sea. The basement here is commonly considered to be trapped oceanic crust, yet there is a change in orientation of magnetic lineations and gravity features within the basin that might reflect later processes. Line 1 extends ∼225 km from southwest to northeast, while Line 2 extends ∼225 km from northwest to southeast and crosses the observed change in magnetic lineation orientation. Velocities of the sediment layer increase from 2.0 km/s at the seafloor to 3.0–3.4 km/s just above basement, crustal velocities increase from 5.1–5.6 km/s at the top of basement to 7.0–7.1 km/s at the base of the crust, and upper mantle velocities are 8.1–8.2 km/s. Average sediment thickness is 3.8–3.9 km for both profiles. Crustal thickness varies from 6.2 to 9.6 km, with average thickness of 7.2 km on Line 1 and 8.8 km on Line 2. There is no clear change in crustal structure associated with a change in orientation of magnetic lineations and gravity features. The velocity structure is consistent with that of normal or thickened oceanic crust. The observed increase in crustal thickness from west to east is interpreted as reflecting an increase in melt supply during crustal formation.

  1. Are arc-type rocks the products of magma crystallisation? Observations from a simple oceanic arc volcano: Raoul Island, Kermadec Arc, SW Pacific

    NASA Astrophysics Data System (ADS)

    Smith, Ian E. M.; Stewart, Robert B.; Price, Richard C.; Worthington, Timothy J.

    2010-02-01

    Raoul Island is the emergent summit of a large intra-oceanic strato-volcano in what is globally one of the simplest of subduction settings. In this simple setting erupted magmas span the compositional range from basalt to dacite but none have the high Mg-numbers and high Ni and Cr expected of primitive mantle-derived melts. The lavas range from aphyric to highly porphyritic and are characterised by phenocryst assemblages dominated by plagioclase accompanied by clinopyroxene, olivine, orthopyroxene and spinel. Phenocryst core compositions and zoning profiles are remarkably uniform irrespective of total phenocryst content or geochemical composition, indicating a decoupling of melt and crystal components in the system. A consistent model for the Raoul magmatic system is that primitive high-Mg magma generated in a melt column within the underlying mantle wedge is transformed into a series of derivative low-Mg magmas by fractional crystallisation within the lower crust. Low-Mg magma accumulates variable quantities of crystal cargo as it ascends toward the surface through a crystal mush zone. These processes are essentially those that characterise continental subduction-related magmatic systems but differ only in the absence of an evolved crustal component.

  2. Tectonics and petroleum potential of sedimentary basins in the Bering, Okhotsk, Japan seas, and island arcs

    SciTech Connect

    Levin, L.E. )

    1993-09-01

    In this vast region located in the northwestern part of the Pacific rim, basins of two main genetic types possess petroleum potential. These two types are represented by basins of the recent active margin and basins of the transitional zone between analogs of the passive margin and the recent active margin. For basins of the active margin, the mean density of potential resources is estimated at 5000 MT/km[sup 2] or more. The total area of these basins is 324,000 km[sup 2] among which 120,000 km[sup 2] are in the Russian sector. Ultimate resources of hydrocarbons are estimated at 1.62 billing MT of oil equivalent. Basins of the zone, transitional from analogs of the passive margin to the recent active margin, are characterized by a number of factors favorable for petroleum occurrence. One of the important factors is the presence of rift trough and foredeeps that are potential sites for zones of oil and gas accumulation. The age of the rifts varies from the late Cretaceous through the Oligocene-Miocene in the Olyutorsky and Litke basins, to the Neogene in the Okhotsk Sea and Tatar-Japan basins. Only a small area of the rifts has been proven to contain zones of oil and gas accumulation. Based on the structural characteristics, the rifts are subdivided into oil-gas bearing, potentially oil-gas bearing, and nonprospective for hydrocarbon exploration. Potential hydrocarbon resources of basins of this type are estimated to be not less than 15.12 billion MT of oil equivalent including 9.2 billion MT in the Russian sector. New large zones of oil and gas accumulation are expected to be found both on the shallow shelf and in some deep-water basins such as in the Aleutian and Kuril basins.

  3. Double saloon door tectonics in the Japan Sea, Fossa Magna, and the Japanese Island Arc

    NASA Astrophysics Data System (ADS)

    Martin, A. K.

    2011-01-01

    A number of criteria considered diagnostic of double saloon door rifting and seafloor spreading are matched by data from the Japanese Arc. These include: a pair of terranes, SW and NE Honshu, which rotated in opposite directions from 22-21 Ma to 14-11 Ma; rotated terranes which comprise a retro-arc fold/thrust belt attached to an accretionary wedge intruded by a magmatic arc; contemporaneous backarc extension from 24 to 21 Ma which is brought to a halt by progressive collision of the Izu-Bonin and Japan Arcs from 15 to 5 Ma; isolation of blocks of thicker continental crust by areas of thin continental or oceanic crust, during backarc rifting; such isolation may be due to simultaneous rifting or to progressively seaward rifts, associated with ridge jumps towards the subduction zone; opposite rotations are accommodated by subduction rollback demonstrated by seaward migration of the volcanic front from 30-26 Ma to 16-15 Ma; concurrent development of a major arc-orthogonal rift, the Fossa Magna, from 23-18 Ma to 14 Ma, which was thereafter inverted from 15 Ma to the Recent; a northeast propagating rift in the northern Japan Basin demonstrated by the relationship of linear magnetic anomalies to the mapped continent ocean boundary. Driving mechanisms for double saloon door tectonics are discussed in relation to various reconstructions of the northwest Pacific. Opposite rotational torques, leading to opposite terrane rotations, may be caused by rollback of a curved trench hingeline, or by the divergent slab sinking forces of the Pacific and Philippine Sea Plates.

  4. Amchitka Island, Alaska, special sampling project 1997

    SciTech Connect

    U.S. Department of Energy, Nevada Operations Office

    2000-06-28

    This 1997 special sampling project represents a special radiobiological sampling effort to augment the 1996 Long-Term Hydrological Monitoring Program (LTHMP) for Amchitka Island in Alaska. Lying in the western portion of the Aleutian Islands arc, near the International Date Line, Amchitka Island is one of the southernmost islands of the Rat Island Chain. Between 1965 and 1971, the U.S. Atomic Energy Commission conducted three underground nuclear tests on Amchitka Island. In 1996, Greenpeace collected biota samples and speculated that several long-lived, man-made radionuclides detected (i.e., americium-241, plutonium-239 and -240, beryllium-7, and cesium-137) leaked into the surface environment from underground cavities created during the testing. The nuclides of interest are detected at extremely low concentrations throughout the environment. The objectives of this special sampling project were to scientifically refute the Greenpeace conclusions that the underground cavities were leaking contaminants to the surface. This was achieved by first confirming the presence of these radionuclides in the Amchitka Island surface environment and, second, if the radionuclides were present, determining if the source is the underground cavity or worldwide fallout. This special sampling and analysis determined that the only nonfallout-related radionuclide detected was a low level of tritium from the Long Shot test, which had been previously documented. The tritium contamination is monitored and continues a decreasing trend due to radioactive decay and dilution.

  5. Slab melting in the Aleutians: implications of an ion probe study of clinopyroxene in primitive adakite and basalt

    NASA Astrophysics Data System (ADS)

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

    1998-05-01

    An ion probe study of trace elements in Mg-rich clinopyroxene phenocrysts in primitive Aleutian lavas provides constraints on the genesis of Aleutian adakites, and possible insights into the source of common Aleutian magmas. Clinopyroxene (cpx) phenocrysts in the primitive adakites have high Sr and Nd/Yb compared to cpx in Aleutian basalts. In the adakites, Sr and Nd/Yb are highest for high Mg# cpx, and these concentrations decrease toward lower Mg# compositions. These trends are the opposite of those seen in basalt cpx which generally show increasing incompatible trace element contents with decreasing Mg#, and are unlike antithetic compatible-incompatible trace element trends produced by chemical or kinetic effects of crystal growth. Petrographic observations and major and trace element zonation in cpx phenocrysts indicate that primitive Aleutian adakites are in part the product of mixing between primitive and relatively evolved magmas. The adakite trace element signature (high Sr, Nd/Yb) is clearly associated with the primitive mixing end-member. This observation supports the idea that adakites are derived by equilibration of slab melts with mantle olivine, and appears to rule out an origin by melting in the lower crust. Adakites are relatively rare in the Aleutians, but arc-wide correlations between Sr and La/Yb indicates that an adakite-type slab melt component may be present in the magmatic source throughout the arc.

  6. Geochemical and isotopic constraints on island arc, synorogenic, post-orogenic and anorogenic granitoids in the Arabian Shield, Saudi Arabia

    NASA Astrophysics Data System (ADS)

    Robinson, F. A.; Foden, J. D.; Collins, A. S.

    2015-04-01

    The Arabian Shield preserves a protracted magmatic record of repeated amalgamation of juvenile subduction terranes that host granite intrusions ranging in age from the early Neoproterozoic to the Cambrian, which were emplaced into convergent and within-plate settings. Geochronology and whole-rock geochemistry of sampled Saudi Arabian granitoids define and distinguish four discrete age groups: 1) ~ 845-700 Ma island arc and synorogenic granitoids (IA + Syn), 2) ~ 640-610 Ma granitoids from the Nabitah and Halaban Suture (NHSG), 3) ~ 610-600 Ma post-orogenic perthitic (hypersolvus) granitoids (POPG), and 4) < 600 Ma anorogenic aegirine-bearing perthitic (hypersolvus) granitoids (AAPG). Groups 1, 2 and 3 include suites ranging from I-S- to A-type granites that have REE signatures typical of volcanic arc settings and show intra-suite variation that could be controlled by a combination of crustal assimilation and fractional crystallisation. Their mafic parental magmas have N-MORB-, or arc-tholeiite-like geochemistry. By contrast, group 4 A-type granites are more enriched in HREE and in incompatible elements such as Nb, Rb, Ga, Nd, Zr and Y and have lower Ce/Yb and higher Y/Nb ratios. These granitoids are interpreted to have been emplaced into within-plate and back-arc settings. Granitoid data also provide evidence that there may be two distinct mantle sources to the mafic parents of the granite suites. These are distinguished as contaminated and enriched mantle using Nb and Y and Nd isotopes. All granitoid suites are isotopically juvenile (ɛNd + 3 to + 6) and fall between the upper field crustal values of the Paleoproterozoic Khida terrane (ɛNd + 1) and contemporary depleted mantle. However, Nd isotopes distinguish contamination in group 1-3 mafic end-members beneath sutures which are interpreted to be derived from the contemporary MORB-type mantle wedge with subsequent crustal assimilation and fractionation to I- and A-type granitoids. The youngest (after 600 Ma) A

  7. 238U 230Th disequilibria, magma petrogenesis, and flux rates beneath the depleted Tonga-Kermadec island arc

    NASA Astrophysics Data System (ADS)

    Turner, Simon; Hawkesworth, Chris; Rogers, Nick; Bartlett, Jessica; Worthington, Tim; Hergt, Janet; Pearce, Julian; Smith, Ian

    1997-11-01

    The highly depleted intra-oceanic Tonga-Kermadec island arc forms an endmember of arc systems and a unique location in which to isolate the effects of the slab flux. High precision TIMS uranium, thorium, strontium, neodymium, and lead isotopes, along with complete major and trace element data, have been obtained on an extensive sample set comprising fifty-eight lavas along the arc as well as nineteen samples of the subducting sediments at DSDP site 204 just to the east of the Tonga-Kermadec trench. Ca/Ti and Al/Ti ratios extend from values appropriate to an N-MORB source in the southern Kermadecs to very high ratios in Tonga interpreted to reflect increasing degrees of depletion of the mantle wedge due to backarc basalt extraction. The isotope data emphasize the need for four components in the petrogenesis of the lavas: (1) the mantle wedge; (2) a component with elevated 207Pb/ 204Pb towards which the Kermadec and southern Tongan lavas extend; (3) a component characterised by high 206Pb/ 204Pb, Ta/Nd, and low 143Nd/ 144Nd observed only in the northernmost Tongan islands of Tafahi and Niuatoputapu; (4) a fluid component characterised by strong enrichments of Rb, Ba, U, K, Ph, and Sr, relative to Th, Zr, and the REE and producing large 211U excesses (( 230Th/ 238U) = 0.8-0.5) in the more depleted lavas. The mantle wedge (Component 1) is isotopically similar to the source of the Lau BABB. Component 2 is average pelagic sediment on the downgoing Pacific plate as observed at DSDP sites 595/596 and in the upper sections of the sediment pile at DSDP site 204. Mass balance calculations indicate that less than 0.5% is recycled into the arc lavas; essentially all the subducted sediment is returned to the upper mantle (˜0.03 km' yr -1). Exceptionally low concentrations of Ta and Nb relative to Th and the LREE requires that this sediment component is added as a partial melt which was in equilibrium with residual rutile or ilmenite. Component 3 is identified as volcaniclastics

  8. Age, origin, and significance of an unconformity that predates island-arc volcanism in the northern Sierra Nevada

    NASA Astrophysics Data System (ADS)

    Varga, Robert J.; Moores, Eldridge M.

    1981-11-01

    The paleogeographic position of rocks of the northern Sierra Nevada relative to North America has long been the topic of debate. A detailed study of the Lakes Basin region of the northern Sierra Nevada substantiates that the Shoo Fly Complex, of early Paleozoic age, was folded and unconformably overlain by an island-arc sequence in late Paleozoic time. Microfossils recovered during the study represent the first in situ fauna ever collected from the Shoo Fly Complex and provide an Ordovician-Silurian lower limit on the early deformation. Late Jurassic (Nevadan) deformation strongly affected all rocks in the region. Regional considerations suggest that mid-Paleozoic deformation may have been widespread in the Sierra Nevada and could indicate an early phase of an eastward-prograding suture that ultimately resulted in emplacement of the Roberts Mountain allochthon of the Great Basin. *Present address: Union Oil Research Center, Box 76, Brea, California 92621

  9. The geochemistry and petrogenesis of basalts from the Taupo Volcanic Zone and Kermadec Island Arc, S.W. Pacific

    NASA Astrophysics Data System (ADS)

    Gamble, J. A.; Smith, I. E. M.; McCulloch, M. T.; Graham, I. J.; Kokelaar, B. P.

    1993-01-01

    Basalts from the Taupo Volcanic Zone (TVZ), New Zealand, the Kermadec Island Arc (KA) and its back-arc basin, the Havre Trough show systematic variations in trace-element and isotope geochemistry which are attributed to differences in tectonic setting and source heterogeneity along a more or less continuous plate boundary. Basalts from the Kermadec Arc are characterised by low abundances of high field strength elements (HFSE) such as Ti, Zr, Nb, Ta and Hf and have high ratios of Ti/Zr and low ratios of Ti/Sc and Ti/V relative to typical MORB. Basalts from TVZ also show low abundances of the HFS elements relative to MORB but show lower Ti/Zr, higher Ti/V and Ti/Sc ratios and generally higher Zr abundances than KA most basalts. The Havre Trough basalt is mildly alkaline (< 1% normative nepheline) like many back-arc basin basalts from the Pacific rim, contrasting with the hypersthene normative TVZ and KA rocks. It has higher Zr than most TVZ basalts and all KA basalts. Ratios such as Ti/V, Ti/Sc and Ti/Zr are within the range of TVZ and MORB basalts but distinct from KA basalts. The depleted (relative to MORB) HFSE characteristics of the KA and TVZ basalts are complemented by high abundances of large ion lithophile elements (LIL), such as Ba, Rb and K, when compared to MORB, yielding the distinctive LIL-enriched pattern of subduction related rocks on a normalised multi-element plot. In contrast, the Havre Trough basalt is MORB-like. Chondrite-normalised Rare Earth Element (REE) patterns for the TVZ basalts show a field overlapping with that defined by the southern KA (Rumble Sea Mounts), with light REE enriched patterns (Ce/Yb n = ˜ 1.8-3) and flat heavy REE (Tb-Lu). Basalts from the northern KA are typically light REE depleted (Ce/Yb n = 0.5) or slightly enriched (Ce/Yb n = 1.5). The REE pattern of the Havre Trough basalt is distinctive from both the KA and TVZ fields, being richer in the heavy REE, yet similar to many basalts from back-arc basins. Sr and Nd

  10. Tectonic evolution of Early Paleozoic island-arc systems and continental crust formation in the Caledonides of Kazakhstan and the North Tien Shan

    NASA Astrophysics Data System (ADS)

    Degtyarev, K. E.

    2011-01-01

    The extended Saryarka and Shyngyz-North Tien Shan volcanic belts that underwent secondary deformation are traced in the Caledonides of Kazakhstan and the North Tien Shan. These belts are composed of igneous rocks pertaining to Early Paleozoic island-arc systems of various types and the conjugated basins with oceanic crust. The Saryarka volcanic belt has a complex fold-nappe structure formed in the middle Arenigian-middle Llanvirnian as a result of the tectonic juxtaposition of Early-Middle Cambrian and Late Cambrian-Early Ordovician complexes of ensimatic island arcs and basins with oceanic crust. The Shyngyz-North Tien Shan volcanic belt is characterized by a rather simple fold structure and consists of Middle-Late Ordovician volcanic and plutonic associations of ensialic island arcs developing on heterogeneous basement, which is composed of complexes belonging to the Saryarka belt and Precambrian sialic massifs. The structure and isotopic composition of the Paleozoic igneous complexes provide evidence for the heterogeneous structure of the continental crust in various segments of the Kazakh Caledonides. The upper crust of the Shyngyz segment consists of Early Paleozoic island-arc complexes and basins with oceanic crust related to the Saryarka and Shyngyz-North Tien Shan volcanic belts in combination with Middle and Late Paleozoic continental igneous rocks. The deep crustal units of this segment are dominated by mafic rocks of Early Paleozoic suprasubduction complexes. The upper continental crust of the Stepnyak segment is composed of Middle-Late Ordovician island-arc complexes of the Shyngyz-North Tien Shan volcanic belt and Early Ordovician rift-related volcanics. The middle crustal units are composed of Riphean, Paleoproterozoic, and probably Archean sialic rocks, whereas the lower crustal units are composed of Neoproterozoic mafic rocks.

  11. Andaman-Sumatra island arc: II. The December 26, 2004 earthquake as one of the key episodes in seismogenic activation of the arc in the beginning of XXI century

    NASA Astrophysics Data System (ADS)

    Balakina, L. M.; Moskvina, A. G.

    2013-03-01

    The interpretation of the nature and parameters of the source for the earthquake that occurred in Sumatra on December 26, 2004 is suggested. Our study relies on a variety of data on the geological structure of the region, long-term seismicity, spatial distribution of the foreshocks and aftershocks, and focal mechanisms; and the pattern of shaking and tsunami, regularities in the occurrence of the earthquakes, and the genetic relationship between the seismic and geological parameters inherent in various types of seismogenic zones including island arcs. The source of the Sumatran earthquake is a steep reverse fault striking parallel to the island arc and dipping towards the ocean. The length of the fault is ˜450 km, and its probable bedding depth is ˜70-100 km. The magnitude of this seismic event corresponding to the length of its source is 8.9-9.0. The vertical displacement in the source probably reached 9-13 m. The fault is located near the inner boundary of the Aceh Depression between the epicenter of the earthquake and the northern tip of the depression. The strike-slip and strike-slip reverse the faults cutting the island arc form the northern and southern borders of the source. The location and source parameters in the suggested interpretation account quite well for the observed pattern of shaking and tsunami. The Aceh Depression and its environs probably also host other seismic sources in the form of large reverse faults. The Sumatran earthquake, which was the culmination of the seismogenic activation of the Andaman-Sumatra island arc in the beginning of XXI century, is a typical tsunamigenic island-arc earthquake. By its characteristics, this event is an analogue to the M W = 9 Kamchatka earthquake of November 4, 1952. The spatial distribution of the epicenters and the focal mechanisms of the aftershocks indicate that the repeated shocks during the Sumatran event were caused by the activation of a complex system of geological structures in various parts of

  12. Aleutian Ancorinidae (Porifera, Astrophorida): Description of three new species from the genera Stelletta and Ancorina.

    PubMed

    Lehnert, Helmut; Stone, Robert P

    2014-01-01

    Two new species of the genus Stelletta and one new species of Ancorina are described from the Aleutian Islands of Alaska and compared to congeners of the region. This is the first record of the genus Ancorina in the North Pacific Ocean. Stelletta ovalae Tanita 1965 is also reported for the first time from the Bering Sea and Alaska.  PMID:24990051

  13. The volcanic evolution of Martinique Island: Insights from K-Ar dating into the Lesser Antilles arc migration since the Oligocene

    NASA Astrophysics Data System (ADS)

    Germa, Aurélie; Quidelleur, Xavier; Labanieh, Shasa; Chauvel, Catherine; Lahitte, Pierre

    2011-12-01

    The Lesser Antilles island arc bifurcates into two lines in its northern part, with an old branch to the east and a recent active branch to the west. Martinique is located at the southern tip of the separation. The two arcs diverge northward, and at maximum divergence are separated by a 50 km wide depression. Despite this separation, which suggests a jump in volcanism, activity has been almost continuous in Martinique Island with a slow displacement of the eruptive centers to the west. Considering timing of emplacement, previous authors defined three cycles of activity, the old, intermediate and recent arcs, of Late Oligocene-Early Miocene, Mid Miocene and Late Miocene to present ages, respectively. The present study investigates the timing of emplacement of the volcanic units in Martinique Island in order to constrain the activity of the old and intermediate Lesser Antilles arcs, as recorded on this island. Unspiked K-Ar age determinations on groundmass and plagioclase separates (Cassignol-Gillot technique) were conducted on 20 samples from the old and intermediate volcanic chains. Martinique has evolved as eight distinct volcanic centers: (1) Basal Complex and Sainte Anne Series (24.8 ± 0.4-20.8 ± 0.4 Ma) for the old arc; (2) Vauclin-Pitault Chain (16.1 ± 0.2-8.44 ± 0.12 Ma) and (3) South-western Volcanism (9.18 ± 0.16-7.10 ± 0.10 Ma) for the intermediate arc; and (4) Morne Jacob volcano (5.14 ± 0.07-1.54 ± 0.03 Ma), (5) Trois Ilets Volcanism (2.358 ± 0.034 Ma and 346 ± 27 ka), (6) Carbet Complex (998 ± 14 to 322 ± 6 ka), (7) Mount Conil (543 ± 8 to 127 ± 2 ka) and (8) Mount Pelée (126 ± 2 ka to present) for the recent arc ( Germa et al., 2010, 2011a).We propose migration rates of 1.1-1.4 km/Myr westward, toward the back arc region throughout the whole volcanic history of Martinique Island. These rates, together with geochemical evidence for a more enriched signature in the youngest magmas, are consistent with a geodynamic evolution involving the

  14. Multi-Hazards Geophysical Monitoring Through the Eastern Caribbean Islands arc: Strategy, Challenges and Future Development

    NASA Astrophysics Data System (ADS)

    Fournier, N.; Lynch, L.; Robertson, R.; Latchman, J.; Mohais, R.; Ramsingh, C.

    2007-05-01

    The Seismic Research Unit (SRU), at the University of the West Indies, St Augustine, Trinidad, W.I., is responsible for monitoring and studying geological hazards in the English and Dutch speaking islands nestled along the ocean-ocean plate convergence zone in the Eastern Caribbean. The Unit operates a multi-hazards monitoring network that spans over 15 islands. Geophysical monitoring techniques include 11 broadband and 44 short period seismic stations, 4 accelerometers, 4 continuous GPS stations (cGPS) and over 50 ground-deformation benchmarks. This seismic network caters for general earthquake surveillance and study as well as for volcano early-warning. As part of the recent trust to improve tsunami surveillance capabilities in the Caribbean the unit has embarked on a program to upgrade a subset of the seismograph network. Near real-time satellite communications will be installed to improve the present network that is built around terrestrial Internet and telephone media. Additional strong motion accelerometers will also be operated alongside the broadband sensors at the upgraded stations to provide the necessary specifications for tsunami detection. Through real- time data exchanged with adjacent and global networks that are involved in the effort to establish a Tsunami Warning System for the Caribbean and adjacent regions, the Unit's capacity to monitor multiple hazard via the seismological method will be significantly improved. The geodetic monitoring program is a hybrid of near real-time data acquisition and static field surveys. It is principally geared towards volcano ground deformation monitoring. The main challenge while monitoring volcano ground deformation in small islands is the limited control on the reference station which are often located within the potential deformation field (versus been ideally outside any volcano related deformation field). As a result, SRU's strategy is to control reference stations in every island by long-baselines processing

  15. Subsurface hydrographic structures and the temporal variations of Aleutian eddies

    NASA Astrophysics Data System (ADS)

    Saito, Rui; Yasuda, Ichiro; Komatsu, Kosei; Ishiyama, Hiromu; Ueno, Hiromichi; Onishi, Hiroji; Setou, Takeshi; Shimizu, Manabu

    2016-05-01

    Aleutian eddies are mesoscale anticyclonic eddies formed within the Alaskan Stream region between 180° meridian and 170° E south of the Aleutian Islands. They propagate southwestward after the isolation from the Alaskan Stream and pass through the Western Subarctic Gyre. We compared hydrographic structures of three Aleutian eddies observed during summer, west of 170° E (Eddy A) and east of 170° E (Eddies B and C). In each eddy, a subsurface dichothermal water (3.0-4.0 °C) was observed above a subsurface mesothermal water (4.0-4.5 °C). The minimum temperature in the dichothermal water at around a depth of 100 m was colder in Eddy A (2.8 °C) than in Eddies B and C (3.0-3.2 °C). This difference could be ascribed to wintertime cooling and influence of surrounding waters during spring warming period. The wintertime cooling makes the dichothermal water colder for eddies isolated from the Alaskan Stream region for a longer time. Particle-tracking experiments using re-analysis products from a data-assimilative eddy resolving ocean model suggested that the dichothermal water within Eddy A was cooled by the entrainment of surrounding colder water even during the spring warming period. The mesothermal waters at depth around 250 m demonstrated similarity among the observed eddies, and the maximum temperature in the mesothermal water within Eddy A (4.3 °C) was close to that of Eddies B and C (4.2 °C) in the in situ observations. These results indicated that the dichothermal water of Aleutian eddies modifies over time, whereas the mesothermal water maintains the original feature as they propagate southwestward from the Alaskan Stream region to the Western Subarctic Gyre.

  16. Vesiculation Characteristics in Pyroclasts of the 3.1 ka Oneraki Eruption, Raoul Island, Kermadec Arc

    NASA Astrophysics Data System (ADS)

    Rotella, M. D.; Barker, S. J.; Wilson, C. J.; Wright, I. C.; Houghton, B. F.

    2008-12-01

    Raoul Island is the emergent 30 square km portion of a > 200 cubic km volcanic edifice which rises 900 m from the sea floor along the Kermadec ridge. Although the island is composed mainly of basalt and basaltic andesite, the last 4000 years has seen several dacitic explosive eruptions associated with caldera formation [Lloyd & Nathan, N.Z. Geol. Surv. Bull., 1981; Smith et al., J.Volc. Geotherm. Res. v. 156, 2006]. Fall deposits of the 3.1 ka Oneraki eruption, of possible plinian dispersal, were sampled at five stratigraphic levels. The 16-32 mm size pumice clasts of the lower four levels display narrow, unimodal density ranges. The upper level fall deposit shows a bimodal density distribution, reflecting a change in eruption characteristics as dense, degassed fragments were also ejected, but without other signs of any interaction with external water. For this study, qualitative and quantitative vesicularity data have been collected from 16- 32 mm clasts from three of the stratigraphic levels to provide insights to the various processes involved in vesiculation and fragmentation of this magma. Future work will include comparisons of vesicle textures in this eruption to other dry and wet subaerially erupted Raoul deposits, and to submarine deposits of similar composition at Macauley and Healy volcanoes. By characterizing eruption products from these volcanoes and using constraints provided by the different degrees of interaction with water (and at different water depths in submarine examples) we hope to better understand the dynamics of the violent degassing processes driving these eruptions.

  17. The collision zone between the North d'Entrecasteaux Ridge and the New Hebrides island arc. 2. Structure from multichannel seismic data

    USGS Publications Warehouse

    Fisher, M.A.; Collot, J.-Y.; Geist, E.L.

    1991-01-01

    The d'Entrecasteaux zone (DEZ) collides with the central New Hebrides island arc and consists of two subparallel ridges that strike east-west, stand 1-2 km above the surrounding oceanic plate, and subduct obliquely (15??) northward beneath the arc. Rocks dredged from the north ridge as well as reflections evident in multichannel seismic reflection data indicate that this ridge has a volcanic origin. Seismic reflection data collected over the lower arc slope reveal that mass wasting deposits locally make up most of the accretionary wedge. Mass wasting is thought to occur as the accretionary wedge is uplifted in response to the northward oblique subduction of the north ridge. The toe of the north ridge flank marks an abrupt transition in the lithologies that make up the footwall of the interplate decollement. -from Authors

  18. A mid-Permian chert event: widespread deposition of biogenic siliceous sediments in coastal, island arc and oceanic basins

    USGS Publications Warehouse

    Murchey, B.L.; Jones, D.L.

    1992-01-01

    Radiolarian and conodont of Permian siliceous rocks from twenty-three areas in teh the circum-Pacific and Mediterranean regions reveal a widespread Permian Chert Event during the middle Leonardian to Wordian. Radiolarian- and (or) sponge spicule-rich siliceous sediments accumulated beneath high productivity zones in coastal, island arc and oceanic basins. Most of these deposits now crop out in fault-bounded accreted terranes. Biogenic siliceous sediments did not accumulate in terranes lying beneath infertile waters including the marine sequences in terranes of northern and central Alaska. The Permian Chert Event is coeval with major phosphorite deposition along the western margin of Pangea (Phosphoria Formation and related deposits). A well-known analogue for this event is middle Miocene deposition of biogenic siliceous sediments beneath high productivity zones in many parts of the Pacific and concurrent deposition of phosphatic as well as siliceous sediments in basins along the coast of California. Interrelated factors associated with both the Miocene and Permian depositional events include plate reorientations, small sea-level rises and cool polar waters. ?? 1992.

  19. Rethinking Recycling in Arcs

    NASA Astrophysics Data System (ADS)

    Kelemen, P.; Behn, M. D.; Jagoutz, O.

    2012-12-01

    C faster, and in larger volumes at a given time. Subduction erosion rarely, if ever, transports significant amounts of buoyant material deep into the convecting mantle. Because buoyant material can remain part of the crust, it may often be a mistake to add all of the eroded material to the observed arc volume to derive crustal growth rates. Buoyancy instabilities during subduction erosion or arc-arc collision will accumulate felsic arc crust. For example, > 50% of Aleutian arc lavas and exposed plutons are more buoyant than mantle peridotite at 700-800°C, 3-4 GPa. The buoyant material has an average of 60-62 wt% SiO2, molar Mg/(Mg+Fe) 0.4-0.5, and trace elements identical to bulk continental crust, though western Aleutian lavas have the most depleted Sr, Nd and Pb isotope ratios of all arc lavas worldwide. In general, density sorting of arc lithologies, and subsequent partial melting as buoyant rocks rise through the mantle wedge or along a subduction channel, could lead to a kind of double and triple distillation. Incompatible elements such as Th would be enriched in arc crust, retaining correlations with isotopic indicators of a recycled sediment component, while Th-poor, dense, mafic lavas and lower crustal cumulates return to the convecting mantle.

  20. The Marsili Ridge (Southern Tyrrhenian Sea, Italy): An island-arc volcanic complex emplaced on a 'relict' back-arc basin

    NASA Astrophysics Data System (ADS)

    Ventura, G.; Milano, G.; Passaro, S.; Sprovieri, M.

    2013-01-01

    Marsili Seamount (< 1 Ma; Southern Tyrrhenian Sea, Italy) is classically interpreted as the spreading ridge of the about 2 Ma old Marsili oceanic back-arc associated to the Southern Tyrrhenian Sea-Calabrian Arc subduction setting. High resolution bathymetric data show that the ridge extends along a NNE-SSW strike and consists of 4 sectors and 11 major segments. Seafloor failures and central-type activity from an overpressurized sill-like reservoir characterize the central sector, whereas fissural volcanism and passive magma ascent take places at the edges. Cones indicative of high effusion rates concentrate in the axial zone, whereas flat-top shields associated to lower rates are located at the northern tip. Along-axis, lateral magma migration due to a local deepening of the elastic-brittle thickness of the crust develops from the central sector toward the northern tip. The opening of the Marsili back-arc basin vanished from about 1 Ma and the Marsili Ridge formed by passive magma ascent along pre-existing fractures inherited by early spreading activity. The values of the long-term output rate, the ratio between magmatic pressure and tectonic stress, and the morphological features of the lava flows and dikes are consistent with those found in volcanic arc subduction settings. Marsili Ridge represents a volcanic arc edifice emplaced on an older, 'relict' back-arc. The formation of the Marsili Ridge marks the transition from an extensional subduction setting to a compressive one.

  1. Application of Satellite Geodesy in Analyzing the Accelerated Movement of the Back-arc Rifting in the Izu Bonin Islands, Japan

    NASA Astrophysics Data System (ADS)

    Arisa, D.; Heki, K.

    2014-12-01

    The Izu-Bonin islands lies along the convergent boundary between the subducting Pacific plate (PA) and the overriding Philippine Sea plate (PH) in the western Pacific. Nishimura (2011) found that the back-arc rifting goes on behind the Izu arc by studying the horizontal velocities of GNSS stations on the Izu islands. Here we show that this rifting has accelerated in 2004 using GNSS data at Aogashima, Hachijoujima, and Mikurajima stations. The back-arc rifting behind the Izu islands can be seen as the increasing distance between stations in the Izu-Bonin islands and stations located in the stable part of PH. We found that their movement showed clear acceleration around the third quarter of 2004. Obtaining the Euler vector of the PH is necessary to analyzed the movement of each stations relative to the other stations on the same plate. The analyzing of GPS timeseries leads us to one initial conclusion that some accelerated movement started to occur in the third quarter of 2004. This event was closely related to the earthquake on May 29, 2004 in Nankai Trough and September 5, 2004 earthquake near the triple junction of Sagami Trough. The analyzing process help us to understand that this accelerated movement was not the afterslip of any of these earthquakes, but it was triggering these area to move faster and further than it was. We first rule out the best possible cause by constraining the onset time of the accelerated movement, and correlating it with the earthquakes. May 29, 2004 earthquake (M6.5) at the PA-PH boundary clearly lacked the jump which should mark the onset of the eastward slow movement. Moreover, additional velocity vectors do not converge to the epicenter, and onset time that minimizes the post-fit residual is significantly later than May. We therefore conclude that accelerated movement started in 2004 was not due to the afterslip of interplate earthquake in May 29. On the next step we found that the onset time coincides with the occurrence of

  2. Island of Okinawa, Japan

    NASA Technical Reports Server (NTRS)

    1982-01-01

    The island of Okinawa, (26.5N, 128.0E) largest of the Ryukyu Islands, Japan. The Ryukyu island group lies south of the main home islands of Japan in an arc towards the Chinese island Republic of Taiwan. As is typical throughout the Japanese home islands, intense urban development can be observed all over the island in this near vertical view.

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

    SciTech Connect

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

    1988-01-01

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

  4. Crustal structure of the Caribbean-northeastern South America arc-continent collision zone

    NASA Astrophysics Data System (ADS)

    Christeson, Gail L.; Mann, Paul; Escalona, Alejandro; Aitken, Trevor J.

    2008-08-01

    We present the results of a 568-km-long regional wide-angle seismic profile conducted in the southeastern Caribbean that crosses an active island arc, a remnant arc, two basins possibly floored by oceanic crust, an allochthonous terrane of forearc affinity, and the passive margin of northern South America. The velocity structures of the Late Cretaceous Aves Ridge remnant arc and Miocene and younger Lesser Antilles arc are remarkably similar, which implies that magmatic processes have remained moderately steady over time. Crustal thickness is ˜26 km at the Aves Ridge and ˜24 km at the Lesser Antilles arc. In comparison to the Izu-Bonin and Aleutian arcs, the Lesser Antilles arc is thinner and has no evidence for a lower crustal cumulate layer, which is consistent with the estimated low magma production rates of the Lesser Antilles arc. Crustal thickness beneath the Grenada and Tobago basins is 4-10 km, and the velocity structure suggests that these basins could be floored by oceanic crust. A decrease of ˜1 km/s in average seismic velocity of the upper crust is observed from NW to SE across the North Coast fault zone; we argue that this marks the suture between the far-traveled Caribbean arc and the passive margin of the South American continent. Current strike-slip motion between the Caribbean and South American plates is located ˜30 km to the south, and thus material originally deposited on the South American passive margin has now been transferred to the Caribbean plate.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    The Hikurangi subduction margin along North Island, New Zealand accommodates oblique convergence of the Pacific plate westward beneath the Australian plate at 45 mm/yr. Along the southern margin, frontal accretion and pronounced forearc uplift occur inboard of the subducting Hikurangi plateau. In the north, subduction erosion and segmented uplift occur inboard of subducting seamounts along the plateau flank. Prior workers have established a robust foundation for coastal terrace studies along the northern Hikurangi margin (e.g., Berryman et al., 1989; Ota et al., 1992; Berryman, 1993; Wilson et al., 2006, 2007; Clark et al., 2010; Litchfield et al, 2007, 2010). New field observations presented here provide additional constraints on terrace uplift along this erosional subduction margin. Along Raukumara Peninsula (north of Poverty Bay), multiple Holocene to late Pleistocene marine and fluvial terraces occur at varying elevations, recording differential uplift across six coastal segments from Gisborne to East Cape (Ota et al., 1992; Wilson et al., 2007). In this study, two to three late Pleistocene terraces were observed on rocky headlands within the first segment (Gisborne to Whangara) at elevations of 80-185 m above msl. Preliminary correlation with OIS 5a-e sea level high stands (80-125 ka) indicates net uplift at 1.2-1.5 m/ky. Uplifted Holocene wavecut platforms occur in steps along the seaward edge of these terraces, consistent with coseismic uplift. At Makorori Point, an uplifted bench occurs along the modern seacliff at 2.3 m above the cliff base. A fossil gastropod shell from paleo-beach gravels on the platform inner edge yielded a calibrated radiocarbon age of 1680 ×110 ybp. At Turihaua Point, a ≥1 m thick deposit of Holocene beach sands overlies an uplifted wavecut platform at ≥1.5 m above mean sea level. Carbonate-cemented beachrock at the base of the sand deposit yields a calibrated radiocarbon age of 2990 ×70 ybp. At Mahia Peninsula (between Poverty

  6. A Dangling Slab, Amplified Arc Volcanism, Mantle Flow and Seismic Anisotropy in the Kamchatka Plate Corner

    NASA Astrophysics Data System (ADS)

    Park, J.; Levin, V.; Brandon, M. T.; Lees, J.; Peyton, V.; Gordeev, E.; Ozerov, A.

    2001-12-01

    The Kamchatka peninsula in Russian East Asia lies at the junction of a transcurrent plate boundary, aligned with the western Aleutian Islands, and a steeply-dipping subduction zone with near-normal convergence. Seismicity patterns and P-wave tomography argue that subducting Pacific lithosphere terminates at the Aleutian junction, and that the downdip extension (>150km depth) of the slab edge is missing. Seismic observables of elastic anisotropy (SKS splitting and Love-Rayleigh scattering) are consistent with asthenospheric strain that rotates from trench-parallel beneath the descending slab to trench-normal beyond its edge. Present-day arc volcanism is concentrated near the slab edge, in the Klyuchevskoy and Sheveluch eruptive centers. Loss of the downdip slab edge, whether from thermo-convective or ductile instability, and subsequent ``slab-window'' mantle return flow is indicated by widespread Quaternary volcanism in the Sredinny range inland of Klyuchevskoy and Sheveluch, as well as the inferred Quaternary uplift of the central Kamchatka depression. The slab beneath Klyuchevskoy has shallower dip (35o) than the subduction zone farther south (55o) suggesting a transient lofting of the slab edge, either from asthenospheric flow or the loss of downdip load. Such lofting may induce pressure-release melting to supply the Klyuchevskoy and Sheveluch eruptive centers. Petrologic indicators of high magma-peridotite equilibrium temperatures, long residence times for the hydrous arc-volcanic component, and weak expression of subducted sediment flux support the lofting hypothesis, and discourage an alternate interpretation in terms of accelerated slab rollback and/or a heightened influx of subducted volatiles. Over the late Cenozoic, the Komandorsky Basin subducted beneath northern Kamchatka and produced arc volcanics in the Sredinny Range. Several lines of evidence suggest the northeast migration of a plate triple junction (North America/Pacific/Komandorsky) along the

  7. Oblique collision and accretion of the Netherlands Leeward Antilles island arc: A structural analysis of the Caribbean-South American plate boundary zone

    NASA Astrophysics Data System (ADS)

    Beardsley, Amanda Gail

    2007-12-01

    The Netherlands Leeward Antilles volcanic island arc is an ideal natural laboratory to study the evolution of the Caribbean-South American plate boundary. The Leeward Antilles islands (Aruba, Curacao, and Bonaire) are located offshore western Venezuela, within the obliquely convergent diffuse plate boundary zone. Outcrop analysis, microthermometry, and 2D marine seismic reflection data provide evidence of three generations of regional deformation since the Late Cretaceous. Outcrop analysis of structural features, including faults, joints, and veins, characterizes the kinematic history of the islands. Fluid inclusion analysis of quartz and calcite veins coupled with apatite fission-track dating provides the island exhumation history. Finally, marine reflection seismic data processing and interpretation of newly acquired data elucidates offshore structures to integrate with our onshore results. The oldest regional deformation, resulting in both ductile (D1) and brittle (F 1) structures, is attributed to displacement partitioning along the arcuate Caribbean plate boundary. Associated crustal thinning initiated island exhumation, at a rate of 0.18 km/my, from a maximum burial depth of 6 km in the Late Cretaceous (˜89 Ma). Coeval with D1/F1 deformation and exhumation, stretching of the island arc resulted in extensive basin rifting that separated the island blocks. At ˜55 Ma, a change in the relative motion of the Caribbean plate altered plate boundary dynamics. Displacement along the right-lateral Caribbean transform fault and Oca - San Sebastian - El Pilar strike-slip fault system created a wrench tectonic regime within the diffuse plate boundary zone. A second generation of brittle structures (F2) developed while the islands were at a maximum burial depth of 2 km during the Paleocene/Eocene. Since ˜45 Ma, continued motion along the strike-slip fault systems and oblique plate convergence resulted in the youngest generation of structural features (F3). Regional

  8. 75 FR 69597 - Fisheries of the Exclusive Economic Zone Off Alaska; Pacific Cod in the Bering Sea and Aleutian...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-11-15

    ... 2011 harvest specifications for groundfish in the BSAI (75 FR 11778, March 12, 2010). In accordance... Economic Zone Off Alaska; Pacific Cod in the Bering Sea and Aleutian Islands Management Area AGENCY.... ACTION: Temporary rule; closure. SUMMARY: NMFS is prohibiting retention of Pacific cod in the Bering...

  9. 75 FR 792 - Fisheries of the Economic Exclusive Zone Off Alaska; Pacific Cod in the Bering Sea and Aleutian...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-01-06

    .../processors using hook-and-line in the BSAI under Sec. 679.20(d)(1)(iii) on November 16, 2009 (74 FR 59918... catcher Pacific cod by catcher/processors using hook-and-line gear in the Bering Sea and Aleutian Islands.../processors using hook-and-line gear in the BSAI. Classification This action responds to the best...

  10. 78 FR 35771 - Fisheries of the Exclusive Economic Zone Off Alaska; Atka Mackerel in the Bering Sea and Aleutian...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-06-14

    ... (78 FR 13813, March 1, 2013). In accordance with Sec. 679.20(d)(1)(iii), the Regional Administrator... Economic Zone Off Alaska; Atka Mackerel in the Bering Sea and Aleutian Islands Management Area AGENCY.... ACTION: Temporary rule; closure. SUMMARY: NMFS is prohibiting directed fishing for Atka mackerel in...

  11. 75 FR 14498 - Fisheries of the Exclusive Economic Zone Off Alaska; Atka Mackerel in the Bering Sea and Aleutian...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-03-26

    ... groundfish in the BSAI (75 FR 11778, March 12, 2010). In accordance with Sec. 679.20(d)(1)(i), the Regional... Economic Zone Off Alaska; Atka Mackerel in the Bering Sea and Aleutian Islands Management Area AGENCY.... ACTION: Temporary rule; closure. SUMMARY: NMFS is prohibiting directed fishing for Atka mackerel in...

  12. 78 FR 64891 - Fisheries of the Exclusive Economic Zone Off Alaska; Atka Mackerel in the Bering Sea and Aleutian...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-10-30

    ... the BSAI (78 FR 13813, March 1, 2013). In accordance with Sec. 679.20(d)(1)(iii), the Regional... Economic Zone Off Alaska; Atka Mackerel in the Bering Sea and Aleutian Islands Management Area AGENCY.... ACTION: Temporary rule; closure. SUMMARY: NMFS is prohibiting directed fishing for Atka mackerel in...

  13. 78 FR 64892 - Fisheries of the Exclusive Economic Zone Off Alaska; Atka Mackerel in the Bering Sea and Aleutian...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-10-30

    ... by the final 2013 and 2014 harvest specifications for groundfish in the BSAI (78 FR 13813, March 1... Economic Zone Off Alaska; Atka Mackerel in the Bering Sea and Aleutian Islands Management Area AGENCY.... ACTION: Temporary rule; closure. SUMMARY: NMFS is prohibiting directed fishing for Atka mackerel in...

  14. 77 FR 26212 - Fisheries of the Exclusive Economic Zone Off Alaska; Atka Mackerel in the Bering Sea and Aleutian...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-05-03

    ... the final 2012 and 2013 harvest specifications for groundfish in the BSAI (77 FR 10669, February 23... Economic Zone Off Alaska; Atka Mackerel in the Bering Sea and Aleutian Islands Management Area AGENCY.... ACTION: Temporary rule; closure. SUMMARY: NMFS is prohibiting directed fishing for Atka mackerel in...

  15. 76 FR 65975 - Fisheries of the Exclusive Economic Zone Off Alaska; Atka Mackerel in the Bering Sea and Aleutian...

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    2011-10-25

    ... by the final 2011 and 2012 harvest specifications for groundfish in the BSAI (76 FR 11139, March 1... Economic Zone Off Alaska; Atka Mackerel in the Bering Sea and Aleutian Islands Management Area AGENCY.... ACTION: Temporary rule; closure. SUMMARY: NMFS is prohibiting directed fishing for Atka mackerel in...

  16. 77 FR 39441 - Fisheries of the Exclusive Economic Zone Off Alaska; Atka Mackerel in the Bering Sea and Aleutian...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-07-03

    ... the BSAI (77 FR 10669, February 23, 2012). In accordance with Sec. 679.20(d)(1)(iii), the Regional... Economic Zone Off Alaska; Atka Mackerel in the Bering Sea and Aleutian Islands Management Area AGENCY.... ACTION: Temporary rule; closure. SUMMARY: NMFS is prohibiting directed fishing for Atka mackerel in...

  17. 75 FR 6129 - Fisheries of the Exclusive Economic Zone Off Alaska; Atka Mackerel in the Bering Sea and Aleutian...

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    2010-02-08

    ... BSAI (74 FR 7359, February 17, 2009). In accordance with Sec. 679.20(d)(1)(iii), the Regional... Economic Zone Off Alaska; Atka Mackerel in the Bering Sea and Aleutian Islands Management Area AGENCY.... ACTION: Temporary rule; closure. ] SUMMARY: NMFS is prohibiting directed fishing for Atka mackerel in...

  18. 76 FR 10780 - Fisheries of the Exclusive Economic Zone Off Alaska; Atka Mackerel in the Bering Sea and Aleutian...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-02-28

    ... specifications for groundfish in the BSAI (75 FR 11778, March 12, 2010) and inseason adjustment (76 FR 1539... Economic Zone Off Alaska; Atka Mackerel in the Bering Sea and Aleutian Islands Management Area AGENCY.... ACTION: Temporary rule; closure. SUMMARY: NMFS is prohibiting directed fishing for Atka mackerel in...

  19. 78 FR 25878 - Fisheries of the Exclusive Economic Zone Off Alaska; Atka Mackerel in the Bering Sea and Aleutian...

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    2013-05-03

    ... the final 2013 and 2014 harvest specifications for groundfish in the BSAI (78 FR 13813, March 1, 2013... Economic Zone Off Alaska; Atka Mackerel in the Bering Sea and Aleutian Islands Management Area AGENCY.... ACTION: Temporary rule; closure. SUMMARY: NMFS is prohibiting directed fishing for Atka mackerel in...

  20. 76 FR 59924 - Fisheries of the Exclusive Economic Zone Off Alaska; Sharks in the Bering Sea and Aleutian...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-09-28

    ... GOA (76 FR 11139, March 1, 2011) and apportionment of non-specified reserves (76 FR 53840, August 30... Economic Zone Off Alaska; Sharks in the Bering Sea and Aleutian Islands Management Area AGENCY: National...: Temporary rule; closure. SUMMARY: NMFS is prohibiting retention of sharks in the Bering Sea and...

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

    SciTech Connect

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

    1990-06-01

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

  2. Evidence for Hydrous Metasomatism and Slab Melting in the Tabar-Lihir-Tanga-Feni Island Arc, Papua New Guinea

    NASA Astrophysics Data System (ADS)

    Watford, A.; Chadwick, J.; Kamenov, G. D.; Foster, N.

    2013-12-01

    The Tabar-Lihir-Tanga-Feni (TLTF) island arc is located 35-75 km from the northeast Pacific coast of New Ireland Island in Papua New Guinea. These volcanoes are in an extending former forearc region of the inactive Manus-Kilinailau subduction zone, at the boundary between the Pacific and Indo-Australian Plates [1]. Volcanism shifted from New Ireland to the TLTF when Pacific Plate subduction stalled there in the Miocene, when the Ontong Java Plateau impinged on the trench [1, 2]. Fresh volcanic rocks dredged from Tubaf seamount near Lihir island in 2000 (Australian CSIRO Project SHAARC) contain abundant ultramafic xenoliths, making it one of the few locations on Earth where they can be found in a subduction setting. Several xenoliths (2-3 cm in size) and their host lavas from two dredges have been analyzed in this geochemical and petrographic study. Host lavas and xenoliths were mechanically separated, and portions of each were examined for bulk major and some trace elements using X-ray fluorescence, a suite of 29 trace elements was analyzed in the host lavas using ICP-MS, and the chemistry of individual xenolith minerals was evaluated using an electron microprobe. Olivine, ortho- and clinopyroxene crystals in the xenoliths are up to 1 mm in size, and these are crosscut by veins containing smaller crystals of pyroxene, phlogopite, and amphibole, as well as glass and open voids. These veins were previously shown to be evidence of dissolution of primary minerals to form the secondary phases via hydrous metasomatism by fluids from the subducted Pacific slab [2, 3]. The primary olivines in xenoliths have homogenous compositions both within and among the samples (e.g. olivine Mg# 80.03 - 82.42; n=22), but pyroxenes show somewhat more variation (e.g. cpx Mg# 84.33 - 89.21; n=23), with low outliers consistently near and within the metasomatic veins. The host lavas are vesicular, alkali-rich trachybasalts and trachyandesites with abundant phlogopite and amphibole

  3. Structure and deformation of north and central Malaita, Solomon Islands: tectonic implications for the Ontong Java Plateau-Solomon arc collision, and for the fate of oceanic plateaus

    NASA Astrophysics Data System (ADS)

    Petterson, M. G.; Neal, C. R.; Mahoney, J. J.; Kroenke, L. W.; Saunders, A. D.; Babbs, T. L.; Duncan, R. A.; Tolia, D.; McGrail, B.

    1997-12-01

    The island of Malaita, Solomon Islands, represents the obducted southern margin of the Ontong Java Plateau (OJP). The basement of Malaita formed during the first and possibly largest plateau-building magmatic event at ˜122 ± 3 Ma. It subsequently drifted passively northwards amassing a 1-2 km thickness of pelagic sediment overburden. A major change in OJP tectonics occurred during the Eocene, possibly initiated by the OJP passing over the Samoan or Raratongan hotspot. Extension facilitated increased sedimentation and basin formation (e.g., the Faufaumela basin) and provided readily available deep-crustal pathways for alkali basalt and subsequent Oligocene alnöite magmas, with related hydrothermal activity producing limited Ag + Pb mineralisation. Eocene to Mid-Miocene sediments record the input of arc-derived turbiditic volcaniclastic sediment indicating the relative closeness of the OJP to the Solomon arc. The initial collision of the OJP and Solomon arc at 25-20 Ma was of a 'soft docking' variety and did not result in major compressive deformation on Malaita. South-directed subduction of the Pacific Plate briefly ceased at this time but resumed intermittently on a local scale from ˜15 Ma. Subduction of the Australian Plate beneath the Solomon arc commenced at ˜8-7 Ma. Increased coupling between the Solomon arc and the OJP led to the gradual emergence of the OJP at 6-5 through to 4 Ma. The most intense period of compressive to transpressive deformation recorded on Malaita is stratigraphically bracketed at between 4 and 2 Ma, resulting in estimated crustal shortening of between 24 and 46%, and the inclusion of between 1 and 4 km of basement OJP basalts within the larger anticlines. Basement and cover sequences are deformed together in a coherent geometry and there are no major decollement surfaces; the large asymmetrical fold structures of Malaita are likely to be the tip regions of blind thrusts with detachment surfaces between 1 and 4 km beneath the cover

  4. Cold-front driven storm erosion and overwash in the central part of the Isles Dernieres, a Louisiana barrier-island arc

    USGS Publications Warehouse

    Dingler, J.R.; Reiss, T.E.

    1990-01-01

    Tropical and extratropical storms produce significant erosion on the barrier islands of Louisiana. Over the past 100 years, such storms have produced at least 2 km of northward beach-face retreat and the loss of 63% of the surface area of the Isles Dernieres, a low-lying barrier-island arc along the central Louisiana coast. Elevations on the islands within the arc are typically less than 2 m above mean sea level. The islands typically have a washover-flat topography with occasional, poorly developed, dune-terrace topography consisting of low-lying and broken dunes. The central part of the arc consists of salt-marsh deposits overlain by washover sands along the Gulf of Mexico shoreline. Sand thicknesses range from zero behind the beach, to less than 2 m under the berm crest, and back to zero in the first nearshore trough. The sand veneer is sufficiently thin that storms can strip all the sand from the beach face, exposing the underlying marsh deposits. The geomorphic changes produced by cold fronts, a type of extratropical storm that commonly affect the Isles Dernieres between late fall and early spring are described. Between August 1986 and September 1987, repeated surveys along eleven shore-normal transects that covered 400 m of shoreline revealed the timing and extent of cold-front-produced beach change along a typical section of the central Isles Dernieres. During the study period, the beach face retreated approximately 20 m during the cold-front season but did not rebuild during the subsequent summer. Because the volume of sand deposited on the backshore (5600 m3) was less than the volume of material lost from the beach face (19,200 m3), approximately 13,600 m3 of material disappeared. Assuming that underlying marsh deposits decrease in volume in direct proportion to the amount of beach-face retreat, an estimate of the mud loss during the study period is 14,000 m3. Thus, the decrease in volume along the profiles can be accounted for without removing any sand

  5. Tectonic implications for the occurrence of ocean floor, hotspot, and island arc materials within accretionary prisms: Examples from the Mesozoic-Cenozoic NW Pacific Rim

    NASA Astrophysics Data System (ADS)

    Ogawa, Y.; Hirano, N.; Hirano, N.; Taniguchi, H.; Taniguchi, H.; Taniguchi, H.

    2001-12-01

    On-land Mesozoic-Cenozoic accretionary prisms exposed in Japan commonly have basaltic rocks incorporated as blocks into melanges or fault zones during a prolonged history of subduction and/or obduction. Chemical signatures of these basaltic rocks and their mode of occurrence with sedimentary covers and/or associated sedimentary rocks indicate that most of these isolated small basaltic blocks consistently display a WPB chemistry, whereas large slabs of basaltic rocks around the Izu Arc collision zone show MORB chemistry with rare examples of IAT, BABB, and/or WPB affinities. Comparing with the present uniformitarian examples of convergent plate boundaries in the western Pacific that we know through the DSDP and ODP projects and submersible and seismic surveys, we can interpret some of the basaltic material with WPB affinity in the Japanese accretionary prisms as relict edifices of seamounts with hotspot origin. These hotspot-related basaltic rocks are commonly associated with reefal limestones and were incorporated into continental margin melanges either by submarine sliding from the downgoing oceanic plate or by shallow-level offscraping along decollement surfaces during the subduction of oceanic plates. Older, uplifted parts of the fossil accretionary prisms on the continent side further inward from the trench where the deeper levels of accreted material are exposed include larger amounts of basaltic blocks. This observation suggests that significant amount of underplating might have occurred in the deeper levels of oceanic crust along decollement zones at structurally lower depths. The metamorphic belts (e.g.Sambagawa, Chichibu, Shimanto etc.) have commonly alkaline rocks or plateau-type E-MORB basalts without any trace of N-MORB rocks with rare special exceptions. Besides these ordinary accretionary prism examples formed by a simple plate subduction system, another type of accretion resulting from island arc or ridge collision is observed to have occurred in

  6. Igneous history of the Koyukuk terrane, western Alaska: constraints on the origin, evolution, and ultimate collision of an accreted island arc terrane

    USGS Publications Warehouse

    Box, S.E.; Patton, W.W., Jr.

    1989-01-01

    The Koyukuk terrane consists of volcanic, volcaniclastic, and plutonic rocks which range from Late Paleozoic to Early Cretaceous in age. The terrane crops out in a U-shaped belt which is roughly paralleled by outer belts of ultramafic rocks, oceanic plate basalts and cherts, and retrograded blueschist facies rocks of continental protolith. These rocks have been interpreted as components of a volcanic arc terrane that collided with the North American continental margin in Early Cretaceous time. The Koyukuk terrane consists of four time-stratigraphic units: (1) pre-Middle Jurassic basalts, (2) Middle and Late Jurassic granitic rocks, (3) lower Lower Cretaceous volcanic rocks, and (4) upper Lower Cretaceous volcanic rocks. Limited chemical data from the basalts of unit 1 indicate that they were erupted in a nonarc tectonic environment, possibly in an oceanic island or back arc setting. Units, 2, 3, and 4 have the characteristics of subduction-related volcanic rocks. -from Authors

  7. Zircon ages and geochemical compositions of the Manlay ophiolite and coeval island arc: Implications for the tectonic evolution of South Mongolia

    NASA Astrophysics Data System (ADS)

    Zhu, Mingshuai; Baatar, Munkhtsengel; Miao, Laicheng; Anaad, Chimedtseren; Zhang, Fochin; Yang, Shunhu; Li, Yueming

    2014-12-01

    Numerous small dismembered ophiolite fragments occur in South Mongolia, but they are very poorly studied. The lack of age data and geochemical analysis hampers our understanding of the Paleozoic tectonic evolution of the region. We conducted detailed studies on the Manlay ophiolitic complex and Huree volcanic rocks south of the Main Mongolian Lineament (MML) to provide some constraints on these rocks. The Manlay ophiolite consists of dunite, harzburgite, pyroxenite, gabbro, plagiogranite, basalt and chert, locally with chromite mineralization in dunite. The gabbro and plagiogranite yielded SHRIMP zircon weighted mean 206Pb/238U ages of 509 ± 5 Ma and 482 ± 4 Ma, respectively. The basalt and dolerite samples of this complex show enrichment in LREE and LILE and negative Nb, Ta and Ti anomalies, and the chrome spinel from the chromitite lens in the dunite is characterized by high Cr# and low TiO2 contents. These features suggest a supra-subduction zone (SSZ) origin for the ophiolitic complex. The Huree volcanic rocks, ranging from basalt to dacite, display enrichment in LREE and LILE, weak Eu anomalies and distinctly negative Nb, Ta and Ti anomalies, consistent with those of typical magmas in a subduction environment. An andesite sample from this arc yielded a SHRIMP 206Pb/238U zircon age of 487 ± 5 Ma, which is the oldest reliable age for an island arc in South Mongolia. Recognition of an Early Paleozoic ophiolitic complex and a coeval island arc indicates that South Mongolia underwent a period of active volcanism during Late Cambrian to Ordovician. Additionally, the tuff overlying the ophiolitic complex and a granite intruding the ophiolite have SHRIMP zircon U-Pb ages of 391 ± 5 Ma and 304 ± 4 Ma, respectively. Combining the available data, we propose that the Early Paleozoic subduction-accretionary complexes likely constitute the basement of the Late-Paleozoic arc formations and correlate with the Lake Zone in western Mongolia.

  8. Regional setting and characteristics of the Neoproterozoic Wadi Hamama Zn-Cu-Ag-Au prospect: evidence for an intra-oceanic island arc-hosted volcanogenic hydrothermal system

    NASA Astrophysics Data System (ADS)

    Abd El-Rahman, Yasser; Surour, Adel A.; El-Manawi, Abdel Hamid W.; El-Dougdoug, Abdel-Monem A.; Omar, Sayed

    2015-04-01

    The Wadi Hamama area is a volcanogenic Zn-Cu-Au-Ag prospect. It is hosted by a Neoproterozoic bimodal-mafic sequence, which comprises basalt, dacite and rhyolite along with volcaniclastic rocks. The rocks have a low-K tholeiitic affinity and are enriched in large ion lithophile elements over high field strength elements, which indicated their formation in an intra-oceanic island arc tectonic setting. The area was intruded by a tonalite-trondhjemite body, which has an intra-oceanic island arc affinity and later by diorite, which has a cordilleran-margin geochemical affinity. These rock units were intruded by post-tectonic granite dykes, which have a within-plate geochemical signature. There is a quartz-carbonate horizon extending along the contact between the basalt and the volcaniclastic rocks, mainly banded and lapilli tuffs. This horizon is of exhalative origin and is underlain by a mushroom-shaped alteration zone extending from the horizon down to the massive basalt. The footwall alteration is characterized by a silica-rich core surrounded by a thick chlorite sheath. Both the quartz-carbonate horizon and the footwall-altered rocks enclose historical trenches and pits. Sulfide-rich core samples are enriched in Zn, relative to Cu, and in Ag, which indicates the low-temperature nature of the hydrothermal system. The prospect was affected by supergene processes, which led to the widespread occurrence of secondary copper minerals and gold enrichment relative to the leached base metals, especially Zn. The prospect formed through a limited rifting of an intra-oceanic island arc which resulted in the formation of a small-scale volcanogenic Zn-Cu-Ag-Au prospect.

  9. Origin of the oceanic basalt basement of the Solomon Islands arc and its relationship to the Ontong Java Plateau-insights from Cenozoic plate motion models

    USGS Publications Warehouse

    Wells, R.E.

    1989-01-01

    Cenozoic global plate motion models based on a hotspot reference frame may provide a useful framework for analyzing the tectonic evolution of the Solomon Islands convergent margin. A postulated late Miocene collision of the Ontong Java Plateau (OJP) with a NE-facing arc is consistent with the predicted path of the OJP across the Pacific Basin and its Miocene arrival at the trench. Late-stage igneous activity (65-30 Ma) predicted for the OJP as it rode over the Samoan hotspot occurred in correlative stratigraphic sections on Malaita, the supposed accreted flake of OJP in the Solomon Islands arc. Convergence similar to the present velocities between Australia and the Pacific plates was characteristic of the last 43 million years. Prior to 43 Ma Pacific-Australia plate motions were divergent, seemingly at odds with geologic evidence for early Tertiary convergence, particularly in Papua New Guinea. A postulated South Pacific plate may have existed between Australia and the Pacific plate and would have allowed implied northward subduction along the northeastern Australia plate boundary that lasted into the early Eocene. Subsequent reorganization of plate motions in the middle Eocene correlates with middle Eocene marginal basin formation along ridges oblique to the main plate boundary. Cessation of spreading on the Pacific-South Pacific Ridge and its subsequent subduction beneath Asia followed the change in Pacific plate motion at 43 Ma. A trapped remnant of the extinct, NW-trending ridge may still lie beneath the western Philippine Sea. The terminal deformation, metamorphism and ophiolite obduction in the Eocene orogen of the southwest Pacific also correlates with the major change in Pacific plate motion at 43 Ma and the subsequent compression of the dying Eocene arc against outlying continental and oceanic crustal blocks of the Australian plate. The Solomon Islands oceanic basement may represent juxtaposition of oceanic plateaus of the Australian plate beneath

  10. Lava Textures, Magma Crystallization History, and the Dynamics of Merapi and Aleutian Mush Columns

    NASA Astrophysics Data System (ADS)

    Marsh, B. D.; Del Marmol, M. A.

    2014-12-01

    The subsurface dynamics of magma in mush columns beneath arc volcanoes is recorded in the textures of the basic lavas. A detailed comparison of lava textures from large mature volcanoes in Indonesia (Merapi) and the Aleutian Islands (Adak and Atka), shows remarkably similar, often indistinguishable, textures of high alumina basalts (HAB) and basaltic andesites (BA). We suggest a systematic characterization of these distinctive textures into a few simple categories reflecting the subsurface history of crystallization within solidification fronts (SFs) and subsequent transport dynamics. The HABs are strongly plagioclase-phyric and of two main groups: A1 consists of large, idiomorphic, mildly zoned, plagioclase (20-30 vol.%) with small amounts of olivine (2-8%) set in a finely crystalline groundmass of these same phases; A2 is similar, but contains an additional pervasive population of large 'old' plagioclase, rounded, often highly zoned, and sometimes broken; A1+ is a subclass of A1 where traces of 'old' plagioclase are present. Similar categories exist in the BA lavas except overall crystallinity is higher and olivine is replaced by large clinopyroxenes containing or mantled with magnetite. In a temporal stratigraphic sense, the early lavas are generally HAB A1 types and transition into, sometimes alternating, HAB A2 types followed by BA types. The initial establishment of the mush column is by hot, highly mobile primary magmas, followed by increasingly more thermally mature magmas containing debris from disrupted SFs. The detailed nature of this debris, its variation in time, and the volumes give important insights on the size and vigor of the mush column staging chambers.

  11. Sequence stratigraphy, structure, and tectonic history of the southwestern Ontong Java Plateau adjacent to the North Solomon Trench and Solomon Islands Arc

    NASA Astrophysics Data System (ADS)

    Phinney, Eric J.; Mann, Paul; Coffin, Millard F.; Shipley, Thomas H.

    1999-09-01

    The Ontong Java Plateau (OJP) is the largest and thickest oceanic plateau on Earth and one of the few oceanic plateaus actively converging on an island arc. We present velocity determinations and geologic interpretation of 2000 km of two-dimensional, multi-channel seismic data from the southwestern Ontong Java Plateau, North Solomon Trench, and northern Solomon Islands. We recognize three megasequences, ranging in age from early Cretaceous to Quaternary, on the basis of distinct interval velocities and seismic stratigraphic facies. Megasequence OJ1 is early Cretaceous, upper igneous crust of the OJP and correlates with basalt outcrops dated at 122-125 Ma on the island of Malaita. The top of the overlying megasequence OJ2, a late Cretaceous mudstone unit, had been identified by previous workers as the top of igneous basement. Seismic facies and correlation to distant Deep Sea Drilling Project/Ocean Drilling Program sites indicate that OJ2 was deposited in a moderately low-energy, marine environment near a fluctuating carbonate compensation depth that resulted in multiple periods of dissolution. OJ2 thins south of the Stewart Arch onto the Solomon Islands where it is correlated with the Kwaraae Mudstone Formation. Megasequence OJ3 is late Cretaceous through Quaternary pelagic cover which caps the Ontong Java Plateau; it thickens into the North Solomon Trench, and seismic facies suggest that OJ3 was deposited in a low-energy marine environment. We use seismic facies analysis, sediment thickness, structural observations, and quantitative plate reconstructions of the position of the OJP and Solomon Islands to propose a tectonic, magmatic, and sedimentary history of the southwestern Ontong Java Plateau. Prior to 125 Ma late Jurassic and early Cretaceous oceanic crust formed. From 125 to 122 Ma, the first mantle plume formed igneous crust (OJ1). Between 122 and 92 Ma, marine mudstone (OJ2 and Kwaraae mudstone of Malaita, Solomon Islands) was deposited on Ontong Java

  12. Insights on the Quaternary Tectonic Evolution of the SE Indonesia Arc-Continent Collision from the Study of Uplifted Coral Terraces on Sumba Island.

    NASA Astrophysics Data System (ADS)

    Leclerc, F.; Rigaud, S.; Chiang, H. W.; Djamil, Y. S.; Herdiyanti, T.; Johnny, J.; Ildefonso, S.; Meilano, I.; Bijaksana, S.; Abidin, H. Z.; Tapponnier, P.; Wang, X.

    2015-12-01

    Sumba Island is uniquely positioned within the Sunda-Banda forearc, at the transition between oceanic subduction and arc-continent collision. There, the convergence between the Sunda and Australian plates is accommodated along at least three major structures: the megathrust, the Savu backthrust located south of Sumba and the Flores backthrust located north of the volcanic arc. The incipient collision in the vicinity of Sumba is responsible for coastal vertical movements. Quaternary reefal deposits form spectacular uplifted flights of terraces, which directly overlie Mid Miocene - Early Pliocene deep carbonate and volcaniclastic rocks at elevations exceeding 500m. Although aerial fossil reefs extensively rim the northern and eastern coasts of Sumba, studies have been limited to Cape Laundi where an uplift rate of 0.2-0.5 m/kyr is estimated for the last 400 kyr, partly on the basis of alpha-spectrometric U/Th dating. At the island scale, the relief morphology and the hydrographic network point to a N-S asymmetry, indicating a general tilt toward the north. A subducting seafloor asperity and south-dipping normal faults have been postulated to generate this asymmetry. However as the pattern and kinematics of the deformation remain partially determined, structures and processes capable of driving such deformation and accommodating the nascent collision may be undisclosed. New topographic data coupled with field observations and coral mass-spectrometric U/Th dating allow investigating the morphology, stratigraphy and age of the fossil reef terraces at the island scale. Tectonic structures disrupting the topography are identified and their activities are relatively dated with respect to fossil reef terraces. The deformation pattern of Sumba is characterized, especially in Cape Laundi where the uplift rate is re-evaluated. Through a multi-disciplinary study, we intend to reconstruct the tectonic evolution of Sumba island and, at a larger scale, of the collision in SE

  13. Craniometric variation in the Aleutians: integrating morphological, molecular, spatial, and temporal data.

    PubMed

    Ousley, Stephen D; Jones, Erica B

    2010-12-01

    Several hypotheses have been put forward about the origins and evolution of the inhabitants of the Aleutian Islands. Both Hrdlička [The Aleutian and Commander Islands and Their Inhabitants (Philadelphia: Wistar Institute of Anatomy and Biology, 1945)] and Laughlin ["The Alaska gateway viewed from the Aleutian Islands," in Papers on the Physical Anthropology of the American Indian, W. S. Laughlin, ed. (New York: Viking Fund, 1951), 98-126] analyzed cranial morphology and came to somewhat different conclusions using a typological approach and limited analytical methods. Subsequent investigations using morphological data have not significantly improved our understanding of Aleut prehistory. More recently, radiocarbon dating and mitochondrial DNA analyses have shed light on Aleut genetic variation and changes over time, but better morphological methods using multivariate statistical analysis have not yet been used. We analyzed craniometric data using multivariate procedures and found that Aleuts demonstrate significant changes in cranial morphology over time, and these changes correspond to Hrdlička's observations but may not necessarily reflect in-migration. The morphological changes were concentrated in the very aspects of morphology that are easily observable and that Hrdlička most often measured, namely, cranial length, breadth, and height, but they were obscured when craniometric variation as a whole was analyzed. Also, we found that the morphological changes over time were not related to the changes in haplogroup frequencies over time, suggesting that migration into the Aleutians did not play a significant role in producing the morphological changes. However, craniometric variability apparently increases over time, suggesting in-migration, localized selection, and/or greater environmental heterogeneity. Our results contradict Laughlin's observations but may be more in line with his hypothesis of in situ evolutionary changes absent gene flow. In addition to

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

    SciTech Connect

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

    1988-02-01

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

  15. Geochemical Evidence from the Kohistan Complex for Differentiation of Garnet Granulitic lower Crust in Island Arcs by Dehydration Melting of Amphibole-bearing Plutonics: Implications for the Andesite Model of Continental Crustal Growth

    NASA Astrophysics Data System (ADS)

    Garrido, C. J.; Bodinier, J.; Burg, J.; Zeilinger, G.; Hussain, S. S.; Dawood, H.; Gervilla, F.

    2005-12-01

    We report a geochemical study of the Jijal and Sarangar complexes constituting the lower crust of the Mesozoic Kohistan paleo-island arc (N. Pakistan). The Jijal complex is composed of basal peridotites topped by a gabbroic section made up of mafic garnet granulite-with minor lenses of garnet hornblendite and granite-grading up section to hornblende gabbronorite. The Sarangar complex is constituted by metagabbro. Sarangar gabbro and Jijal hornblende gabbronorite have melt-like, LREE-enriched REE patterns similar to those of island arc basalts. These rocks and Jijal garnet granulite define altogether negative covariations of LaN, YbN and (La/Sm)N with Eu* (=2xEuN/SmN+GdN; N= chondrite normalized), and positive covariations of (Yb/Gd)N with Eu*. REE modeling indicates that these covariations cannot be accounted for by high-pressure crystal fractionation of hydrous primitive or derivative andesites. They are consistent with formation of garnet granulites as plagioclase-garnet assemblages with variable trapped melt fractions via either high-pressure crystallization of primitive island arc basalts or dehydration melting of hornblende gabbronorite, providing that the amount of segregated or restitic garnet was low (< 5 wt.%). Field, petrographic, geochemical and experimental evidence is more consistent with formation of Jijal garnet granulite by dehydration melting of Jijal hornblende gabbronorite. Similarly, Jijal garnet-bearing hornblendite lenses were most likely generated by coeval dehydration melting of hornblendites. Furthermore, melting models and geochronological data point to intrusive leucogranites in the overlying Metaplutonic complex as the melts generated by dehydration melting of the plutonic protoliths of Jijal garnet-bearing restites. Consistently with the metamorphic evolution of the Kohistan lower arc crust, dehydration melting occurred at the mature stage of this island arc when shallower hornblende-bearing plutonics were buried to depth exceeding 25

  16. Crustal Structure of the Southern Kyushu-Palau Ridge, the Other Half of the Proto Izu-Bonin-Mariana Island Arc

    NASA Astrophysics Data System (ADS)

    Nishizawa, A.; Kaneda, K.; Katagiri, Y.; Kasahara, J.

    2005-12-01

    The Kyushu-Palau Ridge (KPR) is a bathymetric high extending north-south direction at the center of the Philippine Sea and considered as a remnant of a proto Izu-Bonin-Mariana island arc separated by the backarc spreading of the Shikoku and Parece Vela (Oki-no-Tori-Shima) Basin. We conducted a wide-angle and multi-channel seismic experiment to investigate variation in crustal structures along the KPR. The experiment consisted of four seismic lines that were selected to represent the variations in seafloor topography of the southern KPR. All of the profiles cross the KPR perpendicularly and their profile lengths range from 175 to 375 km. The controlled seismic source was a tuned array of 36 airguns with a total volume of 8,040 inch3. In the wide-angle seismic survey, we shot the airgun array at an interval of 200 m (90 s) for each line. We used 200 ocean bottom seismographs (OBS) at an interval of 5 km as receivers. The travel time and amplitude data obtained by the OBSs were modeled by a tomographic inversion and two-dimensional ray tracing. The maximum crustal thickness beneath the KPR varies from 14 to 20 km according to the profile and the crust is significantly thicker than those of the both sides of each profile, that is, the oceanic crusts of the West Philippine Basin to the west and of the Parece Vela Basin to the east. The thickest crust among the four profiles is found in the region where the KPR connects with the Oki-no-Tori-Shima island. The thicker crust beneath the KPR is mainly due to a fat lower crust. The thick (> 5 km) middle crust with P wave velocity of 6.0-6.3 km/s that characterizes the northern Izu-Bonin island-arc crust does not exist so clearly in our profiles. This may relate to the fact that the southern KPR is deeper in seawater and does not have a mature island arc crust compared with the northern KPR where existence of a 6 km/s layer has been reported previously.

  17. The Pathogenesis of Aleutian Disease of Mink

    PubMed Central

    Porter, David D.; Larsen, Austen E.; Porter, Helen G.

    1973-01-01

    Mink chronically infected with Aleutian disease virus develop a severe necrotizing arteritis affecting muscular arteries. Acute, subacute and healing lesions may be found. Extracellular deposits of host immunoglobulin and complement and, after acid elution, viral antigen can be shown by immunofluorescence technics in areas of fibrinoid necrosis and between proliferating endothelial cells. No intracellular viral antigen was found, indicating that the virus probably does not replicate in vascular structures. The arteritis of Aleutian disease appears to be the result of immune complex deposits in vessel walls. Imagesp[341]-aFig 4p[343]-aFig 1Fig 2Fig 3 PMID:4576760

  18. Unusually large tsunamis frequent a currently creeping part of the Aleutian megathrust

    NASA Astrophysics Data System (ADS)

    Witter, Robert C.; Carver, Gary A.; Briggs, Richard W.; Gelfenbaum, Guy; Koehler, Richard D.; La Selle, SeanPaul; Bender, Adrian M.; Engelhart, Simon E.; Hemphill-Haley, Eileen; Hill, Troy D.

    2016-01-01

    Current models used to assess earthquake and tsunami hazards are inadequate where creep dominates a subduction megathrust. Here we report geological evidence for large tsunamis, occurring on average every 300-340 years, near the source areas of the 1946 and 1957 Aleutian tsunamis. These areas bookend a postulated seismic gap over 200 km long where modern geodetic measurements indicate that the megathrust is currently creeping. At Sedanka Island, evidence for large tsunamis includes six sand sheets that blanket a lowland facing the Pacific Ocean, rise to 15 m above mean sea level, contain marine diatoms, cap terraces, adjoin evidence for scour, and date from the past 1700 years. The youngest sheet and modern drift logs found as far as 800 m inland and >18 m elevation likely record the 1957 tsunami. Previously unrecognized tsunami sources coexist with a presently creeping megathrust along this part of the Aleutian Subduction Zone.

  19. Unusually large tsunamis frequent a currently creeping part of the Aleutian megathrust

    USGS Publications Warehouse

    Witter, Robert C.; Carver, G.A.; Briggs, Richard; Gelfenbaum, Guy R.; Koehler, R.D.; La selle, Seanpaul M.; Bender, Adrian M.; Engelhart, S.E.; Hemphill-Haley, E.; Hill, Troy D.

    2016-01-01

    Current models used to assess earthquake and tsunami hazards are inadequate where creep dominates a subduction megathrust. Here we report geological evidence for large tsunamis, occurring on average every 300–340 years, near the source areas of the 1946 and 1957 Aleutian tsunamis. These areas bookend a postulated seismic gap over 200 km long where modern geodetic measurements indicate that the megathrust is currently creeping. At Sedanka Island, evidence for large tsunamis includes six sand sheets that blanket a lowland facing the Pacific Ocean, rise to 15 m above mean sea level, contain marine diatoms, cap terraces, adjoin evidence for scour, and date from the past 1700 years. The youngest sheet, and modern drift logs found as far as 800 m inland and >18 m elevation, likely record the 1957 tsunami. Modern creep on the megathrust coexists with previously unrecognized tsunami sources along this part of the Aleutian Subduction Zone.

  20. The Role of Philippine Sea Plate to the Genesis of Quaternary Magmas of Northern Kyushu Island, Japan, Inferred from Along-Arc Geochemical Variations

    NASA Astrophysics Data System (ADS)

    Shibata, T.; Yoshikawa, M.; Itoh, J.; Ujike, O.; Miyoshi, M.; Takemura, K.

    2013-12-01

    Quaternary volcanoes on Kyushu Island comprise volcanoes Himeshima, Futagoyama, Yufu-Tsurumi, Kuju, Aso, Kirishima and Sakurajima from north to south alongstrike the volcanic front. Adakitic lavas are observed from Yufu-Tsurumi and Kuju volcanoes in northern Kyushu (Kita et al., 2001; Sugimoto et al., 2007), whereas no Quaternary adakites were observed at Aso (e.g., Hunter, 1998) and the volcanoes south of Aso along the entire Ryukyu arc. Sugimoto et al. (2007) suggested that the trace element and Sr, Nd, and Pb isotopic compositions of adakitic magmas from Yufu-Tsurumi volcano indicate derivation of the magmas by partial melting of the subducting PSP. In contrast, Zellmer et al. (2012) suggested that these adakites may have formed by fractional crystallization of mantle-derived mafic magmas within the garnet stability field in the crust. The Honshu-Kyushu arc transition is a particular favorable setting to address these controversial models for the origin of the adakitic lavas, because of the potential relationship between the PSP materials and the alongstrike variation of the lava chemistry. The Palau-Kyushu ridge divides the oceanic crust of the PSP into northeastern and southwestern segments with ages of 26-15 (Shikoku Basin) and 60-40 Ma (West Philippine Basin), respectively (Mahony et al., 2011). Although there are no clear plate images beneath northern Kyushu, the northern extension of the Palau-Kyushu ridge potentially corresponds to the boundary between the SW Japan and Ryukyu arcs. If adakite genesis was related to the subducted slab rather than the overlying crust, then the spatial distribution of Quaternary adakites should correlate with the age of the subducted PSP. In order to test such correlation and elucidate the petrogenesis of the northern Kyushu adakites, we compiled major and trace elements and Sr-Nd-Pb isotope ratios from volcanoes along the arc front that includes the transition from adakitic to non-adakitic arc volcanism. Comprehensive

  1. Compilation of seismic structural models of the Kyushu-Palau Ridge, paleo-island arc in the Philippine Sea plate, at 13-30 N

    NASA Astrophysics Data System (ADS)

    Nishizawa, A.; Kaneda, K.; Oikawa, M.

    2012-12-01

    The Kyushu-Palau Ridge (KPR) is a 2600 km long bathymetric high extending north-south at the center of the Philippine Sea plate. The origin of the KPR is regarded as a remnant of the proto Izu-Ogasawara (Bonin)-Mariana (IBM) Island arc that was separated by backarc spreading of the Shikoku and Parece Vela Basins in the late Eocene. The extensive seismic explorations were implemented to grasp the spatial distribution of the arc crust of the KPR in 2004-2008 under the Japanese Continental Shelf Survey Project. We carried out 27 seismic reflection and refraction profiles across the ridge between 13 and 30 N and one along the ridge in the northernmost part. We deployed ocean bottom seismographs (OBSs) as a receiver at an average interval of 5 km along each line. A tuned airgun array with a volume of 8,040 cubic inches (132 liters) or a non-tuned airgun array with a volume of 6,000 cubic inches (98 liters) was shot at an interval of 200 m (90 sec) for the wide-angle seismic profiles. Multichannel reflection data using 480 ch. or 240 ch. hydrophone streamer were also collected on the coincident lines. We obtained P-wave velocity models using tomographic inversion, forward modeling with two-dimensional ray tracing and comparison with synthetic seismograms. The maximum crustal thickness for each profile across the KPR varies from 8 to 23 km among the seismic lines. The KPR crusts are roughly thicker in the north than those in the south and are always thicker than the neighboring backarc basin oceanic crusts of the West Philippine Basin to the west and of the Shikoku and Parece Vela Basins to the east. The thick crust is mainly attributed to the lower crust with P-wave velocity of 6.8-7.2 km/s. Pn velocities just beneath the KPR are less than 8 km/s, often accompanying with rather high Vp of 7.2 km/s at the base of the crust. Reflection signals observed in far offsets along several lines suggest some reflectors exist at the depths 23-40 km beneath the KPR. The crustal

  2. Subsidence at Kiska volcano, Western Aleutians, detected by satellite radar interferometry

    USGS Publications Warehouse

    Lu, Zhiming; Masterlark, Timothy; Power, J.; Dzurisin, D.; Wicks, C.

    2002-01-01

    Sequential interferometric synthetic aperture radar images of Kiska, the westernmost historically active volcano in the Aleutian arc, show that a circular area about 3 km in diameter centered near the summit subsided by as much as 10 cm from 1995 to 2001, mostly during 1999 and 2000. An elastic Mogi-type deformation model suggests that the source is within 1 km of the surface. Based on the shallow source depth, the copious amounts of steam during recent eruptions, and recent field reports of vigorous steaming and persistent ground shaking near the summit area, we attribute the subsidence to decreased pore-fluid pressure within a shallow hydrothermal system beneath the summit area.

  3. systematics of island arc crustal amphibolite migmatites from the Asago body of the Yakuno Ophiolite, Japan: a field evaluation of some model predictions

    NASA Astrophysics Data System (ADS)

    Pu, Xiaofei; Brophy, James G.; Tsujimori, Tatsuki

    2014-09-01

    The two most commonly invoked processes for generating silicic magmas in intra-oceanic arc environments are extended fractional crystallization of hydrous island arc basalt magma or dehydration melting of lower crustal amphibolite. Brophy (Contrib Mineral Petrol 156:337-357, 2008) has proposed on theoretical grounds that, for liquids >~65 wt% SiO2, dehydration melting should yield, among other features, a negative correlation between rare earth element (REE) abundances and increasing SiO2, while fractional crystallization should yield a positive correlation. If correct, the REE-SiO2 systematics of natural systems might be used to distinguish between the two processes. The Permian-age Asago body within the Yakuno Ophiolite, Japan, has amphibolite migmatites that contain felsic veins that are believed to have formed from dehydration melting, thus forming an appropriate location for field verification of the proposed REE-SiO2 systematics for such a process. In addition to a negative correlation between liquid SiO2 and REE abundance for liquids in excess of ~65 % SiO2, another important model feature is that, at very high SiO2 contents (75-76 %), all of the REE should have abundances less than that of the host rock. Assuming an initial source amphibolite that is slightly LREE-enriched relative to the host amphibolites, the observed REE abundances in the felsic veins fully support all theoretical predictions.

  4. Late Proterozoic island-arc complexes and tectonic belts in the southern part of the Arabian Shield, Kingdom of Saudi Arabia

    USGS Publications Warehouse

    Greenwood, William R.; Stoeser, D.B.; Fleck, R.J.; Stacey, J.S.

    1983-01-01

    Sr ratios are not included in the appendix, but all rocks more than 660 m.y. old have initial ratios in the range 0.7021-0.7035, with only two greater than 0.7030. Thus, nothing in the Rb-Sr data suggests involvement of an older continental crust during the evolution of the southern Shield. A lead isotope study of ore minerals and potassium feldspars of the Arabian Shield by Stacey and others (1980) also suggests that no older (Archean to early Proterozoic) evolved continental-type crust underlies the southern Shield. An early summary of mapping (Schmidt and others, 1973) suggests that older sialic basement underlies the late Proterozoic layered rocks in the southern Shield. However, subsequent-mapping and the isotopic studies cited above have established that all of these rocks are of late Proterozoic age and that all rocks of the southern Shield that are more than 660 m.y. old have ensimatic or mantle isotopic characteristics. Figure 2 shows, with only two exceptions, that rocks more than 800 m.y. old are present west of the boundary separating the Tayyah and Khadra belts. The exceptions are two poorly controlled Rb-Sr ages obtained by Fleck (1980) on two quartz diorite plutons in the Malahah region (appendix 1, localities 26 and 27). Preliminary uranium-thorium zircon data of Stacey now suggest that one of these quartz diorite plutons (locality 26) has an age of approximately 640 m.y. Therefore, we prefer to discount the two dates of Fleck until further information is available. As noted earlier and as described below, most of the rocks of the southern Arabian Shield have characteristics typical of those formed in the island-arc environment by subduction-related processes. We shall refer to the group of rocks in the western part of the southern Shield, which formed from 1100 to 800 m.y. ago, as the 'older ensimatic-arc complex' and those in the eastern and northwestern parts, which formed from 800 to 690 m.y. ago, as the 'younger marginal-arc compl

  5. Progressive Emergence and Warping of Islands in the Active Banda Arc-Continent Collision As Recorded By Uplifted Coral Terraces: Tectonic and Geohazards Implications

    NASA Astrophysics Data System (ADS)

    Harris, R. A.; Cox, N.; Major, J. R.; Merritts, D. J.; Prasetyadi, C.

    2014-12-01

    Uplifted coral terraces throughout the Banda-Sunda Arc transition reveal how strain is distributed over the past thousand to million years in the active arc-continent collision, and are key to identifying hazardous active faults. U-series age analysis of the lowest coral terraces yields surface uplift rates that vary in a non-systematic way along strike from 0.2 to 1.5 mm/a over short wavelengths of a few kms. For example, coral terraces are tilted varying degrees northward in Sumba, SSE in Savu, NNW in Rote and generally south along the north coast of Timor. In all of these cases the tilt is away from zones of active thrusting and folding. In Sumba the forearc is ramping up and over the northern edge of the Scott Plateau along what is likely a north dipping thrust. In Savu the coral terraces rise where the back of the accretionary wedge is ramping up over the forearc basin on the south dipping Savu Thrust. In Rote coral terraces form on the front of the accretionary wedge where it is ramping up over the subducting Australian continental margin. The north coast of East Timor is likely uplifting due to internal thrusting and closure of the Wetar Strait. Localized uplift of circular islands is associated with diapirism. The diapiric island of Kisar is cored by syn-collisional metamorphic rocks. The association of uplift and warping with short wavelength deformational processes argues against the commonly held interpretation that coral terraces in the Banda arc-continent collision manifest the effects of slab tear or some other lithospheric scale process. The pattern of uplift correlates best with proximity to active faults, folds and diapirs. In terms of geohazards, flights of uplifted coral terraces are the smoking gun for sources of large earthquakes and tsunami. Many of the terraces show signs of co-seismic uplift. Tsunami deposits with young corals are found on some of these terraces as high as 20 m above sea level.

  6. A spatial-seasonal analysis of the oiling risk from shipping traffic to seabirds in the Aleutian Archipelago.

    PubMed

    Renner, Martin; Kuletz, Kathy J

    2015-12-15

    Some of the largest seabird concentrations in the northern hemisphere are intersected by major shipping routes in the Aleutian Archipelago. Risk is the product of the probability and the severity incidents in an area. We build a seasonally explicit model of seabird distribution and combine the densities of seabirds with an oil vulnerability index. We use shipping density, as a proxy for the probability of oil spills from shipping accident (or the intensity chronic oil pollution). We find high-risk (above-average seabird and vessel density) areas around Unimak Pass, south of the Alaska Peninsula, near Buldir Island, and north of Attu Island. Risk to seabirds is greater during summer than during winter, but the month of peak risk (May/July) varies depending on how data is analyzed. The area around Unimak Pass stands out for being at high-risk year-round, whereas passes in the western Aleutians are at high risk mostly during summer. PMID:26602441

  7. New Field Surveys of The Great 1946 Aleutian Tsunami

    NASA Astrophysics Data System (ADS)

    Okal, E. A.; Synolakis, C. E.; Plafker, G.

    We seek to reopen the case of the 1946 Aleutian tsunami, which was the most destruc- tive transpacific event in the past century, despite the relatively moderate size of its parent earthquake. As a result, the exact nature of its source, and in particular whether it requires a submarine landslide, remains controversial. In 1999, we started a system- atic effort to build a modern database of runup and inundation values for the 1946 event throughout the Pacific Basin. At teleseismic distances, we rely on interviews from elderly witnesses whose testimony is then quantified using standard surveying techniques. As of early 2002, we were able to gather about 60 such measurements in the Marquesas, Society and Austral Islands, French Polynesia; and at Easter and Juan Fernandez Islands. They point out to the concentration of high runup values (8 m or more) in a narrow band of epicentral azimuths including Hawaii, the Marque- sas and Easter, but excluding Juan Fernandez. In the near field, we surveyed in 2001 the islands of Unimak and Sanak, based on available Coast Guard reports at Scotch Cap, and on subsisting watermarks such as large logs of driftwood deposited on these unforrested islands. We obtain a maximum runup height of 42 m on the Southern coast of Unimak and of 22 m at Sanak. These preliminary results suggest the combi- nation of a slow earthquake dislocation responsible for the strong far-field directivity of the tsunami, and of a co-seismic underwater landslide necessary to account for the exceptional near-field amplitudes, which are many times larger than the seismic dis- placement at the source for any acceptable seismological model of the dislocation. The existence of a large landslide is also suggested by anectodal reports of post-quake changes in local bathymetry and diminished fisheries productivity, and a preliminary confirmation is found on post-1946 bathymetric charts of the continental slope around 53.75 deg.N and 163.75 deg.W.

  8. Early Cretaceous arc volcanic suite in Cebu Island, Central Philippines and its implications on paleo-Pacific plate subduction: Constraints from geochemistry, zircon U-Pb geochronology and Lu-Hf isotopes

    NASA Astrophysics Data System (ADS)

    Deng, Jianghong; Yang, Xiaoyong; Zhang, Zhao-Feng; Santosh, M.

    2015-08-01

    The Philippine island arc system is a collage of amalgamated terranes of oceanic, continental and island arc affinities. Here we investigate a volcanic suite in Cebu Island of central Philippines, including basalt, diabase dike, basaltic pyroclastic rock and porphyritic andesite. LA-ICP-MS U-Pb geochronology of zircon grains from the porphyritic andesite and pyroclastic rock yielded ages of 126 ± 3 Ma and 119 ± 2 Ma, respectively, indicating an Early Cretaceous age. The age distribution of the detrital zircons from river sand in the area displays a peak at ca. 118 Ma, close to the age of the pyroclastic rock. The early Cretaceous volcanic rocks in the central Philippines were previously regarded as parts of ophiolite complexes by most investigators, whereas the Cebu volcanics are distinct from these, and display calc-alkaline affinity and island arc setting, characterized by high LREE/HREE ratios and low HFSE contents. These features are similar to the Early Cretaceous arc basalts in the Amami Plateau and east Halmahera in the northernmost and southernmost West Philippine Basin respectively. Zircon Hf isotopes of the pyroclastic rocks show depleted nature similar to those of the Amami Plateau basalts, implying the subducted Pacific-type MORB as probable source. Zircon Hf isotopes of the porphyritic andesite show slight enrichment relative to that of the pyroclastic rocks and MORB, indicating subducted sediments as a minor end-member in the source. The Hf isotopic compositions of the volcanic rocks are also reflected in the detrital zircons from the river sands. We propose that the volcanic rocks of Cebu Island were derived from partial melting of sub-arc mantle wedge which was metasomatized by dehydration of subducted oceanic crust together with minor pelagic sediments. Within the tectonic environment of Southeast Asia during Early Cretaceous, the volcanic rocks in Cebu Island can be correlated to the subduction of paleo-Pacific plate. The Early Cretaceous

  9. GLORIA imagery links sedimentation in Aleutian Trench to Yakutat margin via surveyor channel

    SciTech Connect

    Carlson, P.R.; Bruns, T.R.; Mann, D.M.; Stevenson, A.J. ); Huggett, Q.J. )

    1990-06-01

    GLORIA side-scan sonar imagery shows that the continental slope developing along the active margin of the Gulf of Alaska is devoid of large submarine canyons, in spite of the presence of large glacially formed sea valleys that cross the continental shelf. In the western and northern Gulf, discontinuous, actively growing deformation structures disrupt or divert the downslope transport of sediment into the Aleutian Trench. To the east of Middleton Island, the slope is intensively gullied and incised only by relatively small canyons. At the base of the gullied slope between Pamplona Spur and Alsek Valley, numerous small slope gullies coalesce into three turbidity current channels that merge to form the Surveyor deep-sea channel. About 350 km from the margin, the channel crosses the structural barrier formed by the Kodiak-Bowie Seamount chain and heads south for another 150 km where it bends northerly, perhaps influenced by the oceanic basement relief of the Patton Seamounts. The channel, now up to 5 km wide and deeply entrenched to 450 m, continues northerly for 200 km where it intercepts the Aleutian Trench, some 700 km from the Yakutat margin. South of Surveyor Channel, GLORIA imagery revealed evidence of another older channel. The older channel meanders through a gap in the seamount chain and eventually bends northwesterly. This now inactive, largely buried channel may have carried turbidity currents to the Aleutian Trench concurrent with the active Surveyor Channel.

  10. Characterization of magmatic sulfur in the Aegean island arc by means of the δ 34S values of fumarolic H 2S, elemental S, and hydrothermal gypsum from Nisyros and Milos islands

    NASA Astrophysics Data System (ADS)

    Marini, Luigi; Gambardella, Barbara; Principe, Claudia; Arias, Alessia; Brombach, Tatjana; Hunziker, Johannes C.

    2002-06-01

    A δ 34S value of +6.3±1.5‰ was estimated for the rhyodacitic degassing magma present underneath the hydrothermal system of Nisyros, based on the S isotope ratios of H 2S in fumarolic vapors. This value was estimated by modeling the irreversible water-rock mass transfers occurring during the generation of the hydrothermal liquid which separates these fumarolic vapors. The S isotope ratio of the rhyodacitic degassing magma of Nisyros is consistent with fractional crystallization of a parent basaltic magma with an initial δ 34S value of +4‰ (±at least 1.5‰). This positive value could be explained by mantle contamination due to by either transference of fluids derived from subducted materials or involvement of altered oceanic crust, whereas contribution of biogenic sulfides from sediments seems to be negligible or nil. This conclusion agrees with the lack of N 2 and CO 2 from thermal decomposition of organic matter contained in subducted sediments, which is a characteristic of the whole Aegean arc system. Since hydrothermal S at Milos and Santorini has isotope ratios similar to those determined at Nisyros, it seems likely that common controlling processes are active throughout the Aegean island arc.

  11. The origin of the 'fluid' component and its implications for U-Th-Pa disequilibria in island arcs

    NASA Astrophysics Data System (ADS)

    Avanzinelli, R.; Skora, S. E.; Blundy, J.; Elliott, T.

    2011-12-01

    Many arc lavas have two discrete slab-derived components evident from their compositional variations. These components have been interpreted to be melts of subducted sediment and a 'fluid' from the mafic oceanic crust. The 'fluid' signature is seen most clearly in depleted samples that contain the smallest fraction of the sediment component. The provenance of this 'fluid' is reliably pinned by its unradiogenic Pb isotope ratios to be from a MORB-like source. The composition of the 'fluid' phase is marked by strong enrichments in the large, divalent cations, notably Ba, Pb and Sr and (238U/230Th)>1. These characteristics have traditionally been explained by the 'mobility' of such elements in an aqueous fluid. Such fluids are anticipated to be generated during prograde, subduction-metamorphism and to flux elements into the mantle wedge. Yet no experimental dataset of solid-aqueous fluid partitioning replicates the full set of elemental enrichments described above. The recent realisation of the pivotal role of accessory phases in controlling the mobility of elements from the slab provides a more consistent explanation of the chemical characteristics of the 'fluid' phase. Notably rutile and allanite retain the 'immobile' HSFE and REE and fractionate Th from U. The enrichments in the 'fluid' thus simply reflect the displacement of homeless elements. However, Ba will not be mobile until its preferred host, phengite, is exhausted at the wet solidus of the mafic crust. Thus the 'fluid' phase transpires to be a wet melt. The dominant control of accessory phases on the composition of the 'fluid' component also helps in understanding the long-standing puzzle of arc lava 235U-231Pa systematics. By analogy with surface aqueous behaviour, many models have assumed that the 'fluid' adds only U to the mantle wedge, generating 238U-230Th and 235U-231Pa excesses. Yet many lavas with strong 'fluid' signatures and large 238U-230Th excesses have 235U-231Pa deficits. This surprising

  12. Repeated magmatism at 34 Ma and 23-20 Ma producing high magnesian adakitic andesites and transitional basalts on southern Okushiri Island, NE Japan arc

    NASA Astrophysics Data System (ADS)

    Sato, Makoto; Shuto, Kenji; Nohara-Imanaka, Rikako; Takazawa, Eiichi; Osanai, Yasuhito; Nakano, Nobuhiko

    2014-09-01

    The southern part of Okushiri Island in the present-day back-arc margin of the NE Japan arc is one of the rare convergent plate boundaries where similar magma types (high-magnesian adakitic andesite (HMAA) and high-TiO2 basalt (HTB)) have been erupted concurrently at more than one time. Oligocene HMAA can be divided into two types: HMAA-I is characterized by high Sr/Y and low Y, and HMAA-II by relatively low Sr/Y and high Y. HMAA-I is primitive in terms of MgO (8.5 wt.%), Mg# (67), Ni (232 ppm) and Cr (613 ppm) contents, and the most Mg-rich olivine phenocrysts plot within the mantle olivine array in terms of Fo and NiO. The similar Cr versus Ni relations of types I and II HMAA indicate some interaction of slab-derived adakitic melts with mantle peridotite, whereas Ni contents are higher than those of most boninites derived by partial melting of mantle peridotite at a given Cr content. Types I and II HMAA have more enriched Sr and Nd isotopic compositions than N-MORB. The petrography and geochemistry of these rocks, combined with published results on the genesis of high-magnesian andesite (HMA) indicate that types I and II HMAA could be produced by interaction of slab (N-MORB and sediment)-derived adakitic melts with mantle peridotite. The comagmatism of HMAA and HTB is ascribed to the following model. A cool, less hydrous, adakite magma (spherical diapir) would rise from the subducting slab (Pacific Plate) and become more hydrous as a result of its interaction with overlying hydrous peridotite. This hydrated adakitic diapir further ascends and is heated on entering the overlying mantle wedge. Subsequently, the temperature and H2O gradients in the ascending adakitic diapir and surrounding mantle peridotite would have been established. The HTB magma segregated from the surrounding mantle peridotite region (high temperature and low H2O content) at a depth of 60 km or more, whereas the adakitic diapir (low temperature and high H2O content) continued to rise, with its

  13. Implications Of Light And Trace Elements Signatures in Melt Inclusions Of St Vincent And Grenada Island On The Lesser Antilles Arc Behavior

    NASA Astrophysics Data System (ADS)

    Bouvier, A.; Deloule, E.; Métrich, N.

    2008-12-01

    St. Vincent and Grenada islands are located in the south part of the Lesser Antilles arc, generated by the subduction of the Atlantic plate beneath the Caribbean plate. In the both islands, the erupted high-MgO basalts (MgO > 10.0 wt%) are thought to be representative of the primary magmas and to be generated by the melting of a MORB mantle source enriched by fluids derived from the subducted slab [1]. We present here trace element compositions determined by ion probe in melt inclusions (M.I.) trapped in olivines (Fo84-91) from magnesian scoriae, for which light and volatile elements, as stable isotopes were previously measured [2-3]. Their major elements compositions point out a broad variability, but show the primitive character of these M.I. (SiO2 < 50.0 wt%). Grenada M.I. are enriched in K2O (0.4-2.5 wt%) and MgO (up to 12.5 wt%) compared to St. Vincent M.I. (up to 0.85 wt% and 10.0 wt%, respectively). Their trace element patterns encompass those of whole rocks. Compared to St. Vincent, Grenada M.I. recorded more variable trace element compositions. All M.I. patterns are characteristic of subduction zones, with Ba and Sr enrichments associated with pronounced negative Nb anomalies, implying slab-fluids influence, as also demonstrated by high Cl/F ratios (up tp 10.9) [4]. As a whole, REE patterns are enriched and poorly fractionated compared to MORB. The trace element patterns, combined with light element and isotopic compositions, are interpreted in term of variations of degree of mantle partial melting and slab influence, with variable contributions of aqueous fluids released from altered oceanic crust and from sediments, and of sediment melt. Both St. Vincent and Grenada primary magmas record the influence of aqueous fluids, whereas the addition of sediment melt is only identified in Grenada M.I., as Zr positive anomalies (Zr contents up to 1200 ppm), a rare feature in basaltic melts. Although light trace elements and stable isotopes illustrated mostly

  14. Discovery of Seafloor Massive Sulfides in an Andesite-Dacite Knoll Caldera off Present-Day Volcanic Front, Izu-Ogasawara Island Arc, Japan

    NASA Astrophysics Data System (ADS)

    Iizasa, K.; Asada, A.; Lee, S.; Mizuno, K.; Katase, F.; Kojima, M.; Kurozawa, T.

    2015-12-01

    We report the discovery of sulfide mounds with 20 to 30 m high sulfide chimneys in the Higashi-Aogashima hydrothermal field of a Quaternary andesite-dacite knoll caldera at the frontal arc side off Quaternary volcanic front, Izu-Ogasawara island arc, Japan. The discovery was carried out based on the systematic survey method of geological technique and a developed acoustic device using AUV. The knoll caldera 12 km east of Aogashima volcanic island is the size 10 km to 9 km of its rim and 820 m deep at its deepest caldera floor. According to the results of heavy mineral analysis for caldera sediments by a gravity corer, at least two areas were inferred to sites of potential hydrothermal activity associated with seafloor massive sulfides. After the precise acoustic survey using AUV there are many mound-like structures in the both inferred areas on the floor. Two major hydrothermal fields among them so far, which are a conical sulfide mound on the southeast flank of the central cone and a ridge-like mound on the inferred caldera boundary fault in the southeast, were confirmed based on sulfide samples recovered by a gravity corer during the next survey stage. One of them occurs at the water depth of 760 m to 770 m. It has active sulfide chimneys (ca. 20 m high) on the conical sulfide mound of about 40 m in diameter with 20 m high. Samples from the mound are composed of major sphalerite with moderate galena and barite, and minor chalcopyrite and pyrite. Another mound associated with chimneys at the water depth ranging from 740m to 770m on the southeast caldera boundary fault forms a small, east-west trend ridge-like shape. The ridge sizes more than 100 m long with 10 m wide. Chimneys are more than 30 m high. It is inferred that the mound is composed of major sphalerite and moderate barite based on samples cored at the margin of the mound. These results indicate that more than several sulfide mounds would be confirmed in the caldera floor by ROV surveys this September.

  15. The collision zone between the North d'Entrecasteaux Ridge and the New Hebrides Island Arc: 1. Sea Beam morphology and shallow structure

    NASA Astrophysics Data System (ADS)

    Collot, Jean-Yves; Fisher, Michael A.

    1991-03-01

    Sea Beam bathymetric data, closely spaced single-channel seismic reflection sections, and geopotential field data were collected aboard the R/V J. Charcot over the collision zone between the North d'Entrecasteaux Ridge (NDR) and the New Hebrides island arc. The NDR trends east at a small angle (14°) to the plate convergence direction so that the ridge creeps northward along the trench at about 2.5 cm/yr, requiring a continual structural adjustment of the accretionary complex. In this report we study the shallow structure, tectonic erosion, and consequent mass wasting of the accretionary complex, all of which were produced by the collision of the NDR in a complex deformational environment. The accretionary complex in this collision zone can be divided into northern, central, and southern parts. The northern part of the collision zone, which lies north of the leading flank of the ridge, shows a lobate lower accretionary complex that is structured by east to southeast dipping thrust and reverse faults and N60°W trending strike-slip faults; a middle accretionary complex that bulges seaward and appears to be rotated 45°E from the regional arc trend; and an upper accretionary complex that is shaped by slumps and a canyon network. The central part of the collision zone, which directly overlies the crest of the ridge, forms a broad shallow protrusion that is bounded on its northern and southern sides by steep scarps. Rocks forming this protrusion have been uplifted, possibly by as much as 1500-2500 m, and tilted to the north, causing northward block sliding along an extensional detachment surface. The southern part of the collision zone, which lies in the wake of the ridge, is deformed by large slumps and normal faults that trend parallel to the ridge axis. Rocks forming this southern part collapse, causing widespread mass wasting. These geophysical data indicate that normal trench convergence has apparently produced only a few trench-parallel structures confined to the

  16. A structural, petrographic, and isotopic study of the Rapid River area and selected mafic complexes in the northwestern United States: Implications for the evolution of an abrupt island arc-continent boundary

    SciTech Connect

    Aliberti, E.A.

    1988-01-01

    The east side of the Columbia embayment is characterized by an unusually sharp island arc-continent boundary. Detailed mapping, strain analysis, and petrography of three structural levels along portion of this boundary, the Rapid River area, are discussed. From lowest to highest these are the Wallowa terrane, the Rapid River plate (RRP), and the Pollock Mountain plate (PMP). Mineral lineation data indicate that the RRP and the PMP were transported west-northwestward along steeply rooted thrust systems. Sm-Nd and Rb-Sr isotopic studies of three mafic and ultramafic complexes around the periphery of the Columbia embayment indicate that each formed from a separate source area, all within an oceanic environment. Structural, petrographic, and isotopic data support an evolution of the island arc-continent boundary in west-central Idaho characterized by three stages: (1) Initial collision of the amalgamated island arc terrane with the continental margin and the removal of a wedge of material northward along both left- and right-lateral strike-slip faults; (2) Strike-slip faults at the tail end of the wedge merge along a zone of occlusion (ZOO). The strain accommodated by northward removal of the wedge is transferred to compression along this zone resulting in intracontinental subduction and uplift; (3) Thermal weakening of the crust by increased magmatic activity resulted in several tens of kilometers of rapid uplift of material out of the ZOO along steeply rooted thrust faults.

  17. Far-field simulation of the 1946 Aleutian tsunami

    NASA Astrophysics Data System (ADS)

    Okal, Emile A.; Hébert, Hélène

    2007-06-01

    We present hydrodynamic far-field simulations of the Aleutian tsunami of 1946 April 1, using both a dislocation source representing a slow earthquake and a dipolar one modelling a large landslide. The earthquake source is derived from the recent seismological study by López and Okal, while the landslide source was previously used to explain the exceptional run-up at Scotch Cap in the near field. The simulations are compared to a field data set previously compiled from testimonies of elderly witnesses at 27 far-field locations principally in the Austral and Marquesas Islands, with additional sites at Pitcairn, Easter and Juan Fernández. We find that the data set is modelled satisfactorily by the dislocation source, while the landslide fails to match the measured amplitudes, and to give a proper rendition of the physical interaction of the wavefield with the shore, in particular at Nuku Hiva, Marquesas. The emerging picture is that the event involved both a very slow earthquake, responsible for the far-field tsunami, and a major landslide explaining the near-field run-up, but with a negligible contribution in the far field.

  18. Multi-centennial reconstruction of Aleutian climate from coralline algae

    NASA Astrophysics Data System (ADS)

    Williams, B.; Halfar, J.; DeLong, K. L.; Smith, E.; Steneck, R.; Lebednik, P.; Jacob, D. E.; Fietzke, J.; Moore, K.

    2015-12-01

    Long-lived encrusting coralline algae yield robust reconstructions of mid-to-high latitude environmental change from their annually-banded high-magnesium calcite skeleton. The magnesium to calcium ratio measured in their skeleton reflects ambient seawater temperature at the time of formation. Thus, reconstructions from these algae are important to understanding the role of natural modes of climate variability versus that of external carbon dioxide in controlling climate in data sparse regions such as the northern North Pacific Ocean/southern Bering Sea. Here, we reconstruct regional seawater temperature from the skeletons of nine algae specimens from two islands in the Aleutian Archipelago. We find that seawater temperature increased ~1.4°C degrees over the past 350 years. The detrended seawater reconstruction correlates with storminess because storms moving across the North Pacific Ocean bring warmer water to the archipelago. Comparison of the algal seawater temperature reconstruction with instrumental and terrestrial proxy reconstructions reveals that atmospheric teleconnections to North America via the North Pacific storm tracks are not robust before the 20th century. This indicates that North Pacific climate processes inferred from the instrumental records should be cautiously extrapolated when describing earlier non-analogous climates or future climate change.

  19. Basaltic volcanism in the Bering Sea: geochronology and volcanic evolution of St. Paul Island, Pribilof Islands, Alaska

    NASA Astrophysics Data System (ADS)

    Winer, G. S.; Feeley, T. C.; Cosca, M. A.

    2004-07-01

    The evolution of a Pleistocene to Holocene basaltic volcanic field in the back-arc region of the Aleutian subduction system is investigated at St. Paul Island, Alaska, one of the youngest eruptive centers in the Bering Sea basalt province. New 40Ar/ 39Ar and 14C age determinations indicate that subaerial volcanic activity forming the island began as early as 540 ka and has continued nearly to the present; the youngest eruption occurred approximately 3230 years BP. Magmas erupted on St. Paul are basaltic with MgO contents ranging from 14 to 4 wt.% and phenocryst assemblages of olivine+clinopyroxene±plagioclase; all are alkalic. The surface of St. Paul is composed mainly of numerous tephra cones surrounded by coalescing, low-viscosity pahoehoe lava flows. A central highland spans the island from east to west and is constructed of relatively young eruptive centers where rocks show a minimum of weathering and little deformation by faulting. In contrast, older lava flows forming the wave-eroded base of the island are gently to moderately tilted and faulted. Geochronologic, stratigraphic, and geochemical data indicate that eruptive styles on St. Paul evolved from early, mostly effusive eruptions of chemically little evolved lavas that form the base of the island, to more explosive monogenetic scoria cones, to polygenetic centers forming shields by repeated effusive eruptions of evolved low-viscosity lavas. Localization of the monogenetic and polygenetic centers appears to be related to east-west and northeast-southwest trending fault and fissure systems, with polygenetic centers located at intersections of major structures. The combined volcanic and compositional changes on St. Paul Island suggest that the magmatic system as a whole may be trending toward eruption of more evolved magmas related to the progressive development of crustal magma chambers in which crystal fractionation and magmatic differentiation are occurring.

  20. Paleomagnetism of the Samar Ophiolite: Implications for the Cretaceous sub-equatorial position of the Philippine island arc

    NASA Astrophysics Data System (ADS)

    Balmater, Hertz G.; Manalo, Pearlyn C.; Faustino-Eslava, Decibel V.; Queaño, Karlo L.; Dimalanta, Carla B.; Guotana, Juan Miguel R.; Ramos, Noelynna T.; Payot, Betchaida D.; Yumul, Graciano P.

    2015-11-01

    Samar island in the eastern part of Central Philippines is underlain by a complete ophiolite suite, the Samar Ophiolite. We present the first geochronological and paleomagnetic data for the Samar Ophiolite. Whole rock K-Ar dating of two basalt samples yielded an age of 100.2 ± 2.7 Ma and 97.9 ± 2.8 Ma. Thirteen sites in four localities yielded characteristic remanent magnetization with in situ direction of D = 340°, I = - 24°, k = 15, α95 = 11° and tilt-corrected direction of D = 342°, I = - 27°, k = 15, α95 = 11°. These values suggest that the ophiolitic basement rocks of Samar formed in the Late Cretaceous at a paleolatitude of 14°S ± 6°. The paleolatitude is several degrees south of the sub-equatorial positions calculated for the three other Mesozoic ophiolites of the Philippine Mobile Belt (PMB) whose paleomagnetism had been previously studied. The PMB ophiolites in eastern and central Philippines share a common age, geochemistry and paleolatitude with the Halmahera Ophiolite, suggesting that they originated from a Mesozoic supra-subduction zone that spanned a few degrees north of the equator to around 15°S.

  1. Crustal Genesis and Dynamics in the Jurassic Talkeetna Arc

    NASA Astrophysics Data System (ADS)

    Kelemen, P.; Amato, J.; Behn, M.; Blusztajn, J.; Christensen, N.; Clift, P.; Debari, S.; Draut, A.; Greene, A.; Hacker, B.; Hanghoj, K.; Hart, S.; Hirth, G.; Mattinson, J.; Mehl, L.; Pavlis, T.; Rioux, M.; Trop, J.

    2005-12-01

    . Even if Talkeetna mid and lower crust were removed, remaining felsic plutonic and volcanic rocks would be distinct from continental crust. Thus, Talkeetna is similar to Izu-Bonin-Marianas and Tonga, and different from western Aleutian and Kurile island arcs where lavas are similar to continental crust. Quartz diorites and tonalites in a klippe south of the main Talkeetna section have igneous garnet formed from LREE enriched, HREE depleted, high Th/La, felsic melts. Mixing of such melts with primitive basalt, combined with removal of the garnet-bearing residue, could produce crust similar to continental crust. However, such melts are rare in the Talkeetna lava stratigraphy to the north. Olivine fabrics in residual peridotites and ultramafic plutons indicate arc parallel a-axis lineation and arc parallel viscous flow, consistent with seismic anisotropy in many modern arcs. Such fabrics in plutons suggest viscous coupling of lower crust and mantle at some times. But, Moho pyroxenites and lower crustal gabbronorites are almost undeformed. Metamorphic conditions recorded by garnet-bearing rocks are ~ 1000 C and 1 GPa near the Moho and 700 and 0.7 GPa in the klippe, consistent with mantle temperatures of ~1300 C at 45 km beneath this and other arcs.

  2. The Neogene Alert Bay Volcanic Belt of northern Vancouver Island, Canada: Descending-plate-edge volcanism in the arc-trench gap

    NASA Astrophysics Data System (ADS)

    Armstrong, R. L.; Muller, J. E.; Harakal, J. E.; Muehlenbachs, K.

    1985-10-01

    The Alert Bay Volcanic Belt trends northeasterly across northern Vancouver Island, coincident with the trace of the subducted Juan de Fuca—Explorer plate edge. Volcanism began in the west, at Brooks Peninsula, about 8 Ma ago, but occurred in most centers 3.5 ± 1 Ma ago. There is a suggestion of eastward migration of activity and shift from basalt to dacite or rhyolite with time. Most of the volcanism was coincident with a time of rapid changes in the geometry of subduction, as inferred from offshore magnetic patterns, and with a hiatus in mainland, Cascade volcanic arc activity. Geometry and chronometry suggest this is a descending-plate-edge volcanic belt, where disruption of steady-state plate-consumption patterns triggered magma genesis. Chemically the rocks are quite variable, with divergent fractionation trends. One trend resembles that of Mull (Hebrides), with a plagiophyric basalt of transitional alkaline-subalkaline, mildly tholeiitic, and aluminous character which differentiated to clinopyroxene andesite, and eventually to tholeiitic rhyolite and mildly tholeiitic calc-alkaline dacite, both of K-poor magma type. The other trend is like the Cascades, with aluminous, aphyric, calc-alkaline basalt, hornblende and/or hypersthene andesite, and K-poor dacite. This divergent character is also evident in Ba, Rb, Nb, and Zr fractionation trends. Major- and trace-element discriminant diagrams generally identify the basalts as within-plate types. The 87Sr/ 86Sr isotope ratio is relatively low, averaging 0.70325, and shows no trend with rock type or differentiation series. Oxygen in the entire suite is relatively heavy, δ 18O averaging 7.1%. Even the basalts are 18O enriched. Oxygen shows no trend with degree of hydration, rock type, or series. These isotopic and chemical data are compatible with minor crustal contamination of mafic primary magmas, followed by fractional crystallization under different oxidation and hydration conditions.

  3. Re-colonization by common eiders Somateria mollissima in the Aleutian Archipelago following removal of introduced arctic foxes Vulpes lagopus

    USGS Publications Warehouse

    Petersen, Margaret R.; Sonsthagen, Sarah A.; Sexson, Matthew G.

    2015-01-01

    Islands provide refuges for populations of many species where they find safety from predators, but the introduction of predators frequently results in elimination or dramatic reductions in island-dwelling organisms. When predators are removed, re-colonization for some species occurs naturally, and inter-island phylogeographic relationships and current movement patterns can illuminate processes of colonization. We studied a case of re-colonization of common eiders Somateria mollissima following removal of introduced arctic foxes Vulpes lagopus in the Aleutian Archipelago, Alaska. We expected common eiders to resume nesting on islands cleared of foxes and to re-colonize from nearby islets, islands, and island groups. We thus expected common eiders to show limited genetic structure indicative of extensive mixing among island populations. Satellite telemetry was used to record current movement patterns of female common eiders from six islands across three island groups. We collected genetic data from these and other nesting common eiders at 14 microsatellite loci and the mitochondrial DNA control region to examine population genetic structure, historical fluctuations in population demography, and gene flow. Our results suggest recent interchange among islands. Analysis of microsatellite data supports satellite telemetry data of increased dispersal of common eiders to nearby areas and little between island groups. Although evidence from mtDNA is suggestive of female dispersal among island groups, gene flow is insufficient to account for recolonization and rapid population growth. Instead, near-by remnant populations of common eiders contributed substantially to population expansion, without which re-colonization would have likely occurred at a much lower rate. Genetic and morphometric data of common eiders within one island group two and three decades after re-colonization suggests reduced movement of eiders among islands and little movement between island groups after

  4. Indirect food web interactions: Sea otters and kelp forest fishes in the Aleutian archipelago

    USGS Publications Warehouse

    Reisewitz, S.E.; Estes, J.A.; Simenstad, C.A.

    2006-01-01

    Although trophic cascades - the effect of apex predators on progressively lower trophic level species through top-down forcing - have been demonstrated in diverse ecosystems, the broader potential influences of trophic cascades on other species and ecosystem processes are not well studied. We used the overexploitation, recovery and subsequent collapse of sea otter (Enhydra lutris) populations in the Aleutian archipelago to explore if and how the abundance and diet of kelp forest fishes are influenced by a trophic cascade linking sea otters with sea urchins and fleshy macroalgae. We measured the abundance of sea urchins (biomass density), kelp (numerical density) and fish (Catch per unit effort) at four islands in the mid-1980s (when otters were abundant at two of the islands and rare at the two others) and in 2000 (after otters had become rare at all four islands). Our fish studies focused on rock greenling (Hexagrammos lagocephalus), the numerically dominant species in this region. In the mid-1980s, the two islands with high-density otter populations supported dense kelp forests, relatively few urchins, and abundant rock greenling whereas the opposite pattern (abundant urchins, sparse kelp forests, and relatively few rock greenling) occurred at islands where otters were rare. In the 2000, the abundances of urchins, kelp and greenling were grossly unchanged at islands where otters were initially rare but had shifted to the characteristic pattern of otter-free systems at islands where otters were initially abundant. Significant changes in greenling diet occurred between the mid-1980s and the 2000 although the reasons for these changes were difficult to assess because of strong island-specific effects. Whereas urchin-dominated communities supported more diverse fish assemblages than kelp-dominated communities, this was not a simple effect of the otter-induced trophic cascade because all islands supported more diverse fish assemblages in 2000 than in the mid-1980s

  5. 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).

    PubMed

    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. PMID:24860717

  6. Are There Spatial or Temporal Patterns to Holocene Explosive Eruptions in the Aleutian Archipelago? A Work in Progress

    NASA Astrophysics Data System (ADS)

    Martin, C.; Nicolaysen, K. P.; McConville, K.; Hatfield, V.; West, D.

    2013-12-01

    By examining the existing geological and archeological record of radiocarbon dated Aleutian tephras of the last 12,000 years, this study sought to determine whether there were spatial or temporal patterns of explosive eruptive activity. The Holocene tephra record has important implications because two episodes of migration and colonization by humans of distinct cultures established the Unangan/Aleut peoples of the Aleutian Islands concurrently with the volcanic activity. From Aniakchak Volcano on the Alaska Peninsula to the Andreanof Islands (158 to 178° W longitude), 55 distinct tephras represent significant explosive eruptions of the last 12,000 years. Initial results suggest that the Andreanof and Fox Island regions of the archipelago have had frequent explosive eruptions whereas the Islands of Four Mountains, Rat, and Near Island regions have apparently had little or no eruptive activity. However, one clear result of the investigation is that sampling bias strongly influences the apparent spatial patterns. For example field reconnaissance in the Islands of Four Mountains documents two Holocene calderas and a minimum of 20 undated tephras in addition to the large ignimbrites. Only the lack of significant explosive activity in the Near Islands seems a valid spatial result as archeological excavations and geologic reports failed to document Holocene tephras there. An intriguing preliminary temporal pattern is the apparent absence of large explosive eruptions across the archipelago from ca. 4,800 to 6,000 yBP. To test the validity of apparent patterns, a statistical treatment of the compiled data grappled with the sampling bias by considering three confounding variables: larger island size allows more opportunity for geologic preservation of tephras; larger magnitude eruption promotes tephra preservation by creating thicker and more widespread deposits; the comprehensiveness of the tephra sampling of each volcano and island varies widely because of logistical and

  7. The Aleutian Tsunami of 1946: the Compound Earthquake-Landslide Source and Near-Field Modeling

    NASA Astrophysics Data System (ADS)

    Fryer, G. J.; Yamazaki, Y.; McMurtry, G. M.

    2015-12-01

    The tsunami of April 1, 1946, spread death and destruction throughout the Pacific from the Aleutians to Antarctica, and produced exceptional runup, 42 m, at Scotch Cap on Unimak Island in the near field. López & Okal (2006) showed that the triggering earthquake was at least MW = 8.6, large enough to explain the far-field tsunami but still requiring a landslide or other secondary source to achieve the local runup. No convincing landslide was found until von Huene, et al (2014) merged all available multibeam data and reprocessed a old multichannel line to show that a feature on the Aleutian Terrace they call Lone Knoll (LK) is the displaced block of a translational slide. From 210Pb dating of push cores taken near the summit of LK, we find that a disruption in sedimentation occurred in 1946 at one site, but sedimentation was not disrupted at another site nearby. We infer that the slide block moved coherently at a speed close to the threshold for erosion of the hemipelagic clays. From GLORIA sidescan, Fryer, et al (2004) had earlier tentatively identified LK as a landslide deposit, but if the tsunami crossed the shallow Aleutian Shelf at the long-wave speed, that landslide had to extend up to the shelf edge to satisfy the known 48-min travel time to Scotch Cap. The resulting landslide was enormous, and a multibeam survey later in 2004 showed that it could not exist. The slide imaged by von Huene, et al is far smaller, with a headwall 30 km downslope at a depth of 3 km. The greater distance demands that the tsunami travel much faster across the shelf. The huge runup, however, suggests that wave height was a significant fraction of the water depth (only 80 m), so the tsunami probably crossed the Aleutian Shelf as a bore. From modeling the landslide-generated tsunami with a shock-capturing dispersive code we infer that it did indeed cross the shelf as a bore traveling at roughly twice the long-wave speed. We are still exploring the dependence of the tsunami on slide

  8. Soil microbial structure and function post-volcanic eruption on Kasatochi Island and regional controls on microbial heterogeneity

    NASA Astrophysics Data System (ADS)

    Zeglin, L. H.; Rainey, F.; Wang, B.; Waythomas, C.; Talbot, S. L.

    2013-12-01

    Microorganisms are abundant and diverse in soil and their integrated activity drives nutrient cycling on the ecosystem scale. Organic matter (OM) inputs from plant production support microbial heterotrophic life, and soil geochemistry constrains microbial activity and diversity. As vegetation and soil develops over time, these factors change, modifying the controls on microbial heterogeneity. Following a volcanic eruption, ash deposition creates new surfaces where both organismal growth and weathering processes are effectively reset. The trajectory of microbial community development following this disturbance depends on both organic matter accumulation and geochemical constraints. Also, dispersal of microbial cells to the sterile ash surface may determine microbial community succession. The Aleutian Islands (Alaska, USA) are a dynamic volcanic region, with active and dormant volcanoes distributed across the volcanic arc. One of these volcanoes, Kasatochi, erupted violently in August 2008, burying a small lush island in pryoclastic flows and fine ash. Since, plants and birds are beginning to re-establish on developing surfaces, including legacy soils exposed by rapid erosion of pyroclastic deposits, suggesting that recovery of microbial life is also proceeding. However, soil microbial diversity and function has not been examined on Kasatochi Island or across the greater Aleutian region. The project goal is to address these questions: How is soil microbial community structure and function developing following the Kasatochi eruption? What is the relative importance of dispersal, soil OM and geochemistry to microbial community heterogeneity across the Aleutians? Surface mineral soil (20-cm depth) samples were collected from Kasatochi Island in summer 2013, five years after the 2008 eruption, and from eight additional Aleutian islands. On Kasatochi, pryoclastic deposits, exposed legacy soils supporting regrowth of remnant dune wild-rye (Leymus mollis) and mesic meadow

  9. A juvenile oceanic island arc origin for the Archean (ca. 2.97 Ga) Fiskenæsset anorthosite complex, southwestern Greenland: Evidence from oxygen isotopes

    NASA Astrophysics Data System (ADS)

    Polat, Ali; Longstaffe, Fred J.

    2014-06-01

    The Archean (ca. 2.97 Ga) Fiskenæsset layered intrusion, southwestern Greenland, consists of an association of anorthosite, leucogabbro, gabbro, hornblendite, pyroxenite, peridotite and dunite. The intrusion is characterized by well-preserved igneous layering, cumulate texture and primary igneous minerals including olivine, pyroxene, plagioclase, hornblende and chromite. We use new whole-rock (n=36) and mineral (n=32) oxygen isotopic data for all major lithologic units from the best preserved stratigraphic section of the Fiskenæsset Complex at Majorqap qâva to revisit geodynamic and petrogenetic hypotheses proposed for the origin of Archean terranes. The Fiskenæsset Complex has modern mantle-like whole-rock O-isotope compositions (δO18=5.8±0.5‰). Average δO18 values increase from peridotite (δO18=5.0‰), through hornblendite (δO18=5.7‰), gabbro (δO18=5.8‰), pyroxene hornblendite (δO18=6.0‰) and leucogabbro (δO18=6.3‰), to anorthosite (δO18=6.3‰). These whole-rock isotopic compositions reflect the approximate modal abundances of olivine (average δO18=4.9‰), hornblende (average δO18=5.7‰), clinopyroxene (average δO18=6.4‰) and plagioclase (average δO18=6.4‰) in each rock type, as a consequence of mineral fractionation in the magma chamber(s). Field relationships and the absence of crustal contamination suggest that the Fiskenæsset Complex formed in an oceanic setting. Subduction zone-like whole-rock trace element signatures and mantle-like δO18 and initial εNd values are consistent with formation of these rocks in a juvenile oceanic island arc setting. Field and geochemical data from the Fiskenæsset region and adjacent terranes suggest that the origin of Archean crust in southwestern Greenland is consistent with Phanerozoic-like plate tectonic processes rather than density-driven sinking, delamination and diapiric processes requiring formation of greenstone belts and anorthosite complexes on pre-existing continental crust

  10. Resolving rock exhumation versus surface uplift during arc-continent accretion on the island of Timor by integrating thermochronology and micropaleontology data

    NASA Astrophysics Data System (ADS)

    Tate, G. W.; McQuarrie, N.; Van Hinsbergen, D. J.; Bakker, R.; Reiners, P. W.; Willett, S.

    2012-12-01

    The emergence of the island of Timor is the result of active accretion of the Banda volcanic arc to the Australian continent. Since collision began in the latest Miocene, a mountain range over 2,900 m in elevation has been raised, much of the Indonesian throughflow linking the Pacific and Indian Oceans has been closed, and the final accretion stages of slab breakoff and subduction polarity reversal may have begun. New thermochronologic and micropaleontological data from Timor-Leste reveal a detailed history of both rock and surface uplift in the central portion of Timor Island. Micropaleontological data is taken from synorogenic basins in Viqueque near the southern coast and in Caiaco, 120 km to the west of Viqueque and farther to the hinterland. These data indicate surface uplift from lower bathyal depth between 5.5 and 4.4 Ma to upper-middle bathyal depth around 3.3 Ma. Uplift is further suggested by a facies change around 4.4 Ma from deep-marine chalk deposits to clay, turbiditic sandstone and debris flow deposits with fossil wood remains, showing nearby emergence. The data suggest a phase of uplift in these basins of up to 1.4 km in about 1 Myr with an uplift rate of about 1.4 mm/yr. Uplift rates since 3.3 Ma may have dropped to less than 0.2 mm/yr. In the central mountain belt between these synorogenics, thermochronologic data show that rapid exhumation was concurrent with and continued after the rapid surface uplift recorded in the basins. Along the northern coast of Timor, zircon (U-Th)/He ages are 4.4 Ma in the east (at Hilimanu) and young to about 1.5 Ma in the west (at Liquica and Ermera). Thermal models suggest exhumation that was possibly as fast as 6.4 mm/yr from as deep as 9 km. To the south and east of the higher grade zircon (U-Th)/He data, apatite (U-Th)/He ages indicate notably less exhumation. Apatite (U-Th)/He ages from the northern and southern foothills in the east (Manatuto district) vary from 3.5 to 5.5 Ma while ages cluster around 2.0 Ma in

  11. Geology and 40Ar/39Ar geochronology of the medium- to high-K Tanaga volcanic cluster, western Aleutians

    USGS Publications Warehouse

    Jicha, Brian R.; Coombs, Michelle L.; Calvert, Andrew T.; Singer, Brad S.

    2012-01-01

    We used geologic mapping and geochemical data augmented by 40Ar/39Ar dating to establish an eruptive chronology for the Tanaga volcanic cluster in the western Aleutian arc. The Tanaga volcanic cluster is unique in comparison to other central and western Aleutian volcanoes in that it consists of three closely spaced, active, volumetrically significant edifices (Sajaka, Tanaga, and Takawangha), the eruptive products of which have unusually high K2O contents. Thirty-five new 40Ar/39Ar ages obtained in two different laboratories constrain the duration of Pleistocene–Holocene subaerial volcanism to younger than 295 ka. The eruptive activity has been mostly continuous for the last 150 k.y., unlike most other well-characterized arc volcanoes, which tend to grow in discrete pulses. More than half of the analyzed Tanaga volcanic cluster lavas are basalts that have erupted throughout the lifetime of the cluster, although a considerable amount of basaltic andesite and basaltic trachyandesite has also been produced since 200 ka. Major- and trace-element variations suggest that magmas from Sajaka and Tanaga volcanoes are likely to have crystallized pyroxene and/or amphibole at greater depths than the older Takawangha magmas, which experienced a larger percentage of plagioclase-dominated fractionation at shallower depths. Magma output from Takawangha has declined over the last 86 k.y. At ca. 19 ka, the focus of magma flux shifted to the west beneath Tanaga and Sajaka volcanoes, where hotter, more mafic magma erupted.

  12. Characterization of Aleutian disease virus as a parvovirus.

    PubMed Central

    Bloom, M E; Race, R E; Wolfinbarger, J B

    1980-01-01

    We characterized a strain of Aleutian disease virus adapted to growth in Crandall feline kidney cells at 31.8 degrees C. When purified from infected cells, Aleutian disease virus had a density in CsCl of 1.42 to 1.44 g/ml and was 24 to 26 nm in diameter. [3H]thymidine could be incorporated into the viral genome, and the viral DNA was then studied. In alkaline sucrose gradients, Aleutian disease virus DNA was a single species that cosedimented at 15.5S with single-stranded DNA from adeno-associated virus. When the DNA was analyzed on neutral sucrose gradients, a single species was again observed, which sedimented at 21S and was clearly distinct from 16S duplex adeno-associated virus DNA. A similar result was obtained even after incubation under annealing conditions, implying that the bulk of Aleutian disease virus virions contained a single non-complementary strand with a molecular weight of about 1.4 X 10(6). In addition, two major virus-associated polypeptides with molecular weights of 89,100 and 77,600 were demonstrated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of virus purified from infected cultures labeled with [35S]methionine. These data suggest that Aleutian disease virus is a nondefective parvovirus. Images PMID:6252342

  13. Episodes of Aleutian Ridge explosive volcanism

    USGS Publications Warehouse

    Hein, J.R.; Scholl, D. W.; Miller, J.

    1978-01-01

    Earlier workers have overlooked deep-sea bentonite beds when unraveling the Cenozoic volcanic history of an area. In the North Pacific, identification of Miocene and older volcanic episodes is possible only if both altered (bentonite) and unaltered ash beds are recognized. Our study, which includes bentonite beds, shows that volcanism on the Aleutian Ridge and Kamchatka Peninsula has been cyclic. Volcanic activity seems to have increased every 2.5 ?? 10 6 years for the past 10 ?? 106 years and every 5.0 ?? 106 years for the time span from 10 to 20 ?? 10 6 years ago. The middle and late Miocene and the Quaternary were times of greatly increased volcanic activity in the North Pacific and elsewhere around the Pacific Basin. The apparent absence of a volcanic record before the late Miocene at Deep Sea Drilling Project site 192 is the result not of plate motion, as suggested by Stewart and by Ninkovich and Donn, but rather of the diagenesis of ash layers. Major, apparently global volcanic episodes occurred at least twice in the last 20 ?? 106 years. Yet, only one major glacial epoch (the Pleistocene) has occurred. Therefore, even though glaciation coincided with an increase in Quaternary volcanism, the increased volcanism itself may not have been the primary cause of global cooling. Copyright ?? 1978 AAAS.

  14. Heavy metals in fish from the Aleutians: interspecific and locational differences.

    PubMed

    Burger, Joanna; Gochfeld, Michael; Jeitner, Christian; Pittfield, Taryn; Donio, Mark

    2014-05-01

    The objectives of this study were to examine levels of arsenic, cadmium, lead, mercury and selenium in edible tissue of seven species of marine fish collected from several Aleutian islands (in 2004) to determine: (1) interspecific differences, (2) locational differences (among Aleutian Islands), (3) size-related differences in any metal levels within a species, and (4) potential risk to the fish or to predators on the fish, including humans. We also compared metals levels to those of three other fish species previously examined in detail, as well as examining metals in the edible tissue of octopus (Octopus dofleini). Octopus did not have the highest levels of any metal. There were significant interspecific differences in all metal levels among the fish species, although the differences were less than an order of magnitude, except for arsenic (mean of 19,500 ppb in Flathead sole, Hippoglossoides elassodon). Significant intraisland variation occurred among the four sites on Amchitka, but there was not a consistent pattern. There were significant interisland differences for some metals and species. Mercury levels increased significantly with size for several species; lead increased significantly for only one fish species; and cadmium and selenium decreased significantly with size for halibut (Hippoglossus stenolepis). The Alaskan Department of Health and Social Services supports unrestricted consumption of most Alaskan fish species for all people, including pregnant women. Most mean metal concentrations were well below the levels known to adversely affect the fish themselves, or predators that consume them (including humans), except for mercury in three fish species (mean levels just below 0.3 ppm), and arsenic in two fish species. However, even at low mercury levels, people who consume fish almost daily will exceed guideline values from the Centers for Disease Control and the Environmental Protection Agency. PMID:24727640

  15. Heavy metals in fish from the Aleutians: Interspecific and locational differences

    SciTech Connect

    Burger, Joanna; Gochfeld, Michael; Jeitner, Christian; Pittfield, Taryn; Donio, Mark

    2014-05-01

    The objectives of this study were to examine levels of arsenic, cadmium, lead, mercury and selenium in edible tissue of seven species of marine fish collected from several Aleutian islands (in 2004) to determine: (1) interspecific differences, (2) locational differences (among Aleutian Islands), (3) size-related differences in any metal levels within a species, and (4) potential risk to the fish or to predators on the fish, including humans. We also compared metals levels to those of three other fish species previously examined in detail, as well as examining metals in the edible tissue of octopus (Octopus dofleini). Octopus did not have the highest levels of any metal. There were significant interspecific differences in all metal levels among the fish species, although the differences were less than an order of magnitude, except for arsenic (mean of 19,500 ppb in Flathead sole, Hippoglossoides elassodon). Significant intraisland variation occurred among the four sites on Amchitka, but there was not a consistent pattern. There were significant interisland differences for some metals and species. Mercury levels increased significantly with size for several species; lead increased significantly for only one fish species; and cadmium and selenium decreased significantly with size for halibut (Hippoglossus stenolepis). The Alaskan Department of Health and Social Services supports unrestricted consumption of most Alaskan fish species for all people, including pregnant women. Most mean metal concentrations were well below the levels known to adversely affect the fish themselves, or predators that consume them (including humans), except for mercury in three fish species (mean levels just below 0.3 ppm), and arsenic in two fish species. However, even at low mercury levels, people who consume fish almost daily will exceed guideline values from the Centers for Disease Control and the Environmental Protection Agency. - Highlights: • Cadmium, lead, mercury and selenium

  16. Griddlestones from Adak Island, Alaska: Their provenance and the biological origins of organic residues from cooking

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Burned stone slabs, historically called griddlestones, were recovered from Components 1 (2390-2590 RCYPB) and 2 (170-415 RCYBP) at archaeological site ADK-011 on Adak Island, Aleutian Islands, Alaska. The griddlestones show evidence of fire exposure and have a dark, often greasy, matrix of decompose...

  17. U-series, SrNdPb isotope and trace-element systematics across an active island arc-continent collision zone: Implications for element transfer at the slab-wedge interface

    NASA Astrophysics Data System (ADS)

    Hoogewerff, J. A.; Van Bergen, M. J.; Vroon, P. Z.; Hertogen, J.; Wordel, R.; Sneyers, A.; Nasution, A.; Varekamp, J. C.; Moens, H. L. E.; Mouchel, D.

    1997-03-01

    We present U-series, SrNdz.sbnd;Pb isotope and trace-element results of a regional study of geochemical systematics across an island arc-continent collision zone in the East Sunda Arc of Indonesia. Samples from four active volcanoes exhibit a striking compositional range from low-K tholeiitic to ultrapotassic, but all are characterised by high 87Sr/86Sr (0.7053-0.7067), radiogenic lead isotope ratios ( 206Pb/204Pb = 18.99-19.15), low ( 230Th) /( 232Thz) (0.66-0.85), and low 143Nd/144Nd (0.51255-0.51272), except for high 143Nd/144Nd (>0.51286) at the volcanic front. Low ( 230Th) /( 232Th) ratios are also found in terrigenous sediments in front of the arc, which, in combination with Srz.sbnd;Ndz.sbnd;Pb isotopic constraints, indicates that subducted continental material contributes to magma sources in this arc sector. The volcanoes close to the trench show a large excess of 238U over . 230Th (up to 80%) and of 226Ra over 230Th (up to 800%). In addition, they are enriched in elements thought to be mobile in hydrous fluids during slab-wedge transfer, such as Ba, Pb, and Sr. In contrast, Uz.sbnd;Thz.sbnd;Ra systematics are close to equilibrium in the volcanoes behind the front. Abundance patterns of incompatible trace elements in these rocks are similar to those of the terrigenous sediments, so that, in comparison with the arc-front lavas, they possess low Ba/La, Ba/Th, La/Th, Pb/Ce, and Zr/Nb. Higher concentration levels and less interelement fractionation form conspicuous differences with the front volcanics. Our combined isotopic and trace element data are consistent with three-component mixing whereby a slab-derived hydrous fluid and a siliceous melt are both added to the sub-arc mantle source. The hydrous fluid largely controls the input in the shallow part of the subduction zone, whereas the siliceous melt dominates the flux at deeper levels. Sedimentary material is considered to be the primary source of both. The large U-Th-Ra disequilibria at the front

  18. Sources of organochlorine contaminants and mercury in seabirds from the Aleutian archipelago of Alaska: inferences from spatial and trophic variation.

    PubMed

    Ricca, Mark A; Keith Miles, A; Anthony, Robert G

    2008-11-15

    Persistent organochlorine compounds and mercury (Hg) have been detected in numerous coastal organisms of the Aleutian archipelago of Alaska, yet sources of these contaminants are unclear. We collected glaucous-winged gulls, northern fulmars, and tufted puffins along a natural longitudinal gradient across the western and central Aleutian Islands (Buldir, Kiska, Amchitka, Adak), and an additional 8 seabird species representing different foraging and migratory guilds from Buldir Island to evaluate: 1) point source input from former military installations, 2) westward increases in contaminant concentrations suggestive of distant source input, and 3) effects of trophic status (delta15N) and carbon source (delta13C) on contaminant accumulation. Concentrations of Sigma polychlorinated biphenyls (PCBs) and most chlorinated pesticides in glaucous-winged gulls consistently exhibited a 'U'-shaped pattern of high levels at Buldir and the east side of Adak and low levels at Kiska and Amchitka. In contrast, concentrations of Sigma PCBs and chlorinated pesticides in northern fulmars and tufted puffins did not differ among islands. Hg concentrations increased westward in glaucous-winged gulls and were highest in northern fulmars from Buldir. Among species collected only at Buldir, Hg was notably elevated in pelagic cormorants, and relatively high Sigma PCBs were detected in black-legged kittiwakes. Concentrations of Sigma PCBs, dichlorodiphenyldichloroethylene (p,p' DDE), and Hg were positively correlated with delta15N across all seabird species, indicating biomagnification across trophic levels. The east side of Adak Island (a former military installation) was a likely point source of Sigma PCBs and p,p' DDE, particularly in glaucous-winged gulls. In contrast, elevated levels of these contaminants and Hg, along with PCB congener and chlorinated pesticide compositional patterns detected at Buldir Island indicated exposure from distant sources influenced by a combination of

  19. Sources of organochlorine contaminants and mercury in seabirds from the Aleutian archipelago of Alaska: Inferences from spatial and trophic variation

    USGS Publications Warehouse

    Ricca, M.A.; Keith, Miles A.; Anthony, R.G.

    2008-01-01

    Persistent organochlorine compounds and mercury (Hg) have been detected in numerous coastal organisms of the Aleutian archipelago of Alaska, yet sources of these contaminants are unclear. We collected glaucous-winged gulls, northern fulmars, and tufted puffins along a natural longitudinal gradient across the western and central Aleutian Islands (Buldir, Kiska, Amchitka, Adak), and an additional 8 seabird species representing different foraging and migratory guilds from Buldir Island to evaluate: 1) point source input from former military installations, 2) westward increases in contaminant concentrations suggestive of distant source input, and 3) effects of trophic status (??15N) and carbon source (??13C) on contaminant accumulation. Concentrations of ?? polychlorinated biphenyls (PCBs) and most chlorinated pesticides in glaucous-winged gulls consistently exhibited a 'U'-shaped pattern of high levels at Buldir and the east side of Adak and low levels at Kiska and Amchitka. In contrast, concentrations of ?? PCBs and chlorinated pesticides in northern fulmars and tufted puffins did not differ among islands. Hg concentrations increased westward in glaucous-winged gulls and were highest in northern fulmars from Buldir. Among species collected only at Buldir, Hg was notably elevated in pelagic cormorants, and relatively high ?? PCBs were detected in black-legged kittiwakes. Concentrations of ?? PCBs, dichlorodiphenyldichloroethylene (p,p??? DDE), and Hg were positively correlated with ??15N across all seabird species, indicating biomagnification across trophic levels. The east side of Adak Island (a former military installation) was a likely point source of ?? PCBs and p,p??? DDE, particularly in glaucous-winged gulls. In contrast, elevated levels of these contaminants and Hg, along with PCB congener and chlorinated pesticide compositional patterns detected at Buldir Island indicated exposure from distant sources influenced by a combination of atmospheric

  20. THE EXTENT OF SEA FLOOR VOLCANISM AND NATURE OF PRIMITIVE MAGMAS IN THE WESTERN ALEUTIANS

    NASA Astrophysics Data System (ADS)

    Yogodzinski, G. M.; Turka, J.; Portnyagin, M.; Kelemen, P. B.; Vervoort, J. D.; Sims, K. W.; Bindeman, I. N.

    2009-12-01

    Results of the 2005 Western Aleutian Volcano Expedition (WAVE) and the June 2009 cruise of the German-Russian KALMAR project (Kamchatka-Aleutian Margin) include the discovery of seafloor volcanism at the Ingenstrem Depression and at unnamed seamounts located 300 km west of Buldir Island, the westernmost emergent volcano in the Aleutians. The newly discovered features fall on a volcanic line connecting Buldir and other emergent volcanoes to Piip Seamount, which is located in the far west. These discoveries suggest that the surface expression of Aleutian volcanism slips below sea level at 175°E, but is otherwise continuous from 170°W to 167°E. Geochemical results from the Ingenstrem Depression (60 km west of Buldir) define two compositional groups, which provide insight into the nature of primitive Aleutian magmatism. Low-Sr lavas (<700 ppm Sr) are basalts and andesites with moderately enriched trace element patterns (La/Yb 4-8, Sr/Y<30) and relatively radiogenic Sr (87/86=0.7031-0.7033), typical of IAB. High-Sr lavas (>700 ppm) are plagioclase and hornblende-phyric andesites and dacites with fractionated trace element patterns (Sr/Y>50) and low Y (<12 ppm) and HREE. Sr isotopes for all lavas are inversely correlated with Sr/Y and SiO2, so the most felsic samples (65-67% SiO2), which have the highest Sr abundances and most fractionated trace element patterns (Sr/Y>120) are also the most isotopically depleted (87/86<0.7028). Major and trace elements are well correlated with isotopes defining primitive end-members at 87/86<0.7027 (high-Sr), and >0.7032 (low Sr). The narrow range for Nd isotopes (8.5-9.5 epsNd) suggests that the main source of Sr and Nd may be seawater-altered subducted oceanic crust; however, oxygen isotopes on olivine and hornblende separates are similar to MORB for both groups (delta18O=5.1-5.6 per-mil, olivine-equ). Available data do not identify a high-Sr lava with whole-rock Mg# and olivine phenocryst compositions appropriate for equilibration

  1. Cathodic arcs

    SciTech Connect

    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.

  2. Sr-isotopic composition of marbles from the Puerto Galera area (Mindoro, Philippines): additional evidence for a Paleozoic age of a metamorphic complex in the Philippine island arc

    SciTech Connect

    Knittel, U.; Daniels, U.

    1987-02-01

    The Sr-isotopic composition of marbles from the Puerto Galera area (Mindoro, Philippines) is compatible with either a Tertiary or a Paleozoic age. The former is considered as unlikely because nonmetamorphic sediments of that age overlie the metamorphic complex. This implies that the metamorphic complex does not represent the basement of the Philippine arc but is an accreted terrane.

  3. Geochemical components in a Cretaceous island arc: The Th/La-(Ce/Ce*)Nd diagram and implications for subduction initiation in the inter-American region

    NASA Astrophysics Data System (ADS)

    Hastie, Alan R.; Mitchell, Simon F.; Treloar, Peter J.; Kerr, Andrew C.; Neill, Iain; Barfod, Dan N.

    2013-03-01

    Tectonic models of the evolution of the inter-American region show that induced subduction initiation/polarity reversal is required in order to isolate the Caribbean as a separate plate. However, the timing and mechanism of this subduction initiation/reversal are still controversial. In order to shed light on this issue we investigate the geochemistry of arc-derived, ~ 80 Ma, basic to acidic igneous rocks from the Main Ridge Formation (MRF) in central Jamaica. The affinity of the mantle component in the MRF arc rocks can help increase our understanding of the initiation of any new subduction zone in the inter-American region. Trace element geochemistry demonstrates that the MRF mantle source component was N-MORB-like. Conversely, younger circum-Caribbean arc rocks (≤ 75 Ma) have a more enriched plume-like mantle component. Unfortunately, when considering the slab component, some of the most useful trace elements that can be used to identify the affinity of a slab flux in arc lavas (e.g., Ba) have been mobilised by subsolidus alteration processes in the MRF. Consequently, the immobile element Th/La-(Ce/Ce*)Nd discrimination diagram is proposed as a method of determining the affinity of slab components from altered igneous rocks. This diagram identifies sedimentary slab components that have potentially contaminated an arc source region, e.g., continental detritus, volcanic detritus, hydrogenous Fe-Mn oxides, fish debris-rich clay and hydrothermal sediments. In this study, the Th/La-(Ce/Ce*)Nd diagram suggests that the slab component in most of the MRF samples has a composition similar to continental detritus/GLOSS II. Additionally, several MRF samples are derived from a source region that has been fluxed with a subduction component, in part, composed of fish debris and hydrothermal sediments. These results help constrain the timing and mechanism of Cretaceous subduction initiation in the inter-American region. The geochemical components recognised in the MRF rocks

  4. Generation of continental crust in intra-oceanic arcs

    NASA Astrophysics Data System (ADS)

    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 (<10 Ma) have a CI <50, closer to the CI (~20) computed from available average continental crust estimates. Transitional CI values of 50-100 were found in the Aleutians, the Iwo-Jima segment of Izu-Bonin, the L. Antilles, Panama, Nicaragua, and Vanuatu. The geochemical signature of the Costa Rican lavas is controlled by melts from the subducting Galapagos tracks. Iwo-Jima and Vanuatu are in a similar tectonic scenario with subducting intraplate seamounts. Melts from the subducting oceanic crust are thought to significantly control the geochemical signature in the W. Aleutians and Panama. In the L. Antilles and E. Aleutians the continental signature may reflect recycling of a component derived from subducting continental sediments. Most of Izu-Bonin, Marianas, S. Scotia and Tonga arcs with a CI >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

  5. Rock magnetic and petrographical-mineralogical studies of the dredged rocks from the submarine volcanoes of the Sea-of-Okhotsk slope within the northern part of the Kuril Island Arc

    NASA Astrophysics Data System (ADS)

    Rashidov, V. A.; Pilipenko, O. V.; Petrova, V. V.

    2016-07-01

    The rock magnetic properties of the samples of dredged rocks composing the submarine volcanic edifices within the Sea-of-Okhotsk slope of the northern part of the Kuril Island Arc are studied. The measurements of the standard rock magnetic parameters, thermomagnetic analysis, petrographical studies, and microprobe investigations have been carried out. The magnetization of the studied rocks is mainly carried by the pseudo-single domain and multidomain titanomagnetite and low-Ti titanomagnetite grains. The high values of the natural remanent magnetization are due to the pseudo-single-domain structure of the titanomagnetite grains, whereas the high values of magnetic susceptibility are associated with the high concentration of ferrimagnetic grains. The highest Curie points are observed in the titanomagnetite grains of the igneous rocks composing the edifices of the Smirnov, Edelshtein, and 1.4 submarine volcanoes.

  6. Origin of primitive andesites by melt-rock reaction in the sub-arc mantle (Invited)

    NASA Astrophysics Data System (ADS)

    Rapp, R. P.

    2009-12-01

    The genetic relationship between primitive granitoids, including high-Mg andesites (HMAs) and bajaites, and primary granitoids, or "pristine" adakites, has been vigorously debated since Defant and Drummond (1991; henceforth D&D) first applied the term "adakite" to refer to Cenozoic arc magmas (andesites and dacites) "associated with young subducting lithosphere", with low Y and Yb, low high-field strength elements (HFSEs), high Sr, and high Sr/Y and (La/Yb)N ratios "relative to island arc andesite-dacite-rhyolite". These characteristics were attributed to an origin for adakites by partial melting of basaltic crust within the subducting slab (hence "slab melts"). That such a process can produce melts with the characteristics described by D&D has since been largely confirmed by dehydration melting experiments on hydrous metabasalt at ~1-4 GPa. Attention was also drawn to the geochemical similarities between "adakites" and large-ion lithophile element (LILE)-enriched, high-field strength element (HFSE) depleted magnesian andesites (HMAs) from Adak Island in the western Aleutians, first described by Kay (1978), implying a genetic relationship between primary granitoid (adakites) formed by partial melting of basaltic ocean crust in the subducting slab, transformed to garnet-amphibolite or eclogite, and primitive magnesian andesites (HMAs) with high Mg-numbers (Mg# = molar Mg/(Mg+Fe)x100) and high concentrations of Ni and Cr. What then is the true origin of these enigmatic arc magmas, with both crustal and mantle, derivative and primitive, geochemical signatures? Kay (1978) suggested a "hybrid" model, in which "hydrous melting of eclogite (slab melting) results in a small volume of dacitic melt ("pristine adakite"), which rises into the hotter overlying peridotite wedge and equilibrates with olivine and orthopyroxene, reacting with olivine until it becomes andesitic". In this paper, I will discuss the results of melt-rock reaction experiments modelling this peridotite

  7. Magmatic relationships between depleted mantle harzburgites, boninitic cumulate gabbros and subduction-related tholeiitic basalts in the Puerto Plata ophiolitic complex, Dominican Republic: Implications for the birth of the Caribbean island-arc

    NASA Astrophysics Data System (ADS)

    Escuder-Viruete, Javier; Castillo-Carrión, Mercedes; Pérez-Estaún, Andrés

    2014-05-01

    The Lower Cretaceous Puerto Plata ophiolitic complex (PPC) occurs west of the main collisional suture between the Caribbean and North American plates in the northern Dominican Republic, and imposes important constraints on the geochemical and tectonic processes associated with the birth of the Caribbean island-arc. The PPC exposes a tectonically dismembered 3.0-km-thick section of upper mantle harzburgites, lower crustal cumulate gabbroic rocks and upper crustal basaltic pillow lavas, volcanic breccias and pelagic sediments. The harzburgites exhibit a highly depleted signature in terms of their modal compositions, mineral chemistry and whole rock major and trace element contents, suggesting that they are residues after high-degrees of partial melting. Melt modeling suggests that they were similar in trace element characteristics to a boninite. In the crustal sequence, three magmatic episodes have been recognized based on field, mineral and geochemical data. The first phase is composed of the lower layered gabbronorites, which are variably deformed and recrystallized at high-temperature conditions. Trace element modeling suggests that the gabbronorites crystallized from LREE-depleted island-arc tholeiitic (IAT) melts. The second phase is composed of the intermediate layered troctolites (126 Ma), which are undeformed and preserve igneous cumulate textures. Modeling indicates that the troctolites crystallized from boninitic melts. The gabronorite-troctolite substrate was intruded by a third, supra-subduction zone tholeiitic magmatic phase at < 126 Ma, which formed the upper olivine gabbros and gabbronorites. These gabbroic rocks formed from melts similar in composition to the IAT basalts and basaltic andesites of the overlying Los Caños Fm. Contemporaneous Aptian to lower Albian mafic volcanic rocks of the Los Ranchos Fm and Cacheal complex have comparable IAT geochemical and isotopic signatures, suggesting that all of them may have erupted over a single piece of the

  8. High-alumina basalts from the Bogda Mountains suggest an arc setting for Chinese Northern Tianshan during the Late Carboniferous

    NASA Astrophysics Data System (ADS)

    Xie, Wei; Xu, Yi-Gang; Chen, Yi-Bing; Luo, Zhen-Yu; Hong, Lu-Bing; Ma, Liang; Liu, Hai-Quan

    2016-07-01

    Considerable debate persists as to the tectonic setting of the Tianshan Orogen during the Late Paleozoic, with active subduction system and intraplate large igneous provinces as two dominant schools. With aims of providing constraints on this issue, geochronological and geochemical analyses have been carried out on the Late Carboniferous high-Al basaltic lava (HAB) from the Bogda Mountains. These lavas, in conformable contact with the felsic rocks, belong to the Upper Carboniferous Liushugou Group. Zircon SHRIMP U-Pb dating of two felsic ignimbrites further suggest that they were mainly erupted during 315-319 Ma. The Bogda basaltic lava is classified as HAB given their high Al contents > 16% and their chemical resemblance to those from modern arcs such as Aleutian and Kamchatka. They are characterized by strong enrichment in large ion lithophile elements (LILE), strong negative Nb-Ta and Ti anomalies, and distinct positive Pb anomalies. Hence, they are significantly different from the mantle plume-related basalts, as exemplified by those from Siberian, Emeishan, and Tarim large igneous provinces. Instead, their MORB-like Nd-Hf-Pb isotopes and arc-like trace elements indicate that the Bogda HABs may have been generated from a mantle wedge metasomatized by sediment-derived melts. The sector and oscillatory zoning in clinopyroxene phenocrysts in the Bogda HABs is attributable to rapid dynamic crystallization during magma ascent. High Al content is due to delayed plagioclase nucleation likely by the high crystallization pressure rather than water content. Collectively, our data lend support to an island arc environment during the Late Paleozoic, probably related to southward subduction of the Paleo-Tianshan Ocean.

  9. Mt. St. Augustine, Alaska: Geochemical evolution of an eastern Aleutian volcanic center

    SciTech Connect

    Johnson, K.E. . Dept. of Geology); Harmon, R.S. . Kingsley Dunham Centre); Moorbath, S. . Dept. of Earth Sciences); Sigmarsson, O. )

    1993-04-01

    Mt. St. Augustine is a calc-alkaline Quaternary volcano, situated within Cook Inlet, Alaska. The island is composed of low- to medium-K andesite and dacite domes and pyroclastic flows. Major element variations indicate the magmatic evolution is dominantly influenced by fractionation and magma-mixing processes. Incompatible element and isotopic compositions suggest that despite its continental location, crustal assimilation is not significant factor in magmatic evolution. Alkali contents for Augustine are generally lower than elsewhere in the Aleutians (e.g. Augustine Cs/Rb = 0.016--0.024, K/Rb = 372--553; Aleutians Cs/Rb = 0.016--0.17, K/Rb = 231--745). Sr- and Nd-isotope ratios encompass narrow ranges ([sup 87]Sr/[sup 86]Sr = 0.70317--0.70343; [sup 143]Nd/[sup 144]Nd = 0.513011--0.513085), characteristic of uncontaminated mantle-derived melts. U-Th disequilibrium isotopic values also indicate little or no assimilation of evolved continental crust. Pb-isotopic ranges are also relatively restricted ([sup 206]Pb/[sup 204]Pb = 18.62--18.82; [sup 207]Pb/[sup 204]Pb = 15.54--15.57; [sup 208]Pb/[sup 204]Pb = 38.18--38.34) and comparison with north Pacific enriched (OIB) and depleted (MORB) mantle sources suggest the incorporation of only a small percentage of subducted terrigenous sediments. A model for Augustine magma genesis is proposed where parental magmas are generated by 5--20% partial melting of a lherzolite mantle with up to a 5% subducted terrigenous sediment component. The major influence of the thickened continental crust is to prevent the ascent and eruption of basaltic magma. The data exhibit no temporal variations, indicating that the magmatic system which produced the historic eruptions is well established.

  10. Potential for generation of natural gas in sediments of the convergent margin of the Aleutian Trench Area

    SciTech Connect

    Kvenvolden, K.A.; von Huene, R.

    1983-01-01

    Sediment being subducted in the eastern part of the convergent margin of the Aleutian Trench has a potential to generate large volumes of natural gas, perhaps as much as 2.8 x 10/sup 6/ m/sup 3/ of methane per km/sup 3/ of sediment, even though the content of organic carbon in the sediment is very low, averaging about 0.4%. This high potential for gas generation results primarily from the enormous volume of sediment undergoing subduction. Along the eastern Aleutian Arc-Trench system a 3-km thick sheet of sediment is being subducted at a rate of about 60 km per million years. We estimate, based on considerations of the stability requirements for gas hydrates observed as anomalous reflectors in some of our seismic records, and on one measurement in a deep well, that the geothermal gradient in this region is about 30/sup 0/C/km. Such a gradient suggests a temperature regime in which the maximum gas generation in the subducting sediment occurs beneath the upper slope. Thus the sediment of the upper slope, as opposed to that of the shelf and lower slope, could be the most prospective for gas accumulation if suitable reservoirs are present. 40 refs., 11 figs., 3 tabs.

  11. Origin of primitive ultra-calcic arc melts at crustal conditions - Experimental evidence on the La Sommata basalt, Vulcano, Aeolian Islands

    NASA Astrophysics Data System (ADS)

    Lanzo, Giovanni; Di Carlo, Ida; Pichavant, Michel; Rotolo, Silvio G.; Scaillet, Bruno

    2016-07-01

    To interpret primitive magma compositions in the Aeolian arc and contribute to a better experimental characterization of ultra-calcic arc melts, equilibrium phase relations have been determined experimentally for the La Sommata basalt (Som-1, Vulcano, Aeolian arc). Som-1 (Na2O + K2O = 4.46 wt.%, CaO = 12.97 wt.%, MgO = 8.78 wt.%, CaO/Al2O3 = 1.03) is a reference primitive ne-normative arc basalt with a strong ultra-calcic affinity. The experiments have been performed between 44 and 154 MPa, 1050 and 1150 °C and from NNO + 0.2 to NNO + 1.9. Fluid-present conditions were imposed with H2O-CO2 mixtures yielding melt H2O concentrations from 0.7 to 3.5 wt.%. Phases encountered include clinopyroxene, olivine, plagioclase and Fe-oxide. Clinopyroxene is slightly earlier than olivine in the crystallization sequence. It is the liquidus phase at 150 MPa, being joined by olivine on the liquidus between 44 and 88 MPa. Plagioclase is the third phase to appear in the crystallization sequence and orthopyroxene was not found. Experimental clinopyroxenes (Fs7-16) and olivines (Fo78-92) partially reproduce the natural phenocryst compositions (respectively Fs5-7 and Fo87-91). Upon progressive crystallization, experimental liquids shift towards higher SiO2 (up to ~ 55 wt.%), Al2O3 (up to ~ 18 wt.%) and K2O (up to ~ 5.5 wt.%) and lower CaO, MgO and CaO/Al2O3. Experimental glasses and natural whole-rock compositions overlap, indicating that progressive crystallization of Som-1 type melts can generate differentiated compositions such as those encountered at Vulcano. The low pressure cotectic experimental glasses reproduce glass inclusions in La Sommata clinopyroxene but contrast with glass inclusions in olivine which preserve basaltic melts more primitive than Som-1. Phase relations for the La Sommata basalt are identical in all critical aspects to those obtained previously on a synthetic ultra-calcic arc composition. In particular, clinopyroxene + olivine co-saturation occurs at very low

  12. Identification of a nonvirion protein of Aleutian disease virus: mink with Aleutian disease have antibody to both virion and nonvirion proteins.

    PubMed Central

    Bloom, M E; Race, R E; Wolfinbarger, J B

    1982-01-01

    We studied Aleutian disease virus polypeptides in Crandall feline kidney (CRFK) cells. When CRFK cells labeled with [35S]methionine at 60 h postinfection were studied by immunoprecipitation with sera from infected mink, the major Aleutian disease virus virion polypeptides (p85 and p75) were consistently identified, as was a 71,000-dalton nonvirion protein (p71). The peptide maps of p85 and p75 were similar, but the map of p71 was different. p85, p75, and p71 were all precipitated by sera from Aleutian disease virus-infected mink, including those with signs of progressive disease, but heterologous sera raised against purified Aleutian disease virus did not precipitate the nonvirion p71. These results indicated that the nonvirion p71 was unrelated to p85 and p75 and further suggested that mink infected with Aleutian disease virus develop antibody to nonvirion, as well as structural, viral proteins. Images PMID:6287034

  13. The Global Array of Primitve Arc Melts

    NASA Astrophysics Data System (ADS)

    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

  14. Sedimentation and deformation in the Amlia Fracture Zone sector of the Aleutian Trench

    USGS Publications Warehouse

    Scholl, D. W.; Vallier, T.L.; Stevenson, A.J.

    1982-01-01

    subducting oceanic crust. Up-to-arc extensional faulting can be attributed to the downbending of the Pacific plate into the Aleutian subduction zone. The rupturing direction and dip is controlled by zones of crustal weakness that parallel north Pacific magnetic anomalies, which were formed south of a late Cretaceous-early Tertiary spreading center (Kula-Pacific Ridge). The strike of these anomalies is fortuitously nearly parallel to the Amlia sector. The up-to-arc fracturing style may locally assist in elevating blocks of trench deposits to form the toe of the trench's landward slope, which is in part underlain by a compressionally thickened accretionary mass of older trench deposits. Compressional structures that can be related to underthrusting are only indistinctly recorded in the turbidite wedge that underlies the trench floor. ?? 1982.

  15. Combined mantle plume-island arc model for the formation of the 2.9 Ga sumozero-kenozero greenstone belt, SE baltic shield: Isotope and trace element constraints

    NASA Astrophysics Data System (ADS)

    Puchtel, I. S.; Hofmann, A. W.; Amelin, Yu. V.; Garbe-Schönberg, C.-D.; Samsonov, A. V.; Shchipansky, A. A.

    1999-11-01

    The Sumozero-Kenozero greenstone belt in the SE Baltic Shield is ˜400 km long and up to 50 km wide and includes two main units with a total thickness of ˜5 km. The lower unit consists of oceanic plateau-type submarine mafic-ultramafic lavas. The upper unit is made up of island arc-type volcanic BADR (basalt-andesite-dacite-rhyolite)-series rocks and adakite-series subvolcanic rhyolites. Both units are separated by major thrust zones from the 3.2 Ga TTG-gneisses of the Vodla Block microcontinent. Komatiites of the lower unit were derived from a liquid containing ˜30% MgO that erupted at a temperature of ˜1570°C. The komatiite liquid began melting at depths of 300-400 km in a mantle plume. The plume was 250°C hotter than the ambient mantle and had the thermal potential to produce oceanic crust with an average thickness of ˜35 km, which was at least in part unsubductable. The lower unit mafic-ultramafic lavas have high ɛNd(T) of +2.7 ± 0.3, relatively unradiogenic Pb isotope compositions (μ 1 = 8.73 ± 0.20), are depleted in highly incompatible elements, and show Nb-maxima (Nb/Nb∗ = 1.2 ± 0.2, Nb/U = 43 ± 6). These parameters are similar to those found in a number of early Precambrian uncontaminated greenstones and in recent Pacific oceanic flood basalts (OFB). They are regarded as plume source characteristics. The BADR-series mafic-intermediate to felsic volcanic rocks and subvolcanic adakitic-series rhyolites from the upper unit have island arc geochemical signatures (enrichment in highly incompatible elements, large negative HFSE-anomalies, Nb/Nb∗ = 0.32 ± 0.10, Nb/U = 8.8 ± 2.5), but are characterized by high positive ɛNd(T) values of +2.4 ± 1.2, indistinguishable from the lower unit mafic-ultramafic sequences. They represent mantle wedge-derived and slab-derived melts, respectively, erupted in the inner and frontal parts of an intraoceanic island arc. U-Pb zircon age of 2875 ± 2 Ma for the upper unit BADR-series felsic volcanic rocks, and Pb

  16. 75 FR 69600 - Fisheries of the Exclusive Economic Zone Off Alaska; Pacific Ocean Perch in the Eastern Aleutian...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-11-15

    ... Economic Zone Off Alaska; Pacific Ocean Perch in the Eastern Aleutian District of the Bering Sea and... directed fishing for Pacific ocean perch in the Eastern Aleutian District of the Bering Sea and Aleutian... action is necessary to prevent exceeding the 2010 allocation of Pacific ocean perch in this...

  17. 77 FR 34262 - Fisheries of the Exclusive Economic Zone Off Alaska; Pacific Ocean Perch in the Western Aleutian...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-06-11

    ... Economic Zone Off Alaska; Pacific Ocean Perch in the Western Aleutian District of the Bering Sea and... directed fishing for Pacific ocean perch in the Western Aleutian District of the Bering Sea and Aleutian... action is necessary to prevent exceeding the 2012 allocation of Pacific ocean perch in this...

  18. 76 FR 43933 - Fisheries of the Exclusive Economic Zone Off Alaska; Pacific Ocean Perch in the Western Aleutian...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-07-22

    ... Economic Zone Off Alaska; Pacific Ocean Perch in the Western Aleutian District of the Bering Sea and... directed fishing for Pacific ocean perch in the Western Aleutian District of the Bering Sea and Aleutian... action is necessary to prevent exceeding the 2011 allocation of Pacific ocean perch in this...

  19. 75 FR 69601 - Fisheries of the Exclusive Economic Zone Off Alaska; Pacific Ocean Perch in the Central Aleutian...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-11-15

    ... Economic Zone Off Alaska; Pacific Ocean Perch in the Central Aleutian District of the Bering Sea and... directed fishing for Pacific ocean perch in the Central Aleutian District of the Bering Sea and Aleutian... action is necessary to prevent exceeding the 2010 allocation of Pacific ocean perch in this...

  20. 75 FR 69601 - Fisheries of the Exclusive Economic Zone Off Alaska; Pacific Ocean Perch in the Western Aleutian...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-11-15

    ... Economic Zone Off Alaska; Pacific Ocean Perch in the Western Aleutian District of the Bering Sea and... directed fishing for Pacific ocean perch in the Western Aleutian District of the Bering Sea and Aleutian... action is necessary to prevent exceeding the 2010 allocation of Pacific ocean perch in this...

  1. 77 FR 39440 - Fisheries of the Exclusive Economic Zone Off Alaska; Pacific Ocean Perch in the Central Aleutian...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-07-03

    ... Economic Zone Off Alaska; Pacific Ocean Perch in the Central Aleutian District of the Bering Sea and... directed fishing for Pacific ocean perch in the Central Aleutian District of the Bering Sea and Aleutian... action is necessary to prevent exceeding the 2012 allocation of Pacific ocean perch in this...

  2. 76 FR 65972 - Fisheries of the Exclusive Economic Zone Off Alaska; Pacific Ocean Perch in the Eastern Aleutian...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-10-25

    ... Economic Zone Off Alaska; Pacific Ocean Perch in the Eastern Aleutian District of the Bering Sea and... directed fishing for Pacific ocean perch in the Eastern Aleutian District of the Bering Sea and Aleutian... action is necessary to prevent exceeding the 2011 allocation of Pacific ocean perch in this...

  3. Using ecological function to develop recovery criteria for depleted species: sea otters and kelp forests in the Aleutian archipelago

    USGS Publications Warehouse

    Estes, James A.; Tinker, M. Tim; Bodkin, James L.

    2010-01-01

    Recovery criteria for depleted species or populations normally are based on demographic measures, the goal being to maintain enough individuals over a sufficiently large area to assure a socially tolerable risk of future extinction. Such demographically based recovery criteria may be insufficient to restore the functional roles of strongly interacting species. We explored the idea of developing a recovery criterion for sea otters (Enhydra lutris) in the Aleutian archipelago on the basis of their keystone role in kelp forest ecosystems. We surveyed sea otters and rocky reef habitats at 34 island-time combinations. The system nearly always existed in either a kelp-dominated or deforested phase state, which was predictable from sea otter density. We used a resampling analysis of these data to show that the phase state at any particular island can be determined at 95% probability of correct classification with information from as few as six sites. When sea otter population status (and thus the phase state of the kelp forest) was allowed to vary randomly among islands, just 15 islands had to be sampled to estimate the true proportion that were kelp dominated (within 10%) with 90% confidence. We conclude that kelp forest phase state is a more appropriate, sensitive, and cost-effective measure of sea otter recovery than the more traditional demographically based metrics, and we suggest that similar approaches have broad potential utility in establishing recovery criteria for depleted populations of other functionally important species.

  4. Bald eagles and sea otters in the Aleutian Archipelago: indirect effects of trophic cascades.

    PubMed

    Anthony, Robert G; Estes, James A; Ricca, Mark A; Miles, A Keith; Forsman, Eric D

    2008-10-01

    Because sea otters (Enhydra lutris) exert a wide array of direct and indirect effects on coastal marine ecosystems throughout their geographic range, we investigated the potential influence of sea otters on the ecology of Bald Eagles (Haliaeetus leucocephalus) in the Aleutian Islands, Alaska, USA. We studied the diets, productivity, and density of breeding Bald Eagles on four islands during 1993-1994 and 2000-2002, when sea otters were abundant and scarce, respectively. Bald Eagles depend on nearshore marine communities for most of their prey in this ecosystem, so we predicted that the recent decline in otter populations would have an indirect negative effect on diets and demography of Bald Eagles. Contrary to our predictions, we found no effects on density of breeding pairs on four islands from 1993-1994 to 2000-2002. In contrast, diets and diet diversity of Bald Eagles changed considerably between the two time periods, likely reflecting a change in prey availability resulting from the increase and subsequent decline in sea otter populations. The frequency of sea otter pups, rock greenling (Hexagammus lagocephalus), and smooth lumpsuckers (Aptocyclus ventricosus) in the eagle's diet declined with corresponding increases in Rock Ptarmigan (Lagopus mutus), Glaucous-winged Gulls (Larus glaucescens), Atka mackerel (Pleurogrammus monopterygius), and various species of seabirds during the period of the recent otter population decline. Breeding success and productivity of Bald Eagles also increased during this time period, which may be due to the higher nutritional quality of avian prey consumed in later years. Our results provide further evidence of the wide-ranging indirect effects of sea otter predation on nearshore marine communities and another apex predator, the Bald Eagle. Although the indirect effects of sea otters are widely known, this example is unique because the food-web pathway transcended five species and several trophic levels in linking one apex predator

  5. Bald eagles and sea otters in the Aleutian Archipelago: indirect effects of trophic cascades.

    USGS Publications Warehouse

    Anthony, R.G.; Estes, J.A.; Ricca, M.A.; Miles, A.K.; Forsman, E.D.

    2008-01-01

    Because sea otters (Enhydra lutris) exert a wide array of direct and indirect effects on coastal marine ecosystems throughout their geographic range, we investigated the potential influence of sea otters on the ecology of Bald Eagles (Haliaeetus leucocephalus) in the Aleutian Islands, Alaska, USA. We studied the diets, productivity, and density of breeding Bald Eagles on four islands during 1993-1994 and 2000-2002, when sea otters were abundant and scarce, respectively. Bald Eagles depend on nearshore marine communities for most of their prey in this ecosystem, so we predicted that the recent decline in otter populations would have an indirect negative effect on diets and demography of Bald Eagles. Contrary to our predictions, we found no effects on density of breeding pairs on four islands from 1993-1994 to 2000-2002. In contrast, diets and diet diversity of Bald Eagles changed considerably between the two time periods, likely reflecting a change in prey availability resulting from the increase and subsequent decline in sea otter populations. The frequency of sea otter pups, rock greenling (Hexagammus lagocephalus), and smooth lumpsuckers (Aptocyclus ventricosus) in the eagle's diet declined with corresponding increases in Rock Ptarmigan (Lagopus mutus), Glaucous-winged Gulls (Larus glaucescens), Atka mackerel (Pleurogrammus monopterygius), and various species of seabirds during the period of the recent otter population decline. Breeding success and productivity of Bald Eagles also increased during this time period, which may be due to the higher nutritional quality of avian prey consumed in later years. Our results provide further evidence of the wide-ranging indirect effects of sea otter predation on nearshore marine communities and another apex predator, the Bald Eagle. Although the indirect effects of sea otters are widely known, this example is unique because the food-web pathway transcended five species and several trophic levels in linking one apex predator

  6. Microgranular enclaves in island-arc andesites: A possible link between known epithermal Au and potential porphyry Cu-Au deposits in the Tulasu ore cluster, western Tianshan, Xinjiang, China

    NASA Astrophysics Data System (ADS)

    Zhao, Xiaobo; Xue, Chunji; Symons, David T. A.; Zhang, Zhaochong; Wang, Honggang

    2014-05-01

    The successful exploration for porphyry copper deposit in western Tianshan, Xinjiang, faces great challenge. Tulasu basin is an important epithermal gold ore cluster in western Tianshan, which was formed in a southwest-Pacific-type island-arc setting during the late Paleozoic by the southward subduction of the North Tianshan ocean beneath the Yili plate. Porphyry Cu-Au deposits are possibly to be found at depth or adjacent to these epithermal gold deposits. Some sulfide-mineralized microgranular enclaves of monzonite porphyry and microdiorite were found in andesites of the Tawuerbieke gold district, Tulasu basin. The enclaves are randomly distributed, with generally round or subangular shape and commonly clearly defined within their host andesite, and have a chilled surrounding margin of andesite. The monzonite porphyry enclaves (MPE) exhibit porphyritic texture with the phenocrysts of plagioclase and K-feldspar. The microdiorite enclaves (MDE) are mainly composed of plagioclase and hornblende with an aplitic texture and massive structure. The host andesites show porphyritic texture, with the phenocrysts major of plagioclase, minor of hornblende and clinopyroxene. The groundmass consists of short-column plagioclase and minor clinopyroxene with a hyalopilitic texture. Zircon grains from a MPE sample yield a weighted 206Pb/238U age of 356.2 ± 4.3 Ma (n = 13, MSWD = 1.11), which is effectively coincident with the 360.5 ± 3.4 Ma (n = 20, MSWD = 0.61) of an andesite sample within analytical error, indicating that they were coeval. In addition, the MPE, MDE and the andesite samples share similar normalized incompatible element and rare earth element patterns that are characterized by a pronounced enrichment of large ion lithophile elements and a deficit of high field strength elements. Moreover, the samples show similar Nd isotope compositions to the contemporary andesites and basaltic andesites. Detailed petrology, geochronology and geochemistry studies suggest that

  7. Isotope geochemistry of recent magmatism in the Aegean arc: Sr, Nd, Hf, and O isotopic ratios in the lavas of Milos and Santorini-geodynamic implications

    USGS Publications Warehouse

    Briqueu, L.; Javoy, M.; Lancelot, J.R.; Tatsumoto, M.

    1986-01-01

    In this comparative study of variations in the isotopic compositions (Sr, Nd, O and Hf) of the calc-alkaline magmas of the largest two volcanoes, Milos and Santorini, of the Aegean arc (eastern Mediterranean) we demonstrate the complexity of the processes governing the evolution of the magmas on the scale both of the arc and of each volcano. On Santorini, the crustal contamination processes have been limited, effecting the magma gradually during its differentiation. The most differentiated lavas (rhyodacite and pumice) are also the most contaminated. On Milos, by contrast, these processes are very extensive. They are expressed in the 143Nd/144Nd vs. 87Sr/86Sr diagram as a continuous mixing curve between a mantle and a crustal end member pole defined by schists and metavolcanic rocks outcropping on these volcanoes. In contrast with Santorini, the least differentiated lavas on Milos are the most contaminated. These isotopic singularities can be correlated with the geodynamic evolution of the Aegean subduction zone, consisting of alternating tectonic phases of distension and compression. The genesis of rhyolitic magmas can be linked to the two phases of distension, and the contamination of the calc-alkaline mantle-derived magmas with the intermediate compressive phase. The isotopic characteristics of uncontaminated calc-alkaline primitive magmas of Milos and Santorini are directly comparable to those of magmas generated in subduction zones for which a contribution of subducted sediments to partial melts from the mantle is suggested, such as in the Aleutian, Sunda, and lesser Antilles island arcs. However, in spite of the importance of the sediment pile in the eastern Mediterranen oceanic crust (6-10 km), the contribution of the subducted terrigenous materials remains of limited amplitude. ?? 1986.

  8. Cloud Arcs

    Atmospheric Science Data Center

    2013-04-19

    ... causing much of the air near the centers of the arcs to rise. This air spreads out horizontally in all directions as it rises and ... is now quite weak and on meeting the undisturbed air it can rise again slightly - possibly assisting in the formation of new small cumulus ...

  9. Geochronology and geochemistry of rhyolites from Hormuz Island, southern Iran: A new record of Cadomian arc magmatism in the Hormuz Formation

    NASA Astrophysics Data System (ADS)

    Faramarzi, Narges Sadat; Amini, Sadraddin; Schmitt, Axel Karl; Hassanzadeh, Jamshid; Borg, Gregor; McKeegan, Kevin; Razavi, Seyed Mohammad Hosein; Mortazavi, Seyed Mohsen

    2015-11-01

    Hormuz Island, a salt-gypsum dome in the Persian Gulf in southern Iran, is a complex halotectonic melange comprising evaporites, carbonates, volcanic and volcaniclastic rocks, as well as low-grade metamorphic and sedimentary rocks. Based on trace element (including rare earth elements REE) compositions of whole rocks and zircon, Hormuz rhyolites are inferred to have formed from subduction-related magmas generated in an active continental margin setting. Ion microprobe analyses of zircon crystals yielded concordant U-Pb ages with weighted mean 206Pb/238U age of 558 ± 7 Ma (juvenile zircons in contrast to those from previous magmatic episodes or xenocrysts) along with younger and older discordant ages which likely represent Pb loss and the presence of xenocrystic domains, respectively. Trace element ratios and in particular REE patterns of juvenile zircon from Hormuz rhyolites indicate crystallization from continental crustal source rocks typical for subduction environments. The concordant 206Pb/238U zircon age agrees with ages obtained from most other structural zones of Iran which indicate regional consolidation of igneous basement during the Neoproterozoic to Early Cambrian. Furthermore, Hormuz rhyolite ages and compositions correlate with counterparts that co-evolved along the northern margin of Gondwana, and are now preserved along the southern coast of the Persian Gulf. Hormuz rhyolites erupted synchronously with the deposition of carbonates and evaporites, suggesting that volcanism occupied an extensional backarc or retroarc setting. Such depositional environments predominated in the northern Gondwana continental margin where convergent (Proto-Tethyan) and extensional (Najd) tectonic regimes coexisted.

  10. Arc of opportunity.

    PubMed

    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. PMID:21878026

  11. Mount Dutton volcano, Alaska: Aleutian arc analog to Unzen volcano, Japan

    NASA Astrophysics Data System (ADS)

    Miller, T. P.; Chertkoff, D. G.; Eichelberger, J. C.; Coombs, M. L.

    1999-04-01

    Holocene eruptions from Mount Dutton, a small Late Quaternary volcano near the tip of the Alaska Peninsula, bear strong physical and petrologic similarities to the 1990-1995 Unzen Fugendake eruption in Japan. The volcano had a protracted phase of effusive calcalkaline andesitic (54-59 wt.% SiO 2) cone-building in the late Pleistocene followed by an abrupt switch to more silicic (˜65 wt.% SiO 2) lavas, emplaced as a central summit cluster of steep-sided domes beginning in the early Holocene. The flanks of the volcano are mantled by pyroclastic flows, debris flows, and talus formed as a result of gravitational dome collapse. Disequilibrium mineral assemblages, including coexisting quartz and olivine in eruptive episodes ranging from the initial cone-building basaltic andesite lavas to the latest Holocene dacite domes, suggest extensive magma mixing. In addition, up to meter-sized, pillow-like cognate mafic enclaves of hornblende+plagioclase+glass are common in the latest of the summit dacite domes. Mineralogical evidence and bulk chemical data indicate the enclaves represent a high-alumina basalt parent with variable and subordinate reservoir contaminant, and the host lava is reservoir magma with variable and subordinate basaltic contaminant. Mount Dutton's history and petrology can be interpreted as reflecting the monotonous repetitive intrusion of mantle-derived mafic magma into a silicic crystal-rich crustal reservoir. During the Holocene, these injections resulted in the extrusion of partially crystallized, viscous, `sticky' central domes which typically failed by collapse resulting in small volume Merapi-type flowage deposits. We speculate that slow introduction of mafic magma into the silicic chamber leads both to enclave formation and to the effusive eruption style. Mount Dutton volcano experienced severe shallow earthquake swarms in 1984, 1988, and to a lesser extent in 1991; although none of these swarms resulted in an eruption, their epicenter distribution and volcanic-tectonic character indicate they recorded the movement of magma at shallow depth beneath the volcano. The lessons of Unzen and Montserrat suggest that, despite limited tephra production, these small volcanic centers with central dome complexes present a serious hazard to life and property.

  12. Temporal Variation in Fish Mercury Concentrations within Lakes from the Western Aleutian Archipelago, Alaska

    PubMed Central

    Kenney, Leah A.; Eagles-Smith, Collin A.; Ackerman, Joshua T.; von Hippel, Frank A.

    2014-01-01

    We assessed temporal variation in mercury (Hg) concentrations of threespine stickleback (Gasterosteus aculeatus) from Agattu Island, Aleutian Archipelago, Alaska. Total Hg concentrations in whole-bodied stickleback were measured at two-week intervals from two sites in each of two lakes from June 1 to August 10, 2011 during the time period when lakes were ice-free. Across all sites and sampling events, stickleback Hg concentrations ranged from 0.37–1.07 µg/g dry weight (dw), with a mean (± SE) of 0.55±0.01 µg/g dw. Mean fish Hg concentrations declined by 9% during the study period, from 0.57±0.01 µg/g dw in early June to 0.52±0.01 µg/g dw in mid-August. Mean fish Hg concentrations were 6% higher in Loon Lake (0.56±0.01 µg/g dw) than in Lake 696 (0.53±0.01 µg/g dw), and 4% higher in males (0.56±0.01 µg/g dw) than in females (0.54±0.01 µg/g dw). Loon Lake was distinguished from Lake 696 by the presence of piscivorous waterbirds during the breeding season. Mercury concentrations in stickleback from Agattu Island were higher than would be expected for an area without known point sources of Hg pollution, and high enough to be of concern to the health of piscivorous wildlife. PMID:25029042

  13. Geothermal Drilling In The Aleutians Reveals New Insights On Volcanic History Of Akutan Volcano

    NASA Astrophysics Data System (ADS)

    Stelling, P. L.

    2013-12-01

    In 2010, two thermal gradient wells were drilled in the Hot Springs Bay Valley geothermal resource area on Akutan Island, Alaska. Well TG-2 was drilled in the region of hot springs occurrence near the mouth of the valley and reached a depth of 253 m (833'). Well TG-4 was drilled near the head of the valley, closer to the current volcano, and reached a depth of 457 m (1500'). The core recovered from these wells represent the only drill core extracted from an Aleutian volcano to date and reveals an important missing piece of the surficial eruptive and erosional history of the volcano that cannot be determined from surface evaluation of recent eruptive deposits laid down on 500 ka bedrock outcrops. No intrusive rocks were encountered, indicating a rich history of surficial activity. The core is dominated (46% of recovered core) by basaltic lava flow deposits (49-52 wt% SiO2), consistent with other observed deposits on the island. These flows are interspersed with andesite lava flows (20% of core, ranging from 53-58 wt% SiO2), abundant mass wasting deposits (27% of core) and a series of ash and ash tuff layers that are some of the most silicic deposits identified at Akutan (up to 66 wt% SiO2). Ash deposits are restricted to the upper 125 m in both wells, are significantly thicker in TG-4, and are difficult to correlate between the two wells. Mass wasting deposits are diverse, including a subset characterized by matrix-supported heterolithologic breccias enclosed in a crystalline basaltic lava host. A shell-rich zone at 273 meters depth indicates that the transition between sub-marine and sub-aerial activity may be recorded in the core.

  14. Temporal variation in fish mercury concentrations within lakes from the western Aleutian Archipelago, Alaska

    USGS Publications Warehouse

    Kenney, Leah A.; Eagles-Smith, Collin A.; Ackerman, Joshua T.; von Hippel, Frank A.

    2014-01-01

    We assessed temporal variation in mercury (Hg) concentrations of threespine stickleback (Gasterosteus aculeatus) from Agattu Island, Aleutian Archipelago, Alaska. Total Hg concentrations in whole-bodied stickleback were measured at two-week intervals from two sites in each of two lakes from June 1 to August 10, 2011 during the time period when lakes were ice-free. Across all sites and sampling events, stickleback Hg concentrations ranged from 0.37–1.07 µg/g dry weight (dw), with a mean (± SE) of 0.55±0.01 µg/g dw. Mean fish Hg concentrations declined by 9% during the study period, from 0.57±0.01 µg/g dw in early June to 0.52±0.01 µg/g dw in mid-August. Mean fish Hg concentrations were 6% higher in Loon Lake (0.56±0.01 µg/g dw) than in Lake 696 (0.53±0.01 µg/g dw), and 4% higher in males (0.56±0.01 µg/g dw) than in females (0.54±0.01 µg/g dw). Loon Lake was distinguished from Lake 696 by the presence of piscivorous waterbirds during the breeding season. Mercury concentrations in stickleback from Agattu Island were higher than would be expected for an area without known point sources of Hg pollution, and high enough to be of concern to the health of piscivorous wildlife.

  15. GLORIA side-scan imagery of Aleutian basin, Bering Sea slope and Abyssal plain

    SciTech Connect

    Carlson, P.R.; Cooper, A.K.; Gardner, J.V.; Karl, H.A.; Marlow, M.S.; Stevenson, A.J.; Huggett, Q.; Kenyon, N.; Parson, L.

    1987-05-01

    During July-September 1986, about 700,000 km/sup 2/ of continental slope and abyssal plain of the Aleutian basin, Bering Sea, were insonified with GLORIA (Geological Long Range Inclined Asdic) side-scane sonar. A sonar mosaic displays prominent geomorphic features including the massive submarine canyons of the Beringian and the northern Aleutian Ridge slopes and shows well-defined sediment patterns including large deep-sea channels and fan systems on the Aleutian basin abyssal plain. Dominant erosional and sediment transport processes on both the Beringian and the Aleutian Ridge slopes include varieties of mass movement that range from small debris flows and slides to massive slides and slumps of blocks measuring kilometers in dimension. Sediment-flow patterns that appear to be formed by sheet flow rather than channelized flow extend basinward from the numerous canyons and gullies that incise the slopes of the Beringian margin and of Bowers Ridge and some places along the Aleutian Ridge. These Beringian and Bowers canyon sediment sources, however, appear to have contributed less modern sediment to the Aleutian basin than the large, well-defined channel systems that emanate from Bering, Umnak, and Amchitka submarine canyons and extend for several hundred kilometers across the abyssal plain. This GLORIA imagery emphasizes the important contribution of the Aleutian Ridge to modern sedimentation in the deep Bering Sea.

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

    NASA Astrophysics Data System (ADS)

    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

  17. Diffuse CO 2 soil degassing and CO 2 and H 2S concentrations in air and related hazards at Vulcano Island (Aeolian arc, Italy)

    NASA Astrophysics Data System (ADS)

    Carapezza, M. L.; Barberi, F.; Ranaldi, M.; Ricci, T.; Tarchini, L.; Barrancos, J.; Fischer, C.; Perez, N.; Weber, K.; Di Piazza, A.; Gattuso, A.

    2011-10-01

    La Fossa crater on Vulcano Island is quiescent since 1890. Periodically it undergoes "crises" characterized by marked increase of temperature (T), gas output and concentration of magmatic components in the crater fumaroles (T may exceed 600 °C). During these crises, which so far did not lead to any eruptive reactivation, the diffuse CO 2 soil degassing also increases and in December 2005 an anomalous CO 2 flux of 1350 tons/day was estimated by 1588 measurements over a surface of 1.66 km 2 extending from La Fossa crater to the inhabited zone of Vulcano Porto. The crater area and two other anomalously degassing sites (Levante Beach and Palizzi) have been periodically investigated from December 2004 to August 2010 for diffuse CO 2 soil flux. They show a marked variation with time of the degassing rate, with synchronous maxima in December 2005. Carbon dioxide soil flux and environmental parameters have been also continuously monitored for over one year by an automatic station at Vulcano Porto. In order to assess the hazard of the endogenous gas emissions, CO 2 and H 2S air concentrations have been measured by Tunable Diode Laser profiles near the fumaroles of the crater rim and of the Levante Beach area, where also the viscous gas flux has been estimated. In addition, CO 2 air concentration has been measured both indoor and outdoor in an inhabited sector of Vulcano Porto. Results show that in some sites usually frequented by tourists there is a dangerous H 2S air concentration and CO 2 exceeds the hazardous thresholds in some Vulcano houses. These zones should be immediately monitored for gas hazard should a new crisis arise.

  18. Geological evolution and analysis of confirmed or suspected gas hydrate localities: Volume 10, Basin analysis, formation and stability of gas hydrates of the Aleutian Trench and the Bering Sea

    SciTech Connect

    Krason, J.; Ciesnik, M.

    1987-01-01

    Four major areas with inferred gas hydrates are the subject of this study. Two of these areas, the Navarin and the Norton Basins, are located within the Bering Sea shelf, whereas the remaining areas of the Atka Basin in the central Aleutian Trench system and the eastern Aleutian Trench represent a huge region of the Aleutian Trench-Arc system. All four areas are geologically diverse and complex. Particularly the structural features of the accretionary wedge north of the Aleutian Trench still remain the subjects of scientific debates. Prior to this study, suggested presence of the gas hydrates in the four areas was based on seismic evidence, i.e., presence of bottom simulating reflectors (BSRs). Although the disclosure of the BSRs is often difficult, particularly under the structural conditions of the Navarin and Norton basins, it can be concluded that the identified BSRs are mostly represented by relatively weak and discontinuous reflectors. Under thermal and pressure conditions favorable for gas hydrate formation, the relative scarcity of the BSRs can be attributed to insufficient gas supply to the potential gas hydrate zone. Hydrocarbon gas in sediment may have biogenic, thermogenic or mixed origin. In the four studied areas, basin analysis revealed limited biogenic hydrocarbon generation. The migration of the thermogenically derived gases is probably diminished considerably due to the widespread diagenetic processes in diatomaceous strata. The latter processes resulted in the formation of the diagenetic horizons. The identified gas hydrate-related BSRs seem to be located in the areas of increased biogenic methanogenesis and faults acting as the pathways for thermogenic hydrocarbons.

  19. Comparative pathogenicity of four strains of Aleutian disease virus for pastel and sapphire mink.

    PubMed Central

    Hadlow, W J; Race, R E; Kennedy, R C

    1983-01-01

    Information was sought on the comparative pathogenicity of four North American strains (isolates) of Aleutian disease virus for royal pastel (a non-Aleutian genotype) and sapphire (an Aleutian genotype) mink. The four strains (Utah-1, Ontario [Canada], Montana, and Pullman [Washington]), all of mink origin, were inoculated intraperitoneally and intranasally in serial 10-fold dilutions. As indicated by the appearance of specific antibody (counterimmunoelectrophoresis test), all strains readily infected both color phases of mink, and all strains were equally pathogenic for sapphire mink. Not all strains, however, regularly caused Aleutian disease in pastel mink. Infection of pastel mink with the Utah-1 strain invariably led to fatal disease. Infection with the Ontario strain caused fatal disease nearly as often. The Pullman strain, by contrast, almost never caused disease in infected pastel mink. The pathogenicity of the Montana strain for this color phase was between these extremes. These findings emphasize the need to distinguish between infection and disease when mink are exposed to Aleutian disease virus. The distinction has important implications for understanding the natural history of Aleutian disease virus infection in ranch mink. PMID:6193063

  20. Diatoms confirm coseismic uplift and subsidence along the eastern Alaska-Aleutian megathrust

    NASA Astrophysics Data System (ADS)

    Dura, T.; Briggs, R. W.; Engelhart, S. E.; Nelson, A. R.; Horton, B.

    2013-12-01

    The Alaska-Aleutian subduction zone is the source of a series of Mw 8-9.2 20th century ruptures, including the second largest historical earthquake ever recorded in 1964. Paleoseismic studies, employing coastal stratigraphic sequences, have been successfully applied at sites within the 1964 rupture zone, but geologic records are unstudied west of the 1964 rupture. Understanding the behavior of the megathrust is important because a tsunamigenic rupture could damage the west coast of the United States. Investigations in the tidal marshes of Sitkinak Island, off the southwest coast of Kodiak Island, have uncovered stratigraphic evidence of five apparent coseismic land-level changes. Radiocarbon, 210Pb, and 137Cs dating indicate this record may include the 1964 and 1788 earthquakes and some predecessors. Here, we present new paleoecological evidence that independently confirms the inference that at least four of the abrupt lithologic changes in the stratigraphy of Sitkinak Island record coseismic land-level changes. Sudden and lasting changes in fossil diatom assemblages spanning tidal lithologic contacts reveal both coseismic subsidence (mud over peat) and coseismic uplift (peat over mud) during the last 1000 years. Across the contact that may mark the 1964 earthquake, a shift from a brackish, low-marsh diatom assemblage dominated by Diploneis interrupta and Navicula cincta to a tidal flat assemblage containing Actinocyclus normanii and Synedra tabulata indicates a sudden rise in relative sea-level, which we infer to record coseismic subsidence. In contrast, diatoms show evidence of coseismic uplift across the probable 1788 contact. An abrupt transition from a fully marine assemblage containing coastal planktonic and tychoplanktonic taxa to a freshwater marsh assemblage dominated by the salt-intolerant benthic diatom Eunotia fallax is consistent with a sudden and lasting relative sea-level fall. Abrupt changes in lithology across a contact dated about ~575 cal yr

  1. Seismic Activity in Northern Izu-Bonin arc by Ocean Bottom Seismograph Observations

    NASA Astrophysics Data System (ADS)

    Obana, K.; Kamiya, S.; Kodaira, S.; Suetsugu, D.; Takahashi, N.; Sakaguchi, H.

    2006-12-01

    The Izu-Bonin Island arc is an oceanic island arc, where the Pacific plate subducts beneath the Philippine Sea plate. Suyehiro et al. (1996) found a thick andesitic middle crust with velocity of 6 km/s in northern Izu arc. Recent active seismic experiments in the Izu-Bonin arc show significant variations of the thickness of the middle crust along the volcanic front (Kodaira et al, 2005). The thickness of the middle crust shows an inverse correlation with the average P-wave crustal velocity and the SiO2 composition of the Quaternary volcanoes along the arc. Crustal evolution in the oceanic island arc is a process including magma evolution in the mantle wedge. To understand the nature of the crustal evolution in the oceanic island arc, we have to clarify structures in the mantle wedge along the arc in addition to the oceanic island arc crust. We conducted seismicity observations by a temporal ocean bottom seismograph (OBS) network in northern Izu-Bonin arc between Tori-shima and Hachijo-jima (30° to 34°N) to investigate structures of the oceanic island arc crust and the mantle wedge in northern Izu-Bonin arc by seismic tomography. The OBS network consists of 40 pop-up type OBSs with a three-component short-period seismometer. The OBSs were deployed in April 2006 and retrieved in July after about 80-day observations. The OBS data were processed with seismic data recorded at island stations on Hachijo-jima and Aoga-shima. These island stations are operated by National Research Institute for Earth Science and Disaster Prevention. From the preliminary results of the hypocenters, many earthquakes were located along the subducting Pacific plate. Along the volcanic front, shallow earthquake clusters were observed around Tori-shima and Sumisu-Jima islands. Another shallow earthquake cluster was observed near a seamount of echelon chains in the back-arc region of the Izu-Bonin arc. Earthquakes in the fore-arc region show strong attenuation at OBSs in the back-arc region

  2. Os and S isotope studies of ultramafic rocks in the Duke Island Complex, Alaska: variable degrees of crustal contamination of magmas in an arc setting and implications for Ni-Cu-PGE sulfide mineralization

    NASA Astrophysics Data System (ADS)

    Stifter, Eric C.; Ripley, Edward M.; Li, Chusi

    2016-03-01

    The Duke Island Complex is one of the several "Ural-Alaskan" intrusions of Cretaceous age that occur along the coast of SE Alaska. Significant quantities of magmatic Ni-Cu-PGE sulfide mineralization are locally found in the complex, primarily within olivine clinopyroxenites. Sulfide mineralization is Ni-poor, consistent with petrologic evidence which indicates that sulfide saturation was reached after extensive olivine crystallization. Olivine clinopyroxenites were intruded by magmas that produced sulfide-poor, adcumulate dunites. As part of a study to investigate the potential for Ni-rich sulfide mineralization in association with the dunites, a Re-Os and S isotope study of the dunites, as well as sulfide mineralization in the olivine clinopyroxenites, was initiated. Importantly, recent drilling in the complex identified the presence of sulfidic and carbonaceous country rocks that may have been involved in the contamination of magmas and generation of sulfide mineralization. γOs (110 Ma) values of two sulfidic country rocks are 1022 and 2011. δ34S values of the country rocks range from -2.6 to -16.1 ‰. 187Os/188Os ratios of sulfide minerals in the mineralization hosted by olivine clinopyroxenites are variable and high, with γOs (110 Ma) values between 151 and 2059. Extensive interaction with Re-rich sedimentary country rocks is indicated. In contrast, γOs (110 Ma) values of the dunites are significantly lower, ranging between 2 and 16. 187Os/188Os ratios increase with decreasing Os concentration. This inverse relation is similar to that shown by ultramafic rocks from several arc settings, as well as altered abyssal dunites and peridotites. The relation may be indicative of magma derivation from a sub-arc mantle that had experienced metasomatism via slab-derived fluids. Alternatively, the relation may be indicative of minor contamination of magma by crustal rocks with low Os concentrations but high 187Os/188Os ratios. A third alternative is that the low Os

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

    NASA Astrophysics Data System (ADS)

    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.

  4. Mercury and Other Metals in Feathers of Common Eider (Somateria mollissima) and Tufted Puffin (Fratercula cirrhata) from the Aleutian Chain of Alaska

    PubMed Central

    Gochfeld, Michael

    2014-01-01

    We analyzed arsenic, cadmium, chromium, lead, manganese, mercury, and selenium in the feathers of common eiders (Somateria mollissima) and tufted puffins (Fratercula cirrhata) from Amchitka and Kiska islands (Aleutians). Between species, puffins had 10 times higher chromium (arithmetic mean = 1820 ppb), 7.5 times higher selenium (mean = 6600 ppb), and 3 times higher mercury (mean = 2540 ppb) than eiders. Eiders had significantly higher levels of manganese than puffins. Puffins are higher on the food chain than eiders, which is reflected in their generally higher levels of metals in their feathers. Interisland differences were generally small, and there were few significant differences as a function of the three nuclear test locations on Amchitka. The only sex-related difference was that female puffins had higher mercury than males (arithmetic mean of 3060 ppb vs. 2270 ppb). Mean levels of metals in the feathers of puffins and eiders from the Aleutians were low compared with comparable studies elsewhere, and the relatively low levels of metals do not indicate the potential for adverse behavioral or reproductive effects in the birds themselves, nor pose concern for other consumers, including subsistence hunters. PMID:18712499

  5. Basaltic island sand provenance

    SciTech Connect

    Marsaglia, K.M. . Dept. of Geological Sciences)

    1992-01-01

    The Hawaiian Islands are an ideal location to study basaltic sand provenance in that they are a series of progressively older basaltic shield volcanoes with arid to humid microclimates. Sixty-two sand samples were collected from beaches on the islands of Hawaii, Maui, Oahu and Kauai and petrographically analyzed. The major sand components are calcareous bioclasts, volcanic lithic fragments, and monomineralic grains of dense minerals and plagioclase. Proportions of these components vary from island to island, with bioclastic end members being more prevalent on older islands exhibiting well-developed fringing reef systems and volcanic end members more prevalent on younger, volcanically active islands. Climatic variations across the island of Hawaii are reflected in the percentage of weathered detritus, which is greater on the wetter, northern side of the island. The groundmass of glassy, basaltic lithics is predominantly black tachylite, with lesser brown sideromelane; microlitic and lathwork textures are more common than holohyaline vitric textures. Other common basaltic volcanic lithic fragments are holocrystalline aggregates of silt-sized pyroxene or olivine, opaque minerals and plagioclase. Sands derived from alkalic lavas are texturally and compositionally indistinguishable from sands derived from tholeiitic lavas. Although Hawaiian basaltic sands overlap in composition with magmatic arc-derived sands in terms of their relative QFL, QmPK and LmLvLs percentages, they are dissimilar in that they lack felsic components and are more enriched in lathwork volcanic lithic fragments, holocrystalline volcanic lithic fragments, and dense minerals.

  6. Three-dimensional inversion of regional P and S arrival times in the East Aleutians and sources of subduction zone gravity highs

    NASA Astrophysics Data System (ADS)

    Abers, Geoffrey A.

    1994-03-01

    Free-air gravity highs over forearcs represent a large fraction of the power in the Earth's anomalous field, yet their origin remains uncertain. Seismic velocities, as indicators of density, are estimated here as a means to compare the relative importance of upper plate sources for the gravity high with sources in the downgoing plate. P and S arrival times for local earthquakes, recorded by a seismic network in the eastern Aleutians, are inverted for three-dimensional velocity structure between the volcanic arc and the downgoing plate. A three-dimensional ray tracing scheme is used to invert the 7974 P and 6764 S arrivals for seismic velocities and hypocenters of 635 events. One-dimensional inversions show that station P residuals are systematically 0.25-0.5 s positive at stations 0-30 km north of the Aleutian volcanic arc, indicating slow material, while residuals at stations 10-30 km south of the arc are 0.1-0.25 s negative. Both features are explained in three-dimensional inversions by velocity variations at depths less than 25-35 km. Tests using a one-dimensional or a two-dimensional slab starting model show that below 100 km depth, velocities are poorly determined and trade off almost completely with hypocenters for earthquakes at these depths. The locations of forearc velocity highs, in the crust of the upper plate, correspond to the location of the gravity high between the trench and volcanic arc. Free-air anomalies, calculated from the three-dimensional velocity inversion result, match observed gravity for a linear density-velocity relationship between 0.1 and 0.3 (Mg m-3)/(km s-1), when a 50-km-thick slab is included with a density of 0.055±0.005 Mg m-3. Values outside these ranges do not match the observed gravity. The slab alone contributes one third to one half of the total 75-150 mGal amplitude of the gravity high but predicts a high that is much broader than is observed. The inclusion of upper-plate velocity anomalies predicts the correct width of

  7. Modern salt-marsh and tidal-flat foraminifera from Sitkinak and Simeonof Islands, southwestern Alaska

    USGS Publications Warehouse

    Kemp, Andrew C.; Engelhart, Simon E.; Culver, Stephen J.; Nelson, Alan R.; Briggs, Richard W.; Haeussler, Peter J.

    2013-01-01

    We describe the modern distribution of salt-marsh and tidal-flat foraminifera from Sitkinak Island (Trinity Islands) and Simeonof Island (Shumagin Islands), Alaska, to begin development of a dataset for later use in reconstructing relative sea-level changes caused by great earthquakes along the Alaska-Aleutian subduction zone. Dead foraminifera were enumerated from a total of 58 surface-sediment samples collected along three intertidal transects around a coastal lagoon on Sitkinak Island and two intertidal transects on Simeonof Island. Two distinctive assemblages of salt-marsh foraminifera were recognized on Sitkinak Island. Miliammina fusca dominated low-marsh settings and Balticammina pseudomacrescens dominated the high marsh. These two species make up >98% of individuals. On Simeonof Island, 93% of individuals in high-marsh settings above mean high water were B. pseudomacrescens. The tidal flat on Simeonof Island was dominated by Cibicides lobatulus (60% of individuals), but the lower limit of this species is subtidal and was not sampled. These results indicate that uplift or subsidence caused by repeated earthquakes along the Alaska-Aleutian subduction zone could be reconstructed in coastal sediments using alternating assemblages of near monospecific B. pseudomacrescens and low-marsh or tidal-flat foraminifera.

  8. Weld arc simulator

    DOEpatents

    Burr, Melvin J.

    1990-01-30

    An arc voltage simulator for an arc welder permits the welder response to a variation in arc voltage to be standardized. The simulator uses a linear potentiometer connected to the electrode to provide a simulated arc voltage at the electrode that changes as a function of electrode position.

  9. Buldir Depression - A Late Tertiary graben on the Aleutian Ridge, Alaska

    USGS Publications Warehouse

    Marlow, M. S.; Scholl, D. W.; Buffington, E.C.; Boyce, R.E.; Alpha, T.R.; Smith, P.J.; Shipek, C.J.

    1970-01-01

    Buldir Depression is a large, rectilinear basin that lies on the northern edge of the Aleutian Ridge and is aligned with the arcuate chain of active volcanoes on the ridge crest. The depression appears to be a volcanic-tectonic feature, which began to form in Late Tertiary time and which is still forming. It is a graben formed by extensional rifting and accompanied by contemporaneous volcanism on the Aleutian Ridge. Subsidence rates for the depression are estimated at 20-70 cm/1,000 years. Sediments in the depression are 300 m thick and are probably pelagic and turbidite deposits of Pleistocene age. The turbidites were apparently derived from the plateau area of the Aleutian Ridge surrounding the depression. Older sediments on the northern slope of the Aleutian Ridge have a maximum thickness of 550 m and are deformed and slumped toward the Bering Sea. These sediments are postulated to overlie a mid-flank terrace on the northern Aleutian Ridge that titled to the north during the formation of Buldir Depression. ?? 1970.

  10. Microscopic analysis of feather and hair fragments associated with human mummified remains from Kagamil Island, Alaska

    USGS Publications Warehouse

    Dove, C.J.; Peurach, S.C.

    2002-01-01

    Human mummified remains of 34 different infant and adult individuals from Kagamil Island, Alaska, are accessioned in the Department of Anthropology, National Museum of Natural History, Smithsonian Institution. Kagamil Island is one of the small islands in the Island of Four Mountains group of the Aleutian Islands, Alaska and is well known for the mummy caves located on the southwest coast of the island. The Kagamil mummy holdings at the Smithsonian represent one of the largest, best documented and preserved collections of this type. Although these specimens are stored in ideal conditions, many small feather and hair fragments have become loose or disassociated from the actual mummies over the years. This preliminary investigation of fragmentary fiber material retrieved from these artifacts is the first attempt to identify bird and mammal species associated with the mummified remains of the Kagamil Island, Alaska collection and is part of the ongoing research connected with these artifacts.

  11. Gas arc constriction for plasma arc welding

    NASA Technical Reports Server (NTRS)

    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.

  12. Mantle Melting as a Function of Water Content in Arcs

    NASA Astrophysics Data System (ADS)

    Kelley, K. A.; Plank, T.; Newman, S.; Stolper, E.; Grove, T. L.; Parman, S.; Hauri, E.

    2003-12-01

    Subduction zone magmas are characterized by high concentrations of dissolved H2O, presumably derived from the subducted plate and ultimately responsible for melt generation in this tectonic setting. Almost ten years ago, Stolper and Newman (EPSL, 1994) illustrated a linear relationship between the concentration of water (H2Oo) and the fraction of melting (F) in the mantle beneath the Mariana back-arc. Here we report new major element and volatile data for olivine-hosted melt inclusions from the Mariana Islands to test this relationship for melting beneath an arc. Basaltic melt inclusions from the Mariana arc have water contents (2.3-6.1 wt% H2O) significantly higher than all basaltic glasses or melt inclusions from the Mariana back-arc (0.2-2.2 wt% H2O). We use TiO2 as a proxy for F, after correcting for crystal fractionation, and evaluate the Ti source composition with a model based on Ti/Y variations in mid-ocean ridge basalts (MORBs). Each calculated F thus represents the amount of mantle melting for a single melting episode. Even after accounting for mantle depletion, the TiO2 concentrations in Mariana arc magmas record higher extents of mantle melting (F = 10-30%) than recorded in back-arc magmas (F = 5-24%). As a whole, the Mariana arc broadly extends the linear H2Oo-F array defined by the back-arc, although in detail the islands show important differences. Two islands from the Mariana arc (Guguan and Pagan) define a H2Oo-F slope similar to the Mariana back-arc, suggesting similar mantle potential temperature beneath the arc and back-arc ( ˜1360 +/- 20° C). Melts from Agrigan island, however, indicate a steeper slope suggestive both of cooler mantle beneath Agrigan and of along-strike thermal variations beneath the Mariana Islands. Both the arc and back-arc arrays project to finite F at zero water in the mantle, providing evidence for decompression melting in both settings. These relationships may be extended globally to other back-arc and arc systems

  13. Clinical Chemical Studies in Aleutian Disease of Mink

    PubMed Central

    Gershbein, Leon L.; Spencer, Kathryn L.

    1964-01-01

    Clinical chemical determinations were carried out on blood removed by cardiac puncture from 49 mink affected with Aleutian disease and 25 normal animals and the respective differences tested for statistical significance. Blood urea nitrogen, serum total protein and globulin, thymol turbidity, glutamic oxalacetic and glutamic pyruvic transaminases and amylase were definitely elevated in the affected animals whereas serum calcium, albumin and A/G ratio were depressed. No statistically significant difference was apparent between the two groups in the comparison of inorganic phosphorus, alkaline and acid phosphatases, bilirubin, total cholesterol and esters, cephalin-cholesterol flocculation (3+ in each case), sodium, potassium, chloride, CO2-combining power, leucine aminopeptidase and lactic dehydrogenase (means: over 2,000 u./ml.). For both the control and affected mink, the distribution of serum lactic dehydrogenase isozymes resembled that of human homologous serum hepatitis. Electrophoresis of serum proteins confirmed earlier findings of hypergammaglobulinemia in the diseased animals but a fast-moving or pre-albumin component, averaging 4% of the total protein, occurred in both the diseased and normal mink. ImagesFigure 1. PMID:17649484

  14. Detailed transcription map of Aleutian mink disease parvovirus.

    PubMed Central

    Alexandersen, S; Bloom, M E; Perryman, S

    1988-01-01

    We studied the transcription program of Aleutian mink disease parvovirus (ADV) by using a combination of cDNA cloning and sequencing, primer extension, and Northern (RNA) blot hybridization with splice-specific oligonucleotides. The 4.8-kilobase ADV genome was transcribed in the rightward direction, yielding plus-sense polyadenylated transcripts of 4.3 (R1 RNA), 2.8 (R2), 2.8 (R3), 1.1 (RX), and 0.85 (R2') kilobases. Each RNA transcript had potential translation initiation sites within open reading frames, suggesting protein translation, and a scheme encompassing ADV structural and nonstructural proteins is proposed. Each of the five RNA transcripts had a characteristic set of splices and originated from a promoter at nucleotide 152 (map unit 3 [R1, R2, R2', and RX]) or at nucleotide 1729 (map unit 36 [R3]). The transcripts terminated with a poly(A) tail at one of two positions: either at map unit 53 (R2' and RX) or at map unit 92 (R1, R2, and R3). Similarities with and differences from the transcription maps of other parvoviruses are discussed, and possible roles of the unique features found in ADV transcription are related to the special pathogenic features of this virus. Images PMID:2843669

  15. Propagation of back-arc extension into the arc lithosphere in the southern New Hebrides volcanic arc

    NASA Astrophysics Data System (ADS)

    Patriat, M.; Collot, J.; Danyushevsky, L.; Fabre, M.; Meffre, S.; Falloon, T.; Rouillard, P.; Pelletier, B.; Roach, M.; Fournier, M.

    2015-09-01

    New geophysical data acquired during three expeditions of the R/V Southern Surveyor in the southern part of the North Fiji Basin allow us to characterize the deformation of the upper plate at the southern termination of the New Hebrides subduction zone, where it bends eastward along the Hunter Ridge. Unlike the northern end of the Tonga subduction zone, on the other side of the North Fiji Basin, the 90° bend does not correspond to the transition from a subduction zone to a transform fault, but it is due to the progressive retreat of the New Hebrides trench. The subduction trench retreat is accommodated in the upper plate by the migration toward the southwest of the New Hebrides arc and toward the south of the Hunter Ridge, so that the direction of convergence remains everywhere orthogonal to the trench. In the back-arc domain, the active deformation is characterized by propagation of the back-arc spreading ridge into the Hunter volcanic arc. The N-S spreading axis propagates southward and penetrates in the arc, where it connects to a sinistral strike-slip zone via an oblique rift. The collision of the Loyalty Ridge with the New Hebrides arc, less than two million years ago, likely initiated this deformation pattern and the fragmentation of the upper plate. In this particular geodynamic setting, with an oceanic lithosphere subducting beneath a highly sheared volcanic arc, a wide range of primitive subduction-related magmas has been produced including adakites, island arc tholeiites, back-arc basin basalts, and medium-K subduction-related lavas.

  16. Iron isotopic evidence for convective resurfacing of recycled arc-front mantle beneath back-arc basins

    NASA Astrophysics Data System (ADS)

    Nebel, O.; Arculus, R. J.; Sossi, P. A.; Jenner, F. E.; Whan, T. H. E.

    2013-11-01

    observations suggest sub-arc convective flow transports melt-exhausted and metasomatized wedge mantle into deeper mantle regions. Reciprocally, asthenospheric, fertile mantle may supply back-arc ridges distal to the trench by shallow, lateral mantle ingress, insinuating initial wedge mantle depletion in its back-arc region. Here we show that light Fe isotope compositions of the Central Lau Spreading Centre located in the Lau back-arc basin on the farside of the Tonga-Kermadec arc are indicative for derivation from a modified arc-front mantle with elemental and Nd-isotopic memory of former slab fluid addition. We propose that this shallow wedge material has been transported from the sub-arc mantle to the back-arc either convectively or in a buoyant diapir. This implies that melt-depleted mantle in subduction zones is, at least in parts, recycled in a resurfacing loop. This can explain the depletion in back-arc regions, and the progressively depleted nature of island arc sources in maturing arc systems.

  17. Patterns of growth and body condition in sea otters from the Aleutian archipelago before and after the recent population decline

    USGS Publications Warehouse

    Laidre, K.L.; Estes, J.A.; Tinker, M.T.; Bodkin, J.; Monson, D.; Schneider, K.

    2006-01-01

    3In addition to larger asymptotic values for mass and length, the rate of growth towards asymptotic values was more rapid in the 1990s than in the 1960s/70s: sea otters reached 95% of asymptotic body mass and body length 1–2 years earlier in the 1990s.4Body condition (as measured by the log mass/log length ratio) was significantly greater in males than in females. There was also an increasing trend from the 1960s/70s through 2004 despite much year-to-year variation.5Population age structures differed significantly between the 1960s/70s and the 1990s with the latter distribution skewed toward younger age classes (indicating an altered lxfunction) suggesting almost complete relaxation of age-dependent mortality patterns (i.e. those typical of food-limited populations).6This study spanned a period of time over which the population status of sea otters in the Aleutian archipelago declined precipitously from levels at or near equilibrium densities at some islands in the 1960s/70s to < 5% of estimated carrying capacity by the late 1990s. The results of this study indicate an improved overall health of sea otters over the period of decline and suggest that limited nutritional resources were not the cause of the observed reduced population abundance. Our findings are consistent with the hypothesis that the decline was caused by increased killer whale predation.

  18. 50 CFR 600.1103 - Bering Sea and Aleutian Islands (BSAI) Crab species program.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... means a bidder's irrevocable offer, in response to an invitation to bid under this section, to surrender...: (1) Holder of record and person otherwise fully and legally entitled to offer, in the manner this.../privilege vessel owner, title holder of record, and person otherwise fully and legally entitled to offer,...

  19. Aleut Dictionary (Unangam Tunudgusii). An Unabridged Lexicon of the Aleutian, Pribilof, and Commander Islands Aleut Language.

    ERIC Educational Resources Information Center

    Bergsland, Knut, Comp.

    This comprehensive dictionary draws on ethnographic and linguistic work of the Aleut language and culture dating to 1745. An introductory section explains the dictionary's format, offers a brief historical survey, and contains notes on Aleut phonology and orthography, dialectal differences and developments, Eskimo-Aleut phonological…

  20. Rotating arc spark plug

    DOEpatents

    Whealton, John H.; Tsai, Chin-Chi

    2003-05-27

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

  1. Petrology and Geochemistry of Plagioclase-Phyric Basaltic Lava Flows on St. George Island, Alaska: Evidence for a Genetic Link Between Magmatic Centers of the Pribilof Islands

    NASA Astrophysics Data System (ADS)

    Deraps, M. R.; Feeley, T. C.; Underwood, S. J.; Winer, G. S.

    2006-12-01

    St. George and St. Paul Islands, the two largest Pribilof Islands (Alaska), are located 70 km apart in the Bering Sea 400-450 km north of the Aleutian arc front. The islands are centers of alkaline basaltic volcanism associated with the diffuse Bering Sea basalt province. On St. George an extensive history of volcanism (~2.6-1.4 Ma; Mukasa and Andronikov, JGR, submitted) is exposed in high sea cliffs and several NE-SW and E-W trending fault blocks that define the present topography of the island. In contrast, St. Paul is a potentially active volcanic center (~550-3 ka) with numerous young tephra cones and associated lava flows that show minimal erosion and deformation by faulting. Volcanic rocks erupted on St. George are mainly olivine- + clinopyroxene-phyric basalts and trachy-basalts with high to moderate MgO contents (12-8 wt%). In addition, distinct plagioclase-phyric lavas are present at high stratigraphic levels. The plagioclase-phyric lavas are relatively evolved with 47-51 wt% SiO2 and 6.6-4.9 wt% MgO. Chondrite-normalized REE patterns are LREE-enriched with little to no Eu anomalies (Eu/Eu* = 1.03-1.06), indicating that the evolved compositions and plagioclase-rich nature of the flows are not due to phenocryst accumulation. Instead, production of plagioclase-phyric lavas on St. George likely involved a complex set of differentiation processes, including fractional crystallization and magma mixing. This assertion is supported by major and trace element compositions of the rocks, which define distinct trends on chemical variation diagrams relative to less evolved plagioclase-poor rocks. For example, whereas MgO contents of most St. George lavas as a group decrease with increasing SiO2 contents, these elements show a positive linear correlation for plagioclase-phyric lavas. The linear trends of these samples on chemical variation diagrams are best explained by mixing of at least two distinct evolved endmember magmas. Major element mass balance calculations

  2. DC arc weld starter

    DOEpatents

    Campiotti, Richard H.; Hopwood, James E.

    1990-01-01

    A system for starting an arc for welding uses three DC power supplies, a high voltage supply for initiating the arc, an intermediate voltage supply for sustaining the arc, and a low voltage welding supply directly connected across the gap after the high voltage supply is disconnected.

  3. [Arc welder's lung].

    PubMed

    Molinari, Luciana; Alvarez, Clarisa; Semeniuk, Guillermo B

    2010-01-01

    Pneumoconiosis of electric arc welder or siderotic pneumoconiosis was described by Doig and McLaughlin in 1936 as a lung disease caused by chronic inhalation of iron fumes in electric arc welders. We present a case report of electric arc welder siderosis associated with high levels of ferritin, without findings of iron deposit in any other organ. PMID:21163741

  4. The geomorphology of the Chandeleur Island Wetlands

    SciTech Connect

    Debusschere, K.; Penland, S.; Westphal, K. ); Handley, L. ); Michot, T. ); Reed, D.; Seal, R.

    1990-09-01

    The Chandeleur Islands represent the largest and oldest transgressive barrier island arc in the northern Gulf of Mexico. Generated by the transgressive submergence of the St. Bernard delta complex, the Chandeleur Islands form the protective geologic framework for one of the richest areas of salt marsh and seagrass flats in Louisiana. The Chandeleur barrier island arc is 60 km long and consists of five individual islands backed by a linear, multiple bar system enclosing a shallow basin floored by extensive seagrass flats. The northern part of the Chandeleur chain is the highest in relief, elevation, width, and habitat diversity. Nonstorm morphology is predominantly a combination of continuous dunes and dune terraces. Numerous washover channels and large washover fans extend into the backbarrier environment. Further south, the island width decreases and washover flats and terraces dominate the shoreline morphology In the southernmost section, the island arc is fragmented into a series of small islands and shoals separated by tidal inlets. Between 1984 and 1989, aerial videotape, aerial photographic, and bathymetric surveys were used to map and monitor the geomorphic changes occurring along the shoreline and in backbarrier areas. The aerial videotape mapping surveys focused on the impacts of hurricanes Danny, Elena, and Juan on the geomorphology of the islands. Videotape imagery was acquired in July 1984 and in July (prestorm), August (post-Danny), September (post-Elena), and November (post-Juan) 1985. A coastal geomorphic classification was developed to map the spatial and temporal landscape changes between surveys.

  5. Mercury and other metals in eggs and feathers of glaucous-winged gulls (Larus glaucescens) in the Aleutians

    PubMed Central

    Gochfeld, Michael; Jeitner, Christian; Burke, Sean; Volz, Conrad D.; Snigaroff, Ronald; Snigaroff, Daniel; Shukla, Tara; Shukla, Sheila

    2014-01-01

    Levels of mercury and other contaminants should be lower in birds nesting on isolated oceanic islands and at high latitudes without any local or regional sources of contamination, compared to more urban and industrialized temperate regions. We examined concentrations of arsenic, cadmium, chromium, lead, manganese, mercury and selenium in the eggs, and the feathers of fledgling and adult glaucous-winged gulls (Larus glaucescens) nesting in breeding colonies on Adak, Amchitka, and Kiska Islands in the Aleutian Chain of Alaska in the Bering Sea/North Pacific. We tested the following null hypotheses: 1) There were no differences in metal levels among eggs and feathers of adult and fledgling glaucous-winged gulls, 2) There were no differences in metal levels among gulls nesting near the three underground nuclear test sites (Long Shot 1965, Milrow 1969, Cannikin 1971) on Amchitka, 3) There were no differences in metal levels among the three islands, and 4) There were no gender-related differences in metal levels. All four null hypotheses were rejected at the 0.05 level, although there were few differences among the three test sites on Amchitka. Eggs had the lowest levels of cadmium, lead, and mercury, and the feathers of adults had the lowest levels of selenium. Comparing only adults and fledglings, adults had higher levels of cadmium, chromium, lead and mercury, and fledglings had higher levels of arsenic, manganese and selenium. There were few consistent interisland differences, although levels were generally lower for eggs and feathers from gulls on Amchitka compared to the other islands. Arsenic was higher in both adult feathers and eggs from Amchitka compared to Adak, and chromium and lead were higher in adult feathers and eggs from Adak compared to Amchitka. Mercury and arsenic, and chromium and manganese levels were significantly correlated in the feathers of both adult and fledgling gulls. The feathers of males had significantly higher levels of chromium and

  6. Magnesium isotope geochemistry in arc volcanism

    PubMed Central

    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. Magnesium isotope geochemistry in arc volcanism.

    PubMed

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

    2016-06-28

    Incorporation of subducted slab in arc volcanism plays an important role in producing the geochemical and isotopic variations in arc lavas. The mechanism and process by which the slab materials are incorporated, however, are still uncertain. Here, we report, to our knowledge, the first set of Mg isotopic data for a suite of arc lava samples from Martinique Island in the Lesser Antilles arc, which displays one of the most extreme geochemical and isotopic ranges, although the origin of this variability is still highly debated. We find the δ(26)Mg of the Martinique Island lavas varies from -0.25 to -0.10, in contrast to the narrow range that characterizes the mantle (-0.25 ± 0.04, 2 SD). These high δ(26)Mg values suggest the incorporation of isotopically heavy Mg from the subducted slab. The large contrast in MgO content between peridotite, basalt, and sediment makes direct mixing between sediment and peridotite, or assimilation by arc crust sediment, unlikely to be the main mechanism to modify Mg isotopes. Instead, the heavy Mg isotopic signature of the Martinique arc lavas requires that the overall composition of the mantle wedge is buffered and modified by the preferential addition of heavy Mg isotopes from fluids released from the altered subducted slab during fluid-mantle interaction. This, in turn, suggests transfer of a large amount of fluid-mobile elements from the subducting slab to the mantle wedge and makes Mg isotopes an excellent tracer of deep fluid migration. PMID:27303032

  8. Magnesium isotope geochemistry in arc volcanism

    NASA Astrophysics Data System (ADS)

    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.

  9. Relationship of the crustal structure and its deformation from arc to back-arc basin in the eastern Japan Sea deduced from the seismic survey

    NASA Astrophysics Data System (ADS)

    Sato, Takeshi; No, Tetsuo; Miura, Seiichi; Kodaira, Shuichi; Sato, Hiroshi

    2015-04-01

    The Japan Sea is a back-arc basin in the northwestern Pacific. Based on geophysical, geological, and petrological results, it is suggested that the opening of the Japan Sea was initiated by crustal rifting and the separation of Japan Island arcs from the Asian continent in the Early Oligocene, followed by the ocean floor spreading in the Late Oligocene (e.g., Tamaki et al., 1992). After 3.5 Ma, the crustal shortening by a strong compression occurred in the eastern margin (e.g., Sato, 1994). In the eastern margin, because of the extension associated with the opening of the Japan Sea and this shortening, the deformation such as active faults and folds formed have developed and large earthquakes with magnitudes-7 class repeatedly occurred (e.g., Okamura et al., 2007). The Japan Sea has a unique setting in terms of the connection between the back-arc basin opening and the crustal deformation. However, we have little information concerning with a crustal structure formed by the back-arc opening in the margin and the deformation. To obtain the information, we have been carrying out active-source seismic surveys using ocean bottom seismographs (OBSs) and multi-channel streamer system (MCS) to cover the eastern margin of the Japan Sea. The obtained results show a difference in crustal structures between the northern and the southern parts of the eastern Japan Sea. In the northern part from the arc to the back-arc basin, the crust is divided into three types; the rifted island arc crust, the thicker oceanic crust and the oceanic crust, based on the comparison of the P-wave velocity distribution and the crustal thickness of a typical oceanic crust (White et al., 1992) and of the northeastern Japan Island arc crust (Iwasaki et al., 2001). On the other hand, the southern part from the arc to the back-arc basin has two crustal types, which are the rifted island arc crust and the thicker oceanic crust. In the northern part, the deformation is distributed in a structural boundary

  10. Back-arc with frontal-arc component origin of Triassic Karmutsen basalt, British Columbia, Canada

    USGS Publications Warehouse

    Barker, F.; Sutherland, Brown A.; Budahn, J.R.; Plafker, G.

    1989-01-01

    The largely basaltic, ???4.5-6.2-km-thick, Middle to Upper Triassic Karmutsen Formation is a prominent part of the Wrangellian sequence. Twelve analyses of major and minor elements of representative samples of pillowed and massive basalt flows and sills from Queen Charlotte and Vancouver Islands are ferrotholeiites that show a range of 10.2-3.8% MgO (as normalized, H2O- and CO2-free) and related increases in TiO2 (1.0-2.5%), Zr (43-147 ppm) and Nb (5-16 ppm). Other elemental abundances are not related simply to MgO: distinct groupings are evident in Al2O3, Na2O and Cr, but considerable scatter is present in FeO* (FeO + 0.9Fe2O3) and CaO. Some of the variation is attributed to alteration during low-rank metamorphism or by seawater - including variation of Ba, Rb, Sr and Cu, but high-field-strength elements (Sc, Ti, Y, Zr and Nb) as well as Cr, Ni, Cu and rare-earth elements (REE's) were relatively immobile. REE's show chondrite-normalized patterns ranging from light-REE depleted to moderately light-REE enriched. On eleven discriminant plots these analyses fall largely into or across fields of within-plate basalt (WIP), normal or enriched mid-ocean-ridge tholeiite (MORB) and island-arc tholeiite (IAT). Karmutsen basalts are chemically identical to the stratigraphically equivalent Nikolai Greenstone of southern Alaska and Yukon Territory. These data and the fact that the Karmutsen rests on Sicker Group island-arc rocks of Paleozoic age suggest to us that: 1. (1) the basal arc, after minor carbonate-shale deposition, underwent near-axial back-arc rifting (as, e.g., the Mariana arc rifted at different times); 2. (2) the Karmutsen basalts were erupted along this rift or basin as "arc-rift" tholeiitite; and 3. (3) after subsequent deposition of carbonates and other rocks, and Jurassic magmatism, a large fragment of this basalt-sediment-covered island arc was accreted to North America as Wrangellia. The major- and minor-elemental abundances of Karmutsen basalt is modeled

  11. Arc initiation in cathodic arc plasma sources

    DOEpatents

    Anders, Andre

    2002-01-01

    A "triggerless" arc initiation method and apparatus is based on simply switching the arc supply voltage to the electrodes (anode and cathode). Neither a mechanical trigger electrode nor a high voltage flashover from a trigger electrode is required. A conducting path between the anode and cathode is provided, which allows a hot spot to form at a location where the path connects to the cathode. While the conductive path is eroded by the cathode spot action, plasma deposition ensures the ongoing repair of the conducting path. Arc initiation is achieved by simply applying the relatively low voltage of the arc power supply, e.g. 500 V-1 kV, with the insulator between the anode and cathode coated with a conducting layer and the current at the layer-cathode interface concentrated at one or a few contact points. The local power density at these contact points is sufficient for plasma production and thus arc initiation. A conductive surface layer, such as graphite or the material being deposited, is formed on the surface of the insulator which separates the cathode from the anode. The mechanism of plasma production (and arc initiation) is based on explosive destruction of the layer-cathode interface caused by joule heating. The current flow between the thin insulator coating and cathode occurs at only a few contact points so the current density is high.

  12. Monitoring ARC services with GangliARC

    NASA Astrophysics Data System (ADS)

    Cameron, D.; Karpenko, D.

    2012-12-01

    Monitoring of Grid services is essential to provide a smooth experience for users and provide fast and easy to understand diagnostics for administrators running the services. GangliARC makes use of the widely-used Ganglia monitoring tool to present web-based graphical metrics of the ARC computing element. These include statistics of running and finished jobs, data transfer metrics, as well as showing the availability of the computing element and hardware information such as free disk space left in the ARC cache. Ganglia presents metrics as graphs of the value of the metric over time and shows an easily-digestable summary of how the system is performing, and enables quick and easy diagnosis of common problems. This paper describes how GangliARC works and shows numerous examples of how the generated data can quickly be used by an administrator to investigate problems. It also presents possibilities of combining GangliARC with other commonly-used monitoring tools such as Nagios to easily integrate ARC monitoring into the regular monitoring infrastructure of any site or computing centre.

  13. Early hominin biogeography in Island Southeast Asia.

    PubMed

    Larick, Roy; Ciochon, Russell L

    2015-01-01

    Island Southeast Asia covers Eurasia's tropical expanse of continental shelf and active subduction zones. Cutting between island landmasses, Wallace's Line separates Sunda and the Eastern Island Arc (the Arc) into distinct tectonic and faunal provinces. West of the line, on Sunda, Java Island yields many fossils of Homo erectus. East of the line, on the Arc, Flores Island provides one skeleton and isolated remains of Homo floresiensis. Luzon Island in the Philippines has another fossil hominin. Sulawesi preserves early hominin archeology. This insular divergence sets up a unique regional context for early hominin dispersal, isolation, and extinction. The evidence is reviewed across three Pleistocene climate periods. Patterns are discussed in relation to the pulse of global sea-level shifts, as well as regional geo-tectonics, catastrophes, stegodon dispersal, and paleogenomics. Several patterns imply evolutionary processes typical of oceanic islands. Early hominins apparently responded to changing island conditions for a million-and-a-half years, likely becoming extinct during the period in which Homo sapiens colonized the region. PMID:26478140

  14. 75 FR 64957 - Fisheries of the Exclusive Economic Zone Off Alaska; Atka Mackerel in the Bering Sea and Aleutian...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-10-21

    ... fishery in the Eastern Aleutian District and the Bering Sea subarea on September 1, 2010 (75 FR 53606... remain anonymous). Attachments to electronic comments will be accepted in Microsoft Word, Excel,...

  15. Long arc stabilities with various arc gas flow rates

    NASA Astrophysics Data System (ADS)

    Maruyama, K.; Takeda, K.; Sugimoto, M.; Noguchi, Y.

    2014-11-01

    A new arc torch for use in magnetically driven arc device was developed with a commercially available TIG welding arc torch. The torch has a water-cooling system to the torch nozzle and has a nozzle nut to supply a swirling-free plasma gas flow. Its endurance against arc thermal load is examined. Features of its generated arc are investigated.

  16. Towards Understanding the Sunda and Banda Arcs

    NASA Astrophysics Data System (ADS)

    Hall, R.

    2014-12-01

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

  17. The volcanoes of an oceanic arc from origin to destruction: A case from the northern Luzon Arc

    NASA Astrophysics Data System (ADS)

    Lai, Yu-Ming; Song, Sheng-Rong

    2013-09-01

    Volcanoes were created, grew, uplifted, became dormant or extinct, and were accreted as part of continents during continuous arc-continent collision. Volcanic rocks in Eastern Taiwan's Coastal Range (CR) are part of the northern Luzon Arc, an oceanic island arc produced by the subduction of the South China Sea Plate beneath the Philippine Sea Plate. Igneous rocks are characterized by intrusive bodies, lava and pyroclastic flows, and volcaniclastic rocks with minor tephra deposits. Based on volcanic facies associations, Sr-Nd isotopic geochemistry, and the geography of the region, four volcanoes were identified in the CR: Yuemei, Chimei, Chengkuangao, and Tuluanshan. Near-vent facies associations show different degrees of erosion in the volcanic edifices for Chimei, Chengkuangao, and Tuluanshan. Yuemei lacks near-vent rocks, implying that Yuemei's main volcanic body may have been subducted at the Ryukyu Trench with the northward motion of the Philippine Sea Plate. These data suggest a hypothesis for the evolution of volcanism and geomorphology during arc growth and ensuing arc-continent collision in the northern Luzon Arc, which suggests that these volcanoes were formed from the seafloor, emerging as islands during arc volcanism. They then became dormant or extinct during collision, and finally, were uplifted and accreted by additional collision. The oldest volcano, Yuemei, may have already been subducted into the Ryukyu Trench.

  18. Welding arc plasma physics

    NASA Technical Reports Server (NTRS)

    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.

  19. Proceedings of the North Aleutian Basin information status and research planning meeting.

    SciTech Connect

    LaGory, K. E.; Krummel, J. R.; Hayse, J. W.; Hlohowskyj, I.; Stull, E. A.; Gorenflo, L.; Environmental Science Division

    2007-10-26

    The North Aleutian Basin Planning Area of the Minerals Management Service (MMS) is a large geographic area with significant ecological and natural resources. The Basin includes most of the southeastern part of the Bering Sea continental shelf including all of Bristol Bay. The area supports important habitat for a wide variety of species and globally significant habitat for birds and marine mammals including federally listed species. Villages and communities of the Alaska Peninsula and other areas bordering or near the Basin rely on its natural resources (especially commercial and subsistence fishing) for much of their sustenance and livelihood. The offshore area of the North Aleutian Basin is considered to have important hydrocarbon reserves, especially natural gas. In 2006, the MMS released a draft proposed program, Outer Continental Shelf Oil and Gas Leasing Program, 2007-2012 and an accompanying draft programmatic environmental impact statement (EIS). The draft proposed program identified two lease sales proposed in the North Aleutian Basin in 2010 and 2012, subject to restrictions. The area proposed for leasing in the Basin was restricted to the Sale 92 Area in the southwestern portion. Additional EISs will be needed to evaluate the potential effects of specific lease actions, exploration activities, and development and production plans in the Basin. A full range of updated multidisciplinary scientific information will be needed to address oceanography, fate and effects of oil spills, marine ecosystems, fish, fisheries, birds, marine mammals, socioeconomics, and subsistence in the Basin. Scientific staff at Argonne National Laboratory (Argonne) were contracted to assist the MMS Alaska Outer Continental Shelf (OCS) Region in identifying and prioritizing information needs related to the North Aleutian Basin and potential future oil and gas leasing and development activities. The overall approach focused on three related but separate tasks: (1) identification and

  20. Assessment of metals in down feathers of female common eiders and their eggs from the Aleutians: arsenic, cadmium, chromium, lead, manganese, mercury, and selenium

    PubMed Central

    Burger, Joanna; Gochfeld, Michael; Jeitner, Christian; Snigaroff, Daniel; Snigaroff, Ronald; Stamm, Timothy; Volz, Conrad

    2014-01-01

    Concentrations of arsenic, cadmium, chromium, lead, manganese, mercury and selenium were examined in the down feathers and eggs of female common eiders (Somateria mollissima) from Amchitka and Kiska Islands in the Aleutian Chain of Alaska to determine whether there were (1) differences between levels in feathers and eggs, (2) differences between the two islands, (3) positive correlations between metal levels in females and their eggs, and (4) whether there was more variation within or among clutches. Mean levels in eggs (dry weight) were as follows: arsenic (769 ppb, ng/g), cadmium (1.49 ppb), chromium (414 ppb), lead (306 ppb), manganese (1,470 ppb), mercury (431 ppb) and selenium (1,730 ppb). Levels of arsenic were higher in eggs, while chromium, lead, manganese, and mercury were higher in feathers; there were no differences for selenium. There were no significant interisland differences in female feather levels, except for manganese (eider feathers from Amchitka were four times higher than feathers from Kiska). Levels of manganese in eggs were also higher from Amchitka than Kiska, and eider eggs from Kiska had significantly higher levels of arsenic, but lower levels of selenium. There were no significant correlations between the levels of any metals in down feathers of females and in their eggs. The levels of mercury in eggs were below ecological benchmark levels, and were below human health risk levels. However, Aleuts can seasonally consume several meals of bird eggs a week, suggesting cause for concern for sensitive (pregnant) women. PMID:17934788

  1. Elemental and organochlorine residues in bald eagles from Adak Island, Alaska.

    PubMed

    Stout, Jordan H; Trust, Kimberly A

    2002-07-01

    Adak Island is a remote island in the Aleutian Island archipelago of Alaska (USA) and home to various military activities since World War II. To assess the contaminant burden of one of Adak Island's top predators, livers and kidneys were collected from 26 bald eagle (Haliaeetus leucocephalus) carcasses between 1993 and 1998 for elemental and organochlorine analyses. Mean cadmium, chromium, mercury, and selenium concentrations were consistent with levels observed in other avian studies and were below toxic thresholds. However, elevated concentrations of chromium and mercury in some individuals may warrant concern. Furthermore, although mean polychlorinated biphenyl and pp'-dichlorodiphenyldichloroethylene concentrations were below acute toxic thresholds, they were surprisingly high given Adak Island's remote location. PMID:12238368

  2. The nearshore benthic community of Kasatochi Island, one year after the 2008 volcanic eruption

    USGS Publications Warehouse

    Jewett, S.C.; Bodkin, J.L.; Chenelot, H.; Esslinger, G.G.; Hoberg, M.K.

    2010-01-01

    A description is presented of the nearshore benthic community of Kasatochi Island 1012 months after a catastrophic volcanic eruption in 2008. The eruption extended the coastline of the island approximately 400 m offshore, mainly along the south, southeast, and southwest shores, to roughly the 20 m isobath. Existing canopy kelp of Eualaria (Alaria) fistulosa, as well as limited understory algal species and associated fauna (e.g., urchin barrens) on the hard substratum were apparently buried following the eruption. Samples and observations revealed the substrate around the island in 2009 was comprised almost entirely of medium and coarse sands with a depauperate benthic community, dominated by opportunistic pontogeneiid amphipods. Comparisons of habitat and biological communities with other nearby Aleutian Islands, as well as with the Icelandic volcanic island of Surtsey, confirm dramatic reductions in flora and fauna consistent with an early stage of recovery from a large-scale disturbance event. ?? 2010 Regents of the University of Colorado.

  3. 2010 Volcanic activity in Alaska, Kamchatka, and the Kurile Islands: summary of events and response of the Alaska Volcano Observatory

    USGS Publications Warehouse

    Neal, Christina A.; Herrick, Julie; Girina, O.A.; Chibisova, Marina; Rybin, Alexander; McGimsey, Robert G.; Dixon, Jim

    2014-01-01

    The Alaska Volcano Observatory (AVO) responded to eruptions, possible eruptions, volcanic unrest or suspected unrest at 12 volcanic centers in Alaska during 2010. The most notable volcanic activity consisted of intermittent ash emissions from long-active Cleveland volcano in the Aleutian Islands. AVO staff also participated in hazard communication regarding eruptions or unrest at seven volcanoes in Russia as part of an ongoing collaborative role in the Kamchatka and Sakhalin Volcanic Eruption Response Teams.

  4. The geochemistry of the Neogene Halmahera Arc, eastern Indonesia

    NASA Astrophysics Data System (ADS)

    Forde, Emily Jane

    The Halmahera arc is a north-south linear intraoceanic arc cutting across the islands of Halmahera and Bacan in NE Indonesia. The arc is the result of the eastward subduction of the Molucca Sea Plate, accommodating the westward movement of the Pacific and Philippine Sea Plates (PSP) against the Eurasian margin. To the south of the Halmahera arc is a major left-lateral strike-slip fault system: the Sorong Fault Zone (SFZ), which separates the northward movement of Australia from the westward movement of the PSP. This plate boundary has been stable throughout the Neogene to the present day, and has been responsible for the transfer of continental fragments from the Australian margin into the southern Molucca Sea region. K/Ar dating has revealed the migration of volcanism along the length of the Halmahera arc from south to north. The oldest volcanics (ca. 11 Ma) are from Obi, the southernmost island in the region, where volcanism is now extinct. Moving north into Bacan, ages range from 7 Ma to the Quaternary, whereas in central Halmahera they range from 6 - 2 Ma. The present-day arc currently lies to the west of central Halmahera and stretches up the north-west arm of the island. On the basis of spatial, temporal and geochemical variations a possible seven Neogene volcanic centres can be distinguished along the length of the arc. Major element, trace element and Sr-Nd-Pb-O isotopic analyses reveal a wide diversity in geochemical characteristics between the centres. This is due to heterogeneity within the arc mantle wedge, the type of arc crust through which the volcanics were erupted and variations in contribution to the mantle wedge from a subducted component. Volcanic rocks from Obi, central Halmahera and north Bacan display geochemical characteristics typical of intraoceanic arc lavas. The lack of a continental component within these centres enables a greater understanding of the variety of processes and source components affecting arc magmatism in this region

  5. TIGER Arc Modification Application

    SciTech Connect

    Armstrong, Hillary

    1995-03-06

    The application enables the geometric correction of TIGER arcs to a more accurate spatial data set. This is done in a structured automated environment according to Census Bureau guidelines and New Mexico state GIS standards. Arcs may be deleted, added, combined, split, and moved relative to a coverage or image displayed in the background.

  6. The Mw7.9 2014 intraplate intermediate-depth Rat Islands earthquake and its relation to regional tectonics