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Sample records for alaska range orogen

  1. Crustal structure of the alaska range orogen and denali fault along the richardson highway

    USGS Publications Warehouse

    Fisher, M.A.; Pellerin, L.; Nokleberg, W.J.; Ratchkovski, N.A.; Glen, J.M.G.

    2007-01-01

    A suite of geophysical data obtained along the Richardson Highway crosses the eastern Alaska Range and Denali fault and reveals the crustal structure of the orogen. Strong seismic reflections from within the orogen north of the Denali fault dip as steeply as 25?? north and extend downward to depths between 20 and 25 km. These reflections reveal what is probably a shear zone that transects most of the crust and is part of a crustal-scale duplex structure that probably formed during the Late Cretaceous. These structures, however, appear to be relict because over the past 20 years, they have produced little or no seismicity despite the nearby Mw = 7.9 Denali fault earthquake that struck in 2002. The Denali fault is nonreflective, but we interpret modeled magnetotelluric (MT), gravity, and magnetic data to propose that the fault dips steeply to vertically. Modeling of MT data shows that aftershocks of the 2002 Denali fault earthquake occurred above a rock body that has low electrical resistivity (>10 ohm-m), which might signify the presence of fluids in the middle and lower crust. Copyright ?? 2007 The Geological Society of America.

  2. Geophysical data reveal the crustal structure of the Alaska Range orogen within the aftershock zone of the Mw 7.9 Denali fault earthquake

    USGS Publications Warehouse

    Fisher, M.A.; Ratchkovski, N.A.; Nokleberg, W.J.; Pellerin, L.; Glen, J.M.G.

    2004-01-01

    Geophysical information, including deep-crustal seismic reflection, magnetotelluric (MT), gravity, and magnetic data, cross the aftershock zone of the 3 November 2002 Mw 7.9 Denali fault earthquake. These data and aftershock seismicity, jointly interpreted, reveal the crustal structure of the right-lateral-slip Denali fault and the eastern Alaska Range orogen, as well as the relationship between this structure and seismicity. North of the Denali fault, strong seismic reflections from within the Alaska Range orogen show features that dip as steeply as 25?? north and extend downward to depths between 20 and 25 km. These reflections reveal crustal structures, probably ductile shear zones, that most likely formed during the Late Cretaceous, but these structures appear to be inactive, having produced little seismicity during the past 20 years. Furthermore, seismic reflections mainly dip north, whereas alignments in aftershock hypocenters dip south. The Denali fault is nonreflective, but modeling of MT, gravity, and magnetic data suggests that the Denali fault dips steeply to vertically. However, in an alternative structural model, the Denali fault is defined by one of the reflection bands that dips to the north and flattens into the middle crust of the Alaska Range orogen. Modeling of MT data indicates a rock body, having low electrical resistivity (>10 ??-m), that lies mainly at depths greater than 10 km, directly beneath aftershocks of the Denali fault earthquake. The maximum depth of aftershocks along the Denali fault is 10 km. This shallow depth may arise from a higher-than-normal geothermal gradient. Alternatively, the low electrical resistivity of deep rocks along the Denali fault may be associated with fluids that have weakened the lower crust and helped determine the depth extent of the after-shock zone.

  3. Geophysical investigation of the Denali fault and Alaska Range orogen within the aftershock zone of the October-November 2002, M = 7.9 Denali fault earthquake

    USGS Publications Warehouse

    Fisher, M.A.; Nokleberg, W.J.; Ratchkovski, N.A.; Pellerin, L.; Glen, J.M.; Brocher, T.M.; Booker, J.

    2004-01-01

    The aftershock zone of the 3 November 2002, M = 7.9 earthquake that ruptured along the right-slip Denali fault in south-central Alaska has been investigated by using gravity and magnetic, magnetotelluric, and deep-crustal, seismic reflection data as well as outcrop geology and earthquake seismology. Strong seismic reflections from within the Alaska Range orogen north of the Denali fault dip as steeply as 25°N and extend to depths as great as 20 km. These reflections outline a relict crustal architecture that in the past 20 yr has produced little seismicity. The Denali fault is nonreflective, probably because this fault dips steeply to vertical. The most intriguing finding from geophysical data is that earthquake aftershocks occurred above a rock body, with low electrical resistivity (>10 Ω·m), that is at depths below ∼10 km. Aftershocks of the Denali fault earthquake have mainly occurred shallower than 10 km. A high geothermal gradient may cause the shallow seismicity. Another possibility is that the low resistivity results from fluids, which could have played a role in locating the aftershock zone by reducing rock friction within the middle and lower crust.

  4. North-vergent thrust fault between Baltica and Laurentian affinity rocks in the frontal part of Romanzof orogen, NE Brooks Range, Alaska

    NASA Astrophysics Data System (ADS)

    Moore, T. E.; O'Sullivan, P. B.

    2012-12-01

    One of the most striking features of Arctic physiography is the long, linear Canadian Arctic margin of the Arctic Basin, which extends from the Lincoln Sea north of Greenland to the eastern Beaufort Sea and projects into northeastern Alaska. Among other ideas, this margin has been proposed to have developed by sinistral transform faulting in the Middle Devonian as a result of tectonic escape of terranes from the Caledonites (the so-called "Northwest Passage"). The faults on which the transform motion might have occurred, however, have not been recognized along the northern margin of North America. One candidate for such a fault is exposed at the southern boundary of the Sadlerochit Mountains province in the Tertiary frontal part of the NE Brooks Range. In the Plunge Creek area of the Arctic National Wildlife Refuge, a contact between rocks of Laurentian affinity and Baltica affinity is exposed on the back limb of a basement-involved map-scale thrust block formed by Brookian thrusting. The regional unconformity at the base of the Mississippian to Triassic Ellesmerian Sequence provides a near flat-lying datum that overlaps the contact between the pre-Mississippian tectonic units and demonstrates that it was not reactivated by Brookian thrusting. The Sadlerochit Mountains succession to the north of the contact consists of a Neoproterozoic and lower Paleozoic carbonate sequence that rests on metaclastic rocks that yield Grenville-Sveconorwegian (0.95-1.2 Ga) and other Mesoproterozoic detrital zircon U-Pb age populations similar to those reported from the northern parts of Baltica and eastern Greenland. In contrast, the Romanzof Mountains succession to the south consists of Neoproterozoic deep-marine clastic rocks (Neruokpuk Quartzite) and overlying lower Paleozoic chert and argillite. Detrital zircon U-Pb age populations from the Neruokpuk are very similar to those from Laurentian-derived clastic rocks in the Canadian margin of North America. Field relations show that

  5. Deformation during terrane accretion in the Saint Elias orogen, Alaska

    USGS Publications Warehouse

    Bruhn, R.L.; Pavlis, T.L.; Plafker, G.; Serpa, L.

    2004-01-01

    The Saint Elias orogen of southern Alaska and adjacent Canada is a complex belt of mountains formed by collision and accretion of the Yakutat terrane into the transition zone from transform faulting to subduction in the northeast Pacific. The orogen is an active analog for tectonic processes that formed much of the North American Cordillera, and is also an important site to study (1) the relationships between climate and tectonics, and (2) structures that generate large- to great-magnitude earthquakes. The Yakutat terrane is a fragment of the North American plate margin that is partly subducted beneath and partly accreted to the continental margin of southern Alaska. Interaction between the Yakutat terrane and the North American and Pacific plates causes significant differences in the style of deformation within the terrane. Deformation in the eastern part of the terrane is caused by strike-slip faulting along the Fairweather transform fault and by reverse faulting beneath the coastal mountains, but there is little deformation immediately offshore. The central part of the orogen is marked by thrusting of the Yakutat terrane beneath the North American plate along the Chugach-Saint Elias fault and development of a wide, thin-skinned fold-and-thrust belt. Strike-slip faulting in this segment may he localized in the hanging wall of the Chugach-Saint Elias fault, or dissipated by thrust faulting beneath a north-northeast-trending belt of active deformation that cuts obliquely across the eastern end of the fold-and-thrust belt. Superimposed folds with complex shapes and plunging hinge lines accommodate horizontal shortening and extension in the western part of the orogen, where the sedimentary cover of the Yakutat terrane is accreted into the upper plate of the Aleutian subduction zone. These three structural segments are separated by transverse tectonic boundaries that cut across the Yakutat terrane and also coincide with the courses of piedmont glaciers that flow from

  6. Detrital blueschist-Facies metamorphic mineral assemblages in Early Cretaceous sediments of the foreland basin of the Brooks Range, Alaska, and implications for orogenic evolution

    NASA Astrophysics Data System (ADS)

    Till, Alison B.

    1992-12-01

    Detrital metamorphic minerals found in the foreland basin of the Brooks Range were derived from blueschist-facies rocks that now occupy the range's metamorphic core. The metamorphic minerals occur in the Torok Formation and the Nanushuk Group; they are contained in sediments at least as old as middle Albian in age, and may have arrived earlier. The source of the minerals is the blueschist-facies schist belt, the structurally highest, more internal of two structurally and metamorphically distinct belts that occupy the metamorphic core of the Brooks Range. The blueschist facies rocks of the schist belt were exhumed between Late Jurassic and middle Albian time, during the major pulse of contractional deformation in the Brooks Range orogeny, rather than during late stage extensional collapse or postcontractional isostatic rebound, as suggested by other workers. The processes by which the blueschist-facies rocks were uplifted and denuded must have operated during contractional tectonism. Post peak metamorphic structures in the blueschist-facies rocks support their uplift by thrust systems; their unroofing apparently occurred by erosion and possibly by small-scale extensional faulting.

  7. Reindeer ranges inventory in western Alaska

    NASA Technical Reports Server (NTRS)

    George, T. H.

    1981-01-01

    The use of LANDSAT data as a tool for reindeer range inventory on the tundra of northwestern Alaska is addressed. The specific goal is to map the range resource and estimate plant productivity of the Seward Peninsula. Information derived from these surveys is needed to develop range management plans for reindeer herding and to evaluate potential conflicting use between reindeer and caribou. The development of computer image classification techniques is discussed.

  8. Geology of the Byrd Glacier Discontinuity (Ross Orogen): New survey data from the Britannia Range, Antarctica

    USGS Publications Warehouse

    Carosi, R.; Giacomini, F.; Talarico, F.; Stump, E.

    2007-01-01

    Field activities in the Britannia Range (Transantarctic Mountains, Antarctica) highlighted new geological features around the so-called Byrd Glacier discontinuity. Recent field surveys revealed the occurrence of significant amounts of medium- to high-grade metamorphic rocks, intruded by abundant coarse-grained porphyritic granitoids. Most of the granitoids are deformed, with foliation parallel to the regional foliation in the metamorphics. Two main episodes of deformation are observed. Tight to isoclinal folds and penetrative axial plane foliation are related to the D1 phase, open folds to the D2. The main foliation (D1) trends nearly E-W in agreement with the trend in the southern portion of the Byrd Glacier. In most outcrops, granitic dykes are folded and stretched by the D2 deformation, which shows similar characteristics with the D2 deformation south of the Byrd Glacier. This suggests the occurrence in the Ross orogen of an orogen-normal structure south and north of the Byrd Glacier.

  9. Clinoform deposition across a boundary between orogenic front and foredeep - an example from the Lower Cretaceous in Arctic Alaska

    USGS Publications Warehouse

    Houseknecht, David W.; Wartes, Marwan A.

    2013-01-01

    The Lower Cretaceous Fortress Mountain Formation occupies a spatial and temporal niche between syntectonic deposits at the Brooks Range orogenic front and post-tectonic strata in the Colville foreland basin. The formation includes basin-floor fan, marine-slope and fan-delta facies that define a clinoform depositional profile. Texture and composition of clasts in the formation suggest progressive burial of a tectonic wedge-front that included older turbidites and mélange. These new interpretations, based entirely on outcrop study, suggest that the Fortress Mountain Formation spans the boundary between orogenic wedge and foredeep, with proximal strata onlapping the tectonic wedge-front and distal strata downlapping the floor of the foreland basin. Our reconstruction suggests that clinoform amplitude reflects the structural relief generated by tectonic wedge development and load-induced flexural subsidence of the foreland basin.

  10. Crustal implications of bedrock geology along the Trans-Alaska Crustal Transect (TACT) in the Brooks Range, northern Alaska

    USGS Publications Warehouse

    Moore, T.E.; Wallace, W.K.; Mull, C.G.; Adams, K.E.; Plafker, G.; Nokleberg, W.J.

    1997-01-01

    Geologic mapping of the Trans-Alaska Crustal Transect (TACT) project along the Dalton Highway in northern Alaska indicates that the Endicott Mountains allochthon and the Hammond terrane compose a combined allochthon that was thrust northward at least 90 km in the Early Cretaceous. The basal thrust of the combined allochthon climbs up section in the hanging wall from a ductile shear zone, in the south through lower Paleozoic rocks of the Hammond terrane and into Upper Devonian rocks of the Endicott Mountains allochthon at the Mount Doonerak antiform, culminating in Early Cretaceous shale in the northern foothills of the Brooks Range. Footwall rocks north of the Mount Doonerak antiform are everywhere parautochthonous Permian and Triassic shale of the North Slope terrane rather than Jurassic and Lower Cretaceous strata of the Colville Basin as shown in most other tectonic models of the central Brooks Range. Stratigraphic and structural relations suggest that this thrust was the basal detachment for Early Cretaceous deformation. Younger structures, such as the Tertiary Mount Doonerak antiform, deform the Early Cretaceous structures and are cored by thrusts that root at a depth of about 10 to 30 km along a deeper detachment than the Early Cretaceous detachment. The Brooks Range, therefore, exposes (1) an Early Cretaceous thin-skinned deformational belt developed during arc-continent collision and (2) a mainly Tertiary thick-skinned orogen that is probably the northward continuation of the Rocky Mountains erogenic belt. A down-to-the-south zone of both ductile and brittle normal faulting along the southern margin of the Brooks Range probably formed in the mid-Cretaceous by extensional exhumation of the Early Cretaceous contractional deformation. copyright. Published in 1997 by the American Geophysical Union.

  11. Thrust involvement of metamorphic rocks, southwestern Brooks Range, Alaska

    SciTech Connect

    Till, A.B.; Schmidt, J.M.; Nelson, S.W. )

    1988-10-01

    Most models for the tectonic history of the western Brooks Range treat Proterozoic and lower Paleozoic metamorphic rocks exposed in the southern part of the range as passive structural basement vertically uplifted late in the Mesozoic orogenic episode. Mapping in the metamorphic rocks shows that they can de divided into two structurally and metamorphically distinct belts, both of which were folded and thrust during the orogeny. Recognition of these belts and the nature of the contact separating them is critical to construction of accurate tectonic models of the Brooks Range fold and thrust belt.

  12. A Major Out of Sequence Fault in Central Range and Its Implication to Mountain Building Process of Taiwan Orogenic Belt

    NASA Astrophysics Data System (ADS)

    Lee, Y. H.

    2015-12-01

    A Major Out of Sequence Fault in Central Range and Its Implication to Mountain Building Process of Taiwan Orogenic Belt Yuan-Hsi Lee1, Wei Lo2, Wei-Hau Wang1, Tim-Byrne 3, Ruey-Juen Rau 41. Department of Earth and Environmental Sciences, National Chung Cheng University, Taiwan, R.O.C. 2. Department of Materials and Mineral Resources Engineering, Taipei, National Taipei University of Technology, Taiwan, R.O.C. 3. Center for Integrative Geosciences, University of Connecticut, Storrs, CT, USA 4. Department of Earth Science, National Chen-Kung University, Taiwan, R.O.C. Taiwan mountain belt results from collision between Eurasia continental crust and Philippine Sea plate that result in exposing the metamorphic complex with high exhumation rate in eastern Central Range of Taiwan orogenic belt. In this study we combine with field survey, zircon fission track (ZFT), metamorphic grade, and tomography data to identify there exists a major out of sequence fault (MOSF) in eastern Central Range of Taiwan orogenic belt. This MOSF extends from north to south of eastern central Range with several segments and the total length is more than 250 km. The ZFT shows total annealing age of ca.1-3 Ma on the hanging wall and partial annealing ages on the foot wall. The seismicity data indicates the MOSF is still active from central to southern central Range. We consider that the MOSF is related with crustal channel flow in depth. To the western side of crustal flow it shows thrusting mechanism associated with MOSF and the normal faults (or normal shearing zone) develop in eastern side of the crustal channel flow. This crustal channel flow is also related with exposing the metamorphic complex in Central Range that is important mechanism for the mountain building process of Taiwan orogenic belt.

  13. Thermal structure of the Brooks Ranges and Seward Peninsula, Alaska HP-LT units : insights from RSCM thermometry

    NASA Astrophysics Data System (ADS)

    nicolas, Lemonnier; loic, Labrousse; philippe, Agard; Buschendorf Maelianna, Bigot; Frédéric, Mouthereau; Alison, Till

    2013-04-01

    Inner parts of mountain belts expose metamorphic rocks that record the thermal evolution of orogenic wedges, from burial to final exhumation. As such, they provide key constraints for paleogeographic and tectonic reconstructions of convergent zones. In order to understand the relationships between the Pacific subduction system and the Arctic geodynamics, we herein reappraise the key tectonic evolution of the Brooks Ranges (Northern Alaska). High-pressure low-temperature metamorphic rocks cropping out in the Schist belt of the Brooks Ranges, and the Nome Complex schists (Seward Peninsula), were exposed during Early Cretaceous to Paleocene times. Processes and structures responsible for their exhumation (i.e., syn-collisional nappe-stacking or post-collisional extensional detachment), which are still a matter of debate, have direct implications in terms of orogenic boundary conditions and mechanical coupling between subduction processes in southern Alaska and basin response to the north (North Slope). In this study systematic thermometry via Raman Spectrometry (RSCM) of Carbonaceous material along two regional transects in the Schist Belt and Seward Penisula (Nome area) allows the identification of units with contrasting thermal histories and a comparison of the thermal evolutions of the two areas. Geodynamic implications are finally discussed.

  14. Cretaceous Olistostrome Model, Brooks Range, Alaska

    SciTech Connect

    Crane, R.C.

    1985-04-01

    The foothills area of the Brooks Range thrust belt in the area between the Itkillik River and the Etivluk River is composed dominantly of shallow, thrusted olistostrome sheets. Three olistostrome units can be recognized based on the dominant lithology of contained olistoliths and age of the matrix shales. The lower unit is Thithonian to mid-Valanginian in age and is characterized by abundant graywacke and turbidite, mafic rocks, black cherts, olistoliths of Norian-Rhaetic shales, Nuka sands, and glide sheets of Upper Devonian to Lower Mississippian rocks. Olistolights were derived from the Misheguk, Ipnavik, and Nuka Ridge allochthonous sequences. The middle unit is of late Valanginian age and has olistoliths of Norian shales; more abundant Upper Triassic chert; Otuk Formation; variegated, radiolarian, black and white cherts; Siksikpuk facies red, green and black shales; Upper Jurassic graywacke; and minor occurrences of mafic rocks. The unit is characterized by glide sheets of Triassic white and multicolor cherts. Olistoliths are derived from Nuka Ridge and Brooks Range sequences. The upper unit is Hauterivian in age and olistoliths included reworked material from all older units. Olistoliths are few and widely scattered. Isolated outcrops of white chert and conglomerate boulders are characteristic.

  15. Caledonian Deformation in Polydeformed Pre-Mississippian Rocks of the Northeast Brooks Range, Alaska

    NASA Astrophysics Data System (ADS)

    Johnson, B. G.; Toro, J.; Benowitz, J.

    2013-12-01

    In the northeastern Brooks Range of Alaska there are polydeformed metasedimentary and metavolcanic rocks exposed below a major pre-Mississippian unconformity. Elsewhere in northern Alaska it has been challenging to correlate the tectonic fabrics of these early Paleozoic to Neoproterozoic rocks to the different orogenic events of the Arctic because of the strong overprint of Mesozoic and Tertiary Brookian deformation. However, our recent field investigations along the Kongakut and Aichiklik rivers of ANWR have identified an older (pre-Brookian) structural event based on the orientation of penetrative cleavage planes and a contrast in folding style to Brookian structures. Many of the cleavage planes are north dipping and orientated parallel to the axial planes of south-vergent folds. Although metamorphic grade is generally low, in localized areas the cleavage planes contain white micas, whose petrologic and isotopic characteristics indicate that they crystallized during fabric formation. 40Ar/39Ar dating of the white micas yield a metamorphic age of ~400 Ma (Early Devonian). This is evidence for a south-directed structural event which is contemporaneous with Caledonian deformation in East Greenland and Svalbard. Stratigraphicaly, the basement consists of a diverse package of highly deformed marine clastic sediments, and a thick section of basaltic to andesitic flows and volcaniclastic rocks, the Whale Mountain volcanics, which have a sharp southern contact but grade northward and upwards into the clastic rocks. All units are metamorphosed to lower greenschist facies. We are currently investigating the age and geochemical characteristics of the Whale Mountain volcanics to determine their tectonic affinity and role in the assemblage of the North Slope block of Northern Alaska.

  16. Denudation rates across the seaward side of a juvenile orogenic topography, western Cantabrian Range

    NASA Astrophysics Data System (ADS)

    Alvarez-Marron, Joaquina; Menendez-Duarte, R.; Stuart, F.; Fernandez, S.; Grobe, R.; Glasmacher, U. A.; Pallas, R.; Rodes, A.; Braucher, R.; Bourles, D.

    2010-05-01

    The Cantabrian Range in northern Spain reaches average elevations above 1500 m a.s.l. (up to 2700 m). This topography grew by uplift of Variscan basement rocks along the North Spanish coast during minor Iberia-Eurasia convergence since Eocene times. The convergence also caused limited subduction along the margin. The generation of this obvious topography has not coincided with significant exhumation; apatite fission track and He thermochronology suggests that less than 1.5 km has been removed since 80 Ma. Despite this, the landscape in the seaward side of the mountain belt shows features consistent with it not being in equilibrium. Relict landforms, in particular low relief surfaces, are preserved above 600 m in the interfluves of the incised fluvial system. These surfaces are interpreted to have evolved from a pre-Eocene palaeo-landscape. The low relief surface in the Oscos area is perhaps the best example. It covers an area of ~450 km2 at 600 to 1000 m, and is composed of broad, rolling hills and hillslopes that never exceed 15°. The river catchments draining these surfaces drop up to 500 m along short bedrock canyons to join the surrounding incised rivers. Small river basins that flow northwards and drain the lowest ~1000 m topography have incised into the 1.5 Ma old wave-cut platform that rises several tens of metres above sea-level along the coast. In order to investigate the distribution of erosion throughout this seemingly inefficient erosional system, in situ cosmogenic nuclides have been analysed in bedrock and alluvial sediment samples. Cosmogenic 21Ne concentrations in sediments from the river mouths imply that basin-average denudation rates are at least a few tens of mm/kyr. These rates are similar to those measured in active Alpine areas elsewhere in Europe. However, denudation rates measured from bedrock quartz in the Oscos paleosurface are significantly lower (1-5 mm/kyr) similar to rates determined in cratonic areas. This heterogeneous distribution

  17. Deep-seated gravitational slope deformations near the Trans-Alaska Pipeline, east-central Alaska Range, Alaska, USA

    NASA Astrophysics Data System (ADS)

    Newman, S. D.; Clague, J. J.; Rabus, B.; Stead, D.

    2013-12-01

    Multiple, active, deep-seated gravitational slope deformations (DSGSD) are present near the Trans-Alaska Pipeline and Richardson Highway in the east-central Alaska Range, Alaska, USA. We documented spatial and temporal variations in rates of surface movement of the DSGSDs between 2003 and 2011 using RADARSAT-1 and RADARSAT-2 D-InSAR images. Deformation rates exceed 10 cm/month over very large areas (>1 km2) of many rock slopes. Recent climatic change and strong seismic shaking, especially during the 2002 M 7.9 Denali Fault earthquake, appear to have exacerbated slope deformation. We also mapped DSGSD geological and morphological characteristics using field- and GIS-based methods, and constructed a conceptual 2D distinct-element numerical model of one of the DSGSDs. Preliminary results indicate that large-scale buckling or kink-band slumping may be occurring. The DSGSDs are capable of generating long-runout landslides that might impact the Trans-Alaska Pipeline and Richardson Highway. They could also block tributary valleys, thereby impounding lakes that might drain suddenly. Wrapped 24-day RADARSAT-2 descending spotlight interferogram showing deformation north of Fels Glacier. The interferogram is partially transparent and is overlaid on a 2009 WorldView-1 panchromatic image. Acquisition interval: August 2 - August 26, 2011. UTM Zone 6N.

  18. Stratigraphy, structure, and palinspastic synthesis of the western Brooks Range, northwestern Alaska

    USGS Publications Warehouse

    Mayfield, Charles F.; Tailleur, Irvin L.; Ellersieck, Inyo

    1983-01-01

    This report is an effort to describe and decipher the mid-Paleozoic to Lower Cretaceous stratigraphy and the orogenic evolution of the western Brooks Range. The western Brooks Range primarily is composed of stacks of complexly deformed thrust sheets that contain mostly coeval sequences of rocks with slightly different lithologic facies. In order to simplify the thrust-faulted stratigraphy and palinspastic restoration, the rocks are grouped into eight principal structural levels. The lowest structural level is believed to be autochthonous or parautochthonous and above that, each succeeding level is designated allochthon one through seven. Allochthon seven is composed of the remnants of an extensive ophiolite sheet. Allochthon six is composed of pillow basalt with subordinate intermediate volcanic rocks, chert, and Devonian limestone. It is not certain whether this allochthon was formed in a continental or oceanic setting. Allochthons five through one consist of distinctive and coeval sequences of Devonian to Lower Cretaceous sedimentary rocks that were deposited in a continental setting. The present geographic distribution of each structural level is shown on the allochthon map of the western Brooks Range. The stratigraphy of the southern part of northern Alaska has been reconstructed by systematically unstacking lower allochthons to the north of higher allochthons. The palinspastic map that results from this procedure shows that the minimum thrust displacement between allochthon seven and the autochthon is approximately 700 to 800 km. Schematic cross sections drawn across the palinspastic map show how the stratigraphy of the southern part of northern. Alaska most likely appeared prior to the orogeny. During Devonian and Mississippian time, the sedimentary sequences that are now part of allochthons one to five are inferred to have been deposited in an ensialic basin with both northern and southern margins. During Pennsylvanian time, the sequences seem to have become

  19. Geochemical evidence for a brooks range mineral belt, Alaska

    USGS Publications Warehouse

    Marsh, S.P.; Cathrall, J.B.

    1981-01-01

    Geochemical studies in the central Brooks Range, Alaska, delineate a regional, structurally controlled mineral belt in east-west-trending metamorphic rocks and adjacent metasedimentary rocks. The mineral belt extends eastward from the Ambler River quadrangle to the Chandalar and Philip Smith quadrangles, Alaska, from 147?? to 156??W. longitude, a distance of more than 375 km, and spans a width from 67?? to 69??N. latitude, a distance of more than 222 km. Within this belt are several occurrences of copper and molybdenum mineralization associated with meta-igneous, metasedimentary, and metavolcanic rocks; the geochemical study delineates target areas for additional occurrences. A total of 4677 stream-sediment and 2286 panned-concentrate samples were collected in the central Brooks Range, Alaska, from 1975 to 1979. The -80 mesh ( 2.86) nonmagnetic fraction of the panned concentrates from stream sediment were analyzed by semiquantitative spectrographic methods. Two geochemical suites were recognized in this investigation; a base-metal suite of copper-lead-zinc and a molybdenum suite of molybdenum-tin-tungsten. These suites suggest several types of mineralization within the metamorphic belt. Anomalies in molybdenum with associated Cu and W suggest a potential porphyry molybdenum system associated with meta-igneous rocks. This regional study indicates that areas of metaigneous rocks in the central metamorphic belt are target areas for potential mineralized porphyry systems and that areas of metavolcanic rocks are target areas for potential massive sulfide mineralization. ?? 1981.

  20. Timing of ore-related magmatism in the western Alaska Range, southwestern Alaska

    USGS Publications Warehouse

    Taylor, Ryan D.; Graham, Garth E.; Anderson, Eric D.; Selby, David

    2014-01-01

    This report presents isotopic age data from mineralized granitic plutons in an area of the Alaska Range located approximately 200 kilometers to the west-northwest of Anchorage in southwestern Alaska. Uranium-lead isotopic data and trace element concentrations of zircons were determined for 12 samples encompassing eight plutonic bodies ranging in age from approximately 76 to 57.4 millions of years ago (Ma). Additionally, a rhenium-osmium age of molybdenite from the Miss Molly molybdenum occurrence is reported (approx. 59 Ma). All of the granitic plutons in this study host gold-, copper-, and (or) molybdenum-rich prospects. These new ages modify previous interpretations regarding the age of magmatic activity and mineralization within the study area. The new ages show that the majority of the gold-quartz vein-hosting plutons examined in this study formed in the Late Cretaceous. Further work is necessary to establish the ages of ore-mineral deposition in these deposits.

  1. Photogrammetrically Derived Estimates of Glacier Mass Loss in the Upper Susitna Drainage Basin, Alaska Range, Alaska

    NASA Astrophysics Data System (ADS)

    Wolken, G. J.; Whorton, E.; Murphy, N.

    2014-12-01

    Glaciers in Alaska are currently experiencing some of the highest rates of mass loss on Earth, with mass wastage rates accelerating during the last several decades. Glaciers, and other components of the hydrologic cycle, are expected to continue to change in response to anticipated future atmospheric warming, thus, affecting the quantity and timing of river runoff. This study uses sequential digital elevation model (DEM) analysis to estimate the mass loss of glaciers in the upper Susitna drainage basin, Alaska Range, for the purpose of validating model simulations of past runoff changes. We use mainly stereo optical airborne and satellite data for several epochs between 1949 and 2014, and employ traditional stereo-photogrammetric and structure from motion processing techniques to derive DEMs of the upper Susitna basin glaciers. This work aims to improve the record of glacier change in the central Alaska Range, and serves as a critical validation dataset for a hydrological model that simulates the potential effects of future glacier mass loss on changes in river runoff over the lifespan of the proposed Susitna-Watana Hydroelectric Project.

  2. Devonian volcanogenic massive sulfide deposits and occurrences, southern Yukon-Tanana Terrace, eastern Alaska Range, Alaska

    USGS Publications Warehouse

    Lange, I.M.; Nokleberg, W.J.; Newkirk, S.R.; Aleinikoff, J.N.; Church, S.E.; Krouse, H.R.

    1993-01-01

    A belt of volcanogenic massive sulfide deposits extends for over 150km along the southern margin of the Yukon-Tanana terrane of the eastern Alaska Range. Located north of the Denali fault, the Yukon-Tanana terrane forms a major basement unit in east-central Alaska. The volcanogenic massive sulfide deposits are primarily in the Jarvis Creek Glacier subterrane, which consists of a volcanogenic massive sulfide-bearing metavolcanic rock member and a metasedimentary rock member. Two periods of regional metamorphism and penetrative deformation are indicated: an older, Early Cretaceous, amphibolite facies event and a younger, mid-Cretaceous lower greenschist facies event. The occurrence, mineralogy and sulphur isotope values are discussed. -from Authors

  3. Pleistocene onset of Simultaneous and Rapid Exhumation in the Eastern Central Range of the Taiwan Orogenic Belt

    NASA Astrophysics Data System (ADS)

    Singh, S.; Hsu, W. H.; Byrne, T. B.; Ouimet, W. B.; Lee, Y. H.; Chen, Y. G.; Van Soest, M. C.; Hodges, K. V.

    2015-12-01

    The Taiwan orogenic belt is often treated as a steady, southward propagating orogenic system with an erosion rate of 4-6 mm/yr for 5 My. A few recent studies of the exhumation history, however, suggest that the collision was initially simultaneous and that exhumation rates changed through time. To test this hypothesis, we constructed four new age-elevation curves that span the length of the orogen from the Central Cross-Island Hwy (CXIH) in northern Taiwan to Small Ghost Lake (XGH) in the south. The age-elevation curves are based on 10 new zircon (U-Th)/He (ZrnHe), 10 new zircon fission track (ZrnFT) ages and 82 previously published ZrnFT and ZrnHe dates. Samples used for each age-elevation analysis extended map distances, ranging from 11 to 17 km for ZrnHe and 11 to 27 Km for ZrnFT to limit the influence of topography on estimated uplift rates. Three of the sites, CXIH, XGH and the South Cross-Island Hwy, are from the eastern Central Range whereas the fourth, Mt Yu, is from western Central Range. The results show that all four sites record similar exhumation histories from about 5 Ma to the present, except for a slight difference at Mt Yu. For example, the three eastern sites record an apparent increase in exhumation rate from < 1.2 mm/yr. to ~ 3-5 mm/yr. at about 1.5 Ma. At Mt. Yu, however, a similar increase in the rate of exhumation occurs at about 2 Ma. In addition, the zero-age intercepts of the youngest phase of uplift from the three eastern sites suggest the possibility of an additional increase in exhumation rate after ~0.4 Ma that is not recorded at Mt. Yu. Interestingly, Mt Yu is also mapped as a continuation of the Eocene rocks exposed in the Hsüehshan Range rather than part of the Central Range, consistent with the presence of a major structural boundary between Mt Yu and the three areas to the east. These data suggest the following conclusions: 1) the Hsüehshan and Central Ranges appear to have different exhumation histories; 2) the eastern Central

  4. Pressure-temperature history of the Brooks Range and Seward Peninsula, Alaska HP-LT units and geodynamic implications

    NASA Astrophysics Data System (ADS)

    Lemonnier, N.; Labrousse, L.; Agard, P.; Till, A. B.

    2013-12-01

    Metamorphic rocks in the inner zones of mountain belts constitute a marker of vertical movements within orogenic wedges, themselves controled by balance between boundary conditions and volume forces. They provide key evidence for paleogeographic and tectonic reconstruction of convergence zones. In the Arctic, the Amerasian basin opened in cretaceous time and evolved in the upper plate of the Pacific subduction system. The tectonic evolution of the Brooks Range, northern Alaska, is a key issue for understanding possible coupling between these two dynamics. HP-LT metamorphic rocks, now exposed in the Schist belt, Brooks Range, and the Nome Complex, Seward Peninsula, were brought to the surface during Early Cretaceous to Paleocene time. The processes responsible for their exhumation (syn-collisional nappe-stacking or post-collisional extensional detachment) are still a matter of debate, and have direct implications in terms of orogenic boundary conditions and coupling between subduction processes (to the south) and basin response (to the north; the North Slope). Systematic thermometry via Raman Spectrometry (RSCM) on carbonaceous material from regional transects in the Schist Belt and the Seward Peninsula as well as pseudosections calculations allow the determination of units with contrasting pressure-temperature histories and a comparison of thermal evolution of the two areas. Geodynamic implications of their exhumation is then discussed.

  5. The Cold Surface Layer of Kahiltna Glacier, Central Alaska Range

    NASA Astrophysics Data System (ADS)

    Harrison, W. D.; Gusmeroli, A.; Arendt, A. A.; Atwood, D. K.; Kampes, B.; Sanford, M.; Young, J. C.; Aschwanden, A.; Truffer, M.; Herreid, S. J.; Hock, R. M.

    2011-12-01

    In Arctic, sub-Arctic and high-Alpine settings the ablation area of many mountain glaciers is rarely entirely temperate, and a cold near-surface layer of variable thickness, whose temperature remains below freezing throughout the year, can be found. This occurs when summer ablation rates do not melt the near-surface ice enough to remove the cold layer from the previous winter. A cold near-surface layer is a useful climatological parameter because, for example, its thinning over time can be related to climatic warming. In April 2011 we conducted several 100 MHz ground penetrating radar (GPR) surveys in the upper ablation area (˜1200 m a.s.l.) of the Kahiltna glacier, in the central Alaska Range. Surface ice temperatures, measured continuously during the preceding winter remained at ˜-4°C for 6 months. The GPR data showed the presence of a spatially variable, ˜20 m thick, transparent layer which we interpret to be the cold surface layer. A layer of similar thickness was retrieved by airborne IFSAR P-band radar surveys on several Alaskan glaciers. We use these observations to discuss the occurrence of a cold-surface layer in the Alaska Range and its usefulness for glacier monitoring studies.

  6. 2014 Earthquake Swarm in Northwest Brooks Range, Alaska

    NASA Astrophysics Data System (ADS)

    Ruppert, N. A.; Holtkamp, S. G.

    2014-12-01

    An unusual sequence of earthquakes in NW Brooks Range region of Alaska began with two magnitude 5.7 earthquakes within minutes of each other on April 18, 2014. These events were followed by a vigorous aftershock sequence with many aftershocks reaching magnitude 4 and higher. Later, three more magnitude 5.7 earthquakes occurred in the same source region on May 3, June 7 and June 16. Earthquake source mechanisms indicate normal faulting on SE-NW striking fault planes. The source region is located ~20 km NE of the Noatak village and ~40 km S of the Red Dog Mine. A magnitude 5.5 occurred in this area in 1981. The 1981 sequence also exhibited a swarm-like behavior over the course of 6 months. Detection and reporting of these earthquakes is complicated by sparseness of seismic network in NW Alaska. At the time of April 18 earthquake the nearest seismic site was located at the Red Dog Mine, with the next nearest station 350 km away. Following the May 3 event, the Alaska Earthquake Center installed two additional temporary stations, one in Noatak and another in Kotzebue, 85 km S of the source area. Overall, 450 events were reported in this sequence through end of July. The catalog magnitude of completeness with the additional stations was about ~2.2. We applied waveform template matching algorithm to detect additional events in this sequence that could not be detected with the standard network processing. The template matching resulted in ~600 additional event detections. The waveform cross-correlation indicates that most of the events are not repeating sources. From the catalogued events, only 6% of event pairs have correlation coefficients of 0.75 or higher. We were able to identify only a few families of repeating events. Only one family seemed to be present throughout the entire sequence, while other event families were mostly short-lived. We find preliminary evidence that the earthquakes migrated to shallower depths throughout the sequence, consistent with the

  7. Paleoseismic study of the Cathedral Rapids fault in the northern Alaska Range near Tok, Alaska

    NASA Astrophysics Data System (ADS)

    Koehler, R. D.; Farrell, R.; Carver, G. A.

    2010-12-01

    The Cathedral Rapids fault extends ~40 km between the Tok and Robertson River valleys and is the easternmost fault in a series of active south-dipping imbricate thrust faults which bound the northern flank of the Alaska Range. Collectively, these faults accommodate a component of convergence transferred north of the Denali fault and related to the westward (counterclockwise) rotation of the Wrangell Block driven by relative Pacific/North American plate motion along the eastern Aleutian subduction zone and Fairweather fault system. To the west, the system has been defined as the Northern Foothills Fold and Thrust Belt (NFFTB), a 50-km-wide zone of east-west trending thrust faults that displace Quaternary deposits and have accommodated ~3 mm/yr of shortening since latest Pliocene time (Bemis, 2004). Over the last several years, the eastward extension of the NFFTB between Delta Junction and the Canadian border has been studied by the Alaska Division of Geological & Geophysical Surveys to better characterize faults that may affect engineering design of the proposed Alaska-Canada natural gas pipeline and other infrastructure. We summarize herein reconnaissance field observations along the western part of the Cathedral Rapids fault. The western part of the Cathedral Rapids fault extends 21 km from Sheep Creek to Moon Lake and is characterized by three roughly parallel sinuous traces that offset glacial deposits of the Illinoian to early Wisconsinan Delta glaciations and the late Wisconsinan Donnelly glaciation, as well as, Holocene alluvial deposits. The northern trace of the fault is characterized by an oversteepened, beveled, ~2.5-m-high scarp that obliquely cuts a Holocene alluvial fan and projects into the rangefront. Previous paleoseismic studies along the eastern part of the Cathedral Rapids fault and Dot “T” Johnson fault indicate multiple latest Pleistocene and Holocene earthquakes associated with anticlinal folding and thrust faulting (Carver et al., 2010

  8. Neocomian source and reservoir rocks in the western Brooks Range and Arctic Slope, Alaska

    SciTech Connect

    Mull, C.G.; Reifenstuhl, R.R.; Harris, E.E.; Crowder, R.K.

    1995-04-01

    Detailed (1:63,360) mapping of the Tingmerkpuk sandstone and associated rocks in the Misheguk Mountain and DeLong Mountains guadrangles of the western Brooks Range thrust belt documents potential hydrocarbon source and reservoir rocks in the northern foothills of the western Delong Mountains and adjacent Colville basin of northwest Alaska. Neocomian (?) to Albian micaceous shale, litharenite, and graywacke that overlies the Tingmerkpuk represents the onset of deposition of orogenic sediments derived from the Brooks Range to the south, and the merging of northern and southern sediment sources in the Colville basin. Both the proximal and distal Tingmerkpuk facies contain clay shale interbeds and overlie the Upper Jurassic to Neocomian Kingak Shale. Preliminary geochemical data show that in the thrust belt, these shales are thermally overmature (Ro 1.4-1.6), but are good source rocks with total organic content (TOC) that ranges from 1.2 to 1.8 percent. Shale in the overlying Brookian rocks is also thermally overmature (Ro 1.2-1.5 percent), but contains up to 1.8 percent TOC from a dominantly terrigenous source, and has generated gas. In outcrops at Surprise Creek, in the foothills north of the thrust belt, the Kingak (1.9 percent TOC) and underlying Triassic Shublik Formation (4.6 percent TOC) are excellent oil source rocks with thermal maturity close to peak oil generation stage (Ro0.75-0.9 percent). These rocks have lower thermal maturity values than expected for their stratigraphic position within the deeper parts of the Colville basin and indicate anomalous burial and uplift history in parts of the basin. Preliminary apatite fission-track (AFTA) data from the thrust belt indicate a stage of rapid uplift and cooling at about 53.61 Ma.

  9. Deep-seated gravitational slope deformations near the Trans-Alaska Pipeline, east-central Alaska Range

    NASA Astrophysics Data System (ADS)

    Newman, Stephen Delmont, Jr.

    I investigated active deep-seated gravitational slope deformation (DSGSD) near the Trans-Alaska Pipeline and Richardson Highway in the east-central Alaska Range, Alaska, USA. I documented the presence, spatial extent, and rates of DSGSD using field-geology methods and optical, SAR, and D-InSAR remote-sensing images. I also documented and mapped many of the morphological, geological, and structural characteristics of slopes undergoing DSGSD, and constructed conceptual numerical models to better understand potential deformation mechanisms. Results confirm that many large DSGSD slopes in the study area are actively deforming. Deformation rates range from less than a millimetre per month to more than ten centimetres per month, and are spatially and temporally varient within each slope. Deforming slopes are characterized by differential movement of kilometre-scale rock blocks. Recent climatic changes and strong seismic shaking, especially during the recent 2002 Denali Fault earthquake, have exacerbated ongoing deformation. Study-area DSGSDs should be considered capable of generating long-runout rock avalanches that could directly sever the Trans-Alaska Pipeline and Richardson Highway, or that could dam up valleys and lead to the buildup and catastrophic failure of landslide-dammed lakes capable of impacting said infrastructure. Keywords: Deep-seated gravitational slope deformation; sackung; Trans-Alaska Pipeline; geomorphology; InSAR; Alaska Range.

  10. Terrestrial cosmogenic nuclide surface exposure dating of the oldest glacial successions in the Himalayan orogen: Ladakh Range, northern India

    USGS Publications Warehouse

    Owen, L.A.; Caffee, M.W.; Bovard, K.R.; Finkel, R.C.; Sharma, M.C.

    2006-01-01

    Terrestrial cosmogenic nuclide surface exposure dating of moraine boulders and alluvial fan sediments define the timing of five glacial advances over at least the last five glacial cycles in the Ladakh Range of the Transhimalaya. The glacial stages that have been identified are: the Indus Valley glacial stage, dated at older than 430 ka; the Leh glacial stage occurring in the penultimate glacial cycle or older; the Karglacial stage, occurring during the early part of the last glacial cycle; the Bazgo glacial stage, at its maximum during the middle of the last glacial cycle; and the early Holocene Khalling glacial stage. The exposure ages of the Indus Valley moraines are the oldest observed to date throughout the Himalayan orogen. We observe a pattern of progressively more restricted glaciation during the last five glacial cycles, likely indicating a progressive reduction in the moisture supply necessary to sustain glaciation. A possible explanation is that uplift of Himalayan ranges to the south and/or of the Karakoram Mountains to the west of the region may have effectively blocked moisture supply by the south Asian summer monsoon and mid-latitude westerlies, respectively. Alternatively, this pattern of glaciation may reflect a trend of progressively less extensive glaciation in mountain regions that has been observed globally throughout the Pleistocene. ?? 2006 Geological Society of America.

  11. Structural geology of the Gogebic Range, Penokean orogen northern Michigan and Wisconsin

    SciTech Connect

    Klasner, J.S. . Dept. of Geology Geological Survey, Macomb, IL ); Laberge, G.E. . Dept. of Geology Geological Survey, Oshkosh, WI )

    1994-04-01

    The Gogebic Iron Range extends for some 100 km from near Clam Lake, northwestern Wisconsin to Lake Gogebic, westernmost northern Michigan. It consists of an allochthonous package of Early Proterozoic (EP) strata sandwiched between Archean basement rocks on the south and unconformably overlying Middle Proterozoic (MP) Keweenawan strata on the north. Volcanic rocks occur at either end of the Gogebic range, but the central part of the range consists mainly of monoclinically north-dipping sedimentary strata. Initial phases of Penokean deformation detached Early Proterozoic strata from underlying Archean basement and created northverging, bedding-parallel shears in the monoclinal sequence. Exposures of mylonitized rocks at several places along the length of the district demonstrate the allochthonous nature of EP strata. The main zones of detachment are the shaly portions of the Sunday Quartzite and Palms Formation. Bedding and the shear zones were next deformed into northeast and northwest-plunging folds, most prominently at the east and west ends of the range respectively. Subsequent deformation involved faulting of both the Archean and EP strata. During formation and closure of the MP Midcontinent Rift, the Pre-Keweenawan strata were tilted steeply northward along listric thrusts (Cannon et al, 1993), resulting in a northwestern-oriented, strike-parallel, cross-sectional view of the Pre-Keweenan crust.

  12. Cement stratigraphy of the Lisburne Group, northeastern Brooks Range, Alaska

    SciTech Connect

    Carlson, R.C.; Goldstein, R.H. . Geology Dept.)

    1992-01-01

    Cement stratigraphy serves as a descriptive framework for the interpretation of the diagenetic history of the Carboniferous Lisburne Group, northeastern Brooks Range, Alaska. The Lisburne is a sequence of shallow-water, marine carbonate rocks that have experienced a wide spectrum of diagenetic events: early marine diagenesis, early subaerial exposure, significant erosion and karstification following final Lisburne deposition, deep burial of at least 3,000 meters, compressional tectonism, and final uplift into modern mountain ranges. Compositional zones in the calcite cements were identified by using stains for ferroan calcite and cathodoluminescence microscopy. The cements are, from oldest to youngest: A1-nonferroan, nonluminescent or multibanded calcite; B1-nonferroan to low-ferroan, dull luminescent calcite; C1-ferroan, very-dull luminescent calcite; B2-nonferroan, dull luminescent calcite; A2-nonferroan calcite with 1 or 2 sets of nonluminescent and bright zones; C2-ferroan, very-dull luminescent calcite; Be-nonferroan, dull luminescent calcite. Petrographic studies of cross-cutting relationships show that A1 cements predate or are synchronous with surfaces of subaerial exposure within the Lisburne Group. The cross-cutting relationships include truncation of cements by early fractures, non-marine fissure fills, and at clast margins of autoclastic breccias. Similarly, B1 and C1 cements predate the major unconformity at the top of the Lisburne Group, hence, these cements are pre-Permian in age and may well have precipitated from fresh groundwaters introduced during development of the sub-Permian unconformity. B2 and C2 cements are present in the Permian Echooka formation overlying the Lisburne Group and, thus, can be dated as post-Pennsylvanian. B3 cements are Cretaceous or younger in age.

  13. The topographically asymmetrical Alaska Range: Multiple tectonic drivers through space and time

    NASA Astrophysics Data System (ADS)

    Benowitz, Jeffrey

    The topographically segmented, ˜700 km long Alaska Range evolved over the last ˜50 Ma in response to both far-field driving mechanisms and near-field boundary conditions. The eastern Alaska Range follows the curve of the Denali Fault strike-slip system, forming a large arc of high topography across southern Alaska. The majority of the topography in the eastern Alaska Range lies north of the Fault. A region of low topography separates the eastern Alaska Range from the central Alaska Range, where most of the high topography lies south of the Denali Fault. To the west, there is a restraining bend in the Fault. Southwest of the bend, the north-south trending western Alaska Range takes an abrupt 90 degree turn away from the Denali Fault. I applied 40Ar/39Ar thermochronology to over forty granitic samples to constrain the thermal history of the western and eastern Alaska Range. I combine the 40Ar/39Ar analyses with available apatite fission track and apatite (U-Th)/He dating. I then inferred the Alaska Range's exhumation history from the region's rates and patterns of rock cooling. Periods of mountain building within the Alaska Range are related to Paleocene-Eocene ridge subduction and an associated slab window (˜50 Ma to ˜35 Ma), Neogene flat-slab subduction of the Yakutat microplate (˜24 Ma to present), Yakutat microplate latitudinal variation in thickness (˜6 Ma to present), block rotation/migration, and fault reorganization along the Denali Fault. However, it is clear from basin, petrological and thermochronological constraints that not all of the far-field driving mechanisms affected every segment of the Alaska Range to the same degree or at the same time. Alaska Range tectonic reconstruction is also complicated by near-field structural controls on both the timing and extent of deformation. Fault geometry affects both the amount of exhumation (e.g., ˜14 km in the Susitna Glacier region of the eastern Alaska Range) and location of topographic development (e

  14. Spring and aufeis (icing) hydrology in Brooks Range, Alaska

    NASA Astrophysics Data System (ADS)

    Yoshikawa, Kenji; Hinzman, Larry D.; Kane, Douglas L.

    2007-12-01

    Remote sensing studies and field hydrometeorological and geophysical investigations were employed to characterize several aufeis fields in the Brooks Range, Alaska. Geochemical studies were undertaken together with field hydrological measurements to better understand the chemical and thermal properties of stream base flow (groundwater spring) that contributes to winter aufeis development. The spring water temperature was measured at several major aufeis fields using data loggers throughout the year. Aufeis is an important water storage component in the Arctic and influences local ecology and geomorphology. Synthetic aperture radar (SAR) is a useful and sensitive sensor for aufeis detection and for estimating the total volume of storage as well as freeze/thaw conditions. The SAR analysis indicated that the volume of aufeis formed in winter is 27-30% of the annual groundwater discharge in the Kuparuk River. Visible and near-IR satellite imagery indicated many of the high-discharge springs (more than 10-1000 1/s) and aufeis fields are centered around an elevation of 600 m a.s.l. in limestone areas with glacial morphology. Geomorphological investigations indicate that many of springs have continually existed from at least the last glaciation. Microwave data (SAR), thermal infrared, short wave infrared, and visible and near-IR bands were all used to observe the growth, decay, and distribution of aufeis deposits. The remotely sensed data indicate that the distribution of the aufeis deposits today is nearly the same as it was in past colder periods; this was mainly determined by mapping the distributed carbonate precipitates. Also, spring water temperatures and discharge volumes are predictable from the aufeis field size using remotely sensed techniques.

  15. Structural problems of the Brooks Range ophiolite, Alaska

    SciTech Connect

    Harris, R.A.; Bickerstaff, D. . Dept. of Geology); Stone, D.B. . Geophysical Inst.)

    1993-04-01

    Structural and paleogeographic restorations of the Brooks Range ophiolite (hereafter BRO) and other associated mafic and ultramafic bodies of N. Alaska are difficult because of ambiguous relations between sheeted dikes, cover sediments, and steep NW and SE dipping magmatic flow fabrics. Paleomagnetically enhanced structural studies at Misheguk, Avan, and Siniktanneyak Mountains provide new constraints for the initial dip and sequence of deformation for various structural features of the BRO. The angle between magmatic layers near the petrologic moho and the paleomagnetic inclination of these layers is 50--63[degree] at Misheguk. High level gabbro layers that are disrupted by syn- and post-cooling intrusions display a greater variation. Assuming that the characteristic magnetization is primary, and that the primary inclination was > 80[degree], magmatic layers and the moho had initial dips from 17--40[degree]. These layers now dip 40--70[degree]SE suggesting some post-magmatic tilt. The variation of inclinations with depth in the ophiolite suggest that high level gabbro has tilted most. Sheeted dikes are documented at the Maiyumerak and Siniktanneyak ophiolite bodies. At both locations the dikes dip steeply and strike NE-SW. Sedimentary and volcanic flow layers associated with the dikes have the same strike and dip 0--30[degree]. Parallelism between various planar features throughout the BRO indicates that rotations about a vertical axis are either uniform throughout the ophiolite belt or negligible. Assuming the later, the BRO may represent a linear zone of SSZ magmatism that was oriented NE-SW prior to collision. Post-emplacement long wavelength folding of the ophiolite lid can account for its variation in facing direction and some steepening of magmatic layers.

  16. Structure of the Red Dog District, western Brooks Range, Alaska

    USGS Publications Warehouse

    de Vera, Jean-Pierre P.; McClay, K. R.

    2004-01-01

    The Red Dog district of the western Brooks Range of northern Alaska, which includes the sediment-hosted Zn-Pb-Ag ± Ba deposits at Red Dog, Su-Lik, and Anarraaq, contains one of the world's largest reserves of zinc. This paper presents a new model for the structural development of the area and shows that understanding the structure is crucial for future exploration efforts and new mineral discoveries in the district. In the Red Dog district, a telescoped Late Devonian through Jurassic continental passive margin is exposed in a series of subhorizontally stacked, internally imbricated, and regionally folded thrust sheets. These sheets were emplaced during the Middle Jurassic to Late Cretaceous Brookian orogeny and subsequently were uplifted by late tectonic activity in the Tertiary. The thrust sheet stack comprises seven tectonostratigraphically distinct allochthonous sheets, three of which have been subject to regional and detailed structural analysis. The lowermost of these is the Endicott Mountains allochthon, which is overlain by the structurally higher Picnic Creek and Kelly River allochthons. Each individual allochthon is itself internally imbricated into a series of tectonostratigraphically coherent and distinct thrust plates and subplates. This structural style gives rise to duplex development and imbrication at a range of scales, from a few meters to tens of kilometers. The variable mechanical properties of the lithologic units of the ancient passive margin resulted in changes in structural styles and scales of structures across allochthon boundaries. Structural mapping and analysis of the district indicate a dominant northwest to west-northwest direction of regional tectonic transport. Local north to north-northeast transport of thrust sheets is interpreted to reflect the influence of underlying lateral and/or oblique ramps, which may have been controlled by inherited basin margin structures. Some thrust-sheet stacking patterns suggest out

  17. Long Range Program, Library Development in Alaska 1973-1978.

    ERIC Educational Resources Information Center

    Alaska State Dept. of Education, Juneau. Div. of State Libraries.

    A statewide library development program designed to provide total library services to meet educational, informational, and cultural needs of the people of Alaska is outlined in this document. The body of the report is divided into three sections. In the first, the purpose, scope, and development of the plan are summarized. The second section…

  18. 76 FR 77300 - Alaska Federal Lands Long Range Transportation Plan

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-12-12

    ... transportation planning and decision-making processes. Such cooperation is accomplished through developing common... LRTP--This draft plan describes the benefits of and actions for coordinated planning and decision making among federal land management agencies (FLMA) involved in this Alaska Federal Lands Long...

  19. U/Pb dating of subduction-collision in the Brooks Range: implications for Mesozoic geodynamics of Arctic Alaska

    NASA Astrophysics Data System (ADS)

    Lemonnier, Nicolas; Labrousse, Loic; Agard, Philippe; McClelland, Bill; Cobble, Mattew; Till, Alison; Roeske, Sarah

    2016-04-01

    The paleogeographic and geodynamic evolution of Northern Alaska is crucial to understand the connection between the Arctic and Pacific realms. The opening of the Canada Basin (CB) is debated both in terms of inception time (between 190 and 140 Ma) and driving mechanisms. The prevalent model assumes that CB opened in a back-arc position within the Arctic-Alaska-Chukotka (AAC) terrane following a change in subduction polarity from S- to N-dipping subduction The adjacent Brooks Range orogen (BRO) is thought to have formed when the Koyukuk volcanic arc collided with the southern extension of AAC. This collision therefore potentially provides key information for Arctic geodynamics, and for the mechanisms of CB opening, but neither the detailed timing of this collisional history nor its duration are well known. In order to constrain the timing of the collision, we performed in-situ zircon U-Pb SIMS analyses on eclogites from the BRO s.l. (BR and Seward Peninsula), which indicate that peak burial (at 510 ± 60°C, 1.6 ± 0.2 GPa) during continental subduction and subsequent collision occurred at 141 ± 6 Ma (n=10, MSWD = 1.6). Eclogite metamorphism therefore postdates the initial rifting stage of the CB but predates effective sea-floor spreading. Younger zircon domains (114 ± 13 Ma) associated with retrograde assemblages could indicate a late thermal pulse or recrystallisation during exhumation in the collisional wedge. Combined with all available information on timing, these new age constraints are used to build a tectonic model for coeval evolution of the Brooks Range and the Canada Basin. The intra-Kingak "Jurassic Unconformity" at the Jurassic Cretaceous Boundary (Houseknecht, pers. communication) could actually be considered as the signature of the AAC-Koyukuk arc collision stage in the CB.

  20. Alaska

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Though it's not quite spring, waters in the Gulf of Alaska (right) appear to be blooming with plant life in this true-color MODIS image from March 4, 2002. East of the Alaska Peninsula (bottom center), blue-green swirls surround Kodiak Island. These colors are the result of light reflecting off chlorophyll and other pigments in tiny marine plants called phytoplankton. The bloom extends southward and clear dividing line can be seen west to east, where the bloom disappears over the deeper waters of the Aleutian Trench. North in Cook Inlet, large amounts of red clay sediment are turning the water brown. To the east, more colorful swirls stretch out from Prince William Sound, and may be a mixture of clay sediment from the Copper River and phytoplankton. Arcing across the top left of the image, the snow-covered Brooks Range towers over Alaska's North Slope. Frozen rivers trace white ribbons across the winter landscape. The mighty Yukon River traverses the entire state, beginning at the right edge of the image (a little way down from the top) running all the way over to the Bering Sea, still locked in ice. In the high-resolution image, the circular, snow-filled calderas of two volcanoes are apparent along the Alaska Peninsula. In Bristol Bay (to the west of the Peninsula) and in a couple of the semi-clear areas in the Bering Sea, it appears that there may be an ice algae bloom along the sharp ice edge (see high resolution image for better details). Ground-based observations from the area have revealed that an under-ice bloom often starts as early as February in this region and then seeds the more typical spring bloom later in the season.

  1. Late Mesozoic and Cenozoic thermotectonic evolution of the central Brooks Range and adjacent North Slope foreland basin, Alaska: Including fission track results from the Trans-Alaska Crustal Transect (TACT)

    USGS Publications Warehouse

    O'Sullivan, P. B.; Murphy, J.M.; Blythe, A.E.

    1997-01-01

    Apatite fission track data are used to evaluate the thermal and tectonic history of the central Brooks Range and the North Slope foreland basin in northern Alaska along the northern leg of the Trans-Alaska Crustal Transect (TACT). Fission track analyses of the detrital apatite grains in most sedimentary units resolve the timing of structures and denudation within the Brooks Range, ranging in scale from the entire mountain range to relatively small-scale folds and faults. Interpretation of the results indicates that rocks exposed within the central Brooks Range cooled rapidly from paleotemperatures 110?? to 50??C during discrete episodes at ???100??5 Ma, ???60??4 Ma, and ???24??3 Ma, probably in response to kilometer-scale denudation. North of the mountain front, rocks in the southern half of the foreland basin were exposed to maximum paleotemperatures 110??C in the Late Cretaceous to early Paleocene as a result of burial by Upper Jurassic and Cretaceous sedimentary rocks. Rapid cooling from these elevated paleotemperatures also occurred due to distinct episodes of kilometer-scale denudation at ???60??4 Ma, 46??3 Ma, 35??2 Ma, and ???24??3 Ma. Combined, the apatite analyses indicate that rocks exposed along the TACT line through the central Brooks Range and foreland basin experienced episodic rapid cooling throughout the Late Cretaceous and Cenozoic in response to at least three distinct kilometer-scale denudation events. Future models explaining orogenic events in northern Alaska must consider these new constraints from fission track thermochronology. Copyright 1997 by the American Geophysical Union.

  2. A geochemical perspective of Red Mountain: an unmined volcanogenic massive sulfide deposit in the Alaska Range

    USGS Publications Warehouse

    Giles, Stuart A.; Eppinger, Robert G.

    2014-01-01

    The U.S. Geological Survey (USGS) has investigated the environmental geochemistry of a group of unmined volcanogenic massive sulfide (VMS) deposits in the Bonnifield mining district, Alaska Range, east-central Alaska. The spectacularly colored Red Mountain deposit is the best exposed of these and provides excellent baseline geochemical data for natural environmental impacts of acidic rock drainage, metal dissolution and transport, and acidic salt and metal precipitation from an exposed and undisturbed VMS deposit.

  3. 'Extra-regional' strike-slip fault systems in Chile and Alaska: the North Pacific Rim orogenic Stream vs. Beck's Buttress

    NASA Astrophysics Data System (ADS)

    Redfield, T. F.; Scholl, D. W.; Fitzgerald, P. G.

    2010-12-01

    The ~2000 km long Denali Fault System (DFS) of Alaska is an example of an extra-regional strike-slip fault system that terminates in a zone of widely-distributed deformation. The ~1200 km long Liquiñe-Ofqui Fault Zone (LOFZ) of Patagonia (southern Chile) is another. Both systems are active, having undergone large-magnitude seismic rupture is 2002 (DFS) and 2007 (LOFZ). Both systems appear to be long-lived: the DFS juxtaposes terranes that docked in at least early Tertiary time, whilst the central LOFZ appears to also record early Tertiary or Mesozoic deformation. Both fault systems comprise a relatively well-defined central zone where individual fault traces can be identified from topographic features or zones of deformed rock. In both cases the proximal and distal traces are much more diffuse tributary and distributary systems of individual, branching fault traces. However, since their inception the DFS and LOFZ have followed very different evolutionary paths. Copious Alaskan paleomagnetic data are consistent with vertical axis small block rotation, long-distance latitudinal translation, and a recently-postulated tectonic extrusion towards a distributary of subordinate faults that branch outward towards the Aleution subduction zone (the North Pacific Rim orogenic Stream; see Redfield et al., 2007). Paleomagnetic data from the LOFZ region are consistent with small block rotation but preclude statistically-significant latitudinal transport. Limited field data from the southernmost LOFZ suggest that high-angle normal and reverse faults dominate over oblique to strike-slip structures. Rather than the high-angle oblique 'slivering regime' of the southeasternmost DFS, the initiation of the LOFZ appears to occur across a 50 to 100 km wide zone of brittly-deformed granitic and gneissic rock characterized by bulk compression and vertical pathways of exhumation. In both cases, relative plate motions are consistent with the hypothetical style, and degree, of offset, leading

  4. Range expansion of nonindigenous caribou in the Aleutianarchipelago of Alaska

    USGS Publications Warehouse

    Ricca, Mark A.; Weckerly, Floyd W.; Duarte, Adam; Williams, Jeffrey C.

    2012-01-01

    Caribou (Rangifer tarandus) are nonindigenous to all but the eastern-most island of the Aleutian archipelago of Alaska. In 1958–1959, caribou were intentionally introduced to Adak Island in the central archipelago, and the population has at least tripled in recent years subsequent to the closure of a naval air facility. Although dispersal of caribou to adjacent islands has been suspected, no historical documentation has occurred to date. Herein, we report consistent detections of caribou sign on the adjacent island of Kagalaska over 2 summer field seasons (2010–2011), and visual detection of caribou on that island during the summer of 2011. Ecological impacts of caribou on Kagalaska are not strongly apparent at the present time and we do not know how many animals permanently occupy the island. However, establishment of a reproductively viable resident population on Kagalaska is worrisome and could set the stage for a step-wise invasion of additional nearby islands.

  5. Acadian orogen Which Acadian orogen

    SciTech Connect

    Ludman, A. )

    1993-03-01

    The Acadian orogeny is widely viewed as the climactic event in much of the Northern Appalachians, resulting from the closing of one or more ocean basins and the accretion of the Avalonian continent to ancestral North America. Unconformities have traditionally dated the Acadian orogeny as Middle Devonian in the east and Late Middle to Late Devonian in the western part of the orogen. The recent recognition that several post-Acadian'' plutons are actually Late Silurian suggests that the tectonic models are too simplistic; that accretion previously attributed to a Devonian (Acadian) event may have been a two-stage process: Late Silurian (Salinic ) and Acadian sensu stricto; that orogenic activity may have been continuous from Taconian through Acadian'' times. Differences between the records of the Taconic (Ordovician) and Acadian orogenies suggest different plate interactions: near-orthogonal subduction for the former vs transcurrent faulting for the latter as the dominant mechanisms. Distribution of Salinic'' unconformities across the Northern Appalachian orogen in Maine suggests that accretion of Avalon may have been completed by that Silurian event, but faunal provincialities displayed by fossils as young as Early Devonian in terranes bordering the Fredericton Trough argue for later (Devonian) accretion. A further complication is the imprecise knowledge of the extent to which post-Devonian tectonism is responsible for the current terrane configuration in the Northern Appalachians. Alleghenian folding and thrusting is well-established in some areas where post-Acadian (Carboniferous) strata are present, and is now being documented in older rocks in eastern Maine as well: transcurrent faulting as young as post-Mesozoic( ) along the Norumbega Fault Zone; east-directed thrusting involving the Early Devonian Center Pond pluton.

  6. Lower Paleozoic and Proterozoic rocks of Southern Brooks Range, Alaska

    SciTech Connect

    Dillion, J.T.

    1985-04-01

    Lower Paleozoic or Proterozoic basement rocks occur in windows and thrust plates in several areas of the Brooks Range. Uranium-lead radiometric analyses of highly metamorphosed rocks from the Baird Mountains and Ernie Lake area have yielded Proterozoic ages. Structural, stratigraphic, petrologic, and isotopic evidence exists for Proterozoic(.) rocks in the schist belt; around the Chandalar, Arrigetch,and Igikpak plutons; and in the Cosmos Hills window. Fossiliferous, Lower Paleozoic, low-grade metasedimentary rocks occur in the Romanzof Mountains, Doonerak window, and Baird Mountains, and may also surround the Chandalar plutons. Locally, the Lower Paleozoic rocks are unconformably overlain by Devonian to Mississippian metasediments and may stratigraphically overlie older, higher grade metamorphic rocks. Similarities in the stratigraphic settings and lithologies and in fossil ages and affinities allow correlation of the Lower Paleozoic rocks in the southern Brooks Range. Correlation of Lower Paleozoic rocks exposed beneath the Endicott allochthon at the Doonerak fenster with coeval rocks in an overlying thrust plate to the south at Snowsden Mountain is especially significant. A west-trending thrust fault, which is rooted in Lower Paleozoic basement, along the north side of Snowsden Mountain is postulated to account for these relationships. Apparently, the Endicott allochthon roots beneath the Snowsden Mountain thrust fault. Evidence form conodont samples currently being studied by A. Harris may bear on the extent of the Lower Paleozoic rocks in the upper plate of the Snowsden Mountain thrust and in the Chandalar area.

  7. Geospatial compilation of results from field sample collection in support of mineral resource investigations, Western Alaska Range, Alaska, July 2013

    USGS Publications Warehouse

    Johnson, Michaela R.; Graham, Garth E.; Hubbard, Bernard E.; Benzel, William M.

    2015-07-16

    This Data Series summarizes results from July 2013 sampling in the western Alaska Range near Mount Estelle, Alaska. The fieldwork combined in situ and camp-based spectral measurements of talus/soil and rock samples. Five rock and 48 soil samples were submitted for quantitative geochemi­cal analysis (for 55 major and trace elements), and the 48 soils samples were also analyzed by x-ray diffraction to establish mineralogy and geochemistry. The results and sample photo­graphs are presented in a geodatabase that accompanies this report. The spectral, mineralogical, and geochemical charac­terization of these samples and the sites that they represent can be used to validate existing remote-sensing datasets (for example, ASTER) and future hyperspectral studies. Empiri­cal evidence of jarosite (as identified by x-ray diffraction and spectral analysis) corresponding with gold concentrations in excess of 50 parts per billion in soil samples suggests that surficial mapping of jarosite in regional surveys may be use­ful for targeting areas of prospective gold occurrences in this sampling area.

  8. Geospatial compilation of results from field sample collection in support of mineral resource investigations, Western Alaska Range, Alaska, July 2013

    USGS Publications Warehouse

    Johnson, Michaela R.; Graham, Garth E.; Hubbard, Bernard E.; Benzel, William M.

    2015-01-01

    This Data Series summarizes results from July 2013 sampling in the western Alaska Range near Mount Estelle, Alaska. The fieldwork combined in situ and camp-based spectral measurements of talus/soil and rock samples. Five rock and 48 soil samples were submitted for quantitative geochemi­cal analysis (for 55 major and trace elements), and the 48 soils samples were also analyzed by x-ray diffraction to establish mineralogy and geochemistry. The results and sample photo­graphs are presented in a geodatabase that accompanies this report. The spectral, mineralogical, and geochemical charac­terization of these samples and the sites that they represent can be used to validate existing remote-sensing datasets (for example, ASTER) and future hyperspectral studies. Empiri­cal evidence of jarosite (as identified by x-ray diffraction and spectral analysis) corresponding with gold concentrations in excess of 50 parts per billion in soil samples suggests that surficial mapping of jarosite in regional surveys may be use­ful for targeting areas of prospective gold occurrences in this sampling area.

  9. Geological mapping in Doonerak Fenster, Central Brooks Range, Alaska

    SciTech Connect

    Mull, C.C.; Adams, K.E.; Dillon, J.T.

    1985-04-01

    Mapping of the north flank of the Doonerak fenster has traced the Amawk thrust, the sole fault of the Endicott Mountains allochthon, from the North Fork of the Koyukuk River - Mount Doonerak area eastward for more than 40 km (25 mi) to the east plunge of the Doonerak anticline at Koyuktuvuk Creek near the Dietrich River. Mapping has concentrated on the structural style of the area and on the autochthonous or parautochthonous Carboniferous Lisburne Group, Kayak shale, Kekiktuk Conglomerate - which are present along most of the anticline - and Triassic Karen Creek Sandstone, Triassic Shublik Formation, and Permian-Triassic Sadlerochit Group - which are present only in the west. This Triassic to Mississippian section closely resembles the coeval autochthonous to Parautochthonous Ellesmerian section of the subsurface to the north and in the Brooks Range to the northeast.

  10. Structural architecture of the central Brooks Range foothills, Alaska

    USGS Publications Warehouse

    Moore, Thomas E.; Potter, Christopher J.; O'Sullivan, Paul B.

    2002-01-01

    Five structural levels underlie the Brooks Range foothills, from lowest to highest: (1) autochthon, at a depth of ~9 km; (2) Endicott Mountains allochthon (EMA), thickest under the northern Brooks Range (>15 km) and wedging out northward above the autochthon; (3) higher allochthons (HA), with a composite thickness of 1.5+ km, wedging out northward at or beyond the termination of EMA; (4) Aptian-Albian Fortress Mountain Formation (FM), deposited unconformably on deformed EMA and HA and thickening northward into a >7-km-thick succession of deformed turbidites (Torok Formation); (5) gently folded Albian-Cenomanian deltaic deposits (Nanushuk Group). The dominant faulting pattern in levels 2-3 is thin-skinned thrusting and thrust-related folds formed before deposition of Cretaceous strata. These structures are cut by younger steeply south-dipping reverse faults that truncate and juxtapose structural levels 1-4 and expose progressively deeper structural levels to the south. Structural levels 4-5 are juxtaposed along a north-dipping zone of south-vergent folds and thrusts. Stratigraphic and fission-track age data suggest a kinematic model wherein the foothills belt was formed first, by thrusting of HA and EMA as deformational wedges onto the regionally south-dipping authochon at 140-120Ma. After deposition of FM and Torok during mid-Cretaceous hinterland extension and uplift, a second episode of contractional deformation at 60 Ma shortened the older allochthonous deformational wedges (EMA, HA) and overlying strata on north-vergent reverse faults. To the north, where the allochthons wedge out, shortening caused duplexing in the Torok and development of a triangle zone south of the Tuktu escarpment.

  11. Diagenesis of the Lisburne Group, northeastern Brooks Range, Alaska

    SciTech Connect

    Carlson, R.C.; Goldstein, R.H.; Enos, P.

    1995-05-01

    Petrographic cathodoluminescence studies of the cement stratigraphy of the Lisburne Group yield insights on its diagenetic history. Crosscutting relationships between features of subaerial exposure and calcite cements show that early generations of nonferroan, nonluminescent and multibanded-luminescent calcites are synchronous with or postdated by subaerial exposure surfaces within the Lisburne. Surfaces of subaerial exposure occur at 18 horizons within the Lisburne and are distinguished by features as laminated crusts, rhizoliths, autoclastic breccia, fissure fills, mud cracks, and erosional surfaces. Crosscutting relationships also occur between calcite cements and clasts in karst breccias and conglomerates that formed along the sub-Permian unconformity at the top of the Lisburne. The sub-Permian unconformity postdates later generations of calcite cement. These cements formed in the following sequence: nonferroan to low-ferroan, dully luminescent calcite; ferroan, very-dully luminescent calcite; and second generation of nonferroan, multibanded calcite. The crosscutting relationships not only constrain the timing of cement precipitation, but also suggest that the cements probably were precipitated from meteoric groundwaters introduced during subaerial exposure of the Lisburne platform. Late cements in the Lisburne postdate the Permian Echooka Formation. These cements are low-ferroan, moderately-bright to dully luminescent calcite, followed by a second generation of ferroan, very-dully luminescent calcite. Features of compaction and pressure solution are coincident with the precipitation of the late ferroan calcite and further constrain its timing to deep burial of the Lisburne. The youngest phase of calcite cement precipitated in the Lisburne Group is nonferroan, very-dully luminescent calcite. It commonly fills tectonically-induced shear fractures, indicating precipitation after the onset of Cretaceous (and/or Cenozoic) tectonism in the northeastern Brooks Range.

  12. Tectonic evolution of the Brooks Range ophiolite, Alaska

    SciTech Connect

    Harris, R.A. . Dept. of Geology)

    1993-04-01

    Detailed studies of the composition, internal structure, and age of the Brooks Range ophiolite (BRO) and its metamorphic sole reveal new constraints for its tectonic evolution. The BRO consists of six separate thrust masses of consanguineous composition, internal organization, structure and age. Subophiolite metamorphic rocks are locally preserved along its structural base, which is well exposed in several places. The metamorphic sole is locally transitional with mafic volcanic sequences, chert, tuffs, and minor clastic sedimentary material of the Copter Peak Complex, which is correlative with the Angayucham terrane. This terrane is much older than, and chemically distinct from the BRO. The internal structure of the BRO is characterized by NE-SW trending igneous layers that expose the transition zone from crust to mantle. Residual mantle material consists of tectonized peridotite in abrupt contact with dunite pods up to 4 km thick. Ductile and brittle structures of the BRO preserve various phases of its dynamic evolution from a magma body to a fragmented thrust sheet. The earliest deformational effects are recorded by ductile lattice and shape fabrics in dunites and the layered series of the BRO. Magmatic flow planes generally parallel the petrologic moho, and dip 40[degree]--70[degree] to the NW and SE. Flow lineations consistently plunge ESE-ENE from 39[degree]--54[degree]. Igneous laminations and compositional layers represent patterns of magmatic flow in, and plastic deformation of, a cumulate sequence -- not the deposition pattern of cumulate layers. In the upper layered series, amphiboles with a shape-preferred orientation yield Ar/Ar plateau ages of 163--169 Ma. These ages overlap with plateau ages of the same kind from amphibolite of the metamorphic sole. This concordance in age indicates that cooling of the BRO coincided with its tectonic emplacement.

  13. Logs and Geologic Data from a Paleoseismic Investigation of the Susitna Glacier fault, Central Alaska Range, Alaska

    USGS Publications Warehouse

    Personius, Stephen F.; Crone, Anthony J.; Burns, Patricia A.C.; Beget, James E.; Seitz, Gordon G.; Bemis, Sean P.

    2010-01-01

    This report contains field and laboratory data from a paleoseismic study of the Susitna Glacier fault, Alaska. The initial M 7.2 subevent of the November 3, 2002, M 7.9 Denali fault earthquake sequence produced a 48-km-long set of complex fault scarps, folds, and aligned landslides on the previously unknown, north-dipping Susitna Glacier thrust fault along the southern margin of the Alaska Range in central Alaska. Most of the 2002 folds and fault scarps are 1-3 m high, implying dip-slip thrust offsets (assuming a near-surface fault dip of approximately 20 degrees)of 3-5 m. Locally, some of the 2002 ruptures were superimposed on preexisting scarps that have as much as 5-10 m of vertical separation and are evidence of previous surface-rupturing earthquakes on the Susitna Glacier fault. In 2003-2005, we focused follow-up studies on several of the large scarps at the 'Wet fan' site in the central part of the 2002 rupture to determine the pre-2002 history of large surface-rupturing earthquakes on the fault. We chose this site for several reasons: (1) the presence of pre-2002 thrust- and normal-fault scarps on a gently sloping, post-glacial alluvial fan; (2) nearby natural exposures of underlying fan sediments revealed fine-grained fluvial silts with peat layers and volcanic ash beds useful for chronological control; and (3) a lack of permafrost to a depth of more than 1 m. Our studies included detailed mapping, fault-scarp profiling, and logging of three hand-excavated trenches. We were forced to restrict our excavations to 1- to 2-m-high splay faults and folds because the primary 2002 ruptures mostly were superimposed on such large scarps that it was impossible to hand dig through the hanging wall to expose the fault plane. Additional complications are the pervasive effects of cryogenic processes (mainly solifluction) that can mask or mimic tectonic deformation. The purpose of this report is to present photomosaics, trench logs, scarp profiles, and fault slip

  14. An integrated model for the tectonic development of the frontal Brooks Range and Colville Basin 250 km west of the Trans-Alaska Crustal Transect

    USGS Publications Warehouse

    Cole, F.; Bird, K.J.; Toro, J.; Roure, F.; O'Sullivan, P. B.; Pawlewicz, M.; Howell, D.G.

    1997-01-01

    We present a kinematic model for the sequence of deformation and sedimentation in the frontal Brooks Range and adjacent Colville Basin in the Etivluk River region, 250 km west of the Trans-Alaska Crustal Transect (TACT). The model is based on a tectonic subsidence analysis of the foreland basin, combined with structural, stratigraphic, and thermal studies of the northern edge of the Brooks Range thrust belt. We interpret six discrete tectonic events that led to the present-day configuration of the thrust belt in this area: (1) emplacement of ophiolitic allochthons over the distal continental margin rocks in Valanginian time, hundreds of kilometers south of this study, (2) Hauterivian uplift of the Barrow Arch rift margin, affecting the northern part of the Colville Basin, (3) Barremian contraction involving emplacement of distal continental margin and ophiolitic allochthons onto the Endicott Mountains allochthon and creation of a southward dipping flexural basin on the North Slope autochthon, (4) mid-Cretaceous exhumation of imbricated rocks in the Brooks Range during northward propagation of the thrust front into the foreland, (5) minor thrusting in Late Cretaceous-Paleocene in the northern foreland to the northern limit of contractional structures, and (6) regional exhumation of the orogen and the foreland in Paleocene-Eocene time. This sequence of deformation agrees well with a simple model of a forward propagating thrust system. Copyright 1997 by the American Geophysical Union.

  15. Solvent extraction treatment of PCB contaminated soil at Sparrevohn Long Range Radar Station, Alaska

    SciTech Connect

    Weimer, L.D.

    1999-07-01

    This technical paper describes an on-site soil treatment project at the Sparrevohn Long-Range Radar Station (LRRS), Alaska. The project was conducted during the summer of 1996. Sparrevohn LLRS is located approximately 200 miles west of Anchorage, Alaska and is accessible only by aircraft. Polychlorinated biphenyls (PCB) contaminated soil containing between 50 and 350 milligrams/kilogram (mg/kg) was stockpiled on-site. Terra Kleen Response Group, Inc.'s (Terra Kleen's) solvent extraction process successfully treated the stockpiled PCB contaminated soil ({approximately}290 yd{sup 3}). The PCB concentrations in the treated soil were reduced below the target treatment level of 15 mg/kg. On-site solvent extraction treatment realized considerable savings ({gt}$1,000,000) to the Government over the traditional method of hauling and off-site disposal.

  16. An inverted metamorphic field gradient in the central Brooks Range, Alaska and implications for exhumation of high-pressure/low-temperature metamorphic rocks

    USGS Publications Warehouse

    Patrick, B.; Till, A.B.; Dinklage, W.S.

    1994-01-01

    During exhumation of the Brooks Range internal zone, amphibolite-facies rocks were emplaced atop the blueschist/greenschist facies schist belt. The resultant inverted metamorphic field gradient is mappable as a series of isograds encountered as one traverses up structural section. Amphibolite-facies metamorphism occurred at ??? 110 Ma as determined from 40Ar 39Ar analysis of hornblende. This contrasts with 40Ar 39Ar phengite cooling ages from the uderlying schist belt, which are clearly older (by 17-22 m.y.). Fabrics in both the amphibolite-facies rocks and schist belt are characterized by repeated cycles of N-vergent crenulation and transposition that was likely associated with out-of-sequence ductile thrusting in the internal zone of the Brooks Range orogen. Contractional deformation occurred in an overall environment of foreland-directed tectonic transport, broadly synchronous with exhumation of the internal zone, and shortening within the thin-skinned fold and thrust belt. These data are inconsistent with a recently postulated mid-Cretaceous episode of lithospheric extension in northern Alaska. ?? 1994.

  17. Time-space focused intrusion of genetically unrelated arc magmas in the early Paleozoic Ross-Delamerian Orogen (Morozumi Range, Antarctica)

    NASA Astrophysics Data System (ADS)

    Rocchi, S.; Di Vincenzo, G.; Dini, A.; Petrelli, M.; Vezzoni, S.

    2015-09-01

    The growth of continental crust in accretionary orogenic belts takes place through repeated cycles of subduction-accretion of rock units from continental and oceanic magmatic arcs, supra-subduction zone backarcs and forearcs loaded with continent-derived materials. An ancient example relevant to magmatic arc accretion models is represented by the remnants of the Cambrian-Ordovician Ross Orogen in the Morozumi Range, Victoria Land (Antarctica). There, late Neoproterozoic phyllites host an intrusive complex which preserves a remarkably uncommon record of genetically unrelated magma pulses emplaced under a variable stress regime in a short time span: (1) a dominant K-feldspar-phyric granite, (2) fine-grained dioritic stocks and dykes, (3) a peraluminous granite; and (4) a tonalitic-granodioritic dyke swarm. Laserprobe U-Pb zircon dates cluster at late Cambrian times for all these units, yet they carry differential cargoes of relict cores. Unique geochemical-isotopic signatures for both the less evolved magmas (diorite and dyke tonalite) and the most acidic ones (granite and peraluminous granite) indicate that each one of them originated from distinct sources at depth. Additionally, field relationships and chemical evolutionary trends testify for a variety of shallow level open-system processes, such as magma mingling/mixing between diorite and main granite magmas, as well as progressive incorporation of the host schists by the dyke tonalite magma. In summary, crustal growth in the Morozumi intrusive complex was contributed by fresh mantle magma issuing from the metasomatised mantle wedge, while the production of other melts did recycle different crustal portions/layers: the main granite derived from Grenville-age granulitic lower crust; the peraluminous granite from late Proterozoic upper crust, and the tonalite magmas derived from subduction erosion-enriched subarc mantle and evolved by ingestion of local metasedimentary rocks. Overall, the Morozumi intrusive complex

  18. Devonian-Mississippian carbonate sequence in the Maiyumerak Mountains, western Brooks Range, Alaska

    SciTech Connect

    Dumoulin, J.A. ); Harris, A.G. )

    1990-05-01

    Essentially continuous, dominantly carbonate sedimentation occurred from at least the Early Devonian through the Mississippian in the area that is now the Maiyumerak Mountains, western Brooks Range. This succession is in striking contrast to Paleozoic sequences in the eastern Brooks Range and in the subsurface across northern Alaska, where uppermost Devonian-Mississippian clastic and Carboniferous carbonates unconformably overlie Proterozoic or lower Paleozoic metasedimentary or sedimentary rocks. Conodonts obtained throughout the Maiyumerak Mountains sequence indicate that any hiatus is less than a stage in duration, and there is no apparent physical evidence of unconformity within the succession. The sequence is best exposed northwest of the Eli River, where Emsian-Eifelian dolostones (Baird Group) are conformably overlain by Kinderhookian-Osagian sandy limestones (Utukok Formation) and Osagian-Chesterian fossiliferous limestones (Kogruk Formation) of the Lisburne Group. Conodont species assemblages and sedimentary structures indicate deposition in a range of shallow-water shelf environments. The sequence extends at least 30 km, from the Noatak Quadrangle northeast into the Baird Mountains Quadrangle; its easternmost extent has not been definitively determined. The Ellesmerian orogeny, thought to have produced the extensive middle Paleozoic unconformity seen through much of northern Alaska apparently had little effect on this western Brooks Range sedimentary succession.

  19. Lead exposure from indoor firing ranges among students on shooting teams--Alaska, 2002-2004.

    PubMed

    2005-06-17

    CDC recognizes blood lead levels (BLLs) of >/=25 microg/dL in adults and >/=10 microg/dL in children aged Alaska Environmental Public Health Program (EPHP) conducted lead-exposure assessments of school-based indoor shooting teams in the state, after a BLL of 44 microg/dL was reported in a man aged 62 years who coached a high school shooting team in central Alaska. This report summarizes the results of the EPHP investigation of potential lead exposure in 66 members of shooting teams, aged 7-19 years, who used five indoor firing ranges. The findings suggest that improper design, operation, and maintenance of ranges were the likely cause of elevated BLLs among team members at four of the five firing ranges. Public health officials should identify indoor firing ranges that have not implemented lead-safety measures and offer consultation to reduce the risk for lead exposure among shooters, coaches, and employees.

  20. A 2000 year varve-based climate record from the central Brooks Range, Alaska

    SciTech Connect

    Bird, B.W.; Abbott, M.B.; Finney, B.P.; Kutchko, Barbara

    2009-01-01

    Varved minerogenic sediments from glacial-fed Blue Lake, northern Alaska, are used to investigate late Holocene climate variability. Varve thickness measurements track summer temperature recorded at Atigun Pass, located 41 km east at a similar elevation (r2 = 0.31, P = 0.08). Results indicate that climate in the Brooks Range from 10 to 730 AD (varve year) was warm with precipitation inferred to be higher than during the twentieth century. The varve-temperature relationship for this period was likely compromised and not used in our temperature reconstruction because the glacier was greatly reduced, or absent, exposing sub-glacial sediments to erosion from enhanced precipitation.

  1. Range Expansion of Moose in Arctic Alaska Linked to Warming and Increased Shrub Habitat

    PubMed Central

    Tape, Ken D.

    2016-01-01

    Twentieth century warming has increased vegetation productivity and shrub cover across northern tundra and treeline regions, but effects on terrestrial wildlife have not been demonstrated on a comparable scale. During this period, Alaskan moose (Alces alces gigas) extended their range from the boreal forest into tundra riparian shrub habitat; similar extensions have been observed in Canada (A. a. andersoni) and Eurasia (A. a. alces). Northern moose distribution is thought to be limited by forage availability above the snow in late winter, so the observed increase in shrub habitat could be causing the northward moose establishment, but a previous hypothesis suggested that hunting cessation triggered moose establishment. Here, we use recent changes in shrub cover and empirical relationships between shrub height and growing season temperature to estimate available moose habitat in Arctic Alaska c. 1860. We estimate that riparian shrubs were approximately 1.1 m tall c. 1860, greatly reducing the available forage above the snowpack, compared to 2 m tall in 2009. We believe that increases in riparian shrub habitat after 1860 allowed moose to colonize tundra regions of Alaska hundreds of kilometers north and west of previous distribution limits. The northern shift in the distribution of moose, like that of snowshoe hares, has been in response to the spread of their shrub habitat in the Arctic, but at the same time, herbivores have likely had pronounced impacts on the structure and function of these shrub communities. These northward range shifts are a bellwether for other boreal species and their associated predators. PMID:27074023

  2. Range Expansion of Moose in Arctic Alaska Linked to Warming and Increased Shrub Habitat.

    PubMed

    Tape, Ken D; Gustine, David D; Ruess, Roger W; Adams, Layne G; Clark, Jason A

    2016-01-01

    Twentieth century warming has increased vegetation productivity and shrub cover across northern tundra and treeline regions, but effects on terrestrial wildlife have not been demonstrated on a comparable scale. During this period, Alaskan moose (Alces alces gigas) extended their range from the boreal forest into tundra riparian shrub habitat; similar extensions have been observed in Canada (A. a. andersoni) and Eurasia (A. a. alces). Northern moose distribution is thought to be limited by forage availability above the snow in late winter, so the observed increase in shrub habitat could be causing the northward moose establishment, but a previous hypothesis suggested that hunting cessation triggered moose establishment. Here, we use recent changes in shrub cover and empirical relationships between shrub height and growing season temperature to estimate available moose habitat in Arctic Alaska c. 1860. We estimate that riparian shrubs were approximately 1.1 m tall c. 1860, greatly reducing the available forage above the snowpack, compared to 2 m tall in 2009. We believe that increases in riparian shrub habitat after 1860 allowed moose to colonize tundra regions of Alaska hundreds of kilometers north and west of previous distribution limits. The northern shift in the distribution of moose, like that of snowshoe hares, has been in response to the spread of their shrub habitat in the Arctic, but at the same time, herbivores have likely had pronounced impacts on the structure and function of these shrub communities. These northward range shifts are a bellwether for other boreal species and their associated predators.

  3. Chronology of ophiolite crystallization, detachment, and emplacement: Evidence from the Brooks Range, Alaska

    SciTech Connect

    Wirth, K.R.; Bird, J.M. )

    1992-01-01

    {sup 40}Ar/{sup 39}Ar data from early Middle Jurassic ophiolites (187-184 Ma) in the western Brooks Range, Alaska, indicate that detachment - related metamorphism occurred {approximately}20 m.y. after crystallization and {approximately}20 m.y. before emplacement onto the Arctic Alaska margin. High-temperature metamorphic rocks along the basal surfaces of many ophiolites have ages that are contemporaneous with ophiolite crystallization, suggesting that detachment and thrust faulting occur while the lithosphere is young ({lt}10 Ma) and relatively hot. From these relations it has been generally assumed that detachment and initial overthrusting of oceanic lithosphere occur near the site of generation, such as a marginal basin or mid-ocean ridge. The new data from the Brooks Range ophiolites confirm previous indications that some ophiolites have much longer intervals between crystallization, thrust-related metamorphism, and emplacement. On the basis of these new results and data from other ophiolites, the authors propose that ophiolites originating within large ocean basins will generally have longer crystallization-to-emplacement intervals than the more commonly recognized marginal basin-type ophiolites.

  4. Range Expansion of Moose in Arctic Alaska Linked to Warming and Increased Shrub Habitat.

    PubMed

    Tape, Ken D; Gustine, David D; Ruess, Roger W; Adams, Layne G; Clark, Jason A

    2016-01-01

    Twentieth century warming has increased vegetation productivity and shrub cover across northern tundra and treeline regions, but effects on terrestrial wildlife have not been demonstrated on a comparable scale. During this period, Alaskan moose (Alces alces gigas) extended their range from the boreal forest into tundra riparian shrub habitat; similar extensions have been observed in Canada (A. a. andersoni) and Eurasia (A. a. alces). Northern moose distribution is thought to be limited by forage availability above the snow in late winter, so the observed increase in shrub habitat could be causing the northward moose establishment, but a previous hypothesis suggested that hunting cessation triggered moose establishment. Here, we use recent changes in shrub cover and empirical relationships between shrub height and growing season temperature to estimate available moose habitat in Arctic Alaska c. 1860. We estimate that riparian shrubs were approximately 1.1 m tall c. 1860, greatly reducing the available forage above the snowpack, compared to 2 m tall in 2009. We believe that increases in riparian shrub habitat after 1860 allowed moose to colonize tundra regions of Alaska hundreds of kilometers north and west of previous distribution limits. The northern shift in the distribution of moose, like that of snowshoe hares, has been in response to the spread of their shrub habitat in the Arctic, but at the same time, herbivores have likely had pronounced impacts on the structure and function of these shrub communities. These northward range shifts are a bellwether for other boreal species and their associated predators. PMID:27074023

  5. Reindeer range inventory in western Alaska from computer-aided digital classification of LANDSAT data

    NASA Technical Reports Server (NTRS)

    George, T. H.; Stringer, W. J.; Baldridge, J. N.

    1977-01-01

    An inventory of reindeer-range resources was conducted for the USDA Soil Conservation Service of 1.6 million hectares of wildlands in western Alaska using clustering techniques with digital Landsat data. Computer-aided digital analysis produced a provisional map of rangeland types which was used to design the field collection of vegetation and soil types data. This field data facilitated refinement of the inventory map and was used to describe the map units. The informational classes important to range resources were wet, moist and alpine tundra, tidal marsh, brush and open spruce forest. A significant feature of the study was the extraction of acreage figures by administrative boundaries within the study area. In addition to soil and vegetation association map products (at scales of 1:250,000 and 1:63,360) acreage values were tallied from the digital data for each of the four grazing permit areas established by the Bureau of Land Management.

  6. Upper triassic continental margin strata of the central alaska range: Implications for paleogeographic reconstruction

    USGS Publications Warehouse

    Till, A.B.; Harris, A.G.; Wardlaw, B.R.; Mullen, M.

    2007-01-01

    Reexamination of existing conodont collections from the central Alaska Range indicates that Upper Triassic marine slope and basin rocks range in age from at least as old as the late Carnian to the early middle Norian. The conodont assemblages typical of these rocks are generally cosmopolitan and do not define a distinct paleogeographic faunal realm. One collection, however, containsEpigondolella multidentata sensu Orchard 1991c, which appears to be restricted to western North American autochthonous rocks. Although paleogeographic relations cannot be determined with specificity, the present distribution of biofaces within the Upper Triassic sequence could not have been the result of simple accordion-style collapse of the Late Triassic margin.

  7. Crustal Seismic Anisotropy Produced by Rock Fabric Terranes in the Taiwan Central Range Deformational Orogen: Integrative Study Combining Rock Physics, Structural Geology, and Passive/Active-Source Seismology

    NASA Astrophysics Data System (ADS)

    Okaya, D. A.; Ross, Z.; Christensen, N. I.; Wu, F. T.; Byrne, T. B.

    2014-12-01

    The island of Taiwan is currently under construction due to the collision of the northwestern corner of the Philippine Sea plate and the embedded Luzon island arc with the larger continental Eurasian plate. This collision is responsible for the current growth of the Central Range that dominates the eastern half of the island. An international collaboration involving several USA and Taiwan universities and academic institutions was formed to study how the orogen evolves through time and to understand the role of a colliding island arc in mountain building. The project, Taiwan Integrated Geodynamics Research (TAIGER), was funded by NSF-Continental Dynamics and Taiwan National Science Council. The Central Range grows at one of the most rapid rates of uplift in the world, exposing metamorphic rocks that were once at least 10 km deep. The range offers unique opportunities for studies of crustal seismic anisotropy for two major reasons: (1) its geological makeup is conducive for producing crustal seismic anisotropy; that is, the rocks are highly foliated; and (2) a seismological data volume of significant breadth offers extensive coverage of sources and recording stations throughout the region. We carried out a crustal shear wave splitting study by data mining 3300 local earthquakes collected in the TAIGER 2009 sea-land experiment. We used an automated P and S wave arrival time picking method (Ross and Ben-Zion, 2014) applied to over 100,000 event-station pairs. These data were analyzed for shear-wave splitting using the MFAST automated package (Savage et al., 2010), producing 3300 quality shear wave split measurements. The splitting results were then station-averaged. The results show NNE to NE orientation trends that are consistent with regional cleavage strikes. Average crustal shear wave split time is 0.244 sec. These measurements are consistent with rock physics measurements of Central Range slate and metamorphic acoustic velocities. The splits exhibit orientations

  8. Association of deformation and fluid events in the central Brooks Range fold-and-thrust belt, Northern Alaska

    USGS Publications Warehouse

    Moore, Thomas E.; Potter, Christopher J.; O'Sullivan, Paul B.; Shelton, Kevin L.; Underwood, Michael B.

    2003-01-01

    Ocentral Brooks Range consists of two superposed north-directed contractional orogens, one formed between 140-120 Ma and the other at ~60-45 Ma. The older orogen was an arc-continent collisional zone characterized by far-traveled allochthons and relatively low structural relief. The younger orogen is a retroarc thrust belt with relatively low amounts of shortening and high structural relief. Folding and thrusting of the younger episode is superimposed on the thin-skinned deformational wedge of the earlier orogen and also produced a frontal triangle zone in a thick sequence of mid-Cretaceous foreland basin sediments to the north. Stable isotope compositions of calcite and quartz veins indicate two fluid events including: (1) an earlier, higher-temperature (~250-300° C) event that produced veins in deformed Devonian clastic rocks, and (2) a younger, lower-temperature (~150° C) event that deposited veins in deformed Mississippian through Albian strata. The fluids in the first event had variable d18O values, but nearly constant d13C values buffered by limestone lithologies. The vein-forming fluids in the second event had similarly variable d18O values, but with distinctly lower d13C values as a result of oxidation of organic matter and/or methane. Zircon fission track ages demonstrate cooling to temperatures below 200° C between 140-120 Ma for the Devonian rocks, whereas zircon and apatite fission track ages show that Mississippian to Albian rocks were never heated above 200° C and cooled below 110-90° C at ~60-45 Ma. These data are interpreted as indicating that the older, high-temperature fluid event was active during thrusting at 120-140 Ma, and the younger fluid event during deformation at ~60-45 Ma. The data and results presented in this poster will be published in early 2004 in Moore and others (in press).

  9. Preliminary results, Central Gneiss Complex of the Coast Range batholith, southeastern Alaska: the roots of a high-K, calc-alkaline arc?

    USGS Publications Warehouse

    Barker, F.; Arth, Joseph G.

    1984-01-01

    The Central Gneiss Complex (CGC) of the Coast Range batholith is the oldest unit of the batholith east of Ketchikan, Alaska, being dated by the zircon UPb method (by T.W. Stern) at 128-140 Ma. Heterogeneous, layered, commonly migmatitic, orthogneiss of hornblende-biotite quartz diorite, tonalite, quartz monzodiorite and granodiorite compositions (IUGS terminology) form the major part of the CGC. These gneisses show a range of 50-65% SiO2 and are high in Al2O3 (c. 15-19%), K2O (1.5-4%) and Sr (800-900 ppm). Most major elements show coherent, typically magmatic trends with SiO2. La and Rb show maxima at ??? 58% SiO2. Initial 87Sr/86Sr ratios are relatively high and range from 0.7052 to 0.7066. Wallrocks of the CGC are mostly metagraywacke, pelite and metavolcanic rocks at amphibolite facies; they are geochemically dissimilar to the CGC. Major and minor elements of the CGC are very similar to those of high-K orogenic, calc-alkaline andesitic suites. The CGC may have formed largely by fractionation of mantle-derived, high AlKSr basaltic liquid in an ascending diapir, having hornblende, plagioclase, and biotite as major precipitating phases. The CGC probably represents the plutonic equivalent of a continental-margin or Andean arc that formed when the Taku terrane of the Insular belt on the west collided with the previously emplaced (but also allochthonous) Stikine terrane on the east in Late Jurassic or Early Cretaceous time. ?? 1984.

  10. Zoned Cr, Fe-spinel from the La Perouse layered gabbro, Fairweather Range, Alaska

    USGS Publications Warehouse

    Czamanske, G.K.; Himmelberg, G.R.; Goff, F.E.

    1976-01-01

    Zoned spinel of unusual composition and morphology has been found in massive pyrrhotite-chalcopyrite-pent-landite ore from the La Perouse layered gabbro intrusion in the Fairweather Range, southeastern Alaska. The spinel grains show continuous zoning from cores with up to 53 wt.% Cr2O3 to rims with less than 11 wt.% Cr2O3. Their composition is exceptional because they contain less than 0.32 wt.% MgO and less than 0.10 wt.% Al2O3 and TiO2. Also notable are the concentrations of MnO and V2O3, which reach 4.73 and 4.50 wt.%, respectively, in the cores. The spinel is thought to have crystallized at low oxygen fugacity and at temperatures above 900??C, directly from a sulfide melt that separated by immiscibility from the gabbroic parental magma. ?? 1976.

  11. Timing and nature of the Xinlin-Xiguitu Ocean: constraints from ophiolitic gabbros in the northern Great Xing'an Range, eastern Central Asian Orogenic Belt

    NASA Astrophysics Data System (ADS)

    Feng, Zhiqiang; Liu, Yongjiang; Liu, Binqiang; Wen, Quanbo; Li, Weimin; Liu, Qing

    2016-03-01

    Jifeng ophiolitic mélange (ultramafic rocks, meta-basalts and gabbros) crops out in the northern segment of the Great Xing'an Range, the eastern segment of the Central Asian Orogenic Belt, which marks the closure of the Xinlin-Xiguitu Ocean associated with the collision between the Erguna block and Xing'an block. In order to investigate the formation age and magma source of the Jifeng ophiolitic mélange, the gabbros from newly discovered the Jifeng ophiolitic mélange are studied with zircon U-Pb ages, whole-rock geochemistry and zircon Hf isotopes. Zircon U-Pb dating from the ophiolitic gabbros yields U-Pb age of 647 ± 5.3 Ma, which may represent the formation age of the ophiolitic mélange. The gabbros display low SiO2, TiO2, K2O contents, high Na2O, LREE contents and indistinctive REE fractionation [(La/Yb)N = 1.97-2.98]. It shows an E-MORB-like affinity, while the element concentrations of the Jifeng samples are lower than that of E-MORB. More importantly, Nb displays negative anomaly in comparison with Th, which shows a transitional SSZ-type ophiolite signature. Moreover, the ɛ Hf ( t) values of ~647 Ma zircons in the gabbros range from +8.4 to +13.4, and the corresponding Hf single-stage ages ( T DM1) are between 687 and 902 Ma, which is obviously older than the crystallization age of 647 Ma. These geochemical features can be explained as melts from the partial melting of a depleted mantle source meta-somatized by fluids derived from a subducted slab. Accordingly, we conclude that the Jifeng ophiolitic mélange is probably related to transitional SSZ-type ophiolite and developed in an intra-oceanic subduction, which indicates that an ocean (the Xinlin-Xiguitu Ocean) existed between the Erguna block and Xing'an block. The Ocean's formation might be no later than the Neoproterozoic (647 Ma), and it was closed in the Late Cambrian because of the collision between the Erguna block and Xing'an block.

  12. Range expansion of moose in arctic Alaska linked to warming and increased shrub habitat

    USGS Publications Warehouse

    Tape, Ken D.; Gustine, David D.; Reuss, Roger W.; Adams, Layne G.; Clark, Jason A.

    2016-01-01

    Twentieth century warming has increased vegetation productivity and shrub cover across northern tundra and treeline regions, but effects on terrestrial wildlife have not been demonstrated on a comparable scale. During this period, Alaskan moose (Alces alces gigas) extended their range from the boreal forest into tundra riparian shrub habitat; similar extensions have been observed in Canada (A. a. andersoni) and Eurasia (A. a. alces). Northern moose distribution is thought to be limited by forage availability above the snow in late winter, so the observed increase in shrub habitat could be causing the northward moose establishment, but a previous hypothesis suggested that hunting cessation triggered moose establishment. Here, we use recent changes in shrub cover and empirical relationships between shrub height and growing season temperature to estimate available moose habitat in Arctic Alaska c. 1860. We estimate that riparian shrubs were approximately 1.1 m tall c. 1860, greatly reducing the available forage above the snowpack, compared to 2 m tall in 2009. We believe that increases in riparian shrub habitat after 1860 allowed moose to colonize tundra regions of Alaska hundreds of kilometers north and west of previous distribution limits. The northern shift in the distribution of moose, like that of snowshoe hares, has been in response to the spread of their shrub habitat in the Arctic, but at the same time, herbivores have likely had pronounced impacts on the structure and function of these shrub communities. These northward range shifts are a bellwether for other boreal species and their associated predators.

  13. Plate Margin Deformation and Active Tectonics Along the Northern Edge of the Yakutat Terrane in the Saint Elias Orogen, Alaska and Yukon, Canada

    NASA Technical Reports Server (NTRS)

    Bruhn, Ronald L.; Sauber, Jeanne; Cotton, Michele M.; Pavlis, Terry L.; Burgess, Evan; Ruppert, Natalia; Forster, Richard R.

    2012-01-01

    The northwest directed motion of the Pacific plate is accompanied by migration and collision of the Yakutat terrane into the cusp of southern Alaska. The nature and magnitude of accretion and translation on upper crustal faults and folds is poorly constrained, however, due to pervasive glaciation. In this study we used high-resolution topography, geodetic imaging, seismic, and geologic data to advance understanding of the transition from strike-slip motion on the Fairweather fault to plate margin deformation on the Bagley fault, which cuts through the upper plate of the collisional suture above the subduction megathrust. The Fairweather fault terminates by oblique-extensional splay faulting within a structural syntaxis, allowing rapid tectonic upwelling of rocks driven by thrust faulting and crustal contraction. Plate motion is partly transferred from the Fairweather to the Bagley fault, which extends 125 km farther west as a dextral shear zone that is partly reactivated by reverse faulting. The Bagley fault dips steeply through the upper plate to intersect the subduction megathrust at depth, forming a narrow fault-bounded crustal sliver in the obliquely convergent plate margin. Since . 20 Ma the Bagley fault has accommodated more than 50 km of dextral shearing and several kilometers of reverse motion along its southern flank during terrane accretion. The fault is considered capable of generating earthquakes because it is linked to faults that generated large historic earthquakes, suitably oriented for reactivation in the contemporary stress field, and locally marked by seismicity. The fault may generate earthquakes of Mw <= 7.5.

  14. Neogene exhumation in the eastern Alaska Range and its relationship to splay fault activity in the Denali fault system

    NASA Astrophysics Data System (ADS)

    Waldien, T.; Roeske, S.; Benowitz, J.; Allen, W. K.; Ridgway, K.

    2015-12-01

    Dextral oblique convergence in the Denali fault system results from subduction zone strain in the Alaska syntaxis that is partitioned into the upper plate. This convergence is accommodated by dextral-reverse oblique slip on segments of the main strand of the Denali fault in the center of the Alaska Range and by splay faults north and south of the Denali fault at the margins of the Alaska Range. Low-temp. thermochronometry applied to basement rocks bounded by faults within the Denali fault system aids stratigraphic data to determine the timing and locations of exhumation in the Alaska Range, which augment regional seismicity studies aimed at resolving modern fault activity in the Denali fault system. The McCallum Creek and Broxson Gulch faults are north-dipping faults that splay southward from the Denali fault near the Delta River and mark the southern margin of the eastern Alaska Range. Apatite fission track thermochronometry on rocks north of the McCallum Creek fault shows rapid cooling in the hanging wall coeval with basin development in the footwall initiating at the Miocene-Pliocene boundary. Apatite fission track and apatite (U-Th)/He ages from plutonic rocks in the hanging wall of the Broxson Gulch fault, west of the McCallum Creek fault, show final cooling in the Miocene, slightly younger than hanging wall cooling associated with the Susitna Glacier thrust further to the west. Neogene low-temp. cooling ages in the hanging walls of the Susitna Glacier thrust, Broxson Gulch, and McCallum Creek faults suggest that these structures have been accommodating convergence in the Denali fault system throughout the Neogene. More recent cooling in the hanging wall of the McCallum Creek compared to the Susitna Glacier thrust suggests that this fault-related exhumation has migrated eastward throughout the Neogene. Convergence on these splay faults south of the Denali fault results in internal contraction of the crust south of the Denali fault, implying that the Southern

  15. Stratigraphy, structure, and graptolites of an Ordovician and Silurian sequence in the Terra Cotta Mountains, Alaska Range, Alaska

    USGS Publications Warehouse

    Churkin, Michael; Carter, Claire

    1996-01-01

    The geology and graptolite faunas of the Terra Cotta Mountains in south-central Alaska are described. Three new formations of Paleozoic age are named and described; they include graptolitiferous argillaceous rocks, sandstones, and limestones of the Dillinger Terrane. The structure and tectonics of the mapped area arc also discussed. Ninety-five species of Ordovician and Silurian graptolites, including four new species, are described and illustrated. The faunal succession is divided into nine Ordovician and ten Silurian biostratigraphic zones and is correlated with graptolite faunas found elsewhere.

  16. Zirconolite, zircon and monazite-(Ce) U-Th-Pb age constraints on the emplacement, deformation and alteration history of the Cummins Range Carbonatite Complex, Halls Creek Orogen, Kimberley region, Western Australia

    NASA Astrophysics Data System (ADS)

    Downes, Peter J.; Dunkley, Daniel J.; Fletcher, Ian R.; McNaughton, Neal J.; Rasmussen, Birger; Jaques, A. Lynton; Verrall, Michael; Sweetapple, Marcus T.

    2016-04-01

    In situ SHRIMP U-Pb dating of zirconolite in clinopyroxenite from the Cummins Range Carbonatite Complex, situated in the southern Halls Creek Orogen, Kimberley region, Western Australia, has provided a reliable 207Pb/206Pb age of emplacement of 1009 ± 16 Ma. Variably metamict and recrystallised zircons from co-magmatic carbonatites, including a megacryst ~1.5 cm long, gave a range of ages from ~1043-998 Ma, reflecting partial isotopic resetting during post-emplacement deformation and alteration. Monazite-(Ce) in a strongly foliated dolomite carbonatite produced U-Th-Pb dates ranging from ~900-590 Ma. Although the monazite-(Ce) data cannot give any definitive ages, they clearly reflect a long history of hydrothermal alteration/recrystallisation, over at least 300 million years. This is consistent with the apparent resetting of the Rb-Sr and K-Ar isotopic systems by a post-emplacement thermal event at ~900 Ma during the intracratonic Yampi Orogeny. The emplacement of the Cummins Range Carbonatite Complex probably resulted from the reactivation of a deep crustal structure within the Halls Creek Orogen during the amalgamation of Proterozoic Australia with Rodinia over the period ~1000-950 Ma. This may have allowed an alkaline carbonated silicate magma that was parental to the Cummins Range carbonatites, and generated by redox and/or decompression partial melting of the asthenospheric mantle, to ascend from the base of the continental lithosphere along the lithospheric discontinuity constituted by the southern edge of the Halls Creek Orogen. There is no evidence of a link between the emplacement of the Cummins Range Carbonatite Complex and mafic large igneous province magmatism indicative of mantle plume activity. Rather, patterns of Proterozoic alkaline magmatism in the Kimberley Craton may have been controlled by changing plate motions during the Nuna-Rodinia supercontinent cycles (~1200-800 Ma).

  17. Petroleum source potential and thermal maturity of Cantwell Formation (Paleocene), central Alaska Range: a reconnaissance study

    SciTech Connect

    Stanley, R.G.

    1987-05-01

    The Paleocene Cantwell Formation is a sequence of nonmarine sedimentary and volcanic rocks that is widely distributed in the central Alaska Range and locally is more than 3000 m thick. Mudstones and coals in the Cantwell were deposited in a variety of lacustrine and fluvial overbank environments and are of interest as potential source rocks of petroleum. Thirty-eight samples of mudstone and coal were collected from ten outcrops and analyzed using Rock-Eval pyrolysis, vitrinite reflectance (R/sub 0/), and thermal alteration index (TAI). The results suggest that these rocks may be potential sources of gas and possibly oil. Total organic carbon (TOC) in the samples is relatively high, averaging about 2.8% (range 0.5-14.2%) in the mudstones and about 28.8% (range 5.1-50.2%) in the coals. Plots of hydrogen and oxygen indices (HI and OI) on modified van Krevelen diagrams indicate kerogens of types III and IV. In addition, HI values are generally less than 150 and S2/S3 values are generally less than 3, indicating that these kerogens are gas prone. A few samples exhibit somewhat higher values of HI (up to 170) and S2/S3 (up to 18.6) and therefore may be capable of generating small amounts of oil. Values of T/sub max/ (range 437-537/sup 0/C), median R/sub 0/ (range 0.63-4.28), and TAI (range 2.3.-3.8) show that the thermal maturity of the samples varies from mature to postmature with respect to the oil and gas windows.

  18. Changing exhumation patterns during Cenozoic growth and glaciation of the Alaska Range: Insights from detrital thermochronology and geochronology

    NASA Astrophysics Data System (ADS)

    Lease, Richard O.; Haeussler, Peter J.; O'Sullivan, Paul

    2016-04-01

    Cenozoic growth of the Alaska Range created the highest topography in North America, but the space-time pattern and drivers of exhumation are poorly constrained. We analyzed U/Pb and fission-track double dates of detrital zircon and apatite grains from 12 catchments that span a 450 km length of the Alaska Range to illuminate the timing and extent of exhumation during different periods. U/Pb ages indicate a dominant Late Cretaceous to Oligocene plutonic provenance for the detrital grains, with only a small percentage of grains recycled from the Mesozoic and Paleozoic sedimentary cover. Fission-track ages record exhumation during Alaska Range growth and incision and reveal three distinctive patterns. First, initial Oligocene exhumation was focused in the central Alaska Range at ~30 Ma and expanded outward along the entire length of the range until 18 Ma. Oligocene exhumation, coeval with initial Yakutat microplate collision >600 km to the southeast, suggests a far-field response to collision that was localized by the Denali Fault within a weak Mesozoic suture zone. Second, the variable timing of middle to late Miocene exhumation suggests independently evolving histories influenced by local structures. Time-transgressive cooling ages suggest successive rock uplift and erosion of Mounts Foraker (12 Ma) through Denali (6 Ma) as crust was advected through a restraining bend in the Denali Fault and indicate a long-term slip rate ~4 mm/yr. Third, Pliocene exhumation is synchronous (3.7-2.7 Ma) along the length of the Alaska Range but only occurs in high-relief, glacier-covered catchments. Pliocene exhumation may record an acceleration in glacial incision that was coincident with the onset of Northern Hemisphere glaciation.

  19. 33 CFR 334.1280 - Bristol Bay, Alaska; air-to-air weapon range, Alaskan Air Command, U.S. Air Force.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 33 Navigation and Navigable Waters 3 2014-07-01 2014-07-01 false Bristol Bay, Alaska; air-to-air weapon range, Alaskan Air Command, U.S. Air Force. 334.1280 Section 334.1280 Navigation and Navigable... REGULATIONS § 334.1280 Bristol Bay, Alaska; air-to-air weapon range, Alaskan Air Command, U.S. Air Force....

  20. 33 CFR 334.1280 - Bristol Bay, Alaska; air-to-air weapon range, Alaskan Air Command, U.S. Air Force.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 33 Navigation and Navigable Waters 3 2012-07-01 2012-07-01 false Bristol Bay, Alaska; air-to-air weapon range, Alaskan Air Command, U.S. Air Force. 334.1280 Section 334.1280 Navigation and Navigable... REGULATIONS § 334.1280 Bristol Bay, Alaska; air-to-air weapon range, Alaskan Air Command, U.S. Air Force....

  1. 33 CFR 334.1280 - Bristol Bay, Alaska; air-to-air weapon range, Alaskan Air Command, U.S. Air Force.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 33 Navigation and Navigable Waters 3 2013-07-01 2013-07-01 false Bristol Bay, Alaska; air-to-air weapon range, Alaskan Air Command, U.S. Air Force. 334.1280 Section 334.1280 Navigation and Navigable... REGULATIONS § 334.1280 Bristol Bay, Alaska; air-to-air weapon range, Alaskan Air Command, U.S. Air Force....

  2. 33 CFR 334.1280 - Bristol Bay, Alaska; air-to-air weapon range, Alaskan Air Command, U.S. Air Force.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 33 Navigation and Navigable Waters 3 2011-07-01 2011-07-01 false Bristol Bay, Alaska; air-to-air weapon range, Alaskan Air Command, U.S. Air Force. 334.1280 Section 334.1280 Navigation and Navigable... REGULATIONS § 334.1280 Bristol Bay, Alaska; air-to-air weapon range, Alaskan Air Command, U.S. Air Force....

  3. 33 CFR 334.1280 - Bristol Bay, Alaska; air-to-air weapon range, Alaskan Air Command, U.S. Air Force.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 33 Navigation and Navigable Waters 3 2010-07-01 2010-07-01 false Bristol Bay, Alaska; air-to-air weapon range, Alaskan Air Command, U.S. Air Force. 334.1280 Section 334.1280 Navigation and Navigable... REGULATIONS § 334.1280 Bristol Bay, Alaska; air-to-air weapon range, Alaskan Air Command, U.S. Air Force....

  4. Middle Jurassic U-Pb crystallization age for Siniktanneyak Mountain ophiolite, Brooks Range, Alaska

    SciTech Connect

    Moore, T.E. ); Aleinikoff, J.N.; Walter, M. )

    1993-04-01

    The authors report here a U-Pb age for the Siniktanneyak Mountain Ophiolite klippe in the west-central Brooks Range, the first U-Pb ophiolite age in northern Alaska. Like klippen of mafic and ultramafic rocks in the Brooks Range, the Siniktanneyak Mountain klippe is composed of a lower allochthon of Devonian and younger( ) diabase and metabasalt with trace-element characteristics of seamount basalts and an upper allochthon of ophiolite. The ophiolite is partial, consisting of (1) abundant dunite and subordinate harzburgite and wehrlite; (2) cumulate clinopyroxene gabbro, and (3) minor noncumulate clinopyroxene gabbro and subordinate plagiogranite; no sheeted dikes or volcanic rocks are known in the ophilitic allochthon. The plagiogranite forms small dikes and stocks that intrude the noncumulate gabbro and consists of zoned Na-rich plagioclase + clinopyroxene with interstial quartz and biotite. Five fractions of subhedral, tan zircon from the plagiogranite yield slightly discordant U-Pb data with an upper intercept age of 170 [+-] 3 Ma. The U-Pb data indicate that the Siniktanneyak Mountain ophiolite crystallized in the Middle Jurassic and was emplaced by thrusting onto mafic accretionary prism rocks within about 10 m.y. of crystallization. The U-Pb data provide an upper limit to the age of initiation of the Brookian orogeny.

  5. Quantifying the spatial distribution of rapid exhumation from glacial detritus, St. Elias Range (Alaska)

    NASA Astrophysics Data System (ADS)

    Grabowski, D.; Enkelmann, E.; Ehlers, T. A.

    2012-04-01

    We present a provenance analysis, zircon (U-Th)/He thermochronometer cooling ages, and petrologic characterization of exhumation processes active under the Malaspina Glacier, St. Elias Range, Alaska. The collision of the Yakutat Terrane with North America formed the St. Elias Range in southeast Alaska. This region is subject to active faulting, high seismicity, and intense glacial erosion. Recent thermochronology studies document rapid rock exhumation at the Yakutat corner where strike-slip deformation transitions to convergence. Published detrital zircon fission track ages from sand samples of the Seward - Malaspina Glacier yielded a young age population of 2 Ma, suggesting a region of rapid exhumation somewhere in the glacier drainage basin. However, the glaciers cover the area and prevent direct observation and sampling, thereby inhibiting detailed bedrock exhumation studies of the Yakutat corner region. We investigate the lithologies of the bedrock at the Yakutat corner to quantify patterns of rock exhumation using clasts collected from the toe of the Malaspina Glacier. Seven different locations 50 km around the glacier were sampled and lithologies characterized by point counting in the field. In total, 1998 clasts were analyzed. We identified six main lithological groups that are assignable to specific geological units. Most of the detritus is gneiss and granulite (26%), micashist and phyllite (26%), and granite (11%) and are typical lithologies of the Chugach Terrane located at the southern margin of the North American plate. Mafic rocks of amphibolite, gabbro, and basalts (21%), and metapelite, sandstone, quartzite and breccia (14%) were also present and are typical for the colliding Yakutat Terrane. Two percent of the clasts are tightly foliated and mylonitic. These clasts are inferred to originate from the Contact Fault, an old suture zone that has been reactivated during Yakutat Terrane collision. Individual clasts from each sample locality and from all

  6. Magmatic responses to Late Cretaceous through Oligocene tectonic evolution of the western Alaska Range

    NASA Astrophysics Data System (ADS)

    Todd, E.; Jones, J. V., III; Karl, S.; Ayuso, R. A.; Bradley, D. C.; Box, S. E.; Haeussler, P. J.

    2014-12-01

    New geochemistry, U/Pb geochronology, and radiogenic isotopes, together with existing datasets, contribute to a refined model of the petrogenetic history of magmatism in the western Alaska Range. Plutons within the study area were emplaced into Kahiltna basin Mesozoic turbiditic strata. The Kahiltna sequence overlies Mesozoic Peninsular oceanic terrane rocks in the SE half of the basin and Proterozoic to Paleozoic Farewell continental terrane rocks to the NW. This study focuses on successive intrusion suites, most of which are thought to intrude Kahiltna or underlying Farewell terrane rocks, but include older, perhaps more deeply exhumed rocks emplaced in Peninsular terrane basement to the SE. The chemically diverse sequence records magmatism associated with major tectonic reorganization events on the southern Alaska circum-Pacific subduction margin. The oldest pluton suite (~100-80 Ma) is mostly intermediate to evolved calcalkaline granite and coincides with final closure of the Kahiltna basin and a regional transition to transpression-dominated tectonics. The post-closure magmatic pulse (~75-67 Ma) is compositionally varied, including primitive subalkaline melts, peraluminous high-K granites, and a subset of sodic, adakite-like granites. A Paleocene (~63-57 Ma) magmatic flare-up follows, dominated by extremely fractionated subalkaline melts. Rare, more primitive melts of this suite are metaluminous, from gabbro to syenite. This stage may represent relaxed melt productivity or shallowing of the slab dip, yielding more laterally diffuse melting. An early Eocene magmatic hiatus precedes middle Eocene circum-Pacific tectonic reorganization, regionally resulting in initiation of proto-Aleutian/Meshik arc magmatism, and locally in the 44-37 Ma emplacement of subalkaline intermediate to felsic plutons associated with andesite to rhyolite volcanic deposits. An Oligocene (~31-25 Ma) magmatic pulse involved emplacement of a compositionally variable suite ranging from

  7. Permian deposition in the north central Brooks Range, Alaska Constraints for tectonic reconstructions

    USGS Publications Warehouse

    Adams, K.E.; Mull, C.G.; Crowder, R.K.

    1997-01-01

    Two opposing tectonic models have been offered to explain the regional structural relations in the north central Brooks Range fold-thrust belt of northern Alaska. The first suggests that rocks of the northern Endicott Mountains were thrust from south to north over the area of the present Mount Doonerak high and are therefore highly allochthonous. The second implies that the rocks of the northern Endicott Mountains were deposited in a basin that lay north of the Mount Doonerak high and later were thrust a short distance southward onto the northern flank of the high and are thus parautochthonous. To provide stratigraphic constraints for these models, this study examines Permian facies of the north central Brooks Range. Permian rocks in the north central Brooks Range comprise a thin (40 to 160 m thick), fining-upward succession of clastic, storm-influenced shelf deposits. When the rocks of the northern Endicott Mountains are restored south of the Mount Doonerak area, a minimum distance of 80 km, the Permian deposits grade systematically from distal facies (Siksikpuk Formation) in the southwest to proximal facies (Echooka Formation) in the northeast. Facies trends in the reconstructed Permian basin include, from southwest to northeast, (1) an increase in carbonate content and corresponding decrease in silica content, (2) a general darkening and thickening of shaley intervals, (3) an increase in proximal features of storm beds, including coarser, thicker, more abundant, and more closely spaced beds, and (4) an increase in abundance and diversity of the faunal assemblage with a corresponding decrease in age. These stratigraphic relations imply that rocks of the northern Endicott Mountains are allochthonous and structurally overlie a proximal stratigraphic succession similar to that exposed in the Mount Doonerak area and northeastern Brooks Range. Copyright 1997 by the American Geophysical Union.

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

    NASA Astrophysics Data System (ADS)

    Robertson, Peter Benjamin

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

  9. Automated detection of unstable glacier flow and a spectrum of speedup behavior in the Alaska Range

    NASA Astrophysics Data System (ADS)

    Herreid, Sam; Truffer, Martin

    2016-01-01

    Surge-type glaciers are loosely defined as glaciers that experience periodic alterations between slow and fast flow regimes. Glaciers from a variety of mountain ranges around the world have been classified as surge type, yet consensus of what defines a glacier as surge type has not always been met. A common source of dispute is the lack of a succinct and globally applicable delimiter between a surging and nonsurging glacier. The attempt is often a Boolean classification; however, glacier speedup events can vary significantly with respect to event magnitude, duration, and the fraction of the glacier that participates in the speedup. For this study, we first updated the inventory of glaciers that show flow instabilities in the Alaska Range and then quantified the spectrum of speedup behavior. We developed a new method that automatically detects glaciers with flow instabilities. Our automated results show a 91% success rate when compared to direct observations of speedup events and glaciers that are suspected to display unstable flow based on surface features. Through a combination of observations from the Landsat archive and previously published data, our inventory now contains 36 glaciers that encompass at least one branch exhibiting unstable flow and we document 53 speedup events that occurred between 1936 and 2014. We then present a universal method for comparing glacier speedup events based on a normalized event magnitude metric. This method provides a consistent way to include and quantify the full spectrum of speedup events and allows for comparisons with glaciers that exhibit clear surge characteristics yet have no observed surge event to date. Our results show a continuous spectrum of speedup magnitudes, from steady flow to clearly surge type, which suggests that qualitative classifications, such as "surge-type" or "pulse-type" behavior, might be too simplistic and should be accompanied by a standardized magnitude metric.

  10. Structural geology of the Big Bend anticline, Brooks Range Foothills, Alaska

    NASA Astrophysics Data System (ADS)

    Sanders, Cheryl M.

    Big Bend anticline is near the northern edge of the Brooks Range foothills of northern Alaska. The structure of the foothills is a low-taper triangle zone or passive-roof duplex within Brooks Range foreland basin deposits. The dominant structures are detachment folds locally cut by thrust faults and Big Bend anticline is one of these. This research combines detailed surface mapping (1:25,000) with interpretation of aerial photos and satellite imagery of the Big Bend anticline and seismic reflection data from the Umiat anticline to reconstruct its surface and subsurface geometry. The research area surrounds the Big Bend of the Chandler River and covers approximately 10 km2. The mechanical stratigraphy of the area consists of the competent Nanushuk sandstones between two incompetent units-the overlying Seabee and underlying Torok shales. The structure of the area consists of an east-trending anticline with a hinge that branches westward into two open, broad anticlines and an intervening syncline. A forethrust near the southern hinge and a backthrust near the northern hinge have broken through the anticline west of the branch point. Subsurface data of Umiat anticline combined with surface projected cross sections from the study area provide an analog of the subsurface structure in the Big Bend area. These cross sections show gentle anticlines separated by flat bottomed synclines in competent Nanushuk Formation sandstone. The anticlines overly Torok Formation thickened by north vergent folds and thrust faults above a detachment zone. Collectively, these structures form a low-taper triangle zone. Cross section restoration suggests more shortening in the Torok duplex than in the overlying folds and breakthrough faults. Results of this research provide an analog for other anticlines in the region that are currently the focus of oil and gas exploration.

  11. Fracture density as a controlling factor of postglacial fluvial incision rate, Granite Range, Alaska.

    NASA Astrophysics Data System (ADS)

    Champagnac, J.-D.; Sternai, P.; Herman, F.; Guralnik, B.; Beaud, F.

    2012-04-01

    The relations between lithosphere and atmosphere to shape the landscape are disputed since the last two decades. The classical "chicken or egg" problem raised the idea that erosion can promote creation of topography thanks to isostatic compensation of eroded material and subsequent positive feedback. Quaternary glaciations and high erosion rates are supposed to be the main agent of such process. More recently, "tectonic activity" has been considered not only as a rock uplift agent, but also as a rock crusher, that in turn promote erosion, thanks to the reduction of size of individual rock elements, more easily transported. The Granite Range in Alaska presents a contrasted morphology: its western part shows preserved glacial landscape, whereas its eastern part presents a strong fluvial / hillslope imprint, and only a few relicts of glacial surfaces. We quantify these differences by 1) qualitative appreciation of the landscape, 2) quantification of post-glacial erosion, and 3) hypsometric quantification of the landscape. On the field, the eastern part appears to be highly fractured, with many, large, penetrative faults, associated with km-thick fault gouges and cataclasites. The westernmost part shows massive bedrock, with minor, localised faults. Remote-sensed fracture mapping confirms this: fracture density is much higher to the east, where hypsometric parameters (HI and HIP) display anomalies, and where high post-glacial incision (up to 600m) is observed. We provide here an impressive case study for tectonic-erosion interactions through rock crushing effect, and document that half of the sediments coming out of the range come from the ~10% of the most fractured area, all other being equal. This challenges the usual view of tectonic "driving" rock uplift, while erosion removes material: In our case, tectonics is the main erosional agent, rivers and glaciers being (efficient) transport agents.

  12. Conodont biostratigraphy and biofacies of the Wahoo Limestone (Carboniferous), Sadlerochit Mountains, northeast Brooks Range, Alaska

    SciTech Connect

    Krumhardt, A.P. ); Harris, A.G. )

    1990-05-01

    The Wahoo Limestone forms the upper part of the Lisburne Group (Carboniferous) in the Sadlerochit Mountains. The Lisburne Group is a thick (> 600 m) sequence of platform carbonate rocks that extends across the Brooks Range of northern Alaska and beneath the North Slope. At Prudhoe Bay, the Lisburne Group forms a major hydrocarbon reservoir. In the easternmost Sadlerochit Mountains, the Wahool Limestone is divisible into informal lower (64 m) and upper (192 m) members. The basal 46 m is chiefly bryozoan and pelmatozoan packstone that formed on a relatively shallow platform during the latest Mississippian lower muricatus subzone (as shown by the occurrence of the zonal index with representatives of Cavusgnathus). Cavusgnathus is dominant in this part of the section and occurs with representatives of Kladognathus, Ghathodus, Adetognathus, Hindeodus, and Rhachistognathus (in order of decreasing abundance). Declinognathodus noduliferus, the index for the base of the Pennsylvanian, first occurs at 49 m above the base of the Wahoo and 1 m above a discontinuity surface that marks the Mississippian-Pennsylvanian boundary. The unconformity represents the highest conodont subzone of the Mississippian and probably part of the earliest Pennsylvanian. Previously, the Mississippian-Pennsylvanian boundary was placed t the lower-upper Wahoo contact based on endothyroids; conodont data now indicate that this boundary is 15 m lower. The remaining lower Wahoo is possibly of noduliferus-primus zone age and chiefly yields, in order of decreasing abundance, species of Adetognathus, Declinognathodus, and Rhachistognathus, as well as redeposited Mississipian conodonts. The lower 15 m of the upper member of the Wahoo contains silty (5-40%) carbonate rock types that yield very few conodonts. Conodonts no older than the minutus-sinuatus zone are relatively abundant from 15 to 106 m above the base of the upper Wahoo.

  13. Frozen debris lobe morphology and movement: an overview of eight dynamic features, southern Brooks Range, Alaska

    NASA Astrophysics Data System (ADS)

    Darrow, Margaret M.; Gyswyt, Nora L.; Simpson, Jocelyn M.; Daanen, Ronald P.; Hubbard, Trent D.

    2016-05-01

    Frozen debris lobes (FDLs) are elongated, lobate permafrost features that mostly move through shear in zones near their bases. We present a comprehensive overview of eight FDLs within the Dalton Highway corridor (southern Brooks Range, Alaska), including their catchment geology and rock strengths, lobe soil characteristics, surface movement measurements collected between 2012 and 2015, and analysis of historic and modern imagery from 1955 to 2014. Field mapping and rock strength data indicate that the metasedimentary and metavolcanic bedrock forming the majority of the lobe catchments has very low to medium strength and is heavily fractured, thus easily contributing to FDL formation. The eight investigated FDLs consist of platy rocks typical of their catchments, organic debris, and an ice-poor soil matrix; massive ice, however, is present within FDLs as infiltration ice, concentrated within cracks open to the surface. Exposure of infiltration ice in retrogressive thaw slumps (RTSs) and associated debris flows leads to increased movement and various stages of destabilization, resulting in morphological differences among the lobes. Analysis of historic imagery indicates that movement of the eight investigated FDLs has been asynchronous over the study period, and since 1955, there has been an overall increase in movement rates of the investigated FDLs. The formation of surface features, such as cracks, scarps, and RTSs, suggests that the increased movement rates correlate to general instability, and even at their current distances, FDLs are impacting infrastructure through increased sediment mobilization. FDL-A is the largest of the investigated FDLs. As of August 2015, FDL-A was 39.2 m from the toe of the Dalton Highway embankment. Based on its current distance and rate of movement, we predict that FDL-A will reach the Dalton Highway alignment by 2023.

  14. Spectral Characteristics of Vegetation Functional Traits across a Range of Thaw Gradients on Alaska's Seward Peninsula

    NASA Astrophysics Data System (ADS)

    Goswami, S.; Hayes, D. J.; Sloan, V. L.; Liebig, J. A.; Norby, R. J.; Wullschleger, S. D.

    2014-12-01

    The Arctic and Boreal regions are warming rapidly, leading to the thawing of the underlying permafrost and associated changes in vegetation structure and composition. The thawing of ice-rich permafrost drives land surface dynamics called thermokarst, characterized by a variety of geomorphic surface features across high latitude landscapes. The development of these thermokarst or thermo-erosional features depends on factors such as local permafrost conditions, hydrology, geomorphology, vegetation, and climate, but their degree of dependence are not well understood across scales. The structure, functions and traits of the vegetation can work as effective indicators of these landscape changes. Our ability to characterize these vegetation characteristics across a wide range of thaw gradients at the local scale could help us to better understand the dependency as well as the impacts of thermokarst processes on them. This will also help us to develop capabilities to quantify these characteristics and dependencies from local to regional scales by using remote sensing and ecosystem modeling techniques. During the months of June - July of 2013 and 2014, we conducted field surveys at various sites across the central Seward Peninsula in Alaska covering a range of thaw gradients to collect data for vegetation functional traits, ancillary data and also hyperspectral data in the 400-2500 nm range using a field spectrometer. Data were collected from plots established along 50 m transects to capture transitional states of these thaw features from the upland zone, transition zone, and thaw lake basins as well as in polygonal features. Here we discuss the characteristics of vegetation functional traits and how they relate to the ground-based spectral measurements. Some of these findings could be scaled up using airborne and satellite remote sensing data. The findings from this study can improve our understanding of disturbance patterns and their feedbacks to local scale plant and

  15. Geologic strip map along the Hines Creek Fault showing evidence for Cenozoic displacement in the western Mount Hayes and northeastern Healy quadrangles, eastern Alaska Range, Alaska

    USGS Publications Warehouse

    Nokleberg, Warren J.; Aleinikoff, John N.; Bundtzen, Thomas K.; Hanshaw, Maiana N.

    2013-01-01

    Geologic mapping of the Hines Creek Fault and the adjacent Trident Glacier and McGinnis Glacier Faults to the north in the eastern Alaska Range, Alaska, reveals that these faults were active during the Cenozoic. Previously, the Hines Creek Fault, which is considered to be part of the strike-slip Denali Fault system (Ridgway and others, 2002; Nokleberg and Richter, 2007), was interpreted to have been welded shut during the intrusion of the Upper Cretaceous Buchanan Creek pluton (Wahrhaftig and others, 1975; Gilbert, 1977; Sherwood and Craddock, 1979; Csejtey and others, 1992). Our geologic mapping along the west- to west-northwest-striking Hines Creek Fault in the northeastern Healy quadrangle and central to northwestern Mount Hayes quadrangle reveals that (1) the Buchanan Creek pluton is truncated by the Hines Creek Fault and (2) a tectonic collage of fault-bounded slices of various granitic plutons, metagabbro, metabasalt, and sedimentary rock of the Pingston terrane occurs south of the Hines Creek Fault.

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

    NASA Astrophysics Data System (ADS)

    Robertson, Peter Benjamin

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

  17. Sedimentology and stratigraphy of the Kanayut Conglomerate, central Brooks Range, Alaska; report of 1980 field season

    USGS Publications Warehouse

    Nilsen, T.H.; Moore, T.E.; Balin, D.F.; Johnson, S.Y.

    1982-01-01

    The Upper Devonian Kanayut Conglomerate crops out along the crest of the Brooks Range of northern Alaska for a distance of almost 1000 km. It ranges in thickness from 2600 m in the Atigun River area to 700 m south of Anaktuvuk Pass and has been subdivided into four regionally persistent members: (a) the basal sandstone member, consisting of marine sandstone and shale with some conglomerate; (b) the lower shale member, consisting of nonmarine quartzite, conglomerate and shale; (c) the middle conglomerate member, consisting of nonmarine pebble and cobble conglomerate and quartzite; and (d) the Stuver Member, consisting of nonmarine sandstone and shale. The Kanayut conformably overlies the Upper Devonian marine Hunt Fork Shale and is conformably overlain by the Mississippian marine Kayak Shale. The Kanayut is wholly allochthonous and has probably been transported northward on a series of thrust plates. The basal sandstone member of the Kanayut Conglomerate, which overlies prodelta turbidites of the Hunt Fork Shale, contains marginal-marine coarsening-upward channel-mouth bar sequences. It is conformably overlain by the lower shale member. Measured sections of the nonmarine members of the Kanayut show that the lower shale member ranges in thickness from 120 m to 1115 m and consists of fining-upward cycles interpreted to have been deposited by meandering streams on a broad floodplain. These cycles contain, in ascending order, channelized basal conglomerate, trough cross-stratified sandstone, and ripple-marked siltstone. The cycles are interpreted to be channel and point-bar deposits. Individual cycles average about 10 m in thickness and are separated by intervals of black, brown or maroon floodplain shale deposits. These typically contain thin coarsening-upward units that probably represent prograding levee sequences and irregular and ungraded sandstone bodies interpreted to be crevasse-splay deposits. In the Okokmilaga River area, the lower shale member contains a

  18. Mafic and ultramafic rocks of the northwestern Brooks Range of Alaska produce nearly symmetric gravity anomalies

    SciTech Connect

    Morin, R.L. )

    1993-04-01

    An arc of mafic and ultramafic rocks is mapped from Asik Mountain to Siniktanneyak Mountain in the northwestern Brooks Range of Alaska. Gravity data, although not very detailed, have been collected over the region and show some very conspicuous circular or oval gravity highs over portions of the mapped mafic-ultramafic bodies. Bodies which have large associated gravity anomalies are Asik Mountain (80 mGal), Avon Hills (20 mGal), Misheguk Mountain (30 mGal), and Siniktanneyak Mountain (20 mGal). Gabbros of the Siniktanneyak Mountain complex, where the gravity coverage is best, have densities of about 3.0 g/cm[sup 3] while the densities of the surrounding sedimentary rocks are about 2.6 g/cm[sup 3]. Volcanic rocks in the area have average densities of about 2.7 g/cm[sup 3]. Three-dimensional modeling indicates that the largest anomaly, on the southwestern part of the complex, could be caused by a polygonal prism of gabbro with vertical sides, about 6 km across and about 4.5 km deep. A smaller lobe of the anomaly on the northeast of the complex could be caused by another oblong polygonal prism about 4 km long and 2 km wide trending northeast and about 1.5 km deep. Modeling this anomaly with densities lower than gabbro would require greater thicknesses to produce the same anomaly. Modeling each anomaly along this arc in 2 1/2-dimensions shows many possible solutions using different body shapes and different density contrasts. There are several other gravity anomalies in this vicinity which could represent unexposed high density rocks. One such anomaly is in the Maiyumerak Mountains northeast of Asik Mountain (30 mGal). Another anomaly is to the northwest of Asik Mountain (20 mGal). There is also an anomaly at Uchugrak (20 mGal) east of Avan Hills. Although many of the anomalies in this region are poorly controlled, an attempt has been made to interpret the data to show possible solutions.

  19. A 2000 year varve-based climate record from the central Brooks Range, Alaska

    SciTech Connect

    Bird, BW; Abbott, MB; Finney, BP; Kutchko, B

    2009-01-01

    Varved minerogenic sediments from glacial-fed Blue Lake, northern Alaska, are used to investigate late Holocene climate variability. Varve-thickness measurements track summer temperature recorded at Atigun Pass, located 41 km east at a similar elevation (r (2) = 0.31, P = 0.08). Results indicate that climate in the Brooks Range from 10 to 730 AD (varve year) was warm with precipitation inferred to be higher than during the twentieth century. The varvetemperature relationship for this period was likely compromised and not used in our temperature reconstruction because the glacier was greatly reduced, or absent, exposing sub-glacial sediments to erosion from enhanced precipitation. Varve-inferred summer temperatures and precipitation decreased after 730 AD, averaging 0.4A degrees C above the last millennial average (LMA = 4.2A degrees C) from 730 to 850 AD, and 0.1A degrees C above the LMA from 850 to 980 AD. Cooling culminated between 980 and 1030 AD with temperatures 0.7A degrees C below the LMA. Varve-inferred summer temperatures increased between 1030 and 1620 AD to the LMA, though the period between 1260 and 1350 AD was 0.2A degrees C below the LMA. Although there is no equivalent to the European Medieval Warm Period in the Blue Lake record, two warm intervals occurred from 1350 to 1450 AD and 1500 to 1620 AD (0.4 and 0.3A degrees C above the LMA, respectively). During the Little Ice Age (LIA; 1620 to 1880 AD), inferred summer temperature averaged 0.2A degrees C below the LMA. After 1880 AD, inferred summer temperature increased to 0.8A degrees C above the LMA, glaciers retreated, but aridity persisted based on a number of regional paleoclimate records. Despite warming and glacial retreat, varve thicknesses have not achieved pre-730 AD levels. This reflects limited sediment availability and transport due to a less extensive retreat compared to the first millennium, and continued relative aridity. Overall, the Blue Lake record is similar to varve records from the

  20. Digital Data for the Geology of the Southern Brooks Range, Alaska

    USGS Publications Warehouse

    Geologic map compiled by Till, Alison B.; Dumoulin, Julie A.; Harris, Anita G.; Moore, Thomas E.; Bleick, Heather; Siwiec, Benjamin; Digital files prepared by Labay, Keith A.; Wilson, Frederic H.; Shew, Nora

    2008-01-01

    The growth in the use of Geographic Information Systems (GIS) has highlighted the need for digital geologic maps that have been attributed with information about age and lithology. Such maps can be conveniently used to generate derivative maps for manifold special purposes such as mineral-resource assessment, metallogenic studies, tectonic studies, and environmental research. This report is part of a series of integrated geologic map databases that cover the entire United States. Three national-scale geologic maps that portray most or all of the United States already exist; for the conterminous U.S., King and Beikman (1974a,b) compiled a map at a scale of 1:2,500,000, Beikman (1980) compiled a map for Alaska at 1:2,500,000 scale, and for the entire U.S., Reed and others (2005a,b) compiled a map at a scale of 1:5,000,000. A digital version of the King and Beikman map was published by Schruben and others (1994). Reed and Bush (2004) produced a digital version of the Reed and others (2005a) map for the conterminous U.S. The present series of maps is intended to provide the next step in increased detail. State geologic maps that range in scale from 1:100,000 to 1:1,000,000 are available for most of the country, and digital versions of these state maps are the basis of this product. The digital geologic maps presented here are in a standardized format as ARC/INFO export files and as ArcView shape files. The files named __geol contain geologic polygons and line (contact) attributes; files named __fold contain fold axes; files named __lin contain lineaments; and files named __dike contain dikes as lines. Data tables that relate the map units to detailed lithologic and age information accompany these GIS files. The map is delivered as a set 1:250,000-scale quadrangle files. To the best of our ability, these quadrangle files are edge-matched with respect to geology. When the maps are merged, the combined attribute tables can be used directly with the merged maps to make

  1. A serologic survey for antibodies to three canine viruses in wolverines (Gulo gulo) from the Brooks Range, Alaska.

    PubMed

    Dalerum, Fredrik; Shults, Brad; Kunkel, Kyran

    2005-10-01

    Canine distemper virus (CDV), canine parvovirus type 2 (CPV-2), and canine adenovirus type 1 (CAV-1) are pathogens that are typically associated with canids but may cause serious disease in a wide range of other carnivores. From 1998 to 2002, serum samples from 64 wolverines (Gulo gulo) from the Brooks Range, Alaska, were tested for antibodies to CDV, CPV-2, and canine adenovirus (CAV). Four animals tested positive for antibodies to CDV (7%), one for antibodies to CPV-2 (2%), and none for antibodies to CAV. These are similar to antibody prevalence estimates for other large and medium carnivores in North America. PMID:16456170

  2. A comprehensive inventory of the Gulf of Alaska sponge fauna with the description of two new species and geographic range extensions.

    PubMed

    Lehnert, Helmut; Stone, Robert P

    2016-01-01

    Two new species, Hamacantha (Vomerula) cassanoi n. sp. and Prosuberites salgadoi n. sp., are described from the eastern Gulf of Alaska in the North Pacific Ocean. These are the first records of the genera Hamacantha and Prosuberites from Alaska. We also report two geographic range extensions for the region. Geodia japonica Sollas, 1888 was previously known only from Japan and is now recorded from the Gulf of Alaska. We also document the first record of Rhizaxinella cervicornis Thiele, 1898 from the Gulf of Alaska. Our comprehensive inventory of the sponge fauna of the Gulf of Alaska confirms the presence of 52 taxa with an additional 38 taxa suspected of occurring in the region. This is a much lower number of species than that recorded from neighbouring regions like the Aleutian Islands and British Columbia. PMID:27470862

  3. Age, Distribution, and Style of Deformation in Alaska North of 60°N: Implications for Assembly of Alaska

    NASA Astrophysics Data System (ADS)

    Moore, T. E.; Box, S. E.

    2015-12-01

    The structural architecture of Alaska is the product of a complex history of deformation along both the Cordilleran and Arctic margins of North America through interactions with ocean plates and with continental elements of Laurentia, Siberia, and Baltica. We use geological constraints to assign areal deformation to 14 time intervals and map their distributions in Alaska. Alaska can be divided into three domains with differing histories of deformation. The northern domain experienced the Early Cretaceous Brookian orogeny, an oceanic arc-continent collisional orogeny, followed by a mid-Cretaceous extensional overprint. Opening of the oceanic Canada Basin rifted the orogen from the Canadian Arctic margin, producing the bent trends of the orogen. The second domain constitutes the Phanerozoic Peninsular-Wrangellia-Alexander arc terrane and its paired Mesozoic accretionary prisms. Its structural history is unrelated to domains to the north until a shared history of Late Cretaceous deformation. The third domain, situated between the first two domains and roughly bounded by the Cenozoic dextral Denali and Tintina faults, includes the Yukon Composite terrane (Laurentian origin) and the large Farewell (Baltica origin) terrane. These terranes are not linked until Late Cretaceous sedimentary overlap, but we have not identified a shared deformation between these two terranes that might mark their juxtaposition by collisional processes. Similar early Late Cretaceous sedimentary linkages stitch the northern and central domains. Late Late Cretaceous folding and thrusting across much of Alaska south of the Brooks Range correlates temporally with the collision of the southern domain with the remainder of Alaska. Early Cenozoic shortening is mild across much of the state but is significant in the Brooks Range, and correlates in time with dextral faulting, ridge subduction, and rotation of western Alaska. Late Cenozoic shortening is significant in southern Alaska inboard of the

  4. Depositional settings, correlation, and age carboniferous rocks in the western Brooks Range, Alaska

    USGS Publications Warehouse

    Dumoulin, J.A.; Harris, A.G.; Blome, C.D.; Young, L.E.

    2004-01-01

    The Kuna Formation (Lisburne Group) in northwest Alaska hosts the Red Dog and other Zn-Pb-Ag massive sulfide deposits in the Red Dog district. New studies of the sedimentology and paleontology of the Lisburne Group constrain the setting, age, and thermal history of these deposits. In the western and west-central Brooks Range, the Lisburne Group includes both deep- and shallow-water sedimentary facies and local volcanic rocks that are exposed in a series of thrust sheets or allochthons. Deep-water facies in the Red Dog area (i.e., the Kuna Formation and related rocks) are found chiefly in the Endicott Mountains and structurally higher Picnic Creek allochthons. In the Red Dog plate of the Endicott Mountains allochthon, the Kuna consists of at least 122 m of thinly interbedded calcareous shale, calcareous spiculite, and bioclastic supportstone (Kivalina unit) overlain by 30 to 240 m of siliceous shale, mudstone, calcareous radiolarite, and calcareous lithic turbidite (Ikalukrok unit). The Ikalukrok unit in the Red Dog plate hosts all massive sulfide deposits in the area. It is notably carbonaceous, is generally finely laminated, and contains siliceous sponge spicules and radiolarians. The Kuna Formation in the Key Creek plate of the Endicott Mountains allochthon (60-110 m) resembles the Ikalukrok unit but is unmineralized and has thinner carbonate layers that are mainly organic-rich dolostone. Correlative strata in the Picnic Creek allochthon include less shale and mudstone and more carbonate (mostly calcareous spiculite). Conodonts and radiolarians indicate an age range of Osagean to early Chesterian (late Early to Late Mississippian) for the Kuna in the Red Dog area. Sedimentologic, faunal, and geochemical data imply that most of the Kuna formed in slope and basin settings characterized by anoxic or dysoxic bottom water and by local high productivity. Shallow-water facies of th e Lisburne Group in the Red Dog area are present locally in the Endicott Mountains

  5. Origin of narrow terranes and adjacent major terranes occurring along the denali fault in the eastern and central alaska range, alaska

    USGS Publications Warehouse

    Nokleberg, W.J.; Richter, D.H.

    2007-01-01

    Several narrow terranes occur along the Denali fault in the Eastern and Central Alaska Range in Southern Alaska. These terranes are the Aurora Peak, Cottonwood Creek, Maclaren, Pingston, and Windy terranes, and a terrane of ultramafic and associated rocks. Exterior to the narrow terranes to the south is the majorWrangellia island arc composite terrane, and to the north is the major Yukon Tanana metamorphosed continental margin terrane. Overlying mainly the northern margin of the Wrangellia composite terrane are the Kahiltna overlap assemblage to the west, and the Gravina- Nutzotin-Gambier volcanic-plutonic- sedimentary belt to the east and southeast. The various narrow terranes are interpreted as the result of translation of fragments of larger terranes during two major tectonic events: (1) Late Jurassic to mid-Cretaceous accretion of the Wrangellia island arc composite terrane (or superterrane composed of the Wrangellia, Peninsular, and Alexander terranes) and associated subduction zone complexes; and (2) starting in about the Late Cretaceous, dextral transport of the Wrangellia composite terrane along the Denali fault. These two major tectonic events caused: (1) entrapment of a lens of oceanic lithosphere along the suture belt between the Wrangellia composite terrane and the North American Craton Margin and outboard accreted terranes to form the ultramafic and mafic part of the terrane of ultramafic and associated rocks, (2) subsequent dextral translation along the Denali fault of the terrane of ultramafic and associated rocks, (3) dextral translation along the Denali fault of the Aurora Peak, Cottonwood Creek, and Maclaren and continental margin arc terranes from part of the Coast plutonic-metamorphic complex (Coast-North Cascade plutonic belt) in the southwest Yukon Territory or Southeastern Alaska, (4) dextral translation along the Denali fault of the Pingston passive continental margin from a locus along the North American Continental Margin, and (5

  6. Permian and Triassic sedimentation in the northeastern Brooks Range, Alaska: Deposition of the Sadlerochit Group: Reply

    SciTech Connect

    Crowder, R.K. )

    1991-12-01

    This paper was written in defense of this authors previous paper on the Ledge Sandstone member of the Ivishak Formation, Arctic National Wildlife Refuge, Alaska. This author has previously written a paper (Crowder, 1990) which discussed the depositional environments and sedimentation of these reservoir-quality sandstones and conglomerates, and developed a geologic model for source materials and deposition. As a response to this paper, another author (McMillen, 1991) questioned numerous conclusions reached by this author. The former author cited the lack of use of paleocurrent information to determine source areas and the misinterpretation of sandstone body geometry. Both papers and rebuttals have been individually entered into the data base.

  7. Lithostratigraphy, microlithofacies, and conodont biostratigraphy and biofacies of the Wahoo Limestone (Carboniferous), eastern Sadlerochit Mountains, Northeast Brooks Range, Alaska

    SciTech Connect

    Krumhardt, A.P.; Harris, A.G.; Watts, K.F.

    1996-12-31

    The Lisburne Group (chiefly Carboniferous) is a wide-spread succession of platform carbonate rocks that apparently developed along a south-facing passive continental margin in northern Alaska. Marine transgressions onlapped northward across northeast Alaska allowing the Lisburne platform to extend over terrigenous deposits of the Endicott Group and local pre-Mississippian paleotopographic highs. The Wahoo Limestone is the youngest formation of the Lisburne Group in northeasternmost Alaska, ranging from latest Mississippian (latest Chesterian) to Middle Pennsylvanian (at least early Atokan) in age. The Wahoo Limestone was systematically sampled for lithostratigraphy and conodont biostratigraphy and biofacies at a relatively continuous section (about 262 m in thickness) in the eastern Sadlerochit Mountains. Existing Carboniferous conodont zonations could not be readily applied to the study section because most zonal indicators are absent. Species diversity is low for a section that spans at least 10 million years. Twenty-four species, distributed among 14 genera, were identified in 72 productive samples; no new species were distinguished. The following biostratigraphic zones and faunal intervals were recognized: Upper muricatus Subzone (latest Chesterian); noduliferus-primus Zone (earliest Morrowan); minutus Fauna (Morrowan) containing a lower subdivision (lower minutus Fauna of early to middle? Morrowan age); and an Idiognathodus Fauna (Morrowan? to early Atokan). The presence of Idiognathodus incurvus? and Rhachistognathus minutus subspp. above the first occurrence of the foraminifer Pseudostaffella sp. in the uppermost part of the Wahoo Limestone indicates that the youngest beds are early Atokan in age. The Mississippian-Pennsylvanian boundary is placed at 56 m above the base of the lower member of the Wahoo Limestone on the basis of the lowest occurrence of Declinognathodus noduliferus japonicus above forms transitional from Gnathodus girtyl simplex.

  8. New U/Pb ages from granite and granite gneiss in the Ruby geanticline and southern Brooks Range, Alaska ( USA).

    USGS Publications Warehouse

    Patton, W.W.; Stern, T.W.; Arth, Joseph G.; Carlson, C.

    1987-01-01

    New U/Pb zircon ages from the Ray Mountains of central Alaska clarify the plutonic history of the Ruby geanticline and support earlier suggestions that the Ruby geanticline and S Brooks Range were once parts of the same tectonostratigraphic terrane. U/Pb zircon ages of 109 to 112 Ma from the Ray Mountains pluton confirm previously reported mid-Cretaceous K/Ar ages and rule out the possibility that the earliest intrusive phase of the pluton is older than mid-Cretaceous K/Ar ages and rule out the possibility that the earliest intrusive phase of the pluton is older than mid- Cretaceous. New U/Pb zircon ages from 4 granite gneiss samples in the Ray Mountains indicate a Devonian protolith age of 390+ or -12 Ma and suggest that the Ruby geanticline, like the S Brooks Range, underwent a major plutonic event in mid-Paleozoic time.-Authors

  9. Nature and evolution of the lithospheric mantle beneath the eastern Central Asian Orogenic Belt: Constraints from peridotite xenoliths in the central part of the Great Xing'an Range, NE China

    NASA Astrophysics Data System (ADS)

    Pan, Shaokui; Zheng, Jianping; Griffin, W. L.; Xu, Yixian; Li, Xiyao

    2015-12-01

    Our knowledge of the lithospheric mantle beneath the Central Asian Orogenic Belt is still sparse. Petrologic, major- and trace-element studies on the peridotite xenoliths from the Cenozoic volcanic fields in the Aershan area, the central part of the Great Xing'an Range, NE China, provide insights into the nature and evolution of the lithospheric mantle beneath the eastern part of the belt. According to the REE patterns of clinopyroxene, these peridotites can be divided into three groups which show clear differences in microstructure, geochemistry and equilibration temperature. Group 1 xenoliths (LREE-depleted patterns of Cpx) are lherzolites, with protogranular microstructure and high modal Cpx (8-13 wt.%), low Cr# in spinel (< 21.1), high whole-rock CaO and Al2O3 contents and estimated temperatures of 834-849 °C. Group 2 xenoliths (flattened REE patterns of Cpx) are harzburgites, with microstructures transitional between mosaic and tabular and low Cpx content (2-3 wt.%); they have high Cr# in spinel (41.1-49.6), low whole-rock CaO and Al2O3 levels and equilibration temperatures of 1183-1244 °C. Group 1 peridotites represent the newly accreted fertile mantle which was not significantly affected by post-melting enrichment; while Group 2 xenoliths may be older relics of moderately refractory mantle that underwent H2O bearing silicate-melt metasomatism (Ti/Eu > 3300, (La/Yb)N < 1 and occurrence of amphibole). Group 3 peridotites (convex-up REE patterns of Cpx) comprise both lherzolite and harzburgite; they have porphyroclastic microstructures, and show a broad range of Cpx modes (0-7 wt.%), spinel-Cr# (26.5-71.1), bulk rock CaO and Al2O3 contents and temperatures (941-1239 °C). The high TiO2 contents (up to 1.42 wt.%) in spinels of Group 3 imply the involvement of melt/rock reactions. We suggest that the upwelling of asthenospheric material played a key role in modifying the lithospheric mantle underneath the eastern Central Asian Orogenic Belt, and resulted in

  10. Terrain, vegetation, and landscape evolution of the R4D research site, Brooks Range Foothills, Alaska

    USGS Publications Warehouse

    Walker, D. A.; Binnian, Emily F.; Evans, B. M.; Lederer, N. D.; Nordstrand, E.; Webber, P. J.

    1989-01-01

    Maps of the vegetation and terrain of a 22 km2 area centered on the Department of Energy (DOE) R4D (Response, Resistance, Resilience to and Recovery from Disturbance in Arctic Ecosystems) study site in the Southern Foothills Physiographic Province of Alaska were made using integrated geobotanical mapping procedures and a geographic-information system. Typical land forms and surface f orms include hillslope water tracks, Sagavanirktok-age till deposits, nonsorted stone stripes, and colluvial-basin deposits. Thirty-two plant communities are described; the dominant vegetation (51% of the mapped area) is moist tussock-sedge, dwarf-shrub tundra dominated by Eriophorum vaginatum or Carex bigelowii. Much of the spatial variation in the mapped geobotanical characters reflects different-aged glaciated surfaces. Shannon-Wienerin dices indicate that the more mature landscapes, represented by retransported hillslope deposits and basin colluvium, are less heterogeneous than newer landscapes such as surficial till deposits and floodplains. A typical toposequence on a mid-Pleistocene-age surface is discussed with respect to evolution of the landscape. Thick Sphagnum moss layers occur on lower hillslopes, and the patterns of moss-layer development, heat flux, active layer thickness, and ground-ice are seen as keys to developing thermokarst-susceptibility maps.

  11. A geochemical sampling technique for use in areas of active alpine glaciation: an application from the central Alaska Range

    USGS Publications Warehouse

    Stephens, G.C.; Evenson, E.B.; Detra, D.E.

    1990-01-01

    In mountainous regions containing extensive glacier systems there is a lack of suitable material for conventional geochemical sampling. As a result, in most geochemical sampling programs a few stream-sediment samples collected at, or near, the terminus of valley glaciers are used to evaluate the mineral potential of the glaciated area. We have developed and tested a technique which utilizes the medial moraines of valley glaciers for systematic geochemical exploration of the glacial catchment area. Moraine sampling provides geochemical information that is site-specific in that geochemical anomalies can be traced directly up-ice to bedrock sources. Traverses were made across the Trident and Susitna glaciers in the central Alaska Range where fine-grained (clay to sand size) samples were collected from each medial moraine. These samples were prepared and chemically analyzed to determine the concentration of specific elements. Fifty pebbles were collected at each moraine for archival purposes and for subsequent lithologic identification. Additionally, fifty cobbles and fifty boulders were examined and described at each sample site to determine the nature and abundance of lithologies present in the catchment area, the extent and nature of visible mineralization, the presence and intensity of hydrothermal alteration and the existence of veins, dikes and other minor structural features. Results from the central Alaska Range have delineated four distinct multi-element anomalies which are a response to potential mineralization up-ice from the medial moraine traverse. By integrating the lithologic, mineralogical and geochemical data the probable geological setting of the geochemical anomalies is determined. ?? 1990.

  12. Spatial variations in focused exhumation along a continental-scale strike-slip fault: The Denali fault of the eastern Alaska Range

    USGS Publications Warehouse

    Benowitz, J.A.; Layer, P.W.; Armstrong, P.; Perry, S.E.; Haeussler, P.J.; Fitzgerald, P.G.; VanLaningham, S.

    2011-01-01

    40Ar/39Ar, apatite fission-track, and apatite (U-Th)/He thermochronological techniques were used to determine the Neogene exhumation history of the topographically asymmetric eastern Alaska Range. Exhumation cooling ages range from ~33 Ma to ~18 Ma for 40Ar/39Ar biotite, ~18 Ma to ~6 Ma for K-feldspar minimum closure ages, and ~15 Ma to ~1 Ma for apatite fission-track ages, and apatite (U-Th)/He cooling ages range from ~4 Ma to ~1 Ma. There has been at least ~11 km of exhumation adjacent to the north side of Denali fault during the Neogene inferred from biotite 40Ar/39Ar thermochronology. Variations in exhumation history along and across the strike of the fault are influenced by both far-field effects and local structural irregularities. We infer deformation and rapid exhumation have been occurring in the eastern Alaska Range since at least ~22 Ma most likely related to the continued collision of the Yakutat microplate with the North American plate. The Nenana Mountain region is the late Pleistocene to Holocene (~past 1 Ma) primary locus of tectonically driven exhumation in the eastern Alaska Range, possibly related to variations in fault geometry. During the Pliocene, a marked increase in climatic instability and related global cooling is temporally correlated with an increase in exhumation rates in the eastern Alaska Range north of the Denali fault system.

  13. Crustal shortening followed by extensional collapse of the Cordilleran orogenic belt in northwestern Montana: Evidence from vintage seismic reflection profiles acquired in the Swan Range and Swan Valley

    NASA Astrophysics Data System (ADS)

    Rutherford, B. S.; Speece, M. A.; Stickney, M. C.; Mosolf, J. G.

    2013-12-01

    Reprocessing of one 24-fold (96 channel) and four 30-fold (120 channel) 2D seismic reflection profiles have revealed crustal scale reflections in the Swan Range and adjacent Swan River Valley of northwestern Montana. The five reprocessed profiles constitute 142.6 of the 303.3 linear km acquired in 1983-84 by Techo of Denver, Colorado. The four 30-fold profiles used helicopter-assisted dynamite shooting (Poulter method) and the 24-fold profile used the Vibroseis method. Acquisition parameters were state of the art for the time. The Swan Range lies east of the Rocky Mountain Trench and is part of the Cordilleran foreland thrust belt where the Lewis thrust system emplaced a thick slab of Proterozoic Belt Supergroup strata eastward and over Paleozoic and Mesozoic rocks during the Late Cretaceous to early Paleocene Laramide orogeny. Deeply drilled borehole data are absent within the study area; however, we generated a synthetic seismogram from the Arco-Marathon 1 Paul Gibbs well (total depth=5418 m), located approximately 70 km west of the reprocessed profiles, and correlated the well data to surface seismic profiles. Large impedance contrasts in the log data are interpreted to be tholeiitic Moyie sills within the Prichard Formation argillite (Lower Belt), which produce strong reflection events in regional seismic sections and result in highly reflective, east-dipping events in the reprocessed profiles. We estimate a depth of 10 km (3 to 3.5 seconds) to the basal detachment of the Lewis thrust sheet. The décollement lies within Belt Supergroup strata to the west of the Swan River Valley before contacting unreflective, west-dipping crystalline basement beneath the Swan Range--a geometry that results in a wedge of eastward-thinning, autochthonous Belt rocks. Distinct fault-plane signatures from the west-dipping, range-bounding Swan fault--produced by extensional collapse of the over-thickened Cordillera--are not successfully imaged. However, reflections from Cenozoic

  14. Climate Change Impacts on the Cryosphere of Mountain Regions: Validation of a Novel Model Using the Alaska Range

    NASA Astrophysics Data System (ADS)

    Mosier, T. M.; Hill, D. F.; Sharp, K. V.

    2015-12-01

    Mountain regions are natural water towers, storing water seasonally as snowpack and for much longer as glaciers. Understanding the response of these systems to climate change is necessary in order to make informed decisions about prevention or mitigation measures. Yet, mountain regions are often data sparse, leading many researchers to implement simple or enhanced temperature index (ETI) models to simulate cryosphere processes. These model structures do not account for the thermal inertia of snowpack and glaciers and do not robustly capture differences in system response to climate regimes that differ from those the model was calibrated for. For instance, a temperature index calibration parameter will differ substantially in cold-dry conditions versus warm-wet ones. To overcome these issues, we have developed a cryosphere hydrology model, called the Significantly Enhanced Temperature Index (SETI), which uses an energy balance structure but parameterizes energy balance components in terms of minimum, maximum and mean temperature, precipitation, and geometric inputs using established relationships. Additionally, the SETI model includes a glacier sliding model and can therefore be used to estimate long-term glacier response to climate change. Sensitivity of the SETI model to changing climate is compared with an ETI and a simple temperature index model for several partially-glaciated watersheds within Alaska, including Wolverine glacier where multi-decadal glacier stake measurements are available, to highlight the additional fidelity attributed to the increased complexity of the SETI structure. The SETI model is then applied to the entire Alaska Range region for an ensemble of global climate models (GCMs), using representative concentration pathways 4.5 and 8.5. Comparing model runs based on ensembles of GCM projections to historic conditions, total annual snowfall within the Alaska region is not expected to change appreciably, but the spatial distribution of snow

  15. Exploration of the Banda orogen, Indonesia

    SciTech Connect

    Harris, R.A. ); Audley-Charles, M.G. ); Tobing, S.L. )

    1990-06-01

    An integrated geologic evaluation of the late Miocene to present Banda orogen and its petroleum potential is in progress. The focus of the investigation involves sedimentary sections of the NW Australian continental margin incorporated into the Banda orogen. The islands of Timor and Seram, and several other islands throughout the Banda orogenic arc, are the closest exposed lithostratigraphic equivalents of the hydrocarbon producing NW Australian subsurface stratigraphy. Hydrocarbon occurrences are well documented on many of the islands, and over 13 million barrels of oil have been produced from the Bula field in Seram. Recent studies of seeps in Timor and associated stratigraphic, structural, and geochemical relations indicate that (1) oil and gas seeps occur throughout the Permian to Pliocene stratigraphic section; (2) bituminous limestones of the Triassic Aituti Formation are the most likely source for many of the seeps; (3) preliminary geochemical analyses of the oils indicate a mixed terrestrial and marine organic source, and suggest a genetic link between the Aitutu oils and oils seeping from Tertiary reservoirs; (4) triterpane and sterane parameters indicate some of these oils are highly mature; (5) palynomorph coloration, conodont alteration, and clay mineralogy data yield paleotemperature estimates in the range of hydrocarbon generation from much of the pre-rift sequence (Permian-Jurassic); (6) structural modeling suggests that the initial decollement zone of the orogenic wedge formed near the Jurassic breakup unconformity of the underthrust NW Australian margin, imbricating the post-rift sequence; (7) in Timor and Seram the decollement has stepped to deeper levels involving prerift sequences that form structural culminations in the core of the orogen. The culminations are expressed as topographic highs as in New Guinea and Oman.

  16. Spatial variability of biotic and abiotic tree establishment constraints across a treeline ecotone in the Alaska Range

    USGS Publications Warehouse

    Stueve, K.M.; Isaacs, R.E.; Tyrrell, L.E.; Densmore, R.V.

    2011-01-01

    Throughout interior Alaska (USA), a gradual warming trend in mean monthly temperatures occurred over the last few decades (;2-48C). The accompanying increases in woody vegetation at many alpine treeline (hereafter treeline) locations provided an opportunity to examine how biotic and abiotic local site conditions interact to control tree establishment patterns during warming. We devised a landscape ecological approach to investigate these relationships at an undisturbed treeline in the Alaska Range. We identified treeline changes between 1953 (aerial photography) and 2005 (satellite imagery) in a geographic information system (GIS) and linked them with corresponding local site conditions derived from digital terrain data, ancillary climate data, and distance to 1953 trees. Logistic regressions enabled us to rank the importance of local site conditions in controlling tree establishment. We discovered a spatial transition in the importance of tree establishment controls. The biotic variable (proximity to 1953 trees) was the most important tree establishment predictor below the upper tree limit, providing evidence of response lags with the abiotic setting and suggesting that tree establishment is rarely in equilibrium with the physical environment or responding directly to warming. Elevation and winter sun exposure were important predictors of tree establishment at the upper tree limit, but proximity to trees persisted as an important tertiary predictor, indicating that tree establishment may achieve equilibrium with the physical environment. However, even here, influences from the biotic variable may obscure unequivocal correlations with the abiotic setting (including temperature). Future treeline expansion will likely be patchy and challenging to predict without considering the spatial variability of influences from biotic and abiotic local site conditions. ?? 2011 by the Ecological Society of America.

  17. The Effects of Changing Climate on Glaciers in the Central Alaska Range, Alaska, USA: A Case Study on the Kahiltna Glacier

    NASA Astrophysics Data System (ADS)

    Young, J. C.; Arendt, A. A.

    2010-12-01

    This study will develop a set of modeling tools to provide estimates of melt evolution for the Kahiltna Glacier and glaciers of the Central Alaska Range (CAKR), over a number of future climate change scenarios. To parameterize the model, field measurements of mass balance and meteorological variables are being collected on the Kahiltna Glacier. These measurements include winter accumulation surveys along both a centerline transect and several lateral profiles of the main glacier branch, and summer ablation measurements at ten centerline index locations spaced evenly over a range of elevations. Snow density measurements are also being recorded at three elevations. Temperature and relative humidity is being sampled at five of the index locations, and a full meteorological station (measuring temperature, humidity, wind speed and direction, snow accumulation, ice ablation, and solar radiation) will be positioned on the lower ablation area. Here we present preliminary results from the 2010 melt season, comparing data collected on the Kahiltna Glacier to measurements from nearby sites within the CAKR. Data from a single index site monitored by the National Park Service (NPS) is compared to the accumulation and ablation measurements taken at the ten sites visited during 2010 as part of this study, to show the NPS index site’s representativeness at different elevations. Accumulation at these locations is also compared to a nearby snow telemetry (SNOTEL) site to determine whether there is a systematic offset between station data and conditions on the glacier. Lapse rates are calculated from temperature readings at five different elevations, for comparison with data from a meteorological station located in an adjacent glacier basin. From these analyses we provide a preliminary assessment of the extent to which our in situ measurements on the Kahiltna Glacier are representative of regional trends. The project will leverage 20 years of NPS mass balance data for the Kahiltna

  18. Sedimentary response to orogenic exhumation in the northern rocky mountain basin and range province, flint creek basin, west-central Montana

    USGS Publications Warehouse

    Portner, R.A.; Hendrix, M.S.; Stalker, J.C.; Miggins, D.P.; Sheriff, S.D.

    2011-01-01

    Middle Eocene through Upper Miocene sedimentary and volcanic rocks of the Flint Creek basin in western Montana accumulated during a period of significant paleoclimatic change and extension across the northern Rocky Mountain Basin and Range province. Gravity modelling, borehole data, and geologic mapping from the Flint Creek basin indicate that subsidence was focused along an extensionally reactivated Sevier thrust fault, which accommodated up to 800 m of basin fill while relaying stress between the dextral transtensional Lewis and Clark lineament to the north and the Anaconda core complex to the south. Northwesterly paleocurrent indicators, foliated metamorphic lithics, 64 Ma (40Ar/39Ar) muscovite grains, and 76 Ma (U-Pb) zircons in a ca. 27 Ma arkosic sandstone are consistent with Oligocene exhumation and erosion of the Anaconda core complex. The core complex and volcanic and magmatic rocks in its hangingwall created an important drainage divide during the Paleogene shedding detritus to the NNW and ESE. Following a major period of Early Miocene tectonism and erosion, regional drainage networks were reorganized such that paleoflow in the Flint Creek basin flowed east into an internally drained saline lake system. Renewed tectonism during Middle to Late Miocene time reestablished a west-directed drainage that is recorded by fluvial strata within a Late Miocene paleovalley. These tectonic reorganizations and associated drainage divide explain observed discrepancies in provenance studies across the province. Regional correlation of unconformities and lithofacies mapping in the Flint Creek basin suggest that localized tectonism and relative base level fluctuations controlled lithostratigraphic architecture.

  19. Range overlap and individual movements during breeding season influence genetic relationships of caribou herds in south-central Alaska

    USGS Publications Warehouse

    Roffler, Gretchen H.; Adams, Layne G.; Talbot, Sandra L.; Sage, George K.; Dale, Bruce W.

    2012-01-01

    North American caribou (Rangifer tarandus) herds commonly exhibit little nuclear genetic differentiation among adjacent herds, although available evidence supports strong demographic separation, even for herds with seasonal range overlap. During 1997–2003, we studied the Mentasta and Nelchina caribou herds in south-central Alaska using radiotelemetry to determine individual movements and range overlap during the breeding season, and nuclear and mitochondrial DNA (mtDNA) markers to assess levels of genetic differentiation. Although the herds were considered discrete because females calved in separate regions, individual movements and breeding-range overlap in some years provided opportunity for male-mediated gene flow, even without demographic interchange. Telemetry results revealed strong female philopatry, and little evidence of female emigration despite overlapping seasonal distributions. Analyses of 13 microsatellites indicated the Mentasta and Nelchina herds were not significantly differentiated using both traditional population-based analyses and individual-based Bayesian clustering analyses. However, we observed mtDNA differentiation between the 2 herds (FSTM = 0.041, P

  20. Seasonal variability and detection range modeling of baleen whale calls in the Gulf of Alaska, 1999-2002.

    PubMed

    Stafford, Kathleen M; Mellinger, David K; Moore, Sue E; Fox, Christopher G

    2007-12-01

    Five species of large whales, including the blue (Balaenoptera musculus), fin (B. physalus), sei (B. borealis), humpback (Megaptera novaeangliae), and North Pacific right (Eubalaena japonica), were the target of commercial harvests in the Gulf of Alaska (GoA) during the 19th through mid-20th Centuries. Since this time, there have been a few summer time visual surveys for these species, but no overview of year-round use of these waters by endangered whales primarily because standard visual survey data are difficult and costly. From October 1999-May 2002, moored hydrophones were deployed in six locations in the GoA to record whale calls. Reception of calls from fin, humpback, and blue whales and an unknown source, called Watkins' whale, showed seasonal and geographic variation. Calls were detected more often during the winter than during the summer, suggesting that animals inhabit the GoA year-round. To estimate the distance at which species-diagnostic calls could be heard, parabolic equation propagation loss models for frequencies characteristic of each of each call type were run. Maximum detection ranges in the subarctic North Pacific ranged from 45 to 250 km among three species (fin, humpback, blue), although modeled detection ranges varied greatly with input parameters and choice of ambient noise level.

  1. THIAFENTANIL-AZAPERONE-XYLAZINE AND CARFENTANIL-XYLAZINE IMMOBILIZATIONS OF FREE-RANGING CARIBOU (RANGIFER TARANDUS GRANTI) IN ALASKA, USA.

    PubMed

    Lian, Marianne; Beckmen, Kimberlee B; Bentzen, Torsten W; Demma, Dominic J; Arnemo, Jon M

    2016-04-28

    Carfentanil-xylazine (CX) has been the primary drug combination used for immobilizing free-ranging ungulates in Alaska, US since 1986. We investigated the efficacy of a potential new drug of choice, thiafentanil (Investigational New Animal Drug A-3080). Captive trials indicated that thiafentanil-azaperone-medetomidine could provide good levels of immobilization. However, field trials conducted in October 2013 on free-ranging caribou ( Rangifer tarandus granti) calves showed the combination too potent, causing three respiratory arrests and one mortality. The protocol was revised to thiafentanil-azaperone-xylazine (TAX), with good results. The induction time was not significantly different between the two combinations. However, the recovery time was significantly shorter for the TAX group than for the CX group. A physiologic evaluation was performed on 12 animals immobilized on CX and 15 animals on TAX. Arterial blood was collected after induction and again after 10 min of intranasal oxygen supplements (1 L/min). Both groups had significant increases in partial pressure of arterial oxygen after oxygen treatment. There was a concurrent significant increase in partial pressure of arterial carbon dioxide in both groups. Rectal temperature increased significantly in both groups during the downtime, which is consistent with other studies of potent opioids in ungulates. On the basis of our results, we found TAX to be a potential alternative for the current CX protocol for immobilizing free-ranging caribou calves via helicopter darting.

  2. THIAFENTANIL-AZAPERONE-XYLAZINE AND CARFENTANIL-XYLAZINE IMMOBILIZATIONS OF FREE-RANGING CARIBOU (RANGIFER TARANDUS GRANTI) IN ALASKA, USA.

    PubMed

    Lian, Marianne; Beckmen, Kimberlee B; Bentzen, Torsten W; Demma, Dominic J; Arnemo, Jon M

    2016-04-28

    Carfentanil-xylazine (CX) has been the primary drug combination used for immobilizing free-ranging ungulates in Alaska, US since 1986. We investigated the efficacy of a potential new drug of choice, thiafentanil (Investigational New Animal Drug A-3080). Captive trials indicated that thiafentanil-azaperone-medetomidine could provide good levels of immobilization. However, field trials conducted in October 2013 on free-ranging caribou ( Rangifer tarandus granti) calves showed the combination too potent, causing three respiratory arrests and one mortality. The protocol was revised to thiafentanil-azaperone-xylazine (TAX), with good results. The induction time was not significantly different between the two combinations. However, the recovery time was significantly shorter for the TAX group than for the CX group. A physiologic evaluation was performed on 12 animals immobilized on CX and 15 animals on TAX. Arterial blood was collected after induction and again after 10 min of intranasal oxygen supplements (1 L/min). Both groups had significant increases in partial pressure of arterial oxygen after oxygen treatment. There was a concurrent significant increase in partial pressure of arterial carbon dioxide in both groups. Rectal temperature increased significantly in both groups during the downtime, which is consistent with other studies of potent opioids in ungulates. On the basis of our results, we found TAX to be a potential alternative for the current CX protocol for immobilizing free-ranging caribou calves via helicopter darting. PMID:26967141

  3. Pingos in the Brooks Range, northern Alaska, U.S.A.

    USGS Publications Warehouse

    Hamilton, T.D.; Obi, Curtis M.

    1982-01-01

    Some 70 pingos occur at 27 separate localities within and near the Brooks Range. The pingos are distributed through mountain valleys at altitudes up to 725m and in terrain glaciated as recently as late Wisconsinan time. Pingos are particularly abundant in the Koyukuk and Chandalar drainage systems of the south-central Brooks Range, where they may be associated with structural features of regional extent.-from Authors

  4. Deformation and the timing of gas generation and migration in the eastern Brooks Range foothills, Arctic National Wildlife Refuge, Alaska

    USGS Publications Warehouse

    Parris, T.M.; Burruss, R.C.; O'Sullivan, P. B.

    2003-01-01

    Along the southeast border of the 1002 Assessment Area in the Arctic National Wildlife Refuge, Alaska, an explicit link between gas generation and deformation in the Brooks Range fold and thrust belt is provided through petrographic, fluid inclusion, and stable isotope analyses of fracture cements integrated with zircon fission-track data. Predominantly quartz-cemented fractures, collected from thrusted Triassic and Jurassic rocks, contain crack-seal textures, healed microcracks, and curved crystals and fluid inclusion populations, which suggest that cement growth occurred before, during, and after deformation. Fluid inclusion homogenization temperatures (175-250??C) and temperature trends in fracture samples suggest that cements grew at 7-10 km depth during the transition from burial to uplift and during early uplift. CH4-rich (dry gas) inclusions in the Shublik Formation and Kingak Shale are consistent with inclusion entrapment at high thermal maturity for these source rocks. Pressure modeling of these CH4-rich inclusions suggests that pore fluids were overpressured during fracture cementation. Zircon fission-track data in the area record postdeposition denudation associated with early Brooks Range deformation at 64 ?? 3 Ma. With a closure temperature of 225-240??C, the zircon fission-track data overlap homogenization temperatures of coeval aqueous inclusions and inclusions containing dry gas in Kingak and Shublik fracture cements. This critical time-temperature relationship suggests that fracture cementation occurred during early Brooks Range deformation. Dry gas inclusions suggest that Shublik and Kingak source rocks had exceeded peak oil and gas generation temperatures at the time structural traps formed during early Brooks Range deformation. The timing of hydrocarbon generation with respect to deformation therefore represents an important exploration risk for gas exploration in this part of the Brooks Range fold and thrust belt. The persistence of gas high at

  5. Geophysical investigation of a Suture Zone: The Border Ranges Fault of southern Alaska

    NASA Astrophysics Data System (ADS)

    Fisher, Michael A.; von Huene, Roland

    1984-12-01

    The Border Ranges fault separates structurally complex accreted Cretaceous rocks from less deformed middle or late Paleozoic and younger rocks in the Cook-Shelikof basin. Of the five types of geophysical data used to investigate this fault, gravity data give the clearest indication of its presence and crustal structure. For at least 400 km along the fault, gravity anomalies include a +20 to +30 mGal peak along the fault's upper plate and a -40 mGal trough along the lower plate. The paired anomaly can be modeled satisfactorily by a simple step, in a deep dense layer, that lies within 3 km of the projected offshore location of the fault. Relatively low-density rocks lie along the fault's lower plate to a depth of about 10 km, and the upper part of the fault dips within 20° of vertical. Satellite altimetry data show that two circular geoid lows lie along the Border Ranges fault and coincide with lows in free air gravity data. Seismic refraction and seismic reflection data suggest that the large-scale density anomalies that cause both types of lows must lie at depths greater than about 1 km within the margin. Three regional magnetic anomalies (Knik Arm, Seldovia, and Shelikof) terminate at the Border Ranges fault, suggesting that the fault truncates obliquely rocks that lie along its northwest side. Six seismic reflection lines cross the Border Ranges fault, but none of them shows reflections from it. The absence of such reflections probably results from the fault's steep dip and from the presence of strong water bottom multiples in the data. From the Late Jurassic until the early Late Cretaceous, the magmatic arc near the Cook-Shelikof basin was inactive, and we infer that the predominant motion along the Border Ranges fault was strike slip. Resurgent Late Cretaceous magmatism was contemporaneous with uplift of rocks along the northwest side of the Border Ranges fault and with deformation of turbidite sequences in the fault's lower plate. We propose that during the

  6. Seismic images of the Brooks Range fold and thrust belt, Arctic Alaska, from an integrated seismic reflection/refraction experiment

    USGS Publications Warehouse

    Levander, A.; Fuis, G.S.; Wissinger, E.S.; Lutter, W.J.; Oldow, J.S.; Moore, T.E.

    1994-01-01

    We describe results of an integrated seismic reflection/refraction experiment across the Brooks Range and flanking geologic provinces in Arctic Alaska. The seismic acquisition was unusual in that reflection and refraction data were collected simultaneously with a 700 channel seismograph system deployed numerous times along a 315 km profile. Shot records show continuous Moho reflections from 0-180 km offset, as well as numerous upper- and mid-crustal wide-angle events. Single and low-fold near-vertical incidence common midpoint (CMP) reflection images show complex upper- and middle-crustal structure across the range from the unmetamorphosed Endicott Mountains allochthon (EMA) in the north, to the metamorphic belts in the south. Lower-crustal and Moho reflections are visible across the entire reflection profile. Travel-time inversion of PmP arrivals shows that the Moho, at 33 km depth beneath the North Slope foothills, deepens abruptly beneath the EMA to a maximum of 46 km, and then shallows southward to 35 km at the southern edge of the range. Two zones of upper- and middle-crustal reflections underlie the northern Brooks Range above ~ 12-15 km depth. The upper zone, interpreted as the base of the EMA, lies at a maximum depth of 6 km and extends over 50 km from the range front to the north central Brooks Range where the base of the EMA outcrops above the metasedimentary rocks exposed in the Doonerak window. We interpret the base of the lower zone, at ~ 12 km depth, to be from carbonate rocks above the master detachment upon which the Brooks Range formed. The seismic data suggest that the master detachment is connected to the faults in the EMA by several ramps. In the highly metamorphosed terranes south of the Doonerak window, the CMP section shows numerous south-dipping events which we interpret as a crustal scale duplex involving the Doonerak window rocks. The basal detachment reflections can be traced approximately 100 km, and dip southward from about 10-12 km

  7. Lisburne Group (Mississippian-Lower Permian) petrography, paragenesis, and hydrocarbon potential, central Brooks Range, Alaska

    SciTech Connect

    Krutak, P.R.

    1989-03-01

    Subsurface Lisburne Group (Wahoo) rocks at Prudhoe Bay-Kuparuk fields produce 2 million bbl of oil/day and contain 2-3 billion bbl of oil in place. Lisburne reservoirs are early diagenetic dolomites encased in thick platform carbonates. Petrographic and geochemical study of 264 samples from eight newly discovered surface Lisburne sections comprising 4568 ft of strata in the Central Brooks Range provide new data concerning paragenesis and hydrocarbon potential of Lisburne facies farther west. A generalized paragenetic sequence for Lisburne equivalents of this region is (1) initial carbonate skeletal growth (both aragonite and calcite) during the Carboniferous, (2) subsequent recrystallization and inversion of aragonite to calcite, the change to calcite proceeding throughout late Paleozoic and Permian-Triassic time, (3) dolomitization in the Middle and Late Carboniferous, (4) chertification and silicification, postdating slightly or overlapping dolomitization, (5) development of porosity (moldic, intracrystal, etc.) in the middle to late Mesozoic, (6) formation of fracture porosity concurrent with the Brooks Range orogeny during Middle Jurassic-Cretaceous time, (7) oil generation, migration, and emplacement in Late Cretaceous-Tertiary time. Lisburne dolomites from the Central Brooks Range bear heavy hydrocarbons. Rock-Eval pyrolysis indicates part of the section is in the oil window and near the peak wet-gas generation zone. Shale samples from this region display thermal alteration indices and vitrinite reflectance values near the oil floor and also indicate potential for sourcing dry gas. Conodont color alteration indices show part of the Lisburn could produce dry gas.

  8. Facies comparison of autochthonous and allochthonous Permian and Triassic units, north-central Brooks Range, Alaska

    SciTech Connect

    Adams, K.E.

    1985-04-01

    Eight stratigraphic sections of Permian and Triassic rocks have been studied over a 30 km by 150 km area in the Endicott and Philip Smith Mountains of the central Brooks Range. Six of the sections are located on the Endicott Mountains allochthon, and the remaining two are parautochthonous columns in the Mount Doonerak area. The sections record a facies transition between the autochthonous Sadlerochit Group and Shublik Formation of the northeastern Brooks Range and the characteristically siliceous rocks of the allochthonous Siksikpuk and Otuk formations of the western Brooks Range. Laterally continuous and bioturbated beds of fine-grained sandstone, siltstone, and shale dominantly compose the Permian sequence, whereas the Triassic rocks consist of black shales, thin rhythmically bedded siliceous mudstones, and fossiliferous limestones. When the allochthonous sections are restored to a position south of the Mount Doonerak area, a general shallowing trend from southwest to northwest becomes evident within the reconstructed marine basin. To the south and west, the Permian sediments show a marked increase in silica content, with the occurrence of barite and a corresponding decrease in the thickness of the basal, coarser grained clastics. The Triassic formations also document an increase in silica and the presence of barite to the south and west, while becoming significantly sooty and phosphatic to the north and east. Ongoing petrographic and micropaleontologic studies of the field data will clarify these general paleogeographic relationships.

  9. Sandia National Laboratories land use permit for operations at Oliktok Alaska Long Range Radar Station.

    SciTech Connect

    Catechis, Christopher Spyros

    2013-02-01

    The property subject to this Environmental Baseline Survey (EBS) is located at the Oliktok Long Range Radar Station (LRRS). The Oliktok LRRS is located at 70À 30 W latitude, 149À 53 W longitude. It is situated at Oliktok Point on the shore of the Beaufort Sea, east of the Colville River. The purpose of this EBS is to document the nature, magnitude, and extent of any environmental contamination of the property; identify potential environmental contamination liabilities associated with the property; develop sufficient information to assess the health and safety risks; and ensure adequate protection for human health and the environment related to a specific property.

  10. Sedimentology and stratigraphy of the Kanayut Conglomerate, central and western Brooks Range, Alaska; report of 1981 field season

    USGS Publications Warehouse

    Nilsen, T.H.; Moore, T.E.

    1982-01-01

    The Upper Devonian and Lower Mississippian(?) Kanayut Conglomerate forms a major stratigraphic unit along the crest of the Brooks Range of northern Alaska. It crops out for an east-west distance of about 900 km and a north-south distance of about 65 km. The Kanayut is wholly allochthonous and has probably been transported northward on a series of thrust plates. The Kanayut is as thick as 2,600 m in the east-central Brooks Range. It thins and fines to the south and west. The Kanayut forms the middle part of the allochthonous sequence of the Endicott Group, an Upper Devonian and Mississippian clastic sequence underlain by platform limestones of the Baird Group and overlain by platform limestone, carbonaceous shale, and black chert of the Lisburne Group. The Kanayut overlies the marine Upper Devonian Noatak Sandstone or, where it is missing, the marine Upper Devonian Hunt Fork Shale. It is overlain by the marine Mississippian Kayak Shale. The Kanayut Conglomerate forms the fluvial part of a large, coarse-grained delta that prograded to the southwest in Late Devonian time and retreated in Early Mississippian time. Four sections of the Kanayut Conglomerate in the central Brooks Range and five in the western Brooks Range were measured in 1981. The sections from the western Brooks Range document the presence of fluvial cycles in the Kanayut as far west as the shores of the Chukchi Sea. The Kanayut in this area is generally finer grained than it is in the central and eastern Brooks Range, having a maximum clast size of 3 cm. It is probably about 300 m thick. The upper and lower contacts of the Kanayut are gradational. The lower Kanayut contains calcareous, marine-influenced sandstone within channel deposits, and the upper Kanayut contains probable marine interdistributary-bay shale sequences. The members of the Kanayut Conglomerate cannot be differentiated in this region. In the central Brooks Range, sections of the Kanayut Conglomerate at Siavlat Mountain and Kakivilak

  11. Constraints on the development of orogenic style gold mineralisation at Mineral de Talca, Coastal Range, central Chile: evidence from a combined structural, mineralogical, S and Pb isotope and geochronological study

    NASA Astrophysics Data System (ADS)

    Firth, Emily A.; Holwell, David A.; Oliver, Nicholas H. S.; Mortensen, James K.; Rovardi, Matthew P.; Boyce, Adrian J.

    2015-08-01

    Mineral de Talca is a rare occurrence of Mesozoic, gold-bearing quartz vein mineralisation situated within the Coastal Range of northern Chile. Quartz veins controlled by NNW-SSE-trending faults are hosted by Devonian-Carboniferous metasediments of greenschist facies and younger, undeformed granitoid and gabbro intrusions. The principal structural control in the area is the easterly dipping, NNW-SSE-trending El Teniente Fault, which most likely developed as an extensional normal fault in the Triassic but was later reactivated as a strike-slip fault during subsequent compression. A dilational zone in the El Teniente Fault appears to have focussed fluid flow, and an array of NW-SE-trending veins is present as splays off the El Teniente Fault. Mineralised quartz veins typically up to a metre thick occur in three main orientations: (1) parallel to and within NNW-SSE-trending, E-dipping faults throughout the area; (2) along NW-SE-trending, NE-dipping structures which may also host andesite dykes; and (3) rarer E-W-trending, subvertical veins. All mineralised quartz veins show evidence of multiple fluid events with anastomosing and crosscutting veins and veinlets, some of which contain up to 3.5 vol.% base metal sulphides. Mineralogically, Au is present in three textural occurrences, identified by 3D CT scanning: (1) with arsenopyrite and pyrite in altered wall rock and along the margins of some of the veins; (2) with Cu-Pb-Zn sulphides within quartz veins; and (3) as nuggets and clusters of native Au within quartz. Fluid inclusion work indicates the presence of CO2-CH4-bearing fluids with homogenisation temperatures of ˜350 °C and aqueous fluids with low-moderate salinities (0.4-15.5 wt% NaCl eq.) with homogenisation temperatures in the range of 161-321 °C. The presence of Au with arsenopyrite and pyrite in structurally controlled quartz veins and in greenschist facies rocks with evidence of CO2-bearing fluids is consistent with an orogenic style classification for

  12. Structural provinces of the northeastern Brooks Range, Arctic National Wildlife Refuge, Alaska

    SciTech Connect

    Wallace, W.K.; Hanks, C.L. )

    1990-07-01

    The dominant Cenozoic structures of the northeastern Brooks Range are anticlinoria with cores of sub-Mississippian rocks, reflecting a regional north-vergent duplex with a floor thrust in the sub-Mississippian sequence and a roof thrust in the Mississippian Kayak Shale. The number of horses forming each anticlinorium and the structural style of the overlying Mississippian and younger cover sequence varies regionally, providing a basis for dividing the northeastern Brooks Range into structural provinces. In the western province, each anticlinorium contains a single horse, and shortening above the Kayak Shale was accommodated mainly by detachment folds. To the north in the Sadlerochit Mountains, the Kayak Shale is depositionally discontinuous and rocks elsewhere separated by this detachment deformed together. In the eastern province, each anticlinorium contains multiple horses, and shortening above the Kayak Shale was accommodated largely by thrust duplication of Mississippian through Triassic rocks. In the narrow central province, the Devonian Okpilak batholith was detached from its roots, internally shortened along shear zones and by penetrative strain, and transported northward. Because the Kayak Shale is locally absent, the Mississippian and younger cover sequence deformed in part penetratively along with the batholith. 13 figs.

  13. The Cenozoic structural evolution of a fold-and-thrust belt, northeastern Brooks Range, Alaska

    SciTech Connect

    Hanks, C.L. )

    1993-03-01

    A Cenozoic fold-and-thrust belt in the eastern structural province of the northeastern Brooks Range exposes polydeformed low-grade metasedimentary and metavolcanic rocks of the pre-Mississippian basement and its sedimentary cover immediately adjacent to much younger foredeep deposits. Analysis of mesoscopic and map-scale structures in the range-front region suggests that at least one pre-Mississippian deformational event was recorded into the basement sequence by north-vergent fold-and-thrust structures and associated penetrative structures. Most of later Cenozoic shortening of the pre-Mississippian rocks was accommodated by thrust duplication, with little development of penetrative mesoscopic structures. Although separated from the underlying basement rocks by a major regional decollement horizon, Cenozoic deformation in the overlying Mississippian through Lower Cretaceous cover sequence also was primarily by thrust duplication. Although local and regional structural trends within the cover sequence suggest that Cenozoic deformation was north-northwest directed, east-west Cenozoic structural trends within the pre-Mississippian rocks may reflect an inherited pre-Mississippian structural grain and/or pre-Mississippian-age structures reactivated during Cenozoic deformation. A regional balanced cross section of the eastern structural province was constructed. 29 refs., 14 figs.

  14. The Border Ranges shear zone, Glacier Bay National Park, Alaska: An example of an ancient brittle-ductile transition zone

    SciTech Connect

    Smart, K.J. . Dept. of Geological Sciences)

    1992-01-01

    The Border Ranges fault system in southern Alaska forms the tectonic boundary between the Peninsular-Alexander-Wrangellia (PAW) composite terrane and the Chugach terrane. In Glacier Bay National Park, the Border Ranges fault system is a north-northwest trending, 10 kilometer wide zone of ductile shear zones and brittle faults hereafter referred to as the Border Ranges shear zone. Three-dimensional strain analyses of plagioclase lathes in the foliated calc-alkaline plutons reveals a strong flattening fabric with the plane of maximum flattening (XY-plane) oriented northwest-southeast and dipping steeply to the southwest. The distribution and shapes of sub-elliptical mafic enclaves in the calc-alkaline plutons show a similarly oriented flattening fabric. Coeval brittle and ductile deformational processes are indicated by: (1) ductile shear zones narrowing to brittle faults at the outcrop scale; and (2) undulose quartz with subgrain development, kinked biotite, twinned and undulose feldspar, and fractured and twinned hornblende often within a single thin-section. Amphibole geobarometry indicates that two of the calc-alkaline plutons deformed by the shear zone crystallized at pressures of approximately 3 kilobars equivalent to 10 to 12 kilometers depth. Metamorphic mineral assemblages within the mylonites indicate deformation under lower greenschist facies conditions (300--400 C). The shear zone may represent a snapshot of the brittle-ductile transition of an ancient convergent-transform plate boundary. As such, this unique exposure may be an ancient analogue for the brittle-ductile transition of the present day San Andreas fault system.

  15. Drought-induced stomatal closure probably cannot explain divergent white spruce growth in the Brooks Range, Alaska, USA.

    PubMed

    Brownlee, Annalis H; Sullivan, Patrick F; Csank, Adam Z; Sveinbjörnsson, Bjartmar; Ellison, Sarah B Z

    2016-01-01

    Increment cores from the boreal forest have long been used to reconstruct past climates. However, in recent years, numerous studies have revealed a deterioration of the correlation between temperature and tree growth that is commonly referred to as divergence. In the Brooks Range of northern Alaska, USA, studies of white spruce (Picea glauca) revealed that trees in the west generally showed positive growth trends, while trees in the central and eastern Brooks Range showed mixed and negative trends during late 20th century warming. The growing season climate of the eastern Brooks Range is thought to be drier than the west. On this basis, divergent tree growth in the eastern Brooks Range has been attributed to drought stress. To investigate the hypothesis that drought-induced stomatal closure can explain divergence in the Brooks Range, we synthesized all of the Brooks Range white spruce data available in the International Tree Ring Data Bank (ITRDB) and collected increment cores from our primary sites in each of four watersheds along a west-to-east gradient near the Arctic treeline. For cores from our sites, we measured ring widths and calculated carbon isotope discrimination (δ13C), intrinsic water-use efficiency (iWUE), and needle intercellular CO2 concentration (C(i)) from δ13C in tree-ring alpha-cellulose. We hypothesized that trees exhibiting divergence would show a corresponding decline in δ13C, a decline in C(i), and a strong increase in iWUE. Consistent with the ITRDB data, trees at our western and central sites generally showed an increase in the strength of the temperature-growth correlation during late 20th century warming, while trees at our eastern site showed strong divergence. Divergent tree growth was not, however, associated with declining δ13C. Meanwhile, estimates of C(i) showed a strong increase at all of our study sites, indicating that more substrate was available for photosynthesis in the early 21st than in the early 20th century. Our

  16. Drought-induced stomatal closure probably cannot explain divergent white spruce growth in the Brooks Range, Alaska, USA.

    PubMed

    Brownlee, Annalis H; Sullivan, Patrick F; Csank, Adam Z; Sveinbjörnsson, Bjartmar; Ellison, Sarah B Z

    2016-01-01

    Increment cores from the boreal forest have long been used to reconstruct past climates. However, in recent years, numerous studies have revealed a deterioration of the correlation between temperature and tree growth that is commonly referred to as divergence. In the Brooks Range of northern Alaska, USA, studies of white spruce (Picea glauca) revealed that trees in the west generally showed positive growth trends, while trees in the central and eastern Brooks Range showed mixed and negative trends during late 20th century warming. The growing season climate of the eastern Brooks Range is thought to be drier than the west. On this basis, divergent tree growth in the eastern Brooks Range has been attributed to drought stress. To investigate the hypothesis that drought-induced stomatal closure can explain divergence in the Brooks Range, we synthesized all of the Brooks Range white spruce data available in the International Tree Ring Data Bank (ITRDB) and collected increment cores from our primary sites in each of four watersheds along a west-to-east gradient near the Arctic treeline. For cores from our sites, we measured ring widths and calculated carbon isotope discrimination (δ13C), intrinsic water-use efficiency (iWUE), and needle intercellular CO2 concentration (C(i)) from δ13C in tree-ring alpha-cellulose. We hypothesized that trees exhibiting divergence would show a corresponding decline in δ13C, a decline in C(i), and a strong increase in iWUE. Consistent with the ITRDB data, trees at our western and central sites generally showed an increase in the strength of the temperature-growth correlation during late 20th century warming, while trees at our eastern site showed strong divergence. Divergent tree growth was not, however, associated with declining δ13C. Meanwhile, estimates of C(i) showed a strong increase at all of our study sites, indicating that more substrate was available for photosynthesis in the early 21st than in the early 20th century. Our

  17. Young tectonics of a complex plate boundary zone: Indentation, rotation, and escape in Alaska

    NASA Astrophysics Data System (ADS)

    Wallace, W. K.; Ruppert, N. A.

    2012-12-01

    Convergence of thick crust of the Yakutat block with the southern margin of Alaska is widely recognized as a dominant influence on the tectonics of Alaska since at least late Miocene time. It is less clear how this convergence relates to the distribution, type, and orientation of geologic structures, and to the boundaries between the tectonic provinces that they define. We propose that convergence of Yakutat block includes two distinct components that influence deformation and topography in different ways: 1) The crust of the exposed, southern Yakutat block is too thick to subduct, which has caused the collisional St. Elias orogen. Detachment of the upper part of the mafic basement allows delamination and sinking of the remaining mafic crust and lithospheric mantle. The collisional orogen drives rigid counterclockwise rotation of the southern Alaska block south of the arcuate, right-lateral Denali fault. The western boundary of this block is a zone of distributed contraction in the western Alaska Range and Cook Inlet. 2) The northern part of the Yakutat block is thin enough to subduct but thick and buoyant enough to cause localized flat-slab subduction orthogonal to rotation of the southern Alaska block. Consequences include the gently antiformal Talkeetna Mountains that span the forearc basin, a gap in the magmatic arc, and a basement-involved fold-and-thrust belt in the northern Alaska Range. An arcuate oroclinal hinge from southern Alaska to the northeastern Brooks Range reflects indentation since at least Paleocene time. Traction above the subducted Yakutat block along the southern part of this hinge drives current indentation. North of the subducted Yakutat block, indentation is reflected by left-lateral block rotation that accommodates shortening between the Denali and Tintina faults and by contraction farther north along the northern edge of the arcuate northeastern Brooks Range. Western Alaska accommodates both northward indentation and westward convergence

  18. Plutonic rocks of Jurassic age in the Alaska-Aleutian Range batholith: chemical variation and polarity.

    USGS Publications Warehouse

    Reed, B.I.; Miesch, A.T.; Lanphere, M.A.

    1983-01-01

    Plutonic rocks of Jurassic age exposed on the Pacific side of this batholith form a compositionally continuous calc-alkaline suite that ranges from hornblende gabbro to quartz monzonite. Tonalite and quartz diorite are the dominant rock types. Trend-surface analysis of 102 samples indicates that the direction of slope of the trend is approximately normal to the Jurassic magmatic arc. K2O and SiO2 increase towards the E-SE and the other oxides towards the W-NW. If the chemical trends reflect the approximate geometry of a palaeo-subduction zone, the polarity of the Jurassic magmatic arc is to the NW, i.e. subduction was directed towards the SE. Thus the palaeo-subduction zone is on the opposite side of the arc from the position that has generally been assumed, indicating that the Jurassic plutonic rocks were not generated in response to classical Andean-type convergent plate margins. The magmatic arc may have been formed in an intra-ocean environment and subsequently has been rafted northwards and accreted to this part of the N Pacific rim during the late Mesozoic. Middle and Upper Jurassic clastics underlying Cook Inlet to the SE and derived from the magmatic arc are classified as back-arc deposits, rather than as an arc-trench gap sequence.-L.C.H.

  19. The crustal section of the Siniktanneyak Mountain ophiolite, Brooks Range, Alaska

    SciTech Connect

    Bickerstaff, D.; Harris, R.A.; Miller, M.A. . Dept. of Geology and Geography)

    1993-04-01

    Fragments of the upper crustal section of the Brooks Range Ophiolite on the west flank of Siniktanneyak Mountain expose important contact relations and paleohorizontal indicators. The nearly complete crustal sequence faces northwest. Based on field observations, the crustal units encountered at Siniktanneyak Mountain from bottom to top are: (1) layered gabbro, (2) isotropic gabbro, (3) high level and late-stage intrusions of diorite and diabase, (4) rare sheeted dikes, (5) basalt, and (6) a bedded volcanic tuff. Potassium feldspar-bearing pegmatites are also found. Of particular interest is the orientation of the layered gabbro, sheeted dikes, and the bedded volcanic tuff. The steeply dipping gabbro layers strike N-S, the adjacent vertical sheeted dikes strike NE-SW. Bedded volcanic tuff and lavas are flat lying. Contacts within the upper crust units are often covered by talus. Contacts between various plutonic rocks are both sharp and gradational, suggesting syn- and post-cooling intrusions. Contacts between plutonic rock and higher volcanic rock appear to be fault contacts.

  20. Lateral continuity of the Blarney Creek Thrust, Doonerak Windown, Central Brooks Range, Alaska

    SciTech Connect

    Seidensticker, C.M.; Julian, F.E.; Phelps, J.C.; Oldow, J.S.; Avellemant, H.G.

    1985-04-01

    The contact between Carboniferous and lower Paleozoic rocks, exposed along the northern margin of the Doonerak window in the central Brooks Range, is a major thrust fault called the Blarney Creek thrust (BCT). The BCT has been traced over a distance of 25 km, from Falsoola Mountain to Wien Mountain. The tectonic nature of this contact is demonstrated by: (1) omission of stratigraphic units above and below the BCT; (2) large angular discordance in orientation of first-generation cleavage at the BCT; (3) numerous thrust imbricates developed in the upper-plate Carboniferous section that sole into the BCT; and (4) truncation of an upper-plate graben structure at the BCT. Lack of evidence for pre-Carboniferous deformation in the lower plate casts doubt on the interpretation of the contact as an angular unconformity. However, the localized presence below the BCT of Mississippian Kekiktuk Conglomerate and Kayak Shale, in apparent depositional contact with lower Paleozoic rocks, suggests that the BCT follows an originally disconformable contact between the Carboniferous and lower Paleozoic rocks. The juxtaposition of younger over older rocks at the BCT is explained by calling upon the BCT to act as the upper detachment surface of a duplex structure. Duplex development involves initial imbrication of the Carboniferous section using the BCT as a basal decollement, followed by formation of deeper thrusts in the lower Paleozoic section, which ramp up and merge into the BCT.

  1. Structure and petrology of the La Perouse gabbro intrusion, Fairweather Range, southeastern Alaska.

    USGS Publications Warehouse

    Loney, R.A.; Himmelberg, G.R.

    1983-01-01

    The gabbro was intruded during the Middle Tertiary into a Mesozoic granulite-facies metamorphic environment dominated by strike-slip fault movement, compression and possible minor subduction. The asymmetric funnel form of the intrusion is due to subsidence from magmatic loading at high T, coupled with control from pre-existing structures, and not from tectonic compression. The intrusion is 12 X 27 km and has exposed cumulate layering of approx 6000 m. Probe analyses of olivines (24), Ca-poor pyroxenes (28), augites (22) and plagioclases (35) are tabulated. Cumulus mineral compositions in the basal cumulates are: olivine Fo86-71, plagioclase An81-63, bronzite Ca3Mg82Fe15 - Ca4Mg75Fe21, augite Ca45Mg47Fe8 - Ca42Mg48Fe10. The layered gabbro above the basal cumulates consists dominantly of lenticularly interlayered plagioclase-augite-orthopyroxene-olivine, plagioclase-augite- olivine and plagioclase-orthopyroxene-augite cumulates, the composition ranges being olivine Fo75-50, plagioclase An78-42, orthopyroxene and inverted pigeonite Ca2.8Mg76.4Fe20.8 - Ca1.4Mg31.0Fe67.6, augite Ca43.1Mg46.9Fe10.0 - Ca40.5Mg27.1Fe32.4. The most iron-rich pyroxene and albite-rich plagioclase occur in a zone near the margin of the intrusion and are probably related to exchange reactions with the country rock. It is considered that the gabbro did not accumulate by simple fractional crystallization of a single or even several large batches of magma, but by numerous influxes of previously fractionated magma from a deeper reservoir. Conditions of crystallization are interpreted as approx 1055oC, 5.4 kbar and fO2 near the wustite-magnetite buffer.-R.A.H.

  2. Multistory duplexes with forward dipping roofs, north central Brooks Range, Alaska

    USGS Publications Warehouse

    Wallace, W.K.; Moore, T.E.; Plafker, G.

    1997-01-01

    The Endicott Mountains allochthon has been thrust far northward over the North Slope parautochthon in the northern Brooks Range. Progressively younger units are exposed northward within the allochthon. To the south, the incompetent Hunt Fork Shale has thickened internally by asymmetric folds and thrust faults. Northward, the competent Kanayut Conglomerate forms a duplex between a floor thrust in Hunt Fork and a roof thrust in the Kayak Shale. To the north, the competent Lisburne Group forms a duplex between a floor thrust in Kayak and a roof thrust in the Siksikpuk Formation. Both duplexes formed from north vergent detachment folds whose steep limbs were later truncated by south dipping thrust faults that only locally breach immediately overlying roof thrusts. Within the parautochthon, the Kayak, Lisburne, and Siksikpuk-equivalent Echooka Formation form a duplex identical to that in the allochthon. This duplex is succeeded abruptly northward by detachment folds in Lisburne. These folds are parasitic to an anticlinorium interpreted to reflect a fault-bend folded horse in North Slope "basement," with a roof thrust in Kayak and a floor thrust at depth. These structures constitute two northward tapered, internally deformed wedges that are juxtaposed at the base of the allochthon. Within each wedge, competent units have been shortened independently between detachments, located mainly in incompetent units. The basal detachment of each wedge cuts upsection forward (northward) to define a wedge geometry within which units dip regionally forward. These dips reflect forward decrease in internal structural thickening by forward vergent folds and hindward dipping thrust faults. Copyright 1997 by the American Geophysical Union.

  3. High fidelity does not preclude colonization: range expansion of molting Black Brant on the Arctic coast of Alaska

    USGS Publications Warehouse

    Flint, Paul L.; Meixell, Brandt W.; Mallek, Edward J.

    2014-01-01

    High rates of site fidelity have been assumed to infer static distributions of molting geese in some cases. To test this assumption, we examined movements of individually marked birds to understand the underlying mechanisms of range expansion of molting Black Brant (Branta bernicla nigricans) on the Arctic Coastal Plain (ACP) of Alaska. The Teshekpuk Lake Special Area (TLSA) on the ACP was created to protect the primary molting area of Brant. When established in 1977, the TLSA was thought to include most, if not all, wetlands used by molting Brant on the ACP. From 2010 to 2013, we surveyed areas outside the TLSA and counted an average of 9800 Brant per year, representing 29–37% of all molting Brant counted on the ACP. We captured and banded molting Brant in 2011 and 2012 both within the TLSA and outside the TLSA at the Piasuk River Delta and Cape Simpson to assess movements of birds among areas across years. Estimates of movement rates out of the TLSA exceeded those into the TLSA, demonstrating overall directional dispersal. We found differences in sex and age ratios and proportions of adult females with brood patches, but no differences in mass dynamics for birds captured within and outside the TLSA. Overall fidelity rates to specific lakes (0.81, range = 0.49–0.92) were unchanged from comparable estimates obtained in the early 1990s. We conclude that Brant are dispersing from the TLSA into new molting areas while simultaneously redistributing within the TLSA, likely as a consequence of changes in relative habitat quality. Shifts in distribution resulted from colonization of new areas by young birds as well as low levels of directional dispersal of birds that previously molted in the TLSA. Based on combined counts, the overall number of molting Brant across the ACP has increased substantially.

  4. Regional variations in the fluvial Upper Devonian and Lower Mississippian(?) Kanayut Conglomerate, Brooks Range, Alaska

    NASA Astrophysics Data System (ADS)

    Moore, Thomas E.; Nilsen, Tor H.

    1984-03-01

    The wholly allochthonous Upper Devonian and Lower Mississippian(?) Kanayut Conglomerate is one of the most extensive fluvial deposits in North America. It crops out for 950 km along the crest of the Brooks Range in a series of thrust plates and is as thick as 2615 m. The Kanayut forms the fluvial part of a large, coarse-grained delta. The lower part of the Kanayut (the Ear Peak Member) overlies marginal-marine and prodelta turbidite deposits and consists of fining-upward meandering-stream-channel cycles of conglomerate and sandstone within black to maroon floodplain shale deposits. The middle part of the Kanayut (the Shainin Lake Member) lacks shale and consists of fining-upward couplets of channelized conglomerate and parallel- to cross-stratified sandstone interpreted as braidplain deposits. These deposits contain the largest clasts (23 cm) and were deposited during maximum progradation of the fluvial sequence. The upper part of the Kanayut (the Stuver Member), which consists of fining-upward meandering stream cycles similar to those of the lower part, grades upward into overlying Lower Mississippian tidal and marginal-marine deposits. Paleocurrent data and distribution of largest clasts indicate that the Kanayut was deposited by southwest-flowing streams fed by at least two major trunk streams that drained a mountainous region to the north and east. Comparison of stratigraphic and sedimentologic data collected at three selected locations representative of proximal, intermediate and distal parts of the Kanayut basin reveal regional variations in its fluvial character. These include a decrease in total thickness of fluvial strata, an increase in total thickness of associated marine sandstone, the pinch-out of the coarse-grained middle part of the Kanayut and decreases in the conglomerate/sandstone and sandstone/shale ratios from proximal to distal areas of the basin. The coarse-grained parts of the fluvial cycles decrease in thickness and lateral extent from

  5. Regional variations in the fluvial Upper Devonian and Lower Mississippian(?) Kanayut Conglomerate, Brooks Range, Alaska

    USGS Publications Warehouse

    Moore, T.E.; Nilsen, T.H.

    1984-01-01

    The wholly allochthonous Upper Devonian and Lower Mississippian(?) Kanayut Conglomerate is one of the most extensive fluvial deposits in North America. It crops out for 950 km along the crest of the Brooks Range in a series of thrust plates and is as thick as 2615 m. The Kanayut forms the fluvial part of a large, coarse-grained delta. The lower part of the Kanayut (the Ear Peak Member) overlies marginal-marine and prodelta turbidite deposits and consists of fining-upward meandering-stream-channel cycles of conglomerate and sandstone within black to maroon floodplain shale deposits. The middle part of the Kanayut (the Shainin Lake Member) lacks shale and consists of fining-upward couplets of channelized conglomerate and parallel- to cross-stratified sandstone interpreted as braidplain deposits. These deposits contain the largest clasts (23 cm) and were deposited during maximum progradation of the fluvial sequence. The upper part of the Kanayut (the Stuver Member), which consists of fining-upward meandering stream cycles similar to those of the lower part, grades upward into overlying Lower Mississippian tidal and marginal-marine deposits. Paleocurrent data and distribution of largest clasts indicate that the Kanayut was deposited by southwest-flowing streams fed by at least two major trunk streams that drained a mountainous region to the north and east. Comparison of stratigraphic and sedimentologic data collected at three selected locations representative of proximal, intermediate and distal parts of the Kanayut basin reveal regional variations in its fluvial character. These include a decrease in total thickness of fluvial strata, an increase in total thickness of associated marine sandstone, the pinch-out of the coarse-grained middle part of the Kanayut and decreases in the conglomerate/sandstone and sandstone/shale ratios from proximal to distal areas of the basin. The coarse-grained parts of the fluvial cycles decrease in thickness and lateral extent from

  6. Compressional intracontinental orogens: Ancient and modern perspectives

    NASA Astrophysics Data System (ADS)

    Raimondo, Tom; Hand, Martin; Collins, William J.

    2014-03-01

    Compressional intracontinental orogens are major zones of crustal thickening produced at large distances from active plate boundaries. Consequently, any account of their initiation and subsequent evolution must be framed outside conventional plate tectonics theory, which can only explain the proximal effects of convergent plate-margin interactions. This review considers a range of hypotheses regarding the origins and transmission of compressive stresses in intraplate settings. Both plate-boundary and intraplate stress sources are investigated as potential driving forces, and their relationship to rheological models of the lithosphere is addressed. The controls on strain localisation are then evaluated, focusing on the response of the lithosphere to the weakening effects of structural, thermal and fluid processes. With reference to the characteristic features of intracontinental orogens in central Asia (the Tien Shan) and central Australia (the Petermann and Alice Springs Orogens), it is argued that their formation is largely driven by in-plane stresses generated at plate boundaries, with the lithosphere acting as an effective stress guide. This implies a strong lithospheric mantle rheology, in order to account for far-field stress propagation through the discontinuous upper crust and to enable the support of thick uplifted crustal wedges. Alternative models of intraplate stress generation, primarily involving mantle downwelling, are rejected on the grounds that their predicted temporal and spatial scales for orogenesis are inconsistent with the observed records of deformation. Finally, inherited mechanical weaknesses, thick sedimentary blanketing over a strongly heat-producing crust, and pervasive reaction softening of deep fault networks are identified as important and interrelated controls on the ability of the lithosphere to accommodate rather than transmit stress. These effects ultimately produce orogenic zones with architectural features and evolutionary

  7. Geochronology and geochemistry of early Paleozoic igneous rocks of the Lesser Xing'an Range, NE China: Implications for the tectonic evolution of the eastern Central Asian Orogenic Belt

    NASA Astrophysics Data System (ADS)

    Wang, Zhi-wei; Xu, Wen-liang; Pei, Fu-ping; Wang, Feng; Guo, Peng

    2016-09-01

    This paper presents new zircon U-Pb, Hf isotope, and whole-rock major and trace element data for early Paleozoic igneous rocks of the Lesser Xing'an Range, NE China, in order to constrain the early Paleozoic tectonic evolution of the eastern Central Asian Orogenic Belt (CAOB). Zircon U-Pb dating indicates that early Paleozoic magmatic events within the northern Songnen-Zhangguangcai Range Massif (SZM) can be subdivided into four stages: Middle Cambrian (~ 505 Ma), Late Cambrian (~ 490 Ma), Early-Middle Ordovician (~ 470 Ma), and Late Ordovician (460-450 Ma). The Middle Cambrian monzogranites are K-rich, weakly to strongly peraluminous, and characterized by pronounced heavy rare earth element (HREE) depletions, high Sr/Y ratios, low Y concentrations, low primary zircon εHf(t) values (- 6.79 to - 1.09), and ancient two-stage model (TDM2) ages (1901-1534 Ma). These results indicate derivation from partial melting of thickened ancient crustal materials that formed during the amalgamation of the northern SZM and the northern Jiamusi Massif (JM). The Late Cambrian monzonite, quartz monzonite, and monzogranite units are chemically similar to A-type granites, and contain zircons with εHf(t) values of - 2.59 to + 1.78 and TDM2 ages of 1625-1348 Ma. We infer that these rocks formed from primary magmas generated by partial melting of Mesoproterozoic accreted lower crustal materials in a post-collisional extensional environment. The Early-Middle Ordovician quartz monzodiorite, quartz monzonite, monzogranite, and rhyolite units are calc-alkaline, relatively enriched in light REEs (LREEs) and large ion lithophile elements (LILEs; e.g., Rb, Th, and U), depleted in HREEs and high field strength elements (HFSEs; e.g., Nb, Ta, and Ti), and contain zircons with εHf(t) values of - 7.33 to + 4.98, indicative of formation in an active continental margin setting. The Late Ordovician alkali-feldspar granite and rhyolite units have A-type granite affinities that suggest they formed in

  8. Mesozoic and Cenozoic tectonics of the eastern and central Alaska Range: Progressive basin development and deformation in a suture zone

    USGS Publications Warehouse

    Ridgway, K.D.; Trop, J.M.; Nokleberg, W.J.; Davidson, C.M.; Eastham, K.R.

    2002-01-01

    Analysis of late Mesozoic and Cenozoic sedimentary basins, metamorphic rocks, and major faults in the eastern and central Alaska Range documents the progressive development of a suture zone that formed as a result of collision of an island-arc assemblage (the Wrangellia composite terrane) with the former North American continental margin. New basin-analysis, structural, and geochronologic data indicate the following stages in the development of the suture zone: (1) Deposition of 3-5 km of Upper Jurassic-Upper Cretaceous marine strata (the Kahiltna assemblage) recorded the initial collision of the island-arc assemblage with the continental margin. The Kahiltna assemblage exposed in the northern Talkeetna Mountains represents a Kimmeridgian-Valanginian backarc basin that was filled by northwestward-flowing submarine-fan systems that were transporting sediment derived from Mesozoic strata of the island-arc assemblage. The Kahiltna assemblage exposed in the southern Alaska Range represents a Valanginian-Cenomanian remnant ocean basin filled by west-southwestward-flowing submarine-fan systems that were transporting sediment derived from Paleozoic continental-margin strata uplifted in the along-strike suture zone. A belt of retrograde metamorphism and a regional anticlinorium developed along the continental margin from 115 to 106 Ma, roughly coeval with the end of widespread deposition in the Kahiltna sedimentary basins. (2) Metamorphism of submarine-fan deposits of the Kahiltna basin, located near the leading edge of the island-arc assemblage, occurred at ca. 74 Ma, as determined from a new U-Pb zircon age for a synkinematic sill. Coeval with metamorphism of deposits of the Kahiltna basin in the southern part of the suture zone was development of a thrust-top basin, the Cantwell basin, in the northern part of the suture zone. Geologic mapping and compositional data suggest that the 4 km of Upper Cretaceous nonmarine and marginal marine sedimentary strata in this basin

  9. Three-dimensional model of an ultramafic feeder system to the Nikolai Greenstone mafic large igneous province, central Alaska Range

    USGS Publications Warehouse

    Glen, J.M.G.; Schmidt, J.M.; Connard, G.G.

    2011-01-01

    The Amphitheater Mountains and southern central Alaska Range expose a thick sequence of Triassic Nikolai basalts that is underlain by several mafic-ultramafic complexes, the largest and best exposed being the Fish Lake and Tangle (FL-T) mafic-ultramafic sills that flank the Amphitheater Mountains synform. Three-dimensional (3-D) modeling of gravity and magnetic data reveals details of the structure of the Amphitheater Mountains, such as the orientation and thickness of Nikolai basalts, and the geometry of the FL-T intrusions. The 3-D model (50 ?? 70 km) includes the full geographic extent of the FL-T complexes and consists of 11 layers. Layer surfaces and properties (density and magnetic susceptibility) were modified by forward and inverse methods to reduce differences between the observed and calculated gravity and magnetic grids. The model suggests that the outcropping FL-T sills are apparently connected and traceable at depth and reveals variations in thickness, shape, and orientation of the ultramafic bodies that may identify paths of magma flow. The model shows that a significant volume (2000 km3) of ultramafic material occurs in the subsurface, gradually thickening and plunging westward to depths exceeding 4 km. This deep ultramafic material is interpreted as the top of a keel or root system that supplied magma to the Nikolai lavas and controlled emplacement of related magmatic intrusions. The presence of this deep, keel-like structure, and asymmetry of the synform, supports a sag basin model for development of the Amphitheater Mountains structure and reveals that the feeders to the Nikolai are much more extensive than previously known. Copyright 2011 by the American Geophysical Union.

  10. Crimean orogene: A nappe interpretation

    SciTech Connect

    Popadyuk, I.V.; Smirnov, S.E. )

    1993-09-01

    On the International Tectonic Map of Europe, the Crimean orogene presents a structure that has no analog in the Alpine orogenic belt. The Crimean mountain system lacks nappe structures of Alpine age. Its geosynclinal folding deformation is restricted to the Tavria flysch formation, previously dated as Triassic-Liassic. Therefore, the Crimean orogene was considered as the Kimmerian tectonotype. In our model, the Crimean orogene is characterized by nappe structures. The Yayla nappe is composed to Upper Jurassic and Neocomian sediments and is located below the Tavrian nappe, which consists of the Tavrian flysch formation. We dated the age of the Tavrian formation as Hauterivian-Aptian on the basis of published ammonite finds in the stratotype section. Nappe displacements are dated roughly as Austrian (albian) by the occurrence of upper-middle Albian sediments below the nappes and the Upper Cretaceous age of their neoautochthonous sedimentary cover. These north-vergent nappes have a horizontal displacement of about 20 km. In the eastern part of the orogene, these nappe structures were overprinted by Laramide-Savic (Paleocene and end Oligocene-early Miocene) deformations, as evident in the Kerch peninsula. The nature of these late deformation is not clear. The hydrocarbon potential of the prenapping autochthonous series has not yet been studied. Exploration for oil and gas in the Crimean sector of the Black Sea must take the suggested model and its implications into account.

  11. Frozen debris lobes, permafrost slope instability, and a potential infrastructure hazard in the south-central Brooks Range of Alaska

    NASA Astrophysics Data System (ADS)

    Daanen, R. P.; Darrow, M.; Grosse, G.; Jones, B. M.

    2012-12-01

    Here we report on investigations carried out at unusual debris mass-movement features (frozen debris lobes) on permafrost slopes in the south central portion of the Brooks Range of northern Alaska. The features under investigation are located in mountainous terrain near the southern border of continuous permafrost. The frozen debris lobes consist mainly of boulders, cobles, platy gravel sand and silt frozen debris derived from weathering mountain tops. The general dimensions of these lobes are either lobate or tongue shaped with widths up to 500 m and lengths up to 1200 m. In accumulation zones where slopes converge, the debris slowly moves as solifluction lobes, mud flows and potentially sliding toward the valley. These features were previously referred to as stable rock glaciers in the past, as evidenced by a dense cover of vegetation, and exhibiting no known downslope movement. Our investigations however, have shown that these features are indeed moving downslope as a result of creep, slumping, viscous flow, blockfall and leaching of fines in the summer; and in cold seasons by creep and sliding of frozen sediment slabs. Movement indicators observed in the field include toppling trees, slumps and scarps, detachment slides, striation marks on frozen sediment slabs, recently buried trees and other vegetation, mudflows, and large cracks in the lobe surface. Ground-based measurements on one frozen debris-lobe over three years (2008-2010) revealed average movement rates of approximately 1 cm day-1, which is substantially larger than rates measured in historic aerial photography from the 1950s to 1980s. Current observations , through lidar, ifsar, insar and ground based measurements using boreholes, geophysics and repeat photography of these features show an increase in movement activity that could be the result of rising summer temperatures in the region. Warming of ice rich permafrost slopes and frozen debris lobes in the Brooks Range pose a direct threat to the

  12. VEGETATION MEDIATED THE IMPACTS OF POSTGLACIAL CLIMATIC CHANGE ON FIRE REGIMES IN THE SOUTHCENTRAL BROOKS RANGE, ALASKA

    SciTech Connect

    Higuera, P E; Brubaker, L B; Anderson, P M; Hu, F S; Brown, T A

    2008-10-28

    We examine direct and indirect impacts of millennial-scale climatic change on fire regimes in the southcentral Brooks Range, Alaska, using four lake-sediment records and existing paleoclimate interpretations. New techniques are introduced to identify charcoal peaks semi-objectively and detect statistical differences in fire regimes. Peaks in charcoal accumulation rates (CHARs) provide estimates of fire return intervals (FRIs) which are compared between vegetation zones described by fossil pollen and stomata. Climatic warming from ca 15-9 ka BP (calendar years before CE 1950) coincides with shifts in vegetation from herb tundra to shrub tundra to deciduous woodlands, all novel species assemblages relative to modern vegetation. Two sites cover this period and show increased CHARs and decreased FRIs with the transition from herb to shrub tundra ca 13.3-14.3 ka BP. Short FRIs in the Betula-dominated shrub tundra (mean [m] FRI 144 yr; 95% CI 119-170) primarily reflect the effects of flammable, continuous fuels on the fire regime. FRIs increased significantly with the transition to Populus-dominated deciduous woodlands ca 10.5 ka BP (mFRI 251 yr [158-352]), despite evidence of warmer- and drier-than-present summers. We attribute reduced fire activity under these conditions to low flammability of deciduous fuels. Three sites record the mid to late Holocene, when cooler and moister conditions allowed Picea glauca forest-tundra and P. mariana boreal forests to establish ca 8 and 5.5 ka BP. Forest-tundra FRIs did not differ significantly from the previous period (mFRIs range from 131-238 yr), but FRIs decreased with the transition to boreal forest (mFRI 145 yr [129-163]). Overall, fire-regime shifts in the study area showed greater correspondence with vegetation characteristics than with inferred climate, and we conclude that vegetation mediated the impacts of millennial-scale climatic change on fire regimes by modifying landscape flammability. Our findings emphasize the

  13. Accretionary orogens through Earth history

    USGS Publications Warehouse

    Cawood, Peter A.; Kroner, A.; Collins, W.J.; Kusky, T.M.; Mooney, W.D.; Windley, B.F.

    2009-01-01

    Accretionary orogens form at intraoceanic and continental margin convergent plate boundaries. They include the supra-subduction zone forearc, magmatic arc and back-arc components. Accretionary orogens can be grouped into retreating and advancing types, based on their kinematic framework and resulting geological character. Retreating orogens (e.g. modern western Pacific) are undergoing long-term extension in response to the site of subduction of the lower plate retreating with respect to the overriding plate and are characterized by back-arc basins. Advancing orogens (e.g. Andes) develop in an environment in which the overriding plate is advancing towards the downgoing plate, resulting in the development of foreland fold and thrust belts and crustal thickening. Cratonization of accretionary orogens occurs during continuing plate convergence and requires transient coupling across the plate boundary with strain concentrated in zones of mechanical and thermal weakening such as the magmatic arc and back-arc region. Potential driving mechanisms for coupling include accretion of buoyant lithosphere (terrane accretion), flat-slab subduction, and rapid absolute upper plate motion overriding the downgoing plate. Accretionary orogens have been active throughout Earth history, extending back until at least 3.2 Ga, and potentially earlier, and provide an important constraint on the initiation of horizontal motion of lithospheric plates on Earth. They have been responsible for major growth of the continental lithosphere through the addition of juvenile magmatic products but are also major sites of consumption and reworking of continental crust through time, through sediment subduction and subduction erosion. It is probable that the rates of crustal growth and destruction are roughly equal, implying that net growth since the Archaean is effectively zero. ?? The Geological Society of London 2009.

  14. Tertiary tectonics of the Border Ranges Fault system, north-central Chugach Mountains, Alaska: Sedimentation, deformation and uplift along the inboard edge of a subduction complex

    SciTech Connect

    Little, T.A.

    1988-01-01

    In south-central Alaska the Border Ranges Fault system (BRFS) separates lower Paleogene rocks of a forearc basin sequence from a Cretaceous subduction complex. In a north-central part of the Chugach Mountains the upper Paleocene-lower Eocene Chickaloon Formation was deposited along the seaward margin of the forearc basin as an alluvial fan complex. A field study combining geologic mapping of a {approximately}200 km{sup 2} region, stratigraphic studies, K-Ar and fission-track geochronology, metamorphic petrology, and detailed structural analysis of deformed rocks on both sides of the BRFS has been used to reconstruct the Tertiary history of displacements and uplift events along the inboard edge of Alaska's subduction-accretion complex.

  15. Stalled Orogen Linked to East Antarctic Craton Assembly

    NASA Astrophysics Data System (ADS)

    Martos, Y. M.; Ferraccioli, F.; Finn, C.; Bell, R. E.; Jordan, T. A.; Damaske, D.

    2015-12-01

    The interior of East Antarctica is often regarded as a coherent Archean craton surrounded by Paleo to Neoproterozoic orogenic belts. Here we use recent aerogeophysical, satellite magnetic, satellite gravity and passive seismic results in central East Antarctica to challenge this view. Firstly, anomalously thick crust (compared to most other cratons) has been imaged in East Antarctica by both passive seismic and gravity modelling with values up to 60 km (Ferraccioli et al., 2011, Nature; An et al., 2015, JGR). The thick crust underlies both the Gamburtsev Subglacial Mountains and an elevated region between Lake Vostok and Dronning Maud Land, referred to as the East Antarctic Mountain Ranges plateau (An et al., 2015). Second, satellite magnetic data reveal that the Gamburtev Province lies in between the Ruker/Princess Elizabeth Land, Vostok, Nimrod/South Pole and Recovery provinces. The Nimrod/ South Pole province is a Paleo to Meso Proterozoic igneous province formed along the edges of the Archean/Paleoproterozoic Mawson continent (e.g. Goodge and Fanning, 2010 JGR). Our aerogeophysical and sediment provenance data interpretations suggest that the Gamburtsev Province represents a distinct Grenvillian-age orogenic belt. A stalled orogen with thick crust (i.e. an orogen where widespread orogenic collapse and root delamination has not occurred)- is preserved in the interior of East Antarctica resembling e.g. the Paleoproterozoic Trans Hudson Orogen and segments of Grenvillian orogens in Laurentia. The stalled orogen may relate to widespread accretionary and collisional events within Rodinia. However, passive seismic interpretations (An et al., 2015) favour linking crustal thickening to the Pan-African age assembly of Greater India, East Antarctica and Australia within Gondwana (e.g. Aitken et al., 2014 GRL). Further aerogeophysical observations over Princess Elizabeth Land are timely to enable more robust correlations with geological observations and to help dating the

  16. Tectonic framework of petroliferous rocks in Alaska: hydrocarbons

    USGS Publications Warehouse

    Grantz, Arthur; Kirschner, C.E.

    1976-01-01

    Alaska, which contains about 28% of the land and continental shelf of the United States, is estimated by the U.S. Geological Survey to contain about one third of the nation's undiscovered oil and about one sixth of its undiscovered natural gas. The Survey estimates that fields discovered in Alaska through 1972 ultimately may produce about 26 billion bbl of oil and 68 Tcf of natural gas. In northern Alaska, Paleozoic and Mesozoic shelf and slope carbonate and clastic rocks of the Brooks Range orogen were thrust relatively northward over the depressed south margin of the Paleozoic and Mesozoic Arctic platform. A foredeep, the Colville geosyncline, developed across the depressed margin of the platform in earliest Cretaceous time. Detritus from the Brooks Range filled the foredeep and prograded northward to fill the Cretaceous and Tertiary North Chukchi and Umiat-Camden basins and form the progradational Beaufort shelf. The largest petroleum reserves (Prudhoe Bay and associated fields) and the best prospects for additional large discoveries in Alaska lie in the areally extensive upper Paleozoic to Tertiary carbonate and clastic rocks of northern Alaska. In southern Alaska, a series of arc-trench systems developed on oceanic rocks during Jurassic and Cretaceous time. Between these arcs and the metamorphic (continental) terranes of east-central and northern Alaska, large back-arc and arc-trench gap basins received thick volcanic and detrital deposits. These deposits were extensively, and commonly intensely, deformed and disrupted by mid-Jurassic to Tertiary plutonism, Laramide oroclinal bending, wrench faulting, and arc-related compression. This deformation, coupled with low porosity (in part produced by diagenetic mobilization of labile constituents), has left these rocks with only modest, local prospects for petroleum. Laramide events compressed and consolidated ("continentalized") the late Mesozoic back-arc basin deposits and welded them to the older continental

  17. Neogene transpressional foreland basin development on the north side of the central alaska range, usibelli group and nenana gravel, tanana basin

    USGS Publications Warehouse

    Ridgway, K.D.; Thoms, E.E.; Layer, P.W.; Lesh, M.E.; White, J.M.; Smith, S.V.

    2007-01-01

    Neogene strata of the Tanana basin provide a long-term record of a northwardpropagating, transpressional foreland-basin system related to regional shortening of the central Alaska Range and strike-slip displacement on the Denali fault system. These strata are ???2 km thick and have been deformed and exhumed in thrust faults that form the foothills on the north side of the Alaska Range. The lower part of the sedimentary package, the Usibelli Group, consists of 800 m of mainly Miocene strata that were deposited in fluvial, lacustrine, and peat bog environments of the foredeep depozone of the foreland-basin system. Compositional data from conglomerate and sandstone, as well as recycled Upper Cretaceous palynomorphs, indicate that the Miocene foreland-basin system was supplied increasing amounts of sediment from lithologies currently exposed in thrust sheets located south of the basin. The upper part of the sedimentary package, the Nenana Gravel, consists of 1200 m of mainly Pliocene strata that were deposited in alluvial-fan and braidplain environments in the wedge-top depozone of the foreland-basin system. Compositional data from conglomerate and sandstone, as well as 40Ar/39Ar dating of detrital feldspars in sandstone and from granitic clasts in conglomerate, indicate that lithologies exposed in the central Alaska Range provided most of the detritus to the Pliocene foreland-basin system. 40Ar/39Ar dates from detrital feldspar grains also show that two main suites of plutons contributed sediment to the Nenana Gravel. Detrital feldspars with an average age of 56 Ma are interpreted to have been derived from the McKinley sequence of plutons located south of the Denali fault. Detrital feldspars with an average age of 34 Ma are interpreted to have been derived from plutons located north of the Denali fault. Plutons located south of the Denali fault provided detritus for the lower part of the Nenana Gravel, whereas plutons located north of the Denali fault began to

  18. 40Ar/39Ar Dating of Zn-Pb-Ag Mineralization in the Northern Brooks Range, Alaska

    USGS Publications Warehouse

    Werdon, Melanie B.; Layer, Paul W.; Newberry, Rainer J.

    2004-01-01

    The 40Ar/39Ar laser step-heating method potentially can be used to provide absolute ages for a number of formerly undatable, low-temperature ore deposits. This study demonstrates the use of this method by determining absolute ages for Zn-Pb-Ag sediment-hosted massive sulfide deposits and vein-breccia occurrences found throughout a 300-km-long, east-west-trending belt in the northern Brooks Range, Alaska. Massive sulfide deposits are hosted by Mississippian to Pennsylvanian(?) black carbonaceous shale, siliceous mudstone, and lesser chert and carbonate turbidites of the Kuna Formation (e.g., Red Dog, Anarraaq, Lik (Su), and Drenchwater). The vein-breccia occurrences (e.g., Husky, Story Creek, West Kivliktort Mountain, Vidlee, and Kady) are hosted by a deformed but only weakly metamorphosed package of Upper Devonian to Lower Mississippian mixed continental and marine clastic rocks (the Endicott Group) that stratigraphically underlie the Kuna Formation. The vein-breccias are mineralogically similar to, but not spatially associated with, known massive sulfide deposits. The region's largest shale-hosted massive sulfide deposit is Red Dog; it has reserves of 148 Mt grading 16.6 percent zinc, 4.5 percent lead, and 77 g of silver per tonne. Hydrothermally produced white mica in a whole-rock sample from a sulfide-bearing igneous sill within the Red Dog deposit yielded a plateau age of 314.5 Ma. The plateau age of this whole-rock sample records the time at which temperatures cooled below the argon closure temperature of the white mica and is interpreted to represent the minimum age limit for massive sulfide-related hydrothermal activity in the Red Dog deposit. Sulfide-bearing quartz veins at Drenchwater crosscut a hypabyssal intrusion with a maximum biotite age of 337.0 Ma. Despite relatively low sulfide deposition temperatures in the vein-breccia occurrences (162°-251°C), detrital white mica in sandstone immediately adjacent to large vein-breccia zones was partially to

  19. Persistent organic pollutants in the blood of free-ranging sea otters (Enhydra lutris ssp.) in Alaska and California

    USGS Publications Warehouse

    Jessup, David A.; Johnson, Christine K.; Estes, James; Carlson-Bremer, Daphne; Jarman, Walter M.; Reese, Stacey; Dodd, Erin; Tinker, M. Tim; Ziccardi, Michael H.

    2010-01-01

    As part of tagging and ecologic research efforts in 1997 and 1998, apparently healthy sea otters of four age-sex classes in six locations in Alaska and three in California were sampled for persistent organic pollutants (POPs) and other chemicals of ecologic or environmental concern (COECs). Published techniques for the detection of POPs (specifically Σpolychlorinated biphenyls [PCBs], ΣDDTs, Σhexachlorocyclohexanes [HCHs], Σpolycyclic aromatic hydrocarbons [PAHs], Σchlordanes [CHLs], hexachlorobenzene [HCB], dieldrin, and mirex) in the tissue of dead otters were modified for use with serum from live sea otters. Toxic equivalencies (TEQs) were calculated for POPs with proven bioactivity. Strong location effects were seen for most POPs and COECs; sea otters in California generally showed higher mean concentrations than those in Alaska. Differences in contaminant concentrations were detected among age and sex classes, with high levels frequently observed in subadults. Very high levels of ΣDDT were detected in male sea otters in Elkhorn Slough, California, where strong freshwater outflow from agricultural areas occurs seasonally. All contaminants except mirex differed among Alaskan locations; only ΣDDT, HCB, and chlorpyrifos differed within California. High levels of ΣPCB (particularly larger, more persistent congeners) were detected at two locations in Alaska where associations between elevated PCBs and military activity have been established, while higher PCB levels were found at all three locations in California where no point source of PCBs has been identified. Although POP and COEC concentrations in blood may be less likely to reflect total body burden, concentrations in blood of healthy animals may be more biologically relevant and less influenced by state of nutrition or perimortem factors than other tissues routinely sampled.

  20. Persistent organic pollutants in the blood of free-ranging sea otters (Enhydra lutris ssp.) in Alaska and California.

    PubMed

    Jessup, David A; Johnson, Christine K; Estes, James; Carlson-Bremer, Daphne; Jarman, Walter M; Reese, Stacey; Dodd, Erin; Tinker, M Tim; Ziccardi, Michael H

    2010-10-01

    As part of tagging and ecologic research efforts in 1997 and 1998, apparently healthy sea otters of four age-sex classes in six locations in Alaska and three in California were sampled for persistent organic pollutants (POPs) and other chemicals of ecologic or environmental concern (COECs). Published techniques for the detection of POPs (specifically ∑polychlorinated biphenyls [PCBs], ∑DDTs, ∑hexachlorocyclohexanes [HCHs], ∑polycyclic aromatic hydrocarbons [PAHs], ∑chlordanes [CHLs], hexachlorobenzene [HCB], dieldrin, and mirex) in the tissue of dead otters were modified for use with serum from live sea otters. Toxic equivalencies (TEQs) were calculated for POPs with proven bioactivity. Strong location effects were seen for most POPs and COECs; sea otters in California generally showed higher mean concentrations than those in Alaska. Differences in contaminant concentrations were detected among age and sex classes, with high levels frequently observed in subadults. Very high levels of ∑DDT were detected in male sea otters in Elkhorn Slough, California, where strong freshwater outflow from agricultural areas occurs seasonally. All contaminants except mirex differed among Alaskan locations; only ∑DDT, HCB, and chlorpyrifos differed within California. High levels of ∑PCB (particularly larger, more persistent congeners) were detected at two locations in Alaska where associations between elevated PCBs and military activity have been established, while higher PCB levels were found at all three locations in California where no point source of PCBs has been identified. Although POP and COEC concentrations in blood may be less likely to reflect total body burden, concentrations in blood of healthy animals may be more biologically relevant and less influenced by state of nutrition or perimortem factors than other tissues routinely sampled.

  1. Constraints on the metamorphic history of a mélange complex within the easternmost Himalayan orogen, northern Indo-Burma Range, based on P-T pseudosection and thermobarometric studies.

    NASA Astrophysics Data System (ADS)

    Haproff, P. J.; Yin, A.

    2015-12-01

    Despite many petrologic and structural studies surrounding the eastern Himalayan syntaxis, P-T histories of metamorphic rocks within the northern Indo-Burman mélange of the easternmost Himalayas remain largely unknown. We present metamorphic P-T conditions of three schists from successive thrust sheets related to generation of the Himalayan orogen, based on mineral assemblage thermobarometry and pseudosection phase diagrams. Use of the garnet-muscovite-biotite-plagioclase thermobarometer and Ti-in-biotite thermometer yield peak conditions of 676 ± 78°C and 10.6 ± 1.3 kbar for schist (PH-1-8-13-26) thrust atop metavolcanics, mafic schist, and ultramafics of the Indus-Ysangpo suture zone (IYSZ). Within this sample, quartz is recrystallized along grain boundaries and garnets contain no significant compositional zoning. Pseudosections constructed from bulk-rock composition and equilibrium mineral assemblages yield a clockwise P-T path with similar peak garnet amphibolite conditions. At structurally lower levels, garnet chlorite schist (PH-1-8-13-8) from a thrust klippe of the IYSZ record peak temperatures below 650°C. Garnets display growth zoning, with increasing Mn and decreasing Fe and Mg from rim to core. Application of the Ti-in-biotite thermometer to a mafic schist (PH-1-3-13-1B) within the klippe near a southwestward-directed thrust yields a peak temperature of 679 ± 24°C. Our study reveals a complex metamorphic history throughout the northern Indo-Burman mélange zone that likely records metamorphism at deep crustal levels during thrust motion and growth of the Himalayan orogen around the northeastern corner of India.

  2. Rapid movement of frozen debris-lobes: implications for permafrost degradation and slope instability in the south-central Brooks Range, Alaska

    USGS Publications Warehouse

    Daanen, R.P.; Grosse, G.; Darrow, M.M.; Hamilton, T.D.; Jones, Benjamin M.

    2012-01-01

    We present the results of a reconnaissance investigation of unusual debris mass-movement features on permafrost slopes that pose a potential infrastructure hazard in the south-central Brooks Range, Alaska. For the purpose of this paper, we describe these features as frozen debris-lobes. We focus on the characterisation of frozen debris-lobes as indicators of various movement processes using ground-based surveys, remote sensing, field and laboratory measurements, and time-lapse observations of frozen debris-lobe systems along the Dalton Highway. Currently, some frozen debris-lobes exceed 100 m in width, 20 m in height and 1000 m in length. Our results indicate that frozen debris-lobes have responded to climate change by becoming increasingly active during the last decades, resulting in rapid downslope movement. Movement indicators observed in the field include toppling trees, slumps and scarps, detachment slides, striation marks on frozen sediment slabs, recently buried trees and other vegetation, mudflows, and large cracks in the lobe surface. The type and diversity of observed indicators suggest that the lobes likely consist of a frozen debris core, are subject to creep, and seasonally unfrozen surface sediment is transported in warm seasons by creep, slumping, viscous flow, blockfall and leaching of fines, and in cold seasons by creep and sliding of frozen sediment slabs. Ground-based measurements on one frozen debris-lobe over three years (2008–2010) revealed average movement rates of approximately 1 cm day−1, which is substantially larger than rates measured in historic aerial photography from the 1950s to 1980s. We discuss how climate change may further influence frozen debris-lobe dynamics, potentially accelerating their movement. We highlight the potential direct hazard that one of the studied frozen debris-lobes may pose in the coming years and decades to the nearby Trans Alaska Pipeline System and the Dalton Highway, the main artery for transportation

  3. Rapid movement of frozen debris-lobes: implications for permafrost degradation and slope instability in the south-central Brooks Range, Alaska

    NASA Astrophysics Data System (ADS)

    Daanen, R. P.; Grosse, G.; Darrow, M. M.; Hamilton, T. D.; Jones, B. M.

    2012-05-01

    We present the results of a reconnaissance investigation of unusual debris mass-movement features on permafrost slopes that pose a potential infrastructure hazard in the south-central Brooks Range, Alaska. For the purpose of this paper, we describe these features as frozen debris-lobes. We focus on the characterisation of frozen debris-lobes as indicators of various movement processes using ground-based surveys, remote sensing, field and laboratory measurements, and time-lapse observations of frozen debris-lobe systems along the Dalton Highway. Currently, some frozen debris-lobes exceed 100 m in width, 20 m in height and 1000 m in length. Our results indicate that frozen debris-lobes have responded to climate change by becoming increasingly active during the last decades, resulting in rapid downslope movement. Movement indicators observed in the field include toppling trees, slumps and scarps, detachment slides, striation marks on frozen sediment slabs, recently buried trees and other vegetation, mudflows, and large cracks in the lobe surface. The type and diversity of observed indicators suggest that the lobes likely consist of a frozen debris core, are subject to creep, and seasonally unfrozen surface sediment is transported in warm seasons by creep, slumping, viscous flow, blockfall and leaching of fines, and in cold seasons by creep and sliding of frozen sediment slabs. Ground-based measurements on one frozen debris-lobe over three years (2008-2010) revealed average movement rates of approximately 1 cm day-1, which is substantially larger than rates measured in historic aerial photography from the 1950s to 1980s. We discuss how climate change may further influence frozen debris-lobe dynamics, potentially accelerating their movement. We highlight the potential direct hazard that one of the studied frozen debris-lobes may pose in the coming years and decades to the nearby Trans Alaska Pipeline System and the Dalton Highway, the main artery for transportation

  4. The initiation of orogenic margin reverse faulting

    NASA Astrophysics Data System (ADS)

    Bailey, R. C.

    2002-04-01

    Laboratory values of rock friction coefficients suggest that reverse faulting should be very difficult to initiate by simple horizontal compression of the crust. Values of stresses required by Andersonian faulting may be an order of magnitude higher than those actually present in orogenic margins. A simple stress balance calculation shows that the effect of the excess lithostatic pressure under an elevated orogen, if transmitted laterally through a crustal ductile layer to the orogenic margin, is to provide sufficient hydraulic lift under the orogen flanks to initiate reverse faulting by direct lift, even with rock friction coefficients of order 0.8. The required orogenic elevation above surrounding ``normal'' lithosphere is about one fifth of the thickness of the brittle crust of the orogen. This elevation may be as small as 2 km in tectonically active regions. The mechanism works even in the absence of regional lithospheric compressive stresses.

  5. Regional structural framework and petroleum assessment of the Brooks Range foothills and southern coastal plain, National Petroleum Reserve, Alaska

    USGS Publications Warehouse

    Potter, Christopher J.; Moore, Thomas E.; O'Sullivan, Paul B.; Miller, John J.

    2002-01-01

    The transects, along with other seismic-reflection examples, illustrate four play concepts being used in the deformed area for the 2002 U.S. Geological Survey oil and gas assessment of the National Petroleum Reserve-Alaska (NPRA). The Brookian topset structural play includes broad west-northwest-trending anticlines in the Cretaceous Nanushuk Group, developed above structurally thickened Torok mudstones in the incipiently-deformed, most northerly part of the thrust system. The Torok structural play includes prominent anticlines affecting deep-basin sandstones, many of which are detached from folds exposed at the surface. The Ellesmerian structural play includes closures developed in the clastic part of the Ellesmerian sequence, mainly above a detachment in the Shublik Formation. The thrust belt play includes antiformal stacks of allochthonous Endicott Group clastic rocks and Lisburne Group carbonates; these stacks were assembled at about 120 Ma, and were transported to their present positions in the foothills at about 60 Ma.

  6. Tectonic processes during oblique collision: Insights from the St. Elias orogen, northern North American Cordillera

    USGS Publications Warehouse

    Pavlis, T.L.; Picornell, C.; Serpa, L.; Bruhn, R.L.; Plafker, G.

    2004-01-01

    Oblique convergence in the St. Elias orogen of southern Alaska and northwestern Canada has constructed the world's highest coastal mountain range and is the principal driver constructing all of the high topography in northern North America. The orogen originated when the Yakutat terrane was excised from the Cordilleran margin and was transported along margin-parallel strike-slip faults into the subduction-transform transition at the eastern end of the Aleutian trench. We examine the last 3 m.y. of this collision through an analysis of Euler poles for motion of the Yakutat microplate with respect to North America and the Pacific. This analysis indicates a Yakutat-Pacific pole near the present southern triple junction of the microplate and' predicts convergence to dextral-oblique convergence across the offshore Transition fault, onland structures adjacent to the Yakutat foreland, or both, with plate speeds increasing from 10 to 30 mm/yr from southeast to northwest. Reconstructions based on these poles show that NNW transport of the collided block into the NE trending subduction zone forced contraction of EW line elements as the collided block was driven into the subduction-transform transition. This suggests the collided block was constricted as it was driven into the transition. Constriction provides an explanation for observed vertical axis refolding of both earlier formed fold-thrust systems and the collisional suture at the top of the fold-thrust stack. We also suggest that this motion was partially accommodated by lateral extrusion of the western portion of the orogen toward the Aleutian trench. Important questions remain regarding which structures accommodated parts of this motion. The Transition fault may have accommodated much of the Yakutat-Pacific convergence on the basis of our analysis and previous interpretations of GPS-based geodetic data. Nonetheless, it is locally overlapped by up to 800 m of undeformed sediment, yet elsewhere shows evidence of young

  7. Multi-resolution Changes in the Spatial Extent of Perennial Arctic Alpine Snow and Ice Fields with Potential Archaeological Significance in the Central Brooks Range, Alaska

    NASA Astrophysics Data System (ADS)

    Tedesche, M. E.; Freeburg, A. K.; Rasic, J. T.; Ciancibelli, C.; Fassnacht, S. R.

    2015-12-01

    Perennial snow and ice fields could be an important archaeological and paleoecological resource for Gates of the Arctic National Park and Preserve in the central Brooks Range mountains of Arctic Alaska. These features may have cultural significance, as prehistoric artifacts may be frozen within the snow and ice. Globally significant discoveries have been made recently as ancient artifacts and animal dung have been found in melting alpine snow and ice patches in the Southern Yukon and Northwest Territories in Canada, the Wrangell mountains in Alaska, as well as in other areas. These sites are melting rapidly, which results in quick decay of biological materials. The summer of 2015 saw historic lows in year round snow cover extent for most of Alaska. Twenty mid to high elevation sites, including eighteen perennial snow and ice fields, and two glaciers, were surveyed in July 2015 to quantify their areal extent. This survey was accomplished by using both low flying aircraft (helicopter), as well as with on the ground in-situ (by foot) measurements. By helicopter, visual surveys were conducted within tens of meters of the surface. Sites visited by foot were surveyed for extent of snow and ice coverage, melt water hydrologic parameters and chemistry, and initial estimates of depths and delineations between snow, firn, and ice. Imagery from both historic aerial photography and from 5m resolution IKONOS satellite information were correlated with the field data. Initial results indicate good agreement in permanent snow and ice cover between field surveyed data and the 1985 to 2011 Landsat imagery-based Northwest Alaska snow persistence map created by Macander et al. (2015). The most deviation between the Macander et al. model and the field surveyed results typically occurred as an overestimate of perennial extent on the steepest aspects. These differences are either a function of image classification or due to accelerated ablation rates in perennial snow and ice coverage

  8. Ambient tremors in a collisional orogenic belt

    USGS Publications Warehouse

    Chuang, Lindsay Yuling; Chen, Kate Huihsuan; Wech, Aaron G.; Byrne, Timothy; Peng, Wei

    2014-01-01

    Deep-seated tectonic tremors have been regarded as an observation tied to interconnected fluids at depth, which have been well documented in worldwide subduction zones and transform faults but not in a collisional mountain belt. In this study we explore the general features of collisional tremors in Taiwan and discuss the possible generation mechanism. In the 4 year data, we find 231 ambient tremor episodes with durations ranging from 5 to 30 min. In addition to a coseismic slip-induced stress change from nearby major earthquake, increased tremor rate is also highly correlated with the active, normal faulting earthquake swarms at the shallower depth. Both the tremor and earthquake swarm activities are confined in a small, area where the high attenuation, high thermal anomaly, the boundary between high and low resistivity, and localized veins on the surfaces distributed, suggesting the involvement of fluids from metamorphic dehydration within the orogen.

  9. Environmental geochemistry at Red Mountain, an unmined volcanogenic massive sulphide deposit in the Bonnifield district, Alaska Range, east-central Alaska

    USGS Publications Warehouse

    Eppinger, R.G.; Briggs, P.H.; Dusel-Bacon, C.; Giles, S.A.; Gough, L.P.; Hammarstrom, J.M.; Hubbard, B.E.

    2007-01-01

    The unmined, pyrite-rich Red Mountain (Dry Creek) deposit displays a remarkable environmental footprint of natural acid generation, high metal and exceedingly high rate earth element (REE) concentrations in surface waters. The volcanogenic massive sulphide deposit exhibits well-constrained examples of acid-generating, metal-leaching, metal-precipitation and self-mitigation (via co-precipitation, dilution and neutralization) processes that occur in an undisturbed natural setting, a rare occurrence in North America. Oxidative dissolution of pyrite and associated secondary reactions under near-surface oxidizing conditions are the primary causes for the acid generation and metal leaching. The deposit is hosted in Devonian to Mississippian felsic metavolcanic rocks of the Mystic Creek Member of the Totatlanika Schist. Water samples with the lowest pH (many below 3.5), highest specific conductance (commonly >2500 ??S/cm) and highest major- and trace-element concentrations are from springs and streams within the quartz-sericite-pyrite alteration zone. Aluminum, Cd, Co, Cu, Fe, Mn, Ni, Pb, Y, Zn and, particularly, the REEs are found in high concentrations, ranging across four orders of magnitude. Waters collected upstream from the alteration zone have near-neutral pH, lower specific conductance (370 to 830 ??S/cm), lower metal concentrations and measurable alkalinities. Water samples collected downstream of the alteration zone have pH and metal concentrations intermediate between these two extremes. Stream sediments are anomalous in Zn, Pb, S, Fe, Cu, As, Co, Sb and Cd relative to local and regional background abundances. Red Mountain Creek and its tributaries do not, and probably never have, supported significant aquatic life. ?? 2007 AAG/ Geological Society of London.

  10. Re-Os sulfide geochronology of the Red Dog sediment-hosted Zn-Pb-Ag deposit, Brooks Range, Alaska

    USGS Publications Warehouse

    Morelli, R.M.; Creaser, R.A.; Selby, D.; Kelley, K.D.; Leach, D.L.; King, A.R.

    2004-01-01

    The Red Dog sediment-hosted deposit in the De Long Mountains of northern Alaska is the largest Zn producer in the world. Main stage mineralization is characterized by massive sulfide ore and crosscutting subvertical veins. Although the vein mineralization is clearly younger than the massive ore, the exact temporal relationship between the two is unclear. Re-Os geochronology of pyrite is used to determine the absolute age of main stage ore at Red Dog. A 10-point isochron on both massive and vein pyrite yields an age of 338.3 ?? 5.8 Ma and is interpreted to represent the age of main stage ore. The Re-Os data indicate that both massive and vein ore types are coeval within the resolution of the technique. Formation of the Red Dog deposit was associated with extension along a passive continental margin, and therefore the Re-Os age of main stage ore constrains the timing of rifting as well as the age of the host sedimentary rocks. Sphalerite from both massive and vein ore yields imprecise ages and shows a high degree of scatter compared to pyrite. We suggest that the Re-Os systematics of sphalerite can be disturbed and that this mineral is not reliable for Re-Os geochronology. ?? 2004 by Economic Geology.

  11. Ellesmerian (. ) and Brookian deformation in the Franklin Mountains, northeastern Brooks Range, Alaska, and its bearing on the origin of the Canada Basin

    SciTech Connect

    Oldow, J.S.; Ave Lallemant, H.G.; Julian, F.E.; Seidensticker, C.M.

    1987-01-01

    Structural analysis of deformed rocks in the Franklin Mountains, northeastern Alaska, indicates that (1) pre-Carboniferous rocks were transported southeastward during mid-Devonian (Ellesmerian.) thrusting, (2) Cretaceous and older rocks were transported northward during Mesozoic-Cenozoic Brookian thrusting, and (3) the pre-Carboniferous rocks were strongly involved in the Brookian deformation. The strong involvement of these rocks in Brookian structures suggests that the magnitude of northward thrusting during Brookian tectonism is virtually uniform from west to east along the axis of the Brooks Range fold and thrust belt. In addition, the newly recognized southern vergence of pre-Carboniferous structures is comparable with that of coeval structures exposed in Arctic Canada to the east. These data are not easily reconciled with the orocline model for the origin of the Canada Basin but are consistent with left-lateral transport on a north-south-striking transform fault along the Canadian Arctic islands. 19 references.

  12. The Middle Fork Plutonic Complex: A plutonic association of coeval peralkaline and metaluminous magmas in the north-central Alaska Range

    SciTech Connect

    Solie, D.N.

    1988-01-01

    The 57 m.y. Middle Fork Plutonic Complex (MFPC) intrudes Paleozoic metasedimentary rocks south of the Farewell Fault zone in the north-central Alaska Range. Though spatially related to the late Cretaceous - Early Tertiary subduction-related Alaska Range batholith, MFPC is more characteristic of an extensional or anorogenic setting. A swarm of basalt, hawaiite and rhyolite dikes east of the complex intruded, and was intruded by, the plutonic rocks. Approximately 30% of the exposed rock in the 125 km[sup 2] complex is hedenbergite - fayalite syenite, [approx equal]20% is peralkalin arfvedsonite-biotite alkali-feldspar granite (AF granite), and [le]20% is pyroxene-olivine-biotite gabbro. The rest is a mixed unit including clinopyroxene-biotite-amphibole diorite, and hornblende-biotite granite (HB granite). K-Ar and Rb-Sr radiometric dating of rock types shows that they are coeval. Their close spatial and temporal relationships led to complex magmatic interactions. Calculated initial [sup 87]Sr/[sup 86]Sr for gabbro and diorite group is around 0.705 to 0.706. HB granites are heterogeneous, but fall mostly around 0.707 to 0.708. Hypersolvus syenites and AF granites form an isochron with initial [sup 87]Sr/[sup 86]Sr of 0.70965. These groupings suggest that at least three different magmas formed the MFPC; scatter of isotopic data reflects mutual contamination and assimilation. Consanguinous hypersolvus syenite and AF granite mineralogy appears to be controlled by fluorine in the magma chamber. Eruptive stratigraphy, as predicted by intrusive history of MFPC, compares favorably with volcanic stratigraphies of peralkaline volcanic systems worldwide, and MFPC may be modelled as the root zone of a peralkaline volcanic system.

  13. Seasonal and altitudinal variations in snow algal communities on an Alaskan glacier (Gulkana glacier in the Alaska range)

    NASA Astrophysics Data System (ADS)

    Takeuchi, Nozomu

    2013-09-01

    Snow and ice algae are cold tolerant algae growing on the surface of snow and ice, and they play an important role in the carbon cycles for glaciers and snowfields in the world. Seasonal and altitudinal variations in seven major taxa of algae (green algae and cyanobacteria) were investigated on the Gulkana glacier in Alaska at six different elevations from May to September in 2001. The snow algal communities and their biomasses changed over time and elevation. Snow algae were rarely observed on the glacier in May although air temperature had been above 0 ° C since the middle of the month and surface snow had melted. In June, algae appeared in the lower areas of the glacier, where the ablation ice surface was exposed. In August, the distribution of algae was extended to the upper parts of the glacier as the snow line was elevated. In September, the glacier surface was finally covered with new winter snow, which terminated algal growth in the season. Mean algal biomass of the study sites continuously increased and reached 6.3 × 10 μl m-2 in cell volume or 13 mg carbon m-2 in September. The algal community was dominated by Chlamydomonas nivalis on the snow surface, and by Ancylonema nordenskiöldii and Mesotaenium berggrenii on the ice surface throughout the melting season. Other algae were less abundant and appeared in only a limited area of the glacier. Results in this study suggest that algae on both snow and ice surfaces significantly contribute to the net production of organic carbon on the glacier and substantially affect surface albedo of the snow and ice during the melting season.

  14. Mississippian clastic-to-carbonate transition in the northeastern Brooks Range, Alaska: Depositional cycles of the Endicott and Lisburne Groups

    SciTech Connect

    Lepain, D.L.; Crowden, R.K.; Watts, K.F. )

    1990-05-01

    The Ellesmerian sequence in northeastern Alaska consists of a thick succession of Mississippian to Lower Cretaceous platform carbonate and terrigenous clastic rocks. At the base of the Ellesmerian sequence, clastic rocks of the Endicott Group are the lower part of a major transgressive sequence that passes gradationally upward into carbonates of the Lisburne Group. In the Endicott Group, the basal Kekiktuk Conglomerate was deposited in fluvial and marginal marine environments. A broad suite of tidally influenced, shallow-marine environments are recorded in the overlying Kayak Shale. The transition into carbonate platform rocks of the Lisburne Group is recorded in a series of depositional cycles developed within the upper half of the Kayak Shale. In the lower beds of the transition, the depositional cycles are multiple upward-thickening and upward-coarsening successions composed of (1) organic-rich siltstone containing flaser-bedded and lenticular-bedded fine-grained sandstone, (2) fine-grained, ripple-laminated quartzarenite, and (3) an intensely bioturbated horizon of medium- to coarse-grained quartzarenite that contains scattered brachiopods, bryozoa, and crinoids. Each cycle is terminated by a sharp transgressive surface that consists of a thin shale drape. Near the top of the Kayak Shale, the coarse-grained horizons become increasingly replaced by wackestone, grainstone, and coralline boundstone. Despite the lithologic change, the vertical upward-thickening and upward-coarsening cycles continue in the basal limestone of the Lisburne Group. Repeated upward-shallowing episodes, followed by coastal onlap, are likely mechanisms for this cyclicity and suggests a genetic relation between both the clastic and carbonate depositional cycles.

  15. A Reconsideration of Pan African Orogenic Cycle in the Anti-Atlas Mountains, Morocco

    NASA Astrophysics Data System (ADS)

    Hefferan, K. P.; Soulaimani, A.; Samson, S. D.; Admou, H.; Inglis, J.; Saquaque, A.; Heywood, N. C.

    2013-12-01

    The term 'Pan African' orogeny was first proposed in 1964 for a tectonothermal event in Africa ~ 500+/- 50 Ma. Over the past 50 years, the Pan African orogeny has been extended to as much as ~1050-450 Ma and recognized in other Gondwanan continents where regional names such as Brasiliano (South America), Adelaidean (Australian) and Bearmore (Antarctica) have been applied. The Pan African time span of ~500 million years is much longer than any Phanerozoic orogeny. However, it does correlate with time ranges of well defined Phanerozoic orogenic cycles such as the Appalachian cycle, extending from ~1,100 to 250 Ma, and the Cordilleran cycle of ~350 Ma to the present. A significant difference of course is that the Appalachian orogenic cycle has long been recognized as consisting of separate Grenville, Taconic, Acadian and Alleghenian orogenies. Similarly, the Mesozoic-Cenozoic Cordilleran orogenic cycle consists of distinct Antler, Sonoma, Nevadan, Sevier, Laramide and ongoing Cascadian-Andean orogenies. Until recently, the absence of precise geochronology in West Africa has prevented a more refined analysis of individual orogenic events within the Pan-African orogenic cycle. Since 2000, precision geochronologic dating by various researchers in the Anti-Atlas Mountains, Morocco, has provided critical data by which it is now appropriate to designate a Pan African orogenic cycle consisting of three separate orogenic events. We herein propose the following distinct orogenic events in the Anti-Atlas Mountains of Morocco: Iriri-Tichibanine orogeny (750-700 Ma), Bou Azzer orogeny (660-640 Ma) and the WACadomian orogeny (620-580 Ma). Generalized tectonic map of the Anti-Atlas Mountain inliers (Adapted from Ennih and Liégeois, 2008). Geodynamic model of the Pan African orogenic cycle in the Anti-Atlas Mountains. Modified from Walsh et al. (2012) and incorporating ideas from Thomas et al. (2002) and El Hadi et al. (2012).

  16. And the Variscan Orogen Buckled

    NASA Astrophysics Data System (ADS)

    Pastor-Galán, D.; Groenewegen, T.; Gutiérrez-Alonso, G.; Langereis, C. G.

    2013-12-01

    Oroclines are the largest scale folds in nature, and as folds can be produced by bending or by buckling. The most commonly invoked bending mechanisms are indentation (the Himalayan syntaxes) and slab roll-back (The Calabria Arc) whereas buckling usually are commonly related with collision of the apex of ribbon continents along strike (Alaskan oroclines). In Western Europe the tectonostratigraphic zonation of Variscan orogen shows a complex 'S' shape pattern recently interpreted as a double orocline consisting of a northern and southern arc. The northern arc, known as Cantabria-Asturias Arc or Cantabrian Orocline, was developed after closure of the Rheic Ocean and the building and collapse of the Variscan orogenic edifice and, therefore, is considered post-Variscan in age. On the other hand, neither the geometry nor the kinematics of the so-called Central Iberian orocline, situated at the south of the Iberian peninsula are properly known. However, it seems reasonable to think that both oroclines developed at the same time as other coupled oroclines, such as the New England oroclines or the Carpathian oroclines. The particular paleogeography of the Variscan belt in Pangea and the kinematics of the oroclinal formation make impossible the mechanisms of indentation or buckling of a ribbon continent. The occurrence of an intense syn- and slightly post-Cantabrian orocline magmatic event (310-290 Ma) has been linked to the development of the orocline(s) due to the particular spatial-temporal distribution of these post-tectonic granitoids and its isotopic signature which would imply that the oroclines (if synchronous) are thick-skinned. This magmatic pulse has also been interpreted as due to slab roll-back. We present widespread evidences of buckling around the whole orocline at different lithospheric levels and new insights of the particular geometry of the southern orocline which is difficult to reconcile with a roll-back related origin. Therefore, a major change in the

  17. Natural versus anthropogenic dispersion of metals to the environment in the Wulik River area, western Brooks Range, northern Alaska

    USGS Publications Warehouse

    Kelley, K.D.; Hudson, T.

    2007-01-01

    Zinc-lead-silver mineral deposits in the Wulik River region, Alaska, contain an enormous accumulation of Zn. In addition to the giant deposits at Red Dog, at least nine other deposits are known. Natural weathering of these deposits has dispersed metals over a wide region over a long period of time (c. 10 000 years) through transport by stream and groundwater, stream sediments, formation of soils, and perhaps wind-blown atmospheric deposition from weathering of naturally enriched Pb-Zn surface deposits. Anthropogenic input also contributes metals to the environment. Mining of the Red Dog deposit, which began in 1989, produces fine-grained galena and sphalerite concentrates that are transported from the mine site by truck to a storage port facility. Wind-blown dispersion of concentrate dust along the road and around the port facility has been a source of local metal-rich surficial materials. Geochemical and mineralogical characteristics provide a means of distinguishing the natural versus anthropogenic metal sources. Soils over deposits have patterns of increasing metal contents with depth and proximity to the metal-bearing source, whereas ore concentrate dust is localized at the surface. The acidity produced by weathering of the sulphide deposits creates an environment in which elements such as Se and Mo are stable whereas Ca is not. Consequently, high Mo (up to 29 ppm) and Se (up to 17 ppm) and low Ca (<0.4%) concentrations characterize surficial materials near natural deposits. Acidic conditions also yield high Pb-Zn ratios (up to 70) because sphalerite is preferentially dissolved and Zn is mobilized during chemical weathering. In natural materials, secondary jarosite and anglesite are developed, and minor galena is etched and rounded due to a history of chemical and mechanical weathering. In contrast, dust-bearing samples have Pb/Zn ratios that are 0.4 or less, Ca contents are higher (0.2 to 3.6%), and Mo (<10 ppm) and Se (not detected) concentrations are low

  18. Stratigraphic and structural implications of conodont and detrital zircon U-Pb ages from metamorphic rocks of the Coldfoot terrane, Brooks Range, Alaska

    USGS Publications Warehouse

    Moore, T.E.; Aleinikoff, J.N.; Harris, A.G.

    1997-01-01

    New paleontologic and isotopic data from the Emma Creek and Marion Creek schists of the Coldfoot terrane, Arctic Alaska superterrane, central Brooks Range, suggest Devonian and possibly younger ages of deposition for their sedimentary protoliths. Conodonts from marble of the Emma Creek schist, intruded by a roughly 392 Ma orthogneiss, are late Lochkovian (early Early Devonian, between about 408 and 396 Ma) and Silurian to Devonian at two other locations. Spherical to oblong detrital zircons from quartz-mica schist of the overlying Marion Creek schist yield mostly discordant U-Pb data suggestive of provenance ages of 3.0, 2.0-1.8, and 1.5-1.4 Ga; however, several euhedral grains of zircon from Marion Creek quartz-mica schist have concordant U-Pb ages from 370 to 360 Ma. The Marion Creek schist in our study area therefore is at least 26 m.y. younger than the Emma Creek schist. The age data imply that the protolith of the Emma Creek schist is age correlative with Devonian carbonate rocks in the Hammond and North Slope terranes, whereas the Marion Creek schist is age correlative with Upper Devonian and Lower Mississippian clastic sedimentary rocks of the Endicott Group in the Endicott Mountains terrane and shale and carbonate units in the De Long Mountains and Sheenjek River terranes. Consequently, tectonic models restoring the entire Coldfoot terrane beneath partly or wholly coeval rocks of the Hammond, Endicott Mountains, De Long Mountains, and Sheenjek River terranes of the Arctic Alaska superterrane require revision. Alternative reconstructions, including restoration of the Coldfoot terrane inboard of the Endicott Mountains terrane or outboard of the De Long Mountains and Sheenjek River terranes are plausible but require either larger amounts of shortening than previously suggested or indicate problematic facies relations. copyright. Published in 1997 by the American Geophysical Union.

  19. Geochronology of the western and central Brooks Range, Alaska: Implications for the geologic evolution of the Anarraaq and Red Dog Zn-Pb-Ag deposits

    USGS Publications Warehouse

    Rombach, C.S.; Layer, P.W.

    2004-01-01

    A compilation of published geochronology of rocks and minerals from the western and central Brooks Range provides a framework for understanding the complex history of the Brooks Range and northern Alaska. A simplified timeline of events comprises (1) Devonian extension, (2) Mississippian extension and Zn-Pb-Ag mineralization, (3) a passive interval, (4) pre-Brooks Range orogeny rock-formation and thermal event, (5) inception of Brooks Range orogeny, (6) exhumation and the end of main-stage deformation, and (7) subsequent episodic deformation. This compilation is supplemented by new 40Ar/39Ar dates of white mica from the Anarraaq and Red Dog Zn-Pb-Ag (+ barite) deposits from the western Brooks Range. The deposits are hosted in black shale and carbonate rocks of the Late Mississippian-Early Pennsylvanian Kuna Formation. Quartz-pyrite-white mica grains in sedimentary rocks above the Anarraaq deposit yield an age of 195.0 ?? 2.0 Ma, and paragenetically late quartz-pyrite-white mica from the Main orebody at the Red Dog deposit has an age of 126.1 ?? 0.7 Ma. These white micas are much younger than the age of Zn-Pb-Ag mineralization at Red Dog (338 ?? 5.8 Ma Re-Os age of pyrite). The date for white mica from Anarraaq (???195 Ma) appears to be related to a large-scale thermal event in the region immediately before the inception of the Brooks Range orogeny. The white mica from the Red Dog deposit (???126 Ma) correlates with the later stages of the orogeny, a period of blueschist metamorphism, extension, and rapid exhumation, which varied with geographic location. These dates suggest that the Red Dog deposits underwent significant hydrothermal overprinting during multiple episodes of the Brooks Range orogeny. ?? 2004 by Economic Geology.

  20. Late Quaternary glacial relief evolution and fracture-density control on erosion revealed by low-temperature thermochronometry and remote sensing (Granite Range, Alaska)

    NASA Astrophysics Data System (ADS)

    Valla, Pierre; Champagnac, Jean-Daniel; Herman, Frédéric; Lowick, Sally; Guralnik, Benny; Shuster, David; Fellin, Giuditta

    2013-04-01

    Long-term erosion and topographic evolution of mountain belts arise from complex coupling between tectonics, climate and surface processes. The Granite Range (Wrangell-St Elias National Park, Alaska) presents an ideal setting to study such interactions. Its alpine landscape, preserving typical glacial features (U-shaped valleys, cirques), appears highly smoothed in the west, and progressively more rugged towards the east. In the field, this is evidenced by minor and only localized faulting of massive bedrock (granite and paragneiss) in the west, while the eastern part shows highly fractured bedrock (penetrative faults, fault gouges). Remote-sensing analysis confirms that fracture density is much higher towards east, and also reveals high post-glacial incision only in areas associated with high fracture density. To quantify our morphometric observations, we sampled four elevation profiles (~15 samples in total) over an 80-km East-West transect for low-temperature thermochrometry. Apatite (U-Th-Sm)/He dating provides ages between ~10 and 30 Ma, in agreement with published data, and shows apparent low long-term exhumation rates (~0.05-0.1 km/Ma). Preliminary 4He/3He thermochronometry data reveal a more complex exhumation history, with a significant increase since ~6-5 Ma which can be related to either onset of glaciations in Alaska or a major change in tectonic activity occurring at that period. Further data collected within the Granite Range will help to decipher the origin of this late-Miocene acceleration in exhumation. We also performed luminescence thermochronometry measured on feldspar separates from bedrock samples. Our results show a strong East-West gradient in samples saturation ratio. Apparent ages vary from ~250 ka in the western part of the range, towards younger ages of ~30 ka in the east. This pattern reveals spatially variable erosion rates during the late Quaternary associated with a major fracture-density control on erosion, and further supports the

  1. The Border Ranges fault system in Glacier Bay National Park, Alaska: Evidence for major early Cenozoic dextral strike-slip motion

    USGS Publications Warehouse

    Smart, K.J.; Pavlis, T.L.; Sisson, V.B.; Roeske, S.M.; Snee, L.W.

    1996-01-01

    The Border Ranges fault system of southern Alaska, the fundamental break between the arc basement and the forearc accretionary complex, is the boundary between the Peninsular-Alexander-Wrangellia terrane and the Chugach terrane. The fault system separates crystalline rocks of the Alexander terrane from metamorphic rocks of the Chugach terrane in Glacier Bay National Park. Mylonitic rocks in the zone record abundant evidence for dextral strike-slip motion along north-northwest-striking subvertical surfaces. Geochronologic data together with regional correlations of Chugach terrane rocks involved in the deformation constrain this movement between latest Cretaceous and Early Eocene (???50 Ma). These findings are in agreement with studies to the northwest and southeast along the Border Ranges fault system which show dextral strike-slip motion occurring between 58 and 50 Ma. Correlations between Glacier Bay plutons and rocks of similar ages elsewhere along the Border Ranges fault system suggest that as much as 700 km of dextral motion may have been accommodated by this structure. These observations are consistent with oblique convergence of the Kula plate during early Cenozoic and forearc slivering above an ancient subduction zone following late Mesozoic accretion of the Peninsular-Alexander-Wrangellia terrane to North America.

  2. Kinematics of the mosquito terrane, Coldfoot Area, Alaska: Keys to Brooks Range tectonics: Final report, Project No. 2

    SciTech Connect

    Harms, T.A.; Coney, P.J.

    1988-04-01

    Within the large-scale geometry of the Brooks Range, the Angayucham terrane occurs as a vast overthrust sheet. From the north flank of the Ruby terrane it underlies the Koyukuk basin and stretches north as the roof thrust to the various nappe terranes of the Brooks Range. The tectonic relationship of the Ruby terrane to the south flank of the Brooks Range lies largely obscured beneath the Angayucham in the eastern apex of the Koyukuk basin. The Mosquito terrane occurs as a window through the Angayucham at this juncture. The composition and structures of the Mosquito terrane reveal that is the result of shear along a sub-horizontal step or flange within the prominent, through-going dextral strike-slip fault system which cuts across the eastern Koyukuk basin and southeastern Brooks Range. Units of the Mosquito were derived from both the Angayucham and Ruby terranes. A consistent tectonic fabric imposed upon them is kinematically linked to the strike-slip system and indicates a northeasterly direction of transport across the terrane. The presence of Ruby-correlative units within the Mosquito suggests the Ruby underlies the Angayucham and that it is in contact with terrances of the southern Brooks Range at that structural level along high-angle strike-slip faults. These relationships demonstrate that an episode of dextral transpression is the latest in the history of terrane accretion and tectonic evolution of the Brooks Range. 35 refs.

  3. Can nutrient limitations explain low and declining white spruce growth near the Arctic treeline in the eastern Brooks Range, Alaska?

    NASA Astrophysics Data System (ADS)

    Ellison, S.; Sullivan, P. F.

    2014-12-01

    The position of the Arctic treeline is of critical importance for global carbon cycling and surface energy budgets. However, controls on tree growth at treeline remain uncertain. In the Alaskan Brooks Range, 20th century warming has caused varying growth responses among treeline trees, with trees in the west responding positively, while trees in the east have responded negatively. The prevailing explanation of this trend ascribes the negative growth response to warming-induced drought stress in the eastern Brooks Range. However, recent measurements of carbon isotope discrimination in tree rings, xylem sap flow and needle gas exchange suggest that drought stress cannot explain these regional growth declines. Additionally, evidence from the western Brooks Range suggests that nutrient availability, rather than drought stress, may be the proximate control on tree growth. In this study, we investigated the hypothesis that low and declining growth of eastern Brooks Range trees is due to low and declining soil nutrient availability, which may continue to decrease with climate change as soils become drier and microbial activity declines. We compared microclimate, tree performance, and a wide range of proxies for soil nutrient availability in four watersheds along a west-east transect in the Brooks Range during the growing seasons of 2013 and 2014. We hypothesized that soil nutrient availability would track closely with the strong west-east precipitation gradient, with higher rainfall and greater soil nutrient availability in the western Brooks Range. We expected to find that soil water contents in the west are near optimum for nitrogen mineralization, while those in the east are below optimum. Needle nitrogen concentration, net photosynthesis, branch extension growth, and growth in the main stem are expected to decline with the hypothesized decrease in soil nutrient availability. The results of our study will elucidate the current controls on growth of trees near the

  4. Origin of gasoline-range hydrocarbons and their migration by solution in carbon dioxide in Norton basin, Alaska.

    USGS Publications Warehouse

    Kvenvolden, K.A.; Claypool, G.E.

    1980-01-01

    Carbon dioxide from a submarine seep in Norton Sound carries a minor component of gas- and gasoline-range hydrocarbons. The molecular and isotopic compositions of the hydrocarbon gases and the presence of gasoline-range hydrocarbons indicate that these molecules are derived from thermal alteration of marine and/or nonmarine organic matter buried within Norton basin. The gasoline-range hydrocarbon distribution suggests that the hydrocarbon mixture is an immature petroleum-like condensate of lower temperature origin than normal crude oil. The submarine seep provides a natural example in support of a carbon dioxide solution transport mechanism thought to be operative in the migration of hydrocarbons in certain reservoirs.-Authors

  5. Potential tight gas resources in a frontier province - Jurassic through Tertiary strata beneath the Brooks Range foothills, Arctic Alaska

    USGS Publications Warehouse

    Nelson, Philip H.; Bird, Kenneth J.; Houseknecht, David W.; Potter, Christopher J.; Moore, Thomas E.

    2006-01-01

    Beneath the foothills of the Brooks Range, rocks of the Lower Cretaceous-Tertiary Brookian and Jurassic-Lower Cretaceous Beaufortian megasequences have been deeply buried and exhumed, and now exhibit characteristics of 'tight gas sandstones'. The data recovered from drilling, well tests, and cores exhibit the potential for substantial gas reserves over a large area. These data include recovery of gas from drillstem tests, indications of overpressure from well tests and mud weights, low porosity and permeability in sandstones, and vitrinite reflectance values ranging from 1.0 to 2.0 percent throughout substantial depth intervals.

  6. Lithostratigraphy, microlithofacies, and conodont biostratigraphy and biofacies of the Wahoo Limestone (Carboniferous), eastern Sadlerochit Mountains, Northeast Brooks Range, Alaska

    USGS Publications Warehouse

    Krumhardt, A.P.; Harris, A.G.; Watts, K.F.

    1996-01-01

    The lithostratigraphy, microlithofacies, and conodonts are described in a key section of the Wahoo Limestone (Middle Carboniferous); this unit forms a hydrocarbon reservoir at Prudhoe Bay. The Wahoo was deposited in a range of environments on the inner part of a high-energy carbonate ramp. Microfacies and conodont biofacies used together refine paleoenvironmental interpretations. Only 24 conodont species distributed among 14 genera were recognized in a section that spans about 10 million years. Significant conodont collections from the Wahoo across the Northeast Brooks Range are described in an appendix.

  7. Pulmonary Mast Cell Tumor and Possible Paraganglioma in a Free-ranging Pacific Walrus ( Odobenus rosmarus divergens), Barrow, Alaska, USA.

    PubMed

    Seguel, Mauricio; Stimmelmayr, Raphaela; Howerth, Elizabeth; Gottdenker, Nicole

    2016-04-28

    We describe a pulmonary mast cell tumor in a subsistence-harvested free-ranging Pacific walrus (Odobenus rosmarus divergens). Neoplastic cells effacing a focal area of pulmonary parenchyma were characterized by rare metachromatic granules and positive staining for C-kit. We also report co-occurrence of a peribronchial mass with a morphologic and immunohistochemical profile compatible with paraganglioma. PMID:27054472

  8. Pulmonary Mast Cell Tumor and Possible Paraganglioma in a Free-ranging Pacific Walrus ( Odobenus rosmarus divergens), Barrow, Alaska, USA.

    PubMed

    Seguel, Mauricio; Stimmelmayr, Raphaela; Howerth, Elizabeth; Gottdenker, Nicole

    2016-04-28

    We describe a pulmonary mast cell tumor in a subsistence-harvested free-ranging Pacific walrus (Odobenus rosmarus divergens). Neoplastic cells effacing a focal area of pulmonary parenchyma were characterized by rare metachromatic granules and positive staining for C-kit. We also report co-occurrence of a peribronchial mass with a morphologic and immunohistochemical profile compatible with paraganglioma.

  9. Use of LANDSAT imagery for wildlife habitat mapping in northeast and eastcentral Alaska. [winter and summer moose range

    NASA Technical Reports Server (NTRS)

    Lent, P. C. (Principal Investigator)

    1976-01-01

    The author has identified the following significant results. Winter and summer moose range maps of three selected areas were produced (1:63,360 scale). The analytic approach is very similar to modified clustering. Preliminary results indicate that this method is not only more accurate but considerably less expensive than supervised classification techniques.

  10. Mid-Pleistocene climate transition drives net mass loss from rapidly uplifting St. Elias Mountains, Alaska.

    PubMed

    Gulick, Sean P S; Jaeger, John M; Mix, Alan C; Asahi, Hirofumi; Bahlburg, Heinrich; Belanger, Christina L; Berbel, Glaucia B B; Childress, Laurel; Cowan, Ellen; Drab, Laureen; Forwick, Matthias; Fukumura, Akemi; Ge, Shulan; Gupta, Shyam; Kioka, Arata; Konno, Susumu; LeVay, Leah J; März, Christian; Matsuzaki, Kenji M; McClymont, Erin L; Moy, Chris; Müller, Juliane; Nakamura, Atsunori; Ojima, Takanori; Ribeiro, Fabiana R; Ridgway, Kenneth D; Romero, Oscar E; Slagle, Angela L; Stoner, Joseph S; St-Onge, Guillaume; Suto, Itsuki; Walczak, Maureen D; Worthington, Lindsay L; Bailey, Ian; Enkelmann, Eva; Reece, Robert; Swartz, John M

    2015-12-01

    Erosion, sediment production, and routing on a tectonically active continental margin reflect both tectonic and climatic processes; partitioning the relative importance of these processes remains controversial. Gulf of Alaska contains a preserved sedimentary record of the Yakutat Terrane collision with North America. Because tectonic convergence in the coastal St. Elias orogen has been roughly constant for 6 My, variations in its eroded sediments preserved in the offshore Surveyor Fan constrain a budget of tectonic material influx, erosion, and sediment output. Seismically imaged sediment volumes calibrated with chronologies derived from Integrated Ocean Drilling Program boreholes show that erosion accelerated in response to Northern Hemisphere glacial intensification (∼ 2.7 Ma) and that the 900-km-long Surveyor Channel inception appears to correlate with this event. However, tectonic influx exceeded integrated sediment efflux over the interval 2.8-1.2 Ma. Volumetric erosion accelerated following the onset of quasi-periodic (∼ 100-ky) glacial cycles in the mid-Pleistocene climate transition (1.2-0.7 Ma). Since then, erosion and transport of material out of the orogen has outpaced tectonic influx by 50-80%. Such a rapid net mass loss explains apparent increases in exhumation rates inferred onshore from exposure dates and mapped out-of-sequence fault patterns. The 1.2-My mass budget imbalance must relax back toward equilibrium in balance with tectonic influx over the timescale of orogenic wedge response (millions of years). The St. Elias Range provides a key example of how active orogenic systems respond to transient mass fluxes, and of the possible influence of climate-driven erosive processes that diverge from equilibrium on the million-year scale. PMID:26598689

  11. Mid-Pleistocene climate transition drives net mass loss from rapidly uplifting St. Elias Mountains, Alaska

    PubMed Central

    Jaeger, John M.; Mix, Alan C.; Asahi, Hirofumi; Bahlburg, Heinrich; Belanger, Christina L.; Berbel, Glaucia B. B.; Childress, Laurel; Cowan, Ellen; Drab, Laureen; Forwick, Matthias; Fukumura, Akemi; Ge, Shulan; Gupta, Shyam; Konno, Susumu; LeVay, Leah J.; März, Christian; McClymont, Erin L.; Moy, Chris; Müller, Juliane; Nakamura, Atsunori; Ojima, Takanori; Ribeiro, Fabiana R.; Ridgway, Kenneth D.; Romero, Oscar E.; Slagle, Angela L.; Stoner, Joseph S.; St-Onge, Guillaume; Suto, Itsuki; Walczak, Maureen D.; Worthington, Lindsay L.; Bailey, Ian; Enkelmann, Eva; Reece, Robert; Swartz, John M.

    2015-01-01

    Erosion, sediment production, and routing on a tectonically active continental margin reflect both tectonic and climatic processes; partitioning the relative importance of these processes remains controversial. Gulf of Alaska contains a preserved sedimentary record of the Yakutat Terrane collision with North America. Because tectonic convergence in the coastal St. Elias orogen has been roughly constant for 6 My, variations in its eroded sediments preserved in the offshore Surveyor Fan constrain a budget of tectonic material influx, erosion, and sediment output. Seismically imaged sediment volumes calibrated with chronologies derived from Integrated Ocean Drilling Program boreholes show that erosion accelerated in response to Northern Hemisphere glacial intensification (∼2.7 Ma) and that the 900-km-long Surveyor Channel inception appears to correlate with this event. However, tectonic influx exceeded integrated sediment efflux over the interval 2.8–1.2 Ma. Volumetric erosion accelerated following the onset of quasi-periodic (∼100-ky) glacial cycles in the mid-Pleistocene climate transition (1.2–0.7 Ma). Since then, erosion and transport of material out of the orogen has outpaced tectonic influx by 50–80%. Such a rapid net mass loss explains apparent increases in exhumation rates inferred onshore from exposure dates and mapped out-of-sequence fault patterns. The 1.2-My mass budget imbalance must relax back toward equilibrium in balance with tectonic influx over the timescale of orogenic wedge response (millions of years). The St. Elias Range provides a key example of how active orogenic systems respond to transient mass fluxes, and of the possible influence of climate-driven erosive processes that diverge from equilibrium on the million-year scale. PMID:26598689

  12. Mid-Pleistocene climate transition drives net mass loss from rapidly uplifting St. Elias Mountains, Alaska.

    PubMed

    Gulick, Sean P S; Jaeger, John M; Mix, Alan C; Asahi, Hirofumi; Bahlburg, Heinrich; Belanger, Christina L; Berbel, Glaucia B B; Childress, Laurel; Cowan, Ellen; Drab, Laureen; Forwick, Matthias; Fukumura, Akemi; Ge, Shulan; Gupta, Shyam; Kioka, Arata; Konno, Susumu; LeVay, Leah J; März, Christian; Matsuzaki, Kenji M; McClymont, Erin L; Moy, Chris; Müller, Juliane; Nakamura, Atsunori; Ojima, Takanori; Ribeiro, Fabiana R; Ridgway, Kenneth D; Romero, Oscar E; Slagle, Angela L; Stoner, Joseph S; St-Onge, Guillaume; Suto, Itsuki; Walczak, Maureen D; Worthington, Lindsay L; Bailey, Ian; Enkelmann, Eva; Reece, Robert; Swartz, John M

    2015-12-01

    Erosion, sediment production, and routing on a tectonically active continental margin reflect both tectonic and climatic processes; partitioning the relative importance of these processes remains controversial. Gulf of Alaska contains a preserved sedimentary record of the Yakutat Terrane collision with North America. Because tectonic convergence in the coastal St. Elias orogen has been roughly constant for 6 My, variations in its eroded sediments preserved in the offshore Surveyor Fan constrain a budget of tectonic material influx, erosion, and sediment output. Seismically imaged sediment volumes calibrated with chronologies derived from Integrated Ocean Drilling Program boreholes show that erosion accelerated in response to Northern Hemisphere glacial intensification (∼ 2.7 Ma) and that the 900-km-long Surveyor Channel inception appears to correlate with this event. However, tectonic influx exceeded integrated sediment efflux over the interval 2.8-1.2 Ma. Volumetric erosion accelerated following the onset of quasi-periodic (∼ 100-ky) glacial cycles in the mid-Pleistocene climate transition (1.2-0.7 Ma). Since then, erosion and transport of material out of the orogen has outpaced tectonic influx by 50-80%. Such a rapid net mass loss explains apparent increases in exhumation rates inferred onshore from exposure dates and mapped out-of-sequence fault patterns. The 1.2-My mass budget imbalance must relax back toward equilibrium in balance with tectonic influx over the timescale of orogenic wedge response (millions of years). The St. Elias Range provides a key example of how active orogenic systems respond to transient mass fluxes, and of the possible influence of climate-driven erosive processes that diverge from equilibrium on the million-year scale.

  13. Foraminiferal zonation and carbonate facies of Carboniferous (Mississippian and Pennsylvanian) Lisburne group, central and eastern Brooks range, Arctic Alaska

    USGS Publications Warehouse

    Armstrong, Augustus K.; Mamet, Bernard L.; Dutro, J. Thomas

    1970-01-01

    The Lisburne Group carbonate rocks of the central and eastern Brooks Range contain foraminiferal assemblages assigned to zones of late Tournaisian (Osage) to early Moscovian (Atoka) age. Representatives of both Eurasiatic and American cratonic microfaunas permit correlation with the original Carboniferous type sections in western Europe as well as with the standard Mississippian and Pennsylvanian sequences in the Mid-Continent region of North America. Correlation anomalies in the lower part of the sequence are discussed.

  14. Composition and sources of atmospheric dusts in snow at 3200 meters in the St. Elias Range, southeastern Alaska, USA

    USGS Publications Warehouse

    Hinkley, T.K.

    1994-01-01

    Dusts in snow from the accumulation zone in the St. Elias Range appear from their chemical compositions to have come from terranes of rocks of ferromagnesian composition. These dusts, with respect to their composition and to the moderate degree of variation that occurs through a depositional year, are similar those deposited in Greenland. The high portion of the St. Elias Range is isolated from dominance by any local dust source terranes, because of altitude and the extent of the surrounding glacierized and snow-covered region. In Greenland the altitude is typically lower, but local sources are even less likely to dominate the character of the dusts deposited into the ice record there. The similar compositions and moderate compositional variations of dusts from these two places bear on the question of whether the dusts that are transported over long distances by the atmosphere under modern and glacial-period conditions are uniform and representative of a broad regional or even hemispheric background dust. The dusts in the snow were measured by means of a suite of major, minor, and trace rock-forming metals chosen to give information about rock types, their constituent minerals, degree of degradation (weathering), and energies of atmospheric uptake from source. The variations in amounts of rock dust through the year in the St. Elias Range snowpack have no time-stratigraphic correspondence to the also large variations in concentrations of other species that are not constituents of rock-derived dusts, such the anions chloride, sulfate, and nitrate; the highs and lows of the two types of materials are apparently completely independent. The structure revealed by the moderately fine-scale sampling of the present study (??? 10 increments/y) serves as a background for the interpretation of analysis of ice core samples, in which annual layers may be too compressed to permit analysis of sub-annual samples. ?? 1994.

  15. Composition and sources of atmospheric dusts in snow at 3200 meters in the St. Elias Range, southeastern Alaska, USA

    NASA Astrophysics Data System (ADS)

    Hinkley, Todd K.

    1994-08-01

    Dusts in snow from the accumulation zone in the St. Elias Range appear from their chemical compositions to have come from terranes of rocks of ferromagnesian composition. These dusts, with respect to their composition and to the moderate degree of variation that occurs through a depositional year, are similar those deposited in Greenland. The high portion of the St. Elias Range is isolated from dominance by any local dust source terranes, because of altitude and the extent of the surrounding glacierized and snow-covered region. In Greenland the altitude is typically lower, but local sources are even less likely to dominate the character of the dusts deposited into the ice record there. The similar compositions and moderate compositional variations of dusts from these two places bear on the question of whether the dusts that are transported over long distances by the atmosphere under modern and glacial-period conditions are uniform and representative of a broad regional or even hemispheric background dust. The dusts in the snow were measured by means of a suite of major, minor, and trace rock-forming metals chosen to give information about rock types, their constituent minerals, degree of degradation (weathering), and energies of atmospheric uptake from source. The variations in amounts of rock dust through the year in the St. Elias Range snowpack have no time-stratigraphic correspondence to the also large variations in concentrations of other species that are not constituents of rock-derived dusts, such the anions chloride, sulfate, and nitrate; the highs and lows of the two types of materials are apparently completely independent. The structure revealed by the moderately fine-scale sampling of the present study (≈ 10 increments/y) serves as a background for the interpretation of analysis of ice core samples, in which annual layers may be too compressed to permit analysis of sub-annual samples.

  16. Mechanisms of doubly-vergent vs. single-sided orogens: insights from numerical modelling

    NASA Astrophysics Data System (ADS)

    Vogt, K.; Matenco, L. C.; Gerya, T.; Cloetingh, S.

    2014-12-01

    Zones of continent collision form mountain ranges with high topographies and complex geometries. Compressional stresses during ongoing convergence result in crustal thickening and localized deformation, where crustal material is transported and redistributed within the orogen. We use numerical high-resolution thermo-mechanical models to investigate the physical processes of continent collision zones and its implications on rock exhumation. We demonstrate that compression of two continental blocks, separated by a rheologically weak suture zone can result in (i) doubly-vergent (Fig. A) or (ii) single-sided orogens (Fig. B), with distinct geometries, deformation and exhumation patterns. The transition between these different modes of collision is strongly controlled by the rheology of the continental lithosphere and therefore its temperature distribution. Doubly-vergent orogens form at relatively high thermal gradients, while single-sided orogens are typical for lower ones. Doubly-vergent orogens (Fig. A) are formed in response to the gradual accretion of crustal material to the upper plate along retro-shears. In these models continental subduction results in upper plate deformation and nested exhumation against retro-shears. Typical examples include the collision recorded by the Swiss Alps and the Pyrenees. In contrast, single-sided orogens are characterized by large-scale lower plate deformation and are accompanied by the subduction of lower crustal material (Fig. B). Modeling infers that shortening and associated exhumation will gradually propagate towards the foreland. In this situation, no significant retro-shear formation is observed, which is in agreement with recent physical modelling studies on deformation of the continental lithosphere [Willingshofer et al., 2013]. Natural examples of such single sided orogens are common in the Mediterranean (Carpathians, Dinarides, Apennines, Betics) or the SE Asia subduction zones. We conclude that deformation and

  17. K-Ar geochronology of the Survey Pass, Ambler River and Eastern Baird Mountains quadrangles, southwestern Brooks Range, Alaska

    USGS Publications Warehouse

    Turner, Donald L.; Forbes, R.B.; Mayfield, C.F.

    1978-01-01

    We report 76 previously unpublished K-Ar mineral ages from 47 metamorphic and igneous rocks in the southwestern Brooks Range. The pattern of radiometric ages is complex, reflecting the complex geologic history of this area. Local and regional radiometric evidence suggests that the southern Brooks Range schist belt has, at least in part, undergone a late Precambrian metamorphism and that the parent sedimentary and igneous rocks for the metamorphic rocks dated as late Precambrian are at least this old (Precambrian Z). This schist terrane experienced a major thermal event in mid-Cretaceous time, causing widespread resetting of nearly all K-Ar mica ages. A series of apparent ages intermediate between late Precambrian and mid-Cretaceous are interpreted as indicating varying amounts of partial argon loss from older rocks during the Cretaceous event. The schist belt is characterized by dominant metasediments and subordinate metabasites and metafelsites. Blueschists occur within the schist belt from the Chandalar quadrangle westward to the Baird Mountains quadrangle, but geologic evidence does not support the existence of a fossil subduction zone.

  18. K-Ar ages of allochthonous mafic and ultramafic complexes and their metamorphic aureoles, Western Brooks Range, Alaska

    SciTech Connect

    Boak, J.L.; Turner, D.L.; Wallace, W.K.; Moore, T.E.

    1985-04-01

    New K-Ar ages from allochthonous mafic and ultramafic complexes of the western Brooks Range (Brooks Range ophiolite) show that igneous rocks yielded ages nearly identical to those of underlying metamorphic aureole rocks. Dated rocks of the Misheguk igneous sequence from Tumit Creek consist of (1) hornblende gabbro with minor greenschist and lower grade alteration, hornblende age 147.2 +/- 4.4 Ma; and (2) hornblende-bearing diorite, also slightly altered, age 155.8 +/- 4.7 Ma. Both samples come from presumed higher levels of the Misheguk sequence. Dated samples of metamorphic aureole rocks come from outcrops near Kismilot Creek and lie structurally beneath the Iyikrok Mountain peridotite body. The rocks consist of amphibolite and garnet-bearing biotite-hornblende gneiss considered to be metamorphosed Copter igneous sequence and related sedimentary rocks. Hornblende ages are 154.2 +/- 4.6 Ma and 153.2 +/- 4.6 Ma. metamorphism is clearly related to the structurally overlying perioditite, as the degree of alteration decreases downward. The authors suggest that the K-Ar ages of these rocks represent the effects of thermal metamorphism post-dating igneous crystallization, and are related to tectonic emplacement of the complex. Earlier K-Ar data on igneous rocks give similar ages and have been interpreted as reflecting tectonothermal events. The age of igneous crystallization of the mafic and ultramafic rocks of the Misheguk igneous sequence remains uncertain.

  19. Northern Alaska

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Seasonal ice in the Beaufort Sea off Alaska's North Slope has begun its spring retreat. This true color MODIS image from March 18, 2002, shows the pack ice in the Chuckchi Sea (left) and Beaufort Sea (top) backing away from its winter position snug up against Alaska's coasts, beginning its retreat into the Arctic Ocean. While not as pronounced in the Beaufort and Chukchi Seas as other part of the Arctic, scientists studying Arctic sea ice over the course of the century have documented dramatic changes in the extent of Arctic sea ice. It retreats farther in the summer and does not advance as far in the winter than it did a half-century ago. Both global warming and natural variation in regional weather systems have been proposed as causes. Along the coastal plain of the North Slope, gray-brown tracks (see high-resolution image) hint at melting rivers. South of the North Slope, the rugged mountains of the Brooks Range make a coast-to-coast arc across the state. Coming in at the lower right of the image, the Yukon River traces a frozen white path westward across half the image before veering south and out of view. Credit: Jacques Descloitres, MODIS Land Rapid Response Team, NASA/GSFC

  20. Investigation of a slowly deforming, glacially debuttressed rock slope in the Alaska Range using InSAR, LiDAR and two-dimensional numerical modeling

    NASA Astrophysics Data System (ADS)

    Newman, S. D.; Clague, J. J.; Rabus, B.; Shugar, D. H.

    2010-12-01

    Field investigation of a large, actively deforming rock slope at Fels Glacier in the east-central Alaska Range during summer 2010 confirmed the presence of more than 100 normal and antislope scarps and numerous other deformation features indicative of deep-seated gravitational slope deformation. Movement is occurring on foliation planes in micaceous schist in response to debuttressing of the slope by rapid downwasting and retreat of Fels Glacier during the twentieth and early twenty-first centuries. Deformation at this slope poses a hazard to strategic infrastructure, including the Alyeska Pipeline and Richardson Highway, both of which are less than 4 km away. We have analyzed RADARSAT-1 (RSAT-1) datasets from the summers of 2003-2008 and confirmed average line-of-sight displacement rates as large as 1 cm/month using the D-InSAR technique. Additionally, speckle-tracking analysis of 2002 RSAT-1 data confirms significant deformation of the slope in response to the 2002 Denali Earthquake (M 7.9), which ruptured the Denali fault less than 4 km from the site. We have recently acquired 45 single-look-complex and spotlight RADARSAT-2 (RSAT-2) scenes spanning the period from January to December 2010 to further characterize recent slope deformation using D-InSAR. We have also constructed preliminary 2-D numerical models of the deforming slope, constrained by field, LiDAR and InSAR datasets, to better characterize the nature of past, present and future deformation at the site.

  1. Cumberland batholith, Trans-Hudson Orogen, Canada: Petrogenesis and implications for Paleoproterozoic crustal and orogenic processes

    NASA Astrophysics Data System (ADS)

    Whalen, Joseph B.; Wodicka, Natasha; Taylor, Bruce E.; Jackson, Garth D.

    2010-06-01

    Large volume, plutonic belts, such as the ˜ 221,000 km 2, ca. 1.865-1.845 Ga Cumberland batholith (CB) of the Trans-Hudson Orogen in Canada, are major components of Paleoproterozoic orogenic belts. In many cases, they have been interpreted as continental arc batholiths. The petrogenesis and tectonic context of the CB and implications for crustal growth and recycling are interpreted herein based on a 900 km geochemical-isotopic (Nd-O) transect across it and into granitoid plutons within bounding Archean cratons in central and southern Baffin Island. The mainly granulite grade CB, emplaced over an age span of between 14 and 24 Ma, consists mainly of high-K to shoshonitic monzogranite and granodiorite, but also includes low- and medium-K granitoid rocks. Metaluminous to slightly peraluminous compositions and δ 18O (VSMOW) values (+ 6 to + 10‰) indicate derivation from infracrustal (I-type) sources. ɛ Nd 1.85 Ga signatures (- 12 to - 2) of both mafic and felsic units suggest a dominance of evolved sources. Isotopic signatures in the interior of the CB (- 2 to - 7) are more radiogenic than those within Archean domains in central (- 8 to - 15) and southern (- 5 to - 19) Baffin Island. The isotopic transect is interpreted as 'imaging' an accreted microcontinental block (Meta Incognita) and bounding Archean cratons. The CB includes granites of arc, within-plate (A-type) and post-collisional affinity and volumetrically minor mafic rocks with both arc and non-arc features. (La/Yb) CN and Sr/Y values range from < 1 to 225 and < 1 to 611, respectively. In these respects, some CB granitoid rocks resemble Paleozoic adakitic granites, interpreted as partial melts of greatly thickened crust within post-collisional settings, such as Tibet. Thus, the CB likely encompasses various non-consanguineous magmatic suites generated at deep- to mid-crustal depths. Although CB granitoid rocks undoubtedly had important crustal sources, it is hard to assess the relative contribution of

  2. Organochlorine contaminant concentrations in multiple tissues of free-ranging Steller sea lions (Eumetopias jubatus) in Alaska.

    PubMed

    Beckmen, Kimberlee B; Keogh, Mandy J; Burek-Huntington, Kathleen A; Ylitalo, Gina M; Fadely, Brian S; Pitcher, Kenneth W

    2016-01-15

    The relationships of selected organochlorine (OC) contaminants between blubber, blood, feces, and milk of young, free-ranging Steller sea lions (Eumetopias jubatus) were examined. Both between and within each tissue there was considerable individual variation. In spite of the variation, similar patterns were observed across the tissues for most of the selected PCB congeners. In all four tissues, the major PCB congeners were PCB101, PCB118, PCB138, and PCB153. The most prominent congener, both as a weight (ng/g lipid) and as a percentage of summed PCBs (∑PCBs), was PCB 153. Comparisons between paired tissues showed that ∑DDTs in blubber samples were related to concentrations in blood, feces, and milk. The ∑PCBs in blubber were related to concentrations in milk and fecal samples, though the relationship with feces was weak. Our findings show milk samples, in particular, are useful for assessing OCs in young sea lions. Blubber concentrations of PCB101, PCB118, and PCB138 were an order of magnitude higher than those in milk, supporting the biomagnification of these PCB congeners in SSL tissues. The findings indicate alternative tissues may be used as indicators of relative contaminant exposure in lieu of surgical blubber biopsy. PMID:26524270

  3. Micromorphologic evidence for paleosol development in the Endicott group, Siksikpuk formation, Kingak(?) shale, and Ipewik formation, western Brooks range, Alaska

    USGS Publications Warehouse

    Dumoulin, Julie A.; White, Tim

    2005-01-01

    Micromorphologic evidence indicates the presence of paleosols in drill-core samples from four sedimentary units in the Red Dog area, western Brooks Range. Well-developed sepic-plasmic fabrics and siderite spherules occur in claystones of the Upper Devonian through Lower Mississippian(?) Kanayut Conglomerate (Endicott Group), the Pennsylvanian through Permian Siksikpuk Formation (Etivluk Group), the Jurassic through Lower Cretaceous Kingak(?) Shale, and the Lower Cretaceous Ipewik Formation. Although exposure surfaces have been previously recognized in the Endicott Group and Kingak Shale on the basis of outcrop features, our study is the first microscopic analysis of paleosols from these units, and it provides the first evidence of subaerial exposure in the Siksikpuk and Ipewik Formations. Regional stratigraphic relations and geochemical data support our interpretations. Paleosols in the Siksikpuk, Kingak, and Ipewik Formations likely formed in nearshore coastal-plain environments, with pore waters subjected to inundation by the updip migration of slightly brackish ground water, whereas paleosols in the Kanayut Conglomerate probably formed in a more distal setting relative to a marine basin.

  4. Organochlorine contaminant concentrations in multiple tissues of free-ranging Steller sea lions (Eumetopias jubatus) in Alaska.

    PubMed

    Beckmen, Kimberlee B; Keogh, Mandy J; Burek-Huntington, Kathleen A; Ylitalo, Gina M; Fadely, Brian S; Pitcher, Kenneth W

    2016-01-15

    The relationships of selected organochlorine (OC) contaminants between blubber, blood, feces, and milk of young, free-ranging Steller sea lions (Eumetopias jubatus) were examined. Both between and within each tissue there was considerable individual variation. In spite of the variation, similar patterns were observed across the tissues for most of the selected PCB congeners. In all four tissues, the major PCB congeners were PCB101, PCB118, PCB138, and PCB153. The most prominent congener, both as a weight (ng/g lipid) and as a percentage of summed PCBs (∑PCBs), was PCB 153. Comparisons between paired tissues showed that ∑DDTs in blubber samples were related to concentrations in blood, feces, and milk. The ∑PCBs in blubber were related to concentrations in milk and fecal samples, though the relationship with feces was weak. Our findings show milk samples, in particular, are useful for assessing OCs in young sea lions. Blubber concentrations of PCB101, PCB118, and PCB138 were an order of magnitude higher than those in milk, supporting the biomagnification of these PCB congeners in SSL tissues. The findings indicate alternative tissues may be used as indicators of relative contaminant exposure in lieu of surgical blubber biopsy.

  5. Orogenic gold deposits: a proposed classification in the context of their crustal distribution and relationship to other gold deposit types

    USGS Publications Warehouse

    Groves, D.I.; Goldfarb, R.J.; Gebre-Mariam, M.; Hagemann, S.G.; Robert, F.

    1998-01-01

    The so-called 'mesothermal' gold deposits are associated with reginally metamorphosed terranes of all ages. Ores were formed during compressional to transpressional deformation processes at convergent plate margins in accretionary and collisional orogens. In both types of orogen, hydrated marine sedimentary and volcanic rocks have been added to continental margins during tens to some 100 million years of collision. Subduction-related thermal events, episodically raising geothermal gradients within the hydrated accretionary sequences, initiate and drive long-distance hydrothermal fluid migration. The resulting gold-bearing quartz veins are emplaced over a unique depth range for hydrothermal ore deposits, with gold deposition from 15-20 km to the near surface environment. On the basis of this broad depth range of formation, the term 'mesothermal' is not applicable to this deposit types as a whole. Instead, the unique temporal and spatial association of this deposit type with orogeny means that the vein systems are best termed orogenic gold deposits. Most ores are post-orogenic with respect to to tectonism of their immediate host rocks, but are simultaneously syn-orogenic with respect to ongoing deep-crustal, subduction-related thermal processes and the prefix orogenic satisfies both these conditions. On the basis of their depth of formation, the orogenic deposits are best subdivided into epizonal (12 km) classes.

  6. Reconnaissance exploration geochemistry in the central Brooks Range, northern Alaska: Implications for exploration of sediment-hosted zinc-lead-silver deposits

    USGS Publications Warehouse

    Kelley, K.D.; Kelley, D.L.

    1992-01-01

    A reconnaissance geochemical survey was conducted in the southern Killik River quadrangle, central Brooks Range, northern Alaska. The Brooks Range lies within the zone of continuous permafrost which may partially inhibit chemical weathering and oxidation. The minus 30-mesh and nonmagnetic heavy-mineral concentrate fractions of sediment samples were chosen as the sample media for the survey so that mechanical rather than chemical dispersion patterns would be enhanced. A total of 263 sites were sampled within the southern half of the Killik River quadrangle at an average sample density of approximately one sample per 12 km2. All samples were submitted for multi-element analyses. In the western and central Brooks Range, several known sediment-hosted Zn-Pb-Ag(-Ba) deposits occur within a belt of Paleozoic rocks of the Endicott Mountains allochthon. Exploration for this type of deposit in the Brook Range is difficult, due to the inherently high background values for Ba, Zn and Pb in shale and the common occurrence of metamorphic quartz-calcite veins, many of which contain traces of sulfide minerals. Stream sediments derived from these sources produce numerous geochemical anomalies which are not necessarily associated with significant mineralization. R-mode factor analysis provides a means of distinguishing between element associations related to lithology and those related to possible mineralization. Factor analysis applied to the multi-element data from the southern Killik River quadrangle resulted in the discovery of two additional Zn-Pb-Ag mineral occurrences of considerable areal extent which are 80-100 km east of any previously known deposit. These have been informally named the Kady and Vidlee. Several lithogeochemical element associations, or factors, and three factors which represent sulfide mineralization were identified: Ag-Pb-Zn (galena and sphalerite) and Fe-Ni-Co-Cu (pyrite ?? chalcopyrite) in the concentrate samples and Cd-Zn-Pb-As-Mn in the sediment

  7. Diurnal and seasonal patterns of ecosystem CO{sub 2} efflux from upland tundra in the foothills of the Brooks Range, Alaska, U.S.A.

    SciTech Connect

    Oberbauer, S.F.; Gillespie, C.T.; Cheng, Weixin

    1996-08-01

    Carbon dioxide efflux and soil microenvironment were measured in three upland tundra communities in the foothills of the Brooks Range in arctic Alaska to determine the magnitude of CO{sub 2} efflux rates and the relative importance of the belowground factors that influence them. Gas exchange and soil microenvironment measurements were made weekly between 14 June and 31 July 1990. The study communities included lichen-heath, a sparse community vegetated by lichens and dwarf ericaceous shrubs on rocky soils, moist Cassiope dwarf-shrub heath tundra, dominated by Carex and evergreen and deciduous shrubs on relatively deep organic soils, and dry Cassiope dwarf-shrub heath of stone-stripe areas, which was of intermediate character. Rates of CO{sub 2} efflux were similar for the three communities until mid-season when they peaked at rates between 4.9 and 5.9 g m{sup {minus}2} d{sup {minus}1}. Following the mid-season peak, the rates in all three communities declined, particularly in the lichen-heath. Seasonal patterns of CO{sub 2} efflux, soil temperature, and soil moisture suggest changing limitations to CO{sub 2} efflux, soil temperature, and soil moisture suggest changing limitations to CO{sub 2} efflux over the course of the season. Rates of carbon dioxide efflux followed changes in soil temperature early in the season when soil moisture was highest. Mid-season efflux appeared to be limited by soil, moss, and lichen hydration until the end of July, when temperature again limited efflux. Differences between the communities were related to microenvironmental differences and probable differences in carbon quality. The presence of peat-forming mosses is suggested to play an important role in differences in efflux and micro-environment among the communities. 32 refs., 3 figs., 4 tab.

  8. Drivers and Estimates of Terrain Suitability for Active Layer Detachment Slides and Retrogressive Thaw Slumps in the Brooks Range and Foothills of Northwest Alaska, USA

    NASA Astrophysics Data System (ADS)

    Balser, A.; Jones, J.

    2015-12-01

    Active layer detachment sliding and retrogressive thaw slumping are important modes of upland permafrost degradation and disturbance in permafrost regions, and have been linked with climate warming trends, ecosystem impacts, and permafrost carbon release. In the Brooks Range and foothills of northwest Alaska, these features are widespread, with distribution linked to multiple landscape properties. Inter-related and co-varying terrain properties, including surficial geology, topography, geomorphology, vegetation and hydrology, are generally considered key drivers of permafrost landscape characteristics and responses to climate perturbation. However, these inter-relationships as collective drivers of terrain suitability for active layer detachment and retrogressive thaw slump processes are poorly understood in this region. We empirically tested and refined a hypothetical model of terrain factors driving active layer detachment and retrogressive thaw slump terrain suitability, and used final model results to generate synoptic terrain suitability estimates across the study region. Spatial data for terrain properties were examined against locations of 2,492 observed active layer detachments and 805 observed retrogressive thaw slumps using structural equation modelling and integrated terrain unit analysis. Factors significant to achieving model fit were found to substantially hone and constrain region-wide terrain suitability estimates, suggesting that omission of relevant factors leads to broad overestimation of terrain suitability. Resulting probabilistic maps of terrain suitability, and a threshold-delineated mask of suitable terrain, were used to quantify and describe landscape settings typical of these features. 51% of the study region is estimated suitable terrain for retrogressive thaw slumps, compared with 35% for active layer detachment slides, while 29% of the study region is estimated suitable for both. Results improve current understanding of arctic landscape

  9. Trace elements in Zn Pb Ag deposits and related stream sediments, Brooks Range Alaska, with implications for Tl as a pathfinder element

    USGS Publications Warehouse

    Graham, G.E.; Kelley, K.D.; Slack, J.F.; Koenig, A.E.

    2009-01-01

    The Zn-Pb-Ag metallogenic province of the western and central Brooks Range, Alaska, contains two distinct but mineralogically similar deposit types: shale-hosted massive sulphide (SHMS) and smaller vein-breccia occurrences. Recent investigations of the Red Dog and Anarraaq SHMS deposits demonstrated that these deposits are characterized by high trace-element concentrations of As, Ge, Sb and Tl. This paper examines geochemistry of additional SHMS deposits (Drenchwater and Su-Lik) to determine which trace elements are ubiquitously elevated in all SHMS deposits. Data from several vein-breccia occurrences are also presented to see if trace-element concentrations can distinguish SHMS deposits from vein-breccia occurrences. Whole-rock geochemical data indicate that Tl is the most consistently and highly concentrated characteristic trace element in SHMS deposits relative to regional unmineralized rock samples. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses of pyrite and sphalerite indicate that Tl is concentrated in pyrite in SHMS. Stream sediment data from the Drenchwater and Su-Lik SHMS show that high Tl concentrations are more broadly distributed proximal to known or suspected mineralization than As, Sb, Zn and Pb anomalies. This broader distribution of Tl in whole-rock and particularly stream sediment samples increases the footprint of exposed and shallowly buried SHMS mineralization. High Tl concentrations also distinguish SHMS mineralization from the vein-breccia deposits, as the latter lack high concentrations of Tl but can otherwise have similar trace-element signatures to SHMS deposits. ?? 2009 AAG/Geological Society of London.

  10. Influence of the Kingak Shale ultimate shelf margin on frontal structures of the Brooks Range in the National Petroleum Reserve in Alaska

    USGS Publications Warehouse

    Stier, Natalie E.; Connors, Christopher D.; Houseknecht, David W.

    2014-01-01

    The Jurassic–Lower Cretaceous Kingak Shale in the National Petroleum Reserve in Alaska (NPRA) includes several southward-offlapping depositional sequences that culminate in an ultimate shelf margin, which preserves the depositional profile in southern NPRA. The Kingak Shale thins abruptly southward across the ultimate shelf margin and grades into condensed shale, which is intercalated with underlying condensed shale and chert of the Upper Triassic Shublik Formation and overlying condensed shale of the Lower Cretaceous pebble shale unit and the gamma-ray zone (GRZ) of the Hue Shale. This composite of condensed shale forms a thin (≈300-meter) and mechanically weak section between much thicker and mechanically stronger units, including the Sadlerochit and Lisburne Groups below and the sandstone-prone foredeep wedge of the Torok Formation above. Seismic interpretation indicates that the composite condensed section acted as the major detachment during an Early Tertiary phase of deformation in the northern foothills of the Brooks Range and that thrust faults step up northward to the top of the Kingak, or to other surfaces within the Kingak or the overlying Torok. The main structural style is imbricate fault-bend folding, although fault-propagation folding is evident locally, and large-displacement thrust faults incorporate backthrusting to form structural wedges. The Kingak ultimate shelf margin served as a ramp to localize several thrust faults, and the spatial relationship between the ultimate shelf margin and thrust vergence is inferred to have controlled many structures in southern NPRA. For example, the obliqueness of the Carbon Creek anticline relative to other structures in the foothills is the result of northward-verging thrust faults impinging obliquely on the Kingak ultimate shelf margin in southwestern NPRA.

  11. On the link between orogenic shortening and back-arc extensional collapse in low topography orogens

    NASA Astrophysics Data System (ADS)

    Matenco, L. C.

    2012-04-01

    Classical models of orogenic evolution assume that back arc basins form in the hinterland of orogens, collapsing the upper plate above oceanic subduction zones. This is a common characteristic commonly thought to apply to all low-topography orogens of Mediterranean type driven by the fast roll-back of subducted slabs, or other analogues such as the Miocene to recent evolution of the SE Asia subduction zones. This extension may take place far at the interior of the upper plate, as is the case in various segments of the Carpathians or in the core of the SE Asian domain, but in most cases of the Dinarides, Apennines or Hellenides it take place superposed or far into the foreland of oceanic suture zones. Therefore, the term back-arc extension in many cases is misleading, as exhumation along major detachment zones takes place in the core of the orogen (Rif, Betics), in the accreted crustal material of the lower plate (Apennines, Dinarides) or even in a presumed former fore-arc (Aegean, Sunda-Banda arc). In all these subduction zones, collision has largely duplicated crustal blocks from the lower plate and has gradually shifted subduction zone far towards the lower plate. As a result, crustal thickening takes place in the foreland of the orogen, in contrast with the typical crustal roots of the high convergence orogens, such as the Alps or Himalaya. This demonstrate an active shift of the main subduction zone, the position of slabs detected by teleseismic mantle tomography is displaced to the foreland and cannot be connected with the position of the lower plate crust beneath the orogen. This shift is associated with large scale magmatism with unusual large crustal signatures, atypical for subduction related magmas. These observations demonstrate the need for an active reconsideration of existing orogenic models which should include displacements of subduction zones during orogenic shortening and an active investigation of the role of continental subduction and associated

  12. UNIT, ALASKA.

    ERIC Educational Resources Information Center

    Louisiana Arts and Science Center, Baton Rouge.

    THE UNIT DESCRIBED IN THIS BOOKLET DEALS WITH THE GEOGRAPHY OF ALASKA. THE UNIT IS PRESENTED IN OUTLINE FORM. THE FIRST SECTION DEALS PRINCIPALLY WITH THE PHYSICAL GEOGRAPHY OF ALASKA. DISCUSSED ARE (1) THE SIZE, (2) THE MAJOR LAND REGIONS, (3) THE MOUNTAINS, VOLCANOES, GLACIERS, AND RIVERS, (4) THE NATURAL RESOURCES, AND (5) THE CLIMATE. THE…

  13. Radiolarian biostratigraphy of the Otuk Formation in and near the National Petroleum Reserve in Alaska

    SciTech Connect

    Blome, C.D.; Reed, K.M.; Tailleur, I.L.

    1989-01-01

    Bedded chert is a common rock type in the Brooks Range orogen of northern Alaska and is locally abundant in all parts of the orogen except the northeast Brooks Range. Pennsylvanian to Jurassic radiolarian chert is especially widespread in the west, in and adjacent to the De Long Mountains. The Cretaceous Brookian orogeny superposed and disordered the bedded chert sequences. Initial foreshortening and subsequent Laramide-style deformation created a complex of Carboniferous to Jurassic sedimentary deposits that has been rearranged into a stack of thrust sheets, each distinguished by its own physical, paleontologic, and tectonic characteristics. Biostratigraphic control in this study was inadequate to refine many of the earlier paleontologic syntheses. Verification of the ages for radiolarian cherts was particularly difficult because the only age-diagnostic megafossils were found in the younger horizons. The older parts of the Otuk Formation have yielded few useful megafossils. This study includes radiolarian faunas from lithostratigraphic sections through the Otuk Formation that include shale, chert, and limestone of Triassic through Early Jurassic age. This biostratigraphic scheme for the Otuk Formation is based on radiolarian and molluscan faunal assemblages from measured sections, as well as correlation with radiolarian faunas described in recent reports (through 1987) concerning Triassic faunas from Baja California, Oregon, British Columbia, and Japan.

  14. Orogen styles in the East African Orogen: A review of the Neoproterozoic to Cambrian tectonic evolution

    NASA Astrophysics Data System (ADS)

    Fritz, H.; Abdelsalam, M.; Ali, K. A.; Bingen, B.; Collins, A. S.; Fowler, A. R.; Ghebreab, W.; Hauzenberger, C. A.; Johnson, P. R.; Kusky, T. M.; Macey, P.; Muhongo, S.; Stern, R. J.; Viola, G.

    2013-10-01

    The East African Orogen, extending from southern Israel, Sinai and Jordan in the north to Mozambique and Madagascar in the south, is the world´s largest Neoproterozoic to Cambrian orogenic complex. It comprises a collage of individual oceanic domains and continental fragments between the Archean Sahara-Congo-Kalahari Cratons in the west and Neoproterozoic India in the east. Orogen consolidation was achieved during distinct phases of orogeny between ∼850 and 550 Ma. The northern part of the orogen, the Arabian-Nubian Shield, is predominantly juvenile Neoproterozoic crust that formed in and adjacent to the Mozambique Ocean. The ocean closed during a protracted period of island-arc and microcontinent accretion between ∼850 and 620 Ma. To the south of the Arabian Nubian Shield, the Eastern Granulite-Cabo Delgado Nappe Complex of southern Kenya, Tanzania and Mozambique was an extended crust that formed adjacent to theMozambique Ocean and experienced a ∼650-620 Ma granulite-facies metamorphism. Completion of the nappe assembly around 620 Ma is defined as the East African Orogeny and was related to closure of the Mozambique Ocean. Oceans persisted after 620 Ma between East Antarctica, India, southern parts of the Congo-Tanzania-Bangweulu Cratons and the Zimbabwe-Kalahari Craton. They closed during the ∼600-500 Ma Kuungan or Malagasy Orogeny, a tectonothermal event that affected large portions of southern Tanzania, Zambia, Malawi, Mozambique, Madagascar and Antarctica. The East African and Kuungan Orogenies were followed by phases of post-orogenic extension. Early ∼600-550 Ma extension is recorded in the Arabian-Nubian Shield and the Eastern Granulite-Cabo Delgado Nappe Complex. Later ∼550-480 Ma extension affected Mozambique and southern Madagascar. Both extension phases, although diachronous,are interpreted as the result of lithospheric delamination. Along the strike of the East African Orogen, different geodynamic settings resulted in the evolution of

  15. Orogen styles in the East African Orogen: A review of the Neoproterozoic to Cambrian tectonic evolution☆

    PubMed Central

    Fritz, H.; Abdelsalam, M.; Ali, K.A.; Bingen, B.; Collins, A.S.; Fowler, A.R.; Ghebreab, W.; Hauzenberger, C.A.; Johnson, P.R.; Kusky, T.M.; Macey, P.; Muhongo, S.; Stern, R.J.; Viola, G.

    2013-01-01

    The East African Orogen, extending from southern Israel, Sinai and Jordan in the north to Mozambique and Madagascar in the south, is the world́s largest Neoproterozoic to Cambrian orogenic complex. It comprises a collage of individual oceanic domains and continental fragments between the Archean Sahara–Congo–Kalahari Cratons in the west and Neoproterozoic India in the east. Orogen consolidation was achieved during distinct phases of orogeny between ∼850 and 550 Ma. The northern part of the orogen, the Arabian–Nubian Shield, is predominantly juvenile Neoproterozoic crust that formed in and adjacent to the Mozambique Ocean. The ocean closed during a protracted period of island-arc and microcontinent accretion between ∼850 and 620 Ma. To the south of the Arabian Nubian Shield, the Eastern Granulite–Cabo Delgado Nappe Complex of southern Kenya, Tanzania and Mozambique was an extended crust that formed adjacent to theMozambique Ocean and experienced a ∼650–620 Ma granulite-facies metamorphism. Completion of the nappe assembly around 620 Ma is defined as the East African Orogeny and was related to closure of the Mozambique Ocean. Oceans persisted after 620 Ma between East Antarctica, India, southern parts of the Congo–Tanzania–Bangweulu Cratons and the Zimbabwe–Kalahari Craton. They closed during the ∼600–500 Ma Kuungan or Malagasy Orogeny, a tectonothermal event that affected large portions of southern Tanzania, Zambia, Malawi, Mozambique, Madagascar and Antarctica. The East African and Kuungan Orogenies were followed by phases of post-orogenic extension. Early ∼600–550 Ma extension is recorded in the Arabian–Nubian Shield and the Eastern Granulite–Cabo Delgado Nappe Complex. Later ∼550–480 Ma extension affected Mozambique and southern Madagascar. Both extension phases, although diachronous,are interpreted as the result of lithospheric delamination. Along the strike of the East African Orogen, different geodynamic settings

  16. Evidence for multiple mechanisms of crustal contamination of magma from compositionally zoned plutons and associated ultramafic intrusions of the Alaska Range

    USGS Publications Warehouse

    Reiners, P.W.; Nelson, B.K.; Nelson, S.W.

    1996-01-01

    Models of continental crustal magmagenesis commonly invoke the interaction of mafic mantle-derived magma and continental crust to explain geochemical and petrologic characteristics of crustal volcanic and plutonic rocks. This interaction and the specific mechanisms of crustal contamination associated with it are poorly understood. An excellent opportunity to study the progressive effects of crustal contamination is offered by the composite plutons of the Alaska Range, a series of nine early Tertiary, multiply intruded, compositionally zoned (peridotite to granite) plutons. Large initial Sr and Nd isotopic contrasts between the crustal country rock and likely parental magmas allow evaluation of the mechanisms and extents of crustal contamination that accompanied the crystallization of these ultramafic through granitic rocks. Three contamination processes are distinguished in these plutons. The most obvious of these is assimilation of crustal country rock concurrent with magmatic fractional crystallization (AFC), as indicated by a general trend toward crustal-like isotopic signatures with increasing differentiation. Second, many ultramafic and mafic rocks have late-stage phenocryst reaction and orthocumulate textures that suggest interaction with felsic melt. These rocks also have variable and enriched isotopic compositions that suggest that this felsic melt was isotopically enriched and probably derived from crustal country rock. Partial melt from the flysch country rock may have reacted with and contaminated these partly crystalline magmas following the precipitation and accumulation of the cumulus phenocrysts but before complete solidification of the magma. This suggests that in magmatic mush (especially of ultramafic composition) crystallizing in continental crust, a second distinct process of crustal contamination may be super-imposed on AFC or magma mixing involving the main magma body. Finally, nearly all rocks, including mafic and ultramafic rocks, have (87Sr

  17. Using crystal records to investigate the parentage of orogenic andesites

    NASA Astrophysics Data System (ADS)

    Kent, A. J.; Koleszar, A. M.

    2011-12-01

    The role of andesitic magmas in continental growth and differentiation and in material fluxes related to subduction zones continues to be an active research topic. The high proportion of andesitic magmas erupted in convergent margin settings contrasts with much more limited evidence for the presence of true andesitic liquids. This suggests that magma mixing plays a dominant role in andesite genesis, consistent with the prevalence of disequilibrium textures and mineral assemblages evident in many orogenic andesites. The high proportion of andesitic magma erupted in convergent margins can be related to the link between mafic recharge, which results in magma mixing to produce andesitic magmas, and eruption initiation. We describe this process as recharge filtering, as it results in preferential eruption of mixed andesites relative to the mafic and felsic components that combine to produce them. Many discussions about andesites also revolve around the relative importance of crustal and mantle contributions. This information is crucial for understanding andesite genesis, although owing to the prevalence of mixing, bulk rock compositions may be difficult to interpret. Fortunately a range of techniques based on the study of crystalline material lets us explore the compositions and origins of the parental magmas involved in formation of orogenic andesite magmas in greater detail. Important records reside in the abundance and composition of erupted phenocryst phases, together with their entrained mineral and melt inclusions, and the relatively long timescales required for crystal re-equilibration, relative to the often-shorter timescales of mixing and eruption mean that phenocrysts primarily preserve information about their parental melts. Phenocrysts from a wide range of orogenic andesites show evidence for contributions from a diversity of mafic and felsic parental melts. This is reflected in major, trace and isotopic compositions, and interactions between these melts are

  18. Convergence rate controls seismicity styles in collision orogens

    NASA Astrophysics Data System (ADS)

    Dal Zilio, Luca; van Dinther, Ylona; Gerya, Taras

    2016-04-01

    The 25 April 2015 Mw 7.8 Gorkha earthquake in Nepal resulted from the unzipping of the previously locked Main Himalayan Thrust (MHT) fault, along which the Himalayan wedge is thrust over India. Strong ground shaking caused the collapse of more than half a million homes, killing more than 8500 people. Can such a large magnitude event also occur within the populated European Alps? Or is there a distinctly different seismicity pattern in different orogens? We show that their long-term seismicity patterns are indeed different and that their differences can be explained by a single parameter: their convergence rate. To do so we present the first self-consistent seismic cycle model for continental collisional margins. We use the viscoelastoplastic continuum Seismo-Thermo-Mechanical model (STM) validated for seismic cycle applications against a laboratory model (van Dinther et al., 2013a) and natural observations (van Dinther et al., 2013b), which includes Drucker-Prager plasticity and spontaneous rupture events governed by strongly rate-dependent friction. The 2-D model setup consists of two continental plates separated by an oceanic plate, in which the incipient subduction phase is followed by collisional orogeny. Results show the physically consistent spontaneous emergence of complex rupture paths, both on and off the main frontal thrust. These off-main frontal thrust events within the upper and lower plate complement the main frontal thrust seismicity leading to a Gutenberg-Richter frequency-magnitude distribution. This is a key observational feature of seismicity, which is typically not reproduced in seismic cycle models. The range of simulated b-values agrees with natural ranges, as we observe values from 0.97 up to 1.25 for convergence rates decreasing from 5 to 1 cm/yr. Decreasing convergence rates thus lead to relatively larger amounts of smaller earthquakes (increasing b-value) and lower maximum magnitudes. This change in b-value also observed to corresponds to

  19. Structural Implications of new Geologic Mapping and a Detailed Gravity Traverse in the Brooks Range Foothills, Chandler Lake Quadrangle, Northern Alaska

    NASA Astrophysics Data System (ADS)

    Peapples, P. R.; Saltus, R. W.; Swenson, R.; Brown, P. J.

    2005-12-01

    A fold and thrust belt in northern Alaska occupies the structural transition from the imbricate thrust sheets (or allochthons) of the Brooks Range to the North Slope coastal plain. Understanding this complexly deformed zone is critical to hydrocarbon assessment in the state-owned lands south of Prudhoe Bay. New geologic mapping and geophysical studies are focused on this important region. Detailed (1:63,360 scale) geologic mapping along the drainages of Tiglukpuk Creek and the Siksikpuk River documents exposures of deep structural levels and provides important constraints for a structural model of this region. A south-to-north structural transect encompasses the transition from the highly deformed thrust sheets of the Endicott Mountains Allochthon (EMA) at the mountain front to the inferred triangle zone at the Tuktu Escarpment 45 miles to the north. Mississippian Carbonates to Triassic siliciclastics make up the EMA north of the mountain front where there is an abrupt transition in structural style from north-vergent asymmetric overturned folding to gentle warping above shallowly dipping fault ramps. Tiglukpuk Anticline represents a fenster where the EMA is overlain in thrust contact by a melange of more distal Ipnavik River Allochthon (IRA) rocks. Parallel synclinoria contain the Okpikruak siliciclastics of the IRA assemblage and the Brookian syntectonic siliciclastics of the Fortress Mountain formation, carried atop the EMA thrust sheets during the latest phase of deformation. This complex structural style abruptly ends at the Tuktu Escarpment which likely represents a backthrust/triangle zone that places shallow north dipping coarse clastics of the Nanushuk Formation over the less competent and highly deformed Torok shale. The structural complexity and associated steeply dipping strata in the foothills belt were not well imaged by existing conventional seismic data in this region. To provide additional subsurface control, we collected ground station gravity

  20. Testing models of orogen exhumation using zircon (U-Th)/He thermochronology: Insight from the Ligurian Alps, Northern Italy

    NASA Astrophysics Data System (ADS)

    Maino, Matteo; Dallagiovanna, Giorgio; Dobson, Katherine J.; Gaggero, Laura; Persano, Cristina; Seno, Silvio; Stuart, Finlay M.

    2012-08-01

    Testing models of orogen exhumation requires precise constraint of the time-temperature paths of the exhumed rocks. The zircon (U-Th)/He (ZHe) thermochronometer has a closure temperature of ~ 140-210 °C, and can provide temporal constraints on the exhumation history of rocks through a thermal range which crucially corresponds the onset of brittle behaviour of an exhuming orogen. We performed ZHe analyses to test the existing contradictory models for the exhumation of the Ligurian Alps. The ZHe ages indicate a very rapid (1.3-6.8 mm/yr) and southward migrating exhumation of the orogen between ~ 32 and 25 Ma. These high exhumation rates are unique within the Alpine belt and cannot be reconciled with existing geodynamic models of the evolution of the Ligurian Alps. We propose a model of tectonic denudation via detachment accomplished in the shallowest crust (< 5 km) as a result of the last orogenic phase of extension.

  1. Predictive mapping of prospectivity for orogenic gold in Uganda

    NASA Astrophysics Data System (ADS)

    Herbert, Sarah; Woldai, Tsehaie; Carranza, Emmanuel John M.; van Ruitenbeek, Frank J. A.

    2014-11-01

    Integration of enhanced regional geo-datasets has facilitated new geological interpretation and modelling of prospectivity for orogenic gold in southwestern Uganda. The geo-datasets include historical geological maps, geological field data, digital terrain models, Landsat TM data and airborne geophysical data. The study area, bordered by the western branch of the East African Rift, covers a range of different aged terranes including the Archaean basement gneisses, Palaeoproterozoic volcano-sedimentary Buganda Toro Belt, Mesoproterozoic clastic sedimentary Karagwe Ankolean Belt and several outliers of undeformed Neoproterozoic sediments. The mineral systems approach to practical exploration targeting requires a framework to link conceptual models of mineralisation with available data. A conceptual model requires good understanding of key processes and their timing within the geodynamic history of an area. The challenge is that processes cannot be mapped, only their results or effects. In this study, a district-scale (1:100,000) investigation is considered appropriate given the scarcity of geological information and the absence of world-renowned gold deposits in southwestern Uganda. At this scale of orogenic gold mineral systems understanding, evidence for the source of gold, active pathways and the physical traps are considered critical. Following the mineral system approach, these processes critical to orogenic gold systems are translated into district-scale mappable proxies using available regional-scale datasets. Tectono-stratigraphic domains, mantle indicators and gold occurrences represent the “source of gold” as a critical process. Zones of hydrothermal alteration were extracted from radiometric data, structures involved in the orogenies and terrane contacts were extracted to represent the active pathway as a critical process and finally the physical throttle is represented by rheological contrasts and geological complexity. Then, the knowledge

  2. Flood frequency in Alaska

    USGS Publications Warehouse

    Childers, J.M.

    1970-01-01

    Records of peak discharge at 183 sites were used to study flood frequency in Alaska. The vast size of Alaska, its great ranges of physiography, and the lack of data for much of the State precluded a comprehensive analysis of all flood determinants. Peak stream discharges, where gaging-station records were available, were analyzed for 2-year, 5-year, 10-year, 25-year, and 50-year average-recurrence intervals. A regional analysis of the flood characteristics by multiple-regression methods gave a set of equations that can be used to estimate floods of selected recurrence intervals up to 50 years for any site on any stream in Alaska. The equations relate floods to drainage-basin characteristics. The study indicates that in Alaska the 50-year flood can be estimated from 10-year gaging- station records with a standard error of 22 percent whereas the 50-year flood can be estimated from the regression equation with a standard error of 53 percent. Also, maximum known floods at more than 500 gaging stations and miscellaneous sites in Alaska were related to drainage-area size. An envelope curve of 500 cubic feet per second per square mile covered all but 2 floods in the State.

  3. The Development of Three-Dimensional Gravity Inversion Software Applied to the Location and Geometry of the Border Ranges Fault System, South-Central Alaska

    NASA Astrophysics Data System (ADS)

    Cardenas, R.; Doser, D. I.; Mankhemthong, N.; Baker, M. R.

    2012-12-01

    Summary The Border Ranges Fault (BRFS) system bounds the Cook Inlet and Susitna Basins, an important petroleum province within south-central Alaska. The inversion utilizes gravity data constrained with geophysical, borehole, and surface geological information. The gravity inversion software was developed and tested by comparing and verifying several plausible structural models using several layers of geologic structure along the BRFS. The novel inversion approach involves directly modeling known geology, initially free-air corrected data, and revising a priori uncertainties on the geologic model to allow comparisons to alternative interpretations. Previous modeling of the BRFS using geophysical data has been limited due to the complexity of local geology and structure, both of shallow crustal features and the deeper subduction zone. Since this inversion is based on a sequence of gridded surfaces, it is feasible to develop software to help build these gridded geologic models. The gravity surveys are used in conjunction with known topology to create gridded surfaces. The software uses a Generalized, Nonlinear Least-Squares criterion to calculate the density solution of each gridded surface based on forward computations involving semi-infinite vertical line elements. The user has the capacity to observe the gravity misfit and make adjustments to the "a priori" information upon careful examination of each computed structural model. By varying several input parameters, the user can yield a range of plausible density models for making comparisons to several interpretations. Forward Model Computations The gravitational contributions are computed using a geophysics formulation, namely the vertical line element. g = πR2Gρ( x2 + y2 + z2)-1/2 Each line element is semi-infinite and extends from the top to the bottom of each structural layer. The contribution of the body to the gravity measurement will be computed as a volume integral and added to the overall contributions of

  4. Sulfur and oxygen isotopes in barite deposits of the western Brooks Range, Alaska, and implications for the origin of the Red Dog massive sulfide deposits

    USGS Publications Warehouse

    Johnson, C.A.; Kelley, K.D.; Leach, D.L.

    2004-01-01

    Sulfur and oxygen isotope analyses have been obtained for barite samples from the giant stratiform sulfide barite deposits at Red Dog in the western Brooks Range of Alaska, from stratiform barite deposits elsewhere in the Red Dog district, and from stratiform and vein and breccia barite occurrences in the central Brooks Range. Twelve of the 15 deposits studied lie within middle to Upper Mississippian black shale and chert units. The data reveal two different patterns on ?? 34S versus ??18O plots. The first, which is best illustrated by the barite deposit at Anarraaq, shows linear trends with slopes that vary with barite texture. For most samples, ??34S and ??18O values are both higher than the values characteristic of Mississippian marine sulfate. The second pattern, which is evident at the Red Dog deposits, shows no correlation between ??34S and ??18. In most samples, ??18O is below the value for Mississippian marine sulfate. Comparisons with sulfate in modern marine environments suggest a possible model for the mineralizing process. Anarraaq-type barite formed at sea-floor vents where ascending fluids carrying barium and methane encountered sulfate-bearing pore waters or bottom waters. Barite deposition was accompanied by the reduction of sulfate to H2S by means of microbially mediated anaerobic methane oxidation. Red Dog-type barite was formed in a manner similar to Anarraaq-type barite but was over-printed by a massive sulfide-forming event. Red Dog sulfides precipitated where metal-bearing hydrothermal fluids encountered pore waters that had been charged with H2S by anaerobic methane oxidation. Textural and isotopic evidence indicates that the sulfide bodies grew by consuming the available H2S and then by reductively dissolving barite. Dissolution of barite caused barium to be released to higher stratigraphic levels where it was reprecipitated on encountering sulfate. Isotopic evidence is pre sented for a link between methane venting and barite formation and

  5. Late Paleozoic orogeny in Alaska's Farewell terrane

    USGS Publications Warehouse

    Bradley, D.C.; Dumoulin, J.; Layer, P.; Sunderlin, D.; Roeske, S.; McClelland, B.; Harris, A.G.; Abbott, G.; Bundtzen, T.; Kusky, T.

    2003-01-01

    Evidence is presented for a previously unrecognized late Paleozoic orogeny in two parts of Alaska's Farewell terrane, an event that has not entered into published scenarios for the assembly of Alaska. The Farewell terrane was long regarded as a piece of the early Paleozoic passive margin of western Canada, but is now thought, instead, to have lain between the Siberian and Laurentian (North American) cratons during the early Paleozoic. Evidence for a late Paleozoic orogeny comes from two belts located 100-200 km apart. In the northern belt, metamorphic rocks dated at 284-285 Ma (three 40Ar/39Ar white-mica plateau ages) provide the main evidence for orogeny. The metamorphic rocks are interpreted as part of the hinterland of a late Paleozoic mountain belt, which we name the Browns Fork orogen. In the southern belt, thick accumulations of Pennsylvanian-Permian conglomerate and sandstone provide the main evidence for orogeny. These strata are interpreted as the eroded and deformed remnants of a late Paleozoic foreland basin, which we name the Dall Basin. We suggest that the Browns Fork orogen and Dall Basin comprise a matched pair formed during collision between the Farewell terrane and rocks to the west. The colliding object is largely buried beneath Late Cretaceous flysch to the west of the Farewell terrane, but may have included parts of the so-called Innoko terrane. The late Paleozoic convergent plate boundary represented by the Browns Fork orogen likely connected with other zones of plate convergence now located in Russia, elsewhere in Alaska, and in western Canada. Published by Elsevier B.V.

  6. GEOPHYSICS. Layered deformation in the Taiwan orogen.

    PubMed

    Huang, T-Y; Gung, Y; Kuo, B-Y; Chiao, L-Y; Chen, Y-N

    2015-08-14

    The underthrusting of continental crust during mountain building is an issue of debate for orogens at convergent continental margins. We report three-dimensional seismic anisotropic tomography of Taiwan that shows a nearly 90° rotation of anisotropic fabrics across a 10- to 20-kilometer depth, consistent with the presence of two layers of deformation. The upper crust is dominated by collision-related compressional deformation, whereas the lower crust of Taiwan, mostly the crust of the subducted Eurasian plate, is dominated by convergence-parallel shear deformation. We interpret this lower crustal shearing as driven by the continuous sinking of the Eurasian mantle lithosphere when the surface of the subducted plate is coupled with the orogen. The two-layer deformation clearly defines the role of subduction in the formation of the Taiwan mountain belt. PMID:26273051

  7. Tectono-metamorphic evolution of the internal zone of the Pan-African Lufilian orogenic belt (Zambia): Implications for crustal reworking and syn-orogenic uranium mineralizations

    NASA Astrophysics Data System (ADS)

    Eglinger, Aurélien; Vanderhaeghe, Olivier; André-Mayer, Anne-Sylvie; Goncalves, Philippe; Zeh, Armin; Durand, Cyril; Deloule, Etienne

    2016-01-01

    The internal zone of the Pan-African Lufilian orogenic belt (Zambia) hosts a dozen uranium occurrences mostly located within kyanite micaschists in a shear zone marking the contact between metasedimentary rocks attributed to the Katanga Neoproterozoic sedimentary sequence and migmatites coring domes developed dominantly at the expense of the pre-Neoproterozoic basement. The P-T-t-d paths reconstructed for these rocks combining field observations, microstructural analysis, metamorphic petrology and thermobarometry and geochronology indicate that they have recorded burial and exhumation during the Pan-African orogeny. Both units of the Katanga metasedimentary sequence and pre-Katanga migmatitic basement have underwent minimum peak P-T conditions of ~ 9-11 kbar and ~ 640-660 °C, dated at ca. 530 Ma by garnet-whole rock Lu-Hf isochrons. This suggests that this entire continental segment has been buried up to a depth of 40-50 km with geothermal gradients of 15-20 °C.km- 1 during the Pan-African orogeny and the formation of the West Gondwana supercontinent. Syn-orogenic exhumation of the partially molten root of the Lufilian belt is attested by isothermal decompression under P-T conditions of ~ 6-8 kbar at ca. 530-500 Ma, witnessing an increase of the geothermal gradients to 25-30 °C·km- 1. Uranium mineralizations that consist of uraninite and brannerite took place at temperatures ranging from ~ 600 to 700 °C, and have been dated at ca. 540-530 Ma by U-Pb ages on uraninite. The main uranium deposition thus occurred at the transition from the syn-orogenic burial to the syn-orogenic exhumation stages and has been then partially transposed and locally remobilized during the post-orogenic exhumation accommodated by activation of low-angle extensional detachment.

  8. Southern Alaska as an Example of the Long-Term Consequences of Mountain Building Under the Influence of Glaciers

    NASA Technical Reports Server (NTRS)

    Meigs, Andrew; Sauber, Jeanne

    2000-01-01

    Southern Alaska is a continent-scale region of ongoing crustal deformation within the Pacific-North American plate boundary zone. Glaciers and glacial erosion have dictated patterns of denudation in the orogen over the last approx. 5 My. The orogen comprises three discrete topographic domains from south to north, respectively: (1) the Chugach/St. Elias Range; (2) the Wrangell Mountains; and (3) the eastern Alaska Range. Although present deformation is distributed across the orogen, much of the shortening and uplift are concentrated in the Chugach/St. Elias Range. A systematic increase in topographic wavelength of the range from east to west reflects east-to-west increases in the width of a shallowly-dipping segment of the plate interface, separation of major upper plate structures, and a decrease in the obliquity of plate motion relative to the plate boundary. Mean elevation decays exponentially from approx. 2500 m to approx. 1100 m from east to west, respectively. Topographic control on the present and past distribution of glaciers is indicated by close correspondence along the range between mean elevation and the modern equilibrium line altitude of glaciers (ELA) and differences in the modern ELA, mean annual precipitation and temperature across the range between the windward, southern and leeward, northern flanks. Net, range- scale erosion is the sum of: (1) primary bedrock erosion by glaciers and (2) erosion in areas of the landscape that are ice-marginal and are deglaciated at glacial minima. Oscillations between glacial and interglacial climates controls ice height and distribution, which, in turn, modulates the locus and mode of erosion in the landscape. Mean topography and the mean position of the ELA are coupled because of the competition between rock uplift, which tends to raise the ELA, and enhanced orographic precipitation accompanying mountain building, which tends to lower the ELA. Mean topography is controlled both by the 60 deg latitude and maritime

  9. Metamorphic facies map of Alaska

    SciTech Connect

    Dusel-Bacon, C.; O-Rourke, E.F.; Reading, K.E.; Fitch, M.R.; Klute, M.A.

    1985-04-01

    A metamorphic-facies of Alaska has been compiled, following the facies-determination scheme of the Working Group for the Cartography of the Metamorphic Belts of the World. Regionally metamorphosed rocks are divided into facies series where P/T gradients are known and into facies groups where only T is known. Metamorphic rock units also are defined by known or bracketed age(s) of metamorphism. Five regional maps have been prepared at a scale of 1:1,000,000; these maps will provide the basis for a final colored version of the map at a scale of 1:2,500,000. The maps are being prepared by the US Geological Survey in cooperation with the Alaska Division of Geological and Geophysical Surveys. Precambrian metamorphism has been documented on the Seward Peninsula, in the Baird Mountains and the northeastern Kuskokwim Mountains, and in southwestern Alaska. Pre-Ordovician metamorphism affected the rocks in central Alaska and on southern Prince of Wales Island. Mid-Paleozoic metamorphism probably affected the rocks in east-central Alaska. Most of the metamorphic belts in Alaska developed during Mesozoic or early Tertiary time in conjuction with accretion of many terranes. Examples are Jurassic metamorphism in east-central Alaska, Early Cretaceous metamorphism in the southern Brooks Range and along the rim of the Yukon-Kovyukuk basin, and late Cretaceous to early Tertiary metamorphism in the central Alaska Range. Regional thermal metamorphism was associated with multiple episodes of Cretaceous plutonism in southeastern Alaska and with early Tertiary plutonism in the Chugach Mountains. Where possible, metamorphism is related to tectonism. Meeting participants are encouraged to comment on the present version of the metamorphic facies map.

  10. A Storm-by-Storm Analysis of Alpine and Regional Precipitation Dynamics at the Mount Hunter Ice Core Site, Denali National Park, Central Alaska Range

    NASA Astrophysics Data System (ADS)

    Saylor, P. L.; Osterberg, E. C.; Kreutz, K. J.; Wake, C. P.; Winski, D.

    2014-12-01

    In May-June 2013, an NSF-funded team from Dartmouth College and the Universities of Maine and New Hampshire collected two 1000-year ice cores to bedrock from the summit plateau of Mount Hunter in Denali National Park, Alaska (62.940291, -151.087616, 3912 m). The snow accumulation record from these ice cores will provide key insight into late Holocene precipitation variability in central Alaska, and compliment existing precipitation paleorecords from the Mt. Logan and Eclipse ice cores in coastal SE Alaska. However, correct interpretation of the Mt. Hunter accumulation record requires an understanding of the relationships between regional meteorological events and micrometeorological conditions at the Mt. Hunter ice core collection site. Here we analyze a three-month window of snow accumulation and meteorological conditions recorded by an Automatic Weather Station (AWS) at the Mt. Hunter site during the summer of 2013. Snow accumulation events are identified in the Mt. Hunter AWS dataset, and compared on a storm-by-storm basis to AWS data collected from the adjacent Kahiltna glacier 2000 m lower in elevation, and to regional National Weather Service (NWS) station data. We also evaluate the synoptic conditions associated with each Mt. Hunter accumulation event using NWS surface maps, NCEP-NCAR Reanalysis data, and the NOAA HYSPLIT back trajectory model. We categorize each Mt. Hunter accumulation event as pure snow accumulation, drifting, or blowing snow events based on snow accumulation, wind speed and temperature data using the method of Knuth et al (2009). We analyze the frequency and duration of events within each accumulation regime, in addition to the overall contribution of each event to the snowpack. Preliminary findings indicate that a majority of Mt. Hunter accumulation events are of pure accumulation nature (55.5%) whereas drifting (28.6%) and blowing (15.4%) snow events play a secondary role. Our results will characterize the local accumulation dynamics on

  11. Trans-Alaska Crustal Transect and continental evolution involving subduction underplating and synchronous foreland thrusting

    USGS Publications Warehouse

    Fuis, G.S.; Moore, T.E.; Plafker, G.; Brocher, T.M.; Fisher, M.A.; Mooney, W.D.; Nokleberg, W.J.; Page, R.A.; Beaudoin, B.C.; Christensen, N.I.; Levander, A.R.; Lutter, W.J.; Saltus, R.W.; Ruppert, N.A.

    2008-01-01

    We investigate the crustal structure and tectonic evolution of the North American continent in Alaska, where the continent has grown through magmatism, accretion, and tectonic underplating. In the 1980s and early 1990s, we conducted a geological and geophysical investigation, known as the Trans-Alaska Crustal Transect (TACT), along a 1350-km-long corridor from the Aleutian Trench to the Arctic coast. The most distinctive crustal structures and the deepest Moho along the transect are located near the Pacific and Arctic margins. Near the Pacific margin, we infer a stack of tectonically underplated oceanic layers interpreted as remnants of the extinct Kula (or Resurrection) plate. Continental Moho just north of this underplated stack is more than 55 km deep. Near the Arctic margin, the Brooks Range is underlain by large-scale duplex structures that overlie a tectonic wedge of North Slope crust and mantle. There, the Moho has been depressed to nearly 50 km depth. In contrast, the Moho of central Alaska is on average 32 km deep. In the Paleogene, tectonic underplating of Kula (or Resurrection) plate fragments overlapped in time with duplexing in the Brooks Range. Possible tectonic models linking these two regions include flat-slab subduction and an orogenic-float model. In the Neogene, the tectonics of the accreting Yakutat terrane have differed across a newly interpreted tear in the subducting Pacific oceanic lithosphere. East of the tear, Pacific oceanic lithosphere subducts steeply and alone beneath the Wrangell volcanoes, because the overlying Yakutat terrane has been left behind as underplated rocks beneath the rising St. Elias Range, in the coastal region. West of the tear, the Yakutat terrane and Pacific oceanic lithosphere subduct together at a gentle angle, and this thickened package inhibits volcanism. ?? 2008 The Geological Society of America.

  12. Crustal Development in the Northeast Asian Orogenic Belt and its comparison with the Central Asian Orogenic Belt

    NASA Astrophysics Data System (ADS)

    Jahn, Bor-ming

    2016-04-01

    The Northeast Asian Orogenic Belt is a Mesozoic-Cenozoic accretionary orogenic collage, and it constitutes the northern and principal part of the "Nipponides" (Sengor and Natal'in, 1996). The tectonic framework was formed in Mesozoic and Cenozoic, and it continues to evolve along the modern Pacific arc-trench systems. Generally, a oceanward younging of tectonic units may be discerned, but such a simple pattern is disrupted in many places by extensive strike-slip faulting, most of which is left-lateral. In this talk, the issue of crustal development in the sector of Sikhote-Alin and Japanese Islands will be discussed based on the geochemical and isotopic analyses of granitoids that intruded in various tectonostratigraphic terrains. The majority of granitoids in the NE Asian Orogenic Belt formed from Jurassic to late Cenozoic, with Cretaceous as the dominant period of granitic magmatism and tectonothermal events. A few Early Paleozoic granitic rocks (500 to 450 Ma) have been identified in SW Japan (Kurosegawa Belt) as well as in NE Japan (Kitakami Belt), among them the ca. 500 Ma diorites and tonalites of southern Kitakami are the oldest rocks in Japan and interpreted as the first TTG crust of proto-Japan (Isozaki et al., 2015). Cretaceous granitoids are widespread in Sikhote-Alin and in NE and SW Japan. However, granitoids were emplaced only in the Cenozoic in Sakhalin (ca. 44 - 42 Ma) and Hokkaido (45, 37 and 18 Ma). Most granitoids from Sikhote-Alin are of I-type and have ISr = 0.7040 to 0.7083, and ɛNd(T) = +3.0 to -6.0 (mostly 0 to -5). The Sr-Nd isotopic data fall within the range of granitoids from SW Japan (0.704 to 0.712; +5.0 to -13.0), and the data of Cretaceous granitoids from Sikhote-Alin and SW Japan overlap almost completely. The Cenozoic granitoids of Hokkaido are characterized by ISr = 0.7044 - 0.7061, ɛNd(T) = +1.0 to +4.7, and Sm-Nd model-1 ages = 400-1000 Ma. This is remarkably similar to the Sakhalin granitoids with ISr = 0.7047 - 0.7050,

  13. Landscape- and decadal-scale changes in the composition and structure of plant communities in the northern foothills of the Brooks Range of Arctic Alaska

    NASA Astrophysics Data System (ADS)

    Mercado-Díaz, J. A.; Gould, W. A.

    2010-12-01

    Scientists have predicted an increase in vascular plant cover in some tundra ecosystems as a result of global climate change. In Arctic Alaska, observational studies have documented increases in shrub cover for some regions; however, only a few studies have provided detailed quantitative evidence supporting the existence such changes. To address these shortcomings, we analyzed plant community data from 156 1m2 vegetation plots located at two 1km2 grids in Toolik Lake, Alaska. This data covered the time period from 1989-2008. After 18 years, we found that the relative abundance of vascular vegetation have increased by 16%, while the relative abundance of nonvascular vegetation decreased by 19%. Mean plant canopy height has experienced an increase from 4.4 cm in 1990 to 6.5 cm in 2008 and the extent and complexity of the canopy have increased over time from about 60% to 80%. Species diversity was also significantly reduced. While major vegetation changes in other tundra regions have been attributed to gradual increases in surface air temperature, changes documented in this study were apparently promoted by increasing soil moisture conditions that resulted from increased summer rainfall in our region. These results support the idea that tundra ecosystems in this region of the Alaskan Arctic are experiencing significant increases in aboveground standing crop and a shift in carbon allocation to vascular plants vs. bryophytes. These changes will likely affect important ecosystem processes like snow re-deposition, winter biological activities, nutrient cycling and could ultimately result in significant feedbacks to climate.

  14. Crustal structure and orogenic material budget in the west central Pyrenees

    NASA Astrophysics Data System (ADS)

    Teixell, Antonio

    1998-06-01

    Surface and subsurface data are combined to construct a crustal-scale cross section of the western central Pyrenees (France and Spain) at the boundary between the European and Iberian plates. The position of Moho reflections in the ECORS-Arzacq reflection profile suggests a tectonic wedge of European crust and upper mantle had indented the Iberian plate at lower crustal levels. The European wedge is overlain by an upper, Iberian wedge thus constituting a double (stacked) wedge geometry. The upper wedge was delaminated and deformed giving rise to the Pyrenean orogenic prism, manifested as a bivergent fan in upper crustal levels. The underthrust lower Iberian plate has been imaged to depths of 55-60 km, but crustal budget considerations based on a palinspastic reconstruction require that this continental root subducted to depths up to 90 km. Total orogenic contraction calculated from surface structures is about 75-80 km, which was accomplished between the latest Cretaceous and the early Miocene at an averaged rate of 1.2 mm/yr. Consistent with these moderate values, exhumation of the orogen is much less than in the more shortened eastern parts of the range. Paleozoic basement and preorogenic Mesozoic rocks are little eroded, and much of the exhumation involved cannibalization of early foreland basins, which once covered the entire, poorly emergent orogen at this transect. This resulted in a continuous process of sediment recycling and, coupled with a considerable lateral arrival of material, a bulk negative erosion-sedimentation budget.

  15. The East African Orogen: Accretion versus Collision

    NASA Astrophysics Data System (ADS)

    Kröner, A.; Muhongo, S.; Sommer, H.; Vogt, M.

    2003-04-01

    The East African Orogen is an extensive Neoproterozoic (Pan-African) orogenic belt extending from Arabia to Mozambique and containing elements of both accretion and collision tectonics. The predominantly upper crustal northern part (Arabian-Nubian Shield, ANS) consists of Neoproterozoic juvenile arc assemblages that accreted onto the African continent along ophiolite-decorated sutures. In contrast, the tectonic evolution of the predominantly middle to lower crustal southern part (Mozambique belt, MB) is still poorly understood, and simple continental collision models as previously applied are not compatible with new isotopic and petrological data. Published Nd isotopic systematics and our new zircon ages demonstrate that large parts of the high-grade MB in Tanzania consists of late Archaean to Palaeoproterozoic granitoid gneisses which may either constitute an extension of the Tanzania craton to the E, reworked during the Pan-African orogeny, or these rocks may constitute a separate terrane, or terranes, tectonically interdigitated with Neoproterozoic gneisses, similar to the situation in Madagascar. Small-scale tectonic interlayering of >1800 Ma and 650-800 Ma gneisses have been documented at several localities, and the amount of pre-Neoproterozoic crust in the MB appears to be ˜70% or more. Relatively small volumes of ˜1000-1100 Ma granitoids have so far only been recorded in southern Tanzania, and their significance in the orogenic evolution and their relation to more extensive rocks of this age in northern Mozambique are not known. High-grade metamorphism in the MB of Tanzania led to granulite and charnockite formation and occurred at 620-640 Ma, slightly earlier than in Mozambique (˜615 Ma) but significantly earlier than in Malawi (˜550-580 Ma) and in Madagascar (˜550-560 Ma). The significance of these age differences is not understood. Petrological data suggest both clockwise and anti-clockwise PT path for the metamorphic assemblages, suggesting that

  16. Gravitational removal of volcanic arc roots in Cordilleran orogens

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  17. Geologic map of Alaska

    USGS Publications Warehouse

    Wilson, Frederic H.; Hults, Chad P.; Mull, Charles G.; Karl, Susan M.

    2015-12-31

    This Alaska compilation is unique in that it is integrated with a rich database of information provided in the spatial datasets and standalone attribute databases. Within the spatial files every line and polygon is attributed to its original source; the references to these sources are contained in related tables, as well as in stand-alone tables. Additional attributes include typical lithology, geologic setting, and age range for the map units. Also included are tables of radiometric ages.

  18. Seismic anisotropy and mantle creep in young orogens

    USGS Publications Warehouse

    Meissner, R.; Mooney, W.D.; Artemieva, I.

    2002-01-01

    Seismic anisotropy provides evidence for the physical state and tectonic evolution of the lithosphere. We discuss the origin of anisotropy at various depths, and relate it to tectonic stress, geotherms and rheology. The anisotropy of the uppermost mantle is controlled by the orthorhombic mineral olivine, and may result from ductile deformation, dynamic recrystallization or annealing. Anisotropy beneath young orogens has been measured for the seismic phase Pn that propagates in the uppermost mantle. This anisotropy is interpreted as being caused by deformation during the most recent thermotectonic event, and thus provides information on the process of mountain building. Whereas tectonic stress and many structural features in the upper crust are usually orientated perpendicular to the structural axis of mountain belts, Pn anisotropy is aligned parallel to the structural axis. We interpret this to indicate mountain-parallel ductile (i.e. creeping) deformation in the uppermost mantle that is a consequence of mountain-perpendicular compressive stresses. The preferred orientation of the fast axes of some anisotropic minerals, such as olivine, is known to be in the creep direction, a consequence of the anisotropy of strength and viscosity of orientated minerals. In order to explain the anisotropy of the mantle beneath young orogens we extend the concept of crustal 'escape' (or 'extrusion') tectonics to the uppermost mantle. We present rheological model calculations to support this hypothesis. Mountain-perpendicular horizontal stress (determined in the upper crust) and mountain-parallel seismic anisotropy (in the uppermost mantle) require a zone of ductile decoupling in the middle or lower crust of young mountain belts. Examples for stress and mountain-parallel Pn anisotropy are given for Tibet, the Alpine chains, and young mountain ranges in the Americas. Finally, we suggest a simple model for initiating mountain parallel creep.

  19. Scientific communications: Re-Os sulfide (bornite, chalcopyrite, and pyrite) systematics of the carbonate-hosted copper deposits at ruby creek, southern brooks range, Alaska

    USGS Publications Warehouse

    Selby, D.; Kelley, K.D.; Hitzman, M.W.; Zieg, J.

    2009-01-01

    New Re-Os data for chalcopyrite, bornite, and pyrite from the carbonate-hosted Cu deposit at Ruby Creek (Bornite), Alaska, show extremely high Re abundances (hundreds of ppb, low ppm) and contain essentially no common Os. The Re-Os data provide the first absolute ages of ore formation for the carbonate-hosted Ruby Creek Cu-(Co) deposit and demonstrate that the Re-Os systematics of pyrite, chalcopyrite, and bornite are unaffected by greenschist metamorphism. The Re-Os data show that the main phase of Cu mineralization pre dominantly occurred at 384 ?? 4.2 Ma, with an earlier phase possibly at ???400 Ma. The Re-Os data are consistent with the observed paragenetic sequence and coincide with zircon U-Pb ages from igneous rocks within the Ambler metallogenic belt, some of which are spatially and genetically associated with regional volcanogenic massive sulfide deposits. The latter may suggest a temporal link between regional magmatism and hydrothermal mineralization in the Ambler district. The utility of bornite and chalcopyrite, in addition to pyrite, contributes to a new understanding of Re-Os geochronology and permits a refinement of the genetic model for the Ruby Creek deposit. ?? 2009 Society of Economices Geologists, Inc.

  20. Evaluate ERTS imagery for mapping and detection of changes of snowcover on land and on glaciers. [Cascade Range, Washington and Tweedsmuir Glacier, Alaska

    NASA Technical Reports Server (NTRS)

    Meier, M. F. (Principal Investigator)

    1974-01-01

    The author has identified the following significant results. The area of snowcover on 10 individual drainage basins in the North Cascades, Washington, has been determined by use of a semi-automatic radiance threshold technique. The result is a unique record of the changing water storage as snow in these important hydrologic units, the runoff of which is utilized for hydroelectric power, dilution of wastes and heat, support of salmon migration, and irrigation. These data allow a new type of hydrologic modelling to proceed which should permit more accurate forecasts of streamflow. A new technique has been developed for measuring snow-covered area or snowline altitude semi-automatically. This variable contour overlay method permits the snowcover to be matched efficiently to the best fit contour of altitude. The motion of the Yentna Glacier during the concluding phase of its surge was successfully measured by a flicker technique using images of two dates. It appears that displacements as small as 100 to 200 m can be measured. Motion of the Tweedsmuir Glacier in Alaska was measured using ERTS-1 images enlarged to 1:50,000. Changes detected included a shock wave moving down the glacier, the margin expanding, the moraine pattern deforming, and the marginal valley deepening.

  1. The thermal-mechanical evolution of crustal orogenic belts at convergent plate boundaries: A reappraisal of the orogenic cycle

    NASA Astrophysics Data System (ADS)

    Vanderhaeghe, Olivier

    2012-05-01

    Convergent plate boundaries are characterized by the development of crustal orogenic wedges and orogenic plateaus but also by gravitational collapse of previously thickened crust leading to the opening of intermontane and eventually oceanic back-arc basins. Foreland and extensional sedimentary basins in the plate boundary region are filled by the erosional products of the orogenic crust. Metamorphic rocks forming orogenic crust attest to burial and exhumation under contrasted geothermal gradients. These features portray the crustal orogenic cycle and are first-order indicators of the thermal and mechanical evolution of the crust within the plate boundary region. This evolution is controlled by complex interactions among (i) the dynamic balance among forces that arise from plate-tectonic, gravitational potential energy, and buoyancy, (ii) the thermal balance between deformation-induced and radioactive heat production and heat advection related to subduction, orogenic deformation, and magma transfer, and (iii) the mass transfer balance between uplift and erosion. To account for these geological characteristics, a generic model, that integrates results from physical modeling, is proposed for the thermal-mechanical evolution of crustal orogenic belts and for its implication in controlling the transition between the different phases of the orogenic cycle. In this model, the transition from low to high geothermal gradient is associated with increased heat production in the thickened crust owing to radioactive decay and deformation. Partial melting and rheologic weakening of the thermally mature thickened crust triggers gravity-driven lateral flow of the lower crust and controls the transition from wedge to orogenic plateau. Destruction of the orogenic crust is achieved in part by erosion but mostly by gravitational collapse. The style of extension is controlled by the rheology of the crust at the onset of gravitational collapse and its evolution as the crust thins and

  2. Coal resources of Alaska

    SciTech Connect

    Sanders, R.B.

    1982-01-01

    In the late 1800s, whaling ships carried Alaskan coal, and it was used to thaw ground for placer gold mining. Unfortunate and costly political maneuvers in the early 1900s delayed coal removal, but the Alaska Railroad and then World War II provided incentives for opening mines. Today, 33 million acres (about 9% of the state) is classified as prospectively valuable for coal, much of it under federal title. Although the state's geology is poorly known, potential for discovery of new fields exists. The US Geological Survey estimates are outdated, although still officially used. The total Alaska onshore coal resource is estimated to be 216 to 4216 billion tons of which 141 billion tons are identified resources; an additional 1430 billion tons are believed to lie beneath Cook Inlet. Transportation over mountain ranges and wetlands is the biggest hurdle for removal. Known coal sources and types are described and mapped. 1 figure.

  3. Mantle refertilization and magmatism in old orogenic regions: The role of late-orogenic pyroxenites

    NASA Astrophysics Data System (ADS)

    France, Lydéric; Chazot, Gilles; Kornprobst, Jacques; Dallai, Luigi; Vannucci, Riccardo; Grégoire, Michel; Bertrand, Hervé; Boivin, Pierre

    2015-09-01

    Pyroxenites and garnet pyroxenites are mantle heterogeneities characterized by a lower solidus temperature than the enclosing peridotites; it follows that they are preferentially involved during magma genesis. Constraining their origin, composition, and the interactions they underwent during their subsequent evolution is therefore essential to discuss the sources of magmatism in a given area. Pyroxenites could represent either recycling of crustal rocks in mantle domains or mantle originated rocks (formed either by olivine consuming melt-rock reactions or by crystal fractionation). Petrological and geochemical (major and trace elements, Sr-Nd and O isotopes) features of xenoliths from various occurrences (French Massif-Central, Jordan, Morocco and Cameroon) show that these samples represent cumulates crystallized during melt percolation at mantle conditions. They formed in mantle domains at pressures of 1-2 GPa during post-collisional magmatism (possibly Hercynian for the French Massif-Central, and Panafrican for Morocco, Jordan and Cameroon). The thermal re-equilibration of lithospheric domains, typical of the late orogenic exhumation stages, is also recorded by the samples. Most of the samples display a metasomatic overprint that may be either inherited or likely linked to the recent volcanic activity that occurred in the investigated regions. The crystallization of pyroxenites during late orogenic events has implications for the subsequent evolution of the mantle domains. The presence of large amounts of mantle pyroxenites in old orogenic regions indeed imparts peculiar physical and chemical characteristics to these domains. Among others, the global solidus temperature of the whole lithospheric domain will be lowered; in turn, this implies that old orogenic regions are refertilized zones where magmatic activity would be enhanced.

  4. Possible Cretaceous Arctic terrestrial ecosystem dynamics based on a rich dinosaur record from Alaska

    NASA Astrophysics Data System (ADS)

    Fiorillo, A. R.; McCarthy, P. J.; Flaig, P. P.

    2010-12-01

    The widespread occurrence of large-bodied herbivores, specifically hadrosaurian and ceratopsian dinosaurs, in the Cretaceous of Alaska presents a proxy for understanding polar terrestrial ecosystem biological productivity in a warm Arctic world. These dinosaurs lived in Alaska at time when this region was at or near current latitudes. Thus these dinosaurs present a paradox. The warmer Cretaceous high-latitude climate, likely related to higher levels of CO2, may have increased plant productivity but the polar light regime fluctuations must have limited the available food during the winter months. The most detailed sedimentological data available regarding the paleoenvironments supporting these dinosaurs are from the Prince Creek Formation of northern Alaska and to a lesser extent the Cantwell Formation of the Alaska Range. The sediments of the Late Cretaceous Prince Creek Formation represent a continental succession deposited on a high-latitude, low-gradient, alluvial/coastal plain. The Prince Creek Formation records numerous paleosols that are consistent with seasonality and successional vegetative cover. Drab colors in fine-grained sediments, abundant carbonaceous plant material, and common siderite nodules and jarosite suggest widespread reducing conditions on poorly-drained floodplains influenced in more distal areas by marine waters. In addition, these rocks contain high levels of organic carbon and charcoal. Carbonaceous root-traces found ubiquitously within all distributary channels and most floodplain facies, along with common Fe-oxide mottles, indicate that the alluvial system likely experienced flashy, seasonal, or ephemeral flow and a fluctuating water table. The flashy nature of the alluvial system may have been driven by recurring episodes of vigorous seasonal snowmelt in the Brooks Range orogenic belt as a consequence of the high paleolatitude of northern Alaska in the Late Cretaceous. The presence of dinosaurian megaherbivores suggests that water was

  5. Alaska Resource Data File, Noatak Quadrangle, Alaska

    USGS Publications Warehouse

    Grybeck, Donald J.; Dumoulin, Julie A.

    2006-01-01

    This report gives descriptions of the mineral occurrences in the Noatak 1:250,000-scale quadrangle, Alaska. The data presented here are maintained as part of a statewide database on mines, prospects and mineral occurrences throughout Alaska.

  6. Orogenic delamination - dynamics, effects, and geological expression

    NASA Astrophysics Data System (ADS)

    Ueda, Kosuke; Gerya, Taras

    2010-05-01

    Unbundling of continental lithosphere and removal of its mantle portion have been described by two mutually rather exclusive models, convective thinning and integral delamination. Either disburdens the remaining lithosphere, weakens the remainder, and causes uplift and extension. Increased heat flux is likely to promote high-degree crustal melting, and has been viewed as a source for voluminous granitic intrusions in late or collapsing orogenic settings. Collapse may be driven by any of gravitational potential differences from orogen to foreland, by stress inversion in the unburdened domain, or by suction of a retreating trench. In this study, we investigate prerequisites, mechanism, and development paths for orogeny-related mantle lithosphere removal. Our experiments numerically reproduce delamination which self-consistently results from the dynamics of a decoupling collision zone. In particular, it succeeds without a seed facilitating initial separation of layers. External shortening of a continent - ocean - continent assembly, such as to initiate oceanic subduction, is lifted before the whole oceanic part is consumed, leaving slab pull to govern further convergence. Once buoyant continental crust enters, the collision zone locks, and convergence diminishes. Under favourable conditions, delamination then initiates close to the edge of the mantle wedge and at deep crustal levels. While it initially separates upper crust from lower crust according to the weakness minimum in the lithospheric strength profile, the lower crust is eventually also delaminated from the subducting lithospheric mantle, owing to buoyancy differences. The level of delamination within the lithosphere seems thus first rheology-controlled, then density-controlled. Subduction-coupled delamination is contingent on retreat and decoupling of the subducting slab, which in turn is dependent on effective rheological weakening of the plate contact. Weakening is a function of shear-heating and hereby of

  7. Developing a Validated Long-Term Satellite-Based Albedo Record in the Central Alaska Range to Improve Regional Hydroclimate Reconstructions

    NASA Astrophysics Data System (ADS)

    Kreutz, K. J.; Godaire, T. P.; Burakowski, E. A.; Winski, D.; Campbell, S. W.; Wang, Z.; Sun, Q.; Hamilton, G. S.; Birkel, S. D.; Wake, C. P.; Osterberg, E. C.; Schaaf, C.

    2015-12-01

    Mountain glaciers around the world, particularly in Alaska, are experiencing significant surface mass loss from rapid climatic shifts and constitute a large proportion of the cryosphere's contribution to sea level rise. Surface albedo acts as a primary control on a glacier's mass balance, yet it is difficult to measure and quantify spatially and temporally in steep, mountainous settings. During our 2013 field campaign in Denali National Park to recover two surface to bedrock ice cores, we used an Analytical Spectral Devices (ASD) FieldSpec4 Standard Resolution spectroradiometer to measure incoming solar radiation, outgoing surface reflectance and optical grain size on the Kahiltna Glacier and at the Kahiltna Base Camp. A Campbell Scientific automatic weather station was installed on Mount Hunter (3900m) in June 2013, complementing a longer-term (2008-present) station installed at Kahiltna Base Camp (2100m). Use of our in situ data aids in the validation of surface albedo values derived from Moderate Resolution Imaging Spectroradiometer (MODIS) and Landsat satellite imagery. Comparisons are made between ASD FieldSpec4 ground measurements and 500m MODIS imagery to assess the ability of MODIS to capture the variability of surface albedo across the glacier surface. The MODIS MCD43A3 BRDF/Albedo Product performs well at Kahiltna Base Camp (<5% difference from ASD shortwave broadband data), but low biases in MODIS albedo (10-28% relative to ASD data) appear to occur along the Kahiltna Glacier due to the snow-free valley walls being captured in the 500m MODIS footprint. Incorporating Landsat imagery will strengthen our interpretations and has the potential to produce a long-term (1982-present) validated satellite albedo record for steep and mountainous terrain. Once validation is complete, we will compare the satellite-derived albedo record to the Denali ice core accumulation rate, aerosol records (i.e. volcanics and biomass burning), and glacier mass balance data. This

  8. A multi-proxy reconstruction of temperature and aridity from lake sediments north of the Brooks Range, Alaska for the past 30,000 years

    NASA Astrophysics Data System (ADS)

    Huang, Y.; Russell, J. M.; Longo, W. M.; Daniels, W.; Giblin, A. E.

    2015-12-01

    Paleoclimate reconstructions from the northern Alaska tundra since the LGM have mainly relied on paleoecological proxies such as pollen and chironomids. However, lack of trees, non-analogue assemblages, and limited species diversity present significant challenges to quantitative reconstructions. The abnormally warm LGM conditions implied by pollen assemblages, supported by the CCSM3 but contradicted by CCSM4 simulations, have been a source of great confusion. Here we present a synthesis of results from a NSF-funded project, aiming at utilizing a full suite of organic geochemical and paleolimnological proxies, in conjunction with model comparison, to quantitatively reconstruct temperature and moisture changes since the LGM. Compound specific hydrogen isotopic ratios of plant leaf waxes from Lake E5 near Toolik Lake suggest summer temperature at the LGM is ~ 7 degrees colder than the early Holocene and there is a temperature decline of 2-3 degrees over the Holocene, coherent with greenhouse and insolation forcings respectively. A similar LGM to present temperature gradient is found in the alkenone-inferred early summer temperatures, although an expanded Arctic sea ice in the early Holocene significantly suppressed this temperature. The LGM to present temperature gradient is further supported by temperatures inferred by br-GDGTs from our sediment core, which also display an early Holocene to present temperature decline of 2 to 3 degrees. Our paleotemperature data are supported by model results using CCSM4, with its use of newer generation ice sheet configuration, indicating lower LGM temperatures than present. Our paleohydrological reconstructions based on hydrogen isotopic contrast between inferred precipitation and lake water isotopic ratios, and carbon isotopic fractionation of terrestrial plant leaf waxes, suggesting an arid last glacial relative to the Holocene. This presentation will also summarize all geochemical measurements including TOC, bulk C and N

  9. Distribution of strain rates in the Taiwan orogenic wedge

    NASA Astrophysics Data System (ADS)

    Mouthereau, F.; Fillon, C.; Ma, K.-F.

    2009-07-01

    To constrain the way Eurasian crust is accreted to the Taiwan orogenic wedge we investigate the present-day 3D seismogenic deformation field using the summation of 1129 seismic moment tensors of events ( Mw > 4) covering a period of 11 years (1995 to 2005). Based on the analysis of the principal strain-rate field, including dilatation and maximum shear rates, we distinguish four domains. Domain I comprises the Coastal Plain and the Western Foothills. It is mainly contractional in both the horizontal plane and in cross-section. Domain II comprises the eastern Western Foothills, the Hsuehshan Range and the Backbone Range. It is characterized by the highest contraction rates of 10 - 6 yr - 1 in association with area expansion in cross-section and area contraction in the horizontal plane. Domain III corresponds to the Central Range. It is characterized by area contraction in cross-section and area expansion in the horizontal plane. The maximum contractional axis is typically low and plunges ~ 30°E. Extension is larger, horizontal and strikes parallel to the axis of the mountain range. Domain IV corresponding to the Coastal Range and offshore Luzon Arc shows deformation patterns similar to domain II. This seismogenic strain-rate field, which is found in good agreement with the main features of the geodetic field, supports shortening within a thick wedge whose basal décollement is relatively flat and located in the middle-to-lower crust > 20 km. The east plunges of maximum strain-rate axes below the Central Range argue for the development of top-to-the-east transport of rocks resulting from the extrusion of the whole crust along west-dipping crustal-scale shear zones. The study of seismogenic strain rates argues that the initiation of subduction reversal has already started in the Taiwan collision domain.

  10. Serum chemistry reference ranges for Steller sea lion (Eumetopias jubatus) pups from Alaska: stock differentiation and comparisons within a North Pacific sentinel species.

    PubMed

    Lander, Michelle E; Fadely, Brian S; Gelatt, Thomas S; Rea, Lorrie D; Loughlin, Thomas R

    2013-12-01

    Blood chemistry and hematologic reference ranges are useful for population health assessment and establishing a baseline for future comparisons in the event of ecosystem changes due to natural or anthropogenic factors. The objectives of this study were to determine if there was any population spatial structure for blood variables of Steller sea lion (Eumetopias jubatus), an established sentinel species, and to report reference ranges for appropriate populations using standardized analyses. In addition to comparing reference ranges between populations with contrasting abundance trends, data were examined for evidence of disease or nutritional stress. From 1998 to 2011, blood samples were collected from 1,231 pups captured on 37 rookeries across their Alaskan range. Reference ranges are reported separately for the western and eastern distinct population segments (DPS) of Steller sea lion after cluster analysis and discriminant function analysis (DFA) supported underlying stock structure. Variables with greater loading scores for the DFA (creatinine, total protein, calcium, albumin, cholesterol, and alkaline phosphatase) also were greater for sea lions from the endangered western DPS, supporting previous studies that indicated pup condition in the west was not compromised during the first month postpartum. Differences between population segments were likely a result of ecological, physiological, or age related differences. PMID:24419664

  11. Coupled delamination and indentor-escape tectonics in the southern part of the c. 650-500 Ma East African/Antarctic Orogen

    NASA Astrophysics Data System (ADS)

    Jacobs, J.; Thomas, R. J.; Ueda, K.; Kleinhanns, I.; Emmel, B.; Kumar, R.; Engvik, A.; Bingen, B.

    2009-12-01

    molasse in the north covers almost the entire North African platform, probably resulting from a long lasting high standing mountain range (no delaminated root), the molasse deposits of the southern EAAO are comparatively smaller, possibly resulting from the rapid and mechanical thinning of the orogen in the south (delaminated root).

  12. A geologic framework for mineralization in the western Brooks Range

    USGS Publications Warehouse

    Young, Lorne E.

    2004-01-01

    The Brooks Range is a 950-km-long north-vergent fold and thrust belt, which was formed during Mesozoic convergence of the continental Arctic Alaska terrane and the oceanic Angayucham terrane and was further shortened and uplifted in Tertiary time. The Arctic Alaska terrane consists of parautochthonous rocks and the Endicott Mountains and De Long Mountains subterranes. The Endicott Mountains allochthon of the western Brooks Range is the setting for many sulfide and barite occurrences, such as the supergiant Red Dog zinc-lead mine. Mineralization is sediment hosted and most commonly is present in black shale and carbonate turbidites of the Mississippian Kuna Formation. The reconstructed Kuna basin is a 200 by +600 km feature that represents the culmination of a remarkable chain of events that includes three fluvial-deltaic and two or more orogenic cycles, Middle Devonian to Mississippian episodes of extension and igneous activity, and the emergence of a seaward Lower Proterozoic landmass that may have constituted a barrier to marine circulation. Mississippian extension and related horst-and-graben architecture in the western Brooks Range is manifested in part by strong facies variability between coeval units of allochthons and structural plates. Shallow marine to possibly nonmarine arkose, platform to shelf carbonate, slope-to-basin shale, chert and carbonate turbidites, and submarine volcanic rocks are all represented in Mississippian time. The structural setting of Mississippian sedimentation, volcanism, and mineralization in the Kuna basin may be comparable to documented Devono-Mississippian extensional sags or half-grabens in the subsurface north of the Brooks Range. Climate, terrestrial ecosystems, multiple fluvial-deltaic aquifers, and structural architecture affected the liberation, movement, and redeposition of metals in ways that are incompletely understood.

  13. In the footsteps of Robert Marshall: Proposed research of white spruce growth and movement at the tree limit, central Brooks Range, Alaska

    SciTech Connect

    Droessler, T.D.

    1992-03-01

    The proposed research will quantify white spruce growth and document its latitudinal stability at the tree limit in the central Brooks Range over the life span of the living trees. The goal is to link tree growth and tree position to summer temperature and precipitation. Historical records from 1929 to 1938 from work by Robert Marshall have been used to identify tree limit sites and provide information to interpret the present location of the tree limit.

  14. Structural analysis of terrane accretions in the eastern Brooks Range and adjacent areas in central Alaska and Canada. Technical progress report No. 6

    SciTech Connect

    Coney, P.J.; Harms, T.A.

    1985-03-14

    Work on radiolarian separation and identification of samples from the Sylvester Allochthon is nearing completion. A preliminary chronostratigraphic chart showing the age range and lithologic type of all dated units has been drawn. The comparative petrography of lithologies from the Sylvester Allochthon and the Angayucham and Mosquito Terranes, and from deformed clastic rocks of the Venetie Terrane is being studied. Several preliminary structure sections have been drawn across the Sylvester Terrane. (ACR)

  15. Depositional framework and regional correlation of pre-Carboniferous metacarbonate rocks of the Snowden Mountain area, central Brooks Range, Northern Alaska

    USGS Publications Warehouse

    Dumoulin, J.A.; Harris, A.G.

    1994-01-01

    This report describes lithofacies, conodont biostratigraphy and biofacies, and depositional environments of Proterozoic(?) through Devonian metacarbonate rocks in the Snowden Mountain area. These rocks are correlated with successions on the Seward Peninsula and across the Brooks Range. Lithologic and paleobiogeographic data suggest that these successions formed along a single continental margin which had faunal exchange with both North America and Siberia, rather than on a series of discrete platforms juxtaposed by later tectonic events.

  16. Transience and Glacial Erosion in South Central Alaska

    NASA Astrophysics Data System (ADS)

    Valentino, J.; Spotila, J. A.; Owen, L. A.; Buscher, J.

    2013-12-01

    It is documented that a glacial presence in active orogenic belts undergoing rapid rock uplift will increase erosion rates often matching rates of rock uplift. Glacial erosion seems to have shaped the mass balance of numerous mountain ranges and tectonic settings, but the Kenai Peninsula and Chugach Mountains of south central Alaska do not conform to this pattern. The Kenai Peninsula is an uplifted forearc forming above the Aleutian subduction zone and the Chugach Mountains are the continuation of the orogenic belt around Prince William Sound. This mountain belt is comprised of accreted Mesozoic island arcs, which were sequentially metamorphosed from the cretaceous through the Tertiary. Geomorphic analysis and past studies, including Buscher et al. (2008) and Arkle et al. (2013), show that the Chugach Mountains and Kenai Peninsula are similar to the Saint Elias Mountains in the Yakutat collision zone with regards to topographic ruggedness. The region is dominated by alpine glaciers, ice fields, and extensive valley glaciers that are actively eroding the topography through headwall erosion and valley glacier down cutting. Despite this, there is a low background long term erosion rate of <0.1-0.2 mm/yr (Buscher et al, 2008). This suggests a transient landscape that has not yet fully adjusted to onset of erosive glacial conditions. Through the use of four dating techniques spanning different timescales, we aim to quantify erosion rates in the Kenai and Chugach Mountains. (U-TH)/He thermochronometry (106-7 yr), He/He thermochronometry (105-6 yr), OSL thermochronometry (105-6 yr), and 10Be and 36CL cosmogenic dating (103-4 yr), are being used in conjunction to test if short-term rates exceed long-term rates, thereby indicating a transient response to late Cenozoic glaciations. This analysis will also address how landscapes respond to the onset of glacial conditions and subsequent climate fluctuations. The history of exhumation and erosion will also characterize the role

  17. How Orogen-scale Exhumed Strike-slip Faults Initiate

    NASA Astrophysics Data System (ADS)

    Cao, S.; Neubauer, F.

    2015-12-01

    Orogen-scale strike-slip faults present one the most important geodynamic processes affecting the lithosphere-asthenosphere system. In specific subtypes, faulting is virtually initiated along hot-to-cool boundaries, e.g. at such of hot granite intrusions or metamorphic core complexes to cool country rocks. Such fault zones are often subparallel to mountain ranges and expose a wide variety of mylonitic, cataclastic and non-cohesive fault rocks, which were formed at different structural levels of the crust and are stacked within each other ("telescoping"). Exhumation of rocks is, therefore, a common feature of such strike-slip faults implying major transtensive and/or transpressive processes accompanying pure strike-slip motion. The hot-to-cool thermal structure across the fault zone significantly influences the physical fault rock properties. One major question is how and where a major strike-slip initiates and further development. Here, we propose a model in which major continental exhumed strike-slip faults potentially evolve along rheologically weak zones such as plutons or margins of metamorphic complexes. As an example, we propose a model for the Ailao Shan-Red River (ASRR) fault, SE Asia, which initiated along the edge of a plutonic belt and evolved in response to India-Asia collision with four tectonic phases.

  18. Paleozoic orogens in New England, USA

    USGS Publications Warehouse

    Robinson, P.; Tucker, R.D.; Bradley, D.; Berry, H.N.; Osberg, P.H.

    1998-01-01

    Stratigraphy and isotope geochronology in the crystalline core of the Appalachians suggest revised interpretations of the extent, nature and timing of Paleozoic orogens in New England. Five major episodes of magmatism, deformation, and high-grade regional metamorphism are recognized: Taconian (455-442 Ma), Acadian (423-385 Ma), Neo-Acadian (366-350 Ma), Late Pennsylvanian (300-290 Ma) and Alleghanian (280-260 Ma). In the Taconian, the passive margin of Laurentia was subducted below a complex magmatic arc lasting from 480 to 442 Ma, founded in part on continental crust of a Medial New England terrane with possible affinities with Amazonia. Questions about Medial New England involve its coherence as a single plate, and the nature of its underlying crust. The Acadian began in Late Silurian as a collision between the amalgamated Laurentia-Medial New England and outer belts of Composite Avalon along a cryptic suture in coastal Maine, and progressed northwestward to the Connecticut Valley basin by mid-Devonian. Tonalitic-granitic magmatism and up to granulite-facies metamorphism culminated in Early Devonian, possibly tied to lithospheric detachment below the subducting northwestern plate and consequent asthenosphere upwelling. Newly discovered Neo-Acadian Late Devonian to Early Mississippian tonalitic-granitic magmatism, up to granulite-facies metamorphism, and severe deformation in central Massachusetts took place in a plate context poorly understood. Late Pennsylvanian effects include magmatism, metamorphism, and deformation near south New England gneiss domes and the Sebago batholith, and development of the right-lateral Norumbega fault system. Permian Alleghanian effects include penetrative deformation, granitic intrusions and up to sillimanite-grade metamorphism of Pennsylvanian beds in southeastern New England. These last two episodes relate to the arrival of Africa.

  19. Tectonic setting and metallogenesis of volcanogenic massive sulfide deposits in the Bonnifield Mining District, Northern Alaska Range: Chapter B in Recent U.S. Geological Survey studies in the Tintina Gold Province, Alaska, United States, and Yukon, Canada--results of a 5-year project

    USGS Publications Warehouse

    Dusel-Bacon, Cynthia; Aleinikoff, John N.; Premo, Wayne R.; Paradis, Suzanne; Lohr-Schmidt, Ilana; Gough, Larry P.; Day, Warren C.

    2007-01-01

    This paper summarizes the results of field and laboratory investigations, including whole-rock geochemistry and radiogenic isotopes, of outcrop and drill core samples from volcanogenic massive sulfide (VMS) deposits and associated metaigneous rocks in the Wood River area of the Bonnifield mining district, northern Alaska Range (see fig. 1 of Editors’ Preface and Overview). U-Pb zircon igneous crystallization ages from felsic rocks indicate a prolonged period of Late Devonian to Early Mississippian (373±3 to 357±4 million years before present, or Ma) magmatism. This magmatism occurred in a basinal setting along the ancient Pacific margin of North America. The siliceous and carbonaceous compositions of metasedimentary rocks, Precambrian model ages based on U-Pb dating of zircon and neodymium ages, and for some units, radiogenic neodymium isotopic compositions and whole-rock trace-element ratios similar to those of continental crust are evidence for this setting. Red Mountain (also known as Dry Creek) and WTF, two of the largest VMS deposits, are hosted in peralkaline metarhyolite of the Mystic Creek Member of the Totatlanika Schist. The Mystic Creek Member is distinctive in having high concentrations of high-field-strength elements (HFSE) and rare-earth elements (REE), indicative of formation in a within-plate (extensional) setting. Mystic Creek metarhyolite is associated with alkalic, within-plate basalt of the Chute Creek Member; neodymium isotopic data indicate an enriched mantle component for both members of this bimodal (rhyolite-basalt) suite. Anderson Mountain, the other significant VMS deposit, is hosted by the Wood River assemblage. Metaigneous rocks in the Wood River assemblage span a wide compositional range, including andesitic rocks, which are characteristic of arc volcanism. Our data suggest that the Mystic Creek Member likely formed in an extensional, back-arc basin that was associated with an outboard continental-margin volcanic arc that included

  20. A comparison of geochemical exploration techniques and sample media within accretionary continental margins: an example from the Pacific Border Ranges, Southern Alaska, U.S.A.

    USGS Publications Warehouse

    Sutley, S.J.; Goldfarb, R.J.; O'Leary, R. M.; Tripp, R.B.

    1990-01-01

    The Pacific Border Ranges of the southern Alaskan Cordillera are composed of a number of allochthonous tectonostratigraphic terranes. Within these terranes are widespread volcanogenic, massive sulfide deposits in and adjacent to portions of accreted ophiolite complexes, bands and disseminations of chromite in accreted island-arc ultramafic rocks, and epigenetic, gold-bearing quartz veins in metamorphosed turbidite sequences. A geochemical pilot study was undertaken to determine the most efficient exploration strategy for locating these types of mineral deposits within the Pacific Border Ranges and other typical convergent continental margin environments. High-density sediment sampling was carried out in first- and second-order stream channels surrounding typical gold, chromite and massive sulfide occurrences. At each site, a stream-sediment and a panned-concentrate sample were collected. In the laboratory, the stream sediments were sieved into coarse-sand, fine- to medium-sand, and silt- to clay-size fractions prior to analysis. One split of the panned concentrates was retained for analysis; a second split was further concentrated by gravity separation in heavy liquids and then divided into magnetic, weakly magnetic and nonmagnetic fractions for analysis. A number of different techniques including atomic absorption spectrometry, inductively coupled plasma atomic emission spectrometry and semi-quantitative emission spectrography were used to analyze the various sample media. Comparison of the various types of sample media shows that in this tectonic environment it is most efficient to include a silt- to clay-size sediment fraction and a panned-concentrate sample. Even with the relatively low detection limits for many elements by plasma spectrometry and atomic absorption spectrometry, anomalies reflecting the presence of gold veins could not be identified in any of the stream-sediment fractions. Unseparated panned-concentrate samples should be analyzed by emission

  1. Strong imprint of past orogenic events on the thermochronological record

    NASA Astrophysics Data System (ADS)

    Braun, Jean

    2016-06-01

    Using a simple solution to the heat conduction equation, I show how, at the end of an orogenic event, the relaxation of isotherms from a syn-orogenic advection-dominated geometry to a post-orogenic conduction-dominated geometry leads to the creation of a thick iso-age crustal layer. Subsequent erosion of this layer yields peculiar age-elevation profiles and detrital age distributions that cannot be easily interpreted using traditional techniques. I illustrate these points by using a simple analytical solution of the heat equation as well as a transient, three-dimensional numerical model. I also demonstrate that the age of the end of an orogenic event is so strongly imprinted in the thermochronological record that it erases most of the information pertaining to the orogenic phase itself and the subsequent isostatically-driven exhumation. The concept is used to explain two thermochronological datasets from the Himalayas and demonstrate that their most likely interpretation involves the sudden interruption of extremely fast exhumation accommodated by movement along the South Tibetan Detachment in the Higher Himalayas around 15 Ma.

  2. Linking magmatism with collision in an accretionary orogen

    NASA Astrophysics Data System (ADS)

    Li, Shan; Chung, Sun-Lin; Wilde, Simon A.; Wang, Tao; Xiao, Wen-Jiao; Guo, Qian-Qian

    2016-05-01

    A compilation of U-Pb age, geochemical and isotopic data for granitoid plutons in the southern Central Asian Orogenic Belt (CAOB), enables evaluation of the interaction between magmatism and orogenesis in the context of Paleo-Asian oceanic closure and continental amalgamation. These constraints, in conjunction with other geological evidence, indicate that following consumption of the ocean, collision-related calc-alkaline granitoid and mafic magmatism occurred from 255 ± 2 Ma to 251 ± 2 Ma along the Solonker-Xar Moron suture zone. The linear or belt distribution of end-Permian magmatism is interpreted to have taken place in a setting of final orogenic contraction and weak crustal thickening, probably as a result of slab break-off. Crustal anatexis slightly post-dated the early phase of collision, producing adakite-like granitoids with some S-type granites during the Early-Middle Triassic (ca. 251–245 Ma). Between 235 and 220 Ma, the local tectonic regime switched from compression to extension, most likely caused by regional lithospheric extension and orogenic collapse. Collision-related magmatism from the southern CAOB is thus a prime example of the minor, yet tell-tale linking of magmatism with orogenic contraction and collision in an archipelago-type accretionary orogen.

  3. Linking magmatism with collision in an accretionary orogen.

    PubMed

    Li, Shan; Chung, Sun-Lin; Wilde, Simon A; Wang, Tao; Xiao, Wen-Jiao; Guo, Qian-Qian

    2016-01-01

    A compilation of U-Pb age, geochemical and isotopic data for granitoid plutons in the southern Central Asian Orogenic Belt (CAOB), enables evaluation of the interaction between magmatism and orogenesis in the context of Paleo-Asian oceanic closure and continental amalgamation. These constraints, in conjunction with other geological evidence, indicate that following consumption of the ocean, collision-related calc-alkaline granitoid and mafic magmatism occurred from 255 ± 2 Ma to 251 ± 2 Ma along the Solonker-Xar Moron suture zone. The linear or belt distribution of end-Permian magmatism is interpreted to have taken place in a setting of final orogenic contraction and weak crustal thickening, probably as a result of slab break-off. Crustal anatexis slightly post-dated the early phase of collision, producing adakite-like granitoids with some S-type granites during the Early-Middle Triassic (ca. 251-245 Ma). Between 235 and 220 Ma, the local tectonic regime switched from compression to extension, most likely caused by regional lithospheric extension and orogenic collapse. Collision-related magmatism from the southern CAOB is thus a prime example of the minor, yet tell-tale linking of magmatism with orogenic contraction and collision in an archipelago-type accretionary orogen. PMID:27167207

  4. Linking magmatism with collision in an accretionary orogen

    PubMed Central

    Li, Shan; Chung, Sun-Lin; Wilde, Simon A.; Wang, Tao; Xiao, Wen-Jiao; Guo, Qian-Qian

    2016-01-01

    A compilation of U-Pb age, geochemical and isotopic data for granitoid plutons in the southern Central Asian Orogenic Belt (CAOB), enables evaluation of the interaction between magmatism and orogenesis in the context of Paleo-Asian oceanic closure and continental amalgamation. These constraints, in conjunction with other geological evidence, indicate that following consumption of the ocean, collision-related calc-alkaline granitoid and mafic magmatism occurred from 255 ± 2 Ma to 251 ± 2 Ma along the Solonker-Xar Moron suture zone. The linear or belt distribution of end-Permian magmatism is interpreted to have taken place in a setting of final orogenic contraction and weak crustal thickening, probably as a result of slab break-off. Crustal anatexis slightly post-dated the early phase of collision, producing adakite-like granitoids with some S-type granites during the Early-Middle Triassic (ca. 251–245 Ma). Between 235 and 220 Ma, the local tectonic regime switched from compression to extension, most likely caused by regional lithospheric extension and orogenic collapse. Collision-related magmatism from the southern CAOB is thus a prime example of the minor, yet tell-tale linking of magmatism with orogenic contraction and collision in an archipelago-type accretionary orogen. PMID:27167207

  5. Paleozoic sedimentary rocks in the Red Dog Zn-Pb-Ag district and vicinity, western Brooks Range, Alaska: provenance, deposition, and metallogenic significance

    USGS Publications Warehouse

    Slack, John F.; Dumoulin, Julie A.; Schmidt, J.M.; Young, L.E.; Rombach, Cameron

    2004-01-01

    The distribution and composition of Paleozoic strata in the western Brooks Range may have played a fundamental role in Zn-Pb mineralization of the Red Dog district. In our model, deposition and early lithification of biogenic chert and bedded siliceous rocks in the upper part of the Kuna Formation served as a regional hydrologic seal, acting as a cap rock to heat and hydrothermal fluids during Late Mississippian base-metal mineralization. Equally important was the iron-poor composition of black shales of the Kuna Formation (i.e., low Fe/Ti ratios), which limited synsedimentary pyrite formation in precursor sediments, resulting in significant H2S production in pore waters through the interaction of aqueous sulfate with abundant organic matter. This H2S may have been critical to the subsurface deposition of the huge quantities of Zn and Pb in the district. On the basis of this model, we propose that low Fe/Ti and S/C ratios in black shale sequences are potential basin-scale exploration guides for giant sediment-hosted, stratiform Zn-Pb-Ag deposits.

  6. Geochemistry and geochronology of carbonate-hosted base metal deposits in the southern Brooks Range, Alaska: temporal association with VMS deposits and metallogenic implications

    USGS Publications Warehouse

    Kelly, Karen; Slack, John; Selby, David

    2009-01-01

    The Brooks Range contains enormous accumulations of zinc and copper, either as VMS or sediment-hosted deposits. The Ruby Creek and Omar deposits are Cu-Co stratabound deposits associated with dolomitic breccias. Numerous volcanogenic Cu-Zn (+/-Ag, Au) deposits are situated ~20 km north of the Ruby Creek deposit. The carbonate-hosted deposits consist of chalcopyrite and bornite that fill open spaces, replace the matrix of the breccias, and occur in later cross-cutting veins. Cobaltiferous pyrite, chalcocite, minor tennantite-tetrahedrite, galena, and sphalerite are also present. At Ruby Creek, phases such as carrollite, renierite, and germanite occur rarely. The deposits have undergone post-depositional metamorphism (Ruby Creek, low greenschist facies; Omar, blueschist facies). The unusual geochemical signature includes Cu-Co +/- Ag, As, Au, Bi, Ge, Hg, Sb, and U with sporadic high Re concentrations (up to 2.7 ppm). New Re-Os data were obtained for chalcopyrite, bornite, and pyrite from the Ruby Creek deposit (analyses of sulfides from Omar are in progress). The data show extremely high Re abundances (hundreds of ppb, low ppm) and contain essentially no common Os. The Re-Os data provide the first absolute ages of ore formation for the Ruby Creek deposit and demonstrate that the Re-Os systematics of pyrite, chalcopyrite, and bornite are unaffected by greenschist metamorphism. The Re-Os data show that the main phase of Cu mineralization occurred at 384 +/-4.2 Ma, which coincides with zircon U-Pb ages from igneous rocks that are spatially and genetically associated with VMS deposits. This suggests a temporal link between regional magmatism and hydrothermal mineralization.

  7. Origin of the Red Dog Zn-Pb-Ag deposits, Brooks Range, Alaska: Evidence from regional Pb and Sr isotope sources

    USGS Publications Warehouse

    Ayuso, R.A.; Kelley, K.D.; Leach, D.L.; Young, L.E.; Slack, J.F.; Wandless, G.; Lyon, A.M.; Dillingham, J.L.

    2004-01-01

    Pb and Sr isotope data were obtained on the shale-hosted Zn-Pb-Ag Red Dog deposits (Qanaiyaq, Main, Aqqaluk, and Paalaaq), other shale-hosted deposits near Red Dog, and Zn-Pb-Ag sulfide and barite deposits in the western and central Brooks Range. The Red Dog deposits and other shale-hosted Zn-Pb-Ag deposits near Red Dog are hosted in the Mississippian Kuna Formation, which is underlain by a sequence of marine-deltaic clastic rocks of the Upper Devonian to Lower Mississippian Endicott Group. Ag-Pb-Zn vein-breccias are found in the Endicott Group. Galena formed during the main mineralization stages in the Red Dog deposits and from the Anarraaq and Wulik deposits have overlapping Pb isotope compositions in the range 206Pb/204Pb = 18.364 to 18.428, 207Pb/204Pb = 15.553 to 15.621, and 208Pb/204Pb = 38.083 to 38.323. Galena and sphalerite formed during the main ore-forming stages in the Red Dog deposits define a narrow field on standard uranogenic and thorogenic Pb isotope diagrams. Lead in sulfides of the Red Dog district is less radiogenic (238U/204Pb: ?? = 9.51-9.77) than is indicated by the average crustal lead evolution model (?? = 9.74), a difference consistent with a long history of evolution at low ratios of ?? before the Carboniferous. The homogeneous regional isotopic reservoir of Pb may indicate large-scale transport and leaching of minerals with various ?? ratios and Th/Pb ratios. Younger and genetically unrelated fluids did not significantly disturb the isotopic compositions of galena and sphalerite after the main mineralization event in the Red Dog district. Some pyrite shows evidence of minor Pb remobilization. The overall lead isotope homogeneity in the shale-hosted massive sulfide deposits is consistent with three types of control: a homogeneous regional source, mixing of lead during leaching of a thick sedimentary section and fluid transport, or mixing at the site of deposition. Isotopic variability of the hydrothermal fluids, as represented by galena

  8. 40Ar/39Ar cooling history of the Albany Mobile Belt, Albany-Fraser Orogen, Western Australia

    NASA Astrophysics Data System (ADS)

    Scibiorski, Elisabeth; Tohver, Eric; Jourdan, Fred

    2013-04-01

    The Albany-Fraser Orogen of southwestern Australia is a Grenville-age orogenic belt that marks the suturing of the Yilgarn Craton of Western Australia to the Mawson Craton of South Australia and Antarctica. The Albany Mobile Belt is situated in the west of the orogen and consists of three geological domains: the Nornalup Zone, the Biranup Zone and the Northern Foreland. The crustal genesis and nature of boundaries between these domains is unknown. 40Ar/39Ar thermochronology of biotite and muscovite grains from a 250 km transect across all three domains in the Albany Mobile Belt is used to study the exhumation and cooling history of the amphibolite to granulite facies orogenic root. Previously published geochronological data dates peak amphibolite or granulite facies metamorphism in the Nornalup Zone, Biranup Zone and Northern Foreland at ca. 1170 Ma, ca. 1180 Ma and ca. 1210 - 1180 Ma respectively. All samples reported in this study yielded well defined plateau ages consistent with Stage II of the Albany-Fraser Orogeny (1215 - 1140 Ma). Four biotites from the Nornalup Zone give cooling ages ranging from 1144 ± 5 Ma to 1168 ± 5 Ma, one biotite from the Biranup Zone gives a cooling age of 1159 ± 5 Ma, and four muscovites from the Northern Foreland give statistically indistinguishable cooling ages ranging from 1157 ± 6 Ma to 1164 ± 5 Ma, with a weighted mean age of 1159 ± 6 Ma (P = 0.10). The new cooling ages imply that the three domains had been brought to a similar structural level (12 - 17 km depth) by ca. 1158 Ma, and have shared a common geological history since that time. This suggests that Stage II tectonic activity may have ended at ca. 1158 Ma in the Albany Mobile Belt, 20 Myr earlier than previously assumed. A cooling rate of 25°C/Myr for the Biranup Zone was calculated based on the 20 Myr interval between peak granulite-facies metamorphism and the cooling of the domain through the estimated biotite closure temperature (ca. 300°C) by ca. 1159 Ma

  9. Alaska's Children, 1997.

    ERIC Educational Resources Information Center

    Douglas, Dorothy, Ed.

    1997-01-01

    These four issues of the "Alaska's Children" provide information on the activities of the Alaska Head Start State Collaboration Project and other Head Start activities. Legal and policy changes affecting the education of young children in Alaska are also discussed. The Spring 1997 issue includes articles on brain development and the "I Am Your…

  10. Alaska's Economy: What's Ahead?

    ERIC Educational Resources Information Center

    Alaska Review of Social and Economic Conditions, 1987

    1987-01-01

    This review describes Alaska's economic boom of the early 1980s, the current recession, and economic projections for the 1990s. Alaska's economy is largely influenced by oil prices, since petroleum revenues make up 80% of the state government's unrestricted general fund revenues. Expansive state spending was responsible for most of Alaska's…

  11. Alaska Natives & the Land.

    ERIC Educational Resources Information Center

    Arnold, Robert D.; And Others

    Pursuant to the Native land claims within Alaska, this compilation of background data and interpretive materials relevant to a fair resolution of the Alaska Native problem seeks to record data and information on the Native peoples; the land and resources of Alaska and their uses by the people in the past and present; land ownership; and future…

  12. Alaska Women: A Databook.

    ERIC Educational Resources Information Center

    White, Karen; Baker, Barbara

    This data book uses survey and census information to record social and economic changes of the past three decades and their effects upon the role of Alaska women in society. Results show Alaska women comprise 47% of the state population, an increase of 9% since 1950. Marriage continues as the predominant living arrangement for Alaska women,…

  13. Textural, compositional, and sulfur isotope variations of sulfide minerals in the Red Dog Zn-Pb-Ag deposits, Brooks Range, Alaska: Implications for Ore Formation

    USGS Publications Warehouse

    Kelley, K.D.; Leach, D.L.; Johnson, C.A.; Clark, J.L.; Fayek, M.; Slack, J.F.; Anderson, V.M.; Ayuso, R.A.; Ridley, W.I.

    2004-01-01

    The Red Dog Zn-Pb deposits are hosted in organic-rich mudstone and shale of the Mississippian Kuna Formation. A complex mineralization history is defined by four sphalerite types or stages: (1) early brown sphalerite, (2) yellow-brown sphalerite, (3) red-brown sphalerite, and (4) late tan sphalerite. Stages 2 and 3 constitute the main ore-forming event and are volumetrically the most important. Sulfides in stages 1 and 2 were deposited with barite, whereas stage 3 largely replaces barite. Distinct chemical differences exist among the different stages of sphalerite. From early brown sphalerite to later yellow-brown sphalerite and red-brown sphalerite, Fe and Co content generally increase and Mn and Tl content generally decrease. Early brown sphalerite contains no more than 1.9 wt percent Fe and 63 ppm Co, with high Mn (up to 37 ppm) and Tl (126 ppm), whereas yellow-brown sphalerite and red-brown sphalerite contain high Fe (up to 7.3 wt %) and Co (up to 382 ppm), and low Mn (<27 ppm) and Tl (<37 ppm). Late tan sphalerite has distinctly lower Fe (< 0.9 wt %) and higher Tl (up to 355 ppm), Mn (up to 177 ppm), and Ge (426 ppm), relative to earlier sphalerite. Wide ranges in concentrations of Ag, Cu, Pb, and Sb characterize all sphalerite types, particularly yellow-brown sphalerite and red-brown sphalerite, and most likely reflect submicroscopic inclusions of galena, chalcopyrite and/or tetrahedrite in the sphalerite. In situ ion microprobe sulfur isotope analyses show a progression from extremely low ??34S values for stage 1 (as low as -37.20???) to much higher values for yellow-brown sphalerite (mean of 3.3???; n = 30) and red-brown sphalerite (mean of 3.4; n = 20). Late tan sphalerite is isotopically light (-16.4 to -27.2???). The textural, chem ical, and isotopic data indicate the following paragenesis: (1) deposition of early brown sphalerite with abundant barite, minor pyrite, and trace galena immediately beneath the sea floor in unconsolidated mud; (2) deposition

  14. Deep seismic structure and tectonics of northern Alaska: Crustal-scale duplexing with deformation extending into the upper mantle

    USGS Publications Warehouse

    Fuis, G.S.; Murphy, J.M.; Lutter, W.J.; Moore, T.E.; Bird, K.J.; Christensen, N.I.

    1997-01-01

    Seismic reflection and refraction and laboratory velocity data collected along a transect of northern Alaska (including the east edge of the Koyukuk basin, the Brooks Range, and the North Slope) yield a composite picture of the crustal and upper mantle structure of this Mesozoic and Cenozoic compressional orogen. The following observations are made: (1) Northern Alaska is underlain by nested tectonic wedges, most with northward vergence (i.e., with their tips pointed north). (2) High reflectivity throughout the crust above a basal decollement, which deepens southward from about 10 km depth beneath the northern front of the Brooks Range to about 30 km depth beneath the southern Brooks Range, is interpreted as structural complexity due to the presence of these tectonic wedges, or duplexes. (3) Low reflectivity throughout the crust below the decollement is interpreted as minimal deformation, which appears to involve chiefly bending of a relatively rigid plate consisting of the parautochthonous North Slope crust and a 10- to 15-km-thick section of mantle material. (4) This plate is interpreted as a southward verging tectonic wedge, with its tip in the lower crust or at the Moho beneath the southern Brooks Range. In this interpretation the middle and upper crust, or all of the crust, is detached in the southern Brooks Range by the tectonic wedge, or indentor: as a result, crust is uplifted and deformed above the wedge, and mantle is depressed and underthrust beneath this wedge. (5) Underthrusting has juxtaposed mantle of two different origins (and seismic velocities), giving rise to a prominent sub-Moho reflector. Copyright 1997 by the American Geophysical Union.

  15. Alaska volcanoes guidebook for teachers

    USGS Publications Warehouse

    Adleman, Jennifer N.

    2011-01-01

    Alaska’s volcanoes, like its abundant glaciers, charismatic wildlife, and wild expanses inspire and ignite scientific curiosity and generate an ever-growing source of questions for students in Alaska and throughout the world. Alaska is home to more than 140 volcanoes, which have been active over the last 2 million years. About 90 of these volcanoes have been active within the last 10,000 years and more than 50 of these have been active since about 1700. The volcanoes in Alaska make up well over three-quarters of volcanoes in the United States that have erupted in the last 200 years. In fact, Alaska’s volcanoes erupt so frequently that it is almost guaranteed that an Alaskan will experience a volcanic eruption in his or her lifetime, and it is likely they will experience more than one. It is hard to imagine a better place for students to explore active volcanism and to understand volcanic hazards, phenomena, and global impacts. Previously developed teachers’ guidebooks with an emphasis on the volcanoes in Hawaii Volcanoes National Park (Mattox, 1994) and Mount Rainier National Park in the Cascade Range (Driedger and others, 2005) provide place-based resources and activities for use in other volcanic regions in the United States. Along the lines of this tradition, this guidebook serves to provide locally relevant and useful resources and activities for the exploration of numerous and truly unique volcanic landscapes in Alaska. This guidebook provides supplemental teaching materials to be used by Alaskan students who will be inspired to become educated and prepared for inevitable future volcanic activity in Alaska. The lessons and activities in this guidebook are meant to supplement and enhance existing science content already being taught in grade levels 6–12. Correlations with Alaska State Science Standards and Grade Level Expectations adopted by the Alaska State Department of Education and Early Development (2006) for grades six through eleven are listed at

  16. Pn anisotropic tomography under the entire Tienshan orogenic belt

    NASA Astrophysics Data System (ADS)

    Zhou, Zhigang; Lei, Jianshe

    2015-11-01

    We present a new anisotropic tomography of the uppermost mantle under the Tienshan orogenic belt and surrounding regions using a number of Pn arrival-time data hand-picked from portable seismic stations and chosen from the Xinjiang provincial observation bulletins and the EHB datasets. Our results exhibit prominent lateral heterogeneities in the study region. Distinct low-velocity anomalies are visible under the tectonically active regions, such as the Tienshan orogenic belt and western Kunlun Mountains, whereas pronounced high-velocity anomalies are imaged beneath the stable blocks, such as the Kazakh shield, the Junggar, Tarim, Qaidam, and Turpan-Hami basins, and the Tajik depression. Most strong earthquakes (Ms > 7.0) are mainly distributed along the transition zone of high to low velocity anomalies, suggesting a possible correlation between the strong earthquakes and the upper mantle structure. The fast directions of Pn anisotropy beneath the Tienshan orogenic belt are generally parallel to its striking orientation, whereas those beneath Pamir show a northward arc-shaped distribution. The Pn fast-velocity directions on the boundaries of the Kazakh shield and the Tarim and Junngar basins are approximately perpendicular to the strike of the Tienshan orogenic belt. By integrating with previous findings, our results suggest that the Tarim and Kazakh lithospheric materials could have underthrusted beneath the Tienshan orogenic belt that leads to the hot mantle material upwelling under the Tienshan orogenic belt, which is attributable to the Indo-Asian collision. These dynamic processes could play important roles in the Tienshan mountain building.

  17. The Impact of Partial Melting in the Orogenic Cycle

    NASA Astrophysics Data System (ADS)

    Rey, P. F.; Teyssier, C.; Whitney, D. L.

    2010-12-01

    Open source, community driven numerical codes available at geodynamics.org allow geologists to model orogenic processes including partial melting and its consequences during orogenic cycles. Here we explore the role of partial melting during continental subduction and its impact on the evolution of orogenic plateaux and that of migmatite-cored metamorphic core complexes. Continental subduction and orogenic plateaux: Numerical experiments show that when continental slabs buried into the mantle meet their solidus, crustal melt is confined to the slab during its ascent and ponds at the Moho (Fig. 1a). The displaced overlying crust is extruded horizontally into the weak lower crust of the continent, resulting in Earth’s surface uplift to form an orogenic plateau, and Moho downward motion to accommodate the influx of material into the lower crust. This model suggests a link between continental subduction, melting and the build up of orogenic plateaux, and show that partial melting may be a significant process in exhumation of ultrahigh-pressure (UHP) rocks. Model results are consistent with the common association of UHP rocks and migmatite. Growth and destruction of orogenic plateaux: The lateral growth of orogenic plateaux is often attributed to the flow of the plateau weak partially melted lower crust into its foreland in some cases over a distance > 1500 km in 15 myr. Using pre-thickening temperatures compatible with Tibet’s uplift history, we show that mass redistribution processes are dynamically coupled, and that CFE velocities are limited to less than 1 cm.yr-1 (~150 km in 15 myr) by cooling and crystallization of the melted channel in the foreland and by any upward deviation into metamorphic domes of the melted channel by extension in the plateau (Fig. 1b). Gravitational collapse and metamorphic core complexes: Localization of extension in the upper crust triggers convergent flow in the partially molten deep crust channel. This convergent flow leads to the

  18. Hyperspectral surveying for mineral resources in Alaska

    USGS Publications Warehouse

    Kokaly, Raymond F.; Graham, Garth E.; Hoefen, Todd M.; Kelley, Karen D.; Johnson, Michaela R.; Hubbard, Bernard E.

    2016-07-07

    Alaska is a major producer of base and precious metals and has a high potential for additional undiscovered mineral resources. However, discovery is hindered by Alaska’s vast size, remoteness, and rugged terrain. New methods are needed to overcome these obstacles in order to fully evaluate Alaska’s geology and mineral resource potential. Hyperspectral surveying is one method that can be used to rapidly acquire data about the distributions of surficial materials, including different types of bedrock and ground cover. In 2014, the U.S. Geological Survey began the Alaska Hyperspectral Project to assess the applicability of this method in Alaska. The primary study area is a remote part of the eastern Alaska Range where porphyry deposits are exposed. In collaboration with the Alaska Division of Geological and Geophysical Surveys, the University of Alaska Fairbanks, and the National Park Service, the U.S. Geological Survey is collecting and analyzing hyperspectral data with the goals of enhancing geologic mapping and developing methods to identify and characterize mineral deposits elsewhere in Alaska.

  19. Spatially Concentrated Erosion Focuses Deformation Within the Himalayan Orogenic Wedge: Sutlej Valley, NW Himalaya, India

    NASA Astrophysics Data System (ADS)

    Thiede, R. C.; Arrowsmith, J.; Bookhagen, B.; McWilliams, M.; Sobel, E. R.; Strecker, M. R.

    2004-12-01

    Long-term erosion processes in the NW-Himalaya have not only shaped the distribution of topography and relief, but may also exert a regional control on the kinematic history of the Himalayan orogenic wedge. The topographic front of the orogenic wedge forms the southern margin of the High Himalaya and may be related to subsurface structures such as a crustal ramp or a blind thrust. Drastic along- and across-strike erosional gradients characterize the modern Himalaya and range from high-erosion regions along the southern High Himalayan front where monsoonal precipitation is able to penetrate far into the range, to low-erosion sectors across the moderately elevated Lesser Himalaya to the south and the high-elevation, arid sectors to the north. Published paleo-elevation estimates from the Thakkhola Graben (Nepal) suggest that by ~11 Ma the southern Tibetan Plateau and probably the High Himalaya had been uplifted to elevations comparable to the recent conditions. Thus, the presently observed pronounced erosional gradients have likely existed across the orogen since then. However, the cause of high rock-uplift and exhumation rates along distinct segments of the southern front of the High Himalaya are still a matter of debate. New apatite fission track (AFT) and 40Ar/39Ar data sampled along an orogen-perpendicular transect following the Sutlej Valley, approximately perpendicular to the Himalayan orogen, constrain the distribution patterns of rapid cooling related to rock uplift and exhumation. Combined with published thermochronologic data, this comprehensive AFT dataset from south of the High Himalaya mountain front to the interior of the Tethyan Himalaya allows us to derive a regional uplift and exhumation scenario. Our new 40Ar/39Ar ages ranging between 17 and 4 Ma reveal diachronous exhumation of two crystalline nappes (Higher and Lesser Himalayan crystalline) during Miocene-Pliocene time. In contrast, the AFT data ranging from 1.3 to 4.6 Ma indicate synchronous, fast

  20. Tularemia in Alaska, 1938 - 2010

    PubMed Central

    2011-01-01

    Tularemia is a serious, potentially life threatening zoonotic disease. The causative agent, Francisella tularensis, is ubiquitous in the Northern hemisphere, including Alaska, where it was first isolated from a rabbit tick (Haemophysalis leporis-palustris) in 1938. Since then, F. tularensis has been isolated from wildlife and humans throughout the state. Serologic surveys have found measurable antibodies with prevalence ranging from < 1% to 50% and 4% to 18% for selected populations of wildlife species and humans, respectively. We reviewed and summarized known literature on tularemia surveillance in Alaska and summarized the epidemiological information on human cases reported to public health officials. Additionally, available F. tularensis isolates from Alaska were analyzed using canonical SNPs and a multi-locus variable-number tandem repeats (VNTR) analysis (MLVA) system. The results show that both F. t. tularensis and F. t. holarctica are present in Alaska and that subtype A.I, the most virulent type, is responsible for most recently reported human clinical cases in the state. PMID:22099502

  1. Tularemia in Alaska, 1938 - 2010.

    PubMed

    Hansen, Cristina M; Vogler, Amy J; Keim, Paul; Wagner, David M; Hueffer, Karsten

    2011-01-01

    Tularemia is a serious, potentially life threatening zoonotic disease. The causative agent, Francisella tularensis, is ubiquitous in the Northern hemisphere, including Alaska, where it was first isolated from a rabbit tick (Haemophysalis leporis-palustris) in 1938. Since then, F. tularensis has been isolated from wildlife and humans throughout the state. Serologic surveys have found measurable antibodies with prevalence ranging from < 1% to 50% and 4% to 18% for selected populations of wildlife species and humans, respectively. We reviewed and summarized known literature on tularemia surveillance in Alaska and summarized the epidemiological information on human cases reported to public health officials. Additionally, available F. tularensis isolates from Alaska were analyzed using canonical SNPs and a multi-locus variable-number tandem repeats (VNTR) analysis (MLVA) system. The results show that both F. t. tularensis and F. t. holarctica are present in Alaska and that subtype A.I, the most virulent type, is responsible for most recently reported human clinical cases in the state. PMID:22099502

  2. The role of thrust faulting in the formation of the eastern Alaska Range: Thermochronological constraints from the Susitna Glacier Thrust Fault region of the intracontinental strike-slip Denali Fault system

    NASA Astrophysics Data System (ADS)

    Riccio, Steven J.; Fitzgerald, Paul G.; Benowitz, Jeff A.; Roeske, Sarah M.

    2014-11-01

    Horizontal-slip along restraining bends of strike-slip faults is often partitioned into a vertical component via splay faults. The active Susitna Glacier Thrust Fault (SGTF), as shown by its initiation of the 2002 M7.9 Denali Fault earthquake, lies south of, and intersects the dextral strike-slip Denali Fault. Geochronology and thermochronology data from samples across the SGTF constrain the region's tectonic history and the role of thrusting in the formation of the eastern Alaska Range south of the Denali fault. U-Pb zircon ages indicate intrusion of plutons in the footwall (~57 Ma) and hanging wall (~98 Ma). These U-Pb zircon ages correlate to those from the Ruby Batholith/Kluane Terrane ~400 km east along the Denali Fault, supporting geologic correlations and hence constraints on long-term slip rates. 40Ar/39Ar mica and K-feldspar data from footwall and hanging wall samples (~54 to ~46 Ma) reflect cooling following magmatism and/or regional Eocene metamorphism related to ridge subduction. Combined with apatite fission track data (ages 43-28 Ma) and thermal models, both sides of the SGTF acted as a coherent block during the Eocene and early Oligocene. Contrasting apatite (U-Th)/He ages across the Susitna Glacier (~25 Ma footwall, ~15 Ma hanging wall) suggest initiation of faulting during the middle Miocene. Episodic cooling and exhumation is related to thrusting on known or hypothesized faults that progressively activate due to varying partition of strain along the Denali Fault associated with changing kinematics and plate interaction (Yakutat microplate collision, flat-slab subduction and relative plate motion change) at the southern Alaskan plate margin.

  3. Comparison of Arctic clouds between European Center for Medium-Range Weather Forecasts simulations and Atmospheric Radiation Measurement Climate Research Facility long-term observations at the North Slope of Alaska Barrow site

    NASA Astrophysics Data System (ADS)

    Zhao, Ming; Wang, Zhien

    2010-12-01

    This study evaluated the European Center for Medium-Range Weather Forecasts (ECMWF) model-simulated clouds and boundary layer (BL) properties based upon Atmospheric Radiation Measurement Climate Research Facility observations at the North Slope of Alaska site during 1999-2007. The ECMWF model-simulated near-surface humidity had seasonal dependent biases as large as 20%, while also experiencing difficulty representing BL temperature inversion height and strength during the transition seasons. Although the ECMWF model captured the seasonal variation of surface heat fluxes, it had sensible heat flux biases over 20 W m-2 in most of the cold months. Furthermore, even though the model captured the general seasonal variations of low-level cloud fraction (LCF) and liquid water path (LWP), it still overestimated the LCF by 20% or more and underestimated the LWP over 50% in the cold season. On average, the ECMWF model underestimated LWP by ˜30 g m-2 but more accurately predicted ice water path for BL clouds. For BL mixed-phase clouds, the model predicted water-ice mass partition was significantly lower than the observations, largely due to the temperature dependence of water-ice mass partition used in the model. The ECMWF model captured the general response of cloud fraction and LWP on large-scale vertical motion changes but overpredicted the magnitude of the difference, especially for LWP. The new cloud and BL schemes of the ECMWF model that were implemented after 2003 only resulted in minor improvements in BL cloud simulations in summer. These results indicate that significant improvements in cold season BL and mixed-phase cloud processes in the model are needed.

  4. The Capricorn Orogen Passive source Array (COPA) in Western Australia

    NASA Astrophysics Data System (ADS)

    Gessner, K.; Yuan, H.; Murdie, R.; Dentith, M. C.; Johnson, S.; Brett, J.

    2015-12-01

    COPA is the passive source component of a multi-method geophysical program aimed at assessing the mineral deposits potential of the Proterozoic Capricorn Orogen. Previous results from the active source surveys, receiver functions and magnetotelluric studies show reworked orogenic crust in the orogen that contrasts with more simple crust in the neighbouring Archean cratons, suggesting progressive and punctuated collisional processes during the final amalgamation of the Western Australian craton. Previous seismic studies are all based on line deployment or single station analyses; therefore it is essential to develop 3D seismic images to test whether these observations are representative for the whole orogen. With a careful design that takes advantage of previous passive source surveys, the current long-term and short-term deployments span an area of approximately 500 x 500 km. The 36-month total deployment can guarantee enough data recording for 3D structure imaging using body wave tomography, ambient noise surface wave tomography and P- and S-wave receiver function Common Conversion Point (CCP) stacking techniques. A successive instrument loan from the ANSIR national instrument pool, provided 34 broadband seismometers that have been deployed in the western half of the orogen since March 2014. We expect approximately 40-km lateral resolution near the surface for the techniques we propose, which due to low frequency nature of earthquake waves will degrade to about 100 km near the base of the cratonic lithosphere, which is expected at depths between 200 to 250 km. Preliminary results from the first half of the COPA deployment will be presented in the light of the hypotheses that 1) distinct crustal blocks can be detected continuously throughout the orogen (using ambient noise/body wave tomography); 2) distinct lithologies are present in the crust and upper mantle across the orogen (using receiver function CCP images); and 3) crustal and lithosphere deformation along

  5. Curved orogen and syntaxes formation during subduction and collision

    NASA Astrophysics Data System (ADS)

    Bajolet, F.; Replumaz, A.; Faccenna, C.; Lainé, R.

    2012-04-01

    The sustained convergence between India and Asia with successive stages of oceanic subduction, continental subduction and continental collision has lead to the formation of the Tibetan plateau while the Himalayan orogenic front acquired an arcuate shape convex toward the South. The Indian plate is bounded by north-south strike-slip faults, which accommodate a large indentation of Asia, between two oceanic subductions, beneath Makran to the west, beneath Indonesia to the east. Two syntaxes formed at both east and west termination of the Himalayan orogenic front at the transition between Indian and Asian plates. In order to better understand this particular configuration, we performed analog experiments at the Laboratory of Experimental Tectonics of Roma TRE to simulate, at the scale of the mantle - lithosphere system, the mechanics of the indentation process. The configuration is set to drive the India indenter towards the Asian continent with a motor-controlled-piston, to simulate far field stresses necessary for indentation. In particular, we test (1) which geometry and rheological parameters favor arcuate orogen and syntaxes formation, (2) what are the consequences on the topography of both the orogenic front and the plateau, and (3) how they relate with the subduction/collision dynamics. The setup is composed of a subducting and an overriding plate made of visco-elastic silicone putty, floating on low-viscosity syrup simulating the asthenosphere. The subducting plate simulates an oceanic lithosphere followed by a continental indenter (analog for the Indian craton) flanked or not by oceans (analog for Makran and Indonesian domains), while the upper continental plate simulates the Tibetan plateau. Results show that the curvature of the orogen and syntaxes' formation are primarily controlled by the strength and gravitational potential energy of the upper plate, and the shape of the subducting plate. A relatively strong upper plate flanked by oceans leads to a

  6. Proterozoic orogens in southern Peninsular India: Contiguities and complexities

    NASA Astrophysics Data System (ADS)

    Chetty, T. R. K.; Santosh, M.

    2013-12-01

    The Precambrian terranes of southern Peninsular India have been central to discussions on the history of formation and breakup of supercontinents. Of particular interest are the Proterozoic high grade metamorphic orogens at the southern and eastern margins of the Indian shield, skirting the 3.4 Ga Dharwar craton which not only preserve important records of lower crustal processes and lithospheric geodynamics, but also carry imprints of the tectonic framework related to the assembly of the major Neoproterozoic supercontinents - Rodinia and Gondwana. These Proterozoic orogens are described as Southern Granulite Terrane (SGT) in the southern tip and the Eastern Ghats Mobile Belt (EGMB) in the eastern domains of the peninsula. The contiguity of these orogens is broken for a distance of ˜400 km and disappears in the Bay of Bengal. These orogens expose windows of middle to lower crust with well-preserved rock records displaying multiple tectonothermal events and multiphase exhumation paths.Recent studies in these orogens have led to the recognition of discrete crustal blocks or terranes separated by major shear zone systems, some of which represent collisional sutures. The SGT and EGMB carry several important features such as fold-thrust tectonics, regional granulite facies metamorphism of up to ultrahigh-temperature conditions in some cases, multiple P-T paths, development of lithospheric shear zones, emplacement of ophiolites, presence of alkaline and anorthositic complexes, development of crustal-scale "flower structures", transpressional strains, and reactivation tectonics. A heterogeneous distribution of different metamorphic and magmatic assemblages with distinct spatial and temporal strain variations in shaping the fabric elements in different blocks is identified. Both EGMB and SGT share a common transpressional deformation history during the latest Neoproterozoic characterized by the steepening of the initial low angle crustal scale structures leading to a

  7. Paleozoic tectonic history of the Arctic basin north of Alaska

    USGS Publications Warehouse

    Churkin, M.

    1969-01-01

    The geology of the margin of the Canada Basin, together with geophysical data, leads me to reject the continental subsidence theory for the origin of the deep Canada Basin. Instead, the Canada Basin is, I believe, a true and probably very ancient ocean basin floored by oceanic crust and rimmed by an early Paleozoic geosynclinal belt. In the Upper Devonian, uplifts in this circumarctic geosyncline, accompanied by granitic intrusion, produced a wedge of coarse clastic sediments (exogeosyncline) that spread southward onto adjoining areas of Alaska, Canada, and Siberia. In both northern Alaska and the Canadian Arctic Islands, thick sequences of upper Paleozoic and younger strata were deposited unconformably on the rocks of the early Paleozoic geosyncline, showing a similarity in tectonic history between the areas. The Paleozoic history of the southern rim of the Canada Basin resembles that of other mobile belts bordering North America. The movement of the floor of the Arctic Ocean against the continental crust of North America (sea-floor spreading) would provide a mechanism to account for the long history of orogenic activity along the basin margin. The sharp bend in the structural elements of southern Alaska (the Alaska orocline) has been cited as evidence of clockwise rotation of the Arctic Islands of Canada from Alaska and the Soviet Arctic to their present position during the Mesozoic. However, the geologic and geophysical evidence available indicates that the Arctic basin has a longer history, extending into the Paleozoic, and that this bend in Alaskan structures may have been largely caused by spreading of the Pacific sea floor against the continental margin in the Gulf of Alaska.

  8. Accretion tectonics and crustal structure in Alaska

    USGS Publications Warehouse

    Coney, P.J.; Jones, D.L.

    1985-01-01

    The entire width of the North American Cordillera in Alaska is made up of "suspect terranes". Pre-Late Cretaceous paleogeography is poorly constrained and the ultimate origins of the many fragments which make up the state are unclear. The Prince William and Chugach terranes accreted since Late Cretaceous time and represent the collapse of much of the northeast Pacific Ocean swept into what today is southern Alaska. Greater Wrangellia, a composite terrane now dispersed into fragments scattered from Idaho to southern Alaska, apparently accreted into Alaska in Late Cretaceous time crushing an enormous deep-marine flysch basin on its inboard side. Most of interior eastern Alaska is the Yukon Tanana terrane, a very large entirely fault-bounded metamorphic-plutonic assemblage covering thousands of square kilometers in Canada as well as Alaska. The original stratigraphy and relationship to North America of the Yukon-Tanana terrane are both obscure. A collapsed Mesozoic flysch basin, similar to the one inboard of Wrangellia, lies along the northern margin. Much of Arctic Alaska was apparently a vast expanse of upper Paleozoic to Early Mesozoic deep marine sediments and mafic volcanic and plutonic rocks now scattered widely as large telescoped sheets and Klippen thrust over the Ruby geanticline and the Brooks Range, and probably underlying the Yukon-Koyukuk basin and the Yukon flats. The Brooks Range itself is a stack of north vergent nappes, the telescoping of which began in Early Cretaceous time. Despite compelling evidence for thousands of kilometers of relative displacement between the accreted terranes, and large amounts of telescoping, translation, and rotation since accretion, the resulting new continental crust added to North America in Alaska carries few obvious signatures that allow application of currently popular simple plate tectonic models. Intraplate telescoping and strike-slip translations, delamination at mid-crustal levels, and large-scale lithospheric

  9. "Taconic" arc magmatism in the central Brooks Range, Alaska: New U-Pb zircon geochronology and Hf isotopic data from the lower Paleozoic Apoon assemblage of the Doonerak fenster

    NASA Astrophysics Data System (ADS)

    Strauss, J. V.; Hoiland, C. W.; Ward, W.; Johnson, B.; McClelland, W.

    2015-12-01

    The Doonerak fenster in the central Brooks Range, AK, exposes an important package of early Paleozoic volcanic and sedimentary rocks called the Apoon assemblage, which are generally interpreted as para-autochthonous basement to the Mesozoic-Cenozoic Brookian fold-thrust belt. Recognition in the 1970's of a major pre-Mississippian unconformity within the window led to correlations between Doonerak and the North Slope (sub-) terrane of the Arctic Alaska Chukotka microplate (AACM); however, the presence of arc-affinity volcanism and the apparent lack of pre-Mississippian deformation in the Apoon assemblage makes this link tenuous and complicates Paleozoic tectonic reconstructions of the AACM. Previous age constraints on the Apoon assemblage are limited to a handful of Middle Cambrian-Silurian paleontological collections and five K-Ar and 40Ar/39Ar hornblende ages from mafic dikes ranging from ~380-520 Ma. We conducted U-Pb geochronologic and Hf isotopic analyses on igneous and sedimentary zircon from the Apoon assemblage to test Paleozoic links with the North Slope and to assess the tectonic and paleogeographic setting of the Doonerak region. U-Pb analyses on detrital zircon from Apoon rocks yield a spectrum of unimodal and polymodal age populations, including prominent age groups of ca. 420-490, 960-1250, 1380­-1500, 1750-1945, and 2650-2830 Ma. Hf isotopic data from the ca. 410-490 Ma age population are generally juvenile (~7-10 ɛHf), implying a distinct lack of crustal assimilation during Ordovician-Silurian Doonerak arc magmatism despite its proximity to a cratonic source terrane as indicated by an abundance of Archean and Proterozoic zircon in the interbedded siliciclastic strata. These data are in stark contrast to geochronological data from the non-Laurentian portions of the AACM, highlighting a prominent tectonic boundary between Laurentian- and Baltic-affinity rocks at the Doonerak window and implying a link to "Taconic"-age arc magmatism documented along

  10. Glaciers of North America - Glaciers of Alaska

    USGS Publications Warehouse

    Molnia, Bruce F.

    2008-01-01

    Glaciers cover about 75,000 km2 of Alaska, about 5 percent of the State. The glaciers are situated on 11 mountain ranges, 1 large island, an island chain, and 1 archipelago and range in elevation from more than 6,000 m to below sea level. Alaska's glaciers extend geographically from the far southeast at lat 55 deg 19'N., long 130 deg 05'W., about 100 kilometers east of Ketchikan, to the far southwest at Kiska Island at lat 52 deg 05'N., long 177 deg 35'E., in the Aleutian Islands, and as far north as lat 69 deg 20'N., long 143 deg 45'W., in the Brooks Range. During the 'Little Ice Age', Alaska's glaciers expanded significantly. The total area and volume of glaciers in Alaska continue to decrease, as they have been doing since the 18th century. Of the 153 1:250,000-scale topographic maps that cover the State of Alaska, 63 sheets show glaciers. Although the number of extant glaciers has never been systematically counted and is thus unknown, the total probably is greater than 100,000. Only about 600 glaciers (about 1 percent) have been officially named by the U.S. Board on Geographic Names (BGN). There are about 60 active and former tidewater glaciers in Alaska. Within the glacierized mountain ranges of southeastern Alaska and western Canada, 205 glaciers (75 percent in Alaska) have a history of surging. In the same region, at least 53 present and 7 former large ice-dammed lakes have produced jokulhlaups (glacier-outburst floods). Ice-capped volcanoes on mainland Alaska and in the Aleutian Islands have a potential for jokulhlaups caused by subglacier volcanic and geothermal activity. Because of the size of the area covered by glaciers and the lack of large-scale maps of the glacierized areas, satellite imagery and other satellite remote-sensing data are the only practical means of monitoring regional changes in the area and volume of Alaska's glaciers in response to short- and long-term changes in the maritime and continental climates of the State. A review of the

  11. Tectonic and kinematics of curved orogenic systems: insights from AMS analysis and paleomagnetism

    NASA Astrophysics Data System (ADS)

    Cifelli, Francesca; Mattei, Massimo

    2016-04-01

    During the past few years, paleomagnetism has been considered a unique tool for constraining kinematic models of curved orogenic systems, because of its great potential in quantifying vertical axis rotations and in discriminating between primary and secondary (orocline s.l.) arcs. In fact, based on the spatio-temporal relationships between deformation and vertical axis rotation, curved orogens can be subdivided as primary or secondary (oroclines s.l.), if they formed respectively in a self-similar manner without undergoing important variations in their original curved shape or if their curvature in map-view is the result of a bending about a vertical axis of rotation. In addition to the kinematics of the arc and the timing of its curvature, a crucial factor for understanding the origin of belts curvature is the knowledge of the geodynamic process governing arc formation. In this context, the detailed reconstruction of the rotational history is mainly based on paleomagnetic and structural analyses (fold axes, kinematic indicators), which include the magnetic fabric. In fact, in curved fold and thrust belts, assuming that the magnetic lineation is tectonically originated and formed during layer-parallel shortening (LPS) before vertical axis rotations, the orientation of the magnetic lineation often strictly follows the curvature of the orogeny. This assumption represents a fundamental prerequisite to fully understand the origin of orogenic arcs and to unravel the geodynamic processes responsible for their curvature. We present two case studies: the central Mediterranean arcs and the Alborz Mts in Iran. The Mediterranean area has represented an attractive region to apply paleomagnetic analysis, as it shows a large number of narrow arcs, whose present-day shape has been driven by the space-time evolution of the Mediterranean subduction system, which define a irregular and rather diffuse plate boundary. The Alborz Mts. form a sinuous range over 1,200 km long, defining

  12. Alaska Volcano Observatory

    USGS Publications Warehouse

    Venezky, Dina Y.; Murray, Tom; Read, Cyrus

    2008-01-01

    Steam plume from the 2006 eruption of Augustine volcano in Cook Inlet, Alaska. Explosive ash-producing eruptions from Alaska's 40+ historically active volcanoes pose hazards to aviation, including commercial aircraft flying the busy North Pacific routes between North America and Asia. The Alaska Volcano Observatory (AVO) monitors these volcanoes to provide forecasts of eruptive activity. AVO is a joint program of the U.S. Geological Survey (USGS), the Geophysical Institute of the University of Alaska Fairbanks (UAFGI), and the State of Alaska Division of Geological and Geophysical Surveys (ADGGS). AVO is one of five USGS Volcano Hazards Program observatories that monitor U.S. volcanoes for science and public safety. Learn more about Augustine volcano and AVO at http://www.avo.alaska.edu.

  13. Exhumation of the southern Pyrenean fold-thrust belt (Spain) from orogenic growth to decay

    NASA Astrophysics Data System (ADS)

    Rushlow, Caitlin R.; Barnes, Jason B.; Ehlers, Todd A.; Vergés, Jaume

    2013-07-01

    The deformation and exhumation history of an orogen reflects the interactions between tectonic and surface processes. We investigate orogenic wedge deformation, erosion, and sedimentation in the Pyrenees by (a) quantifying the spatiotemporal patterns of exhumation across the southern fold-thrust belt (FTB) with bedrock apatite fission track (AFT) thermochronology and (b) comparing the results with existing deformation, exhumation, and sedimentation chronologies. Eighteen new samples record exhumation during and after orogenesis between 90 and 10 Ma. Rocks from the range core (Axial Zone) record rapid exhumation that progresses east to west and north to south, consistent with patterns of tectonically driven uplift. Synorogenic sediments shed into piggyback basins on the southern fold-thrust belt during mountain building retain a detrital exhumation signal from the Axial Zone. In contrast, samples from other structural positions record exhumation of the thin-skinned Pyrenean thrust sheets, suggesting sediment burial and heating of sufficient magnitudes to reset the AFT system (>~3 km). In some locations, exhumation of these fold-thrust structures is likely an erosional response to thrust-driven rock uplift. We identify an exhumation phase ~25-20 Ma that occurs along the central and eastern Spanish Pyrenees at the boundary between thick- and thin-skinned portions of the wedge. We suggest that this distributed exhumation event records (a) a taper response in the southern orogenic wedge to sediment loading and/or (b) a shift to wetter, stormier climate conditions following convergence-driven uplift and full topographic development. A final exhumation phase between ~20 and 10 Ma may record the excavation of the southern fold-thrust system following base level lowering in the Ebro Basin.

  14. Erosion and Sediment Transport Across Pronounced Topographic and Climatic Gradients in the Himalayan Orogen

    NASA Astrophysics Data System (ADS)

    Strecker, M. R.; Bookhagen, B.

    2014-12-01

    The interaction between the NW-directed trajectories of moisture transport associated with the Indian Summer Monsoon circulation and the high topography of the Himalayan orogen results in one of the most efficient orographic barriers on Earth. The steep topographic gradients, the impact of focused rainfall along the southern flank of the range, and northward shifts of rainfall during frequent intensified Indian Summer Monsoons are responsible for an efficient erosional regime, with some of the highest known erosion rates. The spatiotemporal correlation between various topographic, tectonic, climatic, and exhumational phenomena in this region has resulted in the formulation of models of possible long-term erosional and tectonic feedback processes that drive the lateral expansion and vertical growth of the mountain belt. However, despite an increase in thermochronologic, cosmogenic radionuclide, and sedimentological datasets that help explain the underlying mechanisms, the true nature of these relationships is still unclear and controversies particularly exist concerning the importance of the different forcing factors that drive exhumation and, ultimately, deformation. Here, we synthesize and assess these controversies with observations from studies conducted perpendicular to and along strike of the orogen, and combine them with our new basin-wide erosion-rate data from the Sutlej Valley in the NW Himalaya. In our regional comparison we highlight the importance of large river systems and climate-controlled aspects of weathering concerning fluvial mass distribution as there appear to be positive feedbacks between tectonics and surface processes. In contrast, observations from smaller catchments along the orogenic front suggest a negative correlation. Similar to other environments with steep topographic and climatic gradients, our observations from the Sutlej catchments emphasize that erosional processes in the Himalayan realm are most efficient in geomorphic

  15. Structural inversion of the Tamworth Belt: Insights into the development of orogenic curvature in the southern New England Orogen, Australia

    NASA Astrophysics Data System (ADS)

    Phillips, G.; Robinson, J.; Glen, R.; Roberts, J.

    2016-05-01

    The middle to late Permian Hunter Bowen Event is credited with the development of orogenic curvature in the southern New England Orogen, yet contention surrounds the structural dynamics responsible for the development of this curvature. Debate is largely centred on the roles of orogen parallel strike-slip and orogen normal extension and contraction to explain the development of curvature. To evaluate the dynamic history of the Hunter Bowen Event, we present new kinematic reconstructions of the Tamworth Belt. The Tamworth Belt formed as a Carboniferous forearc basin and was subsequently inverted during the Hunter Bowen Event. Kinematic reconstructions of the Tamworth Belt are based on new maps and cross-sections built from a synthesis of best-available mapping, chronostratigraphic data and new interpretations of depth-converted seismic data. The following conclusions are made from our study: (i) the Hunter Bowen Event was dominantly driven by margin normal contraction (east-west shortening; present-day coordinates), and; (ii) variations in structural style along the strike of the Tamworth Belt can be explained by orthogonal vs. oblique inversion, which reflects the angular relationship between the principal shortening vector and continental-arc margin. Given these conclusions, we suggest that curvature around the controversial Manning Bend was influenced by the presence of primary curvature in the continental margin, and that the Hastings Block was translated along a sinistral strike-slip fault system that formed along this oblique (with respect to the regional east-west extension and convergence direction) part of the margin. Given the available temporal data, the translation of the Hastings Block took place in the Early Permian (Asselian) and therefore preceded the Hunter Bowen Event. Accordingly, we suggest that the Hunter Bowen Event was dominantly associated with enhancing curvature that was either primary in origin, or associated with fault block translation

  16. Alaska's renewable energy potential.

    SciTech Connect

    Not Available

    2009-02-01

    This paper delivers a brief survey of renewable energy technologies applicable to Alaska's climate, latitude, geography, and geology. We first identify Alaska's natural renewable energy resources and which renewable energy technologies would be most productive. e survey the current state of renewable energy technologies and research efforts within the U.S. and, where appropriate, internationally. We also present information on the current state of Alaska's renewable energy assets, incentives, and commercial enterprises. Finally, we escribe places where research efforts at Sandia National Laboratories could assist the state of Alaska with its renewable energy technology investment efforts.

  17. Extension of the Mid- to Lower Crust with Orogenic Inheritance: Examples from the Death Valley Region (Western US), and the Mauleon Basin (Southwestern France).

    NASA Astrophysics Data System (ADS)

    Lima, R. D.; Hayman, N. W.; Kelly, E. D.; Lavier, L. L.

    2015-12-01

    Continental margins exhibit a range of widths and symmetries defined by the strain patterns that arise during extension and rifting. An important pattern in this respect is the early localization of extension into necking zones. The rheology of the lower crust plays a large role in this localization, and can be affected by inherited orogenic structures, fabrics, and mineral assemblages. Here, we further evaluate the role of orogenic fabrics in continental extension using microstructural observations and thermodynamic modeling of geological sections exposed in the Funeral and Black Mountains of the Death Valley region, California, and from the Mauleon Basin, France. The Death Valley region sits within the Basin-and-Range region of broadly distributed Cenozoic extension, over a relatively flat and deep moho. In contrast, in the Mauleon basin, Cretaceous extension accommodated mantle exhumation, and was strongly localized in older Hercynian orogenic crust. In both areas, mid- to lower crustal rocks are characterized by inherited migmatitic fabrics overprinted by zones of localized, extensional fabrics. Mineral assemblages that formed over a P-T cooling path define the fabrics in each field area. The high-temperature fabrics record decompression-melting due to late- to post-orogenic collapse. Yet, the two field areas show contrasting retrograde assemblages, which are hypothesized to have resulted from changes in the local effective bulk composition produced by differences in melt segregation. At subsequent extensional stages, mid- to lower crustal deformation resulted in the transposition of the inherited post-orogenic fabrics, documented with quartz fabric analysis (including EBSD). The two contrasting regions show how the rheology of inherited orogenic lower crust responds to differences in melt-segregation and metamorphic histories, potentially controlling margin structural evolution.

  18. Detrital Zircon U-Pb Age Populations in Time and Space in the Arctic Alaska Terrane

    NASA Astrophysics Data System (ADS)

    Moore, T. E.

    2010-12-01

    The Arctic Alaska Terrane (ATT) occupies the only margin of the Ameriasia Basin whose origin and position since Paleozoic time is incompletely known. To better understand its tectonic history, detrital zircon (DZ) U-Pb ages from about 75 samples of clastic strata were obtained from representative parts of the ATT in northern Alaska. The oldest known strata of the AAT are Neoproterozoic clastic rocks exposed in the northeastern Brooks Range. DZ dating of these rocks show that they contain abundant ~1.8 Ga zircons and subordinate populations that indicate derivation from the northwest part of Laurentia. Upper Neoproterozoic strata in the Brooks Range, in contrast, contain populations dominated by ~600 Ma zircons. The latter ages are similar to those in parts of the ATT outside of northern Alaska, including the Seward Peninsula, Chukotka, and Wrangel Island that are thought to have been derived from the Timanian orogen of northern Baltica. Similar DZ populations have also been obtained from Silurian sandstones of the Lisburne Peninsula, suggesting that much of the western and southern parts of AAT may have formed in or near northern Baltica. A third group of DZ ages were found in deformed clastic rocks that were deposited across large parts of the North Slope in the Silurian and/or Devonian and are also present in parautochthonous settings in the Brooks Range. These rocks typically are dominated by DZ ages of 390-470 Ma, and sometimes contain subordinate non-Laurentian populations of ~1.5 Ga. These DZ ages, the underlying rocks of probable Baltic and Laurentian affinity, and evidence of significant deformation indicate that the ATT may have been constructed by Caledonian tectonism in the Silurian and Devonian. Following Devonian deformation, Mississippian to Triassic platform strata of the Ellesmerian Sequence were deposited on a regional unconformity. DZ ages from these rocks appear to reflect the compositions of the sub-unconformity units and indicate that Timanian

  19. A unified model for gold mineralisation in accretionary orogens and implications for regional-scale exploration targeting methods

    NASA Astrophysics Data System (ADS)

    Hronsky, Jon M. A.; Groves, David I.; Loucks, Robert R.; Begg, Graham C.

    2012-04-01

    Accretionary orogens are the sites of long-lived convergent margin tectonics, both compressional and extensional. They are also the hosts to the majority of the world's important gold deposits. A very diverse range of deposit types occurs within accretionary orogens, commonly in close proximity in space and time to each other. These include porphyry and associated high-sulphidation Au-Cu-Ag deposits, classic low-sulphidation Au-Ag deposits, low-sulphidation Au deposits centred on alkalic intrusive complexes, Carlin-type Au deposits, Au-rich volcanic-hosted massive sulphide deposits, orogenic Au deposits, intrusion-related Au deposits and iron oxide Cu-Au deposits. Empirical patterns of spatial distribution of these deposits suggest there must be fundamental generic controls on gold metallogeny. Various lines of evidence lead to the proposal that the underlying key generic factor controlling accretionary orogen gold metallogeny is regional-scale, long-term, pre- and syn-subduction heterogeneous fertilisation of the lithospheric mantle that becomes a source of mineralisation-associated arc magma or hydrothermal fluid components. This process provides a gold-enriched reservoir that can be accessed later in a diverse range of tectonomagmatic settings. Based on this concept, a unified model is proposed in which the formation of a major gold deposit of any type requires the conjunction in time and space of three essential factors: a fertile upper-mantle source region, a favourable transient remobilisation event, and favourable lithospheric-scale plumbing structure. This framework provides the basis for a practical regional-scale targeting methodology that is applicable to data-poor regions.

  20. Taconic plate kinematics as revealed by foredeep stratigraphy, Appalachian Orogen

    USGS Publications Warehouse

    Bradley, D.C.

    1989-01-01

    Destruction of the Ordovician passive margin of eastern North America is recorded by an upward deepening succession of carbonates, shales, and flysch. Shelf drowning occurred first at the northern end of the orogen in Newfoundland, then at the southern end of the orogen in Georgia, and finally in Quebec. Diachronism is attributed to oblique collision between an irregular passive margin, that had a deep embayment in Quebec, and at least one east dipping subduction complex. The rate of plate convergence during collision is estimated at 1 to 2 cm/yr, and the minimum width of the ocean that closed is estimated at 500 to 900 km. The drowning isochron map provides a new basis for estimating tectonic transport distances of four of these allochthons (about 165 to 450 km), results not readily obtained by conventional structural analysis. -Author

  1. Alaska Library Directory, 1996.

    ERIC Educational Resources Information Center

    Jennings, Mary, Ed.

    This directory of Alaska's Libraries lists: members of the Alaska Library Association (AkLA) Executive Council and Committee Chairs; State Board of Education members; members of the Governor's Advisory Council on Libraries; school, academic and public libraries and their addresses, phone and fax numbers, and contact persons; personal,…

  2. Renewable Energy in Alaska

    SciTech Connect

    Not Available

    2013-03-01

    This report examines the opportunities, challenges, and costs associated with renewable energy implementation in Alaska and provides strategies that position Alaska's accumulating knowledge in renewable energy development for export to the rapidly growing energy/electric markets of the developing world.

  3. Alaska geothermal bibliography

    SciTech Connect

    Liss, S.A.; Motyka, R.J.; Nye, C.J.

    1987-05-01

    The Alaska geothermal bibliography lists all publications, through 1986, that discuss any facet of geothermal energy in Alaska. In addition, selected publications about geology, geophysics, hydrology, volcanology, etc., which discuss areas where geothermal resources are located are included, though the geothermal resource itself may not be mentioned. The bibliography contains 748 entries.

  4. Paleozoic tectonics of the Ouachita Orogen through Nd isotopes

    SciTech Connect

    Gleason, J.D.; Patchett, P.J.; Dickinson, W.R.; Ruiz, J. . Dept. of Geosciences)

    1992-01-01

    A combined isotopic and trace-element study of the Late Paleozoic Ouachita Orogenic belt has the following goals: (1) define changing provenance of Ouachita sedimentary systems throughout the Paleozoic; (2) constrain sources feeding into the Ouachita flysch trough during the Late Paleozoic; (3) isolate the geochemical signature of proposed colliding terranes to the south; (4) build a data base to compare with possible Ouachita System equivalents in Mexico. The ultimate aim is to constrain the tectonic setting of the southern margin of North America during the Paleozoic, with particular emphasis on collisional events leading to the final suturing of Pangea. Nd isotopic data identify 3 distinct groups: (1) Ordovician passive margin sequence; (2) Carboniferous proto-flysch (Stanley Fm.), main flysch (Jackfork and Atoka Fms.) and molasse (foreland Atoka Fm.); (3) Mississippian ash-flow tuffs. The authors interpret the Ordovician signature to be essentially all craton-derived, whereas the Carboniferous signature reflects mixed sources from the craton plus orogenic sources to the east and possibly the south, including the evolving Appalachian Orogen. The proposed southern source is revealed by the tuffs to be too old and evolved to be a juvenile island arc terrane. They interpret the tuffs to have been erupted in a continental margin arc-type setting. Surprisingly, the foreland molasse sequence is indistinguishable from the main trough flysch sequence, suggesting the Ouachita trough and the craton were both inundated with sediment of a single homogenized isotopic signature during the Late Carboniferous. The possibility that Carboniferous-type sedimentary dispersal patterns began as early as the Silurian has important implications for the tectonics and paleogeography of the evolving Appalachian-Ouachita Orogenic System.

  5. Jurassic sedimentary basins in the Central Asian orogenic belt

    SciTech Connect

    Bebeshev, I.I.

    1995-05-01

    The principal stages of development of Jurassic sedimentary basins (from their origin to the end of their existence) in the Central Asian orogenic belt are considered. The interrelations of the basins with the surrounding paleorises are investigated. Paleogeographic maps are compiled representing the evolution of paleolandscapes and revealing their interrelations in space and time for each stage. Areas with the highest prospects for coal are found.

  6. Environmental geochemical study of Red Mountain--an undisturbed volcanogenic massive sulfide deposit in the Bonnifield District, Alaska range, east-central Alaska: Chapter I in Recent U.S. Geological Survey studies in the Tintina Gold Province, Alaska, United States, and Yukon, Canada--results of a 5-year project

    USGS Publications Warehouse

    Eppinger, Robert G.; Briggs, Paul H.; Dusel-Bacon, Cynthia; Giles, Stuart A.; Gough, Larry P.; Hammarstrom, Jane M.; Hubbard, Bernard E.

    2007-01-01

    Water samples with the lowest pH values, highest specific conductances, and highest major- and trace-element concentrations are from springs and streams within the quartz-sericite-pyrite alteration zone. Aluminum, As, Cd, Co, Cu, Fe, Mn, Ni, Pb, Y, and particularly Zn and the REEs are all found in high concentrations, ranging across four orders of magnitude. Waters collected upstream from the alteration zone have near-neutral pH values, lower specific conductances, lower metal concentrations, and measurable alkalinities. Water samples collected downstream of the alteration zone have pH values and metal concentrations intermediate between these two extremes. Stream sediments are anomalous in Zn, Pb, S, Fe, Cu, As, Co, Sb, and Cd relative to local and regional background abundances. Red Mountain Creek and its tributaries do not support, and probably never have supported, significant megascopic faunal aquatic life.

  7. Orogenic gold and geologic time: A global synthesis

    USGS Publications Warehouse

    Goldfarb, R.J.; Groves, D.I.; Gardoll, S.

    2001-01-01

    Orogenic gold deposits have formed over more than 3 billion years of Earth's history, episodically during the Middle Archean to younger Precambrian, and continuously throughout the Phanerozoic. This class of gold deposit is characteristically associated with deformed and metamorphosed mid-crustal blocks, particularly in spatial association with major crustal structures. A consistent spatial and temporal association with granitoids of a variety of compositions indicates that melts and fluids were both inherent products of thermal events during orogenesis. Including placer accumulations, which are commonly intimately associated with this mineral deposit type, recognized production and resources from economic Phanerozoic orogenic-gold deposits are estimated at just over one billion ounces gold. Exclusive of the still-controversial Witwatersrand ores, known Precambrian gold concentrations are about half this amount. The recent increased applicability of global paleo-reconstructions, coupled with improved geochronology from most of the world's major gold camps, allows for an improved understanding of the distribution pattern of orogenic gold in space and time.

  8. The crust-mantle interaction in continental subduction channels: Zircon evidence from orogenic peridotite in the Sulu orogen

    NASA Astrophysics Data System (ADS)

    Li, Hai-Yong; Chen, Ren-Xu; Zheng, Yong-Fei; Hu, Zhaochu

    2016-02-01

    A combined secondary ion mass spectrometer and laser ablation-(multicollector)-inductively coupled plasma mass spectrometer study of zircon U-Pb ages, trace elements, and O and Hf isotopes was carried out for orogenic peridotite and its host gneiss in the Sulu orogen. Newly grown zircon domains exhibit weak zoning or no zoning, relatively low Th/U ratios (<0.1), low heavy rare earth element (HREE) contents, steep middle rare earth element-HREE patterns, negative Eu anomalies, and negative to low δ18O values of -11.3 to 0.9‰ and U-Pb ages of 220 ± 2 to 231 ± 4 Ma. Thus, these zircons would have grown from metasomatic fluids during the early exhumation of deeply subducted continental crust. The infiltration of metasomatic fluids into the peridotite is also indicated by the occurrence of hydrous minerals such as amphibole, serpentine, and chlorite. In contrast, relict zircon domains exhibit magmatic zircon characteristics. Their U-Pb ages and trace element and Hf-O isotope compositions are similar to those for protolith zircons from ultrahigh-pressure metamorphic rocks in the Dabie-Sulu orogenic belt. Thus, these relict magmatic zircons would be physically transported into the peridotite by metasomatic fluids originated from the deeply subducted continental crust. Therefore, the peridotite underwent metasomatism by aqueous solutions derived from dehydration of the deeply subducted continental crust during the early exhumation. It is these crustally derived fluids that would have brought not only such chemical components as Zr and Si but also tiny zircon grains from the deeply subducted crustal rocks into the peridotite at the slab-mantle interface in continental subduction channels. As such, the orogenic peridotite records the crust-mantle interaction at the deep continental subduction zone.

  9. Orogenic structural inheritance and rifted passive margin formation

    NASA Astrophysics Data System (ADS)

    Salazar Mora, Claudio A.; Huismans, Ritske S.

    2016-04-01

    Structural inheritance is related to mechanical weaknesses in the lithosphere due to previous tectonic events, e.g. rifting, subduction and collision. The North and South Atlantic rifted passive margins that formed during the breakup of Western Gondwana, are parallel to the older Caledonide and the Brasiliano-Pan-African orogenic belts. In the South Atlantic, 'old' mantle lithospheric fabric resulting from crystallographic preferred orientation of olivine is suggested to play a role during rifted margin formation (Tommasi and Vauchez, 2001). Magnetometric and gravimetric mapping of onshore structures in the Camamu and Almada basins suggest that extensional faults are controlled by two different directions of inherited older Brasiliano structures in the upper lithosphere (Ferreira et al., 2009). In the South Atlantic Campos Basin, 3D seismic data indicate that inherited basement structures provide a first order control on basin structure (Fetter, 2009). Here we investigate the role of structural inheritance on the formation of rifted passive margins with high-resolution 2D thermo-mechanical numerical experiments. The numerical domain is 1200 km long and 600 km deep and represents the lithosphere and the sublithospheric mantle. Model experiments were carried out by creating self-consistent orogenic inheritance where a first phase of orogen formation is followed by extension. We focus in particular on the role of varying amount of orogenic shortening, crustal rheology, contrasting styles of orogen formation on rifted margin style, and the time delay between orogeny and subsequent rifted passive formation. Model results are compared to contrasting structural styles of rifted passive margin formation as observed in the South Atlantic. Ferreira, T.S., Caixeta, J.M., Lima, F.D., 2009. Basement control in Camamu and Almada rift basins. Boletim de Geociências da Petrobrás 17, 69-88. Fetter, M., 2009. The role of basement tectonic reactivation on the structural evolution

  10. Meso-Cenozoic building of the northern Central Asian Orogenic Belt: thermotectonic history of the Tuva region

    NASA Astrophysics Data System (ADS)

    De Grave, Johan; De Pelsmaeker, Elien; Zhimulev, Fedor; Glorie, Stijn; Buslov, Mikhail; Van den haute, Peter

    2014-05-01

    The Tuvinian and West-Sayan mountain ranges (West Sayan, Shapshal, Tannu Ola and Sengilen Range) form part of the Central Asian Orogenic Belt (CAOB), and more specifically they align along the Altai-Sayan-Hangai zone of the CAOB in South Siberia and Mongolia. Its Precambrian-Palaeozoic basement has been subjected to Meso-Cenozoic tectonic reactivation. Two North-South transects across the mountain belts and intervening Meso-Cenozoic basins of Tuva were sampled for apatite fission-track (AFT) thermochronology in order to elucidate the thermal history of the Tuvinian basement in relation to Meso-Cenozoic reactivation of the CAOB. Mainly Palaeozoic granitoid basement was targeted for sampling. Most AFT ages of these granitoids are Late Cretaceous and range between 55 and 115 Ma. Mean lengths of confined fission tracks are relatively long with most values between 13 and 14 µm. Thermal history modeling shows a rapid Late Jurassic - Cretaceous cooling for the sampled Tuvinian crystalline rocks, related to exhumation of the Palaeozoic basement. This exhumation is most likely related to the building and subsequent orogenic collapse of the Mongol-Okhotsk orogen that formed between the Siberian and North China - Mongolian (Sino-Korean or Amurian) continental blocks during the Late Mesozoic. Far-field effects of this orogeny and its collapse, affected the Baikal, Altai and Sayan units of the Central Asian Orogenic Belt, including the Tuvinian basement. After a Palaeogene period of stability, thermal history models for some samples hint at a renewed period of basement cooling during the Neogene. In support of this Neogene event, a single sample from the main West Sayan fault zone contains an apatite population with ~2 Ma reset AFT ages. This is interpreted in the framework of ongoing building of the modern Central Asian orogens and associated fault movements and exhumation of the basement, presumably related with the ongoing India-Eurasia convergence. Sediments derived from

  11. Late-stage orogenic processes: How to link surface motion with distinct lithospheric processes

    NASA Astrophysics Data System (ADS)

    Neubauer, F.; Heberer, B.

    2009-04-01

    There is still a lack of knowledge of surface expression caused by deep-seated lithospheric processes, and how such processes could be distinguished from other, e.g. climate-induced, surface processes like denudation. Surface expressions of deep-seated lithospheric processes in convergent settings are expected to have been long-lived and to show large wave-length structures creating a dynamic topography (Wortel and Spakman, 2000; Cloetingh and Ziegler, 2007). Resulting continent-continent collisional orogens are bivergent, and the principal vergency of collisional orogens is controlled by the previous subduction of oceanic lithosphere (Beaumont et al., 1996). A number of tectonic processes are shown to be active during late orogenic phases and these processes particularly result in specific patterns of surface uplift and denudation of the evolving orogens as well as subsidence in the associated foreland basin. A number of these processes are not fully understood. Late-stage orogenic processes include, among others, slab break-off, slab delamination respectively of lithospheric roots, back-thrusting, tectonic indentation and consequent orogen-parallel lateral extrusion and formation of Subduction-Transform Edge Propagator (STEP) faults acting on the subducting lithosphere (Molnar and Tapponnier, 1975; Wortel and Spakman, 2000; Ratschbacher et al., 1991; Govers and Wortel, 2005). Here, we discuss these processes mainly in terms of their near-surface geological expressions within the orogen and the associated foreland basins, and how these processes could be distinguished by such geological features. We also show distinct theoretical models applied to the arcuate Alpine-Balkan-Carpathian-Dinaric system, which is driven by the oblique convergence of Africa-Europe. Slab-break-off results in lateral orogen-parallel migration of sharp subsidence in a linear belt in front of the slab window, coupled subsidence and subsequent uplift/basin inversion of peripheral foreland

  12. Rapid exhumation of deep crust in an obliquely convergent orogen: The Kaoko Belt of the Damara Orogen

    NASA Astrophysics Data System (ADS)

    Foster, David A.; Goscombe, Ben D.; Gray, David R.

    2009-08-01

    The exhumation of deep crustal rocks and juxtaposition of structural-metamorphic domains from different depths in a transpressional orogen may occur during the prograde evolution of the orogen by vertical extrusion or during the retrograde evolution of the orogen via extension. Metamorphic petrology, kinematics, and thermochronology of strike-slip shear zones in the Kaoko Belt of the Damara Orogen are used to evaluate extrusion and extension processes in this transpressional orogen. Mineral assemblages and deformation mechanisms record shearing at pressures of 4-6 kbar and temperatures of ˜550°C for the Three Palms mylonite zone, 600-650°C for the Purros mylonite zone, and ˜630-700°C for the Village and Khumib mylonite zones. The Three Palms mylonite zone, which separates the accreted Coastal Terrane from the former passive margin of the Congo Craton, exhibits progressive deformation during decreasing temperatures through lower greenschist facies and into the brittle field, with consistent oblique normal shear indicators. Lower-temperature fabrics and brittle features also overprint the Village mylonite zone. The 207Pb-206Pb (titanite) and 40Ar/39Ar (hornblende, muscovite, and biotite) data indicate rapid cooling, at rates of 30-100°C/Ma, of all high-grade structural domains in the core of the Kaoko Belt between circa 535 and 525 Ma, which is about 20-30 Ma younger then peak metamorphism. The 40Ar/39Ar data from synkinematic muscovite fish in the retrograde shear zone assemblages indicate that the Khumib, Village, and Three Palms mylonite zones were actively deforming at temperatures below 350°C at circa 530-524 Ma. These data indicate that the high-grade metamorphic rocks of the Kaoko were rapidly exhumed and juxtaposed after the main transpressive deformation by oblique extension. Reactivation of the shear zones and tectonic exhumation of high-grade structural domains from beneath the accreted Coastal Terrane was caused by collision in the Damara Belt and

  13. Alaska marine ice atlas

    SciTech Connect

    LaBelle, J.C.; Wise, J.L.; Voelker, R.P.; Schulze, R.H.; Wohl, G.M.

    1982-01-01

    A comprehensive Atlas of Alaska marine ice is presented. It includes information on pack and landfast sea ice and calving tidewater glacier ice. It also gives information on ice and related environmental conditions collected over several years time and indicates the normal and extreme conditions that might be expected in Alaska coastal waters. Much of the information on ice conditions in Alaska coastal waters has emanated from research activities in outer continental shelf regions under assessment for oil and gas exploration and development potential. (DMC)

  14. Thermo-kinematic evolution of the Annapurna-Dhaulagiri Himalaya, central Nepal: The Composite Orogenic System

    NASA Astrophysics Data System (ADS)

    Parsons, A. J.; Law, R. D.; Lloyd, G. E.; Phillips, R. J.; Searle, M. P.

    2016-04-01

    The Himalayan orogen represents a "Composite Orogenic System" in which channel flow, wedge extrusion, and thrust stacking operate in separate "Orogenic Domains" with distinct rheologies and crustal positions. We analyze 104 samples from the metamorphic core (Greater Himalayan Sequence, GHS) and bounding units of the Annapurna-Dhaulagiri Himalaya, central Nepal. Optical microscopy and electron backscatter diffraction (EBSD) analyses provide a record of deformation microstructures and an indication of active crystal slip systems, strain geometries, and deformation temperatures. These data, combined with existing thermobarometry and geochronology data are used to construct detailed deformation temperature profiles for the GHS. The profiles define a three-stage thermokinematic evolution from midcrustal channel flow (Stage 1, >700°C to 550-650°C), to rigid wedge extrusion (Stage 2, 400-600°C) and duplexing (Stage 3, <280-400°C). These tectonic processes are not mutually exclusive, but are confined to separate rheologically distinct Orogenic Domains that form the modular components of a Composite Orogenic System. These Orogenic Domains may be active at the same time at different depths/positions within the orogen. The thermokinematic evolution of the Annapurna-Dhaulagiri Himalaya describes the migration of the GHS through these Orogenic Domains and reflects the spatial and temporal variability in rheological boundary conditions that govern orogenic systems.

  15. Brookian structural plays in the National Petroleum Reserve, Alaska

    USGS Publications Warehouse

    Potter, Christopher J.; Moore, Thomas E.

    2003-01-01

    As part of the U.S. Geological Survey assessment of undiscovered oil and gas resources in the National Petroleum Reserve-Alaska (NPRA), two structural plays were assessed in thrust-faulted and folded Upper Cretaceous rocks of the Brookian megasequence. These are the Brookian Topset Structural Play and the Torok Structural Play, located in the Brooks Range foothills and the southern part of the coastal plain, within the Tertiary-age frontal part of the Jurassic to Tertiary Brooks Range orogenic belt. A new regional structural interpretation, developed through regional seismic analyses, reconnaissance field investigations, and new thermal constraints, guided the geologic evaluation and risking of these plays. Volumetric parameters were derived from seismic reflection data, well data and oil and gas field analogs. The fundamental elements of the Brookian Topset Structural Play, exemplified by the undeveloped Umiat oil field, include: (1) reservoirs in Nanushuk Group and uppermost Torok Formation shallow-marine to nonmarine sandstones draped over anticlines caused by structural thickening in underlying Torok mudstones; (2) seals provided by overlying shale drapes in the Nanushuk, and locally by thrust faults; (3) Torok, gamma-ray-zone (GRZ) or pebble shale source rocks; (4) remigration of hydrocarbons from early formed (Late Cretaceous) stratigraphic traps disrupted by 60 Ma thrusting, into newly formed structural traps. The 60 Ma thrusting was probably accompanied by new generation and migration of natural gas resulting from late structural thickening and tectonic loading. Subsurface data from the Umiat field and other seismic reflection data within the play area indicate that the structural traps are commonly compartmentalized by thrust faults. The fundamental elements of the Torok Structural Play, exemplified by the undeveloped East Kurupa gas accumulation just south of NPRA, include: (1) reservoirs in lower Torok Formation basin-floor sandstones, and perhaps in

  16. Late-orogenic, post-orogenic, and anorogenic granites: Distinction by major-element and trace-element chemistry and possible origins

    SciTech Connect

    Rogers, J.J.W.; Greenberg, J.K. )

    1990-05-01

    Granites classified into four categories based solely on tectonics of occurrence and associated rock types also have compositional characteristics that are consistent within groups and different among groups. Orogenically related granites include late-orogenic varieties (LO) associated with calc-alkaline batholiths, and post-orogenic varieties (PO), which occur in broad zones of isolated diapiric plutons in recently deformed orogenic belts. Inclined REE patterns, moderate Sr contents, and K{sub 2}O-SiO{sub 2} relationships show that late-orogenic granites formed by fractionation of plagioclase, clinopyroxene, and amphibole from calcalkaline magmas. Flatter REE patterns and K{sub 2}O contents near 5%, plus the absence of associated magmatic rocks, indicate that the post-orogenic granites developed by partial melting of subduction-produced mafic/intermediate magmatic rocks. Both the late- and post-orogenic granites can be part of material newly added to continental crust as a result of orogeny. Anorogenic granites in anorthosite/rapakivi complexes (AR) or alkaline ring complexes (RC) have LIL contents too high to have been equilibrated with a mafic mineral assemblage. These anorogenic rocks probably formed by partial melting of preexisting sialic crust and do not represent new crustal increment.

  17. Libraries in Alaska: MedlinePlus

    MedlinePlus

    ... this page: https://medlineplus.gov/libraries/alaska.html Libraries in Alaska To use the sharing features on ... JavaScript. Anchorage University of Alaska Anchorage Alaska Medical Library 3211 Providence Drive Anchorage, AK 99508-8176 907- ...

  18. 75 FR 53331 - Alaska Native Claims Selection

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-08-31

    ... Interest to Hadohdleekaga, Incorporated, for the Native village of Hughes, Alaska, pursuant to the Alaska... Hughes, Alaska, and are located in: Kateel River Meridian, Alaska T. 9 N., R. 23 E., Sec. 5....

  19. Alaska telemedicine: growth through collaboration.

    PubMed

    Patricoski, Chris

    2004-12-01

    The last thirty years have brought the introduction and expansion of telecommunications to rural and remote Alaska. The intellectual and financial investment of earlier projects, the more recent AFHCAN Project and the Universal Service Administrative Company Rural Health Care Division (RHCD) has sparked a new era in telemedicine and telecommunication across Alaska. This spark has been flamed by the dedication and collaboration of leaders at he highest levels of organizations such as: AFHCAN member organizations, AFHCAN Office, Alaska Clinical Engineering Services, Alaska Federal Health Care Partnership, Alaska Federal Health Care Partnership Office, Alaska Native health Board, Alaska Native Tribal health Consortium, Alaska Telehealth Advisory Council, AT&T Alascom, GCI Inc., Health care providers throughout the state of Alaska, Indian Health Service, U.S. Department of Health and Human Services, Office of U.S. Senator Ted Steens, State of Alaska, U.S. Department of Homeland Security--United States Coast Guard, United States Department of Agriculture, United States Department of Defense--Air Force and Army, United States Department of Veterans Affairs, University of Alaska, and University of Alaska Anchorage. Alaska now has one of the largest telemedicine programs in the world. As Alaska moves system now in place become self-sustaining, and 2) collaborating with all stakeholders in promoting the growth of an integrated, state-wide telemedicine network.

  20. Alaska: A frontier divided

    SciTech Connect

    O'Dell, R. )

    1986-09-01

    The superlatives surrounding Alaska are legion. Within the borders of the 49th US state are some of the world's greatest concentrations of waterfowl, bald eagles, fur seals, walrus, sea lions, otters, and the famous Kodiak brown bear. Alaska features the highest peak of North America, the 20,320-foot Mount McKinley, and the longest archipelago of small islands, the Aleutians. The state holds the greatest percentage of protected wilderness per capita in the world. The expanse of some Alaskan glaciers dwarfs entire countries. Like the periodic advance and retreat of its glaciers, Alaska appears with some regularity on the national US agenda. It last achieved prominence when President Jimmy Carter signed the Alaska National Interest Lands Conservation Act in 1980. Since then the conflict between environmental protection and economic development has been played out throughout the state, and Congress is expected to turn to Alaskan issues again in its next sessions.

  1. Provenance of Cretaceous trench slope sediments from the Mesozoic Wandashan Orogen, NE China: Implications for determining ancient drainage systems and tectonics of the Paleo-Pacific

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

    The Wandashan Orogen of NE China is a typical accretionary orogen related to Paleo-Pacific subduction. The Raohe Complex, as a major part of the orogen, consists of mid-Triassic to mid-Jurassic radiolarian chert and intraoceanic igneous rocks in an accretionary prism overlain by weakly sheared terrestrial-sourced clastic trench slope sediments. Sensitive high-resolution ion microprobe U-Pb dating and LA-MC-ICPMS Hf isotopic analysis of detrital zircons from the terrestrial-sourced Yongfuqiao Formation sandstone show that most zircons are Phanerozoic (90%): 140-150 Ma (10%), 180-220 Ma (25%), 240-270 Ma (15%), 300-360 Ma (15%), 391-395 Ma (3%), and 450-540 Ma (20%), whereas 10% are Precambrian in age. About 90% of the zircons have ɛHf(t) values ranging from +11.1 to -12.8. This suggests that the major provenance of the trench slope sediments was from the adjacent eastern segment of the Central Asian Orogenic Belt and the Jiamusi Block. The age of the Yongfuqiao Formation is constrained to the earliest Cretaceous, which represents the accretion time of the mid-Triassic to mid-Jurassic oceanic complexes. When compared with the Mino Complex in Japan and the Tananao Complex in Taiwan, three different provenances are identified suggesting three ancient drainage systems which transported sediments from NE China, North China, and South China to the Paleo-Pacific subduction-accretion system.

  2. The appalachian-Ouachita orogen in the United States

    SciTech Connect

    Hatcher, R.D. Jr.; Thomas, W.A.; Viele, G.W.

    1989-01-01

    This book presents information from more than 1,000 sources in academia, state and federal agencies, and industry on the geology and geophysics of the crustal plates in the Appalachian and Ouachita mountains of the U.S. Discusses the tectonics, magnetic and gravity anomaly patterns, regional stress fields, thermal aspects, seismicity, and neotectonics of the area. Other topics include energy resources of the Appalachian orogen; stratigraphy, sedimentology, and depositional setting of reorogenic rocks; and mineral deposits and resources of the Ouachita Mountains. Includes separate maps and charts.

  3. Asymmetric gravitational spreading - Analogue experiments on the Svecofennian orogen

    NASA Astrophysics Data System (ADS)

    Nikkilä, Kaisa; Korja, Annakaisa; Koyi, Hemin; Eklund, Olav

    2015-04-01

    Over-thickened orogenic crust may suffer from rheological, gravitational and topographical unbalancing resulting in discharging via gravitational spreading. If the thickened orogen is also hot, then increased temperature may reduce the viscosity of the crust that may induce large-scale horizontal flow. The effect of flow on the crustal architecture has previously been modeled with symmetric two-way spreading or asymmetric one- or two-way spreading (like channel flow) experiments. Most models do not take into account of the contrasting mechanical properties of the juxtaposed terranes. We have made analogue experiments to study gravitational one-way spreading and the interplay between two crustal blocks with contrasting rheological properties. The models are 3 cm thick replicas of 60 km thick crust. They have three horizontal layers representing strong lower, weak middle and brittle upper crust. The models have cuts to study the effect of inherited crustal-scale weakness zones. The experiments have been conducted within a large centrifuge in the Hans Ramberg Tectonic Laboratory at Uppsala University. The analogue models propose that asymmetric, unilateral flow has different effect on the contrasting crustal units, in both horizontal and vertical directions. The laterally heterogeneous crust flows towards the direction of extension, and it rotates and extends the pre-existing weakness zones. The weakness zones facilitate exhumation and they increase strain rate. The weakness zones split the crust into subblocks, which stretch individually and which may show signatures of compression or rotation. The changes in thickness of the model reflect changes in the layers, which may thin or thicken depending on the mechanical properties of crustal layers. A consequence of this the total amount of flattening is less than the model extension. The results are compared to geophysical and geological data from Precambrian Svecofennian orogen in Fennoscandia. The comparison suggest

  4. Tectonic evolution of the Qinling orogen, China: Review and synthesis

    NASA Astrophysics Data System (ADS)

    Dong, Yunpeng; Zhang, Guowei; Neubauer, Franz; Liu, Xiaoming; Genser, Johann; Hauzenberger, Christoph

    2011-05-01

    This contribution reviews the tectonic structure and evolution of the Qinling orogenic belt, which extends east-west nearly 2500 km across Central China and is a giant orogenic belt formed by the convergence and collision between North China and South China Blocks. The principal tectonic elements including metamorphic basement and its Neoproterozoic to Triassic cover, ophiolitic sutures, nature and ages of granitoid belts, provenance studies and tectonometamorphic studies of metamorphic belts allow tracing the polarity of two stages of plate convergence and collision and the further tectonic history. In this review, we present new distribution maps of the Early Paleozoic ophiolites and associated volcanics in the Shangdan suture zone and the Middle Devonian-Middle Triassic ophiolitic melange in the Mianlue suture zone, as well as the maps of granitoid and metamorphic belts displaying various ages (Silurian-Devonian, Triassic, Late Jurassic-Early Cretaceous). These maps allow better constrain the polarity of subduction and collision. We also discuss the significance of the Early Cretaceous Yanshanian events, which represent a linkage between tectonic events in the Tethyan and East China/Pacific realms. Two ophiolitic sutures, the Shangdan suture zone in the north and the Mianlue suture in the south, have been intensively studied during the past two decades. The Qinling Orogen is divided into the North Qinling and the South Qinling Belts by the Shangdan suture zone, and this suture zone is thought to represent the major suture separating the North China and South China Blocks. However, the timing and processes of convergence between these two blocks have been disputed for many years, and Silurian-Devonian or Late Triassic collision has been proposed as well. Based on the recent results, a detailed convergent evolutionary history between the North China and South China Blocks along the Shangdan suture is here proposed. The Mianlue suture zone is well documented and

  5. Alaska looks HOT!

    SciTech Connect

    Belcher, J.

    1997-07-01

    Production in Alaska has been sluggish in recent years, with activity in the Prudhoe Bay region in the North Slope on a steady decline. Alaska North Slope (ANS) production topped out in 1988 at 2.037 MMbo/d, with 1.6 MMbo/d from Prudhoe Bay. This year operators expect to produce 788 Mbo/d from Prudhoe Bay, falling to 739 Mbo/d next year. ANS production as a whole should reach 1.3 MMbo/d this year, sliding to 1.29 MMbo/d in 1998. These declining numbers had industry officials and politicians talking about the early death of the Trans-Alaskan Pipeline System-the vital link between ANS crude and markets. But enhanced drilling technology coupled with a vastly improved relationship between the state government and industry have made development in Alaska more economical and attractive. Alaska`s Democratic Gov. Tommy Knowles is fond of telling industry {open_quotes}we`re open for business.{close_quotes} New discoveries on the North Slope and in the Cook Inlet are bringing a renewed sense of optimism to the Alaska exploration and production industry. Attempts by Congress to lift a moratorium on exploration and production activity in the Arctic National Wildlife Refuge (ANWR) have been thwarted thus far, but momentum appears to be with proponents of ANWR drilling.

  6. Low-temperature thermochronology of the northern Thomson Orogen: Implications for exhumation of basement rocks in NE Australia

    NASA Astrophysics Data System (ADS)

    Verdel, Charles; Stockli, Daniel; Purdy, David

    2016-01-01

    The Tasmanides of eastern Australia record much of the Phanerozoic tectonic development of the retreating Pacific-Australia plate boundary and are an oft-cited example of an orogen that has undergone "tectonic mode switching." To begin to constrain the timing of exhumation of basement rocks that are now exposed in portions of the NE Tasmanides, we measured apatite and zircon (U-Th)/He ages from the Thomson Orogen and overlying Paleozoic strata in the back-arc of the New England Orogen in NE Australia. Zircon (U-Th)/He ages from basement samples (including those recovered from boreholes at depths of up to 1.1 km) are characterized by large inter- and intra-sample variability and range from approximately 180 Ma (Early Jurassic) to 375 Ma (Late Devonian). (U-Th)/He zircon ages from several individual samples are negatively correlated with effective uranium (eU), a pattern that is also true of the dataset as a whole, suggesting that variations in U and Th zoning and radiation damage are partially responsible for the age variability. The oldest zircon (U-Th)/He cooling ages coincide with the formation of regionally extensive Late Devonian-early Carboniferous back-arc basins, suggesting that Late Devonian extension played a significant role in exhumation of parts of the northern Thomson Orogen. Apatite (U-Th)/He ages from a basement sample and a late Permian sandstone in the overlying Bowen Basin, which are also marked by intra-sample variability and age-eU correlations, span from the Early Cretaceous through Oligocene, in general agreement with previous apatite fission track data. In conjunction with observations of key geologic relationships and prior K-Ar and 40Ar/39Ar data, our results suggest four overall phases in the thermal history of the northern Thomson Orogen: (1) Cambrian-early Silurian metamorphism during the Delamerian and Benambran Orogenies; (2) protracted cooling during the Late Devonian through mid-Permian that likely resulted from extensional

  7. Active Tectonics in crossroads of an evolving orogen and morphological consequences: Anatolia

    NASA Astrophysics Data System (ADS)

    Koral, Hayrettin

    2016-04-01

    Anatolia lies in a curved setting of the active Alpine Mountain Range and is located in crossroads of the European and Asian terrains. It is one of the fastest deforming land in the world, manifested by seismicity, characteristic landforms and GPS measurements. Active tectonics in Anatolia provides not only a comparable geological model for the past orogens, but also a laboratory case for morphological consequences of an orogenic processes. Anatolia comprise different tectonic subsettings with its own characteristics. Northern part is influenced by tectonic characteristics of the Black Sea Basin, the Pontides and the Caucasian Range; northwestern part by the Balkanides; eastern-southeastern part by the Bitlis-Zagros suture; and south-southwestern part by the eastern Mediterranean subduction setting. Much of its present tectonic complexity was inherited from the convergence dominant plate tectonic setting of the platelets prior to the Middle-Neogene. Beginning about 11 Ma ago, the deformed and uplifted landmass unable to accommodate further deformation in Anatolia and ongoing tectonic activity gave rise to rearrangement of tectonic forces and westerly translational movements. Formation of major strike-slip faults in Anatolia including the North and East Anatolian Faults and a new platelet called the Anatolian Plate are the consequences of this episode. Such change in the tectonic regime has led to modification of previously-formed landscape, modification and sometimes termination of previously-formed basins. Evidence is present in the Plio-Quaternary stratigraphy, tectonic characteristics and morphology of the well-studied areas. This presentation will discuss active tectonic features of the northwestern, southwestern and eastern Anatolian subsettings and their influence on morphology that is closely related to sites of pre-historical human settlement.

  8. Plume-orogenic lithosphere interaction recorded in the Haladala layered intrusion in the Southwest Tianshan Orogen, NW China

    NASA Astrophysics Data System (ADS)

    He, Peng-Li; Huang, Xiao-Long; Xu, Yi-Gang; Li, Hong-Yan; Wang, Xue; Li, Wu-Xian

    2016-03-01

    The plume-orogenic lithosphere interaction may be common and important for the generation of large igneous provinces. The information regarding such a process is recorded by the Haladala gabbroic intrusion (~300 Ma), the largest layered ultramafic-mafic intrusion hosting V-Ti magnetite deposits in the Southwest Tianshan Orogen, NW China. The Haladala gabbros exhibit unfractionated chondrite-normalized rare earth element patterns with negative Nb and Ta anomalies and positive Pb anomaly on the primitive mantle-normalized multielement variation diagram. They are characterized by low initial Sr isotopes, slightly decoupled but high positive bulk rock ɛNd(t) and ɛHf(t), and high 207Pb/204Pb and 208Pb/204Pb relative to 206Pb/204Pb, delineating a DUPAL signature in the sources. The Haladala gabbros cannot be arc or postcollisional magmatism, given the lack of hydrous minerals and low K contents, respectively. This is further supported by the relatively low oxygen fugacity required for the gradual enrichment of V-Ti magnetite during the magma fractionation and by an overall anhydrous mantle source suggested by troctolite mineral assemblage (olivine + plagioclase). The emplacement age of the Haladala gabbros is identical to that of the Wajilitag kimberlites in the Tarim's interior, which have been interpreted as the first magmatic expression of the Tarim mantle plume. We thus propose that the Haladala gabbroic intrusion was generated in a hybrid geodynamic setting in which the Southwest Tianshan Orogen was impacted by an upwelling mantle plume. In this sense, the Haladala layered gabbroic intrusion records the early phase of magmatism of the Tarim plume, which was preferentially emplaced in a lithospheric weak zone.

  9. The Pan-African nappe tectonics in the Shackleton Range

    USGS Publications Warehouse

    Buggisch, W.; Kleinschmidt, G.

    2007-01-01

    In memory of Campbell Craddock: When J. Campbell Craddock (1972) published his famous 1:5 000 000 map of the Geology of Antarctica, he established major units such as the East Antarctic Craton, the early Palaeozoic Ross, the Mesozoic Ellsworth, and the Cenozoic Andean orogens. It is already evident from this map, that the strike of the Ellsworth Mountains and the Shackleton Range is perpendicular to palaeo-Pacific and modern Pacific margins. While the Ellsworth-Whitmore block is classified as a rotated terrane, the Ross-aged orogen of the Shackleton Range requires another interpretation. The discovery of extended tectonic nappes with south directed transport in the southern Shackleton Range and west transport in the north established a plate tectonic scenery with a subduction dominated Ross Orogen in the Transantarctic Mountains and a transpressive tectonic regime in the Shackleton Range during the final closing of the Mozambique Ocean.

  10. Moho Depth of the Yakutat Terrane, Southern Alaska

    NASA Astrophysics Data System (ADS)

    Christeson, G. L.; Van Avendonk, H. J.; Gulick, S. P.; Pavlis, G. L.; Hansen, R. A.

    2011-12-01

    The Yakutat terrane, a thickened oceanic plateau, is currently colliding with southern Alaska forming the Chugach-St. Elias orogen. Two-dimensional marine seismic profiles acquired during the STEEP project map the Moho of the terrane at a constant depth of 30-32 km over a distance >300 km from the Bering Glacier east to the Dangerous River Zone, and over a distance of >100 km from the Transition fault north towards Yakutat Bay. However, Moho depth of the terrane is poorly constrained to the north beneath the Chugach-St. Elias mountains. Fortunately, good Moho reflections are observed by land-based seismometers recording the marine shots of the STEEP project over source-receiver offsets up to 200 km. We will use these data to invert for Yakutat terrane Moho depth. We will first use all first-arriving energy to do a three-dimensional tomographic inversion for crustal velocity structure, and then will invert all interpreted Moho reflections for Moho depth. The results should give us new insights into the tectonic processes associated with the Chugach-St. Elias orogen.

  11. Origin and structure of major orogen-scale exhumed strike-slip

    NASA Astrophysics Data System (ADS)

    Cao, Shuyun; Neubauer, Franz

    2016-04-01

    The formation of major exhumed strike-slip faults represents one of the most important dynamic processes affecting the evolution of the Earth's lithosphere and surface. Detailed models of the potential initiation and properties and architecture of orogen-scale exhumed strike-slip faults and how these relate to exhumation are rare. In this study, we deal with key properties controlling the development of major exhumed strike-slip fault systems, which are equivalent to the deep crustal sections of active across fault zones. We also propose two dominant processes for the initiation of orogen-scale exhumed strike-slip faults: (1) pluton-controlled and (2) metamorphic core complex-controlled strike-slip faults. In these tectonic settings, the initiation of faults occurs by rheological weakening along hot-to-cool contacts and guides the overall displacement and ultimate exhumation. These processes result in a specific thermal and structural architecture of such faults. These types of strike-slip dominated fault zones are often subparallel to mountain ranges and expose a wide variety of mylonitic, cataclastic and non-cohesive fault rocks, which were formed at different structural levels of the crust during various stages of faulting. The high variety of distinctive fault rocks is a potential evidence for recognition of these types of strike-slip faults. Exhumation of mylonitic rocks is, therefore, a common feature of such reverse oblique-slip strike-slip faults, implying major transtensive and/or transpressive processes accompanying pure strike-slip motion during exhumation. Some orogen-scale strike-slip faults nucleate and initiate along rheologically weak zones, e.g. at granite intrusions, zones of low-strength minerals, thermally weakened crust due to ascending fluids, and lateral borders of hot metamorphic core complexes. A further mechanism is the juxtaposition of mechanically strong mantle lithosphere to hot asthenosphere in continental transform faults (e.g., San

  12. Alaska Resource Data File: Chignik quadrangle, Alaska

    USGS Publications Warehouse

    Pilcher, Steven H.

    2000-01-01

    Descriptions of the mineral occurrences can be found in the report. See U.S. Geological Survey (1996) for a description of the information content of each field in the records. The data presented here are maintained as part of a statewide database on mines, prospects and mineral occurrences throughout Alaska. There is a website from which you can obtain the data for this report in text and Filemaker Pro formats

  13. Post-orogenic thermal evolution of newborn Archean continents

    NASA Astrophysics Data System (ADS)

    Jaupart, C.; Mareschal, J.-C.

    2015-12-01

    The post-orogenic thermal evolution of newborn cratons in the Archean is marked by high-temperature metamorphism and plutonic activity that lag accretion by several tens of million years. The source of the heat that is required remains controversial. Here, we show that such late activity is consistent with the thermal evolution of new continental crust that adjusts to heat released by radioactive decay. Quantitative results depend on the total amount of radioactive elements in the newborn crust. Using heat flow and heat production data from the Archean Superior Province of the Canadian Shield, we show that temperatures ≈800-900 °C were reached in the lower crust a few tens of million years after the final accretion event. The timing of post-orogenic metamorphism is sensitive to the thermal structure acquired at the end of accretion. For the Superior Province, the relatively short time-lag between the end of accretion and metamorphism suggests that the lithosphere was thin or had been heated up by sustained magma percolation.

  14. Continuation of the New England Orogen, Australia, beneath the Queensland Plateau and Lord Howe rise

    USGS Publications Warehouse

    Mortimer, N.; Hauff, F.; Calvert, A.T.

    2008-01-01

    Greywacke, argillite, greyschist and hypabyssal igneous rocks have been obtained from an Ocean Drilling Program core on the Queensland Plateau and from xenoliths in a volcanic breccia dredged from the crest of the Lord Howe Rise. Low to intermediate detrital quartz contents, 260-240 Ma K-Ar ages, and only moderately radiogenic Sr and Nd isotope compositions, suggest a correlation with the New England Orogen of eastern Australia, rather than with Australia's Lachlan Orogen or other adjacent geological provinces. Our results indicate that the New England Orogen terranes continue towards New Zealand at least as far as the southern Lord Howe Rise. The projected offshore boundaries of the major east Australian orogens are now known with more confidence, and do not appear to require any major cross-orogen offsets.

  15. Chapter 32: Geology and petroleum potential of the Arctic Alaska petroleum province

    USGS Publications Warehouse

    Bird, K.J.; Houseknecht, D.W.

    2011-01-01

    The Arctic Alaska petroleum province encompasses all lands and adjacent continental shelf areas north of the Brooks Range-Herald Arch orogenic belt and south of the northern (outboard) margin of the Beaufort Rift shoulder. Even though only a small part is thoroughly explored, it is one of the most prolific petroleum provinces in North America with total known resources (cumulative production plus proved reserves) of c. 28 BBOE. The province constitutes a significant part of a displaced continental fragment, the Arctic Alaska microplate, that was probably rifted from the Canadian Arctic margin during formation of the Canada Basin. Petroleum prospective rocks in the province, mostly Mississippian and younger, record a sequential geological evolution through passive margin, rift and foreland basin tectonic stages. Significant petroleum source and reservoir rocks were formed during each tectonic stage but it was the foreland basin stage that provided the necessary burial heating to generate petroleum from the source rocks. The lion's share of known petroleum resources in the province occur in combination structural-stratigraphic traps formed as a consequence of rifting and located along the rift shoulder. Since the discovery of the super-giant Prudhoe Bay accumulation in one of these traps in the late 1960s, exploration activity preferentially focused on these types of traps. More recent activity, however, has emphasized the potential for stratigraphic traps and the prospect of a natural gas pipeline in this region has spurred renewed interest in structural traps. For assessment purposes, the province is divided into a Platform assessment unit (AU), comprising the Beaufort Rift shoulder and its relatively undeformed flanks, and a Fold-and-Thrust Belt AU, comprising the deformed area north of the Brooks Range and Herald Arch tectonic belt. Mean estimates of undiscovered, technically recoverable resources include nearly 28 billion barrels of oil (BBO) and 122 trillion

  16. Orogenic gold: Common or evolving fluid and metal sources through time

    NASA Astrophysics Data System (ADS)

    Goldfarb, Richard J.; Groves, David I.

    2015-09-01

    Orogenic gold deposits of all ages, from Paleoarchean to Tertiary, show consistency in chemical composition. They are the products of aqueous-carbonic fluids, with typically 5-20 mol% CO2, although unmixing during extreme pressure fluctuation can lead to entrapment of much more CO2-rich fluid inclusions in some cases. Ore fluids are typically characterized by significant concentrations of CH4 and/or N2, common estimates of 0.01-0.36 mol% H2S, a near-neutral pH of 5.5, and salinities of 3-7 wt.% NaCl equiv., with Na > K > > Ca,Mg. This fluid composition consistency favors an ore fluid produced from a single source area and rules out mixing of fluids from multiple sources as significant in orogenic gold formation. Nevertheless, there are broad ranges in more robust fluid-inclusion trapping temperatures and pressures between deposits that support a model where this specific fluid may deposit ore over a broad window of upper to middle crustal depths. Much of the reported isotopic and noble gas data is inconsistent between deposits, leading to the common equivocal interpretations from studies that have attempted to define fluid and metal source areas for various orogenic gold provinces. Fluid stable isotope values are commonly characterized by the following ranges: (1) δ18O for Precambrian ores of + 6 to + 11‰ and for Phanerozoic ores of + 7 to + 13‰; (2) δD and δ34S values that are extremely variable; (3) δ13C values that range from - 11 to - 2‰; and (4) δ15N of + 10 to + 24‰ for the Neoarchean, + 6.5 to + 12‰ for the Paleoproterozoic, and + 1.5 to + 10‰ for the Phanerozoic. Secular variations in large-scale Earth processes appear to best explain some of the broad ranges in the O, S, and N data. Fluid:rock interaction, particularly in ore trap areas, may cause important local shifts in the O, S, and C ratios. The extreme variations in δD mainly reflect measurements of hydrogen isotopes by bulk extraction of waters from numerous fluid inclusion

  17. Magnetic constraints on the thermal evolution of a collapsing orogen

    NASA Astrophysics Data System (ADS)

    Platzman, Ellen

    2002-06-01

    The thermal evolution of an orogen undergoing late-stage extension was investigated using rock magnetic properties of a suite of mafic dyke rocks affected by greenschist facies metamorphism in the internal zones of the Betic Cordillera, southern Spain. The natural remanent magnetization (NRM) in the dykes intruded into the lowest geological unit is made up of up to three components. The lowest temperature component (LT) is in the direction of the present day magnetic field and is believed to be a chemical remanent magnetization (CRM) or viscous remanent magnetization (VRM) acquired in the recent magnetic field. The intermediate temperature (IT) component unblocked between 200°C and 450°C is thought to be largely a thermoviscous overprint acquired during metamorphism. This component is carried by either primary or authogenic sulfides and low-unblocking temperature magnetite. The component of magnetization with the highest blocking temperature (HT) is isolated above 450°C and is interpreted as the primary component of remanent magnetization. It is most likely that this component is carried by magnetite that resides in the plagioclase and has been shielded from the metamorphism, which transformed most of the original magnetite to metamorphic amphibole, chlorite and biotite. Thermal demagnetization of these dykes separates the IT overprint from the HT primary remanence at a sharp junction occurring at 450°C. For single domain grains this translates to a peak palaeotemperature in the natural sample of approximately 370°C, which is close to the estimated temperature experienced by the greenschist facies country rocks (400°C). In contrast, results obtained from a dyke that is intruded into an overlying weakly metamorphosed geological unit, indicates that temperatures only reached about 175°C in this unit. These results are consistent with temperatures deduced from geological constraints and they imply that between 4 and 6 km of section has been removed between the

  18. Deformation Partitioning Processes in a Mid-crustal Detachment System, the Ketilidian Orogen, South Greenland

    NASA Astrophysics Data System (ADS)

    McCaffrey, K.; Grocott, J.; Garde, A.; Hamilton, M.; Chadwick, B.

    2001-12-01

    The upper crust in convergent margins is commonly segmented into fault-bounded blocks or terranes. The mechanism(s) by which orogen-parallel movement and/or rotation of these blocks takes place in convergent margins remains an open question. Models require sub-horizontal detachments within or at the base of the lithosphere in addition to vertical strike-parallel boundaries. We present an example of an exposed mid-crustal detachment system in which vertical and lateral deformation partitioning can be demonstrated. We present a model of how the detachment system developed and suggest that it provides one possible mechanism for decoupling in cordilleran-style orogenic belts. Continental growth by juvenile magmatic arc processes is typified by the Palaeoproterozoic (c.1800 Ma) Ketilidian orogen which formed in response to oblique convergence between an oceanic plate and an Archaean craton. The core of this orogen is a 100-200 km wide, NE-trending continental magmatic arc, the Julianehaab batholith (JB), that was constructed by calc-alkaline magmas emplaced between c.1855-1795 Ma. To the south-east beyond the outboard margin of the batholith, the Psammite (PsZ) and Pelite Zones (PeZ) with a minimum width of c. 100 km, comprise deformed and metamorphosed arkosic, calcareous, semipelitic, pelitic and minor metavolcanic rocks, with an estimated pre-erosional thickness of over 15 km. These zones are collectively interpreted as the relics of a forearc basin. Transpression during early deformation (D1) was partitioned into sinistral strike-slip in the magmatic arc rocks of the JB and SE-directed thrusting in the sedimentary and volcaniclastic sequences of the proximal forearc (PsZ). Subsequently, D1 fabrics in the PsZ were overprinted and transposed in an intense, flat-lying, D2 ductile shear zone with arc-parallel stretching lineations and top-ENE kinematic indicators. The D2 shear zone is interpreted as a mid-crustal partitioning detachment that lay beneath a domain of

  19. Accretion of southern Alaska

    USGS Publications Warehouse

    Hillhouse, J.W.

    1987-01-01

    Paleomagnetic data from southern Alaska indicate that the Wrangellia and Peninsular terranes collided with central Alaska probably by 65 Ma ago and certainly no later than 55 Ma ago. The accretion of these terranes to the mainland was followed by the arrival of the Ghost Rocks volcanic assemblage at the southern margin of Kodiak Island. Poleward movement of these terranes can be explained by rapid motion of the Kula oceanic plate, mainly from 85 to 43 Ma ago, according to recent reconstructions derived from the hot-spot reference frame. After accretion, much of southwestern Alaska underwent a counterclockwise rotation of about 50 ?? as indicated by paleomagnetic poles from volcanic rocks of Late Cretaceous and Early Tertiary age. Compression between North America and Asia during opening of the North Atlantic (68-44 Ma ago) may account for the rotation. ?? 1987.

  20. Stress Dynamics of Magma Activity during Orogenic Evolution: An Example from Kinmen Island, SE China

    NASA Astrophysics Data System (ADS)

    Chen, Ping-Chuan; Yeh, En-Chao; Lin, Jian-Wei; Lee, Chi-Yu; Chen, Rou-Fei; Lin, Wayne; Hsieh, Pei-Shan; Lin, Cheng-Kuo; Iizuka, Yoshiyuki

    2016-04-01

    During orogeny, a mountain belt experienced different orogenic stages with various conditions of temperature, pressure, stress and fluid pressure. The speculation, that the orogenic stresses evolve from reverse faulting via strike-slip faulting to normal faulting stress regimes corresponding to syn-orogenic, post-orogenic and an-orogenic stage respectively, has been proposed but has not been proved yet. Here we report the study of dikes from Kinmen Island can shed light on understanding the stress evolution of orogeny. The Kinmen Island, located in the southeastern continental margin of Mainland China, cropped out the middle to lower crust of NE structural grain, which was experienced deformation and metamorphism during Late Yenshanian Orogeny(LYO). Based on previous studies of geochemistry, geochronology, and P-T conditions, various types of dike have been identified. They are syn-orognic dikes of amphibolite (130-110Ma), post-orogenic dikes of pegmatite and aplite (110-100Ma), and an-orogenic dike of gabbro (94-76Ma). During syn-orogenic stage of LYO, dike intrusion appeared as low-angle dip, which reflected that reverse faulting regime and horizontal maximum stress direction in E-W orientation. In post-orogenic stage, stress would be divided into two sub-stages. The early one was strike-slip faulting regime and horizontal maximum stress was in NW-SE orientation. The late one was normal faulting regime and horizontal maximum stress direction returned to E-W orientation. Finally, an-orogenic dike intrusion striked NE-SW with vertical dip, which displayed that normal faulting regime and NE-SW horizontal maximum stress direction. Our observation is consistent with the expected stress evolution during orogeny. Deviatoric stresses from new findings were decreased at early post-orogenic stage but increased after late post-orogenic stage, indicating the change of fluid pressure ratio with time. The spatiotemporal variation of stress field might be suggested the change

  1. Magmatic and metamorphic belts and plutonic-metamorphic complexes of southeastern Alaska

    SciTech Connect

    Brew, D.A.; Himmelberg, G.R.; Ford, A.B.; Loney, R.A. . Branch of Alaskan Geology Univ. of Missouri, Columbia, MO . Dept. of Geology)

    1993-04-01

    The Cordilleran orogen in southeastern Alaska includes 24 distinct magmatic belts, ranging in age from Cambrian to Holocene, that are defined by map relations, lithology, age, and chemical composition. The youngest magmatic features are Quaternary-age pre- and post-glacial volcanic rocks that occur in three major fields in the region, as well as in isolated locations. Cenozoic magmatic features consist of four major and three minor belts. The major Tkope-Portland Peninsula belt of Oligocene age includes both volcanic and plutonic rocks. The major calcalkalic Coast Mountains belt of early and middle Eocene age is the single largest magmatic feature of the region. Early Tertiary and latest Cretaceous magmatism is represented by the major calcalkalic great tonalite sill belt, a remarkable long and narrow feature along the west side of the Coast Mountains. Cretaceous and Jurassic intrusive rocks occur in five major belts and two minor belts in the region and Paleozoic intrusive rocks occur in four major and two minor belts. The three major plutonic-metamorphic complexes (PMC), from east to west, are: the Coast PMC in the Coast Mountains; the Glacier Bay-Chichag of plutonic complex (Chugach MC) in the northern outer islands. The Coast PMC records dynamothermal and regional contact metamorphic events related to regional plutonism within several juxtaposed terranes; its lengthy and complicated history is related to the Late Cretaceous collision of the Alexander and Wrangellia terranes and the Gravina overlap assemblage to the west against the Yukon prong and Stikine terrane to the east. The relatively simple Glacier Bay PC history is recorded as the roots of a Late Jurassic through late Early Cretaceous island arc that probably developed during the early stages of the above tectonic event. The complicated Chugach MC history developed during and after the Late Cretaceous collision of the Chugach terrane with the Wrangellia and Alexander terranes.

  2. USGS Alaska State Mosaic

    USGS Publications Warehouse

    ,

    2008-01-01

    The Alaska State Mosaic consists of portions of scenes from the Multi-Resolution Land Characteristics 2001 (MRLC 2001) collection. The 172 selected scenes have been geometrically and radiometrically aligned to produce a seamless, relatively cloud-free image of the State. The scenes were acquired between July 1999 and September 2002, resampled to 120-meter pixels, and cropped to the State boundary. They were reprojected into a standard Alaska Albers projection with the U.S. National Elevation Dataset (NED) used to correct for relief.

  3. Proterozoic collisional tectonism in the Trans-Hudson orogen, Saskatchewan

    SciTech Connect

    Bickford, M.E.; Chiarenzelli, J.R.; Van Schmus, W.R. ); Collerson, K.D. ); Lewry, J.F. )

    1990-01-01

    Isotopic and structural data from the juvenile Reindeer zone of the Trans-Hudson orogen, northern Saskatchewan, indicate a pre-1.85 Ga thermotectonic event, possibly reflecting arc-continent collision, followed by a more extensive, nappe-forming, ca. 1.83-1.80 Ga thermotectonism during terminal continent-continent collision. Preliminary data from the adjacent, ensialic Cree Lake zone suggest high-grade reworking of Archean crust by the pre-1.85 Ga event. In the Rae province to the west, high-grade metamorphism and reworking of Archean crust occurred about 2.0 Ga and may be related to the formation of the coeval Taltson magmatic zone.

  4. Neoproterozoic and Paleozoic accretionary orogens exposed at different crustal levels

    NASA Astrophysics Data System (ADS)

    Kroener, A.

    2002-12-01

    Accretionary orogens in the upper crust are dominated by trench and forearc deposits, obducted ophiolite fragments, exotic terranes and well defined structural boundaries such as major shear zones. The Neoproterozoic Arabian-Nubian shield (ANS) of western Arabia and NE Africa, the huge terrain of the Neoproterozoic to Palaeozoic Central Asian mobile belt (CAMB) and the present Indonesian Archipelago are prime examples of such orogens. In the ANS and CAMB, field relationships, rock associations, differences in structural style and metamorphic grade, and geochronology have led to the recognition of terrane assemblages that are related to processes of lateral accretion as now observed in the southwest Pacific and lasting for several hundred my. In the ANS, ocean crust and arc formation began about 900 Ma ago, and terrane accretion was completed by ~600 Ma, whereas in the CAMB the oldest oceanic crust formed some 1000 Ma ago, and terrane accretion continued into the late Palaeozoic. Typical rock associations are trench and forearc sediments, island-arc volcanics, calc-alkaline granitoids, dismembered ophiolite suites and gneissic rocks (microcontinents?) constituting exotic terranes and mostly of distinctly older age and more complex tectono-metamorphic history than the surrounding lower grade rocks. Shear zones frequently separate the terranes and in the ANS also constitue seismic discontinuities extending to the lower crust. The middle to lower crustal high grade assemblages of the Neoproterozoic Mozambique belt (MB) of East Africa, Madagascar, southernmost India, Sri Lanka and East Antarctica are considered to be a deep crustal analogue to the upper crustal accretionary belts described above. Typical characteristics are (1) voluminous calc-alkaline granitoid suites, now layered gneisses, and interpreted as root zones of arc terranes, (2) tectonic interdigitation of Archaean to Palaeoproterozoic gneisses with Neoproterozoic rocks, probably brought about during

  5. Review: groundwater in Alaska (USA)

    USGS Publications Warehouse

    Callegary, J.B.; Kikuchi, C.P.; Koch, J.C.; Lilly, M.R.; Leake, S.A.

    2013-01-01

    Groundwater in the US state of Alaska is critical to both humans and ecosystems. Interactions among physiography, ecology, geology, and current and past climate have largely determined the location and properties of aquifers as well as the timing and magnitude of fluxes to, from, and within the groundwater system. The climate ranges from maritime in the southern portion of the state to continental in the Interior, and arctic on the North Slope. During the Quaternary period, topography and rock type have combined with glacial and periglacial processes to develop the unconsolidated alluvial aquifers of Alaska and have resulted in highly heterogeneous hydrofacies. In addition, the long persistence of frozen ground, whether seasonal or permanent, greatly affects the distribution of aquifer recharge and discharge. Because of high runoff, a high proportion of groundwater use, and highly variable permeability controlled in part by permafrost and seasonally frozen ground, understanding groundwater/surface-water interactions and the effects of climate change is critical for understanding groundwater availability and the movement of natural and anthropogenic contaminants.

  6. Metabasalts as sources of metals in orogenic gold deposits

    NASA Astrophysics Data System (ADS)

    Pitcairn, Iain K.; Craw, Dave; Teagle, Damon A. H.

    2015-03-01

    Although metabasaltic rocks have been suggested to be important source rocks for orogenic gold deposits, the mobility of Au and related elements (As, Sb, Se, and Hg) from these rocks during alteration and metamorphism is poorly constrained. We investigate the effects of increasing metamorphic grade on the concentrations of Au and related elements in a suite of metabasaltic rocks from the Otago and Alpine Schists, New Zealand. The metabasaltic rocks in the Otago and Alpine Schists are of MORB and WPB affinity and are interpreted to be fragments accreted from subducting oceanic crust. Gold concentrations are systematically lower in the higher metamorphic grade rocks. Average Au concentrations vary little between sub-greenschist (0.9 ± 0.5 ppb) and upper greenschist facies (1.0 ± 0.5 ppb), but decrease significantly in amphibolite facies samples (0.21 ± 0.07 ppb). The amount of Au depleted from metabasaltic rocks during metamorphism is on a similar scale to that removed from metasedimentary rocks in Otago. Arsenic concentrations increase with metamorphic grade with the metabasaltic rocks acting as a sink rather than a source of this element. The concentrations of Sb and Hg decrease between sub-greenschist and amphibolite facies but concentration in amphibolite facies rocks are similar to those in unaltered MORB protoliths and therefore unaltered oceanic crust cannot be a net source of Sb and Hg in a metamorphic environment. The concentrations of Au, As, Sb, and Hg in oceanic basalts that have become integrated into the metamorphic environment may be heavily influenced by the degree of seafloor alteration that occurred prior to metamorphism. We suggest that metasedimentary rocks are much more suitable source rocks for fluids and metals in orogenic gold deposits than metabasaltic rocks as they show mobility during metamorphism of all elements commonly enriched in this style of deposit.

  7. Paleozoic and Paleoproterozoic Zircon in Igneous Xenoliths Assimilated at Redoubt Volcano, Alaska

    NASA Astrophysics Data System (ADS)

    Bacon, C. R.; Vazquez, J. A.; Wooden, J. L.

    2010-12-01

    Historically active Redoubt Volcano is a basalt-to-dacite cone constructed upon the Jurassic-early Tertiary Alaska-Aleutian Range batholith. New SHRIMP-RG U-Pb age and trace-element concentration results for zircons from gabbroic xenoliths and crystal-rich andesitic mush from a late Pleistocene pyroclastic deposit indicate that ~310 Ma and ~1865 Ma igneous rocks underlie Redoubt at depth. Two gabbros have sharply terminated prismatic zircons that yield ages of ~310 Ma. Zircons from a crystal mush sample are overwhelmingly ~1865 Ma and appear rounded due to incomplete dissolution. Binary plots of element concentrations or ratios show clustering of data for ~310-Ma grains and markedly coherent trends for ~1865-Ma grains; e.g., ~310-Ma grains have higher Eu/Eu* than most of the ~1865-Ma grains, the majority of which form a narrow band of decreasing Eu/Eu* with increasing Hf content which suggests that ~1865-Ma zircons come from igneous source rocks. It is very unlikely that detrital zircons from a metasedimentary rock would have this level of homogeneity in age and composition. One gabbro contains abundant ~1865 Ma igneous zircons, ~300-310 Ma fluid-precipitated zircons characterized by very low U and Th concentrations and Th/U ratios, and uncommon ~100 Ma zircons. We propose that (1) ~310 Ma gabbro xenoliths from Redoubt Volcano belong to the same family of plutons dated by Aleinikoff et al. (USGS Circular 1016, 1988) and Gardner et al. (Geology, 1988) located ≥500 km to the northeast in basement rocks of the Wrangellia and Alexander terranes and (2) ~1865 Ma zircons are inherited from igneous rock, potentially from a continental fragment that possibly correlates with the Fort Simpson terrane or Great Bear magmatic zone of the Wopmay Orogen of northwestern Laurentia. Possibly, elements of these Paleoproterozoic terranes intersected the Paleozoic North American continental margin where they may have formed a component of the basement to the Wrangellia

  8. Gas hydrate resources of northern Alaska

    USGS Publications Warehouse

    Collett, T.S.

    1997-01-01

    Large amounts of natural gas, composed mainly of methane, can occur in arctic sedimentary basins in the form of gas hydrates under appropriate temperature and pressure conditions. Gas hydrates are solids, composed of rigid cages of water molecules that trap molecules of gas. These substances are regarded as a potential unconventional source of natural gas because of their enormous gas-storage capacity. Most published gas hydrate resource estimates are highly simplified and based on limited geological data. The gas hydrate resource assessment for northern Alaska presented in this paper is based on a "play analysis" scheme, in which geological factors controlling the accumulation and preservation of gas hydrates are individually evaluated and risked for each hydrate play. This resource assessment identified two gas hydrate plays; the in-place gas resources within the gas hydrates of northern Alaska are estimated to range from 6.7 to 66.8 trillion cubic metres of gas (236 to 2,357 trillion cubic feet of gas), at the 0.50 and 0.05 probability levels respectively. The mean in-place hydrate resource estimate for northern Alaska is calculated to be 16.7 trillion cubic metres of gas (590 trillion cubic feet of gas). If this assessment is valid, the amount of natural gas stored as gas hydrates in northern Alaska could be almost seven times larger then the estimated total remaining recoverable conventional natural gas resources in the entire United States.

  9. Ocean Observing System Demonstrated in Alaska

    NASA Astrophysics Data System (ADS)

    Schoch, G. Carl; Chao, Yi

    2010-05-01

    To demonstrate the utility of an ocean observing and forecasting system with diverse practical applications—such as search and rescue, oil spill response (perhaps relevent to the current Gulf of Mexico oil spill), fisheries, and risk management—a unique field experiment was conducted in Prince William Sound, Alaska, in July and August 2009. The objective was to quantitatively evaluate the performance of numerical models developed for the sound with an array of fixed and mobile observation platforms (Figure 1). Prince William Sound was chosen for the demonstration because of historical efforts to monitor ocean circulation following the 1989 oil spill from the Exxon Valdez tanker. The sound, a highly crenulated embayment of about 10,000 square kilometers at approximately 60°N latitude along the northern coast of the Gulf of Alaska, includes about 6900 kilometers of shoreline, numerous islands and fjords, and an extensive system of tidewater glaciers descending from the highest coastal mountain range in North America. Hinchinbrook Entrance and Montague Strait are the two main deep water connections with the Gulf of Alaska. The economic base of communities in the region is almost entirely resource-dependent. For example, Cordova's economy is based on commercial fishing and Valdez's economy is supported primarily by the trans-Alaska oil pipeline terminal.

  10. Integrated resource inventory for southcentral Alaska (INTRISCA)

    NASA Technical Reports Server (NTRS)

    Burns, T.; Carson-Henry, C.; Morrissey, L. A.

    1981-01-01

    The Integrated Resource Inventory for Southcentral Alaska (INTRISCA) Project comprised an integrated set of activities related to the land use planning and resource management requirements of the participating agencies within the southcentral region of Alaska. One subproject involved generating a region-wide land cover inventory of use to all participating agencies. Toward this end, participants first obtained a broad overview of the entire region and identified reasonable expectations of a LANDSAT-based land cover inventory through evaluation of an earlier classification generated during the Alaska Water Level B Study. Classification of more recent LANDSAT data was then undertaken by INTRISCA participants. The latter classification produced a land cover data set that was more specifically related to individual agency needs, concurrently providing a comprehensive training experience for Alaska agency personnel. Other subprojects employed multi-level analysis techniques ranging from refinement of the region-wide classification and photointerpretation, to digital edge enhancement and integration of land cover data into a geographic information system (GIS).

  11. Geology of the Alaska-Juneau lode system, Alaska

    USGS Publications Warehouse

    Twenhofel, William Stephens

    1952-01-01

    The Alaska-Juneau lode system for many years was one of the worlds leading gold-producing areas. Total production from the years 1893 to 1946 has amounted to about 94 million dollars, with principal values in contained gold but with some silver and lead values. The principal mine is the Alaska-Juneau mine, from which the lode system takes its name. The lode system is a part of a larger gold-bearing belt, generally referred to as the Juneau gold belt, along the western border of the Coast Range batholith. The rocks of the Alaska-Juneau lode system consist of a monoclinal sequence of steeply northeasterly dipping volcanic, state, and schist rocks, all of which have been metamorphosed by dynamic and thermal processes attendant with the intrusion of the Coast Range batholith. The rocks form a series of belts that trend northwest parallel to the Coast Range. In addition to the Coast Range batholith lying a mile to the east of the lode system, there are numerous smaller intrusives, all of which are sill-like in form and are thus conformable to the regional structure. The bedded rocks are Mesozoic in age; the Coast Range batholith is Upper Jurassic and Lower Cretaceous in age. Some of the smaller intrusives pre-date the batholith, others post-date it. All of the rocks are cut by steeply dipping faults. The Alaska-Juneau lode system is confined exclusively to the footwall portion of the Perseverance slate band. The slate band is composed of black slate and black phyllite with lesser amounts of thin-bedded quartzite. Intrusive into the slate band are many sill-like bodies of rocks generally referred to as meta-gabbro. The gold deposits of the lode system are found both within the slate rocks and the meta-gabbro rocks, and particularly in those places where meta-gabbro bodies interfinger with slate. Thus the ore bodies are found in and near the terminations of meta-gabbro bodies. The ore bodies are quartz stringer-lodes composed of a great number of quartz veins from 6

  12. Signature of Cenozoic orogenic movements in combustion metamorphic rocks: mineralogy and geochronology (example of the Salair-Kuznetsk Basin transition)

    SciTech Connect

    Novikov, I.S.; Sokol, E.V.; Travin, A.V.; Novikova, S.A.

    2008-06-15

    Cenozoic combustion metamorphic (CM) complexes produced by fossil natural coal fires are widespread at range-basin junctions worldwide. Large-scale fires accompany the initial orogenic phases as fresh coal-bearing strata become drawn into the aeration zone as a result of crustal deformation. In combustion metamorphism, the protolith melts to different degrees either into ferrous basic paralava or in glassy clinker. The melt rocks have a phase composition favorable for Ar-40/Ar-39 dating of ignition coeval with the onset of each episode in Late Cenozoic orogenic events. We suggest an algorithm providing correct Ar-40/Ar-39 age determination of CM rocks followed by well-grounded geological interpretation and test the new approach on melt rocks from the Kuznetsk Coal Basin. Paralava samples were dated by Ar-40/Ar-39 incremental heating and the isotope ratios were corrected for Ca-, Cl-, and K-derived Ar isotopic interferences. The interpretation of age-spectrum results was checked against internal and external criteria. The former were plateau and isochrone ages and the latter included the so-called 'couple criterion' and conventional relative ages inferred from geological and stratigraphic evidence. As a result, we distinguished two groups of dates for combustion metamorphic events bracketed between 1.2 {+-} 0.4 and 0.2 {+-} 0.3 Ma. The older ages represent rocks in the western edge of the Prokopievsk-Kiselevsk block of the Salair zone and the younger dates correspond to those in its eastern edge. The reported dates record the time when the fault boundaries of the blocks were rejuvenated during recent activity and the block accreted to the Salair orogenic area as a submontane step. The suggested approach to the choice of objects, classification of rocks, and interpretation of Ar-40/Ar-39 spectra is universal and can be practiced in any area of combustion metamorphism.

  13. Alaska Glaciers and Rivers

    NASA Technical Reports Server (NTRS)

    2007-01-01

    The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Terra satellite captured this image on October 7, 2007, showing the Alaska Mountains of south-central Alaska already coated with snow. Purple shadows hang in the lee of the peaks, giving the snow-clad land a crumpled appearance. White gives way to brown on the right side of the image where the mountains yield to the lower-elevation Susitna River Valley. The river itself cuts a silver, winding path through deep green forests and brown wetlands and tundra. Extending from the river valley, are smaller rivers that originated in the Alaska Mountains. The source of these rivers is evident in the image. Smooth white tongues of ice extend into the river valleys, the remnants of the glaciers that carved the valleys into the land. Most of the water flowing into the Gulf of Alaska from the Susitna River comes from these mountain glaciers. Glacier melt also feeds glacier lakes, only one of which is large enough to be visible in this image. Immediately left of the Kahiltna River, the aquamarine waters of Chelatna Lake stand out starkly against the brown and white landscape.

  14. Alaska Mathematics Standards

    ERIC Educational Resources Information Center

    Alaska Department of Education & Early Development, 2012

    2012-01-01

    High academic standards are an important first step in ensuring that all Alaska's students have the tools they need for success. These standards reflect the collaborative work of Alaskan educators and national experts from the nonprofit National Center for the Improvement of Educational Assessment. Further, they are informed by public…

  15. Suicide in Northwest Alaska.

    ERIC Educational Resources Information Center

    Travis, Robert

    1983-01-01

    Between 1975 and 1979 the Alaskan Native suicide rate (90.9 per 100,000) in Northwest Alaska was more than seven times the national average. Alienation, loss of family, low income, alcohol abuse, high unemployment, and more education were factors related to suicidal behavior. Average age for suicidal behavior was 22.5. (Author/MH)

  16. Alaska's Young Entrepreneurs.

    ERIC Educational Resources Information Center

    Knapp, Marilyn R.

    1989-01-01

    Describes Edgecumbe Enterprises, a four-year-old fish exporting venture run by Mt. Edgecumbe High School in Sitka, Alaska, and the students' meeting with business leaders in Tokyo, Japan. The young entrepreneurs spent two weeks studying the Japanese marketing structure. (JOW)

  17. Seismology Outreach in Alaska

    NASA Astrophysics Data System (ADS)

    Gardine, L.; Tape, C.; West, M. E.

    2014-12-01

    Despite residing in a state with 75% of North American earthquakes and three of the top 15 ever recorded, most Alaskans have limited knowledge about the science of earthquakes. To many, earthquakes are just part of everyday life, and to others, they are barely noticed until a large event happens, and often ignored even then. Alaskans are rugged, resilient people with both strong independence and tight community bonds. Rural villages in Alaska, most of which are inaccessible by road, are underrepresented in outreach efforts. Their remote locations and difficulty of access make outreach fiscally challenging. Teacher retention and small student bodies limit exposure to science and hinder student success in college. The arrival of EarthScope's Transportable Array, the 50th anniversary of the Great Alaska Earthquake, targeted projects with large outreach components, and increased community interest in earthquake knowledge have provided opportunities to spread information across Alaska. We have found that performing hands-on demonstrations, identifying seismological relevance toward career opportunities in Alaska (such as natural resource exploration), and engaging residents through place-based experience have increased the public's interest and awareness of our active home.

  18. Current Ethnomusicology in Alaska.

    ERIC Educational Resources Information Center

    Johnston, Thomas F.

    The systematic study of Eskimo, Indian, and Aleut musical sound and behavior in Alaska, though conceded to be an important part of white efforts to foster understanding between different cultural groups and to maintain the native cultural heritage, has received little attention from Alaskan educators. Most existing ethnomusical studies lack one or…

  19. Alaska's Cold Desert.

    ERIC Educational Resources Information Center

    Brune, Jeff; And Others

    1996-01-01

    Explores the unique features of Alaska's Arctic ecosystem, with a focus on the special adaptations of plants and animals that enable them to survive in a stressful climate. Reviews the challenges facing public and private land managers who seek to conserve this ecosystem while accommodating growing demands for development. Includes classroom…

  20. Venetie, Alaska energy assessment.

    SciTech Connect

    Jensen, Richard Pearson; Baca, Michael J.; Schenkman, Benjamin L.; Brainard, James Robert

    2013-07-01

    This report summarizes the Energy Assessment performed for Venetie, Alaska using the principals of an Energy Surety Microgrid (ESM) The report covers a brief overview of the principals of ESM, a site characterization of Venetie, a review of the consequence modeling, some preliminary recommendations, and a basic cost analysis.

  1. Late Proterozoic-Paleozoic evolution of the Arctic Alaska-Chukotka terrane based on U-Pb igneous and detrital zircon ages: Implications for Neoproterozoic paleogeographic reconstructions

    USGS Publications Warehouse

    Amato, J.M.; Toro, J.; Miller, E.L.; Gehrels, G.E.; Farmer, G.L.; Gottlieb, E.S.; Till, A.B.

    2009-01-01

    The Seward Peninsula of northwestern Alaska is part of the Arctic Alaska-Chukotka terrane, a crustal fragment exotic to western Laurentia with an uncertain origin and pre-Mesozoic evolution. U-Pb zircon geochronology on deformed igneous rocks reveals a previously unknown intermediate-felsic volcanic event at 870 Ma, coeval with rift-related magmatism associated with early breakup of eastern Rodinia. Orthogneiss bodies on Seward Peninsula yielded numerous 680 Ma U-Pb ages. The Arctic Alaska-Chukotka terrane has pre-Neoproterozoic basement based on Mesoproterozoic Nd model ages from both 870 Ma and 680 Ma igneous rocks, and detrital zircon ages between 2.0 and 1.0 Ga in overlying cover rocks. Small-volume magmatism occurred in Devonian time, based on U-Pb dating of granitic rocks. U-Pb dating of detrital zircons in 12 samples of metamorphosed Paleozoic siliciclastic cover rocks to this basement indicates that the dominant zircon age populations in the 934 zircons analyzed are found in the range 700-540 Ma, with prominent peaks at 720-660 Ma, 620-590 Ma, 560-510 Ma, 485 Ma, and 440-400 Ma. Devonian- and Pennsylvanian-age peaks are present in the samples with the youngest detrital zircons. These data show that the Seward Peninsula is exotic to western Laurentia because of the abundance of Neoproterozoic detrital zircons, which are rare or absent in Lower Paleozoic Cordilleran continental shelf rocks. Maximum depositional ages inferred from the youngest detrital age peaks include latest Proterozoic-Early Cambrian, Cambrian, Ordovician, Silurian, Devonian, and Pennsylvanian. These maximum depositional ages overlap with conodont ages reported from fossiliferous carbonate rocks on Seward Peninsula. The distinctive features of the Arctic Alaska-Chukotka terrane include Neoproterozoic felsic magmatic rocks intruding 2.0-1.1 Ga crust overlain by Paleozoic carbonate rocks and Paleozoic siliciclastic rocks with Neoproterozoic detrital zircons. The Neoproterozoic ages are

  2. Identification, definition and mapping of terrestrial ecosystems in interior Alaska

    NASA Technical Reports Server (NTRS)

    Anderson, J. H. (Principal Investigator)

    1973-01-01

    The author has identified the following significant results. A transect of the Tanana River Flats to Murphy Dome, Alaska was accomplished. The transect includes an experimental forest and information on the range of vegetation-land form types. Multispectral black and white prints of the Eagle Summit Research Area, Alaska, were studied in conjunction with aerial photography and field notes to determine the characteristics of the vegetation. Black and white MSS prints were compared with aerial photographs of the village of Wiseman, Alaska. No positive identifications could be made without reference to aerial photographs or ground truth data. Color coded density slice scenes of the Eagle Summit Research Area were produced from black and white NASA aerial photographs. Infestations of the spruce beetle in the Cook Inlet, Alaska, were studied using aerial photographs.

  3. Asthma and American Indians/Alaska Natives

    MedlinePlus

    ... Minority Population Profiles > American Indian/Alaska Native > Asthma Asthma and American Indians/Alaska Natives In 2014, 218, ... Native American adults reported that they currently have asthma. American Indian/Alaska Native children are 30% more ...

  4. Time-slice maps showing age, distribution, and style of deformation in Alaska north of 60° N.

    USGS Publications Warehouse

    Moore, Thomas E.; Box, Stephen E.

    2016-08-29

    Fork orogeny), Early and Late Jurassic deformation in the Peninsular-Wrangellia terranes, and Early Cretaceous deformation in northern Alaska (early Brookian orogeny) show that within-terrane amalgamation events occurred prior to assembly of Alaska. Widespread episodes of deformation in the Late Cretaceous and early Cenozoic, in contrast, affected multiple terranes, indicating they occurred during or following the time of assembly of most of Alaska.The primary deformational event in northern Alaska was the Late Jurassic and Early Cretaceous (early) Brookian orogeny, which affected most terranes north and west of the early Cenozoic Tintina, Victoria Creek, Kaltag, and Poorman dextral-slip faults in central Alaska. In southern Alaska, formation of the southern Alaska accretionary complex (Chugach, Prince William, Yakutat terranes) and associated magmatism in the Peninsular-Wrangellia terrane began near the Triassic-Jurassic boundary and continued episodically throughout the remainder of the Mesozoic and the Cenozoic. The collision of these terranes with the Farewell and Yukon Composite terranes in central Alaska is recorded by contractional deformation that emanated from the intervening basins in the Late Cretaceous. The boundary between northern and central Alaska is constrained to late Early Cretaceous but is enigmatic and not obviously marked by contractional deformation. Early Cenozoic shortening and transpressional deformation is the most widespread event recorded in Alaska and produced the widespread late Brookian orogenic event in northern Alaska. Middle and late Cenozoic shortening and transpression is significant in southern Alaska inboard of the underthrusting Yakutat terrane at the Pacific margin subduction zone as well as in northeastern Alaska.

  5. Tectonic stress evolution in the Pan-African Lufilian Arc and its foreland (Katanga, DRC): orogenic bending, late orogenic extensional collapse and transition to rifting

    NASA Astrophysics Data System (ADS)

    Kipata, M. L.; Delvaux, D.; Sebagenzi, M. N.; Cailteux, J.; Sintubin, M.

    2012-04-01

    Between the paroxysm of the Lufilian orogeny at ~ 550 Ma and the late Neogene to Quaternary development of the south-western branch of the East African rift system, the tectonic evolution of the Lufilian Arc and Kundelungu foreland in the Katanga region of the Democratic Republic of Congo remains poorly unknown although it caused important Cu-dominated mineral remobilizations leading to world-class ore deposits. This long period is essentially characterized by brittle tectonic deformations that have been investigated by field studies in open mines spread over the entire arc and foreland. Paleostress tensors were computed for a database of 1450 fault-slip data by interactive stress tensor inversion and data subset separation, and the relative succession of 8 brittle deformation events established. The oldest brittle structures observed are related to the Lufilian brittle compressional climax (stage 1). They have been re-oriented during the orogenic bending that led to the arcuate shape of the belt. Unfolding the stress directions from the first stage allows to reconstruct a consistent NE-SW direction of compression for this stage. Constrictional deformation occurred in the central part of the arc, probably during orogenic bending (Stage 2). After the orogenic bending, a sequence of 3 deformation stages marks the progressive onset of late-orogenic extension: strike-slip deformations (stages 3-4) and late-orogenic arc-parallel extension (stage 5). It is proposed that these 3 stages correspond to orogenic collapse. In early Mesozoic, NW-SE compression was induced by a transpressional inversion, interpreted as induced by far-field stresses generated at the southern active margin of Gondwana (stage 6). Since then, this region was affected by rift-related extension, successively in a NE-SW direction (stage 7, Tanganyika trend) and NW-SE direction (stage 8, Moero trend).

  6. Focused rock uplift above the subduction décollement at Montague and Hinchinbrook Islands, Prince William Sound, Alaska

    USGS Publications Warehouse

    Ferguson, Kelly M; Armstrong, Phillip A; Arkle Jeanette C,; Haeussler, Peter J.

    2014-01-01

    Megathrust splay fault systems in accretionary prisms have been identified as conduits for long-term plate motion and significant coseismic slip during subduction earthquakes. These fault systems are important because of their role in generating tsunamis, but rarely are emergent above sea level where their long-term (million year) history can be studied. We present 32 apatite (U-Th)/He (AHe) and 27 apatite fission-track (AFT) ages from rocks along an emergent megathrust splay fault system in the Prince William Sound region of Alaska above the shallowly subducting Yakutat microplate. The data show focused exhumation along the Patton Bay megathrust splay fault system since 3–2 Ma. Most AHe ages are younger than 5 Ma; some are as young as 1.1 Ma. AHe ages are youngest at the southwest end of Montague Island, where maximum fault displacement occurred on the Hanning Bay and Patton Bay faults and the highest shoreline uplift occurred during the 1964 earthquake. AFT ages range from ca. 20 to 5 Ma. Age changes across the Montague Strait fault, north of Montague Island, suggest that this fault may be a major structural boundary that acts as backstop to deformation and may be the westward mechanical continuation of the Bagley fault system backstop in the Saint Elias orogen. The regional pattern of ages and corresponding cooling and exhumation rates indicate that the Montague and Hinchinbrook Island splay faults, though separated by only a few kilometers, accommodate kilometer-scale exhumation above a shallowly subducting plate at million year time scales. This long-term pattern of exhumation also reflects short-term seismogenic uplift patterns formed during the 1964 earthquake. The increase in rock uplift and exhumation rate ca. 3–2 Ma is coincident with increased glacial erosion that, in combination with the fault-bounded, narrow width of the islands, has limited topographic development. Increased exhumation starting ca. 3–2 Ma is interpreted to be due to rock uplift

  7. Crustal Structure across the Appalachian Orogen in Pennsylvania from P-wave receiver functions

    NASA Astrophysics Data System (ADS)

    Arroyo, G.; Nyblade, A.; Homman, K.

    2014-12-01

    Crustal structure across the Appalachian Orogen from eastern Ohio to New Jersey is investigated using P-wave receiver functions to estimate Moho depths and crustal Vp/Vs ratios. Data for this study comes from the PASEIS and the USArray Transportable Array. The PASEIS seismic network includes 22 broadband seismic stations throughout Pennsylvania that were in installed in February 2013. Preliminary results from H-K stacking show that Moho depth varies greatly across the Appalachians, ranging from 53 km in northern Pennsylvania to only 32 km just west of the New Jersey border. The thickest crust can be found nearest to Lake Erie, and a relatively thick crust is maintained in northeastern Pennsylvania and along the Pennsylvania-Ohio border. Crustal thickness decreases to the southeast, and a rather sharp decrease can be seen well before the start of the Allegheny Front. Crustal thickness remains relatively uniform between 43 and 45km in the Appalachian Mountains, and decreases to 33-38km in the Piedmont province. Vp/Vs values range from 1.75 to 1.83, with no observable pattern to the variation.

  8. The geometries and development of late orogenic strike-slip faults

    NASA Astrophysics Data System (ADS)

    Anderson, M. W.; Peacock, D. C. P.

    2003-04-01

    Strike-slip faults are commonly the final phase of contraction in orogenic belts, occurring when the folds have locked-up and the thrusts have become too steep for further displacement to occur. Where the maximum stress axis (sigma1) is perpendicular to the orogenic belt (i.e. pure shear), the strike-slip faults are conjugate and represent strike-perpendicular shortening and necessary strike-parallel extension. An example of such behaviour occurs in the steeply dipping Silurian sandstones and shales in Kirkcudbrightshire, in the Southern Uplands of Scotland. If sigma1 is at ~ 70°; to the strike of the orogenic belt, the conjugate strike-slip faults become asymmetric. One set of strike-slip faults occurs at a high angle to the strike of bedding, and the conjugate set has a ramp-flat trajectory across steeply dipping beds. An example of this behaviour occurs in the steeply dipping Silurian turbidites at Ardglass, in the Longford-Down terrane of Northern Ireland. If sigma1 is at a lower angle to the orogenic belt (i.e. transpression), one set of strike-slip faults tends to dominate. In some cases, the dominant strike-slip fault set is parallel to the strike of the orogenic belt, the Caledonian-age Great Glen Fault of Scotland being such an example. In other cases, block rotation occurs on the set of strike-slip faults that are at a high angle to the orogenic belt, as in the Variscan Orogenic Belt of SW England. An annulus model is presented to illustrate the variations in geometries of late-orogenic strike-slip faults from pure shear to transpression.

  9. Landscape Evolution in Orogens with Significant Lateral Advection of Rock: Insights from Numerical Simulations of Fault-Bend Folds

    NASA Astrophysics Data System (ADS)

    Miller, S. R.; Slingerland, R. L.; Kirby, E.

    2002-12-01

    Steady-state orogens must balance lateral as well as vertical rock motions by erosion, but how this balance is effected and what its topographic signature might be are open questions. Here we explore the conditions necessary to achieve a topographic steady state above fault-bend folds, a major class of topography-forming orogenic structures in which lateral motion is significant. Field observations indicate that many active fault-bend folds, such as those underlying the Siwalik Hills, Nepal, and the foothills of the Kyrgyz Range, Kyrgyzstan, have only their backlimbs preserved, implying the achievement of at least exhumational steady state. To determine if their topography and drainage networks are at steady-state we have conducted numerical experiments using CHILD, a landscape evolution model. Rock particle motions above a fault bend were modeled using a planar ramp dipping at 30° along which slip occurs at 20 mm/yr. Results indicate that the system achieves a topographic steady-state in which the drainage divide lies above the ramp tip, but drainage nets continuously evolve because longitudinal streams are advected into transverse streams draining the back limb. Transverse streams draining the back of the fold are significantly less concave (θ < 0.4) than streams draining the front (θ > 1), supporting the notion that stream longitudinal profiles reflect lateral advection of their beds in addition to intrinsic hydrologic controls.

  10. Educating medical students for Alaska.

    PubMed

    Fortuine, R; Dimino, M J

    1998-01-01

    Because Alaska does not have its own medical school, it has become part of WAMI (Washington, Alaska, Montana, Idaho), an educational agreement with the University of Washington School of Medicine (UWSM). Each year, 10 Alaskans are accepted into the entering class of UWSM and spend their first year at the University of Alaska Anchorage (UAA). UWSM third- and fourth-year medical students can obtain some of their clinical experience in Alaska. To meet the needs of Alaska, students are chosen based on academic and personal records, as well as the likelihood of their returning to Alaska for practice. To this end, over the last seven years 30% of accepted students have come from rural communities and 10% are Alaska Natives. The curriculum for the first year includes several sessions dedicated to Alaska health problems, cross-cultural issues, and Alaska's unique rural health care delivery system. Students do two preceptorships--one with a private primary care physician and one with a physician at the Alaska Native Medical Center. Additionally, students have the option to spend a week at a rural site to learn about the community's health care system. An Alaska track is being developed whereby an Alaskan UWSM student can do most of the third year in state via clerkships in family medicine, obstetrics/gynecology, psychiatry, internal medicine, and pediatrics. All UWSM students at the end of their first year can elect to participate for one month in the R/UOP (Rural/Underserved Opportunities Program), which includes several Alaska sites. The overall goals of these approaches are to educate UWSM students, especially Alaskans, about the state's health needs and health care system and to encourage UWSM graduates to practice in the state.

  11. Significant Alaska minerals

    SciTech Connect

    Robinson, M.S.; Bundtzen, T.K.

    1982-01-01

    Alaska ranks in the top four states in gold production. About 30.5 million troy oz have been produced from lode and placer deposits. Until 1930, Alaska was among the top 10 states in copper production; in 1981, Kennecott Copper Company had prospects of metal worth at least $7 billion. More than 85% of the 20 million oz of silver derived have been byproducts of copper mining. Nearly all lead production has been as a byproduct of gold milling. Molybdenum is a future Alaskan product; in 1987 production is scheduled to be about 12% of world demand. Uranium deposits discovered in the Southeast are small but of high grade and easily accessible; farther exploration depends on improvement of a depressed market. Little has been done with Alaskan iron and zinc, although large deposits of the latter were discovered. Alaskan jade has a market among craftspeople. A map of the mining districts is included. 2 figures, 1 table.

  12. Seabirds in Alaska

    USGS Publications Warehouse

    Hatch, Scott A.; Piatt, John F.

    1995-01-01

    Techniques for monitoring seabird populations vary according to habitat types and the breeding behavior of individual species (Hatch and Hatch 1978, 1989; Byrd et al. 1983). An affordable monitoring program can include but a few of the 1,300 seabird colonies identified in Alaska, and since the mid-1970's, monitoring effotrts have emphasized a small selection of surface-feeding and diving species, primarily kittiwakes (Rissa spp.) and murres (Uria spp.). Little or no information on trends is available for other seabirds (Hatch 1993a). The existing monitoring program occurs largely on sites within the Alaska Maritime National Wildlife Refuge, which was established primarily for the conservation of marine birds. Data are collected by refuge staff, other state and federal agencies, private organizations, university faculty, and students.

  13. 47 CFR 80.469 - Maritime mobile repeater stations in Alaska.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 5 2010-10-01 2010-10-01 false Maritime mobile repeater stations in Alaska. 80... Maritime mobile repeater stations in Alaska. (a) Maritime mobile repeater stations are authorized to extend...) On a secondary basis, maritime mobile repeater stations may be authorized to extend the range of...

  14. Late Paleozoic orogenic episodes, Trans-Pecos Texas

    SciTech Connect

    Muehlberger, W.R. . Dept. of Geological Sciences)

    1993-04-01

    The onset of the Ouachita orogeny is marked by the absence of rock of Early Mississippian age. This is interpreted to be the result of the narrowing of the trans-equatorial seaway between North America and the oncoming South American plate. Foredeep filling (Pulse I) began in Early Meramecian time with northward-prograding Tesnus Fm siliciclastic turbidites. Pulse 2 began in Atokan time with northward-prograding siliciclastic turbidites of the Haymond Fm. The thrust belt to the south had now intersected the edge of the NAm carbonate platform as shown by clasts of Middle Cambrian carbonates, as well as Ouachita facies clasts, and rounded clasts of Precambrian quartzite, metarhyolite, and gneiss of unknown source. During Late Pennsylvanian time deltaic sediments prograded across the Marathon region into the southern Permian Basin (Gaptank Fm). In Early Wolfcampian time (Pulse 3), all these units were translated on the Dugout Creek thrust, then (Pulse 4 ) translated finally on a frontal imbricate before deposition of Upper Wolfcampian units across the eroded toes of the thrust sheets. Permian Basin orogenic phases parallel those outlined above. Transgressive clastics from the south and the subdivision of the earlier broad, shallow Tobosa Basin into the uplifts and basins that characterize the Permian Basin began in the Mississippian and became prominent structural units by Late Mississippian time.

  15. Tectonic evolution of the western Kunlun orogenic belt, western China

    NASA Astrophysics Data System (ADS)

    Zhihong, Wang

    2004-11-01

    The western Kunlun orogenic belt in western China evolved through the development of a large subduction-accretionary complex, including flysch sediments and granitic plutons, and by collision of three terranes, namely the North and South Kunlun and Karakorum-Qiangtang blocks from the early Paleozoic to the early Mesozoic. North-dipping subduction of the Paleo-Tethys ocean beneath the Kunlun terranes, which may have commenced in the Cambrian, produced an early Paleozoic Andean-type magmatic arc on the South Kunlun, and a marginal back arc basin, represented by the early Paleozoic Oytag-Kudi ophiolite belt, between the North and South Kunlun. A northward subduction zone consumed the basin and the young, hot upper plate lithosphere was obducted southward onto the South Kunlun following closure of the basin. This resulted in collision of the North and South Kunlun in the early Devonian. Continuous northward subduction of Paleo-Tethys resulted in the development of a Carboniferous-Triassic magmatic arc, and a back arc rifting sequence composed of the Carboniferous to Permian carbonates and clastic sediments on the North and South Kunlun terranes. The Paleo-Tethys ocean finally closed in the late Triassic-early Jurassic, when the Kunlun and Karakorum-Qiangtang blocks were accreted, with the Kara-Kunlun accretionary prism marking their suture zone.

  16. Lithosphere delamination and topography evolution in collisional orogens

    NASA Astrophysics Data System (ADS)

    Li, Z. H.; Liu, M.; Gerya, T.

    2015-12-01

    Systematic high-resolution thermo-mechanical numerical models are conducted in order to better understand the behavior of deep mantle lithosphere and surface topography response during continental collision. In the models with similar rheological properties for the pro- (subducting) and retro- (overriding) continental plates, subduction mode is preferred, with localized topography uplift and mountain building. However, if the effective viscosities of the retro-plate are decreased, then delamination of the lithospheric mantle may occur there, which results in large-scale topography buildup and plateau formation. Several other factors that may also influence the delamination dynamics are further investigated, e.g., plastic weakening of the lithospheric mantle, density contrast between the lithospheric and asthenospheric mantle, convergence velocity, as well as the possible lower crust eclogitization effects. Based on the series of numerical simulations, the delamination processes in collisional orogens are summarized into three modes: (1) pro-plate delamination, (2) retro-plate delamination, and (3) a transitional double-plates (both the pro- and retro-plate) delamination. The controlling factors, as well as the geological applications in nature, of the variable delamination modes are also discussed.

  17. Aniakchak Crater, Alaska Peninsula

    USGS Publications Warehouse

    Smith, Walter R.

    1925-01-01

    The discovery of a gigantic crater northwest of Aniakchak Bay (see fig. 11) closes what had been thought to be a wide gap in the extensive series of volcanoes occurring at irregular intervals for nearly 600 miles along the axial line of the Alaska Peninsula and the Aleutian Islands. In this belt there are more active and recently active volcanoes than in all the rest of North America. Exclusive of those on the west side of Cook Inlet, which, however, belong to the same group, this belt contains at least 42 active or well-preserved volcanoes and about half as many mountains suspected or reported to be volcanoes. The locations of some of these mountains and the hot springs on the Alaska Peninsula and the Aleutian Islands are shown on a map prepared by G. A. Waring. Attention has been called to these volcanoes for nearly two centuries, but a record of their activity since the discovery of Alaska is far from being complete, and an adequate description of them as a group has never been written. Owing to their recent activity or unusual scenic beauty, some of the best known of the group are Mounts Katmai, Bogoslof, and Shishaldin, but there are many other beautiful and interesting cones and craters.

  18. Moho depth model from GOCE gravity gradient data for the Central Asian Orogenic Belt

    NASA Astrophysics Data System (ADS)

    Guy, Alexandra; Holzrichter, Nils; Ebbing, Jörg

    2016-04-01

    GOCE gravity gradient data are used together with published seismic data to determine the Moho geometry and the isostatic state of the Central Asian Orogenic Belt (CAOB). The CAOB is an accretionary orogen formed during the Palaeozoic at the periphery of the Siberian cratonic nucleus by the successive amalgamation of different types of crust (cratonic, oceanic, passive margin, magmatic arc, back-arc, ophiolites, accretionary wedge) followed by an oroclinal bending during Permian-Triassic times. This large area was and is still of great interest for geoscientific studies mainly because of its potential in mineral and fossil resources and also for its outstanding, but still misunderstood, geodynamic evolution. However, the geophysical investigations remain scarce due to the remoteness of the area. A systematic analysis of the crustal thickness has been omitted yet, although the geometry of the crust-mantle boundary (Moho boundary) provides crucial information on the evolution of the lithosphere and on the coupling between upper mantle and the crust - particularly interesting for oroclinal bending processes. In this study, the gravity gradient data of GOCE are used to investigate the topography of the Moho for Mongolia and its surroundings. In addition, we used inversion of gravity data and calculation of the isostatic Moho from topographic data to the World Gravity Map (WGM) 2012 satellite-terrestrial model of the Earth's gravity anomalies and these results are compared together with those obtained for the GOCE gravity data. The results of the gravity inversion are constrained by the few xenolith studies and the seismic data available: the receiver function seismic method for north and central Mongolia, deep seismic sounding and seismic reflection profiles in northern China; and tomography in southern Siberia. Then, the effects of isostatic compensation are evaluated by the comparison between the results of the gravity inversion and the isostatic Moho. Finally, a 3D

  19. Sediment supply from the Betic-Rif orogen to basins through Neogene

    NASA Astrophysics Data System (ADS)

    Iribarren, L.; Vergés, J.; Fernàndez, M.

    2009-09-01

    We present a quantification of total and partial (divided by time slices) sedimentary volumes in the Neogene basins of the Betic-Rif orogen. These basins include the Alboran Sea, the intramontane basins, the Guadalquivir and Rharb foreland basins and the Atlantic Margin of the Gibraltar Arc. The total volume of Neogene sediments deposited in these basins is ~ 209,000 km 3 and is equally distributed between the internal (Alboran Basin and intramontane basins) and the external basins (foreland basins and Atlantic Margin). The largest volumes are recorded by the Alboran Basin (89,600 km 3) and the Atlantic Margin (81,600 km 3). The Guadalquivir and Rharb basins amount 14,000 km 3 and 14,550 km 3, respectively whereas the intramontane basins record 9235 km 3. Calculated mean sediment accumulation rates for the early-middle Miocene show an outstanding asymmetry between the Alboran basin (0.24 mm/yr) and the foreland basins (0.06-0.07 mm/yr) and the Atlantic Margin (0.03 mm/yr). During the late Miocene, sedimentation rates range between 0.17 and 0.18 mm/yr recorded in the Alboran Basin and 0.04 mm/yr in the intramontane basins. In the Pliocene-Quaternary, the highest sedimentation rates are recorded in the Atlantic Margin reaching 0.22 mm/yr. Sedimentary contribution shows similar values for the inner and outer basins with a generalized increase from late Miocene to present (from 3500 to 6500 km 3/My). Interestingly, the Alboran Basin records the maximum sedimentary contribution during the late Miocene (5500 km 3/My), whereas the Atlantic Margin does during the Pliocene-Quaternary (6600 km 3/My). The spatial and time variability of the sediment supply from the Betic-Rif orogen to basins is closely related to the morphotectonic evolution of the region. The high sedimentation rates obtained in the Alboran Basin during the early-middle Miocene are related to active extensional tectonics, which produced narrow and deep basins in its western domain. The highest sedimentary

  20. Linking the Timescales of Orogenic growth and Climatic Feedback in Southern New Zealand: A Pilot Study

    NASA Astrophysics Data System (ADS)

    Batt, G. E.; Zwingmann, H.

    2008-12-01

    Orogenic systems are the rejuvenating engines of the Global Earth system, converting the thermal and kinetic energy of tectonic processes into uplift of the landscape that, in turn, drives erosion and renews the fertility of the biosphere. Understanding the relationships between tectonic uplift, erosion, and local climate, however, lags behind quantitative understanding of other areas of Earth Systems Science. The challenge in developing this field lies in the requirement of independently documenting the long-term evolution of these three systems for a given region. Although sensitive chronometric constraint has long been successfully derived for climatic and structural systems, an inability to constrain the temporal evolution of topography has represented a fundamental deficiency in our understanding. Without such chronometric constraint, correlation and testing of models of fundamental links between tectonic forcing and climate variation remain essentially arbitrary and artificial. We present here the results of a pilot investigation into the feasibility of dating authigenic illite extracted from Miocene-Recent paleosols and weathered surfaces formed during the development of the Southern Alps of New Zealand. Chamberlain et al. (1999) have previously attributed a stable isotope signature resolved in Kaolinite from these weathered horizons as recording development of strongly asymmetric climatic zonation as a consequence of Mio-Pliocene growth of the Southern Alps. By re-visiting this approach to assessing the topographic record of the orogen through isotopic proxy measurements, and combining this with direct chronological constraint of the weathered materials making up this record, we hope to examine the potential of developing a robust framework in which to investigate and model the linked processes of mountain growth and local scale climatic effects. Initial results have been mixed. Clay fractions have been separated from 7 variably weathered paleosols and

  1. Sedimentation in detachment-dominated extensional orogens: Examples from the Mojave extensional belt, California

    SciTech Connect

    Travis, C.J.; Dokka, R.K. )

    1990-06-01

    Recent studies of syntectonic sedimentary rocks of the early Miocene Mojave Extensional Belt (MEB) provide new data on sediment dispersal within an evolving continental extensional orogen. Sediment dispersal within the MEB apparently reflects the evolution of the major tectonic elements of the belt. Sediments deposited in the breakaway zone of the Daggett terrane in the Newberry Mountains were derived from unextended regions to the southwest and from intraterrane tilted fault blocks to the northeast. Sediment dispersal patterns near transfer zones are typically perpendicular to extensional axes. In the Daggett terrane, coarse clastic materials were transported northwestward from unextended areas across the Kane Springs transfer fault into upper plate fault-bounded basins. Sequences accumulated in the hanging walls of upper plate tilted fault blocks exhibit geometries similar to those of breakaway zones, but show differences in thickness and textural attributes. Intraterrane arching is indicated by dispersal patterns in conglomerates of the central Cady Mountains in the Daggett terrane. Locally, detachment faulting may be succeeded by high-angle, normal faulting. In the Waterman terrane, this has resulted in relative uplift and the development of a metamorphic core complex in the Waterman Hills-Mitchell Range area. The uplift and unroofing history of the Waterman Hills is recorded in the thick deposits of the formation of Ross Canyon and the Barstow Formation of the Mud Hills.

  2. Active shortening within the Himalayan orogenic wedge implied by the 2015 Gorkha earthquake

    NASA Astrophysics Data System (ADS)

    Whipple, Kelin X.; Shirzaei, Manoochehr; Hodges, Kip V.; Ramon Arrowsmith, J.

    2016-09-01

    Models of Himalayan neotectonics generally attribute active mountain building to slip on the Himalayan Sole Thrust, also termed the Main Himalayan Thrust, which accommodates underthrusting of the Indian Plate beneath Tibet. However, the geometry of the Himalayan Sole Thrust and thus how slip along it causes uplift of the High Himalaya are unclear. We show that the geodetic record of the 2015 Gorkha earthquake sequence significantly clarifies the architecture of the Himalayan Sole Thrust and suggests the need for revision of the canonical view of how the Himalaya grow. Inversion of Gorkha surface deformation reveals that the Himalayan Sole Thrust extends as a planar gently dipping fault surface at least 20-30 km north of the topographic front of the High Himalaya. This geometry implies that building of the high range cannot be attributed solely to slip along the Himalayan Sole Thrust over a steep ramp; instead, shortening within the Himalayan wedge is required to support the topography and maintain rapid rock uplift. Indeed, the earthquake sequence may have included a moderate rupture (Mw 6.9) on an out-of-sequence thrust fault at the foot of the High Himalaya. Such internal deformation is an expected response to sustained, focused rapid erosion, and may be common to most compressional orogens.

  3. Rural Alaska Mentoring Project (RAMP)

    ERIC Educational Resources Information Center

    Cash, Terry

    2011-01-01

    For over two years the National Dropout Prevention Center (NDPC) at Clemson University has been supporting the Lower Kuskokwim School District (LKSD) in NW Alaska with their efforts to reduce high school dropout in 23 remote Yup'ik Eskimo villages. The Rural Alaska Mentoring Project (RAMP) provides school-based E-mentoring services to 164…

  4. Alaska Native Land Claims. [Textbook].

    ERIC Educational Resources Information Center

    Arnold, Robert D.; And Others

    Written for students at the secondary level, this textbook on Alaska Native land claims includes nine chapters, eight appendices, photographs, maps, graphs, bibliography, and an index. Chapters are titled as follows: (1) Earliest Times (Alaska's first settlers, eighteenth century territories, and other claimants); (2) American Indians and Their…

  5. GeoFORCE Alaska, A Successful Summer Exploring Alaska's Geology

    NASA Astrophysics Data System (ADS)

    Wartes, D.

    2012-12-01

    Thirty years old this summer, RAHI, the Rural Alaska Honors Institute is a statewide, six-week, summer college-preparatory bridge program at the University of Alaska Fairbanks for Alaska Native and rural high school juniors and seniors. This summer, in collaboration with the University of Texas Austin, the Rural Alaska Honors Institute launched a new program, GeoFORCE Alaska. This outreach initiative is designed to increase the number and diversity of students pursuing STEM degree programs and entering the future high-tech workforce. It uses Earth science to entice kids to get excited about dinosaurs, volcanoes and earthquakes, and includes physics, chemistry, math, biology and other sciences. Students were recruited from the Alaska's Arctic North Slope schools, in 8th grade to begin the annual program of approximately 8 days, the summer before their 9th grade year and then remain in the program for all four years of high school. They must maintain a B or better grade average and participate in all GeoFORCE events. The culmination is an exciting field event each summer. Over the four-year period, events will include trips to Fairbanks and Anchorage, Arizona, Oregon and the Appalachians. All trips focus on Earth science and include a 100+ page guidebook, with tests every night culminating with a final exam. GeoFORCE Alaska was begun by the University of Alaska Fairbanks in partnership with the University of Texas at Austin, which has had tremendous success with GeoFORCE Texas. GeoFORCE Alaska is managed by UAF's long-standing Rural Alaska Honors Institute, that has been successfully providing intense STEM educational opportunities for Alaskan high school students for over 30 years. The program will add a new cohort of 9th graders each year for the next four years. By the summer of 2015, GeoFORCE Alaska is targeting a capacity of 160 students in grades 9th through 12th. Join us to find out more about this exciting new initiative, which is enticing young Alaska Native

  6. The nature of orogenic crust in the central Andes

    NASA Astrophysics Data System (ADS)

    Beck, Susan L.; Zandt, George

    2002-10-01

    The central Andes (16°-22°S) are part of an active continental margin mountain belt and the result of shortening of the weak western edge of South America between the strong lithospheres of the subducting Nazca plate and the underthrusting Brazilian shield. We have combined receiver function and surface wave dispersion results from the BANJO-SEDA project with other geophysical studies to characterize the nature of the continental crust and mantle lithospheric structure. The major results are as follows: (1) The crust supporting the high elevations is thick and has a felsic to intermediate bulk composition. (2) The relatively strong Brazilian lithosphere is underthrusting as far west (65.5°W) as the high elevations of the western part of the Eastern Cordillera (EC) but does not underthrust the entire Altiplano. (3) The subcrustal lithosphere is delaminating piecemeal under the Altiplano-EC boundary but is not completely removed beneath the central Altiplano. The Altiplano crust is characterized by a brittle upper crust decoupled from a very weak lower crust that is dominated by ductile deformation, leading to lower crustal flow and flat topography. In contrast, in the high-relief, inland-sloping regions of the EC and sub-Andean zone, the upper crust is still strongly coupled across the basal thrust of the fold-thrust belt to the underthrusting Brazilian Shield lithosphere. Subcrustal shortening between the Altiplano and Brazilian lithosphere appears to be accommodated by delamination near the Altiplano-EC boundary. Our study suggests that orogenic reworking may be an important part of the "felsification" of continental crust.

  7. Lithosphere profiles across Central Asian Orogenic Belt in Uzbekistan

    NASA Astrophysics Data System (ADS)

    Sidorova, Irina

    2014-05-01

    This study was made with complex geophysical and geological observations by the DSS-MRW seismic profiles, which cross CAOB in the southern Tien Shan in part of Uzbekistan. The southern Tien Shan is situated along the SW margin of the Central Asian Orogenic Belt-one of key region for understanding both the amalgamation of Eurasia and the Phanerozoic growth of the CAOB itself. The aim of our study was to reveal new features, which characteristic of the upper mantle rocks, related to morphology of bodies. their physical properties, consisting mainly in their contrasting values for contiguous blocks, and general increased velocity and density of the rocks they contain. The most interesting results were obtained by three DSS profiles in Central Kyzylkum: anomalous geological objects (Muruntau, Kokpatas, Kuldjuktau and other) having anomalous high velocity and density values, have been mapped at different depths within the part of CAOB. The alteration zones, the tectonic faults and circular structures related to the cones and calderas determined these methods and checked by group truth studies may the target areas to explore for some new deposits.New regional features have been revealed:they include peculiarities of the Earth's crust's deep geological structure and spatial distribution of deposits:they are contrast areas of the earth's crust geoblocks with anomalously high and low seismic and density parameters. Mapping of these zones helps select new ways in th search for mineral deposits. All the final products was created using ArcGIS and RS methodologies:1)DEM on the base of SRTM dataset;2) 3-D models of crustal basement and Moho surface;3) 3-D potential fields modeling;4) tabular database of tectonic, boreholes data;5)various types of original geological information concerning the Paleozoic to present geological evolution of the region.

  8. 2013 Alaska Performance Scholarship Outcomes Report

    ERIC Educational Resources Information Center

    Rae, Brian

    2013-01-01

    In accordance with Alaska statute the departments of Education & Early Development (EED) and Labor and Workforce Development (DOLWD), the University of Alaska (UA), and the Alaska Commission on Postsecondary Education (ACPE) present this second annual report on the Alaska Performance Scholarship (APS). Among the highlights: (1) In the public…

  9. Eruptive history and petrology of Mount Drum volcano, Wrangell Mountains, Alaska

    USGS Publications Warehouse

    Richter, D.H.; Moll-Stalcup, E. J.; Miller, T.P.; Lanphere, M.A.; Dalrymple, G.B.; Smith, R.L.

    1994-01-01

    Mount Drum is one of the youngest volcanoes in the subduction-related Wrangell volcanic field (80x200 km) of southcentral Alaska. It lies at the northwest end of a series of large, andesite-dominated shield volcanoes that show a northwesterly progression of age from 26 Ma near the Alaska-Yukon border to about 0.2 Ma at Mount Drum. The volcano was constructed between 750 and 250 ka during at least two cycles of cone building and ring-dome emplacement and was partially destroyed by violent explosive activity probably after 250 ka. Cone lavas range from basaltic andesite to dacite in composition; ring-domes are dacite to rhyolite. The last constructional activity occured in the vicinity of Snider Peak, on the south flank of the volcano, where extensive dacite flows and a dacite dome erupted at about 250 ka. The climactic explosive eruption, that destroyed the top and a part of the south flank of the volcano, produced more than 7 km3 of proximal hot and cold avalanche deposits and distal mudflows. The Mount Drum rocks have medium-K, calc-alkaline affinities and are generally plagioclase phyric. Silica contents range from 55.8 to 74.0 wt%, with a compositional gap between 66.8 and 72.8 wt%. All the rocks are enriched in alkali elements and depleted in Ta relative to the LREE, typical of volcanic arc rocks, but have higher MgO contents at a given SiO2, than typical orogenic medium-K andesites. Strontium-isotope ratios vary from 0.70292 to 0.70353. The compositional range of Mount Drum lavas is best explained by a combination of diverse parental magmas, magma mixing, and fractionation. The small, but significant, range in 87Sr/86Sr ratios in the basaltic andesites and the wide range of incompatible-element ratios exhibited by the basaltic andesites and andesites suggests the presence of compositionally diverse parent magmas. The lavas show abundant petrographic evidence of magma mixing, such as bimodal phenocryst size, resorbed phenocrysts, reaction rims, and

  10. New geomorphic data on the active Taiwan orogen: A multisource approach

    NASA Technical Reports Server (NTRS)

    Deffontaines, B.; Lee, J.-C.; Angelier, J.; Carvalho, J.; Rudant, J.-P.

    1994-01-01

    A multisource and multiscale approach of Taiwan morphotectonics combines different complementary geomorphic analyses based on a new elevation model (DEM), side-looking airborne radar (SLAR), and satellite (SPOT) imagery, aerial photographs, and control from independent field data. This analysis enables us not only to present an integrated geomorphic description of the Taiwan orogen but also to highlight some new geodynamic aspects. Well-known, major geological structures such as the Longitudinal Valley, Lishan, Pingtung, and the Foothills fault zones are of course clearly recognized, but numerous, previously unrecognized structures appear distributed within different regions of Taiwan. For instance, transfer fault zones within the Western Foothills and the Central Range are identified based on analyses of lineaments and general morphology. In many cases, the existence of geomorphic features identified in general images is supported by the results of geological field analyses carried out independently. In turn, the field analyses of structures and mechanisms at some sites provide a key for interpreting similar geomorphic featues in other areas. Examples are the conjugate pattern of strike-slip faults within the Central Range and the oblique fold-and-thrust pattern of the Coastal Range. Furthermore, neotectonic and morphological analyses (drainage and erosional surfaces) has been combined in order to obtain a more comprehensive description and interpretation of neotectonic features in Taiwan, such as for the Longitudinal Valley Fault. Next, at a more general scale, numerical processing of digital elevation models, resulting in average topography, summit level or base level maps, allows identification of major features related to the dynamics of uplift and erosion and estimates of erosion balance. Finally, a preliminary morphotectonic sketch map of Taiwan, combining information from all the sources listed above, is presented.

  11. Geologic framework of the Alaska Peninsula, southwest Alaska, and the Alaska Peninsula terrane

    USGS Publications Warehouse

    Wilson, Frederic H.; Detterman, Robert L.; DuBois, Gregory D.

    2015-01-01

    The boundaries separating the Alaska Peninsula terrane from other terranes are commonly indistinct or poorly defined. A few boundaries have been defined at major faults, although the extensions of these faults are speculative through some areas. The west side of the Alaska Peninsula terrane is overlapped by Tertiary s

  12. Geologic framework of the Alaska Peninsula, southwest Alaska, and the Alaska Peninsula terrane

    USGS Publications Warehouse

    Wilson, Frederic H.; Detterman, Robert L.; DuBois, Gregory D.

    2015-01-01

    The boundaries separating the Alaska Peninsula terrane from other terranes are commonly indistinct or poorly defined. A few boundaries have been defined at major faults, although the extensions of these faults are speculative through some areas. The west side of the Alaska Peninsula terrane is overlapped by Tertiary sedimentary and volcanic rocks and Quaternary deposits.

  13. Bryophytes from Tuxedni Wilderness area, Alaska

    USGS Publications Warehouse

    Schofield, W.B.; Talbot, S. S.; Talbot, S.L.

    2002-01-01

    The bryoflora of two small maritime islands, Chisik and Duck Island (2,302 ha), comprising Tuxedni Wilderness in western lower Cook Inlet, Alaska, was examined to determine species composition in an area where no previous collections had been reported. The field study was conducted from sites selected to represent the totality of environmental variation within Tuxedni Wilderness. Data were analyzed using published reports to compare the bryophyte distribution patterns at three levels, the Northern Hemisphere, North America, and Alaska. A total of 286 bryophytes were identified: 230 mosses and 56 liverworts. Bryum miniatum, Dichodontium olympicum, and Orthotrichum pollens are new to Alaska. The annotated list of species for Tuxedni Wilderness expands the known range for many species and fills distribution gaps within Hulte??n's Central Pacific Coast district. Compared with bryophyte distribution in the Northern Hemisphere, the bryoflora of Tuxedni Wilderness primarily includes taxa of boreal (61%), montane (13%), temperate (11%), arctic-alpine (7%), cosmopolitan (7%), distribution; 4% of the total moss flora are North America endemics. A brief summary of the botanical exploration of the general area is provided, as is a description of the bryophytes present in the vegetation and habitat types of Chisik and Duck Islands.

  14. Crustal Architecture along BABEL and FIRE profiles - Insight in the Growth of the Svecofennian Orogen

    NASA Astrophysics Data System (ADS)

    Korja, Annakaisa

    2016-04-01

    The Precambrian Svecofennian orogen is characterized by LP- HT metamorphism and voluminous granitoid magmatism that usually develop in transitional to plateau stages of a collisional orogeny. Deep seismic reflection profiles BABEL and FIRE have been interpreted using PURC concepts: prowedge, retrowedg, uplifted plug, subduction conduit and elevated plateau. BABEL profiles image a transitional orogen with several nuclei displaying prowedge-uplifted plug-retrowedge architecture above paleo-subduction conduits. Prowedge and -continent are on the south-southwestern side and retrowedge and -continent on the north-northwestern side. This implies a long-lived southwesterly retreating convergent margin, where transitional accretionary orogens have developed. FIRE1-3 profiles images a hot orogen with a pronounced super-infra structure, typical of an elevated plateau stage, below the Central Finland Granitoid Complex. Large volumes of granitoid intrusions suggest large scale melting of the middle and/or lower crust. Reflection structures, analogue and numerical modeling suggest midcrustal flow. The plateau is flanked by prowedges that are characterized by HT-LP migmatite belts. The Svecofennian orogeny has progressed to an elevated plateau stage in the thickest core of the orogen, west of the arc-continent collision zone.

  15. Early Cretaceous extensional reworking of the Triassic HP-UHP metamorphic orogen in Eastern China

    NASA Astrophysics Data System (ADS)

    Lin, Wei; Ji, Wenbin; Faure, Michel; Wu, Lin; Li, Qiuli; Shi, Yonghong; Scharer, Urs; Wang, Fei; Wang, Qingchen

    2015-11-01

    Corresponding to the Early Mesozoic continental subduction between the North China Block (NCB) and the South China Block (SCB), the Tongbaishan-Hong'an-Dabieshan-Sulu massifs are famous for their HP-UHP metamorphism. More than 50% of the HP-UHP Orogenic Belt was significantly reworked by Early Cretaceous extensional tectonics. This Early Cretaceous event with a fast cooling period, at 130-120 Ma, superimposed on the Early Mesozoic HP-UHP orogenic belt and intensively changed the architecture of this orogen. Each individual segment documents different Early Cretaceous extensional structures, namely the central Tongbaishan domain is a metamorphic core complex (MCC) represented by an A-type non-cylindrical antiform; the central Dabieshan domain is a typical Cordilleran-type migmatite-cored MCC; the Southern Sulu UHP domain is a "wedge-shaped" structure exhumed by a simple detachment fault. These late stage extensional structures expose the previous HP-UHP orogenic belt as fragments along the NCB-SCB boundary. The geodynamic setting of this Early Cretaceous extensional tectonics along the HP-UHP orogen is a part of a 1000 km-scale crustal extension belt that is widespread in eastern Eurasia continent from Trans-Baikal to the central part of SCB. Convective erosion or delamination of the mantle lithosphere might be considered as a possible mechanism for mantle removal.

  16. Early Cretaceous extensional reworking of the Triassic HP-UHP metamorphic orogen in Eastern China

    NASA Astrophysics Data System (ADS)

    Lin, W.; Ji, W.; Faure, M.; Wu, L.; Li, Q. L.; Shi, Y.; Scharer, U.; Wang, F.; Wang, Q.

    2015-12-01

    Corresponding to the Early Mesozoic continental subduction between the North China Block (NCB) and the South China Block (SCB), the Tongbaishan-Hong'an-Dabieshan-Sulu massifs are famous for their HP-UHP metamorphism. More than 50% of the HP-UHP Orogenic Belt was significantly reworked by Early Cretaceous extensional tectonics. This Early Cretaceous event with a fast cooling period, at 130-120 Ma, superimposed on the Early Mesozoic HP-UHP orogenic belt and intensively changed the architecture of this orogen. Each individual segment documents different Early Cretaceous extensional structures, namely the central Tongbaishan domain is a metamorphic core complex (MCC) represented by an A-type non-cylindrical antiform; the central Dabieshan domain is a typical Cordilleran-type migmatite-cored MCC; the Southern Sulu UHP domain is a "wedge-shaped" structure exhumed by a simple detachment fault. These late stage extensional structures expose the previous HP-UHP orogenic belt as fragments along the NCB-SCB boundary. The geodynamic setting of this Early Cretaceous extensional tectonics along the HP-UHP orogen is a part of a 1000 km-scale crustal extension belt that is widespread in eastern Eurasia continent from Trans-Baikal to the central part of the South China Block. Convective erosion or delamination of the mantle lithosphere might be considered as a possible mechanism for mantle removal.

  17. Mantle Transition Zone Discontinuities Beneath Alaska

    NASA Astrophysics Data System (ADS)

    Dahm, H. H.; Gao, S. S.; Liu, K. H.; Yang, B.

    2015-12-01

    The 410 and 660 km discontinuities (d410 and d660) beneath Alaska and adjacent areas are imaged by stacking radial receiver functions recorded by about 400 broadband seismic stations with up to 30 years of recording period, using the 1D IASP91 earth model. Significant and spatially systematic variations in the apparent depths of the d410 and d660 are observed. The mean apparent depth of d410 and d660 for the entire study area is 416±1.87 km and 664±1.83 km, respectively. The variations of the apparent depths of d410 and d660 result in a complex mantle transition zone (MTZ) structure. Central and south-central Alaska are characterized by a normal MTZ thickness, suggesting that the subducting Pacific slab does not thermally affect the upper MTZ. Beneath the Yakutat microplate, a complex MTZ structure is observed with an overall thin MTZ thickness, coinciding with a low velocity zone and thin lithospheric thickness revealed by previous seismic tomography and receiver function studies. Two large regions with hot MTZ are mapped beneath NNW and NNE Alaska with abnormal temperature ranges between +360 and +390 °K. Despite of the complexity of the MTZ structure beneath Alaska, the mean MTZ thickness for the entire Alaskan orocline is 247 ±2.76 km, suggesting normal MTZ temperature on average. For the majority of the areas, our study shows that lateral upper mantle velocity variations contribute the bulk of the observed apparent undulations of the MTZ discontinuities.

  18. Tracking glaciers with the Alaska seismic network

    NASA Astrophysics Data System (ADS)

    West, M. E.

    2015-12-01

    More than 40 years ago it was known that calving glaciers in Alaska created unmistakable seismic signals that could be recorded tens and hundreds of kilometers away. Their long monochromatic signals invited studies that foreshadowed the more recent surge in glacier seismology. Beyond a handful of targeted studies, these signals have remained a seismic novelty. No systematic attempt has been made to catalog and track glacier seismicity across the years. Recent advances in understanding glacier sources, combined with the climate significance of tidewater glaciers, have renewed calls for comprehensive tracking of glacier seismicity in coastal Alaska. The Alaska Earthquake Center has included glacier events in its production earthquake catalog for decades. Until recently, these were best thought of as bycatch—accidental finds in the process of tracking earthquakes. Processing improvements a decade ago, combined with network improvements in the past five years, have turned this into a rich data stream capturing hundreds of events per year across 600 km of the coastal mountain range. Though the source of these signals is generally found to be iceberg calving, there are vast differences in behavior between different glacier termini. Some glaciers have strong peaks in activity during the spring, while others peak in the late summer or fall. These patterns are consistent over years pointing to fundamental differences in calving behavior. In several cases, changes in seismic activity correspond to specific process changes observed through other means at particular glacier. These observations demonstrate that the current network is providing a faithful record of the dynamic behavior of several glaciers in coastal Alaska. With this as a starting point, we examine what is possible (and not possible) going forward with dedicated detection schemes.

  19. Silver in the Gulf of Alaska

    NASA Astrophysics Data System (ADS)

    Gallon, C.; Flegal, A.

    2009-12-01

    Dramatic increases in coal combustion in Asia over the last three decades have induced the transport of substantial atmospheric emissions over the North Pacific Ocean, where they can potentially alter trace element biogeochemical cycles in oceanic surface waters and North America. These perturbations have recently been evidenced by measurements of elevated silver, which is a geochemical marker of coal combustion, in surface waters of the North Pacific, where this metal now appears to be the most contaminated trace element, relative to its natural concentration. However measurements there have been few and far between since they were first made over two decades ago. We partially fill this void by presenting vertical profiles of silver concentration (HR-ICPMS) measured in archived samples from the VERTEX VII (Vertical Transport and Exchange) cruise (1989), which covered a North South transect extending to the Alaska Gyre, as well as in new samples from the GoA (Gulf of Alaska) cruise (2007) collected in the Alaska Gyre. Our results confirm that within the water column, silver exhibits a nutrient type behavior, as was previously observed in other oceanic waters. In intermediate depth waters, concentrations in all the profiles are higher than those measured in the southern hemisphere and North East Pacific in the early 1980s, and in the range of those reported more recently in the Western and Central North Pacific. In the Alaska Gyre, water samples collected 20 years apart present comparable silver concentrations. Measurements from this study also confirm that silver is significantly correlated with dissolved silica, with plots of Ag versus Si showing a concave shape typical of Pacific waters, suggesting that the biogeochemical cycles of these two elements are linked.

  20. 78 FR 53137 - Flint Hills Resources Alaska, LLC, BP Pipelines (Alaska) Inc., ConocoPhillips Transportation...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-08-28

    ...Phillips Transportation Alaska, Inc., ExxonMobil Pipeline Company; Notice of Complaint Take notice that on... formal complaint against BP Pipelines (Alaska) Inc., ConocoPhillips Transportation Alaska, Inc.,...

  1. Porphyry copper assessment of the Central Asian Orogenic Belt and eastern Tethysides: China, Mongolia, Russia, Pakistan, Kazakhstan, Tajikistan, and India: Chapter X in Global mineral resource assessment

    USGS Publications Warehouse

    Mihalasky, Mark J.; Ludington, Stephen; Hammarstrom, Jane M.; Alexeiev, Dmitriy V.; Frost, Thomas P.; Light, Thomas D.; Robinson,, Gilpin R.; Briggs, Deborah A.; Wallis, John C.; Miller, Robert J.; Bookstrom, Arthur A.; Panteleyev, Andre; Chitalin, Andre; Seltmann, Reimar; Guangsheng, Yan; Changyun, Lian; Jingwen, Mao; Jinyi, Li; Keyan, Xiao; Ruizhao, Qiu; Jianbao, Shao; Gangyi, Shai; Yuliang, Du

    2015-01-01

    The U.S. Geological Survey collaborated with international colleagues to assess undiscovered resources in porphyry copper deposits in the Central Asian Orogenic Belt and eastern Tethysides. These areas host 20 known porphyry copper deposits, including the world class Oyu Tolgoi deposit in Mongolia that was discovered in the late 1990s. The study area covers major parts of the world’s largest orogenic systems. The Central Asian Orogenic Belt is a collage of amalgamated Precambrian through Mesozoic terranes that extends from the Ural Mountains in the west nearly to the Pacific Coast of Asia in the east and records the evolution and final closure of the Paleo-Asian Ocean in Permian time. The eastern Tethysides, the orogenic belt to the south of the Central Asian Orogenic Belt, records the evolution of another ancient ocean system, the Tethys Ocean. The evolution of these orogenic belts involved magmatism associated with a variety of geologic settings appropriate for formation of porphyry copper deposits, including subduction-related island arcs, continental arcs, and collisional and postconvergent settings. The original settings are difficult to trace because the arcs have been complexly deformed and dismembered by younger tectonic events. Twelve mineral resource assessment tracts were delineated to be permissive for the occurrence of porphyry copper deposits based on mapped and inferred subsurface distributions of igneous rocks of specific age ranges and compositions. These include (1) nine Paleozoic tracts in the Central Asian Orogenic Belt, which range in area from about 60,000 to 800,000 square kilometers (km2); (2) a complex area of about 400,000 km2 on the northern margin of the Tethysides, the Qinling-Dabie tract, which spans central China and areas to the west, encompassing Paleozoic through Triassic igneous rocks that formed in diverse settings; and (3) assemblages of late Paleozoic and Mesozoic rocks that define two other tracts in the Tethysides, the 100

  2. Trans-Alaska pipeline

    SciTech Connect

    Not Available

    1991-07-01

    The Trans-Alaska Pipeline system transports nearly 25 percent of the nation's domestically produced crude oil. Since operations began in 1977, the system has delivered over 8 billion barrels of oil to Port Veldez for shipment. This paper reports that concerns have been raised about whether the system is meeting special engineering design and operations requirements imposed by federal and state regulators. GAO found that the five principal federal and state regulatory agencies have not pursued a systematic, disciplined, and coordinated approach to regulating the Trans-Alaska Pipeline System. Instead, these agencies have relied on the Alyeska Pipeline Service Company, which runs the system, to police itself. It was only after the Exxon Valdez spill and the discovery of corrosion that the regulators began to reevaluate their roles and focus on issues such as whether Alyeska's operating and maintenance procedures meet the pipelines, special engineering design and operating requirements, or whether Alyeska can adequately respond to a large oil spill. In January 1990, the regulators established a joint office to provide more effective oversight of the system. GAO believes that central leadership and a secured funding sources may help ensure that this office provides adequate oversight.

  3. Architecture of orogenic belts and convergent zones in Western Ishtar Terra, Venus

    NASA Technical Reports Server (NTRS)

    Head, James W.; Vorderbruegge, R. W.; Crumpler, L. S.

    1989-01-01

    Linear mountain belts in Ishtar Terra were recognized from Pioneer-Venus topography, and later Arecibo images showed banded terrain interpreted to represent folds. Subsequent analyses showed that the mountains represented orogenic belts, and that each had somewhat different features and characteristics. Orogenic belts are regions of focused shortening and compressional deformation and thus provide evidence for the nature of such deformation, processes of crustal thickening (brittle, ductile), and processes of crustal loss. Such information is important in understanding the nature of convergent zones on Venus (underthrusting, imbrication, subduction), the implications for rates of crustal recycling, and the nature of environments of melting and petrogenesis. The basic elements of four convergent zones and orogenic belts in western Ishtar Terra are identified and examined, and then assess the architecture of these zones (the manner in which the elements are arrayed), and their relationships. The basic nomenclature of the convergent zones is shown.

  4. Remagnetization and orogenic fluids: testing the hypothesis in the central Appalachians

    NASA Astrophysics Data System (ADS)

    Elmore, R. Douglas; Kelley, Jeff; Evans, Mark; Lewchuk, Michael T.

    2001-03-01

    Palaeomagnetic and geochemical studies on Devonian sedimentary rocks in the Valley and Ridge province in West Virginia indicate that the hypothesized relationship between orogenic fluids and remagnetization is not straightforward. The Helderberg Group, an aquitard, and the Oriskany Formation, a palaeoaquifer, both contain similar, synfolding late Palaeozoic chemical remanent magnetizations (CRMs) residing in magnetite. The results from the Oriskany Formation are consistent with remagnetization by orogenic fluids because the unit contains geochemical evidence for the migration of such fluids. In contrast, there is no geochemical evidence for the widespread migration of orogenic fluids into the Helderberg Group and thus the CRM cannot be related to such fluids. Another remagnetization mechanism, which remains elusive, must be responsible for the CRM in the Helderberg Group.

  5. Mechanical model for subduction-collision tectonics of Alpine-type compressional orogens

    NASA Astrophysics Data System (ADS)

    Beaumont, Christopher; Ellis, Susan; Hamilton, Juliet; Fullsack, Philippe

    1996-08-01

    Alpine-type orogens are characterized by three distinct convergent tectonic phases: subduction with deformation that has primarily single vergence, a transition from subduction to collision, and continental collision with double vergence. Although the Cenozoic history of the European Alps has additional complexities, a mechanical explanation for these three phases would provide the necessary crustal-scale framework in which to develop an understanding of the smaller-scale processes. We present results from a simple numerical model, which explain the mechanics of these three phases as a consequence of the changing buoyancy of the lithosphere subducted beneath the orogen. The development and exhumation of a subduction complex, suture zone, and basement nappe stack (Piemont suture, Penninic Nappes); the presence of a crustal-scale back fold and thrust (Insubric Line); and uplift of basement on the pro- (European) side of the orogen (external basement massifs) may be explained as a simple consequence of changing dynamics during the transition from subduction to collision.

  6. Reconciling the detrital zircon record and crustal growth within juvenile accretionary orogens

    NASA Astrophysics Data System (ADS)

    Spencer, C. J.; Cawood, P. A.; Roberts, N. M. W.

    2014-12-01

    Ancient cratons are generally characterised by Archaean cores surrounded by Proterozoic accretionary belts with large volumes of juvenile crust. Their crustal growth histories provide important insights into the genesis of continents and orogenic evolution. Whole-rock and detrital zircon isotopic studies are often used to deduce those histories, but the extent to which representative lithologies within the orogens are reliably sampled for such studies is not well established. This is especially true in cases where juvenile, zircon-poor mafic crust comprises a significant proportion of an orogen such as the East African (0.8-0.5 Ga), Namaqua-Natal (1.2-1.0 Ga), Trans-Hudson (1.9-1.8 Ga), and Kola (2.5 Ga). In particular, the Mesoproterozoic Namaqua-Natal orogenic belt (NNO) fringing the Kalahari Craton is a case in point in which Nd isotopic studies of whole-rock outcrop samples and U-Pb-Hf isotopic studies of detrital zircons from sediments of the Orange River (which drains the NNO) show different crust-formation ages and proportions of new and reworked crustal material. We hypothesise that this discrepancy is due to biasing of the detrital zircon record towards felsic rocks. Understanding the representative nature of the crustal archive preserved in detrital zircons remains critical for many studies of crustal evolution. We present data that: (a) addresses the scale of potential bias within an accretionary orogen containing large proportions of juvenile material, (b) demonstrates how the whole-rock and detrital zircon records can be reconciled for the Namaqua-Natal orogen to start, and (c) can be used to evaluate the effect of zircon bias on previous crustal growth models.

  7. Conodont thermal maturation patterns in Paleozoic and Triassic rocks, Northern Alaska - geologic and exploration implications

    SciTech Connect

    Harris, A.G.; Lane, H.R.; Tailleur, I.L.

    1985-04-01

    Metamorphism and thermal maturation patterns of sedimentary rocks in the Brooks Range, Alaska are discussed. Thermal patterns are based on conodont color alteration indices (CAI). Exploration significance of this study is given.

  8. Reconciling competing models for the tectono-stratigraphic zonation of the Variscan orogen in Western Europe

    NASA Astrophysics Data System (ADS)

    Murphy, J. Brendan; Quesada, Cecilio; Gutiérrez-Alonso, Gabriel; Johnston, Stephen T.; Weil, Arlo

    2016-06-01

    The Late Paleozoic Variscan orogen in Europe is the result of convergence and collision between Laurussia and Gondwana during closure of the Rheic Ocean. The orogen is divided into tectonostratigraphic zones that have a distinct curvature (Ibero-Armorican Arc, IAA) and record the Late Cambrian-Early Ordovician opening of the Rheic Ocean, the migration of terranes from the Gondwanan margin towards Laurussia, as well as the closure of that ocean and development of the IAA. Three models have emerged to explain the distribution of tectonostratigraphic zones:

  9. Basin-mountain structures and hydrocarbon exploration potential of west Junggar orogen in China

    NASA Astrophysics Data System (ADS)

    Wu, X.; Qi, X.; Zheng, M.

    2015-12-01

    Situated in northern Xinjiang, China, in NE-SW trend, West Junggar Orogen is adjacent to Altai fold belt on the north with the Ertix Fault as the boundary, North Tianshan fold belt on the south with the Ebinur Lake Strike-slip Fault as the boundary, and the Junggar Basin on the southeast with Zaire-Genghis Khan-Hala'alat fold belt as the boundary. Covering an area of about 10×104 km2 in China, there are medium and small intermontane basins, Burqin-Fuhai, Tacheng, Hefeng and Hoxtolgay, distributing inside the orogen. Tectonically West Junggar Orogen lies in the middle section of the Palaeo-Asian tectonic domain where the Siberia, Kazakhstan and Tarim Plates converge, and is the only orogen trending NE-SW in the Palaeo-Asian tectonic domain. Since the Paleozoic, the orogen experienced pre-Permian plate tectonic evolution and post-Permian intra-plate basin evolution. Complex tectonic evolution and multi-stage structural superimposition not only give rise to long term controversial over the basin basement property but also complex basin-mountain coupling relations, structures and basin superimposition modes. According to analysis of several kinds of geological and geophysical data, the orogen was dominated by compressive folding and thrust napping from the Siberia plate in the north since the Late Paleozoic. Compressive stress weakened from north to south, corresponding to subdued vertical movement and enhanced horizontal movement of crustal surface from north to south, and finally faded in the overthrust-nappe belt at the northwest margin of the Junggar Basin. The variation in compressive stress is consistent with the surface relief of the orogen, which is high in the north and low in the south. There are two kinds of basin-mountain coupling relationships, i.e. high angle thrusting and overthrusting and napping, and two kinds of basin superimposition modes, i.e. inherited and progressive, and migrating and convulsionary modes. West Junggar orogen has rich oil and gas

  10. Brittle tectonic history document the late- to post-orogenic evolution in the Lufilian Arc, RDCongo

    NASA Astrophysics Data System (ADS)

    Kipata, Louis; Delvaux, Damien; Ntabwoba Sebagenzi, Mwene; Cailteux, Jean-Jacques; Sintubin, Manuel

    2013-04-01

    Pan-African orogenic processes in Centra Africa involve intracontinental collision but also late-orogenic and intraplate processes that occurred in dominantly brittle conditions and can be documented by fault kinematic analysis and paleostress reconstructions. The Congo and Tanzania cratons in Central Africa are surrounded by Pan-African belts orogenic belts which all entered almost synchronously in collision stage in the early Paleozoic. While their tectonic history up to the collision stage is increasingly better documented by ductile deformation and metamorphic studies, their late evolution remain poorly known as soon as they enter in the brittle deformation regime. This results in an incomplete understanding of the orogenic processes, especially when the transition from ductile to the brittle regime occurred at the end of the orogenic compression. In this case, the last compressional stages and the entire late orogenic extension and extensional collapse stages remain undocumented. This is the case for the Lufilian orogeny which developed along the southern margin of the Congo Craton in Central Africa during the pan-African and was marked by a collisional event with crustal thickening and white schist formation at 550-530 Ma. The Lufilian Arc which forms the external part of the Lufilian orogeny developed as an arcuate fold-and-thrust belt. Its foreland is formed by the Kundelungu plateau, between the Bangweulu block and the Kibaran belt. This entire region is also tectonically active, as part of the incipient SW branch of the East African rift system. The long period between the paroxysm of the Lufilian orogeny and the late Neogene to Quaternary rifting has been investigated by fault-kinematic analysis and paleostress reconstruction in open mines spread over the entire arc and foreland. Paleostress tensors were computed from 23 sites totaling 1900 fault-slip data by interactive stress tensor inversion and data subset separation, and a succession of 8 brittle

  11. Heavy minerals in surficial sediments from lower Cook Inlet, Alaska

    USGS Publications Warehouse

    Wong, F.L.

    1984-01-01

    Amphiboles, orthopyroxenes, and clinopyroxenes dominate the heavy mineral suite of surficial sediments in lower Cook Inlet, Alaska. Sources for these sediments include the igneous arc terrane of the northeast Alaska Range, reworked intrabasinal sediments, and local drainages in lower Cook Inlet. The distribution of these deposits is a reflection of both the tidal currents and the prevailing southerly net movement from the head of Cook Inlet. The heavy mineral studies concur with similar findings from gravel analyses, clay mineral investigations, and quartz microtexture observations. ?? 1984 Springer-Verlag New York Inc.

  12. Geologic Map of the Nulato Quadrangle, West-Central Alaska

    USGS Publications Warehouse

    Patton, W.W.; Moll-Stalcup, E. J.

    2000-01-01

    Introduction The Nulato quadrangle encompasses approximately 17,000 km2 (6,500 mi2) of west-central Alaska within the Yukon River drainage basin. The quadrangle straddles two major geologic features-the Yukon-Koyukuk sedimentary basin, a huge triangle-shaped Cretaceous depression that stretches across western Alaska from the Brooks Range to the Yukon delta; and the Ruby geanticline,a broad uplift of pre-Cretaceous rocks that borders the Yukon-Koyukuk basin on the southeast. The Kaltag Fault crosses the quadrangle diagonally from northeast to southwest and dextrally offsets all major geologic features as much as 130 km.

  13. Margin Architecture and Sediment Flux as Controls on Submarine Fan Development: Tectonic-Climate Interactions in the Gulf of Alaska

    NASA Astrophysics Data System (ADS)

    Gulick, S. P. S.; Montelli, A.; Swartz, J. M.; Morey, S.; Jaeger, J. M.; Mix, A. C.; Reece, R.; Somchat, K.; Wagner, P. F.; Worthington, L. L.

    2015-12-01

    The oblique collision of the Yakutat microplate into southeast Alaska generates the St. Elias Mountains, a coastal orogen with significant moisture from the Gulf of Alaska resulting in large, temperate glacial systems that expand to and eventually cross the continental shelf during glacial maxima. We present an overview of the evolution of sediment routing on this margin from integration of seismic images, updated age models and core-log-seismic correlations from IODP Expedition 341 drilling sites, and mapping efforts from shelf, slope, and fan. We focus on the three dominant glacial systems during the climatically important intensification of Northern Hemisphere glaciation at the Plio-Pleistocene transition and the further intensification of glaciation since the mid-Pleistocene transition. Along strike, sediment delivery to deepwater from the three glacial systems varied according to Pleistocene shelf accommodation space. The Alsek crossed a narrower shelf with a bedrock high near the shelf edge; the Malaspina-Hubbard system crossed an undeformed, ~1 km deep shelf; the Bering-Bagley system crossed a several km deep shelf deforming as an active fold and thrust belt. The Malaspina and Bering catchments exhibit high exhumation rates onshore due to the Yakutat collision and upon reaching the shelf edge these glaciers generate trough mouth fans (TMFs) on the adjacent continental slope but only after first filling the available accommodation with glacigenic sediment and lowering the slope gradient through progradation. The Alsek crosses the shelf earliest but never with sufficient sediment flux to generate a TMF. An east-west transition in adjacent deepwater submarine channels that feed and generate the Surveyor Fan suggests that shelf accommodation and sediment flux are primary controls on sediment routing from orogen to submarine fan. Both of these parameters are in turn a function of initial tectonic architecture and ongoing orogen dynamics.

  14. Recent sedimentation, northeastern Port Valdez, Alaska

    NASA Astrophysics Data System (ADS)

    Palmer, Harold D.

    1981-09-01

    Sediments accumulating on the northeastern shore of Port Valdez, a fjord leading to Prince William Sound in southern Alaska, are derived from both deltaic and alluvial fan processes. The resulting thick wedge of Recent silts, sands, shells and gravels lies atop irregular ridges of local graywacke bedrock and scattered till deposits. Seismic reflection profiling augmented by soil borings indicates that rapid infilling and upbuilding has occurred at this site. Evidence of slumping suggests general instability of steep submarine slopes in an area characterized by strong earthquakes and large tidal ranges.

  15. Trans-Hudson Orogen of North America and Himalaya-Karakoram-Tibetan Orogen of Asia: Structural and thermal characteristics of the lower and upper plates

    NASA Astrophysics Data System (ADS)

    St-Onge, Marc R.; Searle, Michael P.; Wodicka, Natasha

    2006-08-01

    The Trans-Hudson Orogen (THO) of North America and the Himalaya-Karakoram-Tibetan Orogen (HKTO) of Asia preserve a Paleoproterozoic and Cenozoic record, respectively, of continent-continent collision that is notably similar in scale, duration and character. In THO, the tectonothermal evolution of the lower plate involves (1) early thin-skinned thrusting and Barrovian metamorphism, (2) out-of-sequence thrusting and high-T metamorphism, and (3) fluid-localized reequilibration, anatexis, and leucogranite formation. The crustal evolution of the Indian lower plate in HKTO involves (1) early subduction of continental crust to ultrahigh pressure (UHP) eclogite depths, (2) regional Barrovian metamorphism, and (3) widespread high-T metamorphism, anatexis, and leucogranite formation. The shallow depths of the high-T metamorphism in HKTO are consistent with early to mid-Miocene ductile flow of an Indian lower plate midcrustal channel, from beneath the southern Tibetan Plateau to the Greater Himalaya. Melt weakening of the lower plate in THO is not observed at a similar scale probably due to the paucity of pelitic lithologies. Tectonothermal events in the upper plate of both orogens include precollisional accretion of crustal blocks, emplacement of Andean-type plutonic suites, and high-T metamorphism. Syncollisional to postcollisional events include emplacement of garnet-biotite-muscovite leucogranites, anatectic granites, and sporadic metamorphism (up to 90 Myr following the onset of collision in THO). Comparing the type and duration of tectonothermal events for THO and HKTO supports the notion of tectonic uniformitarianism for at least the later half of dated Earth history and highlights the complementary nature of the rock record in an older "exhumed" orogen compared to one undergoing present-day orogenesis.

  16. Alaska Seismic Network Upgrade and Expansion

    NASA Astrophysics Data System (ADS)

    Sandru, J. M.; Hansen, R. A.; Estes, S. A.; Fowler, M.

    2009-12-01

    AEIC (Alaska Earthquake Information Center) has begun the task of upgrading the older regional seismic monitoring sites that have been in place for a number of years. Many of the original sites (some dating to the 1960's) are still single component analog technology. This was a very reasonable and ultra low power reliable system for its day. However with the advanced needs of today's research community, AEIC has begun upgrading to Broadband and Strong Motion Seismometers, 24 bit digitizers and high-speed two-way communications, while still trying to maintain the utmost reliability and maintaining low power consumption. Many sites have been upgraded or will be upgraded from single component to triaxial broad bands and triaxial accerometers. This provided much greater dynamic range over the older antiquated technology. The challenge is compounded by rapidly changing digital technology. Digitizersand data communications based on analog phone lines utilizing 9600 baud modems and RS232 are becoming increasingly difficult to maintain and increasingly expensive compared to current methods that use Ethernet, TCP/IP and UDP connections. Gaining a reliable Internet connection can be as easy as calling up an ISP and having a DSL connection installed or may require installing our own satellite uplink, where other options don't exist. LANs are accomplished with a variety of communications devices such as spread spectrum 900 MHz radios or VHF radios for long troublesome shots. WANs are accomplished with a much wider variety of equipment. Traditional analog phone lines are being used in some instances, however 56K lines are much more desirable. Cellular data links have become a convenient option in semiurban environments where digital cellular coverage is available. Alaska is slightly behind the curve on cellular technology due to its low population density and vast unpopulated areas but has emerged into this new technology in the last few years. Partnerships with organizations

  17. Amchitka, Alaska Site Fact Sheet

    SciTech Connect

    2011-12-15

    Amchitka Island is near the western end of the Aleutian Island chain and is the largest island in the Rat Island Group that is located about 1,340 miles west-southwest of Anchorage, Alaska, and 870 miles east of the Kamchatka Peninsula in eastern Russia. The island is 42 miles long and 1 to 4 miles wide, with an area of approximately 74,240 acres. Elevations range from sea level to more than 1,100 feet above sea level. The coastline is rugged; sea cliffs and grassy slopes surround nearly the entire island. Vegetation on the island is low-growing, meadow-like tundra grasses at lower elevations. No trees grow on Amchitka. The lowest elevations are on the eastern third of the island and are characterized by numerous shallow lakes and heavily vegetated drainages. The central portion of the island has higher elevations and fewer lakes. The westernmost 3 miles of the island contains a windswept rocky plateau with sparse vegetation.

  18. The crustal structures from Wuyi-Yunkai orogen to Taiwan orogen: the onshore-offshore wide-angle seismic experiment of TAIGER and ATSEE projects

    NASA Astrophysics Data System (ADS)

    Kuochen, H.; Kuo, N. Y. W.; Wang, C. Y.; Jin, X.; Cai, H. T.; Lin, J. Y.; Wu, F. T.; Yen, H. Y.; Huang, B. S.; Liang, W. T.; Okaya, D. A.; Brown, L. D.

    2015-12-01

    The crustal structure is key information for understanding the tectonic framework and geological evolution in the southeastern China and its adjacent area. In this study, we integrated the data sets from the TAIGER and ATSEE projects to resolve onshore-offshore deep crustal seismic profiles from the Wuyi-Yunkai orogen to the Taiwan orogen in southeastern China. Totally, there are three seismic profiles resolved and the longest profile is 850 km. Unlike 2D and 3D first arrival travel-time tomography from previous studies, we used both refracted and reflected phases (Pg, Pn, PcP, and PmP) to model the crustal structures and the crustal reflectors. 40 shots, 2 earthquakes, and about 1,950 stations were used and 15,319 arrivals were picked among three transects. As a result, the complex crustal evolution since Paleozoic era are shown, which involved the closed Paleozoic rifted basin in central Fujian, the Cenozoic extension due to South China sea opening beneath the coastline of southern Fujian, and the on-going collision of the Taiwan orogen.

  19. How does the mid-crust accommodate deformation in large, hot collisional orogens? A review of recent research in the Himalayan orogen

    NASA Astrophysics Data System (ADS)

    Cottle, John M.; Larson, Kyle P.; Kellett, Dawn A.

    2015-09-01

    The presence of hot, weak crust is a central component of recent hypotheses that seek to explain the evolution of continent-continent collisions, and in particular may play an important role in accommodating the >3000 km of convergence within the Himalaya-Tibetan collision over the last ˜55 Myr. Models that implicate flow of semi-viscous midcrustal rocks south toward the front of the Himalayan orogen, 'channel flow', are able to account for many geologic observations in the Himalaya, while alternative models of collision, particularly 'thrust-wedge taper', demonstrate that much of the observed geology could have formed in the absence of a low-viscosity mid-crustal layer. Several recent studies, synthesized here, have prompted a shift from initial assumptions that channel flow and thrust-wedge taper processes are by definition mutually exclusive. These new studies reveal the presence of several tectonometamorphic discontinuities in the midcrust that appear to reflect a continuum of deformation in which both channel- and wedge-type processes operate in spatially and temporally distinct domains within the orogen, and further, that the system may migrate back and forth between these types of behavior. This continuum of deformation styles within the collisional system is of crucial importance for explaining the evolution of the Himalayan orogen and, hence, for understanding the evolution of Earth's many continent-continent collision zones.

  20. Sulfur- and lead-isotope signatures of orogenic gold mineralisation associated with the Hill End Trough, Lachlan Orogen, New South Wales, Australia

    NASA Astrophysics Data System (ADS)

    Downes, P. M.; Seccombe, P. K.; Carr, G. R.

    2008-11-01

    The Hill End Trough (HET) is a deformed middle Silurian to Early Devonian sediment-dominated rift within the northeastern Lachlan Orogen. The HET hosts the Hill End, Hargraves, Napoleon Reefs, Stuart Town and Windeyer low-sulfide orogenic gold deposits. Adjacent to the HET are the Bodangora and Gulgong gold deposits. In this study we present 91 new sulfur- and 18 new lead-isotope analyses and collate a further 25 sulfur- and 32 lead-isotopes analyses from unpublished sources for these deposits. Larger gold deposits in the HET have near 0 δ34S‰ values indicating that sulfur in these systems was sourced from a magmatic reservoir. The dominant lead isotope signature for HET-hosted deposits reflects a crustal source however some mantle-derived lead has been introduced into the HET. Sulfur- and lead-isotopic results suggest that gold was sourced from mantle-derived magmatic units beneath the HET. The study supports earlier studies at Hill End by concluding that the majority of orogenic gold mineralisation in and adjacent to the HET formed during the Early Carboniferous period.

  1. Feeding the ';aneurysm': Orogen-parallel mass flux into Nanga Parbat and the western Himalayan syntaxis

    NASA Astrophysics Data System (ADS)

    Whipp, D. M.; Beaumont, C.; Braun, J.

    2013-12-01

    Over the last ~2 Ma, exhumation of the Nanga Parbat-Haramosh massif (NPHM) in the western Himalayan syntaxis region has occurred at rates that are more than double the exhumation rates in the central Himalaya (up to 13 mm/a). Coupled with surface elevations comparable to the rest of the Himalaya, this suggests an additional source of mass flux, over and above that supplied by normal convergence, is required to sustain localized, very rapid exhumation of the NPHM. The ';tectonic aneurysm' model provides an explanation for localized, rapid exhumation in the NPHM based on incision by the Indus River, but the source of the excess mass is not clear. One source capable of providing the requisite crustal mass is orogen-parallel (OP) mass transport as a result of strain partitioning along the Himalayan thrust front, where convergence is variably oblique, with obliquity up to ~40°. Conceptual and analog models of strain partitioning in convergent orogens have indicated how orogen-normal thrust motion results in OP mass transport within oblique orogenic wedges. However, there has been no quantitative demonstration that this may lead to the development of NPHM-type structures. We use geometrically simple 3D mechanical numerical experiments of an obliquely convergent orogen to demonstrate that the OP mass transport flux resulting from strain partitioning is capable of sustaining syntaxis topography and rapid exhumation rates. The model design includes a frictional-plastic orogenic wedge with predefined weak shear zones at its base and rear, and a neighboring plateau underlain by low-viscosity middle-lower crust. The geometry of the orogen thrust front is segmented, such that there is a region of oblique convergence at 45° obliquity bounded by two regions of orogen-normal convergence. Analytical and numerical results show that strain partitioning in the critical wedge orogen requires both the basal and rear shear zones to be very weak, with angles of internal friction of ~2

  2. Size and perspective in Alaska.

    PubMed

    Towle, Jim

    2006-01-01

    By far America's largest state, Alaska has only 350 members, so effective communication matters in overcoming distance. Alaska has led the way in direct reimbursement, diversity in leadership, member involvement, and a distinctive lifestyle for its practitioners. The tripartite structure of organized dentistry is crucial in building understanding the issues involved in providing oral health care to the members of this vast state. PMID:17585733

  3. Alaska Athabascan stellar astronomy

    NASA Astrophysics Data System (ADS)

    Cannon, Christopher M.

    Stellar astronomy is a fundamental component of Alaska Athabascan cultures that facilitates time-reckoning, navigation, weather forecasting, and cosmology. Evidence from the linguistic record suggests that a group of stars corresponding to the Big Dipper is the only widely attested constellation across the Northern Athabascan languages. However, instruction from expert Athabascan consultants shows that the correlation of these names with the Big Dipper is only partial. In Alaska Gwich'in, Ahtna, and Upper Tanana languages the Big Dipper is identified as one part of a much larger circumpolar humanoid constellation that spans more than 133 degrees across the sky. The Big Dipper is identified as a tail, while the other remaining asterisms within the humanoid constellation are named using other body part terms. The concept of a whole-sky humanoid constellation provides a single unifying system for mapping the night sky, and the reliance on body-part metaphors renders the system highly mnemonic. By recognizing one part of the constellation the stargazer is immediately able to identify the remaining parts based on an existing mental map of the human body. The circumpolar position of a whole-sky constellation yields a highly functional system that facilitates both navigation and time-reckoning in the subarctic. Northern Athabascan astronomy is not only much richer than previously described; it also provides evidence for a completely novel and previously undocumented way of conceptualizing the sky---one that is unique to the subarctic and uniquely adapted to northern cultures. The concept of a large humanoid constellation may be widespread across the entire subarctic and have great antiquity. In addition, the use of cognate body part terms describing asterisms within humanoid constellations is similarly found in Navajo, suggesting a common ancestor from which Northern and Southern Athabascan stellar naming strategies derived.

  4. Alaska Interagency Ecosystem Health Work Group

    USGS Publications Warehouse

    Shasby, Mark

    2009-01-01

    The Alaska Interagency Ecosystem Health Work Group is a community of practice that recognizes the interconnections between the health of ecosystems, wildlife, and humans and meets to facilitate the exchange of ideas, data, and research opportunities. Membership includes the Alaska Native Tribal Health Consortium, U.S. Geological Survey, Alaska Department of Environmental Conservation, Alaska Department of Health and Social Services, Centers for Disease Control and Prevention, U.S. Fish and Wildlife Service, Alaska Sea Life Center, U.S. Environmental Protection Agency, and Alaska Department of Fish and Game.

  5. Operation IceBridge Alaska

    NASA Astrophysics Data System (ADS)

    Larsen, C.

    2015-12-01

    The University of Alaska Fairbanks (UAF) has flown LiDAR missions for Operation IceBridge in Alaska each year since 2009, expanding upon UAF's airborne laser altimetry program which started in 1994. These observations show that Alaska's regional mass balance is -75+11/-16 Gt yr-1 (1994-2013) (Larsen et al., 2015). A surprising result is that the rate of surface mass loss observed on non-tidewater glaciers in Alaska is extremely high. At these rates, Alaska contributes ~1 mm to global sea level rise every 5 years. Given the present lack of adequate satellite resources, Operation IceBridge airborne surveys by UAF are the most effective and efficient method to monitor this region's impact on global sea level rise. Ice depth measurements using radar sounding have been part of these airborne surveys since 2012. Many of Alaska's tidewater glaciers are bedded significantly below sea level. The depth and extent of glacier beds below sea level are critical factors in the dynamics of tidewater retreat. Improved radar processing tools are being used to predict clutter using forward simulation. This is essential to properly sort out true bed returns, which are often masked or obscured by valley wall returns. This presentation will provide an overview of the program, highlighting recent findings and observations from the most recent campaigns, and focusing on techniques used for the extrapolation of surface elevation changes to regional mass balances.

  6. Active thrusting within the Himalayan orogenic wedge in the Kashmir Himalayas

    NASA Astrophysics Data System (ADS)

    Gavillot, Y.

    2011-12-01

    Numerous lines of evidence indicate that significant distributed deformation occurs within the Himalayan fold-thrust belt. Active thrust faults lie as much as 100 km north of the active thrust front. Whereas geochemical and topographical data provide circumstantial evidence for internal deformation in Nepal, new mapping demonstrates that an active emergent thrust fault system extends stepwise from the Balakot-Bagh fault (source of the Mw 7.6 2005 Kashmir earthquake in Pakistan) more than 200 km to the southeast on the Riasi fault (RT). The RT with a fault length of ~70 km, is a ~50° northeast-dipping reverse fault system, which sits ~40 km north of the deformation front in the Kashmiri Himalaya of northwest India. Our mapping demonstrates that the Riasi thrust consists of two strands. The northern strand, Main Riasi thrust (MRT) strand, places Precambrian Sirban Limestone on folded unconsolidated (Pleistocene?) conglomerates. Undeformed younger alluvial deposits (Holocene?) overlyie the MRT, which implies no Holocene (?) surface rupture on this strand. To the south, the surface expression of the Riasi frontal thrust (RFT) includes a fault scarp and offset ~10 ka terrace deposits dated with 36CL depth profiles. OSL and 10Be depth profile dating indicate an age range between ~80 ka to ~30 ka for the Bidda terrace in the upper plate of the MRT, yielding estimates of long-term uplift rate of 5.0 ± 2.2 mm/yr, slip rate of 6.4 ± 2.9 mm/yr, and shortening rate of 4.1 ± 1.9mm/yr. Given a ~34 mm/yr India-Asia convergence rate in the NW Himalaya, our results indicate that internal deformation within the orogenic belt accounts for at least ~10% of the total India-Eurasia plate convergence, with remaining shortening absorbed mainly at the deformation front.

  7. Distribution of active faulting along orogenic wedges: Minimum-work models and natural analogue

    NASA Astrophysics Data System (ADS)

    Yagupsky, Daniel L.; Brooks, Benjamin A.; Whipple, Kelin X.; Duncan, Christopher C.; Bevis, Michael

    2014-09-01

    Numerical 2-D models based on the principle of minimum work were used to examine the space-time distribution of active faulting during the evolution of orogenic wedges. A series of models focused on thin-skinned thrusting illustrates the effects of arid conditions (no erosion), unsteady state conditions (accretionary influx greater than erosional efflux) and steady state conditions (accretionary influx balances erosional efflux), on the distribution of fault activity. For arid settings, a general forward accretion sequence prevails, although a significant amount of internal deformation is registered: the resulting fault pattern is a rather uniform spread along the profile. Under fixed erosional efficiency settings, the frontal advance of the wedge-front is inhibited, reaching a steady state after a given forward propagation. Then, the applied shortening is consumed by surface ruptures over a narrow frontal zone. Under a temporal increase in erosional efficiency (i.e., transient non-steady state mass balance conditions), a narrowing of the synthetic wedge results; a rather diffuse fault activity distribution is observed during the deformation front retreat. Once steady balanced conditions are reached, a single long-lived deformation front prevails. Fault activity distribution produced during the deformation front retreat of the latter scenario, compares well with the structural evolution and hinterlandward deformation migration identified in southern Bolivian Subandes (SSA) from late Miocene to present. This analogy supports the notion that the SSA is not in steady state, but is rather responding to an erosional efficiency increase since late Miocene. The results shed light on the impact of different mass balance conditions on the vastly different kinematics found in mountain ranges, suggesting that those affected by growing erosion under a transient unbalanced mass flux condition tend to distribute deformation along both frontal and internal faults, while others

  8. From orogenic collapse to rifting ; structures of the South China Sea

    NASA Astrophysics Data System (ADS)

    Pubellier, M.; Chan, L. S.; Chamot Rooke, N.; Shen, W.; Ringenbach, J. C.

    2009-04-01

    The opening of the South China Sea has been a matter of debate for many years because of its internal structure, the differences between the conjugate margins and the variations of rifting and spreading directions. Although it is considered as being a back-arc basin, it is not sitting directly above a subduction zone, and the rifting process lasted for an unusually long duration. Among the specific characteristics is the early phase of rifting which took place early in place of the former Yanshanian andean-type mountain range. This stage is marked by narrow basins filled with deformed conglomerate, and initiated around 70My ago within a framework where the oblique subduction marked by igneous activity and ductile wrench faults, was replaced by orogenic collapse. The rifting stage is marked by Eocene syntectonic normal faults and occasional volcanics centres and has proceeded from NW-SE to NS extension. The NW stretching created at least two aborted basins which remained at rift stage. Extension was followed by spreading from 33 to ~20 Ma in the South China Sea. The ocean floor spreading also changed direction to NW-SE with a propagator inside the Sunda shelf from 20 to 17My ago. However the propagator opening implies that deformation is also taken by rifting around a southern wedge which in turn created strain inside the thinned crust. Another extension parallel to the margin is also observed althought the spreading was in process. The southward motion of the southern conjugate margin was later accommodated by its subduction beneath the NW Borneo wedge until completion of the Proto South China Sea subduction. Variations of rifting spreading through time and variations of structural styles are discussed in terms of boundary forces acting to the SE.

  9. Detrital mica K/Ar ages for Devonian-Pennsylvanian strata of the north central Appalachian Basin: Dominance of the Acadian Orogen as provenance

    SciTech Connect

    Aronson, J.L. . Dept. of Geological Sciences); Lewis, T.L. . Dept. of Geological Sciences)

    1992-01-01

    Detrital micas were separated from: the Upper Devonian Walton Sandstone and Ohio Shale; Lower Mississippian Berea Sandstone; Upper Mississippian Mauch Chunk Formation; and the Lower-Middle Pennsylvanian Pottsville and Allegheny Sandstones. A total of 12 separates were conventionally dated, the only biotite being from the Allegheny Formation sandstone, from which a muscovite was also dated. The total range in dates for the study was encompassed by the Allegheny sample of 414 m.y. (muscovite) to 361 m.y. (biotite), each date having an uncertainty of about [+-] 9 m.y. Excluding this sample, a narrower range of Early to Middle Devonian dates from 406--371 m.y. is obtained. For the Walton Sandstone of the proximal Catskill Wedge and for the northeast OH samples of the distal Catskill Wedge, all deposited within Late Devonian-Early Mississippian time, a very narrow span of 20 m.y. is obtained entirely within Early Devonian time and only approximately 30 m.y. older than deposition. All of these provenance ages have been previously found as primary ages of crystallization or cooling therefrom of regional metamorphism and plutonism in the Acadian Orogen of New England. The mean provenance ages are so close to the age of deposition of the distal Devonian/mississippian Catskill strata as to preclude almost any Precambrian contribution from either the Canadian Shield or the uplifted cores of the Orogen. These results support the paleocurrent and paleoenvironmental analysis of the northeast OH section by Lewis (1988) and argue against the classic Bedford Delta interpretation sourced from the north. Furthermore, the Acadian Orogen persisted as the major provenance for the clastic pulses that prograded into the central Appalachian Basin after the post-Catskill transgression, at least up until Middle Pennsylvanian time.

  10. Geologic map of the Christian quadrangle, Alaska

    USGS Publications Warehouse

    Brosge, W.P.; Reiser, H.N.

    2000-01-01

    Most of the Christian quadrangle is in the Porcupine Plateau; the northwestern part is in the southern Brooks Range, and the southern quarter is in the Yukon Flats. Outcrops of bedrock are poor or lacking, except in the Brooks Range. Although large valley glaciers have moved through the Porcupine Plateau, along the East Fork Chandalar and Vanticlese Creek, most of the upland areas in the Porcupine Plateau have not been eroded by ice. Consequently the rocks are deeply weathered and many outcrops in the low hills east of the East Fork are only soil and rubble. The southern quarter of the quadrangle in the Yukon Flats is covered with unconsolidated glacial and alluvial deposits. The Christian quadrangle is at the east end of the southern Brooks Range schist belt. Here three geologic terranes that originate well south of the Brooks Range intersect the subterranes of the southern Brooks Range along northward-directed thrust faults and northeast-striking strike slip faults. The displaced terranes from the south have been mapped by Jones and others (1987), as the schist of the Ruby terrane, the mafic rocks and phyllite of the Tozitna terrane, and the graywacke of the Venetie terrane. The typical rocks of the southern Brooks Range Arctic Alaska terrane at this intersection are the carbonate and clastic rocks of the Hammond subterrane, and the schist of the Coldfoot subterrane. The Coldfoot schist ends at a probable strike-slip fault about 10 miles west of the Christian quadrangle. At that place the mafic rocks and phyllites of the Angayucham terrane that form the south flank of most of the Brooks Range veer sharply northeastward across the Coldfoot subterrane schist and terminate it. A small fragment of the Endicott Mountains subterrane of the Arctic Alaska terrane also lies within the Christian quadrangle, but the main body of this subterrane lies north of the quadrangle.

  11. Evidence of Early Cretaceous transpression in the Sulu orogenic belt, eastern China

    NASA Astrophysics Data System (ADS)

    Wang, Jun; Chang, Su-Chin; Lin, Peijun; Zhu, Xiaoqing; Fu, Yongtao; Zhang, Haichun

    2016-09-01

    Recent studies have documented marine turbidites with syn-sedimentary deformation features in the central Sulu orogenic belt of eastern China. These units preserve essential information on the Late Mesozoic evolution of the Sulu orogenic belt. Referred to as the Baxiandun Formation, the turbidites exhibit similar lithologic characteristics to nearby units such as the Lingshandao Formation that have been well studied even though precise geochronologic constraints are lacking for a more precise correlation. This study reports detrital zircon Usbnd Pb age data that correlate the Baxiandun Formation turbidites of the central Sulu orogenic belt to the Early Cretaceous Lingshandao Formation. We also report Al-in-hornblende emplacement depth estimates for granitic intrusions of the Sulu orogenic belt's Laoshan mountain. A sharp contact between the Laoshan granites and the marine Baxiandun Formation indicates that the Baxiandun basin rapidly subsided to the emplacement depth of the Laoshan plutons. Lateral correlation among the marine turbidites, the Lingshandao and Baxiandun Formations, combined with information established by previous studies indicates initiation of transpressional tectonics at 122-121 Ma. Transpression ceased with the emplacement of the Laoshan granites, whose A1-type composition indicates a return to extensional tectonics at ca. 111 Ma.

  12. The role of radiogenic heat in prolonged intraplate reworking: The Capricorn Orogen explained?

    NASA Astrophysics Data System (ADS)

    Korhonen, Fawna J.; Johnson, Simon P.

    2015-10-01

    Links between intraplate crustal deformation and the thermal regime of the lithosphere have been investigated using numerical models, but these conceptual models must be tested using well-constrained natural systems. The Proterozoic Capricorn Orogen of Western Australia is ideally suited for such a study; after arc accretion, it records a protracted history of intracrustal differentiation and over one billion years of subsequent tectonic reworking. The early addition of juvenile arc material initially reduced the heat production of the crust, whereas subsequent recycling of the deep crust ultimately produced radiogenic granites in the shallow crust. Using whole rock and magmatic zircon compositions, we show that the shallow crust of the Capricorn Orogen has been progressively enriched in heat-producing elements with time. The high heat production is mainly controlled by thorium, concentrated in LREE-enriched phosphates that grew during the late stages of crystallization of crustally-derived granites. Using a numerical model, we investigate the thermal effects of this evolved crustal stratification and compare them with quantitative data on the pressure-temperature-time evolution of a non-magmatic Mesoproterozoic reworking event. The results provide new information concerning the process by which the thermal conditions necessary for the reworking of orogenic crust are generated and sustained for prolonged timescales (>110 Ma). Furthermore, we demonstrate that perturbations to the radiogenic crust lead to warmer geotherms and consequent lithospheric weakening, which has a fundamental control on intraplate reworking of long-lived orogens.

  13. Paleomagnetic data from the New England Orogen (eastern Australia) and implications for oroclinal bending

    NASA Astrophysics Data System (ADS)

    Shaanan, Uri; Rosenbaum, Gideon; Pisarevsky, Sergei; Speranza, Fabio

    2015-11-01

    Orogenic curvatures (oroclines) are common in modern and ancient orogens, but the geodynamic driving forces of many oroclines remain controversial. Here we focus on the New England oroclines of eastern Australia, the formation of which had been previously broadly constrained to the Early-Middle Permian. This time interval encompasses periods of both back-arc extension (at ~ 300-280 Ma) and subsequent contractional deformation (Hunter-Bowen Orogeny) that commenced at ~ 270 Ma along the paleo-Pacific and Gondwanan subduction plate boundary. We present new paleomagnetic data from volcanic rocks that were extruded during the transition from extension to contraction (at ~ 272 Ma), and we show that the oroclinal structure must have formed prior to the emplacement of the volcanic rocks. Our results thus indicate that oroclinal bending in the southernmost New England Orogen has been completed prior to the onset of Middle Permian contractional deformation. It is therefore concluded that the oroclines have likely formed during back-arc extension, and that a major contribution to the orogenic curvature was driven by trench retreat.

  14. Post-collisional magmatism in the central East African Orogen: The Maevarano Suite of north Madagascar

    USGS Publications Warehouse

    Goodenough, K.M.; Thomas, Ronald J.; De Waele, B.; Key, R.M.; Schofield, D.I.; Bauer, W.; Tucker, R.D.; Rafahatelo, J.-M.; Rabarimanana, M.; Ralison, A.V.; Randriamananjara, T.

    2010-01-01

    Late tectonic, post-collisional granite suites are a feature of many parts of the Late Neoproterozoic to Cambrian East African Orogen (EAO), where they are generally attributed to late extensional collapse of the orogen, accompanied by high heat flow and asthenospheric uprise. The Maevarano Suite comprises voluminous plutons which were emplaced in some of the tectonostratigraphic terranes of northern Madagascar, in the central part of the EAO, following collision and assembly during a major orogeny at ca. 550 Ma. The suite comprises three main magmatic phases: a minor early phase of foliated gabbros, quartz diorites, and granodiorites; a main phase of large batholiths of porphyritic granitoids and charnockites; and a late phase of small-scale plutons and sheets of monzonite, syenite, leucogranite and microgranite. The main phase intrusions tend to be massive, but with variably foliated margins. New U-Pb SHRIMP zircon data show that the whole suite was emplaced between ca. 537 and 522 Ma. Geochemically, all the rocks of the suite are enriched in the LILE, especially K, and the LREE, but are relatively depleted in Nb, Ta and the HREE. These characteristics are typical of post-collisional granitoids in the EAO and many other orogenic belts. It is proposed that the Maevarano Suite magmas were derived by melting of sub-continental lithospheric mantle that had been enriched in the LILE during earlier subduction events. The melting occurred during lithospheric delamination, which was associated with extensional collapse of the East African Orogen. ?? 2009 Natural Environment Research Council.

  15. New isotopic ages and the timing of orogenic events in the Cordillera Darwin, southernmost Chilean Andes

    NASA Astrophysics Data System (ADS)

    Hervé, F.; Nelson, E.; Kawashita, K.; Suárez, M.

    1981-10-01

    The Cordillera Darwin, a structural culmination in the Andes of Tierra del Fuego, exposes an orogenic core zone that has undergone polyphase deformation and metamorphism. Some of the classic problems of orogenic zones have remained unanswered in the Cordillera Darwin: the age of deformed plutonic rocks, the distinction of structurally reactivated basement and metamorphosed cover rocks, and the timing of orogenic events. This study addresses and partially answers these questions. A well-constrained Rb-Sr isochron age of157±8m.y. and an initial 87Sr/ 86Sr ratio of 0.7087 obtained from a pre-tectonic granitic suite suggest a genetic relation between this suite and Upper Jurassic silicic volcanic rocks in the cover sequence (Tobifera Formation), and also suggest involvement of continental crust in formation of these magmas. A poorly constrained Rb-Sr isochron age of240±40m.y. obtained from supposed basement schists is consistent with field relations in the area which suggest a late Paleozoic/early Mesozoic metamorphism for these pre-Late Jurassic rocks. However, because of scatter in the data and the uncertainties involved in dating metasedimentary rocks, the significance of the isotopic age is dubious. Compilation of previously published ages in the area [9] with new mineral ages reported here indicate that "early Andean" orogenic events occurred between 100 and 84 m.y. ago, and that subduction-related magmatism has contributed, probably discontinuously, to the crustal evolution of the region throughout the Mesozoic.

  16. Extreme variation of sulfur isotopic compositions in pyrite from the Qiuling sediment-hosted gold deposit, West Qinling orogen, central China: an in situ SIMS study with implications for the source of sulfur

    NASA Astrophysics Data System (ADS)

    Chen, Lei; Li, Xian-hua; Li, Jian-wei; Hofstra, Albert H.; Liu, Yu; Koenig, Alan E.

    2015-08-01

    High spatial resolution textural (scanning electron microscope (SEM)), chemical (electron microprobe (EMP)) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS)), and sulfur isotopic (secondary ion mass spectrometry (SIMS)) analyses of pyrite from the Qiuling sediment-hosted gold deposit (232 ± 4 Ma) in the West Qinling orogen, central China were conducted to distinguish pyrite types and gain insights into the source and evolution of sulfur in hydrothermal fluids. The results reveal an enormous variation (-27.1 to +69.6 ‰) in sulfur isotopic composition of pyrite deposited during three paragenetic stages. Pre-ore framboidal pyrite, which is characterized by low concentrations of As, Au, Cu, Co, and Ni, has negative δ34S values of -27.1 to -7.6 ‰ that are interpreted in terms of bacterial reduction of marine sulfate during sedimentation and diagenesis of the Paleozoic carbonate and clastic sequences, the predominant lithologies in the deposit area, and the most important hosts of many sediment-hosted gold deposits throughout the West Qinling orogen. The ore-stage hydrothermal pyrite contains high concentrations of Au, As, Cu, Sb, Tl, and Bi and has a relatively narrow range of positive δ34S values ranging from +8.1 to +15.2 ‰. The sulfur isotope data are comparable to those of ore pyrite from many Triassic orogenic gold deposits and Paleozoic sedimentary exhalative (SEDEX) Pb-Zn deposits in the West Qinling orogen, both being hosted mainly in the Devonian sequence. This similarity indicates that sulfur, responsible for the auriferous pyrite at Qiuling, was largely derived from the metamorphic devolatization of Paleozoic marine sedimentary rocks. Post-ore-stage pyrite, which is significantly enriched in Co and Ni but depleted in Au and As, has unusually high δ34S values ranging from +37.4 to +69.6 ‰, that are interpreted to result from thermochemical reduction of evaporite sulfates in underlying Cambrian sedimentary rocks with very

  17. Improving Student Achievement in Alaska. Alaska Goals 2000 Annual Report, 1997-98.

    ERIC Educational Resources Information Center

    Alaska State Dept. of Education, Juneau.

    Alaska Goals 2000 is part of a coordinated, statewide effort to improve public education for all students in Alaska. In 1997-1998, 90% of Alaska's federal funding was used to fund grants to local school districts, and 10% was used to fund state-level activities through the Alaska Department of Education. During 1997-1998, curriculum frameworks and…

  18. Alaska K-12 & School Choice Survey: What Do Voters Say about K-12 Education? Polling Paper No. 3

    ERIC Educational Resources Information Center

    DiPerna, Paul

    2011-01-01

    The "Alaska K-12 & School Choice Survey" project, commissioned by The Friedman Foundation for Educational Choice and conducted by Braun Research Incorporated (BRI), measures Alaska registered voters' familiarity and views on a range of K-12 education issues and school choice reforms. The author and his colleagues report response levels and…

  19. Transient and Steady-State Kinematic Response to Erosional Forcing in an Orogenic Wedge: Sandbox Perspective

    NASA Astrophysics Data System (ADS)

    Cruz, L.; Teyssier, C.; Annia, F.; Take, A.

    2005-12-01

    The evolution of orogens is highly affected by surface processes that control mass distribution. Transportation and redistribution of mass at the Earth's surface modifies the gravitational load and alters the stress field and kinematics within orogens. We explore the role of asymmetric erosion, indenter dip angle, and flux steady/non-steady state in determining the patterns of deformation and exhumation in doubly-sided orogenic wedges. In our analogue model, shortening of the orogen is driven by rigid indenters, represented by Plexiglas wedged blocks (35 and 70 degrees) that deform a non-cohesive dry Coulomb material (walnut shells) representing crustal material. Three end-member erosional scenarios are considered. In the first case, erosion is not applied, and thus the doubly-sided orogenic wedge evolves without restraints (non-steady state). In the second case, erosion is concentrated solely on the indenters side of the orogen (retrowedge), and in the third case, erosion is focused on the flank opposite to the indenter side (prowedge). In the last two cases, steady-state conditions were present in the middle stages of shortening. Strain and exhumation were calculated using displacement fields from 2D particle image velocimetry (PIV analysis). In the three cases, the model deforms as a combination of lateral compaction and localization of strain in shear bands. In the early stages of deformation, a "pop-up" structure develops, bounded by a fore-shear on the front and a back-shear toward the indenter. As deformation continues, a new fore-shear develops, and the previous one remains inactive and is passively pushed up the wedge. In the case of no erosion, the old fore-shears rotate slightly toward the indenter, and the shear bands evolve to steeply dipping structures. In the case of retrowedge erosion, the old fore-shears back rotate toward the indenter, and the shear bands evolve to shallowly dipping structures. In the case of prowedge erosion, old fore

  20. Progressive orogenic deformation recorded in a mylonite sample from the Dent Blanche Basal Thrust (Pennine Alps)

    NASA Astrophysics Data System (ADS)

    Kirst, Frederik; Froitzheim, Nikolaus; Nagel, Thorsten

    2013-04-01

    The Dent Blanche Basal Thrust (DBBT) represents an Alpine reverse fault along which the continental Dent Blanche Nappe was thrust onto the ocean-derived Combin Zone. Ductile NW-directed shearing associated with Early Tertiary nappe emplacement was localized along this fault resulting in the formation of intensely sheared rocks. These basal mylonites have locally been overprinted by later deformation phases associated with post-nappe compression. In the following, microstructures of a mylonite sample from a locality near the village Ollomont in the Valpelline of Italy are described and correlated with orogen-scale deformational events. The penetrative mylonitic foliation (S1) dips to the E (88/23) and is defined by a distinct metamorphic layering consisting of alternating, sub-mm thin layers of quartz and fine-grained silicates, mainly white mica ± epidote ± feldspar. The mylonitic stretching lineation (L1) is an aggregate lineation that dips to the ESE (119/19). In some parts, a grain shape preferred orientation of quartz grains defines an oblique foliation which probably developed as a result of combined subgrain rotation and grain boundary migration during simple shear deformation (Passchier & Trouw, 2005). The orientation of elongated quartz grains indicates top-NW shearing and is interpreted to reflect the bulk shear sense during nappe emplacement (D1). This type of dynamically recrystallised quartz also indicates deformation at temperatures around 500°C (Stipp et al., 2002). In most parts of the Ollomont mylonite, a secondary foliation (S2) and lineation (L2) are produced by a SE-dipping crenulation cleavage with NE-dipping (47/17) axes. In some spots, this non-penetrative feature is only slightly developed and gradational whereas in others it is a discrete compressional crenulation cleavage with large fold amplitudes in microlithons. This secondary foliation is interpreted to have formed as a result of late-stage orogen-perpendicular (NW-SE) shortening (D2

  1. Alaska GeoFORCE, A New Geologic Adventure in Alaska

    NASA Astrophysics Data System (ADS)

    Wartes, D.

    2011-12-01

    RAHI, the Rural Alaska Honors Institute is a statewide, six-week, summer college-preparatory bridge program at the University of Alaska Fairbanks for Alaska Native and rural high school juniors and seniors. A program of rigorous academic activity combines with social, cultural, and recreational activities. Students are purposely stretched beyond their comfort levels academically and socially to prepare for the big step from home or village to a large culturally western urban campus. This summer RAHI is launching a new program, GeoFORCE Alaska. This outreach initiative is designed to increase the number and diversity of students pursuing STEM degree programs and entering the future high-tech workforce. It uses Earth science as the hook because most kids get excited about dinosaurs, volcanoes and earthquakes, but it includes physics, chemistry, math, biology and other sciences. Students will be recruited, initially from the Arctic North Slope schools, in the 8th grade to begin the annual program of approximately 8 days, the summer before their 9th grade year and then remain in the program for all four years of high school. They must maintain a B or better grade average and participate in all GeoFORCE events. The carrot on the end of the stick is an exciting field event each summer. Over the four-year period, events will include trips to Fairbanks, Arizona, Oregon and the Appalachians. All trips are focused on Earth science and include a 100+ page guidebook, with tests every night culminating with a final exam. GeoFORCE Alaska is being launched by UAF in partnership with the University of Texas at Austin, which has had tremendous success with GeoFORCE Texas. GeoFORCE Alaska will be managed by UAF's long-standing Rural Alaska Honors Insitute (RAHI) that has been successfully providing intense STEM educational opportunities for Alaskan high school students for almost 30 years. The Texas program, with adjustments for differences in culture and environment, will be

  2. Alaska Native Education Study: A Statewide Study of Alaska Native Values and Opinions Regarding Education in Alaska.

    ERIC Educational Resources Information Center

    McDowell Group, Juneau, AK.

    This document contains four reports detailing a four-phase research project on Alaska Natives' attitudes and values toward education. A literature review examines the history of Native education in Alaska, issues in research on American Indian and Alaska Native education, dropout studies, student assessment, language and culture, learning styles,…

  3. Profile: American Indian/Alaska Native

    MedlinePlus

    ... million American Indians and Alaska Natives. Typically, this urban clientele has less accessibility to hospitals; health clinics ... IHS and tribal health programs. Studies on the urban American Indian and Alaska Native population have documented ...

  4. Visualizing the sedimentary response through the orogenic cycle using multi-dimensional scaling

    NASA Astrophysics Data System (ADS)

    Spencer, C. J.; Kirkland, C.

    2015-12-01

    Changing patterns in detrital provenance through time have the ability to resolve salient features of an orogenic cycle. Such changes in the age spectrum of detrital minerals can be attributed to fluctuations in the geodynamic regime (e.g. opening of seaways, initiation of subduction and arc magmatism, and transition from subduction to collisional tectonics with arrival of exotic crustal material). These processes manifest themselves through a variety of sedimentary responses due to basin formation, transition from rift to drift sedimentation, or inversion and basement unroofing. This generally is charted by the presence of older detrital zircon populations during basement unroofing events and is followed by a successive younging in the detrital zircon age signature either through arrival of young island arc terranes or the progression of subduction magmatism along a continental margin. The sedimentary response to the aforementioned geodynamic environment can be visualized using a multi-dimensional scaling approach to detrital zircon age spectra. This statistical tool characterizes the "dissimilarity" of age spectra of the various sedimentary successions, but importantly also charts this measure through time. We present three case studies in which multi-dimensional scaling reveals additional useful information on the style of basin evolution within the orogenic cycle. The Albany-Fraser Orogeny in Western Australia and Grenville Orogeny (sensu stricto) in Laurentia demonstrate clear patterns in which detrital zircon age spectra become more dissimilar with time. In stark contrast, sedimentary successions from the Meso- to Neoproterozoic North Atlantic Region reveal no consistent pattern. Rather, the North Atlantic Region reflects a signature consistent with significant zircon age communication due to a distal position from an orogenic front, oblique translation of terranes, and complexity of the continental margin. This statistical approach provides a mechanism to

  5. Tectonic controls of Mississippi Valley-type lead-zinc mineralization in orogenic forelands

    USGS Publications Warehouse

    Bradley, D.C.; Leach, D.L.

    2003-01-01

    Most of the world's Mississippi Valley-type (MVT) zinc-lead deposits occur in orogenic forelands. We examine tectonic aspects of foreland evolution as part of a broader study of why some forelands are rich in MVT deposits, whereas others are barren. The type of orogenic foreland (collisional versus Andean-type versus inversion-type) is not a first-order control, because each has MVT deposits (e.g., Northern Arkansas, Pine Point, and Cevennes, respectively). In some MVT districts (e.g., Tri-State and Central Tennessee), mineralization took place atop an orogenic forebulge, a low-amplitude (a few hundred meters), long-wavelength (100-200 km) swell formed by vertical loading of the foreland plate. In the foreland of the active Banda Arc collision zone, a discontinuous forebulge reveals some of the physiographic and geologic complexities of the forebulge environment, and the importance of sea level in determining whether or not a forebulge will emerge and thus be subject to erosion. In addition to those on extant forebulges, some MVT deposits occur immediately below unconformities that originated at a forebulge, only to be subsequently carried toward the orogen by the plate-tectonic conveyor (e.g., Daniel's Harbour and East Tennessee). Likewise, some deposits are located along syn-collisional, flexure-induced normal and strike-slip faults in collisional forelands (e.g., Northern Arkansas, Daniel's Harbour, and Tri-State districts). These findings reveal the importance of lithospheric flexure, and suggest a conceptual tectonic model that accounts for an important subset of MVT deposits-those in the forelands of collisional orogens. The MVT deposits occur both in flat-lying and in thrust-faulted strata; in the latter group, mineralization postdated thrusting in some instances (e.g., Picos de Europa) but may have predated thrusting in other cases (e.g., East Tennessee).

  6. SVM-based base-metal prospectivity modeling of the Aravalli Orogen, Northwestern India

    NASA Astrophysics Data System (ADS)

    Porwal, Alok; Yu, Le

    2010-05-01

    The Proterozoic Aravalli orogen in the state of Rajasthan, northwestern India, constitutes the most important metallogenic province for base-metal deposits in India and hosts the entire economically viable lead-zinc resource-base of the country. The orogen evolved through near-orderly Wilson cycles of repeated extensional and compressional tectonics resulting in sequential opening and closing of intracratonic rifts and amalgamation of crustal domains during a circa 1.0-Ga geological history from 2.2 Ga to 1.0 Ga. This study develops a conceptual tectonostratigraphic model of the orogen based on a synthesis of the available geological, geophysical and geochronological data followed by deep-seismic-reflectivity-constrained 2-D forward gravity modeling, and links it to the Proterozoic base-metal metallogeny in the orogen in order to identify key geological controls on the base-metal mineralization. These controls are translated into exploration criteria for base-metal deposits, validated using empirical spatial analysis, and used to derive input spatial variables for model-based base-metal prospectivity mapping of the orogen. A support vector machine (SVM) algorithm augmented by incorporating a feature selection procedure is used in a GIS environment to implement the prospectivity mapping. A comparison of the SVM-derived prospectivity map with the ones derived using other established models such as neural-networks, logistic regression, and Bayesian weights-of-evidence indicates that the SVM outperforms other models, which is attributed to the capability of the SVM to return robust classification based on small training datasets.

  7. 77 FR 13683 - Alaska Federal Lands Long Range Transportation Plan

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-03-07

    ..., 2011, at 76 FR 77300, the FHWA published a notice in the Federal Register inviting comments to the.... Dated: February 27, 2012. Clara H. Conner, Division Engineer, Western Federal Lands Highway Division, FHWA, Vancouver, Washington. BILLING CODE 4910-36-M...

  8. Malaspina Glacier, Alaska

    NASA Technical Reports Server (NTRS)

    2001-01-01

    This image from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument on NASA's Terra satellite covers an area of 55 by 40 kilometers (34 by 25 miles) over the southwest part of the Malaspina Glacier and Icy Bay in Alaska. The composite of infrared and visible bands results in the snow and ice appearing light blue, dense vegetation is yellow-orange and green, and less vegetated, gravelly areas are in orange. According to Dr. Dennis Trabant (U.S. Geological Survey, Fairbanks, Alaska), the Malaspina Glacier is thinning. Its terminal moraine protects it from contact with the open ocean; without the moraine, or if sea level rises sufficiently to reconnect the glacier with the ocean, the glacier would start calving and retreat significantly. ASTER data are being used to help monitor the size and movement of some 15,000 tidal and piedmont glaciers in Alaska. Evidence derived from ASTER and many other satellite and ground-based measurements suggests that only a few dozen Alaskan glaciers are advancing. The overwhelming majority of them are retreating.

    This ASTER image was acquired on June 8, 2001. With its 14 spectral bands from the visible to the thermal infrared wavelength region, and its high spatial resolution of 15 to 90 meters (about 50 to 300 feet), ASTER will image Earth for the next six years to map and monitor the changing surface of our planet.

    ASTER is one of five Earth-observing instruments launched December 18,1999, on NASA's Terra satellite. The instrument was built by Japan's Ministry of Economy, Trade and Industry. A joint U.S./Japan science team is responsible for validation and calibration of the instrument and the data products. Dr. Anne Kahle at NASA's Jet Propulsion Laboratory, Pasadena, Calif., is the U.S. science team leader; Bjorn Eng of JPL is the project manager. ASTER is the only high-resolution imaging sensor on Terra. The Terra mission is part of NASA's Earth Science Enterprise, along-term research and

  9. Timing and climatic drivers for glaciation across semi-arid western Himalayan-Tibetan orogen

    NASA Astrophysics Data System (ADS)

    Dortch, Jason M.; Owen, Lewis A.; Caffee, Marc W.

    2013-10-01

    Mapping and forty-seven new 10Be ages help define the timing of glaciation in the Ladakh and Pangong Ranges in Northwest India. Five new local glacial stages are defined for the Ladakh Range. From oldest to youngest these include: the Ladakh-4 glacial stage at 81 ± 20 ka; the Ladakh-3 glacial stage (not dated); the Ladakh-2 glacial stage at 22 ± 3 ka; the Ladakh-1 glacial stage (not dated); and the Ladakh Cirque glacial stage at 1.8 ± 0.4 ka. Three local glacial stages are defined for the Pangong Range, which include: the Pangong-2 glacial stage at 85 ± 15 ka; the Pangong-1 glacial stage at 40 ± 3 ka; and the Pangong Cirque glacial stage at 0.4 ± 0.3 ka. The new 10Be ages are combined with 645 recalculated 10Be ages from previous studies to develop the first regional framework of glaciation across the dryland regions of the Greater Himalaya, Transhimalaya, Pamir and Tian Shan at the western end of the Himalayan-Tibetan orogen. Nineteen regional glacial stages are recognized that are termed semi-arid western Himalayan-Tibetan stages (SWHTS). These include: SWHTS 9 at 311 ± 32 ka; SWHTS 7 at 234 ± 44 ka [tentative]; SWHTS 6 at 146 ± 18 ka; SWHTS 5E at 121 ± 11 ka; SWHTS 5A at 80 ± 5 ka; SWHTS 5A- at 72 ± 8 ka; SWHTS 4 at 61 ± 5 ka; SWHTS 3 at 46 ± 4 ka; SWHTS 2F at 30 ± 3 ka; SWHTS 2E at 20 ± 2 ka; SWHTS 2D at 16.9 ± 0.7 ka; SWHTS 2C at 14.9 ± 0.8 ka; SWHTS 2B at 13.9 ± 0.5 ka; SWHTS 2A at 12.2 ± 0.8 ka; SWHTS 1E at 8.8 ± 0.3 ka [tentative]; SWHTS 1D at 6.9 ± 0.2 ka [tentative]; SWHTS 1C at 3.8 ± 0.6 ka; SWHTS 1B at 1.7 ± 0.2 ka; and SWHTS 1A at 0.4 ± 0.1 ka. Regional glacial stages older than 21 ka are broadly correlated with strong monsoons. SWHTS that are 21 ka or younger, have smaller uncertainties and broadly correlate with global ice volume given by marine Oxygen Isotope Stages, and northern hemisphere climatic events (Oldest Dryas, Older Dryas, Younger Dryas, Roman Humid Period, and Little Ice Age).

  10. Rock uplift at the transition from flat-slab to normal subduction: The Kenai Mountains, Southeast Alaska

    NASA Astrophysics Data System (ADS)

    Valentino, Joshua D.; Spotila, James A.; Owen, Lewis A.; Buscher, Jamie T.

    2016-03-01

    The process of flat-slab subduction results in complex deformation of overlying forearcs, yet how this deformation decays with distance away from the zone of underthrusting is not well understood. In south central Alaska, flat-slab subduction of the Yakutat microplate drives shortening and rock uplift in a broad coastal orogenic belt. Defined limits of the zone of underthrusting allow testing how orogenesis responds to the transition from flat-slab to normal subduction. To better understand forearc deformation across this transition, apatite (U-Th)/He low temperature thermochronometry is used to quantify the exhumation history of the Kenai Mountains that are within this transition zone. Measured ages in the northern Kenai Mountains vary from 10-20 Ma and merge with the exhumation pattern in the Chugach Mountains to the northeast, where high exhumation occurs due to flat-slab-related deformation. In the southern Kenai Mountains, however, ages increase to 30-50 Ma across a transition near Seward, Alaska, above the zone from flat-slab to normal subduction. These ages are relatively old in comparison to ages determined in other studies in southern Alaska and suggest minimal exhumation. Furthermore, transitions in topographic expression of the coastal orogen also occur at the margin of Yakutat underthrusting. These observations suggest that either deformation associated with flat-slab subduction requires tens of kilometers to decay with distance away from the zone of underthrusting, or that orogenesis in the Kenai Mountains is driven by a distinct tectonic cause. A potential driver of deformation is underplating of thick sediments, specifically the Surveyor Submarine Fan, along the Aleutian Megathrust, analogous to the tectonic mechanism responsible for the emergence of the Kodiak Island forearc. If correct, this may represent a recent tectonic transition in the region, given the minimal exhumation of the rugged Kenai Mountains despite the presence of an erosion

  11. Population structure and genetic diversity of moose in Alaska.

    PubMed

    Schmidt, Jennifer I; Hundertmark, Kris J; Bowyer, R Terry; McCracken, Kevin G

    2009-01-01

    Moose (Alces alces) are highly mobile mammals that occur across arboreal regions of North America, Europe, and Asia. Alaskan moose (Alces alces gigas) range across much of Alaska and are primary herbivore consumers, exerting a prominent influence on ecosystem structure and functioning. Increased knowledge gained from population genetics provides insights into their population dynamics, history, and dispersal of these unique large herbivores and can aid in conservation efforts. We examined the genetic diversity and population structure of moose (n = 141) with 8 polymorphic microsatellites from 6 regions spanning much of Alaska. Expected heterozygosity was moderate (H(E) = 0.483-0.612), and private alleles ranged from 0 to 6. Both F(ST) and R(ST) indicated significant population structure (P < 0.001) with F(ST) < 0.109 and R(ST) < 0.125. Results of analyses from STRUCTURE indicated 2 prominent population groups, a mix of moose from the Yakutat and Tetlin regions versus all other moose, with slight substructure observed among the second population. Estimates of dispersal differed between analytical approaches, indicating a high level of historical or current gene flow. Mantel tests indicated that isolation-by-distance partially explained observed structure among moose populations (R(2) = 0.45, P < 0.01). Finally, there was no evidence of bottlenecks either at the population level or overall. We conclude that weak population structure occurs among moose in Alaska with population expansion from interior Alaska westward toward the coast.

  12. Trends in Alaska's People and Economy.

    ERIC Educational Resources Information Center

    Leask, Linda; Killorin, Mary; Martin, Stephanie

    This booklet provides data on Alaska's population, economy, health, education, government, and natural resources, including specific information on Alaska Natives. Since 1960, Alaska's population has tripled and become more diverse, more stable, older, less likely to be male or married, and more concentrated. About 69 percent of the population…

  13. Kilbuck terrane: Oldest known rocks in Alaska

    SciTech Connect

    Box, S.E. ); Moll-Stalcup, E.J.; Wooden, J.L. ); Bradshaw, J.Y. )

    1990-12-01

    The Kilbuck terrane in southwestern Alaska is a narrow, thin crustal sliver or flake of amphibolite facies orthogneiss. The igneous protolith of this gneiss was a suite of subduction-related plutonic rocks. U-Pb data on zircons from trondhjemitic and granitic samples yield upper-intercept (igneous) ages of 2,070 {plus minus}16 and 2,040 {plus minus}74 Ma, respectively. Nd isotope data from these rocks suggest that a diorite-tonalite-trondhjemite suite ({epsilon}{sub Nd}(T) = +2.1 to +2.7; T is time of crystallization) evolved from partial melts of depleted mantle with no discernible contamination by older crust, whereas a coeval granitic pluton ({epsilon}{sub Nd}(T) = {minus}5.7) contains a significant component derived from Archean crust. Orthogneisses with similar age and Nd isotope characteristics are found in the Idono complex 250 km to the north. Early Proterozoic rocks are unknown elsewhere in Alaska. However, Phanerozoic plutons cutting several continental terranes in Alaska (southern Brooks Range and Ruby, Seward, and Yukon-Tanana terranes) have Nd isotope compositions indicative of Early Proterozoic (or older) crustal components that could be correlative with rocks of the Kilbuck terrane. Rocks with similar igneous ages in cratonal North America are rare, and those few that are known have Nd isotope compositions distinct from those of the Kilbuck terrane. Conversely, provinces with Nd model ages of 2.0-2.1 Ga are characterized by extensive 1.8 Ga or younger plutonism, which is unknown in the Kilbuck terrane. At present the case for a North American parentage of the Kilbuck terrane is not compelling. The possibility that the Kilbuck terrane was displaced from provinces of similar age in other cratons (e.g., Australian, Baltic, Guiana, and west African shields), or from the poorly dated Siberian craton, cannot be excluded.

  14. Alaska Pipeline Insulation

    NASA Technical Reports Server (NTRS)

    1979-01-01

    Crude oil moving through the 800-mile Trans-Alaska Pipeline must be kept at a relatively high temperature, about 180 degrees Fahrenheit, to maintain the fluidity of the oil. In Arctic weather, that demands highly effective insulation. General Electric Co.'s Space Division, Valley Forge, Pennsylvania, provided it with a spinoff product called Therm-O-Trol. Shown being installed on the pipeline, Therm-O-Trol is a metal-bonded polyurethane foam especially formulated for Arctic insulation. A second GE spinoff product, Therm-O-Case, solved a related problem involved in bringing hot crude oil from 2,000-foot-deep wells to the surface without transferring oil heat to the surrounding permafrost soil; heat transfer could melt the frozen terrain and cause dislocations that might destroy expensive well casings. Therm-O-Case is a double-walled oil well casing with multi-layered insulation which provides an effective barrier to heat transfer. Therm-O-Trol and Therm-O-Case are members of a family of insulating products which stemmed from technology developed by GE Space Division in heat transferlthermal control work on Gemini, Apollo and other NASA programs.

  15. Alexander Archipelago, Southeastern Alaska

    NASA Technical Reports Server (NTRS)

    2002-01-01

    West of British Columbia, Canada, and south of the Yukon Territory, the southeastern coastline of Alaska trails off into the islands of the Alexander Archipelago. The area is rugged and contains many long, U-shaped, glaciated valleys, many of which terminate at tidewater. The Alexander Archipelago is home to Glacier Bay National Park. The large bay that has two forks on its northern end is Glacier Bay itself. The eastern fork is Muir inlet, into which runs the Muir glacier, named for the famous Scottish-born naturalist John Muir. Glacier Bay opens up into the Icy Strait. The large, solid white area to the west is Brady Icefield, which terminates at the southern end in Brady's Glacier. To locate more interesting features from Glacier Bay National Park, take a look at the park service map. As recently as two hundred years ago, a massive ice field extended into Icy Strait and filled the Glacier Bay. Since that time, the area has experienced rapid deglaciation, with many large glaciers retreating 40, 60, even 80 km. While temperatures have increased in the region, it is still unclear whether the rapid recession is part of the natural cycle of tidewater glaciers or is an indicator of longer-term climate change. For more on Glacier Bay and climate change, read an online paper by Dr. Dorothy Hall, a MODIS Associate Science Team Member. Credit: Jacques Descloitres, MODIS Land Rapid Response Team, NASA/GSFC

  16. Alaska Energy Inventory Project: Consolidating Alaska's Energy Resources

    NASA Astrophysics Data System (ADS)

    Papp, K.; Clough, J.; Swenson, R.; Crimp, P.; Hanson, D.; Parker, P.

    2007-12-01

    Alaska has considerable energy resources distributed throughout the state including conventional oil, gas, and coal, and unconventional coalbed and shalebed methane, gas hydrates, geothermal, wind, hydro, and biomass. While much of the known large oil and gas resources are concentrated on the North Slope and in the Cook Inlet regions, the other potential sources of energy are dispersed across a varied landscape from frozen tundra to coastal settings. Despite the presence of these potential energy sources, rural Alaska is mostly dependent upon diesel fuel for both electrical power generation and space heating needs. At considerable cost, large quantities of diesel fuel are transported to more than 150 roadless communities by barge or airplane and stored in large bulk fuel tank farms for winter months when electricity and heat are at peak demands. Recent increases in the price of oil have severely impacted the price of energy throughout Alaska, and especially hard hit are rural communities and remote mines that are off the road system and isolated from integrated electrical power grids. Even though the state has significant conventional gas resources in restricted areas, few communities are located near enough to these resources to directly use natural gas to meet their energy needs. To address this problem, the Alaska Energy Inventory project will (1) inventory and compile all available Alaska energy resource data suitable for electrical power generation and space heating needs including natural gas, coal, coalbed and shalebed methane, gas hydrates, geothermal, wind, hydro, and biomass and (2) identify locations or regions where the most economic energy resource or combination of energy resources can be developed to meet local needs. This data will be accessible through a user-friendly web-based interactive map, based on the Alaska Department of Natural Resources, Land Records Information Section's (LRIS) Alaska Mapper, Google Earth, and Terrago Technologies' Geo

  17. From slab rollback to orogenic plateau formation - a numerical modeling study of ocean-continent subduction systems

    NASA Astrophysics Data System (ADS)

    Wolf, Sebastian; Huismans, Ritske S.; Rondenay, Stéphane

    2016-04-01

    The crustal structures of overriding plates in subduction settings around the world can vary between a wide range of deformation styles, ranging from extensional structures and back arc opening induced by slab roll back as in the Hellenic subduction zone to large, plateau-like orogens such as the central Andes. Both end member types have been intensively studied over the last decades and a range of hypotheses have been proposed to explain their characteristics. Here we model ocean-continent collision using lithospheric scale plane-strain thermo-mechanical models, which also account for phase changes of rocks which enter the eclogite stability field. We consider the oceanic plate velocity, back-arc crustal strength, back-arc lithospheric strength, subduction interface strength, strain weakening thresholds in the crust and mantle flow patterns as the main variables in upper plate deformation and conducted a sensibility study with those parameters. The influence of eclogitized lower continental crust is also accounted for and shows to have a modulating effect. To verify and discuss our modeling results, we also present a comparison of the models with natural subduction systems.

  18. The Carthage-Colton mylonite zone (Adirondack Mountains, New York): The site of a cryptic suture in the Grenville Orogen

    SciTech Connect

    Mezger, K.; Pluijm, B.A. van der; Essene, E.J.; Halliday, A.N. )

    1992-09-01

    U-Pb ages were determined on metamorphic sphenes and monazites from the Late Proterozoic Adirondack Highlands and Lowlands in the vicinity of the Carthage-Colton mylonite zone. Monazites were extracted from metapelites, and sphenes were separated from marbles, calc-silicate gneisses, and granite gneisses in order to determine the timing and the duration of metamorphism as well as the cooling histories for rocks on either side of the mylonite zone. Monazite ages from the Lowlands range from 1,171-1,137 Ma; sphene ages in the Lowlands range from 1,156-1,103 Ma, those from the Highlands immediately to the east of the mylonite zone range from 1,050-982 ma. The ages indicate that the last high-grade metamorphism in the Highlands is ca. 100 m.y. younger than in the Lowlands and that both terranes had separate cooling histories at least until ca. 1,000 Ma. Sphenes from within the Carthage-Colton mylonite zone yield ages of about 1,098 Ma, which are distinct from sphene ages on either side of the shear zone. The mineral ages, structures, and metamorphic histories suggests that the Carthage-Colton mylonite zone is a fundamental tectonic boundary within the Proterozoic Grenville Orogen of North America.