Recent Exhumation in the Chugach, St. Elias, and Fairweather Ranges, Alaska

NASA Astrophysics Data System (ADS)

Spotila, J. A.; Berger, A. L.; McAleer, R. J.

2006-12-01

The motion of the Yakutat block into North America has produced a band of crustal deformation that begins near the tip of the Aleutian megathrust, continues through the eastern Chugach Range and St. Elias Mountains, and wraps southeastward along the Fairweather transform. Because of the extreme climate of the southern Alaska margin, this oblique collision has developed under the intense action of glacial erosion for the past few million years. This makes this orogen suitable for investigating the nature of feedbacks between climate, tectonics, and topography. We have measured the spatial and temporal patterns of exhumation at scales of orogenic evolution using apatite (U-Th)/He dating. In conjunction with previously published (U-Th)/He and fission-track ages (O'Sullivan and Currie, 1996; O'Sullivan et al., 1997; Buscher et al., 2002; Spotila et al., 2004; Johnston, 2005; Meigs et al., 2006; Perry et al., 2006), our new low-temperature cooling ages are beginning to reveal patterns of vertical strain localization on individual structures and in climatic zones, as well as the balance between tectonic influx and erosional efflux in the orogen. Data obtained thus far form a rough bull's eye pattern of concentric rings of cooling ages in the core of the orogen that become older with distance away from focused exhumation near the bend in the plate boundary. A similar bull's eye of young ages occurs along the Fairweather Range southeast of the bend and continuing to Glacier Bay, such that the zone of rapid exhumation is actually boomerang in shape. This is surprising, given that geologic and geodetic data indicate the Fairweather fault is pure strike-slip. Uplift and exhumation of the Fairweather corridor instead implies plate motion is oblique, with a significant component of partitioned shortening. Further west within the core of the Yakutat collision, the youngest apatite helium ages, less than 1 Ma, occur in a band along the coast that extends westwards from Mt. St

Age, distribution and style of deformation in Alaska north of 60°N: Implications for assembly of Alaska

USGS Publications Warehouse

Moore, Thomas; Box, Stephen E.

2016-01-01

The structural architecture of Alaska is the product of a complex history of deformation along both the Cordilleran and Arctic margins of North America involving oceanic plates, subduction zones and strike-slip faults and with continental elements of Laurentia, Baltica, and Siberia. We use geological constraints to assign regions of deformation to 14 time intervals and to map their distributions in Alaska. Alaska can be divided into three domains with differing deformational histories. Each domain includes a crustal fragment that originated near Early Paleozoic Baltica. The Northern domain experienced the Early Cretaceous Brookian orogeny, an oceanic arc-continent collision, followed by mid-Cretaceous extension. Early Cretaceous opening of the oceanic Canada Basin rifted the orogen from the Canadian Arctic margin, producing the bent trends of the orogen. The second (Southern) domain consists of Neoproterozoic and younger crust of the amalgamated Peninsular-Wrangellia-Alexander arc terrane and its paired Mesozoic accretionary prism facing the Pacific Ocean basin. The third (Interior) domain, situated between the first two domains and roughly bounded by the Cenozoic dextral Denali and Tintina faults, includes the large continental Yukon Composite and Farewell terranes having different Permian deformational episodes. Although a shared deformation that might mark their juxtaposition by collisional processes is unrecognized, sedimentary linkage between the two terranes and depositional overlap of the boundary with the Northern domain occurred by early Late Cretaceous. Late Late Cretaceous deformation is the first deformation shared by all three domains and correlates temporally with emplacement of the Southern domain against the remainder of Alaska. Early Cenozoic shortening is mild across interior Alaska but is significant in the Brooks Range, and correlates in time with dextral faulting, ridge subduction and counter-clockwise rotation of southern Alaska. Late Cenozoic

Coeval emplacement and orogen-parallel transport of gold in oblique convergent orogens

NASA Astrophysics Data System (ADS)

Upton, Phaedra; Craw, Dave

2016-12-01

Varying amounts of gold mineralisation is occurring in all young and active collisional mountain belts. Concurrently, these syn-orogenic hydrothermal deposits are being eroded and transported to form placer deposits. Local extension occurs in convergent orogens, especially oblique orogens, and facilitates emplacement of syn-orogenic gold-bearing deposits with or without associated magmatism. Numerical modelling has shown that extension results from directional variations in movement rates along the rock transport trajectory during convergence, and is most pronounced for highly oblique convergence with strong crustal rheology. On-going uplift during orogenesis exposes gold deposits to erosion, transport, and localised placer concentration. Drainage patterns in variably oblique convergent orogenic belts typically have an orogen-parallel or sub-parallel component; the details of which varies with convergence obliquity and the vagaries of underlying geological controls. This leads to lateral transport of eroded syn-orogenic gold on a range of scales, up to > 100 km. The presence of inherited crustal blocks with contrasting rheology in oblique orogenic collision zones can cause perturbations in drainage patterns, but numerical modelling suggests that orogen-parallel drainage is still a persistent and robust feature. The presence of an inherited block of weak crust enhances the orogen-parallel drainage by imposition of localised subsidence zones elongated along a plate boundary. Evolution and reorientation of orogen-parallel drainage can sever links between gold placer deposits and their syn-orogenic sources. Many of these modelled features of syn-orogenic gold emplacement and varying amounts of orogen-parallel detrital gold transport can be recognised in the Miocene to Recent New Zealand oblique convergent orogen. These processes contribute little gold to major placer goldfields, which require more long-term recycling and placer gold concentration. Most eroded syn-orogenic

Geologic maps of the eastern Alaska Range, Alaska (1:63,360 scale)

USGS Publications Warehouse

Nokleberg, Warren J.; Aleinikoff, John N.; Bond, Gerard C.; Ferrians, Oscar J.; Herzon, Paige L.; Lange, Ian M.; Miyaoka, Ronny T.; Richter, Donald H.; Schwab, Carl E.; Silva, Steven R.; Smith, Thomas E.; Zehner, Richard E.

2015-01-01

This report provides a description of map units for a suite of 44 inch-to-mile (1:63,360-scale) geologic quadrangle maps of the eastern Alaska Range. This report also contains a geologic and tectonic summary and a comprehensive list of references pertaining to geologic mapping and specialized studies of the region. In addition to the geologic maps of the eastern Alaska Range, this package includes a list of map units and an explanation of map symbols and abbreviations. The geologic maps display detailed surficial and bedrock geology, structural and stratigraphic data, portrayal of the active Denali fault that bisects the core of the east–west-trending range, and portrayal of other young faults along the north and south flanks of the range.

A range extension for Carex sartwellii in interior Alaska

Treesearch

Mark Winterstein; Teresa N Hollingsworth; Carolyn Parker

2016-01-01

Our documentation of Sartwell’s Sedge, Carex sartwellii, on nine shrinking lakes during fieldwork in the central Yukon Flats, Alaska, represents a range extension for this species. Previously, its range extended as far northwest as Yukon, Canada, with a reported, but lost collection, from Alaska in 1895. Two earlier collections from the Yukon Flats...

Post-orogenic evolution of mountain ranges and associated foreland basins: Initial investigation of the central Pyrenees

NASA Astrophysics Data System (ADS)

Bernard, Thomas; Sinclair, Hugh; Ford, Mary; Naylor, Mark

2017-04-01

Mountain topography, including surrounding foreland basins, results from the long-term competition between tectonic and surface processes linked to climate. Numerous studies on young active mountain ranges such as the Southern Alps, New Zealand and Taiwan, have investigated the interaction between tectonics, climate and erosion on the topographic landscape. However most of the mountain ranges in the world are in various stages of post-orogenic decay, such as the European Alps, Urals, Caledonides, Appalachians and Pyrenees. The landscape evolution of these decaying mountains, which involve relatively inactive tectonics, should appear simple with progressive and relatively uniform erosion resulting in a general lowering of both elevation and topographic relief. However, in a number of examples, post-orogenic systems suggest a complex dynamism and interactions with their associated foreland basins in term of spatio-temporal variations in erosion and sedimentary flux. The complexity and transition to post-orogenesis is a function of multiple processes. Underpinning the transition to a post-orogenic state is the competition between erosion and crustal thickening; the balance of these processes determines the timing and magnitude of isostatic rebound and hence subsidence versus uplift of the foreland basin. It is expected that any change in the parameters controlling the balance of erosion versus crustal thickening will impact the topographic evolution and sediment flux from the mountain range and foreland basin to the surrounding continental margin. This study will focus on the causes and origins of the processes that define post-orogenesis. This will involve analyses of low-temperature thermochronological and topographic data, geodynamical modelling and sedimentological analyses (grainsize distribution). The Pyrenees and its associated northern retro-foreland basin, the Aquitaine basin, will form the natural laboratory for the project as it is one of the best

Estimates of late Cenozoic climate change relevant to Earth surface processes in tectonically active orogens

NASA Astrophysics Data System (ADS)

Mutz, Sebastian G.; Ehlers, Todd A.; Werner, Martin; Lohmann, Gerrit; Stepanek, Christian; Li, Jingmin

2018-04-01

The denudation history of active orogens is often interpreted in the context of modern climate gradients. Here we address the validity of this approach and ask what are the spatial and temporal variations in palaeoclimate for a latitudinally diverse range of active orogens? We do this using high-resolution (T159, ca. 80 × 80 km at the Equator) palaeoclimate simulations from the ECHAM5 global atmospheric general circulation model and a statistical cluster analysis of climate over different orogens (Andes, Himalayas, SE Alaska, Pacific NW USA). Time periods and boundary conditions considered include the Pliocene (PLIO, ˜ 3 Ma), the Last Glacial Maximum (LGM, ˜ 21 ka), mid-Holocene (MH, ˜ 6 ka), and pre-industrial (PI, reference year 1850). The regional simulated climates of each orogen are described by means of cluster analyses based on the variability in precipitation, 2 m air temperature, the intra-annual amplitude of these values, and monsoonal wind speeds where appropriate. Results indicate the largest differences in the PI climate existed for the LGM and PLIO climates in the form of widespread cooling and reduced precipitation in the LGM and warming and enhanced precipitation during the PLIO. The LGM climate shows the largest deviation in annual precipitation from the PI climate and shows enhanced precipitation in the temperate Andes and coastal regions for both SE Alaska and the US Pacific Northwest. Furthermore, LGM precipitation is reduced in the western Himalayas and enhanced in the eastern Himalayas, resulting in a shift of the wettest regional climates eastward along the orogen. The cluster-analysis results also suggest more climatic variability across latitudes east of the Andes in the PLIO climate than in other time slice experiments conducted here. Taken together, these results highlight significant changes in late Cenozoic regional climatology over the last ˜ 3 Myr. Comparison of simulated climate with proxy-based reconstructions for the MH and

Structure and thermochronology of the metamorphic core of the Brooks Range, Alaska

NASA Astrophysics Data System (ADS)

Toro, Jaime

1999-11-01

Detailed field studies were undertaken in two key areas of the Central Belt of the Brooks Range: (1) the north flank of Mt. Igikpak in the Survey Pass Quadrangle and (2) in the Shishakshinovik Pass area in the eastern Ambler River Quadrangle. In both areas structural, stratigraphic, petrologic, 40Ar/39Ar, apatite fission-track and U-Pb data were used to constrain the kinematic and thermal history of metamorphic rocks of those areas. North of the Mt. Igikpak massif a crustal section ˜15 km thick is exposed. There are upper greenschist facies rocks in the deeper portions, and very low grade metamorphic rocks at higher structural levels. Two foliations are found: a higher grade relict S1 fabric and a lower grade S 2 fabric that controls the metamorphic layering. 40Ar/ 39Ar analyses from S1 white mica in the low-grade rocks at the northern end of the transect indicate that peak M1 metamorphism occurred before ˜112 Ma. We ascribe M1 to shortening that occurred during collision of an island arc against the Arctic Alaska margin. S 2 involved the retrogression of earlier assemblages. Kinematic indicators on S2 are top-to-the-north. A rapid cooling event from 500 +/- 50°C to 300 +/- 50°C took place between ˜98 and ˜90 Ma. The driving mechanism for ductile deformation during S2, and for rapid cooling documented by our thermochronologic data, was probably the gravitational collapse of the core of the orogen, over-thickened during the preceding collision. At Shishakshinovik Pass there are Mississippian Lisburne Group strata surrounded by metamorphic rocks typical of the Central Belt of the Brooks Range. All the rocks at Shishakshinovik Pass are intensely deformed, so that one cannot distinguish between an autochthonous and an allochthonous sequence. Furthermore the Mississippian rocks, instead of being attached to the underlying basement, are in the hanging wall of a northwest dipping shear zone. Based on the variations in metamorphic grade and the 40Ar/ 39Ar

Orogenic inheritance in Death Valley region, western US Basin and Range: implications for Neogene crustal extension.

NASA Astrophysics Data System (ADS)

Lima, R. D.; Hayman, N. W.; Prior, M. G.; Stockli, D. F.; Kelly, E. D.

2016-12-01

Deformation and temperature evolution during orogenic stages may influence later fabric development, thus controlling large-scale extensional processes that can occur millions of years later. Here, we describe pressure-temperature and fabric evolution from the Death Valley (DV) region and show how inherited fabrics, formed in late orogenic stages during Late Cretaceous time, influenced later Neogene age Basin and Range (BR) extension. The DV region is one of the most extended and thinned regions in the western US BR province, and the two of the ranges that bound the eastern valley expose basement rocks exhumed during the Neogene extension. In the Funeral range, it has been established that older (Precambrian) basement underwent Mesozoic age syn-deformational metamorphism during the Sevier-Laramide orogeny. In contrast, the Black Mountains record widespread tectonic stretching and magmatism of Miocene age on Precambrian basement, and have, overall, been lacking previous evidence of Mesozoic metamorphism and fabric development. In the Funeral Range Late Cretaceous migmatitic fabrics were overprinted by zones of high-strain fabrics formed due to melt-consuming reaction that define an overall P-T cooling path likely during late- to post-orogenesis. These fabrics form interconnected layers of quartz + biotite aggregates, in which individual quartz grains lack evidence of intracrystalline plastic deformation and show consistently random [c]-axis microfabrics. This suggests coupled reaction-diffusion processes that favored diffusion-assisted creep. New geochronometric results of melt products in the Black Mountains show evidence of partial melting of Late Cretaceous age. Contrasting with the neighboring Funeral Range, overprinting by extensional fabrics of Miocene age is widespread, and consists of high-strain, anastomosing foliation composed of retrograde products from preexisting, higher-temperature fabrics. These include interconnected fine-grained chlorite + quartz

Late Paleozoic orogeny in Alaska's Farewell terrane

USGS Publications Warehouse

Bradley, D.C.; Dumoulin, Julie A.; 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.

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.

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.

Proterozoic geochronological links between the Farewell, Kilbuck, and Arctic Alaska terranes

USGS Publications Warehouse

Bradley, Dwight C.; McClelland, William C.; Friedman, Richard M.; O'Sullivan, Paul B.; Layer, Paul; Miller, Marti L.; Dumoulin, Julie A.; Till, Alison B.; Abbott, J. Grant; Bradley, Dan B.; Wooden, Joseph L.

2014-01-01

New U-Pb igneous and detrital zircon ages reveal that despite being separated by younger orogens, three of Alaska’s terranes that contain Precambrian rocks—Farewell, Kilbuck, and Arctic Alaska—are related. The Farewell and Kilbuck terranes can be linked by felsic magmatism at ca. 850 Ma and by abundant detrital zircons in the Farewell that overlap the ca. 2010–2085 Ma age range of granitoids in the Kilbuck. The Farewell and Arctic Alaska terranes have already been linked via correlative Neoproterozoic to Devonian carbonate platform deposits that share nearly identical faunas of mixed Siberian and Laurentian affinity. New igneous ages strengthen these ties. Specifically, 988, 979, and 979 Ma metafelsites in the Farewell terrane are close in age to a 971 Ma granitic orthogneiss in the Arctic Alaska terrane. Likewise, 852, 850, 845, and 837 Ma granitic orthogneisses, metafelsite, and rhyolite in the Farewell terrane are similar to the reported 874 to 848 Ma age range of metarhyolites in the Arctic Alaska terrane. The Kilbuck and Arctic Alaska terranes have been previously linked on the basis of provenance: detrital zircons from the Carboniferous Nuka Formation in the Arctic Alaska terrane range from 2013 to 2078 Ma, overlapping the age of Kilbuck granitoids. A new 849 Ma age of a Kilbuck granitoid strengthens the proposed connection. Among the other new results from Kilbuck terrane is a 2085 Ma zircon from a granitoid that now stands as the oldest tightly dated rock in Alaska. We conclude that the Kilbuck, Farewell, and Arctic Alaska terranes were not independent entities with unique geologic histories but instead are related pieces of the circum-Arctic tectonic puzzle.

Soda Creek springs - metamorphic waters in the eastern Alaska Range

USGS Publications Warehouse

Richter, D.H.; Donaldson, D.E.; Lamarre, R.A.

1973-01-01

The Soda Creek springs are a group of small, cold mineral springs on the southern flank of the eastern Alaska Range. The spring waters contain anomalous concentrations of carbon dioxide, sodium, chlorine, sulfate, boron, and ammonia and are actively precipitating deposits of calcite and aragonite. Sparingly present in these deposits are mixed-layer illite-montmorillonite clays and zeolite minerals. Low-temperaturemetamorphic reactions in subjacent marine sedimentary rocks of Jurassic and Cretaceous age may have produced the fluids and silicate minerals. With only a few exceptions, cool bicarbonate-rich springs in Alaska are concentrated south of the Denali fault system in south-central Alaska, southeastern Alaska, and along the Kaltag-Tintina fault system. These areas are characterized by active or recently activetectonism, major faults and folds, and an abundance of marine sedimentary rocks.

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.

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.

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

Linkages and feedbacks in orogenic systems: An introduction

USGS Publications Warehouse

Thigpen, J. Ryan; Law, Richard D.; Merschat, Arthur J.; Stowell, Harold

2017-01-01

Orogenic processes operate at scales ranging from the lithosphere to grain-scale, and are inexorably linked. For example, in many orogens, fault and shear zone architecture controls distribution of heat advection along faults and also acts as the primary mechanism for redistribution of heat-producing material. This sets up the thermal structure of the orogen, which in turn controls lithospheric rheology, the nature and distribution of deformation and strain localization, and ultimately, through localized mechanical strengthening and weakening, the fundamental shape of the developing orogenic wedge (Fig. 1). Strain localization establishes shear zone and fault geometry, and it is the motion on these structures, in conjunction with climate, that often focuses erosional and exhumational processes. This climatic focusing effect can even drive development of asymmetry at the scale of the entire wedge (Willett et al., 1993).

Late Cenozoic Climate Change and its Implications on the Denudation of Orogen Syntaxes

NASA Astrophysics Data System (ADS)

Mutz, Sebastian; Ehlers, Todd

2017-04-01

The denudation history of active orogens is often interpreted in the context of modern climate gradients. Despite the influence of climatic conditions on erosion rates, information about paleoclimate evolution is often not available and thus not considered when denudation histories are interpreted. In this study, we analyze output from paleoclimate simulations conducted with ECHAM5-wiso at T159 (ca. 80x80km) resolution. Specifically, we analyze simulations of pre-industrial (PI, pre-1850), Mid-Holocene (MH, ca. 6ka), Last Glacial Maximum (LGM, ca. 21ka) and Pliocene (PLIO, ca. 3ka) climates and focus on a selection of orogen syntaxes as study regions (e.g. Himalaya, SE Alaska, Cascadia, and Central Andes). For the selected region, we carry out a cluster analysis using a hybrid of hierarchical and k-means clustering procedures using mean annual temperature (MAT), temperature amplitude, mean annual precipitation (MAP), precipitation amplitude and u-wind and v-wind in different months to provide a general overview of paleoclimates in the study regions. Additionally, we quantify differences between paleoclimates by applying two-group linear discrimination analyses to the simulation output for a similar selection of variables. Results indicate the largest differences to the PI climate are observed for the LGM and PLIO climates in the form of widespread cooling and reduced precipitation in the LGM and warming and enhanced precipitation during the PLIO. These global trends can be observed for most locations in the investigated areas, but the strength varies regionally and the trends in precipitation are less uniform than trends in temperatures. The LGM climate shows the largest deviation in annual precipitation from the PI climate, and shows enhanced precipitation in the temperate Andes, and coastal regions for both SE Alaska and the US Pacific Northwest Pacific. Furthermore, LGM precipitation is reduced in the western Himalayas and enhanced in the eastern Himalayas

Legacy K/Ar and 40Ar/39Ar geochronologic data from the Alaska-Aleutian Range batholith of south-central Alaska

USGS Publications Warehouse

Koeneman, Lisa L.; Wilson, Frederic H.

2018-04-06

Sample descriptions and analytical data for more than 200 K/Ar and 40Ar/39Ar analyses from rocks of the Alaska-Aleutian Range batholith of south-central Alaska are reported here. Samples were collected over a period of 20 years by Bruce R. Reed and Marvin A. Lanphere (both U.S. Geological Survey) as part of their studies of the batholith.

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.

Magnitude of crustal shortening and structural framework of the easternmost Himalayan orogen, northern Indo-Burma Ranges of northeastern India

NASA Astrophysics Data System (ADS)

Haproff, P. J.; Yin, A.

2016-12-01

Along-strike variation in crustal shortening throughout the Himalayan orogen has been attributed to (1) diachronous, eastward-increasing convergence, or (2) localized controls including pre-collisional stratigraphic configuration and climate. In this study, we present new geologic maps and balanced cross-sections across the easternmost segment of the Himalayan orogen, the N-S-trending N. Indo-Burma Ranges of northeastern India. First order structures are NE-dipping, km-wide ductile thrust shear zones with mylonitic fabrics indicating top-to-the SW motion. Major structures include the Mayodia klippe and Hunli window, generated during folding of the SW-directed Tidding thrust and duplexing of Lesser Himalayan rocks (LHS) at depth. Reconstruction of two balanced cross-sections yields minimum shortening estimates of 70% (48 km) and 71% (133 km), respectively. The widths of the orogen for each transect are 21 km and 54 km, respectively. Our percent strain values are comparable to that of western Arunachal Himalaya, reflecting eastward-increasing strain due to counterclockwise rotation of India during convergence or along-strike variation in India's subduction angle. However, shortening magnitudes much less than that of the Sikkim (641 km), Bhutan (414-615 km), and western Arunachal Himalaya (515-775 km) could signal eastward increasing shortening of a unique Himalayan stratigraphic framework, evidenced by few GHC rocks, absence of Tethyan strata, and an extensive subduction mélange and forearc complex.

Venus orogenic belt environments - Architecture and origin

NASA Astrophysics Data System (ADS)

Head, James W.; Vorder Bruegge, Richard W.; Crumpler, L. S.

1990-08-01

Orogenic belt environments (Danu, Akna, Freyja, and Maxwell Montes) in Western Ishtar Terra, Venus, display a range of architectural elements, including (from the center of Western Ishtar outward) an inboard plateau (Lakshmi Planum), the linear orogenic belts themselves, outboard plateaus, steep scarps bounding Ishtar, adjacent linear foredeeps and outboard rises, and outboard low-lying volcanic plains. The main elements of the architecture are interpreted to be due to the convergence, underthrusting, and possible subduction of lowland plains at the margins of a preexisting tessera plateau of thicker crust.

Flow of ultra-hot Precambrian orogens and the making of crustal layering in Phanerozoic orogenic plateaux

NASA Astrophysics Data System (ADS)

Chardon, Dominique; Gapais, Denis; Cagnard, Florence; Jayananda, Mudlappa; Peucat, Jean-Jacques

2010-05-01

Reassessment of structural / metamorphic properties of ultra-hot Precambrian orogens and shortening of model weak lithospheres support a syn-convergence flow mode on an orogen scale, with a large component of horizontal finite elongation parallel to the orogen. This orogen-scale flow mode combines distributed shortening, gravity-driven flow, lateral escape, and three-dimensional mass redistribution of buried supracrustal rocks, magmas and migmatites in a thick fluid lower crust. This combination preserves a nearly flat surface and Moho. The upper crust maintains a nearly constant thickness by real-time erosion and near-field clastic sedimentation and by ablation at its base by burial of pop-downs into the lower crust. Steady state regime of these orogens is allowed by activation of an attachment layer that maintains kinematic compatibility between the thin and dominantly plastic upper crust and a thick "water bed" of lower crust. Because very thin lithospheres of orogenic plateaux and Precambrian hot orogens have similar thermomechanical structures, bulk orogenic flow comparable to that governing Precambrian hot orogens should actually operate through today's orogenic plateaux as well. Thus, syn-convergence flow fabrics documented on exposed crustal sections of ancient hot orogens that have not undergone collapse may be used to infer the nature of flow fabrics that are imaged by geophysical techniques beneath orogenic plateaux. We provide a detailed geological perspective on syn-convergence crustal flow in relation to magma emplacement and partial melting on a wide oblique crustal transition of the Neoarchean ultra-hot orogen of Southern India. We document sub-horizontal bulk longitudinal flow of the partially molten lower crust over a protracted period of 60 Ma. Bulk flow results from the interplay of (1) pervasive longitudinal transtensional flow of the partially molten crust, (2) longitudinal coaxial flow on flat fabrics in early plutons, (3) distributed, orogen

Deciphering the Transitional Tectonics of the Southern Alaska Margin Through Gulf Sedimentology and Geophysics: IODP Expedition 341

NASA Astrophysics Data System (ADS)

Reece, R.; Gulick, S. P. S.; Jaeger, J. M.

2014-12-01

Southern Alaska is a complex amalgam of tectonic environments, centered on the subduction/collision of the Yakutat Block with North America. Along the Aleutians in the west, the Pacific Plate subducts normally beneath North America, with a gradually shallowing subduction angle towards the Yakutat Terrane to the east. The western region of the Yakutat Block undergoes nearly flat-slab subduction beneath North America, whereas it transitions to collision in the northeast, which is the primary driver for the growth of the Chugach-St. Elias orogen. Farther to the east, the collisional system transitions to a transform boundary with the Fairweather-Queen Charlotte fault system. The collisional system contributes to farfield tectonic effects in many regions, including northern Alaska and the Pacific Plate, but also combines with glaciation to drive sedimentation in the Gulf of Alaska. Glaciation has periodically increased in the St. Elias Range since the Miocene, but began dominating erosion and spurred enhanced exhumation since the intensification of Northern Hemisphere glaciation, at ~2.5 Ma. Results from IODP Expedition 341 show the first appearance of ice-rafted debris and a doubling of Gulf sedimentation at site U1417 at this age, and a major increase in sedimentation at ~1 Ma at sites U1417 and U1418. Glacigenic sediment flux into the Gulf of Alaska represents the majority of accumulation in the deepwater Surveyor Fan, and was the impetus for formation of the Surveyor Channel system. Climate events correlate to three major differentiable sequences across the Surveyor Fan that have been previously mapped using seismic reflection profiles. The change in morphology observed throughout the sequences allows us to characterize the influence that a glaciated orogen can have in shaping margin processes and the sediment pathways from source to sink. IODP Expedition 341 results allow us to now apply this method at higher resolution time scales (i.e., 100 kyr). We will explore

Topographic evolution of orogens: The long term perspective

NASA Astrophysics Data System (ADS)

Robl, Jörg; Hergarten, Stefan; Prasicek, Günther

2017-04-01

The landscape of mountain ranges reflects the competition of tectonics and climate, that build up and destroy topography, respectively. While there is a broad consensus on the acting processes, there is a vital debate whether the topography of individual orogens reflects stages of growth, steady-state or decay. This debate is fuelled by the million-year time scales hampering direct observations on landscape evolution in mountain ranges, the superposition of various process patterns and the complex interactions among different processes. In this presentation we focus on orogen-scale landscape evolution based on time-dependent numerical models and explore model time series to constrain the development of mountain range topography during an orogenic cycle. The erosional long term response of rivers and hillslopes to uplift can be mathematically formalised by the stream power and mass diffusion equations, respectively, which enables us to describe the time-dependent evolution of topography in orogens. Based on a simple one-dimensional model consisting of two rivers separated by a watershed we explain the influence of uplift rate and rock erodibility on steady-state channel profiles and show the time-dependent development of the channel - drainage divide system. The effect of dynamic drainage network reorganization adds additional complexity and its effect on topography is explored on the basis of two-dimensional models. Further complexity is introduced by coupling a mechanical model (thin viscous sheet approach) describing continental collision, crustal thickening and topography formation with a stream power-based landscape evolution model. Model time series show the impact of crustal deformation on drainage networks and consequently on the evolution of mountain range topography (Robl et al., in review). All model outcomes, from simple one-dimensional to coupled two dimensional models are presented as movies featuring a high spatial and temporal resolution. Robl, J., S

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

Subduction and Slab Advance at Orogen Syntaxes: Predicting Exhumation Rates and Thermochronometric Ages with Numerical Modeling

NASA Astrophysics Data System (ADS)

Nettesheim, Matthias; Ehlers, Todd A.; Whipp, David M.

2017-04-01

The change in plate boundary orientation and subducting plate geometry along orogen syntaxes may have major control on the subduction and exhumation dynamics at these locations. Previous work documents that the curvature of subducting plates in 3D at orogen syntaxes forces a buckling and flexural stiffening of the downgoing plate. The geometry of this stiffened plate region, also called indenter, can be observed in various subduction zones around the world (e.g. St. Elias Range, Alaska; Cascadia, USA; Andean syntaxis, South America). The development of a subducting, flexurally stiffened indenter beneath orogen syntaxes influences deformation in the overriding plate and can lead to accelerated and focused rock uplift above its apex. Moreover, the style of deformation in the overriding plate is influenced by the amount of trench or slab advance, which is the amount of overall shortening not accommodated by underthrusting. While many subduction zones exhibit little to no slab advance, the Nazca-South America subduction and especially the early stages of the India-Eurasia collision provide end-member examples. Here, we use a transient, lithospheric-scale, thermomechanical 3D model of an orogen syntaxis to investigate the effects of subducting a flexurally stiffened plate geometry and slab advance on upper plate deformation. A visco-plastic upper-plate rheology is used, along with a buckled, rigid subducting plate. The free surface of the thermomechanical model is coupled to a landscape evolution model that accounts for erosion by fluvial and hillslope processes. The cooling histories of exhumed rocks are used to predict the evolution of low-temperature thermochronometer ages on the surface. With a constant overall shortening for all simulations, the magnitude of slab advance is varied stepwise from no advance, with all shortening accommodated by underthrusting, to full slab advance, i.e. no motion on the megathrust. We show that in models where most shortening is

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

PubMed

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 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 resulted in the evolution

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

A Paleozoic Japan-type subduction-accretion system in the Beishan orogenic collage, southern Central Asian Orogenic Belt

NASA Astrophysics Data System (ADS)

Song, Dongfang; Xiao, Wenjiao; Windley, Brian F.; Han, Chunming; Tian, Zhonghua

2015-05-01

Magmatic arcs ascribed to oceanic lithosphere subduction played a dominant role in the construction of the accretionary Central Asian Orogenic Belt (CAOB). The Beishan orogenic collage, situated between the Tianshan Orogen to the west and the Inner Mongolia Orogen to the east, is a key area to understanding the subduction and accretionary processes of the southern CAOB. However, the nature of magmatic arcs in the Beishan and the correlation among different tectonic units along the southern CAOB are highly ambiguous. In order to investigate the subduction-accretion history of the Beishan and put a better spatial and temporal relationship among the tectonic belts along the southern CAOB, we carried out detailed field-based structural geology and LA-ICP-MS zircon U-Pb geochronological as well as geochemical studies along four cross-sections across crucial litho-tectonic units in the central segment of the Beishan, mainly focusing on the metamorphic assemblages and associated plutons and volcanic rocks. The results show that both the plutonic and volcanic rocks have geochemical characteristics similar to those of subduction-related rocks, which favors a volcanic arc setting. Zircons from all the plutonic rocks yield Phanerozoic ages and the plutons have crystallization ages ranging from 464 ± 2 Ma to 398 ± 3 Ma. Two volcanic-sedimentary rocks yield zircons with a wide age range from Phanerozoic to Precambrian with the youngest age peaks at 441 Ma and 446 Ma, estimated to be the time of formation of the volcanic rocks. These new results, combined with published data on ophiolitic mélanges from the central segment of the Beishan, favor a Japan-type subduction-accretion system in the Cambrian to Carboniferous in this part of the Paleo-Asian Ocean. The Xichangjing-Niujuanzi ophiolite probably represents a major suture zone separating different tectonic units across the Beishan orogenic collage, while the Xiaohuangshan-Jijitaizi ophiolitic mélange may represent a

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

Geosphere - Cryosphere Interactions in the Saint Elias orogen, Alaska and Yukon (Invited)

NASA Astrophysics Data System (ADS)

Bruhn, R. L.; Sauber, J. M.; Forster, R. R.; Cotton, M. M.

2009-12-01

North America's largest alpine and piedmont glaciers occur in the Saint Elias orogen, where microplate collision together with the transition from transform faulting to subduction along the North American plate boundary, create extreme topographic relief, unusually high annual precipitation by orographic lift, and crustal displacements induced by both tectonic and glacio-isostatic deformation. Lithosphere-scale structure dominates the spatial pattern of glaciation; the piedmont Bering and Agassiz-Malaspina glaciers lay along deeply eroded troughs where reverse faults rise from the underlying Aleutian megathrust. The alpine Seward and Bagley Ice Valley glaciers flow along an early Tertiary plate boundary that has been reactivated by reverse faulting, and also by dextral shearing at the NW end of the Fairweather transform fault. Folding above a crustal-scale fault ramp near Icy Bay localizes orographic uplift of air masses, creating alpine glaciers that spill off the highlands into large ice falls, and rapidly dissect evolving structure by erosion. The rate and orientation of ice surface velocities, and the location of crevassing and folding partly reflect changes in basal topography of the glaciers caused by differential erosion of strata, and juxtaposition of variably oriented structures across faults. The effects of basal topography on ice flow are investigated using remote sensing measurements and analog models of glacier flow over uneven topography. Deformation of the ice in turn affects englacial hydrology and sub-ice fluvial systems, potentially impacting ice mass balance, on-set of surging, and loci of glacier quakes. The glaciers impact tectonics by localizing uplift and exhumation within the orogen, and modulating tectonic stress fields as ice masses wax and wane. This is particularly evident in crustal seismicity rates at annual to decadal time scales, while stratigraphy of coastal terraces record both earthquake deformation and glacial isostasy over

A Tale of Two Orogens: Comparing Crustal Processes in the Proterozoic Trans-Hudson and Grenville Orogens, Eastern Canada

NASA Astrophysics Data System (ADS)

Darbyshire, F. A.; Bastow, I. D.; Gilligan, A.; Petrescu, L.

2016-12-01

The Precambrian core of North America is an assemblage of Archean cratons and Proterozoic orogenic belts, preserving over 3 billion years of Earth history. Here we focus on two of the largest collisional orogens, using recent and ongoing seismological studies to probe their present-day structure and tectonic history. The 1.8 Ga collision between the Western Churchill and Superior cratons, along with microcontinental and island arc terranes, formed the Trans-Hudson Orogen (THO), a collisional belt similar in scale and shape to the present-day Himalaya-Karakoram-Tibet Orogen (HKTO). In the Mesoproterozoic, a series of collisions reworked the SE margin of the Superior craton and added new material over a period of several hundred Ma, culminating in the Grenvillian orogeny and the assembly of the supercontinent Rodinia. The Grenville Orogen is thought to have been a large, hot, long-lived plateau which subsequently underwent orogenic collapse. While similar in spatial scale, the Trans-Hudson and Grenville Orogens have significantly different tectonic histories, notably in terms of longevity and tectonic evolution. Comparison of these collisional belts with each other, and with the HTKO, provide valuable insights into plate-tectonic history. Recently a number of broadband seismograph installations have allowed a detailed study of present-day crustal structure beneath the THO and the Grenville. Receiver-function and surface wave studies provide information on crustal thickness variations, bulk crustal composition and crustal heterogeneity. The crust beneath the orogens is generally thicker, more mafic and more heterogeneous than that beneath neighbouring Archean and Phanerozoic domains, with significant along-strike variability and Moho complexity. We review and interpret the new crustal structure information in the context of the tectonic processes affecting the two contrasting orogens.

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.

Geochemical reanalysis of historical U.S. Geological Survey sediment samples from the northeastern Alaska Range, Healy, Mount Hayes, Nabesna, and Tanacross quadrangles, Alaska

USGS Publications Warehouse

Werdon, Melanie B.; Granitto, Matthew; Azain, Jaime S.

2015-01-01

The State of Alaska’s Strategic and Critical Minerals (SCM) Assessment project, a State-funded Capital Improvement Project (CIP), is designed to evaluate Alaska’s statewide potential for SCM resources. The SCM Assessment is being implemented by the Alaska Division of Geological & Geophysical Surveys (DGGS), and involves obtaining new airborne-geophysical, geological, and geochemical data. As part of the SCM Assessment, thousands of historical geochemical samples from DGGS, U.S. Geological Survey (USGS), and U.S. Bureau of Mines archives are being reanalyzed by DGGS using modern, quantitative, geochemical-analytical methods. The objective is to update the statewide geochemical database to more clearly identify areas in Alaska with SCM potential. The USGS is also undertaking SCM-related geologic studies in Alaska through the federally funded Alaska Critical Minerals cooperative project. DGGS and USGS share the goal of evaluating Alaska’s strategic and critical minerals potential and together created a Letter of Agreement (signed December 2012) and a supplementary Technical Assistance Agreement (#14CMTAA143458) to facilitate the two agencies’ cooperative work. Under these agreements, DGGS contracted the USGS in Denver to reanalyze historical USGS sediment samples from Alaska. For this report, DGGS funded reanalysis of 670 historical USGS sediment samples from the statewide Alaska Geochemical Database Version 2.0 (AGDB2; Granitto and others, 2013). Samples were chosen from the northeastern Alaska Range, in the Healy, Mount Hayes, Nabesna, and Tanacross quadrangles, Alaska (fig. 1). The USGS was responsible for sample retrieval from the National Geochemical Sample Archive (NGSA) in Denver, Colorado through the final quality assurance/quality control (QA/QC) of the geochemical analyses obtained through the USGS contract lab. The new geochemical data are published in this report as a coauthored DGGS report, and will be incorporated into the statewide geochemical

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

2015-12-08

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.

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

Deformation Styles Along the Southern Alaska Margin Constrained by GPS

NASA Astrophysics Data System (ADS)

Elliott, J.; Freymueller, J. T.; Larsen, C. F.

2009-12-01

The present-day deformation observed in southcentral and southeast Alaska and the adjacent region of Canada is controlled by two main factors: ~ 50 mm/yr relative motion between the Pacific plate and North America and the Yakutat block’s collision with and accretion to southern Alaska. Over 45 mm/yr of NW-SE directed convergence from the collision is currently accommodated within the St. Elias orogen. The Fairweather, St. Elias, and Chugach ranges show the spectacular consequences of the relative tectonic motions, but the details of the plate interactions have not been well understood. Here we present GPS data from a network of over 170 campaign sites across the region. We use the data to constrain block models and forward models that characterize the nature and extent of the tectonic deformation along the Pacific-Yakutat-North America boundary. Tectonics in southeast Alaska can be described by block motion, with the Pacific plate bounding the region to the west. The fastest block motions occur along the coastal regions. The Yakutat block has a velocity of 51 ± 2.7 mm/yr towards N22 ± 2.5 deg W relative to North America. This velocity has a magnitude almost identical to that of the Pacific plate, but the azimuth is more westerly. The northeastern edge of the Yaktuat block is deforming, represented in our model by two small blocks outboard of the Fairweather fault. East of that fault, the Fairweather block rotates clockwise relative to North America, resulting in transpression along the Duke River and Eastern Denali faults. There is a clear transfer of strain from the coastal region hundreds of kilometers eastward into the Northern Cordillera block, confirming earlier suggestions that the effects of the Yakutat collision are far-reaching along its eastern margin. In contrast, deformation along the leading edge of the Yakutat collision is relatively narrowly focused within the southern half of the St. Elias orogen. The current deformation front of the Yakutat

Reworked crustal of early Paleozoic WuYi Orogen revealed by receiver function data

NASA Astrophysics Data System (ADS)

Wei, Y.; Duan, Y.; Tian, X.; Zhao, Y.

2017-12-01

Intraplate orogenic belt, which occurs at the rigid and undeformable plate interiors, is a distinct new type of orogen rather than an interplate or plate marginal orogenic belt, whose deformation occurs exclusively at plate margins. Therefore, intraplate orogenic belts are the most obvious exception to the plate-tectonic paradigm, they are uncommon in Earth's history. The early Paleozoic Wuyi orogen in South China is one of the few examples of intraplate orogen, and is a key to understanding the process of intraplate orogenesis and global early Paleozoic geodynamics. In this study, we select teleseismic records from 45 mobile linear seismic stations deployed in Wuyi Mountain and 58 permanent stations setting in Jiangxi and Fujian provinces, from January 2011 to December 2012, and calculate the crustal thickness and average crustal Vp/Vs ratio using the H-κ stacking method. The main results include the following: 1) the crustal average Poission's ratio shows an increase tendency from land to sea, the interior of Wuyi orogen belt with an low ration less than 0.23, and the coastline with high ration which is up to 0.28, which indicate a very heterogeneous crustal structure and composition in Wuyi orogen and coast belt. 2) the crustal thickness ranges 28-34 km and shows a tendency of thinning from inland to coast in the region of SE China margin, which maight mean the eastern Eurasia lithospheric is extension and thinning induced by the subducted paleo-Pacific slab. To conclusion, we assume that Wuyi orogen experienced upper crustal thickening, lower crust and lithosphere delamination during the early Paleozoic orogeny, and lithosphere extension in Mesozoic. This research is founded by the Natural Science Foundation of China (41174052 and 41604048).

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

USGS Publications Warehouse

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

2016-01-01

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.

A 400-year ice core melt layer record of summertime warming in the Alaska Range

NASA Astrophysics Data System (ADS)

Winski, D.; Osterberg, E. C.; Kreutz, K. J.; Wake, C. P.; Ferris, D. G.; Campbell, S. W.; Baum, M.; Raudzens Bailey, A.; Birkel, S. D.; Introne, D.; Handley, M.

2017-12-01

Warming in high-elevation regions has socially relevant impacts on glacier mass balance, water resources, and sensitive alpine ecosystems, yet very few high-elevation temperature records exist from the middle or high latitudes. While many terrestrial paleoclimate records provide critical temperature records from low elevations over recent centuries, melt layers preserved in alpine glaciers present an opportunity to develop calibrated, annually-resolved temperature records from high elevations. We present a 400-year temperature record based on the melt-layer stratigraphy in two ice cores collected from Mt. Hunter in the Central Alaska Range. The ice core record shows a 60-fold increase in melt frequency and water equivalent melt thickness between the pre-industrial period (before 1850) and present day. We calibrate the melt record to summer temperatures based on local and regional weather station analyses, and find that the increase in melt production represents a summer warming of at least 2° C, exceeding rates of temperature increase at most low elevation sites in Alaska. The Mt. Hunter melt layer record is significantly (p<0.05) correlated with surface temperatures in the central tropical Pacific through a Rossby-wave like pattern that induces high temperatures over Alaska. Our results show that rapid alpine warming has taken place in the Alaska Range for at least a century, and that conditions in the tropical oceans contribute to this warming.

Escape tectonics and the extrusion of Alaska: Past, present, and future

USGS Publications Warehouse

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

2007-01-01

The North Pacific Rim is a tectonically active plate boundary zone parts of which may be characterized as a laterally moving orogenic stream. Crustal blocks are transported along large-magnitude strike-slip faults in western Canada and central Alaska toward the Aleutian-Bering Sea subduction zones. Throughout much of the Cenozoic, at and west of its Alaskan nexus, the North Pacific Rim orogenic Stream (NPRS) has undergone tectonic escape. During transport, relatively rigid blocks acquired paleomagnetic rotations and fault-juxtaposed boundaries while flowing differentially through the system, from their original point of accretion and entrainment toward the free face defined by the Aleutian-Bering Sea subduction zones. Built upon classical terrane tectonics, the NPRS model provides a new framework with which to view the mobilistic nature of the western North American plate boundary zone. ?? 2007 The Geological Society of America.

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).

Continental Evolution Involving Subduction Underplating and Synchronous Foreland Thrusting: Evidence from the Trans-Alaska Crustal Transect

NASA Astrophysics Data System (ADS)

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.; Lutter, W. J.; Saltus, R. W.; Ruppert, N. A.

2010-12-01

We investigated 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 1980’s and early 1990’s, 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 to be 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 north-vergent, crustal-scale duplexes that overlie a ramp on autochthonous North Slope crust. There, 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 widely separated regions include “flat-slab” subduction and an “orogenic-float” model. In the Neogene, the collision of the Yakutat terrane (YAK), in southern Alaska, correlates with renewed compression in northeast Alaska and northwest Canada, in a fashion somewhat similar to the tectonics in the Paleogene. The Yakutat terrane, riding atop the subducting Pacific oceanic lithosphere (POL), spans a newly interpreted tear in the POL. East of the tear, POL is interpreted to subduct steeply and alone beneath the Wrangell arc volcanoes because the overlying YAK has been left behind as tectonically underplated rocks beneath the rising St. Elias Range in the coastal region. West of the tear, the YAK and POL are interpreted to subduct together at a gentle

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

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.

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

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, Peter 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.

Stratigraphic variation in petrographic composition of Nanushuk Group sandstones at Slope Mountain, North Slope, Alaska: A section in Geologic studies in Alaska by the U.S. Geological Survey, 1998

USGS Publications Warehouse

Johnsson, Mark J.; Sokol, Nikolas K.

2000-01-01

Fluvial, deltaic, and marine sediments of the Nanushuk Group (Albian to Cenomanian), North Slope, Alaska, record Early Cretaceous orogenic events in the Brooks Range to the south. The 1,060-m section at Slope Mountain is part of the Lower Cretaceous Umiat Delta, shed from the Endicott and De Long Mountains subterranes in the central Brooks Range. These sandstones are litharenites dominated by metasedimentary lithic fragments. Subtle and previously unrecognized stratigraphic variations in composition (up-section increases in metasedimentary lithic fragments, volcanic lithic fragments, and quartz interpreted to be of metamorphic origin) reflect a combination of facies migration and changes in provenance associated with unroofing of the ancestral Brooks Range. We recognize stratigraphic variation in sandstone composition at Slope Mountain whereas previous workers have not, probably because of our use of finely subdivided point-counting categories. The source of the volcanic lithic fragments in the Nanushuk Group remains enigmatic; the most likely candidate is a now-eroded volcanic arc, perhaps a volcanic superstructure to granitic rocks of the Ruby terrane to the south.

A 400-Year Ice Core Melt Layer Record of Summertime Warming in the Alaska Range

NASA Astrophysics Data System (ADS)

Winski, Dominic; Osterberg, Erich; Kreutz, Karl; Wake, Cameron; Ferris, David; Campbell, Seth; Baum, Mark; Bailey, Adriana; Birkel, Sean; Introne, Douglas; Handley, Mike

2018-04-01

Warming in high-elevation regions has societally important impacts on glacier mass balance, water resources, and sensitive alpine ecosystems, yet very few high-elevation temperature records exist from the middle or high latitudes. While a variety of paleoproxy records provide critical temperature records from low elevations over recent centuries, melt layers preserved in alpine glaciers present an opportunity to develop calibrated, annually resolved temperature records from high elevations. Here we present a 400-year temperature proxy record based on the melt layer stratigraphy of two ice cores collected from Mt. Hunter in Denali National Park in the central Alaska Range. The ice core record shows a sixtyfold increase in water equivalent total annual melt between the preindustrial period (before 1850 Common Era) and present day. We calibrate the melt record to summer temperatures based on weather station data from the ice core drill site and find that the increase in melt production represents a summer warming rate of at least 1.92 ± 0.31°C per century during the last 100 years, exceeding rates of temperature increase at most low-elevation sites in Alaska. The Mt. Hunter melt layer record is significantly (p < 0.05) correlated with surface temperatures in the central tropical Pacific through a Rossby wave-like pattern that enhances high temperatures over Alaska. Our results show that rapid alpine warming has taken place in the Alaska Range for at least a century and that conditions in the tropical oceans contribute to this warming.

Devonian magmatism in the Timan Range, Arctic Russia - subduction, post-orogenic extension, or rifting?

NASA Astrophysics Data System (ADS)

Pease, V.; Scarrow, J. H.; Silva, I. G. Nobre; Cambeses, A.

2016-11-01

Devonian mafic magmatism of the northern East European Craton (EEC) has been variously linked to Uralian subduction, post-orogenic extension associated with Caledonian collision, and rifting. New elemental and isotopic analyses of Devonian basalts from the Timan Range and Kanin Peninsula, Russia, in the northern EEC constrain magma genesis, mantle source(s) and the tectonic process(es) associated with this Devonian volcanism to a rift-related context. Two compositional groups of low-K2O tholeiitic basalts are recognized. On the basis of Th concentrations, LREE concentrations, and (LREE/HREE)N, the data suggest two distinct magma batches. Incompatible trace elements ratios (e.g., Th/Yb, Nb/Th, Nb/La) together with Nd and Pb isotopes indicate involvement of an NMORB to EMORB 'transitional' mantle component mixed with variable amounts of a continental component. The magmas were derived from a source that developed high (U,Th)/Pb, U/Th and Sm/Nd over time. The geochemistry of Timan-Kanin basalts supports the hypothesis that the genesis of Devonian basaltic magmatism in the region resulted from local melting of transitional mantle and lower crust during rifting of a mainly non-volcanic continental rifted margin.

Neoproterozoic, Paleozoic, and Mesozoic granitoid magmatism in the Qinling Orogen, China: Constraints on orogenic process

NASA Astrophysics Data System (ADS)

Wang, Xiaoxia; Wang, Tao; Zhang, Chengli

2013-08-01

The Qinling Orogen is one of the main orogenic belts in Asia and is characterized by multi-stage orogenic processes and the development of voluminous magmatic intrusions. The results of zircon U-Pb dating indicate that granitoid magmatism in the Qinling Orogen mainly occurred in four distinct periods: the Neoproterozoic (979-711 Ma), Paleozoic (507-400 Ma), and Early (252-185 Ma) and Late (158-100 Ma) Mesozoic. The Neoproterozoic granitic magmatism in the Qinling Orogen is represented by strongly deformed S-type granites emplaced at 979-911 Ma, weakly deformed I-type granites at 894-815 Ma, and A-type granites at 759-711 Ma. They can be interpreted as the products of respectively syn-collisional, post-collisional and extensional setting, in response to the assembly and breakup of the Rodinia supercontinent. The Paleozoic magmatism can be temporally classified into three stages of 507-470 Ma, 460-422 Ma and ˜415-400 Ma. They were genetically related to the subduction of the Shangdan Ocean and subsequent collision of the southern North China Block and the South Qinling Belt. The 507-470 Ma magmatism is spatially and temporally related to ultrahigh-pressure metamorphism in the studied area. The 460-422 Ma magmatism with an extensive development in the North Qinling Belt is characterized by I-type granitoids and originated from the lower crust with the involvement of mantle-derived magma in a collisional setting. The magmatism with the formation age of ˜415-400 Ma only occurred in the middle part of the North Qinling Belt and is dominated by I-type granitoid intrusions, and probably formed in the late-stage of a collisional setting. Early Mesozoic magmatism in the study area occurred between 252 and 185 Ma, with the cluster in 225-200 Ma. It took place predominantly in the western part of the South Qinling Belt. The 250-240 Ma I-type granitoids are of small volume and show high Sr/Y ratios, and may have been formed in a continental arc setting related to subduction

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

USGS Publications Warehouse

Fuis, G.S.; Moore, Thomas 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.

Trophic ecology of introduced populations of Alaska blackfish (Dallia pectoralis) in the Cook Inlet Basin, Alaska.

PubMed

Eidam, Dona M; von Hippel, Frank A; Carlson, Matthew L; Lassuy, Dennis R; López, J Andrés

2016-07-01

Introduced non-native fishes have the potential to substantially alter aquatic ecology in the introduced range through competition and predation. The Alaska blackfish ( Dallia pectoralis ) is a freshwater fish endemic to Chukotka and Alaska north of the Alaska Range (Beringia); the species was introduced outside of its native range to the Cook Inlet Basin of Alaska in the 1950s, where it has since become widespread. Here we characterize the diet of Alaska blackfish at three Cook Inlet Basin sites, including a lake, a stream, and a wetland. We analyze stomach plus esophageal contents to assess potential impacts on native species via competition or predation. Alaska blackfish in the Cook Inlet Basin consume a wide range of prey, with major prey consisting of epiphytic/benthic dipteran larvae, gastropods, and ostracods. Diets of the introduced populations of Alaska blackfish are similar in composition to those of native juvenile salmonids and stickleback. Thus, Alaska blackfish may affect native fish populations via competition. Fish ranked third in prey importance for both lake and stream blackfish diets but were of minor importance for wetland blackfish.

Trophic ecology of introduced populations of Alaska blackfish (Dallia pectoralis) in the Cook Inlet Basin, Alaska

PubMed Central

Eidam, Dona M.; Carlson, Matthew L.; Lassuy, Dennis R.; López, J. Andrés

2016-01-01

Introduced non-native fishes have the potential to substantially alter aquatic ecology in the introduced range through competition and predation. The Alaska blackfish (Dallia pectoralis) is a freshwater fish endemic to Chukotka and Alaska north of the Alaska Range (Beringia); the species was introduced outside of its native range to the Cook Inlet Basin of Alaska in the 1950s, where it has since become widespread. Here we characterize the diet of Alaska blackfish at three Cook Inlet Basin sites, including a lake, a stream, and a wetland. We analyze stomach plus esophageal contents to assess potential impacts on native species via competition or predation. Alaska blackfish in the Cook Inlet Basin consume a wide range of prey, with major prey consisting of epiphytic/benthic dipteran larvae, gastropods, and ostracods. Diets of the introduced populations of Alaska blackfish are similar in composition to those of native juvenile salmonids and stickleback. Thus, Alaska blackfish may affect native fish populations via competition. Fish ranked third in prey importance for both lake and stream blackfish diets but were of minor importance for wetland blackfish. PMID:28082763

Extreme mass flux from the glaciated, collisional St. Elias Orogen: Preliminary results from IODP Expedition 341 (Invited)

NASA Astrophysics Data System (ADS)

Gulick, S. P.; Jaeger, J. M.

2013-12-01

Integrated Ocean Drilling Program Expedition 341 drilled a cross-margin transect to investigate the linkages between global climate change, modification of the dynamics of surficial processes, and subsequent tectonic responses. The Gulf of Alaska (GoA) borders the St. Elias orogen, the highest coastal mountain range on Earth. Exp. 341 drilled five sites within a regional seismic reflection grid that spans from the distal Surveyor Fan to the continental shelf. More than 3000 m of high-quality core coupled with seismic reflection profiles collected with nested vertical resolution allows us to address the major objectives of drilling in the GoA. These objectives were to: 1) document the tectonic response of an active orogenic system to late Miocene to recent climate change; 2) establish the timing of advance/retreat phases of the northern Cordilleran ice sheet to test its relation to dynamics of other global ice sheets; 3) implement an expanded source-to-sink study of the interactions between glacial, tectonic, and oceanographic processes responsible for creation of one of the thickest Neogene high-latitude continental margin sequences; 4) understand the dynamics of productivity, nutrients, freshwater input to the ocean, and ocean circulation in the northeast Pacific and their role in the global carbon cycle, and 5) document the spatial and temporal behavior of the geomagnetic field at extremely high temporal resolution in an under-sampled region of the globe. The Exp. 341 cross-margin transect discovered transitions in sediment accumulation rates from >100 m/Ma at the distal site to > 1000 m/Ma in the proximal fan, slope and on the continental shelf that provide a telescoping view of strata formation from the Miocene to the Holocene. Complete recovery and development of spliced sedimentary records of the Pleistocene through Holocene were achieved at the distal, proximal, and slope Sites U1417, U1418, and U1419, respectively, because of exceptional piston core

Discriminating fluid source regions in orogenic gold deposits using B-isotopes

NASA Astrophysics Data System (ADS)

Lambert-Smith, James S.; Rocholl, Alexander; Treloar, Peter J.; Lawrence, David M.

2016-12-01

The genesis of orogenic gold deposits is commonly linked to hydrothermal ore fluids derived from metamorphic devolatilization reactions. However, there is considerable debate as to the ultimate source of these fluids and the metals they transport. Tourmaline is a common gangue mineral in orogenic gold deposits. It is stable over a very wide P-T range, demonstrates limited volume diffusion of major and trace elements and is the main host of B in most rock types. We have used texturally resolved B-isotope analysis by secondary ion mass spectrometry (SIMS) to identify multiple fluid sources within a single orogenic gold ore district. The Loulo Mining District in Mali, West Africa hosts several large orogenic gold ore bodies with complex fluid chemistry, associated with widespread pre-ore Na- and multi-stage B-metasomatism. The Gara deposit, as well as several smaller satellites, formed through partial mixing between a dilute aqueous-carbonic fluid and a hypersaline brine. Hydrothermal tourmaline occurs as a pre-ore phase in the matrix of tourmalinite units, which host mineralization in several ore bodies. Clasts of these tourmalinites occur in mineralized breccias. Disseminated hydrothermal and vein hosted tourmaline occur in textural sites which suggest growth during and after ore formation. Tourmalines show a large range in δ11B values from -3.5 to 19.8‰, which record a change in fluid source between paragenetic stages of tourmaline growth. Pre-mineralization tourmaline crystals show heavy δ11B values (8-19.8‰) and high X-site occupancy (Na ± Ca; 0.69-1 apfu) suggesting a marine evaporite source for hydrothermal fluids. Syn-mineralization and replacement phases show lighter δ11B values (-3.5 to 15.1‰) and lower X-site occupancy (0.62-0.88 apfu), suggesting a subsequent influx of more dilute fluids derived from devolatilization of marine carbonates and clastic metasediments. The large, overlapping range in isotopic compositions and a skew toward the

Detrital zircon geochronology of quartzose metasedimentary rocks from parautochthonous North America, east-central Alaska

USGS Publications Warehouse

Dusel-Bacon, Cynthia; Holm-Denoma, Christopher S.; Jones, James V.; Aleinikoff, John N.; Mortensen, James K.

2017-01-01

We report eight new U-Pb detrital zircon ages for quartzose metasedimentary rocks from four lithotectonic units of parautochthonous North America in east-central Alaska: the Healy schist, Keevy Peak Formation, and Sheep Creek Member of the Totatlanika Schist in the northern Alaska Range, and the Butte assemblage in the northwestern Yukon-Tanana Upland. Excepting 1 of 3 samples from the Healy schist, all have dominant detrital zircon populations of 1.9–1.8 Ga and a subordinate population of 2.7–2.6 Ga. Three zircons from Totatlanika Schist yield the youngest age of ca. 780 Ma. The anomalous Healy schist sample has abundant 1.6–0.9 Ga detrital zircon, as well as populations at 2.0–1.8 Ga and 2.7–2.5 Ga that overlap the ages from the rest of our samples; it has a minimum age population of ca. 1007 Ma.Detrital zircon age populations from all but the anomalous sample are statistically similar to those from (1) other peri-Laurentian units in east-central Alaska; (2) the Snowcap assemblage in Yukon, basement of the allochthonous Yukon-Tanana terrane; (3) Neoproterozoic to Ordovician Laurentian passive margin strata in southern British Columbia, Canada; and (4) Proterozoic Laurentian Sequence C strata of northwestern Canada. Recycling of zircon from the Paleoproterozoic Great Bear magmatic zone in the Wopmay orogen and its Archean precursors could explain both the Precambrian zircon populations and arc trace element signatures of our samples. Zircon from the anomalous Healy schist sample resembles that in Nation River Formation and Adams Argillite in eastern Alaska, suggesting recycling of detritus in those units.

Nesting by Golden Eagles on the North Slope of the Brooks Range in Northeastern Alaska

USGS Publications Warehouse

Young, Donald D.; McIntyre, Carol L.; Bente, Peter J.; McCabe, Thomas R.; Ambrose, Robert E.

1995-01-01

Twenty-two Golden Eagle (Aquila chrysaetos) nesting territories and 31 occupied eagle nests were documented on the north slope of the Brooks Range in northeastern Alaska, 1988-1990, in an area previously thought to be marginal breeding habitat for eagles. The mean number of young/successful nest was 1.25 in 1988, 1.27 in 1989, and 1.13 in 1990; means did not differ significantly among years. Eighty percent (20/25) of the nestlings for which age was estimated were assumed to have successfully fledged. Nesting success was 79% (11/14) in 1989, the only year nesting success could be determined. Laying dates ranged from 23 March (1990) to 11 May (1989) with mean estimated laying dates differing significantly among years. Annual variation in nesting phenology coincided with annual differences in snow accumulations during spring. These results indicate that Golden Eagles consistently and successfully breed at the northern extent of their range in Alaska, although, productivity may be lower than that for eagles at more southern latitudes.

Tectonochemistry of the Brooks Range Ophiolite, Alaska

NASA Astrophysics Data System (ADS)

Biasi, J.; Asimow, P. D.; Harris, R. A.

2017-12-01

The Brooks Range Ophiolite (BRO), recently estimated to be 1800km2 in area, is the largest ophiolite in the Western Hemisphere. However, due to its remote location, it remains one of the least studied. Mineral exploration and reconnaissance-level mapping of the ophiolite were done in the 1970s and 1980s. Some chemical analyses were also performed, but since that time the BRO has received little attention. Over the subsequent 25+ years, the study of ophiolites has advanced greatly. These early studies found that the BRO lies in the structurally highest position in the Brooks Range, and its obduction probably coincided with the collision between the Koyukuk Arc and the Arctic-Alaska continental margin. It is therefore important to determine the tectonic setting in which the BRO formed if one wants to understand the tectonic history of the Northern Cordillera during the Jurassic/Cretaceous. Here we present new tectonochemistry data from the BRO. This includes whole-rock data (via XRF), trace element data (via XRF and ICP-MS), and mineral chemistries (via Electron Microprobe). Using immobile element fingerprinting, we constrain the tectonic setting in which the BRO formed and how this information ties in with other events in the Northern Cordillera's history. The fingerprinting results are supplemented by Cr-in-spinel data and Al-in-olivine thermometry.

Microdiamonds from the European Variscan Orogenic Belt

NASA Astrophysics Data System (ADS)

Kotkova, J.; Jakubova, P.; Whitehouse, M.; Fedortchouk, Y.

2014-12-01

Diamond, along with coesite, has been discovered recently in the continental crustal rocks of the European Variscan orogenic belt, namely the Bohemian Massif (BM). In addition to the garnet-phengite gneiss in Germany, western BM, microdiamond occurs in major rock forming minerals - garnet, kyanite - and in zircon in ultrahigh-pressure rocks overprinted under high-pressure granulite facies conditions (c. 16-20 kbar, c. 1000°C) in the northern and eastern BM. Well-preserved 10-30 μm-sized microdiamonds from northern BM exhibit diverse morphologies (SEM data) depending upon the host rock type. Octahedral diamond occurs in felsic garnet-kyanite-feldspar-quartz rock (metasediment), whereas intermediate garnet-clinopyroxene-feldspar-quartz rock contains a cubo-octahedral variety. Diamond morphology can be thus controlled by solid impurities available in the medium of crystallization (K- vs. Ca-bearing fluids or melts), as shown by experiments. Pointed-bottom negatively oriented trigonal etch pits on the octahedral diamond faces developed due to diamond resorption at CO2-dominated environment (less than 50 wt % of H2O, experimental data), possibly by action of a residual fluid. SIMS determined δ13C values range from -22 to -21 ‰ for the felsic rock and from - 26 to - 33 for the intermediate one, corresponding to the typical range of organic carbon δ13C and inconsistent with a significant mantle carbon (δ13C ~ - 5 ‰) input. Diamond-bearing domains in zircon, also analysed by SIMS, yielded a Variscan U-Pb age of c. 340 Ma. The present stage of knowledge allows us to conclude that (i) metamorphic diamonds in the BM occur in lithologies of metasedimentary character, and their carbon source was organic; (ii) crustal-derived CO2-rich fluids with impurities played an important role in diamond formation and dissolution; (iii) diamonds formed during the Variscan orogenic cycle and (iv) diamonds are best preserved in the external domain of the Variscan orogenic belt.

Lateral thinking: 2-D interpretation of thermochronology in convergent orogenic settings

NASA Astrophysics Data System (ADS)

Batt, Geoffrey E.; Brandon, Mark T.

2002-05-01

Lateral motion of material relative to the regional thermal and kinematic frameworks is important in the interpretation of thermochronology in convergent orogens. Although cooling ages in denuded settings are commonly linked to exhumation, such data are not related to instantaneous behavior but rather to an integration of the exhumation rates experienced between the thermochronological 'closure' at depth and subsequent exposure at the surface. The short spatial wavelength variation of thermal structure and denudation rate typical of orogenic regions thus renders thermochronometers sensitive to lateral motion during exhumation. The significance of this lateral motion varies in proportion with closure temperature, which controls the depth at which isotopic closure occurs, and hence, the range of time and length scales over which such data integrate sample histories. Different chronometers thus vary in the fundamental aspects of the orogenic character to which they are sensitive. Isotopic systems with high closure temperature are more sensitive to exhumation paths and the variation in denudation and thermal structure across a region, while those of lower closure temperature constrain shorter-term behaviour and more local conditions. Discounting lateral motion through an orogenic region and interpreting cooling ages purely in terms of vertical exhumation can produce ambiguous results because variation in the cooling rate can result from either change in kinematics over time or the translation of samples through spatially varying conditions. Resolving this ambiguity requires explicit consideration of the physical and thermal framework experienced by samples during their exhumation. This can be best achieved through numerical simulations coupling kinematic deformation to thermal evolution. Such an approach allows the thermochronological implications of different kinematic scenarios to be tested, and thus provides an important means of assessing the contribution of

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

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.

What Can Modern River Profiles Tell Us about Orogenic Processes and Orogen Evolution?

NASA Astrophysics Data System (ADS)

Whipple, K. X.

2008-12-01

Numerous lines of evidence from theory, numerical simulations, and physical experiments suggest that orogen evolution is strongly coupled to atmospheric processes through the interrelationships among climate, topography, and erosion rate. In terms of orogenic processes and orogen evolution, these relationships are most important at the regional scale (mean topographic gradient, mean relief above surrounding plains) largely because crustal deformation is most sensitive to erosional unloading averaged over sufficiently long wavelengths. For this reason, and because above moderate erosion rates (> 0.2 mm/yr) hillslope form becomes decoupled from erosion rate, attention has focused on the river network, and even on particularly large rivers. We now have data that demonstrates a monotonic relationship between erosion rate and the channel steepness index (slope normalized for differences in drainage area) in a variety of field settings. Consequently, study of modern river profiles can yield useful information on recent and on-going patterns of rock uplift. It is not yet possible, however, to quantitatively isolate expected climatic and lithologic influences on this relationship. A combination of field studies and theoretical analyses are beginning to reveal the timescale of landscape response, and thus the topographic memory of past conditions. At orogen scale, river profile response to a change in rock uplift rate is on the order of 1-10 Myr. Because of these long response times, the modern profiles of large rivers and their major tributaries can potentially preserve an interpretable record of rock uplift rates since the Miocene and are insensitive to short-term climatic fluctuations. Only significant increases in rock uplift rate, however, are likely to leave a clear topographic signature. Strategies have been developed to differentiate between temporal and spatial (tectonic, climatic, or lithologic) influences on channel profile form, especially where spatially

'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

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.

Bedrock geologic map of the northern Alaska Peninsula area, southwestern Alaska

USGS Publications Warehouse

Wilson, Frederic H.; Blodgett, Robert B.; Blome, Charles D.; Mohadjer, Solmaz; Preller, Cindi C.; Klimasauskas, Edward P.; Gamble, Bruce M.; Coonrad, Warren L.

2017-03-03

The northern Alaska Peninsula is a region of transition from the classic magmatic arc geology of the Alaska Peninsula to a Proterozoic and early Paleozoic carbonate platform and then to the poorly understood, tectonically complex sedimentary basins of southwestern Alaska. Physiographically, the region ranges from the high glaciated mountains of the Alaska-Aleutian Range to the coastal lowlands of Cook Inlet on the east and Bristol Bay on the southwest. The lower Ahklun Mountains and finger lakes on the west side of the map area show strong effects from glaciation. Structurally, a number of major faults cut the map area. Most important of these are the Bruin Bay Fault that parallels the coast of Cook Inlet, the Lake Clark Fault that cuts diagonally northeast to southwest across the eastern part of the map area, and the presently active Holitna Fault to the northwest that cuts surficial deposits.Distinctive rock packages assigned to three provinces are overlain by younger sedimentary rocks and intruded by widely dispersed latest Cretaceous and (or) early Tertiary granitic rocks. Much of the east half of the map area lies in the Alaska-Aleutian Range province; the Jurassic to Tertiary Alaska-Aleutian Range batholith and derivative Jurassic sedimentary rocks form the core of this province, which is intruded and overlain by the Aleutian magmatic arc. The Lime Hills province, the carbonate platform, occurs in the north-central part of the map area. The Paleozoic and Mesozoic Ahklun Mountains province in the western part of the map area includes abundant chert, argillite, and graywacke and lesser limestone, basalt, and tectonic mélange. The Kuskokwim Group, an Upper Cretaceous turbidite sequence, is extensively exposed and bounds all three provinces in the west-central part of the map area.

Linking time-Temperature history of the Aquitaine basin with post-orogenic evolution of the Pyrenees : new insights from borehole thermochronology

NASA Astrophysics Data System (ADS)

Fillon, Charlotte; Calassou, Sylvain; Mouthereau, Frédéric; Pik, Raphaël; Bellahsen, Nicolas; Gautheron, Cécile

2017-04-01

Within their sedimentary record, foreland basins document vertical movements of the lithosphere, climatic changes, paleogeograhic evolution but also history of exhumation of the adjacent mountain belt. Comparing vertical movements in a range and in its foreland is key to identify processes involved in growth and destruction of mountain belts. The Aquitaine basin, geomorphologically stable since the early Pyrenean orogenesis has the potential to help understanding the driving mechanisms during the late to post-orogenic phases, but the lack of outcrops makes the studies particularly difficult to achieve. To bring a new point of vue on the processes involved in the Cenozoic exhumation of this range, we present new low-Temperature thermochronology data from boreholes of the Aquitaine basin. With the objectives to study rift-related to post-orogenic processes, numerous low-T thermochronological ages ( 300 across the range) have been published, documenting pre-, syn- , and post-orogenic exhumation in the Pyrenees. Using thermal modeling of a new low-T database in the western Axial Zone, we show that a late Miocene (around 10 Ma) uplift occured in the western Pyrenees, which generalizes the post-orogenic signal already detected in the south central Pyrenees. In previous studies, we linked the post-orogenic exhumation in the Southern Pyrenees to the excavation of the foreland valleys caused by the opening of the endorheic Ebro basin towards the Mediterranean Sea. To the West, the tectonic out-of sequence reactivation of the Gavarnie thrust has been invoked to explain the late Miocene AHe ages in the Bielsa massif. These new data might lead us to re-think the causes for such an exhumation signal during "post-orogenic" times. We thus summarize all evidences for the post-orogenic phase and attempt to provide explanation for it: is exhumation driven by Aquitaine foreland basin evolution? Does it reflect a tectonic reactivation of the Pyrenees? or is the signature of a regional

3D Thermal/Mechanical Evolution Of The Plate Boundary Corner In SE Alaska

NASA Astrophysics Data System (ADS)

Barker, A.; Koons, P.; Upton, P.; Pavlis, T.; Chapman, J.

2007-12-01

The St Elias orogen of southeast Alaska forms part of an actively deforming plate boundary corner. The corner accommodates the transition from a strike-slip lateral boundary to a convergent normal boundary. Oblique convergence of the Yakutat microplate into the corner generates early stage tectonic characteristics associated with other corner systems (e.g. Himalayan Eastern Syntaxis). In combination with the high relief, the extreme erosive processes of the region redistribute crustal material, partition tectonic strain, and influence the advection of deep crustal material. The evolution of the convergent corner is investigated using 3D numerical models and sandbox analog models. Preliminary model results indicate the deformation partitions into a narrow two-sided orogen along the lateral boundary. The pattern transitions into a wider zone of shortening bounded by inboard and outboard directed thrusts along the frontal boundary. The inclusion of erosion boundary conditions leads to nascent tectonic aneurysm behavior, involving increased strain localization and focused vertical advection of deep crustal material. Thermal models, using the 3D velocity field from these mechanical solutions, show a vertical deflection (towards the surface) of isotherms beneath the eroding region. Sensitivity of the aneurysm behavior is related to the efficiency of the imposed erosion rate (i.e. greater erosion rates led to greater bedrock uplift rates). Higher erosion rates are localized within zones containing major glacier systems in SE Alaska: Bering Glacier, Bagley Icefield, Malaspina Glacier, and Seward Glacier. Combined thermal/mechanical solutions identify the glacier valleys as rheological weakspots, defined by localized strain and differential advection of deep crustal material.

Mass elevation and lee effects markedly lift the elevational distribution of ground beetles in the Himalaya-Tibet orogen

PubMed Central

Schmidt, Joachim; Böhner, Jürgen; Brandl, Roland; Opgenoorth, Lars

2017-01-01

Mass elevation and lee effects markedly influence snow lines and tree lines in high mountain systems. However, their impact on other phenomena or groups of organisms has not yet been quantified. Here we quantitatively studied their influence in the Himalaya–Tibet orogen on the distribution of ground beetles as model organisms, specifically whether the ground beetle distribution increases from the outer to the inner parts of the orogen, against latitudinal effects. We also tested whether July temperature and solar radiation are predictors of the beetle’s elevational distribution ranges. Finally, we discussed the general importance of these effects for the distributional and evolutionary history of the biota of High Asia. We modelled spatially explicit estimates of variables characterizing temperature and solar radiation and correlated the variables with the respective lower elevational range of 118 species of ground beetles from 76 high-alpine locations. Both July temperature and solar radiation significantly positively correlated with the elevational ranges of high-alpine beetles. Against the latitudinal trend, the median elevation of the respective species distributions increased by 800 m from the Himalayan south face north to the Transhimalaya. Our results indicate that an increase in seasonal temperature due to mass elevation and lee effects substantially impact the regional distribution patterns of alpine ground beetles of the Himalaya–Tibet orogen and are likely to affect also other soil biota there and in mountain ranges worldwide. Since these effects must have changed during orogenesis, their potential impact must be considered when biogeographic scenarios based on geological models are derived. As this has not been the practice, we believe that large biases likely exist in many paleoecological and evolutionary studies dealing with the biota from the Himalaya-Tibet orogen and mountain ranges worldwide. PMID:28339461

Rotund versus skinny orogens: Well-nourished or malnourished gold?

USGS Publications Warehouse

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

2001-01-01

Orogenic gold vein deposits require a particular conjunction of processes to form and be preserved, and their global distribution can be related to broad-scale, evolving tectonic processes throughout Earth history. A heterogeneous distribution of formation ages for these mineral deposits is marked by two major Precambrian peaks (2800-2555 Ma and 2100-1800 Ma), a singular lack of deposits for 1200 m.y. (1800-600 Ma), and relatively continuous formation since then (after 600 Ma). The older parts of the distribution relate to major episodes of continental growth, perhaps controlled by plume-influenced mantle overturn events, in the hotter early Earth (ca. 1800 Ma or earlier). This worldwide process allowed preservation of gold deposits in cratons, roughly equidimensional, large masses of buoyant continental crust. Evolution to a less episodic, more continuous, modern-style plate tectonic regime led to the accretion of volcano-sedimentary complexes as progressively younger linear orogenic belts sorrounding the margins of the more buoyant cratons. The susceptibility of these linear belts to uplift and erosion can explain the overall lack of orogenic gold deposits at 1800-600 Ma, their exposure in 600-50 Ma orogens, the increasing importance of placer deposits back through the Phanerozoic since ca. 100 Ma, and the absence of gold deposits in orogenic belts younger than ca. 50 Ma.

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, Thomas 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.

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.

Lithospheric controls on the formation of provinces hosting giant orogenic gold deposits

USGS Publications Warehouse

Bierlein, F.P.; Groves, D.I.; Goldfarb, R.J.; Dube, B.

2006-01-01

Ages of giant gold systems (>500 t gold) cluster within well-defined periods of lithospheric growth at continental margins, and it is the orogen-scale processes during these mainly Late Archaean, Palaeoproterozoic and Phanerozoic times that ultimately determine gold endowment of a province in an orogen. A critical factor for giant orogenic gold provinces appears to be thickness of the subcontinental lithospheric mantle (SCLM) beneath a province at the time of gold mineralisation, as giant gold deposits are much more likely to develop in orogens with subducted oceanic or thin continental lithosphere. A proxy for the latter is a short pre-mineralisation crustal history such that thick SCLM was not developed before gold deposition. In constrast, orogens with protracted pre-mineralisation crustal histories are more likely to be characterised by a thick SCLM that is difficult to delaminate, and hence, such provinces will normally be poorly endowed. The nature of the lithosphere also influences the intrinsic gold concentrations of potential source rocks, with back-arc basalts, transitional basalts and basanites enriched in gold relative to other rock sequences. Thus, segments of orogens with thin lithosphere may enjoy the conjunction of giant-scale fluid flux through gold-enriched sequences. Although the nature of the lithosphere plays the crucial role in dictating which orogenic gold provinces will contain one or more giant deposits, the precise siting of those giants depends on the critical conjunction of a number of province-scale factors. Such features control plumbing systems, traps and seals in tectonically and lithospherically suitable terranes within orogens. ?? Springer-Verlag 2006.

Geodynamic processes and deformation in orogenic belts

NASA Astrophysics Data System (ADS)

Dennis, John G.; Jacoby, Wolfgang R.

1980-03-01

The development of geosynclines and orogenic belts is related to lithosphere convergence. Initial sediment accumulation implying subsidence, and volcanic activity implying extension and rise of geotherms, are in most cases followed by folding and thrusting suggesting compression and by uplift. In terms of recent analogs, sediment accumulation and crustal extension are characteristic of back-arc spreading; subsequent compression would indicate continent—continent collision; and rise of geotherms most likely requires localized thermal flow (convection) in the asthenosphere. These events are here shown to agree with Andrews and Sleep's (1974) numerical model of asthenosphere flow at converging plate margins. Orthogeosynclinal subsidence appears to be a consequence of subcrustal ablation and lithosphere extension and thinning in active marginal basins. Arc and Andean type magmatism mark the reappearance of ablated and transported, relatively low-density subcrustal material. Collision slows and eventually stops the local convection cell, resulting in local heat accumulation and hence high- T, low- P metamorphism and granitization while marginal basin (orthogeosynclinal) deposits are being compressed into Alpine style orogenic structures. Moreover, closing of the marginal basin leads to subsidiary subduction, which in turn may be responsible for some Alpine style structures. Oceanic trench deposits may become incorporated in orogenic zones, as high- P, low- T metamorphic belts (thalassogeosynclines). Dynamic uplift is a fundamental characteristic of orogeny. Most rising and sinking in orogenic zones can be linked to those asthenosphere processes which are a consequence of Andrews-Sleep convection.

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

... 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. (a... enforced by the Commander, Alaskan Air Command, U.S. Air Force, Seattle, Washington, or such agencies as he...

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

... 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. (a... enforced by the Commander, Alaskan Air Command, U.S. Air Force, Seattle, Washington, or such agencies as he...

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

... 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. (a... enforced by the Commander, Alaskan Air Command, U.S. Air Force, Seattle, Washington, or such agencies as he...

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

... 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. (a... enforced by the Commander, Alaskan Air Command, U.S. Air Force, Seattle, Washington, or such agencies as he...

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

... 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. (a... enforced by the Commander, Alaskan Air Command, U.S. Air Force, Seattle, Washington, or such agencies as he...

Publications - RI 2009-3 | Alaska Division of Geological & Geophysical

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Lateral variations in lithospheric and landscape evolution at both ends of the Himalaya-Tibet orogen

NASA Astrophysics Data System (ADS)

Zeitler, P. K.; Schmidt, J. L.; Meltzer, A.

2015-12-01

At the broadest scale, like many orogens the Himalaya encompass a range of orogenic features that are remarkably similar along much of the length of the mountain belt and its neighboring terranes. At one scale of consideration, these similarities appear to be a signal that fundamental processes associated with lithospheric collision have been active. However, the vast size of the Himalaya and Tibet, the different climate regimes experienced by the orogen across time and space, and the along-strike variations in the continental and arc margins that faced one another before collision, make it at once remarkable that any similarities exist, and important to more critically evaluate their nature. The eastern and western Himalayan syntaxes confound any attempt to generalize too much about the Himalaya-Tibet orogen. By area these features occupy at least 25% of the orogenic belt, and compared to the "main" portions of the arc they show clear differences in their lithospheric structures, landscapes, and evolution. The boundary and initial conditions that shaped the eastern and western indentor corners were and are different, as is the nature and timing of erosional exhumation. Some of the most active geologic processes on Earth have recently been in play within the syntaxes, and the evolution of landscapes and fluvial systems, important in developing the sedimentary record of the Himalaya-Tibet system, has been complex and variable in space and time. Southeasternmost Tibet and the Lhasa Block in particular exemplify this complexity both in its complex topographic evolution linked to surface processes and climate, and in lateral variability in lithospheric structure. Taking a system viewpoint, an important question to debate is the degree to which there are features in the Himalaya-Tibet system that are robustly emergent, given the broad boundary conditions of the continental collision plus the suite of local and regional geodynamical processes that have operated during

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

Crustal Structure beneath Alaska from Receiver Functions

NASA Astrophysics Data System (ADS)

Zhang, Y.; Li, A.

2017-12-01

The crustal structure in Alaska has not been well resolved due to the remote nature of much of the state. The USArray Transportable Array (TA), which is operating in Alaska and northwestern Canada, significantly increases the coverage of broadband seismic stations in the region and allows for a more comprehensive study of the crust. We have analyzed P-receiver functions from earthquake data recorded by 76 stations of the TA and AK networks. Both common conversion point (CCP) and H-K methods are used to estimate the mean crustal thickness. The results from the CCP stacking method show that the Denali fault marks a sharp transition from thick crust in the south to thin crust in the north. The thickest crust up to 52 km is located in the St. Elias Range, which has been formed by oblique collision between the Yakutat microplate and North America. A thick crust of 48 km is also observed beneath the eastern Alaska Range. These observations suggest that high topography in Alaska is largely compensated by the thick crust root. The Moho depth ranges from 28 km to 35 km beneath the northern lowlands and increases to 40-45 km under the Books Range. The preliminary crustal thickness from the H-K method generally agrees with that from the CCP stacking with thicker crust beneath high mountain ranges and thinner crust beneath lowlands and basins. However, the offshore part is not well constrained due to the limited coverage of stations. The mean Vp/Vs ratio is around 1.7 in the Yukon-Tanana terrane and central-northern Alaska. The ratio is about 1.9 in central and southern Alaska with higher values at the Alaska Range, Wrangell Mountains, and St. Elias Range. Further data analyses are needed for obtaining more details of the crustal structure in Alaska to decipher the origin and development of different tectonic terranes.

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.

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.

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).

Facts About Alaska, Alaska Kids' Corner, State of Alaska

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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

Axial Belt Provenance: modern river sands from the core of collision orogens

NASA Astrophysics Data System (ADS)

Resentini, A.; Vezzoli, G.; Paparella, P.; Padoan, M.; Andò, S.; Malusà, M.; Garzanti, E.

2009-04-01

Collision orogens have a complex structure, including diverse rock units assembled in various ways by geodynamic processes. Consequently, orogenic detritus embraces a varied range of signatures, and unravelling provenance of clastic wedges accumulated in adjacent foreland basins, foredeeps, or remnant-ocean basins is an arduous task. Dickinson and Suczek (1979) and Dickinson (1985) recognized the intrinsically composite nature of orogenic detritus, but did not attempt to establish clear conceptual and operational distinctions within their broad "Recycled Orogenic Provenance". In the Alpine and Himalayan belts, the bulk of the detritus is produced by focused erosion of the central backbone of the orogen, characterized by high topography and exhumation rates (Garzanti et al., 2004; Najman, 2006). Detritus derived from such axial nappe pile, including slivers of thinned continental-margin lithosphere metamorphosed at depth during early collisional stages, has diagnostic general features, which allows us to define an "Axial Belt Provenance" (Garzanti et al., 2007). In detail, "Axial Belt" detrital signatures are influenced by metamorphic grade of source rocks and relative abundance of continental versus oceanic protoliths, typifying distinct subprovenances. Metasedimentary cover nappes shed lithic to quartzolithic detritus, including metapelite, metapsammite, and metacarbonate grains of various ranks; only amphibolite-facies metasediments supply abundant heavy minerals (e.g., almandine garnet, staurolite, kyanite, sillimanite, diopsidic clinopyroxene). Continental-basement nappes shed hornblende-rich quartzofeldspathic detritus. Largely retrogressed blueschist to eclogite-facies metaophiolites supply albite, metabasite and foliated antigorite-serpentinite grains, along with abundant heavy minerals (epidote, zoisite, clinozoisite, lawsonite, actinolitic to barroisitic amphiboles, glaucophane, omphacitic clinopyroxene). Increasing metamorphic grade and deeper

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.

Oblique contractional reactivation of inherited heterogeneities: Cause for arcuate orogens

PubMed Central

Sokoutis, D.; Willingshofer, E.; Brun, J.‐P.; Gueydan, F.; Cloetingh, S.

2017-01-01

Abstract We use lithospheric‐scale analog models to study the reactivation of pre‐existing heterogeneities under oblique shortening and its relation to the origin of arcuate orogens. Reactivation of inherited rheological heterogeneities is an important mechanism for localization of deformation in compressional settings and consequent initiation of contractional structures during orogenesis. However, the presence of an inherited heterogeneity in the lithosphere is in itself not sufficient for its reactivation once the continental lithosphere is shortened. The heterogeneity orientation is important in determining if reactivation occurs and to which extent. This study aims at giving insights on this process by means of analog experiments in which a linear lithospheric heterogeneity trends with various angles to the shortening direction. In particular, the key parameter investigated is the orientation (angle α) of a strong domain (SD) with respect to the shortening direction. Experimental results show that angles α ≥ 75° (high obliquity) allow for reactivation along the entire SD and the development of a linear orogen. For α ≤ 60° (low obliquity) the models are characterized by the development of an arcuate orogen, with the SD remaining partially non‐reactivated. These results provide a new mechanism for the origin of some arcuate orogens, in which orocline formation was not driven by indentation or subduction processes, but by oblique shortening of inherited heterogeneities, as exemplified by the Ouachita orogen of the southern U.S. PMID:28670046

Crustal structure and evolution of the Trans-Hudson orogen: Results from seismic reflection profiling

NASA Astrophysics Data System (ADS)

Baird, D. J.; Nelson, K. D.; Knapp, J. H.; Walters, J. J.; Brown, L. D.

1996-04-01

A 400-km-long deep seismic reflection transect across northeastern Montana and northern North Dakota reveals the crustal-scale structural fabric of the Early Proterozoic Trans-Hudson orogen beneath the Williston basin. Comparison with deep seismic reflection data across the Canadian portion of the same orogen ˜700 km to the north reveals first-order similarities in crustal architecture but documents significant along-strike variation in orogenic evolution. Both transects display a broad crustal-scale antiform axial to the orogen. In the north, geologic data suggest that this antiform is cored by an Archean microcontinent. In the south, west dipping reflections on the western flank of the antiform extend from the upper crust to the uppermost mantle and truncate prominent subhorizontal lower crustal reflections of the Archean Wyoming craton. Within the Wyoming craton, the eastern limit of east dipping midcrustal reflections coincides with the subsurface age boundary between the craton and the Early Proterozoic Trans-Hudson orogen as interpreted from potential field and drill core data. On the basis of subsurface geochronologic data from the crystalline basement and by analogy with the Glennie domain within the exposed Trans-Hudson orogen in Canada, we suggest that the southern antiform is cored by an Archean crustal fragment that was caught up in the terminal collision of the Wyoming and Superior cratons during Hudsonian orogeny. The eastern side of the Trans-Hudson orogen is characterized on both seismic transects by predominantly east dipping crustal penetrating reflections. We interpret the easterly dip of these reflections as evidence that the Superior province was thrust westward over the interludes of the orogen during terminal collision. Although juvenile Early Proterozoic terranes characterize the exposed segment of the Trans-Hudson orogen in Canada, limited drill core information within the Dakota segment of the orogen shows a predominance of granulitic

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

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.

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

Environmental Impact Statement for the Modernization and Enhancement of Ranges, Airspace, and Training Areas in the Joint Pacific Alaska Range Complex in Alaska. Volume 2 - Appendices A through L

DTIC Science & Technology

2013-06-01

enhanC;enwnlswonld ~nahle reoJ istk. jolll l training artd ta.~ti 1g to sup pori omergi ng tedwolo~ttt.», respond lo recent balllefiold...The military uses the JPARC to conduct testing and training and lo support joint exercises and mission rehearsals. The JPARC was originally developed...68th Ave. and Elmore Rd.) 4477 Pike’s Landing.Road Anchorage, Alaska 99507-2599 Fairbanks, Alaska 99709 I 0 a.m. to noon and I :00 lo 5:00p.m. I 0

A cryptic Gondwana-forming orogen located in Antarctica.

PubMed

Daczko, Nathan R; Halpin, Jacqueline A; Fitzsimons, Ian C W; Whittaker, Joanne M

2018-05-30

The most poorly exposed and least understood Gondwana-forming orogen lies largely hidden beneath ice in East Antarctica. Called the Kuunga orogen, its interpolation between scattered outcrops is speculative with differing and often contradictory trends proposed, and no consensus on the location of any sutures. While some discount a suture altogether, paleomagnetic data from Indo-Antarctica and Australo-Antarctica do require 3000-5000 km relative displacement during Ediacaran-Cambrian Gondwana amalgamation, suggesting that the Kuunga orogen sutured provinces of broadly Indian versus Australian affinity. Here we use compiled data from detrital zircons offshore of East Antarctica that fingerprint two coastal subglacial basement provinces between 60 and 130°E, one of Indian affinity with dominant ca. 980-900 Ma ages (Indo-Antarctica) and one of Australian affinity with dominant ca. 1190-1140 and ca. 1560 Ma ages (Australo-Antarctica). We combine this offshore compilation with existing and new onshore U-Pb geochronology and previous geophysical interpretations to delimit the Indo-Australo-Antarctic boundary at a prominent geophysical lineament which intersects the coast east of Mirny at ~94°E.

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.

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.

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

Deformation Partitioning: The Missing Link Between Outcrop-Scale Observations And Orogen-Scale Processes

NASA Astrophysics Data System (ADS)

Attia, S.; Paterson, S. R.; Jiang, D.; Miller, R. B.

2017-12-01

Structural studies of orogenic deformation fields are mostly based on small-scale structures ubiquitous in field exposures, hand samples, and under microscopes. Relating deformation histories derived from such structures to changing lithospheric-scale deformation and boundary conditions is not trivial due to vast scale separation (10-6 107 m) between characteristic lengths of small-scale structures and lithospheric plates. Rheological heterogeneity over the range of orogenic scales will lead to deformation partitioning throughout intervening scales of structural development. Spectacular examples of structures documenting deformation partitioning are widespread within hot (i.e., magma-rich) orogens such as the well-studied central Sierra Nevada and Cascades core of western North America: (1) deformation partitioned into localized, narrow, triclinic shear zones separated by broad domains of distributed pure shear at micro- to 10 km scales; (2) deformation partitioned between plutons and surrounding metamorphic host rocks as shown by pluton-wide magmatic fabrics consistently oriented differently than coeval host rock fabrics; (3) partitioning recorded by different fabric intensities, styles, and orientations established from meter-scale grid mapping to 100 km scale domainal analyses; and (4) variations in the causes of strain and kinematics within fold-dominated domains. These complex, partitioned histories require synthesized mapping, geochronology, and structural data at all scales to evaluate partitioning and in the absence of correct scaling can lead to incorrect interpretations of histories. Forward modeling capable of addressing deformation partitioning in materials containing multiple scales of rheologically heterogeneous elements of varying characteristic lengths provides the ability to upscale the large synthesized datasets described above to plate-scale tectonic processes and boundary conditions. By comparing modeling predictions from the recently developed

Role of mantle dynamics in rebuilding the Tianshan Orogenic Belt in NW China: A seismic tomographic investigation

NASA Astrophysics Data System (ADS)

He, Chuansong; Santosh, M.

2018-05-01

The Tianshan orogenic belt, Junggar terrane and Altai terrane are located at the southwestern part of the Central Asian Orogenic Belt (CAOB). Here, we investigate the velocity structure beneath the Xinjiang region in NW China, which includes the Tarim terrane, Tianshan orogenic belt, Junggar terrane and Altai terrane with a view to evaluate the mantle dynamics based on teleseismic data recorded by 103 seismic stations. Our tomographic results show both high and low velocity perturbations beneath the Tianshan orogenic belt. We suggest that the high velocity perturbations beneath this orogenic belt might represent the northward subducted lithosphere of the Tarim Basin and the southward subducted lithosphere of the Junggar Basin. The low velocity structure beneath the Tianshan orogenic belt might represent asthenosphere upwelling that triggered the extensive magmatism which contributed to rebuilding of the Tianshan orogenic belt.

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

Publications - PIR 2008-1 | Alaska Division of Geological & Geophysical

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investigations in the Brooks Range Foothills and North Slope, Alaska: Alaska Division of Geological & interpretations of the Nanushuk Formation exposed along the Colville River near the confluences with the Awuna and Surveys Skip to content State of Alaska myAlaska My Government Resident Business in Alaska

Publications - PIR 2008-1A | Alaska Division of Geological & Geophysical

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of recent geologic field investigations in the Brooks Range Foothills and North Slope, Alaska: Alaska Surveys Skip to content State of Alaska myAlaska My Government Resident Business in Alaska ; Tectonics; Thermal History; Thrust; Toolik River; Torok Formation; Turbidites; Turonian; Valanginian Top of

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

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.

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.

Continental origin of the Gubaoquan eclogite and implications for evolution of the Beishan Orogen, Central Asian Orogenic Belt, NW China

NASA Astrophysics Data System (ADS)

Saktura, Wanchese M.; Buckman, Solomon; Nutman, Allen P.; Belousova, Elena A.; Yan, Zhen; Aitchison, Jonathan C.

2017-12-01

The Gubaoquan eclogite occurs in the Paleozoic Beishan Orogen of NW China. Previously it has been interpreted as a fragment of subducted oceanic crust that was emplaced as a mélange within continental rocks. Contrary to this, we demonstrate that the Gubaoquan eclogite protolith was a Neoproterozoic basic dyke/sill which intruded into Proterozoic continental rocks. The SHRIMP Usbnd Pb zircon dating of the metamorphic rims of the Gubaoquan eclogite yields an age 466 ± 27 Ma. Subdued heavy rare earth element abundances and lack of negative Eu anomalies of the metamorphic zircon domains confirm that this age represents eclogite facies metamorphism. The host augen orthogneiss has a Usbnd Pb zircon age of 920 ± 14 Ma, representing the timing of crystallization of the granitic protolith. A leucogranitic vein which intrudes the eclogite has a Usbnd Pb zircon age of 424 ± 8.6 Ma. This granitic vein marks the end of high-grade metamorphism in this area. The overcomplication of tectonic history of the Beishan Orogen is partially caused by inconsistent classifications and nomenclature of the same rock units and arbitrary subdivisions of Precambrian blocks as individual microcontinents. In an attempt to resolve this, we propose a simpler model that involves the partial subduction of the northern passive margin of the Dunhuang Block beneath the active continental margin developing on the Mazongshan-Hanshan Block to the north. Ocean closure and continental collision during the Late Ordovician resulted in continental thickening and eclogite facies metamorphism recorded by the mafic dykes/sills (now the Gubaoquan eclogite). In the light of the new data, the tectonothermal evolution of the Beishan Orogen is reviewed and integrated with the evolution of the Central Asian Orogenic Belt.

Publications - PIR 2008-1C | Alaska Division of Geological & Geophysical

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investigations in the Brooks Range Foothills and North Slope, Alaska: Alaska Division of Geological & Surveys Skip to content State of Alaska myAlaska My Government Resident Business in Alaska content DGGS PIR 2008-1C Publication Details Title: Evaluation of stratigraphic continuity between the

Controlling factors of spatial and temporal preservation of the geochronological signal in sediments during an orogenic cycle

NASA Astrophysics Data System (ADS)

Rat, Juliette; Mouthereau, Frédéric; Bernet, Matthias; Brichau, Stéphanie; Balvay, Mélanie; Garzanti, Eduardo; Ando, Sergio

2017-04-01

Detrital content of sediments preserved in basins provide constraints on the nature of source rocks, dynamics of sediment transport, and potentially on tectonics and climate changes. U-Pb dating method on detrital zircon is ideally suited for provenance studies due to the ability of U-Pb age data to resist several orogenic cycles. However, with the aim to track sediment source evolution over a single orogenic cycle and determine characteristic time and parameters controlling the geochronological signal preservation throughout the cycle from rifting, mountain building to post-collision evolution, low-temperature thermochronology combined with sediment petrography are more appropriate than the U-Pb dating approach taken alone. To better understanding processes at play in the long-term geochronological signal preservation we focus on the sediment record associated with the Iberia plate tectonic evolution, which is part of the OROGEN research project, co-financed by BRGM, TOTAL & CNRS. The Iberian plate recorded a period of extension in the Late Jurassic, followed during the Early Cretaceous (Aptian-Albian) by a major thinning event documented by thick syn-rift sediments in intraplate basins and plate-scale heating/cooling of the Iberia crust, as argued by published fission track ages. Paleogeographic reconstructions that are based on stratigraphic and lithofacies analyses in northern Iberia (Iberian Range, Pyrenees and Basque-Cantabrians Range), describe a large domain of continental/fluvial and shallow-marine siliciclastic deposition. The related detrital content was then recycled during the subsequent Pyrenean orogenic phase in the Ebro foreland basin, and eventually transfer to the Mediterranean realm during post-orogenic re-excavation of the Ebro basin. In this study, we complete the published time-temperature paths in the mesozoic syn-rift basins by providing new thermo-chronological analyses of well-dated syn-collision and post-collision stratigraphic sections

Alaska Department of Revenue - Alaska Film Office

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State Employees Alaska Film Office Alaska Film Office State of Alaska HOME CREDIT PROGRAM PUBLIC REPORTING CPA ECONOMIC DEVELOPMENT CONTACT US State of Alaska > Department of Revenue > Alaska Film Office > Text Size: A+ | A- | A Text Only Effective July 1, 2015, the film production incentive

Tertiary uplift of the Mt. Doonerak antiform, central Brooks Range, Alaska: Apatite fission track evidence from the Trans-Alaska Crustal Transect

USGS Publications Warehouse

O'Sullivan, P. B.; Moore, Thomas E.; Murphy, J.M.; Oldow, J.S.; Ave Lallemant, H.G.

1998-01-01

The Mt. Doonerak antiform is a northeast-trending, doubly plunging antiform located along the axial part of the central Brooks Range. This antiform is a crustal-scale duplex estimated to have a vertical displacement of ~15 km. The antiform folds the Amawk thrust, which separates relatively less displaced lower plate rocks in a window in the core of the antiform from allochthonous upper plate rocks of the Endicott Mountains allochthon. Because regional geological relations indicate that displacement on the Amawk thrust occurred between early Neocomian and early Albian time, uplift of the antiform is post-early Neocomian in age.Zircon fission-track data from the Mt. Doonerak antiform suggest -8-12 km of vertical denudation has occurred within the antiform region since -70-65 Ma. whereas apatite fission-track data indicate the antiform has experienced a minimum of -46 km of denudation since late Oligocene time. Following rapid denudation at -24 + 3 Ma, the rocks have experienced continued denudation to present surface conditions at a slower rate.We conclude from the relative relations and timing that the Mt. Doonerak duplex was constructed in part during the late Oligocene by reactivation of an older duplex formed during the latest Cretaceous to Paleocene. Deformation and uplift of Oligocene age for the axial part of the Brooks Range orogen is anomalously young, but it is the same age as the youngest episode of north-vergent contractional uplift in the northeastern Brooks Range. Because the Mt. Doonerak antiform displays structural characteristics similar to those of antiforms in the northeastern Brooks Range and because both regions experienced simultaneous rapid denudation, we suggest that the Mt. Doonerak antiform formed in response to an episode of contractional deformation that affected both areas in the late Oligocene.

77 FR 13683 - Alaska Federal Lands Long Range Transportation Plan

Federal Register 2010, 2011, 2012, 2013, 2014

2012-03-07

...: Notice of extension of comment period. SUMMARY: On December 12, 2011, via a Federal Register notice, we... to Federal Lands in the Alaska region over the next 20 years. We requested comments be submitted by March 12, 2012. With this notice, we extend that comment period from 90 days to 120 days. DATES: Please...

An isotopic perspective on growth and differentiation of Proterozoic orogenic crust: From subduction magmatism to cratonization

NASA Astrophysics Data System (ADS)

Johnson, Simon P.; Korhonen, Fawna J.; Kirkland, Christopher L.; Cliff, John B.; Belousova, Elena A.; Sheppard, Stephen

2017-01-01

The in situ chemical differentiation of continental crust ultimately leads to the long-term stability of the continents. This process, more commonly known as 'cratonization', is driven by deep crustal melting with the transfer of those melts to shallower regions resulting in a strongly chemically stratified crust, with a refractory, dehydrated lower portion overlain by a complementary enriched upper portion. Since the lower to mid portions of continental crust are rarely exposed, investigation of the cratonization process must be through indirect methods. In this study we use in situ Hf and O isotope compositions of both magmatic and inherited zircons from several felsic magmatic suites in the Capricorn Orogen of Western Australia to highlight the differentiation history (i.e. cratonization) of this portion of late Archean to Proterozoic orogenic crust. The Capricorn Orogen shows a distinct tectonomagmatic history that evolves from an active continental margin through to intracratonic reworking, ultimately leading to thermally stable crust that responds similarly to the bounding Archean Pilbara and Yilgarn Cratons. The majority of magmatic zircons from the main magmatic cycles have Hf isotopic compositions that are generally more evolved than CHUR, forming vertical arrays that extend to moderately radiogenic compositions. Complimentary O isotope data, also show a significant variation in composition. However, combined, these data define not only the source components from which the magmas were derived, but also a range of physio-chemical processes that operated during magma transport and emplacement. These data also identify a previously unknown crustal reservoir in the Capricorn Orogen.

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

Slow recovery of lichen on burned caribou winter range in Alaska tundra: potential influences of climate warming and other disturbance factors

Treesearch

Randi Jandt; Kyle Joly; C. Randy Meyers; Charles Racine

2008-01-01

Lichen regeneration timelines are needed to establish sound fire management guidelines for caribou (Rangifer tarandus) winter range. Paired burned and unburned permanent vegetative cover transects were established after 1981, 1977, and 1972 tundra fires in northwestern Alaska to document regrowth of tundra vegetation including caribou forage...

Publications - RDF 2016-6 v. 1.1 | Alaska Division of Geological &

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Alaska's Mineral Industry Reports AKGeology.info Rare Earth Elements WebGeochem Engineering Geology Alaska 345.0 K Metadata - Read me Keywords Alaska Range; Analyses; Analyses and Sampling; Analytical Lab

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

What controls deformation in a bent three-dimensional orogen? An example from the Bolivian Andes

NASA Astrophysics Data System (ADS)

Kaislaniemi, L.; Whipp, D. M., Jr.

2017-12-01

The width of orogens is thought to be affected by both erosional intensity and strength of the rocks. Along-strike variation of the orogen width can be expected to reflect shifts in these factors. An example of such variation can be found around the Bolivian orocline, which is a change in the orientation of the central Andes, in central Bolivia, from N-S south of 18°S to roughly NW-SE in the north. This bend coincides with 50% reduction in the width of the orogen east of the Altiplano, an approximately eight-fold increase in the annual precipitation, and the presence of a basement arch that reduces the thickness of relatively weak Paleozoic sediments upon which the orogen detaches. This has led to uncertainty about whether the growth of the orogen is controlled primarily by climate (erosion) or tectonics (strength of the basal detachment). We study deformation in a segmented orogen using 3D geodynamic models to understand how along-strike variations in rainfall and basal detachment strength affect orogen deformation and growth of the frontal part of the Andean fold-and-thrust belt (FTB). We calculate the visco-plastic deformation in the retro-wedge of an Andean-style orogen using the finite element software DOUAR (Braun et al. 2008) coupled to the surface process model FastScape (Braun & Willett 2013). The model design includes the basement, the Altiplano, and the FTB east of the plateau. A weak basal detachment zone is prescribed. Strain softening allows development of new faults and free evolution of the detachment zone. The effects of varying rock strength and varying precipitation are considered to determine the primary control(s) on the geometry and evolution of curved orogens. Results show that both increased precipitation and stronger detachment zone can explain differences in the width of the FTB, as reflected in the topography. These factors, however, lead to different structural evolution of the orogen: Weak basal detachment zone promotes growth of the

The eastern Central Asian Orogenic Belt: formation and evolution

NASA Astrophysics Data System (ADS)

Xu, Bei; Xu, Wenliang

2017-08-01

The Central Asian Orogenic Belt (CAOB) extends from the northern Eurasian continent in the west via Mongolia, Inner Mongolia and northeast part of China to the Russia Far East in the east. It is characterized by complex trench-arc-basin subduction system, exotic terrane (microcontinents) accretion, massive generation of juvenile crust during the Neoproterozoic-Phanerozoic (e.g., Jahn et al., 2000, 2004; Sengör et al., 1993). A lot of papers about formation and evolution of the CAOB have been published and new field observations and geochemical data for key areas of the CAOB challenge to previous assessments. Several areas previously defined as juvenile are now shown to have mixed crustal compositions. For example, Kröner et al. (2014, in press) estimated that the distribution of various crustal provinces is truly juvenile crustal material ca. 20%, mixed crust ca. 30%, old crust ca. 50%，respectively, in the CAOB, similar to those in other accretionary orogens through Earth history. A two-stage model for the evolution of the CAOB has been suggested based on recent data from the Eastern Tianshan and Beishan (Gao et al., 2011; Su et al., 2011; Chen et al., 2016; Wang et al., 2017), which suggests the process of the formation and evolution of the CAOB includes closure of the Paleo Asian ocean (PAO), formation of orogenic belt before the late Paleozoic and crustal extension and magmatism resulted from plume upon the young orogenic belt after the late Paleozoic. This new model changes previous concept that the CAOB developed through the Paleozoic and is supported by recent researches on the eastern CAOB.

Paleozoic tectonics of the Ouachita Orogen through Nd isotopes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gleason, J.D.; Patchett, P.J.; Dickinson, W.R.

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. Ndmore » 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.« less

Evaluating Precipitation Elevation Gradients in the Alaska Range using Ice Core and Alpine Weather Station Records

NASA Astrophysics Data System (ADS)

McConnell, E.; Osterberg, E. C.; Winski, D.; Kreutz, K. J.; Wake, C. P.; Campbell, S. W.; Ferris, D. G.; Birkel, S. D.

2016-12-01

Precipitation in Alaska is sensitive to the Aleutian Low (ALow) pressure system and North Pacific sea-surface temperatures, as shown by the increase in Alaskan sub-Arctic precipitation associated with the 1976 shift to the positive phase of the Pacific Decadal Oscillation (PDO). Precipitation in the high-elevation accumulation zones of Alaskan alpine glaciers provides critical mass input for glacial mass balance, which has been declining in recent decades from warmer summer temperatures despite the winter precipitation increase. Twin >1500-year ice cores collected from the summit plateau of Mount Hunter in Denali National Park, Alaska show a remarkable doubling of annual snow accumulation over the past 150 years, with most of the change observed in the winter. Other alpine ice cores collected from the Alaska and Saint Elias ranges show similar snowfall increases over recent decades. However, although Alaskan weather stations at low elevation recorded a 7-38% increase in winter precipitation across the 1976 PDO transition, this increase is not as substantial as that recorded in the Mt. Hunter ice core. Weather stations at high-elevation alpine sites are comparatively rare, and reasons for the enhanced precipitation trends at high elevation in Alaska remain unclear. Here we use Automatic Weather Station data from the Mt. Hunter drill site (3,900 m a.s.l) and from nearby Denali climber's Base Camp (2,195 m a.s.l.) to evaluate the relationships between alpine and lowland Alaskan precipitation on annual, seasonal, and storm-event temporal scales from 2008-2016. Both stations are located on snow and have sonic snow depth sounders to record daily precipitation. We focus on the role of variable ALow and North Pacific High strength in influencing Alaskan precipitation elevational gradients, particularly in association with the extreme 2015-2016 El Niño event, the 2009-2010 moderate El Niño event, and the 2010-2011 moderate La Niña event. Our analysis will improve our

Paleozoic Orogens of Mexico and the Laurentia-Gondwana Connections: an Update

NASA Astrophysics Data System (ADS)

Ortega-Gutierrez, F.

2009-05-01

The present position of Mexico in North America and the fixist tectonic models that prevailed prior to the seventies of the past century, have considered the main Paleozoic tectonic systems of Mexico as natural extensions of the orogens that fringed the eastern and southern sides of the Laurentian craton. Well known examples of pre-Mesozoic orogens in Mexico are the Oaxacan, Acatlan, and Chiapas polymetamorphic terranes, which have been correlated respectively with the Grenville and Appalachian-Ouachitan orogens of eastern North America. Nonetheless, several studies conducted during the last decade in these Mexican orogenic belts, have questioned their Laurentian connections, regarding northwestern Gondwana instead as the most plausible place for their birth and further tectonic evolution. This work pretends to approach the problem by briefly integrating the massive amount of new geological information, commonly generated through powerful dating methods such as LA-ICPM-MS on detrital zircon of sedimentary and metasedimentary units in the Paleozoic crustal blocks, which are widely exposed in southern and southeastern Mexico. The Acatlan Complex bears the closest relationships to the Appalachian orogenic system because it shows thermotectonic evidence for opening and closure of the two main oceans involved in building the Appalachian mountains in eastern Laurentia, whereas two other Paleozoic terranes in NW and SE Mexico, until recently rather geologically unknown, may constitute fundamental links between the Americas for the last-stage suturing and consolidation of western Pangea. The buried basement of the Yucatan platform (400,000 squared km) on the other hand, remains as one of the most relevant problems of tectonostratigraphic correlations across the Americas, because basement clasts from the Chicxulub impact ejecta reveal absolute and Nd-model ages that suggest close Gondwanan affinities. Major changes in the comprehension of the Paleozoic orogens in Mexico

Evidence for large-scale imbrication during Eocene syn-orogenic exhumation of the Hellenic subduction channel (Cyclades, Greece)

NASA Astrophysics Data System (ADS)

Grasemann, Bernhard; Huet, Benjamin; Schneider, David; Rice, Hugh; Lemonnier, Nicolas; Tschegg, Cornelius

2017-04-01

In the Cyclades, Miocene post-orogenic back-arc extension overprinted the exhumed syn- orogenic Eocene subduction channel. Whereas the exact geometry and kinematics of the syn-orogenic exhumation are still controversial, but must have involved a floor thrust and an apparent normal fault at the roof, the post-orogenic extension, leading to the exhumation of Cordilleran-type metamorphic core complexes, is well constrained by several major detachment systems. On the island of Milos, which is part of the South Aegean Volcanic Arc, minor outcrops of schist occur. New data indicate that these witnessed Eocene blueschist facies metamorphism at 8.5 kbar and 400°C, but escaped the Miocene extensional overprint, as they lie in the hanging wall of the West Cycladic Detachment System. In contrast, eclogite pebbles in "Green Lahars" on Milos yield metamorphic conditions of 19.5 kbar at 550°C. Both high-pressure units belong to the Cycladic Blueschist Unit and can only have been juxtaposed by thrusting. This indicates that two nappes, the newly defined Cycladic Blueschist Nappe and the overlying Cycladic Eclogite Nappe, both comprising rocks of the Cycladic Blueschist Unit, exist on Milos. These nappes probably also form the other Cycladic islands, separated by a syn-orogenic thrust, which we name the Trans Cycladic Thrust. The Trans Cycladic Thrust, which traces the orientation of the syn-orogenic exhumation channel, is partly offset by the post-orogenic Miocene extensional detachment systems. As a result of the Mid- to Late Miocene clockwise crustal block rotation, the syn-orogenic channel, and hence the Trans Cycladic Thrust, bends through 90° at Milos, changing from a W-E trending to a N-S trending extrusion-related stretching lineation. Restoration of the Miocene block-rotation and extension results in syn-orogenic thrusting kinematics (top-SSW) in the Cycladic Blueschist Nappe and along the Trans Cycladic Thrust and syn-orogenic apparent normal faulting kinematics (top

Susitna Glacier, Alaska

NASA Image and Video Library

2010-09-13

Folds in the lower reaches of valley glaciers can be caused by powerful surges of tributary ice streams. This phenomenon is spectacularly displayed by the Sustina Glacier in the Alaska Range as seen by NASA Terra spacecraft.

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.

Tectonothermal evolution of the Triassic flysch in the Bayan Har Orogen, Tibetan plateau

NASA Astrophysics Data System (ADS)

Wang, Hejing; Rahn, Meinert; Zhou, Jian

2018-01-01

The Bayan Har Orogen comprises a major part of the "Qingzang-Dianxi fold region" in western China. It preserves important information of the tectono-thermal evolution covering the time span from the closure of the Paleo-Tethys Ocean up to the formation of the Himalayas. Low temperature metamorphic indicators, such as mineral assemblages, illite "crystallinity" (IC), chlorite "crystallinity" (CC), illite polytype, b-cell dimension of K-white micas, geothermometry of selected minerals were analyzed. The values of Kübler index (KI) of the Triassic flysch in the Bayan Har Orogen range from 0.23-1.63°Δ2θ while Árkai index (ÁI) in a range of 0.21-0.60°Δ2θ. Iso-thermal zones mapped with KI describe a pair of anchizones and an anchiregion within the Bayan Har Orogen: the "Giant Yushu Anchizone" in the southwest (extending > 750 km long and 100 km wide), the "Zaling-Eling-Lakes Anchizone" in the center (about 150 km long and 40 km wide) and the "Xing-Tong-Zhe Anchiregion" in the northeast (covering an area of roughly 60,000 km2). They are separated by diagenetic zones. Peak metamorphic conditions are estimated around 280-330 °C and a low to intermediate (N. New Hampshire) pressure type. A slight change with increasing then decreasing pressure was observed from SW to NE. The relationship between anchimetamorphic pattern of Triassic flysch and large-scale folds and faults indicates syn- to post structural metamorphism. Compression at the end of the Triassic, induced by the interaction of the Tarim, North China and Indian blocks caused the closure of the Paleo-Tethys Ocean and led to the folding of the Triassic flysch within the Paleo-Tethys Ocean basin. Anchimetamorphism may have been caused by crustal thickening of > 10 km due to an accretionary wedge setting and a temperature increase in those rocks due to burial. Such a regional metamorphic pattern would provide important information for reconstruction of palaeotectonic-palaeogeograph and the evolutionary history

Malaspina Glacier, Alaska

NASA Image and Video Library

2003-05-01

Malaspina Glacier in southeastern Alaska is considered the classic example of a piedmont glacier. Piedmont glaciers occur where valley glaciers exit a mountain range onto broad lowlands, are no longer laterally confined, and spread to become wide lobes.

Staff - Nina T. Harun | Alaska Division of Geological & Geophysical Surveys

Science.gov Websites

mapping of the Upper Jurassic Naknek Formation in a footwall syncline associated with the Bruin Bay fault Ivishak Formation in the northeastern Brooks Range, Alaska: University of Alaska Fairbanks, M.S. thesis Triassic Ivishak Formation in the Sadlerochit Mountains, northeastern Alaska: Alaska Division of Geological

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.

Metabolic syndrome: prevalence among American Indian and Alaska native people living in the southwestern United States and in Alaska.

PubMed

Schumacher, Catherine; Ferucci, Elizabeth D; Lanier, Anne P; Slattery, Martha L; Schraer, Cynthia D; Raymer, Terry W; Dillard, Denise; Murtaugh, Maureen A; Tom-Orme, Lillian

2008-12-01

Metabolic syndrome occurs commonly in the United States. The purpose of this study was to measure the prevalence of metabolic syndrome among American Indian and Alaska Native people. We measured the prevalence rates of metabolic syndrome, as defined by the National Cholesterol Education Program, among four groups of American Indian and Alaska Native people aged 20 years and older. One group was from the southwestern United States (Navajo Nation), and three groups resided within Alaska. Prevalence rates were age-adjusted to the U.S. adult 2000 population and compared to rates for U.S. whites (National Health and Nutrition Examination Survey [NHANES] 1988-1994). Among participants from the southwestern United States, metabolic syndrome was found among 43.2% of men and 47.3% of women. Among Alaska Native people, metabolic syndrome was found among 26.5% of men and 31.2% of women. In Alaska, the prevalence rate varied by region, ranging among men from 18.9% (western Alaska) to 35.1% (southeast), and among women from 22.0% (western Alaska) to 38.4 % (southeast). Compared to U.S. whites, American Indian/Alaska Native men and women from all regions except western Alaska were more likely to have metabolic syndrome; men in western Alaska were less likely to have metabolic syndrome than U.S. whites, and the prevalence among women in western Alaska was similar to that of U.S. whites. The prevalence rate of metabolic syndrome varies widely among different American Indian and Alaska Native populations. Differences paralleled differences in the prevalence rates of diabetes.

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

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.

Scaling the Teflon Peaks: Rock type and the generation of extreme relief in the glaciated western Alaska Range

USGS Publications Warehouse

Ward, Dylan J.; Anderson, Robert S.; Haeussler, Peter J.

2012-01-01

Parts of the Alaska Range (Alaska, USA) stand in prominent exception to the “glacial buzzsaw hypothesis,” which postulates that terrain raised above the ELA is rapidly denuded by glaciers. In this paper, we discuss the role of a strong contrast in rock type in the development of this exceptional terrain. Much of the range is developed on pervasively fractured flysch, with local relief of 1000–1500 m, and mean summit elevations that are similar to modern snow line elevations. In contrast, Cretaceous and Tertiary plutons of relatively intact granite support the range's tallest mountains (including Mt. McKinley, or Denali, at 6194 m), with 2500–5000 m of local relief. The high granitic peaks protrude well above modern snow lines and support many large glaciers. We focus on the plutons of the Denali massif and the Kichatna Mountains, to the west. We use field observations, satellite photos, and digital elevation data to demonstrate how exhumation of these plutons affects glacier longitudinal profiles, the glacial drainage network, and the effectiveness of periglacial processes. In strong granite, steep, smooth valley walls are maintained by detachment of rock slabs along sheeting joints. These steep walls act as low-friction surfaces (“Teflon”), efficiently shedding snow. Simple scaling calculations show that this avalanching may greatly enhance the health of the modern glaciers. We conclude that, in places such as Denali, unusual combinations of rapid tectonic uplift and great rock strength have created the highest relief in North America by enhancing glacial erosion in the valleys while preserving the peaks.

Shear fabrics reveal orogen-parallel deformations, NW Lesser Garhwal Himalaya, Uttarakhand, India

NASA Astrophysics Data System (ADS)

Biswas, T.; Bose, N.; Mukherjee, S.

2017-12-01

Shear deformation along the Himalayan belt is poorly understood unlike that across the orogen. Field observations and structural analysis along Bhagirathi river section along the National Highway 34 reveals NW Lesser Himalaya (Garhwal region, India) suffered both compression and extension parallel to the orogenic belt and thus forms a unique venue of great structural and tectonic interest. Meso-scale ductile- and brittle shear fabrics, such as S-C, C-P, Y-P, Y-S; are emphasized describing such deformations. Extensional shear fabric strikes N43oE and compressional shear fabrics N39.5oE, which are at a low-angle with the orogenic trend. Our study reviews orogen parallel deformation, both extension as well as compression, taking examples from other part of the world (e.g., Central Andes, N Apennines and SW Alps) and from other terrains in the Himalaya. Proposed models are evaluated and compared with the study area. The results shows that the pre-existing remnant structures (e.g., the Delhi-Haridwar ridge) on the under-thrusting Indian shield/plate plays a vital role in modifying thin-skinned tectonics along with migration of the eastward extrusion of the Tibetian plateau (hinterland deformation) into the Himalayan foreland.

Geochemical evidence for Paleozoic crustal growth and tectonic conversion in the Northern Beishan Orogenic Belt, southern Central Asian Orogenic Belt

NASA Astrophysics Data System (ADS)

Yuan, Yu; Zong, Keqing; He, Zhenyu; Klemd, Reiner; Jiang, Hongying; Zhang, Wen; Liu, Yongsheng; Hu, Zhaochu; Zhang, Zeming

2018-03-01

The Beishan Orogenic Belt is located in the central southernmost part of the Central Asian Orogenic Belt (CAOB), which plays a key role in understanding the formation and evolution of the CAOB. Granitoids are the documents of crustal and tectonic evolution in orogenic belts. However, little is known regarding the petrogenesis and geodynamic setting of the widely distributed Paleozoic granitoids in the Northern Beishan Orogenic Belt (NBOB). The present study reveals significant differences concerning the petrogenesis and tectonic setting of early and late Paleozoic granitoids from the NBOB. The early Paleozoic granitoids from the 446-430 Ma Hongliuxia granite complex of the Mazongshan unit and the 466-428 Ma Shibanjing complex of the Hanshan unit show classic I-type granite affinities as revealed by the relative enrichment of LILEs and LREEs, pronounced depletions of Nb, Ta and Ti and the abundant presence of hornblende. Furthermore, they are characterized by strongly variable zircon εHf(t) values between - 16.7 and + 12.8 and evolved plagioclase Sr isotopic compositions of 0.7145-0.7253, indicating the involvement of both juvenile and ancient continental crust in the magma source. Thus, we propose that the early Paleozoic granitoids in the NBOB were generated in a subduction-related continental arc setting. In contrast, the late Paleozoic 330-281 Ma granitoids from the Shuangjingzi complex of the Hanshan unit exhibit positive zircon εHf(t) values between + 5.8 and + 13.2 and relatively depleted plagioclase Sr isotopic compositions of 0.7037-0.7072, indicating that they were mainly formed by remelting of juvenile crust. Thus, an intra-plate extensional setting is proposed to have occurred during formation of the late Paleozoic granitoids. Therefore, between the early and late Paleozoic, the magma sources of the NBOB granitoids converted from the reworking of both juvenile and ancient crusts during a subduction-induced compressional setting to the remelting of

What happens along the flank and corner of a continental indenter? Insights from the easternmost Himalayan orogen and constraints on the models of the India-Asia collision

NASA Astrophysics Data System (ADS)

Haproff, P. J.; Yin, A.; Zuza, A. V.

2017-12-01

Investigations of continental collisions often focus on thrust belts oriented perpendicular to the plate-convergence direction and exclude belts that bound the flanks of a continental indenter despite being crucial to understanding the collisional process. Research of the Himalayan orogen, for example, has mostly centered on the east-trending thrust belt between the eastern and western syntaxes, resulting in inadequate examination of the north-trending Indo-Burma Ranges located along the eastern margin of India. To better understand the development of the entire Himalayan orogenic system, we conducted field mapping across the Northern Indo-Burma Range (NIBR), situated at the intersection of the eastern Himalaya and Indo-Burma Ranges. Our research shows that major lithologic units and thrust faults of the Himalaya extend to the NIBR, suggesting a shared geologic evolution. The structural framework of the NIBR consists of a southwest-directed thrust belt cored by a hinterland-dipping duplex, like the Himalaya. However, the Northern Indo-Burma orogen is distinct based on (1) the absence of the Tethyan Himalayan Sequence and southern Gangdese batholith, (2) the absence of the South Tibetan detachment, (3) crustal shortening greater than 80%, (4) an incredibly narrow orogen width of 7-33 km, (5) exposure of an ophiolitic mélange complex as a klippe, (6) and right-slip shear along the active range-bounding thrust fault. Furthermore, lithospheric deformation along the flank and northeast corner of India is characterized by right-slip transpression partitioned between the thrust belt and right-slip faults. Such a regime is interpreted to accommodate both contraction and clockwise rotation of Tibetan lithosphere around India, consistent with existing continuum deformation and rotation models.

Timing of sediment-hosted Cu-Ag mineralization in the Trans-Hudson orogen at Janice Lake, Wollaston Domain, Saskatchewan, Canada

NASA Astrophysics Data System (ADS)

Perelló, José; Valencia, Víctor A.; Cornejo, Paula; Clifford, John; Wilson, Alan J.; Collins, Greg

2018-04-01

The Janice Lake Cu-Ag mineralization in the Wollaston Domain of northern Saskatchewan is hosted by a metasedimentary sequence in the upper part of the Wollaston Supergroup of the Trans-Hudson orogen. The Wollaston Supergroup was deposited between 2070 and 1865 Ma in a foreland basin setting constructed over Archean basement of the Hearne craton. The Trans-Hudson orogen underwent final collision and peak metamorphism at 1810 Ma, during consolidation of Laurentia and its amalgamation with the Columbia supercontinent. Titanite is a common constituent of the post-peak metamorphic assemblages of Trans-Hudson lithotectonic units and accompanied disseminated sediment-hosted Cu sulfide mineralization at Janice Lake. Titanite crystals, intergrown with chalcocite over a strike-length of 2 km of Cu-bearing stratigraphy, were dated by the ID-TIMS and LA-ICP-MS U-Pb methods, returning an age range from 1780 to 1760 Ma and a weighted average age of 1775 ± 10 Ma. The titanite ages effectively date the associated chalcocite-dominated sediment-hosted Cu-Ag mineralization and its formation during initial post-orogenic uplift and cooling, 30 myr after peak metamorphism. The age-range and tectonic setting of the Janice Lake mineralization confirms that sediment-hosted Cu mineralization was an integral part of the metallogenic endowment of Columbia and that its emplacement coincided with the continental-scale Trans-Hudson orogeny rather than with diagenesis and extensional basin development 100 myr earlier.

Seismic component of the STEEP project, Alaska: Results of the first field season

NASA Astrophysics Data System (ADS)

Hansen, R. A.; Estes, S.; Stachnik, J.; Lafevers, M.; Roush, J.; Sanches, R.; Fuerst, E.; Sandru, J.; Ruppert, N.; Pavlis, G.; Bauer, M.

2005-12-01

STEEP (SainT Elias Erosion/tectonics Project) is a five year, multi-disciplinary study that addresses evolution of the highest coastal mountain range on Earth - the St. Elias Mountains of southern Alaska and northwestern Canada. The overall goal of the project is to develop a comprehensive model for the St. Elias orogen that accounts for the interaction of regional plate tectonic processes, structural development, and rapid erosion. The seismic component of this project includes passive seismic experiment utilizing the IRIS PASSCAL Program instruments. The total project consists of 22 new, telemetered, digital broad band seismic stations, most accessible by helicopter only. There are 12 existing short period stations in the area. Eight new stations were installed in the coastal region in June 2005. Freewave IP radios provide the telemetry to the newly installed VSAT at the Bering Glacier camp site. The challenge was to find ice-free locations, on bedrock, large enough to install equipment and still have a helicopter landing zone nearby. The stations consist of Quanterra Q330 digitizers with baler, a STS-2 seismometer installed in a vault, a Freewave IP radio, a Scala 900 Mhz antenna, twenty 100 AH rechargeable batteries with a 2400AH backup Celair primary battery, and three solar panels mounted on hut. The acquired data is recorded in real time at the Alaska Earthquake Information Center located in Fairbanks and is incorporated into the standard data processing procedures. High quality data allows for more reliable automatic earthquake detections in the region with lower magnitude threshold. In addition to tectonic earthquakes, glacial events that occur within the vast ice fields of the region are also regularly detected. Broadband instruments complement regional broadband network for more reliable calculations of the regional moment tensors.

Some aspects of the role of rift inheritance on Alpine-type orogens

NASA Astrophysics Data System (ADS)

Tugend, Julie; Manatschal, Gianreto; Mohn, Geoffroy; Chevrot, Sébastien

2017-04-01

Processes commonly recognized as fundamental for the formation of collisional orogens include oceanic subduction, arc-continent and continent-continent collision. As collisional belts result from the closure of oceanic basins and subsequent inversion of former rifted margins, their formation and evolution may also in theory be closely interlinked with the initial architecture of the former rifted margins. This assumption is indeed more likely to be applicable in the case of Alpine-type orogens, mainly controlled by mechanical processes and mostly devoid of arc-related magmatism. More and more studies from present-day magma-poor rifted margins illustrate the complex evolution of hyperextended domains (i.e. severely thinned continental crust (<10 km) and/or exhumed serpentinized mantle with relatively minor magmatic additions) between unequivocal continental and oceanic domains. In this contribution, we compare the deep structure of the Pyrenean and Alpine belts to discuss some aspects of the relative role of rift-inherited hyperextension and collisional processes in building Alpine-type orogens. The Pyrenees and Western to Central Alps respectively result from the inversion of a Late Jurassic to Mid Cretaceous and an Early to Middle Jurassic rift system eventually floored by hyperextended crust, exhumed mantle and/or proto-oceanic crust. In spite of uncertainties on the initial width of the hyperextended and proto-oceanic domains, the rift-related pre-collisional architecture of the Alps shows many similarities with that proposed for the Pyrenees. Remnants of these domains occur in the internal parts of both orogens, but they are largely affected by orogeny-related deformation and show a HP-LT to HT-MP metamorphic overprint in the Alps as a result of a polyphase deformation history. Yet, recent high-resolution tomographic images across the Pyrenees (PYROPE) and the Alps (CIFALPS) reveal a surprisingly comparable present-day overall crustal and lithospheric structure

Generation of post-collisional normal calc-alkaline and adakitic granites in the Tongbai orogen, central China

NASA Astrophysics Data System (ADS)

Zhang, Wen-Xiang; Zhu, Liu-Qin; Wang, Hao; Wu, Yuan-Bao

2018-01-01

Post-collisional granites are generally generated by partial melting of continental crust during orogenic extension. The occurrence of normal calc-alkaline granites following adakitic granites in a collisional orogen is frequently supposed as a sign of tectonic regime transition from compression to extension, which has been debated yet. In this paper, we present a comprehensive study of zircon U-Pb ages, Hf-O isotopes, as well as whole-rock major and trace elements and Sr-Nd isotopes, for Tongbai and Jigongshan post-collisional granitic plutons in the Tongbai orogen. Zircon U-Pb dating yields intrusion ages of ca. 140 and 135 Ma for the Tongbai and Jigongshan plutons, respectively, suggesting they are post-collisional granites. These granites are high-K calc-alkaline series, metaluminous to weakly peraluminous with A/CNK ratios of 0.85-1.08. The Tongbai gneissic granites are normal calc-alkaline granite, having variable SiO2 (61.93-76.74 wt%) and Sr/Y (2.9-38.9) and (La/Yb)N (1.7-30.1) ratios with variably negative Eu anomalies (0.41-0.92). They have relatively high initial Sr isotope ratios of 0.707571 to 0.710317, and low εNd(t) (- 15.74 to - 11.09) and εHf(t) (- 17.6 to - 16.9) values. Their Nd and Hf model ages range from 2.2 to 1.8 Ga and 2.3 to 2.2 Ga. On the contrary, the Jigongshan granites show higher SiO2 (66.56-72.11 wt%) and Sr/Y (30.1-182.0) and (La/Yb)N (27.4-91.4) ratios with insignificant Eu anomalies (0.73-1.00), belonging to adakitic granite. They have Isr = 0.707843-0.708366, εNd(t) = - 19.83 to - 17.59, and εHf(t) = - 26.0 to - 23.5. Their Nd and Hf model ages vary from ca. 2.5 to 2.4 Ga and ca. 2.8 to 2.6 Ga. The Tongbai and Jigongshan granites are characterized by mantle-like zircon δ18O values (5.17-5.46‰). These geochemical features suggest that the Tongbai and Jigongshan granites were derived from partial melting of Paleoproterozoic and Archean continental crust, respectively. Fractional crystallization affected the geochemical

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.

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).

Devonian post-orogenic extension-related volcano-sedimentary rocks in the northern margin of the Tibetan Plateau, NW China: Implications for the Paleozoic tectonic transition in the North Qaidam Orogen

NASA Astrophysics Data System (ADS)

Qin, Yu; Feng, Qiao; Chen, Gang; Chen, Yan; Zou, Kaizhen; Liu, Qian; Jiao, Qianqian; Zhou, Dingwu; Pan, Lihui; Gao, Jindong

2018-05-01

The Maoniushan Formation in the northern part of the North Qaidam Orogen (NQO), NW China, contains key information on a Paleozoic change in tectonic setting of the NQO from compression to extension. Here, new zircon U-Pb, petrological, and sedimentological data for the lower molasse sequence of the Maoniushan Formation are used to constrain the timing of this tectonic transition. Detrital zircons yield U-Pb ages of 3.3-0.4 Ga with major populations at 0.53-0.4, 1.0-0.56, 2.5-1.0, and 3.3-2.5 Ga. The maximum depositional age of the Maoniushan Formation is well constrained by a youngest detrital zircon age of ∼409 Ma. Comparing these dates with geochronological data for the region indicates that Proterozoic-Paleozoic zircons were derived mainly from the NQO as well as the Oulongbuluk and Qaidam blocks, whereas Archean zircons were probably derived from the Oulongbuluk Block and the Tarim Craton. The ∼924, ∼463, and ∼439 Ma tectonothermal events recorded in this region indicate that the NQO was involved in the early Neoproterozoic assembly of Rodinia and early Paleozoic microcontinental convergence. A regional angular unconformity between Devonian and pre-Devonian strata within the NQO suggests a period of strong mountain building between the Oulongbuluk and Qaidam blocks during the Silurian, whereas an Early Devonian post-orogenic molasse, evidence of extensional collapse, and Middle to Late Devonian bimodal volcanic rocks and Carboniferous marine carbonate rocks clearly reflect long-lived tectonic extension. Based on these results and the regional geology, we suggest that the Devonian volcano-sedimentary rocks within the NQO were formed in a post-orogenic extensional setting similar to that of the East Kunlun Orogen, indicating that a major tectonic transition from compression to extension in these two orogens probably commenced in the Early Devonian.

Publications - PIR 2008-1B | Alaska Division of Geological & Geophysical

Science.gov Websites

., Preliminary results of recent geologic field investigations in the Brooks Range Foothills and North Slope Surveys Skip to content State of Alaska myAlaska My Government Resident Business in Alaska content DGGS PIR 2008-1B Publication Details Title: Measured section and facies analysis of the Lower

Earthquake activity along the Himalayan orogenic belt

NASA Astrophysics Data System (ADS)

Bai, L.; Mori, J. J.

2017-12-01

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

Lithosphere structure of the west Qinling orogenic belt revealed by deep seismic reflection profile

NASA Astrophysics Data System (ADS)

Wang, H.

2009-12-01

The west Qinling orogen located in the northeastern margin of the Qinghai-Tibet plateau, is transformation zone between the N-S-trending and E-W-trending tectonics in the Chinese continent. Further study of the fine crust structure of the west Qinling orogen and its relationships with surrounding basins have very important significance for understanding tectonic response of the northeastern margin of the plateau about collision convergence of the Indian block and Asian block and learning formation and evolution of the plateau. In 2009, we reprocessed the data of the Tangke-Hezuo deep seismic reflection profiles collected in 2004 across the west Qinling orogen and the northern Songpan block. The new results show the lithosphere fine structure of the west Qinling orogen. Reflection features indicate that an interface at 6.0-7.0s (TWT) divided the crust into the upper and lower crust, whose structural style and deformation are totally different. Integrating geological data, we deduce that the interface at 6.0-7.0s (depth with 18-21 km) was the basement detachment, which made deformation decoupled of the upper and lower crust. The multi-layered reflections in the upper crust reveal the sedimentary covers of the west Qinling orogen, disclose the thickness of the various structure layer and deformation degree, and provide a basis for the prospective evaluation of a multi-metallic mineral and energy exploration. The north dipping strong reflection characteristics of the lower crust in the west Qinling orogen constituted imbricate structure, such imbricate structural features provide seismology evidence for researching the west Qinling thrusting toward the northern Songpan block, and have great significance for studying formation and evolution of the Songpan-Garze structure. Moho reflections are observed around 17.0-17.2s, characterized by nearly horizontal reflections, which implies the west Qinling orogen underwent an intense extension post orogeny caused the lithosphere

Rare Clear View of Alaska [annotated

NASA Image and Video Library

2017-12-08

On most days, relentless rivers of clouds wash over Alaska, obscuring most of the state’s 6,640 miles (10,690 kilometers) of coastline and 586,000 square miles (1,518,000 square kilometers) of land. The south coast of Alaska even has the dubious distinction of being the cloudiest region of the United States, with some locations averaging more than 340 cloudy days per year. That was certainly not the case on June 17, 2013, the date that the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite acquired this rare, nearly cloud-free view of the state. The absence of clouds exposed a striking tapestry of water, ice, land, forests, and even wildfires. Snow-covered mountains such as the Alaska Range and Chugach Mountains were visible in southern Alaska, while the arc of mountains that make up the Brooks Range dominated the northern part of the state. The Yukon River—the longest in Alaska and the third longest in the United States—wound its way through the green boreal forests that inhabit the interior of the state. Plumes of sediment and glacial dust poured into the Gulf of Alaska from the Copper River. And Iliamna Lake, the largest in Alaska, was ice free. The same ridge of high pressure that cleared Alaska’s skies also brought stifling temperatures to many areas accustomed to chilly June days. Talkeetna, a town about 100 miles north of Anchorage, saw temperatures reach 96°F (36°C) on June 17. Other towns in southern Alaska set all-time record highs, including Cordova, Valez, and Seward. The high temperatures also helped fuel wildfires and hastened the breakup of sea ice in the Chukchi Sea. NASA image courtesy Jeff Schmaltz, LANCE MODIS Rapid Response Team at NASA GSFC. Caption by Adam Voiland. Instrument: Terra - MODIS More info: 1.usa.gov/102MAEj Credit: NASA Earth Observatory NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar

Timing of crust formation and recycling in accretionary orogens: Insights learned from the western margin of South America

NASA Astrophysics Data System (ADS)

Bahlburg, Heinrich; Vervoort, Jeffrey D.; Du Frane, S. Andrew; Bock, Barbara; Augustsson, Carita; Reimann, Cornelia

2009-12-01

Accretionary orogens are considered major sites of formation of juvenile continental crust. In the central and southern Andes this is contradicted by two observations: siliciclastic fills of Paleozoic basins in the central Andean segment of the accretionary Terra Australis Orogen consist almost exclusively of shales and mature sandstones; and magmatic rocks connected to the Famatinian (Ordovician) and Late Paleozoic magmatic arcs are predominantly felsic and characterized by significant crustal contamination and strongly unradiogenic Nd isotope compositions. Evidence of juvenile crustal additions is scarce. We present laser ablation (LA)-ICPMS U-Pb ages and LA-MC-ICPMS Hf isotope data of detrital zircons from seven Devonian to Permian turbidite sandstones incorporated into a Late Paleozoic accretionary wedge at the western margin of Gondwana in northern Chile. The combination with Nd whole-rock isotope data permits us to trace the evolution of the South American continental crust through several Proterozoic and Paleozoic orogenic cycles. The analyzed detrital zircon spectra reflect all Proterozoic orogenic cycles representing the step-wise evolution of the accretionary SW Amazonia Orogenic System between 2.0 and 0.9 Ga, followed by the Terra Australis Orogen between 0.9 and 0.25 Ga. The zircon populations are characterized by two prominent maxima reflecting input from Sunsas (Grenville) age magmatic rocks (1.2-0.9 Ga) and from the Ordovician to Silurian Famatinian magmatic arc (0.52-0.42 Ga). Grains of Devonian age are scarce or absent from the analyzed zircon populations. The Hf isotopic compositions of selected dated zircons at the time of their crystallization ( ɛHf ( T) ; T = 3.3-0.25 Ga) vary between - 18 and + 11. All sandstones have a significant juvenile component; between 20 and 50% of the zircons from each sedimentary rock have positive ɛHf ( T) and can be considered juvenile. The majority of the juvenile grains have Hf-depleted mantle model ages (Hf

The main features of the Uralian Paleozoic magmatism and the epioceanic nature of the orogen

NASA Astrophysics Data System (ADS)

Fershtater, G. B.

2013-02-01

The 2000 km Uralian Paleozoic orogen is situated on the western flank of the Uralo-Mongolian folded belt. It is characterized by an abundant variety of magmatic rocks and related ore deposits. Uralian Paleozoic magmatism is entirely subduction-related. It is proposed that the Uralian orogen represents a cold mobile belt in which the mantle temperature was 200 to 500 °C cooler than in the adjacent areas; a situation which is similar to the modern West Pacific Triangle Zone including Indonesia, the Philippine Islands, and southern Asia. During the course of the geological evolution of the Uralian orogen, the nature of the magmatism has changed from basic rocks of indisputable mantle origin (460-390 Ma) to mantle-crust gabbro-granitic complexes (370-315 Ma) followed by pure crustal granite magmatism (290-250 Ma). This order in rock type and age reflects the evolution of Paleozoic magmatic complexes from the beginning of subduction to the final stages of the orogen development.

Publications - RI 2015-6 | Alaska Division of Geological & Geophysical

Science.gov Websites

., Schwab, C.E., Silva, S.R., Smith, T.E., and Zehner, R.E. Publication Date: Sep 2015 Publisher: Alaska , C.E., Silva, S.R., Smith, T.E., and Zehner, R.E., 2015, Geologic maps of the eastern Alaska Range

Mineral deposits and metallogeny of Alaska

USGS Publications Warehouse

Goldfarb, Richard J.; Meighan, Corey J.; Meinert, Lawrence D.; Wilson, Frederic H.

2016-01-01

Alaska, the largest State within the United States, and mainly located north of latitude 60°, is an important part of the Circum-Arctic region. Alaska is a richly endowed region with a long and complex geologic history. The mining history is short by world standards but nevertheless there are a number of world-class deposits in Alaska, of which Red Dog and Pebble are among the largest of their respective types in the world. Alaska is a collection of geologic terranes or regions having distinct histories, most of which were tectonically assembled in the period from 400 million years to 50 million years ago (late Paleozoic through early Tertiary). They now occur as numerous fault-bounded blocks in the northernmost part of the North American Cordillera on the western margin of the Laurentian craton. These terranes are comprised of rocks ranging in age from Paleoproterozoic to Recent.

Complex high-strain deformation in the Usagaran Orogen, Tanzania: structural setting of Palaeoproterozoic eclogites

NASA Astrophysics Data System (ADS)

Reddy, S. M.; Collins, A. S.; Mruma, A.

2003-11-01

The Palaeoproterozoic Usagaran Orogen of Tanzania contains the Earth's oldest reported examples of subduction-related eclogite facies rocks. Detailed field mapping of gneisses exposed in the high-grade, eclogite-bearing part of the orogen (the Isimani Suite) indicates a complex deformation and thermal history. Deformation in the Isimani Suite can be broadly subdivided into five events. The first of these (D 1), associated with formation of eclogite facies metamorphism, is strongly overprinted by a pervasive deformation (D 2) at amphibolite facies conditions, which resulted in the accumulation of high strains throughout all of the exposed Isimani rocks. The geometry of foliations and lineations developed during D 2 deformation are variable and have different shear directions that enable five D 2 domains to be identified. Analysis of these domains indicates a geometrical and kinematic pattern that is interpreted to have formed by strain and kinematic partitioning during sinistral transpression. U-Pb SHRIMP zircon ages from a post-D 2 granite and previously published geochronological data from the Usagaran eclogites indicate this deformation took place between 2000 ± 1 Ma and 1877 ± 7 Ma (at 1σ error). Subsequent greenschist facies deformation, localised as shear zones on boundaries separating D 2 domains, have both contractional and extensional geometries that indicate post-1877 Ma reactivation of the Isimani Suite. This reactivation may have taken place during Palaeoproterozoic exhumation of the Usagaran Orogen or may be the result of deformation associated with the Neoproterozoic East African Orogen. U-Th-Pb SHRIMP zircon ages from an Isimani gneiss sample and xenocrysts in a "post-tectonic" granite yield ˜2.7 Ga ages and are similar to published Nd model ages from both the Tanzanian Craton and gneiss exposed east of the Usagaran belt in the East African Orogen. These age data indicate that the Isimani Suite of the Usagaran Orogen reflects reworking of Archaean

Crustal surface wave velocity structure of the east Albany-Fraser Orogen, Western Australia, from ambient noise recordings

NASA Astrophysics Data System (ADS)

Sippl, C.; Kennett, B. L. N.; Tkalčić, H.; Gessner, K.; Spaggiari, C. V.

2017-09-01

Group and phase velocity maps in the period range 2-20 s for the Proterozoic east Albany-Fraser Orogen, Western Australia, are extracted from ambient seismic noise recorded with the 70-station ALFREX array. This 2 yr temporary installation provided detailed coverage across the orogen and the edge of the Neoarchean Yilgarn Craton, a region where no passive seismic studies of this scale have occurred to date. The surface wave velocities are rather high overall (>3 km s-1 nearly everywhere), as expected for exposed Proterozoic basement rocks. No clear signature of the transition between Yilgarn Craton and Albany-Fraser Orogen is observed, but several strong anomalies corresponding to more local geological features were obtained. A prominent, NE-elongated high-velocity anomaly in the northern part of the array is coincident with a Bouguer gravity high caused by the upper crustal metamorphic rocks of the Fraser Zone. This feature disappears towards longer periods, which hints at an exclusively upper crustal origin for this anomaly. Further east, the limestones of the Cenozoic Eucla Basin are clearly imaged as a pronounced low-velocity zone at short periods, but the prevalence of low velocities to periods of ≥5 s implies that the uppermost basement in this area is likewise slow. At longer periods, slightly above-average surface wave velocities are imaged below the Eucla Basin.

Provenance and petrofacies, Upper Devonian sandstones, Philip Smith Mountains and Arctic quandrangles, Brooks Range, Alaska: Final report, Project No. 3

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anderson, A.V.; Coney, P.J.

1987-11-01

Late Devonian sandstone beds are exposed as allochthonous sequences that extend for over 1000 km along the east-west strike of the Brooks Range in northern Alaska. These horizons, at least in part, record Late Devonian tectonism and deposition along the southern margin of the Arctic Alaska block. This study identifies clastic petrofacies in the western Philip Smith Mountains and southern Arctic quadrangles and infers the composition of the source terrane. The paleogeography is not known and the original distribution of lithofacies is uncertain, owing to the extensive post-depositional tectonism. In the study area the sandstones are exposed along rugged mountainmore » tops and high ridges. Although exposures are excellent, access is often difficult. Samples were collected from exposures near the western end of the Chandalar Shelf, Atigun Pass, and the Atigun River valley in the Philip Smith Mountains quadrangle and from the Crow Nest Creek and Ottertail Creek areas in the Arctic quadrangle. 34 refs., 17 figs.« less

Alaska Air National Guard

Science.gov Websites

Skip to content State of Alaska myAlaska My Government Resident Business in Alaska Visiting Alaska Symbol Visit 168th Wing Website State of Alaska myAlaska My Government Resident Business in Alaska

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.

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.

Geologic studies in Alaska by the U.S. Geological Survey, 1988

USGS Publications Warehouse

Dover, James H.; Galloway, John P.

1989-01-01

This volume continues the annual series of U.S. Geological Survey (USGS) reports on geologic investigations in Alaska. Since 1975, when the first of these collections of short papers appeared under the title "The United States Geological Survey in Alaska: Accomplishments during 1975," the series has been published as USGS circulars. This bulletin departs from the circular style, in part to provide a more flexible format for longer reports with more depth of content, better documentation, and broader scope than is possible for circular articles.The 13 papers in this bulletin represent a sampling of research activities carried out in Alaska by the USGS over the past few years. The topics addressed range from mineral resource studies (including natural gas) and geochemistry, Quaternary geology, basic stratigraphic and structural problems, and the use of computer graphics in geologic map preparation, to the application of geochronology to regional tectonic problems. Geographic areas represented are numbered on figure 1 and include the North Slope (1) and Brooks Range (2, 3) of Arctic Alaska, Seward Peninsula (4), interior Alaska (5-9), and remote locations of the Alaska Peninsula (10, 11) and southeast Alaska (12, 13).Two bibliographies following the reports of investigations list (1) reports about Alaska in USGS publications released in 1988 and (2) reports about Alaska by USGS authors in publications outside the USGS in 1988. A bibliography and index of the short papers in past USGS circulars devoted to Geological Research and Accomplishments in Alaska (1975-1986) is published as USGS Open-File Report 87-420.

Geology and origin of epigenetic lode gold deposits, Tintina Gold Province, Alaska and Yukon: Chapter A 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

Goldfarb, Richard J.; Marsh, Erin E.; Hart, Craig J.R.; Mair, John L.; Miller, Marti L.; Johnson, Craig; Gough, Larry P.; Day, Warren C.

2007-01-01

-rich and 18O-rich crustal fluids, most commonly of low salinity. The older group of ores includes the low-grade intrusion-related gold systems at Fort Knox near Fairbanks and those in Yukon, with fluids exsolved from fractionating melts at depths of 3 to 9 kilometers and forming a zoned sequence of auriferous mineralization styles extending outward to the surrounding metasedimentary country rocks. The causative plutons are products of potassic mafic magmas generated in the subcontinental lithospheric mantle that interacted with overlying lower to middle crust to generate the more felsic ore-related intrusions. In addition, the older ores include spatially associated, high-grade, shear-zonerelated orogenic gold deposits formed at the same depths from upward-migrating metamorphic fluids; the Pogo deposit is a relatively deep-seated example of such. The younger gold ores, restricted to southwestern Alaska, formed in unmetamorphosed sedimentary rocks of the Kuskokwim basin within 1 to 2 kilometers of the surface. Most of these deposits formed via fluid exsolution from shallowly emplaced, highly evolved igneous complexes generated mainly as mantle melts. However, the giant Donlin Creek orogenic gold deposit is a product of either metamorphic devolatilization deep in the basin or of a gold-bearing fluid released from a flysch-melt igneous body.

Metallogenesis and tectonics of the Russian Far East, Alaska, and the Canadian Cordillera

USGS Publications Warehouse

Nokleberg, Warren J.; Bundtzen, Thomas K.; Eremin, Roman A.; Ratkin, Vladimir V.; Dawson, Kenneth M.; Shpikerman, Vladimir I.; Goryachev, Nikolai A.; Byalobzhesky, Stanislav G.; Frolov, Yuri F.; Khanchuk, Alexander I.; Koch, Richard D.; Monger, James W.H.; Pozdeev, Anany I.; Rozenblum, Ilya S.; Rodionov, Sergey M.; Parfenov, Leonid M.; Scotese, Christopher R.; Sidorov, Anatoly A.

2005-01-01

The Proterozoic and Phanerozoic metallogenic and tectonic evolution of the Russian Far East, Alaska, and the Canadian Cordillera is recorded in the cratons, craton margins, and orogenic collages of the Circum-North Pacific mountain belts that separate the North Pacific from the eastern North Asian and western North American Cratons. The collages consist of tectonostratigraphic terranes and contained metallogenic belts, which are composed of fragments of igneous arcs, accretionary-wedge and subduction-zone complexes, passive continental margins, and cratons. The terranes are overlapped by continental-margin-arc and sedimentary-basin assemblages and contained metallogenic belts. The metallogenic and geologic history of terranes, overlap assemblages, cratons, and craton margins has been complicated by postaccretion dismemberment and translation during strike-slip faulting that occurred subparallel to continental margins. Seven processes overlapping in time were responsible for most of metallogenic and geologic complexities of the region (1) In the Early and Middle Proterozoic, marine sedimentary basins developed on major cratons and were the loci for ironstone (Superior Fe) deposits and sediment-hosted Cu deposits that occur along both the North Asia Craton and North American Craton Margin. (2) In the Late Proterozoic, Late Devonian, and Early Carboniferous, major periods of rifting occurred along the ancestral margins of present-day Northeast Asia and northwestern North America. The rifting resulted in fragmentation of each continent, and formation of cratonal and passive continental-margin terranes that eventually migrated and accreted to other sites along the evolving margins of the original or adjacent continents. The rifting also resulted in formation of various massive-sulfide metallogenic belts. (3) From about the late Paleozoic through the mid-Cretaceous, a succession of island arcs and contained igneous-arc-related metallogenic belts and tectonically paired

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Accretionary and collisional orogenesis in the south domain of the western Central Asian Orogenic Belt (CAOB)

NASA Astrophysics Data System (ADS)

Cai, Keda; Long, Xiaoping; Chen, Huayong; Sun, Min; Xiao, Wenjiao

2018-03-01

The Central Asian Orogenic Belt (CAOB) was the result of long-lived multi-stage tectonic evolution, including Proterozoic to Paleozoic accretion and collision, Mesozoic intracontinental modification, and Cenozoic rapid deformation and uplift. The accretionary and collisional orogenesis of its early history generated a huge orogenic collage consisting of diverse tectonic units including island arcs, ophiolites, accretionary prisms, seamounts, oceanic plateaus and micro-continents. These incorporated orogenic components preserved valuable detailed information on orogenic process and continental crust growth, which make the CAOB a key region to understanding of continental evolution, mantle-crust interaction and associated mineralization. The western CAOB refers to the west region in North Xinjiang of China and circum-Balkash of Kazakhstan, with occurrences of the spectacular Kazakhstan orocline and its surrounding mountain belts. Because orogenic fabrics of this part mostly preserve their original features caused by the interactions among the southern Siberian active margin in the north and the Tarim Craton in the south, the western CAOB can be regarded as an ideal region to study the processes of the accretionary and collisional orogenesis and associated mineralization. Since a large number of researchers have been working on this region, research advances bloom strikingly in a short-time period. Therefore, we, in this special issue, focus on these new study advances on the south domain of the western CAOB, including the Kazakhstan collage system, Tianshan orogenic belt and Beishan region, and it is anticipated that this issue can draw more attention from the international research groups to be interested in the studies on orogenesis of the CAOB.

Downed woody material in southeast Alaska forest stands.

Treesearch

Frederic R. Larson

1992-01-01

Data collected in conjunction with the multiresource inventory of southeast Alaska in 1985-86 included downed wood along 234 transects at 60 locations. Transects occurred in 11 forest types and 19 plant associations within the entire southeastern Alaska archipelago. Downed wood weights in forest types ranged from 1232 kilograms per hectare (0.6 ton per acre) in muskeg...

Geochemistry, 40Ar/39Ar geochronology, and geodynamic implications of Early Cretaceous basalts from the western Qinling orogenic belt, China

NASA Astrophysics Data System (ADS)

Zhang, Feifei; Wang, Yuejun; Cawood, Peter A.; Dong, Yunpeng

2018-01-01

The Qinling-Dabie orogenic belt was formed by the collision of the North and South China Cratons during the Early Mesozoic and subsequently developed into an intracontinental tectonic process during late Mesozoic. Field investigations identified the presence of late Mesozoic basalts in the Duofutun and Hongqiang areas in the western Qinling orogenic belt. The petrogenesis of these basalts provides an important constraint on the late Mesozoic geodynamics of the orogen. The representative basaltic samples yield the 40Ar/39Ar plateau age of about 112 Ma. These samples belong to the alkaline series and have SiO2 ranging from 44.98 wt.% to 48.19 wt.%, Na2O + K2O from 3.44 wt% to 5.44 wt%, and MgO from 7.25 wt.% to 12.19 wt.%. They demonstrate the right-sloping chondrite-normalized REE patterns with negligible Eu anomalies (1.00-1.10) and PM-normalized patterns enriched in light rare earth element, large ion lithophile element and high field strength element, similar to those of OIB rocks. These samples additionally show an OIB-like Sr-Nd isotopic signature with εNd(t) values ranging from +6.13 to +10.15 and initial 87Sr/86Sr ratios from 0.7028 to 0.7039, respectively. These samples are geochemically subdivided into two groups. Group 1 is characterized by low Al2O3 and high TiO2 and P2O5 contents, as well as high La/Yb ratios (>20), being the product of the high-pressure garnet fractionation from the OIB-derived magma. Group 2 shows higher Al2O3 but lower P2O5 contents and La/Yb ratios (<20) than Group 1, originating from asthenospheric mantle with input of delaminated lithospheric component. In combination with available data, it is proposed for the petrogenetic model of the Early Cretaceous thickened lithospheric delamination in response to the asthenospheric upwelling along the western Qinling orogenic belt.

Zircon (U-Th)/He evidence for pre-Eocene orogenic exhumation of eastern North Pyrenean massifs, France

NASA Astrophysics Data System (ADS)

Ternois, Sébastien; Vacherat, Arnaud; Pik, Raphaël; Ford, Mary; Tibari, Bouchaïb

2017-04-01

Orogens and their associated foreland basins are considered as part of a single dynamic system evolving from an early, non equilibrated, growth stage to a late, mature, steady-state stage. Most of our understanding in foreland basins, in particular early convergence-stage deposition, comes from the subducting plate, so that the classic paradigm for foreland basins is the pro-wedge. Models that clearly depict the relationship between erosion of the orogenic wedge and sedimentation into its associated foreland basin only focus on the late post-orogenic phase. Relatively little is known and understood about the very long phase of initiation of orogenesis. In the doubly wedged Pyrenean orogen, where we know and understand relatively little about how the early retro-wedge developed, the record of the onset of orogenic denudation from massifs is quite limited, not only in time but also in space. As part of the OROGEN project funded by TOTAL and the BRGM, this study presents first single-grain zircon (U-Th)/He data from two Palaeozoic massifs of the external Northern Pyrenean Zone, the Agly and Salvezines massifs. It aims at constraining the exhumation history of eastern Pyrenean massifs and understanding what is their significance for early orogenic wedge growth. The Pyrenean orogeny was generated from end Santonian (84 Ma) to Oligocene-Miocene due to convergence of the Iberian and European plates. Aquitaine foreland basin history (Ariège region) indicates that convergence took place in two phases, Campanian to Maastrichian and Eocene, separated by a quiet Paleocene phase. Yet, only Eocene cooling events are recorded by low-temperature thermochronometers in the central Pyrenean massifs (Arize and Trois-Seigneurs). Nine bedrock samples were collected along a WNW-ESE traverse (Salvezines and Saint-Arnac granites, Belesta-Caramany gneisses) and analysed for ZHe dating. Zircon (U-Th)/He data for the Agly and Salvezines massifs, together with forward modelling of data for

Evaluation of the Orogenic Belt Hypothesis for the Formation of Thaumasia, Mars

NASA Astrophysics Data System (ADS)

Nahm, A. L.; Schultz, R. A.

2008-12-01

The Thaumasia Highlands (TH) and Solis Planum are two of the best-known examples of compressional tectonics on Mars. The TH is a region of high topography located in the southern portion of the Tharsis Province, Mars. Solis Planum is located in eastern Thaumasia. Two hypotheses for the formation of this region have been suggested: sliding on a weak horizon or thrusting analogous to orogenic wedges on Earth. Both hypotheses require a shallowly dipping to sub-horizontal weak horizon below Thaumasia. Wrinkle ridges in Solis Planum are also inferred to sole into a décollement. If Thaumasia formed by thrusting related to sliding on a décollement, then certain conditions must be met as in critical taper wedge mechanics (CTWM) theory. If the angle between the surface slope and the basal décollement is less than predicted by the critical taper equation, the 'subcritical' wedge will deform internally until critical taper is achieved. Once the critical taper has been achieved, internal deformation ceases and the wedge will slide along its base. Formation of orogenic belts on Earth (such as the Central Mountains in Taiwan) can be described using CTWM. This method is applied here to the Thaumasia region on Mars. The surface slope (alpha) was measured in three locations: Syria Planum-Thaumasia margin, Solis Planum, and the TH. Topographic slopes were compared to the results from the critical taper equation. Because the dip of the basal décollement (beta) cannot be measured directly as on Earth, the dip angle was varied at 0 - 10 degrees; these values span the range of likely values based on terrestrial wedges. Pore fluid pressure (lambda) was varied between 0 (dry) and 0.9 (overpressured); these values span the full range of this important unknown parameter. Material properties, such as the coefficients of internal friction and of the basal décollement, were varied using reasonable values. Preliminary results show that for both reasonable (such as lambda = 0, mu b = 0

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

The St. Elias orogen as an early stage in the development of indentor corners: Initial results from the STEEP project

NASA Astrophysics Data System (ADS)

Pavlis, T. L.; Bruhn, R. L.; Koons, P.; Berger, A.; Spotila, J.; Barker, A.; Chapman, J.; Doser, D.; Pavlis, G.

2006-12-01

The actively deforming St. Elias orogen of southern Alaska is developed at the transition between the Aleutian trench and the Queen Charlottes transform, and has produced a "one sided" indentor corner as the collided block has been carried obliquely into the subduction-transform transition. A distinctive feature generated within this evolving corner is a 90o bend in the suture at the western edge of the orogen that is associated with a refolding of earlier thin-skinned fold-thrust systems in the collided block. The refolding is recognizable in the area between the bent suture and a major glacial valley, the Bering Glacier, but is absent to the east. Bruhn et al. (2004, GSAB) used this observation to infer an active structure along the Bering Glacier, and speculated that the refolding may be active. New data collected as part of the St. Elias Erosion and tectonics Project (STEEP) provides support for this hypothesis from two observations: 1) clear evidence that many of the hundreds of surface ruptures in this region represent fault-scarps-- probably representing fold-related, bedding- plane slip during refolding; and 2) extremely young (locally <500Ka) U-Th-He apatite cooling ages just west of the Bering Glacier are consistent with the hypothesis of an active structure along the glacial valley. However, young cooling ages to the east of the Bering Glacier as well as geomorphology suggest that at least one of the fold-thrust belt structures is also active, indicating that the interplay of active faults is complex. Additional support for active deformation along the Bering Glacier comes from the spatial distribution of seismicity between the Bering Glacier and Bagley icefield and these observations should be further constrained as data are obtained from the new STEEP broadband seismic network in the area. Analog (sand) and numerical models suggest that this type of feature can originate as the indentor is driven into the corner through a variable vertical axis

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

The Pico do Itapeva Formation: A record of gravitational flow deposits in an Ediacaran intracontinental basin, southern Brasília Orogen, SE Brazil

NASA Astrophysics Data System (ADS)

Caputo Neto, V.; Ribeiro, A.; Nepomuceno, F. O.; Dussin, I. A.; Trouw, R. A. J.

2018-07-01

The Pico do Itapeva Formation is a key metasedimentary unit to the understanding of the extensional events that occurred between the late stage of the southern Brasília Orogen collision and the main collision in the central Ribeira Orogen. The formation crops out in a 20 km long NE-trending narrow belt in the Mantiqueira mountain range in eastern São Paulo State, Brazil. It is located in the interference zone of the southern Brasília and the central Ribeira orogens and records deformation and greenschist facies metamorphism (biotite zone) related to the Brasiliano orogeny. The Pico do Itapeva Formation rests unconformably on a metaigneous substratum of the Socorro-Guaxupé Nappe/Embu Terrane and, on the southern side, is truncated by a steep SE-dipping dextral reverse shear zone. It consists of a coarsening- and thickening-upward succession, with minimum thickness of 800 m, composed of lutite, arkose and conglomerate. These rocks constitute three distinct lithofacies associations: LAI- arkose, arkose-lutite composite beds, lutite and fine conglomerate beds; LAII- arkose, pebbly arkose and scarce lutite and; LAIII- conglomerate and pebbly arkose. Most of the beds are massive; graded beds, dish and convolute structures occur locally. Bed thickness varies from thin to very thick and amalgamated bodies constitute up to 30m thick strata. Three mappable units at scale 1:20,000 were recognized based on different proportions of the three lithofacies associations. The deposits are interpreted as the record of mass flows and associated processes in a fan delta setting developed in an intermontane rift basin. U-Pb LA-ICP-MS detrital zircon ages suggest the maximum depositional age at ca. 611 Ma and the basin evolution is interpreted in the range between 611 and 580 Ma during an inter-orogenic stage between the Brasília and Ribeira orogenies.

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Rare Clear View of Alaska [high res

NASA Image and Video Library

2017-12-08

On most days, relentless rivers of clouds wash over Alaska, obscuring most of the state’s 6,640 miles (10,690 kilometers) of coastline and 586,000 square miles (1,518,000 square kilometers) of land. The south coast of Alaska even has the dubious distinction of being the cloudiest region of the United States, with some locations averaging more than 340 cloudy days per year. That was certainly not the case on June 17, 2013, the date that the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite acquired this rare, nearly cloud-free view of the state. The absence of clouds exposed a striking tapestry of water, ice, land, forests, and even wildfires. Snow-covered mountains such as the Alaska Range and Chugach Mountains were visible in southern Alaska, while the arc of mountains that make up the Brooks Range dominated the northern part of the state. The Yukon River—the longest in Alaska and the third longest in the United States—wound its way through the green boreal forests that inhabit the interior of the state. Plumes of sediment and glacial dust poured into the Gulf of Alaska from the Copper River. And Iliamna Lake, the largest in Alaska, was ice free. The same ridge of high pressure that cleared Alaska’s skies also brought stifling temperatures to many areas accustomed to chilly June days. Talkeetna, a town about 100 miles north of Anchorage, saw temperatures reach 96°F (36°C) on June 17. Other towns in southern Alaska set all-time record highs, including Cordova, Valez, and Seward. The high temperatures also helped fuel wildfires and hastened the breakup of sea ice in the Chukchi Sea. NASA image courtesy Jeff Schmaltz, LANCE MODIS Rapid Response Team at NASA GSFC. Caption by Adam Voiland. Instrument: Terra - MODIS More info: 1.usa.gov/102MAEj Credit: NASA Earth Observatory NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar

Seismological Constraints on Lithospheric Evolution in the Appalachian Orogen

NASA Astrophysics Data System (ADS)

Fischer, K. M.; Hopper, E.; Hawman, R. B.; Wagner, L. S.

2017-12-01

Crust and mantle structures beneath the Appalachian orogen, recently resolved by seismic data from the EarthScope SESAME Flexible Array and Transportable Array, provide new constraints on the scale and style of the Appalachian collision and subsequent lithospheric evolution. In the southern Appalachians, imaging with Sp and Ps phases reveals the final (Alleghanian) suture between the crusts of Laurentia and the Gondwanan Suwannee terrane as a low angle (<15°) southward-dipping interface that soles into a flat-lying mid-crustal detachment. The suture location near the top of the crust coincides closely with the northern limit of the Suwannee terrane reconstructed from its lower Paleozoic shelf strata (Boote and Knapp, 2016). The observed suture geometry implies over 300 km of head-on shortening across a plate boundary structure similar in scale to the Himalayan mid-crustal detachment. While the suture and other structures from the Alleghanian collision are preserved in the upper and mid-crust, the lower crust and mantle lithosphere beneath this region have been significantly modified by later processes. Ps receiver functions, wavefield migration and SsPmp modeling reveal that crustal thickness reaches a maximum of 58 km (beneath high elevations in the Blue Ridge terrane) and decreases to 29-35 km (beneath lower elevations in the Carolina and Suwannee terranes). Given metamorphic estimates of unroofing (Duff and Kellogg, 2017) isostatic arguments indicate crustal thicknesses were 15-25 km larger at the end of the orogeny, indicating a thick crustal root across the region. The present-day residual crustal root beneath the Blue Ridge mountains is estimated to have a density contrast with the mantle of only 104±20 kg/m3. This value is comparable to other old orogens but lower than values typical of young or active orogens, indicating a loss of lower crustal buoyancy over time. At mantle depths, the negative shear velocity gradient that marks the transition from

Tectonic evolution of the Black Sea orogene belt and the history of opening of the Black Sea basin

DOE Office of Scientific and Technical Information (OSTI.GOV)

Uesuemezsoy, S.

1988-08-01

The Black Sea basin is surrounded by successive orogenic belts of Hercynian, Cimmerian, and Alpine ages. The Rhodope, Thracian, western Pontian, and Transcaucasian (RTPT) blocks of Precambrian age were involved by the circum-Black Sea orogene belts. The Hercynian orogene was documented in the Balkanide, Great Caucasian, Kriastide, southern Pontian, and Transcaucasian belts. The Cimmerian orogene extended north and south of the Black Sea. The southern Cimmerian orogene was represented by the circum-Rhodope and East Thracian-Strandja-Kuere belts. The northern Cimmerian orogene belt extended along the Dobruca-Crimean and southern slope belts. Following the demise of the Black Sea Cimmerian basin, the northernmostmore » oceanic branch extending from Nish-Trajan through the present Black Sea to the intra-Transcaucasian basin, was opened within the Hercynian and Cimmerian consolidated terrain in the Late Jurassic. The other oceanic branch, extending from Izmir-Ankara through circum Kirsehir to various basins, was opened within the Paleotethyan collision belt, considered to be eastern extension of the Pindus basin. The Nish-Trajan sector of the northernmost basin was closed in the middle Cretaceous, and the Moesian platform re-fused to the Getic-Serbo-Macedonian-Rhodope belt. The easternmost extension of the intra-Transcaucasian basin disappeared in the Late Cretaceous. Consequently, the northernmost oceanic branch was reduced to the present Black Sea basin.« less

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

Anatexis of mafic and felsic lower crust: Geochemistry and Nd, Sr and Pb isotopes of late-orogenic granodiorites and leucogranites (Damara orogen, Namibia)

NASA Astrophysics Data System (ADS)

Osterhus, Lennart; Jung, Stefan

2010-05-01

The Damara orogen (Namibia) represents a well-exposed and deeply eroded orogenic mobile belt consisting of the north-south trending Kaoko belt and the northeast-southwest trending intracontinental Damara belt. The latter has been subdivided into a Northern, a Central and a Southern Zone based on stratigraphy, metamorphic grade, structure and geochronology. The late-orogenic granodioritic to leucogranitic Gawib pluton is a cross-cutting, pear-shaped post-tectonic stock within the southern Central Zone which is elsewhere dominated by basement rocks, high-grade metasedimentary rocks of the Tinkas Formation and syn-orogenic granites (Salem-type). The non-foliated granodiorites consist of plagioclase, quartz, microcline, hornblende and biotite whereas the leucogranites consist of microcline, quartz, plagioclase and biotite. Major element variation of the granodiorites show two distinct magma types were some samples have high TiO2, MgO and Fe2O3 and low Al2O3 and others have low TiO2, MgO and Fe2O3 and high Al2O3. Based on high REE, Nb, Zr and Y concentrations some granodiorites can be classified as A-type granitoids. Strontium concentrations are high in the granodiorites (up to 939 ppm) and decrease to < 200 ppm in the leucogranites. Rb/Sr ratios are low (1) in the leucogranites. Granodiorites have moderately radiogenic initial 87Sr/86Sr ratios (0.7088-0.7132), strongly negative initial ɛ Nd values (ca. -12) and comparatively unradiogenic Pb isotope data, the latter obtained on acid-leached feldspar separates. Leucogranites have more radiogenic initial 87Sr/86Sr ratios (0.7223-0.7336) and more negative initial ɛ Nd values (ca. -18). Pb isotopes tend to be less radiogenic than in the granodiorites. The mean crustal residence ages of the granodiorites, expressed as depleted mantle Nd model ages, are ca. 2.0 Ga but the leucogranites tend to have older Nd model ages (2.5 Ga). Therefore, a likely source for the granodiorites and leucogranites is a sequence of mafic to

Alaska Tidal Datum Portal - Alaska Tidal Datum Calculator | Alaska Division

Science.gov Websites

Coastal Hazards Program Guide to Geologic Hazards in Alaska MAPTEACH Tsunami Inundation Mapping Energy Portal main content Alaska Tidal Datum Portal Unambiguous vertical datums in the coastal environment are projects to ensure protection of human life, property, and the coastal environment. January 2017 - Update

High-pressure metamorphism in the southern New England Orogen: Implications for long-lived accretionary orogenesis in eastern Australia

NASA Astrophysics Data System (ADS)

Phillips, G.; Offler, R.; Rubatto, D.; Phillips, D.

2015-09-01

New geochemical, metamorphic, and isotopic data are presented from high-pressure metamorphic rocks in the southern New England Orogen (eastern Australia). Conventional and optimal thermobarometry are augmented by U-Pb zircon and 40Ar/39Ar phengite dating to define pressure-temperature-time (P-T-t) histories for the rocks. The P-T-t histories are compared with competing geodynamic models for the Tasmanides, which can be summarized as (i) a retreating orogen model, the Tasmanides formed above a continuous, west dipping, and eastward retreating subduction zone, and (ii) a punctuated orogen model, the Tasmanides formed by several arc accretion, subduction flip, and/or transference events. Whereas both scenarios are potentially supported by the new data, an overlap between the timing of metamorphic recrystallization and key stages of Tasmanides evolution favors a relationship between a single, long-lived subduction zone and the formation, exhumation, and exposure of the high-pressure rocks. By comparison with the retreating orogen model, the following links with the P-T-t histories emerge: (i) exhumation and underplating of oceanic eclogite during the Delamerian Orogeny, (ii) recrystallization of underplated and exhuming high-pressure rocks at amphibolite facies conditions coeval with a period of rollback, and (iii) selective recrystallization of high-pressure rocks at blueschist facies conditions, reflecting metamorphism in a cooled subduction zone. The retreating orogen model can also account for the anomalous location of the Cambrian-Ordovician high-pressure rocks in the Devonian-Carboniferous New England Orogen, where sequential rollback cycles detached and translated parts of the leading edge of the overriding plate to the next, younger orogenic cycle.

Evolving lithospheric flexure and paleotopography of the Pyrenean Orogen from 3D flexural modeling and basin analysis

NASA Astrophysics Data System (ADS)

Curry, M. E.; van der Beek, P.; Huismans, R. S.; Muñoz, J. A.

2017-12-01

The Pyrenees are an asymmetric, doubly-vergent orogen with retro- and pro- foreland basins that preserve a record of deformation since the Mesozoic. The extensive research and exploration efforts on the mountain belt and flanking foreland basins provide an exceptional dataset for investigating geodynamics and surface processes over large spatial and temporal scales in western Europe. We present the results of a numerical modeling study investigating the spatio-temporal variation in lithospheric flexure in response to the developing orogen. We employ a finite element method to model the 3D flexural deformation of the lithosphere beneath the Pyrenean orogen since the onset of convergence in the late Cretaceous. Using subsurface, geophysical, and structural data, we describe the evolving geometry of both the French Aquitaine and Spanish Ebro foreland basins at the present (post-orogenic), the mid-Eocene (peak orogenic), the Paleocene (early orogenic), and the end of the Cretaceous (pre- to early orogenic). The flexural modeling provides insight into how both the rigidity of the lithosphere and the paleotopographic load have varied over the course of orogenesis to shape the basin geometry. We find that the overriding European plate has higher rigidity than the subducting Iberian plate, with modern Effective Elastic Thickness (EET) values of 20 ± 2 and 12 ± 2 km, respectively. Modeling indicates that the modern rigidity of both plates decreases westward towards the Bay of Biscay. The lithospheric rigidity has increased by 50% since the Mesozoic with early Cenozoic EET values of 13 ± 2 and 8 ± 1 km for the European and Iberian plates, respectively. The topographic load began increasing with convergence in the late Cretaceous, reaching modern levels in the central and eastern Pyrenees by the Eocene. In contrast, the topographic load in the western Pyrenees was 70% of the modern value in the Eocene, and experienced topographic growth through the Oligo-Miocene. The

The susceptibility of large river basins to orogenic and climatic drivers

NASA Astrophysics Data System (ADS)

Haedke, Hanna; Wittmann, Hella; von Blanckenburg, Friedhelm

2017-04-01

Large rivers are known to buffer pulses in sediment production driven by changes in climate as sediment is transported through lowlands. Our new dataset of in situ cosmogenic nuclide concentration and chemical composition of 62 sandy bedload samples from the world largest rivers integrates over 25% of Earth's terrestrial surface, distributed over a variety of climatic zones across all continents, and represents the millennial-scale denudation rate of the sediment's source area. We can show that these denudation rates do not respond to climatic forcing, but faithfully record orogenic forcing, when analyzed with respective variables representing orogeny (strain rate, relief, bouguer anomaly, free-air anomaly), and climate (runoff, temperature, precipitation) and basin properties (floodplain response time, drainage area). In contrast to this orogenic forcing of denudation rates, elemental bedload chemistry from the fine-grained portion of the same samples correlates with climate-related variables (precipitation, runoff) and floodplain response times. It is also well-known from previous compilations of river-gauged sediment loads that the short-term basin-integrated sediment export is also climatically controlled. The chemical composition of detrital sediment shows a climate control that can originate in the rivers source area, but this signal is likely overprinted during transfer through the lowlands because we also find correlation with floodplain response times. At the same time, cosmogenic nuclides robustly preserve the orogenic forcing of the source area denudation signal through of the floodplain buffer. Conversely, previous global compilations of cosmogenic nuclides in small river basins show the preservation of climate drivers in their analysis, but these are buffered in large lowland rivers. Hence, we can confirm the assumption that cosmogenic nuclides in large rivers are poorly susceptible to climate changes, but are at the same time highly suited to detect

Home, Alaska Oil and Gas Conservation Commission, State of Alaska

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Earthquakes in Alaska

USGS Publications Warehouse

Haeussler, Peter J.; Plafker, George

1995-01-01

Earthquake risk is high in much of the southern half of Alaska, but it is not the same everywhere. This map shows the overall geologic setting in Alaska that produces earthquakes. The Pacific plate (darker blue) is sliding northwestward past southeastern Alaska and then dives beneath the North American plate (light blue, green, and brown) in southern Alaska, the Alaska Peninsula, and the Aleutian Islands. Most earthquakes are produced where these two plates come into contact and slide past each other. Major earthquakes also occur throughout much of interior Alaska as a result of collision of a piece of crust with the southern margin.

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

Linking orogen and peripheral foreland basin: conceptual model and application to the Southalpine-Dinaric (Friuli) orocline

NASA Astrophysics Data System (ADS)

Heberer, Bianca; Neubauer, Franz

2010-05-01

Surface uplift and rock exhumation within an orogen are generally a consequence of convergence, and can often be linked with subsidence in a peripheral foreland. Since vertical loads act on the entire lithosphere, these processes can, therefore, be considered as plate-scale processes. Here, we propose a conceptual model for this linkage for the Friuli orocline and its surrounding units. The Friuli orocline stretches from the ENE-trending Southern Alps to the SE-trending Dinarides. There, two Neogene stages of convergence and associated deformation can be differentiated: (1) a Mid-Late Miocene phase of increased surface uplift and intra-orogenic subsidence of sedimentary basins reflecting intra-orogenic crustal-scale folding. Depocentres are e.g. the flexural Belluno, Ljubljana and Klagenfurt basins. (2) A second stage of convergence during Late Pliocene-Pleistocene times led to overall surface uplift in the orogen and contemporaneous pronounced subsidence in the peripheral foreland basin (Venetian platform and the northern Adriatic Sea). We propose, that the spatially variable extent of subsidence originates in variably strong orogen-basin coupling, i.e. weak coupling during stage 1 vs. strong coupling during stage 2. This interpretation is based on the apatite fission track age pattern, the distribution of intra-orogenic Neogene sediment basins and subsidence analyses in the foreland basin (Barbieri et al., 2007). Available low-temperature thermochronological data for the Southern Alps and the NW Dinarides are sparse, in contrast to a dense network of primarily apatite fission track ages north of the Periadriatic lineament (e.g. summarized by Luth & Willingshofer, 2008). AFT ages adjacent to the eastern Periadriatic Lineament mainly range from 15 to 25 Ma (Hejl, 1997; Fodor et al., 2008). Detrital studies on Oligocene to Miocene sediments from the Venetian foreland basin yielded dominant age groups clustering roughly around 20 and 30 Ma (Stefani et al., 2008

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

Alaska and the Alaska Federal Health Care Partnership

DTIC Science & Technology

2002-08-01

SUPPLEMENTARY NOTES The original document contains color images. 14. ABSTRACT The intent of the Alaska Federal Healthcare Partnership is to expand clinical and... intent of the Alaska Federal Healthcare Partnership is to expand clinical and support capabilities of the Alaska Native Medical Center (ANMC), Third...the formation of the Partnership. Although lengthy, the information is essential to appreciate the magnitude of the Partnership and the intent behind

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).

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.

Nature and provenance of the Beishan Complex, southernmost Central Asian Orogenic Belt

NASA Astrophysics Data System (ADS)

Zheng, Rongguo; Li, Jinyi; Xiao, Wenjiao; Zhang, Jin

2018-03-01

The ages and origins of metasedimentary rocks, which were previously mapped as Precambrian, are critical in rebuilding the orogenic process and better understanding the Phanerozoic continental growth in the Central Asian Orogenic Belt (CAOB). The Beishan Complex was widely distributed in the southern Beishan Orogenic Collage, southernmost CAOB, and their ages and tectonic affinities are still in controversy. The Beishan Complex was previously proposed as fragments drifted from the Tarim Craton, Neoproterozoic Block or Phanerozoic accretionary complex. In this study, we employ detrital zircon age spectra to constrain ages and provenances of metasedimentary sequences of the Beishan Complex in the Chuanshanxun area. The metasedimentary rocks here are dominated by zircons with Paleoproterozoic-Mesoproterozoic age ( 1160-2070 Ma), and yield two peak ages at 1454 and 1760 Ma. One sample yielded a middle Permian peak age (269 Ma), which suggests that the metasedimentary sequences were deposited in the late Paleozoic. The granitoid and dioritic dykes, intruding into the metasedimentary sequences, exhibit zircon U-Pb ages of 268 and 261 Ma, respectively, which constrain the minimum deposit age of the metasedimentary sequences. Zircon U-Pb ages of amphibolite (274 and 216 Ma) indicate that they might be affected by multi-stage metamorphic events. The Beishan Complex was not a fragment drifted from the Tarim Block or Dunhuang Block, and none of cratons or blocks surrounding Beishan Orogenic Collage was the sole material source of the Beishan Complex due to obviously different age spectra. Instead, 1.4 Ga marginal accretionary zones of the Columbia supercontinent might have existed in the southern CAOB, and may provide the main source materials for the sedimentary sequences in the Beishan Complex.

Basin-mountain structures and hydrocarbon exploration potential of west Junggar orogen in China

NASA Astrophysics Data System (ADS)

Wu, Xiaozhi; He, Dengfa; Qi, Xuefeng

2016-04-01

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

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

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.

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

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.

Resident, State of Alaska

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Skip to content State of Alaska myAlaska My Government Resident Business in Alaska Visiting Alaska State Employees State of Alaska Search Home Quick Links Departments Commissioners Employee Whitepages State Government Jobs Federal Jobs Starting a Small Business Living Get a Driver License Get a Hunting

Visitor, State of Alaska

Science.gov Websites

Skip to content State of Alaska myAlaska My Government Resident Business in Alaska Visiting Alaska State Employees State of Alaska Search Home Quick Links Departments Commissioners Employee Whitepages State Government Jobs Federal Jobs Starting a Small Business Living Get a Driver License Get a Hunting

Selected 1966-69 interior Alaska wildfire statistics with long-term comparisons.

Treesearch

Richard J. Barney

1971-01-01

This paper presents selected interior Alaska forest and range wildfire statistics for the period 1966-69. Comparisons are made with the decade 1956-65 and the 30-year period 1940-69, which are essentially the total recorded statistical history on wildfires available for Alaska.

Shear-wave splitting observations of mantle anisotropy beneath Alaska

NASA Astrophysics Data System (ADS)

Bellesiles, A. K.; Christensen, D. H.; Entwistle, E.; Litherland, M.; Abers, G. A.; Song, X.

2009-12-01

Observations of seismic anisotropy were obtained from three different PASSCAL broadband experiments throughout Alaska, using shear-wave splitting from teleseismic SKS phases. The MOOS (Multidisciplinary Observations Of Subduction), BEAAR (Broadband Experiment Across the Alaska Range), and ARCTIC (Alaska Receiving Cross-Transects for the Inner Core) networks were used along with selected permanent broadband stations operated by AEIC (Alaska Earthquake Information Center) to produce seismic anisotropy results for the state of Alaska along a north south transect from the active subduction zone in the south, through continental Alaska, to the passive margin in the north. The BEAAR network is in-between the ARCTIC and MOOS networks above the subducting Pacific Plate and mantle wedge and shows a tight ~90 degree rotation of anisotropy above the 70km contour of the subducting plate. The southern stations in BEAAR yield anisotropy results that are subparallel to the Pacific Plate motion as it subducts under North America. These stations have an average fast direction of -45 degrees and 1.03 seconds of delay on average. The MOOS network in south central Alaska yielded similar results with an average fast direction of -30 degrees and delay times of .9 seconds. In the north portion of the BEAAR network the anisotropy is along strike of the subduction zone and has an average fast direction of 27 degrees with an average delay time of 1.4 seconds, although the delay times above the mantle wedge range from 1 to 2.5 seconds and are directly correlated to the length of ray path in the mantle wedge. This general trend NE/SW is seen in the ARCTIC stations to the north although the furthest north stations are oriented more NNE compared to those in BEAAR. The average fast direction for the ARCTIC network is 40 degrees with an average delay time of 1.05 seconds. These results show two distinct orientations of anisotropy in Alaska separated by the subducting Pacific Plate.

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

Applications of satellite telemetry to wildlife research and management in Alaska

USGS Publications Warehouse

Fancy, S.G.; Harris, R.B.; Douglas, David C.; Pank, L.F.; Whitten, Kenneth R.; McCabe, Thomas R.; Amstrup, Steven C.; Garner, G.W.

1988-01-01

Since 1984, the Alaska Fish and Wildlife Research Center, in cooperation with the Alaska Department of Fish and Game and several other agencies, has used the Argos Data Collection and Location System to address wildlife research and management problems in Alaska and other parts of North America. The use of satellite telemetry has overcome some of the logistical problems of working in remote areas in an arctic environment, where harsh weather, darkness, worker safety considerations, extensive movements by some species, and high costs of locating study animals often result in small incomplete data sets. As of September 1988, 241 satellite transmitters (PPTs) have been deployed on large mammals, including 109 on polar bears in the Bering, Beaufort and Chukchi seas; 74 on caribou in northern Alaska and northwestern Canada; 22 on brown bears in northern Alaska and Kodiak Island, Alaska; 12 on muskoxen in northeastern Alaska and Greenland; 7 on wolves in northern Alaska; 7 on walrus in the Bering and Chuckchi seas; 4 on mule deer in Idaho; 2 on elk in Wyoming; 2 on moose in southcentral Alaska; and 2 on Dall sheep int the Brooks Range of northern Alaska. The Argos DCLS has provided more than 19,000 and 66,000 locations for polar bears and caribou, respectively, and has been used to document the international ranges of these species and to address specific management questions in a cost-effective manner. The precision of locations provided by the Argos DCLS was examined using transmitters placed on the ground or on buildings and compared to the precision from that prior to deployment, presumably because of the proximity of the antenna to the animal's body. The mean error of locations for PTTs on captive animals was 954 m(+or- 1324 SD; median -553 m; n -330). Sensors for determining ambient temperature, short- and long-term indices of animal activity immersion of transmitters in saltwater, and dive depths, were developed and tested. The long-term activity index indicated

Alaska Seismic Hazards Safety Commission

Science.gov Websites

State Employees ASHSC State of Alaska search Alaska Seismic Hazards Safety Commission View of Anchorage and Commissions Alaska Seismic Hazards Safety Commission (ASHSC) main contant Alaska Seismic Hazards Safety Commission logo Alaska Seismic Hazards Safety Commission (ASHSC) - Mission The Alaska Seismic

Structure, metamorphism, and geochronology of the Cosmos Hills and Ruby Ridge, Brooks Range schist belt, Alaska

USGS Publications Warehouse

Christiansen, Peter B.; Snee, Lawrence W.

1994-01-01

The boundary of the internal zones of the Brooks Range orogenic belt (the schist belt) is a fault contact that dips toward the hinterland (the Yukon-Koyukuk province). This fault, here referred to as the Cosmos Hills fault zone, juxtaposes oceanic rocks and unmetamorphosed sedimentary rocks structurally above blueschist-to-greenschist facies metamorphic rocks of the schist belt. Near the fault contact, schist belt rocks are increasingly affected by a prominent, subhorizontal transposition foliation that is locally mylonitic in the fault zone. Structural and petrologic observations combined with 40Ar/39Ar incremental-release geochronology give evidence for a polyphase metamorphic and deformational history beginning in the Middle Jurassic and continuing until the Late Cretaceous. Our 40Ar/39Ar cooling age for Jurassic metamorphism is consistent with stratigraphic and other evidence for the onset of Brooks Range orogenesis. Jurassic metamorphism is nearly everywhere overprinted by a regional greenschist-facies event dated at 130–125 Ma. Near the contact with the Cosmos Hills fault zone, the schist belt is increasingly affected by a younger greenschist metamorphism that is texturally related to a prominent foliation that folds and transposes an older fabric. The 40Ar/39Ar results on phengite and fuchsite that define this younger fabric give recrystallization ages ranging from 103 to less than 90 Ma. We conclude that metamorphism that formed the transposition fabric peaked around 100 Ma and may have continued until well after 90 Ma. This age for greenschist metamorphism is broadly synchronous with the depositional age of locally derived, shallow-marine clastic sedimentary strata in the hanging wall of the fault zone and thus substantiates the interpretation that the fault zone accommodated extension in the Late Cretaceous. This extension unroofed and exhumed the schist belt during relative subsidence of the Yukon-Koyukuk province.

Late Mesozoic deformations of the Verkhoyansk-Kolyma orogenic belt, Northeast Russia

NASA Astrophysics Data System (ADS)

Fridovsky, Valery

2016-04-01

The Verkhoyansk-Kolyma orogenic belt marks the boundary between the Kolyma-Omolon superterrane (microcontinent) and the submerged eastern margin of the North Asian craton. The orogenic system is remark able for its large number of economically viable gold deposits (Natalka, Pavlik, Rodionovskoe, Drazhnoe, Bazovskoe, Badran, Malo-Tarynskoe, etc.). The Verkhoyansk - Kolyma orogenic belt is subdivided into Kular-Nera and the Polousny-Debin terranes. The Kular-Nera terrane is mainly composed of the Upper Permian, Triassic, and Lower Jurassic black shales that are metamorphosed at lower greenschist facies conditions. The Charky-Indigirka and the Chai-Yureya faults separate the Kular-Nera from the Polousny-Debin terrane that is predominantly composed of the Jurassic flyschoi dturbidites. The deformation structure of the region evolved in association with several late Mesozoic tectonic events that took place in the north-eastern part ofthe Paleo-Pacific. In Late Jurassic-Early Cretaceous several generations of fold and thrust systems were formed due to frontal accretion of the Kolyma-Omolon superterrane to the eastern margin of the North Asian craton.Thrusting and folding was accompanied by granitic magmatism, metamorphic reworking of the Late Paleozoic and the Early Mesozoic sedimentary rocks, and formation of Au-Sn-W mineralization. Three stages of deformation related to frontal accretion can be distinguished. First stage D1 has developed in the north-eastern part of the Verkhoyansk - Kolyma orogenic belt. Early tight and isoclinal folds F1 and assosiated thrusts are characteristic of D1. Major thrusts, linear concentric folds F2 and cleavage were formed during D2. The main ore-controlling structures are thrust faults forming imbricate fan systems. Frontal and oblique ramps and systems of bedding and cross thrusts forming duplexes are common. It is notable that mineralized tectonized zones commonly develop along thrusts at the contacts of rocks of contrasting competence

Alaska exceptionality hypothesis: Is Alaska wilderness really different?

Treesearch

Gregory Brown

2002-01-01

The common idiom of Alaska as “The Last Frontier” suggests that the relative remoteness and unsettled character of Alaska create a unique Alaskan identity, one that is both a “frontier” and the “last” of its kind. The frontier idiom portrays the place and people of Alaska as exceptional or different from the places and people who reside in the Lower Forty- Eight States...

Association of orogenic activity with the Ordovician radiation of marine life

NASA Technical Reports Server (NTRS)

Miller, A. I.; Mao, S.

1995-01-01

The Ordovician radiation of marine life was among the most substantial pulses of diversification in Earth history and coincided in time with a major increase in the global level of orogenic activity. To investigate a possible causal link between these two patterns, the geographic distributions of 6576 individual appearances of Ordovician vician genera around the world were evaluated with respect to their proximity to probable centers of orogeny (foreland basins). Results indicate that these genera, which belonged to an array of higher taxa that diversified in the Middle and Late Ordovician (trilobites, brachiopods, bivalves, gastropods, monoplacophorans), were far more diverse in, and adjacent to, foreland basins than they were in areas farther removed from orogenic activity (carbonate platforms). This suggests an association of orogeny with diversification at that time.

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.

Cenozoic landforms and post-orogenic landscape evolution of the Balkanide orogen: Evidence for alternatives to the tectonic denudation narrative in southern Bulgaria

NASA Astrophysics Data System (ADS)

Gunnell, Y.; Calvet, M.; Meyer, B.; Pinna-Jamme, R.; Bour, I.; Gautheron, C.; Carter, A.; Dimitrov, D.

2017-01-01

Continental denudation is the mass transfer of rock from source areas to sedimentary depocentres, and is typically the result of Earth surface processes. However, a process known as tectonic denudation is also understood to expose deep-seated rocks in short periods of geological time by displacing large masses of continental crust along shallow-angle faults, and without requiring major contributions from surface erosion. Some parts of the world, such as the Basin and Range in the USA or the Aegean province in Europe, have been showcased for their Cenozoic tectonic denudation features, commonly described as metamorphic core-complexes or as supradetachment faults. Based on 22 new apatite fission-track (AFT) and 21 helium (AHe) cooling ages among rock samples collected widely from plateau summits and their adjacent valley floors, and elaborating on inconsistencies between the regional stratigraphic, topographic and denudational records, this study frames a revised perspective on the prevailing tectonic denudation narrative for southern Bulgaria. We conclude that conspicuous landforms in this region, such as erosion surfaces on basement-cored mountain ranges, are not primarily the result of Paleogene to Neogene core-complex formation. They result instead from "ordinary" erosion-driven, subaerial denudation. Rock cooling, each time suggesting at least 2 km of crustal denudation, has exposed shallow Paleogene granitic plutons and documents a 3-stage wave of erosional denudation which progressed from north to south during the Middle Eocene, Oligocene, Early to Middle Miocene, and Late Miocene. Denudation initially prevailed during the Paleogene under a syn-orogenic compressional regime involving piggyback extensional basins (Phase 1), but subsequently migrated southward in response to post-orogenic upper-plate extension driven by trench rollback of the Hellenic subduction slab (Phase 2). Rare insight given by the denudation pattern indicates that trench rollback

The effect of flexural isostasy on the response time of orogenic systems

NASA Astrophysics Data System (ADS)

Braun, J.; Margirier, A.; Guerit, L.

2017-12-01

The concept of orogenic steady-state implies that mountain belts can reach a dynamic balance between uplift and erosion in order to maintain a quasi-constant shape. The final morphology of the mountain will be a function of the relative efficiency between uplift and erosion and is therefore likely to be modulated by climate. However, reaching such a steady-state cannot be instantaneous and there must exist a time lag between the onset of convergence and the full development of the mountain topography. Similarly, when an orogenic system is subject to a marked change in convergence rate or in climatic conditions, it takes a certain time for it to adapt to such a change and develop a new steady-state morphology. It is during these transient phases that the nature and efficiency of the interactions between tectonics and climate are most likely to be constrained by observations and understood. The duration of this transient stage remains, however, poorly constrained and understood. As shown by many authors (Whipple and Tucker, 1999, for example) the rate at which tectonic systems evolve to reach steady-state is likely controlled by climate and rock strength, which both determine the efficiency of erosional processes, and the rate of uplift. Here we show that isostasy also plays a very important role in determining the length of the transient phase and that, depending on the level of isostatic adjustment, which in turn depends on the flexural strength of the underlying lithosphere, isostasy can change the time it takes for an orogenic system to reach steady-state by an order of magnitude, i.,e. from a few millions to a few tens of millions of years. This has very important implications. It may explain why many young orogenic systems display an increase in uplift and erosion rate millions of years after the onset of collision and that, in these situations, such an increase does not require a steady change in tectonic and/or climate conditions/forcing. We also show that

Frequency dependent Lg attenuation in south-central Alaska

USGS Publications Warehouse

McNamara, D.E.

2000-01-01

The characteristics of seismic energy attenuation are determined using high frequency Lg waves from 27 crustal earthquakes, in south-central Alaska. Lg time-domain amplitudes are measured in five pass-bands and inverted to determine a frequency-dependent quality factor, Q(f), model for south-central Alaska. The inversion in this study yields the frequency-dependent quality factor, in the form of a power law: Q(f) = Q0fη = 220(±30) f0.66(±0.09) (0.75≤f≤12Hz). The results from this study are remarkably consistent with frequency dependent quality factor estimates, using local S-wave coda, in south-central Alaska. The consistency between S-coda Q(f) and Lg Q(f) enables constraints to be placed on the mechanism of crustal attenuation in south-central Alaska. For the range of frequencies considered in this study both scattering and intrinsic attenuation mechanisms likely play an equal role.

A discussion on the tectonic implications of Ediacaran late- to post-orogenic A-type granite in the northeastern Arabian Shield, Saudi Arabia

NASA Astrophysics Data System (ADS)

Robinson, F. A.; Bonin, B.; Pease, V.; Anderson, J. L.

2017-03-01

The transition from late-orogenic to post-orogenic magmatism following major orogenic episodes such as the Neoproterozoic to Cambrian East African Orogen (EAO) is an important, yet not well-understood geological event marking the cessation of subduction-controlled magmatism between buoyant lithospheric fragments. Forming the northern part of the EAO in the Arabian-Nubian Shield are three granitic suites that successively intruded the same northeastern area and post-date the 640 Ma major orogenic episode: (1) 620-600 Ma alkali feldspar (hypersolvous) granite with alkaline/ferroan/A-type geochemistry, (2) 599 Ma granite cumulates (some garnet-bearing) with calc-alkaline/magnesian affinities, and (3) 584-566 Ma alkali feldspar (hypersolvous) granite (aegirine-bearing) with a distinctive peralkaline/ferroan/A-type signature. Combining whole-rock geochemistry from the southern and northern Arabian Shield, suites 1 and 2 are suggested to be products of late-orogenic slab tear/rollback inducing asthenospheric mantle injection and lower crustal melting/fractionation toward A-type/ferroan geochemistry. Suite 3, however, is suggested to be produced by post-orogenic lithospheric delamination, which replaced the older mantle with new asthenospheric (rare earth element-enriched) mantle that ultimately becomes the thermal boundary layer of the new lithosphere. Major shear zones, such as the 620-540 Ma Najd Fault System (NFS), are some of the last tectonic events recorded across the Arabian Shield. Data presented here suggest that the NFS is directly related to the late-orogenic (620-600 Ma) slab tear/rollback in the northeastern Shield as it met with opposing subduction polarity in the southern Shield. Furthermore, this study infers that east and west Gondwana amalgamation interacted with opposing convergence reflected by the NFS.

Synchronous partial melting, deformation, and magmatism: evidence from in an exhumed Proterozoic orogen

NASA Astrophysics Data System (ADS)

Levine, J. S. F.; Mosher, S.

2017-12-01

Older orogenic belts that now expose the middle and lower crust record interaction between partial melting, magmatism, and deformation. A field- and microstructural-based case study from the Wet Mountains of central Colorado, an exhumed section of Proterozoic rock, shows structures associated with anatexis and magmatism, from the grain- to the kilometer-scale, that indicate the interconnection between deformation, partial melting, and magmatism, and allow reconstructions of the processes occurring in hot active orogens. Metamorphic grade, along with the degree of deformation, partial melting, and magmatism increase from northwest to southeast. Deformation synchronous with this high-grade metamorphic event is localized into areas with greater quantities of former melt, and preferential melting occurs within high-strain locations. In the less deformed northwest, partial melting occurs dominantly via muscovite-dehydration melting, with a low abundance of partial melting, and an absence of granitic magmatism. The central Wet Mountains are characterized by biotite dehydration melting, abundant former melt and foliation-parallel inferred melt channels along grain boundaries, and the presence of a nearby granitic pluton. Rocks in the southern portion of the Wet Mountains are characterized by partial melting via both biotite dehydration and granitic wet melting, with widespread partial melting as evidenced by well-preserved former melt microstructures and evidence for back reaction between melt and the host rocks. The southern Wet Mountains has more intense deformation and widespread plutonism than other locations and two generations of dikes and sills. Recognition of textures and fabrics associated with partial melting in older orogens is paramount for interpreting the complex interplay of processes occurring in the cores of orogenic systems.

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

78 FR 53137 - Flint Hills Resources Alaska, LLC, BP Pipelines (Alaska) Inc., ConocoPhillips Transportation...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-08-28

... DEPARTMENT OF ENERGY Federal Energy Regulatory Commission [Docket Nos. OR13-31-000] Flint Hills Resources Alaska, LLC, BP Pipelines (Alaska) Inc., ConocoPhillips Transportation Alaska, Inc., ExxonMobil... (Alaska) Inc., ConocoPhillips Transportation Alaska, Inc., and ExxonMobil Pipeline Company (collectively...

Carboniferous - Early Permian magmatic evolution of the Bogda Range (Xinjiang, NW China): Implications for the Late Paleozoic accretionary tectonics of the SW Central Asian Orogenic Belt

NASA Astrophysics Data System (ADS)

Wali, Guzalnur; Wang, Bo; Cluzel, Dominique; Zhong, Linglin

2018-03-01

The Late Paleozoic magmatic evolution of the Bogda Range (Chinese North Tianshan) is important for understanding the accretionary history of the Central Asian Orogenic Belt. We investigated the Carboniferous and Lower Permian volcanic and sedimentary sequences of the Daheyan section, southern Bogda Range, and present new zircon U-Pb ages and whole-rock geochemical data for the volcanic rocks. One Carboniferous rhyolite is dated at 298 ± 8 Ma; a Permian basalt yielded many Proterozoic zircon xenocrysts, and its maximum age (∼297 Ma) is constrained by the detrital zircon ages of the sandstone that stratigraphically underlies it. These volcanic rocks belong to calc-alkaline series. We further synthesize previous geochronological, geochemical and isotopic data of magmatic and sedimentary rocks in the Bogda Range. The available data indicate that the magmatism occurred continuously from 350 Ma to 280 Ma. A comprehensive analysis allows us to propose that: (1) the Carboniferous to Early Permian magmatic rocks of the Bogda Range generally show consistent arc-type features; (2) increasing mantle input through time suggests intra-arc extension in a supra-subduction zone; (3) the localized occurrence of Early Permian alkaline pillow basalts and deep water sediments close to the major shear zone advocate a transtensional crustal thinning during the transition from Carboniferous convergence to Early Permian transcurrent tectonics; (4) occurrence of a large number of Proterozoic zircon xenocrysts in the Late Paleozoic magmatic rocks, and Proterozoic detrital zircons in the coeval clastic sediments suggest a continental or transitional basement of the Bogda Arc; (5) subduction in the Bogda area terminated prior to the deposition of Middle Permian terrestrial sediments.

Fault Dating in the US Rockies and Large Regional Extent of Deformation Pulses Along the Sevier Orogen of North America.

NASA Astrophysics Data System (ADS)

van der Pluijm, B.; Lynch, E. A.; Pana, D.; Yonkee, A.

2017-12-01

Recent Ar dating of clay-rich fault rock in the Canadian Rockies identified multiple orogenic pulses: Late Jurassic (163-146 Ma), Mid-Cretaceous (103-99 Ma), Late Cretaceous (76-72 Ma) and Eocene (54-52 Ma; Pana and van der Pluijm, GSAB 2015). New dating in the US Rockies combined with ages in the most frontal section along an Idaho-Wyoming transect show a remarkably similar age pattern: Meade Thrust, 108-102 Ma; (S)Absaroka Thrust, 73 Ma; Darby-Bear Thrust, 56-50 Ma. These radiometric fault ages in the US Rockies match field and tectono-stratigraphic predictions, analogues to those in the Canadian Rockies. Thus, a remarkably long (>1500km) lateral tract along the North American Sevier orogen is characterized by at least three major orogenic pulses that are structurally contiguous. These orogenic pulses are progressively younger in the direction of easterly thrust fault motion (toward cratonic interior) and are separated by long periods of relative tectonic quiescence. We interpret the extensive regional continuity of deformation pulses and tectonic quiescence along the Sevier Orogen as the result of three plate reorganization events in western North America since the Late Jurassic.

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.

A crustal model of the ultrahigh-pressure Dabie Shan orogenic belt, China, derived from deep seismic refraction profiling

USGS Publications Warehouse

Wang, Chun-Yong; Zeng, Rong-Sheng; Mooney, W.D.; Hacker, B.R.

2000-01-01

We present a new crustal cross section through the east-west trending ultrahigh-pressure (UHP) Dabie Shan orogenic belt, east central China, based on a 400-km-long seismic refraction profile. Data from our profile reveal that the cratonal blocks north and south of the orogen are composed of 35-km-thick crust consisting of three layers (upper, middle, and lower crust) with average seismic velocities of 6.0±0.2 km/s, 6.5±0.1 km/s, and 6.8±0.1 km/s. The crust reaches a maximum thickness of 41.5 km beneath the northern margin of the orogen, and thus the present-day root beneath the orogen is only 6.5 km thick. The upper mantle velocity is 8.0±0.1 km/s. Modeling of shear wave data indicate that Poisson's ratio increases from 0.24±0.02 in the upper crust to 0.27±0.03 in the lower crust. This result is consistent with a dominantly felsic upper crustal composition and a mafic lower crustal composition within the amphibolite or granulite metamorphic facies. Our seismic model indicates that eclogite, which is abundant in surface exposures within the orogen, is not a volumetrically significant component in the middle or lower crust. Much of the Triassic structure associated with the formation of the UHP rocks of the Dabie Shan has been obscured by post-Triassic igneous activity, extension and large-offset strike-slip faulting. Nevertheless, we can identify a high-velocity (6.3 km/s) zone in the upper (<5 km depth) crustal core of the orogen which we interpret as a zone of ultrahigh-pressure rocks, a north dipping suture, and an apparent Moho offset that marks a likely active strike-slip fault.

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

Climate Drivers of Alaska Summer Stream Temperature

NASA Astrophysics Data System (ADS)

Bieniek, P.; Bhatt, U. S.; Plumb, E. W.; Thoman, R.; Trammell, E. J.

2016-12-01

The temperature of the water in lakes, rivers and streams has wide ranging impacts from local water quality and fish habitats to global climate change. Salmon fisheries in Alaska, a critical source of food in many subsistence communities, are sensitive to large-scale climate variability and river and stream temperatures have also been linked with salmon production in Alaska. Given current and projected climate change, understanding the mechanisms that link the large-scale climate and river and stream temperatures is essential to better understand the changes that may occur with aquatic life in Alaska's waterways on which subsistence users depend. An analysis of Alaska stream temperatures in the context of reanalysis, downscaled, station and other climate data is undertaken in this study to fill that need. Preliminary analysis identified eight stream observation sites with sufficiently long (>15 years) data available for climate-scale analysis in Alaska with one station, Terror Creek in Kodiak, having a 30-year record. Cross-correlation of summer (June-August) water temperatures between the stations are generally high even though they are spread over a large geographic region. Correlation analysis of the Terror Creek summer observations with seasonal sea surface temperatures (SSTs) in the North Pacific broadly resembles the SST anomaly fields typically associated with the Pacific Decadal Oscillation (PDO). A similar result was found for the remaining stations and in both cases PDO-like correlation patterns also occurred in the preceding spring. These preliminary results demonstrate that there is potential to diagnose the mechanisms that link the large-scale climate system and Alaska stream temperatures.

Observations of Inland Snowpack-driven Bromine Chemistry near the Brooks Range, Alaska

NASA Astrophysics Data System (ADS)

Peterson, P.; Pöhler, D.; Sihler, H.; Zielcke, J.; S., General; Friess, U.; Platt, U.; Simpson, W. R.; Nghiem, S. V.; Shepson, P. B.; Stirm, B. H.; Pratt, K.

2017-12-01

The snowpack produces high amounts of reactive bromine in the polar regions during spring. The resulting atmospheric bromine chemistry depletes boundary layer ozone to near-zero levels and alters oxidation of atmospheric pollutants, particularly elemental mercury. To improve our understanding of the spatial extent of this bromine chemistry in Arctic coastal regions, the Purdue Airborne Laboratory for Atmospheric Research (ALAR), equipped with the Heidelberg Imaging differential optical absorption spectroscopy (DOAS) instrument, measured the spatial distribution of BrO, an indicator of active bromine chemistry, over northern Alaska during the March 2012 BRomine Ozone Mercury Experiment (BROMEX). Here we show that this bromine chemistry, commonly associated with snow-covered sea ice regions in the Arctic Ocean, is active 200 km inland in the foothills of the Brooks Range. Profiles retrieved from limb-viewing measurements show this event was located near the snowpack surface, with measured BrO mole ratios of 20 pmol mol-1 in a 500 m thick layer. This observed bromine chemistry is likely enabled by deposition of transported sea salt aerosol or gas phase bromine species from prior activation events to the snowpack. These observations of halogen activation hundreds of km from the coast suggest the impacts of this springtime bromine chemistry are not restricted to sea ice regions and directly adjacent coastal regions.

40 Ma of hydrothermal W mineralization during the Variscan orogenic evolution of the French Massif Central revealed by U-Pb dating of wolframite

NASA Astrophysics Data System (ADS)

Harlaux, Matthieu; Romer, Rolf L.; Mercadier, Julien; Morlot, Christophe; Marignac, Christian; Cuney, Michel

2018-01-01

We present U-Pb thermal ionization mass spectrometer (TIMS) ages of wolframite from several granite-related hydrothermal W±Sn deposits in the French Massif Central (FMC) located in the internal zone of the Variscan belt. The studied wolframite samples are characterized by variable U and Pb contents (typically <10 ppm) and show significant variations in their radiogenic Pb isotopic compositions. The obtained U-Pb ages define three distinct geochronological groups related to three contrasting geodynamic settings: (i) Visean to Namurian mineralization (333-327 Ma) coeval with syn-orogenic compression and emplacement of large peraluminous leucogranites (ca. 335-325 Ma), (ii) Namurian to Westphalian mineralization (317-315 Ma) synchronous with the onset of late-orogenic extension and emplacement of syn-tectonic granites (ca. 315-310 Ma) and (iii) Stephanian to Permian mineralization (298-274 Ma) formed during post-orogenic extension contemporaneous with the Permian volcanism in the entire Variscan belt. The youngest ages (276-274 Ma) likely reflect the reopening of the U-Pb isotopic system after wolframite crystallization and may correspond to late hydrothermal alteration (e.g. ferberitization). Our results demonstrate that W(±Sn) mineralization in the FMC formed during at least three distinct hydrothermal events in different tectono-metamorphic settings over a time range of 40 Ma.

Red alder potential in Alaska

Treesearch

Allen Brackley; David Nicholls; Mike Hannan

2010-01-01

Over the past several decades, red alder has established itself as a commercially important species in the Pacific Northwest. Once considered a weed species, red alder now commands respect within many markets, including furniture, architectural millwork, and other secondary manufactured products. Although red alder's natural range extends to southeast Alaska, an...

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.

A comparative analysis of pre-Silurian crustal building blocks of the northern and the southern Appalachian orogen

USGS Publications Warehouse

Hibbard, J.P.; van Staal, C.R.; Rankin, D.W.

2007-01-01

The New York promontory serves as the divide between the northern and southern segments of the Appalachian orogen. Antiquated subdivisions, distinct for each segment, implied that they had lithotectonic histories that were independent of each other. Using new lithotectonic subdivisions we compare first order features of the pre-Silurian orogenic 'building blocks' in order to test the validity of the implication of independent lithotectonic histories for the two segments. Three lithotectonic divisions, termed here the Laurentian, Iapetan, and the peri-Gondwanan realms, characterize the entire orogen. The Laurentian realm, composed of native North American rocks, is remarkably uniform for the length of the orogen. It records the multistage Neoproterozoic-early Paleozoic rift-drift history of the Appalachian passive margin, formation of a Taconic Seaway, and the ultimate demise of both in the Middle Ordovician. The Iapetan realm encompasses mainly oceanic and magmatic arc tracts that once lay within the Iapetus Ocean, between Laurentia and Gondwana. In the northern segment, the realm is divisible on the basis of stratigraphy and faunal provinciality into peri-Laurentian and peri-Gondwanan tracts that were amalgamated in the Late Ordovician. South of New York, stratigraphic and faunal controls decrease markedly; rock associations are not inconsistent with those of the northern Appalachians, although second-order differences exist. Exposed exotic crustal blocks of the peri-Gondwanan realm include Ganderia, Avalonia, and Meguma in the north, and Carolinia in the south. Carolinia most closely resembles Ganderia, both in early evolution and Late Ordovician-Silurian docking to Laurentia. Our comparison indicates that, to a first order, the pre-Silurian Appalachian orogen developed uniformly, starting with complex rifting and a subsequent drift phase to form the Appalachian margin, followed by the consolidation of Iapetan components and ending with accretion of the peri

Transient Landscape Evolution is Characteristic of Post-Orogenic Decay: An Example from the Southern Appalachians, U.S.A.

NASA Astrophysics Data System (ADS)

Gallen, S. F.

2016-12-01

Long-term landscape evolution in post-orogenic settings remains an outstanding question in the geosciences. Despite conventional wisdom that topography in dead orogens will slowly and steadily decay through time, observations from around the globe show that dynamic, unsteady (e.g. transient) landscape evolution is the norm. Unraveling the mechanisms that drive unsteadiness in dead orogens is paramount to understanding the stratigraphic record of offshore basins and the geologic factors that contribute to the high biodiversity common in these settings. Here we address the enigma of unsteady post-orogenic landscape evolution with a study of the geomorphology of southern Appalachians, U.S.A. We focus on the 58,000 km2 Upper Tennessee River Basin that covers portions of the fold-and-thrust belt (Valley and Ridge), foreland basin (Appalachian Plateau), and a deeply exhumed thrust sheet (Blue Ridge) of this dead orogen. Using published millennial-scale erosion rates and quantitative analysis of fluvial topography, we show that this region is in a transient state of adjustment to 400 m of base level fall. Ongoing adjustment to base level drop is observed as a zone of high erosion rates, steep river channels and numerous knickpoints located upstream of and surrounding the contact between the Valley and Ridge and adjacent lithotectonic units. We argue that the association of adjusting landscapes and the Valley and Ridge contact is due to the rapid response time of rivers incising soft Valley and Ridge rocks, relative to the harder metamorphic rocks in the Blue Ridge and resistant capstone in the Appalachian Plateau. We propose that base level fall was triggered by incision through the Appalachian Plateau capstone into underlying weaker rocks that set off a wave of transient adjustment, drainage reorganization and ultimately capture of the paleo-Upper Tennessee Basin. Our results indicate that transient landscape evolution is characteristic of post-orogenic settings, as

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

Some aspects of active tectonism in Alaska as seen on ERTS-1

NASA Technical Reports Server (NTRS)

Gedney, L. D.; Vanwormer, J. D.

1973-01-01

ERTS-1 imagery is proving to be exceptionally useful in delineating structural features in Alaska which have never been recognized on the ground. Previously unmapped features such as seismically active faults and major structural lineaments are especially evident. Among the more significant results of this investigation is the discovery of an active strand of the Denali fault. The new fault has a history of scattered seismicity and was the scene of a magnitude 4.8 earthquake on October 1, 1972. Perhaps of greater significance is the disclosure of a large scale conjugate fracture system north of the Alaska Range. This fracture system appears to result from compressive stress radiating outward from around the outside of the great bend of the Alaska Range at Mt. McKinley.

Crustal Structure of the Yakutat Microplate: New Constraints for Understanding the Evolution of Subduction and Collision in southern Alaska

NASA Astrophysics Data System (ADS)

Worthington, L. L.; van Avendonk, H. J.; Gulick, S. P.; Christeson, G. L.; Pavlis, T. L.

2010-12-01

Flat-slab subduction and accretion of the Yakutat (YAK) microplate in southern Alaska characterizes the most recent iteration in the process of terrane accretion that has built the tectonic assemblage of the Canada-Alaska Cordillera since the Mesozoic. Despite the potentially pivotal role of the Yakutat collision in the evolution and deformation of the North American Cordillera, major questions regarding locations of active faults and velocity structure and thickness of the Yakutat block itself have gone unanswered. We present results of a 2008 marine seismic reflection/refraction survey acquired as part of the St. Elias Erosion and Tectonics Project (STEEP), a multi-disciplinary NSF-Continental Dynamics project aimed at structural evolution and geodynamics related to the YAK collision. An onshore-offshore wide-angle refraction profile shows YAK crustal thickness ranging from ~15 km near the Bering Glacier to ~35 km east of the Dangerous River Zone (DRZ), with calculated lower crustal velocities potentially >7km/s. Crustal velocity and structure are continuous across the DRZ on the YAK shelf, which is historically described as a vertical boundary between continental crust on the east and oceanic basement on the west. Instead, we observe a gradual shallowing of elevated crustal velocities associated with a basement high observed on coincident marine reflection data near the DRZ. Crustal velocity and thicknesses are comparable to the Kerguelen oceanic plateau and the Siletz terrane, thus supporting the oceanic plateau theory for the origin of the YAK microplate. The observed variable crustal thickness indicates that the YAK slab may be slightly wedge-shaped, thinning in the direction of subduction. The thickest portion of the offshore YAK is entering the orogen near the eastern syntaxis, where the Fairweather fault system encounters a restraining bend as its orientation changes from north-south to east-west. It follows that observations of elevated exhumation rates

Post-collisional magmatism in the central East African Orogen: The Maevarano Suite of north Madagascar

NASA Astrophysics Data System (ADS)

Goodenough, K. M.; Thomas, R. 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.

2010-04-01

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.

Early tectonic evolution of the Thomson Orogen in Queensland inferred from constrained magnetic and gravity data

NASA Astrophysics Data System (ADS)

Spampinato, Giovanni P. T.; Betts, Peter G.; Ailleres, Laurent; Armit, Robin J.

2015-05-01

The crustal architecture as well as the kinematic evolution of the Thomson Orogen in Queensland is poorly resolved because the region is concealed under thick Phanerozoic sedimentary basins and the basement geology is known from limited drill holes. Combined potential field and seismic interpretation indicates that the Thomson Orogen is characterized by prominent regional NE- and NW-trending structural grain defined by long wavelength and low amplitude geophysical anomalies. The 'smooth' magnetic signature is interpreted to reflect deeply buried source bodies in the mid- to lower crust. Short wavelength positive magnetic features that correlate with negative gravity anomalies are interpreted to represent shallower granitic intrusions. They appear to be focused along major fault zones that might have controlled the locus for magmatism. The eastern Thomson Orogen is characterized by a prominent NE structural grain and orthogonal faults and fold interference patterns resulting in a series of troughs and highs. The western Thomson Orogen consists of a series of NW-trending structures interpreted to reflect reverse faults. Sedimentation and basin development are interpreted to have initiated in the Neoproterozoic to Early Cambrian during E-W- to ENE-WSW extension, possibly related to the Rodinia break-up. This extensional event was followed by Late Cambrian shortening recorded in the Maneroo Platform and the Diamantina River Domain which possibly correlates with the Delamerian Orogeny. Renewed deposition and volcanism occurred during the Ordovician and may have continued until Late Silurian, resulting in thinned Proterozoic basement crust and extensive basin systems that formed in a distal continental back-arc environment. Our interpretation places the Thomson Orogen to the west of the Neoproterozoic passive margin preserved in the Anakie Inlier. The region is likely to represent the internal extensional architecture during the Rodinia break-up that has been

Structural development of an Archean Orogen, Western Point Lake, Northwest Territories

NASA Astrophysics Data System (ADS)

Kusky, Timothy M.

1991-08-01

The Point Lake orogen in the central Archean Slave Province of northwestern Canada preserves more than 10 km of structural relief through an eroded antiformal thrust stack and deeper anastomosing midcrustal mylonites. Fault restoration along a 25 km long transect requires a minimum of 69 km slip and 53 km horizontal shortening. In the western part of the orogen the basal decollement places mafic plutonic/volcanic rocks over an ancient tonalitic gneiss complex. Ten kilometers to the east in the Keskarrah Bay area, slices of gneiss unroofed on brittle thrusts shed molasse into several submerged basins. Conglomerates and associated thinly bedded sedimentary rocks are interpreted as channel, levee, and overbank facies of this thrust-related sedimentary fan system. The synorogenic erosion surface at the base of the conglomerate truncates premetamorphic or early metamorphic thrust faults formed during foreland propagation, while other thrusts related to hinterland-progressing imbrication displace this unconformity. Tightening of synorogenic depositional troughs resulted in the conglomerates' present localization in synclines to the west of associated thrust faults and steepening of structural dips. Eastern parts of the orogen consist of isoclinally folded graywackes composed largely of Mutti and Ricci-Lucchi turbidite facies B, C, and D, interpreted as submarine fan deposits eroded from a distant volcanic arc. Thrust faults in the metasedimentary terrane include highly disrupted slate horizons with meter-scale duplex structures, and recrystallized calcmylonites exhibiting sheath folds and boudin trains with very large interboudin distances. The sequence of fabric development and the overall geometry of this metasedimentary terrane strongly resembles younger forearc accretionary prisms. Conditions of deformation along the thrusts parallel the regional metamorphic zonation: amphibolite facies in the basal decollement through greenschist facies shear zones to cataclastic

Ichthyophonus in sport-caught groundfishes from southcentral Alaska

USGS Publications Warehouse

Harris, Bradley P.; Webster, Sarah R.; Wolf, Nathan; Gregg, Jacob L.; Hershberger, Paul

2018-01-01

This report of Ichthyophonus in common sport-caught fishes throughout the marine waters of southcentral Alaska represents the first documentation of natural Ichthyophonus infections in lingcod Ophiodon elongates and yelloweye rockfish Sebastes ruberrimus. In addition, the known geographic range of Ichthyophonus in black rockfish S. melanops has been expanded northward to include southcentral Alaska. Among all species surveyed, the infection prevalence was highest (35%, n = 334) in Pacific halibut Hippoglossus stenolepis. There were no gross indications of high-level infections or clinically diseased individuals. These results support the hypothesis that under typical conditions Ichthyophonus can occur at high infection prevalence accompanied with low-level infection among a variety of fishes throughout the eastern North Pacific Ocean, including southcentral Alaska.

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.

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

Distribution and characteristics of metamorphic belts in the south- eastern Alaska part of the North American Cordillera

USGS Publications Warehouse

Brew, D.A.; Himmelberg, G.R.; Loney, R.A.; Ford, A.B.

1992-01-01

The Cordilleran orogen in south-eastern Alaska includes 14 distinct metamorphic belts that make up three major metamorphic complexes, from east to west: the Coast plutonic-metamorphic complex; the Glacier Bay-Chichagof plutonic-metamorphic complex; and the Chugach plutonic-metamorphic complex. Each of these complexes is related to a major subduction event. The metamorphic history of the Coast complex is lengthy and is related to the Late Cretaceous collision of the Alexander and Wrangellia terranes and the Gravina overlap assemblage to the west against the Stikine terrane to the east. The metamorphic history of the Glacier Bay-Chichagof complex is relatively simple and is related to the roots of a Late Jurassic to late Early Cretaceous island arc. The metamorphic history of the Chugach is complicated and developed during and after the Late Cretaceous collision of the Chugach terrane with the Wrangellia and Alexander terranes. -from Authors

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

Comparative analysis of alternative co-production approaches to conservation science in Alaska

NASA Astrophysics Data System (ADS)

Trammell, E. J.

2017-12-01

Co-production has been suggested as an important tool for reducing the gap between science and management. Although co-production can require substantial investments in time and relationship building, there are a range of possible approaches that can be utilized that honor the focus and intent of co-production. I present here a comparison of three efforts that range from relatively simple, to complex and exhaustive, that illustrate diverse approaches to co-production of conservation science in Alaska. The first example highlights a workshop-based approach to identify long-term environmental monitoring needs in Alaska, while the second example describes stakeholder-driven scenarios that identified stressors to salmon in southcentral Alaska. The third example describes a 2-year cooperative agreement to develop management questions as part of a rapid ecoregional assessment in central Alaska. Results suggest that careful stakeholder selection is essential to successful co-production. Additionally, all three examples highlight the potential disconnect between management questions and specific management decisions, even when working directly with resource managers. As the focus of the Alaska Climate Science Center will be on co-production of climate science over the next 5 years, I conclude with some key pathways forward for successful co-production efforts in the future.

Flat-topped mountain ranges: Their global distribution and value for understanding the evolution of mountain topography

NASA Astrophysics Data System (ADS)

Calvet, Marc; Gunnell, Yanni; Farines, Bernard

2015-07-01

Extensive tracts of low-gradient topography in steep mountain ranges, either forming rangetop plateaus or terraced pediments on range flanks, are widely distributed in mountain belts around the world. Before the advent of plate tectonics, such populations of planar landforms were interpreted as vestiges of a post-orogenic raised peneplain, i.e., a low-gradient land surface resulting from the decay, during long intervals of base-level stability, of a previous mountain range that was subsequently raised once again to great elevations-thus forming a new mountain range. This two-stage model has been challenged by theories that advocate continuity in tectonic processes and more gradual changes in base level, and thus expect a more immediate and proportionate response of geomorphic systems. Here we present a global survey of erosion surfaces in mountain ranges and put existing theories and empirical evidence into a broad perspective calling for further research into the rates and regimes of long-term mountain evolution. The resulting library of case studies provides opportunities for comparative analysis and helps to classify the landform mosaics that are likely to arise from the interplay between (i) crustal regimes, which at convergent plate margins need be neither uniform nor steady at all times; (ii) radiation-driven and gravity-driven geomorphic regimes, which are mainly determined by crustal boundary conditions and climate; and (iii) paleogeography, through which clues about base-level changes can be obtained. We examine intracratonic and plate-margin settings, with examples from thin-skinned fold belts, thick-skinned fold belts, island-arc and other subduction-related settings, and bivergent collisional orogens. Results reveal that the existence of erosion surfaces is not a simple function of geodynamic setting. Although some erosion surfaces are pre-orogenic, evidence about their predominantly post-orogenic age is supported by apatite fission-track and helium

Critical elements in Carlin, epithermal, and orogenic gold deposits

USGS Publications Warehouse

Goldfarb, Richard J.; Hofstra, Albert H.; Simmons, Stuart F.

2016-01-01

Carlin, epithermal, and orogenic gold deposits, today mined almost exclusively for their gold content, have similar suites of anomalous trace elements that reflect similar low-salinity ore fluids and thermal conditions of metal transport and deposition. Many of these trace elements are commonly referred to as critical or near-critical elements or metals and have been locally recovered, although typically in small amounts, by historic mining activities. These elements include As, Bi, Hg, In, Sb, Se, Te, Tl, and W. Most of these elements are now solely recovered as by-products from the milling of large-tonnage, base metal-rich ore deposits, such as porphyry and volcanogenic massive sulfide deposits.A combination of dominance of the world market by a single country for a single commodity and a growing demand for many of the critical to near-critical elements could lead to future recovery of such elements from select epithermal, orogenic, or Carlin-type gold deposits. Antimony continues to be recovered from some orogenic gold deposits and tellurium could potentially be a primary commodity from some such deposits. Tellurium and indium in sphalerite-rich ores have been recovered in the past and could be future commodities recovered from epithermal ores. Carlin-type gold deposits in Nevada are enriched in and may be a future source for As, Hg, Sb, and/or Tl. Some of the Devonian carbonaceous host rocks in the Carlin districts are sufficiently enriched in many trace elements, including Hg, Se, and V, such that they also could become resources. Thallium may be locally enriched to economic levels in Carlin-type deposits and it has been produced from Carlin-like deposits elsewhere in the world (e.g., Alsar, southern Macedonia; Lanmuchang, Guizhou province, China). Mercury continues to be recovered from shallow-level epithermal deposits, as well as a by-product of many Carlin-type deposits where refractory ore is roasted to oxidize carbon and pyrite, and mercury is then

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.

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

PubMed

Stueve, Kirk M; Isaacs, Rachel E; Tyrrell, Lucy E; Densmore, Roseann V

2011-02-01

Throughout interior Alaska (U.S.A.), a gradual warming trend in mean monthly temperatures occurred over the last few decades (approximatlely 2-4 degrees C). 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.

Kyanite-bearing migmatites in the central Adirondack Mountains: Implications for late to post-orogenic metamorphism and melting in a collisional orogen

NASA Astrophysics Data System (ADS)

Reeder, J.; Metzger, E. P.; Bickford, M. E.; Leech, M. L.

2016-12-01

Sillimanite-rich felsic migmatites exposed at Ledge Mountain in the Central Adirondack Highlands (AH) represent the only location in the AH where kyanite is found. The texturally young kyanite is overprinted on sillimanite in largely undeformed pegmatitic leucosomes, suggesting a late episode of melting taking place deeper than previously thought, and requiring a counter-clockwise P-T path. A final phase of anatexis ca. 1050 Ma in the Eastern AH is consistent with an influx of fluid or decompression from extension in sillimanite-bearing migmatites. Temperatures both from this study and previous work are consistent with granulite-facies metamorphism; however, the presence of kyanite requires higher pressure conditions corresponding to deeper burial of rocks exposed in the central Adirondacks. The Adirondacks are associated with the Grenville Province of eastern North America, that formed during four orogenic events. The most recent (Grenville) orogeny consisted of two stages: crustal thickening and granulite facies metamorphism during the Ottawan phase (ca 1090-1020) then metamorphism and melting in the kyanite field during the much shorter Rigolet pulse (ca 1005-980 Ma). Preliminary U-Pb SHRIMP zircon ages from Ledge Mountain kyanite-bearing migmatites suggest that melting in the Central AH persisted into the Rigolet phase. On the basis of mineral composition and chemistry and the presence of distinctive quartz-sillimanite nodules, the Ledge Mountain migmatites closely resemble the K-rich phase of the Ottawan-age Lyon Mountain granite (LMG) and may represent LMG that was metamorphosed to sillimanite grade and then overprinted by a higher pressure, lower temperature assemblage. Kyanite-bearing felsic anatectites of Rigolet age have previously been observed only in the western portion of the Grenville Province. Documentation of a counterclockwise P-T path and post-Ottawan melting in the Ledge Mountain migmatites requires re-evaluation of current tectonic models for

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

USGS Publications Warehouse

Chen, Lei; Li, Xian-hua; Li, Jian-wei; Hofstra, Albert H.; Liu, Yu; Koenig, Alan E.

2015-01-01

High spatial resolution textural (scanning electron microscope (SEM)), chemical (electron microprobe (EMP)) and laser ablation-inductively coupled plasma-mass spec- trometry (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 concentra- tions of As, Au, Cu, Co, and Ni, has negative δ34S values of −27.1 to −7.6‰ that are interpreted in terms of bacterial re- duction of marine sulfate during sedimentation and diagenesis of the Paleozoic carbonate and clastic sequences, the predom- inant 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 con- tains high concentrations of Au, As, Cu, Sb, Tl, and Bi and hasa 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 de- posits 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 sig- nificantly 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 reduc- tion of evaporite sulfates in underlying Cambrian sedimentary

Board-Foot and cubic-foot volume tables for Alaska-cedar in southeast Alaska.

Treesearch

Donald J. DeMars

1996-01-01

Four tables give cubic-foot and board-foot volume estimates for Alaska-cedar given breast-height diameter outside bark (DBHOB) and either total tree height or number of logs to a 6-inch top. The values for DBHOB and total tree height (or number of logs in the tree) that are in the tables have been limited to the ranges these variables had in the sample data.

Genetic differentiation of Alaska Chinook salmon: the missing link for migratory studies.

PubMed

Templin, William D; Seeb, James E; Jasper, James R; Barclay, Andrew W; Seeb, Lisa W

2011-03-01

Most information about Chinook salmon genetic diversity and life history originates from studies from the West Coast USA, western Canada and southeast Alaska; less is known about Chinook salmon from western and southcentral Alaska drainages. Populations in this large area are genetically distinct from populations to the south and represent an evolutionary legacy of unique genetic, phenotypic and life history diversity. More genetic information is necessary to advance mixed stock analysis applications for studies involving these populations. We assembled a comprehensive, open-access baseline of 45 single nucleotide polymorphisms (SNPs) from 172 populations ranging from Russia to California. We compare SNP data from representative populations throughout the range with particular emphasis on western and southcentral Alaska. We grouped populations into major lineages based upon genetic and geographic characteristics, evaluated the resolution for identifying the composition of admixtures and performed mixed stock analysis on Chinook salmon caught incidentally in the walleye pollock fishery in the Bering Sea. SNP data reveal complex genetic structure within Alaska and can be used in applications to address not only regional issues, but also migration pathways, bycatch studies on the high seas, and potential changes in the range of the species in response to climate change. © 2011 Blackwell Publishing Ltd.

Geologic studies in Alaska by the U.S. Geological Survey, 1990

USGS Publications Warehouse

Bradley, Dwight C.; Ford, Arthur B.

1992-01-01

This collection of papers continues the annual series of U.S. Geological Survey (USGS) reports on geologic investigations in Alaska. From 1975 through 1988, the series was published as USGS circulars. The first of these appeared under the title "The United States Geological Survey in Alaska: Accomplishments during 1975," and the series continued to the last annual circular entitled "Geologic studies in Alaska by the U.S. Geological Survey during 1987," which reflects a title change made in 1986. This 1990 volume continues the bulletin format started in 1988. As in 1989, this volume separates shorter contributions as Geologic Notes from more extensive Articles.This 1990 volume of 18 Articles and 4 Geologic Notes represents the broad range of USGS research activities carried out in Alaska over the past few years. These studies include topics on mineral and other resources such as gold (Y eend), platinum-group elements (Cathrall and Antweiler), coal (Roberts, Stricker, and Affolter), and petroleum (Howell, Bird, and others). Many other investigations provide background geochemical (Kilburn, Box, and others) and geologic data needed for resource evaluation as well as for determining the general geologic framework of Alaska, as in stratigraphic, sedimentologic, and paleontologic and radiometric age studies (Blodgett, Clough, and others; Box and Elder; Dickinson and Skipp; Marincovich and Moriya; McLean and Stanley; Stanley, Flores, and Wiley; Roeske, Pavlis, and others); geophysics (Sampson, Labson, and Long); structure and tectonic evaluations (Bradley and Kosky; Clendenen, Sliter, and Byrne; Karl; Csejtey; Howell, Johnsson, and others); and geomorphic and late Quaternary studies (Carter and Hillhouse; Galloway, Huebner, and others; McGimsey, Richter, and others; Nelson and Carter). These studies span nearly the entire State from the North Slope and Brooks Range to interior, southwestern, and south-central Alaska (fig. 1).Two bibliographies (White) at the end of the

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

NASA Astrophysics Data System (ADS)

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

2017-10-01

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

Retaining Quality Teachers for Alaska.

ERIC Educational Resources Information Center

McDiarmid, G. Williamson; Larson, Eric; Hill, Alexandra

This report examines the demand for teachers, teacher turnover, and teacher education in Alaska. Surveys were conducted with school district personnel directors, directors of Alaska teacher education programs, teachers who exited Alaska schools in 2001, and rural and urban instructional aides. Alaska is facing teacher shortages, but these are…

Fisheries Education in Alaska. Conference Report. Alaska Sea Grant Report 82-4.

ERIC Educational Resources Information Center

Smoker, William W., Ed.

This conference was an attempt to have the fishing industry join the state of Alaska in building fisheries education programs. Topics addressed in papers presented at the conference include: (1) fisheries as a part of life in Alaska, addressing participation of Alaska natives in commercial fisheries and national efforts; (2) the international…

Traces of Old Glaciations in East-central Alaska

NASA Astrophysics Data System (ADS)

Duk-Rodkin, A.; Barendregt, R. W.; Weber, F.

2001-12-01

The East-central Alaska record of glaciations is similar to that preserved in the west-central Yukon. Surficial geologic mapping of the Yukon-Tanana upland has indicated at least 5 glacial periods including at least one early Holocene. The two earliest glaciations are of pre-Mid Pleistocene age and followed regional erosion and renewed uplift ca.4 Ma. The earliest glaciation of west-central Yukon occurred between 2.6 and 2.9 Ma, forming a continuous carapace of ice covering all the mountain ranges except for a small part of the Dawson Range. This first glaciation was also the most extensive in the region, and resulted in the NW diversion of Yukon River into Alaska by the Cordilleran Ice Sheet. Stratigraphic evidence of 6 glaciations of pre-Mid Pleistocene age is preserved in the western Canadian sector of the Tintina Trench. The limits of these glaciations have been mapped in Yukon on the basis of glacial landforms and the distribution of erratics. Although morphological features of older glaciations (Plio-Pleistocene) are generally not well preserved, there is relatively good control on the distribution of glacial features for two of the older glaciations in Mt.Harper, Alaska. Stratigraphic evidence of at least 3 older glaciations is found in the Goodpastor River. An initial magnetostratigraphic study of three sites in east-central Alaska have yielded normal magnetic polarities only. The sites are:(1) a relatively weathered lowermost till outcropping along Goodpastor River on the Yukon-Tanana upland,(2) an extremely weathered high level moraine (609m) on the western side of the Gerstle River, near Granite Mt.in the Alaska Range and (3)ca.914m pediment containing glacial erratics and a luvisol at its surface, located on Tok River, Tanana Valley, Alaska Range. The normal polarity of the first site likely indicates a Brunhes age rather than a normal subchron within the Matuyama Reversed Chron based on the modest degree of weathering of the till and lack of any

Home ranges and movements of arctic fox (Alopex lagopus) in western Alaska

USGS Publications Warehouse

Anthony, R. Michael

1997-01-01

During the period from 1985 to 1990, radio collars were attached to 61 arctic foxes (Alopex lagopus) in the coastal region of the Yukon-Kuskokwim Delta in western Alaska. Radio tracking using hand-held receivers from aircraft, and from fixed towers was conducted to determine daily and seasonal movements of foxes. Intensive radio tracking of 18 foxes from May through July indicated that males used larger areas (x=10.22i??6.18 km2) than females (x=4.57i??1.94 km2) regardless of breeding status. Generally foxes were relocated near (x=3.4i??2.4 km) their summer home ranges during other seasons of the year. There were no complex social groups of foxes among the marked population. Foxes did not have a definitive preference for any plant community, probably because of the even distribution and abundance of prey throughout all communities. Thirty foxes were relocated repeatedly during a period of at least 10 months, which included the denning season of one year and the breeding season of the next. Of 24 confirmed deaths of collared foxes, 16 were caused by shooting or trapping by local residents and 8 had unidentified causes. Maximum distance moved between relocations was 48.4 km. Males moved farther from initial capture sites in the winter following capture than did females, largely because of greater than 20 km movements by two foxes. There were no seasonal differences in movements between males and females.

The recent warming of permafrost in Alaska

NASA Astrophysics Data System (ADS)

Osterkamp, T. E.

2005-12-01

This paper reports results of an experiment initiated in 1977 to determine the effects of climate on permafrost in Alaska. Permafrost observatories with boreholes were established along a north-south transect of Alaska in undisturbed permafrost terrain. The analysis and interpretation of annual temperature measurements in the boreholes and daily temperature measurements of the air, ground and permafrost surfaces made with automated temperature loggers are reported. Permafrost temperatures warmed along this transect coincident with a statewide warming of air temperatures that began in 1977. At two sites on the Arctic Coastal Plain, the warming was seasonal, greatest during "winter" months (October through May) and least during "summer" months (June through September). Permafrost temperatures peaked in the early 1980s and then decreased in response to slightly cooler air temperatures and thinner snow covers. Arctic sites began warming again typically about 1986 and Interior Alaska sites about 1988. Gulkana, the southernmost site, has been warming slowly since it was drilled in 1983. Air temperatures were relatively warm and snow covers were thicker-than-normal from the late 1980s into the late 1990s allowing permafrost temperatures to continue to warm. Temperatures at some sites leveled off or cooled slightly at the turn of the century. Two sites (Yukon River Bridge and Livengood) cooled during the period of observations. The magnitude of the total warming at the surface of the permafrost (through 2003) was 3 to 4 °C for the Arctic Coastal Plain, 1 to 2 °C for the Brooks Range including its northern and southern foothills, and 0.3 to 1 °C south of the Yukon River. While the data are sparse, permafrost is warming throughout the region north of the Brooks Range, southward along the transect from the Brooks Range to the Chugach Mountains (except for Yukon River and Livengood), in Interior Alaska throughout the Tanana River region, and in the region south of the

Alaska Mental Health Board

Science.gov Websites

State Employees Alaska Mental Health Board DHSS State of Alaska Home Divisions and Agencies Alaska Pioneer Homes Behavioral Health Office of Children's Services Office of the Commissioner Office of Substance Misuse and Addiction Prevention Finance & Management Services Health Care Services Juvenile

Publications - STATEMAP Project | Alaska Division of Geological &

Science.gov Websites

., 2008, Surficial-geologic map of the Salcha River-Pogo area, Big Delta Quadrangle, Alaska: Alaska , Engineering - geologic map, Alaska Highway corridor, Delta Junction to Dot Lake, Alaska: Alaska Division of geologic map of the Salcha River-Pogo area, Big Delta Quadrangle, Alaska: Alaska Division of Geological

Stable Isotopic Constraints on the Geographic Sources of Marijuana in Alaska

NASA Astrophysics Data System (ADS)

Booth, A. L.; Wooller, M. J.; Haubenstock, N. A.; Howe, T. A.

2007-12-01

Marijuana in Alaska can have numerous sources. Confiscated plants are known to originate either from within the state (e.g., Fairbanks and the Matanuska-Susitna Valley) or from numerous areas outside the state (e.g., Latin America, Canada and the contiguous United States). Latin America reportedly supplies a large percentage of the marijuana currently distributed in the lower 48 states of the U.S.A. However, in more remote areas of the country such as Fairbanks, Alaska, the supply proportions from different geographic areas are not well known. This is due to an insufficient ability to trace source regions from which confiscated marijuana was originally grown. As such, we have analyzed multiple stable isotopes (C, N, O and H) preserved in marijuana samples to identify the likely geographic source from which the marijuana originated (Drug Enforcement Agency license # RW0324551). These samples were confiscated in Fairbanks, Alaska and supplied to us by the University of Alaska Fairbanks (UAF) Police Department. Among 36 marijuana plant samples, we found an unexpectedly large range in the stable carbon isotope compositions (‰13C = -62.2‰ to -24.4‰), with twelve of the 36 samples exhibiting exceedingly low δ13C (-36.1‰ to -62.2‰) relative to typical δ13C of other C3 plants. Interior growing conditions (e.g., hydroponics and/or greenhouses) and a variety of CO2 sources (e.g., CO2 from tanks and fermentation CO2 generators) frequently supplied to growing marijuana to improve yields may account for these exceptionally low δ13C values. Stable oxygen and hydrogen isotope compositions (δ18O and δD vs. V-SMOW) of the marijuana samples were found to range from 10.0‰ to 27.6‰ and -197.1‰ to -134.9‰ respectively. The large range of values suggests that the samples originated from multiple sources ranging from low to high latitudes. δ15N of the marijuana samples also exhibited a large range (-7.0‰ to 14.8‰). This project has implications for the

Petrological and zircon evidence for the Early Cretaceous granulite-facies metamorphism in the Dabie orogen, China

NASA Astrophysics Data System (ADS)

Gao, Xiao-Ying; Zhang, Qiang-Qiang; Zheng, Yong-Fei; Chen, Yi-Xiang

2017-07-01

An integrated study of petrology, mineralogy, geochemistry, and geochronology was carried out for contemporaneous mafic granulite and diorite from the Dabie orogen. The results provide evidence for granulite-facies reworking of the ultrahigh-pressure (UHP) metamorphic rock in the collisional orogen. Most zircons from the granulite are new growth, and their U-Pb ages are clearly categorized into two groups at 122-127 Ma and 188 ± 2 Ma. Although these two groups of zircons show similarly steep HREE patterns and variably negative Eu anomalies, the younger group has much higher U, Th and REE contents and Th/U ratios, much lower εHf(t) values than the older group. This suggests their growth is associated with different types of dehydration reactions. The older zircon domains contain mineral inclusions of garnet + clinopyroxene ± quartz, indicating their growth through metamorphic reactions at high pressures. In contrast, the young zircon domains only contain a few quartz inclusions and the garnet-clinopyroxene-plagioclase-quartz barometry yields pressures of 4.9 to 12.5 kb. In addition, the clinopyroxene-garnet Fe-Mg exchange thermometry gives temperatures of 738-951 °C. Therefore, the young zircon domains would have grown through peritectic reaction at low to medium pressures. The younger granulite-facies metamorphic age is in agreement not only with the adjacent diorite at 125 ± 1 Ma in this study but also the voluminous emplacement of coeval mafic and felsic magmas in the Dabie orogen. Mineral separates from both mafic granulite and its adjacent diorite show uniformly lower δ18O values than normal mantle, similar to those for UHP eclogite-facies metaigneous rocks in the Dabie orogen. In combination with major-trace elements and zircon Lu-Hf isotope compositions, it is inferred that the protolith of mafic granulites shares with the source rock of diorites, both being a kind of mafic metasomatites at the slab-mantle interface in the continental subduction channel

An accuracy assessment of positions obtained using survey- and recreational-grade Global Positioning System receivers across a range of forest conditions within the Tanana Valley of interior Alaska

Treesearch

Hans-Erik Andersen; Tobey Clarkin; Ken Winterberger; Jacob Strunk

2009-01-01

The accuracy of recreational- and survey-grade global positioning system (GPS) receivers was evaluated across a range of forest conditions in the Tanana Valley of interior Alaska. High-accuracy check points, established using high-order instruments and closed-traverse surveying methods, were then used to evaluate the accuracy of positions acquired in different forest...

Hillslope response to knickpoint migration in the Southern Appalachians: Implications for the evolution of post-orogenic landscapes

USGS Publications Warehouse

Wegmann, S.F.G.; Franke, K.L.; Hughes, S.; Lewis, R.Q.; Lyons, N.; Paris, P.; Ross, K.; Bauer, J.B.; Witt, A.C.

2011-01-01

The southern Appalachians represent a landscape characterized by locally high topographic relief, steep slopes, and frequent mass movement in the absence of significant tectonic forcing for at least the last 200 Ma. The fundamental processes responsible for landscape evolution in a post-orogenic landscape remain enigmatic. The non-glaciated Cullasaja River basin of south-western North Carolina, with uniform lithology, frequent debris flows, and the availability of high-resolution airborne lidar DEMs, is an ideal natural setting to study landscape evolution in a post-orogenic landscape through the lens of hillslope-channel coupling. This investigation is limited to channels with upslope contributing areas >2.7 km2, a conservative estimate of the transition from fluvial to debris-flow dominated channel processes. Values of normalized hypsometry, hypsometric integral, and mean slope vs elevation are used for 14 tributary basins and the Cullasaja basin as a whole to characterize landscape evolution following upstream knickpoint migration. Results highlight the existence of a transient spatial relationship between knickpoints present along the fluvial network of the Cullasaja basin and adjacent hillslopes. Metrics of topography (relief, slope gradient) and hillslope activity (landslide frequency) exhibit significant downstream increases below the current position of major knickpoints. The transient effect of knickpoint-driven channel incision on basin hillslopes is captured by measuring the relief, mean slope steepness, and mass movement frequency of tributary basins and comparing these results with the distance from major knickpoints along the Cullasaja River. A conceptual model of area-elevation and slope distributions is presented that may be representative of post-orogenic landscape evolution in analogous geologic settings. Importantly, the model explains how knickpoint migration and channel- hillslope coupling is an important factor in tectonically-inactive (i

Detrital zircon geochronology of pre- and syncollisional strata, Acadian orogen, Maine Appalachians

USGS Publications Warehouse

Bradley, Dwight C.; O'Sullivan, Paul B.

2017-01-01

northwest. Next, southeasterly parts of this succession were deformed in the Acadian orogeny, shedding detritus towards the northwest into what remained of the basin. Finally, by Pragian time, all strata in the Central Maine Basin had been deformed and detritus from this new source accumulated as the Tarratine Formation in a new incarnation of the foreland basin. Silurian-Devonian strata from the Central Maine Basin have similar detrital zircon age distributions to coeval rocks from the Arctic Alaska and Farewell terranes of Alaska and the Northwestern terrane of Svalbard. We suggest that these strata were derived from different segments of the 6500-km-long Appalachian-Caledonide orogen.

Seismic anisotropies of the Songshugou peridotites (Qinling orogen, central China) and their seismic implications

NASA Astrophysics Data System (ADS)

Cao, Yi; Jung, Haemyeong; Song, Shuguang

2018-01-01

Though extensively studied, the roles of olivine crystal preferred orientations (CPOs or fabrics) in affecting the seismic anisotropies in the Earth's upper mantle are rather complicated and still not fully known. In this study, we attempted to address this issue by analyzing the seismic anisotropies [e.g., P-wave anisotropy (AVp), S-wave polarization anisotropy (AVs), radial anisotropy (ξ), and Rayleigh wave anisotropy (G)] of the Songshugou peridotites (dunite dominated) in the Qinling orogen in central China, based on our previously reported olivine CPOs. The seismic anisotropy patterns of olivine aggregates in our studied samples are well consistent with the prediction for their olivine CPO types; and the magnitude of seismic anisotropies shows a striking positive correlation with equilibrium pressure and temperature (P-T) conditions. Significant reductions of seismic anisotropies (AVp, max. AVs, and G) are observed in porphyroclastic dunite compared to coarse- and fine-grained dunites, as the results of olivine CPO transition (from A-/D-type in coarse-grained dunite, through AG-type-like in porphyroclastic dunite, to B-type-like in fine-grained dunite) and strength variation (weakening: A-/D-type → AG-type-like; strengthening: AG-type-like → B-type-like) during dynamic recrystallization. The transition of olivine CPOs from A-/D-type to B-/AG-type-like in the forearc mantle may weaken the seismic anisotropies and deviate the fast velocity direction and the fast S-wave polarization direction from trench-perpendicular to trench-oblique direction with the cooling and aging of forearc mantle. Depending on the size and distribution of the peridotite body such as the Songshugou peridotites, B- and AG-type-like olivine CPOs can be an additional (despite minor) local contributor to the orogen-parallel fast velocity direction and fast shear-wave polarization direction in the orogenic crust such as in the Songshugou area in Qinling orogen.

Partial melting of amphibolites in the Eastern Segment of the Sveconorwegian orogen, southern Sweden.

NASA Astrophysics Data System (ADS)

Brophy, E.; Hansen, E. C.; Möller, C.; Huffman, M.

2017-12-01

Mafic migmatites with amphibolitic melanosome and tonalitic leucosome are a common feature in continental collision orogenic zones. However, the anatexis of mafic rocks has received much less attention than anatexis in felsic, intermediate or pelitic compositions. We examined mafic migmatites along a traverse within the Eastern Segment of the 1.14-0.9 Ga Sveconorwegian orogen, between Forsheda and Fegen southern Sweden. This traverse occurs in the center of a >150 km metamorphic transition from sub-greenschist facies in the east to high-pressure granulite and eclogite facies in the west (Möller and Andersson, unpublished metamorphic map). The Eastern Segment is a parautochthonous belt made up of rocks of the Fennoscandian shield that were deformed and metamorphosed during the Sveconorwegian orogeny. Within the traverse amphibolite bodies occur within migmatitic felsic to intermediate orthogneisses. The first appearance of tonalitic leucosome in amphibolite was observed towards the eastern edge of the traverse and continued to occur sporadically westward ranging in abundance (by outcrop area) from 0 to 25 %. The mineral assemblage in amphibolite is hbl + plag ( An30) + qtz + bt ± grt ± ilm ± ttn ± py ± SO2-rich scp. No examples of peritectic pyroxene associated with leucosome were found. The lack of peritectic pyroxene suggests that a water-rich phase was present at the onset of anatexis. The highly variable amount of leucosome further suggests that the amount of melt generated was determined by the amount of water available. Together these suggest that partial was driven by the local influx of a water-rich fluid. In the higher grade portions further west migmatitic amphibolite with tonalitic leucosome occurs in two varieties: one with peritectic pyroxene and relatively small amounts of leucosome, interpreted as forming by water-undersaturated dehydration melting, and another without peritectic pyroxene and with larger amounts of leucosome which is interpreted

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

Petrogenesis and tectonic implications of the Early Paleozoic granites in the western segment of the North Qilian orogenic belt, China

NASA Astrophysics Data System (ADS)

Wang, Nan; Wu, Cai-Lai; Lei, Min; Chen, Hong-Jie

2018-07-01

Early Paleozoic granitic magmatism in the North Qilian orogenic belt records a complete Wilson cycle and provides critical geological clues for unraveling the regional tectonic history. In this study, we report the results of zircon U-Pb ages, Hf isotopic analysis and systematic whole-rock geochemical data for the Late Ordovician Hongliuhe granite and Early Silurian Qingshan monzogranite in the western segment of the North Qilian orogenic belt to constrain their emplacement ages, petrogenesis, and regional evolution history. U-Pb dating reveals that the Hongliuhe granite was emplaced around 453-452 Ma, and the Qingshan monzogranite was emplaced about 440-438 Ma. A geochemical study shows that the two granites belong to the calc-alkaline to high-K calc-alkaline series. The Hongliuhe granite shows adakitic and peraluminous features, while the Qingshan monzogranite belongs to metaluminous to weak peraluminous granites. Zircons in the Hongliuhe granite show εHf(t) values ranging from -15.1 to +11.7 with two-stage Hf model ages (tDM2) of 687-2398 Ma, whereas zircons in the Qingshan monzogranite show εHf(t) values ranging from +5.7 to +11.0 with two-stage Hf model ages from 814 to 1057 Ma. The geochemical characteristics indicate that the Hongliuhe granite was a transitional I/S-type granite and was generated from a thickened lower crust with the addition of minor Paleo- to Mesoproterozoic crustal materials, which left a rutile + garnet + pyroxene ± plagioclase residue. The Qingshan monzogranite formed from the partial melting of mafic crust with minor mantle-derived materials, and the fractionation of Ti-bearing phases, apatite and pyroxene occurred during the magma's evolution, which left an amphibole and plagioclase residue. We infer that the Hongliuhe granite formed during the northward subduction of the North Qilian Ocean, while the Qingshan monzogranite was generated during the post-collision stage between the Qilian and Alxa blocks. This observation indicates

Geophysical identification and geological Implications of the Southern Alaska Magnetic Trough

USGS Publications Warehouse

Saltus, R.W.; Hudson, T.L.; Wilson, Frederic H.

2003-01-01

The southern Alaska magnetic trough (SAMT) is one of the fundamental, crustal-scale, magnetic features of Alaska. It is readily recognized on 10 km upward-continued aeromagnetic maps of the state. The arcuate SAMT ranges from 30 to 100 km wide and extends in two separate segments along the southern Alaska margin for about 1200 km onshore (from near the Alaska/Canada border at about 60 degrees north latitude to the Bering Sea) and may continue an additional 500 km or more offshore (in the southern Bering Sea). The SAMT is bordered to the south by the southern Alaska magnetic high (SAMH) produced by strongly magnetic crust and to the north by a magnetically quiet zone that reflects weakly magnetic interior Alaska crust. Geophysically, the SAMT is more than just the north-side dipole low associated with the SAMH. Several modes of analysis, including examination of magnetic potential (pseudogravity) and profile modeling, indicate that the source of this magnetic trough is a discrete, crustal-scale body. Geologically, the western portion of the SAMT coincides to a large degree with collapsed Mesozoic Kahiltna flysch basin. This poster presents our geophysical evidence for the extent and geometry of this magnetic feature as well as initial geological synthesis and combined geologic/geophysical modeling to examine the implications of this feature for the broad scale tectonic framework of southern Alaska.

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…

Cooperative Alaska Forest Inventory

Treesearch

Thomas Malone; Jingjing Liang; Edmond C. Packee

2009-01-01

The Cooperative Alaska Forest Inventory (CAFI) is a comprehensive database of boreal forest conditions and dynamics in Alaska. The CAFI consists of field-gathered information from numerous permanent sample plots distributed across interior and south-central Alaska including the Kenai Peninsula. The CAFI currently has 570 permanent sample plots on 190 sites...

Appellate Courts - Alaska Court System

Science.gov Websites

Court Cases Appellate Case Management System Oral Argument Supreme Court Calendar, Court of Appeals , which contains the Alaska cases excerpted from P.2d and P.3d. The Pacific Reporter or the Alaska the Alaska cases excerpted from P.2d and P.3d. The Pacific Reporter or the Alaska Reporter is

Alaska looks HOT!

DOE Office of Scientific and Technical Information (OSTI.GOV)

Belcher, J.

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 andmore » 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.« less

Alaska Tidal Datum Portal | Alaska Division of Geological & Geophysical

Science.gov Websites

Engineering Geology Alaska Tidal Datum Portal Climate and Cryosphere Hazards Coastal Hazards Program Guide to Portal Unambiguous vertical datums in the coastal environment are critical to the evaluation of natural human life, property, and the coastal environment. January 2017 - Update Summary Alaska Tidal Datum

Alaska Job Center Network

Science.gov Websites

Job Centers Toll-free in Alaska (877)724-2539 *Workshop Schedules are linked under participating Job : midtown.jobcenter@alaska.gov Employers: anchorage.employers@alaska.gov Toll free Anchorage Employer Phone: 1-888-830 -1149 Phone: 842-5579 Fax: 842-5679, Toll Free: 1-800-478-5579 Job Seekers & Employers

The pre-Devonian tectonic framework of Xing'an-Mongolia orogenic belt (XMOB) in north China

NASA Astrophysics Data System (ADS)

Xu, Bei; Zhao, Pan; Wang, Yanyang; Liao, Wen; Luo, Zhiwen; Bao, Qingzhong; Zhou, Yongheng

2015-01-01

A new tectonic division of the Xing'an-Mongolia orogenic belt (XMOB) in north China has been presented according to our research and a lot of new data of tectonics, geochronology and geochemistry. Four blocks and four sutures have been recognized in the XMOB, including the Erguna (EB), Xing'an-Airgin Sum (XAB), Songliao-Hunshandake (SHB), and Jiamusi (JB), and Xinlin-Xiguitu (XXS), Xilinhot-Heihe (XHS), Mudanjiang (MS) and Ondor Sum-Yongji sutures (OYS). The framework of the XMOB is characterized by a tectonic collage of the blocks and orogenic belts between them. Different Precambrian basements have been found in the blocks, including the Neoproterozoic metamorphic rocks and plutons in the EB, the Neoproterozoic metamorphic rocks in western and eastern of segments of the XAB, Mesoproterozoic and Neoproterozoic metamorphic rocks in middle segments of the XAB, respectively, the Neoproterozoic metamorphic rocks and Mesoproterozoic volcanic rocks and plutons in the SHB, and Neoproterozoic metamorphic rocks in the JB. The XXS resulted from a northwestward subduction of the XAB beneath the EB during the Cambrian, which was followed by the forming of the XHS and OYS in the northwest and south margins of the SHB in the Silurian, respectively. The MS was caused by a westward subduction of the JB beneath the east margin of the SHB during the middle Devonian. The three Cambrian, Silurian and middle Devonian events indicate that the XMOB belongs to a pre-middle Devonian multiple orogenic belt in the Central Asian Orogenic Belt (CAOB). Forming of the XMOB suggests that the southeast part of the Paleo Asian Ocean closed before the middle Devonian.

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

USGS Publications Warehouse

Dumoulin, Julie A.; Harris, Anita G.; Blome, Charles D.; Young, Lorne 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.

Assessment of undiscovered petroleum resources of the Arctic Alaska Petroleum Province

USGS Publications Warehouse

Houseknecht, David W.; Bird, Kenneth J.; Garrity, Christopher P.

2012-01-01

The Arctic Alaska Petroleum Province encompasses all lands and adjacent continental shelf areas north of the Brooks Range-Herald arch tectonic belts and south of the northern (outboard) margin of the Alaska 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 about 28 billion barrels of oil equivalent. For assessment purposes, the province is divided into a platform assessment unit, comprising the Alaska rift shoulder and its relatively undeformed flanks, and a fold-and-thrust belt assessment unit, comprising the deformed area north of the Brooks Range and Herald arch tectonic belts. Mean estimates of undiscovered, technically recoverable resources include nearly 28 billion barrels of oil and 122 trillion cubic feet of nonassociated gas in the platform assessment unit and 2 billion barrels of oil and 59 trillion cubic feet of nonassociated gas in the fold-and-thrust belt assessment unit.

An isotopic perspective on growth and differentiation of Proterozoic orogenic crust: From subduction magmatism to cratonization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnson, Simon P.; Korhonen, Fawna J.; Kirkland, Christopher L.

The in situ chemical differentiation of continental crust ultimately leads to the long-term stability of the continents. This process, more commonly known as ‘cratonization’, is driven by deep crustal melting with the transfer of those melts to shallower regions resulting in a strongly chemically stratified crust, with a refractory, dehydrated lower portion overlain by a complementary enriched upper portion. Since the lower to mid portions of continental crust are rarely exposed, investigation of the cratonization process must be through indirect methods. In this study we use in situ Hf and O isotope compositions of both magmatic and inherited zircons frommore » several felsic magmatic suites in the Capricorn Orogen of Western Australia to highlight the differentiation history (i.e. cratonization) of this portion of late Archean to Proterozoic orogenic crust. The Capricorn Orogen shows a distinct tectonomagmatic history that evolves from an active continental margin through to intracratonic reworking, ultimately leading to thermally stable crust that responds similarly to the bounding Archean Pilbara and Yilgarn Cratons.« less

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…

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,…

Alaska Board of Forestry

Science.gov Websites

Natural Resources / Division of Forestry Alaska Board of Forestry The nine-member Alaska Board of Forestry advises the state on forest practices issues and provides a forum for discussion and resolution of forest management issues on state land. The board also reviews all proposed changes to the Alaska Forest Resources

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.

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…

Alaska's renewable energy potential.

DOE Office of Scientific and Technical Information (OSTI.GOV)

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.

Climate Variability and Surface Processes in Tectonically Active Orogens: Insights From the Southern Central Andes and the Northwest Himalaya

NASA Astrophysics Data System (ADS)

Strecker, M. R.; Bookhagen, B.

2008-12-01

The Southern Central Andes of NW Argentina and the NW Himalaya are important orographic barriers that intercept moisture-bearing winds associated with monsoonal circulation. Changes in both atmospheric circulation systems on decadal to millennial timescales fundamentally influence differences in the amount and location of rainfall in both orogens. In India, the eastern arm of the monsoonal circulation draws moisture from the Bay of Bengal and transports humid air masses along the southern Himalayan front to the northwest. There, at the end of the monsoonal conveyer belt, rainfall is diminished and moisture typically does not reach far into the orogen interior. Similar conditions apply to the NW Argentine Andes, which are located within the precipitation regime of the South American Monsoon. Here, pronounced local relief blocks humid air masses from the Amazon region, resulting in extreme gradients in rainfall that leave the orogen interior dry. However, during negative ENSO years (La Niña) and intensified Indian Summer Monsoon years, moisture penetrates farther into the Andean and Himalayan orogens, respectively. Structurally pre- conditioned valley systems may enhance this process and funnel moisture far into the orogen interior. The greater availability of moisture increases runoff, lateral scouring of mountin streams, and ultimately triggers intensified hillslope processes on decadal to centennial timescales. In both environments, the scenario of intensified present-day surface processes and rates is analogous to protracted episodes of enhanced mass removal from hillslopes via deep-seated landslides during the early Holocene and late Pleistocene. Apparently, these episodes were also associated with transient storage of voluminous conglomerates and lacustrine deposits in narrow intermontane basins. Subsequently, these deposits were incised, partly removed, and the fluvial systems adjusted themselves to the pre-depositional base levels through a readjustment and

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

College Persistence of Alaska Native Students: An Assessment of the Rural Alaska Honors Institute, 1983-88.

ERIC Educational Resources Information Center

Gaylord, Thomas A.; Kaul, Gitanjali

Despite efforts by educators, full participation by Alaska native students in the state's colleges and universities has not yet been achieved. Alaska Natives are the state's only racial group that is underrepresented in enrollments at the University of Alaska (UA). This report examines the contribution of the Rural Alaska Honors Institute (RAHI)…

The eastern larch beetle in Alaska.

Treesearch

Richard A. Werner

1986-01-01

The eastern larch beetle (Dendroctonus simplex LeConte) exists throughout the range of tamarack (Larix laricina (Du Roi) K. Koch) in interior Alaska where it has a 1-year life cycle. Beetles overwinter as adults in the bark of the trunk below snowline in infested trees. Tamarack trees that are slow growing because of repeated...

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.

Geologic framework of the Aleutian arc, Alaska

USGS Publications Warehouse

Vallier, Tracy L.; Scholl, David W.; Fisher, Michael A.; Bruns, Terry R.; Wilson, Frederic H.; von Huene, Roland E.; Stevenson, Andrew J.

1994-01-01

The Aleutian arc is the arcuate arrangement of mountain ranges and flanking submerged margins that forms the northern rim of the Pacific Basin from the Kamchatka Peninsula (Russia) eastward more than 3,000 km to Cooke Inlet (Fig. 1). It consists of two very different segments that meet near Unimak Pass: the Aleutian Ridge segment to the west and the Alaska Peninsula-the Kodiak Island segment to the east. The Aleutian Ridge segment is a massive, mostly submerged cordillera that includes both the islands and the submerged pedestal from which they protrude. The Alaska Peninsula-Kodiak Island segment is composed of the Alaska Peninsula, its adjacent islands, and their continental and insular margins. The Bering Sea margin north of the Alaska Peninsula consists mostly of a wide continental shelf, some of which is underlain by rocks correlative with those on the Alaska Peninsula.There is no pre-Eocene record in rocks of the Aleutian Ridge segment, whereas rare fragments of Paleozoic rocks and extensive outcrops of Mesozoic rocks occur on the Alaska Peninsula. Since the late Eocene, and possibly since the early Eocene, the two segments have evolved somewhat similarly. Major plutonic and volcanic episodes, however, are not synchronous. Furthermore, uplift of the Alaska Peninsula-Kodiak Island segment in late Cenozoic time was more extensive than uplift of the Aleutian Ridge segment. It is probable that tectonic regimes along the Aleutian arc varied during the Tertiary in response to such factors as the directions and rates of convergence, to bathymetry and age of the subducting Pacific Plate, and to the volume of sediment in the Aleutian Trench.The Pacific and North American lithospheric plates converge along the inner wall of the Aleutian trench at about 85 to 90 mm/yr. Convergence is nearly at right angles along the Alaska Peninsula, but because of the arcuate shape of the Aleutian Ridge relative to the location of the plates' poles of rotation, the angle of convergence

Electrifying Alaska

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reinemer, V.

Alaska's diverse systems for electric power include only 4% by private utilities. Large distances and small markets make transmission impractical for the most part. Rates are variable, although the state average is low. Energy sources, except nuclear, are abundant: half the US coal reserves are in Alaska. In addition, it has geothermal, tidal, biomass, solar, wind, and hydroelectric power. Energy construction and study programs are centered in the Alaska Power Authority and include using waste heat from village diesel generators. Hydro potential is good, but access, distances, and environmental effects must be considered. The Terror Lake, Tyee Lake, Swan Lake,more » and Susitna projects are described and transmission construction, including the 345-kW Railbelt intertie, is discussed. 1 figure.« less

Orogenic, Ophiolitic, and Abyssal Peridotites

NASA Astrophysics Data System (ADS)

Bodinier, J.-L.; Godard, M.

2003-12-01

of ophiolites (mid-ocean ridges versus supra-subduction settings - e.g., Nicolas, 1989). In addition, the mantle structures and mineralogical compositions of tectonically emplaced mantle rocks may be obscured by deformation and metamorphic recrystallization during shallow upwelling, exhumation, and tectonic emplacement. Metamorphic processes range from high-temperature recrystallization in the stability field of plagioclase peridotites ( Rampone et al., 1993) to complete serpentinization (e.g., Burkhard and O'Neill, 1988). Some garnet peridotites record even more complex evolutions. They were first buried to, at least, the stability field of garnet peridotites, and, in some cases to greater than 150 km depths ( Dobrzhinetskaya et al., 1996; Green et al., 1997; Liou, 1999). Then, they were exhumed to the surface, dragged by buoyant crustal rocks ( Brueckner and Medaris, 2000).Alternatively, several peridotite massifs are sufficiently well preserved to allow the observation of structural relationships between mantle lithologies that are larger than the sampling scale of mantle xenoliths. It is possible in these massifs to evaluate the scale of mantle heterogeneities and the relative timing of mantle processes such as vein injection, melt-rock reaction, deformation, etc… Detailed studies of orogenic and ophiolitic peridotites on centimeter- to kilometer-scale provide invaluable insights into melt transfer mechanisms, such as melt flow in lithospheric vein conduits and wall-rock reactions (Bodinier et al., 1990), melt extraction from mantle sources via channeled porous flow ( Kelemen et al., 1995) or propagation of kilometer-scale melting fronts associated with thermalerosion of lithospheric mantle ( Lenoir et al., 2001). In contrast, mantle xenoliths may be used to infer either much smaller- or much larger-scale mantle heterogeneities, such as micro-inclusions in minerals ( Schiano and Clocchiatti, 1994) or lateral variations between lithospheric provinces ( O

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

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.

Prevalence of Hypertension and Associated Risk Factors in Western Alaska Native People: The Western Alaska Tribal Collaborative for Health (WATCH) Study.

PubMed

Jolly, Stacey E; Koller, Kathryn R; Metzger, Jesse S; Day, Gretchen M; Silverman, Angela; Hopkins, Scarlett E; Austin, Melissa A; Boden-Albala, Bernadette; Ebbesson, Sven O E; Boyer, Bert B; Howard, Barbara V; Umans, Jason G

2015-10-01

Hypertension is a common chronic disease and a key risk factor in the development of cardiovascular disease. The Western Alaska Tribal Collaborative for Health study consolidates baseline data from four major cohorts residing in the Norton Sound and Yukon-Kuskokwim regions of western Alaska. This consolidated cohort affords an opportunity for a systematic analysis of high blood pressure and its correlates in a unique population with high stroke rates over a wide age range. While the prevalence of hypertension among western Alaska Native people (30%, age-standardized) is slightly less than that of the US general population (33%), cardiovascular disease is a leading cause of mortality in this rural population. The authors found that improvement is needed in hypertension awareness as about two thirds (64%) of patients reported awareness and only 39% with hypertension were controlled on medication. Future analyses assessing risk and protective factors for incident hypertension in this population are indicated. © 2015 Wiley Periodicals, Inc.

Prevalence of Hypertension and Associated Risk Factors in Western Alaska Native People: The Western Alaska Tribal Collaborative for Health (WATCH) Study

PubMed Central

Jolly, Stacey E.; Koller, Kathryn R.; Metzger, Jesse S.; Day, Gretchen M.; Silverman, Angela; Hopkins, Scarlett E.; Austin, Melissa A.; Boden-Albala, Bernadette; Ebbesson, Sven O.E.; Boyer, Bert B.; Howard, Barbara V.; Umans, Jason G.

2014-01-01

Hypertension is a common chronic disease and a key risk factor in the development of cardiovascular disease. The Western Alaska Tribal Collaborative for Health Study consolidates baseline data from four major cohorts residing in the Norton Sound and Yukon-Kuskokwim regions of western Alaska. This consolidated cohort affords an opportunity for a systematic analysis of high blood pressure and its correlates in a unique population that has high stroke rates over a wide age range. While the prevalence of hypertension among western Alaska Native people (30%, age-standardized) is slightly less than that of the U.S. general population (33%), cardiovascular disease is a leading cause of mortality in this rural population. We found that improvement is needed in hypertension awareness as about two-thirds (64%) reported awareness and only 39% with hypertension were controlled on medication. Future analyses assessing risk and protective factors for incident hypertension in this population are indicated. PMID:25644577

Signature of Cenozoic orogenic movements in combustion metamorphic rocks: mineralogy and geochronology (example of the Salair-Kuznetsk Basin transition)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Novikov, I.S.; Sokol, E.V.; Travin, A.V.

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 interpretationmore » 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.« less

Publications - GMC 193 | Alaska Division of Geological & Geophysical

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Surveys Skip to content State of Alaska myAlaska My Government Resident Business in Alaska Visiting Alaska State Employees DGGS State of Alaska search Alaska Division of Geological & Geophysical materials: Alaska State F #1, washed cuttings (13,980' - 13,990'); West Mikkelsen State #1, Canning River

Publications - GMC 327 | Alaska Division of Geological & Geophysical

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drill holes of the Coal Creek tin property of the Talkeetna Mountains D-6 Quadrangle of the Alaska Range and assays of cores from 1980, 1981, and 1982 drill holes of the Coal Creek tin property of the

Alaska's State Forests

Science.gov Websites

Conservation Education Timber Management Wildland Fire & Aviation Burn Permits Firewise Alaska Brochure (PDF) Fire Management Plans Fire Assignments Annual Fire Statistics Fire Terms Glossary Incident Business Management Grants Become an Alaska Firewise Community Community Wildland Fire Protection Plans

Orogenic inheritance and continental breakup: Wilson Cycle-control on rift and passive margin evolution

NASA Astrophysics Data System (ADS)

Schiffer, C.; Petersen, K. D.

2016-12-01

Rifts often develop along suture zones between previously collided continents, as part of the Wilson cycle. The North Atlantic is such an example, formed where Pangaea broke apart along Caledonian and Variscan sutures. Dipping upper mantle structures in E. Greenland and Scotland, have been interpreted as fossil subduction zones and the seismic signature indicates the presence of eclogite and serpentinite. We speculate that this orogenic material may impose a rheological control upon post-orogenic extension and we use thermo-mechanical modelling to explore such effects. Our model includes the following features: 1) Crustal thickness anomalies, 2) Eclogitised mafic crust emplaced in the mantle lithosphere, and 3) Hydrated mantle peridotite (serpentinite) formed in a pre-rift subduction setting. Our models indicate that the inherited structures control the location and the structural and magmatic evolution of the rift. Rifting of thin initial crust allows for relatively large amounts of serpentinite to be preserved within the uppermost mantle. This facilitates rapid continental breakup and serpentinite exhumation. Magmatism does not occur before continental breakup. Rifts in thicker crust preserve little or no serpentinite and thinning is more focused in the mantle lithosphere, rather than in the crust. Continental breakup is therefore preceded by magmatism. This implies that pre-rift orogenic properties may determine whether magma-poor or magma-rich conjugate margins are formed. Our models show that inherited orogenic eclogite and serpentinite are deformed and partially emplaced either as dipping structures within the lithospheric mantle or at the base of the thinned continental crust. The former is consistent with dipping sub-Moho reflectors often observed in passive margins. The latter provides an alternative interpretation of `lower crustal bodies' which are often regarded as igneous bodies. An additional implication of our models is that serpentinite, often

49 CFR 71.11 - Alaska zone.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 49 Transportation 1 2010-10-01 2010-10-01 false Alaska zone. 71.11 Section 71.11 Transportation Office of the Secretary of Transportation STANDARD TIME ZONE BOUNDARIES § 71.11 Alaska zone. The sixth zone, the Alaska standard time zone, includes the entire State of Alaska, except as provided in § 71.12...

The trans-Alaska pipeline controversy: Technology, conservation, and the frontier

DOE Office of Scientific and Technical Information (OSTI.GOV)

Coates, P.A.

1991-01-01

The Trans-Alaska Pipeline was the object of perhaps the most passionately fought conservation battle in the U.S. Although numerous authors documented the pipeline construction during its construction, there is, surprisingly, no previous scholarly treatment of this event written by an historian. Coates is an environmental historian who views the most interesting aspect of the controversy to be [open quote]its relationship to earlier engineering projects and technological innovations in Alaska and the debates that accompanied them.[close quotes] Thus, he describes how the conservationist and environmental ideas arose during numerous earlier major Alaskan projects and controversies, including the Alaska Highway (1938-41), Canolmore » Pipeline (1943-45), exploration of Naval Petroleum Reserve Number Four (Pet 4, 1944-1953), DEWline (1953-57), oil development in the Kenai National Moose Range (1957-58), statehood (1958), the creation of the Arctic Wildlife Refuge (1960), Project Chariot (1958-63), and Rampart Dam (1959-67). The history starts with the acquisition of Alaska in 1867 and finishes about the time of the Valdez oil spill in 1989.« less

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.

Late orogenic processes between Baltica and Siberia cratons during the building of Pangea

NASA Astrophysics Data System (ADS)

Puchkov, V.

2003-04-01

Since the Middle Carboniferous, the territory between the Baltica, Kazakhstania and Siberia plates have been part of the continental crust, the last oceanic crust having by then been subducted. At this time continent-continent collision started and proceeded until the latest epochs of the Paleozoic, forming the Uralide orogen. Two features of this collision standout: 1) The northward movement of the Kazakhstanian block between the Baltica and Siberia plates resulted in a large-scale oroclinal bend of structures in West Siberia, which is well expressed in the magnetic field, as well as in the exposed Kazakhstanian structures, and 2) The orogenic event affected the whole territory between the Baltica and Siberia cratons, including the Kazakhstanian continent. A series of intermontane molasse basins are distributed throughout the orogen and in some places, like Bolshoi Karatau, are affected by Late Paleozoic deformation. Continent-continent collision had ceased by the end of the Permian, and in many places Triassic sediments unconformably overly the orogen. Triassic sedimentary sequences are typically coarse-grained (eventually proluvial), evidencing a new stage of mountain building, though many researchers have attributed this to a superplume event. The reason being the widespread flood basalt eruptions that took place not only between, but also on the cratons under discussion. There is a point of view that the break-up of the supercontinents (e.g., Pangea and Rodinia) was preceded by such a superplume event, passing to formation of linear graben systems and then to oceanic spreading. In the case under discussion, the process was arrested (the West Siberian basin with its grabens is often called a "failed ocean"). There is reason to suspect that the Paleozoic collision that led to formation of the Uralides left an enclosed ocean basin in the North, between the Baltica and Siberia plates. Only in the Early Jurassic, with the advent of the Old Kimmerian collision did

76 FR 82114 - Amendment of VOR Federal Airways V-320 and V-440; Alaska

Federal Register 2010, 2011, 2012, 2013, 2014

2011-12-30

...-1014; Airspace Docket No. 11-AAL-19] RIN 2120-AA66 Amendment of VOR Federal Airways V-320 and V-440... amends two VHF Omnidirectional Range (VOR) Federal airways in Alaska, V-320 and V-440, due to the... proposed rulemaking to amend VOR Federal airways V-320 and V-440 in Alaska, due to the relocation of the...

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.

Sand petrology and focused erosion in collision orogens: the Brahmaputra case

NASA Astrophysics Data System (ADS)

Garzanti, Eduardo; Vezzoli, Giovanni; Andò, Sergio; France-Lanord, Christian; Singh, Sunil K.; Foster, Gavin

2004-03-01

The high-relief and tectonically active Himalayan range, characterized by markedly varying climate but relatively homogeneous geology along strike, is a unique natural laboratory in which to investigate several of the factors controlling the composition of orogenic sediments. Coupling of surface and tectonic processes is most evident in the eastern Namche Barwa syntaxis, where the Tsangpo-Siang-Brahmaputra River, draining a large elevated area in south Tibet, plunges down the deepest gorge on Earth. Here composition of river sands changes drastically from lithic to quartzofeldspathic. After confluence with the Lohit River, draining the Transhimalayan-equivalent Mishmi arc batholiths, sediment composition remains remarkably constant across Assam, indicating subordinate contributions from Himalayan tributaries. Independent calculations based on petrographical, mineralogical, and geochemical data indicate that the syntaxis, representing only ∼4% of total basin area, contributes 35±6% to the total Brahmaputra sediment flux, and ∼20% of total detritus reaching the Bay of Bengal. Such huge anomalies in erosion patterns have major effects on composition of orogenic sediments, which are recorded as far as the Bengal Fan. In the Brahmaputra basin, in spite of very fast erosion and detrital evacuation, chemical weathering is not negligible. Sand-sized carbonate grains are dissolved partially in mountain reaches and completely in monsoon-drenched Assam plains, where clinopyroxenes are selectively altered. Plagioclase, instead, is preferentially weathered only in detritus from the Shillong Plateau, which is markedly enriched in microcline. Most difficult to assess is the effect of hydraulic sorting in Bangladesh, where quartz, garnet and epidote tend to be sequestered in the bedload and trapped on the coastal plain, whereas cleavable feldspars and amphiboles are concentrated in the suspended load and eventually deposited in the deep sea. High-resolution petrographic and

Geology of the Prince William Sound and Kenai Peninsula region, Alaska

USGS Publications Warehouse

Wilson, Frederic H.; Hults, Chad P.

2012-01-01

The Prince William Sound and Kenai Peninsula region includes a significant part of one of the world’s largest accretionary complexes and a small part of the classic magmatic arc geology of the Alaska Peninsula. Physiographically, the map area ranges from the high glaciated mountains of the Alaska and Aleutian Ranges and the Chugach Mountains to the coastal lowlands of Cook Inlet and the Copper River delta. Structurally, the map area is cut by a number of major faults and postulated faults, the most important of which are the Border Ranges, Contact, and Bruin Bay Fault systems. The rocks of the map area belong to the Southern Margin composite terrane, a Tertiary and Cretaceous or older subduction-related accretionary complex, and the Alaska Peninsula terrane. Mesozoic rocks between these two terranes have been variously assigned to the Peninsular or the Hidden terranes. The oldest rocks in the map area are blocks of Paleozoic age within the mélange of the McHugh Complex; however, the protolith age of the greenschist and blueschist within the Border Ranges Fault zone is not known. Extensive glacial deposits mantle the Kenai Peninsula and the lowlands on the west side of Cook Inlet and are locally found elsewhere in the map area. This map was compiled from existing mapping, without generalization, and new or revised data was added where available.

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

Publications - RDF 2015-5 | Alaska Division of Geological & Geophysical

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Surveys Skip to content State of Alaska myAlaska My Government Resident Business in Alaska Visiting Alaska State Employees DGGS State of Alaska search Alaska Division of Geological & Geophysical Alaska's Mineral Industry Reports AKGeology.info Rare Earth Elements WebGeochem Engineering Geology Alaska

Publications - RI 2009-2 | Alaska Division of Geological & Geophysical

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Surveys Skip to content State of Alaska myAlaska My Government Resident Business in Alaska Visiting Alaska State Employees DGGS State of Alaska search Alaska Division of Geological & Geophysical Alaska's Mineral Industry Reports AKGeology.info Rare Earth Elements WebGeochem Engineering Geology Alaska

Publications - RDF 2016-3 | Alaska Division of Geological & Geophysical

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Surveys Skip to content State of Alaska myAlaska My Government Resident Business in Alaska Visiting Alaska State Employees DGGS State of Alaska search Alaska Division of Geological & Geophysical Alaska's Mineral Industry Reports AKGeology.info Rare Earth Elements WebGeochem Engineering Geology Alaska

Publications - RDF 2016-5 | Alaska Division of Geological & Geophysical

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Surveys Skip to content State of Alaska myAlaska My Government Resident Business in Alaska Visiting Alaska State Employees DGGS State of Alaska search Alaska Division of Geological & Geophysical Alaska's Mineral Industry Reports AKGeology.info Rare Earth Elements WebGeochem Engineering Geology Alaska

Publications - RDF 2014-22 | Alaska Division of Geological & Geophysical

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Surveys Skip to content State of Alaska myAlaska My Government Resident Business in Alaska Visiting Alaska State Employees DGGS State of Alaska search Alaska Division of Geological & Geophysical Alaska's Mineral Industry Reports AKGeology.info Rare Earth Elements WebGeochem Engineering Geology Alaska

Publications - RDF 2015-8 | Alaska Division of Geological & Geophysical

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from the Tonsina area, Valdez Quadrangle, Alaska: Alaska Division of Geological & Geophysical Surveys Skip to content State of Alaska myAlaska My Government Resident Business in Alaska Visiting Alaska State Employees DGGS State of Alaska search Alaska Division of Geological & Geophysical

Publications - RDF 2015-16 | Alaska Division of Geological & Geophysical

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rocks collected in 2015 in the Wrangellia mineral assessment area, Alaska: Alaska Division of Geological Surveys Skip to content State of Alaska myAlaska My Government Resident Business in Alaska Visiting Alaska State Employees DGGS State of Alaska search Alaska Division of Geological & Geophysical

Publications - RDF 2015-9 | Alaska Division of Geological & Geophysical

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samples from the Zane Hills, Hughes and Shungnak quadrangles, Alaska: Alaska Division of Geological & Surveys Skip to content State of Alaska myAlaska My Government Resident Business in Alaska Visiting Alaska State Employees DGGS State of Alaska search Alaska Division of Geological & Geophysical

Detrital zircon age and isotopic constraints on the provenance of turbidites from the southernmost part of the Beishan orogen, NW China

NASA Astrophysics Data System (ADS)

Guo, Q. Q.; Chung, S. L.; Lee, H. Y.; Xiao, W.; Hou, Q.; Li, S.

2017-12-01

The Altaids in Central and East Asia is one of the largest accretionary orogenic collages in the world. The Beishan orogen, linked the Tianshan and Xingmeng orogens, occupy a key position to trace the terminal processes of the Altaids. It comprises an assemblage of magmatic arcs and ophiolitic mélanges. The Permian clastic turbidites, situated between the Huaniushan arc and the Shibanshan arc, are the youngest reported deep-marine clasts in the Beishan orogen. They are separated into the Liuyuan turbidites (NT) to the north and the Heishankou turbidites (ST) to the south by the Liuyuan complex. Detrital zircon grains from the NT yielded a wide range, from 254-3111 Ma, with two age clusters at 273 Ma and 424 Ma, indicating they provenance from the Huaniushan arc to the north. Those from the ST yielded ages from 260-2209 Ma, with age clusters at 270 Ma, 295 Ma, 420 Ma and 878 Ma, indicating the provenance from the Shibanshan arc to the south. The youngest three grains from the NT yield a weighted mean age of 260 Ma and those from the ST an age of 255 Ma, indicating an End-Permian maximum depositional age. The Precambrian zircons of the NT have diverse ɛHf(t) values (-12.6 to +10.4), while those of the ST from -6 to -2.6, indicating distinguishing histories of their provenances. The NT have more positive ɛNd(t) values than the ST, suggesting more juvenile or less evolved crustal components in the source. Two contrasting provenances, together with data in the literature, define the latest suture in the Beishan region at 240-250 Ma. The younger peak of U-Pb analysis results of detrital zircons from the northern part of the final suture zone in the southern Altaids is younging eastward from 288 Ma to 247 Ma, which may characterize the closure of the Paleo-Asian Ocean from west to east in about 40 Ma. This identification of the latest suture in the southern Altaids provides new constraints on the Paleo-Asian Ocean - specifically the nature and timing of the end of the

Alaska geology revealed

USGS Publications Warehouse

Wilson, Frederic H.; Labay, Keith A.

2016-11-09

This map shows the generalized geology of Alaska, which helps us to understand where potential mineral deposits and energy resources might be found, define ecosystems, and ultimately, teach us about the earth history of the State. Rock units are grouped in very broad categories on the basis of age and general rock type. A much more detailed and fully referenced presentation of the geology of Alaska is available in the Geologic Map of Alaska (http://dx.doi.org/10.3133/sim3340). This product represents the simplification of thousands of individual rock units into just 39 broad groups. Even with this generalization, the sheer complexity of Alaskan geology remains evident.

Publications - PDF 96-17 | Alaska Division of Geological & Geophysical

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Surveys Skip to content State of Alaska myAlaska My Government Resident Business in Alaska the Fairbanks Mining District, Alaska, scale 1:63,360 (15.0 M) Digital Geospatial Data Digital © 2010 Webmaster State of Alaska myAlaska My Government Resident Business in Alaska Visiting Alaska State

Publications - MP 156 | Alaska Division of Geological & Geophysical Surveys

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Skip to content State of Alaska myAlaska My Government Resident Business in Alaska Visiting Alaska /29446 Publication Products Report Report Information mp156.pdf (126.0 K) Digital Geospatial Data Digital State of Alaska © 2010 Webmaster State of Alaska myAlaska My Government Resident Business in Alaska

Alaska Administrative Manual

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Search the Division of Finance site DOF State of Alaska Finance Home Content Area Accounting Charge Cards Administrative Manual Table of Contents Contains State of Alaska accounting/payroll policies and information clarifying accounting and payroll procedures. Policies are carried out through standard statewide procedures

Publications - GMC 410 | Alaska Division of Geological & Geophysical

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) Keywords Geochemistry; Rare Earth Elements Top of Page Department of Natural Resources, Division of Surveys Skip to content State of Alaska myAlaska My Government Resident Business in Alaska Visiting Alaska State Employees DGGS State of Alaska search Alaska Division of Geological & Geophysical

Publications - GMC 409 | Alaska Division of Geological & Geophysical

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) Keywords Geochemistry; Rare Earth Elements Top of Page Department of Natural Resources, Division of Surveys Skip to content State of Alaska myAlaska My Government Resident Business in Alaska Visiting Alaska State Employees DGGS State of Alaska search Alaska Division of Geological & Geophysical

Publications - GMC 183 | Alaska Division of Geological & Geophysical

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Surveys Skip to content State of Alaska myAlaska My Government Resident Business in Alaska Visiting Alaska State Employees DGGS State of Alaska search Alaska Division of Geological & Geophysical materials: AK State C #1, Bush Federal #1, Echooka Unit #1, Fin Creek Unit #1, E. De K. Leffingwell #1, Nora

Alaska Native Education: Issues in the Nineties. Alaska Native Policy Papers.

ERIC Educational Resources Information Center

Kleinfeld, Judith

This booklet identifies several crucial problems in Alaska Native education, for example: (1) Fetal Alcohol Syndrome (FAS) and Fetal Alcohol Effects (FAE) occur in Alaska Native populations at relatively high rates and can produce mental retardation, hyperactivity, attention deficits, and learning disabilities; (2) while many Native rural school…

Crustal Deformation Rates and Mountain Building In Southern Alaska

NASA Astrophysics Data System (ADS)

Sauber, J.; Pavlis, T.; King, R.

In southern Alaska the northwest directed subduction of the Pacific plate, vp=51mm/yr,isaccompaniedbyaccretionoftheYakutatterranetocontinentalAlaska (va, 33-44mm/yr). The convergence, va, has been accommodated within a deforming zone that becomes increasingly wider and topographically lower from east to west (width, 80 to 120 km; average topographic height, 2500 to 1100m, respectively, Meigs and Sauber, 2000). This systematic change is correlated with an increase in the length of the shallowly dipping segment of the downgoing plate, a divergence of ma- jor upper plate structures, and a decrease in the obliquity of the Pacific plate motion relative to interior Alaska. In the Yakataga and Yakutat segments of the Pacific-North American plate boundary zone of south central Alaska recent crustal shortening and strike-slip faulting occurs offshore in the Gulf of Alaska (1970, MW =6.7; 1987-1988, MS = 6.9, 7.6, 7.6) and onshore in the Chugach-St. Elias mountains (1979, MS = 7.2). Prior great earthquakes in the region occurred in 1899 (MW = 8.1, Yakataga; MW = 8.1, Yakutat Bay). We have used GPS observations made between 1993 and 2001 to estimate short-term deformation rates. For coastal sites the horizontal defor- mation rate and orientation range from 26 to 36 mm/yr at N30-43W and the vertical uplift rates range from 6 to 23 mm/yr. Further inland above the down-dip portion of the locked zone the rate decreases to 8-15 mm/yr and the orientation is N15-26W. Fi- nite element modeling was used to calculate deformation rates and stresses associated with a shallow locked zone ( 40 km) and with ice mass fluctuations. If the elastic strain accumulated on the locked plate interface since the two 1899 earthquakes was seismically released on a single fault, it would correspond to a M 8.0 earthquake.

Alaska Public Offices Commission, Department of Administration, State of

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Visiting Alaska State Employees State of Alaska Department of Administration Alaska Public Offices Commission Alaska Department of Administration, Alaska Public Offices Commission APOC Home Commission Filer ; AO's Contact Us Administration > Alaska Public Offices Commission Alaska Public Offices Commission

Prehistoric Alaska: The land

USGS Publications Warehouse

Wilson, Frederic H.; Weber, Florence R.; Rennick, Penny

1994-01-01

Many Alaskans know the dynamic nature of Alaska’s landscape firsthand. The 1964 earthquake, the 1989 eruption of Mount Redoubt volcano, the frequent earthquakes in the Aleutians and the ever-shifting meanders of the Yukon and Kuskokwim rivers remind them of constant changes to the land. These changes are part of the continuing story of the geologic growth and development of Alaska during hundreds of millions of years. By geologic time, Alaska has only recently come into existence and the dynamic processes that formed it continue to affect it. The landscape we see today has been shaped by glacier and stream erosion or their indirect effects, and to a lesser extent by volcanoes. Most prominently, if less obviously, Alaska has been built by slow movements of the Earth’s crust we call tectonic or mountain-building.During 5 billion years of geologic time, the Earth’s crust has repeatedly broken apart into plates. These plates have recombined, and have shifted positions relative to each other, to the Earth’s rotational axis and to the equator. Large parts of the Earth’s crust, including Alaska, have been built and destroyed by tectonic forces. Alaska is a collage of transported and locally formed fragments of crusts As erosion and deposition reshape the land surface, climatic changes, brought on partly by changing ocean and atmospheric circulation patterns, alter the location and extent of tropical, temperate and arctic environments. We need to understand the results of these processes as they acted upon Alaska to understand the formation of Alaska. Rocks can provide hints of previous environments because they contain traces of ocean floor and lost lands, bits and pieces of ancient history.

Publications - GMC 370 | Alaska Division of Geological & Geophysical

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(249.0 K) Keywords Rare Earth Elements Top of Page Department of Natural Resources, Division of Surveys Skip to content State of Alaska myAlaska My Government Resident Business in Alaska Visiting Alaska State Employees DGGS State of Alaska search Alaska Division of Geological & Geophysical

Publications - GMC 159 | Alaska Division of Geological & Geophysical

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Surveys Skip to content State of Alaska myAlaska My Government Resident Business in Alaska Visiting Alaska State Employees DGGS State of Alaska search Alaska Division of Geological & Geophysical State #1, Kuparuk Unit #1, Mikkelsen Bay State 13-09-19, Ravik State #1, Pt. Thomson Unit #2, West

From the plutonic root to the volcanic roof of a continental magmatic arc: a review of the Neoproterozoic Araçuaí orogen, southeastern Brazil

NASA Astrophysics Data System (ADS)

Gonçalves, Leonardo; Alkmim, Fernando F.; Pedrosa-Soares, Antônio; Gonçalves, Cristiane C.; Vieira, Valter

2018-01-01

The Araçuaí-West Congo orogen (AWCO) is one of the various components of the Brasiliano/Pan-African orogenic network generated during the amalgamation of West Gondwana. In the reconstructions of Gondwana, the AWCO, encompassing the Araçuaí orogen of South America and the West Congo belt of Southwestern Africa, appears as a tongue-shaped orogenic zone embraced by the São Francisco-Congo craton. Differing from the vast majority of the known orogens owing to its singular confined setting, the AWCO contains a large amount of orogenic igneous rocks emplaced in all stages of its tectonic evolution. We present new and revised information about the oldest Ediacaran granitic assemblage, the G1 Supersuite, which together with the Rio Doce Group defines the Rio Doce magmatic arc, and then we propose a new tectonic setting for the arc. Field relationships and mineralogical compositions of the G1 Supersuite allow us to characterize three lithofacies associations, Opx-bearing rocks, enclave-rich Tonalite-Granodiorite and enclave-poor Granite-Tonalite, suggesting different crustal levels are exposed in the central part of the Araçuaí orogen. The region is interpreted to represent a tilted crustal section, with deep arc roots now exposed along its western border. Chemically, these plutonic associations consist mostly of magnesian, metaluminous to slightly peraluminous, calc-alkaline to alkali-calcic and medium- to high-K acidic rocks. The dacitic and rhyolitic rocks of the Rio Doce Group are mainly magnesian, peraluminous, calcic to calc-alkaline, and medium- to high-K acidic rocks. Zircon U-Pb data constrain the crystallization of the granitoids between ca. 625 and 574 Ma, while the age of the metamorphosed volcanic rocks is around ca. 585 Ma. Thus, within errors, these rock associations likely belong to the same magmatic event and might represent the subduction-related, pre-collisional, evolution of the Araçuaí orogen. In addition, whole-rock Sm-Nd isotopic compositions

Vegetation and terrain mapping in Alaska using Landsat MSS and digital terrain data

USGS Publications Warehouse

Shasby, Mark; Carneggie, David M.

1986-01-01

During the past 5 years, the U.S. Geological Survey's (USGS) Earth Resources Observation Systems (EROS) Data Center Field Office in Anchorage, Alaska has worked cooperatively with Federal and State resource management agencies to produce land-cover and terrain maps for 245 million acres of Alaska. The need for current land-cover information in Alaska comes principally from the mandates of the Alaska National Interest Lands Conservation Act (ANILCA), December 1980, which requires major land management agencies to prepare comprehensive management plans. The land-cover mapping projects integrate digital Landsat data, terrain data, aerial photographs, and field data. The resultant land-cover and terrain maps and associated data bases are used for resource assessment, management, and planning by many Alaskan agencies including the U.S. Fish and Wildlife Service, U.S. Forest Service, Bureau of Land Management, and Alaska Department of Natural Resources. Applications addressed through use of the digital land-cover and terrain data bases range from comprehensive refuge planning to multiphased sampling procedures designed to inventory vegetation statewide. The land-cover mapping programs in Alaska demonstrate the operational utility of digital Landsat data and have resulted in a new land-cover mapping program by the USGS National Mapping Division to compile 1:250,000-scale land-cover maps in Alaska using a common statewide land-cover map legend.

LearnAlaska Portal

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Orogen-transverse tectonic window in the Eastern Himalayan fold belt: A superposed buckling model

NASA Astrophysics Data System (ADS)

Bose, Santanu; Mandal, Nibir; Acharyya, S. K.; Ghosh, Subhajit; Saha, Puspendu

2014-09-01

The Eastern Lesser Himalayan fold-thrust belt is punctuated by a row of orogen-transverse domal tectonic windows. To evaluate their origin, a variety of thrust-stack models have been proposed, assuming that the crustal shortening occurred dominantly by brittle deformations. However, the Rangit Window (RW) in the Darjeeling-Sikkim Himalaya (DSH) shows unequivocal structural imprints of ductile deformations of multiple episodes. Based on new structural maps, coupled with outcrop-scale field observations, we recognize at least four major episodes of folding in the litho-tectonic units of DSH. The last episode has produced regionally orogen-transverse upright folds (F4), the interference of which with the third-generation (F3) orogen-parallel folds has shaped the large-scale structural patterns in DSH. We propose a new genetic model for the RW, invoking the mechanics of superposed buckling in the mechanically stratified litho-tectonic systems. We substantiate this superposed buckling model with results obtained from analogue experiments. The model explains contrasting F3-F4 interferences in the Lesser Himalayan Sequence (LHS). The lower-order (terrain-scale) folds have undergone superposed buckling in Mode 1, producing large-scale domes and basins, whereas the RW occurs as a relatively higher-order dome nested in the first-order Tista Dome. The Gondwana and the Proterozoic rocks within the RW underwent superposed buckling in Modes 3 and 4, leading to Type 2 fold interferences, as evident from their structural patterns.

Large along-strike variations in the onset of Subandean exhumation: Implications for Central Andean orogenic growth

USGS Publications Warehouse

Lease, Richard O.; Ehlers, T.A.; Enkelmann, E.

2016-01-01

Plate tectonics drives mountain building in general, but the space-time pattern and style of deformation is influenced by how climate, geodynamics, and basement structure modify the orogenic wedge. Growth of the Subandean thrust belt, which lies at the boundary between the arid, high-elevation Central Andean Plateau and its humid, low-elevation eastern foreland, figures prominently into debates of orogenic wedge evolution. We integrate new apatite and zircon (U-Th)/He thermochronometer data with previously published apatite fission-track data from samples collected along four Subandean structural cross-sections in Bolivia between 15° and 20°S. We interpret cooling ages vs. structural depth to indicate the onset of Subandean exhumation and signify the forward propagation of deformation. We find that Subandean growth is diachronous south (11 ± 3 Ma) vs. north (6 ± 2 Ma) of the Bolivian orocline and that Subandean exhumation magnitudes vary by more than a factor of two. Similar north-south contrasts are present in foreland deposition, hinterland erosion, and paleoclimate; these observations both corroborate diachronous orogenic growth and illuminate potential propagation mechanisms. Of particular interest is an abrupt shift to cooler, more arid conditions in the Altiplano hinterland that is diachronous in southern Bolivia (16-13 Ma) vs. northern Bolivia (10-7 Ma) and precedes the timing of Subandean propagation in each region. Others have interpreted the paleoclimate shift to reflect either rapid surface uplift due to lithosphere removal or an abrupt change in climate dynamics once orographic threshold elevations were exceeded. These mechanisms are not mutually exclusive and both would drive forward propagation of the orogenic wedge by augmenting the hinterland backstop, either through surface uplift or spatially variable erosion. In summary, we suggest that diachronous Subandean exhumation was driven by piecemeal hinterland uplift, orography, and the outward

The antioxidant level of Alaska's wild berries: high, higher and highest.

PubMed

Dinstel, Roxie Rodgers; Cascio, Julie; Koukel, Sonja

2013-01-01

In the last few years, antioxidants have become the stars of the nutritional world. Antioxidants are important in terms of their ability to protect against oxidative cell damage that can lead to conditions, such as Alzheimer's disease, cancer and heart disease--conditions also linked with chronic inflammation. The antioxidant and anti-inflammatory effects of Alaska's wild berries may have the potential to help prevent these diseases. To discover the antioxidant levels of Alaska wild berries and the ways these antioxidant levels translate when preservation methods are applied to the berry. This research centred on both the raw berries and products made from the berries. In the first year, a variety of wild berries were tested to discover their oxygen radical absorption capacity (ORAC) in the raw berries. The second level of the research project processed 4 different berries--blueberries, lingonberries, salmonberries, highbush cranberries--into 8 or 9 products made from these berries. The products were tested for both ORAC as well as specific antioxidants. The Alaska wild berries collected and tested in the first experiment ranged from 3 to 5 times higher in ORAC value than cultivated berries from the lower 48 states. For instance, cultivated blueberries have an ORAC scale of 30. Alaska wild dwarf blueberries measure 85. This is also higher than lower 48 wild blueberries, which had a score of 61. All of the Alaskan berries tested have a level of antioxidant considered nutritionally valuable, ranging from 19 for watermelon berries to 206 for lingonberries on the ORAC scale. With the processed products made from 4 Alaska wild berries, one of the unexpected outcomes of the research was that the berries continued to have levels of antioxidants considered high, despite the effects of commonly used heat-processing techniques. When berries were dehydrated, per gram ORAC values increased. Alaska wild berries have extraordinarily high antioxidant levels. Though cooking

Publications - MP 142 | Alaska Division of Geological & Geophysical Surveys

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Skip to content State of Alaska myAlaska My Government Resident Business in Alaska Visiting Alaska State Employees DGGS State of Alaska search Alaska Division of Geological & Geophysical Surveys Home Industry Reports AKGeology.info Rare Earth Elements WebGeochem Engineering Geology Alaska Tidal Datum

Publications - SR 70 | Alaska Division of Geological & Geophysical Surveys

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Publications - MP 38 | Alaska Division of Geological & Geophysical Surveys

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Skip to content State of Alaska myAlaska My Government Resident Business in Alaska Visiting Alaska State Employees DGGS State of Alaska search Alaska Division of Geological & Geophysical Surveys Home Industry Reports AKGeology.info Rare Earth Elements WebGeochem Engineering Geology Alaska Tidal Datum

Publications - SR 45 | Alaska Division of Geological & Geophysical Surveys

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Publications - MP 43 | Alaska Division of Geological & Geophysical Surveys

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Publications - MP 149 | Alaska Division of Geological & Geophysical Surveys

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Presentations - Wypych, Alicja and others, 2015 | Alaska Division of

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Geological & Geophysical Surveys Skip to content State of Alaska myAlaska My Government Resident Business in Alaska Visiting Alaska State Employees DGGS State of Alaska search Alaska Division of (AVO) Mineral Resources Alaska's Mineral Industry Reports AKGeology.info Rare Earth Elements WebGeochem

Sections | Alaska Division of Geological & Geophysical Surveys

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Publications - RDF 2015-7 | Alaska Division of Geological & Geophysical

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, Geochemical reanalysis of historical U.S. Geological Survey sediment samples from the northeastern Alaska Surveys Skip to content State of Alaska myAlaska My Government Resident Business in Alaska Visiting Alaska State Employees DGGS State of Alaska search Alaska Division of Geological & Geophysical

Presentations - Twelker, Evan and others, 2014 | Alaska Division of

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magmatic Ni-Cu-Co-PGE system in the Talkeetna Mountains, central Alaska (poster): Society of Economic Geological & Geophysical Surveys Skip to content State of Alaska myAlaska My Government Resident Business in Alaska Visiting Alaska State Employees DGGS State of Alaska search Alaska Division of

76 FR 81247 - Fisheries of the Exclusive Economic Zone Off Alaska; Groundfish of the Gulf of Alaska; Amendment 88

Federal Register 2010, 2011, 2012, 2013, 2014

2011-12-27

... Atmospheric Administration 50 CFR Part 679 Fisheries of the Exclusive Economic Zone Off Alaska; Groundfish of... Exclusive Economic Zone Off Alaska; Groundfish of the Gulf of Alaska; Amendment 88 AGENCY: National Marine... conservation, management, safety, and economic gains realized under the Central Gulf of Alaska Rockfish Pilot...

78 FR 11988 - Migratory Bird Subsistence Harvest in Alaska; Harvest Regulations for Migratory Birds in Alaska...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-02-21

...-management process involving the Service, the Alaska Department of Fish and Game, and Alaska Native... developed under a co-management process involving the Service, the Alaska Department of Fish and Game, and... Fish and Game's request to expand the Fairbanks North Star Borough excluded area to include the Central...

Wood and fish residuals composting in Alaska

Treesearch

David Nicholls; Thomas Richard; Jesse A. Micales

2002-01-01

The unique climates and industrial mix in southeast and south central Alaska are challenges being met by the region's organics recyclers. OMPOSTING wood residuals in Alaska has become increasingly important in recent years as wood processors and other industrial waste managers search for environmentally sound and profitable outlets. Traditionally, Alaska?s...

Dental caries in rural Alaska Native children--Alaska, 2008.

PubMed

2011-09-23

In April 2008, the Arctic Investigations Program (AIP) of CDC was informed by the Alaska Department of Health and Social Services (DHSS) of a large number of Alaska Native (AN) children living in a remote region of Alaska who required full mouth dental rehabilitations (FMDRs), including extractions and/or restorations of multiple carious teeth performed under general anesthesia. In this remote region, approximately 400 FMDRs were performed in AN children aged <6 years in 2007; the region has approximately 600 births per year. Dental caries can cause pain, which can affect children's normal growth and development. AIP and Alaska DHSS conducted an investigation of dental caries and associated risk factors among children in the remote region. A convenience sample of children aged 4-15 years in five villages (two with fluoridated water and three without) was examined to estimate dental caries prevalence and severity. Risk factor information was obtained by interviewing parents. Among children aged 4-5 years and 12-15 years who were evaluated, 87% and 91%, respectively, had dental caries, compared with 35% and 51% of U.S. children in those age groups. Among children from the Alaska villages, those aged 4-5 years had a mean of 7.3 dental caries, and those aged 12-15 years had a mean of 5.0, compared with 1.6 and 1.8 dental caries in same-aged U.S. children. Of the multiple factors assessed, lack of water fluoridation and soda pop consumption were significantly associated with dental caries severity. Collaborations between tribal, state, and federal agencies to provide effective preventive interventions, such as water fluoridation of villages with suitable water systems and provision of fluoride varnishes, should be encouraged.

Environmental Restoration of Diesel-Range Organics from Project Chariot, Cape Thompson, Alaska

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kautsky, Mark; Hutton, Rick; Miller, Judy

The Chariot site is located in the Ogotoruk Valley in the Cape Thompson region of northwest Alaska. Project Chariot was part of the Plowshare Program, created in 1957 by the US Atomic Energy Commission (AEC), a predecessor agency of the US Department of Energy (DOE), to study peaceful uses for atomic energy. Project Chariot began in 1958 when a scientific field team chose Cape Thompson as a potential site to excavate a harbor using a series of nuclear explosions. AEC, with assistance from other agencies, conducted more than 40 pretest bioenvironmental studies of the Cape Thompson area between 1959 andmore » 1962; however, the Plowshare Program work at the Project Chariot site (Figure 1) was cancelled because of strong public opposition [1]. No nuclear explosions were ever conducted at the site.« less

Publications - GMC 53C | Alaska Division of Geological & Geophysical

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Alaska's Mineral Industry Reports AKGeology.info Rare Earth Elements WebGeochem Engineering Geology Alaska Paleozoic through Tertiary sandstones, North Slope, Alaska Authors: Alaska Research Associates Publication through Tertiary sandstones, North Slope, Alaska: Alaska Division of Geological & Geophysical Surveys

Geometry, kinematics and tectonic models of the Kazakhstan Orocline, Central Asian Orogenic Belt

NASA Astrophysics Data System (ADS)

Li, Pengfei; Sun, Min; Rosenbaum, Gideon; Yuan, Chao; Safonova, Inna; Cai, Keda; Jiang, Yingde; Zhang, Yunying

2018-03-01

The Central Asian Orogenic Belt (CAOB) is one of the largest accretionary orogens on Earth and is characterized by the occurrence of tight oroclines (Kazakhstan and Tuva-Mongolian oroclines). The origin of these large-scale orogenic curvatures is not quite understood, but is fundamentally important for understanding crustal growth and tectonic evolution of the CAOB. Here we provide an outline of available geological and paleomagnetic data around the Kazakhstan Orocline, with an aim of clarifying the geometry, kinematics and geodynamic origin of the orocline. The Kazakhstan Orocline is evident in a total magmatic image, and can be traced by the continuation of high magnetic anomalies associated with the Devonian Volcanic Belt and the Late Devonian to Carboniferous Balkhash-Yili arc. Paleomagnetic data show ∼112-126° clockwise rotation of the northern limb relative to the southern limb in the Late Devonian to Early Carboniferous, as well as ∼15-28° clockwise rotation of the northern limb and ∼39-40° anticlockwise rotation of the southern limb relative to the hinge of the orocline during the Late Carboniferous to Permian. We argue that the Kazakhstan Orocline experienced two-stage bending with the early stage of bending (Late Devonian to Early Carboniferous; ∼112-126°) driven by slab rollback, and the later stage (Late Carboniferous to Permian; 54-68°) possibly associated with the amalgamation of the Siberian, Tarim and Baltic cratons. This new tectonic model is compatible with the occurrence of rift basins, the spatial migration of magmatic arc, and the development of large-scale strike-slip fault systems during oroclinal bending.

Linkages Between Critical Wedges and Crustal Channels Using 2-D Coupled Thermomechanical Finite Element Models: Implications for Himalayan Orogenic Evolution

NASA Astrophysics Data System (ADS)

Sparks, S. A.; Thigpen, J. R.

2017-12-01

In continental tectonics, questions remain regarding the dominant mechanisms of shortening accommodation during orogen evolution. Two quantitatively-supported models, critical wedge and channel flow, have been applied to the Himalaya and proposed for other large collisional systems. These two models represent fundamentally distinct mechanisms for accommodating shortening in collisional systems and until recently have been viewed as mutually exclusive. While there remains support for these mechanisms being incompatible end-members, in more recent studies it has been proposed that either: (1) both geodynamic mechanisms may operate simultaneously yet in spatially distinct parts of the larger composite orogenic system or (2) both mechanisms are present yet they operate at temporally distinct intervals, wherein the orogen progressively develops through stages dominated by mid-crustal channel flow followed by shallow thrust stacking and duplex development. In both scenarios, the mechanism active at each stage in orogen evolution is presumably dependent upon local to regional scale rheological conditions (as a function of orogen dynamic and thermal evolution) that are likely to be transient in both space and time. However, questions regarding the dynamic, mechanical, and thermal-kinematic relationships of such a system remain. Also, while field observations and deformation records derived from analyses of transects within the Himalaya can be interpreted in such a way to be consistent with a unified model, numerical models that predict the behavior of interactions between the end-member models have - until now - not existed. Here, we present results from 2-D coupled thermomechanical finite-element numerical experiments that examine the necessary conditions for mechanical compatibility between the channel and critical wedge by focusing on the role of rheology. These model results will eventually allow us to make preliminary comparisons between model-derived stress

Geomorphic Consequences of Volcanic Eruptions in Alaska: A Review

USGS Publications Warehouse

Waythomas, Christopher F.

2015-01-01

Eruptions of Alaska volcanoes have significant and sometimes profound geomorphic consequences on surrounding landscapes and ecosystems. The effects of eruptions on the landscape can range from complete burial of surface vegetation and preexisting topography to subtle, short-term perturbations of geomorphic and ecological systems. In some cases, an eruption will allow for new landscapes to form in response to the accumulation and erosion of recently deposited volcaniclastic material. In other cases, the geomorphic response to a major eruptive event may set in motion a series of landscape changes that could take centuries to millennia to be realized. The effects of volcanic eruptions on the landscape and how these effects influence surface processes has not been a specific focus of most studies concerned with the physical volcanology of Alaska volcanoes. Thus, what is needed is a review of eruptive activity in Alaska in the context of how this activity influences the geomorphology of affected areas. To illustrate the relationship between geomorphology and volcanic activity in Alaska, several eruptions and their geomorphic impacts will be reviewed. These eruptions include the 1912 Novarupta–Katmai eruption, the 1989–1990 and 2009 eruptions of Redoubt volcano, the 2008 eruption of Kasatochi volcano, and the recent historical eruptions of Pavlof volcano. The geomorphic consequences of eruptive activity associated with these eruptions are described, and where possible, information about surface processes, rates of landscape change, and the temporal and spatial scale of impacts are discussed.A common feature of volcanoes in Alaska is their extensive cover of glacier ice, seasonal snow, or both. As a result, the generation of meltwater and a variety of sediment–water mass flows, including debris-flow lahars, hyperconcentrated-flow lahars, and sediment-laden water floods, are typical outcomes of most types of eruptive activity. Occasionally, such flows can be quite

Geomorphic consequences of volcanic eruptions in Alaska: A review

USGS Publications Warehouse

Waythomas, Christopher F.

2015-01-01

Eruptions of Alaska volcanoes have significant and sometimes profound geomorphic consequences on surrounding landscapes and ecosystems. The effects of eruptions on the landscape can range from complete burial of surface vegetation and preexisting topography to subtle, short-term perturbations of geomorphic and ecological systems. In some cases, an eruption will allow for new landscapes to form in response to the accumulation and erosion of recently deposited volcaniclastic material. In other cases, the geomorphic response to a major eruptive event may set in motion a series of landscape changes that could take centuries to millennia to be realized. The effects of volcanic eruptions on the landscape and how these effects influence surface processes has not been a specific focus of most studies concerned with the physical volcanology of Alaska volcanoes. Thus, what is needed is a review of eruptive activity in Alaska in the context of how this activity influences the geomorphology of affected areas. To illustrate the relationship between geomorphology and volcanic activity in Alaska, several eruptions and their geomorphic impacts will be reviewed. These eruptions include the 1912 Novarupta–Katmai eruption, the 1989–1990 and 2009 eruptions of Redoubt volcano, the 2008 eruption of Kasatochi volcano, and the recent historical eruptions of Pavlof volcano. The geomorphic consequences of eruptive activity associated with these eruptions are described, and where possible, information about surface processes, rates of landscape change, and the temporal and spatial scale of impacts are discussed.A common feature of volcanoes in Alaska is their extensive cover of glacier ice, seasonal snow, or both. As a result, the generation of meltwater and a variety of sediment–water mass flows, including debris-flow lahars, hyperconcentrated-flow lahars, and sediment-laden water floods, are typical outcomes of most types of eruptive activity. Occasionally, such flows can be quite

Publications - MP 150 | Alaska Division of Geological & Geophysical Surveys

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Skip to content State of Alaska myAlaska My Government Resident Business in Alaska Visiting Alaska larger work. Please see DDS 3 for more information. Digital Geospatial Data Digital Geospatial Data Business in Alaska Visiting Alaska State Employees

Publications - RI 2011-4 | Alaska Division of Geological & Geophysical

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Surveys Skip to content State of Alaska myAlaska My Government Resident Business in Alaska district, Circle Quadrangle, Alaska, scale 1:50,000 (16.0 M) Digital Geospatial Data Digital Geospatial Business in Alaska Visiting Alaska State Employees

The pre-orogenic detrital zircon record of the Variscan orogeny: Preliminary results

NASA Astrophysics Data System (ADS)

Stephan, Tobias; Kroner, Uwe

2017-04-01

To test plate-tectonic constellations in consideration of the long-term development of sedimentary transport paths, temporally and spatially highly resolved records of provenance analysis are mandatory. The interpretation of existing studies focus on small-scale areas within an orogen thereby neglecting the differing distribution of provenance data in the entire orogenic system. This study reviews a large data set of compiled geochronological data to document the development of pre-orogenic tectonic units on the example of the Variscan orogeny. Constrained by tectonic and geological models, the temporal distribution of U-Pb detrital zircon ages, used as a proxy for sedimentary provenance, shows that some minima and maxima of zircon abundance are nearly synchronous for thousands of kilometres along the orogeny. Age spectra of Precambrian to Lower Palaeozoic samples were constructed on the basis of 38729 U-Pb ages from 685 samples that were compiled from 102 publications. The age compilation combines thermal ionization mass spectrometry (TIMS), laser ablation-inductively coupled plasma-mass spectrometer (LA-ICP-MS), sensitive high-resolution ion microprobe (SHRIMP), and secondary ion mass spectrometry (SIMS) analyses. The data was re-processed using a common age calculation and concordance filter to ensure comparability. The concordance of each zircon grain was calculated from 206Pb/238U and 207Pb/235U ages to guarantee that only concordant grains, i.e., with <10% normal and <5% reverse discordance, were included in the age compilation. In order to ignore a metamorphic overprint and hence a blur of the younger age spectra, the compilation is constrained to age data older than 400 Ma only. If a precise sample age is not documented by the author, the weighted-mean age of the youngest zircon population (n > 3) is used for the maximum age of deposition. In addition to the location of >600 samples, the precise depositional ages result in a spatially and temporally high

Carbonatitic metasomatism in orogenic dunites from Lijiatun in the Sulu UHP terrane, eastern China

NASA Astrophysics Data System (ADS)

Su, Bin; Chen, Yi; Guo, Shun; Chu, Zhu-Yin; Liu, Jing-Bo; Gao, Yi-Jie

2016-10-01

Among orogenic peridotites, dunites suffer the weakest crustal metasomatism at the slab-mantle interface and are the best lithology to trace the origins of orogenic peridotites and their initial geodynamic processes. Petrological and geochemical investigations of the Lijiatun dunites from the Sulu ultrahigh-pressure (UHP) terrane indicate a complex petrogenetic history involving melt extraction and multistage metasomatism (carbonatitic melt and slab-derived fluid). The Lijiatun dunites consist mainly of olivine (Fo = 92.0-92.6, Ca = 42-115 ppm), porphyroblastic orthopyroxene (En = 91.8-92.8), Cr-spinel (Cr# = 50.4-73.0, TiO2 < 0.2 wt.%) and serpentine. They are characterized by refractory bulk-rock compositions with high MgO (45.31-47.07 wt.%) and Mg# (91.5-91.9), and low Al2O3 (0.48-0.70 wt.%), CaO (0.25-0.44 wt.%) and TiO2 (< 0.03 wt.%) contents. Whole-rock platinum group elements (PGE) are similar to those of cratonic mantle peridotites and Re-Os isotopic data suggest that dunites formed in the early Proterozoic ( 2.2 Ga). These data indicate that the Lijiatun dunites were the residues of 30% partial melting and were derived from the subcontinental lithospheric mantle (SCLM) beneath the North China craton (NCC). Subsequent carbonatitic metasomatism is characterized by the formation of olivine-rich (Fo = 91.6-92.6, Ca = 233-311 ppm), clinopyroxene-bearing (Mg# = 95.9-96.7, Ti/Eu = 104-838) veins cutting orthopyroxene porphyroblasts. Based on the occurrence of dolomite, mass-balance calculation and thermodynamic modeling, carbonatitic metasomatism had occurred within the shallow SCLM (low-P and high-T conditions) before dunites were incorporated into the continental subduction channel. These dunites then suffered weak metasomatism by slab-derived fluids, forming pargasitic amphibole after pyroxene. This work indicates that modification of the SCLM beneath the eastern margin of the NCC had already taken place before the Triassic continental subduction. Orogenic

New Orogenic Model for Taiwan Collision Zone Inferred From Three-dimensional P- and S-wave Velocity Structures and Seismicity

NASA Astrophysics Data System (ADS)

Nagai, S.; Hirata, N.; Sato, H.

2008-12-01

The island of Taiwan is located in the site of ongoing arc-continent collision zone between the Philippine Sea Plate (PSP) and the Eurasian Plate (EUP). Numerous geophysical and geological studies are done in and around Taiwan to develop various models to explain the tectonic processes in the Taiwan region. However, their details have not been known enough, especially under the Central Range. We suggest a new orogenic model for Taiwan orogeny, named 'Upper Crustal Stacking Model', inferred from our tomographic images using three temporary seismic networks with the Central Weather Bureau Seismic Network. These three temporary networks are the aftershock observation after the 1999 Chi-Chi Taiwan earthquake and two dense array observations across central and southern Taiwan, respectively. Tomographic images by the double-difference tomography [Zhang and Thurber, 2003] show a lateral alternate variation of high- and low-velocity, which are well correlated to surface geology and separated by east-dipping boundaries. These images have reliable high-resolution by dense arrays to be able to discuss this alternate variation. We found three high-velocity zones (> 6.0km/s). The westernmost zone corresponds to the subducting EUP. Other two zones are located beneath the Hsuehshan Range and the Eastern Central Range with trends of eastward dipping, respectively. And, we could image low-velocity zone located beneath Backbone Range between the two high-velocity zones clearly. We interpret that these east-dipping high- and low-velocity zones can be divided into two layered blocks and the subducting EUP, each of which consists of a high-velocity body under low-velocity one. Layered blocks can be interpreted as stacked thrust sheets between the subducting EUP and the Northern Luzon Arc, a part of PSP. These thrust sheets are parts of upper- and mid-crust detached from the subducting EUP. The model of continental subduction followed by buoyancy-driven exhumation can explain the

The United States Geological Survey in Alaska: Accomplishments during 1984

USGS Publications Warehouse

Bartsch-Winkler, Susan B.

1985-01-01

This circular contains short reports about many of the geologic studies carried out in Alaska by the U.S. Geological Survey and cooperating agencies during 1984. The topics cover a wide range in scientific and economic interest.

Publications - AR 2010 | Alaska Division of Geological & Geophysical

Science.gov Websites

Visiting Alaska State Employees DGGS State of Alaska search Alaska Division of Geological & Geophysical DGGS AR 2010 Publication Details Title: Alaska Division of Geological & Geophysical Surveys Annual Report Authors: DGGS Staff Publication Date: Jan 2011 Publisher: Alaska Division of Geological &

Alaska Geochemical Database - Mineral Exploration Tool for the 21st Century - PDF of presentation

USGS Publications Warehouse

Granitto, Matthew; Schmidt, Jeanine M.; Labay, Keith A.; Shew, Nora B.; Gamble, Bruce M.

2012-01-01

The U.S. Geological Survey has created a geochemical database of geologic material samples collected in Alaska. This database is readily accessible to anyone with access to the Internet. Designed as a tool for mineral or environmental assessment, land management, or mineral exploration, the initial version of the Alaska Geochemical Database - U.S. Geological Survey Data Series 637 - contains geochemical, geologic, and geospatial data for 264,158 samples collected from 1962-2009: 108,909 rock samples; 92,701 sediment samples; 48,209 heavy-mineral-concentrate samples; 6,869 soil samples; and 7,470 mineral samples. In addition, the Alaska Geochemical Database contains mineralogic data for 18,138 nonmagnetic-fraction heavy mineral concentrates, making it the first U.S. Geological Survey database of this scope that contains both geochemical and mineralogic data. Examples from the Alaska Range will illustrate potential uses of the Alaska Geochemical Database in mineral exploration. Data from the Alaska Geochemical Database have been extensively checked for accuracy of sample media description, sample site location, and analytical method using U.S. Geological Survey sample-submittal archives and U.S. Geological Survey publications (plus field notebooks and sample site compilation base maps from the Alaska Technical Data Unit in Anchorage, Alaska). The database is also the repository for nearly all previously released U.S. Geological Survey Alaska geochemical datasets. Although the Alaska Geochemical Database is a fully relational database in Microsoft® Access 2003 and 2010 formats, these same data are also provided as a series of spreadsheet files in Microsoft® Excel 2003 and 2010 formats, and as ASCII text files. A DVD version of the Alaska Geochemical Database was released in October 2011, as U.S. Geological Survey Data Series 637, and data downloads are available at http://pubs.usgs.gov/ds/637/. Also, all Alaska Geochemical Database data have been incorporated into

Alaska State Legislature

Science.gov Websites

The Alaska State Legislature search menu Home Senate Current Members Past Members By Session search Home Get Started About the Legislative Branch Legislative Branch The Legislative Branch is responsible for enacting the laws of the State of Alaska and appropriating the money necessary to operate the

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

Alaska Workforce Investment Board

Science.gov Websites

! Looking for a job? Click here. About Us Board Member Documents Phone: (907) 269-7485 Toll Free: (888) 412 : 907-269-7485 Toll Free: 888-412-4742 Fax: 907-269-7489 State of Alaska myAlaska My Government Resident

The evolving Alaska mapping program.

USGS Publications Warehouse

Brooks, P.D.; O'Brien, T. J.

1986-01-01

This paper describes the development of mapping in Alaska, the current status of the National Mapping Program, and future plans for expanding and improving the mapping coverage. Research projects with Landsat Multispectral Scanner and Return Vidicon imagery and real- and synthetic-aperture radar; image mapping programs; digital mapping; remote sensing projects; the Alaska National Interest Lands Conservation Act; and the Alaska High-Altitude Aerial Photography Program are also discussed.-from Authors

Publications - GMC 16 | Alaska Division of Geological & Geophysical Surveys

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Skip to content State of Alaska myAlaska My Government Resident Business in Alaska Visiting Alaska Geologic Data Index (AGDI) Volcanology Alaska Volcano Observatory (AVO) Mineral Resources Alaska's Mineral and Facilities Staff Seismic and Well Data Data Reports Contact Us Frequently Asked Questions Ask a

Publications - RDF 2010-2 | Alaska Division of Geological & Geophysical

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Prospect; Trace Elements; Trace Metals; Triassic; Wrangellia Terrane; geoscientificInformation Top of Page Surveys Skip to content State of Alaska myAlaska My Government Resident Business in Alaska Visiting Alaska State Employees DGGS State of Alaska search Alaska Division of Geological & Geophysical

Publications - RDF 2015-6 | Alaska Division of Geological & Geophysical

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Sediments; Trace Elements; Trace Geochemical; Trace Metals; geoscientificInformation Top of Page Department Surveys Skip to content State of Alaska myAlaska My Government Resident Business in Alaska Visiting Alaska State Employees DGGS State of Alaska search Alaska Division of Geological & Geophysical

Alaska Natives assessing the health of their environment.

PubMed

Garza, D

2001-11-01

The changes in Alaska's ecosystems caused by pollution, contaminants and global climate change are negatively impacting Alaska Natives and rural residents who rely on natural resources for food, culture and community identity. While Alaska commerce has contributed little to these global changes and impacts, Alaska and its resources are nonetheless affected by the changes. While Alaska Natives have historically relied on Alaska's land, water and animals for survival and cultural identity, today their faith in the safety and quality of these resources has decreased. Alaska Natives no longer believe that these wild resources are the best and many are turning to alternative store-bought foods. Such a change in diet and activity may be contributing to a decline in traditional activities and a decline in general health. Contaminants are showing up in the animals, fish and waters that Alaska Natives use. Efforts need to be expanded to empower Alaska Native Tribes to collect and analyze local wild foods for various contaminants. In addition existing information on contaminants and pollution should be made readily available to Alaska residents. Armed with this type of information Alaska Native residents will be better prepared to make informed decisions on using wild foods and materials.

Publications - GMC 171 | Alaska Division of Geological & Geophysical

Science.gov Websites

Arco Alaska Inc. Delta State #2 well Authors: Pawlewicz, Mark Publication Date: 1990 Publisher: Alaska , Vitrinite reflectance data of cuttings (3270'-10760') from the Arco Alaska Inc. Delta State #2 well: Alaska

Publications - RDF 2012-3 | Alaska Division of Geological & Geophysical

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Assessment Project; Trace Elements; geoscientificInformation Top of Page Department of Natural Resources Surveys Skip to content State of Alaska myAlaska My Government Resident Business in Alaska Visiting Alaska State Employees DGGS State of Alaska search Alaska Division of Geological & Geophysical

Publications - RDF 2005-4 | Alaska Division of Geological & Geophysical

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District; Trace Elements; Trace Metals; Tungsten; Uranium; Vanadium; Yttrium; Zinc; Zirconium Top of Page Surveys Skip to content State of Alaska myAlaska My Government Resident Business in Alaska Visiting Alaska State Employees DGGS State of Alaska search Alaska Division of Geological & Geophysical

Publications - RDF 2016-2 | Alaska Division of Geological & Geophysical

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, Major-oxide and trace-element geochemistry of mafic rocks in the Carboniferous Lisburne Group, Ivishak Surveys Skip to content State of Alaska myAlaska My Government Resident Business in Alaska Visiting Alaska State Employees DGGS State of Alaska search Alaska Division of Geological & Geophysical

Publications - RDF 2000-4 | Alaska Division of Geological & Geophysical

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Oxides; Palladium; Platinum; Rare Earth Elements; STATEMAP Project; Trace Metals Top of Page Department Surveys Skip to content State of Alaska myAlaska My Government Resident Business in Alaska Visiting Alaska State Employees DGGS State of Alaska search Alaska Division of Geological & Geophysical

The Ross Orogen and Lachlan Fold Belt in Marie Byrd Land, Northern Victoria Land and New Zealand: implication for the tectonic setting of the Lachlan Fold Belt in Antarctica

USGS Publications Warehouse

Bradshaw, J.D.

2007-01-01

Correlation of the Cambrian Delamerian Orogen of Australia and Ross Orogen of the Transantarctic Mountains widely accepted but the extension of the adjacent Lachlan Orogen into Antarctica is controversial. Outside the main Ross-Delamerian belt, evidence of this orogeny is preserved at Mt Murphy in Marie Byrd Land and the in Takaka Terrane of New Zealand. In all pre-break- configurations of the SW Pacific, these two areas are far removed from the Ross-Delamerian belt. Evidence from conglomerates in the Takaka Terrane, however, shows that in Late Cambrian times it was adjacent to the Ross Orogen. This indicates major tectonic displacements within Gondwana after the Cambrian and before break-up. The Lachlan Orogen formed in an extensional belt in a supra-subduction zone setting and the Cambrian rocks of Marie Byrd Land and New Zealand are interpreted as parts of a rifted continental ribbon on the outboard side of the Lachlan belt.

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…

Influence of forest canopy and snow on microclimate in a declining yellow-cedar forest of southeast Alaska

Treesearch

Paul E. Hennon; David V. D' Amore; Dustin T. Witter; Melinda B. Lamb

2010-01-01

Site factors predispose yellow-cedar (Chamaecyparis nootkatensis D. Don (Spach)) to a widespread climate-induced mortality in southeast Alaska. We investigated the influence of canopy cover and snow on microclimate at two small watersheds across a range of declining yellow-cedar stands on Baranof and Chichagof Islands in southeast Alaska. Two...

The evolution of a Gondwanan collisional orogen: A structural and geochronological appraisal from the Southern Granulite Terrane, South India

NASA Astrophysics Data System (ADS)

Plavsa, Diana; Collins, Alan S.; Foden, John D.; Clark, Chris

2015-05-01

Gondwana amalgamated along a suite of Himalayan-scale collisional orogens, the roots of which lace the continents of Africa, South America, and Antarctica. The Southern Granulite Terrane of India is a generally well-exposed, exhumed, Gondwana-forming orogen that preserves a record of the tectonic evolution of the eastern margin of the East African Orogen during the Ediacaran-Cambrian (circa 600-500 Ma) as central Gondwana formed. The deformation associated with the closure of the Mozambique Ocean and collision of the Indian and East African/Madagascan cratonic domains is believed to have taken place along the southern margin of the Salem Block (the Palghat-Cauvery Shear System, PCSS) in the Southern Granulite Terrane. Investigation of the structural fabrics and the geochronology of the high-grade shear zones within the PCSS system shows that the Moyar-Salem-Attur shear zone to the north of the PCSS system is early Paleoproterozoic in age and associated with dextral strike-slip motion, while the Cauvery shear zone (CSZ) to the south of the PCSS system can be loosely constrained to circa 740-550 Ma and is associated with dip-slip dextral transpression and north side-up motion. To the south of the proposed suture zone (the Cauvery shear zone), the structural fabrics of the Northern Madurai Block suggest four deformational events (D1-D4), some of which are likely to be contemporaneous. The timing of high pressure-ultrahigh temperature metamorphism and deformation (D1-D3) in the Madurai Block (here interpreted as the southern extension of Azania) is constrained to circa 550-500 Ma and interpreted as representing collisional orogeny and subsequent orogenic collapse of the eastern margin of the East African Orogen. The disparity in the nature of the structural fabrics and the timing of the deformation in the Salem and the Madurai Blocks suggest that the two experienced distinct tectonothermal events prior to their amalgamation along the Cauvery shear zone during the

Alaska Native Participation in the Civilian Conservation Corps. Alaska Historical Commission Studies in History No. 206.

ERIC Educational Resources Information Center

Sorensen, Connor; And Others

The report is a finding aid to the sources which document the 1937 federal policy decision mandating that 50% of the enrollees in the Civilian Conservation Corps (CCC) in Alaska must be Alaska Natives and provides a list of the Native CCC projects in Alaska. The finding aid section is organized according to the location of the collections and…

Rayleigh Wave Phase Velocities in Alaska from Ambient Noise Tomography

NASA Astrophysics Data System (ADS)

Pepin, K. S.; Li, A.; Yao, Y.

2016-12-01

We have analyzed ambient noise data recorded at 136 broadband stations from the USArray Transportable Array and other permanent seismic networks in Alaska and westernmost Canada. Daily cross-correlations are obtained using vertical component seismograms and are stacked to form a single trace for each station pair. Rayleigh wave signals are extracted from the stacked traces and are used to calculate phase velocities in the Alaska region. Preliminary phase velocity maps show similar trends to those from previous studies, but also yield new anomalies given the wider geographical range provided by the Transportable Array. At short periods (6-12s), a high velocity anomaly is observed directly northeast of the Fairweather-Queen Charlotte fault, and a high velocity trend appears in the eastern Yukon terrane between the Denali and Tintina fault, probably reflecting mafic igneous crustal rocks. Significantly slow anomalies are present at the Prince William Sound, Cook Inlet, and the basins in southwestern and central Alaska, indicating sediment effects. The slow anomalies gradually shift to southeastern and south-central Alaska with increasing period (up to 40s), corresponding to the Wrangell volcano belt and the volcano arc near Cook Inlet. A broad high-velocity zone is also observed in central Alaska to the north of the Denali fault at long periods (30-40s). The Yakutat terrane is characterized as a high-velocity anomaly from period 14s to 25s but not imaged at longer periods due to poor resolution.

78 FR 4435 - BLM Director's Response to the Alaska Governor's Appeal of the BLM Alaska State Director's...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-01-22

... Bureau of Land Management (BLM) is publishing this notice to explain why the BLM Director is rejecting... Director's Response to the Alaska Governor's Appeal of the BLM Alaska State Director's Governor's... the BLM Alaska State Director. The State Director determined the Governor's Finding was outside the...

Publications - SR 37 | Alaska Division of Geological & Geophysical Surveys

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Skip to content State of Alaska myAlaska My Government Resident Business in Alaska Visiting Alaska Section; Resource Assessment; Tyonek Formation; Type Section Top of Page Department of Natural Resources State Employees DGGS State of Alaska search Alaska Division of Geological & Geophysical Surveys Home

Presentations - Twelker, Evan and others, 2014 | Alaska Division of

Science.gov Websites

Resident Business in Alaska Visiting Alaska State Employees DGGS State of Alaska search Alaska Division of Details Title: Preliminary results from 2014 geologic mapping in the Talkeetna Mountains, Alaska Lande, Lauren, 2014, Preliminary results from 2014 geologic mapping in the Talkeetna Mountains, Alaska

Publications - RDF 2004-2 | Alaska Division of Geological & Geophysical

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; Trace Elements; Trace Metals; Tungsten; Vanadium; Yttrium; Zinc; Zirconium Top of Page Department of Surveys Skip to content State of Alaska myAlaska My Government Resident Business in Alaska Visiting Alaska State Employees DGGS State of Alaska search Alaska Division of Geological & Geophysical

Publications - SR 32 | Alaska Division of Geological & Geophysical Surveys

Science.gov Websites

DGGS SR 32 Publication Details Title: Oil and gas basins map of Alaska Authors: Ehm, Arlen Publication ): Alaska Statewide Bibliographic Reference Ehm, Arlen, 1983, Oil and gas basins map of Alaska: Alaska Sheets Sheet 1 Oil and gas basins map of Alaska, scale 1:2,500,000 (21.0 M) Keywords Alaska Statewide

Modes of orogen-parallel stretching and extensional exhumation in response to microplate indentation and roll-back subduction (Tauern Window, Eastern Alps)

NASA Astrophysics Data System (ADS)

Scharf, A.; Handy, M. R.; Favaro, S.; Schmid, S. M.; Bertrand, A.

2013-09-01

The Tauern Window exposes a Paleogene nappe stack consisting of highly metamorphosed oceanic (Alpine Tethys) and continental (distal European margin) thrust sheets. In the eastern part of this window, this nappe stack (Eastern Tauern Subdome, ETD) is bounded by a Neogene system of shear (the Katschberg Shear Zone System, KSZS) that accommodated orogen-parallel stretching, orogen-normal shortening, and exhumation with respect to the structurally overlying Austroalpine units (Adriatic margin). The KSZS comprises a ≤5-km-thick belt of retrograde mylonite, the central segment of which is a southeast-dipping, low-angle extensional shear zone with a brittle overprint (Katschberg Normal Fault, KNF). At the northern and southern ends of this central segment, the KSZS loses its brittle overprint and swings around both corners of the ETD to become subvertical, dextral, and sinistral strike-slip faults. The latter represent stretching faults whose displacements decrease westward to near zero. The kinematic continuity of top-east to top-southeast ductile shearing along the central, low-angle extensional part of the KSZS with strike-slip shearing along its steep ends, combined with maximum tectonic omission of nappes of the ETD in the footwall of the KNF, indicates that north-south shortening, orogen-parallel stretching, and normal faulting were coeval. Stratigraphic and radiometric ages constrain exhumation of the folded nappe complex in the footwall of the KSZS to have begun at 23-21 Ma, leading to rapid cooling between 21 and 16 Ma. This exhumation involved a combination of tectonic unroofing by extensional shearing, upright folding, and erosional denudation. The contribution of tectonic unroofing is greatest along the central segment of the KSZS and decreases westward to the central part of the Tauern Window. The KSZS formed in response to the indentation of wedge-shaped blocks of semi-rigid Austroalpine basement located in front of the South-Alpine indenter that was part

Detrital zircon geochronology of the Adams Argillite and Nation River Formation, east-central Alaska, U.S.A

USGS Publications Warehouse

Gehrels, G.E.; Johnsson, M.J.; Howell, D.G.

1999-01-01

The Cambrian Adams Argillite and the Devonian Nation River Formation are two sandstone-bearing units within a remarkably complete Paleozoic stratigraphic section in east-central Alaska. These strata, now foreshortened and fault-bounded, were originally contiguous with miogeoclinal strata to the east that formed as a passive-margin sequence along the northwestern margin of the North American continent. Seventy-five detrital zircon grains from the Adams Argillite and the Nation River Formation were analyzed in an effort to provide constraints on the original sources of the grains, and to generate a detrital zircon reference for miogeoclinal strata in the northern Cordillera. Thirty-five single zircon grains from a quartzite in the Adams Argillite yield dominant age clusters of 1047-1094 (n = 6), 1801-1868 (n = 10), and 2564-2687 (n = 5) Ma. Forty zircons extracted from a sandstone in the Nation River Formation yield clusters primarily of 424-434 (n = 6), 1815-1838 (n = 6), 1874-1921 (n = 7), and 2653-2771 (n = 4) Ma. The Early Proterozoic and Archean grains in both units probably originated in basement rocks in a broad region of the Canadian Shield. In contrast, the original igneous sources for mid-Protcrozoic grains in the Adams Argillite and ??? 430 Ma grains in the Nation River Formation are more difficult to identify. Possible original sources for the mid-Proterozoic grains include: (1) the Grenville Province of eastern Laurentia, (2) the Pearya terrane along the Arctic margin, and (3) mid-Proterozoic igneous rocks that may have been widespread along or outboard of the Cordilleran margin. The ??? 430 Ma grains may have originated in: (1) arc-type sources along the Cordilleran margin, (2) the Caledonian orogen, or (3) a landmass, such as Pearya, Siberia, or crustal fragments now in northern Asia, that resided outboard of the Innuitian orogen during mid-Paleozoic time. Copyright ?? 1999, SEPM (Society for Sedimentary Geology).

Climate change and health effects in Northwest Alaska.

PubMed

Brubaker, Michael; Berner, James; Chavan, Raj; Warren, John

2011-01-01

This article provides examples of adverse health effects, including weather-related injury, food insecurity, mental health issues, and water infrastructure damage, and the responses to these effects that are currently being applied in two Northwest Alaska communities. In Northwest Alaska, warming is resulting in a broad range of unusual weather and environmental conditions, including delayed freeze-up, earlier breakup, storm surge, coastal erosion, and thawing permafrost. These are just some of the climate impacts that are driving concerns about weather-related injury, the spread of disease, mental health issues, infrastructure damage, and food and water security. Local leaders are challenged to identify appropriate adaptation strategies to address climate impacts and related health effects. IMPLEMENTATION PROCESS: The tribal health system is combining local observations, traditional knowledge, and western science to perform community-specific climate change health impact assessments. Local leaders are applying this information to develop adaptation responses. The Alaska Native Tribal Health Consortium will describe relationships between climate impacts and health effects and provide examples of community-scaled adaptation actions currently being applied in Northwest Alaska. Climate change is increasing vulnerability to injury, disease, mental stress, food insecurity, and water insecurity. Northwest communities are applying adaptation approaches that are both specific and appropriate. The health impact assessment process is effective in raising awareness, encouraging discussion, engaging partners, and implementing adaptation planning. With community-specific information, local leaders are applying health protective adaptation measures.

Climate change and health effects in Northwest Alaska

PubMed Central

Brubaker, Michael; Berner, James; Chavan, Raj; Warren, John

2011-01-01

This article provides examples of adverse health effects, including weather-related injury, food insecurity, mental health issues, and water infrastructure damage, and the responses to these effects that are currently being applied in two Northwest Alaska communities. Background In Northwest Alaska, warming is resulting in a broad range of unusual weather and environmental conditions, including delayed freeze-up, earlier breakup, storm surge, coastal erosion, and thawing permafrost. These are just some of the climate impacts that are driving concerns about weather-related injury, the spread of disease, mental health issues, infrastructure damage, and food and water security. Local leaders are challenged to identify appropriate adaptation strategies to address climate impacts and related health effects. Implementation process The tribal health system is combining local observations, traditional knowledge, and western science to perform community-specific climate change health impact assessments. Local leaders are applying this information to develop adaptation responses. Objective The Alaska Native Tribal Health Consortium will describe relationships between climate impacts and health effects and provide examples of community-scaled adaptation actions currently being applied in Northwest Alaska. Findings Climate change is increasing vulnerability to injury, disease, mental stress, food insecurity, and water insecurity. Northwest communities are applying adaptation approaches that are both specific and appropriate. Conclusion The health impact assessment process is effective in raising awareness, encouraging discussion, engaging partners, and implementing adaptation planning. With community-specific information, local leaders are applying health protective adaptation measures. PMID:22022304

Publications - GMC 395 | Alaska Division of Geological & Geophysical

Science.gov Websites

investigations of the diatom stratigraphy of Borehole TA8, Portage Alaska: Alaska Division of Geological & Visiting Alaska State Employees DGGS State of Alaska search Alaska Division of Geological & Geophysical DGGS GMC 395 Publication Details Title: Preliminary investigations of the diatom stratigraphy of

76 FR 45217 - Fisheries of the Exclusive Economic Zone Off Alaska; Central Gulf of Alaska Rockfish Program...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-07-28

..., management, safety, and economic gains realized under the Rockfish Pilot Program and viability of the Gulf of...-BA97 Fisheries of the Exclusive Economic Zone Off Alaska; Central Gulf of Alaska Rockfish Program... available for public review and comment. The groundfish fisheries in the exclusive economic zone of Alaska...

Review: groundwater in Alaska (USA)

USGS Publications Warehouse

Callegary, J.B.; Kikuchi, C.P.; Koch, Joshua 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.

Alaska Department of Labor and Workforce Development

Science.gov Websites

Market Information Alaska Job Centers Hot Topics Get Paid to Learn a Trade! Apprenticeship Alaska Career USAJOBS - Federal Gov. Jobs Apprenticeship Alaska Career Information System Veterans' Services Youth

Tourism in rural Alaska

Treesearch

Katrina Church-Chmielowski

2007-01-01

Tourism in rural Alaska is an education curriculum with worldwide relevance. Students have started small businesses, obtained employment in the tourism industry and gotten in touch with their people. The Developing Alaska Rural Tourism collaborative project has resulted in student scholarships, workshops on website development, marketing, small...

76 FR 270 - Alaska: Adequacy of Alaska Municipal Solid Waste Landfill Permit Program

Federal Register 2010, 2011, 2012, 2013, 2014

2011-01-04

...] Alaska: Adequacy of Alaska Municipal Solid Waste Landfill Permit Program AGENCY: Environmental Protection... approved Municipal Solid Waste Landfill (MSWLF) permit program. The approved modification allows the State..., EPA issued a final rule (69 FR 13242) amending the Municipal Solid Waste Landfill (MSWLF) criteria in...

Origin of unusual HREE-Mo-rich carbonatites in the Qinling orogen, China

NASA Astrophysics Data System (ADS)

Song, Wenlei; Xu, Cheng; Smith, Martin P.; Kynicky, Jindrich; Huang, Kangjun; Wei, Chunwan; Zhou, Li; Shu, Qihai

2016-11-01

Carbonatites, usually occurring within intra-continental rift-related settings, have strong light rare earth element (LREE) enrichment; they rarely contain economic heavy REE (HREE). Here, we report the identification of Late Triassic HREE-Mo-rich carbonatites in the northernmost Qinling orogen. The rocks contain abundant primary HREE minerals and molybdenite. Calcite-hosted fluid inclusions, inferred to represent a magmatic-derived aqueous fluid phase, contain significant concentrations of Mo (~17 ppm), reinforcing the inference that these carbonatitic magmas had high Mo concentrations. By contrast, Late Triassic carbonatites in southernmost Qinling have economic LREE concentrations, but are depleted in HREE and Mo. Both of these carbonatite types have low δ26Mg values (-1.89 to -1.07‰), similar to sedimentary carbonates, suggesting a recycled sediment contribution for REE enrichment in their mantle sources. We propose that the carbonatites in the Qinling orogen were formed, at least in part, by the melting of a subducted carbonate-bearing slab, and that 10 Ma younger carbonatite magmas in the northernmost Qinling metasomatized the thickened eclogitic lower crust to produce high levels of HREE and Mo.

Origin of unusual HREE-Mo-rich carbonatites in the Qinling orogen, China

PubMed Central

Song, Wenlei; Xu, Cheng; Smith, Martin P.; Kynicky, Jindrich; Huang, Kangjun; Wei, Chunwan; Zhou, Li; Shu, Qihai

2016-01-01

Carbonatites, usually occurring within intra-continental rift-related settings, have strong light rare earth element (LREE) enrichment; they rarely contain economic heavy REE (HREE). Here, we report the identification of Late Triassic HREE-Mo-rich carbonatites in the northernmost Qinling orogen. The rocks contain abundant primary HREE minerals and molybdenite. Calcite-hosted fluid inclusions, inferred to represent a magmatic-derived aqueous fluid phase, contain significant concentrations of Mo (~17 ppm), reinforcing the inference that these carbonatitic magmas had high Mo concentrations. By contrast, Late Triassic carbonatites in southernmost Qinling have economic LREE concentrations, but are depleted in HREE and Mo. Both of these carbonatite types have low δ26Mg values (−1.89 to −1.07‰), similar to sedimentary carbonates, suggesting a recycled sediment contribution for REE enrichment in their mantle sources. We propose that the carbonatites in the Qinling orogen were formed, at least in part, by the melting of a subducted carbonate-bearing slab, and that 10 Ma younger carbonatite magmas in the northernmost Qinling metasomatized the thickened eclogitic lower crust to produce high levels of HREE and Mo. PMID:27857170

Origin of unusual HREE-Mo-rich carbonatites in the Qinling orogen, China.

PubMed

Song, Wenlei; Xu, Cheng; Smith, Martin P; Kynicky, Jindrich; Huang, Kangjun; Wei, Chunwan; Zhou, Li; Shu, Qihai

2016-11-18

Carbonatites, usually occurring within intra-continental rift-related settings, have strong light rare earth element (LREE) enrichment; they rarely contain economic heavy REE (HREE). Here, we report the identification of Late Triassic HREE-Mo-rich carbonatites in the northernmost Qinling orogen. The rocks contain abundant primary HREE minerals and molybdenite. Calcite-hosted fluid inclusions, inferred to represent a magmatic-derived aqueous fluid phase, contain significant concentrations of Mo (~17 ppm), reinforcing the inference that these carbonatitic magmas had high Mo concentrations. By contrast, Late Triassic carbonatites in southernmost Qinling have economic LREE concentrations, but are depleted in HREE and Mo. Both of these carbonatite types have low δ 26 Mg values (-1.89 to -1.07‰), similar to sedimentary carbonates, suggesting a recycled sediment contribution for REE enrichment in their mantle sources. We propose that the carbonatites in the Qinling orogen were formed, at least in part, by the melting of a subducted carbonate-bearing slab, and that 10 Ma younger carbonatite magmas in the northernmost Qinling metasomatized the thickened eclogitic lower crust to produce high levels of HREE and Mo.

Presentations - Twelker, Evan and Lande, Lauren, 2015 | Alaska Division of

Science.gov Websites

Geological & Geophysical Surveys Skip to content State of Alaska myAlaska My Government Resident Business in Alaska Visiting Alaska State Employees DGGS State of Alaska search Alaska Division of (AVO) Mineral Resources Alaska's Mineral Industry Reports AKGeology.info Rare Earth Elements WebGeochem

Geochemical and Sm-Nd isotope-geochemical patterns of metavolcanic rocks, diabase, and metagabbroids on the northeastern flank of the South Mongolian-Khingan orogenic belt

NASA Astrophysics Data System (ADS)

Smirnov, Yu. V.; Sorokin, A. A.

2017-05-01

The first results of geochemical and Sm-Nd isotope-geochemical studies of metavolcanic rocks, metagabbroids, and diabase of the Nora-Sukhotino terrane, the least studied part of the South Mongolian-Khingan orogenic belt in the system of the Central Asian orogenic belt are reported. It is established that the basic rocks composing this terrane include varieties comparable with E-MORB, tholeiitic, and calc-alkaline basalt of island arc, calc-alkaline gabbro-diabase, and gabbroids of island arcs. Most likely, these formations should be correlated with metabasalt and associated Late Ordovician gabbro-amphibolite of the Sukdulkin "block" of the South Mongolian-Khingan orogenic belt, which are similar to tholeiite of intraplate island arcs by their geochemical characteristics.

IMPROVING SCIENCE EDUCATION AND CAREER OPPORTUNITIES IN RURAL ALASKA:The Synergistic Connection between Educational Outreach Efforts in the Copper Valley, Alaska.

NASA Astrophysics Data System (ADS)

Solie, D. J.; McCarthy, S.

2004-12-01

The objective of the High frequency Active Auroral Research Program (HAARP) Education Outreach is to enhance the science education opportunities in the Copper Valley region in Alaska. In the process, we also educate local residents about HAARP and its research. Funded jointly by US Air Force and Navy, HAARP is located at Gakona Alaska, a very rural region of central Alaska with a predominantly Native population. The main instrument at HAARP is a vertically directed, phased array RF transmitter which is primarily an ionospheric research tool, however, its geophysical research applications range from terrestrial to near-space. Research is conducted at HAARP in collaboration with scientists and institutions world-wide. The HAARP Education Outreach Program, run through the University of Alaska Geophysical Institute has been active for over six years and in that time has become an integral part of science education in the Copper Valley for residents of all ages. HAARP education outreach efforts are through direct involvement in local schools in the Copper River School District (CRSD) and the Prince William Sound Community College (PWSCC), as well as public lectures and workshops, and intern and student research programs. These outreach efforts require cooperation and coordination between the CRSD, PWSCC, the University of Alaska Fairbanks Physics Department and the NSF sponsored Alaska Native Science & Engineering Program (ANSEP) and HAARP researchers. The HAARP Outreach program also works with other organizations promoting science education in the region, such as the National Park Service (Wrangell- St. Elias National Park) and the Wrangell Institute for Science and Environment (WISE) a newly formed regional non-profit organization. We work closely with teachers in the schools, adapting to their needs and the particular scientific topic they are covering at the time. Because of time and logistic constraints, outreach visits to schools are episodic, occurring roughly

Looking at the roots of the highest mountains: the lithospheric structure of the Himalaya-Tibet and the Zagros orogens. Results from a geophysical-petrological study

NASA Astrophysics Data System (ADS)

Tunini, L.; Jimenez-Munt, I.; Fernandez, M.; Villasenor, A.; Afonso, J. C.; Verges, J.

2013-12-01

The Himalaya-Tibet and Zagros orogens are the two most prominent mountain belts built by continental collision. They are part of a huge belt of Cenozoic age which runs from the Pyrenees to Burma. In its central sector, the collision with the southern margin of the Eurasian plate has resulted not only in the building of mountain ranges over the north-eastern edges of the Arabian and Indian plates but also in widespread deformation 1000-3000 km from the suture zones. Zagros and Himalaya-Tibet orogens share many geodynamic processes but at different rates, amount of convergence and stage of development. The study of their present-day structures provides new insights into their quasi coeval collisional event pointing out differences and similarities in the mountain building processes. We present 2D crust and upper mantle cross-sections down to 400 km depth, along four SW-NE trending profiles. Two profiles cross the Zagros Mountains, running from the Mesopotamian Foreland Basin up to the Alborz and Central Iran. Two other profiles run through the Himalaya-Tibetan orogen: the western transect crosses the western Himalaya, Tarim Basin, Tian Shan Mountains and Junggar Basin; the eastern transect runs from the Indian shield to the Beishan Basin, crossing the eastern Himalaya, Tibetan Plateau, Qaidam Basin and Qilian Mountains. We apply the LitMod-2D code which integrates potential fields (gravity and geoid), isostasy (elevation) and thermal (heat flow and temperature distribution) equations, and mantle petrology. The resulting crust and upper mantle structure is constrained by available data on elevation, Bouguer anomaly, geoid height, surface heat flow and seismic data including P- and S-wave tomography models. Our results show distinct deformation patterns between the crust and the lithospheric mantle beneath the Zagros and Himalaya-Tibetan orogens, indicating a strong strain partitioning in both areas. At crustal level, we found a thickening beneath the Zagros and the

Ice Surface Morphology and Flow on Malaspina Glacier, Alaska: Implications for Regional Tectonics in the Saint Elias Orogen

NASA Technical Reports Server (NTRS)

Cotton, Michelle M.; Bruhn, Ronald L.; Sauber, Jeanne; Burgess, Evan; Forster, Richard R.

2014-01-01

The Saint Elias Mountains in southern Alaska are located at a structural syntaxis where the coastal thrust and fold belt of the Fairweather plate boundary intersects thrust faults and folds generated by collision of the Yakutat Terrane. The axial trace of this syntaxis extends southeastward out of the Saint Elias Mountains and beneath Malaspina Glacier where it is hidden from view and cannot be mapped using conventional methods. Here we examine the surface morphology and flow patterns of Malaspina Glacier to infer characteristics of the bedrock topography and organization of the syntaxis. Faults and folds beneath the eastern part of the glacier trend northwest and reflect dextral transpression near the terminus of the Fairweather fault system. Those beneath the western part of the glacier trend northeast and accommodate folding and thrust faulting during collision and accretion of the Yakutat Terrane. Mapping the location and geometry of the structural syntaxis provides important constraints on spatial variations in seismicity, fault kinematics, and crustal shortening beneath Malaspina Glacier, as well as the position of the collisional deformation front within the Yakutat Terrane. We also speculate that the geometrical complexity of intersecting faults within the syntaxis formed a barrier to rupture propagation during two regional Mw 8.1earthquakes in September 1899.

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…

Ediacaran 2,500-km-long synchronous deep continental subduction in the West Gondwana Orogen

NASA Astrophysics Data System (ADS)

Ganade de Araujo, Carlos E.; Rubatto, Daniela; Hermann, Joerg; Cordani, Umberto G.; Caby, Renaud; Basei, Miguel A. S.

2014-10-01

The deeply eroded West Gondwana Orogen is a major continental collision zone that exposes numerous occurrences of deeply subducted rocks, such as eclogites. The position of these eclogites marks the suture zone between colliding cratons, and the age of metamorphism constrains the transition from subduction-dominated tectonics to continental collision and mountain building. Here we investigate the metamorphic conditions and age of high-pressure and ultrahigh-pressure eclogites from Mali, Togo and NE-Brazil and demonstrate that continental subduction occurred within 20 million years over at least a 2,500-km-long section of the orogen during the Ediacaran. We consider this to be the earliest evidence of large-scale deep-continental subduction and consequent appearance of Himalayan-scale mountains in the geological record. The rise and subsequent erosion of such mountains in the Late Ediacaran is perfectly timed to deliver sediments and nutrients that are thought to have been necessary for the subsequent evolution of sustainable life on Earth.

Movements of juvenile Gyrfalcons from western and interior Alaska following departure from their natal areas

USGS Publications Warehouse

McIntyre, Carol L.; Douglas, David C.; Adams, Layne G.

2009-01-01

Juvenile raptors often travel thousands of kilometers from the time they leave their natal areas to the time they enter a breeding population. Documenting movements and identifying areas used by raptors before they enter a breeding population is important for understanding the factors that influence their survival. In North America, juvenile Gyrfalcons (Falco rusticolus) are routinely observed outside the species' breeding range during the nonbreeding season, but the natal origins of these birds are rarely known. We used satellite telemetry to track the movements of juvenile Gyrfalcons during their first months of independence. We instrumented nestlings with lightweight satellite transmitters within 10 d of estimated fledging dates on the Seward Peninsula in western Alaska and in Denali National Park (Denali) in interior Alaska. Gyrfalcons spent an average of 41.4 ± 6.1 d (range  =  30–50 d) in their natal areas after fledging. The mean departure date from natal areas was 27 August ± 6.4 d. We tracked 15 individuals for an average of 70.5 ± 28.1 d post-departure; Gyrfalcons moved from 105 to 4299 km during this period and tended to move greater distances earlier in the tracking period than later in the tracking period. Gyrfalcons did not establish temporary winter ranges within the tracking period. We identified several movement patterns among Gyrfalcons, including unidirectional long-distance movements, multidirectional long- and short-distance movements, and shorter movements within a local region. Gyrfalcons from the Seward Peninsula remained in western Alaska or flew to eastern Russia with no movements into interior Alaska. In contrast, Gyrfalcons from Denali remained in interior Alaska, flew to northern and western Alaska, or flew to northern Alberta. Gyrfalcons from both study areas tended to move to coastal, riparian, and wetland areas during autumn and early winter. Because juvenile Gyrfalcons dispersed over a large geographic area and across three

Relationship Between Earthquake b-Values and Crustal Stresses in a Young Orogenic Belt

NASA Astrophysics Data System (ADS)

Wu, Yih-Min; Chen, Sean Kuanhsiang; Huang, Ting-Chung; Huang, Hsin-Hua; Chao, Wei-An; Koulakov, Ivan

2018-02-01

It has been reported that earthquake b-values decrease linearly with the differential stresses in the continental crust and subduction zones. Here we report a regression-derived relation between earthquake b-values and crustal stresses using the Anderson fault parameter (Aϕ) in a young orogenic belt of Taiwan. This regression relation is well established by using a large and complete earthquake catalog for Taiwan. The data set consists of b-values and Aϕ values derived from relocated earthquakes and focal mechanisms, respectively. Our results show that b-values decrease linearly with the Aϕ values at crustal depths with a high correlation coefficient of -0.9. Thus, b-values could be used as stress indicators for orogenic belts. However, the state of stress is relatively well correlated with the surface geological setting with respect to earthquake b-values in Taiwan. Temporal variations in the b-value could constitute one of the main reasons for the spatial heterogeneity of b-values. We therefore suggest that b-values could be highly sensitive to temporal stress variations.

76 FR 303 - Alaska: Adequacy of Alaska's Municipal Solid Waste Landfill Permit Program

Federal Register 2010, 2011, 2012, 2013, 2014

2011-01-04