tertiary extensional faulting and evolving ductile brittle transition zones in the northern snake range and vicinity new insights from seismic data new geologic mapping and high resolution seismic data from east central nevada shed light on the evolution of the northern snake range decollement nsrd and its relation to the present basins and ranges we suggest that the nsrd originated in oligocene time as a flat 20 km wide 7 km deep zone of decoupling between localized ductile stretching below and more widely distributed high angle normal faulting above younger east dipping normal faults cut the western part of the nsrd forming the tilted fault blocks and highly asymmetric grabens that constitute the duck creek range duck creek valley and schell creek range spring valley and folded the nsrd to its present antiformal geometry these youngest faults flatten into pervasive subhorizontal reflectors at a depth of 10 to 15 km that we interpret as the youngest ductile brittle transition

mesozoic tectonics and metamorphism in the pequop mountains and wood hills region northeast nevada implications for the architecture and evolution of the sevier orogen discussion and reply the pequop mountains wood hills east humboldt range region northeast nevada exposes a nearly continuous cross section of precambrian to mesozoic strata representing middle to upper crustal levels of the mesozoic hinterland of the sevier orogen these rocks preserve the transition from unmetamorphosed mesozoic upper crust to partially melted middle crust integration of new structural metamorphic and u pb thermochronologic data from the wood hills and pequop mountains coupled with a regional tectonic reconstruction reveals substantial cretaceous metamorphism contraction and extension in the sevier hinterland in northeast nevada we report two phases of contraction not previously recognized that are accommodated by top to the southeast thrust faults the windermere and independence thrusts contraction was succeeded by two phases of extension along west rooted normal faults the late cretaceous pequop fault and tertiary mary9s river fault system the earliest phase of thrust faulting resulted in as much as 30 km of crustal thickening and an estimated minimum of 69 km of shortening along an inferred fault called the windermere thrust the timing of this thrusting event is bracketed between late jurassic ca 153 ma and late cretaceous 84 ma relaxation of crustal isotherms following and perhaps during thrusting resulted in barrovian style metamorphism of footwall rocks and partial melting of metapelite at deep levels peak metamorphism was attained ca 84 ma and by this time hinterland crustal thickening had reached a maximum during 84 75 ma another minor pulse of shortening and thickening along the independence thrust was followed by partial exhumation of the metamorphic rocks and as much as 10 km of crustal thinning along the pequop fault thus the interval from 84 to 75 ma in northeast nevada marks a fundamental and apparently permanent change from horizontal contraction to extension in the upper to middle crust in the hinterland final exhumation of the metamorphic rocks was accomplished by the tertiary mary9s river fault system our data indicate that much of the metamorphism and some of the contraction in the sevier hinterland in northeast nevada which was previously thought to be largely late jurassic is actually cretaceous in age furthermore the data indicate that widespread metamorphism of the middle crust is a byproduct of tectonic burial and that hinterland and foreland thrust faulting were coeval suggesting that thrust faults in the sevier orogen do not form a simple foreland younging sequence

incremental 40ar 39ar thermochronology of mylonitic rocks from the northern snake range nevada a 40ar 39ar thermochronologic study of muscovite biotite and potassium feldspar from footwall rocks of the northern snake range decollement nevada was undertaken in order to constrain the timing and temperatures of mylonitic deformation during extension and the subsequent cooling uplift history of these mylonitic rocks mylonitic deformation has been bracketed between 37 ma and about 24 ma and minimum temperatures during ductile thinning were about 300 c mineral cooling ages along the east flank of the range suggest a minimum tmax gradient of about 55 c ma this steep thermal gradient is the result of a localized heat source and or shearing of colder rocks with older cooling histories over hotter rocks with younger cooling histories although mylonitic deformation may have spanned a 13 m y period 37 ma to 24 ma deformation was not synchronous throughout the range on the west flank of the range age spectra from muscovite and microcline samples indicate that rocks were at temperatures well below 325 c and deformation had ceased by 30 ma while on the east flank of the range lower plate rocks were at temperatures above 325 c and ductile deformation was still ongoing this is also reflected in chrontours of published k ar muscovite ages along with 40ar 39ar ages which monotonically decrease in age from west to east these data provide evidence for a temperature difference across the range within the same structural horizon from about 30 to 24 ma these relations suggest a lateral thermal gradient the east flank of the range cooling more slowly than the west flank alternatively the data suggest either an eastward dip of lower plate units prior to the onset of tertiary mylonitic deformation or that layering dipped eastward due to deformation in an east dipping top to the east shear zone both cases result in differential cooling of lower plate units as they pass through a series of subhorizontal isotherms the 40ar 39ar data along with published finite strain structural and quartz petrofabric data provide constraints on the formation and geometric evolution of metamorphic core complex detachment faults

ocean forcing of the greenland ice sheet calving fronts and patterns of retreat identified by automatic satellite monitoring of eastern outlet glaciers 1 we have developed an automatic method to identify changes in the position of calving glacier margins using daily modis imagery application of the method to 32 ocean terminating glaciers in east greenland produced 26 802 margin positions for a 10 year long period 2000 2009 we report these high resolution data and show that the glaciers exhibit seasonal cycles with magnitudes of advance and retreat proportional to glacier width despite similar seasonality there is a distinct difference between the interannual trends of calving front positions north and south of 69 n all glaciers above this latitude showed very limited or no change when seasonality was excluded while glaciers south of 69 n retreated significantly between 2001 and 2005 2 3 km on average approximately 26 of the retreat of southern glaciers was regained by readvance from 2005 to 2009 to explain the latitudinal boundary of glacier dynamics we review basic climatic factors including summer and winter atmospheric forcing sea ice conditions and ocean temperature we conclude that the southern retreats were strongly influenced by warm oceanic conditions associated with increased transport of subtropical waters to the irminger sea and to fjords and coastal regions south of 69 n northern glaciers remained stable despite significant increase in runoff in this region because fjords at latitudes higher than 69 n are less exposed to subtropical waters the southern retreats illustrate sensitive behavior of calving glaciers and we hypothesize that the calving fronts retreated because they were exposed to rapid ice front melting

cenozoic tectonism in the central basin and range magnitude rate and distribution of upper crustal strain a wealth of pre cenozoic geologic markers across the central basin and range province defined mainly by thrust faults developed within a miogeoclinal wedge makes it one of the best areas on earth to reconstruct large scale continental extension we use this 100 000 km 2 region bounded by the southern sierra nevada on the west and the colorado plateau on the east to illustrate the concepts of correlation and misalignment for regional strain markers and of strain compatibility and kinematic viability in palinspastic reconstructions the results indicate 250 to 300 km of west northwest motion of the sierra away from the plateau accommodated by both crustal thinning and north south shortening tertiary intermontane basin deposits and mineral cooling ages of deeply exhumed rocks constrain the overall kinematics of motion most of the westward motion occurred between 16 and 5 ma at rates near 2 cm yr slowing to 1 to 1 5 cm yr in the last 5 ma we have quantified the partitioning of strain between vertical crustal thinning via normal faults and map view plane strain via conjugate strike slip faults by placing a grid of 10 x 10 km elements on a retrodeformed map of the region and measuring the increase in area of grid elements between the undeformed and present day grids this analysis yields a maximum finite elongation of the basin and range at 36 n to 37 n of 3 4 oriented n73 w map view area balance shows that 20 percent of this elongation is compensated by north south shortening and 80 percent by crustal thinning this yields an average thinning factor for the upper crust of 2 7 between the sierra and plateau inconsistent with the hypothesis that neogene deformation in the central basin and range is predominantly dextral shear plane strain these results in concert with the observation that the southern sierra nevada has similar crustal thickness to the central basin and range support the hypothesis of large scale eastward flow of sierran deep crust during extension

turbulent structure in unsteady depth varying open channel flows turbulence measurements over a smooth wall in unsteady depth varying open channel flows were conducted by the simultaneous use of a two component laser doppler anemometer lda and a water wave gauge in the present study velocity measurements in the viscous sublayer of highly unsteady flow have been first conducted to evaluate the friction velocity independently of the log law the von karman constant was calculated using this friction velocity it was proven then that the value of was really a constant of 0 41 even in unsteady open channel flows next statistical structures of mean velocity and turbulence characteristics were investigated across the whole flow from the near wall region up to the free surface in particular turbulence measurements near the depth varying water surface zone of flood flow were conducted successfully for the first time with the lda such measurements have been impossible with conventional velocity instruments such as hot film anemometers mean velocity profiles and turbulence characteristics were revealed in both the rising and the falling stages of the flood period

rapid eocene extension in the robinson district white pine county nevada constraints from 40ar 39ar dating precise 40ar 39ar ages on pretectonic syntectonic and posttectonic rhyolites from the robinson mining district which is within a highly extended domain in east central nevada indicate that extreme extension 400 occurred in fewer than 900 k y during the eocene the duration of extension is tightly delimited by an eocene lacustrine unit that was horizontal prior to extension and by younger rhyolitic units the rhyolites represent at least five eruptive episodes including the preextensional and synextensional rhyolite of white hill emplaced between 37 6 and 37 4 ma and the postextensional rhyolite of garnet hill emplaced at 36 7 ma although some of it is perhaps as old as 37 1 ma thus the duration of extreme extension at robinson was between 0 9 and 0 3 m y comparable to or shorter than other highly extended areas in western north america the extensional domain in east central nevada is a composite feature produced by localized episodic rapid extension that began in early eocene time and continued to at least middle miocene time

profile of a paleo orogen high topography across the present day basin and range from 40 to 23 ma records of past topography connect earth s deep interior to the surface reflecting the distribution of heat and mass past crustal structure and plate interactions many tectonic reconstructions of the north american cordillera suggest the presence of an altiplano like plateau in the location of the modern basin and range with conflicting timing and mechanisms for the onset of surface lowering extension and orogen collapse here we show through a paleotopographic profile that from the eocene to the oligocene a high broad orogen stretched across nevada with a distinct crest that divided a continuous westward draining slope extending to central california from an internally drained eastern nevada plateau this paleo orogen maintained demonstrably higher than modern elevations reaching 3500 m in the late oligocene despite the long term high gravitational potential energy of the crust supporting this topography surface lowering extension did not occur until the transition to a transform margin changed the external kinematic framework of the system maximum surface lowering was spatially decoupled from brittle upper crustal extension requiring a large component of mid crustal flow

magnitude of crustal extension across the northern basin and range province constraints from paleomagnetism abstract the magnitude of crustal extension across the northern basin and range province is a matter of longstanding controversy estimates range from 10 to 300 recently published estimates of extension across the southern basin and range province 36 n are in the range of 80 100 thus the larger values suggested for the northern part of the province 40 n seem to require substantial counterclockwise rotation of the sierra nevada during tertiary extension paleomagnetic data from the range however limit rotation to 4 10 at the 95 confidence level these limits combined with estimates of extension near the garlock fault allow severe constraints to be placed on the magnitude of extension across more northerly parts of the province we conclude that the maximum extension at 40 n is about 50 and that values of 39 12 188 43 km are likely

late holocene hydroclimate inferences for the northern great basin from little lake elko county nevada usa abstract prominent lunette dunes 500 800 m long 50 80 m wide and up to 5 m tall are present on the floor of the independence valley in northeast nevada usa these dunes border the downwind margins of circular playas at the end of a drainage descending from the east humboldt mountains which terminates in an ephemeral water body named little lake gastropod shells from the little lake playa yield radiocarbon ages of 400 cal yr bp after correction for a hard water effect a similar age was obtained for shells from the crest of one of the lunettes deeper sediment in this lunette yielded shell ages clustering around 600 cal yr bp this pattern suggests two intervals of relatively persistent water at little lake both of which ended with lake desiccation and deflation of sediment and shells to the adjacent lunette shells from the crest of another lunette yielded radiocarbon ages between 3800 and 1750 cal yr bp this dune therefore is considerably older and accumulated over a much longer stretch of time using the global surface water explorer years between 1984 and 2018 were identified in which little lake contained water in most of the available summer imagery these years form three clusters 1984 1987 1997 2000 and 2017 2018 snow water equivalent swe is greater in the mountains snow makes up a greater percent of total annual precipitation and palmer drought severity index is more positive in this region in years when water is present in little lake compared with those in which the lake remains dry values of the pdo are also higher in years when little lake holds water although the hydrology of little lake may be influenced to an unknown degree by upstream water diversions this overall pattern implies that the lake and its associated lunettes are a sensitive recorder of late holocene hydroclimate variability in the northern great basin

on the hydrography of the northeast water polynya the water masses and circulation in the area of the northeast water polynya located on the east greenland shelf north of 79 n are described on the basis of an r v polarstern cruise during spring and summer 1993 the baroclinic flow shows northward components close to the east greenland coast and eastward components at the northern limit of the polynya an anticyclonic half circle is formed by this and the southward flowing east greenland current in the south the circle is not closed the upper water column occupied by polar water is affected by this circulation pattern while deeper waters in the trough system of the area seem to spread independently different types of deep waters are found in different troughs all being of atlantic origin though they seem not to be directly connected to return atlantic water it is shown that what is called polar water must be formed at least partly on the greenland shelf and that deepwater formation does not occur in the investigated area

sierra nevada basin and range transition near reno nevada two stage development at 12 and 3 ma relative and absolute elevations of the sierra nevada and adjacent basin and range province timing of their differentiation and location amount and timing of strike slip movement between them are controversial the provincial boundary near reno developed in two stages 1 at ca 12 ma the 700 km 2 verdi boca sedimentary basin formed across what was to become the boundary probably as a result of a small magnitude but regional extensional episode that affected much of the western basin and range 2 at 3 ma the basin was complexly faulted and folded during a larger magnitude extensional episode that established the modern sierran structural and topographic boundary in this area the boundary is really a transition zone with a western edge along the donner pass california fault zone which is farther west than previously placed both episodes appear to have resulted from east west extension only which suggests that northwest motion of the sierra nevada relative to the basin and range shown by geodetic data began after 3 ma or was taken up farther east

the snake range decollement an exhumed mid tertiary ductile brittle transition the snake range decollement srd in east central nevada separates supracrustal rocks extended by normal faulting from ductilely deformed igneous and metamorphic rocks a well known stratigraphy unaffected by earlier faulting permits analysis of both upper and lower plate strain leading to a better understanding of how vastly different rock types and deformational styles are juxtaposed along low angle faults in metamorphic core complexes middle cambrian to permian upper plate rocks are cut by two generations of ne trending east directed normal faults both generations were initiated as high angle 60 planar faults that flattened abruptly into the srd and rotated domino style to low angles yielding a total rotation of bedding of about 80 90 faulting is tertiary in age as 35 m y old volcanic rocks are involved and resulted in about 450 500 extension in a n55w s55e direction the srd developed as a subhorizontal surface 6 7 km deep at the top of the cambrian pioche shale lower plate granitic rocks and their late precambrian cambrian metamorphic country rocks were involved in progressive ductile to brittle extension at low greenschist grade forming a penetrative subhorizontal foliation and n55 70w lineation that increases in intensity eastward and upward toward the srd stretching and thinning in the lower plate is coaxial and comparable in magnitude to upper plate extension and is interpreted as synchronous k ar ages ranging from 20 to 40 m y in the lower plate suggests the n snake range represents a tertiary thermal anomaly we conclude that the srd developed as a ductile brittle transition zone at 6 7 km depth gravity data suggests that the gently domed srd is cut by younger basin and range faults but the geology of adjacent ranges suggests that the srd does not continue more than 60 km in any given direction the lack of stratigraphic omission across the srd rules out large amounts of movement on a surface that originally cut downsection and we suggest that extensional detachment faults such as the srd can be developed locally as boundaries between brittlely extended rocks and underlying ductile extension and intrusion

implications of selected subsurface data on the structural form and evolution of some basins in the northern basin and range province nevada and utah

paleogeographic and tectonic implications of the golconda allochthon southern toiyabe range nevada the golconda allochthon in the southern toiyabe range nevada is composed of several thrust slices of rocks that belong to three age categories early paleozoic early triassic and late paleozoic these slices were stacked mainly during the sonoma orogeny that occurred between permian and late early triassic time the late paleozoic rocks composing the bulk of the allochthon range in age between mississippian and late permian and contain four lithotypes that occur in the following structural order above the golconda thrust terrigenous hemipelagic volcanogenic and pelagic the upper paleozoic rocks were deformed several times during their eastward emplacement onto the north american continental margin the deformation involved isoclinal folding and thrusting of these rocks into slices the slices were openly and gently folded during emplacement and sporadic mesoscopic folds were formed along their boundaries post thrust movements along slice boundaries formed kink bands and related folds in slate and chert interbeds the kinks were later deformed when the golconda thrust was reactivated further contraction during the sonoma orogeny or possibly later was accommodated by imbrication of slices of early triassic and their unconformably underlying lower paleozoic rocks

rock deformation studies in the mineral mountains and sevier desert of west central utah implications for upper crustal low angle normal faulting the cave canyon detachment a low angle normal fault that crops out in the mineral mountains west central utah has been interpreted as a hanging wall splay of a much larger structure the sevier desert detachment that was influential in development of the idea that low angle normal faults play a role in crustal extension the cave canyon detachment provides expectations for the deformational features that might be expected along the hypothesized sevier desert detachment which is not exposed in outcrop and is inferred to exist primarily on the basis of seismic reflection data the footwall of the cave canyon detachment is characterized by a 200 m thick granite cataclasite which exhibits a clear decrease in grain size and increase in microfracture density as the fault surface is approached undulatory extinction in quartz and feldspar and abundant quartz deformation lamellae at distances more than 200 m from the fault surface are interpreted as related to cooling of the miocene granite rather than to normal faulting although mylonitic textures have previously been described in the granite we found no evidence for mylonitization in the footwall rocks the hanging wall of the detachment is characterized by 9 m of deformed partially dolomitized limestone with a 2 m thick carbonate mylonite at the contact deformation features include dynamic recrystallization grain size reduction development of twinning with a strong preferred orientation some grain size layering and undulatory extinction close to the fault static recrystallization overprints fossils and ooids at distances greater than 9 m drill cuttings and some core recovered at similar distances above and below the hypothesized sevier desert detachment show no evidence for localized deformation arco hole in the rock no 1 arco meadow federal no 1 and argonaut energy federal no 1 wells fossils and ooids are undeformed in paleozoic carbonate rocks within 3 m below the contact and sandstone and conglomerate with rounded clasts lacking more than background levels of microfracturing are found in samples within 3 m above the contact these features contrast markedly with those of the cave canyon detachment which was active at a considerably shallower and cooler level in the crust 5 km and 300 c than is implied for paleozoic rocks beneath the sevier desert once hanging wall rocks are restored along the hypothesized detachment 9 14 km and 280 425 c at the locations studied the very different character of the two surfaces reinforces our earlier suggestion that beneath much of the sevier desert basin the base of the tertiary section is an unconformity rather than a low angle normal fault

metamorphic evolution of the luning fencemaker fold thrust belt nevada illite crystallinity metamorphic petrology and 40ar 39ar geochronology abstract the luning fencemaker fold thrust belt lftb of nevada accommodated substantial mesozoic shortening in the back arc region of the u s cordillera metamorphic grade in this belt has not been studied and timing of deformation is not well defined in this study we present new data on metamorphic grade and age of deformation in the northern lftb we focus on the d1 phase of deformation which accommodated most shortening in the belt metamorphic grade was established by petrographic study and microtextural analysis of deformed metasedimentary rocks bulk x ray diffraction and illite crystallinity analyses of slates and phyllites and microprobe analyses of metamorphic mica these techniques indicate that metamorphism during d1 deformation occurred under anchizone to epizone grade conditions at temperatures probably near 300 c timing of d1 deformation was investigated by 40ar 39ar whole rock dating of slates and phyllites age spectra indicate that d1 deformation occurred before 142 144 ma late

geology and k ar geochronology of the paradise peak mine and the relationship of pre basin and range extension to early miocene precious metal mineralization in west central nevada the paradise peak mine is a major gold silver mercury deposit located in the southwestern part of the paradise range near the eastern edge of the walker lane in the western great basin nevada the tertiary volcanic rocks of the area can be divided into a sequence of 26 to 24 ma intermediate lavas a sequence of 24 to 22 ma silicic ash flow tuffs and a sequence of 20 to 15 ma intermediate lavas we classify these rocks as the older middle and younger sequences sedimentary rocks and latites and basalts 12 ma old or younger locally overlie the younger intermediate lavas south of the mine silicified rhyolite tuff in the lower part of the middle tuff sequence is the principal host of the precious metal ore most ore occurs under an acid leached zone of alunitic alteration and is contained in hydrothermal breccias that crosscut early quartz pyrite and alunite alteration field relations and k ar ages of hypogene alunite indicate that precious metal mineralization and alunitic and silicic alteration formed at about 19 to 18 ma several million years after eruption of the main host rock mineralization formed during high angle faulting related to crustal extension low angle normal faults are present 5 km northeast of the paradise peak mine but they formed more than 2 ma after formation of the paradise peak deposit silicic and alunitic alteration and precious metal mineralization are generally absent in areas of low angle faulting regional stratigraphic relations and k ar ages indicate that volcanism changed from silicic ash flow tuffs to intermediate lavas at about 20 to 19 ma regionally extensive angular unconformities indicate that a period of pre basin and range crustal extension occurred between about 22 to 19 ma this extension was penecontemporaneous with the shift in the style of volcanism and with gold silver mineralization in the paradise peak mine and in the goldfield and tonopah districts of western nevada the close temporal and spatial relationships of precious metal mineralization with pre basin and range extension suggest that extension was a major factor in the genesis of early miocene precious metal deposits in the western great basin

the subglacial cavity and implied dynamics under nioghalvfjerdsfjorden glacier ne greenland seismic depth soundings on nioghalvfjerdsfjor den glacier nfg ne greenland reveal an overdeepened trough under thefloating glacier the maximum depth of the trough reaches more than 900m below sea level mass balance calculations indicate considerable ice loss due to strong subglacial melting with a mean melt rate of 8ma 1 the geometry of the cavity and water mass characteristics from ctd measurements suggest the existence of a well de ned regional circulation system warm saline and rather densewaterfollows theinwardinclining basalslope through the deep valley of dijmphna sund towards the grounding line shallow ridges at the eastern glacier front prevent this watermassenteringfromthatdirection thecomparatively cold fresh and less dense melt water follows the subglacial ice topography leaving the cavity through the gaps towards the east the abundance of subglacial melt water east of nfg is most probably one of the main reasons for the semi permanent sea ice cover in this region cold water masses upwelling in the northeast water polynia and detected by satellite remote sensing are very likely influenced and mod ied by the subglacial melt water production

paleobotanical evidence for high altitudes in nevada during the miocene leaf physiognomy provides estimates of environmental parameters including mean annual enthalpy which is a thermodynamic parameter of the atmosphere that varies with altitude analyses of 12 mid miocene floras from western nevada indicate that this part of the basin and range province stood 3 kilometers above sea level at 15 to 16 million years ago which is 1 to 1 5 kilometers higher than its present altitude much if not all of the collapse to present day altitudes seems to have been achieved by 13 million years ago the crust in much of this area has been extended and thinned throughout the past 40 to 50 million years and the isostatic balance of a thinning crust requires subsidence not uplift as suggested by previous paleobotanical work

geometry and kinematics of the grant range brittle detachment system eastern nevada u s a an end member style of upper crustal extension documenting the range of styles of normal faulting is fundamental to understanding crustal extension here geologic mapping field relationships and deformed and restored cross sections illustrate the geometry and kinematic development of a system of west vergent detachment faults in the grant range in eastern nevada faults exhibit brecciation and stratigraphic cutoff angles of 5 15 at all structural levels and deform a 10 km thick section of paleozoic and paleogene rocks the fault system is folded across an anticlinal culmination which grew during extension as indicated by progressively increasing interlimb angles and incision in the axial zone the eastern limb consists of an imbricate stack of faults that were emplaced from bottom to top in the western limb several faults exhibit apparent thrust relationships the oldest faults are cut by a 29 ma dike and the highest preserved fault cuts 32 ma volcanic rocks that restore to paleodepths of 1 km retrodeformation of folding and minimal structural relief and angularity across a paleogene unconformity indicate the faults were active at 5 15 angles retrodeformation of offset indicates 49 km 98 extension we propose a model of stationary sustained isostatic uplift and incision at the culmination axis a fixed hinge with updip excision producing bottom to top growth of the imbricate stack and downdip excision producing apparent thrust relationships the fault system exhibits similarities to core complex detachment systems though it is confined to upper crustal levels and there are no preserved high angle or listric normal faults indicating a unique extension style dominated by low angle excision

partitioning effects from ocean and atmosphere on the calving stability of kangerdlugssuaq glacier east greenland we use the 7 km retreat of kangerdlugssuaq glacier kg east greenland to examine the mechanisms interactions and relative significance of atmospheric forcing and ice ocean interactions hydrographic data from 1991 1993 and 2004 show that subtropical waters are common in kangerdlugssuaq fjord kf and that surface waters were warm in 2004 relative to 1991 and 1993 the main water column was nonetheless warmest in 1991 we contend that while flow of subtropical waters into fjords provides a setting in which rapid glacier retreat can occur the triggering of retreat depends on additional environmental factors the climatic variables standing out in our study of kg and kf are air temperature and katabatic winds both had strong positive anomalies during winter 2004 05 when kg retreated we show that proglacial ice melange was absent and that fjord freeze up did not occur until 11 april 2005 due to warm and windy conditions we demonstrate that this setting is unusual and hypothesize that exposure to open water in winter months caused the retreat calculation of ice front melt rates shows that discharge of basal meltwater first from runoff and subsequently from frictional basal heating should intensify the interaction between glacier and fjord

denmark strait during the late glacial maximum and marine isotope stage 3 sediment sources and transport processes abstract the sediment records from north and south of denmark strait cores ps2644 and md99 2323 and on the kangerlussuaq trough mouth fan ktmf md99 2260 are evaluated for the period 12 to 60 cal ka bp with the goal of evaluating 1 the relative roles of the greenland and iceland ice sheets in sediment composition 2 the processes of sediment supply and 3 the relationship if any between the atmospheric derived ice core records and glacial marine sediment history these questions were addressed using counts of coarse 2 mm ice rafted debris ird magnetic susceptibility grain size spectra and sediment mineral composition a significant difference in these variables occurred between ms3 and mis2 with the latter showing small to modest abrupt changes in felsic and mafic minerals and in ird compared to larger and less variable changes during mis2 the dominant bedrock source archived in the cores is the cenozoic basaltic outcrops from east greenland and iceland 60 but there are frequent pulses of felsic rich sediments 17 36 which coincided with greenland stadials there is also a persistent detrital carbonate input the largest shift in most sediment proxies occurred 28 30 cal ka bp reflecting the sustained expansion of the ice sheets the grain size spectra on the snorri drift md99 2323 reflected complex depositional histories involving the supply of poorly sorted glacially derived sediment sand silt and clay and reworking by bottom currents

the snake range decollement interpreted as a major extensional shear zone geological and geophysical constraints suggest that the snake range decollement of east central nevada is a major tertiary low angle normal fault zone this interpretation is consistent with all existing data and alleviates problems that result if large displacement across the decollement is excluded miller et al 1983 based on published surface geology and cocorp seismic reflection profiling we have constructed cross sections that suggest approximately 60 km of normal displacement on the decollement advantages of this interpretation over models that exclude large displacement are that it provides for overburden consistent with kyanite grade metamorphism of footwall rocks predicts reasonable crustal thicknesses before and after extension without invoking unexposed mantle derived tertiary intrusions at depth and explains contrasting metamorphism and structural styles of hanging wall and footwall without requiring an extreme geothermal gradient during regional metamorphism and extensional strain the present domal shape of the decollement is interpreted to result at least partly from reverse drag above an underlying younger detachment related to much of the extension in ranges to the west of the snake range

north and northeast greenland ice discharge from satellite radar interferometry ice discharge from north and northeast greenland calculated from satellite radar interferometry data of 14 outlet glaciers is 3 5 times that estimated from iceberg production the satellite estimates obtained at the grounding line of the outlet glaciers differ from those obtained at the glacier front because basal melting is extensive at the underside of the floating glacier sections the results suggest that the north and northeast parts of the greenland ice sheet may be thinning and contributing positively to sea level rise

variations in felsic versus mafic sources in the western nordic seas during mis 1 to mis 4 abstract the goal of this paper is to employ quantitative methods to first describe the spatial variations in the quantitative non clay and clay mineral composition of seafloor surface sediments secondly use those data to describe the temporal variations in mineral compositions of nine cores that extend variously between the present day and 85 ka bp and thirdly describe regional variations in the transport of felsic versus mafic rich glacial marine sediments at four sites close to denmark strait k mean clusters of recent seafloor samples n 156 distinguished four mineral facies which characterize a range of mafic to felsic compositions these samples serve as a training set to identify the down core mineral facies in eight cores n 1053 the degree of provenance mixing is measured by fuzzy clustering on an unsupervised cluster analysis classification decision trees validate the mineral facies only 6 misclassified and indicate that variations in the weight of pyroxene are of primary importance in defining cluster membership mineral compositions identify two end member core sites jm07 174gc greenland sea and lo9 18 reykjanes ridge while the cores north and south of the greenland faroes ridge cores ps2644 md99 2274 2280 and 2323 are a mixture of mafic rich and felsic rich mineral facies variations in magnetic susceptibility and quartz wt exhibit coherent runs of values above or below their medians in three of the cores occurred indicating that these cannot be ascribed to random variations p

history and kinematics of cenozoic extension in the northern toiyabe range lander county nevada since earliest oligocene time 15 km of extension has occurred along a major gently dipping normal fault system and a younger more steeply dipping system of normal faults in the northern toiyabe range in central nevada the bernd canyon fault is the structurally lowest of the gently dipping faults in this area it dips 12 28 west and is similar to well known detachment faults paleozoic rocks in the hanging wall are cut by subsidary gently dipping normal faults and are tilted 40 to more than 90 to the east the early oligocene intracaldera tuff of hall creek is the oldest cenozoic unit present in the hanging wall and is tilted 28 58 eastward successively younger units have systematically decreasing dips and record a history of progressive possibly episodic extension bedding in greenschist grade lower paleozoic rocks in the footwall of the bernd canyon fault intersects the fault at angles of 5 to 25 and is arched across the range unlike many other detachment faults the bernd canyon fault contains early oligocene and younger volcanic and sedimentary units in the footwall that may be correlated to units in the hanging wall and they record a similar tilting history sequential untilting of successively older tertiary units suggests that the bernd canyon fault was initiated at a dip of 50 60 and was rotated to a dip of 25 30 during progressive extension before being cut and further rotated by younger faults restoration of tertiary units also suggests that the doming of paleozoic units across the range is a tertiary feature and that associated low bedding to fault angles in the footwall of the bernd canyon fault are the result of penetrative inhomogeneous simple shear deformation of the footwall including faults outside the area of detailed study 20 km of east west extension occurred across a domain that is now 45 km long north south by 35 km wide east west extension apparently began in earliest oligocene time before or perhaps synchronously with the onset of volcanism and it continued into the pliocene epoch tilt directions of oligocene volcanic rocks calcite veining near the detachment and elongate fossils in footwall units indicate that the extension direction on the detachment and related faults may have been nearly east west to possibly east northeast west southwest changing tilt directions in younger rocks suggest that the extension direction switched to west northwest east southeast at some time palinspastic restoration of normal faults also suggests that oligocene basins were initially bounded by high angle faults and had topographically elevated footwalls the restoration implies that the styles of miocene to recent basin and range faulting and pre miocene pre basin and range faulting are closely similar

present and past climate control on fjord glaciations in greenland implications for ird deposition in the sea calving of icebergs is the dominant ablation mechanism for large outlet glaciers from the greenland ice sheet except in northernmost greenland where bottom melting from floating glaciers dominates this difference is controlled by present climate conditions glacial geological evidence indicates that the transition between the associated types of fjord glaciations moved north south in response to past climate change in cold periods local melt out of debris from the bottom of an increasing number of floating glaciers reduces the potential for iceberg transport of ird thus the marine ird signal of greenland origin is not a simple cold climate signal our findings are discussed in the context of the ongoing debate about the kind of ice transporting ird icebergs or sea ice

the chronology of cenozoic volcanism and deformation in the yerington area western basin and range and walker lane high precision 40 ar 39 ar isotopic ages obtained from cenozoic volcanic rocks and subvolcanic intrusions document the age of initiation and the temporal evolution of extensional and strike slip faulting in the western basin and range province in the northern wassuk range faulting began between ca 26 and 24 7 ma both normal and strike slip faults are bracketed between 23 1 and 22 2 ma and between 15 and 14 ma these ages document inception of the ancestral walker lane a northwest trending zone of right transtensional faulting in western nevada that separated extending crust on the east from the unextended sierra nevada block on the west at lat 39 n we speculate that the southwesterly migrating episodic oligocene early miocene east west extensional faulting in the basin and range thinned and weakened the crust allowing right slip faults to develop in the walker lane in response to san andreas right shear in california southwest of the walker lane there was no faulting prior to 15 ma here in the yerington district andesitic magmatism began at ca 15 ma and was followed by 150 east west extension along closely spaced 1 2 km normal faults with up to 4 km of offset each proffett 1977 these faults tilted older cenozoic rocks 35 40 w our new 40 ar 39 ar ages substantially revise earlier k ar ages of the timing of extension and establish that andesite lava flows cut by normal faults are 13 8 15 ma and that these faults are intruded by 12 6 13 0 ma dacites rapid extension is thus bracketed to a 0 7 1 7 m y interval at 95 confidence indicating local east west strain rates of 2 4 10 14 s 5 10 mm yr following this period lower rates of extension prevailed near yerington along more widely spaced normal oblique slip faults that localized clastic sedimentation of the wassuk group between 11 and 8 ma these faults and sedimentary rocks are more abundant southwest of yerington in a belt parallel to the walker lane in previously little extended crust from 7 ma to present normal right oblique slip faults with a lower rate of extension than the previous two periods produced the modern ranges near yerington and extend 100 km southwest of the walker lane which continues to be the locus of strike slip faulting thus since 15 ma the margin of the basin and range has moved progressively 100 km west creating the broad walker lane belt and lower strain rates near yerington

relations between hinterland and foreland shortening sevier orogeny central north american cordillera the tectonic relations between foreland and hinterland deformation in noncollisional orogens are critical to understanding the overall development of orogens the classic central cordilleran foreland fold and thrust belt in the united states late jurassic to early tertiary sevier belt and the more internal zones to the west central nevada thrust belt provide data critical to understanding the developmere of internal and external parts of orogens the garden valley thrust system part of the central nevada thnkst belt crops out in south central nevada within a region generally considered to be the hinterland of the jurassic to eocene sevier thrust belt the thrust system consists of at least four principal thrust plates composed of strata as young as pennsylvanian in age that are unconformably overlain by rocks as old as oligocene suggesting that contraction occurred between those times new u pb dates on intrusions that postdate contraction combined with new paleomagnetic data showing significant tilting of one area prior to intrusion suggest that regionally these thrusts were active before 85 100 ma the thrust faults are characterized by long relatively steeply dipping ramps and associated folds that are broad and open to close upright and overturned although now fragmented by cenozoic crustal extension individual thrusts can be correlated from range to range for tens to hundreds of kilometers along strike we correlate the structurally lowest thrust of the garden valley thrust system the golden gate mount irish thrust southward with the gass peak thrust of southern nevada this correlation carries the following regional implications at least some of the slip across jurassic to mid cretaceous foreland thrusts in southern nevada continues northward along the central nevada thrust belt rather than noaheastward into utah this continuation is consistent with age relations which indicate that thrusts in the type sevier belt in central utah are synchronous with or younger than the youngest thrusts in southern nevada this in turn implies that geometrically similar sevier belt thrusts in utah must die out southward before they reach nevada that slip along the southem nevada thrusts is partitioned

velocity deformation model for unsteady open channel flows over smooth and rough beds abstracta one dimensional depth averaged velocity deformation model is developed to study the characteristics of the unsteady flows in open channels the vertical profile of the streamwise velocity is expressed in a power series and the coefficients of the velocity are evaluated by using the unsteady equation of motion a concise form of the friction velocity for unsteady nonuniform flow is then proposed by utilizing the coefficients of the power series the applicability of the model is validated with experimental data producing reasonably good agreement between the model results and the observed data finally the deformation of velocity at the surface is assured by comparing velocity distribution of numerical model with the computational results from a previous model

is the sevier desert reflection of west central utah a normal fault a prominent west dipping reflection that can be traced in seismic reflection profiles over an area of 7000 km 2 beneath the sevier desert basin of west central utah is generally referred to as the sevier desert detacbment and is widely regarded as one of tbe best examples of an upper crustal low angle normal fault the absence of evidence for fault related deformation in drill cuttings and core from two industry boreholes that intersect this feature casts doubt on the fault interpretation the existing interpretation is based mainly on the observation that high angle normal faulting is restricted largely to tertiary sedimentary and volcanic rocks above the reflection an alternative explanation is tbat the bigh angle faults are related to the withdrawal of early deposited lacustrine salt which even today is as much as 2 km thick reevaluation of the seismic data suggests that the sevier desert reflection consists of two spatially and genetically distinct segments a shallow segment here interpreted as an unconformity between paleozoic and tertiary strata and a fortuitously aligned deeper segment that is traceable to mid and lower crustal levels and that appears to represent a thrust fault related to the cretaceous sevier orogeny

circulation and water masses of the east greenland shelf the water masses and circulation over the northern greenland continental shelf are described based on two cruises to the region during the summers of 1979 and 1984 the cold polar water over the shelf was found to increase notably in salinity toward the shelf break and the east greenland polar front a colder more saline and relatively isolated fraction of the polar water was identified just above the atlantic intermediate water of the front a middepth layer stable in time indicates little vertical heat exchange warm atlantic intermediate water was found to intrude close to the coast via a newly defined system of troughs in the shelf the polar water was found to circulate over the shelf in a clockwise gyre baroclinic transports northward near the coast with 0 58 sv mean flow and southward elsewhere with 1 47 sv mean flow yielded a net southward transport in the east greenland current of 0 89 sv

zircon and apatite u th he evidence for paleogene and neogene extension in the southern snake range nevada usa despite decades of study the timing rates and magnitude of extension in the basin and range are poorly quantified in some areas this study integrates new zircon and apatite u th he analyses zrnhe and aphe with published thermochronologic data to quantify these extensional parameters in the southern snake range ssr of east central nevada the new zrnhe dates range from 40 7 4 9 ma in the western ssr to 21 0 3 3 ma near the present day trace of the southern snake range decollement ssrd and the aphe dates range from 15 1 2 4 ma in the central ssr to 13 6 0 7 ma closest to the ssrd trace these new and previously published low temperature thermochronologic cooling ages were inverted for the extensional history of the ssr using a bayesian monte carlo method incorporating pecube the posterior extensional histories indicate three significant pulses of extension occurred during the paleogene and neogene 1 50 45 to 38 ma eocene 2 33 30 to 23 ma oligocene and 3 23 20 to 10 8 ma miocene modeled rates of extension were low at 0 5 mm a 1 however more rapid rates possibly occurred during the eocene and the miocene based on posterior histories net cumulative extension from posterior histories is 19 8 to 34 9 km with a mean of 29 7 km about 10 18 km of extension occurred during the eocene and oligocene model results indicate no relationship between extension and magmatism in the ssr our new model results and interpretations also indicate extensional collapse of the nevadaplano initiated prior to 17 ma

flow resistance in natural turbulent channel flows the need for a fluvial fluid mechanics in fluvial environments feedbacks among flow bed forms sediment and macrophytes result in a complex fluid dynamics the assumptions underpinning standard tools in hydraulics are commonly violated and alternative approaches must be formulated i argue that we should question the assumption that classical notions in fluid mechanics provide the foundations for the techniques of the future recent work on turbulent dissipation interscale modulation of the dynamics intermittency and the role of complex forcings is discussed an agenda for future work is proposed that involves improving our characterization of complex forcings and developing better understanding of the behavior of the velocity gradient tensor in complex fluvial environments this leads to the formulation of modeling tools relevant to fluvial fluid mechanics rather than a reliance on methods developed elsewhere one avenue by which such methods might be developed is suggested based on the stretched spiral vortex as a baseline topology this would result in a nonequilibrium model for turbulence that has greater potential to capture the dynamics in which we are interested although these ideas are raised in the context of a future fluvial fluid mechanics they are applicable to any situation where turbulent flows are forced in complicated ways

evolution of a late mesozoic back arc fold and thrust belt northwestern great basin u s a abstract the luning fencemaker fold and thrust belt was active from the middle or late jurassic through the early cretaceous and involves rocks of the mesozoic marine province of the northwestern great basin rocks of the marine province were deposited in a back arc basin bound on the west by the sierran arc they are underlain by simatic crust formed either in a paleozoic marginal basin formed on the west coast of north america or in an exotic oceanic arc accreted to north america in the permo triassic deposition in the marine province was localized by the underlying simatic crust which later controlled the locus of back arc thrusting to the south in areas of the back arc region overlying continental crust mesozoic rocks are terrestrial volcanic and volcanogenic deposits rocks of this area are not disrupted by thrusts of significant magnitude until the southwestern end of the sevier thrust belt is encountered during contraction the luning fencemaker thrust belt underwent several hundred kilometers of nw se shortening which was not developed in the sierra nevada to the west the arc and back arc regions were separated by a regionally extensive left lateral fault system that was active during back arc thrusting the marine province was partially coupled with the sierra nevada during transpressional motion on the left lateral fault resulting in imbrication and emplacement of the luning fencemaker thrust belt in the continental region to the south decoupling was more complete and only minor thrusting was associated with the southerly displacement of the sierran arc farther south where the paleozoic miogeoclinal hingeline was encountered conditions apparently changed and the sevier thrust belt developed timing relations suggests that the andean type margin of the western united states had paired back arc thrust belts luning fencemaker and sevier for much of the late mesozoic the belts were separated by a region that underwent relatively minor internal shortening the intervening region probably was decoupled at depth and the thrust belts may have shared a decollement development of the luning fencemaker thrust belt and the associated left lateral fault system extended over a period of 40 50 m y and is best explained as a product of plate convergence the nw se shortening axis for the thrust belt and the inferred left slip on the strike slip fault are not compatible with the generally accepted right oblique subduction proposed for the sierran arc since the early triassic they suggest an interval of left oblique convergence for the middle to late jurassic and early cretaceous regionally developed structures indicate a return to right oblique convergence in the late early cretaceous

spatial and temporal variation of cenozoic surface elevation in the great basin and sierra nevada the surface uplift of mountain belts caused by tectonism plays an important role in determining the long term climate evolution of the earth however the general lack of information on the paleotopography of mountain belts limits our ability to identify the links and feedbacks between topography tectonics and climate change on geologic time scales here we present a 1 8 o and d record of authigenic minerals for the northern great basin that captures the timing and magnitude of regional surface uplift and subsidence events in the western united states during the cenozoic authigenic calcite smectite and chert 1 8 o values suggest the northern great basin region experienced 2km of surface uplift between the middle eocene and early oligocene followed by 1 to 2km of surface subsidence in the southern great basin and or sierra nevada since the middle miocene these data when combined with previously published work show that the surface uplift history varied in both space and time surface uplift migrated from north to south with high elevations in southern british columbia and northeastern washington in the middle eocene and development of surface uplift in north and central nevada in the oligocene this pattern of north to south surface uplift is similar to the timing of magmatism in the western cordillera a result that supports tectonic models linking magamtism with removal of mantle lithosphere and or a subducting slab

paleomagnetic results from the central sierra nevada constraints on reconstructions of the western united states paleomagnetic results from three plutons of the central sierra nevada limit the motion of the sierra nevada relative to the north american craton to 5 8 of poleward motion and 7 11 of clockwise rotation since about 90 ma the indicated rotation and translation are not significant at the 95 confidence level a new tectonic model is presented that is consistent with all available paleomagnetic data from the sierra nevada great valley klamaths oregon coast range cascades and western nevada the paleogeographic reconstructions of this model associate the displacement of major crustal blocks with basin and range extension starting at about 30 ma this model accounts for about 15 of clockwise rotation of the klamaths and southern cascades about 2 of clockwise rotation of the sierra nevada and great valley and 26 of clockwise rotation of the oregon coast range since 30 ma the model is consistent with 40 of clockwise rotation of the oregon coast range before 30 ma as proposed by magill and cox 1980 the amount of basin and range extension in this model at latitude 41 n is 225 km directed e w and at latitude 35 n is 245 km directed wsw ene

reynolds stress and bed shear in nonuniform unsteady open channel flow expressions for the reynolds stress and bed shear stress are developed for nonuniform unsteady flow in open channels with streamwise sloping beds assuming universal logarithmic velocity distribution law and using the reynolds and continuity equations of two dimensional open channel flow the computed reynolds stress distributions are in agreement with experimental data

cainozoic evolution of the state of stress and style of tectonism of the basin and range province of the western united states cainozoic evolution of the modern plate boundary along the western united states from subduction to a predominantly transform boundary coincided with a change from compressional to extensional deformation in the western united states extensions tectonism responsible for the modern basin and range province appears to represent a unique late stage episode of a much longer period of extension initiated in an in tra arc setting contemporaneously with calc alkaline magmatism basin range extension is distinguished from early extension on the basis of angular unconformities differences in fault trends and spacing and associated magmatism basaltic prebasin range extension i e extension preceding the break up of the region into ranges resembling the modern ones was under way locally by at least 30 ma and is now recognized by faulted and highly tilted strata exposed in uplifted range blocks by large regions of the crust underlain by passively emplaced subvolcanic batholiths and by the thickness and distribution of stratigraphic units locally high strain rates that accompanied early extensions of as much as 50 100 are implied data on preferentially orientated dyke swarms and fault slip vectors indicate a strikingly uniform wsw ene least principal stress orientation in the period ca 20 10 ma during this early extension the change from early extension to basin range style faulting of the upper 15 km of crust which resulted in broadly spaced ranges 25 35 km crest crest spacing was time transgressive and probably not abrupt locally both types occurred concurrently southern basin and range block faulting occurred largely in the period 13 10 ma in response to a stress field orientated similarly to that responsible for the early extension in contrast northern basin and range block faulting developed after 10 ma and continues to the present in response to a stress field orientated approximately 45 clockwise to the earlier stress field this modern stress field with a wnw ese to e w directed least principal stress characterizes the entire modern basin and range province and rio grande rift region the 45 change in least principal stress orientation is consistent with superposition of dextral shear associated with the development of the san andreas transform fault inclusion of pre basin range extension may help resolve the discrepancy between estimates of 15 30 for basin range block faulting and total extension estimates of 100 300 for the basin and range province

tracking changes in crustal thickness during orogenic evolution with sr y an example from the north american cordillera global compilations indicate that the geochemistry of arc magmatism is sensitive to moho depth magmatic products are prevalent throughout the history of cordilleran orogenesis and can be employed to constrain the timing of changes in crustal thickness as well as the magnitude of those changes we investigate temporal variations in crustal thickness in the united states cordillera using sr y from intermediate continental arc magmas our results suggest that crustal thickening began during the late jurassic to early cretaceous and culminated with 55 65 km thick crust at 85 95 ma crustal thicknesses remained elevated until the mid eocene to oligocene after which time crustal thicknesses decreased to 30 40 km in the miocene the results are consistent with independent geologic constraints and suggest that sr y is a viable method for reconstructing crustal thickness through time in convergent orogenic systems

miocene unroofing of the canyon range during extension along the sevier desert detachment west central utah this is the published version copyright 2001 american geophysical union all rights reserved

cenozoic and mesozoic structure of the eastern basin and range province utah from cocorp seismic reflection data cocorp seismic reflection data collected from the eastern basin and range in west central utah provide information on cenozoic extensional tectonics mesozoic thrusting and their interrelationships those data show a series of remarkably continuous low angle reflectors that extend more than 120 km perpendicular to strike and can be traced as deep as 15 20 km over that distance none of these events are significantly cut by any high angle normal faults a major detachment beneath the sevier desert can be traced from a surface zone of normal faulting to a depth of 12 15 km with a regional apparent westward dip of 12 tentative correlation of upper and lower plate events suggests 30 60 km of extensional displacement on this detachment whether this structure is a reactivated mesozoic thrust is uncertain west steepening splays off the end of the detachment reach depths of 20 km and may represent a major mesozoic ramp or zones of distributed ductile shearing during extension some events are interpreted to be mesozoic thrusts of which at least one beneath the house range has been reactivated during the cenozoic the snake range decollement dips gently east and has a sense of cenozoic displacement opposite to that of other cenozoic detachments farther east deep events are most numerous beneath the east side of the sevier desert where they occur to depths of 30 km at the top of or perhaps partly within the anomalously low velocity upper mantle

eocene extension of early eocene lacustrine strata in a complexly deformed sevier laramide hinterland northwest utah and northeast nevada new data from a small enclave that did not undergo significant neogene tectonism in northwest utah document eocene tilting normal faulting land folding of the early eocene lacustrine white sage formation this deformation was part of a complexly deformed eocene sevier laramide hinterland that underwent east west contraction and extension in different areas and ultimately gave way to widespread oligocene extension in the eastern great basin such mixed mode supracrustal eocene tectonism may reflect local adjustments to maintain a state of regional gravitational equilibrium or may record responses to changing plate convergence rates at the west edge of the continent

experimental study on the triggering mechanisms and kinematic properties of large debris flows in wenjia gully debris flows are typically caused by natural terrain landslides triggered by intense rainfalls if an incoming mountain torrent flows along sloping channels at high velocity huge amounts of sediment from landslide dams and eroded channel beds will be entrained into the flows to form debris flows it is likely that large debris flows are due to the failure of many landslide dams of different scales due to bank slides or collapses bed erosion and solid transport the catastrophic debris flows that occurred in wenjia gully wenchuan earthquake area china on august 13 2010 two years after the mega earthquake were caused by intense rainfall and the serious erosion of sloping channels in the wake of the incident experimental tests were conducted to better understand the process of sediment erosion and entrainment on the channel bed and the formation of debris flows the results show that the bed erosion bank collapses and channel widening caused by erosion accounted for the triggering and scale amplification of downstream debris flows in the wenjia gully event this study illustrates how the hazardous process of natural debris flows can begin several kilometers upstream and how such a complex cascade of geomorphic events failure of landslide dams and erosion of the sloping bed can lead to catastrophic discharges neglecting recognition of these hazardous geomorphic and hydrodynamic processes may result in high cost c 2014 elsevier b v all rights reserved

the ice cover in the greenland and norwegian seas the seasonal sea ice cover of the northern north atlantic is reviewed comprising the ice of the east greenland current the ice cover around svalbard and the ice of the barents sea as far east as franz josef land the review considers various types of ice cover 1 the fast ice along the coasts and in fjords including sikussak or very old fast ice of exceptional thickness 2 the transition zone between the fast ice and the main pack including the positions and causes of recurring winter polynyas and the nature of the shear zone in ne greenland 3 the constitution dynamics and seasonal extent of the drifting pack ice including interannual variations 4 the processes of air ice ocean interaction which occur in the marginal ice zone where the pack ice is influenced by an open ocean boundary

reappraisal of the relationship between the northern nevada rift and miocene extension in the northern basin and range province the northern nevada rift is a prominent mafic dike swarm and magnetic anomaly in north central nevada inferred to record the middle miocene 16 5 15 0 ma extension direction in the northern basin and range province in the western united states from the 245 250 rift direction basin and range extension is inferred to have shifted 45 clockwise to a modern direction of 290 300 during the late miocene the region surrounding the northern nevada rift was actively extending while the rift formed and these domains are all characterized by extension oriented 280 300 this direction is distinctly different from the rift direction and nearly identical to the modern basin and range direction although the rate structural style and distribution of basin and range extension appear to have undergone a significant change in the late miocene ca 10 ma the overall spreading direction does not middle miocene extension was directed perpendicular to the axis of the thickest crust formed during mesozoic shortening and this orientation may reflect gravitational collapse of this thick crust orientation of northern nevada rift dikes may reflect a short lived regional stress field related to the onset of yellowstone hotspot volcanism

western united states extension how the west was widened abstract cenozoic extension in the western united states presents a complex interrelation of extension volcanism and plate boundary tectonics that defeats simple notions of active or passive rifting forces driving extension can originate at plate boundaries through basal traction basal normal forces or from buoyancy forces internal to the crust and lithospheric mantle the latter two are most responsible for driving extension where it is observed in the basin and range the complex evolution of the northern basin and range probably represents removal or alteration of mantle lithosphere interacting with buoyancy stored in the crust in contrast crustal buoyancy forces combined with a divergent plate boundary between about 28 and 16 ma to drive extension in the southern basin and range the central basin and range most likely extended as a result of boundary forces external to itself but arising from buoyancy forces elsewhere in the western united states

thermochronological constraints on the timing and magnitude of miocene and pliocene extension in the central wassuk range western nevada apatite fission track and u th he thermochronological data provide new constraints on the timing of faulting and exhumation of the wassuk range western nevada where east dipping normal faults have accommodated large magnitude ene wsw oriented extension extensional deformation has resulted in the exhumation of structurally coherent fault blocks that expose sections of preextensional mostly granitic upper crust in the grey hills and central wassuk range these fault blocks display westward tilts of 60 and expose preextensional paleodepths of up to 8 5 km based on the structural reconstruction of tilted preextensional tertiary andesite flows that unconformably overlie mesozoic basement rocks apatite fission track and u th he thermochronological data from the fault blocks constrain the onset of rapid footwall exhumation at 15 ma fission track modeling results indicate rapid fault block exhumation occurred between 15 and 12 ma which is in agreement with miocene volcanic rocks that bracket the tilting history in addition fission track and u th he data suggest reduced rates of cooling following major extension as well as renewed cooling related to active high angle faulting along the present day range front starting at 4 ma thermochronological data from structurally restored fault blocks indicate a preextensional miocene geothermal gradient of 27 5 c km the thermochronological constraints on the timing of extensional faulting and the eruptive history in the wassuk range imply a model for extension where crustal heating and volcanism precede the onset of rapid large magnitude extension and where synextensional magmatism is suppressed during the highest rates of extension

a tibetan model for the early tertiary western united states a comparative study of the geology of the early tertiary western united states and the modern tibetan and turkish iranian plateaux indicates that these three regions situated in the hinterland of major orogenic belts share a common taphrogenic evolutionary path both the tibetan and turkish iranian plateaux have high mean elevations above sea level 5 km and 2 0 2 5 km respectively have experienced fast uplift and widespread unroofing during the last 10 8 ma and are undergoing extension nearly perpendicular to the plate convergence direction successive accretionary and collisional events accompanied by significant shortening and underplating during the formation of these plateaux resulted in the generation of overthickened continental crust 50 km that is currently in the process of extending a two stage magmatism characterized by widespread calc alkaline volcanism followed and or overlapped by bimodal basaltic to rhyolitic volcanism occurs synchronously with crustal extension and thinning the plateaux in general have an internal closed drainage system and are drained by antecedent rivers near their edges the early tertiary western us cordillera displayed similar geological and geomorphic features to those observed in the tibetan and turkish iranian plateaux in the aftermath of a prolonged mesozoic orogeny and underwent an orogenic collapse starting around mid tertiary time a n trending crustal welt with a maximum thickness of 60 km and an elevation around 3 km formed a highland with alpine flora in the hinterland of the cordilleran orogenic belt and separated internal drainage basins and saline lakes on the east from major flood plains of antecedent river systems on the west this highland subsequently became the locus of crustal extension metamorphic core complex formation and wide spread calcalkaline volcanism 9ignimbrite flare up9 this early stage of orogenic collapse was followed by the basin and range extension characterized by block faulting and bimodal volcanism starting around 18 16 ma the basin and range extension and associated subsidence resulted in development of the great basin with a mean elevation of 1 5 km above sea level and a crustal thickness of 30 km similarities in the post orogenic evolutionary paths of these three regions indicate that continental lithosphere reacts to overthickening in a consistent way through large scale crustal remobilization and extensional collapse regardless of the mode and nature of its orogenic build up

unsteady bed shear stresses induced by navigation laboratory observations time dependent bed shear stresses induced by the passage of a barge tow have been measured with hot film shear stress sensors in a 1 25 scale model conditions typical of those observed for upper mississippi river navigation traffic were simulated in the experimental facility two sets of experiments were carried out the first set consisted of simultaneous shear stress measurements at different locations for a variety of flow depths and boat operating conditions providing space time distributions of ensemble averaged wall shear stresses the second set included a large number of realizations gathered for one particular flow condition at a single position allowing analysis of the time evolution of the turbulence characteristics i e standard deviation of the bed shear stresses the results of the first set of experiments show that for all the experimental conditions the basic patterns of the shear stress are similar with two regions of high shear stress associated with the passage of the bow and the

overview of the cocorp 40 n transect western united states the fabric of an orogenic belt the cocorp 40 n transect of the cordillera of the western united states crosses tectonic features ranging in age from proterozoic to recent and provides an acoustic cross section of a complex orogen affected by extension compression magmatism and terrane accretion the key features of the transect centered on the basin and range province include 1 asymmetric seismic fabrics in the basin and range including west dipping reflections in the eastern part of the province and predominantly subhorizontal ones in the west 2 a pronounced reflection moho at 30 2 km and locally as deep as 34 km in the basin and range with no clear sub mono reflections and 3 complex dipping reflections and diffractions locally as deep as 48 km in the colorado plateau and sierra nevada the eastern part of the transect shot above known and inferred precambrian crystalline basement probably records features related to the entire history of the orogen locally perhaps as old as 1800 ma in this region major paleotectonic features probably controlled subsequent structural development in title western half of the transect however most reflectors are probably no older than mesozoic within the basin and range province there appears to be a strong cenozoic overprint that is characterized by asymmetric half grabens low angle normal faults and a pervasive subhorizontal system of reflections in the lower crust no one model of intracontinental extension is universally applicable processes that produce or are accompanied by thermal anomalies magmatism enhanced ductility and extension appear to be essential in developing a highly layered lower crust

on the generation of the northeast water polynya in spring and summer of 1993 a multidisciplinary survey of the northeast water new polynya located on the continental shelf northeast of greenland was undertaken by r v polarstern hydrographic and remotely sensed data from this expedition are analyzed with respect to the generation and the seasonal development of the new its formation is concluded to result from the combined effect of a fast ice barrier extending perpendicular from the coast and bridging a trough system and a northward flowing coastal current the fast ice barrier protects the region downstream of it from ice import while current driven ice export continues the temporal development and spatial distribution of hydrographie parameters in the new is primarily controlled by its generation mechanism continental and sea ice melt induce vertical stability in certain parts of the polynya giving rise to enhanced primary production there

dam break outburst flood propagation and transient hydraulics a geosciences perspective summary dam break outburst floods are sudden short lived and high magnitude discharges of water and sediment propagating over an initially dry terrain both field observations by geoscientists and experimental measurements by engineers have produced understanding of outburst floods but neither approach has satisfactorily supplied data that is directly of use to hazard managers this study draws together those two literature groups and provides new experimental data to test hypotheses concerning the effect of a series of external controls on resultant longitudinal flow propagation and transitory hydraulics these external controls form experimental treatments and are i the height of the lock gate raise as a surrogate for dam breach evolution and initial hydrograph ii bed roughness and iii suspended sediment concentration these control both horizontal and vertical fluid motion the latter of which is a key property for controlling aeration bed shear stress and turbulence intensity the experimental treatments show that outburst floods on horizontal beds can be identified to possess three longitudinal flow regimes firstly there is a short acceleration due to the reservoir pressure level i e the depth of impounded water secondly channel flow quickly converges to an inertial regime the third flow regime is viscous and dominated by channel bed friction flow depth increases in the inertial regime then decreases in the viscous regime experiments herein show that the timing of the peaks at a point down channel of each hydraulic quantity varies most notably peak bed shear stress precedes flow velocity which precedes peak flow depth a point of inflexion occurs with distance down channel that is a manifestation of the transition from accelerating to decelerating flows these external controls and the effects of them on longitudinal and vertical motion are analysed statistically and quantitative relationships are derived to underpin the resultant conceptual model this conceptual model should serve as a platform for future probabilistic and process based modelling of outburst floods

the role of mantle delamination in widespread late cretaceous extension and magmatism in the cordilleran orogen western united states extension during plate convergence and mountain building is widely recognized yet the causes of synconvergent extension remain controversial here we propose that delamination of lithospheric mantle aided by decoupling of the crust from the mantle via a reduction in the viscosity of the lower crust through heating incursion of fl uids and partial melting explains many enigmatic yet prevalent aspects of the metamorphic magmatic and kinematic history of the sevier laramide orogen of the western united states during the late cretaceous extension heating anatexis magmatism and perhaps rock uplift were widespread during a restricted time interval in the late cretaceous 75 67 ma along the axis of maximum crustal thickening within the mojave sector of the sevier orogen and to a lesser extent within the interior of the idaho utah wyoming sector to the north similar processes may have been active in the peninsular range sierran western mojave and salinian segments of the mesozoic cordilleran arc these processes are viewed as predictable consequences of the thermal rheological and dynamic state of the overlying crust following delamination of mantle lithosphere beneath isostatically compensated mountain belts the proposed delamination would have occurred immediately prior to eastward propagation of lowangle subduction of the farallon plate during the inception of the laramide orogeny following delamination extension and anatexis of the north american crust were aided locally by egress of slab derived fl uids from the low angle farallon slab we suggest that lithospheric delamination may have aided in the shallowing of the slab to achieve lowangle subduction geometry delamination has been proposed to be common in areas of thickened continental lithosphere in the terminal phase or late in orogenesis the late cretaceous delamination event proposed here for the sevier laramide orogen occurred during protracted plate convergence and was synchronous with and followed by continued shortening in the external part of the orogen

high elevation of the nevadaplano during the late cretaceous during the late cretaceous central nevada may have been a high elevation plateau the nevadaplano some geodynamic models of the western us require thickened crust and high elevations during the mesozoic to drive the subsequent tectonic events of the cenozoic while other models do not to test the hypothesis of high elevations during the late mesozoic we used carbonate clumped isotope thermometry to determine the temperature contrast between late cretaceous to paleocene carbonates atop the putative plateau in nevada versus carbonates from relatively low paleoelevation central utah site lacustrine carbonates from the nevada site preserve summer temperatures 13 c cooler than summer temperatures from paleosol carbonates from the utah site after correcting for 1 2 c of secular climatic cooling between the times of carbonate deposition at the two sites this 13 c temperature difference implies an elevation difference between the two sites of 2 2 3 1 km including uncertainties from age estimation and climate change broadens this estimate to 2 km our findings support crustal thickness estimates and cenozoic tectonic models that imply thickened crust and high elevation in nevada during the mesozoic

overview tectonic implications of cenozoic volcanism in coastal california cenozoic volcanic rocks of coastal california were erupted west of the magmatic arc trend related to subduction along the continental margin two assemblages representing discrete pulses of mid tertiary oligocene miocene and mid miocene volcanism occupied relatively compact tracts as restored palinspastically prior to disruption and dispersal by tectonic displacements within the neogene san andreas transform system a third assemblage records migratory post mid miocene volcanism at centers located progressively farther north the distribution and petrologic character of all three assemblages reflect slab window magmatism triggered by decompression melting of upwelling mantle paleogeographic reconstructions based on analysis of magnetic anomaly patterns offshore and restoration of on land features prior to san andreas transform slip and associated transrotational deformation indicate the paleotectonic positions of the cenozoic volcanic fields before structural disruption the pulses of mid tertiary and mid miocene volcanism were related to transient episodes of mantle upwelling generated successively by rise trench encounters associated with subduction of the vancouver farallon and monterey arguello plates respectively along the continental margin off southern california migratory post mid miocene volcanism in central california accompanied the incremental expansion of a growing slab window as the mendocino triple junction migrated northward along the continental margin mid miocene columbia river basalt volcanism in the pacific northwest was coeval with the mid miocene pulse of coastal volcanism and may have reflected tectonism induced by the final demise of offshore microplates to allow initial full integration of the san andreas transform as a coherent plate boundary columbia river volcanism may have stemmed from mantle perturbation caused by torsional deformation of the continental block in response to shear imposed by the pacific plate

synorogenic extension localized by upper crustal thickening an example from the late cretaceous nevadaplano synconvergent extension within orogenic systems is often interpreted as gravitational spreading of thickened crust or as a response to thrust belt dynamics however the processes that spatially localize extension during orogenesis are not fully understood here a case study from the united states cordillera demonstrates that localized upper crustal thickening can exert a first order control on the spatial location of synorogenic extension the eureka culmination a 20 km wide north trending anticline with 4 5 km of structural relief in the hinterland plateau of the sevier orogenic belt or nevadaplano in eastern nevada was deformed by two sets of north striking normal faults that pre date late eocene volcanism u th he and fission track thermochronology data collected from paleozoic quartzite in the footwalls of two normal faults demonstrate rapid 10 c m y late cretaceous to paleocene 75 60 ma cooling which we interpret as tectonic exhumation during extension and which was concurrent with late stage shortening in the frontal sevier thrust belt this example illustrates that structural and topographic relief generated within zones of localized upper crustal thickening can spatially focus extension during orogenesis and adds to a growing body of evidence that late cretaceous paleocene extension in the nevadaplano occurred at both mid and upper crustal levels

deep burial of the footwall of the northern snake range decollement nevada metapelitic eocambrian strata from eastern exposures of the footwall of the northern snake range decollement experienced mesozoic amphibolite facies metamorphism and greenschist facies overprint accompanying extreme ductile thinning samples from the hampton creek area where the overprint is weakest contain the assemblage quartz muscovite biotite garnet plagioclase opaque oxides staurolite kyanite tourmaline apatite textural relations and consistency of rim analyses among multiple domains in each sample indicate equilibrium rim pressure temperature estimates were obtained using the garnet biotite fe mg exchange thermometer and the garnet muscovite plagioclase biotite and garnet aluminosilicate plagioclase barometers the results suggest final equilibration at 610 50 c and 810 70 mpa or a depth of 30 3 km about a factor of 3 greater than the stratigraphic depth to the west in the schell creek range correlative strata are contiguous with unmetamorphosed upper paleozoic and tertiary strata from west to east exposures of eocambrian rocks in the two ranges collectively show increasing intensity of crystal plastic deformation metamorphic recrystallization and metamorphic grade from subgreenschist to amphibolite facies and a monotonic decrease in 40 ar 39 ar muscovite ages from mesozoic age to about 23 ma in light of these relations the pressure temperature data suggest that eocambrian strata were inclined eastward during mesozoic metamorphism with 15 20 km of structural relief we interpret the eastward tilting and burial to be the result of west directed thrusting as expressed by folding to the north in the deep creek range unroofing of the deeply buried strata may have occurred partly in cretaceous or early cenozoic time with final unroofing in oligocene and miocene time along the northern snake range decollement these results exclude the hypothesis that the northern snake range decollement initiated as a brittle ductile transition zone within cambrian strata of a little deformed miogeoclinal section and support the hypothesis that it is a major low angle extensional shear zone

a relation among geology tectonics and velocity structure western to central nevada basin and range in the northwestern to central nevada basin and range there are correlations between velocity and specific geologic structures of the crust mapped range bounding faults at the surface can be traced to appreciable 10 km depths based on velocity variations and are consistent with subsurface projections of the faults based on seismic reflection images the limiting depth of the faults as indicated by the velocity variations corresponds to the maximum depth of earthquakes along the seismic profile correlations between velocity and the surface geology show that in the upper crust the pre cenozoic rocks are underlain by high velocity 6 0 km s rocks whereas the tertiary ranges are underlain by lower velocity 4 0 5 7 km s rocks to depths as great as 10 km although the tertiary rocks differ in composition from the mesozoic rocks the lower velocity tertiary rocks may also be attributed to rock masses which are broken 4 0 5 7 km s and the higher velocity mesozoic rocks 6 0 km s may be attributed to largely unbroken rock masses the regional seismicity pattern is consistent with this interpretation as earthquakes are largely confined within or near the base of the low velocity rocks these low velocity highly fractured rocks are laterally distributed in discrete zones suggesting that extension is not uniformly distributed but occurs in discrete highly extended zones beneath these highly extended zones the lower crustal layers show structural evidence of extension and velocity measurements suggest that the lowermost crust has been magmatically underplated the superposition of tertiary volcanic rocks highly fractured upper crust and lower crustal magmatic underplating suggests that the tertiary volcanic rocks originated from lower crustal magmas that migrated to the surface via the highly extended zones the velocity structure of one of the highly extended zones and the lahonton basin resembles that of many continental rifts the velocity structure beneath central nevada however is much more like normal continental crust on the basis of isotopic studies it is concluded that the transition between highly extended crust and more normal crust occurs in the area inferred to be the edge of the north american craton

structural evolution of a mesozoic backarc fold and thrust belt in the u s cordillera new evidence from northern nevada stratigraphic and structural analysis in blue mountain and nearby areas of northern nevada yields new insight into the evolution of the luning fencemaker fold and thrust belt a mesozoic orogenic belt that formed during tectonic closure of a triassic backarc basin three stratigraphic units are defined in blue mountain and correlated with upper triassic norian units in nearby areas these units have a combined structural thickness of 6 km and consist mostly of shale now slate and phyllite quartzose sandstone is much less common and carbonate is rare two phases of deformation affected these strata d 1 deformation is pervasive and was associated with tight to isoclinal folding at various scales widespread cleavage development under low grade metamorphic conditions and reverse faulting this deformation accommodated a minimum of 55 75 northwest southeast shortening with southeast directed tectonic transport d 2 deformation is only locally developed and is manifested by relatively open folds crenulations and a spaced cleavage this phase of deformation accommodated a minor amount of northeast southwest shortening and was not accompanied by metamorphism structures and deformation phases in blue mountain can be correlated with those found in nearby areas the d 1 phase of deformation is pronounced across the entire northern part of the luning fencemaker fold and thrust belt and resulted in structural closure of the backarc basin via development of a ductile fold and thrust belt in the jurassic d 2 is unrelated to development of the fold and thrust belt as a structural province and occurred much later in the middle to late cretaceous the structural evolution of this backarc fold and thrust belt appears to be quite simple and did not evidently involve widespread polyphase deformation data from blue mountain and nearby areas suggest that it is now possible for the first time to map out megascopic structures folds and faults within the interior of the province

late paleogene extensional collapse of the cordilleran foreland fold and thrust belt the cordilleran foreland fold and thrust belt collapsed and spread to the west during a middle eocene to early miocene ca 49 20 ma episode of crustal extension the sedimentary and structural record of this event is preserved in a network of half grabens that extends from southern canada to central utah extensional structures superposed on this allochthonous terrain are rooted to the physical stratigraphy structural relief and sole faults of preexisting thrust fold structures the sole faults dip 3 6 west above an undeformed precambrian crystalline basement and accommodated tectonic transport of a thick up to 20 km eastward tapering hanging wall during regimes of crustal shortening and extension the chronology of tectonism for the foreland fold and thrust belt is established here by dating latest thrusting and initial normal faulting and is best defined where thrusts and normal faults are linked by common detachment surfaces dated movement on two extensionally reactivated thrusts the lewis thrust of northwest montana and southeast british columbia and the medicine butte thrust of southwest wyoming and northeast utah suggests that the hiatus between the end of crustal shortening in the early or early middle eocene and the start of extension in the early middle eocene was brief lateral spreading and extensional basin formation in the cordilleran foreland fold and thrust belt were partly concurrent with formation of metamorphic core complexes and regional magmatism conceptually linking extensional processes that were simultaneously deforming both the hinterland and foreland of the late paleogene cordilleran orogenic wedge is accomplished by applying the extensional wedge coulomb critical taper model the rapid drop in north america pacific plate convergence rate and or steepening of the subducted oceanic slab at ca 50 ma resulted in a large reduction in east west horizontal compressive stress in the cordillera as a result the cordilleran orogenic wedge was left unsupported and it gravitationally collapsed and horizontally spread west until a new equilibrium was established at ca 20 ma subsequently crustal extension and magmatism during the basin and range event ca 17 0 ma overprinted much of this earlier phase of extension

two phase westward encroachment of basin and range extension into the northern sierra nevada 1 structural geophysical and thermochronological data from the transition zone between the sierra nevada and the basin and range province at latitude 39 n suggest 100 km westward encroachment of basin and range extensional deformation since the middle miocene extension accommodated primarily by east dipping normal faults that bound west tilted range forming fault blocks varies in magnitude from 150 in the wassuk and singatse ranges to the east geological and apatite fission track data from exhumed upper crustal sections in the wassuk and singatse ranges point to rapid footwall cooling related to large magnitude extension starting at 14 15 ma farther to the west geological and thermochronological data indicate a younger period of extension in the previously unextended pine nut mountains the carson range and the tahoe truckee depression initiated between 10 ma and 3 ma and incipient post 0 5 ma faulting to the west of the tahoe truckee area these data imply the presence of an extensional breakaway zone between the singatse range and the pine nut mountains at 14 15 ma forming the boundary between the sierra nevada and basin and range at that time in addition fission track data imply a miocene preextensional geothermal gradient of 27 5 c km 1 in the central wassuk range and 20 5 c km 1 in the singatse range much higher than the estimated early tertiary gradient of 10 5 c km 1 for the sierra nevada batholith this might point to a significant increase in geothermal gradients coupled with a likely decrease in crustal strength enabling the initiation of extensional faulting apatite fission track geophysical and geological constraints across the sierra nevada basin and range transition zone indicate a two stage coupled structural and thermal westward encroachment of the basin and range province into the sierra nevada since the middle miocene

turbulence characteristics in supercritical open channel flows effects of froude number and aspect ratio abstractan experimental investigation of supercritical uniform and gradually varied open channel flows is presented for a wide range of froude numbers and flume width to flow depth aspect ratios the instantaneous streamwise and vertical flow velocities were measured in a laboratory flume over the entire width using a two dimensional laser doppler anemometry 2d lda system to determine turbulence intensities and bed and reynolds shear stresses the mean velocity patterns show undulation across the flume indicating the presence of counterrotating secondary current cells these currents redistribute turbulence intensities and bed and reynolds shear stresses across the flume for aspect ratios 4 5 i e narrow open channel flow the velocity dip phenomenon is identified both in the streamwise velocity and the reynolds shear stress distributions for high aspect ratios i e wide open channel flow the strength of secondary currents diminish toward the flume center resulting in a 2d flow farther away

electromagnetic wave surface velocimetry electromagnetic wave surface velocimeters esvs measure the doppler shift in electromagnetic waves reflected from the water surface they provide nonintrusive water surface velocity measurements from bridges and river banks comparisons with laboratory and field tests show very good agreement over a wide range of elevation and planview angles laboratory testing shows comparable results between esv and other measurement techniques when 0 4v1 6 m s and 15 45 field testing at three different locations shows that the optimal operation conditions are at an elevation angle 30 planview angle 13 and 0 30v2 00 m s the ratio of cross section averaged velocity to mean free surface velocity is approximately cfdav0 88 for high flow velocities during floods the standard deviation of the field measurement for these three streams was less than 15 of the mean value

synconvergent surface breaking normal faults of late cretaceous age within the sevier hinterland east central nevada the hinterland of the sevier orogenic belt of western north america is widely interpreted as a cretaceous to paleogene orogenic plateau although evidence for mid crustal extension of late cretaceous age within the sevier hinterland is widespread coeval surface breaking normal fault systems have not been documented new 1 12 000 scale mapping within the type section of the latest cretaceous to eocene sheep pass formation of east central nevada suggests that deposition occurred in response to normal fault movement recording up to 4 km of late cretaceous and paleogene stratigraphic throw intrabasinal normal faulting caused lateral thickness variations within the basal sheep pass formation although upper members are largely unaffected an extensional basin setting best explains the fanning of bedding dips the deposition of megabreccia and the presence of syndepositional normal faults within the sheep pass formation deposition of the basal member of the sheep pass formation is bracketed between ca 81 3 3 7 ma and 66 1 5 4 ma based on the u th he cooling ages of detrital zircons and on a u pb carbonate age derived from the overlying lacustrine limestone member these new data provide the strongest evidence to date for the existence of late cretaceous surface breaking normal faults in the sevier hinterland normal faulting was coeval with mid crustal hinterland extension and with continued contraction within the sevier foreland to the east

thrust timing growth of structural culminations and synorogenic sedimentation in the type sevier orogenic belt western united states most of the regional shortening in the type area of the sevier orogenic belt in central utah was accommodated by displacement on the canyon range neocomian aptian pavant aptian albian paxton cenomanian campanian and gunnison late campanian paleocene thrust systems inception of each thrust system generated synorogenic sediment associated with frontal thrust tip anticlines or triangle zones and older thrust sheets that were elevated above major ramps farther toward the hinterland the sevier culmination a large antiformal duplex cored by crystalline basement rocks developed during paxton and gunnison thrusting west of and structurally beneath the canyon range and pavant thrusts growth of the sevier culmination was coeval with reactivation of the canyon range and pavant thrust systems and produced a second culmination in proterozoic lower cambrian rocks in the canyon range these structural highs provided much of the sediment to the adjacent foreland basin from late cenomanian to late paleocene time and may have helped to maintain critical taper in the thrust belt

the northern nevada rift regional tectono magmatic relations and middle miocene stress direction as defined by the most recent aeromagnetic surveys the north northwest trending northern nevada rift zone extends for at least 500 km from southern nevada to the oregon nevada border at several places along the rift the magnetic anomaly is clearly related to north northwest trending dikes and flows that based on new radiometric dating erupted between 17 and 14 ma and probably during an even shorter time interval the tectonic significance of the rift is dramatized by its length its coincidence in time and space at its northern terminus with the oldest silicic caldera complex along the yellowstone hot spot trend and its parallelism with the subduction zone along the north american coast prior to the establishment of the san andreas fault the northern nevada rift is also equivalent in age trend and composition to feeder dikes that fed the main eruptive pulse 95 volumetrically off the columbia river flood basalts in northern oregon 15 5 16 5 ma because of these similarities both regions are considered to be part of an enormous lithospheric rift that propagated rapidly south southeast and north northwest respectively from a central mantle plume the site of the initial breaching of the north america plate by this plume is probably the mcdermitt volcanic center at the north end off the rift near the oregon nevada border the present north northwest trend of the rift and its internal elements such as dikes and lava filled grabens record the orientation of the arc normal extensional stress in this back arc region at the time of emplacement paleomagnetic evidence presented by others and interpreted to indicate block rotations at three sample localities is not consistent with either a rotation of dikes within the rift or with a regional rotation of the entire rift the present north northwest trend of the rift reflects the state of stress in the basin and range during middle miocene time and is consistent with stress indicators of similar age throughout the basin and range and rio grande rift provinces