crustal reworking at nanga parbat pakistan metamorphic consequences of thermal mechanical coupling facilitated by erosion within the syntaxial bends of the india asia collision the himalaya terminate abruptly in a pair of metamorphic massifs nanga parbat in the west and namche barwa in the east are actively deforming antiformal domes which expose quaternary metamorphic rocks and granites the massifs are transected by major himalayan rivers indus and tsangpo and are loci of deep and rapid exhumation on the basis of velocity and attenuation tomography and microseismic magnetotelluric geochronological petrological structural and geomorphic data we have collected at nanga parbat we propose a model in which this intense metamorphic and structural reworking of crustal lithosphere is a consequence of strain focusing caused by significant erosion within deep gorges cut by the indus and tsangpo as these rivers turn sharply toward the foreland and exit their host syntaxes the localization of this phenomenon at the terminations of the himalayan arc owes its origin to both regional and local feedbacks between erosion and tectonics

thickness and grain size distribution of the 2004 indian ocean tsunami deposits in periya kalapuwa lagoon eastern sri lanka abstract in this paper we describe the sedimentary characteristics of the 2004 indian ocean tsunami deposits in and around periya kalapuwa lagoon sri lanka periya kalapuwa is a coastal lagoon of about 13 km 2 area and has an average depth of about 1 m it is separated from the indian ocean by coastal barrier sand dunes of up to 9 m elevation through which two inlet channels open the lagoon to the ocean this region was hit by three waves during the 2004 indian ocean tsunami the second wave was largest 4 6 m and entered the lagoon not only via the two inlet channels but also by flowing over the sand dunes erosive scars were found on the sand dunes adjacent to the two inlets twenty seven core samples along with trenching and hand auger data show that the tsunami deposits are 9 cm thick on average up to 35 cm in the lagoon and up to 66 cm on the shore and are composed mainly of medium sand mean grain size 1 06 with low mud content 0 61 wt which is similar to the composition of sand from near the erosive scars in the sand dunes mean grain size 0 94 but different from the lagoon deposits mean grain size 1 68 mud content 4 7 wt the distribution of the tsunami deposits was limited to within about 1 km from each inlet the tsunami deposits become thinner and finer grained with increasing distance from the inlets most of the tsunami deposits are massive but some show sedimentary structures single or multiple graded bedding structures parallel laminations defined by layers of heavy minerals and muddy laminations our observations and analyses suggest that the tsunami deposits were formed mainly from sand eroded from sand dunes near the two inlets we estimated the total volume of tsunami sediments to be 83 000 m 3 by assuming that the sediments of the tsunami deposits were supplied only by erosion of sand dunes from near the two inlets this is equivalent to erosion of 83 m 3 of sand per meter of sand dune traversed by the tsunami wave

controls on the strength of coupling among climate erosion and deformation in two sided frictional orogenic wedges at steady state 1 many important insights regarding the coupling among climate erosion and tectonics have come from numerical simulations using coupled tectonic and surface process models however analyses to date have left the strength of the coupling between climate and tectonics uncertain and many questions unanswered we present an approximate analytical solution for two sided orogenic wedges obeying a frictional rheology and in a condition of flux steady state that makes explicit the nature and sensitivity of the coupling between climate and deformation we make the simplifying assumption that the wedge grows in a self similar fashion consistent with airy isostasy such that topographic taper is invariant with orogen width tectonic influx rate and climate we illustrate first how and why the form of the erosion rule matters to orogen evolution and then derive a physically based orogen scale erosion rule we show that steady state orogen width crest elevation and crustal thickness are controlled by the ratio of accretionary flux to erosional efficiency to a power dictated by the erosion process remarkably we show that for most combinations of parameters in the erosion law rock uplift rate is more strongly controlled by erosional efficiency than it is by the accretionary flux further assuming frontal accretion with no underplating the spatial distribution of erosional efficiency dictates the relative rock uplift rates on the pro wedge and retro wedge and the time averaged trajectories of rocks through the orogen the restriction to invariant frictional properties is conservative in these respects systems subject to positive feedback between erosion and rheology will exhibit even stronger coupling among climate erosion and deformation than shown here

mechanics of fold and thrust belts and accretionary wedges cohesive coulomb theory a critically tapered fold and thrust belt or submarine accretionary wedge is one that is on the verge of coulomb failure everywhere including its base where frictional sliding along a decollement is assumed to be occurring cohesion within a wedge can add significantly to the overall strength near the toe the effect of this is to decrease the near toe taper leading to a critical topographic profile that is concave upward if the decollement is planar we obtain an approximate self consistent solution for the state of stress within a thin skinned cohesive critical coulomb wedge and determine the relationship between the wedge taper and its strength and basal friction the theory is then applied to the presently deforming fold and thrust belt of western taiwan fitting of theoretical critical wedge shapes to topographic profiles and measurements of the step up angles of thrust faults from the basal decollement are used to constrain the taiwan wedge strength parameters an attractive assertion fully consistent with all the observations is that the mechanics of fold and thrust belts and accretionary wedges is governed by normal frictional and fracture strengths of rocks measured in the laboratory in particular if byerlee s law b 0 85 is adopted as the coefficient of sliding friction on the base we find a coefficient of internal friction 0 9 1 0 in the wedge and a wedge cohesion so 5 20 mpa other solutions having strengths and ambient stresses up to 4 times lower than this can also however satisfy the data

cooling and uplift patterns in the lepontine alps south central switzerland and an age of vertical movement on the insubric fault line 96 new fission track ft apatite and zircon k ar and rb sr biotite and muscovite ages are presented for 19 samples mainly acid gneisses from a 40 km traverse through the lepontine alps in the maggia valley south central switzerland plotting measured mineral ages against assumed system closure temperatures yields cooling rates for each sample the entire profile shows a fairly uniform late neogene recent mean uplift rate of 0 5 mm a confirmed by a gradient of ft apatite age with elevation cooling from higher temperatures occurred earlier in the south where uplift rates of 2 2 mm a in the steep belt root zone indicate 9 km early miocene uplift of the northern pennine block this uplift started before 23 ma and is interpreted as resulting from a major phase of backthrusting along the insubric line and as dating the formation of the mylonite belt estimated cooling rates constrain the timing of lepontine mid tertiary metamorphism 3 schematic models are proposed which also consider published rb sr k ar mica and hornblende and u pb monazite ages slow cooling differential initial heating and subsequent cooling of different parts of the central alps and post 38 ma cooling with syntectonic metamorphism at 27 ma are postulated as alternative interpretations of isotopic data and geologic evidence from extrapolation between k ar and rb sr mica ages and apatite ft ages 240 50 c is proposed as the closure temperature for the retention of fission tracks in zircon

late cenozoic uplift of mountain ranges and global climate change chicken or egg the high altitudes of most mountain ranges have commonly been ascribed to late cenozoic uplift without reference to when crustal thickening and other tectonic processes occurred deep incision and recent denudation of these mountain ranges abundant late cenozoic coarse sediment near them and palaeobotanical evidence for warmer climates where high mountain climates today are relatively cold have traditionally been interpreted as evidence for recent uplift an alternative cause of these phenomena is late cenozoic global climate change towards lower temperatures increased alpine glaciation a stormier climate and perturbations to humidity vegetative cover and precipitation

geophysical insights into the transition fault debate propagating strike slip in response to stalling yakutat block subduction in the gulf of alaska on the basis of faulting mapped on seismic reflection and bathymetric data seismicity current plate motions and evidence that the yakutat block may be anomalously thick we propose a tectonic model for yakutat pacific interactions including the often debated transition fault to the east deformation associated with the queen charlotte fairweather fault system is extending offshore facilitating westward propagation of strike slip motion along the eastern segment of the transition fault to the west the oblique slip pamplona zone and transition faults merge at an embayment in the continental margin where a north south dextral strike slip fault within the pacific plate illuminated by the 1987 1992 earthquake swarm intersects the pacific yakutat tectonic boundary these fault patterns are consistent with modern plate motions and reflect a plate boundary reorganization that may be caused by resistance to subduction by the yakutat block a possible moderate sized oceanic plateau

the transition from strike slip to oblique subduction in southeastern alaska from seismological studies abstract body waveform modeling of 11 moderate to large earthquakes within southeastern alaska has been incorporated with earthquake relocations and the results of previous seismicity studies to examine the transition from strike slip to oblique subduction in southeastern alaska in the sitka region of extreme southeastern alaska earthquakes indicate seismic slip is parallel to the direction of motion between north america and the pacific plate as the plate margin begins to bend to the west near cross sound and encounters the southeastern edge of the yakutat block partitioning of seismic slip is evident both onshore and offshore although the largest earthquakes magnitude 6 0 in this region have slip parallel to plate motion most moderate sized events have slip vectors rotated clockwise from plate motion offshore the 1973 cross sound sequence indicates that the southern end of the transition zone is seismogenic with the pacific plate being thrust beneath the yakutat block while onshore strike slip faulting has occurred along the fairweather border ranges and denali faults in the st elias region thrust faulting is occurring along and above the plate interface moderate sized events in the st elias show a mix of slip vector orientations in the pamplona zone slip vectors of offshore earthquakes and deformation directions determined onshore from gps studies show a counter clockwise rotation relative to plate motion suggesting that a change in strain field occurs just west of the st elias region

from tectonically to erosionally controlled development of the himalayan orogen whether variations in the spatial distribution of erosion influ ence the location style and magnitude of deformation within the himalayan orogen is a matter of debate we report new 40 ar 39 ar white mica and apatite fission track aft ages that measure the vertical component of exhumation rates along an 120 km wide ne sw transect spanning the greater sutlej region of northwest india the 40 ar 39 ar data indicate that first the high himalayan crystalline units cooled below their closing temperature during the early to middle miocene subsequently lesser himalayan crys talline nappes cooled rapidly indicating southward propagation of the orogen during late miocene to pliocene time the aft data in contrast imply synchronous exhumation of a ne sw oriented 80 3 40 km region spanning both crystalline nappes during the pliocene quaternary the locus of pronounced exhumation de fined by the aft data correlates with a region of high precipita tion discharge and sediment flux rates during the holocene this correlation suggests that although tectonic processes exerted the dominant control on the denudation pattern before and until the middle miocene erosion may have been the most important factor since the pliocene

new constraints on the motion of the fairweather fault alaska from gps observations 1 gps velocities from sites near to the fairweather fault in southern alaska are combined with line length data from geodetic surveys by the u s geological survey usgs to estimate the slip rate and locking depth of the fairweather fault using dislocation theory we perform a weighted least squares inversion of the geodetic data and obtain a best fitting slip rate of 45 6 2 0 mm yr and locking depth of 9 0 0 8 km the slip rate we estimate is one of the highest observed across any strike slip fault we also include the dalton creek segment of the denali fault in our model and estimate a slip rate of 3 8 1 4 mm yr for this section of the fault this is substantially lower than the rate observed for the denali fault segment to the northwest which ruptured in the november 3 2002 mw 7 9 denali fault earthquake

geometry of eclogite facies structural features implications for production and exhumation of ultrahigh pressure and high pressure rocks western gneiss region norway 1 well preserved eclogite facies structural features in metamorphosed gabbro and diorite gneiss in baltica crust formed at a minimum depth of 60 70 km during the scandian orogeny allow direct inferences to be made regarding the geometry of folds kinematics and original structural orientations related to production and exhumation of high pressure rocks folds associated with eclogite facies fabrics are isoclinal to tubular with axes parallel to the trend of a stretching lineation strain estimates and l s or l s fabrics indicate that these structures were formed in a constrictional strain field locally they are well preserved in eclogite facies mylonite zones at least 40 m thick that cut proterozoic gabbro and adjacent gneiss where steeply dipping they show a north side up shear sense across a younger northeast trending shallowly plunging amphibolite facies anticlinorium formed in a constrictional noncoaxial strain field where original structural facing direction can be inferred small circle rotation of the eclogite facies lineation about the anticline axis indicates that the relative motion vector of baltica with respect to overlying imbricated crust and laurentia was oriented 320 in a present day reference frame this result is identical to the orientation of the relative motion vector estimated from paleomagnetic plate reconstructions and consistent with late silurian to early devonian oblique sinistral convergence between baltica and laurentia results of this study indicate that coherent baltica crust at 60 70 km depth experienced subvertical and horizontal shortening while extending toward the foreland during tops southeast thrusting parallel to plate motion high pressure rocks were progressively imbricated and stacked along eclogite facies mylonite zones with the deforming zone separating coherent baltica crust from imbricated basement above the constrictional strains under eclogite facies conditions are interpreted to have resulted from stretching associated with sinking of the cool dense mantle lithosphere

deformation during terrane accretion in the saint elias orogen alaska the saint elias orogen of southern alaska and adjacent canada is a complex belt of mountains formed by collision and accretion of the yakutat terrane into the transition zone from transform faulting to subduction in the northeast pacific the orogen is an active analog for tectonic processes that formed much of the north american cordillera and is also an important site to study 1 the relationships between climate and tectonics and 2 structures that generate large to great magnitude earthquakes the yakutat terrane is a fragment of the north american plate margin that is partly subducted beneath and partly accreted to the continental margin of southern alaska interaction between the yakutat terrane and the north american and pacific plates causes significant differences in the style of deformation within the terrane deformation in the eastern part of the terrane is caused by strike slip faulting along the fairweather transform fault and by reverse faulting beneath the coastal mountains but there is little deformation immediately offshore the central part of the orogen is marked by thrusting of the yakutat terrane beneath the north american plate along the chugach saint elias fault and development of a wide thin skinned fold and thrust belt strike slip faulting in this segment may be localized in the hanging wall of the chugach saint elias fault or dissipated by thrust faulting beneath a north northeast trending belt of active deformation that cuts obliquely across the eastern end of the fold and thrust belt superimposed folds with complex shapes and plunging hinge lines accommodate horizontal shortening and extension in the western part of the orogen where the sedimentary cover of the yakutat terrane is accreted into the upper plate of the aleutian subduction zone these three structural segments are separated by transverse tectonic boundaries that cut across the yakutat terrane and also coincide with the courses of piedmont glaciers that flow from the topographic backbone of the saint elias mountains onto the coastal plain the malaspina fault pamplona structural zone separates the eastern and central parts of the orogen and is marked by reverse faulting and folding onshore most of this boundary is buried beneath the western or agassiz lobe of the malaspina piedmont glacier the boundary between the central fold and thrust belt and western zone of superimposed folding lies beneath the middle and lower course of the bering piedmont glacier

coupling glacial erosion and tectonics at active orogens a numerical modeling study 1 climate change indirectly alters the distribution of tectonic uplift at active orogens by modifying the action of surface processes which in turn alters mountain topography the impact of alpine glaciation on tectonic activity is explored here the predictions of previous analytical critical wedge models are compared with the output of a numerical model that explicitly couples rock uplift produced by convergence with surface erosion glacial and fluvial and erosive processes are calculated over a two dimensional grid which uses an ice evolution model to calculate the rate of glacial erosion due to ice sliding tectonic uplift is determined by a two dimensional finite element convergence model the simulations performed support the predictions of previous one dimensional analytical modeling of fluvially dominated orogens increasing precipitation decreases orogen width by the one quarter power the simulations show that glacially dominated landscapes have similar dependencies the total glacial erosion yield is determined to be proportional to the glacial coverage sublinearly dependent on the precipitation rate and linearly dependent on the glacial erosion constant that relates erosion with sliding speed climate also determines the distribution of tectonic uplift in the model if the equilibrium line altitude ela is high and glacial processes are limited to peak regions the center of the mountain range experiences the highest rate of rock uplift extensive glaciation increases rock uplift rates on the flanks of the range the style of glacial erosion is also important a simple glacial buzzsaw does not create the same tectonic response as models that physically simulate glacial erosion the simulations support the idea that a climate cooling of the magnitude recorded in the late cenozoic has the potential to more than double the rate of rock uplift in appropriate orogens the implications of the model are discussed for observations from the olympic mountains of washington state the southern alps of new zealand the alaskan coastal range and the southern andes

a decade of sedimentation in ice contact proglacial lakes bering glacier ak abstract bathymetric surveys during the 1991 2000 decade in two ice contact proglacial lakes on the eastern sector of bering piedmont lobe captured the buildup effects of the 1993 1995 surge following ice front advance of 1 0 1 5 km into tsivat and tsiu lakes the basins were significantly altered by surge related sedimentation including the impact of a subglacial outburst into tsivat lake the subsequent changes in basin shape size and morphology were monitored by six bathymetric surveys measured changes in water depth serve as a proxy for determining increments of sediment accumulation upwelling ice front vents fed by subglacial tunnels transported suspended fine sediment directly into the lake system the rate of suspension settling within both lakes varied from 0 6 to 1 2 m year 1 prior to the surge suspended load during surge years increased sixfold from 1 7 to 13 9 g l 1 accompanied by increased sediment accumulation of 2 2 3 1 m year 1 vent related aggradation and subsequent filling of tsivat lake caused sediment bypassing to tsiu lake where encroachment by delta growth contributed to a postsurge rate of bottomset accumulation of 3 0 m year 1 the total sediment influx from subglacial sources is represented by the sum of bathymetrically determined accumulation plus an estimated volume of sediment that remained suspended thus passing through the lake system total sediment flux along the eastern bering piedmont lobe from 1991 to 2000 is approximately 227 million cubic meters

u th he thermochronometry mapping 3d geometry using micro x ray tomography and solving the associated production diffusion equation u th he ages reflect the combined effects of he particles loss due to diffusion and he ingrowth due to radioactive decay of u and th series furthermore the particles are emitted with sufficient kinetic energy that they can travel in theory up to 20 m and as a result particles may be ejected beyond the crystal edges to circumvent this problem a correction factor must be applied which is essentially based on the geometry of the crystals farley k a wolf r and silver l 1996 the effect of long alpha stopping distances on u th he dates geochimica et cosmochimica acta 60 4223 4229 this strongly limits the application of the technique to crystals of appropriate geometries we present here a method to compute the effects of ejection for u th he dating by taking into account the 3d morphology of individual crystals determined with micro x ray tomography we also develop a model which solves the diffusion equation for the crystals that have been imaged we then couple this model with an inversion algorithm to extract the range of thermal histories that the rocks may have experienced this technique is applied to detrital samples from rocks collected in the southern alps of new zealand a region of high exhumation rate

geophysical characteristics of the continental crust along the lithoprobe eastern canadian shield onshore offshore transect ecsoot a review the eastern canadian shield onshore offshore transect ecsoot of the lithoprobe program included 1200 km of normal incidence seismic profiles and seven wide angle seismic profiles across archean and proterozoic rocks of labrador northern quebec and the surrounding marine areas archean crust is 33 44 km thick p wave velocity increases downwards from 6 0 to 6 9 km s there is moderate crustal reflectivity but the reflection moho is unclear archean crust that stabilized in the proterozoic is similar except for greater reflectivity and a well defined moho proterozoic crust has similar or greater thickness variable lower crustal velocities and strong crustal reflectivity geodynamic processes of paleoproterozoic growth of the canadian shield are similar to those observed in modern collisional orogens the suturing of the archean core zone and superior provinces involved whole crustal shearing top to west in the core zone linked to thin skinned deformation in the new quebec orogen the torngat orog

punctuated thrust deformation in the context of doubly vergent thrust wedges implications for the localization of uplift and exhumation understanding uplift and exhumation in orogenesis requires integrating the effects of both climatic and tectonic forcing punctuated thrust activity is widely documented from field studies in a range of mountain belts the potential for climatic forcing of thrust activity has been a subject of recent debate here we use a modeling approach to analyze the behavior of individual thrust units in the context of asymmetric doubly vergent thrust wedges the model predicts that rates of surface uplift frontal accretion and exhumation should be punctuated on a time scale linked to thrust sheet geometry and convergence rates this time scale ranges from 0 1 to 5 m y for various settings and should be calculated before external forcings such as climate are invoked

thermotectonic history of mt logan yukon territory canada implications of multiple episodes of middle to late cenozoic denudation abstract the extreme relief of the st elias mountains including mt logan is suggestive of a young mountain belt new apatite fission track data indicate that the mt logan massif experience rapid low temperature cooling during three distinct periods during the middle eocene middle miocene and pliocene each cooling episode the magnitude of which varies due to temporal variations in recorded paleogeothermal gradients can be tentatively linked to a tectonic cause eocene cooling may be due to re equilibration of isotherms following normal faulting caused by a combination of thermal weakening of the crust and a decrease in regional compressional stress due to the 43 ma change in relative motions between the pacific and north american plates the cause of miocene cooling is problematic and could reflect denudation in response to initial underplating of the yakutat terrane or a recorded change in heat flow unrelated to denudation pliocene cooling reflects erosion due to surface uplift that produced the spectacular present day topography of the st elias mountians this surface uplift is probably related to the coeval significant change in relative motion between the north american and pacific plates and or resistance to subduction by the yakutat terrane

erosion and exhumation in accretionary orogens experimental and geological approaches 1 this study examines the role of erosion on exhumation and deformation history of accretionary orogens through experimental and geological methods fault propagation kinematics and exhumation rates in an eroded thrust wedge are analyzed through scaled sandbox simulations by testing different parameters friction rheologic layering and sediment input output ratio a model coulomb wedge is submitted to erosion under flux steady state conditions that is the volume of eroded material remains equal to the volume of newly accreted material maintaining a constant surface slope during shortening results show that the way of exhumation depends on the internal dynamics of thrust wedges and conversely on how this dynamics is modified by erosion in the eroded thrust wedges the diversity of exhumation patterns is controlled by the mode of fault propagation depending on the basal friction high or low the vertical component of exhumation is generally higher for the wedges with high basal friction than for low friction wedges the uplift of material occurs along a cluster of subvertical thrusts in the middle part of the eroded thrust wedge with low basal friction the material is exhumed along a series of inclined 20 50 thrusts in the rear of the high friction wedge the zone of maximum exhumation is generally localized in the middle part of the thrust wedge and migrates toward the backstop with continued shortening the vertical exhumation rate increases with time and the material accreted later is rapidly transferred to the main exhumation zone compared to the material accreted during the early stages the exhumation occurs at rates 2 times faster in the wedges with half the thickness than in full thickness wedges the total quantity of eroded material at the end of convergence constitutes 36 50 of initial model area for the thrust wedges with low basal friction and 20 40 for the high basal friction wedges the extent of basal underplating increases with total shortening the area of basal underplated material constitutes up to 30 and 40 of the eroded thrust wedge area for the models with low and high basal friction respectively presence of decollements in the accreted series allows underplating of thrust units developing an anticlinal stack whose growth and location is favored by erosion our results are compared to different present day active and ancient convergent orogens himalaya taiwan southern alps of new zealand and cascadia orogen allowing the different specific exhumation processes to be characterized

mechanical model for the tectonics of doubly vergent compressional orogens a mechanical model of crustal shortening and deformation driven by the relative convergence of rigid underlying mantle plates explains many features of convergent orogens results based on numerical models and supported by sandbox models show that a coulomb crustal layer subject to basal velocity boundary conditions corresponding to asymmetric detachment and subduction of the underlying mantle passes through three stages of orogenic growth 1 block uplift bounded by step up shear zones 2 development of a low taper wedge over the underthrusting mantle plate and 3 development of a low taperwedge overlying the overthrusting mantle plate and verging in the opposite direction when modified by isostasy basal viscous flow surface erosion and denudation and sedimentation the resultant model orogens exhibit a variety of styles with characteristics in common with small rapidly denuded orogens large orogens with plateaus and extensional characteristics and active subduction margins with doubly vergent accretionary wedges and deformed fore arc basins

architecture kinematics and exhumation of a convergent orogenic wedge a thermochronological investigation of tectonic climatic interactions within the central st elias orogen alaska abstract the kinematics and architecture of orogenic systems along the leading edges of accreting terranes may be heavily influenced by climate but little research has been devoted to the long term effects of glacial erosion on orogenesis here we use low temperature apatite and zircon u th he and fission track thermochronometry along with subsidiary structural relationships and seismicity to develop a new architectural model of the st elias orogen in southern alaska which is one of the best examples of a glaciated orogenic wedge worldwide these data illustrate that the orogen consists of a deformational backstop on the leeward flank and a rapidly deforming and eroding thin skinned fold and thrust belt on the windward flank a structure beneath the bagley ice field separates these distinct deformational domains which we propose is a backthrust that makes the orogen doubly vergent thermochronometry within the orogenic wedge suggests that denudation and deformation are strongly influenced by glacial erosion long term exhumation at rates of up to 4 mm yr is concentrated within a narrow zone along the windward flank where glacier equilibrium lines intersect the orogenic wedge the onset of enhanced glaciation also coincided with a marked acceleration in exhumation across the orogenic wedge accelerated backthrust motion and a major shift in deformation away from the north american yakutat terrane suture chugach st elias fault we propose that accelerated glacial erosion forced the redistribution of strain along the backthrust and an en echelon array of forethrusts that lie beneath the zone of heaviest glaciation which in turn are systematically truncated by the backthrust this focusing of deformation matches predictions from analytical models of orogenic wedges and implies a high degree of coupling between climate and tectonics in this glacially dominated orogen

depositional and microfaunal response to pliocene climate change and tectonics in the eastern gulf of alaska abstract the yakataga formation provides an excellent record of pliocene paleoclimate in the gulf of alaska and northeastern pacific ocean evidence for glaciomarine influence and paleoclimatic change includes the distribution of ice rafted debris and diamictite planktic and benthic foraminiferal biofacies and variable sediment accumulation rates three paleoclimatically defined intervals within the pliocene yakataga formation are recognized in onshore and offshore sections interval p1 5 35 to 4 2 ma contains the first evidence of neogene glaciomarine deposition in the form of ice rafted debris and rare diamictite interval p2 4 2 to 3 0 3 5 ma exhibits a reduction in glaciomarine influence and warming to cool temperate conditions interval p3 3 0 3 5 to 1 8 ma contains massive amounts of glaciomarine diamictite and correlates with other evidence indicating the onset of major northern hemisphere glaciation sediment accumulation rate and foraminiferal based paleobathymetric curves show some correlation to the above paleoclimatic subdivision but also significant independent relationships indicating a strong tectonic influence on those parameters comparison of the yakataga record to odp sites in the north pacific shows that there is good agreement in the ice proximal yakataga and deep sea records of pliocene paleoclimate change

exhumation rates in the st elias mountains alaska abstract reprocessing and interpretation of seismic profiles from the gulf of alaska in the vicinity of the st elias mountains indicate that over 3000 km 3 of sediment were deposited on the ocean shelf since the end of the last glacial epoch approximately 10 000 years ago this estimate of the sediment volume does not include material moved out of the region by long shore currents transportation from the shelf to deeper waters or material trapped in fiords and basins on and near land thus an estimated sedimentation rate offshore of 7 9 mm year and the average erosion rate of 5 1 mm year from the st elias mountains derived from the estimated sedimentation rate represent minimum estimates we infer that these estimated rates are not typical of the approximately 5 m y history of mountain building in the area but rather they represent the result of efficient erosion by glaciers during this interglacial period

two sided orogen collision and erosion from the sandbox to the southern alps new zealand in continental collision zones the indentor is of approximately the same vertical dimension as the material being deformed thereby allowing material to move over the indentor and out of the deforming orogen this simple constraint on the height of the indentor differs from that imposed by the bulldozer model of wedge deformation and results in the formation of an orogen with two opposite dipping topographic slopes these two wedges are mechanically coupled and the mechanics are strongly influenced by the erosion conditions imposed on the wedge where the growing mountains perturb prevailing moisture laden winds the erosion pattern is highly asymmetric erosional work being concentrated at the toe of the steep wedge facing the indentor the inboard wedge concentration of erosional energy results in concentration of mechanical energy in the same region and produces the distinctive geological and geophysical patterns associated with continental collision these include rapid uplift and exposure of deep crustal assemblages adjacent to the indentor accompanied by high crustal heat flow and anomalously low seismicity the outcrop pattern along the inboard wedge evolves from that of a crustal cross section currently exposed in the southern alps to one dominated by repetitive nappe structures consisting predominantly of lower crustal units as in the western alps of europe the other wedge the outboard wedge undergoes relatively little erosion is broad with a more gentle surface slope and maintains an outcrop pattern consisting of upper crustal material

relation of ongoing deformation rates to the subduction zone process in southern alaska the rate and orientation of ongoing strain associated with subduction of the pacific plate and the accretion of the yakutat terrane to southern alaska has been estimated at 13 sites from global positioning system measurements made in june 1993 and 1995 along the gulf of alaska coast near cape yakataga the average rate of deformation relative to fairbanks was 38 mm yr at n32 w further inland above the region where the dip of the downgoing pacific plate changes from about 10 to 30 the deformation rate was 12mm yr at n26 w in the sourdough paxson area the deformation rate drops to 2 5 mm yr and suggests a low short term deformation rate across the denali fault elastic straining of the overriding plate due to back slip on a main thrust zone with an average dip of about 10 can account for the overall rate and distribution of short term compressional strain across south central alaska above the transitional region between unstable and stable sliding we suggest that strain associated with 15 mm yr of right lateral strike slip occurs also if the strain accumulated since the two 1899 earthquakes both mw 8 1 from the offshore pamplona fault zone to south of the border ranges fault down dip width 100 km was seismically released on a single fault it would correspond to a m 8 1 earthquake

change in motion of pacific plate at 5 myr bp alignments of volcanoes such as the hawaiian seamount chain record the passage of oceanic plates over mantle plumes or hot spots and changes in the orientation of a seamount chain may indicate changes in the direction of motion of the plate within the hotspot frame of reference1 this hypothesis can be tested for the pacific plate by comparing data from the hawaiian volcanoes with tectonic movements inferred from the geology of adjacent plates we have now found that the motion of the pacific plate changed to a more northerly direction 5 myr ago probably as a result of the detachment of a piece of pacific sea floor which had been subducted beneath the fiji plateau during the tertiary