laramide exhumation of the bighorn mountains wyoming an apatite u th he thermochronology study we report u th he apatite ages from the crystalline core of the bighorn mountains and compare the exhumation history derived from those ages with the exhumation history determined from sedimentary rocks in the adjacent powder river and bighorn basins our u th he apatite ages range from 62 to 369 ma and represent a pre laramide he partial retention zone that was deformed and uplifted at ca 65 5 ma the geometry of the he partial retention zone indicates that the basement in the bighorn mountains is deformed into a doubly plunging anticline the preservation of a pre laramide partial retention zone in the upper few hundred meters of precambrian basement indicates that in general the temperature at the cambrian unconformity did not exceed the apatite he closure temperature this is difficult to reconcile with evidence from adjacent basins for thick sequences of sedimentary rocks 3 4 km prior to 65 ma and normal modern geothermal gradients either the range was never deeply buried 2 3 km its geothermal gradient has been low 20 c since at least the mesozoic or our apatites have higher u th he closure temperatures 80 90 c than those measured for other apatites

implications for magmatic processes at ontong java plateau from volatile and major element contents of cretaceous basalt glasses 1 major elements cl co2 and h2o were determined in unaltered tholeiitic basalt glasses from drilling program sites 803d and 807c on ontong java plateau ojp and sites 462a in nauru basin nb and 802a in east mariana basin emb glasses are moderately evolved mg 53 60 with low na2o indicating they formed by large extents of melting extent of melting is less for glasses from ojp than from emb requiring faster or more focused mantle upwelling or a longer period of activity for ojp glasses within each hole define 1 3 different compositional types each compositional type is made up of many glass bounded flow units whose chemistry is identical within analytical uncertainty suggesting that each compositional type formed during a single eruptive episode with multiple magma surges the lack of diversity within each type also suggests that the magmatic system was large and well buffered major element chemistry also requires that significant shallow crystallization occurred during plateau formation and limits the amount of deep crystallization that might be responsible for the thick crust of the plateau chlorine contents are constant within each compositional type and are 580 ppm in type a and 850 ppm in types c g from hole 807c and 360 ppm in glasses from hole 803d glasses from 802a and 462a have 240 ppm and 1975 ppm cl respectively cl k ratios range from 0 2 to 2 33 well above mid ocean ridge basalt morb mantle values 0 07 suggesting that most liquids assimilated hydrothermally altered material as they ascended and crystallized high cl k ratios also suggest that abundant hydrothermal activity may have accompanied plateau formation low dissolved co2 i e co32 contents in one ojp compositional type 54 ppm in 807c type a are similar to those on shallow sections of the mid ocean ridge and are consistent with a maximum depth of eruption of 1320 250 m in contrast to the greater eruption depths inferred from fossils in the overlying sediments our proposed eruption depth falls in the morb field on a plot of depth versus na8 0 supporting a ridge or near ridge origin the shallow depth estimate allows for more postformation subsidence and diminishes the importance but does noteliminate the need for additional processes such as prolonged underplating to account for ojp s shallow depth higher co2 in other glasses including types c g from hole 807c suggests that some liquids were oversaturated with co2 when emplaced and therefore did not travel far from their point of eruption h2o contents are similar to morb and range from 0 13 wt for nb to 0 25 wt 807c types c g to 0 49 wt 807c type a ratios of h2o to rare earth elements ree are slightly higher than most morb and are similar to those from northern mid atlantic ridge mar which has distinctively high h2o h2o ce constant in depleted through enriched morb ranges from 200 to 400 compared to 220 380 for northern mar glasses and 150 250 for morb elsewhere and 500 for arc related glasses the slightly higher h2o contents in the ojp mantle source could have contributed very little to the extensive melting that built the plateau so a substantial temperature anomaly is still required

pedogenic carbonate proxies for amount and seasonality of precipitation in paleosols the depth to carbonate nodular bk horizon in soils d in cm is correlated with mean annual precipitation p in mm so that bk horizons are deep in subhumid regions but shallow in semiarid regions previous quantifications of this relationship are unchanged by this new compilation of 807 soils p 137 24 6 45 d 0 013 d 2 where r 2 0 52 and standard error s e 147 mm in most north american postglacial soils the bk horizon is thin and well defined whereas in monsoonal tropical soils of pakistan and kenya the bk horizon is thick and diffuse data from 675 modern soils define the relationship between the thickness of soil with nodules t in cm and mean annual range of precipitation m in mm difference between monthly means of wettest and driest months m 0 79 t 13 71 where r 2 0 58 and s e 22 mm the relationship between carbonate nodule size s in cm and soil age a in ka is quantified by 9 radiocarbon dated soils from las cruces new mexico a 3 92 s 0 34 where r 2 0 57 and s e 1 8 k y these transfer functions are applied to reconstructing paleoclimatic change from paleocene eocene paleosols of the north horn formation and flagstaff limestone of axhandle canyon utah the terminal paleocene spike of warmth recorded by fossil plants in nearby wyoming was coincident with a brief peak in both mean annual precipitation and mean annual range of precipitation in utah

mesozoic aseismic ridges on the farallon plate and southward migration of shallow subduction during the laramide orogeny we propose that an aseismic ridge of late jurassic and early cretaceous age on the farallon plate was subducted beneath the unites states cordillera during the laramide orogeny the relative buoyancy of the aseismic ridge caused shallow subduction which resulted in a magmatic lull 70 40 ma in the existing near trench magmatic arc and laramide uplift and faulting of crystalline basement 1000 1500 km inland from the trench the timing and latitudinal limits of the subduction of the aseismic ridge are similar to the timing and latitudinal limits of both the laramide orogeny and the magmatic lull in the western cordillera because the north northeast trending aseismic ridge was moving northeast relative to the north american plate the point of collision of the aseismic ridge with north america and therefore the locus of shallow subduction migrated southward with time causing the well documented southward migration of the magmatic lull

u th he thermochronology of the ottawa embayment eastern canada the temperature time history of an ancient intracratonic rift basin abstractthe ottawa embayment is an intracratonic rift basin in eastern north america that preserves a unique and eventful history through deep time we report single grain zircon and apatite u th he and biotite 40ar 39ar data from samples collected along a 250 km transect across the crystalline rift flank and through the sedimentary sequences of the embayment the data sets show significant intrasample age dispersions and we investigate the influence of zircon crystallinity and nonideal crystal shapes on he diffusion through the application of raman spectroscopy and x ray microcomputed tomography ultimately we utilize the relationship between radiation damage and helium diffusion to quantify observed age dispersion we integrate our age data from the basement and overlying sedimentary unit of the embayment with regional geology to utilize multisample inverse modeling to reveal viable thermal histories that we then further evaluate by using the forward modeling method to improve our understanding of t

the correction for sediment loading on the seafloor available measurements of sediment velocity and density indicate that a factor of 600 m s 1 of two way sediment reflection time will correct seafloor depth to yield basement depth in the absence of sediment loading this simple linear relation is derived from the results of six deep drill holes in abyssal sediments of the north and south atlantic oceans the relation predicts the sediment correction with an accuracy of about 50 m regardless of the lithology sampled down to a depth of 1 5 s of reflection time the cost wells on the u s continental shelf and empirical relations among velocity density porosity and depth provide estimates of the deeper behavior of abyssal sediments and suggest that the 600 m s 1 factor continues to provide a satisfactory sediment correction to a depth of 3 s

phanerozoic low temperature evolution of the uruguayan shield along the south american passive margin the crystalline basement of uruguay was assembled during the brasiliano orogeny in the neoproterozoic era and was later affected by discrete tectonic activity a new multi method low temperature dataset including u th he ages from both zircon and apatite t t modelling and k ar dating of fine sericite fractions and fault gouge reveal a detailed post orogenic geological history spanning the phanerozoic eon the juxtaposition of the terranes that compose the area was achieved in the ediacaran period and post collision was marked by intense exhumation in which the crystalline basement reached near surface conditions by the early to mid palaeozoic regional subsidence promoted sedimentation in the parana basin until the permian covering and reheating much of the basement that is at present exposed afterwards deposition and volcanism were mostly confined to its current limits regional exhumation of the shield during the permo triassic exposed much of the northern portion of the basement and the south was further affected by the opening of the south atlantic ocean during the mesozoic little exhumation affected the uruguayan shield during the cenozoic as reflected in its modest topography the reactivation of inherited neoproterozoic structures influenced the development of mesozoic basins and the present day landscape supplementary material supplementary data sample locations u th he data and k ar data are available at https doi org 10 6084 m9 figshare c 3702043

zircon titanite and apatite u th he ages and age eu correlations from the fennoscandian shield southern sweden craton cores far from plate boundaries have traditionally been viewed as stable features that experience minimal vertical motion over 100 1000 ma time scales here we show that the fennoscandian shield in southeastern sweden experienced several episodes of burial and exhumation from 1800 ma to the present apatite titanite and zircon u th he ages from surface samples and drill cores constrain the long term low temperature history of the laxemar region single grain titanite and zircon u th he ages are negatively correlated 104 838 ma for zircon 160 945 ma for titanite with effective uranium eu u 0 235 th a measurement proportional to radiation damage apatite ages are 102 258 ma and are positively correlated with eu these correlations are interpreted with damage diffusivity models and the modeled zircon he age eu correlations constrain multiple episodes of heating and cooling from 1800 ma to the present which we interpret in the context of foreland basin systems related to the neoproterozoic sveconorwegian and paleozoic caledonian orogens inverse time temperature models constrain an average burial temperature of 217 c during the sveconorwegian achieved between 944 ma and 851 ma and 154 c during the caledonian achieved between 366 ma and 224 ma subsequent cooling to near surface temperatures in both cases could be related to long term exhumation caused by either post orogenic collapse or mantle dynamics related to the final assembly of rodinia and pangea our titanite he age eu correlations cannot currently be interpreted in the same fashion however this study represents one of the first examples of a damage diffusivity relationship in this system which deserves further research attention

the surface tectonics of mantle lithosphere delamination following ocean lithosphere subduction insights from physical scaled analogue experiments many postulated lithospheric removal events occur in regions with an earlier history of subduction but the relationship between the two processes has not been explored in this work we use physical scaled analogue experiments to investigate the evolution from ocean lithosphere subduction to collision and possible delamination of the mantle lithosphere from the crust we test how varying the magnitude of plate convergence alters the behavior of the subduction delamination model our experiments show that a retreating ocean proplate can evolve to continental mantle lithosphere delamination negative surface topography is supported at the delamination hinge and this migrates back with the peeling lithosphere with high plate convergence delamination is suppressed rather the crust and mantle lithosphere split at the collision zone in a form of flake tectonics as oncoming procrust is accreted on top of the retroplate and the promantle lithosphere subducts below localized high topography develops at this zone of crustal accretion and thickening the results suggest that delamination may be a continental continuation of plate retreat and that lithospheric removal is triggered by the transition from one process to another

jurassic cretaceous boundary age and mid ocean ridge type mantle source for shatsky rise basalt sills cored in lowermost berriasian sediments on shatsky rise in the northwest pacific yield a mean 4 0 ar 3 9 ar incremental heating age of 144 6 0 8 ma providing a minimum estimate on the age of the jurassic cretaceous boundary the largest part of the rise was emplaced at rates similar to those of several continental flood basalts the rise formed at an oceanic triple junction and the sills as well as lavas from two dredge sites exhibit an ocean ridge type nd pb sr isotope signature this signature is provisionally consistent with either a perisphere or meteorite impact model but is not predicted by the plume head model of plateau formation however no model can yet be rejected given the very sparse sampling of shatsky rise

volcanic evolution of the submarine super volcano tamu massif of shatsky rise new insights from formation microscanner logging imagery tamu massif the southernmost plateau of shatsky rise is recently reported as the largest single volcano known on earth this work seeks to understand the type of volcanism necessary to form such an anomalously large single volcano by integrating core and high resolution wireline logging data in particular resistivity imagery obtained by the formation microscanner in integrated ocean drilling program hole u1347a located on the eastern flank of tamu massif was used to construct a logging based volcanostratigraphy this model revealed two different volcanic stages formed tamu massif i the core part of the massif s basaltic basement was formed by a construction phase of volcanism with cyclic eruption events from a steady state magma supply and ii the very topmost basaltic section was formed by a depositional phase of volcanism during which long traveling lava flows were deposited from a distant eruption center

a differential equation for specific catchment area 1 analysis of the behavior of specific catchment area in a stream tube leads to a simple nonlinear differential equation describing the rate of change of specific catchment area along a flow path the differential equation can be integrated numerically along a flow path to calculate specific catchment area at any point on a digital elevation model without requiring the usual estimates of catchment area and width the method is more computationally intensive than most grid based methods for calculating specific catchment area so its main application is as a reference against which conventional methods can be tested this is the first method that provides a benchmark for more approximate methods in complex terrain with both convergent and divergent areas not just on simple surfaces for which analytical solutions are known preliminary evaluation of the d8 m8 digital elevation model networks demon and d methods indicate that the d method is the best of those methods for estimating specific catchment area but all methods overestimate in divergent terrain

subsidence of the west siberian basin effects of a mantle plume impact comparison of modeling results with observed subsidence patterns from the west siberian basin provides new insight into the origin of the siberian traps and constrains the temperature size and depth of an impacting mantle plume head during and after the eruption of the siberian traps at the permian triassic boundary 250 ma we compare subsidence patterns from one dimensional conductive heat flow models to observed subsidence from backstripping studies of wells in the basin this results in a best fit scenario with a 50 km thick initial plume head with a temperature of 1500 c situated 50 km below the surface and an initial regional crustal thickness of 34 km in agreement with published values backstripping and modeling results agree very well including a 60 90 m y delay between the rifting phase and the first regional sedimentation regional subsidence patterns indicate that the plume head was present across a minimum area of 2 5 106 km2 these results re emphasize the viability of a mantle plume origin for the siberian traps provide important constraints on the dynamics of mantle plume heads and suggest a thermal control for the subsidence of the west siberian basin

structural and sedimentological development of footwall growth synclines along an intraforeland uplift east central bighorn mountains wyoming structural sedimentological and provenance data from paleogene synorogenic deposits of the east central flank of the bighorn mountains provide new information about the development of footwall growth synclines the evolution of fault related folds and the erosional unroofing history of intraforeland uplifts three conglomerate units the upper conglomerate member of the fort union formation and the kingsbury and moncrief members of the wasatch formation are incorporated within an asymmetric east verging growth syncline in the footwall of the main range bounding thrust system three stages of footwall deformation are recorded within these conglomerates analysis of mapped progressive unconformities retrodeformed balanced cross sections and conglomerate clast composition data define these stages as part of a continuum of deformation associated with the development of footwall growth synclines development of an anticline syncline pair marked the earliest stage of growth syncline formation stage i rotation of the shared fold limb resulted in amplification of the growth syncline fine grained synorogenic sediment derived from easily eroded mesozoic mudstone bypassed the growth syncline during this stage by the end of lebo shale deposition an average of 12 1 of shortening and 6 46 km of uplift had occurred along the range margin continued growth syncline development was marked by the deposition of the kingsbury conglomerate the kingsbury conglomerate was derived from resistant middle and lower paleozoic carbonate strata in the uplifted source terrane intraformational unconformities recording as much as 55 of bed rotation were developed within the kingsbury conglomerate as fold limb rotation occurred coeval with deposition cross sections indicate that during this early stage of fault related folding an average of 16 9 shortening and 8 12 km of uplift occurred along the eastern flank of the bighorn mountains end of stage i the intermediate stage stage ii of footwall growth syncline development involved partial truncation of the growth syncline by the advancing thrust faults and deposition of the moncrief conglomerate the lower portion of the moncrief conglomerate was rotated basinward in the developing growth syncline the final stage of deformation stage iii was dominated by the thrust faulting of middle and lower paleozoic strata eastward over steeply dipping mesozoic strata and rotated eocene synorogenic conglomerate during this stage of deformation the moncrief conglomerate was deformed as the initially blind thrusts propagated into the near surface conglomerate deposits truncated the entire footwall syncline and overrode the synorogenic conglomerate package cross sections in areas where this final stage of deformation is well developed indicate that an average of 24 1 shortening and 9 7 km of uplift had occurred along the eastern margin of the bighorn mountains the caliber of synorogenic deposition in the powder river basin was linked directly to the lithologic composition of the bighorn mountains approximately half of the 3 6 km thick source stratigraphic section of the eastern bighorn mountains was eroded prior to accumulation of conglomerate the majority of this eroded material was derived from mesozoic mudstone and poorly indurated sandstone that were incapable of generating coarse detritus the first paleogene conglomerates deposited along the east central bighorn mountains therefore do not represent the initiation of laramide uplift but instead represent the exposure of coarse clast forming rock types from the lower half of the hanging wall stratigraphic section i e the mississippian madison limestone and ordovician bighorn dolomite

using hilltop curvature to derive the spatial distribution of erosion rates 1 erosion rates dictate the morphology of landscapes and therefore quantifying them is a critical part of many geomorphic studies methods to directly measure erosion rates are expensive and time consuming whereas topographic analysis facilitates prediction of erosion rates rapidly and over large spatial extents if hillslope sediment flux is nonlinearly dependent on slope then the curvature of hilltops will be linearly proportional to erosion rates in this contribution we develop new techniques to extract hilltop networks and sample their adjacent hillslopes in order to test the utility of hilltop curvature for estimating erosion rates using high resolution 1 m digital elevation data published and new cosmogenic radionuclide analyses in the feather river basin california suggest that erosion rates vary by over an order of magnitude 10 to 250 mm kyr 1 hilltop curvature increases with erosion rates allowing calibration of the hillslope sediment transport coefficient which controls the relationship between gradient and sediment flux having constraints on sediment transport efficiency allows estimation of erosion rates throughout the landscape by mapping the spatial distribution of hilltop curvature additionally we show that hilltop curvature continues to increase with rising erosion rates after gradient limited hillslopes have emerged hence hilltop curvature can potentially reflect higher erosion rates than can be predicted by hillslope gradient providing soil production on hilltops can keep pace with erosion finally hilltop curvature can be used to estimate erosion rates in landscapes undergoing a transient adjustment to changing boundary conditions if the response timescale of hillslopes is short relative to channels

exhumation of high pressure rocks driven by slab rollback rocks metamorphosed under high pressure hp and ultra high pressure uhp conditions in subduction zones come back to the surface relatively soon after their burial and at rates comparable to plate boundary velocities in the mediterranean realm their occurrence in several belts related to a single subduction event shows that the burial exhumation cycle is a recurrent transient process using the calabria apennine and aegean belts as examples we show that the exhumation of hp rocks is associated in time and space with the subduction of small continental lithosphere blocks that triggers slab rollback creating the necessary space for the exhumation of the buoyant continental crust that was deeply buried just before the buoyancy force of the subducted crust increases until this crust detaches from the downgoing slab it then exhumes at a rate that depends directly on the velocity of trench retreat to become part of the overriding plate heated from below by the asthenosphere that flows into the opening mantle wedge the exhumed crust weakens and undergoes core complex type extension responsible for a second stage of exhumation at a lower rate the full sequence of events that characterizes this model crust mantle delamination slab rollback and trench retreat hp rock exhumation asthenosphere heating and core complex formation arises entirely from the initial condition imposed by the subduction of a small continental block no specific condition is required regarding the rheology and erosion rate of hp rocks the burial exhumation cycle is transient and can recur every time a small continental block is subducted

long term tectonothermal history of laramide basement from zircon he age eu correlations abstract the long term 1 ga thermal histories of cratons are enigmatic with geologic data providing only limited snapshots of their evolution we use zircon u th he zircon he thermochronology and age composition correlations to understand the proterozoic phanerozoic thermal history of archean wyoming province rocks exposed in the northern laramide ranges of western north america zircon he ages from the wind river range 54 dates and bighorn mountains 32 dates show negative correlations with effective uranium eu a proxy for radiation damage zircon dates from the bighorns are between 960 ma low eu and 20 ma high eu whereas samples from the wind rivers are between 582 ma low eu and 33 ma high eu we applied forward modeling using the zircon radiation damage and annealing model zrdaam to understand this highly variable dataset a long term t t path that is consistent with the available geologic constraints successfully reproduced age eu correlations the best fit to the wind rivers data involves two phases of rapid cooling at 1800 1600 ma and 900 700 ma followed by slower cooling until 525 ma during the phanerozoic these samples were heated to maximum temperatures between 160 and 125 c prior to laramide cooling to 50 c between 60 and 40 ma data from the bighorn mountains were successfully reproduced with a similar thermal history involving cooler phanerozoic temperatures of 115 c and earlier laramide cooling between 85 and 60 ma our results indicate that age eu correlations in zircon he datasets can be applied to extract long term thermal histories that extend beyond the most recent cooling event in addition our results constrain the timing magnitude and rates of cooling experienced by archean wyoming province rocks between recognized deformation events including the 1 ga period represented by the regionally extensive great unconformity

numerical investigations of the mantle plume initiation model for flood basalt events recent studies have linked both the eruption of continental flood basalts and the emplacement of large oceanic plateaus to the initial phase of mantle plume activity i e the plume head model here we develop this concept further through numerical models of a large thermal diapir rising through the mantle and impinging upon the base of the lithosphere a finite element analysis in axisymmetric geometry is used to model the dynamics of solid state convective flow and heat transport in the mantle and an anhydrous batch melting model is used to estimate melt volumes and compositions obtained from partial melting in the shallow mantle we explore the effects of a number of model variables including mantle viscosity structure plume temperature and diameter and the mechanical response of the lithosphere our study emphasizes cases in which the lithosphere does not undergo significant extension prior to large scale melting a standard model is found to be consistent with some observed characteristics of flood basalt plume initiation events this model includes an initial diapir of radius 400 km and initial excess temperature 350oc rising through a mantle of viscosity 102 pa s and impinging beneath a model oceanic lithosphere 100 ma in age if lithospheric extension does not occur melting is almost entirely sublithospheric the melt volume produced is 3 5x106 km 3 and its composition has high mgo content 15 20 wt a time sequence of precursory central axial uplift of several kilometers followed by major melting volcanism is a robust feature of all the models regardless of mantle viscosity structure or lithospheric response low viscosity in the upper mantle compresses the timescale for these events and results in a constriction of the plume head initially impinging on the lithosphere the radial extent of the melting region about 500 km at the time of maximum melt production is only slightly affected by the upper mantle viscosity for nonrifting lithosphere no significant melt generation occurs for initial plume excess temperatures less than about 300oc the initial plume radius has only a modest effect upon the volume of melt obtained the most important aspect of lithospheric response is whether or not the uppermost crust and lithosphere above 40 km depth undergo extension otherwise the ductile strength of the lower lithosphere has little effect if the lithosphere is allowed to extend freely the melt volume increases by about an order of magnitude and it is comparable with some of the largest oceanic plateaus such as ontong java if continental or oceanic flood basalt events occur on old nonrifting lithosphere the primary melts are likely to be much more mgo rich than the basalts erupted at the surface this is consistent with abundant evidence for olivine fractionation in many flood basalt provinces along with the occurrence of picrite lavas and we hypothesize that fractionation occurs at a density trap at the crust mantle boundary moho at this stage and following it is likely that significant lower crustal and mantle lithospheric contamination of mantle plume derived magmas may occur both isotopically and in the trace elements the sequence and timing of both precursory and post magmatic events in the vast well exposed oceanic flood basalt terrane known as wrangellia se alaska british columbia are consistent with the predictions of our model the uplift predicted by our models is of order 2 4 km if we require that mantle plumes are hot enough to melt beneath unrifted lithosphere effects not modeled here such as small scale convection and hydrous melting will tend to reduce the model excess temperature and uplift in order to better understand the relation between mantle plumes and large igneous provinces several important advances are required implementation of a fractional melting model some realistic assessment of melt transport through the mantle and crust and a fully three dimensional convection model

contrasting responses of rb sr systematics to regional and contact metamorphism laramie mountains wyoming usa archean supracrustal sequences of pelitic quartzitic calcareous and mafic compositions in the central laramie mountains wyoming have been affected by two metamorphic events a 1 78 ga amphibolite grade regional metamorphism and a 1 43 ga contact metamorphism resulting from the intrusion of the laramie anorthosite complex lac rb sr whole rock isotopic data from both outside and within the lac contact aureole define a linear array that lies along a 1 78 ga isochron this date has been independently established as the time of amphibolite facies regional metamorphism associated with collision of the archean wyoming province and the proterozoic colorado province along the cheyenne belt the rb sr isotopic data require that sr was redistributed during regional metamorphism on a scale of at least tens of metres although within the 2 km wide aureole of lac the pelitic rocks were thermally metamorphosed at temperatures greater than 800 c none of the whole rock rb sr data from samples within the lac aureole show evidence of resetting at 1 43 ga it is interpreted that the regional metamorphism involved fluid transport which facilitated sr isotopic resetting whereas the contact metamorphism occurred in a relatively dry environment in which isotopic mobility was restricted to centimetre scale or less rb sr data for biotite feldspar and whole rock from a regional metamorphosed pelitic schist give an isochron age of 1450 40 ma which is interpreted as a cooling age resulting from crustal uplift rb sr data for biotite quartz feldspar and whole rock from a pelitic schist affected by contact metamorphism give an isochron age of 1420 43 ma the time of isotopic re equilibration in response either to crustal uplift or to both contact metamorphism and crustal uplift this study demonstrates that although the response of isotopic systems to metamorphism is complex isotopic data provide insight into metamorphic processes that is difficult to obtain by other means

elevation or alteration evaluation of isotopic constraints on paleoaltitudes surrounding the eocene green river basin low oxygen isotope values 16 relative to peedee belemnite standard obtained from microbial carbonates of the green river formation have been interpreted as evidence for snowmelt and high elevations surrounding this early eocene lake basin however low values from microbial precipitates could also represent a diagenetic overprint we investigate these alternate hypotheses by measuring the oxygen isotope composition of altered and unaltered freshwater bivalves from the basin we analyzed subannual samples from 3 individuals and bulk samples from 54 individuals subannual samples exhibit clear seasonal fluctuations in oxygen isotope values these fluctuations are large enough to require seasonal shifts in temperature and or the oxygen isotope value of the lake water however the lowest value of any unaltered sample either bulk or high resolution corresponds to lake water 18 o of 12 relative to standard mean ocean water and is not low enough to require the addition of snowmelt to the lake a few bulk samples exhibit very low oxygen isotope values which would seem to suggest snowmelt however these samples also show clear evidence of calcite in x ray diffraction patterns demonstrating the presence of diagenetic precipitates given that 1 diagenetic alteration is a plausible explanation of very low 18 o values 2 alteration has not been examined in microbial carbonates and 3 unaltered aragonitic bivalves provide no independent evidence for low 18 o values for lake waters we conclude that robust isotopic evidence for high elevations surrounding the green river basin during the eocene is currently lacking

proterozoic multistage ca 1 1 and 0 8 ga extension recorded in the grand canyon supergroup and establishment of northwest and north trending tectonic grains in the southwestern united states the grand canyon supergroup records at least two distinct periods of intracratonic extension and sedimentation in the late mesoproterozoic and neoproterozoic new 40 ar 39 ar age determinations indicate that the mesoproterozoic unkar group was deposited between ca 1 2 and 1 1 ga basins in which the unkar group was deposited and the related northwest striking faults were created by northeast southwest extension which was contemporaneous with regional northwest southeast grenville contraction new u pb data indicate that the neoproterozoic chuar group was deposited between 800 and 742 ma sedimentary and tectonic studies show that chuar deposition took place during east west extension and resulting normal slip across the butte fault this event is interpreted to be an intracratonic response to the breakup of rodinia and initiation of the cordilleran rift margin laramide monoclines of the grand canyon region have north and northwest trends reactivate faults that originated at the time of unkar and chuar deposition and can be traced for great distances hundreds of kilometers from the grand canyon we use the distribution of monoclines in the southwest to infer the extent of proterozoic extensional fault systems the 1 1 ga northwest trending structures and ca 800 700 ma north trending extensional structures created regional fault networks that were tectonically inverted during formation of the ancestral rocky mountains and laramide contraction and reactivated during tertiary extension

raising the colorado plateau shallow marine rocks exposed on the 2 km high 45 km thick colorado plateau in the western united states indicate that it was near sea level during much of the phanerozoic isostatic calculations however illuminate the difficulty in maintaining a 45 km thick crust at or near sea level we propose that an isostatically balanced 30 km thick proto colorado plateau crust was thickened during the late cretaceous to early tertiary by intracrustal flow out of an overthickened sevier orogenic hinterland this plateau would have been supported by a thick 70 km crustal root which is proposed to have been the source region for hot and weak mid crustal material that flowed eastward from the plateau toward the low elevation proto colorado plateau

diffusion of helium in radiation damaged zircon abstract diffusion of helium was characterized in natural zircon that had been implanted with kr at a range of energies to simulate the effects of alpha recoil in natural radiation damage polished slabs of zircon oriented either normal or parallel to c were implanted with kr ions at a series of energies to produce a damaged region 1 m in thickness then implanted with 100 kev 3he at a dose of 1 1015 3he cm2 which placed the 3he within the region damaged by the kr ion implantation the implanted zircons were annealed isothermally in pt capsules in 1 atm furnaces at temperatures ranging from 51 to 252 c and times ranging from 15 min to 3 weeks 3he distributions following experiments were measured with nuclear reaction analysis using the reaction 3he d p 4he for diffusion in zircon normal to c we obtain the following arrhenius relation d 1 7 10 8 exp 71 2 kj mol 1 rt m2 sec 1 this activation energy for diffusion is about half of the value for he diffusion in zircon from the same sample locality but without kr implantation measured with an otherwise similar experimental and analytical approach cherniak et al 2009 he diffusivities in the kr implanted material are also significantly faster further he diffusivities normal and parallel to c in the kr implanted zircon are similar in contrast to the marked diffusional anisotropy with differences of two orders of magnitude for diffusion normal and parallel to c observed for he diffusion in this zircon in samples not implanted with kr these data indicate that heavily damaged zircon will have very limited retentivity of helium only those zircons larger than a few hundred m will have mean closure temperatures exceeding typical earth surface temperatures mean closure temperatures for he in highly damaged zircon will be about 200 c lower than those for relatively undamaged zircon at 200 c equivalent amounts of he will be lost from severely damaged zircon at a rate about a million times faster than from relatively undamaged zircon for retentivity of he comparable to that for low damage zircon at 200 c the severely damaged zircon would require residence temperatures of 10 c

statistical modelling of annealing kinetics of fission tracks in zircon reassessment of laboratory experiments abstract we remodel the annealing kinetics of fission tracks fts in zircon to fit data from 43 laboratory experiments in three earlier publications using spontaneous ft lengths in zircon from the nisatai dacite heating temperature and time are in the ranges of 350 912 c and 10 3 104 h respectively the data sets illustrate a transition in annealing process at a certain temperature zone in order to express the annealing behavior involving the possible transitional process with improved goodness of fit two types of models are constructed the hybrid linear model that consists of the fanning linear model at high temperature and the parallel linear model at low temperature connected with a transitional temperature zone and the parallel curvilinear model that approximates smoothly the transition in the annealing process the validity of the extrapolation of the model to geological time scale is confirmed by comparison with some deep borehole core data the length estimates by the hybrid linear model agree well with the borehole data whilst the estimates by the parallel curvilinear model show a significant disagreement with highly annealed borehole samples although this model provides good agreement with the experimental data for the hybrid linear model estimates of the partial annealing zone corresponding to isothermal heating for 106 and 107 years are 281 352 c and 262 330 c where the top and bottom of the partial annealing zone are defined by the mean length reduction ratio of 0 4 and 0 8 respectively

the influence of vegetation on debris flow initiation during extreme rainfall in the northern colorado front range we explored regional influences on debris flow initiation throughout the colorado front range colorado usa by exploiting a unique data set of more than 1100 debris flows that initiated during a 5 day rainstorm in 2013 using geospatial data we examined the influence of rain hillslope angle hillslope aspect and vegetation density on debris flow initiation in particular we used a greenness index to differentiate areas of high tree density from grass and bare soil the data demonstrated an overwhelming propensity for debris flow initiation on south facing hillslopes however when the debris flow density was analyzed with respect to total rainfall and greenness we found that most debris flows occurred in areas of high rainfall and low tree density regardless of hillslope aspect these results indicate that present day tree density exerts a stronger influence on debris flow initiation locations than aspect driven variations in soil and bedrock properties that developed over longer time scales

mesoproterozoic burial of the kaapvaal craton southern africa during rodinia supercontinent assembly from u th he thermochronology abstract we present the and zhe data for basement samples across the kaapvaal craton to investigate the cratonic burial and erosion history during the assembly and breakup of the rodinia supercontinent the and zhe dates vary from 1187 to 135 ma and 997 to 32 ma respectively both are negatively correlated with effective u concentration consistent with lower he retentivity at higher radiation damage dose the oldest the dates combined with volcanic rocks that document the basement was at the surface at 1 4 ga require heating to 130 c at 1 0 1 2 ga to cause complete he loss from the titanites we attribute this mesoproterozoic heating event to widespread burial of the craton during rodinia supercontinent assembly by sediments shed from the namaqua natal orogen on the craton s margin later neoproterozoic paleozoic erosion re exhumed the basement to the surface spatial variability in zhe data patterns can be explained by geologically reasonable differences in phanerozoic karoo basin burial and erosion the mesoproterozoic and karoo burial phases are analogous in that their detritus was derived from similarly located orogens during two different supercontinent cycles mesoproterozoic deposition across the kaapvaal craton may be part of a more global signal of burial and erosion during rodinia assembly and breakup our dataset illustrates the power of the and zhe thermochronology for detecting missing proterozoic depositional events in the rock record

bathymetry of shatsky rise northwest pacific ocean implications for ocean plateau development at a triple junction oceanic plateaus are large igneous edifices thought to have been created by nascent mantle plumes but owing to sparse data their origins remain uncertain understanding plateau evolution is important because they are significant ocean features and may provide clues about mantle plume dynamics we constructed a bathymetry map of shatsky rise a large pacific plateau combining multibeam and wide beam echosounder data from 87 cruises and u s navy multibeam contours the rise consists of three large isolated volcanic edifices massifs surrounded by nearly normal lithosphere a linear volcanic ridge and a group of about 80 scattered seamounts massif flank slopes are typically gentle 1 5 and often parallel magnetic lineations or fracture zones the slope angles imply effusive volcanism similar to flood basalts whereas the rise shape suggests formation near the pacific izanagi farallon triple junction with modification of volcano flanks by spreading ridge tectonics edifice sizes and inferred ages imply a trend of decreasing volume and age from southwest to northeast furthermore gaps between massifs suggest episodic volcanism existing data are broadly consistent with the plume head hypothesis wherein the largest edifice formed by massive plume head eruptions the ridge formed from the plume tail and the two massifs in between represent a transition seamounts east of the rise are morphologically distinct which suggests that they may have been formed by a different source or mechanism than shatsky rise proper

influence of radiation damage on titanite he diffusion kinetics titanite is a common u th bearing accessory mineral that previous study suggested has a u th he closure temperature tc of 210 175 c although it has been recognized that radiation damage influences the he retentivity of apatite and zircon this effect has not been documented in titanite we acquired 51 the analyses from 11 archean basement samples across the kaapvaal craton south africa the the dates range from 20 to 1200 ma and are negatively correlated with their 10 970 ppm span of effective uranium concentration eu raman spectra acquired for 4 of these samples display peak broadening with increasing eu 4he diffusion experiments on the same 4 samples suggest tc values that vary by 175 c estimated alpha dose versus tc for our results and published the diffusion data document tc values of 150 210 c at alpha doses 50 1016 g with a sharp decrease in he retentivity above this threshold this damage diffusivity pattern is similar to zircon but the damage level at which the reduction in retentivity occurs appears to be lower for titanite because titanite typically has substantially lower eu than zircon for the same protracted thermal history the dates are likely to record higher temperature portions of the history than zircon u th he dates the results demonstrate that the dating can access a much larger temperature range and potentially be used to decipher more detailed time temperature paths than previously thought

effect of alpha damage annealing on apatite u th he thermochronology recent data on he diffusion challenge the temperature sensitivity of apatite u th he thermochronology the damage induced by recoil of u and th decay series during emission of particles recoil damage has been proposed to modify he diffusion properties through time however we propose that annealing of these irradiation defects may be an important phenomenon and may be significant in case of slowly cooled or reheated basement rocks to test this hypothesis we developed a quantitative model including an explicit treatment of recoil damage annealing and their effect on he diffusion kinetics and calibrate it against literature data our model is based on two hypotheses 1 helium is in equilibrium between an apatite crystal and its defects and 2 alpha recoil damage annealing can be described analogously to fission track annealing this model has been embedded into a monte carlo simulation of helium production ejection diffusion and applied to data from the french massif central a complex slowly cooled terrain with burial reheating where the thermal history has been constrained by previous fission track ft data including ft length distributions u th he ages are close to the ft ages from the same samples and are generally reproducible among replicates but some samples present he age dispersion that is not correlated with crystal size our model reproduces the massif central data very well except for three samples where he ages are older than corresponding ft ages we show that annealing of irradiation damage has an important impact on retentivity of helium and that the he content he is only a rough approximation of the damage level in particular our results show that independence of he ages on crystal sizes in case of reheated samples is a clear indication of the higher he retentivity induced by recoil defects and that an explicit treatment of defect annealing is required for a correct interpretation of u th he ages in such a case more generally a correlation with the crystal size can bring information on the thermal path only if the age of defects well represented by the fission track age is available due to the dependence of the partial retention zone on damages conversely in case of rapid cooling or for samples having low u and th contents damage effects can be ignored without significant effects on he ages

tectonic geomorphology of the san andreas fault zone from high resolution topography an example from the cholame segment abstract high resolution topographic data along fault zones are important aids in the delineation of recently active breaks a 15 km long portion of the south central san andreas fault saf along the southern cholame segment contains well preserved tectonic landforms such as benches troughs scarps and aligned ridges that indicate recurring earthquake slip recently acquired lidar topographic data along the entire southern saf b4 project have shot densities of 3 4 m 2 computed from the lidar returns digital elevation models dems of 0 25 to 0 5 m resolution using local binning with inverse distance weighting and 0 8 m or larger search radii depict the tectonic landforms at paleoseismic sites well enough to assess them confidently mapping of recently active breaks using a lidar only based approach compares well with aerial photographic and field based methods the fault zone varies in width from meters to nearly 1 km and is comprised of numerous en echelon meter to kilometer length overlapping sub parallel fault surfaces bounding differentially moving blocks that elongate parallel to the saf the semantic variations of what constitutes active and the importance of secondary traces influence the breadth and complexity of the resulting fault trace maps

impact origin for the greater ontong java plateau abstract the 120 ma ontong java plateau and neighboring contemporaneous nauru east mariana and probably pigafetta basin flood basalts in the western equatorial pacific ocean comprise the earth s largest flood basalt province geophysical geochemical and geodynamic evidence from the province are difficult to reconcile with mantle plume models absence of an obvious hotspot source or track minor crustal uplift associated with emplacement minor total subsidence compared with normal oceanic crust or other oceanic plateaus and submarine ridges high degrees of melting at shallow upper mantle depths low water contents of basalts enrichment of platinum group elements in basalts and a 300 km deep seismically slow mantle root are more consistent with the consequences of an impacting bolide an object 20 km in diameter impacting relatively young 20 myr pacific lithosphere and penetrating into the uppermost asthenosphere would have initiated massive decompression melting in the upper mantle and may have resulted in emplacement of the greater ontong java plateau

tectonic setting of the midcontinent rift system abstract the continental lithosphere which hosts the midcontinent rift mcr system comprises a crustal assemblage ranging in age from 3 6 to 1 5 ga the most voluminous igneous activity along the mcr occurred within late archean 2 7 ga crust presumably due to magmatism associated with a rising mantle plume two major arms of the rift extend to the southeast and the southwest where rifting magmatism and sedimentation were confined to a 2000 km long rift that cuts through the various crustal provinces ranging in age from 3 6 to 1 5 ga tensional reactivation of pre existing crustal discontinuities may have influenced the location of parts of the mcr however direct cause and effect are difficult to distinguish for want of sufficient exposures the most active phases of magmatism and rifting occurred between 1109 and 1087 ma a u pb age of 1097 ma for the southern end of the mcr shows that magmatic activity was synchronous throughout its length there is evidence of rifting and magmatism prior to 1109 ma but there is little evidence of magmatism after 1087 ma rifting may have effectively ceased by that time rifting may have ceased as a result of compressional forces being exerted on the foreland during the grenville collisional event spanning 1030 970 ma and compressional reactivation of normal faults may have resulted in partial inversion of the mcr chemical data and u pb and sm nd isotopic data for igneous rocks along the rift are similar to those for mcr rocks in the lake superior area which are best explained in terms of a mantle plume model however since the distal arms of the mcr were developed in proterozoic lithosphere and did not involve nearly as much magmatism as in the lake superior area mantle plume sources may not have been as important in formation of the distal magmas data from the buried arms are also consistent with the mafic magmas being derived by decompression melting of proterozoic lithosphere during rifting

paleogeographic and paleotectonic setting of laramide sedimentary basins in the central rocky mountain region in the rocky mountain region between central montana and central new mexico sedimentologically isolated nonmarine basins were produced by basement deformation during the laramide orogeny within the area formerly occupied by a broad late cretaceous foreland basin in which laterally continuous marine facies had accumulated previously laramide structures of varying trend and scale reflect heterogeneity of crustal strain caused by shear between the continental lithosphere and an underlying subhorizontal slab of subducted oceanic lithosphere laramide basins include perimeter basins along the cratonic periphery of the arcuate laramide province axial basins along a north south intramontane trend and ponded basins located farther west closer to the overthrust belt twelve specific stratigraphic and sedimentologic criteria for the onset duration and termination of laramide deformation allow the chronology of basin development to be inferred independently for each basin maastrichtian initiation of laramide deformation was approximately synchronous throughout the laramide province but termination of laramide deformation was systematically diachronous from north to south between early and late eocene time widespread eocene erosion surfaces truncate syntectonic laramide sequences and are overlain by largely volcanic and volcaniclastic post laramide strata of eocene age in the north and oligocene age in the south fluvial depositional systems draining toward the great plains were dominant in perimeter and axial basins but ponded basins were occupied at times by large lakes that served as regional sediment traps paleocene drainages from ponded basins also led eastward toward the continental interior but partly interconnected lakes that developed within several ponded basins by mid eocene time were either closed hydrologically or else they drained westward into the tyee paleoriver of the pacific northwest

mantle convection and the recent evolution of the colorado plateau and the rio grande rift valley the colorado plateau contains late cretaceous marine strata that are at a mean elevation of 2 km the timing and amount of uplift since the cretaceous has generated considerable debate with the exception of a few studies topography supported by vertical stresses generated by viscous fl ow in the mantle has not been explicitly considered to contribute to the elevation of this region herein we compute the viscous fl ow beneath north america that is driven by density anomalies inferred from joint seismic geodynamic modeling we fithat the colorado plateau overlies a strong mantle upwelling that is coupled to the sinking farallon slab currently beneath the eastern united states consequently the colorado plateau is currently a focused dynamic topography high within the western u s cordillera moreover this strong upwelling impacts the base of the lithosphere at an oblique angle east of the plateau directly below the rio grande rift we attribute this fl ow as being responsible for some of the recent magmatic activity along the jemez lineament as well as contributing to the recent rifting process in the rio grande rift valley

influence of crystal size on apatite u th he thermochronology an example from the bighorn mountains wyoming near surface tectonic and geomorphic processes involve cooling of rocks through low temperatures 50 200 c because rates of helium diffusion in apatite titanite and zircon are sensitive to temperature variations in this range uranium thorium helium thermochronometry u th he dating is well suited to establishing the timing and rates of these processes in the geologic record however because fractional loss of he is controlled by crystal size such that larger crystals retain a larger fraction of radiogenic he u th he ages must vary not only with thermal history but also with crystal size here we present crystal size correlated he ages from co existing apatites from the bighorn mountains wyoming that range from 100 to 350 ma these correlations are a sensitive indicator of the rock s thermal history in a temperature range below the system s nominal closure temperature t c 70 c for apatite and are consistent with a thermal history involving residence in the upper 2 3 km of crust since the precambrian with maximum temperatures of 65 80 c just prior to laramide orogenic exhumation the influence of crystal size on he ages will be most apparent in rocks where temperatures have been in the range of partial he retention for long periods of time 30 70 c for 10 7 years in such cases accurate interpretation of u th he ages must incorporate the effect of crystal size and this method may provide insights to thermal histories of rocks in previously inaccessible low temperature ranges

subsidence and growth of pacific cretaceous plateaus abstract the ontong java manihiki and shatsky oceanic plateaus are among the earth s largest igneous provinces and are commonly believed to have erupted rapidly during the surfacing of giant heads of initiating mantle plumes we investigate this hypothesis by using sediment descriptions of deep sea drilling project dsdp and ocean drilling program odp drill cores to constrain plateau subsidence histories which reflect mantle thermal and crustal accretionary processes we find that total plateau subsidence is comparable to that expected of normal seafloor but less than predictions of thermal models of hotspot affected lithosphere if crustal emplacement was rapid then uncertainties in paleo water depths allow for the anomalous subsidence predicted for plumes with only moderate temperature anomalies and volumes comparable to the sources of modern day hotspots such as hawaii and iceland rapid emplacement over a plume head of high temperature and volume however is difficult to reconcile with the subsidence reconstructions an alternative possibility that reconciles low subsidence over a high temperature high volume plume source is a scenario in which plateau subsidence is the superposition of 1 subsidence due to the cooling of the plume source and 2 uplift due to prolonged crustal growth in the form of magmatic underplating this prolonged crustal growth and uplift scenario may explain the low and thus submarine relief during plume initiation the late stage eruptions found on ontong java 90 ma and manihiki 70 ma a large portion of the high seismic velocity lower crust and the widespread normal faults observed throughout and along the margins of the three plateaus such late stage underplating may have occurred continuously or in discrete stages over 30 m y and implies lower magmatic fluxes than previously estimated

paleo elevation and subsidence of 145ma shatsky rise inferred from co2 and h2o in fresh volcanic glass abstract shatsky rise a large mesozoic oceanic plateau in the northwest pacific consists of three massifs tamu ori and shirshov that formed near a mid ocean ridge triple junction published depth estimates imply that shatsky rise has not subsided normally like typical oceanic lithosphere we estimated paleo eruption depths of shatsky rise massifs on the basis of dissolved co2 and h2o in volcanic glass and descriptions of cores recovered from five sites of integrated ocean drilling program expedition 324 initial maximum elevations of shatsky rise are estimated to be 2500 3500 m above the surrounding seafloor and the ensuing subsidence of shatsky rise is estimated to be 2600 3400 m we did not observe the anomalously low subsidence that has been reported for both shatsky rise and the ontong java plateau although we could not resolve whether shatsky rise originated from a hot mantle plume or non plume fusible mantle uplift and subsidence histories of shatsky rise for the both cases are constrained based on the subsidence trend from the center of tamu massif 2600 m toward the flank of ori massif 3400 m in the case of a hot mantle plume origin shatsky rise may have formed on young 5 ma pre existing oceanic crust with a total crustal thickness of 20 km for this scenario the center of shatsky rise is subsequently uplifted by later prolonged crustal growth forming the observed 30 km thickness crust for a non plume origin shatsky rise may have formed at the spreading ridge center as initially thick crust 30 km thickness with later reduced subsidence caused by the emplacement of a buoyant mass perhaps a refractory mantle residuum beneath the center of shatsky rise

apatite u th he thermochronometry using a radiation damage accumulation and annealing model helium diffusion from apatite is a sensitive function of the volume fraction of radiation damage to the crystal a quantity that varies over the lifetime of the apatite using recently published laboratory data we develop and investigate a new kinetic model the radiation damage accumulation and annealing model rdaam that adopts the effective fission track density as a proxy for accumulated radiation damage this proxy incorporates creation of crystal damage proportional to production from u and th decay and the elimination of that damage governed by the kinetics of fission track annealing the rdaam is a version of the helium trapping model hetm shuster d l flowers r m and farley k a 2006 the influence of natural radiation damage on helium diffusion kinetics in apatite earth planet sci lett 249 148 161 calibrated by helium diffusion data in natural and partially annealed apatites the chief limitation of the hetm now addressed by rdaam is its use of he concentration as the radiation damage proxy for circumstances in which radiation damage and he are not accumulated and lost proportionately from the crystal by incorporating the rdaam into the hefty computer program we explore its implications for apatite u th he thermochronometry we show how u th he dates predicted from the model are sensitive to both effective u concentration eu and details of the temperature history the rdaam predicts an effective he closure temperature of 62 c for a 28 ppm eu apatite of 60 m radius that experienced a 10 c ma monotonic cooling rate this is 8 c lower than the 70 c effective closure temperature predicted using commonly assumed durango diffusion kinetics use of the rdaam is most important for accurate interpretation of u th he data for apatite suites that experienced moderate to slow monotonic cooling 1 0 1 c ma prolonged residence in the helium partial retention zone or a duration at temperatures appropriate for radiation damage accumulation followed by reheating and partial helium loss under common circumstances the rdaam predicts u th he dates that are older sometimes much older than corresponding fission track dates nonlinear positive correlations between apatite u th he date and eu in apatites subjected to the same temperature history are a diagnostic signature of the rdaam for many but not all thermal histories observed date eu correlations in four different localities can be explained with the rdaam using geologically reasonable thermal histories consistent with independent fission track datasets the existence of date eu correlations not only supports a radiation damage based kinetic model but can significantly limit the range of acceptable time temperature paths that account for the data in contrast these datasets are inexplicable using the durango diffusion model the rdaam helps reconcile enigmatic data in which apatite u th he dates are older than expected using the durango model when compared with thermal histories based on apatite fission track data or other geological constraints it also has the potential to explain at least some cases in which u th he dates are actually older than the corresponding fission track dates

late cretaceous early eocene laramide uplift exhumation and basin subsidence in wyoming crustal responses to flat slab subduction low angle subduction of the farallon oceanic plate during the late cretaceous early eocene is generally considered as the main driver forming the high rocky mountains in wyoming and nearby areas how the deformation was transferred from mantle to upper crust over the great duration of deformation 40 myr is still debated here we reconstruct basin subsidence and compile paleoelevation thermochronology and provenance data to assess the timing magnitude and rates of rock uplift during the laramide deformation we reconstruct rock uplift as the sum of surface uplift and erosion constrained by combining paleoelevation and exhumation with regional stratigraphic thickness and chronostratigraphic information the amount and rate of rock uplift of individual laramide ranges was less than 2 4 4 8 km 0 21 0 32 mm yr during the early maastrichtian paleocene stage 1 and increased to more than 3 km 0 38 0 60 mm yr during the late paleocene early eocene stage 2 our quantitative constraints reveal a two stage development of the laramide deformation in wyoming and an increase of rock uplift during stage 2 associated with enhanced intermontane basin subsidence exhumation and uplift during stage 1 is consistent with eastward migration of cordilleran deformation associated with low angle subduction whereas the change in exhumation during stage 2 seems to follow a southwestward trend which requires an alternative explanation we here suggest that the increase of rock uplift rate during the late paleocene early eocene and the southwestward younging trend of uplift may be a response to the rollback and associated retreating delamination of the farallon oceanic slab

impact of flow routing on catchment area calculations slope estimates and numerical simulations of landscape development 1 flow routing across real or modeled topography determines the modeled discharge and wetness index and thus plays a central role in predicting surface lowering rate runoff generation likelihood of slope failure and transition from hillslope to channel forming processes in this contribution we compare commonly used flow routing rules as well as a new routing rule to commonly used benchmarks we also compare results for different routing rules using airborne laser swath mapping alsm topography to explore the impact of different flow routing schemes on inferring the generation of saturation overland flow and the transition between hillslope to channel forming processes as well as on location of saturation overland flow finally we examined the impact of flow routing and slope calculation rules on modeled topography produced by geomorphic transport law gtl based simulations we found that different rules produce substantive differences in the structure of the modeled topography and flow patterns over alsm data our results highlight the impact of flow routing and slope calculation rules on modeled topography as well as on calculated geomorphic metrics across real landscapes as such studies that use a variety of routing rules to analyze and simulate topography are necessary to determine those aspects that most strongly depend on a chosen routing rule

investigation of early eocene water vapor transport and paleoelevation using oxygen isotope data from geographically widespread mammal remains the oxygen isotope composition 18 o of apatite from mammalian tooth enamel can be used to infer the 18 o value of ingested water which is in turn related to that of precipitation stored in surface reservoirs therefore the 18 o value of phosphate from fossil tooth enamel can be used to infer the 18 o value of these reservoirs in the past in this paper tooth enamel from a semiaquatic mammal taxon coryphodon collected from five early eocene localities in north america is used to construct patterns in 18 o values of river water for this time period at all localities the 18 o value of river water 18 o r is estimated to have been higher during the early eocene relative to present day north american rivers although the 18 o vs latitude gradient was shallower during the eocene higher 18 o r values are consistent with warmer eocene air masses being able to hold more water vapor and with an increase in the poleward transport of both moisture and latent heat the regular decrease in 18 o r with latitude indicates that global atmospheric circulation patterns and hydrological transport were not much different from those of the present although the shallower 18 o vs latitude gradient during the eocene may reflect regional differences in precipitation evaporation and river recharge at a more regional scale the 18 o value of river water can provide insight into topographic relief during the early eocene in the case of intermontane basins of wyoming differences in average 18 o r values between basins indicate that laramide mountain relief was on the order of 475 m it is suggested that anomalously low 18 o r values reported previously do not provide unambiguous evidence for permanent snow at higher elevations and may instead reflect brief episodes of cooler winters and or altered atmospheric circulation patterns

fission track thermochronology of the wind river range wyoming evidence for timing and magnitude of laramide exhumation fission track analysis of wind river range basement rocks provides information about the timing magnitude and cooling that occurred in response to laramide uplift eighty samples were collected from precambrian rock along six traverses in the northern central and southern parts of the range over 5 km of elevation apatite fission track ages and track length data suggest that the range did not have a uniform thermal history during late mesozoic and cenozoic time zircon fission track ages are precambrian implying that these rocks have not been at temperatures higher than 200 c 9 10 km burial depth since precambrian time apatite ages from the northeastern and southwestern flanks of the range suggesst that cooling may have initiated in the wind river range by about 85 ma but was definitely occurring by 75 ma data from the green river lakes area and fremont peak in the northern part of the range indicate that cooling was occurring by 62 ma and was most rapid between 60 and 57 ma apparent rates of exhumation vary from 94 m m y to 246 m m y in this part of the range the central part of the range records this same period of rapid cooling but structural and topographic relief are not as great ages from the southern part of the range suggest that uplift and erosion may have been initiated earlier there but continued at much slower rates 34 m m y over a longer period of time than in the north samples from a drill hole in the central wind river range have apatite ages ranging from 37 ma to 86 ma and suggest a significant cooling event at approximately 42 ma involving nearly 2 km of the rock column timing magnitudes and apparent rates of exhumation have varied spatially in the wind river range

carving and adaptive drainage enforcement of grid digital elevation models 1 an effective and widely used method for removing spurious pits in digital elevation models consists of filling them until they overflow however this method sometimes creates large flat regions which in turn pose a problem for the determination of accurate flow directions in this study we propose to suppress each pit by creating a descending path from it to the nearest point having a lower elevation value this is achieved by carving i e lowering the terrain elevations along the detected path carving paths are identified through a flooding simulation starting from the river outlets the proposed approach allows for adaptive drainage enforcement whereby river networks coming from other data sources are imposed to the digital elevation model only in places where the automatic river network extraction deviates substantially from the known networks an improvement to methods for routing flow over flat regions is also introduced detailed results are presented over test areas of the danube basin

lithospheric gravitational potential energy and past orogenesis implications for conditions of initial basin and range and laramide deformation gravitational body forces i e buoyancy forces have come to be seen as critical to the evolution of orogens nevertheless constraining the role of body forces in specific geologic scenarios is made difficult by the substantial number of poorly constrained physical parameters needed to fully relate forces to deformation by separating the calculation of buoyancy forces from the calculation of the resulting deformation models based on relatively simple descriptions of the lithosphere can yield geologically useful constraints among these are the importance of paleoelevation in driving syn and postcontractional extension and in localizing contractional strain although such phenomena have been considered in more complex models of continental deformation the simpler analysis presented here clearly establishes first order limits on lithospheric structures and paleoelevations consistent with buoyancy driven deformation in the early cenozoic great basin of the western united states we show that the low elevations inferred in much of the geologic literature are inconsistent with a body force origin for observed extensional tectonism east of the colorado plateau localization of laramide deformation coincides with pre laramide subsidence of the western interior seaway this subsidence prestressed the lithosphere making the southern rocky mountains the weak link in responding to regional compressional stress

deep submarine pyroclastic eruptions theory and predicted landforms and deposits submarine pyroclastic eruptions at depths greater than a few hundred meters are generally considered to be rare or absent because the pressure of the overlying water column is sufficient to suppress juvenile gas exsolution so that magmatic disruption and pyroclastic activity do not occur consideration of detailed models of the ascent and eruption of magma in a range of sea floor environments shows however that significant pyroclastic activity can occur even at depths in excess of 3000 m in order to document and illustrate the full range of submarine eruption styles we model several possible scenarios for the ascent and eruption of magma feeding submarine eruptions 1 no gas exsolution 2 gas exsolution but no magma disruption 3 gas exsolution magma disruption and hawaiian style fountaining 4 volatile content builds up in the magma reservoir leading to hawaiian eruptions resulting from foam collapse 5 magma volatile content insufficient to cause fragmentation normally but low rise speed results in strombolian activity and 6 volatile content builds up in the top of a dike leading to vulcanian eruptions we also examine the role of bulk interaction steam explosivity and contact surface steam explosivity as processes contributing to volcaniclastic formation in these environments we concur with most earlier workers that for magma compositions typical of spreading centers and their vicinities the most likely circumstance is the quiet effusion of magma with minor gas exsolution and the production of somewhat vesicular pillow lavas or sheet flows depending on effusion rate the amounts by which magma would overshoot the vent in these types of eruptions would be insufficient to cause any magma disruption the most likely mechanism of production of pyroclastic deposits in this environment is strombolian activity due to the localized concentration of volatiles in magma that has a low rise rate magmatic gas collects by bubble coalescence and ascends in large isolated bubbles which disrupt the magma surface in the vent producing localized blocks bombs and pyroclastic deposits another possible mode of occurrence of pyroclastic deposits results from vulcanian eruptions these deposits being characterized by the dominance of angular blocks of country rocks deposited in the vicinity of a crater should be easily distinguishable from strombolian and hawaiian eruptions however we stress that a special case of the hawaiian eruption style is likely to occur in the submarine environment if magmatic gas buildup occurs in a magma reservoir by the upward drift of gas bubbles in this case a layer of foam will build up at the top of the reservoir in a sufficient concentration to exceed the volatile content necessary for disruption and hawaiian style activity the deposits and landforms are predicted to be somewhat different from those of a typical primary magmatic volatile induced hawaiian eruption specifically typical pyroclast sizes might be smaller fountain heights may exceed those expected for the purely magmatic hawaiian case cooling of descending pyroclasts would be more efficient leading to different types of proximal deposits and runout distances for density flows would be greater potentially leading to submarine pyroclastic deposits surrounding vents out to distances of tens of meters to a kilometer in addition flows emerging after the evacuation of the foam layer would tend to be very depleted in volatiles and thus extremely poor in vesicles relative to typical flows associated with hawaiian style eruptions in the primary magmatic gas case we examine several cases of reported submarine volcaniclastic deposits found at depths as great as 3000 m and conclude that submarine hawaiian and strombolian eruptions are much more common than previously suspected at mid ocean ridges furthermore the latter stages of development of volcanic edifices seamounts formed in submarine environments are excellent candidates for a wide range of submarine pyroclastic activity due not just to the effects of decreasing water depth but also to 1 the presence of a summit magma reservoir which favors the buildup of magmatic foams enhancing hawaiian style activity and episodic dike emplacement which favors strombolian style eruptions and 2 the common occurrence of alkalic basalts the co2 contents of which favor submarine explosive eruptions at depths greater than tholeiitic basalts these models and predictions can be tested with future sampling and analysis programs and we provide a checklist of key observations to help distinguish among the eruption styles

anomalous uplift and subsidence of the ontong java plateau inferred from co2 contents of submarine basaltic glasses the ontong java plateau in the western pacific is anomalous compared to other oceanic large igneous provinces in that it appears to have never formed a large subaerial plateau paleoeruption depths at 122 ma estimated from dissolved h2o and co2 in submarine basaltic glass pillow rims vary from 1100 m below sea level mbsl on the central part of the plateau to 2200 3000 mbsl on the northeastern edge our results suggest maximum initial uplift for the plateau of 2500 3600 m above the surrounding seafloor and 1500 400 m of postemplacement subsidence since 122 ma our estimates of uplift and subsidence for the plateau are significantly less than predictions from thermal models of oceanic lithosphere and thus our results are inconsistent with formation of the plateau by a high temperature mantle plume two controversial possibilities to explain the anomalous uplift and subsidence are that the plateau 1 formed as a result of a giant bolide impact or 2 formed from a mantle plume but has a lower crust of dense garnet granulite and or eclogite neither of these possibilities is fully consistent with all available geological geophysical and geochemical data the origin of the largest magmatic event on earth in the past 200 m y thus remains an enigma

midcontinent u s fault and fold zones a legacy of proterozoic intracratonic extensional tectonism the u s continental interior midcontinent contains numerous fault and fold zones seismic and drilling data indicate that some of these zones first formed as proterozoic eocambrian rift faults but the origin of most remains enigmatic we propose that the enigmatic fault and fold zones also began as proterozoic eocambrian normal faults we base our hypothesis on the following 1 enigmatic zones parallel known rifts 2 the structural style of enigmatic zones mirrors the structural style of known rifts 3 the map pattern of some enigmatic zones e g the la salle deformation belt of illinois resembles the map pattern of contemporary rifts and 4 it is easier to rupture an intact craton by normal faulting than by reverse or strike slip faulting these zones along with known rifts represent the legacy of widespread extensional tectonism that brittlely broke up the craton into fault bounded blocks prior to deposition of phanerozoic platform cover once formed midcontinent fault and fold zones remained weak allowing cratonic blocks to jostle relative to one another during the phanerozoic thereby inverting faults and creating transpressional or transtensional structural assemblages localizing seismicity and channeling or releasing ore generating fluids

comparison of gully erosion estimates using airborne and ground based lidar on santa cruz island california abstract gully erosion removes comparatively large volumes of soil from small areas it is often difficult to quantify the loss of soil because the footprint of individual gullies is too small to be captured by most generally available digital elevation models dems such as the usgs national elevation dataset airborne lidar light detection and ranging has the potential to provide the required data density but an even newer class of ground based sensors may provide better local resolution at lower cost in this study we compared digital elevation models produced by airborne and ground based lidar systems with ground based geomorphic and geodetic survey data to determine their utility in quantifying volumetric soil loss due to gully erosion in a heavily degraded watershed 7 55 10 2 km 2 on southwestern santa cruz island in southern california volumetric estimates of the eroded sediment were produced by comparing the lidar derived dems of the gully system to a modeled pre erosion surface average point densities were significantly higher for the ground based lidar system and provided more detailed information however its limited scanning footprint and side looking orientation presented serious challenges in collecting continuous data from deeply incised gullies making the airborne system preferable for this type of investigation and likely for most applications where heavy topographic shadowing is prevalent

three dimensional landscape process modelling the effect of dem resolution many landscape models have been developed over the past decades however relatively little is known about handling the effects of changing spatial and temporal resolutions therefore resolution effects remain a factor of uncertainty in many hydrological and geomorphological modelling approaches in this paper we present an experimental multi scale study of landscape process modelling emphasis was laid on quantifying the effect of changing the spatial resolution upon modelling the processes of erosion and sedimentation a simple single process model was constructed and equal boundary conditions were created using artificial digital elevation models dems eliminated effects of landscape representation the only variable factors were dem resolution and the method of flow routing both steepest descent and multiple flow directions our experiments revealed an important dependency of modelled erosion and sedimentation rates on these main variables the general trend is an increase of erosion predictions with coarser resolutions an artificial mathematical overestimation of erosion and a realistic natural modelling effect of underestimating resedimentation cause this increasing the spatial extent eliminates the artificial effect while at the same time the realistic effect is enhanced both effects can be quantified and are expected to increase within natural landscapes the modelling of landscape processes will benefit from integrating these types of results at different resolutions

magnetic lineations within shatsky rise northwest pacific ocean implications for hot spot triple junction interaction and oceanic plateau formation oceanic plateaus are major ocean features yet their origins and development are poorly understood many are huge piles of basalt and it is widely accepted that mantle plumes are their source perhaps from eruptions of the voluminous head of an emerging plume shatsky rise is a basaltic plateau that formed during a period of geomagnetic reversals unlike many mid cretaceous plateaus so magnetic data can help us understand its tectonic history in this study we analyzed magnetic anomaly data from 131 cruises over and around shatsky rise and constructed a magnetic lineation chart for tectonic interpretation a significant finding is that magnetic lineations are traceable through low parts of the rise between volcanic massifs indicating nearly normal lithosphere and between large volcanic edifices many lineations form bights near the rise axis and show former locations of the pacific izanagi farallon triple junction they indicate that the junction was in a ridge ridge ridge rrr configuration and closely followed the rise axis from chron m20 146 ma to chron m4 127 ma lineation and bight geometries indicate that the triple junction jumped northeastward at least nine times often apparently in response to volcanic activity from the mantle plume some jumps however appear related to ridge reorientations numerous features within the rise are parallel to lineations or lineation offsets implying that the plateau formed near the triple junction and was modified by ridge faulting most of our observations support the hypothesis that shatsky rise was formed by a mantle plume that captured a triple junction

post laramide oligocene uplift in the wind river range wyoming in late oligocene time the crest of the wind river range was uplifted from an erosion surface that formed during laramide late cretaceous early eocene deformation this uplift created the highest peaks in the wyoming foreland and is indicated by rejuvenation of the range as a sediment source and by the physiography of the peaks differential movement of basement blocks in the core of the range is identified by apatite fission track data we distinguish this deformation from earlier laramide compression and neogene normal faulting and speculate that it occurred when precambrian shear zones were reactivated in response to local flexural stress in the laramide subsidence uplift couple

geomorphic response to uplift along the dragon s back pressure ridge carrizo plain california we used high resolution topography geomorphic mapping of active surface processes and geologic mapping to study the topographic and erosional response of small drainage basins to rock uplift along the dragon s back pressure ridge along the san andreas fault in the carrizo plain california we infer the history of deformation experienced by 40 small drainage basins formed in poorly consolidated sedimentary rocks a space for time substitution directly images the erosional and topographic responses to deformation progressive deformation and rock uplift are accompanied by increases in channel steepness and basin relief as uplift ceases channel concavity rapidly increases causing channels to undercut hillslopes this undercutting promotes the consumption of hillslopes by landsliding this undercutting also causes basin relief to be greatest after uplift has stopped this analysis indicates that channels of the dragon s back pressure ridge respond to changes in rock uplift rates over thousands of years whereas hillslope processes may take more than an order of magnitude longer to adjust to changes in rock uplift rates our study directly measures changes in erosional processes due to the initiation and cessation of rock uplift which can typically only be inferred using numerical models by direct field observations

minimizing the grid resolution dependence of flow routing algorithms for geomorphic applications the results of flow routing methods currently used in the geomorphic literature depend on grid resolution this poses a problem for landscape evolution models which must be independent of grid resolution to the greatest extent possible here i illustrate a refinement of currently used flow routing algorithms that yields unit contributing areas i e contributing areas per unit width of flow with minimal grid resolution effects i illustrate the application of this method in idealized topography in high resolution digital elevation models dems of real world topography and by integration into a landscape evolution model for ridge and valley topography the landscape evolution model produces grid resolution independent results in a more straightforward way than previous models for this type of landscape

the influence of natural radiation damage on helium diffusion kinetics in apatite abstract stepwise degassing diffusion experiments on 39 different apatite samples using radiogenic 4he and proton induced 3he reveal a range in closure temperature tc from 50 to 115 c for a cooling rate of 10 c myr there is no correlation between helium diffusion and apatite chemistry including f cl ratio but the closure temperature is positively correlated with the radiogenic 4he concentration 4he in each sample we argue that 4he is a proxy for a sample s natural exposure to actinide radioactivity below the closure temperature and that helium diffusion in apatite is impeded by radiation induced damage to the apatite structure the kinetics must therefore be an evolving function of time measured diffusivities thus reflect a snapshot in time and cannot alone be applied to the thermochronometric interpretation of a given sample the effect of radiation damage on helium diffusion appears to far exceed other known controls on helium diffusivity including grain size our diffusion data are well described by a previously proposed quantitative model that consists of two arrhenius relations one for volume diffusion through undamaged mineral structure and one for release of helium from radiation damage traps the unknown parameters in this trapping model were determined from the diffusion experiments and allow us to develop a tentative mathematical function that relates diffusivity to temperature and 4he by inserting this function into a 4he production diffusion model we have explored how these results affect the interpretation of apatite u th he thermochronometry the model predicts that the effective 4he closure temperature of apatite will vary with cooling rate and effective u concentration eu and may differ from the commonly assumed tc of 70 c by up to 15 c the 4he partial retention zone will look similar to previous expectations but its depth will depend on accumulation time and on eu most notably samples subjected to reheating after accumulation of substantial radiation damage will be more retentive than previously expected these predictions are consistent with recent observations of unexpected apatite u th he ages in some settings

channel planform geometry and slopes from freely available high spatial resolution imagery and dem fusion implications for channel width scalings erosion proxies and fluvial signatures in tectonically active landscapes article i nfo the rapid expansion of high spatial resolution optical sensors and imagery over the last decade presents ex ceptional opportunities for quantifying visible attributes of geomorphic systems in this study we detail a simple robust methodology changeom to extract continuous channel width and centerline datasets for single thread channels using freely available high spatial resolution imagery currently available in google earth and bing maps comparisons with a global dataset of field and lidar derived channel widths indicate minimal errors associated with the imagery and changeom methodology b1 overall while examples from the goriganga river indian himalaya and the yakima river wa usa emphasize the benefit of em pirical width values over established channel width scalings in deciphering fluvial responses to complex landscape forcings in tectonically active regions additionally accurate centerline delineation from the changeom methodology provides improved sinuosity measurements and when fused with coarse resolution digital elevation models dems removes along profile shortening and coincident increases in reach scale channel slope lastly comparisons of aster gdem v2 srtm v4 1 and lidar channel profiles extracted in moderate to high relief regions demonstrate the inferiority of the aster gdem for channel slope calcula tions despite the apparent spatial resolution advantages 9 the methodology presented here will facili tate new discoveries in the fluvial environment that have historically been difficult due to access and imagery resolution issues and provide greater perspective on channel signatures and responses to a host of landscape forcings especially in tectonically active bedrock and lower order drainage systems

an automated knickzone selection algorithm kz picker to analyze transient landscapes calibration and validation streams commonly respond to base level fall by localizing erosion within steepened convex knickzone reaches localized incision causes knickzone reaches to migrate upstream such migrating knickzones dictate the pace of landscape response to changes in tectonics or erosional efficiency and can help quantify the timing and source of base level fall identification of knickzones typically requires individual selection of steepened reaches a process that is tedious subjective and has no efficient means to measure knickzone size we construct an algorithm to automate this procedure by selecting the bounds of knickzone reaches in a space drainage area normalized framework an automated feature calibrates algorithm parameters to a subset of knickzones handpicked by the user the algorithm uses these parameters as consistent criteria to identify knickzones objectively and then the algorithm measures the height length and slope of each knickzone reach we test the algorithm on 1 10 and 30 m resolution dems of six catchments trunk stream lengths 2 1 5 4 km on santa cruz island southern california on the 1 m dem algorithm selected knickzones confirm 93 of handpicked knickzone positions n 178 to a spatial accuracy 100 m 88 to an accuracy within 50 m and 46 to an accuracy within 10 m using 10 and 30 m dems accuracy is similar 88 86 to 100 m and 82 to 50 m n 38 36 respectively the algorithm enables efficient regional comparison of the size and location of knickzones with geologic structures mapped landforms and hillslope morphology thereby facilitating approaches to characterize the dynamics of transient landscapes

comparison of grid based algorithms for computing upslope contributing area 1 terrain attributes based on upslope contributing area a are used widely in distributed hydrologic models several grid based algorithms are available for estimating a in this study five algorithms d8 8 mfd demon and d were compared quantitatively on two undulating agricultural fields 63 and 109 ha in northeastern colorado global positioning system gps data 0 02 m accuracy were used to generate grid digital elevation models dems at 5 10 and 30 m cell sizes relative differences between a values estimated using single and multiple direction algorithms increased with decreasing grid cell size relative differences were greatest along ridges and side slopes and differences decreased where the terrain became more convergent multiple direction algorithms mfd demon and d allowing for flow divergence are recommended on these undulating terrains for 5 and 10 m grids where a is most sensitive to the algorithm selection

variety and origin of magmas on shatsky rise northwest pacific ocean 1 shatsky rise consists of thick 30 km maximum basaltic crust with various geochemical compositions geochemistry data indicate that four magma types exist on the plateau namely normal low ti high nb and u1349 types the normal type is the most abundant in volume and appears on all three large edifices of the plateau tamu ori and shirshov massifs composition of the normal type is similar to normal mid ocean ridge basalt n morb composition but with slight relative enrichment of the more incompatible elements the low ti type is distinguished from the normal type basalt by slightly lower ti content at a given mgo composition of the high nb type is characterized by distinctively high contents of incompatible trace elements u1349 type basalts are composed of more primitive and depleted compositions compared with the others the normal type basalts constitute 94 of the lava units of the oldest tamu massif and non normal types i e the other three types basalts comprise 57 on the younger ori massif implying that geochemical compositions may have become heterogeneous with time petrological examination demonstrates that compositions of the normal low ti and high nb type basalts evolved through fractional crystallization of olivine plagioclase and augite in shallow magma chambers 200 mpa model calculations of immobile trace elements estimate that the normal type basalt can be formed by 15 melting of a depleted mantle source in the presence of residual garnet this degree of melting is similar to n morb but the larger effect of residual garnet during petrogenesis implies that a greater depth of melting

combining geomorphometry feature extraction techniques and earth surface processes research the way forward abstract in recent years the wealth of technological development revolutionised our ability to collect data in geosciences due to the unprecedented level of detail of these datasets geomorphologists are facing new challenges giving more in depth answers to a broad er range of fundamental questions across the full spectrum of the earth s and planetary processes this contribution builds on the existing literature of geomorphometry the science of quantitative land surface analysis and feature extraction translate land surface parameters into extents of geomorphological elements it provides evidence of critical themes as well as emerging fields of future research in the digital realm supporting the likely effectiveness of geomorphometry and feature extractions as they are advancing the theoretical empirical and applied dimension of geomorphology the review further discusses the role of geomorphometric legacies and scientific reproducibility and how they can be implemented in the hope that this will facilitate action towards improving the transparency and efficiency of scientific research and accelerate discoveries in geomorphology in the current landscape substantial changes in landforms ecosystems land use hydrological routing and direct anthropogenic modifications impact systems across the full spectrum of geomorphological processes although uncertainties in the precise nature and likelihood of changes exist geomorphometry and feature extraction can aid exploring process regimes and landscape responses taken together they can revolutionise geomorphology by opening the doors to improved investigations crossing space and time scales blurring the boundaries between traditional approaches and computer modelling and facilitating cross disciplinary research ultimately the exploitation of the available wealth of digital information can help to translate our understanding of geomorphic processes which is often based on observations of past or current conditions into the rapidly changing future

thick skinned deformation of the archean wyoming province during proterozoic arc continent collision two major mylonite zones are exposed in the southeastern archean wyoming province the cheyenne belt which marks the boundary between the wyoming and colorado provinces and the laramie peak shear zone across which archean rocks have been uplifted differentially at least 10 km between the two mylonite zones is a 60 100 km wide belt of archean migmatitic gneiss which has been intruded by diabase dikes and peridotites and contains enclaves of high grade metasedimentary rocks we interpret this belt of high grade rocks as a tectonically reactivated block of archean crust uplifted during the development of the cheyenne belt collisional zone at ca 1 8 ga this block does not exhibit a decreasing metamorphic gradient away from the mylonite zone but is at uniformly high grade thus rather than a thick skinned thrust ramp model for uplift we invoke vertical uplift along a high angle reverse fault without rotation this style of uplift may be a tectonic response to transpression underplating or tectonic interfingering at depth during collisional orogeny and it may be a more common feature of basement uplifts within foreland fold and thrust belts than has been previously recognized

flexural versus dynamic processes of subsidence in the north american cordillera foreland basin 1 dynamic subsidence related to subduction is an important process in retroarc foreland basin systems dynamic subsidence in the north american retroarc foreland has been proposed as dominant in the late cretaceous however questions remain about the nature of the subcrustal load and the basin response to such processes we present new isopach data using 130 data points covering a large portion of the u s and a revised flexural analysis of the sevier foreland higher rigidity associated with the wyoming craton can best model flexural subsidence directly prior to 81 ma we constrain the transition from flexural to nonflexural subsidence to 81 ma and correlate this with large late cretaceous progradation the locus of subsidence and the location of the subducted shatsky oceanic plateau suggest that dynamic loading from viscous flow above the subducting plate is the mechanism driving dynamic subsidence in the retroarc foreland basin of the north american cordillera

fault slip and exhumation history of the willard thrust sheet sevier fold thrust belt utah relations to wedge propagation hinterland uplift and foreland basin sedimentation

deciphering a 2 gyr long thermal history from a multichronometer u th he study of the phalaborwa carbonatite kaapvaal craton south africa