sims zircon u pb geochronology and sr nd isotopes of ni cu bearing mafic ultramafic intrusions in eastern tianshan and beishan in correlation with flood basalts in tarim basin nw china constraints on a ca 280 ma mantle plume zircon sims u pb dating of the poshi hongshishan bijiashan and huangshan ni cu bearing and xiangshan ni cu ti fe bearing mafic ultramafic intrusions in the eastern tianshan and beishan rift yields a relatively restricted range of 278 6 ma to 284 0 ma the histogram of compiled age data of basalts in the tarim basin and mafic ultramafic intrusions in the eastern tianshan and beishan rift has a peak of 280 ma which probably represents the time of mantle plume activity the basalts have lower end t values in the range of 9 2 1 7 and mg of 2 wt indicating that they were generated directly from a peripheral zone of the mantle plume by low degree of melting the mafic ultramafic intrusions have higher end t of 1 3 11 2 and mg of 33 90 and lower tio2

base level buffers and buttresses a model for upstream versus downstream control on fluvial geometry and architecture within sequences abstract the effects of downstream base level control on fluvial architecture and geometry are well explored in several broadly similar sequence stratigraphic models cretaceous dakota group strata u s western interior have characteristics reflecting combined downstream and upstream base level controls that these models cannot address particularly three layers of amalgamated channel belt sandstone within this group thicken and are continuous for distances 300 km along dip that stretch the reasonable lengths for which these models are intended to apply as well architecture in up dip reaches records repeated valley scale cut and fill cycles this contrasts with equivalent strata down dip which record channel scale lateral migration with no such valley scale cycles apparent we here introduce the concept of buffers and buttresses to address these observations we assume that river longitudinal profiles are each anchored down dip to some physical barrier e g the sea strand etc that we refer to as a buttress buttress shift is considered the primary downstream control on base level profiles extrapolated up dip from the buttress over any modeled duration of buttress shift can range widely because of high frequency variability in upstream base level controls e g discharge etc all these potential profiles however are bounded above by the profile of highest possible aggradation and below by the profile of maximum possible incision these upper and lower profiles are buffers and they envelop the available fluvial preservation space thickness of the buffer zone is determined by variability in upstream controls and should increase up dip to the limit of downstream profile dominance dakota valley scale surfaces record repeated cut and fill cycles driven by up dip controls and are confined between thick stable buffers equivalent strata down dip record lateral reworking within a thinner channel scale buffer zone that was positioned by downstream controls regression exposed slopes similar to the buffer zone thus buffers were stable for long distances and durations this prompted dip extensive lateral reworking of strata into upstream valley scale and downstream channel scale sheets buffers and buttresses provide a broadly applicable model for fluvial preservation that captures upstream vs downstream base level controls on geometry and architecture the model lends general insights into dip oriented variations in fluvial architecture production of sheet vs lens geometry total preservation volumes for fluvial systems and variations in these factors related to contrasting climatic conditions and basin physiography the model can be amended to existing sequence stratigraphic approaches in order to capture dip oriented variations in sequence architecture

routing graded sediments in streams applications a one dimensional numerical model has been tested in simulating the movement of well graded sediments through a stream reach the model is applied to two laboratory flumes and two alluvial channel reaches found in the literature three of these examples are under steady state flow conditions and the other is under unsteady flow conditions in the unsteady flow situation the flow computations are done by using a water routing scheme based on the kinematic wave equations this scheme needs adjustment of one parameter the sediment model also needs adjustment of only one parameter which is the erodibility parameter the model predicts water and sediment discharges coming out of each reach size distributions of these transported materials size distributions of the bed material or the armor coat and changes in bed elevations comparisons of these predictions are made with the measurements available from these examples and are found to be promising

birth death and resurrection the life cycle of suprasubduction zone ophiolites 1 suprasubduction zone ssz ophiolites display a consistent sequence of events during their formation and evolution that suggests that they form in response to processes that are common to all such ophiolites this sequence includes the following 1 birth which entails the formation of the ophiolite above a nascent or reconfigured subduction zone this stage is typically characterized by the eruption of arc tholeiite lavas and the formation of layered gabbros and sheeted dike complex 2 youth during which is continued melting of refractory asthenosphere depleted during birth occurs in response to fluid flux from the subducting slab with extensional deformation of the older plutonic suite eruption of refractory lavas and the intrusion of wehrlite pyroxenite 3 maturity with the onset of semistable arc volcanism typically calc alkaline as the subduction zone matures and stabilizes and the intrusion of quartz diorite and eruption of silicic lavas and 4 death which is the sudden demise of active spreading and ophiolite related volcanism which in many cases is linked to collision with an active spreading center and the onset of shallow underthrusting of the buoyant spreading axis expressed as dikes and lavas with oceanic basalt compositions that crosscut or overlie rocks of the older suites 5 resurrection with emplacement by obduction onto a passive margin or accretionary uplift with continued subduction the early stages 1 3 may be diachronous and each stage may overlap in both time and space the existence of this consistent progression implies that ophiolite formation is not a stochastic event but is a natural consequence of the ssz tectonic setting

the badenian evaporite basin of the northern carpathian foredeep as a model of a meromictic selenite basin the hydrography and brine flow patterns in the middle miocene badenian evaporite basin of the northern carpathian foredeep in ukraine poland and the czech republic are reconstructed based on studies of the peculiar conformably oriented bottom grown gypsum crystals present in the selenite deposits along the basin margin the crystal apices are turned in a similar horizontal direction that is interpreted as the product of consistent flow of the bottom brines during crystal formation similarly the regular millimetre scale growth zoning in these crystals presumably reflects the annual stratification mixing pattern in the brine column typical of monomictic basins in the central deeper parts of the basin deposition was dominated by nachloride and the selenitic facies are lacking these central areas are interpreted as being meromictic during the oriented selenite deposition the permanent pycnocline separated a mixolimnion at the surface from an anoxic euxinic monimolimnion at the bottom where direct evaporative crystallization of gypsum was not possible the mixolimnion which extended far onto the shallow margin of the basin showed only a seasonal annual pycnocline and monomictic hydrography oriented selenites grew just in this mixolimnetic marginal zone under predominantly counterclockwise

reassessment of continental growth during the accretionary history of the central asian orogenic belt we argue that the production of mantle derived or juvenile continental crust during the accretionary history of the central asian orogenic belt caob has been grossly overestimated this is because previous assessments only considered the palaeozoic evolution of the belt whereas its accretionary history already began in the latest mesoproterozoic furthermore much of the juvenile growth in central asia occurred in late permian and mesozoic times after completion of caob evolution and perhaps related to major plume activity we demonstrate from zircon ages and nd hf isotopic systematics from selected terranes within the caob that many neoproterozoic to palaeozoic granitoids in the accreted terranes of the belt are derived from melting of heterogeneous precambrian crust or through mixing of old continental crust with juvenile or short lived material most likely in continental arc settings at the same time juvenile growth in the caob occurred during the latest neoproterozoic to palaeozoic in oceanic island arc settings and during accretion of oceanic island arc and precambrian terranes however taking together our data do not support unusually high crust production rates during evolution of the caob significant variations in zircon ehf values at a given magmatic age suggest that granitoid magmas were assembled from small batches of melt that seem to mirror the isotopic characteristics of compositionally and chronologically heterogeneous crustal sources we reiterate that the chemical characteristics of crustally derived granitoids are inherited from their source s and cannot be used to reconstruct tectonic settings and thus many tectonic models solely based on chemical data may need re evaluation crustal evolution in the caob involved both juvenile material and abundant reworking of older crust with varying proportions throughout its accretionary history and we see many similarities with the evolution of the sw pacific and the tasmanides of eastern australia

association of redeposited salt breccias and potash evaporites in the lower miocene of stebnyk carpathian foredeep west ukraine abstract potash evaporites of the lower miocene vorotyshcha suite are sandwiched in salt breccias in the ukrainian part of the carpathian foreland basin these breccias have traditionally been interpreted as tectonically deformed units related to the overthrust nappes of the carpathians most clasts consist of intrabasinal sandstone marlstone halite and anhydrite but exotic clasts consisting of rocks that are characteristic of the carpathian flysch rocks are also present breccia beds are intercalated with salt layers containing chevron crystals and cubic hopper crystals and some layers are composed of detrital salt these salt layers rarely display graded bedding or cross lamination and continue over great distances there are also slump structures associated with the bedded salts the salinity in the vorotyshcha basin was extremely high but intermittent inflows caused brine dilution so that it could maintain halite precipitation for a long time during long periods of evaporative concentration and reduced inflow brines in the basin could reach the sylvite saturation level so that potash chlorides and sulfates started to precipitate the potash precipitated subaqueously on the basis of evidence from the study of fluid inclusions the depth of the brine is interpreted to have been 20 30 m in agreement with the supposed brine stratification in a basin subjected to influxes of sediment laden waters the breccias are debris flow deposits they are commonly tectonically deformed but analysis of the relation of breccias to evaporites suggests that both were formed in water ten to a few tens of meters deep it therefore seems that halite breccias in other foreland basins could have had a sedimentary origin

incision of alluvial channels in response to a continuous base level fall field characterization modeling and validation along the dead sea abstract the dramatic lake level drop of the dead sea during the twentieth century 30 m provides a field scale experiment in transport limited incision of gravel bed channels in response to quasi continuous base level fall at approximately constant rate we apply a one dimensional numerical incision model based on a linear diffusion equation to seven ephemeral channels draining into the dead sea the model inputs include the measured twentieth century lake level curve annual shoreline location i e annual channel lengthening following the lake level drop reconstructed longitudinal profiles of each of the channels based on mapped and surveyed terraces and the current profiles of the active channels the model parameters included the diffusion coefficient and the upstream derived sediment flux both were first calibrated using a set of longitudinal profiles of known ages and then validated using additional sets of longitudinal profiles the maximum at station total incision observed at each of the studied channels was significantly less then the total lake level drop and varied in response to both drainage area and lake bathymetry the model applied predicted degradation rates and the pattern of degradation with high accuracy this suggests that sediment flux in the modeled channels is indeed linearly dependent on slope further support for this linear dependency is provided by a linear correlation between the diffusion coefficient and the mean annual rain volume over each basin a proxy for discharge the model presented could be a valuable tool for planning in rapid base level fall environments where incision may risk infrastructure

mathematical modeling of graded river profiles numerical modeling of the longitudinal profiles of rivers at grade is accomplished using the basic equations of open channel flow sediment transport equations and empirical relations for downstream variation in flow discharge sediment discharge sediment caliber and channel width only in some cases are the computed stream profiles fit exactly by any one of the commonly supported mathematical function analogs to graded profile form exponential logarithmic or power function but in most cases any of these functions can provide a fit with a degree of error smaller than would be noted in treating field data profiles dominated by spatial change in fluid and sediment discharge are distinctly power functions while profiles dominated by sediment size reduction are not necessarily exponential in form other important controls on profile shape are the degree of downstream width change in response to increasing discharge and the general range of sediment size a dynamic model of a river s approach to grade

rapid incision of a small coarse and steep fan delta in response to base level fall the case of nahal qedem the dead sea israel the dead sea has been continuously dropping 0 4 1 0 m yr 1 since the middle of the 20th century and thus provides a unique field laboratory for studying in real time the response of drainage systems to a non tectonic base level fall the aim of this work is to study the short term ongoing erosive response to a rapid base level drop in a small steep fronted erodible fan delta setting the work explores the controls of the steep qedem fan delta guided by its clinoform structure on its incision longitudinal profiles of the fan delta and of its entrenched channel were measured in the field sedimentary facies changes fluviatile shallow lacustrine and beach were followed along exposures the existence of large boulders provided an opportunity to examine the uncertain role of armouring and boulder flux on incision the field study was combined with digital elevation models dems that were extracted from pairs of overlapping aerial photos maps of erosion and deposition were prepared using a change detection algorithm the longitudinal profile of the entrenched channel was found to be steep and linear the outlet temporarily hangs elevated and ungraded above the retreating lake level indicating years without incision flow events which cause lags in response to the rapid lake level drop in spite of the large boulders the small drainage basin and precipitation volume over the basin of the qedem the recorded vertical incision rates in the unconsolidated sediments are as high as 0 8 m yr 1 i e similar to those of the largest wadis draining to the dead sea the steep front of the fan delta is suggested to be a main factor controlling the efficient incision a unique transport mechanism of rolling boulders following undercutting contributed to the entrenchment efficiency copyright 2010 john wiley sons ltd

evidence for late stage fluvial activity in kasei valles mars 1 two inner channels in the southern branch of kasei valles are among the best preserved examples of fluvial erosion on mars attributes of the channels include arcuate alcoves perched boulders and a concave up longitudinal profile all of which are consistent with the interpretation that these channels were carved by a newtonian fluid the sharp concavity of the longitudinal profile is comparable to a terrestrial alluvial system with a minimum work profile the shape of the profile suggests that the system was in a quasi equilibrium state but was not active long enough to achieve grade associated with these channels is a platy meter scale texture identified in high resolution mars orbiter camera images although a lava flow could explain many of the material properties of the platy surface texture we speculate that this texture in the immediate proximity to the southern kasei valles inner channels may be related to waning floodwaters moving through the inner channels and is a mudflow deposit

stream networks and long term surface uplift in the new madrid seismic zone stream networks are sensitive to low rates of surface uplift and can be used to decipher the history of large earthquakes even where faults do not rupture the surface as in intraplate seismic zones statistical analysis of alluvial network data from topographic maps in the new madrid seismic zone in the central united states shows that stream segment gradients deviate the most from an estimated natural stream profile where surface uplift is greatest evidence of cumulative deformation distilled from stream network patterns represents at least several meters of differential surface uplift during holocene time which suggests that more than one cycle of surface deformation occurred

teaching geomorphology through spreadsheet modelling abstract geomorphology like most scientific disciplines has evolved from a descriptive stage through quantification to modelling of processes and outcomes indeed high resolution modelling has been termed the third branch of science for its ability to generate high quality hypotheses testable in turn through field mapping and laboratory experimentation i teach the principles and basic applications of modelling using microcomputer spreadsheets these serve as transparent boxes in which graphical output is generated in response to numerical input and more importantly in which the modeler student can see the equations and order of steps unlike traditional black box models the technology is widely available and familiarity with it can be assumed required or taught at the undergraduate level modelling can be taught through a series of spreadsheet exercises in which students while learning topical material in a traditional sequence progress from a simple cookbook exercise through more realistic process based exercises to the level of addressing a previously unstudied research question at each step the model can be used to generate testable hypotheses i have worked with scarp evolution stream longitudinal profiles and glacier reconstructions and plan to include eolian soil development mass wasting and coastal processes in additional exercises the first year of use of this technique in a junior level geomorphology course clarified the strengths and weaknesses of the modelling approach the strengths involve students learning the capabilities and flaws of modelling a stronger understanding of causeeffect relationships and the effects of time on landforms the weaknesses involve time commitment supervision in model implementation and limitations to student ability to independently pursue openended research

cambrian to early silurian ophiolite and accretionary processes in the beishan collage nw china implications for the architecture of the southern altaids the mechanism of continental growth of the altaids is currently under debate between models invoking continuous subduction accretion or punctuated accretion by closure of multiple ocean basins we use the yueyashan xichangjing ophiolite belt of the beishan collage southern altaids to constrain the earliest oceanic crust in the southern palaeo asian ocean five lithotectonic units were identified from s to n the huaniushan block a sedimentary passive margin the structurally incoherent yueyashan xichangjing ophiolite complex a coherent sedimentary package and the mazongshan island arc with granitic rocks we present a structural analysis of the accretionary complex which is composed of the incoherent ophiolitic melange and coherent sedimentary rocks to work out the tectonic polarity a new weighted mean 206 pb 238 u age of 533 1 7 ma from a plagiogranite in the yueyashan xichangjing ophiolite indicates that the ocean floor formed in early cambrian time furthermore we present new geochemical data to constrain the tectonic setting of the yueyashan xichangjing ophiolite the yueyashan xichangjing ophiolite was emplaced as a result of northward subduction of an oceanic plate beneath the mazongshan island arc to the north in late ordovician to early silurian time together with data from the literature our work demonstrates that multiple overlapping periods of accretion existed in the palaeozoic in the northern and southern altaids therefore a model of multiple accretion by closure of several ocean basins is most viable

aridity is expressed in river topography globally it has long been suggested that climate shapes land surface topography through interactions between rainfall runoff and erosion in drainage basins1 4 the longitudinal profile of a river elevation versus distance downstream is a key morphological attribute that reflects the history of drainage basin evolution so its form should be diagnostic of the regional expression of climate and its interaction with the land surface5 9 however both detecting climatic signatures in longitudinal profiles and deciphering the climatic mechanisms of their development have been challenging owing to the lack of relevant global data and to the variable effects of tectonics lithology land surface properties and human activities10 11 here we present a global dataset of 333 502 river longitudinal profiles and use it to explore differences in overall profile shape concavity across climate zones we show that river profiles are systematically straighter with increasing aridity through simple numerical modelling we demonstrate that these global patterns in longitudinal profile shape can be explained by hydrological controls that reflect rainfall runoff regimes in different climate zones the most important of these is the downstream rate of change in streamflow independent of the area of the drainage basin our results illustrate that river topography expresses a signature of aridity suggesting that climate is a first order control on the evolution of the drainage basin a global dataset of river longitudinal profiles shows that river profiles become straighter with increasing aridity and numerical modelling suggests that this can be explained by rainfall runoff regimes in different climate zones

spatial and temporal analysis of hillslope channel coupling and implications for the longitudinal profile in a dryland basin author s michaelides katerina hollings rory singer michael bliss nichols mary h nearing mark a

continental growth of northwest china the northwest corner of china is the most interior part of central asia and includes parts of the siberian tarim and kazakhstan plates where the junggar and tarim basins are separated by the east west trending tianshan range a preliminary terrane map divides the area into thirteen separate areas which are classified into four types l continental 2 oceanic crust 3 island arc 4 composite the boundaries for these terranes are faults that have been previously defined either by geologic mapping or holocene activity passive consolidation of the southern margin of paleo asia is marked by accretion and subduction of the paleo tethys oceanic basins and by development of volcanic arcs paleomagnetic data indicate that the major plates and associated smaller terranes did not reach final consolidation until the permian or later the stratigraphic record reveals development of intracontinental basins in the late carboniferous followed by the pan asian thermal event that gave rise to widespread intrusion of a type granites of late paleozoic age the frontal collision of india along the southern border of asia in the paleocene reactivated nearly all of the older major strike slip and thrust faults formed during the late paleozoic consolidation of paleo asia the complex nature of the continental growth of central asia has produced and destroyed many varieties of sutures and reconstruction of the original plate and terrane configurations therefore is enigmatic

carboniferous and cretaceous mafic ultramafic massifs in inner mongolia china a shrimp zircon and geochemical study of the previously presumed integral hegenshan ophiolite abstract we present shrimp zircon ages and whole rock geochemical data to identify mafic ultramafic massifs of early carboniferous and early cretaceous ages from northern inner mongolia china the early carboniferous massifs chongenshan xiaobaliang wusnihei comprise predominantly lherzolite and minor gabbroic rocks zircons from a microgabbro e nd t 9 8 and a plagiogranite e nd t 9 yielded weighted mean 206 pb 238 u ages of 354 7 ma and 333 4 ma that we interpret as reflecting the time of zircon and magma crystallization a volcanic breccia resting unconformably on the ultramafic rocks serpentinites has an eruption age of 300 2 ma and provides a younger minimum time limit for the emplacement of the early carboniferous mafic ultramafic massifs in contrast the early cretaceous mafic ultramafic massifs hegenshan chaogenshan consist predominantly of harzburgite a pegmatoid gabbro and a rodingite e nd t 10 6 from the hegenshan massif have magmatic zircon ages of 139 2 ma and 132 7 ma respectively the chaogenshan massif is concentrically zoned with an ultramafic core dominantly harzburgite dunite subordinate lherzolite surrounded by gabbro with minor hornblendite and an outermost volcano sedimentary sequence metabasaltic flows metapelites we dated zircons from a leuocogabbro 125 2 ma e nd t 10 6 a coarse grained gabbro 142 4 ma and a metabasalt 134 2 ma zircon xenocrysts ca 152 492 ma are ubiquitous in these and other associated rocks a coarse grained gabbro and a diabase as in the hegenshan rocks ca 152 468 ma the youngest detrital zircon in outer zone garnet schist i e metapelite has an age of 132 2 ma accordingly we conclude that the northern inner mongolia lherzolite dominant and harzburgite dominant massifs are temporally and genetically unrelated their emplacement is attributed to asthenospheric upwelling and consequent lithospheric extension during periods of orogenic quiescence in the southern central asian orogenic belt

river incision and terrace formation in the late cenozoic of europe abstract late cenozoic environmental changes which affected european rivers are reviewed focusing especially on those of mid pleistocene times c 1 2 0 8 ma or around mis 22 and thereafter these involved dominating but fluctuating cold climate periglacial conditions shorter but major episodes of glaciation and brief interglacials there were also related sea level and tectonic responses the known history of european rivers in this period is individually varied but is predominantly marked by multiple stages of episodic incision the form of which changed in style at around the mid pleistocene transition it is suggested that the nature of climatic oscillations the dating of incision episodes and the processes that achieve this incision are as yet insufficiently understood fluvial process studies suggest that the onset of incision may broadly relate to changes in slope discharge sediment load and calibre and bedrock erodibility and these may all have been transformed as the direct or indirect result of mid pleistocene climatic changes common properties of basal sediments on strath terraces suggest that it was during the extended but variable cold stage episodes that both valley deepening and lateral widening occurred and that climatic change was the principal driver of episodic deep valley incision

petrogenesis and implications for tectonic setting of cambrian suprasubduction zone ophiolitic rocks in the central beishan orogenic collage northwest china abstract the hongliuhe ophiolite is a fragment of the early paleozoic oceanic crust situated in a suture zone central to the beishan orogenic collage which is a subset to the central asian orogenic belt in northwest china it has lithologic geochemical and chronological similarities to the yueyashan xichangjing ophiolite 400 km east along strike allowing for correlative interpretations of marginal seafloor spreading processes the hongliuhe ophiolite is explored in this study with complete petrologic geochemical and structural descriptions the ultramafic body comprises cumulate layered lherzolite and gabbro plutonic lithologies tectonized with syn magmatic extension a u pb age of 520 3 5 8 ma was obtained by shrimp analysis of zircons from a pegmatitic gabbro the ultramafic rocks are variably depleted and some show refertilization of lile s consistent with slab dehydration in a supra subduction mantle wedge mineral chemistry shows high cr 36 82 populations of spinel and wide ranging lower mg 8 50 consistent with known forearc peridotite chemistry partially re equilibrated by tectonism or through staged magmatism olivine and pyroxene chemistries are consistent with this interpretation a thin volcanic cover is interlayered with red cherts and has a bimodal set of geochemical signatures both island arc tholeiite and calc alkaline they bear distinct nb ta anomalies consistent with slab derived fluid initiated melting in a supra subduction environment coarse volcaniclastic turbidites infilled paleo topography along the ophiolite and they are interbedded with quartzofeldspathic sandstones indicating an initial proximity to an arc the sandstones contain detrital spinel with analyses showing relation to both the ophiolite and possibly a secondary alkalic volcanic source the supracrustal sequence continues with a thick contiguous covering of margin related rocks including interlayered limestone pyroclastic and siliciclastic rocks and basalts as a constraint on emplacement we provide an u pb zircon shrimp date 413 6 3 5 ma from an undeformed granitoid body intruded within the overlying stratigraphy the entire analysis paints a picture of subduction rollback related extension affecting the margin of an emerging or mature arc just prior to a known magmatic cycle that ended with a collision in the devonian at the latest this suture is one of many in the beishan and our interpretation provides evidence in a long running debate supporting accretionary orogenesis in an island arc archipelago as the main system for growing sialic crust in the paleozoic central asia

channel adjustment of an unstable coarse grained stream opposing trends of boundary and critical shear stress and the applicability of extremal hypotheses channel adjustments in the north fork toutle river and the toutle river main stem were initiated by deposition of a 2 5 km3 debris avalanche and associated lahars that accompanied the catastrophic eruption of mount st helens washington on 18 may 1980 channel widening was the dominant process in combination adjustments caused average boundary shear stress to decrease non linearly with time and critical shear stress to increase non linearly with time at the discharge that is equalled or exceeded 1 per cent of the time these trends converged by 1991 1992 so that excess shear stress approached minimum values extremal hypotheses such as minimization of unit stream power and minimization of the rate of energy dissipation minimum stream power are shown to be applicable to dynamic adjustments of the toutle river system maximization of the darcy weisbach friction factor did not occur but increases in relative bed roughness caused by the concomitant reduction in hydraulic depths and bed material coarsening were documented predictions of stable channel geometries using the minimum stream power approach were unsuccessful when compared to the 1991 1992 geometries and bed material characteristics measured in the field it is concluded that the predictions are not applicable because the study reaches are not truly stable and cannot become so until a new floodplain has been formed by renewed channel incision retreat of stream side hummocks and establishment of riparian vegetation to limit the destabilizing effects of large floods further prediction of energy slope and consequently stream power by the sediment transport equations is inaccurate because of the inability of the equations to account for significant contributions of finer grained sand and gravel bank materials relative to the coarsened channel bed from bank retreat and from upstream terrace erosion

modelling of icecap glaciation of the northern rocky mountains of montana abstract the extent of the lastglacial icecap over the northern rocky mountains of montana has been inferred only from cursory correlation of its marginal deposits which leaves several significant unresolved controversies those controversies all involve the maximum altitude and shape of that interconnected ice mass and include 1 the source of the two medicine piedmont lobe local or cordilleran ice 2 correlation of terminal deposits of the flathead lobe late lastglacial early lastglacial or prelastglacial and 3 regional paleoclimate at last glacial maximum dominant westerlies or local easterlies theoretical reconstructions of the glacial surface along major flowlines constrained by ice marginal features nunataks and breached divides throughout the region tentatively resolve those issues the two medicine lobe was dominantly composed of northeast flowing local ice not ice of northwestern canadian cordillera origin flathead lobe deposits include lastglacial deposits both supported by and without a component from the swan valley there is evidence of only a regional westerly flow of moisture across the region in addition a proglacial lake 60 km long occupied the swan valley during the early stages of deglaciation although subject to revision from fieldwork glacial process modelling remains one of the few geological arenas in which rigorous process modelling can be used to predict the evolution of form

sedimentology of badenian middle miocene gypsum in eastern galicia podolia and bukovina west ukraine primary gypsum is the main evaporite mineral in the middle miocene badenian of the west ukraine the lower part of the gypsum sequence is built of autochthonous gypsum while the upper part is composed of allochthonous gypsum that formed following a major tectonically induced change in basin morphology this change resulted in the destruction of the gypsum deposited on the margins of the basin and formation of redeposition features autochthonous gypsum facies were deposited in two main environments 1 giant gypsum intergrowths precipitated from highly concentrated brines 2 very shallow subaqueous gypsum deposited in a vast brine pan the brine pan was characterized by a facies mosaic that reflects an interplay of concentrated brines from the central part of the evaporite basin and diluted brines due to the influx of continental meteoric waters the facies continuum microbial gypsum bedded selenite massive selenite sabre gypsum indicates increasing salinity of the brine with time this type of facies pattern has been established in recent salinas that are analogous to badenian gypsum in their lateral facies changes however the pattern of facies distribution with respect to the open sea in the badenian basin is opposite to that found in recent salinas the pattern of the badenian gypsum facies in the ukraine indicates that facies repetition may have been related to climatically controlled salinity changes and not to depth changes as is commonly used to explain the repetition of sulphate facies in a vertical succession

cambrian ophiolite complexes in the beishan area china southern margin of the central asian orogenic belt abstract we present zircon ages and geochemical data for cambrian ophiolite complexes exposed in the beishan area at the southern margin of the central asian orogenic belt caob the complexes consist of the xichangjing xiaohuangshan and hongliuhe yushishan ophiolites which both exhibit complete ophiolite stratigraphy chert basalt sheeted dikes gabbro mafic and ultramafic cumulates and serpentinized mantle peridotites zircon grains of gabbro samples yielded 206 pb 238 u ages of 516 8 521 4 528 3 and 535 6 ma that reflect the timing of gabbro emplacement the geochemical data of the basaltic rocks show enrichment in large ion lithophile elements and depletion in the high field strength elements relative to normal mid oceanic ridge basalt nmorb in response to aqueous fluids or melts expelled from the subducting slab the gabbro samples have higher whole rock initial 87 sr 86 sr ratios and lower positive e nd t values than nmorb these geochemical signatures resulted from processes or conditions that are unique to subduction zones and the ophiolites are therefore likely to have formed within a supra subduction zone ssz environment we suggest that the cambrian ophiolite complexes in the beishan area formed within a ssz setting reflecting an early paleozoic subduction of components of the paleo central asian ocean and recording an early paleozoic southward subduction event in the southern caob along the northern margin of the tarim and north china cratons

amount and controls of the quaternary denudation in the ardennes massif western europe it is still debated whether the primary control on the middle pleistocene denudation of the uplifted ardennes massif western europe is tectonic or climatic here based on geomorphological observations we calculate the amount of river incision and interfluve denudation in the meuse basin upstream of maastricht since 0 7 ma and we show that the main response to tectonic forcing was incision this allows us to provide first order estimates of the tectonic and climatic contributions to the denudation of the ardennes from a dataset of 71 remnants of a terrace level dated 0 7 ma we first derive a basin scale functional relationship linking incision with distances to the regional base level lc and to the source ls in the ourthe basin pertaining to the ardennian part of the meuse basin expressed as i i0 1 a lcb lsc i0 being the incision measured at the basin outlet this relationship calculates that river incision has removed 84 km3 of rock in the meuse basin upstream of maastricht since 0 7 ma in the same time 292 km3 were eroded from the interfluves a comparison of these volumes shows that the tectonically forced river incision accounts for 22 of the total post 0 7 ma denudation furthermore the mean denudation rate corresponding to our geomorphological estimate of the overall denudation in the meuse basin since 0 7 ma amounts to 27 mm ky a figure significantly lower than the 40 mm ky mean rate derived from 10be studies of terrace deposits of the meuse schaller et al 2004 this suggests that taken as a basin average the 10be derived rate is overestimated probably due to an overrepresentation of the erosion products of the rapidly incising valleys in the alluvial deposits copyright 2009 john wiley sons ltd

accretionary growth and crust formation in the central asian orogenic belt and comparison with the arabian nubian shield kroner a windley b f badarch g tomurtogoo o hegner e jahn b m gruschka s khain e v demoux a and wingate m t d 2007 accretionary growth and crust formation in the central asian orogenic belt and comparison with the arabian nubian shield in hatcher r d jr carlson m p mcbride j h and martinez catalan j r eds 4 d framework of continental crust geological society of america memoir 200 p 181 209 doi 10 1130 2007 1200 11 for permission to copy contact editing geosociety org 2007 the geological society of america all rights reserved kroner kroener mail uni mainz de windley brian windley btinternet com tomurtogoo igmr magicnet mn hegner hegner lmu de jahn jahn earth sinica edu tw khain khain ginras ru demoux demoux uni mainz de wingate mwingate tsrc uwa edu au

the mid langhian flooding in the eastern central paratethys integrated stratigraphic data from the transylvanian basin and se carpathian foredeep the mid langhian badenian flooding fully reconnected the semi isolated central paratethys realm with the mediterranean and thereby drastically changed the middle miocene paleogeography of central europe due to the scattered stratigraphic record and scarcity of independent age constraints in some areas the precise age and underlying mechanism are still debated we present integrated chronostratigraphic data from five sections in the eastern part of the system to reconstruct the flooding event distal from the strait to the mediterranean by applying modern mediterranean biochronology planktonic foraminifera and calcareous nannofossils supplemented by an 40ar 39ar age on a tuff we demonstrate that the widespread open marine settings in the nw transylvanian basin were definitely installed after 14 9 ma mmi4d biozone and in most areas before 14 4 ma in the marginal study area in the se carpathian foredeep fully marine conditions likely set in slightly later 14 6 14 4 ma there short lived marine incursions into the brackish environment occurred since the latest burdigalian pre flooding phase the new ages overlap with the flooding in the majority of the central paratethys 14 9 14 4 ma and with marine overflow into the black sea 14 85 ma we suggest that the transgression was driven by subsidence of the pannonian basin by creating accommodation space and diminishing barriers between sub basins but was likely enhanced by a global sea level rise finally we speculate that the scarcity of all calcareous material in the se carpathian foredeep before the mid langhian flooding might be related to pulses of nutrient rich brackish and low ph water from the neighboring black sea basin

middle cambrian granites in the dunhuang block nw china mark the early subduction of the southernmost paleo asian ocean abstract the formation and evolution of the central asian orogenic belt caob were closely associated with the opening and closure of the so called paleo asian ocean pao the subduction of the southern pao is expected to have resulted in widespread paleozoic arc magmatism in the southernmost caob however the precise location and timing of such subduction remain uncertain the dunhuang block dhb in the southernmost caob is thought to have recorded such subduction in this contribution we report the results of the zircon u pb ages hf isotopes and whole rock geochemical data for the lianghu dapokouzi and xiaowan plutons in the northeastern dhb nw china zircon u pb dating reveals that these plutons formed at ca 510 ma the middle cambrian and may represent the oldest arc related magmatism in the dhb geochemically the dapokouzi pluton is characterized by high sio2 70 7 71 2 wt na2o 5 11 5 26 wt al2o3 15 5 15 6 wt and sr 730 733 ppm contents high sr y 380 398 ratios moderate mg 49 50 values low mgo 0 61 wt k2o 2 00 2 01 wt and y 1 84 1 93 ppm contents and weakly positive eu 1 39 1 44 anomalies indicating geochemical affinities of adakitic rocks they have positive ehf t values 11 2 to 13 9 close to the depleted mantle line and young two stage model ages tdm2 571 742 ma all the geochemical characteristics show that the dapokouzi pluton was derived from the remelting of juvenile crust with addition of minor metasomatized mantle derived materials and a residue phase dominated by garnet bearing amphibolite similarly the lianghu and xiaowan plutons have high sio2 70 2 74 4 wt and al2o3 12 8 14 3 wt low mgo 0 61 1 01 wt with mg values of 35 43 and k2o 0 43 1 55 wt contents compared to the dapokouzi pluton they exhibit low sr 121 155 ppm and y 15 3 23 1 ppm contents low sr y 5 25 9 54 ratios and cr ni co concentrations and pronouncedly positive ehf t values 11 0 to 14 7 indicating that the magmas originated from the remelting of juvenile lower crust followed by significant fractional crystallization at relatively shallow crustal depths data from this and previous studies convincingly suggest the dhb was located in a thickened continental arc setting during the early paleozoic probably related to the early subduction of the pao lithosphere crustal thickening as indicated by the geochemical signature of the dapokouzi pluton was most likely associated with the underplating of mantle derived mafic magmas during the slab subduction this study therefore highlights that the subduction of the southern pao might have initiated prior to 510 ma possibly dating back to the early cambrian

evolution of a permian intraoceanic arc trench system in the solonker suture zone central asian orogenic belt china and mongolia abstract the identification of a fossil arc trench system from the ophiolite decorated solonker suture zone in the southernmost central asian orogenic belt caob enables us to constrain the timing of pre subduction extension ca 299 290 ma subduction initiation ca 294 280 ma ridge trench collision ca 281 273 ma and slab break off ca 255 248 ma in the permian a fraction of proto arc crust ca 45 km long up to 8 km wide is preserved as a volcanic plutonic sequence and is juxtaposed against a wide ca 30 80 km forearc melange this proto arc crust comprises two distinct magma series island arc tholeiite iat and mid ocean ridge basalt morb both of which have strong supra subduction zone ssz geochemical signatures zircons from a gabbro and a plagiogranite yielded weighted mean 206pb 238u ages of 284 0 4 0 and 288 0 6 0 ma the forearc melange consists of numerous ophiolite fragments and continental margin derived olistoliths blocks that predate the ophiolite the olistoliths are best represented by a gabbroic block 291 8 2 3 ma that contains granite xenoliths 312 6 1 8 and 313 6 3 1 ma other dated blocks include a trondhjemite 323 9 2 7 ma a gabbro 296 6 1 7 ma and a tonalite 294 9 2 4 ma small bodies of diabase andesite and diorite in the forearc melange exhibit a wide variety of geochemical signatures we dated zircons from an n morb like diabase 274 4 2 5 ma an e morb like diabase 252 5 2 3 ma a transitional sanukitoid adakite andesite 250 2 2 4 ma a sanukitoid high mg diorite 251 8 1 1 ma and an anorthosite 252 2 1 7 ma the n morb like diabase contains ca 301 394 ma zircon xenocrysts suggesting assimilation of trench sediments when a spreading ridge intersected a trench the other dated rocks simultaneously formed near the permian triassic boundary and captured abundant zircon xenocrysts ca 269 295 ma ca 301 495 ma and ca 923 2501 ma our new formation ages constrain a magmatic episode in response to slab break off beneath a fossil forearc in a young post collisional setting and the youngest xenocryst ages ca 269 273 ma may define the maximum depositional age of trench sediments

sediment transport and unit stream power function basic fluid mechanics and turbulence theories are applied to show that suspended sediment concentration at a given depth of an open channel flow is a function of the turbulence energy production rate at that depth depth averaged suspended sediment concentration can be obtained by integrating a function of the turbulence energy production rate over the depth of flow which in turn is a function of unit stream power total sediment concentration can also be expressed as a function of unit stream power following the foresaid and a procedure similar to that proposed by einstein comparisons of seven total load equations indicate that equations derived from the concept that the rate of sediment transport should be related to the rate of energy dissipation of the flow are more accurate than other equations for both laboratory flumes and natural rivers

post evaporitic restricted deposition in the middle miocene chokrakian karaganian of east crimea ukraine abstract in the middle miocene of east crimea gypsum evaporites formed in a shallow basin from mixed seawater nonmarine waters are overlain by marl siltstone and claystone which contain a few horizons of stromatolitic limestone the thickness and abundance of the stromatolitic horizons increase up the section in the siliciclastic portion of the section a very poor and taxonomically impoverished assemblage of benthic foraminifers jadammina nonion haynesina astrononion and eponides is recorded it is typical for a shallow water marsh or lagoon environment with a lowered salinity accordingly the brackish conditions prevailing during gypsum precipitation in east crimea continued afterwards although at the end of evaporite deposition the basin became desiccated and then it was rapidly reflooded by brackish water the impoverished biota and the occurrence of microbialites in the ptashkino section indicate extremely unfavourable conditions for most living organisms during the deposition of both the terrigenous and carbonate beds the water salinity thus was probably not only lowered but also anomalous in composition if compared to normal marine water the occurrence of carbonate stromatolitic horizons is probably related to the periodic shallowing of the basin caused by a drop of the lake water table driven by climatic factors the resulted changes allowed for a growth of the bizarre microbial serpulid communities that gave birth to most of the stromatolites in karaganian time the eastern paratethys was a huge lake isolated from the tethys this lake responded to any climatic fluctuation that in turn might lead to water level oscillations in humid climate periods the lake could be open with a surface outflow and when it was drier it could be a closed system without surface outflow gypsum evaporites and stromatolitic carbonates are clear evidence of strong evaporation in a dry climate that probably induced water level fall in the whole basin however all the time the environmental conditions were predominantly brackish even during gypsum precipitation as suggested by the chemical composition of fluid inclusions in gypsum similar conditions may be expected in other evaporite hosted predominantly brackish basins such as some messinian basins of the eastern mediterranean where some evaporites were deposited in the oligohaline to mesohaline conditions typical of the lago mare deposits

fluvial archives a valuable record of vertical crustal deformation abstract the study of drainage network response to uplift is important not only for understanding river system dynamics and associated channel properties and fluvial landforms but also for identifying the nature of crustal deformation and its history in recent decades geomorphic analysis of rivers has proved powerful in elucidating the tectonic evolution of actively uplifting and eroding orogens here we review the main recent developments that have improved and expanded qualitative and quantitative information about vertical tectonic motions the effects of horizontal deformation are not addressed channel long profiles have received considerable attention in the literature and we briefly introduce basic aspects of the behaviour of bedrock rivers from field and numerical modelling perspectives before describing the various metrics that have been proposed to identify the information on crustal deformation contained within their steady state characteristics then we review the literature dealing with the transient response of rivers to tectonic perturbation through the production of knickpoints propagating through the drainage network inverse modelling of river profiles for uplift in time and space is also shown to be very effective in reconstructing regional tectonic histories finally we present a synthetic morphometric approach for deducing the tectonic record of fluvial landscapes as well as the erosional imprint of tectonic forcing sedimentary deposits such as fluvial terrace staircases are also considered as a classical component of tectonic geomorphology we show that these studies have recently benefited from rapid advances in dating techniques allowing more reliable reconstruction of incision histories and estimation of incision rates the combination of progress in the understanding of transient river profiles and larger more rigorous data sets of terrace ages has led to improved understanding of river erosion and the implications for terrace profile correlation i e extrapolation of local data to entire profiles finally planform changes in fluvial systems are considered at the channel scale in alluvial rivers and regional level in terms of drainage reorganisation examples are given of how numerical modelling can efficiently combine with topographic data to shed new light on the dis equilibrium state of drainage systems across regional drainage divides

impact of tectonics on drainage network evolution of suru basin kargil n w himalaya jammu and kashmir india the main objective of this paper is to work out quantitative measurement of various geomorphic parameters as well as analysis of geomorphic landforms to study the tectonic character of suru basin morphometric analysis being widely used to assess the drainage characteristics of the river basins has also been found to be a useful tool to delineate tectonically active zones a number of parameters including the mountain front sinuosity asymmetry factor transverse topography symmetry hypsometry longitudinal profile and the shape parameters have been used the low mountain front sinuosity values 1 4 indicate that the tectonic forces dominate over erosive activity also the asymmetry factor 66 98 suggests that the right side of the basin has experienced uplift with the development of unpaired river terraces hypsometric integral 0 96 convex up hypsometric curve and the gps data of year 2011 2013 indicate that the relief of the basin is high relative to mean is in youthful stage and actively uplifting at the rate of 2 18 0 99 mm year the shape parameters further suggest that the suru river basin having lower elongation ratio is indicative of elongate shape of basin with tectonic forces outpacing the erosion power area altitude analysis of the suru river basin indicates that about 72 of the area of the basin is steeply to very steeply sloping and 28 area is moderately to gently sloping the area altitude indicates 72 area of basin could slide when there is slight shift in terms of tectonic disturbance in addition to the geomorphic indices the field investigations reveal tectonically unstable character exhibit a complex topography and varied quaternary sedimentation the major geomorphic landforms viz alluvial terraces alluvial fans debris cone scree and talus cone at the foothills are present throughout the valley with tectonic structures like micro folds back tilted beds deeply incised valleys faults and tectonic deposits ophiolites indicating that the tectonic activity has affected the basin the synergized results of geomorphometry field investigations and gps data indicate that the suru basin is tectonically active and uplifting

tectono geomorphic indices of the erin basin ne kashmir valley india abstract the present study aims to assess the tectonic activity in the erin basin ne kashmir on the basis of several relevant geomorphic indices and field observations we use digital elevation model srtm and survey of india soi topographic maps in gis environment to compute the geomorphic indices the indices i e convex hypsometric curve high hypsometric integral value h i 0 5 low basin elongation ratio eb 0 17 low mountain front sinuosity values s mf 1 08 average low valley floor width ratios vf 4 suggest that the area is tectonically active moreover prominent irregularities knickpoints knickzones along longitudinal profile of the erin river even in homogenous resistant lithology panjal trap and anomalous stream gradient index sl values reflect that the erin basin is dissected by two faults ef 1 and ef 2 with nnw sse and ssw nne trends respectively the results of this preliminary study further substantiate the recent gps studies which argue that the maximum strain is accumulating in the ne part of the kashmir himalaya

accretionary and collisional orogenesis in the south domain of the western central asian orogenic belt caob abstract the central asian orogenic belt caob was the result of long lived multi stage tectonic evolution including proterozoic to paleozoic accretion and collision mesozoic intracontinental modification and cenozoic rapid deformation and uplift the accretionary and collisional orogenesis of its early history generated a huge orogenic collage consisting of diverse tectonic units including island arcs ophiolites accretionary prisms seamounts oceanic plateaus and micro continents these incorporated orogenic components preserved valuable detailed information on orogenic process and continental crust growth which make the caob a key region to understanding of continental evolution mantle crust interaction and associated mineralization the western caob refers to the west region in north xinjiang of china and circum balkash of kazakhstan with occurrences of the spectacular kazakhstan orocline and its surrounding mountain belts because orogenic fabrics of this part mostly preserve their original features caused by the interactions among the southern siberian active margin in the north and the tarim craton in the south the western caob can be regarded as an ideal region to study the processes of the accretionary and collisional orogenesis and associated mineralization since a large number of researchers have been working on this region research advances bloom strikingly in a short time period therefore we in this special issue focus on these new study advances on the south domain of the western caob including the kazakhstan collage system tianshan orogenic belt and beishan region and it is anticipated that this issue can draw more attention from the international research groups to be interested in the studies on orogenesis of the caob

longitudinal profiles in simple alluvial systems theoretical considerations suggest that exponential or quadratic functions are apt for describing the longitudinal profiles of aggrading alluvial systems that are unaffected by significant lateral inputs of water or sediment a new set of field data confirms this for individual sedimentary links along a wandering gravel bed river in british columbia canada each link is viewed as a simple alluvial system without major water or sediment inputs within which grain size typically fines downstream in a relatively systematic manner such homogeneous reaches are suitable for the investigation of simple profile form it is found that quadratic approximations are the most flexible descriptor for link longitudinal profiles overall the river forms an irregularly cuspate long profile structured by these fundamental length scale units both link gradients and link fining rate reflect size selective aggradation associated with the bounding lateral inputs

geochemical conditions of deposition in the upper devonian prypiac and dnipro donets evaporite basins belarus and ukraine abstract earlier studies of individual fluid inclusions in salt minerals of some devonian evaporite basins showed that the brines in those basins were of chloride type with a high concentration of ca2 the genetic significance of this occurrence was subject to different interpretations we have studied in detail samples taken from the east european dnipro donets and prypiac evaporite basins aiming to establish the chemical composition of fluid inclusions in studied evaporites and then using other geochemical information to establish a geochemical model of the devonian evaporite basins our study showed that salt deposition in the devonian dnipro donets and prypiac evaporite basins was because of intensive evaporation of mainly marine brines of chloride type with a relatively high ca2 content in turn the ratios between na k and mg corresponded to ratios in recent marine brines salt minerals precipitated in bottom water conditions the occurrence of one phase fluid inclusions indicates the temper

longitudinal profile development into bedrock an analysis of hawaiian channels analysis of topographic maps of rivers incised into dated hawaiian lava flows shows that the long term average bedrock erosion rate along certain reaches is linearly related to stream power field observations suggest that two processes may control hawaiian channel downcutting 1 stream power dependent erosion including abrasion of the channel bed by transported particles and 2 step wise lowering caused by knickpoint propagation modeling results indicate that a simple stream power dependent erosion law predicts the straight to weakly convex longitudinal profiles characteristic of kauai channels but is insufficient to predict two other characteristic features the upslope propagation of knickpoints and the straight 5 8 channel slopes below the knickpoints thus more than this single transport law is apparently required to model bedrock channel incision field surveys also indicate that significant portions of the channel lengths below the knickpoints are mantled with large boulders we propose that

onlap offlap and the origin of unconformity bounded depositional sequences christie blick n 1991 onlap ofttap and the origin of unconformity bounded depositional sequences mar geol 97 35 56 unconformity bounded depositional sequences represent the fundamental building blocks of sedimentary successions they are typically characterized by onlap at the base and by offlap at the top and they tend to be markedly asymmetrical with onlap accounting for a larger part of any cycle of sedimentation than offlap offlap cannot be attributed solely to erosional truncation but instead implies that sequence boundaries develop over a finite interval of time depositional sequences are commonly associated with a cyclic arrangement of facies but transgressive regressive cycles are out of phase with respect to sequence boundaries which in down dip locations are both overlain and underlain by progradational deposits and hence form during times of regression of the shoreline these observations are used to develop some ideas about the origin of unconformity bounded sequences with reference to the inter related roles of changes in depositional base level and sediment supply in particular it is shown than onlap and offlap are due to lateral migration of a line of critical bypassing defined so as to incorporate the effects of sediment loading and compaction as well as the rate of change of elevation with respect to sea level downward shifts in onlap may be achieved by either an increase in the rate of eustatic fall or a decrease in the rate of tectonic subsidence and it is premature to assume that eustatic and tectonic controls on sea level may be distinguished solely on the basis of the frequency of depositional cyclicity small shifts in the position of onlap can also be produced by changes in sediment supply and more attention needs to be paid to the influence of sediment supply in the development of minor boundaries unconformities related to eustatic fluctuations are thought to correspond approximately to times of relatively rapid sea level fall inflection points but questions remain about the existence of possible leads and lags of up to cycle and hence about the degree to which sequence boundaries of eustatic origin may vary in age both within a given basin and from one basin to another

progressive accretionary tectonics of the beishan orogenic collage southern altaids insights from zircon u pb and hf isotopic data of high grade complexes abstract high grade gneissic rocks of the southern altaids in central asia bear one of the key elements needed to solve a basic architectural controversy in accretionary orogenesis high grade gneissic rocks widely crop out across the beishan orogenic collage southern altaids mapped as the beishan complex or dunhuang group which was previously regarded as neoarchean to paleoproterozoic crystalline basement but without systematic field geochronological and geochemical data this study provides field geochemical and zircon u pb and hf isotopic data for gneissic rocks from the beishan complex geochemical data show that the gneissic rocks were probably formed in a subduction environment most zircons from the beishan complex are magmatic origins because their th u ratios are mostly in the range of 1 0 0 1 they show age peaks at 494 ma 464 ma and 375 ma with a few precambrian ages zircon hf isotopic compositions indicate that both old and juvenile materials were involved in the formation of the beishan complex which is different from the basement rocks of the tarim craton both in radiometric age and hf isotopic composition all these data thus do not support a uniform precambrian basement in the beishan area as previously proposed but instead the beishan complex probably formed in a subduction accretion environment combined with regional geology and geochemical data we conclude that the beishan orogenic collage was characterized by progressive long lived accretionary tectonics during late precambrian to paleozoic time therefore shedding light on the controversy regarding the architecture of accretionary orogens

global river slope a new geospatial dataset and global scale analysis abstract a rivers longitudinal gradient i e slope is a key parameter in fluvial hydrology hydraulics and geomorphology it affects a multitude of fluvial variables such as flow velocity and sediment transport limitations in river slope data both its availability and accuracy constrain the fidelity of fluvial modeling particularly at larger or global scales traditional slope calculation algorithms cannot accurately predict river slopes as these are based on cell by cell calculation which is only suitable for hillslopes and small mountainous streams this paper presents a methodology for calculating global river slope and a procedure to upscale it for relatively coarse resolution suitable for global scale modeling the methodology is based on a simple principle of calculating slope from elevation depression over the length of a river segment which is automated to allow global scale calculations version 1 0 of the global river slope glors geospatial dataset is introduced and shown to be a step improvement over a previous product nhdplus for the contiguous united states and compares favorably to observed slope data collected from the literature statistical analysis of earth s continents and large basins highlights interesting spatial trends a semi empirical regression analysis between basin average river slope and other basin scale parameters show that terrain slope accounts for 67 of the variability in basin average river slope with average discharge sediment load and basin temperature contributing additional improvements to global predictions of 3 4 and 3 respectively

downstream variation in stream power abstract stream power has a significant influence on many form and process attributes of the fluvial system using a similar approach to that suggested by d m lawler in 1992 and 1995 a model is developed to explore how stream power might vary in the downstream direction based on the assumption that the longitudinal profile of the river has an exponential form no particular discharge is necessarily specified but near bankfull flows are regarded as significant morphologically and one such discharge is the focus here total stream power per unit channel length qs is predicted to peak at an intermediate location the position of which depends on the ratio b where b and are the downstream rates of change of discharge and slope respectively if b is a relatively conservative quantity then the form of the longitudinal profile and in particular its degree of concavity will have the major influence on the position of maximum stream power specific stream power w is even more sensitive to and is expected to peak closer to the headwaters about half way between source and the location of the stream power maximum although this will depend on how channel width w varies with distance from source the model is tested along three connected streams of different size in the catchment of the river trent taking advantage of a relationship between mean annual flood and link magnitude which enables this near bankfull discharge to be estimated at any point within the network the model is verified in so far as stream power does attain a mid basin maximum but the observed and predicted locations of the maxima do not always correspond largely because of the distinctive variation in discharge and especially slope along individual pathways for example maximum power lies far downstream along the trent because of the large increase in mid basin discharge associated with a series of large closely spaced tributaries the importance of slope is borne out by the near headwater locations for specific power maxima which tend to be further upstream than predicted along all three rivers as a result of the steepness of upper reaches the variety of geomorphic settings produces deviations from expectation which has implications for the movement and storage of material in the fluvial system

stream channel convexity induced by continuous base level lowering the dead sea israel abstract the dead sea level has dropped from 388 4 m in 1896 to 417 2 m in 2004 and continues to fall rapidly reaching a record of 1 m y drop such a dramatic base level fall on time scales of several tens of years makes the dead sea area a unique field laboratory the aim of this study is to examine the effect of the lowering dead sea as a base level on the longitudinal profiles of channels on the formation of knick points and on the sinuosity field studies were made along the lower courses of creeks which drain lakeward precise longitudinal profile measurements and their fitting to linear and logarithmic curves show they are planar to slightly convex the short convexity the absence of hydrological or lithological control and former experimental results of profile response to base level fall suggest that the convexity results from the recent continuous rapid drop of the dead sea the convexity is also an inheritance of the paleo morphology i e the original convex front of the fan deltas and coastal scarps following channel incision slope displacement and diffusion the erodible substrate and the high stream power prevented preservation of nickpoints along the main channels sinuosity of the meandering thalwegs remained low 1 1 1 2 indicating no response to the base level lowering along the steep slopes although the stream channels are incised in soft sediments the base level induced entrenchment dies out within 1000 m or less from the receding shoreline the channel profiles demonstrate different phases of adjustment to the lowering base level the uniqueness of the dead sea case is that contrary to former field and experimental studies the system is in a continuous relaxation period without reaching a final adjustment the channels are trapped in their convex form following a rapid on going base level fall upon exposed paleo fan deltas

geochemistry and petrogenesis of 270 ma ni cu pge sulfide bearing mafic intrusions in the huangshan district eastern xinjiang northwest china implications for the tectonic evolution of the central asian orogenic belt abstract the central asian orogenic belt caob is composed of remnants of microcontinents island arcs and ophiolites the presence of voluminous phanerozoic a type granites suggest that continental growth occurred through addition of juvenile crust and the presence of mafic ultramafic intrusions provides direct evidence for a mantle contribution the origin of the mafic ultramafic intrusions in the huangshan area eastern xinjiang has been debated because of the lack of precise age data or trace element and isotopic analyses we have studied the geology petrology geochemistry and geochronology of two of the intrusions the huangshanxi and huangshandong intrusions both are typical layered mafic ultramafic intrusions composed of diorite troctolite norite gabbronorite gabbro wehrlite websterite and lherzolite with systematic geochemical variations that are consistent with the following crystallization sequence ol chr ol pyx chr cpx pl and hbl bt igneous zircons separated from a diorite in the huangshanxi intrusion yield a 269 2 ma shrimp u pb age the rocks are enriched in rb ba u k sr relative to th and lree depleted in nb ta relative to th and exhibit positive end values 6 7 to 9 3 ni cu pge sulfide mineralization occurs in the lower parts of the intrusions primarily strata bound within wehrlite or lherzolite and locally stratiform along the margins of the intrusions the parental magmas appear to have been derived from a mantle source that was previously contaminated by subduction of oceanic crust and to have been variably contaminated by upper continental crustal components the intrusions appear to have formed by plume related activity within a continental setting likely related to post orogenic extension following carboniferous amalgamation of arc related terranes in the caob this plume activity was most likely also responsible for providing heat sources to generate large amounts of a type granites across the caob

zircon ages and hf isotopic compositions of ordovician and carboniferous granitoids from central inner mongolia and their significance for early and late paleozoic evolution of the central asian orogenic belt abstract we present zircon ages and hf in zircon isotopic data for plutonic rocks and review the evolution of central inner mongolia china in the early and late paleozoic zircons of a granodiorite yielded a 206 pb 238 u age of 472 3 ma that reflects the time of early paleozoic magmatism zircon ages were also obtained for a tonalite 329 3 ma quartz diorite 320 3 ma and granite vein 297 2 ma our results in combination with published zircon ages and geochemical data document distinct magmatic episodes in central inner mongolia the dated samples are mostly granodiorite tonalite and quartz diorite in composition with intermediate to high silica high na 2 o 3 08 4 26 wt low k 2 o 0 89 2 86 wt and high na 2 o k 2 o and sr y ratios their chondrite normalized ree patterns are characterized by lree enrichment in mantle normalized multi element variation diagrams they show typical negative nb and ta anomalies and all samples display positive e hf t and e nd t values and low i sr the ordovician rocks however show higher sr y and la yb ratios than the carboniferous samples implying that the older granitoids represent adakitic granitoids and the carboniferous granitoids are typical subduction related arc granitoids but also with adakite like compositions the results are compatible with the view that the central asian orogenic belt caob in inner mongolia evolved through operation of several subduction systems with different polarities an early middle paleozoic subduction and accretion system along the northern margin of the north china craton and the southern margin of the mongolian terrane and late paleozoic northward subduction along the northern orogen and exhumation of a high pressure metamorphic terrane on the northern margin of the north china craton

zircon ages of metamorphic and magmatic rocks within peridotite bearing melanges crucial time constraints on early carboniferous extensional tectonics in the chinese tianshan abstract we dated and geochemically characterized peridotite bearing melanges in the chinese south tianshan and within the main tianshan shear zone the yushugou tonghuashan melange in the chinese south tianshan exposes a tectonic juxtaposition of a diapirically emplaced metaperidotite predominantly lherzolite massif with a high grade metamorphic terrane ca 10 km long protolith age ca 445 466 ma metamorphic zircons of a mafic granulite end t 5 0 yielded a weighted mean 206pb 238u age of 341 8 ma that we interpret as the time of granulite facies metamorphism the youngest zircon rims of an intermediate granulite end t 4 3 have a mean age of 332 13 ma that records a retrogressive metamorphic event these ages determine the timing ca 341 332 ma of mantle diapirism through continental crust a dolerite dike end t 2 3 emplaced into metaperidote has a crystallization age of 335 5 ma that on the basis of geochemistry we interpret as representing e morb oib magmatism that accompanied mantle diapirism an undeformed pink granite end t 3 6 intrudes the melange matrix and has an emplacement age of 324 5 ma thus providing an upper time limit for a tectonic movement that led to melange formation the older time limit of deformation ca 362 352 ma is constrained by the youngest ages of thermo tectonically modified zircons in a mylonitized metagabbro and a foliated meta andesite magmatic zircons in the meta andesite end t 3 3 and a dacite end t 5 6 have eruption ages of 433 4 ma and 435 3 ma that date formation of the melange matrix a microgabbro dike end t 10 0 cutting metasediments i e melange matrix has an emplacement age of 279 3 ma and contains abundant zircon xenocrysts ranging in age from archean to late paleozoic similarly a dolerite dike a meta andesite an intermediate granulite and a metagabbro all contain inherited precambrian to paleozoic zircons we accordingly conclude that the melange was formed by mantle diapirism in the early carboniferous and was subsequently affected by an early permian volumetrically minor mafic episode two foliated garnet granites end t 7 0 and 6 9 in direct contact with metaperidotite within the main tianshan shear zone have emplacement ages of 341 2 ma and 329 4 ma that reflect an early carboniferous episode of crustal anatexis they also contain neoproterozoic zircon xenocrysts also within the main tianshan shear zone a gabbro end t 8 7 has an emplacement age of 297 3 ma and contains abundant neoproterozoic to late paleozoic zircon xenocrysts based on the regional geological relationships we associate early carboniferous mantle diapirism and crustal anatexis with lower crustal delamination induced asthenospheric upwelling the numerous precambrian zircon xenocrysts support a chinese tianshan tarim connection the early permian mafic episode coincided in time with the development of an early permian unconformity in the chinese north tianshan

gypsum facies transitions in basin marginal evaporites middle miocene badenian of west ukraine in the middle miocene badenian gypsum basin of the carpathian foredeep west ukraine three main zones of gypsum development occur in the peripheral parts of the basin zone i consists entirely of stromatolitic gypsum formed in a nearshore zone zone ii is located more basinward and is characterized by stromatolitic gypsum in the lower part of the section overlain by a sabre gypsum unit zone iii occurs in still more basinward areas and is characterized by giant gypsum intergrowths or secondary nodular gypsum pseudomorphs of these in the lowermost part overlain by stromatolitic gypsum sabre gypsum and then by clastic gypsum units correlation between these facies and zones has been achieved using lithological marker beds and surfaces of particular importance for correlation is a characteristic marker bed usually 20 40 cm thick of cryptocrystalline massive gypsum occurring in zones ii and iii the marker was not distinguished in zone i possibly because this bed is older than the entire gypsum section of that zone these new results strongly suggest that the deposition of giant gypsum intergrowth facies and stromatolitic gypsum facies was coeval in some sections of zones i and ii limestone intercalations have been recorded within the upper part of the gypsum sections considerable scatter of the 18o and 13c values of these limestones indicates variable diagenetic overprints of marine carbonates but a marine provenance of the limestones is confirmed by microfacies analysis some of the limestones are coeval with an intercalation of gypsarenitic mostly laminated gypsum occurring in the sabre gypsum unit of zones ii and iii badenian gypsum formed in extremely shallow water to subaerial environments on broad very low relief areas of negligible brine depth which could be affected by rapid transgressions stable isotope 34s 18o studies of the gypsum demonstrate that the sulphate was of sea water origin or was derived from dissolution of miocene marine evaporites investigations of individual inclusions in the gypsum indicate decreased water salinity when compared with modern marine derived calcium sulphate saturated water groundwater influences are indicated by high calcium sulphate contents of the brines in the evaporite basin the chemical composition of badenian waters was thus a mixture of relic sea water depleted in nacl groundwater enriched in calcium sulphate and surface run off

a non plume model for the permian protracted 266 286 ma basaltic magmatism in the beishan tianshan region xinjiang western china abstract the convenient mantle plume model for the permian protracted mafic ultramafic intrusions and mafic dykes 266 286 ma in the beishan tianshan region northern xinjiang western china can be rejected because their temporal spatial distribution does not show a hotspot track predicted by such model new zircon u pb ages reveal that two small mafic dyke clusters podong 280 5 2 ma luodong 266 2 3 2 ma that are separated by only 20 km in the pobei area the southernmost part of the beishan tianshan region have a large age difference of 18 ma the older mafic dykes are characterized by nearly flat mantle normalized rare earth element patterns pronounced negative nb ta anomalies and positive e nd t values from 5 5 to 7 5 similar to the majority of the permian mafic ultramafic intrusions in the region the younger mafic dykes are characterized by significant light rare earth element enrichments as well as pronounced negative nb ta anomalies plus lower e nd t 1 2 to 2 6 values and higher initial 87 sr 86 sr ratios than the older mafic dykes the observed compositional variations can be explained by source mantle heterogeneity plus different degrees of crustal contamination overall the permian mafic ultramafic rocks in the beishan tianshan region are geochemically consistent with the products of basaltic magmatism induced by lithospheric delamination and asthenosphere upwelling in a convergent tectonic zone

a mid palaeozoic ocean continent transition in the mazongshan subduction accretion complex beishan nw china new structural chemical and age data constrain the petrogenesis and tectonic evolution

geochronology and geochemistry of early permian mafic ultramafic complexes in the beishan area xinjiang nw china implications for late paleozoic tectonic evolution of the southern altaids abstract the hongshishan and pobei mafic ultramafic complexes outcrop in the beishan area in the southernmost altaids they consist of olivine gabbros dunites and pyroxenites zircons from olivine gabbros from the hongshishan complex yield a u pb age for emplacement of 281 8 2 6 ma the olivine gabbros have low sio 2 47 08 48 66 tio 2 0 14 0 29 mno 0 07 0 09 and k 2 o 0 06 0 09 but high mg values 81 t fe 2 o 3 4 93 6 29 the hongshishan and pobei mafic ultramafic complexes are characterized by negative anomalies in high field strength elements zr hf nb ta which we interpret as arc related signatures they also have spikes in large ion lithophile fluid mobile elements ba u pb sr and high mobile immobile element ratios i e primitive mantle normalized sr nd ba la 1 which are attributed to an aqueous fluid component in the source zircon hf isotopes indicate that the source magma was derived either from a depleted mantle with some crustal contamination or from an enriched mantle these data are interpreted to indicate that the hongshishan and pobei mafic ultramafic complexes were emplaced in the early permian subduction related environment which suggests that the paleo asian ocean in the southernmost part of altaids did not close until after early permian

drainage organization on the newly emerged dead sea bed israel abstract the organization of distributary drainage systems on the emerging coastal areas of the dead sea was studied following a rapid base level fall of 24 m during the period 1945 2002 which made the emerging pristine coastal zone a natural field laboratory photogrammetric digital elevation models were extracted to identify different emerged areas and to quantify erosion and deposition processes visual interpretation of orthophotos was used in order to recognize different drainage networks and to delineate the receding shoreline the remotely sensed data were backed by field surveys including measurement of longitudinal profiles the study demonstrates the spatial variability of runoff allocation from prograding fans to the emerging areas and the variable drainage responses three distinct environments were revealed on the emerged areas from the coast to the land deeply incised channels which are the main transmitters of the base level effect headward dendritic coalescing systems that are the reversal of the diverging channel system on alluvial fans and areas with unconfined sheet flowouts which are detached from base level control the threshold gradient of erosion on the emerged areas is 3 headward erosion was uncoupled with the lake level drop i e the rate of headward entrenchment increased with time despite an almost constant base level fall

the most ancient ophiolite of the central asian fold belt u pb and pb pb zircon ages for the dunzhugur complex eastern sayan siberia and geodynamic implications abstract ophiolitic rocks with a zircon age of 1020 ma occur in the dunzhugur complex of east sayan siberia and are part of a neoproterozoic to early palaeozoic segment of the central asian fold belt the most spectacular suite is exposed along the oka and bokson rivers where a complete ophiolite sequence with mantle tectonites a layered sequence composed of dunite wehrlite and pyroxenite a gabbro section a sheeted diabase dyke complex and basaltic pillow lavas are exposed petrologic and geochemical data suggest that all members of the ophiolite originally belonged to the same cogenetic mafic ultramafic crustal section and support a supra subduction zone setting in a fore arc rifting environment for its origin two multigrain zircon size fractions from a plagiogranite are both slightly discordant but yielded a combined mean 207pb 206pb age of 1020 10 ma evaporation of three additional fractions of three to four grains each from the same sample produced a mean 207pb 207pb age of 1019 9 0 7 ma that we consider to most closely reflect the time of igneous crystallization of the plagiogranite this is the oldest ophiolite so far dated from the central asian fold belt the southern margin of the siberian craton and the palaeo asian ocean were established at the end of the mesoproterozoic at least 1000 ma ago during the time interval 1000 570 ma one or several large ocean basins existed between baltica siberia kazakhstan tarim and northern china and these blocks are therefore unlikely to have been part of the supercontinent rodinia rifting initiation of subduction and marginal basin formation began prior to 1000 ma and continued through 570 ma the dunzhugur ophiolite of eastern sayan provides evidence for the early opening of the palaeo asian ocean not later than 1000 ma ago

colorado river long profile metrics knickzones and their meaning abstract the numerical analysis of river long profiles has a rich history and is experiencing a rejuvenation with the advent of improved terrain models and computational tools the highly variable profile and the unusual hydrology of the green colorado river system crossing the colorado plateau provide an example that is germane to debates about transient versus equilibrium knickzone features about the controls of baselevel change due to drainage integration or differential uplift and the role of adjustments to climate hydrology and changing bedrock in order to explore these controls in more detail we define objective geologic study reaches along the green colorado river calculate unit stream power and develop a discharge adjusted steepness index kqsn that avoids the scaling assumptions in substituting contributing area for discharge which are erroneous in this dryland setting determining the nature of knickzones is key and the colorado plateau is a prime setting for study because of the legacy of previous work and a burst of new research and debate the four canyon knickzones along the green colorado are characterized by energy expenditure an order of magnitude greater than in intervening reaches and our kqsn proxy tracks stream power well the strong coincidence of the grand canyon cataract canyon and eastern uinta knickzones with stronger bedrock and mass movement inputs suggests they are pinned equilibrium adjustments to greater bed resistance with the possible exception of desolation canyon as a transient feature marked by anomalous profile convexity along the trunk drainage the knickzone anomalies become greater downstream this and patterns of kqsn in headwater tributaries correspond to some proposed sources of broad mantle driven uplift but they do not match other proposed uplift patterns thus a poorly understood decoupling of topography and proposed uplift exists in some regions