the effects of rock uplift and rock resistance on river morphology in a subduction zone forearc oregon usa relationships between riverbed morphology concavity rock type and rock uplift rate are examined to independently unravel the contribution of along strike variations in lithology and rates of vertical deformation to the topographic relief of the oregon coastal mountains lithologic control on river profile form is reflected by convexities and knickpoints in a number of longitudinal profiles and by general trends of concavity as a function of lithology volcanic and sedimentary rocks are the principal rock types underlying the northern oregon coast ranges between 46 30 and 45 n where mixed bedrock alluvial channels dominate average concavity is 0 57 in this region in the alluviated central oregon coast ranges between 45 and 44 n values of concavity are on average the highest 0 82 south of 44 n however bedrock channels are common and 0 73 mixed bedrock alluvial channels characterize rivers in the klamath mountains from 43 n south 0 64 rock uplift rates of 0 5 mm a 1 mixed bedrock alluvial channels and concavities of 0 53 0 70 occur within the northernmost coast ranges and klamath mountains for rivers flowing over volcanic rocks 0 53 and 0 72 for reaches crossing sedimentary rocks whereas channel type and concavity generally co vary with lithology along much of the range rivers between 44 5 and 43 n do not follow these trends concavities are generally greater than 0 70 alluvial channels are common and river profiles lack knickpoints between 44 5 and 44 n despite the fact that lithology is arguably invariant moreover rock uplift rates in this region vary from low 0 5 mm a 1 to subsidence 0 mm a 1 these observations are consistent with models of transient river response to a decrease in uplift rate conversely the rivers between 44 and 43 n have similar concavities and flow on the same mapped bedrock unit as the central region but have bedrock channels and irregular longitudinal profiles suggesting the river profiles reflect a transient response to an increase in uplift rate if changes in rock uplift rate explain the differences in river profile form and morphology it is unlikely that rock uplift and erosion are in steady state in the oregon coastal mountains copyright 2006 john wiley sons ltd

detrital modes and provenance of the stilo capo d orlando formation miocene southern italy the stilo capo d orlando formation sco fm is a miocene clastic unit nonconformably covering the basement of the southern portion of the calabria peloritani arc cpa a small scale terrane which was accreted onto the apennines maghrebides orogenic system during neogene time the sco fm is composed of conglomerate sandstone and mudrock deposited in a marine environment through the action of gravity currents detrital modes of sandstones and conglomerates of the sco fm indicate a local provenance in fact petrological parameters can be matched directly with nearby basement lithologies two petrofacies with distinctive parameters are present a northern petrofacies is predominantly composed of plutonic and low grade metamorphic detritus and was derived from the serre massif which is mostly made of late hercynian plutons intruded into metasedimentary rocks a southern petrofacies is mostly composed of metamorphic detritus and was derived from the aspromonte and the peloritani mountains which are predominantly composed of middle to high grade metamorphic rocks petrological results place important constraints on the geodynamic evolution of the cpa according to several authors the arc is composed of two sectors microterranes with different geological histories and partly composed of contrasting rock types whose timing of juxtaposition is debated early cretaceous against middle late miocene that is much before or soon after deposition of the sco fin the sco fm crops out only in the southern sector of the cpa and does not contain any detritus derived from the northern sector in spite of a favourable sediment palaeodispersal system this fact indicates that the amalgamation of the two sectors probably took place after deposition of the sco fm

mobility of rare earth and other elements during crystallization of peralkaline silicic lavas abstract pantellerite lavas of the dormant caldera volcano mayor island new zealand have thick nonhydrated obsidian selvages at the tops and bases and crystalline microspherulitic interiors the flows were chemically homogeneous on emplacement but the crystalline portions have lost significant na f cl cs y and ree percentage losses of y and ree may exceed 60 ce yb ratios decrease by as much as 20 but eu eu ratios are unchanged loss of y and ree is attributed to the expulsion at near solidus temperatures of y ree 3 chloride complexes but other complexing agents may have contributed to this mobility na is also lost in the same manner groundwater has introduced mg and sr and leached or redistributed na cs and halogens analysis of hydrated glassy plinian pumice shows that secondary hydration has not affected y and ree concentrations the elements na mg f cl sr cs y and ree are highly mobile during the crystallization of peralkaline silicic melts and should not be used in petrogenetic evaluations these elements but not y and ree are also redistributed during secondary hydration processes magmas of undersaturated peralkaline composition will be similarly affected

regional uplift and local tectonic deformation recorded by the quaternary marine terraces on the ionian coast of northern calabria southern italy abstract the setting of a flight of marine terraces along a 65 km long section of the ionian coast of northern calabria is the result of the interaction between interglacial sea levels regional uplift and local fault related elevation changes seven terraces with corresponding palaeoshoreline angles at elevations ranging from 12 m to 420 m were recognised by aerial photo interpretation and field surveying the terraces were correlated to the oxygen isotope stages 1 5a 5c 5e 7 9 15 which correspond to the 7 81 102 124 215 330 and 600 ka highstands of the palaeosea level curve the 600 ka long regional ascent of the terraces took place at an average uplift rate of 0 67 mm yr this value slightly but progressively increases southward along the coastline the elevation of the strandlines is related to the activity of tectonic structures three cases were analysed allowing us 1 to recognise the height anomalies of the terraces on the sibari plain as the result of cumulated coseismic deformation caused by the normal castrovillari fault and on this basis calculate a minimum slip rate and a mean recurrence time for a single event of deformation 2 to exclude the presence of significant vertical deformations and consequently activity on the easternmost section of the normal pollino fault and 3 to hypothesise the presence of an hitherto unknown active fault responsible for the strong vertical displacements of the flight of terraces near the river avena finally we find the ratio of the rate of regional uplift to the average rates of local tectonic deformation to be 2 to 3 1

sedimentology of a marine intermontane pleistocene gilbert type fan delta complex in the crati basin calabria southern italy the crati basin is a pliocene holocene extensional basin filled by the progradation of different types of marine fan delta systems coarse grained gilbert type fan deltas developed during the pleistocene they represent the sedimentary response to a strong differential uplift involving the basin margins and the basin itself the differential uplift was responsible for the fragmentation of the basin into several sub basins into which these fan deltas prograded the protection and lateral confinement by structural highs steep coastlines and the absence of strong tidal action in the adjacent ionian sea allowed the regular progradation of these fan deltas in the restricted gulfs and narrow embayments of the crati basin for the classical gilbert type fan deltas in lacustrine settings homopycnal inflow favours a rapid mixing of water masses and deposition of sediment close to the river mouth in the case of the example described here the density contrast between the sea water and the inflowing river water caused the separation of the muddy fraction from the coarse sandy and conglomeratic part of the sediment this allowed the development of steep mud poor coarse grained delta foresets slope instability features slump scars conglomeratic flow slides are fairly scarce in the proximal parts of the san lorenzo del vallo system towards the north where protection from the ionian sea was less they increase in importance

importance of a stochastic distribution of floods and erosion thresholds in the bedrock river incision problem 1 fluvial erosion of bedrock occurs during occasional flood events when boundary shear stress exceeds a critical threshold to initiate incision therefore efforts to model the evolution of topography over long timescales should include an erosion threshold and should be driven by a stochastic distribution of erosive events however most bedrock incision models ignore the threshold as a second order detail in addition climate is poorly represented in most landscape evolution models so the quantitative relationship between erosion rate and measurable climatic variables has been elusive here we show that the presence of an erosion threshold when combined with a well constrained probabilistic model of storm and flood occurrence has first order implications for the dynamics of river incision in tectonically active areas first we make a direct calculation of the critical shear stress required to pluck bedrock blocks for a field site in new york second we apply a recently proposed stochastic threshold bedrock incision model to a series of streams in california with known tectonic and climatic forcing previous work in the area has identified a weak relationship between channel gradient or relief and rock uplift rate that is not easily explained by simpler detachment limited models the results with the stochastic threshold model show that even low erosion thresholds which are exceeded in steep channels during high frequency flood events fundamentally affect the predicted relationship between gradient and uplift rate in steady state rivers in a manner consistent with the observed topography this correspondence between theory and data is however nonunique models in which a thin alluvial cover may act to inhibit channel incision in the low uplift rate zone also provide plausible explanations for the observed topography third we explore the broader implications of the stochastic threshold model to the development of fluvial topography in active tectonic settings we suggest that continued field applications of geomorphic models including physically meaningful thresholds and stochastic climate distributions are required to advance our knowledge of interactions among surficial climatic and crustal processes

ferrar magmatic province rocks discovered in new zealand implications for mesozoic gondwana geology on the basis of similar ages major and trace element concentrations and sr nd and pb isotopic ratios we correlate the kirwans dolerite of western new zealand with jurassic low ti tholeiites of the well known ferrar magmatic province of gondwana field relations and preliminary paleomagnetic data also support this correlation although the 1 km 2 kirwans dolerite is the first and so far only ferrar correlative to be reported from new zealand it considerably increases the known shape and areal extent of the ferrar province to close to the paleo gondwana margin the presence of ferrar rocks in new zealand can be used to test several models of ferrar magma genesis and gondwana regional tectonics

nd and sr isotope compositions of different phases of surface sediments in the south pacific extraction of seawater signatures boundary exchange and detrital dust provenance the radiogenic isotope composition of neodymium nd and strontium sr are useful tools to investigate present and past oceanic circulation or input of terrigenous material we present nd and sr isotope compositions extracted from different sedimentary phases including early diagenetic fe mn coatings unclean foraminiferal shells fossil fish teeth and detritus of marine surface sediments core tops covering the entire midlatitude south pacific comparison of detrital nd isotope compositions to deep water values from the same locations suggests that boundary exchange has little influence on the nd isotope composition of western south pacific seawater concentrations of rare earth elements ree and al ca ratios of unclean planktonic foraminifera suggest that this phase is a reliable recorder of seawater nd isotope composition the signatures obtained from fish teeth and nondecarbonated leachates of bulk sediment fe mn oxyhydroxide coatings also agree with unclean foraminifera direct comparison of nd isotope compositions extracted using these methods with seawater nd isotope compositions is complicated by the low accumulation rates yielding radiocarbon ages of up to 24 kyr thus mixing the signal of different ocean circulation modes this suggests that different past seawater nd isotope compositions have been integrated in authigenic sediments from regions with low sedimentation rates combined detrital nd and sr isotope signatures indicate a dominant role of the westerly winds transporting lithogenic material from south new zealand and southeastern australia to the open south pacific the proportion of this material decreases toward the east where supply from the andes increases and contributions from antarctica cannot be ruled out

effects of bedrock landslides on cosmogenically determined erosion rates abstract the successful quantification of long term erosion rates underpins our understanding of landscape formation the topographic evolution of mountain ranges and the mass balance within active orogens the measurement of in situ produced cosmogenic radionuclides crns in fluvial and alluvial sediments is perhaps the method with the greatest ability to provide such long term erosion rates although deep seated bedrock landsliding is an important erosional process in active orogens its effect on crn derived erosion rates is largely unquantified we present a numerical simulation of cosmogenic nuclide production and distribution in landslide dominated catchments to address the effect of bedrock landsliding on erosion rates results of the simulation indicate that the temporal stability of erosion rates determined from crn concentrations in sediment decreases with increased ratios of landsliding to bedrock weathering rates within a given catchment area and that as the frequency of landsliding increases larger catchment areas must be sampled in order to accurately evaluate long term erosion rates in addition results of this simulation suggest that sediment sampling for crns is the appropriate method for determining long term erosion rates in regions dominated by mass wasting processes whereas bedrock surface sampling for crns may generally underestimate long term erosion rates response times of crn concentrations to changes in erosion rate indicate that climatically driven cycles of erosion may be detected but that complete equilibration of crn concentrations to new erosional conditions may take tens of thousands of years comparison of simulated crn derived erosion rates with a new data set of such rates from the nepalese himalaya underscore the conclusions drawn from the model results

late quaternary uplift and valley evolution in the northern apennines lamone catchment abstract the topographic evolution of mountain chains is fundamentally dictated by the balance of erosional and tectonic processes in the northern apennines several questions about the late holocene to present deformation style and uplift rates are still open we consider a typical ne facing drainage basin focusing on all the geomorphic markers capable of supplying direct or indirect information regarding tectonic forcing on the landscape characteristics of altitude and relief drainage pattern river profile and fluvial response expressions were found to be in good agreement indicating that the most recent tectonic activity consists of a general persistent uplift of the chain associated with an extensional regime where different sectors are distinguished through differential uplift such differences have been found to act both along and transverse to the chain causing similar coherent patterns of response in erosional processes the geomorphology of the catchment displays several features which together with the long sustained tectonic forcing indicate the near attainment of a dynamic equilibrium between the rates of tectonic forcing and erosional processes creating steady state topography

geochemical characterization evolution and source of a mesozoic accretionary wedge the torlesse terrane new zealand whole rock major and trace element compositions of quartzofeldspathic permian cretaceous sandstones of the torlesse terrane new zealand display progressive changes which compare well with published petrographic data chemical indices in three permian early late triassic rakaia subterrane petrofacies show small contrasts as do the modes reflecting original source compositions a late triassic rakaia petrofacies displays sharp increases in sio 2 al 2 o 3 k 2 o na 2 o th sc la sc ce sc la n y n and decreases in ti zr and v la consistent with partial cannibalistic recycling and a small influx of lithic volcanic detritus in the post collisional late jurassic early cretaceous pahau subterrane sio 2 al 2 o 3 remains high but other indices decrease to levels seen in the permian due to recycling of the earlier rakaia petrofacies and influx of 10 30 mafic intermediate volcaniclastic detritus derived from inboard volcanogenic terranes the results are confirmed by additional suites including mudstones which cover a larger area but also show that some spatial variation occurs within the terrane as a whole whole rock data and chemical index of alteration indices indicate that the torlesse was derived from a relatively unweathered source with granodioritic bulk composition comparisons with data from a proposed rakaia source in the new england and hodgkinson orogens of eastern australia suggest that the observed chemical and modal compositions cannot be simply derived from that area as presently exposed

the pounamu terrane a new cretaceous exotic terrane within the alpine schist new zealand tectonically emplaced deformed and metamorphosed during collision of the lip hikurangi plateau with zealandia abstract the petrologically renowned haast schist previously acknowledged as having formed by jurassic collision and amalgamation of the exotic rakaia and indigenous caples terranes during late mesozoic orogenesis contains a component of the alpine schist whose protolith was deposited in the mid cretaceous an air fall tuff deposited on the ophiolitic pounamu ultramafic belt pub has an eruption age of 108 ma the pub is in tectonic contact to the east with rakaia terrane derived alpine schist of triassic age and is overlain by turbiditic metasediments that have cretaceous 109 140 ma detrital zircon populations the dominant zircon component of these sediments is permo triassic compatible with autocannibalistic reworking from the torlesse composite terrane reconnaissance analysis of the alpine schist indicates that cretaceous protoliths extend at east 200 km along strike while possible correlatives elsewhere in new zealand suggest that the original basin may have been thousands of kilometres in extent models for the emplacement of these exotic cretaceous sediments the proposed pounamu terrane are explored our favoured interpretation is that the cretaceous alpine schist protoliths were deposited in an ensimatic sedimentary basin north of earlier mesozoic subduction zones multi phase deformation and metamorphism occurred during collision of the lip hikurangi plateau with zealandia resulting in the emplacement of an ophiolite pub soled allochthonous thrust sheet of the pounamu terrane onto the previously metamorphosed rakaia otago schist caples massif based on new and regional evidence this collision and the climactic metamorphism of the pounamu terrane occurred at 72 ma

origin of the torlesse terrane and coeval rocks south island new zealand the carboniferous to lower cretaceous torlesse terrane and haast schist derivatives constitute the major part of the complexly deformed facies of the eastern province of new zealand strata consist mainly of quartzofeldspathic graywacke and mudstone intercalated with minor but widely distributed conglomerate and volcanics with associated chert and limestone clastic rocks were deposited largely by sediment gravity flow mechanisms in a deep marine environment also present are a few highly fossiliferous shallow marine and terrestrial deposits of limited areal extent which rest unconformably on or in fault contact with torlesse flysch several periods of deformation are recognized and melange is present on both local and regional scales metamorphism ranges from zeolite to greenschist facies the bulk of the rocks fall into five areally extensive and mutually exclusive fossil zones of the following ages permian atomodesma middle triassic early late triassic torlessia late triassic monotis and late jurassic early cretaceous contacts between major fossil zones are mainly tectonic petrographic analysis permits subdivision of torlesse sandstones into five major petrofacies that correspond in age to the five major fossil zones the sandstone petrofacies mainly arkosic together with the composition of conglomerate clasts mainly indurated torlesse rocks indicate that the source terrane was a continental volcano plutonic arc probably part of gondwanaland coupled with autocannibalistic reworking of older uplifted torlesse rocks in contrast to the quartzofeldspathic nature of the torlesse coeval sedimentary rocks of the eastern province are volcanogenic they are thought to represent related forearc basin maitai murihiku terranes and trench complex caples terrane deposits derived from a volcanic island arc brook street terrane three petrofacies are established for maitai murihiku and caples sandstones the petrofacies indicate a common evolving immature to submature volcanic island arc source for these terranes a reconstruction of new zealand s eastern and western provinces is proposed in permian and triassic times the torlesse was deposited in trench slope or borderland basins along a trench transform margin fronting a continental volcano plutonic arc source western province gondwanaland deposition was spasmodic but voluminous and was accompanied by concurrent deformation and accretion resulting in parallel belts of torlesse rock younging outward from the gondwanaland margin at the same time the brook street terrane volcanic arc and associated terranes were forming to the west of the torlesse site separated from gondwanaland by a marginal sea in latest triassic or early jurassic times the torlesse was rafted into the volcanic arc system via transform faulting approximately parallel to the gondwana margin the collision event resulted in tectonic thickening of torlesse and caples rocks at the plate interface and metamorphism to haast schist the source was then dominated by older partly metamorphosed torlesse terrane newly uplifted along the collision front closing of the marginal sea behind the brook street terrane in late jurassic early cretaceous times resulted in juxtapositioning with the western province gondwanaland along the median tectonic line

field evidence for rapid downstream fining of river gravels through selective transport doubts have been expressed about the ability of either abrasion or sorting to explain strong downstream fining of river gravels we describe pronounced fining over a short distance in a scottish river that has no human disturbance or lateral input of water and sediment measured abrasion rates are far too small to explain observed downstream fining but bed load trap measurements and the dispersion of magnetic tracer pebbles in six subreaches both show sorting during transport the observed downstream fining is also simulated well by a numerical sediment routing model using hydraulic and transport laws consistent with our field measurements the geomorphological cause of the strong fining is slope reduction above a local base level control in this common situation the development of downstream fining is part of the river9s tendency to minimize downstream variation in bed load transport rates and can proceed far more rapidly than the major aggradation otherwise required for equilibration

middle jurassic within plate granites in west antarctica and their bearing on the break up of gondwanaland five post tectonic granitic plutons isolated within the central ellsworth whitmore mountains crustal block in west antarctica form a distinctive geochemical suite all have some characteristics of s type granites and are atypical of active continental margins they range in composition from a within plate granite wpg end member with the lowest 87 sr 86 sr initial ratio 0 707 to granites with a much more marked crustal signature and high initial ratios 0 722 the granitic suite was emplaced over a restricted middle jurassic time interval at the same time as the extensive ferrar karoo tasman mafic suite and just prior to the disintegration of the supercontinent gondwanaland petrogenetic modelling suggests that the wpg end member could have been derived entirely by differentiation of the enriched mantle derived ferrar magma and the end member with the highest initial ratio by partial melting of a crustal source low initial 143 nd 144 nd ratios and proterozoic model ages are compatible with a precambrian crustal component but may alternatively as in the case of ferrar supergroup magmas reflect partial inheritance from enriched lithospheric mantle geochemically coupled to the lower crust since precambrian differentiation data from these granites are consistent with large scale underplating of mafic magma and crustal melting in response to a thermal disturbance in the gondwanaland lithosphere related in some way to break up of the supercontinent

high resolution seismic images of potentially seismogenic structures beneath the northwest canterbury plains new zealand 1 the transpressional boundary between the australian and pacific plates in the central south island of new zealand comprises the alpine fault and a broad region of distributed strain concentrated in the southern alps but encompassing regions further to the east including the northwest canterbury plains low to moderate levels of seismicity e g 2 m 5 events since 1974 and 2 m 4 0 in 2009 and holocene sediments offset or disrupted along rare exposed active fault segments are evidence for ongoing tectonism in the northwest plains the surface topography of which is remarkably flat and even because the geology underlying the late quaternary alluvial fan deposits that carpet most of the plains is not established the detailed tectonic evolution of this region and the potential for larger earthquakes is only poorly understood to address these issues we have processed and interpreted high resolution 2 5 m subsurface sampling interval seismic data acquired along lines strategically located relative to extensive rock exposures to the north west and southwest and rare exposures to the east geological information provided by these rock exposures offer important constraints on the interpretation of the seismic data the processed seismic reflection sections image a variably thick layer of generally undisturbed younger i e 59 ka quaternary sedimentary sequence that shows evidence of moderate faulting and folding during and subsequent to deposition these quaternary units are in unconformable contact with late cretaceous tertiary interbedded sedimentary and volcanic rocks that are highly faulted folded and tilted the lowest imaged unit is largely reflection free permian triassic basement rocks quaternary age deformation has affected all the rocks underlying the younger alluvial sediments and there is evidence for ongoing deformation eight primary and numerous secondary faults as well as a major anticlinal fold are revealed on the seismic sections folded sedimentary and volcanic units are observed in the hanging walls and footwalls of most faults five of the primary faults represent plausible extensions of mapped faults three of which are active the major anticlinal fold is the probable continuation of known active structure a magnitude 7 1 earthquake occurred on 4 september 2010 near the southeastern edge of our study area this predominantly right lateral strike slip event and numerous aftershocks ten with magnitudes 5 within one week of the main event highlight the primary message of our paper that the generally flat and topographically featureless canterbury plains is underlain by a network of active faults that have the potential to generate significant earthquakes

geomorphic expression of active tectonics in a rapidly deforming forearc sila massif calabria southern italy we examine the tectonic geomorphology of la sila calabria southern italy a high standing 1500 m plateau surrounded by crustal extension with map dem and field data these data are used to constrain a simple geodynamic model that describes short wavelength deformation of the plateau rim topographic metrics including drainage patterns river longitudinal profiles and swath profiles are consistent with field stratigraphic relationships collectively suggesting that local tectonic deformation is embedded within a broader regional uplift that has increased the mean elevation of the sila plateau during the quaternary the concavity steepness and length gradient index of modeled river longitudinal profiles proved to be the most useful metrics for recording the effects of locally active faults a previously unrecognized horst on the northeastern portion of the plateau was identified with these data nevertheless the core of the sila plateau remains relatively undeformed with respect to its flanks which are characterized by steep fault bounded escarpments active extension has dropped base level for and unloaded the plateau rim causing deep fluvial incision and associated flexural uplift of the footwall this footwall uplift helps maintain a separate external and nearly radial drainage away from the plateau along its flanks and a nearly closed drainage for the plateau interior a drainage divide roughly correlates with the plateau rim inhibiting the process of drainage integration through the sila interior and subsequent landscape dissection as a result geomorphic processes driving erosion of the sila upland are lagging behind the tectonic processes that have driven rock uplift leading to an overall increase in mean surface elevation these results underscore the importance of the lag times a landscape may endure in transforming from one tectonic and base level condition to another we conclude that the calabrian forearc has a similar geomorphic evolution as the more northern apennines consistent with the emerging view that growth of apennine topography has been recent quaternary rapid and possibly decoupled from rock deformation in the orogenic wedge

limits to quantifying climate driven changes in denudation rates with cosmogenic radionuclides abstract the hypothesis that climate change significantly modifies the denudation history of an orogen can be tested by reconstructing catchment wide denudation histories cosmogenic radionuclides measured in sediment deposits of known age e g a sequence of fluvial terraces offer one approach for quantifying catchment wide paleo denudation rates we present a numerical model and two case studies that evaluate the utility of this technique for reconstructing different denudation histories the concentration of cosmogenic beryllium 10 10 be is calculated for a sequence of sediments produced from climate driven variations in the mean denudation rate of a drainage basin at sea level and high latitude the model accounts for the nucleonic and muonic production and decay of 10 be as sediment is eroded and stored in deposits of different ages two scenarios for different climate driven denudation histories are considered 1 a sinusoidal variation in the input denudation rate with free parameters of periodicity 23 41 100 kyr amplitude 0 1 0 5 1 0 and mean denudation rate 0 01 0 1 1 0 mm yr 1 2 a climate driven denudation history based on oscillations of a global benthic foraminiferal oxygen isotope 18 o record over the last 2 myr results from both scenarios suggest cosmogenic radionuclides measured in a system with high denudation rates 0 5 mm yr 1 longer periodicity 100 kyr and low amplitude have the highest potential for reconstructing climate driven paleo denudation rates unfortunately the high denudation rates preferred in the theoretical consideration are not suitable for paleo denudation rate determination due to overprinting of nuclides accumulated during denudation by post depositional decay and irradiation hence a compromise between the capability to determine changes in paleo denudation rates and the determination of true denudation rates has to be accepted application of the model to previous data sets from northwest europe and southwest north america produce a good agreement but highlight the need for future work to consider how geomorphic processes e g landsliding respond to climate change and influence catchment wide denudation rates in addition other climate proxies than the benthic foraminiferal 18 o record should be used for specific sample locations

ion microprobe upb zircon geochronology of granitic magmatism in the western province of the south island new zealand abstract zircon u pb isotopic systems are described for three mid palaeozoic and four late mesozoic granites from the western province of the south island new zealand the granites chosen are representative of the major plutons in this region two distinct episodes of palaeozoic magmatism have been identified middle devonian 380 ma and early carboniferous 330 ma the mesozoic granites are all mid cretaceous in age and range from 120 to 110 ma the o sullivans granite forming a large part of the karamea batholith has a crystallisation age of 377 7 4 1 ma and the windy point granite from the paparoa batholith has an age of 328 6 4 4 ma further west the granite at cape foulwind has a similar age of 327 3 6 2 ma from east to west the cretaceous granites appear to decrease in age the separation point batholith is dated at 118 ma the oldest phase at separation point gave an age of 116 6 1 9 ma and the youngest phase the pearse granodiorite gave the same age within error at 119 4 2 3 ma the mount olympus pluton in nw nelson gave an age of 111 4 2 0 ma and the same age is found for the buckland granite which forms most of the paparoa batholith at 109 6 1 7 ma inherited zircon components as old as 1700 ma have been identified in many of the granites and distinct components are present at 1000 and 500 600 ma this pattern of zircon ages has also been observed in granites from the lachlan fold belt and in ordovician sediments from se australia and new zealand however it is not clear whether the old zircons are derived from the lower crust from the incorporation of upper crustal material or both the palaeozoic granites can be broadly correlated with rocks of similar age in antarctica se australia and tasmania that formed part of the gondwana supercontinent the cretaceous granites are probably part of an extensive mesozoic magmatic arc that can be traced from south america through west antarctica and on into new zealand

deposition and deformation of an early cretaceous trench slope basin deposit torlesse terrane new zealand studies of modern convergent margins have highlighted the variety of depositional environments and deformational processes that occur in this tectonic setting and provide analogues by which ancient uplifted sequences can be interpreted the whatarangi formation is an early cretaceous trench slope basin deposit preserved within accretionary prism rocks of the pahau torlesse terrane of new zealand and is distinguished from the underlying accreted rocks by its younger age different depositional history structural style and metamorphic grade and lack of oceanic volcanic outcrops furthermore the whatarangi formation records the types of processes inferred to occur in modern slope basins sediments were derived from sources on the western side of the basin and were deposited mainly by gravity flows on channelized base of slope aprons the narrow elongate shape of the basin resulted in restricted longitudinal flow of the sandy turbidity currents and deposition of finer sediment farther down the inner trench slope or in the trench deformation of the turbidites produced open to tight asymmetric folds that are concentrated along the western margin and lower half of the formation the folds are best described by a model of simple shear and formed in response to active west over east thrusting in the underlying prism cleavage was initiated prior to folding in response to overall shortening of the basin with subsequent development of an axial planar cleavage in the tightest folds the compositional similarity between the slope basin strata and accreted sedimentary rocks of the aorangi range has important implications for the early cretaceous tectonic history of the torlesse terrane the sediments were eroded from an uplifted accretionary prism and an acid igneous source and the deposition of these sediments in upslope basins and the trench suggests that all the pahau sediments could have been transported from these transversely located sources

channel changes in badlands stripping of the vegetation and soil from a 13 hectare site in virginia underlain by coastal plain sediments created a rapidly evolving badland topography two types of channels developed 1 sand bed alluvial channels were graded to transport the bed material load supplied from slope erosion with available runoff but they also generally eroded their beds slowly and 2 steeper bedrock floored channels incised rapidly in bedrock channels the erosion rate was proportional to the 4 9ths power of drainage area and the 2 3rds power of gradient these exponents are consistent with a model in which the erosion rate is proportional to the bed shear during high flows due to rapid mass wasting and reduced runoff the alluvial channels became as much as 50 steeper during the winter than the summer with an attendant yearly cycle of winter aggradation and summer entrenchment the gradients their seasonal variability and their downstream hydraulic geometry were consistent with the predictions of total load transport formulas for sand beds and high loads the hydraulic geometry of alluvial channels in the virginia badlands were similar to that on the morrison formation in the western united states

tectonic significance of ductile deformation in low grade sandstones in the mesozoic otago subduction wedge new zealand this study demonstrates how ductile strain measurements can determine the tectonic evolution of a large and long lived subduction wedge we provide a synthesis of the geology of the south island of new zealand with an emphasis on a wedge tectonics perspective that contrasts with a traditional view that interprets new zealand geology in the context of terrane collision and accretion we argue that the otago subduction wedge evolved in a steady fashion throughout its 290 to 105 ma history in response to accretion of trench fill and abyssal plain sediments and slow erosion of a subaerially exposed forearc high maximum temperatures for rocks in the flanks of the forearc high were no greater than 150 to 300 c with solution mass transfer active as the dominant ductile mechanism the 54 studied samples provide information about the absolute ductile strains acquired all along their flow path from the site of accretion to exhumation in the forearc high we use tensor averages to estimate strain at a regional scale these show plane strain uniaxial flattening given that the tensor averages for sy and sx are close to one on average sz is approximately 0 77 and this is balanced by a mass loss of about 23 percent the average z direction is sub horizontal in the prowedge and moderately plunging in the retrowedge a difference attributed to spatial variations in the mode of accretion we infer that rocks presently in the pro side of the otago high were sourced by frontal accretion and those in the retro side were underplated this result highlights the important role of accretion in determining the style of within wedge deformation and also demonstrates the benefit of using a tensor averaging approach to examine regional strain

crustal thickening of the early cretaceous paleo pacific gondwana margin abstract the cause of 7 to 25 km of early cretaceous thickening of parts of the new zealand gondwana margin has been argued to be due to tectonic or magmatic processes new insights into this event have been gained from examination of the grebe mylonite zone an extensive amphibolite facies early cretaceous ductile shear zone that separates volcanic arc rocks of the outboard median batholith from metasedimentary and intrusive rocks of the western province inboard median batholith at lake manapouri in southwest new zealand ar ar and u pb geochronology shows that here exhumation of the outboard median batholith began 128 ma syn kinematic magmatism was taking place at 121 ma and measurable displacement had ceased by 116 ma although the mylonite zone is currently subvertical a combination of thermochronological cooling profiles lineation orientations and back rotation of tilted tertiary unconformities indicate that it most likely formed as an oblique sinistral reverse fault that dipped 60 e and therefore displaced the outboard median batholith over the margin of the western province however the high original angle of this and other compressional shear zones in analogous structural positions the apparent absence of a regional thrust or nappe sheet s and the subtly different ages of thickening for different areas indicate that tectonic loading can have played only one part in the crustal thickening event another factor was the contemporaneous emplacement of 30 000 km 3 of mafic to felsic magma which was likely accommodated by vertical depression of the middle and lower crust tectonic and magmatic processes leading to crustal thickening were therefore not mutually exclusive

the role of slab detachment processes in the opening of the western central mediterranean basins some geological and geophysical evidence abstract a review of the geological and geophysical data from the central and western mediterranean region and the present day upper mantle structure derived from tomographic studies are utilized in order to define the oligocene recent geodynamic evolution for the area in line with previous work we suggest that the miocene quaternary opening of the western and central mediterranean basins is the result of back arc extension due to the roll back toward the southeast of a northwestward subducting african slab in a geodynamic setting pinned between the alpine and betic collisional zones we find however that this general pattern is complicated by four different detachment events which occurred beneath the alps early oligocene the betic chain aquitanian northern africa langhian and the apennines late miocene pliocene we show that each of these events determines a major tectonic reorganization within the european plate

plutonic lithics in ignimbrites of taupo volcanic zone new zealand sources and conditions of crystallisation abstract plutonic rock fragments occur as rare accessory lithics within some of the ignimbrites erupted from calderas and caldera complexes in central taupo volcanic zone tvz new zealand the two main suites of plutonic lithics are 1 medium to fine grained granitoids and 2 fine grained dolerites and microdiorites the granitoids are mostly medium grained rocks with both equigranular and granophyric intergrowth textures the latter indicating rapid crystallisation at shallow crustal levels biotite is the predominant mafic phase in most granitoid samples although rare hornblende and orthopyroxene bearing granitoids also occur glass occurs in some granitoid samples from rotoiti ignimbrite indicating that these samples were incompletely crystallised prior to eruption dolerite and microdiorite fragments typically contain abundant hornblende and up to 10 vesicular interstitial glass sio2 abundances in the granitoids range between 70 3 and 77 9 they are weakly metaluminous to weakly peraluminous and show an enrichment in large ion lithophile lil elements rb k ba and a depletion in nb relative to morb similar to recent tvz rhyolitic volcanic rocks chemically and petrographically the granitoids fall into two distinct groups high sr granodiorites 120 205 ppm sr and chemically more evolved low sr monzogranites 26 65 ppm sr with an apparent compositional gap between the two eu eu anomalies and strong correlations between al2o3 cao and sr indicate that compositional variation between the two granitoid groups is dominantly controlled by plagioclase fractionation the high and low sr groups coincide with the highest and lowest sr concentrations observed in tvz rhyolites ree data and sr nd pb and o isotope ratios for granitoids are comparable to published data for tvz rhyolites and consequently they are considered to represent crystallised portions of zoned silicic magma chambers associated with quaternary tvz volcanic activity and not fragments of older pre tvz basement most granitoids are regarded as comagmatic with their host ignimbrites but those from rotoiti ignimbrite have different mineral assemblages and whole rock chemistry to the host ignimbrite these fragments appear to be incompletely crystallised portions of an earlier magma system possibly the same system that generated the matahina ignimbrite dolerites and microdiorites are geochemically similar to evolved high alumina basalts erupted from the central tvz and are considered to be intrusive equivalents

orographic precipitation and the relief of mountain ranges 1 the influence of climate on the relief of mountain ranges has long been supposed but has received little quantitative investigation the simplified system of a longitudinal river profile in a bedrock channel coupled to a physically based model of orographic precipitation is used to explore how orographically influenced patterns of precipitation affect the relief of fluvially sculpted mountain ranges it is shown that the impact on the orography depends on the nature of the precipitation regime significant changes in relief also occur for imposed temperature changes of realistic magnitude although the ability of the relief to respond to any given change depends sensitively on its response time and the timescale of the forcing

mesozoic radiolarian faunas from the antarctic peninsula age tectonic and palaeoceanographic significance new assemblages of radiolaria including some of the few occurrences of high southern latitude jurassic and cretaceous radiolarian faunas show that several localities in the lemay group of alexander island range in age from latest jurassic earliest cretaceous to at least albian by demonstrating that sedimentation and deformation in the lemay group was diachronous younging oceanwards to the northwest these new age assessments support the model of the lemay group as an accretionary complex the polarity of subduction beneath alexander island was not affected by arc collisions from at least the lower jurassic to the oligocene and such a long period of continuous accretion appears to be unusual deposition of the lemay group spans the kimmeridgian to albian sedimentation in the fossil bluff group fore arc basin thus making the earlier concept of the lemay group as pre jurassic basement untenable allochthonous latest jurassic earliest cretaceous radiolarian assemblages with some supposed tethyan affinities are present in the lemay group in contrast an in situ latest jurassic assemblage from the nordenskjold formation of the back arc basin and a further jurassic assemblage from a probable trench slope basin have characteristics believed diagnostic of high latitudes the biogeographic affinities of radiolarians from cherts in the lemay group accretionary complex suggest that both these cherts and associated basalts are far travelled slices of the phoenix plate rocks from the probable trench slope basin formerly assigned to the younger fossil bluff group fore arc basin sequence now appear to be part of a new previously unrecognized formation

plate detachment asthenosphere upwelling and topography across subduction zones this study analyzes the topography across subduction zones considering the separate contributions of the crust and the mantle lithosphere to the observed surface elevation we have found a transition from a region where the overriding plate is coupled to the descending slab and pulled down along with it to a region where the overriding plate floats freely on the asthenosphere when the subducting slab retreats oceanward rapidly this transition is abrupt and the edge of the overriding plate is uplifted we propose that at some point during rapid slab rollback the overriding plate detaches and rebounds like a boat released from its keel this event is associated with suction of asthenospheric material into the gap that is opened between the plates up to the base of the crust as a result the forearc uplifts and magmatism in the arc increases

late cretaceous to early tertiary subduction history of the antarctic peninsula quantitative estimates of the rates and azimuths of phoenix plate convergence with the antarctic peninsula have been derived from plate rotation calculations for two periods in the late cretaceous and early tertiary 83 0 67 7 and 61 1 53 4 ma published marine magnetic anomaly identifications and flow lines interpreted from gravity anomaly maps were used in simple spherical geometry calculations to derive phoenix pacific stage rotations these were combined with published pacific antarctic rotation data to determine contemporaneous phoenix antarctic stage rotations the results indicate a significant change in azimuths of relative motion between the late cretaceous and early tertiary late cretaceous and perhaps earlier oblique subduction probably caused migration of fore arc slivers along the margin resulting in variations in width of the accretionary prism comparison between synthetic magnetic profiles and a 900 km long magnetic profile across ocean floor produced at the antarctic phoenix ridge during the early tertiary establishes the time of a major decrease in spreading rate and hence also in convergence rate as chron c23r 52 3 ma the associated change in subduction dynamics may have caused the dextral transtensional deformation observed in the george vi sound region and initiated uplift of blueschist facies rocks now exposed on smith island the calculated convergence history does not provide a simple explanation for the occurrence of high mg andesite lavas on alexander island which were erupted more than 20 ma before the antarctic phoenix ridge arrived at the margin the existence of these lavas implies either earlier subduction of another ridge or slab break up beneath alexander island

the hohonu batholith of north westland new zealand granitoid compositions controlled by source h 2 o contents and generated during tectonic transition geochemical studies on the hohonu batholith of the west coast south island new zealand have recognised two distinct but chemically related suites of mid cretaceous granitoids the suites are characterised by restricted radiogenic isotopic compositions sr i 0 7062 to 0 7085 nd i 4 4 to 6 1 and represent melting of a mafic lithosphere source followed by interaction with ordovician metasediments the two suites te kinga suite and deutgam suite are distinguished by contrasting contents of al2o3 na2o sr ba eu and hree attributable to different residual asssemblages controlled by differing h2o contents during melting of a metabasaltic source the relatively mafic metaluminous i type deutgam suite represents magmas derived by dehydration melting in equilibrium with an amphibolitic plagioclase amphibole residue in contrast the peraluminous high silica compositions of the te kinga suite were produced by melting at higher h2o contents reducing the stability of plagioclase and resulting in a melt in equilibrium with a plagioclase free eclogitic garnet amphibole residue residual plagioclase during generation of the deutgam suite resulted in lower al2o3 na2o sr ba and eu contents whereas residual garnet during generation of the te kinga suite resulted in depleted hree contents the mid cretaceous granitoids of the hohonu batholith were generated during a period of rapid tectonic transition from crustal thickening during collision to crustal thinning and core complex formation during extension

landscape response to tectonic forcing digital elevation model analysis of stream profiles in the mendocino triple junction region northern california the topographic evolution of orogens is fundamentally dictated by rates and patterns of bedrock channel incision quantitative field assessments of process based laws are needed to accurately describe landscape uplift and denudation in response to tectonics and climate we evaluate and calibrate the shear stress or similar unit stream power bedrock incision model by studying stream profiles in a tectonically active mountain range previous work on emergent marine terraces in the mendocino triple junction region of northern california provides spatial and temporal control on rock uplift rates digital elevation models and field data are used to quantify differences in landscape morphology associated with along strike northwest to southeast changes in tectonic and climatic conditions analysis of longitudinal profiles supports the hypothesis that the study area channels are in equilibrium with current uplift and climatic conditions consistent with theoretical calculations of system response time based on the shear stress model within uncertainty the profile concavity of the trunk streams is constant throughout the study area 0 43 as predicted by the model channel steepness correlates with uplift rate these data help constrain the two key unknown model parameters the coefficient of erosion k and the exponent associated with channel gradient n this analysis shows that k cannot be treated as a constant throughout the study area despite generally homogeneous substrate properties for a reasonable range of slope exponent values n best fit values of k are positively correlated with uplift rate this correlation has important implications for landscape evolution models and likely reflects dynamic adjustment of k to tectonic changes due to variations in orographic precipitation and perhaps channel width sediment load and frequency of debris flows the apparent variation in k makes a unique value of n impossible to constrain with present data

esr dating and the human evolution contribution to the chronology of the earliest humans in europe abstract in the last 20 years the electron spin resonance esr dating method has allowed the establishment of a chronological time frame over most of the history of human evolution despite many difficulties found for esr dating of bones and carbonates tooth enamel dated by esr has been proven as a reliable method in its application to fossil teeth and quartz both of the latter materials have allowed dating of early and middle pleistocene sites which are not datable using other methods such as the argon argon method in particular recent discoveries of human remains in western europe have been proposed to be sites of the earliest arrival of humans there and have been dated to the early pleistocene by esr using quartz and tooth enamel combined esr and u series dating of fossil herbivore teeth are the only means of dating layers from which such ancient remains have been recovered in western europe good examples are the sites of atapuerca gran dolina spain and visogliano italy which have been dated using tooth enamel when no bones and teeth can be found in prehistoric sites esr dating on quartz extracted from sediments has been used to date sites whose ages range over the entire quaternary period we present here two examples that occur in fluvial terraces of the river creuse france and at monte poggiolo site italy where several artefacts of an archaic pebble industry have been recovered

downstream changes in the lithology and grain size of fluvial gravels the watarase river japan evidence of the role of abrasion in downstream fining two processes have been considered to explain downstream grain size reduction in gravel bed rivers hydraulic sorting by which finer grains are transported faster and farther than coarse grains and abrasion by which individual particles are diminished in size most studies on the cause of downstream fining in rivers emphasize hydraulic sorting as the dominant fining mechanism however broken boulders are often observed in the bed material of japanese rivers also grain size changes may be correlated with the difference in resistance to breakdown among lithologies the purpose of this study is to use the lithologic composition of bed material on the watarase river to demonstrate that some downstream fining cannot be explained by hydraulic sorting alone the study reach on the watarase river flows on a dissected alluvial fan which means that the river is no longer aggrading the study reach is influenced only slightly by input of gravel from tributaries bed gravel in the study reach consists of several lithologies andesite quartz porphyry sandstone hornfels and chert the grain size distribution and lithology of the river bed material were examined at nine sites there are two principal results 1 size distribution of the gravel is strongly related to lithology andesite boulders or large cobbles make up the framework sizes in the upstream part of the study reach while chert pebbles make up the framework sizes in the downstream part there are few andesite pebbles or chert boulders in the river bed 2 longitudinal changes in the composition of each size class show selective transportation by lithology in every gravel size because the mobility of gravel depends mainly on its size hydraulic sorting by lithology does not occur within the same size class these results indicate clearly that particle abrasion occurs in the watarase river and is responsible at least in part for the downstream decrease in particle size of bed material

origins of large volume rhyolitic volcanism in the antarctic peninsula and patagonia by crustal melting voluminous rhyolitic volcanism along the palaeo pacific margin of gondwana was marked by three principal episodes of magmatism the first of these v1 is essentially coincident with the main episode of karoo ferrar magmatism at 184 ma a younger v2 episode occurred at 168 ma and a third episode v3 occurred in the interval 157 153 ma we evaluate the origin of v1 and v2 rhyolites from the antarctic peninsula using major and trace element and isotopic sr nd o data an isotopically uniform 87sr 86sri 0 707 endi 3 andesite dacite magma was generated as a result of anatexis of grenvillian age hydrous mafic lower crust linked to earlier arc related underplating the lower crustal partial melts would have mixed with fractionated components of the mafic underplate followed by subsequent storage and homogenization early jurassic v1 rocks of the southern antarctic peninsula are interpreted as melts of upper crustal paragneiss which have mixed with the isotopically uniform magma in upper crustal magma chambers the v2 rhyolites are the result of assimilation fractional crystallization of the isotopically uniform magma this occurred in upper crustal magma chambers involving assimilants with similar isotopic composition to that of the magma a continental margin setting was crucial in developing hydrous readily fusible lower crust lower crustal anatexis was in response to mafic underplating associated with the discovery shona bouvet group of plumes thought to be responsible for the karoo magmatic province the progression old to young of volcanism from ne to sw in patagonia and south to north in the antarctic peninsula is consistent with migration away from the mantle plumes towards the proto pacific margin of gondwana during rifting and break up

automatic grain sizing of vertical exposures of gravelly deposits abstract the grain size distribution gsd is a key indicator in stratigraphy and morphology it is a basic tool used by a variety of disciplines geology geomorphology archeology ecology and engineering automatic grain sizing ags has been developed to estimate the gsd of surfaces in a rapid and effortless manner yet the traditional bulk method time consuming and laborious is still in use for the determination of the gsd of coarse grained sedimentary deposits and of the near subsurface of landforms principally river beds the ags technique is examined here in its application to the stratigraphic record and to the subsurface images processed by ags and manual samples of coarse grained deposits in section were compared for evaluation of accuracy and determination of the extent of validation of the ags technique the ags often achieves results very similar to field counting especially when the largest grains are accounted for in the size of the sampling area and when photographs are taken afar without flash best results are provided when two images of the same sediment are taken at close range and also from afar to combine their gsds hence overcoming errors generated by resolution sampling area and grain size the computed errors are larger than those in prior studies yet remain reasonably small even though results are not bias corrected axes exposed in an outcrop very likely differ from those exposed on the surface and sediment properties and lighting conditions vary although results indicate a 25 burial effect the performance of the ags for sections is high unlike prior application of ags for riverbed surface openwork gravels conglomerate sections and the near subsurface include a matrix resulting in a somewhat larger mean irreducible error the technique may be utilized in studies of conglomerate texture allowing the evaluation of entire gsds under difficult sampling conditions an example use of ags to subsurface gsd evaluation is provided among others enabling an easy and fast method to calculate extent of armoring

numerical and analytical models of cosmogenic radionuclide dynamics in landslide dominated drainage basins 1 in many tectonically active regions on earth landslides dominate sediment delivery to channels while cosmogenic radionuclides crn represent a valuable tool to document basin averaged erosion rates a better understanding of crn dynamics in these systems is required before erosion rates can be reliably inferred from crn concentrations the stochastic nature of landslides results in variability of crn concentrations in both alluvial and hillslope samples that is both difficult to document and poorly understood to guide sampling strategies we developed a 2 d plan view model to simulate the influence of landslides on crn dynamics we employ a sediment mixing model in which concentrations of crns from material eroded by both landslides and steady processes are combined to evaluate how best to infer erosion rates from crn concentrations this model is further used to test a new analytical solution for the distribution of crn concentrations on hillslopes in a landslide prone system results suggest that for landscapes dominated by deep 5 m landslides only large drainage basins 100 km2 provide consistently reliable estimates of erosion rates from crn concentrations for landscapes dominated by shallow landslides 0 7 2 m smaller basins can produce reliable estimates results further suggest that the distribution of concentrations from hillslope samples could be used to deduce the relative contribution of material derived from landslide and steady processes these findings underscore the need to consider carefully the sources of natural variability in sampling and analyzing crns if properly done the variability can reveal useful information about geomorphic processes in landslide prone areas

provenance of the sedimentary rakaia sub terrane torlesse terrane south island new zealand the use of igneous clast compositions to define the source abstract the permian to late triassic rakaia sub terrane part of the torlesse superterrane of the new zealand eastern province is an accretionary complex that comprises an enormous volume of quartzofeldspathic sandstones and mudstones with subsidiary conglomerates plus minor oceanic assemblages the field of provenance analysis has undergone a revolution with the development of single crystal isotope dating techniques using mainly silt to sand sized single mineral grains fine sand and mud may be transported over thousands of kilometres with potential problems for provenance studies reinforcing the need for caution when interpreting provenance evidence from single heavy mineral grains this study focuses on coarser grained rocks notably conglomerates which involve much shorter transport distances and therefore may be used to trace proximal sources a detailed rock sampling programme and geochronological geochemical and sr nd isotope analysis of igneous clasts from four conglomerates boundary creek te moana mckenzie pass and lake hill have broadly characterised the igneous source for the rakaia sub terrane shrimp u pb zircon ages of rakaia sub terrane igneous clasts define three distinct periods of magmatic crystallisation the first period ranges in age from 292 to 243 ma permian to middle triassic with two clusters recognisable a minor early permian one ranging in age from 292 to 277 ma and a major late permian to middle triassic one from 258 to 243 ma all these clasts are confined to the kazanian permian te moana the dorashamian permian mckenzie pass and the carnian late triassic lake hill conglomerates the clasts which are subduction related calc alkaline to high k calc alkaline and metaluminous to peraluminous range in lithology from andesite to rhyolite and their plutonic equivalents many clasts at lake hill have chemical compositions characteristic of partial melts of a source of basaltic composition in equilibrium with amphibole pyroxene garnet adakites indicative of a thick crust in the clast source area the second period comprises carboniferous calc alkaline metaluminous to weakly peraluminous clasts of the permian boundary creek conglomerate ranging in age from 356 to 325 ma the third group consists of two cambrian clasts a monzogranite from te moana c 497 8 ma and a dacite from lake hill c 517 ma geochronology geochemistry and sr nd isotopes of rakaia igneous clasts correlate broadly with those of permian to triassic plutons and volcanics from the amundsen and ross provinces of marie byrd land thus the antarctic sector of the panthalassan margin of gondwana is the probable source for the rakaia sub terranes as opposed to the other postulated sources in eastern australia

how well can hillslope evolution models explain topography simulating soil transport and production with high resolution topographic data the morphology of hillslopes is a direct refl ection of tectonic forcing and climatic and biologic processes that drive soil production mobilization and transport soil transport on hillslopes affects river incision by providing tools for channel abrasion and controls the distribution of sediment that infl uences aquatic habitat although numerous hillslope transport relationships have been proposed over the past 60 years a comprehensive analysis of model predictions for a real landscape has not been performed here we use high resolution topographic data obtained via airborne laser swath mapping alsm to simulate the long term evolution of oregon coast range hillslopes and test three published transport models and a new model that accounts for nonlinear depth and slopedependent transport analysis of one dimensional steady state solutions for these four models suggests that plots of gradient curvature may be diagnostic for distinguishing model predictions to evaluate two dimensional model predictions for our fi eld site we assumed local steady state erosion for a 72 000 m 2 sequence of hillslopes and valleys after calibrating each of the four models we imposed constant base level lowering for cells within the valley network simulated 500 000 yr of soil production and transport and determined which transport model best preserved morphologic patterns that describe the current landscape form models for which fl ux varies proportionally with hillslope gradient generated broadly convex hilltops inconsistent with the sharp crested steep sided slopes of our study site whereas the two nonlinear slope dependent models produced convex planar slopes consistent with current hillslope form our proposed nonlinear slope and depth dependent model accounts for how soil thickness controls the magnitude of biogenic disturbances that drive transport this model best preserved the current landscape form particularly the narrow sharply convex hilltops characteristic of the oregon coast range according to our formulation which provides an explicit linkage for relating the distribution of biota to hillslope processes the degree of hilltop convexity varies nonlinearly with the ratio of erosion rate to maximum soil production rate highlighting the profound infl uence of soil depth on hillslope evolution

the mid cretaceous transition from basement to cover within sedimentary rocks in eastern new zealand evidence from detrital zircon age patterns detrital zircon u pb ages for 30 late jurassic and cretaceous sandstones from the eastern province of eastern new zealand combined with previously published geochronological and palaeontological data constrain the time of deposition in the pahau and waioeka terranes of the cretaceous accretionary margin of zealandia and their adjacent cover strata the zircon age patterns also constrain possible sediment source areas and mid cretaceous geodynamic models of the transition from basement accretionary wedge to passive margin cover successions pahau terrane deposition was mainly barremian to aptian but continued locally through to late albian time with major source areas in the adjacent kaweka and waipapa terranes and minor inputs from the inboard median batholith waioeka terrane deposition was mainly albian with distinctive and exclusive sediment sources principally from the median batholith but with minor inputs from the western province alternative tectonic models to deliver such exclusive median batholith and western province derived sediment to the mid cretaceous zealandia continental margin are 1 the creation of a rift depression across zealandia or 2 sinistral displacement of south zealandia with respect to north zealandia to expose western province rocks directly at the zealandia margin detrital zircon age patterns of cretaceous cover successions of the eastern province of eastern new zealand demonstrate purely local sources in the adjacent kaweka and waipapa terranes cretaceous zircon components show a decline in successions of late early cretaceous age and disappear by late late cretaceous time suggesting the abandonment or loss of access to both the median batholith and western province as sediment sources

river systems and their sediment flux indo gangetic plains northern bihar india river systems of part of the himalayan foreland northern bihar plains india are described in terms of their channel morphology hydrology and suspended sediment characteristics a simple classification of the river systems based mainly on the source area characteristics is proposed i mountain fed ii foothills fed iii plains fed and iv mixed fed rivers distinct differences are noted between these classes of river systems most rivers show evidence of channel movement mainly by avulsion but cut offs also occur locally the mountain fed rivers are characterized by very high discharge and low suspended sediment concentration and the plains fed rivers have relatively low discharge and high suspended sediment concentration the foothill fed rivers have moderate values of discharge and suspended sediment concentration the mountain fed rivers have built megafans of large extent whereas the foothills fed and plains fed rivers have formed muddy interfan areas semi quantitative estimates of water and sediment flux suggest that about 99 9 of the mass transfer into the plains is water with the remaining 0 1 being sediment and that 10 s of the latter 0 01 of the total is retained in the basin the remainder being transferred to the bengal fan

jurassic tectonic history of the otago schist new zealand a regional reanalysis of the otago schist shows that ductile mesoscopic structures can be interpreted as elements of a single progressive heterogeneous noncoaxial jurassic deformation related to juxtaposition of the caples and torlesse terranes stretching lineations are parallel oblique and perpendicular to the orogen in various parts of otago but changes in trend are generally unrelated to the terrane boundary structural geometry and rare shear criteria indicate that the caples terrane overthrust the torlesse terrane from the south and west but precise transport directions are not known being model dependent macroscopic recumbent folds may be present in the schist but mainly in the form of partially developed nappe structures truncated by zones of retransposed foliation and or high strain

source to sink analysis in an eocene rifted lacustrine basin margin of western shaleitian uplift area offshore bohai bay basin eastern china abstract during the eocene the western shaleitian uplift and its adjacent sags constituted a source to sink s2s system on an active lacustrine basin margin with a steeply dipping boundary fault we integrated a range of data types with subsurface observations from the western offshore bohai bay basin obbb that allowed us to quantify the size and classification of catchment fluvial segments and analyze the sedimentary architecture and sediment fluxes of the proximal fan delta system we then discovered quantitative coupling relationships among the parameters of ancient source to sink segments results show that in the study area the bedrock of the western shaleitian uplift is composed of proterozoic migmatized granites or granites on the basis of paleogeomorphology reconstruction we established classification standards for multi scale catchment units divided the provenance into four third order catchment units obtained quantitative parameters of the catchment unit area a catchment relief r and total sediment discharge qs calculated by bqart model and then confirmed the scales and distribution cross sectional area scs of sediment transport pathways furthermore we analyzed tectonic subsidence sediment dispersal patterns and sediment fluxes of fan delta systems qf using seismic sedimentology in the third member of the eocene shahejie formation es3 finally we used quantitative multivariate statistical analysis of the parameters involved in the source to sink segments to 1 show the proportional range between total sediment fluxes of fan delta qf and sediment discharge qs from catchment largest rate of qf qs in the lower part of es3 smallest rate of qf qs in the middle part of es3 and the range from 30 to 70 and 2 arrange the mainly controlled parameters in terms of their importance i e rate of tectonic subsidence catchment area catchment relief and cross sectional area of sediment transport pathway are listed in order of importance this study can provide an effective way of quantifying and ordering the parameters important in that controlling a complex ancient source to sink system thus helping to achieve an understanding of the process of tectono sedimentary evolution on a rifted lacustrine basin margin

sandstone provenance and sediment dispersal in a complex tectonic setting taranaki basin new zealand abstract mineralogical geochemical and detrital zircon data from key reservoir intervals in taranaki basin are integrated with paleogeography and basement maps to provide a synthesis of changes in sediment provenance and sandstone composition through time results show that sandstone composition and quality in taranaki is strongly related to sediment provenance and basin history late cretaceous syn rift deposits display clear evidence for first cycle erosion from local basement rocks dominated by granites of the median batholith a ne sw trending shoreline belt developed through the paleocene which was associated with a gradual increase in sandstone maturity that peaked during the eocene passive margin phase sediment provenance continued to be primarily from granitoids with transport directions from the s sw to n ne progressive quartz enrichment is interpreted to be a result of cleaning through longshore drift longer transport distances and enhanced chemical weathering due to warmer paleoclimates we also invoke a component of eroded and recycled cretaceous paleocene sediment linked to an episode of uplift in the south a transition period ensued from the late eocene to early miocene associated with a change in basin tectonics from passive margin to active margin compositional and detrital zircon u pb data indicate that rocks to the east of taranaki basin became emergent with progressive erosion of cretaceous eocene cover rocks and underlying basement terranes minor southward propagating uplift of the eastern basin margin was initiated in the latest eocene and by the late oligocene provenance and sedimentation patterns had clearly changed with the earliest miocene strata sourced from eastern metasedimentary basement rocks the eastern province continued to be a major sediment source through the active margin phase but mixed with the re appearance of granite reworked sources and miocene volcaniclastic detritus these changes in sediment provenance through time are displayed on a set of eight sediment dispersal maps which can be used to help predict composition and hence reservoir quality in undrilled parts of the basin

fission track analysis of the crystalline basement rocks of the calabrian arc southern italy evidence of oligo miocene late orogenic extension and erosion abstract fission track analysis is used to provide low temperature and time constraints on the late orogenic cooling and exhumational history of the crystalline basement rocks of the calabrian arc southern italy 65 samples yielded 57 apatite fission track ages 54 zircon fission track ages and 25 apatite confined fission track length distributions interpretation of this data reveals a phase of increased cooling rates related to exhumation between approximately 35 ma mid oligocene and 15 ma middle miocene evidence from the sedimentary record indicates significant oligo miocene erosion related to this period of exhumation new chronological constraints are also applied to localised late orogenic extensional tectonism that has recently been identified within the basement rocks of the calabrian arc this information is used to produce a new model of the oligo miocene tectonic evolution of the calabrian arc it proposes that the crystalline basement rocks were part of a critical orogenic wedge between the mid oligocene and the middle miocene

the lower jurassic hanson formation of the transantarctic mountains implications for the antarctic sector of the gondwana plate margin the hanson formation antarctica consists of interbedded sandstones and tuffaceous rocks of early jurassic age the sandstones pebbly to medium grained range between quartzo feldspathic and volcaniclastic with some of the former being coarse grained arkoses that imply proximal sources geochronology of detrital zircons provides evidence for source rock ages whereas sandstone petrology demonstrates a mixed provenance tuffaceous strata are reworked fine to very fine grained tuffs resulting from distal plinian eruptions dated tuffs provide time constraints on the duration of volcanism the sandstones and tuffs accumulated in a rift environment geochemically the tuffs are rhyolitic in composition and the sr and nd isotope data together with the patterns on multi element diagrams suggest they were derived from a volcanic arc which is interpreted to have been located along the west antarctic gondwana margin the silicic volcanism extends the distribution and timing of magmatism in the early jurassic along that margin the early jurassic extensional regime was delimited by the plate margin region and the east antarctic craton the rift valley system along the east antarctic craton margin in which the hanson strata accumulated was the focus for subsequent emplacement of the intrusive and extrusive rocks of the lower jurassic ferrar large igneous province the early jurassic extensional rifts may have been reactivated during cretaceous cenozoic development of the west antarctic rift system

the role of crustal and mantle sources in the genesis of granitoids of the antarctic peninsula and adjacent crustal blocks abstract magmatic rocks from the antarctic peninsula show marked variations in isotope composition which reflect changes in the geodynamic evolution of the peninsula through time most antarctic peninsula granitoids formed as a result of subduction they fall on well defined trends on plots of nd 207 pb 204 pb and 18 o against 87 sr 86 sr i between a component derived from subduction modified mantle or juvenile basaltic underplate ndi 6 207 pb 204 pb 15 61 18 o 5 5 87 sr 86 sr nd 7 207 pb 204 pb 15 67 18 o 10 87 sr 86 sr 0 709 a small group of granitoids emplaced before or during gondwana break up plot on distinct trends towards high 87 sr 86 sr i compositions reflecting mixing between melts derived from proterozoic lower crust and melts of middle upper crustal rocks ndi 9 207 pb 204 pb 15 64 18 o 10 87 sr 86 sr 0 726 with little or no input of new material derived from the mantle or from juvenile basaltic underplate these granitoids are thought to have formed as a result of crustal attenuation during the initial rifting phase of gondwana break up similar trends are shown by data from granitoids of the adjacent crustal blocks of west antarctica the isotope data suggest that an enriched ferrar karoo type lithosphere was not involved in the genesis of granitoids of the antarctic peninsula or of the ellsworth whitmore mountains crustal block

a new active tectonic model for the construction of the northern apennines mountain front near bologna italy 1 we integrate existing and new geologic data retreating trench extension and accretion tectonics retreat project particularly on the origin growth and activity of the mountain front at bologna italy into a new model that explains apennine orogenesis in the context of a slab rollback upper plate retreat process the bologna mountain front is an actively growing structure driving rock uplift 1 mm year cored by a midcrustal flat ramp structure that accommodates ongoing shortening driven by adria subduction at a rate of 2 5 mm year the data we use are assembled from river terraces and associated pleistocene growth strata geodesy including releveling surveys reinterpretation of published reflection lines and a new high resolution reflection line these data constrain a simple trishear model that inverts for blind thrust ramp depth dip and slip apennine extension is recognized both in the foreland as high angle normal faults and modest stretching in the carapace of the growing mountain front and in the hinterland with larger normal faults that accomplish some crustal thinning as the upper plate retreats this coevolution of extension and shortening shares some notable characteristics with other basement involved collisional orogens including the early tertiary laramide orogeny in the american west and the oligocene to miocene evolution of the alps we propose a possible relationship between underplating and the development of the po as a sag basin as a quaternary phenomenon that may also apply to past periods of apennine deformation tortonian continued shortening on the structure beneath the bologna mountain front represents by far the most important and underappreciated seismogenic source in the front of the northern apennines

relation between rock uplift and denudation from cosmogenic nuclides in river sediment in the central alps of switzerland 1 a north south traverse through the swiss central alps reveals that denudation rates correlate with recent rock uplift rates in both magnitude and spatial distribution this result emerges from a study of in situ produced cosmogenic 10be in riverborne quartz in central alpine catchments as a prerequisite we took care to investigate the potential influence of shielding from cosmic rays due to snow glaciers and topographic obstructions to calculate a possible memory from last glacial maximum lgm glaciation and to identify a watershed size that is appropriate for systematic sampling mean denudation rates are 0 27 0 14 mm a for the alpine foreland and 0 9 0 3 mm a for the crystalline central alps the measured cosmogenic nuclide derived denudation rates are in good agreement with post lgm lake infill rates and are about twice as high as denudation rates from apatite fission track ages that record denudation from 9 to 5 ma in general denudation rates are high in areas of high topography and high crustal thickness the similarity in the spatial distribution and magnitude of denudation rates and those of rock uplift rates can be interpreted in several ways 1 postglacial rebound or climate change has introduced a transient change in which both uplift and denudation follow each other with a short lag time 2 the amplitude of glacial to interglacial changes in both is small and is contained in the scatter of the data 3 both are driven by ongoing convergence where their similarity might hint at some form of long term quasi steady state or 4 enhanced continuous quaternary erosion and isostatic compensation of the mass removed accounts for the distribution of present day rock uplift

integrated analyses constraining the provenance of sandstones mudstones and conglomerates a case study the laojunshan conglomerate qilian orogen northwest china the qilian orogenic belt in the northern tibetan plateau connects the altaids to the north with the tethyan orogenic system to the south and occupies a key tectonic position in the evolution and assembly of asia the belt con tains a wide range of subduction accretion related petrotectonic units the early middle devonian laojunshan con glomerate deposited unconformably upon cambrian silurian strata along the northern margin of the north qilian terrane contains a record of the late paleozoic tectonism of the qilian orogen its provenance and tectonic setting are critical in understanding not only the tectonic evolution of tibetan plateau but paleozoic global reconstructions as well the composition of clastic conglomerates and heavy mineral assemblages of sandstones suggests that coeval mafic felsic metamorphic and sedimentary rocks were the main sources the geochemistry of volcanic clasts and paleocurrent and paleogeographic data suggest derivation from subduction accretion complexes in the north qilian terrane the geochemistry of siltstones and mudstones indicates that the laojunshan conglomerate was derived from an arc and accumulated in an active continental margin geochemical data of granitoid clasts suggest that they were de rived from ordovician silurian subduction related magmatic rocks mafic and ultramafic clasts chromite and magne tite decrease upwards in the stratigraphy whereas metamorphic sedimentary and granitoid clasts and garnet increase these data imply that mafic rocks were the predominant source during initial deposition regional studies suggest that the north china plate subducted southwards and produced subduction related arc magmatism along the southern margin of the north qilian terrane during the early middle devonian therefore we interpret the laojunshan conglomerate as a fore arc basin fill

provenance of permian triassic and ordovician metagraywacke terranes in new zealand evidence from 40ar 39ar dating of detrital micas single crystal 40 ar 39 ar ages of detrital micas from greenland group ordovician low grade metagraywackes of the west coast south island new zealand indicate a source area having muscovite age patterns of 490 515 ma the detrital muscovite ages are characteristic of granitoid and gneiss terranes of the ross adelaide fold belt of antarctica therefore the source area for the greenland group sedimentary rocks was the immediately adjacent pacific margin of gondwana similar age determinations for rakaia terrane permian triassic torlesse supergroup metagraywackes of the wellington and canterbury regions of new zealand indicate that their source area included rocks having prominent muscovite cooling ages populations of 210 290 ma 80 and 410 460 ma 15 the torlesse detrital muscovite age data thus suggest that the source area of the metagraywackes was not within the lachlan fold belt of southeast australia and analogues in antarctica nor in the adjacent ross adelaide fold belt rather the rakaia terrane of the torlesse metagraywackes is a true suspect terrane derived from a source area within the hunter bowen fold belt of northeast australia and the immediately adjacent older orogens of eastern queensland

dynamic equilibrium among erosion river incision and coastal uplift in the northern and central apennines italy erosion river incision and uplift rates in the northern and central apennines italy since 0 9 ma are determined from new cosmogenic nuclide data beryllium 10 concentrations in modern and middle pleistocene sediments indicate erosion rates from 0 20 to 0 58 mm yr these rates are similar to estimates of sediment yield 0 12 0 44 mm yr river incision 0 35 mm yr and uplift 0 01 1 0 mm yr rates inferred from other methods that integrate landscape process rates since the early pleistocene these rates of landscape change are significantly lower than long term exhumation rates of 1 2 mm yr since ca 4 5 ma inferred from thermochronometry collectively these data suggest that hillslope erosion and river incision rates in the northern and central apennines have balanced local uplift rates for 1 my but that exhumation rates have slowed significantly since emergence of the mountain chain in the pliocene this condition of dynamic equilibrium was potentially achieved within ca 3 ma similar to some model predictions of hillslope and fluvial system adjustment

the pre cenozoic magmatic history of the thurston island crustal block west antarctica new rb sr and k ar geochronological data are presented for the majority of known pre cenozoic outcrops in thurston island the jones mountains and the western eights coast which collectively represent the basement geology of the thurston island crustal block of west antarctica almost all are of calc alkaline igneous or metaigneous rocks and indicate long standing proximity to a magmatic arc the observable history began with late carboniferous 309 5 ma emplacement of mantle derived orthogneiss precursors in eastern thurston island nd model ages from these and later igneous rocks suggest that the underlying crust is no older than about 1200 1400 ma throughout the area a variety of cumulate gabbros was emplaced soon after gneiss formation followed by crust contaminated diorites that have triassic mineral cooling dates of 240 220 ma in the nearby jones mountains the oldest exposed rock is a muscovite bearing granite with an early jurassic age of 198 2 ma its initial 87sr 86sr ratio of 0 710 and ndt values of 5 to 7 indicate either anatexis or at least a high degree of crustal input during magma genesis this belongs to a suite of such granites known throughout the antarctic peninsula and related to earliest rifting of the gondwana supercontinent the subsequent evolution of the thurston island area was dominated by i type magmatism apparently in two major episodes at 152 142 ma late jurassic granites and 125 110 ma early cretaceous bimodal suite most of these magmas had initial 87sr 86sr ratios of 0 705 0 706 and ndt values of 2 to 4 and were derived from slightly enriched mantle or from juvenile lower crust they are thought to signify subduction of pacific ocean floor as in the adjacent parts of west antarctica although the late jurassic episode was of greater intensity in thurston island than elsewhere the cretaceous magmatism was intense and of andean type between 100 and 90 ma volcanism in the jones mountains became predominantly silicic with increasing incorporation of crustal components initial 87sr 86sr ratios of 0 706 0 709 and ndt values of 3 to 6 as subduction related magmatism ceased in this part of the margin

residual topography lithospheric structure and sunken slabs in the central mediterranean abstract the central mediterranean comprises subduction collision and backarc extension all in a relatively small area in this paper we analyze the topography of this region examining the influence of subducting slabs on overriding plates we take the observed surface elevation remove the contribution of the crust to it and use the residual topography to identify regions that are unusually low unusually high or normal then we calculate lithospheric thickness where local isostasy applies the results provide information about the structure of the lithosphere in this complex region and about the vertical tectonics in particular we found a difference between the south tyrrhenian subduction zone and the apennines consistent with the processes of slab rollback and slab break off respectively in the south tyrrhenian the edge of the oceanic plate is strongly pulled down whereas the edge of the overriding plate the calabrian peninsula is uplifted this opposite trend indicates weak plate coupling that is the subducting slab which is rapidly rolling back hangs almost entirely on the oceanic plate and the overriding plate is free in contrast in the apennines high residual topography and uplifting are detected on both sides of the mountain belt consistent with complete break off of the subducted lithosphere

transient channel incision along bolinas ridge california evidence for differential rock uplift adjacent to the san andreas fault 1 the rates and spatial distribution of active deformation provide critical constraints on the geodynamics of deforming lithosphere yet such data are often difficult to acquire in eroding landscapes where poor preservation of geomorphic or stratigraphic markers hinders strain reconstruction recent advances in understanding of the relationship between bedrock channel profile form and erosion rate have led to their use as an index of rock uplift rate in steady state landscapes here we extend this analysis to landscapes experiencing a transient increase in erosion rate using an example from the marin county region of northern california we characterize channel and hillslope gradients in a series of small watersheds along a monolithologic portion of the franciscan terrane in marin county channel steepness indices vary strongly from north to south along the ridge and correspond with the progressive development of relief on threshold hillslopes along valley walls these patterns argue that recent channel incision has engendered a transient adjustment of hillslope gradient as incision outpaces soil production rates these differences in landscape form and inferred incision rate are explained by differential rock uplift within the region east of the san andreas fault relationships between channel gradient and incision rate suggest a threefold to fivefold difference in incision rate across the region and place a minimum bound on differential rock uplift rates our study highlights how landscape analysis can place bounds on the distribution of earth deformation in both space and time and thus lends insight into the processes driving that deformation

limestone and chert in tectonic blocks from the esk head subterrane south island new zealand the esk head subterrane is a continuous belt generally 10 20 km wide of tectonic melange and broken formation on the south island of new zealand this subterrane separates older and younger parts of the torlesse terrane which is an extensive accretionary prism composed mostly of quartzo feldspathic submarine fan deposits ranging from permian to early cretaceous in age the torlesse is the most pacific ward of several permian and mesozoic accreted terranes in new zealand that record tectonic amalgamation and ultimate accretion against the pacific facing gondwana margin the esk head subterrane of the torlesse is especially informative because it includes within it conspicuous tectonic blocks of submarine basalt and a variety of basalt associated seamount and sea floor limestones and cherty rocks thought to be representative of the subducted plate limestones in tectonic blocks are of late triassic and probably jurassic ages and include 1 submarine cemented pelagic bivalve geopetal packstone grainstone 2 brachiopod bryozoan encrinite and 3 radiolarian pelagic lime mudstone most of the triassic blocks have been dated using conodonts which have remarkably low color alteration index cai values paleogeographic inferences drawn from megafossils bioclasts and radiolarians as well as from carbonate cements indicate deposition of the oceanic sedimentary rocks at paleolatitudes somewhat lower than that of the new zealand part of the gondwana margin but higher than paleoequatorial latitudes these oceanic sediments and their basaltic substrates were evidently emplaced in the torlesse accretionary prism following off scraping from an extensive subducting oceanic plate probably the phoenix plate which was obliquely convergent with the northwest trending gondwana margin during late jurassic and or early cretaceous time

sedimentology and structure of the trench slope to forearc basin transition in the mesozoic of alexander island antarctica the mesozoic forearc of alexander island antarctica is one of the few places in the world where the original stratigraphic relationship between a forearc basin and an accretionary complex is exposed newlydiscovered sedimentary rocks exposed at the western edge of the forearc basin fill the kimmeridgian albian fossil bluff group record the events associated with the basin formation these strata are assigned to the newly defined selene nunatak formation bathonian and atoll nunataks formation bathonian tithonian within the fossil bluff group the selene nunatak formation contains variable thicknesses of conglomeratesand sandstones predominantly derived from the lemay group accretionary complex upon which it is unconformable the formation marks emergence and subsequent erosion of the inner forearc area it is conformably overlain by the1 km thick atoll nunataks formation characterized by thinly bedded mudstones and silty mudstones representing a marine transgression followed by trench slope deposition the atoll nunataks formation marks a phase of subsidence possibly in response to tectonic events in the accretionary prism that are known to have occurred at about the same time the atoll nunataks formation is conformably overlain by the himalia ridge formation a thick sequence of basin wide arc derived conglomerates this transition from fine to coarse grained deposition suggests that a well developed depositional trough and hence trench slope break had formed by that time the atoll nunataks formation therefore spans the formation of the forearc basin and marks the transition from trench slope to forearc basin deposition

deformation of the 125 ka marine terrace in italy tectonic implications in peninsular italy marine terraces and shorelines created during oxygenisotope substage 5e known historically as the tyrrhenian highstand provide a reliable and homogeneous datum of vertical motions during the past 125 000 years published accounts of 121 locations on the tyrrhenian inner edge were reinterpreted and used to calculate both local and regional uplift rates the data show arching of southern italy between the tyrrhenian and the adriatic coasts and of the calabrian arc between the sangineto and the longi taormina tectonic lineaments at rates of up to 1 2 mm yr for the past 125 ka they also suggest that the present configuration of the southern apennines is the product of post early pleistocene regional uplift superimposed on tortonian to early pleistocene thrusting uplift patterns are characterised by different wavelength in different geodynamic settings suggesting a close link with the depth of the causative tectonic sources

provenance analysis using conglomerate clast lithologies a case study from the pahau terrane of new zealand abstract the field of provenance analysis has undergone a revolution with the development of single crystal isotope dating techniques using mainly silt to sand sized single minerals this study focuses on coarser grained rocks notably conglomerates which involve much shorter transport distances and therefore may be used to trace proximal sources the torlesse terranes part of the new zealand eastern province are accretionary complexes that comprise an enormous volume of quartzofeldspathic sandstones and mudstones with subsidiary conglomerates plus minor oceanic assemblages two terranes are recognised in the south island the permian to late triassic rakaia terrane and the late jurassic to early cretaceous pahau terrane geochronology geochemistry and sr nd isotopes of igneous clasts from pahau terrane conglomerates identify the median tectonic zone s l as a major contributor of detritus to the pahau depositional basin shrimp u pb zircon ages of igneous clasts range from 128 to 123 ma and from 147 to 135 ma calc alkaline clasts of the latter range are indistinguishable in age chemical composition and petrogenesis from the calc alkaline granitoids of the darran suite whereas alkaline clasts correlate with the electric granite both parts of the median tectonic zone an early jurassic calc alkaline rhyolite clast from kekerengu 188 3 ma correlates with the bounty island granite campbell plateau the petrography and geochemistry of pahau terrane sandstone clasts indicate the recycling of permian to early late triassic older rakaia terrane rocks this is further supported by the detrital zircon age data igneous conglomerate clasts are capable of placing exceptionally tight constraints on pahau provenance and on its mesozoic tectonic setting within the southwest pacific margin of gondwana they provide the best evidence yet that the pahau terrane is locally derived

spatially averaged long term erosion rates measured from in situ produced cosmogenic nuclides in alluvial sediment spatially averaged erosion rates of small catchments can be accurately inferred from the concentrations of cosmogenic nuclides in stream sediment here we test this technique at two catchments by comparing erosion rates inferred from cosmogenic nuclides with rates of alluvial fan deposition over the past 16 000 years these two independent estimates agree within one standard error demonstrating that cosmogenic nuclide signatures of stream sediment can be used to measure spatially averaged long term erosion rates using this technique we show that long term erosion rates are an exponential function of average hillslope gradient at these sites

detrital zircon age patterns and provenance in late paleozoic early mesozoic new zealand terranes and development of the paleo pacific gondwana margin permian triassic strata from parapara peak in the takaka terrane western province new zealand are dominated by detrital zircon peaks at ca 240 ma comparable to the torlesse terrane of the eastern province this contrasts with lower paleozoic strata onekaka schist which is comparable to other lower paleozoic terranes including adjacent buller terrane from the gondwana margin that are characterized by detrital zircon patterns with characteristic peaks at ca 500 650 ma and ca 1000 1150 ma a less distinct peak around 1400 1700 ma and scattered archean ages these data indicate the close proximity of the eastern and western provinces by permian time and a probable source region of parapara peak strata and torlesse terrane in the new england fold belt of southeast australia

samarium neodymium elemental and isotopic systematics in sedimentary rocks abstract trace element sm nd th sc and nd isotopic data for sedimentary rocks are examined in order to evaluate 1 1 possible secular trends in the composition of the sedimentary mass and upper continental crust 2 2 the role of tectonic setting in controlling the chemical and nd isotopic composition of the sedimentary mass when plotted against either sedimentation age or average provenance age determined mainly from nd model ages sm nd in sedimentary rocks decreases abruptly from about 0 21 to 0 19 at the archean proterozoic transition consistent with a change towards a more felsic upper crustal composition the change is only somewhat less pronounced for turbidite sediments than for those of continental affinity a trend toward increasing sm nd approaching or exceeding archean values is observed for phanerozoic turbidites this latter change is interpreted as indicating undifferentiated young crust as a component in the sediment which has been lost from the older post archean record due to sedimentary and igneous intracrustal recycling processes when plotted against sedimentation age th sc ratios exhibit a trend directly comparable to that of sm nd in this case th sc increases abruptly at the archean proterozoic boundary from about 0 5 to 1 0 and then decreases to about 0 7 during the phanerozoic nd isotopic composition of modern sediments is affected by tectonic association with those deposited at active margin settings tending to have higher nd reflecting younger provenance and higher and more scattered sm nd reflecting less homogenized and differentiated provenance it is likely that these distinctions can be traced back for about 1 2 ga but with the current data base are not readily resolved in older sedimentary rocks the degree to which the preserved sedimentary mass is open to new additions from the mantle either through replacement during sedimentary recycling or sediment mass growth is highly variable but averages about 15 25 during the phanerozoic

geologic constraints on bedrock river incision using the stream power law denudation rate in unextended terranes is limited by the rate of bedrock channel incision often modeled as work rate on the channel bed by water and sediment or stream power the latter can be generalized as ka m s n where k represents the channel bed s resistance to lowenng whose variation with lithology is unknown a is drainage area a surrogate for discharge s is local slope and m and n are exponents whose values are debated we address these uncertainties by simulating the lowering of ancient river profiles using the finite difference method we vary m n and k to match the evolved profile as closely as possible to the corresponding modern river profile over a time period constrained by the age of the mapped paleoprofiles we find at least two end member incision laws ka 0 3 0 5 s for australian rivers with stable base levels and k f a 0 1 0 2 s n for rivers in kauai subject to abrupt base level change the long term lowering rate on the latter expression is a function of the frequency and magnitude of knickpoint erosion characterized by k f incision patterns from japan and california could follow either expression if they follow the first expression with m 0 4 k varies from 10 7 10 6 m 0 2 yr for granite and metamorphic rocks to 10 5 10 4 m 0 2 yr for volcaniclastic rocks and 10 4 10 2 m 0 2 yr for mudstones this potentially large variation in k with lithology could drive strong variability in the rate of long term landscape change including denudation rate and sediment yield

uplift history of the sila massif southern italy deciphered from cosmogenic 10be erosion rates and river longitudinal profile analysis 1 the sila massif in the calabrian arc southern italy is a key site to study the response of a landscape to rock uplift here an uplift rate of 1 mm yr has imparted a deep imprint on the sila landscape recorded by a high standing low relief surface on top of the massif deeply incised fluvial valleys along its flanks and flights of marine terraces in the coastal belt in this framework we combined river longitudinal profile analysis with hillslope erosion rates calculated by 10be content in modern fluvial sediments to reconstruct the long term uplift history of the massif cosmogenic data show a large variation in erosion rates marking two main domains the samples collected in the high standing low relief surface atop sila provide low erosion rates from 0 09 0 01 to 0 13 0 01 mm yr conversely high values of erosion rate up to 0 92 0 08 mm yr characterize the incised fluvial valleys on the massif flanks the analyzed river profiles exhibit a wide range of shapes diverging from the commonly accepted equilibrium concave up form generally the studied river profiles show two or more frequently three concave up segments bounded by knickpoints and characterized by different values of concavity and steepness indices the wide variation in cosmogenic erosion rates and the non equilibrated river profiles indicate that the sila landscape is in a transient state of disequilibrium in response to a strong and unsteady uplift not yet counterbalanced by erosion

a fluvial record of active fault propagation folding salsomaggiore anticline northern apennines italy 1 fault propagation folds offer the potential to relate folding to underlying fault propagation and slip provided that fold kinematics can be established fluvial terraces have been recognized as kinematic indicators but precise relationships between surface uplift and various folding mechanisms remain largely unexplored this study takes advantage of a well preserved progressively deformed suite of middle pleistocene to recent fluvial terraces above a growing fault propagation fold at the apennine mountain front northern italy to constrain the recent fold kinematics and place them in the context of a longer growth history gleaned from older growth strata the geometry of straths and overlying terrace deposits defines a fixed anticlinal hinge a rolling synclinal hinge proxies for fault tip propagation rates rock uplift rates and tilting rates and how these features and rates vary over the last 800 ka along 15 km of strike length field studies are augmented with dem based quantitative geomorphic analyses that document catchment hypsometry mean anticlinal hinge elevation and long profile form notably long term rock uplift rates using incision as a proxy are uniformly correlated with fault propagation and associated synclinal hinge migration mean anticlinal hinge elevation and variations in catchment hypsometries channels that cross the forelimb at a high angle to the fold hinge generally have higher concavities but channel steepness commonly thought to reflect rock uplift is more strongly adjusted to rock type this study elucidates a new understanding of a complex fold growth history extending back at least 10 ma and provides a novel demonstration of how fluvial terraces may be utilized to constrain fault related fold kinematics

a frost buzzsaw mechanism for erosion of the eastern southern alps new zealand article in the southern alps new zealand large gradients in precipitation b 1t o 12 m year 1 and rock uplift b 1t o 10 mm year 1 produce distinct post glacial geomorphic domains in which landslide driven sediment production dominates in the wet rapid uplift western region and rockfall controls erosion in the drier low uplift eastern region because the western region accounts for b25 of the active orogen the dynamics of erosion in the extensive eastern region are of equal importance in estimating the relative balance of uplift and erosion across the southern alps here we assess the efficacy of frost cracking as the primary rockfall mechanism in the eastern southern alps using air photo and topographic analysis of scree slopes cosmogenic radionuclide dating of headwalls paleo climate data and a numerical model of headwall temperature currently active scree slopes occur at a relatively uniform mean elevation 1450 m and their distribution is independent of hillslope aspect and rock type consistent with the notion that frost cracking which is maximized between 3 and 8 c may control rockfall erosion headwall erosion rates of 0 3 to 0 9 mm year 1 measured using in situ 10 be and 26 al in the cragieburn range confirm that rockfall erosion is active in the late holocene at rates that roughly balance rock uplift models of the predicted depth of frost activity are consistent with the scale of fractures and scree blocks in our field sites also vegetated paleo scree slopes are ubiquitous at elevations lower than active scree slopes consistent with the notion that lower temperatures during the last glacial advance induced pervasive rockfall erosion due to frost cracking our modeling suggests temporally averaged peak frost cracking intensity occurs at 2300 m a s l the approximate elevation of the highest peaks in the central southern alps suggesting that the height of these peaks may be limited by a frost buzzsaw

devonian sedimentation in the xiqingshan mountains implications for paleogeographic reconstructions of the sw qinling orogen abstract the qinling orogen between the north china and yangtze plates comprises various accreted and collisional terranes recording the evolution of the proto tethyan ocean and the formation of east asia knowledge of the provenance and tectonic setting of a thick succession of e w striking devonian sedimentary rocks sandwiched tectonically between the shangdan and mianlue ophiolitic suture zones in this belt is essential to understanding the evolution of the qinling orogen and the assembly of the north china and yangtze plates during the late paleozoic systematic studies of the devonian sedimentary facies in the xiqingshan mountains indicate the northern margin of the south qinling belt was uplifted prior to the early devonian lower devonian sandstones are dominated by feldspathic litharenite q 12 31 f 18 37 l 40 65 indicative of a continental arc derivation detrital zircon u pb data demonstrate that the lower and middle devonian sandstones were derived respectively from ca 770 ma and ca 400 ma felsic arc related magmatic sources devonian sedimentation in the xiqingshan mountains is interpreted to have occurred in a foreland basin between the yangtze plate and the north qinling continental arc

distinguishing between tectonic and lithologic controls on bedrock channel longitudinal profiles using cosmogenic 10be erosion rates and channel steepness index abstract knickpoints in fluvial channel longitudinal profiles and channel steepness index values derived from digital elevation data can be used to detect tectonic structures and infer spatial patterns of uplift however changes in lithologic resistance to channel incision can also influence the morphology of longitudinal profiles we compare the spatial patterns of both channel steepness index and cosmogenic 10be determined erosion rates from four landscapes in italy where the geology and tectonics are well constrained to four theoretical predictions of channel morphologies which can be interpreted as the result of primarily tectonic or lithologic controls these data indicate that longitudinal profile forms controlled by unsteady or nonuniform tectonics can be distinguished from those controlled by nonuniform lithologic resistance in each landscape the distribution of channel steepness index and erosion rates is consistent with model predictions and demonstrates that cosmogenic nuclide methods can be applied to distinguish between these two controlling factors

distribution of active rock uplift along the eastern margin of the tibetan plateau inferences from bedrock channel longitudinal profiles 1 current models of long term river incision into bedrock suggest that the local rate of differential rock uplift should exert a primary control on the gradient of channel longitudinal profiles however discrimination of this effect from the influence of variations in substrate erodibility sediment flux precipitation and transient changes in profile shape has proved difficult in practice here we investigate the controls on the spatial distribution of bedrock channel gradients adjacent to the sichuan basin in an effort to assess the degree and nature of active deformation along this margin of the tibetan plateau analysis of river longitudinal profiles utilizing a channel steepness index a measure of profile gradient normalized for drainage area reveals a zone of anomalously steep channels adjacent to the topographic front of the plateau margin channel profiles are systematically less steep in their headwater reaches on the plateau and in their lower reaches east of the plateau margin comparison of steepness indices to mapped lithologic variations reveals that lithology has only a limited influence on channel gradient in this field area we observe no systematic relationship between steepness indices and upstream drainage area channels of all size are steeper near the plateau margin we argue that these systematic changes are not readily explained as a consequence of increased sediment flux or of orographic precipitation we are led to conclude that steep channel profiles along the topographic front of the plateau reflect active differential rock uplift between this region and the foreland

implications of sediment flux dependent river incision models for landscape evolution 1 developing a quantitative understanding of the factors that control the rate of river incision into bedrock is critical to studies of landscape evolution and the linkages between climate erosion and tectonics current models of long term river network incision differ significantly in their treatment of the role of sediment flux we analyze the implications of various sediment flux dependent incision models for large scale topography in an attempt 1 to identify quantifiable and diagnostic differences between models that could be detected from topographic data or from the transient responses of perturbed systems and 2 to explain the apparent ubiquity of mixed bedrock alluvial channels in active orogens although certain forms of the various models can be discarded as inconsistent with morphological data we find that the relative intrinsic concavity indices of detachment and transport limited systems defined herein largely dictate whether the various models can be tied to distinctive steady state morphologies preliminary data suggest that no such diagnostic differences may exist and other methods must be developed to test models accordingly we develop and explore differences in the scaling behavior of topographic relief and the extent of detachment versus transport limited channels as a function of rock uplift rate that may allow discrimination among various models further we explore potentially diagnostic differences in the rates and patterns of transient channel response to changes in rock uplift rate in addition to general differences between detachment and transport limited systems our analysis identifies an interesting hysteresis in landscape evolution hybrid channels at the threshold between detachment and transport limited conditions are expected to act as detachment limited systems in response to an increase in rock uplift rate or base level fall and as transport limited systems in response to a decrease in rock uplift rate especially during postorogenic topographic decline the analyses presented set the stage for field studies designed to test quantitatively the various river incision models that have been proposed